SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF NIOBIUM(IV) AMIDO COMPLEXES AND A NIOBIUM(V) BIS(IMIDO) COMPLEX

NbCl4(thf)(2) and 4 equiv of LiNPh(2) react to give the homoleptic Nb(TV) compound Nb(NPh(2))(4). The reactions of NbX(4)(thf)(2) (X = Cl, Br) with 2 equiv of lithium bis(trimethylsilyl)amide lead to the Nb(IV) amido halide complexes Nb(N(SiMe(3))(2))(2)X(2), but the reaction of NbCl4(PMe(3))(2) with 2 equiv of LiNH(2,6-C6H3-i-Pr-2) gives the Nb(V) bis(imido) complex Nb(N-2,6-C6H3-i-Pr-2)(2)Cl(PMe(3))(2). A better preparation of the bis(imide) involves reacting [Nb(NEt(2))(2)Cl-3](2) sequentially with 2 equiv of LiNH(2,6-C6H3-i-Pr-2) and PMe(3). Crystal data (Mo K alpha radiation, lambda = 0.71073 Angstrom): Nb(NPh(2))(4), C48H40N4Nb, T = -50 degrees C, a = 10.596(3), b = 11.622(4), c = 16.177(5), alpha = 86.75(2)degrees, beta = 80.63(2)degrees, gamma = 80.33(3)degrees, triclinic, space group <P(1)over bar >, Z = 2; Nb(N(SiMe(3))(2))(2)Br-2, C12H36Br2N2NbSi4, a = 16.802(1) Angstrom, b = 8.7345(6) Angstrom, c = 20.388(2) Angstrom, beta = 121.241(6)degrees, monoclinic, space group C2/c, Z = 4; Nb(N-2,6-C6H3-i-Pr-2)(2)Cl(PMe(3))2, C30H52ClN2NbP2, a = 17.1309(11) Angstrom, b = 9.6722(7) Angstrom, c = 20.7702(15) Angstrom, beta = 95.934(6), monoclinic, space group P2(1)/c, Z = 4.