Synthesis, structure and reactivity studies of tungsten-triosmium mixed-metal compounds

Abstract

There has been considerable current interest in the synthesis and study of cluster complexes due to their potential as models for the behavior of small unsaturated molecules on catalytic metal surfaces. One of the characteristic features of metal cluster chemistry is the promotion of bond scission and bond formation reactions of such small organic ligands. The reaction of $Os_3(CO)_9(C_2Ph_2)$ with $CpW(CO)_2(CTol)$ produces an alkylidyne-alkyne complex $CpWOs_3(CO)_{10}(μ_3 - η^2 - C_2Ph_2)(μ_3 - CTol)$ (1), which is converted to two isomeric allyl complexes $CpWOs_3(CO)_{10}(μ_3 - η^3 - C_3Ph_2Tol)$ (2 and 3) upon thermolysis. Complex 3, in which the allyl ligand is π-coordinated to the tungsten atom, undergoes consecutive allyl C-C bond cleavage to afford trialkylidyne complex $CpWOs_3(CO)_9(μ_3 - CPh)_2(μ_3-CTol)$ (5) via alkylidyne-alkyne complex $CpWOs_3(CO)_{10}(μ_3 - η^2 - C_2Ph_2)(μ_3 - CTol)$ (4), together with formation of $CpWOs_3(CO)_8(μ_3 - η^2 - perp - C_2Ph_2)(μ_3-CTol)$ (6) as a minor product. Initial decarbonylation of $CpWOs_3(CO)_{11}(μ_3 - CTol)$ (7) with $Me_3NO/MeCN$ followed by reaction with dihydrogen and water produces a dihydrido complex $CpWOs_3(CO)_{10}(μ_3 - CTol)(μ - H)_2$ (8), a "butterfly" cluster with a 60 VE, and an oxo complex $CpWOs_3(CO)_{10}(μ - O)(μ_3 - CTol)$ (10), respectively. Complex 8 reacts either with carbon monoxide to produce the starting alkylidyne complex 7 by reductive elimination of dihydrogen or with $PPh_3$ to afford a 62 VE "butterfly" complex $CpWOs_3(CO)_{10}(PPh_3)(μ_3 - CTol)(μ - H)_2$ (12). Thermolysis of 8 in the presence of water gives a hydrido oxo alkylidene complex syn-$CpWOs_3(CO)_9(μ - O)(μ - CHTol)(μ - H)$ (9a), in which the tolyl substituent on the alkylidene carbon is oriented syn to the μ-oxo ligand. Thermolysis of 10 at 110 induces decarbonylation to give a tetrahedral alkylidyne complex $CpWOs_3(CO)_9(μ - O) (μ_3 - CTol)$ (11), which is reversibly converted back to 10 upon exposure to c...