Synthesis of molybdenocene(IV) and tungstenocene(IV) tropolonato complexes: Its derivative containing calix[4]arene moiety

Article abstract of DOI:10.1016/j.jorganchem.2005.07.118

The cationic di-μ-hydroxo dinuclear complexes of molybdenocene and tungstenocene [Cp₂M(μ-OH)₂MCp₂]⁺ (Cp = η-C₅H₅; M = Mo or W) react with tropolone to afford corresponding tropolonato complexes [Cp₂M(trop)]⁺ (trop = C₇H₅O₂). The products were investigated by IR, ¹H NMR, and ¹³C NMR spectroscopy as well as by X-ray crystallography (M = W). The structure shows that the central metal is surrounded by a distorted tetrahedral array of the two centers of cyclopentadienyl ligands and the two oxygen atoms of tropolonato ligand. The reaction has been extended to the synthesis of calix[4]arene receptor functionalized at the 1,3-positions of the upper rim with two tropolonato-molybdenocene centers.

Full text of DOI:10.1016/j.jorganchem.2005.07.118

Journal of Organometallic Chemistry 691 (2006) 282–286
www.elsevier.com/locate/jorganchem
Synthesis of molybdenocene(IV) and tungstenocene(IV)
tropolonato complexes: Its derivative containing calix[4]arene moiety
a,
b
a
a
a
Makoto Minato *, Jian-Guo Ren , Masahiko Kasai , Koji Munakata , Takashi Ito
a
Department of Materials Chemistry, Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku,
Yokohama 240-8501, Japan
b
Department of Chemistry, Shanxi University, Taiyuan 030006, China
Received 7 June 2005; received in revised form 19 July 2005; accepted 21 July 2005
Available online 14 October 2005
Abstract
The cationic di-l-hydroxo dinuclear complexes of molybdenocene and tungstenocene [Cp2M(l-OH)2MCp2]+ (Cp = g-C5H5;
M = Mo or W) react with tropolone to afford corresponding tropolonato complexes [Cp2M(trop)]+ (trop = C7H5O2). The products were
1
investigated by IR, H NMR, and 13C NMR spectroscopy as well as by X-ray crystallography (M = W). The structure shows that the
central metal is surrounded by a distorted tetrahedral array of the two centers of cyclopentadienyl ligands and the two oxygen atoms of
tropolonato ligand. The reaction has been extended to the synthesis of calix[4]arene receptor functionalized at the 1,3-positions of the
upper rim with two tropolonato-molybdenocene centers.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Molybdenocene; Tungstenocene; Tropolone; Calix[4]arene
1. Introduction
ited interesting reactivity patterns leading to new chemis-
try. For example, they reacted with tertiary phosphines in
alcoholic solvents to yield novel alkoxo complexes
[Cp2M(PR3)(R0O)]+ [3b]. It occurred to us that these di-
l-hydroxo dinuclear complexes might be useful precursors
for the molybdenocene and tungstenocene tropolonato
complexes. Although there are many molybdenum and
tungsten tropolonato complexes [4], none has been re-
ported on complexes also containing a Cp ligand.
Tropolonato ligand ðC7H5Oꢀ; tropÞ, which is known to
2
form a series of chelate complexes with metal ions, is the
seven-membered ring analogue of the benzenoid catecho-
lato ligand [1]. Tropolonato complexes are also broadly
similar to analogous b-diketonato complexes, although
there are often very significant differences [2]. In compari-
son with catecholato or b-diketonato complexes relatively
little information is available regarding the chemistry of
the tropolonato complexes. In the course of our studies
on the chemistry of metallocene derivatives of the group
6 transition metals, we decided to make molybdenocene
and tungstenocene tropolonato complexes.
2. Results and discussion
2.1. Synthesis of molybdenocene(IV) and
tungstenocene(IV) tropolonato complexes
We have previously described the preparation of the cat-
ionic di-l-hydroxo dinuclear complexes of molybdenocene
and tungstenocene [Cp2M(l-OH)2MCp2]+ (Cp = g-C5H5;
M = Mo (1a) or W (1b)) [3]. These complexes have exhib-
The reactions of 1 with tropolone under argon in meth-
anol at 50 ꢁC for 5 h afforded the tropolonato complexes
(M = Mo (2a), W (2b)) in almost quantitative yields
(Scheme 1). The resulting complexes were not soluble in
a non-polar solvent, such as benzene or toluene, but solu-
ble in methanol and DMSO. They were found to be stable
*
Corresponding author. Fax: +81 45 339 3933.
