有機磷配位基對仿生釕-硫產氫團簇之光催化產氫研究

Abstract

具燃燒無汙染和再生性優勢的氫氣為替代性能源研究中的重要候選者。產氫酶(hydrogenases)是一群對氫分子和質子進行可逆氧化環原反應的酵素，由於鐵產氫酶([FeFe] hydrogenases)擁有高效率產氫活性，許多效仿他的活性部位-氫簇分子(H-cluster)結構已作為仿生性的催化劑，並應用於光催化產氫領域裡。 過去研究中，合成的釕-磷基產氫團簇Ru2-S2-P(o-tol)3在額外添加1當量P(o-tol)3時，於光催化裂解甲酸系統中有傑出的催化產氫效率。我們目標為解答Ru2-S2進行有機磷基的雙取代時能否提升團簇的催化效率，並欲探討磷化合物對釕-產氫團簇催化活性的影響。因此我們合成不同的釕-雙磷基產氫團簇(Ru2-S2-di-P-ligands)，藉X-光單晶繞射儀(single-crystal X-ray)鑑定及分析Ru2-S2-(PLY)2, Y=1-5 和Ru2-S2-PL2-PL3的結構，並將這些團簇應用於光催化產氫系統中以探討其對產氫效率的影響；另外烷基磷化物和Ru2-S2以額外添加至光催化系統中的方式測試產氫效率，也鑑定出Ru2-S2-(PL7)4和Ru2-S2-(PL8)2的結構。 產氫測試結果顯示Ru2-S2-di-P-ligands沒有明顯提升產氫催化活性；Ru2-S2 / PL6和Ru2-S2 / PL7在照光45分鐘後，分別達到TOF為15753和18420的高產氫效率。在光反應監控實驗中，傅里葉轉換紅外光譜(FTIR)的結果證明，立體障礙大的PL2易從Ru2-S2離去，並再配位到其他的Ru2-S2衍生物。而在以電子撞擊式質譜儀(EI-MS)的反應監控中，我們推測可能有Ru2-S2-formate複合物存在，儘管進一步的結構確認與預期不同，但仍得到兩個由光催化生成的新產物(Ru2-S2-P(o-tol)2和Ru2-S2-[P(o-tol)2THF])。當逐漸了解有機磷基和釕-產氫團簇的關聯，此研究可幫助我們了解反應機制並發展新型的釕-產氫團簇和有機磷基，應用在未來光催化氫能源工業中。

Hydrogen has been regarded as a promising alternative energy candidate. Hydrogenases are enzymes that catalyze the reversible reduction of protons to hydrogen (H+ + 2 e-↔ H2). Due to the high catalytic activity of [FeFe] hydrogenases, their active sites (the H-clusters), have been reconstructed and used as photochemical catalysts for solar-driven hydrogen research. In a previous study, the combination of a biomimetic ruthenium-based H-cluster [Ru2-S2-P(o-tol)3] with one equivalent of P(o-tol)3 promoted the excellent efficiency for formic acid (FA) decomposition in photocatalytic systems. Our goal was to determine if there was an improvement efficiency when the Ru2-S2 was substituted with two phosphine ligands (P-ligands). We then attempted to investigate the PL2 effects on catalytic activity by using the Ru2-S2 complex in a photocatalytic system. Artificial ruthenium H-clusters coordinated with aryl P-ligands were synthesized. Ru2-S2-(PLY)2, Y=1‒5 and Ru2-S2-PL2-PL3 were purified and characterized by single crystal X-ray structure determination. These Ru2-S2-di-P-ligands complexes were used as a catalyst for decomposition of formic acid in the photocatalytic system. On the other hand, the combinations of Ru2-S2 and several kinds of alkyl phosphine were used for in situ catalysis. The Ru2-S2-(PL7)4 structure was also determined by X-ray. The observation suggests that Ru2-S2 linked with di-P-Ligands has no significant improvement on H2 generation efficiency. The PL6 and PL7 showed excellent efficiency (TOF 15753 h-1 and 18420 h-1) after 45 min. A further mechanism of study for PL2 effects on Ru2-S2 complexes were monitored in a photocatalytic system. FTIR (Fourier transform infrared spectroscopy) results indicate that the bulky PL2 is easily eliminated from the Ru2-S2-PL2 and back coordinates with other Ru2-S2 species. In EI-MS, the results present the possibility of Ru2-S2-formate complex. Although the results structure are not in line with expectations, two new photo-induced complexes (Ru2-S2-P(o-tol)2 and Ru2-S2-[P(o-tol)2THF]) were found and characterized by X-ray. When more information about the association between the artificial ruthenium H-cluster and P-ligands is obtained, the catalytic mechanism will become gradually clearer. These results could help us develop new Ru-carbonyl precursors or P-ligands for improving the efficiency of hydrogen production.