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

Abstract

Reactions of NbCp′Cl 4 (Cp′=η 5-C 5H 4SiMe 3) and TaCp*Cl 2Me 2 (Cp*=η 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- i Pr 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- i Pr 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 t Bu, 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 i Pr 2, 19; NH t Bu, 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, i Pr) 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.