H/D exchange in diazine ligands coordinated to Co(III) and their related quaternized salts in alkaline D/sub 2/O solution using NMR spectroscopy - A case for comparison

The Co(III) diazine complexes [(NH/sub 3/)/sub 5/CoPhtz)](ClO/sub 4/)/sub 3/(1), [(NH/sub 3/)/sub 5/CoPydz)] (ClO/sub 4/)/sub 3/ (2), [(NH/sub 3/)/sub 5/Co(3-Me-Pydz)](ClO/sub 4)/sub 3/ (3) and [(NH/sub 3/)/sub 5/Co(3-MePhtz)](ClO/sub 4/)/sub 3/ (4) undergo OD/sup -/ -catalyzed H/D exchange at the position ortho to the coordinated nitrogen atom. Rate constants for H/D exchange of these complexes at 25 degree centigrade were obtained in alkaline D/sub 2/O solution using NMR spectroscopy. These reactions follow the rate low k/sub obs/ = k/sub ex/ [OD] with k/sub wx/M/sup -1/s/sup -1/ (25 degree centi grade, I=0.5) = 8 x 10/sup -4/ (1), 1 x 10/sup -4/ (2), 6 x 10/sup -5/, 5.5 x 10/sup -4/ (4). These reactions are considerably slower than H/D exchange at position ortho to quaternary nitrogen in he N-methylphthalazinium (5) and N-methylpyridazinium perchlorate (6). This difference may attributed to a steric effect between (NH/sub 3/)/sub 5/Co/sup 3+/ moiety and the ortho proton in [(NH/sub 3/)/sub 5/Co(diazine)] complexes. The N-alkylated diazines are found to undergo a variety of reactions in alkaline solution. 5 gives 2-methyl-1,2-dihydrophthalazine (7) and 2-methylphthalazone (8) or 1-hydroxy-2-methyl-1,2-dihydrophthalazine (9) depending on the concentration of OH'. 6 gives tetracycle 2-methyl-la, 2,4a,5,8a,8b,8c-octahydro-1-oxa-2,3,5a,6-tetrazafuro[1,2,3,4-def] fluorine (10 all of these different reactions were investigated by NMR spectroscopy. (author)