Synthesis of Charge-Compensated Octacarbonyltriruthenium Monocarbollide Complexes

The charge-compensated monocarbon carboranes nido-7-NR3-7-CB10H12 react with [Ru3(CO)12] in toluene at reflux temperatures to give the triruthenium complexes [Ru3(CO)8(η5-7-NR3-7-CB10H10)] [NR3 = NMe3 (1a), NH2But (1b), and NMe2But (1c)]. The molecular structure of 1a has been established by X-ray crystallography. The metal atoms form an essentially isosceles triangle. One Ru atom carries two terminal CO groups and the nido-7-NMe3-7-CB10H10 cage, coordinated in a pentahapto manner. The two boron atoms in the β-sites with respect to the carbon in the CBBBB ring form exopolyhedral three-center, two-electron B−H⇀Ru bonds to the other two Ru atoms. These metal atoms also carry three essentially terminally attached CO ligands. Treatment of 1a with PPh3 in toluene gave, after column chromatography of the mixture, [Ru3(μ-H)(μ3-σ: η5-7-NMe3-7-CB10H9)(CO)7(PPh3)] (2), whereas reaction with CNBut affords [Ru3(CO)7(CNBut)(η5-7-NMe3-7-CB10H10)] (3). The structure of 2 has been established by X-ray crystallography. The molecule has a triangular array of ruthenium atoms. As in 1a, one metal center Ru(1) carries two CO groups and forms a closo-icosahedral RuCB10 framework by coordination in a pentahapto manner to the open face of a nido-CB10 fragment. A second Ru atom is ligated by two CO molecules and the PPh3 group, the latter being transoid to Ru(1), while the third Ru atom is terminally attached to three CO molecules. The Ru(2)−Ru(3) connectivity is bridged by a hydrido ligand, and in addition both of these metal atoms are linked to the CB10 framework through boron atoms in the β-sites of the CBBBB ring coordinated to Ru(1). Atom Ru(2) forms a three-center, two-electron B−H⇀Ru bond, while atom Ru(3) forms an Ru−B σ-bond, with the result that the nido-7-NMe3-7-CB10H9 group bridges the Ru3 triangle via η5-CBBBB, B−H⇀Ru, and B−Ru interactions. The NMR data for the new compounds are reported and discussed in relation to their structures.