1,2-Migration of phosphorus-centered anions on ate-type copper carbenoids and its application for the synthesis of new potent phosphine ligands

Article abstract of DOI:10.1021/ol052520a

(Chemical Equation Presented) Diorganophosphide anions, which usually function as nontransferable ligands on mixed cuprates, undergo smooth 1,2-migration on ate-type copper carbenoids. Phosphinodisilylmethylcoppers prepared by this protocol are converted into the corresponding phosphines, which can be used as bulky, highly basic and air-stable ligands.

Full text of DOI:10.1021/ol052520a

ORGANIC
LETTERS
2005
Vol. 7, No. 25
5713-5715
1,2-Migration of Phosphorus-Centered
Anions on Ate-type Copper Carbenoids
and Its Application for the Synthesis of
New Potent Phosphine Ligands
Junichi Kondo,† Hidenori Someya,† Hidenori Kinoshita,† Hiroshi Shinokubo,‡
Hideki Yorimitsu,† and Koichiro Oshima*,†
Department of Material Chemistry, Graduate School of Engineering,
Kyoto UniVersity, Kyoto-daigaku Katsura, Nishikyo-ku, Kyoto 615-8510, Japan,
and Department of Chemistry, Graduate School of Science, Kyoto UniVersity,
Sakyo-ku, Kyoto 606-8502, Japan
oshima@orgrxn.mbox.media.kyoto-u.ac.jp
Received October 18, 2005
ABSTRACT
Diorganophosphide anions, which usually function as nontransferable ligands on mixed cuprates, undergo smooth 1,2-migration on ate-type
copper carbenoids. Phosphinodisilylmethylcoppers prepared by this protocol are converted into the corresponding phosphines, which can be
used as bulky, highly basic and air-stable ligands.
Organocopper reagents are an extremely valuable family of
organometallic compounds that are widely used in organic
synthesis.1 Among them, mixed cuprates have been devel-
oped to improve the reactivity and thermal stability by
introducing “dummy” ligands. These reagents often employ
cyano, silylmethyl, alkynyl, 2-thienyl, and mesityl groups
as the carbon-based dummy groups.1 Heteroatom-based ones
include phenylsulfanyl, N-imidazolyl, dialkylamino, and
dialkylphosphino groups.2,3 However, in the course of our
recent study on 1,2-migration of various groups via ate-type
copper carbenoids, we have found that nontransferable car-
bon-based anionic ligands transfer efficiently.4 Here we wish
to report the 1,2-migration of phosphorus-centered anions,
such as Ph2P- or (c-C6H11)2P-, which are generally expected
to exhibit no migratory aptitude on cuprates in other con-
ventional reactions.3 The migratory phosphination afforded
new phosphines useful in transition-metal-catalyzed reac-
tions.5
Initially, we chose dihalosilylcarbenoid as a test case to
examine the feasibility of the phosphination via 1,2-migration
on cuprates (Scheme 1). An addition of n-BuLi to a THF
Scheme 1. Diphosphination via Double 1,2-Migration of
Phosphorus-Centered Anion on Ate-type Copper Carbenoid
† Graduate School of Engineering, Kyoto University.
‡ Graduate School of Science, Kyoto University.
(1) (a) Modern Organocopper Chemistry; Krause, N., Ed.; Wiley-
VCH: Weinheim, Germany, 2000. (b) Organocopper Reagents; Taylor,
R. J. K., Ed.; Oxford University Press: Oxford, 1994. (c) Lipshutz, B. H.
In Organometallics in Synthesis; Schlosser, M., Ed.; Wiley: Chichester,
2002; p 665.
(2) (a) Phenylsulfanyl: Posner, G. H.; Whitten, C. E.; Sterling, J. J. J.
Am. Chem. Soc. 1973, 95, 7788. (b) N-Imidazolyl: Lipshutz, B. H.; Fatheree,
P.; Hagen, W.; Stevens, K. L. Tetrahedron Lett. 1992, 33, 1041.
solution of Ph2MeSiCHCl2 (1) provided dichlorosilylmeth-
yllithium 2 with the quantitative deprotonation. Lithium
10.1021/ol052520a CCC: $30.25
© 2005 American Chemical Society
Published on Web 11/16/2005

