Low-coordinate germylene and stannylene heterocycles featuring sterically tunable bis(amido)silyl ligands

Article abstract of DOI:10.1021/ic101485a

A series of monomeric heterocyclic metallylenes [{ⁱPr ₂Si(NR)₂}M:] (M = Ge and Sn; R = Dipp = 2,6- ⁱPr₂C₆H₃ or SiPh₃) have been prepared. Preliminary atom-transfer chemistry involving the new low-valent germylenes with the chalcogen sources Me₃NO and S₈ yielded the corresponding dimeric oxo-and sulfido complexes (e.g., [{ ⁱPr₂Si(NDipp)₂}Ge-(μ-E)]₂; E = O and S). Structural analyses of the metallylenes and their oxidized products reveal that incorporation of the umbrella-shaped triarylsilyl groups (SiPh ₃) within the NSiN chelate confers additional steric protection about the group 14 centers relative to a Dipp group. The inclusion of sterically modifiable-SiAr₃ (Ar = aryl) units as part of a bis(amido) ligand array represents a new approach in this field and holds considerable promise with regard to attaining increasingly higher degrees of steric bulk.

Full text of DOI:10.1021/ic101485a

Inorg. Chem. 2010, 49, 9709–9717 9709
DOI: 10.1021/ic101485a
Low-Coordinate Germylene and Stannylene Heterocycles featuring Sterically
Tunable Bis(amido)silyl Ligands
S. M. Ibrahim Al-Rafia, Paul A. Lummis, Michael J. Ferguson, Robert McDonald, and Eric Rivard*
Department of Chemistry, University of Alberta, 11227 Saskatchewan Drive, Edmonton, Alberta,
Canada T6G 2G2
Received July 24, 2010
A series of monomeric heterocyclic metallylenes [{iPr2Si(NR)2}M:] (M = Ge and Sn; R = Dipp = 2,6-iPr2C6H3 or SiPh3)
have been prepared. Preliminary atom-transfer chemistry involving the new low-valent germylenes with the chalcogen
sources Me3NO and S8 yielded the corresponding dimeric oxo- and sulfido complexes (e.g., [{iPr2Si(NDipp)2}Ge-
(μ-E)]2; E = O and S). Structural analyses of the metallylenes and their oxidized products reveal that incorporation of
the umbrella-shaped triarylsilyl groups (SiPh3) within the NSiN chelate confers additional steric protection about the
group 14 centers relative to a Dipp group. The inclusion of sterically modifiable -SiAr3 (Ar = aryl) units as part of a
bis(amido) ligand array represents a new approach in this field and holds considerable promise with regard to attaining
increasingly higher degrees of steric bulk.
Introduction
amide (or amido) ligand frameworks are prominently fea-
tured in the isolation of low-coordinate main group species
that exhibit unusual bonding arrangements and reactivity.3
The widespread success of nitrogen-containing ligands is
derived from their ability to act as both σ- and π-donors
and their ease of tunability, with the latter property being a
direct result of the modular nature of their syntheses; conse-
quently, a significant level of steric and electronic control
over chemical reactivity of the ligated element can be
achieved.1-3
The development of sterically encumbered ligands that
contain anionic nitrogen donor sites (NR2-) has played a
pivotal role in advancing our overall knowledge of funda-
mental chemical reactivity throughout the Periodic Table.1
For example, these studies have led to the discovery of many
novel metal-mediated small molecule/bond activation pro-
cesses which are often elaborated upon later to yield synthe-
tically important catalytic transformations.2 Moreover
The above-mentioned successes have inspired us to focus
research efforts toward the synthesis of new bis(amido)
chelates that bear very hindered flanking groups at nitrogen.
Specifically, this paper describes the development of the
dianionic chelates [NSiN]Dipp and [NSiN]SiPh3 (Chart 1)
and their use to access low-coordinate complexes of Ge(II)
and Sn(II). Moreover, illustrative chalcogen atom-transfer
chemistry has been explored in order to gauge the relative
steric coverage offered by the newly developed NSiN ligands.
*Corresponding author. E-mail: erivard@ualberta.ca.
(1) Lappert, M.; Power, P.; Protchenko, A.; Seeber, A. Metal Amide
Chemistry; John Wiley and Sons Ltd.: West Sussex, UK, 2008.
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(b) Cummins, C. C.; Schaller, C. P.; Van Duyne, G. D.; Wolczanski, P. T.; Chan,
A. W. E.; Hoffmann, R. J. Am. Chem. Soc. 1991, 113, 2985. (c) Fryzuk, M. D.
Can. J. Chem. 1992, 70, 2839. (d) Schrock, R. R. Acc. Chem. Res. 1997, 30, 9.
(e) Cummins, C. C. Chem. Commun. 1998, 1777. (f) Macbeth, C. E.; Golombek,
A. P.; Young, V. G., Jr.; Yang, C.; Kuzera, K.; Hendrich, M. P.; Borovik, A. S.
Science 2000, 289, 938. (g) Gade, L. H. Acc. Chem. Res. 2002, 35, 575.
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Results and Discussion
Ligand Precursor Syntheses. The amine ligand precur-
sors, (RNH)2SiiPr2 (R = Dipp = 2,6-iPr2C6H3, 1; R =
SiPh3, 2) were assembled using the general protocol out-
lined in Scheme 1. Starting from the readily available
primary amines, DippNH2 and Ph3Si-NH2,4 the target
chelates 1 and 2 were prepared in modest yields via two-
step procedures and isolated as colorless moisture-sensitive
solids (55 and 67% overall yields for 1 and 2, respectively).
ꢀ
ꢀ
Lappert, M. F.; Power, P. P.; Riviere, P.; Riviere-Baudet, M. Dalton Trans. 1977,
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H.; Solouki, B.; Wagner, M. Angew. Chem., Int. Ed. 1992, 31, 1485. (g) West, R.;
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Schmidbaur, H. J. Am. Chem. Soc. 1999, 121, 9758. (i) Stahl, L. Coord. Chem.
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Nozaki, K. Science 2006, 314, 113. (l) Wright, R. J.; Brynda, M.; Fettinger, J. C.;
Betzer, A. R.; Power, P. P. J. Am. Chem. Soc. 2006, 128, 12498.
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r
2010 American Chemical Society
Published on Web 09/15/2010
pubs.acs.org/IC

9710 Inorganic Chemistry, Vol. 49, No. 20, 2010
Al-Rafia et al.
Chart 1. Dianionic Bis(amido)silyl Ligands Developed in This Work
molecular structures of 3 and 4, while Table 1 lists relevant
data associated with structure refinement and solution.
As shown above, compounds 3 and 4 adopt similar
overall geometries with planar four-membered NSiNM
rings (M = Ge and Sn) and trigonal planar coordination
involving the chelating nitrogen atoms. The Ge-N and
Sn-N bond distances in 3 and 4 were 1.8627(10) and
˚
2.067(2) A (avg.), respectively, while nearly identical
Si-N endocyclic bond lengths were observed in both
complexes [1.7471(10) in 3; 1.745(2) A avg. in 4]. Com-
˚
pound 3 represents the first uncomplexed germylene
heterocycle featuring an NSiNGe core to be structurally
authenticated by crystallography. The analogous Ge(II)
heterocycle, [Me2Si(NtBu)2Ge:] was prepared by Veith as a
stable yellow oil, and this species was shown to be mono-
meric in benzene solvent by cryoscopic measurements.9,10
Russell and co-workers recently reported the synthesis of
astructurallyrelated tin(II) heterocycle, [{Ph2Si(NDipp)2}-
Sn:].7b As with 4, a planar NSiNSn unit was present,
however the Sn-N bond distances in the diphenylsilane
Scheme 1. Preparation of the Monomeric Germylenes and Stannylenes,
3-6
˚
analogue were elongated [2.101(6) and 2.259(5) A] with
7
respect to those found in 4 [2.067(2) A (avg.)]. Moreover,
˚
The identity of 1 and 2 was established using a combina-
tion of NMR and IR spectroscopy, satisfactory elemental
analyses (C, H, N), and single-crystal X-ray crystallogra-
phy (Figure 1). Despite the steric crowding present at the
nitrogen centers in both 1 and 2, all associated metrical
parameters, including intrachain Si-N and adjacent
Si-C(iPr) bond distances, were within expected values
in accordance with the molecular structures depicted in
Scheme 1.
