[n + n]-Heterometallomacrocyclic complexes (n ≥ 2) prepared from platinum(ii)-centred ditopic 2,2′:6′,2″-terpyridine ligands: dimensional cataloguing by pulsed-field gradient spin-echo NMR spectroscopy

Abstract

The reaction of 4′-(2-propyn-1-oxy)-2,2′:6′,2″-terpyridine (HCCCH₂Oterpy) with trans-[PtI₂(PR₃)₂] (R = Et, ⁿBu, Ph) results in the regioselective formation of the metalloditopic ligands trans-[Pt(CCCH₂Oterpy)₂(PR₃)₂], crystallographic data for which are presented. Each ditopic ligand reacts with FeCl₂·4H₂O to give heterometallomacrocycles, the smallest of which is a [2 + 2] macrocycle, confirmed structurally for R = Et. The NMR spectroscopic data confirm the formation of symmetrical species, i.e. macrocyclic and not polymeric species. The distribution of products has been investigated using pulsed-field gradient spin-echo (PGSE) diffusion NMR spectroscopy, and indicates that the kinetic products from the reactions of 1, 2 or 3 (L) with iron(II) are [Fe_nL_n]²ⁿ⁺ with n = 2, 3 or 4. For L = 1 and 2, these mixtures of products convert in solution to the thermodynamically favoured [Fe₂L₂]⁴⁺.