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

The hydroxy-bridged dimer [(COD)Ir(mu(2)-OH)](2) (COD = 1,5-cyclooctadiene) cleanly cleaves C-H bonds in indene and cyclopentadiene to produce (COD)Ir(eta(3)-indenyl) and (COD)Ir(eta(5)-C5H5), respectively. The kinetics of the formation of (COD)Ir(eta(3)-indenyl) are consistent with a mechanism that involves coordination of indene to [(COD)Ir(mu(2)-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)(mu(4)-O)(mu(3)-O)(mu(2)-OH), a dehydration product of [(COD)Ir(mu(2)-OH)](2), is presented.