Synthesis, Structure, and Reactivity of Mixed-Ligand Dinuclear Ruthenium Polyhydrido Complexes Supported by 1,4,7-Trimethyl-1,4,7-triazacyclononane and Bulky Phosphine Ligands

To construct electronically and sterically
anisotropic reaction
sites of dinuclear cluster, mixed-ligand diruthenium pentahydrido
complexes [Cn*Ru­(μ-H)3Ru­(H)2(PR3)2]+ (Cn* = 1,4,7-trimethyl-1,4,7-triazacyclononane;
R = Cy (3a), iPr (3b), cyclopentyl (Cyp, 3c)) were synthesized by the reaction
of [Cn*RuH­(H2)2]+ (1) with Ru­(H)2(H2)2(PR3)2 (R = Cy (2a) iPr (2b), Cyp (2c)). The treatment of 3a–c with KH afforded the corresponding
neutral tetrahydrido complexes Cn*Ru­(μ-H)3RuH­(PR3)2 (R = Cy (4a), iPr (4b), Cyp (4c)). The structures
of 3 and 4 were confirmed by X-ray diffraction
studies. Introduction of the Cn* ligand into the cluster increased
the electron density at the Cn*-ligated metal center and significantly
stimulated reactivitiy toward molecular nitrogen and carbon dioxide.
Complexes 3a–c reacted with molecular
nitrogen to produce the terminal dinitrogen complexes [Cn*Ru­(N2)­(μ-H)2RuH­(PR3)2]+ (R = Cy (5a), iPr
(5b), Cyp (5c)), which readily underwent
dimerization to form the bridging dinitrogen complexes [(μ-N2)­{RuCn*­(μ-H)2RuH­(PR3)2}2]2+ (R = iPr
(6b), Cyp (6c)), through the liberation
of N2. Cationic complexes 3a–c reacted with CO2 to produce the bridging formato
complexes [Cn*Ru­(μ-η1:η1-O2CH)­(μ-H)2Ru­(H2)­(PR3)2]+ (R = Cy (7a), iPr (7b), Cyp (7c)), whereas
neutral 4a–c reacted with CO2 to form the carbonyl complexes [Cn*Ru­(CO)­(μ-H)2RuH­(PR3)2]+ (R = Cy (9a), iPr (9b), Cyp
(9c)), via cleavage of the CO bond.