Interconversion of Ruthenium-O(CH2CH2PCy2)2 Alkylidene and Alkylidyne Hydride Complexes

The species (Cy3P)(2)RuX2(CHPh) (X = Cl, Br) react with the ancillary ligand O(CH2CH2PCy2)(2) to yield the alkylidene species (POP-Cy)RuX2(CHPh) (X = Cl 1, Br 2). Subsequent reaction of 1 and 2 with GaX3 generates the alkylidyne hydride salts [(POP-Cy)RuHX(CPh)][GaX4] (X = Cl 3, Br 4). Treatment of 3 and 4 with the donor ligand pyridine converts these alkylidyne hydrides to the Ru-alkylidene complexes [(POP-Cy)Ru(py)X(CHPh)][GaX4] (X = Cl 5, Br 6). The complexes 5 and 6 are also formed directly by addition of the Lewis acid-base adduct (py)GaX3 to 1 and 2, respectively. The alkylidyne hydride species 3 and 4 are also quantitatively converted back to alkylidene species 1 and 2 by addition of excess Bu4NX (X = Cl, Br), respectively. Similarly treatment of 5 and 6 with [Et3NH]X or [Bu4N]X (X = Cl, Br) resulted in the re-formation of 1 and 2. These data demonstrate that the interconversion of alkylidene and alkylidyne hydride is energetically facile. This view is supported by crystallographic and preliminary DFT data.