The complex [RuCl(dppe)(2)]PF6, 1, dppe = Ph(2)PCH(2)CH(2)PPh(2), is prepared by reacting cis-RuCl2(dppe)(2) with NaPF6. It has a distorted trigonal bipyramidal geometry with a Ru(P)(2)Cl "Y" shaped equatorial plane. In weakly coordinating solvents it is mainly five-coordinate. Under FAB MS conditions it is ionized to [RuCl(PF6)(dppe)(2)](+) It reacts with Cl- or L = CO, CH3CN to give complexes cis-RuCl2(dppe)(2) or cis-[Ru(Cl)(L)(dppe)(2)]PF6, respectively. Dihydrogen reacts with 1 to give trans-[Ru(H-2)Cl(dppe)(2)]PF6, 2a The reaction of HA, A = BF4 or PF6, with complexes trans-RuH(Cl)(dppe)n or trans-RuHCl(depe)(2), depe = PEt(2)CH(2)CH(2)PEt(2), gives dihydrogen complexes trans-[Ru(H-2)Cl(dppe)(2)]A, 2a, and trans-[Ru(H-2)Cl(depe)(2)]A, 2b. The H-H distances in complexes 2 are longer than those found in analogous complexes trans-[Ru(H-2)H(diphos)(2)](+) 3 probably because of the pi effect of the Cl-. Associated with the H-H lengthening is a dramatic reduction in the pK(a) of 2a (6) vs 3a (15). An electron-rich trihydride complex [Ru(H)(3)(dppf)(2)](+) (4)1 dppf = 1,1’-bis(diphenylphosphino)ferrocene, with no H-H bond is found to be, paradoxically, the most acidic (pK(a) approximate to 4). Bond dissociation energies calculated for complexes 2a, 3a, and 4 from pK, and electrochemical data also suggest that the amount of the H-H bonding has a major influence on the acidity of the complexes. Complex 2a in CH2Cl2, under Ar appears to slowly lose HCl at 233 K; it reacts with CO at 273 K to give HCl and trans-[Ru(CO)H(dppe)(2)](+) and with H-2 in the presence of Na+ to give 3a. Complex 1 crystallizes in the space group P2(1)/c with a 12.427(2) Angstrom, b = 15.565(3) Angstrom, c = 26.759(5) Angstrom, beta = 95.94(3)degrees, V = 5148.1 Angstrom(3), and D-calcd = 1.391 g cm(-3) for Z = 4. Least squares refinement of the model based on 4383 observed reflections (F > 6.0 sigma(F)) converged to a final R(F) = 5.4%. Complex 2a crystallizes in the space group P2(1)/n with a = 15.315(1) Angstrom, b = 17.479(1) Angstrom, c = 18.608(1) Angstrom, beta = 101.79(1)degrees, V =4875.9(7) Angstrom(3), and D-calcd = 1.472 g cm(-3) for Z = 4.Least squares refinement of the model based on 9208 observed reflections (F > 4.0 sigma(F)) converged to a final R( )=F 5.1%. There is electron density associated with the H-2 ligand trans to the chloride in octahedral 2a..