Nickel Nanoparticles as Racemization Catalysts for Primary Amines

Abstract

By combining bases that are known to racemize benzylic amines with a nickel(II) salt, active nickel nanoparticles were obtained that can be used as catalysts in the racemization of both aliphatic and benzylic primary amines. The nanoparticles are stable in the ionic liquid tetrabutylammonium bromide and can complete most racemizations within a few hours with excellent selectivity. The problem of the incompatibility of the strongly reducing racemization catalyst and the enzymatic amine resolution catalyst was overcome by using a two‐pot system with a biphasic racemization step. Consecutive contact of a nonane layer that contained the amine with the acylating enzyme and with the racemizing Ni nanoparticles in the ionic liquid allowed the 50 % amide yield limit of a kinetic resolution to be successfully surpassed.

Liquid Nickel Salts: Synthesis, Crystal Structure Determination, and Electrochemical Synthesis of Nickel Nanoparticles

“…[61][62][63] They can be synthesized in many different ways, such as pyrolysis [64] or sputtering, [65] but the most commonw ay is chemical reduction of NiCl 2 (sometimes microwave assisted) with reducing agentss uch as hydrogen, hydrazine and NaBH 4 ,i nt he presence of stabilizers such as hexadecylamine (HAD) and trioctylphosphine oxide (TOPO). [66][67][68][69] In this work, Ni nanoparticles were synthesized electrochemically.…”

Lipases: Valuable catalysts for dynamic kinetic resolutions

“…In addition to Pd, Ni nanoparticles (Geukens et al, 2013) and cheaper metals such as Raney-Co and Raney- Ni (A.N. Parvulescu et al, 2008) have been described as heterogeneous catalysts for racemization of amines, the latter being useful for one-pot chemoenzymatic DKR of aliphatic amines, though only at high temperature (70-80°C) and with long reaction times (48-96 h).…”

ChemInform Abstract: Heterogeneous Chemoenzymatic Catalyst Combinations for One‐Pot Dynamic Kinetic Resolution Applications

“…Further development of the nickel-based racemization of amines has led to the utilization of nickel nanoparticles (2-4nma ccording to HRTEM). [35] The efficiency was thereby substantially enhanced resulting in shorter reaction times and lower catalystl oadings. Stabilization of the nickel nanoparticles was achieved by using ionic liquids.…”

“…However,D KR still required at wo-pot system separating the kineticr esolution and racemization reactions to individual reaction steps. [35] The twopot reactionw as achieved by first executing KR using nonane as the solvent. The organic solutionw as then combined with an ionic-liquid phase forming ab iphasic combination.…”