Two routes to bis(μ-diphenylphosphino)methane diplatinum halides bridged by sulfur monoxide

Article abstract of DOI:10.1021/om9905815

The new compounds Pt₂(μ-diphenylphosphinomethane)₂(μ-SO)X₂, with X = Cl and I, have been prepared and characterized. One route was to use Pt₂-(μ-dppm)₂X₂ to trap the sulfur monoxide liberated from decomposition of a suiting, intermediate formed from the oxidation of a thioketone sulfoxide with hydrogen peroxide, catalyzed by CH₃ReO₃ (MTO). The second and preferable route consists of the oxidation of Pt₂(μ-dppm)₂-(μ-S)X₂ with hydrogen peroxide, catalyzed by CH₃ReO₃ (MTO). The X-ray structural analysis of Pt₂(μ-dppm)₂-(μ-SO)Cl₂ showed that it has an A-frame structure in which the bridge sulfur atom has the geometry of a distorted trigonal bipyramid.

Full text of DOI:10.1021/om9905815

5420
Organometallics 1999, 18, 5420-5422
Tw o Rou tes to Bis(µ-d ip h en ylp h osp h in o)m eth a n e
Dip la tin u m Ha lid es Br id ged by Su lfu r Mon oxid e
Ruili Huang, Ilia A. Guzei, and J ames H. Espenson*
Ames Laboratory and Department of Chemistry,
Iowa State University of Science and Technology, Ames, Iowa 50011
Received J uly 26, 1999
Summary: The new compounds Pt2(µ-diphenylphosphi-
nomethane)2(µ-SO)X2, with X ) Cl and I, have been
prepared and characterized. One route was to use Pt2-
(µ-dppm)2X2 to trap the sulfur monoxide liberated from
decomposition of a sultine intermediate formed from the
oxidation of a thioketone sulfoxide with hydrogen per-
oxide, catalyzed by CH3ReO3 (MTO). The second and
preferable route consists of the oxidation of Pt2(µ-dppm)2-
(µ-S)X2 with hydrogen peroxide, catalyzed by CH3ReO3
(MTO). The X-ray structural analysis of Pt2(µ-dppm)2-
(µ-SO)Cl2 showed that it has an “A-frame” structure in
which the bridge sulfur atom has the geometry of a
distorted trigonal bipyramid.
complexes have been made with Pd17,18 and Ni,19 not
through direct SO insertion but by oxidation of a µ-S
complex. With that in mind, we carried out a parallel
(and superior) synthesis of 3 based on an oxidation
reaction, eq 3.
The use of simple chemical methods to generate and
study reactive molecules has attracted some attention,
but relatively little attention has been paid to sulfur
monoxide.1,2 Until now, the main method for generating
SO has been the pyrolysis of episulfoxides1,3-5 and other
sulfoxides of varying structures.6,7 The reactive SO
molecule has been trapped as a thiophene-1-oxide with
dienes and trienes.8,9 Certain transition metal com-
plexes have also been used to trap SO.10 Atoms and
small molecules are known to insert into the Pt-Pt bond
of the platinum(I) complex Pt2(µ-dppm)2X2, 1 (X ) Cl,
Br, I), to produce so-called A-frame molecules Pt2(µ-
dppm)2X2(µ-Y), 2, Y ) S, SO2, CH2 (from CH2N2), CO,
etc.11-15
We recently uncovered a reaction (eq 1) that gradually
generates SO in solution.16 Sulfur monoxide was then
either oxidized or, in separate experiments, trapped
with a diene. We reasoned that SO logically could also
be trapped by the Pt(I) complex 1, eq 2, to form Pt2(µ-
dppm)2(µ-SO), 3.
The lemon-yellow compounds 1 and the yellow 2 (µ-
S) were prepared by established procedures.20,21 From
reaction 322 a pure yellow product, 3a , was isolated in
92% yield. Recrystallization from chloroform-hexane
afforded yellow crystals. The product was identified and
characterized by elemental analysis, NMR,23 and single-
crystal X-ray diffraction.24 The iodide derivative 3b was
similarly obtained in 86% yield as a yellow solid and
(6) Dover, F. H.; Solomon, K. E. J . Phys. Chem. 1980, 84, 3024.
(7) Chow, Y. L.; Tam, J . N. S.; Blier, J . W. J . Chem. Soc., Chem.
Commun. 1970, 1604.
(8) Dodson, R. M.; Sauers, F. R. J . Chem. Soc., Chem. Commun.
1967, 1189.
(9) Dodson, R. M.; Nelson, J . P. J . Chem. Soc., Chem. Commun.
1969, 1159.
(10) Schenk, W. A. Angew. Chem., Int. Ed. Engl. 1987, 26, 98.
(11) Puddephatt, R. J . J . Chem. Soc. Rev. 1983, 12, 99.
(12) Balch, A. L. Adv. Chem. Ser. 1982, 196, 243.
(13) Brown, M. P.; Fisher, J . R.; Franklin, S. J .; Puddephatt, R. J .;
Thomson, M. A. Adv. Chem. Ser. 1982, 196, 231.
(14) Muralidharan, S.; Espenson, J . H.; Ross, S. A. Inorg. Chem.
1986, 25, 2557.
(15) Brant, P.; Benner, L. S.; Balch, A. L. Inorg. Chem. 1979, 18,
3422.
(16) Huang, R.; Espenson, J . H. J . Org. Chem. 1999, 64, 6374.
(17) Lee, C.-L.; Besenyei, G.; J ames, B. R.; Nelson, D. A.; Lilga, M.
A. J . Chem. Soc., Chem. Commun. 1983, 1175.
(18) Besenyei, G.; Lee, C.-L.; Gulinski, J .; Rettig, S. J .; J ames, B.
R.; Nelson, D. A.; Lilga, M. A. Inorg. Chem. 1987, 26, 3622.
(19) Gong, J . K.; Fanwick, P. E.; Kubiak, C. P. J . Chem. Soc., Chem.
Commun. 1990, 1190.
(20) Brown, M. P.; Puddephatt, R. J .; Rashidi, M.; Seddon, K. R. J .
Chem. Soc., Dalton Trans. 1977, 951.
(21) Brown, M. P.; Fisher, J . R.; Franklin, S. J .; Puddephatt, R. J .
J . Chem. Soc., Chem. Commun. 1978, 749.
(22) Compound 2a (250 mg, 0.20 mmol) and MTO (2.5 mg, 10 µmol)
in 15 mL of chloroform were treated with 1 equiv of hydrogen peroxide.
1H NMR showed that reaction 3 was complete upon mixing. The
product was obtained by column chromatography on silica gel with
chloroform as eluent.
This reaction was successful, providing what we
believe is the first µ-SO complex of platinum. Related
(23) 1H NMR (CDCl3) of 3a : δ 7.00-7.90 (aromatic, m, 40 H); 4.12
(CH2, m, 2 H); 2.87 (CH2, m, 2H). 31P: δ 16.12, 13.51 ppm. Elemental
analysis for Pt2Cl2P4C50H44SO: C, found 46.00 (calcd 46.99), H 3.61
(3.47), S 1.85 (2.51), P 10.14 (9.69). The calcd values assume the
analyzed compound is solvent (chloroform) free, whereas the crystal-
lographic sample contained 3.3 CHCl3, to which we attribute the figure
for C being low. As little as 0.14 CHCl3 would make the comparison of
C be 46.00 (46.52 calcd).
(1) Abu-Yousef, I. A.; Harpp, D. N. J . Org. Chem. 1997, 62, 8366.
(2) Abu-Yousef, I. A.; Harpp, D. N. Tetrahedron Lett. 1995, 36, 201.
(3) Hartzell, G. E.; Paige, J . N. J . Am. Chem. Soc. 1966, 88, 2616.
(4) Hartzell, G. E.; Paige, J . N. J . Org. Chem. 1967, 32, 459.
(5) Saito, S. Tetrahedron Lett. 1968, 4961.
10.1021/om9905815 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 11/17/1999

Notes
Organometallics, Vol. 18, No. 25, 1999 5421
pm, indicates the absence of direct Pt-Pt bonding.
The Pt-S distances, 226.2 pm, are equal. Structures of
these binuclear A-frame bis(diphenylphosphino)methane
(dppm) complexes have been reported: Pd2Cl2(µ-SO)-
(µ-dppm)2 (5),17,18 Pd2Cl2(µ-SO2)(µ-dppm)2 (6),27 Pd2Cl2-
(µ-S)(µ-dppm)2 (7),27 Ni2Cl2(µ-SO)(µ-dppm)2 (8),19 Ir2-
(CO)2(µ-N-tol)(µ-dppm)2,26 and Rh2(CO)2(µ-S)(µ-dppm)2.28
Their Pt analogues, however, have not been structurally
characterized.
Complexes 3a and 5-8 exhibit very similar structural
features, Table 1. In 3a , two different tilt geometries of
the SO oxygen atom were observed. The occupancy
factors for oxygen atom disorder were refined to 0.66
for O(1) and 0.34 for O(2), a feature also observed for 5
and 8. The S-O bond distance is 142.8 pm, comparable
to those found for 5 (140 pm)17,18 and 8 (144, 146 pm).
Complex 3a contains pyramidal S, located equidistant
from both metal centers. The O-S-O and Pt-S-Pt
angles about the S atom are close to 90°, while the
Pt-S-O angles are near 120°. These values are in
excellent agreement with the bond angle in 5, but the
same angles in 6-8 (except for O-S-O) were much
closer to 111°. The two six-membered rings Pt-S-Pt-
P-C-P exhibit boat conformations similar to those in
5 and 8, with atoms C(13) and C(38) on the same side
of the P-Pt-P-P-Pt-P plane. Two Pt and four P
atoms are planar within 9 pm. The coordination envi-
ronment about Pt(1) and Pt(2) is that of a slightly
distorted square plane with the coordination angles in
the range 87.81(8)-92.99(7)° and 87.60(8)-92.84(7)°,
respectively. The ligating atoms lie alternatively 9 pm
around Pt(1) and 14 pm around Pt(2) above and below
the least-squares planes of PtP2SCl. This diagonal twist
toward tetrahedral geometry has also been observed in
5-8. The platinum-chlorine and platinum-phosphorus
parameters are similar to those for the palladium and
nickel complexes.
F igu r e 1. Perspective view of Pt2(dppm)2Cl2(µ-SO), 3a ,
with thermal ellipsoids at the 30% probability level. The
two fractionally occupied oxygen positions are shown as
O(1) and O(2). Selected bond lengths (pm) and bond angles
(deg): Pt(1)-Pt(2) ) 326.9(2); Pt(1)-Cl(1) ) 240.98(19); Pt-
(2)-Cl(2) ) 241.13(18); Pt(1)-S ) 226.2(2); Pt(1)-P(1) )
231.5(2); Pt(1)-P(3) ) 231.54(19); Pt(2)-S ) 226.2(2); Pt-
(2)-P(2) ) 231.5(2); Pt(2)-P(4) ) 231.2(2); S-O(1) ) 142.8-
(7); S-O(2) ) 142.8(7); Cl(1)-Pt(1)-S ) 172.22(7); P(1)-
Pt(1)-P(3) ) 176.32(7); Cl(2)-Pt(2)-S ) 171.26(8); P(2)-
Pt(2)-P(4) ) 174.26(7); Pt(1)-S-Pt(2) ) 92.57(7); Pt(1)-
S-O(1) ) 118.2(4); Pt(1)-S-O(2) ) 120.2(5); Pt(2)-S-O(1)
) 118.4(4); Pt(2)-S-O(2) ) 120.4(6); O(1)-S-O(2) )
89.8(7).
Preparation of SO-bridged dimetallic complexes by
oxidation of the corresponding S-bridged complexes has
limited precedent. In addition to the palladium complex
5, one also finds Mo2(NTol)2(S2P(OEt)2)2(µ-O2CMe)(µ-
SR)(µ-SO) 929 and Mn2Cp2(CO)4(µ-SO) 10.30,31 Com-
pounds 3a , 5, the nickel complex 8 (from Ni(cod)2, dppm,
and thionyl chloride), and 9 all have pyramidal M2SO
units, whereas compound 10 has a planar M2SO unit.
The locations of the oxygen atom were disordered in 3a ,
5, and 8 but not in 9 and 10. In 10 the planar Mn2SO
unit renders it incapable of that disorder; the lack of
disorder in compound 9 was due to the two orientations
being grossly inequivalent.
Previous methods used for the preparation of the SO-
bridged complexes 5,17,18 8,19 9,29 and 1030,31 usually
needed very low temperature (-20 to -95 °C), an inert
atmosphere (under N2, 8 and 9), the avoidance of light
(9), and/or the use of a concentrated oxidizing reagent
(30% H2O2, 5). The nickel complex 8 was obtained in
characterized by NMR.25 Without the MTO catalyst, the
reaction under similar conditions is >103 times slower.
When a second equivalent of peroxide was used, the
µ-S compounds were further oxidized to the previously
known µ-SO2 complexes,14,20 4a (X ) Cl) and 4b (X )
I). These yellow compounds were isolated and purified
by column chromatography on silica gel with 5% methyl
alcohol in chloroform as eluent. The spectroscopic data
matched the known materials.26
The A-frame structure of 3a is depicted by the ORTEP
diagram shown in Figure 1. The platinum atoms exhibit
a distorted square-planar geometry, in which the bond
angles for Cl-Pt-S and P-Pt-P are 171-177°, slightly
deviant from linearity. The Pt-Pt distance in 3a , 326.9
(24) Crystallographic data for 3a : C53.33H17.33Cl12OP4Pt2S, tetrago-
nal, P41, a ) 21.1745(8) Å, b ) 21.1745(8) Å, c ) 14.2897(8) Å, V )
6406.9(5) Å3, Z ) 4, T ) 183(2) K, Dcalcd ) 1.737 Mg/m3, R(F) ) 3.89%
for 14518 independently observed (I g 2σ(I)) reflections (3° e 2θ e
57°). All hydrogen atoms were included in the structure factor
calculation at idealized positions and were allowed to ride on the
neighboring atoms with relative isotropic displacement coefficients. The
oxygen atom is disordered over two positions in a 66:34 ratio. There
are also 3.33 solvate molecules of chloroform in the asymmetric unit.
All software and sources of the scattering factors are contained in the
SHELXTL (version 5.1) program library (G. Sheldrick, Bruker Analyti-
cal X-ray Systems, Madison, WI, 1988).
(27) Balch, A. L.; Benner, L. S.; Olmstead, M. M. Inorg. Chem. 1979,
18, 2996.
(28) Kubiak, C. P.; Eisenberg, R. J . Am. Chem. Soc. 1977, 99,
6129.
(29) Wang, R.; Mashuta, M. S.; Richardson, J . F.; Noble, M. E. Inorg.
Chem. 1996, 35, 3022.
(30) Lorenz, I.-P.; Messelha¨user, J .; Hiller, W.; Conrad, M. J .
Organomet. Chem. 1986, 316, 228.
(25) 1H NMR/CDCl3: δ 7.00-7.90 (aromatic, m, 40 H), 4.48 (CH2,
m, 2 H), 2.61 (CH2, m, 2 H) ppm. 31P NMR/CDCl3: δ 12.66, 9.88 ppm.
(26) Changquing, Y.; Sharp, P. R. Inorg. Chem. 1995, 34, 55.
(31) Lorenz, I.-P.; Messelha¨user, J .; Hiller, W.; Haug, K. Angew.
Chem., Int. Ed. Engl. 1985, 24, 228.

5422 Organometallics, Vol. 18, No. 25, 1999
Ta ble 1. Selected Str u ctu r a l P a r a m eter s for 3a a n d 5-8
Notes
dM-X/pm
M‚‚‚M
complex
M-Cl
M-S
M-P
M-S-M
Pt2Cl2(µ-SO)(µ-dppm)2 3a
Pd2Cl2(µ-SO)(µ-dppm)2 5a
Pd2Cl2(µ-SO2)(µ-dppm)2 6a b,c
Pd2Cl2(µ-SO2)(µ-dppm)2 6bb,c
Pd2Cl2(µ-S)(µ-dppm)2 7c
327.0(2)
322.5(4)
338.3(4)
322.0(4)
325.8(2)
330.8(1)
241.1(1)
240.2(9)
238.1(4)
238.1(4)
237.2(5)
237.2(5)
226.2(2)
227.3(5)
223.4(4)
224.1(4)
229.8(5)
212.7(2)
231.5(2)
233.7(7)
234.4(4)
235.9(19)
231.6(13)
222.7(12)
92.57(7)
90.4(3)
98.4(4)
91.9(4)
90.3(2)
NiCl2(µ-SO)(µ-dppm)2 8d
101.98(7)
a
b
d
References 17, 18. 6a , 6bstwo independent molecules. c Reference 27. Reference 19.
20-25% yield, compared to 60-95% for the others.
Complexes 5 and 9 decompose quickly when taken out
of solution or exposed to air or light. The µ-SO complexes
of platinum, 3a and 3b, are very stable as crystals and
in solution. They are not sensitive to laboratory light
or oxygen and can be kept unchanged for months. The
oxidation of the µ-S complexes by H2O2/MTO provides
the superior means for generating them. This reaction
proceeds in air in a few minutes at room temperature,
affording a product that can be isolated and purified in
high yield.
Su m m a r y. This research has provided the first
examples of sulfur monoxide-bridged diplatinum phos-
phines. Direct insertion of sulfur monoxide was used,
as was the oxidation of the µ-S compound with hydrogen
peroxide in an MTO-catalyzed reaction. To our knowl-
edge, this is the first µ-SO compound prepared by direct
insertion of sulfur monoxide into a metal-metal bond.
The structure was confirmed spectroscopically and
crystallographically.
Complexes 1 are known to react with S and SO2 to
yield, respectively, 2, Y ) S, and 4, Y ) SO2. Trapping
by 1 of the SO released during reaction 1 also provides
1
the µ-SO product, confirmed by comparison of the H
NMR spectra. In a typical experiment 4,4′-difluo-
rothiobenzophenone S-oxide (40 mM) and MTO (12 mM)
were dissolved in acetonitrile containing 0.1 M trifluo-
romethanesulfonic acid. Hydrogen peroxide (80 mM)
was added, followed by 1a (7.5 mM). After 1.5 h, during
Ack n ow led gm en t. This research was supported by
a grant from the National Science Foundation (CHE-
9625349). Some experiments were conducted with the
use of the facilities of the Ames Laboratory.
1
which time the H spectrum was monitored, 1.0 mM 3a
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
cedures for the synthesis of and spectroscopic data for 3a ,b
and 4a ,b, and X-ray diffraction data for 3a . This material is
available free of charge via the Internet at http://pubs.acs.org.
was found in the reaction mixture. The various reactions
are shown in eqs 1, 2, and 4. The low yield of the desired
product is a consequence of the SO trap, 1a , itself being
rapidly oxidized by H2O2/MTO, a point that was inde-
pendently confirmed.
OM9905815