PHOSPHORANE IMINATO COMPLEXES OF NIOBIUM AND TANTALUM - CRYSTAL-STRUCTURES OF [NBCL4((NPPR3)-PR-I)(CH3CN)], [NBCL3((NPPR3)-PR-I)(2)], [TACL4((NPPR3)-PR-I)](2), AND [TACL3((NPPR3)-PR-I)(2)]

The title compounds have been prepared from the pentachlorides of niob ium and tantalum with the silylated phosphorane imine Me(3)SiNP(i)Pr(3 ). They are characterized by IR spectroscopy and crystal structure det erminations. NbCl4((NPPr3)-Pr-i)(CH3CN)]. Space group Pna2(1), Z = 4, 2102 observed unique reflections, R = 0.022. Lattice dimensions at -50 degrees C: a = 1627.2, b = 876.3, c = 1335.3 pm. The compound forms m onomeric molecules with the acetonitrile molecule in trans position to the phosphorane iminato group. This group shows a short NbN distance of 178.2 pm with a NbNP bond angle of 165.2 degrees. [NbCl3((NPPr3)-Pr -i)(2)]. Space group Cc, Z = 4, 2534 observed unique reflections, R = 0.046. Lattice dimensions at 20 degrees C: a = 1302.65, b = 1321.69, c = 1672.04 pm, beta = 111.713 degrees. The compound forms monomeric mo lecules with a distorted bipyramidal surrounding of the niobium atom a nd equatorially arranged phosphorane iminato groups. [TaCl4((NPPr3)-Pr -i)](2). Space group Pbca, Z = 4, 1537 observed unique reflections, R = 0.037. Lattice dimensions at -40 degrees C: a = 1420.6, b = 1483.9, c = 1622.0 pm. The compound forms centrosymmetric dimeric molecules wi th dissimilarly long Ta2Cl2 bridges and equatorially arranged phosphor ane iminato groups. [TaCl3((NPPr3)-Pr-i)(2)]. Space group Cc, Z = 4, 5 737 observed uni que reflections, R = 0.039. Lattice dimensions at -50 degrees C: a = 1303.9, b = 1327.2, c = 1682.1 pm, beta = 111,92 degre es. The compound is isotypical with the corresponding niobium compound .