Hybrid Diborolyl/Dicarbaboranyl Triple-Deckers: [(μ5-Cyclopentadienyl)cobalt][μ,η5-1,3-diborolyl)cobalt[dicarba-heptacarboranyl and -nonacarboranyl Complexes

The three‐component reactions of the sandwich anion [(η5‐C5H5)Co(η5‐Et4MeC3B2)]− (4‐H)− and various dicarbaborane anions with metal halides are described. Thus, (4‐H)−, nido‐4,5‐C2B6H9− (5), and CoCl2 form the 30VE triple‐decker [η5‐C5H5)Co(μ,η5‐Et4MeC3B2)Co(η5‐2,3‐C2B5H7)] (6). An analogous three‐component reaction of (4‐H)−, arachno‐4,5‐C2B7H−2 (7), and CoCl2 yields [(η5‐C5H5)Co(μ,η5‐Et4‐MeC3B2)Co(η5‐6,9‐C2B7H9)] (8), which rearranges on heating (57°C) to give the 1,6‐isomer [(η5‐C5H5)Co(μ,η5‐Et4‐MeC3B2)Co(η5‐1,6‐C2B7H9)] (9) with an activation energy of 127 · 10 kJ/mol. The thermodynamically most stable 1,10‐isomer [(η5‐C5H5)Co(μ,η5‐Et4MeC3B2)Co(η5‐1,10‐C2B7H9)] (10) is formed by heating of 9 at 180°C. An alternative route to 9 is provided by the reaction of arachno‐6,8‐C2B7H12− (11) with (4‐H)− and CoCl2. The analogous reaction with RhCl3 leads to [(η5‐C5H5)Co(μ,η5‐Et4MeC3B2)Rh(1,6‐C2B7H9)] (15) and unexpectedly to closo‐2‐(η5‐C5H5)Co(1,6‐C2B7H9) (12). The constitutions of the described compounds are derived from their 1H‐, 11B‐, 13C‐NMR data as well as mass spectral data. The X‐ray structure analyses of 10 and 12 show the expected metal complexes with a CoC2B7H9 framework. In 10 the carbon atoms occupy the capping positions of a bicapped square antiprism. The short Co‐Co distance of 3.20 Å is in agreement with the 30VE configuration of 10. In both 10 and 12, the distance from the cobalt to the four‐coordinate C4 is the shortest Co‐to‐cage atom distance.