Enhanced Hydride Donation Achieved Molybdenum Catalyzed Direct N-Alkylation of Anilines or Nitroarenes with Alcohols: From Computational Design to Experiment

Abstract

An example of homogeneous Mo-catalyzed direct N-alkylation of anilines or nitroarenes with alcohols is presented. The DFT aimed design suggested the easily accessible bis-NHC-Mo(0) complex features a strong hydride-donating ability, achieving effective N-alkylation of anilines or challenging nitroarenes with alcohols. The enhanced hydride-donating strategy should be useful in designing highly active systems for borrowing hydrogen transformations.

Half-Sandwich Iridium Complexes with Hydrazone Ligands: Synthesis and Catalytic Activity in N-Alkylation of Anilines or Nitroarenes with Alcohols via Hydrogen Autotransfer

“…Although many efforts have been made, harsh conditions such as high reaction temperatures (>100 °C), using unstable catalysts or high catalyst loadings, are often required to obtain acceptable yields. Additionally, it is still a challenging process to realize the direct N -alkylation between nitroarenes and alcohols, and the efficient homogeneous transition-metal catalysts for it were rarely reported . In continuation to our previous study on the synthesis and catalytic activity of half-sandwich metal complexes for various organic reactions, we herein report the N , O -chelate half-sandwich iridium complexes with aromatic hydrazone ligands as the efficient catalysts for alcohol amination reactions using amine or nitroarenes as substrates (Scheme ).…”

Disarming the alkoxide trap to access a practical FeCl3 system for borrowing-hydrogen N-alkylation

“…In addition, according to previous studies, the tetradentate NHC ligand-coordinated nonprecious d 6 metal complex tends to adopt a non-coplanar geometry. [49][50][51][52][53] To verify the feasibility of this design and evaluate the potential of the most Earth-abundant metal, iron, as an appropriate candidate for this system, based on our previous studies on d 6 metal complexes, 29,45,46,54 we selected representative nonprecious d 6 metals (Cr 0 , Mn 1+ , Fe 2+ , Co 3+ ) as metal chloride precursors, and benzyl alcohol and aniline as substrates for DFT studies. On the basis of our previous research, 29,46 the thermodynamics of the key intermediate metal hydride and the kinetics of the hydrogenation transition states (this step is the rate-determining step for this reaction) would be critical points to evaluate the catalytic performance.…”

“…In terms of sustainability, the use of Earth-abundant metals continues to be a long-standing goal of chemical research. 24 In this respect, much effort has been devoted to developing catalyst systems based on Mn, [25][26][27][28][29][30] Fe, [31][32][33][34][35][36][37][38] Co, [39][40][41] and Ni 42,43 for the N-alkylation of amines with alcohols, and other nonprecious metals -Cr, 44 Mo, 45 and W [44][45][46] have also been developed very recently (Scheme 1a-2). Further developments in phosphine-or pyridine-based complexes are highly desirable to improve their activity and performance.…”

“…Therefore, using an easy to operate Fe(III) metal source to achieve higher catalytic activity at a lower temperature is a big challenge for the iron-catalyzed N-alkylation reaction. Based on our previous studies on Mn 29,48 and Mo, 45 the chelation of bis-NHC metal carbonyl complexes performs better than that of pyridine metal carbonyl complexes in catalyzing N-alkylation reactions. As a strong σ-donor and π-acceptor, the strong-field ligand NHCs may be able to help the in situ reduction of Fe(III) to Fe(II) and stabilize the Fe(II) center via NHC chelating to achieve borrowing-hydrogen N-alkylation under mild reaction conditions.…”

Iridium complex immobilized on a high-nitrogen containing covalent triazine framework derived from 2,5-pyrazinedicarbonitrile as a recyclable catalyst for the selective N-alkylation of aminobenzenesulfonamides with alcohols

“…In recent years, considerable attention has been directed to the N -alkylation of amines with alcohols as alkylating agents instead of alkyl halides based on hydrogen autotransfer processes or a hydrogen-borrowing strategy, 3 using Ir, 4 Ru, 5 Pd, 6 Co, 7 Fe, 8 Mn, 9 Ni, 10 Re 11 and Mo 12 complexes. In this process, alcohols are first dehydrogenated to form aldehydes, and then the condensation between amines and the resulting aldehydes occurs to afford imine intermediates, which are further hydrogenated to produce N -alkylated amines.…”