Titre du document / Document title

Palladium(II) allyl complexes of chiral diphosphazane ligands: ambident coordination behaviour and stereodynamic studies in solution

Auteur(s) / Author(s)

MANDAL Swadhin K. ; NAGANA GOWDA G. A. ; KRISHNAMURTHY Setharampattu S. ; NETHAJI Munirathinam ;

Résumé / Abstract

The chemistry of η₃-allyl palladium complexes of pyrazolyl substituted diphosphazane ligands, Ph²P(E)N(R)-PPh(N²C³HMe²-3,5) [E = lone pair, R = CHMe² (1); E = lone pair, R = (S)-*CHMePh (2); E = S, R = CHMe² (3)] bearing a stereogenic phosphorus centre has been investigated and the complexes, [Pd(η₃-1,3-R'²-C³H³){κ₂-Ph²P(E)-N(R)PPh(N2C3HMe2-3,5)}](PF⁶) [E = lone pair or sulfur; R = CHMe² or (S)-*CHMePh; R' = H, Me or Ph; 4-13], have been isolated. Detailed NMR studies reveal that these complexes exist as a mixture of isomers in solution. The structures of four complexes have been determined by X-ray crystallography and only one isomer is observed in the solid state in each case. The allyl complexes formed by ligands 1 and 2 display a P,N-coordination mode except the 1,3-diphenyl allyl complex, [Pd(η₃-1,3-Ph²-C³H³){κ₂-Ph²PN(CHMe²)PPh(N2C3HMe2-3,5)}](PF6) (8), which shows the presence of both P,N- and P,P-coordinated isomers in solution with the former predominating. On the other hand, the complexes bearing the diphosphazane monosulfide ligand 3 display P,S-coordination. Two-dimensional phase sensitive ₁H-₁H NOESY and ROESY measurements indicate that several of the above allyl palladium complexes undergo syn-anti and/or cis-trans isomerization in solution through an η₁-intermediate formed by the opening of the η₃-allyl group selectively at the trans position with respect to the phosphorus centre. Preliminary investigations show that the diphosphazanes (1 and (SR)-2) function as efficient auxiliary ligands for catalytic allylic alkylation reactions but lead to only low levels of enantiomeric excess.

Revue / Journal Title

Dalton transactions    ISSN  1477-9226 

Source / Source

2003, n^o5, pp. 1016-1027 [12 page(s) (article)]

Langue / Language

Anglais

Editeur / Publisher

Royal Society of Chemistry, Cambridge, ROYAUME-UNI  (2003) (Revue)

Localisation / Location

INIST-CNRS, Cote INIST : 130 A, 35400011240794.0380