Symmetrical biaryl synthesis via rhodium catalyzed dimerization of aryl mercuric salts

Vinyl- and arylmercuric halide salts undergo reaction with rhodium (I) and (III) catalysts, preferably in the presence of lithium chloride to provide essentially quantitative yields of the corresponding 1,3 dienes and biaryls respectively. Importantly, the reaction is stereospecific and is especially valuable for synthesis of symmetrical functionally substituted dienes, biaryls and polyenes.

BACKGROUND OF THE INVENTION 
Conjugated dienes are of considerable importance in organic chemistry in 
and of themselves. In addition, they are extremely important for use in 
the well known Diels-Alder reaction. Many conjugated dienes, biaryls and 
polyenes are used as intermediates for synthesis reactions and as monomers 
for the formation of polymeric reaction products. For example, the 
preparation of polybutadiene rubber. 
One problem often encountered with prior art processes for the formation of 
conjugated dienes is that the reaction procedures often are unsuitable for 
the preparation of functionally substituted dienes. Thus, if the diene 
being prepared is functionally substituted with, for example, a carboxyl 
group, a carbonyl group, an amino group, an ester group, or the like, 
often the reactive site in any synthesis reaction will be at the 
functional group rather than the formation of the desired conjugated 
diene. As a result, very few functional groups have been incorporated into 
these reactions. 
In addition, the preparation of conjugated dienes often encounters the 
difficulty that the stereospecificity of the reaction starting material is 
lost in the coupling procedure to prepare the conjugated diene. This is 
important in many syntheses since the stereochemistry can and indeed often 
does affect the ultimate reaction properties of any polymers which are 
formed. 
Accordingly, there is a real need in the art for the development of a new 
process for the preparation of symmetrical conjugated dienes and polyenes 
which both tolerates functionality and which produces symmetrical dienes, 
stereospecifically, in high yields. This invention has as one of its 
primary objectives the satisfaction of the above described needs, with 
respect to synthesis of conjugated dienes by a catalytic synthesis 
procedure. 
My earlier application related to a useful new method for the symmetrical 
dimerization of readily available vinylmercuric chlorides which employed 
stoichiometric amounts of palladium chloride and lithium chloride and 
provided 1,3-dienes in excellent yield. It has now been found that similar 
results can be achieved by use of rhodium catalysts thereby eliminating 
the previously required stoichiometric amount of expensive palladium 
chloride. 
It has also been discovered that nearly quantitative yields of biaryl 
compounds can be obtained by dimerization of aryl-mercurials in accord 
with a similar rhodium catalyzed reaction. 
SUMMARY OF THE INVENTION 
In summary, the invention provides for the first time a convenient, 
stereospecific, rhodium catalyzed synthesis of 1,3 dienes, and biaryls via 
vinylmercurials and arylmercurials, respectively. 
Importantly, reactions occur without any adverse effect upon functionally 
substituted groups.

DETAILED DESCRIPTION OF THE INVENTION 
In accordance with the process of this invention for synthesis of dienes 
from vinylmercurials, a vinylmercuric halide of the general formula 
##STR1## 
is dimerized in the presence of a rhodium (I) or (III) catalyst. In the 
formula for the vinylmercuric halide, X represents the anion of that 
compound and may be any of the common inorganic anions such as nitrate, 
acetate, phosphate, sulfate, chloride, bromide, iodide or the like. 
However, it is most preferable that X represents a monovalent inorganic 
anion which is a halide and more particularly is either chloride, bromide 
or iodide. 
The value of R is not critical and depends upon the precise conjugated 
diene which one desires to prepare. Generally R may be hydrogen or an 
organic hydrocarbon radical which is either saturated or unsaturated. The 
radical may be functionally substituted to provide, for example, keto 
groups, carboxylic acid groups, hydroxy groups, ester groups, amino 
groups, or other functional substituents. It may be an alkyl, acyl, aryl, 
aralkyl, alkenyl, alkynyl, straight or branched chains, or cyclic 
derivatives of the above, including heterocyclics. 
