Chiral osmium complexes with sterically bulky schiff-base ligands. Crystal structures of Os(IV) derivatives and the reactivity and catalytic cyclopropanation of alkenes with EDA

Article abstract of DOI:10.1021/ic0481935

The syntheses and reactivities of sterically encumbered trans-dioxoosmium(VI) complexes containing Schiff-base ligands bis(3,5-di-tert-butylsalicylidene)-1,2-cydohexane-diamine (H₂Bu- salch) and bis(3,5-dibromosalicylidene)-1,2-cyclohexane-diamine (H ₂Br-salch) are described. Reactions of [Os^VI(Bu-salch) O₂] (1a) and [Os^VI(Br-salch)O₂] (1b) with PPh₃, p-X-arylamines (X = NO₂, CN), N₂H ₄·H₂O, Ph₂NNH₂, SOCl ₂, CF₃CO₂H, Br₂, and I₂ under reducing conditions gave [Os^II(Br-salch)(OPPh₃) ₂] (2), [Os^VI(Br-salch)(p-X-C₆H ₄NH)₂] (3), [μ-O{Os^IV(Bu-salch)(p-NO ₂C₆H₄-NH)}₂] (4), [Os ^II(Br-salch)(N₂)(H₂O)] (5), [Os ^IV(Bu-salch)(OH)(Cl)] (6), [Os^IV(Bu-salch)(OH) ₂] (7), [Os^IV(Bu-salch)-Cl₂] (8), [Os ^IV(Bu-salch)(CF₃CO₂)₂] (9), [Os ^IV(Bu-salch)Br₂] (10), and [Os^IV(Bu-salch) I₂] (11), respectively. X-ray crystal structure determinations of [Os^IV(Br-salch)(p-NO₂C₆H₄NH) ₂] (3a), [Os^IV(Br-salch)(p-CNC₆H ₄NH)₂] (3b), 6, 8, 9, and 11 reveal the Os-N(amido) distances to be 1.965(4)-1.995(1) A for the bis(amido) complexes, Os-Cl distances of 2.333(8)-2.3495(1) A for 6 and 8, Os-O(CF₃CO ₂) distances of 2.025(6)-2.041(6) A for 9, and Os-I distances of 2.6884(6)-2.6970(6) A for 11. Upon UV irradiation, (1S,2S)-(1a) reacted with aryl-substituted alkenes to give the corresponding epoxides in moderate yields, albeit with no enantioselectivity. The (1R,2R)-6 catalyzed cyclopropanation of a series of substituted styrenes exhibited moderate to good enantioselectivity (up to 79% ee) and moderate trans selectivity.

Full text of DOI:10.1021/ic0481935

Inorg. Chem. 2005, 44, 3942−3954
Chiral Osmium Complexes with Sterically Bulky Schiff-Base Ligands.
Crystal Structures of Os(IV) Derivatives and the Reactivity and Catalytic
Cyclopropanation of Alkenes with EDA
Jing Zhang,† Jiang-Lin Liang,† Xian-Ru Sun,† Hai-Bing Zhou,† Nian-Yong Zhu,† Zhong-Yuan Zhou,‡
Philip Wai Hong Chan,*,† and Chi-Ming Che*,†
Department of Chemistry and Open Laboratory of Chemical Biology of the Institute of Molecular
Technology for Drug DiscoVery and Synthesis, The UniVersity of Hong Kong, Pokfulam Road,
Hong Kong, P. R. China, and Department of Applied Biology and Chemical Technology,
The Hong Kong Polytechnic UniVersity, Hung Hom, Kowloon, Hong Kong, P. R. China
Received December 22, 2004
The syntheses and reactivities of sterically encumbered trans-dioxoosmium(VI) complexes containing Schiff-base
t
ligands bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diamine (H2 Bu-salch) and bis(3,5-dibromosalicylidene)-1,2-
cyclohexane-diamine (H2Br-salch) are described. Reactions of [OsVI(tBu-salch)O2] (1a) and [OsVI(Br-salch)O2] (1b)
with PPh3, p-X
conditions gave [OsII(Br-salch)(OPPh3)2] (2), [OsIV(Br-salch)(p-X-C6H4NH)2] (3), [
NH)
−
arylamines (X
)
NO2, CN), N2H4
‚
H2O, Ph2NNH2, SOCl2, CF3CO2H, Br2, and I2 under reducing
-O-
OsIV(tBu-salch)(p-NO2C6H4-
2] (4), [OsII(Br-salch)(N2)(H2O)] (5), [OsIV(tBu-salch)(OH)(Cl)] (6), [OsIV(tBu-salch)(OH)2] (7), [OsIV(tBu-salch)-
µ
{
}
Cl2] (8), [OsIV(tBu-salch)(CF3CO2)2] (9), [OsIV(tBu-salch)Br2] (10), and [OsIV(tBu-salch)I2] (11), respectively. X-ray
crystal structure determinations of [OsIV(Br-salch)(p-NO2C6H4NH)2] (3a), [OsIV(Br-salch)(p-CNC6H4NH)2] (3b), 6, 8,
9, and 11 reveal the Os
distances of 2.333(8) 2.3495(1) Å for 6 and 8, Os
distances of 2.6884(6) 2.6970(6) Å for 11. Upon UV irradiation, (1S,2S)-(1a) reacted with aryl-substituted alkenes
−
N(amido) distances to be 1.965(4)
−
1.995(1) Å for the bis(amido) complexes, Os
−Cl
−
−O(CF3CO2) distances of 2.025(6)
−2.041(6) Å for 9, and Os
−I
−
to give the corresponding epoxides in moderate yields, albeit with no enantioselectivity. The (1R,2R)-6 catalyzed
cyclopropanation of a series of substituted styrenes exhibited moderate to good enantioselectivity (up to 79% ee)
and moderate trans selectivity.
Introduction
complexes has rendered them to be an invaluable model
system for understanding the physical and spectroscopic
properties of their ruthenium analogues, which should be
more reactive toward organic transformations. Previous
works by Che and co-workers had described a one-pot
synthesis of trans-[OsVI(salen)O2] [salen ) N,N′-bis(sali-
cylidene)ethylenediamine] and the susceptibility of this
complex to undergo reduction in the presence of PPh3 and
thiols.2a In view of these works showing that dioxoruthenium-
(VI) porphyrins are useful catalysts for a number of organic
transformations,3,4 we were intrigued with the possibility of
developing similar chemistry with ruthenium and osmium
complexes containing inexpensive Schiff-base ligands. In-
deed, chiral metal Schiff-base complexes have been dem-
onstrated to be versatile catalysts for enantioselective organic
transformation reactions. Pioneering work by Nakamura and
co-workers showed that chiral (Schiff-base)cobalt(II) com-
The chemistry of dioxoosmium(VI) complexes containing
multianionic Schiff-base ligands has come under increasing
scrutiny in recent years.1,2 Unlike their ruthenium counter-
parts, the greater stability of dioxoosmium(VI) Schiff-base
* Authors to whom correspondence should be addressed. Fax: (852)
2857 1586. Tel: (852) 2859 2154. E-mail: cmche@hku.hk (C.-M.C.);
pwhchan@hkucc.hku.hk (P.W.H.C.).
† The University of Hong Kong.
‡ The Hong Kong Polytechnic University.
(1) (a) Lay, P. A.; Harman, W. D. AdV. Inorg. Chem. 1991, 37, 219. (b)
Lynch, W. E.; Lintvedt, R. L.; Shui, X. Q. Inorg. Chem. 1991, 30,
1014. (c) Wong, T.-W.; Lau, T.-C.; Wong, W.-T. Inorg. Chem. 1999,
38, 6181.
(2) (a) Che, C.-M.; Cheng, W.-K.; Mak, T. C. W. Inorg. Chem. 1986,
25, 703. (b) Che, C.-M.; Cheng, W.-K.; Mak, T. C. W. Inorg. Chem.
1988, 27, 250. (c) Cheng, W.-K.; Wong, K.-Y.; Tong, W.-F.; Lai,
T.-F.; Che, C.-M. J. Chem. Soc., Dalton Trans. 1992, 91. (d) Yip,
K.-L.; Yu, W.-Y.; Chan, P.-M.; Zhu, N.-Y.; Che, C.-M. J. Chem. Soc.,
Dalton Trans. 2003, 3556.
3942 Inorganic Chemistry, Vol. 44, No. 11, 2005
10.1021/ic0481935 CCC: $30.25
© 2005 American Chemical Society
Published on Web 04/27/2005

Chiral Osmium Complexes with Schiff-Base Ligands
Scheme 1
plexes are effective catalysts for asymmetric methylene
transfer reactions.5 Jacobsen and Katsuki showed that chiral
manganese(III) Schiff-base complexes catalyzed highly
enantioselective alkene epoxidation and C-H bond oxida-
tions.6 More recently, Katsuki et al. reported that Ru(II), Co-
(II), and Co(III) Schiff-base complexes catalyzed cyclopro-
panation of alkenes with good to high cis diastereo- and
enantioselectivities.6c,7 The applications of chiral ruthenium-
(II) and manganese(III) Schiff-base complexes in stereose-
lective nitrene transfer reactions to CdC bonds and insertion
to saturated C-H bonds have also been reported.6,8 Herein,
we present the synthesis and characterization of trans-
dioxoosmium(VI) complexes supported by the sterically
encumbered chiral Schiff-base ligands bis(3,5-di-tert-butyl-
crystallographic analysis. We also describe a chiral osmium-
(IV) Schiff-base-catalyzed protocol for alkene cyclopropa-
nation with ethyl diazoacetate (EDA) that was accomplished
with moderate trans selectivity and moderate to good
enantioselectivities (Scheme 1).
t
salicylidene)-1,2-cyclohexane-diamine (H2 Bu-salch) and bis-
(3,5-dibromosalicylidene)-1,2-cyclohexane-diamine (H2Br-
salch) and the reactivities of these compounds toward PPh3,
amines, hydrazines, and nucleophiles under reducing condi-
tions and alkenes under photolytic conditions. The trans-
osmium(IV) Schiff-base complexes obtained from these
reactions have been structurally characterized by X-ray
Results and Discussion
A. Dioxoosmium(VI) Schiff-Base Complexes [OsVI(tBu-
salch)O2] (1a) and [OsVI(Br-salch)O2] (1b). i. Synthesis.
A number of first row transition metal complexes containing
chelating multianionic ligands have been extensively studied
for their catalytic activities in carbon-carbon, carbon-
oxygen, and carbon-nitrogen bond formation reactions.6-8
This is in contrast to only a handful reports on the chemistry
of late transition metal Schiff-base complexes. Previous
works by us2 and others1c,9 showed that certain [OsVI(Schiff-
base)O2] complexes could be readily prepared by reacting
the corresponding Schiff-base ligand with K2[OsO2(OH)4].
However, a similar reaction of K2[OsO2(OH)4] with either
(3) For works by us, see: (a) Leung, W. H.; Che, C.-M. J. Am. Chem.
Soc. 1989, 111, 8812. (b) Ho, C.; Leung, W.-H.; Che, C.-M. J. Chem.
Soc., Dalton Trans. 1991, 2933. (c) Lai, T.-S.; Zhang, R.; Cheung,
K.-K.; Kwong, H.-L.; Che, C.-M. Chem. Commun. 1998, 1583. (d)
Liu, C.-J.; Yu, W.-Y.; Peng, S.-M.; Mak, T. C. W.; Che, C.-M. J.
Chem. Soc., Dalton Trans. 1998, 1805. (e) Lai, T.-S.; Kwong, H.-L.;
Zhang, R.; Che, C.-M. J. Chem. Soc., Dalton Trans. 1998, 3559. (f)
Liu, C.-J.; Yu, W.-Y.; Che, C.-M.; Yeung, C.-H. J. Org. Chem. 1999,
64, 7365. (g) Zhang, R.; Yu, W.-Y.; Lai, T.-S.; Che, C.-M. Chem.
Commun. 1999, 409; Chem. Commun. 1999, 757. (h) Zhang, R.; Yu,
W.-Y.; Lai, T.-S.; Che, C.-M. Chem. Commun. 1999, 1791. (i) Zhang,
R.; Yu, W.-Y.; Wong, K.-Y.; Che, C.-M. J. Org. Chem. 2001, 66,
8145. (j) Zhang, R.; Yu, W.-Y.; Sun, H.-Z.; Liu, W.-S.; Che, C.-M.
Chem.sEur. J. 2002, 8, 2495.
(4) For works by others, see: (a) Groves, J. T.; Quinn, R. Inorg. Chem.
1984, 23, 3844. (b) Groves, J. T.; Quinn, R. J. Am. Chem. Soc. 1985,
107, 5790. (c) Groves, J. T.; Ahn, K. H. Inorg. Chem. 1987, 26, 3831.
(d) Tavares, M.; Ramasseul, R.; Marchon, J. C. Catal. Lett. 1990, 4,
163. (e) Ohtake, H.; Higuchi, T.; Hirobe, M. J. Am. Chem. Soc. 1992,
114, 10660. (f) Tokita, Y.; Yamaguchi, K.; Watanabe, Y.; Morishima,
I. Inorg. Chem. 1993, 32, 329. (g) Le Maux, P.; Bahri, H.; Simonneaux,
G. Chem. Commun. 1994, 1287. (h) Le Maux, P.; Bahri, H.;
Simonneaux, G.; Toupet, L. Inorg. Chem. 1995, 34, 4691. (i) Morice,
C.; Le Maux, P.; Simonneaux, G. Tetrahedron Lett. 1996, 37, 6701.
(j) Bailey, A. J.; James, B. R. Chem. Commun. 1996, 2343. (k) Gross,
Z.; Ini, S. J. Org. Chem. 1997, 62, 5514. (l) Morice, C.; Le Maux, P.;
Simonneaux, G.; Toupet, L. J. Chem. Soc., Dalton Trans. 1998, 4165.
(m) Morice, C.; Le Maux, P.; Moinet, C.; Simonneaux, G. Inorg. Chim.
Acta 1998, 273, 142. (n) Gross, Z.; Ini, S. Org. Lett. 1999, 1, 2077.
(o) Chen, C.-Y.; Cheng, S.-H.; Su, Y. O. J. Electroanal. Chem. 2000,
487, 51.
t
H2 Bu-salch or H2Br-salch failed to result in metal complex-
ation. In this work, trans-dioxoosmium(VI) Schiff-base
complexes 1a and 1b were prepared through a modification
of the literature method.1c,2,9 Treatment of K2[OsO2(OH)4]
t
(0.27 mmol) with either H2 Bu-salch or H2Br-salch (0.27
mmol) in a solution of MeOH (25 mL) containing a few
drops of HCl followed by treatment with 2,6-lutidine at room
temperature gave 1a and 1b in yields of 70 and 65%,
respectively (Figure 1). Under these conditions, (1R,2R)- and
(1S,2S)-1a were also prepared from the reactions of K2[OsO2-
t
(OH)4] with (1R,2R)- and (1S,2S)-H2 Bu-salch. The enan-
tiopurities of these two latter complexes were determined
on the basis of circular dichroism spectroscopy ([φ](1R,2R)-1a
+ [φ](1S,2S)-1a ≈ 0).10 The addition of HCl was essential for
the synthesis; presumably, proton was used to remove the
strongly coordinated OH- group.
ii. Reactivity. Previous studies demonstrated that
[OsVI(14TMC)O2]2+ (14TMC ) 1,4,7,11-tetramethyl-1,4,7,11-
cyclotetraazanonane) and [OsVI(CN)4O2](Ph4As)2 are power-
ful photo-oxidants, undergoing light-induced oxygen atom
transfer reactions with trialkylphosphines, dialkylsulfides, and
alkenes.11 In light of these works, we reasoned that similar
(5) Nakamura, A.; Konisi, A.; Tatsuno, Y.; Otsuka, S. J. Am. Chem. Soc.
1978, 100, 3443.
(6) (a) Mu¨ller, P. In AdVances in Catalytic Processes; Doyle, M. P., Ed.;
JAI Press: Greenwich, CT, 1997; Vol. 2, p 113. (b) Jacobsen, E. N.;
Wu, M. H. In ComprehensiVe Asymmetric Catalysis; Jacobsen, E. N.,
Pfaltz, A., Yamamoto, H., Eds.; Springer: New York, 1999; p 607-
649. (c) Katsuki, T. In Catalytic Asymmetric Synthesis, 2nd ed.; Ojima,
I., Ed.; Wiley-VCH: New York, 2000; p 287.
(7) (a) Fukuda, T.; Katsuki, T. Tetrahedron 1997, 53, 7201. (b) Uchida,
T.; Irie, R.; Katsuki, T. Tetrahedron 2000, 56, 3501. (c) Niimi, T.;
Uchida, T.; Irie, T.; Katsuki, T. Tetrahedron Lett. 2000, 41, 3647. (d)
Uchida, T.; Saha, B.; Katsuki, T. Tetrahedron Lett. 2001, 42, 2521.
(8) For recent reviews, see: (a) Mu¨ller, P.; Fruit, C. Chem. ReV. 2003,
103, 2905. (b) Katsuki, T. Synlett 2003, 281. For recent examples,
see: (c) Noda, K.; Hosoya, N.; Irie, R.; Ito, Y.; Katsuki, T. Synlett
1993, 469. (d) Nishikori, H.; Katsuki, T. Tetrahedron Lett. 1996, 37,
9245. (e) Kohmura, Y.; Katsuki, T. Tetrahedron Lett. 2001, 42, 3339.
(f) Liang, J.-L.; Yu, X.-Q.; Che C.-M. Chem. Commun. 2002, 124.
(g) Omura, K.; Uchida, T.; Irie, R.; Katsuki, T. Chem. Commun. 2004,
2060.
(9) (a) Anson, F. C.; Collins, T. J.; Gipson, S. L.; Keech, J. T.; Krafft, T.
E.; Peake, G. T. J. Am. Chem. Soc. 1986, 108, 6593. (b) Muller, J.
G.; Takeuchi, K. J. Inorg. Chem. 1987, 26, 3634.
(10) See the Supporting Information for circular dichroism spectra of
(1R,2R)- and (1S,2S)-1a.
Inorganic Chemistry, Vol. 44, No. 11, 2005 3943

Zhang et al.
dioxoosmium(VI) moiety was no longer present. Under these
conditions, styrene oxide along with benzaldehyde were
furnished in 23 and 28% yield, respectively, on the basis of
gas chromatography (GC) analysis (Table 1, entry 1).
However, the epoxidation of styrene was found to be non-
enantioselective. Similar photochemical reactions with cis-
and trans-â-methylstyrene and 1,2-dihydronaphthalene with
(1S,2S)-1a gave the corresponding epoxidation products in
moderate yields (Table 1, entries 2-4). The reaction of
cyclooctene with (1S,2S)-1a gave no epoxidation product
1
detected by either H NMR or GC analysis.
In the absence of either UV irradiation or a reductant,
neither [OsVI(tBu-salch)O2] (1a) nor [OsVI(Br-salch)O2] (1b)
was found to react with styrene, ethanol, 1,3-dimethyl-
imidazolidine-2-thione, or aniline under a variety of condi-
tions, such as at temperature up to 80 °C and with the use
of excess reactants. In contrast, reaction of 1a with 6 equiv
of PPh3 in MeCN at room temperature for 8 h gave a green
solution. Analysis of the solution by FAB mass spec-
trometry revealed the presence of cluster peaks that could
be assigned to [Os(tBu-salch)(PPh3)], [Os(tBu-salch)(OPPh3)-
(OH)], and [Os(tBu-salch)(OPPh3)(PPh3)]. No [Os(tBu-salch)-
(MeCN)m]n+ species were found. The analogous reaction of
1b with 6 equiv of PPh3 in MeCN at room temperature, on
the other hand, furnished [OsII(Br-salch)(OPPh3)2] (2a) as
the sole product in 60% yield, and tentatively characterized
on the basis of IR measurements and FAB mass spectrometry
(see the Experimental Section).12
Figure 1. Dioxoosmium(VI) and osmium(IV) Schiff-base complexes
prepared in this work.
Table 1. Light-Induced Oxidation of Alkenes with 1aa
The bis(amido)osmium(IV) complexes [OsIV(Br-salch)(p-
NO2C6H4NH)2] (3a) and [OsIV(Br-salch)(p-CNC6H4NH)2]
(3b) were obtained in 30% yields when 1b was treated with
2 equiv of either p-nitro- or p-cyanoaniline in the presence of
hydrazine hydrate. Under similar conditions, the analogous
reaction of 1a with p-nitroaniline, however, gave the dinu-
clear µ-oxo-bridged complex 4 in 50% yield. Complex 4, [µ-
O-{OsIV(tBu-salch)(p-NO2C6H4NH)}2], was characterized by
elemental analyses and FAB mass spectrometry. While no
reaction was found between 1a and hydrazine hydrate in di-
methylformamide (DMF), the reaction of hydrazine hydrate
with 1b in DMF gave the dinitrogen complex [OsII(Br-salch)-
(N2)(H2O)] (5) in 50% yield. Structural elucidation of 5 was
based on elemental analyses and IR spectroscopy (see later
section).13 With diphenylhydrazine hydrochloride, [OsIV(tBu-
salch)(OH)(Cl)] (6) was preferentially furnished in 80% yield,
and no mono- or bis(hydrazido)osmium(IV) complex could
be detected by either 1H NMR spectroscopy or mass spectro-
metry. This is different from the analogous reaction of [Os-
(Por)O2] with diphenylhydrazine.14 [OsIV{1R,2R}(tBu-salch)-
(OH)(Cl)] (6) was similarly obtained from the reaction of
diphenylhydrazine hydrochloride with [OsVI{1R,2R}(tBu-
salch)O2] (1a). Repetition of this reaction with Et3N to re-
a Reaction conditions: (1S,2S)-1a/alkene ) 1:100; degassed 2:1 CH2Cl2/
MeCN; UV irradiation for 24 h; analyzed by GC analysis. b Yield
determined by GC analysis and based on the (1S,2S)-1a used. c Not detected.
reactivities could be observed for [OsVI{1S,2S}(tBu-salch)-
O2] (1a) when it is subjected to UV irradiation (Table 1).
Thus, when a degassed CH2Cl2/MeCN (2:1 v/v) solution
containing 1 equiv of (1S,2S)-1a and 100 equiv of styrene
was placed in a photochemical reactor (Rayonet RPR-100)
and irradiated with an array of 16 low-pressure mercury arc
lamps (RPR-2537) over a 24 h period, a color change from
orange to green was observed. Analysis of the crude reaction
mixture obtained after photolysis by fast atom bombardment
(FAB) mass spectrometry revealed the presence of cluster
peaks at m/z 737, 753, 767, 769, and 1522 that could be
assigned to [Os(tBu-salch)], [Os(tBu-salch)O], 1a, [Os(tBu-
salch)(OH)2], and [{Os(tBu-salch)(O)}2O], respectively (see
Figure S16 in the Supporting Information). In addition, the
ν(OsO2) stretch at 832 cm-1 detected by IR spectroscopic
analysis (see later section) disappeared, suggesting that the
(12) Che, C.-M.; Lai, T.-F.; Chung, W.-C.; Schaefer, W. P.; Gray H. B.
Inorg. Chem. 1987, 26, 3907.
(13) (a) Albertin, G.; Antoniutti, S.; Baldan, D.; Bordignon, E. Inorg. Chem.
1995, 34, 6205. (b) Li, Z. Y.; Huang J.-S.; Chan, M. C.-W.; Cheung,
K.-K.; Che, C.-M. Inorg. Chem. 1997, 36, 3064. (c) Coia, G. M.;
Devenney, M.; White, P. S.; Meyer, T. J.; Wink, D. A. Inorg. Chem.
1997, 36, 2341.
(11) (a) Che, C.-M.; Yam, V. W. W.; Tang, W.-T. Chem. Commun. 1988,
100. (b) Yam, V. W. W.; Che, C.-M. New J. Chem. 1989, 13, 707.
(c) Yam, V. W. W.; Che, C.-M. Coord. Chem. ReV. 1990, 97, 93.
(14) Leung, S. K.-Y.; Huang J.-S.; Zhu, N.-Y.; Cheung, K.-K.; Che, C.-
M. Inorg. Chem. 2003, 42, 7266.
3944 Inorganic Chemistry, Vol. 44, No. 11, 2005

Chiral Osmium Complexes with Schiff-Base Ligands
Table 2. 1H NMR Spectra of 1a, 3a, 3b, and 6-11
Ha signal
(d, 2H)
Hb signal
(d, 2H)
Hc signal
(s, 2H)
Hd signal
(m, 2H)
He-Hh signal
tBu
p-X-C6H4NH
complex
(m, 8H)
(4 × s, 32H)a
(m, 8H)
1a
3a
3b
6
7
8
9
10
11
7.14
7.53
7.52
6.99, 6.81
6.41
8.04
7.56
8.44
8.82
7.66
7.86
7.77
10.58, 10.37
8.30
12.43
10.40
13.07
13.73
8.38
9.38
9.23
9.38, 8.30
5.35
16.44
14.07
19.31
22.15
3.98
3.92
4.00
2.86, 2.61
3.17
4.94
6.31
6.49
8.35
3.81, 2.04, 1.73, 1.48
2.24-0.86
3.31, 2.19, 1.68
1.32, 1.58
8.02, 6.92a
7.46, 7.08b
1.27, 0.85
2.32, 2.29, 0.57, 0.39
1.91, 1.28
2.37, -0.21
1.96, 0.34
2.46, -0.27
2.56, 0.31
1.69, 1.12, -0.07
1.99, 0.15, -1.27
2.31, 0.70, 0.42, -0.01
2.00, 0.08, -0.27, -1.49
2.00, 1.49, 0.31, -1.89
a X ) NO2. b X ) CN.
place KOH preferentially gave [OsIV(tBu-salch)(OH)2] (7)
in 60% yield. Thus, the role of diphenylhydrazine in these
reactions could be that of a reductant. The reaction of [OsVI-
(tBu-salch)O2] (1a) with either SOCl2 or CF3CO2H under re-
ducing conditions (i.e., N2H4‚H2O and PPh3, respectively),
on the other hand, afforded [OsIV(tBu-salch)Cl2] (8) and [OsIV-
(tBu-salch)(CF3CO2)2] (9) in 70 and 40% yield, respectively.
Similarly, the analogous reaction of 1a with either Br2 or I2 in
the presence of N2H4‚H2O gave [OsIV(tBu-salch)Br2] (10) and
[OsIV(tBu-salch)I2] (11) in 50 and 80% yield, respectively
(Figure 1).
Under alkylating conditions, the reaction of 8 with either
MeLi or PhLi was found to result in the formation of an
amorphous brown solid. Although analysis of the reaction
mixtures by conventional spectroscopic means was unable
to elucidate the product(s) obtained, the detection of no
stretching frequencies that could be assigned to the Schiff-
base ligand by IR spectroscopy suggests that demetalation
had occurred during the course of these reactions.
of these signals to 3.95-3.98 ppm relative to those of the
free ligand which are located in the 3.30-3.33 ppm region.
This is comparable to the data noted for [OsVI(R-salen)O2]
and [OsVI(R-saltmen)O2] {R ) Pr, Bu, (3-Me)Bu; H2-
(saltmen) ) N,N′-(1,1,2,2-tetramethylethylene)bis(salicyl-
idenamine)}.2b A marked downfield shift of the equatorial
and axial CH protons of the cyclohexane ring in 1a to 2.03-
2.17 and 2.78-2.83 ppm, respectively, has also been
observed. In the free ligand, these signals appear as a
multiplet at 1.41-1.95 ppm. For 1a, 3a, 3b, and 7-11, where
the axial ligands are equivalent, only one set of signals
corresponding to the two azomethine, four ArCH, and four
tBu groups is observed. For 6 with different axial ligands, a
total of 10 signals for the 2 azomethine, 8 ArCH protons,
and 4 tBu groups of the Schiff-base ligand are found (Figure
2). As depicted in Table 2, the chemical shift of the
azomethine Hc protons shifts upfield by 0.15 ppm from 3a
to 3b. This upfield shift is attributed to the strong electron-
withdrawing effect of the NO2 substituent in 3a. A similar
trend of the chemical shift of Hc from 6 to 8 has also been
found. Replacing an axial Cl ligand in 8 with a OH ligand,
as in 6, results in an upfield shift of the Hc signal by > 7.0
ppm. A further upfield shift of the Hc signal to 5.35 ppm is
observed when the Cl ligand in 6 (Hc signal ) 8.30 and
9.38 ppm) is further replaced by another OH ligand, as in 7.
i
t
iii. Characterization. Complexes 1-11 are stable in the
solid state and in solution. Exposure of a CDCl3 solution
containing 7, for example, to air at room temperature for 1
month was found to result in no noticeable decomposition
1
on the basis of H NMR spectroscopic analysis.
The 1H NMR spectra of 1a, 3a, 3b, and 6-11 exhibit well-
resolved signals at normal fields. This is consistent with the
diamagnetic nature of related dioxoosmium(VI) and osmium-
(IV) Schiff-base complexes reported in the literature.2a-c The
spectral data are summarized in Table 2. The insolubility of
1b and 5 in various deuterated solvents renders characteriza-
tion of these complexes by NMR and UV-vis spectroscopy
difficult.
1
An inspection of the H NMR data of [OsIV(tBu-salch)-
X2] (8, X ) Cl; 9, X ) CO2CF3; 10, X ) Br; 11, X ) I),
listed in Table 2, shows a significant downfield shift of the
Schiff-base ligand proton signals on going from 9 f 8 f
10 f 11. This trend apparently correlates to the π-bonding
interaction of the axial halide ligands with Os(IV), which
would be most pronounced for the soft iodide ligand. The
dπ{Os(IV)}-pπ(X-) interaction would compete with the
π-bonding interaction between Os(IV) and the coordinated
Schiff-base ligand and, hence, affecting the ring current-
deshielding effect. Similar trends have also been reported
in NMR studies on the Schiff-base2a,c-d and porphyrinato15
complexes of ruthenium and osmium.
1
The H NMR spectrum of 1a in CDCl3 features the
azomethine and ArCH protons shifted downfield to 8.38,
7.66, and 7.14 ppm relative to the respective signals of the
free Schiff-base ligand at 7.29, 6.80, and 7.30 ppm, which
is assignable to a deshielding effect by the axial oxo ligands
(see the Supporting Information). A similar effect on the
bridging methylene protons in 1a causes an observed shift
Inorganic Chemistry, Vol. 44, No. 11, 2005 3945

Zhang et al.
Figure 2. 1H NMR spectrum of 6 in CDCl3.
Table 3. UV-Vis Spectral Data of 1a, 2, 3a, 3b, and 4-11 in CH2Cl2
Table 4. Electrochemical Data for the Osmium Schiff-Base Complexes
1a, 3a, 3b, and 6-11 in CH2Cl2
complex
λ )
max/nm (log ꢀ/dm3 mol-1 cm-1
potential (V)a
1a
2
272(4.17), 307(4.04), 377(3.72), 437(3.48)
356(4.17), 432(4.27)
complex
oxidation
first reduction
3a
3b
4
5
6
7
8
9
10
11
378(4.22), 653(4.23)
390(4.00), 634(4.10)
384(4.75), 409(4.73), 463(4.57)
349(4.07), 399(4.10)
269(4.48), 347(4.14), 398(4.35), 702(4.00)
268(4.43), 370(4.33), 425(4.40), 594(3.76)
270(4.44), 310(4.08), 343(4.05), 406(4.28), 760(4.08)
233(4.47), 265(4.32), 338(3.96), 392(4.22), 756(4.00)
270(4.36), 327(4.01), 348(4.00), 411(4.27), 788(4.04)
271(4.45), 345(4.19), 414(4.48), 854(4.11)
1a
3a
3b
6d
7d
8
9
10
11
0.78,b 1.14b
-1.39b
-0.89b
-1.09b
-1.00e
-1.33e
-0.77e
-0.64e
-0.74e
-0.72e
0.57,c 1.21c
0.41,b 1.00c
0.51,c 0.85,c 1.05c
0.17,c 0.71,c 1.06c
0.75,e 1.50c
0.89,e 1.53c
0.73,e 1.49c
0.69,e 1.22c
a Versus that of the Cp2Fe+/0 couple. b Quasi-reversible. c Irreversible.
d Several irreversible oxidation waves are observed. e Reversible.
The UV-vis data of 1a, and 2-11 are summarized in
Table 3. The UV-vis spectrum of 1a (see Figure S4 in the
Supporting Information) shows absorption bands at 272, 307,
and 377 nm and a shoulder at 437 nm. The high energy bands
at 272 and 307 nm, with respective log ꢀ values of 4.17 and
4.04 dm3 mol-1 cm-1, are dominated by intraligand charge-
transfer transitions of the coordinated Schiff-base ligands,
although the spin-allowed pπ(O2-) f Os(VI) charge-transfer
transition of related trans-dioxoosmium(VI) complexes was
reported to occur at a similar spectral region (ca. 300 nm).2b,16
Complexes 3a, 3b, and 6-11 exhibit a low energy band with
λmax lying between 594 and 854 nm. The λmax value red-
shifts by 2535 cm-1 on going from 6 to 8 and to 11 (Figures
S5-S6 in the Supporting Information). We attribute this low
energy absorption band as pπ(phenolate) f Os(IV) with pπ-
(axial ligand) f Os(IV) charge-transfer character.
electrochemical data (vs Cp2Fe+/0 couple) for these com-
plexes are tabulated in Table 4. The cyclic voltammogram
of 1a, shown in Figure 3, reveals two quasi-reversible
oxidation waves and a quasi-reversible reduction wave. The
reduction wave at -1.39 V is assigned to the reduction of
Os(VI) to Os(V). The quasi-reversible oxidation couples of
1a at 0.78 and 1.14 V are interesting because related
dioxoosmium(VI) Schiff-base complexes were found to show
irreversible oxidation at potentials 0.92-0.95 V.2b The two
oxidation couples of 1a are attributed to ligand-centered
oxidation because reversible oxidation couples with E1/2
values of 0.69-0.89 V have also been found for the related
Os(IV) complexes [OsIV(tBu-salch)X2] (8, X ) Cl; 9, X )
CO2CF3; 10, X ) Br; 11, X ) I). The cyclic voltammograms
of 8-11 also reveal an irreversible oxidation wave at Epa
values ranging from 1.22 to 1.53 V (see the Supporting
Information). The potentials for the first and second oxida-
tions of 8-11 are more anodic than those for the related
[OsIV(salen)(OR)2] (R ) Me, Et, iPr) complexes (0.36-0.50
V).2c In addition, the E1/2 for the first oxidation couple
becomes less anodic along the sequence 9 f 8 f 10 f 11.
Cyclic voltammetry was used to examine the redox
properties of 1a, 2, 3a, 3b, and 6-11 in CH2Cl2. The
(15) (a) Huang, J.-S.; Leung, S. K.-Y.; Cheung, K.-K.; Che, C.-M. Chem.s
Eur. J. 2000, 6, 2971. (b) Li, Y.; Huang, J.-S.; Xu, G.-B.; Zhu, N.;
Zhou, Z.-Y.; Che, C.-M.; Wong, K.-Y. Chem.sEur. J. 2004, 10, 3486.
(16) Miskowski, V. M.; Gray, H. B.; Hopkins, M. D. AdV. Transition Met.
Coord. Chem. 1996, 1, 159 and references therein.
3946 Inorganic Chemistry, Vol. 44, No. 11, 2005

Chiral Osmium Complexes with Schiff-Base Ligands
Figure 3. Cyclic voltammogram trace of 1a, in CH2Cl2 at 298 K with 0.1
M (Bu4N)PF6 as a supporting electrolyte (scan rate ) 100 mVs-1; Cp2Fe+/-
) 0.27 V; working electrode ) pyrolytic graphite).
Figure 4. Perspective view of 3a. Hydrogen atoms and solvent molecules
have been omitted for clarity. Selected bond lengths (Å) and angles (deg):
Os-O(1) 2.005(9), Os-O(2) 2.033(7), Os-N(1) 2.025(9), Os-N(2) 1.968-
(11), Os-N(3) 1.995(10), Os-N(5) 1.979(10), N(1)-C(7) 1.28(14), N(2)-
C(9) 1.498(18), O(1)-Os-N(1) 94.0(4), N(2)-Os-N(3) 91.9(4), N(2)-
Os-N(5) 90.0(4), N(3)-Os-O(1) 89.1(4), N(3)-Os-O(2) 90.2(3), N(3)-
Os-N(1) 89.6(4), N(5)-Os-N(1) 88.0(4), C(21)-N(3)-Os 126.1(8),
C(27)-N(5)-Os 128.8(9).18
This trend of E1/2 values is in accord with a decrease in the
inductive effect of the axial ligands, which follow the order
CF3CO2 > Cl > Br > I. In contrast, the cyclic voltammo-
grams of 3a and 3b revealed an irreversible oxidation peak
with Epa at 0.57 and 0.41 V for 3a and 3b, respectively. The
irreversibility could be due to the electrochemical generation
of an Os(V)-N (amido) complex. Similarly, for 6 and 7,
several irreversible oxidation peaks in the 0.30-1.33 V
region are found, which we tentatively assign to the oxidative
deprotonation of the Os(IV)-OH moiety.
assigned to the ν(OH) stretch. The positive ion FAB spectra
of 1a and 1b each exhibit three signals that can be attributed
to the parent ion [M]+ and the [M - O]+ and [M - 2O]+
fragments. For 2-11, the positive ion FAB spectra of these
complexes revealed ion clusters assignable to the parent ion
[M]+ and the [M - (axial ligand)n]+ fragments.
The cyclic voltammograms of 3a, 3b, and 6-11 also show
a reversible/quasi-reversible Os(IV)/Os(III) couple at E1/2
ranging from -0.49 to -1.33 V. A comparison of the
electrochemical data revealed that the E1/2 of Os(IV)/Os(III)
couples follow the trend 9 > 8, 10, 11 > 6 > 7, which
parallels the increase in π-donor strength of the axial ligands.
As OH- ligand is a strong σ- and π-donor, the Os(IV) site
would be more electron rich because of strong pπ(OH-)-
dπ{Os(IV)} π-bonding interaction. The axial halide ligands
have little effect on the E1/2 of Os(IV)/Os(III) couple.
IR spectroscopic measurements of 1a and 1b reveal a νas-
(OsO2) stretch at 833 cm-1 for 1a and one at 841 cm-1 for
1b. In both 1a and 1b, the absence of a ν(OH) stretch
indicates that the phenolic OH groups of the H2salch ligand
are deprotonated. Bands at ca. 1640 and 1560 cm-1 are
assigned to ν(CdN) and ν(CO), respectively. For 2, peaks
at 1420, 1155, and 1066 cm-1, assignable to ν(P-Ph), and
at 1121 cm-1, assignable to ν(PdO), are consistent with the
stretching frequencies of the axial OPPh3 ligands. The IR
spectra of 3a-c and 4 exhibit one sharp and three medium
NH stretching bands at 3290, 3296, 3329, and 3278 cm-1,
respectively. These stretching frequencies are higher than
that observed for [Os(TPP)(PhNH)2] [H2(TPP) ) meso-
tetrakis(phenyl)porphyrin] at 3253 cm-1 13 but lower than that
for [Os(Tp)(NHPh)(Cl)2] [Tp ) hydro-tris(1-pyrazolyl)-
borate] at 3519 cm-1.17 The IR spectrum of 5 reveals a band
at 2017 cm-1 attributed to the ν(N2) stretch.13 For 6 and 7,
sharp medium bands located at 3533 and 3557 cm-1 are
B. Structures of 3a, 3b, 6, 8, 9, and 11.18 Complexes 3a
and 3b were recrystallized from CHCl3/acetone, whereas 6,
8, and 9 were recrystallized from n-hexane/CHCl3, and 11
was recrystallized from Et2O/CH2Cl2 at room temperature.
Perspective views of 3a-b, 6, 8, 9 and 11 are depicted in
Figures 4-9. The crystal data and structural refinements are
given in Table 5.18
As shown in Figures 4 and 5, the axial ligands of 3a and
3b adopt a configuration where the aryl rings of the axial
ligands are situated away from the cyclohexane ring,
presumably to minimize unfavorable steric interactions with
the Schiff-base ligand. The aromatic rings of the axial ligands
sit in planes that are nearly perpendicular to the plane of the
Schiff-base ligand, with dihedral angles between these planes
equal to 80.4 and 85.1° for 3a and 85.3 and 88.5° for 3b.
The amido aryl rings in these complexes are also located in
the same plane with respect to each other, with dihedral
angles between the planes occupied by the aryl rings of the
amido ligands equal to 14.5° in 3a and 4° in 3b. The
structures of 6, 8, and 11, depicted in Figures 6,7, and 9,
(17) Crevier, T. J.; Bennett, B. K.; Soper, J. D.; Bowman, J. A.; Dehestani,
A.; Hrovat, D. A.; Lovell, S.; Kaminsky, W.; Mayer, J. M. J. Am.
Chem. Soc. 2001, 123, 1059.
(18) CCDC 228404-228408 and 254698 contain the supplementary
crystallographic data for this paper. These data can be obtained free
of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK. Fax: +44 1223
336033. E-mail: deposit@ccdc.cam.ac.uk).
Inorganic Chemistry, Vol. 44, No. 11, 2005 3947

Zhang et al.
meso-tetrakis(p-chlorophenyl)porphyrin] and 1.749(7) Å in
[OsV(Tp)(Cl)2(NH)].20 They are, however, shorter than the
Os-N (amido) distance in [Os3(µ-dan)(CO)10] [2.165 Å; H2-
(dan) ) 1,8-diaminonaphthalene].21 The average Os-Cl
distances in 6 and 8 [2.333(8)-2.349(1) Å] are similar, but
they are slightly shorter than related values in [OsIV(NPPh3)-
(salophen)(Cl)] [H2(salopen) ) N,N′-bis(salicylidene)o-phe-
nylenediamine; 2.424(5) Å]1c and [Os(bpb)(PPh3)(Cl)] [H2-
(bpb) ) N,N′-bis(2′-pyridinecarboxamide)-1,2-benzene;
2.410(4) Å].22 The Os-OH distance of 6 is 1.94(2) Å, which
is comparable to that for Os-O(OiPr) in [OsIV(salen)(OiPr)2]
[1.92(3) Å].2c In 9, the average Os-O(CF3CO2) distance is
2.033 Å, which is longer than that in 6. The bond angles
between the axial ligands in 8 and 11 are 179 and 177°,
respectively, which are close to the 180° value required for
linearity. In comparison, the analogous angles between the
two axial ligands in 6 and 9 are 170 and 167°, respectively,
suggesting the Os-axial ligand moieties in these complexes
to be slightly bent.
Figure 5. Perspective view of 3b. Hydrogen atoms and solvent molecules
have been omitted for clarity. Selected bond lengths (Å) and angles (deg):
Os-O(1) 2.039(4), Os-O(2) 2.021(3), Os-N(1) 2.005(5), Os-N(2) 1.965-
(4), Os-N(4) 2.021(4), Os-N(6) 1.975(4), N(1)-C(7) 1.29(7), N(1)-Os-
N(2) 89.8(2), N(2)-Os-O(1) 89.9(2), N(2)-Os-N(4) 90.1(2), N(4)-Os-
O(1) 177.2(1), N(4)-Os-O(2) 92.7(2), N(6)-Os-O(2) 90.7(1), N(6)-
Os-N(1) 89.5(1), C(14)-N(2)-Os(1) 132.1(4), C(28)-N(6)-Os(1)
130.8(4).18
At this juncture, it is worthy to highlight that the crystal
structures of 3a, 3b, 8, 9, and 11 not only show the chirality
of the bonding environment around the osmium atom, but
they also conform to an idealized C2 molecular geometry
with a pseudo-2-fold axis passing through the metal center
and the midpoint of the bridging cyclohexane bond. In 6,
respectively, reveal that the axial ligands, which are sterically
less demanding than those of the arylamido groups of 3a
and 3b, are also situated in planes that are at near right angles
to the plane of the Schiff-base ligand. The average axial
ligand-Os-N (imine) angle is between 86 and 94° in 6, 89
and 92° in 8, and 87 and 90° in 11. The axial Cl and OH
ligands in 6 are disordered. A perspective view of 9 is
depicted in Figure 8. The plane occupied by the two CF3-
CO2 axial ligands is slightly tilted by ca. 10° from the
idealized perpendicular plane with respect to the plane of
the Schiff-base ligand. Presumably, in this conformation, any
unfavorable steric interactions between the CF3CO2 axial
ligands and the Schiff-base ligand are kept to a minimum.
Ligand chelation in 3a, 3b, 6, 8, 9, and 11 is found to result
in a minimal distortion of the Os atom from the calculated
least-squares plane of the Schiff-base ligand, with the metal
in each complex sitting in the plane of the ligand. For each
complex, the five-membered chelate ring comprising Os, the
two N (imine) atoms, and the bridging C (cyclohexane)
atoms sit in a gauche form, so that the two vicinal C atoms
bonded to the bridging C (cyclohexane) are staggered with
respect to each other.
1
the axial ligands are different, consistent with H NMR
analysis of this complex.
C. [OsIV{1R,2R}(tBu-salch)(OH)(Cl)] (6) Catalyzed
Organic Reactions. In the literature, Schiff-base complexes
of Cr(V)23 and Mn(III)12,24 are known to catalyze C-O bond
formation reactions. Jacobsen and co-workers showed that
[MnIII{1S,2S}(tBu-salch)Cl]+ catalyzed the epoxidation of
alkenes with enantioselectivities of up to 98% ee.24 In this
work, when (1R,2R)-6 (2 mol %) was treated with a CH2Cl2
solution containing 1 equiv of styrene and 1.5 equiv of
PhIdO, no epoxidation was found on the basis of GC
analysis. Similarly, no aziridination product was detected by
either 1H NMR spectroscopy or GC analysis for the reaction
of (1R,2R)-6 (2 mol %) with 1 equiv of styrene and 1.5 equiv
of PhIdNTs. In contrast, when 1.5 equiv of EDA was slowly
added dropwise to a CH2Cl2 solution containing styrene (1
equiv) and (1R,2R)-6 (1 mol %) at room temperature,
2-phenyl-cyclopropanecarboxylic acid ethyl ester was fur-
nished in 50% yield and with a trans/cis ratio of 2.1:1.25 On
the basis of high-performance liquid chromatography (HPLC)
The average Os-N (amido) distances in 3a and 3b are
1.987 and 1.97 Å, respectively. These distances are slightly
longer than that found in [OsIV(Tp)(NHPh)(Cl)2] [1.919(6)
Å],17 though similar to that of the Ru-NHAr bond [1.956-
(7) Å] in [RuIV(TTP)(p-Cl-PhNH)2] [H2(TTP) ) meso-
tetrakis(tolyl)porphyrin].19 The Os-N (amido) distances in
3a and 3b are also longer than the Os-N (imido) distance
of 1.775 Å in [OsVI(4-Cl-TPP)(NtBu)2]13b [H2(4-Cl-TPP) )
(20) Huynh, M. H. V.; White, P. S.; John, K. D.; Meyer, T. J. Angew.
Chem., Int. Ed. 2001, 40, 4049.
(21) Cabeza, J. A.; Noth, H.; Rosales-Hoz, M. D. J.; Sanchez-Cabrera, G.
Eur. J. Inorg. Chem. 2000, 2327.
(22) Che, C.-M.; Cheng, W.-K.; Mak, T. C. W. Chem. Commun. 1986,
200.
(23) O’Mahony, C. P.; McGarrigle, E. M.; Renehan, M. F.; Ryan, K. M.;
Kerrigan, N. J.; Bousquet, C.; Gilheany, D. G. Org. Lett. 2001, 3,
3435.
(24) (a) Jacobsen, E. N.; Zhang, W.; Muci, A. R.; Ecker, J. R.; Deng L. J.
Am. Chem. Soc. 1991, 113, 7063. (b) Larrow J. F.; Jacobsen, E. N. J.
Am. Chem. Soc. 1994, 116, 12129.
(19) Huang, J.-S.; Sun, X.-R.; Leung, S. K.-Y.; Cheung, K.-K.; Che, C.-
M. Chem.sEur. J. 2000, 6, 334.
3948 Inorganic Chemistry, Vol. 44, No. 11, 2005

Chiral Osmium Complexes with Schiff-Base Ligands
Figure 6. Perspective view of 6. Hydrogen atoms and solvent molecules have been omitted for clarity. Selected bond lengths (Å) and angles (deg):
Os-Cl(1) 2.333(8), Os-O(1) 1.94(2), Os-O(3) 1.996(6), Os-O(4) 1.98(6), Os-N(1) 1.994(8), Os-N(2) 1.983(8), N(1)-C(7) 1.281(11), N(2)-C(22)
1.296(11), Cl(1)-Os-O(1) 170.1(9), Cl(1)-Os-O(3) 93.0(3), Cl(1)-Os-N(2) 87.8(3), O(1)-Os-O(4) 86.8(11), O(1)-Os-N(1) 93.7(12), O(3)-Os-
N(1) 93.3(3), O(3)-Os-N(2) 176.4(3).18
Figure 7. Perspective view of 8. Hydrogen atoms and solvent molecules have been omitted for clarity. Selected bond lengths (Å) and angles (deg):
Os-Cl(1) 2.3495(10), Os-Cl(2) 2.349(1), Os-O(1) 1.976(2), Os-O(2) 1.962(2), Os-N(1) 1.991(3), Os-N(2) 1.997(3), N(1)-C(7) 1.305(4), N(2)-C(22)
1.302(4), Cl(1)-Os-Cl(2) 178.99(3), Cl(1)-Os-O(1) 88.26(8), Cl(1)-Os-N(2) 91.79(9), Cl(2)-Os-O(1) 90.74(8), Cl(2)-Os-N(1) 91.36(9), N(1)-
Os-O(1) 91.0(2), N(1)-Os-O(2) 173.7(1).18
analysis, the enantiomeric excess of the trans product was
determined to be 38% ee whereas that of the cis-cyclopro-
pane (65% ee) was much higher (Table 6, entry 1). Under
similar conditions, cyclopropanation of a series of styrene
derivatives bearing either an electron-donating or -withdraw-
ing substituent at the para position with (1R,2R)-6 gave the
corresponding 2-(p-substituted phenyl)-cyclopropanecarbox-
ylic acid ethyl ester products in 49-63% yields and trans/
cis ratios of up to 2.7:1, along with enantioselectivities of
up to 79% ee (entries 2-5). The results are listed in Table
6. A survey of other osmium complexes prepared in this work
for similar reactivity showed that neither 5 nor 7 exhibited
any catalytic activity toward alkene cyclopropanation in
reaction with styrene and EDA, on the basis of a GC analysis
of the reaction mixture.
A series of competition experiments was performed to
investigate the product ratios of the cyclopropane esters
formed by the reaction of C6H5CHdCH2 versus that of p-X-
C6H4CHdCH2 (X ) MeO, Me, Cl, CF3) with EDA in the
presence of 6 (EDA/alkene/6 ) 200:100:1). The ratios of
the corresponding cyclopropane esters, defined as the relative
rate constants kX/kH, were determined on the basis of GC
analysis. This gave log kX/kH values of 0.525 (X ) OMe),
0.24 (X ) Me), 0.148 (X ) Cl), and -0.40 (X ) CF3),
which suggested that cyclopropanes derived from alkenes
substituted with an electron-donating group are more reactive
than styrene, whereas those with electron-withdrawing para
substituents retard the carbene group transfer process. Fitting
(by the least-squares method) the log kX/kH data to the σ+
(25) During preparation of this manuscript, Nguyen and co-workers reported
a ruthenium(II) Schiff-base-catalyzed alkene cyclopropanation pro-
cedure. See: (a) Miller, J. A.; Jin, W.; Nguyen, S. T. Angew. Chem.,
Int. Ed. 2002, 41, 2953. (b) Miller, J. A.; Hennessy, E. J.; Marshall,
W. J.; Scialdone, M. A.; Nguyen S. B. T. J. Org. Chem. 2003, 68,
7884.
Inorganic Chemistry, Vol. 44, No. 11, 2005 3949

Zhang et al.
Figure 8. Perspective view of 9. Hydrogen atoms and solvent molecules have been omitted for clarity. Selected bond lengths (Å) and angles (deg):
Os-O(1) 1.954(5), Os-O(2) 1.959(5), Os-O(3) 2.025(6), Os-O(5) 2.041(6), Os-N(1) 2.013(6), Os-N(2) 1.998(6), N(1)-C(7) 1.295(9), N(2)-C(22)
1.317(10), O(1)-Os-O(3) 87.9(2), O(1)-Os-N(1) 89.6(2), O(1)-Os-N(2) 168.3(3), O(2)-Os-O(3) 85.1(2), O(3)-Os-O(5) 167.0(2), N(1)-Os-O(3)
100.3(3), N(1)-Os-O(5) 90.9(3), N(1)-Os-N(2) 81.6(2).18
Figure 9. Perspective view of 11. Hydrogen atoms and solvent molecules have been omitted for clarity. Selected bond lengths (Å) and angles (deg):
Os(1)-I(1) 2.6884(6), Os(1)-I(2) 2.6970(6), Os(1)-O(1) 1.976(4), Os(1)-O(2) 1.981(4), Os(1)-N(2) 1.998(5), Os(1)-N(1) 1.999(5), N(1)-C(7) 1.318-
(7), N(2)-C(20) 1.304(7), O(1)-Os(1)-I(1) 88.23(11), N(2)-Os(1)-I(1) 89.10(13), I(1)-Os(1)-I(2) 177.37(2), O(1)-Os(1)-O(2) 96.70(17), N(2)-Os-
(1)-N(1) 83.0(2).18
scale results in reasonable linearity (R ) 0.95), with a F+
value of -0.66 ( 0.09 (see the Supporting Information).
Although the mechanism is currently unclear, it would not
be unreasonable to speculate that the reaction occurs via the
initial formation of a metallocarbenoid intermediate that has
been shown or proposed to be a reactive species in a number
of related ruthenium and osmium systems.25-28 Although
attempts to isolate such osmium-carbene species proved
treatment of 1 mmol of (1R,2R)-6 with EDA (0.2 mmol) in
CH2Cl2 (5 mL) over an 18 h period at room temperature by
FAB mass spectrometry revealed a cluster of peaks with
(26) (a) Woo, L. K.; Smith, D. A. Organometallics 1992, 11, 2344. (b)
Smith, D. A.; Reynolds, D. N.; Woo, L. K. J. Am. Chem. Soc. 1993,
115, 2511. (c) Wolf, J. R.; Hamaker, C. G.; Djukic, J.-P.; Kodadek,
T.; Woo, L. K. J. Am. Chem. Soc. 1995, 117, 9194.
(27) For recent reviews, see: (a) Che, C.-M.; Huang, J.-S. Coord. Chem.
ReV. 2002, 231, 151. (b) Lebel, H.; Marcoux, J.-F.; Molinaro, C.;
Charette, A. B. Chem. ReV. 2003, 103, 977. (c) Maas, G. Chem. Soc.
ReV. 2004, 33, 183.
29
unsuccessful with either Ph2CN2 or EDA as a carbene
source, analysis of the reaction mixture obtained from the
3950 Inorganic Chemistry, Vol. 44, No. 11, 2005

Chiral Osmium Complexes with Schiff-Base Ligands
Table 5. Crystal Data and Structure Refinement for Complexes 3a, 3b, 6, 8, 9, and 1118
3a‚1.5CHCl3
3b
6
formula
MR
C32H26Br4N6O6Os‚1.5CHCl3
1279.50
C34H26Br4N6O2Os
1060.46
C36H52ClN2O3Os
786.45
λ [Å]
T [K]
0.71073
253
0.71073
294
0.71073
301
cryst syst
space group
a [Å]
monoclinic
P21/n
12.574(3)
orthorhombic
P212121
12.9219(16)
monoclinic
P21/n
18.688(2)
b [Å]
17.4000(4)
17.563(2)
11.941(1)
c [Å]
19.254(4)
18.195(2)
20.078(2)
R [deg]
â [deg]
γ [deg]
V [Å3]
Z
90
104.25(3)
90
4082.9(16)
4
2.082
7.384
90
90
90
4129.3(9)
90
94.43(2)
90
4467.1(8)
4
4
F
cacld [mg m-3
]
1.772
6.997
2104
1.169
2.943
1596
µ(Mo KR) [mm-1
F(000)
]
2446
index ranges
-13 e h e 14,
-19 e k e 19,
-21 e l e 21
19063
-16 e h e 16,
-22 e k e 22,
-23 e l e 16
28099
-22 e h e 22,
-13 e k e 12,
-23 e l e 23
22173
reflns collected
independent reflns
refinement method
params
5921
9438
7467
full-matrix least-squares on F2
312
full-matrix least-squares on F2
478
full-matrix least-squares on F2
406
GOF
0.94
1.01
1.09
final R indices [I > 2σ(I)]a
largest diff. peak:hole [eÅ-3
R1 ) 0.051, wR2 ) 0.12
1.346/-1.879
R1 ) 0.039, wR2 ) 0.077
0.940/-0.522
R1 ) 0.059, wR2 ) 0.2
1.308/-1.29
]
8
9
11
formula
MR
C36H52Cl2N2O2Os
805.90
C40H54F6N2O6Os
963.05
C36H52I2N2O2Os
988.80
λ [Å]
T [K]
0.71073
294
0.71073
293
0.71073
301
cryst syst
space group
a [Å]
triclinic
P1
12.1571(11)
triclinic
P1h
12.681(3)
orthorhombic
Pbca
12.522(3)
b [Å]
13.3553(12)
14.074(3)
24.059(5)
c [Å]
13.3721(12)
14.727(3)
26.455(5)
R [deg]
â [deg]
γ [deg]
V [Å3]
Z
69.7
81.066(2)
71.178(2)
1925.4(3)
67.2
72.51
85.65
2308.3(9)
90
90
90
7970(3)
2
2
8
F
cacld [mg m-3
]
1.390
3.481
816
1.386
2.828
972
1.648
4.779
3840
µ(Mo KR) [mm-1
F(000)
]
index ranges
-15 e h e 15,
-17 e k e 16,
-14 e l e 17
13050
-14 e h e 14,
-13 e h e 13,
-27 e k e 28,
-30 e l e 25
21005
-16 e k e 17,
-17 e l e 17
12321
reflns collected
independent refls
refinement method
params
8735
6928
5956
full-matrix least-squares on F2
389
full-matrix least-squares on F2
full-matrix least-squares on F2
383
484
GOF
0.81
1.0
0.50
final R indices [I > 2σ(I)]a
largest diff. peak:hole [eÅ-3
R1 ) 0.045, wR2 ) 0.11
1.059/-0.933
R1 ) 0.044, wR2 ) 0.11
0.851/-1.617
R1 ) 0.028, wR2 ) 0.056
0.724/-0.584
]
2
a R1 ) Σ|/Fo| - |Fc||/Σ|Fo|; wR2 ) [Σw(|/Fo| - |Fc|)2|/Σw|Fo| ]1/2
.
values centered at m/z 821 and 907 that match the respective
formulations. Analysis of the FAB mass spectrum also
showed cluster peaks with values centered at m/z 752, 767,
769, and 786 that could be assigned to [Os(tBu-salch)(OH)],
1a, 7, and (1R,2R)-6, respectively. However, FAB mass
spectrometric analysis of isolated fractions obtained from
purification of the crude reaction mixture by column chro-
matography showed a marked decrease in the intensity of
the signal at m/z 821, assigned to [Os(tBu-salch)(CHCO2-
Et)], the complete disappearance of the m/z 907 signal
[Os(tBu-salch)(CHCO2Et)] and [Os(tBu-salch)(CHCO2Et)2]
(28) For works by us, see: (a) Lo, W.-C.; Che, C.-M.; Cheng, K.-F.; Mak,
T. C. W. Chem. Commun. 1997, 1205. (b) Che, C.-M.; Huang, J.-S.;
Lee, F.-W.; Li, Y.; Lai, T.-S.; Kwong, H.-L.; Teng, P.-F.; Lee, W.-
S.; Lo, W.-C.; Peng, S.-M.; Zhou, Z.-Y. J. Am. Chem. Soc. 2001,
123, 4119. (c) Li, Y.; Huang, J.-S.; Zhou, Z.-Y.; Che C.-M. Chem.
Commun. 2003, 1362; Chem. Commun. 2003, 3052. (d) Zhou, C.-Y.;
Chan, P. W. H.; Yu, W.-Y.; Che, C.-M. Synthesis 2003, 9, 1403. (e)
Zhang, J.-L.; Chan, P. W. H.; Che, C.-M. Tetrahedron Lett. 2003, 44,
8733. (f) Zhou, C.-Y.; Yu, W.-Y.; Chan, P. W. H.; Che, C.-M. J.
Org. Chem. 2004, 69, 7072. (g) Li, Y.; Chan, P. W. H.; Zhu, N.-Y.;
Che C.-M.; Kwong, H.-L. Organometallics 2004, 23, 54.
(29) Miller, J. B. J. Org. Chem. 1959, 24, 560.
Inorganic Chemistry, Vol. 44, No. 11, 2005 3951

Zhang et al.
Table 6. [OsIV{1R,2R}(tBu-salch)(OH)(Cl)] (6) Catalyzed Cyclopropanation of Alkenes with EDAa
a Reaction conditions: catalyst/styrene/EDA ) 1:100:150; CH2Cl2; 40 °C; EDA; addition over 10 h and stirring for 24 h. b Isolated yield based on the
amount of alkene consumed. c Determined by GC analysis with tribromobenzene as an internal standard. d Determined by analytical GC column. e Determined
by HPLC using chiral OJ column. In addition to the cyclopropane adduct, diethyl fumarate and diethyl maleate were obtained as side products, but the yields
of these latter compounds were not determined.
assigned to [Os(tBu-salch)(CHCO2Et)2], and the appearance
of a cluster of peaks centered at m/z 1522 that could be
assigned to [µ-O-{Os(tBu-salch)O}2]. In addition, the forma-
tion of diethyl fumarate was detected by 1H NMR spectros-
copy in monitoring the reaction of 19 µmol of (1R,2R)-6
with EDA (1.2 µmol) in CDCl3 (1 mL) over a 10 h period
at room temperature (see the Supporting Information). Thus,
the inability to isolate the osmium-carbenoid species in the
pure form could be due to its instability; similar observations
in related ruthenium and osmium systems have previously
been reported.25-28
selectivity. When treated with EDA, (1R,2R)-6 was shown
to catalyze alkene cyclopropanation with moderate trans
selectivity and moderate to good enantioselectivities. Our
studies lead us to speculate that EDA decomposition in the
presence of (1R,2R)-6 gives a metallocarbenoid intermediate
that undergoes carbene transfer via a carboradical species
that cyclizes to give the cyclopropane. Product formation
was shown to occur more quickly for reactions derived from
alkenes substituted with an electron-donating group compared
to those derived from electron-withdrawing substituted
alkenes.
Conclusion
Experimental Section
In this article, we describe the synthesis of trans-
dioxoosmium(VI) containing sterically bulky Schiff-base
complexes. The reactions of 1a with PPh3 were shown to
give a complex mixture of products, but the analogous
reaction of 1b with PPh3 furnished 2. In addition, reactions
of 1b with arylamines gave the bis(amido)osmium(IV)
Schiff-base complexes 3a and 3b in moderate yields.
Reaction of 1a with p-nitroaniline is the only example where
the µ-oxo-bridged Os(IV) Schiff-base complex 4 was
preferentially furnished. With hydrazine compounds, the
expected bis(hydrazido)osmium(IV) Schiff-base complexes
were not obtained. These reactions preferentially furnish 5,
6, and 7 in good yields. Reaction of 1a with either thionyl
chloride, trifluoroacetic acid, bromine, or iodine under
reducing conditions, on the other hand, gave the expected
Os(IV) complexes 8-11 in good yields. 1H NMR spectros-
copy and X-ray crystallographic analyses reveal that the
ligands in these complexes form a chiral environment around
the metal center. Upon UV irradiation, (1S,2S)-1 was
demonstrated to undergo light-induced epoxidation with a
series of alkenes in moderate yields, albeit with no enantio-
General Considerations. 3,5-Di-tert-butyl-2-hydroxybenzalde-
hyde (99%; Aldrich), trans-(()-(1R,2R)- and (1S,2S)-1,2-cyclo-
hexanediamine (99%; Aldrich), OsO4 (99.8%; Aldrich), 4-nitroa-
niline (99%+; Aldrich), 4-chloroaniline (98%; Aldrich), and 1,1-
diphenylhydrazine hydrochloride (97%; Aldrich) were all purchased
and used as received. All of the solvents used were of AR grade.
K2[OsVIO2(OH)4] was prepared following the literature procedure.30
Bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diamine (H2tBu-
salch) and bis(3,5-dibromosalicylidene)-1,2-cyclohexane-diamine
(H2Br-salch) were prepared from the reaction of 3,5-di-tert-butyl-
2-hydroxybenzaldehyde or 3,5-dibromo-2-hydroxybenzaldehyde
with 1,2-cyclohexanediamine in ethanol (2:1), respectively.
1
Instrumentation. H NMR spectra were recorded on either a
Bruker DPX 300 or a Bruker DPX 400 spectrometer at 300 or 400
MHz. The chemical shifts (δ, ppm) were reported relative to
tetramethylsilane (TMS). IR spectra were measured on a Bio-Rad
FT-IR spectrometer. UV-vis spectra were recorded on a Hewlett-
Packard 8452A Diode Array spectrophotometer. FAB mass spectra
were measured on a Finnigan MAT 95 mass spectrometer using
3-nitrobenzyl alcohol as the matrix. HPLC measurements were
(30) Malin, J. M. Inorg. Synth. 1980, 20, 61.
3952 Inorganic Chemistry, Vol. 44, No. 11, 2005

