New fossils of small and medium-sized bovids from the Early Site of Shanshenmiaozui in Nihewan Basin, North China

发布时间：2022年12月30日

New fossils of small and medium-sized bovids from the Early Site of Shanshenmiaozui in Nihewan Basin, North China

张贝

Abstract An array of rare-earth bis(aminobenzyl) complexes supported by imidazolin-2-iminato ligands were synthesized and structurally characterized. These complexes showed high activity towards ortho-Csp2–H alkylation of 2-alkylpyridines and benzylic Csp3–H alkylation of 2,6-dialkylpyridines with alkenes. A wide range of alkyl or aryl substituted olefin substrates are compatible, providing an atom-economical route to linear or branched alkylated pyridine derivatives in moderate to high yields (45 examples, up to 99% yield). The primary study suggested that the asymmetric version of Csp3–H alkylation of 2,4,6-collidine with allylbenzene was feasible with chiral imidazolin-2-iminato-ligated scandium(III) complexes, and good yield with moderate enantioselectivity was obtained (84% yield, 84:16 er). Mechanistic investigations including kinetic isotope effect (KIE) experiments and density functional theory (DFT) calculations shed light on the catalytic cycle and the origin of enantiocontrol.