Mechanism of Anion-Catalyzed C–H Silylation Using TMSCF₃: Kinetically-Controlled CF₃-Anionoid Partitioning As a Key Parameter

The mechanism of anion-catalyzed C–H silylation by R3SiCF3 reagents has been investigated using homogeneous TBAT-initiation, in situ and stopped-flow 19F NMR spectroscopy 2H-KIE, LFER, deuterium-labeled crossover, structure-selectivity quantitation (TMSCF3/TESCF3), carbene trapping, DFT-calculations. Analysis the kinetics reactions 1,3-difluorobenzenes (2), generation ArSiMe3 Me3SiF as a function concentration [2], [TMSCF3], [TBAT], show that CF3-anionoid is active intermediate. reversibly released from siliconate [(CF3)2SiMe3]− undergoes partitioning through rate-limiting arene deprotonation (1H/2H KIE 9.5) to generate (via transient aryl anionoid) fluoroform (CF3H), competition with F-anion transfer TMSCF3 CF2 TMSF. [2]/[TMSCF3] ratio directly proportionally controls partition, favor deprotonation. Higher concentrations TBAT lower lead faster rates generation. Use homologous TESCF3 reagent leads anion catalysis an increased selectivity toward Perfluoroalkenes, generated CF2, capture leading progressive inhibition anion-catalysis. Inhibition suppressed styrene additive trap efficiency process enhanced slow-addition (1) maintain high [2]/[1].