Syntheses and applications of soluble polyisobutylene (PIB)-supported transition metal catalysts

摘要

Soluble polymer supports facilitate the recovery and recycling of expensivetransition metal complexes. Recently, polyisobutylene (PIB) oligomers have been foundto be suitable polymer supports for the recovery of a variety of transition metal catalystsusing liquid/liquid biphasic separations after a homogeneous reaction. Our work hasshown that PIB-supported Ni(II) and Co(II) ?-diketonates prepared from commerciallyavailable vinyl terminated PIB oligomers possess catalytic activity like that of their lowmolecular weight analogs in Mukaiyama epoxidation of olefins.Carboxylic acid terminated PIB derivatives can act as carboxylate ligands forRh(II) cyclopropanation catalysts. An achiral PIB-supported Rh(II) carboxylate catalystshowed good activity in cyclopropanation of styrene in hydrocarbon solvents, and couldbe easily recycled nine times by a post reaction extraction. Further application of PIBsupports in asymmetric cyclopropanation reactions were investigated using PIBsupportedarenesulfonyl Rh(II) prolinates derived from L-proline as examples. The PIBsupportedchiral Rh carboxylates demonstrated moderate activity and were recovered and reused for four to five cycles. The prolinate catalyst prepared from PIB-anisole alsoshowed encouraging enantioselectivity and about 8% ee and 13% ee were observed ontrans- and cis-cyclopropanation product respectively.Finally, PIB oligomers can be modified in a multi step sequence to prepare PIBsupportedchiral bisoxazolines that can in turn be used to prepare active, recyclable PIBsupportedCu(I) bisoxazoline complexes for olefin cyclopropanation. These chiralcopper catalysts showed moderate catalytic activity and good stereoselectivity incyclopropanation of styrene. A chiral ligand prepared from D-phenylglycinol providedthe most effective stereo control and gave the trans- and cis-cyclopropanation product in94% ee and 68% ee respectively. All three PIB-supported chiral bisoxazoline-Cu(I)catalysts could be reused five to six times.