Influence of the Counterion on the Synthesis of Cyclic Carbonates Catalyzed by Bifunctional Aluminum Complexes

Abstract

New bifunctional aluminum complexes have been prepared with the aim of studying the effect of a counterion on the synthesis of cyclic carbonates from epoxides and carbon dioxide (CO2). Neutral ligand 1 was used as a precursor to obtain four novel mesylate, chloride, bromide, and iodide zwitterionic NNO ligands (2–5). The reaction of these ligands with 1 or 2 equiv of AlR3 (R = Me, Et) allowed the synthesis of mono- and bimetallic bifunctional aluminum complexes [AlR2(κ2-mbpzappe)]­X [X = Cl, R = Me (6), Et (7); X = Br, R = Me (8), Et (9); X = I, R = Me (10), Et (11)] and [{AlR2(κ2-mbpzappe)}­(μ-O)­{AlR3}]­X [X = MeSO3, R = Me (12), Et (13); X = Cl, R = Me (14), Et (15); X = Br, R = Me (16), Et (17); X = I, R = Me (18), Et (19)] via alkane elimination. These complexes were studied as catalysts for the synthesis of cyclic carbonates from epoxides and CO2. Iodide complex 11 showed to be the most active catalyst for terminal epoxides, whereas bromide complex 9 was found to be the optimal catalyst when internal epoxides were used, showing the importance of the nucleophile cocatalyst on the catalytic activity.

Zinc Imine Polyhedral Oligomeric Silsesquioxane as a Quattro‐Site Catalyst for the Synthesis of Cyclic Carbonates from Epoxides and Low‐Pressure CO2

“…Cyclic carbonates are characterized by a range of applications, for instance: monomers for polymerization, substrates in organic synthesis, green solvents, or electrolytes for lithium‐ion batteries [48, 49] . From the above reasons, a number of research groups have focused their attention on the preparation of efficient catalytic systems for cyclic carbonate synthesis including metal complexes with imine, [50–54] aminophenolate, [55, 56] porphyrin, [57, 58] or other ligands [59–62] . Also, an organocatalytic approach has actively been investigated [63–65] …”

A Mechanistic Analysis of Trimethylanilinium Salt Degradation: Implications for Methylation and Cross-coupling Applications

“…From these experiments, the hypothesised trend of thermally unstable anilinium salts leading to more efficient methylation did not hold. Indeed, three of the most thermally unstable anilinium iodides 2a-4a and 15a -all carrying strong electron-withdrawing aryl substituents -led to measurable quantities of SNAr products (18)(19)(20)(21) and poor yields of desired methylation products. Indeed, analysis of thermal degradation versus O-methylation efficiency within the anilinium salt library revealed that only those unstable salts bearing no resonance withdrawing aryl substituents served as efficient methylating reagents.…”

“…Applications and divergent reactivity of trimethylanilinium salts. N,N,N-trimethylanilinium salts have found wide-ranging applications in synthesis, spanning phase-transfer catalysis, 1 supramolecular ion-pairing catalysis, 2,3 host-guest binding studies, 4 O-methylation, 5 O-arylation, 6 heteroatom arylations, 7 C-H methylation, 8 C-arylation, [9][10][11] fluorine radiolabeling, [12][13][14][15] organometallic ligand design, [16][17][18][19][20][21] antimicrobial polymer design, 22 and a range of metal-catalysed cross-coupling methodologies. [23][24][25][26][27][28][29] The dichotomy of arylation versus methylation reactivity, while important for optimising the above-listed applications, is rarely studied in detail.…”

Diethylene Glycol/NaBr Catalyzed CO2 Insertion into Terminal Epoxides: From Batch to Continuous Flow

“…A plethora of such systems active for terminal, internal and trisubstituted epoxides have been reported so far. [6] In view of more sustainable protocols, special emphasis has been devoted to non-endangered metal catalysts [7] such as salts and complexes of Fe, Al, Co and Zn, [8][9][10][11] and, even more interesting, some of these systems have proved efficient in continuous-flow (CF) mode, i. e. under highly reliable conditions for process optimization, intensification and upscaling. [12] One of the first CF-examples described a Co II -salen complex immobilized on MCM-41 silica gel: at T = 110°C, p(CO 2 ) = 125 bar and F = 10-20 mL • h À 1 , in the presence of tetrabutylammonium bromide (TBAB) as a co-catalyst, ethylene oxide (EO) was converted up to 86 % into ethylene carbonate (EC) with > 99 % selectivity.…”