155889-92-2Relevant 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.
Zerovalent palladium and platinum complexes containing rigid bidentate nitrogen ligands and alkenes: Synthesis, characterization, alkene rotation and substitution reactions. X-ray crystal structure of [bis((2,6-diisopropylphenyl)imino)acenaphthene](maleic anhydride)palladium(0)
Van Asselt, Rob,Elsevier, Cornelis J.,Smeets, Wilberth J. J.,Spek, Anthony L.
, p. 1521 - 1531 (2008/10/08)
A number of zerovalent palladium and platinum M(NN)(alkene) complexes, containing the rigid bidentate nitrogen ligands bis(arylimino)acenaphthene (Ar-BIAN) and bis(phenylimino)camphane (Ph-BIC) have been synthesized and characterized. Stable complexes were obtained with electron poor alkenes, such as dimethyl fumarate, fumaronitrile, maleic anhydride, and tetracyanoethylene. Complexes bearing asymmetric Ar-BIAN or Ph-BIC ligands occurred as mixtures of isomers. From IR, UV, and 1H and 13C NMR spectroscopy and from substitution reactions it was concluded that the back-donation of electron density from the metal to the alkene is the major factor determining the stability of the complexes. Some of the complexes show fluxional behavior on the NMR time scale, which was explained by rotation of the alkene around the metal-alkene bond. The estimated rotation barriers of 50-69 kJ/mol for Pd and >72 kJ/mol for Pt are high as compared to reported values for other palladium and platinum alkene complexes. From a study of alkene substitution reactions of Pd(Ar-BIAN)(alkene) complexes it appeared that alkene substitution occurs via a fast associative mechanism for complexes containing Ph-BIAN or p-Tol-BIAN ligands and via a slower dissociative mechanism for complexes containing o,o′-i-Pr2C6H3-BIAN. Substitution of the p-Tol-BIAN ligand in Pd(p-Tol-BIAN) (alkene) by o,o′-i-Pr2C6H3-BIAN is also observed and is explained by initial dissociation of the alkene. Whereas the spectroscopic and crystal data point to M(II)-metallacyclopropane type structures, the reactivity points rather to M(0)-alkene type complexes. The X-ray crystal structure of Pd(o,o′-i-Pr2C6H3-BIAN)(maleic anhydride) has been determined. Crystals are triclinic, space group P1, with a = 10.9931(9) ?, b = 11.7313(5) ?, c = 14.7906(13)?, α = 86.276(5)°, β = 81.936(7)°, γ = 71.273(5)°, Z = 2, and final R = 0.055 for 3702 reflections with I > 2.5σ(I).
