Reactivity of Carboranylacetylenes towards Cobalt Complexes

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Abstract
The reaction of 1,6‐diiodo‐C4B2 nido‐carborane derivative 1 with RC2Li (R = Me, SPh) yields the corresponding carboranylacetylenes 2b,c. Treatment of the PPh2‐substituted nido‐carborane 3a with PhC2ZnCl in the presence of a catalytic amount of Pd(PPh3)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 Pd0‐catalyzed Nigishi‐type cross‐coupling reaction; the basal boron atom is blocked by the n‐butyl group. The 1,3‐dicarboranyl‐substituted (η4‐cyclobutadiene)cobalt complexes 5a,c are obtained from the reactions of 2a,c with stoichiometric amounts of CpCo(C2H4)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)

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