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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 |

REPOSITORIES: biostudies-literature

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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.

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

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