[go: up one dir, main page]
Previous Article in Journal
Structural Evolution of Olivine during Mechanochemically Assisted Mineral Carbonation under CO2 Flow
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Inorganics
Volume 12
Issue 10
10.3390/inorganics12100270
inorganics-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Synthesis and Characterization of Extremely Bulky Aminopyridinate Ligands and a Series of Their Groups 1 and 2 Metal Complexes

by
Arif M. Earsad
,
Albert Paparo
,
Matthew J. Evans
and
Cameron Jones
*
School of Chemistry, Monash University, P.O. Box 23, Melbourne, VIC 3800, Australia
*
Author to whom correspondence should be addressed.
Inorganics 2024, 12(10), 270; https://doi.org/10.3390/inorganics12100270 (registering DOI)
Submission received: 24 September 2024 / Revised: 14 October 2024 / Accepted: 14 October 2024 / Published: 15 October 2024
(This article belongs to the Special Issue Development and Applications of Sterically Demanding Ligands in Main Group Chemistry)
Browse Figures
Figure 1
<p>The bulky aminopyridinate ligand <b>I</b> (Trip = 2,4,6-triisopropylphenyl and Dip = 2,6-diisopropylphenyl).</p> "> Figure 2
<p>Molecular structure of HAmPy<sup>3</sup> (25% thermal ellipsoids are shown; hydrogen atoms, except the amine proton, omitted). Selected bond lengths (Å) and angles (°): N(1)-C(1) 1.342(2), C(1)-N(2) 1.380(2), N(1)-C(1)-N(2) 114.24(13).</p> "> Figure 3
<p>Molecular structures of <b>1</b> (<b>top</b>) and <b>4</b> (<b>bottom</b>) (25% thermal ellipsoids are shown; hydrogen atoms omitted; TCHP, Trip, C(H)Ph<sub>2</sub> and/or cyclohexyl groups shown as wireframe for clarity). See <a href="#inorganics-12-00270-t001" class="html-table">Table 1</a> for relevant metrical parameters.</p> "> Figure 4
<p>Molecular structure of compound <b>5</b> (25% thermal ellipsoids are shown; hydrogen atoms omitted; isopropyl, ethyl and C(H)Ph<sub>2</sub> groups shown as wireframe for clarity). Selected bond lengths (Å) and angles (°): I(1)-Mg(1) 2.741(1), Mg(1)-O(2) 2.064(3), Mg(1)-N(2) 2.091(3), Mg(1)-O(1) 2.126(3), Mg(1)-N(1) 2.185(3), N(1)-C(1) 1.364(5), N(2)-C(1) 1.348(5), N(2)-Mg(1)-N(1) 63.64(13), N(2)-C(1)-N(1) 112.6(3).</p> "> Figure 5
<p>Molecular structures of the monomer unit of compound <b>6</b> (<b>top</b>), and compound <b>8</b> (<b>bottom</b>) (25% thermal ellipsoids are shown; hydrogen atoms omitted; isopropyl, and C(H)Ph<sub>2</sub> groups shown as wireframe for clarity). Selected bond lengths (Å) and angles (°) for <b>6</b>: Na(1)-N(2) 2.299(2), Na(1)-N(1) 2.4254(19), N(1)-C(1) 1.380(3), C(1)-N(2) 1.329(3), Na(1)-C(16)’ 2.828(3), Na(1)-C(17)’ 3.014(3), N(2)-Na(1)-N(1) 57.65(7), N(2)-C(1)-N(1) 114.66(19). Selected bond lengths (Å) and angles (°) for <b>8</b>: K(1)-N(2) 2.612(4), K(1)-N(1) 2.777(4), N(1)-C(1) 1.393(6), C(1)-N(2) 1.321(6), K(1)-toluene cent. 2.988(5), N(2)-K(1)-N(1) 50.41(11), N(2)-C(1)-N(1) 115.8(4).</p> "> Figure 6
<p>Molecular structure of compound <b>9</b> (25% thermal ellipsoids are shown; hydrogen atoms omitted; isopropyl and C(H)Ph<sub>2</sub> groups shown as wireframe for clarity). Selected bond lengths (Å) and angles (°): N(1)-C(1) 1.372(6), C(1)-N(2) 1.350(7), N(3)-C(60) 1.374(6), N(4)-C(60) 1.341(6), Mg(1)-N(2) 2.009(4), Mg(1)-N(1) 2.155(4), Mg(2)-N(4) 2.011(4), Mg(2)-N(3) 2.066(4), Mg(1)-O(1) 2.014(4), I(1)-Mg(2) 2.7123(19), I(1)-Mg(1) 2.7531(16), I(2)-Mg(2) 2.6782(18), N(2)-Mg(1)-N(1) 65.46(16), N(2)-C(1)-N(1) 111.9(4), N(4)-Mg(2)-N(3) 67.03(15), N(4)-C(60)-N(3) 112.0(4).</p> "> Scheme 1
<p>Synthesis of aminopyridine pro-ligands HAmPy<sup>1−5</sup> (dba = dibenzylideneacetone; dppp = 1,3-bis(dipehylphospino)propane; TCHP = 2,4,6-tricyclohexylphenyl; Ar* = C<sub>6</sub>H<sub>2</sub>(CHPh<sub>2</sub>)<sub>2</sub>Me-2,6,4; Ar<sup>†</sup> = C<sub>6</sub>H<sub>2</sub>(CHPh<sub>2</sub>)<sub>2</sub>Pr<span class="html-italic"><sup>i</sup></span>-2,6,4).</p> "> Scheme 2
<p>Synthesis of compounds <b>1</b>–<b>4</b> (delocalization within the aminopyridinate ligands is not depicted).</p> "> Scheme 3
<p>Synthesis of compounds <b>5</b>–<b>8</b>.</p> ">
Versions Notes

Abstract

:
High-yielding synthetic routes to five new extremely bulky aminopyridine pro-ligands were developed, viz. (C5H3N-6-Ar1)N(H)Ar2-2; Ar1 = Trip, Ar2 = TCHP (HAmPy1), Ar* (HAmPy2) or Ar† (HAmPy3); Ar1 = TCHP, Ar2 = Ar* (HAmPy4) or Ar† (HAmPy5) (Trip = 2,4,6-triisopropylphenyl, TCHP = 2,4,6-tricyclohexylphenyl, Ar* = C6H2(CHPh2)2Me-2,6,4, Ar† = C6H2(CHPh2)2Pri-2,6,4. Four of these were deprotonated with LiBun in diethyl ether to give lithium aminopyridinate complexes which were dimeric for the least bulky ligand, [{Li(AmPy1)}2] or monomeric for the bulkier aminopyridinates, i.e., in [Li(AmPy2−4)(OEt2)]. One aminopyridine was deprotonated with MeMgI to give monomeric [Mg(AmPy3)I(OEt2)2]. When treated with sodium or potassium mirrors or 5% w/w Na/NaCl, over-reduction occurred, leading to the alkali metal aminopyridinates, [M(AmPy3)(η6-toluene)] (M = Na or K) or [{Na(AmPy3)}∞]. An attempted reduction of [Mg(AmPy3)I(OEt2)2] with a dimagnesium(I) compound led only to partial loss of diethyl ether and the formation of [(AmPy3)Mg(μ-I)2Mg(AmPy3)(OEt2)]. All prepared complexes have potential as ligand transfer reagents in salt metathesis reactions with metal halide complexes.

1. Introduction

The chemistry of low-oxidation-state main-group complexes has seen rapid advances over the past two decades, regularly giving rise to new compound types that would previously have been thought to be incapable of ambient existence. Much of the success in this field derives from the development of numerous very bulky N-donor anionic ligand types that kinetically stabilize coordinated low-oxidation-state metal centres against undergoing disproportionation reactions [1,2,3,4,5,6,7,8,9]. The majority of such ligands are bi- or polydentate, which further provides thermodynamic stability to chelated metal centres. Of the many ligand types developed, mono-anionic N,N-donors, including β-diketiminates [RC(RCNR)2]− [10], amidinates [RC(NR)2]− [11], and guanidinates [R2NC(NR)2]− [12] (R = H, alkyl, aryl, silyl etc.), have been the most widely employed.
Although closely related to amidinates, aminopyridinate ligands, [(C5R4N)NR-2]−, have rarely been used to stabilize low-oxidation-state main-group compounds. This is perhaps surprising, considering that this ligand class has been widely applied in the preparation of low-oxidation-state d- and f-block metal compounds. These compounds, and their “normal” oxidation-state counterparts, have found numerous applications in synthesis, catalysis, and materials chemistry [13,14,15]. In order to stabilize low-oxidation-state d-block compounds, a variety of bulky aminopyridinate ligands have been developed, primarily from the group of Kempe [15,16]. These typically have bulky aryl groups installed at the amino N-centre and at the 6-position of the pyridine. As far as we are aware, the bulkiest of such aminopyridinates is I (Figure 1), which is substituted by Trip (2,4,6-triisopropylphenyl) and Dip (2,6-diisopropylphenyl) groups [16]. Its complexes can exhibit a degree of electronic delocalization over the NCN fragment, as is the case for related amidinate ligands. In this study, we report the synthesis of a series of aminopyridinate ligands that are significantly bulkier than I. We also describe the synthesis of a range of groups 1 and 2 metal complexes that have potential as reagents or precursors for the preparation of low-oxidation-state metal complexes.

