Synthesis and characterization of OsH2Cl[kappa N,kappa O-(ON = CR2)]((PPr3)-Pr-i)(2) (CR2 = C(CH2)(4)CH2, R = CH3): Influence of the L-2 ligand on the nature of the H-2 unit in OsH2ClL2((PPr3)-Pr-i)(2) (L-2 = ON = CR2, NH = C(Ph)C6H4) complexes

The dihydride-dichloro complex OsH2Cl2((PPr3)-Pr-i)(2) (1) reacts with cycl ohexanone oxime and acetone oxime in the presence of Et3N to give the dihyd ride derivatives OsH2Cl{kappa N,kappa O-[ON=C(CH2)(4)CH2]}(PiPr(3))(2) (2) and OsH2Cl{kappa N,kappa O-[ON=C(CH3)(2)]}((PPr3)-Pr-i)(2) (3), respectivel y. The structure of 2 has been determined by X-ray diffraction. The geometr y around the osmium atom can be described as a distorted pentagonal bipyram id, with the triisopropylphosphine ligands occupying two relative trans pos itions. 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)degrees. In solution the hydride ligands of 2 and 3 undergo an intramolec ular thermally activated site exchange process, The activation parameters o ff;his process are Delta H-double dagger = 11.9(+/-0.7) kcal mol(-1) and De lta(double dagger) = -0.5(+/-1.4) cal mol(-1) K-1 for 2 and Delta H-double dagger = 11.7(+/-0.8) kcal mol(-1) and Delta S-double dagger = -0.8(+/-2.0) cal mol(-1) K-1 for 3. To understand why complexes 2 and 3 are dihyride de rivatives, while the previously reported complex OsCl-{NH=C(Ph)C6H4}(eta(2) -H-2)((PPr3)-Pr-i)(2) is an elongated dihydrogen-compound, a quantitative t heoretical analysis of the interaction between the H-2 moiety and the OsClL 2(PH3)(2)(L-2 = ON=CH2, NH=CHCH=CH) complex fragments, along the oxidative addition pathway, is also reported.