192073-95-3Relevant academic research and scientific papers
Synthetic, structural, and redox studies of arene alkyl complexes of tantalum(III) supported by aryloxide and arenethiolate ligands
Arney, David S. J.,Fox, Peter A.,Bruck, Michael A.,Wigley, David E.
, p. 3421 - 3430 (2008/10/08)
A series of η6-hexamethylbenzene alkyl and aryl complexes of tantalum(III) supported by aryloxide and arenethiolate ligands have been prepared, characterized, and compared to their halide analogues. Thus, (η6-C6Me6)Ta(OAr)2Cl (1, Ar = 2,6-C6H3iPr2) reacts with MeMgBr at low temperature to afford (η6-C6Me6)Ta(OAr)2Me (3). Low-temperature alkylation of (η6-C6Me6)Ta(OAr)Cl2 (2) with 2 equiv of RMgBr forms (η6-C6Me6)Ta(OAr)R2 (4, R = Me; 5, R = Et) and with 2 equiv of RLi affords (η6-C6Me6)Ta(OAr)R2 (6, R = CH2SiMe3; 7, R = Ph). Complexes 3-7 are more stable than their halide precursors; no products arising from α- or β-H elimination processes were identified upon thermolysis. In addition to NMR studies of these compounds, cyclic voltammetry experiments show two oxidation processes; the Ta(III) ? Ta(IV) couple is quasi-reversible, and the Ta(IV) → Ta(V) process is irreversible. Molecules of 5 exhibit a folded arene ligand with π-electron localization (diene-diyl structure) and normal ethyl ligands (no evidence for agostic interactions). Under the appropriate conditions, (η6-C6Me6)Ta(OAr)Cl2 (2) can be monoalkylated using 1 equiv of LiCH2SiMe3 or LiPh to afford (η6-C6Me6)Ta(OAr)(CH2SiMe 3)Cl (8) and (η6-C6Me6)Ta(OAr)(Ph)Cl (9). However, attempts to monoalkylate (η6-C6Me6)Ta(OAr)Cl2 with 1 equiv of either MeMgBr or EtMgBr provide the double-exchange products (η6-C6Me6)Ta(OAr)(Me)Br (10) and (η6-C6-Me6)Ta(OAr)(Et)Br (11), respectively. The metathesis product (η6-C6Me6)Ta(OAr)(Et)Cl (12) is isolated in good yield upon attempts to alkylate (η6-C6Me6)Ta(OAr)(CH2SiMe 3)Cl (8) with ZnEt2. However, (η6-C6Me6)Ta(OAr)(CH2SiMe 3)Cl (8) reacts with PhLi to afford (η6-C6-Me6)Ta(OAr)(CH2SiMe 3)Ph (13). The halide alkyl complexes (η6-C6Me6)Ta(OAr)(Et)Br (11) and (η6-C6Me6)Ta(OAr)(CH2SiMe 3)Cl (8) react with LiBEt3H to provide the hydrido complexes (η6-C6Me6)Ta(OAr)(Et)H (14) and (η6-C6Me6)Ta(OAr)(CH2SiMe 3)H (15), respectively. The arenethiolate complexes (η6-C6Me6)Ta(OAr)(SAr′)Cl (16) (Ar′ = 2,4,6-C6H2iPr3) and (η6-C6-Me6)Ta(OAr)(S(mes))Cl (17) (mes = 2,4,6-C6H2Me3) are formed upon reacting (η6-C6Me6)-Ta(OAr)Cl2 (2) with the appropriate lithium arenethiolate reagent, and the characterization of these species is discussed.
