Combination Catalysts Consisting of a Homogeneous Catalyst Tethered to a Silica-Supported Palladium Heterogeneous Catalyst: Arene Hydrogenation
Combination Catalysts Consisting of a Homogeneous Catalyst Tethered to a Silica-Supported Palladium Heterogeneous Catalyst: Arene Hydrogenation
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DOI：
10.1021/ja9710058
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发表时间：
1997-07
影响因子：
15
通讯作者：
Hanrong Gao;R. J. Angelici
中科院分区：
文献类型：
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作者：
Hanrong Gao;R. J. Angelici
过去几十年来，连接到有机或无机载体上的过渡金属配合物催化剂受到了广泛关注，因为它们原则上可以结合均相和非均相催化剂的优点。这种配合物可以通过配合物中的配体很容易地束缚在二氧化硅表面上，该配体具有与SiO2上的表面羟基反应的烷氧基或氯硅烷官能团。二氧化硅负载的多相金属催化剂（例如 Pd-SiO2、Rh-SiO2 和 Pt-SiO2）也具有表面羟基，可用于束缚过渡金属配合物均相催化剂。这些组合催化剂由负载金属 (TCSM) 催化剂上的束缚络合物组成（图 1），可以通过两种催化剂组分的协同作用发挥作用。对于不饱和有机底物的氢化反应，人们可能会想象这些 TCSM 催化剂的作用方式是，H2 在负载金属（例如 Pd、Rh 或 Pt）上被激活，产生的氢原子溢出到二氧化硅上，在二氧化硅上它们可以与不饱和有机底物反应，同时由束缚络合物配位和激活。 TCSM 催化剂的这种作用机制取决于众所周知的负载金属催化剂上的氢溢出现象。3 在其他机制中，束缚络合物可能更直接地与负载金属上活化的分子相互作用。在本文中，我们报告了一个据我们所知的第一个例子，即负载金属（TCSM）催化剂上的系链配合物，其芳烃加氢活性大大高于单独的系链配合物或负载金属的活性。事实上，在 1 atm H2 和 40 °C 的温和条件下，其活性高于任何报道的均相或固定化金属配合物催化剂。通过将异氰化铑配合物 RhCl[CN(CH2)3Si(OC2H5)3]3 或 RhCl(CO)[CN(CH2)3Si(OC2H5)3]2 与二氧化硅负载的钯金属催化剂 (Pd-SiO2) 结合来制备两种 TCSM 催化剂。异氰化铑配合物 RhCl(CO)[CN(CH2)3Si(OC2H5)3]2 (Rh-CNR2) 是通过 [Rh(CO)2Cl]2 与 4 当量 CN(CH2)3Si(OC2H5)3 在甲苯中反应制备的，反应类似于合成 RhCl(CO)[CNBu]2 的反应。根据用于制备RhCl[CN(2,6-二甲苯基)]3的程序，通过[Rh(COD)Cl]2(COD)环辛二烯)与6当量的CN(CH2)3Si(OC2H5)3反应制备复合物RhCl[CN(CH2)3Si(OC2H5)3]3(Rh-CNR3)。将含有RhCl(CO)[CN(CH2)3Si(OC2H5)3]2或RhCl[CN(CH2)3Si(OC2H5)3]3的甲苯溶液与二氧化硅负载的钯催化剂Pd-SiO2(Pd,10wt%)一起回流4小时。过滤后，将固体用甲苯洗涤，然后在室温下真空干燥。所得系留催化剂Rh-CNR2/Pd-SiO2（Rh含量，1.10 wt%）和Rh-CNR3/PdSiO2（Rh含量，1.35 wt%）给出了带有ν(CN-)和ν(CO)带的红外光谱（DRIFTS）（RhCNR2/Pd-SiO2为2197（s）和2017（s）cm-1； Rh-CNR3/PdSiO2 的 2176 (s) 和 2124 (w) cm-1）在位置和相对强度上与未束缚的 Rh-CNR2 和 Rh-CNR3 配合物的位置和相对强度非常相似，4,8 这表明配合物在束缚到 Pd-SiO2 表面后保留了其结构。在 TCSM 催化剂或单独的均相和非均相催化剂存在下，在 1 atm H2 下搅拌的同时，在 40 °C 下，甲苯氢化成甲基环己烷的速率（表 1）通过 H2 吸收速率来确定。催化剂从一开始就具有活性，但 1 小时后，Rh-CNR2/Pd-SiO2 的 TOF（周转频率）值增加到最大值 4.8，6.5 小时后，RhCNR3/Pd-SiO2 的 TOF（周转频率）值增加到最大值 5.5。在最大 TOF 水平几个小时后，活性略有下降。从表1中的数据可以看出，Rh-CNR2/Pd-SiO2催化剂活性（通过最大TOF、周转数（TO）或H2吸收来测量）比简单的多相SiO2负载的Pd（Pd-SiO2）、仅与SiO2连接的RhCNR2络合物（Rh-CNR2/SiO2）、仅配体的活性至少高7倍(CN(CH2)3Si(OC2H5)3) 与 Pd-SiO2(CNR/PdSiO2) 或均相催化剂 (Rh-CNR2) 相连，即使与 Rh-CNR2/Pd-SiO2 中的 6.3 μmol 相比，即使具有相对大量的 Rh (20 μmol)。