RHODIUM(III) CHLORIDE 1
Rhodium(III) Chloride
RhCl3" 3H2O
EtOH, K2CO3
(3)
RhCl3
100 °C
51%
NPh NHPh
[10049-07-7] Cl3Rh (MW 209.26)
RhCl3" 3H2O
InChI = 1/3ClH.Rh/h3*1H;/q;;;+3/p-3/f3Cl.Rh/h3*1h;/q3*-1;m/
Ph 2.5 h Ph H
N
N (4)
rCl3Rh/c1-4(2)3
100%
Ph
Ph
InChIKey = SONJTKJMTWTJCT-ZUBXHIFLCV
(hydrate)
Furthermore, rhodium trichloride can isomerize strained carbo-
[20765-98-4]
cycles (eq 5).4 In comparison, IrIII, RuIII, and PtIV are effective in
(isomerizes alkenes and strained carbocycles;1 reduction
bringing about similar rearrangements; FeIII, NiII, and HgII are not
precatalyst;5 oxidation catalyst7)
active in the same fashion. Deuterium exchange studies indicate
that this process most likely involves a metal hydride.
ć%
Physical Data: mp 450 C.
Solubility: insol water; sol aq sodium hydroxide, aq potassium
CO2Et CO2Et
cyanide.
RhCl3
H
+ (5)
Form Supplied in: available as anhydrous solid and hydrated
MeOH, 70 °C
CO2Et
solid.
88% 12%
Analysis of Reagent Purity: elemental analysis.
Reductions. A mixture of Sodium Borohydride and rhodium
trichloride forms a selective reagent for the reduction of aromatic
systems (eq 6).5 This method does not affect carboxylic acids,
Original Commentary
esters, or amides; ketones are partially reduced; alkenes are com-
petitively reduced. The fact that aromatic nuclei typically require
Jeffrey A. McKinney
severe conditions for reduction underscores the usefulness of this
Zeneca Pharmaceuticals, Wilmington, DE, USA
mild process.
Isomerizations. Rhodium trichloride catalyzes the isomeriza-
CO2H CO2H
tion of alkenes, typically generating the thermodynamically more
NHCOMe NHCOMe
NaBH4, RhCl3
(6)
stable isomer. The exposure of an arylmethylenechroman-4-one
EtOH, 2 h, 30 °C
to this reagent results in the efficient migration of the exocyclic
94%
alkene (eq 1).1a This example nicely illustrates the mild nature of
the isomerization method as basic media induce degradation of
the chroman-4-one, acidic media do not produce a reaction, and
Rhodium trichloride, in the presence of the phase transfer cat-
Raney Nickel affords a mixture of the desired alkene isomer and
alyst Aliquat 336, serves as a hydrogenation catalyst that prefer-
a reduced compound. Enones to which alkenes are attached are
entially reduces alkenes in the presence of aromatic nitro groups
transformed into phenols upon reaction with rhodium trichloride
(eq 7).6 In general, the reduction of the nitro functionality is the
(eq 2).2 Unsaturated imines are converted to anilines via an anal-
most facile hydrogenation process.
ogous process (eq 3).2 This reagent also allows the removal of an
allyl protecting group from a wide variety of heteroatoms through
an isomerization hydrolysis pathway (eq 4).3
RhCl3, Aliquat 336
(7)
H2, MeNO2, 7 h
70%
NO2 NO2
Ph Ph
RhCl3" 3H2O
EtOH, CHCl3
(1) Oxidation. Phase transfer catalysis allows the oxidation of
O O O O
70 °C, 2 h
alkenes to proceed in the presence of rhodium trichloride (eq 8).7
100%
Tetrabutylammonium hydrogen sulfate (THS) is of general use
as a catalyst. Other quaternary ammonium salts will also serve
this role. Mechanistically, it is thought that this reaction is analo-
gous to the Wacker oxidation. This is in contrast to another report
describing the use of rhodium trichloride as a homogeneous
O
HO
oxidation catalyst.8
RhCl3" 3H2O
EtOH, 100 °C
(2)
RhCl3" 3H2O
62%
O2, benzene, H2O
1-Decene 2-Decanone (8)
THF, CuCl2
44%
Avoid Skin Contact with All Reagents
2 RHODIUM(III) CHLORIDE
Acetylene Hydration. Rhodium trichloride in acidic media RhCl3 3H2O
·
NO2 NH2 (13)
catalyzes the hydration of Acetylene (eq 9).9 The rate of this reac-
80% aq. TMEDA
100 °C, CO
tion is accelerated by the introduction of ligating additives such as
57%
Lithium Chloride In comparison, Ruthenium(III) Chloride also
catalyzes alkyne hydration but at one-third the rate of rhodium
trichloride.
