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Probing steric influences on electrophilic phosphonium cations: a comparison of [(3,5-(CF3)2C6H3)3PF]+ and [(C6F5)3PF]+Electronic supplementary information (ESI) available: Spectral data. CCDC 1851570 and 1851571. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c8dt02594k
The electrophilic phosphonium cation (EPC) salt [(3,5-(CF 3 ) 2 C 6 H 3 ) 3 PF][B(C 6 F 5 ) 4 ] ( 2 ) is prepared via oxidation of the precursor phosphine with XeF 2 and subsequent abstraction of fluoride with [Et 3 Si(tol)][B(C 6 F 5 ) 4 ]. The Lewis acidity of 2 is evaluated by experimental and co...
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| Main Authors: | , , , , , |
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| Format: | Article |
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| Summary: | The electrophilic phosphonium cation (EPC) salt [(3,5-(CF
3
)
2
C
6
H
3
)
3
PF][B(C
6
F
5
)
4
] (
2
) is prepared
via
oxidation of the precursor phosphine with XeF
2
and subsequent abstraction of fluoride with [Et
3
Si(tol)][B(C
6
F
5
)
4
]. The Lewis acidity of
2
is evaluated by experimental and computational methods and by preliminary catalysis testing. Exchange reactions of
2
and [(C
6
F
5
)
3
PF][B(C
6
F
5
)
4
] with their respective difluorophosphoranes are studied by 2D
19
F-
19
F NOESY/EXSY and selective 1D
19
F NMR exchange spectroscopy (SEXSY) experiments affording comparative rates of fluoride exchange. Collectively, although these data show that
2
is less Lewis acidic than [(C
6
F
5
)
3
PF][B(C
6
F
5
)
4
], the improved access to the P center of
2
provides a kinetic acceleration for fluoride exchange and catalysis where the transition states are more sterically demanding.
The electrophilic phosphonium cation (EPC) salt [(3,5-(CF
3
)
2
C
6
H
3
)
3
PF][B(C
6
F
5
)
4
] (
2
) can display catalytic activity greater than its thermodynamic acidity would suggest. The role of steric factors is explored. |
|---|---|
| ISSN: | 1477-9226 1477-9234 |
| DOI: | 10.1039/c8dt02594k |