Metal Vapour Synthesis of an Organometallic Barium(0) Synthon

A hydrocarbon-soluble barium anthracene complex was prepared by means of metal vapour synthesis. Reaction of 9,10-bis(trimethylsilyl)anthracene (Anth′′) with barium vapour gave deep purple Ba(Anth′′) which after extraction with diethyl ether crystallised as the cyclic octamer [Ba(Anth′′)⋅Et${}_2$O]${}_8$. Dissolution in benzene or toluene led to replacement of the Et${}_2$O ligand with a softer arene ligand and isolation of Ba(Anth′′)⋅arene. Diffusion ordered spectroscopy (DOSY NMR ) measurements in benzene-d${}_6$ indicate solution species with a molecular weight that equals a trimeric constitution. Natural population analysis (NPA) assigned charges of +1.70 and −1.70 to Ba and Anth′′, respectively, relating to highly ionic Ba${}^{2+}$/Anth′′${}^{2-}$ bonding. Preliminary reactivity studies with air, Ph${}_2$C=NPh, or H${}_2$ show that the complex reacts as a Ba${}^0$ synthon by release of neutral Anth′′. This soluble molecular Ba0/BaII redox synthon provides new routes for the syntheses of barium complexes under mild conditions.