Joan Albert

Cyclometallation reactions of N-(benzylidene)benzylamines with palladium compounds

Abstract The cyclometallation of p-RC6H4CHNCH2C6H2, (R = H, Cl, NO2) by PdX2 (X = Cl, AcO) has been studied. In every case the cyclometallation occurs with formation of a five-membered ring containing the methine group. The structure of these compounds [ PdX( p -RC 6 H 3 CHN CH2C6H5)]2, derived from 1H NMR spectra, are different from those reported previously. Reaction of these compounds with PEt3 gives the compounds [PdX(p-RC6H3CHNCH2C6H5)(PEt3)2] but with an excess of PPh3 only the complexes [ PdX( p -RC 6 H 3 CHN CH2C6H5)(PPh3)] are formed.

Cyclopalladation of the primary amine (R)-(+)-1-(1-naphthyl)ethylamine: a new resolving agent for monodentate phosphines

Abstract The cyclopalladation of the primary amine ( R )-(+)-1-(1-naphthyl)ethylamine, available commercially, is described. The resolution of the monodentate phosphine trans -PPh 2 (2-HOC 6 H 10 ) by means of the dinuclear cyclopalladated derivative is also reported

Cyclometallation of 2-phenylaniline and (R)-α-methylbenzylamine by palladium(II) acetate. X-ray molecular structure of [Pd{2−(2′−NH2C6H4)C6H4}Br(PPh3)]

The action of palladium(II) acetate on the primary amines 2-phenylaniline and (R)-α-methylbenzylamine and subsequent treatment with LiBr allows the preparation of the corresponding cyclopalladated dimers [Pd(CN)Br]2 (1a and 1b respectively). Mononuclear compounds [Pd(CN)Br(L)], 3 (L = py−d5) and 2 (L = PPh3), have ben obtained by reaction of 1 with py-d5 and PPh3. Addition of PPh3 to chloroform solutions of 2 produces a rapid exchange between coordinated and free PPh3. 31P{1H} NMR at variable temperature suggests that this exchange proceeds for 2a through the fast equilibrium [Pd(CN)Br(PPh3)2]⇔[P(CN)Br(PPh3)], while the usual mechanism in substitution reactions in d8 planar square complexes is involved in the case of 2b. The X-ray crystal structure of 2a has been determined. 2a crystallizes in the triclinic space group P1 with a = 12.182(3), b = 10.502(2), c = 9.998(2) A, α = 99.24(2), β = 94.69(2) and γ = 99.13(2)°.

Optically active palladacycles containing imines derived from 1-(1-naphthyl)ethylamine: new resolving agents for P-chiral phosphines

Abstract The synthesis of the new palladium metallacycles containing imines derived from 1-(1-naphthyl)ethylamine is reported. These new organometallic complexes have been used to resolve the P-chiral ligand benzylcyclohexylphenylphosphine. The absolute configuration of ( R C , S P )-[PdCl{2-[HCN-CH(Me)C 10 H 6 ]-3-ClC 6 H 3 }(PBzCyPh)] has been determined by single crystal X-ray analysis.

CHIRAL CYCLOPALLADATED COMPOUNDS FOR ENANTIOMERIC PURITIES OF FUNCTIONALIZED PHOSPHINES BY MEANS OF MULTINUCLEAR NMR

Abstract The application of the cyclopalladated compound [Pd(2-{Z-( R )-CHMeN=CH-2′,6′-Cl 2 C 6 H 3 }C 6 H 4 )Cl] 2 for the enantiomeric excess determination of functionalized phosphines is presented. The X-ray structure determination of diastereomeric complex [Pd(2-{Z-( R )-CHMeN=CH-2′,6′-Cl 2 C 6 H 3 }C 6 H 4 )Cl{( R , R )-PPh 2 (2-OHC 6 H 1 0 )}] is also reported.

Cyclometallation of 3,5 disubstituted N-benzylideneamines by palladium(II). Synthesis and X-ray crystal structure of [Pd(3,5-F2C6H2CHNC6H5)Br(PPh3)2]

