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Influence of the Ligand of Palladium(0) Complexes on the Rate of the Oxidative Addition of Aryl and Activated Alkyl Bromides: Csp 2 −Br versus Csp 3 −Br Reactivity and Selectivity
Author(s) -
Noverges Pedro Bárbara,
MedioSimón Mercedes,
Jutand Anny
Publication year - 2017
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201700041
Subject(s) - chemistry , oxidative addition , regioselectivity , palladium , reductive elimination , medicinal chemistry , ligand (biochemistry) , reactivity (psychology) , aryl , alkyl , stereochemistry , catalysis , organic chemistry , receptor , alternative medicine , pathology , medicine , biochemistry
Kinetic data obtained by means of electrochemical techniques are used to characterize the reactivity of aryl bromides and activated alkyl bromides in the oxidative addition to palladium(0) complexes generated from three precursors: Pd 0 (PPh 3 ) 4 , {Pd 0 (dba) 2 +2 PPh 3 } (dba=dibenzylideneacetone) and {Pd 0 (dba) 2 +2 P( o ‐Tol) 3 } in dimethylformamide (DMF) at 25 °C. It is established that, for the investigated substrates 1 – 6 and 7 – 11 , the oxidative addition at the Csp 3 −Br bond is much faster than that at the Csp 2 −Br bond if the palladium(0) is ligated by two PPh 3 . This explains why the regioselectivity in Suzuki–Miyaura reactions performed from substrates bearing both Csp 2 −Br and Csp 3 −Br groups is in favor of the substitution at the Csp 3 −Br bond. This is in agreement with DFT calculations, which propose a S N 2‐type mechanism from the bis‐ligated Pd 0 (PPh 3 ) 2 . The oxidative addition at the Csp 2 −Br bond is much faster if the palladium(0) is ligated by P( o ‐Tol) 3 than by PPh 3 , in agreement with the DFT calculations, which support a concerted mechanism involving the mono‐ligated Pd 0 [P( o ‐Tol) 3 ] as the reactive species. This explains why the regioselectivity in Suzuki–Miyaura reactions performed from substrates bearing both Csp 2 −Br and Csp 3 −Br groups might be in favor of the substitution at the Csp 2 −Br bond if the ligand is P( o ‐Tol) 3 .