31P NMR probes of chemical dynamics: paramagnetic relaxation enhancement of the (1)H and (31)P NMR resonances of methyl phosphite and methylethyl phosphate anions by selected metal complexes.
31P NMR probes of chemical dynamics: paramagnetic relaxation enhancement of the (1)H and (31)P NMR resonances of methyl phosphite and methylethyl phosphate anions by selected metal complexes.
复制标题
化学动力学的 31P NMR 探针：通过选定的金属配合物增强亚磷酸甲酯和磷酸甲乙酯阴离子的 (1)H 和 (31)P NMR 共振的顺磁弛豫。
DOI：
10.1021/ic010728w
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发表时间：
2001
影响因子：
4.6
通讯作者：
Crumbliss,AL
中科院分区：
文献类型：
--
作者：
Summers,JS;Hoogstraten,CG;Britt,RD;Base,K;Shaw,BR;Ribeiro,AA;Crumbliss,AL
亚磷酸甲酯（（CH_3 O）P（H）（O）_2-; MeOPH）和磷酸甲乙酯（（CH_3 O）P（OCH_2CH_3）（O）_2-; MEP）是一类对顺磁性金属离子具有显著的~（31）PT_2弛豫速率的阴离子配体。由Mn（H2O）62+离子和水溶性锰（III）卟啉（MnIIITMPyP 5+）引起的31 P NMR谱线增宽的温度依赖性表明顺磁弛豫增强的程度是阴离子探针与顺磁中心物理接触的速率的量度（即，进入内配位层）;即πΔνpar=kassn[M]，其中Δν巴黎为顺磁性和反磁性溶液中共振线宽之差，kassn为磷配体与金属M缔合的二级速率常数。比较31 PT 1和T2弛豫增强表明，金属离子的快速T2弛豫是由与电子自旋的标量相互作用引起的。MeOPH（1H-P）的磷结合质子通过MnIIITMPyP 5+的弛豫在大部分可观察到的温度范围内显示出中间交换动力学。1H − PT 2增强的场强依赖性和31 PT 2的独立性支持这些断言。与31 PT 2的情况一样，1H-PT 2弛豫增强是由于电子自旋的标量相互作用。核磁共振数据的标量耦合解释得到了Mn（H2O）62+与亚磷酸甲酯的P-氘代类似物CH 3 OP（2 H）（O）2-相互作用的脉冲EPR研究的支持。电子与~（31）P和~ 2 H核的标量耦合常数分别为4.6和0.10MHz。与此相反，顺磁性离子的甲氧基和乙氧基1H共振的MeOPH和MEP的影响是弱的，证据表明，这些核的弛豫发生的偶极机制。MeOPH和MEP的1H和31 P核的弛豫灵敏度的广泛变化使我们能够研究所观察到的核与顺磁中心之间的相互作用强度的差异如何影响NMR T2弛豫。我们建议，这些阴离子配体探针可用于研究锰配合物的配体交换反应性，而不需要变温研究。当满足以下条件时，31 PT 2由化学缔合动力学确定：（T2 M，P/T2 M，H）（ΔνP/ΔνHP− 1）< 0.2其中T2 M，PandT 2 M，H是31 P和1H核在探针与金属结合时的横向弛豫时间，Δν P和Δν HP分别是31 P和1H −P核的顺磁线加宽。我们认为，利用EPR和NMR实验结果，可以估算一般金属配合物的T_2M，P/T_2M，H比值。
Methyl phosphite ((CH3O)P(H)(O)2-; MeOPH) and methylethyl phosphate ((CH3O)P(OCH2CH3)(O)2-; MEP) are two members of a class of anionic ligands whose31PT2relaxation rates are remarkably sensitive to paramagnetic metal ions. The temperature dependence of the31P NMR line broadenings caused by the Mn(H2O)62+ion and a water-soluble manganese(III) porphyrin (MnIIITMPyP5+) indicates that the extent of paramagnetic relaxation enhancement is a measure of the rate at which the anionic probes come into physical contact with the paramagnetic center (i.e., enter the inner coordination shell); that is, πΔνpar=kassn[M], where Δνparis the difference between the line widths of the resonance in paramagnetic and diamagnetic solutions, andkassnis the second-order rate constant for association of the phosphorus ligand with the metal, M. Comparison of the31PT1andT2relaxation enhancements shows that rapidT2relaxation by the metal ion is caused by scalar interaction with the electronic spin. Relaxation of the phosphorus-bound proton of MeOPH (1H−P) by MnIIITMPyP5+displayed intermediate exchange kinetics over much of the observable temperature range. The field strength dependence of1H−PT2enhancement and the independence of the31PT2support these assertions. As in the case of the31PT2, the1H−PT2relaxation enhancement results from scalar interaction with the electronic spin. The scalar coupling interpretation of the NMR data is supported by a pulsed EPR study of the interactions of Mn(H2O)62+with the P-deuterated analogue of methyl phosphite, CH3OP(2H)(O)2-. The electron to31P and2H nuclear scalar coupling constants were found to be 4.6 and 0.10 MHz, respectively. In contrast, the effects of paramagnetic ions on the methoxy and ethoxy1H resonances of MeOPH and MEP are weak, and the evidence suggests that relaxation of these nuclei occurs by a dipolar mechanism. The wide variation in the relaxation sensitivities of the1H and31P nuclei of MeOPH and MEP permits us to study how differences in the strengths of the interactions between an observed nucleus and a paramagnetic center affect NMRT2relaxations. We propose that these anion ligand probes may be used to study ligand-exchange reactivities of manganese complexes without requiring variable temperature studies. The31PT2is determined by chemical association kinetics when the following condition is met: (T2M,P/T2M,H)(ΔνP/ΔνHP− 1) < 0.2 whereT2M,PandT2M,Hare the transverse relaxation times of the31P and1H nuclei when the probe is bound to the metal, and ΔνPand ΔνHPare the paramagnetic line broadenings of the31P and1H−P nuclei, respectively. We assert that the ratioT2M,P/T2M,Hcan be estimated for a general metal complex using the results of EPR and NMR experiments.