Pierre Le Gendre

Aza-boron-dipyrromethenes (aza-BODIPYs) are established fluorescent imaging agents derived from aza-DIPY ligands coordinated to boron. While many modifications of the aza-DIPY core have optimized the photophysical properties, replacing boron with a metal ion remains underexplored. Here, we report four zirconium-based aza-DIPY complexes (aza-ZrDIPYs) and show that this substitution enables bimodal NIR-I fluorescence and photoacoustic imaging. The complexes were fully characterized and evaluated photophysiologically. The bromo derivative, aza-ZrDIPY-Br, displayed particularly favorable dual-mode properties. It showed low in vitro cytotoxicity and an effective uptake in two human cell lines. In mice bearing subcutaneous U87-MG glioblastoma tumors, intravenous or peritumoral administration led to passive tumor accumulation, with tumor-to-background ratios of up to 5 (photoacoustic) and 2 (optical). These results highlight aza-ZrDIPY-Br as a promising bimodal probe for tumor imaging, with future work aimed at improving specificity through active targeting.

In search of an alternative to the dominant industrial processes, facilitated mostly by transition-metal catalytic systems, current economic and environmental aspects are leading to a growing interest in the chemistry and application of main group element-based catalysts and materials. Mono- and dinuclear boron and aluminum complexes bearing a biguanide ligand (substituted 4,6-dimethoxypyrimidin-2-yl-guanidinate; L) were prepared by deprotonation of LH₂ with BH₃·Me₂S, BF₃·Et₂O, Me₃Al, or Me₂AlCl or, in some cases, by transmetallation reactions of the lithium complex. Complexes were characterized by multinuclear NMR and sc-XRD analyses. Two coordination isomers, where the central atoms can occur both in the four- and six-membered N,N'-chelate ring, were found for homobimetallic aluminum and boron biguanide complexes. A thorough study was performed to understand the formation and isomerization process, where thermally and kinetically conducted isomerization was explored. The relative Gibbs free energies of optimized structures and hypothetical arrangements were calculated and compared in order to support the described isomerization. The activity of selected complexes was tested in the ring-opening polymerization (ROP) of rac-lactide. While the boron complexes are inactive, dimethylaluminum species show moderate activity and good control over the polymer mass and dispersity after ⁱPrOH co-initiation. Furthermore, the species effectively promote hydroboration of unsaturated C-C bonds.

Herein, we report the synthesis of a series of new bis(phenoxy-amidine) dichloro and bis(dimethylamido) Ti and Zr complexes [(FA)₂MX₂]. In the solid state, all the structures showed a distorted octahedral geometry around the metal center with the same O-trans, N-cis, X-cis configuration. Remarkably, NMR spectroscopic study of (FA)₂MX₂ complexes in solution shows that all complexes exist only as a C₂-symmetric isomer. The direct alkylation of (L4)₂TiCl₂ and (L4)₂ZrCl₂ by two equivalents of PhCH₂MgCl and/or Me₃SiCH₂MgCl yielded the corresponding dialkyl complexes without alkylation of the amidine moieties. The (FA)₂Ti and Zr complexes are active in ethylene polymerization upon activation by MAO at 25-50 °C in toluene, at 5 bar ethylene pressure, providing linear (ultra) high-molecular-weight PE (M_w up to 2,154,000 g·mol^-1 for the soluble fraction), yet with very broad distributions (M_w/M_n = 14-408), testifying an abundant multisite behavior. Complexes with ^tBu substituents on the ligand aryloxy ring showed better polymerization productivity (up to 230 kg_PE·mol_cat^-1·h^-1). The (L4)₂MX₂ complexes, upon activation with MAO, are also slightly active toward styrene (2 to 39 kg_PS·mol_cat^-1·h^-1 at 25-100 °C) giving polystyrenes with an atactic microstructure and molecular weight characteristics (Đ = 1.77-1.86) indicative of a single-site behavior.

The correlation between delocalization (DI) and penetration ( p ) indexes partitions bonding interactions into bond types. This methodology was applied to the bonding analysis of Ti/Ir heterobimetallic complexes derived from ambiphilic phosphides.

Heteroleptic and homoleptic complexes of zinc with phenoxyimine and phenoxyamidine ligands are used as alternatives to currently used tin catalysts in the transesterification reaction of methyl acrylate and N,N‐ dimethylethanolamine in the synthesis of N,N‐ dimethylaminoethyl acrylate. A large screening of phenoxyimine and three generations of phenoxyamidine ligands has been undertaken and used to determine the best catalysts in terms of conversion and selectivity. All of the catalysts tested show significant improvement in activity over catalysts currently well‐established in industrial processes such as dibutyltin oxide or Ti(O ⁱ Pr) ₄ . The catalytic charges can be decreased significantly (10–20×) still affording good conversions and selectivities. A series of heteroleptic and homoleptic zinc complexes with phenoxyimine and phenoxyamidine ligands have been tested for the transesterification of methyl acrylate with N,N ‐dimethylethanolamine. All the catalysts demonstrated a substantial increase in activity compared to dibutyltin oxide, a well‐established catalyst that is currently used in industry for this reaction.

Discrete yttrium and lanthanum complexes supported by new bis(phenoxy‐amidine) ligands have been prepared in high yields. Some of these so‐called FAlen ligands, when coordinated onto the large La ³⁺ in contrast to the small Y ³⁺ , can adopt an η ³ coordination mode of both amidine moieties. These La‐FAlen complexes, either previously isolated or conveniently prepared in situ, act as highly efficient ROP catalysts of simple and functional β‐propiolactones rac ‐BL ^R (R = Me, CH ₂ O i Pr, CH ₂ OSi t BuMe ₂ ) under mild conditions, returning the corresponding linear polymers PBL ^R with high control over the molecular weights and narrow dispersities. More uniquely, when substituents with appropriate bulkiness are installed on the phenoxy and amidine moieties, the polymers all feature high isotacticity ( P _m up to 0.93). High activity and isoselectivity are maintained, no matter the nature and polarity of the solvent used.

Discrete yttrium and lanthanum complexes supported by new bis(phenoxy‐amidine) ligands have been prepared in high yields. Some of these so‐called FAlen ligands, when coordinated onto the large La ³⁺ in contrast to the small Y ³⁺ , can adopt an η ³ coordination mode of both amidine moieties. These La‐FAlen complexes, either previously isolated or conveniently prepared in situ, act as highly efficient ROP catalysts of simple and functional β‐propiolactones rac ‐BL ^R (R = Me, CH ₂ O i Pr, CH ₂ OSi t BuMe ₂ ) under mild conditions, returning the corresponding linear polymers PBL ^R with high control over the molecular weights and narrow dispersities. More uniquely, when substituents with appropriate bulkiness are installed on the phenoxy and amidine moieties, the polymers all feature high isotacticity ( P _m up to 0.93). High activity and isoselectivity are maintained, no matter the nature and polarity of the solvent used.