2. Results and Discussion

At the outset of this study, five extremely bulky aminopyridine pro-ligands, HAmPy1−5, were prepared by variations of the method used to synthesise protonated I (Scheme 1) [16]. That is, 6-aryl-2-bromopyridines II were synthesized by a nickel-catalysed Kumada coupling of 2,6-dibromopyridine with the appropriate aryl Grignard reagent (see Supporting Information for the crystal structure of II; Ar1 = 2,4,6-tricyclohexylphenyl, TCHP). Subsequent palladium-catalysed couplings of II with bulky anilines afforded the desired aminopyridine in high isolated yields. Using this approach, aminopyridines which were substituted with combinations of four very bulky aryl groups were accessed.
All HAmPy1−5 compounds are thermally stable colourless solids. Their NMR spectra are fully consistent with their proposed structures. The crystal structure of one example, HAmPy3, was obtained, and its molecular structure is depicted in Figure 2. This shows it to be monomeric, with a localized exocyclic N-Cpy single bond. It is clear that the extremely large N-aryl substituent (viz. Ar†, C6H2(CHPh2)2Pri-2,6,4) makes this ligand significantly bulkier than the protonated version of I. Accordingly, the deprotonated aminopyridinate counterparts of HAmPy1−5 should provide a high degree of steric shielding to N,N-coordinated metal centres.
To assess the possibility of deprotonating the aminopyridines, ether solutions of the HAmPy1−4 compounds were treated with LiBun at 0 °C, then the reaction solutions were warmed to room temperature. The removal of volatiles in vacuo, followed by the recrystallization of the residues from hexane, afforded the lithium aminopyridinates 1–4 in high isolated yields as colourless crystalline solids (Scheme 2). Interestingly, compounds 2–4 are ether-coordinated monomers, while compound 1 is an amido N-bridged dimer. It seems likely that these differences arise from the seemingly lower steric bulk of the aminopyridinate ligand in 1, compared to those in 2–4. Despite these differences, compounds 1–4 all have the potential to act as ligand transfer reagents in salt metathesis reactions with main-group metal halide complexes. This is a typical pathway to β-diketiminato, amidinato, and guanidinato main-group metal halide complexes, which can act as precursors to low-oxidation-state systems via reduction processes [1,2,3,4,5,6,7,8,9].
The solution-state NMR spectra for compounds 1–4 are reminiscent of their solid-state structures, which, for 1 and 4, are depicted in Figure 3. Compounds 2 and 3 are structurally analogous to 4, so their molecular structures can be found in the Supporting Information. Relevant metrical parameters for all the Li aminopyridinate complexes are compiled in Table 1. As alluded to above, compound 1 is a dimer which associates through N-centres which bridge three-coordinate N,N-chelated Li atoms that exhibit heavily distorted T-shaped geometries. Related structurally characterized dimeric Li aminopyridinates have been previously reported, but only where the aminopyridinate ligand is less bulky and the Li atoms are further coordinated by Lewis bases, e.g., as in [{(C5H3N-6-Me)N(SiMe3)Li(OEt2)}2] [17]. Compounds 2–4 are monomeric, with the Li atoms N,N-chelated by the aminopyridinate ligand, while additionally being ligated by a molecule of diethyl ether. This gives rise to a distorted trigonal planar geometry for the metal in each case. A lithium complex of aminopyridinate I, viz. [Li(κ2-N,N-I)(OEt2)], has been reported to have an analogous monomeric structure [16]. In all complexes 1–4, the Li-Namide and Li-Npy distances are similar, while the Cpy-Namide distance is shorter than that for a normal single bond. This is suggestive of a degree of electronic delocalization over the NCN fragment, as has been described for other Li aminopyridinate compounds, e.g., [Li(κ2-N,N-I)(OEt2)] [16].
In the next phase of this study, we sought to prepare a bulky aminopyridinato magnesium iodide complex, which could potentially be reduced to give a bulky aminopyridinate stabilized dimagnesium(I) compound, “(AmPy3)Mg-Mg(AmPy3)”. Although such compounds are unknown, we have previously described a similar reductive synthesis of a closely related guanidinato dimagnesium(I) system [18]. With that said, and with a view to form dimagnesium(I) compounds, reductions of aminopyridinato magnesium halides have been previously attempted, but these were not successful, perhaps because the aminopyridinate ligands involved were less bulky than those reported here [19]. The pro-ligand we chose for this study was HAmPy3, which was readily deprotonated in its reaction with ethereal solutions of MeMgI. This gave rise to a high yield (86%) of aminopyridinato magnesium iodide complex 5 as a colourless solid (Scheme 3).
The solution-state NMR spectroscopic data for 5 reflect its structure in the solid state. The molecular structure of the compound (Figure 4) shows it to be monomeric, with the Mg centre being chelated by the aminopyridinate ligand, while also being ligated by two diethyl ether molecules. The distorted trigonal bipyramidal coordination sphere is completed by a terminal iodide. It should be noted that, although the final r-factors for the crystal structure are acceptable, the reflection data completeness is low (84.2% to a resolution of 0.833 Å; Cu Kα radiation; see Table S1). This arises due to the crystal of the compound slowly decomposing during the X-ray data collection. Despite this, the molecular connectivity of the molecule is unambiguous. There are only three previously structurally characterized aminopyridinato magnesium halides, and none of those are ether-coordinated monomers [19,20]. An examination of the N-Mg and Cpy-Namide distances in the compound indicate that, like in 1–4, there is a degree of delocalization over the NCN moiety, but this is seemingly less than in those lithium complexes.
With compound 5 in hand, we explored its reduction, as a toluene solution, using sodium or potassium mirrors, 5% w/w Na/NaCl [21], or the dimagnesium(I) compound, [{(MesNacNac)Mg}2] (MesNacNac = [{(Mes)NC(Me)}2CH)]−, Mes = mesityl) [22]. In all of the reactions with the alkali metals, over-reduction occurred, leading to high yields of the sodium and potassium aminopyridinate complexes 6–8 (Scheme 3), with an accompanying black precipitate, which was presumably magnesium metal. At this stage, it is unsure why the reaction with a sodium mirror in toluene gave toluene-free 6, while the almost equivalent reaction with 5% w/w Na/NaCl gave toluene-coordinated 7. No reduction of 5 with [{(MesNacNac)Mg}2] occurred, although, as the reaction was carried out in toluene, a partial loss of diethyl ether from 5 led to the isolation of a few colourless crystals of the iodide-bridged dinuclear system, [(AmPy3)Mg(μ-I)2Mg(AmPy3)(OEt2)] 9. Like the lithium aminopyridinates, compounds 6–8 have potential for use as ligand transfer reagents in salt metathesis reactions with metal halide complexes.
The solid-state structures of compounds 6–8 were determined, and the molecular structures of 6 and 8 can be found in Figure 5. As compound 7 is structurally analogous to 8, its molecular structure can be found in the Supporting Information. Compound 6 is polymeric, with the Na centre of each monomer unit being N,N-chelated by the ligand while, at the same time, having an intramolecular η3-interaction with one of the flanking phenyl groups of the Ar† fragment. The polymer is assembled through η2-interactions between the sodium centres and a different flanking phenyl group of another monomer unit. The Na-Namide distance is significantly shorter than the Na-Npy separation, which may indicate a lesser degree of electronic delocalization over the NCN fragment than that in the lithium aminopyridinates. The structure of 8 (and 7) is similar, in that the metal centre is N,N-chelated by the ligand and has an intramolecular η3-interaction with a Ar† phenyl group. However, instead of forming a polymer, the coordination sphere of the potassium atom is satisfied by η6-coordination to a molecule of toluene.
The magnesium iodide complex 9 is dinuclear in the solid state, with two N,N-chelated magnesium atoms connected through iodide bridges (Figure 6). One of the magnesium centres, Mg(1), is further coordinated by a molecule of diethyl ether, giving it a heavily distorted trigonal bipyramidal geometry, while the other, Mg(2) is ether-free and has a distorted tetrahedral environment. All of the N-Mg bonds are of a similar length, which, in combination with the short C-Namid distance, indicates electronic delocalization over the NCN fragments, as is the case with the mononuclear species 5. The structure of the compound is comparable to those of several previously reported halide-bridged diethyl-ether-coordinated magnesium aminopyridinate complexes [19].

