Hybrid Diborolyl/Dicarbaboranyl Triple‐Deckers: [(μ 5 ‐Cyclopentadienyl)cobalt][μ,η 5 ‐1,3‐diborolyl)cobalt[dicarba‐heptacarboranyl and ‐nonacarboranyl Complexes

The three‐component reactions of the sandwich anion [(η 5 ‐C 5 H 5 )Co(η 5 ‐Et 4 MeC 3 B 2 )] − ( 4 ‐H) − and various dicarbaborane anions with metal halides are described. Thus, ( 4 ‐H) − , nido ‐4,5‐C 2 B 6 H 9 − ( 5 ), and CoCl 2 form the 30VE triple‐decker [η 5 ‐C 5 H 5 )Co(μ,η 5 ‐Et 4 MeC 3 B 2 )Co(η 5 ‐2,3‐C 2 B 5 H 7 )] ( 6 ). An analogous three‐component reaction of ( 4 ‐H) − , arachno ‐4,5‐C 2 B 7 H − 2 ( 7 ), and CoCl 2 yields [(η 5 ‐C 5 H 5 )Co(μ,η 5 ‐Et 4 ‐MeC 3 B 2 )Co(η 5 ‐6,9‐C 2 B 7 H 9 )] ( 8 ), which rearranges on heating (57°C) to give the 1,6‐isomer [(η 5 ‐C 5 H 5 )Co(μ,η 5 ‐Et 4 ‐MeC 3 B 2 )Co(η 5 ‐1,6‐C 2 B 7 H 9 )] ( 9 ) with an activation energy of 127 · 10 kJ/mol. The thermodynamically most stable 1,10‐isomer [(η 5 ‐C 5 H 5 )Co(μ,η 5 ‐Et 4 MeC 3 B 2 )Co(η 5 ‐1,10‐C 2 B 7 H 9 )] ( 10 ) is formed by heating of 9 at 180°C. An alternative route to 9 is provided by the reaction of arachno ‐6,8‐C 2 B 7 H 12 − ( 11 ) with ( 4 ‐H) − and CoCl 2 . The analogous reaction with RhCl 3 leads to [(η 5 ‐C 5 H 5 )Co(μ,η 5 ‐Et 4 MeC 3 B 2 )Rh(1,6‐C 2 B 7 H 9 )] ( 15 ) and unexpectedly to closo ‐2‐(η 5 ‐C 5 H 5 )Co(1,6‐C 2 B 7 H 9 ) ( 12 ). The constitutions of the described compounds are derived from their 1 H‐, 11 B‐, 13 C‐NMR data as well as mass spectral data. The X‐ray structure analyses of 10 and 12 show the expected metal complexes with a CoC 2 B 7 H 9 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.