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

Abstract

A series of bis metallacyclic compounds [M(THF)(x)UN*(CH(2)SiMe(2)N{SiMe(3)})(2)](n) [M = Na (2), Li (3), or K (4), N* = N(SiMe(3))(2)] were isolated from reactions of UCl(4) or [UN*(3)Cl] with MN* or by treatment of [UN*(2)(CH(2)SiMe(2)N{SiMe(3)})] (1) or [UN*(3)] with MN*, MH, or LiCH(2)SiMe(3) in tetrahydrofuran (THF). Crystals of 2a x 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*(CH(2)SiMe(2)N{SiMe(3)})(2)] (2d) and [Na(15-crown-5)][UN*(CH(2)SiMe(2)N{SiMe(3)})(2)] (2e) were formed upon addition of the crown ether. The crystal structures of 2a-2e and 4b exhibit the same [UN*(CH(2)SiMe(2)N{SiMe(3)})(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)U(2)N*(2)(OC{=CH(2)}SiMe(2)N{SiMe(3)})(4)] (5b) and [Na(15-crown-5)UN*(OC{=CH(2)}SiMe(2)N{SiMe(3)})(2)] (5c) in the presence of the crown ether. Thermal decomposition of 5b gave [Na(2)(THF)U(OC{=CH(2)}SiMe(2)N{SiMe(3)})(3)](2) (6), the product of CO insertion into the putative tris metallacycle [Na(2)(THF)(x)U(CH(2)SiMe(2)N{SiMe(3)})(3)]. The crystal structures of 5b, 5c, and 6 show the interaction of the Na atoms with the exocyclic C=CH(2) bonds. Diffusion of CO(2) into a THF solution of 2 led to the formation of [Na(THF)(x)UN*(OC{O}CH(2)SiMe(2)N{SiMe(3)})(2)] (7) which crystallized from pyridine/pentane to give [Na(THF)(2)(py)(2)UN*(OC{O}CH(2)SiMe(2)N{SiMe(3)})(2)] x 0.5 py (8 x 0.5 py), the first crystallographically characterized complex resulting from CO(2) insertion into a M(CH(2)SiMe(2)N{SiMe(3)}) metallacycle. Compound 2 reacted with I(2) to give [UN*(CH(2)SiMe(2)N{SiMe(3)})(N{SiMe(3)}SiMe(2)CH(2)I)] (9) which would represent a new type of so-called "pendulum" systems resulting from a degenerate sigma bond metathesis reaction of U-C and C-I bonds.

Carbon monoxide and carbon dioxide insertion chemistry of f-block N-heterocyclic carbene complexes

“…5 Reactions that can form carbon-carbon bonds are rare in general, and the direct dimerisation of CO to afford OCCO is energetically uphill by +73 kcal mol −1 , and particularly rare. 1 Though the insertion of CO into metal alkyl, amido and hydride bonds is now well documented for Group 4 and f-block metal complexes, [6][7][8][9][10][11][12][13][14] there are only two complexes which bind and reductively couple carbon monoxide to date; the sterically congested, trivalent, 18,19 The incorporation of a pendant borane group to provide a hydride source has recently been used to address the second challenge in CO coupling -the formation of the reduced C-C and C-H bonds, the 4 ] is borane activated to form Re-CH 2 -O-BR 3 which couples with a second carbonyl equivalent. 20 As yet, no catalytic C-C coupling or oligomerisation reactions exist for carbon monoxide at low pressures or temperatures.…”

Exploring Synthetic Routes to Heteroleptic UIII, UIV, and ThIV Bulky Bis(silyl)amide Complexes

“…Thus, we postulate that the bulkier N** ligand hinders the third substitution; the Lewis acidic An IV centers in the disubstituted intermediates then promote deprotonation of one of the coordinated N** ligands by basic KN**, leading to cyclometallation. Similar complexes have previously been synthesized in An IV N′′ chemistry, such as [An(N′′) 2 {N(SiMe 3 )(SiMe 2 CH 2 ‐κ 2 ‐ N , C )}] (An = Th, U), and [An(N′′){N(SiMe 3 )(SiMe 2 CH 2 ‐κ 2 ‐ N , C )} 2 ] – (An = Th, U); unlike the N** complexes 7 and 8 the N′′ cyclometallates have been made deliberately in higher yields, thus their further chemistry has been investigated…”

“…[10e] Formally four‐coordinate 8 is similarly disordered; in addition to the N** and cyclometallated ligands the Th IV center is disordered above and below the N 3 plane by 0.2666(7) Å. The structure of 8 is reminiscent of [K(DME)][Th(N′′){N(SiMe 3 )(SiMe 2 CH 2 ‐κ 2 ‐ N , C )} 2 ],[25c] and the bond lengths/angles are comparable, so we do not comment on this further.…”

Direct hydrosilylation by a zirconacycle with β-hydrogen

“…A singlet resonance at 3.29 ppm in the 1 H NMR spectrum of 3 was assigned to the methoxy group, and only one SiH signal was detected at 4.50 ppm. That signal was assigned by 1 H- 29 Si HMQC and COSY experiments; the latter showed scalar coupling to the ZrCH 2 proving that the SiH is part of the cyclic structure. As in 1, the (C 5 H 5 ) 2 , CH 2 , and SiMe 2 groups are diastereotopic.…”

“…The low temperature NMR signals corresponding to 10 were sharper and better resolved. At 220 K, four 29 Si resonances were observed at 11.4, -4.6, -61.1 and -63.9 ppm.…”