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) SO
2Ph] L
2 and their
N-bound isomers, Ru
+Cp (NCCH
-SO
2Ph) L
2 have been synthesized by the reactions of RuCp-ClL
2 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.
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