Synthesis of aryliron complexes by palladium-catalyzed transmetalation between [CpFe(CO)2I] and aryl Grignard reagents and their chemistry directed toward organic synthesis

Article abstract of DOI:10.1021/om800560m

Palladium-catalyzed transmetalation between [CpFe-(CO)₂I] and aryl Grignard reagents emerges as a new method for the synthesis of [CpFe(CO)₂Ar]. The aryliron complexes thus formed are useful arylmetal reagents that become active upon oxidation or UV irradiation.

Full text of DOI:10.1021/om800560m

Copyright 2008
Volume 27, Number 16, August 25, 2008
American Chemical Society
Communications
Synthesis of Aryliron Complexes by Palladium-Catalyzed
Transmetalation between [CpFe(CO)2I] and Aryl Grignard Reagents
and Their Chemistry Directed toward Organic Synthesis
Shigeo Yasuda, Hideki Yorimitsu,* and Koichiro Oshima*
Department of Material Chemistry, Graduate School of Engineering, Kyoto UniVersity,
Kyoto-daigaku Katsura, Nishikyo-ku, Kyoto 615-8510, Japan
ReceiVed June 17, 2008
synthesis of [CpFe(CO)2Ar].2 Here we report a new efficient
Summary: Palladium-catalyzed transmetalation between [CpFe-
method for the synthesis of [CpFe(CO)2Ar] under palladium
catalysis. Several transformations of [CpFe(CO)2Ar] are also
disclosed, which will be useful in organic synthesis.3,4
(CO)2I] and aryl Grignard reagents emerges as a new method
for the synthesis of [CpFe(CO)2Ar]. The aryliron complexes
thus formed are useful arylmetal reagents that become actiVe
upon oxidation or UV irradiation.
As reported previously,2a our attempt at a substitution reaction
of [CpFe(CO)2I] (1) with phenylmagnesium bromide in the
absence of a catalyst resulted in failure, affording a poor yield
of [CpFe(CO)2Ph] (2a), a significant amount of [CpFe(CO)2]2
(3), and recovered 1 (Table 1, entry 1). After extensive screening
of the reaction conditions, we found that a combination of
palladium acetate and diamine 4 efficiently catalyzes the phe-
Thanks to the ubiquity of iron, organoiron compounds
represent rare organic transition-metal compounds that we can
use stoichiometrically in organic synthesis. However, the
potential of organoiron compounds have not been fully devel-
oped.1
Among organoiron compounds, the coordinatively saturated
aryldicarbonylcyclopentadienyliron complexes [CpFe(CO)2Ar]
are easy to handle and hence can be useful as arylmetal reagents
in organic synthesis. However, little is known about the concise
(2) The reaction of [CpFe(CO)2I] with phenylmagnesium bromide was
reported to result in a less than 12% yield of [CpFe(CO)2Ph]: (a) Li, H.-J.;
Turnbull, M. M. J. Organomet. Chem. 1991, 419, 245–249. The reaction
with highly reactive aryllithium: (b) Butler, I. R.; Lindsell, W. E.; Preston,
P. N. J. Chem. Res., Synop. 1981, 185. The palladium-catalyzed reactions
of aryl iodides with [CpFe(CO)2]ZnCl, the preparation of which requires
NaK2.8: (c) Artamkina, G. A.; Mil’chenko, A. Y.; Bumagin, N. A.;
Beletskaya, I. P.; Reutov, O. A. Organomet. Chem., USSR 1988, 1, 17–20.
The reactions of diaryliodonium and triarylsulfonium salts with [CpFe(CO)2]-
Na: (d) Nesmeyanov, A. N.; Chapovsky, Y. A.; Polovyanyuk, I. V.;
Makarova, L. G. J. Organomet. Chem. 1967, 7, 329–337. Decarbonylation
of [CpFe(CO)2(ArCO)], which is available from [CpFe(CO)2]Na and
ArCOCl: (e) Hunter, A. D.; Szigety, A. B. Organometallics 1989, 8, 2670–
2679, and references cited therein.
