Fluoride-Promoted Cross-Coupling Reactions of Alkenylsilanols. Elucidation of the Mechanism through Spectroscopic and Kinetic Analysis

• Published in: Journal of the American Chemical Society Vol. 126; no. 15; pp. 4865 - 4875
• Main Authors: Denmark, Scott E, Sweis, Ramzi F, Wehrli, Daniel
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 21.04.2004; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Multidisciplinary; Exact sciences and technology; Hydrogen Bonding; Kinetics; Kinetics and mechanisms; Magnetic Resonance Spectroscopy; Organic chemistry; Palladium - chemistry; Physical Sciences; Quaternary Ammonium Compounds - chemistry; Reactivity and mechanisms; Science & Technology; Silanes - chemistry; Thiophenes - chemistry; CARBON BOND FORMATION; ARYL BROMIDES; MILD; AMINATION; REAGENTS; TRIPHENYLARSINE; ZEROVALENT PALLADIUM COMPLEXES; ORGANIC HALIDES; OXIDATIVE ADDITION; STILLE REACTION; Platinoid Compounds; Five membered ring; Catalytic reaction; Transition metal Compounds; Silicon Organic compounds; Organic silane; Experimental study; Chemical coupling; Sulfur heterocycle; Cocatalyst; Reaction mechanism; Kinetic parameter; Rate constant; Palladium compound; Catalyst activity
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja037234d

The mechanism of the palladium-catalyzed cross-coupling reaction of (E)-dimethyl-(1-heptenyl)silanol ((E)-1) and of (E)-diisopropyl-(1-heptenyl)silanol ((E)-2) with 2-iodothiophene has been investigated through spectroscopic and kinetic analysis. A common intermediate in cross-coupling reactions of several types of organosilicon precursors has been identified as a hydrogen-bonded complex between tetrabutylammonium fluoride (TBAF) and a silanol. The order in each component has been determined by plotting the initial rates of the cross-coupling reaction at varying concentrations. These data provide a mechanistic picture that involves a fast and irreversible oxidative insertion of palladium into the aryl iodide and a subsequent turnover-limiting transmetalation step achieved through a fluoride-activated disiloxane derived from the particular silanol employed. The inverse order dependence of TBAF at high concentration is consistent with a pathway that proceeds through a hydrogen-bonded complex which is the lowest energy silicon species in solution.