Protic NNN and NCN Pincer‐Type Ruthenium Complexes Featuring (Trifluoromethyl)pyrazole Arms: Synthesis and Application to Catalytic Hydrogen Evolution from Formic Acid

Abstract

NNN and NCN pincer-type ruthenium(II) complexes featuring two protic pyrazol-3-yl arms with at rifluoromethyl (CF 3 )g roup at the 5-position weres ynthesized and structurally characterized to evaluate the impacto ft he substitution on the properties and catalysis. The increased Brønsted acidity by the highly electron-withdrawing CF 3 pendants was demonstrated by protonation-deprotonation experiments.B yc ontrast, the IR spectra of the carbonyl derivatives as well as the cyclic voltammogram indicated that the electron density of the ruthenium atom is negligibly influenced by the CF 3 group.C atalysis of these complexes in the decomposition of formic acid to dihydrogen and carbon dioxide was also examined. The NNNp incer-type complex 1a with the CF 3 group exhibited ah igherc atalytic activity than the tBu-substituted analogue 1b.I na ddition, the bis(CF 3 -pyrazolato) ammine derivative 4 catalyzed the reaction even in the absence of base additives.

Rhenium-catalysed reactions in chemical synthesis: selected case studies

“…[38][39][40][41][42][43][44][45] Classical approaches for the synthesis of transition metal vinylidene complexes exploit 1,2-alkyl or 1,2-hydrogen shifts of internal, [46][47][48][49] or terminal alkynes. [50][51][52][53] These activation pathways are also often invoked in many associated transitionmetal-catalysed reactions employing alkyne substrates. [54][55][56][57] Jia and co-workers demonstrated the first example of C-C bond cleavage of internal propargyl alcohols to access rhenium viny-lidene complexes in 2018 (Scheme 1B).…”

An Update on Formic Acid Dehydrogenation by Homogeneous Catalysis

“…In 2011, Nozaki introduced an Ir−PNP complex to demonstrate the reversible FA dehydrogenation providing TOF of 120,000 h −1 in tert ‐butanol during the first minute at 80 °C . A great number of catalysts bearing pincer type ligands were also investigated in the selective FA decomposition under different conditions . These studies are described in section 4.…”

Recent Progress with Pincer Transition Metal Catalysts for Sustainability

“…Kuwata showed a series of ruthenium-NNN pincer complexes bearing protic (trifluoromethyl)pyrazole arms for formic acid dehydrogenation [404]. The complexes were synthetized and characterized, and the impact of the perturbations on the catalytic properties was Scheme 25.…”