(3) Butler, I. R.; Cullen, W. R.; Lindsell, W. E.; Preston, P. N.; Rettig,
S. J. J. Chem. Soc., Chem. Commun. 1987, 439–441.
(4) The coordination chemistry of [CpFe(CO)2Ar] has been summarized:
Kerber, R. C. In ComprehensiVe Organometallic Chemistry II; Abel, E. W.,
Stone, F. G. A., Wilkinson, G., Eds.; Elsevier: Oxford, U.K., 1995; Vol. 7,
Chapter 2.
* To whom correspondence should be addressed. E-mail: yori@
orgrxn.mbox.media.kyoto-u.ac.jp (H.Y.); oshima@orgrxn.mbox.media.
kyoto-u.ac.jp.(K.O.).
(1) (a) Pearson, A. J. Iron Compounds in Organic Synthesis; Academic
Press: London, 1994. (b) Pearson, A. J. Pure Appl. Chem. 1983, 55, 1767–
1779. (c) Kno¨lker, H.-J. Curr. Org. Synth. 2004, 1, 309–331. (d) Kno¨lker,
H.-J. Chem. ReV. 2000, 100, 2941–2961. (e) Kno¨lker, H.-J. Chem. Soc.
ReV. 1999, 28, 151–157. (f) Ru¨ck-Braun, K.; Mikula´s, M.; Amrhein, P.
Synthesis 1999, 727–744. (g) Li, C.-L.; Liu, R.-S. Chem. ReV. 2000, 100,
3127–3161. (h) Abd-El-Aziz, A. S.; Bernardin, S. Coord. Chem. ReV. 2000,
203, 219–267. (i) Donaldson, W. A. Curr. Org. Chem. 2000, 4, 837–868.
(j) Nakazawa, H.; Itazaki, M.; Kamata, K.; Ueda, K. Chem. Asian J. 2007,
2, 882–888. (k) Anson, C. E.; Malkov, A. V.; Roe, C.; Sandoe, E. J.;
Stephenson, G. R. Eur. J. Org. Chem. 2008, 196–213, and references cited
therein.
10.1021/om800560m CCC: $40.75
2008 American Chemical Society
Publication on Web 07/26/2008

4026 Organometallics, Vol. 27, No. 16, 2008
Communications
Table 1. Ligand Effect on Palladium-Catalyzed Arylation of 1
Table 2. Palladium-Catalyzed Arylation of 1 with ArMgBr
entry
Ar
2
yield/%
1
4-MeC6H4
4-PhC6H4
4-MeOC6H4
4-ClC6H4
4-FC6H4
2b
2c
2d
2e
2f
80
87
yield/%
2
entry
1a
2
3
4
5
6
7
ligand
none
2a
3
1
3a
4
62 (90b)
74
5
51
9
5
6
5
87
73
32
15
45
73
87
81
28
87
6
2-MeC6H4
2g
21
PPh3
38
37
31
<1
7
4
5
4
8
2
5
P(c-C6H11)3
DPPEb
TMEDAc
4
2,2′-bipyridyl
IPr · HCle
4
a Performed at -20 °C for 2 h. b Yield determined by 1H NMR
analysis of the crude product.
Scheme 1. Synthesis of Aryliron Complex from ArMgCl · LiCl
8
3
9d
10f
<1
<6
59
<1
a In the absence of Pd(OAc)2. PhMgBr (2.0 equiv) was used. b 1,2-
Bis(diphenylphosphino)ethane (10 mol %). c N,N,N′,N′-Tetramethylethylenedi-
amine. d PhMgBr (1.6 equiv) was used. e 12 mol %. f 5 mol % of
Pd(OAc)2, 6 mol % of 4, 0 °C, 15 min.
Scheme 2
nylation reaction (entry 7).5 The phenylation is regarded as
palladium-catalyzed transmetalation between [CpFe(CO)2I] and
phenylmagnesium bromide.
The choice of the ligand is important. The use of phosphine
ligands favored the formation of 3 (entries 3-5). The N-
heterocyclic carbene ligand IPr · HCl6 did not work well (entry
9). Palladium acetate by itself had high catalytic activity (entry
2). TMEDA and 2,2′-bipyridyl showed slightly lower activity
than diamine 4 (entries 6-8). Diamine 4 was so efficient that
the reaction went to completion at 0 °C within 15 min with 5
mol % of the palladium catalyst (entry 10).
