Formation of an iron(II) carbene-thiolato complex by insertion of carbon monoxide into an Si-C bond

Article abstract of DOI:10.1002/anie.200352916

Fischer carbenes - a new angle: The insertion of carbon monoxide into an Si-C bond of the Fe^II complex 1, which contains a tripodal thiolato ligand (see scheme), yields the Fischer carbene-thiolato complex 2, whose molecular structure reveals the presence of a bonding interaction between the carbene carbon atom and the thiolato sulfur atoms.

Full text of DOI:10.1002/anie.200352916

Communications
Carbene Complexes
Formation of an Iron(ii) Carbene–Thiolato
Complex by Insertion of Carbon Monoxide into
À
an Si C Bond**
Masahiro Yuki, Tsukasa Matsuo, and
Hiroyuki Kawaguchi*
The carbene carbon atom in Fischer carbene complexes is
well known to be susceptible to nucleophilic attack. Hence,
complexes A bearing both Fischer carbene and thiolato
ligands would be in equilibrium with the thiametalacyclopro-
pane form B.[1] Although the existence of an equilibrium
between A and B was supported by NMR spectroscopy and
reactivity studies,[1a] such complexes are scarce.[2–4] A possible
reason for this paucity lies in facile intramolecular nucleo-
philic substitution to form the RS-substituted carbene com-
plex C.
Scheme 1. Synthesis of 1–3. a) 3BuLi then [Fe(CF3SO3)2(CH3CN)2],
THF; b) CO, THF, À488C; c) THF, RT.
An X-ray crystallographic study of 1 (Figure 1) showed
that the iron atom is bound to the three sulfur donors and one
À
THF molecule with an average Fe S distance of 2.301 Š and
In our studies of transition-metal complexes of thiolato
ligands,[5] we designed and synthesized the tridentate ligand
[
TMSS3Si]3À (H3[TMSS3Si] = tris(3-trimethylsilyl-2-mercaptophe-
nyl)methylsilane).[6] On attempting to carbonylate an iron(ii)
complex of [TMSS3Si]3À, namely 1, we encountered an unex-
pected formation of a stable Fischer carbene–thiolato com-
plex 3 (Scheme 1). Intriguingly, 3 exhibits a bonding inter-
action of the Fischer carbene carbon atom with the thiolato
ligand.[7]
Figure 1. Structure of the anion of 1 with 50% ellipsoids. Selected
À
À
bond lengths [Š] and angles [8]: Fe S(1) 2.2798(9), Fe S(2) 2.3097(9),
À
À
Fe S(3) 2.3129(9), Fe O 2.130(2); S(1)-Fe-S(2) 106.02(3), S(1)-Fe-S(3)
112.00(3), S(2)-Fe-S(3) 122.62(3), S(1)-Fe-O 100.81(6), S(2)-Fe-O
110.13(7), S(3)-Fe-O 103.14(7).
Treatment of [Fe(CF3SO3)2(CH3CN)2]with 1 equiv of
Li3(TMSS3Si) followed by cation exchange with PPh4Br
afforded PPh4[Fe(TMSS3Si)(thf)]( 1). The magnetic moment
of 1 is typical of tetrahedral FeII centers (meff = 4.77 mB).
Despite line-broadening and a paramagnetic shift of the
resonances, the 1H NMR spectrum exhibits five signals
ascribed to the [TMSS3Si]3À ligand, and this suggests that the
solution structure is consistent with C3 symmetry.
[8]
À
an Fe O distance of 2.130(2) Š. The iron center has a
tetrahedral environment with slight compression of the S-Fe-
S angles (av 113.58). The S-Fe-O angles average 104.78. The
bridging Si(1) atom assumes a tetrahedral geometry, and the
atoms Fe and Si(1) are separated by 3.3701(9) Š. The strain in
the eight-membered {FeS2C4Si} ring of 1 is relieved by
propeller twisting of the [TMSS3Si]3À ligand, which leads to
average S-Fe-Si-C torsion angles of 41.98.
Complex 1 smoothly reacted with 1 atm of CO in THF at
À488C to give the diamagnetic carbonyl derivative
(PPh4)[Fe(TMSS3Si)(CO)3] (2). The 1H NMR spectrum of 2
indicates that the symmetric coordination of the [TMSS3Si]3À
ligand is retained. The 13C{1H} NMR resonance of the
carbonyl ligands is found at d = 209.6 ppm. The IR spectrum
of 2 displays two carbonyl stretching bands at 2052 and
[*] Dr. M. Yuki, Dr. T. Matsuo, Prof. Dr. H. Kawaguchi
Coordination Chemistry Laboratories
Institute for Molecular Science
Myodaiji, Okazaki, 444-8585 (Japan)
Fax: (+81)564-55-5245
E-mail: hkawa@ims.ac.jp
[**] This work was supported by a Grant-in-Aid for Scientific Research
(No. 14703008) and Priority Areas (No. 14078101 “Reaction Con-
trol of Dynamic Complexes”) from Ministry of Education, Culture,
Sports, Science, and Technology, Japan.
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DOI: 10.1002/anie.200352916
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Angewandte
Chemie
1990 cmÀ1, indicative of a facial tricarbonyl geometry. Com-
plex 2 is stable at low temperature, but is unstable in solution
at ambient temperature. On warming to room temperature,
the red solution gradually turned green, and complete
conversion to complex 3 occurred.
of doublets (2JC,C = 11, 7 Hz) and is accompanied by two
doublets of doublets ascribed to two terminal carbonyl
ligands at d = 213.6 (J = 11, 2 Hz) and 220.1 ppm (J = 7,
2 Hz). The chemical shift of the carbene carbon atom shows
that this center is shielded relative to typical Fischer carbene
complexes (220–350 ppm),[13] a difference that may arise from
the interaction between the carbene carbon atom and the
thiolato sulfur atom. In the IR spectrum, the carbonyl bands
of 3 (1993, 1928 cmÀ1) are at lower wavenumber than those of
2 because of the higher s-donor/p-acceptor ratio of the
carbene ligand relative to CO.
The crystal structure of 3 revealed an unprecedented
Fischer carbene–thiolato complex (Figure 2).[8] The coordi-
Scheme 2 shows the likely sequence of events in the
formation of 3 from 2. This transformation is presumed to
Figure 2. Structure of the anion of 3 with 50% ellipsoids. Selected
À
À
bond lengths [Š] and angles [8]: Fe S(1) 2.334(1), Fe S(2) 2.299(1),
À
À
À
À
Fe S(3) 2.281(1), Fe C(29) 1.981(4), Fe C(30) 1.818(5), Fe C(31)
À
À
À
1.745(5), S(2) C(29) 1.872(4), Si(1) O(1) 1.652(3), O(1) C(29)
À
1.409(5), C(21) C(29) 1.487(6); S(1)-Fe-S(2) 97.96(5), S(1)-Fe-S(3)
170.21(5), S(2)-Fe-S(3) 87.32(6), S(2)-Fe-C(29) 51.2(1), S(2)-Fe-C(30)
107.8(2), C(29)-Fe-C(31) 96.1(2), C(30)-Fe-C(31) 104.9(2), Fe-S(2)-
C(29) 55.6(1), Fe-C(29)-S(2) 73.2(2), Fe-C(29)-O(1) 126.0(3), Fe-C(29)-
C(21) 117.2(3), S(2)-C(29)-O(1) 114.8(3), S(2)-C(29)-C(21) 110.2(3),
O(1)-C(29)-C(21) 109.5(3).
Scheme 2. Proposed mechanism for the transformation of 2 into 3.
involve loss of one CO ligand and h1/h3 rearrangement of one
nation environment of the iron center is best described as
distorted octahedral, with two mutually cis carbonyl ligands
and a new [TMSS3Si]-derived tetradentate ligand in which the
original trithiolato ligand has been transformed into a
of the arylthiolate groups, followed by migratory insertion of
À
the CO ligand into an Si C bond and subsequent capture of
the liberated CO. This would yield an acyl intermediate with a
dearomatized ring, which could then undergo a net [1,3]-silyl
migration to give a carbene species due to the high
oxophilicity of the silicon atom. In arylthiolato complexes
p coordination at the aryl substituent is uncommon. However,
our recent finding that the arylthiolato ligand SC6H3-2,6-
(SiMe3)2 can bind to the metal center though the aryl moiety
could provide support for the h1/h3 rearrangement of this
proposed mechanism.[5] Although carbonylation of early
transition-metal and actinide complexes is well known to
À
carbene–trithiolato moiety by insertion of CO into an Si C
À
bond. The Fe C(29) bond length of 1.981(4) Š is at the long
[9]
À
end of known Fe C(carbene) bonds, and the C(29) atom
has trigonal-planar geometry, as evidenced by the sum of
À
angles at C(29) of 352.78. The Fe S bond lengths, which range
from 2.299(1) to 2.334(1) Š, are typical of low-spin FeII
thiolato complexes.[10] It is noteworthy that the thiolato
sulfur atom S(2) is in close proximity to the carbene carbon
atom C(29), although the separation of 1.872(4) Š is longer
À
produce enolate complexes via insertion of CO into Si C
3
[11]
than a normal C S single bond (C(sp ) S 1.82 Š). Longer
À
bonds,[14] this kind of intramolecular transformation is rare for
late-transition-metal complexes. Recently, it was reported
À
À
C S bonds (1.87–1.92 Š) have been observed for sulfur atoms
bonded to spiro carbon atoms.[12] This structural feature
suggests that substantial bonding interaction occurs between
the vacant p orbital of the carbene carbon atom and the lone
pair of the thiolato sulfur atom. This notion is also supported
that a platinum complex with Ph2P NSiMe3 ligands under-
=
À
went insertion of CO into the N Si bond and subsequent
migration of the SiMe3 group to generate an N,O-substituted
carbene.[15]
À
by the elongation of the C(29) O(1) distance (1.409(5) Š)
relative to those of Fischer carbene complexes.
To gain some insight into the kinetics of the formation of
3, we monitored the disappearance of CO stretching absorp-
tions in the IR spectrum of 2 from 277 to 296 K. The resulting
data gave first-order plots with excellent correlation coeffi-
cients (R2 > 0.997). An Arrhenius plot yielded values of
DH° = 125.3 Æ 3.3 kJmolÀ1 and DS° = 122 Æ 11 JmolÀ1 KÀ1.
Together with the observation that the rate of the reaction
Spectroscopic data of 3 are consistent with the solid-state
structure. The 1H NMR spectrum reveals a total lack of
symmetry in solution, as evidenced by three SiMe3 singlets. In
the 13C{1H} NMR spectrum of 3-13C, prepared with 13CO, the
carbene carbon atom resonates at d = 128.6 ppm as a doublet
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Communications
is slower in the presence of CO, the positive entropy of
Keywords: carbene ligands · insertions · iron · S ligands ·
tripodal ligands
.
activation suggests a rate-limiting step involving CO loss from
2. The formation of 3 might be driven by strain in the large
chelate rings in 2.
Finally, preliminary reactivity studies were carried out
with 3. Treatment of 3 with 1 equiv of methyl iodide gave a
mixture of three products in which one of the three thiolato
donors of the [TMSS3Si]3À ligand was methylated according to
NMR spectroscopic data. The carbene moiety remains intact
during the course of the reaction, in which a dithio(thioe-
ther)carbene ligand is formed. On the other hand, complex 3
was inert toward nucleophiles such as PEt3.
[1]a) G. N. Glavee, R. J. Angelici, J. Am. Chem. Soc. 1989, 111,
3598 – 3603; b) D. Steinborn, Angew. Chem. 1992, 104, 392 – 412;
Angew. Chem. Int. Ed. Engl. 1992, 31, 401 – 421.
[2]A variety of thiametallacyclopropane complexes has been
reported: a) K. Miki, Y. Kai, N. Yasuoka, N. Kasai, Bull.
Chem. Soc. Jpn. 1981, 54, 3639 – 3647; b) E. Rudulfo de Gil, L. F.
Dahl, J. Am. Chem. Soc. 1969, 91, 3751 – 3756; c) R. A. Doyle,
R. J. Angelici, J. Organomet. Chem. 1989, 375, 73 – 84; d) F. R.
Kreißl, N. Ullrich, J. Organomet. Chem. 1992, 440, 335 – 339.
[3]N-Heterocyclic carbene complexes containing thiolato ligands
are known: a) R. F. R. Jazzar, P. H. Bhatia, M. F. Mahon, M. K.
Whittlesey, Organometallics 2003, 22, 670 – 683; b) D. Sellmann,
W. Prechtel, F. Knoch, M. Moll, Inorg. Chem. 1993, 32, 538 – 546.
[4]A carbene complex with 1,1-ethylenedithiolato ligands was
recently reported: J. Vincente, M. T. Chicote, S. Huertas, P. G.
Jones, Inorg. Chem. 2003, 42, 4268 – 4274.
In summary, we have synthesized the novel iron(ii)
trithiolato complex 1 containing the tripodal [TMSS3Si]3À
ligand. Carbene–thiolato complex 3 was prepared by reaction
À
of 1 with CO, in which insertion of CO into an Si C bond took
place. Since the coordinated THF molecule of 1 is labile, the
trithiolato complex 1 could be a useful reagent for exploring
the chemistry of iron–sulfur compounds relevant to the active
sites in metalloenzymes. We are currently investigating the
reactivity of 1 and 3.
[5]T. Komuro, T. Matsuo, H. Kawaguchi, K. Tatsumi, J. Am. Chem.
Soc. 2003, 125, 2070 – 2071.
[6]The synthesis of H
[
TMSS3Si]is based on the well-known ortho-
3
lithiation of lithium thiophenolate by nBuLi/N,N,N’,N’-tetrame-
thylethylenediamine in hexane: a) G. D. Figuly, C. K. Loop, J. C.
Martin, J. Am. Chem. Soc. 1989, 111, 654 – 668; b) E. Block, V.
Eswarakrishnan, M. Gernon, G. Ofori-Okai, C. Saha, K. Tang, J.
Zubieta, J. Am. Chem. Soc. 1989, 111, 658 – 665; c) M. Yuki, T.
Komuro, T. Matsuo, H. Kawaguchi, K. Tatsumi, unpublished
reasults.
Experimental Section
1: A solution of Li3[TMSS3Si], prepared by reaction of H3[TMSS3Si]
(428 mg, 0.729 mmol) with BuLi (1.58m, 1.42 mL, 2.21 mmol) in THF
(10 mL), was added to [Fe(CF3SO3)2(CH3CN)2](317 mg,
0.728 mmol). The mixture was stirred for 15 min at room temper-
ature, and a solution of PPh4Br (305 mg, 0.727 mmol) in CH3CN
(3.5 mL) was added. After removal of the solvent in vacuo, recrystal-
lization of the residue from THF/Et2O afforded pale-yellow rods of 1
(643 mg, 84%); elemental analysis (%) calcd for C56H67FeOPS3Si4: C
63.97, H 6.42, S 9.15; found: C 63.83, H 6.53, S 8.67; 1H NMR
([D8]THF, 500 MHz, 238C): d = 20.1 (br, w1/2 = 21 Hz, 3H), 17.7 (br,
[7]A bonding interaction between a carbene carbon atom and a
neighboring chloro ligand was recently reported for the N-
heterocyclic carbene complex of trichlorooxovanadium(v): C. D.
Abernethy, G. M. Codd, M. D. Spicer, M. K. Taylor, J. Am.
Chem. Soc. 2003, 125, 1128 – 1129.
