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 n (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. # 2002 Elsevier Science B.V. All rights reserved.