Synthesis, characterization, and catalytic properties of new electrophilic iridium(III) complexes containing the (R)-(+)-2,2,′-binaphthyl Ligand

摘要

The oxidative addition of MeI to the Ir(I) square-planar complex IrI(CO)((R)-(+)-BINAP) where (R)-(+)-BINAP = (R)-(+)-2,2′- bis(diphenylphosphino)-1,′-binaphthyl)) results in the formation of two diastereomers in a 2:1 ratio of the Ir(III) oxidative addition product IrI _2(CO)(Me)((R)-(+)-BINAP) (4a and 4b) in a 85% overall yield. Upon iodide abstraction from the diastereomeric mixture with 2 equiv of AgSbF _6 in the presence of diethyl isopropylidene malonate (DIM), two diastereomers of the dicationic complex [Ir(CO)(Me)(DIM)((R)-(+)-BINAP)] [SbF_6]_2 (5) are formed in a 90% yield with a ratio of 9:1. One diastereomer of the diiodide complex 4 and one diastereomer of the dicationic complex 5 have been characterized by X-ray diffraction. An anion exchange reaction of 5 with NaBAr_4~(1-) (BAr_4~(1-) = B(3,5-(CF_3)_2C_6H _3)_4) affords [Ir(CO)(Me)(DIM)((R)-(+)-BINAP)][BAr _4~f]_2 (6) in quantitative yield. Both 5 and 6 are active Lewis acid catalysts for the polarized Nazarov cyclization and the Diels-Alder reaction. In the Nazarov cyclization, when NaBAr_4~f is added as a cofactor for the reaction catalyzed by 5 or 6, the resultant oxyallyl cation intermediate from the 4π conrotation undergoes a Wagner-Meerwein rearrangement to afford spirocyclic cyclopentenones in modest to good yields.