Preferably R is a lower, C.sub.12 and below, saturated or unsaturated, 
substituted or unsubstituted, alkyl, alkenyl, phenyl, or aralkyl group. 
As depicted in the general formula for the vinylmercuric halide salt, two 
hydrogen moieties are shown. However, it is to be understood that, if 
desired, the hydrogen moieties may be replaced with organic radicals such 
as those previously described to represent R. 
The starting material for the diene synthesis reaction of this invention, 
namely, vinylmercuric halides, are readily available through acetylene 
addition reactions, see for example, 
R. c. larock and H. C. Brown, J. Organometal Chem., 36, 1 (1972). 
R. c. larock, S. K. Gupta, and H. C. Brown, J. Amer. Chem. Soc., 94, 4371 
(1972). 
H. staub, K. P. Zeller and H. Leditschke, In Houben-Weyl's "Methoden der 
Organischen Chemie", Fourth Ed., Vol. 13, G. Thieme Verlag, Stuttgart, 
1974, Pt. 2b, pp. 192-199. 
which are incorporated herein by reference. 
Turning now to the biaryl synthesis, the starting materials are 
arylmercurials, ArHgX or Ar.sub.2 Hg, preferably arylmercurial halide 
salts. Biaryls are usually prepared by the dimerization of aryl halides by 
copper (Ullmann reaction) or zerovalent nickel reagents, or through the 
reaction of aromatic Grignard or lithium reagents, with any variety of 
inorganic salts. The Ullmann reaction suffers several disadvantages. It is 
best carried out with aryl iodides which are often difficult to obtain in 
high isomeric purity. It is incompatible with amine, amide, and hydroxyl 
functionality, and it usually requires basic solvents and temperatures in 
excess of 200.degree. C for extended reaction times. The nickel (O) 
reagents are not readily available and are difficult to handle. The use of 
the highly reactive arylmagnesium and -lithium reagents is limited by the 
incompatibility of these organometallics with a variety of important 
organic functional groups. 
It has now been found, just like the dimerization of vinylmercurials with 
rhodium catalyzed reactions, the corresponding reaction of arylmercuric 
salts in the presence of rhodium catalysts can be used to achieve a new 
route to biaryls. 
The aryl compound (ArHgX) has the same X moiety as the vinylmercuric 
compound. The aryl moiety may be alkylaryl, a functionally substituted 
aryl such as a keto, hydroxy, nitro, sulfur, or oxygen substituted aryl, 
it may be a naphthalene ring containing compound, an anthracene ring 
containing compound, a diaryl compound or the like. Preferably, it is an 
aryl, either functionally substituted or non-substituted, or a C.sub.1 
-C.sub.12 alkylaryl mercurial compound. 
The catalyst for the dimerization reactions described herein is either a 
rhodium (I) or (III) catalyst and is preferably a rhodium I or rhodium III 
complex. Using such catalysts vinylmercuric salts and arylmercuric salts 
are dimerized in high yield and isomeric purity. 
The catalyst may be rhodium per se but is preferably a rhodium salt and is 
most preferably a rhodium (I) or (III) complex. Rhodium I complex salts 
are well known and are generally prepared by the reduction of rhodium 
(III) salts in the presence of a selected ligand such as phosphines, 
dienes, carbon monoxide and the like. Such complexes are readily available 
from specialty chemical houses and by synthesis in accordance with the 
Osborne et al. article, which is incorporated by reference in a later part 
of this application. 
The amount of catalyst may vary from 0.01% up to about 10% of an equivalent 
of the vinylmercuric salt or the arylmercuric salt depending upon whether 
the reaction is conducted in the presence of certain organic solvents or 
in the presence of an added source of chloride ions, such as lithium 
chloride. Where added chloride ion source is employed, i.e., over and 
above the amount from the vinyl or aryl salt, catalyst amounts on the 
lower end of the range may be employed. 
