Alkynylcarbyne(bipyridine)dicarbonyl(triflouroacetato) complexes—synthesis and detection of reversible association in solution

A series of alkynylcarbyne(bipyridine)(dicarbonyl)trifluoroacetato complexes, [CF3COO(LL)(CO)2MCCCR] (M=W, Mo; LL=2,2′-bipyridine, 4,4′-dimethyl 2,2′-bipyridine; R=SiMe3, Ph, p-Tol, t-Bu), has been prepared by sequential reaction of [M(CO)6] with Li[CCR], trifluoroacetic anhydride, and LL. All complexes were fully characterized. Concentrated solutions of these complexes exhibit two sets of ν(CO) absorptions (instead of the expected one set (A1/B1). The ratio A1/B1:A1*/B1* is concentration-dependent and decreases with increasing concentration of the complexes in solution. This phenomenon is discussed on the basis of a reversible association of complex molecules to form dimers and oligomers prior to precipitation and crystallization.