Steric Control of Cyclometallation Reactions in Schiff-Base Complexes of Cobalt(I) Containing an Anchoring Diphenylphosphanyl Group

Abstract

2-(Diphenylphosphanyl)alkyliminobenzaldehydes(2-Ph2PC6H4CHNR) react with [CoCH3(PMe3)4] forming five-membered metallacycles in complexes [(2-Ph2PC6H4CNR-C,P)Co(PMe3)3] [1: R = C2H5, 2: R = CH(CH3)2, 3: R = cyclo-C6H11] while the ortho-metallation pathway is selectively followed in the formation of [{2-Ph2PC6H3(CHNR)-C1,P}Co(PMe3)3] [4: R = C(CH3)3]. The presence of a four-membered cobaltocycle in the molecular structure of 4 was confirmed by X-ray analysis. Carbonylation of 2 and 3 gives the monocarbonyl derivatives [(2-Ph2PC6H4CNR-C,P)Co(CO)(PMe3)2] [5: R = CH(CH3)2, 6: R = cyclo-C6H11] while 4 undergoes ring expansion by insertion forming [{2-Ph2PC6H3(CHNR)CO-C,P}Co(CO)(PMe3)2] [7: R = C(CH3)3]. Monosubstitution occurs under 1 bar of ethene giving the π-ethene complexes [(2-Ph2PC6H4CNR-C,P)Co(C2H4)(PMe3)2] [8: R = CH(CH3)2, 9: R = cyclo-C6H11] and [{2-Ph2PC6H3(CHNR)-C1,P}Co(C2H4)(PMe3)2] [10: R = C(CH3)3]. The molecular structure of 9 shows an equatorial π-ethene ligand. Iodomethane oxidizes 2 and 3 to afford the cobalt(II) complexes [(2-Ph2PC6H4CNR-C,P)CoI(PMe3)2] [11: R = CH(CH3)2, 12: R = cyclo-C6H11] and oxidatively adds to 4 to give mer-trans-[{2-Ph2PC6H3(CHNR)-C1,P}CoI(CH3)(PMe3)2] [13: R = C(CH3)3]. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)