The synthesis of Ar-BIAN ligands (Ar-BIAN ) bis(aryl)acenaphthenequinonediimine) having strong electron-withdrawing substituents on the aryl ring is reported. Most of these derivatives had escaped isolation in a pure form up to now. A quantitative scale of coordination strength of the newly synthesized ligands in the complexes Pd 0 (L)(DMFU) (DMFU ) dimethylfumarate) and Pd II (L)(OAc) 2 has been measured. The series also includes some previously known Ar-BIAN ligands, phenanthroline, bipyridine, and Ph-DAB (Ph-DAB ) diphenyldiazabutadiene). A good correlation is observed for the Ar-BIAN ligands between the Hammet σ constants of the substituents of the aryl group and the relative binding constant with respect to Ph-BIAN. The values for the F constant for the Pd(L)(DMFU) and Pd(L)(OAc) 2 series are respectively -1.57 and -3.44, indicating that electron-rich ligands bind more strongly in both series, but the effect is much stronger in the Pd(II) series. The observed effect is relevant to the question of the effective oxidation state of palladium in the Pd(L)(DMFU) complex. Phenanthroline and bipyridine are stronger ligands than any Ar-BIAN compound, whereas Ph-DAB is the weakest ligand of all. The sterically hindered 2,6-Pr i 2 C 6 H 3 -BIAN binds less strongly than its basicity would suggest.

Warum in die Ferne schweifen, wenn das Gute liegt so nah: Die Aktivität des Palladium‐Phenanthrolin‐Katalysatorsystems für die Carbonylierung von Nitrobenzol zu Methylphenylcarbamaten wird durch Zugabe organischer Phosphorsäuren gesteigert – doch ausgerechnet die einfache, dazu billige, leicht abtrennbare und nichttoxische Phosphonsäure H3PO3 erwies sich als bester Zusatz.

Palladium-phenanthroline complexes catalyze both the nitroarene carbonylation reaction and the amine oxidative carbonylation reaction to give, depending on the conditions, carbamates and ureas. There is evidence that the key step in both processes is the amine carbonylation. Here, we show that when the reaction is run in methanol key intermediate compounds have the general formula [Pd(RPhen)(COOMe)(2)] (1) (RPhen = 1,10-phenanthroline or one of its substituted derivatives). The kinetics of the reaction of 1 with toluidine in the presence of a carboxylic or phosphorus acid is first-order with respect to complex, acid, and toluidine. A CO atmosphere is also required for the reaction to proceed. Acid dimerization was shown not to be influential under the concentration conditions examined, but reaction between the acid and toluidine is not negligible and a correction has to be applied. Diphenylphosphinic acid is more effective than any carboxylic acid in promoting this reaction, as also observed under catalytic conditions. A series of equilibria and an irreversible acid-assisted proton transfer explain the observed data. Formation of an adduct between complexes of the kind 1 and CO was spectroscopically observed when RPhen = 2,9-Me(2)Phen. Several analogous complexes were also spectroscopically characterized and the X-ray structure of [Pd(2,9-Me(2)Phen)Cl(2)(CO)] was solved. This shows an asymmetric coordination of the nitrogen ligand. Kinetic measurements were also conducted under catalytic conditions. An Eyring plot shows that the effect of the acidic promoter is to decrease the DeltaS(double dagger) value, whereas no positive effect is observed on DeltaH(double dagger). A temperature-dependent correction for the reaction between the acid and aniline and phenanthroline present under the reaction conditions has to be applied. Comparison of the results obtained under stoichiometric and catalytic conditions strongly supports the view that 1 is involved even in the latter and that the acid is acting as a bifunctional promoter.

A new family of promoters, based on phosphorus acids, is reported for the catalytic carbonylation of nitrobenzene to methyl phenylcarbamate by palladium-phenanthroline complexes. With the new promoters, unprecedented reaction rates (TOF up to 6000/h) and catalyst stability (TON up to 10 5 ) could be reached. The best promoter is phosphoric acid, which is also very cheap, nontoxic and easily separable from the reaction products.

The synthesis of Ar,Ar'-BIAN ligands (Ar,Ar'-BIAN = bis(aryl)acenaphthenequinonediimine) having different aryl groups bound to the two nitrogen atoms is reported for the first time. The ligands were obtained by two different strategies: (i) by a transimination reaction starting from a symmetric Ar,Ar-BIAN ligand having aryl groups bearing strongly electron-withdrawing substituents or (ii) by a two-step-one-pot sequence. The ligands synthesized have been chosen so that the electronic difference between the two aryl groups is very large, but the steric difference is variable and, in one case, the ligand is almost sterically symmetric. The coordination strength of the new ligands towards three palladium complexes has been measured by a competition experiment following a protocol previously described by us. The coordination strength of the mixed ligands is the mean of those of the corresponding symmetric counterparts. The X-ray crystal structure of a palladium pi-allyl complex of the electronically asymmetric-sterically symmetric ligand (3,5-(CF(3))(2)C(6)H(3)),(3,5-Me(2)C(6)H(3))-BIAN has been solved, together with those of the two symmetric analogues to allow a comparison. Despite the fact that the dodecafluorinated ligand has a K(eq) value about three orders of magnitude lower than the non-fluorinated counterpart, no notable difference is observed in the N-Pd and Pd-C(allyl) distances in the three complexes. Calculations at the density functional level confirm that Pd-BIAN distances are not strictly correlated to the coordination energies, which are in qualitative agreement with the spectroscopic evidence. The bond length is thus not a good indication of the bond strength in these cases.