{4-t-Bu-2,6-[P(O)(O-i-Pr)2]2C6H 2Sn}2: An intramolecularly coordinated organotin(I) compound with a Sn-Sn single bond, its disproportionation toward a diorganostannylene and elemental tin, and its oxidation with PhI(OAc) 2

Article abstract of DOI:10.1021/ic3005954

Syntheses of the intramolecularly coordinated organotin(I) compound {4-t-Bu-2,6-[P(O)(O-i-Pr)₂]₂C₆H ₂Sn}₂ (2), which crystallized in two different pseudopolymorphs 2 and 2·C₇H₈, of the diorganostannylene {4-t-Bu-2,6-[P(O)(O-i-Pr)₂]₂C ₆H₂}₂Sn (3) and of the organotin(II) acetate 4-t-Bu-2,6-[P(O)(O-i-Pr)₂]₂C₆H ₂SnOAc (4) are reported. The compounds were characterized by multinuclear NMR, IR (3 and 4), UV-vis spectroscopy (2), electrospray ionization mass spectrometry (3 and 4), and single-crystal X-ray diffraction analyses. Density functional theory calculations on compound 2 revealed the stabilizing effect of the intramolecular P=O → Sn coordination.

Full text of DOI:10.1021/ic3005954

Article
pubs.acs.org/IC
{4-t-Bu-2,6-[P(O)(O-i-Pr)2]2C6H2Sn}2: An Intramolecularly Coordinated
Organotin(I) Compound with a Sn−Sn Single Bond, Its
Disproportionation toward a Diorganostannylene and Elemental Tin,
and Its Oxidation with PhI(OAc)2
Michael Wagner, Christina Dietz, Stefan Krabbe, Stephan G. Koller, Carsten Strohmann,
and Klaus Jurkschat*
Lehrstuhl fur Anorganische Chemie II, Technische Universitat Dortmund, 44221 Dortmund, Germany
̈
̈
S
* Supporting Information
ABSTRACT: Syntheses of the intramolecularly coordinated
organotin(I) compound {4-t-Bu-2,6-[P(O)(O-i-
Pr)2]2C6H2Sn}2 (2), which crystallized in two different
pseudopolymorphs 2 and 2·C7H8, of the diorganostannylene
{4-t-Bu-2,6-[P(O)(O-i-Pr)2]2C6H2}2Sn (3) and of the
organotin(II) acetate 4-t-Bu-2,6-[P(O)(O-i-Pr)2]2C6H2SnOAc
(4) are reported. The compounds were characterized by
multinuclear NMR, IR (3 and 4), UV−vis spectroscopy (2),
electrospray ionization mass spectrometry (3 and 4), and
single-crystal X-ray diffraction analyses. Density functional
theory calculations on compound 2 revealed the stabilizing
effect of the intramolecular PO → Sn coordination.
For many years, we have been interested in the synthesis and
characterization of low-valent organoelement compounds
containing the O,C,O-coordinating pincer-type ligand {4-t-
Bu-2,6-[P(O)(O-i-Pr)2]2C6H2}−, hereafter referred to as R.17
We isolated and characterized a number of transition-metal
carbonyl complexes of the type R[M]SnSn[M]R (R = 4-t-Bu-
2,6-[P(O)(O-i-Pr)2]2C6H2; [M] = Cr(CO)5, Mo(CO)5, W-
(CO)5, Fe(CO)4) by reacting the organochloridostannylene
complexes R[M]SnCl with potassium tri-sec-butylboranate,
K[B-sec-Bu3H], to give the corresponding hydride derivatives
R[M]SnH, which, in turn, smoothly convert into R[M]SnSn-
[M]R and H2.17f,g In a continuation of these studies, we here
report the analogous reaction of RSnCl (1) with K[B-sec-
Bu3H], potassium graphite, C8K, or sodium naphthalenide,
respectively, to finally give the corresponding organotin(I)
compound RSnSnR (2). Furthermore, we investigate the
thermal stability of the latter compound and exemplarily
demonstrate its reactivity toward oxidation with PhI(OAc)2.
INTRODUCTION
■
The heavy formal analogues of alkynes (“distannynes”) have
been known since the pioneering work of Power et al.1 Such
compounds, like the corresponding germanium2 and silicon3
congeners, are of great interest with regard to their bonding
theory. Depending on the organic substituents, single-, double-,
and triple-bonded structures have been proposed.4 Organotin-
(I) compounds have been used for the activation of small
molecules, e.g., dihydrogen, cyclopentadiene, cyclooctatetraene,
azobenzene, and P4.5 Also, Lewis base adducts with isonitriles
are known.6
Elemental sulfur, selenium, and tellurium respectively were
used for oxidation of the intramolecularly coordinated
organotin(I) compound B,7a−c (Chart 1) whereas Power et
al. used pyridine N-oxide to produce an oxygen-bridged
distannylene.7d
Following the works by Power et al., intramolecularly N,C,N-
coordinating pincer-type ligands, and amidine as well as β-
diketiminate ligands, have been employed for the synthesis of
tin(I) compounds of the types B−E, which are thermodynami-
cally stabilized (Chart 1).5f,8a,b,c
Intramolecularly coordinated diorganostannylenes have also
been known since 1981 by work from Zuckerman et al.9
Crystallographically characterized examples F−L10−16 are
shown in Chart 2. These compounds demonstrate that
intramolecular Lewis base-Lewis acid interactions are an
alternative to exclusively bulky substituents for the stabilization
of stannylenes.