additional molecular interactions were observed in
[{Ph2Si(NDipp)2}Sn:] involving the flanking aryl rings
of the Dipp groups and adjacent Sn centers, resulting in
the formation of a weakly associated coordination poly-
mer with close intermolecular Sn η6 aryl(centroid)
3 3 3
7b
contacts of ca. 3.2 A. By contrast, compound 4 is rig-
˚
orously monomeric with no close-range intermolecular
˚
interactions observed within 4.0 A. This difference in
solid-state packing is a likely consequence of added intra-
ligand repulsion in 4. The presence of encumbered iPr2Si
and Dipp groups within the same heterocycle results in
the aryl rings in 4 being pushed even further toward the Sn
center, leading to greater steric coverage.11 This effect is
observed both in the solid-state structure of 4, wherein
the Si-N-C(ipso, Dipp) angles are considerably wide
[134.98(10) and 137.71(10)°], and via the presence of
Synthesis of the Monomeric N-heterocyclic Germylenes
and Stannylenes, 3-6. In order to verify the ability of our
bis(amido)silyl ligands, [NSiN]Dipp and [NSiN]SiPh3, to
stabilize low-coordinate environments, we targeted the
preparation of divalent heavy carbene analogues, R2Ge:
and R2Sn:, termed hereafter as germylenes and stannylenes.5
Following established procedures,3d,6,7 the aryl-substituted
bis(amine), 1, was reacted with two equivalents of nBuLi in
Et2O to generate the dilithiated precursor, [{iPr2Si-
(NDipp)2}Li2], Li2[NSiN]Dipp. This reagent could be iso-
lated in pure form as a THF solvate,8 however, purification
was not necessary for our syntheses given that the in situ
generated dilithio salt, Li2[NSiN]Dipp, still underwent clean
i
spectroscopically distinct Pr environments within the
Dipp ligands (by 1H and 13C{1H} NMR) due to restricted
rotation of the Dipp groups. In the less hindered ana-
logue, [{Ph2Si(NDipp)2}Sn:], the exocyclic Si-N-C(ipso,
Dipp) angles are reduced to 130.2(2) and 132.7(2)°, while
i
free rotation of the Dipp moieties, and a single Pr
metathesis chemistry with GeCl2 dioxane and SnCl2 to give
3
the target Ge(II) and Sn(II) complexes, [{iPr2Si(NDipp)2}-
M:] (M = Ge, 3; M = Sn, 4; Scheme 1). High-quality crys-
tals of 3 and 4 were subsequently grown from diethyl ether,
and single-crystal X-ray crystallography confirmed the
presence of rigorously monomeric heterocycles with dicoor-
dinate Ge(II) and Sn(II) centers. Figure 2 contains the
environment, is observed by NMR spectroscopy at ambient
temperature.7b The Ge(II) heterocycle 3 possesses a similar
overall geometry as its heavier congener 4, with correspond-
ingly wide Si-N-C(ipso) angles of 139.41(8)° observed.
In order to further expand the potential tunability of our
dianionic chelates, we decided to install umbrella-shaped
(9) (a) Veith, M. Angew. Chem., Int. Ed. 1987, 26, 1. (b) Veith, M.; Grosser,
M. Z. Naturforsch., B: J. Chem. Sci. 1982, 37, 1375.
(5) (a) Neumann, W. P. Chem. Rev. 1991, 91, 311. (b) Lappert, M. F. Main
Group Metal Chem. 1994, 17, 183. (c) Haaf, M.; Schmedake, T. A.; West, R. Acc.
Chem. Res. 2000, 33, 704. (d) Weidenbruch, M. J. Organomet. Chem. 2002,
646, 39. (e) Mizuhata, Y.; Sasamori, T.; Tokitoh, N. Chem. Rev. 2009, 109, 3479.
(6) (a) Fink, W. Helv. Chim. Acta 1964, 47, 498. (b) Bush, R. P.; Lloyd, N. C.
J. Chem. Soc. A 1969, 257.
€
(10) For related work on N-heterocyclic germylenes, see (a) Kuhl, O.;
€
Lonnecke, P.; Heinicke, J. Polyhedron 2001, 20, 2215. (b) Tokitoh, N.;
Kishikawa, K.; Okazaki, R.; Sasamori, T.; Nakata, N.; Takeda, N. Polyhedron
2002, 21, 563. (c) K€uhl, O. Coord. Chem. Rev. 2004, 248, 411. (d) Zabula, A. V.;
Hahn, F. E.; Pape, T.; Hepp, A. Organometallics 2007, 26, 1972.
(7) (a) Hill, M. S.; Hitchcock, P. B. Organometallics 2002, 21, 3258.
(b) Mansell, S. M.; Russell, C. A.; Wass, D. F. Inorg. Chem. 2008, 47, 11367.
(8) Repeating the lithiation of 1 in THF, followed by crystallization of the
product from a hexanes/THF mixture, led to the isolation of the dilithiated
(11) (a) Spencer, D. J. E.; Aboelella, N. W.; Reynolds, A. M.; Holland,
P. L.; Tolman, W. B. J. Am. Chem. Soc. 2002, 124, 2108. (b) Stanciu, C.;
Richards, A. F.; Fettinger, J. C.; Brynda, M.; Power, P. J. Organomet. Chem.
2006, 691, 2540. (c) Wolf, R.; Brynda, M.; Ni, C.; Long, G. J.; Power, P. P. J. Am.
Chem. Soc. 2007, 129, 6076. (d) Zhu, Z.; Fischer, R. C.; Ellis, B. D.; Rivard, E.;
Merrill, W. A.; Olmstead, M. M.; Power, P. P.; Guo, J. D.; Nagase, S.; Pu, L.
Chem.;Eur. J. 2009, 15, 5263.
ligand, Li2[NSiN]Dipp 3THF in quantitative yield. X-ray crystallography
3
showed the structure of this species, prior to desolvation of THF, to be
{[NSiN]DippLi(THF)2}{Li(THF)4}. See Supporting Information for com-
plete crystallographic details.

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9711
Figure 1. Molecular structures of (DippNH)2SiiPr2 (1) and (Ph3SiNH)2SiiPr2 (2) with thermal ellipsoids presented at the 30% probability level. All
carbon-bound hydrogen atoms and solvate molecules have been omitted for clarity. Primed atoms are related to unprimed via a two-fold rotation axis that
˚
bisects the N-Si-N angle in 1. Selected bond lengths (A) and angles (°) with bracketed values belonging to a second molecule within the asymmetric unit:
Compound 1:Si(1)-N(1) 1.7397(11) [1.7413(11)], Si(1)-C(1)1.8896(13) [1.8873(13)];N(1)-Si(1)-N(1)0 115.04(8)[116.74(8)], C(1)-Si(1)-C(1)0 116.86(9)
[116.82(9)]. Compound 2: Si(1)-N(1) 1.7391(16), Si(1)-N(2) 1.7402(19), Si(2)-N(1) 1.7228(16), Si(3)-N(2) 1.7182(16), Si(1)-C(1) 1.892(2), Si(1)-C(4)
1.892(2); N(1)-Si(1)-N(2) 114.43(8), Si(1)-N(1)-Si(2) 139.33(10), Si(1)-N(2)-Si(3) 140.09(11), C(1)-Si(1)-C(4) 116.31(9).
Figure 2. Molecular structures of heterocycles 3-6 with thermal ellipsoids at the 30% probability level. Primed atoms for 3 are related to unprimed via a
˚
two-fold rotational axis upon which the Ge and Si atoms are located. Selected bond lengths (A) and angles (°): Compound 3: Ge(1)-N(1) 1.8627(10),
Si(1)-N(1) 1.7471(10); N(1)-Ge(1)-N(1)0 81.26(6), N(1)-Si(1)-N(1)0 87.94(7), C(1)-Si(1)-C(1)0 112.72(12), Si(1)-N(1)-C(11) 139.41(8). Compound 4:
Sn(1)-N(1) 2.0709(12), Sn(1)-N(2) 2.0631(12), Si(1)-N(1) 1.7440(12), Si(1)-N(2) 1.7463(12); N(1)-Sn(1)-N(2) 74.60(5), N(1)-Si(1)-N(2) 91.74(6),
C(1)-Si(1)-C(4) 111.87(7), Si(1)-N(1)-C(11) 137.71(10), Si(1)-N(2)-C(31) 134.98(10). Compound 5: Ge(1)-N(1) 1.8834(14), Ge(1)-N(2)
1.8829(14), Si(1)-N(1) 1.7210(14), Si(2)-N(2) 1.7164(14), Si(3)-N(1) 1.7458(14), Si(3)-N(2) 1.7481(14); N(1)-Ge(1)-N(2) 83.31(6), N(1)-Si(3)-N-
(2) 91.53(7), C(1)-Si(3)-C(4) 110.52(10), Si(3)-N(1)-Si(1) 146.23(9), Si(3)-N(2)-Si(2) 140.19(9). Compound 6: Sn(1)-N(1) 2.0888(15), Sn(1)-N(2)
2.0882(15), Si(1)-N(1) 1.7102(16), Si(2)-N(2) 1.7083(16), Si(3)-N(1) 1.7402(16), Si(3)-N(2) 1.7446(16);N(1)-Sn(1)-N(2) 76.28(6), N(1)-Si(3)-N(2)
95.51(8), C(1)-Si(3)-C(4) 109.50(11), Si(3)-N(1)-Si(1) 146.51(10), Si(3)-N(2)-Si(2) 140.14(9).
triarylsilyl groups at the nitrogen-donor sites, [NSiN]SiPh3
(Chart 1). The SiAr3 groups (Ar = aryl) not only provide
a wide swath of steric bulk that radiates outward from the
Si centers, but should allow for further ligand modification
via chemical functionalization of the peripheral Ar
groups.12
The syntheses of the Ge(II) and Sn(II) complexes
[{[NSiN]SiPh3}Ge:] (5) and [{[NSiN]SiPh3}Sn:] (6) pro-
ceeded in a similar fashion as for the less hindered Dipp
analogues, 3 and 4 (Scheme 1), with the noted exception
that the triphenylsilyl-substituted heterocycles exhibited
(12) Watkin, J. G.; Click, D. R. Polymerization Catalysts containing
Electron Withdrawing Amide Ligands. WO Patent 9845039, 1998.

