Kinetics and Mechanism of Indene C–H Bond Activation by [(COD)Ir(μ_2-OH)]_2

Abstract

The hydroxy-bridged dimer [(COD)Ir(μ_2-OH)]_2 (COD = 1,5-cyclooctadiene) cleanly cleaves C–H bonds in indene and cyclopentadiene to produce (COD)Ir(η^3-indenyl) and (COD)Ir(η^5-C_(5)H_5), respectively. The kinetics of the formation of (COD)Ir(η^3-indenyl) are consistent with a mechanism that involves coordination of indene to [(COD)Ir(μ_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(μ_4-O)(μ_3-O)(μ_2-OH), a dehydration product of [(COD)Ir(μ_2-OH)]_2, is presented.

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