Synthesis and characterization of an amidinate-stabilized bisgermylene oxide and sulfide

Article abstract of DOI:10.1021/om101194f

The synthesis and characterization of the amidinate-stabilized bisgermylene oxide and sulfide [L²Ge-E-GeL²] (E = O (2), S (3); L ² = Bu^tC(NAr)₂, Ar = 2,6-Prⁱ ₂C₆H₃) are described. Compound 2 was prepared by the reaction of two equivalents of [L²GeCl] (1) with Me ₃NO and two equivalents of KC₈ in THF. It is proposed that the reaction proceeds through an [L²Ge^I] intermediate, which then reacts with Me₃NO to form 2. Similarly, the reaction of two equivalents of 1 with elemental sulfur and two equivalents of KC₈ in THF afforded 3. Compounds 2 and 3 have been characterized by NMR spectroscopy and X-ray crystallography.

Full text of DOI:10.1021/om101194f

NOTE
pubs.acs.org/Organometallics
Synthesis and Characterization of an Amidinate-Stabilized
Bisgermylene Oxide and Sulfide
Shu-Hua Zhang and Cheuk-Wai So*
Division of Chemistry and Biological Chemistry, Nanyang Technological University, Singapore 637371
S Supporting Information
b
ABSTRACT: The synthesis and characterization of the amidi-
nate-stabilized bisgermylene oxide and sulfide [L2Ge-E-
GeL2] (E = O (2), S (3); L2 = ButC(NAr)2, Ar = 2,6-Pri2C6H3)
are described. Compound 2 was prepared by the reaction of two
equivalents of [L2GeCl] (1) with Me3NO and two equivalents
of KC8 in THF. It is proposed that the reaction proceeds
through an [L2GeI] intermediate, which then reacts with Me3NO to form 2. Similarly, the reaction of two equivalents of 1 with
elemental sulfur and two equivalents of KC8 in THF afforded 3. Compounds 2 and 3 have been characterized by NMR spectroscopy
and X-ray crystallography.
table heavier group 14 dicarbene analogues of composition
[L4Ge-GeL4] with sulfur to form an [L4Ge-S-GeL4] inter-
mediate, which then undergoes an oxidation with elemental
sulfur to form [L4Ge(S)-S-Ge(S)L4]. However, [L4Ge-S-
GeL4] was not isolated from the reaction mixture. To the best of
our knowledge, bisgermylene chalcogenides [RGe-E-GeR]
have not been reported and structurally characterized.
Recently, we reported the synthesis and characterization of the
first isolable silylsilylene [L1SiSi(Cl){(NBut)2C(H)Ph}].4 It is
stable at room temperature under anaerobic conditions because
it benefits from electronic stabilization and steric protection by
the amidinate ligand. It is anticipated that the amidinate ligand is
capable of stabilizing low-valent germanium chalcogenides.
Herein, we report the synthesis and characterization of an
amidinate-stabilized bisgermylene oxide and sulfide [L2Ge-
E-GeL2] (E = O (2), S (3); L2 = ButC(NAr)2, Ar = 2,6-
Pri2C6H3).
:: ::
S
RE-ER (R = supporting ligand; E = low valent Si, Ge, Sn, Pb)
have attracted much attention in the past few years. These
:: ::
compounds comprise an E-E single bond and a lone pair of
electrons at each E atom.1 The formal oxidation state of each E
atom is þ1. They can be synthesized successfully by incorporat-
ing sterically hindered substituents at the heavier group 14
elements. For example, the amidinate-stabilized disilylene and
:: ::
digermylene [LE-EL] (E = Si, Ge, L = L1 = PhC(NBut)2;
E = Ge, L = L2 = ButC(NAr)2, Ar = 2,6-Pri2C6H3),1a,c,d
N-heterocyclic carbene-stabilized dichlorodisilylene [L3f(Cl)
Si-Si(Cl)rL3] (L3 = :C{N(Ar)CH}2),1e pyridyl-1-azaallyl
digermylene [L4Ge-GeL4] (L4 = N(SiMe3)C(Ph)C(SiMe3)-
(C5H4N-2)),1b and diaryldistannylene [LArSn-SnLAr] [LAr
=
2,6-(Me2NCH2)2C6H3] were synthesized and structurally
characterized.1g The reactions of stable heavier group 14 dicar-
bene analogues were reported.2 Recently, Roesky et al. showed
that [L1Si-SiL1] reacted with N2O in toluene to afford [L1Si(μ-
O)-O-Si(μ-O)L1]2, which contains two four-membered dis-