carbenoid 2 was sequentially treated with CuCN‚2LiCl (1.1
equiv in THF) and lithium diphenylphosphide (2.5 equiv in
THF) at -78 °C, and the mixture was allowed to warm
gradually to 0 °C. After quenching with sulfur and dilute
HCl aq., extractive workup followed by purification afforded
the pentavalent phosphorus compound 3. This result indicates
the generation of copper species 4 through the double 1,2-
migrations of diphenylphosphino groups on ate-type copper
carbenoid. Desilylation of 4 took place upon hydrolysis to
yield 3.
Next, we attempted the monophosphination of chlorodisi-
lylcarbenoid 8a, which was instantly prepared by mixing
(Ph2MeSi)2CCl2 (5a) with n-BuLi (1.0 equiv) in THF at -78
°C (Scheme 2). In a similar way as described above, lithium
Figure 1. ORTEP drawing of the phosphine sulfide 6b. Hydrogen
atoms were omitted for clarity. The thermal ellipsoids were at the
50% probability level.
Scheme 2. Monophosphination of Chlorodisilylcarbenoids
DFT calculations at the B3LYP/6-31G* level show that 9a
is expected to have a large cone angle (Supporting Informa-
tion, Figure S1).8d,9 The electron-donating silylmethyl group
1
should enhance the basicity of 9a. J(77Se-31P) coupling
constants of the phosphine selenides SedPR3 are commonly
used to estimate the relative basicities of the parent phos-
phines PR3. In our case, the selenide of 9a marked 690
Hz, which indicates that 9a has a comparable basicity to
P(t-Bu)3 (SedP(t-Bu)3, 686 Hz) and stronger basicity than
PPh3 (SedPPh3, 735 Hz).8
The phosphine 9a is expected to have some unique
chemical properties due to its steric and electronic effects,
which are induced by silyl substitution at the R-position.
Consequently, we have examined the use of this silicon-
bearing phosphine 9a as a ligand of two typical transition-
metal-catalyzed reactions.10 Scheme 3 shows the preliminary
carbenoid 8a was treated with 1.1 equiv of CuCN and 1.2
equiv of Ph2PLi. The mixture was stirred at 0 °C and
quenched with sulfur and aqueous NH4Cl. Disilylmeth-
ylphosphine sulfide 6a was obtained in 84% yield as a sole
product.6 The reactions of 5b and 5c having two other silyl
groups, PhMe2Si and Me3Si, respectively, proceeded in the
same manner. (c-C6H11)2PLi was also applicable to this
reaction protocol and furnished the corresponding phosphine
sulfides despite slight decreases in yields. Furthermore, we
could isolate the trivalent phosphines 9a and 9b in good
yields without sulfurization.7
Scheme 3. Ligand 9a in Transition-Metal-Catalyzed Reactions
Importantly, these (disilylmethyl)diphenylphosphines 9a
and 9b show much higher air-stability than the parent
PPh2Me. The structure of the phosphine sulfide 6b was
unambiguously elucidated by X-ray crystallographic analysis,
as shown in Figure 1. Clearly, two large silyl groups sterically
hinder the environment of the phosphorus center. In addition,
(3) (a) Bertz, S. H.; Dabbagh, G.; Villacorta, G. M. J. Am. Chem. Soc.
1982, 104, 5824. (b) Bertz, S. H.; Dabbagh, G. J. Org. Chem. 1984, 49,
1119. (c) Martin, S. F.; Fishpaugh, J. R.; Power, J. M.; Giolando, D. M.;
Jones, R. A.; Nunn, C. M.; Cowley, A. H. J. Am. Chem. Soc. 1988, 110,
7226.
(4) (a) Inoue, A.; Kondo, J.; Shinokubo, H.; Oshima, K. J. Am. Chem.
Soc. 2001, 123, 11109. (b) Kondo, J.; Ito, Y.; Shinokubo, H.; Oshima, K.
Angew. Chem., Int. Ed. 2004, 43, 106. (c) Kondo, J.; Inoue, A.; Ito, Y.;
Shinokubo, H.; Oshima, K. Tetrahedron 2005, 61, 3361.
(5) We recently described new methods for the synthesis of organo-
phosphorus compounds. See: (a) Hirano, K.; Yorimitsu, H.; Oshima, K.
Org. Lett. 2004, 6, 4873. (b) Sato, A.; Yorimitsu, H.; Oshima, K. Angew.
Chem., Int. Ed. 2005, 44, 1694. (c) Ohmiya, H.; Yorimitsu, H.; Oshima,
K. Angew. Chem., Int. Ed. 2005, 44, 2368.
results of the Heck reaction with aryl bromide and ethyl
acrylate to exploit the basicity and bulkiness of 9a.11 We
were pleased to find that the desired Heck product was
obtained in good yield at 85 °C in the presence of tetrabu-
tylammonium chloride with ligand 9a. In contrast, the same
transformation with PPh3 or under ligandless conditions
resulted in diminished yield (34 or 6% yield, respectively).
The Heck reaction with aryl bromide generally needs high
reaction temperatures over 120 °C,12 and these milder
(6) We could not detect the byproduct, R,R-bis(methyldiphenylsilyl)-
acetonitrile, which was derived via 1,2-migration of the cyano group.
5714
Org. Lett., Vol. 7, No. 25, 2005

