含磷硫四牙基雙三角錐三價銅錯合物之生成研究

Abstract

為了瞭解酵素如何裂解氧氣，三價銅錯合物的生成是相當重要的訊息。目前文獻中單核三價銅錯合物並不多見，其中大部分屬於四配位平面四方構形。將三腳四牙配位基P(C6H3-3-SiMe3-2-SH)3 (H3PS3′)去質子化後與CuCl2及 [PPN]Cl在MeCN與CH2Cl2混合溶劑下反應，會發生自身氧化還原反應得到 [PPN][PS3′CuCl] (1) 和 [PPN][CuCl2]，利用X光單晶繞射、X光吸收光譜及核磁共振光譜證實錯合物1為逆磁雙三角錐構形的三價銅錯合物。在乙腈或二氯甲烷下，藉循環伏安儀會觀察到錯合物1出現不可逆的氧化及還原峰，可知錯合物1不是電化學安定的化合物。由不同反應條件下錯合物1的產率變化，可推測此自身氧化還原反應的機制應為：雙核銅二價錯合物與去質子化的PS3′3−配位基鍵結，雙核銅之間經由內部電子轉移，形成錯合物1與 [PPN][CuCl2]。通入氧氣會將 [PPN][CuCl2] 氧化成二價銅物質再進行自身氧化還原反應，可提高錯合物1的產率。此研究提供了有用的資訊以進一步了解五配位雙三角錐構形之三價銅錯合物的特徵。

Formation of copper(III) complexes is of great importance for the understanding of dioxygen cleavage in enzymatic systems. However, there are only few examples of structurally characterized mononuclear CuIII complexes, most of them possessing square-planar geometry. The tripodal tetradentate ligand P(C6H3-3-SiMe3-2-SH)3 (H3PS3′) was deprotonated by NaH, and further reacted with CuCl2 in MeCN/THF mixed solvent. The disproportionation of copper(II) species occurred to form [PPN][PS3′CuCl] (1) and [PPN][CuCl2]. The X-ray structure, X-ray absorption spectrum and NMR spectra of 1 unambiguously indicate that complex 1 is a diamagnetic copper(III) species with a trigonal bipyramidal geometry. Cyclic voltammogram analysis of 1 shows irreversible redox waves in either MeCN or CH2Cl2 revealing that complex 1 is an electrochemically unstable species. Based on yield analysis for the formation of 1 under different conditions, we propose that disproportionation of copper(II) species occurs through an inner-sphere electron transfer as dimeric copper(II) species encounters deprotonated PS3′3− ligand. The dimeric copper(II) species will be regenerated from resulting copper(I), [PPN][CuCl2], by O2 oxidation. This study provides useful insight for further understanding the characteristic of the five-coordination trigonal bipyramidal copper(III) complexes.