Activation of aldehydes by exocyclic iridium(i)-η 4 :π 2 -diene complexes derived from 1,3-oxazolidin-2-ones.

The Ir(i) complexes [TpMe2 Ir(η4 -1,4-diene)] 2b and 2c react thermally with a variety of aromatic aldehydes, 3a-e, to generate the metallabicyclic compounds 4e-k and the Fischer-type carbenes 5a-b in moderate yields. These reactions are proposed to take place with the initial formation of η1 -aldehyde adducts as key intermediates. The formation of the metallabicyclic compounds 4e-k involves a formal decarboxylation process at the exo-2-oxazolidinone diene and an ortho metallation of the aromatic ring. The generation of the Fischer-type carbenes 5a-b is the result of a series of metal-based rearranged intermediates with no decarboxylation observed. Treatment of the η4 -diene complex 2b with a variety of Lewis bases induces a change in the binding mode of the diene ligand from η4 :π2 to η2 :σ2 to form the Ir(iii) derivatives 6b-d of composition TpMe2 Ir-(η4 :π2 -1,4-diene)(L) (L = CO, MeCN, and C5 H5 N). A study of reactions of complex 2b with either mono- or poly-deuterated aldehydes was performed to understand the mechanisms of such processes. The results of these studies were used to determine plausible formation mechanisms of the metallabicyclic compounds 4e-4k and Fischer-type carbenes 5a-b compound series. These mechanisms were corroborated by density functional theory (DFT) calculations of the free energy profiles.