Facile oxidative addition of the phosphorous-selenium bond to Pd(0) and Pt(0) complexes and development of Pd-catalyzed regio- and stereoselective selenophosphorylation of alkynes

Full text of DOI:10.1021/ja9608860

7000
J. Am. Chem. Soc. 1996, 118, 7000-7001
Facile Oxidative Addition of the
Phosphorous-Selenium Bond to Pd(0) and Pt(0)
Complexes and Development of Pd-Catalyzed
Regio- and Stereoselective Selenophosphorylation of
Alkynes
Li-Biao Han, Nami Choi, and Masato Tanaka*
National Institute of Materials and
Chemical Research, Tsukuba, Ibaraki 305, Japan
ReceiVed March 19, 1996
Transition metal complex-catalyzed addition of E-E (E ) a
heteroatom) bonds to carbon-carbon unsaturated bonds, as
exemplified by the Pd- and Pt-catalyzed double silylations and
related reactions,1 is generally characterized by its high product
yield and selectivity under mild reaction conditions and hence
is particularly attractive from the synthetic viewpoint. Although
mechanistic details are variant depending on the identity of E,
most of these additions may be overall envisioned to proceed
Via a simple sequence of oxidative addition of the E-E bond
to the transition metal complex, insertion of an alkene or alkyne,
and reductive elimination. Heteroatom compounds having
B-B,2 Si-Si,1 Sn-Sn,3 S-S,4 and Se-Se4 bonds undergo
such reactions, and some of them are now widely used in organic
synthesis. However, similar reactions for organophosphorous
compounds have never been documented.5 Now we wish to
disclose herein (1) the facile oxidative addition of a phosphorous-
selenium bond to Pd(0) and Pt(0) complexes which represents
the first example of phosphorous-heteroatom bond additions
to transition metal complexes and (2) the first palladium-
catalyzed regio- and stereoselective selenophosphorylation of
alkynes with selenophosphates6,7 affording synthetically versatile
(Z)-1-(diphenoxyphosphinyl)-2-(phenylseleno)alkenes.8
Figure 1. Molecular structure of trans-Pd(PhSe)[P(O)(OPh)2][PEt3]2
(1a). Selected bond lengths (Å) and angles (deg): Pd-Se ) 2.518(9),
Pd-P(1) ) 2.351(2), Pd-P(2) ) 2.351(3), Pd-P(3) ) 2.275(2), Se-
Pd-P(1) ) 86.90(5), Se-Pd-P(2) ) 89.58(6), Se-Pd-P(3) ) 174.01-
(6), P(1)-Pd-P(2) ) 164.02(9), P(1)-Pd-P(3) ) 95.72(7), P(2)-
Pd-P(3) ) 89.33(7).
of the reaction by NMR spectroscopy indicated that both of
the starting materials disappeared completely within 0.5 h, while
two new signals centered at 68.0 and 16.8 ppm appeared in 31
P
NMR. The former was a triplet having a coupling constant of
14.1 Hz, assignable to P(O)(OPh)2, and the latter was a doublet
with the same coupling constant, assignable to PEt3 ligating to
Pd. Evaporating the solvent afforded a brown oil. Upon
addition of hexane to the oil followed by slow cooling from
room temperature to -30 °C overnight, orange crystals pre-
cipitated out. Both its NMR and analytical data were in good
agreement with the structure of trans-Pd(PhSe)[P(O)(OPh)2]-
[PEt3]2 (1a),9 which was unambiguously confirmed by the X-ray
crystallographic analysis (Figure 1). The complex has a slightly
distorted square-planar geometry with bond distances of Se-
Pd and Pd-P(3) being 2.518 and 2.275 Å, respectively. The
two PEt3 ligands (PhSe and P(O)(OPh)2 groups) are bound to
the palladium center in the positions trans to each other. Very
similarly, the reaction of PhSeP(O)(OEt)2 with Pd(PEt3)3
afforded trans-Pd(PhSe)[P(O)(OEt)2][PEt3]2 (1b) in 87% yield
as a yellow solid.9 Platinum(0) complexes were also as reactive
as their palladium(0) analogues. For example, when Pt(PEt3)3
was allowed to react with PhSeP(O)(OPh)2 at room temperature,
the color of the solution immediately changed from orange to
pale yellow, and trans-Pt(PhSe)[P(O)(OPh)2][PEt3]2 (1c) was
obtained in 95% yield as an off-white solid.9
When 1 equiv of PhSeP(O)(OPh)2 was added to Pd(PEt3)3
in C6D6 at room temperature, the color of the solution im-
mediately turned from pale-orange to brown (eq 1). Monitoring
(1) For recent reviews, see: (a) Horn, K. A. Chem. ReV. 1995, 95, 1317.
