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Intramolecular Change Distribution and Related Properties in a Series of 3,6-Di- tert -butylbenzoquinonatocobalt Complexes Containing Piperidine

2001; Oxford University Press; Volume: 74; Issue: 2 Linguagem: Inglês

10.1246/bcsj.74.305

1348-0634

Ok‐Sang Jung, Young‐A Lee, Sung Ho Park, Yun Ju Kim, Kyung Ho Yoo, Dong Chan Kim,

Metal-Catalyzed Oxygenation Mechanisms

Abstract A series of cobalt-benzoquinone complexes containing piperidine derivatives as a coligand, [Co(3,6-dbq)2(N-N)], (N-N = 1,1′-methylenedipiperidine (mdp), 1,1′-methylenebis(3-methylpiperidine) (mbmp), 1-methyl-4-(methylamino)piperidine (mmap); 3,6-dbq = 3,6-di-tert-butyl-1,2-benzoquinone) have been prepared and characterized. The crystal structure of [Co(3,6-dbq)2(mmap)]•0.5Me2CO (P1-, a = 11.524(2) Å, b = 12.565(4) Å, c = 14.160(3) Å, α = 80.65(2)°, β = 82.15(2)°, γ = 87.39(2)°, V = 2003.6(8) Å3, R = 0.0763) proves that the molecule exists as low-spin [CoIII(3,6-dbsq)(3,6-dbcat)(mmap)] (3,6-dbsq = 3,6-di-tert-butyl-1,2-semiquinonato; 3,6-dbcat = 3,6-di-tert-butylcatecholato) in the solid state. According to magnetic, spectroscopic, and thermal analyses, [CoIII(3,6-dbsq)(3,6-dbcat)(mmap)] is locked up to 431 K while [CoII(3,6-dbsq)2(mdp)] and [CoII(3,6-dbsq)2(mbmp)] are changed to their corresponding low spin CoIII forms at (below) T1/2 = 215 K and 271 K, respectively. The transition temperature (T1/2) between CoIII/CoII varies as mbmp < mdp << mmap, which appears to be associated with electronic versus steric effects of the piperidine coligands. In particular, [Co(3,6-dbq)2(mdp)] reveals a two-step spin conversion centered at 208 K and 298 K with a plateau of 90 deg.