Mechanism of silver-mediated di-tert-butylsilylene transfer from a silacyclopropane to an alkene.
Kinetic studies of the reactions of cyclohexene silacyclopropane 1 and monosubstituted alkenes in the presence of 5 mol % of (Ph3P)2AgOTf suggested a possible mechanism for silver-mediated di-tert-butylsilylene transfer. The kinetic order in cyclohexene silacyclopropane 1 was determined to be one. Inverse kinetic saturation behavior (rate inhibition) was observed in monosubstituted alkene and cyclohexene concentrations. Saturation kinetic behavior in catalyst concentration was observed. A reactive intermediate, a silylsilver complex, was observed using low temperature 29Si NMR spectroscopy. Competition experiments between substituted styrenes and a deficient amount of 1 correlated well with the Hammett equation and provided a rho value of -0.62 +/- 0.02 using sigmap constants. These data support a mechanism involving reversible silver-promoted di-tert-butylsilylene extrusion from 1 followed by irreversible concerted electrophilic attack of the silylsilver intermediate on the alkene.
Driver
Tom G
TG
Department of Chemistry, University of California, Irvine, California 92697-2025, USA.
Woerpel
K A
KA
D000475:Alkenes / Q000737:chemistry*; D002384:Catalysis; D003510:Cyclohexanes / Q000737:chemistry; D053138:Cyclohexenes; D003521:Cyclopropanes / Q000737:chemistry*; D007700:Kinetics; D012821:Silanes / Q000737:chemistry*; D012834:Silver / Q000737:chemistry*; D013816:Thermodynamics
D000475:Alkenes; D003510:Cyclohexanes; D053138:Cyclohexenes; D003521:Cyclopropanes; D012821:Silanes; C052568:cyclohexene; D012834:Silver