合成仿生性釕磷基氫團簇並應用於光催化產氫

Abstract

氫氣已成為替代能源研究的一個新趨勢，在大自然界中，氫化酶(hydrogenase)可藉由催化氫分子與氫質子間的可逆氧化還原反應(2H+ + 2e- ↔ H2)來產生氫氣。鐵-鐵產氫酶([FeFe]H2ase)活性位的催化結構稱為氫簇分子(H-cluster)，包含了一個二鐵二硫的單元，其結構為一個雙硫架橋雙鐵錯合物，此結構可作為仿生性光催化劑，並應用於光催化產氫上。 我們的目標在於模擬氫簇分子(H-cluster)的化學結構，以釕金屬置換其中心的鐵金屬，並把八個不同推拉電子特性及立體結構障礙的磷化合物共價接上模擬氫簇分子，合成仿生性釕磷基氫團簇。在此論文中我們成功合成出 Ru-HP1 , Ru-HP2, Ru-HP3, Ru-HP4 , Ru-HP5, Ru-HP6, Ru-HP7和Ru-HP8，並藉由X-光單晶繞射儀(single-crystal X-ray)進行結構鑑定及分析。而這八個釕磷基氫團簇的產氫效率也拿來和未共價接上磷化合物的氫簇分子Ru-H 作比較，並應用於兩種不同質子來源(水及甲酸)的光催化產氫系統中來探討其對產氫效率的影響。結果顯示，在氫氣產生效率的比較上，在甲酸系統下的產氫效率比水來的高。而有機相中，有推電子官能基的磷化合物對產氫效率的影響高於拉電子官能基的磷化合物，以釕磷基氫團簇而言，Ru-HP4 的產氫效率(照光三小時後的TOF為6447)高於Ru-H 外加P(o-tol)3的產氫效率(照光三小時後的TOF為5532)，而不同比例的Ru-HP4 和額外添加的P(o-tol)3對光催化產氫效率也會造成影響，Ru-HP4/P(o-tol)3 (1:1)可以得到最好的產氫效率(照光三小時後的TOF為8305)。此外，有機相產氫的機制也利用31P NMR來進行分析，在整個光催化產氫的循環中， Ru-H 和P(o-tol)3都是不會被消耗的。在我們的研究中，希望此仿生性釕磷基氫團簇能應用於未來光催化氫能源工業上。

Hydrogen, a gaseous energy, has recently become a trend in alternative energy research. In nature, hydrogenases (H2ase) can catalyze reversible hydrogen reduction of proton (H++2e-↔H2). The active site of [FeFe]H2ase called the H-cluster, which includes 2Fe2S subunit. The structure of the 2Fe2S subunit is a dithiolate-bridged diiron complex and has been used as a biomimetic photochemical catalyst for light-driven hydrogen generation. Our aim is to mimic the structure of the H-cluster. We take ruthenium substitutes for the central metal iron and take eight different P-ligands with different electronic and steric effects to substitute for the CO ligand of H-cluster to synthesize ruthenium-phosphine H-clusters. In this research, ruthenium-phosphine H-clusters, Ru-HP1, Ru-HP2, Ru-HP3, Ru-HP4, Ru-HP5, Ru-HP6, Ru-HP7, and Ru-HP8 are synthesized and characterized by single crystal X-ray structure determination. The hydrogen generation efficiency of eight ruthenium-phosphine H-clusters were compared with Ru-H with non-covalently linked P-ligands and were applied as catalysts in light-driven hydrogen generation from different proton sources such as water and formic acid. The results show that hydrogen generation obtained from formic acid is better than that obtained from water. In the organic phase, the P-ligands with an electron donating functional group has higher hydrogen generation efficiency than the P-ligands with an electron withdrawing functional group. For ruthenium-phosphine H-clusters, Ru-HP4 had the better efficiency (TOF is 6447 after three hours of irradiation) than Ru-H in the presence of P(o-tol)3 (TOF is 5532 after three hours of irradiation). Ru-HP4 in the presence of a different ratio of P(o-tol)3 influenced the hydrogen generation efficiency. The Ru-HP4/P(o-tol)3 (1:1) had the best efficiency (a TOF of 8305) after three hours of photoirradiation. The mechanism for the organic phase was proposed after 31P NMR analyses were performed. From the catalytic mechanism for hydrogen generation, P(o-tol)3 (a substitute in the catalytic cycle) and Ru-H (a recycling photocatalyst in the catalytic cycle) could not be consumed in this system. In the future, ruthenium-phosphine H-clusters are promising catalysts in the light-driven hydrogen production industry.