3. Materials and Methods

3.1. General Considerations

All manipulations were carried out using standard Schlenk and glove box techniques under an atmosphere of high-purity dinitrogen. Toluene, THF, and hexane were distilled over molten potassium, while diethyl ether was distilled over 1:1 Na/K alloy. Benzene-d6 was stored over a mirror of sodium and degassed three times via freeze-pump-thawing before use. The 1H, 13C{1H}, and 7Li NMR spectra were recorded on a Bruker AvanceIII 600 spectrometer and were referenced to the residual resonances of the solvent used or external 1 M LiCl. Mass spectra were collected using an Agilent Technologies 5975D inert MSD with a solid-state probe. FTIR spectra were collected as Nujol mulls on an Agilent Cary 630 attenuated total reflectance (ATR) spectrometer. Microanalyses were carried out at the Science Centre, London Metropolitan University. Melting points were determined in sealed glass capillaries under dinitrogen and are uncorrected. The starting materials, 6-Trip-2-Br-pyridine [16], (TCHP)MgBr [23], (TCHP)NH2 [24], Ar*NH2 [25], Ar†NH2 [26], 5% w/w Na/NaCl [21], and [{(MesNacNac)Mg}2] [22], were prepared by procedures detailed in the literature. All other reagents were used as received from Sigma-Aldrich, St Lois, MO, USA.

