三角雙錐三價銅磷亞胺錯合物之合成機制與取代反應探討

Abstract

三角雙錐構形的三價銅錯合物[PPN][(TMSPS3)CuIII(NCBH3)] (2)，可視為是CH3CN配位在三價銅的類似物[PPN][(TMSPS3)CuIII(NCCH3)]，經由[PPN][(TMSPS3)CuIII(Cl)] (1) 和氰基硼氫化鈉(NaBH3CN)反應生成。另外，(TMSPS3)CuIII(NH=PPh3) (3) 可藉由錯合物1在THF下加入NaOMe而得，推測其反應機制是由NaOMe先與THF中少量的水產生OH-陰離子，及時生成的OH-陰離子再將[PPN]+打斷，產生O=PPh3以及NH=PPh3，生成的NH=PPh3會配位上三價銅金屬中心形成五配位的錯合物3。經由外加不同配位基(負電荷的N3-和電中性的DABCO)逐量滴定錯合物3，可知反應為1:1的配位基交換，並以UV-vis光譜儀觀測其變化，求得形成[PPN][TMSPS3CuIII(N3)]和TMSPS3CuIII(DABCO)的Keq分別為0.25和0.15，此結果顯示NH=PPh3的鍵結能力比DABCO和N3-強，推測可能與軸位配位基的鹼性及推電子能力有關。A trigonal bipyramidal copper(III) complex, [PPN][(TMSPS3)CuIII(NCBH3)] (2), an analogue of [PPN][(TMSPS3)CuIII(NCCH3)], was synthesized from the reaction of [PPN][(TMSPS3)CuIII(Cl)] (1) with sodium cyanoborohydride (NaBH3CN) in THF. Interestingly, complex 1 was converted to (TMSPS3)CuIII(NH=PPh3) (3) in THF as NaOMe was added. The added NaOMe is proposed to react with trace of water in THF solution to produce OH- anion. Then, the in-situ produced OH- anion attacks [PPN]+, and generates O=PPh3 and NH=PPh3. Further, NH=PPh3 coordinates to the copper(III) center to form the five-coordinate copper(III) complex. UV-vis titration of 3 by adding N3- (Keq = 0.25) or DABCO (Keq = 0.15) complies 1:1 ligand exchange in solution. This result demonstrates that the binding ability of NH=PPh3 ligand is strong than that of DABCO and N3-. This finding is related to basicity and donor capacity of the axial ligand.