Oxorhenium(V) Complexes with Pyrazole Based Aryloxide Ligands and Application in Olefin Epoxidation

We synthesized and characterized a set of new oxorhenium(V) complexes coordinated by various pyrazole containing phenol (L1−L3) and naphthol ligands (L4−L7). Depending on the starting material, we were able to selectively synthesize monosubstituded or disubstituted complexes of the type [ReOBr2L(PPh3)] (1−7; L = L1−L7) and [ReOClL2] (L = L1 8; L2 9; L4 10; L6 11), respectively. All complexes are stable to air and moisture, both in solid state as well as in solution. Furthermore, the cationic oxorhenium(V) complex [ReO(L1)2(NCMe)](OTf) (8a) was obtained upon chloride abstraction with silver triflate from 8. All new complexes were able to catalyze the epoxidation of cis-cyclooctene in yields up to 64%. The ease of preparation and their tolerance to air and moisture, as well as the simple ligand modifications, make them an interesting class of novel catalysts. An attempted reduction of perchlorate ClO4− with complex 8 was unsuccessful. Molecular structures of complexes 1, 4, 6, 7, 8, 8a, 10, and 11 were determined by single crystal X-ray diffraction analyses.

本研究合成并表征了一系列新型氧化铑(V)配合物，这些配合物由多种含吡唑基团的酚类配体（L1−L3）和萘酚类配体（L4−L7）所配位。根据起始原料的不同，我们能够选择性地合成单取代或双取代的[ReOBr2L(PPh3)]型（1−7；L = L1−L7）和[ReOClL2]型（L = L1 8；L2 9；L4 10；L6 11）配合物。所有配合物在固态和溶液状态下均对空气和水分稳定。此外，通过用氯化银三氟化物从化合物8中提取氯离子，成功获得了阳离子氧化铑(V)配合物[ReO(L1)2(NCMe)](OTf)（8a）。所有新合成的配合物均能催化顺式环辛烯的环氧化反应，产率高达64%。其制备的简便性、对空气和水分的耐受性，以及配体的简单修饰，使它们成为一类引人注目的新型催化剂。尝试用化合物8还原高氯酸根ClO4−未能成功。通过单晶X射线衍射分析确定了配合物1、4、6、7、8、8a、10和11的分子结构。