3.2. Syntheses of New Complexes

Preparation of 6-TCHP-2-bromopyridine, II (Ar1 = TCHP). 2,6-Dibromopyridine (7.91 g, 33.4 mmol), THF (35 mL), tricyclohexylphosphine (0.021 g, 0.075 mmol), and [(DME)NiBr2] (0.012 g, 0.0375 mmol) were added to a Schlenk flask under dinitrogen. A diethyl ether solution of (TCHP) MgBr (35.2 mmol) was then added to the stirred suspension, resulting in a beige precipitate. The reaction mixture was then heated at reflux for three days. Water (50 mL) and CHCl3 (50 mL) were then added carefully to the reaction mixture, and the resultant suspension transferred to a separating funnel. The organic phase was collected, and the residue was extracted with CHCl3 (80 mL). The combined organic phases were washed with brine (50 mL) and dried over Na2SO4. Volatiles were removed in vacuo to afford a white precipitate, which was recrystallised from hexane at –30 °C to give II as a colourless crystalline solid. Yield, 9.62 g (60%). M.p.: >260 °C; 1H NMR (benzene-d6, 600 MHz, 298 K): δ 1.01–2.57 (m, 33H, Cy-H), 6.73 (t, 1H, J = 7.6 Hz, pyAr-H), 6.90 (dd, 1H, J = 7.4, 0.8 Hz, pyAr-H), 6.98 (dd, 1H, J = 7.8, 0.8 Hz, pyAr-H), 7.22 (s, 2H, Ar-H); 13C{1H} NMR (benzene-d6, 151 MHz, 298 K): δ 26.3, 26.4, 27.0, 27.2, 34.6, 34.7, 34.9, 41.9, 45.3 (Cy-C), 120.2, 123.8, 125.7, 135.7, 137.5, 141.8, 145.7, 148.4, 148.4, 161.8 (pyAr-C, Ar-C); IR (ATR) ν (cm−1) = 1035 (m), 986 (s), 953 (m), 893 (m), 863 (s), 846 (m), 809 (vs), 782 (vs), 769 (vs), 752 (s), 677 (s); Acc. mass calc. for C29H38BrN (MH+): 480.2188; found: 480.2262.
Preparation of HAmPy1. Compound II (Ar1 = Trip) (2.75 g, 7.63 mmol), 1,3-bis(diphenylphosphino)propane (0.12 g, 0.28 mmol), [Pd2(dba)3] (0.13 g, 0.14 mmol), and sodium tert-butoxide (0.830 g, 8.6 mmol) were added to a Schlenk flask. After the addition of a toluene (30 mL) solution of (TCHP)NH2 (2.606 g, 7.63 mmol) to the flask, the resultant mixture was heated at 95 °C for 72 h. The reaction mixture was then cooled to room temperature, and water (50 mL) and diethyl ether (50 mL) were added. The organic phase was separated, and the remaining residue was extracted with diethyl ether (60 mL). The combined organic phases were washed with brine (50 mL) and dried over Na2SO4. Volatiles were removed under reduced pressure. The resulting red solid was purified by column chromatography (SiO2/CH2Cl2) to give the title compound as a colourless solid. Yield, 3.00 g (65%). M.p.: 230–233 °C; 1H NMR (benzene-d6, 600 MHz, 298 K): δ 1.16–1.26 (m, 5H, Cy-H), 1.27 (d, 6H, J = 7.0 Hz, CH(CH3)2), 1.31 (d, 6H, J = 7.0 Hz, CH(CH3)2), 1.32–1.37 (m, 5H, Cy-H), 1.40 (d, 6H, J = 7.0 Hz, CH(CH3)2), 1.51–1.85 (m, 18H, Cy-H), 1.98–2.01 (m, 2H, Cy-H), 2.53–2.58 (m, 1H, Cy-H), 2.90 (sept, 1H, J = 7.0 Hz, CH(CH3)2), 3.02–3.06 (m, 2H, Cy-H), 3.10 (sept, 2H, J = 7.0 Hz, CH(CH3)2), 5.88–5.90 (m, 1H, pyAr-H), 5.98 (br s, 1H, NH), 6.54 (dd, 1H, J = 7.2, 0.8 Hz, pyAr-H), 6.93–6.97 (m, 1H, pyAr-H), 7.21 (s, 2H, Ar-H), 7.27 (s, 2H, Ar-H); 13C{1H} NMR (benzene-d6, 151 MHz, 298 K): δ 24.5, 24.5, 24.8, 24.9 (CH(CH3)2), 26.6, 26.7, 27.4 (Cy-C), 30.9 (CH(CH3)2), 30.9 (Cy-C), 35.0 (CH(CH3)2), 35.1, 39.9, 39.9, 45.3 (Cy-C), 103.5, 115.1, 115.1, 120.8, 123.5, 128.3, 132.8, 137.4, 138.0, 146.7, 147.2, 147.6, 148.6, 159.4, 160.0 (pyAr-C, Ar-C); IR (ATR) ν (cm−1) = 3398 (w, NH), 1584 (s), 1571 (vs), 1065 (m), 985 (m), 879 (s), 865 (m), 804 (s), 753 (m), 733 (s), 697 (m), 662 (m); Acc. mass calc. for C44H62N2 (MH+): 619.4913; found: 619.4977.
Preparation of HAmPy2. The compound was prepared by a similar procedure used for HAmPy1, but using II (Ar1 = Trip) (2.75 g, 7.63 mmol) and Ar*NH2 (3.35 g, 7.63 mmol). Yield, 2.97 g (55%). M.p.: >260 °C; 1H NMR (benzene-d6, 600 MHz, 298 K): δ 1.25 (d, 6H, J = 7.0 Hz, CH(CH3)2), 1.27–1.28 (m, 6H, CH(CH3)2), 1.31 (d, 6H, J = 7.0 Hz, CH(CH3)2), 1.89 (s, 3H, CH3), 2.90 (sept, 1H, J = 7.0 Hz, CH(CH3)2), 3.02 (sept, 2H, J = 7.0 Hz, CH(CH3)2), 5.55 (br s, 1H, NH), 5.80 (d, 1H, J = 8.3 Hz, pyAr-H), 5.92 (s, 2H, CHPh2), 6.51–6.53 (m, 1H, pyAr-H), 6.92–7.23 (m, 25H, Ar-H, pyAr-H); 13C{1H} NMR (benzene-d6, 151 MHz, 298 K): δ 21.4 (CH3), 24.4, 24.5, 24.8 (CH(CH3)2), 30.9, 35.0 (CH(CH3)2), 52.9 (CHPh2), 103.1, 115.2, 116.0, 120.8, 126.6, 128.0, 128.3, 128.6, 130.0, 134.7, 137.1, 138.0, 143.6, 145.2, 146.7, 148.6, 158.0, 159.4 (pyAr-C, Ar-C); IR (ATR) ν (cm−1) = 3403 (w, NH), 1078 (m), 1032 (m), 986 (m), 879 (m), 796 (m), 765 (m), 742 (s), 697 (vs); Acc. mass calc. for C53H54N2 (MH+): 719.4287; found: 719.4358.
Preparation of HAmPy3. The compound was prepared by a similar procedure used for HAmPy1, but using II (Ar1 = Trip) (2.75 g, 7.63 mmol) and Ar†NH2 (3.56 g, 7.63 mmol). Yield, 3.42 g (60%). M.p.: 250–255 °C; 1H NMR (benzene-d6, 600 MHz, 298 K): δ 1.26 (d, 6H, J = 7.0 Hz, CH(CH3)2), 1.31 (d, 6H, J = 7.0 Hz, CH(CH3)2), 2.49 (sept, 1H, J = 7.1 Hz, CH(CH3)2), 2.90 (sept, 1H, J = 7.0 Hz, CH(CH3)2), 3.02 (sept, 2H, J = 7.1 Hz, CH(CH3)2), 5.56 (br s, 1H, NH), 5.80–5.82 (m, 1H, pyAr-H), 5.94 (s, 2H, CHPh2), 6.51–6.54 (m, 1H, pyAr-H), 6.90–6.93 (m, 1H, pyAr-H), 6.98–7.23 (m, 24H, Ar-H); 13C{1H} NMR (benzene-d6, 151 MHz, 298 K): δ 24.0, 24.4, 24.5, 24.8 (CH(CH3)2), 30.9, 34.2, 35.0 (CH(CH3)2), 53.1 (CHPh2), 103.2, 115.2, 120.8, 126.6, 127.3, 128.6, 129.9, 135.0, 137.1, 137.8, 143.7, 145.0, 146.7, 147.9, 148.6, 157.9, 159.3 (pyAr-C, Ar-C); IR (ATR) ν (cm−1) = 3396 (w, NH), 1099 (m), 1072 (m), 1030 (m), 984 (m), 876 (m), 796 (s), 760 (m), 741 (s), 696 (vs); acc. mass calc. for C55H58N2 (MH+): 747.4600; found: 747.4657.
Preparation of HAmPy4. The compound was prepared by a similar procedure used for HAmPy1, but using II (Ar1 = TCHP) (3.66 g, 7.63 mmol) and Ar*NH2 (3.35 g, 7.63 mmol). Yield, 3.20 g (50%).
M.p.: 250–260 °C; 1H NMR (benzene-d6, 600 MHz, 298 K): δ 1.17–2.64 (m, 33H, Cy-H), 1.91 (s, 3H, CH3), 5.67 (br s, 1H, NH), 5.87 (d, 1H, J = 9.0 Hz, pyAr-H), 5.99 (s, 2H, CHPh2), 6.58 (d, 1H, J = 7.2 Hz, pyAr-H), 6.93–6.98 (m, 1H, pyAr-H), 6.99–7.25 (m, 24H, Ar-H); 13C{1H} NMR (benzene-d6, 151 MHz, 298 K): δ 21.4 (CH3), 26.7, 27.5, 27.6, 27.7, 35.0, 35.0, 35.2, 41.9, 45.6 (Cy-C), 52.8 (CHPh2), 115.5, 122.1, 126.7, 128.7, 129.9, 135.1, 137.3, 138.3, 143.6, 145.3, 145.7, 147.6, 158.6, 159.8 (pyAr-C, Ar-C); IR (ATR) ν (cm−1) = 3393 (w, NH), 1076 (m), 1031 (m), 860 (m), 800 (m), 745 (s), 698 (vs); Acc. mass calc. for C62H66N2 (MH+): 839.5226; found: 839.5302.
