Activated Mn-MACHO Complexes Form Stable CO2 Adducts.

Manganese(I) carbonyl complexes bearing a MACHO-type ligand (HN(CH2 CH2 PR2 )2 ) readily react in their amido form with CO2 to generate 4-membered {Mn-N-C-O} metallacycles. The stability of the adducts decreases with the steric demand of the R groups at phosphorous (R=isopropyl>adamantyl). The CO2 -adducts display generally a lower reactivity as compared to the parent amido complexes. These adducts can thus be interpretated as masked forms of the active amido catalysts and potentially play important roles as off-loop species or branching points in catalytic transformations of carbon dioxide.

Pd(II)-catalyzed carboxylation of aromatic C─H bonds with CO2.

The carboxylation of nonactivated C─H bonds provides an attractive yet hitherto largely elusive chemical process to synthesize carboxylic acids by incorporation of CO2 into the chemical value chain. Here, we report on the realization of such a reaction using simple and nonactivated arenes as starting materials. A computationally designed Pd(II) complex acts as organometallic single-component catalyst, and apart from a base, necessary for thermodynamic stabilization of the intermediates, no other additives or coreagents are required. Turnover numbers up to 102 and high regioselectivities are achieved. The potential of this catalytic reaction for "green chemistry" is demonstrated by the synthesis of veratric acid, an intermediate for pharmaceutical production, from CO2 and veratrol.

Factors Governing the Catalytic Insertion of CO2 into Arenes - A DFT Case Study for Pd and Pt Phosphane Sulfonamido Complexes.

The potential of Pd/Pt complexes for catalytic carboxylation of arenes with CO2 is investigated by means of computational chemistry. Recently we reported that the bis[(2-methoxyphenyl)phosphino]-benzenesulfonamido palladium complex 1 inserts CO2 reversibly in its Pd-C(aryl) bond generating carboxylato complex 2. In the present work we study how geometric and electronic factors of various ligands and substrates influence the overall activation barrier (energy span, ES) of a potential catalytic cycle for arene carboxylation comprising this elementary step. The tendency of the key intermediates to dimerize and thus deactivating the potential catalysts is examined as well as the role of the base, which inevitably is needed to stabilize the reaction product. We show that Pd and Pt complexes I(Pd)-L16-S1 and I(Pt)-L16-S1 do not dimerize, enable the computation of complete catalytic cycles, and show interestingly low ES values of 26.8 and 24.5 kcal/mol, respectively.

Chiral colloids: homogeneous suspension of individualized SiO2 helical and twisted nanoribbons.

Finely tuned chiral nanometric silica fibers were synthesized based on sol-gel chemistry using organic self-assembly as a template. The optimization of the sol-gel process in acidic conditions allowed us to reduce the transcription time by a factor of 10. These nanohelices were successfully fragmented while preserving the fine internal structures from several micrometers to several hundreds of nanometers in length by a sonication method previously reported for carbon nanotubes. By carefully choosing the nature of the solvent, the sonication power, pH in the case of water, and densification of the silica walls by freeze-drying, the homogeneous and stable colloidal suspensions of individualized chiral nanometric silica ribbons with controlled length were obtained.