New Protocol for the Synthesis of S-Thioesters from Benzylic, Allylic and Tertiary Alcohols with Thioacetic Acid.

A new one-pot solvent-less reaction to convert benzylic, allylic, ferrocenyl or tertiary alcohols into S-thioesters, bench-stable and less odorous precursors of the corresponding thiols, which is based on reactions in neat thioacetic acid in the presence of tetrafluoroboric acid, is presented. Reaction monitoring by NMR and GC of the benzyl alcohol conversion indicated the intermediate formation of benzyl acetate and benzyl thionoacetate (PhCH2 OC(S)CH3 ) prior to the slower conversion to the final S-benzyl thioacetate product. Increasing the HBF4 concentration enhanced the reaction rate, giving good to excellent yield (up to 99 %) for a large scope of alcohols. Control experiments, with support of DFT calculations, have revealed a thermodynamically favorable, though requiring HBF4 -activation, disproportionation of CH3 C(O)SH to CH3 C(O)OH and CH3 C(S)SH, the latter immediately decomposing to H2 S and (MeC)4 S6 but also generating the hitherto unreported [MeC(O)C(Me)S]2 (µ-S)2 . Kinetic investigations demonstrated that the rate of benzyl alcohol conversion is second-order in [PhCH2 OH] and second order in [HBF4 ], while the rate of conversion of the benzyl acetate intermediate to S-benzyl thioacetate is second order in [PhCOOMe] and fourth order in [HBF4 ]. The DFT calculations rationalize the need to two alcohol molecules and two protons to generate the reactive benzyl cation.

Hydrogenation and dehydrogenation of N-heterocycles under Cp*Co(III)-catalysis.

To realize the goal of a carbon-free energy economy, it is crucial to discover reactions that utilize sustainable resources as alternatives to fossil feedstocks. In this study, a well-defined, air-stable Cp*Co(III)-catalyst for transfer hydrogenation of quinoline derivatives and oxidative dehydrogenation of cyclic amines in water is developed. While the former reaction is promoted by formic acid as a transfer hydrogenation reagent, the latter is mediated by molecular oxygen as the sole oxidant. These processes provide new avenues for the investigation of air-stable cobalt catalysts for environmentally benign hydrogenation and dehydrogenation reactions.

Acetate ion addition to and exchange in (1,5-cyclooctadiene)rhodium(I) acetate: relevance for the coagulation of carboxylic acid-functionalized shells of core-crosslinked micelle latexes.

The solution behavior of complex [Rh(COD)(µ-OAc)]2 in the absence and presence of PPN+OAc- in dichloromethane has been investigated in detail by multinuclear NMR spectroscopy. Without additional acetate ions, the compound shows dynamic behavior at room temperature, consistent with an inversion of its C2v structure. Addition of PPN+OAc- reveals an equilibrated generation of [Rh(COD)(OAc)2]-. Rapid exchange is observed at room temperature between the neutral dimer and the anionic mononuclear complex, as well as between the anionic complex and free acetate. Lowering the temperature to 213 K freezes the exchange between the two Rh complexes, but fast exchange between the anionic Rh complex and free acetate maintains coalesced Me (1H and 13C) and COO (13C) NMR resonances. DFT calculations support the experimental data and lean in favour of a dissociative mechanism for the acetate exchange in [Rh(COD)(OAc)2]-. The acetate ligands in complex [Rh(COD)(µ-OAc)]2 are also exchanged in a biphasic (water/organic) system with the methacrylic acid (MAA) functions of hydrosoluble [MMA0.5-co-PEOMA0.5]30 copolymer chains (PEOMA = poly(ethylene oxide) methyl ether methacrylate), resulting in transfer of the Rh complex to the aqueous phase. Exchange with the MAA functions in the same polymer equally takes place for the chloride ligands of [Rh(COD)(µ-Cl)]2. The latter phenomenon rationalizes the coagulation of a core-crosslinked micelle (CCM) latex, where MMA functions are present on the hydrophilic CCM shell, when a dichloromethane solution of [Rh(COD)(µ-Cl)]2 is added.

