Synthesis of Heteroleptic Uranium (μ-η6:η6-C6H6)2- Sandwich Complexes via Facile Displacement of (η5-C5Me5)1- by Ligands of Lower Hapticity and Their Conversion to Heteroleptic Bis(imido) Compounds

Reactivity studies on the sterically crowded [(C5Me5)(2)U](2)(mu-eta(6):eta(6)-C6H6), 1, have revealed that eta(1)-ligands can displace one of the normally inert (eta(5)-C5Me5)(1-) ligands in each metallocene unit to form a series of heteroleptic bimetallic sandwich complexes of nonplanar (C6H6)(2-), namely, [(C5Me5)(X)U](2)(mu-eta(6):eta(6)-C6H6), where X = N(SiMe3)(2), OC6H2(CMe3)(2)-2,6-Me-4, and CH(SiMe3)(2). Displacement by an amidinate is also possible, that is, X = (PrNC)-Pr-i(Me)(NPr)-Pr-i. This allows the multielectron reactivity of the (mu-eta(6):eta(6)-C6H6)(2-) sandwich complexes to be studied as a function of ancillary ligands. Specifically, the reaction of 1 with K[N(SiMe3)(2)], previously found to form {((CMe5)-Me-5)[(Me3Si)(2)N]U}(2)(C6H6), 2, also occurs with K[OC6H2(CMe3)(2)-2,6-Me-4], Li[CH(SiMe3)(2)], and Li[(PrNC)-Pr-i(Me)(NPr)-Pr-i] to form {(C5Me5)[4-Me-2,6-(Me3C)(2)C6H2O]U}(2)(C6H6), 3, {(C5Me5)[(Me3Si)(2)CH]U}(2)(C6H6), 4, and {(C5Me5)[(PrNC)-Pr-i(Me)(NPr)-Pr-i]U}(2)(C6H6), 5, respectively. The reactivity of 2-5 vis-6-vis 1 has been compared with the substrates 1,3,5,7-cyclooctatetraene (C8H8) and 1-azidoadamantane (AdN(3)). Complex 1 acts as a six electron reductant to convert three equiv of C8H8 to [(C5Me5)(C8H8)U](2)(mu-eta(3)-eta(3)-C8H8), whereas the sterically less crowded 2-5 provide only four electrons to reduce two equiv of C8H8 generating U4+ products of formula (C5Me5)(X)U(C8H8). With AdN(3), complexes 1, 2, and 5 react similarly to form bis(imido) U6+ complexes, (C5Me5)(X)U(=NAd)(2). Complexes 2 and 5 also form the ligand redistribution product, (C5Me5)(2)U(=NAd)(2). The reaction of 4 with AdN(3) generates at least three imido complexes: (C5Me5)(2)U(=NAd)(2) from reduction and ligand redistribution, (C5M5)[AdN(3)CH(SiMe3)(2)-kappa N-2(1,2)]U(=NAd)(2), from reduction and insertion, and (C5Me5)(eta(5):kappa N-C(5)Me(4)CH(2)NAd)U(=NAd), from reduction, ligand redistribution, metalation, and insertion.