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Organomercury Compounds in Organic Synthesis.

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Organomercury Compounds in Organic Synthesis
By Richard C. Larock[*]
Organomercurials have been known since 1850 and many synthetic routes to these compounds
presently exist. The ability of these compounds to accommodate a wide variety of functional
groups and to tolerate quite diverse reaction conditions makes them attractive as synthetic
intermediates. While the ~~lv~mercuration-demercuration
and divalent carbon transfer reactions
remain the most widely used of the organomercurial reactions, a number of new synthetic
procedures employing organomercurials have been developed in recent years. Many of these
involve transmetallation reactions with palladium salts.
1. Introduction
Organomercurials wereamong the first organometallic compounds to have been prepared over 125 years ago. Early
interest in their medicinal use encouraged chemists to synthesize many organomercurials. Although these compounds
found increasing utility in the synthesis of other organometallic
compounds, their low chemical reactivity towards organic
substrates limited their early use in organic synthesis. With
the development of the more reactive Grignard and organolithium reagents, interest in the synthetic applications of these
compounds waned. However, with the increasing interest in
recent years in the development of organometallic reagents
which will undergo mild carbon-carbon bond formation and
yet tolerate a variety of functionality, the organomercurials
have seen a rebirth of interest. The ready availability of these
compounds, their ability to accommodate essentiallyall important organic functional groups, and their remarkable chemical
and thermal stability have made them attractive as synthetic
intermediates. These factors plus the ease with which these
compounds undergo transmetallation reactions with a number
of transition metals, most notably palladium, have provided
a large number of new procedures which should prove of
interest to the synthetic organic chemist.
This review will only very briefly outline some of the methods
of synthesis of organomercurials which have proven useful
in the development of these compounds as reagents and intermediates in organic synthesis. The major portion of the review
will then cover a number of new synthetic applications of
these compounds. Only those reactions whose generality has
been established will be covered. No attempt will be made
to cover any of the uses of mercury salts as oxidizing agents
in organic chemistry. The use of mercury(I1) oxide in this
respect has already been extensively reviewed[’].
2. Synthesis of Organomercury Compounds
Today a wide variety of synthetic procedures exist for the
preparation of organomercurials. These methods have been
reviewed in two recent books[’. ’I. Only those reactions which
lead to synthetically valuable organomercury reagents or intermediates will be mentioned here.
The direct synthesis of organomercurials from organic
halides and metallic mercury or mercury amalgams is rather
limited [eq. (
However, methyl, methylene, benzyl, propR-X
+ Hg .+ R-Hg-X
(1)
argyl and several allylic and 0-acylvinyl iodides undergo
a facile reaction in the presence of light, Alkyl bromides will
react when activated by electron withdrawing groups, but
alkyl chlorides are generally unreactive. Utilization of mercury
amalgams usually results in formation of the corresponding
diorganomercury compounds of type HgR2, but the yields
are generally low.
Organomercurials are most commonly prepared from the
corresponding organolithium or -magnesium compounds [eqs.
(2) and (3)]‘’]. However, the severe limitations on functionality
RLi + HgX2
+
RMgX + HgX2
RHgX + LiX
.+
RHgX
(2)
+ MgXz
(3)
and the already numerous synthetic applications of these
highly reactive organometallics severely restrict the synthetic
utility of the resulting organomercury compounds.
Halomethylmercury compounds have proven very valuable
as carbene transfer reagents. They are most readily obtained
by carbanion displacement reactions on organomercury
halides [eq. (4)]C61.A large number of these reagents have
RHgX
+ HCX3 + KOC(CH3)3
)-
THF
RHgCX3
+ HOC(CH3)3 + KX
(4)
been prepared and many are now commercially available.
Their utility as transfer reagents will be discussed in Section
4.
The mercuration of organoboranes offers a very valuable
method for the synthesis of organomercurials containing a
variety of functional groups[’1. Primary trialkylboranes, readily
available via hydroboration of terminal olefins, undergo a
rapid quantitative reaction with mercury(ri) acetate at room
temperature to give the corresponding alkylmercury acetates
[eq. (5)][*1.Treatment with aqueous sodium chloride provides
BH3
3RCH=CH2 -(RCHzCH2)3B
3 Hg(OAc)*
)
[*] Prof. Richard C. Larock
Department of Chemistry
Iowa State University
Ames, Iowa 5001 1 (USA)
Angrw. Ckem. Int. Ed. Engl. 17, 27-37 ( 1 9 7 8 )
~RCH~CH~H~OAC
(5)
excellent yields of the alkylmercury chlorides. Secondary alkyl
groups do not react under these mild conditions allowing
27
with saturated aqueous solutions of mercury(I1) chloride and
sodium chloride to give the corresponding trans-p-chlorovinylmercury([[) chlorides [eq. (l2)]["1. We have also recently
the use of dicyclohexylborane for selective hydroboration-mercuration [eq. (611.Dialkylmercury compounds can be prepared
s
R-C-C-CH
bH
3. NaCl
in a similar manner[']. Secondary alkylmercury compounds
are readily obtained from internal olefins via hydroborationmercuration using mercury alkoxides [eq. (7)]['". "I.
HKli
---+
R.cl\,C=C,/H
NaCl
observed analogous addition reactions with alkynylamines in
dilute hydrochloric acid [(eq. (1 3)]['*]. Ketones, carboxylic
?
2 R-C-C-CH
I
N
'
R 'R
+
2 HC1
+ 3 HgC12-
(13)
HzO
The hydroboration-mercuration of alkynes can be controlled to give either alkylidenebis(mercury(t1) chlorides) [eq.
(8)]['21 or vinylmercury(1r) chlorides [eq. (9)][13,141.The dicy2 BH3
B(°CH3)2
RC-CH
4 HOCHj
2H ~ C I ~
RCH,C\H
B(OCH3)2
HgCl
RCH,C$
3Na0H
(8)
HgCl
acids and esters containing a CC triple bond also undergo
similar addition reactions [eq. ( 14)][''9 '"I.
0
r"
R-CE
RC-CH
R
C-C-X
II
HgClz
X = R', OH, O R '
cl\ /c-x
c=c
'
R
hgC1
(9)
L
The most important route to arylmercurials is undoubtedly
the direct mercuration of aromatic compounds [eq. (1 5)][" "I.
" O H g Y
clohexylborane route (Route a) to vinylmercurials gives excellent yields from terminal alkynes and has been shown to
tolerate functional groups[' 31. The "pyrocatecholborane" procedure (Route b) is superior for the conversion of internal
alkynes to vinyl mercurial^['^!
In a protic solvent mercury salts react directly with alkenes
to form a wide variety of very valuable p-substituted organomercurials [eq. (I O)][' 'I. These reactions have proven exceedY
RCH=CHz
I
+ HgXz + HY -,RCHCHzHgX + HX
(10)
ingly useful for the Markownikoff functionalization of alkenes
when employed in conjunction with a demercuration step,
and will be discussed in detail in Section 3.
At this time we will discuss only the analogous alkyne
addition reactions which lead to organomercurials useful in
other synthetic transformations. Mercury(I1) acetate readily
reacts with internal alkynes in acetic acid to give p-(acetoxy)vinylmercurials. Depending upon reaction conditions, 2butyne gives either the trans or the cis addition product [eq.
(1 1)][161. Certain propargylic alcohols and diols react readily
+ HY
(15)
This reaction has been extensively studied from both a
mechanistic and synthetic standpoint. It generally exhibits
the characteristics of a typical electrophilic aromatic substitution reaction and is facilitated by highly ionic mercury salts
and by electron donating groups on the aromatic ring. Arylmercurials containing a large variety of organic functional
groups have been prepared in this manner.
The direct mercuration of aromatic compounds has one
major drawback. It often results in mixtures of 0, rn, and
p isomers. This complication can be easily avoided by employing diazonium salts[231.Copper promotes the facile displacement of nitrogen from the double salts of aryldiazonium halides
and mercury([[) halides [eq. (16)]. With excess copper and
ArN2X.HgX2+ 2Cu + ArHgX + 2CuX + N 2
(16)
aqueous ammonia diarylmercury compounds are produced.
These reactions also proceed in high yield when copper([)
chloride is employed.
Arylhydrazines can also be directly converted into arylmercurials upon treatment with mercury([[) acetate and copper(r1)
acetate [eq. (1 7)][241.
CHsCGCCH3
J
H3C\
H3CCO/
8
28
/CH3
C=C
\HgOAc
ArNHNH2 + Hg(0Ac)Z + Cu(OAc)* + ArHgOAc
I
0
II
H3CCO\
/CH3
/c="
H3C
HgOAc:
(17)
The thermal decarboxylation of the mercury(1r) salts of
arenecarboxylates provides an alternate method for the synthesis of arylmercurials, but appears limited to aryl groups
containing strong electron withdrawing groups [eq. ( 18)y2?
Angew. Chem. Int.
Ed. Engl. 17, 27-37 (1978)
2
Hg
r D ! O ) 2
ro)z
Hg + 2 COz
(18)
The photochemical or peroxide initiated decomposition of
aliphatic or aromatic mercury carboxylates proceeds under
much milder conditions and often provides excellent yields
of the corresponding organomercury carboxylates [eq.
(19)][261.
0
II
( R 8 0 )zHg
---+
RHgOCR
+
COz
Although this discussion of the preparation of organomercurials has been kept purposely short, it is obvious that a
wide variety of methods for their synthesis exist and that
a substantial number of these methods are quite general and
accommodate considerable organic functionality. With this
in mind we are ready to explore some of the synthetic applications of these compounds.
3. Solvomercuration-Demercuration Reactions
I
RCH=CHz
-----+
RCHCHzHgX
-
Y
I
RCHCH,
MOAck
HzOl THF
R
NaB&
CH(OH)CH,
fluoroacetate [eq. (22)]f3*].Fair yields of unsaturated alcohols
can also be obtained from conjugated dienes [eq. (23)]. When
/H
,c =c
H
' CH=CHz
-
H3C\
/H
,c=c\
H
FHCH,
OH
two equivalents of mercury(I1) salt are employed, diols are
obtained in high yields [eq. (24)], except in those cases where
HzC=CH(CHz),CH=CHz
-
PH
YH
CH3CH(CHz),CHCH3
(24)
hydroxyl participation can result in the formation of tetrahydrofurans or tetrahydropyrans [eq. (25)][391.These results are
best explained by two consecutive Markownikoff additions.
Cyclic ether formation from dienes and unsaturated alcohols
has been reported by a number of workers and can often
proceed in high
A number of interesting cyclic and
polycyclic ethers have been prepared in this manner. One
can take advantage of these reactions to convert cyclohexenols
into cis-l,2-diols [eq. (26)][41'.
R HCH, ( 2 1 )
NaOH
a very convenient procedure for the Markownikoff hydration
of alkenes, nicely complementing hydroboration-oxidation.
Although many P-hydroxyalkylmercurialshave been isolated
from this reaction["], and a few subsequently reduced with
various reducing agents, the recent work of H . C. Brown
et al. on the in situ oxymercuration-demercuration of alkenes using sodium tetrahydridoborate as the reducing agent
provides the most convenient procedure[281.This procedure
is applicable to mono-, di-, tri- and tetraalkyl, as well as
phenyl substituted alkenes. The relative rates of hydroxymercuration have also been determined[291:
Angew. Chem. Int. Ed. Engl. 17, 27-37 (1978)
FH=CHz
(2 0 )
very general method for the Markownikoff functionalization
of alkenes. Its advantages over other procedures are: (1) extremely mild reaction conditions are involved, (2) considerable
functionality is accommodated, (3) carbon skeletal rearrangements are rare, and (4)numerous nucleophiles, Y, can be
employed. We shall only very briefly cover each of the different
types of solvomercuration adducts which can be formed and
the major methods by which they can be demercurated. Primary emphasis will be on those procedures which accomplish
the above transformation in situ, without isolation of the
intermediate organomercurial, as these are clearly the synthetically more appealing procedures.
The oxymercuration-demercuration reaction is the most
widely used synthetic procedure [eq. (21)]. It provides
RCH=CHz
The regio- and stereochemistry of this reaction have been
thoroughly
30-341.
The reaction generally
involves a trans-Markownikoff addition. However, with certain strained alkenes such as n ~ r b o r n e n e [and
~ ~ trans-cyclooc]
tene and -n0nene[~~1
cis-addition occurs. Substituted cyclohexenes give almost exclusively the axial a l c o h 0 1 [ ~
~ ~Optically
341.
active alcohols can also be obtained by employing chiral
mercury(I1) c a r b o ~ y l a t e s [37!~ ~ ,
The oxymercuration-demercuration of dienes has proven
quite interesting. The monohydration of unsymmetrical dienes
can be accomplished using one equivalent of mercury(l1) tri-
H&\
The solvomercuration-demercuration of alkenes is probably
the most important synthetic method employing intermediate
organomercurials [eq. (2011. This sequence has provided a
Y
R2C=CH2 > RCH=CH2 > cis-RCH=CHR >
> trans-RCH=CHR > R,C=CHR > R2C=CR2
1. N a B b
',
2. ZnIHOAc
I
Alkenes and dienes readily undergo alkoxymercurationdemercuration when an alcohol is used as the solvent [eq.
(27)]. Although numerous P-alkoxymercurials have been pre29
0
pared using mercury(@ acetate[”], and some of these subsequently demercurated, mercury(I1) trifluoroacetate appears to
OR‘
RCH=CH2
Hg(QzCCFdz
___*
R’OH
::
I
RCHCHZHgOzCCF,
NaBH4
= ONHCCH
(27)
PR’
RCHCH,
NaOH
be a far superior reagent and, when employed in conjunction
with an in situ alkaline NaBH4 reduction, provides a very
convenient route to highly branched ethers[42!
Peroxymercuration has also been achieved using mercury(r1)
carboxylates and both hydrogen peroxide and tert-butyl hydroperoxide [eq. (28)][43]1.
The alkyl tert-butyl peroxides can
rBuOOH
RCH=CH2
YOtBu
RCHCHZHgOzCR’
Hg(0zCR’h
NaBH4
NaOH
YOtBu
RCHCH,
be demercurated with NaBH4[441.Cyclic peroxides can also
be prepared from dienes by this approach[451.
Solvomercuration reactions can also prove useful for the
synthesis of esters and lactones. In the absence of a protic
solvent mercuric acetate will add directly to a l k e n e ~ ‘ ~The
~].
monoaddition of mercury(I1) acetate to dienes provides an
improved method for the monohydration of symmetrical
~~]
dienes [eq. (29)][47J.Both acyclic[481and b i ~ y c l i c [ y,&-unOAc
A number of other mercury salts will also add across the
double bonds of alkenes. In this manner f l - a z i d ~ [ ~p-nitr0[~~1,
~],
fl-fluoro[601and fl-(trinitromethyl)[601mercurials have been
prepared.
There are only a few examples of carbon-carbon bond
formation via sohomercuration reactionsI6’! Certain aromatic compounds react with alkenes in the presence of mercury(I1)
salts to give p-aryl alcohols or carboxylates, as well as 1,2diarylalkanes. 1,3-Dicarbonyl compounds also undergo coupling with ethylene and mercury(r1) salts.
The mercuration of alkynes has been much less thoroughly
studied and appears rather limited in its synthetic utility[62!
Hydroxymercuration conditions provide a convenient method
for the catalytic hydrolysis of alkynes to ketones. Alkoxymercuration generally produces ketals directly, although enol
ethers have been obtained. Enol acetates can also be obtained
if acetic anhydride is used as the solvent.
A few comments on the methods of demercuration should
be made before concluding this section[63! Although hydrazine
has been employed as a reducing agent, it generally gives
poor yields. LiAIH4 has also been used, but offers no advantages over the widely used NaBH4 procedure. This latter
procedure usually proceeds in very high yield, although free
radicals are involved and rearrangement products are sometimes observed[641.O n the other hand, sodium amalgam provides a valuable method for the stereospecific replacement
of mercury by deuterium[65].
OH
NaOH_J&
.,/.
