Deprotonation of [7-(1′-closo-1′,2′-C2B10H11)-nido-7,8-C2B9H11]− and reaction
with [Rh(PPh3)3Cl] results in isomerization
of the metalated cage and the formation of [8-(1′-closo-1′,2′-C2B10H11)-2-H-2,2-(PPh3)2-closo-2,1,8-RhC2B9H10] (1). Similarly, deprotonation/metalation
of [8′-(7-nido-7,8-C2B9H11)-2′-(p-cymene)-closo-2′,1′,8′-RuC2B9H10]− and [8′-(7-nido-7,8-C2B9H11)-2′-Cp*-closo-2′,1′,8′-CoC2B9H10]− affords [8-{8′-2′-(p-cymene)-closo-2′,1′,8′-RuC2B9H10}-2-H-2,2-(PPh3)2-closo-2,1,8-RhC2B9H10] (2) and [8-(8′-2′-Cp*-closo-2′,1′,8′-CoC2B9H10)-2-H-2,2-(PPh3)2-closo-2,1,8-RhC2B9H10]
(3), respectively, as diastereoisomeric mixtures. The
performances of compounds 1–3 as
catalysts in the isomerization of 1-hexene and in the hydrosilylation
of acetophenone are compared with those of the known single-cage species
[3-H-3,3-(PPh3)2-closo-3,1,2-RhC2B9H11] (I) and [2-H-2,2-(PPh3)2-closo-2,1,12-RhC2B9H11] (V), the last two compounds
also being the subjects of 103Rh NMR spectroscopic studies,
the first such investigations of rhodacarboranes. In alkene isomerization
all the 2,1,8- or 2,1,12-RhC2B9 species (1–3, V) outperform the 3,1,2-RhC2B9 compound I, while for hydrosilylation
the single-cage compounds I and V are better
catalysts than the double-cage species 1–3.