9712 Inorganic Chemistry, Vol. 49, No. 20, 2010
Al-Rafia et al.
Table 1. Crystallographic Data for Compounds 1-5
1b
2c
3
4
5
empirical formula
fw
C30H50N2Si
466.81
C42H46N2Si3
663.08
0.37 ꢀ 0.21 ꢀ 0.18
monoclinic
P21
C30H48GeN2Si
537.38
0.40 ꢀ 0.37 ꢀ 0.36
monoclinic
C2/c
C30H48N2SiSn
583.48
0.42 ꢀ 0.39 ꢀ 0.35
monoclinic
P21/c
C42H44GeN2Si3
733.65
0.53 ꢀ 0.39 ꢀ 0.09
monoclinic
P21/n
cryst dimens (mm3)
cryst syst
space group
0.46 ꢀ 0.44 ꢀ 0.43
trigonal
P3121
unit cell dimensions
˚
˚
b (A)
˚
c (A)
a (A)
10.2694(3)
10.5347(9)
15.3080(13)
12.1157(10)
10.4149(4)
23.1176(8)
13.4528(5)
16.6257(7)
11.2475(4)
17.6079(7)
8.6077(9)
25.628(3)
17.1827(18)
46.7860(14)
R (°)
β (°)
γ (°)
111.6950(10)
107.5710(4)
110.7814(4)
91.3020(10)
3
˚
V (A )
4273.0(2)
6
1.088
1815.4(3)
2
1.213
3087.9(2)
4
1.156
3078.4(2)
4
1.259
3789.5(7)
4
1.286
Z
D (g cm-3
)
abs coeff (mm-1
T (K)
)
0.102
0.163
1.050
0.888
0.935
173(1)
55.10
38035
6589 (0.0201)
6421
299
0.0331
0.0894
0.282/-0.268
173(1)
52.92
14514
7441 (0.0232)
7063
425
0.0349
0.0940
0.533/-0.217
173(1)
55.00
13517
3556 (0.0112)
3371
155
0.0240
0.0701
0.317/-0.235
173(1)
55.02
26638
7080 (0.0116)
6777
307
0.0208
0.0574
0.437/-0.392
173(1)
55.26
33203
8784 (0.0301)
7290
433
0.0331
0.0983
0.577/-0.561
2θmax (°)
total data
unique data (Rint
)
obs data [I > 2σ(I)]
params
R1 [I > 2σ(I)]a
wR2 [all data]a
max/min ΔF (e-
A
)
-3
˚
P
P
P
P
a R1 = ||Fo|-|Fc||/ |Fo|; wR2 = [ w(Fo2 - Fc2)2/ w(Fo4)]1/2
.
b Flack parameter = 0.05(8). c Flack parameter = 0.17(7).
significantly reduced solubility in organic solvents.13 As a
consequence of the hydrolytically prone Si-N and Ge-N/
Sn-N linkages within 5 and 6, these compounds
react readily with trace quantities of moisture to yield
Ph3Si-O-SiPh3 as a soluble byproduct (identified by
strategy for the stabilization/isolation of low-coordinate
environments.
Initial Atom-Transfer Chemistry Involving Germylenes
3 and 5. Divalent germylenes (R2Ge:) and stannylenes
(R2Sn:) exhibit diverse reaction chemistry due to their
dual donor/acceptor nature and proclivity for oxidative
bond forming reactions.5,15 As mentioned earlier, intra-
molecular steric repulsions within the NSiNM hetero-
cycles 3-6 lead to the positioning of the flanking groups
at nitrogen (Dipp or SiPh3) in closer proximity to the
group 14 center. This effect should be quite useful in un-
covering new forms of bonding, whereby kinetic stabili-
zation is required to suppress undesired side-reactions.16
One such example would be the isolation of heavy ana-
logues of ketones, with the isolation of a stable silicone
derivative (R2SidO) being a highly desirable target.17,18
In order to benchmark the steric coverage offered by our
chelates with respect to known ligands, we explored
preliminary chalcogen atom-transfer chemistry involving
the germylenes 3 and 5 with the goal of isolating hitherto
unknown (or rare) examples of GedE multiple bonds
(E = group 16 element).5e
X-ray crystallography and H and 13C{1H} NMR).14
1
However when 5 and 6 are handled under strictly anhy-
drous conditions, these compounds are quite thermally
stable, with no noticeable signs of decomposition in the
solid state up to 300 °C (under N2).
High-quality crystals of 5 and 6 for X-ray diffraction
studies were obtained from diethyl ether and their mo-
lecular structures are presented as part of Figure 2. These
triarylsilyl-capped heterocycles display a higher degree of
intramolecular repulsion involving the backbone posi-
tioned iPr2Si groups relative to the Dipp analogues, 3 and
i
4. These Pr2Si SiPh3 interactions cause the -SiPh3
3 3 3
moieties to be tilted forward toward the Ge and Sn centers
to produce highly distorted Si(endo)-N-Si(exo) angles
[Si(3)-N(1)-Si(1,2) angles =146.23(9) and 140.10(9)
for 5; 146.51(10)° and 140.14(9)° for 6]. Furthermore,
space filling models indicate that the -SiPh3 groups
create a much deeper steric pocket about the capping
Ge and Sn centers with respect to the coverage offered by
the flanking Dipp groups in 3 and 4, hence the use of
triarylsilyl groups as structural motifs is a promising
Interaction of the arylamido germylene [{[NSiN]Dipp}-
Ge:] 3 with the chalcogen sources Me3NO and S8 (one
atomic equiv) afforded a new Ge product in each case;
notably, the products obtained exhibited analogous
NMR spectroscopic signatures, suggesting that these
products were of similar structure in solution. X-ray
(13) For the use of SiPh3 groups in ligands, see:(a) Bartlett, R. A.; Power,
P. P. J. Am. Chem. Soc. 1987, 109, 6509. (b) Bott, S. G.; Sullivan, A. C.
J. Chem. Soc., Chem. Commun. 1988, 1577. (c) Wehmschulte, R. J.; Power, P. P.
Inorg. Chem. 1998, 37, 6906. (d) Bindl, M.; Stade, R.; Heilmann, E. K.; Picot, A.;
Goddard, R.; F€urstner, A. J. Am. Chem. Soc. 2009, 131, 9468.
€
(15) (a) Veith, M.; Notzel, M.; Huch, V. Z. Anorg. Allg. Chem. 1994, 620,
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(c) Rakebrandt, H. -J.; Klingebiel, U. Z. Anorg. Allg. Chem. 1997, 623, 1264.
(16) Power, P. P. Chem. Rev. 1999, 99, 3463.
(14) For spectroscopic data, see: (a) Blankenship, C.; Cremer, S. E.
J. Organomet. Chem. 1989, 371, 19. Crystals of non-solvated Ph3SiOSiPh3
and those containing toluene solvate were isolated in separate reactions, and
identified by comparison of their unit cell parameters with those found in the
literature: (b) Glidwell, C.; Liles, D. C. Acta Crystallogr. 1978, B34, 124. (c)
Honle, W.; Manriquez, V.; von Schnering, H. G. Acta Crystallogr. 1990, C46,
1982.
(17) (a) Robison, R.; Kipping, F. S. J. Chem. Soc. Trans. 1908, 24, 25.
(b) Tokitoh, N.; Okazki, R. Coord. Chem. Rev. 2000, 210, 251. (c) Okazaki, R.;
Tokitoh, N. Acc. Chem. Res. 2000, 33, 625.
(18) (a) Yao, S.; Xiong, Y.; Brym, M.; Driess, M. J. Am. Chem. Soc. 2007,
129, 7268. (b) Yao, S.; Brym, M.; van Wu€llen, C.; Driess, M. Angew. Chem., Int.
Ed. 2007, 46, 4159. (c) Yao, S.; Xiong, Y.; Driess, M. Chem. Commun. 2009,
6466. (d) Yao, S.; Xiong, Y.; Driess, M. Chem.;Eur. J. 2010, 16, 1281.

