Hexyne Complexes of Molybdenum ( II ) and Tungsten ( II ) Containing 2 , 2 '-Bipyridine . X-Ray Crystal Structure of [ MoI 2 ( CO ) ( bipy ) ( 7 2-EtC 2 Et ) ]

Reaction of [MI2(CO)(NCM e)(j/2-EtC2Et)2] (M = Mo,W) with one equivalent of 2,2 -bipyri­ dine (bipy) in CH2C12 at room temperature gives either the neutral complex, [MoI2(CO)(bipy)(?72-EtC2Et)] (1) or the cationic complex, [W I(CO)(bipy)(/72-EtC2Et)2]I (2). The neutral molybdenum complex 1, has been crystallographically characterised, and has a pse«do-octahedral geometry with the iodo-ligand trans to the 3-hexyne, and with the bipy, carbon monoxide and other iodo-ligand occupying the equatorial face. 13C NM R studies show the 3-hexyne is donating four electrons to the molybdenum in 1. the cationic tungsten complex, [WI(CO)(bipy)(7 2-EtC2E t)2]I (2).