Three new complexes, [Fe(LN 4 H 2 )Cl 2 ] + , [Fe(LN 4 H 2 )(Cat)] + , and [Fe(LN 4 H 2 )(DBC)] + , were synthesized by using the tetradentate macrocyclic ligand LN 4 H 2 (where LN 4 H 2 , Cat, and DBC stand for 2,11-diaza[3,3](2,6) pyridinophane, catecholate, and 3,5-di-tert-butylcatecholate, respectively). The structure of [Fe(LN 4 H 2 )Cl 2 ] + was determined by X-ray diffraction. It crystallizes in the monoclinic space group C2/c with a = 9.613(1), b = 11.589(1), c = 14.063(2) Å , β=110.20(2)°, V = 1541.9(3) Å 3 , and Z = 4. These complexes were found to catalyze the oxidation of catechol groups using O 2 . This was performed in various organic solvents at 20°C. The reaction
Molecular composite knots have been prepared from transition
metal-assembled precursors via a Glaser
acetylenic coupling reaction. The templating metal is
copper(I), and the coordinating fragments incorporated
into
the final structure are 1,10-phenanthroline-type chelates.
The compounds are composite knots as opposed to
prime
knots such as the classical trefoil knot. By combining two tied
open-chain fragments in a cyclodimerization reaction,
the simplest composite knots are obtained as a mixture of two
topological diastereomers. The minimum number of
crossing points used to represent the molecules in a plane is six.
Due to the complexity of the entangled precursors
and to the several cyclization possibilities, the formation yield of
composite knots is only modest (∼3%). On the
other hand, the compound has been fully characterized by ES-MS
(molecular weight, 4037.8) and by 1H NMR
spectroscopy, including 2D NMR (NOESY).
Remote site deprotonation of a coordinated imidazole ligand switches the reduction potential of coordinated iron over a narrow pH range from +0.920 to 20.460 V.
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