Hydride-Carbyne to Carbene Transformation in an Osmium-Acetate-Bis(triisopropylphosphine) System: Influence of the Coordination Mode of the Carboxylate and the Reaction Solvent

The bis-solvato hydride-allenylidene complex [OsH(CCCPh2)(CH3CN)2(PiPr3)2]BF4 (1) reacts with acetic acid to give the hydride-carbyne [OsH(κ2-O2CCH3)(⋮CCHCPh2)(PiPr3)2]BF4 (2), which in 1,2-dichloroethane under reflux is stable and does not evolve into its five-coordinate carbene isomer. In acetonitrile at room temperature, complex 2 is in equilibrium with [OsH{κ1-OC(O)CH3}(⋮CCHCPh2)(CH3CN)(PiPr3)2]BF4 (4; ΔH° = −6.4 ± 0.3 kcal·mol-1, ΔS° = −22.9 ± 1.1 eu). At 353 K, complex 4 is transformed into the carbene [Os{κ1-OC(O)CH3}(CHCHCPh2)(CH3CN)2(PiPr3)2]BF4 (5; 40%), which is obtained in high yield (88%) by reaction of [Os(CHCHCPh2)(CH3CN)3(PiPr3)2][BF4]2 with sodium acetate in 2-propanol. The hydride-carbyne to carbene transformation is analyzed by DFT calculations.双溶剂合氢化物-联烯亚基配合物[OsH(=C=C=CPh₂)(CH₃CN)₂(PiPr₃)₂]BF₄（编号1）与乙酸反应，生成氢化物-卡拜配合物[OsH(κ²-O₂CCH₃)(≡CCH=CPh₂)(PiPr₃)₂]BF₄（编号2）；该配合物在回流的1,2-二氯乙烷中稳定存在，不会转化为其五配位卡宾异构体。在室温乙腈(CH₃CN)中，配合物2与[OsH{κ¹-OC(O)CH₃}(≡CCH=CPh₂)(CH₃CN)(PiPr₃)₂]BF₄（编号4；ΔH° = −6.4 ± 0.3 kcal·mol⁻¹，ΔS° = −22.9 ± 1.1 熵单位(entropy unit, eu)）处于化学平衡状态。在353 K条件下，配合物4会转化为卡宾配合物[Os{κ¹-OC(O)CH₃}(=CHCH=CPh₂)(CH₃CN)₂(PiPr₃)₂]BF₄（编号5，产率40%）；而通过[Os(=CHCH=CPh₂)(CH₃CN)₃(PiPr₃)₂][BF₄]₂与乙酸钠在异丙醇中反应，可获得产率高达88%的该卡宾配合物5。本研究通过密度泛函理论(Density Functional Theory, DFT)计算，对氢化物-卡拜向卡宾的转化过程进行了分析。