Spin-Orbit Effects in a Thallium Borohydride Stabilized by Coordination to Bis(diisopropylamino)Cyclopropenylidene (BAC)

Reaction of Tl(OTf) with 2 equiv of bis(diisopropylamino)cyclopropenylidene (BAC) in THF results in formation of [Tl(BAC)₂(OTf)] (1) in moderate yields. Subsequent reaction of 1 with [K][H₂-9-BBN] ([H₂-9-BBN]⁻ = dihydrido 9-boratabicyclo[3.3.1]nonane) in THF results in formation of [Tl(BAC)(μ-H₂-9-BBN)]₂ (3), also in moderate yield. Complex 3 is the first reported thallium borohydride. We attribute its thermal stability to the strong donor ability of the BAC co-ligand. Both 1 and 3 exhibit trigonal pyramidal geometries about Tl⁺ in the solid-state, indicative of the presence of stereochemically active lone pairs. The hydride environment in 3 is calculated to exhibit a 3.9 ppm downfield shift attributed to spin-orbit effects from the adjacent Tl center.