Synthesis of Crystallographically Characterizable Bis(cyclopentadienyl) Sc(II) Complexes: (C 5 H 2 t Bu 3 ) 2 Sc and {[C 5 H 3 (SiMe 3 ) 2 ] 2 ScI} 1

• Published in: Journal of the American Chemical Society 2024-02, Vol.146 (5), p.3279-3292
• Main Authors: Queen, Joshua D, Anderson-Sanchez, Lauren M, Stennett, Cary R, Rajabi, Ahmadreza, Ziller, Joseph W, Furche, Filipp, Evans, William J
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.3c11922

The synthesis of previously unknown bis(cyclopentadienyl) complexes of the first transition metal, i.e., Sc(II) scandocene complexes, has been investigated using C H ( Bu) (Cp ), C Me (Cp*), and C H (SiMe ) (Cp ) ligands. Cp ScI, , formed from ScI and KCp , can be reduced with potassium graphite (KC ) in hexanes to generate dark-red crystals of the first crystallographically characterizable bis(cyclopentadienyl) scandium(II) complex, Cp Sc, . Complex has a 170.6° (ring centroid)-Sc-(ring centroid) angle and exhibits an eight-line EPR spectrum characteristic of Sc(II) with = 82.6 MHz (29.6 G). It sublimes at 200 °C at 10 Torr and has a melting point of 268-271 °C. Reductions of Cp* ScI and Cp ScI under analogous conditions in hexanes did not provide new Sc(II) complexes, and reduction of Cp* ScI in benzene formed the Sc(III) phenyl complex, Cp* Sc(C H ), , by C-H bond activation. However, in Et O and toluene, reduction of Cp* ScI at -78 °C gives a dark-red solution, , which displays an eight-line EPR pattern like that of , but it did not provide thermally stable crystals. Reduction of Cp ScI, in THF or Et O at -35 °C in the presence of 2.2.2-cryptand, yields the green Sc(II) metallocene iodide complex, [K(crypt)][Cp ScI], , which was identified by X-ray crystallography and EPR spectroscopy and is thermally unstable. The analogous reaction of Cp* ScI with KC and 18-crown-6 in Et O gave the ligand redistribution product, [Cp* Sc(18-crown-6-κ )][Cp* ScI ], , as the only crystalline product. Density functional theory calculations on the electronic structure of these compounds are reported in addition to a steric analysis using the Guzei method.