Indium-mediated alkyl radical addition to (η6-arene) tricarbonylmanganese complexes in aqueous media

Article abstract of DOI:10.1021/om050721c

Alkyl radical addition to (η⁶-arene)tricarbonylmangenese complexes was investigated with SmI², zinc, or indium as the radical initiator. Among them, the indium-mediated reactions of (η⁶- arene)tricarbonylmangenese cations

Full text of DOI:10.1021/om050721c

Organometallics 2005, 24, 5983-5988
5983
Indium-Mediated Alkyl Radical Addition to
(η6-Arene)tricarbonylmanganese Complexes in Aqueous
Media
Lidong Cao, Meihua Shen, and Chaozhong Li*
Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road,
Shanghai 200032, People’s Republic of China
Received August 20, 2005
Alkyl radical addition to (η6-arene)tricarbonylmangenese complexes was investigated with
SmI2, zinc, or indium as the radical initiator. Among them, the indium-mediated reactions
of (η6-arene)tricarbonylmangenese cations with various alkyl iodides in aqueous media af-
forded the corresponding radical addition-reduction products in moderate to excellent yields.
Complexation of an arene ring with a Cr(CO)3 or Mn-
(CO)3+ moiety significantly reduces the electron density
of the arene ring, thus allowing nucleophilic addition
to occur.1 The reduction of the electron density of the
phenyl ring also encourages the addition of nucleophilic
radicals.2 For example, Merlic and co-workers demon-
strated that ketyl radical addition to Cr(CO)3-complexed
benzene is at least 100 000 times faster than attack on
free benzene.3 However, only a few examples were
reported on radical addition to arene-metal complexes,
most of which dealt with ketyl radical addition to (η6-
arene)Cr(CO)3 complexes.3-5 Recently, we reported the
first examples of radical addition to (η6-arene)tricarbo-
nylmangenese cations (1) by reaction with alkylmercury
halides.5c The alkyl radical added to the phenyl ring in
1 to generate the corresponding 17-valence electron
intermediate, which was presumably further reduced
by alkylmercury halide, leading to the formation of the
stable 18-valence-electron product 2 and to the regen-
eration of an alkyl radical.6 In this reaction the alkyl-
mercury halide served not only as the radical precursor
but also as the reducing agent. This radical chain
process worked well for tert-butylmercury halide, and
an excellent yield of the product 2a was achieved.
However, with isopropylmercury halide the chain pro-
cess was less efficient, while almost no reaction could
be observed for isobutyl- or n-butyl-mercury halide.
Moreover, the high toxicity of alkylmercury halides also
limited the application of the above method in organic
synthesis. To develop general and convenient methods
to conduct the radical reactions, we carried out the
following investigation. We report here that alkyl radi-
cal addition to (η6-arene)Mn(CO)3 complexes can be
+
successfully carried out in aqueous media by reaction
with indium(0) and alkyl iodides.
Results and Discussion
As discussed above and also in the literature,2,5c
+
* To whom correspondence should be addressed. E-mail:
clig@mail.sioc.ac.cn.
successful radical addition to arene-Mn(CO)3 com-
plexes would require both a radical precursor and a
reducing agent. A metal reductant and an alkyl halide
would be an ideal combination to meet this requirement.
Thus, we chose manganese complex 1a as the model
substrate and isopropyl iodide as the radical source to
explore this possibility (eq 1). The results are presented
in Table 1.
(1) For reviews, see: (a) Kane-Maguire, L. A. P.; Honig, E. P.;
Sweigart, D. A. Chem. Rev. 1984, 84, 525. (b) Semmelhack, M. F. In
Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.;
Pergamon: New York, 1991; Vol. 4, p 517. (c) Semmelhack, M. F. In
Comprehensive Organometallic Chemistry II; Abel, E. W., Stone, F.
G. A., Wilkinson, G., Eds.; Pergamon: New York, 1995; Vol. 12, p 979.
(d) Sun, S.; Dullaghan, C. A.; Sweigart, D. A. J. Chem. Soc., Dalton
Trans. 1996, 4493. (e) Pape, A. R.; Kaliappan, K. P.; Kundig, E. P.
Chem. Rev. 2000, 100, 2917. (f) Rose-Munch, F.; Rose, E. Curr. Org.
Chem. 1999, 3, 445. (g) Rose-Munch, F.; Rose, E. Eur. J. Inorg. Chem.
2002, 1269.
(2) For a review article, see: Lin, H.; Shen, M.; Yang, L.; Li, C. Chin.
J. Org. Chem. 2003, 23, 944.
(3) Merlic, C. A.; Miller, M. M.; Hietbrink, B. N.; Houk, K. N. J.
Am. Chem. Soc. 2001, 123, 4904.
(4) (a) Schmalz, H.-G.; Siegel, S.; Bats, J. W. Angew. Chem., Int.
Ed. 1995, 34, 2383. (b) Schmalz, H.-G.; Siegel, S.; Schwarz, A.
Tetrahedron Lett. 1996, 37, 2947. (c) Hoffmann, O.; Schmalz, H.-G.
Synlett 1998, 1426. (d) Schwarz, O.; Brun, R.; Bats, J. W.; Schmalz,
H.-G. Tetrahedron Lett. 2002, 43, 1009. (e) Schmalz, H.-G.; Kiehl, O.;
Gotov, B. Synlett 2002, 1253.
(5) (a) Lin, H.; Yang, L.; Li, C. Organometallics 2002, 21, 3848. (b)
Lin, H.; Yang, L.; Li, C. Chin. J. Chem. 2003, 21, 797. (c) Lin, H.;
Zhang, H.; Yang, L.; Li, C. Org. Lett. 2002, 4, 823.
