Synthesis and characterization of (I) structural models for dimetallic hydrolases and (II) manganese coordination polymers

Abstract

Two series of di-metal(II) complexes [M₂(μ-OH₂)(BzIm) ₄(OAc)₄] and [M₂(μ-OH₂ (4-pic)₄(O₂CPh)₄.(MeOH)₃ (M = Mn, Co, Ni and Mg; BzIm = benzimidazole; 4-pit = 4-picoline; OAc = acetate; O₂CPh = benzoate) have been synthesized and characterized. These two series of di-metallic complexes serve as excellent structural models for the active sites of many known hydrolases. A possible catalytic pathway has been revealed in an unusual reversal of C-O bond lengths in the terminal coordinated acetates.

A series of mono-, di-, tri-, hexa- and poly-manganese complexes were also synthesized and characterized during our effort to study the aqua-bridged di-M²⁺ core.

With the success in the structural models, we turn our focus to the synthesis and characterization of reaction models for dimetallic hydrolases. We hope that the structure of the dirnetalhc core can be retained and polymerized by the two-armed V-donor ligands 4,4'-bipyridyl (4,4'-bpy). A series of manganese coordination polymers were therefore synthesized and characterized. However, our attempt to synthesize a di-Mn²⁺ aqua-bridged polymer with 4,4'-bpy was proved to be unsuccessful. On the other hand, interesting antiferromagnetic coupling was observed in these polymers at low temperatures.

Since we can only obtain Mn coordination polymers with trans Mn-N bonds using 4,4'-bpy, we would like to use another "two-arm" N-donor ligand 1,2-bis(4- pyridyl)ethane (bpe). The ligand bpe possess an extra -CH₂-CH₂- group between the two pyridine rings when compared to 4,4'-bpy, and should introduce higher structual diversity into the coordination polymer. Higher structural diversity is indeed observed, although the targeted aqua-bridged dimetahic polymer cannot be obtained.

Date of Award	1998
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology