(Tetramethylcyclobutadiene)cobalt Complexes with Tricarbollide Ligands

Reactions of the 11‐vertex nido ‐tricarbollide anions [7,8,9‐C 3 B 8 H 11 ] – ( 2a ) and [7,8,10‐C 3 B 8 H 11 ] – ( 3 ) with [Cb*Co(MeCN) 3 ] + or [Cb*Co(C 6 H 6 )] + (Cb* = C 4 Me 4 ) afford the expected cobaltatricarbollides 1‐Cb*‐1,2,3,4‐CoC 3 B 8 H 11 ( 4a ) and 1‐Cb*‐1,2,3,5‐CoC 3 B 8 H 11 ( 5 ), respectively. A similar reaction of the amino‐substituted anion [7‐ t BuNH‐7,8,9‐C 3 B 8 H 10 ] – ( 2b ) is accompanied by polyhedral rearrangement even at room temperature, giving 1‐Cb*‐12‐ t BuNH‐1,2,4,12‐CoC 3 B 8 H 10 ( 7b ). Complex 4a rearranges to the isomeric complex 5 at 110 °C and further to 1‐Cb*‐1,2,4,10‐CoC 3 B 8 H 11 ( 6a ) at 160 °C. The amino‐substituted derivative 1‐Cb*‐10‐ t BuNH‐1,2,4,10‐CoC 3 B 8 H 10 ( 6b ) was obtained by isomerization of 7b at 160 °C. The observed rearrangement sequence for Cb*CoC 3 B 8 H 11 correlates well with the relative stabilities of nonmethylated analogs estimated by DFT calculations. The structures of 4a and 7b were determined by X‐ray diffraction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)