Syntheses and Properties of a Series of Oxo-Centered Triruthenium Complexes and Their Bridged Dimers with Isocyanide Ligands at Terminal and Bridging Positions

Abstract

Seven new oxo-centered triruthenium complexes with 2,6-dimethylphenyl isocyanide (CNXy) as a terminal ligand, [Ru 3 (O)(CH 3 CO 2 ) 6 (CNXy) n (L) 3 - n ] {L = CO, n = 2 ( 1 ); L = pyridine (py), n = 1 ( 2 ); L = 4-(dimethylamino)pyridine (dmap), n = 1 ( 3 ); L = py, n = 2 ( 4 ); L = dmap, n = 2 ( 5 ); n = 3 ( 6 ); L = 5-(4-pyridyl)-10,15,20-triphenylporphine, n = 2 ( 7 )}, three new pyrazine (pz) bridged dimers of triruthenium complexes with terminal isocyanide ligands, [{Ru 3 (O)(CH 3 CO 2 ) 6 (CNXy) n (L) 2 - n } 2 (μ-pz)] {L = py, n = 1 ( 8 ); L = dmap, n = 1 ( 9 ); n = 2 ( 10 )}, and three new 1,4-phenylene diisocyanide bridged dimers, [{Ru 3 (O)(CH 3 CO 2 ) 6 (L) 2 } 2 (μ-CNC 6 H 4 NC)] {L = py ( 11 ); L = dmap ( 12 ); L = CNXy ( 13 )}, were prepared. All the Ru 3 (O) cluster core in these compounds have the formal oxidation state of Ru III 2 Ru II in the isolated state. In contrast to the related carbonyl derivatives, the isocyanide complexes gave triruthenium complexes with more than one isocyanide ligand, reflecting the lower π acidity of isocyanides. In the mixed carbonyl/isocyanide complex [Ru 3 (O)(CH 3 CO 2 ) 6 (CO)(CNXy) 2 ] ( 1 ), the carbonyl and isocyanide ligands compete in π acidity for the Ru 3 (O) cluster core, and as a result 1 undergoes a facile elimination of the CO ligand followed by substitution. With use of this reaction, many other triruthenium isocyanide complexes were prepared. Coordination of isocyanide ligands to these triruthenium complexes causes the redox potentials to be shifted anodically relative to the corresponding pyridine derivatives. The pz bridged dimers, 8 and 9, gave stable one-electron-reduced species which are in the mixed-valence state with respect to the Ru 3 core, as is evidenced by a large redox wave splitting for the Ru III 2 Ru II −pz−Ru III 2 Ru II /Ru III 2 Ru II −pz−Ru III Ru II 2 /Ru III Ru II 2 −pz−Ru I II Ru II 2 process (Δ E 1/2 = 349 mV for 8 and 393 mV for 9 ). On the other hand, 1,4-phenylene diisocyanide bridged Ru 3 dimers 11 − 13 gave no stable mixed-valence state, indicating that the electronic communication between the Ru 3 units through this bridge is negligibly small. The compound [Ru 3 (O)(CH 3 CO 2 ) 6 (CNXy)(py) 2 ] ( 2 ) crystallized in the orthorhombic Pbcn space group with a = 18.393(5) Å, b = 14.428(2) Å, c = 17.396(2) Å, and Z = 4. A comparison of Ru−O(acetate) distances reveals that the site coordinated by the isocyanide ligand is formally Ru(II).