Synthesis and Theoretical Investigation of Diphosphastannylenes

Article abstract of DOI:10.1021/acs.organomet.8b00258

The factors affecting the stabilization of diphosphastannylenes, such as substituent size, steric demand, and type of substituent (aryl, alkyl, silyl) were investigated via a comprehensive DFT and experimental investigation. The influence of various substituents (H, Me, ^tBu, Ph, TMS, Hyp = (Si(SiMe₃)₃)) on the pyramidalization of the phosphorus centers and cone angle determination of those substituents were carried out. Through these considerations, ligand systems capable of isolating a stable Sn(II) species were determined. Synthetic work led to the isolation of dimeric supermesityl(trimethylsily)phosphanides, 2,4,6-tris(t-butyl)phenyl trimethylsilyl lithium phosphanide, 2,4,6-tris(t-butyl)phenyl trimethylsilyl potassium phosphanide, and one hypersilylphosphanide [HypP(SiMe₃)K·DME]. In addition to that, a novel monomeric diphosphastannylene [HypP(SiMe₃)]₂Sn was isolated as well as confirmed by experimental and calculated NMR data and single crystal X-ray analysis.

Full text of DOI:10.1021/acs.organomet.8b00258

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Synthesis and Theoretical Investigation of Diphosphastannylenes
Elisabeth Schwarz,* Stefan K. Mueller, Gernot Weinberger, Ana Torvisco, and Michaela Flock*
Institute of Inorganic Chemistry, Graz University of Technology, Stremayrgasse 9/IV, 8010 Graz, Austria
S
* Supporting Information
ABSTRACT: The factors affecting the stabilization of diphos-
phastannylenes, such as substituent size, steric demand, and type
of substituent (aryl, alkyl, silyl) were investigated via a
comprehensive DFT and experimental investigation. The
t
influence of various substituents (H, Me, Bu, Ph, TMS, Hyp =
(Si(SiMe3)3)) on the pyramidalization of the phosphorus centers
and cone angle determination of those substituents were carried
out. Through these considerations, ligand systems capable of
isolating a stable Sn(II) species were determined. Synthetic work
led to the isolation of dimeric supermesityl(trimethylsily)-
phosphanides, 2,4,6-tris(t-butyl)phenyl trimethylsilyl lithium
phosphanide, 2,4,6-tris(t-butyl)phenyl trimethylsilyl potassium phosphanide, and one hypersilylphosphanide [HypP(SiMe3)-
K·DME]. In addition to that, a novel monomeric diphosphastannylene [HypP(SiMe3)]2Sn was isolated as well as confirmed by
experimental and calculated NMR data and single crystal X-ray analysis.
density into the empty p-orbital on the tetrel (see Figure 1). So
the key to success for the stability of diphosphatetrylenes
INTRODUCTION
■
Diphosphatetrylenes, the heavier analogues of the well-known
diaminotetrylenes, have gained interest in recent years. The
number of publications that examine the analogue cyclic α,α′-
nitrogen-stabilized carbenes (NHC, Arduengo carbene1) is
quite large given that there is just one analogous α,α′-
phosphorus-stabilized compound of this type.2 The acyclic
compounds have, because of their high reactivity, substantial
possibilities in transition metal catalysis while still showing
enough stability for convenient use. Tetrylenes are able to
coordinate to transition metals forming homogeneous
catalysts, as is impressively shown in the work of Lappert3
and Veith.4 In Lappert’s investigations with Pd(II) complexes,
Sn[N(SiMe3)2] acts as a two-electron σ-donor, which is a
successful alternative to the widely used tertiary phosphanes.5
In diaminotetrylenes, stabilization is provided via interaction of
the group 15 element lone pair with the vacant p-orbital on the
group 14 element in oxidation state + II (tetrel atom E = C, Si,
Ge, Sn, Pb). As a result of the large planarization barrier of the
P atom, the effective orbital overlap was discussed as being less
beneficial in diphosphatetrylenes,6 which might be a reason for
the small number of compounds in the literature. However, in
1996, Schleyer et al.7 noted that the inherent p-donor
capabilities of phosphorus should be as large or even larger
than those of nitrogen. Nevertheless, the difference in the
electronegativities (Pauling: N = 3.04, P = 2.19) and the
stronger pyramidalization of the phosphorus might counteract
the effective orbital overlap with the empty p-orbital of the
tetrel atom.
Figure 1. Intramolecular stabilization of diphosphatetrylenes.
should be the determination of substituents that provide
sufficient steric protection, together with decreasing the
pyramidalization of the P atom to obtain optimal orbital
overlap.
In almost all literature known structures, the P atoms are de
facto trigonal pyramidal and no typical π-type interactions
could be determined. In 1977, the first diphosphatetrylene with
t
the rather small Bu substituents, [(tBu2P)]2Sn2, a dimeric
compound,8 was established via NMR spectroscopy. A few
years later, the first monomeric structure (Me3Si)2P2Sn was
confirmed by NMR spectroscopy and cryoscopy;9 red-orange
crystals were isolated but decomposed while storing at reduced
temperature. Since TMS (=SiMe3) and tBu are similar in their
steric demand, this indicates that silyl substituents might be
more favorable for the stabilization of monomeric diphospha-
In order to use the tetrylenes for subsequent chemical
reactions, the steric shielding should be small enough to allow
access to the reactive tetrel center. At the same time, stability
needs to be increased by intramolecular donation of electron
Received: April 25, 2018
© XXXX American Chemical Society
A
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tetrylenes compared to alkyl ligands. The first structurally
characterized diphosphastannylene was isolated by Driess in
1995,10 bearing sterically demanding silyl substituents R1R2,
on the pyramidal P atom, with R1 = −Si(2,4,6-iPr3C6H2)2F or
−Si(tBu)(2,4,6-iPr3 C6 H2)F and R2 = −Si(tBu)-
(2,4,6-iPr3C6H2)F. A bis(phosphanyl) stannylene was isolated
by Westerhausen in 1998. Here, bulky phospholide sub-
stituents were used.11,12 The stabilization via formation of
phosphastannenocenes was also mentioned by Brym and
Jones.12
reported monomeric diphosphatetrylenes, these ligands feature
neither aromatic nor any additional electron donating moieties.
Computational Approach. For more insight, a DFT
investigation of phosphorus ligands with aryl, alkyl, and silyl
substituents on the phosphorus atoms was carried out. Owing
to the fact that larger substituents are essential for kinetic
stabilization, greater focus was placed on 2,4,6-tris(t-butyl)-
phenyl−PR2 (Mes*PR2), which is comparable to the bulky
aromatic substituents (Dipp, Tripp) used in literature known
diphosphastannylenes, and HypPR2, Hyp = (Si(SiMe3)3)), as a
sterically demanding silyl substituent.
In 2007, an NMR experiment characterizing monomeric
Mes2
diphosphastannylene, [ArMes P(Ph)]2Sn (Ar
= C6H3−
A closer look at the influence of the substituent choice on
the planarization using Mes*PR2 and HypPR2 as root
2
2,6(C6H2−2,4,6-Me3)), was reported by Rivard.13 In 2005
and 2012, comparatively small diphosphatetrylenes,
[(Me3Si)2−CH]P(C6H4−2-SMe)2E (E = Ge, Sn) and [(Ph)-
t
backbones with R = H, Me, Bu, TMS, Hyp, and Ph was
taken. Comparing the results for both types of phosphanes, the
Mes*backbone, seen in Table 1, appears particularly suitable
(C6H3−2,6- CH2NMe2)2P]2Sn were isolated by Izod14 and
15
̌
̌
Reznicek. In both cases, additional stabilization of discrete
monomers was reached by intramolecular base stabilization via
a sulfur or a nitrogen lone pair.
Table 1. mPW1PW91/SDD DFT Calculated Geometry
Data for Mes*PR2
All of the above-mentioned and literature known monomeric
diphosphastannylenes feature rather bulky and sterically
demanding alkyl, aryl, or silyl substituents11 on the pyramidal
phosphorus atoms. Izod16 recently also added π-stabilized
diphosphatetrylenes to this type of compound, in which one of
the phosphorus atoms actually has a planar configuration.
These diphosphatetrylenes (R2P)2E [E = Ge, Sn; R = Dipp
(2,6-iPr3C6H2) or Tripp (2,4,6-iPr3C6H2)]16 show stabilization
via pπ−pπ interaction of one trigonal-planar P center.
Nevertheless, the substituents used in these compounds are
rather bulky groups.
R
H
Me
tBu
TMS
Hyp
Ph
P−C [Å]
P−R [Å]
ΣP [°]
1.90
1.44
293.4
1.89
1.89
319.9
1.90
1.96
341.8
1.89
2.34
351.9
1.90
2.48
359.9
1.86
1.87
326.3
for lowering the pyramidalization of the P atom. Focusing on
the Bu, TMS, and Hyp substituents, a stronger effect on the
t
pyramidalization for the silyl substituents was observed.
Although the TMS group is isomorphic20 and similar in size
t
to the Bu ligand, the bond angle sum (ΣP) increases by 10
degrees going from tBu (ΣP = 341.8°) to TMS (ΣP = 351.9°).
This indicates that the type (aryl, alkyl, silyl) of substituent is
as essential as its size. A second aromatic group, Ph, does not
seem to enhance planarity.
As suggested by Izod, stabilization in diphosphastannylenes
could be fortified by a strong PE multiple bond character.16
Such a strong intramolecular stabilization could allow the use
of smaller substituents for stable tetrylenes. However, what is
missing is an understanding in what factors of the ligand,
including substituent size, steric demand, and kind of
substituent (aryl, alkyl, silyl), affect isolation and stabilization
of novel compounds. DFT calculations were used to explore
A similar trend is noted for the HypPR2 compounds (see
Table 2). However, the bond angle sums around P are
Table 2. mPW1PW91/SDD DFT Calculated Geometry
Data for HypPR2
i
t
the influence of various substituents (H, Me, Pr, Bu, Ph,
TMS, Hyp = (Si(SiMe3)3)) on the pyramidalization of the
phosphorus center. Cone angle determination of those
substituents was carried out. Through these considerations, a
ligand system capable of isolating a stable Sn(II) species, was
determined.
R
H
Me
tBu
TMS
Hyp
Ph
P−Si [Å]
P−R [Å]
ΣP [°]
2.36
1.44
287.0
2.36
1.90
303.1
2.41
1.95
321.5
2.36
2.35
333.1
2.43
2.49
341.7
2.38
1.88
312.1
approximately 20° smaller for both, tBu and TMS. Only Hyp3P
has a rather high bond angle sum with 341.7°. These results
suggest a superiority of the Mes*PR2 substituent for forming
EP double bonds.
RESULTS AND DISCUSSION
■
As noted before, Izod16 recently characterized diphosphas-
tannylenes and -germylenes, bearing rather bulky, aromatic
substituents (Dipp, Tripp), where one of the phosphorus
centers is planar, and a PE double bond is formed.
Diphosphatetrylenes with smaller silyl substituents on the P
atoms, have not been isolated so far, although SiMe3 groups
have been used as sterically demanding, stabilizing substituents
for several years in group 14 chemistry.17 In 2006, Hassler et al.
reported on several phosphanes and diphosphanes featuring a
bulky −Si(SiMe3)3 group, among others, the simple hyper-
silylphosphane [(SiMe3)3Si−PH2].18 The hypersilyl moiety
[(SiMe3)3Si−] provides great steric protection to neighboring
groups while generally not being reactive itself, if not
specifically targeted.18 It was shown that backbone systems
featuring a hypersilyl moiety can be functionalized, which
might make them ideal precursors for the synthesis of novel
α,α′-P-tetrylenes.18,19 Unlike the ligands of all previously
Calculations of Cone Angles. Steric bulk of ligands is
usually determined by Tolman θ or solid cone angles Θ,21
which both suffer from some disadvantages such as the
imprecision with asymmetric and polydentate ligands or for
solid angles, only providing a picture of the ligand in a frozen
state.21 In contrast, the “exact cone angle method”21 is a more
convenient technique for determining exact cone angles θ° via
finding the most acute circular cone, containing all ligand
atoms over a quadratic equation for the cosine of the cone
angle. The size of the cone angle describes the ability of
shielding an active metal center. Commonly used phosphane
ligands show values around 200°.22 Using the exact cone angle
method,21 Dipp and Tripp substituents used by Izod6,16 have
cone angles of 204 to 205°. For the diphosphastannylenes
B
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Figure 2. Schematic diagram of diphosphatetrylene cone angles.
Table 3. mPW1PW91/SDD DFT Calculated Data for the Global Minimum of (Mes*PR)2Sn
substituent
∑P(P)′ [deg]
P−R/P′−R [Å]
P−Sn/P′−Sn [Å]
P−Sn−P [deg]
ΔH−L [eV]
tBu
TMS
Hyp
325.4 (360.0)
347.0 (360.0)
331.5 (359.9)
2.00/1.98
2.34/2.35
2.38/2.40
2.70/2.52
2.36/2.35
2.61/2.56
104.2
110.3
112.1
3.05
3.25
3.03
Table 4. mPW1PW91/SDD DFT Calculated Data for the Global Minimum of (HypPR)2Sn
substituent
∑P(P)′ [deg]
P−R/P′−R [Å]
P−Sn/P′−Sn [Å]
P−Sn−P [deg]
ΔH−L [eV]
tBu
TMS
Hyp
309.7 (360.0)
328.0 (328.0)
317.3 (358.9)
1.96/1.94
2.35/2.36
2.57/2.71
2.68/2.51
2.58/2.61
2.71/2.57
102.0
98.82
118.0
3.16
3.11
2.04
studied here, (Mes*RP)2Sn and (HypRP)2Sn, with R = H, Me,
or Ph, values from 150 to 165° were obtained, making them
less suitable for stabilizing monomeric diphosphatetrylenes.
For the Hyp backbone, the TMS and tBu ligands have values of
197 and 198°, respectively. In comparison, the Mes*backbone
with R = TMS has a value for the cone angle of 167°, while tBu
with 178° might still be in a reasonable range (see Figure 2). In
were detected. The P−Sn−P angle is 110.3°, slightly wider.
Only for this compound a conformer with two almost planar P
atoms, ∑P(P)′ = 355.6° (355.0°), was found. This conformer
was the least stable one, with a ΔH of 20 kJ/mol. The Hyp
substituted compound shows an increased P−Sn−P′ angle,
because of the ligand size, which can be seen in Table 3.
The global minima of compounds (HypPR)2Sn have usually
two pyramidal phosphorus centers. NBO analyses show in
these cases interactions between the P lone pairs and the
empty p-orbital on the Sn with lower delocalization energies
(E2 = 15−30 kcal/mol). Only for (HyptBuP)2Sn and
(Hyp2P)2Sn a global minimum with a planar P center was
detected. For (HyptBuP)2Sn, all of the minima are rather close
in energy (ΔH = 3.1−16.5 kJ/mol). The global minimum
structure has Sn−P distances of 2.51 and 2.69 Å, and the P
bond angle sums are 360 and 309.7°. For the analogous
compound with R = TMS, four minima were found only 1.7 to
3.4 kJ/mol less stable than the global minimum, and another
four minima were located with ΔH = 8.8 to 24.8 kJ/mol. The
global minimum is quite symmetric; both Sn−P distances are
2.59 Å, and both P atoms are pyramidal with a bond angle sum
of 328°. A restricted scan for the planarization of one P center
shows a very small barrier of approximately 5 kJ/mol. In the
case of R = Hyp, there is a significant difference in the Sn−P
distances, with 2.57 and 2.70 Å as seen in Table 4. This
indicates reduced pyramidal environment on the second P
atom, and indeed, the bond angles are 358.9 and 317.3°. The
P−Sn−P bond angle (118°) is wider than in the TMS
substituted compound (98.8°). The literature known silyl
substituted compound isolated by Driess10 has a P−Sn bond
length of 2.567 Å and a P−Sn−P angle of 98.78°, similar to
(HypTMSP)2Sn as seen in Table 4.
t
summary, the Hyp backbone in combination with a Bu or
TMS ligand seems to provide enough steric stabilization for
the isolation of monomeric diphosphatetrylenes. Both back-
t
bone systems with special emphasis on R = Bu, TMS, and
Hyp, were considered for DFT calculations on diphosphas-
tannylenes.
In a brief summary in Tables 3 and 4, the calculated data for
the lowest energy minimum of each compound can be found
(coordinates for all geometries are given in the Supporting
Information). For every compound, four to five stable
minimum geometries were located. At least one of those
configurations had a planar P center, which indicates a higher
overlap of the orbitals and therefore a stronger stabilization. In
these conformers, one shorter P−Sn bond was detected,
caused by the π-type interaction, which was also confirmed by
NBO analyses, resulting in high delocalization energies (E2 =
115−185 kcal/mol). Simultaneously, the P−Sn bond of the
second P center was significantly elongated and shows only a
weak interaction of this type. In the case of (Mes*RP)2Sn, all
of the global minima, except for R = H, have one planar P
t
atom. For R = Bu, the global minimum is 15 kJ/mol more
stable than the other minima. The Sn−P distances are 2.52 and
2.71 Å, with a P−Sn−P angle of 104.2°. The bond angle sums
of the P atoms are 360 and 325°, respectively. For the TMS
substituted compound, bond angle sums of 347.0 and 360.0°
C
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Scheme 1. Reaction Route to Sn(PMes*TMS)2
Figure 3. 2,4,6-Tris(t-butyl)phenyl trimethylsilyl lithium phosphanide 2a obtained by X-ray diffraction analysis. All noncarbon atoms shown as 30%
shaded ellipsoids. Hydrogen atoms have been omitted for clarity.
Concerning the NMR data, two shifts in the 31P NMR
should be detected if a compound has one pyramidal and one
planar P center. These shifts differ in a quite remarkable
manner. The shifts for the planar phosphorus atom are
calculated to occur in our investigated stannylenes in a region
from 22 to 52 ppm, while the pyramidal phosphorus centers
resonate in the high field from −139 to −125 ppm. In the
solid-state 31P(1H) MAS NMR spectra of the Dipp substituted
compound isolated by Izod,16 shifts at 95.8 ppm (P−Sn =
2620 Hz) and −66.2 ppm (P−Sn = 1180 Hz) occurred,16
which matches their DFT calculations. In a toluene-d8 solution,
only a 31P NMR peak at −25.1 ppm with a P−Sn coupling of
1300 Hz was found. This was attributed to small barriers of
inversion.16 Our calculations on a simpler model, (PPh2)2Sn,
predict an inversion barrier of 2.4 kJ/mol.
As mentioned before, tetrylenes are interesting candidates
for complementing transition metal compounds in catalytic
processes. Particularly the activation of small molecules, such
as H2 and NH3, arouses great interest. Schoeller23 noted that
HOMO−LUMO gaps, ΔH−L, and singlet−triplet energy
separations, ΔES−T, are essential in the reactions with small
molecules. Smaller gaps lead to lower activation barriers and
are therefore favorable.16 Recently, it was mentioned24 that by
the use of phosphido ligands, the values for ΔES−T can be
lowered to values below 63 kJ·mol−1. In diaminotetrylenes, the
values are around 88 kJ·mol−1 or higher. Literature known
germylenes,25 which were tested for H2 activation, show
HOMO−LUMO gap values from 3.4 to 3.6 eV. Compared
with our results, we can see that in all Sn conformers seen in
Tables 3 and 4, the HOMO−LUMO energy gaps are between
2.04 and 3.25 eV. If we take a closer look at our TMS
substituted compounds, (Mes*PTMS)2 Sn and
(HypPTMS)2Sn, the absorption maximum for the Mes*com-
pound is at 531 nm (red-purple), and the absorption maximum
for the Hyp compound is at 676 nm (green blue). This
indicates a smaller HOMO−LUMO gap for the (HypPTMS2)-
Sn, which could be confirmed with our DFT calculation; the
ΔH−L value for the Hyp compound is 3.11 eV, while the
Mes*compound has a wider gap of 3.25 eV. The ΔES−T could
be calculated with 128.5 kJ·mol−1 for (Mes*PTMS)2Sn and
178.7 kJ·mol−1 for (HypPTMS)2Sn. This makes these
compounds ideal candidates for the activation of small
D
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Figure 4. Structure of 2,4,6-Tris(t-butyl)phenyl trimethylsilyl potassium phosphanide]·DME 2b obtained by X-ray diffraction analysis. All
noncarbon atoms shown as 30% shaded ellipsoids. Hydrogen atoms have been omitted for clarity.
molecules. For the purpose of employing the insight gained
from the calculations, we have chosen to apply the ligands tBu
and TMS for the synthesis of stable diphosphastannylenes in
the form of Mes*RP−Sn−PRMes*and HypRP−Sn−PRHyp.
Experimental Approach. Mes*PH2 (or supermesityl-
phosphanide [LiPMes2)(OEt2)]2,28 with P−Li bonds of
2.483 and 2.479 Å. In the case of the potassium phosphanide
2b, each metal atom is coordinated to DME. The P−K bond
lengths are 3.264 and 3.228 Å, comparable to the literature
known P3K bridged [3]ferrocenophane.29 This compound has
P−K bond lengths of 3.581 and 3.333 Å. The K···H−C
contacts are as well within reported values for a K···H−C
(2.845, 3.062, 3.101, 3.238 Å) agostic interaction.
The attempted tetrylene synthesis via reaction of Me-
s*PHosphanide with the corresponding Sn(II) halides (SnCl2,
SnBr2) yielded a dark red solution and a red-brown precipitate.
Further interpretation of this precipitate was difficult because
of the poor solubility in any common solvent. The reaction
solution was further analyzed via NMR. A 31P signal at −392.1
ppm and a 119Sn signal at 1292 ppm were detected. The red
solution was stored at reduced temperature in order to gain
crystals for a structure determination. Two kinds of crystals
could be isolated. Apart from yellow crystals, which were
analyzed to be Mes*−P = P−Mes*, a quite common side
product in the reaction of lithium silylphosphides with
halides,30,31 small red crystals were formed. Unfortunately, X-
ray diffraction analysis of these was not possible because of
poor crystal quality.
18
PH2) 1 and (SiMe3)3Si−PH2 (HypPH2) were chosen as
convenient synthetic starting points in the synthesis of
silylphosphanes, which can act as stabilizing ligands for
n
diphosphatetrylenes. The lithiation of Mes*PH2 1 with BuLi
is well-known and yields the phosphanide Mes*PHLi.
Straightforward salt elimination reaction with TMS-Cl yields
the silaphosphane Mes*P(TMS)H 3. A subsequent reaction
n
with BuLi and a salt elimination reaction with TMS-Cl leads
n
to Mes*P(TMS)2 4. The deprotonation reaction with BuLi
can also yield the diphosphene, a common side product (see
Scheme 1).26
A reaction of Mes*P(TMS)2 seems more complicated;
however, reaction of 4 with nBuLi causes an almost quantitative
(>99%) abstraction of one trimethylsilyl group, resulting in a
clean lithium phosphanide 2a. Si−P cleavage by nBuLi, as well
as lithiation of primary and secondary phosphanes, is a well-
known reaction. However, solid-state structures of 2a and 2b
have not been reported to date. Crystals suitable for X-ray
diffraction analysis of these were gained from a mixture of n-
hexane and toluene (see Figures 3 and 4). A P−C bond length
was observed with a length of 1.872 Å for the lithium
phosphanide 2a and 1.887 Å for the potassium phosphanide
2b; the values for the P−Si bond (2.226 and 2.211 Å) are in a
reasonable region. Both phosphanides crystallize as dimers
consisting of two metal atoms bridged by two Mes*TMSP
ligands in a P−M−P−M central ring (M = Li, K). In the case
of 2a, one Li coordination center is saturated by ether, while
the second Li atom is stabilized by agostic interactions from
the t-butyl groups of the Mes*ligand, with a coordination
number of 2. The values for these Li···H−C contacts are within
reported values for a Li···H−C (2.140, 2.365, and 2.745 Å)
agostic interaction.27 The P−Li bond lengths are 2.505 and
2.412 Å, comparable to the literature known lithium
In the literature, an NMR pattern similar to ours was found
for a compound isolated by Westerhausen,32 a tin−phosphorus
cubane with SitBu3 groups on P. It shows a 31P signal at −452.1
1
ppm and a 119Sn peak at 1234 ppm with a JSn−P coupling
3
constant of 788 Hz and a JSn−P coupling constant of 84 Hz.
Since this compound shows an upfield shift compared to our
analyzed reaction solution, and carbon substituents on P were
found to rather form cages, we suppose the formation of
multinuclear Sn−P cage structures as mentioned by Wright.33
According to our calculations, [HypPK−SiMe3] is an ideal
candidate for synthesizing a stable stannylene. The synthesis of
[HypPK−SiMe3] has been described before18 but was
modified for this work. The replacement of toluene with 1,2-
dimethoxyethane (DME) results in similarly high yields
(>85%), making the addition of 18-crown-6 obsolete and the
E
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Figure 5. Disordered diagram of dipotassium salt 5 obtained by X-ray diffraction analysis. All noncarbon atoms shown as 30% shaded ellipsoids.
Hydrogen atoms have been omitted for clarity.
Scheme 2. Reaction to Sn(PTMSHyp)2
Figure 6. Solid-state structure of stannylene 6 obtained by X-ray diffraction analysis. All noncarbon atoms shown as 30% shaded ellipsoids.
Hydrogen atoms have been omitted for clarity.
reaction able to be handled at room temperature. Crystals
suitable for X-ray diffraction analysis were obtained after
removal of the solvent and recrystallization from toluene with
slow evaporation of the solvent at room temperature.
Compound 5 crystallizes in a dimeric structural pattern, as
seen in 2a and 2b with a four membered P−K−P−K central
F
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ring (see Figure 5). Each of the potassium ions is further
stabilized via a dimethoxyethane molecule and agostic
interactions to the methyl groups on the hypersilyl moiety.
However, [HypPK−SiMe3] displays whole molecule disorder
(Supporting Information).
calculations predict coupling constants of 1517 Hz.10 The
1
1J
119Sn−P
coupling, as well as the slightly smaller J
117Sn−P
(1423
Hz) coupling, can also clearly be observed via 31P NMR
spectroscopy (see Figure 8). These coupling constants are
considerably larger than those reported for Sn−P single bonds
(700−1000 Hz)10 and also larger than the coupling constants
found for ligands in dimeric stannylenes (∼1000−1200 Hz).8
A tin ferrocenophane dimer34 shows a 119Sn shift at +418 ppm
A reaction of [HypPK−SiMe3] 5 in diethyl ether with
tin(II)bromide diluted in THF (see Scheme 2) led to an
immediate change of color to a rich emerald green. After
replacement of the solvents with toluene and filtration, dark
green needles were obtained at low temperatures (−30 °C).
Analysis via X-ray diffraction gave the molecular structure of a
novel diphosphastannylene [HypP−(SiMe3)]2Sn (see Figure
6) with two pyramidal P centers as predicted by DFT
calculations. There are neither solvent molecules coordinating
to the stannylene nor can any agostic intramolecular or
intermolecular interactions be observed. In accordance to our
calculations at the level of density functional theory (M06L/
IGLO-II//mPW1PW91/SDD), a predicted absorption at 676
nm for the donor free stannylene, resulting in a green color,
was observed. If a solvent molecule would have been
coordinated to the metal center, this would have a direct
influence on the HOMO−LUMO gap, resulting in an
absorption at 495 nm. A UV/vis value was measured at 665
nm for this compound. Also in agreement with our calculated
data (see Table 5), the Sn−P bond lengths and angles match
1
with JSn−P coupling constants of 702 Hz for the more
deshielded P and another 1JSn−P coupling constant of 1179 Hz
for the phosphorus nucleus resonating at higher field,34
showing that coupling constants for dimeric compounds are
in between (700−1200 Hz).
Compound 6 has two pyramidal P centers and shows a
sharp 31P peak at −104.9 ppm, in agreement with our
calculated data of −125 ppm.
This matches the data for comparable literature known
compounds,10 with 31P shifts at −102.5 and −121.5 ppm. 6 has
two stereogenic centers. The molecular structure and the
calculated minimum structures with ΔH ≤ 3 kJ/mol are D,L-
conformations. In solution a mixture of D,L- and meso-forms
cannot be entirely ruled out, although the 119Sn and the 31P
NMR peaks are quite sharp with line widths at half height of 37
and 3.5 Hz, respectively.
Studies concerning the proposed reactivity toward small
molecules, such as H2 or NH3, are ongoing.
Table 5. mPW1PW91/SDD DFT Calculated and
Experimental Data for the Monomeric
Diphosphastannylene 6
Conclusion. Through DFT calculations, a series of
phosphorus ligands with different characteristics, such as size,
steric demand, and type of substituent (aryl, alkyl, silyl) were
evaluated for their ability to stabilize low valent tin(II)
compounds. The effect of various substituents (H, Me, tBu, Ph,
TMS, Hyp = (Si(SiMe3)3)) on the pyramidalization of the
phosphorus center were explored. In addition, the steric
demand of these substituents was evaluated through exact cone
angle determinations. The most promising substituents on
bond lengths
exp. [Å]
calc. [Å]
P1−Sn
P2−Sn
2.53
2.56
2.59
2.60
bond angles [deg]
Σα(P) [deg]
P−Sn−P
306.1/321.4
98.95(6)
328.0/328.0
101.0
t
(Mes*PR)2Sn and (HypPR)2Sn (R = Bu, TMS, Hyp) were
the experimentally observed values. Compound 6 has Sn−P
bond lengths of 2.53 and 2.56 Å and a P−Sn−P angle of
98.96°, resulting in a v-shape. These values are similar to those
of Driess’ compounds, which have P−Sn bond lengths of 2.57
Å and a P−Sn−P angle of 98.78°.10
used in calculating the structures and HOMO−LUMO gap,
giving an idea on their reactivity. Our combination of
calculations and synthetic results indicate that the intra-
molecular stabilization via formation of a SnP double bond
is less important than previously considered. NBO analysis
showed that in conformers with one planar P center, strong π-
type interactions occur. At the same time, the second P center
is considerably weakened as expressed by an elongation of the
P−Sn bond. Consequently, steric shielding needs to be
increased to ensure stabilization. In case of two pyramidal P
centers, simultaneous interaction between the lone pair of both
P centers with the empty p-orbital of the Sn is found but yields
comparably low delocalization energies. Calculations for
(Mes*PTMS)2Sn reveal conformers with planar P centers
and a cone angle of 176°, which according to the literature
should lead to the isolation of stable stannylene species.
Experimentally, however, the use of this substituent combina-
tion did not give the desired results. In contrast, the
combination of Hyp and TMS on the phosphorus centers
does not have planar P atoms but has a larger steric demand
with a cone angle of 197°. This led to a novel stable tin(II)
species, (Hyp*PTMS)2Sn, confirmed by experimental and
calculated data. The solid-state structure shows no donor
coordination to the metal center and no further interactions.
Compound 6 shows a downfield 119Sn shift at 1467 ppm
(see Figure 7), comparable to the compound isolated by Driess
1
with a 119Sn shift of 1551 ppm and a J Sn−P coupling constant
119
of 1682 Hz. As expected for a tin atom substituted by two
phosphorus moieties, the signal of 6 is a triplet with a J
coupling constant of 1486 Hz (see Figure 8), where our DFT
1
119Sn−P
Figure 7. 119Sn NMR resonance of 6 in the lowfield region.
G
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Article
Figure 8. 31P NMR resonance of 6.
Mercury 300 MHz spectrometer from Varian at 25 °C. Chemical
shifts are given in parts per million (ppm) relative to TMS (δ = 0
ppm) regarding 1H, 13C, and 29Si. Coupling constants (J) are reported
in hertz (Hz). All NMR spectra were measured in C6D6.
EXPERIMENTAL SECTION
■
General Procedures. All reactions, unless otherwise stated, were
carried out using either standard Schlenk line techniques or in a
glovebox under nitrogen atmosphere. All dried and deoxygenated
solvents were obtained from a solvent drying system (Innovative
Technology, Inc.). C6D6 has been destilled over sodium and stored
under nitrogen atmosphere. n-Butyl lithium and potassium tert-
butylate were bought from Aldrich and used as delivered.
Dichlorotetramethyldisilane has been prepared following standard
procedures.35 HypP(SiMe3)K 5 was prepared following procedures
previously published.18,19
Because of the air, moisture, and, in the case of the stannylene,
light, sensitivity of our compounds, we were unable to obtain
meaningful elemental analysis results. This is a common problem
observed in tin(II) species and alkaline metal complexes. Alkaline
compounds, such as the reported phospanides, were already described
before to be extremely reactive, and immediate decomposition at
room temperature is very likely.36,37
X-ray Diffraction. All crystals suitable for single crystal X-ray
diffractometry were removed from a vial or a Schlenk under N2 and
immediately covered with a layer of silicone oil. A single crystal was
selected, mounted on a glass rod on a copper pin, and placed in the
cold N2 stream provided by an Oxford Cryosystems cryostream. XRD
data collection was performed for compounds 2a, 2b, 5, and 6 on a
Bruker APEX II diffractometer with use of an Incoatec microfocus
sealed tube with Mo Kα radiation (γ = 0.71073 Å) and a CCD area
detector. Empirical absorption corrections were applied using
SADABS or TWINABS.42,43 The structures were solved with use of
the intrinsic phasing option in SHELXT and refined by the full-matrix
least-squares procedures in SHELXL.44−46 The space group assign-
ments and structural solutions were evaluated using PLATON.47,48
Non-hydrogen atoms were refined anisotropically. All other hydrogen
atoms were located in calculated positions corresponding to standard
bond lengths and angles and refined using a riding model. Disorder as
observed for compounds 2a, 2b, and 5 was handled by modeling the
occupancies of the individual orientations using free variables to refine
the respective occupancies of the affected fragments (PART).49 In
some cases, the similarity SAME restraint, the similar-ADP restraint
SIMU, and the rigid-bond restraint DELU, as well as the constraints
EXYZ and EADP, were used in modeling disorder to make the ADP
values of the disordered atoms more reasonable. In some cases, the
distances between arbitrary atom pairs were restrained to possess the
same value using the SADI instruction, and in some cases, distance
restraints (DFIX) to certain target values were used. In some tough
cases of disorder, anisotropic Uij values of the atoms were restrained
(ISOR) to behave more isotropically. Disordered positions for the
coordinated ether in 2,4,6-tris(t-butyl)phenyl trimethylsilyl lithium
phosphanide 2a were refined using 70/30 split positions. Disordered
The purity of all reported compounds was established by the
absence of impurities, detected by NMR measurement for all nuclei
(1H, 13C, 29Si, 31P, and 119Sn NMR).
Computational Details. All calculations have been carried out
using the Gaussian09 program package38 on a computing cluster with
blade architecture. For all calculations except calculations of magnetic
shielding, the mPW1PW91 hybrid functional39 was used. Magnetic
shielding was calculated using the M06L40 pure functional as
implemented in Gaussian09. For optimizations and calculation of
frequencies, the basis set combination denoted by SDD as
implemented in Gaussian0938was used. For calculation of UV/vis
absorptions and NMR magnetic shielding, the all electron IGLO-II41
basis set was used. The magnetic shielding of H3P04 (σ31P = 624.7)
was used as reference.
1
NMR. H (300.2 MHz), 13C (75.5 MHz), 29Si (59.6 MHz), 119Sn
(111.8 MHz), and 31P (121.5 MHz) NMR spectra were recorded on a
H
DOI: 10.1021/acs.organomet.8b00258
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
positions for a SiMe3 group, a coordinated DME, and a methyl group
in a t-butyl group in compound [2,4,6-tris(t-butyl)phenyl trimethyl-
silyl potassium phosphanide]·DME 2b were refined using 50/50, 50/
50, and 55/45 split positions, respectively. In addition to poor crystal
quality for compound [HypP(SiMe3)K·DME] 5, resulting in high
RINT values and low bond precision, whole molecule disorder was
refined using 60/40 split positions. Despite multiple least-squares
refinement cycles, proper convergence of the refinement was not
achieved and attributed to poor crystal quality and not incorrect atom
assignments. All agostic interactions for presented compounds fall
within reported values27,50 and are based on a Cambridge Structural
Database search.51 CCDC 1838937−1838940 contain the supple-
mentary crystallographic data for compounds 2a, 2b, 5, and 6
respectively. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
(Me3Si)3Si), −0.53 ppm (1Si, d, JSiP = 78.9 Hz, Me3Si). 31P NMR
(C6D6, 293 K): δ −355.8 ppm.
Synthesis of [HypP(SiMe3)]2Sn 6. A solution of HypP(SiMe3)K·
DME (0.92 g, 1.91 mmol) in 6 mL of DME was cooled to −50 °C
and slowly added to a cooled (−50 °C) suspension of SnBr2 (0.27g,
0.96 mmol) in 10 mL of THF in a 100 mL Schlenk flask via cannula
under vigorous stirring. Upon addition, the reaction solution turned
to dark green. The reaction was allowed to warm up to room
temperature and was vigorously stirred for 16 h. After removal of
solvents under reduced pressure, the residue was dissolved in pentane
and filtered from salts. Crystals suitable for X-ray diffraction analysis
were obtained from pentane at −30 C. Yield: 0.72 g. 1H NMR (C6D6,
293 K): δ 0.35 ppm (27H, broad s, (Me3Si)3Si), 0.50 ppm (9H, d,
3JHP = 3.6 Hz, Me3Si). 13C NMR (C6D6, 293 K): δ 2.7 ppm (18C,
2
4
broad s, (Me3Si)3Si), 6.5 ppm (6C, dd, JCP = 7.2 Hz, JCP = 6.0 Hz,
Me3Si). 29Si NMR (C6D6, 293 K): δ −91.5 ppm (2Si, dd, 1JSiP = 79.6
3
2
Crystallographic data and details of measurements and refinement
for compounds 2a, 2b, 5, and 6 can be found in the Supporting
Information.
Hz, JSiP = 10.8 Hz, (Me3Si)3Si), −9.9 ppm (6Si, dd, JSiP = 5.0 Hz,
4JSiP = 3.8 Hz, (Me3Si)3Si), 6.1 ppm (2Si, dd, JSiP = 51.5 Hz, JSiP
=
=
1
3
5.0 Hz, Me3Si). P NMR (C6D6, 293 K): δ −104.9 ppm (1J
31
117SnP
1423 Hz, J SnP = 1486 Hz); 119Sn NMR (C6D6, 293 K): δ 1467 ppm
1
119
Synthesis. Synthesis of 2,4,6-Tris(t-butyl)phenyl Trimethylsilyl
Lithium Phosphanide 2a. 2,4,6-Tris(t-butyl)phenyl trimethylsilyl
phosphane (0.40 g, 1.14 mmol) was dissolved in 5 mL of THF. 0.82
mL of 1.6 M n-butyl lithium (1.15 eq, 1.31 mmol) in hexanes was
added dropwise at RT. The color of the reaction solution changed to
yellow, and the solution was stirred for an additional 2 h. After
evaporation of all volatile components, the solid residue was
redissolved in n-hexane. After 1 week at −30 °C, crystals suitable
for X-ray diffraction analysis can be isolated from this solution. Yield:
0.19 g, 42%. 1H NMR (C6D6, 293 K): δ 0.15 ppm (9H, d, SiMe3, 3JHP
= 3.9 Hz), 3.66 ppm (18H, o-t-Bu) 3.91 ppm (9H, p- t-Bu) 7.16 ppm
(2H, d, arom., 4JHP = 1.8 Hz). 13C NMR (C6D 6, 293 K): δ 4.33 ppm
(SiMe3, d, 2JCP = 12.8 Hz), 31.2 ppm (o-CMe3, d, 3JCP = 8.1 Hz), 33.3
1
117
( J
= 1486 Hz)
SnP
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00258.
S1_Bonds and angles 1: Selected bond lengths and
angles for presented and reference solid-state diphos-
phastannylene structures; S2_Bonds and angles 2:
Selected bond lengths and angles for presented
phosphanide structures 2a, 2b, 5; S3_Crystallographic
data: Data and details of measurements for compounds
2a, 2b, 5, 6; S4_DFT: mpw1pw91/sdd calculated data
of various conformers of diphosphastannylenes
ppm (o-CMe3, d, 4JCP = 8.8 Hz), 34.7 ppm (p-CMe ), 38.8 ppm (p-
3
2
CMe3), 118.7 ppm (arom., d, JCP = 3.7 Hz), 121.1 ppm (arom., d,
2JCP = 4.25 Hz), 149.8 ppm (arom.), 157.6 ppm (arom.). 29Si NMR
(C6D6, 293 K): δ 7.94 ppm (d, 1JSiP = 21.8 Hz). 31P NMR (C6D6, 293
K): δ −151.4 ppm.
Synthesis of [2,4,6-Tris(t-butyl)phenyl Trimethylsilyl Potassium
Phosphanide]·DME 2b. 2,4,6-Tris(t-butyl)phenyl bis-trimethylsilyl
phosphane (0.13 g, 0.28 mmol) was dissolved in 3 mL of DME. A
solution of 0.035 g (0.31 mmol) of KOtBu in 2 mL of DME was
added dropwise at RT. The colorless solution changed to yellow
immediately and was subsequently stirred for 2 h. After evaporation of
all volatile components, the residue was redissolved in n-hexane. After
1 week at −30 °C, crystals suitable for X-ray diffraction analysis could
(HypPR)2Sn and (Mes*PR)2Sn); S5_NMR: H, 31P,
1
29Si, 119Sn, and 13C NMR of presented compounds
reported in the Experimental section; S5_Crystallo-
graphic data: Data and details of measurements for
compounds 2a, 2b, 5, 6 (PDF)
1
be isolated from this solution. Yield: 0.11 g, 82%. H NMR (C6D6,
S7_DFT.xyz: Cartesian coordinates (.xyz) of all
investigated compounds (XYZ)
293 K): δ 0.24 ppm (9H, d, SiMe3, 3JHP = 3.6 Hz), 1.40 ppm (9H, p-t-
Bu), 1.99 ppm (18H, o- t-Bu), 3.00 ppm (4H, DME CH2), 7.11 ppm
(2H, broad s, arom.). 13C NMR (C6D6, 293 K): δ 4.0 ppm (SiMe3, d,
Accession Codes
3
2JCP = 13.4 Hz), 31.2 ppm (o-CMe3, d, JCP = 8.1 Hz), 33.4 ppm (o-
CCDC 1838937−1838940 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
4
CMe3, d, JCP = 8.8 Hz), 34.5 ppm (p-CMe ), 38.5 ppm (p-CMe3),
3
2
58.3 ppm (DME), 71.2 ppm (DME), 118.8 ppm (arom., d, J
=
CP
12.8 Hz), 118.9 ppm (arom.), 143.4 ppm (arom.), 156.0 ppm
(arom.). 29Si NMR (C6D6, 293 K): δ −0.83 ppm (d, 1JSiP = 58.4 Hz).
31P NMR (C6D6, 293 K): δ −143.1 ppm.
Synthesis of [HypP(SiMe3)K·DME] 5. HypP(SiMe3)2 (1.00 g, 2.4
mmol) and KOtBu (0.28 g, 2.5 mmol) were brought into a Schlenk
flask under inert atmosphere. Dissolution of the solid, colorless educts
in 6 mL of 1,2-dimethoxyethane (DME) at 0 °C led to an immediate
change of color to intense yellow. After the mixture was vigorously
stirred for 24 h, all volatile components were removed under reduced
pressure. The residue was redissolved in a mixture of pentane and
toluene. Crystals suitable for X-ray diffraction analysis were obtained
from this solution at −30 °C. Yield: 0.98 g, 87%. 1H NMR (C6D6, 293
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: elisabeth.schwarz@tugraz.at; Phone: +43 316 873
32101 (E.S.)
*E-mail: michaela.flock@tugraz.at; Phone: +43 316 873 32101
(M.F.)
