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

: The saturated trihydride IrH3 {κ3 -P,O,P-[xant(Pi Pr2)2 ]} (1; xant(Pi Pr2)2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene) activates the B-H bond of two molecules of pinacolborane (HBpin) to give H2 and the hydride-boryl derivatives IrH2(Bpin){κ3 -P,O,P-[xant(Pi Pr2)2]} (2) and IrH(Bpin)2 {κ3 -P,O,P-[xant(Pi Pr2)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 the dihydride 2 as a common intermediate. The C-H bond activation of the arenes is the rate determining step of both cycles, being the C-H oxidative addition to 3 faster than to 2 . Results from the 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.