Synthesis and structures of the [benzamidinato]~(3-) complexes Li_3(tmeda)(L~1)]_2 and [Li(thf) _4][Li_5(L~2)(OEt_2)_2] [L~1 = N(SiMe_3)C(Ph)N(SiMe_3) and L~2 = N(SiMe_3)C(C_6H_4-4)NPh]

摘要

Reduction at ambient temperature of each of the lithium benzamidinates [Li(L~1)(tmeda)] or [{Li(L~2)(OEt_2) _2}_2] with four equivalents of lithium metal in diethyl ether or thf furnished the brown crystalline [Li_3(L ~1)(tmeda)] (1) or [Li(thf)_4][Li_5(L ~2)_2(OEt_2)_2] (2), respectively. Their structures show that in each the [N(R~1)C(R~3)NR ~2]~(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 R~3 approximate to being double bonds. Multinuclear NMR spectra in C_6D_6 and C _7D_8 show that 1 and 2 exhibit dynamic behaviour. [The following abbreviations are used: L~1 = N(SiMe_3)C(Ph) N(SiMe_3); L~2 = N(SiMe_3)C(C_6H _4Me-4)N(Ph); tmeda = (Me_2NCH_2-)_2; thf = tetrahydrofuran.] This reduction is further supported by a DFT analysis.