5 COORDINATION MODES OF 4-AMINOPYRIMIDINE WITH YDROXY-ETHYLETHYLENEDIAMINETRIACETATORUTHENATE(II)

The complex [Ru(II)(hedta)(4NH2pym)]-, hedta3- = N-hydroxyethylethylen ediaminetriacetate, 4NH2pym = 4-aminopyrimidine, exists at pH 7 as fiv e different coordination isomers, which are most readily distinguished by their electrochemical waves in comparison with the 2-aminopyridine (2NH2py) complex. The 2NH2py complex exhibits N(1) (pyridine bound), exo-NH2 (amine bound) and N(1), NH2-chelated species. The 4NH2pym comp lex forms N(1), exo-amine and N(3), NH2-chelated isomers analogues to the 2NH2py Species, but also engages in eta2 (olefin bound) coordinati on of the dearomatized 4NH2pym ring in C(5)-C(6), and another eta2 typ e of complex involving electron density between N(1) and N(3) of the r ing (eta3 form). N(1), eta2 and eta3 isomers have also been detected f or unsubstituted pyrimidine (pym), 4-methylprimidine (4CH3pym) and 2-a minopyrimidine (2NH2pym). Electrochemical waves (V versus NHE) for the five isomers are assigned as follows: (Ru(II/III)) exo-NH2 (0.06 V), N(1) (0.29 V), eta2(0.49 V), (Ru(III/IV))eta3(0.76 V); N(3), NH2-chela ted (1.09 V).