Any polar organic solvent capable of dissolving the catalyst and the aryl 
or vinylmercuric salt may be employed, but it has been found that the 
yield increases steadily with the polarity of the solvent, and in 
particular, seems to be best when the solvent is an organic phosphorous 
containing solvent. Typical solvents which may be employed to produce the 
biaryl and diene products of this invention include tetrahydrofuran, 
acetonitrile, pyridine, acetone, methyl alcohol, dimethyl sulfoxide, N, 
N-dimethyl formamide, and organic phosphorous containing polar solvents 
such as hexamethylphosphoramide. The preferred solvent is 
hexamethylphosphoramide since the highest yields of product, consistent 
with maintaining stereospecificity, are achieved. 
As previously mentioned, in order to achieve high yields of the symmetrical 
conjugated dienes, or biaryls in accord with the synthesis reaction, it is 
preferred that reaction be conducted in the presence of added amounts of 
halide ions. By the term added amounts of halide ions is meant amounts of 
halide ions in excess of the amount which may otherwise be provided by the 
aryl or vinylmercuric salt, if that salt is a halide salt. It is preferred 
that additional amounts of halide ions be added because such has been 
found essential to providing high yields of symmetrical conjugated dienes 
and biaryls which maintain the stereochemistry of the aryl or 
vinylmercuric salt. The source of the additional halide ions may be any 
metal salt which is soluble in the reaction solvent. Preferably the metal 
salt is an alkali metal halide salt with the alkali metal being sodium, 
potassium or lithium. Most preferably the alkali metal is lithium and the 
salt is lithium chloride. 
It is preferred that the reaction be conducted at room temperature or lower 
temperatures for preparation of conjugated dienes. Generally satisfactory 
results are obtained at temperatures within the range of from about 
0.degree. C to about 25.degree. C with satisfactory results being obtained 
at room temperature. However, for dimerization of arylmercurials it is 
preferred that the reaction be within the range of 60.degree. C to 
90.degree. C and preferably 70.degree. C to 85.degree. C. 
To summarize for a moment, the synthesis route for the preparation of the 
symmetrical, stereospecific, conjugated dienes in accord with the process 
of this invention may be represented by the following equation, which 
assumes that the vinylmercury compound is a vinylmercuric chloride, and 
which assumes that the rhodium catalyst employs added amounts of lithium 
chloride as an additional chloride ion source. 
##STR2## 
The reaction is advantageous over prior art processes of preparing 
conjugated dienes in that it obtains the desired product in high yield, 
often in excess of 90%. In addition, the reaction is stereospecific and 
maintains the stereospecific relationship of the vinylmercuric halide so 
that one can predictably prepare cis or trans isomers. In addition, the 
reaction is highly tolerant of the presence of functional groups 
substituted on the R moiety or in place of the hydrogen moieties of the 
vinylmercuric salt. It is the entire combination of reaction conditions 
which produces high yields, the tolerance to functional groups, and the 
stereospecificity. The obtaining of high yields and control of the 
stereochemistry of the isomer produced appears to be a function of the 
organomercuric halide starting material in combination with suitable 
solvents. It is preferred that the reaction temperature be room 
temperature or lower since better yields and higher stereospecificity are 
observed at lower temperatures. 
The overall reaction for dimerization of the biaryls may be represented as 
follows: 
##STR3## 
This reaction has all of the advantages previously listed for the 
vinylmercurial dimerization reaction. 
The following examples are offered to further illustrate but not limit the 
process of this invention. 
EXAMPLES OF SYNTHESIS OF DIENES VIA VINYLMERCURIALS AND RHODIUM CATALYSIS 
In these initial examples the effect of 10% of a variety of commercially 
available rhodium(I) and (III) complexes on the room temperature 
dimerization of trans-1-hexenylmercuric chloride in HMPA (equation below) 
was studied. The results are summarized in Table 1. 
Table 1. 
