Diiron acetylide complexes: Molecular structures of [Fe2(CO)4(mu-C CPh)(mu-PPh2)(mu-dppm)] and [Fe-2(CO)(3)(Ph2PC CPh)(mu-C CPh)(mu-PPh2)(mu-dppm)]

The synthesis and X-ray crystal structures of two diiron acetylide complexes [Fe-2(CO)(4-n)(Ph2PC=CPh)(n)(mu-C=CPh)(n)(mu-PPh2)(mu-dppm)](1, n = 0; 2, n - 1) are presented together with the synthesis of [Fe-2(CO)(3){P(OEt)(3)}(mu-C=CPh)(mu-PPH2)(mu-dppm)] 3; structural comparisons made with related phosphido-bridged diiron complexes are used to elucidate the role of ground state structural changes in the sigma-pi acetylide fluxionality. (C) 1997 Elsevier Science S.A.