No abstract

No abstract

distillation at 120°C (oven temperature) and lo-' mbar, formed a glassy solid. Recrystallization from pentane at -78°C afforded 980 mg (87%) of colorless crystals (isomerically pure): m.p. = 9 0 T A 63 :37 mixture of the isomers 6c .7c is present in the mother liquor. Received: November 12, 1985 [Z 1533 IE] German version: Angew. Chem. 98 (1986) 265 [I] Review: G. Mark1 in Houben-Weyl: Methoden der Organirchen Chemie. 4.

oxidation. Since four electrons are required for the formation of an 02-molecule, a water-oxidation can only be achieved if the 1 e-processes can be efficiently coupled. This is obviously not the case in homogeneous phases, but is so in heterogeneous phases.The heterogeneous water-oxidation system described here is of special interest with regard to the evolution of oxygen in photosynthesis. It has already been suggested['.'-'] that the microheterogeneous environment around the manganese centers and the close proximity of the manganese atoms to one another are responsible for water-splitting in photosynthesis. This is supported by our finding that the complexes 1 and 2 are only catalytically active in the solid form. It is conceivable that four molecules of the binuclear manganese complex may be oxidized by four adjacent Ce'" ions to produce a four-electron depletion center on the surface. This oxidizing center would then lead to the four-electron oxidation of two molecules of weakly bound water with subsequent evolution of oxygen.