Preparation of Ruthenium Azirinyl Complexes and Reversed Regiospecificity of the Carbonyl Insertion Reaction

Electrophilic addition of organic halides to [Ru]CN (1; [Ru] = Cp(PPh3)2Ru) gave the
cationic isocyanide complexes {[Ru]CNCH2R}X (R = CN, 2a; R = CHCH2, 2b; R = Ph,
2c), which reacted with base (n-Bu4NOH or n-Bu4NF) to give the three-membered-ring
azirinyl complexes. For the azirinyl complex with a phenyl group 3c, three isomers, assigned
as ruthenium 2H- and 1H-azirinyl complexes, are observed at −20 °C. Reaction of the methyl
isocyanoacetate complex {[Ru]C⋮NCH2COOMe}X (2d) with n-Bu4NOH causes hydrolysis
of the ester group to give the ruthenium oxazolone complex 4d. The insertion of the CO
group of acetone, aldehyde, ester, and amide into the C−C bond of the three-membered
azirinyl ring of 3a−c yields a variety of five-membered oxazolinyl complexes 5−7. The
regiospecificity of the insertion differs from that observed in the photochemically induced
carbonyl insertion in the organic azirine system. The diastereoselectivity in the formation
of 5−7 is controlled by steric effects. In the formation of the pentamethylcyclopentadienyl
oxazolinyl ruthenium complex 7a*, the intermediate 8a* is isolated before cyclization.
Molecular structures of 7a* and 8a* have been determined by single-crystal X-ray diffraction
analysis. Treatment of 7 with hydride gave [Ru]CN and alcohol.