Synthesis of 1,1′-diphospha[4]ferrocenophanes by molybdenum-catalyzed ring-closing metathesis

Article abstract of DOI:10.1021/om021058k

A variety of 1,1′-diphospha[4]ferrocenophanes were prepared in good to moderate yield with the interannular ring-closing metathesis reaction of diallyl-1,1′-diphosphaferrocenes using the Schrock's molybdenum-carbene catalyst. The Grubbs' ruthenium metathesis catalyst was found inactive for these Lewis basic phosphorus-containing substrates.

Full text of DOI:10.1021/om021058k

1174
Organometallics 2003, 22, 1174-1176
Syn th esis of 1,1′-Dip h osp h a [4]fer r ocen op h a n es by
Molybd en u m -Ca ta lyzed Rin g-Closin g Meta th esis
Masamichi Ogasawara,*,† Takashi Nagano, and Tamio Hayashi*,‡
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo,
Kyoto 606-8502, J apan
Received December 31, 2002
Sch em e 1. P r ep a r a tion of
Dia llyl-1,1′-d ip h osp h a fer r ocen es 2
Summary: A variety of 1,1′-diphospha[4]ferrocenophanes
were prepared in good to moderate yield with the
interannular ring-closing metathesis reaction of diallyl-
1,1′-diphosphaferrocenes using the Schrock’s molybde-
num-carbene catalyst. The Grubbs’ ruthenium metath-
esis catalyst was found inactive for these Lewis basic
phosphorus-containing substrates.
Recently, Richards and co-workers reported a novel
synthetic method of [4]ferrocenophanes by the ring-
closing metathesis (RCM) reaction of 1,1′-diallylfer-
rocenes1 using Grubbs’ ruthenium catalyst RuCl2(dC-
HPh)(PCy3)2.2a Shortly after this report, we independently
found analogous reactions and reported that the me-
tathesis route could be applied to preparation of a
variety of bridged metallocenes of Fe(II), Ru(II), Zr(IV),
and Hf(IV).3 In the same period, Erker described ap-
plication of the RCM method for preparing ansa-
zirconocene species.4 In certain cases, the metathesis
reactions proceed in a diastereoselective fashion1,3 and
either meso- or dl-bridged metallocenes could be selec-
tively prepared with a proper choice of reaction condi-
tions and the ruthenium-carbene catalysts, RuCl2-
to give the corresponding lithium 2-allylphospholides.8c,d
Subsequent reaction of the lithium phospholides with
FeCl2 afforded diallyldiphosphaferrocenes 2.8 Because
2a -d possess two unsymmetrically substituted η5-
phospholyl ligands which are planar chiral, two dia-
stereomeric forms, meso- and dl-isomers, are possible
in theory. Among the diphosphaferrocenes used for this
study, 2c was isolated as a mixture of meso- and dl-
isomers after appropriate purification. For 2a and 2b,
the 31P NMR spectra of crude products showed existence
of the corresponding meso- and dl-isomers. One of the
two isomers, however, was selectively crystallized, and
thus meso-2a and dl-2b were isolated in diastereomeri-
cally pure forms. For 2d , the complexation of the free
phospholyl anion to the Fe(II) center proceeded in a
(dCHPh)(PCy3)2 or RuCl2(dCHPh)(PCy3)(IMes-H2).2b
2a
In this communication, we wish to report the prepara-
tion of 1,1′-diphospha[4]ferrocenophanes5 using similar
metathesis reactions of diallyldiphosphaferrocenes. For
the RCM synthesis of the diphospha[4]ferrocenophanes,
the Grubbs’ ruthenium catalyst was ineffective, but
Schrock’s molybdenum carbene complex Mo(dCHCMe2-
Ph)(dNC6H3-2,6-iPr2)(OC(CF3)2Me)26 was found to be an
active catalyst for the Lewis basic phosphorus-contain-
ing substrates.7
Synthesis of 2,2′-diallyl-1,1′-diphosphaferrocenes 2 is
illustrated in Scheme 1. P-Chlorophospholes,8 which
were prepared from 1-substituted-undeca-1,7-diyn-10-
enes (1) using zirconocene-mediated reaction reported
by Fagan and Nugent,9 were treated with lithium metal
(7) For RCM reactions of phosphorus-containing compounds, see:
(a) Leconte, M.; J ourdan, I.; Pagano, S.; Lefebvre, F.; Basset, J .-M. J .
