Hybrid diborolyl/dicarbaboranyl triple-deckers: [(mu(5)-cyclopentadienyl)cobalt][mu,eta(5)-1,3-diborolyl)cobalt]dicarba-heptacarboranyl and -nonacarboranyl complexes

The three-component reactions of the sandwich anion [(eta(5)-C5H5)Co(eta(5)-Et(4)MeC(3)B(2))](-) (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 [(eta(5)C(5)H(5))Co(mu,eta(5)-Et(4)MeC(3)B(2))Co(eta(5)-2,3-C2B5H7)] (6) An analogous three-component reaction of (4-H)(-), arachno-4,5-C2B7H12- (7), and CoCl2 yields [(eta(5)-C5H5)Co(mu,eta(5)-Et(4)MeC(3)B(2)) Co(eta(5)-6,9-C2B7H9)] (8), which rearranges on heating (57 degrees C) to give the 1,6-isomer [(eta(5)-C5H5)Co(mu,eta(5)-Et(4)MeC(3)B(2))Co(eta(5)-1,6-C2B7H9)] (9) With an activation energy of 127 +/- 10 kJ/mol. The thermodynamically most stable 1,10-isomer [(eta(5)-C5H5)Co(mu,eta(5)-Et(4)MeC(3)B(2))Co(eta(5)-1,10-C2B7H9)] (10) is formed by heating of 9 at 180 degrees 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 [(eta(5)-C5H5)Co(mu,eta(5)-Et(4)MeC(3)B(2))Rh(1,6-C2B7H9)] (15) and unexpectedly to closo-2-(eta(5)-C5H5)Co(1,6-C2B7H9) (12). The constitutions of the described compounds are derived from their H-1-,B-11-, C-13-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 Angstrom 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.