Alternating copolymerization of carbon monoxide and olefins by single-site metal catalysis

Following palladium catalyzed methoxycarbonylation by hyperpolarized NMR spectroscopy: a parahydrogen based investigation

When the reaction of Pd(OTf)₂(bcope) with diphenylacetylene, carbon monoxide and parahydrogen is probed, hyperpolarised NMR signals (blue) are seen.

Hollow and Microporous Organic Polymers Bearing Sulfonic Acids: Antifouling Seed Materials for Polyketone Synthesis

The reactor fouling is a notorious obstacle in managing continuous synthetic processes of polyketones. The fouling raises synthetic costs and reduces the bulk density of polymers. Thus, efficient seed materials are required for antifouling performance. Hollow microporous organic polymers (HMOPs) were prepared using ZIF-8 nanoparticles as templating materials. Sulfonic groups were incorporated into HMOP via a post synthetic approach. The resultant HMOP-SO₃H (20-90 μg/mL in methanol) showed successful catalyst activation and antifouling performance in polyketone synthesis.

Effect of chalcogens on CO insertion into the palladium-methyl bond of [(N^N^X)Pd(CH3)](+) (X = O, S, Se) and on CO/ethylene copolymerisation

Neutral chloromethylpalladium(II) complexes, [Pd(Cl)(CH3)(L)] (1a-5a) with ligands κ(2)-N^S-2-((3,5-di-tert-butyl-1H-pyrazol-1-yl)methyl)-6-(phenylthiomethyl)pyridine (L1), κ(2)-N^S-2-((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-6-(phenylthiomethyl)pyridine (L2), κ(2)-N^Se-2-((3,5-di-tert-butyl-1H-pyrazol-1-yl)methyl)-6-(phenylselanylmethyl)pyridine (L3), κ(2)-N^Se-2-((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-6-(phenylselanylmethyl)pyridine (L4), and κ(2)-N^N-2-((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-6-(phenoxymethyl)pyridine (L5) have been synthesised and characterised by various spectroscopic techniques. Ligands L1-L4 exhibit Npy^S/Se bidentate coordination whereas L5 shows an Npy^Npz bidentate coordination mode in their corresponding neutral palladium complexes. Abstraction of chloride in neutral palladium complexes with NaBAr4 (BAr4 = tetrakis[3,5-bis(trifluoromethyl)-phenyl]borate) resulted in the formation of the cationic palladium complexes 1b-5b, in which L1-L4 adopt a tridentate Npz^Npy^X (X = S or Se) coordination mode in their respective cationic palladium complexes (1b-4b) whilst L5 in complex 5b adopts a Npy^Npz bidentate coordination mode and the palladium centre is stabilized by the weakly coordinating acetonitrile. Compounds 1b-5b readily undergo CO insertion into the Pd-CH3 bond to form Pd-acyl that determines their ability to catalyse CO/ethylene copolymerisation to polyketones.

Enantioselective small molecule synthesis by carbon dioxide fixation using a dual Brønsted acid/base organocatalyst

Carbon dioxide exhibits many of the qualities of an ideal reagent: it is nontoxic, plentiful, and inexpensive. Unlike other gaseous reagents, however, it has found limited use in enantioselective synthesis. Moreover, unprecedented is a tool that merges one of the simplest biological approaches to catalysis-Brønsted acid/base activation-with this abundant reagent. We describe a metal-free small molecule catalyst that achieves the three component reaction between a homoallylic alcohol, carbon dioxide, and an electrophilic source of iodine. Cyclic carbonates are formed enantioselectively.

Synthesis of Sequence-Regulated Polymers: Alternating Polyacetylene through Regioselective Anionic Polymerization of Butadiene Derivatives

We hereby report a strategy to synthesize sequence-regulated substituted polyacetylenes using living anionic polymerization of designed monomers, that is, 2,4-disubstituted butadienes. It is found that proper substituents, such as 2-isopropyl-4-phenyl, lead to nearly 100% 1,4-addition during the polymerization, thus, giving product with high regioregularity, precise molecular weight, and narrow molecular weight distribution. The product is convertible into sequence-regulated substituted polyacetylene by oxidative dehydrogenation using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Block copolymers containing polyacetylene segment are also prepared. Owing to the versatility of the anionic reactions, the present strategy can serve as a powerful tool of precise control on polymer chain microstructure, architecture, and functionalities in the same time.

Carbonylation of ethene catalysed by Pd(II)-phosphine complexes

This review deals with olefin carbonylation catalysed by Pd(II)-phosphine complexes in protic solvents. In particular, the results obtained in the carbonylation with ethene are reviewed. After a short description of the basic concepts relevant to this catalysis, the review treats in greater details the influence of the bite angle, skeletal rigidity, electronic and steric bulk properties of the ligand on the formation of the products, which range from high molecular weight perfectly alternating polyketones to methyl propanoate. It is shown that the steric bulk plays a major role in directing the selectivity. Particular emphasis is given to the factors governing the very active and selective catalysis to methyl propanoate, including the mechanism of the catalytic cycles with diphosphine- and monophosphine-catalysts. A brief note on the synthesis of methyl propanoate using a “Lucite” type catalyst in ionic liquids is also illustrated. A chapter is dedicated to the carbonylation of olefins in aqueous reaction media. The nonalternating CO-ethene copolymerization is also treated.

Ortho-phosphinobenzenesulfonate: a superb ligand for palladium-catalyzed coordination-insertion copolymerization of polar vinyl monomers

Ligands, Lewis bases that coordinate to the metal center in a complex, can completely change the catalytic behavior of the metal center. In this Account, we summarize new reactions enabled by a single class of ligands, phosphine-sulfonates (ortho-phosphinobenzenesulfonates). Using their palladium complexes, we have developed four unusual reactions, and three of these have produced novel types of polymers. In one case, we have produced linear high-molecular weight polyethylene, a type of polymer that group 10 metal catalysts do not typically produce. Secondly, complexes using these ligands catalyzed the formation of linear poly(ethylene-co-polar vinyl monomers). Before the use of phosphine-sulfonate catalysts, researchers could only produce ethylene/polar monomer copolymers that have different branched structures rather than linear ones, depending on whether the polymers were produced by a radical polymerization or a group 10 metal catalyzed coordination polymerization. Thirdly, these phosphine-sulfonate catalysts produced nonalternating linear poly(ethylene-co-carbon monoxide). Radical polymerization gives ethylene-rich branched ethylene/CO copolymers copolymers. Prior to the use of phosphine-sulfonates, all of the metal catalyzed processes gave completely alternating ethylene/carbon monoxide copolymers. Finally, we produced poly(polar vinyl monomer-alt-carbon monoxide), a copolymerization of common polar monomers with carbon monoxide that had not been previously reported. Although researchers have often used symmetrical bidentate ligands such as diimines for the polymerization catalysis, phosphine-sulfonates are unsymmetrical, containing two nonequivalent donor units, a neutral phosphine, and an anionic sulfonate. We discuss the features that make this ligand unique. In order to understand all of the new reactions facilitated by this special ligand, we discuss both the steric effect of the bulky phosphines and electronic effects. We provide a unified interpretation of the unique reactivity by considering of the net charge and the enhanced back donation in the phosphine-sulfonate complexes.