Angewandte
Chemie
(Scheme 1) with potassium graphite (KC8) in THF, which
afforded air-sensitive, orange-red crystals of 2 (5.21% yield).
Compound 2 is highly soluble in solvents such as diethyl ether,
toluene, and THF. It has been characterized by elemental
analysis, spectroscopic methods, and X-ray structural analysis.
equivalents hydrazine and diphosphine.[16] It is interesting to
I
I
À
mention that a bis(carbene) with a C C bond has not been
reported to date.
In conclusion, we have prepared and fully characterized a
I
I
À
compound with a Si Si bond, which is stabilized by bulky
1
The H and 13C NMR spectra of 2 (in [D8]THF) display one
amidinate ligands. Compound 2 exhibits a gauche-bent
À
set of resonances that result from the amidinate ligand. The
resonances show a downfield shift relative to that of 1 and also
from chlorosilylene.[10] The shift is probably due to the lower
oxidation state of the silicon center (+ I in 2) compared to
silylene, where normally a formal oxidation state at the Si
geometry, and the Si Si bond shows no multiple-bond
character. Currently we are exploring the reactivity of
compound 2.
center of + II is observed. The resonance of 2 in the 29Si NMR Experimental Section
All manipulations were carried out in an inert atmosphere of
spectrum in [D8]THF (75.71 ppm) is further downfield than
dinitrogen using standard Schlenk techniques or in a dinitrogen-
filled glove box. Solvents were dried over molecular sieves and
distilled prior to use. The NMR spectra were recorded in C6D6 and
[D8]THF. The chemical shifts d are given relative to SiMe4. The EI
mass spectrum was obtained using a Finnigan MAT 8230 instrument.
Elemental analyses were performed by the Institut fꢁr Anorganische
Chemie, Universitꢂt Gꢃttingen. The melting point was measured in a
sealed glass tube on a Bꢁchi B-540 melting point apparatus and was
uncorrected.
À
that of RClSi SiClR, (d = 38.4 ppm; R = 1,3-bis-(2,6-diiso-
propylphenyl)imidazol-2-ylidene).[8] We were also curious to
measure the NMR spectrum in nonpolar solvent (C6D6), and
in the 29Si NMR spectrum, 2 resonates at d = 76.29 ppm. So
there is very little downfield shift in the 29Si NMR spectrum.
The molecular ion of 2 appeared as the most abundant peak in
the EI mass spectrum at m/z 518.3.
The molecular structure of 2 is shown in Figure 1.[12]
Compound 2 crystallizes in the monoclinic space group
C2/c. The coordination environment of each of the Si atoms
exhibits a distorted tetrahedral geometry. The coordination
2: THF (50 mL) was added to a mixture of 1 (1.49 g, 4.08 mmol)
and potassium graphite (1.65 g, 12.24 mmol) at À788C. The resulting
red mixture was stirred overnight. The solvent was then removed in
vacuo, and the residue was extracted with toluene (50 mL). The
insoluble precipitate was filtered off and the red filtrate was
concentrated to yield orange-red crystals of 2 (0.11 g, 5.21%).
1
M.p.:155–1608C. H NMR (200 MHz, [D8]THF, 258C): d = 1.23 ppm
(s, 36H, tBu), 7.34–7.38 ppm (m, 10H, Ph); 13C{1H} NMR
(75.47 MHz, [D8]THF, 258C): d = 32.19 (CMe3), 53.36 (CMe3),
128.42, 129.91, 130.95, 131.95, 134.35, 136.49, (Ph), 146.32 ppm
(NCN); 29Si{1H} NMR (59.62 MHz, [D8]THF, 258C): d = 75.71 ppm;
1H NMR (200 MHz, C6D6, 258C): d = 1.18 ppm (s, 36H, tBu), 7.22–
7.30 ppm (m, 10H, Ph); 13C{1H} NMR (125.75 MHz, C6D6, 258C): d =
32.01 (CMe3), 53.73 (CMe3), 127.71, 128.19, 128.40, 129.21, 130.32,
135.98 (Ph), 145.67 ppm (NCN); 29Si{1H} NMR (99.36 MHz, C6D6,
258C): d = 76.29 ppm; EI-MS: m/z(%): 518.3 [M+] (100). Elemental
analysis (%) calcd for C30H46N4Si2 (518.33): C 69.44, H 8.94, N 10.80;
found: C 68.26, H 8.63, N 11.06.
Figure 1. ORTEP view (50% ellipsoid probability) of compound 2.
Hydrogen atoms have been removed for clarity. Selected bond lengths
[ꢃ] and angles [8] Si1–Si1A 2.413(2), Si1–N2 1.866(4), Si1–N1
1.874(4), C1–N1 1.467(6), C9–N1 1.331(6); N2-Si1-N1 69.52(18),
N2-Si1-Si1A 102.15(14), C9-N1-C1 130.09(3).
Received: June 3, 2009
Revised: July 22, 2009
Published online: October 2, 2009
Keywords: N ligands · potassium · reduction · silicon
.
sites of the Si centers are each occupied by the N atoms of the
amidinato ligand and by the other Si atom. The lone pair of
each Si atom occupies the remaining coordination site of the
tetrahedral geometry. The X-ray structural analysis of 2
[2] Y. Apeloig, R. Pauncz, M. Karni, R. West, W. Steiner, D.
À
reveals that the Si Si core is sterically well-shielded by the
[3] Experimental determinations of DES–T in SiH2: a) A. Kasdan, E.
À
two amidinate ligands. The central Si Si bond (2.413(2) ꢀ) is
only about 0.07 ꢀ longer than the sum of the Si covalent radii
ˇˇ ´
(2.34 ꢀ)[13] and about 0.05 ꢀ longer than the Si Si single bond
À
in a-silicon (2.36 ꢀ).[14] The value is 5.17% larger than the
longest disilene bond (2.29 ꢀ)[6] and 14.6% longer than the
reported disilyne bond (2.06 ꢀ),[7] and it also compares well
with that of the SiI dimer reported by Robinson et al.
(2.393 ꢀ).[8] The sum of the bond angles of the Si atoms in 2
(282.358 average) compares very well with literature values.[15]
Compound 2 possesses a gauche-bent conformation. This
structural feature of 2 is akin to that of the GeI dimer,[11] which
also favors a gauche-bent geometry, as do the isolobal
[5] Reviews elaborating on the CGMT model: a) M. Driess, H.
[6] a) N. Tokitoh, H. Suzuki, R. Okazaki, K. Ogawa, J. Am. Chem.
Angew. Chem. Int. Ed. 2009, 48, 8536 –8538
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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