Expanded Ligands Based upon Iron(II) Coordination Compounds of Asymmetrical Bis(terpyridine) Domains

Abstract

The synthesis and characterization of two tritopic ligands containing a 2,2':6',2″-terpyridine (tpy) metal binding domain and either a 3,2':6',3″- or a 4,2':6',4″-tpy domain are detailed. The synthetic routes to these ligands involved the [Pd(dppf)Cl₂]-catalyzed coupling of a boronic ester-functionalized 2,2':6',2″-tpy with bromo-derivatives of 3,2':6',3″-tpy or 4,2':6',4″-tpy. The 2,2':6',2″-tpy domains of the tritopic ligands preferentially bind Fe²⁺ in reactions with iron(II) salts leading to the formation of two homoleptic iron(II) complexes containing two peripheral 3,2':6',3″-tpy or 4,2':6',4″-tpy metal-binding sites, respectively. These iron(II) complexes are potentially tetratopic ligands and represent expanded versions of tetra(pyridin-4-yl)pyrazine.

Keywords: 2,2′:6′,2″-terpyridine; 3,2′:6′,3″-terpyridine; 4,2′:6′,4″-terpyridine; expanded ligand; iron(II).