Phosphine-free pincer-ruthenium catalyzed biofuel production: high rates, yields and turnovers of solventless alcohol alkylation,Catalysis Science & Technology

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Phosphine-free pincer-ruthenium catalyzed biofuel production: high rates, yields and turnovers of solventless alcohol alkylation
Catalysis Science & Technology ( IF 4.4 ) Pub Date : 2020-10-08 , DOI: 10.1039/d0cy01679a
Kanu Das _{1,

2,

3,

4} , Eileen Yasmin _{1,

2,

3,

4} , Babulal Das _{1,

2,

3,

4} , Hemant Kumar Srivastava _{3,

4,

5,

6} , Akshai Kumar _{1,

2,

3,

4,

7}

Affiliation

Phosphine-free pincer-ruthenium carbonyl complexes based on bis(imino)pyridine and 2,6-bis(benzimidazole-2-yl) pyridine ligands have been synthesized. For the β-alkylation of 1-phenyl ethanol with benzyl alcohol at 140 °C under solvent-free conditions, (^Cy2NNN)RuCl₂(CO) (0.00025 mol%) in combination with NaOH (2.5 mol%) was highly efficient (ca. 93% yield, 372 000 TON at 12 000 TO h⁻¹). These are the highest reported values hitherto for a ruthenium based catalyst. The β-alkylation of various alcohol combinations was accomplished with ease which culminated to give 380 000 TON at 19 000 TO h⁻¹ for the β-alkylation of 1-phenyl ethanol with 3-methoxy benzyl alcohol. DFT studies were complementary to mechanistic studies and indicate the β-hydride elimination step involving the extrusion of acetophenone to be the overall RDS. While the hydrogenation step is favored for the formation of α-alkylated ketone, the alcoholysis step is preferred for the formation of β-alkylated alcohol. The studies were extended for the upgradation of ethanol to biofuels. Among the pincer-ruthenium complexes based on bis(imino)pyridine, (^Cy2NNN)RuCl₂(CO) provided high productivity (335 TON at 170 TO h⁻¹). Sterically more open pincer-ruthenium complexes such as (^Bim2NNN)RuCl₂(CO) based on the 2,6-bis(benzimidazole-2-yl) pyridine ligand demonstrated better reactivity and gave not only good ethanol conversion (ca. 58%) but also high turnovers (ca. 2100) with a good rate (ca. 710 TO h⁻¹). Kinetic studies indicate first order dependence on concentration of both the catalyst and ethanol. Phosphine-free catalytic systems operating with unprecedented activity at a very low base loading to couple lower alcohols to higher alcohols of fuel and pharmaceutical importance are the salient features of this report.

中文翻译：

无磷的cer式钌催化的生物燃料生产：无溶剂醇烷基化反应的高产率，高收率和周转率

合成了基于双（亚氨基）吡啶和2,6-双（苯并咪唑-2-基）吡啶配体的无膦钳式钌羰基配合物。在无溶剂条件下，在140°C下用苯甲醇将1-苯基乙醇与苄醇进行β-烷基化反应，（^Cy2 NNN）RuCl ₂（CO）（0.00025 mol％）与NaOH（2.5 mol％）的结合非常有效（约93％的产率，在12000 TO h ^-1时为37.2万吨。这是迄今为止基于钌的催化剂的最高报道值。轻松完成各种醇组合的β-烷基化反应，最终在19 000 TO h ^-1达到380000 TON1-苯基乙醇与3-甲氧基苄醇的β-烷基化反应。DFT研究是对机理研究的补充，并指出涉及苯乙酮挤出的β-氢化物消除步骤成为整个RDS。尽管有利于形成α-烷基化的酮的氢化步骤，但是对于形成β-烷基化的醇，醇解步骤是优选的。研究扩大了将乙醇升级为生物燃料的研究。在基于双（亚氨基）吡啶的钳-钌络合物中，（^Cy2 NNN）RuCl ₂（CO）提供了高生产率（在170 TO h ^-1时为335 TON ）。在空间上更开放的钳式钌络合物，例如（^Bim2 NNN）RuCl ₂基于2,6-双（苯并咪唑-2-基）吡啶配体的（CO）表现出更好的反应性，不仅具有良好的乙醇转化率（约58％），而且具有高营业额（约2100）和良好的转化率（约710 TO h ^-1）。动力学研究表明，催化剂和乙醇的浓度均一阶依赖。本报告的主要特点是，无磷催化剂体系在极低的碱负荷下以空前的活性运行，可将低级醇与高级醇偶合，具有重要的医学意义。

更新日期：2020-11-03

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