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Phase‐Transfer Activation of Transition Metal Catalysts
Author(s) -
Tuba Robert,
Xi Zhenxing,
Bazzi Hassan S.,
Gladysz John A.
Publication year - 2015
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.201502403
Subject(s) - catalysis , dissociation (chemistry) , chemistry , ligand (biochemistry) , substrate (aquarium) , metal , phase (matter) , transition metal , aqueous solution , liquid phase , aqueous two phase system , photochemistry , combinatorial chemistry , chemical engineering , inorganic chemistry , organic chemistry , thermodynamics , biochemistry , oceanography , receptor , physics , engineering , geology
Abstract With metal‐based catalysts, it is quite common that a ligand (L) must first dissociate from a catalyst precursor (L′ n ML) to activate the catalyst. The resulting coordinatively unsaturated active species (L′ n M) can either back react with the ligand in a k −1 step, or combine with the substrate in a k 2 step. When dissociation is not rate determining and k −1 [L] is greater than or comparable to k 2 [substrate], this slows the rate of reaction. By introducing a phase label onto the ligand L and providing a suitable orthogonal liquid or solid phase, dramatic rate accelerations can be achieved. This phenomenon is termed “phase‐transfer activation”. In this Concept, some historical antecedents are reviewed, followed by successful applications involving fluorous/organic and aqueous/organic liquid/liquid biphasic catalysis, and liquid/solid biphasic catalysis. Variants that include a chemical trap for the phase‐labeled ligands are also described.