同样，Rh-CNR3/Pd-SiO2 的活性至少比 Pd-SiO2、均质 Rh-CNR3、系链 Rh-CNR3/SiO2 或 CNR/Pd-SiO2 高 9 倍。最活跃的 TCSM 催化剂 Rh-CNR3/Pd-SiO2 的最大周转频率为 5.5 mol H2/(mol Rh min)，周转数 (1) (a) Hartley, F. R. 负载金属催化剂； Reidel：荷兰多德雷赫特，1985 年。(b) Iwasaka, Y. 定制金属催化剂； Reidel：东京，1986 年。(c) Cornils，B.； Hermann, W. A. 应用有机金属化合物均相催化； VCH：魏因海姆，1996；第 351 页。 (2) (a) Blumel，J. Inorg。化学。 1994, 33, 5050。(b) Capka, M.；恰科娃，M.；沃德齐米日，美国；舒伯特，U. J. Mol。加塔尔。 1992, 74, 335。(c) Allum, K. G.；汉考克，R.D.；豪厄尔，I.V.；麦肯齐，S.；皮特凯斯利，R.C.；罗宾逊，P.J.J.Organomet。化学。 1975, 87, 203。(d) 卡普卡，M.； Hetflejs，J. 收集。捷克语。化学。交流。 1974, 39, 154。(e) Pugin, B. J. Mol。加塔尔。答：化学。 1996, 107, 273。(f) Czakova, M.；卡普卡，M. J. 摩尔。加塔尔。 1981, 11, 313。 (3) (a) Pajonk, G. M.；泰希纳，S.J.； Germain, J. E. SpilloVer，《吸附物种》；爱思唯尔：阿姆斯特丹，1983 年。(b) Conner, W. C., Jr.；帕琼克，GM； Teichner，S.J.AdV。加塔尔。 1986, 34, 1。(c) Conner, W. C., Jr.； Falconer，J.L.化学。修订版。 1995, 95, 759。(d) Inui, T.；藤本，K.；内岛，T.； Masai, M. 催化溢出效应的新方面； Elsevier：阿姆斯特丹，1993。 (4) RhCl(CO)[CN(CH2)3Si(OC2H5)3]2 的选定数据：1H NMR (CDCl3) δ 3.82 (q, 12H, OCH2CH3), 3.67 (t, 4H, CNCH2), 1.90 (m, 4H, CH2CH2CH2), 1.21 (t, 18H, OCH2CH3), 0.75 (t, 4H, SiCH2); IR（在甲苯中）ν(CN-) 2192 (s) cm-1，ν(CO) 1996 (s) cm-1。 (5) 麦克莱弗蒂，J.A.；威尔金森，G. Inorg。合成器。 1990, 28, 84. (6) (CH3CH2O)3SiCH2CH2CH2NC 由 (CH3CH2O)3SiCH2CH2CH2NHCHO 和 Cl3COC(dO)Cl 制备，遵循为合成其他烷基异氰化物而开发的程序（Skorna, G.；Ugi, I. Angew. Chem., Int. Ed. Engl. 1977， 16, 259); IR（CH2Cl2 中），ν(CN-) 2150 cm-1； 1H NMR (CDCl3)δ 3.81(q，6H，OCH2CH3)，3.38(m，2H，CCH2)，1.78(m，2H，CH2CH2CH2)，1.20(t，9H，OCH2CH3)，0.72(t，2H，SiCH2)。 (7) 迪明，A. J. J. Organomet。化学。 1979, 175, 105. (8) RhCl[CN(CH2)3Si(OC2H5)3]3 的选定数据: 1H NMR (CDCl3) δ 3.82 (q, 18H, OCH2CH3), 3.58 (t, 4H, CNCH2), 3.46 (t, 2H, CNCH2), 1.85 (m, 6H，CH2CH2CH2)，1.23(t，27H，OCH2CH3)，0.73(t，6H，SiCH2)； IR（在甲苯中）ν(CN-) 2158 (s), 2119 (m) cm-1。肛门。 C30H63O9N3Si3ClRh 的计算值：C，43.28； H，7.63； N，5.05。实测值：C，42.70； H，7.37； N，4.57。 (9)佐丹奴，G.；克拉布特里 (Crabtree)，R. H. Inorg。合成器。 1990, 28, 88。 (10) 山本 Y.；山崎，H.J.Organomet。化学。 1977, 140, C33。 (11)采用初湿法制备Pd-SiO2，用H2PdCl4水溶液浸渍SiO2，在500℃下煅烧4h，并在380℃下用H2还原4h。图 1. TCSM 催化剂的概念图，该催化剂由负载型金属非均相催化剂上的系链均相络合物催化剂组成。第6937章化学。苏克。 1997, 119, 6937-6938