NaBHa
4. Carbene Transfer
saturated carboxylic acids form y-lactones when treated with
mercury(r1) acetate [eq. (30)].
a-Halomethylmercury compounds have found extensive use
in organic synthesis as carbene transfer reagents. They have
proven particularly useful for the synthesis of cyclopropanes
from alkenes [eq. (33)]. The utility of these compounds has
The aminomercuration of alkenes has been reported by
a number of workers [eq. (31)][47*50-521
. B0th mercury(I1)
N R;
RCH=CH2
+
2 HNRh
+
HgX,
-+
RkHCHZHgX
(31)
chloride and acetate, as well as primary and secondary alkyl
and aryl amines, have been allowed to react with a wide
variety of alkenes. The reaction has also been extended to
the synthesis of heterocyclic amines by employing unsaturated
amines and d i e n e ~ [ ~ ~A . variety
~ ~ ] . of reducing agents have
been used to reduce the mercurial^[^^, 51, 54, 551.
The amidomercuration of alkenes can readily be accomplished using mercury(1r) nitrate and nitriles followed by hywith sodium amalgam or NaBH4
d r o l y s i ~ [571.
~ ~Reduction
.
gives high yields of the corresponding amide [eq. (32)]. LiAIH4
reduction gives the corresponding secondary amineCs71.
30
been extensively studied by Seyferth et al. and several reviews
have appeared recently[66- 681. Rather than repeat those
reviews, we shall primarily concentrate on the synthetic utility
of these reagents, pointing out the advantages and disadvantages.
The majority of these carbene transfer reactions have
employed phenyl(trihalomethy1)mercury compounds. In
general, these reagents appear to reversibly dissociate “free”
O
H
:cc1, +
gC Cl, R r
;c=c:
-
O H g B r + :CCl,
- 2c
(34)
(35)
fast
Angew. Chem. Int. Ed. Engl. 17, 27-37 (1978)
carbenes which then rapidly react with the alkene to generate
701. Clean transfer of
cyclopropanes [eqs. (34) and (35)][699
the more nucleophilic halide (I > Br > Cl) from carbon to mercury is observed in these reactions, apparently by a concerted
intramolecular rearrangementf711.The relative rates of reaction of various halomethylmercurials follow the same order
(I > Br > C1). Replacement of the phenyl group by a cyclohexyl
group has also been observed to facilitate reaction[72!
Apparently, not all transfer reactions of this type proceed
via a carbene intermediate however. For example, (BrCH&Hg
appears to involve a direct transfer of the CH2 moiety from
the mercurial to the alkene[73! Under certain circumstances
trihalomethyl carbanions can also be involved in these reactions. In those cases where the carbene is not readily thermally
released by the mercurial, iodide ion can be employed to
displace the trihalomethyl anion which subsequently decomposes to a carbene [eqs. (36) and (37)][74-76!
%F,
-
:CF2 + F'
is-':".
+
---+
---+
(38)
The addition of dihalocarbenes to arylacetylenes has provided a convenient route to aryl substituted cyclopropenones
[eq. (39)][78,791. This reaction fails with dialkylacetylenes.
(3 7)
The cr-halomethylmercurialshave proven very valuable for
the synthesis of cyclopropanes for a number of reasons. They
proceed at reasonable temperatures under neutral reaction
conditions, avoiding the introduction of strong bases or other
potentially reactive reagents which are generally necessary
for the formation of other transfer reagents. Thus, potentially
serious side reactions between the actual carbene transfer
reagent and reagents used to generate this species are avoided.
Furthermore, the organomercurial reagent itself is generally
inert to most substrates with which one desires to carry out
a reaction. The phenylmercury(I1) halide by-product in these
reactions is also inert and usually precipitates from solution
during reaction. It can also be easily reused in the preparation
of additional transfer reagents. The insolubility of the resultant
mercurial allows it to be removed from the cyclopropane
product by simple filtration. These reactions can also generally
be run in a variety of solvents. In general, one can employ
an equimolar ratio of alkene and organomercurial and temperatures of 50--100°C. Under these conditions simple alkenes
give essentially quantitative yields. Those alkenes, such as
ethylene, trans-stilbene, tetrachloroethylene, trimethyl(viny1)silane and 3,3-dimethyl-l-pentene, which are generally unreactive towards other carbene reagents give satisfactory yields
with the mercurial reagents. Alkenes, such as acrylonitrile,
methyl acrylate and vinyl acetate which readily polymerize
in the presence of base or reagents which generate the trihalomethyl carbanion, also give good yields with these reagents.
A large number of functional groups are apparently accommodated by this reaction.
There are, however, several limitations to the use of these
reagents. The most obvious one is the need to prepare and
isolate the intermediate organomercurial. However, a number
of literature procedures presently exist for the preparation
of these compounds. The presence of certain functional groups
in the alkene can also create problems. Carboxylic acids,
alcohols and amines all react with these reagents. Reactions
with a number of other functional groups can occur in the
absence of carbon-carbon double bonds and a number of
Angew. Chem. Int. Ed. Engl. 17, 27-37 (1978)
unusual heterocyclic compounds can be prepared in this manner.
These reagents have found other uses in organic synthesis
as well. Stork has utilized dichlorocarbene additions to enol
acetates as a means of ring expanding cyclic ketones to enones
[eq. (38)]["1.
Organoboranes, derived from terminal alkenes via hydroboration, are readily coupled in good yield upon treatment
with bromodichloromethyl(pheny1)mercury [eq. (40)][801.
