Reaction of pyrones with triosmium clusters

Article abstract of DOI:10.1021/om030250z

A report on the reaction of pyrones with triosmium clusters was presented. The reactions were quantitative and were judged by infrared (IR) spectroscopy. The aromaticity of the pyrone rings was found to increase slightly and the non-carbonyl carbon adjacent to the metalation site was relatively electron-deficient.

Full text of DOI:10.1021/om030250z

Organometallics 2003, 22, 3639-3648
3639
Articles
Rea ction of P yr on es w ith Tr iosm iu m Clu ster s
Qi Lin and Weng Kee Leong*
Department of Chemistry, National University of Singapore, Kent Ridge, Singapore 119260
Received April 4, 2003
Reaction of Os3(CO)10(NCCH3)2, 2, with coumarin, chromone, R-pyrone, γ-pyrone, or
2-methyl-3-hydroxy-γ-pyrone afforded the products Os3(CO)10(µ-H)(µ-L), 3, in which the
pyrone is anchored onto the triosmium framework via the exocyclic oxygen and orthometa-
lation; the major product for the last pyrone is Os3(CO)9(µ-H)(µ-γ-C6H5O3), 5, coordinated
via the hydroxyl group rather than an orthometalation. The cluster Os3(CO)10(µ-H)(µ-OH),
7, formed H-bonded adducts, 8, with unsubstituted pyrones; the OH functioned as the
H-donor.
In tr od u ction
One current impetus in organometallic cluster chem-
istry has been the hope that the multinuclear cluster
core may imbue unusual reactivity to a cluster-bound
organic substrate. Indeed, this has been very elegantly
demonstrated in the quinoline system by the group of
Rosenberg.1 It is thus of interest to examine the
chemistry of cluster-bound organic substrates. A pre-
requisite for such studies is the anchoring of the organic
substrate onto a cluster. Much effort has been expended
on investigating the interaction of N-heterocycles with
triosmium clusters. Thus osmium clusters containing
ligands from the quinoline, pyridine, pyrazole, imida-
zole, and pyrrole families are known.2 In contrast, there
F igu r e 1. Molecular structures of clusters 3.
are very few osmium clusters known that contain
The pyrones are an important class of O-heterocycles
that occur in many naturally occurring compounds such
as several steroids and kojic acid and in important drugs
such as the anticoagulant warfarin. The R- and γ-pyrone
ring systems possess little aromaticity, the former
behaving more like an unsaturated lactone and the
latter a vinylogous lactone. It is possible, however, to
aromatize them via electrophilic attack at the exocyclic
oxygen.4 In this paper, we would like to report our
investigations into the reaction of two triosmium clus-
ters, namely, Os3(CO)10(CH3CN)2, 2, and Os3(CO)10(µ-
H)(µ-OH), 7, with a number of representative pyrones
in order to map out their behavior with organometallic
clusters, particularly in relation to their binding onto
the cluster.
O-heterocycles.3
* Corresponding author.
(1) (a) J oynal, A. M.; Bergman, B.; Holmquist, R.; Smith, R.;
Rosenberg, E.; Ciurash, J .; Hardcastle, K.; Roe, J .; Vazquez, V.; Roe,
C.; Kabir, S.; Roy, B.; Alam, S. and Azam, K. A. Coord. Chem. Rev.
1999, 190-192, 975. (b) Kabir, S. E.; Kolwaite, D. S.; Rosenberg, E.;
Hardcastle, K. I.; Cresswell, W. and Grindstaff, J . Organometallics
1995, 14, 3611. (c) Abedin, M. J .; Bergman, B.; Holmquist, R.; Smith,
R.; Rosenberg, E.; Ciurash, J .; Hardcastle, K.; Roe, J .; Vazquez, V.;
Roe, C.; Kabir, S. E.; Roy, B.; Alam, S. and Azam, K. A. Coord. Chem.
Rev. 1999, 192, 975. (d) Bergman, B.; Holmquist, R.; Smith, R.;
Rosenberg, E.; Ciurash, J .; Hardcastle, K. I.; Visi, M. J . Am. Chem.
Soc. 1998, 120, 12818.
(2) See for example: (a) Shapley, J . R.; Samkoff, D. E.; Bueno, C.;
Churchill, M. R. Inorg. Chem. 1982, 21, 634. (b) Yin, C. C.; Deeming,
A. J . J . Chem. Soc., Dalton Trans. 1975, 2091. (c) Burgess, K.; J ohnson,
B. F. G.; Lewis, J . J . Organomet. Chem. 1982, 233, C55. (d) Deeming,
A. J .; Peters, R.; Hursthouse, M. B.; Backer-Dirks, J . D. J . J . Chem.
Soc., Dalton Trans. 1982, 787. (e) Yin, C. C.; Deeming, A. J . J . Chem.
Soc., Dalton Trans. 1982, 2563. (f) Deeming, A. J .; Whittaker, C.; Arce,
A. J .; De Sanctis, Y. J . Organomet. Chem. 1997, 540, 67. (g) Leadbeater,
N. E.; Lewis, J .; Raithby, P. R.; Ward, G. P. Eur. J . Inorg. Chem. 1998,
1479. (h) Day, M. W.; Hardcastle, K. I.; Deeming, A. J .; Arce, A. J .; De
Sanctis, Y. Organometallics 1990, 9, 6. (i) Chao, M.-H.; Kumaresan,
S.; Wen, Y.-S.; Lin, S.-C.; Hwu, J . R.; Lu, K.-L. Organometallics 2000,
19, 714.
Resu lts a n d Discu ssion
The reaction of 2 with excess coumarin, chromone,
R-pyrone, γ-pyrone, or 2-methyl-3-hydroxy-γ-pyrone at
elevated temperatures afforded products with the mo-
lecular formula Os3(CO)10(µ-H)(µ-L), 3 (L ) R-C9H5O2
(a ); γ-C9H5O2 (b); R-C5H3O2 (c); γ-C5H3O2 (d ); 2-Me-3-
OH-γ-C5HO2 (e)), as illustrated below (Figure 1).
