Aqueous Organometallic Chemistry: Synthesis, Structure, and Reactivity of the Water-Soluble Metal Hydride CpRu(PTA) 2 H

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 25 ° C = 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: Δ H ⧧ = 68 ± 2 kJ/mol; Δ S ⧧ = −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 .