Diborane and Bis(boryl) Complexes of Osmium Stabilized in the Coordination Sphere of [Cp*Os] (Cp* = η⁵-C₅Me₅)

Electron-precise osmium boron complexes have been synthesized and structurally characterized with similarity to [B2H6]. Thermolysis of an unstable intermediate, generated from the reaction of [(Cp*OsBr2)2], 1, and [LiBH4·THF], with CO gas led to the formation of colorless [Cp*Os(CO)2(η2-B2H5)], 2. Complex 2 is analogous to diborane(6) [B2H6], in which one of the bridging hydrogens is replaced by a [Cp*Os(CO)2] fragment. With an objective to isolate Os-diborane species supported by aryl chalcogenide fragments, we have treated 1 with an in situ generated chalcogenoborate species [LiBH3(SePh)]. The reaction yielded [(Cp*Os)2(μ-(HB)O(BH)-κ2B:κ2B)(μ-SePh)2], 3, in which an oxadiborirane unit is coordinated to two [Cp*Os] fragments. In contrast, the thermolysis of an osmium intermediate, generated from the reaction of [(Cp*OsBr2)2], 1, and [LiBH4·THF], with [S2Ph2] yielded a bis(boryl) complex, [(Cp*Os)2(μ-HBS(1,2-C6H4)BS-κ2B:κ2B:κ2S)(μ-SPh)], 4. All the complexes have been characterized by multinuclear NMR and IR spectroscopies, mass spectrometry, and single-crystal X-ray diffraction studies. Additionally, density functional theory (DFT) calculations are carried out that afford insight into the bonding of complexes 2–4.