Qualitative Estimation of the Single-Electron Transfer Step Energetics Mediated by Samarium(II) Complexes: A “SOMO–LUMO Gap” Approach

International audienceLanthanide II organometallic complexes usually initiate reactions via a single-electron transfer (SET) from the metal to a bonded substrate. Extensive mechanistic studies were carried out for lanthanide III complexes in which no change of oxidation state is involved. Some case-dependent strategies were reported by our group in order to account for a SET event in organometallic computed studies. In the present study, we show that analysis of DFT orbital spectra allows differentiating between exothermic and endothermic electron transfer. This methodology appears to be general; it allows differentiating between lanthanide centers and substituent effects on metallocenes. For that purpose, we considered mainly various samarocene adducts as well as a SmI2 complex explicitly solvated by THF. Comparison between DFT methods and ab initio (CAS-SCF and HF) computational level revealed that the SOMO–LUMO gap computed at the DFT B3PW91 level, in combination with small-core RECPs and standard basis sets, offers a qualitative estimation of the energetics of the SET that is in line with both CAS-SCF calculations and experimental results when available. This orbital-based approach, based on DFT calculation, affords a fast and efficient methodology for pioneer exploration of the reactivity of lanthanide(II) mediated by SET

Theoretical treatment of one electron redox transformation of a small molecule using f-element complexes

International audienceThe theoretical treatment of single electron transfer (SET) of the redox chemistry mediated by f-element complexes is reviewed and summarized. The different computational strategies to account for the SET energy are presented and commented on the basis of the subsequent mechanistic investigation. Moreover, the mechanistic investigation of the subsequent reactivity, mainly in the field of heteroallene activation, using DFT-based approaches is also summarized. All reported reactivities are found to involve formation of bimetallic species and share in common the formation of the same key intermediate in which the substrate is doubly reduced and stabilized by two oxidized metal centers. Modern computational methods are found to efficiently account for such reactivity

Easy and Quantitative Access to Fe(II) and Fe(III) Diarylalkynyl-phosphine Oxides Featuring [Fe(dppe)Cp*] Endgroups: Terminal P=O Functionality Blocks the Dimerisation of the Fe(III) Derivatives

International audienceA series of paramagnetic di(aryl)alkynylphosphine oxides [PF6] featuring an open-shell [Fe(κ(2)-dppe)(η(5)-C5Me5)](+) endgroup were obtained by oxidation of their neutral Fe(II) parents 3a-c, themselves obtained in a simple and nearly quantitative fashion from the corresponding Fe(II) metallophosphines 1a-c. The new organometallic radicals were characterised by NMR and ESR and were shown to be perfectly stable in solution, in contrast to species such as 1a-b[PF6] which readily dimerise

To Bend or Not To Bend: Experimental and Computational Studies of Structural Preference in Ln(Tp iPr 2 ) 2 (Ln = Sm, Tm)

International audienceThe synthesis and characterization of Ln(TpiPr2)2 (Ln = Sm, 3Sm; Tm, 3Tm) are reported. While the simple 1H NMR spectra of the compounds indicate a symmetrical solution structure, with equivalent pyrazolyl groups, the solid-state structure revealed an unexpected, “bent sandwich-like” geometry. By contrast, the structure of the less sterically congested Tm(TpMe2,4Et)2 (4) adopts the expected symmetrical structure with a linear B–Tm–B arrangement. Computational studies to investigate the origin of the unexpected bent structure of the former compounds indicate that steric repulsion between the isopropyl groups forces the Tp ligands apart and permits the development of unusual interligand C–H···N hydrogen-bonding interactions that help stabilize the structure. These results find support in the similar geometry of the Tm(III) analogue [Tm(TpiPr2)2]I, 3Tm+, and confirm that the low symmetry is not the result of a metal–ligand interaction. The relevance of these results to the general question of the coordination geometry of MX2 and M(C5R5)2 (M = heavy alkaline earth and Ln(II), X = halide, and C5R5 = bulky persubstituted cyclopentadienyl) complexes and the importance of secondary H-bonding and nonbonding interactions on the structure are highlighted