Positional Isomers of Isocyanoazulenes as Axial Ligands Coordinated to Ruthenium(II) Tetraphenylporphyrin: Fine-Tuning Redox and Optical Profiles

Mahtab Fathi-Rasekh; Gregory T Rohde; Mason D Hart; Toshinori Nakakita; Yuriy V Zatsikha; Rashid R Valiev; Mikhail V Barybin; Victor N Nemykin

doi:10.1021/acs.inorgchem.9b01030

Positional Isomers of Isocyanoazulenes as Axial Ligands Coordinated to Ruthenium(II) Tetraphenylporphyrin: Fine-Tuning Redox and Optical Profiles

Inorg Chem. 2019 Jul 15;58(14):9316-9325. doi: 10.1021/acs.inorgchem.9b01030. Epub 2019 Jun 26.

Authors

Mahtab Fathi-Rasekh¹, Gregory T Rohde², Mason D Hart³, Toshinori Nakakita³, Yuriy V Zatsikha⁴, Rashid R Valiev^{5

6}, Mikhail V Barybin³, Victor N Nemykin^{1

4}

Affiliations

¹ Department of Chemistry and Biochemistry , University of Minnesota Duluth , 1039 University Drive , Duluth , Minnesota 55812 , United States.
² Marshall School , Duluth , Minnesota 55811 , United States.
³ Department of Chemistry , University of Kansas , 1567 Irving Hill Road , Lawrence , Kansas 66045 , United States.
⁴ Department of Chemistry , University of Manitoba , 144 Dysart Road , Winnipeg , MB R3T 2N2 , Canada.
⁵ Tomsk State University , 36, Lenin Avenue , 634050 Tomsk , Russia.
⁶ University of Helsinki , P.O. Box 55, FIN-00014 Helsinki , Finland.

PMID: 31240923
DOI: 10.1021/acs.inorgchem.9b01030

Abstract

Two isomeric ruthenium(II)/5,10,15,20-tetraphenylporphyrin complexes featuring axially coordinated redox-active, low-optical gap 2- or 6-isocyanoazulene ligands have been isolated and characterized by NMR, UV-vis, and magnetic circular dichroism (MCD) spectroscopic methods, high-resolution mass spectrometry, and single-crystal X-ray crystallography. The UV-vis and MCD spectra support the presence of the low-energy, azulene-centered transitions in the Q band region of the porphyrin chromophore. The first coordination sphere in new L₂RuTPP complexes reflects compressed tetragonal geometry. The redox properties of the new compounds were assessed by electrochemical and spectroelectrochemical means and correlated with the electronic structures predicted by density functional theory and CASSCF calculations. Both experimental and theoretical data are consistent with the first two reduction processes involving the axial azulenic ligands, whereas the oxidation profile (in the direction of increasing potential) is exerted by the ruthenium ion, the porphyrin core, and the axial azulenic moieties.