HYDRIDE COMPLEXES OF RUTHENIUM AND RELATED METALS - PREPARATION AND STRUCTURES OF CP(PME(3))(2)RUH AND [CP(PME(3))(2)RUH2]BF4

The reaction of Cp(PMe(3))(2)RuCl with either KOMe in MeOH or LiAlH4 in Et(2)O produces the hydride Cp(PMe(3))(2)RuH (1) in high yield. Protonation of 1 with HX quantitatively generates the dihydrides [Cp(PMe(3))(2)RuH2]X (X = Cl (2), BF4 (3), B[3,5-(CF3)(2)C6H3](4) (4)). The spectroscopic data on 3 indicate a classical dihydride configuration with no evidence for a dihydrogen tautomer. The pK(a) of 3 in CH2Cl2 is 13.9, and the contribution of the ancillary ligands to the pK(a) value is discussed. X-ray crystal structures of hydride 1 and dihydride 3 have been determined. Hydride 1 exhibits a ''three-legged piano stool'' geometry, while the cation of 3 exhibits a ''four-legged piano stool'' geometry, consistent with the classical dihydride configuration. A comparison of the structures of 1 and 3 with related d(6) Cp'L(2)MH, d(4) Cp'L(2)MH(2), and d(6) Cp'L(2)M(eta(2)-H-2) complexes (Cp' = eta(5)-C5H5, eta(5)-C(5)Me(5), eta(5)-C(5)H(5)Me) reveals several general structural trends. First, the angle between the Cp' plane and the ML(2) plane lies in the range 59-79 degrees (mean 67.6(13)degrees) for d(6) CP'L(2)MH complexes but is in the range 86-90 degrees (mean 87.6(4)degrees) for d(4) Cp'L(2)MH(2) complexes and has a mean value of 56.1(8)degrees for known d(6) Cp'L(2)M(eta(2)-H-2) complexes. Second, the angle between the M-H vector and the normal to the ML(2) plane is generally less than 10 degrees (mean 7.9(12)degrees) for the d(6) Cp'L(2)MH complexes, while in d(4) Cp'L(2)MH(2) complexes the M-H vector is shifted toward the ML(2) plane, increasing this angle by ca. 20 degrees (mean 30.0(20)degrees). The corresponding angle in d(6) Cp'L(2)M(eta(2)-H-2) complexes has a mean value of 15.5(18)degrees. Third, the L-M-L' angles in d(6) Cp'L(2)MH complexes (range 84-101 degrees, mean 93.0(19)degrees) are typically smaller that the corresponding angles in d(4) CP'L(2)MH(2) complexes (range 101-111 degrees, mean 107.2(10)degrees).