Reaction of H-2 with RuCl2(CO)L(2) (L = P(t)Bu(2)Me) in benzene forms RuHCl(CO)L(2) and HCl. The latter reacts with RuCl2(CO)L(2) to give [LH][Ru2Cl5(CO)(2)L(2)] and [LH]Cl. The Ru2Cl5(CO)(2)L(2)(-) ion is detected (NMR) as several isomers, and is shown by X-ray diffraction to have a face-shared bioctahedral structure : LCl(OC)Ru(mu-Cl)(3)Ru(CO)ClL(-). The loss of phosphine from Ru(II) is triggered by electrophilic attack, but not directly on P or on the Ru-P bond. It is shown (low-temperature NMR studies) that HCl reacts with RuHCl(CO)L(2) to give initially RuCl2(H-2)(CO)L(2), in which H-2 is trans to Cl. From this study, and also direct observation of the reaction of HCl with RuCl2(CO)L(2) to produce Ru2Cl5(CO)(2)L(2)(-), the Bronsted basicity of chloride in RuCl2(CO)L(2) is established. This accounts for its reaction with PhC(2)H and NEt(3) to give Ru(C(2)Ph)Cl(CO)L(2). Crystallographic data (-173 degrees C) for [P(t)Bu(2)MeH][Ru2Cl5(CO)(2)(P(t)Bu(2)Me)(2)] : a = 16.418(2)Angstrom, b = 12.578(2)Angstrom, c = 20.044(3)Angstrom, beta = 103.38(1)degrees with Z = 4 in space group P2(1)/a.