【作者】 李金金；

【导师】 李光兴；

【作者基本信息】 华中科技大学 ， 材料物理与化学， 2011， 博士

【摘要】 长期以来,金一直被认为是惰性的,因此其在催化领域的应用研究被忽略。然而,二十世纪八十年代初期,发现金作为催化剂在CO低温氧化和乙烯氢氯化中有非常好的活性,于是人们成功地将金催化剂用于多种反应中,如多相的氧化反应、水煤气转换反应等和均相的C-C键的形成、炔的水合作用和加氢反应等。然而,与其他贵金属催化剂相比较,金催化剂的普适性和通用性研究仍然相对比较局限。其中特别是与多相金的催化相比较,对均相金配合物催化剂的研究还远远不够。在目前金催化剂研究领域中,有关在羰化领域中的研究报道很少,而本课题组在羰化领域研究多年,取得一些成果,所用催化剂包括铜、钴、钯等。而在均相催化反应中,金属配合物催化的甲醇氧化羰化反应最具有代表性,而金与铜为同一族元素,Au（Ⅲ）与Pd（II）具有相同的d8电子结构,于是我们首先以甲醇氧化羰化反应为模板探讨Au（Ⅲ）/Schiff base催化剂的催化性能。在Au（Ⅲ）/Schiff base/CuCl₂催化剂中,经过对一系列Schiff base配体的筛选,发现[AuCl₂（bipy）]Cl/CuCl₂催化剂的活性最高,在120℃,Pco/Po2=2:1,P总=3.0MPa,反应时间4h条件下,甲醇的转化率达到14.7%,DMC选择性为92.5%,反应中未见Au（0）生成,表明在Schiff base配体和CuCl₂的共同作用下,能够稳定Au（Ⅲ）,而且该催化剂经过重复使用6次,活性基本保持不变,其他Au（Ⅲ）/Schiff base/CuCl₂经过6次使用,活性也能基本保持。虽然Au（Ⅲ）/Schiff base/CuCl₂催化剂在甲醇氧化羰化反应中能保持较好的催化性能,但是CuCl₂的助催化作用不可忽略,为了排除原本在甲醇氧化羰化反应中具有一定活性的CuCl₂的影响,我们研究出了一种新型均相催化体系Au（Ⅲ）/Schiff base/卤化物,在甲醇氧化羰化反应中表现出较好活性,系统研究了希夫碱配体种类、反应温度,反应压力、卤化物添加剂用量和种类对催化剂活性的影响,结果表明在120℃,Pco/Po2=2:1,P总=3.0MPa,反应时间3h,甲醇/Au（Ⅲ） = 5060,KI/Au（Ⅲ） = 4,在[AuCl₂（phen）]Cl/KI催化剂上,甲醇转化率、DMC选择性以及反应TOF分别为10.8%、98%和138.9h^-1,与传统催化剂相比,活性大大提高。为探讨均相金催化剂的普适性,我们将Au（Ⅲ）/Schiff base/卤化物催化剂应用于亚硝酸酯羰化反应制备碳酸酯中,研究了配体种类、卤化物添加剂种类和用量对反应活性的影响,结果表明,在T=80℃,Pco=3.0MPa,反应5h,KI为卤化物添加剂,KI/Au（Ⅲ）=4,[AuCl₂（phen）]Cl/KI在反应中的活性最好,亚硝酸乙酯转化率达到78.2%,DEC选择性大于90%。并且对其他亚硝酸酯也具有相同的反应活性。反应过程中无单质金生成,表明在该催化体系中,即使处于强还原气氛CO中,Schiff base/卤化物配合物体系能很好地稳定Au（Ⅲ）离子,使其仍然能保持较好的活性。而后采用Au（Ⅲ）/Schiff base/CuCl₂催化剂,研究了[AuCl₂（phen）]Cl/KI/CuCl₂在亚硝酸乙酯羰化反应中的催化性能,考察了CuCl₂用量以及[AuCl₂（phen）]Cl/KI/CuCl₂的重复使用性能,发现加入4倍CuCl₂后,DEC选择性由91.7%增大至99%,且该催化剂还具有一定的重复使用性能。采用UV-vis、ESI-MS以及循环伏安法研究探讨了[AuCl₂（phen）]Cl/KI在羰化反应中的机理,认为[AuI2（phen）]+可能为反应的活性中间体,阐述了希夫碱配体和碘化物在反应中的作用,提出了[AuCl₂（phen）]Cl/KI在甲醇氧化羰化反应中的可能机理。在亚硝酸酯羰化反应中,提出了与传统钯催化不同的反应机理,Au（Ⅲ）先与底物亚硝酸酯作用,形成Au（Ⅲ） （OR）（NO）物种,然后进行CO的配位与插入反应,得到Au（Ⅲ） （COOR）（NO）物种,然后另一分子ROH的亲核进攻,通过解离得到产物,Au（Ⅲ）在亚硝酸酯和碘化物的作用下,重新进入下一轮催化循环。更多还原

