Molecular Oxygen and Sulfur Reactivity of a Cyclotriveratrylene Derived Trinuclear Copper(I) Complex

Our continuing efforts into developing copper coordination chemistry relevant to dioxygen-processing copper proteins has led us to design and synthesize a cyclotriveratrylene (CTV)-based trinucleating ligand, CTV-TMPA, which employs tetradentate tris(2-pyridylmethyl)-amine chelates (TMPA) for their copper ion binding sites. Binding of three copper ions per CTV-TMPA unit was established by various chemical and spectroscopic methods such as UV-vis and resonance Raman (rR) spectroscopies. The following complexes were observed: A tricopper(I) complex [(CTV-TMPA)Cu-3(I)](3+) (1), a CO adduct [(CTV-TMPA)Cu-3(I)(CO)(3)](3+) (1-CO; nu(C=O) = 2094 cm(-1)) a triphenylphosphine adduct [(CTV-TMPA)Cu-3(I)(PPh3)(3)](3+) (1-PPh3), a tricopper(II) complex [(CTV-TMPA)Cu-3(II)](3+) (1-Ox), and its tris-monochloride or tris-monobromide adducts. Also, introduction of dioxygen to the -80 degrees C solutions of 1 leads to O-2-adducts, the first example of a synthetic copper complex which can stabilize a mononuclear Cu-II-superoxo and dinuclear peroxo species simultaneously within one complex {[Cu] = 1.53 mM in THF: (mu-1,2-peroxo complex, lambda(max) = 543 (epsilon 9650) nm): nu(O-O) = 825 ((Delta O-18(2)) = -47) cm(-1); nu(Cu-O) = 506 ((Delta O-18(2)) = -26) cm(-1): (superoxo complex, lambda(max) = 427 (epsilon 3150) nm): nu(O-O) = 1129 ((Delta O-18(2)) = -60) cm(-1); nu(Cu-O) = 463 ((Delta O-18(2)) = -27) cm(-1)}. Elemental sulfur reacts reversibly with 1 leading to a (proposed) hexanuclear species [{(CTV-TMPA)Cu-3(II)}(2)(mu-1,2-S-2(2-))(3)](6+) (1-S) {lambda(max) = 544 (epsilon 7270) nm}, possessing one dicopper(II)-disulfide structural type: {THF solvent) nu(S-S) = 489 ((Delta S-34) = -10) cm(-1); nu(Cu-S) = 307 ((Delta S-34) = -5) cm(-1)}. Derivation of spectroscopic, structural, and chemical conclusions were aided by the study of a close mononuclear analogue with one pyridyl group of the TMPA parent possessing a 6-CH2OCH3 substituent, this being part of the CTV-TMPA architecture.