Grégory Danoun

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, 3^Me; Et, 3^Et) complexes have a room temperature half-life of more than 17 h, while the one-electron reduction of 3^Me 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, 3^Me, 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.

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.

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 Cp^ttt ligand (Cp^ttt = 1,2,4-tris(tert-butyl)cyclopentadienyl). This complex demonstrates the ability to cleave and hydrogenate dinitrogen under smooth 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 U^IV dimer featuring an end-on coordinated (N₂)^4– bridging ligand, the cornerstone of the observed reactivity

Palladium chemistry is widely studied since the 1950’s, 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 its 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 pentamethylcy-clopentadienyl and bipym for 2,2’bipyrimidine). As such, the Cp*2Yb(bipym)Pd(Me)3(R) (R = Me, 3Me; Et, 3Et) complexes have 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 ho-molysis, 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 reac-tivity with 3@crypt leads to forming a free methyl radical, as shown by EPR reaction trapping.

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 smooth 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.

Herein, we report the synthesis of a Ce(iii)-based complex, [Ce^IIITREN^TIPS], possessing a redox potential of −3.2 V vs. Cp₂Fe^0/+ under light irradiation which enables C–Cl and C–F bond activation on very stable chemicals including POPs and PFAS.

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.

Reversible light isomerization in organometallic complexes of lanthanides: the low-energy wavelengths favor the cis isomer, and the high-energy wavelengths favor the trans isomer.

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.