reaction conditions can be attributed to the bulky and highly
basic nature of 9a.11,12b
stimulated us to find a new way to prepare π-allylpalladium
species with a combination of Pd2(dba)3, 9a, and tetrabuty-
lammonium fluoride. This was indeed the case, and the
reaction of diethyl malonate with allyl alcohol exclusively
afforded monoallylated product in 86% yield without forma-
tion of the diallylated product. Both crotyl alcohol and its
regioisomer, 3-buten-2-ol, provided the corresponding linear
and branched products in comparable ratios (linear/branched
) 59:41 and 56:44, respectively). The comparable ratios
suggest the formation of the π-allylpalladium intermediate.
In conclusion, we have demonstrated 1,2-migration of
phosphorus-centered anions on ate-type copper carbenoids.
Additionally, we have applied (disilylmethyl)diphenylphos-
phine as a bulky and electron-rich ligand to transition-metal-
catalyzed reactions. Further studies are now underway to
elucidate the effects of (disilylmethyl)diphenylphosphines in
transition-metal-catalyzed reactions.
We also attempted to utilize this phosphine 9a for Tsuji-
Trost reaction with the direct use of allylic alcohol.13 Tsuji-
Trost reaction with allyl alcohol as the allyl source usually
requires acidic activators for the hydroxy group, such as
inorganic acids or Lewis acids. Several other catalytic
examples have been recently reported which utilize π-al-
lylpalladium complexes bearing diphosphinidenecyclobutene
ligands13a or water-soluble palladium complex in an aque-
ous-organic biphasic system.13b These precedent works
(7) Classical synthetic methods of silylmethyl- and bis(silyl)methylphos-
phines were reported. See: (a) Appel, R.; Schoeler, H. F. Chem. Ber. 1979,
112, 1068. (b) Holmes-Smith, R. D.; Osei, R. D.; Stobart, S. R. J. Chem.
Soc., Perkin Trans. 1 1983, 861. (c) Appel, R.; Haubrich, G.; Knoch, F.
Chem. Ber. 1984, 117, 2063. (d) Wolfsberger, W. Chemiker Zeitung 1989,
113, 349. (e) Kawashima, T.; Mitsuda, N.; Inamoto, N. Bull. Chem. Soc.
Jpn. 1991, 64, 708. (f) Bennett, M. A.; Edwards, A. J.; Harper, J. R.;
Khimyak, T.; Willis, A. C. J. Organomet. Chem. 2001, 629, 7. (g) Wang,
L.; Chen, X.; Huang, S.; Liu, D. Shanxi Daxue Xuebao, Ziran Kexueban
2004, 27, 160.
(8) (a) Allen, D. W.; Taylor, B. F. J. Chem. Soc., Dalton Trans. 1982,
51. (b) Socol, S. M.; Verkade, J. G. Inorg. Chem. 1984, 23, 3487. (c)
Andersen, N. G.; Keay, B. A. Chem. ReV. 2001, 101, 997. (d) Niyomura,
O.; Iwasawa, T.; Sawada, N.; Tokunaga, M.; Obora, Y.; Tsuji, Y.
Organometallics 2005, 24, 3468. (e) The selenide of 9a was prepared
according to the reported procedure in ref 7a.
Acknowledgment. This work was supported by Grants-
in-Aid for Scientific Research and COE Research from the
Ministry of Education, Culture, Sports, Science and Technol-
ogy, Government of Japan. J.K. and H.K. acknowledge JSPS
for financial support. The authors also would like to thank
Prof. Dr. M. Shimizu and Mr. K. Nomura for crystallographic
analysis.
(9) Tolman, C. A. Chem. ReV. 1977, 77, 313.
(10) Transition-metal-catalyzed reactions with dendritic phosphine ligands
containing silylmethylphosphine units were reported. See: Benito, M.;
Rossell, O.; Seco, M.; Muller, G.; Ordinas, J. I.; Font-Bardia, M.; Solans,
X. Eur. J. Inorg. Chem. 2002, 2477.
Supporting Information Available: Detailed experi-
mental procedures, characterization data of compounds, and
X-ray crystallographic data for 6b in CIF format. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(11) Shaughnessy, K. H.; Kim, P.; Hartwig, J. F. J. Am. Soc. Chem.
1999, 121, 2123.
(12) (a) Beletskaya, I. P.; Cheprakov, A. V. Chem. ReV. 2000, 100, 3009.
(b) Littke, A. F.; Fu, G. C. J. Am. Chem. Soc. 2001, 123, 6989.
(13) (a) Ozawa, F.; Okamoto, H.; Kawagishi, S.; Yamamoto, S.; Minami,
T.; Yoshifuji, M. J. Am. Chem. Soc. 2002, 124, 10968. (b) Kinoshita, H.;
Shinokubo, H.; Oshima, K. Org. Lett. 2004, 6, 4085 and references therein.
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