The carbonylation of allylic halides and prop-2-en-1-ol catalysed by
triethylphosphine complexes of rhodium
Abstract
In ethanol, [RhX(CO)(PEt
3
)
2
] added directly or
formed in situ from
[Rh
2
(OAc)
4
]·2MeOH
(OAc = O
2
CMe) and PEt
3
or
[Rh(OAc)(CO)(PEt
3
)
2
] catalysed the carbonylation
of CH
2
![[double bond, length as m-dash]](https://www.rsc.org/images/entities/char_e001.gif)
CHCH
2
X (X = Cl, Br or
I) to ethyl but-3-enoate with CH
2
CHCH
2
OEt
as a side product. Small amounts of the isomerisation product, ethyl
but-2-enoate were produced but no base was required for the reaction.
The selectivity of the reaction is in the order Cl > Br > I and
prop-2-en-1-ol can be successfully carbonylated to prop-2-enyl
but-3-enoate by the same system using 3-chloroprop-1-ene as a promoter.
3-Fluoropropene was not carbonylated, but in the presence of
H
2
underwent hydroformylation to produce acetals.
3-Chlorobut-1-ene and 1-chlorobut-2-ene both produced ethyl
pent-3-enoate and 3-ethoxybut-1-ene. In situ and ex
situ NMR and IR spectroscopic studies have been used to show that
the first step of the reaction is oxidative addition to give
[Rh(CH
2
CHCH
2
)Cl
2
(CO)(PEt
3
)
2
] for which thermodynamic parameters have been
obtained. Both 3-chlorobut-1-ene and 1-chlorobut-2-ene give
[Rh(CH
2
CHCHMe)Cl
2
(CO)(PEt
3
)
2
] but with different E∶Z ratios. The
detailed mechanism of the oxidative addition is discussed. The CO
inserts into the Rh–C bond to give
[Rh(COCH
2
CHCH
2
)Cl
2
(CO)(PEt
3
)
2
], from which but-3-enoyl chloride reductively
eliminates to react with ethanol to give the observed products.
High-pressure IR and high-pressure NMR studies reveal that
[RhX(CO)(PEt
3
)
2
] (X = Cl or Br)
reacts with CO to give
[RhX(CO)
2
(PEt
3
)
2
], which exists as two
isomeric forms. The compound [Rh(OAc)(CO)(PEt
3
)
2
]
catalyses the formation of prop-2-enyl ethanoate from 1-chloroprop-2-ene
and sodium ethanoate. A mechanism is proposed.
CHCH
2
X (X = Cl, Br or
I) to ethyl but-3-enoate with CH
2
CHCH
2
OEt
as a side product. Small amounts of the isomerisation product, ethyl
but-2-enoate were produced but no base was required for the reaction.
The selectivity of the reaction is in the order Cl > Br > I and
prop-2-en-1-ol can be successfully carbonylated to prop-2-enyl
but-3-enoate by the same system using 3-chloroprop-1-ene as a promoter.
3-Fluoropropene was not carbonylated, but in the presence of
H
2
underwent hydroformylation to produce acetals.
3-Chlorobut-1-ene and 1-chlorobut-2-ene both produced ethyl
pent-3-enoate and 3-ethoxybut-1-ene. In situ and ex
situ NMR and IR spectroscopic studies have been used to show that
the first step of the reaction is oxidative addition to give
[Rh(CH
2
CHCH
2
)Cl
2
(CO)(PEt
3
)
2
] for which thermodynamic parameters have been
obtained. Both 3-chlorobut-1-ene and 1-chlorobut-2-ene give
[Rh(CH
2
CHCHMe)Cl
2
(CO)(PEt
3
)
2
] but with different E∶Z ratios. The
detailed mechanism of the oxidative addition is discussed. The CO
inserts into the Rh–C bond to give
[Rh(COCH
2
CHCH
2
)Cl
2
(CO)(PEt
3
)
2
], from which but-3-enoyl chloride reductively
eliminates to react with ethanol to give the observed products.
High-pressure IR and high-pressure NMR studies reveal that
[RhX(CO)(PEt
3
)
2
] (X = Cl or Br)
reacts with CO to give
[RhX(CO)
2
(PEt
3
)
2
], which exists as two
isomeric forms. The compound [Rh(OAc)(CO)(PEt
3
)
2
]
catalyses the formation of prop-2-enyl ethanoate from 1-chloroprop-2-ene
and sodium ethanoate. A mechanism is proposed.
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