Cobalt‐catalyzed alternating and nonalternating copolymerization of carbon monoxide with aziridine

Catalysts CH₃COCo(CO)₃PPh₃ ( 1 ) and HCo(CO)₃PPh₃ ( 2 ) catalyze the copolymerization of aziridine and carbon monoxide. Catalyst 2 can be conveniently generated in situ via reaction of Na⁺Co(CO)₄, N,N‐dimethylanilinium chloride, and PPh₃. The copolymerization alternates at high catalyst loadings to produce poly(β‐alanine). The end groups of the poly(β‐alanine) product are characterized by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry and by comparison of the ¹H NMR spectra of the polymer and a stepwise synthesized model compound. At low catalyst loadings, the polymer product contains both the β‐alanine units and amine units because of nonalternating enchainment of the comonomers. The characterization of the amine units is again supported by comparison of the ¹H NMR spectra of the polymers and the stepwise synthesized model compounds. The molecular weights of the polymers are determined by gel permeation chromatography. The thermal stability of the polymers is probed by differential scanning calorimetry and thermogravimetric analysis. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 376–385, 2003     

Mechanistic Aspects of a Highly Active Dinuclear Zinc Catalyst for the Co‐polymerization of Epoxides and CO2

The dinuclear zinc complex reported by us is to date the most active zinc catalyst for the co‐polymerization of cyclohexene oxide (CHO) and carbon dioxide. However, co‐polymerization experiments with propylene oxide (PO) and CO₂ revealed surprisingly low conversions. Within this work, we focused on clarification of this behavior through experimental results and quantum chemical studies. The combination of both results indicated the formation of an energetically highly stable intermediate in the presence of propylene oxide and carbon dioxide. A similar species in the case of cyclohexene oxide/CO₂ co‐polymerization was not stable enough to deactivate the catalyst due to steric repulsion.     

Palladium catalyzed ethylene-carbon monoxide alternating copolymerization

A new [(PPh₂CH₂CH₂CH₂PPh₂)Pd(CH₃CN)₂](BF₄)₂/CH₃OH catalyst for olefin/carbon monoxide alternating copolymerization has been found which is far more active and more stable than previous monodente phosphine Pd catalysts. Methanol is a coinitiator as well as a chain transfer agent. Protonic acid is not a coinitiator but causes chain transfers. In the absence of methanol, the copolymerization was characterized by long induction period and slow rate © 1992 John Wiley & Sons, Inc.     

The cobalt-catalyzed alternating copolymerization of epoxides and carbon monoxide: a novel approach to polyesters

The metal-catalyzed synthesis of polyolefins, polyketones, and polycarbonates is well-known in academia and is already successfully applied in industrial processes. Still missing, however, is the metal-catalyzed synthesis of aliphatic polyesters, as one of the most important biodegradeable polymer families. We report here on the cobalt-catalyzed alternating copolymerization of propylene oxide and carbon monoxide, affording atactic and isotactic polyhydroxybutyrates (PHB). The postulated mechanism is supported by online ATR-IR analytics.     

Synthesis of heterobimetallic Ru-Mn complexes and the coupling reactions of epoxides with carbon dioxide catalyzed by these complexes

The heterobimetallic complexes [(eta5-C5H5)Ru(CO)(mu-dppm)Mn(CO)4] and [(eta5-C5Me5)Ru(mu-dppm)(mu-CO)2Mn(CO)3] (dppm = bis-diphenylphosphinomethane) have been prepared by reacting the hydridic complexes [(eta5-C5H5)Ru(dppm)H] and [(eta5-C5Me5)Ru(dppm)H], respectively, with the protonic [HMn(CO)5] complex. The bimetallic complexes can also be synthesized through metathetical reactions between [(eta5-C5R5)Ru(dppm)Cl] (R = H or Me) and Li+[Mn(CO)5]-. Although the complexes fail to catalyze the hydrogenation of CO2 to formic acid, they catalyze the coupling reactions of epoxides with carbon dioxide to yield cyclic carbonates. Two possible reaction pathways for the coupling reactions have been proposed. Both routes begin with heterolytic cleavage of the RuMn bond and coordination of an epoxide molecule to the Lewis acidic ruthenium center. In Route I, the Lewis basic manganese center activates the CO2 by forming the metallocarboxylate anion which then ring-opens the epoxide; subsequent ring-closure gives the cyclic carbonate. In Route II, the nucleophilic manganese center ring-opens the ruthenium-attached epoxide to afford an alkoxide intermediate; CO2 insertion into the RuO bond followed by ring-closure yields the product. Density functional calculations at the B3LYP level of theory were carried out to understand the structural and energetic aspects of the two possible reaction pathways. The results of the calculations indicate that Route II is favored over Route I.     