Treatment of an alkyl iodide with SmI2 to generate
an alkyl radical is well documented.7 Thus, we first
tested the SmI2/i-PrI system. The reaction of 1a with
10.1021/om050721c CCC: $30.25 © 2005 American Chemical Society
Publication on Web 10/26/2005

5984 Organometallics, Vol. 24, No. 24, 2005
Cao et al.
Table 1. Synthesis of 2b via the Reaction of 1a at
Table 2. Synthesis of 2a via Reaction of 1a with
20 °C
In(0)/t-BuI
time yield
entry
H2O:CH3CN
temp (°C)
time (h)
yield (%)a
entry
metal (equiv)
solvent
(h)
(%)a
1
2
3
4
5
6
7
8
1:3
20
20
20
40
70
70
70
70
2
24
24
10
10
10
10
10
trace
46
1
2
3
4
5
6
7
8
9
SmI2 (4)b
SmI2 (4)b
SmI2 (4)b
Zn (2)c
THF
2
2
15
38
12
10
31
25
17
88
85
1:3
CH3CN
3:1
49
CH3CN/HMPA (12:1)
sat. NH4Cl
sat. NH4Cl/CH3CN (2:1)
sat. NH4Cl/CH3CN (1:2)
sat. NH4Cl/CH3CN (2:1)
2
1:2
47
10
10
10
10
10
10
2:1
46
Zn (2)c
1:2
62
Zn (2)c
CH3CN
H2O
trace
50
Zn (3)c
Zn (5)/CuI (0.5)d H2O/CH3CN (3:1)
a Isolated yield based on 1a.
In (3)e
H2O
a Isolated yield based on 1a. b Two equivalents of i-PrI was
employed. c Four equivalents of i-PrI was employed. d Ultrasonic
irradiation was used. e Six equivalents of i-PrI was employed.
radical addition showed a better performance in aceto-
nitrile,5c we used acetonitrile as the cosolvent to enhance
the solubility of i-PrI, and a higher yield (31%) was
achieved when the ratio of saturated NH4Cl solution to
CH3CN was 2:1 (entry 5, Table 1). Increasing the
amount of zinc did not show much difference in the
product yield (entry 7, Table 1). Since the presence of
CuI as the catalyst significantly enhanced the zinc-
mediated radical reactions in aqueous media,10b we
carried out the reaction of 1a with Zn/CuI under
ultrasonic irradiation, and the product 2b was thus
obtained in 88% yield (entry 8, Table 1).
It should be noted that the above zinc-mediated
radical addition showed a different reactivity pattern
from the nucleophilic addition of alkylzinc reagents such
as IZn(CH2)3OAc in THF, in which alkylation of the
manganese cation at the C-2 position of THF was
observed.11
Although a satisfactory yield was achieved with Zn/
CuI as the radical initiator, the requirement of ultra-
sonic irradiation was undesirable. We then turned our
attention to indium metal. Indium-mediated radical
reactions have gained increasing popularity over the
past few years and have become a useful tool in organic
synthesis under environmentally benign conditions.12,13
To our delight, the treatment of 1a with indium (3
equiv) and isopropyl iodide (6 equiv) in pure water at
room temperature for 10 h afforded the addition product
2b in 85% yield (entry 9, Table 1). Compared to zinc in
saturated NH4Cl solution (entry 4, Table 1), indium was
obviously more effective in initiating the radical reac-
tion.
We then tested other alkyl iodides in the indium-
mediated reaction to explore the generality of this
method. However, when tert-butyl iodide was employed,
only a trace amount of the expected product 2a could
be detected. Thinking that this might be attributed to
the lower solubility of tert-butyl iodide than isopropyl
iodide in water, we conducted the following experiments
to optimize the reaction conditions (eq 2). The results
are summarized in Table 2.
i-PrI (2 equiv) and SmI2 (4 equiv) in THF at room
temperature for 2 h afforded the expected product 2b
in only 15% yield (entry 1, Table 1). When the reaction
was carried out in acetonitrile, the yield of 2b was
improved to 38% (entry 2, Table 1). Introduction of
HMPA resulted in a decrease of yield (12%), while the
direct reduction product of 1a, (η5-cyclohexadienyl)-
tricarbonylmanganese complex 3, was obtained in about
50% yield (entry 3, Table 1).8 Varying the amount of
i-PrI or SmI2 or changing the reaction temperature did
not result in any improvement. Under the above opti-
mized condition (CH3CN, rt), 2a was achieved in 59%
yield by reaction of 1a with t-BuI, while no 2e could be
obtained in the reaction of 1a with n-BuI. This differ-
ence might be rationalized by the relative efficiencies
of generation of the alkyl radicals (t-Bu > i-Pr > n-Bu).
In all the above cases, the direct reduction of 1a was,
more or less, always observed.
It should be mentioned that we also tested the
possibility of ketyl radical addition to (η6-arene)Mn-
(CO)3+ by reaction with SmI2 and a carbonyl compound.
However, in sharp contrast to the success in ketyl
radical addition to (η6-arene)Cr(CO)3 complexes,3-5
under various experimental conditions screened, only
the direct reduction product 3 was observed. The easy
reduction of 1a should be attributed to the much
stronger electron-withdrawing effect of Mn(CO)3+ than
Cr(CO)3.
We next selected zinc as the radical initiator. Zinc-
mediated radical reactions in aqueous media have
received considerable attention from both economical
and environmental points of view.9,10 The reaction of 1a
with zinc (2 equiv) and i-PrI (4 equiv) in saturated
ammonium chloride solution at rt for 10 h afforded the
product 2b in 10% yield (entry 4, Table 1). Since the
+
(6) Zaworotko et al. reported that the reactions of arene-Mn(CO)3
cations with trialkylaluminum could involve an electron-transfer
process. However, the proposed mechanism was single-electron transfer
to arene-Mn(CO)3+ to form the neutral 19-electron complex rather than
+
alkyl radical addition to arene-Mn(CO)3 to form the 17-electron
intermediates. See: Gaudet, M. V.; Hanson, A. W.; White, P. S.;
Zaworotko, M. J. Organometallics 1989, 8, 286.
