Organometallic iron(III) complexes supported by MePhTIM macrocycle: An attempt of π-acidity tuning

Reported herein are the syntheses and characterization of the phenylacetylide complex trans-[Fe(III)(MePhTIM)(C₂Ph)₂]⁺(2), σ−phenyl complex trans-[Fe(III)(MePhTIM)(Ph)₂]⁺(3), and their precursor trans-[Fe(III)(MePhTIM)Cl₂]⁺(1), all of which are supported by the tetra-imine macrocycle MePhTIM (2,9,-dimethyl-3,10-diphenyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene). All the new complexes were investigated using mass spectrometry, electronic absorption spectroscopy and cyclic and differential pulse voltammetry techniques. The molecular structures of compounds 1, 2, and 3 were established using single-crystal X-ray diffraction analysis, and their electronic structures (both ground and excited state) analyzed using density functional theory (DFT) calculations. The complexes display rich redox characteristics including a reversible Fe^III/II reduction and a MePhTIM reduction. TD-DFT calculations show that the introduction of MePhTIM-based π(phenyl) orbitals, namely π(phenyl_macro), yields new charge transfer bands for 1 and 2. Furthermore, a greater stabilization of the Fe dπ orbitals for all complexes in comparison to their analogous TIM (2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene) counterparts is evident from electrochemistry and DFT results.