pH‐Dependent Catalytic Activity and Chemoselectivity in Transfer Hydrogenation Catalyzed by Iridium Complex with 4,4′‐Dihydroxy‐2,2′‐bipyridine

Abstract

Transfer hydrogenation catalyzed by an iridium catalyst with 4,4'-dihydroxy-2,2'-bipyridine (DHBP) in an aqueous formate solution exhibits highly pH-dependent catalytic activity and chemoselectivity. The substantial change in the activity is due to the electronic effect based on the acid-base equilibrium of the phenolic hydroxyl group of DHBP. Under basic conditions, high turnover frequency values of the DHBP complex, which can be more than 1000 times the value of the unsubstituted analogue, are obtained (up to 81 000 h(-1) at 80 degrees C). In addition, the DHBP catalyst exhibits pH-dependent chemoselectivity for alpha,beta-unsaturated carbonyl compounds. Selective reduction of the C=C bond of enone with high activity are observed under basic conditions. The ketone moieties can be reduced with satisfactory activity under acidic conditions. In particular, pH-selective chemoselectivity of the C=O versus C=C bond reduction was observed in the transfer hydrogenation of cinnamaldehyde.

A visible-light-driven transfer hydrogenation on CdS nanoparticles combined with iridium complexes

“…This trend is in agreement with those made with HCOONa as the reducing agent in water. 13 The used CdS sample was filtered and further characterized. No iridium nanoparticles could be observed in the TEM image (Fig.…”

“…13 This inspires us to improve the efficiency in the current photocatalytic system by the optimization of the pH value of solution. As shown in Fig.…”

Ion–Molecule Reactions of “Rollover” Cyclometalated [Pt(bipy−H)]+ (bipy=2,2′‐bipyridine) with Dimethyl Ether in Comparison with Dimethyl Sulfide: An Experimental/Computational Study

“…For example, Periana and coworkers investigated the heterolytic C À H bond activation of methane and benzene with a cyclometalated Pt II complex as well as catalytic methane hydroxylation using an Ir III NNC pincer complex in acidic solution; [7,8] another study deals with transfer hydrogenation mediated by a cyclometalated Ir III compound. [9] 2,2'-Bipyridine (bipy) and related heterocycles, which are versatile ligands in the coordination chemistry of transition metals, [10] are well suited for the formation of cyclometalated compounds. Moreover, it has been shown that cyclometalated [PtA C H T U N G T R E N N U N G (bipyÀH)] + (1) can formally dehydrosulfurize a variety of thioethers in the gas phase; [11] especially in the reaction with dimethyl sulfide, efficient oxidative C À C bond coupling and concomitant formation of neutral ethene was observed.…”

Triazolopyridines. Part 30. Hydrogen transfer reactions; pyridylcarbene formation

“…For this reason, the scientific community has been directing considerable research effort into catalytic transfer hydrogenation, [6][7][8] which favors use of hydrogen donors (alcohols, diimides, amines, hydrocarbons or formic acid) and avoids molecular hydrogen. Ruthenium, 9-11 rhodium, [12][13][14][15] iridium, [16][17][18][19] and nickel 20 are the metals most frequently used as catalysts. Organocatalytic transfer hydrogenation using dihydropyridines as hydride donors and Brönsted acid catalysis has also been intensively investigated.…”