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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Sterically hindered Re- and Mn-CO2 reduction catalysts for solar energy conversion
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Sterically hindered Re- and Mn-CO2 reduction catalysts for solar energy conversion

机译：用于太阳能转换的空间妨碍重新和Mn-CO 2还原催化剂

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Novel molecular Re and Mn tricarbonyl complexes bearing a bipyridyl ligand functionalised with sterically hindering substituents in the 6,6'-position, [M(HPEAB)(CO)(3)(X)] (M/X = Re/Cl, Mn/Br; HPEAB = 6,6'-{N-(4-hexylphenyl)-N(ethyl)-amido}-2,2'-bipyridine) have been synthesised, fully characterised including by single crystal X-ray crystallography, and their propensity to act as catalysts for the electrochemical and photochemical reduction of CO2 has been established. Controlled potential electrolysis showed that the catalysts are effective for electrochemical CO2-reduction, yielding CO as the product (in MeCN for the Re-complex, in 95:5 (v/v) MeCN : H2O mixture for the Mn-complex). The recyclability of the catalysts was demonstrated through replenishment of CO2 within solution. The novel catalysts had similar reduction potentials to previously reported complexes of similar structure, and results of the foot-of-the-wave analysis showed comparable maximum turnover rates, too. The tentative mechanisms for activation of the pre-catalysts were proposed on the basis of IR-spectroelectrochemical data aided by DFT calculations. It is shown that the typical dimerisation of the Mn-catalyst was prevented by incorporation of sterically hindering groups, whilst the Re-catalyst undergoes the usual mechanism following chloride ion loss. No photochemical CO2 reduction was observed for the rhenium complex in the presence of a sacrificial donor (triethylamine), which was attributed to the short triplet excited state lifetime (3.6 ns), insufficient for diffusion-controlled electron transfer. Importantly, [Mn(HPEAB)(CO)(3)Br] can act as a CO2 reduction catalyst when photosensitised by a zinc porphyrin under red light irradiation (lambda > 600 nm) in MeCN : H2O (95:5); there has been only one reported example of photoactivating Mn-catalysts with porphyrins in this manner. Thus, this work demonstrates the wide utility of sterically protected Re- and Mn-diimine carbonyl catalysts, where the rate and yield of CO-production can be adjusted based on the metal centre and catalytic conditions, with the advantage of suppressing unwanted side-reactions through steric protection of the vacant coordination site.
机译：载有在6,6'-位置的空间逆转取代基官能化的双吡啶基配体的新型分子Re和Mn三羰基配合物，[M（HPEAB）（CO）（3）（x）]（M / x = RE / Cl，Mn / Br; HPEAB = 6,6' - {N-（4-己基苯基）-N（乙基）-Amido} -2,2'-Bi吡啶）已经合成，完全表征包括单晶X射线晶体学，和已经建立了作为CO 2电化学和光化学减少的催化剂的倾向。受控电位电解显示，催化剂对电化学CO2还原是有效的，得到CO作为产物（在MECN中，在RE-Complex中，在95：5（v）MECN：Mn-复合物中的H 2 O混合物）。通过在溶液中补充CO 2来证明催化剂的再循环性。新型催化剂对先前报道的类似结构复合物具有类似的降低电位，并且载足分析的结果也显示出可比的最大周转率。基于DFT计算的IR-SpectraEtrochemical数据提出了激活预催化剂的暂定机制。结果表明，通过掺入空间妨碍基团来防止Mn催化剂的典型二聚化，而再催化剂经历氯离子损失后的常用机制。对于牺牲供体（三乙胺）存在的铼络合物中没有观察到光化学二氧化碳还原，其归因于短三重素激发状态寿命（3.6ns），不足以扩散控制的电子转移。重要的是，[Mn（HPEAB）（CO）（CO）（CO）（3）BR]在MECN：H 2 O（95：5）中的红光照射（Lambda> 600nm）下的锌卟啉在卟啉在卟啉（Lambda> 600nm）中的发光时，可以用作CO 2还原催化剂;以这种方式只有一个报道的用卟啉与卟啉相磷催化剂的实施例。因此，该作业证明了本空间保护的重新和Mn-二亚胺羰基催化剂的宽泛积，其中可以基于金属中心和催化条件调节共同速率和产率，其优点是抑制不需要的副反应通过空置协调场所的空间保护。

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