RCH2CHZCH=CHCH2R (40)
Treatment of aldehydes and ketones with these same mercurials and triphenylphosphane provides an interesting route
to a variety of vinyl halides [eq. (41)][8',82! This Wittig-like
RX=O
+ C6H5HgCHBr2+ (C6H&P
---t
R2C=CHBr
(41)
reaction quite likely proceeds through an intermediate phosphorus ylide.
All told, the halomethyl(pheny1)mercury reagents have
proven extremely valuable for the synthesis of halocyclopropanes and exhibit a number of other interesting reactions
which appear to possess considerable synthetic potential.
5. Halogenation of Organomercury Compounds
Organomercurials generally react quite readily with chlorine, bromine and iodine to give the corresponding organic
halides [eqs. (42) and (43)]. This reaction has been widely
+
RzHg Xz + RHgX + RX
RHgX + Xz -+ HgXz + RX
X=CI. Br. I
(42)
(43)
used to determine the position of the mercury atom in organomercurials. Synthetically, however, it is of rather limited importance since the usual starting materials for the preparation
of organomercurials are either (1) organic halides themselves,
(2) compounds derived from organic halides (organomagnesium or -lithium compounds), or (3) compounds readily
halogenated directly (organoboranes, arenes, diazonium salts).
31
There are perhaps several noteworthy exceptions however.
Several reports indicate that the halogenation of organomercurials prepared by solvomercuration reactions provides a
convenient method for the synthesis of P-substituted organic
halides [eq. (44)][83-871. Equally valuable is the bromination
the conversion of alkenes directly to ketones [eq. (48)][961.
If ethylene glycol is employed as the solvent the 1,3-dioxolane
can be obtained directly [eq. (49)]Lg71.
n
oCHzCHzoH
I
RCHCHzHgOAc
RCH=CHz
RCH=CHz
--+
PX x2
'lI
RCH-CHz
--+
Y
I
X
I
RCH-CHz
(44)
Y = -OH, -OR'; X = B r , I
of vinylmercury bromides which can apparently be controlled
to give either the retained or inverted vinyl bromide simply
by changing the solvent [eq. (45)][88]. The iodination of
(45)
alken~l-[*~I,
alkynyl-[90,911 and a r y l m e r ~ u r i a l salso
~ ~ ~appears
]
to be of preparative utility.
It is interesting to note that the in situ iodination of n-alkylmercuric acetates derived from the mercuration of tri-n-alkylboranes gives the corresponding acetates and not the iodides,
although the iodides are apparently intermediates in this reaction [eq.(46)][931.I n situ bromination provides the corresponding alkyl bromides[941.
32
(49)
proceeds through intermediate P-hydroxy and P-keto mercurials. While the palladium reaction apparently gives good
yields of ketones from internal olefins, the chromium trioxide
procedure gives only 20-56 % yields.
Arylmercunals have been oxidized in high yield to phenols
by first treating with borane and then oxidizing the resulting
arylborane [eq. (51)][991.
Thermolysis of a large number of vinylmercury salts leads,
often in high yields, to the corresponding vinyl oxygen and
sulfur derivatives and metallic mercury [eq. (52)][100-106!
A
CHZ=CHHgX +CHz=CHX
+ Hg
(52)
0
-OAr, -SAr, -SR, -OTs, -SCN, -SEOR,
This reaction seems to be quite general and would appear
to have some synthetic utility.
Diary1 sulfides can be prepared by heating diarylmercurials
and sulfur to 190-250°C [eq. (53)][107-1101.
At 140-180°C
Ar-Hg-Ar
Sa
Ar-S-Ar
19&250*C
(53 1
using either alkyl or arylmercury chlorides in sulfolane, good
yields of the corresponding disulfides can be obtained instead
[eq.(54)]t111!
2 RH g Cl
tertiary alkylmercurials yield the corresponding tertiary alcohols upon ozonolysis, this reaction is of little value due to
the limited availability of these organomercurials.
The oxidation of either hydroxy- or methoxymercuration
products with catalytic amounts of palladium(11) chloride and
copper(I1) chloride provides a very convenient method for
R CH,
(50)
?
The large majority of organomercurials are very stable towards oxygen. On the other hand, organomercurials are readily
oxidized by 0zone1~~].
Primary alkylmercurials give the corresponding carboxylic acid, plus all carboxylic acids possible
from stepwise loss of carbon. Secondary organomercurials
give good yields of ketones. This reaction would appear to
be of value for the synthesis of u-substituted ketones from
alkenes via solvomercuration-oxidation [eq. (47)]. Although
3 cuCll
0x6
An analogous ketone preparation can be achieved by
employing chromium trioxide and only a catalytic amount
of mercury(I1) acetate [eq. (50)][981.This reaction presumably
X = -OC!R,
6. Oxidation and Sulfur Displacement Reactions
cat. PdCll
S8
140-180"c
R-S-S-R
(54)
7. Dimerization of the Organic Moiety of Organomercury Compounds
Transition metals have proven useful for the dimerization
of a number of organomercurials. Dibenzylmercury and a
number of diarylmercurials can be dimerized by heating with
finely divided nickel, palladium, platinum, copper, gold or
silver metals [eq. (55)][1121.Silver powder has been used to
synthesize biferrocenyl[' 13], as well as biphenylenet' 1 4 * l 1 'I,
Angew. Chem. l n t . Ed. Engl. 17,27-37 ( 1 9 7 8 )
-+.An
r-Ar
Ar-ISg-Ar
+ Hg
(55)
octafluorobiphenylene[' '61, benzo[a]biphenylene[' ' 71 and triphenylene[' from cyclic arylmercurials.