(b) Sharma, H. K.; Pannell, K. H. Chem. ReV. 1995, 95, 1351. See also:
(c) Tanaka, M.; Uchimaru, Y.; Lautenschlager, H.-J. Organometallics 1991,
10, 16. (d) Finckh, W.; Tang, B.-Z.; Lough, A.; Manners, I. Organometallics
1992, 11, 2904.
(2) (a) Ishiyama, T.; Matsuda, N.; Miyaura, N.; Suzuki, A. J. Am. Chem.
Soc. 1993, 115, 11018. (b) Iverson, C. N.; Smith, M. R., III. J. Am. Chem.
Soc. 1995, 117, 4403.
(3) (a) Mitchell, T. N.; Amamria, A.; Killing, H.; Rutschow, D. J.
Organomet. Chem. 1983, 241, C45. (b) Killing, H.; Mitchel, T. N.
Organometallics 1984, 3, 1318. (c) Piers, E.; Skerlj, R. T. J. Chem. Soc.,
Chem. Commun. 1986, 626.
(4) Kuniyasu, H.; Ogawa, A.; Miyazaki, S.; Ryu, I.; Sonoda, N. J. Am.
Chem. Soc. 1991, 113, 9796.
(5) We have recently reported the activation of P-H bonds by transition
metal complexes: Han, L.-B.; Tanaka, M. J. Am. Chem. Soc. 1996, 118,
1571.
(6) (Phenylseleno)phosphates PhSeP(O)(OR)2 (R ) Et, Ph) used in this
study were readily prepared by adding corresponding (RO)2P(O)Cl at -78
°C to a THF solution of PhSeLi which was in situ generated by the reaction
of PhLi with Se and purified by column chromatography on silica gel (Et2O/
hexane ) 1/5-1/1). The yields were acceptable (55-63%). These seleno-
phosphates were colorless in their pure forms. However, they were
occasionally contaminated by a trace of (PhSe)2 and could become pale
yellow.
(7) Only very limited studies have been documented on these compounds.
For preparations of (alkylseleno)phosphates, see: (a) Melnik, Y. G. Ukr.
Khim. Zh. (Russ. Ed.) 1993, 59, 654. (b) Dybowski, P.; Krawczyk, E.;
Skowronska, A. Synthesis 1992, 601. (c) Markowka, A.; Buchowiecki, W.
Bull. Acad. Pol. Sci., Ser. Sci. Chim. 1973, 21, 455. (d) Kataev, E. G.;
Mannafov, T. G.; Kostina, G. I. Zh. Obshch. Khim. 1968, 38, 363. For
their reactivities, halogenlysis: (e) Krawiecka, B. Phosphorus, Sulfur, Silicon
Relat. Elem. 1991, 62, 199. (f) Markowska, A. Bull. Acad. Pol. Sci., Ser.
Sci. Chim. 1967, 15, 153. Alcolysis: (g) Wozniak, L. A.; Krzyzanowska,
B.; Stec, W. J. J. Org. Chem. 1992, 57, 6057.
Catalytic addition of selenophosphates to alkynes (seleno-
phosphorylation) was readily realized on the basis of the
foregoing findings. Thus, when Pd(PPh3)4 (35 mg, 3 mol %)
(9) 1H (300 MHz) and 31P (121.5 MHz) NMR spectral data of 1 in C6D6.
