Preparation, X‑ray Structures, Spectroscopic, and Redox Properties of Di- and Trinuclear Iron–Zirconium and Iron–Hafnium Porphyrinoclathrochelates

The first hybrid di- and trinuclear iron­(II)–zirconium­(IV) and iron­(II)–hafnium­(IV) macrobicyclic complexes with one or two apical 5,10,15,20-tetraphenylporphyrin fragments were obtained using transmetalation reaction between n-butylboron-triethylantimony-capped or bis­(triethylantimony)-capped iron­(II) clathrochelate precursors and dichlorozirconium­(IV)- or dichlorohafnium­(IV)-5,10,15,20-tetraphenylporphyrins under mild conditions. New di- and trinuclear porphyrinoclathrochelates of general formula FeNx3((Bn-Bu)­(MTPP)) and FeNx3(MTPP)2 [M = Zr, Hf; TPP = 5,10,15,20-tetraporphyrinato­(2-); Nx = nioximo­(2-)] were characterized by one-dimensional (1H and 13C­{1H}) and two-dimensional (COSY and HSQC) NMR, high-resolution electrospray ionization mass spectrometry, UV–visible, and magnetic circular dichroism spectra, single-crystal X-ray diffraction experiments, as well as elemental analyses. Redox properties of all complexes were probed using electrochemical and spectroelectrochemical approaches. Electrochemical and spectroelectrochemical data suggestive of a very weak, if any, long-range electronic coupling between two porphyrin π-systems in FeNx3(MTPP)2 complexes. Density functional theory and time-dependent density functional theory calculations were used to correlate spectroscopic signatures and redox properties of new compounds with their electronic structures.