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The Al(OR F ) 3 /H 2 O/Phosphane [R F = C(CF 3 ) 3 ] System – Protonation of Phosphanes and Absolute Brønsted Acidity
Abstract The synthesis of the classical, neutral donor–acceptor adducts Ph 2 MeP–/Ph 3 P–/Ph 3 As–Al(OR F ) 3 and H 2 O–Al(OR F ) 3 [ 1 , 2 , 3 , 4 , OR F = OC(CF 3 ) 3 ] is reported. The intermediate H 2 O–Al(OR F ) 3 ( 4 ) was generated by substitution of PhF in PhF–Al(OR F ) 3 with H 2 O and was...
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| Published in: | European journal of inorganic chemistry 2013-06, Vol.2013 (17), p.3054-3062 |
|---|---|
| Main Authors: | , , , , , |
| Format: | Article |
| Language: | English |
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| Online Access: | Get full text |
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| Summary: | Abstract
The synthesis of the classical, neutral donor–acceptor adducts Ph
2
MeP–/Ph
3
P–/Ph
3
As–Al(OR
F
)
3
and H
2
O–Al(OR
F
)
3
[
1
,
2
,
3
,
4
, OR
F
= OC(CF
3
)
3
] is reported. The intermediate H
2
O–Al(OR
F
)
3
(
4
) was generated by substitution of PhF in PhF–Al(OR
F
)
3
with H
2
O and was analyzed in a long‐term NMR study over 22 days. This Brønsted acidic system was used in orienting experiments to protonate phosphanes such as PMePh
2
, PPh
3
, PCy
3
, P(
t
Bu)
3
, and PCy
2
[2,4,6‐(
i
Pr)
3
C
6
H
2
]. Depending on the use of one or two equivalents of PhF–Al(OR
F
)
3
, the new weakly coordinating anions [(R
F
O)
3
Al(μ‐OH)Al(OR
F
)
3
]
–
or [HOAl(OR
F
)
3
]
–
were obtained. However, in dependence of the steric bulk of the phosphanes, stable and unreactive R
3
P–Al(OR
F
)
3
adducts were also observed in the NMR experiments. The absolute acidity of the key H
2
O–Al(OR
F
)
3
adduct was evaluated by the relaxed COSMO cluster‐continuum (rCCC, COSMO = conductor‐like screening model) model in fluorobenzene solution. For a 0.001
M
solution of H
2
O–Al(OR
F
)
3
, the medium acidity resulted as –986 kJ mol
–1
or a pH
abs
value of 173. Long‐term hydrolysis of H
2
O–Al(OR
F
)
3
(
4
), probably to give HOR
F
and HOAl(OR
F
)
2
followed by trimerization, gave [HOAl(OR
F
)
2
]
3
(
10
), which was identified by X‐ray diffraction. |
|---|---|
| ISSN: | 1434-1948 1099-0682 |
| DOI: | 10.1002/ejic.201300031 |