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

Abstract

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.

Small Molecule Activation Mediated by a Thorium Terminal Imido Metallocene

“…Diamide 5 can be converted to imido 1 at approximately 140°C /0.01 mmHg, but no equilibrium between diamide 5 and imido 1 is detected by 1 H NMR spectroscopy (in the temperature range of 20−100°C) because of the rather small amount of formed imido or rapid chemical exchange. 9 Under similar reaction conditions, reaction of 1 with 1 equiv of Ph 2 NH also affords the desired mixed diamide [η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 Th(NH-p-tolyl)(NPh 2 ) (6) (Scheme 2). In contrast to diamide 5, an equilibrium between diamide 6 and imido 1 is detected at temperatures above 80°C by 1 H NMR can be converted to diamide 5 by reaction with p-toluidine at 70°C (Scheme 1), again supporting the notion that 5 is more stable than 6.…”

“…Overall, these results imply that the formation of an actinide-imido metallocene starting from the corresponding diamide derivatives by amine elimination strongly depends on the substituents on the amide group. 3w, 9 The molecular structure of [η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 Th-(NH-p-tolyl)(NPh 2 ) (6) is depicted in Figure 5. The orientation of the cyclopentadienyl rings is nearly eclipsed, and the two amido-groups (NH-p-tolyl and NPh 2 ) are oriented on either side of the eclipsed Me 3 C-groups.…”

“…The N−Th−N angle is 91.2(2)°, identical to that (91.2(1)°) found in [η 5 -1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 Th(NH-p-tolyl) 2 (5). 9 However, the Th− N(1) distance (2.418(5) Å) is longer than that of Th−N(2) (2.266(4) Å) and the average Th−N distance (2.283(3) Å) of 5, 9 which can presumably be attributed to the increased steric bulk of the Ph 2 N group and which also contributes to the decreased stability of diamide 6 and the facile release of the Ph 2 N group.…”

“…8−10 Gratifyingly, complex 1 shows a rich reaction chemistry including the activation of element sulfur, 9 Si−H bonds, 11 and NN bonds in diazoalkanes. 12 Furthermore, it is also an important intermediate in the catalytic hydroamination of internal acetylenes, 9 an efficient catalyst for the trimerization of PhCN, 9 and a useful synthon for the preparation of oxido a n d s u l fi 8 Encouraged by this broad reactivity, we are now extending our studies to small molecule activation mediated by 1. Herein, we report on some observations concerning the reactions of the imido thorium metallocene 1 with pyridine derivatives, amines, boranes, chlorosilane, selenium, and its organic derivatives, and α,β-unsaturated organic molecules.…”

C‐H‐Aktivierung mit Komplexen der f‐Block‐Elemente

“…Der vorgeschlagene Mechanismus (Schema 23) weist ¾hn-lichkeiten zur H-Abstraktion durch das Uranyl-Ion [76] auf und bençtigt einen Elektrontransfer zum Uran, gefolgt von homolytischen C-H-und U N-Bindungsspaltungen. Die Autoren bestätigen die These aus einer vorangegangen Studie von Kiplinger und Kollegen, [73] 3 C 5 H 2 , R = p-Tolyl oder 67: Cp = Cp*, R = 2,6-Dimethylphenyl; Abbildung 2) gehen eine [2+2]-Cycloaddition mit Nitrilen [77] und Alkinen [77,78] ein und aktivieren gleichzeitig C-H-Bindungen [78b] der Alkine, was zur Bildung der Mono(acetylido)thorium-Amidokomplexe führt.…”