Competitive and Selective Csp³Br versus Csp²Br Bond Activation in Palladium‐Catalysed Suzuki Cross‐Coupling: An Experimental and Theoretical Study of the Role of Phosphine Ligands

Abstract

Phosphine ligands have been demonstrated to have an effect on reactivity and selectivity in the competitive intramolecular palladium-catalysed Suzuki-Miyaura coupling of dibromo sulfoxide 1a possessing two different hybridised electrophilic carbons. It was found that the bromine bond to the sp(3)-hybridised carbon is selectively replaced in the presence of unhindered phosphines such as PPh(3) or xantphos. The use of hindered phosphine ligands such as P(o-tol)(3) and P(1-naphthyl)(3) reversed the selectivity, conducting the cross-coupling at the Csp(2)-Br. Identical trends were observed in external competition experiments carried out with bromomethyl sulfoxide and different substituted bromoarenes. DFT and DFT/MM calculations showed that the selectivity observed is mainly due to the different facility of the ligands to dissociate. Bisphosphine catalysts favour coupling at the sp(3) carbon, whereas monophosphine catalysts prefer the sp(2) carbon.

Oxidative Additions of Aryl Halides to Palladium Proceed through the Monoligated Complex

“…Finally, theoretical calculations provided us with key insights into the structure and bonding of the ions we observed experimentally and allowed a detailed description of the mechanism of OA in the gas phase. Oxidative addition of ArX bonds to Pd 0 centers has been previously used to calibrate the performance of theoretical methods to compute energy barriers,34 and the competition with other activation processes has been shown to depend on the coordination number of the reacting complex35, 36 and on the nature of the para ‐substituent on the aryl halide 37…”

Mediumeffekte in Palladium‐katalysierten Kreuzkupplungen und Implikationen bezüglich der katalytisch aktiven Spezies

“…[8][9][10][11][12] Außerdem demonstrierte Fu einen bemerkenswerten Ligandeneffekt in Pd-Kupplungen des Chloraryltriflats 1 (Schema 1). [7,13] PCy 3 führte zur Kupplung an der C-OTfBindung, PtBu 3 dagegen ausschließlich zur Reaktion an der C-Cl-Bindung. [7] DFT-Rechnungen wurden angewendet, um die Ursachen dieser Chemoselektivität zu erkunden.…”

Application of the Palladium‐Catalysed Norbornene‐Assisted Catellani Reaction Towards the Total Synthesis of (+)‐Linoxepin and Isolinoxepin

“…With both ortho positions substituted, the steric congestion around the palladium centre increases, driving the decarbopalladation of norbornene to give the aryl–Pd II intermediate VI . sp 3 –sp 3 coupling between the alkyl and norbornyl groups is not seen, presumably due to the high activation barrier of this type of coupling with a monodentate triarylphosphine ligand 11. Echavarren and co‐workers proposed an alternative mechanism involving a dinuclear Pd II species that proceeds via intermediate VII 12.…”