Novel metallacycle complexes from bis(oxazolinyl)pyridine-rhodium(I) species and diynes

Article abstract of DOI:10.1021/om0202221

A study was performed on novel metallacycle complexes from bis(oxazolinyl)pyridine-rhodium(I) species and diynes. The complexes were analyzed using x-ray crystallography and showed the catalytic activity for cycloaddition of diynes and several alkynes. It was found that the complexes had an octahedral configuration with the rhodacyclopentadiene skeleton.

Full text of DOI:10.1021/om0202221

2572
Organometallics 2002, 21, 2572-2574
Communications
Novel Meta lla cycle Com p lexes fr om
Bis(oxa zolin yl)p yr id in e-Rh od iu m (I) Sp ecies a n d Diyn es
Hisao Nishiyama,* Eiko Niwa, Tomohiro Inoue, Yosuke Ishima, and
Katsuyuki Aoki
School of Materials Science, Toyohashi University of Technology, Tempaku-cho, Toyohashi,
Aichi, 441-8580 J apan
Received March 25, 2002
Summary: The reaction of [Rh(coe)2Cl]2 (coe ) cis-
cyclooctene), bis(oxazolinyl)pyridine (pybox), and diynes
(O(CH2CtCCO2Me)2 and PhCtCCH2OCH2CtCCO2-
Me) gave new types of metallacycle complexes, which
were analyzed by X-ray crystallography and showed
catalytic activity for cycloaddition of diynes and several
alkynes.
The reaction of pybox-dh and [Rh(coe)2Cl]2 (2:1 mol
ratio) with the diyne 1 was carried out in an absolute
tetrahydrofuran (THF) solution at 25-30 °C for 17 h.
Chromatographic separation of the reaction residue
gave thermally stable orange solids, which proved to be
the corresponding rhodacycle complex 2, in 68% yield
(Scheme 1).6 Structural elucidation of 2 was performed
by NMR spectroscopy and X-ray crystallographic analy-
sis (Figure 1). The complex 2 has an octahedral config-
uration with the rhodacyclopentadiene skeleton, where
the two carbon atoms (C1 and C4) are located at an
equatorial position and an axial position, respectively.
The rhodacycle moiety also proved to be a typical
metallacyclopentadiene,1b-d not a metallacyclopen-
tatriene, as postulated for some ruthenium complexes:7
2.0 Å, Rh-C1; 1.34 Å, C1-C2; 1.44 Å, C2-C3; 1.35
Å, C3-C4; 2.04 Å, C4-Rh; 80.5°, C1-Rh-C4.1b-d The
two methoxycarbonyl groups of 2 are located just
filling the spaces over the pybox plane and by the
side of the chloride atom, respectively. Accordingly,
Metallacycle complexes have been intensively studied
as important intermediates for the cyclotrimerization
of alkynes and/or diynes in terms of mechanistic view
and discovery of new efficient catalysts.1-3 In the course
of our research on nitrogen-based ligands and catalytic
reactions with their transition-metal complexes,4 we
found that the oxidative addition reaction of alkyl
chlorides (e.g. CH2Cl2 and ClCH2CO2Me) to pybox-RhI-
Cl species generated in situ from pybox and [Rh-
(coe)2Cl]2 proceeds to form stable pybox-RhIII-alkyl
complexes.5a In this context, the existence of such
rhodium(I) species with certain tridentate nitrogen
ligands (κ3-N,N,N type) has recently been proved by
isolation and X-ray analysis by other chemists.3b,c,h On
the basis of these findings, we thought that diynes could
add to the in situ pybox-RhICl species to oxidatively
cyclize and to give new types of metallacycles, pybox-
rhodacyclopentadienes.
(3) For metallacycles of other transition metals, see the following.
For Ir: (a) Collman, J . P.; Kang, J . W.; Little, W. F.; Sullivan, M. F.
