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Reactions of the Ni(0) Compound Ni(PPh3)4 with Unactivated Alkyl Halides: Oxidative Addition Reactions Involving Radical Processes and Nickel(I) Intermediates
Organometallics ( IF 2.5 ) Pub Date : 2018-07-20 , DOI: 10.1021/acs.organomet.8b00244 Ryley Kehoe 1 , Markshun Mahadevan 1 , Adeela Manzoor 1 , Gillian McMurray 1 , Patrick Wienefeld 1 , Michael C. Baird 1 , Peter H. M. Budzelaar 2
Organometallics ( IF 2.5 ) Pub Date : 2018-07-20 , DOI: 10.1021/acs.organomet.8b00244 Ryley Kehoe 1 , Markshun Mahadevan 1 , Adeela Manzoor 1 , Gillian McMurray 1 , Patrick Wienefeld 1 , Michael C. Baird 1 , Peter H. M. Budzelaar 2
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Reactions of the nickel(0) compound NiL4 (L = PPh3) with alkyl halides RX involve initial inner-sphere halogen atom abstraction from the alkyl halides to form alkyl radicals R· and halonickel(I) metalloradical species NiX(PPh3)2,3. The radical pairs then undergo combination within the solvent cage to give the square planar nickel(II) compounds NiRX(PPh3)2. Radical intermediacy is demonstrated persuasively by observations that the relative rates vary in the orders tert-butyl > sec-butyl > n-butyl and RI > RBr > RCl, while density functional theory calculations indicate that the radical mechanism provides a lower energy pathway than do alternative, more conventional pathways. The product of the reaction of Ni(PPh3)4 with methyl iodide, NiMeI(PPh3)2, decomposes in solution to ethane and NiI(PPh3)2,3, but when RX = EtI, n-BuI, sec-BuI, tert-BuI, the alkyl-nickel products undergo rapid β-hydrogen elimination to give the hydride NiHI(PPh3)2 plus the corresponding alkene(s). Reactions also occur in which a portion of the alkyl radicals diffuses from the solvent cage and abstracts hydrogen from NiHI(PPh3)2 to form alkanes RH and Ni(I) species NiI(PPh3)2. As a result, NiHI(PPh3)2 is invariably a minor product while the major products are alkanes RH, alkenes R–H, and NiI(PPh3)2. Hydride NiHI(PPh3)2 is found to decompose to H2 and NiI(PPh3)2 but is stable at low temperatures where it exhibits unusual NMR behavior because of exchange involving free PPh3 and the bis- and trisphosphine species, NiHI(PPh3)2 and NiHI(PPh3)3. Present in all of the reactions are paramagnetic, substitution-labile Ni(I) metalloradical species. As a result, resonances of PPh3, ethylene, and the smaller iodoalkenes are generally broad and shifted because of exchange between free and coordinated ligands.
中文翻译：
Ni（0）化合物Ni（PPh 3）4与未活化的烷基卤的反应：涉及自由基过程和镍（I）中间体的氧化加成反应
镍（0）化合物NiL 4（L = PPh 3）与卤代烷RX的反应涉及从卤代烷中提取初始的内球卤原子，形成烷基基团R·和卤代酮（I）金属原子NiX（PPh 3）。2,3。然后将这些自由基对在溶剂笼中进行合并，以得到方形的平面镍（II）化合物NiRX（PPh 3）2。通过观察到相对速率以叔丁基>仲丁基> n的顺序变化而有说服力地证明了自由基的中介作用-丁基和RI> RBr> RCl，而密度泛函理论计算表明，与其他更常规的途径相比，自由基机理提供的能量途径更低。的Ni（PPH的反应的产物3）4用甲基碘，NiMeI（PPH 3）2，在分解溶液中的乙烷和NII（PPH 3）2,3，但是当RX = ETI，Ñ -BuI，仲- BuI，叔-BuI，烷基镍产物经过快速的β-氢消除，得到氢化物NiHI（PPh 3）2加上相应的烯烃。还发生反应，其中一部分烷基自由基从溶剂笼中扩散出来，并从NiHI（PPh 3）2提取氢，从而形成链烷烃RH和Ni（I）物种NiI（PPh 3）2。结果，NiHI（PPh 3）2始终是次要产物，而主要产物是烷烃RH，烯烃RH和NiI（PPh 3）2。发现氢化物NiHI（PPh 3）2分解为H 2和NiI（PPh 3）2但在低温下稳定，由于涉及游离PPh 3以及双-和三膦物种NiHI（PPh 3）2和NiHI（PPh 3）3的交换，它表现出不同寻常的NMR行为。存在于所有反应中的是顺磁性，不稳定取代的Ni（I）金属原子。结果，由于自由的和配位的配体之间的交换，PPh 3，乙烯和较小的碘代烯烃的共振通常是宽泛的并且发生位移。
更新日期：2018-07-21
中文翻译：
Ni（0）化合物Ni（PPh 3）4与未活化的烷基卤的反应：涉及自由基过程和镍（I）中间体的氧化加成反应
镍（0）化合物NiL 4（L = PPh 3）与卤代烷RX的反应涉及从卤代烷中提取初始的内球卤原子，形成烷基基团R·和卤代酮（I）金属原子NiX（PPh 3）。2,3。然后将这些自由基对在溶剂笼中进行合并，以得到方形的平面镍（II）化合物NiRX（PPh 3）2。通过观察到相对速率以叔丁基>仲丁基> n的顺序变化而有说服力地证明了自由基的中介作用-丁基和RI> RBr> RCl，而密度泛函理论计算表明，与其他更常规的途径相比，自由基机理提供的能量途径更低。的Ni（PPH的反应的产物3）4用甲基碘，NiMeI（PPH 3）2，在分解溶液中的乙烷和NII（PPH 3）2,3，但是当RX = ETI，Ñ -BuI，仲- BuI，叔-BuI，烷基镍产物经过快速的β-氢消除，得到氢化物NiHI（PPh 3）2加上相应的烯烃。还发生反应，其中一部分烷基自由基从溶剂笼中扩散出来，并从NiHI（PPh 3）2提取氢，从而形成链烷烃RH和Ni（I）物种NiI（PPh 3）2。结果，NiHI（PPh 3）2始终是次要产物，而主要产物是烷烃RH，烯烃RH和NiI（PPh 3）2。发现氢化物NiHI（PPh 3）2分解为H 2和NiI（PPh 3）2但在低温下稳定，由于涉及游离PPh 3以及双-和三膦物种NiHI（PPh 3）2和NiHI（PPh 3）3的交换，它表现出不同寻常的NMR行为。存在于所有反应中的是顺磁性，不稳定取代的Ni（I）金属原子。结果，由于自由的和配位的配体之间的交换，PPh 3，乙烯和较小的碘代烯烃的共振通常是宽泛的并且发生位移。
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