Synthesis Of Six-membered N-heterocyclic Carbene Precursors With A Functionalized Backbone And Application Of NHC-Metal Complexes

The design and synthesis of various new six-membered cyclic formamidinium salts with functional group and applications of metal complexes have been reported in this paper.First, new six-membered cyclic formamidinium salts with a3,4-dihydroquinazoline core3、6a-d、9、11a-c、13and15a-b have been prepared from substituent benzaldehyde and fully characterized by NMR, MS and IR spectroscopies.Then, the backbone-functionalized six-membered cyclic formamidinium salts19with a methoxyl-containing or with monocarbonyl-containing backbone22and23have been prepared from substituent formamidinium.A series of novel3,4-dihydroquinazolin-2-ylidene-based rhodium(I) complexes26a-g were prepared by the reaction of [Rh(cod)Cl]2from the deprotonation of the corresponding formamidinium salts with KN(SiMe3)2. The structure of complex26e-g was also confirmde by its X-ray single-crystal diffraction study. By the v(CO) values of the corresponding dicarbonyl Rh complexes, the3,4-dihydroquinazol-2-ylidenes are stronger electron donors.Last, the catalytic activity of the Rh complexes was studied in detail. Complexes18b are highly active in the arylation of carbonyl compounds in98%yield. Moreover, the3,4-dihydroquinazolin-2-ylidenes are powerful precatalysts in palladium-catalyzed Suzuki cross-coupling reactions at room temperature with two ppm scale catalyst loading with TONs of up to425000.