RESULTS AND DISCUSSION
■
The reaction of 1 in tetrahydrofuran (THF) with potassium tri-
sec-butylboranate (K[B-sec-Bu3H]) gave, after 30 min, a crude
reaction mixture, the 31P NMR spectrum of which showed
three major intense resonances at δ 16.7 (integral 16, RH), 32.8
[J(31P−117/119Sn) = 81 Hz, integral 32, signal a], and 34.1
[J(31P−117/119Sn) = 90 Hz, integral 36, signal b], respectively,
Received: March 21, 2012
Published: May 24, 2012
© 2012 American Chemical Society
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reaction mixture. The assignment of the NMR signals to the
latter compound gets support from a recent finding by Roesky/
Stalke and co-workers, who reported the intramolecularly
coordinated organotin(II) hydride R′SnH (R′ = 2,6-[Ar′NC-
(Me)]2C6H3; Ar′ = 2,6-i-Pr2C6H3) with a 1J(119Sn−1H) of
112.9 Hz.18
Chart 1. Common Distannynes and Related Tin(I)
Complexes
The reaction of 1 with excess KC8 in toluene or deuterated
benzene provided 2 after a reaction time of approximately 4 h
or less than 90 min with sonification (Scheme 1). A prolonged
Scheme 1. Synthesis of Compound 2
reaction time caused the reaction mixture to turn black because
of decomposition. From the reaction mixture mentioned above,
2 was obtained as a crystalline material that is well soluble in
common organic solvents such as toluene and benzene but less
in hexanes and that is extremely sensitive toward moisture and
oxygen.
Notably, when stoichiometric amounts of KC8 were used,
only part of the organochloridostannylene 1 was converted to
give compound 2, even after prolonged reaction time.
Single crystals of compound 2 suitable for X-ray diffraction
analysis were obtained as two different pseudopolymorphs.
Crystallization from toluene/hexane at −20 °C gave single
Chart 2. Crystallographically Characterized Intramolecularly
Coordinated Diorganostannylenes
crystals of 2 (space group P1), whereas crystallization from
̅
toluene/hexane at −80 °C provided single crystals of the
toluene solvate 2·C7H8 (space group C2/c, isolated from
reduction with NaC8H10 after workup). The molecular
structures are shown in Figure 1. Selected interatomic distances
and angles are given in Table 1.
In the crystal of 2, the Sn(1) and Sn(2) atoms are each four-
coordinate and exhibit distorted pseudo-trigonal-bipyramidal
configuration, with the O(1)/O(2) and O(3)/O(4) atoms
occupying the axial positions at Sn(1) and Sn(2), respectively.
The equatorial positions are occupied by C(1)/Sn(2)/lone pair
(at Sn1) and C(31)/Sn(1)/lone pair (at Sn2). The distortion
from the ideal geometry is manifested by the O(1)−Sn(1)−
O(2) and O(3)−Sn(1)−O(4) angles of 151.27(14) and
150.01(13)°, respectively, being the result of ligand constraint,
as well as by the C(1)−Sn(1)−Sn(2) [97.87(16)°] and
C(31)−Sn(2)−Sn(1) [98.14(16)°] angles, which indicate the
lone electron pair at the Sn atoms to be stereochemically active.
The two latter angles as well as the Sn(1)−Sn(2) distance of
3.0486(6) Å clearly indicate the Sn−Sn interaction to be a
single bond. This bond length is close to the Sn−Sn distance
reported for E [3.0685(9) Å]8c but longer than those in the
related compounds B [2.9712(12) Å]8a and D [2.8981(9) Å]5f
(Chart 1), which are also characterized by intramolecular donor
stabilization. The shortest Sn−Sn distance reported so far for a
ArSnSnAr-type compound is 2.6461(3) Å for Ar = 4-t-Bu-2,6-
Dipp2C6H3 (Dipp = 2,6-i-Pr2C6H3).8e The intramolecular Sn−
O distances vary between 2.459(4) [Sn(1)−O(1)] and
2.527(5) Å [Sn(1)−O(2)] and are somewhat longer than the
corresponding distances [2.430(2) and 2.427(2) Å] in the
organochloridostannylene 1.17d The C(1)−Sn(1)−Sn(2)−
and five minor intense resonances between δ 36.0 and 36.4
(total integral 16, not assigned). After 5 h, signal (b)
completely disappeared and the intensity of signal (a)
increased. The 119Sn NMR spectrum of the same sample
revealed a broad resonance at δ 385 (ν1/2 248 Hz, signal c).
With caution but supported by the results described below, the
31P NMR signal (a) and the 119Sn NMR signal (c) are assigned
to 2. However, all attempts to isolate compound 2 from the
reaction mixture failed.
In a second analogous experiment, a solution in THF was
obtained, the 31P NMR spectrum of which revealed a ratio
between signals (a) and (b) of 1:3. The 119Sn NMR spectrum
of the same sample revealed a triplet resonance at δ 50
1
[J(119Sn−31P) = 93 Hz, signal d]. In the H-coupled 119Sn
NMR spectrum, this resonance changed into a doublet of
1
triplet resonance [J(119Sn−31P) = 93 Hz and J(119Sn−1H) =
1
116 Hz]. The H NMR spectrum revealed a singlet resonance
at δ 12.78 [J(1H−117/119Sn) = 117 Hz, signal e]. The signals
(b), (d), and (e) are assigned with caution to the organotin(II)
hydride RSnH, which, however, we failed to isolate from the
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Figure 1. Molecular structure of compound 2 in the crystal of 2 (left) and in the crystal of 2·C7H8 (right) (ORTEP presentation at 30% probability
of the depicted atoms). H atoms are omitted for clarity. The toluene molecule was removed by PLATON/SQUEEZE.19 Symmetry code: A) 0.5 − x,
0.5 − y, 1 − z.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for 2, 2·C7H8, Optimized 2 (C1 and Ci Symmetry), and Optimized
Hypothetical 2′ with O(3) Turned Away
2 (X = 2; Y = 31) 2·C7H8 (X = Y = 1A) calculated 2 (C1) (X = 2; Y = 31) calculated 2 (Ci) (X = Y = 1A) 2′ (X = 2; Y = 31)
Sn(1)−Sn(X)
Sn(1)−C(1)
Sn(2)−C(31)
Sn(1)−O(1)
Sn(1)−O(2)
Sn(2)−O(3)
Sn(2)−O(4)
3.0486(6)
2.238(6)
2.254(6)
2.459(4)
2.527(5)
2.510(4)
2.504(4)
2.9588(5)
2.232(4)
3.083
2.292
2.291
2.537
2.565
2.573
2.544
3.083
2.287
3.055
2.307
2.305
2.573
2.557
2.510(3)
2.470(3)
2.533
2.570
2.357
C(1)−Sn(1)−O(1)
C(1)−Sn(1)−O(2)
O(2)−Sn(1)−O(1)
C(1)−Sn(1)−Sn(X)
O(1)−Sn(1)−Sn(X)
O(2)−Sn(1)−Sn(X)
C(31)−Sn(2)−O(4)
C(31)−Sn(2)−O(3)
O(4)−Sn(2)−O(3)
C(31)−Sn(2)−Sn(1)
O(3)−Sn(2)−Sn(1)
O(4)−Sn(2)−Sn(1)
P(1)−O(1)−Sn(1)
P(2)−O(2)−Sn(1)
P(3)−O(3)−Sn(2)
P(4)−O(4)−Sn(2)
76.41(19)
74.87(19)
151.27(14)
97.87(16)
82.47(11)
100.93(11)
75.09(17)
75.01(17)
150.01(13)
98.14(16)
94.59(11)
87.42(11)
115.7(2)
75.57(11)
75.70(11)
151.24(9)
94.03(9)
89.89(6)
90.71(6)
75.6
75.6
75.2
150.8
92.6
90.5
90.8
75.0
74.8
149.1
93.8
90.2
85.9
78.7
75.2
150.9
93.3
88.8
92.8
75.4
75.2
150.6
93.4
99.2
90.5
90.5
94.3
114.48(14)
116.52(14)
114.4
114.1
113.7
115.5
114.5
114.9
114.3
113.9
115.1(2)
115.2(2)
116.8(2)
117.0
171.3
C(1)−Sn(1)−Sn(2)−C(Y)
174.4(2)
180
177.3
180
C(31) dihedral angle of 174.4(2)° corresponds to other trans-
bent tin(I) compounds like in ArSnSnAr (Ar = 4-t-Bu-2,6-
Dipp2C6H3) with 180°, whereas gauche-bent structures are
observed for B [82.7(4)°],8a C,8b and D [83.36(7)°].5f Both
aromatic planes are not parallel but twisted by 18°.