______________________________________ 
##STR4## 
##STR5## 
RHODIUM CATALYZED 
DIMERIZATION OF TRANS-1- 
HEXENYLMERCURIC CHLORIDE.sup.a 
Exam- 
ples Rhodium Complex Diene Yield (%).sup.b 
______________________________________ 
1 ClRh(PPh.sub.3).sub.3 
28 
2 ClRh(CO) (PPh.sub.3).sub.2 
74 
3 [ClRh(CH.sub.2CH.sub.2).sub.2 ].sub.2 
70 
4 [ClRh(COD)].sub.2.sup.c 
81 
5 [ClRh(CO).sub.2 ].sub.2 
87 
6 [ClRh(CO).sub.2 ].sub.2 /LiCl.sup.d 
95 
7 RhCl.sub.3 . nH.sub.2 O.sup.e 
61 
8 RhCl.sub.3 . nH.sub.2 O.sup.e /LiCl.sup.d 
94 
______________________________________ 
.sup.a All reactions were run with 10% "rhodium" per vinylmercurial (5% 
dimeric rhodium complex) for 6 hours at room temperature in HMPA 
(hexamethylphosphoramide) under a nitrogen atmosphere. 
.sup. b All yields were determined by GLC analysis using an internal 
standard. 
.sup.c COD = 1,5-cyclooctadiene. 
.sup.d Two equivalents of lithium chloride per vinylmercurial were 
employed. 
.sup.e n is approximately 2.3. 
All of the rhodium complexes studied proved to be catalytic. The rhodium 
(I) complexes generally appear to be more effective than rhodium 
trichloride. In all reactions, the trans,trans-diene was obtained in 98% 
or greater stereospecificity. Unlike the earlier palladium reactions of my 
parent application, low temperatures are no longer necessary to achieve 
high stereospecificity. While the large majority of the diene product is 
formed in the first 6 hours, the yields can be slightly improved by 
letting the reaction run longer (up to 24 hours). As in my earlier 
application work with palladium chloride, the addition of lithium chloride 
(2 equiv. per vinylmercurial) can substantially improve the yield of 
diene. The combination of lithium chloride and [ClRh(CO).sub.2 ].sub.2 or 
RhCl.sub.3.nH.sub.2 O appeared to be the most effective catalyst. A 
comparison of these two complexes at various catalyst concentrations 
demonstrated the superiority of the rhodium (I) complex (Table II). Even 
at concentrations as low as 0.01% and in the presence of air, this 
catalyst gives a 95% yield of trans,trans-5,7 dodecadiene from 
trans-1-hexenylmercuric chloride. The effect of other solvents on this 
reaction was not significant, it was found that one need not use HMPA 
since diethyl ether or tetrahydrofuran (THF) work equally well. (Table 
II). 
The full scope of this reaction has been investigated on a variety of 
vinylmercuric chlorides, and the yields are indicated in Table III. 
Vinylmercurials derived from terminal alkynes give excellent yields of the 
corresponding dienes. The more sterically hindered vinylmercurials derived 
from internal alkynes react much more sluggishly and even after heating at 
75.degree. C for 24 hours still give only very poor yields of 1,3-dienes. 
Table II. 
______________________________________ 
Comparison of Rhodium Catalyst Activity 
##STR6## 
Sol- Concen- Yield 
Ex. Rhodium Catalyst 
vent tration(%).sup.a 
(%).sup.b 
______________________________________ 
9 RhCl.sub.3 . nH.sub.2 O.sup.c /LiCl 
HMPA 10 100 
10 1 85 
11 [ClRh(CO).sub.2 ].sub.2 /LiCl 
10 98 
12 1 100 
13 0.01 90 
14 95.sup.d 
15 Et.sub.2 O 
1 90 
16 THF 78.sup.e 
17 99 
______________________________________ 
.sup.a Percent "rhodium" per vinylmercurial. 
.sup.b Analysis by GLC using an internal standard. 
.sup.c n is approximately 2.3. 
.sup.d Reaction run in the presence of air (all others are under 
nitrogen). 
.sup.e No lithium chloride used. 
Table III. 
