Synthesis of Ar-BIAN Ligands (Ar-BIAN = Bis(aryl)acenaphthenequinonediimine) Having Strong Electron-Withdrawing Substituents on the Aryl Rings and Their Relative Coordination Strength toward Palladium(0) and -(II) Complexes

Abstract

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.

Catalyst activity or stability: the dilemma in Pd-catalyzed polyketone synthesis

“…For Ar-BIANs, (E,E) and (E,Z) isomers are possible regarding to the relative configuration of the aryl rings with respect to the C=N imine bonds. In general, only the E,E isomer is observed for symmetrical Ar-BIANs, 19 but a variable amount of the E,Z isomer is always found in the case of nonsymmetrical Ar,Ar′-BIAN derivatives [16][17][18]20 and for alkyl-BIANs. 22,23 For both ligands 3 and 7, the 1 H NMR spectrum recorded at room temperature in CDCl 3 and CD 2 Cl 2 , respectively, indicated the presence in solution of the E,E isomer only.Though this was expected for the latter, it is surprising for the former.…”

“…The synthetic methodology for ligand 7 is based on the well known condensation reaction of acenaphthenequinone with 3,5-difluoro aniline in the presence of ZnCl 2 as templating agent. 19,20 The synthesis of the new nonsymmetrical Ar,Ar′-BIAN 3 was performed by the transimination reaction between the zinc derivative of ligand 7 and 3,4,5-trimethoxy aniline (Scheme 1), similarly to what was previously described by some of us for other nonsymmetrical Ar,Ar'-BIAN derivatives. 16 The reaction proceeds quickly and the mixed ligand could be isolated in 52 % yield after chromatographic purification.…”

“…This catalytic behavior is different from that found by us for analogous palladium complexes with ligands belonging to the family of 1,10-phenanthroline 21 that over a range of 90 h showed a linear dependence of CO uptake with time, in agreement with the stronger coordinating capability of phenanthroline ligands with respect to that of Ar-BIANs. 20 The comparison of the CO uptake curves of precatalyst 1b with those of complexes 4b and 5b…”

“…In previous papers some of us have shown that the logarithm of the relative coordinating strength of substituted Ar-BIAN ligands shows a good correlation with the Hammett σ constants. 20,38 When two substituents were present, the correlation was maintained if the sum of the two individual σ was employed, whereas ligands having different substituents on the two aryl rings followed the same trend if the arithmetic average of the Hammett σ constants for the two rings was employed in the correlation. 16 In general, this corresponds to employing for both symmetrical and nonsymmetrical ligands the value of Σσ/2 (where the sum is extended to all substituents on the two rings),which is also shown in Table 2.…”

Combined Low Temperature Rapid Scan and1H NMR Mechanistic Study of the Protonation and Subsequent Benzene Elimination from a (Diimine)platinum(II) Diphenyl Complex Relevant to Arene C−H Activation

“…The Ar-BIAN ligands, 138,161,171 the Ar-BICAT precursor 172 Ar'N=C(Cl)-C(Cl)=NAr' with Ar' = 4-MeC 6 H 4 , and Ph 2 Pt(SMe 2 ) 2 120 were prepared according to published procedures.…”