Synthesis and Characterization of the First Sandwich Complex of Trivalent Thorium:  A Structural Comparison with the Uranium Analogue

Abstract

Reduction of the bulky 8-annulene thorium complex [Th{COT(TBS)2}2] (COT(TBS)2 = η-C8H6(tBuMe2Si)2-1,4) by potassium yields the anionic compound {Th[COT(TBS)2]2}K·(DME)2, which was crystallographically characterized and is the first sandwich complex of Th(III). EPR spectroscopy indicates that the molecule possesses a 6d1 ground state. A structural comparison is made with the isostructural uranium(III) complex and the thorium(IV) parent compound.

New sandwich complexes of di- and trivalent ytterbium: Reduction of Yb(3+) by a bulky cyclooctatetraenyl dianion

“…1 also shows that the t-butyl groups at silicon are both pointing away from the central ytterbium in order to minimize unfavorable steric repulsion by the Cp * ligand on the opposite side of the molecule. The same phenomenon has been reported for the anionic thorium(III) complex (DME) 2 K[Th (COT TBS ) 2 ] [12] As depicted in Fig. 2, the blue product 4 is a salt consisting of a [K(DME) 4 ] þ cation and a [Yb(COT TBS ) 2 ] À sandwich monoanion.…”

“…A similar result was reported for the uranocene derivative U(COT TBS ) 2 . The 1 H NMR spectrum of this compound exhibited SiMe 2 proton resonances at d À16.7 and À21.2 ppm [12]. Fig.…”

“…Unlike the previously reported lithium derivative Li 2 (COT TBS )$ THF [12], the potassium precursor [K(DME)] 2 (COT TBS ) (2) is a white, crystalline solid which is easily obtained as a well-defined starting material which does not lose the coordinated DME upon drying under vacuum. According to its 1 H NMR data compound 2 contains one DME ligand per potassium ion, so that the structure (Scheme 1) can be assumed to be analogous to the previously reported COT 000 derivative [13b].…”

“…The bulky silyl-substituted cyclooctatetraenyl ligand [C 8 H 6 (SiMe 2 t Bu) 2 -1,4] 2À (¼COT TBS ) was first reported by Cloke et al and successfully employed in the synthesis and characterization of the first sandwich complex of trivalent thorium [12]. The precursor 1,4-bis(t-butyldimethylsilyl)cycloocta-2,5,7-triene (1) is easily accessible in a one-pot reaction starting from cycloocta-1,5-diene.…”

“…Products isolated from such reactions include not only the anionic sandwich complexes [Ln(COT 00 ) 2 ] À [8,9] and the chloro-bridged dimers [(COT 00 )Ln(m-Cl)THF)] 2 [7a,b], but also unusual cluster-centered multidecker sandwich complexes [10] as well as the triple-deckers Ln 2 (COT 00 ) 3 [2]. Besides the COT 00 ligand, other bulky cyclooctatetraenyl dianions such as 1,4-bis(triisopropylsilyl)cyclooctatetraenyl (¼COT 1,4-SiiPr3 ) [11], 1,4-bis(t-butyldimethylsilyl) cyclooctatetraenyl (¼COT TBS ) [12] and 1,3,6-tris(trimethylsilyl) cyclooctatetraenyl (¼COT 000 ) [13] have also been successfully employed in organolanthanide chemistry. Only with the use of the latter an unprecedented ytterbium(II) tetra-decker sandwich complex, Cp * Yb(m-COT 000 )Yb(m-COT 000 )YbCp * , has become available starting with ytterbium(II) diiodide [13b].…”