Preparation of HAmPy5. The compound was prepared by a similar procedure used for HAmPy1, but using II (Ar1 = TCHP) (3.66 g, 7.63 mmol) and Ar†NH2 (3.56 g, 7.63 mmol). Yield, 3.30 g (50%).
M.p.: 250–260 °C; 1H NMR (benzene-d6, 600 MHz, 298 K): δ 0.99 (d, 6H, J = 7.0 Hz, CH(CH3)2), 1.17–2.62 (m, 33H, Cy-H), 2.52 (sept, 1H, J = 6.8 Hz, CH(CH3)2), 5.69 (br s, 1H, NH), 5.89 (d, 1H, J = 8.2 Hz, pyAr-H), 6.01 (s, 2H, CHPh2), 6.57 (d, 1H, J = 7.0 Hz, pyAr-H), 6.96 (m, 1H, pyAr-H), 7.00–7.25 (m, 24H, Ar-H); 13C{1H} NMR (benzene-d6, 151 MHz, 298 K): δ 24.1 (CH(CH3)2), 26.7, 27.5, 27.6, 27.7 (Cy-C), 34.2 (CH(CH3)2), 34.9, 35.0, 35.2, 41.9, 45.6 (Cy-C), 53.0 (CHPh2), 103.4, 115.5, 122.1, 126.7, 127.3, 128.4, 128.6, 128.7, 129.8, 130.0, 135.3, 137.3, 138.3, 143.5, 143.7, 145.2, 145.7, 147.5, 148.1, 158.6, 159.8 (pyAr-C, Ar-C); IR (ATR) ν (cm−1) = 3396 (w, NH), 1033 (m), 985 (m), 862 (m), 800 (m), 746 (m), 699 (vs); Acc. mass calc. for C64H70N2 (MH+): 867.5539; found: 867.5603.
Preparation of [{Li(AmPy1)}2], 1. LiBun in n-hexane (0.63 mL, 1.6 M, 1.0 mmol) was slowly added to a stirred solution of HAmPy1 (0.62 g, 1.0 mmol) in diethyl ether (30 mL) at 0 °C. After complete addition, the mixture was stirred and warmed slowly to room temperature over 2 h. The reaction mixture was then reduced to dryness under vacuum and the residue was extracted with hexane (20 mL). The solvent volume was then reduced to 10 mL in vacuo. Upon standing overnight, colourless crystals of 1 were obtained. Yield, 0.56 g (90%). M.p.: 250–255 °C; 1H NMR (toluene-d8, 600 MHz, 298 K): δ 1.22–2.98 (m, 33H, Cy-H), 1.25 (d, 6H, J = 7.0 Hz, CH(CH3)2), 1.30 (d, 6H, J = 7.0 Hz, CH(CH3)2), 1.37 (d, 6H, J = 7.0 Hz, CH(CH3)2), 2.89 (sept, 1H, J = 7.0 Hz, CH(CH3)2), 3.04 (sept, 2H, J = 7.0 Hz, CH(CH3)2), 5.80–5.84 (m, 1H, pyAr-H), 5.86 (d, 1H, J = 8.0 Hz, pyAr-H), 6.49 (d, 1H, J = 7.0 Hz, pyAr-H), 7.17 (s, 2H, Ar-H), 7.21 (s, 2H, Ar-H); 13C{1H} NMR (toluene-d8, 151 MHz, 298 K): δ 24.4, 24.5, 24.8 (CH(CH3)2), 26.6, 26.7, 27.4, 27.5 (Cy-C), 30.9 (CH(CH3)2), 35.0 (Cy-C), 35.1 (CH(CH3)2), 39.9, 45.3 (Cy-C), 103.4, 115.0, 120.7, 123.3, 124.7, 127.6, 128.3, 128.6, 132.7, 137.3, 138.1, 146.6, 147.0, 147.5, 148.4, 159.4, 160.0 (pyAr-C, Ar-C); IR (ATR) ν (cm−1) = 1154 (m), 1117 (m), 1075 (m), 1031 (m), 984 (m), 876 (m), 799 (m), 747 (m), 698 (vs). N.B. A reproducible microanalysis could not be obtained for this compound due to its high air and moisture sensitivity.
Preparation of [Li(AmPy2)(OEt2)], 2. LiBun in n-hexane (0.63 mL, 1.6 M, 1.0 mmol) was slowly added to a stirred solution of HAmPy2 (0.72 g, 1.0 mmol) in diethyl ether (30 mL) at 0 °C. After complete addition, the mixture was stirred and warmed slowly to room temperature over 2 h. The reaction mixture was reduced to dryness under vacuum and the residue was extracted with hexane (20 mL). The solvent volume was reduced to 10 mL. Upon standing overnight, colourless crystals of 2 were obtained. Yield, 0.68 g (85%). M.p.: 220–225 °C; 1H NMR (benzene-d6, 600 MHz, 298 K): δ 0.43 (t, 6H, J = 7.0 Hz, OCH2CH3), 1.25–1.28 (m, 18H, CH(CH3)2), 2.08 (s, 3H, CH3), 2.64 (q, 4H, J = 7.0 Hz, OCH2CH3), 2.84 (sept, 1H, J = 7.0 Hz, CH(CH3)2), 3.25 (sept, 2H, J = 7.0 Hz, CH(CH3)2), 5.74 (dd, 1H, J = 8.6 Hz, 0.8 Hz, pyAr-H), 5.96 (dd, 1H, J = 6.8 Hz, 0.8 Hz, pyAr-H), 6.05 (s, 2H, CHPh2), 6.92–7.31 (m, 25H, pyAr-H, Ar-H); 13C{1H} NMR (benzene-d6, 151 MHz, 298 K): δ 14.1 (OCH2CH3), 21.5 (CH3), 24.6, 24.8, 25.0 (CH(CH3)2), 30.6, 34.9 (CH(CH3)2), 53.0 (CH(Ph)2), 65.9 (OCH2CH3), 103.4, 105.3, 120.4, 125.7, 126.1, 127.9, 128.1, 128.2, 128.4, 128.4, 129.5, 129.6, 129.9, 130.5, 137.6, 139.2, 140.1, 145.2, 146.1, 146.7, 147.8, 147.9, 156.8, 167.6 (pyAr-C, Ar-C); 7Li NMR (benzene-d6, 155 MHz, 298 K): δ 0.70; IR (ATR) ν (cm−1) = 1155 (m), 1067 (m), 1031 (m), 990 (m), 786 (m), 764 (m), 740 (m), 698 (vs). N.B. A reproducible microanalysis could not be obtained for this compound due to its high air and moisture sensitivity.
Preparation of [Li(AmPy3)(OEt2)], 3. This compound was prepared by a similar procedure used for 2, but using HAmPy3 (0.75 g, 1.0 mmol). Yield, 0.78 g (95%). M.p.: 235–240 °C; 1H NMR (benzene-d6, 600 MHz, 298 K): δ 0.46 (t, 6H, J = 7.2 Hz, OCH2CH3), 1.10 (d, 6H, J = 7.0 Hz, CH(CH3)2), 1.25–1.29 (m, 18H, CH(CH3)2), 2.64 (sept, 1H, J = 7.0 Hz, CH(CH3)2), 2.67 (q, 4H, J = 7.2 Hz, OCH2CH3), 2.84 (sept, 1H, J = 7.0 Hz, CH(CH3)2), 3.25 (sept, 2H, J = 7.0 Hz, CH(CH3)2), 5.67 (dd, 1H, J = 8.6 Hz, 0.9 Hz, pyAr-H), 5.95 (dd, 1H, J = 7.0 Hz, 0.9 Hz, pyAr-H), 6.06 (s, 2H, CHPh2), 6.88 (dd, 1H, J = 9.7 Hz, 6.8 Hz, pyAr-H), 6.94–7.35 (m, 24H, Ar-H); 13C{1H} NMR (benzene-d6, 151 MHz, 298K): δ 14.2 (OCH2CH3), 24.6, 24.6, 24.8, 25.0 (CH(CH3)2), 30.6, 34.1, 34.9 (CH(CH3)2), 53.2 (CHPh2), 65.9 (OCH2CH3), 103.6, 105.3, 120.3, 125.6, 126.1, 126.7, 128.3, 128.4, 128.4, 128.7, 129.6, 130.0, 130.5, 137.5, 139.2, 139.9, 140.9, 143.5, 145.3, 146.3, 146.7, 147.9, 148.2, 156.8, 167.6 (pyAr-C, Ar-C). 7Li NMR (benzene-d6, 155 MHz, 298 K): δ 0.79; IR (ATR) ν (cm−1) = 1154 (m), 1076 (m), 1031 (m), 991 (m), 784 (m), 737 (m), 699 (vs). N.B. A reproducible microanalysis could not be obtained for this compound due to its high air and moisture sensitivity.
Preparation of [Li(AmPy4)(OEt2)], 4. This compound was prepared by a similar procedure used for 2, but using HAmPy4 (0.84 g, 1.0 mmol). Yield, 0.73 g (80%). M.p.: 240–242 °C; 1H NMR (benzene-d6, 600 MHz, 298 K): δ 0.60 (br t, 6H, OCH2CH3), 1.18–2.82 (m, 33H, Cy-H), 2.08 (s, 3H, CH3), 2.81 (br q, 4H, OCH2CH3), 5.89 (d, 1H, J = 8.6 Hz, pyAr-H), 6.03 (d, 1H, J = 6.8 Hz, pyAr-H), 6.13 (s, 2H, CH(Ph)2), 6.93–7.13 (m, 25H, pyAr-H, Ar-H); 13C{1H} NMR (benzene-d6, 151 MHz, 298 K): δ 14.5 (OCH2CH3), 21.5 (CH3), 26.6, 26.7, 27.5, 27.8, 35.3, 35.3, 35.6, 41.5, 45.5 (Cy-C), 52.6 (CHPh2), 65.9 (OCH2CH3), 103.8, 105.6, 121.8, 125.6, 126.2, 128.3, 128.5, 129.5, 129.6, 130.5, 137.8, 139.6, 139.7, 145.7, 145.7, 146.4, 146.8, 147.9, 157.3, 168.0 (pyAr-C, Ar-C). 7Li NMR (benzene-d6, 155 MHz, 298 K): δ 0.82; IR (ATR) ν (cm−1) = 1154 (m), 1076 (m), 1032 (m), 990 (m), 863 (m), 787 (m), 699 (vs). N.B. A reproducible microanalysis could not be obtained for this compound due to its high air and moisture sensitivity.
