Solid-State NMR and DFT Studies on the Formation of Well-Defined Silica-Supported Tantallaaziridines: From Synthesis to Catalytic Application

Cyclic Ureate Tantalum Catalyst for Preferential Hydroaminoalkylation with Aliphatic Amines: Mechanistic Insights into Substrate Controlled Reactivity

The efficient and catalytic amination of unactivated alkenes with simple secondary alkyl amines is preferentially achieved. A sterically accessible, N,O-chelated cyclic ureate tantalum catalyst was prepared and characterized by X-ray crystallography. This optimized catalyst can be used for the hydroaminoalkylation of 1-octene with a variety of aryl and alkyl amines, but notably enhanced catalytic activity can be realized with challenging N-alkyl secondary amine substrates. This catalyst offers turnover frequencies of up to 60 h^-1, affording full conversion at 5 mol% catalyst loading in approximately 20 min with these nucleophilic amines. Mechanistic investigations, including kinetic isotope effect (KIE) studies, reveal that catalytic turnover is limited by protonolysis of the intermediate 5-membered azametallacycle. A Hammett kinetic analysis shows that catalytic turnover is promoted by electron rich amine substrates that enable catalytic turnover. This more active catalyst is shown to be effective for late stage drug modification.

Catalytic and Atom-Economic Csp3 -Csp3 Bond Formation: Alkyl Tantalum Ureates for Hydroaminoalkylation

Atom-economic and regioselective Csp3 -Csp3 bond formation has been achieved by rapid C-H alkylation of unprotected secondary arylamines with unactivated alkenes. The combination of Ta(CH₂ SiMe₃ )₃ Cl₂ , and a ureate N,O-chelating-ligand salt gives catalytic systems prepared in situ that can realize high yields of β-alkylated aniline derivatives from either terminal or internal alkene substrates. These new catalyst systems realize C-H alkylation in as little as one hour and for the first time a 1:1 stoichiometry of alkene and amine substrates results in high yielding syntheses of isolated amine products by simple filtration and concentration.

Early transition metal-catalyzed C–H alkylation: hydroaminoalkylation for Csp3–Csp3 bond formation in the synthesis of selectively substituted amines

Protecting group, directing group, and external oxidant free synthesis of structurally diverse amines.