(7) For reviews on SmI2-mediated radical reactions, see: (a) Molan-
der, G. A. In Radicals in Organic Synthesis; Renaud, P., Sibi, M. P.,
Eds.; Wiley-VCH: New York, 2001; Vol. 1, p 153. (b) Molander, G. A.;
Harris, C. R. Chem. Rev. 1996, 96, 307.
(8) Direct reduction of arenetricarbonylmanganese cations with
NaBH4 or LiAlH4 was reported in the literature. See: Winkhaus, G.;
Pratt, L.; Wilkinson, G. J. Chem. Soc. 1961, 3807.
(9) For reviews, see: (a) Li, C.-J. Chem. Rev. 1993, 93, 2023. (b)
Lubineau, R.; Ange, J.; Queneau, Y. Synthesis 1994, 741. (c) Li, C.-J.
Tetrahedron 1996, 52, 5643. (d) Podlech, J.; Maier, T. C. Synthesis
2003, 633. (e) Li, C.-J.; Wang, D. Chemtracts 2003, 16, 59.
To increase the solubility of tert-butyl iodide, aceto-
nitrile was again used as the cosolvent. The reaction in
water/acetonitrile solution at room temperature was
very slow. After 24 h, the expected product 2a was

Indium-Mediated Alkyl Radical Addition
Organometallics, Vol. 24, No. 24, 2005 5985
Table 3. In(0)-Mediated Alkyl Radical Addition to
Manganese Complexes 1 in Aqueous Media
than the primary butyl radical (entries 1 and 5, Table
3). These phenomena are in line with the observations
in many other indium-mediated radical reactions.13 This
trend (2° > 3° > 1° radicals) is different from that in
the reactions of 1 with alkylmercury halides (3° > 2° >
1° radicals).5c The benzene complex 1a gave higher
yields of reductive alkylation products than the toluene
complex 1b or the isopropylbenzene complex 1c, which
in turn showed better performance than the anisole
complex 1d. These results indicate the sensitivity of the
radical addition toward the electron densities of the
arene ring in 1. With regard to the regioselectivity in
the reactions of 1b-d, meta-addition was preferred for
1b,c, while exclusively meta-addition was achieved for
methoxy-substituted complex 1d (entries 13-15, Table
3). The increase of the bulkiness of alkyl radicals
inhibited the ortho-addition, and thus only meta- and
para-addition products could be detected in the reaction
of tert-butyl radical (entry 6, Table 3). The above
regioselectivity pattern is similar to that in the nucleo-
philic addition reactions with Grignard reagents14-23 or
organolithium reagents16,19-21,24-25 but slightly better
than that in the reactions of 1b with alkylmercury
halides.5c
To further demonstrate the advantage of the above
methodology, we prepared alkyl iodides 7a-e bearing
various functional groups and carried out their reactions
with complex 1a (Table 4). As can be seen in Table 4,
the corresponding radical addition products 8a-e were
achieved in satisfactory yields. The trans-substituted
substrate 7d gave the product 8d as the mixture of two
stereoisomers in 6:1 ratio determined by HPLC. Sur-
prisingly, the reaction of trans-2-iodocyclohexanol 7e
with 1a produced exclusively the trans isomer 8e, whose
structure was unambiguously determined by its X-ray
diffraction experiment (Figure 1). Although the reason
for the different behaviors between 7d and 7e is still
unclear, the excellent stereoselectivity in the case of 7e
might be attributed to the possible coordination of In-
(I) to the hydroxyl group, which could impose a signifi-
cant steric effect on the radical addition.
entry
Z
R
temp (°C) product yield (%)a o:m:pb
1
H
H
H
H
H
Me
Me
Me
Me
t-Bu
70
40
40
40
70
70
40
40
40
50
50
50
50
50
50
2a
2b
2c
2d
2e
4a
4b
4c
4d
5b
5c
5d
6b
6c
6d
62
96
83
91
35
36
66
72
50
86
71
60
45
42
40
2
i-Pr
3
c-hexyl
s-Bu
n-Bu
t-Bu
i-Pr
c-hexyl
s-Bu
4
5
6
0:93:7
21:67:12
8:80:12
15:75:10
2:67:31
1:70:29
2:67:31
0:100:0
0:100:0
0:100:0
7
8
9
10
11
12
13
14
15
i-Pr i-Pr
i-Pr c-hexyl
i-Pr s-Bu
OMe i-Pr
OMe c-hexyl
OMe s-Bu
a Isolated yield based on 1. b Determined by HPLC.
isolated in 46% yield (entries 1 and 2, Table 2). Chang-
ing the ratio of water to acetonitrile showed little
difference (entry 3, Table 2). Increasing the reaction
temperature to 40 °C resulted in a faster reaction, and
2a was obtained in 47% yield within 10 h (entry 4, Table
2). When the reaction was carried out at 70 °C with H2O/
CH3CN in a 1:2 ratio as the solvent, the yield of 2a
jumped to 62% (entry 6, Table 2). The advantage of the
mixed solvent was further evidenced by running the
reaction in H2O or CH3CN alone, which gave 2a in lower
yields (entries 7 and 8, Table 2).
Thus, we used H2O/CH3CN (1:2, v/v) as the solvent
and conducted the reactions of manganese complexes
1a-d with a number of alkyl iodides of typical structure
(eq 3). The results are summarized in Table 3.