Tetraene Amination Carbocyclization. The cyclization of
RhCl3
1,3,8,10-tetraene with secondary amines in the presence of RhCl3
(9)
C2H2 H2O MeCHO
and PPh3 results in the formation of a cyclopentane ring with the
new ring substituents having predominantly the cis stereochem-
istry (eq 14),14 while the palladium-catalyzed cyclization gives the
Hydrosilylation Catalyst. The hydrosilylation of
trans isomers.15 2,2,2-Trifluoroethanol is the solvent of choice.
Ä…,²-unsaturated esters to form dimethylketene trimethylsilyl
acetals is catalyzed by rhodium trichloride (eq 10).10 The use of
O
rhodium trichloride rather than Chlorotris(triphenylphosphine)
O
RhCl3, PPh3
Rhodium(I), the typical rhodium catalyst employed, results in a EtO
+
EtO
2,2,2-trifluoroethanol
faster reaction with improved yields and product purities.
N
75 °C
H
O 67%
TMSH MeO OTMS
CO2Me
(10)
RhCl3" 6H2O
O
75%
EtO
(14)
EtO
N
O
O
First Update
Yoshiya Fukumoto & Naoto Chatani
Oxidative Cyclization. With a stoichiometric amount of
Osaka University, Osaka, Japan
Cu(OAc)2·H2O as the oxidant, RhCl3·3H2O can function as an
efficient catalyst for the oxidative cyclization of 2,3-bisindolyl-
Isomerizations. RhCl3·3H2O can be used to catalyze the
maleimides to give indocarbazoles (eq 15).16 Under an O2 atmos-
cycloisomerization of cyclopropenyl ketones to give 2,3,5- phere, the amount of Cu(OAc)2·H2O used can be reduced to a
trisubstituted furans (eq 11). Other transition-metal com- catalytic amount without a loss in product yields.
plexes such as RuCl3·3H2O, PdCl2, PdCl2(CH3CN)2, and
PdBr2(PhCN)2 also show catalytic activity as well. Bn
N
OO
O
O O
OEt
RhCl3 3H2O
· RhCl3 3H2O
·
(11)
EtO
acetone, reflux
Cu(OAc)2 (stoichiometric) or
58%
Bu Cu(OAc)2 (catalytic), O2
O
Bu
N N
90 120 °C, DMF
H H
78%
Bn
Reductions. Rhodium(III) chloride catalyzes the hydrogena-
N
tion of diethyl vinylphosphonate in water or ethanol without the
OO
need for any external hydrogen source. Monoethyl ethylphospho-
nate is produced as the single product in almost quantitative yield
(15)
by the in situ hydrolysis of the primary product, diethyl ethylphos-
phonate (eq 12).12
N N
H H
OEt OEt
RhCl3 3H2O
·
OEt OH
(12)
P P
H2O, 100 °C or
O O
EtOH, 80 °C
Addition of Aryl- and Alkenylboronic Acids to Aldehy-
>99%
des. The combination of RhCl3·3H2O, an imidazolium salt, and
Aromatic nitro compounds undergo reduction to aniline deriva- NaOMe catalyzes the arylation and alkenylation of aldehydes
tives under water-gas shift reaction conditions in 80% aqueous with boronic acids (eq 16).17 Other rhodium complexes, such as
TMEDA solutions (eq 13).13 Some functional groups, such as Rh(acac)(coe)2 and [Rh(OAc)2]2, can also be used as catalysts, but
amino, fluoro, chloro, and nitrile, are compatible under the they are less active. While the addition is highly chemoselective
reaction conditions. The turnover frequencies for the production for aldehydes, other carbonyl groups such as ketones and amides
of substituted anilines are increased as the substituents become remain intact. N-Heterocyclic carbene derived from I functions as
more electron-releasing. the actual ligand, which is formed in situ.
