Regioselective double hydrophosphination of terminal arylacetylenes catalyzed by an iron complex

Article abstract of DOI:10.1021/ja304818c

The first catalytic double hydrophosphination of alkynes was achieved by reaction with diarylphosphines in the presence of an iron catalyst. The double hydrophosphination proceeded regioselectively and effectively for various secondary arylphosphines and

Full text of DOI:10.1021/ja304818c

Communication
pubs.acs.org/JACS
Regioselective Double Hydrophosphination of Terminal
Arylacetylenes Catalyzed by an Iron Complex
Masahiro Kamitani, Masumi Itazaki, Chihiro Tamiya, and Hiroshi Nakazawa*
Department of Chemistry, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan
S
* Supporting Information
Table 1. Reaction of PPh2H with PhCCH in the Presence
a
ABSTRACT: The first catalytic double hydrophosphina-
tion of alkynes was achieved by reaction with diary-
lphosphines in the presence of an iron catalyst. The double
hydrophosphination proceeded regioselectively and effec-
tively for various secondary arylphosphines and terminal
alkynes to give 1,2-bisphosphinoethane derivatives.
of Fe Catalysis
b
c
entry
Fe cat.
solvent
neat
cat. /mol%
yield /%
1
CpFe(CO)2Me
CpFe(CO)2Me
CpFe(CO)2Me
CpFe(CO)2Me
CpFe(CO)2Me
CpFe(CO)2Me
CpFe(CO)2Me
Cp*Fe(CO)2Me
FeCl2
5
94
d
2
hexane
toluene
THF
5
NR
d
3
5
NR
hosphines have been widely used as versatile and
d
4
5
NR
P
indispensable ligands for various transition metals because
the properties of transition metal complexes can be easily tuned
by varying the substituents on the phosphorus atoms.1
Appropriate selections of phosphines have realized the
stabilization, isolation, and even structural characterization of
reactive complexes, as well as control of the activity and
selectivity of transition metal catalysts. Among several methods
for the preparation of phosphines, the addition of a P−H bond
to an unsaturated C−C bond is one of the most attractive
methods because it produces no undesired compounds as
byproducts.2 Additions of P−H bonds in P(V) compounds to
alkynes promoted by a transition metal catalyst have been
reported.3,4 These additions have been referred to as
hydrophosphinylation and hydrophosphonylation, depending
on the substituents on the P(V) atom (Scheme 1). Reduction
d
5
acetonitrile
neat
5
NR
e
6
2.5
1
32
e
7
neat
13
8
neat
5
92
d
9
neat
5
NR
d
10
11
FeCl3
neat
5
NR
d
Fe(CO)5
neat
5
NR
a
Reaction conditions: 110 °C, [PPh2H]/[phenylacetylene] = 2:1.
b
c
d
e
Based on [Ph2PH]. Isolated yield. No reaction. Phenylacetylene
was completely consumed, but the single hydrophosphination
compound was also formed.
reactant such as PR2H and/or a product such as PR2R′ to a
transition metal catalyst to form a coordinatively saturated
complex, leading to a decrease in or complete loss of catalytic
activity. Double hydrophosphination of an alkyne is especially
difficult because the product serves as a bidentate ligand, which
binds to a transition metal catalyst more strongly than a
monodentate ligand because of the chelate effect.7 If double
hydrophosphination of an alkyne could be achieved with a
transition metal, it would be a convenient and atom-efficient
method to obtain bidentate 1,2-phosphinated ethane deriva-
tives such as bis(diphenylphosphino)ethane (dppe). To our
best knowledge, there are only a few stoichiometric double
hydrophosphinations of alkynes,8 and no such catalytic reaction
using a transition metal catalyst has been reported.9 In this
Communication, we describe the first example of catalytic
double hydrophosphination of various alkynes promoted by an
iron catalyst.
Scheme 1. P−H Bond Addition to Alkyne
PPh2H (465 mg, 2.50 mmol), PhCCH (137 μL, 1.25
mmol), and CpFe(CO)2Me (12.0 mg, 0.125 mmol, corre-
sponding to 5 mol% based on PPh2H) (Cp stands for η5-C5H5)
were charged in a Schlenk tube under a nitrogen atmosphere.
