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

Abstract

The isolation of six isomeric, low-symmetry, dicobaltacarboranes with bicapped hexagonal antiprismatic cage structures, always in low yield, is described from reactions in which 13-vertex cobaltacarborane anions and sources of cobalt-containing cations were present. The vertex-to-centroid distance (VCD) and boron-H distance (BHD) methods are used to locate the correct C atom positions in the cages, thus allowing the compounds to be identified as 1,13-Cp2-1,13,2,10-closo-Co2C2B10H12 (1), 1,8-Cp2-3-OEt-1,8,2,10-closo-Co2C2B10H11 (2), 1,13-Cp2-1,13,2,9-closo-Co2C2B10H12 (3), 1,8-Cp2-1,8,2,4-closo-Co2C2B10H12 (4), 1,13-Cp2-1,13,2,4-closo-Co2C2B10H12 (5) and 1,8-Cp2-1,8,2,5-closo-Co2C2B10H12 (6). It is shown that a common alternative method of cage C atom identification, using refined (as B) U(eq) values, does not work well, at least in these cases. Having identified the correct isomeric forms of the six dicobaltacarboranes, their syntheses are tentatively rationalised in terms of the direct electrophilic insertion of a {CpCo(+)} fragment into [CpCoC2B10](-) anions and it is demonstrated that compounds 1, 4, 5 and 6 can be successfully prepared by deliberately performing such reactions.

Reduction-induced facile isomerisation of metallacarboranes: synthesis and crystallographic characterisation of 4-Cp-4,1,2-closo-CoC2B9H11

“…11 This takes to six the number of isomers of CpCoC 2 B 9 H 11 to be isolated by low-temperature routes, and experiments targeting the remaining isomers yet to be afforded by conventional chemistry (9,1,2-, 2,1,9-and 9,1,7-) are currently in hand.…”

“…2) as part of which the identities of the cage C atoms were unambiguously determined by both the vertex-to-centroid distance 10 and boron-hydrogen distance 11 methods. 2) as part of which the identities of the cage C atoms were unambiguously determined by both the vertex-to-centroid distance 10 and boron-hydrogen distance 11 methods.…”

Carborane Substituents Promote Direct Electrophilic Insertion over Reduction–Metalation Reactions

“…Reduction [3] and boron-hydrogen distance [4] methods (see the Supporting Information for experimental, spectroscopic,a nd crystallographic details of all new compounds). Thes tructure of 2 is shown in Figure 1.…”

How to Make 8,1,2‐closo‐MC2B9 Metallacarboranes

“…Note that in compounds 7-10, 12 and 13 at least one of the cage C atoms has only an H substituent, so it is particularly important that the cage C and cage B atoms are correctly distinguished in crystallographic studies. For this purpose we have used the recently reported VCD [19] and BHD [20] methods, both of which gave the same unambiguous results, allowing us to be completely confident that, for example, 7 and 12 are correctly described as 8,1,2-closo-MC2B9 species. In conclusion, the first examples of metallacarboranes with 8,1,2-closo-MC2B9 architectures to be crystallographically characterised, compounds 1, 6 and 7, are reported.…”