Reduction of Activated Alkenes by P^III/P^V Redox Cycling Catalysis

Abstract

The carbon–carbon double bond of unsaturated carbonyl compounds was readily reduced by using a phosphetane oxide catalyst in the presence of a simple organosilane as the terminal reductant and water as the hydrogen source. Quantitative hydrogenation was observed when 1.0 mol % of a methyl‐substituted phosphetane oxide was employed as the catalyst. The procedure is highly selective towards activated double bonds, tolerating a variety of functional groups that are usually prone to reduction. In total, 25 alkenes and two alkynes were hydrogenated to the corresponding alkanes in excellent yields of up to 99 %. Notably, less active poly(methylhydrosiloxane) could also be utilized as the terminal reductant. Mechanistic investigations revealed the phosphane as the catalyst resting state and a protonation/deprotonation sequence as the crucial step in the catalytic cycle.

Catalytic Hydrodefluorination via Oxidative Addition, Ligand Metathesis, and Reductive Elimination at Bi(I)/Bi(III) Centers

“…2b , 2c Located in the middle of the p-block, group 15 elements have recently been identified as privileged candidates to unfold redox catalysis, 3 as exemplified by the success of redox cycling using P and Bi redox couples in various catalytic reactions. 4 − 6 In this endeavor, our group reported catalytic C(sp 2 )–F and C(sp 2 )–OTf/ONf bond formation proceeding through canonical cross-coupling steps in a Bi(III)/Bi(V) manifold ( Figure 1 B). 5 However, in contrast to other pnictogens, Bi possesses additional low-valent redox manifolds to be exploited.…”

C–H Functionalization of Benzothiazoles via Thiazol-2-yl-phosphonium Intermediates

“…Our interest in phosphonium ions stems from reactions that use phosphines as Lewis base catalysts with typical Michael acceptors, which, in the presence of water and other protic additives, produce vinylphosphonium intermediates (Scheme a) . We hypothesized that the distinctly different outcomes these reactions have in the presence of alcohols (oxidation of C3 of the ynone) and water (reduction of C3) are the consequence of the differences in the reactivity of the pentavalent phosphorus intermediates generated in these processes. If this is also reflected in the reactivity of arylphosphonium salts, the easily accessible heteroarylphosphonium salts would become valuable intermediates in the regioselective functionalization of heterocycles.…”