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.
Résumé / Abstract
The chemistry of η3
-allyl palladium complexes of pyrazolyl substituted diphosphazane ligands, Ph2
-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
) [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
)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 1
H 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 TitleDalton transactions
Source / Source
5, pp. 1016-1027 [12 page(s) (article)]
Langue / Language
Editeur / Publisher
Royal Society of Chemistry, Cambridge, ROYAUME-UNI
Localisation / Location
INIST-CNRS, Cote INIST : 130 A, 35400011240794.0380
Nº notice refdoc (ud4) : 15127076