Under certain conditions transition metal salts have also
proven highly efficient for the dimerization of both aryl and
vinylmercurials. Recently, several new procedures have been
developed for the dimerization of vinylmercurials. We have
observed that symmetrical 1,3-dienes and polyenes can be
obtained in excellent yields by treating vinylmercury chlorides
with lithium chloride and stoichiometric amounts of palladium
chloride in hexamethylphosphoramide (HMPA) at 0°C [eq.
(56)][1'91.When benzene is used as the solvent an unusual
"head-to-tai1"dimerization occurs instead [eq. (57)]['201.Catalytic procedures also exist for the symmetrical dimerization.
bromide to give low to modest yields of coupled products
under these conditions. The highly reactive a-mercurated carbony1 compounds are readily alkylated at room temperature
even in the absence of catalysts['3'.'321.
Transition metal reagents can also be used to promote
alkylation. Whitesides has reported an interesting copper reaction which results in overall alkylation of an organomercurial
[eq. (60)][1331.Unfortunately, this procedure appears to have
no advantages over the direct use of organocuprates since
alkyl lithium reagents are required in both procedures.
Recently, we have observed that organorhodium(I1I)compounds will couple with both aryl- and vinylmercurials and
we are presently studying the generality and synthetic utility
of this reaction [eq. (61)]['341.
Ph\
,H
c=c\
H/
Thus, Vedejs and Weeks have reported that cis- and trans-dipropenylmercury are catalytically dimerized by tetrakis(tripheny1phosphane)palladium(o)[eq. (58)]['211. More recently, we have
cat. Pd(PPh3k
Hg
------=P
(
Ji3C\
+ Hg
H/C=CT)z
(58)
observed that rhodium([) and rhodium(rI1)salts very efficiently
catalyze the dimerization of both aryl and vinyl groups of
organomercury chlorides [eq. (59)]['221. Palladium chloride
R\
/H
cat. [CIRh(CO)& or RhC13
c=c\
2
H'
HgCl
2 LiCI
R\
H'
HgCl
H N V g C 1
2.
1 . NaBH4/H2
H2C=CHz/LtzPdCb
OA Rr '
\
,
(62)
R
directly without reduction and methyl acrylate gives the 3-trans
substituted propenoate [eq. (63)] (see Section 9).
,,3c=c\H
OH,
H
/
(59)
,C=C\
H
K
Hi-.$vgcl
H2C=CHC@CH3,
a
0T;J
"3
/COzCH3
(63)
4k
LilPdCb
O E :
R
plus copper(11) chloride" 231or copper
or palladium
acetate alone['251,have also been reported to dimerize arylmercurials. Surprisingly little use seems to have been made of
any of these reactions for the synthesis of biaryls.
To date, alkylmercurials other than allylmercury iodide" "1
and benzylmercurials[' ' have not been dimerized in good
yield.
(61)
Bergstrom and Ruth have been able to alkylate, allylate
and alkenylate 5-(ch1oromercury)nucleosidesby taking advantage of previously reported organopalladium reactions [eq.
(62)][1351.Use of ally1 chloride gives the 5-ally1 derivative
H
, c=c/
ph\
/H
/C=C
H
\ CH3
+ CH,RhIz(PPh3)2
R
Both aryl- and vinylmercurials also undergo a smooth coupling with allylic halides when palladium chloride plus lithium
chloride is employed as a catalyst. Heck reports that arylmercuric halides give 31-87 % yields of allylaromatics [eq.
(@)I['361. We have found that vinylmercurials give similar
F1
O H g C l + CHZ=CHCHCH3
LIPdCIs
cua2
cat.
8. Reactions of Organomercury Compounds with Alkylating Reagents
In general, organomercurials are quite inert towards alkyl
halides. Only under forcing conditions will arylmethyl halides
alkylate dibutylmercury and arylmercurials['26 - '"1 . The
yields in these reactions are generally quite low. However,
these reactions can be carried out at -15 to -20°C if aluminum bromide is added[' 301.Diphenyl- and dibenzylmercury
react with methyl iodide, ethyl bromide, chloromethyl methyl
ether, benzyl bromide, p-nitrobenzyl bromide, and benzhydryl
Angew. Chem. I n t . Ed. Engl. 1 7 , 27-37 ( 1 9 7 8 )
yields of 1,4-dienes [eq. (65)][1371.It is especially noteworthy
that both these reactions tolerate a number of functional
(CH3)3C\
/H
/c=c\
H
HeCl
7'
+ CH2=CHCHCH3
cat.
L!lPdC&
THF
33
groups, occur at or below room temperature, and result in
transposition of the double bond of the allylic halide. These
reactions apparently proceed as indicated below [eqs. (66)
to (68)].
+
RHgCl
-
PdC14Zo
+
RPdC1,20
c1
+ CH,=CH&HCH,
RPdC1;'
[
-
Y
C1,Pd
I
RCHzCH-CHCH,
HgC1,
(66)
C1,Pd
RCH2&H-&CH3]20
+
RCHzCH=CHCH,
+
PdCl."
(67)
(68)
9. Alkene Substitution and Addition Reactions
In 1968 Heck reported a number of interesting reactions
of organomercurials and alkenes promoted by palladium salts.
