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

Buil, María
L.; Collado, Alba; Esteruelas, Miguel A.; Gómez-Gallego, Mar; Izquierdo, Susana; Nicasio, Antonio I.; Oñate, Enrique; Sierra, Miguel A.

doi:10.1021/acs.organomet.1c00068.s001

om1c00068_si_001.pdf (4.16 MB)

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

journal contribution

posted on 2021-04-01, 10:18 authored by María L. Buil, Alba Collado, Miguel A. Esteruelas, Mar Gómez-Gallego, Susana Izquierdo, Antonio I. Nicasio, Enrique Oñate, Miguel A. Sierra

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)(η⁴-C₈H₁₂)]₂ (M = Rh (1), Ir (2)) and [M(μ-OH)(η⁴-C₈H₁₂)]₂ (M = Rh (3), Ir (4)) with 1,3-bis(6′-methyl-2′-pyridylimino)isoindoline (HBMePHI). Complex 1 reacts with HBMePHI, in dichloromethane, to afford equilibrium mixtures of 1, the mononuclear derivative RhCl(η⁴-C₈H₁₂){κ¹-N_py-(HBMePHI)} (5), and the binuclear species [RhCl(η⁴-C₈H₁₂)]₂{μ-N_py,N_py-(HBMePHI)} (6). Under the same conditions, complex 2 affords the iridium counterparts IrCl(η⁴-C₈H₁₂){κ¹-N_py-(HBMePHI)} (7) and [IrCl(η⁴-C₈H₁₂)]₂{μ-N_py,N_py-(HBMePHI)} (8). In contrast to chloride, one of the hydroxide groups of 3 and 4 promotes the deprotonation of HBMePHI to give [M(η⁴-C₈H₁₂)]₂(μ-OH){μ-N_py,N_iso-(BMePHI)} (M = Rh (9), Ir (10)), which are efficient precatalysts for the acceptorless and base-free dehydrogenation of secondary alcohols. In the presence of KO^tBu, 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.