Binuclear Complexes with an Aminocarbene−Cyclopropenylidene Unit as Bridging Ligand:  Facile Migration of Carbonylmetal Fragments in Carbene Complexes^†

The sequential reaction of the (dimethylamino)ethynylcarbene complexes [(CO)(5)M=C-(NMe2)CdropCH] (1a-c: M = W (a), Mo (b), Cr (c)) with BuLi, [M(CO)(6)], and CF3SO3CH3 affords homobinuclear complexes with an aminocarbene-cyclopropenylidene bridging ligand, [(CO())5M=C(NMe2)C=C(OMe)CdropM(CO)(5)] (3a-c). Two isomeric heterobinuclear complexes (4xy and 4yx) are formed in the reaction Of [(CO)(5)M=C(NMe2)CdropCH] (1) with BuLi, [M'(CO)(6)] (M not equal M': W, Mo, Cr), and CF3SO3CH3. 4xy and 4yx differ in the relative distribution of the metals M and M': [(CO)(5)M=C(NMe2)C=C(OMe)C=M'(CO)(5)] (4xy) and [(CO)(5)M'=C(NMe2)C=C(OMe)C=M(CO)(5)] (4yx). The 4xy/4yx ratios obtained by the two different possible reaction sequences are similar. Complexes 4xy and 4yx do not interconvert. The reaction of Cis-[(CO)(4)(Me3P)W=C(NMe2)CH] with BuLi, [W(CO)(6)], and CF3SO3CH3 likewise gives two isomers, CiS-[(CO)(4)(Me3P)W=C(NMe2)C=C(OMe)C=W(CO)(5)] (7) and [(CO)(5)W=C(NMe2)C=C(OMe)C=M(PMe3)(CO)(4)] (8). These results demonstrate the facile migration of carbonylmetal fragments along a carbon chain. The structures of the complexes 3b,c and 7 have been established by X-ray structural analyses.