Preparation of RSn(I)-Sn(I)R with two unsymmetrically coordinated Sn(I) atoms and subsequent gentle activation of P4

Article abstract of DOI:10.1021/ja207538g

This article reports the reduction of [{2,6-iPr₂C ₆H₃NC(CH₃)}₂C₆H ₃SnCl] (1) with potassium graphite to afford a new distannyne [{2,6-iPr₂C₆H₃NC(CH₃)} ₂C₆H₃Sn]₂ (2) with a Sn-Sn bond. The most striking phenomenon of 2 is the presence of two differently coordinated Sn atoms (one is three-coordinated, the other is four-coordinated). The Sn-Sn bond length in 2 is 2.8981(9) A, which is very close to that of a Sn-Sn single bond (2.97-3.06 A). To elucidate the nature of the Sn-Sn bond, DFT calculation is carried out that shows there is no multiple bond character in 2. Furthermore, the reaction of 2 with white P₄ affords the tetraphosphabicylobutane derivative 3. This is the first example of gentle activation of white phosphorus by a compound with low valent Sn atoms. Note that, unlike 2, in 3 both Sn atoms are four-coordinated.

Full text of DOI:10.1021/ja207538g

ARTICLE
pubs.acs.org/JACS
Preparation of RSn(I)ꢀSn(I)R with Two Unsymmetrically Coordinated
Sn(I) Atoms and Subsequent Gentle Activation of P4
Shabana Khan,† Reent Michel,† Johannes M. Dieterich,‡ Ricardo A. Mata,*,‡ Herbert W. Roesky,*,†
Jean-Philippe Demers,§ Adam Lange,§ and Dietmar Stalke*,†
†Institut f€ur Anorganische Chemie, Georg-August-Universit€at, Tammannstrasse 4, D-37077 G€ottingen, Germany
‡Institut f€ur Physikalische Chemie, Georg-August-Universit€at, Tammannstrasse 6, D-37077, G€ottingen, Germany
§Max-Planck-Institut f€ur biophysikalische Chemie, Am Faßberg11, D-37077 G€ottingen, Germany
S Supporting Information
b
ABSTRACT: This article reports the reduction of [{2,6-
iPr2C6H3NC(CH3)}2C6H3SnCl] (1) with potassium graphite
to afford a new distannyne [{2,6-iPr2C6H3NC(CH3)}2C6H3Sn]2
(2) with a SnꢀSn bond. The most striking phenomenon of 2 is
the presence of two differently coordinated Sn atoms (one is
three-coordinated, the other is four-coordinated). The SnꢀSn
bond length in 2 is 2.8981(9) Å, which is very close to that of a SnꢀSn single bond(2.97ꢀ3.06 Å). To elucidate the nature of the SnꢀSn
bond, DFT calculation is carried out that shows there is no multiple bond character in 2. Furthermore, the reaction of 2 with white P4
affords the tetraphosphabicylobutane derivative 3. This is the first example of gentle activation of white phosphorus by a compound with
low valent Sn atoms. Note that, unlike 2, in 3 both Sn atoms are four-coordinated.
Scheme 1. Multiply and Singly Bonded Alkyne Analogues
of Tin
’ INTRODUCTION
One of the vital research areas in modern main-group chemistry
is focused on the synthesis of heavier group 14 homologues of
alkynes, and pursuing their reactivity. The comprehension that
steric protection could be employed to overcome the kinetic
instability smoothed the progress of the chemistry of low-valent
heavier group 14 elements. In recent years a number of alkyne
analogues of Si, Ge, and Sn have been reported. The remarkable
progress in this area is reflected by reviews devoted to this topic.1
The first alkyne analogue of tin, namely, dark blue-green distan-
nyne [ArSnSnAr; Ar = 2,6-Dipp2C6H3 (Dipp = 2,6-iPr2C6H3)]
(A), was reported by Power et al. in 2002.2 Following this the same
group isolated a series of distannynes by altering the Ar ligand
through replacement of the p-hydrogen of the central aryl ring with
various substituents (tBu, Cl, OMe, SiMe3, GeMe3).3 A new type of
intramolecularly coordinated distannyne, [{2,6-(Me2NCH2)2-
C6H3}Sn]2 (B), was prepared by Jambor et al. in 2008.4
The isolation of an amidinato stabilized distannyne [ArSnSnAr;
Ar = 4-tBuC6H4C(NDipp)2]5 was reported by Jones et al.
