Syntheses, structures and ligand dissociation kinetics of Vitamin B12 model compounds with exceptionally poor electron donating groups, LCo(DH)2CHX2 (X = Cl or Br)
Syntheses, structures and ligand dissociation kinetics of Vitamin B12 model compounds with exceptionally poor electron donating groups, LCo(DH)2CHX2 (X = Cl or Br)
复制标题
具有极差给电子基团 LCo(DH)2CHX2（X = Cl 或 Br）的维生素 B12 模型化合物的合成、结构和配体解离动力学
DOI：
10.1016/s0020-1693(00)86294-5
复制
发表时间：
1988
影响因子：
2.8
通讯作者：
E. Zangrando
中科院分区：
文献类型：
--
作者：
Chen Qiuhao;L. Marzilli;N. B. Pahor;L. Randaccio;E. Zangrando
本文报道了维生素B_（12）模型化合物LCo（DH）_2CHX_2（X = Cl和Br，L =不同的中性N-和P-配体）的合成和配体解离动力学，以及CHCl_2衍生物（L = py（1）和1，5，6-三甲基苯并咪唑Me_3Bzm（2））的晶体结构。化合物1的晶胞参数a = 9.617（1），B= 12.601（2），c= 15.586（2）°，β = 95.44（1）°; 2晶体属于空间群P1，晶胞参数a = 8.867（2），B= 10.719（2），c= 13.345（2）Å，α = 94.81（2），β = 90.89（1），γ = 105.63（2）°。用Patterson和Fourier方法解出两种结构，并用最小二乘法修正，最终R值为0.037（1）和0.036（2），利用3474（1）和4435（2）的独立反射，轴向N <$Co <$C碎片的特征在于Co <$N和Co <$C的距离分别为2.045（2）和1.995（2）μ in 1和2.043（2）μ in 2。和1.983（2）μ in 2。在py和Me 3Bzm烷基钴肟中，Co C键长是迄今为止报道的最小值。L配体的置换遵循SN 1 LIM行为，相应的速率常数取决于L的性质，在CHCl 2衍生物中从2-氨基吡啶的2.42 X 10− 1 s − 1变化到P（OMe）3的1.99 X 10−5s− 1。动力学结果证实了CHBr_2的供电子能力低于CHCl_2的结论，但Cl和Br的电负性则相反.动力学和结构性质之间的一些关系进行了讨论。
The syntheses and ligand dissociation kinetics of vitamin B12model compounds LCo(DH)2CHX2with X = Cl and Br and L = different neutral N- and P- ligands are reported together with the crystal structures of the CHCl2derivatives with L = py (1) and 1,5,6-trimethylbenzimidazole, Me3Bzm (2). Compound1crystallizes in the space groupP21/nwith cell parametersa= 9.617(1),b= 12.601(2),c= 15.586(2) Å, β = 95.44(1)°; 2 crystallizes in the space groupP1 with cell parametersa= 8.867(2),b= 10.719(2),c= 13.345(2) Å, α = 94.81(2), β = 90.89(1), γ = 105.63(2)°. The two structures were solved by Patterson and Fourier methods and refined by least-squares methods to finalRvalues of 0.037 (1) and 0.036 (2), using 3474 (1) and 4435 (2) independent reflections.The axial NCoC fragment is characterized by CoN and CoC distances of 2.045(2) and 1.995(2) Å in1and 2.043(2) and 1.983(2) Å in2, respectively. The CoC bond lengths have the smallest values so far reported in both py and Me3Bzm alkylcobaloximes.The displacement of the L ligand followed SN1 LIM behaviour and the corresponding rate constants depend upon the nature of L and vary in CHCl2derivatives from 2.42 X 10−1s−1for 2-aminopyridine to 1.99 X 10−5s−1for P(OMe)3. For fewer CHBr2analogs the rate constants were smaller.Kinetic results confirm previous findings that the donating ability of CHBr2is less than that of CHCl2, although the electronegativity of Cl and Br species would suggest an opposite trend. Some relationships between kinetic and structural properties are discussed.