Kinetic determination of transition metal-alkyl bond dissociation energies: application to organocobalt compounds related to B12 coenzymes
Kinetic determination of transition metal-alkyl bond dissociation energies: application to organocobalt compounds related to B12 coenzymes
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DOI：
10.1021/ja00366a046
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发表时间：
1982-05
影响因子：
15
通讯作者：
T. T. Tsou-T.;Loots Melanie;J. Halpern
中科院分区：
文献类型：
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作者：
T. T. Tsou-T.;Loots Melanie;J. Halpern
尽管它们在各种有机金属、生化和催化过程中具有广泛的意义，但很少有过渡金属-烷基键解离能得到可靠的测定，这在很大程度上反映了用于此类测定的方法的有限适用性。本文所述的研究最终揭示了某些有机钴化合物的热分解是通过钴碳键的均解离解进行的，并证明了这种键的离解能可以从动力学测量中推断出来。这些有机钴化合物与辅酶B12类似物4,5的相关性，以及该方法测定其他过渡金属-烷基键解离能的进一步潜力，增强了人们对这些研究结果的兴趣。我们的研究涉及有机钴希夫碱化合物[py (saloph) Co-R]（其中py=吡啶，saloph= myv -双（水杨基）-邻苯二胺，R=烷基或苄基）的热分解，在吡啶溶液中，在低于100℃的温度下，在有效的自由基陷阱（如氢供体，«-C8H17SH（缩写为XH））的存在下，这些化合物的热分解速度可以方便地测量。当R= -丙基或异丙基（即含氢的烷基）时，反应生成丙烯和丙烷的混合物，表现出与方案1相对应的动力学和产物分布，其中[ComR]=[py (saloph) Co-C3H7]和[Co11]=[py (saloph) Con]。7、8
Despite their widespread significance for various organometallic, biochemical, and catalytic processes, 1 few transition-metal-alkyl bond dissociation energies have been determined reliably, reflecting in considerable degree the limited applicability of the methods available for such determinations. 2, 3 The studies described in this communication reveal conclusively that the thermal decomposition of certain organocobalt compounds proceeds via homolytic cobalt-carbon bond dissociation and demonstrate that the dis-sociation energies of such bonds can be deduced from kinetic measurements. Interest in the results of these studies is enhanced by the relevance of these organocobalt compounds as coenzyme B12 analogues4, 5 andby the further potential of the method for the determination of other transition-metal-alkyl bond dissociation energies. Our studies relate to the thermal decompositions of organocobalt Schiff base compounds [py (saloph) Co-R](where py= pyridine, saloph= MyV-bis (salicylidene)-o-phenylenediamine and R= alkyl or benzyl), which were found to proceedat conveniently meas-urable rates in pyridine solution6 at temperatures below 100 C in the presence of an efficient radical trap such as the hydrogen donor,«-C8H17SH (abbreviated XH). When R=«-propyl or isopropyl (ie, an alkyl containing a ß hydrogen), the reaction yielded a mixture of propene and propane, exhibiting the kinetics and productdistribution corresponding toScheme I where [ComR]=[py (saloph) Co-C3H7] and [Co11]=[py (saloph) Con]. 7, 8