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9713
Scheme 2. Chalcogen Transfer Chemistry Used to Generate the
Oxo- and Sulfido-Bridged Germane Dimers (7-9)
Figure 4. Molecular structure of 8 [{[NSiN]Dipp}Ge(μ-S)]2 with thermal
ellipsoids presented at the 30% probability level. All hydrogen atoms and
ether solvate molecules omitted for clarity. Primed atoms related to
˚
unprimed by an inversion center. Selected bond lengths (A) and angles
(°): Ge(1)-S(1) 2.1992(3), Ge(1)-S(1)0 2.2577(3), Ge(1)-N(1) 1.8344(9),
Ge(1)-N(2) 1.8471(9), Si(1)-N(1) 1.7606(9), Si(1)-N(2) 1.7675(10),
Si(1)-C(1) 1.8925(13), Si(1)-C(4) 1.8755(13); S(1)-Ge(1)-S(1)0 95.956-
(10), Ge(1)-S(1)-Ge(1)0 84.043(10), N(1)-Ge(1)-N(2) 83.65(4), N-
(1)-Si(1)-N(2) 88.19(4), C(1)-Si(1)-C(4) 109.35(6), Si(1)-N(1)-C-
(11) 137.62(9), Si(1)-N(2)-C(31) 138.00(8), Ge(1)-N(1)-C(11) 128.19-
(7), Ge(1)-N(2)-C(31) 128.18(7).
[Ge{N(SiMe3)2}2(μ-O)]2, was synthesized by Lappert and
co-workers through the direct reaction of the germanium-
(II) bisamide, Ge{N(SiMe3)2}2 with molecular oxygen.19
Dimeric [Ge{N(SiMe3)2}2(μ-O)]2 features a similar planar
Ge2O2 core, as in 7 with Ge-O distances ranging from
˚
1.804(11) to 1.836(10) A and accompanying Ge-N dis-
19
tances that vary from 1.8317(10) to 1.830(10) A. For
˚
further comparison, the centrosymmetric diarylgermone
dimer, [(2,6-Et2C6H3)2Ge(μ-O)]2, exhibited an average
˚
Ge-O bond length of 1.817(3) A and an endocyclic
O-Ge-O angle of 87.6(1)°;20 this O-Ge-O bond angle
compares well with those found in 7 [86.43(8) and
86.51(8)°]. Notably, the Ge-N distances in 7 are ca.
˚
0.03 A shorter than in 3, while the intraring N-Ge-N
Figure 3. Molecular structure of 7 [{[NSiN]Dipp}Ge(μ-O)]2 with thermal
ellipsoids presented at the 30% probability level. All hydrogen atoms and
angles are slightly wider in 7 [84.10(6) and 83.79(10)°]
relative to the corresponding angle of 81.26(6)° in the
Ge(II) precursor 3. The decrease in the observed Ge-N
bond lengths upon oxidation of 3 with Me3NO is likely
due to a reduction in the covalent radii on going from a
formal Ge(II) site in 3 to a Ge(IV) center in 7.21
The formation of a dimeric arrangement in 7 under-
scores the difficulty associated with isolating a monomer-
ic germanone (R2GedO) under ambient conditions; a
major factor for the lack of success thus far lies in the
highly polar nature of the Ge-O π-bond, which makes
this unit prone to dimerization/oligomerization to yield
thermodynamically more stable σ-linkages (and the for-
mation of extended Ge-O rings and/or chains).22-24
˚
ether solvate molecules omitted for clarity. Selected bond lengths (A) and
angles (°): Ge(1)-O(1) 1.8045(18), Ge(1)-O(2) 1.8063(19), Ge(2)-O(1)
1.8044(19), Ge(2)-O(2) 1.8032(18), Ge(1)-N(1) 1.828(2), Ge(1)-N(2)
1.833(2), Ge(2)-N(3) 1.830(2), Ge(2)-N(4) 1.828(2), Si(1)-N(1)
1.768(2), Si(1)-N(2) 1.763(2), Si(1)-C(1) 1.879(3), Si(1)-C(4) 1.877(3),
Si(2)-N(3) 1.761(2), Si(2)-N(4) 1.762(2), Si(2)-C(7) 1.878(30, Si(2)-C-
(10) 1.878(3); O(1)-Ge(1)-O(2) 86.43(8), N(1)-Ge(1)-N(2) 84.10(10),
O(1)-Ge(2)-O(2)86.51(8), N(1)-Si(1)-N(2) 87.95(11),C(1)-Si(1)-C-
(4) 112.08(14), Si(1)-N(1)-C(21) 134.65(19), Si(1)-N(2)-C(41) 135.79-
(19), Ge(1)-N(1)-C(21) 131.27(19), Ge(1)-N(2)-C(41) 129.17(19),
N(3)-Si(2)-N(4) 87.78(11), C(7)-Si(2)-C(10) 111.86(14), Si(2)-N-
(3)-C(61) 135.34(19), Si(2)-N(4)-C(81) 134.57(19), Ge(2)-N(3)-C-
(61) 130.43(18), Ge(2)-N(4)-C(81) 130.12(18).
crystallography substantiated the successful transfer of
chalcogen atoms to germanium in both instances and
revealed the formation of the corresponding oxo- and
sulfido-bridged dimers, [{iPr2Si(NDipp)2}Ge(μ-E)]2 (E =
O and S, 7 and 8, Scheme 2, Figures 3 and 4).
(19) Ellis, D.; Hitchcock, P. B.; Lappert, M. F. J. Chem. Soc., Dalton
Trans. 1992, 3397.
(20) Masamune, S.; Batcheller, S. A.; Park, J.; Davis, W. M.; Yamashita,
O.; Ohta, Y.; Kabe, Y. J. Am. Chem. Soc. 1989, 111, 1888.
(21) Bokii, N. G.; Yu, T.; Struchkov, T.; Kolesnikov, S. P.; Rogozhin,
I. S.; Nefedov, O. M. Izv. Akad. Nauk SSSR, Ser. Khim 1975, 4, 812.
(22) (a) Trinquier, G.; Barthelat, J. C.; Satge, J. J. Am. Chem. Soc. 1982,
104, 5931. (b) Kapp, J.; Remko, M.; Schleyer, P. v. R. J. Am. Chem. Soc. 1996,
118, 5745.
The oxo-bridged dimer [{[NSiN]Dipp}Ge(μ-O)]2 7 con-
tains planar NSiNGe and Ge2O2 arrays that are mutually
rotated by 73.0 and 71.6°, with average endocyclic
˚
Ge-O and Ge-N bond lengths of 1.805(4) and 1.830(5) A.
A related amide-substituted 1,3-cyclodigermoxane,

9714 Inorganic Chemistry, Vol. 49, No. 20, 2010
Al-Rafia et al.
these dimers are similar to that found in the precursor 3 as
evidenced by only minor deviations in the Si-N-C(ipso,
Dipp) angles in all three complexes. This suggests that the
degree of repulsion between the cofacial Dipp groups in
the dimers 7 and 8 was minimal. In order to more tho-
roughly compare the steric effects created by the Dipp
and SiPh3 groups within our chelates, we explored ana-
logous chalcogen-transfer chemistry with the triarylsilyl-
substituted germylene, 5.
Interaction of the Ph3Si-flankedgermylene[{[NSiN]SiPh3}-
Ge:] (5) with Me3NO did not yield any products that
could be isolated in pure form. However treatment of 5
with elemental sulfur yielded a clean product that was
marginally soluble in diethyl ether. Single-crystal X-ray
crystallography (Figure 5), later identified the compound
as the sterically congested germanethione dimer
[{[NSiN]SiPh3}Ge(μ-S)]2 (9). As with the less hindered
derivative [{[NSiN]Dipp}Ge(μ-S)]2 (8), the Ge2S2 core in
9 was found to be planar with similar Ge-S distances of
Figure 5. Molecularstructure of[{[NSiN]SiPh3}Ge(μ-S)]2 9 with thermal
ellipsoids presented at the 30% probability level with primed atoms
related to nonprimed by an inversion center. All hydrogen atoms and
ether solvate molecules have been omitted for clarity. Selected bond
˚
2.2197(5) and 2.2484(5) A and with slightly narrower
0
˚
lengths (A) and angles (°): Ge(1)-S(1) 2.2197(5), Ge(1)-S(1)
intraring S-Ge-S angles of 94.28(2)°; the Ge-S bond
lengths in 9 are in the range expected for single bonds
2.2484(5), Ge(1)-N(1) 1.8534(13), Ge(1)-N(2) 1.8519(13), Si(1)-N(1)
1.7337(14), Si(2)-N(2) 1.7326(14), Si(3)-N(1) 1.7704(14), Si(3)-N(2)
1.7675(14); S(1)-Ge(1)-S(1)0 94.28(2), N(1)-Ge(1)-N(2) 85.38(6), N-
(1)-Si(3)-N(2) 90.49(6), C(1)-Si(3)-C(4) 110.96(9), Si(3)-N(1)-Si-
(1) 131.13(8), Si(3)-N(2)-Si(2) 134.47(8), Ge(1)-N(1)-Si(1)
136.91(8), Ge(1)-N(2)-Si(2) 133.22(8).
