Manganese-catalysed transfer hydrogenation of esters

Authors thank the University of St Andrews, and the EPSRC Centre for Doctoral Training in Critical Resource Catalysis (CRITICAT) for financial support [Ph.D. studentship to CO; Grant code: EP/L016419/1].Manganese catalysed ester reduction using ethanol as reductant in place of dihydrogen is reported. High yields can be achieved for a range of substrates using 1 mol% of a Mn(I) catalyst, with an alkoxide promotor. The catalyst is derived from a tridentate P,N,N ligand.Publisher PDFPeer reviewe

Manganese catalyzed hydrogenation of enantiomerically pure esters

The authors thank the EPSRC for DTG funding for MBW. The technical support staff at St Andrews are also gratefully acknowledged. The research data supporting this publication can be accessed at: dx.doi.org/10.17630/29308cf7-b6b6- 4b1b-809b-a12fe91b250fA manganese-catalyzed hydrogenation of esters has been accomplished with TON up to 1000, using cheap, environmentally benign, potassium carbonate and simple alcohols as activator and solvent, respectively. The weakly basic conditions lead to good functional group tolerance and enable the hydrogenation of enantiomerically enriched α-chiral esters with essentially no loss of stereochemical integrity.PostprintPeer reviewe

Hydrogenation reactions using group III to group VII transition metals

Catalytic hydrogenations using catalysts derived from the following elements are reviewed: scandium, yttrium, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, rhenium, and manganese. There are procedures for reducing a wide range of organic compounds using catalysts from this range of non-precious metals. Titanium catalysts have quite an extensive literature and feature some impressive results, although they have not been attracting much recent interest. Mn-based hydrogenation catalysis is only recently established and is showing very promising results, both for pure hydrogenation reaction and other redox type processes. The utility of many of the catalyst systems is compared to precious metal systems; currently the protocols using most of the mentioned non-precious systems are significantly more expensive processes than those using the best precious metal catalysts due to the cost of additives and high catalyst loading. It is envisaged that in the years ahead further research will transform the most promising leads into truly effective and competitive catalysts. It is worth noting that manganese catalysts are very much only just beginning to be researched, yet are already showing utility; Mn catalysts represent the most promising systems discussed in this chapter.</p

Manganese Catalyzed Hydrogenation of Enantiomerically Pure Esters

A manganese-catalyzed hydrogenation of esters has been accomplished with TONs up to 1000, using cheap, environmentally benign, potassium carbonate and simple alcohols as activator and solvent, respectively. The weakly basic conditions lead to good functional group tolerance and enable the hydrogenation of enantiomerically enriched α-chiral esters with essentially no loss of stereochemical integrity

A highly active manganese catalyst for enantioselective ketone and ester hydrogenation

A new hydrogenation catalyst based onamanganese complex of a chiral P,N,N ligand has been found to be especially active for the hydrogenation of esters down to 0.1 mol% catalyst loading, and gives up to 97% ee in the hydrogenation of pro-chiral deactivated ketones at 30-50 degrees C.</p

A highly active manganese catalyst for enantioselective ketone and ester hydrogenation

A new hydrogenation catalyst based on a manganese complex of a chiral P,N,N ligand has been found to be especially active for the hydrogenation of esters down to 0.1 mol% catalyst loading, and gives up to 97% e.e. in the hydrogenation of pro-chiral deactivated ketones at 30-50 oC

Corrigendum::A highly active manganese catalyst for enantioselective ketone and ester hydrogenation (Angew. Chem. Int. Ed. (2017), 56, (5825-5828), 10.1002/anie.201702406)

In this Communication, Figure 2 displays structure diagrams for the RC,SP isomer of ligand 3 and its complexes, and the X-ray structures of the SC,RP isomers of complexes 4 and 5 b whereas the figure caption incorrectly refers only to the SC,RP enantiomers. The structures of the SC,RP isomers of 3–5 are therefore shown here. In Table 1, the use of catalyst 5 a refers to the SC,RP isomer, giving the R enantiomers of the hydrogenation products. The authors apologize for the labeling error and lack of clarity.</p

Sensitized 1‑Acyl-7-nitroindolines with Enhanced Two-Photon Cross Sections for Release of Neurotransmitters

Precise photochemical control, using two-photon excitation (2PE), of the timing and location of activation of glutamate is useful for studying the molecular and cellular physiology of the brain. Antenna-based light harvesting strategies represent a general method to increase the sensitivity to 2PE of otherwise insensitive photoremovable protecting groups (PPGs). This was applied to the most commonly used form of “caged” glutamate, MNI-Glu. Computational investigation showed that a four- or six-carbon linker attached between the 4-position of thioxanthone (THX) and the 4-position of the 5-methyl derivative of MNI-Glu (MMNI-Glu) would position the antenna and PPG close to one another to enable Dexter energy transfer. Nine THX-MMNI-Glu conjugates were prepared and their photochemical properties determined. Installation of the THX antenna resulted in a red shift of the absorption (λmax = 385–405 nm) along with increased quantum yield compared to the parent compound MNI-Glu (λmax = 347 nm). The THX-MMNI-Glu conjugate with a four-carbon linker and attachment to the 4-position of THX underwent photolysis via 1PE at 405 and 430 nm and via 2PE at 770 and 860 nm, yielding glutamate. The two-photon uncaging action cross section (δu) was 0.11 and 0.29 GM at 770 and 860, respectively, which was greater than for MNI-Glu (0.06 and 0.072 GM at 720 and 770 nm, respectively). The THX sensitizer harvested the light via 2PE and transferred its resulting triplet energy to MMNI-Glu. Release of glutamate through 2PE at 860 nm from the compound (100 μM) activated iGluSnFR, a genetically encoded, fluorescent glutamate sensor, on the surface of cells in culture, portending its usefulness in studies of neurophysiology in acute brain slice

Sensitized 1‑Acyl-7-nitroindolines with Enhanced Two-Photon Cross Sections for Release of Neurotransmitters

Precise photochemical control, using two-photon excitation (2PE), of the timing and location of activation of glutamate is useful for studying the molecular and cellular physiology of the brain. Antenna-based light harvesting strategies represent a general method to increase the sensitivity to 2PE of otherwise insensitive photoremovable protecting groups (PPGs). This was applied to the most commonly used form of “caged” glutamate, MNI-Glu. Computational investigation showed that a four- or six-carbon linker attached between the 4-position of thioxanthone (THX) and the 4-position of the 5-methyl derivative of MNI-Glu (MMNI-Glu) would position the antenna and PPG close to one another to enable Dexter energy transfer. Nine THX-MMNI-Glu conjugates were prepared and their photochemical properties determined. Installation of the THX antenna resulted in a red shift of the absorption (λmax = 385–405 nm) along with increased quantum yield compared to the parent compound MNI-Glu (λmax = 347 nm). The THX-MMNI-Glu conjugate with a four-carbon linker and attachment to the 4-position of THX underwent photolysis via 1PE at 405 and 430 nm and via 2PE at 770 and 860 nm, yielding glutamate. The two-photon uncaging action cross section (δu) was 0.11 and 0.29 GM at 770 and 860, respectively, which was greater than for MNI-Glu (0.06 and 0.072 GM at 720 and 770 nm, respectively). The THX sensitizer harvested the light via 2PE and transferred its resulting triplet energy to MMNI-Glu. Release of glutamate through 2PE at 860 nm from the compound (100 μM) activated iGluSnFR, a genetically encoded, fluorescent glutamate sensor, on the surface of cells in culture, portending its usefulness in studies of neurophysiology in acute brain slice