The major differences in the structure of 2·C7H8 compared
to that of its pseudopolymorph 2 are (i) the shorter Sn−Sn
distance of 2.9588(5) Å, (ii) the smaller C(1)−Sn(1)−Sn(1A)
angle of 94.0(1)°, and (iii) the bigger C(1)−Sn(1)−Sn(1A)−
C(1A) dihedral angle of 180°. The latter is a consequence of
the molecule having a center of inversion. The range of the
intramolecular Sn−O distances of 2.470(3) and 2.510(3) Å is
narrower.
The fact that compound 2 exhibits pseudopolymorphism in
the solid state is interesting. Pseudopolymorphs were also
found for the related transition-metal-substituted ditin com-
pounds [Cr(CO5)]RSn−SnR[Cr(CO)5], with Sn−Sn distances
varying between 2.8923(4) and 3.1443(3) Å.17f This fact is also
reflected by Mossbauer spectroscopy and points to different
̈
bond situations maybe induced by packing forces.
To gain insight into the bonding situation, density functional
theory (DFT) calculations20 [the B3LYP/def2-SVP level of
theory combined with the Stuttgart−Koln effective core
̈
potential (ECP) for tin]21 were performed. The bond lengths
and angles of the optimized structure (based on the crystal data
for 2 and 2·C7H8) are given in Table 1. Taking into account the
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level of theory and gas-phase calculations, the data are in fairly
good agreement with the values obtained from the crystal
structure. The Sn1−Sn2 distance of 3.083 Å is also in
agreement with the calculations reported for compound D
(Chart 1), giving a Sn−Sn distance of 3.046 Å.5f Natural bond
orbital (NBO) calculations were performed. The lone pairs
(NAO) were located in orbitals with 86% s character. The Sn−
Sn and Sn−Cipso bonds are composed of orbitals with
predominant p character. So, the Sn−Sn bond can be described
as a single bond. Interestingly, the DFT calculations gave the
same Sn−Sn distance for both C1 and Ci symmetry, with C1
being energetically favored by 1 kJ/mol only. The other bond
distances and angles are also almost identical. This supports the
interpretation of the different Sn−Sn distances found for 2 and
2·C7H8 to originate from crystal-packing effects.8b,e,f,22
pincer-type ligands. All of our attempts so far at obtaining such
compounds by a nucleophilic substitution reaction with a
variety of metal halides including HgCl2 and the corresponding
organolithium species had failed.
The reaction was monitored by 31P NMR showing a first-
order decay with deviations for higher conversions (see Figure
S1 in the Supporting Information). From the solution,
compound 3 was obtained as a yellow single-crystalline
material of its toluene solvate, 3·C7H8, which is well soluble
in THF, toluene, and benzene and became colorless upon
removal of the solvate toluene in vacuo. The molecular
structure of compound 3·C7H8 is shown in Figure 2, and
selected bond distances and angles are given in the figure
caption.
To elucidate the importance of PO···Sn coordination, a
rotation about one C−P bond by 180° was performed. The
validity of this approach is supported by the fact that the
molecular structure in the solid state of the protonated ligand 3-
t-Bu-1,5-[P(O)(O-i-Pr)2]2C6H3 (RH) shows a rotamer in
which both PO O atoms are turned away from H-1.17d
For the geometry-optimized structure of the hypothetical
isomer with one 3-fold-coordinated Sn atom, the energy is 45
kJ/mol higher than the energy of the optimized structure of
compound 2. This indicates an attractive Sn−O interaction and
illustrates the importance of the latter for stabilization of
compound 2.
The identity of compound 2 is retained in solution. Thus, the
119Sn NMR spectrum shows a triplet resonance at δ 359
1
[J(119Sn−31P) = 81 Hz] with a J(119Sn−117Sn) coupling of
1455 Hz. To the best of our knowledge, this is the first time
that a 119Sn−117Sn coupling was observed for a ArSnSnAr
compound. The 31P NMR shows a singlet resonance at δ 33.1
that is flanked by J(31P−117/119Sn) satellites of 82 Hz and that
indicates the four P atoms to be equivalent. The 13C NMR
spectrum shows the resonance for the C(1) atom at δ 195,
which is high-frequency-shifted compared to the corresponding
signal in compound 1 (δ 187).17d
The UV−vis spectrum of compound 2 in toluene shows
absorption maxima at 505 and 372 nm. The spectrum is similar
to that of other tin(I) compounds.8a,b
As mentioned above, compound 2 is very sensitive toward
water and oxygen. A solution of 2 that had been exposed to
moist air immediately decolorized, and its 31P NMR spectrum
showed a single resonance at δ 16.4 that is assigned to the
protonated ligand RH.
