Structural Diversity in Cyanido Thorocene Complexes

(Cot)2Th (1) was found to react with Na*CN (Cot = η8-C8H8; Na* = Na­(18-crown-6)) or the
ammonium salts NR4CN (R = Et, nBu) in pyridine
to give a variety of anionic products, depending on the (Cot)2Th:MCN ratio and the nature of M+ (Na*+ or NR4+). When it was treated with 1 mol equiv
of NR4CN (R = Et, nBu) or Na*CN, (Cot)2Th (1) was transformed into the anionic monocyanide
derivative [Th­(Cot)2(CN)]− (2–) with a bent geometry and crystallized
either as a binuclear complex with a Th–CN–Na
ligation mode in [(Cot)2Th­(μ-CN)]­[Na*] (2[Na*]) or as a 1D coordination polymer in {[(Cot)2Th­(μ-CN)]­[NEt4]}∞ (2[NEt4]) due
to the presence of Th–CN–Th bridges. The structure of 2[NEt4] is remarkable because it is different from
that of [(Cot)2U­(CN)]­[NEt4], where the cyanide
is terminal, and because it evidences two available coordination sites
on the bent-thorocene fragment, suggesting that the anionic species
[(Cot)2Th­(μ-CN)­Th­(Cot)2]− (4) and [(Cot)2Th­(CN)2]2– (5) could be obtained. In the presence of 0.5 mol equiv
of NnBu4CN in pyridine, 1 was indeed transformed into the binuclear complex [{(Cot)2Th}2(CN)]­[NnBu4] (4[NnBu4]), which was characterized by X-ray diffraction, as
well as its analogue [{(Cot)2Th}2(μ-CN)]­[Na*­(py)2]·2py (4[Na*­(py)2]·2py)
obtained under similar conditions. Crystallization of [(Cot)2Th­(CN)]­[NnBu4] (2[NnBu4]) did not afford a polymeric compound analogous to 2[NEt4] but gave crystals of 4[NnBu4] and of the trinuclear compound [{(Cot)2Th­(μ-CN)}2Th­(Cot)2]­[NnBu4]2·py (3[NnBu4]2·py). Thorocene 1 rapidly
reacted with 2 mol equiv of NnBu4CN to give
the dianionic complex [(Cot)2Th­(CN)2]­[NnBu4]2 (5[NnBu4]2). However, with an excess of NEt4CN, only the monocyanide compound 2[NEt4]
could be obtained from 1, likely as the result of distinct
solubilities. The reactions reported here illustrate the chemical
potential of thorocene which, in contrast to (Cot)2U, can
easily trap strongly coordinating anions and evidence that [Th­(CN)]q− species such as 2– may be useful building blocks for the
formation of polymetallic derivatives and clusters. Crystal structures
show that compounds 2–5 exhibit an
unusual bent-thorocene moiety, a long-sought and rare geometry for
bis­(cyclooctatetraenyl) complexes.