Oxidative addition of Ph3PCHCHO to [Os3(CO)10(MeCN)2]

Abstract

(Triphenylphosphoranylidene)ethanal (Ph₃PCHCHO) rapidly adds at room temperature or below to [Os₃(CO)₁₀(MeCN)₂] to give the light-sensitive isomeric clusters [Os₃(µ-H)(µ-Ph₃PCCHO)(CO)₁₀]1(39%) and [Os₃(µ-H)(µ-Ph₃PCHCO)(CO)₁₀]2(34%) derived by C–H bond cleavage at the CHCHO and CHCHO positions respectively. Rates of oxidative addition are higher than for aldehydes or alkenes because of the greater nucleophilicity of this reagent; a reaction step involving co-ordination at osmium rather than subsequent C–H cleavage is probably rate-determining. Cluster 1 decarbonylates in daylight to give [Os₃(µ-H)(µ₃-Ph₃PCCHO)(CO)₉]3 containing the µ₃-ligand co-ordinated through an alkylidene bridge and a formyl group (X-ray structure). Cluster 3 is photochemically stable but thermally decarbonylates to give [Os₃(µ-H)₂(µ₃-C₆H₄PPh₂CCHO)(CO)₈]5(X-ray structure) by orthometallation at one Ph ring of the triphenylphosphonium group. Like its isomer 1, the decacarbonyl 2 also decarbonylates in visible light to give in this case two isomers of 3, [Os₃(µ-H)(µ₃-Ph₃PCHCO)(CO)₉]4a and 4b, which differ only in the stereochemistry at the carbon atom Ph₃PCHCO. Selection of one crystal from a mixture of 4a and 4b allowed the crystal structure of isomer 4a to be determined.