Oxo complexes of osmium(IV) formed via dioxygen activation. X-ray structures of [OsX(dcpe)2]PF6 (X = CL, Br), [OsCl(η2-O2)(dcpe)2]BPH4, and [OsCl(O)(dcpe)2]BPh4 (dcpe = 1,2-bis(dicyclohexylphosphino)ethane)

Article abstract of DOI:10.1021/ic0002420

Dioxygen addition to the 16-electron complexes [OsX(P-P)₂]⁺ (3) gives the dioxygen adducts [OsCl(η²-O₂)-(P-P)₂]⁺ (3), which in turn react with HCl gas to give the novel osmium(IV) oxo complexes trans-[OsX(O)-(P-P)₂]⁺ (5) (X = Cl, Br; P-P = 1,2-bis(dicyclohexylphosphino)ethane (dcpe), 1,2-bis(diethylphosphino)ethane (depe), 1,2-bis((2R,5R)-2,5-dimethylphospholano)benzene (Me-duphos)). The complexes [OsX(dcpe)₂]⁺ (X = Cl, Br) (3) are studied by X-ray crystallography and are shown to have a 'Y-shaped' coordination geometry in the equatorial plane. The X-ray structural analysis of [OsCl(η²-O₂)(dcpe)₂]⁺ (4a) reveals an exceptionally short O-O bond (1.315(5) A). trans-[OsCl(O)(dcpe)₂]⁺ (5a), the first oxo complex of osmium(IV) investigated crystallographically, exhibits a long Os-O distance of 1.834(3) A. The reactivity of 4 and 5 as oxidants is described. The dioxygen complex 4a transfers one oxygen atom to PPh₃ (to give Ph₃PO) or oxidizes iodide ions to triiodide ions in the presence of anhydrous HCl. In both reactions, the corresponding oxo species 5a is quantitatively formed as the only metal-containing product. Oxo complexes 5 are surprisingly stable and unreactive toward standard reducing agents such as phosphines.

Full text of DOI:10.1021/ic0002420

Inorg. Chem. 2000, 39, 4903-4912
4903
Oxo Complexes of Osmium(IV) Formed via Dioxygen Activation. X-ray Structures of
[OsX(dcpe)2]PF6 (X ) Cl, Br), [OsCl(η2-O2)(dcpe)2]BPh4, and [OsCl(O)(dcpe)2]BPh4 (dcpe
) 1,2-Bis(dicyclohexylphosphino)ethane)
Peter Barthazy, Michael Wo1rle,† Heinz Ru1egger,‡ and Antonio Mezzetti*
Laboratory of Inorganic Chemistry, Swiss Federal Institute of Technology, ETH Zentrum,
CH-8092 Zu¨rich, Switzerland
ReceiVed March 6, 2000
Dioxygen addition to the 16-electron complexes [OsX(P-P)2]+ (3) gives the dioxygen adducts [OsCl(η2-O2)-
(P-P)2]+ (3), which in turn react with HCl gas to give the novel osmium(IV) oxo complexes trans-[OsX(O)-
(P-P)2]+ (5) (X ) Cl, Br; P-P ) 1,2-bis(dicyclohexylphosphino)ethane (dcpe), 1,2-bis(diethylphosphino)ethane
(depe), 1,2-bis((2R,5R)-2,5-dimethylphospholano)benzene (Me-duphos)). The complexes [OsX(dcpe)2]+ (X )
Cl, Br) (3) are studied by X-ray crystallography and are shown to have a “Y-shaped” coordination geometry in
the equatorial plane. The X-ray structural analysis of [OsCl(η2-O2)(dcpe)2]+ (4a) reveals an exceptionally short
O-O bond (1.315(5) Å). trans-[OsCl(O)(dcpe)2]+ (5a), the first oxo complex of osmium(IV) investigated
crystallographically, exhibits a long Os-O distance of 1.834(3) Å. The reactivity of 4 and 5 as oxidants is described.
The dioxygen complex 4a transfers one oxygen atom to PPh3 (to give Ph3PO) or oxidizes iodide ions to triiodide
ions in the presence of anhydrous HCl. In both reactions, the corresponding oxo species 5a is quantitatively
formed as the only metal-containing product. Oxo complexes 5 are surprisingly stable and unreactive toward
standard reducing agents such as phosphines.
Introduction
on dioxygen activation by ruthenium porphyrin complexes5 and
has found applications in catalytic oxidation reactions.6 How-
ever, because of the intrinsic difficulties associated with
dioxygen activation,1 advancements in this area have been much
slower than those for alternative methods utilizing single-oxygen
donors as oxidants in “shunt” pathways, such as those in Mn-
salen catalytic systems.7,8
Despite the large variety of transition metals and ligands
employed, all catalytic processes cited above have a number of
features in common. The active species is often a five-coordinate
complex [MXL4] containing four ligands L (often incorporated
in chelating ligands favoring a planar geometry). The ligand X
trans to the active site fine-tunes the reactivity of the system.
The catalytic cycle is generally thought to involve an oxo species
of the type [MX(O)L4]+. However, although the involvement
of oxo complexes2 in olefin epoxidation9 and alkane hydroxy-
lation10 reactions is an established fact, well-documented
examples of the formation of oxo complexes from molecular
Despite its enormous potential, the use of molecular oxygen
in transition-metal-catalyzed oxidation reactions is relatively
rare.1 Rather than dioxygen, most industrial processes exploit
partially reduced forms of this molecule, e.g., peroxides, as well
as catalysts based on metal centers in high oxidation states, often
with d0 or d2 configurations, which easily form oxo complexes.2
Nature instead uses processes where the metal centers are in
low oxidation states, typically with d6 configurations, and
operates with the most readily available oxidant, i.e., dioxygen.3
As several natural systems are based on the heme ferryl moiety,
much effort has been directed toward developing biomimetic
catalytic systems based on iron porphyrin complexes.4 Replace-
ment of the central atom with other members of the iron triad
along with retention of the d6 electronic configuration of the
central atom offers an opportunity to vary the catalytic species.
This approach was developed by Groves in his pioneering work
* Corresponding author. E-mail: mezzetti@inorg.chem.ethz.ch.
† X-ray structures.
(5) (a) Groves, J. T.; Quinn, R J. Am. Chem. Soc. 1985, 107, 5790. (b)
Groves, J. T.; Quinn, R. Inorg. Chem. 1984, 23, 3844. (c) Groves, J.
T.; Ahn, K. H. Inorg. Chem. 1987, 26, 3831.
‡ 2D NMR studies.
(1) (a) Ebner, J.; Riley, D. In ActiVe Oxygen in Chemistry; Foote, C. S.,
Valentine, J. S., Greenberg, A., Liebman, J. F., Eds.; Blackie Academic
and Professional Publishers: London, 1995; Chapter 6. (b) See also
refs 1a-f in ref 16 below.
(2) (a) Nugent, W. A.; Mayer, J. M. Metal-Ligand Multiple Bonds;
Wiley: New York, 1988. (b) See also refs 3b-f in ref 16 below.
(3) (a) Ho, R. Y. N.; Liebman, J. F.; Valentine, J. S. In ActiVe Oxygen in
Biochemistry; Valentine, J. S., Foote, C. S., Greenberg, A., Liebman,
J. F., Eds.; Blackie Academic and Professional Publishers: London,
1995. (b) See also refs 2b-f in ref 16 below.
(4) (a) Sheldon, R. A., Ed. Metalloporphyrins in Catalytic Oxidations;
Dekker: New York, 1994. (b) Montanari, F., Casella, L., Eds.
Metalloporphyrins Catalyzed Oxidations; Kluwer: Dordrecht, The
Netherlands, 1994. For seminal papers, see: (c) Balch, A. L.; Chan,
Y. W.; Cheng, R. S.; LaMar, G. N.; Latos, B.; Grazinsky, L.; Denner,
M. W. J. Am. Chem. Soc. 1984, 106, 7779 and references therein.
(6) Selected papers: (a) Bailey, C. L.; Drago, R. S. J. Chem. Soc., Chem.
Commun. 1987, 179. (b) Lai, T. S.; Zhang, R.; Cheung, K. K.; Kwong,
H. L.; Che, C. M. Chem. Commun. 1998, 1583. (c) Neumann, R.;
Dahan, M. Nature 1997, 388, 353. (d) Neumann. R.; Dahan, M. J.
Am. Chem. Soc. 1998, 120, 11969.
(7) Jacobsen, E. N. In Catalytic Asymmetric Synthesis; Ojima, I., Ed.;
VCH Publishers: New York, 1993; Chapter 4.2.
(8) Ito, Y. N.; Katsuki, T. Bull. Chem. Soc. Jpn. 1999, 72, 603.
(9) Representative papers: (a) Dobson, J. C.; Seok, W. K.; Meyer, T. J.
Inorg. Chem. 1986, 25, 1513. (b) Che, C. M.; Li, C. K.; Tang, W. T.;
Yu, W. Y. J. Chem. Soc., Dalton Trans. 1992, 3153. (c) Goldstein,
A. S.; Beer, R. H.; Drago, R. S. J. Am. Chem. Soc. 1994, 116, 2424.
(d) Stultz, L. K.; Binstead, R. A.; Reynolds, M. S.; Meyer, T. J. J.
Am. Chem. Soc. 1995, 117, 2520 and ref 1 therein. (e) Lai, T. S.;
Kwong, H. L.; Zhang, R.; Che, C. M. J. Chem. Soc., Dalton Trans.
1998, 3559.
10.1021/ic0002420 CCC: $19.00 © 2000 American Chemical Society
Published on Web 09/28/2000

4904 Inorganic Chemistry, Vol. 39, No. 21, 2000
Barthazy et al.
Scheme 1
Scheme 2
Chart 1
Results and Discussion
The Six-Coordinate Complexes [OsX2(P-P)2]. The six-
coordinate complexes trans-[OsX2(P-P)2] (1) and cis-[OsX2-
(P-P)2] (2) are the precursors for the five-coordinate, 16-
electron species [OsX(P-P)2]+ (3). By a variation of the
published procedures, the dcpe14 and depe (depe ) 1,2-bis-
(diethylphosphino)ethane)17 derivatives trans-[OsX2(P-P)2]
(P-P ) dcpe, X ) Cl (1a), Br (1b); P-P ) depe, X ) Cl
(1c)) were prepared by ligand metathesis from [OsX2(PPh3)3]18
and the appropriate diphosphine ligand (2 equiv) in refluxing
toluene. However, this synthetic method failed with Me-duphos
(Me-duphos ) (-)-1,2-bis((2R,5R)-2,5-dimethylphospholano)-
benzene),19 giving a monosubstituted binuclear species, most
likely [(Me-duphos)(PPh3)Os(µ-Cl)3Os(PPh3)(Me-duphos)]Cl,
instead of the disubstituted mononuclear complex. Therefore,
cis-[OsCl2(depe)2] (2c) and cis-[OsCl2(Me-duphos)2] (2d) were
prepared by heating [(PEt2Ph)3Os(µ-Cl)3Os(PEt2Ph)3]Cl with the
neat diphosphine ligand.17 In this series, the Me-duphos deriva-
tive 2d is new. It shows two pseudotriplets (AA′XX′ spin
system) in the 31P NMR spectrum, indicating that a single
diastereomer (either ∆ or Λ) is formed.
The Five-Coordinate Complexes [OsX(P-P)2]PF6. The
five-coordinate dcpe derivatives are easily prepared by reacting
trans-[OsX2(dcpe)2] (X ) Cl (1a), Br (1b)) with a strong halide
scavenger (Scheme 2). Thus, 1a,b smoothly form [OsCl(dcpe)2]-
PF6 ([3a]PF6) and [OsBr(dcpe)2]PF6 ([3b]PF6) upon addition
of TlPF6. When dry, the five-coordinate species [3a,b]PF6 are
air-stable in the solid state for months.
In the case of the least bulky diphosphine, depe, dissociation
of chloride from trans-[OsCl2(depe)2] (1c) does not occur under
the above conditions, whereas the more labile cis-[OsCl2(depe)2]
(2c) reacts with TlPF6 in CH2Cl2 or CHCl3. However, instead
of the 16-electron species [OsCl(depe)2]+ (3c), the dioxygen
complex [OsCl(η2-O2)(depe)2]+ (4c) is isolated when standard
Schlenk techniques are employed under argon. The putative
intermediate [OsCl(depe)2]+ is so reactive toward traces of O2
that we were not able to observe it by monitoring the reaction
between cis-[OsCl2(depe)2] and TlPF6 with 31P NMR spectros-
copy in CD2Cl2 solutions under argon. Thus, in view of the
extreme reactivity of 3c and its structural analogy to 3a,b,d, its
isolation was not further pursued.
oxygen are rare in nonbiomimetic systems of the iron triad.5,11
Indeed, most oxo complexes of ruthenium and osmium are
formed by oxidation of coordinated water12 or oxene transfer
from a terminal oxidant.4,13
We recently found that the five-coordinate, 16-electron
complexes [OsX(dcpe)2]+, 3 (X ) H, Cl; dcpe ) 1,2-bis-
(dicyclohexylphosphino)ethane),14 activate molecular oxygen,15
and that the resulting complex trans-[OsCl(η2-O2)(dcpe)2]+ (4a)
forms the oxo species trans-[OsCl(O)(dcpe)2]+ (5a) (Scheme
1).16 Complexes 3-5 belong to the series [OsXOnP4]+, which
features a variable number of oxygen atoms n (n ) 0, 1, 2)
with the same ligand set. These species share all the com-
monalities mentioned above, as they are five-coordinate com-
plexes of the iron triad, contain an ancillary ligand X that tunes
their electronic properties, and include an oxo species formed
from molecular oxygen. We show herein that this chemistry
can be generalized to other five-coordinate complexes [OsX-
(P-P)2]+ (2) (X ) Cl, Br; P-P ) diphosphine; Chart 1) and
report their reactions with O2 to give trans-[OsX(η2-O2)(P-
P)2]+ (4) and, eventually, the oxo complexes trans-[OsX(O)-
(P-P)2]+ (5).
(10) Representative papers: (a) Groves, J. T.; Nemo, T. E. J. Am. Chem.
Soc. 1983, 105, 6243. (b) Goldstein, A. S.; Drago, R. S. J. Chem.
Soc., Chem. Commun. 1991, 21. (c) Bailey, A. J.; Griffith, W. P.;
Savage, P. D. J. Chem. Soc., Dalton Trans. 1995, 3537.
(11) (a) Bourgault, M.; Castillo, A.; Esteruelas, M. A.; On˜ate, E.; Ruiz, N.
Organometallics 1997, 16, 636. (b) Molina-Svendsen, H.; Bojesen,
G.; McKenzie, C. J. Inorg. Chem. 1998, 37, 1981. (c) Camenzind, M.
J.; James, B. R.; Dolphin, D. J. Chem. Soc., Chem. Commun. 1986,
1137. (d) Hay-Motherwell, R. S.; Wilkinson, G.; Hussain-Bates, B.;
Hursthouse, M. B. Polyhedron 1993, 12, 2009.
(12) See, for instance: (a) Takeuchi, K. J.; Thompson, M. S.; Pipes, D.
W.; Meyer, T. J. Inorg. Chem. 1986, 25, 1845. (b) Dobson, J. C.;
Takeuchi, K. J.; Popes, D. W.; Geselowitz, D. A.; Meyer, T. J. Inorg.
Chem. 1986, 25, 2357. (c) Pipes, D. W.; Meyer, T. J. Inorg. Chem.
1986, 25, 4042. (d) Che, C. M.; Lai, T. F.; Wong, K. Y. Inorg. Chem.
1987, 26, 2289. (e) Marmion, M. E.; Takeuchi, K. J. J. Am. Chem.
Soc. 1988, 110, 1472. (f) Che, C. M.; Cheng, W. K.; Yam, V. W. W.
J. Chem. Soc., Dalton Trans. 1990, 3095. (g) Cheng, C. C.; Goll, J.
G.; Neyhart, G. A.; Welch, T. W.; Singh, P.; Thorp, H. H. J. Am.
Chem. Soc. 1995, 117, 2970. (h) Cheng, W. C.; Yu, W. Y.; Zhu, J.;
Cheung, K. K.; Peng, S. M.; Poon, C. K.; Che, C. M. Inorg. Chim.
Acta 1996, 242, 105. (i) Catalano, V. J.; Heck, R. A.; Immoos, C. E.;
O¨ hman, A.; Hill, M. G. Inorg. Chem. 1998, 37, 2150.
In the case of Me-duphos, cis-[OsCl2(Me-duphos)2] (2d)
smoothly reacts with TlPF6, giving [OsCl(Me-duphos)2]PF6
([3d]PF6). The new compound was characterized by 31P and
1H NMR spectroscopy and elemental analysis. The 31P room-
temperature NMR spectrum, consisting of two sharp triplets at
δ 76.1 and 42.6 (J ) 5.5 Hz), suggests that the complex has a
stereochemically rigid TBP structure and is present as a single
diastereomer (either ∆ or Λ) under these conditions.
(13) See, for instance: (a) Leung, T.; James, B. R.; Dolphin, D. Inorg.
Chim. Acta 1983, 79, 180. (b) Aoyagi, K.; Yukawa, Y.; Shimizu, K.;
Mukaida, M.; Takeuchi, T.; Kakihana, H. Bull. Chem. Soc. Jpn. 1986,
59, 1493. (c) Leung, W. H.; Che, C. M. J. Am. Chem. Soc. 1989, 111,
8812.
In general, halide dissociation is apparently favored in the
sterically crowded dcpe complexes 1a,b. In the other cases, the
(14) Mezzetti, A.; Del Zotto, A.; Rigo, P. J. Chem. Soc., Dalton Trans.
1990, 2515.
(15) Mezzetti, A.; Zangrando, E.; Del Zotto, A.; Rigo, P. J. Chem. Soc.,
Chem. Commun. 1994, 1597.
(16) Barthazy, P.; Wo¨rle, M.; Mezzetti, A. J. Am. Chem. Soc. 1999, 121,
480.
(17) Chatt, J.; Hayter, R. G. J. Chem. Soc. 1961, 896.
(18) Hoffman, P. R.; Caulton, K. G. J. Am. Chem. Soc. 1975, 97, 4221.
(19) For synthesis and application of Me-duphos, see, for instance: Burk,
M. J.; Gross, M. F.; Harper, T. G.; Kalberg, C. S.; Lee, J. R.; Martinez,
J. P. Pure Appl. Chem. 1996, 68, 37.

Oxo Complexes of Osmium(IV)
Inorganic Chemistry, Vol. 39, No. 21, 2000 4905
Br distance in the bromo derivative 3b is 2.481(2) Å, shorter
than the 2.5738(6) Å distances in the reference compound trans-
[OsBr2(dppe)2].28 Taking into account the unsaturated nature
of these complexes, the axial Os-P distances in both 3a and
3b appear exceptionally long with respect to literature val-
ues.21,26,29 An interesting feature in both 3a and 3b is the
envelope conformation of the chelate rings with the flap on a
C atom.
Reaction of [OsX(P-P)2]PF6 with O2. The 16-electron
species 3a,b reacted quantitatively with O2 in CH2Cl2, forming
the dioxygen complexes [OsX(η2-O2)(dcpe)2]+ (X ) Cl (4a),
Br (4b)) within hours. The depe derivative [OsCl(η2-O2)-
(depe)2]+ (4c) was prepared directly from six-coordinate 2c by
reaction with TlPF6 and O2 in CH3OH. The light green
complexes 4a-c were characterized by 31P and 1H NMR
spectroscopy, mass spectrometry (FAB+), and elemental analy-
sis. Although the ν(O-O) stretching band was unassignable
owing to the crowding of the 800-900 cm-1 IR spectral region,
the X-ray structure of 4a reported below gives definitive
evidence of the η2-O2 linkage. The 31P NMR spectra of 4a-c
consist of one sharp singlet in the range δ +10 to -10,
consistent with rapid internal reorientation rendering all P atoms
equivalent. In contrast, the 31P NMR spectra of the related
complexes [MH(η2-O2)(P-P)2] (M ) Ru, Os) show broad
signals at room temperature, possibly due to the hindered
propeller-like rotation of the η2-O2 ligand.15,30,31
Figure 1. ORTEP view of [OsCl(dcpe)2]+ (3a) (30% probability
ellipsoids). Selected bond distances (Å) and angles (deg): Os-Cl,
2.371(1); Os-P(1), 2.282(1); Os-P(3), 2.321(1); Os-P(2), 2.422(1);
Os-P(4), 2.417(1); Cl-Os-P(1), 122.38(4); P(1)-Os-P(3), 92.58-
(4); Cl-Os-P(2), 88.05(4); P(1)-Os-P(4), 102.06(4); Cl-Os-P(3),
144.86(4); P(2)-Os-P(3), 101.50(4); Cl-Os-P(4), 85.78(4); P(2)-
Os-P(4), 173.75(4); P(1)-Os-P(2), 82.08(4); P(3)-Os-P(4), 83.10-
(4).
more labile cis isomer 2 has to be used, exploiting the stronger
trans effect of P as compared to Cl. The reactivity trend also
suggests that the increasing basicity of the P-P ligand labilizes
the halide, as observed for trans-[OsCl2(dcpe)2] as compared
to trans-[OsCl2(dppe)2] (dppe ) 1,2-bis(diphenylphosphino)-
ethane). The latter species, which contains a less basic and less
bulky diphosphine, does not react with TlPF6, and the corre-
sponding five-coordinate complex has been prepared from cis-
[OsCl2(dppe)2].20 Steric and electronic effects apparently co-
operate in stabilizing the Lewis-acidic 16-electron complexes
containing the more basic and more bulky phosphines.
X-ray Structures of [OsX(dcpe)2]PF6 (X ) Cl, Br). The
five-coordinate nature of 3a and 3b was confirmed by X-ray
analysis (Figure 1 and Figure S1 (Supporting Information)).
Selected interatomic distances and angles of 3a and 3b are given
in the caption to Figure 1 and in Table S2 (Supporting
Information), respectively. The five-coordinate cations [OsX-
(dcpe)2]+ (X ) Cl (3a), Br (3b)) have a Y-shaped, distorted
trigonal bipyramidal structure, similar to that found in [OsCl-
(dppe)2]+,21 as well as in the ruthenium analogues with dcpe22
and other diphosphines.23,24 This is as expected for π-stabilized
16-electron complexes.25 The “Y-plane” is further distorted, with
two largely different P-Os-X angles, as already observed in
the ruthenium analogues.22-24 Support for the role played by
the π-donation from the chloride ligand comes from the Os-
Cl distance of 2.371(1) Å, which is ca. 0.06 Å shorter than those
in trans-[OsCl2(dppe)2] (2.434(1) Å).26,27 Similarly, the Os-
The dioxygen complex [OsCl(η2-O2)(depe)]+ (4c) is probably
the cationic species observed by Chatt and Hayter upon
dissolution of cis-[OsCl2(depe)2] in water.17 In the series, the
Me-duphos derivative [OsCl(Me-duphos)2]+ (3d) is the least
reactive toward O2. Upon exposure to air of a CDCl3 solution,
the five-coordinate complex 3d remains unchanged to a great
extent and no diamagnetic η2-O2 complex is formed, as indicated
by the 31P NMR spectrum. The 1H NMR spectrum of the
solution indicates that traces (∼1%) of a paramagnetic complex
are formed, which we tentatively formulate as the corresponding
oxo complex by analogy with the other [OsX(O)(P-P)2]+
species (see below). The latter probably derives from an
undetected dioxygen adduct present at low concentration in
equilibrium with 3d. Finally, for the dppe complex, no reaction
with O2 was observed.20
X-ray Structure of [OsCl(η2-O2)(dcpe)2]BPh4 ([4a]BPh4).
X-ray-quality crystals of [4a]BPh4 were grown from CH2Cl2/
PriOH. The complexes [OsBr(η2-O2)(dcpe)2]+ (4b) and [OsCl-
(η2-O2)(depe)2]+ (4c) decomposed to the oxo complexes during
the crystallization process. This prevented growing crystals of
their salts with [PF6]-, [BPh4]-, or [BAr4]- (BArF, Ar ) 3,5-
bis(trifluoromethyl)phenyl).
The formally seven-coordinate cation [OsCl(η2-O2)(dcpe)2]+
can be described as a distorted pentagonal bipyramid, with two
P atoms, the Cl atom, and the two O atoms approximately in
the equatorial plane and with two mutually trans axial P atoms
(Figure 2, Table S3 (Supporting Information)).32 The Os-Cl
(20) Maltby, P. A.; Schlaf, M.; Steinbeck, M.; Lough, A.; Morris, R. H.;
Klooster, W. T.; Koetzle, T. F.; Srivastava, R. C. J. Am. Chem. Soc.
1996, 118, 5396.
(21) Lough, A. J.; Morris, R. H.; Schlaf, M. Acta Crystallogr., Sect. C
1996, 52, 2193.
(22) Mezzetti, A.; Del Zotto, A.; Rigo, P.; Bresciani Pahor, N. J. Chem.
Soc., Dalton Trans. 1989, 1045.
(23) Chin, B.; Lough, A. J.; Morris, R. H.; Schweitzer, C. T.; D’Agostino,
C. Inorg. Chem. 1994, 33, 6278.
(24) Batista, A. A.; Centeno Cordeiro, L. A.; Oliva, G. Inorg. Chim. Acta
1993, 203, 185.
(25) (a) Caulton, K. G. New J. Chem. 1994, 18, 25. (b) Riehl, J. F.; Jean,
Y.; Eisenstein, O.; Pe´lissier, M. Organometallics 1992, 11, 729. (c)
Johnson, T. J.; Folting, K.; Streib, W. E.; Martin, J. D.; Huffman, J.
C.; Jackson, S. A.; Eisenstein, O.; Caulton, K. G. Inorg. Chem. 1995,
34, 488 and references therein.
(26) Levason, W.; Champness, N. R.; Webster, M. Acta Crystallogr., Sect.
C 1993, 49, 1884.
(27) A mean value of 2.435(9) Å is found for five complexes of the type
trans-[OsCl2(PPhR2)4], as retrieved in the Cambridge Structural
Database.
(28) Lough, A. J.; Morris, R. H.; Schlaf, M. Z. Kristallogr. 1995, 210,
973.
(29) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D.
G.; Taylor, R. J. Chem. Soc., Dalton Trans. 1989, S1.
(30) Jime´nez-Tenorio, M.; Puerta, M. C.; Valerga, P. Inorg. Chem. 1994,
33, 3515.
(31) Martelletti, A.; Gramlich, V.; Zu¨rcher, F.; Mezzetti, A. New J. Chem.
1999, 199.

4906 Inorganic Chemistry, Vol. 39, No. 21, 2000
Barthazy et al.
discovery of [RuH(η2-O2)(P-P)2]+.30 Most of these new η2-O2
derivatives are complexes of the type [MH(η2-O2)(P-P)2]+ (M
) Ru, Os)30-33 or [Ru(η2-O2)(Cp*)(P-P)]+ (Cp* ) C5Me5).35
The present investigation contributes to the assessment of the
electronic requirements for dioxygen activation by relatively
electron-rich but coordinatively unsaturated Ru(II) and Os(II)
complexes of the [MX(P-P)2]+ series. In this class of com-
pounds, the osmium derivatives show a higher tendency to bind
O2 than the ruthenium analogues. As the five-coordinate
complexes [MX(P-P)2]+ generally react rapidly with both
neutral and anionic donors, such as halide, CO, H2, and
nitriles,14,22,37 this is probably a thermodynamic effect, as
supported by the following considerations.
Dioxygen adducts of ruthenium are formed only when several
strong σ-donors (the hydride and basic P-P ligands) enhance
the electron density at the metal. Thus, the five-coordinate [RuH-
(P-P)2]+ complexes form [RuH(η2-O2)(P-P)2]+ (P-P ) dcpe31
or 1,2-bis(diisopropylphosphino)ethane30 (dippe)), whereas the
chloro analogue [RuCl(dcpe)2]+ is stable in solutions exposed
to air for short periods of time and does not form a (detectable)
dioxygen adduct.22 In the case of [OsX(dcpe)2]+, O2 activation
occurs also when less basic X and P-P ligands are combined,
as in [OsH(dppe)2]+ 33a and [OsCl(dcpe)2]+.15 Indeed, the higher
energy of the d orbitals of Os as compared to Ru favors the
shift of electron density from the metal to the dioxygen ligand
that stabilizes the M(η2-O2) linkage. The effect of the donor
properties of the anionic ligand X is clearly visible in the series
[OsX(η2-O2)(P-P)2]+, where the O-O distance increases on
going from chloride (a weak donor) to hydride (a strong donor)
(Table 1). In this class of compounds, the chloro derivatives
[OsCl(η2-O2)(P-P)2]+ (4a-c) reported herein are the dioxygen
complexes that are stabilized by the least basic ligands.
However, some stable dioxygen adducts of osmium are formed
even in the presence of a π-acid ligand, as in [OsHCl(η2-O2)-
(CO)(PR3)2] (R ) c-C6H11, Pri).36b
Figure 2. ORTEP view of trans-[OsCl(η2-O2)(dcpe)2]+ (4a) (30%
probability ellipsoids).
Table 1. O-O and Os-O Bond Distances (Å) in
[OsX(η2-O2)(P-P)2]PF6
O-O
Os-O
ref
[OsCl(η2-O2)(dcpe)2]PF6 1.315(5) 2.006(3), 2.041(4) this work
[OsH(η2-O2)(dcpe)2]PF6 1.45(1)
2.045(8), 2.037(8) 15
[OsH(η2-O2)(dppe)2]PF6 1.430(5) 2.061(4), 2.064(3) 33a
distance in the (formally seven-coordinate) 4a (2.380(1) Å) is
similar to that in five-coordinate 3a (2.371(1) Å), whereas the
Os-P distances are even longer than those in 3a,b. The Os-
P4 arrangement shows a tetrahedral distortion, with the P(1) and
P(3) atoms bent away from the coplanar dioxygen ligand (P(1)-
Os-P(3) ) 162.46(4)°). The axial P atoms are only slightly
bent toward the dioxygen (P(2)-Os-P(4) ) 175.91(4)°). Both
chelate rings show an envelope conformation with the flap on
a C atom.
Despite structural analogies, 4a displays a much shorter O-O
distance (1.315(5) Å) than [OsH(η2-O2)(P-P)2]+ (dcpe,15 1.45-
(1) Å; dppe,33a 1.430(5) Å; Table 1) and among the shortest
ever found for a dioxygen complex.29,34 Unfortunately, the
Os-O distances are not a reliable probe of the Os-O bond
strengths in 4a, as the η2-coordination mode of the dioxygen
ligand is slightly distorted. Thus, the Os-O(2) distance is longer
by 0.035(4) Å than Os-O(1) and the O(2)-O(1)-Os angle
(72.5(2)°) is larger than O(1)-O(2)-Os (69.6(2)°). Comparison
with [OsH(η2-O2)(P-P)2]+ (Table 1) shows an enhanced
interaction between Os and one of the O atoms of η2-O2.
Although these features invite speculation about distortion of
the η2-coordination toward η1, their magnitudes are so small
that they could be the effect of crystal packing as well.
Bonding in [MX(η2-O2)(P-P)2]+. Examples of dioxygen
adducts of d6 complexes of Ru(II)30,31,35 and Os(II)33,36 have
been increasing in number, in particular since the recent
Besides the nature of the metal M (M ) Ru or Os) and the
donor properties of the ligand X (X ) halide or H), the
electronic and steric properties of the diphosphine fine-tune the
reactivity of [MX(P-P)2]+ toward O2. As described above, the
reactivity of the five-coordinate species [OsCl(P-P)2]+ toward
dioxygen increases with increasing basicity and decreasing steric
bulk of the P-P ligand along the series dppe < Me-duphos ,
dcpe < depe.
The structural data available for [MX(η2-O2)(P-P)2]+ (M )
Ru, Os; X ) Cl, H) in the solid state and in solution provide
further insight into the bonding in 4a-c, taking into account
that the η2-O2 ligand is a π-acceptor and the chloride a weak
π-donor. The Peq-Os-Peq angle is much larger in 4a (162.46-
(4)°) than in the hydride analogue [OsH(η2-O2)(dcpe)2]+ (136.3-
(1)°). As the steric crowding in chloro derivatives 4 is higher
than that in the hydride analogues, this effect is more likely
electronic than steric. For the related [MH(η2-H2)(P-P)2]+
(35) Other η2-O2 complexes of Ru(II): (a) Kirchner, K.; Mauthner, K.;
Mereiter, K.; Schmid, R. J. Chem. Soc., Chem. Commun. 1993, 892.
(b) De los rios, I.; Tenorio, M. J.; Padilla, J.; Puerta, M. C.; Valerga,
P. J. Chem. Soc., Dalton Trans. 1996, 377. (c) Sato, M.; Asai, M. J.
Organomet. Chem. 1996, 508, 121. (d) Takahashi, Y.; Hikichi, S.;
Akita, M.; Moro-oka, Y. Chem. Commun. 1999, 1491. (e) Jia, G. C.;
Ng, W. S.; Chu, H. S.; Wong, W. T.; Yu, N. T.; Williams, I. D.
Organometallics 1999, 18, 3597.
(36) (a) Moers, F. G.; ten Hoedt, R. W. M.; Langhout, J. P. J. Inorg, Nucl.
Chem. 1974, 36, 2279. (b) Esteruelas, M. A.; Sola, E.; Oro, L. A.;
Meyer, U.; Werner, H. Angew. Chem., Int. Ed. Engl. 1988, 27, 1563.
(c) For related species, see: Maddock, S. M.; Rickard, C. E. F.; Roper,
W. R.; Wright, L. J. J. Organomet. Chem. 1996, 510, 267.
(37) Mezzetti, A.; Del Zotto, A.; Rigo, P.; Farnetti, E. J. Chem. Soc., Dalton
Trans. 1991, 1525.
(32) This is largely formal and implies that 4b could be described as a
peroxo complex of Os(IV). However, the alternative description as a
six-coordinate dioxygen complex of Os(II) (featuring a distorted
octahedral coordination) seems more appropriate in view of the short
O-O distance and is normally used throughout this paper.
(33) (a) Bartucz, T. Y.; Golombek, A.; Lough, A. J.; Maltby, P. A.; Morris,
R. H.; Ramachandran, R.; Schlaf, M. Inorg. Chem. 1998, 37, 1555.
(b) Tenorio, M. J.; Puerta, M. C.; Salcedo, I.; Valerga, P. J. Organomet.
Chem. 1998, 564, 21.
(34) Hill, H. A.; Tew, D. G. In ComprehensiVe Coordination Chemistry;
Wilkinson, G., McCleverty, J. A., Eds.; Pergamon: Oxford, U.K.,
1987; Vol. 2, p 318.

Oxo Complexes of Osmium(IV)
Inorganic Chemistry, Vol. 39, No. 21, 2000 4907
Figure 3. Partial (π-bonding) correlation diagram of the Cl-Os-η2-
O2 fragment. Only the dxz orbital has the correct symmetry for
interacting with π*(O2).
complex, it has been shown that the bending of two trans P
atoms away from the dihydrogen ligand enhances the dπ-
(M)fσ*(η2-H2) back-bonding.38 This is because closing the
equatorial P-Ru-P angle rehybridizes the dxz orbital and raises
its energy. Such a distortion is necessary in [OsH(η2-O2)-
(dcpe)2]+, where it improves the overlap with the π* orbitals
of O2. In [OsCl(η2-O2)(P-P)2], closing one P-Ru-P angle is
both unfavorable (because Cl is larger than H) and unnecessary,
as the dxz orbital is destabilized by the pπ orbital of the chloro
ligand (Figure 3).25 This is consistent with a weaker dπ(Os)fπ*-
(η2-O2) binding component in 4a than in [OsH(η2-O2)(dcpe)2]+
due to Cl being an overall weaker donor than hydride, as
discussed above for the O-O and Os-O bond distances.
Variable-temperature NMR spectroscopy data support the
above interpretation. Thus, the hydride analogues [MH(η2-O2)-
(P-P)2]+ (M ) Ru, Os) show fluxional behavior in solution
that is possibly due to the hindered propeller-like rotation of
the η2-O2 ligand.15,30,31 Their room-temperature 31P NMR spectra
show two broad humps that resolve into two pseudotriplets at
low temperature. In contrast, the 31P NMR spectra of the halo
derivatives 4a-c consist of one sharp singlet, indicating rapid
rotation of η2-O2 on the NMR time scale due to lower energy
barriers. This is contrary to expectation based on steric argu-
ments and consistent with a larger dπ(Os)fπ*(η2-O2) binding
component in chloro derivative 4a than in [OsH(η2-O2)(dcpe)2]+.
The overall bonding pattern in the Cl-Os-(η2-O2) moiety
features a three-orbital, four-electron push-pull interaction
between the chloro ligand and the dioxygen ligand analogous
to the case of the Cl-M-CO moiety (Figure 3).25 Accordingly,
the Os-Cl distance in the formally seven-coordinate 4a (2.380-
(1) Å) is similar to that in the five-coordinate 3a (2.371(1) Å).
This is again contrary to the expectation based on steric effects
and suggests that π-donation plays similar roles in both
complexes.
Figure 4. UV-visible monitoring of the reaction of 4a with I- in the
presence of anhydrous HCl.
ized) products. Heating under vacuum mainly produces dcpe
dioxide. A similar behavior has been observed for [OsH(η2-
O2)(dcpe)2]+.15 Complex 4a reacts slowly with carbon monoxide
in CH2Cl2 solution, but 31P NMR spectroscopy and stripping
of the effluent gases in aqueous Ba(OH)2 indicated that neither
the carbonyl complex [OsCl(CO)(dcpe)2]+ nor CO2 was formed.
All of the dioxygen complexes 4a-c are stable in the solid
state, but decomposition to the oxo species trans-[OsX(O)(P-
P)2]+ slowly occurs in CH2Cl2 solution. Simple storing of 4a-c
in CH2Cl2 solution yields the corresponding oxo complexes
within 3 d. As independent experiments show that traces of acids
greatly accelerate this reaction, we conclude that the reaction
is triggered by traces of HCl formed by the decomposition of
the chlorinated solvent over time (Scheme 1) or, alternatively,
by traces of water incorporated during the preparation of 4.
Accordingly, as the [PF6]- anion is always associated with small
amounts of acids (or water), changing the anion Y- in [OsCl-
(P-P)2]Y to [BPh4]- or [BAr4]- substantially increases the
stability of the dioxygen complex. In contrast, [OsH(η2-O2)-
(dcpe)2]+ is stable in solution for longer periods of time.15
Neither the fate of the “lost” oxygen atom nor the mechanism
of this reaction could be assessed. However, we rule out that
the above reaction occurs by dissociation of O2 from [OsCl-
(η2-O2)(dcpe)2]+ (4a) followed by formation of a peroxo-bridged
intermediate,3,6c,d as O2 coordination in 4a is essentially ir-
reversible, as discussed above, and five-coordinate 3a does not
react with the dioxygen complex 4a.16
In conclusion, the stronger Os-O bonds (and weaker O-O
bond) in [OsH(η2-O2)(P-P)2]+ than in 4a are due to hydride
being a much stronger donor than Cl. As the Osf(η2-O2)
electron transfer is mediated by a π-effect, the dπ(Os)-π*(O2)
overlap is maximized by the distortion of the equatorial P-M-P
angle in the hydride complexes and by the dπ(Os)-pπ(Cl) four-
electron destabilization in the case of 4. The weaker Os-(η2-
O2) bonding and smaller dπ-π* overlap in 4 are possibly
reflected in the distortion of the η2-coordination toward η1. This
could explain the unusual reactivity of 4 as compared to the
hydride analogues.
Oxidation Reactions with [OsX(η2-O2)(P-P)2]+ (4). The
oxygen-transfer reactivity of 4a with a number of substrates
was studied. The test reactions were generally performed with
[OsCl(η2-O2)(dcpe)2]+ (4a), but 4b and 4c showed similar
reactivity when used in selected instances. [4a]BPh4 oxidizes
I- (as [NBu4]I) to triiodide, forming trans-[OsCl(O)(dcpe)2]+
(5a) in the presence of anhydrous HCl in CH2Cl2 according to
eq 1. Monitoring of the reaction by UV-visible spectroscopy
[OsCl(η2-O2)(dcpe)2]+ + 3I- + 2H+ f
trans-[OsCl(O)(dcpe)2]+ + I3- + H2O (1)
Reactivity of [OsX(η2-O2)(P-P)2]+. We investigated the
reversibility of dioxygen addition to five-coordinate 3a. Pho-
tolysis of 4a (Xe lamp) in CH2Cl2 solution gives small amounts
of five-coordinate 3a (20%) together with other (uncharacter-
at 365 nm shows quantitative formation of [I3]- and 5a based
on the absorbance trace of the reaction after correction for the
absorbance of the oxo complex (Figure 4). The 31P NMR
spectrum of the reaction solution indicates quantitative disap-
pearance of 4a, whereas only the typical signals of 5a are visible
(38) (a) Van Der Sluys, L. S.; Eckert, J.; Eisenstein, O.; Hall, J. H.;
Huffman, J. C.; Jackson, S. A.; Koetzle, T. F.; Kubas, G. J.; Vergamini,
P. J.; Caulton, K. G. J. Am. Chem. Soc. 1990, 112, 4831. (b) Maseras,
F.; Koga, N.; Morokuma, K. Organometallics 1994, 13, 4008.

4908 Inorganic Chemistry, Vol. 39, No. 21, 2000
Barthazy et al.
1
in the H NMR spectrum. No reaction occurs without acid.
Complex 4a also oxidizes triphenylphosphine in the presence
of HCl under argon (eq 2). The stoichiometry of reaction 2 is
[OsCl(η2-O2)(dcpe)2]+ + [Ph3PH]Cl f
trans-[OsCl(O)(dcpe)2]+ + Ph3PO + HCl (2)
well-defined, as [Ph3PH]Cl is added to 4a (1:1 mole ratio) to
give 5a and Ph3PO in almost quantitative yields, as measured
by 31P NMR spectroscopy. The reaction is complete within 10
min, and the coordinated diphosphines are not oxidized.39
Acid-promoted oxygen transfer has been proposed for other
peroxo complexes.1,40 In contrast to what is observed for M(η2-
O2) complexes (M ) Pt, Rh),41 it seems unlikely that reaction
1 involves acid hydrolysis of 4a, since the use of aqueous HCl
gives yet unidentified products instead of 5a and extraction of
freshly prepared CH2Cl2 solutions of 5a with aqueous titanyl
sulfate does not reveal the presence of H2O2. Finally, 5a does
not re-form 4a upon treatment with H2O2.
Figure 5. Partial correlation diagram of a d4 [Os(O)L5] complex.
Table 2. 1H and 13C NMR Data (Obtained in CDCl3) for
trans-[OsCl(O)(depe)2]BPh4 ([5c])BPh4)
assignta
δ(1H)
R2(1H),b s-1
δ(13C)
The oxidation of a number of organic substrates has been
attempted. Complex 4a does not epoxidize olefins (styrene) or
quinone-like substrates (menadione), oxidize aldehydes (ben-
zaldehyde) or alcohols (PriOH, tert-butyl alcohol, CH3OH), or
hydroxylate alkanes (adamantane). In contrast, the dioxygen
ligand of the ruthenium analogue [RuH(η2-O2)(dcpe)2] displays
moderate nucleophilic behavior and oxidizes aldehydes to the
corresponding carboxylic acids.31 With TCNE an immediate
reaction occurs, but the TCNE radical anion is formed instead
of the epoxide. We also tested whether 5a shows haloperoxidase
reactivity in the presence of bromide ions.42 However, the acidic
hydrolysis of the dioxygen complex 4a in the presence of [NBu4]-
Br and 1,3,5-trimethoxybenzene or 2,3-dimethoxytoluene does
not give the corresponding brominated derivatives (not even
traces). This also disfavors the possibility that HOCl is formed
in the reaction of 4a with HCl (Scheme 1).
trans-[OsX(O)(P-P)2]BPh4. The osmium(IV) complexes
[OsX(O)(P-P)2]+ (X ) Cl, P-P ) dcpe, 5a; X ) Br, P-P )
dcpe, 5b; X ) Cl, P-P ) depe, 5c) were prepared from the
corresponding dioxygen complexes 4a-c and fully character-
ized. As mentioned above, the d4 oxo complexes 5a-c are
formed by oxygen transfer from the dioxygen adducts 4a-c
(Scheme 1) and the reaction is accelerated by gaseous HCl. The
light green or brownish complexes 5a-c are stable in the solid
state and in solution. The Me-duphos analogue [OsCl(O)(Me-
duphos)2]+ is formed only in traces, as discussed above. We
have previously reported that 5a is paramagnetic with an
effective magnetic moment µeff of 3.05 µB at 300 K,16 a value
near the spin-only value for two unpaired electrons. This is
explained by the molecular orbital ordering of octahedral oxo
complexes with a d4 configuration based on C4V symmetry as
discussed by Mayer (Figure 5).43 In the case of the d4 complexes
[OsX(O)(P-P)2]+, two d electrons fill the dxy orbital, and the
remaining two occupy the two degenerate dxz and dyz orbitals
with parallel spins.
CH3(Cl)
CH3(O)
CH2(Cl)
CH2(O)
CH2(BB)
1.5
29.0
6.9, -4.1
34.0, 12.3
15.1, 8.1
45
240
195, 350
320, 635
155, 205
-26.6
+34.2
-122.2
+173.8
-85.4
a (Cl) and (O) denote the chloride and oxo hemispheres, respectively;
(BB) denotes the diphosphine backbone. b Transverse relaxation rates
R2 estimated from line widths.
NMR Spectroscopy. Although no 31P NMR signals can be
observed (at least at room temperature), the H and 13C NMR
1
spectra are sufficiently resolved in the diamagnetic areas and
feature well-defined paramagnetic regions with relatively small
isotropic shifts. Most of the signals could be assigned by a
combination of one- and two-dimensional NMR techniques
(Table 2). In the depe derivative trans-[OsCl(O)(depe)2]+ (5c),
there are two inequivalent methyl groups belonging to the two
hemispheres in which the oxo and the chloro substituents reside,
respectively. On the basis of the assumptions (i) that most of
the unpaired spin density is located either on the oxo ligand or
between it and the metal and (ii) that the dipolar term dominates
the relaxation behavior of the adjacent protons, we assign the
slowly relaxing methyl protons resonating in the diamagnetic
region of the spectrum at δ 1.5 to the group in the Cl
hemisphere.
Despite the considerable transverse relaxation rates R2 (Table
2) of the diastereotopic protons in the ethyl CH2 groups, it
proved possible to relate these to their respective CH3’s by
means of a 2D TOCSY experiment. The backbone CH2 protons
are consequently assigned to the remaining two signals. All 13
C
resonances were assigned on this basis by means of H-13C
2D-heteronuclear multiple-quantum coherence spectroscopy. It
is interesting to note that the chemical shifts of the carbons
residing in the oxo hemisphere are isotropically shifted toward
higher frequency, whereas those of the carbons belonging to
the chloride hemisphere and the chelate backbone are below
the TMS frequency.
1
(39) Although [OsCl(Me-duphos)2]+ (3d) probably forms a very labile
dioxygen adduct, PPh3 is not oxidized in the presence of 3d (1 equiv)
under O2 in CDCl3.
The dcpe derivatives 5a and 5b are completely analogous in
structure and spectroscopic properties to 5c. However, the
interpretation process is more demanding in view of 12 and 22
inequivalent C and H atoms to be assigned, requiring the use
(40) (a) van Asselt, A.; Trimmer, M. S.; Henling, M. S.; Bercaw, J. E. J.
Am. Chem. Soc. 1988, 110, 8254 and ref 12 therein. (b) Conte, V.; Di
Furia, F.; Moro, S. J. Mol. Catal. A: Chem. 1997, 120, 93.
(41) Selected papers: (a) Sen, A.; Halpern, J. J. Am. Chem. Soc. 1977, 99,
8337. (b) Bhaduri, S.; Casella, L.; Ugo, R.; Raithby, P. R.; Zuccaro,
C.; Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1979, 1624.
(42) Butler, A. Coord. Chem. ReV. 1999, 187, 17.
of 2D methods. A contour plot of a section of the H-13C
1
heteronuclear multiple-quantum coherence spectrum for trans-
[OsBr(O)(dcpe)2]BPh4 ([5b]BPh4) (Figure 6) in CDCl3 at room
temperature shows the wide spread of shifts in the carbon
dimension. Indeed, with the exception of that of one R-carbon,
(43) Mayer, J. M.; Thorn, D. L.; Tulip, T. H. J. Am. Chem. Soc. 1985,
107, 7454.

Oxo Complexes of Osmium(IV)
Inorganic Chemistry, Vol. 39, No. 21, 2000 4909
Figure 7. ORTEP view of trans-[OsCl(O)(dcpe)2]+ (5a) (30% prob-
ability ellipsoids).
Figure 8. Correlation diagram of the Cl-OsdO fragment.
Figure 6. 1H-13C heteronuclear multiple-quantum coherence spectrum
of [5b]BPh4. Cross-peaks labeled with an asterisk are vertically
expanded by a factor of 8; BB denotes the chelate backbone resonances.
The Os-oxo linkage deserves discussion. The Os-O(1)
distance in 5a (1.834(3) Å) is much longer than those in
osmium(VI) oxo complexes (ca. 1.72 Å),2,29,44 e.g., in the (E)-
styryl complex [OsCl(O)2((E)-CHdCHPh)(PPri)2] (d(Os-O) )
1.70(1), 1.72(1) Å).11a The lengthening of the Os-O bond in
5a is due to the two additional electrons in the (dxy)2(dxz)1(dyz)1
configuration as compared to the d2 osmium(VI) systems. A
partial, qualitative correlation diagram (Figure 8) indicates that
the degenerate dxz and dyz orbitals have antibonding character
with respect to the Os-O bond.2 Their partial occupation by
parallel spins is confirmed by the magnetic data.2,12d,13b
Qualitative MO considerations explain further structural
features. The Os-Cl bond is much longer in 5a (2.442(1) Å)
than in five-coordinate 3a (2.371(1) Å) and in the η2-O2 complex
4a (2.380(1) Å). The opposite trend is expected on the basis of
the ionic radius contraction upon going from Os(II) to Os(IV).
The straightforward explanation is that both the dioxygen
complex 4a and the 16-electron species 3a are stabilized by pπ
f dπ donation from the halide, although via different mecha-
nisms, as discussed above.25,45 In contrast, 5a contains two
π-donors, a strong one, the oxo ligand,2 and a much weaker
one, the chloro ligand (Figure 8),25 and the d4 metal center has
two electrons occupying the antibonding dxz and dyz orbitals.
This results in a 2-fold five-electron pπ-dπ destabilizing
interaction between the oxo and chloro lone pairs and the half-
filled dxz and dyz orbitals of osmium (Figure 8), which possibly
explains the longer Os-Cl bond. Although it has been suggested
that pπ-dπ destabilization energies are very small,46 the present
1
The dashed wavy line separates signals assigned to H and 13C nuclei
in the two hemispheres (see text).
all resonances can be unambiguously assigned. It is again to be
noted that the signals belonging to carbons in the two different
hemispheres of the complex are in well-separated shift regions,
whereas no such distinction can be made for the respective
hydrogens. This allows structural assignments, as the 13C
chemical shifts of both (equivalent) C atoms of the chelate
backbone are in the negative range as are those of the R-carbons
of the cyclohexyl groups in the chloride hemisphere (RCH(Cl),
Table S4 (Supporting Information)). Indeed, the chelate ring
present in the solid phase for 5a exhibits an envelope conforma-
tion with a tip into this part of the molecule (see below).
X-ray Structure of [5a]BPh4. Crystals of trans-[OsCl(O)-
(dcpe)2]BPh4 ([5a]BPh4) were grown from CH2Cl2/PriOH. An
ORTEP view of 5a is shown in Figure 7, and structural data
are provided in Table S5 (Supporting Information). The complex
cation features a slightly distorted octahedral geometry with an
O(1)-Os-Cl angle of 175.1(1)°. The OsP4 arrangement shows
a tetrahedral distortion with P(1) and P(3) below the mean plane
(both by -0.12 Å) and P(2) and P(4) above it (both by 0.09
Å). In agreement with the higher oxidation state of 5a, the Os-P
distances are significantly shorter than those in 4a. The bite
angles of about 82° are normal for dcpe. As already observed
for 3a,b and 4a, the chelate rings have an envelope conforma-
tion. The Os, P(1), P(2), and C(14) atoms are nearly coplanar
((0.04 Å), and C(13) is displaced 0.71 Å from their mean plane
toward Cl. In the second chelate ring, Os, P(3), P(4), and C(39)
are coplanar within (0.1 Å and C(40) is displaced 0.44 Å from
their mean plane in the Cl hemisphere.
(44) Marshman, R. W.; Bigham, W. S.; Wilson, S. R.; Shapley, P. A.
Organometallics 1990, 9, 1341.
(45) For examples of π-stabilized 16-electron complexes, see: Barthazy,
P.; Hintermann, L.; Stoop, R. M.; Wo¨rle, M.; Mezzetti, A.; Togni, A.
HelV. Chim. Acta 1999, 82, 2448 and references therein.

4910 Inorganic Chemistry, Vol. 39, No. 21, 2000
Barthazy et al.
structural data show that such effects are sizable, at least when
a strong donor, such as an oxo ligand, is involved.47
Although the oxo complexes 5 are not useful oxidants, the
discovery of stable phosphine oxo complexes is important, as
ruthenium analogues of trans-[OsCl(O)(P-P)2]+ have been
invoked as intermediates in catalytic olefin epoxidation. It has
been suggested that complexes of the type [RuCl(P-P)2]+ and
the related [RuCl(PNNP)]+ complexes (PNNP ) tetradentate
ligands with P and N donors) catalyze the asymmetric epoxi-
dation of olefins with hydrogen peroxide and PhIO as oxidants
and with the involvement of oxo species of Ru(IV).51
Reactivity of trans-[OsX(O)(P-P)2]+. Most of the reactions
were performed with trans-[OsCl(O)(dcpe)2]+ (5a), but trans-
[OsBr(O)(dcpe)2]+ (5b) and trans-[OsCl(O)(depe)2]+ (5c) show
very similar reactivity. The oxo complexes 5 do not react with
CO (1 atm, 20 °C), transfer oxene to isonitriles, thioethers, and
styrene, or react with these substrates in other ways. Stoichio-
metric oxidation of alcohols does not take place in CDCl3 at
room temperature. However, some [OsH3(dcpe)2]+ 37 is formed
in refluxing methanol, together with decomposition products.
This suggests that the protic solvent is able to protonate the
oxygen and reduce the complex under forcing conditions. To
test the possibility of reoxygenating the oxo species 5a, we
treated it with H2O2 or O2, but the η2-O2 complex 4a was not
formed in either case.
The d4 osmium oxo complexes reported to date have been
prepared by oxidation of the corresponding aquo complexes
of the general formula [Os(OH2)N5]2+ (N ) sp2 or sp3
N-donor).12a-c,f These species are highly reactive or unstable
toward disproportionation to the point that the osmium(IV)
oxidation state is sometimes considered as “missing”.12a-c,f Also,
a high reactivity is expected for octahedral d4 oxo complexes
owing to their reduced Os-O bond order (Figure 5).2 Thus,
we were surprised to find that 5a reacts with nucleophiles (PR3
and SR2) sluggishly or does not react at all. Complex 5a reacts
with PPh3 (in an NMR tube sealed under vacuum to exclude
traces of O2), giving Ph3PO (20%) and a small amount of 3a
(ca. 5% by 31P NMR), together with other unidentified products
after 14 d (eq 3). The 1H NMR spectrum of the reaction solution
Conclusion
The main reaction of the dioxygen complexes [OsX(η2-O2)-
(dcpe)2]+ (4) is the loss of one oxygen atom to form trans-
[OsX(O)(P-P)2]+ (5). The reactivity of coordinated dioxygen
is analogous to that of peroxide. The investigations concerning
the reactivity of the oxo species 5 show clearly that these
osmium complexes are much less reactive than their Fe and
Ru analogues. This can be qualitatively explained by considering
that the metal center becomes softer (and the oxo species less
electrophilic) upon going from 3d to 5d metals. This effect is
reinforced upon going from iron porphyrins to [RuCl(PNNP)]+
and [OsCl(P-P)2]+ as the ligand set is changed from N4 to P2N2
(a drastic change as the extensive π interactions in the
metalloporphyrin are lost) and, finally, to P4. Besides the
significance of trans-[OsX(O)(P-P)2]+ with respect to nonbio-
mimetic dioxygen activation, its isolation and characterization
lend support to previous mechanistic speculations regarding the
catalytic epoxidation of olefins catalyzed by [RuCl(P-P)2]+.
Experimental Section
General Details. All operations were carried out under argon using
standard Schlenk techniques or in a glovebox (Braun) under purified
nitrogen. Solvents were purified by standard methods. All chemicals
used were of reagent grade or comparable purity. 1,2-Bis((2R,5R)-2,5-
dimethylphospholano)benzene (Me-duphos) was purchased from Strem.
The ligand dcpe and trans-[OsCl2(dcpe)2] were prepared as previously
reported (see ref 14). Yields are based on the metal. Infrared spectra
were recorded on a Perkin-Elmer Paragon 1000 FT-IR spectrometer,
and UV-visible spectra, on a Kontron Instruments Uvikon 922
spectrophotometer. Microanalyses were performed by the Laboratory
of Microelemental Analysis at the Organic Laboratories of the ETH
trans-[OsCl(O)(dcpe)2]+ + Ph3P f
[OsCl(dcpe)2]+ + Ph3PO (3)
indicates that 5a is still present after this time, but other
unidentified paramagnetic complexes are formed. The reaction
with PMe3 is not significantly faster. As a comparison, the d4
oxo species [Ru(O)(TMP)] (TMP ) the 5,10,15,20-tetramesi-
tylporphyrin dianion) readily oxidizes PPh3 under analogous
conditions.48
1
Zu¨rich. H, 13C{1H}, and 31P{1H} and 2D correlation NMR spectra
The above results suggest that the dissociation energy of the
OsdO bond is lower than 125 kcal mol-1, the dissociation
energy of the P-O bond in PPh3.49 This appears reasonable
also in view of the long Os-O distance (1.834(3) Å) and the
presence of two π-antibonding electrons discussed above.
Provided that reaction 3 is thermodynamically favored, its low
rate points to the existence of a kinetic barrier. As the dcpe and
depe analogues 5a and 5c react similarly, we suspect that the
nature of the kinetic barrier is electronic rather than steric. A
possible explanation is that the attack of the incoming nucleo-
phile on the LUMO’s of 5, the degenerate dxz and dyz orbitals,
must be preceded by electron pairing (Figure 5).50 Thus, the
attack on complexes 5 requires either geometrical rearrangement
were obtained with Bruker Avance 250, 300, 400, and 500 spectrom-
1
eters. H (and 13C) and 31P chemical shifts are relative to TMS and
external 85% H3PO4, respectively. Mass spectrometry was carried out
by the Analytic Service of the Organic Laboratories at the ETH Zu¨rich.
NaBArF was prepared by a literature method.52
cis-[OsCl2(depe)2], 2c. An improved synthesis for 2c was as
follows: [(PEt2Ph)3Os(µ-Cl)3Os(PEt2Ph)3]Cl (1.021 g, 0.672 mmol) and
depe (1.24 g, 6.0 mmol) were heated together without solvent for 12
h. The resulting colorless solid was extracted with boiling hexane (50
mL) to remove diethylphenylphosphine. The resulting white microc-
rystals were filtered off and washed twice with hexane. Yield: 829
1
mg (92%). H NMR (CDCl3): δ 1.0-32.7 (m, 48 H, CH2, CH3). 31P
2
NMR: δ 19.4 (t, 2 P, JPP′ ) 8.8 Hz), 10.9 (t, 2 P). Other data are as
in ref 17.
2
cis-[OsCl2(Me-duphos)2], 2d. [(PEt2Ph)3Os(µ-Cl)3Os(PEt2Ph)3]Cl
(541 mg, 0.356 mmol) and Me-duphos (459 mg, 1.50 mmol, 1.05 equiv)
were heated together without solvent for 12 h. Diethylphenylphosphine
or the involvement of the high-energy dz orbital.
(46) Holland, P. L.; Andersen, R. A.; Bergman, R. G. Comments Inorg.
Chem. 1999, 21, 115.
(47) Mayer, J. M. Comments Inorg. Chem. 1988, 8, 125.
(48) Cheng, S. Y. S.; James, B. R. J. Mol. Catal. A: Chem 1997, 117, 91.
(49) Data from: Sawyer, D. T. Oxygen Chemistry; Oxford University
Press: New York, 1991; p 77.
(50) The spin barrier is not present in oxygen transfers from diamagnetic
octahedral d2 systems, as recently discussed for rhenium(V) oxo
complexes: Seymore, S. B.; Brown, S. N. Inorg. Chem. 2000, 39,
325.
(51) (a) Bressan, M.; Morvillo, A. Inorg. Chem. 1989, 28, 950. (b) Morvillo,
A.; Bressan, M. J. Mol. Catal. A: Chem. 1997, 125, 119. (c) Maran.
F.; Morvillo, A.; d’Alessandro, N.; Bressan, M. Inorg. Chim. Acta
1999, 288, 122. (d) Stoop, R. M.; Bauer, C.; Setz, P.; Wo¨rle, M.;
Wong, T. Y. H.; Mezzetti, A. Organometallics 1999, 18, 5691. (e)
Stoop, R. M.; Mezzetti, A. Green Chem. 1999, 39.
(52) Brookhart, M.; Rix, F. C.; DeSimone, J. M.; Barabak, J. C. J. Am.
Chem. Soc. 1992, 114, 5894.

Oxo Complexes of Osmium(IV)
Inorganic Chemistry, Vol. 39, No. 21, 2000 4911
was separated from the resulting pale yellow oil by distillation under
reduced pressure at 200 °C. The solid residue was then crushed and
vacuum-dried, yielding a pale-yellow powder. Yield: 612 mg (98%).
1H NMR (CDCl3): δ 9.79 (br, 2 H, Ph H), 9.58 (br, 2 H, Ph H), 9.3
(br, 4 H, Ph H), 5.40-5.30 (m, 2 H, CH), 4.98-4.78 (m, 6 H, CH,
CH2), 4.77-4.59 (m, 2 H, CH), 4.41-4.25 (m, 2 H, CH), 4.09-3.30
31P NMR: δ -8.6 (s, 4 P). MS (FAB+): m/z 1148 ([M + H]+, 100),
1131 ([M - O]+, 48), 1115 ([M - 2O]+, 20), 965 ([M - O - 2C6H11]+,
4), 709 ([M - O - dcpe]+, 8). Anal. Calcd for C76H116BBrO2OsP4:
C, 62.24; H, 7.97; O, 2.18. Found: C, 62.27; H, 8.11; O, 2.46.
[OsCl(η2-O2)(depe)2]PF6, [4c]BPh4. Complex 2c (67 mg, 0.1 mmol)
and TlPF6 (35 mg, 0.1 mmol) were dissolved in MeOH (10 mL). After
10 min of stirring, the TlCl that formed was filtered off, the volume of
the solution was reduced under vacuum, and hexane (10 mL) was added.
The resulting precipitate was then filtered off and treated with NaBPh4
as described for [4b]BPh4. Yield: 49 mg (60%). This substance
contained traces of [5c]BPh4. 1H NMR (CDCl3): δ 2.54-1.85 (m, 24
H, CH2), 1.55-0.86 (m, 24 H, CH3). 31P NMR: δ 9.6 (s, 4 P). MS
(FAB+): m/z 671 (M+, 95), 656 ([M - O + H]+, 64), 640 ([M - 2O
+ H]+, 100), 205 ([depe - H]+, 10). Anal. Calcd for C44H68BClO2-
OsP4: C, 53.42; H, 6.93. Found: C, 53.52; H, 6.89.
trans-[OsCl(O)(dcpe)2]PF6, [5a]PF6. [3a]PF6 (1.286 g, 1.06 mmol)
was dissolved in CH2Cl2 (50 mL) and PriOH (100 mL), and the solution
was was stirred in air for 2 d. Evaporation of the CH2Cl2 under vacuum
yielded [5a]PF6 as a light brown solid. Yield: 1.04 g (80%). 1H
NMR: see Table 2. 31P NMR (CDCl3): δ -143 (septet, 1 P, PF6, 1JPF
) 710 Hz). MS (FAB+): m/z 1087 (M+, 100), 1071 ([M - O]+, 12),
921 ([M - 2C6H11]+, 19), 665 ([M - dcpe]+, 9). Anal. Calcd for C52H96-
ClF6OOsP5: C, 50.70; H, 7.85; O, 1.30; Cl, 2.88. Found: C, 50.46; H,
7.99; O, 1.53; Cl, 3.09.
(m, 18 H, CH2, wherefrom δ 3.73 (dd, 6 H, CH3, JHH′ ) 7 Hz, JPH
)
14 Hz)), 3.13 (dd, 6 H, CH3, JHH′ ) 7 Hz, JPH ) 13 Hz), 2.49 (dd, 6
H, CH3, JHH′ ) 7 Hz, JPH ) 14 Hz), 2.14 (dd, 6 H, CH3, JHH′ ) 7 Hz,
JPH ) 16 Hz). 31P NMR (CDCl3): δ 40.2 (t, 2 P, 2JPP′ ) 9.0 Hz), 37.5
(t, 2 P). MS (FAB+): m/z 874 (M+, 16), 839 ([M - Cl]+, 100). Anal.
Calcd for C36H56Cl2OsP4: C, 49.48; H, 6.46. Found: C, 49.49; H, 6.43.
[OsCl(dcpe)2]BPh4, [3a]BPh4. A simplified synthesis was em-
ployed: trans-[OsCl2(dcpe)2] (3.04 g, 2.75 mmol) and TlPF6 (960 mg,
2.75 mmol) were suspended in CH2Cl2 (50 mL), and the mixture was
stirred overnight at room temperature. The thallium chloride that formed
was filtered off, PriOH (40 mL) was added, and CH2Cl2 was removed
under vacuum to yield a dark brown precipitate of [3a]PF6. Yield: 2.38
g (71%). A slurry of [3a]PF6 (121.6 mg, 0.10 mmol) and NaBPh4 (171
mg, 0.50 mmol) was stirred for 10 min in CH2Cl2 (10 mL). Addition
of methanol (40 mL) and evaporation of CH2Cl2 under vacuum gave
brown [3a]BPh4, which was filtered off and vacuum-dried. Yield: 119
mg (86%). Analytical and spectroscopic data were as reported in ref
14.
[OsBr(dcpe)2]PF6, [3b]PF6. An improved synthesis was again
employed: trans-[OsBr2(dcpe)2] (4.20 g, 3.5 mmol) and TlPF6 (1.22
g, 3.5 mmol) were suspended in CH2Cl2 (50 mL), and the mixture was
stirred overnight at room temperature. The thallium bromide that formed
was filtered off, PriOH (40 mL) was added, and CH2Cl2 was removed
under vacuum, yielding an almost black precipitate. Yield: 3.99 g
(87%).31P NMR (CDCl3): δ 40.8 (t, 2 P, 2JPP′ ) 1.8 Hz), 26.7 (t, 2 P,
2JPP′ ) 1.8 Hz). Analytical data were as in ref 14.
trans-[OsCl(O)(dcpe)2]BPh4, [5a]BPh4. [5a]PF6 (123.1 mg, 0.10
mmol) and NaBPh4 (171 mg, 0.50 mmol) were dissolved in CH2Cl2
(10 mL). Addition of CH3OH (40 mL) and evaporation of CH2Cl2 under
vacuum yielded a light brown precipitate, which was filtered off and
vacuum-dried. Yield: 125 mg (89%). 1H NMR (CDCl3): δ 7.39 (s, 8
H, Ph H), 7.09 (t, 8 H, Ph H, JHH′ ) 7.4 Hz), 6.93 (t, 4 H, Ph H, JHH′
) 7.1 Hz); for 5a data, see Table 2. UV-vis (CH2Cl2) λmax, nm (ꢀmax
,
M-1 cm-1): 350 (2200), 410 (sh), 480 (sh), 575 (sh). MS (FAB+):
m/z 1087 (M+, 100), 1071 ([M - O]+, 12), 921 ([M - 2C6H11]+, 19),
665 ([M - dcpe]+, 9). Anal. Calcd for C76H116BClOOsP4: C, 64.92;
H, 8.31; O, 1.14; Cl, 2.52. Found: C, 64.74; H, 8.38; O, 1.13; Cl,
2.43.
