Synthesis, crystal structures and quantum chemical calculations of novel phosphonium salt-1, 5-diphospha-3-phosphonia-tricyclo pentane cations

10^TH ANNUAL Chemistry & Mass Spectrometry Congress

OCTOBER 18-19, 2017 OSAKA, JAPAN

Mutasem Z Bani-Fwaz and Ahmed E Fazary

King Khalid University, KSA

Posters & Accepted Abstracts: Chem Sci J

Abstract :

This work deals with reactions between the kinetically stable 2-tert-butyl-1�»3-phospha-alkyne, tBu C=P, and various halodiorganylphosphines (X=Cl, Br). The isolated ionic salts with the 2, 4-di-tert-butyl-3, 3-diorganyl-1�»3, 5�»3-diphospha3-phosphonia-tricyclo [2.1.0.02,5]-pentane cations, [R2C2tBu2P3]ï�� (R=ethyl, isopropyl, methyl, phenyl), were characterized by spectroscopic methods; additionally, the results of X-ray structure analyses were confirmed by quantum chemical calculations which were performed on the hydrogen substituted phosphonium and phosphenium cations. As for the phosphonium cation ([H2P(CH)2P2]ï��) generated from our work the conventional trigonal bipyramidal framework of point group C2v represents the absolute minimum on the potential energy surface. To our surprise this situation is followed by a second one which has to be attributed to the so-called housene structure of point group C1 showing a somewhat higher energy value +77.9 kJ/mol. Quite a reverse situation is encountered for the phosphenium cation [P(CH)2P2]ï��. Here the pseudo square-based pyramidal nido structure of point group C2v known from Russellâ��s tetrachloroaluminate(III) compound is found to be the only minimum on the potential energy surface. A phosphenium cation with a trigonal bipyramidal framework of point group C2v is higher in energy only by 35.7 kJ/mol but due to one imaginary frequency it has to be considered the structure of a transition state. The opened housene structure corresponds neither to a minimum nor to a saddle point on the potential energy surface. In the pseudo square-based pyramidal nido structure (point group C2v) of the phosphenium cation [P(CH)2P2]ï�� the s-orbital and all p-orbitals of the apical four-coordinate phosphorus atom are used to form two P-C and two P-P bonds. Further addition of two hydrogen atoms to entail the phosphonium cation [H2P(CH)2P2]ï�� of point group symmetry C2 not only increases the coordination number of the apical phosphorus atom to six but also requires two electrons and two orbitals for P-H bonding. banifawaz@yahoo.com