Characterization and Reactivity of the Tetrametallic Pd2-Mo2 Complex Ph(Bu)P(η5 C5H4)Mo(CO)3Pd(m-I)2PdMo(CO)3(η5-C5H4)P(Ph)Bu and its Use to Model Pd Catalyzed Cross-Coupling Reactions Leading to M-CºC Bonds

The mechanism of the Pd-catalyzed cross-coupling reaction between tributyltin acetylides and metal iodides has been investigated with the use of a model Mo precursor bearing a ligand with appropriate steric and electronic properties. This study has allowed us to intercept the tetrametallic Pd2-Mo2 complex Ph(Bu)P(è5-C5H4)Mo(CO)3Pd(í-I)2PdMo(CO)3(è5-C5H4)-P(Ph)Bu, which is a precursor to the catalytically active solvento complex Ph(Bu)P(è5-C5H4)Mo(CO)3PdI(DMF). Both complexes play a key role in Pd-catalyzed cross-coupling reactions between tributyltin acetylides and metal iodides, leading to metal-ó-alkynyls. The catalytic cycle for such a reaction has been further elucidated, especially with regard to the role of the ligands in the metal iodide for the stabilization and/or detection of the intermediates as well as for the formation of the M-alkynyl product.