Transition metal complex catalysts tethered to organic or inorganic supports1 have received much attention in the past few decades because they can, in principle, combine the advantages of homogeneous and heterogeneous catalysts. Such complexes can be easily tethered on silica surfaces through a ligand in the complex which has alkoxyor chlorosilane functional groups that react with surface hydroxyl groups on the SiO2. Silica-supported heterogeneous metal catalysts such as Pd-SiO2, Rh-SiO2, and Pt-SiO2 also have surface hydroxyl groups that could be used to tether transition metal complex homogeneous catalysts. These combination catalysts consisting of a tethered complex on a supported metal (TCSM) catalyst (Figure 1) could function by synergistic action of both catalyst components. For hydrogenation reactions of unsaturated organic substrates, one might imagine that these TCSM catalysts could function in a way that H2 is activated on the supported metal (e.g., Pd, Rh, or Pt) with the resulting hydrogen atoms spilling over onto the silica where they could react with the unsaturated organic substrate that is simultaneously coordinated and activated by the tethered complex. This mechanism for the functioning of a TCSM catalyst depends on the well-known phenomenon of hydrogen spillover on supported metal catalysts.3 In other mechanisms, the tethered complex may interact more directly with molecules that are activated on the supported metal. In this paper, we report an example, the first to our knowledge, of a tethered complex on a supported metal (TCSM) catalyst, whose activity for the hydrogenation of arenes is substantially higher than that of the tethered complex or the supported metal separately. In fact, its activity is higher than that of any reported homogeneous or immobilized metal complex catalyst under the mild conditions of 1 atm of H2 and 40 °C. Two TCSM catalysts were prepared by tethering either of the rhodium isocyanide complexes, RhCl[CN(CH2)3Si(OC2H5)3]3 or RhCl(CO)[CN(CH2)3Si(OC2H5)3]2, to a silica-supported palladium metal catalyst (Pd-SiO2). The rhodium isocyanide complex RhCl(CO)[CN(CH2)3Si(OC2H5)3]2 (Rh-CNR2) was prepared by the reaction of [Rh(CO)2Cl]2 with 4 equiv of CN(CH2)3Si(OC2H5)3 in toluene, in a reaction similar to that described for the synthesis of RhCl(CO)[CNBu]2. The complex RhCl[CN(CH2)3Si(OC2H5)3]3 (Rh-CNR3) was prepared in the reaction of [Rh(COD)Cl]2 (COD ) cyclooctadiene) with 6 equiv of CN(CH2)3Si(OC2H5)3 according to a procedure used for the preparation of RhCl[CN(2,6-xylyl)]3. The toluene solution containing RhCl(CO)[CN(CH2)3Si(OC2H5)3]2 or RhCl[CN(CH2)3Si(OC2H5)3]3 