遷移金属シアノカルバニオンの構造と反応性

抄録

Structure and reactivity of C- and N-bound isomers of transition metal cyanocarbanions are described. A series of C-bound ruthenium phosphine complexes, RuCp [CH (CN) SO₂Ph] L₂ and their N-bound isomers, Ru⁺Cp (NCCH^-SO₂Ph) L₂ have been synthesized by the reactions of RuCp-ClL₂ with the sodium salt of (phenylsulfonyl) acetonitrile and subsequent ligand exchange reactions. Structural characterization by X-ray diffraction indicated that carbanion moiety of the C-bound complexes has complete α-metalated structure, while that of the N-bound ones has zwitter ionic structure. Interconversions between C- and N-bound complexes have been observed upon heating, where relative stabilities of the C- and N-bound complexes are drastically changed depending mainly on the steric factors of ligands. The intra- and intermolecular mechanisms of the C-N interconversions were explored by means of kinetic studies and DFT calculations. The N-bound complexes have proven to show high catalytic activities for aldol and Michael reactions of nitriles. Kinetic studies revealed that the catalytic reaction proceeds via direct C-C bond formation of N-bound complexes and subsequent nitrile exchange reaction.