Figure 2. Molecular structure of compound 3·C7H8 (ORTEP
presentation at 30% probability of the depicted atoms and atom
numbering scheme). H atoms are omitted for clarity. The toluene
molecule was removed by PLATON/SQUEEZE.19 Symmetry code: A)
1 − x, y, 0.5 − z. Selected interatomic distances (Å): Sn(1)−C(1)
2.295(2), Sn(1)−O(1) 2.4970(14), Sn(1)−O(2) 3.1302(14), P(1)−
O(1) 1.476(2), P(2)−O(2) 1.462(2). Selected bond angles (deg):
C(1)−Sn(1)−C(1A) 99.10(10), C(1)−Sn(1)−O(1) 74.57(6), C(1)−
Sn(1)−O(1A) 76.99(6), O(1)−Sn(1)−O(1A) 135.51(7), O(1)−
Sn(1)−O(2) 133.11(4).
The Sn atom is four-coordinate and exhibits a distorted
pseudo-square-pyramidal configuration, with the C(1), C(1A),
O(1), and O(1A) atoms occupying the equatorial positions and
the lone electron pair occupying the apical position. The
C(1)−Sn(1)−C(1A) angle [99.10(10)°] is similar to the
corresponding angle in (o-Me2NCH2C6H4)2Sn, F [100.5(1)
°].10 In the latter compound, however, the configuration of the
Sn atom is distorted pseudo-trigonal-bipyramidal because the
N(1)−Sn(1)−N(2) angle is 164.9(1)° whereas the O(1)−
Sn(1)−O(1A) angle [135.51(7)°] in 3·C7H8 is considerably
smaller. The intramolecular O(1)−Sn(1) distance of
2.4970(14) Å is similar to the Sn−O distances found for
2·C7H8 and 2 but longer than the corresponding distances in
the organochloridostannylene 1. Notably, the O(2)−Sn(1)
distance of 3.1302(14) Å is shorter than the sum of the van der
Waals radii of tin and oxygen (3.69 Å).23 The nonequivalence
of the two phosphonyl moieties is also reflected in the IR
spectrum, showing two ν(PO) absorptions at 1176 and 1254
cm−1 that correspond to the coordinating and noncoordinating
phosphonyl moieties, respectively.
Compound 2 is not stable at room temperature and, in a
C6D6 solution in a sealed tube, disproportionates within a few
weeks into elemental tin and the corresponding diorgano-
stannylene SnR2 (3; Scheme 2). Notably, this is the first metal
derivative containing two {4-t-Bu-2,6-[P(O)(O-i-Pr)2]2C6H2}−
Scheme 2. Disproportionation of Compound 2 To Give
Elemental Tin and the Diorganostannylene 3
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To the best of our knowledge, it is the first time that the
products of decomposition of a distannyne have been
identified. Unidentified products and elemental tin were
described by Jones et al.8c A disproportionation reaction similar
to that described above was also observed for SnBr.24
The 119Sn and 31P NMR spectra of compound 3 show a
quintet resonance at δ 3 [J(119Sn−31P) = 101 Hz] and a singlet
resonance at δ 28.3 [J(31P−117/119Sn) = 100 Hz], respectively,
indicating the four P atoms to be equivalent on the respective
NMR time scales. The 119Sn resonance is considerably low-
frequency-shifted compared to those of F (δ 169),10 2,6-
(Me2NCH2)2C6H3SnC6H4Me-4 (δ 209.6), and (8-
Me2NC10H6)2Sn, I (δ 188.3).25 A chemical shift difference of
the same order of magnitude was observed between compound
1 (δ −99)17d and 2,6-(Me2NCH2)2C6H3SnCl (δ 155.6).26 The
1H NMR of compound 3 shows only one signal for the OCH
protons and only two doublets for the CH(CH3)2 methyl
protons, indicating fast exchange as well. The electrospray
ionization mass spectrometry (ESI-MS, positive mode)
spectrum shows a mass cluster centered at m/z 1043.5 that is
assigned to [M + H]+.
Figure 3. Molecular structure of compound 4 (ORTEP presentation
at 30% probability of the depicted atoms and atom numbering
scheme). H atoms are omitted for clarity. Selected interatomic
distances (Å): Sn(1)−C(1) 2.234(5), Sn(1)−O(1) 2.455(3), Sn(1)−
O(2) 2.421(3), Sn(1)−O(3) 2.112(3), Sn(1)−O(4) 3.121(3), P(1)−
O(1) 1.507(3), P(2)−O(2) 1.488(3). Selected bond angles (deg):
C(1)−Sn(1)−O(3) 84.02(15), C(1)−Sn(1)−O(1) 75.82(15), C(1)−
Sn(1)−O(2) 76.83(15), O(1)−Sn(1)−O(2) 152.20(11).
The reaction of in situ generated organotin(I) compound 2
with PhI(OAc)2 gave the organotin(II) acetate RSnOAc (4) as
a colorless crystalline material that is well soluble in THF and
toluene (Scheme 3). Notably, along this reaction, formation of
Scheme 3. Oxidation of in Situ Generated 2 with the
Hypervalent Reagent PhI(OAc)2 To Give the
reported for other tin(II) acetates. Other structurally
characterized members are (acac)Sn(OAc),27c Ca[Sn-
(OAc)3]2,27d Sn(OAc)2,27e and Sn(OAc)2·[SC(NH2)2].27f
The Sn(1)···O(4) distance of 3.121(3) Å is shorter than the
sum of the van der Waals radii of tin and oxygen (see above)
but too long to be regarded as bonding. Consequently, the
acetate moiety shows a monodentate coordination mode. The
Intramolecularly Coordinated Organotin(II) Acetate 4
νCOOasym
̃
is observed at 1641 cm−1.
