軸位配基可置換之三角雙錐三價銅錯合物的電子結構及反應特性
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2016
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本研究承繼實驗室先前的工作，合成出三角雙錐構形的三價銅錯合物[PPN][Cu(TMSPS3)(Cl)] (錯合物1)。根據製備條件與錯合物1產率的關係以及DFT理論計算的結果，推測錯合物1和一同生成的一價銅副產物，是經由TMSPS3–Cu2Cl4中間體，進行熱力學驅動之二價銅自身氧化還原反應而產生。藉UV–vis光譜監測錯合物1與外加配基的滴定，結果符合配位基與氯離子的1:1置換平衡反應，而不同配位基之相對結合常數為：N3− (Keq = 18)、DABCO (8)、pyridine (0.13)、2,6-lutidine (0.0010)，此結果也解釋了錯合物1在溶液中的半穩定性質。據此進而合成了軸位配基衍生之錯合物：[PPN][Cu(TMSPS3)(N3)] (錯合物2)、[Cu(TMSPS3)(DABCO)] (錯合物3)和[PPN][Cu(TMSPS3)(NCS/Cl)] (錯合物4/1)。量測錯合物1–3之銅和硫元素的X-ray K-edge吸收光譜，可證實：銅離子的正三價氧化態、三角雙錐配位場造成錯合物LUMO(3dz2貢獻)的抬升、及銅—硫之間的高度共價性。這些結果指出Cu(TMSPS3)配位基團內的電子密度補償效應 (S→Cu)，一方面穩定了中心的三價銅離子，一方面也削弱了其軸位配基結合對靜電作用的需求。氰根配位的衍生物 [PPN][Cu(TMSPS3)(CN)] (錯合物5) 是由錯合物1和NaOH於CH3CN中反應而得；並藉NMR、UV–vis、IR等光譜跡象歸結：應有cyanomethide配位的三價銅中間體存在，從而引發CH3CN溶劑的C–CN鍵斷裂。此外，Sc(OTf)3會將錯合物1所配位的氯離子拔除，使三價銅片段裸露並導致二聚體[Cu(TMSPS3)]2 (錯合物6) 的形成。以上結果有助於未來高價銅催化劑的開發。
A trigonal bipyramidal copper(III) complex, [PPN][Cu(TMSPS3)(Cl)] (complex 1), was synthesized following our previous studies. Basing on the correlation between yields and preparation conditions as well as DFT calculations, we propose a thermodynamically favored copper(II) disproportionation occurs within a TMSPS3–Cu2Cl4 intermediate, producing complex 1 and a copper(I) side-product. UV–vis titrations of complex 1 with various additive ligands, such as N3− (Keq = 18), DABCO (8), pyridine (0.13) and 2,6-lutidine (0.0010), comply 1:1 ligand–chloride exchange in solution, hence clarifying the semi-stability of complex 1 in solution phase. Derivatized [PPN][Cu(TMSPS3)(N3)] (complex 2), [Cu(TMSPS3)(DABCO)] (complex 3) and [PPN][Cu(TMSPS3)(NCS/Cl)] (complex 4/1) were then accordingly synthesized. Cu and S K-edge X-ray absorption spectra of complexes 1–3 reveal theelevated LUMO (3dz2 feathered) in TBP ligand field with their +3 oxidation state of copper and the Cu–thiolate covalency. These indicate the electron density compensation (S→Cu) within Cu(TMSPS3) moiety, which not only stabilizes copper(III) center but also supresses the electrostatic demand for the axial ligand binding. A cyano derivative, [PPN][Cu(TMSPS3)(CN)] (complex 5), was isolated from the reaction of complex 1 with NaOH in CH3CN; and a cyanomethide-bound copper(III) intermediate is evidenced by NMR, UV–vis, and IR spectra, responsible for the C–CN bond cleavage of CH3CN solvent. Additionally, chloride of complex 1 is abstracted by Sc(OTf)3, which exposes the copper(III) moiety and leads the formation of dimeric [Cu(TMSPS3)]2 (complex 6). These results facilitate further development of high-valent copper catalysts.
A trigonal bipyramidal copper(III) complex, [PPN][Cu(TMSPS3)(Cl)] (complex 1), was synthesized following our previous studies. Basing on the correlation between yields and preparation conditions as well as DFT calculations, we propose a thermodynamically favored copper(II) disproportionation occurs within a TMSPS3–Cu2Cl4 intermediate, producing complex 1 and a copper(I) side-product. UV–vis titrations of complex 1 with various additive ligands, such as N3− (Keq = 18), DABCO (8), pyridine (0.13) and 2,6-lutidine (0.0010), comply 1:1 ligand–chloride exchange in solution, hence clarifying the semi-stability of complex 1 in solution phase. Derivatized [PPN][Cu(TMSPS3)(N3)] (complex 2), [Cu(TMSPS3)(DABCO)] (complex 3) and [PPN][Cu(TMSPS3)(NCS/Cl)] (complex 4/1) were then accordingly synthesized. Cu and S K-edge X-ray absorption spectra of complexes 1–3 reveal theelevated LUMO (3dz2 feathered) in TBP ligand field with their +3 oxidation state of copper and the Cu–thiolate covalency. These indicate the electron density compensation (S→Cu) within Cu(TMSPS3) moiety, which not only stabilizes copper(III) center but also supresses the electrostatic demand for the axial ligand binding. A cyano derivative, [PPN][Cu(TMSPS3)(CN)] (complex 5), was isolated from the reaction of complex 1 with NaOH in CH3CN; and a cyanomethide-bound copper(III) intermediate is evidenced by NMR, UV–vis, and IR spectra, responsible for the C–CN bond cleavage of CH3CN solvent. Additionally, chloride of complex 1 is abstracted by Sc(OTf)3, which exposes the copper(III) moiety and leads the formation of dimeric [Cu(TMSPS3)]2 (complex 6). These results facilitate further development of high-valent copper catalysts.
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三角雙錐三價銅, 配位基親和力, X-ray吸收, 碳—氰鍵裂解, 密度泛函理論, trigonal copper(III), ligand affinity, X-ray absorption, C–CN bond cleavage, density-functional theory