TY - JOUR
T1 - Catalytic N-H Bond Formation Promoted by a Ruthenium Hydride Complex Bearing a Redox-Active Pyrimidine-Imine Ligand
AU - Kim, Sangmin
AU - Kim, Junho
AU - Zhong, Hongyu
AU - Panetti, Grace B.
AU - Chirik, Paul J.
N1 - Publisher Copyright:
© 2022 American Chemical Society. All rights reserved.
PY - 2022/11/16
Y1 - 2022/11/16
N2 - The synthesis of a piano-stool ruthenium hydride, [(Ε5-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 [(Ε5-C5Me5)RuCl2]nwith one equivalent PmIm ligand in the presence of zinc and sodium methoxide resulted in the isolation of the diruthenium complex, [(Ε5-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, [(Ε5-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 [(Ε5-C5Me5)Ru(PmIm)H] generated the 17-electron metalloradical, [(Ε5-C5Me5)Ru(PmIm)], which was characterized by EPR spectroscopy. The C-C bond forming process was reversible as the irradiation of [(Ε5-C5Me5)Ru(PmIm)]2generated [(Ε5-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.
AB - The synthesis of a piano-stool ruthenium hydride, [(Ε5-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 [(Ε5-C5Me5)RuCl2]nwith one equivalent PmIm ligand in the presence of zinc and sodium methoxide resulted in the isolation of the diruthenium complex, [(Ε5-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, [(Ε5-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 [(Ε5-C5Me5)Ru(PmIm)H] generated the 17-electron metalloradical, [(Ε5-C5Me5)Ru(PmIm)], which was characterized by EPR spectroscopy. The C-C bond forming process was reversible as the irradiation of [(Ε5-C5Me5)Ru(PmIm)]2generated [(Ε5-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.
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U2 - 10.1021/jacs.2c07800
DO - 10.1021/jacs.2c07800
M3 - Article
C2 - 36326751
AN - SCOPUS:85141742270
SN - 0002-7863
VL - 144
SP - 20661
EP - 20671
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 45
ER -