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

A series of bis metallacyclic compounds [M(THF)(x)UN*(CH2SiMe2N{SiMe3})(2)](n) [M = Na (2), Li (3), or K (4), N* = N(SiMe3)(2)] were isolated from reactions of UCl4 or [UN*Cl-3] 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 [Na-2(THF)U2N2*(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 [Na-2(THF)U(OC{=CH2}SiMe2N{SiMe3})(3)](2) (6), the product of CO insertion into the putative tris metallacycle [Na-2(THF)(x)U(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)(x)UN*(OC{O}CH2SiMe2N{SiMe3})(2)] (7) which crystallized from pyridine/pentane to give [Na(THF)(2)(py)(2)UN*(OC{O}CH2SiMe2N{SiMe3})(2)]center dot 0.5py (8.0.5py), the first crystallographically characterized complex resulting from CO2 insertion into a M(CH2SiMe2N{SiMe3}) metallacycle. Compound 2 reacted with l(2) to give [UN*(CH2SiMe2N{SiMe3})(N{SiMe3}SiMe(2)CH(2)l)] (9) which would represent a new type of so-called "pendulum" systems resulting from a degenerate a bond metathesis reaction of U-C and C-l bonds.