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

Abstract

The complex RuH2(H2)2(PiPr3)2 (1) was prepared by the protonation of [K(18-crown-6)][RuH5(PiPr3)2] with 1,3-benzenedimethanol. The observation of H−H and M−H vibrations, short T1(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(PiPr3)2 provide evidence for two dihydrogen and two hydride ligands. Under an atmosphere of N2, complex 1 readily forms an equilibrium mixture of the dinitrogen complexes RuH2(N2)2(PiPr3)2 (2) and {RuH2(N2)(PiPr3)2}2(μ-N2) (3), which readily reverts to 1 under an atmosphere of H2. Slow evaporation of a pentane solution of 1 under an atmosphere of N2 gas resulted in the isolation of colorless crystals of 3. Complex 1 is very unstable with respect to loss of H2 and forms the trihydride-bridged classical polyhydride dimer (PiPr3)2(H)Ru(μ-H)3Ru(H)2(PiPr3)2 (4) under an argon atmosphere or under vacuum at room temperature. Exposure of a solution of 4 to H2 gas results in the gradual regeneration of 1. Similarly, the known bis(dihydrogen) complex RuH2(H2)2(PCy3)2 (5) was also prepared by protonation of [K(18-crown-6)][RuH5(PCy3)2]. An attempt to isolate RuH2(H2)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(μ-H)3Ru(H2)(PPh3)2 (7). The crystal structures of 3, 4, and 7 are reported.