Acetate exchange mechanism on a Zr12 oxo hydroxo cluster: relevance for reshaping Zr-carboxylate coordination adaptable networks.

The kinetics and mechanism of the acetate ligand exchange with free acetic acid in [Zr6O4(OH)4(O2CCH3)12]2, used as a molecular model of crosslink migration in [Zr6O4(OH)4(carboxylate)12-n(OH)n]-based coordination adaptable networks with vitrimer-like properties, has been thoroughly investigated by dynamic 1H NMR and DFT calculations. The compound maintains its C2h-symmetric Zr12 structure in CD2Cl2 and C6D6, while it splits into its Zr6 subunits in CD3OD and D2O. In the Zr12 structure, the topologically different acetates (3 chelating, 6 belt-bridging, 2 intercluster-bridging and 1 inner-face-bridging) of the Zr6 subunits behave differently in the presence of free CH3COOH: very fast exchange for the chelating (coalesced resonance at room temperature), slower exchange for the belt-bridging (line broadening upon warming), no observable exchange up to 65 °C (by EXSY NMR) for the intercluster- and inner-face-bridging. The rates of the first two exchange processes have zero-order dependence on [CH3COOH]. Variable-temperature line broadening studies yielded ΔH‡ = 15.0 ± 0.4 kcal mol-1, ΔS‡ = 8 ± 1 cal mol-1 K-1 (-30 to +25 °C range in CD2Cl2) for the chelating acetates and ΔH‡ = 22.7 ± 1.6, 22.9 ± 2.1 and 20.6 ± 1.0 kcal mol-1 and ΔS‡ = 13 ± 5, 14 ± 6 and 9 ± 3 cal mol-1 K-1, respectively (+25 to +70 °C range in C6D6), for three distinct resonances of magnetically inequivalent belt-bridging acetates. With support of DFT calculations, these results point to an operationally associative mechanism involving a rate-determining partial dissociation to monodentate acetate, followed by rapid acid coordination and proton transfer. The cluster µ3-OH ligands accelerate the exchange processes through H-bonding stabilization of the coordinatively unsaturated intermediate. The lower exchange barrier for the chelated vs. bridging acetates is associated to the release of ring strain. The results presented in this investigation may help the interpretation of carboxylate exchange phenomena in other systems and the design of new carboxylate-based materials.

A mononuclear cobalt(III) carboxylate complex with a fully O-based coordination sphere: CoIII-O bond homolysis and controlled radical polymerisation from [Co(acac)2(O2CPh)].

The addition of benzoyl peroxide to [CoII(acac)2] in a 1 : 2 ratio selectively produces [CoIII(acac)2(O2CPh)], a diamagnetic (NMR) mononuclear CoIII complex with an octahedral (X-ray diffraction) coordination geometry. It is the first reported mononuclear CoIII derivative with a chelated monocarboxylate ligand and an entirely O-based coordination sphere. The compound degrades in solution quite slowly by homolytic CoIII-O2CPh bond cleavage upon warming above 40 °C to produce benzoate radicals and can serve as a unimolecular thermal initiator for the well-controlled radical polymerisation of vinyl acetate. Addition of ligands (L = py, NEt3) induces benzoate chelate ring opening and formation of both cis and trans isomers of [CoIII(acac)2(O2CPh)(L)] for L = py under kinetic control, then converting quantitatively to the cis isomer, whereas the reaction is less selective and equilibrated for L = NEt3. The py addition strengthens the CoIII-O2CPh bond and lowers the initiator efficiency in radical polymerisation, whereas the NEt3 addition results in benzoate radical quenching by a redox process. In addition to clarifying the mechanism of the radical polymerisation redox initiation by peroxides and rationalizing the quite low efficiency factor for the previously reported [CoII(acac)2]/peroxide-initiated organometallic-mediated radical polymerisation (OMRP) of vinyl acetate, this investigation provides relevant information on the CoIII-O homolytic bond cleavage process.

IrI(η4-diene) precatalyst activation by strong bases: formation of an anionic IrIII tetrahydride.

