Expanding the steric coverage offered by bis(amidosilyl) chelates: Isolation of low-coordinate N-heterocyclic germylene complexes

Article abstract of DOI:10.1021/ic300495k

The synthesis and coordination chemistry of a series of dianionic bis(amido)silyl and bis(amido)disilyl, [NSiN] and [NSiSiN], chelates with N-bound aryl or sterically modified triarylsilyl (SiAr₃) groups is reported. In order to provide a consistent comparison of the steric coverage afforded by each ligand construct, various two-coordinate N-heterocyclic germylene complexes featuring each ligand set were prepared and oxidative S-atom transfer chemistry was explored. In the cases where clean oxidation transpired, sulfido-bridged centrosymmetric germanium(IV) dimers of the general form [LGe(μ-S)]₂ (L = bis(amidosilyl) ligands) were obtained in lieu of the target monomeric germanethiones with discrete Ge=S double bonds. These results indicate that the reported chelates possess sufficient conformational flexibility to allow for the dimerization of LGe=S units to occur. Notably, the new triarylsilyl groups (4-RC₆H₄)₃Si- (R = ^tBu and ⁱPr) still offer considerably expanded degrees of steric coverage relative to the parent congener, -SiPh_3, and thus the use of substituted triarylsilyl groups within ligand design strategies should be a generally useful concept in advancing low-coordination main group and transition-metal chemistry.

Full text of DOI:10.1021/ic300495k

Article
pubs.acs.org/IC
Expanding the Steric Coverage Offered by Bis(amidosilyl) Chelates:
Isolation of Low-Coordinate N-Heterocyclic Germylene Complexes
Sean K. Liew, S. M. Ibrahim Al-Rafia, James T. Goettel, Paul A. Lummis, Sean M. McDonald,
Leah J. Miedema, Michael J. Ferguson, Robert McDonald, and Eric Rivard*
Department of Chemistry, University of Alberta, 11227 Saskatchewan Drive, Edmonton, Alberta, Canada, T6G 2G2
S
* Supporting Information
ABSTRACT: The synthesis and coordination chemistry of a series of
dianionic bis(amido)silyl and bis(amido)disilyl, [NSiN] and [NSi-
SiN], chelates with N-bound aryl or sterically modified triarylsilyl
(SiAr3) groups is reported. In order to provide a consistent
comparison of the steric coverage afforded by each ligand construct,
various two-coordinate N-heterocyclic germylene complexes featuring
each ligand set were prepared and oxidative S-atom transfer chemistry
was explored. In the cases where clean oxidation transpired, sulfido-
bridged centrosymmetric germanium(IV) dimers of the general form
[LGe(μ-S)]2 (L = bis(amidosilyl) ligands) were obtained in lieu of the
target monomeric germanethiones with discrete GeS double bonds.
These results indicate that the reported chelates possess sufficient
conformational flexibility to allow for the dimerization of LGeS
units to occur. Notably, the new triarylsilyl groups (4-RC6H4)3Si (R
= tBu and iPr) still offer considerably expanded degrees of steric coverage relative to the parent congener, SiPh3, and thus the
use of substituted triarylsilyl groups within ligand design strategies should be a generally useful concept in advancing low-
coordination main group and transition-metal chemistry.
by the new triarylsilyl side groups with the tighter steric pocket
inherent to an [NSiSiN] chelate, we hope to prepare low-
coordinate complexes with concomitantly unique forms of
chemical bonding and/or reactivity. Specifically, this paper
describes the preparation of reactive two-coordinate germylene
complexes supported by new bulky silylamido ligands and
subsequent atom transfer chemistry involving these low valent
Ge(II) complexes and elemental sulfur.8 A further rationale for
exploring the coordination chemistry of Ge(II) is that
germanium can be regarded as a steric atomic model for first
row transition metals, thus the chemistry in this paper should
serve as a guide for the future use of our sterically hindered
silylamido ligands in the realm of d-block chemistry.
INTRODUCTION
■
The preparation of complexes that contain ligands with high
degrees of steric coverage has had a tremendous influence in
expanding the range of chemical transformations that can be
mediated by inorganic elements.1 A parallel strategy that is
prominent in synthetic inorganic chemistry is the design of
ligand classes with readily modifiable steric and electronic
properties, thus enabling key structure−function relationships
to be elucidated in a rapid manner. As a consequence,
breakthroughs in ligand development can translate into the
discovery of novel bond activation processes2 and often
provides access to new bonding environments throughout the
Periodic Table.3
With the above-mentioned concepts in mind, there has been
considerable focus on exploring the synthesis and coordination
chemistry of complexes supported by silylamido chelates.
Silylamido ligands each contain Si−N linkages as part of their
chelate backbones, and hallmarks of these ligands include their
ease of synthesis and the ability to alter the ligand donor
properties by changing the substituent bound at either the
intraligand silicon or nitrogen centers.1e,4,5
Motivated by our prior work involving formally dianionic
bis(amido)silyl [NSiN] ligands,6 we now introduce a series of
[NSiSiN] chelates bearing elongated tetramethyldisilyl,
−SiMe2−SiMe2−, backbones in conjunction with new sterically
expanded triarylsilyl, (4-RC6H4)3Si−, umbrella-shaped moieties
(R = tBu and iPr).7 By combining the greater radial bulk offered
EXPERIMENTAL SECTION
■
General. All reactions were performed using standard Schlenk
techniques under an atmosphere of nitrogen or in a nitrogen-filled
glovebox (Innovative Technology, Inc.). Solvents were dried using a
Grubbs-type solvent purification system9 manufactured by Innovative
Technology, Inc., and degassed (freeze−pump−thaw method) and
stored under an atmosphere of nitrogen prior to use. n-Butyl lithium
(1.6 M solution in hexanes), GeCl2·dioxane, SnCl2, Li[NH2],
magnesium, iodine, and elemental sulfur were purchased from Aldrich
and used as received. Dichloroditolylsilane and dichlorotetramethyldi-
silane were obtained from Gelest, degassed (freeze−pump−thaw), and
Received: March 5, 2012
Published: April 24, 2012
© 2012 American Chemical Society
5471
dx.doi.org/10.1021/ic300495k | Inorg. Chem. 2012, 51, 5471−5480

Inorganic Chemistry
Article
Table 1. Crystallographic Data for Compounds 2−5
2
3
4·tol·THF
5
empirical formula
fw
C28H46GeN2Si2
539.44
C28H46N2Si2Sn
585.54
C67H108Ge2N4SiOS2Si4
1307.2
C27H33ClSi
421.07
cryst dimens (mm3)
cryst syst
space group
unit cell dimensions
a (Å)
0.61 × 0.29 × 0.18
monoclinic
P21/n
0.64 × 0.53 × 0.22
triclinic
0.32 × 0.10 × 0.07
triclinic
0.48 × 0.40 × 0.37
triclinic
P1
̅
P1
̅
P1
̅
13.5706(4)
15.5783(5)
14.5196(4)
90
9.1347(5)
10.0168(5)
19.1344(10)
76.6557(5)
86.6259(5)
66.6516(5)
1562.99(14)
2
9.960(2)
14.101(3)
15.228(3)
102.871(3)
93.857(3)
107.097(2)
1972.6(8)
1
10.1381(3)
11.5933(4)
11.6907(4)
83.9233(3)
65.1785(3)
89.4459(3)
1239.19(7)
2
b (Å)
c (Å)
α (deg)
β (deg)
97.2967(3)
90
γ (deg)
V (Å3)
3044.69(13)
4
Z
ρ (g cm−3
)
1.177
1.244
1.100
1.128
abs coeff (mm−1
)
1.102
0.911
0.913
0.213
T (K)
173(1)
55.18
173(1)
173(1)
173(1)
2θmax (deg)
total data
55.10
50.50
55.26
26915
14072
14188
11052
unique data (Rint)
obs data [I > 2σ(I)]
params
7038 (0.0159)
6181
7151 (0.0072)
6802
7124 (0.0641)
5240
5692 (0.0095)
5111
298
302
363
262
a
R1 [I > 2σ(I)]
0.0250
0.0763
0.0186
0.0870
0.0497
a
wR2 [all data]
0.0586
0.2703
0.1428
max/min Δρ (e− Å−3
)
0.467/−0.309
0.531/−0.332
1.865/−1.461
0.963/−0.491
a
R1 = ∑||Fo| − |Fc||/∑|Fo|; wR2 = [∑w(Fo − Fc2)2/∑w(Fo )]1/2
.
2
4
stored under an N2 atmosphere prior to use. Anhydrous Me3NO
(Aldrich) was recrystallized from a dry and degassed DMF/hexanes
mixture (−35 °C). 4-iPrC6H4Br, 4-tBuC6H4Br, Li[NHDipp] (Dipp =
2,6-iPr2C6H3), and MesCNO (Mes = 2,4,6-Me3C6H2) were prepared
according to literature procedures.10−13 1H, 13C{1H}, and 29Si{1H}
NMR spectra were recorded with either Varian iNova-400 or iNova-
500 spectrometers and referenced externally to SiMe4 (1H, 13C{1H},
and 29Si). Elemental analyses and mass spectrometry were performed
by the Analytical and Instrumentation Laboratory at the University of
Alberta. Infrared spectra were recorded with a Nic-Plan FTIR
Microscope. Melting points were obtained in sealed glass capillaries
under nitrogen using a MelTemp melting point apparatus and are
uncorrected.
