جلوگیری از شکستن پیوند Pd-NHC و سوییچ کردن از سیستم کاتالیستی نانومقیاس به کاتالیست مولکولی
مقاله شیمی جلوگیری و ممانعت از شکستن پیوند Pd-NHC و سوییچ کردن از سیستم کاتالیستی نانومقیاس به کاتالیست مولکولی آمین ها و دما به عنوان فعال کننده کاتالیزور در ادامه از جم شیمی دانلود نمایید. مقاله Preventing Pd-NHC bond cleavage and switching from nano-scale to molecular catalytic systems: amines and temperature as catalyst activators در ژورنال انجمن سلطنتی شیمی Royal Society of Chemistry i منتشر شده است.
ABSTRACT: Many reactions catalyzed by Pd complexes with N-heterocyclic carbene (NHC) ligands are performed in the presence of amines which usually act as coupling reagents or mild bases. However, amines can react with Pd/NHC complexes in a number of ways: enhancing molecular catalysis, causing the catalyst deactivation or triggering the ligandless modes of catalysis by producing NHC-free active palladium species. This study gains insight into conditions required for the efficient use of amines as activators of molecular Pd/NHC catalysis and preventing the undesirable reductive cleavage of the Pd-NHC bond in catalytic systems. Reactions of Pd/NHC complexes with various amines within a temperature range of 25–140 °C and thermal stability of the resulting amino-complexes are examined. The results indicate the major influence of the amine structure and reaction temperature on the catalyst transformations. In particular, thermal decomposition of Pd/NHC complexes with aliphatic amine ligands predominantly leads to the reductive Pd-NHC bond cleavage, while deprotonation of the complexes with primary and secondary aliphatic amine ligands in the presence of strong bases at 25–60 °C promotes the activation of molecular Pd/NHC catalysis. Efficient Pd-PEPPSI complex – amine systems suitable for the strong-base-promoted C-S cross-coupling reactions between aryl halides and thiols are suggested on the basis of these findings.
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