After the reaction mixture was heated at 110 °C for 3 days, the
of the products from P(V) to P(III) affords phosphines.5 A
more straightforward method to obtain phosphines is the
addition of a P−H bond of a P(III) compound to an alkyne,
which is referred to as hydrophosphination (Scheme 1).2
However, examples of hydrophosphination catalyzed by a
transition metal complex are limited.6 One of the reasons
presumably the main reasonstems from the coordination of a
Received: May 26, 2012
Published: July 9, 2012
© 2012 American Chemical Society
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Journal of the American Chemical Society
Communication
volatile materials were removed under reduced pressure. The
residue was washed with hexane and dried under vacuum to
give 1,2-bis(diphenylphosphino)-1-phenylethane (1a) in 94%
yield (Table 1, entry 1). In this reaction, PPh2H and PhCCH
served as both reagents and solvents. Interestingly and
importantly, when the reaction was performed in an organic
solvent such as hexane, toluene, THF, or acetonitrile, the
double hydrophosphination product was not obtained; rather,
CpFe(CO)(PPh2H){C(O)Me} was formed (entries 2−5), as
determined by comparison from the NMR data of the reaction
mixture to those from the authentic complex.10 Even when the
amount of CpFe(CO)2Me was reduced from 5 mol% to 2.5
mol% or 1 mol%, the PhCCH was completely consumed.
However, both the single and double hydrophosphination
compounds were produced (entries 6 and 7). Some other iron
complexes were also examined as catalyst precursors. Cp*Fe-
(CO)2Me (Cp* stands for η5-C5Me5) showed similar catalytic
activity (entry 8). In contrast, FeCl2, FeCl3, and Fe(CO)5
showed no catalytic activity, even for the single hydro-
phosphination reaction (entries 9−11).11
Table 2. Double Hydrophosphination of PR2H with Alkynes
Promoted by CpFe(CO)2Me
a
b
entry
R
R′
compd
yield /%
1
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
p-Me-C6H4
p-tBu-C6H4
p-MeO-C6H4
p-NH2-C6H4
p-F-C6H4
1b
1c
1d
1e
1f
95
73
82
72
91
91
77
27
0
2
3
4
5
6
3-pyridyl
1g
1h
1i
7
3-thiophenyl
2-pyridinyl
8
c
9
alkyl
−
10
11
12
p-Me-C6H4
Ph
Ph
Ph
1j
92
73
0
p-MeO-C6H4
1k
−
d
alkyl
a
Reaction conditions: 110 °C, 3 days, 10 mL Schlenk tube, [PR2H]/
b
c
[phenylacetylene]/[CpFe(CO)2Me] = 20:10:1. Isolated yield. Alkyl
= n-hexyl, cyclohexyl, benzyl. Alkyl = Hex, Bu.
d
c
t
In the reactions shown in entries 2−5 of Table 1,
CpFe(CO)(PPh2H){C(O)Me} was produced, indicating that
this iron complex could be a catalyst precursor. The reaction of
PhCCH with 2 equiv of PPh2H in the presence of 5 mol% of
CpFe(CO)(PPh2H){C(O)Me} was examined, and it was
revealed that the iron complex is catalytically active for the
double hydrophosphination reaction (Scheme 2).
(entries 10 and 11). However, alkylphosphines, PR2H (R =
t
cHex Bu), did not afford any hydrophosphination product
(entry 12).
All hydrophosphination compounds were characterized by
1H, 13C, and 31P NMR. The molecular structures of 1b and 1d
were confirmed by X-ray diffraction (Figure 1). In both cases,
Scheme 2. Double Hydrophosphination Promoted by
CpFe(CO)(PPh2H){C(O)Me} Complex
Because the double hydrophosphination of a CC triple
bond is unprecedented, we examined further instances of this
reaction by utilizing different combinations of secondary
phosphines and alkynes. The results are summarized in Table
2, where the reaction conditions employed were the same as
those shown in entry 1 of Table 1. Various para-substituted
phenylacetylenes were effectively converted into double
hydrophosphination products (entries 1−6), whether the
substituent was an electron-donating or electron-withdrawing
group. It should be noted that the NH2 group remains intact
during the reaction (entry 4), indicating that the reactive and
coordinative amino group did not disturb this catalytic system.
