Mori Kohsuke, Yamaguchi Kazuya, Hara Takayoshi, Mizugaki Tomoo, Ebitani Kohki, Kaneda Kiyotomi
Department of Chemical Science and Engineering, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan.
J Am Chem Soc. 2002 Oct 2;124(39):11572-3. doi: 10.1021/ja020444q.
Achieving precise control of active species on solid surfaces is one of the most important goals in the development of highly functionalized heterogeneous catalysts. The treatment of hydroxyapatites with PdCl(2)(PhCN)(2) gives two new types of hydroxyapatite-bound Pd complexes. Using the stoichiometric hydroxyapatite, Ca(10)(PO(4))(6)(OH)(2), we found that monomeric PdCl(2) species can be grafted on its surface, which are easily transformed into Pd(0) particles with narrow size distribution in the presence of alcohols. Such metallic Pd species can effectively promote alcohol oxidation using molecular oxygen and are shown to give a remarkably high TON of up to 236 000. Another monomeric Pd(II) phosphate complex can be generated at a Ca-deficient site of the nonstoichiometric hydroxyapatite, Ca(9)(HPO(4))(PO(4))(5)(OH), affording a catalyst with Pd(II) structure and high activity for the Heck and Suzuki reactions. To the best of our knowledge, the PdHAP are one of the most active heterogeneous catalysts for both alcohol oxidation under an atmospheric O(2)() pressure and the Heck reaction reported to date. These Pd catalysts are recyclable in the above organic reactions. Our approach to catalyst preparation based on the control of Ca/P ratios of hydroxyapatites represents a particularly attractive method for the nanoscale design of catalysts.
实现对固体表面活性物种的精确控制是开发高功能化多相催化剂最重要的目标之一。用PdCl₂(PhCN)₂处理羟基磷灰石可得到两种新型的羟基磷灰石结合的钯配合物。使用化学计量的羟基磷灰石Ca₁₀(PO₄)₆(OH)₂，我们发现单体PdCl₂物种可以接枝到其表面，在醇存在下，这些物种很容易转化为尺寸分布窄的Pd(0)颗粒。这种金属钯物种可以有效地利用分子氧促进醇氧化，并且显示出高达236000的显著高的TON。另一种单体Pd(II)磷酸盐配合物可以在非化学计量的羟基磷灰石Ca₉(HPO₄)(PO₄)₅(OH)的缺钙位点生成，得到一种具有Pd(II)结构且对Heck反应和Suzuki反应具有高活性的催化剂。据我们所知，PdHAP是迄今为止报道的在大气O₂压力下进行醇氧化以及Heck反应中最具活性的多相催化剂之一。这些钯催化剂在上述有机反应中可循环使用。我们基于控制羟基磷灰石的Ca/P比来制备催化剂的方法是一种特别有吸引力的催化剂纳米级设计方法。
