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

Abstract

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{κN,κO-[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.

Preparation, Spectroscopic Characterization, X-ray Structure, and Theoretical Investigation of Hydride−, Dihydrogen−, and Acetone−OsTp Complexes: A Hydridotris(pyrazolyl)borate−Cyclopentadienyl Comparison

“…In contrast to 3 , the skeleton of 2 is rigid in solution. The behavior of this κ 2 -Tp complex agrees well with that previously observed for related OsH 3 (YZ)(P i Pr 3 ) 2 and OsH 2 X(YZ)(P i Pr 3 ) 2 (X = halogen, YZ = chelating ligand) species, where the presence of two bulky phosphine ligands appears to prevent the necessary movements for the interconversion between polyhedra. , …”

“…Previous theoretical calculations on hydride site exchanges in related trihydride species suggest that the process takes place through dihydrogen transition states. 34b,c, That for the exchange in 3t has been located ( TS1 ; Figure ). It lies 11.2 kcal·mol -1 above 3t and has the coordinated H(1C)−H(1B) molecule parallel disposed to the P−Os−N(5) direction, with the atoms H(1C) and H(1B) separated by 0.925 Å.…”

Synthesis, Characterization, and Theoretical Study of Stable Hydride−Azavinylidene Osmium(IV) Complexes

“…Solvents were dried by the usual procedures and distilled under argon prior to use. The starting materials OsH 2 Cl 2 (P i Pr 3 ) 2 ( 1 ), ( 3 ), and OsH 2 Cl{κ- N ,κ- O [ONC(CH 3 ) 2 ]}(P i Pr 3 ) 2 ( 5 ) were prepared by the published method. , …”

Δ2- and Δ3-Azaosmetine Complexes as Intermediates in the Stoichiometric Imination of Phenylacetylene with Oximes

“…These precedents prompted us to study the reactions of the dihydride−dichloro complex OsH 2 Cl 2 (P i Pr 3 ) 2 with acetone oxime, cyclohexanone oxime, and phenylacetylene. In an initial stage, the oximes were introduced into the metallic center and the oxygen atom was eliminated by reaction of the resulting oximate compounds with HCl (Scheme ). The alkyne was introduced into the osmium atom by treatment of OsHCl 2 (NCR 2 )(P i Pr 3 ) 2 [CR 2 = CMe 2 , with Ag[CF 3 SO 3 ] at room temperature and the subsequent addition of phenylacetylene at −25 °C.…”