Anatoly K. Yatsimirsky

Some complexes of palladium(II) with C-phenylglycine and its derivatives. Cyclopalladation of N,N-dimethyl-C-phenylglycine ethyl ester

Abstract The reaction of both D-C-phenylglycine and its methyl ester with palladium(II) acetate in acetic acid solvent gives the acetato-bridged dimer [PdL(OAc) 2 ] 2 and the monomeric complex [PdL 2 (OAc) 2 ]. On the basis of IR and 1 H NMR measurements it is suggested that the ligands are bonded to the metal in a monodentate fashion, amine nitrogen being a donor group. N,N-Dimethyl-C-phenylglycine ethyl ester reacts with Pd(II) acetate in acetic acid or chloroform and Li 2 PdCl 4 in aqueous dioxane in the presence of sodium acetate to afford the cyclopalladated species [Pd{Me 2 NCH(CO 2 Et)C 6 H 4 }X] 2 , where X = OAc or Cl. The assignment of the ortho-metallated compounds has been made on the basis of 1 H NMR data. Some characteristic reactions of these cyclopalladated complexes are presented.

Palladium(II)-catalyzed oxidation of substituted benzenes to biaryls by tris(trifluoroacetato)thallium(III)

Abstract The method of oxidation of substituted benzenes to 4,4′-biaryls by Tl(III) trifluoroacetate catalyzed by Pd(II) acetate is presented. The reactions proceed in the completely homogeneous solution of arene.

Palladium(II)-catalyzed oxidative coupling of arenes by thallium(III)

Abstract Oxidation of benzenes with electron-donating and moderate electron-withdrawing substituents by thallium(III) trifluoroacetate in the presence of catalytic amounts of palladium(II) acetate affords biaryls in good yields. The GLC study of the isomer distribution has shown that 4,4 -biaryls are the major products. Thus, the pure 4,4 -biaryls can be easily isolated either by recrystallization or column chromatography. The competitive experiments and kinetic study using arenes and arylthallium derivatives as starting materials as well as quenching experiments have demonstrated the first step of the reaction to be fast thallation of arene to form arylthallium intermediate ArTl (OOCCF 3 ) 2 . The latter undergoes the rate-determining transmetallation step reacting with monomeric complex Pd(OAc) 2 , which is formed upon depolymerization of trimer Pd 3 (OAc) 6 . Subsequent fast decomposition of arylpalladium species gives the final reaction products. The thallation of arene and substitution of Tl III for Pd II in ArTl (OOCCF 3 ) 2 are characterized by the slopes of Hammett plots of -5.6 (XXX+) and -3.0 (XXX), respectively.

Comparative study of the mechanism of alkynelation of ortho-palladated benzylamines and acetanilides

Abstract The ortho -palladated derivate of N,N -dimethylbenzylamine, the complex [Pd(OAc)(C 6 H 4 CH 2 -NMe 2 ) 2 , reacts with styrene in acetic acid solution with a final product of o -Me 2 NCH 2 C 6 CHue5fbCHC 6 -H 5 . Two parallel second-order pathways, are involved catalysed, respectively by acetic acid ( k 3 ) and perchloric acid ( k H ). The rate constants k 3 and k H at 30°C are 0.021± 0.005 and 6.8 ± 0.5 dm 3 mol −1 s −1 , while the p K a is 4.6. In the case of the corresponding sacetanilide derivative, the complex [Pd(OAc)(C 6 H 4 NHCOMe)] 2 , the catalysis by perchloric acid is much weaker than for the amine complex, the k 3 and k H being 0.0206 ± 0.0005 and 0.049 ± 0.003 dm 3 mol −1 s −1 , respectively. The p K a in this case is 4.5. Despite the great difference in basicity of N,N -dimethylbenzylamine and acetanilide, the values for p K a are very similar, providing evidence that the perchloric acid-catalysed pathway involves the protonation of groups of comparable basicity in both complexes, that is to say the bridging acetates, while the great variation in the values of k H suggests the existence of other route of acid catalysis for amine complexes. The chloro-bridged acetanilided complex [PdCl(C 6 H 4 NHCOMe)] 2 reacts with styrene in various organic solvents without the perchloride acid-catalysed pathway ( k H ). The Hammett equations log k 3 = −(1.58 ± 0.02) − (1.57 ± 0.06)σ m and log k 3 = −(1.49 ± 0.02) − (0.79 ± 0.15)σ P we obtained in acetic acid solution at 30°C varying ring-substituents in the acetanilide complex and styrene, respectively. On the basis of these and previously reporte results the mechanism of the k 3 pathway for acetanilide complexes is discussed.

