Organic syntheses via Transition metal complexes. 72. (2-(acyloxy)ethenyl)carbene complexes by Michael addition of carboxylic acids to alkynylcarbene complexes (M = Cr, W). (2-(acyloxy)ethenyl)ketene imines by ligand disengagement with isocyanide

Article abstract of DOI:10.1021/om00021a025

(2-(Acyloxy)ethenyl)carbene complexes (CO)₅M=C(OEt)-CH=C(OCOR)Ph [(Z)-5] (M = Cr, W; R = Ph, p-Me₂NC₆H₄, CH₃, c-C₇H₇CH₂, PhCH=CPh, Me₂C=CH, 1,4-C₆H₄) are obtained by the addition of carboxylic acids R-CO₂H (4) to alkynylcarbene complexes (CO)₅M=C-(OEt)-C≡CPh (1) (M = Cr, W) in the presence of Et₃N at 20°C in 71-78% isolated yields. The reaction is regio- and stereochemically uniform. (Z)-5g (R = PhCH=CPh), C₃₁H₂₂O₈W, was characterized by X-ray diffraction. It crystallizes in space group P1 with cell parameters a = 10.381(6) A?, b = 11.444(6) A?, c = 13.509(7) A?, α = 107.84(4)°, β = 91.54(4)°, γ = 108.49-(4)°, Z = 2, R₁ = 0.0354, and wR₂ = 0.0811. Ligand disengagement from (Z)-5 with tert-butyl isocyanide (8b) at 20°C results in the formation of [2-(acyloxy)ethenyl]ketene imines t-BuN=C=C(OEt)-CH=C(OCOR)Ph [(Z)-11] (>95% yields).