Inorg. Chem. 1968, 7, 1298. (b) Rappoli, B. J .; Churchill, M. R.; J anik,
T. S.; Rees, W. M.; Atwood, J . D. J . Am. Chem. Soc. 1987, 109, 5145.
(c) O’Connor, J . M.; Pu, L.; Rheingold, A. L. J . Am. Chem. Soc. 1990,
112, 6232. (d) Bianchini, C.; Caulton, K. G.; Chardon, C.; Doublet, M.-
L.; Eisenstein, O.; J ackson, S. A.; J ohnson, T. J .; Meli, A.; Peruzzuni,
M.; Streib, W. E.; Vacca, A.; Vizza, F. Organometallics 1994, 13, 2010.
(e) O’Connor, J . M.; Merwin, R.; Rheingold, A. L.; Adams, M. L.
Organometallics 1995, 14, 2102. (f) Field, L. D.; Ward, A. J .; Turner,
P. Aust. J . Chem. 1999, 52, 1085. (g) O’Connor, J . M.; Closson, A.;
Hiibner, K.; Merwin, R.; Gantzel, P.; Roddick, D. M. Organometallics
2001, 20, 3710. (h) O’Connor, J . M.; Closson, A.; Gantzel, P. J . Am.
Chem. Soc. 2002, 124, 2434. The related cyclotrimerization: (i)
Takeuchi, R.; Tanaka, S.; Nakaya, Y. Tetrahedron Lett. 2001, 42, 2991.
For Ni: (j) Sato, Y.; Nishimata, T.; Mori, M. J . Org. Chem. 1994, 59,
6133. (k) Sato, Y.; Ohashi, K.; Mori, M. Tetrahedron Lett. 1999, 40,
5231. (l) Mori, N.; Ikeda, S.; Odashima, K. Chem. Commun. 2001, 181.
For Pd: (m) Yamamoto, Y.; Nagata, A.; Itoh, K. Tetrahedron Lett. 1999,
40, 5035. For Ru: (n) Yamamoto, Y.; Ogawa, R.; Itoh, K. Chem.
Commun. 2000, 549. (o) Witulski, B.; Stengel, T.; Ferna´ndez-Herna´n-
dez, J . M. Chem. Commun. 2000, 1965.
(4) (a) Nishiyama, H.; Itoh, Y.; Sugawara, Y.; Matsumoto, H.; Park,
S.-B.; Itoh, K. Bull. Chem. Soc. J pn. 1995, 68, 1247. (b) Nishiyama,
H.; Naitoh, T.; Motoyama, Y.; Aoki, K. Chem. Eur. J . 1999, 5, 3509.
(c) Iwasa, S.: Takezawa, F.; Tuchiya, Y.; Nishiyama, H. Chem.
Commun. 2001, 59. (d) Iwasa, S.; Tsushima, S.; Shimada, T.; Nish-
iyama, H. Tetrahedron 2002, 58, 227.
(5) (a) Nishiyama, H.; Horihata, M.; Hirai, T.; Wakamatsu, S.; Itoh,
K. Organometallics 1991, 10, 2706. Related papers for tridentate
nitrogen-ligand-Rh(I) species: (b) Haarman, H. F.; Ernsting, J . M.;
Kranenburg, M.; Kooijman, H.; Veldman, N.; Spek, A. L.; van Leeuwen,
P. W. N. M.; Vrieze, K. Organometallics 1997, 16, 887. (c) Nu¨ckel, S.;
Burger, P. Organometallics 2001, 20, 4359.
(1) For rhodacyclopentadienes and rhodium-catalyzed cyclotrimer-
ization of alkynes, see the following. Review: (a) Mu¨ller, E. Synthesis
1974, 761. The related rhodacycles: (b) Igresias, M.; del Pino, C.; Ros,
J .; Blanco, S, G.; Carrera, S. M. J . Organomet. Chem. 1988, 338, 89.
(c) Bianchini, C.; Masi, D.; Meli, A.; Peruzzini, M.; Vacca, A.; Laschi,
F.; Zanello, P. Organometallics 1991, 10, 636. (d) Bianchini, C.; Meli,
A.; Perzzini, M.; Vacca, A.; Vizza, F. Organometallics 1991, 10, 645.
The related catalysis: (e) Abdulla, K.; Booth, B. L.; Stacy, C. J .
