Eleven-vertex polyhedral metalladicarbaborane chemistry. Reactions of neutral nido-5,6-C2B8H12 and the [nido-6,9-C2B8H10]2− anion to give formally closo isomeric 1-(arene) and 1-(cyclopentadiene)-1,2,4- and 1,2,3-metalladicarbaundecaboranes, and some subs

Reactions between nido-5,6-C2B8H12 (1) and the organometallic halides [{MLCl2}2] (2) [where {ML}={Ru(η6-C6Me6)} (2a), {Ru(η6-p-MeC6H4iPr)} (2b), {Rh(η5-C5Me5)} (2c), and {Os(η6-p-MeC6H4iPr)} (2d)] in the presence of N,N,N′,N′-tetramethylnaphthalene-1,8-diamine (tmnda) in dichloromethane or chloroform have generated a series of the corresponding metalladicarbaboranes [1-L-1,2,4-MC2B8H10] (3, closo 11-vertex numbering system) [where {ML}={Ru(η6-C6Me6)} (3a), {Ru(η6-p-MeC6H4iPr)} (3b), {Rh(η5-C5Me5)} (3c), and {Os(η6-p-MeC6H4iPr)} (3d)] in yields of 48–94%. The substituted species, [5-Br-1-(η6-C6Me6)-1,2,4-RuC2B8H9] (5-Br-3a) and [7-Br-1-(η6-C6Me6)-1,2,4-RuC2B8H9] (7-Br-3a) have been obtained from a similar reaction involving [7-Br-nido-5,6-C2B8H11] (7-Br-1) (combined yield 75%, separated by preparative HPLC). Each of the compounds 5-Br-3a and 7-Br-3a has been resolved into its enantiomers by use of chiral HPLC separation techniques. Analogous reactions between [{MLCl2}2] (2) and the [nido-6,9-C2B8H10]2− anion (species 42−) have produced a series of the isomeric symmetrical complexes [1-L-closo-1,2,3-MC2B8H10] (5) [where {ML}={Ru(η6-C6Me6)} (5a), {Ru(η6-p-MeC6H4iPr)} (5b), {Rh(η5-C5Me5)} (5c) and {Os(η6-p-MeC6H4iPr)} (5d)]; the 2-methyl substituted compound [2-Me-1-(η5-C5Me5)-closo-1,2,3-RhC2B8H9] (2-Me-5c) has been prepared similarly using the [6-Me-nido-C2B8H9]2− anion (species 2-Me-42−) as the starting dicarbaborane. All these compounds are characterised by mass spectrometry and 11B- and 1H-NMR spectroscopy. Single-crystal X-ray diffraction studies have been carried out on compounds 5-Br-3a and 2-Me-5c as two representative examples of the compounds in series 3 and in series 5. The {MC2B8} clusters of compounds 3 have four-membered open faces, generating an ‘isonido’ geometry, whereas those of compounds 5 approximate more to the classical closo cluster geometry. Thermolyses of the {1,2,4-MC2B8} compounds 3a–3d cleanly generate their corresponding {1,2,3-MC2B8} isomers 5a–5d.