Electronic versus steric effects of pyridinophane ligands on Pd(iii) complexes?

Dalton Transactions Pub Date: 2017-12-12 DOI: 10.1039/C7DT04366J

Abstract

Several new PdII and PdIII complexes supported by electronically and sterically tuned tetradentate pyridinophane ligands MeN4OMe, MeN4, and tBuN4 were isolated and fully characterized (MeN4OMe: N,N′-dimethyl-2,11-diaza[3,3](2,6)-para-methoxypyridinophane; MeN4: N,N′-dimethyl-2,11-diaza[3,3](2,6)pyridinophane; tBuN4: N,N′-di-tert-butyl-2,11-diaza[3,3](2,6)pyridinophane). Cyclic voltammetry studies, UV-vis and EPR spectroscopy, and X-ray crystallography were employed to reveal that the steric properties of the N-substituents of the RN4 ligands have a pronounced effect on the electronic properties of the corresponding PdIII complexes, while the electronic tuning of the ligand pyridyl groups has a surprisingly minimal effect. An explanation for these observations was provided by DFT and TD-DFT calculations which suggest that the electronic properties of the PdIII complexes are mainly dictated by their frontier molecular orbitals that have major atomic contributions from the Pd center (mainly the Pd dz2 atomic orbital) and the axial N atom donors.

Graphical abstract: Electronic versus steric effects of pyridinophane ligands on Pd(iii) complexes
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