Effective transmetalation from gold to iron or ruthenium

Article abstract of DOI:10.1021/om200360q

The transmetalation of aryl, alkynyl, and alkyl groups from organogold compounds to iron complexes offers an efficient synthesis of organoiron complexes under very mild conditions. This method could be extended to ruthenium complexes.

Full text of DOI:10.1021/om200360q

COMMUNICATION
pubs.acs.org/Organometallics
Effective Transmetalation from Gold to Iron or Ruthenium
A. Stephen K. Hashmi* and Lise Molinari
Organisch-Chemisches Institut, Ruprecht-Karls-Universit€at Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
S Supporting Information
b
ABSTRACT: The transmetalation of aryl, alkynyl, and alkyl groups
from organogold compounds to iron complexes offers an efficient
synthesis of organoiron complexes under very mild conditions.
This method could be extended to ruthenium complexes.
n the past decade gold has emerged as a powerful tool to
achieve many organic transformations through carbonÀcarbon
temperature and monitoring the reaction by NMR. We were
delighted to detect that within a few minutes the transfer of the
aryl group from gold to iron was complete, leading to the
organoiron complex 3a. The reaction progress was even detect-
able by a color change; the initially dark brown solution had
turned bright yellow. The complex was purified by column
chromatography and isolated in 84% yield. Ph3PAuI could also
be isolated in 87% yield. Then we explored the scope of the
reaction using other organogold compounds. Electron-rich aro-
matic moieties, such as p-tert-butylphenyl, could be transmeta-
lated in excellent yield (Table 1, entry 4). The presence of a
coordinating methoxy substituent on the aromatic ring did not
affect the reaction (Table 1, entry 5), and even the sterically
hindered m-methoxyphenyl moiety (Table 1, entry 6) could be
transmetalated completely; the corresponding organoiron spe-
cies 3d was isolated in 82% yield. Organogold complexes bearing
electron-deficient aryl groups were also investigated. Both the
weakly electron withdrawing fluoro substituent (Table 1, entry 9)
and strongly electron withdrawing nitro group in para position
(Table 1, entry 11) were transferred easily. With the nitro group
in the meta position (Table 1, entry 15), complete ligand
exchange was achieved within 1 h and product 3h could be
isolated in good yield. The transmetalation between the sterically
hindered Hammond furanone gold complex 1i,13 a stable inter-
mediate of a gold-catalyzed cycloisomerization, and iron complex
2a (Table 1, entry 18) was slower than for arylgold species, but
clean conversion at room temperature delivered 3i in good yield.
Focusing onthe influence of the hybridization, the transmetalation
of an sp-hybridized phenylacetylene moiety (Table 1, entry 19)
afforded the organoiron species 3j in excellent yield. In contrast
to the furanone 1i, the transfer of a simpler sp2-hybridized vinyl
group (Table 1, entry 20) did not deliver the expected compound
3k. Monitoring the reaction by 1H and 31P NMR showed
consumption of the vinylgold compound 1k, but instead of the
expected formation of Ph3PAuI at 39 ppm in 31P NMR, one major
peak was observed at 61 ppm. 1H NMR and COSY showed the
presence of two different vinyl species, which were not consistent
with NMR data reported for the desired product 3k. These species
I
or carbonÀheteroatom bond formation.1 The cycloisomeriza-
tions of enynes2 and the hydrofunctionalizations of alkenes,
allenes, and alkynes with nucleophilic heteroatoms are represen-
tative examples.3 These catalysis reactions proceed under very
mild conditions and are based on the high carbophilic character
of gold(I/III) complexes. However, the catalytic cycle for most of
these reactions does not involve changes in the oxidation state of
the catalyst.4 Gold catalysts do not undergo oxidative addition
reactions easily.5 To circumvent this problem, transmetalation of
isolated or in situ generated organogold species to other transi-
tion metals with pronounced redox ability allows broadening
the scope of gold catalysis. Different groups have addressed the
palladium-catalyzed cross-coupling reaction of organogold
compounds.6 While transmetalation between gold and palladium
has since been studied more extensively,7 publications reporting
transmetalation between gold and other metals remain sporadic.8
Blum and co-workers recently reported the nickel-catalyzed cross-
coupling reactions of stoichiometric organogold compounds9 and
studied the transmetalation between organogold and rhodium
complexes.10 Due to the recent success of iron-catalyzed cross-
coupling in organic synthesis,11 we turned our attention to the
transmetalation between gold and iron. Iron is a very cheap and
nontoxic metal, which has proven to be a powerful catalyst in many
reaction types, including cross-coupling. Reports of a transmetalation
step between gold and iron complexes are scarce; van Koten and co-
workers published the transmetalation of an (o-amine)aryl moiety,8c
and Low et al. reported the transmetalation of an alkynyl group.8j
In the search for a stable iron complex as a potential
transmetalation partner, our interest focused on the coordina-
tively saturated piano-stool iron complex. Oshima et al. reported
the synthesis of aryliron compounds using the dicarbonylcyclo-
pentadienyliodoiron complex CpFe(CO)2I (2a) from different
organometallic reagents.12 Their method is efficient but requires
the use of a palladium catalyst and/or different additives. Herein
we report transmetalation between organogold and iron com-
plexes, showing that this type of reaction might be incorporated
in catalytic cycles in the future.
