591231-63-9Relevant academic research and scientific papers
Palladium(II) allyl complexes of chiral diphosphazane ligands: ambident coordination behaviour and stereodynamic studies in solution
Mandal, Swadhin K.,Gowda, G. A. Nagana,Krishnamurthy, Setharmapattu S.,Nethaji, Munirathinam
, p. 1016 - 1027 (2007/10/03)
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.
