Enlargement of the scope of the carbon–carbon coupling reactions between Fischer-type metallaalkylidyne and organopalladium compounds

The carbyne carbon atom of the ‘Fischer-type’ metallaalkylidyne complexes: (η5-C5H5)(CO)2MoC-pTol (1) is readily coupled with the palladated carbon atom of the organometallic compounds [Me(PPh3)Pd(μ-X)]2, (X=Cl, I; 2, 3) affording novel stable μ-alkylidene complexes [{Cp(OC)(μ-OC)Mo}{μ-C(4-Tol)Me}Pd(PPh3)X] (X=Cl, I; 4, 5). Compound 4 has been fully characterised through a crystal structure analysis, which shows that a molybdaalkylidene unit is interacting with a palladium(triphenylphosphine)chloride unit via an alkylidene carbon, the molybdenum and the carbon atom of a carbonyl group. The phosphine and the halide ligands of these new dimetallic complexes can reversibly exchange their role in solution leading to a mixture of isomers in which the phosphine is either cis or trans to the alkylidene carbon atom bridging the two metals. [Me(SEt2)Pd(μ-Cl)]2 (6) led to a chloride bridged dimer (7) through the C–C coupling reaction with 1. Compound 7 allowed the entry into a larger class of μ-alkylidene species structurally related to 4 via bridge-splitting reactions by neutral ligands such as 4-methylpyridine for example to afford 8.