Structural Diversity in Cyanido Thorocene Complexes

Apr 16, 2014 - The structure of 2[NEt4] is remarkable because it is different from that of [(Cot)2U(CN)][NEt4], where the cyanide is terminal, and bec...
1 downloads 0 Views 2MB Size
Download PDF
Article pubs.acs.org/Organometallics

Structural Diversity in Cyanido Thorocene Complexes Alexandre Hervé, Pierre Thuéry, Michel Ephritikhine, and Jean-Claude Berthet* CEA, IRAMIS, NIMBE, CNRS UMR 3299 SIS2M, CEA/Saclay, 91191 Gif-sur-Yvette, France S Supporting Information *

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.

■

complexes of the d transition metals.3−9 The cyanide ion is one of the strongest ligands, with different ligation modes, and it is able to coordinate metal ions in their different oxidation states, affording a rich structural variety. In combination with the f elements, which have strong Lewis acidity, large ionic radii, flexible coordination geometries, mainly polar metal−ligand interactions, and sometimes, as for uranium, numerous oxidation states and unpaired f electrons, attractive compounds with novel physicochemical properties are expected to be obtained. The discovery of a novel class of linear metallocenes, e.g. [(C5Me5)2An(CN)5][NEt4]n (n = 2, 3), with uranium,6−8 is a good illustration of such a development giving rise to further experimental and theoretical studies. The latter have evidenced the important contributions of the 5f orbitals and 5f

INTRODUCTION For fundamental reasons as well as industrial and environmental challenges, it is crucial to better understand the properties of the 5f elements (some of which are too radioactive or unstable to be easily handled). Thus, comparison of the chemical behavior of similar complexes of the actinides and/or the lanthanides gives information on the influence of the f orbitals in the metal−ligand bonding and on the effects of the 5f/4f contraction on the chemical reactivity of these ions, as they become progressively harder and more ionic along the series.1,2 For such studies, organometallic species of the actinides are particularly attractive because of the large variety of available ligands, which enables solubility in organic solvents and facile 1H NMR detection. For the past decade, we have developed the cyanide chemistry of uranium and the lanthanides, a field poorly explored in contrast to the attention paid to the cyanide © 2014 American Chemical Society

Received: March 10, 2014 Published: April 16, 2014 2088

dx.doi.org/10.1021/om500252v | Organometallics 2014, 33, 2088−2098

Organometallics

Article

were distilled immediately before use. Deuterated pyridine (Eurisotop) was distilled over K and stored over 3 Å molecular sieves in the glovebox. NnBu4CN (95%), NEt4CN (94%), KCN, and NaCN (Aldrich) were dried at 80 °C under vacuum for 20 h and kept under argon. (Cot)2Th (1) was synthesized as previously described,14 but from ThCl4(dme)2.21 IR samples were prepared as Nujol mulls between KBr round cell windows and the spectra recorded on a Perkin-Elmer FT-IR 1725X spectrometer. The 1H and 13C{1H} NMR spectra were recorded on a 200 MHz spectrometer and referenced internally using the residual protio solvent resonances relative to tetramethylsilane (δH 0). The spectra were recorded at 21 °C when not otherwise specified. The 1H NMR signals of pyridine-d5 were referenced at δH 8.57, 7.41, and 7.0 and the signals of THF-d8 at δH 3.56 and 1.71; the 13C NMR signals of pyridine-d5 were referenced at δc 150.4, 135.9, and 123.9 and those of THF-d8 at δc 67.40 and 25.50. The 1H NMR signal of K2C8H8 is at δH 6.67 in pyridine-d5 and δH 5.67 in THF-d8, and that of C8H8 is at δH 5.64 in pyridine-d5.22 Elemental analyses were performed by Analytische Laboratorien at Lindlar (Germany) or by Medac Ltd. at Chobham (Surrey, U.K.). The measured carbon content is very often too low, as previously observed by different authors, which was interpreted as due to thorium carbide formation.18−20,23 Caution! Depleted uranium (primary isotope 238U) is a weak α emitter (4.197 MeV) with a half-life of 4.47 × 109 years, and natural thorium (primary isotope 232Th) is a weak α emitter (4.012 MeV) with a half-life of 1.41 × 1010 years; all of the manipulations and reactions should be carried out in monitored fume hoods or in a glovebox, in a laboratory equipped with α- and β-counting equipment. Caution! Cyanide reagents should always be handled with caution, under anhydrous conditions and an inert atmosphere or in a ventilated hood, as hydrolysis can lead to formation of very toxic HCN. NnBu4CN: 1H NMR (pyridine-d5) δH 3.44 (t, 8H, J = 7.7 Hz, NCH2CH2CH2CH3), 1.67 (quint, 8H, J = 7.2 Hz, NCH2CH2CH2CH3) 1.24 (sext, J = 7.5 Hz, 8H, NCH2CH2CH2CH3), 0.75 (t, 12H, J = 7.2 Hz, NCH2CH2CH2CH3); 13C{1H} NMR (pyridine-d5) δC 168.2 (CN), 59.4 (CH2), 24.8 (CH2), 20.6 (CH2), 14.4 (CH3); IR (KBr/Nujol) ν(CN) 2050 cm−1. Synthesis of (Cot) 2 Th (1). A flask was charged with ThCl4(DME)2 (3.0 g, 5.4 mmol) and K2Cot (1.98 g, 10.8 mmol), and THF (50 mL) was condensed into it. The yellow reaction mixture was stirred for 48 h at 23 °C. The solvent was then evaporated off and the residue dried under vacuum for 12 h. Toluene (100 mL) was then condensed, and Soxhlet extraction for 5−6 days permitted isolation of 1 as a bright yellow microcrystalline powder (1.83 g, 77%). Anal. Calcd for C16H16Th: C, 43.64; H, 3.66. Found: C, 41.60; H, 3.50. 1H NMR (THF-d8): δH 6.50 (s, 8 H, Cot). 13C{1H} NMR (THF-d8): δc 107.67 (s, 8H, CH of Cot). 1H NMR (pyridine-d5): δH 6.28 (s, 8 H, Cot). 13 C{1H} NMR (pyridine-d5): δc 104.92 (s, 8 H, CH of Cot); in the latter case the compound is the pyridine adduct (Cot)2Th(py).19 Synthesis of [(Cot)2Th(CN)][Na(18-c-6)] (2[Na*]).18 A 50 mL round-bottom flask was charged with 1 (100 mg, 0.23 mmol), NaCN (35.0 mg, 0.71 mmol), and 18-crown-6 (60.0 mg, 0.23 mmol), and pyridine (15 mL) was condensed into it. The orange suspension was transformed into an orange solution, and after 20 h at room temperature the solvent was evaporated off and the product extracted in THF (20 mL). Evaporation of the solvent and washing of the yellow residue with hot toluene (15 mL) afforded the pure product [(Cot)2Th(CN)][Na(18-crown-6)] as a yellow powder (140 mg, 82%). Anal. Calcd for C29H40NNaO6Th: C, 46.22; H, 5.35; N, 1.86; Na, 3.05. Found: C, 41.40; H, 4.97; N, 2.03; Na, 2.65. 1H NMR (pyridine-d5): δH 6.60 (s, 16 H, Cot), 3.22 (s, 24 H, OCH2). 1H NMR (THF-d8): δH 6.07 (s, 16 H, CH of Cot), 3.57 (s, 24 H, OCH2). 13 C{1H} NMR (pyridine-d5): δC 175.5 (CN), 103.0 (Cot), 70.4 (CH2O). 13C{1H} NMR (THF-d8): δC 164.3 (CN), 102.5 (Cot), 70.8 (OCH2). IR (KBr/Nujol): ν(CN)= 2108 cm−1. Yellow crystals of 2[Na*] were obtained by slow diffusion of Et2O into a pyridine solution or by slowly cooling a hot THF solution of 2[Na*]. Synthesis of [(Cot)2Th(CN)][NEt4] (2[NEt4]). A 50 mL roundbottom flask was charged with 1 (80 mg, 0.18 mmol) and NEt4CN (26.9 mg, 0.16 mmol), and pyridine (5 mL) was condensed into it.