using the Mg(I) dimer [{Mes(Nacnac)Mg}]2, (MesNacnac =
[(MesNCMe)2CH], Mes =2,4,6-Me3C6H2) as a reducing agent.6
The bonding in the alkyne analogues of heavier group 14 elements
has been the subject of considerable discussion.7 In contrast to the
triple bond of acetylene, which has a bond order of 3, calculation
shows that the bond order in A is ca. 2, whereas in B it is about 1.
Therefore, it can be envisaged that two types of alkyne analogues of
tin are possible: (a) two Sn atoms are connected by a triple bond (I)
and (b) two Sn atoms are connected by a σ-bond and each holds a
lone pair of electrons (II) (Scheme 1). However, it is unquestion-
able that all these alkyne analogues of tin show marked lone pair
character and decreasing π-overlap of the involved atoms.
Our formal entry in this chemistry started in 2008 with the
isolation of a bis(germylene) (PhC(NtBu)2Ge)2,8a which was
followed by the discovery of analogous bis(silylene)
(PhC(NtBu)2Si)2.8b However, attempts to stabilize the bis-
(stannylene) with the support of the same amidinato ligand
was unsuccessful.8c The selection of the correct ligand has
been critical in the synthesis of these compounds, and it is
already known that additional N-donation to stannylenes is
advantageous in the synthesis of Sn(o-C6H4PPh2NSiMe3)2.9
Therefore, we turned our attention toward the pincer-based
ligand, which has a long history of stabilizing transition
metals10 due to the firm tridentate coordination mode. Re-
cently Dostꢀal et al. employed successfully the pincer ligand
to stabilize monomeric compounds with Sb(I) and Bi(I).11
Accordingly, we treated [{2,6-iPr2C6H3NC(CH3)}2C6H3-
SnCl] (1) with KC8 and isolated a new type of bis-stannylene
2 with two unsymmetrically coordinated Sn atoms in the same
framework.
Received: August 10, 2011
Published: September 29, 2011
r
2011 American Chemical Society
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Scheme 2. Preparation of Compound 2
’ RESULT AND DISCUSSION
The reduction of 1 with 1 equiv of KC8 in THF afforded the
bis(stannylene) derivative 2 in 30% yield (Scheme 2). Upon
reduction, immediately a deep blue color developed, which
turned dark green after 14 h of stirring. The removal of the
solvent in vacuum followed by extraction with toluene yielded a
dark green solid. Recrystallization of 2 from n-pentane at 0 °C
afforded extremely air- and moisture-sensitive dark green crystals
of 2 suitable for X-ray crystallography.12 Compound 2 crystallizes
in the monoclinic space group P21/c (Figure 1). The most salient
feature of 2 is the presence of two differently coordinated Sn
atoms in the +1 oxidation state. This is the first example of an
alkyne analogue of main group elements where both metals are
unsymmetrically coordinated. The Sn1 atom is four-coordinated
with distorted tetrahedral geometry and coordinated by two
nitrogen atoms (N3 and N4) of both the pendant arms with
bond lengths for Sn1ꢀN3 and Sn1ꢀN4 of 2.6879(17) and
2.4129(16) Å, respectively. The Sn2 atom is further coordinated
to only one nitrogen atom (N2) at a distance of 2.2228(16) Å
and hence adopts a distorted trigonal pyramidal geometry. The
Sn2ꢀN2 bond length is the shortest among all of the SnꢀN
interactions. The pendant N1 is turned away from the tin atom.