3-Pyridyl and 3-thiophenyl derivatives were also converted into
the corresponding diphosphines (entries 6 and 7). Although
the 2-pyridyl derivative showed a low isolated yield due to its
high solubility in hexane that was used for purification of the
product, the phosphine was converted into the corresponding
diphosphine in 78% yield, according to the 31P NMR
measurement (entry 8). In contrast, n-hexyl-, cyclohexyl-, and
benzylacetylene did not undergo hydrophosphination (entry
9). In addition, internal alkynes such as diphenylacetylene and
dimethylacetylene dicarboxylate (DMAD) did not undergo
hydrophosphination. These results suggest that this catalytic
system is effective for terminal arylacetylenes but not for
alkylacetylenes and internal alkynes. P(p-MeC6H4)2H and P(p-
MeOC6H4)2H also reacted with PhCCH to give double
hydrophosphination products in the present catalytic system
Figure 1. ORTEP drawings of 1b and 1d with 50% thermal ellipsoidal
plots. Hydrogen atoms are omitted for simplicity.
the two sp carbons in the starting alkyne were changed to sp3
carbons, and each of them has one PPh2 group. The carbon−
carbon bond lengths are 1.538 and 1.545 Å, showing that they
are single bonds. The two phosphorus atoms were not oxidized.
The reaction of 1 equiv of PhCCH, 2 equiv of PPh2H, and
0.1 equiv of CpFe(CO)2Me was monitored by 31P NMR
(without H decoupling). A plot of the amounts of phosphorus-
containing compounds as functions of time is shown in Figure
2. The amount of PPh2H decreased constantly. The single
hydrophosphination product with Z configuration (2-Z)12
increased for 12 h after the reaction started and then decreased
gradually. In contrast, very little (E)-vinylphosphine (2-E)13
was formed. The double hydrophosphination product (1a)
constantly increased with time. This time-dependence curve
lets us envision the following catalytic profile: PPh2H reacts
with PhCCH to give 2-Z selectively, which then reacts with
PPh2H to afford 1a; a very small degree of isomerization of 2-Z
to 2-E takes place. The molar ratio of 1a:2-Z:2-E:PPh2H after
48 h was 84:7:4:5.
The proposed mechanism for the catalytic reaction of Ph2PH
with phenylacetylene is shown in Scheme 3. CO insertion into
the Fe−Me bond in CpFe(CO)2Me and PPh2H coordination
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Journal of the American Chemical Society
Communication
insertion into the Fe−P bond), G→H (PPh2H coordination),
and H→B (reproduction of B with formation of (Ph2P)C-
(Ph)HCH2(PPh2)). In this catalytic cycle, species D and G are
in equilibrium with catalytically inactive D′ and G′, respectively.
These equilibria may be responsible for the relatively slow
reaction: it takes about 3 days to finish the catalytic reaction.
We conducted some additional experiments to check
whether the radical pathway can be ruled out. When more
than 1 equiv of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)
or galvanoxyl was used as a radical inhibitor, diphenylphosphine
was converted into the corresponding phosphine oxide even
without an iron catalyst.18 When 5 mol% (vs phosphine) of the
radical inhibitor was added under standard conditions (Table 1,
entry 1), a large amount of double hydrophosphination
compound and a small amount of phosphine oxide were
formed. We also conducted several reactions under light-
shielding conditions and under an argon atmosphere, but no
significant difference was observed. It has been reported that a
radical reaction of PPh2H with alkyne promoted by AIBN or
photoirradiation yielded only the single hydrophosphination
product, but never yielded the double hydrophosphination
product in one pot.12 These results indicate that our catalytic
reaction does not occur via a radical pathway, although a radical
pathway cannot be ruled out completely.
Figure 2. Plot of the amounts of phosphorus-containing compounds
as functions of time in the reaction of CpFe(CO)2Me, phenyl-
◆ ■
▲
,
acetylene, and diphenylphosphine in 1:10:20 ratio at 110 °C.
,
,
●
and stand for 1a, 2-Z, 2-E, and diphenylphosphine.
take place to give A. As mentioned above, A can be isolated
when the reaction is performed in an organic solvent.
Conversion of A into B with a PPh2 ligand occurs either via
P−H oxidative addition and HC(O)Me elimination14 or via
concerted HC(O)Me elimination from the coordinated PPh2H
and the C(O)Me ligand. PhCCH coordinates to B through
the CC triple bond to give C. The phosphide iron complex,
CpFe(CO)(PMes2), which is similar to B, has been reported
previously to be reactive with an unsaturated bond in
isothiocyanate.15 The PhCCH in C inserts into the Fe−P
bond to form D. The phosphorus atom in D may coordinate to
the iron center to give D′, and they may be in equilibrium.15,16
Relevant alkyne insertion into the M−P bond (M = Ni, Pd, Pt,
Rh) was suggested by DFT calculation.17 The second PPh2H
coordinates to D to form E, which is converted into B with
PhHCCH(PPh2) generation. Complex B goes into Cycle 1
when it reacts with PhCCH. Alternatively, B may react with
the PhHCCH(PPh2) produced in Cycle 1 to go into Cycle 2,
which consists of B→F (olefin coordination), F→G (olefin
Hydrophosphination involving cationic species has been
proposed.19 A cationic iron complex bearing PRH2, [CpFe-
(CO)2(PRH2)]+, was reported to undergo hydrophosphination
to alkynes and alkenes.19b This cationic complex reacted with
DMAD to give a double hydrophosphination product, whereas
DMAD did not undergo hydrophosphination in our reaction
system. Therefore, it is highly likely that a cationic iron complex
bearing phosphine as a ligand is not involved in our catalytic
cycle.
