Scope and Mechanistic Analysis for Chemoselective Hydrogenolysis of Carbonyl Compounds Catalyzed by a Cationic Ruthenium Hydride Complex with a Tunable Phenol Ligand

Authors

Nishantha Kumara Kalutharage, Marquette University
Chae S. Yi, Marquette UniversityFollow

Document Type

Article

Language

eng

Format of Original

10 p.

Publication Date

8-2-2015

Publisher

American Chemical Society

Source Publication

Journal of the American Chemical Society

Source ISSN

1520-5126

Original Item ID

DOI: 10.1021/jacs.5b06097, PubMed Central: PMID: 26235841

Abstract

A cationic ruthenium hydride complex, [(C₆H₆)(PCy₃)(CO)RuH]⁺BF₄^– (1), with a phenol ligand was found to exhibit high catalytic activity for the hydrogenolysis of carbonyl compounds to yield the corresponding aliphatic products. The catalytic method showed exceptionally high chemoselectivity toward the carbonyl reduction over alkene hydrogenation. Kinetic and spectroscopic studies revealed a strong electronic influence of the phenol ligand on the catalyst activity. The Hammett plot of the hydrogenolysis of 4-methoxyacetophenone displayed two opposite linear slopes for the catalytic system 1/p-X-C₆H₄OH (ρ = −3.3 for X = OMe, t-Bu, Et, and Me; ρ = +1.5 for X = F, Cl, and CF₃). A normal deuterium isotope effect was observed for the hydrogenolysis reaction catalyzed by 1/p-X-C₆H₄OH with an electron-releasing group (k_H/k_D = 1.7–2.5; X = OMe, Et), whereas an inverse isotope effect was measured for 1/p-X-C₆H₄OH with an electron-withdrawing group (k_H/k_D = 0.6–0.7; X = Cl, CF₃). The empirical rate law was determined from the hydrogenolysis of 4-methoxyacetophenone: rate = k_obsd[Ru][ketone][H₂]⁻¹ for the reaction catalyzed by 1/p-OMe-C₆H₄OH, and rate = k_obsd[Ru][ketone][H₂]⁰ for the reaction catalyzed by 1/p-CF₃-C₆H₄OH. Catalytically relevant dinuclear ruthenium hydride and hydroxo complexes were synthesized, and their structures were established by X-ray crystallography. Two distinct mechanistic pathways are presented for the hydrogenolysis reaction on the basis of these kinetic and spectroscopic data.

Comments

Accepted version. Journal of the American Chemical Society, Vol 137, No. 34 (August 2, 2015): 11105-11114. DOI. © 2015 American Chemical Society. Used with permission.

Recommended Citation

Kalutharage, Nishantha Kumara and Yi, Chae S., "Scope and Mechanistic Analysis for Chemoselective Hydrogenolysis of Carbonyl Compounds Catalyzed by a Cationic Ruthenium Hydride Complex with a Tunable Phenol Ligand" (2015). Chemistry Faculty Research and Publications. 468.
https://epublications.marquette.edu/chem_fac/468