Poly(methimazolyl)silanes: Syntheses and molecular structures

Article abstract of DOI:10.1021/om1004989

A new class of multidentate "scorpionate" ligands is readily obtained from the reactions of methimazole with a range of organochlorosilanes. A recurrent structural feature to emerge is the intramolecular S-capping of the tetrahedral inner Si coordination

Full text of DOI:10.1021/om1004989

Organometallics 2010, 29, 5607–5613 5607
DOI: 10.1021/om1004989
Poly(methimazolyl)silanes: Syntheses and Molecular Structures†
Jorg Wagler,*,‡,^ Thomas Heine,§ and Anthony F. Hill^
€
‡
€
Institut fu€r Anorganische Chemie, Technische Universitat Bergakademie Freiberg, D-09596 Freiberg,
Germany, ^Research School of Chemistry, The Australian National University, Canberra, ACT 0200,
Australia, and §School of Engineering and Science, Jacobs University Bremen, D-28759 Bremen, Germany
Received May 20, 2010
A new class of multidentate “scorpionate” ligands is readily obtained from the reactions of
methimazole with a range of organochlorosilanes. A recurrent structural feature to emerge is the
intramolecular S-capping of the tetrahedral inner Si coordination spheres, the nature of which is
responsive to the substitution pattern at silicon.
Scheme 1
Within the past decade methimazole (H-mt) and related
2-mercaptoimidazoles have attracted considerable interest, as
they are the essential building block in 2-mercapto-1,3-diazol-3-yl
borates (Scheme 1), a class of multidentate ligands that exhibits
surprising features in transition metal complex chemistry.
Since the first reports on methimazolylborates by Reglinski
et al.,1 the coordination chemistry of this class of ligands has
been widely investigated2 and a range of coordination modes
have been identified (Scheme 1) that reveal striking differences
between methimazolylborate and pyrazolylborate coordina-
tion chemistries. Among these was the discovery of the first
metallaboratranes (Scheme 1, κ3-B,S,S0 and κ4-B,S,S0,S00
coordination modes), which included transannular metal-
boron dative bonding.3
Despite these extensive investigations of methimazolylbo-
rates and related compounds, silicon analogues (i.e., methima-
zolyl-substituted silanes) have not been reported until recently,
when we published selected mt-substituted silanes that can
undergo a variety of reactions with transition metal complexes:
PhCl2Si(mt) was shown to react with (Ph3P)2Pt(C2H4) under
insertion of Pt(0) into the mt-ligand’s CdS bond and forma-
(COT) = 1,3,5-cyclooctatriene] with Ph(H)Si(mt)2 proved the
Si-H bond to be a third reactive site for attaching methima-
zolylsilanes to transition metals6 (Scheme 2).
For further investigations of methimazolylsilanes, with
particular focus on the intramolecular coordination properties
of their S-donor functions, wehave now extended the library of
structurally characterized mt-substituted silanes and report
herein full details of their synthesis and characterization.
tion of an imidazol-2-yl-Pt(II)-complex-stabilized silane-
thione.4 Metallasilatranes (comprising formal PdfSi and
PtfSi dative bonds) became accessible from ClSi(mt)3 (or
Si(mt)4) in reactions with MCl2(PPh3)2 (M = Pd, Pt),5 and the
reaction of Ru(COD)(COT) [(COD) =1,5-cyclooctadiene,
† Part of the Dietmar Seyferth Festschrift.
*Corresponding author. E-mail: joerg.wagler@chemie.tu-freiberg.de.
(1) Garner, M.; Reglinski, J.; Cassidy, I.; Spicer, M. D.; Kennedy,
A. R. Chem. Commun. 1996, 1975.
(2) (a) Crossley, I. R.; Hill, A. F.; Willis, A. C. Organometallics 2005,
24, 4889. (b) Foreman, M. R. S.-J.; Hill, A. F.; Tshabang, N.; White, A. J. P.;
Williams, D. J. Organometallics 2003, 22, 5593. For selected reviews on the
coordination chemistry of methimazolylborates, -boranes, and related sys-
tems please see: (c) Spicer, M. D.; Reglinski, J. Eur. J. Inorg. Chem. 2009,
1553. (d) Fontaine, F.-G.; Boudreau, J.; Thibault, M.-H. Eur. J. Inorg. Chem.
2008, 5439. (e) Kuzu, I.; Krummenacher, I.; Meyer, J.; Armbruster, F.;
Breher, F. Dalton Trans. 2008, 5836.
Results and Discussion
In general, the reactions between organochlorosilanes and
methimazole in the presence of triethylamine as sacrificial
base provided easy access to a variety of methimazolylsilanes
(Scheme 3), thus serving as a general approach for their
synthesis.
(3) (a) Hill, A. F.; Owen, G. R.; White, A. J. P.; Williams, D. J.
Angew. Chem., Int. Ed. 1999, 38, 2759. (b) Crossley, I. R.; Hill, A. F.; Willis,
A. C. Organometallics 2006, 25, 289. (c) Crossley, I. R.; Hill, A. F.; Willis,
A. C. Organometallics 2005, 24, 1062. (d) Crossley, I. R.; Hill, A. F.; Willis,
A. C. Organometallics 2010, 29, 326, and references therein.
(4) Brendler, E.; Hill, A. F.; Wagler, J. Chem.;Eur. J. 2008, 14, 11300.
(5) Wagler, J.; Brendler, E. Angew. Chem., Int. Ed. 2010, 49, 624.
According to Scheme 3, a range of mono-, bis-, and tris-
(methimazolyl)silanes as well as tetrakis(methimazolyl)silane
(6) Hill, A. F.; Neumann, H.; Wagler, J. Organometallics 2010, 29,
1026.
r
2010 American Chemical Society
Published on Web 10/13/2010
pubs.acs.org/Organometallics

5608 Organometallics, Vol. 29, No. 21, 2010
Wagler et al.
Scheme 2
In sharp contrast with 2-mercapto-azolinyl-substituted
stannanes (e.g., 2-mercaptobenzothiazolinylstannanes),
which clearly exhibit hypercoordinate Sn atoms due to
four-membered Sn(N-C-S) chelates,8 the combination
of the thermodynamically disadvantaged S-Si bond and
the rather rigid Si-bound methimazol-3-yl moiety offers
only limited geometric freedom for the variability of the
S-Si distances. Although all of these Si-S separations are
shorter than the sum of the van der Waals radii, one can
discern rather attractive versus rather repulsive contacts
by analysis of the Si-N-C(S) and Si-N-C(C) angles
(Table 1, Scheme 4). In case of S-Si separations of about
˚
3.41 3.43 A (e.g., in compounds PhMeSi(mt)2, EtSi-
3 3 3
(mt)3, PhSi(mt)3, and PhClSi(mt)2) the Si-N-C angles
at the methimazol-3-yl moiety are similar. Significantly
shorter S-Si separations cause significant bond angle
deformations by means of smaller Si-N-C(S) versus
wider Si-N-C(C) angles, thus hinting at S-Si attraction.
