Deoxygenation of Epoxides with Carbon Monoxide

Abstract

The use of carbon monoxide as a direct reducing agent for the deoxygenation of terminal and internal epoxides to the respective olefins is presented. This reaction is homogeneously catalyzed by a carbonyl pincer‐iridium(I) complex in combination with a Lewis acid co‐catalyst to achieve a pre‐activation of the epoxide substrate, as well as the elimination of CO2 from a γ‐2‐iridabutyrolactone intermediate. Especially terminal alkyl epoxides react smoothly and without significant isomerization to the internal olefins under CO atmosphere in benzene or toluene at 80–120 °C. Detailed investigations reveal a substrate‐dependent change in the mechanism for the epoxide C−O bond activation between an oxidative addition under retention of the configuration and an SN2 reaction that leads to an inversion of the configuration.

LNL-Carbazole Pincer Ligand: More than the Sum of Its Parts

“…Expansion of the reactivity profile of the BIMCA complexes to catalytic epoxide deoxygenation was probed. 237 Using carbon monoxide as a direct deoxygenation agent, 194 was found to catalyze the conversion of propylene oxide into propylene with Lewis acid LiNTf 2 as the cocatalyst, although the complex proved to be unstable at the elevated temperature required for the reaction. However, the iridium(I) analogue 208 showed greater stability and considerably higher activity, which even exceeded the activity of commercially available Further studies provided information on the mechanism of the catalytic reaction (Scheme 34).…”

Bright luminescent lithium and magnesium carbene complexes

“…[41][42][43][44] Similar ligands, which had been studied mainly as NNN pincers (Fig. 1 II), [45][46][47][48][49][50][51][52][53][54][55][56][57] have been pioneered by Bezuidenhout [58][59][60][61][62] (CNC pincer, C: mesoionic carbene MIC; III and IV) and Kunz [63][64][65][66][67][68] (CNC pincer, C: N-heterocyclic carbene NHC; V). Mesoionic carbenes, [69][70][71][72][73][74][75] in general, and 1,2,3-triazolinylidenes, in particular, excel through their donating properties 76,77 and, as such, are expected to stabilize high-valent transition metals.…”

Deoxygenation of Epoxides with Hexamethyldigermane Catalyzed by Au Nanoparticles on TiO2

“…[4] Later, several protocols were developed where in the presence of a catalytic metal, a substance that acts as reducing agent is removing the oxygen atom with generation of the alkene π system. Characteristic examples are: diazo malonate in the presence of Cu(II) [5] or Rh(II), [6] CO catalyzed by Ir(I) [7] or Mn(CO) 5…”

“…Later, several protocols were developed where in the presence of a catalytic metal, a substance that acts as reducing agent is removing the oxygen atom with generation of the alkene π system. Characteristic examples are: diazo malonate in the presence of Cu(II) [5] or Rh(II), [6] CO catalyzed by Ir(I) [7] or Mn(CO) 5 − , [8] trivalent phosphorus compounds catalyzed by Mo(IV) [9] or Re(VII), [10] H 2 catalyzed by MeReO 3 , [11] Zn metal in the presence of NbCl 5 , [12] and alcohols bearing α‐H atoms catalyzed by Mo(IV) [13] . Various other non‐catalytic methods are also known, such as using NaI/ZrCl 4 [14a] or NaI/SnCl 2 , [14b] polyphosphoric acid, [15] and In/InCl [16] .…”