Fluoride-promoted cross-coupling reactions of alkenylsilanols. Elucidation of the mechanism through spectroscopic and kinetic analysis.
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.
Denmark
Scott E
SE
Roger Adams Laboratory, Department of Chemistry, University of Illinois, Urbana, Illinois 61801, USA. denmark@scs.uiuc.edu
Sweis
Ramzi F
RF
Wehrli
Daniel
D
D006860:Hydrogen Bonding; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D010165:Palladium / Q000737:chemistry; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012821:Silanes / Q000737:chemistry*; D013876:Thiophenes / Q000737:chemistry*
D000644:Quaternary Ammonium Compounds; D012821:Silanes; D013876:Thiophenes; D010165:Palladium; C009405:tetrabutylammonium