TERMINAL AND BRIDGED DIPHENYL PHOSPHIDO COMPLEXES DERIVED FROM NIOBOCENE AND GROUP-6 METAL-CARBONYLS (CR, MO, W) - STRUCTURES OF CP(2)NB(L)(MU-PPH(2))CR(CO)(5),S (L=CO, S=CH3COCH3 L=P(OME)(3), S=C6H5CH3)

New terminal monophosphido complexes derived from bent niobocene Cp(2) Nb(L)PPh(2)(L = P(OMe)(3) PMe(2)H) have been prepared by a procedure d escribed earlier for Cp(2)Nb(CO)PPh(2). These metallophosphines have b een used to bind the M(CO)(5) (M = Cr, Mo, W) fragments. The expected dimetallic monobridged complexes of the type Cp(2)Nb(L)(mu-PPh(2))M(CO )(5)(L = CO, P(OMe)(3),PMe(2)H; M = Cr, Mo, W) are formed. When L = CO the dibridged compounds Cp(2)Nb(mu-PPh(2))(mu-CO)M(CO)(4)(M = Cr, W) are also obtained. All new mono- and dimetallic complexes have been ch aracterized by H-1 and P-31 NMR and IR spectroscopies. X-ray diffracti on studies of solvated Cp(2)Nb(CO)(mu-PPh(2))Cr(CO)(5) and Cp(2)Nb(P(O Me)(3))(mu-PPH2)Cr(CO), indicate that the metallic centers in both com plexes are tethered by a single bridge. The large Nb-P-Cr angles (125. 94(8) and 129.11(5)degrees, respectively) and the long Nb-Cr distances (4.653(1) and 4.7575(9) Angstrom, respectively) clearly show the abse nce of metal-metal interaction.