Preparation of [Mg(AmPy3)I(OEt2)2], 5. A 1M solution of MeMgI in diethyl ether (0.5 mL, 0.5 mmol) was added to a stirred solution of HAmPy3 (373 mg, 0.50 mmol) in diethyl ether (10 mL) at –78 °C over a period of 5 min. A colourless precipitate immediately formed. The resultant suspension was warmed to room temperature and stirred for 2 h. The white precipitate of 5 was collected by filtration. The supernatant solution was concentrated and then cooled to –30 °C overnight to give a second crop of 5. Yield, 432 mg (85%). M.p. 250–252 °C; 1H NMR (600 MHz, benzene-d6, 298 K): δ 0.90 (br t, 6H, OCH2CH3), 1.09 (d, 6H, J = 6.8 Hz, CH(CH3)2), 1.18 (d, 6H, J = 6.8 Hz, CH(CH3)2), 1.23 (d, 6H, J = 6.8 Hz, CH(CH3)2), 1.46 (d, 6H, J = 6.8 Hz, CH(CH3)2), 2.63 (sept, 1H, J = 6.8 Hz, CH(CH3)2), 2.81 (sept, 1H, J = 6.8 Hz, CH(CH3)2), 3.06 (sept, 2H, J = 6.8, CH(CH3)2), 3.17 (br q, 4H, OCH2CH3), 4.67 (d, 1H, J = 8.6 Hz, PyAr-H), 5.72 (d, 1H, J = 6.9 Hz, pyAr-H), 6.12–6.17 (m, 1H, pyAr-H), 6.61 (s, 2H, CHPh2) 6.94–7.44 (m, 24H, Ar-H); 13C{1H} NMR (151 MHz, benzene-d6, 298 K): δ 14.7 (OCH2CH3), 24.1, 24.4, 24.4, 26.3 (CH(CH3)2), 30.4, 34.1, 34.9 (CH(CH3)2), 52.4 (CHPh2), 66.8 (OCH2CH3), 106.7, 109.0, 120.8, 126.1, 126.1, 130.2, 130.4, 136.4, 136.9, 141.6, 144.2, 145.8, 147.0, 149.3, 153.9, 168.9 (pyAr-C, Ar-C). ATR-IR: ν = 1031 (m), 798 (m), 743 (m), 695 (vs); MS (EI, 70 eV): m/z (%, fragment) = 746.6 (35.77, [HAmPy3]+). A reproducible microanalysis could not be obtained for this compound due to its air and moisture sensitivity, and the fact that it readily loses diethyl ether of crystallization.
Preparation of [{Na(AmPy3)}∞], 6. A solution of 5 (1.0 g, 1 mmol) in toluene (20 mL) and diethyl ether (1 mL) was stirred vigorously for 3 days over a sodium mirror (230 mg, 10 mmol) at room temperature. The resultant yellowish suspension was filtered, and the filtrate was concentrated under reduced pressure. Subsequent slow cooling to –30 °C over a period of 24 h provided 6 as colourless crystals. Yield, 653 mg (86%). M.p. 245–250 °C; 1H NMR (600 MHz, benzene-d6, 298 K): δ 0.96 (d, 6H, J = 6.8 Hz, CH(CH3)2), 1.25 (d, 12H, J = 6.8 Hz, CH(CH3)2), 1.31 (d, 6H, J = 6.8 Hz, CH(CH3)2), 2.49 (sept, 1H, J = 7.0 Hz, CH(CH3)2), 2.90 (sept, 1H, J = 7.0 Hz, CH(CH3)2), 3.01 (sept, 2H, J = 7.0 Hz, CH(CH3)2), 5.81 (d, 1H, J = 8.2 Hz, pyAr-H), 5.94 (s, 2H, CHPh2), 6.52 (d, 1H, J = 6.8 Hz, pyAr-H), 6.91 (t, 1H, J = 7.4 Hz, pyAr-H) 6.98–7.23 (m, 24H, Ar-H); 13C{1H} NMR (151 MHz, benzene-d6, 298K): δ 24.1, 24.4, 24.5, 24.8 (CH(CH3)2), 30.9, 34.2, 35.0 (CH(CH3)2), 53.1 (CHPh2), 103.2, 115.2, 120.8, 125.7, 126.6, 127.3, 128.6, 128.6, 129.9, 135.1, 137.1, 137.8, 143.7, 145.1, 146.7, 147.9, 148.6, 157.9, 159.4 (pyAr-C, Ar-C). ATR-IR: ν = 1097 (m), 1072 (m), 1030 (m), 876 (m), 834 (m), 796 (s), 741 (m), 696 (vs); MS (EI, 70 eV): m/z (%, fragment) = 746.6 (30.66, [HAmPy3]+). A reproducible microanalysis could not be obtained for this compound due to its air and moisture sensitivity, and the fact that it readily loses toluene of crystallization.
Preparation of [Na(AmPy3)(toluene)], 7. A solution of 5 (1.0 g, 1 mmol) in toluene (20 mL) and diethyl ether (1 mL) was transferred to a Schlenk flask containing a suspension of 5% w/w Na/NaCl (4.60 g, 10 mmol Na) in 10 mL of toluene, then the mixture was stirred for 3 days. The resultant yellowish suspension was filtered, and the filtrate was concentrated under reduced pressure. Subsequent slow cooling to –30 °C over 24 h provided compound 7 as colourless crystals. Yield, 727 mg (84%). M.p. 247–250 °C; 1H NMR (600 MHz, benzene-d6, 298 K): δ 1.08 (d, 6H, J = 6.8 Hz, CH(CH3)2), 1.24–1.26 (m, 12H, CH(CH3)2), 1.27 (d, 6H, J = 6.8 Hz, CH(CH3)2), 2.11 (s, 6H, toluene-CH3), 2.62 (sept, 1H, J = 7.0 Hz, CH(CH3)2), 2.85 (sept, 1H, J = 7.0 Hz, CH(CH3)2), 3.26 (sept, 2H, J = 7.0 Hz, CH(CH3)2), 5.77 (s, 2H, CHPh2), 6.00–6.05 (m, 2H, pyAr-H), 6.68 (t, 1H, J = 7.2 Hz, pyAr-H), 6.86–7.27 (m, 34H, Ar-H); 13C{1H} NMR (151 MHz, benzene-d6, 298 K): δ 21.5 (toluene-CH3), 24.6, 24.7, 25.0, 25.2 (CH(CH3)2), 30.5, 34.2, 35.0 (CH(CH3)2), 53.8 (CHPh2), 103.1, 104.7, 120.5, 124.8, 125.7, 126.2, 126.6, 127.4, 128.3, 128.4, 128.6, 129.3, 129.5, 130.6, 137.1, 137.9, 138.8, 139.8, 140.7, 144.9, 146.7, 147.3, 147.9, 149.0, 158.1, 163.3 (pyAr-C, Ar-C). ATR-IR: ν = 1076 (m), 1030 (m), 984 (m), 875 (m), 767 (m), 742 (s), 697 (vs); MS (EI, 70 eV): m/z (%, fragment) = 746.7 (33.52, [HAmPy3]+). A reproducible microanalysis could not be obtained for this compound due to its air and moisture sensitivity, and the fact that it appears to readily loose toluene of coordination.
Preparation of [K(AmPy3)(toluene)], 8. A solution of 5 (1.0 g, 1 mmol) in toluene (20 mL) and diethyl ether (1 mL) was stirred vigorously for 3 days over a potassium mirror (390 mg, 10 mmol) at room temperature. The resultant reddish suspension was filtered, and the filtrate was concentrated under reduced pressure. Placement at –30 °C for 2 days provided compound 8 as colourless crystals. Yield, 654 mg (75%). M.p. 215–220 °C; 1H NMR (600 MHz, benzene-d6, 298 K) δ = 1.10 (d, 6H, J = 6.8 Hz, CH(CH3)2), 1.25–1.29 (m, 18H, CH(CH3)2), 2.11 (s, 3H, toluene-CH3), 2.64 (sept, 1H, J = 7.0 Hz, CH(CH3)2), 2.87 (sept, 1H, J = 7.0 Hz, CH(CH3)2), 3.32 (sept, 2H, J = 7.0 Hz, CH(CH3)2), 5.81 (s, 2H, CHPh2), 6.00 (d, 1H, J = 6.8 Hz, pyAr-H), 6.13 (d, 1H, J = 8.2 Hz, pyAr-H), 6.61 (t, 1H, J = 7.3 Hz, pyAr-H), 7.01–7.25 (m, 29H, Ar-H); 13C{1H} NMR (151 MHz, benzene-d6, 298K) δ 21.4 (toluene-CH3), 24.7, 24.7, 24.8, 25.6 (CH(CH3)2), 30.6, 34.2, 35.0 (CH(CH3)2), 53.9 (CHPh2), 103.2, 103.7, 120.4, 124.3, 125.7, 126.2, 126.3, 127.2, 128.3, 128.4, 128.6, 129.3, 129.9, 130.6, 136.7, 137.9, 138.2, 138.5, 141.5, 144.8, 146.8, 147.6, 149.3, 149.9, 158.2, 162.6 (pyAr-C, Ar-C); ATR-IR: ν = 1153 (m), 1073 (m), 1031 (m), 983 (m), 875 (m), 797 (m), 741 (s), 696 (vs); MS (EI, 70 eV): m/z (%, fragment) = 746.7 (39.23, [HAmPy3]+). A reproducible microanalysis could not be obtained for this compound due to its air and moisture sensitivity, and the fact that it appears to readily loose toluene of coordination.
Preparation of [(AmPy3)Mg(μ-I)2Mg(AmPy3)(OEt2)], 9. A solution of 5 (500 mg, 0.5 mmol) and [{(MesNacNac)Mg}2] (182 mg, 0.25 mmol) in toluene (20 mL) was stirred overnight at 70 °C, during which time, the initial yellow solution turned red. The reaction mixture was then filtered, and the filtrate was concentrated under reduced pressure. Placement at –30 °C overnight yielded a few colourless crystals of 9. Due to the very low yield of the compound, no spectroscopic data could be obtained.

