A donor-stabilized zwitterionic half-parent phosphasilene and its unusual reactivity towards small molecules

Article abstract of DOI:10.1002/chem.201303906

The stabilization of the labile, zwitterionic half-parent phosphasilene 4 LSi-PH (L=CH[(C=CH₂)CMe(NAr)₂]; Ar=2,6-iPr ₂C₆H₃) could now be accomplished by coordination with two different donor ligands (4-dimethylaminopyridine (DMAP) and 1,3,4,5-tetramethylimidazol-2-ylidene), affording the adducts 8 and 9, respectively. The DMAP-stabilized zwitterionic half-parent phosphasilene 8 is capable of transferring the elusive parent phosphinidene moiety (:PH) to an unsaturated organic substrate, in analogy to the free phosphasilene 4. Furthermore, compounds 4 and 8 show an unusual reactivity of the Si=P moiety towards small molecules. They are capable of adding dimethylzinc and of activating the S-H bonds in H₂S and the N-H bonds in ammonia and several organoamines. Interestingly, the DMAP donor ligand of 8 has the propensity to act as a leaving group at the phosphasilene during the reaction. Accordingly, treatment of 8 with H₂S affords, under liberation of DMAP, the unprecedented thiosilanoic phosphane LSi=S(PH₂) 16 (L=HC(CMe[2,6-iPr₂C₆H₃N])₂). Compounds 4 and 8 react with ammonia both affording LSi(NH₂)PH ₂ 17, respectively.

Full text of DOI:10.1002/chem.201303906

DOI: 10.1002/chem.201303906
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&
Silicon–Phosphorus Chemistry
A Donor-Stabilized Zwitterionic “Half-Parent” Phosphasilene and
Its Unusual Reactivity towards Small Molecules
Kerstin Hansen,[a] Tibor Szilvꢀsi,[b] Burgert Blom,[a] Elisabeth Irran,[a] and Matthias Driess*[a]
Dedicated to Professor Peter Hildebrandt
Abstract: The stabilization of the labile, zwitterionic “half-
parent” phosphasilene 4 L’Si=PH (L’=CH[(C=CH2)CMe(NAr)2];
Ar=2,6-iPr2C6H3) could now be accomplished by coordina-
tion with two different donor ligands (4-dimethylaminopyri-
dine (DMAP) and 1,3,4,5-tetramethylimidazol-2-ylidene), af-
fording the adducts 8 and 9, respectively. The DMAP-stabi-
lized zwitterionic “half-parent” phosphasilene 8 is capable of
transferring the elusive parent phosphinidene moiety (DPH)
to an unsaturated organic substrate, in analogy to the “free”
phosphasilene 4. Furthermore, compounds 4 and 8 show an
unusual reactivity of the Si=P moiety towards small mole-
cules. They are capable of adding dimethylzinc and of acti-
vating the SꢀH bonds in H2S and the NꢀH bonds in ammo-
nia and several organoamines. Interestingly, the DMAP
donor ligand of 8 has the propensity to act as a leaving
group at the phosphasilene during the reaction. Accordingly,
treatment of 8 with H2S affords, under liberation of DMAP,
the unprecedented thiosilanoic phosphane LSi=S(PH2) 16
(L=HC(CMe[2,6-iPr2C6H3N])2). Compounds 4 and 8 react with
ammonia both affording L’Si(NH2)PH2 17, respectively. In ad-
dition, the reaction of 8 with isoproylamine, p-toluidine, and
pentafluorophenylhydrazine lead to the corresponding
phosphanylsilanes L’Si(PH2)NHR (R=iPr 18a; R=C6H5ꢀCH3
18b, R=NH(C6F5) 18c), respectively.
Introduction
age of donor–acceptor effects and/or steric congestion
through the presence of bulky substituents.
Spectroscopic evidence for the first phosphasilene 1 bearing
a Si=P functional group with bulky aryl substituents at the
phosphorus and silicon atoms (Scheme 1) was reported nearly
30 years ago by Bickelhaupt et al.[1] Since this landmark discov-
ery, it took almost a decade for the first isolation of a crystalline
phosphasilene, which was reported by Niecke et al.[2] Since
then, only a few other structurally characterized compounds
featuring a silicon–phosphorus double bond could be realiz-
ed,[3,4] representing heteroatomic Si=P species that break the
“double-bond rule”.[5,6] Unlike the Si=Si bond in disilenes, the
Si=P functional group with three-coordinate silicon and two-
coordinate phosphorus is slightly polar due to the higher elec-
tronegativity of phosphorus versus silicon.[7,8] Nevertheless, the
highly reactive Si=P bond can be stabilized by taking advant-
Comparisons between the parent phosphasilenes H2Si=PH
and H2Si=P(SiH3), on the basis of computations, show that the
SiꢀP p-bond strength in the latter compound is increased and
the SiꢀP bond length is shortened by hyperconjugation effects
due to the silyl substituent at phosphorus.[9] The latter strong
influence of a silyl substituent could be experimentally verified
by us.[4,9,10] In addition, the pronounced s-donor ability of the
silyl group at the phosphorus atom causes a large shielding
effect for the 31P nucleus, while the divalent 29Si atom is de-
shielded. Thermodynamic stabilization of a Si=P system could
[a] K. Hansen, Dr. B. Blom, Dr. E. Irran, Prof. Dr. M. Driess
Department of Chemistry
Metalorganics and Inorganic Materials
Technische Universitꢀt Berlin
Strasse des 17. Juni 135, Sekr. C2
10623 Berlin (Germany)
Fax: (+49)30-314-29734
E-mail: matthias.driess@tu-berlin.de
[b] T. Szilvꢁsi
Department of Inorganic and Analytical Chemistry
Budapest University of Technology and Economics
Szent Gellꢂrt tꢂr 4, 1111 Budapest (Hungary)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201303906.
Scheme 1. Some examples of isolable phosphasilenes.
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also be accomplished by employing intramolecular donor co-
ordination of an amino group at the sp2-silicon center, as
shown in 1991 by Corriu et al.[11] Due to the large shielding of
the respective 31P and 29Si nuclei in the NMR spectra, the latter
phosphasilene is better described by a l4-Si+ꢀPꢀ betaine reso-
nance structure. In contrast, a “push–pull” phosphasilene with
electron-donating silyl groups on the low-coordinate (l3) sili-
con atom and electron-accepting aryl groups at the phospho-
rus reported by Sekiguchi et al.[12] does not show a reverse po-
larization of the Si=P double bond,[13] but instead both nuclei
are extremely deshielded resulting from a paramagnetic contri-
bution.[14] To gain insights into the electronic properties of con-
jugated Si=P functional group, Tamao et al. investigated
a series of p-conjugated phosphasilenes and they established,
on the basis of UV/Vis spectroscopy, that a Si=P moiety can
conjugate with carbon p-electron systems.[15] Interestingly,
these systems bearing the bulky Eind group (Eind=
1,1,3,3,5,5,7,7,-octaethyl-s-hydrindacen-4-yl) are even stable in
air for months in the solid state. It appeared that the steric
protection of l3-coordinate silicon is more important than that
of l2-coordinate phosphorus.[7] Proof for this assertion was re-
ported in 2006 by our group, when the first “half-parent” phos-
phasilenes 3 bearing a PH group was synthesized, which is sta-
bilized by n(P)!s*(SiꢀSi) hyperconjugation.[16] Besides, “half-
parent” phosphasilenes bearing a naked PH moiety, a phospha-
silene bearing a hydride ligand and an amino group on the sili-
con atom, which is stable with or without a coordinated N-het-
erocyclic carbene (NHC) at the silicon center, also exists. The
amino group in this compound is responsible for a substantial
NꢀSiꢀP p-conjugation and concomitant stabilization.[17] One of
the N-donor-stabilized phosphasilenes, compound 2[18,19] with
a low-valent, l4-coordinate silicon atom, was synthesized in
2011 by some of us and Inoue et al.[19] in which an N!Si
donor coordination favors a strong polarization of the Si=P p-
bond and leads to a predominant ylide-like Si+ꢀPꢀ character.
Even more recently, we reported a combination of these latter
described compounds: the zwitterionic, ylide-like “half-parent”
phosphasilene 4,[20] bearing a low-valent, l3-coordinated Si
atom (Scheme 1), which is fragile in solutions at room temper-
ature and undergoes homolytic cleavage to form “free” silylene
L’SiD 5 (L’=CH[(C=CH2)CMe(NAr)2]; Ar=2,6-iPr2C6H3) and parent
phosphinidene (DPH); the latter of which undergoes oligomeri-
zation to (PH)n clusters. In the presence of an NHC as a DPH
trapping agent, however, it was shown that 4 in fact acts as
a transfer reagent of the DPH moiety resulting in the formation
of a phosphaalkene bearing a terminal PH group, again with
concomitant formation of 5.
example of the oxidative addition of ammonia by a transition-
metal complex was published only a few years ago by Hartwig
et al. Thereby, an iridium(I) pincer complex inserts into an NꢀH
bond of ammonia, affording a stable monomeric amido hy-
dride complex.[38] A recent example of NꢀH bond activation in
ammonia by iridium and rhodium complexes was reported by
Oro et al.[52] Low-valent main-group elements are also capable
of activating NꢀH and SꢀH bonds, as shown for the first time
in 2007 by Bertrand et al.[41] In 2009 and 2010, respectively, sev-
eral N-heterocyclic silicon-containing compounds, which could
activate NꢀH and/or SꢀH bonds, were reported.[21,22,46,55] For
example, the zwitterionic N-heterocyclic silylene (NHSi) 5 un-
dergoes the addition of ammonia affording the 1,1-insertion
product 6a. Compound 5 is also capable of activating the
more Brønsted acidic heavier group 15 hydrides EH3 (E=P,
As).[56] In analogy to ammonia, phosphane engages in a 1,1-ad-
dition over the l3-Si center. In contrast, the reaction of AsH3
with 5 yields the donor-stabilized arsasilene 6c. Moreover, the
reaction of 5 with H2S gas results in the formation of the
donor-stabilized silathioformamide 7 (Scheme 2).[21,24,57]
Scheme 2. Reaction of the silylene 5 toward EH3 and H2S (E=N, P, As).
Herein, we report the stabilization of the labile zwitterionic
“half-parent” phosphasilene 4 by filling the formally empty 3p-
orbital of the l3 silicon center with electron density with the
aid of DMAP and a small NHC donor (1,3,4,5-tetramethylimida-
zol-2-ylidene). Furthermore, we describe the unusual reactivity
of these adducts of 4 towards a variety of small molecules:
ZnMe2, H2S, NH3, iPrNH2, H2N(C6H4)(CH3), and H2NNH(C6F5),
which is very different to that of 4 and other isolable phospha-
silenes.
Results and Discussion
The highly ylidic but nevertheless surprisingly fragile phospha-
silene 4 with two essentially localized lone pairs residing on
the phosphorus atom could be described as an adduct of the
silylene 5 and the parent phosphinidene with an empty 3p or-
bital at the l3-coordinate Si atom.[20] Therefore, it seemed rea-
sonable to fill this empty 3p orbital at silicon with electron
density and thereby stabilize this otherwise coordinatively un-
saturated molecule. In fact, stabilization of the labile phospha-
silene 4 could be accomplished by using the two different
donor ligands 4-dimethylaminopyridine (DMAP) and 1,3,4,5-tet-
Within our ongoing research program focusing on small-
molecule bond-activation reactions, mediated by low-valent sil-
icon species,[21–26] we became interested in potentially stabiliz-
ing 4 and exploring its reactivity towards small molecules with
a view of potentially uncovering new and useful reactivity pat-
terns through donor–acceptor stabilization of 4.
The activation of small molecules, particularly that of the Nꢀ ramethylimidazol-2-ylidene (Me4ꢀNHC). In both reactions, com-
H- and SꢀH-containing compounds has been a topic of orga-
noelement chemistry due to the potential of generating new
organic and/or pharmaceutical compounds.[21,22,27–54] The first
pound 4 was synthesized in situ in Et2O according to the litera-
ture procedure[20] and extracted with toluene at which time
one of these two ligands were added at low temperature af-
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free phosphasilene 4, in accordance with expectations. The 31P
chemical shifts of 9 (d(31P)=ꢀ259.8 ppm) is shifted to low
field, whereas that of compound 8 (d(31P)=ꢀ331.9 ppm) is
shifted to high field compared with the resonance of 4 d(31P)=
ꢀ293.9 ppm. The explanation of this phenomenon could be
that the Me4ꢀNHC is a better p-acceptor than DMAP and this
1
trend is in addition reflected in the H NMR spectrum for the
1
proton at the phosphorus atom. According to this, the J(Si,P)
Scheme 3. Synthesis of the donor-stabilized phosphasilenes 8 and 9.
coupling constant of 9 is smaller than that of 8 and they are
1
even smaller still in compound 4 because the J coupling con-
fording the desired new Si=P adducts 8 and 9, respectively,
isolated in low to moderate yields (Scheme 3).
stants are proportional to the s character in the bonding
(Table 1).[59]
Compounds 8 and 9 were isolated as yellow solids and char-
acterized by NMR spectroscopy, high-resolution electrospray
ionization mass spectrometry (HR-ESI-MS) or electron impact
mass spectrometry (EI-MS) and elemental analysis, IR spectros-
copy, and by single-crystal X-ray diffraction (XRD)
analysis. Compared with 4, the stabilized phosphasi-
lenes 8 and 9 are insoluble in n-hexane. Surprisingly,
compound 8 is also insoluble in benzene but slightly
soluble in toluene and well soluble in THF. Com-
pound 9 is only slightly soluble in benzene, toluene,
and THF. Strikingly, in contrast to the highly labile
compound 4, compounds 8 and 9 are perfectly
stable in solution at room temperature for several
months. Even after heating 8 for several hours at
608C in THF, no decomposition occurs. However,
after heating compound 9 for 4 h at 508C and 2 h at
708C in C6D6, 20% of the ligand LH (L=HC(CMe[2,6-
iPr2C6H3N])2) is generated as a decomposition prod-
uct. Despite the stabilization with the donor ligands,
the compounds 8 and 9 are air sensitive and on con-
tact with air turn colorless. The 29Si signals of 8 and 9
are shifted considerably to higher field (Dd=93.1 to
108.5 ppm) in comparison with 4 (Table 1) but are in
The molecular structures of 8 and 9 were confirmed by
using single-crystal XRD analysis[60] (Figure 1). The atoms of the
C3N2 backbone of 8 and 9 are nearly co-planar, which is
a common feature of this ligand. In comparison with the
Figure 1. ORTEP representation of the molecular structure of 8 (left) and 9 (right); ther-
mal ellipsoids are shown with 50% probability; hydrogen atoms are omitted for clarity,
except those of C1, C3, C5, and P1). Selected distances (pm) and angles (deg) of 8: Si1–
P1, 212.05(1); Si1–N1, 174.82(1); Si1–N2,175.51(1); Si1–N3, 188.07(1); C1–C2, 138.76(1);
C4–C5, 145.22(1); N1-Si1-N2, 102.5(1); N1-Si1-N3, 104.1(1); N2-Si1-N3, 100.9(1). Selected
distances (pm) and angles (deg) of 9: Si1–P1, 214.31(10); Si1–N1, 176.4(2); Si1–N2,
177.0(2); Si1–C30, 197.0(3); C1–C2, 137.8(4); C4–C5, 146.8(4); N1-Si1-N2, 100.81(12); N1-
Si1-C30, 105.58(11); N2-Si1-C30, 106.15(12).
the same range as the Me4ꢀNHC!5 (d(29Si)=
ꢀ12.0 ppm) and dmap!5 (d(29Si)=37.4 ppm) ad-
ducts, synthesized in our group.[46,58] This indicates
that the formally empty 3p orbital of the silicon
center is filled with electron density and the silicon
atom is more shielded in comparison with the donor-
“naked” phosphasilene 4, in which the silicon atom adopts
a trigonal-planar coordination geometry, the silicon centers of
Table 1. Selected NMR data of 4, 8, and 9.
both complexes 8 and 9 are coordinated in a distorted-tetrahe-
dral fashion and they are out of the mean plane of the ligand
backbone by 34.8 (8) and 20.1 pm (9), respectively. The angle
between the plane of the DMAP and the ligand backbone
plane in 8 is about 101.38, whereas the Me4ꢀNHC plane is
nearly perpendicular to the ligand backbone plane (938). The
SiꢀP bond lengths in 8 (212.05(1) pm) and 9 (214.31(10) pm)
are slightly longer (2.4% for 8 and 3.5% for 9) than in the
phosphasilene 4 (207.12(10) pm) corresponding to the differ-
ent degrees of polarization in the SiꢀP bond in these three
phosphasilenes. The SiꢀC30(carbene) distance of 197.0(3) pm
in 9 is significantly longer than the typical SiꢀC single bond
NMR data
4[a]
8[b]
9[b]
1H (PH)
[d, ppm]
31P
[d, ppm]
1J(P,H)
[Hz]
29Si{1H}
[d, ppm]
1J(Si,P)
[Hz]
ꢀ0.66
ꢀ2.62
ꢀ1.55
ꢀ293.9
143.0
101.5
186.4
ꢀ331.7
144.1
8.4
ꢀ259.8
144.1
ꢀ7.0[c]
116.4
131.8
[a] [D6]C6H6, 258C. [b] [D8]THF, 258C. [c] C6H5F, lock capillary: [D6]C6H6,
258C.
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Figure 3. HOMO (left) and HOMO-8 (right) of 9.
Figure 2. HOMO (left) and HOMO-8 (right) of 8.
length in organosilanes (187 pm) but similar to the SiꢀC dis-
4, the Si and P atoms contribute equally to the s-bond
tance (201.6(3) pm) of the Me4ꢀNHC!5 adduct.[58] The Siꢀ (50.00%),[20] whereas in 8 and 9 the contribution of the phos-
N3(DMAP) bond length of 188.08(1) pm is almost 7% longer
phorus atom is 54.78 and 56.00%, respectively. In Figures 2
than the SiꢀN1 and SiꢀN2 bond lengths of the ligand. Howev-
and 3, the HOMO-8’s illustrate these SiꢀP s-bonds, with an in-
er, the SiꢀN3 bond length in 8 is much shorter than that of Siꢀ teraction of the hydrogen atom and the lone pair of the phos-
N3 in the dmap!5 adduct (200.5(2) pm),[46] indicating a stron-
ger interaction of the PꢀSiꢀN3 subunit in 8.
phorus, whereas the HOMOs represent the phosphinidene–sily-
lene character.
DFT calculations at the B97-D/cc-pVTZ(PCM=Benzene)//B97-
D/6-31G* level of theory reveals that the formation of 8 and 9
are thermodynamically favored by DG=ꢀ11.3 kcalmolꢀ1 and
ꢀ20.0 kcalmolꢀ1, respectively. Natural Bond Orbital (NBO) and
Wiberg Bond Index (WBI) analyses show the change of the
electronic structure of the Si=P subunit in 8 and 9 in compari-
son with the “donor-free” phosphasilene 4. As a consequence
of the electron donation of DMAP and Me4ꢀNHC, the weak
double-bond character of 4[20] (WBI of Si=P in 4 is 1.68) is com-
pletely eliminated and only the phosphinidene–silylene charac-
ter remains. NBO analysis[60] indicated only one s-type bond
between the Si and P atoms,
Due to the fact that the phosphasilene 4 is able to transfer
the PH moiety to a bulky NHC,[20] we were interested if the sta-
bilized phosphasilenes (8 and 9) could still act as a PH transfer
agent. DFT studies revealed that the formation of the phos-
phaalkene is thermodynamically slightly favorable by DG=
ꢀ3.2 and ꢀ4.6 kcalmolꢀ1, respectively, but the Gibbs free
energy of the transition states TSa and TSb are as expected to
be much higher (Scheme 4). Therefore, harsher reaction condi-
tions are required to obtain the desired phosphaalkene 12 by
using 8 or 9 as a starting material. This was corroborated ex-
perimentally: After heating a solution of 8 and 10 in toluene
which corresponded to the don-
ation of the lone pair of the sily-
lene moiety 5 to the phosphini-
dene moiety, and two lone pairs
on the P atom both in the case
of 8 and 9. WBIs suggest the
same conclusion. In the DMAP-
containing compound 8, the
WBI of the SiꢀP bond is 1.44,
whereas in the stronger s-donor
Me4ꢀNHC-substituted
com-
pound 9, the WBI of the SiꢀP
bond is even lower (1.34). These
bond indices are also reflected
in SiꢀP distances of 8 and 9 (see
above). NBO analysis also reveals
that the s-donor ability of the si-
lylene moiety is enhanced by
the donation of DMAP and Me4ꢀ
NHC and therefore the s-bond is
Scheme 4. Left: [DPH]-Transfer from the phosphasilenes 4, 8, and 9 to the NHC carbene center of 10 to give,
under liberation of 5, 11, and 13, the phosphaalkene 12, respectively. Right: Calculated Gibbs free energy of these
polarized toward the P atom. In reactions. Ar=2,6-diisopropylphenyl; TSa, 11: D=DMAP; TSb, 13: D=Me4ꢀNHC.
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for 5 h at 908C, almost complete conversion to 12 was ob-
served.1 Unfortunately, due to these harsh reaction conditions
the obtained product 11 could not be observed and decom-
poses into free ligand LH (L=HC(CMe[2,6-iPr2C6H3N])2). Never-
theless, the stabilized phosphasilene 8 can act as a PH transfer
agent, in analogy to 4.
To compare the reactivity of 4 to the “half-parent” phospha-
silene 3, we carried out the reactions of 4 with ZnMe2 in pres-
ence of N,N,N’,N’-tetramethylethylenediamine (TMEDA). The
ylide-like structure of 4 favors the 1,2-addition product 14, in
contrast to the analogous reaction with 3, affording the P-zin-
cophosphasilene 15 (Scheme 5).[16] The reaction of the DMAP-
Figure 4. ORTEP representation of the molecular structure of 14 (thermal el-
lipsoids show 50% probability; hydrogen atoms are omitted for clarity,
except those of C1, C3, C5, and P1). Selected distances (pm) and angles
(deg) of 14: Si1–P1, 220.22(1); Si1–N1, 175.62(1); Si1–N2, 177.03(1); Si1–C30,
186.99(1); Zn1–C31, 199.02(1); P1–Zn1: 236.70(2), C1–C2, 135.5(6); C4–C5,
149.7(5); N1-Si1-N2, 106.5(1); N1-Si1-C30, 107.24(17); N2-Si1-C30, 107.99(18);
Si1-P1-Zn1, 106.66(6).
only the [MꢀTMEDAꢀZnMe+2H]+ peak was observed, most
likely due to the lability of the PꢀZn bond.
The reaction of 8 with one equiv of H2S gas at low tempera-
ture resulted in the selective formation of the donor-stabilized
Scheme 5. 1,2-Addition of dimethylzinc to the Si=P bond of 4 to give 14
versus the analogous reaction of 3 with dimethylzinc, affording the P-metal-
lated phosphasilene 15.
thiosilanoic phosphane 16 in analogy to compound
7
(Scheme 2 and 6).[21] The protons of H2S undergo a 1,5-addition
stabilized phosphasilene 8 with ZnMe2 and TMEDA affords the
same product 14 but only with a prolonged reaction time,
which is required for the full conversion. Accordingly, DMAP
has the propensity to be eliminated at the phosphasilene
during the reaction as supported by results of DFT calculations
(see the Supporting Information, Figure S16). The 31P NMR
spectrum of 14 reveals a doublet at d=ꢀ303.4 ppm (1J(P,H)=
173.1 Hz), whereas the 29Si signal at d=7.5 ppm is also split
into a doublet (1J(Si,P)=29.8 Hz). This small 1J(Si,P) coupling
constant is typical for SiꢀP single bonds[9] and indicates that
both Si and P are coordinatively saturated. Suitable crystals of
14 for single-crystal XRD analysis[60] were obtained from a con-
centrated n-hexane solution upon storage at ꢀ308C for several
days (Figure 4). The Si center exhibits a distorted tetrahedral
coordination geometry. The methyl group at the silicon atom
is positioned nearly orthogonal to the plane defined by the
ligand backbone. The SiꢀP distance of 220.22(1) pm is 6.3%
longer then the Si=P bond in 4 and is in the characteristic
range of a SiꢀP bond.[61] The Zn atom is coordinated in a dis-
torted-tetrahedral fashion and the value of the PꢀZn bond
length of 236.70(2) pm is typical for that of zincophospha-
nides.[16,62] Attempts to observe the [M+H]+ peak in the HR-ESI
spectra were unsuccessful despite several attempts. Instead,
Scheme 6. Synthesis of the first thiosilanoic phosphane 16.
over the phosphasilene and protonate the methylene group of
1
the backbone ligand. In the H NMR spectrum, the characteris-
tic signals of the exocyclic methylene groups disappeared and
only one singlet at d=1.53 ppm, corresponding to six chemi-
cally equivalent protons is observed. In the 31P NMR spectrum,
a triplet resonance signal with 29Si satellites at d=ꢀ221.2 ppm
(1J(P,H)=191.7 Hz) is observed, which is less shielded com-
pared with 4 and 5. The doublet of the 29Si chemical shift at
d=ꢀ4.0 ppm (1J(Si,P)=15.0 Hz) is in the same range as with 7
(d(29Si)=16.8 ppm).[21] The molecular structure of 16 could be
elucidated by single-crystal XRD analysis[60] (Figure 5). The
bond lengths of C1ꢀC2=1.5063(1) and C4ꢀC5=1.4996(1)pm
additionally prove that the exocyclic methylene group of 8 is
converted into a methyl group in 16. The silicon atom has
a distorted tetrahedral coordination geometry and is out of
the ligand backbone plane by 76.3 pm. The SiꢀP bond length
of 224.00(2) pm is similar to that observed in 14 and character-
istic for a SiꢀP single bond. The SiꢀS distance of 199.58(1) pm
is only 1 pm longer then the SiꢀS bond length in 7[21] and sig-
nificantly shorter than SiꢀS single bonds.[63]
1
Compound 12 could be synthesized independently by an alternative synthetic
route to compare the NMR data: One equiv of N,N’-1,3-bis(2,6-diisopropyl-
phenyl)-2,2-dichloroimidazol-2-ylidene[74] was reacted with two equiv of lith-
iumphosphite to afford 12 after workup.[60]
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1951
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
in which the latter corresponds to the coupling to
the protons at the nitrogen atom. The 29Si{1H} spec-
trum exhibits a doublet at d=ꢀ26.5 ppm (1J(Si,P)=
7.9 Hz), which is shifted by Dd=18.5 ppm to low
field in comparison with the chemical shift of 6a.[22]
The IR spectrum of 17 displays one weak sharp band
at n˜ =2285 cmꢀ1 for the PꢀH bond and two weak
sharp bands corresponding to the symmetric and
asymmetric vibration of the NH2 group (n˜ =3482 and
3397 cmꢀ1).[64] The composition of 17 could be con-
firmed by HR-ESI mass spectrometry (m/z=
494.31148; 0.02 ppm deviation). Suitable crystals of
17 for single-crystal XRD analysis[60] were obtained
from a concentrated n-hexane solution upon storage
at ꢀ308C for several weeks (Figure 6). In one asym-
metric unit, there are four independent molecules.
The following metric parameters are all averaged
over all four molecules. The silicon atom exhibits
a distorted tetrahedral coordination geometry and is
Figure 5. ORTEP representation of the molecular structure of 16 (thermal ellipsoids show
50% probability; hydrogen atoms are omitted for clarity, except those of C1, C3, C5, and
P1). Selected distances (pm) and angles (deg) of 14: Si1–P1, 224.00(2); Si1–N1, 182.72(1);
Si1–N2, 180.62(1); Si1–S1, 199.58(1); C1–C2, 150.63(1); C4–C5, 149.96(1); N1-Si1-N2,
97.0(1); Si1-P1-S1, 115.24(6).
Beside the activation of ZnMe2 and H2S, compounds 4 and 8
are also capable of activating the NꢀH bonds in ammonia, or-
ganoamines (iPrNH2, H2N(C6H4)(CH3)), and pentafluorophenyl-
hydrazine (H2NNH(C6F5)). Accordingly, an excess of ammonia
gas was bubbled through a diethyl ether solution of 4 and
a toluene solution of 8 at low temperature, respectively
(Scheme 7). The formation of the colorless 1,2-addition product
Figure 6. ORTEP representation of the molecular structure (one of four) of
17 (thermal ellipsoids show 50% probability; hydrogen atoms are omitted
for clarity, except those of C1, C3, C5, P1, and N3). Selected distances (pm)
and angles (deg; average values) of 17: Si1–P1, 223.75; Si1–N1/N2, 173.71;
Si1–N3, 170.00; C1–C2, 136.6; C4–C5, 147.8; N1-Si1-N2, 102.88.
Scheme 7. Synthesis of the 1,2-aminophosphinosilane 17.
17 occurs after 30 min at room temperature. Once again, the
DMAP donor ligand acts as a leaving group during the reac-
1
tion, affording the desired products. In the H NMR spectrum
out of the ligand backbone plane by 48.5 pm. The SiꢀP bond
length of 224.15 pm is similar to that observed in 16 and char-
acteristic for a SiꢀP single bond. The NH2 group at the silicon
atom is positioned nearly orthogonal to the plane defined by
the ligand backbone. The SiꢀN3 bond length of 170.00 pm is
2.2% shorter than the SiꢀN1/N2 bond length of the ligand.