The coordinated bonding between N2 and Sn2 is further
verifiable from the two CꢀN double bond lengths, which are
almost equal (1.287(2) and 1.303(2) Å). The SnꢀN bond
lengths vary from 2.2207 to 2.6879(17) Å and are in good
agreement with those reported in the literature for NfSn
bonds.4,13 The Sn1ꢀSn2 bond length of 2.8981(9) Å in 2 is
considerably shorter than that of B (2.9712(12) Å)4 and other
reported bis-stannylenes3,5 but significantly longer than that of A
(2.6675(4) Å).2 Because of the two unsymmetrically coordinated
Sn atoms the two SnꢀSnꢀC bond angles (C49ꢀSn2ꢀSn1 =
121.26(4)° and C59ꢀSn2ꢀSn1 = 96.63(5)°) differ substantially
from each other. Compound 2 exhibits a gauche-bent geometry
with a torsion angle C49ꢀSn2ꢀSn1ꢀC59 of 83.36(7)°.
Figure 1. Molecular structure of 2. Anisotropic displacement para-
meters are depicted at the 50% probability level. Hydrogen atoms,
disorder of iPr groups, and lattice n-pentane were omitted and 2,6-
iPr2C6H3 groups appear transparent for clarity. Selected bond distances
(Å) and bond angles (deg): Sn1ꢀSn2 2.8981(9), Sn1ꢀN3 2.6879(17),
Sn1ꢀN4 2.4129(16), Sn2ꢀN2 2.2228(16), Sn1ꢀC59 2.1575(18),
Sn2ꢀC49 2.1880(19), N1ꢀC55 1.280(2), N2ꢀC57 1.309(2),
N3ꢀC65 1.287(2), N4ꢀC67 1.303(2); C49ꢀSn2ꢀSn1 121.26(4),
N2ꢀSn2ꢀSn1 99.87(4), N4ꢀSn1ꢀSn2 105.11(4), N3ꢀSn1ꢀSn2
75.42(4), N4ꢀSn1ꢀN3 141.01(5), N4ꢀSn1ꢀC59 72.88(6),
N3ꢀSn1ꢀC59 68.41(6), C59ꢀSn1ꢀSn2 96.63(5), C49ꢀSn2ꢀN2
76.72(6), C59ꢀSn1ꢀSn2ꢀC49 83.36(7).
increased repulsion of the bulky groups, moving the Sn atoms
further apart. Empirical dispersion corrected functionals could be
used to circumvent this problem.16 However, we found that the
optimization convergence was significantly deteriorated with the
use of B3LYP-D. This is linked to the appearance of shallow
potential wells with the added dispersion corrections. Therefore,
we decided to neglect such corrections. The B3LYP/def2-TZVP
electronic density of 2 was also calculated and used for a natural
bond orbital (NBO) analysis.17 We find that a lone pair is located
at each of the Sn atoms (populations of 1.89 and 1.85 electrons).
By observing the natural atomic orbital (NAO) contributions to
each of the pairs, one finds that they are essentially of s-character
(82ꢀ84%, with only 16ꢀ18% p-character; see isosurface plot for
the NBOs in the Supporting Information).
Another question arises about the asymmetric coordination of
the SnꢀSn bond. To achieve further insight, one would have to
compare 2 with a model compound where both Sn atoms are
four-coordinated. However, due to the bulky groups around the
tin atoms, we found it impossible to accommodate a bond
between N1 and the Sn2. Instead, a truncated model structure
To gain some insight into the SnꢀSn bonding, quantum
chemical calculations were performed on 2. The structure was
optimized at the B3LYP/def2-SVP level of theory,14a,b combined
with the relativistic small core (Stuttgart-K€oln ECP) for Sn.14c All
structure optimizations in this work were carried out with the
ORCA program package.15a Single point calculations were
performed with Molpro2010.1.15b The optimized structure
reveals a SnꢀSn bond distance of 3.046 Å, slightly longer than
that of the refined crystal structure but in fairly good agreement
taking into account the level of theory. An overestimation of the
bond length is also expected, since our model is lacking the
description of dispersion interactions. This should lead to an
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Figure 2. Model structures of 2 optimized at the B3LYP/def2-SVP level of theory, with (3ꢀ4) coordination (left) and (4ꢀ4) coordination (right).
