C O M M U N I C A T I O N S
that reported for the monosilylene alkoxides [LSiOtBu] (δ -5.2
ppm) and [LSiOiPr] (δ -13.5 ppm),12 respectively.
The molecular structure of bis-silylene oxide 1 is shown in Figure
1. The Si-O distances in 1 of 1.641(2) and 1.652(2) Å are
comparable to those of siloxysilylene A [1.6442(3) Å and 1.6501(2)
Å] and, thus, typical for silicon-oxygen single bonds of other
disiloxanes.13 Moreover, as expected for an disiloxane-like sys-
tem,13 the Si1-O-Si2 angle of 1 is bent 159.88(15)° and larger
than that observed for a C-OsC moiety of ethers. Accordingly,
DFT calculations of compound 1 revealed that the Si1-O-Si2
angle deformation energy is very small. In fact, the energy
difference between the experimental geometry (159.88°) and linear
Si-OsSi arrangement is only 0.17 kcal mol-1 (see Supporting
Information). The sum of bond angles at Si1 and Si2 are 277.69°
and 275.34°, respectively, which is consistent with the presence of
a lone pair at each silicon center.
Figure 2. Molecular structure of 3. Thermal ellipsoids are drawn at 50%
probability level. Hydrogen atoms are omitted for clarity. The tBu group
on the N3 atom was disordered over two positions (site occupancies 0.76
and 0.24), but only one is shown. Selected bond lengths (Å) and angles
(deg): Si1-Ni1, 2.1969(7); Si2-Ni1, 2.1908(7); Si1-O1, 1.7011(15);
Si1-N1, 1.8929(19); Si1-N2, 1.875(2); Si2-O1, 1.7081(17); Si2-N3,
1.8776(19); Si2-N4, 1.893(2); Si1-O1-Si2, 93.44(8); Si1-Ni1-Si2,
68.90(3); N1-Si1-N2, 69.41(9); N3-Si2-N4, 69.54(8).
and one COD ligand are coordinated to the nickel atom with the
Si1-Ni1-Si2 angle at 68.90(3)°. The Si-O bond lengths in 3
[1.7011 (15) and 1.7081(17) Å] are longer than that in 1 [1.641(2)
and 1.652(2) Å], while the Si1-O-Si2 angle of 3 (93.44(8)°) is
significantly smaller than that in 1. The Ni-Si bond lengths
[2.1908(7) and 2.1969(7) Å] are slightly shorter than those in bis-
silylene nickel complex Ia [2.207(2) and 2.216(2) Å]6a but longer
than those found in bis-silylene nickel complex II (2.1395(8) Å).7
Moreover, the Ni-Si bond lengths of bis-silylene nickel complex
1 are longer than those in ylide-like silylene-nickel complexes
[2.0369(6) and 2.0597(10)].14 The Ni-C distances (2.070-2.090
Å) in 2 are shorter than those in Ni(COD)2 (2.11-2.13 Å)15 and
bis-silylene nickel complex II (2.130-2.146 Å),7 indicating a
somewhat stronger π back-donation from the nickel atom to the
chelating bis-silylene ligand.
Figure 1. Molecular structure of 1. Thermal ellipsoids are drawn at 50%
probability level. Hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and angles (deg): Si1-O1, 1.641(2); Si1-N1, 1.896(3);
Si1-N2, 1.902(3); Si2-O1, 1.652(2); Si2-N3, 1.888(2); Si2-N4, 1.908(3);
Si1-O1-Si2,159.88(15);O1-Si1-N1,104.17(12);O1-Si1-N2,105.35(11);
O1-Si2-N3, 101.96(11); O1-Si2-N4, 104.81(12); N1-Si1-N2, 68.15(10);
N3-Si2-N4, 68.55(11).
In conclusion, we have reported a facile method for the
preparation of the isolable bis-silylene oxide (“disilylenoxane”) 1
by dehydrochloration of the corresponding disiloxane with base.
The reaction of 1 with [Ni(COD)2] leads to the first bis-silylene
oxide nickel complex 3, indicating that 1 could serve as a novel
bidentate ligand for transition-metal chemistry. Investigations on
the reactivity of 1 toward other transition-metal complexes and their
use as molecular catalysts are currently underway.
To probe the chelate coordination ability of 1, its reactivity
toward [Ni(COD)2] (COD ) cycloocta-1,5-diene) was investigated.
A solution of the bis-silylene oxide 1 was added to 1 molar equiv
of [Ni(COD)2] in toluene at room temperature to furnish an intensely
red-colored reaction solution. Recrystallization of the crude product
from a saturated n-hexane solution at -30 °C afforded dark red
crystals of the Ni complex 3 in 91% yield (Scheme 3). The
constitution and composition of 3 could be determined by NMR
spectroscopy, elemental analysis, and ESI mass spectrometry. The
1H NMR spectrum of 3 exhibits one singlet for the tBu groups and
one set of resonances for the COD ligand and Ph groups of the
amidinate ligands. The 29Si NMR spectrum of 3 exhibits one singlet
(δ ) 32.8 ppm), which shows a downfield shift relative to that of
the “free” ligand 1. The observed downfield shift for the 29Si(II)
nuclei in 3 clearly suggests the presence of a bis-silylene chelate
complex.
Acknowledgment. We would like to thank the Deutsche
Forschungsgemeinschaft (DR 226-17-1) and the Cluster of Excel-
cat.tu-berlin.de) as well as the JSPS (fellowship for S.I.) for financial
support of this work.
Supporting Information Available: Experimental details for the
synthesis and spectroscopic data of 1, 2, and 3, DFT calculations and
Cartesian coordinates of 1 (PDF); crystallographic data for 1, 2, and 3
(CIF). This material is available free of charge via the Internet at http://
pubs.acs.org
Scheme 3. Synthesis of 3
References
(1) For reviews on silylene complex, see: (a) Tilley, T. D. In The Chemistry
of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: New
York, 1989; Chapter 24. (b) Eisen, M. S. In The Chemistry of Organic
Compounds; Rappoport, Z., Apeloig, Y., Eds.; Wiley: New York, 1998;
Chapter 35. (c) Ogino, H. Chem. ReV. 2002, 2, 291. (d) Okazaki, M.; Tobita,
H.; Ogino, H. J. Chem. Soc., Dalton Trans. 2003, 493. (e) Waterman, R.;
Hayes, P. G.; Tilley, T. D. Acc. Chem. Res. 2007, 40, 712.
(2) (a) Buechner, W. J. Organomet. Chem. Lib. 1980, 9, 409. (b) Brook, M. A.
Silicon in Organic, Organometallic, and Polymer Chemistry; Wiley: New
York, 2000; pp 382-384 and references cited therein.
This is confirmed by X-ray diffraction analysis; the molecular
structure of 3 is displayed in Figure 2. The two silylene subunits
9
J. AM. CHEM. SOC. VOL. 132, NO. 45, 2010 15891