13-Vertex Carbacobaltaboranes: Synthesis and Molecular Structures of the 4,1,6-, 4,1,8- and 4,1,12-Isomers of Cp*CoC2B10H12

Abstract

Attempted crystallographic studies of the known compounds 4-Cp-4,1,8-closo-CoC2B10H12 and 4-Cp-4,1,12-closo-CoC2B10H12 were frustrated because of disorder which was impossible satisfactorily to model. Thus the family of Cp* compounds 4-Cp*-4,1,6-closo-CoC2B10H12, 4-Cp*-4,1,8-closo-CoC2B10H12 and 4-Cp*-4,1,12-closo-CoC2B10H12 were prepared. The 11B NMR spectroscopic properties of these compounds are closely similar to those of their Cp analogues. All three compounds were studied crystallographically. The 4,1,8- and 4,1,12-species are isomorphous and partially disordered, however the disorder was successfully modelled and structural analyses of 4,1,8- and 4,1,12-MC2B10 compounds are reported for the first time. A new technique for distinguishing between cage C and B atoms in crystallographic study of (hetero)carboranes is reported. The 12-vertex compound 3-Cp*-3,1,2-closo-CoC2B9H11 is formed as a minor co-product along with 4-Cp*-4,1,6-closo-CoC2B10H12 and is believed to result from partial degradation of the latter. The 12-vertex species has also been subjected to crystallographic analysis.

Asymmetric 1,8/13,2,x-M2C2B1014-vertex metallacarboranes by direct electrophilic insertion reactions; the VCD and BHD methods in critical analysis of cage C atom positions

“…We present evidence which suggests that these compounds are not formed by 2-e reduction and metallation of 13-vertex CoC 2 B 10 species (although in some cases they were first isolated from reactions in which this was the intention) rather that they may arise as the result of direct electrophilic attack by a metal fragment cation on a [CoC 2 B 10 ] − monoanion. Crucial to rationalising their synthesis is the identification of the correct positions of the cage C atoms in the crystallographically-determined structures (in no cases do the C atoms carry exo-polyhedral substituents other than H) and for this we have used both the recently reported vertex-tocentroid distance (VCD) method 12 and a complementary approach, the boron-H distance (BHD) method which we first communicated in 2002 13 but for which we now provide more detail.…”

Synthesis, structure and properties of mixed-sandwich cobalta- and ferra-carboranes with ‘carbon-atoms-adjacent’ C2B9 and C2B10 systems

“…2, 134.4, 128.9, 128.4, 127.2, 125.6 (aryl C), 91.9 (C 5 H 5 ), 77.9 (CHOH), 46.8 (C 6 H 4 CH 2 ), cage carbons were not observed. 11 …”

“…Thermal rearrangement of the cage atoms is a very common phenomenon in d-block metallacarboranes of the C 2 B 9 and C 2 B 10 systems [11,13]. As revealed by 11 B NMR spectra, 2 is stable even in refluxing dichlorobenzene (180 C) for 3 days, indicating that CAd metallacarboranes are much more thermally stable than their CAp counterparts.…”

“…It is assumed that the strong base attacks one of the cage boron atoms on the C 2 B 4 bonding face of 2 to give [(h 5 -C 5 Co were obtained as the by-products in the synthesis of [(h 5 -C 5 H 5 )(h 6 -C 2 B 10 H 12 )]Co and [(h 5 -C 5 Me 5 )(h 6 -C 2 B 10 H 12 )]Co, respectively [2,11].…”

“…[19d] (h 5 -C 5 H 5 )(h 6 -C 2 B 10 H 12 )Fe (11) þ0.16 [2] (h 5 -C 5 H 5 )(h 5 -C 2 B 9 H 11 )Fe (12) À0.08 [19a] a All potentials were given relative to ferrocenium/ferrocene. Pt working electrode: 100 mVs À1 ; recorded in CH 3 CN with n-Bu 4 NPF 6 (0.10 M) as supporting electrolyte.…”