(3) (a) Azam, K. A.; Deeming, A. J .; Kimber, R. E.; Shukla, P. R. J .
Chem. Soc., Dalton Trans. 1976, 1853. (b) Arce, A. J .; De Sanctis, Y.;
Deeming, A. J . J . Organomet. Chem. 1986, 311, 371. (c) Boyer, E.;
Deeming, A. J .; Randle, N. P.; Bates, P. B.; Hursthouse, M. B. J . Chem.
Soc., Dalton Trans. 1987, 551. (d) Tunik, S. P.; Balova, I. A.; Borovitov,
M. E.; Nordlander, E.; Haukka, M.; Pakkanen, T. A. J . Chem. Soc.,
Dalton Trans. 2002, 827.
(4) Gilchrist, T. L. Heterocyclic Chemistry, 3rd ed.; Longman:
Singapore, 1997.
10.1021/om030250z CCC: $25.00 © 2003 American Chemical Society
Publication on Web 08/01/2003

3640 Organometallics, Vol. 22, No. 18, 2003
Ta ble 1. Sp ectr oscop ic a n d An a lytica l Da ta for All P r od u cts
Lin and Leong
Anal. (calcd)
cluster
IR [ν(CO)/cm-1
2106w, 2068s, 2054s,
]
1H NMR [δ/(ppm)]a
J
H-H [Hz]
MS [m/z]
C
H
3a
8.44(s, H4), 7.6-7.2(4H, m,
benzo), -12.8(s, OsHOs)a
23.13
(22.89) (0.61)
0.39
2024s, 2012w(sh),
2006s, 1996m, 1988w (sh), 1977w
2105w, 2066s, 2053s,
2036w, 2022s, 2007s,
1993m, 1986w(sh), 1975w
2106w, 2068s, 2054s,
4
3b
3c
8.18(s, H2), 7.94(d, H5), 7.67
(m, H7), 7.49(d, H8), 7.42(m,
H6), -12.8(s, OsHOs)b
8.06(dd, H6), 7.42(dd, H4),
6.30(dd, H5), -13.1(s, OsHOs)
3J 56 ) 3J 78 ) 8.2, J 57
)
-
22.86
(22.89) (0.61)
0.44
4J 68 ) 1.6
3J 45 ) 4.9, J 46 ) 1.6,
947.6d 945.7e 18.88
0.31
(19.03) (0.43)
4
2024s, 2012w(sh), 2006s,
1996m, 1987w(sh), 1977w
2106w, 2066s, 2053s, 2023s,
2006s, 1994m, 1987w(sh), 1975w
2106w, 2066s, 2054s, 2023s,
2007s, 1994m, 1987w(sh), 1976w
2112w, 2077s, 2060s, 2030s,
2014s, 2005m(sh), 1993w, 1985w
2102w, 2059s, 2022m(sh),
2019vs, 2003s, 1987w, 1982vw(sh), 1941w (s, 3H, Me), -9.3(s, OsHOs)
2126w, 2082vw, 2069m,
2049s, 2022m, 2008m,
1994w, 1983w, 1937w
3J 56 ) 6.6
3J 56 ) 5.0
3d
3e
4
7.99(s, H2), 7.66(d, H6), 6.33
(d, H5), -13.0(s, OsHOs)
19.11
0.64
(19.03) (0.43)
19.33 0.70
(19.67) (0.62)
7.84(s, H6), 5.51(s, OH), 2.39
(3H, s, Me), -12.9(s, OsHOs)
6.85(dd, H4), 6.11(d, H5), 5.71
(d, H3), -13.6(s, OsHOs)
3J 34 ) 9.1, J 45 ) 6.6
947.7d 944.6e
f
f
3
5
7.78(d, H6), 6.73(d, H5), 2.46
3J 56 ) 5.0
19.24
(18.99) (0.64)
0.46
3
6
8.09(d, H5), 7.84(d, H3), 7.74
(t, H7), 7.63(t, H2), 7.60(d, H8),
7.37(t, H6), 7.00(d, H1), -14.5
(s, OsHOs)
7.71(d, H4), 753(t, H7), 7.50
(d, H5), 7.31(d, H8), 7.27(t, H6),
6.37(d, H3), 0.42(s, OH), -12.64
(s, OsHOs)b
3J 23 ) 3J 67 ) 7.4, J 12
f
f
) 3J 56 ) 3J 78 ) 8.2, J 57
) 4J 68 ) 1.6
4
3J 34 ) 10, J 56 ) 3J 78
)
22.54
(22.48) (0.79)
0.45
3
8a
8b
8c
2108vw, 2067s, 2057m,
2019s, 1997m, 1990vw(sh),
1983w, 1978w(sh)
8.2, J 57 ) 4J 57 ) 1.6
4
3
2109vw, 2068s, 2058m,
2021s, 2000m, 1989w(sh),
1983w
8.22(d, H5), 7.85(d, H2), 7.68
(m, H7), 7.46(d, H8), 7.41(m,
H6), 6.34(d, H3), 0.52(s,
3J 23 ) 5.8, J 56 ) 8.2,
22.31
(22.48) (0.79)
0.49
3J 78 ) 8.2
OH), -12.62(s, OsHOs)
2109vw, 2068s, 2059m,
2022s, 2002m, 1990w(sh),
1984w, 1978w(sh)
8.36(2H, d, H1 & H8), 7.77
(2H, t, H3 & H6), 7.52(2H, d,
H4 & H5), 7.39(2H, t, H2 & H7),
0.59(s, OH),c-13.12(s, OsHOs)c
7.70(2H, d, H2 & H6), 6.31(2H,
d, H3 & H5), 0.70(s, OH), -12.65
(s, OsHOs)
3J ) 8.2, 4J ) 1.6
25.99
(25.94) (0.95)
0.88
8d
8e
9
2109vw, 2068s, 2058m,
2020s, 1990w, 1982w,
1978w(sh)
3J 23 ) 3J 56 ) 6.2
18.74
(18.67) (0.63)
0.54
3
2109vw, 2068s, 2058m,
2021s, 2015m(sh), 1999w,
1983w, 1978w(sh), 1761vs
2118m, 2089s, 2063vs,
2045w, 2029s, 2018m,
2003m, 1999m(sh), 1984vw
2102w, 2073vs, 2037s,
2016m, 2003m, 1968vw
6.44(d, H6), 6.12(ddd, H4), 5.71
(d, H3), 5.05(t, H5), 0.60(s, OH),c
-13.09(s, OsHOs)c
5.40(s, H5), 1.89(3H, s, Me), -11.9
(s, OsHOs), -14.1(s, OsHOs).
