American Chemical Society
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Synthesis and Characterization of OsH2Cl[κNO-(ONCR2)](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 = ONCR2, NHC(Ph)C6H4) Complexes

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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 Tomàs
The 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{κNO-[ONC(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 = ONCH2, NHCHCHCH) complex fragments, along the oxidative addition pathway, is also reported.