Simple alkenes undergo vinylic hydrogen substitution reactions [eq. (6911'' 381. In the reactions of alkenes containing
RHgX
+ PdXz + CHz=CHY
+
RCH=CHY
(69)
allylic hydrogens a mixture of isomeric substituted alkenes
is obtained. These reactions are apparently limited to arylmercurials, alkoxycarbonylmercurials, and alkylmercurials which
do not contain P-hydrogen atoms['38. 1391. A large number
of functional groups are apparently accommodated by this
reaction.
The reaction apparently involves the following sequence
of reactions [eqs. (70) to (73)][140,141!When the original
RHgX
+
R P d X + HgXz
PdXz
R P d X + CHz=CHY
RCHZ-CHY
I
PdX
HPdX
-
-
approximately 2 M copper(1r) chloride, P-arylalkyl chlorides
are produced instead [eq. (75)][143! This reaction appears
(70)
+ RCHz-FHY
PdX
valuable for the synthesis of a-halocarbonyl compounds [eq.
(7611.
The reaction of primary and secondary allylic alcohols takes
an entirely different course and produces 3-arylaldehydes and
ketones respectively, although in low yield [eq. (77)][144!
A r H g C l + CHz=CHCHzOH + LiPdC1,
CH,CN
?
ArCH,CH,& H
(77)
Apparently, the initial alkylpalladium compound obtained
upon addition of the aryl palladium species to the carbon-carbon double bond preferentially eliminates a hydride from
the carbon containing the hydroxyl group, producing an enol
of the eventual carbonyl compound.
The reaction of enol esters provides 2-arylaldehydes and
ketones, albeit generally in quite low yield [eq. (78)]['451.
OAc
ArHgCl
+
I
CH,=CCH,
cat. LizPdCb
0
11
(78)
ArCHzCCH,
CUClZ
The reaction of organomercurials, palladium salts and conjugated dienes gives low to moderate yields of n-allylpalladium
compounds [eq. (79)][146! Quite surprisingly, the reaction
R H g C l + LiPdC1,
RCH=CHY + H P d X
---+
+
CH,=CHCH=CH,
--+
R = a r y l , benzyl, methyl
H
(79)
I
HX
+
Pd
(73)
alkene contains allylic hydrogens, palladium hydride elimination can occur in more than one direction leading to an
isomeric mixture. These reactions can be made catalytic in
palladium if a reoxidant such as copper(I1)chloride is employed
to oxidize the palladium metal back to palladium(I1).
The intermediate organopalladium addition compounds
from the alkoxycarbonylmercurial addition reactions can be
trapped by carbonylation, providing a novel synthesis of substituted succinic esters [eq. (74)][142!
-
of vinylmercurials, palladium chloride and simple alkenes produces quite high yields of n-allylpalladium compounds also
(CH3)3C,
,H
/C =c
H
'HgC1
+
Li,PdCl,
+
CHz=CHCOzC2HS
co
e C H = C H z + CIHgCOzCH,
Pdc12
CHjOH
(741
[eq. (80)][147! The n-allylpalladium compounds are apparently
produced by a palladium hydride rearrangement [eq. (Sl)].
PdCl
I
(CH3),CCH=CHCHzCHC02C,H,
If the reaction of arylmercurials and alkenes is run in the
presence of catalytic amounts of palladium chloride and
--+
PdCl
(CH,),CCH=CH~HCH,CO~C~H~
ArHgCl
+
CH2=CHR
+
cat. WCIZ
2CuC12c1
ArCHzCHR
34
(75)
The palladium promoted addition of organic groups from
organomercurials to carbon-carbon double bonds appears
to be a very general reaction. The reactions also accommodate
Angew. Chem. I n t . Ed. Engl. 17, 27-37 (1978)
a large number of functional groups. Unfortunately, however,
they cannot be employed with organomercurials possessing
P-hydrogens and many reactions give rather low yields.
Nevertheless, the ease with which carbon-carbon bond formation occurs suggests considerable synthetic utility.
The direct carbonylation of organomercurials by carbon
monoxide is of limited synthetic
15'1.
It requires
high temperatures and pressures and generally gives only
very poor yields. However, palladium salts readily promote
the carbonylation of organomercurials. For example, Henry
has reported that ethylmercury(r1)chloride reacts with palladium chloride and carbon monoxide at atmospheric pressure
to give propionic acid upon aqueous workup" 521. Similarly,
arylmercurials give acid chlorides in acetonitrile, esters in
alcohol solvents, and anhydrides when palladium acetate is
employed. Unfortunately, the yields are generally low.
On the other hand, vinylmercurials are readily carbonylated
at low temperatures and one atmosphere carbon monoxide
if lithium chloride and palladium chloride are
Depending on the solvent used, one obtains excellent yields
of either a$-unsaturated carboxylic acids or esters [eq. (82)].
C
,
H
/H
=c\
COOH
-
H
R\
/
/C=C,
H
HgCl
-
R\
H
,c=c1
H
'COOR'
cat. CO*(CO)B
C O ------+
A r z C = O + Hg
hv
(84)
11. Acylation of Organomercury Compounds
Most organomercurials are unreactive towards acid halides.
However, a few arylmercury chlorides have been acylated
to give the corresponding ketones [eq. (S5)]['28.1291. a-MercuAiigew. Chem. Int. Ed. Engl. 17, 27-37 (1978)
0
I1
A r C R + HgC1,
(85)
rated carbonyl compounds react readily with acid halides to
produce the corresponding enol esters [eq. (86)][132!