was generated by removing the iPr groups. From this model
structure, two isomers were optimized at the B3LYP/def2-SVP
level of theory. In the first structure we kept the coordination
pattern of 2. In the second isomer, the N1ꢀC55ꢀC49ꢀSn2
dihedral angle was rotated to build a coordination between N1
and Sn2. Both structures are shown in Figure 2. The SnꢀSn
bond distance in the 3- and 4-coordinated model is in agreement
with that found in 2 (3.040 Å compared to 3.046 Å), showing that
the modifications introduced have only a marginal impact on the
SnꢀSn bonding. Moreover it is feasible to compare the hypothe-
tical 4ꢀ4 case and observe the force of the coordination on the
Figure 3. 119Sn solid-state NMR cross-polarization spectra of bis-
(stannylene) 2. The spectra were recorded at 8.2 and 11 kHz MAS on
a 9.4 T spectrometer. Isotropic chemical shifts are indicated by arrows.
SnꢀSn bond. We find that the changes are minimal; the bond
length is increased by only 0.003 Å. Therefore, the asymmetrical
coordination does not seem to strengthen or weaken the SnꢀSn
bond. Furthermore, comparing the energies of the two models at
the B3LYP/def2-TZVP level of theory, we find that the 4ꢀ4
coordination is favored by 7.6 kcal/mol. This indicates that the
asymmetrical coordination in 2 is due to steric strain introduced
by the iPr groups and unrelated to any strengthening of the
SnꢀSn bond.
In a report from 2010, entitled “Main-group elements as
transition metals” Power pointed out that main group elements
in lower oxidation states show remarkable resemblance to transi-
tion metals due to the presence of frontier orbitals with small
energy separations.19 As a result, it is expected that, like transition
metals, compounds with low-valent group 14 elements can also
activate P4, and indeed there are recent reports on the activation
of P4 by carbenes20 and silylenes.21 Although the reactions of P4
with tetraphenyl tin or dimethyl tin hydride were known,22 so far
no gentle activation of P4 with a compound containing low valent
Ge or Sn has been demonstrated. In line with this observation
Driess et al. mentioned that the germanium analogue of N-
hetrocyclic silylene [LGe, (L = CH[(CdCH2)CMe][N(2,6-
iPr2C6H3)]2)] is resistant toward P4 even in boiling toluene
owing to the lower reduction potential of Ge versus Si (inert-pair
effect).21a The only example of P4 activation where a compound
with low valent Sn was used is the synthesis of a species with
composition of Sn4P3. Thiscompound was obtained by treatment
of SnCl2 with KBH4 in the presence of white phosphorus under
hydrothermal conditions (EtOH, 160 °C, autoclave, 10 h).23
Although several reactions of distannynes with various organic
substrates have been reported,24,25 surprisingly no reaction with
phosphorus has been mentioned so far. As a result, there is a high
quest for the mild activation of P4 by a compound with low valent
Sn atoms. Herein, we show for the first time activation of the P4
tetrahedron by compound 2 with low valent Sn(I) atoms.
The 1H and 13C NMR data confirm the presence of
two chemically different environments for 2,6-bis[N-(20,60-
diisopropylphenyl)ketimino] phenyl moiety and methyl group
attached to imino group in 2. However, despite numerous
attempts, an 119Sn NMR resonance could not be detected in
solution. This is presumably due to the broadening of resonance
to undetectable level caused by the chemical shift anisotropies
induced by the tin environment which was also mentioned by
Power et al.2 The UVꢀvis spectrum of 2 in toluene shows three
absorption maxima at 424.8, 457.3, and 561.3 nm and are in line
with the reported compounds.2ꢀ5 The EI-MS spectrum exhibits
the most abundant peak with highest relative intensity at m/z 599
that indicates half the fragment of the molecule. Furthermore the
structure of 2 was strongly supported by 119Sn CP-MAS NMR
investigations.
Two highly anisotropic resonances were detected in the 119Sn
solid-state NMR (Figure 3). CP-MAS experiments carried at two
MAS frequencies identified the isotropic chemical shifts at 134
and 115 ppm (referenced to Me4Sn). The cross-polarization
build-up curves confirm that both tin sites are nonprotonated.
