Manganese PNP-pincer catalyzed isomerization of allylic/homo-allylic alcohols to ketones – activity, selectivity, efficiency

Abstract

Manganese PNP pincer complexes are excellent catalysts for the isomerization of allylic alcohols to the ketones. The reaction proceeds via a dehydrogenation/hydrogenation mechanism as shown by DFT calculations and deuterium labelling.

Well-Defined Phosphine-Free Manganese(II)-Complex-Catalyzed Synthesis of Quinolines, Pyrroles, and Pyridines

“…Under the reaction conditions, aliphatic as well as cyclic ketones were also well tolerated (62−73%) (59 and 60). Interestingly, the reaction proceeded smoothly with a heteroatom-containing acetophenone derivative in moderate yield (76%) (61). The reaction of acetophenone and 4-iodoacetophenone with 3-aminopropan-1-ol also afforded the expected products in moderate yields (62 and 63).…”

“…The relative Gibbs free energies of all the states were calculated using the LANL2DZ basis set for Mn and 6-31G** basis set for nonmetal elements. The base-mediated activation of the precatalyst Mn1 generated the intermediate II . Then 2-aminobenzyl alcohol was activated via a metal–ligand cooperative pathway where the proton was transferred to the imido-N in the ligand backbone followed by the formation of Mn-alkoxy species III (Δ G = 1.66 kcal/mol) .…”

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

“…Isomerization of 7b into 7a represents a rare example of a Mn-catalyzed allylic alcohol isomerization reaction . Typically, isomerization of allylic alcohols requires a precious-metal catalyst .…”

“…Typically, isomerization of allylic alcohols requires a precious-metal catalyst . Nickel, molybdenum, iron, and cobalt have been utilized, , and only one manganese catalyst has been reported . The allylic alcohol isomerization capability of the HL Ph Mn­(CO) 3 Br and base system in toluene was tested for the three different allyl alcohols 7b , 10b , and 11b and gave quantitative conversion (Scheme ).…”

Manganese-catalyzed hydrogenation, dehydrogenation, and hydroelementation reactions

“…The only report on the manganese-catalyzed isomerization of allylic and homoallylic alcohols to the corresponding carbonyl product was disclosed by Vries (Scheme 84). 419 Ph MACHO–Mn( i )-complex Mn39 catalyzed the reaction in the presence of a catalytic amount of KO t Bu at 120 °C. The detailed DFT study revealed the involvement of the dehydrogenation/hydrogenation sequence, which was further verified by the isolation of the α,β-unsaturated ketone intermediate and a deuterium labeling experiment (Scheme 85).…”