This phenomenon is found for S-Si caps trans to N-Si
and Cl-Si bonds. For the S-Si caps trans to C-Si bonds
a widening of the Si-N-C(S) angle is observed in many
cases, thus indicating rather repulsive forces. In the hydride-
bearing compounds Me(H)Si(mt)2 and Ph(H)Si(mt)2, how-
ever, both the S-Si interactions trans to N-Si and trans to
C-Si bonds seem rather attractive, and these compounds
exhibit the shortest S-Si separations of both the trans-C-Si
and trans-N-Si class.
This leads to the conclusion that both the S-Si capping trans
to N-Si/Cl-Si and trans to C-Si are electronically attractive.
Repulsive interactions due to the steric bulk of further substit-
uents at the Si atom, however, may cause a net repulsion for the
weaker S-Si capping trans to C-Si bonds in compounds
Me2Si(mt)2 and Ph2Si(mt)2 or rather balanced situations in
compounds PhMeSi(mt)2, PhSi(mt)3, and PhClSi(mt)2.
The general choice of the tetrahedral faces to be S-capped
may be driven by a combination of sterically favorable arrange-
ments of the Si-bound substituents, attractions of S-Si caps,
and intramolecular C-H-π contacts. Figure 2 illustrates this
intramolecular “S-Si capping þ C-H-π-contact” feature,
which appears in the above molecular structures.
The hydrogen atom in 4-position of each of the methima-
zol-3-yl moieties (i.e., H4, H8, and H12 in Figure 2) points to
π-electron-rich atoms of a neighboring substituent, thus
forcing the S atom of its own methimazol-3-yl moiety (S1,
S2, and S3, respectively) to cap the tetrahedral face opposite
this hydrogen contact acceptor. This model explains why
none of the 2-fold methimazolyl-substituted silanes exhibit
two S-Si contacts trans to N-Si (which might be electro-
nically favorable as regards N-Si-S electrostatic inter-
actions): The S-capping of one tetrahedral face trans to the
second methimazolyl moiety results in the setting up of a
hydrogen contact to this methimazolyl group and allows
Scheme 3
were prepared and their molecular structures were determined
by single-crystal X-ray diffraction analysis (Figures 1 and 2,
Table 1). A common feature of these methimazolylsilane
molecules (and the previously reported examples, see Sup-
porting Information) is the n-fold S-capped tetrahedral envi-
ronment of the silicon atom (n = number of methimazolyl
moieties per silane molecule). The S-Si separations range
˚
from 3.17 to 3.50 A; thus, they are shorter than the sum of
7
the van der Waals radii (3.9 A), and effects on the bonding
˚
properties within the methimazolylsilane molecules should
result therefrom. In the molecules of compounds Me2Si(mt)2,
Me(H)Si(mt)2, PhMeSi(mt)2, Ph(H)Si(mt)2, and PhSi(mt)3
both S-Si-capping trans to N-Si and trans to C-Si bonds
are encountered. Comparison of the S-Si separations reveals
that those trans to an N-Si bond are generally shorter than
those trans to a C-Si bond (Table 1). Similar behavior is
observed for compound PhClSi(mt)2, which exhibits shorter
S-Si capping trans to a Cl-Si bond versus longer S-Si
separation trans to C-Si. As to the origin of the Si-S
separations observed, electrostatic attraction between Si
and S atoms is in general reasoned by their electropositive
and electronegative nature, respectively. Orbital interactions
(electron donation into σ* MOs) might also contribute to
the overall electronic situation, as indicated by the results
of X-ray crystallography. The S-Si interaction appears
to influence the trans-disposed N-Si bonds. In Table 1 the
N-Si bond lengths are listed and a general trend of N-Si
bond lengthening is observed (in compounds Me2Si(mt)2,
Me(H)Si(mt)2, PhMeSi(mt)2, Ph(H)Si(mt)2, PhSi(mt)3, and
ClSi(mt)3) for those connections bearing a trans-Si-S cap.
Natural bond orbital (NBO) analysis of PhHSi(mt)2 as a
representative example, however, proved S-localized lone
pairs to comprise only up to 3% Si-contribution. Further-
more, an atoms in molecules (AIM) analysis did not reveal a
bond critical point between Si and S atoms (for details see the
Supporting Information).
ꢀ
ꢀ
ꢁ ꢁ
(8) (a) Martincova, J.; Dostal, L.; Taraba, J.; Ruzicka, A.; Jambor, R.
ꢀ
ꢀ
J. Organomet. Chem. 2007, 692, 3415. (b) Martincova, J.; Dostal, L.;
Taraba, J.; Jambor, R. J. Organomet. Chem. 2007, 692, 908. (c) Xantho-
poulou, M. N.; Hadjikakou, S. K.; Hadjiliadis, N.; Kubicki, M.; Skoulika, S.;
Bakas, T.; Baril, M.; Butler, I. S. Inorg. Chem. 2007, 46, 1187. (d) Ma, C.;
Jiang, Q.; Zhang, R. Polyhedron 2004, 23, 779. (e) Ma, C.; Jiang, Q.; Zhang,
R. Appl. Organomet. Chem. 2003, 17, 623. (f) Xanthopoulou, M. N.;
Hadjikakou, S. K.; Hadjiliadis, N.; Sch€urmann, M.; Jurkschat, K.; Michae-
lides, A.; Skoulika, S.; Bakas, T.; Binolis, J.; Karkabounas, S.; Charalabo-
poulos, K. J. Inorg. Biochem. 2003, 96, 425. (g) de Sousa, A. P. G.; Silva,
R. M.; Cesar, A.; Wardell, J. L.; Huffman, J. C.; Abras, A. J. Organomet.
ꢀ
ꢀ ꢀ
Chem. 2000, 605, 82. (h) Susperregui, J.; Bayle, M.; Leger, J. M.; Deleris, G.
J. Organomet. Chem. 1998, 556, 105.
(7) Bondi, A. J. Phys. Chem. 1964, 68, 441.

Article
Organometallics, Vol. 29, No. 21, 2010 5609
Figure 1. Molecular structures of Me3Si(mt) (one of the two crystallographically independent molecules), Me2Si(mt)2, Me(H)Si(mt)2,
PhMeSi(mt)2 in PhMeSi(mt)2 0.5 toluene, Ph2Si(mt)2 in Ph2Si(mt)2 0.5toluene, and EtSi(mt)3 in EtSi(mt)3 CH2Cl2 (ORTEP
diagrams with 50% probability ellipsoids, C-bound hydrogen atoms and solvent molecules, if applicable, omitted for clarity).
3
3
3
as a result of net repulsive or net attractive Si-S capping, these
hydrogen contacts may play a secondary role only. Compar-
ison between the structural features of Me2Si(mt)2 and PhMe-
Si(mt)2 (Table 1) supports this conclusion: Both the structures
of Me2Si(mt)2 and PhMeSi(mt)2 bear one S-Si cap trans to
C-Si and one trans to Si-N each. The increased Lewis acidity
of the Si atom in PhMeSi(mt)2 (as a result of replacing an
sp3 C atom by a more electronegative sp2 C atom in the
coordination sphere) causes a shortening of both S-Si
˚
˚
separations (by 0.074 A trans to C-Si, 0.067 A trans to
˚
N-Si). The difference in the S-Si distances is 0.133 A for
compound Me2Si(mt)2. Unlike Me2Si(mt)2, compound
PhMeSi(mt)2 bears a phenyl group and exhibits hydrogen
contacts between this π-electron system and one methi-
mazolyl group, the analogue of which could not establish
such contacts in Me2Si(mt)2. The difference in S-Si
separations within this molecule, however, is similar
˚
(0.126 A).
With respect to the question whether S-Si interactions
in these methimazolylsilanes can be regarded as Si-hyper-
coordination, differing opinions can be found in the
literature. S-Si capping with similar S-Si separations
Figure 2. Molecular structure of PhSi(mt)3 in PhSi(mt)3 toluene
3
(ball-and-stick diagram, atomic spheres of arbitrary size, most
hydrogen atoms and toluene molecule omitted for clarity). Selected
˚
(i.e., ca. 3.05-3.48 A) has also been reported for ligands
of higher flexibility, the S-Si separations of which cannot
be regarded as a sole result of steric constraints. In the
dithiocarboxylate-bearing silanes reported by Kano et al.,
these S-Si distances are discussed in terms of Si-hyper-
coordination.9 Similar S-Si separations were also found
for a series of O-silylated thiobenzoates PhC(dS)O-SiR3
(R=Ph, O-C6H3-2,6-Me2, O-tBu), but the authors inter-
pret this result as a lack of intramolecular interaction.10
Our experimental (single-crystal XRD) observations, i.e.,
the systematic trends in the slight dependence of the S-Si
separation on the substitution pattern about the Si atom,
provide support for the presence of weak intramolecular
donor-acceptor interactions. Si-hypercoordination (i.e.,
more than four donor atoms in the first coordination
sphere) is usually indicated by a notable shift of the 29Si
C-H π(X) (X = C, N) hydrogen contacts* (indicated by thin
3 3 3
˚
arrows). H X distances [A] and C-H X angles [deg]:
3 3 3 3 3 3
C4-H4 C13 2.84, 102.6; C8-H8 N1 2.82, 99.6; C-H8
3 3 3 3 3 3
3 3 3
C1 2.89, 117.5; C12-H12 N3 2.88, 99.0; C12-H12 C5 2.91,
3 3 3
3 3 3
119.0; C18-H18 N3 2.74, 107.4. (*The hydrogen atoms in
3 3 3
this structure have been refined in idealized positions, i.e., with
2
C(sp )-H bond lengths restrained to 0.950 A.)
˚
only for generating the second S-Si cap trans to one of the
other substituents. The complete absence of S-Si capping
trans to N-Si in compounds Ph2Si(mt)2 and PhClSi(mt)2
may be a result of further hydrogen contacts within the
system of methimazolyl and phenyl substituents. As the
intramolecular C-H π(X) distances and the capping
3 3 3
S-Si separations indicate rather weak interactions, inter-
molecular packing effects in the crystal may contribute to the
favorable molecular conformation.
(9) Kano, N.; Nakagawa, N.; Kawashima, T. Angew. Chem., Int. Ed.
2001, 40, 3450.
(10) Wojnowski, W.; Wojnowska, M.; Grubba, R.; Konitz, A.;
Regarding the Si-N-C(C) and Si-N-C(S) bond angle
deformation and S-Si separations, which have been discussed
Pikies, J. Z. Anorg. Allg. Chem. 2008, 634, 730.

5610 Organometallics, Vol. 29, No. 21, 2010
Wagler et al.
˚
Table 1. Selected Si-S Separations and Si-N Bond Lengths [A] and Angles [deg] of Compounds Me3Si(mt), Me2Si(mt)2, Me(H)Si(mt)2,
PhMeSi(mt)2 0.5toluene, Ph(H)Si(mt)2, Ph2Si(mt)2 0.5toluene, EtSi(mt)3 CH2Cl2, PhSi(mt)3 toluene, PhClSi(mt)2 toluene,
3
3
3
3
3
PhCl2Si(mt), and ClSi(mt)3, Which Are Affected by the S-Si Cappinga
compd
S
trans to
d(Si-S)
N
d(Si-N)
Si-N-C(S)
Si-N-C(C)
Me3Si(mt)
S1
C
3.451(1)
125.9(1)
126.2(1)
N1
N3
1.800(2)
1.780(2)
Me2Si(mt)2
S1
S2
N3
C
3.367(1)
3.500(1)
123.4(1)
127.7(1)
128.6(1)
124.1(1)
N1
1.775(2)
Me(H)Si(mt)2
PhMeSi(mt)2
Ph(H)Si(mt)2
Ph2Si(mt)2
S1
S2
C
N1
3.321(1)
3.180(1)
122.2(2)
119.1(1)
128.5(2)
132.6(2)
N1
N3
1.771(2)
1.768(2)
S1
S2
C
N1
3.426(1)
3.300(1)
126.0(1)
122.3(1)
126.0(1)
129.5(1)
N1
N3
1.785(1)
1.769(1)
S1
S2
C
N1
3.292(1)
3.167(1)
121.6(1)
119.2(1)
128.8(1)
132.3(1)
N1
N3
1.776(1)
1.759(1)
S1
S2
C
C
3.480(1)
3.452(1)
127.0(1)
127.2(1)
124.3(1)
124.5(1)
N1
N3
N3
N5
N1
1.769(2)
1.765(2)
1.767(1)
1.761(1)
1.777(1)
EtSi(mt)3
PhSi(mt)3
S1
S2
S3
S1
S2
S3
N3
N5
N1
C
N1
N3
3.419(1)
3.385(1)
3.319(1)
3.422(1)
3.349(1)
3.353(1)
125.1(1)
125.0(1)
122.3(1)
126.3(1)
123.5(1)
123.5(1)
125.3(1)
126.1(1)
129.0(1)
125.1(1)
126.9(1)
126.9(1)
N1
N3
N5
1.756(1)
1.763(1)
1.751(1)
PhClSi(mt)2
S1
S2
C
Cl
3.403(1)
3.317(1)
125.2(1)
122.9(1)
125.9(1)
128.5(1)
N1
N3
1.752(2)
1.751(2)
PhCl2Si(mt)
ClSi(mt)3
S1
Cl
3.243(1)
120.9(1)
130.3(1)
N1
N3
1.753(1)
1.742(1)
S1
S2
S3
N3
Cl
N1
3.386(1)
3.331(1)
3.302(1)
124.9(1)
123.8(1)
121.7(1)
126.3(1)
127.6(1)
126.9(1)
N1
N5
1.752(1)
1.735(1)
a Trans-N Si-S separations and their respective trans-disposed Si-N bonds are highlighted in bold. The structure of Si(mt)4 suffers effects of disorder,
thus the structural parameters are not listed.
(indolyl)2SiPhCl (-23.7 ppm).13 These differences, how-
Scheme 4
ever, do not represent any significant hint at hypercoordi-
nation because replacement of one indolyl group of the
latter by pyrrole causes an even greater upfield shift of
(indolyl)(pyrrolyl)SiPhCl (-31.7 ppm).13 Hence, although
X-ray diffraction data hint at intramolecular Si-S interac-
tions, these effects exert only marginal impact on the 29Si
NMR properties of methimazolylsilanes. In this context we
need topoint out that 29Si NMR data reported in our paper are
NMR signal to higher field (with respect to molecular
systems that lack the additional donor sites).11 Compar-
solution-state NMR data, and the molecular architectures as
found crystallographically do not persist in solution (only one
ison of the 29Si NMR data of some of above methimazo-
set of signals was found 1H and 13C NMR spectroscopically for
lylsilanes with structurally related molecules that lack the
capping S-donor function, however, does not support a
the mt moieties of the bis-, tris-, and tetrakis(methimazolyl)
concept of Si-hypercoordination in terms of significantly
silanes). Nonetheless, rotation of the methimazolyl moiety
upfield-shifted 29Si resonances upon coordination of the
about the Si-N bond should retain the sulfur atoms in close
proximity to the Si atom. This was confirmed by a potential
energy surface scan (PES) of a rotation about the Si-N bond of
Cl3Si(mt) (Figure 3). According to the only slightly altered
additional donors: The 29Si NMR shift of Me3Si(mt) (15.8 ppm)
is similar to that of trimethylsilylimidazole (14.1 ppm);12
the resonances of PhCl2Si(mt) (-17.0 ppm) and PhClSi(mt)2
(-28.5 ppm) are slightly upfield-shifted with reference to the
Si-S separations along the rotation coordinate (ranging
between 3.39 and 3.60 A), similar shielding of the Si nucleus can
be expected. The energy barrier associated with the rotation
indolyl-substituted silanes (indolyl)SiPhCl2 (-12.6 ppm)13 and
˚
(11) For reviews on hypercoordinate silicon compounds see for
example: (a) Chuit, C.; Corriu, R. J. P.; Reye, C.; Young, J. C. Chem.
8 kcal/mol), which may furthermore be lowered by solvent
Rev. 1993, 93, 1371. (b) Tacke, R.; P€ulm, M.; Wagner, B. Adv. Organomet.
Chem. 1999, 44, 221. (c) Kost, D.; Kalikhman, I. Adv. Organomet. Chem.
2004, 50, 1. (d) Voronkov, M. G.; Trofimova, O. M.; Bolgova, Yu. I.;
Chernov, N. F. Russ. Chem. Rev. 2007, 76, 825.
about the Si-N bond of our model compound Cl3Si(mt) (ca.
effects, indicates both the possibility of rotation in solution and
(12) Komarova, T. N.; Larina, L. I.; Abramova, E. V.; Dolgushin,
G. V. Russ. J. Gen. Chem. 2007, 77, 1089.
(13) Frenzel, A.; Gluth, M.; Herbst-Irmer, R.; Klingebiel, U. J.
Organomet. Chem. 1996, 514, 281.

Article
Organometallics, Vol. 29, No. 21, 2010 5611
Scheme 5
Scheme 6
substituent), and we also reported it for ClSi(mt)3 in CDCl3
(δ -41.2, -50.5, and -59.1 ppm, assigned to Cl2Si(mt)2,
ClSi(mt)3, and Si(mt)4, respectively).5 For the latter we have
now shown that in the solid state only ClSi(mt)3 is present
(one signal at -50.1 ppm), whereas the three signals emerge
upon dissolution in CDCl3.
Figure 3. Potential energy surface scan (PES) of a torsion about
the Si-N bond in Cl3Si(mt) by 60ꢀ in steps of 10ꢀ, calculated at
the PBE-DþZORA/TZ2P level. Red spots represent the relative
energies ΔE (in kcal/mol); black diamonds represent the calcu-
lated difference in 29Si NMR shift Δδ (in ppm).
This feature of multicomponent solutions in CDCl3, which
has only been observed for those methimazolylsilanes bear-
ing both N-Si and Cl-Si bonds, was ascribed to ligand
scrambling since those methimazolylsilanes devoid of Cl-Si
bonds were found to produce only one set of signals in their
1H and 13C NMR spectra as well as only one 29Si NMR peak.
The latter observation excludes traces of water being the
source of the reproducible emerging of the sets of signals
(e.g., signals of silanols or siloxanes), since Cl-free methima-
zolylsilanes were also found to be highly sensitive toward
moisture and other OH-protic reagents such as alcohols and
would therefore have to exhibit similar behavior. Whereas
ligand scrambling at Cl-Si-functionalized methimazolylsi-
lanes represents a potential disadvantage of these com-
pounds with respect to their applicability as stable ligands
in coordination chemistry, this ligand scrambling has how-
ever proven useful for providing the ligand scrambling
products as starting materials in a decelerated fashion. It
renders them useful precursors when slow crystallization is
preferred rather than spontaneous precipitation, e.g., in the
synthesis of metallasilatranes, Scheme 6.
In addition, the facile N-Si versus Cl-Si exchange within
the methimazolylsilane systems opens further routes toward
methimazolylsilanes. Instead of synthesizing methimazolyl-
silanes along the base-supported route as depicted in
Scheme 3, a transsilylation between Me3Si(mt) and a chlor-
osilane might prove the better alternative, especially when
the product reveals poor solubility in THF and might pre-
cipitate with the byproduct Et3NHCl. In a particular case,
i.e., the synthesis of ClSi(mt)3, SiCl4 was successfully reacted
with Me3Si(mt) to give the desired product in good yield and
without Et3NHCl as potential impurity.
a preference for the conformations with S-capped tetrahedral
faces in the Si coordination sphere. The latter should render
the 29Si NMR shifts in solution similar to those of the solids, as
the predominant conformation will contribute predominantly
to δ29Si. Accordingly, for ClSi(mt)3 (which exhibits chemically
different mt ligands in the solid state, i.e., trans-S-capped
and noncapped Si-N bonds) only one mt-related set of signals
1
was detected in solution H and 13C NMR spectra, and 29Si
NMR spectroscopy revealed similar chemical shifts in solution
(-50.5 ppm in CDCl3) and the solid state (-50.1 ppm).
Although the methimazolylsilanes Ph2Si(mt)2, EtSi(mt)3,
and PhSi(mt)3 require the presence of N-methylimidazole
(NMI) as catalyst when prepared in THF solution, their
formation seems favored in chlorinated solvents such as
chloroform or dichloromethane. Whereas donors such as
NMI may support nucleophilic substitution reactions at Si
by formation of reactive higher-coordinate Si complexes,14
solvents such as CHCl3 may support ionic Si-Cl bond
dissociation,15 thus also supporting nucleophilic substitu-
tion reactions at Si. When dissolved in CDCl3 compound
PhClSi(mt)2 gives rise to three signals of similar intensity
in the 29Si solution NMR spectrum (δ -17.0, -28.5, and
-39.9 ppm for PhCl2Si(mt), PhClSi(mt)2, and PhSi(mt)3,
respectively) (Scheme 5).4 Assignment was made by analyz-
ing these compounds separately in thf or toluene solution,
where they remained the predominant species for many
hours. The same effect has been observed for EtClSi(mt)2
in CDCl3 (signals at δ 0.0, -12.6, and -24.0 ppm, which
were assigned to EtCl2Si(mt), EtClSi(mt)2, and EtSi(mt)3,
respectively, according to the systematic upfield shift by
ca. 10 ppm upon replacing one Si-bound Cl atom by a mt
In conclusion, we have found that a variety of methima-
zolylsilanes are accessible via straightforward syntheses from
methimazole and the respective chlorosilane in the presence
of triethylamine as sacrificial base, whereas more bulky
substituents at the silicon atom required a catalyst (NMI)
to promote complete methimazolyl substitution. The silanes
reported herein add to this essentially unexplored class of
N-silylated methimazoles, which represent tempting “scor-
pionate”-like systems for further investigation as ligands
in transition metal coordination chemistry. In addition to
(14) (a) Brendler, E.; Heine, T.; Hill, A. F.; Wagler, J. Z. Anorg. Allg.
Chem. 2009, 635, 1300. (b) Bassindale, A. R.; Parker, D. J.; Taylor, P. G.;
Turtle, R. Z. Anorg. Allg. Chem. 2009, 635, 1288. (c) Wagler, J.; Hill, A. F.
Organometallics 2007, 26, 3630.
(15) (a) Kost, D.; Kingston, V.; Gostevskii, B.; Ellern, A.; Stalke, D.;
Walfort, B.; Kalikhman, I. Organometallics 2002, 21, 2293. (b) Wagler, J.;
€
Bohme, U.; Brendler, E.; Roewer, G. Z. Naturforsch. B 2004, 59, 1348.

5612 Organometallics, Vol. 29, No. 21, 2010
Wagler et al.
exhibiting interesting molecular structural features by means of
S-capped tetrahedral Si coordination spheres, the Si-N bonds
of methimazolylsilanes appeared to be both kinetically labile
and thermodynamically capable of undergoing intermolecular
mt versus Cl ligand exchange reactions. This feature renders
methimazolylsilanes potential methimazolyl transfer reagents.
The latter was proven both in the syntheses of the first
methimazolyl-bridged metallasilatranes5 and by the successful
synthesis of ClSi(mt)3 along a transsilylation route, namely,
starting from SiCl4 and Me3Si(mt). The applicability of methi-
mazolylsilanes as methimazolyl-transfer reagents for syntheses
of silicon-free methimazolyl-bridged complexes such as ClSn-
(μ-mt)4PdCl,16 which could only be prepared in traces so far,
will be explored in further studies.
and the mixture was stirred at room temperature for 1 h. The
hydrochloride precipitate was then filtered off and washed with
ether (100 mL). From the combined filtrate and washings the
volatiles were removed under reduced pressure, and the resulting
solid was recrystallized from hexane (50 mL). Upon storage at
room temperature for 1 day, the crystals were separated from the
supernatant by decantation and dried in vacuo. Yield: 11.6 g (62.2
mmol, 89%). Mp: 58 ꢀC. Anal. Found (%): C 44.72, H 7.53, N
15.09. Calcd for C7H14N2SSi: C 45.12, H 7.57, N 15.03. 1H NMR
(CDCl3, 300 MHz): δ 0.59 (s, 9 H, SiCH3), 3.58 (s, 3 H, NCH3),
[6.57 (d, 1 H, 2.4 Hz), 6.72 (d, 1 H, 2.4 Hz)(methimazole)]. 13C
NMR (CDCl3, 300 MHz): δ -0.6 (SiCH3), 34.5 (NCH3), 117.8,
119.8 (methimazole CH), 167.1 (CdS). 29Si NMR (CDCl3,
300 MHz): δ 15.8. Crystal structure analysis of Me3Si(mt):
C7H14N2;SSi, CCDC-773426, T 100(2) K, orthorhombic, Pnma,
3
˚
˚
˚
˚
a 13.9036(6) A, b 7.0905(2) A, c 21.1015(9) A, V 2080.26(14) A ,
Z 8, μ(Mo KR) 0.373 mm-1, θmax 32ꢀ, 16935 reflections (3838
unique, Rint 0.0602), 133 parameters, S 1.042, R1/wR2 [I > 2σ(I )]
0.0354/0.0577, R1/wR2 (all data) 0.0793/0.0857, residual electron
Experimental Section
General Considerations. Unless otherwise indicated, the che-
micals used were commercially available. Due to the general
hydrolytic sensitivity of both chlorosilanes and methimazolylsi-
lanes, all following manipulations were carried out under an
inert atmosphere of dry argon. Toluene and THF were distilled
from sodium/benzophenone prior to use. Triethylamine and
dichloromethane were distilled from calcium hydride, and
-3
˚
density (highest peak, deepest hole) 0.462/-0.408 e A
.
