Unusual coordination modes of arylthiolates in Mo{η5-SC6H3-2,6- (SiMe3)2}{η7-SC6 H3-2,6-(SiMe3)2}

Article abstract of DOI:10.1021/ja029541+

Treatment of MoCl₃(thf)₃ with LiSC₆H₃-2,6-(SiMe₃)₂ (LiSAr) resulted in formation of the π-sandwiched bis-arylthiolato complex, Mo{η⁵-SC₆H₃-2,6-(SiMe₃

Full text of DOI:10.1021/ja029541+

Published on Web 02/01/2003
Unusual Coordination Modes of Arylthiolates in
Mo{η5-SC6H3-2,6-(SiMe3)2}{η7-SC6H3-2,6-(SiMe3)2}
Takashi Komuro,† Tsukasa Matsuo,‡ Hiroyuki Kawaguchi,*,‡ and Kazuyuki Tatsumi*,†
Research Center for Materials Science, and Department of Chemistry, Graduate School of Science,
Nagoya UniVersity, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan, and Coordination Chemistry Laboratories,
Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan
Received December 2, 2002 ; E-mail: i45100a@nucc.cc.nagoya-u.ac.jp; hkawa@ims.ac.jp
Although arylthiolate ligands are ubiquitous in transition-metal
coordination chemistry, they are invariably S-bonded for either
terminal or bridging coordination. This is probably because the
affinity of transition-metal elements for thiolate sulfurs is strong
relative to the metal-aryl π interactions. In contrast, analogous
aryloxide complexes have occasionally been found to assume π
coordination geometries at the aryl substituents, in an η5-pentadienyl
or an η3-allyl bonding manner, leaving the CdO portion intact.1
As a part of our ongoing study on activation of small molecules
by means of coordinatively unsaturated transition-metal complexes,2
we were interested in preparation of molybdenum complexes of
the 2,6-disubstituted arylthiolates, SC6H3-2-Ph-6-SiMe3 and SC6H3-
2,6-(SiMe3)2. This contribution describes the reactions of MoCl3-
Figure 1. Molecular structure of 1. Selected bond distances [Å]: Mo-
(thf)3 with the lithium salts of these arylthiolates, which resulted
in isolation of the unexpected π-sandwiched bis-arylthiolato
complex, Mo{η5-SC6H3-2,6-(SiMe3)2}{η7-SC6H3-2,6-(SiMe3)2} (1).
We also report here that the π-bonding in 1 is labile and that the
reaction with acetonitrile gave rise to the S-bonded bis-arylthiolato
complex carrying three acetonitrile molecules, one of which is
coordinated in an η2-mode, Mo{SC6H3-2,6-(SiMe3)2}2(η1-CH3CN)2-
(η2-CH3CN) (2).
Treatment of MoCl3(thf)3 with 3 equiv of LiSC6H3-2-Ph-6-SiMe3
in Et2O, and subsequent removal of LiCl, afforded the expected
tris-arylthiolato complex of Mo(III), Mo(SC6H3-2-Ph-6-SiMe3)3 (3)
(see Scheme 1), as an analytically pure dark-purple crystalline solid
in 67% yield.3 According to the X-ray analysis, complex 3 has a
three-legged piano-stool structure with three arylthiolate sulfurs and
a π-bonded phenyl substituent of one arylthiolate ligand.4 The
coordination geometry at molybdenum(III) is similar to that of Mo-
(SC6H3-2,6-Mes2)3,4a and the geometric parameters are not unusual.
S(1) 2.562(1); Mo-C(1) 2.111(4); Mo-C(2) 2.339(4); Mo-C(3) 2.360(4);
Mo-C(4) 2.280(4); Mo-C(5) 2.335(4); Mo-C(6) 2.317(4); Mo-C(13)
2.448(4); Mo-C(14) 2.302(4); Mo-C(15) 2.313(4); Mo-C(16) 2.327(4);
Mo-C(17) 2.295(4); Mo-C(18) 2.369(4); S(1)-C(1) 1.754(4); S(2)-C(13)
1.709(4).
m/z 604, and the IR spectrum indicating the absence of an SH
moiety. Obviously reduction from Mo(III) to Mo(II) took place
during the reaction, and the yield of 1 is relatively low (29%), partly
because we were forced to rinse the crude product with HMDSO
repeatedly to remove the disulfide, {SC6H3-2,6-(SiMe3)2}2.
The X-ray crystal structure analysis confirmed the formulation
of 1 and revealed its unusual coordination geometry (Figure 1).
There are two immediate observations in the structure: (1) the aryl
group of each ligand is π-bonded to Mo, and (2) one CdS group
bends significantly toward Mo while the other is far away from
the metal center, and thereby the molecule is unsymmetric. Close
inspection of the C-C bond distances in either of the arylthiolates
suggests that they are classified into two groups: four short C-C
bonds among C(2)-C(6) (or C(14)-C(18)) (1.382(7)-1.426(6) Å)
vs two long C(1)-C(2), C(1)-C(6), (or C(13)-C(14), C(13)-
C(18)) bonds (1.450(6)-1.459(6) Å). Thus, the aryl rings behave
like pentadienyl ligands. This bonding feature would provide 16
electrons at the Mo(II) center, and the additional π-coordination
of one CdS bond makes the complex an 18-electron system. The
η7-SC6H3-2,6-(SiMe3)2 ligand is folded by 14.9° at the C(2)-C(6)
vector due to the coordination of the CdS group. Consequently
the C(1)-S(1) bond is elongated, while the Mo-C(1) bond
(2.111(4) Å) is substantially shorter than the other Mo-C bonds.
In the η5-SC6H3-2,6-(SiMe3)2 ligand, the C(13)-S(2) bond length
of 1.709(4) Å is between single and double bonds, indicating
π-electron delocalization over the five “pentadienyl” carbon atoms
and the CdS bond. The CdS group bends away from the metal
center by 10.8°, resulting in the long Mo-C(13) distance of
2.449(5) Å.
Scheme 1
On the other hand, we isolated reddish-brown crystals from the
analogous reaction between MoCl3(thf)3 and 3 equiv of LiSC6H3-
2,6-(SiMe3)2. The product was formulated as Mo{SC6H3-2,6-
(SiMe3)2}2 (1), based on the elemental analysis,5 the EI mass
spectrum showing an isotope cluster of the parent ion centered at
The Mo(II) complex 1 is diamagnetic, and the 1H NMR spectrum
in benzene-d6 shows two sets of proton signals in a 1:1 intensity
† Nagoya University.
‡ Institute for Molecular Science.
9
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J. AM. CHEM. SOC. 2003, 125, 2070-2071
10.1021/ja029541+ CCC: $25.00 © 2003 American Chemical Society

C O M M U N I C A T I O N S
at the aryl portion to form a π-sandwich Mo(II) complex, which
would open a new facet of transition-metal thiolate chemistry.
Lability of the π-aryl coordination of 1 and the presence of η1-
and η2-CH3CN ligands in 2 suggest that these complexes are useful
for exploration of the chemistry of coordinatively unsaturated low-
valent molybdenum complexes.4,8,11 Further study of the reactivity
of 1 and 2 is currently underway.
Acknowledgment. This work was supported by Grant-in-Aid
for Scientific Research on Priority Areas (No. 14078101, 14078211
“Reaction Control of Dynamic Complexes”) from Ministry of
Education, Culture, Sports, Science, and Technology, Japan.
Figure 2. Molecular structure of 2. Selected bond distances [Å] and angles
(deg): Mo-S(1) 2.355(3); Mo-S(2) 2.352(3); Mo-N(1) 1.98(2); Mo-
N(2) 2.14(1); Mo-N(3) 2.15(1); Mo-C(25) 1.98(2); S(1)-C(1) 1.81(1);
S(2)-C(13) 1.78(1); N(1)-C(25) 1.24(2); N(2)-C(27) 1.15(2); N(3)-C(29)
1.16(2); S(1)-Mo-S(2) 128.5(1); N(2)-Mo-N(3) 162.1(5); Mo-S(1)-
C(1) 110.2(3); Mo-S(2)-C(13) 108.7(4); N(1)-C(25)-C(26) 141(1).
Supporting Information Available: Experimental procedures,
analytical data, spectroscopic data (PDF), and X-ray crystallographic
files (in CIF format) for 1, 2, and 3. This material is available free of
charge via the Internet at http://pubs.acs.org.
References
ratio for both the aromatic and trimethylsilyl groups. The 13C and
29Si NMR spectra also indicate that the two SC6H3-2,6-(SiMe3)2
ligands are chemically inequivalent.5 The aryl ring proton reso-
nances are all shifted upfield compared with those of HSC6H3-2,6-
(SiMe3)2 (7.45(d) and 7.06(t) ppm). A similar trend was noticed in
the 13C{1H} NMR spectrum, except for one resonance at 174.0
ppm, which may be assigned to the uncoordinated thiocalbonyl
carbon.6 These observations suggest that the unsymmetric π-sand-
wich structure of 1 is preserved and rigid in solution.
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Although the unsymmetric π-sandwich structure of 1 appears to
be rigid at the NMR time scale, lability of the aryl-Mo bond was
manifested by its reaction with acetonitrile. Thus, dissolution of 1
in CH3CN at room temperature led to a rapid color change to deep
green. A diamagnetic sky-blue crystalline product, formulated as
Mo{SC6H3-2,6-(SiMe3)2}2(CH3CN)3 (2),7 was obtained from the
CH3CN solution in 76% yield. The X-ray derived structure of 2 is
given in Figure 2, which reveals a trigonal bipyramidal coordination
geometry of Mo(II) with two S-bonded arylthiolates and three
acetonitrile molecules. Interestingly, one acetonitrile molecule
adopts an η2-coordination mode at an equatorial site, while the other
two show normal η1-coordination at the axial sites. The π-bonded
CH3CN orients perpendicular to the equatorial plane, and the
C(25)-N(1) bond is longer by 0.08 Å than the corresponding bonds
of η1-CH3CN. This upright conformation is electronically favored