electron configuration in the stability of these compounds, which display unprecedented reactivity.9 Apart from the ubiquitous cyclopentadienyl ligands, the Cot dianion (Cot = η8-C8H8) and its substituted derivatives also play a particular role toward the f-block elements, highlighting differences between the f elements and the d transition metals. The geometry of the C8 ring is particularly well adapted to the large size of the actinides and lanthanides and favors the formation of a unique series of linear π-sandwich compounds of formula [(Cot)2M]q− viewed as ferrocene-type10 representatives for the f elements until the discovery of the uranium(V) anion [(C7H7)2U]3−.11 Since 1968, the date of the characterization of the first bis(Cot) compound with uranium(IV),12,13 many studies, mainly based on the tetravalent compounds (Cot)2U and (Cot)2Th14 (1) and their trivalent lanthanide analogues [(Cot)2Ln]−,13 demonstrated the inability of these species to coordinate ligands as the result of the large steric pressure around the metal center. However, recent studies have changed this generally accepted idea. In 2008, the characterization of [(Cot)2U(CN)][NR4] revealed that ligands could coordinate onto a bis(Cot) species with bending of the (Cot)2Mf moiety and that the cyanide ion has the proper size and shape to insert between the two Cot rings of uranocene, which is the most stable and most covalent (Cot)2Mf compound.15 More recently, Evans, Edelmann, and co-workers reported that bulky substituents on the Cot ligand can also induce bending in the [(1,4-(Ph3Si)2C8H6)2M]q− compounds (M = Ce, q = 1; M = U, q = 0).16 These results were an incitement to further investigations with other ligands and actinocenes. In particular, we decided to compare the chemical behavior of the actinocenes (Cot)2An of the two natural actinides (An = U, Th). In addition to requiring minimal laboratory precautions in terms of radiation safety, these ions show quite similar ionic radii (rTh4+ ≈ rU4+ + 0.05 Å)17 but have high-energy 5f orbitals and above all distinct 5f electron numbers (U4+(5f2) and Th4+(5f0)), which should induce distinct chemical reactivity. Our recent preliminary work on the coordination chemistry of (Cot)2An (U, Th) clearly evidenced the unique behavior of (Cot)2Th (1) which, in contrast to its uranium counterpart, can readily trap neutral or anionic ligands to afford unprecedented bent compounds [(Cot)2Th(L)]q− (L = py, tBuNC, bipyridine; CN−, N3−, and H− anions).18−20 The striking distinct coordination behavior of the Th4+ and U4+ ions led us to compare the reactivity of the actinocenes (Cot)2An (An = U, Th) in the presence of the cyanide ion, with the aim of isolating a variety of thorium cyanide complexes. Here, we report the reactions of (Cot)2Th with some cyanide salts and the formation of a series of new bent anionic complexes. The rich variety of compounds and structures that are obtained is strongly dependent on the nature of the countercation (Na+, NR4+) and of the [(Cot)2Th]:CN ratio. These results contrast with the paucity of derivatives obtained from (Cot)2U.

■

EXPERIMENTAL SECTION

The complexes described below are oxygen and moisture sensitive. Syntheses and manipulations of the compounds were conducted under an ultrahigh-purity argon atmosphere with rigorous exclusion of air and water, using Schlenk-vessel and vacuum-line techniques or in a glovebox. The solvents, toluene, pentane, and tetrahydrofuran were dried over a mixture of sodium−benzophenone and pyridine over potassium and 2089

dx.doi.org/10.1021/om500252v | Organometallics 2014, 33, 2088−2098

Organometallics

Article

4[NnBu4] were deposited by slow diffusion of diethyl ether into a concentrated pyridine solution of 4[NnBu4]. Pale yellow crystals of 4[Na*(py)2]·2py were also obtained by slow diffusion of pentane into a pyridine solution of a mixture of 1 (11.4 mg, 0.026 mmol), NaCN (5 mg, 0.103 mmol), and 18-crown-6 (3.4 mg, 0.013 mmol) which was first heated to 100 °C for 24 h. Synthesis of [(Cot)2Th(CN)2][NnBu4]2 (5[NnBu4]2). A 25 mL round-bottom flask was charged with 1 (80 mg, 0.18 mmol) and NnBu4CN (106.4 mg, 0.36 mmol), and pyridine (20 mL) was condensed into it. After 2 h at 70 °C, the pale blue solution was stirred for an additional 15 h at room temperature. The solvent was then evaporated off and the yellow solid washed twice with hot toluene (10 mL) before drying under vacuum for 15 h at 23 °C (178 mg, 100%). 5[NnBu4]2 is slightly soluble in THF and insoluble in toluene. Anal. Calcd for C50H88N4Th: C, 61.45; H, 9.08; N, 5.73. Found: C, 60.39; H, 9.41; N, 6.12. 1H NMR (pyridine-d5): δH 6.57 (s, 16 H, CH of Cot), 3.16 (t, 16H, J = 8.2 Hz, CH2), 1.52 (m, 16H, CH2), 1.19 (m, 16H, CH2), 0.74 (t, 24H, J = 7.2 Hz, CH3). 13C{1H} NMR (pyridine-d5): δC 172.8 (CN), 102.0 (Cot), 59.1 (CH2), 24.5 (CH2), 20.5 (CH2), 14.3 (CH3). IR (KBr/Nujol): ν(CN) 2084 cm−1. Large yellow crystalline platelets of 5[NnBu4]2 were obtained after slow diffusion of Et2O into a pyridine solution. Although giving a rough model of the structure, the quality of the X-ray data was very poor. Crystals suitable for X-ray diffraction were obtained, in an NMR tube, by dissolution of 5[NnBu4]2 (10 mg) in hot THF (0.6 mL); large yellow platelets were deposited from the yellow solution almost quantitatively upon slow cooling to room temperature. Reactions of Uranocene and Na*CN or NR4CN. (a) An NMR tube was charged with (Cot)2U (10 mg, 0.022 mmol), NaCN (5 mg, 0.1 mmol), 18-crown-6 (5.9 mg, 0.022 mmol), and pyridine-d5 (0.5 mL). The green suspension was heated to 90 °C for 48 h, leading to a dark green solution containing large crystals of (Cot)2U. As for [(Cot)2U(CN)][NR4], the color varies from dark green to red upon the lighting conditions. The 1H NMR spectrum showed the formation of [{(Cot)2U(CN)][Na*] and the presence of residual uranocene (δH −37.5). 1H NMR (pyridine-d5): δH 3.31 (s, 24 H, CH2O), −32.44 (s, 32 H, CH of Cot). 13C{1H} NMR (pyridine-d5): δC 133.0 (Cot), 70.49 (CH2O). (b) An NMR tube was charged with (Cot)2U (15 mg, 0.033 mmol). 0.5 mol equiv of NnBu4CN (4.8 mg, 0.016 mmol). and pyridine-d5 (0.5 mL). The green reaction mixture was heated for 48 h to 90 °C, giving a green solution containing [(Cot)2U(CN)][NnBu4] (δH (cot) −31.7) and large dark green crystals of (Cot)2U (checked by X-ray diffraction). (c) An NMR tube was charged with [(Cot)2U(CN)][NEt4] (8.4 mg, 0.014 mmol), 1 mol equiv of (Cot)2U (6.3 mg, 0.014 mmol), and pyridine-d5 (0.5 mL). The green reaction mixture was heated for 24 h at 90 °C, giving a green-brown solution containing green crystals of (Cot)2U. The 1H NMR spectrum showed 3 singlets at δH 4.45, 1.93, and −32.15 in the ratio 8/12/16 corresponding to the starting product [(Cot)2U(CN)][NEt4].15 (d) An NMR tube was charged with (Cot)2U (10.0 mg, 0.022 mmol), 1 mol equiv of NnBu4CN (6.3 mg, 0.022 mmol), and pyridined5 (0.5 mL). After 30 min at 90 °C, the 1H NMR spectrum of the brown solution showed the quantitative formation of [(Cot)2U(CN)][NnBu4] (δ(cot) −31.7). The reaction also proceeded in THF, but partial or total release of the cyanide ion with precipitation of (Cot)2U was observed in CH2Cl2, toluene, and acetonitrile. Attempts to oxidize [(Cot)2U(CN)][NR4] with AgI led to a dark green solution and formation of uranocene. After addition of another 1 equiv of NnBu4CN to the solution, it was stirred for 15 h at room temperature; the 1H NMR spectrum showed a unique U−Cot singlet shifted to δH −31.3. Diffusion of Et2O led to the formation of a brown oil. (e) An NMR tube was charged with (Cot)2U (10.4 mg, 0.023 mmol), 2 mol equiv of NEt4CN (7.7 mg, 0.046 mmol), and pyridine-d5 (0.5 mL). The tube was heated to 90 °C for 20 h, affording a brown solution. The 1H NMR signal of the Cot ligand, in comparison to that of [(Cot)2U(CN)][NEt4], was shifted by ca. 1 ppm to δH − 31.4, as previously mentioned,15 but the brown crystals which were deposited

