A concerted mechanism for the transfer of the thiophosphinoyl group from aryl dimethylphosphinothioate esters to oxyanionic nucleophiles in aqueous solution.
A concerted mechanism for the transfer of the thiophosphinoyl group from aryl dimethylphosphinothioate esters to oxyanionic nucleophiles in aqueous solution.
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DOI：
10.1021/ja0501565
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发表时间：
2005-05
影响因子：
15
通讯作者：
I. Onyido;K. Świerczek;Jamie W. Purcell;A. Hengge
中科院分区：
文献类型：
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作者：
I. Onyido;K. Świerczek;Jamie W. Purcell;A. Hengge
关于芳基硫代膦酸酯水解的早期工作导致了矛盾的机理结论。为了解决这种机制的模糊性，我们已经测量了线性自由能关系（β（nuc）和β（lg））和动力学同位素效应的含氧阴离子与芳基二甲基膦硫代酸酯的反应。对于亲核试剂对4-硝基苯基二甲基硫代膦酸酯的攻击，对于酚盐亲核试剂，β（nuc）= 0.47 +/- 0.05（pK（a）或= 11）。跨越离去基团（4-硝基苯酚盐，pK（a）7.14）的pK（a）范围内的曲线线性表明存在协同机制。更碱性的亲核试剂的β（nuc）值低得多，表明在限速亲核攻击之前去溶剂化步骤的重要性。一系列取代的芳基二甲基硫代膦酸酯与亲核试剂HO（-）（β = -0.54 +/-0.03）和PhO（-）（β = -0.52 +/-0.09）的反应给出了相同的β值（lg）。一个显着更好的Hammett相关性得到与西格玛（-）比与西格玛或西格玛度，如预期的过渡态涉及限速裂解的P-OAr键。在键断裂位置的（18）O KIE（（18）k = 1.0124 +/- 0.0008）表明P-O键断裂约40%，离去基团的（15）N KIE（（15）k = 1.0009 +/- 0.0003）表明离核物在过渡态携带约三分之一的负电荷。因此，LFER和KIE数据都与协同反应一致，不支持分步机制。
Earlier work on the hydrolysis of aryl phosphinothioate esters has led to contradictory mechanistic conclusions. To resolve this mechanistic ambiguity, we have measured linear free energy relationships (beta(nuc) and beta(lg)) and kinetic isotope effects for the reactions of oxyanions with aryl dimethylphosphinothioates. For the attack of nucleophiles on 4-nitrophenyl dimethylphosphinothioate, beta(nuc) = 0.47 +/- 0.05 for phenoxide nucleophiles (pK(a) or= 11). Linearity of the plot in the range that straddles the pK(a) of the leaving group (4-nitrophenoxide, pK(a) 7.14) is indicative of a concerted mechanism. The much lower value of beta(nuc) for the more basic nucleophiles reveals the importance of a desolvation step prior to rate-limiting nucleophilic attack. The reactions of a series of substituted aryl dimethylphosphinothioate esters give the same value of beta(lg) with the nucleophiles HO(-) (beta= -0.54 +/- 0.03) and PhO(-) (beta = -0.52 +/- 0.09). A significantly better Hammett correlation is obtained with sigma(-) than with sigma or sigma degrees , as expected for a transition state involving rate-limiting cleavage of the P-OAr bond. The (18)O KIE at the position of bond fission ((18)k = 1.0124 +/- 0.0008) indicates the P-O bond is approximately 40% broken, and the (15)N KIE in the leaving group ((15)k = 1.0009 +/- 0.0003) reveals the nucleofuge carries about a third of a negative charge in the transition state. Thus, both the LFER and KIE data are consistent with a concerted reaction and disfavor a stepwise mechanism.