26b
˚
(2.17-2.25 A). Particularly noteworthy is the signifi-
cant degree of intramolecular repulsion in 9 involving
proximal SiPh3 groups that are mutually located on the
same side of the plane created by the central Ge2S2 core.
These -SiPh3 Ph3Si- interactions lead to very large
3 3 3
Notably, Veith’s heterocyclic germylene, [Me2Si(NtBu)2-
Ge:], also participates in smooth oxo-transfer chemistry
with Me3NO, however due to the reduced steric bulk in this
system relative to 3, a trimeric product [{Me2Si(NtBu)2}-
Ge(μ-O)]3 containing a Ge3O3 core was obtained.15a
The sulfido dimer [{[NSiN]Dipp}Ge(μ-S)]2 (8) (Figure 4)
has an overall structure that mirrors the oxo-bridge dimer
7 with the primary difference being the presence of an
molecular distortions, as revealed by a widening of the Ge-
N-SiPh3 angles [Ge-N-SiPh3 angles =133.22(8) and
136.91(8)°] relative to in the less-hindered precursor 5
[121.13(8) and 127.42(8)°]. This effect is in stark contrast
to the sulfido-dimer 8 where little perturbation of the
Dipp groups is observed relative to the free germylene 3. It
is tempting to postulate that the addition of bulk to the
aryl groups in 9 would result in further repulsion between
the SiAr3 units and a steric preference for monomeric
species with discrete GedO and GedS double bonds.
Fortunately the synthesis of related ligands featuring
substituted SiAr3 groups should be feasible,28 thus en-
abling us to directly test our hypothesis in the near future.
˚
expanded Ge2S2 core [Ge-S = 2.1992(3) and 2.2577(3) A]
due to the larger covalent radius of S relative to O.25 It
is salient to mention that an example of a stable mono-
meric germanethione has been isolated at ambient tem-
perature, [Tbt(Tip)GedS] (Tbt = 2,4,6-{(Me3Si)2CH}-
C6H2; Tip = 2,4,6-iPr3C6H2),26,27 and that this species
˚
contains a significantly short Ge-S distance [2.049(3) A]
Conclusions
that is consistent with a GedS double bond. Inspection of
the structures of 7 and 8 reveals that the flanking Dipp
groups can readily twist away from the germanium-
chalcogen rings, thus providing a pathway for the dimer-
ization of any putative GedO and GedS double bonds
initially formed. In addition, the relative positions be-
tween the Dipp groups in 7 and 8 and the Ge centers in
A series of low-coordinate group 14 complexes featuring
sterically encumbered bis(amido)silyl ligands has been re-
ported. The ligand systems employed are hindered enough to
facilitate the isolation of rigorously monomeric, two-coordi-
nate germylenes and stannylenes, and preliminary work
indicates that these species undergo clean chalcogen-transfer
chemistry with Me3NO and S8 to give centrosymmetric
dimers with Ge2E2 cores (E = O and S). The structural data
in this paper suggests that [NSiN]SiPh3 and related ligands
featuring modified triarylsilyl groups would be useful for
supporting low-coordination environments involving transi-
tion-metal elements.29 Consequently, we are currently ex-
ploring this avenue of study in our laboratory.
(23) Khabashesku, V. N.; Boganov, S. E.; Kudin, K. N.; Margrave, J. L.;
Nefedov, O. M. Organometallics 1998, 17, 5041.
ꢀ
ꢁ
(24) (a) Barrau, J.; Rima, G.; Lavayssiere, H.; Dousse, G.; Satge, J.
J. Organomet. Chem. 1983, 246, 227. (b) Tokitoh, N.; Matsumoto, T.; Okazaki,
R. Chem. Lett. 1995, 1087. (c) Weidenbruch, M.; Sturmann, M.; Kilian, H.; Pohl,
S.; Saak, W. Chem. Ber. 1997, 130, 735. (d) Samuel, M. S.; Jennings, M. C.;
Baines, K. M. J. Organomet. Chem. 2001, 636, 130. (e) Iwamoto, T.; Masuda,
H.; Ishida, S.; Kabuto, C.; Kira, M. J. Organomet. Chem. 2004, 689, 1337.
ꢁ
ꢁ
(25) Cordero, B.; Gomez, V.; Platero-Plats, A. E.; Reves, M.; Echeverrıa,
(28) (a) Steele, A. R.; Kipping, F. S. J. Chem. Soc. 1929, 357. (b) Maruoka,
K.; Ito, T.; Araki, Y.; Shirasaka, T.; Yamamoto, H. Bull. Chem. Soc. Jpn. 1988,
61, 2975. (c) Osakada, K.; Koizumi, T.; Sarai, S.; Yamamoto, T. Organometallics
1998, 17, 1868. (d) Lambert, J. B.; Lin, L. J. Org. Chem. 2001, 66, 8537.
(29) (a) Tsai, Y.-C.; Lin, Y.-M.; Yu, J.-S. K.; Hwang, J.-K. J. Am. Chem.
Soc. 2006, 128, 13980. (b) Tsai, Y.-C.; Lu, Y.-M.; Lin, Y.-M.; Hwang, J.-K.; Yu,
J.-S. Chem. Commun. 2007, 4125.
ꢁ
J.; Cremades, E.; Barragan, F.; Alvarez, S. Dalton Trans. 2008, 2832.
(26) (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.
(27) For reports concerning base-stabilized germanethiones, see:
(a) Veith, M.; Becker, S.; Huch, V. Angew. Chem., Int. Ed. 1989, 28, 1237.
(b) Nagendran, S.; Roesky, H. W. Organometallics 2008, 27, 457.

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9715
Table 2. Crystallographic Data for Compounds 6-9
6
7
8
9
empirical formula
fw
C42H44N2Si3Sn
779.75
0.46 ꢀ 0.24 ꢀ 0.08
monoclinic
P21/n
C68H116Ge2N4O4Si2
1255.01
C64H106Ge2N4OS2Si2
1213.01
C92H108Ge2N4O2S2Si6
1679.66
cryst dimens (mm3)
cryst syst
space group
0.49 ꢀ 0.45 ꢀ 0.12
0.49 ꢀ 0.45 ꢀ 0.12
0.52 ꢀ 0.45 ꢀ 0.40
triclinic
P-1
monoclinic
P21/n
triclinic
P-1
unit cell dimensions
˚
˚
b (A)
˚
c (A)
a (A)
8.6497(7)
25.761(2)
17.1292(13)
12.8221(6)
15.7103(7)
19.1054(9)
82.9780(10)
78.9340(10)
79.303(10)
3696.4(3)
4
1.128
0.890
173(1)
50.50
16 911
14.0842(6)
14.8807(7)
16.6170(8)
11.766(2)
13.955(3)
15.759(3)
65.862(2)
72.296(2)
71.013(2)
2188.5(7)
1
1.274
0.866
173(1)
55.30
19 736
R (°)
β (°)
γ (°)
91.3450(10)
105.8690(10)
3
˚
V (A )
3815.8(5)
4
1.357
0.796
173(1)
55.06
33 162
8760 (0.0228)
7616
3349.9(3)
2
1.203
1.036
173(1)
55.10
29 458
7700 (0.0156)
7028
Z
D (g cm-3
)
abs coeff (mm-1
T (K)
)
2θmax (°)
total data
unique data (Rint
)
16 911 (0.0323)
13 235
696
0.0411
0.1229
10 089 (0.0096)
9505
530
0.0313
0.0903
observed data [I > 2σ(I)]
params
433
375
R1 [I > 2σ(I)]a
wR2 [all data]a
0.0284
0.0787
0.559/-0.695
0.0211
0.0582
0.444/-0.197
difference map ΔF (e-
A
)
1.164/-0.584
0.995/-0.330
-3
˚
P
P
P
P
a R1 = ||Fo| - |Fc||/ |Fo|; wR2 = [ w(Fo2 - Fc2)2/ w(Fo4)]1/2
.
Experimental Section
the crystal cooled to -100 °C. The data were corrected for ab-
sorption33 through use of a multiscan model (SADABS34 [2, 5, 6]
or TWINABS35 [7]) or through Gaussian integration from
indexing of the crystal faces (1, Li2[NSiN]Dipp, 3, 4, 8, 9). Struc-
tures were solved using the direct methods programs SHELXS-
9736 (1, Li2[NSiN]Dipp, 2, 7, 9) and SIR9737 (5, 6, 8) or the
Patterson search/structure expansion facilities within the
DIRDIF-200838 program system (3,4). Refinements were completed
using the program SHELXL-97.31 Hydrogen atoms were as-
signed positions based on the sp2 or sp3 hybridization geome-
tries 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.