__________________________________________________________________________ 
Synthesis of Dienes and Polyenes 
Example 
Vinylmercurial 
Catalyst.sup.a 
Solvent 
Diene Yield (%).sup.b 
__________________________________________________________________________ 
18 
##STR7## RhCl.sub.3 . nH.sub.2 O 
HMPA 
##STR8## 65 
19 [ClRh(CO.sub.2 ].sub.2 100 
20 THF 84 
21 
##STR9## RhCl.sub.3 . nH.sub.2 O 
HMPA 
##STR10## 85 
22 [ClRh(CO).sub.2 ].sub.2 100 
23 THF 99 
24 
##STR11## RhCl.sub.3 . nH.sub.2 O 
HMPA 
##STR12## 98 
25 [ClRh(CO).sub.2 ].sub.2 100(88) 
26 THF 100 
27 
##STR13## RhCl.sub.3 . nH.sub.2 O 
HMPA 
##STR14## 24.sup.c 
28 [ClRh(CO).sub.2 ].sub.2 35.sup.c 
29 
##STR15## 
##STR16## (90) 
30 THF (97) 
31 
##STR17## HMPA 
##STR18## (92) 
__________________________________________________________________________ 
.sup.a 1% " Rhodium" and 2 equiv lithium chloride per vinylmercurial; 
.sup.b GLC analysis (isolated yield); 
.sup.c Reactions run at 75.degree. C. 
EXAMPLES OF BIARYL SYNTHESIS 
Using conditions similar to those worked out for the synthesis of dienes 
([ClRh(CO).sub.2 ].sub.2 and lithium chloride), the effect of different 
catalyst concentrations, temperatures, and solvents on the dimerization of 
both phenylmercuric chloride and diphenylmercury (Table IV) was studied. 
Phenylmercuric chloride proved significantly less reactive than any of the 
vinylmercuric chlorides examined earlier and reaction temperatures greater 
than room temperature were required to obtain a reasonable rate of 
reaction. A reaction temperature of 80.degree. C was quite sufficient and 
all subsequent work was done at this temperature. Catalyst concentrations 
as low as 1% proved effective. Increasing or decreasing the amount of 
catalyst resulted in lower yields of biphenyl. Polar solvents proved most 
effective, with acetonitrile somewhat less effective than HMPA. 
Table IV. 
__________________________________________________________________________ 
[ClRh(CO).sub.2 ].sub.2 Catalyzed Dimerization of Arylmercurials.sup.a 
Arylmercuric Catalyst Temp 
Yield 
Example 
chloride.sup.b 
Biaryl 
Solvent 
concentration(%).sup.c 
(.degree. C) 
(%).sup.d 
__________________________________________________________________________ 
32 
##STR19## 
##STR20## 
THF 1 66 15.sup.e 
33 25 
34 MeOH 65 24 
35 CH.sub.3 CN 82 65 
36 HMPA 1 25 25 
37 0.5 80 61 
38 1 81 
39 2 67 
40 1 125 78 
41 
##STR21## 1 25 36 
42 1 80 66 
__________________________________________________________________________ 
.sup.a All reactions were run for 24 hr. with 2 equiv lithium chloride pe 
arylmercurial under a nitrogen atmosphere. 
.sup.b One mmol phenylmercuric chloride or 0.5 mmol diphenylmercury. 
.sup.c Percent "rhodium" per vinylmercurial. 
.sup.d GLC analysis using an internal standard. 
.sup.e No lithium chloride present. 
The generality of the above described approach to the synthesis of biaryls 
(equation below) 
##STR22## 
(Table V) was studied. In general, the yields of biaryl are comparable to 
those obtained by other routes. However, the reaction proceeds at much 
lower temperatures than the Ullmann reaction and significantly lower than 
those of Kretchmer's procedure. 
Table V. 
______________________________________ 
Synthesis of Biaryls 
Iso- 
Ex- lated 
am- Arylmercuric Yield Mp(.degree. C) 
ple Chloride Biaryl (%) (lit mp) 
______________________________________ 
43 
##STR23## 
##STR24## 84 62-65.5 (70.5) 
44 
##STR25## 
##STR26## 92 120-121.5 (121-122) 
45 
##STR27## 
##STR28## 88 177-178 (175) 
46 
##STR29## 
##STR30## 88 277-278.5 (272) 
47 
##STR31## 
##STR32## 53 202-202.5 (200) 
48 
##STR33## 
##STR34## 40 312-313 (320) 
49 
##STR35## 
##STR36## 94 185-186 (187-8) 
50 
##STR37## 
##STR38## 70 oil 
51 
##STR39## 
##STR40## 96 32-33 (32.5) 
______________________________________ 
The ease with which arylmercurials are obtained through direct 
electrophilic aromatic mercuration of arenes and the high isomeric purity 
obtained by simple recrystallization of these stable organometallics 
recommends their use in organic synthesis. The mild conditions for 
dimerization and ease of isolation, plus the high isomeric purity of the 
products makes this a valuable new route to symmetrical biaryls. 
