Preparation and Coordination Properties Including Catalytic Activities of a Bulky 2-Methyl-3-thioxo-1,3-diphosphapropene

Article abstract of DOI:10.1021/ol036330g

(Matrix presented) 2-Methyl-3,3-diphenyl-3-thioxo-1-(2,4,6-tri-tert- butylphenyl)-1,3-diphosphapropene, which bears a P=C-P=S skeleton, was prepared and used as a ligand of transition-metal complexes. The palladium complexes containing the ligated 3-thioxo-1,3-diphophapropene were stable and used for catalytic reactions such as cross-couplings and direct conversion of allyl alcohol to allylaniline.

Full text of DOI:10.1021/ol036330g

ORGANIC
LETTERS
2004
Vol. 6, No. 3
425-427
Preparation and Coordination Properties
Including Catalytic Activities of a Bulky
2-Methyl-3-thioxo-1,3-diphosphapropene
Hongze Liang, Shigekazu Ito, and Masaaki Yoshifuji*
Department of Chemistry, Graduate School of Science, Tohoku UniVersity,
Aoba, Sendai 980-8578, Japan
yoshifj@mail.tains.tohoku.ac.jp
Received November 29, 2003
ABSTRACT
2-Methyl-3,3-diphenyl-3-thioxo-1-(2,4,6-tri-tert-butylphenyl)-1,3-diphosphapropene, which bears a PdC−PdS skeleton, was prepared and used
as a ligand of transition-metal complexes. The palladium complexes containing the ligated 3-thioxo-1,3-diphophapropene were stable and
used for catalytic reactions such as cross-couplings and direct conversion of allyl alcohol to allylaniline.
Chemistry of the low-coordinated phosphorus compounds
has greatly developed in the past decades,1 and we have
reported a number of phosphaethenes kinetically stabilized
by a bulky 2,4,6-tri-tert-butylphenyl (hereafter abbreviated
to Mes*) group.2 Previously we reported preparation of the
1,3-diphosphapropene derivatives 1 and 2, which were used
as ligands for transition-metal complexes.3 Compounds 1 and
2, both carrying a low-coordinated sp2 phosphorus atom and
a normal sp3 phosphino group, displayed a stepwise coor-
dination pattern by way of a monodentate to a chelation
mode.3,4 Moreover, a palladium complex containing the
ligated 2 displayed a catalytic activity for the Sonogashira
cross-coupling reaction.3b Recently, low-coordinated phos-
phorus compounds have been utilized for synthetic cata-
lysts,5,6 and especially, transition-metal complexes containing
the ligated 3,4-diphosphinidenecyclobutene (DPCB) deriva-
tives have been available for several unique catalytic
reactions.7 These results prompted us to develop novel low-
coordinated phosphorus compounds which can be used as
ligands for synthetic catalytic reactions. Previously, we
reported sulfurizations of 1 affording the corresponding
3-thioxo-1,3-diphosphapropenes 3 that consist of the PdC-
PdS skeleton, and indeed, 3 behaved as P,S-chelating ligands
(5) Reviews: Weber. L. Angew. Chem., Int. Ed. 2002, 41, 563. (b)
Mathey, F. Angew. Chem., Int. Ed. 2003, 42, 1578.
(6) Catalysts containing phosphaethenes: (a) Ionkin, A.; Marshall, W.
Chem. Commun. 2003, 710. (b) Daugulis, O.; Brookhart, M.; White, P. S.
Organometallics 2002, 21, 5935. (c) Doux, M.; Me´zailles, N.; Melaimi,
M.; Ricard, L.; Le Floch, P. Chem. Commun. 2002, 1566. (d) Breit, B.;
Winde, R.; Mackewitz, T.; Paciello, P.; Harms, K. Chem. Eur. J. 2001, 7,
3106. (e) Keim, W.; Appel, R.; Gruppe, S.; Knoch, F. Angew. Chem., Int.
Ed. Engl. 1987, 26, 1012.