3J 34 ) 9.6, J 45 ) 3J 56
18.71
(18.67) (0.63)
0.42
3
) 5.2, J 46 ) 1.8
18.97 0.66
(18.99) (0.64)
18.03 0.30
10
5.61(s, H3), 1.90(3H, s, Me)
(17.70) (0.33)
a
b
d
f
The integration is 1H unless otherwise indicated. In CD2Cl2. c In d8-toluene. FAB-MS, M+. e FAB-MS, M-. Unstable compound.
The clusters 3 have been characterized spectroscopi-
cally and analytically (Table 1), and for 3a -d , by single-
crystal X-ray crystallographic studies as well; the
common atomic numbering scheme and selected bond
parameters for clusters 3a -d are given in Table 2.
The pyrones in the clusters 3 are bound to the cluster
core via the exocyclic (ketonic) oxygen and an ortho-
metalation; this is similar to that found in N-heterocy-
cles1,2 and other O-heterocycles.3 In contrast to the
benzo derivatives of those systems, however, we have
not observed any product resulting from metalation of
the benzo ring in coumarin or chromone. The pyrones
are bound axially with respect to the triosmium plane;
the dihedral angles between the Os3 and the pyrone
planes are about 97 ( 1°. The bond parameters for the
O-heterocycles in 3a -d suggest that the bonding within
the heterocycles is not much affected by coordination
to the cluster.5 A noticeable structural feature common
to all the clusters is the shortening of the Os-CO bond
trans to the O donor atom; the sum of the Os-C and
C-O bond lengths6 for this carbonyl is the shortest
(except for 3b, where the disorder of the chromone ring
renders the associated bond parameters less reliable)
and reflects the increase in π-back-donation into this
carbonyl.
example, the absence of the H3 resonance at about δ
6.4 ppm compared to the spectrum of chromone indi-
cates that metalation has occurred at C3. The singlet
at δ 8.2 ppm is therefore assigned to H2; the assign-
ments of the remaining resonances of 3b are in ac-
cordance with those of free chromone.
It is thus observed that, on bonding to the clusters,
1
the H resonances of the pyrones are shifted downfield.
In particular, that for the proton on the carbon atom
adjacent to the metalated site exhibits a very large
downfield shift (>0.3 ppm). This suggests that the
aromaticity of the pyrone rings is increased slightly and
that the non-carbonyl carbon adjacent to the metalation
site is relatively electron-deficient. Interestingly, the
hydroxyl resonance in 3e is narrow (width < 0.2 ppm),
unlike the very broad signal (width > 3 ppm) in the free
pyrone, and suggests that exchange of the hydroxyl H
with adventitious water is inhibited on attachment of
the pyrone onto the cluster.
In the reaction of R-pyrone, another product, 4, was
also isolated. This product is thermally unstable; at-
tempts at crystallization at low temperature afforded
only 3c and other unidentified decomposition products.
(5) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,
A. G.; Taylor, R. J . Chem. Soc., Perkin Trans. 1987, S1.
(6) Leong, W. K.; Einstein, F. W. B.; Pomeroy, R. K. J . Cluster Sci.
1996, 7, 121.
(7) Handbook of Proton-NMR Spectra and Data; Asahi Research
Center Co., Ltd., Ed.; Academic Press Inc: J apan, 1986.
1
The H NMR spectra of 3a -e have been assigned by
comparison with the resonances for the free pyrones.7
Thus in the 1H NMR spectrum of 3b (Figure 2) for

Reaction of Pyrones with Triosmium Clusters
Organometallics, Vol. 22, No. 18, 2003 3641
F igu r e 2. 1H NMR spectra and tentative assignments for 3b (left) and chromone (right).
1
Ta ble 2. Com m on Atom ic Nu m ber in g Sch em e a n d
A comparison of the H NMR spectrum of 4 with that
of R-pyrone (Figure 3) suggests that C6 has been
metalated. This would also imply that, in contrast to
the clusters 3, the 1H resonances for the pyrone in 4
are shifted upfield; that for H3 is particularly large. This
would be consistent with a loss of aromaticity on
bonding at the endocyclic oxygen, which is expected to
reduce the aromatic canonical form of R-pyrone.
Selected Bon d P a r a m eter s for Clu ster s 3a -d
Similarly, the major product from the reaction of
2-methyl-3-hydroxy-γ-pyrone was a second product, Os3-
(CO)9(µ-H)(µ-γ-C6H5O3), 5. The molecular structure of
5 has been determined by a single-crystal X-ray crystal-
lographic study, and the ORTEP diagram is shown in
Figure 4, together with selected bond parameters.
Unlike in 3e, cluster 5 has the hydroxyl group involved
in coordination to the cluster, rather than an ortho-
metalation. The bond parameters associated with the
pyrone again suggest that the effect on the pyrone on
binding to the cluster is small. The higher yield of 5
compared to 3e suggests that the cleavage of the O-H
bond in the hydroxyl group of 2-methyl-3-hydroxy-γ-
pyrone is more favored than orthometalation, as may
be expected.