The 119Sn and 31P NMR spectra of compound 4 showed a
triplet resonance at δ −229 [J(119Sn−31P) = 106 Hz] and a
singlet resonance at δ 36.3 [J(31P−119/117Sn) = 100 Hz],
respectively. The 1H NMR spectrum showed one broad
resonance for the OCH protons and two doublets for the
CH(CH3)2 methyl protons. Accordingly, the 13C NMR
revealed one signal for the CH C atom and two signals for
the CH(CH3)2 C atom, respectively. This indicates the Sn atom
to be configurationally not stable, very likely as result of Sn−O
bond dissociation being fast on the corresponding NMR time
scales. However, this was not investigated further. ESI-MS
showed a mass cluster centered at m/z 1219.4 that is assigned
to [RSnOAcSnR]+.
the chloridostannylene 1 as a major byproduct by in situ
nucleophilic substitution of compound 4 with sodium chloride
was observed. Formation of compound 4 was also observed by
reacting the chloridostannylene 1 with silver acetate or
thallium(I) acetate.17f
The molecular structure of compound 4 is shown in Figure 3,
and selected bond distances and angles are given in the figure
caption.
Like in the organochloridostannylene 1,17d the Sn atom in
compound 4 is four-coordinate and exhibits a distorted pseudo-
trigonal-bipyramidal configuration, with the O(1) and O(2)
atoms occupying the axial positions. The equatorial positions
are occupied by the C(1) and O(3) atoms and the lone
electron pair. The distortion from the ideal geometry is
manifested by deviation of the O(1)−Sn(1)−O(2)
[152.20(11)°] and C(1)−Sn(1)−O(3) [84.02(15)°] angles
from 180° and 120°, respectively. Notably, the latter angle is
the smallest among the C−Sn−X angles measured within the
series of heteroleptic organostannylenes of the type RSnX (X =
Cl, Br, I, SPh).17d
CONCLUSION
■
The intramolecularly coordinated pincer ligand-based
organotin(I) compound (2) showing a Sn−Sn single bond
has been prepared by reduction of the corresponding
heteroleptic organostannylene 1 with potassium graphite
(C8K). The many attempts in vain to obtain compound 2 by
other reducing reagents such as anthracene·Mg·3THF, sodium
biphenylide, K-Selectride (K[B-sec-Bu3H]), or [{(MesNacNac)-
Mg}2] indicates C8K to be superior for such reactions. The
major reason for this is very likely the simple workup procedure
that includes one filtration only, avoiding other separation
techniques and thermal stress. On the other hand, however,
consecutive reactions for which isolation of 2 is not required
The Sn(1)−O(1) and Sn(1)−O(2) distances are close to the
corresponding distances in compound 117d (see above). The
Sn(1)−O(3) distance of 2.112(3) Å is in the range of 2.079(3)
Å ({[2,6-(Me2NCH2)2C6H3](O2CCH3)Sn}[2-(Me2-NCH2)-
C6H4]PdCl)27a and 2.188(4) Å ([{Cr(CO)5}2Sn(OAc)2]2−)27b
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Inorganic Chemistry
Article
removed in vacuo, yielding compound 2. Yield: 1.10 g, 75%. 1H NMR
(C6D6, 400.13 MHz): δ 0.96 (d, 3J(1H−1H) = 6.0 Hz, 12H,
are most conveniently performed using sodium napthalenide.
DFT calculations revealed the importance of the intramolecular
PO → Sn coordination for stabilization of compound 2.
Such coordination has become an alternative for steric
protection by bulky substituents to stabilize tin(I) species.
Compound 2 easily undergoes disproportionation to give the
corresponding diorganostannylene 3 and elemental tin.
Compound 3 could not be obtained by alternative reactions,
and this illustrates the synthetic potential of the organotin(I)
species 2. The straightforward oxidation of compound 2 with
PhI(OAc)2 to give the organotin(II) acetate 4 is a motivation
to look for other such oxidation reactions. The results on these
investigations will be presented in a forthcoming paper.
3
CH(CH3)2), 1.21 (d, J(1H−1H) = 6.0 Hz, 12H, CH(CH3)2), 1.25−
1.27 (not resolved, 30H, C(CH3)3 + CH(CH3)2), 1.56 (d, 3J(1H−1H)
= 6.0 Hz, 12H, CH(CH3)2), 4.47−4.55 (m, 4H, CH(CH3)2), 5.45−
5.53 (m, 4H, CH(CH3)2), 7.98 (d, 3J(31P−1H) = 13.3 Hz, 4H, CHaryl).
13C{1H} NMR (C6D6, 100.61 MHz): δ 24.0−24.1 (m, CH(CH3)2),
24.4−24.5 (m, CH(CH3)2), 24.6−24.7 (m, CH(CH3)2), 25.2−25.3
(m, CH(CH3)2), 31.7 (s, C(CH3)3), 34.7 (s, C(CH3)3), 70.8−70.9 (m,
CH(CH3)2), 71.9−72.0 (m, CH(CH3)2), 131.7 (dd, C3/5aryl
,
,
,
4
2J(13C−31P) = 17.0 Hz, J(13C−31P) = 4.4 Hz), 133.4 (dd, C2/6aryl
1J(13C−31P) = 190 Hz, 3J(13C−31P) = 24.3 Hz), 147.4 (t, C4aryl
3J(13C−31P) = 13.1 Hz), 195.0 (t, C1aryl
,
2J(13C−31P) = 36.0 Hz).
31P{1H} NMR (C6D6, 121.49 MHz): δ 33.06 (J(31P−119/117Sn) = 82
Hz, 1J(31P−13C) = 192 Hz). 119Sn{1H} NMR (C6D6, 111.92 MHz): δ
1
359 (J(119Sn−31P) = 81 Hz, J(119Sn−117Sn) = 1455 Hz). UV−vis
EXPERIMENTAL SECTION
■
[toluene, λmax (ε)]: 505 (10660), 372 (9480). Because of extreme air
sensitivity, microanalysis was not performed. Single crystals of 2
suitable for X-ray diffraction analysis were grown from a toluene/
hexanes solution at −20 °C.
General Procedures. All reactions were carried out under an
atmosphere of dry argon in flame-dried glassware using Schlenk
techniques. The solvents used for reactions and the preparation of
NMR samples were purified by distillation from appropriate drying
agents under argon.