Olefin π-complex formation and kinetics of oxidative dimerisation in the palladium(II) acetate system

Abstract The kinetics of oxidative dimerisation of styrene to 1,4-diphenyl- 1,3-butadiene in the presence of palladium(II) acetate has been studied in acetic acid containing sodium acetate with reference to the reactivity of various palladium(II) species existent in these conditions. The most reactive species is Pd 3 (OAc) 6 which does not form detectable complexes with styrene. Dimeric species, Na 2 Pd 2 (OAc) 6 , is the next, and, in this case, reaction involves intermediate π-complex formation. The monomeric species, Na 2 Pd(OAc) 4 , is unreactive. Another type of monomeric species, Pd(OAc) 2 (HOAc) 2 , formed at low palladium(II) concentration in the sodium acetate- free system, is also unreactive in oxidation reaction but forms intensively absorbing π-complexes with styrene. The role of π-complexes and reaction mechanism is discussed assuming the rate determining φ-vinyl complex formation, by direct electrophilic substitution.

Reaction of ortho-palladated dimethylbenzylamine with styrene: Unexpected salt effect

Treatment of ortho-palladated complex I with styrene in benzene - acetic acid mixture gives complex IV. The reaction is strongly accelerated in the presence of NaClO4 or LiClO4.

An approach to isoindole skeleton via ortho palladation

Abstract An acid-induced cyclisation of the products of vinylation of ortho palladated NN-dimethylbenzylamines by 3-buten-2-one (II) leads to isoindolinium derivatives (IV) as confirmed by an X-ray structural study.

Initial state and transition state solvation in oxidative dimerization of styrenein the presence of Palladium(II) acetate in various solvents

Abstract Kinetics of oxidative dimerization of styrene to give E,E,-1,4-diphenyl-1,3-butadiene in the presence of palladium(II) acetate has been studied in 12 solvents. In all solvents studied, the reaction obeyed the second order kinetics. Activation parameters (ΔH ≠ , ΔS ≠ , and ΔG ≠ ) were evaluated and isokinetic relationship between ΔH ≠ and ΔS ≠ was established. The trimeric structure of palladium(II) acetate has been supported by spectrophotometric measurements in all solvents except acetonitrile. From the solubility data of palladium(II) acetate its Gibbs free energies of transfer (δμ o Pd ) from heptane (reference solvent) to the respective solvent were calculated. The same values for styrene (δμ o St ) were obtained from the partition constants of styrene between solvents studied and the phase of cross-linked polymer. From δμ o Pd , δμ o St , and δΔ values transfer functions of transition state δμ ≠ were calculated. Correlations of transfer functions of the initial state and the transition state with empirical solvent parameters were examined and used in discussion of a reaction mechanism.

Boric acid effect ont he hydrolysis of 4-nitrophenyl 2,3-dihydroxybenzoate: mimic of borate inhibition of serine proteases

Boric acid inhibits the hydrolysis of deprotonated 4-nitrophenyl 2,3-dihydroxybenzoate which proceeds iwth intramolecular general base assistance. This effect is opposite to previously reported borate catalysis of the hydrolysis of salycilic acid esters and mimics borate inhibition of serine proteases.

Ester hydrolysis catalysed by ortho-palladated aryl oximes

Hydrolysis of 4-nitro- and 2,4-dinitro-phenyl carboxylates proceeds catalytically in the presence of ortho-palladated aryl oximes 4. The catalytic reaction involves two active species, identified as aquated complexes 4 with protonated (kAH path) and deprotonated (kA path) oximate groups, respectively. Both species contain a weakly basic coordinated hydroxide anion manifested in the kAH path. Other cyclopalladated hydroxo complexes 8, lacking an oxime group, are shown to react with 2,4-dinitrophenyl acetate with rate constants ca. ten times greater than those expected from their basicity. The rate constants kA obey a Bronsted correlation (β ca. 1) with the pKa of the coordinated oxime group. In neutral solution, palladated oximes react with esters ca. 103 times faster than the respective free oximes. The O-acyl oxime intermediate undergoes very fast hydrolysis through intramolecular attack by the coordinated hydroxide. Factors ensuring the combination of fast acylation and deacylation steps are discussed with reference to some related systems.