Application of a Stable and Soluble Dibenzylbarium Reagent in the Synthesis of a Barium Imido Cluster

This is the authors' abstract. We don't add key points for this paper.

The complex (DMAT) 2 Ba·(THF) 2 (DMAT = 2-dimethylamino-α-trimethylsilylbenzyl) was prepared by a salt metathesis reaction between (DMAT)K and BaI 2 in THF, and crystals were isolated in 83% yield. This monomeric complex dissolves well in aromatic or ethereal solvents and is also stable at higher temperatures in solution. Structural details and NMR parameters reveal a high degree of charge delocalization in the DMAT aryl ring. Comparison with identical Ca and Sr complexes, (DMAT) 2 Ae·(THF) 2 (Ae = Ca and Sr), shows that the extent of delocalization increases down group 2: Ca < Sr < Ba. Due to chirality at the benzylic carbon, in solution the heterochiral R, S -isomer and homochiral R, R / S, S -isomers exist in equilibrium. A temperature-dependent NMR study gives an estimate of the Ae–C and Ae–N bond energies which decrease down the group: Ca > Sr > Ba. Although the DMAT carbanion is stabilized by resonance and negative hyperconjugation, (DMAT) 2 Ba·(THF) 2 is still a very potent deprotonation reagent. Double deprotonation of Ph 3 SiNH 2 gave the first Ba imido complex. A similar reaction using (DMAT) 2 Sr·(THF) 2 gave the analogue Sr imido complex. Comparison with reported structures shows trends for the full series [(Ph 3 SiN)Ae·(THF)] 4 (Ae = Mg, Ca, Sr, and Ba) which crystallize as tetramers with very stable, ionically bound heterocubane Ae 4 N 4 cores.