The synthesis of a piano-stool ruthenium hydride, [(Î•5-C5Me5)Ru(PmIm)H] (PmIm = (N-(1,3,5-trimethylphenyl)-1-(pyrimidin-2-yl)ethan-1-imine), for the dual purpose of catalytic dihydrogen activation and subsequent hydrogen atom transfer for the formation of weak chemical bonds is described. The introduction of a neutral, potentially redox-active PmIm supporting ligand was designed to eliminate the possibility of deleterious C(sp2)-H reductive coupling and elimination that has been identified as a deactivation pathway with related rhodium and iridium catalysts. Treatment of [(Î•5-C5Me5)RuCl2]nwith one equivalent PmIm ligand in the presence of zinc and sodium methoxide resulted in the isolation of the diruthenium complex, [(Î•5-C5Me5)Ru(PmIm)]2, arising from the C-C bond formation between two PmIm chelates. Addition of H2to the ruthenium dimer under both thermal and blue light irradiation conditions furnished the targeted hydride, [(Î•5-C5Me5)Ru(PmIm)H], which has a relatively weak DFT-calculated Ru-H bond dissociation free energy (BDFE) of 47.9 kcal/mol. Addition of TEMPO to [(Î•5-C5Me5)Ru(PmIm)H] generated the 17-electron metalloradical, [(Î•5-C5Me5)Ru(PmIm)], which was characterized by EPR spectroscopy. The C-C bond forming process was reversible as the irradiation of [(Î•5-C5Me5)Ru(PmIm)]2generated [(Î•5-C5Me5)Ru(PmIm)H] and a piano-stool ruthenium complex containing an enamide ligand derived from H-atom abstraction from the PmIm chelate. Equilibration studies were used to establish an experimental estimate of the effective Ru-H BDFE, and a value of 50.8 kcal/mol was obtained, in agreement with the observed loss of H2and the DFT-computed value. The ruthenium hydride was an effective catalyst for the thermal catalytic hydrogenation of TEMPO, acridine, and a cobalt-imido complex and for the selective reduction of azobenzene to diphenylhydrazine, highlighting the role of this complex in catalytic weak bond formation using H2as the stoichiometric reductant.
|Number of pages||11|
|Journal||Journal of the American Chemical Society|
|Publication status||Published - 2022 Nov 16|
Bibliographical noteFunding Information:
This research was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Catalysis Science program, under Award DE-SC0006498. S.K. acknowledges a Samsung Scholarship for partial financial support.
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All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry