Reactions of dimesityldioxoosmium(VI) with bidentate N-heterocycles. Crystal structure of a dioxoosmium(VI) complex containing a molecular square

Article abstract of DOI:10.1021/om950531+

The interaction of OsO₂(mes)₂ (mes = mesityl) with pyz (pyrazine) gave the pyrazinebridged dimer [OsO₂(mes)₂]₂(μ-pyz) (1), which has been characterized by X-ray crystallography. The structure around Os in 1 is square pyramidal, with the pyrazine, two oxo ligands, and one mesityl group in the square plane. The Os-O distance and O-Os-O angle are 1.71 A? and 147.5°, respectively. The reaction of OsO₂(mes)₂ with 4,4′-bpy (4,4′-bipyridyl) and bpe (trans-1,2-bis(4-pyridyl)ethylene) in Et₂O gave the oligomeric [OsO₂(mes)₂L]_n (L = 4,4′-bpy (2), bpe (3)) in good yields. The ¹H NMR spectra of 2 and 3 indicate that L's are coordinated in a symmetric fashion in these oligomers. The reaction of OsO₂(mes)₂ with 4,4′-bpy in CHCls followed by slow evaporation afforded the crystalline tetramer [OsO₂-(mes)₂(μ-4,4′-bpy)]₄ (4). The crystal structure of the tetramer 4 contains the square-planar [Os(4,4′-bpy)]₄ core with octahedral local geometry around each Os. The Os-O distance and O-Os-O angle are 1.6 A? and 159°, respectively. Treatment of OsO₂(mes)₂ with CNpy (4-cyanopyridine) gave [OsO₂(mes)₂]·[OsO₂(mes) ₂(CNpy)] (5). The structure of 5 consists of the four-coordinate [OsO₂(mes)₂] and five-coordinate [OsO₂(mes)₂(CNpy)] moieties, which are linked together via the Os=O?Os interaction. The Os-O distances in the [OsO₂(mes)₂] and [OsO₂(mes)₂(CNpy)] moieties in 5 are 1.69 and 1.71 A?, respectively. The (Os)O?Os distance is 2.78 A?, and the Os-O?Os angle is 170°. The Os-O stretching frequency for the above dimesityldioxoosmium(VI) complexes correlates well with the Os-O bond order and the coordination environment around Os.

Full text of DOI:10.1021/om950531+

Organometallics 1996, 15, 1497-1501
1497
Rea ction s of Dim esityld ioxoosm iu m (VI) w ith Bid en ta te
N-Heter ocycles. Cr ysta l Str u ctu r e of a Dioxoosm iu m (VI)
Com p lex Con ta in in g a Molecu la r Squ a r e
Wa-Hung Leung,*,† J ack Y. K. Cheng,‡ Tom S. M. Hun,† Chi-Ming Che,*,‡
Wing-Tak Wong,‡ and Kung-Kai Cheung‡
Departments of Chemistry, The Hong Kong University of Science and Technology,
Clear Water Bay, Kowloon, Hong Kong, and The University of Hong Kong,
Pokfulam Road, Hong Kong
Received J uly 11, 1995X
The interaction of OsO2(mes)2 (mes ) mesityl) with pyz (pyrazine) gave the pyrazine-
bridged dimer [OsO2(mes)2]2(µ-pyz) (1), which has been characterized by X-ray crystal-
lography. The structure around Os in 1 is square pyramidal, with the pyrazine, two oxo
ligands, and one mesityl group in the square plane. The Os-O distance and O-Os-O angle
are 1.71 Å and 147.5°, respectively. The reaction of OsO2(mes)2 with 4,4′-bpy (4,4′-bipyridyl)
and bpe (trans-1,2-bis(4-pyridyl)ethylene) in Et2O gave the oligomeric [OsO2(mes)2L]n (L )
1
4,4′-bpy (2), bpe (3)) in good yields. The H NMR spectra of 2 and 3 indicate that L’s are
coordinated in a symmetric fashion in these oligomers. The reaction of OsO2(mes)2 with
4,4′-bpy in CHCl3 followed by slow evaporation afforded the crystalline tetramer [OsO2-
(mes)2(µ-4,4′-bpy)]4 (4). The crystal structure of the tetramer 4 contains the square-planar
[Os(4,4′-bpy)]4 core with octahedral local geometry around each Os. The Os-O distance
and O-Os-O angle are 1.6 Å and 159°, respectively. Treatment of OsO2(mes)2 with CNpy
(4-cyanopyridine) gave [OsO2(mes)2]‚[OsO2(mes)2(CNpy)] (5). The structure of 5 consists of
the four-coordinate [OsO2(mes)2] and five-coordinate [OsO2(mes)2(CNpy)] moieties, which
are linked together via the OsdO‚‚‚Os interaction. The Os-O distances in the [OsO2(mes)2]
and [OsO2(mes)2(CNpy)] moieties in 5 are 1.69 and 1.71 Å, respectively. The (Os)O‚‚‚Os
distance is 2.78 Å, and the Os-O‚‚‚Os angle is 170°. The Os-O stretching frequency for
the above dimesityldioxoosmium(VI) complexes correlates well with the Os-O bond order
and the coordination environment around Os.
In tr od u ction
that certain trans-dioxo-Os(VI) complexes possess long-
lived photoemissive excited states4 prompted us to
synthesize polynuclear and macrocyclic complexes con-
taining the oxo-osmium moiety. Additionally, the ν(Os-
O) value can serve as a probe of the coordination
geometry around Os in the oxo-osmium-containing
polymers both in solution and in the solid state.
Coordinately unsaturated OsO2(mes)2 (mes ) mesityl)
has a high affinity for pyridine5 and, hence, would be
expected to be a good building block for polymers of the
type [OsO2(mes)2L]n (L ) bidentate bridging ligand, e.g.
pyrazine, 4,4′-bipyridyl). We herein describe the reac-
tions of OsO2(mes)2 with bidentate N-heterocycles and
the crystal structures of dimeric and macrocyclic com-
plexes containing the [OsO2(mes)2] moiety.
One- and two-dimensional network materials con-
taining transition metals have attracted much attention
due to their interesting catalytic, electrical, and optical
properties.1 Of particular interest are “molecular square”
materials based on metals and bipyridines, which have
been shown to recognize organic molecules and to
catalyze reactions.2 The rich redox chemistry of oxo-
osmium complexes3 coupled with the recent findings
* To whom correspondence should be addressed.
† The Hong Kong University of Science and Technology.
‡ The University of Hong Kong.
X Abstract published in Advance ACS Abstracts, February 1, 1996.
(1) See for example: (a) Hirsch, A.; Hanack, M. In Conjugated
Polymeric Materials: Opportunities in Electronics, Optoelectronics and
Molecular Electronics; Bredas, J . L., Chance, R. R., Eds.; Kluwer: New
York, 1990; p 163. (b) Schultz, H.; Lehmann, H.; Rein, M.; Hanack,
M. Struct. Bonding 1991, 74, 41.
Exp er im en ta l Section
(2) (a) Robinson, R.; Abrahams, B. F.; Batten, S. R.; Gable, R. W.;
Hoskins, B. F.; Liu, J . In Supramolecular Architecture; Bein, T., Ed.;
ACS Symposium Series 499; American Chemical Society: Washington,
DC, 1992; Chapter 12, and references cited therein. (b) Fujita, M.;
Yazaki, J .; Ogura, K. J . Am. Chem. Soc. 1994, 116, 1151. (c) Fujita,
M.; Kwon, Y. J .; Washizu, S.; Ogura, K. J . Am. Chem. Soc. 1994, 116,
1151. (d) Stang, P. J .; Zhdankin, V. V.J . Am. Chem. Soc., 1993, 115,
9808. (e) Stang, P. J .; Cao, D. H. J . Am. Chem. Soc. 1994, 116, 4981.
(f) Stang, P. J .; Chen, K. J . Am. Chem. Soc. 1995, 117, 1667. (g) Stang,
P. J .; Cao, D. H.; Saito, S.; Arif, A. M.J . Am. Chem. Soc. 1995, 117,
6273. (h) Rauter, H.; Hillgeris, E. C.; Erxleben, A.; Lippert, B. J . Am.
Chem. Soc. 1994, 116, 616.
(3) (a) Che, C.-M.; Yam, V. W.-W. Adv. Inorg. Chem. 1992, 39, 233.
(b) Che, C.-M.; Cheng, W.-K.; Yam, V. W.-W. J . Chem. Soc., Dalton
Trans. 1990, 3095. (c) Che, C.-M.; Cheng, W.-K.; Mak, T. C. W. J .
Chem. Soc., Chem. Commun. 1986, 200. (d) Che, C.-M.; Cheng, W.-K.
J . Am. Chem. Soc. 1986, 108, 4644.
Solvents were purified and distilled prior to use. 1H NMR
spectra (in CDCl3) were recorded on a J EOL EX400 spectrom-
eter. Chemical shifts (δ, ppm) were reported with reference
to SiMe4. Infrared spectra were recorded on a Perkin-Elmer
(4) (a) Che, C.-M.; Yam, V. W.-W.; Cho, K.-C.; Gray, H. B. J . Chem.
Soc., Chem. Commun. 1987, 948. (b) Yam, V. W.-W.; Che, C.-M. Coord.
Chem. Rev. 1990, 97, 93. (c) Schindler, S.; Castner, E. W., J r.; Creutz,
C.; Sutin, N. Inorg. Chem. 1993, 32, 4200.
(5) (a) Starvopolous, P.; Edwards, P. G.; Behling, T.; Wilkinson, G.;
Motevalli, M.; Hursthouse, M. B. J . Chem. Soc., Dalton Trans. 1987,
169. (b) McGrilligan, B. S.; Arnold, J .; Wilkinson, G.; Hussain-Bates,
B.; Hursthouse, M. B. J . Chem. Soc., Dalton Trans. 1990, 2465. (c)
Chin, K.-F.; Cheng, Y.-K.; Cheung, K.-K.; Guo, C.-X.; Che, C.-M. J .
Chem. Soc., Dalton Trans. 1995, 2967.
0276-7333/96/2315-1497$12.00/0 © 1996 American Chemical Society

1498 Organometallics, Vol. 15, No. 5, 1996
Ta ble 1. Su m m a r y of Cr ysta l Da ta a n d Exp er im en ta l Deta ils
Leung et al.
1
4
5
formula
Mr
color, habit
cryst syst
space group
a/Å
b/Å
c/Å
C40H46N2O4Os2
999.21
blue, block
monoclinic
P21/n (No. 14)
9.452(2)
8.970(4)
22.451(2)
90.0
92.97(1)
90.0
1901.0(6)
[C28H30N2O2Os]4
616.76
C42H48N2O4Os2
1025.25
black, block
monoclinic
P21/n (No. 14)
13.672(2)
13.539(2)
21.406(5)
90.0
93.01(2)
90.0
3957(1)
4
black, block
tetragonal
I41/9 (No. 88)
18.318(5)
18.318(5)
31.465(6)
90.0
90.0
90.0
10 558.3(1)
4
1.552
R/deg
â/deg
γ/deg
V/Å3
Z
2
Dc/g cm-3
1.746
1.721
F(000)
968
4864
1992
diffractometer
Rigaku
298
67.14
3594
Enraf-Nonius
298
48.6
Rigaku
298
64.54
T/K
µ(Mo KR)/ cm-1
no. of unique rflns
no. of observed rflns (I > 3.00σ(I0))
weighting scheme
Ra
3525
1962
7288
3991
2530
4Fo2/[σ2(Fo2) + 0.004(Fo2)2]
4Fo2/[σ2(Fo2) + 0.065Fo2)2]
0.040
4Fo2/[σ2(Fo2) + 0.003Fo2)2]
0.032
0.035
1.81
+0.73 to -0.59
0.04
0.036
1.85
+0.95 to -1.01
a
Rw
0.053
1.195
+1.14 to -1.13
Sb
residual electron density/e Å-3
a
2
b
R ) Σ |Fo| - |Fc|/Σ|Fo|; Rw ) [w (|Fo| - |Fc|)2/Σw|Fo| ]1/2
.
S ) [Σ w(|Fc| - |Fo|)2/(Nobs - Nparam)]1/2
.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 1
16 PC FT-IR spectrophotometer. Elemental analyses were
performed by Medac Ltd., Brunel University, U.K.
OsO2(mes)2 was synthesized according to the literature
method.5a The ligands pyz (pyrazine), 4,4′-bpy (4,4′-bipyridyl),
bpe (trans-1,2-bis(4-pyridyl)ethylene), and CNpy (4-cyanopy-
ridine) were purchased from Aldrich and used as received.
Syn th esis of [OsO2(m es)2]2(µ-p yz) (1). To a solution of
OsO2(mes)2 (50 mg, 0.11 mmol) in Et2O (10 mL) was added
pyz (9 mg, 0.05 mmol), and the mixture was stirred at room
temperature for 1 h. The volatiles were pumped off, and the
residue was extracted with hexane/Et2O. Slow evaporation
of the extracts afforded dark crystals, which were suitable for
a diffraction study (yield 44 mg, 80%). 1H NMR: δ 2.33 (s,
12H, o-CH3), 2.53 (s, 6H, p-CH3), 6.99 (s, 4H, Hm), 8.60 (d, 4H,
pyz). IR (Nujol, cm-1): 900 (ν(OsO2)). Anal. Calcd for
[C40H46N2O4Os2]: C, 48.0; H, 4.8; N, 2.8. Found: C, 47.6; H,
5.0; N, 2.5.
Syn th esis of [OsO2(m es)2(µ-4,4′-bp y)]n (2). To a solution
of OsO2(mes)2 (50 mg, 0.11 mmol) in Et2O (10 mL) was added
a slight excess of 4,4′-bpy (25 mg, 0.16 mmol), and the mixture
was stirred for 15 min, during which a copious amount of
brown precipitate was formed. The solid was collected, washed
with ether, and dried in air (yield 60 mg, 90%). 1H NMR: δ
2.32 (s, 12H, o-CH3), 2.45 (s, 24H, p-CH3), 6.94 (s, 4H, Hm),
7.59 (d, 4H, pyridyl proton), 8.70 (d, 4H, pyridyl proton). Anal.
Calcd for [C28H30N2O2Os]: C, 54.3; H, 5.0; N, 4.8. Found: C,
54.5; H, 4.9; N, 4.5. IR (Nujol, cm-1) 868 ν(OsO2).
Syn th esis of [OsO2(m es)2(µ-bp e)]n (3). This was pre-
pared as for 2 from OsO2(mes)2 (50 mg, 0.11 mmol) and bpe
(20 mg, 0.11 mmol) in Et2O (10 mL), isolated as a brown solid
(yield 60 mg, 86%). 1H NMR: δ 2.31 (s, 24H, o-CH3), 2.47 (s,
12H, p-CH3), 7.26 (s, 2H, CH)C), 7.49 (d, 4H, pyridyl proton),
8.54 (d, 4H, pyridyl proton). IR (Nujol, cm-1): 864 (ν(OsO2)),
1610 (ν(CdC)). Anal. Calcd for [C30H32N2O2Os]: C, 56.1; H,
5.0; N, 4.4. Found: C, 55.7; H, 5.3; N, 4.1.
Syn th esis of [OsO2(m es)2(µ-4,4′-bp y)]4 (4). To a solution
of OsO2(mes)2 (50 mg, 0.11 mmol) in CHCl3 (10 mL) was added
1 equiv of 4,4′-bpy (18 mg, 0.11 mol) and the solution was left
to stand at room temperature for 2 days. Upon slow evapora-
tion, dark green crystals were formed and collected (yield: 34
mg, 50%). 1H NMR: δ 2.32 (s, 12H,o-CH3), 2.45 (s, 6H, p-CH3),
6.94 (s, 4H, Hm), 7.59 (d, 4H, pyridyl proton), 8.70 (d, 4H,
pyridyl proton). IR (Nujol, cm-1): 865, 859 (ν(OsO2)). Anal.
Calcd for [C28H30N2O2Os]4: C, 54.3; H, 5.0; N, 4.8. Found: C,
54.5; H, 4.9; N, 4.5.
