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

• Main Authors: Kriti Pathak, Chandan Nandi, Jean-François Halet, Sundargopal Ghosh
• Format: Article
• Language: English
• Published: MDPI AG 2021-04-01
• Series: Inorganics
• Subjects: cobaltaborane; decaborane; eleven-vertex cluster; <i>nido</i> cluster; metallaborane; mixed-metal cluster
• Online Access: https://www.mdpi.com/2304-6740/9/4/28

Synthesis, isolation, and structural characterization of unique metal rich diamagnetic cobaltaborane clusters are reported. They were obtained from reactions of monoborane as well as modified borohydride reagents with cobalt sources. For example, the reaction of [Cp*CoCl]₂ with [LiBH₄<b>·</b>THF] and subsequent photolysis with excess [BH₃<b>·</b>THF] (THF = tetrahydrofuran) at room temperature afforded the 11-vertex tricobaltaborane <i>nido</i>-[(Cp*Co)₃B₈H₁₀] (<b>1</b>, Cp* = <i>η</i>⁵-C₅Me₅). The reaction of Li[BH₂S₃] with the dicobaltaoctaborane(12) [(Cp*Co)₂B₆H₁₀] yielded the 10-vertex <i>nido</i>-2,4-[(Cp*Co)₂B₈H₁₂] cluster (<b>2</b>), extending the library of dicobaltadecaborane(14) analogues. Although cluster <b>1</b> adopts a <i>classical</i> 11-vertex-<i>nido</i>-geometry with one cobalt center and four boron atoms forming the open pentagonal face, it disobeys the Polyhedral Skeletal Electron Pair Theory (PSEPT). Compound <b>2</b> adopts a perfectly symmetrical 10-vertex-<i>nido</i> framework with a plane of symmetry bisecting the basal boron plane resulting in two {CoB₃} units bridged at the base by two boron atoms and possesses the expected electron count. Both compounds were characterized in solution by multinuclear NMR and IR spectroscopies and by mass spectrometry. Single-crystal X-ray diffraction analyses confirmed the structures of the compounds. Additionally, density functional theory (DFT) calculations were performed in order to study and interpret the nature of bonding and electronic structures of these complexes.