Abstract
The chemistry of Cp2V2(CO)5 (I) with alkynes is reported. In non-coordinating solvents, I reacts with large, electron-poor alkynes to give the cyclobutadiene complexes CpV(CO)2(C4R4), which are not formed from photolysis of CpV(CO)4 in the presence of alkyne. Smaller, more basic alkynes give simple monomeric adduct products of the type CpV(CO)2(RCCR). This latter product is the only one obtained if coordinating solvents are employed. It is demonstrated that coupling to form the cyclobutadiene ligand occurs on the dimer. The dimeric intermediate, produced at low temperature and observed at low temperature by IR and NMR, is believed to have the formula Cp2V2(CO)4(μ-RCCR) (X). Cp2V2(CO)5 is active as a catalyst precursor in the photochemical hydrogenation of diphenyl acetylene to cis-stilbene. The mechanism appears to proceed through a Cp2V2(CO)4(alkyne) intermediate.
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