Treatment of 8 with isopropylamine, p-toluidine, and penta-
fluorophenylhydrazine in toluene at low temperature yields in
the corresponding L’Si(PH2)NHR (L’=CH[(C=CH2)CMe(NAr)2];
Ar=2,6-iPr2C6H3) compounds 18a–c with a small amount of
of 17, each proton at the phosphorus atom reveals a doublet
of doublets at d=0.99 and 1.03 ppm, respectively, with a large
1J(P,H) coupling constant of 189.3 Hz and a small J(H,H) cou-
2
pling constant of 12.1 Hz. Thus, the two protons at the phos-
phorus atom are not chemical equivalent, but the difference in
the chemical shift between these two protons is so small that
the roof effect is observed at a spectrometer frequency of
400.13 MHz. To prove this coupling pattern and the roof effect,
1
the H NMR spectrum was measured at different spectrometer
1
frequencies. At a spectrometer frequency of 200.13 Hz, the two
protons reveal a single resonance, whereas at a frequency of
700.17 Hz, the two resonances exhibit only a small roof effect
with the same coupling constants. The protons at the nitrogen
atom reveal a broad signal at d=0.86 ppm in the 1H NMR
spectrum. The proton-coupled 31P NMR spectrum shows at d=
the free ligand LH (Scheme 8). In the H NMR spectra of 18a–c,
each proton at the phosphorus atom reveals a doublet of dou-
blets with a pronounced roof effect, as observed in compound
17 (Table 2). The 31P{1H} resonance signals as well as the
29Si{1H} resonance signals are rather similar to 17. Unfortunately
1
the J(Si,P) of 18c is not visible. Corresponding to secondary
ꢀ252.8 ppm a triplet of triplets (1J(P,H)=189.3, J(P,H)=2.7 Hz),
amines, the IR spectrum of 18a–c reveals for the NꢀH bond
3
Chem. Eur. J. 2014, 20, 1947 – 1956
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1952
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
purified nitrogen. Solvents were dried by standard methods and
freshly distilled prior use. The starting material L’SiPH 4 (L’=
CH[(C=CH2)CMe(NAr)2]; Ar=2,6-iPrC6H3) were prepared according
1
to literature procedures.[20] Solution H, 13C, 31P, and 29Si NMR spec-
tra were recorded on Bruker Avance II 400 MHz (1H: 400.13, 13C:
100.61; 29Si: 79.49 MHz), Bruker Avance II 200 MHz (1H: 200.13, 13C:
50.32 MHz), or on Bruker Avance III 700 MHz (1H: 700.17 MHz) spec-
trometers. The NMR signals are reported relative to the residual
solvent peaks (1H: [D6]C6H6: 7.16; 13C: [D6]C6H6: 128.0 ppm), or an
external standard (19F: CCl3F: 0.0, 31P: 85% H3PO4: 0.0; 29Si: TMS:
0.0 ppm). EI mass spectra were recorded on a Finnigan MAT95S,
ESI- and APCI mass spectra on LTQ Orbitrap XL and the raw data
evaluated using the XCalibur computer program. IR spectra were
recorded on a PerkinElmer Spectrum 100 FTIR. UV/Vis spectra were
recorded with an Analytik Jena Specord S600 Spectrometer in
10 mm quartz cuvettes. Elemental analyses were performed with
a Thermo Finnigan Flash EA 1112 Series. Crystals were mounted on
a glass capillary in perfluorinated oil and measured in a cold N2
flow. The data were collected on an Oxford Diffraction Xcalibur S
Sapphire at 150 K (MoKa radiation, l=0.71073 ꢂ). The structures
were solved by direct methods and refined on F2 with the SHELX-
97 software package.[65] The positions of the H atoms were calcu-
lated and considered isotropically according to a riding model. For
the final refinement on compound 9, the contributions of disor-
dered solvent molecules were removed from the diffraction data
with SQUEEZE in PLATON.[66,67]
Scheme 8. Synthesis of the 1,2-addition products 18a–c. 18a: R=iPr; 18b:
R=tolyl; 18c: R=NH(C6F5).
Table 2. Selected NMR data of 17 and 18a–c.
NMR Data
17[a]
0.99
18a[a]
18b[a]
18c[a]
1H(PHH’)
[ppm]
1H(PHH’)
[ppm]
1J(P,H)
[Hz]
2J(H’,H)
[Hz]
31P
[ppm]
29Si{1H}
[ppm]
1J(Si,P)
[Hz]
1.80
0.84
1.21
1.03
189.3
12.1
1.86
190.2
11.6
0.88
188.8
12.0
1.23
191.5
11.7
ꢀ252.8
ꢀ26.5
7.9
ꢀ254.7
ꢀ27.7
4.0
ꢀ254.3
ꢀ31.4
6.4
ꢀ264.0
ꢀ23.1
–
[a] [D6]C6H6, 258C.
Syntheses
Compound 8: A solution of DMAP (86.1 mg, 0.70 mmol) in toluene
(5 mL) at ꢀ908C was added through a teflon cannula to a stirred
solution of 4 (336 mg, 0.70 mmol) in toluene (50 mL) at ꢀ908C.
The resulting yellow solution was allowed to warm up to room
temperature and stirred for a further 30 min. All volatiles were re-
moved in vacuo and the residue was washed three times with n-
hexane (10 mL). The obtained yellow residue was extracted three
times with toluene (50 mL) and the filtrate was concentrated to
10 mL and left at ꢀ308C for three days to the afford a yellow crys-
talline product, which was separated from the mother liquor by fil-
one sharp vibration (18a: n˜ =3391 cmꢀ1, 18b: n˜ =3401 cmꢀ1
and 18c: n˜ =3351 cmꢀ1).[64]
,
Conclusion
The fragile zwitterionic “half-parent” phosphasilene 4 could be
drastically stabilized by using DMAP and 1,3,4,5-tetramethylimi-
dazol-2-ylidene, which coordinate to the low-coordinate silicon
center. The latter coordination results in a substantial decrease
in the bond order of the Si=P bond compared with the
“donor-free” compound 4 and virtually no p-bonding exists be-
tween Si and P in 8 and 9. Essentially, compounds 8 and 9 can
be thought of as donor-stabilized silylene–phosphinidene ad-
ducts. Remarkably, compounds 8 and 9 are still capable of
acting as transfer reagents of parent phosphinidene (DPH) to
unsaturated organic substrates (bulky NHC) at relatively harsh
reaction conditions. Furthermore, compounds 4 and 8 show
striking reactivity towards a variety of small molecules and
were shown to add dimethylzinc and activate the SꢀH bonds
in H2S and the NꢀH bonds in ammonia and in several organoa-
mines to give unprecedented thiosilanoic phosphane and
phosphanylsilane derivatives.