Organomet. Chem. 1985, 293, 103. (f) Grigg, R.; Scott, R.; Stevenson,
P. J . Chem. Soc., Perkin Trans. 1 1988, 1357. (g) Amer, I.; Bernstein,
T.; Eisen, M.; Blum, J .; Peter, K.; Vollhardt, K. P. C. J . Mol. Catal.
1990, 60, 313. (h) Ceccon, A.; Gambaro, A.; Santi, S.; Venzo, A. J . Mol.
Catal. 1991, 69, L1. (i) McDonald, F. E.; Zhu, H. Y. E.; Homquist, C.
R. J . Am. Chem. Soc. 1995, 117, 6605. (j) Kotha, S.; Brahmachary, E.
Tetrahedron Lett. 1997, 38, 3561. (k) Witulski, R.; Stengel, T. Angew.
Chem., Int. Ed. 1999, 38, 2426.
(2) General reviews of alkyne cyclotrimerization: (a) Vollhardt, K.
P. C. Angew. Chem., Int. Ed. Engl. 1984, 23, 539. (b) Shore, N. E. In
Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.;
Pergamon: Oxford, U.K., 1991; Vol. 5, p 1129. (c) Grotjahn, D. B. In
Comprehensive Organometallic Chemistry II; Abel, E. W., Stone, F.
G. A., Wilkinson, G., Eds.; Pergamon: Oxford, U.K., 1995; Vol. 12, p
741. (d) Ojima, I.; Tzamarioudaki, M.; Li, Z.; Donovan, R. J . Chem.
Rev. 1996, 96, 635. (e) Malacria, M. Chem. Rev. 1996, 96, 289. (f)
Bo¨nnemann, H.; Brijoux, W. Transition Metals for Organic Synthesis;
Beller, M., Bolm, C., Eds; Wiley-VCH: Weinheim, Germany, 1998; Vol.
1, p 114.
10.1021/om0202221 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 05/29/2002

Communications
Organometallics, Vol. 21, No. 13, 2002 2573
Sch em e 2
Ta ble 1. Cycloa d d ition of Diyn e 1 a n d Alk yn es
w ith P ybox-Rh Ca ta lystsa
alkyne R
run no.
cat.
(amt, equivd) time (h) product yieldb (%)
1
2
3
4
5
6
7
2
2
2
2
2
Ph (5)
Ph (10)
4
2
30
72
24
5
3
3
4
5
6
3
5
74
84
68
47
0
n-Bu (7)
SiMe3 (7)
CO2Me (7)
F igu r e 1. Molecular structure of the pybox-rhodacycle
complex 2 showing 30% thermal ellipsoids.
in situc Ph (7)
72
23
in situc SiMe3 (7)
72
a
Sch em e 1
Conditions: 1 (0.2 mmol), 2 (0.01 mmol), chlorobenzene (2 mL).
Isolated yield based on 1. The dimer of the diyne was obtained
b
in ca. 5-20% yield. c In situ catalyst prepared by mixing of pybox-
dh (0.015 mmol) and [Rh(coe)2Cl]2 (0.005 mmol) in chlorobenzene
d
(2 mL). With respect to 1.
Ch a r t 1
one of the proton signals for the methoxy groups ap-
pears at higher magnetic field by the shielding effect
of the pybox plane: for two CH3O, δ 3.23 and 3.82
ppm.
We attempted in turn the catalytic cycloaddition of
the diyne 1 and some alkynes, such as phenylacetylene,
1-hexyne, and (trimethylsilyl)acetylene, by using the
complex 2 (5 mol %) as a catalyst. Although the
oxidative cyclization of the diyne giving 2 took place at
room temperature, the cycloaddition process needed
higher temperature to give the corresponding adducts
3-5 in good yields (Scheme 2, Table 1); no reaction
occurs below 60 °C. A 7-10-fold excess of alkynes is
necessary to obtain higher yields in order to decrease
(1) self-trimerization of alkynes 3-5 and (2) formation
of 2 + 1 adducts of alkyne/diyne or diyne/alkyne. As
alkynes, dimethyl acetylenedicarboxylate and methyl
propiolate were employed, but not to give the corre-
sponding adducts by formation of their trimers and
some amounts of the 2 + 1 adducts. Alternatively, an
in situ catalyst, the mixture of pybox-dh and [Rh-
(coe)2Cl]2, was also applicable for this purpose to give
similar results (runs 6 and 7).
