Metal cluster compounds steric factors

Phosphorus-substituted carborane ligands can be mono-, bi-, or multidentate when they react with a metal center. Factors affecting this behavior include the structural features of the carborane cage (i.e., whether it is the ortho, meta, or para isomer, or has the closo or nido structure), the substitution pattern of the carborane cluster, the number and kind of donor atoms, and the electronic and steric properties of the ligand. All these factors have an influence on the catalytic activity of the metal complex. For example, the carborane cluster can act as an electron acceptor or electron donor at the phosphorus atom [22,29]. The donor atoms adjacent to phosphorus can act as labile ligands that block the coordination site at the metal until a substrate approaches. In nido cluster compounds, the metal ion can bind in two ways through the phosphorus substituent or by the decapped face of the cluster, whereby the former option is the most stable. In nido-carborme chemistry, B-H-Rh and... 

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