Phase‐Transfer Activation of Transition Metal Catalysts. Issue 45 (4th September 2015)

• Record Type: Journal Article
• Authors: Tuba, Robert; Xi, Zhenxing; Bazzi, Hassan S.; Gladysz, John A.
• Is Part Of: Chemistry. Volume 21:Issue 45(2015)
• Page Start: 15894
• Page End: 15906
• Publication Date: 2015-09-04
• Subjects: biphasic catalysis -- fluorous solvents -- olefin metathesis -- phase transfer -- polymerization; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201502403
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: With metal‐based catalysts, it is quite common that a ligand (L) must first dissociate from a catalyst precursor (L′ n ML) 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. Abstract : A turn of phase : With many homogeneous transition metal catalysts, a ligand L must first dissociate from a precursor to generate the active species. Dramatic rate accelerations can be observed when a "phase label" is added to the ligand, and the reaction is conducted in the presence of an orthogonal liquid or solid phase that is similar in nature (hydrophilic, fluorophilic, lipophilic, etc.). This phenomenon is termed "phase‐transfer activation".