3a
3ba
3c
3d
Bond Lengths (Å)
Os(1)Os(2)
Os(2)Os(3)
Os(3)Os(1)
Os(1)O(1)
Os(2)C(2)
O(1)C(1)
C(1)C(2)
C(2)C(3)
C(3)C(4)/C(3)O(4)
C(4)C(5)/O(4)C(5)
C(5)O(6)/C(5)C(6)
O(6)C(1)/C(6)C(1)
2.9327(4) 2.9089(6) 2.9321(17) 2.9062(4)
2.8990(4) 2.8925(6) 2.9414(15) 2.9136(4)
2.8750(4) 2.8977(6) 2.9092(14) 2.8884(4)
2.135(5)
2.159(7)
1.226(9)
1.464(10) 1.35(3)
1.365(10) 1.40(3)
1.446(10) 1.39(2)
2.16(2)
2.14(3)
1.38(2)
2.135(10) 2.127(5)
2.150(14) 2.146(7)
1.260(17) 1.263(9)
1.460(19) 1.443(12)
1.39(2)
1.41(2)
1.368(11)
1.360(10)
1.324(13)
1.336(14)
1.390(10) 1.260(15) 1.32(3)
1.378(9)
1.357(9)
1.394(14) 1.38(2)
1.460(13) 1.373(16) 1.434(10)
Bond Angles (deg)
Os(2)Os(1)Os(3)
Os(1)Os(2)Os(3)
Os(1)Os(3)Os(2)
O(1)Os(1)Os(2)
C(2)Os(2)Os(1)
59.880(10) 59.754(14) 60.47(4)
59.073(10) 59.931(14) 59.38(2)
61.047(10) 60.314(14) 60.15(4)
82.75(14) 83.3(6)
82.68(19) 83.7(9)
60.370(10)
59.513(9)
60.117(10)
83.66(16)
82.5(2)
That the pyrones appear to favor metalation at the
ortho position to the exocyclic oxygen prompted us to
examine the case with xanthone, in which it is not
possible for orthometalation to the exocyclic oxygen to
occur. The reaction afforded one major product, 6.
Monitoring by IR spectroscopy showed that 6 decom-
posed slowly to afford Os3(CO)12, 1. The 1H NMR
spectrum of 6 (Figure 5) showed seven sets of non-
equivalent resonances, indicating metalation of the
xanthone has occurred; none of these were singlets, thus
pointing to C1, C4, C5, or C8 as the possible metalation
sites. The benzo resonances H5 to H8 may be assigned
by comparison with that in free xanthone, leaving the
resonances for the metalated ring, which are shifted
upfield with respect to the benzo resonances. This
suggests that the endocyclic oxygen is bonded to the
clusters, just as in 4; the tentative structure for 6 is as
given in the inset to Figure 5.
83.0(3)
83.2(4)
97.4(4)
Dihedral angle between 97.7(2)
96.9(9)
96.0(2)
Os(1)Os(2)Os(3) and
Os(1)O(1)C(1)C(2)Os(2)
a
Disorder of chromone.
Consistent with this was the observation that the
relative amounts of 3c and 4 obtained depended on the
reaction temperature employed. Thus in refluxing hex-
ane, they were obtained in about equal amounts,
whereas in refluxing toluene, the amount of 4 obtained
was negligible.
The IR spectrum of 4 in the carbonyl stretch region
is very similar to that of the clusters 3, suggesting
similar number and arrangement of carbonyl ligands
in the two; this is also supported by the FAB-MS, which
showed a cluster of peaks centered at m/z 947.7,
corresponding to M+.
The cluster Os3(CO)10(µ-H)(µ-OH), 7, has recently

3642 Organometallics, Vol. 22, No. 18, 2003
Lin and Leong
F igu r e 3. 1H NMR spectra and tentative assignments for 4 (left) and R-pyrone (right).
The reactions were quantitative, as judged by IR
spectroscopy. These H-bonded adducts are surprisingly
thermally quite stable. For instance, the decomposition
of 8a in hexane became significant only when heated
in a Carius tube above 100 °C, whereupon cluster
decomposition occurred to afford Os3(µ-H)2(CO)10 (iden-
tified spectroscopically). On the other hand, they are
completely transformed back to 7 during attempts at
TLC separation on silica.
The formation of such O-H- - -O hydrogen bonds is
novel; they are the first examples of a bridging OH
group directly coordinated to a cluster core participating
as H-donors, in contrast to the more common examples
involving cluster-bound organic ligands with free hy-
droxyl functions.9 Preliminary investigations suggest
that the H-bonding also occurs with other ketones such
F igu r e 4. ORTEP diagram (50% probability thermal ellip-
soids, organic hydrogens omitted) and selected lengths (Å)
and angles (deg) for 5. Os(1)Os(2) ) 2.8000(4); Os(1)Os(3)
) 2.8180(4); Os(2)Os(3) ) 2.7642(4); Os(1)O(3) ) 2.185(5);
Os(2)O(3) ) 2.142(5); Os(2)O(4) ) 2.164(5); Os(3)C(31) )
1.937(7); O(1)C(6) ) 1.350(11); O(1)C(2) ) 1.353(9); C(2)C(3)
) 1.355(10); C(2)C(7) ) 1.483(11); C(3)O(3) ) 1.364(8);
C(3)C(4) ) 1.421(10); C(4)O(4) ) 1.276(9); C(4)C(5) )
1.417(10); C(5)C(6) ) 1.321(13); Os(2)Os(1)Os(3) ) 58.948(9);
Os(3)Os(2)Os(1) ) 60.851(9); Os(2)O(3)Os(1) ) 80.62(16);
C(3)O(3)Os(2) ) 111.3(4); C(4)O(4)Os(2) ) 112.8(4).
1
as benzophenone. The H resonance at 0.35 ppm for the
OH group in cluster 7 is, for those cases in which it is
observable, shifted downfield in 8; this resonance for
cluster 7 has been verified by the disappearance of the
signal upon the addition of D2O, which also confirms
that this hydrogen is very labile. The capability of the
bridging OH group to form an H-bond implies that it is
acidic, and in that sense, cluster 7 behaves as an alcohol.
