Selected homoleptic metal β-diketiminates MIL and MIIL2 [MI = Li or K, MII = Mg, Ca or Yb; L: LPh = N(SiMe3)C(Ph)}2CH, LBut = N(SiMe3)C(Ph)C(H)C(But)N(SiMe3), L* = N(C6H3Pri2-2,6)C(Me)}2CH] have been studied by cyclic voltammetry (CV). The primary reduction (Epred, the peak reduction potential measured vs. SCE in thf containing 0.2 M [NBu4][PF6] with a scan rate 100 mV sâ1 at a vitreous carbon electrode at ambient temperature) is essentially ligand-centred: Epred being ca.
â2.2 V (LiLPh and KLPh) and â2.4 V [Mg(LPh)2, LiLBut and Ca(LPh)2], while LiL* is significantly more resistant to reduction (Epred = â3.1 V). These observations are consistent with the view that the two (LPh) or single (LBut) C-phenyl substituent(s), respectively, are available for Ï-electron-delocalisation of the reduced species, whereas the N-aryl substituents of L* are unable to participate in such conjugation for steric reasons. The primary reduction process was reversible on the CV-time scale only for LiLBut, Ca(LPh)2 and Yb(LPh)2. For the latter this occurs at a potential ca. 500 mV positive of Ca(LPh)2, consistent with the notion that the LUMO of Yb(LPh)2 has substantial metal character. The successive reversible steps, each separated by ca. 500 mV, indicate that there is strong electronic communication between the two ligands of Yb(LPh)2. The overall three-electron transfer sequence shows that the final reduction level corresponds to [YbII(LPh)2â(LPh)3â]. DFT calculations on complexes Li(LPh)(OMe2)2 and Li2(LPh)(OMe2)3 showed that both HOMO and LUMO orbitals are only based on the ligand with a HOMOâLUMO gap of 4.21 eV. Similar calculations on a doubly reduced complex Yb(µ-LPh)Li(OMe2)}2 demonstrated that there is a considerable Yb atomic orbital contribution to the HOMO and LUMO of the complex.
选定的均配
金属
β-二酮timinates MIL 和 MII
L2 [MI = Li 或 K,MII = Mg、Ca 或 Yb; L: LPh = N(SiMe3)C(Ph)}2CH, LBut = N(SiMe3)C(Ph)C(H)C(But)N(SiMe3), L* = N(C6H3Pri2-2,6) )C(Me)}2CH]已通过循环伏安法(CV)进行了研究。初级还原(Epred,在含有 0.2 M [NBu4][PF6] 的 thf 中相对于 SCE 测量的峰值还原电位,在环境温度下在
玻璃碳电极上扫描速率为 100 mV s±1)基本上是以
配体为中心的: Epred 大约是。
≤2.2 V(LiLPh 和 KLPh)和 ≤2.4 V [Mg(LPh)2、LiLBut 和 Ca(LPh)2],而 LiL* 明显更耐还原(Epred = ≤3.1 V) 。这些观察结果与以下观点一致:两个(LPh)或单个(LBut)C-苯基取代基分别可用于还原物质的α-电子离域,而L的N-芳基取代基* 由于空间原因无法参与此类缀合。仅 LiLBut、Ca(LPh)2 和 Yb(LPh)2 的初级还原过程在 CV 时间尺度上是可逆的。对于后者,这种情况发生的可能性约为。 Ca(LPh)2 的 500 mV 正值,与 Yb(LPh)2 的 LUMO 具有显着
金属特性的概念一致。连续的可逆步骤,每个步骤间隔约。 500 mV,表明Yb(LPh)2 的两个
配体之间存在强电子通讯。整体三电子转移序列显示最终还原
水平对应于[YbII(LPh)2→(LPh)3→]。对配合物 Li(LPh)(OMe2)2 和 Li2(LPh)(OMe2)3 的 DFT 计算表明 HOMO 和 LUMO 轨道均仅基于 HOMO-LUMO 能隙为 4.21 eV 的
配体。对双还原络合物 Yb(µ-LPh)Li(OMe2)}2 的类似计算表明,Yb 原子轨道对该络合物的 HOMO 和 LUMO 有相当大的贡献。