(6) Complex 2: orange-red solid, dec pt 233-235 °C. IR (KBr):
ν
1686, 1680 cm-1 1H NMR (300 MHz, CDCl3, Me4Si): δ 3.23 (s, 3 H),
.
3.78 (m, 2 H), 3.82 (s, 3 H), 4.03 (m, 2 H), 4.62 (s, 2 H, OCH2), 4.70 (s,
2 H, OCH2), 4.93 (t, J ) 9.9 Hz, 4 H, OCH2), 7.94 (d, J ) 7.8 Hz), 8.19
(t, J ) 7.8 Hz × 2). 13C NMR (75.5 MHz, CDCl3, Me4Si): δ 50.40, 50.81,
51.39 (d, J ) 1.4 Hz), 66.92, 70.51, 72.69, 124.37, 125.89 (d, J ) 35.5
Hz), 138.16, 144.37, 155.26, 160.68 (d, J ) 31.2 Hz), 166.68 (d, J ) 1.7
Hz), 169.70 (d, J ) 1.4 Hz), 174.86, 175.37. X-ray analysis: a single
crystal (0.15 × 0.3 × 0.4 mm) was obtained by recrystallization from
CH2Cl2-n-hexane. Crystal data: C21H21N3O7ClRh, monoclinic, space
group P21/n (No. 14), a ) 10.492(3) Å, b ) 12.290(3) Å, c ) 17.481(4)
Å, â ) 102.61(1)°, V ) 2199.6(7) Å3, Fcalcd ) 1.708 g cm-3, Z ) 4, µ )
9.45 cm-1. The intensity data (2θ < 55.1°) were collected on a Rigaku
AFC-7R diffractometer with graphite-monochromated Mo KR radiation
(λ ) 0.710 69 Å) and the structure was solved by direct methods
(SIR88). The final cycle of refinement was based on 3098 observed
reflection (I > 3.00σ(I)) and 298 variable parameters and converged
with R ) 4.4% and Rw ) 5.0%. The Cambridge Crystallographic
Database file is CCDC-178534.
In the reaction of the diyne monoester 7 (0.2 mmol;
Chart 1) and phenylacetylene (2.0 mmol), the catalytic
cycloaddition using 2 (5 mol %) proceeded smoothly at
80 °C in chlorobenzene for 2 h to give the adduct 9 in
95% yield, but as a mixture of the regioisomer 9a + 9b
(63:37 ratio of the isomer). In this system, the corre-
sponding metallacycle complex could not be isolated at
ambient temperature, probably because of its unstabil-
ity.
On the other hand, it is worthy of note that the
phenyl-diyne-monoester 8 reacted with in situ pybox-
Rh species in a manner similar to the preparation of 2
to give the rhodacycle complex 11 in 75% (purified yield)
as a sole product.8 No stereoisomer was detected, even
in the crude product, by 1H NMR. Interestingly, the
(7) (a) Yamamoto, Y.; Kitahara, H.; Ogawa, R.; Kawaguchi, K.;
Tatsumi, K.; Itoh, K. J . Am. Chem. Soc. 2000, 122, 4310. (b) Ru¨ba, E.;
Mereiter, K.; Schmid, R.; Kirchiner, K. Chem. Commun. 2001, 1996
and references therein.

2574 Organometallics, Vol. 21, No. 13, 2002
Communications
Sch em e 3
benzene at 80 °C resulted in nonstereoselective forma-
tion of the adduct 10a + 10b, in 72% yield (51:49).
