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Computational Studies on Azaphosphiridines, or How to Effect Ring‐Opening Processes through Selective Bond Activation
Author(s) -
Espinosa Arturo,
Streubel Rainer
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201002565
Subject(s) - chemistry , isomerization , ring strain , protonation , ring (chemistry) , bond cleavage , kinetics , medicinal chemistry , valence (chemistry) , stereochemistry , crystallography , catalysis , ion , biochemistry , physics , organic chemistry , quantum mechanics
The relative energies of azaphosphiridine and its isomers, the ring stability towards valence isomerization, and the ring strain, as well as the kinetics and thermodynamics of possible ring‐opening reactions of P III derivatives ( 1 – 5 ) and P V chalcogenides ( 6 – 9 ; O to Te), were studied at high levels of theory (up to CCSD(T)). The barrier to inversion at the nitrogen atom in the trimethyl‐substituted P III derivative 5 increases from 12.11 to 15.25 kcal mol −1 in the P‐ oxide derivative 6 (P V ); the relatively high barrier to inversion at the phosphorus in 5 (75.38 kcal mol −1 ) points to a configurationally stable center (MP2/def2‐TZVPP//BP86/def2‐TZVP). The ring strain for azaphosphiridine 5 (av. 22.6 kcal mol −1 ) was found to increase upon P ‐ oxidation ( 6 ) (30.8 kcal mol −1 ; same level of theory). Various ring‐bond‐activation processes were studied: N‐protonation of P III ( 5 ) and P V ( 6 , 7 ) derivatives leads to highly activated species that readily undergo PN bond cleavage. In contrast, metal chlorides such as LiCl, CuCl, CuCl 2 , BeCl 2 , BCl 3 , AlCl 3 , TiCl 3 , and TiCl 4 show little PN bond activation in 5 and 7 . Remarkably, TiCl 3 selectively activates the CN bond, and induces stronger bond activation for P V ( 6, 7 ) than for P III azaphosphiridines ( 5 ). The ring‐expanding rearrangement of P V azaphosphiridines 6 – 9 to yield P III 1,3,2‐chalcogena‐azaphosphetidines 32 a – d is predicted to be preferred for the heavier chalcogenides 7 – 9 , but not for the P‐ oxide 6 . The first comparative analysis of three bond strength parameters is presented: 1) the electron density at bond critical points, 2) Wiberg’s bond index, and 3) the relaxed force constant. This reveals the usefulness of these parameters in assessing the degree of ring bond activation.