Dataset Information

CO₂ Capture by 2-(Methylamino)pyridine Ligated Aluminum Alkyl Complexes.

ABSTRACT: A set of novel, easily synthesized aluminum complexes, Al[κ²-N,N-2-(methylamino)pyridine]₂R (R = Et, iBu) are reported. When subjected to 1 atm of CO₂ pressure, each hemilabile pyridine arm dissociates and facilitates cooperative activation of the CO₂ substrate reminiscent of a Frustrated Lewis Pair. This reaction has limited precedent for Al/N based Lewis Pair systems, and this is the first system readily shown to sequester multiple equivalents of CO₂ per aluminum center. The ethyl variant then reacts further, inserting a third equivalent of CO₂ into the aluminum alkyl to generate an aluminum carboxylate. Examples of this type of reactivity are rare under thermal conditions. A joint experimental/computational study supports the proposed reaction mechanism.

SUBMITTER: Yokley TW

PROVIDER: S-EPMC7457790 | biostudies-literature | 2020 Aug

REPOSITORIES: biostudies-literature

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CO2 Capture by 2-(Methylamino)pyridine Ligated Aluminum Alkyl Complexes.

Yokley Timothy W TW Tupkar Hrishikesh H Schley Nathan D ND DeYonker Nathan J NJ Brewster Timothy P TP

European journal of inorganic chemistry 20200529 31

A set of novel, easily synthesized aluminum complexes, Al[κ2-N,N-2-(methylamino)pyridine]2R (R = Et, iBu) are reported. When subjected to 1 atm of CO2 pressure, each hemilabile pyridine arm dissociates and facilitates cooperative activation of the CO2 substrate reminiscent of a Frustrated Lewis Pair. This reaction has limited precedent for Al/N based Lewis Pair systems, and this is the first system readily shown to sequester multip ...[more]

PMID: 32879618

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Project description:Interest in O2-dependent aliphatic carbon-carbon (C-C) bond cleavage reactions of first row divalent metal diketonate complexes stems from the desire to further understand the reaction pathways of enzymes such as DKE1 and to extract information to develop applications in organic synthesis. A recent report of O2-dependent aliphatic C-C bond cleavage at ambient temperature in Ni(ii) diketonate complexes supported by a tridentate nitrogen donor ligand [(MBBP)Ni(PhC(O)CHC(O)Ph)]Cl (7-Cl; MBBP = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine) in the presence of NEt3 spurred our interest in further examining the chemistry of such complexes. A series of new TERPY-ligated Ni(ii) diketonate complexes of the general formula [(TERPY)Ni(R2-1,3-diketonate)]ClO4 (1: R = CH3; 2: R = C(CH3)3; 3: R = Ph) was prepared under air and characterized using single crystal X-ray crystallography, elemental analysis, 1H NMR, ESI-MS, FTIR, and UV-vis. Analysis of the reaction mixtures in which these complexes were generated using 1H NMR and ESI-MS revealed the presence of both the desired diketonate complex and the bis-TERPY derivative [(TERPY)2Ni](ClO4)2 (4). Through selective crystallization 1-3 were isolated in analytically pure form. Analysis of reaction mixtures leading to the formation of the MBBP analogs [(MBBP)Ni(R2-1,3-diketonate)]X (X = ClO4: 5: R = CH3; 6: R = C(CH3)3; 7-ClO4: R = Ph; X = Cl: 7-Cl: R = Ph) using 1H NMR and ESI-MS revealed the presence of [(MBBP)2Ni](ClO4)2 (8). Analysis of aerobic acetonitrile solutions of analytically pure 1-3, 5 and 6 containing NEt3 and in some cases H2O using 1H NMR and UV-vis revealed evidence for the formation of additional bis-ligand complexes (4 and 8) but suggested no oxidative diketonate cleavage reactivity. Analysis of the organic products generated from 3, 7-ClO4 and 7-Cl revealed unaltered dibenzoylmethane. Our results therefore indicate that N3-ligated Ni(ii) complexes of unsubstituted diketonate ligands do not exhibit O2-dependent aliphatic C-C bond clevage at room temperature, including in the presence of NEt3 and/or H2O.

Project description:Treatment of an unsymmetrical bis(imino)pyridyl-thiolate zinc(II) complex [Zn(II)(LN(3)S)(OTf)] (1) with LiAlH(4) results in the double reduction of the two imino groups in the ligand backbone, and at the same time causes a rare transmetalation reaction to occur. The products formed in this reaction are two novel aluminium(III) bis(amido)pyridyl-thiolate complexes [(R,S/S,R-[Al(III)(LH(2)N(3)S)(THF)] (2a) and [(R,R/S,S-[Al(III)(LH(2)N(3)S)(THF)] (2b), which are diastereomers of each other. These complexes have been characterized by single-crystal X-ray diffraction and (1)H NMR spectroscopy. Single crystal X-ray structure analysis shows that the Al(III) ion is bound in an almost idealized square pyramidal geometry in 2a, while being held in a more distorted square pyramidal geometry in 2b. The major difference between 2a and 2b arises in the orientation of the terminal methyl groups of the ligand backbone in relation to the Al(III)N(3)S plane. These two complexes are crystallized at different temperatures (room temperature vs -35 °C), allowing for their separate isolation. Structural analysis shows that these complexes are reduced by the formal addition of one hydride ion to each imino group, resulting in a deprotonated bis(amido)pyridyl-thiolate ligand. A detailed analysis of metrical parameters rules out the possibility of pure one- or two-electron reduction of the π-conjugated bis(imino)pyridine framework. (1)H NMR spectra reveal a rich pattern in solution indicating that the solution state structures for 2a and 2b match those observed in the solid-state crystal structures, and reveal that both complexes are severely conformationally restricted. Direct organic synthetic methods failed to produce the reduced bis(amino)pyridyl-thiol ligand in pure form, but during the course of these efforts an unusual unsymmetrical aminopyridyl ketone, 1-(6-(1-(2,6-diisopropylphenylamino)ethyl)pyridin-2-yl)ethanone was synthesized in good yield and can be used as a possible precursor for further ligand development.

Dataset Information

CO₂ Capture by 2-(Methylamino)pyridine Ligated Aluminum Alkyl Complexes.

Publications

CO<sub>2</sub> Capture by 2-(Methylamino)pyridine Ligated Aluminum Alkyl Complexes.

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