Water-soluble bis(4′-[2,2,2-tris(hydroxymethyl)ethoxy]-2,2′:6′,2″-terpyridine)metal complexes

A series of homoleptic metal complexes containing the pentaerythritol-functionalized ligand 1 (4′-(2,2,2-tris(hydroxymethyl)ethoxy)-2,2′:6′,2″-terpyridine) has been synthesized. In MeOH and under microwave conditions, the 2,2,2-tris(hydroxymethyl)ethoxy substituent is cleaved and replaced by a methoxy group originating from the solvent. This has been confirmed from the single crystal structure of [Zn(2)2][PF6]2 (2 = 4′-methoxy-2,2′:6′,2″-terpyridine). The complexes [Zn(1)2][OAc]2, [Fe(1)2]Cl2 and [Co(1)2][PF6]2 were therefore prepared under mild conditions; [Co(1)2][PF6]2 readily oxidizes to [Co(1)2][PF6]3; the conversion of the paramagnetic [Co(1)2]2+ to diamagnetic [Co(1)2]3+ is readily monitored by 1H NMR spectroscopy. The homoleptic complexes are hygroscopic and are highly soluble in water; the most soluble is [Zn(1)2][OAc]2 (71 mmol dm−3). Structural data for 1, [Zn(1)2][PF6]2, 4{[Zn(1)2][PF6]2}·3MeCN, [Zn(1)(OAc-O)2]·2MeOH and 2{[Co(1)2][PF6]3}·1.5MeCN·1.5H2O confirm that dominant packing forces involve hydrogen bonds between pendant 2,2,2-tris(hydroxymethyl)ethoxy units.

Graphical abstractWater-soluble homoleptic complexes with {M(tpy)2} cores and pendant 2,2,2-tris(hydroxymethyl)ethoxy units are reported. Structural data confirm extensive hydrogen bonding involving the pendant functionalities.Figure optionsDownload full-size imageDownload as PowerPoint slide