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.