Diverse outcomes of CO₂ fixation using alkali metal amides including formation of a heterobimetallic lithium–sodium carbamato-anhydride via lithium–sodium bis-hexamethyldisilazide

Abstract

Mixed-metal synergistic activation of CO2 leads to a crystalline mixed-metal carbamato-anhydride polymer.

Recent Advances in the Chemistry of Metal Carbamates

“…Concerning metal alkyls, lithium N,N-dialkylcarbamates were recently prepared starting from n BuLi and CO 2 in the presence of diisopropylamine or pyrrole [165]. A related reaction was reported with NaH, providing a more convenient pathway to Na(O 2 CNEt 2 ) compared to the use of sodium sand [166].…”

“…Analogous equilibria can also explain the solubility of metal carbamates in coordinating solvents [42]. In this regard, THF or TMEDA adducts were recently isolated growing crystals of lithium carbamates [133,165].…”

“…This feature is common to several alkali metal carbamates [ 156 , 177 ], including those of bulky 2,2,6,6-tetramethylpiperidine [ 133 ]. On the other hand, the lithium diisopropyl derivative [(LiO 2 CN i Pr 2 ) 12 ( i Pr 2 NCOOH) 2 ] is a dodecanuclear cluster decorated with a rare carbamic acid ligand [ 47 , 84 , 178 ], whose formation has been ascribed to adventitious hydrolysis [ 165 ].…”

“…Organolithium compounds, Grignard reagents and other d-block and p-block alkyls can be employed to this purpose, hence the generation of the carbamate may proceed through the intermediacy of a metal-amide unit [ 42 ]. These reactions are usually conducted in coordinating solvents (e.g., THF, Et 2 O), which are often found incorporated in the final complex [ 165 , 248 ]. For instance, the reaction of MeMgBr with N -methylaniline and CO 2 in THF leads to the dimer [Mg(O 2 CN(Me)Ph)(THF) 2 Br] 2 , where magnesium shows a trigonal bipyramidal coordination geometry [ 248 ] ( Scheme 24 a).…”

Backbone Reactivity of Lithium β‐Diketiminate (NacNac) Complexes with CO2, tBuNCO and iPrNCO

“…Recently our group joined the growingn umber of scientists interested in the field of CO 2 activation/fixation chemistry.D espite the many studies probingC O 2 fixation, we noted how few considered the insertion of CO 2 into reactive LiÀN bonds, [18] even though such bonds are found in synthetically important lithium (and sodium) amide reagents.O ur study showedt hat reaction between as eries of common utility metal amides and CO 2 resulted in insertion into the MÀN bonds affording ar ange of new metal carbamate complexes with interesting structural motifs (polymeric ladders, carbamato anhydride mixed sodium lithium polymers). [19] Inspired by this study,w ed ecided to expand our effortsi nto researching the popular NacNac ligand,t oe xamine the effects of CO 2 fixation on their lithium derivatives, anticipating CO 2 insertion into the reactiveN ÀLi bondsp resent in theses pecies. Thef act that alkali metal complexes are agentss upremef or transferring the NacNac anion, [20] andnumerousother ligands, adds an extra incentive for elaborating fully the chemistry of alkali metal NacNac complexes.R eported herein are our resultsf ocusing on the fixation of small molecules with lithiumN acNac complexes of the commonly studied 2,6-diisopropylphenyl-b-methyldiketiminate [NacNac(Dipp, Me) or (DIPPBDI) A Figure 1].…”