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

摘要

The full H-1 and Sn-119 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 Troger'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 C-2 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 H-1 NMR spectra for these systems was achieved using dqf-COSY, NOESY, ROESY, H-1-Sn-119 HMQC, H-1-C-13 HSQC and H-1-C-13 HMBC spectroscopy at temperatures that optimised dispersion. The H-1-Sn-119 HMQC was particularly useful in this assignment. The Sn-119 chemical shift is sensitive to the functionality of the porphyrin and to the nature of the axial ligation, and the Sn-119 centre couples to both the ligand protons and the beta-pyrrolic protons. This allows unequivocal identification of the spin systems associated with each metal centre. Copyright (C) 2008 John Wiley & Sons, Ltd.