E-mail address: minato@ynu.ac.jp (M. Minato).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.07.118

M. Minato et al. / Journal of Organometallic Chemistry 691 (2006) 282–286
283
104.9 ppm. The spectrum of complex 2b is almost identical
to those of 2a, supporting the analogous structure as 2a.
The molecular structure of 2b was fully confirmed by
single-crystal X-ray analysis. Dark-red crystals suitable
for X-ray analysis were obtained by recrystallization from
acetone–hexane. The view of the molecular geometry of the
cation is shown in Fig. 1. The more important bond lengths
and bond angles are given in Table 2. A summary of the
crystallographic data is given in Table 3 (see Section 3).
The molecular structure is a neat and simple one; 2b has
geometry typical of bent metallocene. The tropolonato li-
gand exhibits an essentially planar seven-membered ring
Scheme 1.
˚
(mean deviation of the ring atom is 0.017 A). The cyclopen-
tadienyl rings lie above and below this plane. The structure
can be compared with that of the parent tropolone [5] and
complex 1b [3b]. The C–C bond distances for trop ring
to air both in the solid state and in solution. In Table 1, se-
lected spectroscopic data for the complexes 2a,b are col-
lected. The IR spectra of these complexes show a m(C@O)
stretch band at around 1340 cmꢀ1. In the 1H NMR
(CD3OD) spectrum of 2a, besides the singlet signal due
to Cp protons at d 5.89, doublet of doublets (d = 7.67,
2H, J = 10.4, 10.4 Hz, H-4,6), doublet (d = 7.44, 2H,
J = 10.4 Hz, H-3,7), and doublet of doublets (d = 7.37,
1H, J = 10.4, 10.4 Hz, H-5) signals are, respectively, ob-
served. The 13C NMR spectrum of 2a contains four signals
assigned to the tropolonato carbons between 120 and
190 ppm together with the Cp carbon signal at
˚
average 1.395 A, which is compatible with that of the par-
˚
ent tropolone (1.395 A). The W–O bond lengths are nearly
˚
equivalent (2.076(3) and 2.092(3) A). The internal ring an-
gle is O2–W1–O1 = 74.7(1)ꢁ. The C–O bond lengths are
˚
˚
found to average 1.304 A, which is ca. 0.04 A longer than
the C@O double bond length in the parent tropolone but
˚
only slightly shorter than the C–OH single bond (1.333 A).
The average C–C bond distance for the Cp rings in 2b
˚
(1.396 A) is comparable to the average C–C bond distance
Table 1
Selected spectroscopic data for [Cp2M(trop)]+ (M = Mo (2a) and W (2b))
Complexes
1H NMR/ppm
13C NMR/ppm
d (trop)
d (Cp)
d (trop)
2a
7.67 (dd, 2H, J = 10.4, 10.4, H-4,6)
7.44 (d, 2H, J = 10.4, H-3,7)
7.37 (dd, 1H, J = 10.4, 10.4, H-5)
5.89 (s, 10H)
186.5 (C-1,2)
141.2 (C-3,7)
132.5 (C-5)
129.8 (C-4,6)
189.2 (C-1,2)
141.5 (C-3,7)
133.6 (C-5)
2b
7.74 (dd, 2H, J = 10.4, 10.4, H-4,6)
7.57 (d, 2H, J = 10.4, H-3,7)
7.45 (dd, 1H, J = 10.4, 10.4, H-5)
5.90 (s, 10H)
129.7 (C-4,6)
Fig. 1. Molecular structure of 2b.

