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 [(C(5)Me(5))(2)U](2)(mu-eta(6):eta(6)-C(6)H(6)), 1, have revealed that eta(1)-ligands can displace one of the normally inert (eta(5)-C(5)Me(5))(1-) ligands in each metallocene unit to form a series of heteroleptic bimetallic sandwich complexes of nonplanar (C(6)H(6))(2-), namely, [(C(5)Me(5))(X)U](2)(mu-eta(6):eta(6)-C(6)H(6)), where X = N(SiMe(3))(2), OC(6)H(2)(CMe(3))(2)-2,6-Me-4, and CH(SiMe(3))(2). Displacement by an amidinate is also possible, that is, X = (i)PrNC(Me)N(i)Pr. This allows the multielectron reactivity of the (mu-eta(6):eta(6)-C(6)H(6))(2-) sandwich complexes to be studied as a function of ancillary ligands. Specifically, the reaction of 1 with K[N(SiMe(3))(2)], previously found to form {(C(5)Me(5))[(Me(3)Si)(2)N]U}(2)(C(6)H(6)), 2, also occurs with K[OC(6)H(2)(CMe(3))(2)-2,6-Me-4], Li[CH(SiMe(3))(2)], and Li[(i)PrNC(Me)N(i)Pr] to form {(C(5)Me(5))[4-Me-2,6-(Me(3)C)(2)C(6)H(2)O]U}(2)(C(6)H(6)), 3, {(C(5)Me(5))[(Me(3)Si)(2)CH]U}(2)(C(6)H(6)), 4, and {(C(5)Me(5))[(i)PrNC(Me)N(i)Pr]U}(2)(C(6)H(6)), 5, respectively. The reactivity of 2-5 vis-a-vis 1 has been compared with the substrates 1,3,5,7-cyclooctatetraene (C(8)H(8)) and 1-azidoadamantane (AdN(3)). Complex 1 acts as a six electron reductant to convert three equiv of C(8)H(8) to [(C(5)Me(5))(C(8)H(8))U](2)(mu-eta(3)-eta(3)-C(8)H(8)), whereas the sterically less crowded 2-5 provide only four electrons to reduce two equiv of C(8)H(8) generating U(4+) products of formula (C(5)Me(5))(X)U(C(8)H(8)). With AdN(3), complexes 1, 2, and 5 react similarly to form bis(imido) U(6+) complexes, (C(5)Me(5))(X)U(=NAd)(2). Complexes 2 and 5 also form the ligand redistribution product, (C(5)Me(5))(2)U(=NAd)(2). The reaction of 4 with AdN(3) generates at least three imido complexes: (C(5)Me(5))(2)U(=NAd)(2) from reduction and ligand redistribution, (C(5)Me(5))[AdN(3)CH(SiMe(3))(2)-kappa(2)N(1,2)]U(=NAd)(2), from reduction and insertion, and (C(5)Me(5))(eta(5):kappaNu-C(5)Me(4)CH(2)NAd)U(=NAd), from reduction, ligand redistribution, metalation, and insertion.