Preparation of sterically protected 3,4-bis[(2,4,6-tri-tert-butylphenyl)-phosphinidene]cyclobutene derivatives having ring-fused structures

Article abstract of DOI:10.1021/ol017169h

(Formula Presented) Sterically protected 3,4-diphosphinidenecyclobutenes, having ring-fused structures, were prepared. Structures of 8,9-bis[(2,4,6-tri-tert-butylphenyl)-phosphinidene]bicyclo[5.2.0]non-1(7)-ene and its dichloropalladium(II) complex were a

Full text of DOI:10.1021/ol017169h

ORGANIC
LETTERS
2002
Vol. 4, No. 4
569-572
Preparation of Sterically Protected
3,4-Bis[(2,4,6-tri-tert-butylphenyl)-
phosphinidene]cyclobutene Derivatives
Having Ring-Fused Structures
Naoki Yamada,† Keita Abe, Kozo Toyota, and Masaaki Yoshifuji*
Department of Chemistry, Graduate School of Science, Tohoku UniVersity,
Aoba, Sendai 980-8578, Japan
yoshifj@mail.cc.tohoku.ac.jp
Received December 4, 2001
ABSTRACT
Sterically protected 3,4-diphosphinidenecyclobutenes, having ring-fused structures, were prepared. Structures of 8,9-bis[(2,4,6-tri-tert-butylphenyl)-
phosphinidene]bicyclo[5.2.0]non-1(7)-ene and its dichloropalladium(II) complex were analyzed by X-ray crystallography. A geometrical change
induced by the complex formation was exhibited by X-ray crystallographic analysis. The geometrical change in solution was also suggested
by 1H NMR spectroscopy in CDCl3.
Multiple bonds containing the heavier main-group elements
have been of interest for the past two decades.1 By utilizing
an extremely bulky 2,4,6-tri-tert-butylphenyl group (hereafter
abbreviated to the Mes* group) as a sterically protecting
auxiliary, we and others have prepared several double-bonded
phosphorus compounds such as diphosphenes,1a phosphacu-
mulenes,2 and phospharadialenes.3 We have also reported
syntheses of sterically protected 3,4-diphosphinidenecy-
clobutenes 14 and its application as a ligand with confor-
mationally rigid coordination sites.5 Moreover, palladium or
platinum complexes having the 3,4-diphosphinidenecy-
clobutene ligand showed catalytic activities.5c,f-h Thus,
M.; Tachon, C.; El Ouatib, R.; Ramarijaona, O.; Etemad-Moghadam, G.;
Koenig, M. Tetrahedron Lett. 1989, 30, 177. (i) Yoshifuji, M.; Yoshimura,
H.; Toyota, K. Chem. Lett. 1990, 827. (j) Yoshifuji, M.; Toyota, K.;
Yoshimura, H. Chem. Lett. 1991, 491.
(3) Toyota, K.; Tashiro, K.; Yoshifuji, M. Angew. Chem., Int. Ed. Engl.
1993, 32, 1163.
† Fellowships of the Japan Society for the Promotion of Science for
Japanese Junior Scientists.
(1) (a) Yoshifuji, M.; Shima, I.; Inamoto, N.; Hirotsu, K.; Higuchi, T. J.
Am. Chem. Soc. 1981, 103, 4587; 1982, 104, 6167. (b) West, R.; Fink, M.
J.; Michl, J. Science 1981, 214, 1343. (c) Tokitoh, N.; Arai, Y.; Okazaki,
R.; Nagase, S. Science 1997, 277, 78. (d) Stu¨rmann, M.; Saak, W.;
Marsmann, H.; Weidenbruch, M. Angew. Chem., Int. Ed. 1999, 38, 187.
(e) Power, P. P. Chem. ReV. 1999, 99, 3463. (f) Gru¨tzmacher, H.; Fa¨ssler,
T. F. Chem. Eur. J. 2000, 2317. (g) Esucdie´, J.; Ranaivonjatovo, H.; Rigon,
L. Chem. ReV. 2000, 100, 3639. (h) Yoshifuji, M. J. Organomet. Chem.
2000, 611, 210.
