185405-97-4Relevant 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.
Kinetic study of the insertion of norbornadiene into palladium-carbon bonds of complexes containing the rigid bidentate nitrogen ligand bis(arylimino)acenaphthene
Groen, Johannes H.,Delis, Johannes G. P.,Van Leeuwen, Piet W. N. M.,Vrieze, Kees
, p. 68 - 77 (2008/10/08)
The ionic [Pd(C7H8C(O)R)(Ar-BIAN)]X (R = Me, Et, iPr, Ph; X = Cl, Br, I; Ar = p-An, P-FC6H4, P-BrC6H4, p-Tol, Ph, o,o′-Me2C6H3,o,o′-iPr 2C6H3) complexes (1b-12b), bearing the bidentate nitrogen ligand bis(arylimino)acenaphthene (Ar-BIAN), have been synthesized via reaction of the corresponding neutral acylpalladium complexes Pd(C(O)R)X(Ar-BIAN) (1a-12a) with norbornadiene (nbd). For the first time, an extensive kinetic study of this migratory alkene insertion into acyl-palladium bonds of neutral complexes containing α-diimine ligands has been carried out. It has been found that under pseudo-first-order circumstances these reactions follow the rate law kobsd = k1 + k2[nbd], which shows that these reactions proceed via a pathway independent of alkene concentration (k1 pathway) and a pathway dependent on alkene concentration (k2 pathway). The dramatic decrease of the rate constants k1 and k2 upon increasing the steric bulk of the BIAN ligand and the large negative entropy of activation and low enthalpy of activation for both pathways indicate that the k1 and k2 pathways are closely related and involve associative processes. From the influence of solvent, X and C(O)R ligand, steric and electronic properties of the BIAN ligand, the presence of free halide and free BIAN, and the parameters of activation, mechanisms have been proposed for both pathways. The k1 pathway may proceed via a rate-determining solvent-assisted halide or nitrogen dissociation, followed by alkene association and migratory insertion, while the k2 pathway may occur via a rate-determining migratory alkene insertion in a contact ion pair intermediate. This species may be formed via alkene association followed by either halide or nitrogen dissociation.
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.
