Synthesis of Nitrogen Heterocycles Utilizing Molecular Nitrogen as a Nitrogen Source and Attempt to Use Air Instead of Nitrogen Gas

Abstract

Nitrogen fixation using transition metals is a challenging subject. Using a titanium-nitrogen complex, discovered by Yamamoto in 1967, and titanium isocyanate complex, molecular nitrogen could be incorporated into organic compounds to afford various heterocyclic compounds. Furthermore, novel titanium-catalyzed nitrogenation procedure was developed. That is, a THF solution of TiCl 4 or Ti(O i Pr) 4 , and an excess amount of Li and TMSCl was stirred under nitrogen (1 atm) at room temperature overnight and to this solution was added phthalic anhydride. The whole solution was refluxed overnight to afford a phthalimide in over 100 % yield. Using the stoichiometric conditions of the novel nitrogenation, various indole, pyrrole, pyrrolizine, indolizine derivatives and lactams were obtained in good to moderate yields after usual workup. Although the structure of the titanium-nitrogen complex has not been determined yet, the complex is thought to be a mixture of N(TMS) 3 , TiX 2 N(TMS) 2 and XTi=NTMS. Nitrogen in air could be directly fixed using this method, and the natural products, such as monomoline I, lycopodine and pumiliotoxin C, could be synthesized from nitrogen in air as a nitrogen source. CONTENTS 1. Introduction 2. Synthesis of Nitrogen Heterocycles Using Titanium Isocyanate Complex and Palladium Complex

Dinitrogen Fixation: Rationalizing Strategies Utilizing Molecular Complexes

“…Hydrolysis or removal of the silyl groups using CsF allowed for the isolation of a wide variety of N ‐heterocycles, such as indole, quinoline, pyrrole, pyrrolizine and indolizine, [247] even using dry air instead of pure dinitrogen (Scheme 63). [248, 249] …”

Nitrogen Fixation via Splitting into Nitrido Complexes

“…Sobota and co-workers utilized Yamamoto’s putative titanium nitride for C–N bond formation with carbon monoxide and carbon dioxide. , Mori reported a series of papers that followed related methodology for the synthesis of a broad variety of organic amides, pyridines, pyrroles, or amines directly from N 2. − While the mechanisms for these reactions remain unknown, the seminal work of Cummins revived efforts to obtain nitrogenous products beyond ammonia, now utilizing well-defined molecular nitrides that were obtained by N 2 splitting to enable direct functionalization of dinitrogen . This approach provides valuable insight into thermodynamically suitable target compounds and potential kinetic bottlenecks for catalytic transformations of dinitrogen into nitrogenous products.…”

Molecular titanium nitrides: nucleophiles unleashed

“…30–41 Of particular interest are group 4 terminally bound Ti nitrides, expected to be highly ionic given the disparity in Pauling electronegativities between Ti (1.5) and N (3.0). Only in certain cases could the nitride ligand be installed with protecting Lewis acidic groups (Fig.…”