Reactions of (Silyl) (silylene) tungsten and -molybdenum complexes with sulfur reagents

Article abstract of DOI:10.1021/om100875h

Reaction of (silyl)(silylene)tungsten complex Cp*(OC) ₂W(SiMe₃)(=SiMes₂) (1) with sulfur reagents, S₈ and ethylene sulfide 4, afforded cyclic carbene tungsten complex Cp*(S)W{=C(SiMe₃)C(=O)OSi(Mes)₂S} (3) via C=O bond fission of a carbonyl ligand and 1,2-migration of the SiMe₃ group from W to the resulting carbene carbon. In contrast to the tungsten complex, reaction of (silyl)(silylene)molybdenum complex Cp*(OC) ₂Mo(SiMe₃)(=SiMes₂) (2) with 4 gave η²-thiocarbonyl complex Cp*(S)Mo[{η²-S= C(SiMe₃)}C(=O)OSi(Mes)₂S] (5), which would be formed by addition of a sulfur atom to the Mo=C bond of a molybdenum analogue of 3.

Full text of DOI:10.1021/om100875h

6624 Organometallics 2010, 29, 6624–6626
DOI: 10.1021/om100875h
Reactions of (Silyl)(silylene)tungsten and -molybdenum Complexes
with Sulfur Reagents
Takako Muraoka, Tomoko Nakamura, Atsushi Nakamura, and Keiji Ueno*
Department of Chemistry and Chemical Biology, Graduate School of Engineering,
Gunma University, Kiryu 376-8515, Japan
Received September 9, 2010
Summary: Reaction of (silyl)(silylene)tungsten complex Cp*-
caused the elimination of the silylene fragment to give
[Cp*(Me3P)2Os-S-S-Os(PMe3)2Cp*][B(C6F5)4]2 and un-
identified organosilicon compounds.5
(OC)2W(SiMe3)(dSiMes2) (1) with sulfur reagents, S8 and
ethylene sulfide 4, afforded cyclic carbene tungsten complex
Cp*(S)W{dC(SiMe3)C(dO)OSi(Mes)2S} (3) via CdO bond
fission of a carbonyl ligand and 1,2-migration of the SiMe3
group from W to the resulting carbene carbon. In contrast to
the tungsten complex, reaction of (silyl)(silylene)molybdenum
complex Cp*(OC)2Mo(SiMe3)(dSiMes2) (2) with 4 gave η2-
thiocarbonyl complex Cp*(S)Mo[{η2-SdC(SiMe3)}C(dO)-
OSi(Mes)2S] (5), which would be formed by addition of a
sulfur atom to the ModC bond of a molybdenum analogue of 3.
We have reported the synthesis, structure, and properties
of (silyl)(silylene) complexes LnM(SiR3)(dSiR2) (M = Mo,
W, Fe; R = alkyl, aryl).6 These complexes are categorized as
silylene complexes, but show unique reactivity attributable to
the cooperation of the silyl and silylene ligands in the com-
plexes, such as 1,3-R group shift from the silyl to the silylene
ligand and 1,2-silyl shift from the metal to the silylene ligand.
This prompted us to investigate the reactivity of (silyl)(sily-
lene) complexes with sulfur reagents. In this paper, we report
the reaction of (silyl)(silylene)tungsten and -molybdenum
complexes Cp*(OC)2M(SiMe3)(dSiMes2) (1, M = W; 2,
M = Mo; Mes = 2,4,6-(CH3)3C6H2) with sulfur reagents. This
reaction did not cause silylene elimination, as mentioned above
for the silylene Os complex,5 but gave a cyclic carbene complex
and its sulfur adduct in which the silylene fragment remains in
the metallacycle core. Bond fission of a carbonyl ligand also took
place during the reaction to form the carbene ligand.
The reaction of transition metal carbene complexes LnMd
CR2 with sulfur reagents has been investigated intensively,
which afforded a variety of sulfur-containing metal com-
plexes and organic compounds via the initial formation of
η1- or η2-thiocarbonyl-coordinated complexes by addition of
sulfur to the MdC bond.1-3 In contrast to the carbene com-
plexes, only two examples have been reported so far on the
reaction of heavier congeners of carbene complexes, namely,
silylene and germylene complexes LnMdER2 (E = Si, Ge) with
sulfur reagents.4,5 The reaction of germylene complexes P2Pdd
Ge{N(SiMe3)2}2 (P2 = 2PEt3, 2PPh3, Ph2P(CH2)2PPh2) with
COS afforded metallacycles containing Pd, Ge, and S atoms via
addition of S to the PddGe bond.4 As opposed to the germylene
complex, the reaction of silylene Os complex [Cp*(Me3P)2Osd
SiiPr2][B(C6F5)4] (Cp* = η5-C5Me5) with elemental sulfur
Treatment of 1 with S8 in THF at 25 °C for 5 h afforded
cyclic carbene tungsten complex Cp*(S)W{dC(SiMe3)C-
(dO)OSi(Mes)2S} (3) in 65% yield (eq 1). Complex 3 was
also obtained by the reaction of 1 with excess ethylene sulfide
4, although a longer reaction time was required for comple-
tion (C6D6, rt, 26 days). Crystal structure analysis of 3
(Figure 1) revealed the three-legged piano-stool geometry
at the metal, two of which constitute a metallacyclohexene
*To whom correspondence should be addressed. Tel & fax: þ81-277-
30-1260. E-mail: ueno@chem-bio.gunma-u.ac.jp.
˚
fragment. The WdC(32) bond distance (1.935(4) A) is at the
shorter limit for those of typical WdC double bonds in the
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7
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8
˚
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pubs.acs.org/Organometallics
Published on Web 11/22/2010
2010 American Chemical Society

Communication
Organometallics, Vol. 29, No. 24, 2010 6625
Mo-(η2-SdC) cyclic complex Cp*(S)Mo[{η2-SdC(SiMe3)}-
C(dO)OSi(Mes)2S] (5) in 52% yield (eq 2). Elemental anal-
ysis is consistent with the composition of 5. The crystal
structure analysis clearly revealed the Mo-(η2-SdC) cyclic
structure of 5 shown in Figure 2; however, the low quality of
the crystal hampered a detailed discussion (Rw = 0.1547).
The spectroscopic data also support the structure of 5. The
13C NMR resonances assignable to the Mo-(η2-SdC) and
ester carbonyl carbons were observed at 89 and 177 ppm,
respectively, which are within the usual ranges of chemical
shift values in Mo-(η2-SdC) (80-103 ppm)12 and Mo-C-
CO2R (171-178 ppm),13 respectively. The IR spectrum
showed the stretching absorptions of ester carbonyl and
ModS at 1701 and 485 cm-1, respectively.13,14 Complex 5
showed two sharp singlet signals assignable to the o-Me
1
groups at 2.96 and 2.90 ppm in the H NMR spectrum at
293 K, indicating free rotation of the ipso-C-Si bond of the
Mes groups.
Figure 1. ORTEP drawing of 3 (50% probability level). Hydro-
˚
gen atoms are omitted for clarity. Selected bond lengths (A) and
angles (deg): W-C(32) 1.935(4), W-S(1) 2.1476(13), W-S(2)
2.3784(16), S(1)-W-S(2) 110.12(5), S(1)-W-C(32) 104.31(13),
W-C(32)-Si(2) 127.7(2), W-C(32)-C(33) 119.9(3), Si(2)-
C(32)-C(33) 112.3(3).
sum of the three bond angles around C(32) is 360(1)°, which
implies the sp2 hybridization of C(32). The WdS(1)
˚
˚
(2.1476(13) A) and W-S(2) (2.3784(16) A) bond distances
9
˚
are comparable to those of the usual WdS (2.13-2.16 A)
and W-S (2.26-2.52 A)
9b,d,10
Complex 5 seems to form by addition of a sulfur atom to
the ModC bond of a Mo analogue of complex 3, although
such a complex was not detected during the reaction of
complex 2 with excess 4 in C6D6. Attempts to synthesize
the Mo analogue of complex 3 by sulfur abstraction from
˚
bonds, respectively. The
structure of 3 is also supported by spectroscopic data. The
13C NMR spectrum showed resonances for the carbene and
ester carbonyl carbons at 264 and 169 ppm, respectively,
which are within the reported chemical shift ranges corre-
sponding to WdC(SiMe3) (235-276 ppm)8 and W-C-
CO2R (163-181 ppm),11 respectively. In the IR spectrum,
stretching absorptions for the ester carbonyl and WdS were
observed at 1676 and 489 cm-1, respectively.9,11 The 1H
NMR spectrum at 293 K showed a broad signal around
2.8 ppm, which is assignable to o-Me of the Mes groups. The
signal varied from four sharp singlet signals at 213 K to two
sharp singlet signals at 313 K. These spectral changes are
attributable to the restricted rotation of the ipso-C-Si bond
of Mes groups.
15
complex 5 with excess PMe3 in C6D6 at 25 °C failed and
resulted in complete consumption of complex 5 with the
formation of a mixture of SdPMe3 and unidentified com-
plexes. Efforts of sulfur addition to complex 3 to provide a W
analogue of complex 5 were also unsuccessful. The reaction
of complex 3 with excess S8 in C6D6 at 25 °C for 26 days
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Chem. 1999, 592, 46. (b) Malisch, W.; Grun, K.; Fey, O.; Baky, C. A. E.
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C. H. J. Am. Chem. Soc. 1987, 109, 2022. (b) Chen, C.-C.; Fan, J.-S.; Shieh,
S.-J.; Lee, G.-H.; Peng, S.-M.; Wang, S.-L.; Liu, R.-S. J. Am. Chem. Soc.
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Lee, G.-H.; Wang, Y. Organometallics 1997, 16, 4636. (d) Malisch, W.;
Grun, K.; Fried, A.; Reich, W.; Pfister, H.; Huttner, G.; Zsolnai, L.
J. Organomet. Chem. 1998, 566, 271.
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Pizzano, A.; Ruiz, C.; Sanchez, L.; Carmona, E. Inorg. Chem. 1993, 32,
5569. (b) Schenk, W. A.; Rub, D.; Burschka, C. J. Organomet. Chem. 1987,
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Nolan, S. P.; Musaev, D. G.; Morokuma, K. J. Am. Chem. Soc. 1998,
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In contrast to the tungsten complex 1, the reaction
of molybdenum complex 2 with excess 4 in toluene for 8 h
did not afford the corresponding carbene complex but
(9) (a) Faller, J. W.; Kucharczyk, R. R.; Ma, Y. Inorg. Chem. 1990,
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6626 Organometallics, Vol. 29, No. 24, 2010
Muraoka et al.
It should be noted that the transformation proceeds via a
CdO bond fission of one carbonyl ligand16 and migration of
the SiMe3 group to the resulting carbene carbon. The con-
version would start by addition of a sulfur atom to the MdSi
bond to give a M-Si-S three-membered complex that is
similar to that observed for the reaction of germylenepalla-
dium complexes with COS.4 However, the detailed forma-
tion mechanism of complexes 3 and 5 is unclear at present.
Mechanistic aspects as well as reactions with other group 16
elements are under investigation.
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research (Nos. 20655011 and 21750056)
from the Ministry of Education, Culture, Sports, Science and
Technology of Japan.
Supporting Information Available: Text, tables, figures, and a
CIF file on experimental details and X-ray crystallographic
data. This material is available free of charge via the Internet
at http://pubs.acs.org.
Figure 2. ORTEP drawing of 5 (50% probability level). Hydro-
gen atoms are omitted for clarity.
(16) There are only a few reports on the CdO cleavage of carbonyl
ligand on transition metal complexes in which both oxygen and carbon
atoms remain in the resulting complexes: (a) Neithamer, D. R.;
Lapointe, R. E.; Wheeler, R. A.; Richeson, D. S.; Van Duyne, G. D.;
Wolczanski, P. T. J. Am. Chem. Soc. 1989, 111, 9056. (b) Miller, R. L.;
Wolczanski, P. T.; Rheingold, A. L. J. Am. Chem. Soc. 1993, 115, 10422. (c)
Chisholm, M. H.; Hammond, C. E.; Johnston, V. J.; Streib, W. E.; Huffman,
J. C. J. Am. Chem. Soc. 1992, 114, 7056. (d) Dyson, P. J.; Johnson, B. F. G.;
Martin, C. M.; Braga, D.; Grepioni, F. J. Chem. Soc., Chem. Commun. 1995,
771. (e) Adams, H.; Gill, L. J.; Morris, M. J. Organometallics 1996, 15, 464.
(f ) Su, C.-J.; Su, P.-C.; Chi, Y.; Peng, S.-M.; Lee, G.-H. J. Am. Chem. Soc.
1996, 118, 3289.
caused a 10% decomposition of complex 3 without any
isolable products. These results exhibited significant differ-
ences in the sulfur affinity between ModC and WdC bonds.
A tendency similar to our results was also reported in the
sulfur addition reaction of ferrocenyl aminocarbene molyb-
denum and tungsten complexes. Thus, carbene molybdenum
complexes reacted readily (∼5 min) to give the correspond-
ing thioamide complexes, while tungsten analogues required
a much longer reaction time (∼24 h).3f