A NEW TYPE OF TRANSITION-METAL DIMER BASED ON A HEXAPHOSPHINE LIGAND SYSTEM - CO2(CO)4(EHTP)2+ (EHTP = (ET2PCH2CH2)2PCH2P(CH2CH2PET2)2)
A NEW TYPE OF TRANSITION-METAL DIMER BASED ON A HEXAPHOSPHINE LIGAND SYSTEM - CO2(CO)4(EHTP)2+ (EHTP = (ET2PCH2CH2)2PCH2P(CH2CH2PET2)2)
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DOI：
10.1021/ja00311a034
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发表时间：
1985-01-01
影响因子：
15
通讯作者：
MARQUES, EC
中科院分区：
文献类型：
--
作者：
ASKHAM, FR;STANLEY, GG;MARQUES, EC
本文报道了一个新的六元膦配体体系（Et_2PCH_2CH_2）_2PCH_2P（CH_2CH_2PEt_2）_2，1的合成和表征。该配体具有三螯合和桥接两种过渡金属的能力，无论是在封闭模式的MM键合几何结构中，还是在两种金属原子相距6-7 A的开放模式构型中。1与2当量的CoCl 2反应，最初以高产率产生顺磁性双核红棕色Co（II）化合物Co2 Cl 4（eHTP），4，其中eHTP= 1。4的扩展X射线吸收精细结构（EXAFS）谱显示Co-P和Co-Cl键距在2.2-2.4- 1.0范围内，没有Co-Co接触距离小于4.0 μ m，表明4处于开模几何结构。静置时，4解离两个氯配体，形成绿色顺磁性Co2 Cl 2（eHTP）2+络合物5，其从反应混合物中沉淀出来，或者作为氯化物，或者如果使用额外当量的CoCl 2，则作为CoCl 42 '盐。5的CoC_（142）~-盐的EXAFS谱与4的非常相似，表明5也是一种开模几何构型。4或5（单独或混合）与H2/CO（33%CO）和额外当量的CoCl 2在50巴和80 ℃下反应，高产率地形成黄绿色抗磁性Co（I）双核羰基/eHTP络合物[Co 2（CO）4（eHTP）2+][CoCl 42-]，6a，其可以与NaPF 6水溶液复分解，得到黄色PF 6-盐，6 b。6已通过31 P NMR、EXAFS、质谱、IR和晶体结构表征。6 B的晶体属于单斜晶系空间群C2/c，晶胞参数a= 26.464（4）A，B= 12.562（2）A，c= 14.380（3）A，λ = 99.04（1），V= 4721（3）A3，Z= 4。对结构进行精制，得到R= 0.070和Rw= 0.106。该分子位于2重轴上，穿过eHTP配体的桥接亚甲基。该络合物具有eHTP配体的中心双（膦基）甲烷部分，其采用独特的倒置配位几何结构，以得到具有由6.697（1）A分离的两个钴原子的开放模式络合物。钴原子有一个扭曲的三角双锥几何结构，一个羰基配体和两个末端的eHTP配体的磷原子在赤道plane.尽管大量的兴趣，利用过渡金属二聚体和集群作为均相催化剂，很少有这样的系统已被发现，1而更少havebeen被证明是更有效的比单核系统已经知道。两个主要的问题，传统上与研究多核络合物已经在一个逐步和合理的方式合成新的物种和这些多核系统往往容易碎裂成单核络合物，这可能会导致混乱的性质反应物种在溶液中的困难。
The synthesis and characterization of a new hexa-iert-phosphine ligand system,(Et2PCH2CH2) 2PCH2P (CH2CH2PEt2) 2, 1, is described. This ligand has the ability to both tris-chelate and bridge two transition metals, either in a closed-mode, MM bonding geometry, or in an open-mode configuration in which the two metal atoms are 6-7 A apart. Reaction of 1 with 2 equiv of CoCl2 initially produces, in high yields, the paramagnetic, binuclear, red-brown Co (II) compound, Co2Cl4 (eHTP), 4, where eHTP= 1. An Extended X-ray Absorption Fine Structure (EXAFS) spectrum of 4 shows Co-P and Co-Cl bond distances in the 2.2-2.4-Á region and no Co-Co contactdistance less than 4, 0 Á, indicating that 4 is in an open-mode geometry. On standing, 4 dissociates twochloride ligands to form the green, paramagnetic Co2Cl2 (eHTP) 2+ complex, 5, which precipitates out of the reaction mixture, either as the chloride or, if an extra equivalent of CoCl2 is used, the CoCl42'salt. The EXAFS spectrum on the CoC142~ salt of 5 is very similar to thatof 4, indicating that 5 is also in an open-mode geometry. Reaction of 4 or 5 (alone or mixed) with H2/CO (33% CO) and an extra equivalent of CoCl2 at 50 bar and 80 C forms, in high yields, the yellow-green, diamagneticCo (I) binuclear carbonyl/eHTP complex,[Co2 (CO) 4 (eHTP) 2+][CoCl42 “], 6a, which can be metathesized with aqueous NaPF6 to give the yellow PF6~ salt, 6b. 6 has been characterized by and 31P NMR, EXAFS, mass spectroscopy, IR, and a crystal structure. Crystals of 6b belong tothe monoclinic space group C2/c, with unit cell parameters a= 26.464 (4) A, b= 12.562 (2) A, c= 14.380 (3) A, ß= 99.04 (1), V= 4721 (3) A3, and Z= 4. The structure was refined to give R= 0.070 and Rw= 0.106. The molecule lies on a 2-fold axis, passing through the bridging methylene group of the eHTP ligand. The complex has the central bis (phosphino) methane portion of the eHTP ligand adopting a unique inverted coordination geometry to give an open-mode complex with the two cobalt atoms separated by 6.697 (1) A. The cobalt atoms have a distorted trigonal-bipyramidal geometry with one carbonyl ligand and two terminal phosphorus atoms of the eHTP ligand in the equatorial plane.Despite the large amount of interest in utilizing transition-metal dimers and clusters as homogeneous catalysts, few such systems have been discovered, 1 while even fewer havebeen demonstrated to be more effective than mononuclear systems already known. Two major problems traditionally associated with research into polynuclear complexeshave been difficulties insynthesizing new species in a stepwise and rational fashion and the often ready fragmentation of these polynuclear systems into mononuclear complexes which can lead to confusion about the nature of the reactive species in solution.