We started using the simplest reaction conditions, by mixing
the arylgold 1a with iron complex 2a in chloroform at room
Received: April 28, 2011
Published: June 13, 2011
r
2011 American Chemical Society
3457
dx.doi.org/10.1021/om200360q Organometallics 2011, 30, 3457–3460
|

Organometallics
COMMUNICATION
Table 1. Transmetalation between Organogold Compounds and Iron Complexesc
a Reaction was carried out at 60 °C. b Yield determined by NMR. c IPr = [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene].
could not be isolated for characterization. An sp3-hybridized
methyl group could almost be fully transferred to the iron complex
(93% conversion based on 1H and 31P NMR integration), but the
product decomposed upon purification. In order to examine the
reactivity toward transmetalation of other iron complexes, we
tested the transmetalation between representative organogold com-
pounds and the corresponding bromo and chloro iron complexes
(2b,c). The bromo complex 2b showed reactivity comparable
with that of the iodo complex 2a. Though the transmetalation
proceeded slightly more slowly, the yield was not affected
(Table 1, entries 2, 7, 10, 12, 14, and 16). The conversion of
the chloro complex 2c was found to be slow at room temperature,
but upon heating at 60 °C, the organoiron complexes could be
isolated in modest to good yield (Table 1, entries 3, 8, and 17).
To get a more reliable insight into the transmetalation kinetics,
we monitored the reaction by 31P NMR, combining the organo-
gold compounds 1f,h and the three different iron complexes 2aÀc.
Transmetalation between the p-nitrophenylgold complex 1f
(Figure 1) and the iodo iron complex 2b was achieved within
5 min, while with the bromo iron complex 2b, completion was
observed after 15 min. For the chloro complex 2c, after almost
2 h, the conversion reached 67% and did not evolve. As expected
for the m-nitrophenyl group (Figure 2), the reaction was slower
than for 1f with the iron complexes 2a,b and for 2c the trans-
metalation reached only 28% conversion after prolonged re-
action times.
3458
dx.doi.org/10.1021/om200360q |Organometallics 2011, 30, 3457–3460

Organometallics
COMMUNICATION
Table 2. Yield of Gold-Catalyzed Formation of Organoiron 3ja
Figure 1. NMR-monitored kinetics for the formation of 3f (with
respect to Ph3PAuX formation) from complexes 2aÀc.
a The structures of 5 and 6 are as follows:
Figure 2. NMR-monitored kinetics for the formation of 3h (with
respect to Ph3PAuX formation) from complexes 2aÀc.
Next we investigated the influence of organogold ligand
hindrance. A drastic influence on the reactivity was observed with
the organogold species 4a, bearing the very bulky N-heterocyclic
carbene ligand IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-
2-ylidene) and transfer of the p-tolyl group to the iron complex to
form 3a was not observed, although the reaction mixture was
heated to60 °C (Table 1, entry 22). Using the bromo iron complex
2b led to the same result (Table 1, entry 23).
Encouraged by the results for the transmetalation from gold to
iron, we decided to explore another group 8 metal, ruthenium.
