Tetracarbon Metallacarboranes 11

Alternative Title

11-Vertex nido cages: Structures of two isomers of (η⁵-C₅H₅)Co(CH₃)₄C₄B₆H₆


The structures of 2,7,8,10,11- and 9,7,8,10,11- (η5-C5H5)Co(CH3) 4C4B6H6 were determined by single-crystal X-ray diffraction. Both compounds contain 11-vertex CoC4B6 cages having icosahedral-fragment (capped-pentagonal-antiprism) geometry with all four skeletal carbon atoms on the five-membered open face. In the 2,7,8,10,11 system (isomer I) the metal atom is located in the lower (CoB4) belt adjacent to two cage carbon atoms, while in the 9,7,8,10,11 species (isomer II), the metal is on the open rim of the cage. Both complexes contain an idealized mirror plane, which in the case of isomer II is crystallographically imposed. The two isomers were obtained in equal amounts by reaction of (η5-C5H5)Co(CO)2 with (CH3)4C4B8H8 as previously reported, and the present investigation confirms the structures postulated earlier from NMR spectra. In contrast to many other four-carbon carborane and metallacarborane systems, there are no unusual distortions or anomalous features in the skeletal cage structures. However, the three framework C-C interactions are of nearly equal length in isomer II, which has a CoC4 open face; in isomer I, the central C-C bond is substantially shorter than the other two, suggesting a localization of electron density in the central C-C link which probably involves a π-type interaction with cobalt. Crystal data for (η5-C5H5)Co(CH3) 4C4B6H6, isomer I: mol wt 303, space group P21/c, Z = 4; a = 14.638 (3) Å; b = 8.701 (3) Å; c = 13.483 (7) Å; β = 115.74 (4)°; V = 1547 Å3; R = 0.041 for 1309 independent reflections having Fo 2 > 3σ(Fo 2). Crystal data for isomer II: space group Pnma; Z = 4; a = 13.252 (3) Å; b = 12.310 (3) Å; c = 9.521 (2) Å; V = 1553 Å3; R = 0.044 for 1009 independent reflections having Fo 2 > 3σ(Fo 2). © 1981 American Chemical Society.



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© 1981 American Chemical Society (ACS), All rights reserved.