Lapo Luconi

Facing Unexpected Reactivity Paths with ZrIV–Pyridylamido Polymerization Catalysts

This work provides original insights to the better understanding of the complex structure-activity relationship of Zr(IV)-pyridylamido-based olefin polymerization catalysts and highlights the importance of the metal-precursor choice (Zr(NMe(2))(4) vs. Zr(Bn)(4)) to prepare precatalysts of unambiguous identity. A temperature-controlled and reversible σ-bond metathesis/protonolysis reaction is found to take place on the Zr(IV)-amido complexes in the 298-383 K temperature range, changing the metal coordination sphere dramatically (from a five-coordinated tris-amido species stabilized by bidentate monoanionic {N,N(-)} ligands to a six-coordinated bis-amido-mono-amino complexes featured by tridentate dianionic {N(-),N,C(-)} ligands). Well-defined neutral Zr(IV)-pyridylamido complexes have been prepared from Zr(Bn)(4) as metal source. Their cationic derivatives [Zr(IV) N(-),N,C(-)}Bn](+)[B(C(6)F(5))(4)](-) have been successfully applied to the room-temperature polymerization of 1-hexene with productivities up to one order of magnitude higher than those reported for the related Hf(IV) state-of-the-art systems. Most importantly, a linear increase of the poly(1-hexene) M(n) values (30-250 kg mol(-1)) has been observed upon catalyst aging. According to that, the major active species (responsible for the increased M(n) polymer values) in the aged catalyst solution, has been identified.

Photothermally Activated Hybrid Films for Quantitative Confined Release of Chemical Species

Illuminating films of a porous chitosan matrix containing gold nanorods and thermosensitive micelles loaded with a chemical stimulates local photothermal conversion of the gold nanorods. The heat produced activates the ejection of the chemical from the micelles (see scheme), and causes the transient permeabilization of adjacent cell membranes, resulting in a selective cellular uptake of the released chemical with control over spatiotemporal parameters and dosage.

Metal-to-Ligand Alkyl Migration Inducing Carbon–Sulfur Bond Cleavage in Dialkyl Yttrium Complexes Supported by Thiazole-Containing Amidopyridinate Ligands: Synthesis, Characterization, and Catalytic Activity in the Intramolecular Hydroamination Reaction

Neutral Y(III) dialkyl complexes supported by tridentate N(-) ,N,N monoanionic methylthiazole- or benzothiazole-amidopyridinate ligands have been prepared and completely characterized. Studies on their stability in solution revealed progressive rearrangement of the coordination sphere in the benzothiazole-containing system through an unprecedented metal-to-ligand alkyl migration and subsequent thiazole ring opening. Attempts to synthesize hydrido species from the dialkyl precursor led to the generation of a dimeric yttrium species stabilized by a trianionic N(-) ,N,N(-) ,S(-) ligand as the result of metal-to-ligand hydride migration with chemoselective thiazole ring opening and subsequent dimerization through intermolecular addition of the residual YH group to the imino fragment of a second equivalent of the ring-opened intermediate. DFT calculations were used to elucidate the thermodynamics and kinetics of the process, in support of the experimental evidence. Finally, all isolated yttrium complexes, especially their cationic forms prepared by activation with the Lewis acid Ph3 C(+) [B(C6 F5 )4 ](-) , were found to be good candidate catalysts for intramolecular hydroamination/cyclization reactions. Their catalytic performance with a number of primary and secondary amino alkenes was assessed.

“Click” on Tubes: a Versatile Approach towards Multimodal Functionalization of SWCNTs

Organic functionalization of carbon nanotube sidewalls is a tool of primary importance in material science and nanotechnology, equally from a fundamental and an applicative point of view. Here, an efficient and versatile approach for the organic/organometallic functionalization of single-walled carbon nanotubes (SWCNTs) capable of imparting multimodality to these fundamental nanostructures, is described. Our strategy takes advantage of well-established Cu-mediated acetylene-azide coupling (CuAAC) reactions applied to phenylazido-functionalized SWCNTs for their convenient homo-/heterodecoration with a number of organic/organometallic frameworks, or mixtures thereof, bearing terminal acetylene pendant arms. Phenylazido-decorated SWCNTs were prepared by chemoselective arylation of the CNT sidewalls with diazonium salts under mild conditions, and subsequently used for the copper-mediated cycloaddition protocol in the presence of terminal acetylenes. The latter reaction was performed in one step by using either single acetylene derivatives or equimolar mixtures of terminal alkynes bearing either similar functional groups (masked with orthogonally cleavable protecting groups) or easily distinguishable functionalities (on the basis of complementary analytical/spectroscopic techniques). All materials and intermediates were characterized with respect to their most relevant aspects/properties by TEM microscopy, thermogravimetric analysis coupled with MS analysis of volatiles (TG-MS), elemental analysis, cyclic voltammetry (CV), Raman and UV/Vis spectroscopy. The functional loading and related chemical grafting of both primary amino- and ferrocene-decorated SWCNTs were spectroscopically (UV/Vis, Kaiser test) and electrochemically (CV) determined, respectively.