Os(1)-O(1)
Os(1)-N(1)
Os(1)-C(12)
1.722(5)
2.391(6)
2.093(7)
Os(1)-O(2)
Os(1)-C(3)
1.718(5)
2.085(8)
O(1)-Os(1)-O(2)
O(1)-Os(1)-C(3)
O(2)-Os(1)-N(1)
O(2)-Os(1)-C(12)
N(1)-Os(1)-C(12)
147.5(3)
101.0(3)
84.7(3)
93.0(3)
169.9(3)
O(1)-Os(1)-N(1)
O(1)-Os(1)-C(12)
O(2)-Os(1)-C(3)
N(1)-Os(1)-C(3)
C(3)-Os(1)-C(12)
80.3(3)
96.9(3)
107.2(3)
88.6(3)
101.4(3)
Syn th esis of [OsO2(m es)2]‚[OsO2(m es)2(CNp y)] (5). To
a solution of OsO2(mes)2 (50 mg, 0.11 mmol) in Et2O (10 mL)
was added 0.5 equiv of CNpy (6 mg, 0.05 mmol), and the
mixture was stirred at room temperature for 30 min. The
solvent was pumped off, and the residue was washed with
hexane and recrystallized from Et2O/hexane to give dark green
crystals (yield: 45 mg, 80%). 1H NMR: δ 2.32 (s, 24H, o-CH3),
2.52 (s, 12H, p-CH3), 6.98 (s, 8H, Hm), 7.62 (d, 2H, pyridyl),
8.76(d, 2H, pyridyl). IR (Nujol, cm-1): 2239 (ν(C≡N)), 918,
962, 932, 884 (ν(OsO2)). Anal. Calcd for [C42H46N2O4Os2] :
C, 49.3; H, 4.5; N, 2.7. Found: C, 49.0; H, 4.7; N, 2.6.
X-r a y Diffr a ction Mea u r em en ts. Data for 1 and 5 were
collected on a Rigaku AFC7R diffractometer with graphite-
monochromated Mo KR radiation (λ ) 0.710 73 Å) and a 12
kW rotating anode generator. Data for 4 were collected on a
Enraf-Nonius CAD4 diffractometer with graphite-monochro-
mated Mo KR radiation (λ 0.710 73 Å). The structures for 1
and 4 were solved by direct methods, while the structure for
5 was solved by the Patterson method. These three structures
were refined by full-matrix least-squares analyses. All inten-
sity data were corrected for Lorentz and polarization effects.
All non-hydrogen atoms were refined anisotropically. The
hydrogen atoms were generated in their ideal positions (C-H
) 0.95 Å). A summary of crystal data and experimental details
is given in Table 1. Selected bond distances and angles for 1,
4, and 5 are listed in Tables 2-4, respectively.
Resu lts a n d Discu ssion
Syn th eses. The interaction of OsO2(mes)2 with 0.5
equiv of pyz (pyrazine) afforded the pyrazine-bridged
dimer [OsO2(mes)2]2(µ-pyz) (1) in good yield. The solid-
state structure of 1 was characterized by X-ray crystal-

Complexes Containing [OsO2(mes)2]
Organometallics, Vol. 15, No. 5, 1996 1499
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 4
Os-O(1)
Os-N(1)
Os-C(1)
1.738(9)
2.34(2)
2.11(1)
Os-O(2)
Os-N(2)
Os-C(10)
1.76(1)
2.36(1)
2.11(1)
O(1)-Os-O(2)
O(1)-Os-N(2)
O(1)-Os-C(10)
O(2)-Os-C(1)
N(1)-Os-N(2)
N(1)-Os-C(10)
N(2)-Os-C(10)
159.4(4)
83.4(4)
101.2(5)
100.3(5)
87.1(5)
O(1)-Os-N(1)
O(1)-Os-C(1)
O(2)-Os-N(1)
O(2)-Os-C(10)
N(1)-Os-C(1)
N(2)-Os-C(1)
C(1)-Os-C(10)
81.5(5)
94.0(6)
83.9(5)
93.2(6)
88.1(5)
174.8(5)
92.9(6)
177.0(5)
91.9(5)
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 5
F igu r e 1. Perspective view of 1 (50% probability ellip-
soids).
