Sterically Demanding, Bioxazoline-Derived N-Heterocyclic Carbene Ligands with Restricted Flexibility for Catalysis
作者:Gereon Altenhoff、Richard Goddard、Christian W. Lehmann、Frank Glorius
DOI:10.1021/ja045349r
日期:2004.11.1
A unique family of N-heterocycliccarbenes derived from bioxazolines (IBiox) suitable for application in transition-metal catalysis is described. The ligands are electron rich, sterically demanding, and have restricted flexibility. Their usefulness has been demonstrated in the Suzuki-Miyaura cross-coupling of stericallyhinderedarylchlorides and boronic acids. For the first time, tetraortho-substituted
Into the groove: The introduction of a C2‐symmetric N‐heterocyclic carbene ligand with appropriately substituted naphthyl side chains enables the efficient Suzuki–Miyauracoupling to form bulky tetra‐ortho‐substituted biaryls from aryl bromides and chlorides at room temperature. DFT calculations uncover the subtle steric phenomena at play that lead to the superior catalytic performance. Cyoct=cyclooctyl
Pd-PEPPSI-IPent: An Active, Sterically Demanding Cross-Coupling Catalyst and Its Application in the Synthesis of Tetra-Ortho-Substituted Biaryls
作者:Michael G. Organ、Selçuk Çalimsiz、Mahmoud Sayah、Ka Hou Hoi、Alan J. Lough
DOI:10.1002/anie.200805661
日期:2009.3.16
series of N‐heterocyclic carbene catalysts (see picture) were prepared and evaluated in the Suzuki–Miyaura reaction. A variety of sterically encumbered tetra‐ortho‐substituted biaryl products were formed from unreactive aryl chlorides using the isopentyl‐substituted catalyst at temperatures ranging from 65 °C to room temperature. The cyclopentyl‐substituted catalyst was virtually inactive, demonstrating