Quasi Harmonic Lattice Dynamics and Molecular Dynamics calculations for the Lennard-Jones solids

We present Molecular Dynamics (MD), Quasi Harmonic Lattice Dynamics (QHLD) and Energy Minimization (EM) calculations for the crystal structure of Ne, Ar, Kr and Xe as a function of pressure and temperature. New Lennard-Jones (LJ) parameters are obtained for Ne, Kr and Xe to reproduce the experimental pressure dependence of the density. We employ a simple method which combines results of QHLD and MD calculations to achieve densities in good agreement with experiment from 0 K to melting. Melting is discussed in connection with intrinsic instability of the solid as given by the QHLD approximation. (See http://www.fci.unibo.it/~valle for related papers)Comment: 7 pages, 5 figures, REVte

Cleavage of P=O in the Presence of P-N: Aminophosphine Oxide Reduction with In Situ Boronation of the PIII Product

In contrast to tertiary phosphine oxides, the deoxygenation of aminophosphine oxides is effectively impossible due to the need to break the immensely strong and inert PO bond in the presence of a relatively weak and more reactive PN bond. This long-standing problem in organophosphorus synthesis is solved by use of oxalyl chloride, which chemoselectively cleaves the PO bond forming a chlorophosphonium salt, leaving the PN bond(s) intact. Subsequent reduction of the chlorophosphonium salt with sodium borohydride forms the PIII aminophosphine borane adduct. This simple one-pot procedure was applied with good yields for a wide range of PN-containing phosphoryl compounds. The borane product can be easily deprotected to produce the free PIII aminophosphine. Along with no observed PN bond cleavage, the use of sodium borohydride also permits the presence of ester functional groups in the substrate. The availability of this methodology opens up previously unavailable synthetic options in organophosphorus chemistry, two of which are exemplified.AM

Asymmetric synthesis of a tertiary arsine by nucleophilic addition to a chiral phosphine-stabilized arsenium salt

A new method for the asymmetric synthesis of As-chiral tertiary arsines is described. The addition at -95 °C of n-butyllithium to a dichloromethane solution of a phosphine-stabilized arsenium salt of the type (±)-[R P→AsMePh]PF, where RP is an enantiomerically pure, atropisomeric phosphepine derived from lithiated (aR)-2,2'-dimethyl-1,1'-binaphthalene, furnishes (S)-(+)-(n-butyl) methylphenylarsine in 85% enantioselectivity (70% enantiomeric excess) with displacement of the (aR)-phosphepine. The enantioselectivity of the synthesis is lower than the diastereoselectivity of coordination of the (aR )-phosphepine to the prochiral, six-electron methylphenylarsenium ion with which it is in equilibrium in solution by P-As bond dissociation, 94% diastereomeric excess, as determined by NMR spectroscopy at -95 °C. The excess of the S enantiomer of the arsine, however, is consistent with the S 2 mechanism proposed for the reaction and the solution and solid-state structures of the predominant diastereomer of the phosphepine-arsenium complex. A feature of the design of the phosphepine auxiliary is the attachment of a 2-(methoxymethyl)phenyl substituent at phosphorus, the oxygen of which interacts with the arsenic of the arsenium ion, in solution and in the solid state, and facilitates Stereodifferentiation by the chiral phosphepine of the enantiotopic faces of the prochiral, six-electron methylphenylarsenium ion; the significance of this anchimeric interaction is borne out by DFT calculations on a closely related model complex