After refluxing for 15 h, the initially orange solution was transformed into a yellow suspension. Evaporation of the solvent gave a gold-yellow solid of 2[NEt4], which was obtained pure in quantitative yield after washing with toluene (2 × 15 mL) and drying under vacuum for 15 h at 23 °C (96 mg, 100% with respect to NEt4CN). Anal. Calcd for C25H36N2Th: C, 50.33; H, 6.08; N 4.69. Found: C, 48.28; H, 5.81; N, 5.53. The low solubility of the product in organic solvents prevents NMR characterization at room temperature. IR (KBr/Nujol): ν(CN) 2099 cm−1. An NMR tube was charged with (Cot)2Th (10 mg, 0.022 mmol) and 4 mol equiv of NEt4CN (15.1, 0.088 mmol) and pyridine (0.5 mL). After 15 h at 90 °C, the yellow solution was slowly cooled to room temperature and deposited yellow needles of {[(Cot)2Th (μ-CN)][NEt4]}∞. Thin yellow crystalline platelets of this polymer were also obtained by warming at 110 °C a concentrated solution of (Cot)2Th (8 mg, 0.018 mmol) and NEt4CN (12 mg, 0.072 mmol) in pyridine (0.4 mL). Synthesis of [(Cot)2Th(CN)][NnBu4] (2[NnBu4]). A 50 mL roundbottom flask was charged with 1 (150 mg, 0.34 mmol) and NnBu4CN (96.2 mg, 0.34 mmol), and pyridine (20 mL) was condensed into it. The initial orange solution turned progressively yellow-orange, and a small quantity of yellow precipitate was formed. After 15 h at room temperature the solvent was evaporated off and the bright yellow powder of 2[NnBu4] was washed twice with 15 mL of toluene and dried under vacuum for 15 h at 23 °C (209 mg, 87%). 2[NnBu4] is slightly soluble in THF and insoluble in toluene. Attempts to crystallize 2[NnBu4] were unsuccessful. Anal. Calcd for C33H52N2Th: C, 55.92; H, 7.39; N, 3.95. Found: C, 52.40; H, 7.17; N, 4.06. 1 H NMR (pyridine-d5): δH 6.57 (s, 16 H, CH of Cot), 3.02 (t, 8H, J = 8.1 Hz, CH2), 1.44 (m, 8H, CH2), 1.14 (sext, 8H, J = 7.2 Hz, CH2), 0.73 (t, 12H, J = 7.2 Hz, CH3). 1H NMR (THF-d8): δH 6.06 (s, 16 H, CH of Cot), 2.94 (m, 8 H, CH2), 1.60−1.25 (m, 16 H, CH2), 1.01 (t, 12H, J = 6.9 Hz, CH3). 1H NMR (THF-d8, 53 °C): δH 6.08 (s, 16 H, CH of Cot), 3.06 (t, 8 H, J = 7.2 Hz, CH2), 1.60−1.25 (m, 16 H, CH2), 1.01 (t, 12H, J = 7.2 Hz, CH3). 13C{1H} NMR (pyridine-d5): δC 175.6 (CN), 102.9 (Cot), 59.0 (CH2), 24.4 (CH2), 20.5 (CH2), 14.2 (CH3). 13C{1H} NMR (THF-d8): δC 101.8 (Cot), 58.6 (CH2), 24.3(CH2), 20.3 (CH2), 13.8 (CH2), CN not seen. 13 C{1H} NMR (THF-d8, 53 °C): δC 102.3 (Cot), 59.4 (CH2), 25.3 (CH2), 20.6 (CH2), 14.0 (CH2); the signal of CN was not detected. IR (KBr/Nujol): ν(CN) 2106 cm−1. Attempts to crystallize 2[NnBu4] led to the formation of crystals of [{(Cot)2Th(μ-CN)}2Th(Cot)2][NnBu4]2 (3[NnBu4]2) and the bimetallic [{(Cot)2Th}2(μ-CN)][NnBu4] (4[NnBu4]). Thin yellow crystalline platelets of 3[NnBu4]2, suitable for X-ray diffraction, were initially obtained by slow diffusion of Et2O into a pyridine solution of the mixture of Th(Cot)2 (10 mg, 0.022 mmol) and NnBu4CN (6.0 mg, 0.021 mmol) which was heated to 100 °C for 15 min. In another attempt under the same conditions, crystals of the bimetallic [{(Cot)2Th}2(μ-CN)][NnBu4] (4[NnBu4]) were deposited. An NMR tube was charged with 1 (10 mg, 0.022 mmol) and 0.66 mol equiv of NnBu4CN (4.3 mg, 0.015 mmol) and pyridine-d5 (0.5 mL). After 15 h at 90 °C, yellow crystals of 4[NnBu4] were deposited from the yellow-orange solution. The 1H NMR spectrum of the solution showed three Cot−Th signals at δH 6.57, 6.56, and 6.55. Synthesis of [{(Cot)2Th}2(μ-CN)][NnBu4] (4[NnBu4]). A 50 mL round-bottom flask was charged with 1 (100 mg, 0.23 mmol) and NnBu4CN (33.2 mg, 0.12 mmol), and pyridine (15 mL) was condensed into it. The orange suspension progressively turned yellow, and after 15 h at room temperature the solvent was evaporated off. The bright yellow solid of 4[NnBu4] was washed twice with 10 mL of THF and dried under vacuum for 15 h at 23 °C (71.20 mg, 55% with respect to NnBu4CN). 4[NnBu4] is poorly soluble in THF and insoluble in toluene or diethyl ether. Anal. Calcd for C49H68N2Th2: C, 51.21; H, 5.96; N, 2.44. Found: C, 49.53; H, 5.77; N, 2.71. 1H NMR (pyridine-d5): δH 6.57 (s, 32 H, CH of Cot), 3.00 (t, 8 H, J = 7.8 Hz, CH2), 1.43 (m, 8 H, CH2), 1.15 (m, 8H, CH2), 0.72 (t, 12H, J = 7.2 Hz, CH3). 13C{1H} NMR (pyridine-d5): δC 103.1 (Cot), 58.8 (CH2), 24.0 (CH2), 20.1 (CH2), 13.9 (CH3); the signal of CN was not detected. IR (KBr/Nujol): ν(CN) 2098 cm−1. Pale yellow crystals of 2090

dx.doi.org/10.1021/om500252v | Organometallics 2014, 33, 2088−2098

Organometallics

■

from the solution were always shown as being those of [(Cot)2U(CN)][NEt4] by X-ray diffraction. (f) An NMR tube was charged with (Cot)2U (10.0 mg, 0.022 mmol), 5 mol equiv of NnBu4CN (32 mg, 0.11 mmol), and pyridine-d5 (0.5 mL). After 30 min at 90 °C, the 1H NMR spectrum showed a unique U−Cot singlet at δH −30.9. Diffusion of Et2O or pentane led after 2 weeks to the formation of a brown oil. Crossed Th/U Reactions. (a) An NMR tube was charged with [(Cot)2U(CN)][NEt4] (10.0 mg, 0.016 mmol), (Cot)2Th (7.3 mg, 0.016 mmol), and pyridine-d5 (0.5 mL). After 15 h at 90 °C, the green solution contained dark green crystals of (Cot)2U and of 2[NEt4]. (b) An NMR tube was charged with (Cot)2Th (9.9 mg, 0.023 mmol), NnBu4CN (6.4 mg, 0.023 mmol), and pyridine-d5 (0.5 mL). After 1 h at 90 °C, the solution was yellow and the 1H NMR spectrum showed the quantitative formation of [(Cot)2Th(CN)][NnBu4] (δH 6.57). (Cot)2U (10 mg, 0.023 mmol) was then added, and after 1 h at 90 °C, crystals of uranocene (checked by X-ray diffraction) deposited from the dark green solution. The 1H NMR spectrum of the solution showed at least two superimposed Cot−Th signals at δH 6.48 (unidentified species) and a weak and broad Cot−U signal at δH −35.25 that was not attributed to a known species; the nBu4N chain is slightly displaced (3.17 (m), 1.57 (m), 1.24 (m), and 0.78 (t)) in comparison to that of [(Cot)2Th(CN)][NnBu4]. (c) An NMR tube was charged with (Cot)2U (8.0 mg, 0.018 mmol), (Cot)2Th (8.0 mg, 0.018 mmol), NnBu4CN (5.3 mg, 0.019 mmol), and pyridine-d5 (0.5 mL). After 10 min or 3 h at 23 °C, the solution was green and contained many dark green crystals of (Cot)2U (checked by X-ray diffraction). The 1H NMR spectrum showed a unidentified Th−Cot signal centered at δH 6.48 and a weak and broad paramagnetic U−Cot singlet at δH −34.9 (unknown species). The suspension and the NMR spectrum did not change after 3 h on reflux of the solvent; crystals of (Cot)2U and of the trimetallic 3[NnBu4]2 deposited after standing for 15 h at room temperature. Crystallography. The data were collected at 150(2) K on a Nonius Kappa-CCD area detector diffractometer24 using graphitemonochromated Mo Kα radiation (λ = 0.71073 Å). The crystals were introduced into glass capillaries with a protecting coating of “ParatoneN” oil (Hampton Research). The unit cell parameters were determined from 10 frames and then refined on all data. The data (combinations of φ and ω scans giving complete data sets up to θ = 30°, with a minimum redundancy of 4 for 90% of the reflections) were processed with HKL2000.25 Absorption effects were corrected empirically with the program SCALEPACK.25 The structures were solved by direct methods, expanded by subsequent difference Fourier synthesis, and refined by full-matrix least squares on F2 with SHELXL97.26 All non-hydrogen atoms were refined with anisotropic displacement parameters. In the compounds 2[NEt4], 4[NnBu4], and 4[Na*(py)2]·2py, the cyanide ligand is disordered over the two possible positions and each atom has been modeled as 0.5 nitrogen and 0.5 carbon (the four atoms being denoted C1a, N1a, C1b, and N1b when they are not related by a symmetry element), with constraints on positional and displacement parameters. In 3[NnBu4]2· py and 5[NnBu4]2, the cyanide nitrogen and carbon atoms were located so as to give the most satisfying refined displacement parameters (i.e., close to one another for a bridging cyanide or giving the most regular progression from metal to terminal atom in the case of monodentate cyanides). This assignment is unambiguous in 5[NnBu4]2, while disorder cannot be ruled out in 3[NnBu4]2·py (although refinement of a disordered model with different occupancy factors for nitrogen and carbon atoms over the two sites was unsuccessful). The hydrogen atoms were introduced at calculated positions and were treated as riding atoms with an isotropic displacement parameter equal to 1.2 times that of the parent atom (1.5 for CH3). Crystal data and structure refinement parameters are given in Table S1 (see the Supporting Information). The molecular plots were drawn with ORTEP-3.27 CCDC file nos. 988821−988825 contain the supplementary crystallographic data for compounds 2[NEt4], 3[NnBu4]2·py, 4[NnBu4], 4[Na*(py)2]·2py and 5[NnBu4]2, respectively.