[8]Crystal data for 1: C56H67FeOPS3Si4, Mr = 1051.49, crystal
dimensions 0.40 ” 0.25 ” 0.10 mm, a = 26.090(5), b = 14.900(3),
c = 29.470(6) Š, b = 100.560(3)8, V= 11262(4) Š3, monoclinic,
C2/c (no. 15), Z = 8, 1calcd = 1.240 gcmÀ3, F(000) = 4448, m =
5.29 cmÀ1, 42749 measured, 12534 independent, 9455 observed
reflections (F2o > 2sFo2), R1(observed data) = 0.054, wR2(all
data) = 0.137; Crystal data for 3: C55H59FeOPS3Si4, Mr =
1063.41, crystal dimensions 0.45 ” 0.10 ” 0.03 mm, a = 18.717(7),
b = 15.436(6), c = 20.571(8) Š, b = 109.550(4)8, V= 5601(4) Š3,
monoclinic, P21/n (no. 14), Z = 4, 1calcd = 1.261 gcmÀ3, F(000) =
2232, m = 5.35 cmÀ1, 44131 measured, 12801 independent, 7564
observed reflections (Fo2 > 2sFo2), R1(observed data) = 0.075,
wR2(all data) = 0.189. Rigaku Saturn CCD system (1) or
Murcury CCD system (3), MoKa radiation (l = 0.71070 Š),
graphite monochromator, T= 173 K; the structures were
solved by direct methods and refined against F2 for all
independent reflections (heavy atoms with anisotropic temper-
ature factors, H atoms located at calculated positions with
isotropic temperature factors); CCDC-219529 (1) and -219530
(3) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cam-
bridge Crystallographic Data Centre, 12, Union Road, Cam-
bridge CB21EZ, UK; fax: (+ 44)1223-336-033; or deposit@
ccdc.cam.ac.uk).
w
1/2 = 40 Hz, 3H), 8.35 (br, 8H, PPh4+), 8.09 (br, 12H, PPh4+), 6.99
(br, w1/2 = 38 Hz, 27H), À2.90 (br, w1/2 = 27 Hz, 3H), À25.3 ppm (br,
w1/2 = 24 Hz, 3H); magnetic moment: meff = 4.77 mB.
2: A solution of 1 (368 mg, 0.35 mmol) in THF (3 mL) was treated
with 1 atm of CO at À488C for 1 h. The red solution was concentrated
and layered with Et2O at À488C to give 2 (306 mg, 82%) as red
plates; elemental analysis (%) calcd for C55H59FeO3PS3Si4: C 62.12, H
5.59, S 9.05; found: C 61.95, H 5.93, S 8.30; IR (KBr): n˜(CO) = 2052
(s), 1990 cmÀ1 (s); 1H NMR ([D8]THF, 500 MHz, À308C): d = 8.0–7.6
(br, 20H, PPh4+), 7.19 (d, J = 7.3 Hz, 3H, ArH), 7.14 (J = 6.8 Hz, 3H,
ArH), 6.75 (dd, J = 6.8, 7.3 Hz, 3H, ArH), 0.40 (s, 3H, SiMe),
0.27 ppm (s, 27H, SiMe3). 13C{1H} NMR ([D8]THF, 125 MHz,
À308C): d = 209.6 (CO). 29Si{1H} NMR ([D8]THF, 99 MHz, À308C)
d = À7.6 (SiMe3), À18.9 ppm (SiMe).
3: A solution of 2 (306 mg, 0.288 mmol) in THF (7 mL) was
stirred for 2 h at room temperature. The resulting green solution was
evaporated to dryness. The residue was washed with Et2O and
recrystallized from THF/Et2O to give 3 as green plates (229 mg,
75%); elemental analysis (%) calcd for C55H59FeO3PS3Si4: C 62.12, H
5.59, S 9.05; found: C 61.85, H 5.69, S 8.83; IR (KBr): n˜(CO) = 1993
(s), 1928 cmÀ1 (s); 1H NMR ([D8]THF, 500 MHz): d = 8.0–7.5 (m,
20H, PPh4+), 7.64 (d, J = 7.3 Hz, 1H), 7.34 (d, J = 6.7 Hz, 1H), 7.28 (d,
J = 6.7 Hz, 1H), 7.19 (d, J = 7.3 Hz, 1H), 7.16 (d, J = 7.3 Hz, 1H), 6.89
(m, 2H), 6.83 (d, J = 7.3 Hz, 1H), 6.55 (m, 1H), 0.62 (s, 3H, SiMe),
0.331 (s, 9H, SiMe3), 0.325 (s, 9H, SiMe3), 0.28 ppm (s, 3H, SiMe3);
13C{1H} NMR ([D8]THF, 3-13C): d = 219.8 (2JC,C = 11, 2 Hz, CO), 213.3
(J = 7, 2 Hz, CO), 128.9 ppm (J = 11, 7 Hz, Ccarbene); 29Si NMR (DEPT,
[D8]THF, 99 MHz): d = À5.0, À6.3, À8.4 (SiMe3), À15.1 ppm (SiMe).
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