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)]Cl-2 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 H-1 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))center dot 3MeCN, [Zn(1)(OAc-O)(2)]center dot 2MeOH and 2{[Co(1)(2)][PF6](3))center dot 1.5MeCN center dot 1.5H(2)O confirm that dominant packing forces involve hydrogen bonds between pendant 2,2,2-tris(hydroxymethyl)ethoxy units.