Stabilization of vinylic intermediates in the addition, cyclization, and oligomerization reactions of alkynes by coordination of molybdenum and tungsten. The crystal and molecular structure of [W(SC6H4Me-p)[η2-C(CF3)C(CF3)PEt3] (η2-CF3C≡CCF3)(η-C5H5)] and [WCl[η2-C(CF3)C(CF3)CN](η2-CF3C≡CCF3)(η-C5H5)]

Nucleophilic attack of phosphines, phosphites or Me3CNC on the η2-CF3C≡CCF3 (L) complexes L2WBr2(CO) and L2MX(Cp) (Cp = η5-cyclopentadienyl; M = Mo, W, X = Cl, SC6F5; M = W, X = SC6H4Me-p) occurs at an acetylenic C atom to give 1:1 adducts. The products, I [X = SC6H4Me-p, L1 = PEt3 (II); X = Cl, L1 = Me3CNC (III)] were shown by x-ray diffraction to contain a metal-stabilized 1-3 dipolar vinyl ligand L+C(CF3)C-(CF3) η2-coordinated to the W center. The structures of II and III were refined to R 0.038, 0.040, for 2924, 6900 independent reflections, resp.