X-ray Crystallography. Crystals of appropriate quality for X-ray
diffraction studies were removed from either a Schlenk tube under a
stream of nitrogen, or from a vial (glovebox), and immediately covered
with a thin layer of hydrocarbon oil (Paratone-N). A suitable crystal
was then selected, attached to a glass fiber, and quickly placed in a low-
temperature stream of nitrogen.14 All data were collected using a
Bruker APEX II CCD detector/D8 diffractometer using Mo or Cu Kα
radiation, with the crystal cooled to −100 °C. The data were corrected
for absorption through Gaussian integration from indexing of the
crystal faces. Structures were solved using the direct methods
programs SHELXS-9715 (compounds 2, 4, 5, 7, 12, and 13) and
SIR9716 (compound 3), or using the Patterson search/structure
expansion facilities within the DIRDIF-200817 and SHELXD18
program suites (compound 2). Refinements were completed using
the program SHELXL-97.15 Hydrogen atoms were assigned positions
based on the sp2 or sp3 hybridization geometries of their attached
carbon or nitrogen atoms and were given thermal parameters 20%
greater than those of their parent atoms. See Tables 1 and 2 for a
listing of crystallographic data.
C22SC27S and C26SC27S distances restrained to be
2.51(2) Å.
Compound 7: The Si−C31A and Si−C31B distances (involving
disordered positions for the ipso carbon of one of the 4-
isopropylphenyl groups) were constrained to be equal (within 0.02
Å) during the refinement.
Compound 12: The geometries of the isopropyl groups defined by
atoms C27B to C29B and C47B to C49B (the minor orientations)
were restrained to be the same as that of C37 to C39. Additionally, the
phenyl rings defined by atoms C21A to C26A, C21B to C26B, C31B
to C36B, C41A to C46A, and C41B to C46B were constrained to be
idealized hexagons with C−C distances of 1.39 Å.
Compound 13: Attempts to refine peaks of residual electron
density as disordered or partial-occupancy hexane solvent molecules
were unsuccessful. The data were corrected for disordered electron
density through use of the SQUEEZE procedure as incorporated in
PLATON.19 A total solvent accessible void volume of 591 Å3 with a
total electron count of 89 (consistent with two molecules of solvent
hexane or one molecule per asymmetric unit) was found in the unit
cell. The C44B−C47B, C47B−C48B, and C47B−C49B distances
were restrained to be 1.51(1) Å. The C17−C18A, C17−C19A, C17−
C18B, and C17−C19B distances were restrained to be the same by the
SHELX SAME instruction. Additionally, the phenyl ring defined by
carbon atoms C41B to C46B was constrained to be an idealized
hexagon with C−C distances of 1.39 Å.
Synthetic Procedures. Preparation of (DippNH)2Si2Me4 (1).20
To a solution of Li[NHDipp] (1.043 g, 5.69 mmol) in 10 mL
of cold (−35 °C) Et2O was added dropwise a cold (−35 °C)
solution of ClSiMe2SiMe2Cl (0.532 g, 2.84 mmol) in 5 mL of
Et2O. The resulting mixture was slowly warmed to room
temperature and stirred for 12 h to give a yellow solution over a
white precipitate. The reaction mixture was then filtered
through Celite and the volatiles were removed to yield 1 as a
light yellow oil (1.300 g, 98%). 1H NMR (400 MHz, C6D6): δ =
0.25 (s, 12H, SiCH3), 1.21 (d, 24H, 3JHH = 7.2 Hz, CH(CH3)2),
2.28 (s, 2H, NH), 3.47 (septet, 4H, 3JHH = 6.8 Hz, CH(CH3)2),
and 7.07−7.18 (m, 6H, ArH). 13C{1H} NMR (100 MHz,
Special Refinement Conditions. Compound 4: The
following distance restraints were applied to the solvent
tetrahydrofuran molecules: OC, 1.43(1); CC, 1.53(1) Å.
The solvent toluene molecule phenyl ring was constrained to
be an idealized hexagon with CC distances of 1.39 Å, and
5472
dx.doi.org/10.1021/ic300495k | Inorg. Chem. 2012, 51, 5471−5480

Inorganic Chemistry
Article
n
Preparation of [(Me2SiNDipp)2Sn:] (3). A solution of BuLi (0.623
mL, 1.6 M solution in hexanes, 1.00 mmol) was slowly added to a
solution of 1 (0.231 g, 0.50 mmol) in 5 mL of Et2O at −35 °C. The
resulting mixture was warmed to room temperature and stirred for 2 h,
then recooled to −35 °C, and slowly added to a slurry of SnCl2 (0.105
g, 0.55 mmol) in 5 mL of Et2O. Afterward, the reaction mixture was
warmed to room temperature and stirred for 15 h to give a deep
yellow solution over a white precipitate (LiCl). Filtration of the
mixture through Celite yielded a pale yellow solution, which afforded a
pale yellow solid once the solvent was removed (0.266 g, 91%). This
product was recrystallized from cold (−35 °C) Et2O to give 3 as
Table 2. Crystallographic Data for Compounds 7, 12, and 13
7
12
13
empirical
formula
C27H35NSi
C55H78GeN2Si4
C148H188Ge2N4S2Si6
fw
401.65
988.17
2400.86
cryst dimens
(mm3)
0.61 × 0.21 ×
0.16
0.39 × 0.31 ×
0.22
0.22 × 0.12 × 0.09
cryst syst
monoclinic
monoclinic
triclinic
space group
P21/n
P21/n
P1
̅
unit cell dimensions
1
yellow rhomboid-shaped crystals. H NMR (400 MHz, C6D6): δ =
a (Å)
15.0786(16)
18.6549(5)
16.2623(4)
21.0055(5)
90
15.3279(11)
16.5942(12)
16.8715(13)
62.851(3)
66.564(4)
83.170(4)
3493.2(4)
1
3
0.27 (s, 12H, SiCH3), 1.15 (d, 12H, JHH = 6.8 Hz, CH(CH3)2), 1.32
b (Å)
6.8829(7)
23.297(3)
90
(d, 12H, JHH = 6.8 Hz, CH(CH3)2), 3.68 (septet, 4H, 3JHH = 6.8 Hz,
3
c (Å)
CH(CH3)2), 7.07−7.10 (m, 2H, ArH), and 7.19 (d, 4H, 3JHH = 8.0 Hz,
ArH). 13C{1H} NMR (100 MHz, C6D6): δ = 2.2 (SiCH3), 23.2
(CH(CH3)2), 27.7 (CH(CH3)2), 28.1 (CH(CH3)2), 123.8 (ArC),
124.5 (ArC), 141.5 (ArC), and 145.4 (ArC). 29Si{1H} NMR (99 MHz,
C6D6): δ = −2.2. HR-MS, EI (m/z): calcd. for [M+]: 586.22217.
Found: 586.22284 (Δppm =1.1). Mp (°C): 169−171. Anal. calcd for
C28H46N2Si2Sn: C, 57.43; H, 7.92; N, 4.78. Found: C, 57.56; H, 8.06;
N, 4.86.
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
93.6135(14)
90
116.4250(10)
90
2413.0(4)
4
5706.7(2)
4
ρ (g cm−3
)
1.106
1.150
1.141
abs coeff
0.110
1.800
1.668
(mm−1
)
Preparation of [(Me2SiNDipp)2Ge(μ-S)]2 (4). Elemental sulfur (8.3
mg, 0.26 mmol) and 2 (0.149 g, 0.261 mmol) were combined in 5 mL
of Et2O and the resulting reaction mixture was then stirred for 24 h.
Removal of the volatiles yielded a white microcrystalline powder from
which X-ray quality crystals of 4 (needles) were subsequently grown
from a solution of toluene and THF at −35 °C (34 mg, 22%). H
NMR (400 MHz, C6D6): δ = 0.06 (s, 12H, SiCH3), 1.04 (br, 12H,
T (K)
173(1)
173(1)
173(1)
2θmax (deg)
52.80
138.88
140.40
total data
18635
28066
23551
unique data
(Rint)
4941 (0.0351)
10446 (0.0317)
12426 (0.0423)
1
obs data [I > 3734
2σ(I)]
8581
8900
3
CH(CH3)2), 1.23 (d, 12H, JHH = 6.8 Hz, CH(CH3)2), 3.46 (septet,
3
4H, JHH = 6.8 Hz, CH(CH3)2), and 7.02−7.08 (m, 6H, ArH).
params
352
694
696
13C{1H} NMR (100 MHz, C6D6): δ = 1.2 (br, SiCH3), 26.3
(CH(CH3)2), 27.1 (CH(CH3)2), 28.2 (CH(CH3)2), 125.0 (ArC),
126.1 (ArC), 140.0 (ArC), and 148.3 (ArC). 29Si{1H} NMR (80 MHz,
C6D6): δ = −2.5. Mp (°C): 215 (dec.). Anal. calcd. for
C56H92Ge2N4S2Si4: C, 58.84; H, 8.11; N, 4.90; S: 5.61. Found: C,
58.84; H, 8.08; N, 4.82; S, 5.71.
R1 [I >
2σ(I)]
0.0371
0.0675
0.0722
a
wR2 [all
0.1018
0.1928
0.2328
a
data]
max/min Δρ 0.238/−0.233
0.846/−1.623
1.279/−0.829
(e− Å−3
)
Synthesis of (4-iPrC6H4)3SiCl (5). The Grignard reagent,
(4-iPrC6H4)MgBr was first prepared by slowly adding 4-iPrC6H4Br
(29.38 g, 0.148 mol) in 75 mL of THF (75 mL) to dried magnesium
metal (4.20 g, 0.170 mol) in 75 mL of THF, followed by heating of the
solvent to reflux overnight. The resulting brown solution of
(4-iPrC6H4)MgBr was then filtered into a separate flask and, then,
slowly added via cannula to a solution of SiCl4 (5.65 mL, 0.049 mol) in
50 mL of THF at −78 °C. A yellow-green solution was obtained which
was then warmed to room temperature and heated to reflux for 2 days
to yield a pale yellow solution. A 15 mL portion of 1,4-dioxane was
then added to precipitate the MgX2 byproduct (in the form of
MgX2·dioxane; X = Cl and/or Br), and the resulting heterogeneous
mixture was filtered. Removal of the volatiles from the filtrate afforded
a colorless solid that was recrystallized from hexanes (ca. 75 mL; −35
a
2
4
R1 = ∑||Fo| − |Fc||/∑|Fo|; wR2 = [∑w(Fo − Fc2)2/∑w(Fo )]1/2
.
