Theoretical study of formation of pyridines by interaction of a cobaltacyclopentadiene with model nitriles (hydrogen cyanide or trifluoroacetonitrile): Electronic effects of nitriles on the reaction mechanism
Theoretical study of formation of pyridines by interaction of a cobaltacyclopentadiene with model nitriles (hydrogen cyanide or trifluoroacetonitrile): Electronic effects of nitriles on the reaction mechanism
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DOI：
10.1016/j.jorganchem.2010.06.015
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发表时间：
2010-09-01
影响因子：
2.3
通讯作者：
Koga, Nobuaki
中科院分区：
文献类型：
--
作者：
Dahy, AbdelRahman A.;Koga, Nobuaki
用B3 LYP和CCSD（T）方法对HCN与（η（5）-β）环戊二烯钴（1）的反应进行了理论计算。由于它是配位不饱和的，1在三重态比在单重态更稳定。然而，当HCN与1相互作用时，单线态变得更稳定，并且C N键插入单线态的Co-C键中，形成氮杂钴并环庚三烯中间体（4aS）。这种反应可以遵循4aS的两个过程。一种是还原消除，得到保留单重态自旋的eta（4）-吡啶络合物（5aS）。另一种是自旋态转变为三重态，形成更稳定的三重态氮杂钴杂环庚三烯（4 T），然后发生还原消除，得到三重态eta（2）-吡啶络合物（5 bT）。单重态的eta（4）-吡啶络合物（5 bS）是最稳定的吡啶络合物，并且含有与Co原子配位的吡啶环的四个碳原子。5aS或5 bT的重排反应得到5 bS涉及自旋状态的变化。因此，该机制表现出两态反应性。该机理与乙腈的反应不同，在乙腈的反应中，MeCN与钴环戊二烯1的[4 + 2]环加成以单线态发生，而不是插入Co-C键和还原消除。这种差异可以用前线轨道能量的差异来解释，因此给电子基团有利于[4 + 2]环加成，而吸电子基团有利于C N键插入Co-C键。这通过对CF 3CN的反应的计算得到证实。(C)2010年爱思唯尔B。版权所有© 2016
Theoretical calculations on the reaction of HCN with (eta(5)-cyclopentadienyl) cobaltacyclopentadiene (1) were made by using B3LYP and CCSD(T) methods. Since it is coordinatively unsaturated, 1 is more stable in the triplet state than in the singlet state. However, when HCN interacts with 1, the singlet state becomes more stable, and the C N bond inserts into the Co-C bond in the singlet state to form an azacobaltacycloheptatriene intermediate (4aS). The reaction can follow two courses from 4aS. One is reductive elimination to give an eta(4)-pyridine complex (5aS) that retains a singlet spin state. The other involves a change in spin state to the triplet state to form the more stable triplet state azacobaltacycloheptatriene (4T), from which reductive elimination takes place to give a triplet eta(2)-pyridine complex (5bT). The eta(4)-pyridine complex in the singlet state (5bS) is the most stable pyridine complex and contains four carbon atoms of the pyridine ring coordinated to the Co atom. The rearrangement reactions of 5aS or 5bT to give 5bS involve a change in the spin state. The mechanism therefore shows two-state reactivity. This mechanism is different from the reaction of acetonitrile, in which [4 + 2] cycloaddition of MeCN to cobaltacyclopentadiene 1 takes place in the singlet state instead of insertion into the Co-C bond and reductive elimination. This difference can be rationalized in terms of the difference in the energies of the frontier orbitals, so that an electron-donating group favors [4 + 2] cycloaddition and an electron-withdrawing group favors insertion of the C N bond into the Co-C bond. This was confirmed by calculations on the reactions of CF3CN. (C) 2010 Elsevier B. V. All rights reserved.