Article

RESULTS AND DISCUSSION

The synthesis of [(Cot)2U(CN)][NEt4], the first bentactinocene complex, was clear evidence that the linear uranocene could coordinate strong ligands, and this induced further reactivity studies in our group. We first envisaged using [(Cot) 2U(CN)][NEt4] as a metallo ligand to prepare polymetallic cyanide species or clusters. However, reactions of (Cot)2U with 0.5 mol equiv of CN− or the direct combination of [(Cot)2U(CN)]− and (Cot)2U did not give any species involving U−CN−U linkage, whereas the polycyanide species [(Cot)2U(CN)n][NR4]n and the mono-Cot derivatives [(Cot)U(CN)n][NR4]n−2 could not be obtained from U(Cot)2 in the presence of excess cyanide ions.28 In all cases, the only characterized complexes from these reactions were (Cot)2U and/or its monocyanide derivative. As reported recently, (Cot)2U and (Cot)2Th showed distinct coordination behaviors,15,18−20 and the characterization of the bimetallic [{(Cot)2Th}2(μ-H)]− suggested that the use of ambidentate ligands could afford novel polymetallic Th species within the bis(Cot) series. The cyanide ion has C and N coordinating atoms, and its attractiveness when combined with d and f transition metals prompted us to inspect its reactivity with thorocene. Synthesis of [(Cot) 2 Th(CN)][Na*] (2[Na*]) and [(Cot) 2Th(CN)][NR 4] (2[NR4]; R = Et, n Bu). Crystal Structures of 2[Na*] and of the Polymer 2[NEt4]. Addition of excess NaCN to an equimolar mixture of 18-crown-6 and 1 in pyridine gave, after 20 h at room temperature, a yelloworange suspension (Scheme 1). Further extraction in THF of the dried residue afforded pure [(Cot)2Th(CN)][Na*] (2[Na*]; Na* = Na(18-crown-6)), which was deposited as yellow crystals, in high yield. The crystal structure of 2[Na*] was presented in a preliminary communication and will not be discussed further in detail, but a view of 2[Na*] is shown in Figure 1 and selected bond lengths and angles are given in Table 1. Complex 2[Na*] crystallized as a heterobimetallic complex with one bridging cyanide ligand best refined with Th−C and Na−N linkages. The most salient features are the unusual bent geometry of the (Cot)2Th fragment with a Cg···Th···Cg angle of 150° and Th···Cg distances of 2.09 and 2.10 Å (Cg = ring centroid). Although the uranium counterpart [(Cot)2U(CN)][Na*] could not be crystallized, it is expected to have a quite similar geometry in view of the U−CN bond found in [(Cot)2U(CN)][NEt4] and because a U−CN−Na linkage has already been reported in [{(C5Me5)2U}2(μ-CN){(μ-CN)2(Na(THF)}2 ]∞7 and in the amido-metallacycle derivatives [UN* 2 (N,C)(μ-CN)Na*] (N* = N(SiMe 3 ) 3 ; N,C = CH2SiMe2N(SiMe3)) and [UN*(N,O)2(μ-CN)Na(15-crown5)] (N,O = OC(CH2)SiMe2N(SiMe3)).5m A U−CN−Mg bridge was also reported in the metallocene species [(C5Me5)2UCl2(μ-CN)]2Mg(THF)4.6 In contrast, the only other thorium cyanide compound to have been reported, (tBu3C5H2)2Th(NC)(OSiMe3), showed an unprecedented isocyanide Th−NC bonding, which has not been commented upon.5j Formation of 2[Na*] is easier than that of the uranium analogue, requiring less drastic conditions to go to completion. 1 H NMR control experiments relative to the synthesis of [(Cot)2An(CN)][Na*] (An = U, Th) showed residual uranocene always contaminating the product [(Cot)2U(CN)][Na*], whereas the thorium analogue was obtained in a 2091

dx.doi.org/10.1021/om500252v | Organometallics 2014, 33, 2088−2098

Organometallics

Article

Scheme 1. Synthesis of the Bent Cyanido Thorocenes

was of interest in order to determine the possible role of the NR4+ and Na*+ cations in the solid-state organization of the anion 2−, as well as for structural comparisons with the analogous uranium anionic complex [(Cot)2An(CN)]−. Yellow crystalline platelets of 2[NEt4] were obtained upon slow cooling of a pyridine solution of 1 in the presence of excess NEt4CN (4 equiv). Views of the metal ion environment and of the polymeric assemblage in 2[NEt4] are shown in Figure 2, while selected bond lengths and angles are given in Table 2. In contrast to [(Cot)2U(CN)][NEt4], which is mononuclear in the solid state,15 the structure of 2[NEt4] consists of infinite onedimensional zigzag chains of [(Cot)2Th(CN)]− anions linked to one another in an almost face-to-face arrangement, where each bent (Cot)2Th fragment is coordinated in its equatorial plane by two disordered cyanide ions (see the Experimental Section). 2[NEt4] is, after the neutral derivatives (Cot)2Th(L), where L is a bidentate ligand (2,2′-bipy, phen, Me4phen), a rare example of a (Cot)2An species containing two donor atoms in its equatorial girdle and is the first to be anionic. This structure of 2[NEt4] evidences for the first time that 12-coordinate (Cot)2Th(L)2-type compounds, where L is a monodentate ligand, are attainable. Previous attempts at such (Cot)2Th(L)2 species by addition of excess isonitrile tBuNC to (Cot)2Th(NCtBu) were unsuccessful.19 The two cyanide groups on the Th4+ ion are not coplanar, and the C1a′ and N1a atoms are on either side of the plane defined by Th, C1a, and N1a′ (see Figure 2 for labels). The Cg···Th···Cg angle of 140.1° (Cg = ring centroid) is one of the lowest values reported to date, close to that found in the anion [(Cot)2Th(bipy)]− and comparable to those in the other 12-coordinate (Cot)2 Th(bipy) and (Cot)2Th(Me4phen) species.19,20 These angles are generally found to vary within the range 140.0−154.3°, the

Figure 1. View of 2[Na*].18 The hydrogen atoms have been omitted. Displacement parameters are drawn at the 30% probability level.

quantitative fashion. Moreover, the stability of [(Cot)2Th(CN)]− is notably larger than that of [(Cot)2U(CN)]−, which readily releases CN− with formation of (Cot)2U in acetonitrile, CH2Cl2, or toluene. In a manner closely similar to the synthesis of [(Cot)2U(CN)][NEt4],15 treatment of 1 with slightly less than 1 mol equiv of NEt4CN in refluxing pyridine afforded [(Cot)2Th(CN)][NEt4] (2[NEt4]) in almost quantitative yield (Scheme 1). Its poor solubility at room temperature prevented NMR characterization. Elucidation of the crystal structure of 2[NEt4] 2092

dx.doi.org/10.1021/om500252v | Organometallics 2014, 33, 2088−2098

Organometallics

Article

Table 1. Selected Bond Lengths (Å) and Angles (deg) in 2[Na*], 4[Na*(py)2], and 4[NnBu4] [{(Cot)2Th}2(CN)][Na*(py)2]·2py (4[Na*(py)2]·2py)

