135015-47-3Relevant academic research and scientific papers
Method of establishing the Lewis acidity of a metal fragment based on the relative binding strengths of Ar-BIAN ligands (Ar-BIAN = bis(aryl)acenaphthenequinonediimine)
Gasperini, Michela,Ragaini, Fabio
, p. 995 - 1001 (2008/10/09)
The relative coordination strengths of a series of differently substituted Ar-BIAN ligands (Ar-BIAN = bis(aryl)acenaphthenequinonediimine) to a series of palladium complexes in both the formal 0 and 2 oxidation states have been determined. In all cases a good to excellent linearity of log Keq with respect to the Hammett σ constants of the substituents on the aryl fragments of the ligands was observed. The resulting ρ constant is proposed to be a good indication of the Lewis acidity of the metal fragment, a physical quantity for which experimental parameters have been determined only for a limited class of compounds. The obtained parameters allow a comparison not only of different olefin complexes among themselves but also with respect to different metal fragments such as Pd(OAc)2, Pd(Me)Cl, and a π-allyl complex. The Lewis acidity of the olefin complexes is extremely variable and ranges from the less acidic (Pd(Ar-BIAN)(DMFU); DMFU = dimethyl fumarate) to two of the most acidic (Pd(Ar-BIAN)(TCNE) and Pd(Ar-BIAN)(FN); TCNE = tetracyanoethylene, FN = fumarodinitrile) complexes among those examined. A cationic π-allyl complex has the highest Lewis acidity among the complexes examined. The importance of steric effects is examined in some cases.
Divalent palladium and platinum complexes containing rigid bidentate nitrogen ligands and electrochemistry of the palladium complexes
Van Asselt, Rob,Elsevier, Cornelis J.,Amatore, Christian,Jutand, Anny
, p. 317 - 328 (2008/10/08)
The synthesis and characterization of divalent palladium and platinum complexes of the type PdX2(Ar-BIAN) (X = Cl, Br, I, OC(O)Me), PdCl2(Ph-BIC) and PtCl2(Ar-BIAN) is described. These complexes contain the rigid bidentate nitrogen ligands bis(arylimino)-acenaphthene (Ar-BIAN; Ar = Ph, p-MeC6H4, p-MeOC6H4, o,o′-Me2C6H3, o,o′-i-Pr2C6H3) or bis(phenylimino)camphane (Ph-BIC), which act as σ-donor ligands to the metal center, as was deduced from the observed shifts in the IR and NMR spectra of the complexes. Electrochemical reduction of PdCl2(Ar-BIAN) complexes in THF or DMF occurs via two one-electron reductions and affords the complex PdICl(Ar-BIAN).-, which slowly produces some Pd0(Ar-BIAN) complex. PdICl(Ar-BIAN).- reacts with iodomethane, whereas with iodobenzene or bromobenzene no reaction was observed. PdICl(Ar-BIAN).- reacts with free Ar-BIAN or the alkenes dimethyl fumarate, dimethyl maleate, and methyl acrylate, giving complexes of the formulas PdICl(Ar-BIAN)2.- and PdICl(Ar-BIAN)(alkene).-, respectively. A two-electron reduction of the latter afforded Pd0(Ar-BIAN)22- and Pd0(Ar-BIAN)(alkene)2-, respectively, whose further oxidation in two one-electron steps produces Pd0(Ar-BIAN)2 and Pd0(Ar-BIAN)(alkene). The Pd0(Ar-BIAN) complex which is slowly formed from PdICl(Ar-BIAN).- reacts with alkene but directly affords the complexes Pd0(Ar-BIAN)(alkene).- because Pd0(Ar-BIAN)(alkene) complexes are formed at a potential more negative than their first reduction potential. Reoxidation of Pd0(Ar-BIAN)(alkene).- affords Pd0(Ar-BIAN)(alkene) complexes. The results of the electrochemical experiments corroborate earlier mechanistic proposals of exchange of Ar-BIAN ligands in Pd0(Ar-BIAN)(alkene) complexes and homogeneous hydrogenation of electron-poor alkenes by Pd0(Ar-BIAN)(alkene) complexes.
