Mechanistic studies of the transfer dehydrogenation of cyclooctane catalyzed by iridium bis(phosphinite) p-XPCP pincer complexes
Mechanistic studies of the transfer dehydrogenation of cyclooctane catalyzed by iridium bis(phosphinite) p-XPCP pincer complexes
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DOI：
10.1021/ja048393f
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发表时间：
2004-08-04
影响因子：
15
通讯作者：
Brookhart, M
中科院分区：
文献类型：
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作者：
Göttker-Schnetmann, I;Brookhart, M
双（亚膦酸盐）PCP铱螯合物（p-XPCP）IrHCl (5a- F) [X = MeO (5a), Me (5b), H (5c)， F(5d), C6F5 (5e), Ar-F（= 3,5-双（三氟甲基）苯基）（5f）]与NaOtBu在纯环辛烷（COA）中反应生成各自的（p-XPCP）IrH2配合物4a-f和环辛烯（COE）烯烃配合物（p-XPCP）lr(COE) （6a-f）在23度下的1:1混合物。在较高温度下，配合物4和6由于COA与自由COE （6 + COA = 4 + 2COE）的简并转移脱氢而达到平衡，正如温度相关的平衡常数和80°c下的自旋饱和转移实验所表明的那样。在此温度下，COE配合物在核磁共振时间尺度上与自由COE交换，缺电子越多的配合物交换COE的速度越快。交换是游离的，在[COE]中是零阶的。进一步分析表明，在低至- 100℃的温度下，配合物4f对COE进行了化学加氢反应，从而分离出了4f + 2COE—bbb6f + COA的反反应，中间有两个异构体配合物（p-(ArPCP)- p- f）lr(H)(2)(COE) （8f, 8f'）。在-100°c下，与过氘化配合物4f-d（38）进行COE氘化，导致氢进入配合物8f、8f′-d（38）的水合位点，但没有进入配合物4f-d（38）的水合位点，从而使COE在配合物8f、8f′中的迁移插入可逆，并通过配合物4f的速率决定COE配位，从而实现整体COE氘化。
Reaction of bis(phosphinite) PCP iridium pincer complexes (p-XPCP)IrHCl (5a-f) [X = MeO (5a), Me (5b), H (5c), F (5d), C6F5 (5e), Ar-F(= 3,5-bis(trifluoromethyl)phenyl) (5f)] with NaOtBu in neat cyclooctane (COA) generates 1:1 mixtures of the respective (p-XPCP)IrH2 complexes 4a-f and the cyclooctene (COE) olefin complexes (p-XPCP)lr(COE) (6a-f) at 23 degreesC. At higher temperatures, complexes 4 and 6 are equilibrated because of the degenerate transfer dehydrogenation of COA with free COE (6 + COA = 4 + 2COE), as was shown by temperature-dependent equilibrium constants and spin saturation transfer experiments at 80 degreesC. At this temperature, the COE complexes 6 exchange with free COE on the NMR time scale with the more electron-deficient complexes 6 exchanging COE faster. The exchange is dissociative and zero order in [COE]. Further analysis reveals that the stoichiometric hydrogenation of COE by complex 4f, and thus the separated back reaction 4f + 2COE --> 6f + COA proceeds at temperatures as low as - 100 degreesC with the intermediacy of two isomeric complexes (p-(ArPCP)-P-F)lr(H)(2)(COE) (8f, 8f'). COE deuteration with the perdeuterated complex 4f-d(38) at -100 degreesC results in hydrogen incorporation into the hydridic sites of complexes 8f,8f'-d(38) but not in the hydriclic sites of complex 4f-d(38), thus rendering COE migratory insertion in complexes 8f,8f' reversible and COE coordination by complex 4f rate-determining for the overall COE deuteration.