Lanthanide (Substituted-)Cyclopentadienyl Bis(phosphinimino)methanediide Complexes: Synthesis and Characterization

Design and synthesis of high-performance single-molecule magnets (SMMs) have long been a research focus. Inspired by the best dysprosium(III) metallocene SMMs and dysprosium(III) bis(methanediide) SMMs, we assumed dysprosium SMMs, which had electrical neutrality by combining the two types of ligands. As the Dy³⁺ center is coordinated by one (substituted-)cyclopentadienyl (Cp^R) ligand and one methanediide ({C(PPh₂NSiMe₃)₂}^2-) ligand on the axial sites, this ideal structure with linear C_carbene-Dy-Cp_cent would strengthen the magnetic anisotropy and exhibit excellent SMM properties. However, it is not easy to synthesize it in this configuration. We for the first time obtained [Y{C(PPh₂NSiMe₃)₂}(Cp^R)(THF)] (Cp^R = Cp(1), Cp (2), Cp*(3), Cp = C₅H₅, Cp = C₅H₄ tBu, Cp* = C₅Me₅) through the reactions of NaCp/KCp^R and [Y{C(PPh₂NSiMe₃)₂}(I)(THF)₂]. In the molecular structures of 1-3, except for the two expected ligands, one coordination tetrahydrofuran (THF) molecule was also found in each complex. The P-C-P values of 1-3 were 135.46(7), 136.421(8), and 131.43(10)°, respectively, which were far less than 180°. The C_carbene-Y-Cp_cent of 1-3 deviated significantly from the linear shape, which was 118.021, 129.459, and 118.331°, respectively. Such a coordination environment makes the dysprosium congener [Dy{C(PPh₂NSiMe₃)₂}(Cp*)(THF)] (4) whose C_carbene-Dy-Cp_cent (118.295°) was too small to maintain axiality and which almost exhibited no SMM properties. Even though the first exploration of lanthanide (substituted-)cyclopentadienyl bis(phosphinimino)methanediide complexes did not live up to our expectation, it provided great experiences for the future success of high-performance lanthanide (substituted-)cyclopentadienyl methanediide SMMs.