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 [{eta(5)-1,2,4-(Me3C)(3)C5H2}(2)ThMe2] and [{eta(5)-1,3-(Me3C)(2)C5H3}(2)ThMe2] with RNH2 gives diamides [{eta(5)-1,2,4-(Me3C)(3)C5H2}(2)Th-(NHR)(2)] (R=Me (7), p-tolyl (8)) and [{eta(5)-1,3-(Me3C)(2)C5H3}(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 degrees C under vacuum (0.01 mmHg), whereas diamide 8 is converted at 140 degrees C/0.01 mmHg into the primary amine p-tolyl-NH2 and [{eta(5)-1,2,4-(Me3C)(3)C5H2}(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 [{eta(5)-1,2,4-(Me3C)(3)C5H2}(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.