Special Refinement Conditions. Compound 7: The crystal used
for data collection exhibited nonmerohedral twinning. Both
components were indexed with the program CELL_NOW.39
The second twin component can be related to the first compo-
nent by a 180° rotation about the [1 0 0] axis in reciprocal space
and the [1 -0.135 -0.144] axis in real space. Integration
intensities for the reflections from the two components were
written into a SHELXL-97 HKLF 5 reflection file with the data
integration program SAINT (version 7.68 A)40 using all reflec-
tion data (exactly and partially overlapped and nonoverlapped).
The following restraints were applied to the disordered solvent
General. All reactions were performed using standard
Schlenk techniques under an atmosphere of nitrogen or in a
nitrogen-filled glovebox (Innovative Technology, Inc.). Sol-
vents were dried using a Grubbs-type solvent purification
system30 manufactured by Innovative Technology, Inc., degassed
(freeze-pump-thaw method), and stored under an atmosphere
of nitrogen prior to use. Triphenylchlorosilane, n-butyl lithium
(2.5 M solution in hexanes), GeCl2 dioxane, SnCl2, elemental
3
sulfur, 2,6-diisopropylaniline, and lithium amide were pur-
chased from Aldrich and used as received. Dichlorodiisopro-
pylsilane was obtained from Gelest, degassed (freeze-pump-
thaw), and stored over molecular sieves under an N2 atmosphere
prior to use. Anhydrous trimethylamine N-oxide was recrystal-
lized from dry and degassed DMF (-30 °C). LiNHDipp (Dipp =
2,6-iPr2C6H3) was prepared according to a literature pro-
cedure.31 1H, 13C{1H}, 29Si{1H}, and 119Sn{1H} NMR spectra
were recorded on Varian Inova-400 spectrometer and refer-
enced externally to SiMe4 (1H, 13C{1H}, and 29Si) and SnMe4
(
119Sn). Elemental analyses were performed by the Analytical
and Instrumentation Laboratory at the University of Alberta.
Infrared spectra were recorded using Nic-Plan FTIR micro-
scope. Melting points were obtained in sealed glass capillaries
under nitrogen using a MelTemp melting point apparatus and
are uncorrected.
Et2O molecules: O-C, 1.43(1); C-C, 1.53(1); C C, 2.34(2);
3 3 3
˚
and O C, 2.42(2) A.
3 3 3
X-ray Crystallography. Crystals of appropriate quality for
X-ray diffraction studies were removed either from a Schlenk
tube under a stream of nitrogen or 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.32 All data were collected using a Bruker APEX II
CCD detector/D8 diffractometer using Mo KR radiation, with
Compound 9: The following restraints were applied to the
disordered solvent Et2O molecules: O-C, 1.430(4); C-C,
˚
1.530(4); C C, 2.340(8); and O C, 2.420(8) A.
3 3 3
3 3 3
€
€
(35) Sheldrick, G. M. TWINABS, version 2008/2; Universitat Gottingen:
€
Gottingen, Germany, 2008.
(36) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
(37) 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.
(30) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(31) Patton, J. T.; Feng, S. C.; Abboud, K. A. Organometallics 2001, 20,
3399.
(32) Hope, H. Prog. Inorg. Chem. 1995, 43, 1.
(33) Blessing, R. H. Acta Crystallogr. 1995, A51, 33.
(34) Sheldrick, G. M. SADABS, version 2008/1; Universitat Gottingen:
(38) Beurskens, P. T.; Beurskens, G.; de Gelder, R.; Smits, J. M. M.;
Garcia-Granda, S.; Gould, R. O. DIRDIF-2008; Crystallography Laboratory,
Radboud University: Nijmegen, The Netherlands, 2008.
€
€
(39) Sheldrick, G. M. CELL_NOW, version 2008/2; Universitat Gottingen:
€
Gottingen, Germany, 2008.
€
€
(40) Sheldrick, G. M. SAINT, version 7.68A; Bruker AXS Inc.: Madison,
€
Gottingen, Germany, 2008.
WI, 2008.

9716 Inorganic Chemistry, Vol. 49, No. 20, 2010
Al-Rafia et al.
4
Synthetic Procedures. Preparation of Ph3Si-NH2. Thirty
mL of THF was added to a precooled mixture of Ph3SiCl
(6.02 g, 20.4 mmol) and LiNH2 (0.519 g, 22.4 mmol) at -78 °C.
The reaction mixture was then warmed to room temperature
and stirred overnight to eventually yield a pale-pink solution.
The solvent was then removed under vacuum to give an off-
white oil. Addition of 50 mL dry diethyl ether to the oil resulted
in the precipitation of a white solid (presumably LiCl), and the
mixture was filtered using a filter-tipped cannula. The solvent
was then removed from the colorless filtrate to give a white solid
that was recrystallized from hexane (ca. -30 °C) to give pure
This analysis revealed the presence of the mixed dilithio adduct,
[{iPr2Si(NDipp)2}Li(THF)2][Li(THF)4]. These crystals rapidly
released THF upon exposure to vacuum to yield a pure material
containing three equivalents of THF per [NSiN]Dipp ligand.
Yield of {Li2[NSiN]Dipp 3THF} = 0.238 g (0.34 mol, 98%).
3
1H NMR (C6D6): δ 1.18 (m, 12H, THF), 1.35 (d, 3JHH = 6.9 Hz,
3
24H, CH(CH3)2, Dipp), 1.36 (d, JHH = 7.2 Hz, 12H, CH-
(CH3)2, -SiiPr2-), 1.56 (sept, 3JHH = 7.2 Hz, 2H, CH(CH3)2,
-SiiPr2-), 3.24 (m, 12H, THF), 4.04 (sept, 3JHH = 6.9 Hz, 4H,
CH(CH3)2, Dipp), 6.90 (t, 3JHH = 7.5 Hz, 2H, ArH), and 7.24
3
(d, JHH = 7.5 Hz, 4H, ArH). 13C{1H} NMR (C6D6): δ 20.9
1
Ph3Si-NH2 as a colorless solid (4.5 g, 80% yield). H NMR
(CH(CH3)2, -SiiPr2-), 21.9 (CH(CH3)2, -SiiPr2-), 25.1
(CH(CH3)2, Dipp), 25.5 (β-C (THF)), 27.4 (CH(CH3)2, Dipp),
68.1 (R-C (THF)), 115.1 (ArC), 123.3 (ArC), 141.7 (ArC),
and 157.1 (ArC). Mp (°C) 132-134. Anal. calcd for
(C6D6): δ 0.75 (br, 2H, -NH2), 7.16-7.19 (m, 9H, ArH), and
7.62-7.64 (m, 6H, ArH). 13C{1H} NMR (C6D6): δ 128.1 (ArC),
129.8 (ArC), 135.6 (ArC), and 137.3 (ArC). NMR spectroscopic
data were also obtained in CDCl3 and matched those reported
previously.4
{Li2[NSiN]Dipp 3THF} C42H72O3N2Li2Si: C, 72.58; H, 10.44;
3
N, 4.03. Found: C, 72.54; H, 10.41; N, 4.03.
Preparation of (DippNH)2SiiPr2 (1). To a white slurry of
LiNHDipp (1.67 g, 9.1 mmol) in 35 mL of Et2O at -78 °C
was added dropwise iPr2SiCl2 (0.85 mL, 4.7 mmol). The reaction
mixture was subsequently warmed to room temperature and
stirred for 6 h. The resulting white slurry was filtered with a
filter-tipped cannula to give a clear colorless solution. Concen-
tration of the filtrate to ca. 20 mL followed by cooling to ca.
