REACTIONS OF CARBON-MONOXIDE WITH PHOSPHINE ADDUCTS OF NB(2,4-C7H11)2 - SPONTANEOUS REDUCTION TO NIOBIUM(I) COMPLEXES

The reactions of 17 electron Nb(2,4-C7H11)2(L) species (L = PEt3, PMe2C6H5) with CO lead to the loss of one pentadienyl ligand and formation of the 18 electron Nb(I) complexes Nb(2,4-C7H11)(L)(CO)3 in high yield. One carbonyl ligand may be thermally replaced by a second equivalent of phosphine, yielding ''trans''-Nb(2,4-C7H11)(PMe2Ph)2(CO)2, which adopts something close to a piano-stool geometry with the phosphines located by the open dienyl edge and the central dienyl carbon atom. The Nb(2,4-C7H11)(L)(CO)3. complexes are also susceptible to reduction by alkali metals, presumably leading to Nb(2,4-C7H11)(CO)32-. Oxidation of these species under CO leads to Nb(2,4-C7H11)(CO)4. Structural determinations have been carried out for Nb(2,4-C7H11)(PMe2Ph)(CO)3 and Nb(2,4-C7H11)(PMe2Ph)2(CO)2. For the former the space group is P1 with a = 7.911(5) angstrom, b = 10.490(6) angstrom, c = 12.829(6) angstrom, alpha = 105.61(4)degrees, beta = 95.88(4)degrees, gamma = 107.59(4)degrees, and V = 957.5(8) angstrom3 for Z = 2. The structure has been refined to discrepancy indices of R = 0.031 and R(w) = 0.034. For the latter the space group is P2(1)/c with a = 11.778(2) angstrom, b = 13.966(2) angstrom, c = 15.930(3) angstrom, beta = 96.33(1)degrees for Z = 4. The structure was refined to discrepancy indices of R = 0.037 and R(w) = 0.039.