十五族雙牙基硼陽離子之合成與反應性探討

Abstract

在本論文中，1,2-雙(二苯基膦)乙烷配位之硼陽離子[1]+、(2-二苯基膦)吡啶配位之硼陽離子[3]+、(2-二叔丁基膦)吡啶配位之硼陽離子[4]+ 可被成功被合成，並利用核磁共振光譜鑑定。經由X-ray單晶繞射儀解析，[1]+為含雙膦基之五員環結構，而[3]+則是同時具有膦基及吡啶之高環張力四員環結構。與文獻報導過之十五族雙牙基配位所穩定之硼陽離子比較，[1]+ 與 [3]+ 具有較長的磷-硼鍵、更高的環張力，所以可以使其環形結構在遇到其他受質時更容易斷鍵，進而增強反應性。具有立體障礙更大的二叔丁基的 [4]+ 具有與 [3]+ 相似的11B NMR訊號，顯示 [4]+ 也具有相似的四員環結構。在反應性部分，[1][OTf] 可成功活化三乙基矽烷，產生膦-硼烷加合物1A，也可藉由受阻路易氏酸鹼對(frustrated Lewis pair)之反應機構來活化氫氣，顯示此類十五族雙牙基配位的環形硼陽離子比一般四配位硼陽離子具有更高反應性以及應用的潛力。

DPPE-coordinated boronium [1]+, Ph2P-Py-coordinated boronium [3]+, and tBu2P-Py-coordinated boronium [4]+ have been synthesized and characterized. The structure of [1]+ and [3]+ are confirmed by X-ray diffraction analysis. [1]+ shows a homoleptic five-membered ring, and [3]+ exhibits a highly-strained four-membered ring compared to reported bidendate group 15 ligands coordinated boroniums. Although having bulkier tBu2 group, [4]+ still presents cyclic structure similar to [3]+, which has been verified by 11B NMR spectrum. Reactivity study revealed that [1][OTf] can thermally activate Et3SiH through intramolecular frustrated Lewis pair mechanism to generate DPPE-9-BBN-H adduct (1A). It demonstrated that our cyclic boroniums bearing bidentate group 15 ligands have the potential to enhance the reactivity than usual tetra-coordinated boroniums.