-30 °C produced large colorless blocks of 1 after 2 days (1.16 g,
55%); these crystals were of suitable quality for X-ray crystal-
lography. H NMR (C6D6): δ 1.06 (d, JHH = 6.9 Hz, 12H,
CH(CH3)2, -SiiPr2-), 1.20 (d, 3JHH = 6.6 Hz, 24H, CH(CH3)2,
Dipp), 1.23 (septet, 3JHH = 6.6 Hz, 2H, CH(CH3)2, -SiiPr2-),
2.93 (s, 2H, NH), 3.67 (septet, 3JHH = 6.6 Hz, 4H, CH(CH3)2,
Dipp), and 7.06-7.14 (m, 6H, ArH). 13C{1H} NMR (C6D6): δ
14.3 (CH(CH3)2, -SiiPr2-), 18.5 (CH(CH3)2, -SiiPr2-), 24.0
(CH(CH3)2, Dipp), 28.6 (CH(CH3)2, Dipp), 123.7 (ArC), 124.0
(ArC), 140.1 (ArC), and 143.6 (ArC). 29Si{1H} NMR (C6D6): δ
-11.8. Mp (°C): 104-106. IR (FT-IR microscope): 3394 cm-1
(m, ν(N-H)). Anal. calcd for C30H50N2Si: C, 77.19; H, 10.80; N,
6.00. Found: C, 77.17; H, 10.98; N, 6.05.
Preparation of [{iPr2Si(NDipp)2}Ge:], [NSiN]DippGe (3). To a
solution of 1 (0.233 g, 0.50 mmol) in 6 mL of Et2O was added
dropwise two equiv of BuLi (2.5 M solution in hexanes, 0.40
n
mL, 1.00 mmol) at -35 °C. The reaction mixture was warmed to
room temperature and stirred for 1.5 h to give a pale-yellow
solution. This solution was then added dropwise to a cold (-35
°C) slurry of GeCl2 dioxane (0.115 g, 0.50 mmol) in 5 mL of
3
Et2O. Upon the addition of the lithiated ligand, a purple color
was generated which dissipated rapidly upon stirring. After the
addition was complete, an orange solution was seen over a white
precipitate. The reaction was then warmed to ambient tempera-
ture and stirred overnight. Filtration of the resulting mixture
yielded an orange filtrate from which 3 was isolated as a tan-
colored solid upon removal of the volatiles (0.251 g, 94%).
X-ray quality crystals of 3 (colorless plates) were subsequently
obtained by slowly cooling a solution of 3 in Et2O to -35 °C
1
3
1
3
(2 days). H NMR (C6D6): δ 1.02 (d, JHH = 7.2 Hz, 12H,
3
CH(CH3)2, Dipp), 1.31 (d, JHH = 6.8 Hz, 24H, CH(CH3)2,
Dipp, and iPr2Si, coincident; confirmed by an 1H-13C HMQC
correlation experiment), 1.71 (septet, 3JHH = 6.8 Hz, 2H, CH-
(CH3)2, -SiiPr2-), 3.80 (septet, 3JHH = 6.8 Hz, 4H, CH(CH3)2,
Synthesis of (Ph3SiNH)2SiiPr2 (2). To a solution of Ph3SiNH2
(2.53 g, 9.14 mmol) in 30 mL dry diethyl ether was added
dropwise one equiv of nBuLi (3.66 mL, 9.15 mmol, 2.5 M
solution in hexanes) at 0 °C. The reaction mixture was then
warmed at room temperature and stirred for 3 h. The resulting
white slurry was cooled at -78 °C, then 0.82 mL of Cl2SiiPr2 (0.5
equiv., 4.57 mmol) was added dropwise. After which the reac-
tion was warmed to room temperature and stirred overnight.
The resulting mixture was filtered through Celite to give pale-
orange colored solution, and subsequent removal of volatiles
afforded an orange-colored oil that was recrystallized from
diethyl ether (-35 °C) to give colorless crystals of 2 after 3 days
(2.05 g, 67%). 1H NMR (C6D6): δ 0.69 (septet, 3JHH = 7.6 Hz,
3
Dipp), 7.10 (m, 2H, ArH), and 7.20 (d, JHH = 8.2 Hz, 4H,
ArH). 13C{1H} NMR (C6D6): δ 18.2 (CH(CH3)2, Dipp),
23.5 (CH(CH3)2, Dipp), 24.2 (CH(CH3)2, -SiiPr2-), 28.5
(CH(CH3)2, -SiiPr2-), 123.5 (ArC), 124.4 (ArC), 142.6 (ArC),
and 144.1 (ArC). Mp (°C): 171-173. Anal. calcd for C30H48-
GeN2Si: C, 67.05; H, 9.00; N, 5.21. Found: C, 66.84; H, 9.29;
N, 5.09.
Preparation of [{iPr2Si(NDipp)2}Sn:], [NSiN]DippSn (4). To a
solution of 1 (0.270 g, 0.58 mmol) in 6 mL of Et2O was added
dropwise a solution of nBuLi (2.5 M solution in hexanes, 0.463
mL, 1.16 mmol). The resulting colorless solution was then stir-
red for 1.5 h and added dropwise to a cold (-35 °C) slurry of
SnCl2 (0.128 g, 0.68 mmol) in 4 mL of Et2O. After the addition
was complete (time of addition =15 min.), a red-brown solution
was observed over unreacted SnCl2. The reaction mixture was
then warmed to ambient temperature and stirred for 2 days.
The resulting orange slurry was filtered through Celite, and the
volatiles were removed from the orange filtrate collected to give
a yellow solid (0.336 g, quantitative yield). Crystals of suitable
for X-ray crystallography were subsequently grown by cooling a
saturated solution of 4 in Et2O to -35 °C to afford yellow rods.
3
2H, CH(CH3)2, -SiiPr2-), 0.95 (d, JHH = 7.6 Hz, 12H, CH-
(CH3)2, -SiiPr2-), 1.06 (br, 2H, NH), 7.13-7.18 (m, 18H,
ArH), and 7.71-7.74 (m, 12H, ArH). 13C{1H} NMR (C6D6):
δ 15.4 (CH(CH3)2, -SiiPr2-), 18.5 (CH(CH3)2, -SiiPr2-),
128.1 (ArC), 129.9 (ArC), 136.1 (ArC), and 137.3 (ArC).
29Si{1H} NMR (CDCl3): -18.2 (s, -SiPh3), 1.2 (s, -SiiPr2-).
Mp (°C): 121-123. IR (FT-IR microscope): 3334 cm-1 (m,
ν(N-H)). Anal. calcd for C42H46N2Si3: C, 76.08; H, 6.99; N,
4.22. Found: C, 75.82; H, 6.82; N, 4.22.
3
1H NMR (C6D6): δ 1.04 (d, JHH = 7.6 Hz, 12H, CH(CH3)2,
Preparation of [iPr2Si(NDipp)2]Li2 3THF, {Li2[NSiN]Dipp
3
3
i
Dipp), 1.28 (br, 24H, CH(CH3)2, Dipp and Pr2Si, coincident;
3THF}. Compound 1 (0.163 g, 0.35 mmol) was dissolved in
5 mL of hexanes, and this solution was cooled to -35 °C. To this
solution was added nBuLi (2.5 M solution in hexanes, 280 μL,
0.70 mmol), and stirring of the reaction mixture for 30 min
resulted in the formation of a white slurry. THF (1 mL) was then
added, followed by stirring for 30 min to yield a pale-yellow,
clear solution. The volume of the solution was then concentrated
to ca. 2 mL, and subsequent cooling to -35 °C resulted in the
formation of clear crystals of suitable quality for X-ray analysis.
confirmed by an 1H-13C HMQC correlation experiment), 1.57
(septet, 3JHH = 7.6 Hz, 2H, CH(CH3)2, -SiiPr2-), 3.90 (septet,
3JHH = 6.8 Hz, 4H, CH(CH3)2, Dipp), 7.02 (t, 3JHH = 7.6 Hz,
3
2H, ArH), and 7.20 (d, JHH = 7.6 Hz, 4H, ArH). 13C{1H}
NMR (C6D6): δ 18.4 (CH(CH3)2, Dipp), 23.3 (CH(CH3)2,
Dipp), 24.1 (CH(CH3)2, -SiiPr2-), 28.0 (CH(CH3)2, -SiiPr2-),
123.2 (ArC), 123.4 (ArC), 143.6 (ArC), and 144.8 (ArC).
119Sn{1H} NMR (C6D6): δ 536. Mp (°C): 129-131. Anal. calcd

Article
Inorganic Chemistry, Vol. 49, No. 20, 2010 9717
for C30H48N2SiSn: C, 61.75; H, 8.29; N, 4.80. Found: C, 60.22;
H, 8.65; N, 4.41.
and 6.99-7.10 (m, 12H, ArH). 13C{1H} NMR (C6D6): δ 19.3
(CH(CH3)2, -SiiPr2-), 19.0 (CH(CH3)2, -SiiPr2-), 26.2
(CH(CH3)2, Dipp), 28.4 (CH(CH3)2, Dipp), 123.9 (ArC), 125.7
(ArC), 138.2 (ArC), and 146.9 (ArC). Mp (°C): > 300. Anal.
calcd. for C60H96Ge2N4O2Si2 C, 65.11; H 8.74; N, 5.06. Found:
C, 64.02; H, 8.68; N, 5.03.