Chem. Soc., Chem. Commun. 1995, 857. (b) Leconte, M.; Pagano, S.;
Mutch, A.; Lefebvre, F.; Basset, J .-M. Bull. Soc. Chim. Fr. 1995, 132,
1069. (c) Hanson, P. R.; Stoianova, D. S. Tetrahedron Lett. 1998, 39,
3939. (d) Bujard, M.; Gouverneur, V.; Mioskowski, C. J . Org. Chem.
1999, 64, 2119. (e) Hanson, P. R.; Stoianova, D. S. Tetrahedron Lett.
1999, 40, 3297. (f) Trevitt, M.; Gouverneur, V. Tetrahedron Lett. 1999,
40, 7333. (g) Hetherington, L.; Greedy, B.; Gouverneur, V. Tetrahedron
2000, 56, 2053. (h) Schuman, M.; Trevitt, M.; Redd, A.; Gouverneur,
V. Angew. Chem., Int. Ed. 2000, 39, 2491.
† Present address: Catalysis Research Center, Hokkaido University,
Sapporo 060-0811, J apan. E-mail: ogasawar@cat.hokudai.ac.jp.
‡ E-mail: thayashi@kuchem.kyoto-u.ac.jp.
(1) Locke, A. J .; J ones, C.; Richards, C. J . J . Organomet. Chem. 2001,
637-639, 669.
(2) Schwab, P.; Grubbs, R. H.; Ziller, J . W. J . Am. Chem. Soc. 1996,
118, 100. (b) Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Org. Lett.
1999, 1, 953.
(3) Ogasawara, M.; Nagano, T.; Hayashi, T. J . Am. Chem. Soc. 2002,
124, 9068; J . Am. Chem. Soc. 2002, 124, 12626.
(4) Hu¨erla¨nder, D.; Kleigrewe, N.; Kehr, G.; Erker, G.; Fro¨hlich, R.
Eur. J . Inorg. Chem. 2002, 2633.
(5) Recently, preparation of 1,1′-diphospha[2]ferrocenophane was
reported, see: Deschamps, E.; Ricard, L.; Mathey, F. Organometallics
2001, 20, 1499.
(8) Douglas, T.; Theopold, K. H. Angew. Chem., Int. Ed. Engl. 1989,
28, 8, 1367. (b) Westerhausen, M.; Digeser, J . H.; Gu¨ckel, C.; No¨th,
H.; Knizek, J .; Ponikwar, W. Organometallics 1999, 18, 2491. (c) Sava,
X.; Me´zailles, N.; Maigrot, N.; Nief, F.; Ricard, L.; Mathey, F.; Le Floch,
P. Organometallics 1999, 18, 4205. (d) Sava, X.; Ricard, L.; Mathey,
F.; Le Floch, P. Organometallics 2000, 19, 4899.
(9) Fagan, P. J .; Nugent, W. A. J . Am. Chem. Soc. 1988, 110, 2310.
(b) Fagan, P. J .; Nugent, W. A.; Calabrese, J . C. J . Am. Chem. Soc.
1994, 116, 1880.
(6) Schrock, R. R.; Murdzek, J . S.; Bazan, G. C.; Robbins, J .; Di Mare,
M.; O’Regan, M. J . Am. Chem. Soc. 1990, 112, 3875.
10.1021/om021058k CCC: $25.00 © 2003 American Chemical Society
Publication on Web 02/08/2003

Communications
Organometallics, Vol. 22, No. 6, 2003 1175
Ta ble 1. Molybd en u m -Ca ta lyzed Syn th esis of Br id ged 1,1′-Dip h osp h a fer r ocen esa
entry
substrate (δ 31Pb)
[2]/mol‚L-1c
[5]/mol %
temp
time/h
yield/%d
δ
31Pb
1
2
3
meso-2a (-51.3)
dl-2b (-71.8)
2.8 × 10-3
2.8 × 10-3
1.8 × 10-2
20
20
10
reflux
reflux
23 °C
48
36
15
77 (meso-3a )
51e (dl-3b)
44g (dl-3c)
39h (meso-3c)
61 (meso-3d )
33 (dl-3e)
-87.2
-55.5
-45.4
-83.8
-84.2
-43.9
-91.7
dl- and meso-2cf
(-51.9 and - 55.7)
meso-2d (-55.1)
2e (-53.0)
4
5
3.0 × 10-3
20
20
reflux
reflux
48
36
2.5 × 10-3
31 (4)
a
b
The reaction was carried out in CH2Cl2 in the presence of the molybdenum catalyst 5. Recorded in CDCl3. c Initial concentration of
the substrate. Yield of the isolated product. e The unreacted 2b was recovered in 39% yield. f dl-2c/meso-2c ) 56/44. 79% of theory.
