Novel multidentate pyridyl/thiazolyl ligands containing terpyridine units: Formation of dinuclear and trinuclear double helicate complexes

Three new multidentate N-donor ligands L¹–L³, which containa combination of pyridyl and thiazolyl donor units, have been prepared startingfrom 2,2′:6′,2″-terpyridine. The extended linear sequence of ortho-linkedN-donor heterocycles (five for L¹; six for L²; and seven for L³) is reminiscentof the well-known oligopyridines, although they have different coordinationproperties due to the presence of five-membered thiazolyl rings which result innatural breaks of the ligand backbone into distinct bidentate or terdentatedomains. Thus, the pentadentate ligand L¹ partitions into terdentate andbidentate domains to give a dinuclear double helicate [M₂(L¹)₂]⁴⁺ with Cu(II).The hexadentate ligand L² partitions into two terdentate domains to givedinuclear double helicates [M₂(L²)₂]⁴⁺ with six-coordinate first-row transitionmetals dications (M=Ni and Co). The heptadentate ligand L³ partitions into twoterminal bidentate and a central terdentate domains to give a trinuclear doublehelicate [Cd₃(L³)₂]⁶⁺ with Cd(II). The formation of these complexes highlightsthe fact that the thiazole group is instrumental in instructing thepartitioning of the ligand, which in turn controls the formation of thehelicate complexes.

Three new multidentate N-donor ligands L¹–L³, which containa combination of pyridyl and thiazolyl donor units, have been prepared startingfrom 2,2′:6′,2′′-terpyridine. Several complexes with transition metal ions havebeen prepared. The pentadentate ligand L¹ partitions into terdentate andbidentate domains to give the dinuclear double helicate [Cu₂(L¹)₂]⁴⁺. Thehexadentate ligand L² partitions into two terdentate domains to give dinucleardouble helicates [M₂(L²)]⁴⁺ with Ni and Co. The heptadentate ligand L³partitions into two bidentate and a terdentate domains to give a trinucleardouble helicate [Cd₃(L³)₂]⁶⁺.