LINKING METAL CENTERS WITH 1,4-BIS(DIPHENYLPHOSPHINO)BUT-2-YNE (DPPBU) - SYNTHESES AND MOLECULAR-STRUCTURES OF [(MO(CO)(4)(MU-DPPBU))(2)] AND [(MO(CO)(4)(ETA(2)-DPPBU))(3)(MO(CO))]

Addition of cis-[Mo(CO)(4)(piperidine)] to 1,4-bis(diphenylphosphino)b ut-2-yne (DPPBu) affords [{Mo(CO)(4)(mu-DPPBu)}(2)] (1) and [{Mo(Co)(4 )(eta(2)-DPPBu)}(3){Mo(CO)}] (2), both of which have been characterise d crystallographically. Three different bonding modes of the diphosphi ne are seen in the two complexes. In 1 it bridges molybdenum tetracarb onyl centres via coordination through phosphorus to give a 14-membered ring with a chair-like configuration, while in 2 the diphosphine chel ates molybdenum tetracarbonyl centres, and three of these units are fu rther complexed to a molybdenum carbonyl fragment via coordination of the carbon-carbon triple bonds.