[Cp′FeI]2 as convenient entry into iron-modified pincer complexes: bimetallic η6,κ1-POCOP-pincer iron iridium compounds

Abstract

The synthesis of [(1,2,4-tBu₃C₅H₂)FeI]₂, [Cp′FeI]₂ (1), and its reaction chemistry are described. Complex 1 shows remarkable stability toward ligand redistribution in solution and gas-phase due to kinetic stabilization with respect to formation. In coordinating solvents the dimer is homolytically cleaved to form paramagnetic mono-solvate 16 valence-electron (VE) adducts [Cp′FeI(L)]. These solvent adducts are labile, and 1 is re-established on exposure to dynamic vacuum. Complex 1 was demonstrated to be a suitable synthon for [Cp′Fe]⁺ transfer to Ir pincer complexes and successful η⁶-coordination of this fragment to the arene ring of κ¹-metallated POCOP–iridium pincer complexes [(Cp′Fe)(POCOP)Ir(H)(I)] ([5]⁺+) and [(Cp′Fe)(POCOP)Ir(C₂H₄)] ([7]⁺+) (POCOP = C₆H₃-2,6-(OP^tBu₂)₂) was accomplished. In these heterometallic organometallic complexes, the π- and σ-electrons of the POCOP-pincer phenyl anion are involved in η⁶- and κ¹-coordination to iron(II) and iridium(III) and iridium(I), respectively. [Cp′Fe]⁺ coordination alters the charge distribution in the (POCOP)Ir complex by inducing significant charge transfer from the POCOP aryl π-system to the [Cp′Fe]⁺ fragment, and therefore yielding an electron-poor and more electrophilic iridium center. Density functional theory (DFT) calculations provide a detailed understanding of this effect. Preliminary catalytic studies show that [7]⁺+ is an active catalyst in transfer dehydrogenation between cyclooctane (COA) and tert-butyl ethylene (TBE).