Chemistry of Concerto Molecular Catalysis Based on the Metal/NH Bifunctionality

Abstract

The development of conceptually new bifunctional transition-metal-based catalysts for a wide range of catalytic reactions is described. The bifunctional chiral molecular catalyst based on metalligand cooperation was originally developed for asymmetric transfer hydrogenation of ketones and imines and is now applicable to chemo-and stereoselective reductive and oxidative transformations as well as to enantioselective CC and CN bond formations with a wide scope and high practicability. The structural modification and electronic fine-tuning of the protic amine chelating ligands are crucial to develop unprecedented catalytic reactions. Cp*Ru complexes bearing a diamine (NN) or aminophosphine (PN) ligand readily activate H 2 , and can effect hydrogenation of polar functionalities. The bifunctional Ir complexes promote aerobic oxidative transformation of alcohols into ketones and esters and are applicable to kinetic resolution of racemic secondary alcohols. A novel imido-bridged dirhodium complex, which is a dinuclear variant of the bifunctional mononuclear amido complexes, promotes aerobic oxidation of a secondary alcohol and H 2 . In addition, the metal/NH bifunctional property also affects efficiently enantioselective conjugate additions. The present concerto molecular catalysts offer a great opportunity to open up new fundamentals for stereoselective molecular transformations.

Unsymmetrical Pincer‐Type Ruthenium Complex Containing β‐Protic Pyrazole and N‐Heterocyclic Carbene Arms: Comparison of Brønsted Acidity of NH Groups in Second Coordination Sphere

“…When 2 was treated with two equivalents of a base under H 2 or in 2-propanol, the hydrido complex 4 containing protic NHC and pyrazolato groups was obtained through metal-ligand cooperation.Proton-responsive ligands surrounding a metal play crucial roles in metal-ligand bifunctional catalysis. [1] A variety of protic ligands, such as amines, [2,3] pyrazoles, [4][5][6][7][8][9] imidazoles, [10] oximes, [11, 12] pyridinols, [13] and picoline/lutidine-based chelates, [14] have been used to facilitate the substrate binding, activation, and transformation through noncovalent interactions. Although most of the artificial bifunctional catalysts have only one kind of such protic ligands, metalloenzymes in Nature generally possess two or more structurally differentiated cooperating groups with various ranges of proton affinity in the second coordination sphere, which accelerate biological transformations in a delicate manner.…”

Synthesis of Complexes Containing an Anionic NHC Ligand with an Unsubstituted Ring‐Nitrogen Atom

“…Particularly complexes containing "protic" NHC ligands can be obtained easily this way and these have recently attracted interest as bifunctional catalysts. [14]…”

New Bifunctional Bis(azairidacycle) with Axial Chirality via Double Cyclometalation of 2,2′-Bis(aminomethyl)-1,1′-binaphthyl

“…The metal/NH bifunctional catalysis has become a pivotal concept for redox transformations based on hydrogen transfer between secondary alcohols and ketones [1][2][3][4][5]. From in-depth studies on original (η 6 -arene)Ru catalysts bearing chiral N-sulfonyldiamines (N-N chelate complexes) developed by Noyori and Ikariya [6,7], a fundamental hydrogen delivery process associated with alternating back and forth between 16e amido and 18e hydrido(amine) complexes has been thoroughly realized.…”

“…From in-depth studies on original (η 6 -arene)Ru catalysts bearing chiral N-sulfonyldiamines (N-N chelate complexes) developed by Noyori and Ikariya [6,7], a fundamental hydrogen delivery process associated with alternating back and forth between 16e amido and 18e hydrido(amine) complexes has been thoroughly realized. We have systematically investigated how the interconversion operates in a range of group 8 and 9 metal complexes with protic amine chelates, and we also investigated how ligand modification, by changing the chelating atom, significantly influences the catalyst performance [2,8,9]. In particular, half-sandwich (η 6 -arene)Ru, Cp*Ir, and Cp*Rh complexes containing a five-membered bifunctional C-N chelate ring, which were synthesized by the orthometalation of protic benzylamine derivatives [10][11][12][13], have been applied to efficient bifunctional catalysts based on the amine/amido functionalities (Scheme 1) [14][15][16][17][18][19][20][21][22][23][24][25][26].…”