Aqueous organometallic chemistry:: Synthesis, structure, and reactivity of the water-soluble metal hydride CpRu(PTA)2H

The reaction of CpRu(PTA)(2)Cl (1) with KOH in methanol afforded the water-soluble hydride CpRu(PTA)(2)H (2) in good yield. The solid-state structures of both CpRu(PTA)(2)H and the previously reported CpRu(PTA)(2)Cl are described and exhibit classic piano stool geometries. Complex 2 is one of a very few structurally characterized CpRu(PR(3))(2)H compounds known and the only one that is water-soluble. The ruthenium hydride is stable and soluble (S(25degreesC) = 20 mg/mL) in deoxygenated water; however, the complex does react with chlorinated solvents to yield 1. Complex 2 undergoes H/D exchange with D(2)O, and the kinetics of this process were monitored by (31)P NMR spectroscopy as a function of temperature. Activation parameters for the reaction of 2 with D(2)O were obtained: DeltaH(double dagger) = 68 +/- 2 kJ/mol; DeltaS(double dagger) = -94 +/- 7 J/mol-K. A normal kinetic isotope effect of 7.9 was calculated for the H/D exchange reaction described here. These kinetic parameters suggest an associative mechanism with little Ru-H (or Ru-D) bond cleavage at the transition state. The reaction is postulated to occur via protonation of the hydride ligand of 2 by water followed by deprotonation by the resultant hydroxide. Finally DFT calculations were performed on all complexes and are consistent with the observed solid-state structures of 1 and 2.