iloxane rings bridged by two oxygen atoms.2d The reaction
appears to proceed through an insertion of [L1Si-SiL1] with
N2O to form an [L1Si-O-SiL1] intermediate. The [L1Si-O-
SiL1] intermediate undergoes an oxidation with N2O to form
[L1Si(O)-O-Si(O)L1], which then dimerizes to afford
[L1Si(μ-O)-O-Si(μ-O)L1]2. It is noteworthy that [L1Si-
O-SiL1] was not isolated from the reaction mixture. In contrast,
the reaction of [L1Si-SiL1] with elemental selenium afforded
the di(silaneselone) [L1Si(Se)-Si(Se)L1].3 Selenium does not
insert into the SiI-SiI bond. Jambor et al. reported that [LArSn-
SnLAr] reacted with excess elemental selenium in toluene/
hexane to form [LArSn-Se-SnLAr].2h Similar reaction for a
longer reaction time gave [LArSn(Se)-Se-Sn(Se)LAr]. Leung
et al. showed that the reaction of the digermylene [L4Ge-GeL4]
with excess elemental sulfur afforded [L4Ge(S)-S-Ge(S)L4].1b
The reaction is proposed to proceed through an insertion of
The novel bisgermylene oxide [L2Ge-O-GeL2] (2) was
synthesized by the reaction of two equivalents of [L2GeCl] (1)
with Me3NO and two equivalents of KC8 in THF (Scheme 1).
The reaction was stirred at room temperature for 12 h. After
removal of THF in vacuo, the crude product was characterized by
1H NMR spectroscopy. The spectrum shows that a mixture of 2
(major product) and the digermylene [L2Ge-GeL2]1a (minor
product) was formed. The crude product was extracted with
Et2O to give compound 2 as colorless crystals. An attempt to
isolate [L2Ge-GeL2] by recrystallization failed. However, the
reaction of [L2Ge-GeL2] with one equivalent of Me3NO in
THF did not afford compound 2, confirmed by NMR spectros-
copy. The results suggest that the reaction of 1 with Me3NO and
KC8 proceeds through the formation of a germanium(I) [L2GeI]
intermediate. The intermediate then reacts with Me3NO to form
2, or it dimerizes to form [L2Ge-GeL2]. Moreover, there is no
Received: December 22, 2010
Published: March 09, 2011
r
2011 American Chemical Society
2059
dx.doi.org/10.1021/om101194f Organometallics 2011, 30, 2059–2062
|

Organometallics
NOTE
reaction between 1 and Na2O in THF. The results suggest that
the reaction of 1 with Me3NO and KC8 may not proceed through
a substitution reaction of 1 and the K2O intermediate. The lighter
congener [L1Si-O-SiL1] can be synthesized by the reaction of
[L1SiH(Cl)-O-SiH(Cl)L1] with LiN(SiMe3)2, and the struc-
ture of [L1Si-O-SiL1] has been characterized by X-ray
chlorogermylene [L2GeCl] (265.29°).1a This geometry is con-
sistent with a stereoactive lone pair at the germanium centers.
The lone pair electrons at the germanium centers have a trans
conformation. The Ge(1)-O(1)-Ge(2) angle (147.2(3)°) in 2
is significantly smaller than the Si-O-Si angle in [L1Si-O-
SiL1] (159.88(15)°).5 The Ge-O bonds (1.733(4), 1.766(5) Å)
are comparable with typical Ge-O single bonds (1.75-1.85 Å),7
but they are shorter than that in MamxGeOPri (Mamx =
methylaminomethyl-m-xylyl, 1.856(2) Å).8 The C-N bond
lengths (C(13)-N(1): 1.330(3) Å, C(13)-N(2): 1.343(3)
Å) are approximately between the C-N double and C-N(sp2)
single bond lengths. This geometry shows considerable deloca-
lization throughout the NCN backbone of the ligand.
The molecular structure of 3 with an atomic numbering
scheme is shown in Figure 2. Compound 3 crystallizes in the
triclinic space group P1 incorporating disordered THF molecules
in the asymmetric unit. Disordered THF molecules are omitted
for clarity in Figure 2. Selected bond distances (Å) and angles
(deg) are given in Table 1. The amidinate ligands are bonded in a
N,N0-chelate fashion to the germanium centers, which adopt a
trigonal-pyramidal geometry. The sum of the bond angles at the
Ge(1) and Ge(2) atoms are 256.96° and 255.41°, respectively.
