The Bis Metallacyclic Anion [U(N{SiMe₃}₂)(CH₂SiMe₂N{SiMe₃})₂]⁻

A series of bis metallacyclic compounds [M(THF)xUN*(CH2SiMe2N{SiMe3})2]n [M = Na (2), Li (3), or K (4), N* = N(SiMe3)2] were isolated from reactions of UCl4 or [UN*3Cl] with MN* or by treatment of [UN*2(CH2SiMe2N{SiMe3})] (1) or [UN*3] with MN*, MH, or LiCH2SiMe3 in tetrahydrofuran (THF). Crystals of 2a·1/6n-pentane (x = 0), 2b (x = 1), 2c (x = 2), and 4b (x = 1) were obtained by crystallization of 2 and 4 from pentane, and [Na(18-crown-6)(THF)][UN*(CH2SiMe2N{SiMe3})2] (2d) and [Na(15-crown-5)][UN*(CH2SiMe2N{SiMe3})2] (2e) were formed upon addition of the crown ether. The crystal structures of 2a−2e and 4b exhibit the same [UN*(CH2SiMe2N{SiMe3})2] units which are linked to Na or K atoms via methylene or methyl groups, giving either tight cation−anion pairs (2d and 2e) or one-dimensional (1D) or two-dimensional (2D) polymeric compounds with Na or K atoms in bridging position between methylene groups of adjacent units. Reaction of 2 with CO gave the double insertion derivative [Na2(THF)U2N*2(OC{=CH2}SiMe2N{SiMe3})4] (5b) and [Na(15-crown-5)UN*(OC{=CH2}SiMe2N{SiMe3})2] (5c) in the presence of the crown ether. Thermal decomposition of 5b gave [Na2(THF)U(OC{=CH2}SiMe2N{SiMe3})3]2 (6), the product of CO insertion into the putative tris metallacycle [Na2(THF)xU(CH2SiMe2N{SiMe3})3]. The crystal structures of 5b, 5c, and 6 show the interaction of the Na atoms with the exocyclic C=CH2 bonds. Diffusion of CO2 into a THF solution of 2 led to the formation of [Na(THF)xUN*(OC{O}CH2SiMe2N{SiMe3})2] (7) which crystallized from pyridine/pentane to give [Na(THF)2(py)2UN*(OC{O}CH2SiMe2N{SiMe3})2]·0.5py (8·0.5py), the first crystallographically characterized complex resulting from CO2 insertion into a M(CH2SiMe2N{SiMe3}) metallacycle. Compound 2 reacted with I2 to give [UN*(CH2SiMe2N{SiMe3})(N{SiMe3}SiMe2CH2I)] (9) which would represent a new type of so-called “pendulum” systems resulting from a degenerate σ bond metathesis reaction of U−C and C−I bonds.