The reaction would proceed via a mechanism similar to the
conventional cross-coupling reaction,5c which consists of oxidative
addition of 1 to palladium that generates [Cp(CO)2Fe-Pd-I],
transmetalation with phenylmagnesium bromide, and reductive
elimination that forms the phenyl-iron bond.
column purification under air. Unfortunately, the reaction of 1
with (2-methylphenyl)magnesium bromide failed to afford 2g
in reasonable yield, probably for steric reasons.
(4-Bromophenyl)magnesium reagent, prepared from 4-bro-
moiodobenzene according to the procedure of Knochel,7 also
underwent the arylation reaction at -20 °C, albeit in modest
yield and with a higher catalyst loading (Scheme 1).
[CpFe(CO)2I] is the best starting material for the preparation
of 2a. The corresponding bromide and chloride were arylated
with lower efficiency. The palladium-catalyzed reactions of
[CpFe(CO)2Br] and [CpFe(CO)2Cl] afforded 2a in 53% and
66% yields along with 3 in 24% and 12% yields, respectively.
Advantageously, [CpFe(CO)2I] was more stable in air than
[CpFe(CO)2Br] and [CpFe(CO)2Cl].
The scope of aryl Grignard reagents is summarized in Table
2. Substituents at the 4-positions of aryl Grignard reagents had
little effect on the arylation reaction. An electron-rich
[CpFe(CO)2(4-MeOC6H4)] (2d) was somewhat sensitive to
oxygen, which led to a moderate yield of 2d after silica gel
Although rich coordination chemistry has been reported for
[CpFe(CO)2Ar],4 the application of [CpFe(CO)2Ar] to organic
synthesis has been almost unknown.3 Hence, we examined
several transformations of [CpFe(CO)2Ar] which will be useful
in organic synthesis.
Many oxidative alkoxycarbonylations of [CpFe(CO)2R] with
ceric ammonium nitrate to form RCOOR′ were reported,8
although there have been no reports on the reaction of
[CpFe(CO)2Ar]. We thus optimized conditions for the reaction
of [CpFe(CO)2Ar] to find the conditions in eq 1. Treatment of
2c with ceric ammonium nitrate in a methanol-toluene mixed
solvent at -78 °C for 30 min provided methyl 4-biphenylcar-
boxylate (5) in 89% yield.
(5) Palladium-catalyzed alkynylation reactions of [CpFe(CO)2I] with
1-alkynylstannanes are known: (a) Lo Sterzo, C. J. Chem. Soc., Dalton
Trans. 1992, 1989–1990. (b) Crescenzi, R.; Lo Sterzo, C. Organometallics
1992, 11, 4301–4305. (c) Ricci, A.; Angelucci, F.; Bassetti, M.; Lo Sterzo,
C. J. Am. Chem. Soc. 2002, 124, 1060–1071, and references cited therein.
(d) Long, N. J.; Williams, C. K. Angew. Chem., Int. Ed. 2003, 42, 2586–
2617.
(6) (a) Arduengo, A. J., III; Krafczyk, R.; Schmutzler, R.; Craig, H. A.;
Goerlich, J. R.; Marshall, W. J.; Unverzagt, M. Tetrahedron 1999, 55,
14523–14534. (b) Jafarpour, L.; Stevens, E. D.; Nolan, S. P. J. Organomet.
Chem. 2000, 606, 49–54.
The carbon-iron bond of 2 was robust enough to be
compatible under transition-metal-catalyzed conditions. For
(7) Krasovskiy, A.; Knochel, P. Angew. Chem., Int. Ed. 2004, 43, 3333–
3336.
(8) (a) Bucheister, A.; Klemarczyk, P.; Rosenblum, M. Organometallics
1982, 1, 1679–1684. (b) Stokes, H. L.; Ni, L. M.; Belot, J. A.; Welker,
M. E. J. Organomet. Chem. 1995, 487, 95–104. (c) Jiang, S.; Turos, E.
Organometallics 1993, 12, 4280–4282.

