Abstract
Synthesis and structural details of enantiomerically pure alkaline earth metal complexes (Mg, Ca, Sr, Ba) supported by chiral phosphinoselenoic amides are reported.
Highlights
Efficient synthesis of optically active compounds is one of the most important tasks of synthetic organic chemistry
We introduced various amidophosphine chalcogenide and borane ligands with P, N, E (E 1⁄4 O, S, Se, BH3) as donor atoms, into alkaline earth metal chemistry to study their coordination properties.[13]. These unique ligands are potentially capable of coordinating through the hard nitrogen and phosphorus donor atoms as well as the so E donor atom. Bearing these characteristic features in mind, as well as our continuing interest in highly electropositive alkaline earth metals, catalytic activity and the vast potential of the eld in asymmetric synthesis, we proposed to synthesise various novel chiral alkaline earth metal complexes stabilised by chiral amidophosphine selenoids and boranes, to explore the chemistry of alkaline earth metals in asymmetric synthesis
Chiral phosphinoselenoic amide ligands The chiral phosphinoselenoic amides {HN(R-*CHMePh)(Ph2P(Se))} (1a) and {HN(S-*CHMePh)(Ph2P(Se))} (1b) were prepared in enantiomeric pure forms in a similar method as analogous [Ph2P(Se)NHCHPh2] and [Ph2P(Se)NHCPh3] were prepared, that is, they were synthesised in quantitative yield by the treatment of pure 1,1-diphenyl-N-(1-phenylethyl)phosphinamines {HN(R-*CHMePh)(Ph2P)} and {HN(S-*CHMePh)(Ph2P)} with slight excess elemental selenium in 1 : 1.2 molar ratio at ambient temperature in THF solvent.13c,17 Both the enantiomeric pure compounds 1a and 1b were characterised using standard 1H, 13C{1H}, 31P{1H} NMR spectra, combustion analysis and the solid-state structures were established using single-crystal X-ray diffraction analysis
Summary
A wide variety of chiral phosphorus ligands have been prepared over the years, and their coordination chemistry with various metal ions has been studied extensively.[11]. To achieve our target compounds with high-purity and good yield, we chose chiral phosphineamines HN(R-*CHMePh)(PPh2) and HN(S-*CHMePh)(PPh2), which were originally introduced by Brunner into coordination chemistry of the late transition metals.[14] Roesky et al introduced the same ligands into zirconium chemistry,[15] group 3 and lanthanide chemistry.[16] We synthesise the corresponding enantiomeric pure amidophosphine-selenoids [HN(R-*CHMePh)P(Se)Ph2] (1a) and [HN(S-*CHMePh)P(Se)Ph2] (1b) in order to introduce them into the alkaline earth metal chemistry We envisage that these ligands potentially coordinate through the amido nitrogen and selenium atoms, forming a four-membered metallacycle with a centre metal ion. The details of the ring-opening polymerisation of 3-caprolactone using complexes 5 and 6 are presented
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