(2) (a) Yoshifuji, M.; Toyota, K.; Shibayama, K.; Inamoto, N. Tetrahe-
dron Lett. 1984, 25, 1809. (b) Yoshifuji, M.; Toyota, K.; Inamoto, N. J.
Chem. Soc., Chem. Commun. 1984, 689. (c) Karsch, H. H.; Ko¨hler, F. H.;
Reisacher, H.-U. Tetrahedron Lett. 1984, 25, 3687. (d) Appel, R.; Fo¨lling,
P.; Josten, B.; Siray, M.; Winkhaus, V.; Knoch, F. Angew. Chem., Int. Ed.
Engl. 1984, 23, 619. (e) Ma¨rkl, G.; Sejpka, H.; Dietl, S.; Nuber, B.; Ziegler,
M. Angew. Chem., Int. Ed. Engl. 1986, 25, 1003. (f) Ma¨rkl G.; Kreitmeier,
P. Angew. Chem., Int. Ed. Engl. 1988, 27, 1360. (g) Yoshifuji, M.; Sasaki,
S.; Niitsu, T.; Inamoto, N. Tetrahedron Lett. 1989, 30, 187. (h) Gouygou,
(4) (a) Yoshifuji, M.; Toyota, K.; Murayama, M.; Yoshimura, H.;
Okamoto, A.; Hirotsu, K.; Nagase, S. Chem. Lett. 1990, 2195. (b) Toyota,
K.; Tashiro, K.; Yoshifuji, M. Bull. Chem. Soc. Jpn. 1992, 65, 2297. See,
also: (c) Appel, R.; Winkhaus, V.; Knoch, F. Chem. Ber. 1987, 120, 243.
(d) Ma¨rkl G.; Hennig, R. Liebigs Ann. 1996, 2059.
(5) (a) Toyota, K.; Tashiro, K.; Yoshifuji, M. Chem. Lett. 1991, 2079.
(b) Toyota, K.; Tashiro, K.; Yoshifuji, M.; Miyahara, I.; Hayashi, A.;
Hirotsu, K. J. Organomet. Chem. 1992, 431, C35. (c) Toyota, K.; Masaki,
K.; Abe, T.; Yoshifuji, M. Chem. Lett. 1995, 221. (d) Yoshifuji, M.;
Ichikawa, Y.; Toyota, K.; Kasashima, E.; Okamoto, Y. Chem. Lett. 1997,
87. (e) Yoshifuji, M.; Ichikawa, Y.; Yamada, N.; Toyota, K. Chem.
Commun. 1998, 27. (f) Ikeda, S.; Ohhata, F.; Miyoshi, M.; Tanaka, R.;
Minami, T.; Ozawa, F.; Yoshifuji, M. Angew. Chem., Int. Ed. 2000, 39,
4512. (g) Ozawa, F.; Yamamoto. S.; Kawagishi, S.; Hiraoka, M.; Ikeda,
S.; Minami, T.; Ito, S.; Yoshifuji, M. Chem. Lett. 2001, 972. (h) Minami,
T.; Okamoto, H.; Ikeda, S.; Tanaka, R.; Ozawa, F.; Yoshifuji, M. Angew.
Chem., Int. Ed. 2001, 40, 4501.
10.1021/ol017169h CCC: $22.00 © 2002 American Chemical Society
Published on Web 01/19/2002

expansion of the structure at the 1- and/or 2-position of the
cyclobutene ring and evaluation of the steric and/or electronic
effects of the expansion are of interest from the viewpoints
of coordination chemistry as well as synthetic organic
chemistry. We report here the preparations of 3,4-diphos-
phinidenecyclobutene derivatives having ring-fused struc-
tures.
20% yield; δP )147.9. (E,E)-5c: 11% yield; δP )147.2.
Intermediates 6c as well as 7a-c were observed by 31P NMR
spectroscopic monitoring during the reaction. On the other
hand, plausible intermediates 6a,b were not detected by 31
P
NMR spectroscopic monitoring, probably because the rear-
rangement reaction is faster due to the larger ring strain,
compared to the case of 6c. 6c: 31P{1H} NMR (81 MHz,
THF-C6D6) δP ) -34.8. 7a: δP ) 63.6. 7b: δP ) 63.3.