Rare‐earth‐catalyzed alternating copolymerization of carbon monoxide with styrene

Rare‐earth acetates were used to catalyze the copolymerization reaction of carbon monoxide and styrene. Cupric acetate, 1,10‐phenanthroline, p‐toluenesulfonic acid, and 1,4‐benzoquinone were also added to the catalyst system. The structures of the copolymers obtained were characterized with IR, ¹H NMR, ¹³C NMR, wide‐angle X‐ray diffraction, and elemental analysis methods. The relationship between the catalytic activity and the catalyst composition was studied in detail. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 642–649, 2002; DOI 10.1002/pola.10147     

Synthesis of linear and branched polyketones from the Rh complex catalyzed living alternating copolymerization of (4‐alkylphenyl)allene with CO

Copolymerization of (4‐hexylphenyl)allene and of (4‐dodecylphenyl)allene with carbon monoxide (1 atm) catalyzed by Rh[η³‐CH(Ar′)C{C(CHAr′)CH₂C (CHAr′)CH₂CH₂CHCHAr′}CH₂](PPh₃)₂ (A; Ar′ = C₆H₄OMe‐p) gives the corresponding polyketones: I‐[—CO—C(CHAr)—CH₂—]_n [1: Ar = C₆H₄C₆H₁₃‐p, 2 : Ar = C₆H₄C₁₂H₂₅‐p; I = CH₂C(CHAr′)C(CHAr′)CH₂C(CHAr′)CH₂CH₂CHCHAr′]. Molecular weights of the polyketone prepared from (4‐hexylphenyl)allene and CO are similar to the calculated from the monomer to initiator ratios until the molecular weight reaches to 45,000, indicating the living polymerization. Melting points of the polyketones I‐[—CO—C(CHC₆H₄R‐p)—CH₂—]_n (n = ca. 100) increase in the order R = C₁₂H₂₅ < C₆H₁₃ < C₄H₉ < CH₃ < H. Block and random copolymerization of phenylallene and (4‐alkylphenyl)allene with carbon monoxide gives the new copoly‐ ketones. The polymerization of a mixture of (4‐methylphenyl)allene and smaller amounts of bis(allenyl)benzene under CO afforded the polyketone with a crosslinked structure. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1505–1511, 2000     

Enantioselective,alternating copolymerization of carbon monoxide and olefins

Enantioselective, alternating copolymerizations of carbon monoxide with styrene, dicyclopentadiene, and methylcyclopentadiene dimer were carried out with a palladium catalyst modified by 1,4‐3,6‐dianhydro‐2,5‐dideoxy‐2,5‐bis(diphenyl phosphino)‐L ‐iditol. Chiral diphosphine was proven to be effective at enantioselective copolymerization. In the copolymers, some of the second double bonds of alternating poly(1,4‐ketone) were carbonylated. Optical rotation, elemental analysis, and spectra of ¹H NMR, ¹³C NMR, and IR showed that the copolymers had isotactic, alternating poly(1,4‐ketone) structures. An oxidant and an organic acid were the promoters of the copolymerization. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2919–2924, 2000     

Mechanistic aspects of the copolymerization reaction of carbon dioxide and epoxides,using a chiral salen chromium chloride catalyst

The air-stable, chiral (salen)Cr(III)Cl complex (3), where H(2)salen = N,N'-bis(3,5-di-tert-butyl-salicylidene)-1,2-cyclohexene diamine, has been shown to be an effective catalyst for the coupling of cyclohexene oxide and carbon dioxide to afford poly(cyclohexenylene carbonate), along with a small quantity of its trans-cyclic carbonate. The thus produced polycarbonate contained >99% carbonate linkages and had a M(n) value of 8900 g/mol with a polydispersity index of 1.2 as determined by gel permeation chromatography. The turnover number (TON) and turnover frequency (TOF) values of 683 g of polym/g of Cr and 28.5 g of polym/g of Cr/h, respectively for reactions carried out at 80 degrees C and 58.5 bar pressure increased by over 3-fold upon addition of 5 equiv of the Lewis base cocatalyst, N-methyl imidazole. Although this chiral catalyst is well documented for the asymmetric ring-opening (ARO) of epoxides, in this instance the copolymer produced was completely atactic as illustrated by (13)C NMR spectroscopy. Whereas the mechanism for the (salen)Cr(III)-catalyzed ARO of epoxides displays a squared dependence on [catalyst], which presumably is true for the initiation step of the copolymerization reaction, the rate of carbonate chain growth leading to copolymer or cyclic carbonate formation is linearly dependent on [catalyst]. This was demonstrated herein by way of in situ measurements at 80 degrees C and 58.5 bar pressure. Hence, an alternative mechanism for copolymer production is operative, which is suggested to involve a concerted attack of epoxide at the axial site of the chromium(III) complex where the growing polymer chain for epoxide ring-opening resides. Preliminary investigations of this (salen)Cr(III)-catalyzed system for the coupling of propylene oxide and carbon dioxide reveal that although cyclic carbonate is the main product provided at elevated temperatures, at ambient temperature polycarbonate formation is dominant. A common reaction pathway for alicyclic (cyclohexene oxide) and aliphatic (propylene oxide) carbon dioxide coupling is thought to be in effect, where in the latter instance cyclic carbonate production has a greater temperature dependence compared to copolymer formation.     