Method 2. To a solution of {4-t-Bu-2,6-[P(O)(O-i-Pr)2]2C6H2}-
SnCl (534 mg, 0.87 mmol) in THF (10 mL) was added a solution of
sodium naphthalenide (118 mg, 0.92 mmol, 1.06 equiv) in THF (10
mL) at −90 °C. The red solution was warmed to room temperature
and stirred for 5 min to ensure complete conversion. From this
reaction mixture, a 31P NMR spectrum was recorded. 31P{1H} NMR
(THF, 81.01 MHz, no deuterated solvent, referenced to RH): δ 32.6
(s, J(31P−119/117Sn) = 81 Hz; RSnSnR). After THF had been carefully
removed in vacuo, the dark residue was extracted with toluene (10
mL) and the extract was filtered. The volume of the red filtrate was
reduced to approximately 5 mL, and a few drops of hexanes were
added. The solution was stored at −80 °C to give colorless crystals of
naphthalene and dark-brown crystals of 2·C7H8. The latter were
manually separated from the naphthalene crystals and mounted to the
diffractometer.
The organostannylene 4-t-Bu-2,6-[P(O)(Oi-Pr)2]2C6H2SnCl was
synthesized as described and recrystallized from hexanes prior to
use.17d KC8 and solutions of sodium naphthalenide in THF were
freshly prepared. Iodobenzene diacetate was prepared according to a
literature procedure.28 NMR spectra were recorded on a Bruker AV
DPX-300/AV DRX 400/AV DRX 500 or a Varian Unity Inova/
Mercury instrument at room temperature unless otherwise stated.
Solutions of compound 2 were measured in sealed tubes. NMR
chemical shifts δ are given in ppm and were referenced to Me4Si using
a residual solvent signal (1H, 7.16 ppm; 13C, 128.39 ppm), H3PO4
(85%, 31P), and Me4Sn (119Sn). Elemental analyses were performed on
a LECO-CHNS-932 analyzer. Melting points are uncorrected and
were measured on a Buchi M-560. IR spectra (cm−1) were measured
̈
on a Bruker IFS 28 device as KBr disks. UV−vis spectra were
measured on an Agilent Cary 60 UV−vis device. The ESI-MS spectra
were recorded at positive mode with a Thermoquest−Finnigan
instrument using CH3CN as the mobile phase.
Bis{[2,6-Bis(diisopropoxyphosphonyl)-4-tert-butyl]phenyl}tin(II),
({4-t-Bu-2,6-[P(O)(O-i-Pr)2]2C6H2})2Sn (3). A solution of ({4-t-Bu-2,6-
[P(O)(O-i-Pr)2]2C6H2}Sn)2 (ca. 30 mg) in C6D6 was sealed in a
NMR tube. After a few hours, the deposition of elemental tin was
observed and the 31P NMR spectrum revealed a new signal, the
intensity of which increased with time. After 3 weeks, the 31P NMR
Reaction of 4-t-Bu-2,6-[P(O)(O-i-Pr)2]2C6H2SnCl with K[B-sec-
Bu3H] (K-Selectride). Experiment 1. At 0 °C and under magnetic
stirring, a 1 M solution of K-Selectride in THF (2.5 mL, 2.5 mmol)
was added dropwise within 10 min to a solution of compound 1 (1.51
g, 2.5 mmol) in THF (10 mL). NMR spectra were recorded after t =
0.5 and 5 h.
1
spectrum indicated that the solution contained essentially pure 3. H
3
NMR (C6D6, 500.13 MHz): δ 1.01 (d, J(1H−1H) = 6.5 Hz, 24H,
3
CH(CH3)2), 1.18 (s, 18H, C(CH3)3), 1.29 (d, J(1H−1H) = 6.5 Hz,
24H, CH(CH3)2), 4.56−4.65 (m, 8H, CH(CH3)2), 7.95 (d,
3J(31P−1H) = 14.2 Hz, 4H, CHaryl). 13C{1H} NMR (C6D6, 75.47
MHz): δ 24.2−24.3 (m, CH(CH3)2), 24.7−24.8 (m, CH(CH3)2), 31.6
(s, C(CH3)3), 34.7 (s, C(CH3)3), 70.2−70.3 (m, CH(CH3)2), 132.4
(dd, C3/5aryl, 2J(13C−31P) = 16.7 Hz, 4J(13C−31P) = 5.1 Hz), 137.2 (dd,
t = 0.5 h. 31P{1H} NMR (121.50 MHz, C6D6): δ 16.7 (s, RH,
integral 16), 32.8 (s, J(31P−117/119Sn) = 81 Hz, 2, integral 32), 34.1 (s,
J(31P−117/119Sn) = 90 Hz, RSnH, integral 36), 36.0−36.4 (five minor
intense resonances, not assigned, total integral 16).
t = 5 h. 31P{1H} NMR (121.50 MHz, C6D6): δ 16.7 (s, RH, integral
18), 32.8 (s, J(31P−117/119Sn) = 81 Hz, 2, 59%), 34.9 (s,
J(31P−117/119Sn) = 101 Hz, not assigned, integral 5), 36.1−36.5 (five
minor intense resonances, not assigned, total integral 18). 119Sn{1H}
NMR (111.86 MHz, C6D6): δ 385 (s, ν1/2 = 274 Hz, 2).
C2/6aryl, 1J(13C−31P) = 195 Hz, 3J(13C−31P) = 25.4 Hz), 147.5 (t, C4aryl
,
3J(13C−31P) = 13.4 Hz), 193.0 (t, C1aryl 2J(13C−31P) = 36.0 Hz).
,
31P{1H} NMR (C6D6, 121.49 MHz): δ 28.27 (s, J(31P−119/117Sn) =
1
2
100 Hz, J(31P−13C) = 195 Hz, J(31P−13C) = 36 Hz). 119Sn{1H}
NMR (C6D6, 111.92 MHz): δ 3 (quintet, J(119Sn−31P) = 101 Hz).
The contents of the NMR tube were decanted into a Schlenk flask.
The solvent was removed, and the residue was crystallized from
toluene to yield the toluene solvate 3·C7H8 as a yellow single-
crystalline material. The solvate was removed in vacuo at 40 °C, giving
Experiment 2. At 0 °C and under magnetic stirring, a 1 M solution
of K-Selectride in THF (1.1 mL, 1.1 mmol) was added dropwise to a
solution of compound 1 (700 mg, 1.1 mmol) in THF.