Os(1)-O(1)
Os(1)-N(1)
Os(1)-C(16)
Os(2)-O(4)
Os(2)-C(34)
1.710(7)
2.314(8)
2.11(1)
1.687(7)
2.05(1)
Os(1)-O(2)
Os(1)-C(7)
Os(2)-O(3)
Os(2)-C(25)
1.710(8)
2.06(1)
1.705(7)
2.07(1)
O(1)-Os(1)-O(2)
O(1)-Os(1)-C(16)
O(2)-Os(1)-C(7)
O(2)-Os(1)-C(16)
144.8(3) O(1)-Os(1)-N(1)
92.7(4) O(1)-Os(1)-C(7)
103.5(4) O(2)-Os(1)-N(1)
97.7(4) N(1)-Os(1)-C(7)
85.2(3)
108.4(4)
81.3 (3)
88.3(3)
96.9(4)
101.5(4)
108.6(4)
97.8(4)
N(1)-Os(1)-C(16) 174.7(3) C(7)-Os(1)-C(16)
O(3)-Os(2)-O(4)
O(3)-Os(2)-C(34)
O(4)-Os(2)-C(34)
141.7(4) O(3)-Os(2)-C(25)
96.1(4) O(4)-Os(2)-C(25)
96.1(4) C(25)-Os(2)-C(34)
lography and is shown in Figure 1. The geometry
around Os in 1 is distorted square pyramidal, with the
pyrazine, one mesityl, and two oxo groups in the
equatorial plane. The Os-O distance is ca. 1.721 Å, and
the O-Os-O angle is 147.5(3)°. The Os-N distance of
2.398 Å is significantly longer than a normal OsVI-N
bond (e.g. the Os-N(py) distance in trans-OsO2Cl2(py)2
is ca. 2.101 Å6 ), suggesting lability of the coordinated
pyrazine. Indeed, the IR spectrum of 1 in CCl4 shows
Os-O stretches due to both OsO2(mes)2 (962, 928 cm-1
)
and 1 (900 cm-1). Upon addition of pyz to a CCl4
solution of 1, the 962 and 928 cm-1 bands decrease in
intensity and the 900 cm-1 band increases concomi-
tantly. This indicates that 1 is in equilibrium with
OsO2(mes)2 in solution and the dissociation of pyz in 1
is suppressed by pyz (eq 1).
F igu r e 2. Perspective view of 4 (50% probability ellip-
soids).
materials are insoluble in toluene, acetone, and hexane
and slightly soluble in THF and CHCl3. The value of n
for 2 in THF solution was determined to be ca. 5 by gel
[OsO2(mes)2]2(µ-pyz) a 2OsO2(mes)2 + pyz (1)
1
permeation chromatography. The H NMR spectra of
Further addition of pyz led to appearance of a new
Os-O band at 874 cm-1, which is typical for an
octahedral dimesityldioxoosmium(VI) complex (see be-
low), attributable to the formation of the bis(pyrazine)
adduct trans-OsO2(mes)2(pyz)2 (eq 2).
2 and 3 in CDCl3 show two doublets for the pyridyl
protons, suggesting that the L’s are bridging ligands and
are coordinated symmetrically between two Os centers.
The IR spectra of 2 in both Nujol and CCl4 solution
display Os-O stretches at ca. 868 cm-1, indicative of a
trans disposition of the two oxo ligands.
