Dicationic Ir(III) complexes having labile adjacent sites have been found to be active electrophilic catalysts.  Previously, the complex [IrMe(CO)(dppe)(DIB)](BARF)2 where  dppe = bis(diphenylphosphino)ethane; DIB = o-diiodobenzene and BARF = [B(3,5-C6H3(CF3)2)4], from which DIB readily dissociates, was found to catalyze the Nazarov cyclization rapidly, leading to efficient conversion of divinyl ketones and aryl vinyl ketones into cyclopentenones and indanones, respectively.  These results were also extended to a tandem sequence with a Michael addition following the Nazarov cyclization.  New electrophilic iridium(III) complexes, [IrX(CO)(DIM)((R)-(+)-BINAP)](SbF6)2 (X = Br, Me; DIM = diethylisopropylidenemalonate) have been synthesized and are found to exhibit even higher activity in the catalysis of Nazarov cyclization than the dppe system. Weakly polarized aryl vinyl ketones that show poor reactivity with the dppe catalyst and other catalysts such as Sc(OTf)3 + LiClO4, and Cu(ClO4)2, can be cyclized using catalytic amounts of the BINAP complex with X = Br in the presence of AgSbF6 (1:1) under relatively mild conditions.  A variety of other aryl vinyl ketones with different electron withdrawing groups have been.

Electrophilic iridium chemistry for catalysis of electrocyclization reactions

239th National Meeting (2010)

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