Synthesis and structures of the [benzamidinato]3− complexes Li3(tmeda)(L1)]2 and [Li(thf)4][Li5(L2)(OEt2)2] [L1 = N(SiMe3)C(Ph)N(SiMe3) and L2 = N(SiMe3)C(C6H4-4)NPh]

Abstract

Reduction at ambient temperature of each of the lithium benzamidinates [Li(L¹)(tmeda)] or [{Li(L²)(OEt₂)₂}₂] with four equivalents of lithium metal in diethyl ether or thf furnished the brown crystalline [Li₃(L¹)(tmeda)] (1) or [Li(thf)₄][Li₅(L²)₂(OEt₂)₂] (2), respectively. Their structures show that in each the [N(R¹)C(R³)NR²]³⁻ moiety has the three negative charges largely localised on each of N, N′ and R = Aryl); a consequence is that the “aromatic” 2,3- and 5,6-CC bonds of R³ approximate to being double bonds. Multinuclear NMR spectra in C₆D₆ and C₇D₈ show that 1 and 2 exhibit dynamic behaviour. [The following abbreviations are used: L¹ = N(SiMe₃)C(Ph)N(SiMe₃); L² = N(SiMe₃)C(C₆H₄Me-4)N(Ph); tmeda = (Me₂NCH₂-)₂; thf = tetrahydrofuran.] This reduction is further supported by a DFT analysis.