Regio- and stereocontrol in the alternating copolymerization of olefins with carbon monoxide

Strictly alternating copolymers between olefins and carbon monoxide are synthesized using cationic palladium catalysts modified by phosphorus or nitrogen ligands. Basic chelate diphosphines as the ligand allow the regioregular copolymerization of aliphatic olefins thus affording, e.g. in the case of propene, poly(1-oxo-2-methyltrimethylene). Steric control of the copolymerization process towards the production of overwhelmingly isotactic copolymers is possible particularly when using atropisomeric ligands. In the case of styrene as the substrate and for all ligands employed the copolymerization process is regioregular. Prevailing syndiotactic structure is obtained with 1,10-phenanthroline or 2,2′-bipyridine as the ligand. Chelate thioether ligands allow the preparation of a completely atactic material. For 4-tert-butylstyrene an isotactic structure became accessible by using chiral bisoxazolidines. The prevailing structure of the copolymers of cyclopentene corresponds to a 1,3-enchainment of the olefin units most probably associated with a prevailing diisotactic structure     

Regioselective and stereoselective alternating copolymerization of carbon monoxide with functional olefins

Enantioselective, alternating copolymerizations of carbon monoxide with ω‐undecylenic acid, ethyl acrylate, and butyl acrylate were carried out for the first time with a palladium catalyst modified by 1,4:3,6‐dianhydro‐2,5‐dideoxy‐2,5‐bis(diphenylphosphino)‐L ‐iditol. Optical rotation, elemental analysis, and ¹H NMR,¹³C NMR, and IR spectra showed that the copolymers were optically active, isotactic, alternating poly(1,4‐ketone) or poly(spiroketal) structures. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2027–2036, 2001     

The facile reduction of carbon dioxide to carbon monoxide with an amido-digermyne

Taking the fizz out: A digermyne compound with a Ge?Ge single bond has been shown to quantitatively reduce CO(2) to CO at temperatures as low as -40?°C. The mechanism of this unprecedented reaction has been probed by spectroscopic and computational techniques and involves a metastable intermediate (see picture; Ar*=C(6) H(2) {C(H)Ph(2) }(2) Me-2,6,4).     

A theoretical study on the complete catalytic cycle of the hetero-Pauson-Khand-type [2+2+1] cycloaddition reaction of ketimines,carbon monoxide and ethylene catalyzed by iron carbonyl complexes

The [2+2+1] cycloaddition reaction of 1,4-diazabutadienes, carbon monoxide and ethylene catalyzed by iron carbonyl complexes produces pyrrolidin-2-one derivatives. Only one of the two imine moieties is activated during the catalysis. The mechanism of this cycloaddition reaction is studied by density functional theory at the B3LYP/6-311++G(d,p) level of theory. In accordance with experimental results, a [(diazabutadiene)Fe(CO)(3)] complex of square-pyramidal geometry is used as the starting compound S of the catalytic cycle. Based on experimental experience, the reaction with ethylene is considered to take place before any interaction with carbon monoxide. According to the computational results, the reaction does not proceed by ligand dissociation followed by addition of ethylene and subsequent intramolecular activation steps but by the approach of an ethylene molecule from the base of the square-pyramidal complex. This reaction yields an intermediate I(4) in which ethylene is coordinated to the iron centre and a new C-C bond between ethylene and one of the imine groups is formed. The insertion of a terminal carbon monoxide ligand into the metal-carbon bond between ethylene and iron produces the key intermediate I(7). The reaction proceeds by metal-assisted formation of a lactam P. The catalytic cycle is closed by a ligand-exchange reaction in which the diazabutadiene ligand substitutes P with reformation of S. This reaction pathway is found to be energetically favored over a reductive elimination. It leads to the experimentally observed heterocyclic product P and a reactive [Fe(CO)(3)] fragment.     