Chemical functionalization of N-doped carbon nanotubes: a powerful approach to cast light on the electrochemical role of specific N-functionalities in the oxygen reduction reaction

In this paper, we describe the combination of two different synthetic approaches to carbon nanotube N-decoration/doping: the chemical functionalization with tailored N-pyridinic groups and the classical Chemical Vapor Deposition (CVD) technique. Accordingly, CVD-prepared N-doped CNMs (NMWs) and their N-decorated (chemically functionalized) counterparts (NMW@N1,2) have been prepared and used as metal-free electrocatalysts for the oxygen reduction reaction (ORR). It has been demonstrated that chemical functionalization occurs on the NMW surface sites responsible for their inherent electrochemical properties and “switches them off”. As a result, the ORR promoted by NMW@N1,2 is fully controlled by the appended N-heterocycles. A comparative analysis of N-functionalized samples and N-doped (CVD prepared) materials is used to foster the hypothesis of a unique N-configuration (N-pyridinic) responsible for the overall electrochemical performance in NMWs. In addition to that, original electrochemical insights unveiled during the study are discussed and the truly metal-free action of NMW in ORR catalysis is demonstrated.

Intramolecular Hydroamination Reactions Catalyzed by Neutral and Cationic Group IV Pyridylamido Complexes

ZrIV and HfIV benzyl (neutral or cationic) and amido catalysts stabilized by pyridylamido ligands are found to be good candidates for the intramolecular hydroamination/cyclization of primary and secondary aminoalkenes. In particular, cationic monobenzyl derivatives have shown remarkable catalytic activity for the production of five and six‐membered N‐containing heterocycles from secondary amino alkenes. In addition, ZrIV and HfIV amido derivatives that are produced by a temperature‐controlled prototropic rearrangement have provided evidence of the central role played by the metal coordination sphere in promoting such catalytic transformations efficiently.

Intramolecular σ-Bond Metathesis/Protonolysis on Zirconium(IV) and Hafnium(IV) Pyridylamido Olefin Polymerization Catalyst Precursors: Exploring Unexpected Reactivity Paths

A temperature-controlled metathesis/protonolysis takes place on group 4 amidopyridinate polymerization catalyst precursors. Unraveling this unprecedented reactivity path allowed us to highlight the importance of the metal precursor choice while preparing improved catalytic structures or studying new catalytic processes.

Soft matter nanocomposites by grafting a versatile organogelator to carbon nanostructures

The organic functionalization of either [60]fullerene or MWCNTs with a highly efficient organogelator has allowed the production of novel and homogeneously dispersed soft-nanocomposites. While the nanostructured carbon materials produced by simple mixing do not homogeneously disperse into a preformed gel, C60- and MWCNT-containing gels have been conveniently obtained by covalent functionalization of the carbon lattice with reactive organogelator derivatives. The present study, while emphasizing the gelling properties of a selected class of organogelators, allows the conjugation of the properties of gels and nanostructured carbon materials yielding novel soft-nanocomposites.

Novel yttrium and zirconium catalysts featuring reduced Ar-BIANH2 ligands for olefin hydroamination (Ar-BIANH2 = bis-arylaminoacenaphthylene)

The novel class of bis-arylaminoacenaphthylenes (Ar-BIANH2) was employed for the preparation of zirconium and yttrium complexes to be used as catalysts for cyclohydroamination of a number of primary and secondary aminoalkenes. The complex [(2,6-iPr2C6H3-BIAN)Zr(NMe2)2(η1-NHMe2)] was isolated and completely characterized, including X-ray diffraction analysis. Despite its easy and almost quantitative isolation, it showed only moderate catalytic performance in the intramolecular hydroamination, irrespective of the cyclization precursor used. On the other hand, in situ generated YIII complexes obtained using the same class of ligands were found to be very active, leading to the hydroamination of substrates including those normally reluctant in undergoing cyclization such as those featuring an internal non-activated CC double bond. Electron donating substituents and especially steric hindrance on the ligand improve the performance of the catalysts, allowing us to decrease the catalyst loading to 1 mol% in the latter case.

C 1 and Cs 2-pyridylethylanilido zirconium(IV), yttrium(III) and lutetium(III) complexes: synthesis, characterization and catalytic activity in the isoprene polymerization

Neutral group-IV and rare-earth complexes stabilized by novel Cs and C1-symmetric 2-pyridylethylanilido ligands have been prepared and fully characterized before being scrutinized as catalyst precursors in the isoprene (IP) polymerization. In all the isolated complexes, these ligands coordinate to the metal centers in their monoanionic bidentate form. Tetra-amido ZrIV-complexes from this series (11 and 12) have shown only negligible catalytic activity in the IP polymerization, giving polydienes in traces, irrespective of the activator(s) and reaction conditions used. On the other hand, ternary systems made of a bis-alkyl rare-earth metal complex (13–16), an organoborate and a 10-fold excess of an aluminum-alkyl [pre-catalyst/Al-alkyl/borate = 1 : 10 : 1] are found to initiate the living IP polymerization with complete monomer conversion within a few minutes. The process selectivity has been investigated from different perspectives, analyzing its dependence from the rare-earth metal ion of choice (YIIIvs. LuIII), the ligand type (C1vs. Cs) and the activator(s). Polyisoprenes (PIPs) with a prevalent cis-1,4-motif (up to 67.0%) or mainly featured by vinyl pendant arms in their microstructure (up to 75.7% – 3,4-motif) are obtained.