The reaction of 7 with hydroxyl-substituted pyrones
followed a very different course. Thus the reaction
between 7 and excess 2-methyl-3-hydroxy-γ-pyrone at
temperatures from 25 to 60 °C gave rise to the partial
formation of a complex that has an IR spectrum similar
to that of 8a . However, the complex could not be
separated from 7 despite several attempts at recrystal-
lization. Instead, cluster 5 was obtained as the major
product when the mixture was further heated at 110
°C for 16 h. Presumably, the reaction at higher tem-
perature is primarily driven by the hydroxy substituent
on the pyrone; this is consistent with the behavior of 7
toward simple alcohols.8,13
emerged as another useful precursor for triosmium
cluster synthesis.8,13 The reaction of 7 with coumarin,
chromone, xanthone, γ-pyrone, or R-pyrone afforded the
H-bonded adducts, 8a -e. These were characterized
spectroscopically and analytically (Table 1), and for 8a
and 8d , also by single-crystal X-ray crystallographic
studies; the ORTEP diagram and selected bond lengths
and bond angles for 8a are given in Figure 6.
(8) Lum, M. W.; Leong, W. K. J . Chem. Soc., Dalton Trans. 2001,
2476.
(9) Braga, D.; Grepioni, F. Advances in Molecular Structure Re-
search; J AI: Greenwich; 1995; Vol. 2, p 25.
(10) Azam, K. A.; Deeming, A. J .; Rothwell, I. P.; Hursthouse, M.
B.; New, L. J . Chem. Soc., Chem. Commun. 1978, 1086.
(11) (a) Lu, C. Y.; Einstein, F. W. B.; J ohnston, V. J .; Pomeroy, R.
K. Inorg. Chem. 1989, 28, 4212. (b) Martin, L. R.; Einstein, F. W. B.;
Pomeroy, R. K. Inorg. Chem. 1988, 27, 2986.
(12) Nicholl, J . N.; Vargas, M. D. Inorg. Synth. 1989, 28, 232.
(13) Roberto, D.; Lucenti, E.; Roveda, C.; Ugo, R. Organometallics
1997, 16, 5974.
The reaction between 7 and 6-methyl-4-hydroxy-R-
pyrone at 60 °C afforded the novel cluster Os3(CO)9(µ-
H)2(µ3-R-C6H4O3), 9, in good yield. In refluxing toluene,
another novel cluster, Os4(CO)12(µ4-R-C6H4O3), 10, was
obtained in 13% yield. It was also found that refluxing
9 in toluene gave 10; the results are summarized in
Scheme 1.

Reaction of Pyrones with Triosmium Clusters
Organometallics, Vol. 22, No. 18, 2003 3643
F igu r e 5. 1H NMR spectra and tentative assignments for 6 (left) and xanthone (right).
F igu r e 6. ORTEP diagram (50% probability thermal
ellipsoids, organic hydrogens omitted) and selected lengths
F igu r e 7. ORTEP diagram (50% probability thermal ellip-
(Å) and angles (deg) for 8a . Os(1)Os(2) ) 2.7770(3); Os(1)-
Os(3) ) 2.8195(3); Os(2)Os(3) ) 2.8194(3); Os(1)O(10) )
2.102(5); Os(2)O(10) ) 2.103(4); O(1)C(2) )1.338(8); O(1)C(6)
) 1.392(7); O(7)C(4) ) 1.253(8); C(2)C(3) ) 1.304(10);
C(3)C(4) ) 1.429(9); C(5)C(6) ) 1.381(8); C(4)C(9) )
1.453(8); C(5)C(6) ) 1.353(9); C(5)C(9) ) 1.428(9); C(6)C-
(7) ) 1.419(9); C(7)C(8) ) 1.358(9); C(8)C(10) ) 1.394(9);
Os(2)Os(1)Os(3) ) 60.494(8); Os(1)Os(2)Os(3) ) 60.499(8);
Os(2)Os(3)Os(1) ) 59.006(8); O(10)Os(1)Os(3) ) 80.13(13);
O(10)Os(2)Os(1) ) 48.66(12); Os(1)O(10)Os(2) ) 82.65(16).
soids, organic hydrogens omitted) and selected lengths (Å)
and angles (deg) for 8d . Os(1)Os(2) ) 2.7832(4); C(3)C(4)
) 1.401(14); Os(1)Os(3) ) 2.8196(4); C(9)C(10) ) 1.373(9);
Os(2)Os(3) ) 2.8217(4); Os(1)O(10) ) 2.114(5); Os(2)O(10)
)2.108(6); O(1)C(2) ) 1.291(17); O(1)C(10) ) 1.296(15);
O(3)C(4) ) 1.253(11); C(2)C(3) ) 2.188(18); Os(2)Os(1)Os-
(3) ) 60.475(9) ) O(10)Os(1)Os(3) ) 80.03(16); Os(1)Os-
(2)Os(3) ) 60.402(10); O(10)Os(2)Os(1) ) 48.87(14); Os(2)-
Os(3)Os(1) ) 59.123(9); Os(1)O(10)Os(2) ) 82.5(2).
Clusters 9 and 10 were characterized completely,
including by single-crystal X-ray crystallographic stud-
ies. The ORTEP diagrams are shown in Figures 8 and
9, respectively; selected bond lengths and bond angles
are given in Table 3.
The tetraosmium cluster 10 has a rhombic arrange-
ment of the osmium atoms. Few structural studies on
tetraosmium clusters with such a planar arrangement
of the osmium atoms have been reported, two examples
being Os4(µ-H)(CO)14(SnMe3) and Os4(µ-H)2(CO)13(P-
Me3).11 The pyrone in 10 is coordinated to all four
osmium atoms, and it is situated on one side of the
tetraosmium plane. As in 9, both the pyrone oxygen
atoms are ketonic and the structure depicted in Scheme
1 is consistent with the observed bond parameters. As
for the other clusters in this study, there is a discernible
shortening of the Os-CO bond for the carbonyl trans
to the O-donor.