C6D6): δ = 1.1 (SiCH3), 26.4 (CH(CH3)2), 29.3 (CH(CH3)2),
124.0 (ArC), 124.8 (ArC), 140.6 (ArC), and 144.7 (ArC).
29Si{1H} NMR (99 MHz, C6D6): δ = −7.9. IR (FT-IR
microscope, cm−1): 3384 [m, ν(N−H)]. Anal. calcd. for
C29H51N2Si2: C, 71.98; H, 10.62; N, 5.79. Found: C, 71.04;
H, 10.30; N, 5.76.
n
Preparation of [(Me2SiNDipp)2Ge:] (2). A solution of BuLi (3.5
mL, 1.6 M solution in hexanes, 5.6 mmol) was slowly added to a
solution of 1 (1.30 g, 2.80 mmol) in 6 mL of Et2O at −35 °C. The
resulting mixture was warmed to room temperature and stirred for 2 h,
recooled to −35 °C, and then slowly added to a slurry of
GeCl2·dioxane (0.648 g, 2.80 mmol) in 7 mL of Et2O. The reaction
mixture was then warmed to room temperature and allowed to stir for
15 h to give an orange solution over a white precipitate (LiCl).
Filtration of the mixture through Celite gave an amber solution, which
afforded 2 as pale orange waxy solid upon removal of the volatiles
(1.314 g, 88%). Recrystallization of 2 from hexanes/Et2O at −35 °C
resulted in the formation of large plate-shaped orange crystals of
suitable quality for X-ray crystallography. 1H NMR (400 MHz, C6D6):
1
°C) to give 5 as colorless X-ray quality crystals (7.635 g, 36%). H
NMR (500 MHz, C6D6): δ = 1.07 (d, 18H, JHH = 7.0 Hz,
CH(CH3)2), 2.63 (septet, 3H, JHH = 7.0 Hz, CH(CH3)2), 7.07 (d,
6H, JHH = 8.0 Hz, ArH), and 7.77 (d, 6H, JHH = 8.0 Hz, ArH).
13C{1H} NMR (125 MHz, C6D6): δ = 23.8 (CH(CH3)2), 34.4
(CH(CH3)2), 126.6 (ArC), 131.0 (ArC), 136.0 (ArC), and 151.6
(ArC). 29Si{1H} NMR (99 MHz, C6D6): δ = 1.9. HR-MS, EI (m/z):
calcd. for [M]+: 422.20105. Found: 422.20269 (Δppm = 0.3). Mp
(°C): 156−168. Anal. calcd. for C27H33ClSi: C, 77.01; H, 7.90. Found:
C, 76.79; H, 7.50.
3
3
3
3
3
δ = 0.22 (s, 12H, SiCH3), 1.17 (d, 12H, JHH = 7.2 Hz, CH(CH3)2),
Synthesis of (4-tBuC6H4)3SiCl (6). A 500 mL three-necked round-
bottom flask equipped with a magnetic stirring bar and a condenser
was flushed with nitrogen and then charged with dried magnesium
turnings (1.1 g, 0.046 mol), 10 mL of THF, and a small crystal of
iodine. The mixture was stirred at room temperature until the color of
the iodine faded away and a solution of 1-bromo-4-tert-butylbenzene
(6.0 g, 0.028 mol) in 20 mL of THF was then added dropwise. The
resulting brown solution was refluxed overnight, cooled to room
temperature, and then filtered to remove unreacted magnesium. This
1.29 (d, 12H, 3JHH = 6.8 Hz, CH(CH3)2), 3.55 (septet, 4H, 3JHH = 6.8
Hz, CH(CH3)2), and 7.08−7.18 (m, 6H, ArH). 13C{1H} NMR (100
MHz, C6D6): δ = 0.8 (SiCH3), 23.0 (CH(CH3)2), 27.5 (CH(CH3)2),
28.1 (CH(CH3)2), 123.9 (ArC), 125.5 (ArC), 139.6 (ArC), and 146.4
(ArC). 29Si{1H} NMR (80 MHz, C6D6): δ = −2.5. HR-MS, EI (m/z):
calcd. for [M+]: 540.24115. Found: 540.24176 (Δppm =1.1). Mp (°C)
= ca. 80 (turns red), 126−132 (melts). Anal. calcd. for
C28H46GeN2Si2: C, 62.34; H, 8.59; N, 5.19. Found: C, 62.02; H,
8.83; N, 4.86.
5473
dx.doi.org/10.1021/ic300495k | Inorg. Chem. 2012, 51, 5471−5480

Inorganic Chemistry
Article
solution of aryl magnesium bromide was then added dropwise to a
cold (−78 °C) solution of SiCl4 (1.07 mL, 9.35 mmol) in 20 mL of
THF. The reaction mixture was allowed to warm to room temperature
and then refluxed overnight to yield a pale green solution. Removal of
the volatiles from the solution afforded a white powder that was
redissolved in 15 mL of THF, and then, 6 mL of 1,4-dioxane was
added. The resulting slurry was stirred for 2 h, and the precipitates
were allowed to settle; then, the mother liquor was filtered through
Celite to yield a colorless filtrate. Removal of the volatiles from the
filtrate gave 6 as a white powder that was then recrystallized from THF
(5 mL) to yield spectroscopically pure 6 as colorless crystals (1.87 g,
43%). 1H NMR (400 MHz, CDCl3): δ = 1.34 (s, 27H, C(CH3)3), 7.43
(d, 6H, JHH = 8.4 Hz, ArH), and 7.60 (d, 6H, JHH = 8.4 Hz, ArH).
13C{1H} NMR (100 MHz, CDCl3): δ = 31.4 (C(CH3)3), 35.0
(C(CH3)3), 125.2 (ArC), 130.0 (ArC), 135.3 (ArC), and 153.8 (ArC).
29Si{1H} NMR (80 MHz, C6D6): δ = 1.9. Mp (°C): 233−235. HR-
MS, EI (m/z): calcd. for [M]+: 462.25086. Found: 462.25095 (Δppm
= 0.2).
(CH(CH3)2), 34.4 (CH(CH3)2), 126.1 (ArC), 128.4 (ArC), 134.7
(ArC), 135.6 (ArC), 135.9 (ArC), 136.4 (ArC), 138.7 (ArC), and
149.8 (ArC). 29Si{1H} NMR (80 MHz, C6D6): δ = −17.1 (−SiAr3)
and −20.4 (−Si(tolyl)2−). IR (FT-IR microscope, cm−1): 3330 [br,
ν(N−H)]. Mp (°C): 178−181. Anal. calcd. for C68H82N2Si3: C, 80.73;
H, 8.17; N, 2.77. Found: C, 80.95; H, 8.06; N, 2.77.
Synthesis of [(4-iPrC6H4)3SiNHSiMe2]2 (10). (4-iPrC6H4)3SiNH2
(1.04 g, 2.60 mmol) was dissolved in 20 mL of Et2O and cooled to
−35 °C, and a solution of nBuLi (1.62 mL, 1.6 M solution in hexanes,
2.60 mmol) was added dropwise. The reaction mixture was then
stirred for 3 h, cooled to −35 °C, and dichlorotetramethyldisilane
(0.245 mL, 1.32 mmol) was then added. The resulting cloudy white
suspension was then warmed to room temperature, stirred for 16 h,
and filtered through Celite. Removal of the volatiles from the filtrate
(in vacuo) afforded a viscous yellow oil that was freed from residual
LiCl (as evidenced by a flame test) by redissolving the crude material
in 10 mL of hexanes, followed by filtration through Celite. Removal of
the solvent from the filtrate gave 10 as a spectroscopically pure pale
3
3
1
yellow oil (0.92 g, 77%). H NMR (300 MHz, C6D6): δ = 0.18 (s,
Synthesis of (4-iPrC6H4)3SiNH2 (7). (4-iPrC6H4)3SiCl (6.435 g,
0.0152 mol) and LiNH2 (0.456 g, 0.0199 mol) were combined in 25
mL of THF and the resulting white slurry was stirred overnight. A
slightly turbid reaction mixture was obtained, and the volatiles were
removed under vacuum. The product was extracted with 50 mL of
hexanes, and the LiCl salt was removed by filtration. The resulting
filtrate was cooled to −35 °C to give a crop of colorless crystals, while
further concentration and cooling of the mother liquor yielded
additional pure 7 as a white solid (combined yield of both crops =
4.896 g, 80%). 1H NMR (500 MHz, C6D6): δ = 0.83 (br. s, 2H, NH2),
1.13 (d, 18H, 3JHH = 7.0 Hz, CH(CH3)2), 2.70 (septet, 3H, 3JHH = 7.0
3
12H, Si(CH3)2), 1.02 (br, 2H, NH), 1.14 (d, 36H, JHH = 7.0 Hz,
3
CH(CH3)2), 2.71 (septet, 6H, JHH = 7.0 Hz, CH(CH3)2), 7.14 (d,
3
3
12H, JHH = 8.0 Hz, ArH), and 7.83 (d, 12H, JHH = 8.0 Hz, ArH).
13C{1H} NMR (125 MHz, C6D6): δ = 2.0 (Si(CH3)2), 24.0
(CH(CH3)2), 34.5 (CH(CH3)2), 126.5 (ArC), 135.2 (ArC), 136.3
(ArC), and 150.3 (ArC). 29Si{1H} NMR (79.5 MHz, C6D6): δ = −7.2
(s) and −16.6 (s). IR (FT-IR microscope, cm−1): 3349 [m, ν(N−H)].
