探討同碳雙碳烯與鎳金屬進行分子內碳‒氫活化反應機制及研究其錯合物之氧化還原活性

Abstract

同碳雙碳烯（Carbodicarbene）是一種獨特的碳零價結構，其中心碳原子上具有兩對孤電子對，並由兩個中性電子給予配位基L穩定。在有機金屬和催化領域中，以具有良好的σ給予電子能力的配位基而聞名，與金屬搭配合成錯合物做後續更多元的應用，屬於發展日漸活躍的研究領域。 本論文以同碳雙碳烯作為配位基，合成一系列鎳二價金屬錯合物，此結構是透過同碳雙碳烯中，其中一個甲基側臂進行碳-氫活化形成的。在合成過程中，我們發現部分鎳二價前驅物被還原，隨後形成同碳雙碳烯配位的鎳一價錯合物。因此，我們以研究鎳二價錯合物的形成機制為目標，並根據上述觀察結果提出兩種機制：鹼基輔助碳-氫活化和自由基反彈碳-氫活化。 此外，我們也合成了以同碳雙碳烯和碳烯作為配位基的鎳二價和鈀二價金屬錯合物，用於研究同碳雙碳烯與不同金屬配位後的氧化還原活性。透過單電子氧化反應，我們成功合成並分離出兩種錯合物的氧化物質。藉由X光單晶繞射儀解析其晶體結構，以X光吸收光譜確認中心金屬價數，並以電子順磁共振光譜儀輔佐分析電子結構。結果表明，鎳二價錯合物的氧化主要發生在金屬中心，而鈀二價錯合物的氧化主要發生在同碳雙碳烯的配位基中心。

Carbodicarbenes, a divalent carbon(0) species supported by two neutral donor groups (L), possess two lone pairs of electrons on their central carbon atom. Due to their strong σ donating ability, they have been reliable ligands in organometallic and catalysis. In this work, a series of novel CDC‒nickel(II) complexes were synthesized. They were generated via intramolecular C(sp3)‒H bond activation at one of the CDC methyl side arms. During the synthesis, we found that the nickel(II) precursor was partially reduced, and later formed the CDC‒nickel(I) complex. Accordingly, we sought to investigate the mechanism of formation of CDC‒nickel(II) complexes, and two mechanisms were proposed: base-assisted and radical-rebound C‒H activation. In addition, we have also synthesized nickel(II) and palladium(II) complexes bearing CDC and NHC as ligands. They were used for probing the redox activity of CDC in coordination with different metals. Upon single-electron oxidation, we successfully obtained the oxidized species of both complexes. Their electronic structures were investigated by a combination of EPR, X-ray absorption spectroscopies, and X-ray crystallography. The results indicated that oxidation of the nickel(II) complex occurs mostly on the metal center, whereas that of the palladium(II) complex is CDC ligand-centered.