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

Abstract

The complex (DMAT) 2 Ba•(THF) 2 (DMAT = 2dimethylamino-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.

Metal Vapour Synthesis of an Organometallic Barium(0) Synthon

“…Regardless of the solvent used for crystallisation (benzene, toluene, or Et 2 O), the 1 H, 13 C and 29 Si NMR shifts measured in benzene‐ d 6 are identical. This is explained by complete substitution of the neutral ligand (benzene, toluene, or Et 2 O) by benzene‐ d 6 , as supported by additional signals for the free neutral ligand, and is in agreement with the strong preference for interaction of Ba 2+ , a soft cation, with soft arene ligands [43b,45] . 1 H NMR spectra of 1 ⋅ Et 2 O in toluene‐ d 8 in the temperature range of −70 to +50 °C show hardly any changes (Figure S18).…”

Metal Vapour Synthesis of an Organometallic Barium(0) Synthon

“…The more covalent MgÀ C bonds in Mg(Anth'') • (THF) 2 result in rehybridisation of C towards sp 3 . [43] A similar trend was observed for the aromatic signals in Mg(Anth'') • (THF) 2 (6.50 and 6.75 ppm, THF-d 8 ). [28] They are, however, not as far shifted as those for the anthracene dianion in Na 2 (Anth) (3.36 and 4.25 ppm, THF-d 8 ).…”