[(Cot)2Th(CN)][Na*] (2[Na*]) ⟨Th−C(Cot)⟩ Th···Cga Th−C(1)/N(1) C−N Na−X (X = N, O) Th···Th Cg1···Th···Cg2 Th−C−N Cg···Th−X a

2.80(1) 2.09; 2.10 2.648(4) 1.157(6) Na−N(1) Na−O(2) Na−O(4) Na−O(6)

2.365(4); Na−O(1) 2.527(5) 2.527(4); Na−O(3) 2.656(5) 2.584(5); Na−O(5) 2.539(4) 2.818(6)

150.2 176.4(3) 105.9; 103.9

[{(Cot)2Th}2(CN)] [NnBu4] (4[NnBu4])

2.76(2) 2.09; 2.10 2.638(3) 1.148(6) Na−N(2) 2.457(4); Na−O(1) 2.745(2) Na−O(2) 2.772(3); Na−O(3) 2.724(3)

2.76(2); 2.76(3) 2.09; 2.09; 2.08; 2.09 2.641(3); 2.609(3) 1.162(4)

6.4242(4) 151.3 178.9(4) 104.0; 104.6

6.4113(3) 151.9; 149.9 178.6(3); 178.4(3) 104.3; 103.8; 104.8; 105.2

Cgi are the centroids of the cyclooctatetraenyl rings.

Figure 2. Views of the metal ion environment (left) and of the polymeric chain (right) in 2[NEt4]. Countercations and hydrogen atoms have been omitted. Only one particular position of the disordered cyanide ions is represented. Displacement parameters are drawn at the 50% probability level. Symmetry codes: (i) x + 1/2, 3/2 − y, −z; (j) x − 1/2, 3/2 − y, −z.

[{(Cot)2Th(μ-CN)}2Th(Cot)2][NnBu4]2·py (3[NnBu4]2·py) and [(Cot)2Th(μ-CN)Th(Cot)2][NnBu4] (4[NnBu4]) were obtained in a reproducible manner from a 1:1 mixture of 1 and NnBu4CN in pyridine. Formation of these compounds from 2[NnBu4], in contrast to the 1D polymer of 2[NEt4], shows the major role of the NR4+ countercation in the crystallization of the [(Cot)2Th(CN)][NR4] species. These bi- and trinuclear anions are likely intermediates in the formation of the 1D polymer 2[NEt4]. The single Cot 1H NMR singlet of 2[NnBu4] would be the mean signal of several polynuclear species. The IR spectra of 2[NEt4] and 2[NnBu4] show a single ν(CN) absorption band (2099 and 2106 cm−1, respectively), suggesting the formation of a unique product in the solid state (vide infra) after evaporation of the solvent. Synthesis of the Binuclear Complex [{(Cot)2Th}2(CN)][NnBu4] (4[NnBu4]) and Attempts To Synthesize Mixed Th/U Bimetallic Complexes. Rational syntheses of 3[NnBu4]2 and 4[NnBu4] were attempted by mixing 1 and NnBu4CN in 3:2 and 2:1 ratios, respectively (Scheme 1). The 1 H NMR spectrum in pyridine of the 3:2 crude mixture showed three superimposed Cot signals (δ 6.57−6.55), suggesting the presence of several species in slow equilibrium, and 3[NnBu4]2 was not isolated. In the presence of slightly less than 0.5 mol equiv of NnBu4CN, 1 was transformed into a bright yellow solid for which the elemental analyses and the 1H NMR spectrum indicate formation of the expected binuclear complex [{(Cot)2Th}2(CN)][NnBu4] (4[NnBu4]) as the sole product. The 1H NMR spectrum in pyridine showed a Cot signal at

lower values being related to the more sterically congested 12-coordinate species. The mean Th−C(Cot) distance of 2.84(7) Å is larger by 0.14 and 0.04 Å than in the linear thorocene14b and the 11-coordinate 2[Na*],18 respectively, in agreement with the increase of the metal−ligand distance of ca. 0.05 Å when the coordination number increases by 1. This difference can be compared with that found in the bent and linear uranocenes, where the mean U−C(Cot) distance of (Cot) 2U is shorter by ∼0.082 Å than in its 11-coordinate [(Cot)2U(CN)]− derivative.15 The Th−C(Cot) distance is also comparable to those reported in the neutral derivatives (Cot) 2Th(L2), where L2 is a bidentate ligand (L 2 = bipy (2.82(4) Å), Me4phen (2.81(4) and 2.82(4) Å for the two independent molecules)), and [(Cot)2Th(bipy)]− (2.86(4) Å). The mean Th−C/N distance of 2.630(5) Å is close to the Th−C distance measured in 2[Na*] (2.648(4) Å).18 In order to circumvent the poor solubility of 2[NEt4], and to get more soluble cyanide species detectable by NMR spectroscopy and useful as chemical precursors, the Et4N+ counterion was exchanged for nBu4N+. By mixing 1 and NnBu4CN in a 1:1 ratio in pyridine, [(Cot)2Th(CN)][NnBu4] (2[NBu4]) could be isolated in 87% yield after usual treatment (Scheme 1). The 1H NMR spectra of 2[Na*] and 2[NnBu4] in pyridine-d5 exhibit a singlet corresponding to the Cot ligand at δH 6.60 and 6.57, respectively. These resonances are shifted downfield relative to the δH 6.28 resonance of the precursor (Cot)2Th(py). Attempts to crystallize 2[NnBu4] were unsuccessful, but thin yellow crystalline platelets of the tri- and binuclear complexes 2093

dx.doi.org/10.1021/om500252v | Organometallics 2014, 33, 2088−2098

δH 6.57, a value shifted downfield in comparison to that of (Cot)2Th(py) (δH 6.28), which integrated for 32 H relative to the 36 H of the NnBu4+ ion. 4[NnBu4], obtained in 79% yield, is partially soluble in THF and poorly soluble in toluene. Large yellow crystalline platelets of 4[NnBu4] were also obtained by slow diffusion of Et2O into a pyridine solution. Alternatively, crystals of the derivative 4[Na*(py)2]·2py were also isolated by slow diffusion of pentane into a pyridine solution of a 0.5:1 mixture of 18-crown-6 and 1 in the presence of excess NaCN. Attempts to synthesize mixed Th−(CN)−U compounds have also been carried out by cross-coupling reactions. Different ways have been considered from NnBu4CN (because of the solubility afforded by this countercation), by mixing a 1:1:1 mixture of 1, [(Cot)2U], and NnBu4CN or by treatment of [(Cot)2U(CN)][NEt4] with 1 and conversely by mixing [(Cot)2Th(CN)][NR4] with [U(Cot)2], all in pyridine. The 1 H NMR spectra of these dark green solutions showed intense and unidentified Th−Cot diamagnetic signals (or a mean signal) at δH ∼6.48−6.45 for thorocene cyanide species and a weak and broad paramagnetic U−Cot singlet in the range δH −34.39 to −35.25. In all the cases, crystallization of emerald platelets of uranocene (as checked by X-ray diffraction) occurred, demonstrating that the cyanide ion binds preferentially to Th4+ rather than to U4+ within the bis(Cot) series. Many attempts at crystallization led to crystals of the bi- and trinuclear thorocene compounds 4[NnBu4], 3[NnBu4]2·py, and the expected [(Cot)2Th(CN)U(Cot)2][NR4]2 could never be characterized. Crystal Structures of the Binuclear Complexes 4[N nBu 4] and 4[Na*(py) 2]·2py and the Trinuclear Complex 3[NnBu4]2·py. Views of the anions [{(Cot)2Th}2(μ-CN)]− in 4[NnBu4] and 4[Na*(py)2]·2py are shown in Figure 3, and selected bond lengths and angles are

71.67(9) X1···Th···X2

Figure 3. Views of the anion 4− in the compounds 4[NnBu4] (top) and 4[Na*(py)2] (bottom). Counterions and hydrogen atoms have been omitted. Only one particular position of the disordered cyanide ions is represented. Displacement parameters are drawn at the 30% probability level. Symmetry code: (i) 2 − x, 1 − y, 1 − z.

given in Table 2. As in the oligomeric species [(C5Me5)2Ln (μ-CN)(CNR)]3 (Ln = Sm and R = Cy; Ln = Pr and R = SiMe3),3d,f,4 [(C5Me5)2Sm(μ-CN)]6,3e or [{(C5Me5)2U}2(μ-CN)5{Na(THF)}2]∞,7 the cyanide ligands are disordered

a

106.6; 105.8; 106.7; 105.1 Cg···Th−X

Cgi are the centroids of the cyclooctatetraenyl rings.