EI-MS (m/z): 459 {[(4-iPrC6H4)3SiNHSiMe2]+, 6%}, 401
{[(4-iPrC6H4)3SiNH2]+, 38%}, {[(4-iPrC6H4)3Si]+, 22%}. Anal.
calcd. for C58H50N2Si4: C, 75.92; H, 8.79; N, 3.05. Found: C, 74.29;
H, 8.84; N, 2.81; despite repeated attempts the analyses were
consistently low in C (ca. 2%).
3
Hz, CH(CH3)2), 7.14 (d, 6H, JHH = 8.0 Hz, ArH), and 7.72 (d, 6H,
3JHH = 8.0 Hz, ArH). 13C{1H} NMR (125 MHz, C6D6): δ = 24.1
(CH(CH3)2), 34.5 (CH(CH3)2), 126.3 (ArC), 134.9 (ArC), 136.0
(ArC), and 150.3 (ArC). 29Si{1H} NMR (80 MHz, C6D6): δ = −16.8.
HR-MS, EI (m/z): calcd. for [M]+: 401.25388. Found: 401.25374
(Δppm = 3.9). Mp (°C): 65−70. Anal. calcd. for C27H35NSi: C, 80.74;
H, 8.78; N, 3.49. Found: C, 80.42; H, 8.66; N, 3.48.
Preparation of [{tolyl2Si[(4-iPrC6H4)3SiN]2}Ge:] (11). Compound 9
(0.259 g, 0.256 mmol) was dissolved in 7 mL of Et2O and cooled to
n
−35 °C, and BuLi (320 μL, 1.6 M solution in hexanes, 0.512 mmol)
was added dropwise; the reaction mixture was then allowed to warm to
room temperature and stirred for 3 h. This solution was then added
dropwise to GeCl2·dioxane (59 mg, 0.26 mmol) in 4 mL of Et2O and
stirred overnight to yield a cloudy white mixture. The resulting LiCl
precipitate was separated by filtration, and the volatiles were removed
from the yellow filtrate to give a white solid that was recrystallized
from Et2O at −35 °C to give an analytically pure sample of 11 as a
Synthesis of (4-tBuC6H4)3SiNH2 (8). Compound 6 (1.50 g, 3.2
mmol) and LiNH2 (0.10 g, 4.4 mmol) were combined in 12 mL of
THF and the reagent mixture was stirred for 2 days at room
temperature to give a colorless solution. The solvent was then
removed in vacuo to yield a white powder. The product was then
extracted with 20 mL of Et2O, and the resulting slurry was filtered
through Celite to give a colorless solution. Removal of the volatiles
from the filtrate afforded spectroscopically pure 8 as a white powder
(0.41 g, 28%). 1H NMR (400 MHz, CDCl3): δ = 1.32 (s, 27H,
1
colorless microcrystalline solid (95 mg, 34%). H NMR (500 MHz,
3
C6D6): δ = 1.08 (d, 36H, JHH = 6.5 Hz, CH(CH3)2), 2.08 (s, 6H,
3
tolyl-CH3), 2.63 (septet, 6H, JHH = 6.5 Hz, ArCH(CH3)2), 6.86 (d,
4H, 3JHH = 7.5 Hz, tolyl-ArH), 7.00 (d, 12H, 3JHH = 8.0 Hz, ArH), 7.47
3
3
(d, 4H, JHH = 7.5 Hz, tolyl-ArH), and 7.65 (d, 12H, JHH = 8.0 Hz,
ArH). 13C{1H} NMR (125 MHz, C6D6): δ = 21.5 (tolyl−CH3), 23.9
(CH(CH3)2), 34.3 (CH(CH3)2), 126.1 (ArC), 128.7 (ArC), 133.8
(ArC), 134.7 (ArC), 135.6 (ArC), 136.5 (ArC), 139.1 (ArC), and
149.9 (ArC). 29Si{1H} NMR (80 MHz, C6D6): δ = −3.1
(−Si(tolyl)2−) and −18.9 (−SiAr3). Mp (°C): 245−248. Anal.
calcd. for C68H80GeN2Si3: C, 75.46; H, 7.45; N, 2.59. Found: C,
75.23; H, 7.46; N, 2.56.
C(CH3)3), 7.38 (d, 6H, 3JHH = 8.1 Hz, ArH), and 7.57 (d, 6H, 3JHH
=
8.1 Hz, ArH); the N−H resonance could not be located. 13C{1H}
NMR (100 MHz, CDCl3): δ = 31.4 (C(CH3)3), 34.9 (C(CH3)3),
124.9 (ArC), 133.6 (ArC), 135.2 (ArC), and 152.5 (ArC). HR-MS, EI
(m/z): calcd. for [M]+: 443.30036. Found: 443.30084 (Δppm = 1.1).
IR (FT-IR microscope, cm−1): 3390 [br, ν(N−H)]. Mp (°C): 167−
169. Anal. calcd. for C30H41NSi: C, 81.20; H, 9.31; N, 3.16. Found: C,
81.03; H, 9.07; N, 3.08.
Synthesis of [{Me4Si2[(4-iPrC6H4)3SiN]2}Ge:] (12). Silylamine 10
(0.377 g, 0.410 mmol) was dissolved in 14 mL of Et2O and cooled to
−35 °C, and nBuLi (0.513 mL, 1.6 M solution in hexanes, 0.82 mmol)
was added; the reaction mixture was then allowed to warm to room
temperature and stirred for 3 h. This resulting solution was then added
dropwise to GeCl2·dioxane (95 mg, 0.41 mmol) in 3 mL of Et2O and
stirred overnight to yield a cloudy yellow mixture. The precipitate was
separated by filtration, and the volatiles were removed form the filtrate
to give a tacky yellow solid. This product was recrystallized from 5 mL
of a 5:1 hexanes/hexamethyldisiloxane mixture at −35 °C to yield pale
yellow crystals of 12 of suitable quality for single-crystal X-ray
Preparation of [(4-i PrC6 H4 )3 SiNH]2 Si(tolyl)2 (9).
(4-iPrC6H4)3SiNH2 (0.774 g, 1.92 mmol) was dissolved in 8 mL of
n
Et2O and cooled to −35 °C. A solution of BuLi (1.20 mL, 1.6 M
solution in hexanes, 1.92 mmol) was then added dropwise, followed by
stirring for 3 h. The resulting slurry was then cooled to −35 °C, and
neat di-p-tolyldichlorosilane (0.259 mL, 1.01 mmol) was then added
followed by stirring at room temperature overnight. The reaction
mixture was then filtered to yield a colorless filtrate, and the volatiles
were then removed from the filtrate under vacuum. The crude product
was then recrystallized from hexanes (−35 °C) to yield 9 as a white
microcrystalline solid (0.568 g, 58%). 1H NMR (400 MHz, C6D6): δ =
1
crystallography (154 mg, 38%). H NMR (500 MHz, C6D6) δ = 0.21
3
3
1.14 (d, 36H, JHH = 6.8 Hz, CH(CH3)2), 1.78 (br. s, 2H, NH), 2.08
(s, 12H, Si(CH3)2), 1.12 (d, 36H, JHH = 7.0 Hz, CH(CH3)2), 2.67
(s, 6H, tolyl-CH3), 2.71 (septet, 6H, 3JHH = 6.8 Hz, CH(CH3)2), 6.87
(d, 4H, J = 8.0 Hz, tolyl-ArH), 7.05 (d, 12H, J = 8.0 Hz, ArH), 7.55 (d,
4H, 3JHH = 8.0 Hz, tolyl-ArH), and 7.67 (d, 12H, 3JHH = 8.0 Hz, ArH).
13C{1H} NMR (125 MHz, C6D6): δ = 21.5 (tolyl-CH3), 24.0
3
(septet, 6H, 3JHH = 7.0 Hz, CH(CH3)2), 7.13 (d, 12H, JHH = 8.0 Hz,
3
ArH), and 7.87 (d, 12H, JHH = 8.0 Hz, ArH). 13C{1H} NMR (125
MHz, C6D6): δ = 2.8 (Si(CH3)2), 24.0 (CH(CH3)2), 34.4 (CH-
(CH3)2), 126.2 (ArC), 135.4 (ArC), 137.0 (ArC), and 150.3 (ArC).
5474
dx.doi.org/10.1021/ic300495k | Inorg. Chem. 2012, 51, 5471−5480

Inorganic Chemistry
Article
29Si{1H} NMR (80 MHz, C6D6): δ = −7.2 (−SiMe2SiMe2−) and
−16.6 (−SiAr3). Mp (°C): 80−83 (dec.). Anal. calcd. for
C58H78GeN2Si4: C, 70.49; H, 7.96; N, 2.83. Found: C, 70.83; H,
7.96; N, 2.79.
Group 14 (tetrel) element, thus leading to a more sterically
crowded coordination environment.