(7) (a) Ozawa, F.; Okamoto, H.; Kawagishi, S.; Yamamoto, S.; Minami,
T.; Yoshifuji, M. J. Am. Chem. Soc. 2002, 124, 10968. (b) Minami, T.;
Okamoto, H.; Ikeda, S.; Tanaka, R.; Ozawa, F. Yoshifuji, M.; Angew. Chem.,
Int. Ed. 2001, 40, 4501. (c) Ozawa, F.; Yamamoto, S.; Kawagishi, S.;
Hiraoka, M.; Ikeda, S.; Minami, T.; Ito S.; Yoshifuji, M. Chem. Lett. 2001,
972. (d) Ikeda, S.; Ohhata, F.; Miyoshi, M.; Tanaka, R.; Minami, T.; Ozawa,
F.; Yoshifuji, M. Angew. Chem., Int. Ed. 2000, 39, 4512. (e) Toyota, K.;
Masaki, K.; Abe T.; Yoshifuji, M. Chem. Lett. 1995, 221.
(1) (a) Regitz, M.; Scherer, O. J. Multiple Bonds and Low Coordination
in Phosphorus Chemistry; Georg Thieme Verlag: Stuttgart, 1990. (b) Dillon,
K. B.; Mathey, F.; Nixon, J. F. Phosphorus: The Carbon Copy; Wiley:
Chichester, 1998.
(2) (a) Yoshifuji, M. J. Chem. Soc., Dalton Trans. 1999, 3343. (b)
Yoshifuji, M. J. Organomet. Chem. 2000, 611, 210.
(3) (a) Ito, S.; Yoshifuji, M. Chem. Commun. 2001, 1208. (b) Liang,
H.; Nishide, K.; Ito, S.; Yoshifuji, M. Tetrahedron Lett. 2003, 44, 8297.
(4) Nishide, K.; Ito, S.; Yoshifuji, M. J. Organomet. Chem. 2003, 682,
79.
10.1021/ol036330g CCC: $27.50 © 2004 American Chemical Society
Published on Web 01/07/2004

for transition-metal complexes.8 In this paper, we report
preparation of a bulky 2-methyl-3-thioxo-1,3-diphosphapro-
pene 4 from sulfurization of 2. Compound 4 was used as a
chelating ligand for several transition-metal complexes, and
the palladium complexes were employed for catalytic reac-
tions.
formed. When compound 4 was allowed to react with
W(CO)5(thf) in THF, both of the monocoordinated complex
6 and the chelate complex 710 were obtained as a mixture
(6: 42%; 7: 15%) (Scheme 1). Attempts to isolate 6 [δP
2
329.4, 55.8, JPP 121 Hz] by recrystallization were not
successful, probably due to the instability of 6 in solution.
On the other hand, 6 afforded 7 by release of a CO ligand
together with several desulfurized and/or decomplexed
compounds such as 2 and 4 in solutions.
We next focused on the coordination chemistry of 4 with
palladium reagents for the purpose of obtaining catalysts
including a 3-thioxo-1,3-diphosphapropene [PdC-PdS]
framework. Compound 4 was allowed to react with PdCl2-
(MeCN)2 in dichloromethane at room temperature for 30 min
to give 8 in 84% yield (Scheme 1).11 Complex 8 was an air-
and moisture-insensitive solid and displayed no decomposi-
tion in solutions for several weeks, whereas a palladium
complex of 2 (9) reacted with water in solutions to afford
the complexes including a 1-hydroxy-1,3-diphosphapropane
derivative.3b Attempts to obtain a platinum(II) complex from
4 and PtCl2(cod) (cod ) cycloocta-1,5-diene) were not
successful. The structure of 8 was characterized by the
spectroscopic data and confirmed by X-ray crystallography
(Figure 1), revealing a planar structure around the palladium
As described in our previous paper on the sulfurization,8
1,3-diphosphapropene 23b was allowed to react with an
equivalent amount of sulfur (1/8 S8) in refluxing toluene for
20 h to afford the corresponding sulfurized compound 4 in
an excellent yield (91%) (Scheme 1).9 Compound 4 was an
Scheme 1 a
Figure 1. ORTEP representation of the molecular structure of 8
with 30% probability ellipsoids. Hydrogen atoms and the solvent
molecules (dichloromethane) are omitted for clarity. Selected bond
lengths (Å) and angles (deg): Pd-Cl1 2.319(3), Pd-Cl2
2.307(3), Pd-S 2.284(3), Pd-P1 2.186(3), P2-S 2.012(4), P1-
C1 1.644(9), P1-Mes* 1.806(9), P2-C1 1.779(2), C1-Me
1.50(1), Cl1-Pd-Cl2 93.4(1), Cl1-Pd-S 86.0(1), Cl1-Pd-P1
174.6(1), Cl2-Pd-S 177.9(1), Cl2-Pd-P1 91.1(1), S-Pd-P1
89.60(10), Pd-S-P2 106.7(1), Pd-P1-C1 119.8(3), Pd-P1-
Mes* 128.3(3), C1-P1-Mes* 112.0(4), S-P2-C1 110.0(3), P1-
C1-P2 113.5(5), P1-C1-Me 126.2(7), P2-C1-Me 120.0(7).
