Tantalum Amido and Imido Complexes Supported by Tris[(2-indolyl)methyl]amine, a Tetradentate Trianionic Ligand with Reduced π-Donor Character

Tris[(2-indole)methyl]amine, N(CH2inH)3, may be readily obtained by reaction of methyl 2-bromomethyl-1-indolecarboxylate with NH3 followed by deprotection with NaOMe/MeOH. In its deprotonated form, [N(CH2in)3]3- is an efficient tetradentate trianionic ligand for tantalum, as illustrated by the isolation and structural characterization of [eta 4-N(CH2in)3]Ta(NAr)(NMe2H) (Ar = 2,6-C6H3Pri2), [eta 4-N(CH2in)3]Ta(NMe2)2 and [eta 4-N(CH2in)3]Ta(NMe2)Cl. The [N(CH2in)3]3- ligand has a structural similarity to that of [N(CH2CH2NR)3]3-, but differs electronically from the latter due to its reduced pi-donor capability, a direct result of the nitrogen being a component of the aromatic pi-system of the indolyl fragment.