Challenges in cyclometalation: steric effects leading to competing pathways and η¹,η²-cyclometalated iridium(iii) complexes

Abstract

The iridation of (R)-N,N-dimethyl-1-(1-naphthyl)ethylamine in the presence of a base afforded an assortment of products ranging from organic molecules to coordinated systems and cyclometalated complexes. The transformation affirmed the postulation where steric effects within the coordination sphere favor a β-hydride elimination-like decomposition pathway, competing alongside ortho-metalation, thus leading to iminium intermediates. The same procedure also generated an unprecedented carbocyclic η,η-cycloiridated species that could not be attained from the direct cyclometalation of its organic ligand.

Recent Development in the Synthesis and Catalytic Application of Iridacycles

“…In the same year, the same group carried out the reaction of ( R )‐ N,N ‐dimethyl‐1‐(1‐naphthyl)ethylamine with [IrCp*Cl 2 ] 2 , employing sodium acetate in 1,2‐dichloroethane (DCE) at reflux temperature, in order to gain more insight into the selectivity of cyclometallation [25] . This reaction generated six isolable products: cycloiridated complexes 13 , 15 , and 16 , dimethylamine coordinated complex 14 and organic molecules 1‐acetonaphthone and 1‐ethylnaphthalene, as shown in Scheme 3.…”

“…In the same year, the same group carried out the reaction of (R)-N,N-dimethyl-1-(1-naphthyl)ethylamine with [IrCp*Cl 2 ] 2 , employing sodium acetate in 1,2-dichloroethane (DCE) at reflux temperature, in order to gain more insight into the selectivity of cyclometallation. [25] This reaction generated six isolable products: cycloiridated complexes 13, 15, and 16, dimethylamine coordinated complex 14 and organic molecules 1-acetonaphthone and 1-ethylnaphthalene, as shown in Scheme 3. It was suggested that the formation of 13, 14 and 1-acetonaphthone could start from a β-hydride elimination-like process, 15 could be derived from 13 via a dehydrogenation procedure, and 16 could be formed from the dehydroamination of a complexed cyclic intermediate, hydrogenation of which could produce 1-ethylnaphthalene.…”

“…[27] These iridacycles appeared mostly as a mixture of two diastereoisomers, presumably due to the small difference between their thermodynamic stability. Some examples (21)(22)(23)(24)(25)(26) are shown in Scheme 6.…”