CYCLOPENTADIENYLNIOBIUM(V) PHOSPHINE CHEMISTRY - ADDUCT FORMATION VS REDUCTION X-RAY STRUCTURE OF CPNBCL(4)(PMEPH(2))

The reaction between CpNbCl(4) and the phosphine ligands PMe(x)Ph(3-x) (x = 0, 1, 2, 3) has been investigated. While no reaction occurs with PPh(3), stable adducts are formed with all the other ligands in the a bove series. These have been isolated and characterized by elemental a nalysis, H-1 and P-31-NMR spectroscopy, and an X-ray structural determ ination for the PMePh(2) adduct. The three phosphines PMe(3), PMe(2)Ph , and PMePh(2), however, also engage in a subsequent reduction process with formation of Cl radicals and Nb(IV) complexes. CpNbCl(3)(PMe(3)) (2) has been independently synthesized from CpNbCl(4), Na, and PMe(3) in a 1:1:2 ratio and fully characterized. The relative rate of reducti on depends on the nature of the phosphine, increasing in the order PMe Ph(2) < PMe(2)Ph < PMe(3). X-ray data for CpNbCl(4)(PMePh(2)): monocli nic, C2/c, a = 23.818(2) Angstrom, b = 12.4719(10) Angstrom, c = 15.81 37(12) Angstrom, beta = 106.365(7)degrees, V = 4507.2(6) Angstrom(3), Z = 8, D-x = 1.609 g . cm(-3), mu(Mo K alpha) = 0.603 mm(-1), R = 0.03 49 for 329 parameters and 3989 data with I > 2 sigma(I). The structure shows a distorted pseudooctahedral geometry with the Cp and PMePh(2) ligands occupying two axial coordination sites and the four equatorial Nb-Cl bonds being bent away from the Cp ring.