DIBRIDGED BIMETALLIC COMPLEXES DERIVED FROM BENT NIOBOCENE AND GROUP-6 METAL-CARBONYLS - TRANSMETALATION OF THE PME(2)H LIGAND AND CRYSTAL-STRUCTURE OF CP(2)NB(MU-PPH(2))(MU-CO)CR(CO)(3)(PME(2)H)

The bimetallics Cp(2)Nb(mu-PPh(2))(mu-CO)M(CO)(3)(PMe(2)H) (M = Cr, W) were prepared by UV irradiation of the dinuclear monobridged complexe s Cp(2)Nb(PMe(2)H)(mu-PPh(2))M(CO)(5). These compounds may also be obt ained in good yield directly from metallophosphine Cp(2)Nb(PPh(2))(PMe (2)H) and Cr(CO)(4)(eta(4)-norbomadiene) or W(CO)(4)(piperidine)(2). T heir formations are accompanied by the transfer of the PMe(2)H ligand from Nb to M (M=Cr, W). The Nb-Cr distance of 3.02(1) Angstrom observe d in the structure of Cp(2)Nb(mu-PPh(2))(mu-CO)Cr(CO)(3)(PMe(2)H) indi cates the presence of a direct metal-metal bond and agrees with the P- 31 NMR data.