284
M. Minato et al. / Journal of Organometallic Chemistry 691 (2006) 282–286
Table 2
At present, the structure of 2a remains somewhat
˚
Interatomic distances (A) and angles (ꢁ) for 2b
ambiguous, as no crystals suitable for X-ray diffraction
1
are available. However the similarity of the H and 13C
Distances
W1–O1
W1–C8
W1–C10
W1–C12
W1–C14
W1–C16
O1–C1
C1–C2
C2–C3
C4–C5
C6–C7
2.076(3)
2.268(4)
2.374(4)
2.249(4)
2.272(5)
2.353(5)
1.301(4)
1.402(5)
1.374(6)
1.383(8)
1.399(5)
1.424(6)
1.420(7)
1.43(1)
W1–O2
W1–C9
W1–C11
W1–C13
W1–C15
W1–C17
O2–C7
C1–C7
C3–C4
C5–C6
C8–C9
2.092(3)
2.372(4)
2.271(4)
2.233(5)
2.311(5)
2.290(5)
1.306(5)
1.444(5)
1.376(7)
1.389(6)
1.398(6)
1.395(7)
1.437(7)
1.45(1)
NMR spectra of 2a and 2b, along with the combustion
analysis strongly suggests that 2a and 2b have similar
structures.
2.2. Synthesis of a photosensitive calix[4]arene-based
molybdenocene
It occurred to us that the cationic center of these com-
plexes might interact with anions and neutral electron-rich
molecules. We have envisioned that these complexes can be
assembled to create new hybrid materials, when properly
functionalized. Thus, we decided to incorporate the cat-
ionic component into a calix[4]arene framework. A number
of calix[4]arenes carrying a wide variety of groups on the
upper and lower rims have been prepared in the last dec-
ade. When appropriately modified they provide attractive
platform to which to attach ligating moieties for transition
metal centers [6]. The scope of calix[4]arenes chemistry is
expected to be extended dramatically by incorporation of
metallic centers into the peripheral sites [7,8].
C8–C12
C10–C11
C13–C14
C14–C15
C9–C10
C11–C12
C13–C17
C15–C16
1.357(9)
1.319(9)
Angles
O1–W1–O2
W1–O1–C1
O1–C1–C2
O2–C7–C6
C3–C4–C5
C2–C1–C7
C4–C5–C6
74.7(1)
118.3(2)
118.5(4)
118.2(4)
127.7(4)
126.8(3)
129.3(4)
W1–O2–C7
O2–C7–C1
O1–C1–C7
C5–C6–C7
C2–C3–C4
C1–C2–C3
C1–C7–C6
117.7(2)
114.4(3)
114.7(3)
129.1(5)
130.4(4)
129.0(4)
127.4(4)
The new calixarene-tropolonato–molybdenocene com-
plex has been prepared according to Scheme 2. The molyb-
denocene-tropolonato groups are linked to the upper rim
via photoactive azo spacers in order to change the prop-
erties of the resulting calixarene in response to light.
Literature preparations were used to obtain the required
de-tert-butylated calix[4]arene 3 [9]. The reaction of 3 with
methyl p-toluenesulfonate in the presence of K2CO3 gave
1,3-dimethoxy-calix[4]arene 4 in 93% yield [10]. These
methyl groups were used since their conformational influ-
ence on the calixarene was predictable [11]. Preparation
of the tropolone-diazonium compound 5 was carried out
by using the method of Nozoe [12]. Reaction of 4 with
an excess of the diazonium salt, according to the method
of Taniguchi and co-workers [13], gave 6 in 53% yield.
The reaction of 6 with 1a proceeded in similar fashion as
tropolone and resulted in the formation of the desired
Table 3
Summary of crystal data for 2b
Empirical formula
Formula weight
Temperature
Crystal dimensions
Crystal system
Space group
C25.50H25O5.50SW (2b Æ 1/2acetone)
635.38
23 ꢁC
0.40 · 0.32 · 0.20 mm
monoclinic
C2/c (# 15)
C-centered
Lattice type
Lattice parameters
˚
a (A)
15.15(1)
10.62(1)
30.68(1)
106.34(5)
4739(7)
8
1.781 g/cm3
2496.00
50.06 cmꢀ1
˚
b (A)
˚
c (A)
b (ꢁ)
3
˚
V (A )
Z value
Dcalcd
F(000)
l(Mo Ka)
No. of reflections used for unit cell 14 (25.1–29.9ꢁ)
determination (2h range)
2h max
Scan rate
55.0ꢁ
8.0ꢁ/min (in x) (up to 9 scans)
No. of reflections measured
Total
5941
Unique
5722 (Rint = 0.014)
4529
0.024; 0.037
0.99
No. observations (I > 3.00r(I))
Residuals: R; Rw
GOF
˚
in 1b (1.392 A). The average metal–Cp ring carbon dis-
˚
tances in 2b is 2.299 A, which is slightly shorter than the
˚
2.326 A found in 1b. The internal C–C–C ring angles in
2b range from 102.2ꢁ to 111.1ꢁ, which are compared favor-
ably with the expected internal angle, 108ꢁ, for a planar
pentagon.
