Studies on bis(1′-ortho-carboranyl)benzenes and bis(1′-ortho-carboranyl)biphenyls

Abstract Reactions between the C , C′ -dicopper(I) derivative of ortho -carborane and ortho -, meta - and para -diiodobenzene are reported. The reaction with 1,2-C 6 H 4 I 2 unexpectedly afforded 2,2′-bis(1′- ortho -carboranyl)biphenyl, [HCB 10 H 10 CC 6 H 4 ] 2 2 , whereas reactions with 1,3- or 1,4-C 6 H 4 I 2 provided alternative routes to 1,3-bis(1′- ortho -carboranyl)benzene 3 and 1,4-bis(1′- ortho -carboranyl)benzene 4 , respectively. The crystal structure of the biphenyl derivative 2 revealed significant distortions in the biphenylene framework attributable to the proximity of the two bulky carborane cages. UV absorption spectra and electrochemical data on 2 and 3 showed little electronic communication between the two carborane cages in either, and negligible π-conjugation between the two ortho -phenylene rings in 2 . However, substantial evidence was found of electronic communication between the carborane cages via the para -phenylene bridge in 4 . B3LYP/6-31G ∗ computations have been carried out on compounds 2 and 4 , on 4,4′-bis( ortho -carboranyl)biphenyl 6 and on 1,2-bis(1′- ortho -carboranyl)benzene 7 . Those on 2 , 4 and 6 show the computed geometries to be in very good agreement with the experimental geometries: those on 7 allowed the reported molecular geometry of this compound to be revised and revealed a long cage C–C bond of 1.725(3) A.