Linear and bent oxo-bridged dimers of ruthenium pyrazole nitrosyls

The nitrosylation of RuCl3.(H2O)(x) in thionyl chloride affords anhydrous [ RuCl3(NO)] which, when treated with a variety of ligands L, gives [RuCl3(L) (2)(NO)]. For L = 3,5-dimethylpyrazole (dmpH) it is possible to isolate and characterize the corresponding monomeric complex 1 as well as unusual oxo- bridged dimeric products with nitrosyl ligands trans to the oxo ligand with either a linear geometry, as in trans-O[RuCl2(NO)(dmpH)(2)] (2) and [Cl-4( NO)Ru]O[Ru-(NO)(dmpH)(4)] (4), or with a bent geometry, as in trans-O[RuCl( NO)(dmpH)(mu-dmp)](2) (3). These compounds have been characterized by eleme ntal analysis and vibrational and NMR spectroscopy, as well as by single cr ystal X-ray diffraction. Collectively the structural and spectroscopic data support a delocalized pi-bonding model across the linear ON-Ru-O-Ru-NO fra mework.