A semiempirical quantum mechanical study of cationically catalyzed homopolymerization and copolymerization of vinyl ethers and epoxides

The purpose of this study was to use the semiempirical quantum mechanical computational method, AM1, to investigate vinyl ether cationic homopolymerization, epoxide homopolymerization, and copolymerization of selected vinyl ethers with a model epoxide (cyclohexene oxide). Homopolymerization studies of 19 vinyl ethers showed that activation enthalpies ranged between 0.0 and 15 kcal/mol, and that the enthalpies of reaction for homopolymerization were nearly all exothermic. Homopolymerization of three epoxides predicted low activation enthalpies, some of which were virtually activationless. All ring-opening epoxide polymerizations were exothermic. Copolymerization of three vinyl ethers with cyclohexene oxide gave activation enthalpies that varied between 2.7 and 4.0 kcal/mol, and the enthalpies of reaction for copolymerization were all exothermic.     

(Salan)CrCl,an effective catalyst for the copolymerization and terpolymerization of epoxides and carbon dioxide

The selective transformation of CO₂ and epoxides to afford completely alternating copolymers remains a topic of much interest for the potential utilization of carbon dioxide in chemical synthesis. The use of salicylaldimine (salen)‐metal complexes and their saturated (salan)‐metal versions have proven to be the most effective and robust single‐site catalyst for these processes. Herein, we report on mechanistic aspects of the copolymerization of alicyclic and aliphatic epoxides with CO₂ in toluene solution and in neat epoxides in the presence of a (salan)CrCl/onium salt catalyst system. The activation barriers for both cyclohexene oxide(CHO)/CO₂ and propylene oxide(PO)/CO₂ were shown to be significantly higher in toluene solution than those previously reported for reactions carried out under solventless conditions. Terpolymerization of CHO/vinylcyclohexene oxide/CO₂ was shown via Fineman‐Ross analysis at 60 °C to proceed with little monomer selectivity, for example, r_CHO = 1.03 and r_VCHO = 0.847. On the other hand, terpolymerization of CHO/PO/CO₂ occurred at 25 °C with a propensity for incorporation of PO in the polymer. However, at 40 °C, Fineman‐Ross analysis revealed r_CHO and r_PO values of 0.869 and 1.49, thereby affording a terpolymer with a more equal distribution of monomers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Mechanistic studies of the copolymerization reaction of aziridines and carbon monoxide to produce poly-beta-peptoids

The coupling of carbon monoxide and aziridines has been shown to be selective for comonomer-alternating enchainment in the presence of PhCH2C(O)Co(CO)4 to afford poly-beta-peptoids. In this article, we have investigated the mechanistic aspects of the reaction of CO and N-butylaziridine by means of in situ infrared spectroscopy employing CH3C(O)Co(CO)3L (L = PPh3 (1) and P(o-tolyl)3 (2)) as precatalysts. Precatalyst 1 exists in solution under catalytic conditions as an equilibrium mixture of 1 and CH3C(O)Co(CO)4, and affords both poly-beta-butylalanoid and the corresponding lactam. By way of contrast, precatalyst 2 which possesses the sterically bulky and labile P(o-tolyl)3 ligand, affords only the acyl cobalt tetracarbonyl species in solution during catalysis with concomitant selective production of the copolymer. Kinetic studies conducted with precatalyst 2 showed the coupling reaction to have a first order dependence on catalyst, a first order dependence on N-butylaziridine, and only a slight dependence on the concentration of CO over the pressure range 17-69 bar. The working mechanistic model for the copolymerization reaction involves first aziridine insertion into the cobalt-acyl bond, rate determining ring opening by the cobaltate species, followed by the migratory CO insertion.     

Ruthenium phosphine complexes as catalysts of alternating copolymerization of ethylene and carbon monoxide

The properties of the ruthenium (II) phosphine complexes [Ru(dppe)₂(OTs)₂] and [Ru{PhP(CH₂CH₂CH₂PPh₂)₂}(OTs)₂] as catalysts of alternating copolymerization of ethylene and carbon monoxide were studied. The catalytic activity of these complexes in the absence of cocatalysis is low, but it is substantially increased in the presence of trifluoroacetic acid or 1,4-benzoquinone. These compounds are the first ruthenium complexes which catalyze copolymerization of ethylene and CO. Translated fromAkademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1119–1121, June, 2000.