To prevent dimerization from occurring, the size and shape of R is likely of critical importance. This notion is corroborated by our previous observation that the alkylidyne complex 6a decomposes by bimolecular coupling with formation of the corresponding tolane and the homobimetallic dimer 8 (Scheme 1). Methyl substituents on the silicon linkers do obviously not suffice to prevent metal-metal bonding from occurring. Interestingly though, reaction of 1 with the free ligand 9a failed to afford this product but gave an ill-defined oligomer.