[OsCl(Me-duphos)2]PF6, [3d]PF6. Complex 2d (87 mg, 0.1 mmol)
was dissolved in CH2Cl2 (10 mL), TlPF6 (34 mg, 0.15 mmol) was
added, and the solution was stirred overnight. TlCl was then filtered
off, and PriOH (20 mL) was added. Evaporation of CH2Cl2 under
1
vacuum afforded red microcrystals. Yield: 71 mg (72%). H NMR
trans-[OsBr(O)(dcpe)2]BArF, [5b]BArF. [3b]PF6 (1.00 g, 0.80
mmol) was dissolved in CH2Cl2 (50 mL), and the solution was stirred
in air for 2 d. The resulting complex [OsBr(η2-O2)(dcpe)2]PF6 was
treated with gaseous HCl for 1 min. After 12 h of stirring, the mixture
was filtered, and the filtrate was treated with NaBArF (710 mg, 0.80
(CDCl3): δ 7.85 (br, 2 H, Ph H), 7.54-7.33 (m, 6 H, Ph H), 3.24 (s
br, 2 H, CH), 3.08 (br, 2 H, CH), 2.48-2.32 (m, 4 H, CH), 2.20-2.03
(m, 8 H, CH2), 1.94-1.53 (m, 8 H, CH2), 1.47 (dd, 6 H, CH3, JHH′
)
8 Hz, JPH ) 18 Hz), 1.28 (dd, 6 H, CH3, JHH′ ) 7 Hz, JPH ) 17 Hz),
0.45 (dd, 6 H, CH3, JHH′ ) 7 Hz, JPH ) 14 Hz), 0.27 (dd, 6 H, CH3,
i
mmol). Addition of PrOH (100 mL) and removal of CH2Cl2 under
JHH′ ) 7 Hz, JPH ) 15 Hz). 31P NMR (CDCl3): δ 76.1 (t, 2 P, 2JPP′
)
vacuum gave a brown product. Yield: 1.03 g (66%). 1H NMR
(CDCl3): δ 7.79 (s, 8 H, Ph o-H), 7.63 (s, 4 H, Ph p-H); for 5b data,
see Table 2. MS (FAB+): m/z 1131 (M+, 100), 1115 ([M - O]+, 84),
1049 ([M - HBr]+, 31), 965 ([M - 2C6H11]+, 27). Anal. Calcd for
C84H108BBrF24OOsP4: C, 49.63; H, 5.35. Found: C, 49.63; H, 5.19.
trans-[OsCl(O)(depe)2]PF6, [5c]BPh4. This complex was prepared
similarly to [4c]BPh4, but stirring was prolonged to 12 h before filtration
1
5.5 Hz), 42.6 (t, 2 P), -143 (septet, 1 P, PF6, JPF ) 710 Hz). MS
(FAB+): m/z 839 (M+, 100), 755 ([M - C6H12]+, 8). Anal. Calcd for
C36H56ClF6OsP5: C, 43.97; H, 5.74. Found: C, 43.71; H, 5.91.
[OsCl(η2-O2)(dcpe)2]BPh4, [4a]BPh4. A slurry of [3a]PF6 (0.846
g, 0.70 mmol) and NaBPh4 (1.195 g, 3.5 mmol) in CH2Cl2 (50 mL)
and PriOH (10 mL) was stirred for 10 min, after which more PriOH
(100 mL) was added. CH2Cl2 was then removed under vacuum, and
the precipitate was filtered off and dissolved in CH2Cl2/PriOH (200
mL, 1:1 v/v). This solution was stirred under O2 (1 atm) at room
temperature for 1 h. The CH2Cl2 was then removed under vacuum,
and the resulting light green [4a]BPh4 was filtered off. Yield: 0.751 g
(87%). The presence of CH2Cl2 (0.5 equiv) was supported by 1H NMR
1
and precipitation. Yield: 67 mg (84%). H NMR: see Table 2. 31P
NMR δ -143 (septet, 1 P, PF6, 1JPF ) 710 Hz). MS (FAB+): m/z 656
([M + H]+, 100). Anal. Calcd for C44H68BClOOsP4: C, 54.29; H, 7.04.
Found: C, 54.22; H, 6.88.
Oxidation of Iodide with [4a]BPh4. A CH2Cl2 solution of [4a]BPh4
(0.2 mM, 1 mL) and a CH2Cl2 solution of [NBu4]I (2.0 mM, 1 mL)
were mixed in a UV cuvette. The reaction was initiated by the addition
of one drop of a saturated solution of anhydrous HCl in CH2Cl2. The
spectrum of the reaction solution recorded immediately after the addition
and corrected for the absorbance of 5a indicated that [I3]- was formed
on the basis of the reference for the triiodide ion. Quantitative
conversion (within experimental error) was calculated from absorbance
data at 365 nm. Two measurements gave the same results. No reaction
occurred without addition of acid. Blank experiments omitting HCl
gave no reaction.
1
spectroscopy. H NMR (CDCl3): δ 7.39 (s, 8 H, Ph H), 7.09 (t, 8 H,
Ph H, JHH′ ) 7.4 Hz), 6.93 (t, 4 H, Ph H, JHH′ ) 7.1 Hz), 2.5-2.2 (m,
12 H, PCH2, PCH), 2.2-1.7 (m, 44 H, C6H11), 1.7-1.2 (m, 40 H,
C6H11). 31P NMR (CDCl3): δ -4.0 (s, 4 P). UV-vis (CH2Cl2) λmax
,
nm (ꢀmax, M-1 cm-1): 345 (sh), 435 (sh). MS (FAB+): m/z 1104 ([M
+ H]+, 54), 1087 ([M - O]+, 100), 1071 ([M - 2O]+, 11), 921 ([M
- O - 2C6H11]+, 14), 665 ([M - O - dcpe]+, 8). Anal. Calcd for
C76H116BCl3O2OsP4‚0.5CH2Cl2: C, 62.74; H, 8.05. Found: C, 62.87;
H, 8.09.
[OsBr(η2-O2)(dcpe)2]BPh4, [4b]BPh4. A CH2Cl2 solution of [OsBr-
(dcpe)2]PF6 (56.3 mg, 45 µmol) was stirred under an O2 atmosphere
for 3 h, after which PriOH (30 mL) and NaBPh4 (70 mg, 200 µmol) in
CH2Cl2 (20 mL) were added. CH2Cl2 was removed under vacuum, and
the resulting precipitate was filtered off and vacuum-dried. Yield: 56
mg (85%). 1H NMR (CDCl3): δ 7.85 (s, 8 H, Ph H), 7.4-7.3 (m, 8 H,
Ph H), 7.1-7.0 (m, 4 H, Ph H), 2.4-0.9 (m, 96 H, PCH2, PCH, C6H11).
X-ray Structure Determinations. Crystals of [OsCl(dcpe)2]PF6
([3a]PF6), [OsBr(dcpe)2]PF6 ([3b]PF6), [OsCl(η2-O2)(dcpe)2]BPh4 ([4a]-
BPh4), and trans-[OsCl(O)(dcpe)2]BPh4 ([5a]BPh4) were obtained by
slow evaporation of concentrated CH2Cl2/PriOH solutions of the
respective complexes. Crystals of [3a]PF6 and [3b]PF6 were grown in
a glovebox under purified N2. Data were collected on a Siemens CCD
SMART area detector system equipped, except for the [3b]PF6 study

4912 Inorganic Chemistry, Vol. 39, No. 21, 2000
Barthazy et al.
(four-circle diffractometer Syntex P21), with a normal-focus Mo-target
X-ray tube. Unit cell dimension determinations and data reductions
were performed by standard procedures. An empirical absorption
correction (SADABS) was applied for 3a, 4a, and 5a. The structures
were solved with SHELXS-96 using direct methods and refined by
full-matrix least-squares calculations based on F2 with anisotropic
displacement parameters for all non-H atoms. Disordered atoms were
refined isotropically. Hydrogen atoms (bound to nondisordered C atoms)
were introduced at calculated positions and refined with a riding model
using individual isotropic thermal parameters for each group. Further
details of the crystallographic determinations are given in the Supporting
Information.
Maximum and minimum difference peaks for [3a]PF6 were +0.71
and -0.55 e Å-3; the largest and the mean ∆/σ values were -0.638
and +0.007. In [3b]PF6, cyclohexyl C(15)-C(20) is disordered and
was split between two chair conformations with 64:36 refined oc-
cupancies. Maximum and minimum difference peaks were +3.834 and
-1.907 e Å-3 (at 1.18 Å from Os); the largest and the mean ∆/σ values
were -0.002 and 0.000. In [4a]BPh4, cyclohexyl C(27)-C(32) is
disordered and was split between two conformations with 7:3 refined
occupancies. Maximum and minimum difference peaks were +1.765
and -1.851 e Å-3; the largest and the mean ∆/σ values were +0.014
and 0.000. In [5a]BPh4, cyclohexyl C(47)-C(52) and phenyl C(71)-
C(76) are disordered and were split between two conformations with
equal refined occupancies and isotropic displacement parameters.
Complete results are reported in the Supporting Information.
Supporting Information Available: A listing of NMR data for
5a and 5b, an ORTEP drawing of 3b, and tables of crystal data, X-ray
experimental details, atomic coordinates, thermal parameters, bond
distances, and bond angles along with X-ray crystallographic files, in
CIF format, for [3a]PF6, [3b]PF6, [4a]BPh4, and [5a]BPh4. This material
is available free of charge via the Internet at http://pubs.acs.org.
IC0002420