多牙氮配位基及雙金屬鈀錯合物的合成與其催化應用

Abstract

本篇論文分別合成2,7-bis(2-pyridyl)-1,8-naphthyridine (bpnp) 和 5-phenyl-2,8-bis(2,2’-bipyridin-6-yl)-1,9,10-anthyridine (pbbpa) 作為多牙配位基，利用這些配體與鈀金屬進行錯合反應，探討所生成錯合物的結構和催化應用。多牙氮配位基 bpnp 與乙酸鈀在甲醇和三氟醋酸下反應生成 Pd2(bpnp)(TFA)3(OH) (9)，pbbpa 與 Pd(MeCN)2Cl2 反應，合成出雙金屬錯合物。由於其溶解度不佳，使用六氟磷酸鉀置換陰離子，生成 [Pd2(pbbpa)Cl2](PF6)2 (11)，以核磁共振光譜和質譜分析分別鑑定結構。 論文中比較 9 和 11 對於硝基還原反應之催化活性之差異。在先前的研究工作中發現 [Pd2(pbbpa)Cl2](PF6)2 (11) 經過少量的 NaBH3CN 活化後，能夠在氫氣下還原硝基苯衍生物，而Pd2(bpnp)(TFA)3(OH) (9) 則是可以作為催化劑直接在氫氣下進行該還原反應。另外，對此催化系統的應用範圍做了廣泛性測試，並藉由動力學和可能的反應中間體的實驗，解析此催化的反應機構。發現 9 的催化過程是遵循縮合路徑，由 N-苯基羥胺和亞硝基苯縮合成氧化偶氮苯後，藉由雙金屬的協助進行後續的還原得到苯胺；而 11 的催化過程則和單金屬錯合物 Pd(bpy)(TFA)2 相同，是直接將 N-苯基羥胺還原成產物。

The use of bimetallic complexes as catalysts for the catalytic reactions has received much attraction due to the possible synergistic effect between the metal ions. In this study, a naphthyridine-based multidentate ligand 2,7-bis(2-pyridyl)-1,8-naphthyridine (bpnp) and an anthyridine-based ligand 5-phenyl-2,8-bis(2,2’-bipyridin-6-yl)-1,9,10-anthyridine (pbbpa) were synthesized. Coordination of bpnp with Pd(OAc)2 in a mixture of MeOH and trifluoroacetic acid yielded the dipalladium complex Pd2(bpnp)(TFA)3(OH) (9). Treatment of pbbpa with Pd(MeCN)2Cl2 followed by anion exchange resulted in the formation of [Pd2(pbbpa)Cl2](PF6)2 (11). The structures of both complexes were confirmed by 1H-, 13C-NMR and ESI-HRMS. In a previous work, the resulting complex obtained from treatment of 11 with NaBH3CN was catalytically active toward the reduction of nitroarenes in the presence of H2. In this work, complex 9 showed a similar activity without any pre-treatment. Comparison of the catalytic activity between these complexes was revealed. This catalytic system is applicable for various nitroarenes. The possible reaction mechanism of this catalytic system is established by the kinetic studies and the reactivity of possible intermediates under the catalytic conditions. 9 catalyzed through the condensation pathway, in which N-phenylhydroxylamine and nitrosobenzene formed azoxybenzene, and gave aniline by following reduction with the assistance of dimetal complex. On the other hand, 11 and Pd(bpy)(TFA)2 catalyzed through direct pathway, in which aniline was obtained by reduction of N-phenylhydroxylamine.