Endo and exo cyclopalladated ( E )- N -([1,1'-biphenyl]-2-yl)-1-mesitylmethanimines: Anticancer, antibacterial and antioxidant activities

Photoisomerisation of Exo-Imine Complexes and the Role of MECP in the Reverse Thermal Equilibrium: An Experimental and DFT Computational Investigation

Complexes [MCl2 Cp*]2 (M=Ir, Rh), [RuCl2 (p-cymene)]2 and [Ir(C^N)2 Cl]2 (HC^N=a, phenylpyridine ; b, phenylpyrazole,) react with imine ligands derived from ο-aminophenol to yield complexes with an exocyclic C=N bond which has a cis or trans configuration. The trans isomer is favoured except for sterically crowded complexes Cp*M (M=Ir, Rh) when the imine has a mesityl substituent, for which the cis isomer is favoured. The complexes undergo photoisomerisation in visible light but revert back to the original isomer over time or when heated. The rate of the thermal reverse isomerisation depends on the imine substituent and the metal fragment. DFT calculations correctly reproduce the favoured isomer and suggest that the reverse isomerisation occurs by a rehybridisation at the N atom as found in organic imines. In addition, a triplet state, thermally accessible by a Minimum Energy Crossing Point (MECP) provides a low energy pathway for reverse isomerisation in the case of the half-sandwich complexes.

The Exchange of Cyclometalated Ligands

Reactions of cyclometalated compounds are numerous. This account is focused on one of such reactions, the exchange of cyclometalated ligands, a reaction between a cyclometalated compound and an incoming ligand that replaces a previously cyclometalated ligand to form a new metalacycle: + H-C*~Z ⇄ + H-C~Y. Originally discovered for PdII complexes with Y/Z = N, P, S, the exchange appeared to be a mechanistically challenging, simple, and convenient routine for the synthesis of cyclopalladated complexes. Over four decades it was expanded to cyclometalated derivatives of platinum, ruthenium, manganese, rhodium, and iridium. The exchange, which is also questionably referred to as transcyclometalation, offers attractive synthetic possibilities and assists in disclosing key mechanistic pathways associated with the C-H bond activation by transition metal complexes and C-M bond cleavage. Both synthetic and mechanistic aspects of the exchange are reviewed and discussed.