Cg1···Th−C1/C2, 104.6/106;.0 Cg2···Th−C1/C2. 106.8/106.2 77.19(12)

C(1)−N(1), 1.152(5); C(2)−N(2), 1.138(5) 139.0 Th−C(1)−N(1), 176.0(4); Th−C(2)−N(2), 175.5(3)

2.84(7) 2.17; 2.19 2.625(3); 2.635(3) 6.3335(2) 1.175(4) 140.1 168.2(3)

⟨Th1−C⟩, 2.83(5); ⟨Th2−C⟩, 2.77(3); ⟨Th3−C⟩, 2.77(2) Th(1)···Cg, 2.17. 2.17; Th(2)···Cg, 2.09. 2.08; Th(3)···Cg, 2.09, 2.09 Th(1)−N(1), 2.601(3); Th1−N2, 2.612(3); Th(2)−C(1), 2.608(3); Th3−C2, 2.610(3) Th(1)−Th(2), 6.3493(3); Th(1)−Th(3), 6.3691(3) C(1)−N(1). 1.160(4); C(2)−N(2). 1.160(4) Cg1···Th(1)···Cg2, 142.2; Cg3···Th(2)···Cg4, 151.7; Cg5···Th(3)···Cg6, 152.1 C(1)−N(1)−Th(1), 176.3(3); C(2)−N(2)−Th(1), 175.4(3); N(1)−C(1)−Th(2), 173.7(3); N(2)−C(2)−Th(3), 175.9(3) Cg1/Cg2···Th1−N1, 104.6/105.7; Cg1/Cg2···Th1−N2, 106.1/104.4; Cg3/Cg4···Th2−C1, 105.0/103.4; Cg5/Cg6···Th3−C2, 103.1/104.8 N1−Th1−N2, 72.22(9)

2.84(6) Th···Cg1, 2.20; Th···Cg2, 2.18 Th−C(1), 2.675(5); Th−C(2), 2.685(4)

Article

⟨Th−C(Cot)⟩ Th···Cga Th−C(1)/N(1) Th···Th C−N Cg1···Th···Cg2 Th−C−N

[{(Cot)2Th(CN)}2Th(Cot)2][NnBu4]2·py (3[NnBu4]2·py) {[(Cot)2Th(CN)] [NEt4]}∞ (2[NEt4])

Table 2. Selected Bond Lengths (Å) and Angles (deg) in the Complexes 2[NEt4], 3[NnBu4]2·py, and 5[NnBu4]2

[(Cot)2Th(CN)2][NnBu4]2 (5[NnBu4]2)

Organometallics

2094

dx.doi.org/10.1021/om500252v | Organometallics 2014, 33, 2088−2098

Organometallics

Article

(Th(2) and Th(3)), and also in agreement with the 1:1 molar ratio of 1 and NnBu4CN used in its formation, it is likely that 3[NnBu4]2 results from the coordination of two [(Cot)2Th(CN)]− units onto the neutral (Cot)2Th compound (Scheme 2).

over the two possible positions and each atom has been modeled as a mixture of 0.5 nitrogen and 0.5 carbon (see the Experimental Section). The anion [{(Cot)2Th}2(μ-CN)]− in 4[Na*(py)2]·2py is centrosymmetric, while the two bent (Cot)2Th fragments in 4[NnBu4] are twisted along the Th−CN−Th axis. In the latter case, the two mean planes containing the Th and C1 (or N1) atoms and the two ring centroids in each (Cot)2Th fragment intersect with a dihedral angle of 17.9°. This geometry is quite different from that of the hydride [{(Cot)2Th}2(μ-H)]−, in which the close proximity (Th···Th distance of 4.586 Å) of the two identical bent (Cot)2Th moieties forced them to interlock in an almost perpendicular position for steric reasons. The Th··· Th distance of ca. 6.4 Å in the anions 4− is sufficient to suppress any destabilizing steric interaction between the two thorocene fragments, which can adopt an almost face-to-face arrangement. The Th−N−C angles in the two anions vary from 178.4(3) to 178.9(4)°. They are quite linear in comparison to the angle found in 2[NEt4] (168.2(3)°) or in the monometallic isocyanide compound ( t Bu 3 C 5 H 2 ) 2 Th(OSiMe)(NC) (164.5(7)°).5j The carbon atoms of the C8 rings are planar with a root mean square (rms) deviation of 0.04 Å at most for the two bimetallic anions. The Cg···Th···Cg angles, in the range 149.9−151.9°, are larger by ca. 11° than in 2[NEt4] but similar to that measured in [{(Cot)2Th}2(μ-H)]− (∼150°)18 or in [(Cot)2Th(N3)]− (149°) and can be compared with the angle found in [(Cot)2U(CN)]− (153°).15 The average Th−C(Cot) distance of 2.76 Å is typical for bent 11-coordinate thorocenes,19,20 while the Th−C/Ncyanide bond lengths (2.609(3)−2.641(3) Å) are comparable to the distances in 2[Na*] (2.648(4) Å) and in the trimetallic U(III) species [{(C5Me5)2U(μ-CN)(CNCMe3)}3] (2.582(3)−2.669(4) Å).4 They are similar to the U−C(CN) distance of 2.626(4) Å in [(Cot)2U(CN)]− but notably larger than the Th−NC bond length of 2.454(4) Å in (tBu3C5H2)2Th(OSiMe)3(NC).5j A view of the dianion [{(Cot)2Th(μ-CN)}2Th(Cot)2]2− of 3[NnBu4]2 is shown in Figure 4, and selected bond distances

Scheme 2. Best Representation of 3[NnBu4]2 as Coordination of Two [(Cot)2Th(CN)]− Units on 1

However, although the cyanide nitrogen and carbon atoms were located so as to give the most satisfying refined displacement parameters, disorder cannot be ruled out (see Experimental Section). As in 2[NEt4] or in the bimetallic 4[NnBu4], the [Th(1)]/ [Th(2)] and [Th(1)]/[Th(3)] thorocene fragments of the trimetallic species are twisted along the Th−CN−Th axis and their mean planes (Th, C/N, Cg1, Cg2) intersect with dihedral angles of 19.6 and 9.6°, respectively. This angle is 0 or 17.9° in the two bimetallic complexes 4[Na*(py)2] and 4[NnBu4], and 28.8° in 2[NEt4], which shows the great structural flexibility of these compounds. Here again, the carbon atoms of the C8 rings are coplanar with a maximum rms deviation of 0.038 Å and the Cg···Th···Cg angles deviate notably from linearity, with a value close to 152° for the 11-coordinate Th(2) and Th(3) fragments and 142.2° for the 12-coordinate Th(1) fragment. The two terminal thorocene fragments show quite identical Th−ligand distances, with a mean Th−C(Cot) distance of 2.77(3) Å and Th−C(CN) bond lengths of 2.608(3) and 2.610(3) Å. Structural characteristics of these 11-coordinate Th(2) and Th(3) fragments are similar to those in 2[Na*] and 2[NnBu4]. In the central 12-coordinate fragment, Th(1)−C(Cot) distances are similar but the Cg···Th···Cg obtuse angle is notably smaller (142.2°). The bi-, tri and polynuclear structures of 4[Na*(py)2]·2py, 4[NnBu4], 3[NnBu4]2·py, and 2[NEt4] show that, in the absence of an alkali-metal cation, the cyanide ligand in [Th(Cot)2(CN)]− is easily engaged in Th−CN−Th linkages, indicating that this bent anionic moiety can serve as a metalloligand for the formation of homo- and heteropolymetallics or clusters. The absence of U−CN−U interactions in the analogous uranium derivatives [(Cot)2U(CN)]− and the inability of [(Cot)2U(CN)]− to coordinate (Cot)2U clearly show that thorocene is a stronger Lewis acid than uranocene, in agreement with the distinct electron configuration of U4+ (5f2) and Th4+(5f0) and the less covalent Th−Cot bonding which favors mobility of the Cot dianion around the metal center and makes the approach of ligands easier. Moreover, the presence of 12-coordinate (Cot)2Th(L)2 species in the structures of 2[NEt4] and 3[NnBu4]2 strongly suggests that the bis-cyanide complex [(Cot)2Th(CN)2]2− (52−) would be attainable. Synthesis and Structure of the Bis-Cyanide Complex [(Cot)2Th(CN)2][NnBu4]2 (5[NnBu4]2). In contrast to the poorly soluble MCN reagents (M = Na, K), the ammonium salts NR4CN (R = Et, nBu) favor formation of polyanionic

Figure 4. View of the anion of 3[NnBu4]2. Hydrogen atoms have been omitted. Displacement parameters are drawn at the 30% probability level.

