Bifunctional transition metal‐based molecular catalysts for asymmetric CC and CN bond formation

Abstract

This paper describes the recent advances in the conceptually new bifunctional Ir and Ru catalysts for asymmetric catalytic reactions. These reactions include the enantioselective Michael addition of 1,3-dicarbonyl compounds to cyclic enones and nitroalkenes, and the enantioselective direct amination of alpha-cyanoacetates with diazoesters. The outcome of these reactions in terms of reactivity and selectivity was delicately influenced by the catalyst structures and the reaction conditions including the solvents used. Even with a 1 : 1 molar ratio of donors to acceptors, the reactions proceeded smoothly to give the corresponding chiral adducts with an excellent yield and enantiomeric excess (ee). Preliminary mechanistic studies showed that the key stage of the catalytic cycle is the interaction of the bifunctional catalyst with a pronucleophilic reagent that leads to stereoselective formation of C-, O-, or N-bound complexes. The resulting protonated catalyst bearing metal-bound nucleophiles readily reacts with electrophiles to provide C--C and C--N bond formation products in a highly stereoselective manner.

Variable coordination of amine functionalised N-heterocyclic carbene ligands to Ru, Rh and Ir: C–H and N–H activation and catalytic transfer hydrogenation

“…[1][2][3] In organic synthesis, chelating amine and amido complexes have come to prominence in reactions such as hydrogenation under H 2 , 4 transfer hydrogenation, 5,6 and isomerisation of allylic alcohols.…”

N-heterocyclic carbene tethered amido complexes of palladium and platinum

“…[1][2][3] Wide-ranging applications have been found for bifunctional catalysis, many in asymmetric synthesis, including hydrogenation under H 2 , 4 transfer hydrogenation, 5,6 isomerisation of allylic alcohols, 7 alkene hydroamination, 8 hydrosilylation, 9 Michael addition, 10 C-H activation [11][12][13][14][15] and lactide polymerisation. 16 The most studied of these reactions is the asymmetric transfer hydrogenation between alcohols and carbonyl compounds, catalysed by half-sandwich complexes of Ru, Ir or Rh with a chiral diamine ligand such as N-tosyl-1,2-diphenylethylenediamine.…”

Protonic–Hydridic Bifunctionality: The Protonic (2‐Aminoethyl)dimethylphosphane Ligand in Nitrosyl Tungsten Hydride Complexes

“…Attempted Synthesis of WH(NO)(edmp) 2 Using a hydride donor, the target complex WH(NO)(edmp) 2 was envisaged to be prepared by chloride replacement in WCl(NO)(edmp) 2 . [29][30][31][32] Two preparative routes were considered to lead to WCl(NO)(edmp) 2 .…”

“…"Ionic hydrogenations" and also transfer hydrogenations with similar polar mechanistic background are presently mainly ruthenium and iridium based. [12][13][14][15][16][17][18][19] It is anticipated that related non-noble metal catalyses could were prepared and treated with NaHBEt 3 to obtain the corresponding hydride species WH(NO)(η 2 3 (9a) and L = PMe 3 (9b)] were produced from 7a and 7b by the reaction with NaHBEt 3 . Hydride 8b turned out to be the most stable hydride complex in the given series.…”

“…Denoted as "ionic hydrogenations" or more general as "bifunctional molecular catalysis" they typically occur in the secondary coordination sphere through H -and H + transfers. The bound and strongly polarized H atoms are prone to intra-or intermolecular dihydrogen bonding contacts (-H δ-···H δ+ -), which is assumed to appear in "ionic hydrogenations" of unsaturated molecules, such as olefins, ketones, and imines, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] but their crucial involvement in such reaction courses is as yet not fully established. "Ionic hydrogenations" and also transfer hydrogenations with similar polar mechanistic background are presently mainly ruthenium and iridium based.…”