Bhirud Vinesh A, Ehresmann Justin O, Kletnieks Philip W, Haw James F, Gates Bruce C
Department of Chemical Engineering and Materials Science, University of California at Davis, California 95616, USA.
Langmuir. 2006 Jan 3;22(1):490-6. doi: 10.1021/la052268f.
Mononuclear rhodium complexes with reactive olefin ligands, supported on MgO powder, were synthesized by chemisorption of Rh(C(2)H(4))(2)(C(5)H(7)O(2)) and characterized by infrared (IR), (13)C MAS NMR, and extended X-ray absorption fine structure (EXAFS) spectroscopies. IR spectra show that the precursor adsorbed on MgO with dissociation of acetylacetonate ligand from rhodium, with the ethylene ligands remaining bound to the rhodium, as confirmed by the NMR spectra. EXAFS spectra give no evidence of Rh-Rh contributions, indicating that site-isolated mononuclear rhodium species formed on the support. The EXAFS data also show that the mononuclear complex was bonded to the support by two Rh-O bonds, at a distance of 2.18 A, which is typical of group 8 metals bonded to oxide supports. This is the first simple and nearly uniform supported mononuclear rhodium-olefin complex, and it appears to be a close analogue of molecular catalysts for olefin hydrogenation in solution. Correspondingly, the ethylene ligands bonded to rhodium in the supported complex were observed to react with H(2) to form ethane, and the supported complex was catalytically active for the ethylene hydrogenation at 298 K. The ethylene ligands also underwent facile exchange with C(2)D(4), and exposure of the sample to carbon monoxide led to the formation of rhodium gem dicarbonyls.
通过Rh(C₂H₄)₂(C₅H₇O₂)的化学吸附作用，合成了负载在MgO粉末上的带有活性烯烃配体的单核铑配合物，并通过红外光谱（IR）、¹³C固体核磁共振（¹³C MAS NMR）和扩展X射线吸收精细结构（EXAFS）光谱对其进行了表征。红外光谱表明，前驱体吸附在MgO上时，乙酰丙酮配体与铑发生解离，而乙烯配体仍与铑结合，核磁共振光谱证实了这一点。EXAFS光谱没有显示出Rh-Rh相互作用的证据，这表明在载体上形成了位点隔离的单核铑物种。EXAFS数据还表明，单核配合物通过两个Rh-O键与载体结合，键长为2.18 Å，这是第8族金属与氧化物载体结合的典型键长。这是第一个简单且几乎均匀的负载单核铑-烯烃配合物，它似乎是溶液中烯烃加氢分子催化剂的紧密类似物。相应地，观察到负载配合物中与铑结合的乙烯配体与H₂反应生成乙烷，并且负载配合物在298 K下对乙烯加氢具有催化活性。乙烯配体还能与C₂D₄轻松进行交换，并且将样品暴露于一氧化碳会导致形成铑偕二羰基化合物。
