Much attention has been paid to sulfide-coordinated transition metal complexes, due to their chemistry relevant to the biological and catalytic processes. 1 Although there are several chemical reactivities in which the sulfur atom of the ligands usually acts as the reactive center, 2 C-H bond activation on the sulfur center has not been reported, except for our previous result and that of Rauchfuss et al. on C-H bond activation of acetone promoted by disulfide and monosulfide metal complexes. 3,4 Additionally, the reverse reaction of the olefin insertion into a S-H bridging ligand of a cationic cyclopentadienylmolybdenum complex can also be regarded as a C-H bond activation of a µ-alkanethiolate ligand. 5 This is in strong contrast to the extensive studies on C-H bond activation based upon transition metal centers in organometallic chemistry. 6 In this regard, exploitation of C-H bond activation on a sulfur center of ligands will be a new challenge in chemistry. So far the most widely reported reactions of sulfide, disulfide, hydrosulfide, and polysulfide ligands in the formation of C-S bond(s) are via (a) addition of sulfide, disulfide, and polysulfide ligands to acetylene and its derivatives 7,8 or alkenes; 8,9 (b) olefin insertion into coordinated S-H bonds; 5,10,11 and (c) attack of alkylating reagents on sulfide ligands. 12 Among the several C-S bond formations via inorganic sulfide ligands, chemical reactivities of disulfide ligand are less explored. 3,7e,8a Here, we report the first sulfur-centered activation of an allylic C-H bond of monoolefin, such as 1-pentene and cyclohexene, on a disulfide-bridged dinuclear ruthenium complex, accompanied by formation of C-S bond(s).Addition of an excess of 1-pentene to an acetonitrile solution(2) with 4 equiv of AgCF 3 SO 3 as previously reported, 13,14 at ambient temperature gave yellow crystals of [{Ru(P(OMe) 3 ) 2 (MeCN) 3 } 2 (µ-S 2 )(CH 2 ) 2 -CH(C 2 H 5 )](CF 3 SO 3 ) 4 (3) in a yield of 44% (eq 1). 15 The structure of 3 was confirmed based on the 31 P, 1 H, and 13 C NMR, CHN elemental analysis, and X-ray diffraction analysis. 15,16 Two doublets with an ab pattern (126.4 and 125.7 ppm, 2 J PP ) 81 Hz) and a singlet (125.0 ppm) were observed in the 31 P{ 1 H} NMR spectrum, indicating inequivalency of the two ruthenium atoms in 3. The 1 H and 13 C NMR spectra of 3 also clearly show the pentyl moiety. 15 All of the three NMR spectra with sharp peak profiles show that 3 is diamagnetic, although it is a Ru(III) dinuclear compound. 17 X-ray analysis of 3 reveals that an allylic C-H bond of 1-pentene is cleaved and the two bridging sulfur atoms are bound to two carbon atoms at the 1 and 3 positions of 1-pentene to form a five-membered dithiolane moiety as shown in Figure 1. To our knowledge, this is the first example of allylic C-H bond activation on any sulfide center and two sulfur atoms of the disulfide bridging ligand are bonded to two alkyl carbon atoms. This double C-S bond formation is significant, since only one C-S bond is formed in our previous study on the ...