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

The synthesis of previously unknown bis(cyclopentadienyl) complexes of the first transition metal, i.e., Sc(II) scandocene complexes, has been investigated using C5H2(Bu-t)(3) (Cp-ttt), C5Me5 (Cp*), and C5H3(SiMe3)(2) (Cp '') ligands. (Cp2ScI)-Sc-ttt, 1, formed from ScI3 and KCpttt, can be reduced with potassium graphite (KC8) in hexanes to generate dark-red crystals of the first crystallographically characterizable bis(cyclopentadienyl) scandium(II) complex, (Cp2Sc)-Sc-ttt, 2. Complex 2 has a 170.6 degrees (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 degrees C at 10(-4) Torr and has a melting point of 268-271 degrees C. Reductions of Cp*2ScI and Cp '' 2ScI under analogous conditions in hexanes did not provide new Sc(II) complexes, and reduction of Cp*2ScI in benzene formed the Sc(III) phenyl complex, Cp*Sc-2(C6H5), 3, by C-H bond activation. However, in Et2O and toluene, reduction of Cp*2ScI at -78 degrees 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 '' 2ScI, in THF or Et2O at -35 degrees C in the presence of 2.2.2-cryptand, yields the green Sc(II) metallocene iodide complex, [K(crypt)][Cp '' 2ScI], 5, which was identified by X-ray crystallography and EPR spectroscopy and is thermally unstable. The analogous reaction of Cp*2ScI with KC8 and 18-crown-6 in Et2O gave the ligand redistribution product, [Cp*Sc-2(18-crown-6-kappa O-2,O ')][Cp*2ScI2], 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.