Manganese‐Catalyzed Transfer Hydrogenation of Aldimines

Abstract

The reduction of imines to amines via transfer hydrogenation was achieved promoted by phosphine‐free manganese(I) catalyst. Using isopropanol as reductant, in the presence of tBuOK (4 mol %) and manganese complex [Mn(CO)3Br(κ2N,N‐PyCH2NH2)] (2 mol %), a large variety of aldimines (30 examples) were typically reduced in 3 hours at 80 °C with good to excellent yield.

β-Amino Phosphine Mn Catalysts for 1,4-Transfer Hydrogenation of Chalcones and Allylic Alcohol Isomerization

“…Transfer hydrogenation and dehydrogenation (TH and TdH) are incredibly important transformations in organic synthesis, and the field has been described as experiencing a “golden age” . Despite the large number of metal ions that have been found to carry out TH, the first manganese­(I)-TH catalysts were only discovered recently. − Some of these examples use phosphine-free ligands, , and asymmetric catalysis has been achieved in some instances …”

“…The ever-expanding versatility and unique properties of Mn­(I)-based catalysts are nicely demonstrated by the fact that Mn­(I) catalysts are supported with bidentate ligands more effectively in comparison to iron and ruthenium . For instance, Pidko recently disclosed the use of β-amino glycine derived phosphine ligands in hydrogenation reactions, and others have used bidentate nitrogen-only chelating ligands in TH reactions. While it is commendable that many Mn­(I)-catalyzed TH studies can use cheap, phosphine-free ligands, the exclusion of strong-field supporting ligands destabilizes the low-spin d 6 configuration, resulting in facile electron transfer decompositions to unreactive Mn­(II) species.…”

Manganese—New prominent actor in transfer hydrogenation catalysis

“…A further step has been taken in the field when the groups of Kundu, [19] Khusnutdinova [20] and Sortais [25] demonstrated that their catalytic systems were also able to reduce imines, which are more reluctant substrates towards TH. The catalyst developed by Khusnutdinova was particularly active for the reduction of aldimines, the corresponding amines were produced in good to excellent yields up to 96% in the presence of 0.5 mol% of catalyst at 80 °C.…”

Recent Developments in Dehydrogenative Organic Transformations Catalyzed by Homogeneous Phosphine‐Free Earth‐Abundant Metal Complexes

“…In continuation, later in 2019, Wei and co‐workers have reported the reduction of imines to amines through transfer hydrogenation by manganese‐bidendate aminomethylpyridine complex catalyst under optimized conditions including 2 mol% catalyst 24 in the presence of i PrOH as hydrogen donor and 4 mol% t BuOK as a base at 80 °C for 3 to 18 h (Scheme 16b) [29] …”