λ3‐1,3‐Diphosphacyclobutadiene‐Cobalt Complexes by Cyclodimerization of λ3‐Phosphaalkynes

Abstract λ3‐Phosphaalkynes PCR [R = tert‐butyl (1a) or isopropyl (1b)] react with (η5‐cyclopentadienyl)bis(ethene)cobalt (2) or bis(ethene)(η5‐indenyl)cobalt (3) by displacement of ethene to yield the (η4‐1,3‐diphosphacyclobutadiene)cobalt complexes 4a, b and 5a, b. These are the first reported syntheses of a λ3‐1,3‐diphosphacyclobutadiene (λ3‐1,3‐diphosphete)14,15). Complex 4 reacts smoothly with the lone pairs of the phosphorus atoms to give the dinuclear or trinuclear cobalt complexes 6a, b and 7a, b. The structures of the new complexes 4–7 have been elucidated by spectroscopic methods, especially 13C‐NMR spectroscopy. The X‐ray analyses of 4a and 5a confirm these structures.