Syntheses and Properties of Triruthenium Polyhydrido Complexes Composed of 1,2,4-tri-tert-butylcyclopentadienyl and p‑Cymene Ruthenium Units

Mixed-ligand triruthenium hydrido complexes composed of [Cp‡Ru] (Cp‡ = 1,2,4-tri-tert-butylcyclopentadienyl) and [(p-cymene)­Ru] fragments, [(Cp‡Ru)2{(p-cymene)­Ru}­(μ-H)3(μ3-H)] (3a) and [(Cp‡Ru)­{(p-cymene)­Ru}2(μ-H)2(μ3-H)] (5), were synthesized. While the reaction of [(Cp*Ru)2(μ-H)4] (1a; Cp* = C5Me5) with 0.5 equiv of [(p-cymene)­RuCl2]2 in the presence of 2-propanol and a base did not afford 3a selectively, 5 was exclusively obtained by the reaction of [(Cp‡Ru)­{(p-cymene)­Ru}­(μ-H)3] (2a) with 0.5 equiv of [(p-cymene)­RuCl2]2. Both triruthenium complexes smoothly reacted with P­(OMe)3 to yield the corresponding phosphite adducts 7 and 8; however, the sites for P­(OMe)3 ligation were different in these complexes. While the P­(OMe)3 ligated at one of the [Cp‡Ru] sites in 3a, it ligated at the [(p-cymene)­Ru] site in 5. A quantum theory of an atoms in molecules analysis of these complexes revealed that a direct Ru–Ru interaction was present only at the (p-cymene)­Ru–Ru­(p-cymene) edges, which did not contain a μ-hydrido ligand. Due to the presence of the Ru–Ru bond, complex 5 showed high reactivity toward H/D exchange with deuterated benzene at 25 °C.