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-tet raazacyclotridecane, 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 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 was obtained. The compound crystallizes in the space group P1 (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 - and 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 -. The reactivities of 2-, Ca2+/2-, and [(bpy)2Ru] toward O2 were significantly different. The reaction of 2- with O2 rapidly generated -, apparently by an outer-sphere electron-transfer pathway. In contrast, the oxidation of Ca2+/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], it appeared as though the dinuclear complex [(bpy)2Ru]2(μ-O2) formed upon reaction with O2.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry