Oxidation at a Dimolybdenum(V) Sulfur Bridge. Formation of so and SO2 Bridges. Facile Extrusion of so from the SO2 Bridge

Article abstract of DOI:10.1021/ic951518k

Peroxide oxygenation of μ-thiolate-μ-sulfide Mo(V) dimer complexes of the type [Mo₂(NAr)₂(S₂P(OEt)₂) ₂(μO₂CMe)(μ-SR)(μ-S)] yielded Mo₂(μ-SO) and Mo₂(μ-SO₂) complexes, demonstrating the reactivity sequence μ-S > μ-SO ? μ-SR. Inversion isomers of the pyramidal sulfur site in the μ-SO bridge were observed, and the pyramidicity was confirmed crystallographically. Visible light photolysis of the Mo₂(μ-SO₂) complex liberated SO from the SO₂ bridge and produced Mo₂(μ-O) compounds. Crystallography of analogous Mo₂(μ-S), Mo₂(μ-SO), Mo₂(μ-SO₂), and Mo₂(μ-O) complexes provided structural comparisons related to variations in the bridge functionality. For 2, Mo₂C₃₁H₄₄N₂O₆P ₂S₆: a = 13.604(5) A?, b = 15.280(4) A?, c = 12.502(2) A?, α = 93.36(2)°, β = 112.00 (2)°, γ = 76.01(2)°, triclinic, P1, Z = 2. For 3, Mo₂C₃₁H₄₄N₂O₇P ₂S₆: a = 12.535(2) A?, b = 25.299-(9) A?, c = 13.989(5) A?, β = 99.99(2)°, monoclinic, P2₁/n, Z = 4. For 4, Mo₂C₃₁H₄₄N₂O₈P ₂S₆: a = 12.591(9) A?, b = 25.34(1) A?, c = 14.048(3) A?, β = 100.79(4)°, monoclinic, P2₁/n, Z = 4. For 5, Mo₂C₃₁H₄₄N₂O₇P ₂S₅: a = 13.731(5) A?, b = 19.267(4) A?, c = 16.652(5) A?, β = 104.78(3)°, monoclinic, P2₁/n, Z = 4.

Full text of DOI:10.1021/ic951518k

3022
Inorg. Chem. 1996, 35, 3022-3030
Oxidation at a Dimolybdenum(V) Sulfur Bridge. Formation of SO and SO2 Bridges. Facile
Extrusion of SO from the SO2 Bridge
Runtong Wang, Mark S. Mashuta, John F. Richardson, and Mark E. Noble*
Department of Chemistry, University of Louisville, Louisville, Kentucky 40292
ReceiVed NoVember 29, 1995X
Peroxide oxygenation of µ-thiolate-µ-sulfide Mo(V) dimer complexes of the type [Mo2(NAr)2(S2P(OEt)2)2(µ-
O2CMe)(µ-SR)(µ-S)] yielded Mo2(µ-SO) and Mo2(µ-SO2) complexes, demonstrating the reactivity sequence µ-S
> µ-SO . µ-SR. Inversion isomers of the pyramidal sulfur site in the µ-SO bridge were observed, and the
pyramidicity was confirmed crystallographically. Visible light photolysis of the Mo2(µ-SO2) complex liberated
SO from the SO2 bridge and produced Mo2(µ-O) compounds. Crystallography of analogous Mo2(µ-S), Mo2(µ-
SO), Mo2(µ-SO2), and Mo2(µ-O) complexes provided structural comparisons related to variations in the bridge
functionality. For 2, Mo2C31H44N2O6P2S6: a ) 13.604(5) Å, b ) 15.280(4) Å, c ) 12.502(2) Å, R ) 93.36(2)°,
â ) 112.00 (2)°, γ ) 76.01(2)°, triclinic, P1h, Z ) 2. For 3, Mo2C31H44N2O7P2S6: a ) 12.535(2) Å, b ) 25.299-
(9) Å, c ) 13.989(5) Å, â ) 99.99(2)°, monoclinic, P21/n, Z ) 4. For 4, Mo2C31H44N2O8P2S6: a ) 12.591(9)
Å, b ) 25.34(1) Å, c ) 14.048(3) Å, â ) 100.79(4)°, monoclinic, P21/n, Z ) 4. For 5, Mo2C31H44N2O7P2S5:
a ) 13.731(5) Å, b ) 19.267(4) Å, c ) 16.652(5) Å, â ) 104.78(3)°, monoclinic, P21/n, Z ) 4.
Introduction
halosulfide (S-X) products. (In the structure diagrams shown,
dithiophosphate groups are omitted for clarity. Abbreviations
for organic groups are footnoted.5) With an interest in the
oxygenation of sulfur sites to SOx ligands, studies of the
oxidation of µ-thiolate-µ-sulfide compounds [Mo2(NTo)2(S2-
P(OEt)2)2(µ-O2CMe)(µ-SR)(µ-S)], 2, were undertaken and are
reported presently. These rections have yielded the dimolyb-
dosulfoxides [Mo2(NTo)2(S2P(OEt)2)2(µ-O2CMe)(µ-SR)(µ-SO)],
3, and the dimolybdosulfones [Mo2(NTo)2(S2P(OEt)2)2(µ-O2-
CMe)(µ-SR)(µ-SO2)], 4. Taken together, these constitute a rare
example6,7 of the ability to isolate both µ-SO and µ-SO2 products
from the oxidation of a sulfide bridge. These complexes are
also high-valent, d1 systems; this is in distinct contrast to prior
µ-SO and µ-SO2 compounds which were predominantly orga-
nometallic, low valent, and of high d-electron count.8-11
During the course of these studies, the facile photoextrusion
of SO from the SO2 bridge was also observed, and these results
are included herein.
Biological, atmospheric, and geochemical sulfur transforma-
tions involve a wide range of reactions, many of which are
formal oxidation-reduction processes.1,2 Within these natural
cycles the most common oxidation reactions involve S/S or S/O
bond formation. Metal ions play important roles in many of
these processes, and investigations into the oxidation of sulfur
ligands should therefore impact upon studies related to these
natural transformations.
The oxidations of sulfur bridges in anionic imido-dithio-
phosphato-carboxylato-sulfidomolybdenum(V) dimers such as
[Mo2(NTo)2(S2P(OEt)2)2(µ-O2CMe)(µ-S)2]- (1) have been pre-
viously reported;3,4 those reactions yielded disulfide (S-S) and
Experimental Section
Reactions and manipulations were conducted open to air except as
noted. [Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SBz)(S)], 2 (R ) Bz),3 and
[Mo(NTo)(S2P(OEt)2)S]412 were prepared as previously reported. All
commercial reagents were used as received. Silica gel for chroma-
tography was 100-200 mesh (DAVISIL grade 644). Peracetic acid
(3) Noble, M. E. Inorg. Chem. 1986, 25, 3311.
(4) Lee, J. Q.; Sampson, M. L.; Richardson, J. F.; Noble, M. E. Inorg.
Chem. 1995, 34, 5055.
(5) Abbreviations used in this paper: Me, methyl; Et, ethyl; t-Bu, tert-
butyl; Bz, benzyl; Ar, aryl; Ph, phenyl; To, p-tolyl; Cp, cyclopenta-
dienyl; dppm, bis(diphenylphosphino)methane.
(6) Lorenz, I.-P.; Messelha¨user, J.; Hiller, W.; Conrad, M. J. Organomet.
Chem. 1986, 316, 121. Lorenz, I.-P.; Messelha¨user, J.; Hiller, W.;
Haug, K. Angew. Chem., Int. Ed. Engl. 1985, 24, 228.
(7) Besenyei, G.; Lee, C.-L.; Gulinski, J.; Rettig, S. J.; James, B. R.;
Nelson, D. A.; Lilga, M. A. Inorg. Chem. 1987, 26, 3622.
(8) Ryan, R. R.; Kubas, G. J.; Moody, D. C.; Eller, P. G. Struct. Bonding
1981, 46, 47.
(9) Schenk, W. A. Angew. Chem., Int. Ed. Engl. 1987, 26, 98.
(10) Pandey, K. K. Prog. Inorg. Chem. 1992, 40, 445.
(11) Kubas, G. J. Acc. Chem. Res. 1994, 27, 183.
(12) Sampson, M. L.; Richardson, J. F.; Noble, M. E. Inorg. Chem. 1992,
31, 2726.
X Abstract published in AdVance ACS Abstracts, April 15, 1996.
(1) See, for example, the following. Takakuwa, S. In Organic Sulfur
Chemistry: Biochemical Aspects; Oae, S., Okuyama, T., Eds.; CRC
Press: Boca Raton, FL, 1992; p 1. Brandt, C.; van Eldik, R. Chem.
ReV. 1995, 95, 119. Williamson, M. A.; Rimstidt, J. D. Geochim.
Cosmochim. Acta 1992, 56, 3867.
(2) Oae, S. Organic Sulfur Chemistry: Structure and Mechanism; CRC
Press: Boca Raton, FL, 1991.
S0020-1669(95)01518-7 CCC: $12.00 © 1996 American Chemical Society

Oxidation at a Dimolybdenum(V) Sulfur Bridge
Inorganic Chemistry, Vol. 35, No. 10, 1996 3023
was commercial grade in dilute MeCO2H; it assayed to be 47% total
peroxide. m-Chloroperbenzoic acid was commercial grade which also
contained m-chlorobenzoic acid; it assayed to be 84%. The peroxide
assays were conducted by reaction with excess Ph3P in CDCl3 and
quantitation by 31P NMR spectroscopy; this method gave total peroxide
equivalents and did not distinguish, for example, MeCO3H from H2O2,
which was also present in the commercial reagent.
was photolyzed for 1.5 h. The solution was rotavapped; the residue
was redissolved in a small volume of CHCl3 and chromatographed on
silica gel using CHCl3 as eluent. The second orange band was collected
and rotavapped. The residue was dissolved in CH2Cl2 (1 mL), and
dodecane (6 mL) was added. This mixture was left standing for 2
days for slow precipitation. The slurry was filtered; the solid was
washed (C12H26) and vacuum dried, giving a red-orange powder (0.2115
g, 85%). 31P NMR (ppm): 110.3, (110.2). 1H NMR (ppm): 7.57 d,
7.45 t, 7.35 m, Bz-H; (6.95 d), (6.73 d), 6.65 d, 6.51 d, To-H; 3.9-
4.3 m, POCH2; 3.54 s, Bz-CH2; (2.20 s), 2.09 s, To-CH3; 1.50 s,
O2CCH3; 1.37 t, 1.21 t, POCCH3. Invertomer ratio: 6.2. Selected IR
bands (cm-1): 1545 m, 1447 s, 1013 vs, 961 s, 816 s, 795 m.
The first band in the chromatography workup was separately
identified as [Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SBz)(S)], 2 (R ) Bz).
[Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SMe)(S)], 2 (R ) Me). The
synthesis follows that for 2 (R ) Bz).3 MeBr (40 mL gas, 1.6 mmol)
was slowly added to a solution of [Mo(NTo)(S2P(OEt)2)S]4 (0.8364 g,
0.500 mmol), MeCO2H (72 µL, 1.2 mmol), and Et3N (148 µL, 1.2
mmol) in CH2Cl2. After being stirred for 15 min, the solution was
rotavapped. The residue was dissolved in THF (10 mL). Precipitation
was effected with 2:1 EtOH:H2O (30 mL), and the resulting slurry was
filtered; the solid was washed (4:1 EtOH:H2O) and vacuum dried to
give an orange crystalline product (0.607 g, 67%). Anal. Calcd for
Mo2C25H40N2O6P2S6: C, 33.0; H, 4.4; N, 3.1. Found: C, 33.0; H, 4.3;
N, 2.8. 31P NMR (ppm): (115.2, 4 Hz downfield of major invertomer),
115.2. 1H NMR (ppm): (6.71 d), (6.59 d), 6.57 d, 6.46 d, To-H;
4.0-4.3 m, POCH2; (2.93 s), 2.27 s, SCH3; (2.14 s), 2.08 s, To-CH3;
1.32 t, 1.22 t, POCCH3; 1.27 s, O2CCH3. Invertomer ratio: 5. Selected
IR bands (cm-1): 1545 m, 1449 s, 1011 vs, 964 s, 816 s, 797 m.
[Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SMe)(SO)], 3 (R ) Me). [Mo2-
(NTo)2(S2P(OEt)2)2(O2CMe)(SMe)(S)], 2 (R ) Me; 0.5900 g, 0.648
mmol), and m-chloroperbenzoic acid (84%; 0.1347 g, 0.656 mmol) were
dissolved separately in 6.5 mL of CH2Cl2, and both solutions were
cooled in a CH2Cl2 slush bath (prepared from liquid nitrogen and CH2-
Cl2) for 0.5 h. Under red light, the solution of m-chloroperbenzoic
acid was added to the solution of [Mo2(NTo)2(S2P(OEt)2)2(O2CMe)-
(SMe)(S)] while being stirred; a rinse with CH2Cl2 (6.5 mL) at the
same temperature was used for complete transfer. After being warmed
to -20 °C, the mixture was taken out of the bath and rotavapped. The
residue was redissolved in a small volume of MeCN and chromato-
graphed on silica gel using MeCN as eluent. A flashlight was
occasionally used to check the progress. The second colored band was
collected, and this was rotavapped to a volume of ∼20 mL. H2O (20
mL) was added, and the solution was rotavapped until nearly all MeCN
was removed. The resulting slurry was filtered. The product was
vacuum dried, giving a dark green solid (0.3585 g, 60%). Anal. Calcd
for Mo2C25H40N2O7P2S6: C, 32.4; H, 4.4; N, 3.0. Found: C, 31.5; H,
4.4; N, 2.9. 31P NMR (ppm): (114.7, D), (114.5, C), (114.4, B), 113.7
(A). 1H NMR (ppm): (7.00 br, D), (6.86 br, C), (6.68 d, B), 6.57 d
(A), To-H; 3.9-4.3 m, POCH2; (3.28 br, D), (3.05 s, B), 2.31 s (A),
SCH3; (2.18 s, C), (2.11 s, B), 2.07 s (A), (2.02 s, D), To-CH3; 1.51
s (A), (1.43 s, B), O2CCH3; 1.34 t (A), 1.17 t (A), POCCH3. Invertomer
distribution: 66% A, 20% B, 11% C, 3% D. Selected IR bands (cm-1):
1532 m, 1452 s, 1011 vs, 968 vs, 816 s, 795 m.
1
31P{1H} and H NMR spectra were obtained in CDCl3 (except as
noted) on a Varian XL-300 spectrometer (which was updated during
this work with an Inova300 console) at 121 and 300 MHz or a Bruker
AMX-500 spectrometer at 202 and 500 MHz; results are reported as
downfield shifts from external 85% H3PO4 and internal Me4Si. In the
NMR data listed below, values for minor invertomers are given in
parentheses where these could be distinguished; when four isomers were
distinguishable, the major isomer is A, while the minor isomers are
B-D (least abundant). Infrared data were obtained using a Mattson
Galaxy Series FTIR 5000 spectrometer by diffuse reflectance on KBr
powder mixtures. GC-MS data were obtained on a Hewlett-Packard
5890 Series II gas chromatograph with a Hewlett-Packard 5971A mass
selective detector. Galbraith Laboratories, Inc. (Knoxville, TN)
performed the elemental analyses.
Routine photolyses were conducted in an apparatus of local
construction which consisted of four 20-W, 23-in., cool white fluores-
cent lamps. The lamps were arranged parallel and vertical, with the
internal center of each lamp lying at the corners of a rectangle of
dimensions 6.5 cm × 7.5 cm. The solution to be photolyzed was held
centrally within the four lamps and parallel to the lamps; vertically,
the solution center was near mid-length of the lamps.
All syntheses of [Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SR)(SO)], 3, and
of [Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SR)(SO2)], 4, were conducted
under red light conditions.3 Except during actual photolysis, these
compounds were stored in the dark and were handled under red light
conditions, even as solids.
[Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SBz)(SO)], 3 (R ) Bz). [Mo2-
(NTo)2(S2P(OEt)2)2(O2CMe)(SBz)(S)], 2 (R ) Bz; 0.3947 g, 0.400
mmol), and m-chloroperbenzoic acid (84%; 0.0869 g, 0.42 mmol) were
dissolved separately in 4 mL of CH2Cl2, and both solutions were cooled
in a CH2Cl2 slush bath (prepared from liquid nitrogen and CH2Cl2) for
0.5 h. Under red light, the solution of m-chloroperbenzoic acid was
quickly poured into the solution of [Mo2(NTo)2(S2P(OEt)2)2(O2CMe)-
(SBz)(S)] while being stirred. Additional CH2Cl2 (4 mL) at the same
temperature was used for complete transfer. When the slush bath
warmed to -20 °C, the mixture was taken out of the bath and
rotavapped. The residue was redissolved in a small volume of MeCN,
and this was chromatographed on silica gel using MeCN as eluent. A
flashlight was occasionally used to check the progress. The second
colored band was collected, rotavapped, and redissolved in tetrahy-
drofuran (THF) (1 mL). EtOH:H2O (2:5, 11.5 mL) was used for
precipitation. The slurry was filtered, and the product was vacuum
dried, giving a dark-green powder (0.3032 g, 75%). 31P NMR (ppm):
(114.6, D), (114.2, C), (114.1, B), 113.6 (A). 1H NMR (ppm): (7.71
br), 7.63 d (A), 7.48 t (A), 7.38 m (A), Bz-H; (6.86 br, D), (6.77 br,
C), 6.56 d (A), 6.41 d (A), To-H; (4.43 s, B), 3.59 s (A), (3.29 s, C),
Bz-CH2; 3.9-4.4 m, POCH2; (2.12 s, B), 2.04 s (A), To-CH3; 1.57
s (A), O2CCH3; 1.38 t (A), 1.18 t (A), POCCH3. Invertomer
distribution: 67% A, 20% B, 10% C, 3% D. Selected IR bands (cm-1):
1536 m, 1452 s, 1011 vs, 968 vs, 816 m, 791 m.
[Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SBz)(SO2)], 4 (R ) Bz). Under
red light, MeCO3H (47%; 63 µL, 0.44 mmol) was added to a solution
of [Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SBz)(S)], 2, (R ) Bz; 0.0987 g,
0.100 mmol), in THF (1 mL). After being stirred for 1 min, the solution
was treated with 1:1 EtOH:H2O (4 mL). The resulting precipitate was
filtered and vacuum dried, giving a brown crystalline solid (0.0875 g,
84%). 31P NMR (ppm): (112.2), 112.0. 1H NMR (ppm): (7.74 br),
7.64 m, 7.50 t, 7.40 m, Bz-H; (6.94 br), 6.80 d, 6.39 d, To-H; (4.76
br), 3.55 s, Bz-CH2; 3.9-4.3 m, POCH2; 2.04 s, To-CH3; 1.42 s,
O2CCH3; 1.37 t, 1.16 t, POCCH3. Invertomer ratio: 5. Selected IR
bands (cm-1): 1534 m, 1456 s, 1208 m, 1051 vs, 1011 vs, 968 s, 818
m, 793 m.
[Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SMe)(SO2)], 4 (R ) Me). Under
red light, MeCO3H (47%; 0.25 mL, 1.8 mmol) was added to a solution
of [Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SMe)(S)], 2 (R ) Me; 0.3643 g,
0.400 mmol), in THF (4 mL). After being stirred for 1 min, the solution
was treated with 1:1 EtOH:H2O (16 mL). The resulting precipitate
was filtered and vacuum dried, giving a brown crystalline solid (0.3332
g, 88%). Anal. Calcd for Mo2C25H40N2O8P2S6: C, 31.8; H, 4.3; N,
3.0; S, 20.4. Found: C, 31.8; H, 4.0; N, 2.9; S, 20.7. 31P NMR
(ppm): (112.8), 112.2. 1H NMR (ppm): (6.91 d), 6.81 d, (6.48 d),
6.42 d, To-H; 3.9-4.3 m, POCH2; (3.30 s), 2.32 s, SCH3; (2.10 s),
2.06 s, To-CH3; 1.36 s, O2CCH3; 1.34 t, 1.16 t, POCCH3. Invertomer
ratio: 5.5. Selected IR bands (cm-1): 1535 m, 1454 s, 1209 m, 1051
vs, 1007 vs, 964 s, 816 m, 793 m.
[Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SMe)(O)], 5 (R ) Me).
A
solution of [Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SMe)(SO2)], 4 (R ) Me;
0.2400 g, 0.255 mmol), in CHCl3 (10 mL) in a long tube of 5 mm i.d.
was photolyzed for 1.5 h. The solution was rotavapped; the residue
was redissolved in a small volume of CHCl3 and chromatographed on
[Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SBz)(O)], 5 (R ) Bz). A solu-
tion of [Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SBz)(SO2)], 4 (R ) Bz;
0.2600 g, 0.255 mmol), in CHCl3 (10 mL) in a long tube of 5 mm i.d.

3024 Inorganic Chemistry, Vol. 35, No. 10, 1996
Wang et al.
Table 1. Crystallographic Data
2
3
4
5
formula
fw
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
T, °C
V, Å3
Z
Mo2S6P2O6N2C31H44‚0.9CH3OH
Mo2S6P2O7N2C31H44
1002.89
P21/n (No. 14)
12.535 (2)
25.299 (9)
13.989 (5)
Mo2S6P2O8N2C31H44
1018.88
P21/n (No. 14)
12.591 (9)
25.34 (1)
14.048 (3)
Mo2S5P2O7N2C31H44
970.83
P21/n (No. 14)
13.731 (5)
19.267 (4)
16.652 (5)
1018.93
P1h (No. 2)
13.604 (5)
15.280 (4)
12.502 (2)
93.36 (2)
112.00 (2)
76.01 (2)
22 (1)
99.99 (2)
100.79 (4)
104.78 (3)
23 (1)
4369 (2)
4
23 (1)
4403 (3)
4
23 (1)
4259 (2)
4
2335 (1)
2
λ, Å
0.710 73 (Mo KR)
0.710 73 (Mo KR)
0.710 93 (Mo KR)
0.710 73 (Mo KR)
F
calcd, g cm-3
1.45
1.52
1.54
1.51
µ, cm-1
9.13
0.040
0.042
9.75
0.037
0.037
9.70
0.043
0.043
9.50
0.039
0.040
Ra
Rw
b
2
a R ) Σ||Fo| - |Fc||/Σ|Fo|. b Rw ) [Σw(||Fo| - |Fc||)2/Σw|Fo| ]1/2
.
silica gel using CHCl3 as eluent. The second orange band was collected
and rotavapped. The residue was dissolved in CH2Cl2 (1 mL), and
dodecane (6 mL) was added. This mixture was left standing for 2
days for slow precipitation. The slurry was filtered; the solid was
washed (C12H26) and vacuum dried, giving a red-orange powder (0.2026
g, 89%). Anal. Calcd for Mo2C25H40N2O7P2S5: C, 33.6; H, 4.5; N,
3.1; S, 17.9. Found: C, 33.9; H, 4.6; N, 2.6; S, 18.2. 31P NMR
(ppm): (110.6), 110.5. 1H NMR (ppm): (6.95 d), (6.73 d), 6.69 d,
6.56 d, To-H; 3.9-4.3 m, POCH2; (2.80 s), 2.28 s, SCH3; (2.20 s),
2.12 s, To-CH3; 1.45 s, O2CCH3; 1.34 t, 1.21 t, POCCH3. Invertomer
ratio: 5.0. Selected IR bands (cm-1): 1547 m, 1447 s, 1013 vs, 964
s, 818 m, 793 m, 775 m.
The first band in the chromatography work-up was separately
identified as [Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SMe)(S)], 2 (R ) Me).
Photolysis Reactions. Several sample procedures were as follows.
For photolysis in solution, 4 (R ) Me; 9.4 mg, 10.0 µmol) in CDCl3
(0.4 mL) in a sealed NMR tube was photolyzed for 1.5 h. The 31P
NMR spectrum was then obtained.
tions were applied in each case. Scattering and anomalous dispersion
factors were taken from ref 14. The structures were solved by Patterson
methods and expanded using Fourier techniques. In each case,
hydrogen atom positions were calculated and added to the structure
factor calculations with B set to 1.2Beq of the carbon atom to which
each was bonded; hydrogen atom parameters were not refined. Each
structure was refined by full-matrix, least-squares methods, minimizing
∑w(|Fo| - |Fc|)2, where w ) [σ2(F)]-1
.
For 2 (R ) Bz), an orange block crystal from CH2Cl2/MeOH
measuring 0.46 × 0.40 × 0.36 mm was used for data collection. Three
representative reflections were measured every 60 min; the standards
decreased by 6.0% over the course of data collection, and a linear
correction factor was applied. A partial, disordered methanol was
present and was modeled as three C-O groups, each of 30% occupancy;
hydrogens of the methanol were excluded.
For 3 (R ) Bz), a green-black block crystal from CH2Cl2/n-hexane
measuring 0.45 × 0.35 × 0.30 mm was used for data collection. Three
representative reflections were measured every 60 min; no decay
corrections were applied.
For 4 (R ) Bz), an orange block crystal from C6H5Cl/n-dodecane
measuring 0.40 × 0.30 × 0.30 mm was used for data collection. Three
representative reflections were measured every 60 min; the standards
decreased by 9.8% over the course of data collection, and a linear
correction factor was applied.
For photolysis in the solid state, solid 4 (R ) Bz; 19.8 mg, 20.0
µmol) was sealed inside an NMR tube. The sample tube and the lamps
were positioned horizontally with the solid dispersed along the length
of the tube. The sample was photolyzed for 3.0 h. The tube was then
broken open, CDCl3 was added, and the 31P NMR spectrum was
obtained.
For photolysis with Ph3P present, a solution of 4 (R ) Bz, 10.6 mg,
10.4 µmol) and Ph3P (40.9 mg, 0.156 mmol) in CDCl3 (0.40 mL) was
photolyzed 1.5 h in a septum-capped NMR tube under N2. The 31P
NMR spectrum was then obtained.
For 5 (R ) Bz), an orange block crystal from CH2Cl2/n-hexane
measuring 0.55 × 0.50 × 0.41 mm was used for data collection. Three
representative reflections were measured every 60 min; no decay
corrections were applied. Several dithiophosphate ethyl groups were
disordered and were modeled as follows: C(17)-C(18) was modeled
as two groups in the ratio of 0.70:0.30; C(20) was modeled as two
sites in the ratio of 0.75:0.25; C(21)-C(22) was modeled as two half-
occupancy groups.
For the reaction sequence involving photolysis and then dark reaction
with Ph3P, a solution of 4 (R ) Me; 9.4 mg, 10.0 µmol) in CDCl3 (0.4
mL) in a septum-capped NMR tube under N2 was photolyzed 1.5 h. A
solution of Ph3P (10.5 mg, 40 µmol) in CDCl3 (0.2 mL) was then
syringed into the sample under N2. The solution was left to stand for
1 h in the dark. The 31P NMR spectrum was then obtained.
Photolysis using Corning band-pass filters was conducted using an
apparatus of in-house construction. Results of the photolyses using
filters 3-74 (412, 423), 3-68 (530, 546), 2-63 (582, 602), and 2-58 (631,
650) were compared to a reference reaction using a 9-54 filter. For
comparison, the parenthetical values listed with the filters represent
wavelengths (nm) for 10 and 80% transmittance relative to the 9-54
filter. The sample of 4 (R ) Bz, 10.0 µmol) in CDCl3 (0.40 mL) was
photolyzed directly in a quartz NMR tube for 4.0 min using filtered
light from a 650-W DVY lamp; the lamp-to-tube distance was 45 cm.
Under these conditions, the reference reaction reached 68% completion.
Crystallography. Crystal data and experimental details are given
in Table 1. Data were collected on an Enraf-Nonius CAD4 automated
diffractometer with Mo KR radiation (graphite monochromator), using
the ω-2θ scan technique; computations utilized the teXsan crystal-
lographic software package.13 Cell constants and orientation matrices
were obtained from least-squares refinement. Absorption corrections,
secondary extinction corrections, and Lorentz and polarization correc-
Selected results are given in Tables 2 and 3, and the structures are
shown in Figures 1-4.
Results
For simplicity, the [Mo2(NTo)2(S2P(OEt)2)2(µ-O2CMe)(µ-
SR)(µ-SOx)] dimer groups will be designated RSMo2SOx, which
indicates the thiolate bridge, the dimetal core, and the SOx
bridge; other ligands are invariant in the compounds described
herein. Although various bonding modes are known for SO
and SO2,6-11 the µ-SO and µ-SO2 ligands described herein are
µ2-η1(S) unless otherwise specified.
(13) teXsan: Crystal Structure Analysis Package; Molecular Structure
Corp.: The Woodlands, TX, 1985, 1992.
(14) International Tables for X-Ray Crystallography; Kynoch Press:
Birmingham, England, 1974; Vol. IV, Tables 2.2B, 2.3.1. International
Tables for Crystallography; Kluwer Academic Publishers: Boston,
MA, 1992; Vol. C, Table 4.2.6.8.

Oxidation at a Dimolybdenum(V) Sulfur Bridge
Inorganic Chemistry, Vol. 35, No. 10, 1996 3025
Table 2. Selected Bond Lengths (Å)
2
3
4
5
Mo(1)-Mo(2)
Mo(1)-S(1)
2.8315 (9) 2.8689 (6) 2.9440 (6) 2.6688 (6)
2.443 (2) 2.441 (1) 2.452 (1) 2.444 (1)
Mo(1)-S(2)/O(7)a 2.342 (2) 2.428 (1) 2.427 (1) 1.942 (3)
Mo(1)-S(3)
Mo(1)-S(4)
Mo(1)-O(1)
Mo(1)-N(1)
Mo(2)-S(1)
2.518 (2) 2.514 (2) 2.502 (2) 2.529 (2)
2.548 (2) 2.523 (2) 2.505 (2) 2.541 (2)
2.206 (4) 2.174 (3) 2.184 (3) 2.201 (3)
1.723 (4) 1.726 (4) 1.733 (4) 1.741 (4)
2.443 (2) 2.447 (1) 2.457 (1) 2.447 (2)
Mo(2)-S(2)/O(7)a 2.347 (2) 2.429 (1) 2.420 (1) 1.941 (3)
Mo(2)-S(5)
Mo(2)-S(6)
Mo(2)-O(2)
Mo(2)-N(2)
S(1)‚‚‚S(2)/O(7)a
S(1)-C(25)
S(3)-P(1)
2.519 (2) 2.514 (2) 2.502 (2) 2.537 (2)
2.538 (2) 2.523 (2) 2.507 (2) 2.560 (2)
2.194 (4) 2.165 (3) 2.175 (3) 2.206 (3)
1.719 (4) 1.726 (4) 1.725 (4) 1.726 (4)
3.860 (3) 3.937 (4) 3.885 (3) 3.456 (3)
1.852 (6) 1.856 (4) 1.840 (5) 1.865 (5)
1.986 (3) 1.989 (2) 1.987 (2) 1.996 (2)
1.990 (2) 1.993 (2) 1.995 (2) 1.989 (2)
1.988 (3) 1.989 (2) 1.993 (2) 1.994 (2)
1.991 (3) 1.992 (2) 1.989 (2) 1.990 (3)
1.254 (7) 1.247 (6) 1.262 (6) 1.264 (6)
1.258 (7) 1.268 (5) 1.245 (6) 1.253 (6)
1.380 (6) 1.387 (5) 1.384 (5) 1.376 (6)
1.378 (6) 1.390 (5) 1.385 (5) 1.389 (6)
1.515 (4) 1.467 (3)
S(4)-P(1)
S(5)-P(2)
S(6)-P(2)
O(1)-C(15)
O(2)-C(15)
N(1)-C(1)
N(2)-C(8)
S(2)-O(7)
S(2)-O(8)
Figure 2. ORTEP view of [Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SBz)-
(SO)], 3 (R ) Bz). This view clearly shows the pyramidicity of S(2).
1.469 (4)
a The bridge atom is S(2) for compounds 2-4 and O(7) for
compound 5.
Figure 3. ORTEP view of [Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SBz)-
(SO2)], 4 (R ) Bz).
SO2, 4, from sulfide BzSMo2S, 2, clearly proceeded by way of
SO-bridged BzSMo2SO, 3, eq 2. This compound could be
Figure 1. ORTEP view of [Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SBz)-
(S)], 2 (R ) Bz).
The oxidation of the sulfide bridge of RSMo2S, 2, was
investigated for R ) Bz and Me. Using excess MeCO3H, NMR
spectra revealed quantitative oxygenation to µ-SO2 products
RSMo2SO2, 4, eq 1, and high yields could be isolated with this
(2)
separately prepared and isolated, and best results were obtained
using near-stoichiometric amounts of m-chloroperbenzoic acid
and low temperature (-95 °C). Higher temperatures generally
gave more µ-SO2 product. The ability to isolate µ-SO and
µ-SO2 products from oxidation of dimetal µ-S sites has limited
precedence: [Mn2Cp2(CO)4(µ-S)]6 and [Pd2Cl2(µ-dppm)2(µ-S)]7
were successful, but others were not.15-18 The more common
parallel is with organic sulfide/sulfoxide/sulfone chemistry.19,20
(1)
reagent. High solution yields were also observed using m-
chloroperbenzoic acid, H2O2/HBF4, or t-BuOOH/HBF4. H2O2
or t-BuOOH alone gave no reaction, indicating the need for
some acid catalysis. In a study by NMR spectroscopy using
incremental additions of MeCO3H, the formation of BzSMo2-
(15) Balch, A. L.; Benner, L. S.; Olmstead, M. M. Inorg. Chem. 1979, 18,
2996.
(16) Neher, A.; Heyke, O.; Lorenz, I.-P. Z. Anorg. Allg. Chem. 1989, 578,
185.
(17) Browning, C. S.; Farrar, D. H. Organometallics 1989, 8, 813. Lorenz,
I.-P.; Thurow, K. J. Organomet. Chem. 1995, 496, 191.

3026 Inorganic Chemistry, Vol. 35, No. 10, 1996
Wang et al.
Table 3. Selected Bond Angles (deg)
2
3
4
5
S(1)-Mo(1)-S(2)/O(7)a
S(1)-Mo(1)-S(4)
S(2)/O(7)-Mo(1)-S(3)a
S(3)-Mo(1)-S(4)
O(1)-Mo(1)-N(1)
Mo(2)-Mo(1)-N(1)
Mo(2)-Mo(1)-O(1)
S(1)-Mo(2)-S(2)/O(7)a
S(1)-Mo(2)-S(6)
S(2)/O(7)-Mo(2)-S(5)a
S(5)-Mo(2)-S(6)
O(2)-Mo(2)-N(2)
Mo(1)-Mo(2)-N(2)
Mo(1)-Mo(2)-O(2)
Mo(1)-S(1)-Mo(2)
Mo(1)-S(1)-C(25)
Mo(2)-S(1)-C(25)
Mo(1)-S(2)/O(7)-Mo(2)a
Mo(1)-S(3)-P(1)
Mo(1)-S(4)-P(1)
Mo(2)-S(5)-P(2)
Mo(2)-S(6)-P(2)
S(3)-P(1)-S(4)
107.52 (6)
107.97 (5)
88.71 (5)
82.68 (5)
78.85 (5)
175.0 (2)
94.0 (1)
81.14 (9)
107.74 (5)
89.30 (5)
82.32 (5)
78.50 (5)
178.6 (1)
98.5 (1)
81.33 (9)
71.87 (4)
111.2 (2)
110.8 (2)
72.41 (4)
87.28 (7)
86.95 (7)
87.72 (7)
87.38 (7)
106.9 (1)
106.4 (1)
127.2 (3)
126.7 (3)
175.6 (4)
172.3 (3)
113.7 (2)
113.1 (2)
105.70 (5)
90.17 (5)
83.01 (5)
79.28 (5)
174.2 (2)
94.3 (1)
80.10 (9)
105.76 (5)
91.04 (5)
82.24 (5)
78.93 (6)
177.2 (2)
97.5 (1)
80.42 (9)
73.70 (4)
112.2 (2)
111.9 (2)
74.80 (4)
87.09 (7)
86.83 (7)
87.46 (7)
87.42 (8)
106.7 (1)
106.2 (1)
127.6 (3)
128.0 (3)
175.1 (4)
174.4 (4)
115.3 (2)
114.8 (2)
115.3 (2)
116.1 (2)
114.8 (2)
103.4 (1)
88.74 (5)
83.91 (6)
77.86 (6)
173.8 (2)
96.3 (1)
89.28 (5)
85.93 (9)
78.52 (5)
174.8 (2)
97.5 (1)
83.61 (9)
103.3 (1)
90.18 (5)
85.8 (1)
78.18 (5)
176.2 (2)
98.9 (1)
84.88 (9)
66.13 (4)
109.8 (2)
110.4 (2)
86.8 (1)
87.17 (7)
86.97 (7)
86.93 (7)
86.50 (7)
107.27 (9)
107.8 (1)
122.9 (3)
121.7 (3)
174.9 (4)
171.8 (4)
81.8 (1)
107.35 (6)
87.63 (6)
84.62 (6)
77.97 (7)
173.7 (2)
101.1 (2)
82.3 (1)
70.83 (4)
111.1 (2)
110.8 (2)
74.30 (5)
88.27 (8)
87.32 (8)
88.15 (9)
87.6 (1)
106.4 (1)
106.2 (1)
125.4 (4)
125.3 (4)
172.0 (4)
176.1 (4)
S(5)-P(2)-S(6)
Mo(1)-O(1)-C(15)
Mo(2)-O(2)-C(15)
Mo(1)-N(1)-C(1)
Mo(2)-N(2)-C(8)
Mo(1)-S(2)-O(7)
Mo(2)-S(2)-O(7)
Mo(1)-S(2)-O(8)
Mo(2)-S(2)-O(8)
O(7)-S(2)-O(8)
a The bridge atom is S(2) for compounds 2-4, and O(7) for compound 5.
The isolated RSMo2SO, 3, products were not very stable, and
decomposition was evident within a week of cold storage in
the dark. Solution samples decomposed within days even under
N2. The RSMo2SO2, 4, derivatives were indefinitely stable in
the dark in air-exposed solution; these were, however, consider-
ably light-sensitive.
All products were characterized by IR spectroscopy, NMR
spectroscopy (1H and 31P), and elemental analyses or X-ray
crystallography. IR spectra showed absorptions which are
typical for the [Mo2(NTo)2(S2P(OEt)2)2(µ-O2CMe)] portion.2,21-24
In addition, RSMo2SO2 displayed ν(SO) at 1208 and 1051 cm-1
(R ) Bz) and 1209 and 1051 cm-1 (R ) Me); SO2 deformation
bands could also be assigned at 529 (Bz) and 526 (Me) cm-1
.
These values are consistent with those of prior µ-SO2 com-
plexes.8 The ν(SO) band for RSMo2SO was not observed for
either R ) Me or Bz; the band was expected at lower
wavenumbers and was presumed to be buried under the intense
dithiophosphate bands in the vicinity. Values for ν(SO) in prior
µ-SO complexes extend from 883 to 1100 cm-1 6,7,16,25-30
For
.
those cases where analogous M2(µ-SO) and M2(µ-SO2) com-
Figure 4. ORTEP view of [Mo2(NTo)2(S2P(OEt)2)2(O2CMe)(SBz)-
(O)], 5 (R ) Bz).
(18) Schrier, P. W.; Fanwick, P. E.; Walton, R. A. Inorg. Chem. 1992, 31,
3929.
(19) Oae, S. In Organic Sulfur Chemistry; Oae, S., Ed.; Plenum Press: New
York, 1977; p 383.
(20) Patai, S., Rappoport, Z., Stirling, C. J. M., Eds. The Chemistry of
Sulphones and Sulphoxides; John Wiley & Sons: Chichester, England,
1988.
(21) Lizano, A. C.; Noble, M. E. Inorg. Chem. 1988, 27, 747.
(22) Noble, M. E. Inorg. Chem. 1990, 29, 1337.
(23) Haub, E. K.; Lizano, A. C.; Noble, M. E. J. Am. Chem. Soc. 1992,
114, 2218.
plexes have been reported,6,7,16,30 ν(SO) is of lower energy for
µ-SO than for µ-SO2 bridges. This parallels the pattern for
organic sulfoxides and sulfones.19,31,32
1H and 31P NMR spectra revealed all appropriate resonances
and demonstrated the presence of conformational isomers
associated with inversion at the thiolate sulfur bridge. Sulfur
(24) Haub, E. K.; Richardson, J. F.; Noble, M. E. Inorg. Chem. 1992, 31,
4926.
(25) Ho¨fler, M.; Baitz, A. Chem. Ber. 1976, 109, 3147.
(26) Pandey, K. K. Spectrochim. Acta 1983, 39A, 925.
(27) Herberhold, M.; Schmidkonz, B. J. Organomet. Chem. 1986, 308, 35.
(28) Schenck, W. A.; Karl, U.; Horn, M. R.; Mu¨ssig, S. Z. Naturforsch.,
B: Anorg. Chem., Org. Chem. 1990, 45, 239.
(29) Gong, J. K.; Fanwick, P. E.; Kubiak, C. P. J. Chem. Soc., Chem.
Commun. 1990, 1190.
(30) Heyke, O.; Hiller, W.; Lorenz, I.-P. Chem. Ber. 1991, 124, 2217.

Oxidation at a Dimolybdenum(V) Sulfur Bridge
Inorganic Chemistry, Vol. 35, No. 10, 1996 3027
invertomers have been previously demonstrated for various
µ-thiolate-µ-sulfide dimers RSMo2S, 2; these are depicted
pictorially in the structure diagram for 2 (see Introduction) and
are designated distal and proximal on the basis of the position
of the sulfur substituent relative to the arylimido rings. Distal
and proximal spectroscopic assignments are based on prior
methods.3 For RSMo2SO, four isomers were observed in the
NMR spectra; this indicated additional isomers associated with
a pyramidal SO bridge. The isomers were spectroscopically
assigned as orientations A-D. The isomer distributions in
strated through several studies, some of which employed Ph3P.33
As a control, there was no reaction of BzSMo2SO2 with Ph3P
in the dark, even after 5 days. Photolysis of RSMo2SO2 (R )
Bz or Me) for 1.5 h in the presence of 15- or 16-fold Ph3P
gave clean production of the oxide RSMo2O, 5, with no
formation of the sulfide RSMo2S, 2. One equivalent of Ph3PS
and 1 equiv of Ph3PO were also obtained. These results
represented complete reaction as per eq 3 with quantitative
interception of SO by Ph3P.
When the photolysis and phosphine steps were separated, the
results clearly differed. Photolysis of MeSMo2SO2 alone in
CDCl3 followed afterward by treatment with 4 equiv of Ph3P
in the dark yielded 89% oxide MeSMo2O and 10% sulfide
MeSMo2S, analogous to the cases of RSMo2SO2 as first
indicated above. In addition, a sizable amount of Ph3PS was
observed, but only a trace (<1%) of Ph3PO was present. In a
separate experiment, the vapor phase was sampled after pho-
tolysis and SO2 was identified by GC-MS analysis. These
results indicated that eq 3 was yet the major and initial reaction,
but this was followed by the characteristic disproportionation34,35
of SO to S + SO2, as given overall by eq 4. Post-addition of
CDCl3 were similar for both R ) Me (66% A, 20% B, 11% C,
and 3% D) and R ) Bz (67% A, 20% B, 10% C, and 3% D).
The distal/proximal preference for SO invertomers was 6.4 (Me)
and 6.7 (Bz), while the ratio for SR invertomers was 3.5 (Me)
and 3.4 (Bz). In (CD3)2CO, the isomer distributions were 54%
A, 22% B, 17% C, and 7% D for R ) Me and 59% A, 21% B,
15% C, and 5% D for R ) Bz; the distal/proximal ratios were
3.1 (Me) and 4.2 (Bz) for SO invertomers and 2.5 (Me) and
3.0 (Bz) for SR invertomers. (The spectra showed good
consistency for the ratio measurements which were believed
valid within (0.5.) Thus, the SO ratio was more sensitive to
solvent than the SR ratio. Attempts to examine inversion ratios
in other solvents were thwarted by poor solubility or inadequate
separation of isomer resonances.
Photochemistry. The RSMo2SO2, 4, products are modestly
sensitive to normal lighting in solution and in the solid state,
and samples were handled under red light. Direct photolysis
of MeSMo2SO2 in CDCl3 in a sealed tube for 1.5 h using
fluorescent lights produced 11% of the sulfide MeSMo2S, 2,
and 89% of a new product. Sometimes traces (<2%) of a third
product could be observed, but this product was never identified.
Similar results were obtained for photolysis in air-exposed
solution and for photolysis of BzSMo2SO2. The major photo-
product could be isolated from larger scale reactions, but this
defied spectroscopic identification. X-ray crystallography was
necessary for definitive identification (see below), and the
compound proved to be oxo-bridged RSMo2O, 5 (R ) Me or
Bz). This suggested the loss of one formal equivalent of SO
during the reaction, eq 3.
(4)
Ph3P produced Ph3PS from reaction with elemental sulfur, but
not with SO2. (Reaction of Ph3P with SO2 is not significant at
room temperature without a catalyst.36)
The formation of some sulfide RSMo2S, 2, in these reactions
indicated that a second, minor pathway also existed for the fate
of SO. This minor route involved SO or one of its dispropor-
tionation intermediates acting as a reducing agent for unreacted
RSMo2SO2 to give RSMo2S; this yielded more SO2 and less
elemental sulfur as predicted for eq 4 alone. In the photolysis
of MeSMo2SO2 followed afterward by addition of Ph3P, the
observed amount of Ph3PS corresponded to the observed
distribution of MeSMo2S, 2, and MeSMo2O, 5, as calculated
for these two pathways. The reduction involved oxygen
abstraction and implied the intermediacy of RSMo2SO. This
compound was never observed, however, which therefore
required that its own reduction to RSMo2S was fast. This was
tested by photolyzing BzSMo2SO2 in the presence of MeSMo2-
SO (10 mol %): complete conversion of MeSMo2SO to
MeSMo2S was realized before all BzSMo2SO2 had reacted. This
was true despite the sluggish reactivity of RSMo2SO by itself
(see below). Thus, SO (or one of its disproportionation
intermediates) was indeed abstracting oxygen from RSMo2SO
in a facile process.
The photolysis reaction was also investigated in the solid state.
Photolysis of solid BzSMo2SO2 for 3 h produced 91% oxide
BzSMo2O and 8% sulfide BzSMo2S. The results were strongly
indicative of a unimolecular extrusion of free SO: crystal-
lography of BzSMo2SO2 revealed no close contacts which could
suggest an intermolecular process in the solid state.
(3)
Since fluorescent lights provide visible and some UV
radiation, an attempt was made to estimate the spectral region
for the photoextrusion. Filter studies were conducted for
solution photolysis of BzSMo2SO2 utilizing visible-cutoff filters;
the reactions were compared to a reference using a 9-54 filter
Although intermolecular pathways could be envisioned, a
unimolecular mechanism for extrusion of free SO was demon-
(31) Truce, W. E.; Klingler, T. C.; Brand, W. W. In Organic Sulfur
Chemistry; Oae, S., Ed.; Plenum Press: New York, 1977; p 527.
(32) Zoller, U. In The Chemistry of Sulphones and Sulphoxides; Patai, S.,
Rappoport, Z., Stirling, C. J. M., Eds.; John Wiley & Sons: Chichester,
England, 1988; p 379.
(34) Schenck, P. W.; Steudel, R. Angew. Chem., Int. Ed. Engl. 1965, 4,
402.
(33) The reaction of Ph3P with SO has been implicated: Bonini, B. F.;
Maccagnani, G.; Mazzanti, G.; Pedrini, P.; Piccinelli, P. J. Chem. Soc.,
Perkin Trans. 1 1979, 1720.
(35) Herron, J. T.; Huie, R. E. Chem. Phys. Lett. 1980, 76, 322.
(36) Fluck, E.; Binder, H. Angew. Chem., Int. Ed. Engl. 1965, 4, 359. Smith,
B. C.; Smith, G. H. J. Chem. Soc. 1965, 5516.

3028 Inorganic Chemistry, Vol. 35, No. 10, 1996
Wang et al.
which transmits well below 300 nm. Photolysis using a 3-74
filter gave a slight (∼10%) decrease in reaction, while 3-68
and 2-63 filters slowed the reaction substantially, ∼50 and
∼80%, respectively. A 2-58 filter eliminated the reaction
completely. These results clearly showed the photolysis to be
a visible light process and suggested that the photolysis band
was in a region near 500 nm. The UV-vis spectrum of
BzSMo2SO2 revealed a weak band at ∼550 nm (ꢀ ) 140 M-1
cm-1) and an inflection at ∼470 nm (ꢀ ) 1010 M-1 cm-1);
these rode the tails of strong absorptions at higher energies and
were not well-resolved. By comparison, UV-vis spectra of
BzSMo2S, BzSMo2SO2, and BzSMo2O revealed only one band
in this region at 496 nm (ꢀ ) 1560 M-1 cm-1), 578 nm (ꢀ )
381 M-1 cm-1), and ∼520 nm (ꢀ ) 290 M-1 cm-1), respec-
tively; these, too, lay on higher energy absorption tails.
The µ-SO complexes were photoreactive, but very weakly:
the process was extremely slow and was incomplete after 48 h.
In all cases, the sulfide BzSMo2S was obtained, but other
products were also observed, none of which could be identified.
Reactions incorporating Ph3P produced variable amounts of Ph3-
PO and Ph3PS, but BzSMo2O was not observed; this suggested
other modes of sulfur release from dimer components. Overall,
the results did not provide sufficient product accountability for
useful conclusions.
Crystal Structures. The crystal structures of BzSMo2SO
and of BzSMo2SO2 were undertaken to more fully characterize
the bridge units. The structure of BzSMo2SO is particularly
valuable since the µ-SO linkage is not well-characterized
crystallographically: only three structures were located in the
literature, and two of these were disordered within the SO
unit.6,7,29 The structure of oxide BzSMo2O was undertaken for
definitive identification, as indicated above. With that of
BzSMo2S, the crystal structures herein provide an interesting
comparison of µ-S, µ-SO, µ-SO2, and µ-O units within otherwise
identical complexes.
The lack of disorder in BzSMo2SO can be attributed to the gross
inequivalence of the two orientations, as reflected also in the
solution isomer distribution. The S(2)Mo2 angle in BzSMo2-
SO is 72.41(4)° and is much smaller than the range of 90.4-
(3)-130.78(7)° for SM2 angles in the three complexes cited;
none of the others, however, was a metal-metal bonded system.
The structure of BzSMo2SO2 clearly reveals the SO2 bridge
with perpendicular SO2 and Mo2S groups. The SO2 angle is
114.6(2)°, and the S(2)Mo2 angle is 74.80(4)°. The SO bond
lengths are identical: 1.466(4) and 1.465(4) Å. These are longer
than the bonds of SO2 itself (1.431 Å40) but similar to SO bond
lengths in organic sulfones (typical range, 1.41-1.47 Å37,38).
The SO bonds of BzSMo2SO2 are shorter than that in the above
BzSMo2SO complex; this is in direct parallel to the pattern of
shorter SO bonds in sulfones than in sulfoxides.37,38 Direct SO/
SO2 comparisons using other metallovariants are limited due
to the lack of µ-SO structures, although both [Pd2Cl2(dppm)2-
(SOx)] x ) 1 (disordered)7 and 2 15 have been reported.
Comparisons can be made, however, between the Mo2SO2
structural features of BzSMo2SO2 and those of other M2SO2
systems. Ten crystal structures of dinuclear complexes with
equivalent, metal-metal bonded sites have been previously
reported;41-50 one of these was a lower-valent molybdenum
complex, [Mo2(CN)8(S2)(SO2)]4- 45
The SO bond lengths and
.
the SM2 angle in BzSMo2SO2 are well within the ranges, 1.44-
(1)-1.495(6) Å and 69.6(1)-79.84(7)°, respectively, of those
prior ten structures. The M-S bond lengths of BzSMo2SO2
(2.427(1), 2.420(1) Å), however, are long compared to the prior
range of 2.169(1)-2.369(8) Å. The SO2 angle in BzSMo2SO2
is at the wide end of the range of 107.5(3)-114.3(2)°. If the
structural pool is extended to SO2-bridged dimers with inequiva-
lent metal sites (four more structures30,51,52), then only [(Me5-
Cp)Ni(SO2)(CO)3W(MeCp)]52 exceeds BzSMo2SO2 in M-S
bond length (2.441(1) Å for W-S) and only [(Et3P)BrPd(SO2)-
PdCp(Et3P)]51 exceeds BzSMo2SO2 in SO2 angle (116.0(1)°).
The results of the comparison of the four structures reported
herein are now described. The structure of µ-thiolate-µ-sulfide
BzSMo2S is considered the reference structure; it is similar to
those of related µ-sulfide complexes with a perthiolate (RSS-)
bridge, EtSSMo2S,53 a thiohydroxylamide (H2NS-) bridge, H2-
NSMo2S,24 and, a thiooximate (RCHdNS-) bridge, Me3-
CCHNSMo2S.24 A few common features are as follows. The
imido linkages are linear, and the acetate ligand bridges
symmetrically. The SMo2S cores are nearly planar; for
The results are presented for the Mo2SO and Mo2SO2 features
and then for the comparison of the four compounds as a whole.
All structures are shown in Figures 1-4. Selected metrical
results are listed in Tables 2 and 3.
The SO bridge is revealed in the structure of BzSMo2SO to
be a symmetric, pyramidal Mo2SO unit, consistent with the
observation of invertomers in solution. The sum of the angles
at S(2) is 299.2(5)°; this can be compared to the sum of 293.9-
(5)° for the thiolate sulfur bridge, S(1). O(7) and the benzyl
group are in distal orientations, consistent with the major
solution isomer. The S(2)-O(7) bond length is 1.515(4) Å;
this is longer than SO itself (1.481 Å34) and longer than the SO
bond of organic sulfoxides (typical range, 1.47-1.49 Å37,38) but
still much shorter than the sum of single bond radii (1.70 Å39).
Any comparison to other µ-SO complexes is very limited. The
crystal structures for [Pd2Cl2(dppm)2(SO)]7 and analogous [Ni2-
Cl2(dppm)2(SO)]29 revealed pyramidal M2SO units, but both
were disordered in the location of the O atom with respect to
the two possible pyramidal orientations. The crystal structure
of [Cp2Mn2(CO)4(SO)]6 was not disordered, but the Mn2SO
group was planar and was therefore incapable of that disorder.
The planar SO bond length in [Cp2Mn2(CO)4(SO)] was 1.504-
(4) Å, similar to that for pyramidal SO in the present structure.
(40) Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements; Pergamon
Press: Oxford, England, 1985; p 827.
(41) Meunier-Piret, J.; Piret, P.; van Meerssche, M. Bull. Soc. Chim. Belg.
1967, 76, 374.
(42) Churchill, M. R.; Kalra, K. L. Inorg. Chem. 1973, 12, 1650.
(43) Angoletta, M.; Bellon, P. L.; Manassero, M.; Sansoni, M. J. Orga-
nomet. Chem. 1974, 81, C40.
(44) Cowie, M.; Dwight, S. K. Inorg. Chem. 1980, 19, 209.
(45) Potvin, C.; Bre´geault, J.-M.; Manoli, J.-M. J. Chem. Soc., Chem.
Commun. 1980, 664. Some metrical information was derived from
the Cambridge Data Base.
(46) Herrmann, W. A.; Plank, J.; Ziegler, M. L.; Wu¨lknitz, P. Chem. Ber.
1981, 114, 716.
(47) Mingos, M. P.; Williams, I. D.; Watson, M. J. J. Chem. Soc., Dalton
Trans. 1988, 1509.
(48) Seyferth, D.; Womack, G. B.; Archer, C. M.; Fackler, J. P.; Marler,
D. O. Organometallics 1989, 8, 443.
(49) Mu¨ller, A.; Krickemeyer, E.; Wittneben, V.; Bo¨gge, H.; Lemke, M.
Angew. Chem., Int. Ed. Engl. 1991, 30, 1512.
(37) Hargittai, I. In The Chemistry of Sulphones and Sulphoxides; Patai,
S., Rappoport, Z., Stirling, C. J. M., Eds.; John Wiley & Sons:
Chichester, England, 1988; p 33.
(38) Furukawa, N.; Fujihara, H. In The Chemistry of Sulphones and
Sulphoxides; Patai, S., Rappoport, Z., Stirling, C. J. M., Eds.; John
Wiley & Sons: Chichester, England, 1988; p 541.
(50) Heyke, O.; Beuter, G.; Lorenz, I.-P. J. Chem. Soc., Dalton Trans. 1992,
2405.
(51) Werner, H.; Thometzek, P.; Zenkert, K.; Goddard, R.; Kraus, H.-J.
Chem. Ber. 1987, 120, 365. Thometzek, P.; Zenkert, K.; Werner, H.
Angew. Chem., Int. Ed. Engl. 1985, 24, 516.
(52) Bartlone, A. F.; Chetcuti, M. J.; Navarro, R., III; Shang, M. Inorg.
Chem. 1995, 34, 980.
(53) Noble, M. E.; Williams, D. E. Inorg. Chem. 1988, 27, 749.
(39) Pauling, L. The Nature of the Chemical Bond; Cornell University
Press: Ithaca, NY, 1960.

Oxidation at a Dimolybdenum(V) Sulfur Bridge
Inorganic Chemistry, Vol. 35, No. 10, 1996 3029
BzSMo2S the dihedral angle for MoS2 planes is 179.7(1)°. Metal
bonds to tricoordinate S(1) are longer than those to sulfide S(2);
this has been attributed to π effects.54 The Mo-S(dithiophos-
phate) bond lengths are inversely correlated to Mo-S(bridge)
bond lengths, demonstrating a greater trans influence for the
sulfide bridge, S(2), than for the functionalized sulfur bridge,
S(1).
Generalities for the present four compounds include linear
imido groups, symmetric acetate bridges, and nearly planar
SMo2S cores, but Mo-S(2) bond lengths are substantially
affected. In all compounds, the benzyl thiolate group is in the
distal orientation, corresponding to the major solution isomer.
Structural changes associated with the conversion of µ-S to
µ-SO reveal an expansion of the SMo2S core. The Mo-Mo
bond lengthens and S(2) moves out; the latter is evidenced by
longer Mo-S(2) bonds and a larger cross-core S(1)‚‚‚S(2)
distance while Mo-S(1) bond lengths are unchanged. Some
coligand-to-metal bond lengths decrease: Mo-O(acetate) bond
lengths decrease and Mo-S(dithiophosphate) bonds trans to SO
shorten. The latter indicates a weakened trans influence for
SO. The results overall are consistent with reduced donating
properties of SO vs S, which relaxes the SMo2S core and
shortens some coligand distances. The SMo2S core remains
planar, with a dihedral angle of 178.9(1)° for MoS2 planes.
These trends are not consistently maintained on proceeding
to the SO2-bridged structure, which renders interpretation
difficult. The Mo-Mo bond lengthens substantially, but the
cross-core S(1)‚‚‚S(2) distance shortens and is now intermediate
to those in the µ-S and µ-SO structures. The Mo-S(2) bond
lengths involving SO2 remain the same as for SO. The thiolate
Mo-S(1) bond lengths are modestly longer in BzSMo2SO2. The
MoS2 dihedral angle is 177.9(1)°. All Mo-S(dithiophosphate)
bond lengths in BzSMo2SO2 are at least slightly contracted, and
all are virtually equal, which indicates that there is no trans
influence of µ-SO2 relative to that of µ-SBz.
Discussion
Peroxide oxygenation of the bridge sulfide within RSMo2S
2 proceeded cleanly without evidence of reaction at other ligand
sites including the thiolate. When taken with the observation
of the product distribution obtained with limiting peroxide
equivalents, it is seen that oxygenation reactivity follows the
sequence S > SO . SR. Although steric factors for SBz may
have blocked access to the thiolate site, these would have been
much smaller for SMe. The S > SO comparison and the use
of acidic peroxide reagents are consistent with a mechanism
involving nucleophilic sulfur and electrophilic oxidant.1 The
sulfide bridge of complexes RSMo2S, 2, has proven somewhat
electron-rich in other recent studies.4,55
The classical description8,9 of the bonding of SO2 to a metal
involves neutral SO2 acting as σ-donor and π-acceptor and a
metal with a moderate or high d-electron count to allow for
back-donation into the π-accepting LUMO of SO2. In some
instances, the SO22- unit has been invoked,18,49,56 which is the
extreme of π-acidity to the point of 2e- reduction of the SO2
unit at the expense of d-electrons. While this distinction has
2-
indefinite boundaries, clearly in the present case a µ-SO2
complex with Mo(V) (d1) is the appropriate description, as
opposed to neutral µ-SO2 with Mo(IV) (d2). Despite the formal
distinction, structural differences within the M2SO2 unit are
modest between BzSMo2SO2 and 14 other structures previously
reported for metal-metal bonded dimers. All of the 14 other
compounds were lower valent and of higher d-electron count,
regardless of the formalism invoked.
By analogy, the SO2- bridge is invoked for RSMo2SO.
Structurally, there is a clear distinction between pyramidal and
planar M2SO units, although there are too few structures of
either case for useful comparison. The parallel of the dimo-
lybdosulfoxide RSMo2SO to organic sulfoxides is evidenced
by the pyramidicity of the Mo2SO unit, the inversion isomer-
ization at sulfur, and even the solvent effect57 on isomer
preference.
Although the emphasis of this work had been on S/SO/SO2
bridge conversions, it was of interest to determine whether there
would be any influence on the thiolate bridge of the dimetal
core. The latter, however, proved to be very insensitive to the
changes, even for the µ-O complex. The constancy of the
thiolate did allow a comparison of the trans influence of the
S/SO/SO2/O bridges: as determined by Mo-S(dithiophosphate)
bond lengths, the structural trans influence was in the order µ-S
g µ-O > µ-SO g µ-SO2 ) µ-SBz. The µ-S vs µ-O relationship
is similar to that seen in crystal structures of dithiophosphato-
molybdenum dimers containing one S and one O bridge: in
some cases, Mo-S(dithiophosphate) bonds trans to µ-S are
longer, while in other cases the bond lengths are similar to those
trans to µ-O.58
In this comparison of µ-S, µ-SO, and µ-SO2 structures, some
reference can be made to the series [Pd2Cl2(dppm)2(SOx)], x )
0-2,7,15 although, as noted above, these were not metal-metal
bonded complexes and the SO structure was disordered. Similar
to the case of the present series, some structural features for
the Pd complexes fit a trend, while others were inconsistent.7
The most notable feature for current comparison is that Pd-S
bond lengths varied consistently and decreased in the series:
Pd-S (2.298(5), 2.298(5) Å) > Pd-SO (2.268(8), 2.277(8) Å)
> Pd-SO2 (2.234(4), 2.241(4) Å, two independent molecules).