Synthesis of Me2Si(mt)2. A solution of methimazole (0.80 g,
7.0 mmol) and triethylamine (1.2 g, 12 mmol) in THF (20 mL)
was stirred at ambient temperature, and dimethyldichlorosilane
(0.47 g, 3.6 mmol) was added dropwise. Immediately a precipitate
of triethylammonium chloride formed. The mixture was stored in a
refrigerator (4 ꢀC) overnight and then filtered, and the hydrochlor-
ide washed with THF (10 mL). Removal of the solvent from the
filtrate provided a white powder, recrystallization of which from
toluene (10 mL) afforded colorless crystals of Me2Si(mt)2. The
solution was decanted, and the crystals were dried in vacuo. Yield:
0.85 g (3.00 mmol, 85%). Mp: 168-170 ꢀC. Anal. Found (%): C
42.02, H 5.86, N 19.45. Calcd for C10H16N4S2Si: C 42.22, H 5.67, N
19.70. 1H NMR(CDCl3, 500 MHz): δ1.18 (s, 6 H, Si-CH3), 3.55 (s,
6 H, N-CH3), 6.70-6.74 (m, 4 H, methimazole). 13C NMR
(CDCl3, 500 MHz): δ -1.0 (SiCH3), 34.4 (NCH3), 119.0, 120.0
(methimazole CH), 167.6 (CdS). 29Si NMR (CDCl3, 500 MHz): δ
3.75. Crystal structure analysis of Me2Si(mt)2: C10H16N4S2Si,
˚
chloroform was dried over 4 A molecular sieves.
NMR spectra were recorded on a Varian Inova 500 or Inova
300 spectrometer (SiMe4 as internal standard). Elemental analyses
were carried out by the RSC microanalytical services. Single-
crystal X-ray diffraction data were collected on a NONIUS
KappaCCD diffractometer. Structures were solved with direct
methods and refined with full-matrix least-squares methods.
All non-hydrogen atoms were anisotropically refined. C-Bound
hydrogen atoms were placed in idealized positions and isotropi-
cally refined (riding model). The Si-bound hydrogen atom in the
structure of Me(H)Si(mt)2 was located on residual electron density
maps and isotropically refined without restraints. The absolute
configuration of the non-centrosymmetric structure of Me2Si(mt)2
was determined (Flack parameter: -0.05(6)) Structure solution
and refinement of F2 against all reflections were done with the
software SHELXS-97 and SHELXL-97 (G. M. Sheldrick, Uni-
CCDC-773420, T 200(2) K, orthorhombic, Pna21, a 16.8497(3)
3
˚
˚
˚
˚
A, b 11.5975(2) A, c 7.1424(1) A, V 1395.73(4) A , Z 4, μ(Mo KR)
0.452 mm-1, θmax = 32ꢀ, 34 433 reflections (4767 unique, Rint
0.0682), 154 parameters, S 1.060, R1/wR2 [I > 2σ(I)] 0.0384/
0.0690, R1/wR2 (all data) 0.0751/0.0833, x(Flack) -0.05(6), residual
€
€
versitat Gottingen, 1986-1997). Data of structure determination
and refinement for the herein presented crystal structures can be
found in the respective part of analytical data for each compound.
Crystallographic data (excluding structure factors) for the struc-
tures reported in this paper have been deposited with the Cam-
bridge Crystallographic Centre as supplementary publication nos.
CCDC 773420-773426. Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, Cambridge CB2
1EZ, UK [fax: (int.) þ44-1223/336-033; e-mail: deposit@ccdc.
cam.ac.uk].
-3
˚
electron density (highest peak, deepest hole) 0.228/-0.368 e A
.
Synthesis of Me(H)Si(mt)2. At -5 ꢀC a solution of methima-
zole (0.80 g, 7.0 mmol) and triethylamine (1.2 g, 12 mmol) in
THF (20 mL) was added dropwise to a solution of methyldi-
chlorosilane (0.42 g, 3.6 mmol) in THF (10 mL). Immediately a
precipitate of triethylammonium chloride formed. The mixture
was stored in a refrigerator (4 ꢀC) for 2 h and then filtered, and
the hydrochloride washed with THF (10 mL). Removal of the
solvent from the filtrate provided a white powder, which upon
recrystallization from toluene (10 mL) afforded colorless crys-
tals of Me(H)Si(mt)2. The solution was decanted, and the
crystals were dried in vacuo. Yield: 0.80 g (2.96 mmol, 84%).
Mp: 170-174 ꢀC. Anal. Found (%): C 39.29, H 5.34, N 20.42.
The syntheses of PhClSi(mt)2,4 PhCl2Si(mt),4 ClSi(mt)3,5 Si-
(mt)4,5 and Ph(H)Si(mt)26 have been recently reported elsewhere.
An alternative Synthesis of ClSi(mt)3, via transsilylation,
proceeds as follows: To a solution of Me3Si(mt) (10.0 g, 53.8
mmol) in THF (20 mL) was added SiCl4 (3.00 g, 17.6 mmol) at
room temperature. Within 1 day crystallization of ClSi(mt)3
commenced. Upon storage at room temperature for 7 days the
crystals were separated from the supernatant by decantation,
washed with THF (5 mL), and dried under vacuum. Yield: 6.22 g
(15.4 mmol, 87%). 1H, 13C, and 29Si NMR data correspond to
those previously reported for ClSi(mt)3; 29Si CP/MAS NMR
(δiso -50.1 ppm) confirmed the presence of only one Si species in
the solid state.
1
Calcd for C9H14N4S2Si: C 39.97, H 5.22, N 20.72. H NMR
(CDCl3, 500 MHz): δ 1.23 (d, 3 H, 3 Hz, SiCH3), 3.55 (s, 6 H,
NCH3), 5.78 (q, 1 H, 3 Hz, SiH), 6.74 (d, 2 H, 2.8 Hz), 6.84 (d, 2
H, 2.8 Hz) (methimazole). 13C NMR (CDCl3, 500 MHz): δ -3.3
(SiCH3), 34.3 (NCH3), 119.6, 120.3 (methimazole CH), 167.7
(CdS). 29Si NMR (CDCl3, 500 MHz): δ -18.2 (d, 1JSiH 264 Hz).
Crystal structure analysis of Me(H)Si(mt)2: C9H14N4S2Si,
˚
CCDC-773421, T 100(2) K, monoclinic, P21/c, a 7.4489(2) A,
3
˚
˚
˚
b 19.7998(8) A, c 8.7347(3) A, β 100.361(2)ꢀ, V 1267.25(8) A , Z
4, μ(Mo KR) 0.494 mm-1, θmax 27.5ꢀ, 21 341 reflections (2918
unique, Rint 0.1106), 149 parameters, S 1.034, R1/wR2 [I > 2σ(I )]
0.0433/0.0664, R1/wR2 (all data) 0.0893/0.0958, residual electron
Synthesis of Me3Si(mt). Toa suspensionofmethimazole(8.0 g,
70 mmol) in diethyl ether (150 mL) were added triethylamine
(10.0 g, 99 mmol) and chlorotrimethylsilane (9.0 g, 83 mmol),
-3
˚
density (highest peak, deepest hole) 0.349/-0.323 e A
Synthesis of PhMeSi(mt)2. A solution of methimazole (0.80 g,
.
(16) Wagler, J.; Hill, A. F.; Heine, T. Eur. J. Inorg. Chem. 2008, 4225.
7.0 mmol) and triethylamine (1.2 g, 12 mmol) in THF (20 mL)

Article
Organometallics, Vol. 29, No. 21, 2010 5613
was stirred at ambient temperature, and methylphenyldichlor-
osilane (0.68 g, 3.6 mmol) was added dropwise. Immediately a
precipitate of triethylammonium chloride formed. The mixture
was stirred at 60 ꢀC for 30 min, then stored in a refrigerator
(4 ꢀC) overnight. The hydrochloride was filtered and washed
with THF (10 mL). Removal of the solvent from the filtrate
provided a colorless foam, which upon recrystallization from
toluene (10 mL) afforded colorless crystals of the solvate
H 5.01, N 15.93. Calcd for C25H28N6S3Si: C 55.94, H 5.26, N
15.66. (The lower content in C and H as well as the higher content
in N may result from partial loss of toluene from the crystals.)
1H NMR(CDCl3, 500MHz):δ3.52 (s, 9 H, N-CH3), [6.72 (d, 3 H,
2.5 Hz), 6.90-7.05 (br, 3 H)(methimazole)], [7.40-7.50 (m, 3 H),
7.92 (dd, 2 H, 7.5 Hz, 1.0 Hz)(phenyl)]. 13C NMR (CDCl3,
500 MHz): δ 34.6 (NCH3), 120.4, 121.6 (methimazole), 125.8(i),
128.0 (o,m), 131.9 (p), 136.3 (o,m)(phenyl), 168.4 (CdS). 29Si
(CDCl3, 500 MHz): δ -39.9. Crystal structure analysis of PhSi-
PhMeSi(mt)2 (toluene)0.5. The solution was decanted, and the
3
crystals were briefly dried in vacuo. Yield: 1.20 g (3.06 mmol,
87%). Anal. Found (%): C 54.86, H 5.25, N 14.77. Calcd for
C37H44N8S4Si2: C 56.60, H 5.65, N 14.27. (The slightly lower
content in C and H as well as the higher content in N may result
from partial loss of toluene from the crystals.) 1H NMR (CDCl3,
500 MHz): δ 1.61 (s, 3 H, SiCH3), 3.56 (s, 6 H, NCH3), [6.30 (d, 2
H, 2.5 Hz), 6.68 (d, 2 H, 2.5 Hz)(methimazole)], 7.40-7.60 (m, 5
H, phenyl). 13C NMR (CDCl3, 500 MHz): δ -1.9 (SiCH3), 34.5
(NCH3), 119.5, 120.2 (methimazole CH), 128.5 (o,m), 128.9 (i),
131.3 (p), 134.3 (o,m), 168.0 (CdS). 29Si NMR (CDCl3, 500
(mt)3 toluene: C25H28N6S3Si, CCDC-773425, T 100(2) K, mono-
3
˚
˚
clinic, P21/n, a 12.7358(2) A, b 14.5040(3) A, c 14.6495(3) A,
˚
3
-1
˚
β 93.037(1)ꢀ, V 2702.26(9) A , Z 4, μ(Mo KR) 0.345 mm
,
θ
max = 41ꢀ, 119 198 reflections (17 784 unique, Rint 0.0793), 316
parameters, S 1.082, R1/wR2 [I > 2σ(I )] 0.0421/0.0766, R1/wR2
(all data) 0.1042/0.1128, residual electron density (highest peak,
-3
˚
deepest hole) 0.663/-0.480 e A
.
Synthesis of EtClSi(mt)2. A solution of methimazole (2.50 g,
21.9 mmol) and triethylamine (3.0 g, 29.7 mmol) in THF
(70 mL) was stirred at 0 ꢀC, and ethyltrichlorosilane (1.83 g,
11.2 mmol) was added dropwise. Immediately a precipitate of
triethylammonium chloride formed. The mixture was stored in a
refrigerator (4 ꢀC) overnight. The hydrochloride was filtered
and washed with THF (30 mL). Removal of the solvent from the
filtrate delivered a white powder, which upon recrystallization
from toluene (12 mL) afforded a white powder of EtClSi(mt)2.
The solution was decanted, and the solid was dried in vacuo.
Yield: 2.33 g (7.32 mmol, 67%). The 1H and 13C NMR spectra
(CDCl3) reveal the presence of at least three chemically inde-
pendent ethyl moieties, while the 29Si NMR (CDCl3) spectrum is
consistent with the presence of EtCl2Si(mt), EtClSi(mt)2, and
EtSi(mt)3 suggested by the presence of three signals (δ 0.0,
-12.6, -24.0) in approximate intensity ratio 1:2:1.
Synthesis of EtSi(mt)3. From the above crude EtClSi(mt)2
crystalline EtSi(mt)3 was obtained as dichloromethane solvate
by dissolution of EtClSi(mt)2 (1.36 g, 4.27 mmol) in dichloro-
methane (5.5 mL) followed by addition of diethyl ether (4 mL).
Within 1 day large crystals of EtSi(mt)3.CH2Cl2 formed, which
were separated by decantation and briefly dried in vacuo. Yield:
0.51 g (1.06 mmol, 50%) with respect to the formation of
EtCl2Si(mt) as byproduct. Anal. Found (%): C 37.24, H 4.60,
N 17.56. Calcd for C15H22Cl2N6S3Si: C 37.41, H 4.60, N 17.45.
