Preparation, Mechanism, and Structural Study of Group 6 Transition Metal 2-Substituted η³-Butadienyl Complexes:  Crystal Structure of [WCl(CO)₂{η³-CH₂C(COSBuⁿ)CCH₂}(1,10-phenanthroline)]

The complexes [WCl(CO)₂(η³-CH₂C(COX)CCH₂)L₂] (X = Cl; L₂ = 2,2‘-bipyridyl, 1,10-phenanthroline) (1) containing a 2-substituted butadienyl ligand were isolated from reactions of Ph₄P[WCl(CO)₃L₂] and excess 1,4-dichlorobut-2-yne in chlorinated solvents. Spectroscopic evidence supports analogous reactions for the chromium analogue. Addition of 1 to alcohol, amine, or thiol (HX) gave good yields of the related ester (X = OMe), amide (X = NEt₂), or thiolate (X = SBuⁿ) complexes, respectively. Mechanisms and supporting evidence for the formation of 1 and the ester complex are proposed and discussed. Some differences in reactivity of Ph₄P[MCl(CO)₃L₂] with 1,4-dichlorobut-2-yne in methanol are reported for M = Mo and M = W. The structure of [WCl(CO)₂(η³-CH₂C(COSBuⁿ)CCH₂)(1,10-phenanthroline)] was confirmed by single-crystal X-ray diffraction analysis.