N-1- and eta(2)-pyrimidine linkage isomers in complexes of [Ru-II(hedta)](-)

[Ru-II(hedta)(H2O)](-), hedta(3-) = N-hydroxyethylethylenediaminetriacetate, forms N-1-bound pyrimidine complexes via a kinetically controlled substitution at N-1 with pyrimidine (pym), 4-methylpyrimidine (4CH(3)pym), and 4,6-dimethylpyrimidine (Me(2)pym); k = 31 M(-1) s(-1) for pym. Subsequent to N-1 coordination, an intramolecular redistribution of Ru-II-pyrimidine linkage isomers occurs with the formation of eta(2) attachments, reaching equilibrium with t(1/2)'s Of 28.8 (pym), 24 (4CH(3)pym), and 1 h for Me(2)pym. The N-1 forms exhibit normal Ru-II/III waves at 0.14 (pym), 0.10 (4CH(3)pym), and 0.16 V (Me(2)pym) whereas the eta(2) forms shift to more positive values indicative of better pi-acceptor attachments: 0.50 (pym) and 0.44 V (4CH(3)pym). The ratio of isomers was determined to be as follows by H-1 NMR and C-13 NMR methods: (pym) eta(2)(1,2):eta(2)(5,6):eta(2)(1,6):N-1 of 43:22:33:2;(4CH(3)pym) eta(2)(1,2):eta(2)(5,6):N-1 of 10:33:57; (Menpym) eta(2)(1,2):eta(2)(5,6):N-1 of 6:26:68. H-1 NMR assignments have been made for all the observed N-1, eta(2)(1,2), eta(2)(5,6), and eta(2)(1,6) isomers. C-13 NMR shifts have been identified for the major isomers of pym and 4CH(3)pym and confirmed HH COSY and HC COSY methods. Several important conclusions are drawn: (1) eta(2) isomers of the eta(2)(1,2) type exhibit significant downfield shifts of H2 of ca 1.20 ppm; (2) C-13 NMR shifts of carbon centers in eta(2)-bound diazine rings are downfield of the free ligand by up to +9 ppm and not 40-80 ppm upfield as for eta(2)-olefinic complexes; (3) eta(2) protons of the eta(2)(5,6) type shift significantly less upfield than those for eta(2)-olefin complexes (ca. 0.4-0.8 ppm vs 1.0-2.0 ppm). It was established that the formation of eta(2)-bound pyrimidines of [Ru-II(hedta)](-) occurs concomitantly with the dissociation of a carboxylate donor of the hedta(3-) ligand, C-13 NMR spectra reveal the predicted weighted percentage of freed carboxylates based on the isomer distribution between N-1 with all three glycinato arms of hedta(3-) bound to Ru-II (C-13 resonance at 188 ppm) vs eta(2) forms with two bound glycinato groups and one free glycinato group of hedta(3-) (resonating near 174 ppm).