雙原子碳分子與其錯合物的合成、鑑定與反應性探討

Abstract

與自然環境中存在的 F2、O2 和 N2 雙原子分子相比，單獨雙原子碳 (C2) 是一種具有高活性的分子，僅天然存在於外太空或者星際之間。過去以來不同的 L→C2←L 化合物被許多團隊所研究開發，但其核心 C2 分子的鍵長與鍵結情況卻仍與單獨 C2 有所差異，因此吸引了更多化學家們嘗試以單配位基 L 來穩定C2 分子，但皆未能成功。 然而我們選用了特定具有立體障礙的膦化配位基 (imidazolidin-2-iminato) (L 為 (NHCR=N)2(CH3)P, NHCR 為含氮雜環碳烯)，成功合成了於常溫下可穩定存在於溶液中的單配位基雙原子碳分子 PDC，並且得到其晶體結構加以鑑定。另外我們也藉由不同的實驗來進一步了解 PDC 的反應特性，再嘗試與不同的金屬進行反應，成功合成出了不同的金屬錯合物，並且對個別結構加以進行鑑定和分析。 此外，我們發現 PDC 可做為一種新的類碳烯配位基，其具有優異的σ-予體能力（強於 NHCs 和 CAACs）與稍差的π-受體特性，更通過 Suzuki-Miyaura 交叉耦合實驗來證明 PDC 對於催化反應中所具有的效用。

In contrast to naturally occurring F2, O2 and N2, dicarbon (C2) is a reactive carbon allotrope that naturally exists only in the high temperature medium of stellar space. Various L→C2←L compounds had been studied, but the bonding situation of the central C2 in this motif differs remarkably from that of free C2. So it has fascinated chemists for a long time and numerous experimental attempts to stabilize it with a ligand L have not been successful yet. Here we have prepared and structurally characterized diatomic C2 as mono-ligated complex phosphine stabilized dicarbon (PDC) using a bulky phosphine ligand bearing two imidazolidin-2-iminato groups (L is (NHCR=N)2(CH3)P, where NHCR is a N-heterocyclic carbene). The compound is stable in solution at ambient temperature and has also been isolated in the solid state. The reactivity of PDC has been investigated with a variety of reactions. Different metal complexes supported with the PDC were prepared, and their molecular structures were characterized and analyzed. We explore the use of molecules as a new complementary class of carbene-like ligands featuring strong σ-donor (>NHCs and CAACs) but weak π-acceptor properties. We demonstrate the catalytic utility of the PDC framework by successful implementation for Suzuki-Miyaura cross-coupling.