As can be seen in Table 3, radical addition to cations
1 proceeded smoothly for all the primary, secondary, and
tertiary carbon radicals, and the corresponding addition
products were achieved in moderate to excellent yields.
The secondary alkyl radicals gave the best results, and
the corresponding addition products 2b-d were achieved
in excellent yields (entries 2-4, Table 3). The tertiary
butyl radical gave the higher yield of addition product
The results in Table 4 clearly demonstrated the
advantage of the above radical methodology over the
conventional ionic processes.1,11,14-31 Although the ad-
+
dition of functionalized nucleophiles to arene-Mn(CO)3
complexes gave the corresponding products in reason-
able to high yields, stabilized carbanions such as ketone
enolates or R-ester carbanions were usually em-
(10) For recent examples, see: (a) Liu, X.; Zhu, S.; Wang, S.
Synthesis 2004, 683. (b) Suarez, R. M.; Sestelo, J. P.; Sarandeses, L.
A. Chem. Eur. J. 2003, 9, 4179. (c) Ueda, M.; Miyabe, H.; Nishimura,
A.; Sugino, H.; Naito, T. Tetrahedron: Asymmetry 2003, 14, 2857. (d)
Sugi, M.; Sakuma, D.; Togo, H. J. Org. Chem. 2003, 68, 7629. (e)
Suarez, R. M.; Sestelo, J. P.; Sarandeses, L. A. Synlett 2002, 1435.
(11) Yeh, M.-C. P.; Hwu, C.-C.; Lee, A.-T.; Tsai, M.-S. Organome-
tallics 2001, 20, 4965.
(14) Chung, Y. K.; Williard, P. G.; Sweigart, D. A. Organometallics
1982, 1, 1053.
(15) Jeong, E.; Chung, Y. K. J. Organomet. Chem. 1992, 434, 225.
(16) Lee, S. S.; Lee, J.-S.; Chung, Y. K. Organometallics 1993, 12,
4640.
(17) Pearson, A. J.; Zhu, P. Y. J. Am. Chem. Soc. 1993, 115, 10376.
(18) Woo, K.; Williard, P. G.; Sweigart, D. A.; Duffy, N. W.; Robinson,
B. H.; Simpson, J. J. Organomet. Chem. 1995, 487, 111.
(19) Astley, D. K.; Astley, S. T. J. Organomet. Chem. 1995, 487, 253.
(20) Cao, Y.; Woo, K.; Yeung, L. K.; Carpenter, G. B.; Sweigart, D.
A. Organometallics 1997, 16, 178.
(12) For a review article, see: Li, C.-J.; Chan, T.-H. Tetrahedron
1999, 55, 11149.
(13) For recent examples, see: (a) Yanada, R.; Koh, Y.; Nishimori,
N.; Matsumura, A.; Obika, S.; Mitsuya, H.; Fujii, N.; Takemoto, Y. J.
Org. Chem. 2004, 69, 2417. (b) Yanada, R.; Obika, S.; Nishimori, N.;
Yamauchi, M.; Takemoto, Y. Tetrahedron Lett. 2004, 45, 2331. (c)
Miyabe, H.; Ueda, M.; Nishimura, A.; Naito, T. Tetrahedron 2004, 60,
4227. (d) Sugi, M.; Sakuma, D.; Togo, H. J. Org. Chem. 2003, 68, 7629.
(e) Ueda, M.; Miyaba, H.; Nishimura, A.; Miyata, O.; Takemoto, Y.;
Naito, T. Org. Lett. 2003, 5, 3835. (f) Yanada, R.; Nishimori, N.;
Matsumura, A.; Fujii, N.; Takemoto, Y. Tetrahedron Lett. 2002, 43,
4585. (g) Jang, D. O.; Cho, D. H. Synlett 2002, 631. (h) Miyabe, H.;
Nishimura, A.; Ueda, M.; Naito, T. Chem. Commun. 2002, 1454. (i)
Miyabe, H.; Ueda, M.; Nishimura, A.; Naito, T. Org. Lett. 2002, 4, 131.
(21) Dullaghan, C. A.; Carpenter, G. B.; Sweigart, D. A. Chem. Eur.
J. 1997, 3, 75.
(22) Woo, K.; Cao, Y.; Li, H.; Y. K.; Carpenter, G. B.; Sweigart, D.
A.; Robinson, B. H. J. Organomet. Chem. 2001, 630, 84.
(23) Son, S. U.; Paik, S.-J.; Park, K. H.; Lee, Y.-A.; Lee, I. S.; Chung,
Y. K.; Sweigart, D. A. Organometallics 2002, 21, 239.
(24) Pauson, P. L.; Siegal, J. A. J. Chem. Soc., Dalton Trans. 1975,
1683.
(25) Renard, C.; Valentic, R.; Rose-Munch, F.; Rose, E.; Vaisserman,
J. Organometallics 1998, 17, 1587.

5986 Organometallics, Vol. 24, No. 24, 2005
Cao et al.
Table 4. Reactions of Functionalized Alkyl Iodides
Scheme 1. Proposed Mechanism for
In(0)-Mediated Alkyl Radical Addition to 1
7a-e with Complex 1a
CO2Et or IZn(CH2)2CN to complex 1a afforded the
R-alkylated product rather than the expected â-alky-
lated product because of deprotonation of the acidic
proton R to the ester or cyano group as reported by Yeh
and co-workers.11 A Grignard reagent equivalent to 7a
or 7b would be impossible.14-23 A nucleophilic anionic
reagent equivalent to 7d would result in â-elimination
to give cyclohexene.32,33 Moreover, the ionic processes
require strict anhydrous conditions, while the radical
reactions proceed readily in aqueous media, although
excess amounts of In(0) and alkyl iodides are used.
