| Abstrakt: |
A macrocyclic tetraamido ligand 5,6:(3-pyrido)-12,12-diethyl-2,2,9,9-tetramethyl-3,8,11,13-tetraoxo-1,4,7,10-tetraazacyclotridecane, H41, has been designed to incorporate CoII and CoIII in the primary coordination site and has a secondary bidentate site, comprising pyridine-N and amido-O donor atoms, that coordinates Lewis acids. The complex PPh4[2] was obtained by deprotonation of H41 with lithium diisopropylamide in the presence of CoCl2, followed by air oxidation and precipitation from water by addition of PPh4Cl. The X-ray crystal structure of PPh4[2] was obtained. The compound crystallizes in the space group P&onemacr; (No. 2) with unit cell dimensions a = 12.936(4) Å, b = 13.253(5) Å, c = 13.288(2) Å, α = 93.75(2)°, β = 90.91(2)°, γ = 91.53(3)°, V = 2272.1(1.2) Å3, and Z = 2. Lewis acids can be bound either reversibly as in the case of alkali and alkaline earth cations or irreversibly as found for [(bpy)2Ru]2+ (bpy is 2,2-bipyridine) and [(Me2bpy)2Ru]2+ (Me2bpy is 4,4-(CH3)2-2,2-bipyridine). The Lewis acid in the secondary coordination site broadly modifies the chemistry at CoIII and CoII in [2]- and [2]2-, respectively. The axial binding affinity of the CoIII center for 1-CH3-imidazole was 1 to 2 orders of magnitude larger when divalent Lewis acids were in the secondary coordination site than that for [2]-. The reactivities of [2]2-, Ca2+/[2]2-, and [(bpy)2Ru[2]] toward O2 were significantly different. The reaction of [2]2- with O2 rapidly generated [2]-, apparently by an outer-sphere electron-transfer pathway. In contrast, the oxidation of Ca2+/[2]2- by O2 was a complex reaction in which some of the Ca2+ was consumed and the final species depended on the amount of Ca2+ present at the start of the reaction. Finally, in the case of [(bpy)2Ru[2]], it appeared as though the dinuclear complex [(bpy)2Ru[2]]2(μ-O2) formed upon reaction with O2. |
