Exploitation of a Chemically Non-innocent Acetate Ligand in the Synthesis and Reactivity of Ruthenium Vinylidene Complexes

Reaction of the ruthenium bis-acetate complex cis-Ru(κ2-OAc)2(PPh3)2 with a range of terminal alkynes HCCR (R = Ph, CO2Me, C{OH}Ph2, C{OH}Me2) results in the formation of the vinylidene complexes Ru(κ2-OAc)(κ1-OAc)(CCHR)(PPh3)2. The acetate ligands in these species are fluxional and, in the case where R = Ph, are undergoing fast exchange on the NMR time scale even at 195 K. In the case of the hydroxy-substituted complex Ru(κ2-OAc)(κ1-OAc)(CCHC{OH}Ph2)(PPh3)2 a hydrogen bond exists between the OH group on the γ-position of the vinylidene and the κ1-OAc ligand. This hydrogen bond inhibits the exchange of the OAc ligands, which now becomes slow on the NMR time scale at 215 K. In addition, and in contrast to the Cl-substituted analogues, elimination of water from the hydroxy vinylidene complex does not readily occur, possibly due to the presence of this hydrogen-bonding interaction. Instead, a slow reaction to form Ru(κ2-OAc)(κ1-OAc)(CO)(PPh3)2 is observed with the concomitant formation of H2CCPh2. An analogous process with Ru(κ2-OAc)(κ1-OAc)(CCHC{OH}Me2)(PPh3)2 affords H2CCMe2 and Ru(κ2-OAc)(κ1-OAc)(CO)(PPh3)2.