Manganese(I)‐Catalyzed β‐Methylation of Alcohols Using Methanol as C₁ Source

Abstract

Highly selective β‐methylation of alcohols was achieved using an earth‐abundant first row transition metal in the air stable molecular manganese complex [Mn(CO)2Br[HN(C2H4PiPr2)2]] 1 ([HN(C2H4PiPr2)2]=MACHO‐iPr). The reaction requires only low loadings of 1 (0.5 mol %), methanolate as base and MeOH as methylation reagent as well as solvent. Various alcohols were β‐methylated with very good selectivity (>99 %) and excellent yield (up to 94 %). Biomass derived aliphatic alcohols and diols were also selectively methylated on the β‐position, opening a pathway to “biohybrid” molecules constructed entirely from non‐fossil carbon. Mechanistic studies indicate that the reaction proceeds through a borrowing hydrogen pathway involving metal–ligand cooperation at the Mn‐pincer complex. This transformation provides a convenient, economical, and environmentally benign pathway for the selective C−C bond formation with potential applications for the preparation of advanced biofuels, fine chemicals, and biologically active molecules

Acceptorless Dehydrogenation of Methanol to Carbon Monoxide and Hydrogen using Molecular Catalysts

“…The plateau of the reaction indicates that the reaction reaches an equilibrium defined by the build‐up of the partial pressures of the gaseous products [17d,g] . In order to demonstrate the robustness of the catalytic system, the reaction was performed for a longer period using only 0.5 μmol of complex 1 in 1 mL of MeOH, monitoring the composition of the gas phase of the reaction mixture every 12 h over a total of 84 h. The kinetic profile was largely identical to that shown in Figure 1, reaching a total TON of 3150 for CO and 9230 for H 2 , with only a marginal formation of CO 2 corresponding to a TON of 41.…”

“…Based on these results and previous reports, a plausible catalytic manifold is proposed involving the typical metal‐ligand cooperation [20] of MACHO‐type ligands (Scheme 3). [17g, 21a,b] Complex 1 generates the reactive species Ru II complex ( I ) comprising the cooperative M‐N site [22] . Similarly, the manganese complex 6 can enter an analogous manifold upon activation with the base.…”

Manganese‐Catalyzed Chemoselective Coupling of Secondary Alcohols, Primary Alcohols and Methanol

“…Later on, β‐methylation was achieved using single, well‐defined, precious transition metal complexes [7a,f] . Moreover, Liu, [7e] Morrill, [7d] Kempe [7b] and Leitner [7c] independently described their investigations to afford β‐(di)methylated alcohols using 3d transition metal catalysts such as iron or manganese.…”