1H NMR (CDCl3, 300 MHz): δ 1.25 (t, 3 H, 7.8 Hz, SiCH2CH3),
2.32 (q, 2 H, 7.8 Hz, SiCH2CH3), 3.55 (s, 9 H, NCH3), [6.71 (d,
3 H, 2.4 Hz), 6.74 (d, 3 H, 2.4 Hz)(methimazole)]. 13C NMR
(CDCl3, 300 MHz): δ 7.2, 7.6 (SiCH2CH3), 34.6 (NCH3), 120.3,
120.6 (methimazole CH), 167.9 (CdS). 29Si NMR (CDCl3, 500
MHz): δ -8.9. Crystal structure analysis of (PhMeSi(mt)2)2
toluene: C37H44N8S4Si2, CCDC-773422, T 200(2) K, monocli-
3
˚
nic, P21/c, a 12.5018(2) A, b 7.6542(1) A, c 21.4230(3) A,
˚
˚
3
-1
˚
β 97.356(2)ꢀ, V 2033.12(5) A , Z 2, μ(Mo KR) 0.330 mm
,
θ
max = 32ꢀ, 43 207 reflections (7034 unique, Rint 0.0522), 263
parameters, S 1.062, R1/wR2 [I > 2σ(I )] 0.0470/0.0695, R1/wR2
(all data) 0.1263/0.1362, residual electron density (highest peak,
-3
˚
deepest hole) 0.514/-0.415 e A
.
Synthesis of Ph2Si(mt)2. A solution of methimazole (0.80 g,
7.0 mmol), triethylamine (2.0 g, 20 mmol), and N-methylimida-
zole (0.1 g) in THF (20 mL) was stirred at ambient temperature,
and diphenyldichlorosilane (0.90 g, 3.6 mmol) was added drop-
wise. Immediately a precipitate of triethylammonium chloride
formed. The mixture was stirred at 60 ꢀC for 1 h, then stored in a
refrigerator (4 ꢀC) overnight. The hydrochloride was filtered off
and washed with THF (5 mL). Removal of the solvent from the
filtrate delivered a colorless foam, which upon recrystallization
from toluene (20 mL) afforded colorless crystals of the solvate
Ph2Si(mt)2 (toluene)0.5. The solution was decanted, and the
3
crystals were briefly dried in vacuo. Yield: 1.21 g (2.66 mmol,
76%). Anal. Found (%): C 59.04, H 5.14, N 12.82. Calcd for
C47H48N8S4Si2: C 62.08, H 5.32, N 12.32. (The lower content in
C and H as well as the higher content in N may result from
partial loss of toluene from the crystals.) 1H NMR (CDCl3, 500
MHz): δ 3.56 (s, 6 H, N-CH3), [6.63 (d, 2 H, 2.5 Hz), 6.70 (d, 2 H,
2.5 Hz)(methimazole)], [7.40-7.55 (m, 6 H), 7.84 (dd, 4 H,
8.0 Hz, 1.5 Hz)(phenyl)]. 13C NMR (CDCl3, 500 MHz): δ 34.7
(N-CH3), 120.2, 120.6 (methimazole CH), 128.0 (o,m), 128.3 (i),
131.2 (p), 136.3 (o,m) (phenyl), 168.8 (CdS). 29Si NMR (CDCl3,
MHz): δ -24.0. Crystal structure analysis of EtSi(mt)3 CH2Cl2:
C15H22Cl2N6S3Si, CCDC-773424, T 100(2) K, monoclinic, P21/
3
˚
˚
˚
500 MHz): δ -22.5. Crystal structure analysis of (Ph2Si(mt)2)2
toluene: C47H48N8S4Si2, CCDC-773423, T 200(2) K, triclinic,
n, a 10.8429(1) A, b 17.0694(3) A, c 12.8979(2) A, β 113.057(1)ꢀ,
3
V 2196.47(6) A , Z 4, μ(Mo KR) 0.649 mm-1, θmax 45ꢀ, 117 337
3
˚
˚
˚
˚
P1, a 9.4659(2) A, b 10.2308(3) A, c 12.0804(3) A, R 99.860(2)ꢀ,
reflections (18 099 unique, Rint 0.0550), 248 parameters, S 1.049,
R1/wR2 [I > 2σ(I )] 0.0365/0.0586, R1/wR2 (all data) 0.0861/
0.0923, residual electron density (highest peak, deepest hole)
3
˚
β 97.936(1)ꢀ, γ 91.312(1)ꢀ, V 1140.28(5) A , Z 1, μ(Mo KR)
0.305 mm-1, θmax=28.5ꢀ, 25 025 reflections (5702 unique, Rint
0.0444), 272 parameters, S 1.053, R1/wR2 [I > 2σ(I )] 0.0432/
0.0639, R1/wR2 (all data) 0.1077/0.1166, residual electron den-
-3
˚
0.764/-1.156 e A
.
-3
˚
sity (highest peak, deepest hole) 0.487/-0.390 e A
.
Acknowledgment. This work was supported by a fel-
lowship within the Post-Doctoral Programme of the
German Academic Exchange Service (DAAD) and by
the Australian Research Council (DP0771497).
Synthesis of PhSi(mt)3. A solution of methimazole (10.0 g,
87.7 mmol), triethylamine (10.0 g, 99 mmol), and N-methylimi-
dazole (0.2 g) in THF (120 mL) was stirred at ambient tempera-
ture, and phenyltrichlorosilane (6.25 g, 29.6 mmol) was added
dropwise. Immediately, a precipitate of triethylammonium
chloride formed. The mixture was stirred at 50 ꢀC for 1.5 h,
then stored in a refrigerator (4 ꢀC) overnight. The hydrochloride
was filtered off and washed with THF (100 mL). From the
filtrate the solvent was removed under reduced pressure, and the
resultant white foam was dissolved in hot toluene (40 mL). After
storage at room temperature for 1 day followed by storage at
4 ꢀC for 5 days the solid product (PhSi(mt)3.toluene) was filtered
off, washed with toluene (20 mL), and briefly dried in vacuo.
Yield: 12.6 g (23.5 mmol, 80%). Anal. Found (%): C 51.06,
Supporting Information Available: X-ray crystallographic
files in CIF format (for structure determinations of Me3Si(mt),
Me2Si(mt)2, Me(H)Si(mt)2, PhMeSi(mt)2 0.5toluene, Ph2Si-
3
(mt)2 0.5toluene, EtSi(mt)3 CH2Cl2, and PhSi(mt)3 toluene)
3
3
3
and a pdf document containing ORTEP diagrams of Ph(H)Si-
(mt)2, PhClSi(mt)2, PhCl2Si(mt), ClSi(mt)3, and Si(mt)4 as well
as details of the computational analyses are deposited with the
ACS. This information is available free of charge via the
Internet at http://pubs.acs.org.