Cycloadditions and Retrocycloadditions of Niobium Imido Complexes: An Experimental and Computational Mechanistic Study
Cycloadditions and Retrocycloadditions of Niobium Imido Complexes: An Experimental and Computational Mechanistic Study
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铌亚氨基配合物的环加成和逆环加成：实验和计算机理研究
DOI：
10.1021/acs.inorgchem.2c00428.s001
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发表时间：
2022
影响因子：
4.6
通讯作者：
Arnold, J
中科院分区：
文献类型：
--
作者：
1. Jain, A.;Fostvedt, J. I.;Kriegel, B. M.;Grant, L. N.;Small, D. W.;Bergman, R. G.;Arnold, J
我们证明了β-二酮亚胺基负载的铌（III）酰亚胺配合物与烷基叠氮化物之间的反应性，以形成四氮杂茂配合物（BDI）Nb（NtBu）（RNNNNR）（BDI =N，N-双（2，6-二异丙基苯基）-3，5-二甲基-β-二酮亚胺基; R =环己基（1），苄基（2））。有趣的是，四氮烯配合物1和2可以通过加入适当的烷基叠氮化物相互转化，可能是通过一系列协同的[3 + 2]环加成和逆环加成反应，其中形成π-负载的双（酰亚胺）中间体。在加入烷基异腈后捕获双（亚氨基）中间体，得到五配位双（亚氨基）配合物（BDI）Nb（NtBu）（NCy）（CNR）（R =叔丁基（4a），环己基（4 b））。采用密度泛函理论和密度泛函紧束缚（DFTB）两种计算方法计算了这一多步转变的势能面上的最低能量路径。反应路径计算个别环加成或逆环加成过程沿着的多步反应途径表明，这些转换发生通过一个协调一致的，但高度异步的机制，其中两个键断裂或-使事件不同时发生。在这项工作中使用的DFTB方法突出了它的优点和实用性，研究过渡金属系统。
We demonstrate reactivity between a β-diketiminate-supported niobium(III) imido complex and alkyl azides to form niobatetrazene complexes (BDI)Nb(NtBu)(RNNNNR) (BDI =N,N-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate; R = cyclohexyl (1), benzyl (2)). Intriguingly, niobatetrazene complexes1and2can be interconverted via addition of an appropriate alkyl azide, likely through a series of concerted [3 + 2] cycloaddition and retrocycloaddition reactions in which π-loaded bis(imido) intermediates are formed. The bis(imido) intermediates were trapped upon addition of alkyl isocyanides to yield five-coordinate bis(imido) complexes (BDI)Nb(NtBu)(NCy)(CNR) (R =tert-butyl (4a), cyclohexyl (4b)). Two computational methods─density functional theory and density functional tight binding (DFTB)─were employed to calculate the lowest energy pathway across the potential energy surface for this multistep transformation. Reaction path calculations for individual cycloaddition or retrocycloaddition processes along the multistep reaction pathway showed that these transformations occur via a concerted, yet highly asynchronous mechanism, in which the two bond-breaking or -making events do not occur simultaneously. The use of the DFTB method in this work highlights its advantages and utility for studying transition metal systems.