Metallacycle expansion by alkyne insertion. Chemistry of a new family of ruthenium organometallics

Acetylene and phenylacetylene reacts with carbonylchloro[4-methyl-6-((R-imino)meth phenolato-C,O]bis(triphenylphosphine)ruthenium(II), Ru(RL1)(PPh3)(2)(CO)Cl (3), affording the inserted product carbonylchloro[2-vinyl-4-methyl-6-((R-imino)methyl)phenolato-C,O]bis-(triphenylphosphine ruthenium(II), Ru(RL2,X)(PPh3)(2)(CO)Cl (4), in virtually quantitative yield. The X-ray structures of 4b (R = X = Ph) and 4g (R Et, X = H) have revealed the presence of distorted-octahedral RuC2P2ClO coordination spheres. In the conversion 3 --> 4, the Ru(C,O) chelate ring expands from four-membered to six-membered. The insertion of phenylacetylene is regiospecific, and a reaction model implicating initial Ru-O cleavage and steric control is proposed. The Ru-O bond in 4 is significantly shorter (by similar to 0.14 Angstrom) and stronger than that in 3. This is reflected in the lowering of the ruthenium(III)ruthenium(II) reduction potential by similar to 200 mV. The uncoordinated Schiff base moiety in 4 is present in the hydrogen-bonded iminium-phenolato zwitterionic form, as revealed by the N ... O distance as well as by IR and NMR data.