Reactivity of Carboranylacetylenes towards Cobalt Complexes

The reaction of 1,6‐diiodo‐C 4 B 2 nido ‐carborane derivative 1 with RC 2 Li (R = Me, SPh) yields the corresponding carboranylacetylenes 2b , c . Treatment of the PPh 2 ‐substituted nido ‐carborane 3a with PhC 2 ZnCl in the presence of a catalytic amount of Pd(PPh 3 ) 4 leads to the known basal‐substituted nido ‐carboranylacetylene 2a . The synthesis of apical‐substituted compound 4b is achieved by the substitution of 3b by a Pd 0 ‐catalyzed Nigishi‐type cross‐coupling reaction; the basal boron atom is blocked by the n ‐butyl group. The 1,3‐dicarboranyl‐substituted (η 4 ‐cyclobutadiene)cobalt complexes 5a , c are obtained from the reactions of 2a , c with stoichiometric amounts of CpCo(C 2 H 4 ) 2 . The 1,6‐dialkynyl carborane 6 reacts regioselectively at the basal acetylene group with a stoichiometric amount of CpCo(CO) 2 to give 1,3‐dicarboranyl‐substituted (cyclobutadiene)cobalt complex 7 . The dicarboranyl‐substituted (cyclopentadienone)cobalt complex 8 is formed by the reaction of compound 4b with CpCo(CO) 2 . The new compounds are characterized by NMR spectroscopy, mass spectrometry, and by X‐ray crystal structure analyses for 5a and 8 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)