[OsO2(mes)2]2(µ-pyz) + pyz (excess) a
On the other hand, the reaction of OsO2(mes)2 with
4,4′-bpy in CHCl3 followed by slow evaporation led to
the isolation of the crystalline cyclic tetramer trans-
[OsO2(mes)2(µ-4,4′-bpy)]4 (4), which has been character-
ized by X-ray crystallography. To our knowledge, 4 rep-
resents the first structurally characterized neutral “mo-
lecular square” containing a high-valent organometallic
building block. Figure 2 shows a perspective view of
the molecule. The structure consists of the planar Os4-
(4,4′-bpy)4 moiety with Os and 4,4′-bpy at each corner
and side, respectively. Similar square network struc-
tures have been reported for the related cationic materi-
als [M(4,4′-bpy)2]X (M ) Zn, Cd, Cu; X ) PF6, SiF6),2c
{[Cd(4,4′-bpy)](NO3)}∞,2d and [Pt(dppp)(4,4′-bpy)]4(O3-
SCF3)8 (dppp ) 1,3-bis(diphenylphosphino)propane).2g
2OsO2(mes)2(pyz)2 (2)
One might expect that the formation of polymers of
the type [OsO2(mes)2(L)]n should be favorable for longer
spacers L such as 4,4′-bpy (4,4′-bipyridyl) and bpe
(trans-1,2-bis(4-pyridyl)ethylene). Indeed, the reactions
of OsO2(mes)2 with and bpe led to isolation of such
complexes. However, the nature of the products was
found to be dependent on the experimental conditions.
Treatment of OsO2(mes)2 with 4,4′-bpy and bpe in Et2O
led to immediate precipitation of brown solids analyzed
as [OsO2(mes)2L]n (L ) 4,4′-bpy (2), bpe (3)). These
(6) Imbe, Y.; Umakoshi, K.; Matsuanmid, C.; Sasaki, Y. Inorg. Chem.
1995, 34, 813.

1500 Organometallics, Vol. 15, No. 5, 1996
Leung et al.
Os-O vibrational modes assignable to both the [OsO2-
(mes)2] (918, 932 cm-1) and the [OsO2(mes)2(CNpy)] (884
cm-1) entities.
Bon d in g a n d Str u ctu r e. The structures of OsO2-
(mes)2 and its mono and bis adducts are tetrahedral (I),
square pyramidal (II), and octahedral (III), respectively.
These geometries are in agreement with those predicted
by group theory for d2 dioxometal complexes. Accord-
ingly, the formal Os-O bond orders for I-III are 3, 2.5,
and 2, respectively.7 The Os-N bonds in the adducts
1, 4, and 5 are considerably weaker and longer than a
normal Os-pyridine bond, obviously due to the strong
trans influence of the mesityl ligands. Coordination of
bases to OsO2(mes)2 results in a lowering of the Os-O
bond order and an increase in steric congestion around
Os. This explains why these adducts are unstable in
solution with respect to ligand dissociation. It might
also be noted that the O-Os-O angle (ca. 150°) in the
monoadduct II is significantly smaller than the ideal
value of 180°. The bending of O-Os-O in II can be
explained in terms of the maximization of overlap of the
filled pπ(O) orbital with the vacant dπ(Os) orbital
(of b2 symmetry), which is below the equatorial plane.7
F igu r e 3. Perspective view of 5 (50% probability ellip-
soids).
The local geometry around each osmium is pseudo
octahedral with the two 4,4′-bpy and two mesityl groups
occupying the equatorial plane; the Os-O distance and
O-Os-O angle are ca. 1.75 Å and 159.4°, respectively.
The IR spectrum of 4 in Nujol shows intense Os-O
stretches at 865 and 859 cm-1. There are two stretching
modes for the trans-OsO2 entity, possibly due to the
bending of O-Os-O. Consistent with the solid-state
structure, the 1H NMR spectrum of 4 displays two
doublets for the pyridyl protons, indicative of the
symmetric binding mode of 4,4′-bpy.
In an attempt to prepare the cyanopyridine-bridged
oligomer of OsO2(mes)2, the reaction of OsO2(mes)2 with
CNpy (4-cyanopyridine) has also been investigated. In-
teraction of OsO2(mes)2 with 0.5 equiv of CNpy in Et2O,
followed by recrystallization from hexane/Et2O, led to
the isolation of [OsO2(mes)2]‚[OsO2(mes)2(CNpy)] (5). No
polymeric materials were obtained, even when a stoi-
chiometric amount of CNpy was used. The structure
of 5, shown in Figure 3, consists of a four-coordinate
[OsO2(mes)2] and a five-coordinate [OsO2(mes)2(CNpy)]
moiety, which are linked together via the weak OsdO‚‚‚
Os′ interaction. The geometry of the [OsO2(mes)2]
moiety is pseudotetrahedral, with an Os-O distance
(1.69 Å) similar to that found for OsO2(mes)2.5a The
geometry around Os in the [OsO2(mes)2(CNpy)] moiety
is approximately trigonal bipyramidal with the two oxo
ligands and one mesityl group in the trigonal plane.
