High reactivity of a five-membered cyclic hydrogen phosphonate leading to development of facile palladium-catalyzed hydrophosphorylation of alkenes [11]

Full text of DOI:10.1021/ja000444v

J. Am. Chem. Soc. 2000, 122, 5407-5408
5407
Chart 1
High Reactivity of a Five-Membered Cyclic
Hydrogen Phosphonate Leading to Development of
Facile Palladium-Catalyzed Hydrophosphorylation of
Alkenes
Li-Biao Han, Farzad Mirzaei, Chang-Qiu Zhao, and
Masato Tanaka*
1a was significantly influenced by the nature of the ligand,
alkyldiphenylphosphine like PPh2Me being of choice under similar
conditions. Besides palladium complexes, Ni(PPh3)4 (26% yield,
10 mol % catalyst) and RhCl(PPh3)3 (49% yield) were also
moderately active under similar conditions. However, Pt(CH2d
CH2)(PPh3)2 was nearly inactive.
National Institute of Materials and Chemical Research
Tsukuba, Ibaraki 305-8565, Japan
ReceiVed February 7, 2000
Transition metal-catalyzed addition reactions of heteroatom
compounds across unsaturated carbon linkages are emerging
rapidly as one of the most powerful tools for constructing carbon-
heteroatom bonds.1 However, methodologies for phosphorus
compounds are still limited.1e Organophosphonates RP(O)(OR′)2,
a useful class of compounds in synthetic applications and bio-
logical activity, are traditionally prepared via the classic Arbuzov
reaction of P(OR′)3 with organic halides RX with the concomitant
elimination of an equivalent quantity of R′X.2 A more attractive,
versatile, and clean alternative of high atom economy for their
preparation would be the addition of HP(O)(OR′)2 to alkenes
catalyzed by metal complexes.3 Despite extensive screening of
catalysts, such reactions have never been realized, although the
corresponding Pd-catalyzed hydrophosphorylation of alkynes takes
place efficiently.4,5 Very surprisingly, however, when a fiVe-
membered cyclic hydrogen phosphonate, 4,4,5,5-tetramethyl-1,3,2-
dioxaphospholane 2-oxide (1a),6 was employed as the reactant,
metal-catalyzed additions to alkenes proceeded smoothly to afford
the adducts in high yields (eq 1). Herein are preliminarily
disclosed the synthetic and mechanistic aspects of this unprec-
edented phenomenon.7
Preliminary screening of palladium catalysts revealed that
the procedure using Ph2P(CH2)4PPh2 complexes in 1,4-dioxane
also worked efficiently. For instance, heating an equimolar
mixture of 1a and 1-octene at 100 °C in the presence of PdMe2-
[Ph2P(CH2)4PPh2] (5 mol %) in dioxane afforded a 93% GC yield
of 2a (reaction time ) 15 h).9 Table 1 summarizes the catalytic
reactions run mostly by this procedure, which can be readily
applied to both aliphatic and aromatic alkenes. Thus, ethene and
propene gave near quantitative yields of the adducts. The addition
to 3,3-dimethyl-1-butene, a bulky alkene, also worked well, ending
up with the selective terminal attachment of phosphorus to the
double bond. In contrast, styrene formed a mixture of regioisomers
(R-adduct/â-adduct ) 45/55, 95% total yield). However, the
selectivity for the R-isomer could be markedly improved to 95%
when PdMe2(PPh2Cy)2 was used as the catalyst. Acyclic internal
alkenes were nearly inert under similar conditions. However,
2-norbornene reacted as efficiently as terminal alkenes. Less
strained cyclopentene reacted somewhat slowly and the reactivity
of cyclohexene was even lower.
The hydrophosphorylation is best explained by Scheme 1,
which involves (i) oxidative addition of the H-P bond, (ii)
addition of the H-Pd bond of 3 (hydropalladation) to an alkene
molecule, and (iii) reductive elimination of adduct 2 from 4. The
following observations substantiate these elemental steps. First,
the oxidative addition of 1a with Pd(PCy3)2 readily proceeded at
room temperature to generate 3a as the sole product in 15 min
(eq 2). Phosphonate 1b behaved similarly, but more slowly; the
A mixture of 1a (1 mmol) and 1-octene (1 mmol) in toluene
(2 mL), when heated in the presence of cis-PdMe2(PPh2Me)2 (5
mol %) at 110 °C for 3 h, developed a pale yellow solution, in
which adduct 2a was found by gas chromatography to be formed
in 63% yield.8 Surprisingly similar treatments using noncyclic
and six-membered cyclic hydrogen phosphonates 1b-f did not
form corresponding adducts at all. The reaction of 1-octene with
(1) Recent reviews: (a) Horn, K. A. Chem. ReV. 1995, 95, 1317. (b) Sharma,
H. K.; Pannell, K. H. Chem. ReV. 1995, 95, 1351. (c) Burgess, K.; Ohlmeyer,
M. J. Chem. ReV. 1991, 91, 1179. (d) Beletskaya, I.; Pelter, A. Tetrahedron
1997, 53, 4957. (e) Han, L.-B.; Tanaka, M. Chem. Commun. 1999, 395.
