Reactions of complex ligands 74. Alkyne carbene chromium chelates: Synthesis, structure and carbene dimerization

Article abstract of DOI:10.1016/S0022-328X(97)00072-7

An alkyne-carbene chromium chelate 2, a model complex for the first intermediate of the benzannulation reaction, is generated by low-temperature photodecarbonylation of pentacarbonyl[(tert-butylethynylphenyl)methoxycarbene]chromium 1. X-ray structure determinations and ¹³C NMR studies on both compounds indicate only a weak coordination of the alkyne both in the solid state and in solution. Whereas thermal dimerization of the carbene ligand is directed by less bulky alkyne substituents to give chrysenes, pentacarbonyl complex 1 affords a mixture of stilbene diastereomers.