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Diastereomerism in palladium(II) allyl complexes of P,P-, P,S- and S,S-donor ligands, Ph2P(E)N(R)P(E?)Ph2 [R/CHMe2 or (S)- *CHMePh; E/E?/lone pair or S]: solution behaviour, X-ray crystal structure and catalytic allylic alkylation reactions

Mandal, Swadhin K and Nagana Gowda, GA and Krishnamurthy, Setharampattu S and Zheng, Chong and Li, Shoujian and Hosmane, Narayan S (2003) Diastereomerism in palladium(II) allyl complexes of P,P-, P,S- and S,S-donor ligands, Ph2P(E)N(R)P(E?)Ph2 [R/CHMe2 or (S)- *CHMePh; E/E?/lone pair or S]: solution behaviour, X-ray crystal structure and catalytic allylic alkylation reactions. In: Journal of Organometallic Chemistry, 676 (1-2). pp. 22-37.

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Abstract

The reactions of achiral homodonor diphosphazane ligands, Ph2P(E)N(CHMe2)P(E')Ph-2[E = E' = lone pair (1) or S (2)] with the chloro bridged palladium dimers, [Pd(eta(3)-1,3m R'-R"-C3H3)(mu-Cl)](2) (R', R" = H, Me or Ph) in the presence of NH4PF6 give cationic eta(3)-allyl palladium complexes, [Pd(eta(3)-1 3-R'-R"-C3H3)(L-L')]. Each of these complexes exists as single species in solution except the 1,3-dimethyl allyl complex, which exists as two isomers (syn/syn- and syn/anti-) in solution. Analogous allyl palladium complexes derived from the chiral homodonor diphosphazane ligand, Ph2PN((S)-*CHMePh)PPh2 (3) exist as a single species when the allyl moiety is symmetrical (R' = R" = H or Ph) but a 1:1 mixture of two different face-coordinated diastereomers if the allyl moiety is unsymmetrically substituted (R' not equal R"). The 1,3-dimethyl-allyl complex, [Pd(eta(3)-1,3-Me-2-C3H3 {Ph2PN((S)-*CHMePh)PPh2-k(2)P,P}]PF6 (20) exists as a mixture of two isomers. The major isomer (20a) has the syn/syn-allylic arrangement while the minor isomer (20b) has the syn/anti configuration. These isomers (20a and 20b) equilibrate in solution via a syn-anti isomerisation pathway. Achiral and chiral heterodonor monosulphide ligands, Ph2P(S)N(R)PPh2 [R = CHMe2 (4), (S)-*CHMePh(5)] give rise to allyl palladium complexes which exist as several isomers in solution. The presence of a chiral centre in the ligand 5 enables the observation of two NMR distinguishable face-coordinated diastereomers for its allyl complexes. However, the solid state structure of [Pd(eta(3)-C3H5){Ph2P(S)N((S)-*CHMePh)PPh2-k(2)P,S}]PF6 (27) shows the presence of only one diastereomer. Two-dimensional (2D) phase sensitive H-1-H-1 NOESY and ROESY measurements indicate that the monosulphide complexes undergo exchange by the opening of the eta(3)-allyl group selectively at the trans position with respect to the greater pi-acceptor phosphorus centre to generate a eta(1)-bonded intermediate. Preliminary studies on the use of the ligands 1-5 for catalytic allylic alkylation reactions of an unsymmetrically substituted substrate, (E)-1-phenyl-2-propenyl-acetate are reported.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Elsevier Science.
Keywords: Palladium;Allyl complexes;P ligands;S ligands;Stereodynamics by NMR spectroscopy;Allylic alkylation.
Department/Centre: Division of Chemical Sciences > Sophisticated Instruments Facility
Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited: 18 May 2009 05:43
Last Modified: 08 Jan 2013 06:06
URI: http://eprints.iisc.ernet.in/id/eprint/16779

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