Synthesis and Characterization of RuH2(H2)2(PiPr3)2 and Related Chemistry. Evidence for a Bis(dihydrogen) Structure

The complex RuH 2 (H 2 ) 2 (P i Pr 3 ) 2 ( 1 ) was prepared by the protonation of [K(18-crown-6)][RuH 5 (P i Pr 3 ) 2 ] with 1,3-benzenedimethanol. The observation of H−H and M−H vibrations, short T 1 (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 RuH x D 6 - x (P i Pr 3 ) 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 RuH 2 (N 2 ) 2 (P i Pr 3 ) 2 ( 2 ) and {RuH 2 (N 2 )(P i Pr 3 ) 2 } 2 (μ-N 2 ) ( 3 ), which readily reverts to 1 under an atmosphere of H 2 . Slow evaporation of a pentane solution of 1 under an atmosphere of N 2 gas resulted in the isolation of colorless crystals of 3 . Complex 1 is very unstable with respect to loss of H 2 and forms the trihydride-bridged classical polyhydride dimer (P i Pr 3 ) 2 (H)Ru(μ-H) 3 Ru(H) 2 (P i Pr 3 ) 2 ( 4 ) under an argon atmosphere or under vacuum at room temperature. Exposure of a solution of 4 to H 2 gas results in the gradual regeneration of 1 . Similarly, the known bis(dihydrogen) complex RuH 2 (H 2 ) 2 (PCy 3 ) 2 ( 5 ) was also prepared by protonation of [K(18-crown-6)][RuH 5 (PCy 3 ) 2 ]. An attempt to isolate RuH 2 (H 2 ) 2 (PPh 3 ) 2 ( 6 ) by protonation of K[RuH 5 (PPh 3 ) 2 ] resulted in the in situ formation of an equilibrium mixture of the bis(dihydrogen) complex 6 and the nonclassical dimer (PPh 3 ) 2 (H)Ru(μ-H) 3 Ru(H 2 )(PPh 3 ) 2 ( 7 ). The crystal structures of 3, 4, and 7 are reported.