Synthesis, Structure, and Reactivity of the Sterically Crowded Th~(3+) Complex (C_5Me_5)_3Th Including Formation of the Thorium Carbonyl, [(C_5Me_5)_3Th(CO)][BPh_4]

摘要

The Th~(3+) complex, (C_5Me_5)_3Th, has been isolated despite the fact that tris(pentamethylcyclopentadienyl) complexes are highly reactive due to steric crowding and few crystallographically characterizable Th~(3+) complexes are known due to their highly reducing nature. Reaction of (C_5Me_5)_2ThMe_2 with [Et_3NH][BPh_4] produces the cationic thorium complex [(C_5Me_5)_2ThMe] [BPh_4] that can be treated with KC_5Me_5 to generate (C_5Me_5)_3ThMe, 1. The methyl group on (C_5Me_5)_3ThMe can be removed with [Et_3NH]-[BPh_4] to form [(C_5Me_5)_3Th][BPh_4], 2, the first cationic tris-(pentamethylcyclopentadienyl) metal complex, which can be reduced with KC_8 to yield (C_5Me_5)_3Th, 3. Complexes 1-3 have metrical parameters consistent with the extreme steric crowding that previously has given unusual (C_5Me_5)~- reactivity to (C_5Me_5)_3M complexes in reactions that form less crowded (C_5Me_5)_2M-containing products. However, neither sterically induced reduction nor (η~1-C_5Me_5)~- reactivity is observed for these complexes. (C_5Me_5)_3Th, which has a characteristic EPR spectrum consistent with a d~1 ground state, has the capacity for two-electron reduction via Th~(3+) and sterically induced reduction. However, it reacts with MeI to make two sterically more crowded complexes, (C_5Me_5)_3ThI, 4, and (C_5Me_5)_3ThMe, 1, rather than (C_5Me_5)_2Th(Me)I. Complex 3 also forms more crowded complexes in reactions with I_2, PhCl, and Al_2Me_6, which generate (C_5Me_5)_3ThI, (C_5Me_5)_3ThCl, and (C_5Me_5)_3ThMe, 1, respectively. The reaction of (C_5Me_5)_3Th, 3, with H_2 forms the known (C_5Me_5)_3ThH as the sole thorium-containing product. Surprisingly, (C_5Me_5)_3ThH is also observed when (C_5Me_5)_3Th is combined with 1,3,5,7-cyclooctatetraene. [(C_5Me_5)_3Th][BPh_4] reacts with tetrahydrofuran (THF) to make [(C_5Me_5)_3Th(THF)] [BPh_4], 2-THF, which is the first (C_5Me_5)_3M of any kind that does not have a trigonal planar arrangement of the (C_5Me_5)~- rings. It is also the first (C_5Me_5)_3M complex that does not ring-open THF. [(C_5Me_5)_3Th][BPh_4], 2, reacts with CO to generate a product characterized as [(C_5Me_5)_3Th(CO)][BPh_4], 5, the first example of a molecular thorium carbonyl isolable at room temperature. These results have been analyzed using density functional theory calculations.