Structural Diversity in Cyanido Thorocene Complexes

Abstract

(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.