Part I. Conformational mobility in pentacoordinate zinc(II) and copper(I) complexes. Part II. Redox chemistry of pentacoordinate copper(I): Reaction with dioxygen and electron transfer properties

[摘要] Zinc(II), copper(II), and copper(I) complexes of the pentadentate ligand, ((5-MeimidH)$sb2$DAP) were prepared and studied as their (BF$sb4$)$sp-$ salts. The divalent compounds, (M$sp{m II}$((5-MeimidH)$sb2$DAP)) (BF$sb4$)$sb2$ (M = Zn, Cu), were found to have intermediate geometries between idealized trigonal bipyramidal and square pyramidal structures by x-ray crystallography. It is assumed that (Cu$sp{m I}$((5-MeimidH)$sb2$DAP)) (BF$sb4$) is also pentacoordinate as is its parent compound, (Cu$sp{m I}$((imidH)$sb2$DAP)) (BF$sb4$). In addition to the x-ray structures, the new compounds have been fully characterized, where appropriate, by a battery of techniques for both the solid and solution states. These studies all suggest that the pentacoordinate structures of the solid state are also retained in solution. Variable-temperature proton NMR studies in non-aqueous solvents were used to extensively probe the intramolecular conformational dynamics of (M((5-MeimidH)$sb2$DAP)) $sp{m n+}$ (M = Zn(II), Cu(I)) and two related pentacoordinate systems ((M((imidH)$sb2$DAP)) $sp{m n+}$ and (M((py)$sb2$DAP)) $sp{m {n+}}$). Computer simulation of the temperature-dependent methylene proton regions were used to observe $lambda$ and $delta$ chelate ring conformations. Coalesence rate constants were obtained in four of the six cases. The electron self-exchange rate of the (Cu((5-MeimidH)$sb2$DAP)) $sp{+/2+}$ couple was measured in CD$sb3$CN, as a function of temperature, by dynamic NMR line-broadening techniques. Under controlled conditions ($mu$ = 25 mM), the observed rate constant ranged from 0.9($pm$0.1) $imes$ 10$sp4$ M$sp{-1}$ s$sp{-1}$ (243 K) to 3.9($pm$0.4) $imes$ 10$sp4$ M$sp{-1}$ s$sp{-1}$ (293 K) with activation parameters of $Delta$H$spddagger$ = 12.5 kJ mol$sp{-1}$ and $Delta$S$spddagger$ = $-$116 J mol$sp{-1}$ K$sp{-1}$. The present electron self-exchange rate constant, together with those for two related Cu(I/II) couples ((Cu((imidH)$sb2$DAP)) $sp{+/2+}$ and (Cu((py)$sb2$DAP)) $sp{+/2+}$) indicate a possible relationship between intramolecular dynamics of the Cu(I) species and the electron self-exchange rates of the Cu(I/II) couples. Finally, the reactivity of (Cu$sp{m I}$((5-MeimidH)$sb2$DAP)) $sp+$ towards O$sb2$ was investigated and found to be something other than a reversible process. Although an initial uptake stoichiometry of 2Cu:O$sb2$ was obtained by manometry, a Toepler pump experiment showed that regeneration of Cu(I) proceeded without significant release of O$sb2$.

[发布机构] Rice University