Synthesis and structural characterization of methylindium imino/aminophenolates: Comparison to aluminum analogues and reactivity toward the coupling reactions of carbon dioxide with epoxides

Abstract

We have synthesized methylindium complexes containing a variety of amino- and iminophenolate ligands for structural comparison to their aluminum analogues. The reaction of Me3In with the corresponding amino-/iminophenols resulted in the formation of MeIn(Et2NCH2CH2-abp) (1), MeIn(PyCH2-abp) (2), [MeIn(iPr-abp)]2 (3), MeIn(Ph-salen) (4), MeIn(Etsalan) (5), MeIn(Cy-ip) (6) and MeIn(Mes-ip) (7) [H2(Et2NCH2CH2-abp) = Et2NCH2CH2N(2-OH-3,5-C6H2tBu2)2, H2(PyCH2-abp) = (2-C5H4N)CH2N(2-OH-3,5- C6H2tBu2)2, H2(iPr-abp) = (CH3)2CHN(2-OH-3,5-C6H2tBu2)2, H2(Ph-salen) = 1,2-(NCH-2-OH-3,5-C6H2tBu2)2C6H4, H2(Et-salan) = 1,2-(NMeCH2-2-OH-3,5- C6H2tBu2)2C2H4, H(Cy-ip) = (2-OH-3,5-tBu2-C6H2)CHN(C6H11), and H(Mes-ip) = (2-OH-3,5-tBu2-C6H2CHN(2,4,6-Me3C6H2)]. X-ray crystallography studies show monomeric structures and five-coordinate indium centres for 1 and 2, a dimeric structure via intermolecular In⋯O interactions and fivecoordinate indium centres for 3, and monomeric structures and fourcoordinate indium centres for 6 and 7. DFT calculations were used to rationalize the observed dimeric structure of 3 and monomeric structures of 6 and 7, and gauge the effect of ligand steric bulk and atomic radius in indium versus aluminum on dimerization. Compounds 2 and 5 are active catalysts for coupling reactions of carbon dioxide and propylene oxide to yield propylene carbonate and carbon dioxide with cyclohexene oxide to yield polycyclohexene carbonate. This work provides insight into controlling intermolecular bonding and hence reactivity in indium and aluminum amino-/iminophenolate complexes, and represents one of the first examples of indium complexes as catalysts for the formation of cyclic- or polycarbonates from carbon dioxide and epoxides.