The reaction between [IrCl(COD)]2 and dppe in a 1 : 2 ratio was investigated in detail under three different conditions. [IrCl(COD)(dppe)], 1, is formed at room temperature in the absence of base. In the presence of a strong base at room temperature, hydride complexes that retain the carbocyclic ligand in the coordination sphere are generated. In isopropanol, 1 is converted into [IrH(1,2,5,6-η2:η2-COD)(dppe)] (2) on addition of KOtBu, with k12 = (1.11 ± 0.02) × 10-4 s-1, followed by reversible isomerisation to [IrH(1-κ-4,5,6-η3-C8H12)(dppe)] (3) with k23 = (3.4 ± 0.2) × 10-4 s-1 and k32 = (1.1 ± 0.3) × 10-5 s-1 to yield an equilibrium 5 : 95 mixture of 2 and 3. However, when no hydride source is present in the strong base (KOtBu in benzene or toluene), the COD ligand in 1 is deprotonated, followed by ß-H elimination of an IrI-C8H11 intermediate, which leads to complex [IrH(1-κ-4,5,6-η3-C8H10)(dppe)] (4) selectively. This is followed by its reversible isomerisation to 5, which features a different relative orientation of the same ligands (k45 = (3.92 ± 0.11) × 10-4 s-1; k5-4 = (1.39 ± 0.12) × 10-4 s-1 in C6D6), to yield an equilibrated 32 : 68 mixture of 4 and 5. DFT calculations assisted in the full rationalization of the selectivity and mechanism of the reactions, yielding thermodynamic (equilibrium) and kinetic (isomerization barriers) parameters in excellent agreement with the experimental values. Finally, in the presence of KOtBu and isopropanol at 80 °C, 1 is transformed selectively to K[IrH4(dppe)] (6), a salt of an anionic tetrahydride complex of IrIII. This product is also selectively generated from 2, 3, 4 and 5 and H2 at room temperature, but only when a strong base is present. These results provide an insight into the catalytic action of [IrCl(COD)(LL)] complexes in the hydrogenation of polar substrates in the presence of a base.

Catalyst-Free Thia-Michael Addition to α-Trifluoromethylacrylates for 3D Network Synthesis.

Thia-Michael additions (1,4-additions of a thiol to a Michael acceptor) are generally catalyzed by an external Brønsted or Lewis base. A spontaneous (uncatalyzed) Michael addition of thiols to α-trifluoromethyl acrylates is described, as well as its application to the very efficient preparation of a thermoset. A thorough mechanistic investigation, based on an experimental kinetic study and on DFT calculations, is presented for the addition of arene- and alkanethiols to tert-butyl trifluoromethyl acrylate in polar aprotic solvents, unveiling a probable solvent-assisted proton transfer in the rate-determining step and a considerable lowering of the energy barrier induced by the CF3 group.

Phosphine-Functionalized Core-Crosslinked Micelles and Nanogels with an Anionic Poly(styrenesulfonate) Shell: Synthesis, Rhodium(I) Coordination and Aqueous Biphasic Hydrogenation Catalysis.

Stable latexes containing unimolecular amphiphilic core-shell star-block polymers with a triphenylphosphine(TPP)-functionalized hydrophobic core and an outer hydrophilic shell based on anionic styrenesulfonate monomers have been synthesized in a convergent three-step strategy by reversible addition-fragmentation chain-transfer (RAFT) polymerization, loaded with [RhCl(COD)]2 and applied to the aqueous biphasic hydrogenation of styrene. When the outer shell contains sodium styrenesulfonate homopolymer blocks, treatment with a toluene solution of [RhCl(COD)]2 led to undesired polymer coagulation. Investigation of the interactions of [RhCl(COD)]2 and [RhCl(COD)(PPh3)] with smaller structural models of the polymer shell functions, namely sodium p-toluenesulfonate, sodium styrenesulfonate, and a poly(sodium styrenesulfonate) homopolymer in a biphasic toluene/water medium points to the presence of equilibrated Rh-sulfonate interactions as the cause of coagulation by inter-particle cross-linking. Modification of the hydrophilic shell to a statistical copolymer of sodium styrenesulfonate and poly(ethylene oxide) methyl ether methacrylate (PEOMA) in a 20:80 ratio allowed particle loading with the generation of core-anchored [RhCl(COD)TPP] complexes. These Rh-loaded latexes efficiently catalyze the aqueous biphasic hydrogenation of neat styrene as a benchmark reaction. The catalytic phase could be recovered and recycled, although the performances in terms of catalyst leaching and activity evolution during recycles are inferior to those of equivalent nanoreactors based on neutral or polycationic outer shells.