Although we cannot elucidate the mechanism and
nonstereoselectivity at this stage, we hypothesize that
the cycloaddition concertedly proceeds via direct attack
of alkyne at the diene moiety of the rhodacycle skeleton,
having a 18-electron coordinatively saturated trivalent
rhodium atom (A; Scheme 3), followed by reductive
elimination, releasing the adduct and active pybox-RhI-
Cl species. Other possibilities, such as alkyne insertion
on the cationic and unsaturated alkyne complexes (B
and C) to form the rhodacycloheptatrienes (D and E,
respectively), remain unsolved.9
F igu r e 2. Molecular structure of the pybox-rhodacycle
complex 11 showing 30% thermal ellipsoids.
X-ray analysis of 11 shows that the carbon atom (C4)
bound to the ester part on the diyne skeleton is located
at the apical position, while the carbon atom (C1) bound
to the phenyl group is placed at the equatorial position
(Figure 2): 2.05 Å, Rh-C1; 1.30 Å, C1-C2; 1.43 Å, C2-
C3; 1.38 Å, C3-C4; 2.03 Å, C4-Rh; 78.7°, C1-Rh-C4.
Nevertheless, the cycloaddition of the diyne 8 and phen-
ylacetylene catalyzed by the complexes 11 (5 mol %) in
(8) Complex 11: orange-red solid, dec pt >250 °C. IR (KBr): ν 1660
cm-1 1H NMR (400 MHz, CD2Cl2, Me4Si): δ 3.18 (s, 3 H), 3.8-4.0 (m,
.
Ack n ow led gm en t. This work was supported by a
Grant-in-Aid for Scientific Research from the Ministry
of Education, Science and Culture of J apan (Tokutei A,
412).
2 H), 4.60 (s, 2 H, OCH2), 4.72 (s, 2 H, OCH2), 4.94 (t, J ) 10.0 Hz ×
2, 4 H, OCH2), 7.16 (t, J ) 7.2 Hz × 2, 1H), 7.30 (t, J ) 7.2 Hz × 2,
2H), 7.41 (d, J ) 7.2 H, 2H), 7.97 (d, J ) 8.0 Hz), 8.17 (t, J ) 8.0 Hz
× 2). 13C NMR (100 MHz, CD2Cl2, Me4Si): δ 50.23, 52.25, 67.59, 70.76,
73.04, 122.73 (d, J ) 35.5 Hz), 124.49, 124.99, 127.10, 127.80, 138.27,
144.72, 149.54, 153.57, 167.40, 170.42, 175.31, 175.31, 178.57 (d, J )
30.0 Hz). X-ray analysis: a single crystal (0.1 × 0.4 × 0.5 mm) was
obtained by recrystallization from benzene-ether-hexane-CH2Cl2.
Crystal data: C35H35N3O6ClRh, monoclinic, space group P21/n (No. 14),
a ) 12.229(4) Å, b ) 21.324(5) Å, c ) 13.355(4) Å, â ) 97.58(2)°, V )
3452(1) Å3, Fcalcd ) 1.408 g cm-3, Z ) 4, µ ) 6.18 cm-1. The crystal
contains a 1:1:1 mole ratio of 11, benzene, and ether; the solvent
molecules in the crystal were omitted in Figure 2. The intensity data
(2θ < 55.1°) were collected on a Rigaku AFC-7R diffractometer with
graphite-monochromated Mo KR radiation (λ ) 0.710 69 Å), and the
structure was solved by Patterson methods (DIRDIF92, PATTY). The
final cycle of refinement was based on 2140 observed reflections (I >
3.00σ(I)) and 360 variable parameters and converged with R ) 6.9%
and Rw ) 8.0%. The Cambridge Crystallographic Database file is
CCDC-178535.
Su p p or tin g In for m a tion Ava ila ble: Text giving syn-
thetic procedures for the complexes 2 and 11 and selected
catalytic procedures. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM0202221
(9) For a new observation of metallacyclopentadiene cobalt com-
plexes and their related reactions in terms of reaction mechanism for
cyclotrimerization, see: Diercks, R.; Eaton, B. E.; Gu¨rtzgen, S.;
J alisatgi, S.; Matzger, A. J .; Radde, R. H.; Vollhardt, K. P. C. J . Am.
Chem. Soc. 1998, 120, 8247.