was refluxed with the silica-supported palladium catalyst Pd-SiO2 (Pd, 10 wt %) for 4 h. After filtration, the solid was washed with toluene and then dried in vacuum at room temperature. The resulting tethered catalysts, Rh-CNR2/Pd-SiO2 (Rh content, 1.10 wt %) and Rh-CNR3/PdSiO2 (Rh content, 1.35 wt %), gave IR spectra (DRIFTS) with ν(CN-) and ν(CO) bands (2197 (s) and 2017 (s) cm-1 for RhCNR2/Pd-SiO2; 2176 (s) and 2124 (w) cm-1 for Rh-CNR3/PdSiO2) that are very similar in position and relative intensity to those of the untethered Rh-CNR2 and Rh-CNR3 complexes,4,8 which indicates that the complexes retain their structures after being tethered to the Pd-SiO2 surface. The rates of hydrogenation (Table 1) of toluene to methylcyclohexane at 40 °C while being stirred under 1 atm of H2 in the presence of the TCSM catalysts or the separate homogeneous and heterogeneous catalysts were determined by following the rate of H2 uptake. The catalysts are active from the outset but the TOF (turnover frequency) values increase to a maximum value of 4.8 for Rh-CNR2/Pd-SiO2 after 1 h and to 5.5 for RhCNR3/Pd-SiO2 after 6.5 h. After several hours at the maximum TOF levels, the activities decrease slightly. From the data in Table 1, it can be seen that the Rh-CNR2/Pd-SiO2 catalyst activity (as measured by the maximum TOF, turnover number (TO), or H2 uptake) is at least 7 times greater than that of the simple heterogeneous SiO2-supported Pd (Pd-SiO2), the RhCNR2 complex tethered to just SiO2(Rh-CNR2/SiO2), just the ligand (CN(CH2)3Si(OC2H5)3) tethered to Pd-SiO2(CNR/PdSiO2), or the homogeneous catalyst (Rh-CNR2) even with relatively large amounts of Rh (20 μmol) as compared with 6.3 μmol in Rh-CNR2/Pd-SiO2. Similarly, Rh-CNR3/Pd-SiO2 is at least 9 times more active than Pd-SiO2, homogeneous Rh-CNR3, tethered Rh-CNR3/SiO2, or CNR/Pd-SiO2. The most active TCSM catalyst, Rh-CNR3/Pd-SiO2, has a maximum turnover frequency of 5.5 mol H2/(mol of Rh min) and a turnover number (1) (a) Hartley, F. R. Supported Metal Catalysts; Reidel: Dordrecht, The Netherlands, 1985. (b) Iwasaka, Y. Tailored Metal Catalysts; Reidel: Tokyo, 1986. (c) Cornils, B.; Hermann, W. A. Applied Homogeneous Catalysis with Organometallic Compounds; VCH: Weinheim, 1996; p 351. (2) (a) Blumel, J. Inorg. Chem. 1994, 33, 5050. (b) Capka, M.; Czakova, M.; Wlodzimierz, U.; Schubert, U. J. Mol. Catal. 