Starting from the known bis(amine) 1,20 we were able to
prepare the monomeric germylene and stannylene complexes,
[(Me2SiNDipp)2E:] (E = Ge and Sn; 2 and 3) in high yields of
88 and 91%, respectively. The germanium heterocycle 2 was
obtained as an orange solid of modest stability in the solid state
(decomposition noted at 80 °C under N2), while its tin
congener was isolated as a thermally stable yellow solid (Mp =
169−171 °C). As shown in Figure 1, compounds 2 and 3 adopt
monomeric structures in the solid state with the peripheral,
nitrogen-bound Dipp groups oriented orthogonal to the
ENSiSiN ring planes (E = Ge and Sn). In each heterocycle,
slight canting of the SiMe2 groups relative to one another was
observed with N−Si−Si−N intraring torsion angles of
11.58(6)° and 22.17(6)° for 2 and 3, respectively. As expected,
the Dipp substituents were also bent considerably forward
toward the Ge and Sn centers, as evidenced by the narrow
C(ipso, Dipp)−N−E angles of 113.99(12)° avg. and
117.12(13)° avg. for compounds 2 and 3. For comparison,
the Dipp groups within the four-membered [NSiNE] chelates
[{iPr2Si(NDipp)2}E:] (E = Ge and Sn) were also orthogonal to
the inorganic ring planes, but were positioned further away
from the Group 14 centers as indicated by significantly wider
C(ipso, Dipp)−N−E angles of 124.96(8)° (E = Ge) and
126.30(13)° avg. (E = Sn).6a The backbone Si−Si distances in
heterocycles 2 [2.3339(5) Å] and 3 [2.3269(5) Å] were nearly
identical within experimental error and are in the range
expected for Si−Si single bonds.24
Preparation of [{[(4-iPrC6H4)3SiN]2Si(tolyl)2}Ge(μ-S)]2 (13). To a
mixture of 11 (81 mg, 0.075 mmol) and elemental sulfur (2.4 mg,
0.075 mmol) was added 10 mL of Et2O. The reaction mixture was
stirred overnight at room temperature to give a white suspension that
was then filtered through Celite to obtain a pale yellow solution.
Removal of volatiles from the filtrate afforded 13 as a white powder
(73 mg, 87% yield). X-ray quality crystals were obtained by cooling a
solution of 13 in 2:1 hexanes/hexamethyldisiloxane mixture (6 mL) at
−35 °C for 3 days. 1H NMR (500 MHz, C6D6) δ = 1.14 (d, 36H, 3JHH
= 7.0 Hz, CH(CH3)2), 2.03 (s, 6H, tolyl-CH3) 2.67 (septet, 6H, 3JHH
=
3
7.0 Hz, CH(CH3)2), 6.71 (d, 4H, JHH = 7.5 Hz, ArH), 6.83 (br. d,
12H, 3JHH = 6.5 Hz, ArH), 7.20 (d, 4H, 3JHH = 7.5 Hz, ArH), and 7.41
(br. d, 12H, 3JHH = 6.5 Hz, ArH). 13C{1H} NMR (125 MHz, C6D6): δ
= 21.6 (tolyl-CH3), 24.1 (CH(CH3)2), 34.4 (CH(CH3)2), 125.7
(ArC), 132.4 (ArC), 134.2 (ArC), 136.5 (ArC), 137.3 (ArC), 139.1
(ArC), and 149.1 (ArC); one ArC resonance could not be located. Mp
(°C): >260. Anal. calcd. for C136H160Ge2N4S2Si6: C, 73.29; H, 7.24; N,
2.51. Found: C, 73.45; H, 7.20; N, 2.60.
RESULTS AND DISCUSSION
■
Bis(amidosilyl) [NSiSiN] Chelates and Associated Low-
Coordinate Group 14 Element Chemistry. As mentioned
in the Introduction, we have been exploring ligand design
strategies as a means to access low-coordinate main group
complexes with novel reactivity. An area that would benefit
from such ligand advances would be the synthesis of a silicon
analogue of a ketone, termed a silanone, LSiO (L = bidentate
ligand) or R2SiO. This molecular class has been the target of
scientific investigation for over 100 years but has thwarted
isolation in the condensed phase, as the SiO double bonds in
these targets are anticipated to be highly reactive due to their
polarized nature. The isolation of a silanone will therefore
require sufficient steric shielding from the proximal ligands in
order to suppress the thermodynamically favored formation of
oligomers.21 Although Tamao and co-workers have very
recently reported the elegant synthesis of a monomeric
germanone R2GeO,22 these species and their heavier
chalcogen derivatives (e.g., R2GeS) are still quite rare.8
Drawing inspiration from N-heterocyclic carbene chemistry23
and keeping the above-mentioned synthetic targets in mind, we
decided to prepare low-coordinate, N-heterocyclic Group 14
complexes featuring 5-membered rings (Scheme 1). It was
reasoned that the expanded chelate ring size relative to our
previously reported 4-membered heterocycles, such as Ge-
[NSiN]Dipp ([NSiN]Dipp = [iPr2Si(NDipp)2]),6a would place
the flanking aryl (Dipp) groups in closer proximity to the
Compound 2 represents the first heterocyclic, two-
coordinate, germylene that contains a disilane unit as part of
the ring skeleton.25 Notably, structurally related Sn(II)
disilylamino complexes, [(Me2SiNR)2Sn]1
(R = alkyl
or
2
groups) were prepared by the group of Wrackmeyer.26 When
t
bulky side groups were appended to nitrogen (e.g., R = Bu),
monomeric stannylenes were observed in solution; however
upon decreasing the steric bulk of the substituent at nitrogen,
dimerization via intermolecular Sn···N interactions transpired
and in some instances, monomer−dimer equilibria were
identified using variable-temperature 1H and 119Sn NMR
studies.26 While our hindered stannylene 3 is stable indefinitely
at room temperature and in the presence of light, the less-
sterically protected Sn complexes of Wrackmeyer slowly
decompose in solution when exposed to ambient light; this
process generally leads to ligand redistribution to give the
homoleptic complexes [(Me2SiNR)2]2Sn.26
The high degrees of thermal stability, coupled with the
monomeric nature of the germylene and stannylene complexes
2 and 3, suggest that the consitituent [NSiSiN]Dipp chelates are
promising ligands for the stabilization of other reactive
inorganic bonding environments.27 As a starting point, we
explored chalcogen atom transfer chemistry between the two-
coordinate germylene [(Me2SiNDipp)2Ge:] 2 and elemental
sulfur in order to potentially access a rare example of a stable
species featuring an unsupported GeS double bond.8a
Treatment of 2 with an atomic equivalent of sulfur resulted
in the gradual bleaching of the initially orange colored solution
and the eventual recovery of a white microcrystalline solid. X-
ray crystallographic analysis later revealed the successful
installation of a sulfur atom at Ge; however in place of
isolating the desired monomeric germanethione, a dimeric
complex [(Me2SiNDipp)2Ge(μ-S)]2 (4) was obtained (eq 1;
Figure 1).
Scheme 1. Synthesis of the Bis(amido)disilyl Germylene and
Stannylene Heterocycles [(Me2SiNDipp)2E:] (E = Ge and
Sn; 2 and 3)
5475
dx.doi.org/10.1021/ic300495k | Inorg. Chem. 2012, 51, 5471−5480

Inorganic Chemistry
Article
Figure 1. Molecular structures of [(Me2SiNDipp)2}E:] (E = Ge and Sn; 2 and 3) and [(Me2SiNDipp)2Ge(μ-S)]2 (4) with thermal ellipsoids
presented at the 30% probability level. The hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (deg): Compound
2: Ge−N(1) 1.8615(10), Ge−N(2) 1.8623(10), N(1)−Si(1) 1.7535(11), N(2)−Si(2) 1.7560(11), Si(1)−Si(2) 2.3339(5); N(1)−Ge-N(2)
98.75(5), Si(1)−N(1)−Ge 122.49(6), Si(2)−N(2)−Ge 121.70(6), Si(1)−N(1)−C(11) 123.50(8), C(11)−N(1)−Ge 113.93(8), Si(2)−N(2)−
C(31) 124.26(8), C(31)−N(2)−Ge 114.05(8), N(1)−Si(1)−Si(2) 97.41(4), N(2)−Si(1)−Si(2) 98.00(4). Compound 3: Sn−N(1) 2.0597(11),
Sn−N(2) 2.0646(11), N(1)−Si(1) 1.7477(11), N(2)−Si(2) 1.7533(12), Si(1)−Si(2) 2.3269(5); N(1)−Sn-N(2) 93.35(4), Si(1)−N(1)−Sn
121.05(6), Si(2)−N(2)−Sn 120.45(6), Si(1)−N(1)−C(11) 122.10(9), C(11)−N(1)−Sn 116.79(8), Si(2)−N(2)−C(31) 121.93(9), C(31)−
N(2)−Sn 117.44(8), N(1)−Si(1)−Si(2) 99.47(4), N(2)−Si(1)−Si(2) 100.24(4). Compound 4: Ge−S 2.2763(17), Ge−S′ 2.2245(17), Ge−N(1)
1.853(5), Ge−N(2) 1.840(6), N(1)−Si(1) 1.765(6), N(2)−Si(2) 1.792(6), Si(1)−Si(2) 2.303(3); S−Ge−S(A) 93.39(6), Ge−S−Ge 86.61(6),
N(1)−Ge-N(2) 101.7(2), Ge−N(1)-C(11) 127.3(4), Ge−N(2)−C(31) 130.2(4), N(1)−Si(1)−Si(2) 96.9(2), N(2)−Si(1)−Si(2) 98.2(2).
from the Ge centers). In compound 4, the average Ge−N−
C(ipso, Dipp) angles were 128.8(5)° and indicate that the Dipp
groups in this complex subtend at an angle that is only ca. 3°
wider than in the precursor 2. This data suggests that, despite
some increase in intraligand repulsion involving the Dipp
groups in 4, the overall level of intraligand strain in this dimer is
still relatively low, thus the dimerization of putative
[(Me2SiNDipp)2}GeS] units can still proceed to form 4.
