The equilibrium reaction between tellurium(H) dithiolates and thiols, Te(SR1)(2) + 2HSR(2) reversible arrow Te(SR2)(2) + 2HSR(1) was studied by means of H-1 and Te-125 NMR spectroscopy and ab initio quantum chemical methods. It was found that the reaction is catalyzed by Bronsted acids and bases, the catalytic activity corresponding to the strength of the respective acid or base. Investigation of the initial step of the reaction, Te(SR1)(2) + HSR2 reversible arrow Te(SR1)(SR2) + HSR1, showed it to proceed according to first order kinetics for Te(SR1)(2), HSR2 and for the catalyst. Ab initio geometry optimizations and frequency calculations suggest [Te(SR1)(HSR1)(HSR2)](+) and [Te(SR1)(2)(SR2)](-) to be stable intermediates and not transition states in the acid and base catalyzed reactions, respectively. The reaction hence proceeds via all. additional elimination rather than all S(N)2 mechanism. The catalytic activity displayed by acids and bases call be applied to reduce the temperature in synthesis of thermally labile tellurium(II) dithiolates.
Kinetics and Mechanism of the Nucleophilic Substitution of Tellurium(II) Dialkanethiolates, Te(SR 1 ) 2 with Thiols, HSR 2
作者:Holger Fleischer
DOI:10.1080/10426500590906337
日期:2005.2.23
The equilibrium reaction between tellurium(H) dithiolates and thiols, Te(SR1)(2) + 2HSR(2) reversible arrow Te(SR2)(2) + 2HSR(1) was studied by means of H-1 and Te-125 NMR spectroscopy and ab initio quantum chemical methods. It was found that the reaction is catalyzed by Bronsted acids and bases, the catalytic activity corresponding to the strength of the respective acid or base. Investigation of the initial step of the reaction, Te(SR1)(2) + HSR2 reversible arrow Te(SR1)(SR2) + HSR1, showed it to proceed according to first order kinetics for Te(SR1)(2), HSR2 and for the catalyst. Ab initio geometry optimizations and frequency calculations suggest [Te(SR1)(HSR1)(HSR2)](+) and [Te(SR1)(2)(SR2)](-) to be stable intermediates and not transition states in the acid and base catalyzed reactions, respectively. The reaction hence proceeds via all. additional elimination rather than all S(N)2 mechanism. The catalytic activity displayed by acids and bases call be applied to reduce the temperature in synthesis of thermally labile tellurium(II) dithiolates.
Tellurium(
<scp>II</scp>
) Dialkanethiolates: n
<sub>p</sub>
(S)‐σ*(Te−S′) Orbital Interactions Determine the
<sup>125</sup>
Te NMR Chemical Shift, and the Molecular and Crystal Structure
作者:Holger Fleischer、Norbert W. Mitzel、Dieter Schollmeyer
DOI:10.1002/ejic.200390111
日期:2003.3
thiol HSR. Ab initio calculations of the Te-125 NMRshifts for the model compound Te(SH)(2) (C-2 symmetry) reveal that it also depends strongly on the HSTeS torsion angle. These results can be explained by a model in which pi-type n(p)(S)- sigma*(Te-S') and n(p)(Te)-sigma*(S-H) orbitalinteractionsdetermine the paramagnetic shielding of the tellurium nucleus. ((C) Wiley-VCH Verlag GmbH & Co. KGaA,
通过 TeO2 和 Te(OiPr)(4) 分别与 HSMe 和 HSEt 反应合成了碲 (II) 二甲硫醇盐 Te(SMe)(2) 和二乙硫醇碲 (II) Te(SEt)(2)。在固态下,Te(SMe)(2) 表现出甲基相对于 TeS2 平面的顺式构象 - 这是非官能化有机三硫族化合物前所未有的情况 - 而 Te(SEt)(2) 显示出反式构象。对 Te(SMe)(2) 和 Te(SEt)(2) 进行的从头算计算表明,顺式和反式构象器代表势能表面上的最小值,并由分子内 pi 型 n(S)-sigma 稳定* (Te-S') 轨道相互作用。在固态下,每个化合物的分子通过两个中心对称的 Te2S2 单元与它们的两个相邻单元相连,导致四配位 Te 原子具有扭曲的梯形构型。虽然分子间 Te...S 距离在序列 R = Me < Et < iPr < tBu 中增加,但共价 Te-S 键的长度以相同的顺序减少,这是由于分子间