In summary, an unprecedented catalytic double hydro-
phosphination was achieved in the reaction of a terminal
Scheme 3. Proposed Catalytic Cycle
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Journal of the American Chemical Society
Communication
(8) (a) Tang, L.; Zhang, Y.; Luo, D.; Li, Y.; Mok, K. F.; Yeo, W. C.;
Leung, P. H. Tetrahedron Lett. 2007, 48, 33. (b) Pullarkat, S. A.; Ding,
Y.; Li, Y.; Tan, G. K.; Leung, P. H. Inorg. Chem. 2006, 45, 7455.
(c) Yeo, W. C.; Tee, S. T.; Tan, G. K.; Koh, L. L.; Leung, P. H. Inorg.
Chem. 2004, 43, 8102. (d) Zhang, Y.; Tang, L.; Ding, Y.; Chua, J. F.;
Li, Y.; Yuan, M.; Leung, P. H. Tetrahedron Lett. 2008, 49, 1762.
(e) Treichel, P. M.; Wong, W. K. J. Organomet. Chem. 1978, 157, C5.
(f) Malish, W.; Rehmann, F. J.; Jehle, H.; Reising, J. J. Organomet.
Chem. 1998, 570, 107.
(9) One example of catalytic double hydrophosphination of an alkyne
has been reported in which KOtBu was used. However, this method is
not applicable to hydrophosphines and alkynes bearing functional
group(s) which react with KOtBu. See: (a) Bookham, J. L.; Smithies,
D. M.; Wright, A.; Thornton-Pett, M.; McFarlane, M. J. Chem. Soc.,
Dalton Trans. 1998, 811. (b) Bookham, J. L.; McFarlane, W.;
Thornton-Pett, M.; Jones, S. J. Chem. Soc., Dalton Trans. 1990, 3621.
(10) Adams, H.; Bailey, N. A.; Blenkiron, P.; Morris, M. J. J.
Organomet. Chem. 1993, 460, 73.
(11) When FeCl2 was used, no reaction occurred and the starting
PPh2H and PhCCH were recovered. When Fe(CO)5 was used, the
reaction mixture showed several resonances in the range 50−120 ppm
in the 31P NMR spectrum, which were not attributed to double or
single hydrophosphination products.
(12) Terence, M. N.; Kerstin, H. J. Organomet. Chem. 1991, 409, 163.
(13) Hayashi, M.; Matsuura, Y.; Watanabe, Y. J. Org. Chem. 2006, 71,
9248.
arylalkyne with a secondary arylphosphine using an iron
complex. The key point is that no organic solvent is used; the
arylalkyne and arylphosphine are used as both solvents and
reagents. It should be noted that the iron catalyst, presumably
CpFe(CO)(PPh2), does not suffer considerable (if any) loss of
activity from coordination by PPh2H and the diphosphine
formed.
ASSOCIATED CONTENT
* Supporting Information
■
S
Detailed experimental procedures and characterization of
products. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
nakazawa@sci.osaka-cu.ac.jp
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This research was supported by a Challenging Exploratory
Research (No. 23655056) from the Ministry of Education,
Culture, Sports, Science and Technology, Japan.
(14) Itazaki, M.; Kamitani, M.; Nakazawa, H. Chem. Commun. 2011,
47, 7854.
(15) Malisch, W.; Hirth, U.; Fried, A.; Pfister, H. Phosphorus, Sulfur
Silicon 1993, 77, 17.
REFERENCES
■
(1) For example, see: Tolman, C. A. Chem. Rev. 1977, 77, 313.
(2) (a) Alonso, F.; Beletskaya, I. P.; Yus, M. Chem. Rev. 2004, 104,
3079. (b) Delacroix, O.; Gaumont, A. C. Curr. Org. Chem. 2005, 9,
1851. (c) Mimeau, D.; Delacroixb, O.; Gaumont, A. Chem. Commun.
2003, 2928.
(16) Derrah, E. J.; McDonald, R.; Rosenberg, L. Chem. Commun.