On the basis of the above results, a plausible mech-
anism could be drawn for In(0)-mediated radical addi-
tion reactions, as shown in Scheme 1. The interaction
of an alkyl iodide with indium generates an alkyl
radical, which adds to (η6-benzene)Mn(CO)3 cation to
+
give the corresponding 17-valence-electron intermediate
9. The intermediate 9 is then further reduced presum-
ably by another molecule of indium metal via a single
electron-transfer process to give the stable 18-valence-
electron product 2. The reactivity pattern of alkyl
iodides observed above strongly implies that the genera-
tion of an alkyl radical is the rate-determining step for
the reaction.
Conclusion
a Reaction conditions: 1a (1 equiv), 7 (6 equiv), In (3 equiv), 50
°C, 10 h. b Isolated yield based on 7. c Trans:cis ) 6:1 determined
by HPLC.
In summary, we have demonstrated that alkyl radical
addition to (η6-arene)Mn(CO)3 complexes can be suc-
+
cessfully carried out in aqueous media with indium as
the radical initiator. The reactions exhibit different
reactivity pattern from those of organomercurials. More-
over, the reactions also show excellent tolerance to
various functional groups, thus broadening the scope
of the radical addition, and should be of application in
organic synthesis.
Experimental Section
Typical Procedure for SmI2-Mediated Radical Reac-
tions of 1a. A THF solution of SmI2 (8 mL, 0.8 mmol) was
concentrated in vacuo to give a blue solid, which was diluted
with anhydrous acetonitrile (8 mL). A CH3CN solution of SmI2
was then added to the mixture of (η6-benzene)Mn(CO)3+PF6
-
(28) Miles, W. H.; Smiley, P. M.; Brinkman, H. R. J. Chem. Soc.,
Chem. Commun. 1989, 1897.
(29) Pearson, A. J.; Lee, S.-H.; Gouzoules, F. J. Chem. Soc., Perkin
Trans. 1 1990, 2251.
(30) Miles, W. H.; Brinkman, H. R. Tetrahedron Lett. 1992, 33, 589.
(31) Brookhart, M.; Pinhas, A. R.; Lukacs, A. Organometallics 1982,
1, 1730.
Figure 1. ORTEP drawing of compound 8e.
(32) Larock, R. C. In Comprehensive Organic Transformations;
Wiley: New York, 1999; p 266.
ployed.14,21,26-30 On the other hand, the nucleophilic
addition of the functionalized zinc reagent IZn(CH2)2-
(33) For examples, see: (a) Semmelhack, M. F.; Heinsohn, G. E. J.
Am. Chem. Soc. 1972, 94, 5139. (b) Adachi, T.; Iwasaki, T.; Inoue, I.;
Miyoshi, M. J. Org. Chem. 1979, 44, 1404. (c) Rao, A. V. R.; Yadav, J.
S.; Rao, C. S. Tetrahedron Lett. 1986, 27, 3297. (d) Florent, J. C.;
Ughetto-Monfrin, J.; Monneret, C. J. Org. Chem. 1987, 52, 1051. (e)
Cho, S.; Kang, S.; Keum, G.; Kang, S. B.; Han, S.-Y.; Kim, Y. J. Org.
Chem. 2003, 68, 180. (f) Yu, H.; Li, C. J. Org. Chem. 2004, 69, 142.
(26) Woo, K.; Carpenter, G. B.; Sweigart, D. A. Inorg. Chim. Acta
1994, 220, 297.
(27) Walker, P. J. C.; Mawby, R. J. J. Chem. Soc., Chem. Commun.
1972, 330.

Indium-Mediated Alkyl Radical Addition
Organometallics, Vol. 24, No. 24, 2005 5987
(1a, 72.4 mg, 0.2 mmol)34 and tert-butyl iodide (74 mg, 0.4
mmol) in acetonitrile (4 mL) at room temperature under
nitrogen atmosphere. The mixture was stirred at rt for 2 h. A
saturated NaHSO3 solution (10 mL) was then added to quench
the reaction. The resulting mixture was extracted with ether
(3 × 20 mL). The combined organic phase was washed with
brine (10 mL) and then dried over anhydrous MgSO4. After
removal of solvent under reduced pressure, the crude product
was purified by column chromatography on silica gel with
hexane as the eluent to afford the pure 2a as a yellowish solid.
Yield: 32.4 mg (59%). Mp: 73-75 °C.5c
Typical Procedure for Zn(Cu)-Mediated Radical Re-
actions of 1a. The mixture of manganese complex 1a (72.4
mg, 0.2 mmol), zinc (65 mg, 1 mmol), CuI (19 mg, 0.1 mmol),
i-PrI (0.12 mL, 1.2 mmol), CH3CN (0.5 mL), and H2O (1.5 mL)
in a 10 mL tube was stirred at rt under ultrasonic irradiation
for 10 h. The resulting mixture was extracted with EtOAc (3
× 10 mL). The combined organic phase was washed with brine
and then dried over anhydrous MgSO4. After removal of
solvent under reduced pressure, the crude product was purified
by column chromatography on silical gel with hexane as the
eluent to give pure 2b as a yellowish solid. Yield: 45.7 mg
(88%). Mp: 36 °C.5c
6.3 Hz), 0.74-0.78 (5H, m), 1.25-1.31 (1H, m), 2.02-2.09 (1H,
m), 2.45 (3H, s), 3.48 (2H, dd, J ) 7.2, 13.8 Hz), 4.85 (2H, d,
J ) 7.5 Hz); ortho isomer: δ 0.56 (3H, d, J ) 6.3 Hz), 0.74-
0.78 (5H, m), 1.25-1.31 (1H, m), 1.70 (3H, s), 2.36-2.40 (1H,
m), 3.03-3.09 (1H, m), 4.62 (1H, d, J ) 5.1 Hz), 4.75-4.78
(1H, m), 5.50 (1H, t, J ) 5.4 Hz). EIMS: m/z (rel intensity)
288 (M+, 1), 231 (70), 204 (100), 175 (39), 147 (50), 119 (8), 91
(14), 55 (49). Anal. Calcd for C14H17MnO3: C, 58.32; H, 6.24.
