Analogies between the chemical bonding topologies in metla-olefin complexes and in metallaboranes:the role of three-center two-electron bonding

摘要

Three-center two-electron (2c-2e) interactoins are found both in the C_2M #delta#-bonding in the Dewar-Chatt model of the olefin-metal bond and in theB_2H and B_3 bonding in borane structures based on deltahedra or deltahedral fragments.Incorporation of metals as vertices of boron deltahedra frequently changes their shapes to provide degree 6 and even degree 7 vertices for the metal atoms.In addition,metal incorporaton frequently modifies the core+ surface skeletal bonding of the origninal B_nH_N~(2-) to pure surface bonding consisting mainly or entirely of 3c-2e bonds.In such structures the resulting 3c-2e B_2M bonds are related to the C_2M #delta#-bonding in the Dewar-Chatt model.Theskeletal bonding of deltahedral metallaboranes containing two or more metal verices can also include 2c-2e metal-metal bondig rhrough the center of the deltahedron.