and angles are given in Table 2. In view of the quite identical structural parameters of the two terminal thorocene units 2095

dx.doi.org/10.1021/om500252v | Organometallics 2014, 33, 2088−2098

Organometallics

Article

[(Cot)2Th(CN)(NC)]− of 2[NEt4], while the Th−C(CN) bond lengths (2.675(5) and 2.685(4) Å) are slightly larger, by ∼0.05 Å, than in 2[NEt4] (2.648(4) Å). The C−N distances of the cyanide ligand in all the complexes 2−5 vary within the range 1.138(5)−1.175(4) Å, the smallest values being found in the terminal ligands of 5[NnBu4]2. Infrared Data of the Complexes 2[Na*], 2[NnBu4], 2[NEt4], 4[NnBu4], and 5[NnBu4]2. The IR spectra in Nujol mull of 2[Na*], 2[NnBu4], 2[NEt4], 4[NnBu4], and 5[NnBu4]2 show intense ν(CN) stretching frequencies at 2108, 2106, 2099, 2098, and 2084 cm−1, respectively. The lowest ν(CN) frequency is found for the terminal cyanide ligands of the anion of 5[NnBu4]2.29,30 The ν(CN) band was observed at 2073 cm−1 in the monoanionic compound [(Cot)2U(CN)][NEt4], and the lower frequency reported for this uranium(IV) compound may suggest a weaker U−CN interaction, as ν(CN) decreases with the weakening of the metal−CN bond.31 In the other thorocene cyanide complexes, which all involve cyanide bridges, the ν(CN) frequencies are generally shifted to higher energies. Such increases in ν(CN) values for M−CN−M′ in comparison to terminal M−CN bonding are well documented.30,32 Moreover, the higher ν(CN) value for the heterobinuclear compound 2[Na*] in comparison with that in 4[NnBu4] would suggest that the Th−CN−Na linkage is stronger than the Th−CN−Th bond. Thus, in the formation of homopolynuclear cyanide compounds of the f elements, the presence of alkalimetal salts or of other metal ions (Mg2+, Cu+) should be avoided. It was indeed reported that the nature of M+ in the MCN salts is crucial to the formation of f element cyanide complexes and that the presence of M+ (Na+, K+, or Mg2+) cations can be detrimental to the formation of species involving only an Mf−CN−Mf pattern.7 These ν(CN) frequencies are notably larger than that of 2050 cm−1 in free NEt4CN33 due to the strong σ-donating capacity of the cyanide ligand and the absence of π backbonding from the diamagnetic 5f0 Th4+ ion. They can be compared with the ν(CN) values in a small number of f metal complexes with cyanide bridges such as [(C 5Me5) 2Ce (μ-CN)(CNtBu)] 3 (2102 cm −1 ), 7 [(C 5 Me 5 ) 2 M(μ-CN)(CNtSiMe3)]3 (M = La (2104 cm−1), Pr (2108 cm−1), U (2088 cm−1)),4 and [(C5Me5)2U(μ-CN)]n (2082 cm−1),7 some uranium compounds with terminal cyanides such as [(Cot)2U(CN)][NEt4] (2073 cm−1),15 [(C5Me5)2U(CN)5][NEt4]3 (2091 cm−1),6,8 and [(C5Me5)UO2(CN)3][NEt4]2 (2090, 2069 cm−1),5l and the metallacycles [UN*2(N,C)(CN)][NEt4], [NEt4][UN*(N,N)(CN)2], and [NEt4][UN*(N,O)2(CN)], which are within the close range 2059−2063 cm−1.5m Nevertheless, the range of ν(CN) frequencies of all these compounds evidences that ν(CN) is strongly dependent on the nature of the ancillary ligands. The strong bands in the 600−1000 cm − 1 region can be assigned to the (cyclooctatetraenyl)uranium(IV) linkage.34

polycyanide species, as observed with the preparation of [(C5Me5)2M(CN)3]2− (M = U, Ce), [(C5Me5)2U(CN)3]−, or [(C5Me5)2U(CN)5]3−.6−8 However, as mentioned above, only the polymeric compound 2[NEt4], which precipitated from a mixture of 1 and excess NEt4CN, could be crystallized and characterized. Because the M−CN−M bridges are readily broken by further cyanide ions, and considering the distinct solubility induced by the NnBu4+ versus NEt4+ cation, a different reaction course in the treatment of 1 with NnBu4CN was expected, with formation of the expectedly more soluble [(Cot)2Th(CN)2][NnBu4]2 (5[NnBu4]2) bis-cyanide species. Addition of slightly less than 2 mol equiv of NnBu4CN to a suspension of 1 in pyridine at 70 °C gave rapidly a clear pale green solution of 5[NnBu4]2 as the unique product as observed by 1H NMR experiments (Scheme 1). After the usual workup, 5[NnBu4]2 was isolated as a pale yellow solid in almost quantitative yield. Its 1H NMR spectrum in pyridine-d5 shows a singlet for the Cot signal at δH 6.57, a value similar to that observed in the monocyanide precursor, but with integration of the Cot and NnBu4 signals in the ratio 16H/72H. 5[NnBu4]2 crystallizes readily as large yellow platelets by slow diffusion of diethyl ether into a pyridine solution or by slow cooling to room temperature of a hot THF solution. A similar reaction of (Cot)2U with either 2 mol equiv or excess NEt4CN or NnBu4CN in pyridine (20 h at 90 °C) led to the formation of a species displaying an NMR signal of the Cot ligand shifted downfield (∼1 ppm) in comparison to that of [(Cot)2U(CN)][NR4]. Although the formation of [(Cot)2 U(CN)2][NR4]2 may be suspected in solution, it could not be firmly established by X-ray diffraction. 5[NnBu4]2 is the first bent-thorocene species with a dianionic charge. A view of the dianion [(Cot)2Th(CN)2]2− is shown in Figure 5, and selected bond lengths and angles are given in

Figure 5. View of the anion of 5[NnBu4]2. Hydrogen atoms have been omitted. Displacement parameters are drawn at the 30% probability level.

■

CONCLUSION The present work on the reactivity of thorocene with the cyanide ion expands on our initial report on uranocene, which described the formation of the monomeric cyanide complex [(Cot)2U(CN)]−, the first (Cot)2M species to be coordinated with a bent geometry. Replacing U4+ with Th4+ has a pronounced effect on the reactivity of the (Cot)2An complex, and thorocene shows a greatly varied chemistry in the presence of the cyanide ion. A series of sterically crowded cyanide complexes [{(Cot)2Th}2(CN)]− and [(Cot)2Th(CN)n]q− (n = 1, 2) has

Table 2. The complex is mononuclear with a bent-thorocene moiety coordinated in its equatorial plane to two terminal cyanide ligands unambiguously attached via their carbon atom. As in the other complexes, the C8 rings are planar with a maximum rms deviation of 0.04 Å. The Cg···Th···Cg angle of 139.0° is the lowest ever reported within a bent actinocene and is likely related to the effects of the dianionic charge and steric constraints. The Th−C(Cot) distances average 2.84(6) Å, a value identical with that found in the 12-coordinate anion 2096