Cluster 9 is analogous to the known cluster Os3(CO)9-
(µ-H)2(µ3-C6H4O) obtained from the reaction of 1 with
phenol, in which the phenol has lost its aromatic
character.10 The C-C and C-O bond lengths of the
pyrone in 9 are also consistent with this (depicted in
Scheme 1); thus the C(4)-O(4) and C(5)-C(6) bond
lengths of 1.268(10) and 1.309(13) Å, respectively, are
indicative of double-bond character, while those of the
others are consistent with single-bond character.

3644 Organometallics, Vol. 22, No. 18, 2003
Lin and Leong
Sch em e 1
Ta ble 3. Selected Bon d Len gth s (Å) a n d Bon d An gles (d eg) for 9 a n d 10
bond length
9
10
bond angle
9
10
Os(1)-Os(2)a
Os(1)-Os(3)a
Os(2)-Os(3)
Os(1)-C(3)a
Os(2)-C(3)
Os(3)-O(4)
O(1)-C(6)
O(1)-C(2)
O(2)-C(2)
O(4)-C(4)
C(2)-C(3)
2.8063(4)
2.9464(5)
2.7792(5)
2.187(9)
2.193(9)
2.105(6)
1.379(12)
1.392(11)
1.206(12)
1.268(10)
1.477(12)
1.470(12)
1.416(12)
1.309(13)
1.489(13)
N.A.
2.7039(4)
2.8075(3)
2.8075(3)
2.204(5)
2.204(5)
2.140(5)
1.381(9)
1.363(9)
1.253(9)
1.270(10)
1.420(10)
1.436(10)
1.431(10)
1.334(12)
1.490(10)
2.8063(4)
2.8115(3)
2.157(5)
Os(2)-Os(1)-Os(3)a
Os(3)-Os(2)-Os(1)a
Os(2)-Os(3)-Os(1)a
O(4)-Os(3)-Os(1)a
O(4)-Os(3)-Os(2)
C(3)-Os(1)-Os(3)a
C(3)-Os(2)-Os(3)
O(2)-C(2)-C(3)
57.716(12)
63.672(13)
58.612(12)
82.98(17)
83.85(17)
73.5(2)
77.1(2)
126.2(8)
79.7(3)
61.258(5)
61.214(5)
57.572(10)
84.21(13)
84.21(13)
75.76(18)
75.76(18)
125.3(7)
75.7(2)
122.2(7)
118.0(5)
57.484(10)
121.844(9)
83.68(12)
76.31(18)
Os(1)-C(3)-Os(2)a
O(4)-C(4)-C(3)
122.7(8)
118.6(6)
N.A.
C(4)-O(4)-Os(3)
Os(2)-Os(1)-Os(2A)
Os(3)-Os(2)-Os(1)
O(2)-Os(1)-Os(2)
C(3)-Os(2)-Os(1)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
Os(1)-Os(2A)
Os(1)-Os(2)
Os(1)-O(2)
a
For 10, Os(1) is labeled as Os(2A).
Sch em e 2
Con clu d in g Rem a r k s
pyrones is favored by coordination via the hydroxyl
function. Attachment of the pyrones onto the cluster
core does not appear to significantly affect the structure
of the pyrones. However, NMR evidence suggests en-
hanced aromaticity of the O-heterocycles in clusters 3,
implying that the coordinated pyrones will be more
susceptible to electrophilic attack than the correspond-
ing free pyrones. We have already embarked on inves-
tigating the chemistry of cluster-bound pyrones and will
report some of our findings in a subsequent paper.
The clusters 2 and 7 present different coordinative
capabilities toward various pyrones. Cluster 2 interacts
with pyrones via the ketone function and orthometala-
tion, although the presence of a hydroxyl group tends
to redirect the site of reaction. The reactions of 2 are
summarized in Scheme 2.
Cluster 7 reacts with unsubstituted pyrones to form
H-bonded adducts with its OH group functioning as the
H-donor, while its reaction with hydroxyl-substituted

Reaction of Pyrones with Triosmium Clusters
Organometallics, Vol. 22, No. 18, 2003 3645
Ta ble 4. Rea ction Con d ition s a n d Yield s for 2 w ith Cou m a r in , Ch r om on e, Xa n th on e, or γ-P yr on e
u n d er Reflu x
Ta ble 5. Rea ction Con d ition s a n d Yield s for 2 w ith r-P yr on e, γ-P yr on e, or 2-Meth yl-3-h yd r oxy-γ-p yr on e in
a Closed Vessel
Os3(CO)10(CH3CN)2, 2, and Os3(CO)10(µ-H)(µ-OH), 7, were
prepared according to literature methods.12,13 Os3(CO)12, 1,
from OXKEM, and all other reagents from other commercial
sources, were used as supplied. TLC separations were on plates
coated with K60GF254 of 0.25 or 0.5 mm thickness, and
extracted with dichloromethane.
Exp er im en ta l Section
Gen er a l P r oced u r es. All reactions and manipulations
were carried out under nitrogen by using standard Schlenk
techniques. Solvents were purified, dried, distilled, and stored
under nitrogen prior to use. NMR spectra were recorded on a
Bruker ACF-300 FT-NMR spectrometer as CDCl3 solutions
unless otherwise stated. 1H chemical shifts reported are
referenced against the residual proton signals of the solvents.
ESI spectra were obtained on a Finnigan MAT LCQ, with a
spray voltage of 4.5 kV and capillary temperature of 353 K,
as CH3CN solutions. FAB mass spectra were recorded on a
Finnigan MAT 95XL-T mass spectrometer in a 3NBA matrix.
EI spectra were obtained on a Macromass VG7035, at 70 eV.
