Synthesis, Structure, and Reactivity of the Sterically Crowded Th 3+ Complex (C 5 Me 5 ) 3 Th Including Formation of the Thorium Carbonyl, [(C 5 Me 5 ) 3 Th(CO)][BPh 4 ]

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