Preparation and reactivity of cis-bis(cyclopentadienyldiphenylphosphine) (tetracarbonyl)molybdenum and cis-[1,3-bis(diphenylphosphino)dicyclopentadiene] (tetracarbonyl)molybdenum. X-ray crystal structure of 2[(C5H5)Mo]2(μ-PPh2) 2(CO)(O)·C6H14