Coordination Adaptable Networks: Zirconium(IV) Carboxylates.

Vitrimers are 3D "covalent adaptable networks" (CANs) with flow properties thanks to thermally activated associative exchange reactions. This contribution introduces coordination adaptable networks, or CooANs, that are topologically related to metal-organic frameworks with octahedral Zr6 clusters as secondary building units in a carboxylic acid-functionalized acrylate-methacrylate copolymer matrix. A series of Zr-CooAN-x materials (x=percent of Zr6 loading relative to maximum capacity) was synthesized with x=5, 10, 15, 20, 25, 50 and 100. The mechanical and rheological investigations demonstrate vitrimer-like properties for x up to 50, the crosslink migration being ensured by carboxylate ligand exchange, with relaxation becoming slower as the Zr6 content is increased. The flow activation energy of Zr-CooAN-10 is 92.9±3.6 kJ mol-1 . Rapid (30 min) hot-press reshaping occurs at temperatures in the 50-100 °C range under a 3-ton pressure and does not significantly alter the material properties.

Synthesis and crystal structure of [(Sp )-(2-phenyl-ferrocen-yl)meth-yl]tri-methyl-ammonium iodide di-chloro-methane monosolvate.

As a follow-up to our research on the chemistry of disubstituted ferrocene derivatives, the synthesis and the structure of the title compound, [Fe(C5H5)(C15H19N)]I·CH2Cl2, is described. The cation mol-ecule is built up from a ferrocene disubstituted by a tri-methyl-ammonium methyl group and a phenyl ring. The asymmetric unit contains the iodide to equilibrate the charge and a disordered di-chloro-methane solvate. The disordered model results from a roughly statistical exchange (0.6/0.4) between one Cl and one H. The packing of the structure is stabilized by weak C-H⋯X (X = I, Cl), C-H⋯π(Cp) and C-Cl⋯π(phen-yl) inter-actions, building a three-dimensional network. The cation has planar chirality with Sp (Fc) absolute configuration. The structure of the title compound is compared with related disubstituted (tri-meth-ylammonio)-methyl ferrocenes.

Cobalt-Carbon Bonding in a Salen-Supported Cobalt(IV) Alkyl Complex Postulated in Oxidative MHAT Catalysis.

The catalytic hydrofunctionalization of alkenes through radical-polar crossover metal hydrogen atom transfer (MHAT) offers a mild pathway for the introduction of functional groups in sterically congested environments. For M = Co, this reaction is often proposed to proceed through secondary alkylcobalt(IV) intermediates, which have not been characterized unambiguously. Here, we characterize a metastable (salen)Co(isopropyl) cation, which is capable of forming C-O bonds with alcohols as proposed in the catalytic reaction. Electron nuclear double resonance (ENDOR) spectroscopy of this formally cobalt(IV) species establishes the presence of the cobalt-carbon bond, and accompanying DFT calculations indicate that the unpaired electron is localized on the cobalt center. Both experimental and computational studies show that the cobalt(IV)-carbon bond is stronger than the analogous bond in its cobalt(III) analogue, which is opposite of the usual oxidation state trend of bond energies. This phenomenon is attributable to an inverted ligand field that gives the bond Coδ--Cδ+ character and explains its electrophilic reactivity at the alkyl group. The inverted Co-C bond polarity also stabilizes the formally cobalt(IV) alkyl complex so that it is accessible at unusually low potentials. Even another cobalt(III) complex, [(salen)CoIII]+, is capable of oxidizing (salen)CoIII(iPr) to the formally cobalt(IV) state. These results give insight into the electronic structure, energetics, and reactivity of a key reactive intermediate in oxidative MHAT catalysis.