Maximal intensity is reached after more than 5 ms, indicating a
large distance separation between tin and the nearest proton. The
structure of 2 is further supported by the detection of one-bond
carbonꢀtin J couplings on the two most downfield 13C reso-
nances, which correspond to the carbons covalently bound to tin
(see Supporting Information, Figure S1). The magnitude of the
J couplings (433 and 323 Hz) are in agreement with values in the
literature for one-bond carbonꢀtin coupling.9,18
Treatment of 2 with P4 in toluene in a 1:1 molar ratio at
ambient temperature provided a dark purple solution (Scheme 3).
The removal of the solvent under vacuum followed by recrystalli-
zation in n-pentane afforded purple crystals of 3 suitable for single
crystal X-ray structural determination. The 1H NMR spectrum of
3 shows four doublets for 48 protons of the iPr groups (δ = 0.90,
0.99, 1.20, and 1.27 ppm respectively). A resonance for 12 methyl
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Scheme 3. Preparation of Compound 3
group 14 elements. Therefore, with the synthesis of 3 (cf.
Scheme 3), the selective activation of one of the six PꢀP bonds
in P4 by a heavier group 14 element has been achieved for the first
time. It is noteworthy to mention that in 3 both tin atoms are
symmetrical and four-coordinated and possess distorted tetra-
hedral geometry. The SnꢀP bond lengths in 3 of 2.7189(9) and
2.6096(9) Å fall in the range of those reported in literature for
SnꢀP single bonds.22,27,28 The average PꢀP bond length of
the peripheral phosphorus atoms (2.2242 Å) is very close to
white P4 (2.21 Å) itself and other tetraphosphabicyclobutane
derivatives,26,29 whereas the bridgehead P2ꢀP4 bond length is
2.1528(11) Å. The SnꢀN bond distances vary between 2.456(3)
Å for Sn2ꢀN4 to 2.519(2) Å for Sn2ꢀN3 and are similar to the
SnꢀN distances observed for 2 or reported for pincer-based
bis(stannylene) B.4 The P1ꢀP2ꢀP3 and P1ꢀP4ꢀP3 angles
[82.90(4)°, 83.02(4)°] are significantly larger than the intraring
PꢀPꢀP angles, which are slightly deviated from expected 60°
[57.89(4)ꢀ61.21(4)°]. The P1 and P3 atoms exhibit trigonal-
pyramidal geometry. The P3ꢀP2ꢀP4ꢀP1 torsion angle
(98.41(5)°) is similar to the folding angles reported for the
1,4-R2P4 compounds (92.9ꢀ100.4°) (R = N(SiMe3)2,29a 2,4,6-
tBu3C6H2,29b {(Cp0)(CO)2Fe} (Cp0 = 1,2,4-tBu3C5H2),26a
P{N(SiMe3)2}2,28b 2,6-Dipp2C6H3].28a
’ CONCLUSION
In summary, we have synthesized a new pincer based bis-
stannylene with two unsymmetrically coordinated Sn(I) atoms.
Computational studies show that this asymmetry is due to steric
crowding and has virtually no impact on the Sn(I)ꢀSn(I)
bonding. The SnꢀSnꢀC bending is not induced by a stereo-
chemically active lone pair as it has predominantly s-character.
Reminiscent of d-block metal complexes and N-heterocyclic
carbene and silylene, this new compound has the ability to
activate P4 under ambient condition. This is the first example
of phosphorus activation by a Sn(I) compound.
Figure 4. Molecular structure of compound 3. Anisotropic displacement
parameters are depicted at the 50% probability level. Hydrogen atoms
were omitted for clarity. Selected bond distances (Å) and bond angles
(deg): Sn1ꢀP3 2.7189(9), Sn2ꢀP1 2.6096(9), P1ꢀP2 2.2274(12),
P2ꢀP3 2.2236(12), P1ꢀP4 2.2210(12), P4ꢀP3 2.2248(12), P2ꢀP4
2.1528(11), Sn2ꢀN3 2.519(2), Sn2ꢀN4 2.456(3), Sn1ꢀN2 2.492(2),
Sn1ꢀN1 2.471(2); C35ꢀSn2ꢀP1 104.48(9), N3ꢀSn2ꢀP1 87.18(6),
N4ꢀSn2ꢀP1 91.46(7), N2ꢀSn1ꢀP3 92.63(7), N1ꢀSn1ꢀP3
89.88(6), P2ꢀP1ꢀP4 57.89(4), P1ꢀP4ꢀP3 83.02(4), P4ꢀP3ꢀP2
57.89(4), P3ꢀP2ꢀP1 82.90(4), P3ꢀP2ꢀP4 61.08(4), P3ꢀP4ꢀP2
61.03(4), P1ꢀP4ꢀP2 61.21(4), P1ꢀP2ꢀP4 60.91(4).