Microanalyses were carried out by the Microanalytical Labora-
tory at the National University of Singapore. The clusters
Rea ction s of P yr on es w ith Os3(CO)10(NCCH3)2, 2, u n -
d er Reflu x. In a typical reaction, into a solution of 2 in hexane
or toluene placed in a Schlenk tube fitted with a condenser
was added an excess of the pyrone. The solution was refluxed
under nitrogen, the solvent was then removed under reduced
pressure, and the residue obtained was redissolved in the
minimum volume of dichloromethane and chromatographed
on TLC plates, hexane/CH2Cl2 (4:1 v/v) as mobile phase. The
reaction conditions and yields are summarized in Table 4.

3646 Organometallics, Vol. 22, No. 18, 2003
Ta ble 6. Rea ction s of 7 w ith P yr on esa
Lin and Leong
a
* ) quantitative reaction as judged from IR spectroscopy.
Rea ction s of P yr on es w ith Os3(CO)10(NCCH3)2, 2, in a
Ca r iu s Tu be. In a typical reaction, to a solution of 2 in
cyclohexane or toluene in a Carius tube was added an excess
of the pyrone. The solution was degassed by three freeze-
pump-thaw cycles and heated for 40 min. The solvent was
then removed under reduced pressure, and the residue ob-
tained was redissolved in the minimum volume of dichlo-
romethane and chromatographed. The reaction conditions and
yields are summarized in Table 5.
Rea ction s of P yr on es w ith Os3(CO)10(µ-H)(µ-OH), 7. In
a typical reaction, into a solution of 7 in hexane or toluene
placed in a Schlenk tube fitted with a condenser was added
an excess of the pyrone. The solution was stirred under
nitrogen and monitored by IR spectroscopy. The solvent was
then removed under reduced pressure, and the yellow solid
residue was recrystallized from dichloromethane/hexane at -5
°C to afford yellow crystals of the product. For 2-methyl-3-
hydroxy-γ-pyrone and 6-methyl-4-hydroxy-R-pyrone, the resi-
due obtained after solvent removal was redissolved in the
minimum volume of dichloromethane and chromatographed
on TLC plates with hexane/CH2Cl2 (3:2 v/v) as mobile phase.
The reaction conditions and yields are summarized in Table
6.
Th er m olysis of 9. A solution of 9 (10.7 mg, 0.011 mmol)
in toluene (10 mL) placed in a Schlenk tube fitted with a
condenser was heated at 110 °C under nitrogen for 17 h. The
solvent was removed under reduced pressure, and the residue
obtained was redissolved in the minimum volume of dichlo-
romethane and chromatographed on TLC plates. Elution with
hexane/CH2Cl2 (3:2 v/v) gave unreacted 9 (Rf ) 0.24, yield )
8.3 mg, 78%) and red crystalline 10 (Rf ) 0.50, yield ) 1.2
mg, 8.7%), both identified by their IR spectrum.
Cr ysta l Str u ctu r e Deter m in a tion s. Crystals were grown
from dichloromethane/hexane solutions and mounted on quartz

Reaction of Pyrones with Triosmium Clusters
Organometallics, Vol. 22, No. 18, 2003 3647
Ta ble 7. Cr ysta l a n d Refin em en t Da ta for 3a -d a n d 5
3a
3b
3c
3d
5
empirical formula
fw
temperature, K
cryst syst
space group
a, Å
b, Å
C
19H6O12Os3
C
19H6O12Os3
C
15H4O12Os3
C
15H4O12Os3
C
15H6O12Os3.CH2Cl2
996.84
223(2)
1139.24
223(2)
orthorhombic
Pbcn
25.1390(14)
11.5290(6)
15.2961(9)
90
946.78
223(2)
triclinic
P1h
8.744(5)
9.408(6)
12.860(8)
87.144(11)
79.807(11)
75.337(11)
1007.3(10)
2
946.78
223(2)
1033.72
223(2)
monoclinic
P21/c
9.0029(3)
9.9438(3)
25.7169(8)
90
92.729(1)
90
2299.64(13)
4
2.986
16.826
1848
monoclinic
C2/c
25.9456(3)
10.3497(1)
16.5559(1)
90
94.195(1)
90
4433.83(7)
8
monoclinic
P21/n
7.9711(1)
16.7506(2)
14.9583(1)
90
102.747(1)
90
1948.02(4)
4
c, Å
R, deg
â, deg
90
90
γ, deg
volume, Å3
Z
4433.2(4)
8
2.987
17.218
density (calcd), Mg/m3
abs coeff, mm-1
F(000)
2.987
17.215
3552
3.122
18.935
836
3.228
19.582
1672
3552
cryst size, mm3
θ range for data
collection, deg
no. of reflns collected
no. of ind reflns
0.40 × 0.38 × 0.38
0.315 × 0.245 × 0.215
0.32 × 0.32 × 0.14
0.32 × 0.23 × 0.22
0.14 × 0.12 × 0.10
2.12 to 29.27
2.36 to 28.52
1.61 to 30.35
1.85 to 29.31
2.20 to 30.03
27 598
5505
34 094
5632
7343
5064
14 062
4884
18 990
6671
[R(int) ) 0.0344]
[R(int) ) 0.0628]
[R(int) ) 0.0570]
[R(int) ) 0.0416]
[R(int) ) 0.0483]
completeness, %
(to θ, deg)
91.0 (29.27)
99.8 (28.52)
83.4 (30.35)
91.7 (29.31)
99.3 (30.03)
max. and min. transmn
no. of data/restraints/
params
0.042 and 0.014
5505/0/307
0.105 and 0.041
5632/5/308
0.056 and 0.015
5064/0/271
0.080 and 0.032
4884/0/275
0.284 and 0.202
6671/0/299
goodness-of-fit on F2
final R indices [I>2σ(I)]
1.151
1.217
1.044
1.156
1.102
R1 ) 0.0338,
wR2 ) 0.0805
R1 ) 0.0439,
wR2 ) 0.0855
1.162 and -1.852
R1 ) 0.0440,
wR2 ) 0.1061
R1 ) 0.0538,
wR2 ) 0.1087
1.775 and -1.893
