J. Am. Chem. Soc. 1996, 118, 1571-1572
2
Table 1. Palladium-Catalyzed Addition of (EtO) P(O)H to
1571
Palladium-Catalyzed Hydrophosphorylation of
Acetylenes
Alkynes Wia Oxidative Addition of HP(O)(OR)
2
run
catalyst
time (h)
% adduct yield (2/3)a
b,c
Li-Biao Han and Masato Tanaka*
1
2
3
4
5
6
7
8
5
13
17
6
18
22
72
72
93 (90/10)
92 (89/11)
73 (85/15)
93 (91/9)
89 (86/14)
69 (88/16)
8 (64/36)
9 (68/32)
2
2
2
2
b
b
National Institute of Materials and Chemical Research
Tsukuba, Ibaraki 305, Japan
b,d
b
ReceiVed NoVember 2, 1995
b,c
e
Application of metal complex catalysis to heteroatom chem-
istry is a research field that will vitally grow in the future.
Addition reactions of H-E and E-E′ bonds (E, E′ ) a
heteroatom or group) across unsaturated carbon linkages in
particular are an important class of reactions from a synthetic
e
4
a
Determined by GC. b 3 mol % Pd catalyst, equimolar 1-octyne and
c
(
)
EtO)
2
1 M. Carried out under 1 atm of ethylene. e 5 mol % Pt catalyst,
equimolar phenylacetylene and (EtO) P(O)H in toluene (1 M), 110 °C.
2
1
viewpoint. An exceptional example in this category that has
already been experiencing great industrial success is hydrosi-
lylation. Addition reactions of other group 14 element
compounds and elemental processes behind the catalysis are
also under intense study.3 To the best of our knowledge,
however, the metal-complex-catalyzed addition reaction of the
H-P bond appears to have never been explored.4 Herein are
reported (1) the first entry into this category, namely, palladium-
2
Pd(0) complexes or readily reducible Pd(II) complexes that have
less basic ligands are able to efficiently catalyze the reaction.
Accordingly, as shown in Table 1, cis-PdMe (PPh ) Pd-
2
3 2,
(
CH2dCH2)(PPh3)2, and Pd(PPh3)4 also catalyzed the reaction.
On the other hand, Pd(II) complexes such as PdMe (PEt ) (cis/
2
3 2
trans ) 7/1), PdCl2, Pd(OAc)2, PdCl2(PPh3)2, and PdCl2(PhCN)2
were totally inactive because of either the ligand being too basic
or the complex not being readily reduced to Pd(0) species.8
Worth noting from a mechanistic viewpoint (Vide infra) is that
some platinum complexes were also able to promote the
reaction, albeit sluggishly.
catalyzed hydrophosphorylation of acetylenes, and (2) the first
example of oxidative addition of HP(O)(OR)25 to the Pt(0)
complex generating H-Pt-P(O)(OR)2 species. In the new
catalysis the H-P bond adds across triple bonds under gentle
conditions to afford various alkenylphosphonates in excellent
6
Pd-catalyzed hydrophosphorylation can be easily applied to
other alkynes, thus proving to be a new general methodology
for the synthesis of alkenylphosphonates, which are not readily
yields. Alkenylphosphonates are both synthetically versatile
and biologically active.7
Heating a THF solution (1 mL) of 1-octyne (1 mmol) and
HP(O)(OR)2 (1 mmol) in the presence of cis-PdMe2(PPh2Me)2
6
,9
accessible by conventional methods.
As demonstrated in
Table 2, both aliphatic and aromatic terminal alkynes reacted
efficiently with HP(O)(OMe)2, affording in high yields the
corresponding adducts by regioselective attack of the phosphorus
at the internal carbon of the triple bond. An exceptional case
was the reaction of (trimethylsilyl)acetylene in which only the
terminal carbon was phosphorylated, probably owing to steric
hindrance at the internal carbon. As exemplified by runs 5 and
(
1, 3 mol %) at 67 °C for 5 h under argon resulted in a complete
disappearance of the starting materials. Simple Kugelrohr
distillation afforded the corresponding alkenylphosphonates in
high yields (eq 1).
6
, two phosphoryl groups could be easily introduced to both
triple bonds of the diynes. Under similar conditions, the olefinic
double bond is totally unreactive to the hydrophosphorylation.
Accordingly, 1-ethynylcyclohexene (run 7) underwent the
addition reaction selectively at the triple bond.
