Carboranylamidinates

This Research Report provides an overview on synthesis, structure, and reactivity of the recently discovered carboranylamidinate ligands. Carboranylamidinate anions of the type [(o-C2B10H10C(NHR)(=NR)] (R = iPr, cyclohexyl) are readily accessible via addition of o-lithiocarborane to N,N-carbodiimides RN=C=NR. They combine the highly versatile characteristics of both amidinates and carboranes in one unique ligand system. Unlike simple amidinate anions, the carboranylamidinates coordinate to metal ions not as typical N,N-chelating ligands but adopt an unexpected 2C, N-bonding mode. The free imine functionality in carboranylamidinates can be further deprotonated. The resulting dianions were demonstrated to be excellent starting materials for novel boron-rich heterocycles incorporating e.g. Si, Sn, P, or transition metals such as Ti, Zr, Rh, and Ir. Further modification of the carboranylamidinate cage structure includes the introduction of additional functional groups like SH or SeH as well as the selective removal of a boron atom with formation of novel nido-type dicarbollylamidinate ligands. An initial study already showed that transition metal carboranylamidinates are potentially useful as polymerization catalysts.