The following general procedures are repeated herein only once to show the 
exact procedure employed for the preparation of the rhodium catalyzed 
dienes and binaryls shown in the above tables. 
Reagents 
All chemicals were used directly as obtained commercially unless otherwise 
indicated. HMPA was distilled from lithium aluminum hydride (LAH) under 
vacuum. Pentane was stirred over fuming sulfuric acid, washed with water 
and stored over anhydrous sodium sulfate after distillation. Ether and THF 
were distilled from LAH. 
The vinylmercurials used have all been described elsewhere in this 
application and my earlier parent case, and were prepared using a standard 
hydroboration-mercuration sequence as shown discussed in the incorporated 
references. 
[ClRh(CO).sub.2 ].sub.2 (PCR), [(CH.sub.2 .dbd.CH.sub.2).sub.2 RhCl].sub.2 
(Strem), (1,5-COD RhCl).sub.2 (ROC/RIC), (Ph.sub.3 P).sub.2 Rh(CO)Cl (Alfa 
Inorganics-Ventron), and RhCl.sub.3.nH.sub.2 O (Matthey Bishop) were used 
directly as obtained. Wilkinson's catalyst, (Ph.sub.3 P).sub.3 RhCl, was 
prepared from RhCl.sub.3.nH.sub.2 O according to published procedures of 
Obsborne, et al., Inorganic Synthesis, 10, 67 (1967) which is incorporated 
herein by reference. 
All GLC yields are corrected by the use of appropriate hydrocarbon internal 
standards. 
(Rhodium Catalyzed Dimerization of trans-1-Hexenylmercuric Chloride -- 
Table I) 
The catalytic activity of a variety of different rhodium catalysts was 
examined using the following standard procedure for the dimerization of 
trans-1-hexenylmercuric chloride. The catalyst (0.10 mmol of monomeric, 
and 0.05 mmol of dimeric rhodium catalysts), tetradecane ((internal 
standard, approx. 0.5 mmol) and lithium chloride (2.0 mmol) where 
appropriate were dissolved in HMPA 5 ml) in a 25 ml round bottom flask 
which has been previously flushed with nitrogen. The 
trans-1-hexenylmercuric chloride (1.00 mmol) was added and the reaction 
stirred for 6 hours at room temperature. Ether (5 ml) was then added and 
the mixture analyzed on a 10' 10% DC-550 GLC column. The results are 
included in Table I. 
(Comparison of Rhodium Catalyst Activity--Table II) 
The appropriate amount of RhCl.sub.3.nH.sub.2 O (n.perspectiveto.2.3) (0.1 
or .01 mmol) or [ClRh(CO).sub.2 ].sub.2 (0.05, 0.005 or 0.00005 mmol), 
lithium chloride (2 mmol), and tetradecane were dissolved in 5 ml of the 
appropriate solvent. Trans-1-hexenylmercuric chloride (1 mmol) was added 
and the reaction stirred for 24 hours at room temperature. The yields in 
HMPA were determined by GLC as described above. The ether and THF 
reactions were analyzed by GLC after adding water or saturated ammonium 
chloride solution respectively. 0.01% [ClRh(CO).sub.2 ].sub.2 was achieved 
by adding 0.025 ml. of a solution containing 4.0 mg. of catalyst in 5.0 
ml. HMPA. The results are summarized in Table II. 
(Synthesis of Dienes) 
The following procedure for the synthesis of 
trans,trans-2,2,7,7-tetramethylocta-3,5-diene, is representative. 