Found: C, 58.32; H, 6.30.
Complex 5b: yellowish oil. IR (KBr): ν (cm-1) 1921, 2011.
1H NMR (300 MHz, CDCl3) meta isomer: 0.60 (7H, br), 1.26
(3H, d, J ) 6.9 Hz), 1.40 (3H, d, J ) 6.6 Hz), 2.02-2.10 (1H,
m), 2.14-2.22 (1H, m), 3.23 (1H, dd, J ) 6.0, 13.8 Hz), 3.23
(1H, d, J ) 7.2 Hz), 4.81 (1H, t, J ) 7.5 Hz), 5.63 (1H, d, J )
4.8 Hz); para isomer: δ 0.60 (7H, br), 1.04 (3H, d, J ) 6.9
Hz), 1.26 (3H, d, J ) 6.9 Hz), 2.02-2.10 (1H, m), 2.79-2.89
(1H, m), 3.16 (2H, t, J ) 6.0 Hz), 4.80 (2H, d, J ) 7.8 Hz).
EIMS: m/z (rel intensity) 302 (M+, 1.96), 301 (12), 274 (M+
-
CO, 0.27), 218 (25), 260 (31), 217 (33), 203 (8), 175 (10), 105
(7), 55 (100). HRMS: calcd for C12H19Mn (M+ - 3CO) 218.0870,
found 218.0867.
Complex 5c: yellowish oil. IR (KBr): ν (cm-1) 1920, 2010.
1H NMR (300 MHz, CDCl3) meta isomer: δ 0.31-0.38 (1H,
m), 0.49-0.60 (2H, m), 0.95-1.05 (4H, m), 1.26 (3H, d, J )
6.6 Hz), 1.41 (3H, d, J ) 6.6 Hz), 1.56-1.63 (4H, m), 2.13-
2.22 (2H, m), 3.20 (1H, dd, J ) 5.7, 12.9 Hz), 3.20 (1H, d, J )
7.2 Hz), 4.80 (1H, t, J ) 7.8 Hz), 5.63 (1H, d, J ) 4.5 Hz);
para isomer: δ 0.31-0.38 (1H, m), 0.49-0.60 (2H, m), 0.95-
1.05 (4H, m), 1.03 (3H, d, J ) 6.3 Hz), 1.26 (3H, d, J ) 6.6
Hz), 1.56-1.63 (4H, m), 2.13-2.22 (1H, m), 2.83-2.87 (1H,
m), 3.12 (2H, t, J ) 6.3 Hz), 4.79 (2H, d, J ) 7.8 Hz). EIMS:
m/z (rel intensity) 342 (M+, 0.3), 300 (42), 301 (35), 259 (21),
258 (33), 245 (16), 217 (33), 175 (11), 55 (100). Anal. Calcd for
C18H23MnO3: C, 63.12; H, 6.77. Found: C, 63.09; H, 6.82.
Complex 5d: yellowish oil. IR (KBr): ν (cm-1) 1920, 2012.
1H NMR (300 MHz, CDCl3) meta isomer: δ 0.34-0.45 (1H,
m), 0.56 (3H, d, J ) 6.3 Hz), 0.74-0.80 (5H, m), 1.27 (3H, d,
J ) 6.6 Hz), 1.40 (3H, d, J ) 6.6 Hz), 2.11-2.22 (2H, m), 3.19-
3.29 (2H, m), 4.82 (1H, t, J ) 6.3 Hz), 5.63 (1H, m); para
isomer: δ 0.34-0.45 (1H, m), 0.56 (3H, d, J ) 6.3 Hz), 0.74-
0.80 (5H, m), 1.06 (3H, d, J ) 6.6 Hz), 1.27 (3H, d, J ) 6.6
Hz), 2.11-2.22 (1H, m), 2.79-2.88 (1H, m), 3.12-3.19 (2H,
m), 4.81 (2H, d, J ) 6.3 Hz). EIMS: m/z (rel intensity) 316
(M+, 0.2), 288 (M+ - CO, 2), 259 (32), 232 (44), 203 (18), 175
(33), 55 (100). HRMS: calcd for C13H21Mn (M+ - 3CO)
232.1014, found 232.1024.
Typical Procedure for Indium-Mediated Alkyl Radical
Addition to 1 in Aqueous Media. The mixture of manganese
complex 1a (72.4 mg, 0.2 mmol), indium (68.8 mg, 0.6 mmol),
cyclohexyl iodide (0.155 mL, 1.2 mmol), CH3CN (1.4 mL), and
H2O (0.7 mL) in a 10 mL tube was stirred at 40 °C for 10 h.
Water (5 mL) was added, and the resulting mixture was
extracted with EtOAc (3 × 10 mL). The combined organic
phase was washed with saturated brine and then dried over
anhydrous MgSO4. After removal of solvent under reduced
pressure, the crude product was purified by column chroma-
tography on silical gel with hexane as the eluent to give pure
2c as a yellowish solid. Yield: 50 mg (83%). IR (KBr): ν (cm-1
)
1926, 2002, 2021. 1H NMR (300 MHz, CDCl3): δ 0.37-0.45
(1H, m), 0.49-0.56 (2H, m), 0.92-1.07 (4H, m), 1.57-1.65 (4H,
m), 2.12-2.19 (1H, m), 3.23 (2H, t, J ) 6.0 Hz), 4.80 (2H, t, J
) 6.6 Hz), 5.73 (1H, t, J ) 5.4 Hz). EIMS: m/z (rel intensity)
300 (M+, 7), 216 (100), 189 (20), 161 (20), 133 (20), 91 (9), 83
(5), 55 (47). Anal. Calcd for C15H17MnO3: C, 60.01; H, 5.71.
