Synthesis of Crystallographically Characterizable Bis(cyclopentadienyl) Sc(II) Complexes: (C₅H₂^tBu₃)₂Sc and {[C₅H₃(SiMe₃)₂]₂ScI}^1–

Abstract

The synthesis of previously unknown bis(cyclopentadienyl) complexes of the first transition metal, i.e., Sc(II) scandocene complexes, has been investigated using C 5 H 2 ( t Bu) 3 (Cp ttt ), C 5 Me 5 (Cp*), and C 5 H 3 (SiMe 3 ) 2 (Cp″) ligands. Cp ttt 2 ScI, 1, formed from ScI 3 and KCp ttt , can be reduced with potassium graphite (KC 8 ) in hexanes to generate dark-red crystals of the first crystallographically characterizable bis(cyclopentadienyl) scandium(II) complex, Cp ttt 2 Sc, 2. Complex 2 has a 170.6°(ring centroid)-Sc-(ring centroid) angle and exhibits an eight-line EPR spectrum characteristic of Sc(II) with A iso = 82.6 MHz (29.6 G). It sublimes at 200 °C at 10 −4 Torr and has a melting point of 268−271 °C. Reductions of Cp* 2 ScI and Cp″ 2 ScI under analogous conditions in hexanes did not provide new Sc(II) complexes, and reduction of Cp* 2 ScI in benzene formed the Sc(III) phenyl complex, Cp* 2 Sc(C 6 H 5 ), 3, by C−H bond activation. However, in Et 2 O and toluene, reduction of Cp* 2 ScI at −78 °C gives a dark-red solution, 4, which displays an eight-line EPR pattern like that of 1, but it did not provide thermally stable crystals. Reduction of Cp″ 2 ScI, in THF or Et 2 O at −35 °C in the presence of 2.2.2-cryptand, yields the green Sc(II) metallocene iodide complex, [K(crypt)][Cp″ 2 ScI], 5, which was identified by X-ray crystallography and EPR spectroscopy and is thermally unstable. The analogous reaction of Cp* 2 ScI with KC 8 and 18-crown-6 in Et 2 O gave the ligand redistribution product, [Cp* 2 Sc(18crown-6-κ 2 O,O′)][Cp* 2 ScI 2 ], 6, 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.