Synthesis and Reactions of the Triruthenamonocarboncarborane Cluster Complex [NHMe₃][Ru₃(CO)₈(<i>η</i>⁵-7-CB₁₀H₁₁)]^†

In thf (tetrahydrofuran) at reflux temperatures the compounds [Ru3(CO)12] and [NHMe3][nido-7-CB10H13] give the anionic triruthenium complex [Ru3(CO)8(η5-7-CB10H11)]-, characterized as its [PPh4]+ salt (4a). Protonation of [NHMe3][Ru3(CO)8(η5-7-CB10H11)] (4b) with HBF4·Et2O yields the hydrido cluster complex [Ru3(μ-H)(CO)8(η5-7-CB10H11)] (5), the structure of which has been determined by X-ray diffraction. The molecule has a triangle of ruthenium atoms. One ruthenium atom is ligated by the η5-7-CB10H11 cage system and carries two CO groups, while the other two ruthenium atoms each carry three CO molecules with a hydrido ligand bridging the metal−metal bond which joins them. In addition, these two metal atoms are linked to the cage through two exopolyhedral B−H⇀Ru bonds. These are formed using boron atoms lying in β sites with respect to the carbon in the open face of the nido-CB10H11 fragment ligating the Ru(CO)2 group. Treatment of 4b in thf with [CuCl(PPh3)3] in the presence of TlPF6, or with Ag[BF4] and PPh3, affords the bimetallic complexes [Ru3(μ-H)(CO)7(PPh3){η5-10-M(PPh3)-7-CB10H10}] (M = Cu (6a), Ag (6b)), respectively. The structure of 6a was established by X-ray diffraction. A triangle of ruthenium atoms is formed by Ru(CO)2, Ru(CO)3, and Ru(CO)2(PPh3) units. This triangle is bridged by a nido-10-Cu(PPh3)-7-CB10H10 fragment, the open face of which is η5-coordinated to the Ru(CO)2 group. The two boron atoms lying in the β-sites in the ring coordinated to the Ru(CO)2 moiety form exopolyhedral B−H ⇀ Ru and B−Cu→Ru linkages, respectively, to the Ru(CO)2(PPh3) and Ru(CO)3 groups, which have their Ru−Ru bond bridged by a hydrido ligand. A novel feature of the structure is a three-center−two-electron B−H⇀Cu bond involving the B(2) site in the nido-10-Cu(PPh3)-7-CB10H10 cage system. The reaction between 4b and [AuCl(PPh3)] gives [Ru3(μ-H)(CO)8{η5-10-Au(PPh3)-7-CB10H10}] (6c), the structure of which was also determined by X-ray crystallography. It is similar to that of 6a, except there is no exopolyhedral B−H⇀Au bond supplementing the B(10)−Au→Ru and Au−P bonds.