New heterogeneous hydrogenation catalysts, based on Pd nanoparticles and polypropyleneimine (PPI) dendrimers of the third generation that have been covalently grafted to a silica surface modified with polyallylamine (PAA) have been synthesized. The final products were characterized by TEM, XPS, and solid-state NMR spectroscopy. The synthesized materials are effective catalysts for selective hydrogenation of dienes to monoenes and phenyl acetylene to styrene at very high substrate/Pd ratios with turnover rates higher than related Pd nanoparticle catalysts. The synthesized catalysts can be reused without any loss of activity in the case of styrene and isoprene.

The maximum Cu(II), Ni(II), and Co(II) ion capacities of a silica−poly(ethyleneimine) composite (WP-1) are compared with those of the commercially available iminodiacetic acid chelator resin Amberlite IRC-718. Under batch (static) conditions, IRC-718 exhibits better capacities for these metals than WP-1. Dynamic studies, however, revealed that WP-1 possessed a much higher capacity for all three divalent metals than IRC-718, with relative metal capacities in the order Cu(II) > Co(II) ≈ Ni(II). In the presence of the competing chelator ethylenediaminetetraacetic acid, the Cu(II) capacities of WP-1 and IRC-718 lost 48% and 45%, respectively, of their original adsorption values. Even with this decrease, however, WP-1 maintained a higher Cu(II) capacity than IRC-718. Repeated cycle testing, using Cu(II) solutions at both room temperature and 97 °C, was conducted to compare the long-term stability of each material. WP-1 maintained 94% of its original Cu(II) capacity and maintained structural integrity after 3000 cycles using room temperature copper solutions, while IRC-718 compressed and dropped to 64% of its original capacity. When boiling copper solutions were used, the capacity of WP-1 increased slightly over 1500 cycles, while IRC-718 lost 13% of its original copper capacity and again became compressed, indicating degradation of the polystyrene beads.

Novel catalysts consisting of ruthenium nanoparticles encapsulated in cross‐linked matrices based on the poly(propylene imine) dendrimers of the 1st and 3rd generations have been synthesized with a narrow particle size distribution (3.8 and 1.0 nm, respectively). The resulting materials showed high activity for the hydrogenation of phenols in aqueous media (specific catalytic activity reached turnover frequencies of 2975 h−1 with respect to hydrogen uptake). It has been shown that the use of water as a solvent leads to a 1.5 to 50‐fold increase in the reaction rate depending upon the nature of the substrate. It has been established that unlike the traditional heterogeneous catalysts based on ruthenium, during the hydrogenation of dihydroxybenzenes, the hydrogenation rate decreases in the order: resorcinol>hydroquinone≫catechol. The maximum specific activity for resorcinol was a turnover frequency of 243150 h−1 with respect to hydrogen uptake. The catalyst based on the dendrimer of the 3rd generation containing finer particles has significantly inferior activity to the catalyst based on the dendrimer of the 1st generation by virtue of steric factors, as well as the need for prereduction of the ruthenium oxide contained on the surface. These catalysts showed resistance to metal leaching and may be reused several times without loss of activity.

Silanization of the silica gel surface in the synthesis of silica gel polyamine composites uses (chloropropyl)trichlorosilane (CPTCS). It is possible to substitute a molar fraction of reagent CPTCS with methyltrichlorosilane (MTCS), creating a mixed silane surface layer. Two types of silica gels were modified with a series of MTCS:CPTCS molar ratios. Solid-state CP/MAS 29 Si and 13 C NMR spectroscopies were used to evaluate the surface silane composition. Surface silane coverage was markedly improved for the resulting gels. When polyamines were grafted to the resultant MTCS:CPTCS silane layers, it was shown that the decrease in the number of propyl attachments to the polyamine resulted in increased quantities of "free amines". Optimum MTCS:CPTCS ratios were determined for three polyamines grafted onto one silica gel. A substantial free amine increase was observed for poly(allylamine) (PAA). Metal uptake studies show increases in Cu(II) capacity and/or an improvement in Cu(II) mass-transfer kinetics. The effect of polymer molecular weight upon Cu(II) capacity was investigated for each polyamine. Substantial differences in Cu(II) capacity between 50 000 MW poly(vinylamine) (PVA) and >1000 MW PVA were evident. Similar differences between 25 000 MW poly(ethyleneimine) (PEI) and 1200 MW PEI were found. The mass-transfer kinetics was shown to be improved for composites prepared using a large fraction of MTCS in the reagent silane mixture. This resulted in substantial improvements in the 10% breakthrough Cu(II) capacity for PVA (50 000 MW). PEI composites were further modified to form an amino-acetate ligand. The impact of the MTCS:CPTCS silane ratio on the acetate ligand loading and ultimately on the Cu(II) capacity at pH ) 2 was investigated. A ratio of 12.5:1 was shown to result in an acetate modified PEI composite with a Cu(II) capacity 140% of the Cu(II) capacity of the same composite prepared with "CPTCS only".