7c: δP ) 63.4. The diphosphinidenecyclobutenes (E,E)-5a-c
thus obtained were converted to the (E,Z)-isomers by addition
of catalytic amounts of iodine in benzene.7
In a typical preparative method of 1, alkynylphosphines
2 were used as starting material (Scheme 1). Thus, we
It should be noted that the reaction of BrMgCtC(CH2)3Ct
CMgBr with Mes*P(H)Cl (2 molar equiv) followed by
reactions with tert-butyllithium and 1,2-dibromoethane re-
sulted in the formation of 1,2-dipent-4-ynyl-3,4-diphosphin-
idenecyclobutene (E,E)-8 [δP (CDCl3) ) 153.6, 6% isolated
yield after silica gel column chromatographic and recycling
gel permeation column chromatographic treatments] (Scheme
3).
Scheme 1
prepared R,ω-bis[(2,4,6-tri-tert-butylphenyl)phosphino]diynes
3a-c by reactions of chloro(2,4,6-tri-tert-butylphenyl)-
phosphine2f,6 with BrMgCtCCH2(CH2)nCH2CtCMgBr [pre-
pared from the corresponding diynes 4a-c; Scheme 2]. 3a:
Scheme 3
Scheme 2
Thus, the diphosphinidenecyclobutene fused with a five-
membered ring was not obtained by the present method.
When the reaction of BrMgCtC(CH2)3CtCMgBr with
Mes*P(H)Cl (2 molar equiv) was quenched with water,
monophosphine Mes*P(H)CtC(CH2)3CtCH [δP(CDCl3) )
-101.3 (d, 1JPH ) 244.5 Hz)] and Mes*P(O)H2 [a hydrolyzed
product of unreacted Mes*P(H)Cl] were obtained after gel
permeation column chromatography. We could not find either
the corresponding diphosphine or its derivatives in this
reaction.
1
31P NMR (81 MHz, C6D6) δP ) -101.0 (d, JPH ) 246.7
1
The compound (E,E)-8 was alternatively obtained in 30%
yield in the reaction of Mes*P(H)Cl with BrMgCt
C(CH2)3CtCH followed by addition of tert-butyllithium and
1,2-dibromoethane. In the latter reaction, intermediate bis-
(phosphaallene) 9 was observed [δP(THF-C6D6) ) 75.5]
by 31P NMR spectroscopic monitoring of the reaction. As
shown in Scheme 4, (E,E)-8 was also formed by desilylation
reaction of (E,E)-1,2-bis[5-(trimethylsilyl)pent-4-ynyl]-3,4-
Hz). 3b: δP ) -101.0 (d, JPH ) 246.5 Hz). 3c: δP )
1
-101.5 (d, JPH ) 244.6 Hz).
When the phosphines 3a-c were treated successively with
tert-butyllithium (2 molar equiv) and 1,2-dibromoethane (1
molar equiv), the ring-fused diphosphinidenecyclobutene
derivatives (E,E)-5a-c were obtained. (E,E)-5a: 25% yield
[based on Mes*PH2 used in the preparation of Mes*P(H)-
Cl]; 31P{1H} NMR (81 MHz, CDCl3) δP ) 148.8. (E,E)-5b:
(6) Cowley, A. H.; Kilduff, J. E.; Norman, N. C.; Pakulski, M.; Atwood,
J. L.; Hunter, W. E. J. Am. Chem. Soc. 1983, 105, 4845.
(7) Toyota, K.; Tashiro, K.; Abe, T.; Yoshifuji, M. Heteroatom Chem.
1994, 5, 549.
570
Org. Lett., Vol. 4, No. 4, 2002

P(1), and P(2) were on the same plane within 0.012(8) Å.
The two Mes* groups were nearly perpendicular to this plane
[interplanar angles between the diphosphinidenecyclobutene
plane and the aromatic rings C(10)-C(15) and C(28)-C(33)
are 87.5(3)° and 87.5(2)°, respectively].
Scheme 4
Reaction of (E,E)-5a-c with PdCl2(MeCN)2 in THF gave
1
dichloropalladium(II) complexes 12a-c (Scheme 5). In H
Scheme 5
diphosphinidenecyclobutene 11 [δP(CDCl3) ) 153.9]8 with
tetrabutylammonium fluoride.
