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η 5 ‐P‐ or η 4 ‐P‐Coordination in apically oxygenated phosphoranes? An ab initio study of PH 4 O − , PH 4 O − · E (E = Li + , NH 4 + , and HF) and related fluorinated oxyphosphoranes
Author(s) -
Glaser Rainer,
Streitwieser Andrew
Publication year - 1990
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.540110211
Subject(s) - chemistry , phosphorane , substituent , ab initio , basis set , nucleophile , crystallography , computational chemistry , molecular orbital , phosphine oxide , density functional theory , yield (engineering) , phosphine , stereochemistry , molecule , materials science , organic chemistry , metallurgy , catalysis , biochemistry
Structural optimizations of the apically substituted isomer of PH 4 O − and the diapically substituted isomer of PH 3 FO − with diffuse‐function augmented 3–21G* basis sets and with the 6–31 + G* and 6–31 + + G* basis sets result in P‐η 4 ‐coordination in these anions. The structures obtained are those of a hydride or fluoride ion “solvated” by or complexed with phosphine oxide, rather than phosphoranes. In contrast, 3–21G* basis sets without diffuse functions on the atom in the trans ‐apical position with regard to the oxy‐substituent yield P‐η 5 ‐phosphorane structures that appear to be computational artifacts of the small basis set; the formation of the P‐η 4 ‐geometries is curtailed by the insufficient functional description of the potential trans ‐apical nucleophilic leaving group. The overall neutral apical isomers of PH 4 O − · E(E = Li + , NH 4 + ), the diapical isomer of PH 3 FO − Li + , as well as the model‐solvated apical isomer of PH 4 O − · HF favor P‐η 5 ‐phosphorane geometries at all of these computational levels. The mechanism by which the E‐group alters the electronic structures within PH 4 O a − is discussed based on the geometries, the molecular orbitals, and electron density analysis techniques.