Acetylene and phenylacetylene reacts with carbonylchloro[4-methyl-6-((R-imino)methyl)phenolato- C, O ]bis(triphenylphosphine)ruthenium(II), Ru(RL 1 )(PPh 3 ) 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(RL 2,X)(PPh 3 ) 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 RuC 2 P 2 ClO 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 ∼0.14 Å) and stronger than that in 3 . This is reflected in the lowering of the ruthenium(III)−ruthenium(II) reduction potential by ∼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.
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Ghosh et al. (1998) studied this question.