HETEROLYTIC H-2 ACTIVATION BY DIHYDROGEN COMPLEXES - EFFECTS OF THE LIGAND X IN [M(X)H-2(PH(2)P(CH2)(3)PPH(2))(2)](N+) (M=RU,OS, X=CO, CL, H)

Complexes of the general formula [MXH(2)(dppp)(2)](n+) (M=Ru, Os; X=H, Cl, CO; dppp=1,3-bis (diphenylphosphino)propane) have been prepared a nd characterized, and the effect of the donor/acceptor properties of X on their structure and acidity has been studied. The five-coordinate complexes [MCl(dppp)(2)](+) (M=Ru (1a), Os (1b)) react with H-2 gas in CH2Cl2 to give the complexes [MCl(eta(2)-H-2)(dppp)(2)](+) (M=Ru (2a) , Os (2b)) containing elongated dihydrogen ligands. The molecular stru cture of 2b has been determined by X-ray crystallography (monoclinic, space group P2(1)/n with a=13.314(7) Angstrom, b=18.63(2) Angstrom, c= 23.20(2) Angstrom, beta=94.58(6)degrees, and Z=4). Chlorohydride [OsH( Cl)(dppp)(2)] (3b) reacts with H-2 gas in the presence of Na[BPh(4)] f orming [OsH3(dppp)(2)](+) (4b). Protonation of [OsH2(dppp)(2)] (5b) wi th HBF4 . Et(2)O also gives 4b. A combination of X-ray crystallography (monoclinic, space group P2(1)/n with a=13.392(3) Angstrom, b=25.306( 7) Angstrom, c=21.247(7) Angstrom, beta=91.15(2)degrees, and Z=4) and H-1 and P-31 NMR studies indicate that 4b is a classical trihydride. H ydridocarbonyls [MH(CO)(dppp)(2)](+) (M=Ru (6a), Os (6b)) are protonat ed by F3CSO3H in CD2Cl2 to yield [M(CO)(eta(2)-H-2)(dppp)(2)](2+) (M=R u (7a), Os (7b)), which were characterized in solution. 7a is stable o nly at low temperature. Compound 7b is a highly acidic dihydrogen comp lex with an estimated pK(a) of -6.