Bifunctional aluminum complexes supported by novel zwitterionic NNO-donor scorpionate ligands were found to be efficient bifunctional catalysts for cyclic carbonate synthesis from terminal and internal epoxides in good yields and with broad substrate scope. Neutral scorpionate ligands (1–2) were designed and used as precursors to obtain two novel zwitterionic NNO-heteroscorpionate ligands (3–4). Reaction of 3 or 4 with [AlX3] (X = Me, Et) in a 1:1 or 1:2 molar ratio afforded the mononuclear and dinuclear cationic aluminum complexes [AlX2{κ2-mbpzbdmape}]­I2 (X = Me (5), Et (6)), [AlX2{κ2-mbpzbdeape}]­I2 (X = Me (7), Et (8)), [{AlX2(κ2-mbpzbdmape)}­(μ-O)­{AlX3}]­I2 (X = Me (9), Et (10)), and [{AlX2(κ2-mbpzbdeape)}­(μ-O)­{AlX3}]­I2 (X = Me (11), Et (12)) with elimination of the corresponding alkane. These complexes were investigated as catalysts for cyclic carbonate formation from epoxides and carbon dioxide in the absence of a co-catalyst. Complex 7 was found to be the most active catalyst for cyclic carbonate formation from various epoxides and carbon dioxide.

Metal-free catalysts for cyclic carbonates synthesis.

The coupling reaction of carbon dioxide and terminal, internal, and highly substituted epoxides derived from renewable resources such as furfural, limonene, carvone, carvyl acetate, terpinen-4-ol, or ionone leads to the synthesis of new bioderived cyclic carbonates using an efficient aluminum catalyst under mild and solvent-free reaction conditions. Interestingly, the synthesis of highly substituted bioderived cyclic carbonates can occur with excellent diastereoselectivity, obtaining in some cases one diastereoisomer as the major product. The X-ray crystal structures of two enantiomerically pure carvonebased cyclic carbonates are reported.

Helical aluminium complexes have been prepared and used as catalysts for cyclic carbonate synthesis.

The optimization of an organoaluminum catalytic system for the copolymerization of epoxides and anhydrides is presented. For this purpose, the influence of different variables in the process, such as catalysts, cocatalyst, solvent, or substrates, has been analyzed. Kinetic studies, a proposal for the catalytic mechanism, and full characterization of the copolymers obtained are also discussed. Finally, a new copolymer, poly(limonene succinate), obtained by the optimized catalytic system is reported.

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.

A series of alkyl aluminium complexes based on heteroscorpionate ligands were designed as catalysts for the ring-opening polymerisation of cyclic esters and ring-opening copolymerisation of epoxides and anhydrides. Treatment of AlX3 (X = Me, Et) with ligands bpzbeH [bpzbe = 1,1-bis(3,5-dimethylpyrazol-1-yl)-3,3-dimethyl-2-butoxide], bpzteH [bpzte = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1-para-tolylethoxide], and (R,R)-bpzmmH [(R,R)-bpzmm = (1R)-1-{(1R)-6,6-dimethyl-bicyclo[3.1.1]-2-hepten-2-yl}-2,2-bis(3,5-dimethylpyrazol-1-yl)ethoxide] for 2 hours at 0 °C afforded the mononuclear dialkyl aluminium complexes [AlMe2{κ2-bpzbe}] (1), [AlEt2{κ2-bpzbe}] (2), [AlMe2{κ2-(R,R)-bpzmm}] (3) and [AlEt2{κ2-(R,R)-bpzmm}] (4), and the dinuclear dialkyl complexes [AlMe2{κ2-bpzte}]2 (5) and [AlEt2{κ2-bpzte}]2 (6). The molecular structures of the new complexes were determined by spectroscopic methods and confirmed by X-ray crystallography. The alkyl-containing aluminium complexes can act as highly efficient single-component initiators for the ring-opening polymerisation of ε-caprolactone and l-lactide and for the ring-opening copolymerisation of cyclohexene oxide and phthalic anhydride to give a range of biodegradable polyesters.

Bimetallic motifs mediate the selective activation and functionalization of CO 2 in metalloenzymes and some recent synthetic systems. In this work, we build on the nascent concept of bimetallic frustrated Lewis pairs (FLPs) to investigate the activation and reduction of CO 2 . Using the Fe 0 fragment [(depe) 2 Fe] (depe = 1,2-bis(diethylphosphino)ethane) as base, we modify the nature of the partner Lewis acid to accomplish a divergent and highly chemoselective reactivity towards CO 2 . [Au(PMe 2 Ar)] + irreversibly dissociates CO 2 , Zn(C 6 F 5 ) 2 and B(C 6 F 5 ) 3 yield different CO 2 adducts stabilized by push-pull interactions, while Al(C 6 F 5 ) 3 leads to a rare heterobimetallic CÀ O bond cleavage, and thus to contrasting reduced products after exposure to dihydrogen. Computational investigations provide a rationale for the divergent reactivity, while Energy Decomposition Analysis-Natural Orbital for Chemical Valence (EDA-NOCV) method substantiates the heterobimetallic bonding situation.