Reactivity of dicyclopentadienylbis(diethylamido)uranium(IV). Insertion reactions

Abstract

pentadienyl moieties and transamination, are often plagued by ligand redistribution reactions and concurrent formation of Cp3U(NR2). Cp3U(NEt2) also forms when Cp2U(NEt2)2 is further reacted with cyclopentadiene. Thermal stability also appears to favor the tricyclopentadienyl derivatives since attempted sublimation of some of the products produced Cp3U(NR2)-type compounds. It is clear that steric factors are of utmost importance in this area of chemistry. The combination of two cyclopentadienyl groups and two amide moieties is sometimes sufficient to saturate the coordination sphere of uranium(IV) and stabilize the so formed Cp2UX2 species. However, given a chance, even those species rearrange or react to give the more favored Cp3U containing complexes.Cp2U[NC4Me3(COOEt)]2 appears to be an exception. In this case, the postulated interaction between oxygen of the carboxylate functionality and uranium may account for the added stability. Indeed, as will be seen in the following papers, replacement of the amido gropus by potentially bidentate ligands results in the synthesis of relatively stable Cp2UX2 (X = R2NCS2, R2NCOS, R2NC02, RC02, RCOS) compounds.Acknowledgment. This work was supported at LBL by the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy, under Contract No. W-7405-Eng-48, and at Alberta by the Natural Sciences and Engineering Research Council and the University of Alberta. A.L.A. also thanks the NSERC for a postgraduate fellowship.

Synthesis and Reactivity of a Mixed-Sandwich Uranium(IV) Primary Amido Complex

“…Assignment of this resonance was confirmed by synthesizing U­(COT TIPS2 )­Cp*­(κ 2 -O 2 CND 2 ) and collecting 1 H and 2 H NMR spectroscopic data. The IR spectrum of 3 contained a strong vibrational band at 1611 cm –1 , along with further broad absorptions at 1520–1410 cm –1 , corresponding to symmetric and asymmetric ν C–O vibrations (shifted to 1588 and 1509–1375 cm –1 for 13 C-3 ) and consistent with other reported carbamate ν C–O bands, ,, along with a band at 3424 cm –1 attributable to ν N–H .…”

“…While the study of U–C σ bonds and their ability to insert small molecules has received a significant amount of attention in the literature, U–N σ bonds have been comparatively overlooked and are more typically found as part of “inert” multidentate ligand frameworks supporting uranium metal centers in a range of oxidation states. , Some investigations into the insertion chemistry of U–N bonds with respect to CO and CO 2 have been reported, establishing the formation of U­(IV) carbamoyls and U­(III) and U­(IV) carbamates. − However, uranium–nitrogen multiple bonds have remained of considerable interest, ever since the first reports of UN double bonds in the mid-1980s, , and the latter have subsequently been synthesized within a range of ligand frameworks; , however, only one example of a primary terminal imido linkage, UNH, exists . Molecular, terminal UN triple bonds are extremely rare and until recently had only been observed under matrix isolation or mass spectrometric conditions − or as a proposed intermediate .…”

Formation of Trivalent U–C, U–N, and U–S Bonds and Their Reactivity toward Carbon Dioxide and Acetone

“…Further evidence for the monoanionic character of the carboxylate ligand is obtained by comparison to uranium(VI) carboxylate species, which has similar bond distances and angles. 48 Although studied for uranium(IV) amide complexes, 6,7 examples of the insertion of carbon dioxide into U(III)Àamide bonds is sparse. Stirring either 4-NHPh or 5-NHCH 2 Ph in the presence of small amounts of CO 2 causes an instant conversion to the respective carbamate products Tp* 2 U(k 2 -O 2 CNHPh) (9-O 2 CNHPh) and Tp* 2 U(k 2 -O 2 CNHCH 2 Ph) (10-O 2 CNH-CH 2 Ph) (eq 2).…”

“…Similarly, the uranium bis(acetylide) Cp* 2 U(CCPh) 2 forms Cp* 2 U(κ 2 -O 2 CCCPh) by CO 2 insertion . Amido complexes, such as Cp* 2 U(NEt 2 ) 2 , [(( R ArO) 3 tacn)U(NHMes)] (( R ArO) 3 tacn =1,4,7-tris(3-R-5- tert -butyl-2-hydroxybenzyl)-1,4,7-triazacyclononane, R = tBu, Ad), and other tetrakis(dialkylamido) uranium(IV) derivatives, yield carbamate ligands by insertion of CO 2 into the U–N bond. − Although the insertion chemistry of uranium(IV) sulfido species has had less attention, U–S bonds have been shown to reversibly insert carbon dioxide and carbon disulfide …”

Influence of steric pressure on the activation of carbon dioxide and related small molecules by uranium coordination complexes

“…Other remarkable instances document the insertion of carbon dioxide into a U-N amide bond of U(IV) mesityl amide complexes [(( t-Bu ArO) 3 tacn)U(NHMes)] ( 25) and [(( Ad ArO) 3 tacn)U(NHMes)] . 75 The difference in coordination modes can clearly be observed in the molecular structures of 26 and 28 (Fig. 15).…”