Understanding the Reshaping of Fluorinated Polyester Vitrimers by Kinetic and DFT Studies of the Transesterification Reaction.

Vitrimers are a third class of polymers gathering the mechanical properties and solvent resistance of 3D thermosets and the reprocessability of thermoplastics. This unique behaviour is due to the triggering of certain covalent exchange reactions that allow the network to rearrange upon application of a stimulus. The constitutive feature of vitrimers is the adoption of a glass-like viscosity during the rearrangement of the network, often due to an associative mechanism for the exchange reaction. Transesterification networks are one of the most studied type of vitrimers that usually require the incorporation of a catalyst, implying the associated drawbacks. Following up on a recent report on catalyst-free transesterification vitrimers in which the ester functions are particularly reactive thanks to the presence of fluorine atoms in α- or ß-position, parallel DFT calculations and an experimental kinetic study on model molecules are presented in order to quantitatively assess the effect of neighbouring fluorinated groups on the transesterification reaction rate.

Synthesis and crystallographic studies of 2-(di-phenyl-phosphino-thio-yl)-2-(3-oxobut-1-en-yl)ferrocene.

As a follow-up to our research on the chemistry of disubstituted ferrocene derivatives, the synthesis and the structure of the title compound, 2-(di-phenyl-phosphino-thio-yl)-2-(3-oxobut-1-en-yl)ferrocene, [Fe(C5H5)(C21H18OPS)], are described. The mol-ecule is built up from a ferrocene unit disubstituted by an S-protected di-phenyl-phosphine group and by a methyl-vinyl-ketone chain. The crystal structure features weak C-H⋯O and C-H⋯S inter-actions, which build a two-dimensional network. This structure is compared to that of the related disubstituted di-phenyl-phosphino ferrocene.

Rhodium nanoparticles inside well-defined unimolecular amphiphilic polymeric nanoreactors: synthesis and biphasic hydrogenation catalysis.

Rhodium nanoparticles (Rh NPs) embedded in different amphiphilic core-crosslinked micelle (CCM) latexes (RhNP@CCM) have been synthesized by [RhCl(COD)(TPP@CCM)] reduction with H2 (TPP@CCM = core-anchored triphenylphosphine). The reduction rate depends on temperature, on the presence of base (NEt3) and on the P/Rh ratio. For CCMs with outer shells made of neutral P(MAA-co-PEOMA) copolymer chains (RhNP@CCM-N), the core-generated Rh NPs tend to migrate toward the hydrophilic shell and to agglomerate depending on the P/Rh ratio and core TPP density, whereas the MAA protonation state has a negligible effect. Conversely, CCMs with outer shells made of polycationic P(4VPMe+I-) chains (RhNP@CCM-C) maintain core-confined and well dispersed Rh NPs. All RhNP@CCMs were used as catalytic nanoreactors under aqueous biphasic conditions for acetophenone, styrene and 1-octene hydrogenation. Styrene was efficiently hydrogenated by all systems with high selectivity for vinyl reduction. For acetophenone, competition between benzene ring and carbonyl reduction was observed as well as a limited access to the catalytic sites when using CCM-C. Neat 1-octene was also converted, but the activity increased when the substrate was diluted in 1-nonanol, which is a better core-swelling solvent. Whereas the molecular RhI center was more active than the Rh0 NPs in 1-octene hydrogenation, the opposite trend was observed for styrene hydrogenation. Although Rh NP migration and agglomeration occurred for RhNP@CCM-N, even at high P/Rh, the NPs remained core-confined for RhNP@CCM-C, but only when toluene rather than diethyl ether was used for product extraction before recycling.

Triphenylphosphine-Functionalized Core-Cross-Linked Micelles and Nanogels with a Polycationic Outer Shell: Synthesis and Application in Rhodium-Catalyzed Biphasic Hydrogenations.

