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

Mandal, Swadhin K and Nagana Gowda, GA and Krishnamurthy, Setharampattu S and Nethaji, Munirathinam (2003) Palladium(II) allyl complexes of chiral diphosphazane ligands: ambident coordination behaviour and stereodynamic studies in solution. In: Dalton Transactions (5). pp. 1016-1027.

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Abstract

The chemistry of eta(3)-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(eta(3)-1,3-R'(2)-C3H3){kappa(2)-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(eta(3)-1,3-Ph-2-C3H3 {kappa(2)-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 H-1-H-1 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 eta(1)-intermediate formed by the opening of the eta(3)-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.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to The Royal Society of Chemistry.
Department/Centre: Division of Chemical Sciences > Sophisticated Instruments Facility
Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited: 29 Oct 2009 08:49
Last Modified: 19 Sep 2010 04:55
URI: http://eprints.iisc.ernet.in/id/eprint/17212

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