Half-sandwich dichloro, alkyl chloro, dialkyl, alkyl methyl and amido methyl imido cyclopentadienyl niobium and tantalum(V) complexes. Dynamic behaviour of amido imido tantalum derivatives

摘要

Reactions of NbCp'Cl_4 (Cp' = #eta#~5-C_5H_4SiMe_3) and TaCp~*Cl_2Me_2 (Cp~* = #eta#~5-C_5Me_5) with two equivalents of NHR~1SiMe_3 and two equivalents of CNR~1 (M = Nb, R~1 = 2,6-Me_2C_6H_3; 2,6-~IPr_2C_6H_3; SiMe_3; M = Ta, R~1 = 2,6-Me_2C_6H_3), respectively, gave the dichloro imido derivatives [MCpCl_2(NR~1)] (M = Nb, Cp = Cp', R~1 = 2,6-Me_2C_6H_3, 1; 2,6-~tPr_2C_6H_3, 2; SiMe_3, 3; M = Ta, Cp = Cp~*, 4). Alkyl chloro imido complexes [MCpClR(NR~1)], (R~1 = 2,6-Me_2C_6H_3; M = Nb, Cp = Cp', R = Me, 5; Cp~*, 6; M = Ta, Cp = Cp~*, R = Me, 7; NMe_2, 8; O~tBu, 9) were obtained by treatment of dichloro derivatives 1 and 4 with the appropriate amount of alkylating reagent (5, 7 one equivalent of ZnMe_2; 6 four equivalents of LiCp~*, 8, 9 one equivalent of LiR). When the same reaction was carried out with two equivalents of MgClMe (10) or LiR(R=CH_2SiMe_3, 11; CH_2CMe_3, 12; NMe_2 13) and one equivalent of Mg(CH_2C_6H_5)_2(THF)_2 (14) or Li_2[o-(NSiMe_3)_2C_6H_4] (15) the corresponding dialkyl imido derivatives [MCpR_2(NR~1)], (R~1 = 2,6-Me_2C_6H_3; M = Nb, Cp = Cp', R = Me, 10; CH_2SiMe_3, 11; CH_2CMe_3, 12; NMe_2, 13; CH_2C_6H_5, 14; M = Ta, Cp = Cp~*, R = o-(NSiMe_3)_2C_6H_4, 15) can be prepared. The methyl complexes 5, 7 reacted with one equivalent of LiR to give mixed alkyl methyl and amido methyl imido derivatives [MCpMeR(NR~1)] (R~1 = 2,6-Me_2C_6H_3; M = Nb, Cp = Cp', R = CH_2SiMe_3, 16; NMe_2, 17; M = Ta, Cp = Cp~*, R = NMe_2, 18, N~iPr_2, 19; NH~tBu, 20). All the new complexes were characterized by usual IR and NMR spectroscopic methods. The rotation of 2,6-Me_2C_6H_3 ring and NR_2(R = Me, ~iPr) amido ligands around C_(ipso)(aryl)-N_(imido) and N_(amido)-Ta bonds, respectively, were observed for complexes 8, 18 and 19 and studied by ~1H-DNMR spectroscopy.