a Reagents and conditions: (i) 1/8 S8, toluene, reflux, 20 h; (ii)
medium-pressure Hg lamp (100 W), THF, 21 h; (iii) W(CO)5(THF),
THF, rt, 16 h; (iv) PdCl2(MeCN)2, CH2Cl2, rt, 0.5 h; (v) [(allyl)-
PdCl]2, AgOTf, CH2Cl2, rt, 2 h.
air- and moisture-insensitive colorless solid, and the structure
was characterized by the spectroscopic data.9 Similarly to
the case of 3,8 E/Z isomerization of 4 was observed upon
irradiation (medium-pressure Hg lamp, λ > 300 nm, in THF)
resulting in the formation of a mixture of 4 and 5 in a 5:1
atom.12 The Pd-Cl1 distance is close to the Pd-Cl2 length,
indicating a similar trans effect of the P1 and S atoms. The
P1-C1 distance is within the phosphorus-carbon double
2
ratio after 21 h [5: δP 331.3, 41.2, JPP ) 58 Hz].
To evaluate the properties of 4 as a ligand, at first,
preparation of carbonyltungsten(0) complexes was per-
(8) (a) Ito, S.; Liang, H.; Yoshifuji, M. Chem. Commun. 2003, 398. (b)
Liang, H.; Ito, S.; Yoshifuji, M. Org. Biomol. Chem. 2003, 1, 3054.
(9) 4: colorless crystals; mp 67 °C; 31P{1H} NMR (162 MHz, CDCl3)
(10) 7: brown solid; mp 143 °C dec; 31P{1H} NMR (162 MHz, CDCl3)
2
δ 324.6 (1JPW ) 278 Hz, PdC), 56.9 (PdS), JPP ) 123 Hz.
(11) 8: yellowish-brown solid; mp 218-220 °C; 31P{1H} NMR (162
2
2
δ 314.8 (PdC), 50.9 (PdS), JPP ) 123 Hz.
MHz, CDCl3): δ 277.5 (PdC), 55.5 (PdS), JPP ) 95 Hz.
426
Org. Lett., Vol. 6, No. 3, 2004

bond,1 and an end-on coordination mode was established.
In contrast to the previous report on the metal complexes
including the ligated PdC-PdS skeletons, which displayed
envelope-type skeletons,8 the five-membered ring in 8 is
almost planar [Θ(Pd-P1-C1-P2) 0.4(6)°, Θ(S-Pd-P1-
C1) 4.0(3)°].
silver(I) triflate7a,b to afford the corresponding complex 10
almost quantitatively, and the structure was characterized by
the spectroscopic data.15 Complex 10 did not decompose in
air, whereas the π-allyl complex containing the ligated 1,3-
diphosphapropene (11)16 decomposed in several hours even
in an inert atmosphere.
Complex 8 was applied to catalytic cross-coupling reac-
tions such as the Sonogashira and the Suzuki couplings.13
As described in eqs 1 and 2 (Scheme 2), iodobenzene was
The cationic complex 10 was employed as a catalyst for
the reaction of allyl alcohol with aniline.7a As described in
eq 3 (Scheme 2), 2 mol % of 10 catalyzed the reaction of
allyl alcohol with aniline in an 1:1 molar ratio at room
temperature to afford N-(2-propenyl)aniline in 63% yield
together with a small amount of N,N-di(2-propenyl)aniline
(3%). Although a slightly larger amount of 10 was necessary
for the reaction and the yield was not excellent compared
with the results of catalysts bearing DPCB,7a,b 10 displayed
a considerable catalytic ability for the direct conversion of
allyl alcohol to allylaniline, which has been difficult by use
of catalysts including normal phosphine ligands. The low-
coordinated sp2 phosphorus atom might enhance π-back-
bonding due to the low-lying PdC π* orbital,7a and it might
facilitate the C-O bond cleavage in allyl alcohol.
Scheme 2 a
a Reagents and conditions: (i) 8 (2.5 mol %), CuI (2 mol %),
Et3N, rt, 4 h; (ii) 8 (4 mol %), K2CO3, THF, reflux, 20 h; (iii) 10
(2 mol %), MgSO4, toluene, rt, 2 h.
