Efficient Ruthenium-Catalyzed N-Methylation of Amines Using Methanol

An in situ-generated complex from [RuCp*Cl2]2 and dpePhos ligand is reported as an efficient catalyst in the presence of 5 mol % of LiOtBu for the N-methylation of amines using methanol as the methylating agent at moderate conditions, following hydrogen borrowing strategy. This simple catalyst system provides selective N-monomethylation of substituted primary anilines and sulfonamides as well as N,N-dimethylation of primary aliphatic amines in excellent yields at 40–100 °C with good tolerance to reducible functional groups. The catalytic intermediate Cp*Ru(dpePhos)H was isolated and was shown to be active for methylation in the absence of base.