Novel reactivity of ruthenium alkylidenes in protic solvents: Degenerate alkylidene proton exchange

A novel organometallic transformation is reported in which the alkylidene p rotons of water-soluble ruthenium alkylidenes 1 and 2 undergo nondestructiv e, degenerate exchange with solvent-derived deuterons in perdeuterated prot ic solvents such as D2O and CD3OD. Deuterated alkylidene complex (1-D) was isolated from a solution of alkylidene 1 in D2O, and the new alkylidene was fully characterized by H-1, H-2, C-13, and P-31 NMR spectroscopy and fast- atom bombardment mass spectroscopy (FAB-MS). The rate of alkylidene proton exchange for this transformation was found to correlate with the bulk diele ctric constant of the solvent or solvent mixtures employed. The data suppor t a mechanism for proton exchange involving the dissociation of a chloride ion from the ruthenium metal center. The rate of alkylidene H/D exchange fo r alkylidene 2 was faster than the rate of exchange for alkylidene 1, demon strating that relative rates of exchange are influenced by the electron den sities at the metal centers of these complexes. Several additional rutheniu m alkylidenes were found to undergo analogous alkylidene H/D exchange react ions, including parent alkylidene (Cy3P)(2)Cl2Ru=CHPh (3) in CD2Cl2/CD3OD m ixtures. These data suggest that this novel reactivity may be general for a n entire class of ruthenium alkylidenes provided that protic species are av ailable in solution and that the dielectric constant of the reaction medium is sufficiently high to ionize the halide ligands.