Chiral Osmium Complexes with Schiff-Base Ligands
carried out on a HP 1050 Series HPLC. Cyclic voltammetry was
performed with a Bioanalytical Systems (BAS) model 100 B/W
electrochemical analyzer. A conventional two-compartment elec-
trochemical cell was used. The glassy carbon electrode was polished
with 0.05 mm alumina on a microcloth, sonicated for 5 min in
deionized water, and rinsed with MeCN before use. An Ag/AgNO3
(0.1 M in MeCN) electrode was used as the reference electrode.
All of the solutions were degassed with argon before the experi-
ments. E1/2 values were taken from the average of the cathodic and
anodic peak potentials for the oxidative and reductive waves. The
[µ-O-{[OsIV(tBu-salch)](p-NO2C6H4NH)}2] (4). Yield: 50%.
Anal. Calcd for C84H114N8O9Os2‚2(CH3)2CO: C, 57.61; H, 6.77;
N, 5.97. Found: C, 57.93; H, 6.52; N, 5.82. IR (Nujol, cm-1): νNH
3287. FAB MS: m/z 1761 [M + H]+, 1624 [M - p-NO2C6H4-
NH]+, 1487 [M - 2(p-NO2C6H4NH)]+, 889 [M - p-NO2C6H4NH
- {Os(tBu-salch)}]+, 751 [M - 2(p-NO2C6H4NH) - {Os(tBu-
salch)}]+, 735 [M - 2(p-NO2C6H4NH) - [Os(tBu-salch)] - O]+.
[OsII(Br-salch)(N2)(H2O)] (5). To a DMF (10 mL) solution
containing 1b (20 mg) was added several drops of hydrazine
monohydrate. The reaction mixture was stirred at room temperature
for 10 min, quenched with water (40 mL), filtered, and concentrated
in vacuo to afford a light green solid. The crude product was
recrystallized by slow diffusion of Et2O into a CHCl3 solution.
Yield: 50%. Anal. Calcd for C20H18Br4N4O3Os‚2CHCl3: C, 23.78;
H, 1.81; N, 5.04. Found: C, 23.62; H, 2.20; N, 5.19. IR (KBr pellet,
cm-1): νNtN 2017, νCdN 1638.
E
1/2 value of the ferrocenium/ferrocene couple (Cp2Fe+/0) measured
in the same solution was used as an internal reference.
General Procedure for the Synthesis of Dioxoosmium(VI)-
(Schiff-Base) Complexes 1. A few drops of HCl (2M) was slowly
added to a mixture of K2[OsVIO2(OH)4] (100 mg, 0.27 mmol) and
either H2Br-salch or H2tBu-salch (100 mg, 0.18 mmol) in MeOH
(25 mL). The mixture was then stirred for several minutes. Upon
the addition of 2,6-lutidine (0.1 mL), an orange solid was observed
to slowly precipitate. The crude product was recrystallized by the
diffusion of Et2O into a solution of CH2Cl2.
[OsIV(tBu-salch)(OH)(Cl)] (6).18 A solution of 1,1-diphenylhy-
drazine hydrochloride (220 mg, 1 mmol) and KOH (90 mg, 1.4
mmol) in CH2Cl2 (20 mL) was stirred for 1 h. Complex 1a (40
mg, 0.05 mmol) was added to the resulting brown mixture, and
the reaction was stirred for 1 further day at room temperature. The
brown solution was observed to turn green after evaporation to
dryness. The green residue was loaded on a silica gel column, which
was first eluted with CH2Cl2/n-hexane (1:1 v/v) to remove the brown
band. The green band was eluted with 3% MeOH in CH2Cl2 to
give 6. Yield: 80%. Anal. Calcd for C36H53ClN2O3Os‚0.5C6H14:
C, 56.40; H, 7.28; N, 3.37. Found: C, 56.07; H, 7.26; N, 3.24. 1H
NMR (300 MHz, CDCl3): δ 10.58 (d, 1H, J ) 2.4 Hz), 10.37 (d,
1H, J ) 2.4 Hz), 9.38 (s, 1H), 8.30 (s, 1H), 6.99 (d, 1H, J ) 2.5
Hz), 6.81 (d, 1H, J ) 2.5 Hz), 2.86 (m, 1H), 2.61 (m, 1H), 2.32 (s,
9H), 2.29 (s, 9H), 1.27 (m, 2H), 0.85 (m, 6H), 0.57 (s, 9H), 0.39
(s, 9H). IR (Nujol, cm-1): νOH 3533. FAB MS: m/z 788 [M +
H]+, 771 [M - OH]+, 753 [M - Cl]+, 735 [M - Cl - OH]+.
[OsIV(tBu-salch)(OH)2] (7). This compound was prepared fol-
lowing the procedure of 4 but with NEt3 as the base. Yield: 60%.
Anal. Calcd for C36H54N2O4Os: C, 56.22; H, 7.08; N, 3.64.
[OsVI(tBu-salch)O2](1a).Yield: 70%.Anal.CalcdforC36H52N2O4-
Os: C, 56.37; H, 3.65; N, 6.38. Found: C, 56.20; H, 3.89; N, 7.01.
1H NMR (300 MHz, CDCl3): δ 8.38 (s, 2H), 7.66 (d, 2H, J ) 2.6
Hz), 7.14 (d, 2H, J ) 2.6 Hz), 3.98 (m, 2H), 3.81 (m, 2H), 2.04
(m, 2H), 1.73 (m, 2H), 1.58 (s, 18H), 1.48 (m, 2H), 1.32 (s, 18H).
IR (KBr pellet, cm-1): 1636, 1533, νas(OsdO) 833. FAB MS: m/z
767 [M]+, 751 [M - O]+, 735 [M - 2O]+.
[OsVI(Br-salch)O2] (1b). Yield: 65%. Anal. Calcd for C20H16-
Br4N2O4Os: C, 27.99; H, 1.88; N, 3.26. Found: C, 27.50; H, 1.92;
N, 3.10. IR (KBr pellet, cm-1): 1642, 1581, νas(OsdO) 841. FAB
MS: m/z 858 [M]+, 842 [M - O]+, 826 [M - 2O]+.
[OsII(Br-salch)(OPPh3)2] (2). A solution of MeCN (20 mL)
containing 1b (86 mg, 0.1 mmol) and PPh3 (262 mg, 1 mmol) was
stirred for 24 h. The reaction mixture was filtered and evaporated
to dryness. The brown solid obtained was recrystallized from a
solution of CH2Cl2 and Et2O to give the title compound. Yield:
70%. IR (Nujol, cm-1): ν(P-Ph) 1420, ν(P-Ph) 1155, ν(OdP) 1121,
ν(P-Ph) 1066. FAB MS: m/z 1382 [M + H]+.
1
Found: C, 56.77; H, 7.37; N, 3.56. H NMR (400 MHz, CDCl3):
δ 8.30 (d, 2H, J ) 1.9 Hz), 6.41 (d, 2H, J ) 2.4 Hz), 5.35 (s, 2H),
3.17 (m, 2H), 1.91 (s, 18 H), 1.69 (m, 2H), 1.28 (s, 18H), 1.12 (m,
4H), -0.07 (m, 2H). IR (KBr pellet, cm-1): νOH 3557, 1595, 1524.
FAB MS: m/z 769 [M]+, 752 [M - OH]+, 735 [M - 2OH]+.
[OsIV(tBu-salch)Cl2] (8).18 Complex 1a (100 mg, 0.13 mmol)
was dissolved in CH2Cl2 (15 mL), and one drop of N2H4‚H2O was
subsequently added. Excess SOCl2 (0.1 mL) was slowly added,
and the reaction mixture was stirred overnight. The resulting green
solution was evaporated to dryness. The residue was loaded on an
alumina column with CH2Cl2 as an eluent. The green band was
collected and concentrated to 1-2 mL. The addition of n-hexane
gave a green solid. Crystals of 7 were obtained by slow diffusion
of Et2O into a CH2Cl2 solution. Yield: 70%. Anal. Calcd for
C36H52N2Cl2O2Os: C, 53.65; H, 6.50; N, 3.48. Found: C, 54.02;
General Procedure for the Synthesis of Bis(arylamido)-
osmium(IV) Complexes 3a, 3b, and 4. To a solution of 1 (40
mg, 0.05 mmol) and arylamine (128 mg, 1 mmol) in CH2Cl2 (20
mL) was added one drop of N2H4‚H2O. The mixture was stirred
for 24 h at room temperature. The resulting green solution was
evaporated to dryness. The solid was dissolved in CH2Cl2, which
was purified on a silica gel column with CH2Cl2 as an eluent. The
second green band was eluted with CH2Cl2/acetone (2:1 v/v),
collected, and evaporated to dryness to give the title compound as
a green solid.
[OsIV(Br-salch)(p-NO2C6H4NH)2] (3a).18 Yield: 30%. Anal.
Calcd for C32H26Br4N6O6Os‚2CHCl3: C, 32.85; H, 2.27; N, 6.76.
1
Found: C, 33.01; H, 1.90; N, 6.90. H NMR (300 MHz, acetone-
1
H, 6.32; N, 3.88. H NMR (300 MHz, CDCl3): δ 16.44 (s, 2H),
d6): δ 9.38 (s, 2H), 8.02 (m, 4H), 7.86 (d, 2H, J ) 2.4 Hz), 7.53
(d, 2H, J ) 2.4 Hz), 6.92 (m, 4H), 3.92 (m, 2H), 2.24-0.86 (m,
8H). IR (Nujol, cm-1): νNH 3290. FAB MS: m/z 1101 [M + H]+,
963 [M - p-NO2C6H4NH]+, 826 [M - 2(p-NO2C6H4NH)]+.
[OsIV(Br-salch)(p-CNC6H4NH)2] (3b).18 Yield: 30%. Anal.
Calcd for C34H26Br4N6O2Os‚2.5CH2Cl2: C, 34.44; H, 2.45; N, 6.60.
12.43 (d, 2H, J ) 2.1 Hz), 8.04 (d, 2H, J ) 2.4 Hz), 4.94 (m, 2H),
2.37 (s, 18 H), 1.99 (m, 2H), 0.15 (m, 4H), -0.21 (s, 18H), -1.27
(m, 2H). IR (KBr pellet, cm-1): 1584. FAB MS: m/z 807 [M +
H]+, 772 [M - Cl]+, 735 [M - 2Cl]+.
[OsIV(tBu-salch)(CF3CO2)2] (9).18 To a solution of 1a (78 mg,
0.1 mmol) was added CF3CO2H (16 mL) and PPh3 (150 mg) in
tetrahydrofuran (THF; 20 mL). The reaction mixture was heated
for 1h. Upon cooling to room temperature and removal of the
solvent, the residue was dissolved in CH2Cl2 and purified by silica
gel chromatography with CH2Cl2 as an eluent. The first band was
collected and evaporated to dryness to give the title compound as
1
Found: C, 34.53; H, 2.24; N, 6.69. H NMR (300 MHz, acetone-
d6): δ 9.23 (s, 2H), 7.77 (d, 2H, J ) 2.5 Hz), 7.52 (d, 2H, J ) 2.5
Hz), 7.46 (d, 4H, J ) 9.0 Hz), 7.08 (m, 4H), 4.00 (m, 2H), 3.31
(m, 2H), 2.19 (m, 4H), 1.68 (m, 2H). IR (Nujol, cm-1): νNH 3296,
ν
C≡N 2207. FAB MS: m/z 1060 [M]+, 943 [M - p-CNC6H4NH]+,
826 [M - 2(p-CNC6H4NH)]+.
Inorganic Chemistry, Vol. 44, No. 11, 2005 3953

Zhang et al.
a green solid. Yield: 40%. Anal. Calcd for C40H54F6N2O6Os‚
program on a PC. In all cases, graphite monochromatized Mo KR
radiation (λ ) 0.71073 Å) was used.
0.25C6H14: C, 50.62; H, 5.89; N, 2.85. Found: C, 50.74; H, 5.75;
1
N, 2.64. H NMR (300 MHz, CDCl3): δ 14.07 (s, 2H), 10.40 (d,
Procedure for Photoinduced Oxidation of Alkenes by [OsVI-
{1S,2S}(tBu-salch)O2] (1a). A CH2Cl2/MeCN (2:1 v/v, 150 mL)
solution containing (1S,2S)-1a (65 µmol) and alkene (6.5 mmol)
was placed in a photochemical reactor (Rayonet RPR-100) and
irradiated with an array of 16 low-pressure mercury arc lamps (RPR-
2537) for 24 h. After evaporation of the reaction mixture to dryness,
product yields were determined by GC using an analytic column
2H, J ) 2.4 Hz), 7.56 (d, 2H, J ) 2.4 Hz), 6.31 (m, 2H), 2.31 (m,
2H), 1.96 (s, 18H), 0.70 (m, 2H), 0.42 (m, 2H), 0.34 (s, 18H),
-0.01 (m, 2H). IR (Nujol, cm-1): νCdO 1711. FAB MS: m/z 963
[M]+, 850 [M - CF3CO2]+, 735 [M - 2(CF3CO2)]+.
[OsIV(tBu-salch)Br2] (10). To a solution of 1a (78 mg, 0.1 mmol)
in anhydrous THF (20 mL) was added 2 drops of N2H4‚H2O. After
the reaction mixture was stirred for 20 min at room temperature,
two drops of Br2 solution was added. The reaction was stirred for
1 further day. The resultant green solution obtained was evaporated
to dryness and loaded on a silica gel column, which was eluted
with CH2Cl2 to isolate the green band and furnish the title compound
as a green solid. Yield: 50%. Anal. Calcd for C36H52N2O2Br2Os‚
0.5CH2CL2‚0.25C6H14: C, 47.61; H, 5.95; N, 2.92. Found: C,
47.63; H, 6.09; N, 2.92. 1H NMR (400 MHz, CDCl3): δ 19.31 (s,
2H), 13.07 (s, 2H), 8.44 (s, 2H), 6.49, 2.46 (s, 18H), 2.00 (m, 2H),
1
with tribromobenzene as an internal standard. IR and H NMR
spectroscopy were used to determine the organic and inorganic
products obtained.
Procedure for [OsIV{1R,2R}(tBu-salch)(OH)(Cl)] (6) Cata-
lyzed Cyclopropanation of Alkenes with EDA. A solution of EDA
(1.5 mmol) in CH2Cl2 (5 mL) was added dropwise to a solution of
alkene (1 mmol) and (1R,2R)-5 (0.01 mmol) in CH2Cl2 (5 mL)
over a 10 h period at room temperature under an argon atmosphere.
The mixture was then stirred for an additional 24 h. After
purification by flash chromatography on a short column of silica
gel, substrate conversion and the ratio of trans- to cis-cyclopropyl
esters were determined by GC using an analytic column with
tribromobenzene as an internal standard. Further purification of the
cyclopropyl esters was carried out by column chromatography on
silica gel with n-hexane/EtOAc (20:1 v/v) as an eluent.
Competitive Cyclopropanations Catalyzed by (1R,2R)-6. In
a typical experiment, equimolar amounts of each alkene (1.5 mmol)
and (1R,2R)-6 (0.015 mmol) were dissolved in CH2Cl2 (2 mL) at
room temperature. A solution of EDA (0.3 mmol) in CH2Cl2 (1
mL) was added over a 6 h period. The cyclopropane esters obtained
were analyzed by GC spectroscopy.
0.08 (m, 2H), -0.27 (s, 20H), -1.49 (m, 2H). IR (KBr pellet, cm-1
)
1583. FAB MS: m/z 894 [M]+, 815 [M - Br]+, 735 [M - 2 Br]+.
Synthesis of [OsIV(tBu-salch)I2] (11).18 To a solution of 1a (78
mg, 0.1 mmol) in anhydrous THF (20 mL) was added 2 drops of
N2H4‚H2O. After the reaction mixture was stirred for 20 min at
room temperature, I2 (100 mg) was added. The reaction was stirred
for 1 further day. The resultant brown solution was evaporated to
dryness and loaded onto a silica gel column. Excess I2 was removed
by eluting with n-hexane, and CH2Cl2 was used as an eluent to
isolate the brown band and furnish the title compound as a brown
solid. Yield 80%. Anal. Calcd for C36H52N2O2I2Os‚0.4C6H14: C,
1
44.97; H, 5.67; N, 2.73. Found: C, 44.91; H, 5.72; N, 2.61. H
NMR (400 MHz, CDCl3): δ 22.15 (s, 2H), 13.71 (s, 2H), 8.81 (s,
2H), 8.35 (m, 2H), 2.56 (s, 18H), 1.99 (d, J ) 3.0 Hz, 2H), 1.49
(m, 2H), 0.31 (s, 20H), -1.89 (m, 2H). IR (KBr pellet, cm-1) 1578.
FAB MS: m/z 990 [M]+, 863 [M - I]+, 735 [M - 2I]+.
Acknowledgment. We thank Dr. Po Hung Ko and Siu-
Chung Chan for contributions made to the synthesis and
photochemistry of the dioxoosmium(VI) complexes reported
in this paper. This work is supported by the Area of
Excellence Scheme (AoE/P-10-01) established under the
University Grants Committee, HKSAR, the Hong Kong
Research Grants Council (HKU7384/02P), HKSAR, and The
University of Hong Kong (University Development Fund).
P.W.H.C. wishes to thank The University of Hong Kong
(Small Project Funding Program) for funding.
X-ray Crystallography. Crystals of 3a and 3b were obtained
by slow diffusion of CHCl3 into acetone solutions of either 3a or
3b, whereas those of 6, 8, and 9 were obtained by slow diffusion
of n-hexane into CHCl3 solutions of either 6, 8, or 9, respectively,
and those of 11 was obtained by slow diffusion of Et2O into a CH2-
Cl2 solution containing 11.18 For 3b and 8, the data were collected
on a Bruker SMART CCD diffractometer by employing a crystal
of the dimensions 0.22 × 0.14 × 0.12 mm3 at 294 K and 0.20 ×
0.14 × 0.12 mm3 at 294 K, respectively. The structures were refined
by full-matrix least squares using the SHELXL-9731 program. For
the other four complexes, data collection was made on a MAR
diffractormeter by using a crystal of the dimensions of 0.40 × 0.20
× 0.10 (3a‚1.5CHCl3, at 253 K), 0.50 × 0.20 × 0.20 (6, at 301
K), 0.50 × 0.30 × 0.25 mm3 (9, at 293 K), and 0.50 × 0.12 ×
0.08 mm (11, at 301K). The images were interpreted and the
intensities integrated by using the program DENZO.32 The structures
were solved by direct methods by employing the SHELXS-9733
Supporting Information Available: Circular dichroism spectra
of (1R,2R)- and (1S,2S)-1a, including an 1H NMR spectrum of 1a;
1H NMR spectrum of 7; UV-vis spectra for 1a, 3a, and 6-11;
cyclic voltammograms of 3a, 3b, and 6-11; data and a plot of
linear-free-energy correlation of log kX/kH versus σ+ for reactions
of (1R,2R)-6 with a series of para-substituted styrenes at 298 K;
FAB mass spectra of UV irradiated (1S,2S)-1a; full experimental
details and spectroscopic analysis for the reaction of (1R,2R)-6 with
EDA; and crystallographic data in CIF format for 3a, 3b, 6, 8, 9,
and 11. This material is available free of charge via the Internet at
http://pubs.acs.org.
(31) Sheldrick, G. M. SHELXL97. Programs for Crystal Structure Analysis,
release 97-2; University of Goettingen: Goettingen, Germany, 1997.
(32) Otwinowski, Z.; Minor, W. “Processing of X-ray Diffraction Data
Collected in Oscillation Mode”. Methods in Enzymology, Macromo-
lecular Crystallography, Part A; Carter, C. W., Sweet, R. M., Jr., Eds.;
Academic Press: New York, 1997; Vol. 276, pp 307-326.
IC0481935
(33) Sheldrick, G. M. SHELXS97. Programs for Crystal Structure Analysis,
release 97-2; University of Goetingen: Goettingen, Germany, 1997.
3954 Inorganic Chemistry, Vol. 44, No. 11, 2005