Mesoionic N-heterocyclic olefin catalysed reductive functionalization of CO2 for consecutive N-methylation of amines

A mesoionic N-heterocyclic olefin (mNHO) was introduced as a metal-free catalyst for the reductive functionalization of CO₂ leading to consecutive double N-methylation of primary amines in the presence of 9-borabicyclo[3.3.1]nonane (9-BBN). A wide range of secondary amines and primary amines were successfully methylated under mild conditions. The catalyst sustained over six successive cycles of N-methylation of secondary amines without compromising its activity, which encouraged us to check its efficacy towards double N-methylation of primary amines. Moreover, this method was utilized for the synthesis of two commercially available drug molecules. A detailed mechanistic cycle was proposed by performing a series of control reactions along with the successful characterisation of active catalytic intermediates either by single-crystal X-ray study or by NMR spectroscopic studies in association with DFT calculations.

Mesoionic N-heterocyclic olefin (mNHO) catalysed consecutive N-methylation of primary and secondary amines was accomplished under 1 atm CO₂ pressure in the presence of 9-BBN as a reducing agent nearly at room temperature.     

Selective polycarboxylation of semiconducting single-walled carbon nanotubes by reductive sidewall functionalization

The efficient and controllable synthesis, the detailed characterization, and the chemical postfunctionalization of polycarboxylated single-walled carbon nanotubes SWCNT(COOH)(n) are reported. This innovative covalent sidewall functionalization method is characterized by (a) the preservation of the integrity of the entire σ-framework of SWCNTs; (b) the possibility of achieving very high degrees of addition; (c) control of the functionalization degrees by the variation of the reaction conditions (reaction time, ultrasonic treatment, pressure); (d) the identification of conditions for the selective functionalization of semiconducting carbon nanotubes, leaving unfunctionalized metallic tubes behind; (e) the proof that the introduced carboxylic acid functionalities can serve as versatile anchor points for the coupling to functional molecules; and (f) the application of a subsequent thermal degradation step of the functionalized semiconducting tubes leaving behind intact metallic SWCNTs. Functional derivatives have been characterized in detail by means of Raman, UV-vis/nIR, IR, and fluorescence spectroscopy as well as by thermogravimetric analysis combined with mass spectrometry, atomic force microscopy, and zeta-potential measurements.     

Nickel-catalyzed reductive carboxylation of styrenes using CO2

A nickel-catalyzed reductive carboxylation of styrenes using CO2 has been developed. The reaction proceeds under mild conditions using diethylzinc as the reductant. Preliminary data suggests the mechanism involves two discrete nickel-mediated catalytic cycles, the first involving a catalyzed hydrozincation of the alkene followed by a second, slower nickel-catalyzed carboxylation of the in situ formed organozinc reagent. Importantly, the catalyst system is very robust and will fixate CO2 in good yield even if exposed to only an equimolar amount introduced into the headspace above the reaction.     

Activation of CO2 by a heterobimetallic Zr/Co complex

At room temperature, the early/late heterobimetallic complex Co((i)Pr(2)PNMes)(3)Zr(THF) has been shown to oxidatively add CO(2), generating (OC)Co((i)Pr(2)PNMes)(2)(μ-O)Zr((i)Pr(2)PNMes). This compound can be further reduced under varying conditions to generate either the Zr oxoanion (THF)(3)Na-O-Zr(MesNP(i)Pr(2))(3)Co(CO) or the Zr carbonate complex (THF)(4)Na(2)(CO(3))-Zr(MesNP(i)Pr(2))(3)Co(CO). Additionally, reactivity of the CO(2)-derived product has been observed with PhSiH(3) to generate the Co-hydride/Zr-siloxide product (OC)(H)Co((i)Pr(2)PNMes)(3)ZrOSiH(2)Ph.     

Uranium-mediated reductive conversion of CO(2) to CO and carbonate in a single-vessel, closed synthetic cycle

The new neopentyl (Neop)-substituted tris(aryloxide) U(iii) complex [(((Neop,Me)ArO)(3)tacn)U(III)] reacts with CO(2) to form CO and the bridging carbonate complex [{(((Neop,Me)ArO)(3)tacn)U(IV)}(2)(μ-CO(3))]. The uranium(iv) bridging oxo [{(((Neop,Me)ArO)(3)tacn)U(IV)}(2)(μ-O)] has been determined to be the intermediate in this reaction. For the first time, both U(iv) complexes can be reduced back to the U(iii) starting material. Thus, with KC(8) as reductant, [(((Neop,Me)ArO)(3)tacn)U(III)] engages in a synthetic cycle, in which CO(2) is converted to CO and CO(3)(2-).     

