Mimicking the HDS activity of ruthenium-based catalysts. Homogeneous hydrogenolysis of benzo[b]thiophene
Mimicking the HDS activity of ruthenium-based catalysts. Homogeneous hydrogenolysis of benzo[b]thiophene
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DOI：
10.1021/om9800804
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发表时间：
1998-06-08
期刊：
影响因子：
2.8
通讯作者：
Vizza, F
中科院分区：
文献类型：
--
作者：
Bianchini, C;Meli, A;Vizza, F
[（triphos）RuH（BH_4）]（1）在THF中与KOBut反应，得到了新的三氢配合物K[（triphos）RuH_3]（2）和BH_2 OBut（triphos = MeC（CH_2 PPh_2）（3））。还可以通过在TI-IF中在5倍过量的BH 2 OBut存在下在40 ℃下氢化（30巴H-2）三（乙腈）络合物[（triphos）Ru（NCMe）（3）]（BPh 4）（2）（3）来合成三膦酸酯络合物2。由于MeCN氢化，该反应产生NH 2 Et、NHEt 2、NEt 3和NH3的混合物，随后进行胺再分配反应。化合物2通过在18-冠-6醚存在下从THF/正己烷中重结晶以分析纯形式分离为[K（C12 H24 O 6）][（triphoS）RUH 3]（2a）。在强碱如KOBut存在下，1和3都是在温和反应条件（大于或等于70 ℃，30巴Hz）下在THF中将苯并[B]噻吩（BT）均匀氢解成2-乙基苯硫酚（ETP）的有效催化剂前体。氢解速率随着碱的浓度而增加，这取决于催化剂前体，在催化反应中可以起到多达三种不同的作用。它促进催化活性物质（即16 e（-）片段[（triphos）RuH]（-））的形成和稳定，并加快氢解速率，将ETP产物作为2-乙基硫酚钾盐输送到溶液中。在钛合金阀门密封的蓝宝石管中进行的高压（31）p（H-1）和H-1 NMR实验（HPNMR）表明，在大于或等于70 ℃的THF-d（s）中，2与BT的相互作用选择性地产生二氢硫醇盐络合物K[（triphos）Ru（H）（2）]（o-S（C6 H4）C2 H5）]（5）和乙烯基硫酚盐络合物K[（triphos）Ru（eta（3）-S（C6 H6）CH= CH 2）]（6）在Nz下。即使在室温下，化合物6在THF中通过用HS处理也转化为5。在70 ℃的催化条件下，5和2是唯一的NMR可检测的物质，其平衡浓度取决于温度和碱浓度。氢解反应的机理是钌插入到BT的C-2-S键中得到2-乙烯基硫酚配体，然后乙烯基部分被氢化，硫醇被还原消除。这后一步是由强大的布朗斯台德基地加速。本可溶性络合物催化的氢解反应中可能发生的相似性在化石燃料的加氢脱硫Ru促进的非均相催化剂进行了讨论。
The reaction of [(triphos)RuH(BH4)] (1) in THF with KOBut yields the novel trihydride complex K[(triphos)RuH3] (2) and BH2OBut (triphos = MeC(CH2PPh2)(3)). The ruthenate complex 2 can also be synthesized by hydrogenation (30 bar of H-2) in TI-IF of the tris(acetonitrile) complex [(triphos)Ru(NCMe)(3)](BPh4)(2) (3) in the presence of a 5-fold excess of BH2OBut at 40 degrees C. This reaction produces a mixture of NH2Et, NHEt2, NEt3, and NH3 as a result of MeCN hydrogenation, followed by amine redistribution reactions. Compound 2 is isolated in analytically pure form as [K(C12H24O6)][(triphoS)RUH3] (2a) by recrystallization from THF/n-hexane in the presence of 18-crown-6 ether. In the presence of a strong base such as KOBut, both 1 and 3 are effective catalyst precursors for the homogeneous hydrogenolysis of benzo[b]thiophene (BT) to 2-ethylthiophenol (ETP) in THF under mild reaction conditions (greater than or equal to 70 degrees C, 30 bar of Hz). The hydrogenolysis rate increases with the concentration of the base, which, depending on the catalyst precursor, may play up to three distinct roles in the catalytic reactions. It promotes the formation and stabilization of the catalytically active species (i.e. the 16e(-)fragment [(triphos)RuH](-)) and speeds up the hydrogenolysis rate, delivering the ETP product into the solution as 2-ethylthiophenolate potassium salt. High-pressure (31)p(H-1) and H-1 NMR experiments (HPNMR) in sapphire tubes sealed by titanium-alloy valves show that the interaction of 2 with BT at greater than or equal to 70 OC in THF-d(s) selectively yields the dihydride thiolate complex K[(triphos)Ru(H)(2)(o-S(C6H4)C2H5)] (5) under H-2 and the vinylthiophenolate complex K[(triphos)Ru(eta(3)-S(C6H6)CH=CH2)] (6) under Nz. Compound 6 in THF transforms into 5 by treatment with HS even at room temperature. Under catalytic conditions at 70 degrees C, 5 and 2 are the only NMR-detectable species in equilibrium concentrations that depend on the temperature and on the base concentration. The hydrogenolysis mechanism is proposed to involve C-S insertion of ruthenium into the C-2-S bond of BT to give a 2-vinylthiophenolate ligand, followed by hydrogenation of the vinyl moiety and reductive elimination of the thiol. This latter step is accelerated by the strong Bronsted base. The possible similarity in the hydrogenolysis reactions catalyzed by the present soluble complexes to those occurring in the hydrodesulfurization of fossil fuels over Ru-promoted heterogeneous catalysts is discussed.