Unimolecular amphiphilic nanoreactors with a poly(4-vinyl-N-methylpyridinium iodide) (P4VPMe+ I- ) polycationic outer shell and two different architectures (core-cross-linked micelles, CCM, and nanogels, NG), with narrow size distributions around 130-150 nm in diameter, were synthesized by RAFT polymerization from an R0 -4VPMe+ I- 140 -b-S50 -SC(S)SPr macroRAFT agent by either chain extension with a long (300 monomer units) hydrophobic polystyrene-based block followed by cross-linking with diethylene glycol dimethacrylate (DEGDMA) for the CCM particles, or by simultaneous chain extension and cross-linking for the NG particles. A core-anchored triphenylphosphine (TPP) ligand functionality was introduced by using 4-diphenylphosphinostyrene (DPPS) as a comonomer (5-20 % mol mol-1 ) in the chain extension (for CCM) or chain extension/cross-linking (for NG) step. The products were directly obtained as stable colloidal dispersions in water (latexes). After loading with [RhCl(COD)]2 to yield [RhCl(COD)(TPP@CCM)] or [RhCl(COD)(TPP@NG)], respectively, the polymers were used as polymeric nanoreactors in Rh-catalyzed aqueous biphasic hydrogenation of the model substrates styrene and 1-octene, either neat (for styrene) or in an organic solvent (toluene or 1-nonanol). All hydrogenations were rapid (TOF up to 300 h-1 ) at 25 °C and 20 bar of H2 pressure, the biphasic mixture rapidly decanted at the end of the reaction (<2 min), the Rh loss was negligible (<0.1 ppm in the recovered organic phase), and the catalyst phase could be recycled 10 times without significant loss of catalytic activity.

Synthesis of Nixantphos Core-Functionalized Amphiphilic Nanoreactors and Application to Rhodium-Catalyzed Aqueous Biphasic 1-Octene Hydroformylation.

A latex of amphiphilic star polymer particles, functionalized in the hydrophobic core with nixantphos and containing P(MAA-co-PEOMA) linear chains in the hydrophilic shell (nixantphos-functionalized core-crosslinked micelles, or nixantphos@CCM), has been prepared in a one-pot three-step convergent synthesis using reversible addition-fragmentation chain transfer (RAFT) polymerization in water. The synthesis involves polymerization-induced self-assembly (PISA) in the second step and chain crosslinking with di(ethylene glycol) dimethacrylate (DEGDMA) in the final step. The core consists of a functionalized polystyrene, obtained by incorporation of a new nixantphos-functionalized styrene monomer (nixantphos-styrene), which is limited to 1 mol%. The nixantphos-styrene monomer was synthesized in one step by nucleophilic substitution of the chloride of 4-chloromethylstyrene by deprotonated nixantphos in DMF at 60 °C, without interference of either phosphine attack or self-induced styrene polymerization. The polymer particles, after loading with the [Rh(acac)(CO)2] precatalyst to yield Rh-nixantphos@CCM, function as catalytic nanoreactors under aqueous biphasic conditions for the hydroformylation of 1-octene to yield n-nonanal selectively, with no significant amounts of the branched product 2-methyl-octanal.

Fluoroalkyl Pentacarbonylmanganese(I) Complexes as Initiators for the Radical (co)Polymerization of Fluoromonomers.

The use of [Mn(RF)(CO)5] (RF = CF3, CHF2, CH2CF3, COCF2CH3) to initiate the radical polymerization of vinylidene fluoride (F2C=CH2, VDF) and the radical alternating copolymerization of vinyl acetate (CH2=CHOOCCH3, VAc) with tert-butyl 2-(trifluoromethyl)acrylate (MAF-TBE) by generating primary RF• radicals is presented. Three different initiating methods with [Mn(CF3)(CO)5] (thermal at ca. 100 °C, visible light and UV irradiations) are described and compared. Fair (60%) to satisfactory (74%) polyvinylidene fluoride (PVDF) yields were obtained from the visible light and UV activations, respectively. Molar masses of PVDF reaching 53,000 g·mol-1 were produced from the visible light initiation after 4 h. However, the use of [Mn(CHF2)(CO)5] and [Mn(CH2CF3)(CO)5] as radical initiators produced PVDF in a very low yield (0 to 7%) by both thermal and photochemical initiations, while [Mn(COCF2CH3)(CO)5] led to the formation of PVDF in a moderate yield (7% to 23%). Nevertheless, complexes [Mn(CH2CF3)(CO)5] and [Mn(COCHF2)(CO)5] efficiently initiated the alternating VAc/MAF-TBE copolymerization. All synthesized polymers were characterized by 1H and 19F NMR spectroscopy, which proves the formation of the expected PVDF or poly(VAc-alt-MAF-TBE) and showing the chaining defects and the end-groups in the case of PVDF. The kinetics of VDF homopolymerization showed a linear ln[M]0/[M] versus time relationship, but a decrease of molar masses vs. VDF conversion was noted in all cases, which shows the absence of control. These PVDFs were rather thermally stable in air (up to 410 °C), especially for those having the highest molar masses. The melting points ranged from 164 to 175 °C while the degree of crystallinity varied from 44% to 53%.

