Steroselective Oxidative Addition of Silanes and Hydrogen Halides to the Iridium(I) cis-Phosphine Complexes IrX(CO)(1,2-Bs(diphenylphosphino)ethane), X = Br, CN.
ROCHESTER UNIV NY DEPT OF CHEMISTRY
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The oxidative addition of silanes, RnCl3-nSiH n 3, R Et, Ph, OEt n 2, R Me n 1, R Me, to the IrI cis phosphine complexes IrXCOdppeX Br, CN dppe 1,2-bisdiphenylphosphinoethane has been found to proceed stereoselectively under kinetic control. Of the four possible diastereomers which can form by concerted cis addition of the Si-H bond to the iridiumI center, the one having hydride trans to CO and Si trans to Pdppe is formed initially with 98 steroselectivity. For X Br, this diastereomer is not the thermodynamically favored product. Isomerization of the initially formed silyl hydride product to the equilibrium mixture of diastereomers follows first order kinetics for the triphenylsilyl derivative with k sub 1 0.015min. the rate of isomerization for the kinetic silyl hydride adducts decreases int he order Et3SiH Ph3SiH OEt3SiH Me2C1SiH with the MeCl2SiH derivative not isomerizing even after prolonged heating. The most stable diastereomer for x Br has hydride trans to Br and silyl trans to Pdppe. For X CN, the kinetic isomer with H trans to CO and Si trans to Pdppe is also the most stable isomer, although other isomers are observed to form after initial reaction. Secondary chemistry of the triethylsilyl hydride products for X Br and CN is observed over longer reaction times leading to the formation of IrHX2COdppeX Br, IrH2SiEt3COdppe, and Et3SiSiEt3.
- Organic Chemistry
- Physical Chemistry