Synthesis, properties and structures of the tris(cyclopentadienyl)thorium(III) complexes [Th{eta(5)-C5H3(SiMe2R)(2)-1,3}(3)] (R = Me or Bu-t)

The homoleptic, dark-blue, crystalline (disubstituted-cyclopentadienyl)thor ium(III) complexes [Th{eta (5)-C5H3(SiMe2R)(2)-1,3}(3)] (R = Me 1 or 'Bu 3) were obtained in good yield from the appropriate tris(cyclopentadienyl)tho rium(IV) chloride by treatment with an excess of sodium-potassium alloy in toluene at 20-35 degreesC with sonication. Complex I was also accessible by a similar reduction of [ThCp"Cl-2(2)] [Cp" = eta (5)-C5H3(SiMe3)(2)-1,3]; with possibly a transient Th(II) cyclopentadienyl as intermediate. Complex 1 with wet toluene afforded [(ThCp"(3))(2)( mu -O)] (2); it was unreactive with THF, DME, CO or H-2, but with Na-K alloy in THF it afforded a green, d iamagnetic, readily oxidisable cyclopentadienylthorium complex. Complexes 1 and 3 showed singlet EPR spectra in methylcyclohexane at 298 K, whence it is concluded that they have a 6d(1) rather than a 5f(1) electronic ground s tate. Variable temperature EPR spectra, magnetic measurements and optical s pectra of I are described and discussed. The X-ray structures of crystallin e I and 3 show that each has approximate D-3h, symmetry about the Th atom, which can be regarded as bound to the centroid of each of the three cyclope ntadienyl rings. (C) 2001 Elsevier Science B.V. All rights reserved.