[ClRh(CO).sub.2 ].sub.2 (0.05 mmol) and lithium chloride (20 mmol) were 
placed in a 250 ml round bottom flask equipped with a septum inlet and gas 
inlet tube which has been flushed with nitrogen. HMPA (50 ml) and then 
trans-3,3-dimethyl-1-butenyl-mercuric chloride (10.0 mmol) were added and 
the reaction stirred for 24 hours at room temperature. The reaction 
mixture was poured into water and pentane added. A gray suspension formed 
and was filtered off. The gray residue was washed with pentane. The 
pentane layer was separated and the water layer re-extracted with pentane. 
The combined pentane extracts were washed with water, dried over anhydrous 
sodium sulfate, and the pentane removed under vacuum. A white solid (0.73 
g, 88%, crude mp 74.degree.-77.degree. C, mp 77.degree.-78.degree. C 
(EtOH), lit. mp. 78.degree.-79.degree. C) was obtained. .sup.1 H NMR 
(CCl.sub.4) .delta.1.00 (18H, s, CH.sub.3) and 5.6 (4H, m, vinyl). All 
other dienes were prepared in like manner using the same molar quantities, 
solvent and conditions. The results are reported in Table III. 
The THF preparative reaction was worked up by adding saturated ammonium 
chloride, separating the layers, and washing the aqueous layer with 
hexane. The combined organic layers were then washed with saturated 
ammonium chloride, 3M sodium thiosulfate, and saturated sodium chloride, 
dried over anhydrous sodium sulfate, and the solvent removed. 
All GLC yields were determined on reactions run on one-tenth the above 
scale following GLC analysis procedures identical to those outlined above. 
Internal standard correction factors were determined using authentic diene 
samples. 
([ClRh(CO).sub.2 ].sub.2 Catalyzed Dimerization of Arylmercurials-- 
The effect of catalytic amounts of [ClRh(CO).sub.2 ].sub.2 on the 
dimerization of phenylmercuric chloride and diphenylmercury was examined 
as follows: The appropriate quantity of [ClRh(CO).sub.2 ].sub.2 (0.01, 
0.005 and 0.0025 mmol), lithium chloride (2.0 mmol) and octadecane were 
dissolved in the appropriate solvent (5 ml) in a 25 ml round bottom flask 
equipped with a rubber septum. After adding phenylmercuric chloride (1.0 
mmol) or diphenylmercury (0.50 mmol) the reaction was stirred for 24 hours 
at room temperature or in a preheated oil bath. The HMPA reaction was 
poured into water and ether added. The ether layer was analyzed by GLC on 
a 10' 10% DC-550 column. The THF reactions were analyzed as described 
previously and the methanol and acetonitrile reactions were analyzed 
directly. 
(Synthesis of Biaryls -- Table V) 
The following procedure for the synthesis of 4,4'-bianisole is 
representative. [ClRh(CO).sub.2 ].sub.2 (0.05 mmol) and lithium chloride 
(20 mmol) were dissolved in HMPA (50 ml) in a 250 ml round bottom flask 
equipped with a gas inlet tube and a sidearm fitted with a rubber septum. 
After adding 4-methoxyphenylmercuric chloride (10 mmol) the reaction was 
stirred in a preheated oil bath at 80.degree. C for 24 hours. A puddle of 
metallic mercury was observed. The reaction mixture was then poured onto 
ice and benzene added. After separating the layers, the water was 
re-extracted with benzene. The combined organic layers were washed with 
water, 10% HCl, 3M sodium thiosulfate, water and saturated sodium 
chloride, and dried over anhydrous magnesium sulfate. Removal of the 
solvent under vacuum provided 0.94 g of white solid (88%); mp 
174.5.degree.-175.5.degree. C before recrystallization, mp 
177.degree.-178.degree. C (hexane) (lit. mp. 175.degree. C). 
As has been mentioned previously herein and as shown in Examples 41, 42 and 
44, while the preferred arylmercuric salts are the arylmercuric halide 
salts, satisfactory results are also obtained when diarylmercury salts 
(Ar) .sub.2 Hg are employed, as for example diphenylmercury and 
di-p-tolylmercury. Thus, it is to be understood that the specific 
description given herein for arylmercuric salts is also equally applicable 
to the diarylmercury salts.