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 (HC[triple bond]CCH2Oterpy) with trans-[PtI2(PR3)2] (R = Et, (n)Bu, Ph) results in the regioselective formation of the metalloditopic ligands trans-[Pt(C[triple bond]CCH2Oterpy)2(PR3)2], crystallographic data for which are presented. Each ditopic ligand reacts with FeCl(2).4H(2)O 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(n)L(n)](2n+) with n = 2, 3 or 4. For L = 1 and 2, these mixtures of products convert in solution to the thermodynamically favoured [Fe(2)L(2)](4+).