Synthesis, properties and structures of the tris(cyclopentadienyl)thorium(III) complexes [Th{η5-C5H3(SiMe2R)2-1,3}3] (R=Me or tBu)

Abstract The homoleptic, dark-blue, crystalline (disubstituted-cyclopentadienyl)thorium(III) complexes [Th{η 5 -C 5 H 3 (SiMe 2 R) 2 -1,3} 3 ] (R=Me 1 or t Bu 3 ) were obtained in good yield from the appropriate tris(cyclopentadienyl)thorium(IV) chloride by treatment with an excess of sodium–potassium alloy in toluene at 20–35 °C with sonication. Complex 1 was also accessible by a similar reduction of [ThCp″ 2 Cl 2 ] [Cp″=η 5 -C 5 H 3 (SiMe 3 ) 2 -1,3]; with possibly a transient Th(II) cyclopentadienyl as intermediate. Complex 1 with wet toluene afforded [(ThCp″ 3 ) 2 (μ-O)] ( 2 ); it was unreactive with THF, DME, CO or H 2 , but with Na–K alloy in THF it afforded a green, diamagnetic, 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 state. Variable temperature EPR spectra, magnetic measurements and optical spectra of 1 are described and discussed. The X-ray structures of crystalline 1 and 3 show that each has approximate D 3 h symmetry about the Th atom, which can be regarded as bound to the centroid of each of the three cyclopentadienyl rings.