Reactivity Studies on 2,3,4,5‐Tetraethyl‐1,6‐diiodo‐2,3,4,5‐tetracarba‐ nido ‐hexaborane(6): Synthesis and Structures of New C 4 B 2 nido ‐Carborane Derivatives

The reactivity of the title compound 2,3,4,5‐tetraethyl‐1,6‐diiodo‐2,3,4,5‐tetracarba‐ nido ‐hexaborane(6) ( 1 ) towards a variety of nucleophiles is reported. When 1 is treated with RC 2 Li (R = Ph, t Bu, SiMe 3 , p ‐tolyl) and Ph 2 PLi, the corresponding new C 4 B 2 nido ‐carborane derivatives 2a − d and 3 , respectively, are obtained by selective substitution at the basal B−I group, whereas the apical B−I bond remains inert. The reaction of 1 with K[(η 5 ‐C 5 H 5 )Fe(CO) 2 ] affords the novel species 4 , which contains a CpFe(CO) 2 fragment σ‐bonded to the basal boron atom of the C 4 B 2 cluster. Attempts to isolate 4 by chromatography on silica gel led to cleavage of the Fe−B bond and formation of compound 5 , containing a basal BH vertex, which can be separately prepared by the reaction of 1 and LiBEt 3 H. In the reactions of 1 with PhLi and Me 3 SnLi, respectively, 6a and 7a are formed as the predominant B6‐substituted carborane products. In addition, trace amounts of 1,6‐disubstituted species 6b and 7b are also detected. The substitution at the apical B−I group in 2a with an alkynyl group is effected by a Pd 0 ‐catalyzed Negishi‐type cross‐coupling reaction to give compound 8 . The reaction of 1 and monolithio‐ o ‐carborane affords the C 4 B 2 −C 2 B 10 carborane 10 , while the reaction of 2a and Co 2 (CO) 8 furnishes the double cluster 9 (C 4 B 2 −C 2 Co 2 ). In both 9 and 10 two different types of clusters are directly connected by a B−C bond. Compound 1 reacts with ClZnC 6 H 4 C 6 H 4 ZnCl in the presence of the catalyst Pd(PPh 3 ) 4 to give 11 , in which two C 4 B 2 clusters are linked by a C 6 H 4 C 6 H 4 unit. The constitutions of the products follow from spectroscopic data, and X‐ray diffraction analyses for 2a , 2d , 4 , 8 , 9 , and 10 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)