Conjugate addition of acetylides to complexes of type [M(CO)4{(Ph2P)2CCH2}](M = Cr, Mo, or W): crystal structure of [M(CO)4{(Ph2P)2CCHCHCHPh}] formed by the base-catalysed isomerization of [M(CO)4{(Ph2P)2CHCH2CCPh}]

Abstract

Although treatment of [W(CO)₄{(Ph₂P)₂CCH₂}] with Li(CCPh) resulted in no conjugate addition, in the presence of Me₂NCH₂CH₂NMe₂ smooth addition occurred to give [W(CO)₄{(Ph₂P)₂CHCH₂CCPh}](1c). Similar additions were effected with the corresponding complexes of Cr and Mo, and other acetylides, Li(CCR) where R = C₆H₄Me-p, Me, Prⁿ, or Buⁿ, underwent addition. Treatment of [W(CO)₄{(Ph₂P)₂CHCH₂CCPh}] with KOBu^t in PrⁱOH gave the dienephosphine complex [W(CO)₄{(Ph₂P)₂CCHCHCHPh}](2a); the p-tolylactylide complex [W(CO)₄{(Ph₂P)₂CCHCHCHC₆H₄Me-p}] was also prepared. Crystals of compound (2a) are monoclinic, space group P2₁/c with a= 988.4(3), b= 1 069.7(2), c= 3 233.7(4) pm, β= 94.73(2)°, and Z= 2; final R= 0.0334 and R′= 0.0316 for 3 929 observed reflections. Hydrogen-1 and ³¹P-{¹H} n.m.r. and i.r. data are given.