A list of General Abbreviations appears on the front Endpapers
RHODIUM(III) CHLORIDE 3
O
Aza-Michael Reaction. The aza-Michael addition of car-
RhCl3 3H2O, I
·
bamates to enones in the presence of a RhCl3·3H2O catalyst
+ (HO)2B OMe
H
NaOMe, 80 °C, aq DME
leads to the production of ²-amino ketones (eq 19).20 Not only
93%
RhCl3·3H2O but also several group 7 11 transition-metal salts
OH
in a higher oxidation state such as Re(CO)5, Fe(ClO4)3·9H2O,
RuCl3·xH2O, OsCl3·3H2O, IrCl3·xH2O, PtCl4·5H2O, and
(16)
Aul3·2H2O also exhibit a high catalytic activity.
OMe
O O NHCbz
+
RhCl3 3H2O
N N Cl ·
(19)
+ H2NCbz
Ph Ph
CH2Cl2, rt
94%
I
t-Bu-Amphos, a sterically hindered, water-soluble phosphine
is also an effective ligand for catalytic arylation and alkenylation
reactions in aqueous solvents (eq 17).18 The catalyst species dis- 1. (a) Andrieux, J.; Barton, D. H. R.; Patin, H., J. Chem. Soc., Perkin
Trans. 1 1977, 359. For examples of other enone isomerizations see:
solved in the aqueous solvent can be recycled up to nine times
(b) Grieco, P. A.; Nishizawa, M.; Marinovic, N.; Ehmann, W. J., J. Am.
with little loss in product yields.
Chem. Soc. 1976, 98, 7102. (c) Genet, J. P.; Ficini, J., Tetrahedron Lett.
1979, 1499. (d) Harrod, J. F.; Chalk, A. J., J. Am. Chem. Soc. 1964, 86,
Disulfide Exchange Reaction. Unsymmetrical disulfides are
1776.
formed by a RhCl3·3H2O-catalyzed disulfide exchange reaction
2. Grieco, P. A.; Marinovic, N., Tetrahedron Lett. 1978, 2545.
in an aqueous solvent (eq 18).19
3. Moreau, B.; Lavielle, S.; Marquet, A., Tetrahedron Lett. 1977,
2591.
O
4. Wiberg, K. B.; Bishop, K. C., III, Tetrahedron Lett. 1973, 2727.
RhCl3 3H2O, t-Bu-Amphos
+ (HO)2BCN
H 5. Nishiki, M.; Miyataka, H.; Niino, Y.; Mitsuo, N.; Satoh, T., Tetrahedron
NaOH, 80 °C
Lett. 1982, 23, 193.
aq. CH3CN/H2O or H2O
6. Amer, I.; Bravdo, T.; Blum, J.; Vollhardt, K. P. C., Tetrahedron Lett.
90%
1987, 28, 1321.
OH
7. Januszkiewicz, K.; Alper, H., Tetrahedron Lett. 1983, 24, 5163.
(17)
8. Mimoun, H.; Machirant, M. M. P.; Seree de Roch, I., J. Am. Chem. Soc.
1978, 100, 5437.
CN
9. James, B. R.; Rempel, G. L., J. Am. Chem. Soc. 1969, 91, 863.
t
Bu2P
NMe3Cl
10. Revis, A.; Hilty, T. K., J. Org. Chem. 1990, 55, 2972.
11. Ma, S.; Zhang, J., J. Am. Chem. Soc. 2003, 125, 12386.
t-Bu-Amphos
12. Raghuraman, K.; Pillarsetty, N.; Prabhu, K. R.; Katti, K. K.; Katti,
K. V., Inorg. Chim. Acta 2004, 357, 2933.
NH2 H
13. Mdleleni, M. M.; Rinker, R. G.; Ford, P. C., J. Mol. Catal. A 2003, 204,
N RhCl3 3H2O
·
HOOC S + (HO2CCH2S)2
125.
H2O, 40 °C
O
14. Takacs, J. M.; Lawson, E. C., Organometallics 1994, 13, 4787.
80%
HN O
15. Takacs, J. M.; Zhu, J., J. Org. Chem. 1989, 54, 5193.
excess
HOOC 16. Witulski, B.; Schweikert, T., Synthesis 2005, 1959.
2
17. Fürstner, A.; Krause, H., Adv. Synth. Catal. 2001, 343, 343.
NH2 H
18. Huang, R.; Shaughnessy, K. H., Chem. Commun. 2005, 4484.
N
(18)
HOOC S SCH2CO2H 19. Arisawa, M.; Suwa, A.; Yamaguchi, M., J. Organomet. Chem. 2006, 691,
1159.
O
HN O
20. Kobayashi, S.; Kakumoto, K.; Sugiura, M., Org. Lett. 2002, 4,
1319.
HOOC
Avoid Skin Contact with All Reagents