Alkynyl Selenolate Complexes of Iron, Nickel, and Molybdenum

The successive treatment of terminal alkynes, HCCR (R = C6H4Me-4, SiMe3), with nBuLi and gray selenium affords LiSeCCR, which in turn reacts with [FeCl(CO)2(η-C5H5)], [NiCl(PPh3)(η-C5H5)], and [MoI(CO)3(η-C5H5)] to afford the alkynylselenolato complexes [Fe(SeCCR)(CO)2(η-C5H5)], [Ni(SeCCR)(PPh3)(η-C5H5)], and [Mo(SeCCR)(CO)3(η-C5H5)], two examples of which have been structurally characterized. When [MoI(CO)3{HB(pz)3}] (pz = pyrazol-1-yl) was however employed as the electrophile, low yields of the selenoketenyl complex [Mo(η2-C,C′-SeCCR)(CO)2{HB(pz)3}] were obtained via the presumed intermediacy of the alkynylselenolato complex [Mo(σ-SeCCR)(CO)3{HB(pz)3}], which is perhaps destabilized relative to the selenoketenyl complex by the octahedral enforcer character of the HB(pz)3 ligand.