Heterolytic cleavage of dihydrogen on transition metal sulfides/thiolates has been regarded as the key reaction in hydrogen metabolism in nature [1] and in catalytic desulfurization of fossil fuel. [2] Although there are numerous reports of heterolytic dihydrogen activation, [3, 4] that occurring at metalsulfur bonds is still limited. A representative example is the reaction of [{Rh(triphos)} 2 (m-S) 2 ] 2+ (triphos = tris(diphenylphosphanylethyl)methane) with H 2 to generate [{RhH-(triphos)} 2 (m-SH) 2 ] 2+ . [4a,b] Heterolytic H 2 cleavage was also reported to be promoted by sulfido/thiolato-bridged dinuclear Mo-Mo, [4c-e] Ir-Ir, [4f] and W-Ir [4g] complexes and mononuclear sulfido/thiolato complexes of Ti, [4h-i] Ni, Ru, and Rh. [4j-n] In the course of our studies on transition metal sulfide/thiolate complexes, [5] we found that sulfido-bridged W-Ru complexes activate H 2 in a heterolytic manner. [5c] Here we report heterolytic cleavage of H 2 by the sulfidoand oxo-bridged heterodinuclear germanium-ruthenium complex [(dmp)(dep)Ge(m-S)(m-O)Ru(PPh 3 )] (1; dmp = 2,6dimesitylphenyl, dep = 2,6-diethylphenyl). As we showed previously, the m-S ligand of 1 prefers softer acids, and the m-O ligand harder acids. [6] The synergetic m-sulfide and moxide pair plays an important role in H 2 heterolysis by 1.
Heterodinuclear complex 1 was prepared from [(dmp)-(dep)Ge(SH)(OH)], [RuCl 2 (h 6 -p-cymene)], and PPh 3 according to Scheme 1. [6] No H 2 activation by 1 took place under an atmospheric pressure of dihydrogen even at 90 8C. However, complex 1 was converted slowly to anti and syn isomers of hydroxy hydride complex 2 when heated to 75 8C in toluene under 10 atm of H 2 (Scheme 1, Table 1). As is obvious from the structures of anti-2 and syn-2, H 2 was cleaved heterolytically by 1 into a hydroxy-bound proton on Ge and a hydride ligand on Ru.
Dihydrogen activation was examined under various conditions to obtain insight into the reaction mechanism. Intriguingly, anti-2 is the favored product in the early stage of the reaction (Table 1, entry 1). The relative ratio of syn-2 to anti-2 slowly increases as the reaction proceeds, and eventually syn-2 becomes the exclusive product at 90 8C after 3 days under 7.5 atm H 2 (Table 1, entry 5). The results suggest that the kinetically favored product is anti-2, which gradually isomerizes to the more thermodynamically stable syn-2. Addition of 10 equiv PPh 3 hardly affects the reaction of 1 with H 2 . No significant deceleration of the consumption of 1 was observed, either for the reactions at 75 8C for 6 h (Table 1, entries 1 and 2) or for those at 24 h (Table 1, entries 3 and 4), that is, the rate-determining step does not include PPh 3 dissociation. On the other hand, the subsequent isomerization from anti-2 to syn-2 is clearly decelerated by addition of PPh 3 , as is manifested in the results at 90 8C and 72 h (Table 1, entries 5 and 6). The isomerization appears to be accompanied by dissociation of PPh 3 .