Yang Qiaomu, Yu Xiaojuan, Lapsheva Ekaterina, Pandey Pragati, Smith Patrick W, Gupta Himanshu, Gau Michael R, Carroll Patrick J, Minasian Stefan G, Autschbach Jochen, Schelter Eric J
P. Roy and Diana T. Vagelos Laboratories, Department of Chemistry, University of Pennsylvania 231 S. 34th St. Philadelphia PA 19104 USA
Department of Chemistry, University at Buffalo, State University of New York 732 Natural Sciences Complex Buffalo NY 14260 USA
Chem Sci. 2025 Aug 11. doi: 10.1039/d5sc03222a.
Organometallic cerium(iv) complexes have been challenging to isolate and characterize due to the strongly oxidizing nature of the cerium(iv) cation. Herein, we report two cerium(iv) alkynyl complexes, [Ce(TriNOx)(C[triple bond, length as m-dash]C-SiMe)] (1-Ce) and [Ce(TriNOx)(C[triple bond, length as m-dash]C-Ph)] (1-Ce) (TriNOx = (2--butylhydroxylaminato)benzylamine), that include terminal alkyne moieties. The isostructural thorium analogue [Th(TriNOx)(C[triple bond, length as m-dash]C-SiMe)] (1-Th) was also synthesized and compared with 1-Ce in bond distance, C-NMR spectra, vibrational spectra and electronic structure. The Ce-C bond distances were 2.501(3) Å for 1-Ce and 2.513(5) Å for 1-Ce on the shorter end of the few reported Ce-C single bonds (2.478(3)-2.705(2) Å), possibly indicating significant Ce 5d- and 4f-orbital involvement. C-NMR spectroscopy was also consistent with Ce-C covalency, with significantly deshielded resonances ranging from 185-213 ppm. Such C-NMR shifts demonstrate a strong influence from spin-orbit coupling (SOC) effects, corroborated by computational studies. Raman analysis showed stretching frequencies of 2000 cm (1-Ce) and 2052 cm (1-Ce), indicating the cerium(iv)-alkynyl interaction, compared to the parent HC[triple bond, length as m-dash]CPh (IR = 2105 cm and Raman = 2104 cm). L-edge X-ray absorption measurements revealed a predominant Ce(iv) electronic configuration, and magnetic measurements revealed temperature-independent paramagnetism. Electrochemical studies similarly revealed the electron donating ability of the alkynyl ligands, stronger than either fluoride or imido ligands for the Ce(iv)(TriNOx)-framework, with a cerium(iv/iii) reduction potential of = -1.58 to -1.66 V Fc/Fc. Evidence for a -influence has been observed by evaluating a series including previously reported [Ce(TriNOx)X] complexes with axial ligands X = THF, I, Br, Cl, F, C[triple bond, length as m-dash]C-Ph, C[triple bond, length as m-dash]C-SiMe, NH(3,5-(CF)-Ar), OSiPh, N(M(L))(3,5-(CF)-Ar) [M(L) = Li(TMEDA), K(DME) or Cs(2,2,2-crypt)]. These data stand in contrast with previous reports of an inverse -influence at cerium(iv) and point to differences in involvement of cerium 4f- 5d-orbitals in the electronic structures of the complexes.
由于铈（IV）阳离子具有强氧化性，有机金属铈（IV）配合物的分离和表征一直具有挑战性。在此，我们报道了两种含末端炔基部分的铈（IV）炔基配合物，[Ce(TriNOx)(C≡C-SiMe)]（1-Ce）和[Ce(TriNOx)(C≡C-Ph)]（1-Ce）（TriNOx =（2-丁基羟氨基）苄胺）。还合成了同构的钍类似物[Th(TriNOx)(C≡C-SiMe)]（1-Th），并在键长、碳核磁共振谱、振动光谱和电子结构方面与1-Ce进行了比较。1-Ce的Ce-C键长为2.501(3) Å，1-Ce的为2.513(5) Å，处于少数报道的Ce-C单键（2.478(3)-2.705(2) Å）较短的一端，这可能表明有显著的Ce 5d和4f轨道参与。碳核磁共振光谱也与Ce-C共价性一致，屏蔽显著的共振范围为185 - 213 ppm。这种碳核磁共振位移表明自旋 - 轨道耦合（SOC）效应有很大影响，计算研究证实了这一点。拉曼分析显示1-Ce的νC≡C拉伸频率为2000 cm⁻¹，1-Ce的为2052 cm⁻¹，表明铈（IV） - 炔基相互作用，相比母体HC≡CPh（红外 = 2105 cm⁻¹，拉曼 = 2104 cm⁻¹）。L边X射线吸收测量揭示了主要的Ce(IV)电子构型，磁性测量揭示了与温度无关的顺磁性。电化学研究同样揭示了炔基配体的给电子能力，对于Ce(IV)(TriNOx)骨架，其比氟化物或亚氨基配体更强，铈（IV/III）还原电位为E = -1.58至 -1.66 V vs Fc/Fc⁺。通过评估一系列包括先前报道的[Ce(TriNOx)X]配合物（轴向配体X = THF、I、Br、Cl、F、C≡C-Ph、C≡C-SiMe、NH(3,5-(CF₃)Ar)、OSiPh₃、N(M(L))(3,5-(CF₃)Ar) [M(L) = Li(TMEDA)、K(DME)或Cs(2,2,2-crypt)]）观察到了π-影响的证据。这些数据与先前关于铈（IV）处反向π-影响的报道形成对比，并指出铈4f和5d轨道在配合物电子结构中的参与存在差异。
