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-C ₅H₅), 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.