Configurationally stable asymmetric nitrogen atom in the palladium(II) aminophosphine complex

Abstract

The synthesis of a new optically active aminophosphine ligand i-Pramphos, containing a potentially stereogenic nitrogen atom, from (S)-N-isopropyl-N-methyl-~-methylbenzylamine is described; its complex with palladium(u) chloride was obtained. NMR spectroscopy revealed that the coordination of the arninophosphine with the metal resulted in stereospecific locking of the donor nitrogen atom in only one of two possible configurations.

New principle for palladacycle resolution: diastereoselective monomer to dimer conversion

“…The published examples include routes via diastereomeric derivatives with (S)-a-methylbenzylamine 32 (monodentate N-donor) and (R)-phenylglycinate, 30 (S)-leucinate 31 or (S)-prolinate 33,44 (bidentate N,O-donors) as auxiliary ligands. To our knowledge, before our first report on this subject 44 neither decomposition of such complexes on sorbent nor stereochemistry of this process had been discussed.…”

“…[29][30][31][32][33] The new methodology described here is based on the difference in stability of two diastereomeric palladacycles relative to the achiral sorbent (here it is silica). In order for this technique to be put to practical use, we have to estimate the conditions of its applicability.…”

“…To the best of our knowledge, only two properties of diastereomeric derivatives of palladacycles have been used to date for the separation of their enantiomers: a difference in the solubility of two diastereomers [15][16][17][18][19][20][21][22][23][24][25][26][27][28]47 or in their chromatographic mobility. [29][30][31][32][33] The new methodology described here is based on the difference in stability of two diastereomeric palladacycles relative to the achiral sorbent (here it is silica).…”

“…12,22 From Newman projections of palladacycles along the N-C a bond ( Fig. 1) it becomes clear that in the case of its k(S C )-or d(R C )-stereochemistry spin-spin coupling of a-methine proton will be possible only with one of two NH-protons, while in the case of alternative k(R C )-or d(S C )-conformations efficiency of a-CH interaction with both NH 2 protons will be expected as very similar (as the result of equivalence of the corresponding torsion angles $30°and $150°in the terms of the Carplus-Konroy equation 45 ).…”

“…Two main approaches to enantiomerically pure palladacycles are commonly used: (i) synthesis from optically active ligands (commercially available, 1-8 pre-resolved [9][10][11][12][13] or prepared by asymmetric synthesis 14 ); and (ii) resolution of racemic cyclopalladated compounds by recrystallization [15][16][17][18][19][20][21][22][23][24][25][26][27][28] or chromatographic separation [29][30][31][32][33] of their diastereomeric derivatives. The third method based on the asymmetric activation of the C-H bond under control of an optically active base [34][35][36][37][38][39] or ligand in the palladation agent [40][41][42] is not so popular and used mainly for prochiral substrates.…”