K): δ 0.09 ppm (27H, s, (Me3Si)3Si), 0.17 ppm (9H, d, SiMe3, 3JHP
=
ORCID
3.6 Hz), 1.47 ppm (9H, p-t-Bu) 2.00 ppm (18H, o-t-Bu), 2.96 ppm
Elisabeth Schwarz: 0000-0002-9846-4107
Michaela Flock: 0000-0002-2799-1479
(6H, DME CH3), 3.00 ppm (4H, DME CH2). 13C NMR (C6D6, 293
3
K): δ 2.0 ppm (9C, d, JCP = 12.2 Hz, (Me3Si)3Si), 8.5 ppm (3C, d,
2JCP = 11.6 Hz, Me3Si). 29Si NMR (C6D6, 293 K): δ −94.8 ppm (Si, d,
Notes
2
1JSiP = 118.2 Hz, (Me3Si)3Si), −14.14 ppm (3Si, d, JSiP = 12.6 Hz
The authors declare no competing financial interest.
I
DOI: 10.1021/acs.organomet.8b00258
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(19) Mueller, S. K.; Weinberger, G.; Schwarz, E.; Torvisco, A.;
Dransfeld, A.; Fischer, R. C.; Hassler, K.; Flock, M. Synthesis and
Crystal Structures of Novel Silylsubstituted Diphosphanes. Inorg.
Chim. Acta 2014, 423, 517−523.
REFERENCES
■
(1) Arduengo, A. J.; Harlow, R. L.; Kline, M. A stable crystalline
carbene. J. Am. Chem. Soc. 1991, 113, 361−363.
(2) Martin, D.; Baceiredo, A.; Gornitzka, H.; Schoeller, W. W.;
Bertrand, G. A Stable P-Heterocyclic Carbene. Angew. Chem., Int. Ed.
2005, 44, 1700−1703.
(3) Hitchcock, P. B.; Lappert, M. F.; Misra, M. C. Homoleptic,
three-co-ordinate group 8c noble metal(0) complexes having GeII or
SnII ligands, [M{M′(NR2)2}3](M = Pd or Pt, M′= Ge or Sn, R =
SiMe3), and the X-ray structure of one of them (M = Pd, M′= Sn). J.
Chem. Soc., Chem. Commun. 1985, 0, 863−864.
(4) Veith, M. Cyclic Nitrogen Derivatives of Tetra- and Divalent
Tin. Angew. Chem., Int. Ed. Engl. 1975, 14, 263−264.
(5) Iovkova-Berends, L.; Seiger, M.; Westfeld, T.; Hoffmann, A.;
Herres-Pawlis, S.; Jurkschat, K. Extending the Family of N-
Heterocyclic Heavy Carbene Analogues: Synthesis and Crystal and
Molecular Structures of MeN[CH2C(O)N(R)]2Sn (R
Me2NCH2CH2, PhCH2, Me3CCH2). Eur. J. Inorg. Chem. 2013,
2013, 5836−5842.
(20) Bruckmann, J.; Kruger, C. Tris(n-butyl)phosphine, Tris(tert-
̈
butyl)phosphine and Tris(trimethylsilyl)phosphine. Acta Crystallogr.,
Sect. C: Cryst. Struct. Commun. 1995, 51, 1152.
(21) Bilbrey, J. A.; Kazez, A. H.; Locklin, J.; Allen, W. D. Exact
ligand cone angles. J. Comput. Chem. 2013, 34, 1189−1197.
(22) Immirzi, A.; Musco, A. A method to measure the size of
phosphorus ligands in coordination complexes. Inorg. Chim. Acta
1977, 25, L41−L42.
(23) Frey, G. D.; Lavallo, V.; Donnadieu, B.; Schoeller, W. W.;
Bertrand, G. Facile Splitting of Hydrogen and Ammonia by
Nucleophilic Activation at a Single Carbon Center. Science 2007,
316, 439−441.
(24) Protchenko, A. V.; Bates, J. I.; Saleh, L. M. A.; Blake, M. P.;
Schwarz, A. D.; Kolychev, E. L.; Thompson, A. L.; Jones, C.;
Mountford, P.; Aldridge, S. Enabling and Probing Oxidative Addition
and Reductive Elimination at a Group 14 Metal Center: Cleavage and
Functionalization of E-H Bonds by a Bis(boryl)stannylene. J. Am.
Chem. Soc. 2016, 138, 4555−4564.
(25) Paul, D.; Heins, F.; Krupski, S.; Hepp, A.; Daniliuc, C. G.;
Klahr, K.; Neugebauer, J.; Glorius, F.; Hahn, F. E. Synthesis and
Reactivity of Intramolecularly NHC-Stabilized Germylenes and
Stannylenes. Organometallics 2017, 36, 1001−1008.
=
(6) Izod, K.; Rayner, D. G.; El-Hamruni, S. M.; Harrington, R. W.;
Baisch, U. Stabilization of a Diphosphagermylene through p-p
Interactions with a Trigonal-Planar Phosphorus Center. Angew.
Chem., Int. Ed. 2014, 53, 3636−3640.
́
(7) Kapp, J.; Schade, C.; El-Nahas, A. M.; von Rague Schleyer, P.
̈
Die π-Donorfahigkeit schwerer Elemente ist nicht geringer. Angew.
Chem. 1996, 108, 2373−2376.
(26) Yoshifuji, M. Sterically protected organophosphorus com-
pounds of unusual structures. Pure Appl. Chem. 2017, 89, 281−286.
(27) Scherer, W.; Sirsch, P.; Shorokhov, D.; McGrady, G. S.; Mason,
S. A.; Gardiner, M. G. Valence-Shell Charge Concentrations and
Electron Delocalization in Alkyllithium Complexes: Negative Hyper-
conjugation and Agostic Bonding. Chem. - Eur. J. 2002, 8, 2324−
2334.
(8) du Mont, W.-W.; Kroth, H.-J. Dimeric Bis(di-tert-
butylphosphino)stannanediyl: A Cyclic Phosphorus-Tin Ylide.
Angew. Chem., Int. Ed. Engl. 1977, 16, 792−793.
(9) Goel, S. C.; Chiang, M. Y.; Rauscher, D. J.; Buhro, W. E.
Comparing the properties of homologous phosphido and amido
complexes: synthesis and characterization of the disilylphosphido
complexes {M[P(SiMe3)2]2}2 where M = zinc, cadmium, mercury,
tin, lead and manganese. J. Am. Chem. Soc. 1993, 115, 160−169.
(10) Driess, M.; Janoschek, R.; Pritzkow, H.; Rell, S.; Winkler, U.
Diphosphanyl- and Diarsanyl-Substituted Carbene Homologues:
Germanediyls, Stannanediyls, and Plumbanediyls with Remarkable
Electronic Structures. Angew. Chem., Int. Ed. Engl. 1995, 34, 1614−
1616.
(28) Hey, E.; Raston, C. L.; Skelton, B. W.; White, A. H. J.
Organomet. Chem. 1989, 362, 1−10.
(29) Isenberg, S.; Frenzel, L.-M.; Bruhn, C.; Pietschnig, R.
Metallated [3]Ferrocenophanes Containing P3M Bridges (M = Li,
Na, K). Inorganics 2018, 6, 67.
(30) Sasaki, S.; Yoshifuji, M.; Inamoto, N. Reaction of lithium
(2,4,6-tri-tert-butylphenyl)silylphosphides with haloforms. Arkivoc
2012, ii, 15−23.
