Metal-Rich Metallaboranes: Synthesis, Structures and Bonding of Bi- and Trimetallic Open-Faced Cobaltaboranes

Synthesis, isolation, and structural characterization of unique metal rich diamagnetic cobaltaborane clusters are reported. They were obtained from reactions monoborane as well modified borohydride reagents with cobalt sources. For example, the reaction [Cp*CoCl]2 [LiBH4·THF] subsequent photolysis excess [BH3·THF] (THF = tetrahydrofuran) at room temperature afforded 11-vertex tricobaltaborane nido-[(Cp*Co)3B8H10] (1, Cp* η5-C5Me5). The Li[BH2S3] dicobaltaoctaborane(12) [(Cp*Co)2B6H10] yielded 10-vertex nido-2,4-[(Cp*Co)2B8H12] cluster (2), extending library dicobaltadecaborane(14) analogues. Although 1 adopts a classical 11-vertex-nido-geometry one center four boron atoms forming open pentagonal face, it disobeys Polyhedral Skeletal Electron Pair Theory (PSEPT). Compound 2 perfectly symmetrical 10-vertex-nido framework plane symmetry bisecting basal resulting in two {CoB3} units bridged base by possesses expected electron count. Both compounds characterized solution multinuclear NMR IR spectroscopies mass spectrometry. Single-crystal X-ray diffraction analyses confirmed structures compounds. Additionally, density functional theory (DFT) calculations performed order to study interpret nature bonding electronic these complexes.