Communications
Organometallics, Vol. 27, No. 16, 2008 4027
Scheme 3
instance, the palladium-catalyzed borylation9 of 2h proceeded
smoothly to afford the (borylphenyl)iron complex 2i (eq 2).
Iron complexes 2 reacted with allylic electrophiles under
irradiation with a high-pressure mercury lamp to afford allyl-
arenes 6 (eqs 3 and 4). The reaction would proceed as follows
(Scheme 2): (1) photoinduced dissociation of a carbonyl
ligand,10–12 (2) coordination of an allylic electrophile followed
by migratory insertion,13 and (3) ꢀ-halide elimination.14 It is
worth noting that the reaction of 2i with methallyl tosylate
occurred selectively at the iron-carbon bond without affecting
the boron-carbon bond. This photoinduced additive-free metal-
selective carbon-carbon bond formation opens up a new
possibility of organoiron-based organic synthesis that takes
advantage of the most ubiquitous transition metal.
is, palladium-catalyzed transmetalation between [CpFe(CO)2I]
and aryl Grignard reagents. The iron complexes thus synthesized
are a useful class of arylmetals of significant stability and
become reactive upon oxidation or irradiation. As notably
demonstrated in the reaction of 2i and methallyl tosylate, the
organoiron complexes [CpFe(CO)2Ar] play unique roles as
reagents in organic synthesis.
In summary, we have devised an efficient method for the
synthesis of the series of iron complexes [CpFe(CO)2Ar]: that
Acknowledgment. This work was supported by Grants-
in-Aid for Scientific Research from the MEXT and JSPS.
We thank Professor Koichi Ohe and Dr. Koji Miki at Kyoto
University for allowing us to use a high-pressure mercury
lamp for photochemical reactions.
(9) (a) Ishiyama, T.; Itoh, Y.; Kitano, T.; Miyaura, N. Tetrahedron Lett.
1997, 38, 3447–3450. (b) Ishiyama, T.; Ishida, K.; Miyaura, N. Tetrahedron
2001, 57, 9813–9816. The use of X-Phos, dicyclohexyl[2-(2,4,6-triisopro-
pylphenyl)phenyl]phosphine, in the palladium-catalyzed borylation: (c)
Billingsley, K. L.; Barder, T. E.; Buchwald, S. L. Angew. Chem., Int. Ed.
2007, 46, 5359–5363.
(10) (a) Alt, H. G. Angew. Chem., Int. Ed. Engl. 1984, 23, 766–782.
(b) Olson, A. S.; Seitz, W. J.; Hossain, M. M. Tetrahedron Lett. 1991, 32,
5299–5302. (c) Ku¨ndig, E. P.; Bourdin, B.; Bernardinelli, G. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 1856–1858.
Supporting Information Available: Text giving experimental
details and characterization data for new compounds. This material
is available free of charge via the Internet at http://pubs.acs.org.
OM800560M
(11) It was reported that UV irradiation of [CpFe(CO)2(alkyl)] leads to
homolytic cleavage of the iron-alkyl bond: (a) Giese, B.; Thoma, G. HelV.
Chim. Acta 1991, 74, 1143–1155. (b) Tawarah, K. M.; Jibril, I.; Bani-Fwaz,
M. Z. Transition Met. Chem. 2000, 25, 659–663.
(12) Boryliron complexes are reagents for the borylation of hydrocarbon
upon irradiation: (a) Waltz, K. M.; He, X.; Muhoro, C.; Hartwig, J. F. J. Am.
Chem. Soc. 1995, 117, 11357–11358. (b) Waltz, K. M.; Hartwig, J. F.
Science 1997, 277, 211–213. (c) Waltz, K. M.; Muhoro, C. N.; Hartwig,
J. F. Organometallics 1999, 18, 3383–3393.
(13) (a) Cavell, K. J. Coord. Chem. ReV. 1996, 155, 209–243. (b) Zhang,
Z.; Lu, X.; Xu, Z.; Zhang, Q.; Han, X. Organometallics 2001, 20, 3724–
3728. (c) Hill, R. H.; Becalska, A.; Chiem, N. Organometallics 1991, 10,
2104–2109.
(14) Oxidative addition followed by reductive elimination via an unusual
Fe(IV) oxidation state is an alternative process for the allylation (Scheme
3).