3.3. Crystallographic Details

Crystals suitable for X-ray structural determination were mounted in silicone oil. Crystallographic measurements were carried out at 123(2) K, and were conducted using a Rigaku Synergy diffractometer using a graphite monochromator with Mo Kα radiation (λ = 0.71073 Å) or Cu Kα radiation (λ = 1.54184 Å). The structures were solved by direct methods and refined on F2 by full-matrix least squares (SHELX16) [27] using all unique data. All non-hydrogen atoms were anisotropic, with hydrogen atoms typically included in calculated positions (riding model). Crystal data, details of the data collection, and refinement are given in Table S1 (in Supplementary Materials).

4. Conclusions

In summary, high-yielding synthetic routes to five new extremely bulky aminopyridine pro-ligands, HAmPy1−5, were developed. Four of these were deprotonated with LiBun in diethyl ether to give lithium aminopyridinate complexes 1–4, which were either dimeric or monomeric, depending on the steric bulk of the ligand involved. These have potential as ligand transfer reagents in salt metathesis reactions with metal halide complexes. One aminopyridine was deprotonated with MeMgI to give a monomeric aminopyridinato magnesium iodide complex, 5. Endeavours to reduce this to a dimagnesium(I) compound with sodium or potassium mirrors or 5% w/w Na/NaCl led to over-reduction and a series of Na or K salts of the aminopyridinate ligand, 6–8. An attempted reduction of the bulky aminopyridinato magnesium iodide system with a dimagnesium(I) compound was not successful, yielding magnesium(II) iodide compound, 9. We continue to explore the use of the bulky aminopyridinates developed in this study for the kinetic stabilization of low-oxidation-state main-group complexes.

Supplementary Materials

The following are available online at https://www.mdpi.com/article/10.3390/inorganics12100270/s1, NMR spectra (Figures S1–S31) and crystallographic data (Table S1 and Figures S32–S35) for new compounds.

Author Contributions

Conceptualization, C.J.; methodology, A.M.E. and C.J.; validation, A.M.E., M.J.E. and C.J.; formal analysis, A.M.E., M.J.E. and C.J.; investigation, A.M.E. and C.J.; writing—original draft preparation, C.J.; writing—review and editing, C.J.; supervision, C.J. and A.P.; project administration, C.J.; funding acquisition, C.J. All authors have read and agreed to the published version of the manuscript.

Funding

CJ is grateful to the Australian Research Council for funding part of this work. Moreover, this material is based upon work supported by the Air Force Office of Scientific Research under award number FA2386-21-1-4048.