【Abstract】 The application of gold catalysis in reaction has long been neglected due to the preconceived notion that gold is chemically inert. Due to the pioneering studies of Haruta and other researchers, extraordinarily good catalytic activities were observed with gold catalyst for low-temperature CO oxidation and hydrochlorination of ethyne in the 1980s. Since then, catalysis with gold has gained much attention, and many successful examples have shown that gold catalysts can indeed be applied to several fields of heterogeneous catalysis, such as oxidation reaction,water-gas shift reaction, and in many fields of homogeneous catalysis, e.g., carbon-carbon bond forming reactions, hydration of alkynes and hydrogenation. However, despite the fact that exploration of gold in catalysis has recently surged to unprecedented levels compared with other commonly used noble metal catalysts, the generality and applicability of gold in catalysis remain relatively limited. In particular, while the effectiveness of gold in heterogeneous catalysis has been well- recognized, far less efforts have been spent on study regarding homogeneous gold complexes.Few research in the field of carbonylation using Au complex as a catalyst was reported comparing with other gold catalysis areas. Oxidative carbonylation of methanol catalyzed by metal complex is a typical model reaction in the field of homogeneous catalysis. Recently, some promising results have been achieved in the oxidative carbonylation of alkyl alcohol, aniline, and phenol using Cu, Co, and Pd complexes as catalysts. We considered that the Au（Ⅲ） complexes would be catalytically active in the oxidative carbonylation of methanol due to the following reasons: （1） gold is located in the same group as Cu in the periodic table of elements, allowing Au complex to exhibit similar properties as Cu complex catalyst; and （2） the electronic configuration of Au（Ⅲ） is very similar to that of Pd（II）. In this study, we presented the successful outcome of this endeavor where Au（Ⅲ）/Shiff-base complexes were used as catalysts for the oxidative carbonylation of methanol to dimethyl carbonate （DMC）.We found that the highest activity of the catalyst emerged from [AuCl₂（bipy）]Cl/CuCl₂ in the Schiff base ligand screening test. The conversion and selectivity value of the model reaction were 14.7%, 92.5%, and no Au（0） generated under the reaction conditions: 120℃, Pco/PO2=2:1, P总=3.0MPa, t=4h, indicating that the Schiff base and CuCl₂ could stabilized Au（Ⅲ） in CO atmosphere. After the catalyst reused for 6 times, their activity keep almost unchanged.In the continution of the new catalyst system in the oxidation carbonylation, a new type homogeneous catalytic system was developed, Au（Ⅲ）/Schiff base/halide, which showed good activity in methanol oxidative carbonylation was found. The Schiff base ligand, reaction temperature, pressure, amount and type of halide additives on the catalytic performance was studied in detail. At an optimized condition: 120℃, Pco/Po2==2:1, Ptotal=3.0MPa, 3h, Metnaol/Au（Ⅲ） = 5060（mol/mol）, KI/Au（Ⅲ）=4, on the [AuCl₂（phen）]Cl/KI, the conversion of methanol was 10.8%, the selectivity to DMC was 98% and the TOF was 138.9h-1.The activity of this new catalytic system increased substantially comparing with conventional Cu complex catalyst.To extend the practical application of gold in homogeneous catalysis, the experimental study presented herein describes a homogeneous gold-catalyzed carbonylation of alkyl nitrite to dialkyl carbonate. The ligand type, amount of halide additives were studied in detail. The catalytic esults shows that under 80℃, Pco=3.0MPa, 5h, KI/Au（Ⅲ） = 4（mol/mol）, [AuCl₂（phen）]Cl/KI exhibited the best performance with the conversion of ethyl nitrite 78.2%, the selectivity of DEC 91.7%. This catalytic system is also capable to apply to low-carbon alkyl nitrite, which suggests good selectivity in the production of corresponding carbonate. No Au0 generated in this catalytic system. Both the ligand and promoter play crucial roles in increasing the catalytic activity of the gold ion in a homogeneous reaction. Au（Ⅲ）/Shiff-base/CuCl₂ was then employed as a catalyst in the carbonylation of ethyl nitrite, under the same reaction conditions, on [AuCl₂（phen）]Cl/KI/CuCl₂, the conversion and the selectivity were enhanced up to 80.6% and 99%, and the catalyst could be used for several times.Based on the experimental results of UV-vis, ESI-MS and cyclic voltammetry, the oxidation state of gold during the reaction and the role of KI were discussed. [AuI2（phen）]+ was considered as an intermediate in the reaction. A plausible catalytic cycle mechanism between AuⅢand AuI was proposed in methanol oxidative carbonylation. In alkyl nitrite carbonylation, the reaction mechanism was provided, which was different from the mechanism catalyzed by Pd catalyst system. The RO-NO is first interacts with Au（Ⅲ） to form the Au（Ⅲ）-（OR）（NO） species, and alkyloxycarbonylgold species Au（Ⅲ） （OCOR）（NO） was generated through the insertion of CO. The next step was a nucleophilic attack by the next alkyloxy on the ROH. A dialkyl carbonate is formed with release of nitric oxide （NO） by reductive elimination, and the AuⅢcomplex was regenerated in the presence of alkyl nitrite and iodide, then followed up the catalytic cyclic.更多还原