Synthesis of Ruthenium Polyhydride Clusters with 1,4,7-Triazacyclononane-Type Ligands: Stereo and Electronic Effects of Ancillary Ligands

A ruthenium bis(η2-dihydrogen)-hydrido complex with 1,4,7-triazacyclononane (Cn), [CnRuH(H2)2](BPh4) (2a-BPh4), was prepared. The infrared spectra, longitudinal relaxation time (T1) measurements, and density functional theory calculations reveal that the electron density at the metal center of complex 2a is higher than that of the 1,4,7-trimethyl-1,4,7-triazacyclononane (Cn*) analogue [Cn*RuH(H2)2]+ (2b). Complex 2a-BF4 is converted into the tetranuclear octahydrido cluster complex [(CnRu)4(μ-H)6(μ3-H)2](BF4)4 (3-BF4) via spontaneous dehydrogenation, whereas the dehydrogenation of 2b-PF6 exclusively affords the diruthenium trihydrido complex [(Cn*Ru)2(μ-H)3](PF6)2 (4-PF6).