Hydride complexes of ruthenium and related metals: Preparation and structures of Cp(PMe3)2RuH and [Cp(PMe3)2RuH2]BF4

Article abstract of DOI:10.1021/om00008a051

The reaction of Cp(PMe₃)₂RuCl with either KOMe in MeOH or LiAlH₄ in Et₂O produces the hydride Cp(PMe₃)₂RuH (1) in high yield. Protonation of 1 with HX quantitatively generates the dihydrides [Cp(PMe₃)₂RuH₂]X (X = Cl (2), BF₄ (3), 6[3,5-(CF₃)₂C₆H₃]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 d⁶ Cp′L₂-MH, d1 Cp′L₂MH₂, and d⁶ Cp′L₂M(η²-H₂) complexes (Cp′ = η⁵-C₅H₅) η⁵-C₅Me₅, η⁵-C₅H₅Me) reveals several general structural trends. First, the angle between the Cp′ plane and the ML₂ plane lies in the range 59-79° (mean 67.6(13)°) for d⁶ Cp′L₂MH complexes but is in the range 86-90° (mean 87.6(4)°) for d⁴ Cp′L₂MH₂ complexes and has a mean value of 56.1(8)° for known d⁶ Cp′L₂M(η²-H₂) complexes. Second, the angle between the M-H vector and the normal to the ML₂ plane is generally less than 10° (mean 7.9(12)°) for the d⁶ Cp′L₂MH complexes, while in d⁴ Cp′L₂MH₂ complexes the M-H vector is shifted toward the ML₂ plane, increasing this angle by ca. 20° (mean 30.0(20)°). The corresponding angle in d⁶ Cp′L₂M-(η²-H₂) complexes has a mean value of 15.5(18)°. Third, the L-M-L′ angles in d⁶ Cp′L₂MH complexes (range 84-101°, mean 93.0(19)°) are typically smaller that the corresponding angles in d⁴ Cp′L₂MH₂ complexes (range 101-111°, mean 107.2(10)°).