This trend is in direct contrast to the present BzSMo2SOx results,
for which Mo-S bond lengths were the shortest with µ-S.
In the comparison of structural variations in organic sulfides,
sulfoxides, and sulfones,37 the angles at S are narrowest for
sulfoxides; this pattern is also obtained in the current series for
S(2).
The most unusual feature of the current series of complexes
is the facile photoextrusion of SO from the SO2 bridge of the
dimolybdosulfones RSMo2SO2. Thermal or photolytic extrusion
of SO2 has been established from a variety of -(SO2)-, units
including cyclic sulfones and some M2SO2 complexes.8,9,31,32,59-62
The crystal structure of the oxide-bridged BzSMo2O reveals
a gross contraction of the SMo2O core relative to the above
SMo2S cores, as to be expected. The shortness of the Mo-
O(7) bond lengths along with the much shorter Mo-Mo bond
account for the greatest differences. Mo-S(1) bond lengths
are again unaffected, however, and overall these remained very
consistent in all four compounds. The SMo2O core is nearly
planar (MoSO dihedral angle, 173.2(1)°), albeit less planar than
the SMo2S cores in the above structures. The disparity in Mo-
S(dithiophosphate) bonds indicates a greater trans influence for
µ-O than for µ-SR.
(55) Allred, B. R.; Koffi-Sokpa, E. I.; Noble, M. E. Work in progress.
(56) Farrar, D. H.; Gukathasan, R. R. J. Chem. Soc., Dalton Trans. 1989,
557.
(57) Barbarella, G.; Dembech, P.; Tugnoli, V. Org. Magn. Reson. 1984,
22, 402.
(58) Drew, M. G. B.; Mitchell, P. C. H.; Read, A. R.; Colclough, T. Acta
Crystallogr., Sect. C: Cryst. Struct. Commun. 1981, 37, 1758. Drew,
M. G. B.; Baricelli, P. J.; Mitchell, P. C. H.; Read, A. R. J. Chem.
Soc., Dalton Trans. 1983, 649. Baricelli, P. J.; Drew, M. G. B.;
Mitchell, P. C. H. Acta Crystallogr., Sect. C: Cryst. Struct. Commun.
1983, 39, 843.
(54) Lizano, A. C.; Munchhof, M. G.; Haub, E. K.; Noble, M. E. J. Am.
Chem. Soc. 1991, 113, 9204.

3030 Inorganic Chemistry, Vol. 35, No. 10, 1996
Wang et al.
The extrusion of free SO from the -(SO)- unit is known for
sulfoxides.32,60-66 Although the emphasis here is on bridge
linkages, loss of SO2 from terminal SO2 ligands and loss of SO
from terminal SO ligands have also been reported.8,9,67,68
Despite these, the extrusion of SO from SO2 units is not well-
documented. The dissociation of SO2 itself can give SO + O,
but this is a high-energy process thermally or photolytically.34,69
The release of SO from sulfenes (R2CdSO2) and cyclic sulfinate
esters has been suggested in some studies.70-72
Although the present photoextrusion is extremely unusual, a
mechanism can be proposed based on the following background.
The SO2 bridge can occur as µ2-η2(S,O) between two metal sites;
this has been demonstrated crystallographically in [Mo(CO)2-
(PPh3)(C5H5N)(SO2)]2.73 The analogy for organic compounds
is sulfinate esters, RS(O)OR. Thermal and/or photochemical
isomerization of cyclic sulfones to cyclic sulfinate esters has
been demonstrated,61,62 although the reverse also occurs for
acyclics.59 In the general area of metal-SO2 studies, albeit not
involving SO2 as a µ2 bridge, the terminal η1(S)-SO2 ligand of
the monomeric complex [Ru(NH3)4Cl(SO2)]+ photoisomerizes
to η2(S,O) even in the solid state.74 Another example is the
recent proposal that the terminal SO2 ligand can undergo η2-
η1 (pyramidal and planar) isomerization to electronically buffer
the metal during exchange of coligands.75
(5)
(6)
this scheme, eq 5 is the photoprocess and eq 6 is a thermal
step. The inverse combination of thermal eq 5 and photoequa-
tion 6 is less favored but cannot be eliminated; this would
necessitate an equilibrium for eq 5 which is very far to the left
in order to escape detection by NMR spectroscopy (down to
-50 °C) and in order to maintain reasonable thermal parameters
in the crystal structure of BzSMo2SO2.
The elusive nature of SO has impeded studies of its chemistry
under normal conditions. The present reactions identify an
oxygen abstraction reactivity toward SO2 and SO ligands. The
ability of SO to abstract oxygen has been reported in other
situations: its own disproportionation involves abstraction of
O from its dimer (SO)2; SO also reduces organic N-oxides.76
In the many cases of SO extrusion from organic sulfoxides
and the subsequent reactions of SO, the question of spin state
has been of interest but it has been very contentious. Although
the ground state for SO is a triplet, this and its low-energy singlet
state have been invoked for various mechanisms involving either
concerted or stepwise pathways.61,65,77 Given that background,
and the facile spin conversion available to SO,78 there is
sufficient ambiguity to refrain from any spin-state projections
for the present system.
Based on the metal and organic background for η1-η2
isomerization, the photoextrusion of SO from RSMo2SO2 is
proposed to proceed through a µ2-η2(S,O) intermediate, eq 5,
which then extrudes SO to form the oxide RSMo2O, 5, eq 6. In
(59) Simpkins, N. S. Sulphones in Organic Synthesis; Pergamon Press:
Oxford, England, 1993.
(60) Still, I. W. J. In Organic Sulfur Chemistry; Bernardi, F., Csizmadia,
I. G., Mangini, A., Eds.; Elsevier: Amsterdam, 1985; p 596.
(61) Zoller, U. In Small Ring Heterocycles, Part 1; Hassner, A., Ed.;
Interscience: New York, 1983; p 323.
(62) Still, I. W. J. In The Chemistry of Sulphones and Sulphoxides; Patai,
S., Rappoport, Z., Stirling, C. J. M., Eds.; John Wiley & Sons:
Chichester, England, 1988; p 873.
The observed photoextrusion of SO from the SO2 bridge
further extends the versatility of this important ligand. It is
reasonable to expect that this behavior will be observed
thermally or photolytically for other µ-SO2 complexes (η1 or
η2) or for (mono)metallosulfones M-(SO2)-R or their sulfinate
isomers M-O-S(O)-R. This may not be as well-favored,
however, with lower valent, higher d-electron systems. Indu-
bitably, the oxophilicity of the high-valent molybdenum(V)
contributes driving force for the present process.
(63) Chow, Y. L.; Tam, J. N. S.; Blier, J. E.; Szmant, H. H. J. Chem. Soc.,
Chem. Commun. 1970, 1604.
(64) Chao, P.; Lemal, D. M. J. Am. Chem. Soc. 1973, 95, 920, 922.
(65) Thiemann, C.; Thiemann, T.; Li, Y. Q.; Sawada, T.; Nagano, Y.;
Tashiro, M. Bull. Chem. Soc. Jpn. 1994, 67, 1886.
(66) Abu-Yousef, I. A.; Harpp, D. N. Tetrahedron Lett. 1995, 36, 201.
(67) Schenk, W. A.; Leissner, J.; Burschka, C. Z. Naturforsch., B: Anorg.
Chem., Org. Chem. 1985, 40, 1264.
(68) Heyke, O.; Neher, A.; Lorenz, I.-P. Z. Anorg. Allg. Chem. 1992, 608,
23.
(69) Felder, P.; Haas, B.-M.; Huber, J. R. Chem. Phys. Lett. 1993, 204,
248.
(70) McIntosh, C. L.; de Mayo, P. J. Chem. Soc., Chem. Commun. 1969,
32.
(71) Battaglia, A.; Dondoni, A.; Maccagnani, G.; Mazzanti, G. J. Chem.
Soc., Perkin Trans. 2 1974, 609.
Acknowledgment. This work was supported by research
awards from the National Science Foundation, the Kentucky
EPSCoR Program, and the University of Louisville.
Supporting Information Available: Tables of full crystallographic
parameters, positional and displacement parameters, bond lengths, and
bond angles (27 pages). Ordering information is given on any current
masthead page.
IC951518K
(72) Coates, J. E.; Abbot, F. S. J. Org. Chem. 1977, 42, 3506.
(73) Jarvinen, G. D.; Kubas, G. J.; Ryan, R. R. J. Chem. Soc., Chem.
Commun. 1981, 305.
(74) Johnson, D. A.; Dew, V. C. Inorg. Chem. 1979, 18, 3273.
(75) Shen, J. K.; Basolo, F.; Kubas, G. J. J. Organomet. Chem. 1995, 488,
C1.
(76) Maccagnani, G. In Organic Sulfur Chemistry; Freidlina, R. K.,
Skorova, A. E., Eds.; Pergamon Press: Oxford, England, 1981; p 123.
(77) Swope, W. C.; Lee, Y.-P.; Schaeffer, H. F., III. J. Chem. Phys. 1979,
71, 3761.
(78) Breckenridge, W. H.; Miller, T. A. J. Chem. Phys. 1972, 56, 465.