Chemistry Reference
In-Depth Information
Ph
where
R
=
CH
2
SiMe
3
; ArOH
=
HO
this refers to 6.51 on the previous page.
Ph
Kinetic studies have shown a primary kinetic isotope effect upon deuteration of the
phenolic proton.
7
In some cases ligand exchange reactions restrict the stoichiometry
that can be obtained. One of the most thoroughly studied reactions of this type is
the attempted synthesis of the mono-aryloxide derivative by reaction of trimethyla-
luminum [Al
2
Me
6
] with 2,6-di-
tert
-butyl-4-methylphenol (Eq. 6.52)
137
which leads to
the bis(aryloxide) owing to the two disproportionation reactions shown in Eq. 6.53.
138
2MeH
! 2[
ArO
AlMe
2
]
[Al
2
Me
6
] C 2ArOH
6
.
52
Me
3
C
where
ArOH
=
HO
CH
3
.
Me
3
C
3[
ArO
AlMe
2
]
[Al
2
Me
5
OAr
] C [
ArO
2
AlMe]
[Al
2
Me
5
OAr
]
2
[Al
2
Me
6
] C [
ArO
AlMe
2
]
6
.
53
Me
3
C
where
ArOH
=
HO
CH
3
.
Me
3
C
Changing the aluminium alkyl substrate to [AlBu
3
] allows isolation of the mono-
aryloxide derivative.
89
,
139
3.6.2
By Oxygenation of Metal-Aryl Compounds
Under certain circumstances it is possible to insert oxygen into metal - aryl bonds
leading to the corresponding aryloxide. This reactivity is a subset of the much
larger study of the oxidation of organometallic species in general.
140
,
141
Mechanistic
studies show that for transition metal-aryls, an intermediate peroxo (possibly
2
-
bound) can precede formation of the metal aryloxide function.
142
The oxygenation
of cyclopalladated compounds has been achieved, leading to chelated aryloxides of
palladium.
143
Similarly the treatment of nickel metallacycles with N
2
O can lead to
essentially cyclometallated aryloxides.
144
The addition of electron-deficient olefins
to nickel benzyne complexes can lead to metallacycles which are then oxygenated
to chelating aryloxides.
145
Treatment of the complex [PtMe
PPh
2
C
6
F
5
2
THF
] with
LiOH was found to produce the phenoxide [PtMe
PPh
2
C
6
F
5
2
PPh
2
C
6
F
4
O
].
146
The
reaction is believed to involve attack of coordinated hydroxide at the electrophilic
ortho
carbon of a C
6
F
5
group. Recently the insertion of O
2
into a chromium - phenyl
bond has been investigated.
147
The migration of aryl groups to metal - oxo functions
can lead to metal aryloxides.
148
,
149
More aspects of this reactivity are discussed in
Section 6.2.8.
