Wenshan Ren

Thorium Oxo and Sulfido Metallocenes: Synthesis, Structure, Reactivity, and Computational Studies

The synthesis, structure, and reactivity of thorium oxo and sulfido metallocenes have been comprehensively studied. Heating of an equimolar mixture of the dimethyl metallocene [η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)](2)ThMe(2) (2) and the bis-amide metallocene [η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)](2)Th(NH-p-tolyl)(2) (3) in refluxing toluene results in the base-free imido thorium metallocene, [η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)](2)Th═N(p-tolyl) (4), which is a useful precursor for the preparation of oxo and sulfido thorium metallocenes [η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)](2)Th═E (E = O (5) and S (15)) by cycloaddition-elimination reaction with Ph(2)C═E (E = O, S) or CS(2). The oxo metallocene 5 acts as a nucleophile toward alkylsilyl halides, while sulfido metallocene 15 does not. The oxo metallocene 5 and sulfido metallocene 15 undergo a [2 + 2] cycloaddition reaction with Ph(2)CO, CS(2), or Ph(2)CS, but they show no reactivity with alkynes. Density functional theory (DFT) studies provide insights into the subtle interplay between steric and electronic effects and rationalize the experimentally observed reactivity patterns. A comparison between Th, U, and group 4 elements shows that Th(4+) behaves more like an actinide than a transition metal.

A Base‐Free Thorium–Terminal‐Imido Metallocene: Synthesis, Structure, and Reactivity

The synthesis, structure, and reactivity of a base-free thorium terminal-imido metallocene have been comprehensively studied. Treatment of thorium metallocenes [{η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)}(2)ThMe(2)] and [{η(5)-1,3-(Me(3)C)(2)C(5)H(3)}(2)ThMe(2)] with RNH(2) gives diamides [{η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)}(2)Th(NHR)(2)] (R=Me (7), p-tolyl (8)) and [{η(5)-1,3-(Me(3)C)(2)C(5)H(3)}(2)Th(NH-p-tolyl)(2)] (9), respectively. Diamides 7 and 9 do not eliminate methylamine or p-toluidine, but sublime without decomposition at 150 °C under vacuum (0.01 mmHg), whereas diamide 8 is converted at 140 °C/0.01 mmHg into the primary amine p-tolyl-NH(2) and [{η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)}(2)Th=N(p-tolyl)] (10), which may be isolated in pure form. Imido metallocene 10 does not react with electrophiles such as alkylsilyl halides; however, it reacts with electron-rich or unsaturated reagents. For example, reaction of 10 with sulfur affords the metallacycle [{η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)}(2)Th{N(p-tolyl)S-S}]. Imido 10 is an important intermediate in the catalytic hydroamination of internal alkynes, and an efficient catalyst for the trimerization of PhCN. Density functional theory (DFT) studies provide a detailed understanding of the experimentally observed reactivity patterns.

An Actinide Metallacyclopropene Complex: Synthesis, Structure, Reactivity, and Computational Studies

The synthesis, structure, and reactivity of an actinide metallacyclopropene were comprehensively studied. The reduction of [η(5)-1,2,4-(Me3C)3C5H2]2ThCl2 (1) with potassium graphite (KC8) in the presence of diphenylacetylene (PhC≡CPh) yields the first stable actinide metallacyclopropene [η(5)-1,2,4-(Me3C)3C5H2]2Th(η(2)-C2Ph2) (2). The magnetic susceptibility data show that 2 is indeed a diamagnetic Th(IV) complex, and density functional theory (DFT) studies suggest that the 5f orbitals contribute to the bonding of the metallacyclopropene Th-(η(2)-C═C) moiety. Complex 2 shows no reactivity toward alkynes, but it reacts with a variety of heterounsaturated molecules such as aldehyde, ketone, carbodiimide, nitrile, organic azide, and diazoalkane derivatives. DFT studies complement the experimental observations and provide additional insights. Furthermore, a comparison between Th and group 4 metals reveals that Th(4+) shows unique reactivity patterns.