Synthesis of [{iPr2Si(NSiPh3)2}Ge:], [NSiN]SiPh3Ge (5). To a
solution of 2 (95 mg, 0.14 mmol) in 10 mL of Et2O was added
dropwise two equiv of nBuLi (2.5 M solution in hexanes, 0.120
mL, 0.30 mmol) at -35 °C. The reaction was warmed to room
temperature and stirred overnight to give a yellow solution. The
solution was then added dropwise to a cold (-35 °C) slurry of
Preparation of [{iPr2Si(NDipp)2}Ge(μ-S)]2, {[NSiN]Dipp
-
Ge(μ-S)}2 (8). Ten mL of dry ether was added to a mixture of 4
(60 mg, 0.11 mmol) and one equiv of sulfur (3.7 mg, 0.12 mmol) in a
20 mL scintillation vial in a glovebox. The reaction mixture was
stirred overnight at ambient temperature, which resulted in the
formation of a clear yellow solution. The solution was filter-
ed through Celite, and volatiles were removed in vacuo to give
white solid, which was recrystallized from a toluene/hexanes mix-
ture (5:1 ratio, -35 °C, 10 days). Yield of 8:58mg(91%). 1H NMR
(C6D6): δ0.91 (d, 3JHH = 7.5 Hz, 24H, CH(CH3)2, -SiiPr2-), 1.20
(d, 3JHH = 7.0 Hz, 24H, CH(CH3)2, Dipp), 1.29 (d, 3JHH =7.0Hz,
GeCl2 dioxane (0.035 g, 0.15 mmol) in 5 mL of Et2O. The
3
solution turned red-yellow immediately, and the formation of a
white precipitate was observed. The reaction was then warmed
to ambient temperature and stirred overnight. Filtration of the
resulting mixture yielded a clear yellow filtrate from which 5 was
isolated as a yellow-colored solid upon removal of the volatiles
(88 mg, 84%). X-ray quality crystals (colorless) of 5 were
subsequently obtained by slowly cooling a solution in Et2O
(-35 °C, 5 days). 1H NMR (C6D6): δ 0.81 (septet, 3JHH = 6.4
3
3
Hz, 2H, CH(CH3)2, -SiiPr2-), 0.87 (d, JHH = 6.4 Hz, 12H,
24H, CH(CH3), Dipp), 1.44 (septet, JHH = 7.5 Hz, 4H, CH-
CH(CH3)2, -SiiPr2-), 7.15-7.17 (m, 18H, ArH), and 7.78-
7.80 (m, 12H, ArH). 13C{1H} NMR (C6D6): δ 15.0 (CH(CH3)2,
-SiiPr2-), 17.0 (CH(CH3)2, -SiiPr2-), 128.2 (ArC), 129.9
(ArC), 136.4 (ArC), and 137.3 (ArC). Mp (°C): 196-198. Anal.
calcd for C42H44GeN2Si3: C, 68.75; H, 6.04; N, 3.82. Found: C,
68.76; H, 5.61; N, 3.79.
(CH3)2, -SiiPr2-), 3.96 (septet, 3JHH = 7.0 Hz, 8H, CH(CH3)2,
Dipp), and 6.99-7.17 (m, 12H, ArH). 13C{1H} NMR (C6D6): δ
15.6 (CH(CH3)2, -SiiPr2-), 18.7 (CH(CH3)2, -SiiPr2-), 27.6
(CH(CH3)2, Dipp), 28.2 (CH(CH3)2, Dipp), 124.2 (ArC), 125.6
(ArC), 138.3 (ArC), and 147.6 (ArC). Mp (°C): > 300. Anal. calcd
for C60H96Ge2N4S2Si2: C, 63.27; H, 8.50; N, 4.92. Found: C, 63.55;
H, 8.80; N, 4.59.
Synthesis of [{iPr2Si(NSiPh3)2}Sn:], [NSiN]SiPh3Sn (6). To a
solution of 2 (0.100 g, 0.15 mmol) in 10 mL of Et2O was added
dropwise two equiv of nBuLi (2.5 M solution in hexanes, 0.120
mL, 0.30 mmol) at -35 °C. The reaction was warmed to room
temperature and stirred overnight to give a yellow solution. The
solution was then added dropwise to a cold (-35 °C) slurry of
SnCl2 (0.029 g, 0.15 mmol) in 5 mL of Et2O. The reaction was
then warmed to ambient temperature and stirred overnight to
give a bright-yellow solution over white precipitate. Filtration of
the resulting mixture yielded a bright-yellow filtrate from which
6 was isolated as a yellow-colored solid upon removal of the
volatiles (93 mg, 79%). Crystals of 6 (yellow blocks) were grown
by cooling a saturated ether solution to -35 °C for 5 days. 1H
Synthesis of [{iPr2Si(NSiPh3)2}Ge(μ-S)]2, {[NSiN]SiPh3
-
Ge(μ-S)}2 (9). Diethyl ether (10 mL) was added to a mixture of 5
(51 mg, 0.070 mmol) and sulfur (2.2 mg, 0.069 mmol) in a 20 mL
scintillation vial in a glovebox. The reaction mixture was stirred for
24 h and resulted in the formation of white slurry. The reaction was
filtered, and the volatiles were removed from the filtrate in vacuo to
give a white solid. X-ray quality crystals of 9 were obtained by
redissolving the product in Et2O (8 mL), followed by layering with
hexanes (-35 °C, 9 days). Yield: 18 mg (35%). 1H NMR (C6D6): δ
-0.02 (septet, 3JHH = 7.5 Hz, 2H, CH(CH3)2, -SiiPr2-), 0.51 (d,
3JHH = 7.5 Hz, 12H, CH(CH3)2, -SiiPr2-), 1.15 (septet, 3JHH
=
7.5 Hz, 2H, CH(CH3)2, -SiiPr2-), 1.28 (d, 3JHH = 7.5 Hz, 12H,
CH(CH3)2, -SiiPr2-), 6.97 (t, 3JHH = 7.5 Hz, 24H, ArH), 7.12 (t,
3
NMR (C6D6): δ 0.80 (septet, JHH = 7.2 Hz, 2H, CH(CH3)2,
3
3
-SiiPr2-), 0.94 (d, JHH = 7.2 Hz, 12H, CH(CH3)2, -SiiPr2-),
3JHH = 7.5 Hz, 12H, ArH), and 7.65 (d, JHH = 7.5 Hz, 24H,
7.16-7.19 (m, 18H, ArH), and 7.77-7.79 (m, 12H, ArH).
13C{1H} NMR (C6D6): δ 15.8 (CH(CH3)2, -SiiPr2-), 17.5
(CH(CH3)2, -SiiPr2-), 128.1 (ArC), 129.7 (ArC), 136.3 (ArC),
and 138.9 (ArC). 119Sn{1H} NMR (C6D6): δ 527. Mp (°C):
113-115. Anal. calcd for C42H44N2Si3Sn: C, 64.69; H, 5.69; N,
3.59. Found: C, 65.02; H 5.81; N 3.57.
ArH). The 13C{1H} NMR spectrum was uninformative due to the
low solubility of the product. Mp (°C): > 300. Anal. calcd for
C92H108Ge2N4O2S2Si6 (9 2 Et2O): C, 65.80; H 6.49; N, 3.34.
Found: C, 65.35; H, 6.53; N, 3.23.
3
Acknowledgment. This work was supported by the Natural
Sciences and Engineering Research Council (NSERC-Discov-
ery Grant) and the Canada Foundation for Innovation (CFI-
LOF Grant). In addition the authors would like to thank the
University of Alberta for start-up funding and Alberta Inno-
vates for an Alberta Ingenuity New Faculty Award (E.R.) and a
Ph.D. fellowship (S.M.I.A). We also thank Mr. Mark Miskolzie
for assistance with acquiring 119Sn{1H} NMR data.
Preparation of [{iPr2Si(NDipp)2}Ge(μ-O)]2, {[NSiN]Dipp
-
Ge(μ-O)}2 (7). Toluene (10 mL) was added to a mixture of 3(60mg,
0.11 mmol) and trimethylamine N-oxide (8.3 mg, 0.12 mmol) in a
20 mL scintillation vial in a glovebox. The reaction mixture was
stirred overnight at ambient temperature and resulted in the
formation of a clear pale-yellow solution. The solution was
filtered through Celite, and volatiles were removed in vacuo to
obtain 7 (colorless solid), which was recrystallized from hexanes
(-35 °C, 7 days). Yield: 48mg (78%). 1H NMR(C6D6): δ 0.94 (d,
3JHH = 7.5 Hz, 24H, CH(CH3)2, -SiiPr2-), 1.04 (d, 3JHH = 6.9
Supporting Information Available: X-ray crystallographic
data in CIF format and the molecular structure of Li2-
3
Hz, 24H, CH(CH3)2, Dipp), 1.28 (d, JHH = 6.9 Hz, 24H,
[NSiN]Dipp 6THF along with selected bond lengths and angles.
3
CH(CH3), Dipp), 1.58 (septet, 3JHH = 6.9 Hz, 4H, CH(CH3)2,
-SiiPr2-), 3.77 (septet, 3JHH = 6.9 Hz, 8H, CH(CH3)2, Dipp),
This material is available free of charge via the Internet at http://
pubs.acs.org.