Although lanthanide borohydride precursors are useful building blocks to access molecular lanthanide complexes, the nucleophilic reactivity of the attached [BH4]- unit has not been thoroughly investigated. We herein report the reaction of [La(Cpttt)2(BH4)] (1, Cpttt = 1,2,4-tris(tert-butyl)cyclopentadienyl) toward CO2, leading to the formation of a formate complex, which exists as an equilibrium mixture between the dimeric and monomeric forms in aromatic solvents. 1H DOSY NMR experiments allowed a convenient analysis of the reaction mixture and provided an estimation of the hydrodynamic radii for both species. Hydroborane reagents (BH3, HBPin, H(9-BBN)) further react with the formate complex, leading to the formation of borylated methanol and the corresponding lanthanide boroxide complexes. Preliminary investigations were performed to investigate the viability of 1 as a precatalyst in the hydroboration of CO2. This work highlights the potential application of readily available rare-earth borohydride complexes in the transformation and valorization of CO2.

We report the first structurally characterised coordination solids based on decamethylytterbocene, using bipyridine linkers to form YbCp*2(bipy) and YbCp*2(Me2bipy). Analogous to their mononuclear cousins known for intermediate valence, spectroscopic evidence suggests that YbCp*2(bipy) features a multiconfigurational ground state, composed of a superposition of an open-shell ligand non-innocent 4f13(π*)1 state and a closed- shell 4f14 state. Our findings mark a first step toward increasing electronic correlations in lanthanide-organic frameworks, with the aim of realising materials with coexisting electronic transport and emergent magnetic properties.

Procedures for activating and degrading compounds containing carbon-halogen bonds are highly sought after due to the environmental persistence and potential hazards of such compounds. Such activations are challenging because of the high stability of these bonds, particularly those with C-F bonds. Here, we report on the activation of carbon-halogen bonds, including C-F bonds, by the cerium(iii)-triamidoamine complex CeIIITRENTIPS (1, TRENTIPS = tris-(2-(tri-iso-propylsilylamidoethyl)amine)). Under light irradiation, 1 reaches a strongly negative excited state redox potential, and our measurements enable it to be estimated as -3.2 V relative to Cp2Fe0/+. Hence, the photo-reactivity of 1 with carbon-halogen bonds has been established with numerous examples, including Persistent Organic Pollutants (POPs) and fluorinated compounds. The photoactivation of POPs is rapid, but the photoactive nature of the cerium(iv) products precludes complete conversion. This study provides insight into the activation of POPs that may benefit the future design of photodegradation approaches for these highly problematic compounds.

Palladium chemistry has been widely studied since the 1950s, particularly for cross-coupling reactions. It facilitates breaking C-X bonds through oxidative addition and forming C-C bonds through reductive elimination. These 2 electrons' elementary steps are the key features to construct highly elaborated molecules and explain their exceptional versatility. While Pd(0)/Pd(II) catalytic cycles are well understood, the behavior of Pd(IV) alkyl complexes is less studied, particularly due to their instability. Here, we report the synthesis and characterization by X-ray diffraction, solid-state magnetism, and 1H NMR of several Pd(Alkyl)4 fragments, which demonstrate unusual stability thanks to a Cp*2Yb(bipym) fragment (Cp* is for pentamethylcyclopentadienyl and bipym for 2,2'bipyrimidine). As such, the Cp*2Yb(bipym)Pd(Me)3(R) (R = Me, 3Me; Et, 3Et) complexes have a room temperature half-life of more than 17 h, while the one-electron reduction of 3Me leads to a Pd(Me)4 fragment, 3@crypt, which does not degrade over time. This unusual stability allowed us to study the original reactivities of these Pd(Alkyl)4 fragments other than classical reductive elimination. Thus, we report the first light-induced Pd(IV)-C bond homolysis, which leads to the formation of alkyl radicals. The Cp*2Yb(bipym)PdMe4 complex, 3Me, reacts under irradiation at 370 nm to form the Cp*2Yb(4Me,4H-bipym)PdMe4, 4, and the Cp*2Yb(4Me,4H-bipym)PdMe2, 5, in which the methyl radical couples with the bipym radical. The mechanism of this peculiar reaction has been determined by DFT. Similar reactivity with 3@crypt leads to the formation of a free methyl radical, as shown by EPR reaction trapping.

