Versatile bonding and coordination modes of ditriazolylidene ligands in rhodium(iii) and iridium(iii) complexes

Abstract

Metalation of novel ditriazolium salts containing a trimethylene (–CH₂CH₂CH₂–) or dimethylether linker (–CH₂OCH₂–) was probed with different rhodium(III) and iridium(III) precursors. When using [MCp*Cl₂]₂, a transmetalation protocol via a triazolylidene silver intermediate was effective, while base-assisted metalation with MCl₃via sequential deprotonation of the triazolium salt with KOtBu and addition of the metal precursor afforded homoleptic complexes. The N-substituent on the triazole heterocycle directed the metalation process and led to C_trz,C_trz,C_Ph-tridentate chelating ditriazolylidene complexes for N-phenyl substituents. With ethyl substituents, only C_trz,C_trz-bidentate complexes were formed, while metalation with mesityl substituents was unsuccessful, presumably due to steric constraints. Through modification of the reaction conditions for the metalation step, an intermediate species was isolated that contains a C_trz,C_Ph-bidentate chelate en route to the formation of the tridentate ligand system. Accordingly, C_phenyl–H bond activation occurs prior to formation of the second metal–triazolylidene bond. Stability studies with a C_trz,C_trz,C_Ph-tridentate chelating ditriazolylidene iridium complex towards DCl showed deuterium incorporation at both N-phenyl groups and indicate that C_phenyl–H bond activation is reversible while the C_trz–Ir bond is robust. The flexible linker between the two triazolylidene donor sites provides access to both facial and meridional coordination modes.