Synthesis of Ligand Frameworks Bearing Sterically
Expanded Triarylsilyl Groups, (4-RC6H4)3Si− (R = iPr and
tBu). We have demonstrated in earlier work that replacement of
As shown in Figure 1, compound 4 adopts a centrosym-
Dipp groups by “umbrella-shaped” triphenylsilyl, −SiPh3,
moieties within [NSiN] chelates leads to an increase in the
overall steric bulk of the resulting ligand.6a Building upon this
concept, we targeted the synthesis of sterically expanded
analogues in which the flanking triarylsilyl groups contained
metric structure comprised of two GeNSiSiN heterocycles
joined by a central Ge2S2 array. The overall geometry of this
germanium sulfide complex is reminiscent of that observed
within the previously reported dimers, [{iPr2Si(NDipp)2}Ge(μ-
S)]2 and [{iPr2Si(NSiPh3)2}Ge(μ-S)]2.6a For example, the Ge−
S distances in 4 were 2.2245(17) and 2.2763(17) Å, while in
the above-mentioned dimers featuring [NSiN] chelates,
distances in the range of 2.1992(3)−2.2577(3) Å were
observed.6a The Ge−S distances in 4 are consistent with the
presence of Ge−S single bonds,8b and these bond lengths are
expectedly lengthened in comparison to the GeS double
bond distance of 2.049(3) Å found in [Tbt(Trip)GeS] (Tbt
= 2,4,6-{(Me3Si)2CH}3C6H2; Trip = 2,4,6-iPr3C6H2).8a,b The
backbone-positioned SiMe2 groups in 4 are mutually twisted in
comparison to the nearly eclipsed Me2Si-SiMe2 arrangement
found in the Ge(II) precursor 2, as evidenced by widened N−
Si−Si−N torsion angles of 23.6(3)° in 4 versus 11.58(6)° in 2;
this effect is likely due to an increase in intraligand
Dipp···SiMe2 repulsion in the oxidized dimer
[(Me2SiNDipp)2Ge(μ-S)]2 (4). Another potential indicator of
intraligand repulsion would be the presence of substantial
widening of the Ge−N−C(ipso, Dipp) angles as the cofacial
Dipp groups in 4 are pushed away from each other (and away
t
i
pendant Bu and Pr groups at the para-positions of the aryl
i
t
rings, (4-RC6H4)3Si− (R = Pr and Bu).
Somewhat to our surprise, examples of species with the
i
t
desired triarylsilyl motifs (4-RC6H4)3Si− (R = Pr and Bu)
were unknown in the literature prior to our investigations.
Consequently, new synthetic routes to the requisite nucleo-
philic silylamine ligand precursors (4-RC6H4)3SiNH2 (R = Pr
and Bu) had to be developed. The first step in the general
i
t
procedure outlined in Scheme 2 involved the preparation of the
hindered triarylsilylchlorides, (4-RC6H4)3SiCl (R = iPr and tBu;
5 and 6), via the condensation of in situ generated aryl
Grignard reagents 4-RC6H4MgBr with SiCl4. Fortunately the
selective installation of three aryl groups at silicon was possible
in a high yield, and conversion of the chlorosilanes 5 and 6 into
i
t
the target silylamines (4-RC6H4)3SiNH2 (R = Pr and Bu; 7
and 8) was readily accomplished by treating the chlorosilanes
with a slight excess of Li[NH2] in THF. The hindered silane
reagents 5−8 were each obtained as lipophilic, moisture-
5476
dx.doi.org/10.1021/ic300495k | Inorg. Chem. 2012, 51, 5471−5480

Inorganic Chemistry
Article
Scheme 2. Synthesis of the Hindered Triarylchlorosilane and
Triarylsilylamine Precursors 5−8
Scheme 3. Synthesis of the Silyl and Disilyl Bis(Amine)
Ligand Precursors [(4-iPrC6H4)3SiNH]2Si(tolyl)2 (9) and
[(4-iPrC6H4)3SiNHSiMe2]2 (10)
i
sensitive colorless solids, while the Pr-substituted (cumyl)
derivatives 5 and 7 were characterized further by single-crystal
X-ray crystallography (Figure 2); the metrical parameters for
both 5 and 7 were within expected values and thus no further
discussion is required.
ligand precursors could not be isolated in pure form. One
contributing reason for the lack of success lies in the extreme
solubility of these tert-butylated derivatives that precluded
further purification of the impure products by fractional
crystallization; moreover, attempts to triturate the oily products
with Me3SiOSiMe3 or lyophilization with benzene also failed to
yield tractable products. Motivated by the successful use of iPr-
bound aryl groups within ligand designs to aid in
crystallization/purification,28 we focused our remaining syn-
thetic efforts on [NSiN] and [NSiSiN] chelates bearing
(4-iPrC6H4)3Si− substituents at the ligating nitrogen atoms.
In order to access low-valent germylene complexes, we
followed the established procedure6a outlined in Scheme 4. The
required dilithio-amide precursors, {tolyl2 Si-
[(4-iPrC6H4)3SiN]2}Li2 and {[Me2Si(4-iPrC6H4)3SiN]2}Li2,
were each generated in situ via the reaction of the bis(amines)
n
9 and 10 with 2 equiv of BuLi in diethyl ether, and then
reacted with GeCl2·dioxane to afford the air- and moisture-
sensitive germylenes [{tolyl2Si[(4-iPrC6H4)3SiN]2}Ge:] (11)
and [{Me4Si2[(4-iPrC6H4)3SiN]2}Ge:] (12) in moderate yields.
Compounds 11 and 12 were obtained as colorless and pale
yellow air- and moisture-sensitive solids, respectively, with the
germylene 11 decomposing at 245 °C under a nitrogen
atmosphere, while the disilylamido germylene heterocycle 12
exhibited a much lower decomposition temperature of 80 °C.
We were unable to verify the solid state structure of the 11 by
X-ray crystallography; however, crystals of 12 of suitable quality
for single-crystal X-ray crystallography were obtained from a
cold (−35 °C) hexanes/Me3SiOSiMe3 solution (Figure 3).
T h e fi v e - m e m b e r e d g e r m y l e n e h e t e r o c y c l e
[{Me4Si2[(4-iPrC6H4)3SiN]2}Ge:] (12) is monomeric in the
solid state (Figure 3) with a planar GeNSiSiN ring and
mutually eclipsed backbone SiMe2 groups [N(1)−Si(1)−
Si(2)−N(2) torsion angle = 1.74(6)°]. What is evident upon
inspection of the structure of 12 is that the flanking nitrogen-
bound (4-iPrC6H4)3Si groups serve to create a much tighter
steric pocket about the Ge center when compared to the Dipp
analogue [(Me2SiNDipp)2Ge:] (2). The backbone Si−Si bond
length in 12 [2.3400(15) Å] is the same within experimental
error as the related linkage in 2, while the Ge−N bond lengths
in 12 [1.875(3) and 1.886(3) Å] are typical for single bonding
interactions and suggest a lack of appreciable Ge−N π-bonding
within the heterocycle.
Figure 2. Molecular structures of (4-iPrC6H4)3SiCl (5) and
(4-iPrC6H4)3SiNH2 (7) with thermal ellipsoids at a 30% probability
level. All carbon-bound hydrogen atoms have been omitted for clarity;
values due to a disorded 4-iPrC6H4 group in 7 are listed in brackets.
Selected bond lengths [Å] and angles [deg]. 5: Si−Cl 2.0841(6), Si−
C(11) 1.8573(17), Si−C(21) 1.8605(18), Si−C(31) 1.8569(18); Cl−
Si−C angles: 107.41(6) to 111.64(8), C−Si−C angles: 110.44(8) to
111.64(8). 7: Si−N 1.7144(16), Si−C(11) 1.8679(15), Si−C(21)
1.8721(15), Si−C(31) 1.881(4) [1.884(5)]; N−Si−C angles:
105.3(6) to 113.6(4); C−Si−C angles: 103.4(3) to 109.8(5).
With the silylamine (4-iPrC6H4)3SiNH2 (7) in hand, both
the monosilyl [(4-iPrC6H4)3SiNH]2Si(tolyl)2 9 and disilyl-
bridged [(4-iPrC6H4)3SiNHSiMe2]2 10 ligand precursors were
then prepared using the straightforward one-pot procedures
outlined in Scheme 3. In the case [(4-iPrC6H4)3SiNH]2Si-
(tolyl)2 9, the presence of the backbone-positioned tolyl groups
were used to add structural rigidity to the ligand framework and
to serve as spectroscopic handles. Both bis(amine) precursor 9
and 10 were obtained as analytically pure, moisture-sensitive
materials in 58 and 77% yields, respectively, and exhibited
NMR and IR spectral data consistent with the assigned
structures. We encountered considerable difficulties when we
attempted to construct the ligand analogues to 9 and 10 with
i
para-tBu substituents in place of Pr. For example, when
The Ge(II) centers within the monomeric germylenes 11
and 12 were expected to undergo facile oxidation chemistry to
yield stable products with germanium centers in the +4
oxidation state. As anticipated, the bis(amido)germylene 11
i Pr2 SiCl2 was reacted with in situ generated
[(4-tBuC6H4)3SiNH]Li, complex product mixtures were
obtained from which the desired tert-butylated silylbis(amine)
5477
dx.doi.org/10.1021/ic300495k | Inorg. Chem. 2012, 51, 5471−5480

Inorganic Chemistry
Article
Scheme 4. Synthesis of the Germylene Complexes [{tolyl2Si[(4-iPrC6H4)3SiN]2}Ge:] (11) and
[{Me4Si2[(4-iPrC6H4)3SiN]2}Ge:] (12)
Figure 4. Molecular structure of [{[(4-iPrC6H4)3SiN]2Si(tolyl)2}Ge-
(μ-S)]2 (13) with hydrogen atoms and solvate molecules omitted for
clarity. Selected bond lengths (Å) and angles (deg): Ge−S 2.2253(10),
Ge−S′ 2.2392(9), Ge−N(1) 1.837(3), Ge−N(2) 1.850(3), N(1)−
Si(1) 1.738(3), N(1)−Si(3) 1.764(3), N(2)−Si(2) 1.741(3), N(2)−
Si(3) 1.762(3); S−Ge−S′ 95.14(3), Ge−S−Ge′ 84.86(3), N(1)−Ge-
N(2) 85.68(12), Ge−N(1)−Si(1) 142.01(18), Ge−N(2)−Si(2)
141.76(17), Ge−N(1)−Si(3) 91.85(14), Ge−N(2)−Si(3) 91.43(12),
N(1)−Si(3)−N(2) 85.68(12).