’ EXPERIMENTAL SECTION
All reactions and handling of reagents were performed under an
atmosphere of dry nitrogen or argon using standard Schlenk techniques
or a glovebox where the O2 and H2O levels were usually kept below 1
ppm. Solvents were purified with the M-Braun solvent drying system.
Solution NMR spectra were recorded on Bruker Avance 200, Bruker
Avance 300, and Bruker Avance 500 MHz NMR spectrometers.
Deuterated NMR solvent C6D6 was dried by stirring for 2 days over
Na/K alloy followed by distillation in vacuum and degassed. EI-MS
spectra were obtained with a Finnigan MAT 8230 or a Varian MAT CH5
instrument (70 eV) by EI-MS methods. Elemental analyses were
performed by the Analytisches Labor des Instituts f€ur Anorganische
Chemie der Universit€at G€ottingen.
Synthesis of 1. nBuLi (8 mL, 20 mmol, 2.5 M solution in n-hexane)
was added to a stirred solution of 2,6-bis[N-(20,60-diisopropylphe-
nyl)ketimino]phenyl-1-bromide (5.59 g, 10 mmol) in Et2O (90 mL)
at ꢀ60 °C. The mixture turned to deep red and was stirred for additional
1 h at this temperature. This solution was then added to a precooled
(ꢀ60 °C) solution of SnCl2 (1.90 g, 10 mmol) in Et2O (50 mL), and the
reaction mixture was allowed to warm to room temperature gradually
and stirred for additional 12 h. The solution was filtered through Celite
and concentrated to ca. one-third. Concentration and storing of the
solution at 0 °C in a freezer afforded orange-yellow crystals of 1 (2.00 g,
31.05%). 1H NMR (200 MHz, C6D6, 25 °C) δ 0.90 (m, 12H, CH3), 1.30
(m, 12 H, CH3), 1.94 (s, 6H, CH3-Cd), 2.92ꢀ3.19 (m, 4H, CH-),
6.90ꢀ7.70 (m, 9H, Ph) ppm; 119Sn NMR (C6D6, 111.92 MHz, 25 °C)
protons appears as a sharp singlet (δ = 1.94 ppm). Two septets for
CHMe2 protons resonate at δ = 2.75 and 3.00 ppm. The 119Sn
NMR spectrum exhibits a broad resonance at δ = 703.33 ppm.
The 31P NMR spectrum of 3 displays two resonances (δ = ꢀ97.70
and ꢀ327.32 ppm) confirming the presence of two chemically
different phosphorus. The phosphorus attached to tin appears at
31
δ = ꢀ97.70 ppm as a triplet (1J(31Pꢀ P) = 158 Hz) with tin
satellites. Another phosphorus atom associated to the P4 tetrahe-
31
dron appears as a sharp triplet at δ=ꢀ327.32 ppm ((1J(31Pꢀ P) =
161 Hz). In the EI-MS spectrum the most abundant peak was
observed at m/z 976, which corresponds to the fragment after the
loss of 8 iPr groups.
The constitution of 3 was determined by single crystal X-ray
studies (Figure 4). Compound 3 crystallizes in the monoclinic
space group P21/c.12 The molecular structure reveals the inser-
tion of one P4 tetrahedron into the SnꢀSn bond of 2 to form
a butterfly-like bicyclo[1.1.0]tetraphosphabutane moiety via
selective cleavage of a single PꢀP bond in the P4 tetrahedron.
Similar butterfly-like molecules with a tetraphosphabicyclobu-
tane skeleton have been reported,26 but not with heavier
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Table 1. Crystallographic Data
filtrate was concentrated to about 5 mL and stored at ꢀ32 °C in a
freezer to afford dark colored crystals of 3 (0.18 g, 54.3%). 1H NMR
(500 MHz, C6D6, 25 °C) δ 0.90 (d, 12 H, CH3), 0.99 (d, 12 H, CH3),
1.20 (d, 12 H, CH3), 1.27 (d, 12 H, CH3), 1.94 (s, 12H, CH3-Cd),
2.70ꢀ2.87 (m, 4H, CH-), 2.99ꢀ3.12 (m, 4H, CH-), 7.04ꢀ7.71 (m,
18H, Ph) ppm; 13C{1H} NMR (125.75 MHz, C6D6, 25 °C) δ 17.82
(dC-CH3), 23.87, 24.04, 24.67, 25.11 (CH3), 28.07, 28.05 (-CH),
123.89, 124.01, 125.84, 128.5, 130.06, 138.76, 139.88, 143.69 (Ph),
171.69 (-CdCH3), 182.34 (Cipso) ppm; 31P NMR (121.5 MHz, C6D6,
2 C5H12
3
3
a [Å]
b [Å]
c [Å]
16.411(6)
16.426(6)
25.192(9)
90
14.644(2)
17.463(2)
26.602(2)
90
α [deg]
β [deg]
γ [deg]
V
94.40(2)
104.48(2)
90
31
25 °C) δ ꢀ97.70 (1J(31Pꢀ P) = 158 Hz), ꢀ327.32 ppm ((1J-
90
31
(31Pꢀ P) = 161 Hz); 119Sn NMR (C6D6, 111.92 MHz, 25 °C)
6771(4)
6586.8(13)
4
δ +703.33 ppm. EI-MS: m/z 976 [M+ ꢀ 8iPr] (100%). Anal. Calcd for
C68H86N4P4Sn2 (1320.75): C, 61.84; H, 6.56; N, 4.24. Found: C,
61.19; H, 6.11; N, 4.58.
Z
4
F [Mg/m3]
1.245
1.332
μ [mmꢀ1
]
0.780
0.897
Crystal Data for 2 and 3. Shock cooled crystals were selected and
mounted under nitrogen atmosphere using the X-TEMP2. The data of
2 and 3 were measured on an INCOATEC Mo Microsource with
Quazar mirror optics and a Smart APEX II Ultra detector on a D8
goniometer and are summarized in Table 1.30 The diffractometers were
equipped with a low temperature device and used Mo Kα radiation,
λ = 0.71073 Å. The data sets were integrated with SAINT,31 and an
empirical absorption (SADABS) was applied.32 The structures were
solved by direct methods (SHELXS-97) and refined by full-matrix least-
squares methods against F2 (SHELXL-97).33 All non-hydrogen-atoms
were refined with anisotropic displacement parameters. The hydrogen
atoms were refined isotropically on calculated positions using a riding
model with their Uiso values constrained to equal to 1.5 times the Ueq of
their pivot atoms for terminal sp3 carbon atoms and 1.2 times for all
other carbon atoms. Disordered moieties were refined using bond
length restraints and isotropic displacement parameters restraints.
Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge
Crystallographic Data Center. The crystal data are available from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
F (000)
2656
2728
θ range for data colln [deg]
1.24ꢀ27.86
ꢀ21 e h e 21
ꢀ21 e k e 21
ꢀ33 e l e 33
177456
1.41ꢀ26.04
ꢀ18 e h e 18
ꢀ21 e k e 21
ꢀ32 e l e 32
86017
index range
refl collected
indep refl
16126
12981
max, min transmis.
data/restraints/parameters
goodness of fit on F2
final R-indices [I > 2σ(I)]
0.7456, 0.6971
16126/361/851
1.042
1.0000, 0.8843
12981/512/827
1.072
R1 = 0.0257, wR2
= 0.0561
R1 = 0.0374, wR2
= 0.0871
final R-indices (all data)
largest diff peak and
R1 = 0.0358, wR2
= 0.0609
R1 = 0.0541, wR2
= 0.0981
0.650 and ꢀ0.487
2.311 and ꢀ0.857
hole [e Åꢀ3
]
CCDC number
833290
833291
δ ꢀ20 ppm. EI-MS: m/z 634 [M+] (100%). Anal. Calcd for
C34H43ClN2Sn2 (634.21): C, 64.42; H, 6.84; N, 4.42. Found: C,
63.96; H, 6.12; N, 4.10.
