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Structure–Activity Relationship Analysis of Pd–PEPPSI Complexes in Cross‐Couplings: A Close Inspection of the Catalytic Cycle and the Precatalyst Activation Model
Author(s) -
Nasielski Joanna,
Hadei Nilofaur,
Achonduh George,
Kantchev Eric Assen B.,
O'Brien Christopher J.,
Lough Alan,
Organ Michael G.
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.201000138
Subject(s) - negishi coupling , chemistry , pyridine , carbene , catalysis , halide , reactivity (psychology) , palladium , combinatorial chemistry , coupling reaction , medicinal chemistry , organic chemistry , medicine , alternative medicine , pathology
A series of Pd–N‐heterocyclic carbene (Pd–NHC) complexes with various NHC, halide and pyridine ligands (PEPPSI (pyridine, enhanced, precatalyst, preparation, stabilisation and initiation) precatalysts) were prepared, and the effects of these ligands on catalyst activation and performance were studied in the Kumada–Tamao–Corriu (KTC), Negishi, and Suzuki–Miyaura cross‐coupling reactions. The lowered reactivity of more hindered 2,6‐dimethylpyridyl complex 4 in the Negishi and KTC reactions is consistent with slow reductive dimerisation of the organometallic reaction partner during precatalyst activation. Comparative rate studies of complexes 1 , 4 and 5 in the KTC and Suzuki–Miyaura reactions verify that 4 activated more slowly than the others. A potential on/off mechanism of pyridine coordination to NHC–Pd 0 is also plausible, in which the more basic pyridine stays bound for longer.