Dimetallaborane analogues of pentaborane

Area of Science:

• Organometallic Chemistry
• Boron Chemistry
• Computational Chemistry

Background:

• Dimetallaboranes are organometallic compounds featuring metal-boron cages.
• Understanding their structures is crucial for predicting reactivity and properties.
• Previous studies have focused on specific metal combinations and cage types.

Purpose of the Study:

• To investigate the structural diversity of five-vertex dimetallaboranes Cp2M2B3H7 using computational methods.
• To correlate structure with electronic properties (Wade's rules) for various transition metals.
• To provide insights into the formation and stability of different cage architectures.

Main Methods:

• Density functional theory (DFT) calculations were employed to explore potential energy surfaces.
• Geometries of Cp2M2B3H7 (Cp = η(5)-C5H5) for various transition metals (M = Rh, Ir, Pd, Pt, Ru, Os, Re, Mo, W, Ta) were optimized.
• Wade's electron counting rules were applied to rationalize observed and predicted structures.

Main Results:

• Predicted low-energy structures for Rh and Ir analogs are tetragonal pyramids, consistent with 14 skeletal electrons.
• Two closely related isomers were found for Cp*2Rh2B3H7, matching experimental observations.
• Electron-richer Pd and Pt systems (16 skeletal electrons) exhibit more open structures, analogous to pentaborane-11.
• Hypoelectronic systems (Ru, Os, Re, Mo, W, Ta) favor trigonal bipyramidal structures.
• Rhenium derivatives show unique structures based on a Re2B2 tetrahedron bridged by boron.

Conclusions:

• The study demonstrates a rich structural landscape for dimetallaboranes, heavily influenced by the identity of the transition metals.
• DFT calculations effectively predict diverse cage geometries and isomers.
• The findings provide a theoretical framework for understanding the structure-property relationships in these organoboron compounds.