Scheme 2.

M. Minato et al. / Journal of Organometallic Chemistry 691 (2006) 282–286
285
1
compound 7. Resulting 7 exhibits marked air stability. H
NMR pattern for the ArCH2Ar methylene protons of 7
showed the two pairs of doublets (d 4.25 and 3.70,
J = 13.5 Hz), indicating a cone conformation [14].
UV–Vis spectra of the free (compound 6) and the metal
complexed ligand (compound 7) in pyridine are shown in
Fig. 2.
The spectrum of 6 is characterized by the presence of
one absorption maximum at around 420 nm; this value is
closely similar to published data on 4-arylazo-1-naphthols
[15] and p-nitrophenylazo-substituted calix[4]arenes [16],
suggesting that 6 exists as the azo form. Complexation with
cationic molybdenocene resulted in a large change in the
absorption spectrum. The band at 420 nm decreased con-
siderably and shifted to 470 nm; this shift can be attributed
to the formation of the hydrazone form [15]. The present
result is compatible with the study of Kishimoto and co-
workers [17], who reported that, in tautomerism of 4-(40-
substituted-phenylazo)-1-naphthol [azo form vs. hydrazone
form], the hydrazone form predominates with electron-
withdrawing substituents. In addition to the band at
470 nm, a new peak at longer wavelength (720 nm) ap-
peared. The remarkable red shift of the band of 7 can be
ascribed to the lengthening of the conjugated system in
the diimine form [17]. Thus, in pyridine the hydrazone
form 7A and the diimine form 7B are in equilibrium
(Scheme 3). In methanol, a sole band appeared at around
460 nm, ascribable to the hydrazone form 7A; the longer
wavelength absorption (ꢁ720 nm) due to the diimine form
7B was virtually negligible. These results indicate that the
equilibrium between 7A and 7B is strongly dependent on
the property of media.
Scheme 3.
3. Experimental section
3.1. General procedures
Unless otherwise noted, all manipulations were con-
ducted using standard Schlenk techniques under purified
argon or nitrogen. Commercially available reagent grade
chemicals were used as such without any further purifica-
tion. All solvents were dried by standard methods and were
stored under argon. The synthesis of 1 was presented in a
previous paper [3b].
3.2. Synthesis of [Cp2 M(trop)]+ OTsꢀ (M = Mo (2a),
W (2b))
Tropolone (0.060 g, 0.49 mmol) was added to a slurry of
1a (0.070 g, 0.085 mmol) in 5 mL of methanol. The result-
ing mixture was heated at 50 ꢁC for 5 h to yield a dark-red
solution. The solvent was removed in vacuo, and the resi-
due was washed with hexane and ether. The crude product
was extracted with acetone (20 mL) and then 20 mL of hex-
ane was added. On standing at 0 ꢁC, 2a precipitated as
dark-red crystals (96%). Anal. Calcd for C24H22O5SMo:
C, 55.60; H, 4.28. Found: C, 55.44; H, 4.29%. The tungsten
complex 2b could likewise be obtained as dark-red crystals
(98%).