0
II
CIHgCHzCR'
-
9
OCR
I
CHz=CR' + HgC1z
(86)
Both Pd[P(C6H5)3]4[1591
and aluminum halides['6o. 1 6 1 1
promote rapid acylation of dialkyl- and diarylmercurials [eq.
(87)], but it appears that only one of the two organic groups
9
RzHg + C1CR'
9
+ RCR'
+ RHgCl
of the organomercurial reacts under these conditions. However, vinylmercury chlorides and aluminum trichloride react
readily with acid chlorides to give excellent yields of cr,P-unsaturated ketones with retention of configuration [eq. (88)][162!
12. Conclusion
Diarylketones have also been obtained upon carbonylation
of arylmercurials. Arylmercuric chlorides react with palladium
chloride salts under 50 psig of carbon monoxide to give low
yieldsof diary1 ketones" 54! Rhodium(1)and (HI) complexes give
somewhat better yields and can be run at atmospheric pressure.
These reactions can be accomplished in considerably higher
yield by using either tetracarbonylnickel[' 5 5 1 or octacarbonyldicobalti'56,1571. The latter procedure can also be employed
using only catalytic amounts of the carbonylmetal if the reaction is photolyzed [eq. (84)][158!
+
-
(82)
These reactions can be accomplished with only catalytic
amounts of palladium chloride or palladium on carbon, if
copper(r1) chloride is added as a reoxidant. These reactions
have recently provided a novel new route to butenolides via
carbonylation of the vinylmercurials derived from the addition
of mercury(r1)chloride to alkynyl alcohols [eq. (83)][l7].
ArzHg
II
FI
RCCl +
10. Carbonylation Reactions
R,
0
ArHgCl + ClCR
Organomercurials have been known since 1850. They are
now readily available by a number of routes and possess
a number of characteristics which make them attractive as
synthetic intermediates. Until lately, however, their low chemical reactivity has limited their use in organic synthesis.
Recently, transition metal exchange reactions have been
employed to promote a number of synthetically interesting
reactions. These reactions appear to accommodate a large
number of organic functional groups. However, the two most
widely used reactions of organomercurials remain the carbene
transfer reactions and solvomercuration-demercuration reactions.
Received: Februar 16, 1977 [A 192 [ E l
German version: Angew. Chem. 90,28 (1978)
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Solid Ionic Conductors : Principles and Applications
By Hans R i c k e r t [ * ]
Solid ionic conductors, also called solid electrolytes, transport electric current by means
of ions. The hest known examples of these usually crystalline compounds include doped Z r 0 2 ,
as well as AgI, P-A1203, and CaF2. Ionic conduction in solid electrolytes reaches its maximum
value if a partial lattice of a solid compound undergoes transition at elevated temperature
to a quasimolten state. The ionic conductivity in such solid compounds is then as high as
in molten salts. Solid electrolytes have found many scientific and technological applications;
thus, they can be used to study thermodynamic and kinetic problems, and to build fuel
cells, batteries, sensors, and chemotronic components.
1. Principles
Solid ionic conductors are solid, generally crystalline, compounds in which electric current is carried by charged atoms,
i.e. by ions. The passage of current is thus associated with
mass transfer. Such ionic conductors are called “solid electrolytes”, by analogy to liquid electrolyte solutions, and have
permitted development of a new scientific discipline, viz. solidstate electrochemistry. The associated technology is termed
solid-state ionics, in contrast to solid-state electronics.
The fact of ionic conduction in solids presents two sets
of questions. First, how can ionic conduction arise microscopically at the atomic level, and how large can this ionic conduction become‘? Secondly, what applications are open to solid
conductors in science and technology?
The first set of questions leads us to discuss disorder in
solids. One limiting case is structural disorder-the quasimolten state-of a partial lattice of crystalline compound.
This explains how the ionic conduction in certain solid electrolytes can become as high as that in concentrated electrolyte
solutions or molten salts. However, unlike the liquid electrolytes, solid ionic conductors require no vessel to contain them,
____
[‘I
Prof. Dr. H. Rickert
Lehrstuhl fir Physikalische Chemie der Universitat
Otto-Hahn-Strasse, D-4600 Dortmund 50 (Germany)
Angew. Chem. Int. Ed. Engl. 17, 37-46 (1978)
since they are still solid in spite of their quasimolten partial
lattice. A solid ionic conductor can itself act as container
or as the partition between electrode compartments; this leads
to interesting constructional possibilities in the design of galvanic cells not provided by liquid electrolyte solutions or
molten salts.
We thus come to the second set of questions, those concerning scientific and technological applications. The potential
uses are largely based on the fact that solid electrolytes can
be used to construct galvanic cells (also called elements) suitable for many different purposes; for example, not only for
batteries or fuel cells but also for measurement or control
engineering purposes, for display units, and for the developing
field of chemotronic components. In the scientific area, galvanic cells containing solid electrolytes can be used in both
thermodynamic and kinetic investigations. The importance
of galvanic solid-state cells for thermodynamic investigations
lies in the fact that their EMF provides information about
chemical potentials or thermodynamic activities, partial pressures, and free energies. In kinetic investigations it is also
important that reaction rates can be measured via the electric
current in suitably constructed galvanic cells. The combination
of rate measurement via an electric current with measurement
of thermodynamic quantities via the EMF often permits analysis of kinetic processes. Both engineering applications and
thermodynamic and kinetic studies will be illustrated in this
37
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