This geometry is consistent with a stereoactive lone pair at the
germanium centers. The structure of compound 3 is different
from that of 2. The lone pair electrons at the germanium centers
have a cis conformation. A similar structure can be found in
[L4Ge(S)-S-Ge(S)L4], which is comprised of two GedS
bonds in a cis conformation.1b It is suggested that the electronic
repulsion of lone pair electrons on the Ge-E-Ge skeleton and
the steric hindrance between the amidinate ligands determine the
::
::
crystallography.5 The heavier congeners [RE-O-ER] (E = Sn,
Pb) are still unknown. Power et al. showed that the reaction of
[Ar0EEAr0] (Ar0 = C6H -2,6-Ar2, E = Ge, Sn) with N2O in hexane
30::
or toluene afforded [Ar E(μ-OH)]2.6
Similarly, the reaction of two equivalents of 1 with elemental
sulfur and two equivalents of KC8 in THF afforded [L2Ge-S-
GeL2] (3, Scheme 2). [L2Ge-GeL2] cannot be observed in the
crude product. The reaction of [L2Ge-GeL2] with one equiva-
lent of elemental sulfur in THF afforded 3 and a mixture of
inseparable products, confirmed by NMR spectroscopy. How-
ever, an attempt to isolate 3 by recrystallization failed. It is
proposed that the reaction of 1 with KC8 and elemental sulfur
proceeds through the [L2GeI] intermediate, which then reacts
with elemental sulfur to form 3. The [L2GeI] intermediate can
also dimerize to form [L2Ge-GeL2], which then reacts with
elemental sulfur to form 3. Thus, [L2Ge-GeL2] was not
observed in the crude product. Moreover, 1 did not react with
Na2S in THF to form 3. The results suggest that the reaction of 1
with elemental sulfur and KC8 may not proceed through a
substitution reaction of 1 and the K2S intermediate. The heavier
congener, [LArSn-S-SnLAr], was synthesized by the reaction of
[LArSn-SnLAr] with elemental sulfur.2g
Compounds 2 and 3 were isolated as highly air- and moisture-
sensitive colorless crystalline solids that are soluble in THF and
Et2O. They are stable in solution or the solid state at room
temperature in an inert atmosphere. They have been character-
ized by elemental analysis, spectroscopic methods, and X-ray
crystallography. The 1H and 13C NMR spectra of 2 and 3 display
resonances due to the amidinate ligand.
The molecular structure of 2 with an atomic numbering
scheme is shown in Figure 1. Selected bond distances (Å) and
angles (deg) are given in Table 1. There is a substantial disorder
of the Ge-O-Ge skeleton. The amidinate ligands are bonded in
a N,N0-chelate fashion to the germanium centers, which adopt a
trigonal-pyramidal geometry. The sum of the bond angles at the
Ge(1) and Ge(2) atoms are 269.20° and 250.93°, respectively.
They are comparable with that of the three-coordinated
Scheme 1. Synthesis of 2
Figure 1. Molecular structure of 2 with thermal ellipsoids at the 50%
probability level. Hydrogen atoms are omitted for clarity.
Scheme 2. Synthesis of 3
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dx.doi.org/10.1021/om101194f |Organometallics 2011, 30, 2059–2062

Organometallics
NOTE
Table 1. Selected Bond Distances (Å) and Bond Angles (o)
for Compounds 2 and 3
Ge(1) Ge(2) distance (3.492 Å) is longer than typical Ge-
3 3 3
Ge single bonds (average 2.61 Å), which indicates there is no
bonding between the germanium centers.
2
Ge(1)-O(1)
Ge(1)-N(1)
N(1)-C(13)
Ge(2)-N(1A)
1.733(4) Ge(2)-O(1)
2.026(2) Ge(1)-N(2)
1.330(3) N(2)-C(13)
2.077(2) Ge(2)-N(2A)
1.766(5)
2.055(2)
1.343(3)
2.097(2)
’ EXPERIMENTAL SECTION
All manipulations were carried out under an inert atmosphere of
argon gas using standard Schlenk techniques. Solvents were dried over
and distilled over Na/K alloy prior to use. 1 was prepared as described in
the literature.1a The 1H and 13C NMR spectra were recorded on a JEOL
ECA 400 spectrometer. The NMR spectra were recorded in C6D6. The
chemical shifts δ are relative to SiMe4 for 1H and 13C. Elemental analyses
were performed by the Division of Chemistry and Biological Chemistry,
Nanyang Technological University. Melting points were measured in
sealed glass tubes and were not corrected.
Ge(1)-O(1)-Ge(2) 147.2(3)
N(1)-Ge(1)-O(1)
103.00(16)
92.80(16)
63.73(9)
N(2)-Ge(1)-O(1) 102.47(16) N(1A)-Ge(2)-O(1)
N(2A)-Ge(2)-O(1) 95.98(15) N(1)-Ge(1)-N(2)
Ge(1)-N(1)-C(13) 93.72(16) N(1)-C(13)-N(2)
107.4(2)
C(13)-N(2)-Ge(1) 92.06(15) N(1A)-Ge(2)-N(2A) 62.15(8)
Synthesis of 2. THF (15 mL) was added to a mixture of 1 (1.58 g,
2.99 mmol), Me3NO (0.13 g, 1.69 mmol), and KC8 (0.55 g, 4.01 mmol)
at -78 °C. The reaction mixture was stirred at room temperature for
12 h. Volatiles were removed by vacuum, and the residue was extracted
with Et2O. The resulting green-red solution was filtered, and the filtrate
was concentrated to a volume of approximately 10 mL. Storage of the
solution at room temperature for 1 day afforded colorless block crystals
of 2. Yield: 0.16 g (11%). Mp: 308.9 °C. Anal. Calcd for C58H86Ge2-
N4O: C, 69.60; H, 8.67; N, 5.60. Found: C, 69.43; H, 8.52; N, 5.43. 1H
NMR (395.9 MHz, 21.2 °C): δ 0.91 (s, 18 H, But), 1.07 (d, 3JH-H = 6.3
3
Ge(1)-S(1)
Ge(1)-N(1)
C(13)-N(1)
Ge(2)-N(3)
N(3)-C(42)
2.2512(14) Ge(2)-S(1)
2.2626(14)
2.019(4)
1.338(6)
2.032(4)
1.343(6)
2.048(4)
1.331(7)
2.039(4)
1.333(6)
Ge(1)-N(2)
C(13)-N(2)
Ge(2)-N(4)
N(4)-C(42)
Ge(1)-S(1)-Ge(2) 101.37(6)
N(2)-Ge(1)-S(1) 92.52(13)
N(1)-Ge(1)-S(1) 100.63(13)
N(1)-Ge(1)-N(2) 63.81(16)
N(1)-C(13)-N(2) 107.3(4)
N(3)-Ge(2)-S(1) 100.24(13)
N(3)-Ge(2)-N(4) 63.95(16)
N(3)-C(42)-N(4) 107.3(4)
Hz, 12 H, CH(CH3)2), 1.32 (br s, 24 H, CH(CH3)2), 1.37 (d, 3JH-H
=
3
6.3 Hz, 12 H, CH(CH3)2), 3.63 (sept, JH-H = 6.3 Hz, 4 H, CH-
Ge(1)-N(1)-C(13) 93.6(3)
C(13)-N(2)-Ge(1) 94.7(3)
3
(CH3)2), 3.82 (sept, JH-H = 6.3 Hz, 4 H, CH(CH3)2), 7.04-7.10
ppm (m, 12 H, Ph). 13C NMR (99.5 MHz, 21.4 °C): δ 23.4 (CMe3),
27.6 (CH(CH3)2), 28.4 (CH(CH3)2), 29.5 (CH(CH3)2), 29.6
(CH(CH3)2), 30.6 (CH(CH3)2), 42.3 (CMe3), 123.8, 124.3, 141.1,
144.7, 145.7 (Ph), 175.4 ppm (NCN).
N(4)-Ge(2)-S(1)
91.22(13)
Ge(2)-N(3)-C(42) 94.0(3)
C(42)-N(4)-Ge(2) 94.0(3)
Synthesis of 3. THF (15 mL) was added to a mixture of 1 (1.57 g,
2.98 mmol), S8 (0.0497 g, 0.194 mmol), and KC8 (0.53 g, 3.92 mmol) at
-78 °C. The reaction mixture was stirred at room temperature for 12 h
and filtered. The resulting red-brown solution was concentrated to a
volume of approximately 10 mL. Storage of the solution at room
temperature for 1 day afforded colorless block crystals of 3 2THF.