3.3. Synthesis of 6
To a cold suspension (ice bath temperature) of 5-amino
tropolone (0.501 g, 3.65 mmol) in aqueous 1,4-dioxane
(50%, 8 mL) was added dropwise sulfuric acid (0.6 mL),
then a solution of NaNO2 (0.327 g, 4.74 mmol) in water
(1.2 mL) affording a solution of 5. The reaction of 4 with
NaH was carried out in a separate flask. 4 (0.403 g,
0.891 mmol) suspended in DMF (25 mL) was stirred at
room temperature. NaH (60% oil, 0.399 g, 9.98 mmol)
was added to the flask to dissolve 4, forming a clear homo-
geneous solution. After cooling to 0 ꢁC, to the resulting
solution was added dropwise the aforementioned tropo-
lone-diazonium solution (the temperature was held at 0
to 5 ꢁC to avoid a side reaction). After addition was
complete, the solution was allowed to warm to room
Fig. 2. Absorption spectra of 6 and 7 in pyridine (4 · 10ꢀ5 M).

286
M. Minato et al. / Journal of Organometallic Chemistry 691 (2006) 282–286
temperature and was kept at this temperature for 2 h. The
resulting mixture was adjusted to pH 3.0 by addition of di-
lute HCl and then heated with stirring at 60 ꢁC for 30 min.
Water (40 mL) was added and the resulting precipitate was
repeatedly washed with water and methanol. The dried
crude product was washed with CH2Cl2 and was reprecip-
itated with DMSO-methanol; yield: 0.355 g (53%). IR
(KBr) 3211, 2933, 1709, 1615, 1557, 1469, 1350, 1297,
3.6. UV–Visible spectral measurements
UV–Visible spectra were recorded at room tempera-
ture in a 1-cm quartz cell by using a JASCO V-550
spectrophotometer. Absolute pyridine was used as the
solvent.
Acknowledgements
1
1262, 1210 cmꢀ1; H NMR (DMSO-d6, 20 ꢁC) d 8.04 (d,
4H, J = 11.9 Hz, COCHCH and COHCHCH in the trop-
olone), 7.84 (s, 4H, ArH in the azophenyl moiety), 7.37
(d, 4H, J = 11.9 Hz, COCHCH and COHCHCH in the
tropolone), 7.11 (d, 4H, J = 7.5 Hz, ArH in the methoxy-
phenyl moiety), 6.82 (t, 2H,J = 7.5 Hz, ArH in the meth-
oxyphenyl moiety), 4.24 (d, 4H, J = 12.9 Hz, ArCH2Ar),
3.94 (s, 6H, OCH3), 3.68 (d, 4H, J = 12.9 Hz, ArCH2Ar).
We are grateful to Dr. Mikio Yamasaki of Rigaku
Corporation for an X-ray structure analysis. We grate-
fully acknowledge Professor Yasushi Yokoyama of
Yokohama National University for UV–Vis measure-
ments. We sincerely thank Dr. Takeharu Haino of Hiro-
shima University for helpful and stimulating discussions
on the synthesis of 7. We also thank Dr. Masako Tanaka
of Tokyo Institute of Technology for the elemental
analysis.
3.4. Synthesis of 7
A suspension of 1a (0.159 g, 0.192 mmol) and 6 (0.144 g,
0.192 mmol) in methanol (28 mL) was heated with stirring
at 50 ꢁC for 5 h. After filtration under argon and subse-
quent removal of the solvent under reduced pressure, the
black residue was repeatedly washed with ether to yield 7
(0.160 g, 54%). IR (KBr) 3105, 2925, 1656, 1593, 1557,
References
[1] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, Wiley,
New York, 1988, p. 481.
[2] (a) W.P. Griffith, C.A. Pumphery, A.C. Skapski, Polyhedron 6
(1987) 891;
(b) G. Doyle, J. Organomet. Chem. 132 (1977) 243.
[3] (a) J.-G. Ren, H. Tomita, M. Minato, K. Osakada, T. Ito, Chem.
Lett. (1994) 637;
1
1436, 1348, 1299, 1268, 1190 cmꢀ1; H NMR (DMSO-d6,
20 ꢁC) d 8.22 (d, 4H, J = 12.2 Hz, COCHCH in the tropo-
lone), 7.88 (s, 4H, ArH in the azophenyl moiety), 7.56 (d,
4H, J = 12.2 Hz, COCHCH in the tropolone), 7.11 (d,
4H, J = 7.4 Hz, ArH in the methoxyphenyl moiety), 6.82
(t, 2H,J = 7.4 Hz, ArH in the methoxyphenyl moiety),
6.02 (s, 20H, Cp rings), 4.25 (d, 4H, J = 13.5 Hz, ArCH2-
Ar),3.97(s,6H,OCH3),3.70(d,4H,J = 13.5 Hz,ArCH2Ar).