The structure of (E,E)-5b was confirmed by X-ray
crystallography.9,10 Figure 1 shows a molecular structure of
NMR spectra of 12a-c, signals due to the methylene protons
showed downfield shifts compared with the corresponding
signals of the free ligands (E,E)-5a-c. For example, meth-
ylene signals for 12b appear at δ ) 1.46 (4H, br s), 1.56
(2H, br s), and 1.87 (4H, br s), while those for the free ligand
(E,E)-5b appear at δ ) 0.86 (4H, br s), 1.05 (4H, pseudo t),
and 1.26 (2H, m). Probably the aromatic rings of the Mes*
groups in the free ligands [(E,E)-5a-c] are close to the
methylenes, causing strong shielding effect in the 1H NMR
spectra. This shielding effect might be decreased when the
Mes* groups move away from the methylenes upon coor-
dination of the phosphorus atoms to the metal.
This is demonstrated by the crystal structure analysis of
the ligand and the complex.10 Figure 2 shows the molecular
structures of 12b in the crystal.13,14 The angles C(1)-P(1)-
C(10) and C(3)-P(2)-C(28) become larger upon coordina-
tion, and both aromatic rings move apart from the methylenes
Figure 1. Molecular structure of (E,E)-5b showing the atomic
labeling scheme with thermal ellipsoids (30% probability).
(E,E)-5b.11,12 The methyl groups C(39)-C(41) of a p-tert-
butyl group and the methylenes C(6)-C(8) of the seven-
membered ring were disordered. The atoms C(1)-C(5), C(9),
C(2)-C(4), 93.5(4); C(1)-C(2)-C(5), 132.4(6); C(4)-C(2)-C(5), 134.2-
(6); P(2)-C(3)-C(1), 130.3(4); P(2)-C(3)-C(4), 142.6(5); C(1)-C(3)-
C(4), 87.2(4); C(2)-C(4)-C(3), 92.5(5); C(2)-C(4)-C(9), 134.2(6); C(3)-
C(4)-C(9), 133.4(6).
(13) The structure was solved with SAPI91: Hai-Fu, F.; Structure
Analysis Programs with Intelligent Control, Rigaku Corporation, Tokyo,
Japan, 1991.
(14) Hydrogen atoms and incorporated solvent molecules are omitted
for clarity. Some selected bond lengths (Å) and angles (deg): Pd-P(1),
2.267(2); Pd-P(2), 2.256(2); Pd-Cl(1), 2.329(2); Pd-Cl(2), 2.331(2);
P(1)-C(1), 1.654(9); P(2)-C(3), 1.652(8); C(1)-C(2), 1.46(1); C(3)-C(4),
1.49(1); C(1)-C(3), 1.47(1); C(2)-C(4), 1.38(1); C(2)-C(5), 1.49(1);
C(4)-C(9), 1.47(1); P(1)-C(10), 1.815(8); P(2)-C(28), 1.799(9); P(1)-
Pd-P(2), 85.20(8); Cl(1)-Pd-Cl(2), 93.81(8); P(1)-Pd-Cl(1), 91.23(8);
P(2)-Pd-Cl(2), 89.76(8); Pd-P(1)-C(1), 108.4(3); Pd-P(1)-C(10),
137.5(3); Pd-P(2)-C(3), 108.9(3); Pd-P(2)-C(28), 132.8(3); C(1)-P(1)-
C(10), 114.1(4); C(3)-P(2)-C(28), 118.2(4); P(1)-C(1)-C(2), 152.7(7);
P(1)-C(1)-C(3), 118.9(6); C(2)-C(1)-C(3), 88.4(6); C(1)-C(2)-C(4),
92.8(7); C(1)-C(2)-C(5), 134.8(8); C(4)-C(2)-C(5), 132.4(8); P(2)-
C(3)-C(1), 118.6(6); P(2)-C(3)-C(4), 153.3(7); C(1)-C(3)-C(4), 88.0-
(6); C(2)-C(4)-C(3), 90.9(7); C(2)-C(4)-C(9), 134.2(8); C(3)-C(4)-
C(9), 134.9(8).
(8) Crude compound 11 was obtained in ca. 49% yield [via intermediate
bis(phosphaallene) 10; δP (THF-C6D6) ) 75.8] and used without purifica-
tion. Attempted purification of 11 failed because of partial decomposition
during the isolation process.
