COPPER-ION COMPLEXES WITH DERIVATIZED CHELATING PTERIN LIGANDS

Pterin-copper ion interactions are of interest for possible modeling o f enzyme active site chemistry or in coupling reactions of a redox-act ive metal ion with a redox-active ligand cofactor, Here, we describe t he synthesis of derivatized chelating pterins, provided with enhanced organic solubility by introduction of a pivalolyl group the pterin C2 position and supplied with a good copper ion chelator, through reactio n of the 6-(bromomethyl)pterin with a 2-(2-(methylamino)ethyl)pyridine (to give L') or bis(2-pyrid-2-ylethyl)amine (to give L). Copper(I) an d copper(II) complexes have been synthesized and characterized. The X- ray structure of [L'Cu(CI)(CH3CN)](PF6) (3-PF6) is described [space gr oup P2(1)/c; a = 10.606(3) Angstrom, b = 21.683(3) Angstrom, c = 12.18 8(3) Angstrom; beta = 96.67(2)degrees; Z = 3; V = 2784(1) Angstrom(3)] and compared with the previously reported structure of [LCu(Cl)](PF6) (NaPF6) (1-PF6 . NaPF6). In 3-PF6, the Cu(II) is pentacoordinate, incl uding equatorial ligation to the pterin N5 atom, achieving one of the goals of the ligand design. Unlike other pterin-Cu(II) structures, nei ther 1-PF6 . NaPF6 nor 3-PF6 binds to the pterin carbonyl oxygen atom (off pterin C4). Other solution spectroscopic data (e.g., IR, UV-vis, EPR) and a magnetic moment of 1.91 mu(B) are provided and are consiste nt with the solid-state structure observed. Copper(I) complexes [L'Cu- I](PF6) (5-PF6) and [L'Cu-I](PF6). 0.25CH(2)Cl(2) (6-PF6 . 0.25CH(2)Cl (2)) have been generated and characterized. Observed coordination-indu ced H-1 NMR chemical shifts in 6-PF6 . 0.25CH(2)Cl(2)) are consistent with binding through the pterin pyrazine N5 donor; a W-vis feature at 466 nm (sh, epsilon = 1200) is considered a MLCT transition. A cyclic voltammogram of 6-PF6 . 0.25CH(2)Cl(2) (DMF solvent) reveals reversibl e redox process with E-1/2 = 286 mV (E-1/2 = 546 mV for ferrocene/ferr ocenium; vs Ag/AgCl). [L'Cu-II(CH3CN)](CF3SO3)(2) (4-(CF3SO3)(2)) exhi bits the identical cyclic voltammogram, indicating common solution str uctures. The analogue complex [(MeL)Cu-I(CH3CN)](ClO4) (7-ClO4) (Met = (2-(2-pyridyl)ethyl) (2-pyridylmethyl)methylamine) displays a more ne gative redox potential, E-1/2 = 24 mV, indicating that the pterin pyra zine ring has an electron-withdrawing effect, which may explain the la ck of O-2 reactivity of copper(I) complexes of L arid L'.