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Depending on the chelate ring present, cyclometalated complexes are useful catalysts for various reactions. The reactivity of Ir III and Rh III NHC complexes bearing aliphatic or aromatic N,N'-substituents and thus featuring various metalation sites toward cyclometalation has been investigated. The Rh III complex bearing an N -mesityl- N '-benzyl-NHC does not participate in any cyclometalation, while the Ir III complex reacts under metalation of an ortho -methyl group of the Mes substituent to give complex [ 3 ] with a six-membered chelate ring. The Rh III and Ir III complexes bearing an N - o -tolyl, N -benzyl-NHC undergo sp 2 -CH activation to yield the cyclometalated complexes [ 4 ] and [ 5 ] featuring a five-membered C NHC ∧ C chelate ring. Density functional theory (DFT) studies corroborated the experimental findings., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Thanks to the impressive control that microenvironments within enzymes can have over substrates, many biological reactions occur with high regio- and stereoselectivity. However, comparable regio- and stereoselectivity is extremely difficult to achieve for many types of reactions, particularly photochemical cycloaddition reactions in homogeneous solutions. Here, we describe a supramolecular templating strategy that enables photochemical [4 + 4] cycloaddition of 2,6-difunctionalized anthracenes with unique regio- and stereoselectivity and reactivity using a concept known as the supramolecular approach. The reaction of 2,6-azolium substituted anthracenes H 4 - L (PF 6 ) 2 ( L = 1a-1c ) with Ag 2 O yielded complexes anti -[Ag 2 L 2 ](PF 6 ) 4 featuring an antiparallel orientation of the anthracene groups. Irradiation of complexes anti -[Ag 2 L 2 ](PF 6 ) 4 proceeded under [4 + 4] cycloaddition linking the two anthracene moieties to give cyclodimers anti -[Ag 2 ( 2 )](PF 6 ) 2 . Reaction of 2,6-azole substituted anthracenes with a dinuclear complex [Cl-Au-NHC-NHC-Au-Cl] yields tetranuclear assemblies with the anthracene moieties oriented in syn -fashion. Irradiation and demetallation gives a [4 + 4] syn -photodimer of two anthracenes. The stereoselectivity of the [4 + 4] cycloaddition between two anthracene moieties is determined by their orientation in the metallosupramolecular assemblies., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The Ir III hydrido complexes [ 1 ] and [ 2 ] have been synthesized by the regioselective oxidative addition of the N7-H bond of 8-halogenotheophyllines to [IrCl(coe) 2 ] 2 in the presence of PPh 3 . The use of dppf in this reaction yielded the bimetallic Ir III /Fe II hydrido complexes [ 3 ] and [ 4 ]. X-ray diffraction studies confirmed that complexes [ 1 ]-[ 4 ] feature a theophyllinato ligand coordinated to the metal center in the rarely observed, chelating fashion via the N7 and O1 atoms. In addition, 8-bromoadenine reacts with [IrCl(coe) 2 ] 2 in the presence of PPh 3 to form the Ir III hydrido complex [ 5 ] which features one anionic 8-bromoadeninato and one neutral 8-bromoadenine ligand linked by an intramolecular hydrogen bond. Complex [ 5 ] was characterized by high-resolution mass spectrometry and an X-ray diffraction analysis but could not be analyzed by nuclear magnetic resonance spectroscopy because of its low solubility., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)