31P{1H} NMR (121.50 MHz, THF/C6D6): δ 16.7 (s, RH, integral
30), 32.8 (s, 2, integral 12), 33.4 (s, not assigned, integral 5), 34.1 (s,
J(31P−117/119Sn) = 90 Hz, RSnH, 37%), 36.2 (five minor intense
resonances, not assigned, integral 16). 119Sn{1H} NMR (111.86 MHz,
C6D6): δ 51 (t, J(31P−119Sn) = 92 Hz, RSnH). 119Sn NMR (111.86
MHz, C6D6): δ 51 (dt, J(31P−119Sn) = 92 Hz, J(1H−119Sn) = 116 Hz,
RSnH).
3 as a colorless solid. Mp: >350 °C. IR (KBr): ν
̃
1176 (PO,
coordinating), 1254 (PO, noncoordinating). ESI-MS (CH3CN):
1043.5 [(M + H)+].
[2,6-Bis(diisopropoxyphosphonyl)-4-tert-butyl]phenyltin acetate,
{4-t-Bu-2,6-[P(O)(O-i-Pr)2]2C6H2}SnOAc (4). To a solution of {4-t-Bu-
2,6-[P(O)(O-i-Pr)2]2C6H2}SnCl (534 mg, 0.87 mmol) in THF (10
mL) was added a solution of sodium naphthalenide (118 mg, 0.92
mmol, 1.06 equiv) in THF (10 mL) at −90 °C. The red solution was
warmed to room temperature and stirred for 5 min to ensure complete
conversion. From this reaction mixture, a 31P NMR spectrum was
recorded.
[2,6-Bis(diisopropoxyphosphonyl)-4-tert-butyl]phenyltin(I), ({4-t-
Bu-2,6-[P(O)(O-i-Pr)2]2C6H2}Sn)2 (2). Method 1. To KC8 (764 mg,
5.65 mmol, 2.36 equiv) was added a solution of {4-t-Bu-2,6-[P(O)(O-
i-Pr)2]2C6H2}SnCl (1.474 g, 2.39 mmol) in toluene (18 mL). The
suspension was stirred for 4 h, during which the color of the reaction
mixture turned to red-violet. After filtration over Celite, toluene was
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Table 2. Crystallographic Data for Compounds 2, 2·C7H8, 3·C7H8, and 4
2
2·C7H8
3·C7H8
4
empirical formula
fw [g/mol]
λ [Å]
C44H78O12P4Sn2
1160.32
C44H78O12P4Sn2•C7H8
1252.46
C44H78O12P4Sn•C7H8
1133.77
C24H42O8P2Sn
639.21
0.71073
0.71073
0.71073
0.71073
T [K]
173(2)
173(2)
173(2)
173(2)
cryst syst
cryst size [mm]
space group
a [Å]
triclinic
monoclinic
0.49 × 0.47 × 0.31
C2/c
monoclinic
0.50 × 0.12 × 0.04
C2/c
orthorhombic
0.30 × 0.13 × 0.12
P212121
0.17 × 0.15 × 0.15
P1
̅
12.4462(4)
12.6211(3)
18.0942(5)
82.249(2)
76.873(2)
86.797(2)
2741.82(13)
2
26.493(2)
13.9899(4)
24.0375(10)
90
18.0490(6)
24.1798(8)
13.5944(5)
90
10.1722(9)
16.9303(12)
18.0365(13)
90
b [Å]
c [Å]
α [deg]
β [deg]
117.133(5)
90
103.039(3)
90
90
γ [deg]
V [Å3]
90
7928.7(7)
4
5779.9(3)
4
3106.2(4)
4
Z
ρcalcd[mg/m3]
1.405
1.049
1.303
1.367
μ [mm−1
]
1.080
0.751
0.608
0.965
F(000)
1196
2592
2392
1320
θ range [deg]
2.12−25.50
−15 ≤ h ≤ 15
−15 ≤ k ≤ 15
−21 ≤ l ≤ 21
39817
2.74−25.50
−32 ≤ h ≤ 32
−16 ≤ k ≤ 16
−29 ≤ l ≤ 29
31339
2.28−25.50
−21 ≤ h ≤ 21
−29 ≤ k ≤ 29
−16 ≤ l ≤ 16
16464
2.30−25.50
−8 ≤ h ≤ 12
−20≤ k ≤ 20
−21 ≤ l ≤ 21
18266
index ranges
no. of reflns collected
completeness of θmax [%]
no. of indep reflns/Rint.
no. of reflns obsd with I > 2σ(I)
abs corrn
100.0
99.9
99.9
99.7
10184/0.0463
7236
7372/0.0359
5814
5385/0.0454
4245
5713/0.0679
3023
multiscan
1.0/0.77013
581
multiscan
1.0/0.83142
367 (12)
1.417
multiscan
1.0/0.88045
287
multiscan
1.0/0.79420
371 (66)
0.687
Tmax/Tmin
no. of refined param (restraints)
GOF(F2)
1.100
0.824
R1(F) [I > 2σ(I)]
wR2(F2) (all data)
(Δ/σ)max.
0.0570
0.0460
0.0238
0.0370
0.1662
0.1348
0.0660
0.0495
0.001
0.001
0.000
0.001
largest diff peak/hole [e/Å3]
2.469/−1.378
1.239/−0.510
0.335/−0.255
0.511/−0.568
31P{1H} NMR (THF, 81.01 MHz, no deuterated solvent,
referenced to RH): δ 32.6 (s, J(31P−119/117Sn) = 81 Hz; RSnSnR).
To the red solution was added PhI(OAc)2 (148 mg, 0.46 mmol,
0.53 equiv). The red color disappeared within a few minutes, leaving a
colorless solution. From this reaction mixture, a 31P NMR spectrum
was recorded.
119Sn{1H} NMR (C6D6, 111.92 MHz): δ −229 (J(119Sn−31P) = 106
Hz). IR (KBr) ν
1145 (PO), 1162 (PO), 1641 (COassym). ESI-
̃
MS (CH3CN): 1219.4 [(M + RSn)+]. Elem anal. Calcd for
C24H42O8P2Sn (639.2): C, 45.09; H, 6.62. Found: C, 44.65; H, 6.5.
Crystallography. The crystallographic data are given in Table 2.
