SYNTHESIS OF CHARGE-COMPENSATED OCTACARBONYLTRIRUTHENIUM MONOCARBOLLIDE COMPLEXES

The charge-compensated monocarbon carboranes nido-7-NR(3)-7-CB10H12 re act with [Ru-3(CO)(12)] in toluene at reflux temperatures to give the triruthenium complexes [Ru-3(CO)(8)(eta(5)-7-NR(3)-7-CB10H10)] [NR(3) = NMe(3) (1a), NH(2)Bu(t) (1b), and NMe(2)Bu(t) (1c)]. The molecular s tructure of la has been established by X-ray crystallography. The meta l atoms form an essentially isosceles triangle, One Ru atom carries tw o terminal CO groups and the nido-7-NMe(3)-7-CB10H10 cage, coordinated in a pentahapto manner, The two boron atoms in the beta-sites with re spect 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 atom s also carry three essentially terminally attached CO ligands. Treatme nt of la with PPh(3) in toluene gave, after column chromatography of t he mixture, [Ru-3(mu-H)(mu(3)-sigma: eta(5)-7-NMe(3)-7-CB10H9)(CO)(7)( PPh(3))] (2), whereas reaction with CNBu(t) affords [Ru-3(CO)(7)(CNBu( t))(eta(5)-7-NMe(3)-7-CB10H10)] (3). The structure of 2 has been estab lished by X-ray crystallography, The molecule has a triangular array o f ruthenium atoms. As in 1a, one metal center Ru(1) carries two CO gro ups 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 PPh(3) group, the latt er being transoid to Ru(1), while the third Ru atom is terminally atta ched to three CO molecules. The Ru(2)-Ru(3) connectivity is bridged by a hydride ligand, and in addition both of these metal atoms are linke d to the CB10 framework through boron atoms in the beta-sites of the C BBBB ring coordinated to Ru(1), Atom Ru(2) forms a three-center, two-e lectron B-H --> Ru bond, while atom Ru(3) forms an Ru-B sigma-bond, wi th the result that the nido-7-NMe(3)-7-CB10H9 group bridges the Ru-3 t riangle via eta(5)-CBBBB, B-H --> Ru, and B-Ru interactions. The NMR d ata for the new compounds are reported and discussed in relation to th eir structures.