CO2-induced plasticization phenomena in glassy polymers

A typical effect of plasticization of glassy polymers in gas permeation is a minimum in the relationship between the permeability and the feed pressure. The pressure corresponding to the minimum is called the plasticization pressure. Plasticization phenomena significantly effect the membrane performance in, for example, CO₂/CH₄ separation processes. The polymer swells upon sorption of CO₂ accelerating the permeation of CH₄. As a consequence, the polymer membrane loses its selectivity. Fundamental understanding of the phenomenon is necessary to develop new concepts to prevent it.In this paper, CO₂-induced plasticization phenomena in 11 different glassy polymers are investigated by single gas permeation and sorption experiments. The main objective was to search for relationships between the plasticization pressure and the chemical structure or the physical properties of the polymer. No relationships were found with respect to the glass-transition temperature or fractional free volume. Furthermore, it was thought that polar groups of the polymer increase the tendency of a polymer to be plasticized because they may have dipolar interactions with the polarizable carbon dioxide molecules. But, no dependence of the plasticization pressure on the carbonyl or sulfone density of the polymers considered was observed. Instead, it was found that the polymers studied plasticized at the same critical CO₂ concentration of 36±7 cm³ (STP)/cm³ polymer. Depending on the polymer, different pressures (the plasticization pressures) are required to reach the critical concentration.     

嵌段聚合物PGMA-b-PDEAEMAx的合成及其CO2诱导解组装行为

以甲基丙烯酸二乙基氨基乙酯为疏水段,聚甲基丙烯酸甘油酯为亲水段,采用可逆加成-断裂转移聚合合成了具有不同嵌段比例的甲基丙烯酸甘油酯-b-甲基丙烯酸二乙氨基乙酯二嵌段聚合物(PGMA-b-PDEAEMAx),其结构经1H NMR和GPC表征。聚合物通过自组装形成球形胶束、线性胶束聚集体和囊泡结构;向聚合物溶液中通入CO2后,其自组装解体。     

Ionic diamine rhodium complex catalyzed reductive N-heterocyclization of 2-nitrovinylarenes

Ionic diamine rhodium complex (1) catalyzes the reductive N-cyclization of 2-vinylnitroarenes using carbon monoxide as a reducing agent to afford functionalized indoles. The catalytic system allows direct access to indoles with ester and ketone groups at the 2- or 3-position, in good yields.     

Reduction of CO2 to CO using low-coordinate iron: formation of a four-coordinate iron dicarbonyl complex and a bridging carbonate complex

A reduced diiron(I) complex reacts with CO(2) to give two iron-containing products. One product has a carbonate bridge, which isomerizes rapidly at -70 degrees C and may be derived from an oxodiiron intermediate. The formation of this product releases free CO, which leads to a four-coordinate iron dicarbonyl complex. This product is the first crystallographically characterized example of a four-coordinate iron dicarbonyl species, a moiety that may be present in the active site of Hmd ("iron-sulfur cluster free") hydrogenase.     

Alkyne oligomerization mediated by rhodium complexes with a phosphinosulfonamido ligand and isolation and characterization of a rhodacyclopentadiene complex

Treatment of N-tosyl aziridine with KPPh₂ in THF produces Ph₂PCH₂CH₂NTsK (Ts = p-CH₃C₆H₄SO₂). Reaction of Ph₂PCH₂CH₂NTsK with [Rh₂(μ₂-Cl)₂(NBD)₂] (NBD = norbornadiene) and [Rh₂(μ₂-Cl)₂(COD)₂] (COD = 1,5-cyclooctadiene) produces [Rh(NBD)(Ph₂PCH₂CH₂NTs)] and [Rh(COD)(Ph₂PCH₂CH₂NTs)] (4), respectively. Reaction of Ph₂PCH₂CH₂NTsK with [Ir₂(μ₂-Cl)₂(COD)₂] gives [Ir(COD)(Ph₂PCH₂CH₂NTs)]. Complex 4 is catalytically active for polymerization of arylalkynes and for cyclotrimerization of HCCCOR (R = OEt, Me). The novel metallacycle [Rh(C(CO₂Et)CHC(CO₂Et)CH)(CH(CO₂Et)CCCCO₂Et)(Ph₂PCH₂CH₂NHTs)₂] was isolated from the reaction of 4 with ethyl propiolate. The metallacycle is catalytically active for cyclotrimerization of ethyl propiolate.     

Catalytic C-H functionalization driven by CO as a stoichiometric reductant: application to carbazole synthesis

[reaction: see text] A palladium-catalyzed regioselective C-H bond functionalization driven by CO as the stoichiometric reductant is described. Nitrogen heterocycles, e.g., carbazoles, are accessible in good to excellent yields with use of palladium acetate and 70 psig of carbon monoxide at 140 degrees C.     

The reductive metalation of 1,2-dihalobenzocyclobutenes by NaFe(CO)2Cp and HFe(CO)2Cp

The reactions between cis- and trans-1,2-dibromo- or 1,2-diidobenzocyclobutene and NaFe(CO)₂Cp (NaFp) were investigated. The mechanism of formation of 1,2-bis(cyclopentadienyldicarbonyliron)benzocyclobutene (I) and 1-(cyclopentadienyldicarbonyliron)benzocyclobutene (II) is thought to involve initial formation of benzocyclobutadiene, addition of a Fp radical to benzocyclobutadiene and subsequent addition of a second Fp radical to form I, or hydrogen abstraction from FpH to form II.