Piano-stool ruthenium cymene complexes appeared to be the
proper choice; they behave quite similarly to the corresponding
iron compounds. Complexes 9a,b were both synthesized from the
corresponding dimer. In order to avoid ligand exchange between
chlorinated solventand complex9b, the reaction was carried outin
THF at 40 °C. Two representative organogold compounds were
tested. The activated p-methylphenyl group was transferred to
ruthenium complexes 9a,b, leading to the formation of organor-
uthenium species 10aa,ab in good yields. Transmetalation of a
deactivated m-nitrophenyl group could be achieved even more
efficiently for both chloro and bromo complexes 9a,b (Scheme 2).
We have presented in this publication a very efficient and
mild method for the synthesis of organoiron and -ruthenium
complexes by transmetalation with organogold complexes. This
method also allows the use of a catalytic amount of gold cata-
lyst for the formation of iron phenylacetylene complexes. The
transmetalation from gold to iron and ruthenium might in the
future serve as the basis for combining the very successful iron-
catalyzed coupling methods with gold catalysis. This would
extend the possibilities, which are currently limited to gold/
palladium and gold/nickel systems. On the other hand, this
efficient transmetalation differs from previous work on the trans-
metalation from organozincandorganomagnesiumcompounds or
boronic acids, which requires a palladium catalyst.12a We assume
that, different from the case for zinc, magnesium, or boron, the
high affinity of the soft gold(I) for iodine and bromine creates an
additional driving force for the transmetalation, an effect which
Even though Ph3PAuX (X = I, Br, Cl) could be isolated in very
good yield, our next focus was to achieve the transmetalation using a
catalytic amount of the gold complex. Phenylacetylene seemed to be
the proper choice, as it can easily form the corresponding organogold
complex 1j in the presence of a base, without silver salt activation.
Using Et3N as a base, 10 mol % of Ph3PAuCl with iron complexes
2aÀc at 60 °C led to stoichiometric formation of organoiron 3j in
modest to good yield depending on the iron precursor (Table 2, entry
2). Changing the gold catalyst to the conformationally more flexible
noncyclic amino carbene (NAC)14 ligand 6 gave an excellent yield,
except for the chloro iron complex 2c (Table 2, entry 3). The catalyst
loading could be even reduced to 3 mol % without affecting the yield
of the reaction (Table 2, entry 4). The control experiment showed
that, in the absence of the gold catalyst, the amount of 3j formed was
very low; in the case of 2c it failed completely (Table 2, entry 1).15
To further emphasize the synthetic advantages of this meth-
odology, we decided to test a subsequent coupling reaction of 3j
with 3-bromo-2-methylpropene (7), which had been found by
Oshima and co-workers to be a good coupling partner.8b,d The
conversion was conducted as a one-pot reaction with sequential
addition: first the gold-catalyzed formation of 3j, followed by a
coupling reaction with 7 under UV irradiation. The formation of
the spÀsp3 coupling product 8 could be achieved in 34À46%
yield (Scheme 1).
3459
dx.doi.org/10.1021/om200360q |Organometallics 2011, 30, 3457–3460

Organometallics
COMMUNICATION
Scheme 1. One-Pot spÀsp3 Cross-Coupling Reaction
48, 8243–8246. (c) Shi, Y.; Roth, K. E.; Ramgren, S. D.; Blum, S. A.
J. Am. Chem. Soc. 2009, 131, 18022–18023.
(7) (a) Shi, Y.; Ramgren, S. D.; Blum, S. A. Organometallics 2009,
28, 1275–1277. (b) Shi, Y.; Roth, K. E.; Ramgren, S. D.; Blum, S. A. J. Am.
Chem. Soc. 2009, 131, 18022–18023. (c) Hashmi, A. S.; D€opp, R.;
Lothsch€utz, C.; Rudolph, M.; Riedel, D.; Rominger, F. Adv. Synth. Catal.
2010, 352, 1307–1314. (d) Pe~na-Lꢀopez, M.; Ayꢀan-Varela, M.; Sarandeses,
L. A.; Pꢀerez Sestelo, J. Chem. Eur. J. 2010, 16, 9905–9909. (e) Lauterbach,
T.; Livendahl, M.; Rosellꢀon, A.; Espinet, P.; Echavarren, A. M. Org. Lett.
2010, 12, 3006–3009. (f) Panda, B.; Sarkar, T. K. Tetrahedron Lett. 2010,
51, 301–305.
Scheme 2. Transmetalation between Arylgold Compounds
and Ruthenium Complexes
(8) (a) Cross, R. J.; Davidson, M. F.; McLennan, A. J. J. Organomet.