’ ASSOCIATED CONTENT
Synthesis of 2. To the mixture of 1 (1.27 g, 2.00 mmol) and KC8
(0.270 g, 2.00 mmol) at ꢀ60 °C was added THF (50 mL), and the color
of the solution immediately changed from orange to dark green. The
reaction mixture was stirred for 12 h. The solvent was removed under
reduced pressure, and the residue was extracted with toluene (30 mL).
Recrystallization in n-pentane (25 mL) at 0 °C in a freezer afforded dark
S
Supporting Information. CIF files of 2 and 3, solid state
b
NMR and computational details of 2. This material is available
free of charge via the Internet at http://pubs.acs.org.
green crystals of 2 C5H12 (0.30 g, 25%). 1H NMR (500 MHz, C6D6,
’ AUTHOR INFORMATION
3
25 °C) δ 0.89 ꢀ 1.16 (m, 24 H, CH3), 1.30 (d, 24 H, CH3), 1.85 (s, 3H,
CH3-Cd),1.97 (s, 9H, CH3-Cd), 2.77 (sept, 4H, CH-), 2.95 (sept, 2H,
CH-), 3.29 (sept, 2H, CH-), 7.02ꢀ7.51 (m, 18H, Ph) ppm; 13C{1H}
NMR (125.75 MHz, C6D6, 25 °C) δ 14.23 (dC-CH3), 18.23 (dC-CH3),
20.11, 22.94, 23.59, 24.07, 24.45, 25.33, 25.39, 26.04, (CH3), 28.72,
28.88, 34.38 (-CH), 123.31, 123.61, 123.80, 124.35, 124.52, 125.96,
138.36, 140.56, 142.66, 143.38, 143.69, 146.86 (Ph), 169.78 (-CdCH3),
186.32 (Cipso) ppm; 119Sn NMR (C6D6, 111.92 MHz, 25 °C) we could
not observe any signal in solution. EI-MS: m/z 599 [M+ ꢀ C34H43N2Sn]
Corresponding Author
hroesky@gwdg.de; dstalke@chemie.uni-goettingen.de; rmata@
gwdg.de
’ ACKNOWLEDGMENT
H.W.R. thanks the Deutsche Forschungsgemeinschaft (DFG
RO 224/55-3). S.K. is indebted to Deutscher Akademischer
Austausch Dienst for a research fellowship. J.-P.D. thanks
NSERC of Canada for a scholarship. D.S. is grateful for funding
from the DFG Priority Programme 1178, the DNRF funded
Center for Materials Crystallography (CMC) for support, and
the Land Niedersachsen for providing a fellowship in the
Catalysis for Sustainable Synthesis (CaSuS) Ph.D. program.
A.L. thanks the support of the Deutsche Forschungsgemeinschaft
for Emmy Noether Fellowship.
(100%). For the elemental analysis 2 C5H12 was dried under vacuum
3
overnight to remove 1 molecule of n-pentane. Anal. Calcd for C68H86N4Sn2
(1198.49): C, 68.24; H, 7.24; N, 4.68. Found: C, 68.11; H, 7.01;
N, 4.43.
Synthesis of 3. To a mixture of 2 (0.300 g, 0.25 mmol) and P4
(0.031 g, 0.25 mmol) was added toluene (40 mL) at room tempera-
ture. Immediately after addition, the reaction mixture turned to deep
purple in color. The resulting mixture was stirred for additional 2 h
at room temperature and evaporated under reduced pressure. The
residue was extracted with n-pentane (30 mL), and the deep purple
This paper is dedicated to Professor Robert West.
17893
dx.doi.org/10.1021/ja207538g |J. Am. Chem. Soc. 2011, 133, 17889–17894

Journal of the American Chemical Society
ARTICLE
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