Ligand Influence on the Redox Chemistry of Organosamarium Complexes: Experimental and Theoretical Studies of the Reactions of (C₅Me₅)₂Sm(THF)₂ and (C₄Me₄P)₂Sm with Pyridine and Acridine

Abstract

The reactions of the samarium(II) complexes Tmp 2 Sm (Tmp = 2,3,4,5-tetramethyl-1H-phosphol-1-yl) and Cp* 2 Sm(THF) 2 (Cp* = 1,2,3,4,5-tetramethyl-2,4-cyclopentadien-1-yl) with pyridine were found to be different, despite the fact that the Cp* and Tmp π-ligands are similar in size. With Tmp 2 Sm, a simple adduct, Tmp 2 Sm(pyridine) 2 is isolated, while with Cp* 2 Sm(THF) 2 pyridine is dimerized with concomitant oxidation of samarium to form [Cp* 2 Sm-(C 5 H 5 N)] 2 [μ-(NC 5 H 5 −C 5 H 5 N)]. However, reaction of Tmp 2 Sm with acridine, a better π-acceptor than pyridine, did result in acridine dimerization and the isolation of [Tmp 2 Sm] 2 [μ-(NC 13 H 9 −C 13 H 9 N)]. DFT calculations on the model structures of Tmp 2 Sm and Cp* 2 Sm, and on the single electron transfer step from Sm to pyridine and acridine in these ligand environments, confirmed that, even though the Sm−πligand bonds are mostly ionic, the different electronic properties of the Tmp ligand versus that of Cp are responsible for the difference in reactivity of Tmp 2 Sm and Cp* 2 Sm.■ EXPERIMENTAL SECTION Computational Details. Calculations were performed with the GAUSSIAN 03 suite of programs. 10 DFT was applied by means of the

Reactivity of Bulky Formamidinatosamarium(II or III) Complexes with C═O and C═S Bonds

“…A different loss of aromaticity of benzophenone caused by lanthanoid metals is observed in formation of enolate complexes, 37 and dearomatization of pyridine was observed recently in a reaction of [Sm(Cp* 2 )-(thf) 2 ] with pyridine forming [{Cp* 2 Sm(C 5 H 5 N)} 2 {μ-(NC 5 H 5 −C 5 H 5 N)}]. 38 The redox reaction of 3 with carbon disulfide yielded a samarium(III) complex 5 with a rare thioformyl carbonotrithioate ((SCSCS 2 ) 2− ) bridging ligand (rather than a tetrathiooxalate ligand) in moderate yield (Scheme 4). The poor solubility of the compound in hydrocarbon solvent prevented NMR characterization.…”

Assessment of Density Functionals for Computing Thermodynamic Properties of Lanthanide Complexes

“…Recent work on this subject includes the use of non‐innocent ligands, the reduction of small molecules such as CO 2 , and the development of newly designed luminescent and magnetic compounds . In many studies, quantum chemical methods support the interpretation of experiments by evaluating various physical‐chemical properties of lanthanide complexes; that is, mechanisms of reactions, magnetic coupling, and luminescence properties …”

“…Maron et al . reported an energy comparison between two density functionals, B3PW91 and B3LYP, and the MP2 method, using small core relativistic effective core potentials (RECP), and they chose B3PW91 for further chemical studies . Recently, the performance of several density functionals over energies of diatomic lanthanide molecules was evaluated by Grimmel et al .…”

Chemically and Electrochemically Triggered Assembly of Viologen Radicals: Towards Multiaddressable Molecular Switches

“…55 Following these pioneering works, many reports have established that pyridinyl radicals are indeed prone to σ‐dimerization, mostly through the ortho and para positions of the pyridine rings, but the exact regioselectivity and stereoselectivity of the coupling process have been shown to be essentially determined by steric factors and by the distribution of the electron density in each ring 50. 51, 53, 56–58 Most reported radical‐radical coupling reactions are fully irreversible but the reversibility of σ‐dimerization processes has also been postulated for various radicals59–68 including pyridinyl derivatives 53. 61, 69–74 The proposed dimeric structures produced from 6 2 .…”