(2) (a) Organic Phosphorus Compounds; Kosolapoff, G. M., Maier, L.,
Eds.; Wiley-Interscience: New York, 1972. (b) Handbook of Organophos-
phorus Chemistry; Engel, R., Ed.; Marcel Dekker: New York, 1992. (c)
Corbridge, D. E. C. Phosphorus: An Outline of Its Chemistry, Biochemistry
and Uses, 5th ed., Elsevier: Amsterdam, 1995.
(3) Radical additions of HP(O)(OR)2 to alkenes are well-known (ref 2).
For recent examples, see: (a) Nifant’ev, E. E.; Magdeeva, R. K.; Dolidze, A.
V.; Ingorokva, K. V.; Vasyanina, L. K. Russ. J. Gen. Chem. 1993, 63, 1201.
(b) Nifant’ev, E. E.; Magdeeva, R. K.; Dolidze, A. V.; Ingorokva, K. V.;
Samkharadze, L. O.; Vasyanina, L. K.; Bekker, A. R. Zh. Obshch. Khim. 1991,
61, 96. (c) Nifant’ev, E. E.; Magdeeva, R. K.; Shchepet’eva, N. P. Zh. Obshch.
Khim. 1980, 50, 1744.
conversion of 1b to 3b was 60% after 30 min. Second, the
resulting hydridopalladium species 3a readily reacted with styrene
(6) Compound 1a is a white solid easily prepared from PCl3 or H3PO3 and
pinacol. (a) Zwierrzak, A. Can. J. Chem. 1967, 45, 2501. (b) Munoz, A.;
Hubert, C.; Luche, J.-L. J. Org. Chem. 1996, 61, 6015. Very little is known
about its reactivity. The OsPsO angle in the ring was estimated at ca. 99°,
5° smaller than the normal angle for the acyclic analogues, resulting in a ring-
strain energy of ca. 5-6 kcal/mol, which makes 1a more acidic. (c)
Ovchinnikov, V. V.; Galkin, V. I.; Yarkova, E. G.; Markova, L. E.; Cherkasov,
R. A.; Pudovik, A. N. Zh. Obshch. Khim. 1978, 48, 2424. (d) Newton, M. G.;
Campbell, B. S. J. Am. Chem. Soc. 1974, 96, 7790. (e) Ovchinnikov, V. V.;
Lapteva, L. I.; Sagadeev, E. V.; Konovalov, A. I. Thermochim. Acta 1996,
288, 105. (f) Ovchinnikov, V. V.; Cherezov, S. V.; Cherkasov, R. A.; Pudovik,
A. N. Zh. Obshch. Khim. 1985, 55, 1244.
(7) Great ring-size effect on the hydrolysis of phosphates (RO)3P(O) is
well-established. (a) Hudson, R. F.; Brown, C. Acc. Chem. Res. 1972, 5, 204.
(b) Westheimer, F. H. Acc. Chem. Res. 1968, 1, 70.
(8) 33% of 1a remained unchanged. 2-Octenes (31%, cis/trans ) 36/64),
which was inert toward the hydrophosphorylation under present conditions,
was also formed.
(4) Metal-catalyzed addition to alkenes usually is more difficult to achieve
than the corresponding addition to alkynes. (a) Baker, R. T.; Nguyen, P.;
Marder, T. B.; Westcott, S. A. Angew. Chem., Int. Ed. Engl. 1995, 34, 1336.
(b) Iverson, C. N.; Smith, M. R., III Organometallics 1997, 16, 2757. (c)
Ishiyama, T.; Yamamoto, M.; Miyaura, N. Chem. Commun. 1997, 689. (d)
Suginome, M.; Nakamura, H.; Ito, Y. Angew. Chem., Int. Ed. Engl. 1997, 36,
2516. (e) Kondo, T.; Uenoyama, S.-y.; Fujita, K.-i.; Mitsudo, T.-a. J. Am.
Chem. Soc. 1999, 121, 482.
(9) The reaction can also be conveniently conducted with Pd2(dba)3/
PPh2(CH2)4PPh2 (Pd/P ) 1/2) as the catalyst (82% isolated yield of 2a).
(5) Han, L.-B.; Tanaka, M. J. Am. Chem. Soc. 1996, 118, 1571.