Experimental and Computational Studies on the Reactivity of a Terminal Thorium Imidometallocene towards Organic Azides and Diazoalkanes

The reaction of the base-free terminal thorium imido complex [{η(5)-1,2,4-(Me3C)3C5H2}2Th=N(p-tolyl)] (1) with p-azidotoluene yielded irreversibly the tetraazametallacyclopentene [{η(5)-1,2,4-(Me3C)3C5H2}2Th{N(p-tolyl)N=N-N(p-tolyl)}] (2), whereas the bridging imido complex [{[η(5)-1,2,4-(Me3C)3C5H2]Th(N3)2}2{μ-N(p-tolyl)}2][(n-C4H9)4N]2 (3) was isolated from the reaction of 1 with [(n-C4H9)4N]N3. Unexpectedly, upon the treatment of 1 with 9-diazofluorene, the NN bond was cleaved, an N atom was transferred, and the η(2)-diazenido iminato complex [{η(5)-1,2,4-(Me3C)3C5H2}2Th{η(2)-[N=N(p-tolyl)]}{N=(9-C13H8)}] (4) was formed. In contrast, the reaction of 1 with Me3SiCHN2 gave the nitrilimido complex [{η(5)-1,2,4-(Me3C)3C5H2}2Th{NH(p-tolyl)}{N2CSiMe3}] (5), which slowly converted into [{η(5)-1,2,4-(Me3C)3C5H2}{η(5):κ-N-1,2-(Me3C)2-4-CMe2(CH2NN=CHSiMe3)C5H2}Th{NH(p-tolyl)}] (6) by intramolecular C-H bond activation. The experimental results are complemented by density functional theory (DFT) studies.

Is the bipyridyl thorium metallocene a low-valent thorium complex? A combined experimental and computational study

Bipyridyl thorium metallocenes [η5-1,2,4-(Me3C)3C5H2]2Th(bipy) (1) and [η5-1,3-(Me3C)2C5H3]2Th(bipy) (2) have been investigated by magnetic susceptibility and computational studies. The magnetic susceptibility data reveal that 1 and 2 are not diamagnetic, but they behave as temperature independent paramagnets (TIPs). To rationalize this observation, density functional theory (DFT) and complete active space self-consistent field (CASSCF) calculations have been undertaken, which indicated that Cp′2Th(bipy) has indeed a Th(IV)(bipy2−) ground state (f0d0π*2, S = 0), but the open-shell singlet (f0d1π*1, S = 0) (almost degenerate with its triplet congener) is only 9.2 kcal mol−1 higher in energy. Complexes 1 and 2 react cleanly with Ph2CS to give [η5-1,2,4-(Me3C)3C5H2]2Th[(bipy)(SCPh2)] (3) and [η5-1,3-(Me3C)2C5H3]2Th[(bipy)(SCPh2)] (4), respectively, in quantitative conversions. Since no intermediates were observed experimentally, this reaction was also studied computationally. Whereas coordination of Ph2CS to 2 in its S = 0 ground state is not possible, Ph2CS can coordinate to 2 in its triplet state (S = 1) upon which a single electron transfer (SET) from the (bipy2−) fragment to Ph2CS followed by C–C coupling takes place.

Si–H addition followed by C–H bond activation induced by a terminal thorium imido metallocene: a combined experimental and computational study

The Si–H bond addition to a terminal actinide imido complex was comprehensively studied. The base-free thorium imido [η5-1,2,4-(Me3C)3C5H2]2ThN(p-tolyl) (1) activates Si–H bonds in PhSiH3 or Ph2SiH2 to give the thorium amido hydrido metallocenes [η5-1,2,4-(Me3C)3C5H2]2Th(H)[N(p-tolyl)SiH2Ph] (2) and [η5-1,2,4-(Me3C)3C5H2]2Th(H)[N(p-tolyl)SiHPh2] (3), respectively. Complex 2 readily inserts unsaturated molecules into the Th–H bond, whereas complex 3 reversibly activates an intramolecular aromatic C–H bond to yield [η5-1,2,4-(Me3C)3C5H2]2Th[η2-N,C-{N(p-MeC6H3)(SiHPh2)}] (4) and H2. The experimental results have been complemented by density functional theory (DFT) studies and provide a detailed understanding of the observed reactivity. In addition, a comparison between Th and early transition metals reveals that the Th4+ behaves more like an actinide than a transition metal.