Resonances due to the TsO groupꢀs protons are omitted
throughout. Both 6 and 7 are only soluble in polar solvents
such as DMSO and pyridine. At present, no samples
suitable for combustion analyses are available [18].
(b) J.-G. Ren, H. Tomita, M. Minato, T. Ito, K. Osakada, M.
Yamasaki, Organometallics 15 (1996) 852.
[4] See for example, S. Takekuma, K. Tomoda, M. Sasaki, T. Minem-
atsu, H. Takekuma, Bull. Chem. Soc. Jpn. 77 (2004) 1935.
[5] H. Shimanouchi, Y. Sasada, Acta Cryst. B29 (1973) 81.
[6] (a) C. Wieser, C.B. Dielman, D. Matt, Coordin. Chem. Rev. 165
(1997) 93;
(b) C.B. Dieleman, D. Matt, P.G. Jones, J. Organomet. Chem. 545–
546 (1997) 461.
[7] P.D. Beer, D. Hesek, K.C. Nam, M.G.B. Drew, Organometallics 18
(1999) 3933.
[8] M. Staffilani, K.S.B. Hancock, J.W. Steed, K.T. Holman, J.L.
Atwood, R.K. Juneja, R.S. Burkhalter, J. Am. Chem. Soc. 119 (1997)
6324.
3.5. X-ray crystal structure analysis of 2b
[9] C.D. Gutsche, L. Lin, Tetrahedron 42 (1986) 1633.
[10] J.D. Loon, A. Arduini, A. Coppi, W. Verboom, A. Pochini, R.
Ungaro, S. Harkenna, D.N. Reinhoudt, J. Org. Chem. 55 (1990)
5639.
[11] L.C. Groenen, E. Steinwender, B.T.G. Lutz, J.H. van der Maas,
D.N. Reinhoudt, J. Chem. Soc., Perkin Trans. II (1992) 1893.
[12] T. Nozoe, S. Seto, S. Ebina, S. Ito, J. Am. Chem. Soc. 73 (1951)
1895.
A simple crystal of 2b was grown from an acetone–hex-
ane solution in a fridge, and was mounted on a glass fiber.
All measurements were made on a Rigaku AFC-7R diffrac-
˚
tometer by using Mo Ka radiation (k = 0.71069 A) with
l = 50.06 cmꢀ1 and F(000) = 2496.00 A. The unit-cell
˚
[13] Y. Morita, T. Agawa, E. Nomura, H. Taniguchi, J. Org. Chem. 57
(1992) 3658.
[14] D.R. Stewart, C.D. Gutsche, J. Am. Chem. Soc. 121 (1999) 4136.
[15] E. Fischer, Y.F. Frei, J. Chem. Soc. (1953) 3159.
[16] S. Shinkai, K. Araki, J. Shibata, D. Tsugawa, O. Manabe, J. Chem.
Soc., Perkin Trans. I (1990) 3333.
[17] S. Kishimoto, S. Kitahara, O. Manabe, H. Hiyama, J. Org. Chem. 43
(1978) 3882.
[18] (a) Problems associated with microanalysis of calixarenes have been
previously reported, V. Bo¨hmer, K. Jung, M. Scho¨n, A. Wolff, J.
Org. Chem. 57 (1992) 790;
parameters were obtained from a least-squares refinement
using the setting angles of 14 carefully centered reflections
in the range 25.1ꢁ 6 2h 6 29.9ꢁ. The parameters used dur-
ing the collection of diffraction data are given in Table 3.
The structure was solved and expanded by using Fourier
techniques. The non-hydrogen atoms were refined aniso-
tropically. Hydrogen atoms were included but not refined.
CCDC reference number 270365. See http://www.rsc.
org/suppdata/dt/b2/b209624m/ for crystallographic data
in CIF or other electronic format.
(b) C.D. Gutsche, K.A. See, J. Org. Chem. 57 (1992) 4527.