Direct C−H Borylation of Arenes Catalyzed by Saturated Hydride-Boryl-Iridium-POP Complexes: Kinetic Analysis of the Elemental Steps |
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| Authors: | Prof Dr Miguel A Esteruelas Antonio Martínez Dr Montserrat Oliván Dr Enrique Oñate |
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| Institution: | Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), Centro de Innovación en Química Avanzada (ORFEO-CINQA), Universidad de Zaragoza—CSIC, 50009 Zaragoza, Spain |
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| Abstract: | The saturated trihydride IrH3{κ3-P,O,P-xant(PiPr2)2]} ( 1 ; xant(PiPr2)2=9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene) activates the B−H bond of two molecules of pinacolborane (HBpin) to give H2, the hydride-boryl derivatives IrH2(Bpin){κ3-P,O,P-xant(PiPr2)2]} ( 2 ) and IrH(Bpin)2{κ3-P,O,P-xant(PiPr2)2]} ( 3 ) in a sequential manner. Complex 3 activates a C−H bond of two molecules of benzene to form PhBpin and regenerates 2 and 1 , also in a sequential manner. Thus, complexes 1 , 2 , and 3 define two cycles for the catalytic direct C−H borylation of arenes with HBpin, which have dihydride 2 as a common intermediate. C−H bond activation of the arenes is the rate-determining step of both cycles, as the C−H oxidative addition to 3 is faster than to 2 . The results from a kinetic study of the reactions of 1 and 2 with HBpin support a cooperative function of the hydride ligands in the B−H bond activation. The addition of the boron atom of the borane to a hydride facilitates the coordination of the B−H bond through the formation of κ1- and κ2-dihydrideborate intermediates. |
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| Keywords: | arene borylation B−H activation C−H activation iridium pincer ligand |
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