SYNTHESIS AND REACTIVITY OF LOW-VALENT AMIDO, IMIDO, AZAVINYLIDENE, AND NITRIDO COMPLEXES OF TUNGSTEN

Amido complexes Tp'(CO)2W(NHR) [Tp' = hydridotris(3,5-dimethylpyrazolyl)borate; R = Bu(t), 1a; R = Ph, 1b; R = BU(n), 1c; R = CH2Ph, 1d; R = H, 1e] have been synthesized by reaction of the corresponding amine (NH2R) with Tp'(CO)2WI (2). These ambiphilic amido complexes have been utilized as precursors to both anionic imido complexes, Tp'(CO)2W(NR)- (R = Ph, 3a; R = CH2Ph, 3b; R = H, 3c), and cationic imido complexes, Tp'(CO)2W(NR)+ (R = Bu(t), 5a; R = Ph, 5b; R = Bu(n), 5c; R = CH2Ph, 5d; R = H, 6a; R = CPh3, 6b). Treatment of the unstable anionic imido species 3a-c with PhCH2Br (3a) or Mel (3b,c) leads to the formation of dialkyl substituted amido complexes Tp'(CO)2W(N(R)R') (R = Ph, R' = CH2Ph, 4a; R = CH2Ph, R' = Me, 4b; R = R' = Me, 4c). The structures of 4a and 4c have been confirmed by X-ray diffraction. (4a.CH2Cl2 crystallizes in space group P1BAR with Z = 2, a = 11.452(2) angstrom, b = 11.597(2) angstrom, c = 14.144(2) angstrom, alpha = 86.78(1)-degrees, beta = 84.41(l)-degrees, gamma = 64.37(1)-degrees, R = 3.7%, R(w) = 4.6%; 4c crystallizes in space group P1BAR with Z = 2, a = 11.151(4) angstrom, b = 11.702(3) angstrom, c = 10.391(4) angstrom, alpha = 93.46(3)-degrees, beta = 108.56(3)-degrees, gamma = 63.20(3)-degrees, R = 3.9 %, R(w) = 4.3%.) Reactivity studies were carried out with the cationic nitrene complexes, Tp'(CO)2W(NR)+. Deprotonation of Tp'(CO)2W(NCH2R)+ (R = Pr(n), 5c; R = Ph, 5d) yields azavinylidene complexes, Tp'(CO)2W(N=CHR) (R = Prn, 7a; R = Ph, 7b). The barrier to rotation around the WNC unit of 7a as determined by variable temperature NMR studies is 9.6 kcal/mol. Addition of LiBH4 to the cationic nitrene complex 5b results in formation of a formyl intermediate, Tp'(CO)(CHO)W(NPh) (8), which undergoes hydride migration from carbon to nitrogen to form the amido complex lb at -70-degrees-C. Deprotonation of the parent nitrene cation Tp'(CO)2W(NH)+ (6a) or reaction of [(Ph3P)2N] [N3] with Tp'(CO)2WI (2) yields an unstable nitrido complex Tp'(CO)2WN (9). Complex 9 reacts with a variety of electrophiles (RX) to form both dicarbonyl, [Tp'(CO)2W(NR)][X] (R = H, X = BF4-, 6a; R = CPh3, X = PF6, 6b; R = Me, X = OTf-, 10), as well as monocarbonyl, Tp'(CO)(X)W(NR) (R = Ts, X = Cl, 11a; R = C(O)CH3, X = Cl, 11b; R=C(O)CH3, X=OC(O)CH3, 11c), imido products. The X-ray structures of nitrene complexes Tp'(CO)2W(NPh)+(5b) and Tp'(CO)Cl2W(NTs)(11a) reveal linear imido ligands for both cationic and neutral complexes with WN bond lengths of 1.775(7) and 1.78(1) angstrom, respectively. (5b crystallizes in space group P2(1)/n with Z = 4, a = 10.301(2) angstrom, b = 10.389(2) angstrom, c = 27.816(7) angstrom, beta = 97.69(2)-degrees, R = 3.6%, R(w) = 4.5%; 11a crystallizes in space group P2(1) with Z = 2, a 8.222(3) angstrom, b = 17.256(6) angstrom, c = 9.561(4) angstrom, beta = 100.85(3)-degrees, R = 4.0%, R(w) = 4.6%.)