Data Availability Statement

NMR spectra and crystal data are given in the Supporting Information. Crystal data, details of the data collection and refinement are given in Table S1. Crystallographic data for the structures have been deposited with the Cambridge Crystallographic Data Centre (CCDC no. 2383453-2383463). Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: +44-1223-336033; email: [email protected] or http://www.ccdc.cam.ac.uk).

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

References

  1. Weetman, C.; Inoue, S. The Road Travelled: After Main-Group Elements as Transition Metals. ChemCatChem 2018, 10, 4213–4228. [Google Scholar] [CrossRef]
  2. Hadlington, T.J.; Driess, M.; Jones, C. Low-valent group 14 element hydride chemistry: Towards catalysis. Chem. Soc. Rev. 2018, 47, 4176–4197. [Google Scholar] [CrossRef] [PubMed]
  3. Asay, M.; Jones, C.; Driess, M. N-Heterocyclic Carbene Analogues with Low-Valent Group 13 and Group 14 Elements: Syntheses, Structures, and Reactivities of a New Generation of Multitalented Ligands. Chem. Rev. 2011, 111, 354–396. [Google Scholar] [CrossRef] [PubMed]
  4. Rivard, E.; Power, P.P. Multiple Bonding in Heavier Element Compounds Stabilized by Bulky Terphenyl Ligands. Inorg. Chem. 2007, 46, 10047–10064. [Google Scholar] [CrossRef] [PubMed]
  5. Hicks, J.; Vasko, P.; Goicoechea, J.M.; Aldridge, S. The Aluminyl Anion: A New Generation of Aluminium Nucleophile. Angew. Chem. Int. Ed. 2021, 60, 1702–1713. [Google Scholar] [CrossRef]
  6. Jones, C. Dimeric magnesium(I) β-diketiminates: A new class of quasi-universal reducing agent. Nat. Rev. Chem. 2017, 1, 0059. [Google Scholar] [CrossRef]
  7. Rösch, B.; Harder, S. New horizons in low oxidation state group 2 metal chemistry. Chem. Commun. 2021, 57, 9354–9365. [Google Scholar] [CrossRef]
  8. Evans, M.J.; Jones, C. Low oxidation state and hydrido group 2 complexes: Synthesis and applications in the activation of gaseous substrates. Chem. Soc. Revs. 2024, 53, 5054–5082. [Google Scholar] [CrossRef]
  9. Chu, T.; Nikonov, G.I. Oxidative Addition and Reductive Elimination at Main-Group Element Centers. Chem. Rev. 2018, 118, 3608–3680. [Google Scholar] [CrossRef]
  10. Tsai, Y. The chemistry of univalent metal β-diketiminates. Coord. Chem. Rev. 2012, 256, 722–758. [Google Scholar] [CrossRef]
  11. Chlupaty, T.; Ruzicka, A. Hybrid amidinates and guanidinates of main group metals. Coord. Chem. Rev. 2016, 314, 103–113. [Google Scholar] [CrossRef]
  12. Jones, C. Bulky guanidinates for the stabilization of low oxidation state metallacycles. Coord. Chem. Rev. 2010, 254, 1273–1289. [Google Scholar] [CrossRef]
  13. Kempe, R. The Strained η2-NAmido-NPyridine Coordination of Aminopyridinato Ligands. Eur. J. Inorg. Chem. 2003, 2003, 791–803. [Google Scholar] [CrossRef]
  14. Noor, A. Coordination Chemistry of Bulky Aminopryridinates with Main Group and Transition Metals. Top. Curr. Chem. 2021, 379, 6. [Google Scholar] [CrossRef] [PubMed]
  15. Kempe, R. Rare Earth Polymerization Catalysts Supported by Bulky Aminopyridinato Ligands. Z. Anorg. Allg. Chem. 2010, 636, 2135–2147. [Google Scholar] [CrossRef]
  16. Scott, N.M.; Schareina, T.; Tok, O.; Kempe, R. Lithium and Potassium Amides of Sterically Demanding Aminopyridines. Eur. J. Inorg. Chem. 2004, 2004, 3297–3304. [Google Scholar] [CrossRef]
  17. Engelhardt, L.M.; Jacobsen, G.E.; Junk, P.C.; Raston, C.L.; Skelton, B.W.; White, A.H. Syntheses and structural studies of [2-(6-methyl)pyridyl]- and (8-quinolyl)trimethylsilylamido-lithium complexes. J. Chem. Soc. Dalton Trans. 1988, 1011–1020. [Google Scholar] [CrossRef]
  18. Green, S.P.; Jones, C.; Stasch, A. Stable Magnesium(I) Compounds with Mg-Mg Bonds. Science 2007, 318, 1754–1757. [Google Scholar] [CrossRef]
  19. Noor, A.; Qayyum, S.; Fertig, R. Synthesis and structure of magnesium aminopyridinates and their attempted conversion to magnesium(I) derivatives. Inorg. Chim. Acta 2019, 494, 239–244. [Google Scholar] [CrossRef]
  20. Ried, A.C.A.; Taylor, L.J.; Geer, A.M.; Williams, H.E.L.; Lewis, W.; Blake, A.J.; Kays, D.L. A Highly Active Bidentate Magnesium Catalyst for Amine-Borane Dehydrocoupling: Kinetic and Mechanistic Studies. Chem. Eur. J. 2019, 25, 6840–6846. [Google Scholar] [CrossRef]
  21. Hicks, J.; Juckel, M.; Paparo, A.; Dange, D.; Jones, C. Multigram Syntheses of Magnesium(I) Compounds Using Alkali Metal Halide Supported Alkali Metals as Dispersible Reducing Agents. Organometallics 2018, 37, 4810–4813. [Google Scholar] [CrossRef]
  22. Bonyhady, S.; Jones, C.; Nembenna, S.; Stasch, A.; Edwards, A.; McIntyre, G. β-Diketiminate-Stabilized Magnesium(I) Dimers and Magnesium(II) Hydride Complexes: Synthesis, Characterization, Adduct Formation, and Reactivity Studies. Chem. Eur. J. 2010, 16, 938–955. [Google Scholar] [CrossRef] [PubMed]
  23. Evans, M.J.; Parr, J.P.; Nguyen, D.T.; Jones, C. An isolable stannaimine and its cycloaddition/ metathesis reactions with carbon dioxide. Chem. Commun. 2024, 60, 10350–10353. [Google Scholar] [CrossRef] [PubMed]
  24. Savka, R.; Plenio, H. Metal Complexes of Very Bulky N,N′-Diarylimidazolylidene N-Heterocyclic Carbene (NHC) Ligands with 2,4,6-Cycloalkyl Substituents. Eur. J. Inorg. Chem. 2014, 2014, 6246–6253. [Google Scholar] [CrossRef]
  25. Berthon-Gelloz, G.; Siegler, M.A.; Spek, A.L.; Tinant, B.; Reek, J.N.H.; Markó, I. IPr* an easily accessible highly hindered N-heterocyclic carbene. Dalton Trans. 2010, 39, 1444–1446. [Google Scholar] [CrossRef]
  26. Wong, E.W.Y.; Dange, D.; Fohlmeister, L.; Hadlington, T.J.; Jones, C. Extremely Bulky Amido and Amidinato Complexes of Boron and Aluminium Halides: Synthesis and Reduction Studies. Aust. J. Chem. 2013, 66, 1144–1154. [Google Scholar] [CrossRef]
  27. Sheldrick, G.M. SHELX-16; University of Göttingen: Göttingen, Germany, 2016. [Google Scholar]
Inorganics 12 00270 g001
Figure 1. The bulky aminopyridinate ligand I (Trip = 2,4,6-triisopropylphenyl and Dip = 2,6-diisopropylphenyl).
Figure 1. The bulky aminopyridinate ligand I (Trip = 2,4,6-triisopropylphenyl and Dip = 2,6-diisopropylphenyl).
Inorganics 12 00270 g001
Inorganics 12 00270 sch001
Scheme 1. Synthesis of aminopyridine pro-ligands HAmPy1−5 (dba = dibenzylideneacetone; dppp = 1,3-bis(dipehylphospino)propane; TCHP = 2,4,6-tricyclohexylphenyl; Ar* = C6H2(CHPh2)2Me-2,6,4; Ar† = C6H2(CHPh2)2Pri-2,6,4).
Scheme 1. Synthesis of aminopyridine pro-ligands HAmPy1−5 (dba = dibenzylideneacetone; dppp = 1,3-bis(dipehylphospino)propane; TCHP = 2,4,6-tricyclohexylphenyl; Ar* = C6H2(CHPh2)2Me-2,6,4; Ar† = C6H2(CHPh2)2Pri-2,6,4).
Inorganics 12 00270 sch001
Inorganics 12 00270 g002
Figure 2. Molecular structure of HAmPy3 (25% thermal ellipsoids are shown; hydrogen atoms, except the amine proton, omitted). Selected bond lengths (Å) and angles (°): N(1)-C(1) 1.342(2), C(1)-N(2) 1.380(2), N(1)-C(1)-N(2) 114.24(13).
Figure 2. Molecular structure of HAmPy3 (25% thermal ellipsoids are shown; hydrogen atoms, except the amine proton, omitted). Selected bond lengths (Å) and angles (°): N(1)-C(1) 1.342(2), C(1)-N(2) 1.380(2), N(1)-C(1)-N(2) 114.24(13).
Inorganics 12 00270 g002
Inorganics 12 00270 sch002
Scheme 2. Synthesis of compounds 1–4 (delocalization within the aminopyridinate ligands is not depicted).
Scheme 2. Synthesis of compounds 1–4 (delocalization within the aminopyridinate ligands is not depicted).
Inorganics 12 00270 sch002
Inorganics 12 00270 g003
Figure 3. Molecular structures of 1 (top) and 4 (bottom) (25% thermal ellipsoids are shown; hydrogen atoms omitted; TCHP, Trip, C(H)Ph2 and/or cyclohexyl groups shown as wireframe for clarity). See Table 1 for relevant metrical parameters.
Figure 3. Molecular structures of 1 (top) and 4 (bottom) (25% thermal ellipsoids are shown; hydrogen atoms omitted; TCHP, Trip, C(H)Ph2 and/or cyclohexyl groups shown as wireframe for clarity). See Table 1 for relevant metrical parameters.
Inorganics 12 00270 g003
Inorganics 12 00270 sch003
Scheme 3. Synthesis of compounds 5–8.
Scheme 3. Synthesis of compounds 5–8.
Inorganics 12 00270 sch003
Inorganics 12 00270 g004
Figure 4. Molecular structure of compound 5 (25% thermal ellipsoids are shown; hydrogen atoms omitted; isopropyl, ethyl and C(H)Ph2 groups shown as wireframe for clarity). Selected bond lengths (Å) and angles (°): I(1)-Mg(1) 2.741(1), Mg(1)-O(2) 2.064(3), Mg(1)-N(2) 2.091(3), Mg(1)-O(1) 2.126(3), Mg(1)-N(1) 2.185(3), N(1)-C(1) 1.364(5), N(2)-C(1) 1.348(5), N(2)-Mg(1)-N(1) 63.64(13), N(2)-C(1)-N(1) 112.6(3).
Figure 4. Molecular structure of compound 5 (25% thermal ellipsoids are shown; hydrogen atoms omitted; isopropyl, ethyl and C(H)Ph2 groups shown as wireframe for clarity). Selected bond lengths (Å) and angles (°): I(1)-Mg(1) 2.741(1), Mg(1)-O(2) 2.064(3), Mg(1)-N(2) 2.091(3), Mg(1)-O(1) 2.126(3), Mg(1)-N(1) 2.185(3), N(1)-C(1) 1.364(5), N(2)-C(1) 1.348(5), N(2)-Mg(1)-N(1) 63.64(13), N(2)-C(1)-N(1) 112.6(3).
Inorganics 12 00270 g004
Inorganics 12 00270 g005
Figure 5. Molecular structures of the monomer unit of compound 6 (top), and compound 8 (bottom) (25% thermal ellipsoids are shown; hydrogen atoms omitted; isopropyl, and C(H)Ph2 groups shown as wireframe for clarity). Selected bond lengths (Å) and angles (°) for 6: Na(1)-N(2) 2.299(2), Na(1)-N(1) 2.4254(19), N(1)-C(1) 1.380(3), C(1)-N(2) 1.329(3), Na(1)-C(16)’ 2.828(3), Na(1)-C(17)’ 3.014(3), N(2)-Na(1)-N(1) 57.65(7), N(2)-C(1)-N(1) 114.66(19). Selected bond lengths (Å) and angles (°) for 8: K(1)-N(2) 2.612(4), K(1)-N(1) 2.777(4), N(1)-C(1) 1.393(6), C(1)-N(2) 1.321(6), K(1)-toluene cent. 2.988(5), N(2)-K(1)-N(1) 50.41(11), N(2)-C(1)-N(1) 115.8(4).
Figure 5. Molecular structures of the monomer unit of compound 6 (top), and compound 8 (bottom) (25% thermal ellipsoids are shown; hydrogen atoms omitted; isopropyl, and C(H)Ph2 groups shown as wireframe for clarity). Selected bond lengths (Å) and angles (°) for 6: Na(1)-N(2) 2.299(2), Na(1)-N(1) 2.4254(19), N(1)-C(1) 1.380(3), C(1)-N(2) 1.329(3), Na(1)-C(16)’ 2.828(3), Na(1)-C(17)’ 3.014(3), N(2)-Na(1)-N(1) 57.65(7), N(2)-C(1)-N(1) 114.66(19). Selected bond lengths (Å) and angles (°) for 8: K(1)-N(2) 2.612(4), K(1)-N(1) 2.777(4), N(1)-C(1) 1.393(6), C(1)-N(2) 1.321(6), K(1)-toluene cent. 2.988(5), N(2)-K(1)-N(1) 50.41(11), N(2)-C(1)-N(1) 115.8(4).
Inorganics 12 00270 g005
Inorganics 12 00270 g006
Figure 6. Molecular structure of compound 9 (25% thermal ellipsoids are shown; hydrogen atoms omitted; isopropyl and C(H)Ph2 groups shown as wireframe for clarity). Selected bond lengths (Å) and angles (°): N(1)-C(1) 1.372(6), C(1)-N(2) 1.350(7), N(3)-C(60) 1.374(6), N(4)-C(60) 1.341(6), Mg(1)-N(2) 2.009(4), Mg(1)-N(1) 2.155(4), Mg(2)-N(4) 2.011(4), Mg(2)-N(3) 2.066(4), Mg(1)-O(1) 2.014(4), I(1)-Mg(2) 2.7123(19), I(1)-Mg(1) 2.7531(16), I(2)-Mg(2) 2.6782(18), N(2)-Mg(1)-N(1) 65.46(16), N(2)-C(1)-N(1) 111.9(4), N(4)-Mg(2)-N(3) 67.03(15), N(4)-C(60)-N(3) 112.0(4).
Figure 6. Molecular structure of compound 9 (25% thermal ellipsoids are shown; hydrogen atoms omitted; isopropyl and C(H)Ph2 groups shown as wireframe for clarity). Selected bond lengths (Å) and angles (°): N(1)-C(1) 1.372(6), C(1)-N(2) 1.350(7), N(3)-C(60) 1.374(6), N(4)-C(60) 1.341(6), Mg(1)-N(2) 2.009(4), Mg(1)-N(1) 2.155(4), Mg(2)-N(4) 2.011(4), Mg(2)-N(3) 2.066(4), Mg(1)-O(1) 2.014(4), I(1)-Mg(2) 2.7123(19), I(1)-Mg(1) 2.7531(16), I(2)-Mg(2) 2.6782(18), N(2)-Mg(1)-N(1) 65.46(16), N(2)-C(1)-N(1) 111.9(4), N(4)-Mg(2)-N(3) 67.03(15), N(4)-C(60)-N(3) 112.0(4).
Inorganics 12 00270 g006
Table 1. Selected bond lengths (Å) for complexes 1–4.
Table 1. Selected bond lengths (Å) for complexes 1–4.
1234
C-Namide1.354(3)1.335(3)1.3417(13)1.341(3)
C-Npy1.368(2)1.374(3)1.3739(13)1.374(3)
Namid-Li2.046(4)1.976(5)1.967(2)1.951(4)
Npy-Li2.037(4)1.978(5)2.006(2)2.043(4)
Li-O orLi-N′amid2.010(4)1.893(5)1.905(2)1.900(4)
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Earsad, A.M.; Paparo, A.; Evans, M.J.; Jones, C. Synthesis and Characterization of Extremely Bulky Aminopyridinate Ligands and a Series of Their Groups 1 and 2 Metal Complexes. Inorganics 2024, 12, 270. https://doi.org/10.3390/inorganics12100270

AMA Style

Earsad AM, Paparo A, Evans MJ, Jones C. Synthesis and Characterization of Extremely Bulky Aminopyridinate Ligands and a Series of Their Groups 1 and 2 Metal Complexes. Inorganics. 2024; 12(10):270. https://doi.org/10.3390/inorganics12100270

Chicago/Turabian Style

Earsad, Arif M., Albert Paparo, Matthew J. Evans, and Cameron Jones. 2024. "Synthesis and Characterization of Extremely Bulky Aminopyridinate Ligands and a Series of Their Groups 1 and 2 Metal Complexes" Inorganics 12, no. 10: 270. https://doi.org/10.3390/inorganics12100270

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop