Activation of aldehydes by exocyclic iridium(I)-?4:?2-diene complexes derived from 1,3-oxazolidin-2-ones

The Ir(I) complexes [TpMe2Ir(?4-1,4-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 ?1-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 ?4-diene complex 2b with a variety of Lewis bases induces a change in the binding mode of the diene ligand from ?4:?2 to ?2:?2 to form the Ir(III) derivatives 6b?d of composition TpMe2Ir-(?4:?2-1,4-diene)(L) (L = CO, MeCN, and C5H5N). 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.