89% of theory.
d
g
h
Sch em e 2. Mo-Ca ta lyzed RCM Rou te to
Dip h osp h a [4]fer r ocen op h a n es 3
2). Dilute conditions are important for high yield of the
intramolecular RCM products (except for the reaction
of 2c, vide infra). Under more concentrated conditions,
uncharacterized polymeric/oligomeric products were
formed to a certain extent and the yield of the diphos-
phaferrocenophanes became lower. Among the diallyl-
diphosphaferrocenes examined, 2c showed exceptionally
high reactivity; the RCM reaction of 2c was completed
in a shorter reaction time at the lower temperature with
lower catalyst loading (entry 3). In addition, the me-
tathesis reaction of 2c proceeded in an intramolecular
fashion exclusively, and no polymeric/oligomeric byprod-
ucts were detected by 31P NMR even in the reaction
carried out under the more concentrated conditions.
The diastereomeric mixture of 2c shows the 31P NMR
resonances at δ -51.9 and -55.7 with a 56:44 molar
ratio. After the RCM reaction, a pair of newly formed
diphospha[4]ferrocenophanes 3c show distinctive chemi-
cal shifts in their 31P NMR spectrum; one is at δ -45.4,
which is derived from 2c of δ -51.9, while the other is
in the far upper field region at δ -83.8, which is from
the isomer of δ -55.7. It was assumed that this unusual
upper field shift of the 31P NMR resonance for the latter
would be ascribed to an eclipsed geometry of the two
phosphorus nuclei in the diphosphaferrocenophane
which would happen in the meso-isomer. Indeed, the
X-ray crystal structure analysis clarified the isomer of
3c with the 31P NMR signal at δ -83.8 to be the meso-
isomer (Figure 1). During the metathesis reaction, no
epimerization/racemization at the planar chirality of the
η5-phospholyl ligands was detected. Thus, the stereo-
chemistry of the other diallylphosphaferrocenes 2 and
diphospha[4]ferrocenophanes 3 was assigned on the
basis of the 31P NMR chemical shifts of the RCM
products 3; 2a /3a and 2d /3d were determined to be
meso-isomers, while 2b/3b were assigned to be dl-
isomers.
diastereoselective manner, and meso-2d was obtained
as a single diastereomer.
The obtained diphosphaferrocene 2a was examined
as a potential substrate for the ring-closing metathesis
reaction based on our previous report.3 That is, 2a was
reacted with 3 mol % of RuCl2(dCHPh)(PCy3)2 in
refluxing dichloromethane for 24 h. However, no reac-
tion was observed and the substrate 2a was recovered
in >90% yield. Considering the reported mechanistic
study on the Ru-catalyzed metathesis reaction, which
claims that a critical process for the Ru-catalyzed
metathesis reaction is initial dissociation of one of the
PCy3 ligands from RuCl2(dCHPh)(PCy3)2 giving a 14e-
species,10 the diphosphaferrocene 2a probably deacti-
vated the Ru catalyst by coordinating to the ruthenium
center. The second-generation Grubbs’ catalysts with
imidazolylidene or dihydroimidazolylidene were also
found inactive for the RCM of 2a . We then turned our
attention to Schrock’s molybdenum-carbene complex
Mo(dCHCMe2Ph)(dNC6H3-2,6-iPr2)(OC(CF3)2Me)2 (5).6
As we expected, transformation of 2a into the corre-
sponding 1,1′-diphospha[4]ferrocenophane 3a was ef-
ficiently catalyzed by 20 mol % of the molybdenum
complex 5 (Scheme 2). Thus, a mixture of 2a (50 mg,
110 µmol) and 5 (17 mg, 22 µmol) was dissolved in CH2-
Cl2 (40 mL) and the solution was heated to reflux. The
substrate 2a was completely consumed in 48 h, and 35
mg of 3a (77% yield) was isolated as a bright red
crystalline solid by silica gel chromatography under
nitrogen (Table 1, entry 1). The results of the Mo-
catalyzed RCM reactions of the diallyl-1,1′-diphospha-
ferrocenes are summarized in Table 1. In most cases,
the reactions proceeded smoothly to give the corre-
sponding bridged diphosphaferrocenes in good to mod-
Two independent molecules of slightly different con-
formations are present in the asymmetric unit of meso-
3c (see Supporting Information for details). The X-ray
crystal structure of one of the two molecules of meso-3c
is shown in Figure 1 with selected bond lengths and
angles.11 The two η5-phospholyl moieties are nearly
eclipsed. Because of the C4-bridge, the phosphaferrocene
(11) Crystallographic data for C32H32P2Fe: MW ) 534.40; triclinic;
space group P1h; a ) 14.454(5) Å, b ) 14.801(5) Å, c ) 12.657(4) Å,
R ) 109.6992)°, â ) 97.07(3)°, γ ) 91.86(3)°; V ) 2522.2(2) Å3; Z ) 4;
d ) 1.407 g/cm3; µ ) 7.44 cm-1; F(000) ) 1120.00; crystal dimensions
0.30 × 0.20 × 0.20 mm; 15 265 total reflections collected (I > 3σ(I)),
goodness of fit on F 2.36; R ) 0.057; Rw ) 0.083; maximum/minimum
residual density 1.08/-0.90 e/Å3. Data were collected on a Rigaku
AFC7S diffractometer with graphite-monochromated Mo KR radiation
(λ ) 0.71069 Å). Full details of the crystallographic analysis are
described in the Supporting Information.