Figure 3. Molecular structure of [{Me4Si2[(4-iPrC6H4)3SiN]2}Ge:]
(12) with thermal ellipsoids at a 30% probability level. All hydrogen
atoms and disordered 4-iPrC6H4 groups have been omitted for clarity.
Selected bond lengths [Å] and angles [deg]: Ge−N(1) 1.875(3), Ge−
N(2) 1.886(3), Si(1)−Si(2) 2.3400(15), Si(1)−N(1) 1.744(3),
Si(2)−N(2) 1.745(3), N(1)−Si(3) 1.732(3), N(2)−Si(4) 1.737(3);
N(1)−Ge-N(2) 101.46(13), N(1)−Si(1)−Si(2) 99.30(11), N(2)−
Si(2)−Si(1) 99.53(11), Ge−N(1)-Si(1) 119.99(17), Ge−N(1)-Si(3)
110.55(15), Ge−N(2)-Si(2) 119.56(17), Ge−N(2)-Si(4) 110.07(15).
reacted rapidly with elemental sulfur; however as with 2, the
S bond lengths noted within related sulfido-bridged Ge(IV)
complexes featuring silylamido chelates [2.1992(3) to
2.2577(3)].6a
product obtained was
a sulfido-linked dimer,
[{(4-iPrC6H4)3SiN]2Si(tolyl)2}Ge(μ-S)]2 (13). Due to the
high lipophilicity of 13, the use of hexamethyldisiloxane as a
cosolvent of crystallization was required to obtain crystals of
suitable quality for X-ray crystallography. The refined structure
of 13 is presented in Figure 4 and reveals the formation of a
dimeric germanethione containing a similar Ge2S2 diamond
core arrangement as in 2 and 4; however in 13, the Ge2S2 unit
is much more sterically shielded as a result of interdigitating
cumyl groups (4-iPrC6H4) that are positioned on each side of
the Ge2S2 core. Furthermore, the close intraligand interactions
between the cumyl side groups results in significant intraligand
repulsion which is manifested in the form of wide Ge−N−SiAr3
angles of 141.76(17) and 142.01(18)°. For comparison, the
related angles in [iPr2Si(NSiPh3)2Ge(μ-S)]2 were, on average,
considerably narrower [135.07(11)°].6a Despite the substantial
buckling of the (4-iPrC6H4)3Si− groups in 13, the Ge−S bond
lengths [2.2253(10) and 2.2392(9) Å] were similar to the Ge−
Unfortunately our attempts to react the sterically shielded
germylene [{Me4Si2[(4-iPrC6H4)3SiN]2}Ge:] (12) with ele-
mental sulfur failed to yield clean products that could be
structurally authenticated. When the reaction of 12 with one
atom equiv of sulfur was conducted, significant amounts (ca.
20−30%) of unreacted 12 were noted along with another major
product (ca. 50% spectroscopic yield). Increasing the amount
of sulfur in the reaction to 2 equiv improved the spectroscopic
yield of the major species to ca. 60%; however our efforts to
separate this product from the remaining byproducts (at least
four by 1H NMR) via fractional crystallization were
unsuccessful. At this stage we are unsure if monomeric
germanium polysulfides, such as {Me4Si2[(4-iPrC6H4)3SiN]2}-
Ge(S)x (x = 2, 3, ...), are formed as in the case of the reaction of
Tbt(Trip)Ge: with S8,8 or if bridging sulfido Ge−Sx−Ge
interactions are present. Moreover attempts to selectively
5478
dx.doi.org/10.1021/ic300495k | Inorg. Chem. 2012, 51, 5471−5480

Inorganic Chemistry
Article
oxidize 12 with Me3NO or MesCNO13 to give the germanium-
(IV) oxo complex {Me4Si2[(4-iPrC6H4)3SiN]2}Ge(O) gave
multiple products as evidenced by NMR spectroscopy.
Interestingly, a number of downfield positioned SiMe2
resonances (relative to in 12) were observed and suggested
that oxidation of the backbone Si−Si linkages in 12 to give
siloxane moieties, −SiMe2OSiMe2−, transpired. Support for
this mode of reactivity exists in the literature wherein the
oxidation of Si−Si linkages by Me3NO has been reported by
various groups.29
(2) (a) Cummins, C. C.; Baxter, S. M.; Wolczanski, P. T. J. Am.
Chem. Soc. 1988, 110, 8732. (b) Laplaza, C. E.; Cummins, C. C. Science
1995, 268, 861. (c) Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed.
2001, 40, 3750. (d) Pool, J. A.; Lobkovsky, E.; Chirik, P. J. Nature
2004, 427, 527. (e) Betley, T. A.; Peters, J. C. J. Am. Chem. Soc. 2004,
126, 6252. (f) Gunanathan, C.; Ben-David, Y.; Milstein, D. Science
2007, 317, 790. (g) Ni, C.; Ellis, B. D.; Long, G. J.; Power, P. P. Chem.
Commun. 2009, 2332. (h) Takaoka, A.; Mankad, N. P.; Peters, J. C. J.
Am. Chem. Soc. 2011, 133, 8440. (i) Rodriguez, M. M.; Bill, E.;
Brennessel, W. W.; Holland, P. L. Science 2011, 334, 780.
(3) (a) Okazaki, R.; Tokitoh, N. Acc. Chem. Res. 2000, 33, 625.
(b) Resa, I.; Carmona, E.; Gutierrez-Puebla, E.; Monge, A. Science
2004, 305, 1136. (c) Nguyen, T.; Sutton, A. D.; Brynda, M.; Fettinger,
J. C.; Long, G. J.; Power, P. P. Science 2005, 310, 844. (d) Rupar, P. A.;
Staroverov, V. N.; Baines, K. M. Science 2008, 322, 1360. (e) Wang, Y.;
Robinson, G. H. Chem. Commun. 2009, 5201. (f) Fischer, R. C.;
Power, P. P. Chem. Rev. 2010, 110, 3877. (g) Asay, M.; Jones, C.;
Driess, M. Chem. Rev. 2011, 111, 354. (h) Li, J.; Schenk, C.; Goedecke,
C.; Frenking, G.; Jones, C. J. Am. Chem. Soc. 2011, 133, 18622.
(4) Lappert, M.; Power, P.; Protchenko, A.; Seeber, A. Metal Amide
Chemistry; John Wiley and Sons Ltd.: West Sussex, UK, 2008.
(5) (a) Bradley, D. C.; Hursthouse, M. B.; Rodesiler, P. F. J. Chem.
Soc., Chem. Commun. 1969, 14. (b) Fisher, K. J.; Bradley, D. C. J. Am.
Chem. Soc. 1971, 93, 2058. (c) Davidson, P. J.; Harris, D. H.; Lappert,
M. F. Dalton Trans. 1976, 2268. (d) Cotton, J. D.; Davidson, P. J.;
Lappert, M. F. Dalton Trans. 1976, 2275. (e) Fryzuk, M. D.; MacNeil,
P. A.; Rettig, S. J.; Secco, A. S.; Trotter, J. Orgamometallics 1982, 1,
918. (f) Fryzuk, M. D.; Love, J. B.; Rettig, S. J.; Young, V. G. Science
1997, 275, 1445. (g) Cummins, C. C.; Schrock, R. R.; Davis, W. M.
Angew. Chem., Int. Ed. Engl. 1993, 32, 756. (h) Brynda, M.; Herber, R.;
Hitchcock, P. B.; Lappert, M. F.; Nowik, I.; Power, P. P.; Protchenko,
A.; Ruzicka, A.; Steiner, J. Angew. Chem., Int. Ed. 2006, 45, 4333.
(i) Wright, R. J.; Brynda, M.; Fettinger, J. C.; Betzer, A. R.; Power, P.
P. J. Am. Chem. Soc. 2006, 128, 12498.
CONCLUSION
■
In this work, we report new silylamido chelates featuring
elongated Si−Si bonds within a [NSiSiN] ligand backbone and
introduce the sterically expanded triarylsilyl group, −Si-
i
(C6H4 Pr)3, as a structural motif in ligand design. Although
these chelates provided increased steric coverage relative to pre-
existing silylamido bidentate ligands, our initial attempts to
isolate rare examples of three-coordinate germanium com-
pounds with terminal GeS double bonds led to the formation
of dimeric germanes with exclusively σ-bonded Ge2S2 arrays.
These results suggest that a high degree of structural flexibility
is present within the newly developed amidosilyl ligands, thus
allowing higher than expected coordination numbers to be
attained. Despite such challenges, the ease of synthesis and high
level of substituent control, make the general silylamino ligand
class introduced in this paper of widespread interest to those
seeking to access new inorganic element bonding modes and
reactivity profiles via ligand design.
ASSOCIATED CONTENT
■
(6) (a) Al-Rafia, S. M. I.; Lummis, P. A.; Ferguson, M. J.; McDonald,
R.; Rivard, E. Inorg. Chem. 2010, 49, 9709 and references therein. For
recent reports involving related chelates, see. (b) Yang, D.; Guo, J.;
Wu, H.; Ding, Y.; Zheng, W. Dalton. Trans. 2012, 2187. (c) West, J.
K.; Stahl, L. Organometallics 2012, 31, 2042.
S
* Supporting Information
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
(7) For the effective use of SiAr3 groups (Ar = Ph or tolyl) in ligand
design, see: (a) Bartlett, R. A.; Power, P. P. J. Am. Chem. Soc. 1987,
109, 6509. (b) Danopoulos, A. A.; Redshaw, C.; Vaniche, A.;
Wilkinson, G.; Hussain-Bates, B.; Hursthouse, M. B. Polyhedron
1993, 12, 1061. (c) Bindl, M.; Stade, R.; Heilman, E. K.; Picot, A.;
■
Corresponding Author
*E-mail: erivard@ualberta.ca.
