Comparison of the geometric and molecular orbital structures of (Cp~*Cr)_2B_4H_8 and (Cp~8Re)_2B_4H_8=#eta#~5-C_5Me_5.Structural consequences of delocalized electronic unsaturation in a metallaborane cluster

摘要

Comparison of the structure so two metallaboranes possessing the same borane fragment and ancillary metal ligands but differing transition mletal atoms defines the geometric consequences of the addition (or removal)of two valence electrons from a bicapped tetrahedralmetallaborane cluste rstructure.Likewise the effects of the cluster distortion on electronic structure is explored utilizing approximate molecular orbital calculations on hypothetical(CpMn)_2B_4H_8,Cp=#eta#~5-C_5H_5,as it is changed from the shape characteristic of five skeletal electron pair (sep) (Cp~*Cr)_2B_4H_8 to that of six sep (Cp~8Re)_2B_4H_8,Cp=#eta#~5-C_5Me_5.In doing so it is demonstrated that the observed changesin the metal-metal distance (a counter-intuitive increase with smaller sep) and endohydrogen positoins (more like B-H with smaller sep) (Cp~*Cr0_2B_4bH_8, to that of six sep (Cp~*Re)_2B_4H_8,Cp=#eta#~5-C_5M3.In doing so it is demonstrated that the observed changes in the metal-metaldistance(a counter-intuitive increase counter-intuitive increase with smaller sep).and endohydrogen positions 9more like B-H with smaller sep) are required to electronically accommodate the removal of a pair of electrons from a satuerated bicapped tetrahedral cluster.