Heterogeneously catalyzed efficient alkyne-alkyne homocoupling by supported copper hydroxide on titanium oxide.
Heterogeneously catalyzed efficient alkyne-alkyne homocoupling by supported copper hydroxide on titanium oxide.
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DOI：
10.1002/chem.200901080
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发表时间：
2009-08
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影响因子：
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通讯作者：
T. Oishi;Tatsuyori Katayama;K. Yamaguchi;N. Mizuno
中科院分区：
文献类型：
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作者：
T. Oishi;Tatsuyori Katayama;K. Yamaguchi;N. Mizuno
二炔衍生物是一类重要的天然产物合成、高分子化学、超分子化学和材料科学中的化合物，因为它们可以被转化为各种结构实体。[1-4]因此，许多注意力已经支付给二炔衍生物的合成的有效程序的发展。氧化炔-炔均偶联反应是合成对称二炔衍生物最广泛使用的方法之一。化学计量量的铜盐[5]或催化量的铜盐与适当的氮碱（作为溶剂或配体）和/或添加剂（作为水清除剂）在分子氧存在下[6-15]通常用于氧化性炔-炔同偶联反应。然而，在铜基催化剂作用下，脂肪族炔的偶联反应中，脂肪族二炔的产率仍然普遍较低。[5-13]尽管已经报道钯盐和络合物对于脂族炔的氧化均偶联是活性的，但是这些体系具有使用昂贵的钯催化剂和不可缺少地使用碱和铜盐助催化剂的缺点。对于氧化性炔-炔均偶联，报道的体系大多数是均相的，缺点是催化剂/产物分离困难和（昂贵）催化剂的重复使用。据我们所知，非均相催化氧化炔-炔与分子氧偶联反应的报道很少。[21-23]在已报道的含铜水滑石的非均相体系中，需要过量的添加剂（至少是相对于炔的化学计量量），例如NaOH [20]和N，N，N '，N'-四甲基乙二胺[22]，以获得高产率，需要分子氧的高压（> 20个大气压），[21]和/或范围仅限于乙炔苯。[21]在某些情况下，需要大量的催化剂（含铜水滑石体系[22]为110摩尔%，含铜沸石体系[23]为10-30摩尔%）。因此，没有任何添加剂的有效的非均相体系的发展仍然是具有挑战性的，可以解决上述问题。我们的策略，设计有效的非均相催化剂的各种功能基团的转换是形成单体（或至少主要，如果不是全部）分散的金属氢氧化物物种在适当的载体。[24-29]金属氢氧化物物质将同时具有刘易斯酸和布朗斯台德碱位点，因为通过刘易斯酸和布朗斯台德碱位点的“协同活化”促进了各种官能团转化。[24-29]在此，我们报道了通过容易制备的负载在氧化钛上的氢氧化铜（Cu（OH）x/TiO 2）而没有任何添加剂的有效的非均相催化氧化炔-炔均偶联[Eq.①]。
Diyne derivatives are very important class of compounds in natural product synthesis, polymer chemistry, supramolecular chemistry, and materials science because they can be converted into various structural entities.[1–4] Thus, much attention has been paid to the development of efficient procedures for the synthesis of diyne derivatives. An oxidative alkyne–alkyne homocoupling reaction is one of the most widely used procedures for the synthesis of symmetrical diyne derivatives. Stoichiometric amounts of copper salts [5] or copper salts in catalytic amounts with appropriate nitrogen bases (as solvents or ligands) and/or additives (as water scavengers) in the presence of molecular oxygen [6–15] have typically been used for the oxidative alkyne–alkyne homocoupling reactions. However, yields of aliphatic diynes were still generally low to moderate for the homocoupling reactions of aliphatic alkynes with copper-based catalysts.[5–13] Although palladium salts and complexes have been reported to be active for the oxidative homocoupling of aliphatic alkynes, these systems have the disadvantage of the use of expensive palladium catalysts and the indispensable use of bases and co-catalysts of copper salts.[16–20] As for the oxidative alkyne–alkyne homocoupling, most of the systems reported are homogeneous and have shortcomings in the difficulty in catalyst/product (s) separation and reuse of (expensive) catalysts. As far as we know, there are only a few reports for the heterogeneously catalyzed oxidative alkyne–alkyne homocoupling with molecular oxygen.[21–23] In the reported heterogeneous systems with copper-containing hydrotalcites, excess amounts of additives (at least stoichiometric amounts with respect to alkynes) such as NaOH [20] and N, N, N’, N’-tetramethylethylenediamine [22] are necessary to attain high yields, high pressure of molecular oxygen (> 20atm) is necessary,[21] and/or the scope is limited only to ethynylbenzene.[21] In some cases, large amounts of catalysts (110 mol% for copper-containing hydrotalcite system [22] and 10–30 mol% for copper-containing zeolite system [23]) are required. Therefore, the development of efficient heterogeneous systems without any additives is still challenging and could solve the above-mentioned problems.Our strategy to design efficient heterogeneous catalysts for various functional group transformations is the formation of monomerically (or at least mainly if not wholly) dispersed metal hydroxide species on appropriate supports.[24–29] The metal hydroxide species would possess both Lewis acid and Brønsted base sites, as various functional group transformations have been promoted through the “concerted activation” by Lewis acid and Brønsted base sites.[24–29] Herein, we report the efficient heterogeneously catalyzed oxidative alkyne–alkyne homocoupling by an easily prepared supported copper hydroxide on titanium oxide (Cu (OH) x/TiO2) without any additives [Eq.(1)].