Valery V. Dunina

ortho-palladated α-phenylalkylamines for enantiomeric purity determination of monodentate P∗-chiral phosphines

Abstract Three ortho-palladated complexes were tested as chiral derivatizing agents for enantiomeric excess determination of monodentate P∗-chiral phosphines by 31P NMR analysis. The complexes containing a bulky substituent at the α-C∗- 1e or an N∗-stereocentre 1d are shown to be more efficient as compared to known N-achiral α-methyl substituted analogues. The structure and stereochemistry of the new dimeric complex (S C )- 1 e was established by X-ray analysis.

A RESOLUTION OF THE MONODENTATE P*-CHIRAL PHOSPHINE PBUTC6H4BR-4 AND ITS NMR-DEDUCED ABSOLUTE CONFIGURATION

Abstract Both enantiomers of the monodentate phosphine PBu t C 6 H 4 Br-4 were obtained in an enantiopure state by chromatographic separation of their diastereomeric adducts with a new homochiral ortho -palladated resolving agent derived from α- tert -Bu-substituted tertiary benzylamine. The conformation of the palladacycle and the absolute configuration of the phosphine were determined using 1 H NMR spectroscopy (including NOE technique) and confirmed by an X-ray diffraction study of both diastereomeric complexes. The enantiomers of the resolved phosphine were displaced from the individual diastereomers of the palladium(II) complexes with recovery of the starting resolving agent, and trapped in the form of binuclear coordination complexes of palladium(II).

Steric Promotion of Aromatic C–H Bond Activation in Primary Benzylamines

ortho-Palladation of a sterically crowded primary benzylamine, α-phenylneopentylamine, was accomplished in a moderate yield of 50% in the reaction with the weakest of palladation agents (Li2PdCl4) under very mild conditions, due to a steric promotion of an aromatic C–H bond activation. The structure of dimer 1a thus formed and the palladacycle conformation were established on the basis of 1H-NMR spectroscopy of its mononuclear derivatives with [D5]pyridine (3a) and triphenylphosphane (4a), and an X-ray investi-gation of the latter.

A resolution of monodentate P*-chiral phosphine

Abstract The monodentate phosphine PMeBu t Ph is obtained in enantiopure form by using a new N ∗ -chiral ortho-palladated resolving agent; some advantages of the latter over its N-achiral analogue are shown. The conditions of resolved phosphine displacement from individual diastereomers of palladium(II) complexes are elaborated which allow the starting resolving agent to be recovered.

Enantiomeric discrimination in the complexation of ortho-palladated α-arylalkylamines with the racemic tert-Butylmethylphenylphosphine

Abstract A high degree of diastereoselectivity was achieved in the coordination of monodentate phosphine PMeBu t Ph with dimeric chloro-bridged ortho-palladated complexes in solution due to the modification of the stereoselector structure, namely by the creation of asymmetry in the environment of nitrogen donor atom and by the fitting of substituents sizes in the palladacycle. The stereochemistry of complexation is discussed in the terms of equilibrium constants between two diastereomers of monophosphine complexes estimated from the 31 P NMR data.

First enantiopure phosphapalladacycle with planar chirality. X-Ray study of the racemic dimer and (Spl,SCSN)-diastereomer of its prolinate derivative

Abstract The first P , C -cyclopalladated complex with planar chirality was prepared by direct cyclopalladation of prochiral di- tert -butyl(ferrocenylmethyl)phosphine. Resolution of the racemic dimer was achieved through separation of its diastereomeric ( S )-prolinate derivatives. The palladacycle structure was confirmed by the 1 H NMR spectra of the dimer and its triphenylphosphine adduct and an X-ray diffraction study of the racemic dimeric complex. The absolute configuration of the planar chirality was determined by an X-ray diffraction investigation of one of two diastereomers of the ( S )-prolinate derivative.

Direct ortho -palladation of 2-phenyl-2-oxazoline: Crystal structure of Cl2Pd(OCH2CH2NCPh)2 and Cl(PPh3)Pd(OCH2CH2NCC6H4)

Direct ortho -palladation of sterically non-hindered 2-phenyl-2-oxazoline ( 1 ) using Pd(OAc) 2 and AcONa in AcOH provided di-μ-acetatobis-[2-(2-oxazolinyl)phenyl,1-C,3-N]dipalladium(II) ( 3a ) in a yield of 63%. Dimeric complex 3a was converted into the corresponding μ-chloro analog ( 3b ) by the reaction with LiCl in acetone in quantitative yield. Compound 3b was also obtained in 90% yield by the ligand exchange reaction of oxazoline ( 1 ) with dimeric ortho -palladated complex of N , N -dimethylbenzylamine in a AcOH–CHCl 3 mixture at 50°C. The same reaction at room temperature provided the coordination complex dichlorobis-(2-phenyl-2-oxazoline)palladium(II) ( 2 ); the use of toluene in this reaction (50°C) led to the formation of chloro[ N , N -dimethylbenzylamino]-(2-phenyl-2-oxazoline)palladium(II) ( 5 ). Dimer 3b reacted with 2,4-pentadionate and PPh 3 to yield the corresponding mononuclear derivatives 6 and 7 , respectively. The structures of coordination complex 2 and phosphane adduct 7 were confirmed by X-ray diffraction analysis. Compound 2 has a centrosymmetric structure with strictly planar coordination environment of the palladium center and a close above-plane approach of the ortho -CH bond to the metal center. In adduct 7 , both the palladium coordination sphere and palladacycle are nearly planar.

P*-Chiral phosphapalladacycle as derivatizing agent for enantiomeric purity determination of α-amino acids by means of 31P NMR spectroscopy

Abstract A P*-chiral cyclopalladated complex was shown to be an efficient chiral derivatizing agent for enantiomeric excess determination of α-amino acids by 31 P NMR technique. The main advantages of this type of reagent are discussed.

Asymmetric exchange of cyclopalladated ligands with a high level of asymmetric induction: a new route to optically active phosphapalladacycles

Abstract The first example of an asymmetric CH bond activation with chirality transfer (up to 91% ee) from an enantiopure CN -palladacycle is described. This asymmetric version of cyclopalladated ligand exchange was elaborated in an aprotic medium using prochiral phosphines as substrates and an enantiopure benzylaminate palladacycle bearing a primary amino group and a bulky tert -Bu substituent on the side chain as the palladation agent.

Competition between sp3 and sp2 CH bonds in cyclopalladation of N-methyl-α-tert-butylbenzylamine

Intramolecular palladation of the (sp 3 )CH bond of a tert-butyl group of N-methyl-a-tert-butylbenzylamine can be achieved in competition with (sp 2 )CH bond activation where both possible reactions are equally suitable for five-membered palladacycle formation. Activation of the (sp 3 )CH bond occurs with PdCl4 2 assisted by a secondary amino group as a heterodonor center in a benzylamine ligand; regioselective activation of the (sp 2 )CH bond was achieved with PdI4 2 . To compare, cyclopalladation of the related tertiary amine occurs regioselectively to give ortho-palladated complex as the sole product. The structure of both regioisomeric complexes was confirmed by an X-ray study of their triphenylphosphine adducts. The conformational features of the two five-membered palladacycles is discussed on the base of the 1 H-NMR and X-ray data.