1a: 1H NMR δ 7.88-7.91 (m, 2H), 7.50-7.54 (m, 4H), 6.87-7.16 (m,
9H), 2.08-2.18 (m, 12H), 0.92 (dt, 18H, J ) 7.6 Hz, JH-P ) 16.6 Hz); 31
P
NMR δ 68.0 (t, JP-P(O) ) 14.1 Hz, JP(O)-Se ) 108.4 Hz), 16.8 (d, JP-P(O)
) 14.1 Hz). 1b: 1H NMR δ 7.92-7.95 (m, 2H), 6.89-7.02 (m, 3H), 4.04-
4.30 (m, 4H), 2.10-2.20 (m, 12H), 1.21 (t, 6H, J ) 7.1 Hz), 0.98 (dt, 18H,
J ) 7.1 Hz, JH-P ) 16.5 Hz); 31P NMR δ 66.9 (t, JP-P(O) ) 4.7 Hz, JP(O)-Se
) 120.3 Hz), 16.8 (d, JP-P(O) ) 4.7 Hz). 1c: 1H NMR δ 7.85-7.88 (m,
2H), 7.50-7.54 (m, 4H), 6.87-7.16 (m, 9H), 2.18-2.28 (m, 12H), 0.84-
0.99 (m, 18H); 31P NMR δ 51.8 (t, JP-P(O) ) 25.4 Hz, JP(O)-Se ) 87.2 Hz,
JP(O)-Pt ) 4669.3 Hz), 12.5 (d, JP-P(O) ) 25.4 Hz, JP(O)-Pt ) 2477.0 Hz).
(8) Reviews on the synthetic utility of vinylselenides and vinylphos-
phonates: (a) Comasseto, J. V. J. Organomet. Chem. 1983, 253, 131. (b)
Minami, T.; Motoyoshiya, J. Synthesis 1992, 333.
S0002-7863(96)00886-4 CCC: $12.00 © 1996 American Chemical Society

Communications to the Editor
J. Am. Chem. Soc., Vol. 118, No. 29, 1996 7001
Scheme 1a
Table 1. Pd-Catalyzed Selenophosphorylation of Terminal
Alkynesa
a Only actively reacting ligands are illustrated in the Scheme,
disregarding other incidental ligands that may be bound to palladium.
solvents for the reaction, and good yields of the adduct (87-
91%) were obtained as long as reactions were run at 67 °C as
in the case of THF. Conducting the reaction at higher
temperatures was not beneficial since side reactions such as
oligomerization of the alkyne took place. For example, yields
of the adduct dropped to 86% and 65%, respectively, when the
reactions were run at 80 °C (benzene) and 110 °C (toluene).
Similar temperature dependence was also observed when THF-
d8 was used as the solvent in a sealed NMR tube.
As demonstrated in Table 1, the Pd-catalyzed selenophos-
phorylation could be readily applied to other terminal alkynes,
yielding the corresponding 1-(diphenoxyphosphinyl)-2-(phen-
ylseleno)alkenes in good yields with excellent regio- and
stereoselectivities.12,13 Besides the reaction of 1-octyne, the
reaction of acetylene under atmospheric pressure as well as
functionalized aliphatic alkynes such as those having methoxy
and cyano groups also proceeded efficiently, affording the
adducts in high yields. Multiple PhSe and (PhO)2(O)P groups
could be easily introduced regio- and stereoselectively to
acetylenes having more than one C-C triple bond. For
example, the selenophosphorylation reaction of 1,8-nonadiyne
using 2.2 equiv of PhSeP(O)(OPh)2 afforded the corresponding
product nearly quantitatively. Aromatic alkynes like phen-
ylacetylene and 4-ethynyltoluene also reacted efficiently, and
good yields of the selenophosphorylation products were obtained
in both cases. In contrast to alkynes, alkenes were inert toward
the reaction under the present reaction conditions. Conse-
quently, only the adduct formed by the addition of PhSeP(O)-
(OPh)2 to the triple bond was obtained from 1-ethynylcyclo-
hexene.