3
3
Yield: 0.25 g (15%). Mp: 312.7 °C. Anal. Calcd for 3 2THF,
C66H102Ge2N4O2S: C, 68.27; H, 8.86; N, 4.83. Found: C, 67.91; H,
8.52; N, 4.57. 1H NMR for 3 2THF (395.9 MHz, 21.6 °C): δ 0.91 (s, 18
3
H, But), 1.19 (d, 3JH-H = 6.8 Hz, 12 H, CH(CH3)2), 1.28 (d, 3JH-H
=
4.1 Hz, 12 H, CH(CH3)2), 1.29 (d, 3JH-H = 4.1 Hz, 12 H, CH(CH3)2),
1.39 (d, 3JH-H = 6.8 Hz, 12 H, CH(CH3)2), 1.42 (m, 8 H, THF), 3.57
(m, 8 H, THF), 3.63 (sept, 3JH-H = 6.8 Hz, 4 H, CH(CH3)2), 4.03 (sept,
3JH-H = 6.8 Hz, 4 H, CH(CH3)2), 7.00-7.01 (d, 1 H, Ph), 7.02-7.03
(d, 2 H, Ph), 7.07-7.11 (t, 4 H, Ph), 7.12-7.13 (d, 3 H, Ph), 7.14-7.15
(d, 2 H, Ph). 13C NMR for 3 2THF (99.5 MHz, 21.7 °C): δ 23.0
3
(CH(CH3)2), 23.7 (CH(CH3)2), 26.2 (THF), 28.5 (CH(CH3)2), 28.6
(CH(CH3)2), 28.7 (CH(CH3)2), 29.4 (CMe3), 29.6 (CH(CH3)2), 42.4
(CMe3), 68.2 (THF), 123.7, 124.6, 128.2, 140.1, 145.1, 146.4 (Ph),
172.4 ppm (NCN).
X-ray Data Collection and Structural Refinement. Intensity
data for compounds 2 and 3 were collected using a Bruker APEX II
Figure 2. Molecular structure of 3 with thermal ellipsoids at the 50%
probability level. Disordered THF molecules and hydrogen atoms are
omitted for clarity.
diffractometer. The crystals of 2 and 3 2THF were measured at 103(2)
3
K. The structures were solved by direct phase determination (SHELXS-
97) and refined for all data by full-matrix least-squares methods on F2.9
All non-hydrogen atoms were subjected to anisotropic refinement. The
hydrogen atoms were generated geometrically and allowed to ride on
their respective parents atoms; they were assigned appropriate isotopic
thermal parameters and included in the structure-factor calculations.
conformation of the Ge-E-Ge skeleton in 2 and 3. The
Ge(1)-S(1)-Ge(2) angle (101.37(6)°) in 3 is significantly
smaller than the Ge-O-Ge angle in 2, and it is similar to that in
[L4Ge(S)-S-Ge(S)L4] (101.4(1)°).1b The Ge-S bonds
(2.2512(14) and 2.2626(14) Å) are comparable to typical
Ge-S single bonds (2.21-2.29 Å)7 and the Ge-S single bond
in [L4Ge(S)-S-Ge(S)L4] (2.222(3), 2.226(3) Å).1b The
Selected X-ray crystallographic data of 2 and 3 2THF are summarized in
3
Table 2. The largest diffraction peak and hole values for compound
3 2THF are high because of the disordered THF molecules in the
3
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dx.doi.org/10.1021/om101194f |Organometallics 2011, 30, 2059–2062

Organometallics
NOTE
Table 2. Crystallographic Data for Compounds 2 and
Robinson, G. H. Science 2008, 321, 1069. (f) Fischer, R. C.; Pu, L.;
Fettinger, J. C.; Brynda, M. A.; Power, P. P. J. Am. Chem. Soc. 2006,
128, 11366. (g) Jambor, R.; Kaꢀsnꢁa, B.; Kirschner, K. N.; Sch€urmann, M.;
Jurkschat, K. Angew. Chem., Int. Ed. 2008, 47, 1650. (h) Pu, L.; Twamley,
B.; Power, P. P. J. Am. Chem. Soc. 2000, 122, 3524. (i) Wang, W.; Inoue,
S.; Yao, S.; Driess, M. Chem. Commun. 2009, 2661.
(2) (a) Yeong, H.-X.; Lau, K.-C.; Xi, H.-W.; Lim, K. H.; So, C.-W.
Inorg. Chem. 2010, 49, 371. (b) Yeong, H.-X.; Xi, H.-W.; Lim, K. H.; So,
C.-W. Chem.—Eur. J. 2010, 16, 12956. (c) Sen, S. S.; Roesky, H. W.;
Meindl, K.; Stern, D.; Henn, J.; St€uckl, A. C.; Stalke, D. Chem. Commun.