In conclusion, a novel 3-thioxo-1,3-diphosphapropene (4)
was prepared and functioned as a monodentate and a
chelating ligand. The dichloropalladium(II) complex 8
displayed higher stability than 9 and equivalent catalytic
activities for the Sonogashira and Suzuki cross-coupling. On
the other hand, the cationic allylpalladium(II) complex 10
was useful to the direct conversion of allyl alcohol, indicating
the efficiency of low-coordinated phosphorus compounds as
ligands for transition metal catalysts. Taking these easy
procedures of preparation into consideration, the 3-thioxo-
1,3-diphosphapropene skeleton would be widely used as a
novel system of ligand as well as the 1,3-diphosphapropene
system.
allowed to react with phenylacetylene and phenylboronic acid
in the presence of 8 and some other reagents to afford
diphenylacetylene in 83% yield and biphenyl in almost
quantitative yield,14 respectively. In the case of the Sono-
gashira coupling, p-iodoanisole and phenylacetylene afforded
the corresponding diarylacetylene in 65% yield, although the
Suzuki coupling with p-iodoanisole gave a poor result (1%
yield). Whereas these cross-coupling reactions smoothly
proceeded in the case of iodobenzene, bromobenzene showed
poor reactivity for these reactions. In the reaction of
bromobenzene and phenylacetylene under the catalytic
reaction conditions with 8, diphenylbutadiyne was obtained
almost quantitatively (96%). The low activity of 8 for the
cross-coupling might be attributed to both descending
electron-donating effect of the sp2-phosphorus atom and
enhancing oxidative-addition ability to the C-X bond.1,3b,5
Compound 4 was available for a ligand of a cationic
π-allyl palladium(II) complex as described in Scheme 1.
Indeed, 4 was allowed to react with [(η3-allyl)PdCl]2 and
Acknowledgment. This work was supported in part by
Grants-in-Aid for Scientific Research (Nos. 13304049 and
14044012) from the Ministry of Education, Culture, Sports,
Science and Technology, Japan. H.L. is grateful to the Japan
Society for the Promotion of Science for the Postdoctoral
Fellowships for Foreign Researchers. We thank Prof. Fumi-
yuki Ozawa, Institute of Chemical Research, Kyoto Univer-
sity, for his helpful suggestions.
Supporting Information Available: Experimental details
for preparation of 4, 6-8, 10, and 11, with full characteriza-
tion data. Tables of crystallographic data, atomic coordinates,
anisotropic thermal parameters, and bond lengths and angles
for compound 8 (CIF). This material is available free of
charge via the Internet at http://pubs.acs.org.
(12) Crystal data for 8: C32H42Cl2P2Pd‚1.5CH2Cl2, MW ) 825.40,
triclinic, P-1 (No. 2), a ) 13.0619(9) Å, b ) 14.127(2) Å, c ) 11.692(1)
Å, R ) 108.13(1)°, â ) 109.703(5)°, γ ) 77.28(1)°, V ) 1914.2(4) Å3, Z
) 2, Fcalcd ) 1.432 g cm-1, µMoKR ) 0.994 mm-1, F000 ) 846, 2θmax
)
55.0°, T ) 296 °C, 13 145 measured reflections, 7794 unique reflections
(Rint ) 0.055), R1 ) 0.062 (I > 4σ(I) on F2), RW ) 0.163 (all data), S )
1.57 (378 parameters).
(13) (a) Tykwinski, P. R. Angew. Chem., Int. Ed. 2003, 42, 1566. (b)
Li, C.-J. Angew. Chem., Int. Ed. 2003, 42, 4856. (c) Sonogashira, K. In
Metal-Catalyzed Cross-Coupling Reactions; Diederich, F., Stang, P. J., Eds.;
Wiley-VCH: Weinheim, 1998. (d) Miyaura, N.; Suzuki, A. Chem. ReV.
1995, 95, 2457.
OL036330G
(15) 10: yellow crystals; mp 125 °C; 31P{1H} NMR (162 MHz, CDCl3)
2
(14) Complex 9 catalyzed the Suzuki coupling of iodobenzene and
phenylboronic acid affording biphenyl almost quantitatively under a similar
conditions in eq 2.
δ 289.2 (PdC), 61.0 (PdS), JPP ) 126 Hz.
(16) 11: 31P{1H} NMR (162 MHz, CDCl3) δ 249.8 (PdC), 12.4 (PPh2),
2JPP ) 11 Hz.
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