The delta in 18+delta electron complexes: Importance of the metal/ligand interface for the substitutional reactivity of ''Re(0)'' complexes (alpha-diimine(-))Re-I(CO)(3)(X)
The delta in 18+delta electron complexes: Importance of the metal/ligand interface for the substitutional reactivity of ''Re(0)'' complexes (alpha-diimine(-))Re-I(CO)(3)(X)
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DOI：
10.1021/om950500e
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发表时间：
1996-01-09
期刊：
影响因子：
2.8
通讯作者：
Kaim, W
中科院分区：
文献类型：
--
作者：
Klein, A;Vogler, C;Kaim, W
在取代配体如三苯基膦、氰化物或乙腈存在的情况下，通过EPR和循环伏安法系统地研究了电子转移诱导的（α -二亚胺）Re(CO)(3)（Hal）、Hal = Cl和Br配合物中卤化物稳定的影响因素。所采用的-二亚胺是4种异构体双嘧啶（bdz） 3,3'-联吡嗪、2,2'-联吡嗪、2,2'-和4,4'-联嘧啶以及非芳香- -二亚胺1,4-二叔丁基-1,4-二氮-1,3-丁二烯（dab）和1,3-二叔丁基硫二亚胺（sdi）。为了比较，还研究了配合物(L)Re(CO3)Cl、L = 2,2′-联吡啶、1,4,7,10-四氮菲和eta(2)-2,2′，2′-三吡啶，以及新的阳离子物种[(bdz)Re(CO)(3)(CH3CN)]（+）。在进一步的实验中，采用原位EPR光谱电化学方法研究了原型化合物（bpy）Re(CO)(3)Cl在CO2气氛下还原过程中的初级顺磁中间体。取代敏感性与N-14、Re-185、Re-187和P-31 EPR偶联常数反映的金属配位氮中心的pi分子轨道系数无关，而与氧化还原电位无关。因此，在小dab和sdi配体的配合物中发现了最不稳定的体系，尽管它们易于还原。相比之下，这些非芳香族化合物的配合物表现出电化学可逆的单电子氧化，与吸收最大值相比，使我们能够估计两种情况下MLCT激发态重组能的贡献。对于还原性稳定，主要是金属/配体界面上的小但可变且epr可检测的配体到金属的电子（自旋）转移，它决定了18 + δ价电子中间体的激活程度。
The factors determining the electron transfer-induced halide labilization in complexes (alpha-diimine)Re(CO)(3)(Hal), Hal = Cl and Br, were systematically studied via EPR and cyclic voltammetry in the presence of substituting ligands such as triphenylphosphine, cyanide, or acetonitrile. The alpha-diimines employed were the four isomeric bidiazines (bdz) 3,3'-bipyridazine, 2,2'-bipyrazine, and 2,2'- and 4,4'-bipyrimidine and the nonaromatic alpha-diimines 1,4-di-tert-butyl-1,4-diaza-1,3-butadiene (dab) and 1,3-di-tert-butylsulfurdiimine (sdi). For comparison, the complexes (L)Re(CO3)Cl, L = 2,2'-bipyridine, 1,4,7,10-tetraazaphenanthrene, and eta(2)-2,2',2 ''-terpyridine, and the new cationic species [(bdz)Re(CO)(3)(CH3CN)](+) were also investigated. In a further experiment, in situ EPR spectroelectrochemistry was employed to study the primary paramagnetic intermediates during the reduction of the prototype compound, (bpy)Re(CO)(3)Cl, under a CO2 atmosphere. The susceptibility to substitution was found to be dependent not on the redox potential but on the pi molecular orbital coefficients at the metal-coordinating nitrogen centers which are reflected by N-14, Re-185,Re-187, and P-31 EPR coupling constants. The most labile systems were thus found among the complexes of the small dab and sdi ligands, despite their facile reduction. In contrast, the complexes of these nonaromatic compounds showed an electrochemically reversible one-electron oxidation which, in comparison to the absorption maximum, allowed us to estimate contributions to the reorganization energy of the MLCT excited state in two cases. For the reductive labilization, it is primarily the small but variable and EPR-detectable ligand-to-metal electron (spin) transfer at the metal/ligand interface which determines the extent of activation in 18 + delta valence electron intermediates.