1992, 74, 335. (c) Allum, K. G.; Hancock, R. D.; Howell, I. V.; McKenzie, S.; Pitkethly, R. C.; Robinson, P. J. J. Organomet. Chem. 1975, 87, 203. (d) Capka, M.; Hetflejs, J. Collect. Czech. Chem. Commun. 1974, 39, 154. (e) Pugin, B. J. Mol. Catal. A: Chem. 1996, 107, 273. (f) Czakova, M.; Capka, M. J. Mol. Catal. 1981, 11, 313. (3) (a) Pajonk, G. M.; Teichner, S. J.; Germain, J. E. SpilloVer of Adsorbed Species; Elsevier: Amsterdam, 1983. (b) Conner, W. C., Jr.; Pajonk, G. M.; Teichner, S. J. AdV. Catal. 1986, 34, 1. (c) Conner, W. C., Jr.; Falconer, J. L. Chem. ReV. 1995, 95, 759. (d) Inui, T.; Fujimoto, K.; Uchijima, T.; Masai, M. New Aspects of SpilloVer Effects in Catalysis; Elsevier: Amsterdam, 1993. (4) Selected data for RhCl(CO)[CN(CH2)3Si(OC2H5)3]2: 1H NMR (CDCl3) δ 3.82 (q, 12H, OCH2CH3), 3.67 (t, 4H, CNCH2), 1.90 (m, 4H, CH2CH2CH2), 1.21 (t, 18H, OCH2CH3), 0.75 (t, 4H, SiCH2); IR (in toluene) ν(CN-) 2192 (s) cm-1, ν(CO) 1996 (s) cm-1. (5) McCleverty, J. A.; Wilkinson, G. Inorg. Synth. 1990, 28, 84. (6) (CH3CH2O)3SiCH2CH2CH2NC was prepared from (CH3CH2O)3SiCH2CH2CH2NHCHO and Cl3COC(dO)Cl following a procedure developed for the synthesis of other alkyl isocyanides (Skorna, G.; Ugi, I. Angew. Chem., Int. Ed. Engl. 1977, 16, 259); IR (in CH2Cl2), ν(CN-) 2150 cm-1; 1H NMR (CDCl3) δ 3.81 (q, 6H, OCH2CH3), 3.38 (m, 2H, CNCH2), 1.78 (m, 2H, CH2CH2CH2), 1.20 (t, 9H, OCH2CH3), 0.72 (t, 2H, SiCH2). (7) Deeming, A. J. J. Organomet. Chem. 1979, 175, 105. (8) Selected data for RhCl[CN(CH2)3Si(OC2H5)3]3: 1H NMR (CDCl3) δ 3.82 (q, 18H, OCH2CH3), 3.58 (t, 4H, CNCH2), 3.46 (t, 2H, CNCH2), 1.85 (m, 6H, CH2CH2CH2), 1.23 (t, 27H, OCH2CH3), 0.73 (t, 6H, SiCH2); IR (in toluene) ν(CN-) 2158 (s), 2119 (m) cm-1. Anal. Calcd for C30H63O9N3Si3ClRh: C, 43.28; H, 7.63; N, 5.05. Found: C, 42.70; H, 7.37; N, 4.57. (9) Giordano, G.; Crabtree, R. H. Inorg. Synth. 1990, 28, 88. (10) Yamamoto, Y.; Yamazaki, H. J. Organomet. Chem. 1977, 140, C33. (11) Pd-SiO2 was prepared by the incipient wetness method by impregnation of SiO2 using an aqueous solution of H2PdCl4, calcining at 500 °C for 4 h and reducing with H2 at 380 °C for 4 h. Figure 1. Conceptual illustration of a TCSM catalyst consisting of a tethered homogeneous complex catalyst on a supported metal heterogeneous catalyst. 6937 J. Am. Chem. Soc. 1997, 119, 6937-6938