As compared to terminal alkynes, the hydrophosphorylation
of internal alkynes proceeded a little slower. The addition of
HP(O)(OEt)2 to 4-octyne produced 23 and 82% yields of the
adduct after heating for 15 and 65 h, respectively. The high
stereoselectivity is noteworthy; only the cis isomer could be
In the absence of the catalyst, neither 2 nor 3 could be
detected by GC under the same reaction conditions. In general,
1
observed on H NMR.
Although the detailed mechanism of the hydrophosphorylation
reaction still remains to be clarified, the reaction is envisioned
(
1) (a) Chaloner, P. A. Handbook of Coordination Catalysis in Organic
Chemistry; Butterworth: London, 1986; Chapter 4. (b) Collman, J. P.;
Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applications of
Organotransition Metal Chemistry; University Science Books: Hill Valley,
CA, 1987. (c) ComprehensiVe Organic Synthesis; Trost, B. M., Ed.;
Pergamon Press: Oxford, U.K., 1991; Vol. 8, pp 667-792. (d) Parshall,
G. W.; Ittel, S. D. Homogeneous Catalysis; John Wiley & Sons: New York,
(5) Hydrogen phosphonates exist in two tautomeric forms, HP(O)(OR)2
and P(OR)2(OH), the former being thermodynamically more favored under
ambient conditions. They coordinate, like tertiary phosphines, to transition
metals (Pd, Pt, Ir, Rh, etc.) to form complexes which have been used as
catalysts in organic reactions: (a) Henbest, H. B.; Mitchell, T. R. B. J.
Chem. Soc. C 1970, 785. (b) Roundhill, D. M.; Sperline, R. P; Beaulieu,
W. B. Coord. Chem. ReV. 1978, 26, 263. (c) Bennett, M. A.; Mitchell, T.
R. B. J. Organomet. Chem. 1985, 295, 223.
1
992; pp 25-50.
2) ComprehensiVe Handbook on Hydrosilylation; Marciniec, B., Ed.;
Pergamon Press: Oxford, U.K., 1992.
(
(
3) For recent reviews, see: (a) Horn, K. A. Chem. ReV. 1995, 95, 1350.
(
(
(
b) Sharma, H. K.; Pannell, K. H. Chem. ReV. 1995, 95, 1351. See also:
c) Yamashita, H.; Tanaka, M.; Goto, M. Organometallics 1993, 12, 988.
d) Hada, M.; Tanaka, Y.; Ito, M.; Murakami, M.; Amii, H.; Ito, Y.;
(6) For a recent review, see: Minami, T.; Motoyoshiya, J. Synthesis 1992,
333.
(7) (a) Engel, R. Chem. ReV. 1977, 77, 349. (b) Harnden, M. R.; Parkin,
A.; Parratt, M. J.; Perkins, R. M. J. Med. Chem. 1993, 36, 1345. (c) Breaker,
R. R.; Gough, G. R.; Gilham, P. T. Biochemistry 1993, 32, 9125.
(8) Some of these Pd(II) complexes appeared to react with the phos-
phonate since a distinct color change of the solution was observed upon
mixing these two components.
Nakatsuji, H. J. Am. Chem. Soc. 1994, 116, 8754. (e) Chatani, N.; Amishiro,
N.; Morii, T.; Yamashita, T.; Murai, S. J. Org. Chem. 1995, 60, 1834. (f)
Fu, P.-F.; Brard, L.; Li, Y.; Marks, T. J. J. Am. Chem. Soc. 1995, 117,
7
1
1
157. (g) Shimada, S.; Tanaka, M.; Honda, K. J. Am. Chem. Soc. 1995,
17, 8289. (h) Yamashita, H.; Tanaka, M.; Hond, K. J. Am. Chem. Soc.
995, 117, 8873.
2
(9) Examples of sp -carbon to phosphorus bond-forming reactions are
(
4) For radical and acid- or base-catalyzed addition of H-P, see: (a)
rare: (a) Hirao, T.; Masunaga, T.; Yamada, N.; Oshiro, Y.; Agawa, T. Bull.
Chem. Soc. Jpn. 1982, 55, 909. (b) Xu, Y.; Li, Z.; Xia, J.; Guo, H.; Huang,
Y. Synthesis 1983, 377. (c) Holt, D. A.; Erb, J. M. Tetrahedron Lett. 1989,
30, 5393.
Organic Phosphorus Compounds; Kosolapoff, G. M., Maier, L., Eds.;
Wiley-Interscience: New York, 1972. (b) Goldwhite, H. Introduction to
Phosphorus Chemistry; Cambridge University Press: Cambridge, 1981.
0
002-7863/96/1518-1571$12.00/0 © 1996 American Chemical Society