R1 ) 0.0685,
wR2 ) 0.1768
R1 ) 0.0766,
wR2 ) 0.1895
5.139 and -3.186
R1 ) 0.0311,
wR2 ) 0.0736
R1 ) 0.0401,
wR2 ) 0.0770
1.312 and -1.948
R1 ) 0.0387,
wR2 ) 0.0847
R1 ) 0.0495,
wR2 ) 0.0883
1.884 and -2.784
R indices (all data)
largest diff peak and
hole, e Å-3
Ta ble 8. Cr ysta l a n d Refin em en t Da ta for 8a , 8d , 9, a n d 10
8a
8d
9
10
empirical formula
fw
temperature, K
cryst syst
space group
a, Å
C
19H8O13Os3
C
15H6O13Os3
C
15H6O12Os3
C
18H4O15Os4.1/2CH2Cl2
1014.85
193(2)
monoclinic
C2/c
27.5207(11)
7.4504(3)
23.9268(10)
90
110.838(1)
90
4585.1(3)
8
2.940
16.653
3632
964.80
223(2)
948.80
223(2)
1263.47
223(2)
monoclinic
C2/m
12.5051(6)
11.7989(6)
17.1181(8)
90
97.521(1)
90
2504.0(2)
4
3.352
20.412
2228
monoclinic
P21/n
13.0789(3)
11.6074(2)
14.2418(3)
90
102.461(1)
90
2111.14(8)
4
orthorhombic
P212121
7.3582(3)
8.9915(4)
29.1969(14)
90
b, Å
c, Å
R, deg
â, deg
90
90
γ, deg
volume, Å3
1931.70(15)
4
3.262
19.748
1680
Z
density(cald), Mg/m3
abs coeff, mm-1
F(000)
3.035
18.075
1712
cryst size, mm3
θ range for data collection,
deg
0.36 × 0.34 × 0.28
0.26 × 0.16 × 0.16
0.14 × 0.12 × 0.10
0.30 × 0.22 × 0.19
2.81 to 31.02
2.37 to 26.37
2.37 to 29.46
2.38 to 29.42
no. of reflns collected
no. of ind reflns
completeness, % (to θ, deg)
max. and min. transmn
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I>2σ(I)]
40289
7121 [R(int) ) 0.0326]
97.1 (31.02)
16525
4293 [R(int) ) 0.0380]
99.5 (26.37)
13915
4873 [R(int) ) 0.0436]
93.5 (29.46)
17156
3396 [R(int) ) 0.0382]
93.7 (29.42)
0.070 and 0.030
7121/0/324
1.035
R1 ) 0.0325,
wR2 ) 0.0791
R1 ) 0.0420,
wR2 ) 0.0817
2.359 and -1.185
0.160 and 0.089
4293/0/289
1.057
R1 ) 0.0282,
wR2 ) 0.0640
R1 ) 0.0364,
wR2 ) 0.0668
1.127 and -1.367
0.243 and 0.169
4873/0/279
1.066
R1 ) 0.0342,
wR2 ) 0.0613
R1 ) 0.0385,
wR2 ) 0.0627
1.422 and -1.227
0.113 and 0.064
3396/6/206
1.141
R1 ) 0.0250,
wR2 ) 0.0472
R1 ) 0.0289,
wR2 ) 0.0482
1.250 and -1.086
R indices (all data)
largest diff peak and
hole, e Å-3
extinction coeff
0.00125(5)
fibers. X-ray data were collected on a Bruker AXS APEX
system, using Mo KR radiation, with the SMART suite of
programs.14 Data were processed and corrected for Lorentz and
polarization effects with SAINT15 and for absorption effects
with SADABS.16 Structural solution and refinement were
carried out with the SHELXTL suite of programs.17 Crystal
and refinement data are summarized in Tables 7 and 8.
The structures were solved by direct methods to locate the
heavy atoms, followed by difference maps for the light, non-
hydrogen atoms. Organic hydrogen atoms were placed in
calculated positions. All non-hydrogen atoms were generally
given anisotropic displacement parameters in the final model
(but see below). Metal hydrides not located in the electron
density difference maps were placed in positions calculated
with XHYDEX18 and refined with a fixed isotropic thermal
parameter and riding on one of the osmium atoms it is
(14) SMART version 5.628; Bruker AXS Inc.: Madison, WI, 2001.
(15) SAINT+ version 6.22a; Bruker AXS Inc.: Madison, WI, 2001.
(16) Sheldrick, G. M. SADABS; 1996.
(18) Orpen, G. XHYDEX: A Program for Locating Hydrides in Metal
(17) SHELXTL version 5.1; Bruker AXS Inc.: Madison, WI, 1997.
Complexes; School of Chemistry, University of Bristol: UK, 1997.

3648 Organometallics, Vol. 22, No. 18, 2003
Lin and Leong
attached to. An extinction parameter was refined for 8d , and
9 was refined as a racemic twin.
A dichloromethane solvent molecule was found in 5 and 10;
in the latter, it was disordered about a center of symmetry.
The disorder was modeled with two alternative sites of equal
occupancies, with appropriate restraints applied.
The coumarin ligand in 3b exhibited disorder about a
pseudomirror plane; this was modeled as two sites of equal
occupancies, with appropriate restraints applied. The crystal
of 3c broke off midway through data collection, which ac-
counted for inadequate absorption correction and hence the
large residue about the heavy atoms.
RP 010172), and one of us (Q.L.) thanks the University
for a Research Scholarship.
Su p p or tin g In for m a tion Ava ila ble: Experimental and
refinement details for the crystallographic studies, tables of
crystal data and structure refinement, atomic coordinates,
isotropic and anisotropic thermal parameters, complete bond
parameters, and hydrogen coordinates. Crystallographic data
in CIF format. This material is available free of charge via
the Internet at http://pubs.acs.org.
Ack n ow led gm en t. This work was supported by the
National University of Singapore (Research Grant No.
OM030250Z