t
erate yield. The reaction of 2b, which is with bulky Bu
substituents, was slow, and 39% of the unreacted 2b
was recovered in 36 h with 51% of the bridged 3b (entry
(10) Dias, E. L.; Nguyen, S. T.; Grubbs, R. H. J . Am. Chem. Soc.
1997, 119, 3887.

1176 Organometallics, Vol. 22, No. 6, 2003
Communications
Sch em e 3. Mo-Ca ta lyzed RCM Rea ction of
Tetr a a llyl-1,1′-d ip h osp h a fer r ocen e 2e
tively. Single-bridged meso-3e was not detected in the
reaction mixture. A corollary of this observation is that
the initially formed meso-3e is more reactive than 2e.
Two remaining allyl substituents in meso-3e are forced
to occupy an eclipsed position because of the restricted
rotation of the η5-phospholyl ligands, and thus a second
RCM reaction proceeds rapidly to give 4. As expected,
the double-bridged diphosphaferrocenophane 4, in which
the two phosphorus atoms are eclipsed, shows its 31P
NMR resonance in the high-field region at δ -91.7.
In summary, we have established that the RCM route
of preparing [4]ferrocenophanes could be applied to
preparation of diphosphaferrocene analogues by using
Schrock’s molybdenum carbene complex as a catalyst.
The dl- and meso-isomers of the diphospha[4]ferroceno-
phanes are easily distinguished by their 31P NMR
spectra, in which the latter show the unusual high-field
shift of the resonances.
F igu r e 1. ORTEP drawing of meso-3c with 30% thermal
ellipsoids. Selected bond lengths (Å) and angles (deg):
C(4)-C(15) ) 1.519(8), C(15)-C(16) ) 1.505(9), C(16)-
C(17) ) 1.28(1), C(17)-C(18) ) 1.513(9), Fe(1)-phos-
pholylP(1) ) 1.671(5), Fe(1)-phospholylP(2) ) 1.668(5), C(1)-
P(1)-C(4) ) 89.4(3), C(19)-P(2)-C(22) ) 89.4(3), C(4)-
C(15)-C(16) ) 114.7(5), C(15)-C(16)-C(17) ) 124.4(6),
C(16)-C(17)-C(18) ) 124.9(6), C(17)-C(18)-C(19) )
112.4(6).
framework is slightly distorted, the dihedral angle of
the two phospholyl ligands being 6.4°, which is within
the range of those found in the analogous [4]ferro-
cenophanes.3 The two phenyl substituents are nearly
parallel to each other (7.6° dihedral angle), and π-π
stacking interaction can be seen between them. It is
expected that there is similar π-π attraction between
the two phenyl groups in the nonbridged 2c. The π-π
attraction between the phenyl groups puts the two allyl
groups in 2c in close proximity, assisting the RCM
reaction. The high reactivity and the tendency of
undergoing intramolecular RCM cyclization of 2c can
be ascribed to the π-π attraction.
Ack n ow led gm en t. This work was supported by a
Grant-in-Aid for Scientific Research (the Ministry of
Education, J apan) and the Asahi Glass Foundation (to
M.O.).
Su p p or tin g In for m a tion Ava ila ble: Detailed experi-
mental procedures, compound characterization data, and
crystallographic data for meso-3c. This material is available
free of charge via the Internet at http://pubs.acs.org.
As shown in Scheme 3, the tetraallyldiphosphafer-
rocene 2e gave two RCM products with small amounts
of uncharacterized polymeric/oligomeric products (Table
1, entry 5). The two RCM products were characterized
as single-bridged dl-3e and double-bridged 4, respec-
OM021058K