Co-ordination polymers

Amorphous, low-porosity carbon spheres on the order of a few micrometers in size were prepared by carbonization of squalane (C30H62) in supercritical CO2 at 823 K. The spheres were characterized and used as catalysts’ supports for Pd. Near-edge X-ray absorption fine structure studies of the spheres revealed sp2 and sp3 hybridized carbon. To activate carbons for interaction with a metal precursor, often oxidative treatment of a support is needed. We showed that boiling of the obtained spheres in 28 wt % HNO3 did not affect the shape and bulk structure of the spheres, but led to creation of a considerable amount of surface oxygen-containing functional groups and increase of the content of sp2 hybridized carbon on the surface. This carbon was seen by scanning transmission electron microscopy in the form of waving graphene flakes. The H/C atomic ratio in the spheres was relatively high (0.4) and did not change with the HNO3 treatment. Palladium was deposited by impregnation with Pd acetate followed by reducti...

Pd clusters supported on amorphous, low-porosity carbon spheres for hydrogen production from formic acid.

The term ‘Organometallic-Mediated Radical Polymerization (OMRP)’ encompasses all controlled radical polymerizations that make use of dormant species containing a direct bond between the metal atom and the growing radical chain. There are two versions of such techniques, one resting on the reversible activation of the dormant species by dissociation of the metal–carbon bond (OMRP-RT for ‘reversible termination’) and the other one based on the principle of degenerate transfer, with the growing polymer chain being released by an associative exchange with a second radical (OMRP-DT for ‘degenerative transfer’). The technique has allowed the control of a wide range of monomers from very reactive ones such as AN to vinyl acetate. Transition metals may be involved in a number of other one-electron processes and indeed all of them interplay with OMRP depending on conditions (type and amount of initiator, nature of metal and ligands, coordination number, type of monomer). A general analysis of this interplay is provided in this chapter. In addition to the interplay between dissociative and associative radical exchange processes in the OMRP dormant species, the chain-carrying radical may also interact with the OMRP trapping complex by H • transfer leading to catalytic chain transfer. Finally, transfer of atoms (particularly halogens) may positively or negatively interfere with OMRP. A strategy for the elimination, recovery, and recycling of the metal complex is also discussed.

Organometallic Mediated Radical Polymerization

In this work thermo-responsive ruthenium catalysts, based on the poly(propylene imine) dendrimers cross-linked with the poly(ethylene glycol) diglycidyl ether, have been prepared for the first time. The materials obtained were characterized by X-ray photoelectron spectroscopy and transmission electron microscopy, and tested in the phenol and benzene hydrogenation. Conditions for the metal impregnation into the polymeric matrix were demonstrated to have a great influence both on physical chemical properties of the synthesized catalysts (metal loading, mean particles size, surface structure etc.), and, as a consequence, on their hydrogenation activity and thermo-responsive properties.

Thermo-responsive Ruthenium Dendrimer-based Catalysts for Hydrogenation of the Aromatic Compounds and Phenols

Heterogenized Homogeneous Catalysts

Palladium(II) acetate has been anchored onto a copolymer support containing pyridyl and carboxyl groups. XPS studies showed the Pd 3d binding energies for the recovered catalyst to be less by 1 eV after being used in hydrogenation studies. However, x-ray studies and a chemical test based on KCN treatment failed to reveal any palladium oxide or palladium metal formation in the recovered catalyst. It is presumed that an acetate ligand is lost during hydrogenation, which could be the reason for the lowering of the palladium 3d binding energies in the recovered catalyst. Results of investigations of the hydrogenation of olefins and selectivity of the catalyst toward the hydrogenation of dienes and alkynes are presented. The loss of palladium due to leaching under the reaction conditions employed was found to be very low (<1%/cycle).

Characterization of a Polymer-Bound Palladium Acetate Catalyst and Studies on the Selective Hydrogenation of Dienes and Alkynes

The kinetics of polymerization of acrylamide (AA) initiated by the redox system V(III)(acac)3 -benzoyl peroxide (BPO) in DMF were investigated in the temperature range 40–45°C. A direct second-order reaction between V(III)(acac)3 and BPO was evident from the oxidation kinetics. Rates of polymerization varied as [AA]3/2 and [BPO]½ but were independent of [V(III)(acac)3]. Extensive reduction of primary radicals by V(III)(acac)3 with mutual termination of growing radicals accounts for the kinetics. Degrees of polymerization increased with increasing [AA] and decreased with increasing [BPO] but remained unchanged with variation in [V(III)(acac)3] as required by the mechanism proposed.

V. Mahadevan

Papers

Characterization of a Polymer-Bound Palladium Acetate Catalyst and Studies on the Selective Hydrogenation of Dienes and Alkynes

Redox Polymerization of Acrylamide Initiated by the System Trisacetylacetonato Vanadium(lll)-Benzoyl Peroxide in Dimethylformamide