Insertion, Isomerization, and Cascade Reactivity of the Tethered Silylalkyl Uranium Metallocene (η⁵-C₅Me₄SiMe₂CH₂-κC)₂U

Investigation of the insertion reactivity of the tethered silylalkyl complex (η⁵-C₅Me₄SiMe₂CH₂-κC)₂U (1) has led to a series of new reactions for U−C bonds. Elemental sulfur reacts with 1 by inserting two sulfur atoms into each of the U−C bonds to form the bis(tethered alkyl disulfide) complex (η⁵:η²-C₅Me₄SiMe₂CH₂S₂)₂U (2). The bulky substrate N,N′-diisopropylcarbodiimide, ⁱPrNCNⁱPr, inserts into only one of the U−C bonds of 1 to produce the mixed-tether complex (η⁵-C₅Me₄SiMe₂CH₂-κC)U[η⁵-C₅Me₄SiMe₂CH₂C(ⁱPrN)₂-κ²N,N′] (3). Carbon monoxide did not exclusively undergo a simple insertion into the U−C bond of 3 but instead formed {μ-[η⁵-C₅Me₄SiMe₂CH₂C(NⁱPr)O-κ²O,N]U[OC(C₅Me₄SiMe₂CH₂)CN(ⁱPr)-κ²O,N]₂ (4) in a cascade of reactions that formally includes U−C bond cleavage, C−N bond cleavage of the amidinate ligand, alkyl or silyl migration, U−O, C−C, and C−N bond formations, and CO insertion. The reaction of 3 with isoelectronic tert-butyl isocyanide led to insertion of the substrate into the U−C bond, but with a rearrangement of the amidinate ligand binding mode from κ² to κ¹ to form [η⁵:η²-C₅Me₄SiMe₂CH₂C(N^tBu)]U[η⁵-C₅Me₄SiMe₂CH₂C(NⁱPr)N(ⁱPr)-κN] (5). The product of double insertion of ^tBuNC into the U−C bonds of 1, namely [η⁵:η²-C₅Me₄SiMe₂CH₂C(N^tBu)]₂U (6), was found to undergo an unusual thermal rearrangement that formally involves C−H bond activation, C−C bond cleavage, and C−C bond coupling to form the first formimidoyl actinide complex, [η⁵:η⁵:η³-^tBuNC(CH₂SiMe₂C₅Me₄)(CHSiMe₂C₅Me₄)]U(η²-HCN^tBu) (7).