Found: C, 60.10; H, 5.78.
Complex 2d: yellowish solid. IR (KBr): ν (cm-1) 1914, 2010.
1H NMR (300 MHz, CDCl3): δ 0.58 (3H, d, J ) 6.3 Hz), 0.72-
0.77 (5H, m), 1.32-1.37 (1H, m), 2.11-2.17 (1H, m), 3.23-
3.28 (2H, m), 4.80 (2H, t, J ) 6.3 Hz), 5.72 (1H, t, J ) 5.4 Hz).
EIMS: m/z (rel intensity) 274 (M+, 0.6), 217 (69), 190 (100),
161 (32), 133 (40), 105 (11), 91 (10), 55 (75). Anal. Calcd for
C13H15MnO3: C, 56.94; H, 5.51. Found: C, 56.98; H, 5.59.
Complex 4c: yellowish oil. IR (KBr): ν (cm-1) 1920, 2013.
1H NMR (300 MHz, CDCl3) meta isomer: δ 0.30-0.42 (1H,
m), 0.48-0.60 (2H, m), 0.96-1.06 (4H, m), 1.53-1.63 (4H, m),
1.87 (3H, s), 2.17-2.23 (1H, m), 3.15-3.20 (2H, m), 4.79 (1H,
dd, J ) 5.4, 7.2 Hz), 5.62 (1H, d, J ) 5.1 Hz); para isomer: δ
0.30-0.42 (1H, m), 0.48-0.60 (2H, m), 0.96-1.06 (4H, m),
1.53-1.63 (4H, m), 2.04-2.10 (1H, m), 2.46 (3H, s), 3.06-3.12
(2H, m), 4.85 (2H, d, J ) 6.9 Hz); ortho isomer: δ 0.30-0.42
(1H, m), 0.48-0.60 (2H, m), 0.96-1.06 (4H, m), 1.53-1.63 (4H,
m), 1.70 (3H, s), 2.36-2.39 (1H, m), 3.21-3.22 (1H, m), 4.61
(1H, d, J ) 5.4 Hz), 4.73-4.78 (1H, m), 5.55 (1H, t, J ) 5.4
Hz). EIMS: m/z (rel intensity) 314 (M+, 0.5), 273 (0.8), 230
(100), 203 (15), 175 (22), 147 (21), 91 (7), 55 (26). Anal. Calcd
for C16H19MnO3: C, 61.15; H, 6.09. Found: C, 61.54; H, 6.48.
Complex 4d: yellowish oil. IR (KBr): ν (cm-1) 1928, 2016.
1H NMR (300 MHz, CDCl3) meta isomer: δ 0.56 (3H, d, J )
6.3 Hz), 0.74-0.78 (5H, m), 1.25-1.31 (1H, m), 1.86 (3H, s),
2.15-2.23 (1H, m), 3.17-3.25 (2H, m), 4.78 (1H, t, J ) 5.4
Hz), 5.61 (1H, d, J ) 4.8 Hz); para isomer: δ 0.56 (3H, d, J )
Complex 6b: yellowish oil. IR (KBr): ν (cm-1) 1921, 2014.
1H NMR (300 MHz, CDCl3): δ 0.53 (7H, br), 2.12-2.25 (1H,
m), 3.12-3.23 (2H, m), 3.49 (3H, s), 4.84 (1H, dd, J ) 6.6, 12.6
Hz), 5.67 (1H, d, J ) 5.4 Hz). EIMS: m/z (rel intensity) 247
(M+ - C3H7, 2), 232 (11), 206 (M+ - 3CO, 2), 203 (5), 175 (8),
85 (34), 69 (39), 55 (100). HRMS: calcd for C10H15MnO (M+
3CO) 206.0492, found 206.0503.
-
Complex 6c: yellowish oil. IR (KBr): ν (cm-1) 1918, 2013.
1H NMR (300 MHz, CDCl3): δ 0.35-0.42 (1H, m), 0.49-0.60
(2H, m), 0.96-1.03 (4H, m), 1.50-1.63 (4H, m), 2.25-2.32 (1H,
m), 3.12-3.16 (1H, m), 3.15 (1H, d, J ) 6.0 Hz), 3.48 (3H, s),
4.82 (1H, t, J ) 6.0 Hz), 5.66 (1H, d, J ) 5.1 Hz). EIMS: m/z
(rel intensity) 330 (M+, 0.1), 302 (M+ - CO, 1), 247 (41), 246
(43), 219 (8), 191 (18), 163 (17), 109 (34), 55 (100). HRMS: cald
for C13H19MnO (M+ - 3CO) 246.0797, found 246.0816.
Complex 6d: yellowish oil. IR (KBr): ν (cm-1) 1919, 2014.
1H NMR (300 MHz, CDCl3): δ 0.41-0.52 (1H, m), 0.58 (3H,
m), 0.71-0.82 (5H, m), 2.25-2.32 (1H, m), 3.17-3.23 (2H, m),
3.48 (3H, s), 4.84 (1H, t, J ) 6.6 Hz), 5.66 (1H, d, J ) 4.8 Hz).
EIMS: m/z (rel intensity) 304 (M+, 0.1), 276 (M+ - CO, 1), 247
(38), 220 (34) 191 (19), 163 (21), 109 (48), 55 (100). HRMS:
cald for C11H17MnO (M+ - 3CO) 220.0668, found 220.0660.