Single crystals of compounds 2 and 2·C7H8 were mounted at low
temperature in inert oil under a nitrogen atmosphere by using the
XTemp2 device.29 All intensity data were collected with an XcaliburS
CCD diffractometer (Oxford Diffraction) using Mo Kα radiation at
110 K. The structures were solved with direct methods using SHELXS-
97,30 and refinements were carried out against F2 using SHELXL-97.30
All non-H atoms were refined using anisotropic displacement
parameters. The C−H H atoms were positioned with idealized
geometry and refined using a riding model. In compound 2·C7H8, the
isopropyl groups at O(1′) and O(1″) are affected by disorder; both
have been described by a split model with distance restraints for
stabilization. In compound 4, the tert-butyl group and the atoms
C(13), C(16), and C(26) are also affected by disorder and described
by a split model; their Uij components were restrained to approximate
isotropic behavior. In compounds 2·C7H8 and 3·C7H8, solvate
molecules were found to be severely disordered and removed by
SQUEEZE (PLATON)19 to improve the main part of the structure.
CCDC 870443 (2), 870442 (2·C7H8), 870444 (3·C7H8), and 870445
(4) contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/
cif.
31P{1H} NMR (THF/C6D6, 121.49 MHz): δ 37.14 (s,
J(31P−119/117Sn) = 122 Hz, integral 37; RSnCl), 36.21 (s,
J(31P−119/117Sn) = 102 Hz, integral 49; RSnOAc), 16.37 (s, integral
11, RH). 119Sn{1H} NMR (THF/C6D6, 111.92 MHz): δ −98 (t,
J(119Sn−31P) = 121 Hz, integral 37; RSnCl), −228 (t, J(119Sn−31P) =
106 Hz, integral 53; RSnOAc).
All volatiles were removed in vacuo, and naphthalene was sublimed
at 60 °C. The residue was extracted into toluene (20 mL) and filtered
over Celite. The filtrate was concentrated to give colorless single
crystals suitable for X-ray diffraction analysis. The colorless crystals
were dried in vacuo. Yield: 97 mg, 17%. Mp: 155 °C. 1H NMR (C6D6,
300.13 MHz): δ 1.00 (d, 3J(1H−1H) = 6.2 Hz, 12H, CH(CH3)2), 1.08
3
(s, 9H, C(CH3)3), 1.25 (d, J(1H−1H) = 6.2 Hz, 12H, CH(CH3)2),
1.93 (s, 3H, CH3), 4.63−4.88 (m, 4H, CH(CH3)2), 8.00 (d,
3J(31P−1H) = 13.2 Hz, 2H, CHaryl). 13C{1H} NMR (C6D6, 75.47
MHz): 23.6 (s, CH3), 24.0−24.1 (m, CH(CH3)24), 24.4−24.5 (m,
CH(CH3)2), 31.4 (s, C(CH3)3), 35.0 (t, C(CH3)3, J(13C−31P) = 1.4
2
Hz), 72.2−72.3 (m, CH(CH3)2), 131.9 (dd, C3/5aryl, J(13C−31P) =
17.1 Hz, 4J(13C−31P) = 4.7 Hz), 134.2 (dd, C2/6aryl, 1J(13C−31P) = 193
3
3
Hz, J(13C−31P) = 24.0 Hz), 151.1 (t, C4aryl, J(13C−31P) = 12.7 Hz),
177.3 (s, CO), 187.0 (t, C1aryl, J(13C−31P) = 36.7 Hz). 31P{1H}
2
NMR (C6D6, 121.49 MHz): δ 36.29 (J(31P−119/117Sn) = 100 Hz).
6857
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Inorganic Chemistry
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Computational Details. All calculations were performed with the
Gaussian 03, Revision E.01,31 suite of programs. Full DFT calculations
were carried out with the B3LYP functional21a and def2-SVP basis
127, 17530−17541. (f) Khan, S.; Michel, R.; Dieterich, J. M.; Mata, R.
A.; Roesky, H. W.; Demers, J.-P.; Lange, A.; Stalke, D. J. Am. Chem.
Soc. 2011, 133, 17889−17894.
set.21b For the Sn atom, the Stuttgart−Koln ECP was added.21c
̈
(6) Peng, Y.; Wang, X.; Fettinger, J. C.; Power, P. P. Chem. Commun.
2010, 46, 943−945.
Starting coordinates were obtained from the crystal coordinates.
Harmonic vibrational frequency analyses were performed in order to
determine the nature of the stationary point at the same theoretical
level. Compound 2 was calculated within the C1 and Ci point groups.
All calculated total (self-consistent field) and zero-point energies as
well as standard orientations can be found in the Supporting
Information. In order to perform NBO analyses, the built-in NBO-
3.1 subroutines of the Gaussian program package were used.
(7) (a) Bousk
̌
a, M.; Dostal, L.; Ruzick
a, A.; Benes,
a, M.; Dostal, L.; Proft,
a, A.; Jambor, R. Chem.Eur. J. 2011, 17,
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Pawlis, S.; Jurkschat, K.; Jambor, R. Angew. Chem., Int. Ed. 2012, 51,
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ASSOCIATED CONTENT
* Supporting Information
(8) (a) Jambor, R.; Kasna, B.; Kirschner, K.; Schurmann, M.;
̌
́
̈
■
Jurkschat, K. Angew. Chem., Int. Ed. 2008, 47, 1650−1653; Angew.
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Holzmann, N.; Frenking, G.; Stasch, A. Inorg. Chem. 2011, 50, 12315−
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P. P. J. Am. Chem. Soc. 2003, 125, 11626−11636. (e) Peng, Y.; Fischer,
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Herber, R. H.; Power, P. P. Chem. Sci. 2010, 1, 461−468. (f) Fischer,
R. C.; Pu, L.; Fettinger, J. C.; Brynda, M. A.; Power, P. P. J. Am. Chem.
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S
Kinetic plot, computational data, complete ref 31, and
combined CIF for 2, 2·C7H8, 3·C7H8, and 4. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: klaus.jurkschat@uni-dortmund.de.
■
Notes
The authors declare no competing financial interest.
(9) Bigwood, M. P.; Corvan, P. J.; Zuckerman, J. J. J. Am. Chem. Soc.
1981, 103, 7643−7646.
ACKNOWLEDGMENTS
M.W. is grateful to Technische Universitat Dortmund for a
scholarship.
■
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