Enantioselective Synthesis of Optically Active Polymeric Homo- and Bimetallic Oxalate-Bridged Networks [M2(ox)3]n

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Abstract
The synthesis of the enantiomeric forms of the two- and three-dimensional polymers: {[NBu4][MnCr(ox)3]}n (1) (Bu = n-butyl, ox = oxalate), {[M(bpy)3)][LiCr(ox)3]}n (M = Ni (2), Ru (4)) (bpy = 2,2‘-bipyridine), {[M(bpy)3)][Mn2(ox)3]}n (M = Ni (3), Ru (5)) using resolved [Cr(ox)3]3- and [M(bpy)3]2+ (M = Ni, Ru) species as chiral building blocks, and their structural characterization are reported. The optical activity of these systems arises from the helical chirality of the tris-chelated subunits with Δ or Λ configurations. Bimetallic two-dimensional optically active network 1 results from the stacking of similar metallo-oxalate honeycomblike layers containing [Cr(ox)3]3- units of the same chirality. The assembly of homochiral species leads to optically active three-dimensional 3-connected 10-gon nets 2−5. Solid state circular dichroism (CD) measurements demonstrate the enantiomeric character of the obtained polymers. Absolute configurations of the metal centers have been assigned according to circular dichroism and X-ray diffraction data. Enantiomerically pure single crystals of the two enantiomeric forms, {[RuΔ(bpy)3)][LiΔCrΔ(ox)3]H2O}n (4Δ) and {[RuΛ(bpy)3)][LiΛCrΛ(ox)3]H2O}n (4Λ), have been obtained and the structures determined by X-ray diffraction studies (crystals data: cubic system, space group P213, a (Å) = 15.293(8) (4Δ), 15.289(2) (4Λ), Z = 4).