Preparation and Degradation of Rhodium and Iridium Diolefin Catalysts for the Acceptorless and Base-Free Dehydrogenation of Secondary Alcohols.

Rhodium and iridium diolefin catalysts for the acceptorless and base-free dehydrogenation of secondary alcohols have been prepared, and their degradation has been investigated, during the study of the reactivity of the dimers [M(μ-Cl)(η-CH)] (M = Rh (), Ir ()) and [M(μ-OH)(η-CH)] (M = Rh (), Ir ()) with 1,3-bis(6'-methyl-2'-pyridylimino)isoindoline (HBMePHI). Complex reacts with HBMePHI, in dichloromethane, to afford equilibrium mixtures of , the mononuclear derivative RhCl(η-CH){κ- -(HBMePHI)} (), and the binuclear species [RhCl(η-CH)]{μ- , -(HBMePHI)} (). Under the same conditions, complex affords the iridium counterparts IrCl(η-CH){κ- -(HBMePHI)} () and [IrCl(η-CH)]{μ- , -(HBMePHI)} (). In contrast to chloride, one of the hydroxide groups of and promotes the deprotonation of HBMePHI to give M(η-CH){μ- , -(BMePHI)} (M = Rh (), Ir ()), which are efficient precatalysts for the acceptorless and base-free dehydrogenation of secondary alcohols. In the presence of KO Bu, the [BMePHI] ligand undergoes three different degradations: alcoholysis of an exocyclic isoindoline-N double bond, alcoholysis of a pyridyl-N bond, and opening of the five-membered ring of the isoindoline core.