The direct splitting of H2 and N2 molecules is a challenging reaction that is closely related to the Haber-Bosch ammonia synthesis process. Until now, such reactivity has never been observed in the case of molecular lanthanide species. Here, we show that careful selection of the ligand scaffold allows the isolation and characterization of a kinetically stable but highly reactive LuII complex. This divalent lanthanide species enables direct H2 splitting at room temperature, an unknown reactivity in lanthanide chemistry, which has been fully corroborated by DFT calculations. In addition, the LuII complex readily binds N2, leading to an end-on coordinated diazenido (N2)2- lanthanide complex. The latter can be hydrogenated under very smooth conditions (ca. 1.2 bar H2, ambient temperature) to form a unique LuIII-NH2 complex. Direct N2 hydrogenation and cleavage are thus accessible using low-valent molecular rare-earth metal complexes.

The conversion of dinitrogen into ammonia plays an important role in sustaining life on Earth and serves as a significant building block for our planet's future. The Haber-Bosch process, although a well-established method for converting hydrogen and nitrogen gases into ammonia using metal-based heterogeneous catalysts, requires an extensive industrial infrastructure, limiting its accessibility and flexibility. Molecular systems, whether supported or unsupported, offer the advantage of allowing fine-tuning of the metal properties and the involved elementary steps, which ultimately leads to a better understanding of the transformations. In this context, we present findings on the reactivity of dinitrogen with an organometallic uranium complex featuring the bulky Cpttt ligand (Cpttt = 1,2,4-tris(tert-butyl)cyclopentadienyl). This complex demonstrates the ability to cleave and hydrogenate dinitrogen under mild conditions, at ambient temperature and atmospheric pressure. Most notably, the rich redox chemistry of uranium enables the direct reduction of N2 into a unique formal UIV dimer featuring an end-on coordinated (N2)4- bridging ligand, the cornerstone of the observed reactivity.

Cyclononatetraenyl (Cnt) is a nine-membered monoanionic aromatic ligand. Despite its early discovery in 1963, it has been rarely utilised in coordination chemistry, which is mainly due to its large diameter and easy skeletal rearrangement. Only in 2017, the first lanthanide Cnt complex was synthesised, marking the beginning of a new era in organolanthanide chemistry. Since then, the chemistry displayed by Cnt has expanded rapidly in lanthanide chemistry. Due to the ligand flexibility, both classical planar eta 9-Cnt ligands and heavily bent ones with lower hapticity were found in Ln coordination complexes. These novel structure motifs exhibit reactivity which differs significantly from traditional cyclopentadienyl (Cp) and cyclooctatetraenediide (Cot) complexes. Some of the obtained compounds also show interesting photoluminescence and magnetic properties. This review presents an overview of the synthesis, structure and reactivity of the growing family of lanthanide Cnt compounds.

Three new lanthanide complexes of the general form [Ln(Cnt)(CntInd)] (Ln = Ce, Pr, and Nd; Cnt = cyclononatetraenyl; and CntInd = cyclononatetraenyl-dihydroindene) have been synthesized from the corresponding LnI3 salt and several equivalents of the KCnt ligand. A novel C-C coupling has been observed between one Cnt- moiety and one dihydroindene moiety, originating from the collapse of a Cnt unit. The observed CntInd ligand is dianionic, harboring one more electron than a typical Cnt ligand. The complexes are characterized by X-ray diffraction, 1H NMR, and UV-visible studies. The novel complexes are formed instead of the [Ln(Cnt)3] (Ln = Ce, Pr, and Nd), which are only reported with late lanthanide ions, while lanthanum did not form one or the other complex.

This chapter describes the redox-active ligands (RALs) that have been associated with lanthanide complexes. The ligand families discussed herein are quinones, semiquinones, diimines, diazadienes, imino- and bis(imino)pyridines, nitroxides, and N-heterocycles. The main strategies for obtaining lanthanide complexes containing RALs in their coordination spheres are outlined, and the resulting electronic correlation is discussed from multiple perspectives. The intrinsic physicochemical properties of lanthanides also manifest themselves within the RAL-lanthanide framework. Examples of reactivity enabled by such systems are presented and analyzed. The most salient features and examples will be discussed in this chapter.

