Complete 1H and 119Sn NMR spectral assignment for an asymmetric di[dihydroxotin(IV)] bis‐porphyrin supramolecular host and its corresponding tetraacetato complex

• Published in: Magnetic resonance in chemistry 2009-03, Vol.47 (3), p.257-262
• Main Authors: Brotherhood, Peter R., Luck, Ian J., Crossley, Maxwell J.
• Format: Article
• Language: English
• Subjects: 1H NMR; 1H‐119Sn HMQC; 2D NMR; coordination chemistry; host–guest chemistry; NMR; porphyrin; supramolecular chemistry; tin; Tröger's base
• ISSN: 0749-1581; 1097-458X
• DOI: 10.1002/mrc.2356

The full 1H and 119Sn NMR spectral assignments for a di[dihydroxotin(IV)] bis‐porphyrin supramolecular host I and for the di[diacetatotin(IV)] complex II are presented. Despite the lack of varied chemical functionality in these molecules, all of their 64 proton environments are non‐equivalent. This is due to the asymmetry afforded by the Tröger's base (methanodiazocine) bridge between the porphyrin and quinoxalinoporphyrin macrocycles. The methanodiazocine bridge imparts chirality and concavity on the host framework and the quinoxalino link to one porphyrin macrocycle results in a negation of C2 symmetry. The anisotropy of the aromatic porphyrin and quinoxalinoporphyrin macrocycles results in good dispersion for all 60 signals of the host framework and for the four ligands bound in the axial positions of the tin(IV) centres. The full assignment of the 1H NMR spectra for these systems was achieved using dqf‐COSY, NOESY, ROESY, 1H‐119Sn HMQC, 1H‐13C HSQC and 1H‐13C HMBC spectroscopy at temperatures that optimised dispersion. The 1H‐119Sn HMQC was particularly useful in this assignment. The 119Sn chemical shift is sensitive to the functionality of the porphyrin and to the nature of the axial ligation, and the 119Sn centre couples to both the ligand protons and the β‐pyrrolic protons. This allows unequivocal identification of the spin systems associated with each metal centre. Copyright © 2008 John Wiley & Sons, Ltd. Full 1H and 119Sn NMR spectral assignments for di[dihydroxotin(IV)] bis‐porphyrin I and for di‐[diacetatotin(IV)] complex II are presented. The anisotropy of the aromatic macrocycles results in good dispersion for all 64 proton environments of these asymmetric systems. NOE, 1H‐1H homonuclear and 1H‐13C and 1H‐119Sn heteronuclear bond correlation experiments allow unequivocal identification of the proton spin systems associated with each tin(IV) metal centre.