dx.doi.org/10.1021/om500252v | Organometallics 2014, 33, 2088−2098

Organometallics

Article

Paris XI, 2005. (f) Evans, W. J.; Forrestal, K. J.; Ziller, J. W. J. Am. Chem. Soc. 1998, 120, 9273. (g) del Mar Conejo, M.; Parry, J. S.; Carmona, E.; Schultz, M.; Brennann, J. G.; Beshouri, S. M.; Andersen, R. A.; Rogers, R. D.; Coles, S.; Hursthouse, M. Chem. Eur. J. 1999, 5, 3000. (h) Zi, G.; Jia, L.; Werkema, E. L.; Walter, M. D.; Gottfriedsen, J. P.; Andersen, R. A. Organometallics 2005, 24, 4251. (i) Thomson, R. K.; Graves, C. R.; Scott, B. L.; Kiplinger, J. K. Dalton Trans. 2010, 39, 6826. (j) Ren, W.; Zi, G.; Fang, D. C.; Walter, M. D. J. Am. Chem. Soc. 2011, 133, 13183. (k) Tanase, S.; Reedijk, J. Coord. Chem. Rev. 2006, 250, 2501. (l) Berthet, J. C.; Thuéry, P.; Ephritikhine, M. Chem. Commun. 2007, 604. (m) Bénaud, O.; Berthet, J. C.; Thuéry, P.; Ephritikhine, M. Inorg. Chem. 2011, 50, 12204. (6) Maynadié, J.; Berthet, J. C.; Thuéry, P.; Ephritikhine, M. Organometallics 2007, 26, 4585. (7) Maynadié, J.; Berthet, J. C.; Thuéry, P.; Ephritikhine, M. Organometallics 2007, 26, 2623. (8) Maynadié, J.; Barros, N.; Berthet, J. C.; Thuéry, P.; Maron, L.; Ephritikhine, M. Angew. Chem., Int. Ed. 2007, 46, 2010. (9) Maynadié, J.; Berthet, J. C.; Thuéry, P.; Ephritikhine, M. Chem. Commun. 2007, 486. (10) Werner, H. Angew. Chem., Int. Ed. 2012, 51, 6052. (11) Arliguie, T.; Lance, M.; Nierlich, M.; Ephritikhine, M. J. Chem. Soc., Chem. Commun. 1995, 183. (12) Streitwieser, A.; Müller-Westerhoff, U. J. Am. Chem. Soc. 1968, 90, 7364. (13) Seyferth, D. Organometallics 2004, 23, 3562. (14) (a) Streitwieser, A.; Yoshida, N. J. Am. Chem. Soc. 1969, 91, 7528. (b) Avdeef, A.; Raymond, K. N.; Hodgson, K. O.; Zalkin, A. Inorg. Chem. 1972, 11, 1083. (15) Berthet, J. C.; Thuéry, P.; Ephritikhine, M. Organometallics 2008, 27, 1664. (16) Lorenz, V.; Schmiege, B. M.; Hrib, C. G.; Ziller, J. W.; Edelmann, A.; Blaurock, S.; Evans, W. J.; Edelmann, F. T. J. Am. Chem. Soc. 2011, 133, 1257. (17) Shannon, R. D. Acta Crystallogr., Sect. A 1976, 32, 751. (18) Hervé, A.; Garin, N.; Thuéry, P.; Ephritikhine, M.; Berthet, J. C. Chem. Commun. 2013, 49, 6304. (19) Berthet, J. C.; Thuéry, P.; Garin, N.; Dognon, J. P.; Cantat, T.; Ephritikhine, M. J. Am. Chem. Soc. 2013, 135, 10003. (20) Berthet, J. C.; Thuéry, P.; Ephritikhine, M. C. R. Chim. 2014, DOI: j.crci.2013.09.006. (21) Cantat, T.; Scott, B. L.; Kiplinger, J. L. Chem. Commun. 2010, 46, 919. (22) Simons, L. H.; Lagowski, J. J. Tetrahedron Lett. 2002, 43, 1771. (23) (a) Levanda, C.; Streitwieser, A. Inorg. Chem. 1981, 20, 656. (b) Parry, J. S.; Cloke, F. G. N.; Coles, S. J.; Hursthouse, M. B. J. Am. Chem. Soc. 1968, 90, 6867. (c) Nishiura, M.; Hou, Z.; Wakatsuki, Y. Organometallics 2004, 23, 1359. (24) Hooft, R. W. W. COLLECT; Nonius BV, Delft, The Netherlands, 1998. (25) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307. (26) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112. (27) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565. (28) Berthet, J. C.; Thuéry, P.; Ephritikhine, M. unpublished results. The poly-cyanide mono(Cot) compounds [(Cot)U(CN)4][NEt4]2 and [(Cot)U(CN)5][NEt4]3 were obtained by treatment of (Cot)UI2(THF)2 and (Cot)U(O3SCF3)2 with NEt4CN. The crystal structures of these compounds have been determined by X-ray diffraction: CCDC reference codes NIWNOY and NIWNUE. (29) Lee, I. S.; Long, J. R. Dalton Trans. 2004, 3434. (30) Mock, M. T.; Kieber-Emmons, M. T.; Popescu, C. V.; Gasda, P.; Yap, G. P. A.; Riordan, C. G. Inorg. Chim. Acta 2009, 362, 4553. (31) Bowmaker, G. A.; Hartl, H.; Hurban, V. Inorg.Chem. 2000, 39, 4548. (32) (a) Nakamoto, K. In Infrared and Raman Spectra of Inorganic and Coordination Compounds, 5th ed.; Wiley: New York, 1997; Vol. B, Applications in Coordination, Organometallic and Bioinorganic Chemistry. (b) Scott, M. J.; Holm, R. H. J. Am. Chem. Soc. 1994,

been obtained from (Cot)2Th, depending on the Th:CN ratio and the nature of the M+ cation of the MCN reagent. Structural characterizations of bi-, tri-, and polynuclear cyanide species demonstrated the coordinating ability of [(Cot)2Th(CN)]−, which can trap strong Lewis acid species to form polynuclear entities with [Th]−CN−[Na] or [Th]−CN−[Th] bridges. The polymeric arrangement of the monocyanide complex [(Cot)2Th(CN)][NR4] revealed that not only one but also two coordination sites are available on a bent (Cot)2Th fragment. This species, together with the trinuclear 3[NnBu4]2 and mononuclear 5[NnBu4]2 complexes, is the first (Cot)2Th(L)2 (L = monodentate ligand) complex to be characterized.

■

ASSOCIATED CONTENT

S Supporting Information *

Figures giving 1H and 13C NMR spectra of complexes 2[NnBu4], 4[NnBu4], and 5[NnBu4]2 and a table and CIF files giving crystal data, atomic positions and displacement parameters, anisotropic displacement parameters, and bond lengths and bond angles for 2[NEt4], 3[NnBu34]2·py, 4[NnBu4], 4[Na*(py)2]·2py and 5[NnBu4]2. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: for J.-C.B.: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We thank the Direction of Material Sciences of the Commissariat à l’Energie Atomique et aux Energies Alternatives for financial support.

■

REFERENCES

(1) Evans, W. J. Inorg. Chem. 2007, 46, 3435. (2) (a) Cotton, S. A.; Hart, F. A. The Heavy Transition Elements; MacMillan: London and Basingstoke, U.K., 1975. (b) Soloveichik, G. In Encyclopedia of Inorganic Chemistry; King, R. B., Ed.; Wiley: Chichester, U.K., 1994; Vol. 1, p 2. (c) Edelmann, F. T. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, U.K., 1995; Vol. 4, Chapter 2, p 11. (d) Bagnall, K. W. The Actinides. In Comprehensive Coordination Chemistry; Wilkinson, G., Gillard, R. D., McCleverty, J. A., Eds.; Pergamon Press: Oxford, U.K., 1987; Vol. 3, Chapter 40, p 1129. (e) Santos, A.; Pires de Matos, A.; Maddock, G. Adv. Inorg. Chem. 1989, 34, 65. (3) (a) Kalsotra, B. L.; Multani, R. K.; Jain, B. D. J. Inorg. Nucl. Chem. 1972, 34, 2265. (b) McColm, I. J.; Thompson, S. J. Inorg. Nucl. Chem. 1972, 34, 3801. (c) Bagnall, K. W.; Plews, M. J.; Brown, D.; Fischer, R. D.; Klähne, E.; Landgraf, G. W.; Sienel, G. R. J. Chem. Soc., Dalton Trans. 1982, 1999. (d) Evans, W. J.; Drummond, D. K. Organometallics 1988, 7, 797. (e) Obora, Y.; Ohta, T.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1997, 119, 3745. (f) Evans, W. J.; Montalvo, E.; Foster, S. E.; Harada, K. A.; Ziller, J. W. Organometallics 2007, 26, 2904. (g) Evans, W. J.; Montalvo, E.; Champagne, T. M.; Ziller, J. W.; DiPasquale, A. G.; Rheingold, A. L. Organometallics 2009, 28, 2897. (4) Evans, W. J.; Mueller, T. J.; Ziller, J. W. Chem. Eur. J. 2010, 16, 964. (5) (a) Bagnall, K. W.; Baptista, J. L. J. Inorg. Nucl. Chem. 1970, 32, 2283. (b) McColm, I. J.; Thompson, S. J. J. Inorg. Nucl. Chem. 1972, 34, 3801. (c) Kanellakopulos, B.; Dornberger, E.; Billich, H. J. Organomet. Chem. 1974, 76, C42. (d) Adam, R.; Villiers, C.; Ephritikhine, M.; Lance, M.; Nierlich, M.; Vigner, J. J. Organomet. Chem. 1993, 445, 99. (e) Mehdoui, T. Thèse de Doctorat, Université 2097

dx.doi.org/10.1021/om500252v | Organometallics 2014, 33, 2088−2098

Organometallics

Article

116, 11357. (c) Kettle, S. F. A.; Diana, E.; Boccaleri, E.; Stanghellini, P. L. Inorg. Chem. 2007, 46, 2409. (33) Parry, J. S.; Cloke, F. G. N.; Coles, S. J.; Hursthouse, M. B. J. Am. Chem. Soc. 1999, 121, 6867. (34) (a) Hodgson, K. O.; Mares, F.; Starks, D. F.; Streitwieser, A. J. Am. Chem. Soc. 1973, 95, 8650. (b) Gilbert, T. M.; Ryan, R. R.; Sattelberger, A. P. Organometallics 1988, 7, 2514.

2098

dx.doi.org/10.1021/om500252v | Organometallics 2014, 33, 2088−2098