PHOSPHIDO-BRIDGED HETEROBIMETALLIC COMPLEXES DERIVED FROM NIOBOCENE AND DIIRON NONACARBONYL - CRYSTAL-STRUCTURE OF CP(2)NB(MU-PPH(2))(MU-CO)FE(CO)(3)

The terminal phosphido complexes Cp(2)Nb(CO)PR(2) (R = Ph, Me) prepared by published procedures react with Fe-2(CO)(9) to give a mixture of mono- and dibridged compounds Cp(2)Nb(CO)(mu-PR(2))Fe(CO)(4) and Cp(2)Nb(mu-PR(2))(mu-CO)Fe(CO)(3). Removal by photolysis of one CO from the monobridged complexes produced the dibridged compounds. All new mono- and dimetallic complexes have been characterized by H-1 and P-31 NMR and IR spectroscopy, and EHMO calculations have been carried out on dimethylphosphido derivatives. The complex Cp(2)Nb(mu-PPh(2))(mu-CO)Fe(CO)(3) crystallizes in the triclinic space group P ($) over bar 1 with a = 7.936(7) Angstrom, b = 10.010(7) Angstrom, c = 15.153(8) Angstrom, alpha 91.26(5)degrees, beta = 92.80(6)degrees, gamma = 101.23(6)degrees, V = 1178.8 Angstrom(3), R = 0.046, and Z = 2. The molecular structure reveals a short distance between metallic centers (Nb-Fe = 2.884(2) Angstrom), indicating the existence of a metal-metal bond. Dibridged complexes Cp(2)Nb(mu-PR(2))(mu-CO)Fe(CO)3 (R Ph, Me) did not react with CO, but a good donor Ligand (PMe(2)Ph) displaced the metal-metal bond, leading to new phosphido-monobridged compounds without a metal-metal bond, Cp(2)Nb(CO)(mu-PR(2))Fe(C0)(3)(PMe(2)Ph).