̈
(11) Westerhausen, M.; Digeser, M. H.; Noth, H.; Ponikwar, W.;
Seifert, T.; Polborn, K. 2,5-Diphenyl-3,4-bis(trimethylsilyl)-1-phos-
phacyclopentadienide as a Ligand at Calcium, Strontium, and Tin(II).
Inorg. Chem. 1999, 38, 3207−3214.
(12) Brym, M.; Francis, M. D.; Jin, G.; Jones, C.; Mills, D. P.; Stasch,
A. Facile Transformations of a 1,3,5-Triphosphacyclohexadienyl
Anion within the Coordination Sphere of Group 13 and 14 Elements:
Synthesis of 1,3-Diphosphacyclopentadienyl Complexes and Phos-
phaorganometallic Cage Compounds. Organometallics 2006, 25,
4799−4807.
(13) Rivard, E.; Sutton, A. D.; Fettinger, J. C.; Power, P. P. Synthesis
of the sterically congested diarylphosphines and and the monomeric
Sn(II)-diphosphide. Inorg. Chim. Acta 2007, 360, 1278−1286.
(14) Izod, K.; McFarlane, W.; Allen, B.; Clegg, W.; Harrington, R.
W. An Intramolecularly Base-Stabilized Diphosphagermylene and
Two Unusual Germanium(II) Ate Complexes: A Structural, NMR,
(31) Cowley, A.; Newman, T. Reaction of (Tri(trimethylsilyl)silyl)
lithium with Halophosphines. A Novel Silicon-Halogen Exchange
Reaction. Organometallics 1982, 1, 1412−1413.
̈
(32) Westerhausen, M.; Krofta, M.; Wiberg, N.; Knizek, J.; Noth, H.;
Pfitzner, A. Tetrazinn(II)-und Bariumtrizinn(II)-tetrakis[μ3-tri-ter/-
butyIsilylphosphan-diid]-Verbindungen mit einem Tetrametallatetra-
phosphacuban-Geru
1489−1493.
̈
st. Z. Naturforsch., B: J. Chem. Sci. 1998, 53,
(33) McPartlin, M.; Melen, R.; Naseri, V.; Wright, D. Formation and
Rearrangement of SnII Phosphanediide Cages. Chem. - Eur. J. 2010,
16, 8854−8860.
(34) Kargin, D.; Kelemen, Z.; Krekic, K.; Maurer, M.; Bruhn, C.;
Nyulaszi, L.; Pietschnig, R. [3]Ferrocenophanes with the bi-
sphosphanotetryl bridge: inorganic rings on the way to tetrylenes.
Dalton Trans. 2016, 45, 2180−2189.
and DFT Study. Organometallics 2005, 24, 2157−2167.
̌
(35) Hengge, E.; Pletka, H. D.; Hoefler, F. Preparation and
properties of amino disilanes. Monatsh. Chem. 1970, 101, 325.
(36) Nief, D.; Mercier, F.; Mathey, F. Reactions of (phosphine)-
pentacarbonyltungsten.Synthesis of primary and secondary phos-
phines in the coordination sphere of tungsten. J. Organomet. Chem.
1987, 328, 349−355.
̌
́
̊
̌
̌
(15) Reznícek, T.; Dostal, L.; Ruzicka, A.; Jambor, R. Diphosphas-
tannylenes: Precursors for Phosphorus-Phosphorus Coupling? Eur. J.
Inorg. Chem. 2012, 2012, 2983−2987.
(16) Izod, K.; Evans, P.; Waddell, P. G.; Probert, M. R. Remote
Substituent Effects on the Structures and Stabilities of P = E π-
Stabilized Diphosphatetrylenes (R2P)2E (E = Ge, Sn). Inorg. Chem.
2016, 55, 10510−10522.
̈
(37) Westerhausen, M.; Rotter, T.; Gorls, H.; Birg, C.; Warchhold,
̈
M.; Noth, H. Lithium Bis(triisopropylsilyl)phosphanide and its
(17) Kira, M.; Ishida, S.; Iwamoto, T.; Kabuto, C. The First Isolable
Dialkylsilylene. J. Am. Chem. Soc. 1999, 121, 9722−9723.
(18) Cappello, V.; Baumgartner, J.; Dransfeld, A.; Hassler, K.
Monophosphanes and Diphosphanes with the Hypersilyl Substituent.
Eur. J. Inorg. Chem. 2006, 2006, 4589−4599.
Pentacarbonyltungsten Adduct: Synthesis and Crystal Structures of
the Dimer [(thf)Li-P(SiiPr3)2]2 and the Solvent-Separated Ion Pair
[(thf)4Li]+ [(OC)5W-P(SiiPr3)2]−. Z. Naturforsch., B: J. Chem. Sci.
2005, 60, 766.
J
DOI: 10.1021/acs.organomet.8b00258
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(38) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.;
Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.;
Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.;
Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi,
R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar,
S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox,
J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.;
Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A.
D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J.
Gaussian 09, revision E.01; Gaussian, Inc.: Wallingford, CT, 2009.
(39) Adamo, C.; Barone, V. Exchange functionals with improved
long-range behavior and adiabatic connection methods without
adjustable parameters: The mPW and mPW1PW models. J. Chem.
Phys. 1998, 108, 664.
(40) Zhao, Y.; Truhlar, D. G. A new local density functional for
main-group thermochemistry, transition metal bonding, thermochem-
ical kinetics, and noncovalent interactions. J. Chem. Phys. 2006, 125,
194101.
(41) Kutzelnigg, W.; Fleischer, U.; Schindler, M. Deuterium and Shift
Calculation; NMR Basic Principles and Progress; Springer, 1991; Vol.
23; p 165.
(42) Bruker APEX2 and SAINT; Bruker AXS Inc.: Madison,
Wisconsin, USA, 2012.
(43) Blessing, R. H. An empirical correction for absorption
anisotropy. Acta Crystallogr., Sect. A: Found. Crystallogr. 1995, 51,
33−38.
(44) Sheldrick, G. M. Phase annealing in SHELX-90: direct methods
for larger structures. Acta Crystallogr., Sect. A: Found. Crystallogr. 1990,
46, 467−473.
(45) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr.,
Sect. A: Found. Crystallogr. 2008, 64, 112−122.
(46) Sheldrick, G. M. SHELXT − Integrated space-group and
crystal-structure determination. Acta Crystallogr., Sect. A: Found. Adv.
2015, 71, 3−8.
(47) Spek, A. L. Structure validation in chemical crystallography.
Acta Crystallogr., Sect. D: Biol. Crystallogr. 2009, 65, 148−155.
(48) Spek, A. L. Single-crystal structure validation with the program
PLATON. J. Appl. Crystallogr. 2003, 36, 7−13.
(49) Muller, P.; Herbst-Irmer, R.; Spek, A. L.; Schneider, T. R.;
̈
Sawaya, M. R. Crystal Structure Refinement: A Crystallographer’s Guide
to SHELXL; Oxford University Press, 2006.
(50) Torvisco, A.; Decker, K.; Uhlig, F.; Ruhlandt-Senge, K. Heavy
Alkali Metal Amides: Role of Secondary Interactions in Metal
Stabilization. Inorg. Chem. 2009, 48, 11459−11465.
(51) Allen, F. H. The Cambridge Structural Database: a quarter of a
million crystal structures and rising. Acta Crystallogr., Sect. B: Struct.
Sci. 2002, 58, 380−388.
K
DOI: 10.1021/acs.organomet.8b00258
Organometallics XXXX, XXX, XXX−XXX