Synthesis, structure and benzannulation of chalcogen-tethered Fischer carbene complexes

Addition of PhSH–NEt3 or PhSeNa to Phsingle bondCtriple bond; length of mdashCsingle bondC(OC2H5)double bond; length as m-dashM(CO)5 [M = Cr or W] afforded stable, β-chalcogenide tethered conjugated carbene complexes 3–6 as a mixture of E,Z-isomers. The Z-configuration was ascribed to those isomers that readily yield cyclometallated complexes. Aminolysis with methylamine yielded corresponding amino carbene complexes as mixtures of E,Z-isomers. Alkylation by methyl iodide afforded separable E,Z-isomers of dimethylamino complexes. One-step aminolysis of ethoxy carbene complexes with dimethylamine furnished only the Z-isomer of the dimethylamino complex. The Z-isomer of dimethylamino carbene complexes yielded cyclometallated products on warming. Representative crystal structures of these complexes confirm isomer assignments. Only E-isomers of the S or Se-tethered ethoxy complexes undergo benzannulation reaction with alkynes, with loss of chalcogenide atom.