a Conditions: equimolar PhSeP(O)(OPh)2 and an alkyne in THF (1
M), 3 mol % Pd(PPh3)4, 67 °C, 15-20 h. b Yields refer to isolated
yields after PTLC isolation on silica gel. c 1 atm CHtCH. d 2.2 equiv
of PhSeP(O)(OPh)2 were employed.
was added to a mixture of PhSeP(O)(OPh)2 (389 mg, 1 mmol)
and 1-octyne (110 mg, 1 mmol) in dry THF (1 mL) under argon,
the color of the solution immediately turned from colorless to
reddish brown.10 Heating the mixture at 67 °C overnight
resulted in a complete consumption of the starting materials,
yielding (Z)-1-(diphenoxyphosphinyl)-2-(phenylseleno)-1-octene
(2a) as the sole product (eq 2).11 Evaporation of the solvent
followed by PTLC purification (EtOAc/hexane ) 1/1) afforded
pure 2a in 95% yield as a pale yellow oil. A 5 mmol scale
experiment also gave a similar result (89% isolated yield after
column chromatography; see the supporting information).
On the basis of the results described above, the catalytic
reaction is very likely to proceed Via the oxidative addition of
the P-Se bond of selenophosphates followed by insertion14 of
an alkyne to the resulting species 1 (Scheme 1). However
details, including the preference of the two possible insertion
processes (i.e. selenopalladation Vs phosphinylpalladation) as
well as the regioselectivity, still remain to be clarified in the
forthcoming papers.
The Pd catalyst is essential for this addition reaction. In the
absence of the catalyst, no adduct could be obtained under
similar reaction conditions. Besides Pd(PPh3)4, cis-PdMe2(PPh2-
Me)2 (76% yield) and cis-PdEt2(PPh2Me)2 (82% yield) also
catalyzed the reaction under identical conditions. In contrast,
Pt complexes such as Pt(PPh3)4, Pt(PEt3)3, and Pt(CH2dCH2)-
(PPh3)2 did not show any catalytic activity under similar reaction
conditions despite the ready oxidative addition of P-Se bonds
to the complexes. Benzene and toluene could also be used as
Acknowledgment. L.-B.H. and N.C. are postdoctoral fellowship
awardees from the Research Development Corporation of Japan.
Supporting Information Available: Text describing experimental
details and spectral and/or analytical data of (Z)-1-(diphenoxyphos-
phinyl)-2-(phenylseleno)alkenes and complexes 1a-c; a perspective
view and tables of crystallographic data, atomic coordinates and thermal
parameters, and bond lengths and angles for 1a (24 pages). See any
current masthead page for ordering and Internet access instructions.
JA9608860
(10) When an equimolar mixture of Pd(PPh3)4 and PhSeP(O)(OPh)2 in
C6D6 was stirred at 25 °C, a facile oxidative addition of the P-Se bond of
PhSeP(O)(OPh)2 to Pd(PPh3)4 also took place, as evidenced by the
appearance of three 31P NMR signals centered at 56, 30, and -5 ppm.
Unfortunately, however, we have not succeeded in the isolation of the
resulting complexes; see the supporting information for more details.
(12) As compared to PhSeP(O)(OPh)2, the addition of PhSeP(O)(OEt)2
to alkynes proceeded slower under the same reaction conditions. Thus, after
the THF solution of PhSeP(O)(OEt)2 and 1-octyne was refluxed in the
presence of 3 mol % of Pd(PPh3)4, only 15% of the corresponding adduct
was obtained. Most of the starting materials remained unreacted.
(13) Internal alkynes were unreactive under the present conditions.
(14) Though very sluggish, formation of 2a could be observed by NMR
spectroscopy when 1a was allowed to react in a sealed NMR tube with an
excess of 1-octyne in C6D6 at 100 °C.
1
(11) Other isomers of 2a could not be detected by H NMR. Although
a small amount (< 3%) of an adduct formed by the addition of (PhSe)2 to
the alkyne was also obtained when a (PhSe)2-contaminated selenophosphate
was used, its formation could not be confirmed when carefully purified
PhSeP(O)(OPh)2 was employed.