(9) The structure was solved with SIR92: Altomare, A.; Burla, M. C.;
Camalli, M.; Cascarano, M.; Giacovazzo, C.; Guagliardi, A.; Polidori, G.
J. Appl. Crystallogr. 1994, 27, 435.
(10) The complete crystal data are deposited at at the Cambridge
Crystallographic Data Centre (Nos. CCDC-173600 for (E,E)-5b and CCDC-
173599 for 12b).
(11) Johnson, C. K.; ORTEP-II, Oak Ridge National Laboratory Report,
ORNL-TM-5138, 1976, Oak Ridge, TN.
(12) Hydrogen atoms are omitted for clarity. The atoms [C(6)-C(8) and
C(39)-C(41)] were disordered, but only atoms with a dominant occupancy
factor are displayed. Some selected bond lengths(Å) and angles (deg): P(1)-
C(1), 1.661(6); P(2)-C(3), 1.673(5); C(1)-C(2), 1.472(8); C(3)-C(4),
1.481(7); C(1)-C(3), 1.505(8); C(2)-C(4), 1.351(8); C(2)-C(5), 1.509-
(9); C(4)-C(9), 1.487(10); P(1)-C(10), 1.859(5); P(2)-C(28), 1.830(5);
C(1)-P(1)-C(10), 99.6(2); C(3)-P(2)-C(28), 100.4(2); P(1)-C(1)-C(2),
143.1(4); P(1)-C(1)-C(3), 130.0(4); C(2)-C(1)-C(3), 86.9(5); C(1)-
Org. Lett., Vol. 4, No. 4, 2002
571

chelate-type tetracarbonylmolybdenum complex was ob-
served by 31P NMR spectroscopy, in contrast to the previous
results using (E,E)-5d as follows: The reactions of (E,E)-
5d with an excess amount of Mo(CO)5(thf) or Mo(CO)6 gave
only chelate complex 13 as a stable compound,5a probably
because the Mes*PdC-CdPMes* moiety in (E,E)-5d is
preoriented in favor of chelate formation due to steric
repulsion between the bulky Mes* group and the trimeth-
ylsilyl group. Actually, the angles corresponding to C(1)-
P(1)-C(10) and C(3)-P(2)-C(28) in (E,E)-5d largely
deviate from those in (E,E)-5b [in (E,E)-5d, the angles are
110.7(3)° and 108.0(3)°] and are very close to those for 13
[109.7(2)° and 108.7(2)°].5b This fact suggests that the steric
effect of the substituents at the 1- or 2-position plays an
important role in coordination and in catalytic abilities5c,f-h
of the complexes. Further studies on the properties of the
ring-fused diphosphinidenecyclobutene derivatives are now
in progress.
Figure 2. Molecular structure of 12b showing the atomic labeling
scheme with thermal ellipsoids (30% probability).
in 12b, compared with those in (E,E)-5b [in (E,E)-5b the
angle C(1)-P(1)-C(10) is 99.6(2)° and the angle C(3)-
P(2)-C(28) is 100.4(2)°, whereas in 12b the angle C(1)-
P(1)-C(10) is 114.1(4)° and the angle C(3)-P(2)-C(28)
is 118.2(4)°].
The substantial changes in the angles C(1)-P(1)-C(10)
and/or C(3)-P(2)-C(28) may affect the coordination abili-
ties of the ligands: In the reaction of (E,E)-5b with an excess
amount of Mo(CO)5(thf), neither a chelate complex nor a
monodentate complex was detected by 31P NMR spectro-
scopic monitoring. Moreover, the reaction of (E,E)-5b with
an excess amount of Mo(CO)6 in refluxing 1,4-dioxane led
to decomposition, and no formation of the corresponding
Acknowledgment. A part of this work was supported by
Grants-in-Aid for Scientific Research on Priority Area (Nos.
09239104 and 12020205) from the Ministry of Education,
Science, Sports, Culture and Technology, Japan.
Supporting Information Available: Experimental pro-
cedures and spectroscopic data for compounds (E,E)-5a-c,
(E,Z)-5a-c, 8, and 12a-c, including the crystal data of
(E,E)-5b and 12b. This material is available free of charge
via the Internet at http://pubs.acs.org.
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