Allylpalladium(II) complexes with aminophosphane ligands:: Solution behaviour and X-ray structure of cis-[Pd(η3-CH2CHCHPh){Ph2PCH2CHPhNH(2,6-C6H3iPr2)}][PF6]

A new beta-aminophosphane L-2 [Ph2PCH2CH(Ph)NH(2,6-C(6)H(3)iPr(2))], bearing an asymmetric carbon atom and a vicinal prochiral nitrogen centre and (eta(3)-allyl)palladium complexes of general formula [Pd(eta(3)-C3H4R){eta(2)-Ph2PCH2CH-(Ph)NHAr}][PF6] (1-6) (R = H, Me or Ph and Ar = Ph or 2,6-C(6)H(3)iPr(2)) have been synthesised. NMR spectroscopic studies and a crystal structure analysis of complex 6 (R = Ph, Ar = 2,6-C(6)H(3)iPr(2)) confirmed the highly diastereoselective coordination of the nitrogen atom. Because of the allyl fluxionality and the presence of asymmetric centres, all the complexes exist in solution as mixtures of up to four diastereomers. For the monosubstituted allyl complexes [Pd(eta(3)-C3H4R){Ph2PCH2CH(Ph)NHAr}][PF6] (3-6, R = Me or Ph) only cis/trans-P and endo/exo isomers with syn-oriented allyl substituents have been observed in solution. The diastereomeric distribution is subject to a steric control since a modification of the steric bulk of the allyl substituents and/or N-aryl groups strongly affect the isomers ratio. An X-ray diffraction study of compound 6 reveals a mixture of endo and exo cis-P syn isomers and corresponds to the first cis-P isomer crystal structure for an N,P-ligand allyl complex. A phase-sensitive 2-D NOESY NMR analysis showed that complex I undergoes a selective syn-anti exchange isomerisation, involving exclusively a trans-P opening of the eta(3)-allyl moiety. Therefore, eta(3)-eta(1)- eta(3) rearrangements in allylic complexes 1-6 were assumed to occur via the regioselective formation of a sigma-allyl intermediate. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).