2010, 46, 4592.
(17) Ananikov, V. P.; Beletskaya, I. P. Chem. Asian J. 2011, 6, 1423.
(18) Baker, R. J.; Hashem, E. Helv. Chim. Acta 2010, 93, 1081.
(19) (a) Hoffmann, H.; Diehr, H. J. Chem. Ber. 1965, 98, 363.
(b) Malisch, W.; Klupfel, B.; Schumacher, D.; Nieger, M. J. Organomet.
Chem. 2002, 661, 95.
(3) Hydrophosphinylation: (a) Han, L.-B.; Choi, N.; Tanaka, M.
Organometallics 1996, 15, 3259. (b) Han, L.-B.; Hua, R.; Tanaka, M.
Angew. Chem., Int. Ed. 1998, 37, 94. (c) Han, L.-B.; Zhao, C.-Q.;
Tanaka, M. J. Org. Chem. 2001, 66, 5929. (d) Han, L.-B.; Zhao, C.-Q.;
Onozawa, S.; Goto, M.; Tanaka, M. J. Am. Chem. Soc. 2002, 124, 3842.
(e) Deprele, S.; Montchamp, J.-L. J. Am. Chem. Soc. 2002, 124, 9386.
(f) Nune, S. K.; Tanaka, M. Chem. Commun. 2007, 43, 2858.
(4) Hydrophosphonylation: (a) Han, L.-B.; Tanaka, M. J. Am. Chem.
Soc. 1996, 118, 1571. (b) Zhao, C.-Q.; Han, L.-B.; Goto, M.; Tanaka,
M. Angew. Chem., Int. Ed. 2001, 40, 1929. (c) Goulioukina, N. S.;
Dolgina, T. M.; Beletskaya, I. P.; Henry, J.-C.; Lavergne, D.;
Ratovelomanana-Vidal, V.; Genet, J.-P. Tetrahedron: Asymmetry
2001, 12, 319. (d) Allen, A., Jr.; Manke, D. R.; Lin, W. Tetrahedron
Lett. 2000, 41, 151. (e) Zhao, C.-Q.; Han, L.-B.; Tanaka, M.
Organometallics 2000, 19, 4196. (f) Han, L.-B.; Mirzaei, F.; Zhao, C.-
Q.; Tanaka, M. J. Am. Chem. Soc. 2000, 122, 5407. (g) Mirzaei, F.;
Han, L.-B.; Tanaka, M. Tetrahedron Lett. 2001, 42, 297. (h) Kanada, J.;
Yamashita, K.; Nune, S. K.; Tanaka, M. Tetrahedron Lett. 2009, 50,
6196. (i) Stockland, R. A., Jr.; Taylor, R. I.; Thompson, L. E.; Patel, P.
B. Org. Lett. 2005, 7, 851. (j) Ananikov, V. P.; Khemchyan, L. L.;
Beletskaya, I. P. Synlett 2009, 15, 2375. (k) Ananikov, V. P.;
Khemchyan, L. L.; Beletskaya, I. P.; Starikovac, Z. A. Adv. Synth.
Catal. 2010, 352, 2979.
(5) (a) Allen, A., Jr.; Ma, L.; Lin, W. Tetrahedron Lett. 2002, 43, 3707.
(b) Berk, S. C.; Buchwald, S. L. J. Org. Chem. 1992, 57, 3751.
(6) (a) Takaki, K.; Takeda, M.; Koshoji, G.; Shishido, T.; Takehira,
K. Tetrahedron Lett. 2001, 42, 6357. (b) Kazankova, M. A.; Efimova, I.
V.; Kochetkov, A. N.; Afanas’ev, V. V.; Beletskaya, I. P.; Dixneuf, P. H.
Synlett 2001, 497. (c) Kazankova, M. A.; Efimova, I. V.; Kochetkov, A.
N.; Afanas’ev, V. V.; Beletskaya, I. P. Russ. J. Org. Chem. 2002, 38,
1465. (d) Sadow, A. D.; Togni, A. J. Am. Chem. Soc. 2005, 127, 17012.
(7) (a) Mizuta, T.; Miyaji, C.; Katayama, T.; Ushio, J.; Kubo, K.;
Miyoshi, K. Organometallics 2009, 28, 539. (b) Kovacik, I.; Scriban, C.;
Glueck, D. S. Organometallics 2006, 25, 536. (c) Kondoh, A.;
Yorimitsu, H.; Oshima, K. J. Am. Chem. Soc. 2007, 129, 4099.
11935
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