10.1021/ja000444v CCC: $19.00 © 2000 American Chemical Society
Published on Web 05/20/2000

5408 J. Am. Chem. Soc., Vol. 122, No. 22, 2000
Table 1. Hydrophosphorylation of Alkenesa
Communications to the Editor
Scheme 1
after 16 h. At the same time, deuterated styrenes were observed
(ca. 0.1 mmol in total, R/â-cis/â-trans ) 26/36/38). Note that
the deuterium incorporation ratio at the R- and â-carbons of
styrene is 26/74, which is in fairly good agreement with the
regioisomeric ratio of 5a (R/â ) 82/18) observed in the foregoing
reaction of 3a with styrene (eq 2). Although complex 4a has not
been unambiguously identified, 31P NMR analysis of the mixture
of 3a and styrene displayed weak signals in a 93-100 ppm region,
assignable to Pd-bound P(O) species in 4a. On the other hand,
no species arising from the addition of the P(O)-Pd bond to
styrene was detected. The H-D exchange experiment verifies
that the hydropalladation is a facile process and that the reductive
elimination of 2 from 4 is slow as compared with the backward
reaction to 3 via â-hydrogen elimination. This suggests, fourth,
that the reductive elimination step is rate-determining in the
catalysis. The high reactivity of 1a as compared with the other
hydrogen phosphonates is associated most likely with the reduc-
tive elimination process. Indeed, heating a benzene-d6 solution
of trans-PdMe[P(O)(OR′)2](PEt3)2 [6a, (OR′)2 ) pinacolato] at
70 °C for 1 h resulted in the formation of MeP(O)(OR′)2 in 92%
NMR yield, while its analogue 6b (OR′ ) OMe) remained
unchanged in a similar treatment. The origin of the accelerating
effect of the five-membered ring in the reductive elimination is
ambiguous at this stage. It may be tentatively assumed that a
trigonal bipyramidal transition state (7) is involved, similarly to
a Reaction conditions: an equimolar 1a and an alkene in 1,4-dioxane
(0.5-1 M), 3-5 mol % PdMe2[Ph2P(CH2)4PPh2]2, 100 °C, 15 h. Unless
otherwise noted, only one adduct shown in the table was formed. b GC
yield. The figure in parentheses is the isolated yield after column
chromatography on silica (hexane/i-PrOH ) 10/1 ∼ 2). c Run under 5
atm of pressure of the alkene. d Catalyst: PdMe2(PPh2Cy)2. Regiose-
lectivity of the R-adduct >95%. e 100% exo. f After 44 h of heating.
g After 48 h of heating.
(2 equiv) upon heating at 60 °C for 15 h and at 80 °C for an
additional 4 h to give isomeric adducts 5a (88% yield based on
1a, R/â ) 82/18). In contrast, 3b did not form the corresponding
adducts at all in a similar reaction with styrene. Third, the
extensive H-D exchange between 3a-d and styrene strongly
supports involvement of hydropalladation.10 Thus, styrene (0.2
mmol) was added at room temperature to 3a-d, cleanly generated
in situ by the reaction of Pd(PCy3)2 (0.1 mmol) with 1a-d (0.1
mmol) in toluene-d8. 1H NMR spectroscopy revealed the forma-
tion of ca. 0.04 mmol of 3a in 2 h (eq 3). Upon further stirring,
the hydrolysis of phosphates;7 during the course of reductive
elimination from 4, which has the strained five-membered ring,
the ring oxygens occupy apical and equatorial positions with a
cyclic O-P-O angle of 90°, the strain-free apical/equatorial angle
for a dsp3-hybridized hypervalent phosphorus.
In conclusion, Pd-catalyzed hydrophosphorylation of terminal
and some cyclic alkenes has been made possible by taking
advantage of the exceptionally high reactivity of a five-membered
cyclic hydrogen phosphonate. Further synthetic applications of
this finding and extensions to other heteroatom compounds are
now in progress.
Acknowledgment. We thank the Japan Science and Technology
Corporation (JST) for partial financial support through the CREST (Core
Research for Evolutional Science and Technology) program and for
postdoctoral fellowships to F.M. and C.-Q.Z.
the quantity of 3a reached an equilibrium value (ca. 0.08 mmol)
Supporting Information Available: Text describing experimental
details and spectral and/or analytical data of the products (PDF). This
material is available free of charge via the Internet at http://pubs.acs.org.
(10) Pt-P rather than Pt-H addition was proposed for the Pt-catalyzed
addition of PH3 to acrylonitrile. (a) Wicht, D. K.; Kourkine, I. V.; Lew, B.
M.; Nthenge, J. M.; Glueck, D. S. J. Am. Chem. Soc. 1997, 119, 5039. (b)
Pringle, P. G.; Smith, M. B. J. Chem. Soc., Chem. Commun. 1990, 1701.
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