Oxidative dehydrodimerization of manganese phenylvinylidene complex (η5-C5H5)(CO)2MnCC(H)Ph. X-ray structure of phenyl(trityl)vinylidene complex (η5-C5H5)(CO)2MnCC(CPh3)Ph

The oxidatively induced dehydrodimerization of the manganese vinylidene complex (η5-C5H5)(CO)2MnCC(H)Ph (I) to the bis-vinylidene compound (η5-C5H5)(CO)2MnCC(Ph)C(Ph)CMn(CO)2(η5-C5H5) (II) proceeds via CβH bond homolysis in the radical cation (I+radical dot) and is thought to involve the formally 16-electron mononuclear σ-phenylethynyl cation [(η5-C5H5)(CO)2MnCCPh]+ (III) and the bis-carbyne dication [(η5-C5H5)(CO)2MnCC(Ph)C(Ph)CMn(CO)2(η5-C5H5)]2+ (II2+) as the key sequential intermediates. Compound II2+ was characterized by IR and CV. The reduction of II2+ with (C6H6)2Cr gave II in an 80% yield. Compound II can be prepared more conveniently by treating I with (C5H5)2FeBF4 in the presence of Et3N. The interaction of I with Ph3CPF6 yields the trityl(phenyl)vinylidene complex (η5-C5H5)(CO)2MnCC(CPh3)Ph (IV) as a result of the electrophilic attack of the trityl cation on Cβ followed by the loss of a proton. The structure of IV was established by an X-ray structural analysis.