title: Untethered 4,1,2-MC2B10 supraicosahedral metallacarboranes, their C,C'-dimethyl 4,1,6-, 4,1,8- and 4,1,12-MC2B10 analogues, and DFT study of the (4,)1,2- to (4,)1,6-isomerisations of C2B11 carboranes and MC2B10 metallacarboranes.
abstract: Reduction of the tethered carborane 1,2-μ-(CH(2)SiMe(2)CH(2))-1,2-closo-C(2)B(10)H(10) followed by metallation with {CpCo} or {(p-cymene)Ru} fragments affords both C,C'-dimethyl 4,1,2-MC(2)B(10) and 4,1,6-MC(2)B(10) species. DFT calculations indicate that the barriers to isomerisation of both 4-Cp-4,1,2-closo-CoC(2)B(10)H(12) and 4-(η-C(6)H(6))-4,1,2-closo-RuC(2)B(10)H(12) to their respective 4,1,6-isomers are too high for this to be the origin of the unexpected formation of 4,1,6-MC(2)B(10) products (in marked contrast to the related isomerisation of 1,2-closo-C(2)B(11)H(13) to 1,6-closo-C(2)B(11)H(13)), and, indeed, the 4,1,2-species are recovered unchanged from refluxing toluene. Equally, the DFT-calculated profile for the isomerisation of [7,8-nido-C(2)B(10)H(12)](2-) to [7,9-nido-C(2)B(10)H(12)](2-) suggests that the unexpected formation of 4,1,6-metallacarboranes is unlikely to result from isomerisation of a reduced (nido) carborane following desilylation. Instead, the source of the 4,1,6-MC(2)B(10) compounds is traced to desilylation of 1,2-μ-(CH(2)SiMe(2)CH(2))-1,2-closo-C(2)B(10)H(10) by Li or Na prior to reduction. The supraicosahedral metallacarboranes 1,8-Me(2)-4-Cp-4,1,8-closo-CoC(2)B(10)H(10), 1,12-Me(2)-4-Cp-4,1,12-closo-CoC(2)B(10)H(10) and 1,12-Me(2)-4-(p-cymene)-4,1,12-closo-RuC(2)B(10)H(10) are also reported with all new species characterised both spectroscopically and crystallographically.
authors.affiliation: Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, UK.
authors.forename: Amelia
authors.initials: A
authors.lastname: McAnaw
authors.forename: Maria Elena
authors.initials: ME
authors.lastname: Lopez
authors.forename: Greig
authors.initials: G
authors.lastname: Scott
authors.forename: David
authors.initials: D
authors.lastname: Ellis
authors.forename: David
authors.initials: D
authors.lastname: McKay
authors.forename: Georgina M
authors.initials: GM
authors.lastname: Rosair
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Welch