1428232-72-7Relevant academic research and scientific papers
Mechanism of N,N,N-Amide Ruthenium(II) Hydride Mediated Acceptorless Alcohol Dehydrogenation: Inner-Sphere β-H Elimination versus Outer-Sphere Bifunctional Metal-Ligand Cooperativity
Tseng, Kuei-Nin T.,Kampf, Jeff W.,Szymczak, Nathaniel K.
, p. 5468 - 5485 (2015)
The reversible transformations between ketones and alcohols via sequential hydrogenation-dehydrogenation reactions are efficiently achieved using a single precatalyst HRu(bMepi)(PPh3)2 (bMepi = 1,3-bis(6′-methyl-2′-pyridylimino)isoindolate). The catalytic mechanism of HRu(bMepi)(PPh3)2 mediated acceptorless alcohol dehydrogenation (AAD) has been investigated by a series of kinetic and isotopic labeling studies, isolation of intermediates, and evaluation of Ru(b4Rpi)(PPh3)2Cl (R = H, Me, Cl, OMe, OH) complexes. Two limiting dehydrogenation scenarios are interrogated: inner-sphere β-H elimination and outer-sphere bifunctional double hydrogen transfer. Isotopic labeling experiments demonstrated that the proton and hydride transfer in a stepwise manner. Catalyst modifications suggest that the imine group on the bMepi pincer scaffold is not necessary for catalytic alcohol dehydrogenation. Evaluation of the kinetic experiments and catalyst modifications suggests a pathway whereby HRu(bMepi)(PPh3)2 operates via the inner-sphere β-H elimination mechanism. Following a single PPh3 dissociation, an alcohol substrate can bind and undergo proton transfer followed by a turnover-limiting β-H elimination step. Analysis of the Eyring plot established activation parameters for the β-H elimination reaction as ΔH? = 15(1) kcal/mol and ΔS? = -41(3) eu. AAD reactions using a series of Ru(b4Rpi)(PPh3)2Cl complexes indicated that the ortho-substituted methyl groups of bMepi slightly impede catalytic activity, and electronic modifications of the pincer scaffold have a minimal effect on the reaction rate.
Modular Attachment of Appended Boron Lewis Acids to a Ruthenium Pincer Catalyst: Metal-Ligand Cooperativity Enables Selective Alkyne Hydrogenation
Tseng, Kuei-Nin T.,Kampf, Jeff W.,Szymczak, Nathaniel K.
, p. 10378 - 10381 (2016/09/04)
A new series of bifunctional Ru complexes with pendent Lewis acidic boranes were prepared by late-stage modification of an active hydrogen-transfer catalyst. The appended boranes modulate the reactivity of a metal hydride as well as catalytic hydrogenations. After installing acidic auxiliary groups, the complexes become multifunctional and catalyze the cis-selective hydrogenation of alkynes with higher rates, conversions, and selectivities compared with the unmodified catalyst.
Base-free, acceptorless, and chemoselective alcohol dehydrogenation catalyzed by an amide-derived NNN -ruthenium(II) hydride complex
Tseng, Kuei-Nin T.,Kampf, Jeff W.,Szymczak, Nathaniel K.
supporting information, p. 2046 - 2049 (2013/05/22)
The bmpi (1,3-bis(6′-methyl-2′-pyridylimino)isoindoline) pincer Ru(II) hydride complex catalyzes base-free, acceptorless, and chemoselective dehydrogenation of alcohols with liberation of dihydrogen under moderate (120 C) conditions. Primary alcohols and diols are converted to ester and lactone products with high conversion efficiencies. The catalyst system is remarkably selective for the oxidation of secondary alcohols in the presence of primary alcohols.
