Palladium/Norbornene-Cocatalyzed <i>Ortho</i>-Amination of Aryl Iodides: A Systematic Elucidation of the Mechanisms and Roles of Cs<sub>2</sub>CO<sub>3</sub> Base via Computational and Mass Spectrometric Approaches
Linxing Zhang, Ping Chen, Xuepeng Zhang, Xuepeng Zhang, Chengxi Yang, Tian‐Yu Sun, Xinhao Zhang, Xinhao Zhang, Yun‐Dong Wu
Abstract
The Catellani-type palladium/norbornene-cocatalyzed ortho -amination of aryl halides has been widely applied. Although a Pd(0)/Pd(II)/Pd(IV) mechanism is generally adopted, some key issues remain to be addressed. Combined mass spectrometry (MS) and theoretical study have been carried out, and the following observations and conclusions are obtained: (1) MS studies detected a Cs-containing Pd IV complex ( m / z = 752.0947) to confirm the existence of Pd IV intermediate; (2) density functional theory (DFT) calculations indicate that 2-iodotoluene is more reactive than morpholine–OBz in Pd 0 (PPh 3 ) 2 oxidative addition to form Pd II intermediate; (3) for the Pd II aryl-NBE-palladacycle (ANP) species, Cs 2 CO 3 as a ligand coordinates better than PPh 3 by computation; (4) with the involvement of Cs 2 CO 3, Pd II oxidative addition into morpholine–OBz to form a Pd IV intermediate becomes favored over Pd II oxidative addition into 2-iodotoluene and C(sp 2 )–C(sp 3 ) reductive elimination; and (5) the base effects of Cs 2 CO 3 and K 2 CO 3 are also compared, which are in agreement with the experimental findings that the latter results in a much lower yield.