Synthesis and characterization of RuH2(H2)2(PiPr3)2 and related chemistry.: Evidence for a bis(dihydrogen) structure

The complex RuH2(H-2)(2)((PPr3)-Pr-i)(2) (1) was prepared by the protonation of [K(18-crown-6)]-[RuH5((PPr3)-Pr-i)(2)] with 1,3-benzenedimethanol. The observation of H-H and M-H vibrations, short Tl(min) values of the hydride resonance, the octahedral geometry of the disordered single-crystal X-ray structure of 1, and large averaged H-D coupling constants for RuHxD6-x((PPr3)-Pr-i)(2) provide evidence for two dihydrogen and two hydride ligands. Under an atmosphere of N-2, complex 1 readily forms an equilibrium mixture of the dinitrogen complexes RuH2(N-2)(2)((PPr3)-Pr-i)(2) (2) and {RuH2(N-2)((PPr3)-Pr-i)(2)}(mu-N-2) (3), which readily reverts to 1 under an atmosphere of Hz. Slow evaporation of a pentane solution of 1 under an atmosphere of Na gas resulted in the isolation of colorless crystals of 8. Complex 1 is very unstable with respect to loss of Ha and forms the trihydride-bridged classical polyhydride dimer ((PPr3)-Pr-i)(2)(H)Ru(mu-H)(3)Ru(H)(2)((PPr3)-Pr-i)(2) (4) under an argon atmosphere or under vacuum at room temperature. Exposure of a solution of 4 to Hz gas results in the gradual regeneration of 1. Similarly, the known bis(dihydrogen) complex RuH2(H-2)(2)(PCy3)(2) (5) was also prepared by protonation of [K(18-crown-6)][RuH5(PCy3)(2)]. An attempt to isolate RuH2(H-2)(2)(PPh3)(2) (6) by protonation of K[RuH5(PPh3)(2)] resulted in the in situ formation of an equilibrium mixture of the bis(dihydrogen) complex 6 and the nonclassical dimer (PPh3)(2)(H)Ru(mu-H)(3)Ru(H-2)(PPh3)(2) (7) The crystal structures of 3, 4, and 7 are reported.