2010, 5873. (d) Sen, S. S.; Tavꢀcar, G.; Roesky, H. W.; Kratzert, D.; Hey,
J.; Stalke, D. Organometallics 2010, 29, 2343. (e) Tavꢀcar, G.; Sen, S. S.;
Roesky, H. W.; Hey, J.; Kratzert, D.; Stalke, D. Organometallics 2010,
29, 3930. (f) Sen, S. S.; Kratzert, D.; Stern, D.; Roesky, H. W.;ꢀStalke, D.
Inorg. Chem. 2010, 49, 5786. (g) Bouꢀska, M.; Dostꢁal, L.; Ruꢀziꢀcka, A.;
Beneꢀs, L.; Jambor,ꢀ R. Chem.-Eur. J. 2011, 17, 450. (h) Bouꢀska, M.; Dostꢁal,
L.; de Proft, F.; Ruꢀziꢀcka, A.; Lyꢀcka, A.; Jambor, R. Chem.-Eur. J. 2011, 17,
455.
3 2THF
3
2
3 2THF
3
formula
M
C58H86Ge2N4O
1000.49
colorless
monoclinic
P2(1)/c
12.1248(7)
19.2482(12)
13.3429(6)
90
C66H102Ge2N4O2S
1160.76
color
colorless
triclinic
cryst syst
space group
a/Å
P1
13.4937(15)
13.5639(10)
19.802(2)
98.213(5)
100.902(5)
109.631(3)
3267.6(6)
2
b/Å
c/Å
R/deg
β/deg
119.477(4)
90
γ/deg
V/Å3
2710.9(3)
2
(3) Zhang, S.-H.; Yeong, H.-X.; So, C.-W. Chem.—Eur. J. 2011,
17, 3490.
Z
dcalcd/g cm-3
μ/mm-1
F(000)
cryst size/mm
index range
1.226
1.180
(4) Zhang, S.-H.; Yeong, H.-X.; Xi, H.-W.; Lim, K. H.; So, C.-W.
Chem.—Eur. J. 2010, 16, 10250.
(5) Wang, W.; Inoue, S.; Yao, S.; Driess, M. J. Am. Chem. Soc. 2010,
132, 15890.
(6) Spikes, G. H.; Peng, Y.; Fettinger, J. C.; Steiner, J.; Power, P. P.
Chem. Commun. 2005, 6041.
(7) Baines, K. M; Stibbs, W. G. Coord. Chem. Rev. 1995, 145, 157.
(8) Jutzi, P.; Keitemeyer, S.; Neumann, B.; Stammler, H.-G. Orga-
nometallics 1999, 18, 4778.
1.150
0.995
1068
1244
0.40 ꢁ 0.04 ꢁ 0.04 0.40 ꢁ 0.40 ꢁ 0.10
-17 e h e 9
-27 e k e 27
-15 e l e 19
41 399
-15 e h e 17
-17 e k e 16
-14 e l e 25
14 916
no. of rflns collected
R1, wR2 (I > 2(σ)I)
R1, wR2 (all data)
goodness of fit, F2
(9) Sheldrick, G. M. SHELXL-97; Universit€at G€ottingen: G€ottingen,
Germany, 1997.
0.0589, 0.1446
0.1193, 0.1844
1.061
0.0885, 0.2153
0.1469, 0.2387
1.076
no. of data/restraints/params 8312/0/318
largest diff peak, hole/e Å-3
0.709, -0.777
14 916/274/783
2.199, -1.713
asymmetric unit. The large Ueq(max)/Ueq(min) ratio for compound
3 2THF is due to the Pri groups, which usually show large atomic
3
displacement parameters.
’ ASSOCIATED CONTENT
S
Supporting Information. CIF files giving X-ray data for 2
b
and 3 2THF. This material is available free of charge via the
Internet at http://pubs.acs.org.
3
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: CWSo@ntu.edu.sg.
’ ACKNOWLEDGMENT
This work was supported by the Academic Research Fund
Tier 1 (RG 47/08). The authors thank Dr. Y. Li for X-ray
crystallography.
’ REFERENCES
(1) (a) Green, S. P.; Jones, C.; Junk, P. C.; Lippert, K.-A.; Stasch, A.
Chem. Commun. 2006, 3978. (b) Leung, W.-P.; Chiu, W.-K.; Chong,
K.-H.; Mak, T. C. W. Chem. Commun. 2009, 6822. (c) Nagendran, S.;
Sen, S. S.; Roesky, H. W.; Koley, D.; Grubm€uller, H.; Pal, A.; Herbst-
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