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Synthesis and Characterization of OsH2Cl[κN,κO-(ONCR2)](PiPr3)2 (CR2 = C(CH2)4CH2, R = CH3): Influence of the L2 Ligand on the Nature of the H2 Unit in OsH2ClL2(PiPr3)2 (L2 = ONCR2, NHC(Ph)C6H4) Complexes
journal contribution
posted on 1999-09-21, 00:00 authored by Ricardo Castarlenas, Miguel A. Esteruelas, Enrique Gutiérrez-Puebla, Yves Jean, Agustí Lledós, Marta Martín, Jaume TomàsThe dihydride−dichloro complex OsH2Cl2(PiPr3)2 (1) reacts with cyclohexanone oxime and
acetone oxime in the presence of Et3N to give the dihydride derivatives (2) and OsH2Cl{κN,κO-[ONC(CH3)2]}(PiPr3)2 (3), respectively.
The structure of 2 has been determined by X-ray diffraction. The geometry around the
osmium atom can be described as a distorted pentagonal bipyramid, with the triisopropylphosphine ligands occupying two relative trans positions. The remaining perpendicular
plane is formed by the hydride ligands, the chlorine, and the oximate group, which acts
with a bite angle of 36.6(1)°. In solution the hydride ligands of 2 and 3 undergo an
intramolecular thermally activated site exchange process. The activation parameters of this
process are ΔH⧧ = 11.9(±0.7) kcal mol-1 and ΔS⧧ = −0.5(±1.4) cal mol-1 K-1 for 2 and ΔH⧧
= 11.7(±0.8) kcal mol-1 and ΔS⧧ = −0.8(±2.0) cal mol-1 K-1 for 3. To understand why
complexes 2 and 3 are dihyride derivatives, while the previously reported complex is an elongated dihydrogen compound, a quantitative
theoretical analysis of the interaction between the H2 moiety and the OsClL2(PH3)2 (L2 =
ONCH2, NHCHCHCH) complex fragments, along the oxidative addition pathway, is
also reported.