Direct C−H Borylation of Arenes Catalyzed by Saturated Hydride‐Boryl‐Iridium‐POP Complexes: Kinetic Analysis of the Elemental Steps

The saturated trihydride IrH 3 {κ 3 ‐P,O,P‐[xant(P i Pr 2 ) 2 ]} ( 1 ; xant(P i Pr 2 ) 2 =9,9‐dimethyl‐4,5‐bis(diisopropylphosphino)xanthene) activates the B−H bond of two molecules of pinacolborane (HBpin) to give H 2 , the hydride‐boryl derivatives IrH 2 (Bpin){κ 3 ‐P,O,P‐[xant(P i Pr 2 ) 2 ]} ( 2 ) and IrH(Bpin) 2 {κ 3 ‐P,O,P‐[xant(P i Pr 2 ) 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 κ 1 ‐ and κ 2 ‐dihydrideborate intermediates.