η⁵-P- or η⁴-P-Coordination in Apically Oxygenated Phosphoranes? An Ab Initio Study of PH₄Oˉ, PH₄Oˉ · E (E = Li⁺, NH₄⁺, and HF) and Related Fluorinated Oxyphosphoranes


Structural optimizations of the apically substituted isomer of PH4O- and the diapically substituted isomer of PH3FO- with diffuse-function augmented 3-21G* basis sets and with the 6-31 + G* and 6-31 + + G* basis sets result in P-η4-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-η5-phosphorane structures that appear to be computational artifacts of the small basis set; the formation of the P-η4-geometries is curtailed by the insufficient functional description of the potential trans-apical nucleophilic leaving group. The overall neutral apical isomers of PH4O- · E(E = Li+, NH4+), the diapical isomer of PH3FO-Li+, as well as the model-solvated apical isomer of PH4O- · HF favor P-η5-phosphorane geometries at all of these computational levels. The mechanism by which the E-group alters the electronic structures within PH4Oα- is discussed based on the geometries, the molecular orbitals, and electron density analysis techniques.



International Standard Serial Number (ISSN)

0192-8651; 1096-987X

Document Type

Article - Journal

Document Version


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© 1990 Wiley-Blackwell, All rights reserved.

Publication Date

01 Mar 1990