Kinetics and Mechanism of Indene C–H Bond Activation by [(COD)Ir(μ2-OH)]2

The hydroxy-bridged dimer [(COD)Ir(μ2-OH)]2 (COD = 1,5-cyclooctadiene) cleanly cleaves C–H bonds in indene and cyclopentadiene to produce (COD)Ir(η3-indenyl) and (COD)Ir(η5-C5H5), respectively. The kinetics of the formation of (COD)Ir(η3-indenyl) are consistent with a mechanism that involves coordination of indene to [(COD)Ir(μ2-OH)]2 followed by rate-determining C–H activation from the iridium dimer–indene unit. Transition-state analysis of the Ir and Rh hydroxy dimers indicates that the C–H activation proceeds through a direct deprotonation of indene by the M–OH unit rather than a stepwise oxidative addition/reductive elimination mechanism. The crystal structure of [(COD)Ir]5(μ4-O)(μ3-O)(μ2-OH), a dehydration product of [(COD)Ir(μ2-OH)]2, is presented.