Chem. 1984, 265, c37–c39. (b) Cross, R. J.; Davidson, M. F. J. Chem. Soc.,
Dalton Trans. 1986, 411–414. (c) Contel, M.; Stol, M.; Casado, M. A.;
van Klink, G. P. M.; Ellis, D. D.; Spek, A. L.; van Koten, G. Organome-
tallics 2002, 21, 4556–4559. (d) Bruce, M. I.; Smith, M. E.; Zaitseva,
N. N.; Skelton, B. W.; White, A. H. J. Organomet. Chem. 2003,
670, 170–177. (e) Antonova, A. B.; Bruce, M. I.; Ellis, B. G.; Gaudio,
M.; Humphrey, P. A.; Jevric, M.; Melino, G.; Nicholson, B. K.; Perkins,
G. J.; Skelton, B. W.; Stapleton, B.; White, A. H.; Zaitseva, N. N. Chem.
Commun. 2004, 960–961. (f) Ferrer, M.; Rodríguez, L.; Rossell, O.;
Lima, J. C.; Gꢀomez-Sal, P.; Martín, A. Organometallics 2004, 23,
was also visible in our previous investigation of the gold/palladium
systems.6a,7c Investigations addressing this point are in progress.
€
5096–5099. (g) Robitzer, M.; Bouamaied, I.; Sirlin, C.; Chase, P. A.;
van Koten, G.; Pfeffer, M. Organometallics 2005, 24, 1756–1761. (h)
Bruce, M. I.; Humphrey, P. A.; Melino, G.; Skelton, B. W.; White, A. H.;
Zaitseva, N. N. Inorg. Chim. Acta 2005, 358, 1453–1468. (i) Jones, L. A.;
Sanz, S.; Laguna, M. Catal. Today 2007, 122, 403–406. (j) Khairul,
W. M.; Fox, M. A.; Zaitseva, N. N.; Gaudio, M.; Yufit, D. S.; Skelton,
B. W.; White, A. H.; Howard, J. A. K.; Bruce, M. I.; Low, P. J. Dalton
Trans. 2009, 610–620. (k) Chuchuryukin, A. V.; Huang, R.; Lutz, M.;
Chadwick, J. C.; Spek, A. L.; van Koten, G. Organometallics 2011,
30, 2819–2830.
(9) Hirner, J. J.; Blum, S. A. Organometallics 2011, 30, 1299–1302.
(10) Shi, Y.; Blum, S. A. Organometallics 2011, 30, 177–1779.
(11) (a) Bolm, C.; Legros, J.; Le Paih, J.; Zani, L. Chem. Rev. 2004,
104, 6217–6254. (b) Correa, A.; Garcia Mancheno, O.; Bolm, C. Chem.
Soc. Rev. 2008, 37, 1108–1117. (c) Sherry, B. D.; F€urstner, A. Acc. Chem.
Res. 2008, 41, 1500–1511. (d) Czaplik, W. M.; Mayer, M.; Cvengroꢁs, J.;
von Wangelin, A. J. ChemSusChem 2009, 2, 396–417.
(12) (a) Asada, Y.; Yasuda, S.; Yorimitsu, H.; Oshima, K. Organo-
metallics 2008, 27, 6050–6052. (b) Yasuda, S.; Yorimitsu, H.; Oshima, K.
Organometallics 2008, 27, 4025–4027. (c) Nakaya, R.; Yasuda, S.;
Yorimitsu, H.; Oshima, K. Tetrahedron Lett. 2009, 50, 5274–5276.
(d) Yasuda, S.; Asada, Y.; Yorimitsu, H.; Oshima, K. Materials 2009,
2, 978–991. (e) Yasuda, S.; Yorimitsu, H.; Oshima, K. Organometallics
2010, 29, 273–274. (f) Yasuda, S.; Yorimitsu, H.; Oshima, K. Organo-
metallics 2009, 28, 4872–4875. (g) Yasuda, S.; Yorimitsu, H.; Oshima, K.
Organometallics 2010, 29, 2634–2636.
’ ASSOCIATED CONTENT
S
Supporting Information. Text and figures giving char-
b
acterization data for all products. This material is available free of
charge via the Internet at http://pubs.acs.org.
’ ACKNOWLEDGMENT
This work was supported by Umicore AG & Co. KG and by
the Deutsche Forschungsgemeinschaft (SFB 623).