for a d4 configuration of Mo(II), and can be rationalized in terms
of the optimal π-back-bonding.8b This bonding feature is analogous
to the Mo(II) alkyne complexes, Mo(StBu)2(CNtBu)2(RCtCR′) (R,
R′ ) Ph, H).8
(3) Data for 3: Anal. Calcd for C45H51MoS3Si3: C, 62.25; H, 5.92; S, 11.08.
Found: C, 61.90; H, 6.00; S, 10.82. Crystal data: monoclinic, P21/n
(No. 14), a ) 12.395(5) Å, b ) 17.433(6) Å, c ) 20.061(8) Å, â )
90.849(5)°, V ) 4334(2) Å3, Z ) 4, R1 [I > 2σ(I)] ) 0.055 (wR2 (all
data) ) 0.142, GOF ) 1.01 on F2).
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(5) Data for 1: 1H NMR (C6D6): δ 6.73 (d, 2H), 5.19 (t, 1H), 5.12 (d, 2H),
3.09 (t, 1H), 0.48 (s, 18H, SiMe3), 0.28 (s, 18H, SiMe3). 13C{1H} NMR
(C6D6): δ 174.0, 125.9, 110.1, 106.0, 104.4, 103.2, 95.5, 93.6, 2.9 (SiMe3),
1.6 (SiMe3). 29Si{1H} NMR (C6D6): δ 0.9, -0.5. Anal. Calcd for
C24H42MoS2Si4: C, 47.80; H, 7.02; S, 10.64. Found: C, 47.69; H, 7.07;
S, 10.57. Crystal data: monoclinic, P21/n (No. 14), a ) 11.960(5) Å,
b ) 19.135(8) Å, c ) 13.097(5) Å, â ) 99.847(5)°, V ) 2953.1(20) Å3,
Z ) 4, R1 [I > 2σ(I)] ) 0.050 (wR2 (all data) ) 0.129, GOF ) 1.03 on
F2).
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(7) Data for 2: 1H NMR (C6D6): δ 7.47 (dd, 1H), 7.41 (dd, 1H), 7.38 (dd,
1H), 7.30 (dd, 1H), 6.94 (t, 1H), 6.90 (t, 1H), 3.02 (s, 3H), 1.05 (s, 3H),
0.78 (s, 3H), 0.69 (s, 9H), 0.63 (s, 9H), 0.242 (s, 9H), 0.237 (s, 9H).
13C{1H} NMR (C6D6): δ 226.9 (η2-NCMe), 165.5 (η1-NCMe), 164.9
(η1-NCMe). 29Si{1H} NMR (C6D6): δ -3.1, -3.5, -3.7, -4.6. Anal.
Calcd for C30H51MoN3S2Si4: C, 49.62; H, 7.08; N, 5.79; S, 8.83. Found:
C, 49.26; H, 7.02; N, 5.67; S, 8.35. Crystal data: monoclinic, P21 (No.
4), a ) 11.496(8) Å, b ) 15.287(9) Å, c ) 13.237(9) Å, â ) 114.96(1)°,
V ) 2108(2) Å3, Z ) 2, R1 [I > 2σ(I)] ) 0.059 (wR2 (all data) ) 0.168,
GOF ) 1.01 on F2).
The IR spectrum of 2 exhibits bands at 2261 and 1673 cm-1
,
assignable to the N-C stretching modes of the η1- and η2-CH3CN
ligands, respectively. The 1H NMR spectrum in toluene-d8 consists
of three CH3CN singlets and two sets of the arylthiolate ligands
up to 70 °C,7 at the temperature of which 2 starts to decompose.
Thus, the molecule is not fluxional, and its solid-state structure is
retained in solution. The η2-CH3CN nitrile carbon resonance at
226.9 ppm in the 13C{1H} NMR spectrum shifts downfield
considerably, relative to the η1-CH3CN nitrile carbons, and falls in
the region where CH3CN has been thought to act as a four-electron-
donor ligand.9 Thus, the second π orbital10 may also participate in
the bonding with Mo(II) for 2.
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M.; Tatsumi, K.; Hoffmann, R. Organometallics 1982, 1, 227-230. (b)
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We have established for the first time that the 2,6-disubstituted
arylthiolate ligand SC6H3-2,6-(SiMe3)2 can bind to a metal center
JA029541+
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