Krishna Damodaran - Dirhodium Paddlewheel with Functionalized Carboxylate Bridges: New Building Block for Self-Assembly and Immobilization on Solid Support

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      Inorg.   Chem.,   2012, 51, 4855


      A new dirhodium(II,II) paddlewheel complex,   [Rh2(O2CC6H4COOC2H5)4]   (1), has been synthesized using a predesigned   functionalized carboxylate, namely, 4-(ethoxycarbonyl)benzoate.   The target product has been crystallized from the acetone   solution and structurally characterized as a bis-acetone adduct,   [Rh2(O2CC6H4COOC2H5)4(OCMe2)2]·C6H14  (2). By utilizing the ability of dangling ester   groups to coordinate to open axial ends of neighboring dirhodium   units, 1 can self-assemble to form 2D networks   upon crystallization from solutions of noncoordinating solvents   such as chlorobenzene and chloroform. The resulting   [Rh2(O2CC6H4COOC2H5)4]·2C6H5Cl   (3) and   [Rh2(O2CC6H4COOC2H5)4]·2CHCl3  (4) products have microporous solid state   structures with the pores filled with the corresponding   disordered solvent molecules. Notably, 3 and   4 represent unique examples of 2D extended   frameworks based on dirhodium tetracarboxylate paddlewheel units   devoid of any exogenous ligands. In solution, the dangling ends   of carboxylate bridges of 1 have been   successfully utilized for condensation reaction with the selected   solid support, benzylamine-functionalized polystyrene, allowing   successful heterogenization of dirhodium units through the   equatorial covalent attachment to the substrate. The resulting   solid product was tested as a catalyst in the cyclopropanation   reaction of styrene with methyl phenyldiazoacetate to show good   yields and diastereoselectivity.

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