In a search of transition metal complexes with sulfur dominated coordination spheres and free coordination sites for the binding of small molecules, [Ru(L)('buS5')] complexes with the sterically demanding pentadentate thioether-thiolate ligand 'buS5'2- ( 'buS5'2- = 2,2'-Bis(2-mercapto-3,5-di-t-butylphenylthio)diethylsulfide(2-)) have been synthesized. Reaction of [RuCl3(NO)(PPh3)2] with 3,5-di(t-butyl)benzene-1,2-dithiolate, ′buS2'2-, yields the 16 electron complex [Ru(NO )('buS2')2]- which is isolated as the NBu4+-salt, 1. According to the NMR spectra, 1 contains a two-fold axis or a mirror plane. Alkylation of 1 with bis(β-bromethyl)sulfide under reflux leads stereoselectively to meso-[Ru(NO)('buS5')]Br, [2]Br. Reaction of [2]Br with LiBEt3H yields the barely soluble binuclear complex [Ru('buS5')]2, 3, with [Ru('buS5')Ru(NO)('buS2')('buS2'- C2H4SH)], 4, as a by-product. 4 ·THF, 4a, has been characterized by X-ray structure analysis. Reactions of 3 with σ-π- and σ-ligands yield mononuclear meso-[Ru(L)('buS5')] complexes which have been isolated and characterized with L = CO, PMe3, PPh3, PCy3, pyr, CN-, 5 - 10, NH2NHPh, NH2NHMe, NH2NMe2, NH2Ph und NHEt2, 13-17. Complexes 5 -10 are stable compounds. Complexes 13-17, however, are sensitive towards oxidation and/or substitution. Coordination of L = N2H4 and NH3 to 3 leads to insoluble [Ru(L)('buS5')]x complexes.