Re-cycling carbon dioxide with iron". The synthesis of cyclic organic carbonates in high yield, stereo- and chemo-selectivity was accomplished through the coupling of carbon dioxide and epoxides, catalysed by a novel air-stable and easy-to-handle thioether-triphenolate iron(iii) complex

The preparation and characterization of new Zn(II) complexes of the type [(PPP)ZnR] in which R = Et (1) or N(SiMe(3))(2) (2) and PPP is a tridentate monoanionic phosphido ligand (PPP-H = bis(2-diphenylphosphinophenyl)phosphine) are reported. Reaction of ZnEt(2) and Zn[N(SiMe(3))(2)](2) with one equivalent of proligand PPP-H produced the corresponding tetrahedral zinc ethyl (1) and zinc amido (2) complexes in high yield. Homoleptic (PPP)(2) Zn complex 3 was obtained by reaction of the precursors with two equivalents of the proligand. Structural characterization of 1-3 was achieved by multinuclear NMR spectroscopy ((1)H, (13)C, and (31)P) and X-ray crystallography (3). Variable-temperature (1)H and (31)P NMR studies highlighted marked flexibility of the phosphido pincer ligand in coordination at the metal center. A DFT calculation on the compounds provided theoretical support for this behavior. The activities of 1 and 2 toward the ring-opening polymerization of ε-caprolactone and of L- and rac-lactide were investigated, also in combination with an alcohol as external chain-transfer agent. Polyesters with controlled molecular parameters (M(n), end groups) and low polydispersities were obtained. A DFT study on ring-opening polymerization promoted by these complexes highlighted the importance of the coordinative flexibility of the ancillary ligand to promote monomer coordination at the reactive zinc center. Preliminary investigations showed the ability of these complexes to promote copolymerization of L-lactide and ε-caprolactone to achieve random copolymers whose microstructure reproduces the composition of the monomer feed.

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The aerobic oxidation and oxidative esterification of 5-hydroxymethylfurfural (HMF) catalyzed by gold nanoparticles (AuNPs) supported on a semicrystalline nanoporous multiblock copolymer matrix consisting of syndiotactic poly(styrene)-cis-1,4-poly(butadiene) (sPSB) have been investigated. Depending on the reaction parameters (support nanoporosity, presence of water, solvent, temperature, cocatalyst, oxygen pressure), the conversion of HMF can be finely addressed to the formation of the desired oxidation product, such as 2,5-diformylfuran (DFF), 5-formylfuran-2-carboxylic acid (FFCA), methyl 5-(hydroxymethyl)furan-2-carboxylate (MHMFC), dimethyl furan-2,5-dicarboxylate (DMFC), and furan-2,5-dicarboxylic acid (FDCA), under optimized reaction conditions. The AuNP-sPSB catalyst is highly effective and selective because the polymer support acts as a conveyor and concentrator of the reactants toward the catalytic sites.

The ability of the dichloro{1,4-dithiabutanediyl-2,2‘-bis(4,6-di-tert-butylphenoxy)}titanium complex (1) to catalyze homopolymerization of conjugated dienes and copolymerization of butadiene with styrene is reported. After proper activation with methylalumoxane, 1 resulted active in the trans-1,4 selective polymerization of butadiene and isoprene with good activity. The molecular weight distributions of the polymers are monomodal with the polydispersity indexes, consistent with a single site behavior of the catalyst. Isotactic polystyrene-co-trans-1,4-polybutadiene with an unprecedented architecture, covering a wide range of compositions (x S = 0.15−0.97), were also obtained. The chemo- and stereoselectivity of butadiene insertion and the isospecific styrene polymerization of the title catalyst are retained when the two monomers are copolymerized. The molecular weight distributions are consistent with the material being copolymeric in nature. The reactivity ratios values and the microstructure analysis (by means of 13C NMR) indicate a random distribution of the two monomers in the polymer chain.

Treatment of 2,4-di-tert-butyl-6-(bis(3,5-dimethylpyrazol-1-yl)methyl)phenol (bpzmp-H) as tridentate ligand with aluminum trialkyls affords the corresponding heteroscorpionate aluminum complexes (bpzmp)-AlR 2 (R ) Me (1); R ) Et (2); R ) iBu (3)) in high yield. In the solid state, complexes 1-3 were isolated as racemic mixtures in which each stereoisomer adopts a tetrahedral structure with the bpzmp ligand κ 2 -coordinated to the metal via the phenoxy group and the imino nitrogen of one of pyrazolyl rings. The investigation of the solution structure of 1-3 by means of VT 1 H NMR spectroscopy revealed fluxional exchange between coordinated and noncoordinated pyrazolyl rings, producing interconversion between the two enantiomers. The activation enthalpy (∆H # ) for racemization processes (10.1 ( 0.2 kcal‚mol -1 (1); 11.6 (0.3 kcal‚mol -1 (2); 14.1 ( 0.2 kcal‚mol -1 (3)) was dependent on steric hindrance at the aluminum center. Reaction of 1 or 2 with B(C 6 F 5 ) 3 proceeds through net alkyl abstraction, forming the expected cationic aluminum complexes [(bpzmp)AlR] + [RB(C 6 F 5 ) 3 ] -(R ) Me (4); R ) Et ( 5)), in which the bpzmp fragment acts as a tridentate ligand. The ionization reaction of 3 with Lewis acidic compounds (B(C 6 F 5 ) 3 or [Ph 3 C][B(C 6 F 5 ) 4 ]) proceeds by net β-H abstraction from the isobutyl group, forming [(bpzmp)AliBu] + [HB(C 6 F 5 ) 3 ] -(6) along with isobutene; in contrast, reaction with the Bro ¨nsted acid [HNMe 2 Ph][B(C 6 F 5 ) 4 ] proceeds by protonolysis of the isobutyl group. Complex 4 is active in ringopening polymerization of -caprolactone ( -CL), producing high-molecular-weight polymers. The 1 H NMR monitoring of the reaction between 4 and -CL in 1:1 molar ratio showed that the initiation involves monomer insertion into the Al-O bond of the bpzmp fragment, forming the intermediate [(bpzphe)AlMe] + -[MeB(C 6 F 5 ) 4 ] -(bpzphe ) 2,4-di-tert-butyl-6-(bis(3,5-dimethylpyrazol-1-yl)methyl)phenyl 6-hydroxyhexanoate (8). The growth of the polymer chain occurs through continuous insertions of the monomer in the Al-alkoxide bond.

Glycidol is converted into glycerol carbonate (GC) by coupling with CO in the presence of tetrabutylammonium bromide (TBAB) under mild reaction conditions (T=60 °C, PCO2 =1 MPa) in excellent yields (99 %) and short reaction time (t=3 h). The unusual reactivity of this substrate compared to other epoxides, such as propylene oxide, under the same reaction conditions is clearly related to the presence of a hydroxyl functionality on the oxirane ring. Density functional theory calculations (DFT) supported by H NMR experiments reveal that the unique behavior of this substrate is a result of the formation of intermolecular hydrogen bonds into a dimeric structure, activating this molecule to nucleophilic attack, and allowing the formation of GC. Furthermore, the glycidol/TBAB catalytic system acts as an efficient organocatalyst for the cycloaddition of CO to various oxiranes.

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