Similar bond angles have been found for the related
five-coordinate dioxoosmium(VI) complex [OsO2(mes)-
(ONO2)2]- (O-Os-O angle 146.7(2)°)5b and bis(imido)-
osmium(VI) complex Os(NAr)2(PMe2Ph)I2 (Ar ) 2,6-
diisopropylphenyl, N-Os-N angle 150°).8 For the
above dimesityldioxoosmium(VI) complexes, the ν(Os-
O) value correlates well with the geometry around Os,
the Os-O bond length, and the O-Os-O angle, which
are collected in Table 5. For example, the ν(Os-O)
value varies from 950 cm-1 for tetrahedral to 890 cm-1
for square pyramidal and to 859 cm-1 for octahedral
geometry. The Os-O bond length is, however, less
sensitive to the change in Os-O bond order and
decreases from 1.695 Å or an Os-O double bond to 1.749
Å for an Os-O triple bond.
In summary, we have demonstrated that OsO2(mes)2
reacts with N-bases to give dimeric, tetrameric, and
polymeric complexes, depending on the experimental
conditions. The Os-O stretching frequency provides
valuable information on the solution structure and the
coordination environment around Os for these com-
plexes. The study of their photophysical, catalytic, and
clathration properties is underway.
There is no significant difference between the two Os-O
distances (ca. 1.71 Å) in the [OsO2(mes)2(CNpy)] moiety,
which are similar to those for 1. The OsdO‚‚‚Os′ angle
is ca. 170°, and the (Os)O‚‚‚Os′ distance (ca. 2.78 Å) is
considerably longer than a normal OsVI-O single bond.
The O‚‚‚Os interaction is weak but significant, at least
in the solid state, and can be considered as a donor-
acceptor type. The IR spectrum of 5 shows intense
(7) Lin, Z.; Hall, M. B. Coord. Chem. Rev. 1993, 123, 149.
(8) Schofield, M. H.; Kee, T. P.; Anhaus, J . T.; Schrock, R. R.;
J ohnson, K. H.; Davis, W. M. Inorg. Chem. 1991, 30, 3595.

Complexes Containing [OsO2(mes)2]
Organometallics, Vol. 15, No. 5, 1996 1501
Ta ble 5. Str u ctu r a l a n d Vibr a tion a l Da ta for th e Dim esityld ioxoosm iu m (VI) Com p lexes
geometry
complex
Os-O (Å)
O-Os-Os (deg)
ν(Os-O) (cm-1
)
a
tetrahedral
Os(mes)2O2
1.695
1.69
136.1
141.7
950, 918
932, 918
[OsO2(mes)2] of 5
square pyramidal
1
1.710
1.71
1.714
144.8
144.8
146.7
900
884
899
[OsO2(mes)2(CNpy)] of 5
[OsO2(mes)(ONO2)2]- b
octahedral
4
1.749
1.732
1.72
159.4
162.7
158.5
865, 859
878
870
OsO2(mes)2(tmeda)c
OsO2(mes)2(phen)c
a
b
Reference 5a. Reference 5b. c Reference 5c. Abbreviations: tmeda ) N,N,N′,N′-tetramethylethylenediamine; phen ) 1,10-
phenanthroline.
Su p p or tin g In for m a tion Ava ila ble: Listings of calcu-
lated atomic coordinates, bond distances and angles, and
anisotropic thermal parameters for compounds 1, 4, and 5 (32
pages). Ordering information is given on any current mast-
head page.
Ack n ow led gm en t. Support from The Hong Kong
University of Science and Technology, The University
of Hong Kong, and The Hong Kong Research Grants
Council (Grant No. HKUST 202E/93) is gratefully
acknowledged. We thank Dr. Zhenyang Lin for helpful
discussions.
OM950531+