’ REFERENCES
(1) For representative reviews on gold catalysis see: (a) Dyker, G.
Angew. Chem. 2000, 112, 4407–4409. Angew. Chem., Int. Ed. 2000,
39, 4237–4239. (b) Hashmi, A. S. K. Gold. Bull. 2003, 36, 3–9.
(c) Hashmi, A. S. K. Gold Bull. 2004, 37, 51–65. (d) Hoffmann-R€oder,
A.; Krause, N. Org. Biomol. Chem. 2005, 3, 387–391. (e) Hashmi, A. S. K.
Angew. Chem. 2005, 117, 7150–7154. Angew. Chem., Int. Ed. 2005,
44, 6990–6993. (f) Hashmi, A. S. K.; Hutchings, G. Angew. Chem. 2006,
118, 8064–8105. Angew. Chem., Int. Ed. 2006, 45, 7896–7936. (g) Gorin,
D. J.; Toste, F. D. Nature 2007, 446, 395–403. (h) F€urstner, A.; Davies,
P. W. Angew. Chem. 2007, 119, 3478–3519. Angew. Chem., Int. Ed. 2007,
46, 3410–3449. (i) Jimenez-Nunez, E.; Echavarren, A. M. Chem.
Commun. 2007, 333–346. (j) Hashmi, A. S. K. Chem. Rev. 2007,
107, 3180–3211. (k) Li, Z.; Brouwer, C.; He, C. Chem. Rev. 2008,
108, 3239–3265. (l) Arcadi, A. Chem. Rev. 2008, 108, 3266–3325.
(m) Shen, H. C. Tetrahedron 2008, 64, 3885–3909. (n) Shen, H. C.
Tetrahedron 2008, 64, 7847–7870. (o) Hashmi, A. S. K. Angew. Chem.
2010, 122, 5360–5369. Angew. Chem., Int. Ed. 2010, 49, 5232–5241.
(2) Ma, S.; Yu, S.; Gu, Z. Angew. Chem. 2006, 118, 206–209. Angew.
Chem., Int. Ed. 2006, 45, 200–203.
(13) Liu, L.-P.; Xu, B.; Mashuta, M. S.; Hammond, G. B. J. Am. Chem.
Soc. 2008, 130, 17642–17643.
(14) (a) Bartolomꢀe, C.; Ramiro, Z.; García-Cuadrado, D.; Pꢀerez-Galꢀan,
P.; Raducan, M.; Bour, C.; Echavarren, A. M.; Espinet, P. Organometallics
2010, 29, 951–956. (b) Hashmi, A. S. K.; Hengst, T.; Lothsch€utz, C.;
Rominger, F. Adv. Synth. Catal. 2010, 352, 1315–1337. (c) Hashmi,
A. S. K.; Lothsch€utz, C.; B€ohling, C.; Hengst, T.; Hubbert, C.; Rominger,
F. Adv. Synth. Catal. 2010, 352, 3001–3012.
(15) 3j has been prepared with 10 mol % CuI (with 2b, 75% yield)
before: Villemin, D.; Schigeko, E. J. Organomet. Chem. 1988, 346, C24–C26
and has been prepared under Sonogashira-type conditions.12c
(3) (a) Muzart, J. Tetrahedron 2008, 64, 5815–5849. (b) Hashmi,
A. S. K.; B€uhrle, M. Alrdichim. Acta 2010, 43, 27–33. (c) Rudolph, M.;
Hashmi, A. S. K. Chem. Commun. 2011, 47, 6536–6544.
(4) Corma, A.; Juꢀarez, R.; Boronat, M.; Sꢀanchez, F.; Iglesias, M.;
García, H. Chem. Commun. 2011, 47, 1446–1448.
(5) Hashmi, A. S. K.; Pankajakshan, S.; Rudolph, M.; Enns, E.;
Bander, T.; Rominger, F.; Frey, W. Adv. Synth. Catal. 2009,
351, 2855–2875.
(6) (a) Shi, Y.; Ramgren, S. D.; Blum, S. A. Organometallics 2009,
28, 1275–1277. (b) Hashmi, A. S. K.; Lothsch€utz, C.; D€opp, R.; Rudolph,
M.; Ramamurthi, T. D.; Rominger, F. Angew. Chem., Int. Ed. 2009,
3460
dx.doi.org/10.1021/om200360q |Organometallics 2011, 30, 3457–3460