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Competitive and Selective Csp 3 Br versus Csp 2 Br Bond Activation in Palladium‐Catalysed Suzuki Cross‐Coupling: An Experimental and Theoretical Study of the Role of Phosphine Ligands
Author(s) -
Mollar Cristian,
Besora Maria,
Maseras Feliu,
Asensio Gregorio,
MedioSimón Mercedes
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201001113
Subject(s) - phosphine , chemistry , selectivity , palladium , xantphos , electrophile , reactivity (psychology) , intramolecular force , catalysis , bromine , medicinal chemistry , coupling reaction , sulfoxide , organic chemistry , medicine , alternative medicine , pathology
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 1 a 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.