Synthesis, Structure, and Reactivity of the Sterically Crowded Th3+ Complex (C5Me5)3Th Including Formation of the Thorium Carbonyl, [(C5Me5)3Th(CO)][BPh4]

The Th3+ complex, (CsMes)(3)Th, has been isolated despite the fact that tris(pentamethylcyclopentadienyl) complexes are highly reactive due to steric crowding and few crystallographically characterizable Th3+ complexes are known due to their highly reducing nature. Reaction of (CsMes)(2)ThMe2 with [Et3NH] [BPh4] produces the cationic thorium complex [(CsMes)(2)Th.Me][BPh4.] that can be treated with KCsMes to generate (C(5)Mes)(3)ThMe, 1. The methyl group on (C(5)Mes)(3)ThMe can be removed with [Et3NH][BPh4] to form [(C(5)Mes)(3)Th][BPh4], 2, the first cationic tris(pentamethylcyclopentadienyl) metal complex, which can be reduced with KC8 to yield (C(5)Mes)(3)Th, 3. Complexes 1-3 have metrical parameters consistent with the extreme steric crowding that previously has given unusual (CsMes)- reactivity to (C(5)Mes)(3)M complexes in reactions that form less crowded (C(5)Mes)(2) M-containing products. However, neither sterically induced reduction nor (eta(1)-C(5)Mes)- reactivity is observed for these complexes. (C(5)Mes)(3)Th, which has a characteristic EPR spectrum consistent with a d(1) ground state, has the capacity for two-electron reduction via Th3+ and sterically induced reduction. However, it reacts with MeI to make two sterically more crowded complexes, (C(5)Mes)(3)ThI, 4, and (C(5)Mes)(3)ThMe, 1, rather than (C(5)Mes)Th-2(Me)I. Complex 3 also forms more crowded complexes in reactions with 12, PhCl, and Al2Me6, which generate (C(5)Mes)(3)ThI, (C(5)Mes)(3)ThC1, and (C(5)Mes)(3)ThMe, 1, respectively. The reaction of (C(5)Mes)(3)Th, 3, with H-2 forms the known (CsMes)3ThH as the sole thorium-containing product. Surprisingly, ((C(5)Mes)(3)ThH is also observed when (C(5)Mes)(3)Th is combined with 1,3,5,7-cyclooctatetraene. [(C(5)Mes)(3)Th][BPh4] reacts with tetrahydrofuran (THF) to make [(C(5)Mes)(3)Th(THF)][BPh4]; 2-THF, which is the first (C(5)Mes)(3)3M of any kind that does not have a trigonal planar arrangement of the (CsMes)- rings. It is also the first (C(5)Mes)(3)M complex that does not ring-open THF. [(C(5)Mes)(3)Th][/BPh4], 2, reacts with CO to generate a product characterized as [(C(5)Mes)(3)Th(CO)][BPh4], 5, the first example of a molecular thorium carbonyl isolable at room temperature. These results have been analyzed using density functional theory calculations.