Complex 8a: yellowish oil. IR (KBr): ν (cm-1) 1730, 1920,
2015. 1H NMR (300 MHz, CDCl3): δ 0.68 (3H, d, J ) 6.9 Hz),
1.06-1.12 (1H, m), 1.25 (3H, t, J ) 7.2 Hz), 1.72-1.80 (1H,
(34) Pauson, P. L.; Segal, J. A. J. Chem. Soc., Dalton Trans. 1975,
1677.

5988 Organometallics, Vol. 24, No. 24, 2005
Cao et al.
m), 2.19-2.25 (2H, m), 3.21 (1H, dd, J ) 7.2, 13.5 Hz), 3.23
(1H, dd, J ) 6.3, 13.8 Hz), 4.10 (2H, q, J ) 7.2 Hz), 4.85 (2H,
t, J ) 5.7 Hz), 5.75 (1H, t, J ) 5.4 Hz). EIMS: m/z (rel
intensity) 248 (M+ - 3CO, 11), 231 (4), 217 (22), 189 (6), 174
(17), 133 (10), 105 (27), 55 (100). Anal. Calcd for C15H17MnO5:
C, 54.23; H, 5.16. Found: C, 54.46; H, 5.39.
Hz); cis isomer: δ 0.68-0.90 (2H, m), 0.96-1.18 (2H, m), 1.50-
1.69 (4H, m), 1.82-1.86 (1H, m), 2.07 (3H, s), 2.24-2.31 (1H,
m), 3.19 (2H, t, J ) 6.6 Hz), 4.96-5.01 (1H, m), 5.75 (1H, t, J
) 5.4 Hz). EIMS: m/z (rel intensity) 274 (M+ - 3CO, 0.4), 248
(5), 230 (10), 217 (28), 189 (7), 174 (9), 91 (53), 55 (100).
HRMS: calcd for C14H19MnO2 (M+ - 3CO) 274.0766, found
274.0776.
Complex 8e: yellowish solid. IR (KBr): ν (cm-1) 1919, 2013,
3363. 1H NMR (300 MHz, CDCl3): δ 0.55-0.64 (2H, m), 1.09-
1.19 (2H, m), 1.56-1.66 (4H, m), 1.76-1.87 (1H, m), 2.79-
2.87 (1H, m), 3.11 (1H, t, J ) 6.6 Hz), 3.16-3.27 (1H, m), 3.43
(1H, t, J ) 6.6 Hz), 4.80 (1H, t, J ) 6.3 Hz), 4.86 (1H, t, J )
6.3 Hz), 5.72 (1H, t, J ) 5.1 Hz). 13C NMR (CDCl3): δ 223.2,
96.5, 96.1, 79.6, 73.0, 60.1, 54.6, 37.9, 36.1, 29.7, 25.6, 24.8,
24.4. EIMS: m/z (rel intensity) 316 (M+, 0.1), 232 (M+ - 3CO,
3), 230 (14), 217 (20), 176 (12), 91 (100), 55 (56). Anal. Calcd
for C15H17MnO4: C, 56.97; H, 5.42. Found: C, 57.07; H, 5.66.
Complex 8b: yellowish oil. IR (KBr): ν (cm-1) 1718, 1919,
2013. 1H NMR (300 MHz, CDCl3): δ 0.59 (3H, d, J ) 5.4 Hz),
0.89-1.02 (1H, m), 1.56-1.70 (2H, m), 2.11 (3H, s), 2.14-2.25
(2H, m) 2.32-2.43 (1H, m), 3.26 (2H, m), 4.83 (2H, dd, J )
5.1, 11.0 Hz), 5.73 (1H, t, J ) 5.4 Hz). EIMS: m/z (rel intensity)
316 (M+, 2), 219 (7), 217 (1), 191 (3), 169 (5), 85 (18), 55 (100).
Anal. Calcd for C15H17MnO4: C, 56.97; H, 5.42. Found: C,
57.33; H, 5.44.
Complex 8c: yellowish oil. IR (KBr): ν (cm-1) 1937, 2021,
2247. 1H NMR (300 MHz, CDCl3): δ 0.65 (3H,. d, J ) 5.4 Hz),
0.96-1.10 (1H, m), 1.65-1.79 (2H, m), 2.13-2.22 (2H, m),
2.26-2.37 (1H, m), 3.22 (2H, m), 4.87 (2H, m), 5.76 (1H, t, J
) 5.1 Hz). EIMS: m/z (rel intensity) 299 (M+, 0.7), 165 (41),
149 (23), 132 (35), 91 (25), 55 (79). Anal. Calcd for C14H14-
MnNO3: C, 56.20; H, 4.72; N, 4.68. Found: C, 56.22; H, 4.93;
N, 4.59.
Acknowledgment. This project was supported by
the National Natural Science Foundation of China (No.
20325207 and No. 20272072).
Complex 8d: yellowish oil. IR (KBr): ν (cm-1) 1718, 1737,
1937, 2021. 1H NMR (300 MHz, CDCl3) trans isomer: δ 0.68-
0.90 (2H, m), 0.96-1.18 (2H, m), 1.50-1.69 (4H, m), 1.82-
1.86 (1H, m), 2.05 (3H, s), 2.66 (1H, q, J ) 6.0 Hz), 3.07 (1H,
t, J ) 6.6 Hz), 3.14 (1H, t, J ) 6.6 Hz), 4.45 (1H, dt, J ) 4.8,
9.6 Hz), 4.84 (2H, dd, J ) 7.8, 13.6 Hz), 5.71 (1H, t, J ) 5.4
Supporting Information Available: X-ray crystal data
of 8e in CIF format. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM050721C