Transfer hydrogenation reduction of ketones, aldehydes and imines using chelated iridium(III) N-heterocyclic bis-carbene complexes

A Simple Route to Chelating, Structurally Different Triazole‐Based Bis(N‐heterocyclic carbene) Ligands and Their Coordination to PtII

“…[2,3] Because 1,2,4-triazole undergoes alkylation first at the 1 position and then at the 4 position, [17] we were able to prepare the two distinct ligands with the linker between the 1,1Ј (1) or 4,4Ј (2) positions (Scheme 1). It is important to point out that this simple synthetic procedure leads to subtle but interesting differences in the NHC ligand precursors, which may have interesting consequences, as we will discuss below.…”

“…General Procedures: Ligand precursor o-xylene-4,4Ј-bis(1-n-butyltriazolium) diiodide (2) [3] and complex 4 [18] were prepared according to literature procedures. All other reagents and solvents were used as received from commercial suppliers.…”

“…[2][3][4] Triazolylidenes are an interesting class of NHCs because the presence of the three nitrogen atoms in the azole ring provides asymmetry, reduces the electron donation of the ligand, and allows the trisalkylation of the three nitrogen atoms, [5] which potentially facilitates the preparation of monoazole-based dicarbenes. [6] Specifically, 1,2,4-triazoles are interesting building blocks to bis(chelating) triazoles because the asymmetric distribution of the nitrogens in the azole ring allows two different topologies only by exchanging the positions of the linkers between the azole rings and the terminal wingtips.…”

Donor‐Functionalised N‐Heterocyclic Carbene Complexes of Group 9 and 10 Metals in Catalysis: Trends and Directions

“…[121] In a subsequent paper, [122] the same group expanded the linker and the resulting Ir complex was applied to the transfer hydrogenation of aldehydes (a more challenging reaction due to possible decarbonylation and aldol side reactions in the presence of base) at low catalyst loading (0.1 mol-%). Finally, other chelating bis(carbene) complexes were tested in transfer hydrogenation, [123] notably a bitriazole NHC, [124] however activities were low. An intriguing tripodal NHC complex of Rh III (78, Scheme 10) was described by Peris, displaying good activities (loadings down to 0.001 mol-%) for a range of substrates including imines.…”

Imino Transfer Hydrogenation Reductions

“…In many cases the turnover numbers are impressive. [170][171][172][173][174] The area has been reviewed in some depth. [175][176][177][178] A carbene derived from triazole was used in IPA with K2CO3 as base, for direct reductive amination of aldehydes with primary amines to form secondary amine products.…”