The cyclononatetraenyl (Cnt) ligand is a large monoanionic ligand. It is easily synthesized by ring expansion after cyclopropanation of the cyclooctatetraenyl (Cot) ligand. The Cnt ligand can be reported as the cis-cis-cis-cis (cis) isomer, where the aromatic ring is flat, and all carbon atoms form a homogenous ring, and as the cis-cis-cis-trans (trans) isomer, where one carbon places itself inside the ring. The isomerization from the trans to the cis form has been reported numerous times in previous articles, but no quantitative analysis has been proposed due to contradictory data. This article proposes a detailed analysis involving light in order to rationalize this intrigue concerning isomerization. A careful synthesis at low temperatures and with light protection yields the ligand in its trans form (Cnt-trans). The controlled photo-isomerization of the Cnt-trans ligand is reported herein. A series of divalent or trivalent rare earth complexes, (Cnt)2Sm, and (Cot)(Cnt)Ln (Ln= Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Er, Ho), which synthesis, solid-state X-ray diffraction and solution 1H NMR and UV-Visible measurements, have been revised according to the synthesis using the Cnt-trans ligand. The photo-isomerization of the (Cnt-trans)2Sm evolves to the intermediate (Cnt-cis)(Cnt-trans)Sm and the (Cnt-cis)2Sm complex as the thermodynamical product. The photoisomerization of the trivalent (Cot)(Cnt)Ln complexes highlights the formation of a photostationary state (PSS) after several minutes of irradiation, in which both Cnt-trans and Cnt-cis ligands are present. The ratio of these two forms varies according to metal and irradiation wavelength: while low-energy wavelengths favor the cis isomer, high-energy wavelengths favor the trans isomer. DFT and TD-DFT were performed to provide a tentative orbital explanation.

This article focuses on the synthesis of heterobimetallic complexes of lanthanide and platinum. It describes the synthesis of the Cp*Yb(bipym)PtMe2 complex and its characterization, followed by its reactivity with oxidants, giving access to various Pt + IV compounds of trismethyl (PtMe3) and tetramethyl (PtMe4) fragments. Characterization of the electronic properties of the complexes by magnetic measurements demonstrated that the tetramethyl complex possesses a singlet ground state. The trismethyl fragments, on the other hand, have a ground state that evolves as a function of the ligand saturating the coordination sphere: a singlet for triflate and pyridine and a triplet for iodine, demonstrating the capacity for simple tuning of the electronic structure of these complexes. While the addition of B(C6F5)(3) to the platinum + II bis methyl complex leads to FLP-like reactivity triggering THF opening, reactivity with [Ph3C](+)[BPh4](-) leads to oxidation of the bipym ligand. Furthermore, the light reactivity of the tetramethyl complex indicated the possible transfer of a methyl group, leading to functionalization of the bridging bipym ligand.

Procedures for activating and degrading compounds containing carbon-halogen bonds are highly sought after due to the environmental persistence and potential hazards of such compounds. Such activations are challenging because of the high stability of these bonds, particularly those with C-F bonds. Here, we report on the activation of carbon-halogen bonds, including C-F bonds, by the cerium(III)-triamidoamine complex CeIIITRENTIPS (1, TRENTIPS = tris-(2-(tri-iso-propylsilylamidoethyl)amine). Under light irradiation, 1 reaches a strongly negative excited state redox potential, and our measurements enable it to be estimated as 3.2 V relative to Cp2Fe0/+. Hence, the photo-reactivity of 1 with carbon-halogen bonds has been established with numerous examples, including Persistent Organic Pollutants (POPs) and fluorinated compounds. The photoactivation of POPs is rapid, but the photoactive nature of the cerium(IV) products precludes complete conversion. This study provides insight into the activation of POPs that may benefit the future design of photodegradation approaches for these highly problematic compounds.

Angewandte Chemie International EditionVolume 62, Issue 18 e202381811 Graphical AbstractFree Access Graphical Abstract: Angew. Chem. Int. Ed. 18/2023 First published: 17 April 2023 https://doi.org/10.1002/anie.202381811AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat Volume62, Issue18April 24, 2023e202381811 RelatedInformation

The heterotrinuclear linear arrangement Ln–Pd–Ln has short Ln–Pd distances: does it imply a covalent bond?

At the dawn of the development of structural organometallic chemistry, soon after the discovery of ferrocene, the description of the LnCp3 complexes, featuring large and mostly trivalent lanthanide ions, was rather original and sparked curiosity. Yet, the interest in these new architectures rapidly dwindled due to the electrostatic nature of the bonding between π-aromatic ligands and 4f-elements. Almost 70 years later, it is interesting to focus on how the discipline has evolved in various directions with the reports of multiple catalytic reactivities, remarkable potential in small molecule activation, and the development of rich redox chemistry. Aside from chemical reactivity, a better understanding of their singular electronic nature - not precisely as simplistic as anticipated - has been crucial for developing tailored compounds with adapted magnetic anisotropy or high fluorescence properties that have witnessed significant popularity in recent years. Future developments shall greatly benefit from the detailed reactivity, structural and physical chemistry studies, particularly in photochemistry, electro- or photoelectrocatalysis of inert small molecules, and manipulating the spins' coherence in quantum technology.