New Electrophilic Iridium(I) Complexes: H−H and C−H Bond Heterolysis by [(dfepe)Ir(μ-X)]2(X = O2CCF3, OTf)

New electrophilic dimeric iridium(I) complexes [(dfepe)Ir(μ-X)] 2 (dfepe = (C 2 F 5 ) 2 PCH 2 CH 2 P(C 2 F 5 ) 2; X = O 2 CCF 3, OTf) have been prepared and their reactions with H 2 and cyclopentane examined. Treatment of [(cod)Ir(O 2 CCF 3 )] 2 with dfepe produced an ionic product [(dfepe)Ir(cod)] + [(dfepe)Ir(O 2 CCF 3 ) 2 ] - ( 1 ), which in refluxing benzene rearranged with loss of cyclooctadiene to form [(dfepe)Ir(μ-O 2 CCF 3 )] 2 ( 2 ). The corresponding reaction of [(cod)Rh(O 2 CCF 3 )] 2 with dfepe yielded [(dfepe)Rh(μ-O 2 CCF 3 )] 2 ( 3 ) directly. X-ray diffraction analysis of 2 revealed a hinged dimeric geometry with an unusually large interplanar angle of 82.7° defined by the two 4-coordinate metal centers (Ir(1)−Ir(2) = 4.307 Å). The triflate-bridged analogue of 2 was prepared via an indirect route: addition of 1 equiv of triflic acid to (dfepe)Ir(η 3 -C 3 H 5 ) yielded the allyl hydride complex (dfepe)Ir(η 3 -C 3 H 5 )(H)(OTf) ( 4 ), which eliminated propylene in refluxing heptane to quantitatively afford [(dfepe)Ir(μ-O 3 SCF 3 )] 2 ( 5 ). The structure of 4 was confirmed by X-ray diffraction. In contrast to [(dfepe)Ir(μ-Cl)] 2, the acetate- and triflate-bridged analogues 2 and 5 are reactive toward both H 2 and alkane C−H bonds. Treatment of 2 with H 2 (20 °C) or cyclopentane (150 °C) cleanly afforded (dfepe) 2 Ir 2 (μ-H) 2 (H)(μ-O 2 CCF 3 ) ( 6 ) and CpIr(dfepe), respectively. Surprisingly, the corresponding reactions of 5 are significantly slower, suggesting that the concomitant release of the stronger acid CF 3 SO 3 H may inhibit these heterolysis reactions.