Organometallic Nickel NCN Pincer Complex Promotes L-Lactate Racemization in Water

Abstract

The air-stable and water-soluble salt [(NCNMe+)Ni(NCCH3)](OTf)2 (NCNMe+= 3,5-bis(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-1,2,6-trimethylpyridin-1-ium) was synthesized and characterized. As a partial structural mimic, [(NCNMe+)Ni(NCCH3)]2+ retains the unusual 4-pyridylidene-based pincer framework present in the nickel pincer nucleotide (NPN) active site of lactate racemase. Combined spectroscopic, crystallographic, and computational analyses reveal that the Ni-Cpyridylidene forms primarily a single bond in [(NCNMe+)Ni(NCCH3)]2+, with the pyridylidene backbone acting as a σ donor and weak π-acceptor. Under anaerobic conditions, [(NCNMe+)Ni(NCCH3)](OTf)2 shows lactate racemization reactivity and promotes the partial racemization of L-lactate in water, achieving 63% ee.