The solution structure and dynamics of {(17j-CsMej)zZrNz}zN2, ((11j-CsMej)zZr(CO)I2N2, {(q5-CsMe5)2Zr-(PF3)}2x>, and ((q5-CjMej)2TiN2)2N2 have been studied by IH N M R spectrometry. {(q5-CsMej)2ZrN2J2N2 is observed to undergo mutual exchange of pentamethylcyclopentadienyl ligands between the two sites of the molecule on the time scale of the order of the ' H N M R experiments at 10 OC. Variable-temperature I5N N M R experiments for {(q5-CjMej)2Zr-('5N2)12('5N2) were also carried out, and the results are interpreted on the basis of dissociative exchange of the two terminal dinitrogen ligands with free dissolved N2. The observation that nitrogen dissociation is 5-10 times faster than [q5-CsMes] site exchange suggests a mechanism for ring interchange involving stepwise dissociation-association of terminal IV2 ligands with "inversion" at the zirconium centers. Activation parameters calculated from I5N N M R data are E , = 11 kca1,mol-' and AS* = t I O eu. The observed temperature dependence of the ' H N M R spectra for the isostructural complex ((qs-CsMej)2TiN2}2Nzsuggests that the same mechanism is operative. (($-CsMej)2Zr(C0)}2N2, on the other hand, does not undergo C O dissociation at a rate sufficient to observe [$-CjMes] ring site exchange by ' H N M R spectrometrq even a t 64 "C.Bis(pentamethylcyclopentadienyl) derivatives of titanium and zirconium have proved to be useful congeners to their bis(cyclopentadieny1) analogues by virtue of enhanced stability, solubility, and crystallizability. Dinitrogen complexes of (q5-C5Me5)2Ti and (v5-C5Me5)2Zr are of particular interest in view of the ready protonation and reduction to hydrazine of their ligated N2.3-8 We have recently reported the solid-state structures of {(v5-C5Me5)2Ti)2Nz8 and ((v5-C5Me5)2-ZrN2J2N2' as determined by single-crystal x-ray diffraction methods. I n this paper we report the results of an NMR and IR study of the solution structure and dynamics of {($-CsMe5)2ZrNz}2Nl, its carbonyl and PF3 derivatives, and the titanium analogue. Experimental SectionPhysical Measurements. ' H N M R spectra were recorded on a Varian H R 220 (CW) spectrometer. IsN N M R spectra were obtained at 18.25 M H z on a Bruker WH180 (FT) spectrometer. Computersynthesized spectra were obtained using DNMR3, a general N M R line-shape program with symmetry and magnetic equivalence factoring, written by Binsch and Kleier.9 Infrared spectra were obtained on Perkin-Elmer 180. 225, and 457 and Beckman IR-12 spectrophotometers.Materials. All manipulations were performed on a vacuum line, in a glovebox which was evacuated to <0.05 Torr and filled just prior to use with either prepurified argon or nitrogen, or in a Vacuum Atmospheres glovebox under nitrogen. Nitrogen used in the experiments was prepurified grade rendered rigorously oxygen-and water-free by passage over MnO on vermiculitelo and activated 4A molecules sieves. Toluene, benzene, and 30-60 OC petroleum ether were purified by vacuum transfer first from LiAIH4 and then from "titanocene".Il I ,2,3,4,5-Pentamethylcyclopentadien...