Abstract The action of Pd(AcO) 2 on the imines C 6 R m H 5- m CHN(CH 2 ) n C 6 H 5 have been studied. Five-membered endo metallacyles were obtained from the imines 1a (R = 3,5-F 2 , n = 0), 1b (R = 3,5-F 2 , n = 1), 1c (R = 3,5-(MeO) 2 , n = 0) and 1d (R = 3,5-(MeO) 2 , n = 1), by activation of a C(aromatic)-H bond, in spite of the presence of MeO or F substituents on the carbon atom adjacent to the metallation position. 1 H NMR spectra of the acetate bridged compounds [ P d(C-N )(μ- AcO ) 2 ] ( 2a-d ) obtained show the existence of different isomers in solution. Complexes [ P dBr(C-N )( PPh 3 )] ( 4 ) and [PdBr(C-N)(PPh 3 ) 2 ] ( 5 ) can be obtained by the action of PPh 3 on the new cyclometallated compounds. [Pd(3,5-F 2 C 6 H 2 CH=NC 6 H 5 )Br(PPh 3 ) 2 ] crystallizes in the space group P 2 1 a with a = 20.224(4), b = 17.447(3), c = 12.290(2) A, β = 110.12(3)° and Z = 4. The dihedral angle between the metallated phenyl ring and the coordination plane is 86.6°. An N=CH proton and a fluorine atom ortho to the PdC bond occupy the apical positions in the coordination sphere of the palladium atom.

Oxidative addition of arylhalogen bonds of N-benzylidenbenzylamines to palladium(0) compounds

The oxidative addition of imines 2-Cl,6-XC6H3CHNCH2C6H4-2′-Y, (X  H, Cl; Y  Cl, Br) and 4-NO2C6H4CHNCH2C6H4-2′-Br to [Pd(PPh3)4] and [Pd(dba)2] has been studied. endo Cyclometallated compounds are obtained if the carbonhalogen bonds to be activated are the same in both aromatic rings, and the exo derivatives are obtained only if the benzylic phenyl ring contains an ortho-CBr bond. The activation of the stronger CCl bond, with formation of an endocyclic compound, takes place in preference to that of the weaker CBr bond when the imine 2,6-Cl2C6H3CHNCH2C6H4-2′-Br reacts with [Pd(PPh3)4].

Catalytic C–H Activation of Phenylethylamines or Benzylamines and Their Annulation with Allenes

Tetrahydro-3-benzazepines and tetrahydroisoquinolines are synthesized in one step from allenes and phenylethylamines or benzylamines, respectively. Mechanistically, it is assumed that activation of a C-H bond of an aromatic ring with Pd(II) occurs, directed by the primary amine, leading to the formation of a palladacycle into which an allene then undergoes insertion. The resulting π-allyl intermediate cyclizes to the products by an intramolecular allylic alkylation. The process is particularly useful with 2,3-butadienoates and amines having a quaternary carbon at the α-position.

STERIC AND ELECTRONIC EFFECTS ON E/Z COMPOSITION OF EXOCYCLIC CYCLOPALLADATED N-BENZYLIDENEAMINES

Exocyclic six-membered cyclopalladated dimers 2a-2c, Figure options Download full-size image Download as PowerPoint slide , have been prepared by reaction of palladium(II) acetate with N-benzylidene-2-phenylanilines 1a-1c, RCH=NC6H4-2-C6H5 {1a, R = 2,6-Cl2C6H3; 1b, R = 2,6-F2C6H3 and 1c, R = 2,4,6-(CH3O)3C6H2}, and a subsequent metathesis reaction with LiBr. Reaction of 2 with PPh3 produced mononuclear compounds 3, Figure options Download full-size image Download as PowerPoint slide . Analysis of the 1H NMR methinic region of 2 and 3 revealed their E/Z composition. 2a and 2b present imines in E and Z configuration in an approximate ratio of 1:1, white 2c consists almost exclusively of imines in E configuration. Compounds 3 also present imines in E and Z configuration, the former are more abundant in all cases (≥ 4:1). The crystal structure of 3c with the imine in E configuration has been determined. It crystallizes in the monoclinic space group P21/a with a = 19,258(3) A, b = 13.177(2) A, c = 14.660(2) A and β = 113.78(2)°. Steric and electronic effects on the E/Z composition of 2 and 3 and related exocyclic cyclopalladated N-benzylidenebenzylamines suggest that, for compounds of this type, the E → Z isomerization takes place via a rotation through the N=C bond which is assisted by π back bonding of the palladium(II) center to the iminic function.

Synthesis and resolution of benzylisopropylphenylphosphine, a monodentate P-chiral ligand

Abstract The synthesis of benzylisopropylphenylphosphine by reaction between the benzylphenylphosphide anion and isopropyl chloride and its subsequent resolution by means of an optically active palladium metallacycle is reported. The synthesis of the organometallic complex [Pd(η 3 -2-MeC 3 H 4 )Cl(PBn i PrPh)] is also described, as well as the assignment of the absolute configuration of the coordinated phosphine by mono- and bidimensional proton NMR spectra, using the homochiral palladacycle as a reference point. In order to estimate the height of the energy barrier corresponding to the rotation of the phosphine ligand around the PdP bond, several calculations were performed at the semiempirical PM3(tm) level.