Notes
Goddard, R.; Furstner, A. J. Am. Chem. Soc. 2009, 131, 9468.
(d) Suzuki, E.; Komuro, T.; Kanno, Y.; Okazaki, M.; Tobita, H.
̈
The authors declare no competing financial interest.
Organometallics 2010, 29, 1839. (e) Malassa, A.; Herzer, N.; Gorls, H.;
Westerhausen, M. Dalton Trans. 2010, 5356. (f) Li, J.; Stasch, A.;
Schenk, C.; Jones, C. Dalton Trans. 2011, 10448.
̈
ACKNOWLEDGMENTS
■
This work was supported by the Natural Sciences and
Engineering Research Council (NSERC) of Canada, the
Canada Foundation for Innovation, Alberta Innovates-Tech-
nologies Futures (New Faculty Award to E.R. and a graduate
fellowship to S. M. I. A), and Suncor Energy Inc. (Petro-
Canada Young Innovator Award for E. R.). L.J.M. is grateful to
NSERC for a USRA fellowship. We would also like to thank
Ms. Nupar Dabral, Dr. Tiffany MacDougall, and Mr. Mark
Miskolzie for their kind assistance with obtaining 29Si NMR
data.
(8) For related studies involving chalcogen atom transfer to
germylenes, see: (a) Tokitoh, N.; Matsumoto, T.; Manmaru, K.;
Okazaki, R. J. Am. Chem. Soc. 1993, 115, 8855. (b) Matsumoto, T.;
Tokitoh, N.; Okazaki, R. J. Am. Chem. Soc. 1999, 121, 8811. (c) Veith,
M.; Becker, S.; Huch, V. Angew. Chem., Int. Ed. Engl. 1989, 28, 1237.
(d) Nagendran, S.; Roesky, H. W. Organometallics 2008, 27, 457.
(e) Yao, S.; Xiong, Y.; Driess, M. Chem.Eur. J. 2010, 1281.
(9) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(10) Marvel, C. S.; Johnston, H. W.; Meier, J. W.; Mastin, T. W.;
Whitson, J.; Himel, C. M. J. Am. Chem. Soc. 1944, 66, 914.
(11) Hall, M. A.; Xi, J.; Lor, C.; Dai, S.; Pearce, R.; Dailey, W. P.;
Eckenhoff, R. G. J. Med. Chem. 2010, 53, 5667.
REFERENCES
■
(1) (a) King, R. B.; Bisnette, M. B. J. Organomet. Chem. 1967, 8, 287.
(b) Bradley, D. C.; Chisholm, M. H. Acc. Chem. Res. 1976, 9, 273.
(c) Eaborn, C. J. Organomet. Chem. 1982, 239, 93. (d) Trofimenko, S.
Chem. Rev. 1993, 93, 943. (e) Schrock, R. R. Acc. Chem. Res. 1997, 30,
9. (f) Cummins, C. C. Chem. Commun. 1998, 1777. (g) Power, P. P. J.
Organomet. Chem. 2004, 689, 3904. (h) MacLachlan, E. A.; Fryzuk, M.
D. Organometallics 2006, 25, 1530. (i) Holland, P. L. Acc. Chem. Res.
2008, 41, 905. (j) Wolczanski, P. T. Chem. Commun. 2009, 740.
(12) Patton, J. T.; Feng, S. G.; Abboud, K. A. Organometallics 2001,
20, 3399.
(13) (a) Bode, J. W.; Hachisu, Y.; Matsuura, T.; Suzuki, K.
Tetrahedron Lett. 2003, 44, 3555. (b) Barybin, M. V.; Diaconescu, P.
L.; Cummins, C. C. Inorg. Chem. 2001, 40, 2892.
(14) Hope, H. Prog. Inorg. Chem. 1993, 41, 1.
(15) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
5479
dx.doi.org/10.1021/ic300495k | Inorg. Chem. 2012, 51, 5471−5480

Inorganic Chemistry
Article
(16) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.;
Spagna, R. J. Appl. Crystallogr. 1999, 32, 115.
(17) Beurskens, P. T.; Beurskens, G.; de Gelder, R.; Smits, J. M. M.;
Garcia-Garcia, S.; Gould, R. O. DIRDIF-2008; Crystallography
Laboratory, Radboud University: Nijmegen, The Netherlands, 2008.
(18) Schneider, T. R.; Sheldrick, G. M. Acta Crystallogr. 2002, D58,
1772.
(19) (a) Sluis, P. v.; der; Spek, A. L. Acta Crystallogr. 1990, A46, 194.
(b) Spek, A. L. Acta Crystallogr. 1990, A46, C34. (c) Spek, A. L. J.
Appl. Crystallogr. 2003, 36, 7. (d) PLATON−a multipurpose
crystallographic tool. Utrecht University, Utrecht, The Netherlands.
(20) Jager, F.; Roesky, H. W.; Dorn, H.; Shah, S.; Noltemeyer, M.;
̈
Schmidt, H.-G. Chem. Ber./Receuil 1997, 130, 399.
(21) (a) Steele, A. R.; Kipping, F. S.; Dickinson, R.; Chapman, A. C.
J. Chem. Soc. 1929, 357. (b) Maruoka, K.; Ito, T.; Araki, T.; Shirasaka,
T.; Yamamoto, H. Bull. Chem. Soc. Jpn. 1988, 61, 2975. (c) Mizuhata,
Y.; Sasamori, T.; Tokitoh, N. Chem. Rev. 2009, 109, 3479. (d) Tokitoh,
N.; Kishikawa, K.; Okazaki, R.; Sasamori, T.; Nakata, N.; Takeda, N.
Polyhedron 2002, 21, 563. (e) Witnall, R.; Andrews, L. J. Phys. Chem.
1985, 89, 3261. (f) Khabashesku, V. N.; Boganov, S. E.; Kudin, K. N.;
Margrave, J. L.; Nefedov, O. M. Organometallics 1998, 17, 5041.
(g) Xiong, Y.; Yao, S.; Driess, M. J. Am. Chem. Soc. 2009, 131, 7562.
(h) Muraoka, T.; Abe, K.; Haga, Y.; Nakamura, T.; Ueno, K. J. Am.
Chem. Soc. 2011, 133, 15365.
(22) Li, L.; Fukawa, T.; Matsuo, T.; Hashizume, D.; Fueno, H.;
Tanaka, K.; Tamao, K. Nature Chem. DOI: 10.1038/NCHEM.1305.
(23) (a) Arduengo, A. J.; Harlow, R. L.; Kline, M. J. Am. Chem. Soc.
1991, 113, 361. (b) Arduengo, A. J. Acc. Chem. Res. 1999, 32, 913.
For examples of analogous heavy Group 14 element systems, see
(c) Haaf, M.; Schmiedl, A.; Schmedake, T. A.; Powell, D. R.;
Millevolte, A. J.; Denk, M.; West, R. J. Am. Chem. Soc. 1998, 120,
12714. (d) Herrmann, W. A.; Denk, M.; Behm, J.; Scherer, W.;
Klingan, F. -R.; Bock, H.; Solouki, B.; Wagner, M. Angew. Chem., Int.
Ed. Engl. 1992, 31, 1485. (e) Mansell, S. M.; Herber, R.; Nowik, I.;
Ross, D. H.; Russell, C. A.; Wass, D. F. Inorg. Chem. 2011, 50, 2252
and references therein.
(24) Choi, N.; Asano, K.; Ando, W. Organometallics 1995, 14, 3146.
(25) For examples of four-coordinate Ge(IV) complexes with
NSiSiN chelates, see: Wannagat, v. U.; Seifert, R.; Schlingmann, M.
Z. Anorg. Allg. Chem. 1978, 439, 83.
(26) (a) Horschler, K.; Stader, C.; Wrackmeyer, B. Inorg. Chim. Acta
1986, 117, L39. (b) Stader, C.; Wrackmeyer, B.; Schlosser, D. Z.
Naturforsch. B 1988, 43, 288. (c) Wrackmeyer, B.; Stader, C.;
Horchler, K.; Zhou, H.; Schlosser, D. Inorg. Chim. Acta 1990, 176, 205.
(27) (a) Power, P. P. Chem. Rev. 1999, 99, 3463. (b) West, R.
Polyhedron 2002, 21, 467. (c) Weidenbruch, M. Organometallics 2003,
22, 4348. (d) Jones, C. Coord. Chem. Rev. 2010, 254, 1273. (e) Wang,
Y.; Robinson, G. H. Dalton Trans. 2012, 337. (f) Sen, S. S.; Khan, S.;
Samuel, P. P.; Roesky, H. W. Chem. Sci 2012, 3, 659.
(28) (a) Stanciu, C.; Richards, A. F.; Fettinger, J. C.; Brynda, M.;
Power, P. P. J. Organomet. Chem. 2006, 691, 2540. (b) Rivard, E.;
Power, P. P. Inorg. Chem. 2007, 46, 10047 and references therein.
(29) (a) Sakurai, H.; Hirama, K.; Nakadaira, Y.; Kabuto, C. J. Am.
Chem. Soc. 1987, 109, 6880. (b) Kwak, Y. −W.; Lee, I. −S.; Baek, M.
−K.; Lee, U.; Choi, H. −J.; Ishikawa, M.; Naka, A.; Ohshita, J.; Lee, K.
−H.; Kunai, A. Organometallics 2006, 25, 48. (c) Kai, H.; Ohshita, J.;
Ohara, S.; Nakayama, N.; Kunai, A.; Lee, I. −S.; Kwak, Y. −W. J.
Organomet. Chem. 2008, 693, 3490.
5480
dx.doi.org/10.1021/ic300495k | Inorg. Chem. 2012, 51, 5471−5480