Small carborane ligands as tailorable Cp surrogates. Halogenation, alkylation, and arylation at metal and cage positions on CpX2M(Et2C2B4H4) complexes (M = Ta, Nb)

Synthetic methods for the derivitization of sandwich complexes of the type CpCl2M(2,3-Et2C2B4H4) (M = Ta, Nb) have been further developed via regiospe cific halogenation and alkylation at boron vertexes and at the metal center . Treatment of the parent complexes with elemental halogens or N-halosuccin imides generated B(5)-monohalo, B(4,5)-dihalo, and in some cases B(4,5,6)-t rihalo complexes; these compounds, in turn, reacted with Grignard reagents to give the corresponding B-alkyl and B-aryl derivatives. Similarly, the he terodinuclear bent triple-decker complex Cp*Co((EtC2B3H3)-C-2)Cl2Ta(Et2C2B4 H4) was treated with an excess of N-bromosuccinimide to afford the B-tribro mo derivative 7a. The new compounds were characterized via B-11, H-1, and C -13 NMR, IR, and mass spectroscopy and elemental analysis, augmented by an X-ray diffraction study on 7a and by UV-visible and electrochemical data on some of the complexes.