Ruthenium clusters with nitrogen ligands V ¹. Pyridyl ligands on triruthenium cores. X-ray structures of Ru₃(μ-H)₂(μ-NC₅H₄)₂(CO)₈ and Ru₃(μ₃-η²-PPhCH₂PPh₂) (μ-NC₅H₄)(CO)₈

The reaction between Ru₃(CO)₁₂ and pyridine affords a mixture of Ru₃(μ-H)(μ-NC₅H₄)(CO)₁₀ (1) and Ru₃(μ-H)₂(μ-NC₅H₄)₂(CO)₈ (2). Cluster 2 is the first crystallographically-verified triruthenium cluster with two orthometalated N-heterocycles; these ligands occupy edge-bridging diaxial sites on two of the three Ru-Ru bonds, one on each side of the triruthenium plane, with the hydrido ligands bridging the same Ru-Ru bonds as the pyridyls. Reaction of 1 with dppm gives Ru₃(μ₃-η²-PPhCH₂PPh₂)(μ-NC₅H₄)(CO)₈ (3) in low yield amongst a mixture of products. The structural study confirms that 3 results from dephenylation of the dppm ligand; concomitant loss of the hydrido ligand suggests reductive elimination of benzene. Formal electron counting on this electron precise cluster shows that Ru(1) and Ru(3) are each 0.5e deficient, and Ru(2) is le rich; two "semibridging" carbonyls in the triruthenium plane redistribute electron density from Ru(2) to Ru(1) and Ru(3). Reaction of Ru₃(μ-dppm)(CO)₁₀ with pyridine also affords 3 in low yield. Related reactions with the more flexible bidentate ligand dppe afford more complex mixtures of products. Whereas thermolysis of 1 affords [Ru₂(μ-H)(μ-NC₅H₄)₂(CO)₄(NC₅H₅)₂][Ru₁₀(μ-H)(μ₆-C)(CO)₂₄], thermolyses of 2 or 3 do not lead to tractable products.