Pyridyl-, bipyridyl-, and terpyridyl-functionalised azamacrocycles

A series of azamacrocycles which have been N-functionalised with pendent pyridylmethyl-(pyCH(2)-), bipyridylmethyl-(bipyCH(2)-) and terpyridylmethyl- (terpyCH(2)-) arms have been synthesised and characterised, and some of their coordination chemistry with transition metal ions is reported. By attaching the pendent-arms at the 5- rather than the 6-position of the py, bipy and terpy, new ligands are generated which can be used to form polynuclear metal complexes in a controlled and systematic fashion. Fluorescent pH and transition metal ion sensors have been developed by reacting the azamacrocyclic N-pendent bipyCH(2) arm(s) with cis-[Ru(bipy)(2)Cl-2] to give macrocycles with up to four attached [Ru(bipy)(3)](2+) groups. That based on 1,4,7-triazacyclononane (9N3), with three attached [Ru(bipy)(3)](2+) groups, has a first photo excited state pK(a) of 7.1, and is a useful fluorescent sensor for physiological pH at below micromolar concentrations. The analogous derivative of cyclam (1,4,8,11-tetraazacyclotetradecane) carrying four [Ru(bipy)(3)](2+) groups has a first photo excited state pK(a) of 5.7, allowing kinetic and thermodynamic fluorescence studies of metal ion uptake by an azamacrocycle at neutral pH without complications from protonated species. A pre-organised hexadentate tris(2,2'-bipyridyl) chelating ligand, 1,4,7-tris(2',2 ''-bipyridyl-5'-ylmethyl)-1,4,7-triazacyclononane (L) has been developed, and crystal structures of mononuclear complexes [M(LH)](3+) (M = Ru, Cu) are reported. In [M(LH)](3+) the azamacrocyclic N-atoms are noncoordinating to M, but have a very high affinity for a single proton trapped in the macrocyclic cavity, An analogous and potentially nonadentate ligand has been developed based on 9N3 with three N-pendent terpyCH(2)-arms.