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(CH(2)inH)(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(CH(2)in)(3)](3-) is an efficient tetradentate trianionic ligand for tantalum, as illustrated by the isolation and structural characterization of [eta(4)-N(CH(2)in)(3)]Ta(NAr)(NMe2H) (Ar = 2,6-C6H3Pr2i), [eta(4)-N(CH(2)in)(3)]Ta(NMe2)(2) and [eta(4)-N(CH(2)in)(3)]Ta(NMe2)Cl. The [N(CH(2)in)(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.