Switchable Polymerization Triggered by Fast and Quantitative Insertion of Carbon Monoxide into Cobalt-Oxygen Bonds.

A strategy that uses carbon monoxide (CO) as a molecular trigger to switch the polymerization mechanism of a cobalt Salen complex [salen=(R,R)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine] from ring-opening copolymerization (ROCOP) of epoxides/anhydrides to organometallic mediated controlled radical polymerization (OMRP) of acrylates is described. The key phenomenon is a rapid and quantitative insertion of CO into the Co-O bond, allowing for in situ transformation of the ROCOP active species (Salen)CoIII -OR into the OMRP photoinitiator (Salen)CoIII -CO2 R. The proposed mechanism, which involves CO coordination to (Salen)CoIII -OR and subsequent intramolecular rearrangement via migratory insertion has been rationalized by DFT calculations. Regulated by both CO and visible light, on-demand sequence control can be achieved for the one-pot synthesis of polyester-b-polyacrylate diblock copolymers (D<1.15).

Mechanistic diversity in acetophenone transfer hydrogenation catalyzed by ruthenium iminophosphonamide complexes.

A series of arene ruthenium iminophosphonamide complexes, [(Arene)RuCl{R2P(NR')2}] (1), bearing various arenes and R,R' substituents on the NPN ligand have been investigated as precatalysts in acetophenone transfer hydrogenation in basic and base-free isopropanol. The results clearly demonstrate the presence of two distinct reaction mechanisms, which are controlled by the basicity of the N-atoms. Complexes 1 in which both R' substituents are aryl groups are only active once the neutral hydride complex [(Arene)RuH{R2P(NR')2}] (2) is generated in basic isopropanol, the latter being able to reduce a ketone via a stepwise hydride and proton transfer. On the other hand, complexes in which at least one R' group is Me readily catalyze the reaction in the absence of base. In the latter case, the results of kinetic studies and DFT calculations support an outer-sphere concerted asynchronous hydride and proton transfer assisted by the basic N-atom of the NPN ligand, which promotes catalysis via precoordination of an alcohol molecule by hydrogen bonding.

Oxygen-Triggered Switchable Polymerization for the One-Pot Synthesis of CO2 -Based Block Copolymers from Monomer Mixtures.

Switchable polymerization provides the opportunity to regulate polymer sequence and structure in a one-pot process from mixtures of monomers. Herein we report the use of O2 as an external stimulus to switch the polymerization mechanism from the radical polymerization of vinyl monomers mediated by (Salen)CoIII -R [Salen=N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine; R=alkyl] to the ring-opening copolymerization (ROCOP) of CO2 /epoxides. Critical to this process is unprecedented monooxygen insertion into the Co-C bond, as rationalized by DFT calculations, leading to the formation of (Salen)CoIII -O-R as an active species to initiate ROCOP. Diblock poly(vinyl acetate)-b-polycarbonate could be obtained by ROCOP of CO2 /epoxides with preactivation of (Salen)Co end-capped poly(vinyl acetate). Furthermore, a poly(vinyl acetate)-b-poly(methyl acrylate)-b-polycarbonate triblock copolymer was successfully synthesized by a (Salen)cobalt-mediated sequential polymerization with an O2 -triggered switch in a one-pot process.