Recyclable Tridentate Stable Palladium(II) PCP‐Type Catalysts Supported on Silica for the Selective Synthesis of Lactones

Abstract

Five-or seven-membered ring lactones are synthesized, in good selectivity and high yields, by the cyclocarbonylation reaction of 2-allylphenols, using a tridentate diphosphinoaryl ligand (PCP-type) palladium(II) catalyst immobilized on silica (A) and silica supported dendrimers (B, C and D). These immobilized catalysts, which are highly active and can be recycled by simple filtration in air, and reused with only moderate loss of activity, combine the advantages of heterogeneous and homogeneous catalysts. These complexes are also stable towards oxygen and moisture.

Novel silica immobilized NCN-pincer palladium(II) and platinum(II) complexes: Application as Lewis acid catalysts

“…The physico-chemical properties of the pincer metal complexes allow for a 'hands-on' structural analysis via reversible colorization of pincer platinum materials by SO 2 binding and, in addition, offer various opportunities in catalysis as exemplified by the corresponding pincer palladium materials described in this study. Moreover, the NCN-pincer manifold can be replaced by PCP, SCS, or a variety of other pincer-type combinations and together with specific choices of the metal site this gives access to a variety of catalysts for notable conversions in organic synthesis [20,23,32,45,64].…”

“…Therefore, the metallo-pincer catalysts seem ideally suited for the grafting protocol to an insoluble support like silica as envisaged above. SCS-and PCP-type pincer palladium complexes have earlier been immobilized on silica and their use in aldol and Heck reactions was reported [20,23,32,[49][50][51].…”

“…The properties of silica include thermal and chemical stability under reaction conditions, easily accessible and well-dispersed surface active sites (a high surface area >100 m 2 g −1 is required), and a mesoporous structure which is a prerequisite for liquid phase processes (pore size >20Å to avoid diffusion limitations) [17]. A wide range of homogeneous catalysts has been immobilized on silica and successfully recycled [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33].…”

N‐Heterocyclic Carbene Catalyzed [4+3] Annulation of Enals and o‐Quinone Methides: Highly Enantioselective Synthesis of Benzo‐ε‐Lactones

“…The most applied approach to e-lactones is the Bayer-Villiger oxidation of cyclohexanone. [2,3] In addition, several other interesting methodologies, including metalcatalyzed ring expansion of 3-(2-hydroxyphenyl)cyclobutanones, [4] metal-catalyzed carbonylation of 2-allylphenols, [5] and N-heterocyclic carbene catalyzed ring expansion of aldehydes [6] have been reported. However, most of these approaches are intramolecular reactions.…”

N‐Heterocyclic Carbene Catalyzed [4+3] Annulation of Enals and o‐Quinone Methides: Highly Enantioselective Synthesis of Benzo‐ε‐Lactones

“…The most applied approach to e-lactones is the Bayer-Villiger oxidation of cyclohexanone. [2,3] In addition, several other interesting methodologies, including metalcatalyzed ring expansion of 3-(2-hydroxyphenyl)cyclobutanones, [4] metal-catalyzed carbonylation of 2-allylphenols, [5] and N-heterocyclic carbene catalyzed ring expansion of aldehydes [6] have been reported. However, most of these approaches are intramolecular reactions.…”