1
tration and dried in vacuo for 30 min. Yield: 253 mg (60%). H NMR
1
2
(400.13 MHz, [D8]THF, 258C): d=ꢀ2.62 (d, J(P,H)=144.1, J(Si,H)=
13.2 Hz, 1H, PH), 0.49, 0.73, 0.94, 0.98, 1.17, 1.20, 1.38, 1.43 (each d,
3J(H,H)=6.8 Hz, 3H, CHMe2), 1.51 (s, 3H, NCMe), 2.47 (sept,
3J(H,H)=6.9 Hz, 2H, CHMe2), 2.89 (s, 1H, NCCHH’), 3.20 (s, 6H,
NMe2), 3.65 (s, 1H, NCCHH’), 3.92 (sept, 3J(H,H)=6.9 Hz, 2H,
CHMe2), 5.35 (s, 1H, g-CH), 6.77 (d, 3J(H,H)=7.0 Hz, 1H, DMAP),
7.04 (d, 3J(H,H)=7.0 Hz, 1H, DMAP), 6.90–7.25 (m, 6H, 2ꢃ2,6-
iPr2C6H3), 9.03 (d, 3J(H,H)=7.0 Hz, 1H, DMAP), 9.52 ppm (br, 1H,
DMAP); 13C{1H} NMR (100.61 MHz, [D8]THF, 258C): d=23.2 (NCMe);
24.4, 25.0, 25.4, 25.6, 25.8, 25.9 (d, 6J(C,P)=3.3 Hz), 26.1, 26.5
(CHMe2); 29.0, 29.2, 29.6, 29.7 (CHMe2); 39.6 (NMe2), 86.3 (NCCH2);
105.0 (g-C); 123.8, 124.1, 124.7, 125.1, 127.2, 128.9, 129.6, 139.8,
140.3, 148.3, 148.8, 149.2, 150.4, 157.5 (NC, 2,6 iPr2C6H3). 144.6,
150.6 ppm (DMAP); 29Si{1H} NMR (39.76 MHz, [D8]THF, 258C): d=
8.4 ppm (d, 1J(Si,P)=131.8 Hz); 31P{1H} NMR (161.97 MHz, [D8]THF,
1
258C): d=ꢀ331.7 ppm (s, J(P,Si)=131.8 Hz); 31P NMR (161.97 MHz,
[D8]THF, 258C): d=ꢀ331.7 ppm (dd, 1J(P,H)=144.1, 4J(P,H)=3.9,
1J(P,Si)=131.8 Hz; MS (EI 70 eV): m/z (%)=476 (16, [MꢀDMAP]+),
461 (100, [MꢀDMAPꢀMe]+), 433 (29, [MꢀDMAPꢀiPr]+); elemental
analysis (%) calcd for C36H51N4PSi: C 72.20, H 8.58, N 9.36; found: C
71.65, 8.65, N 9.20; UV/Vis (toluene): lmax =294, 345 nm.
Experimental Section
General considerations
All experiments and manipulations were conducted under dry
anaerobic nitrogen using standard Schlenk techniques or in an
MBraun inert atmosphere dry box containing an atmosphere of
Compound 9: A solution of 1,3,4,5-tetramethylimidazol-2-ylidene
(86.1 mg, 0.70 mmol) in toluene (5 mL) at ꢀ908C was added
through a teflon cannula to a stirred solution of 4 (336 mg,
Chem. Eur. J. 2014, 20, 1947 – 1956
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1953
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
0.70 mmol) in toluene (50 mL) at ꢀ908C. The resulting yellow solu-
tion was warmed to room temperature and stirred for further
30 min. All volatiles were removed in vacuo and the residue was
washed three times with n-hexane (10 mL). The obtained yellow
residue was extracted three times with toluene (50 mL) and the fil-
trate was concentrated to 10 mL and left at ꢀ308C for three days
to afford the yellow crystalline product, which was separated from
the mother liquor by filtration and dried in vacuo for 30 min. Yield:
three times with n-hexane (5 mL). The obtained yellow residue was
extracted three times with toluene (10 mL) and the filtrate was
concentrated to 5 mL and left at ꢀ308C for three days to afford
a yellow crystalline product, which was separated from the mother
liquor by filtration and dried in vacuo for 30 min. Yield: 35.2 mg
1
(69%). H NMR (400.13 MHz, [D8]Tol, 258C): d=0.92, 1.16, 1.30, 1.61
3
1
(each d, J(H,H)=6.8 Hz, 6H, CHMe2); 1.62 (d, J(P,H)=191.7 Hz, 2H,
3
PH2); 1.53 (s, 6H, NCMe); 3.06, 4.41 (each sept, J(H,H)=6.9 Hz, 2H,
1
84.1 mg (20%). H NMR (200.13 MHz, [D8]THF, 258C): d=ꢀ1.55 (d,
CHMe2); 5.10 (s, 1H, g-CH), 6.95–7.20 ppm (m, 6H, 2ꢃ2,6- iPr2C6H3);
13C{1H} NMR (100.61 MHz, [D8]Tol, 258C): d=23.6 (NCMe); 24.2 (d,
6J(C,P)=4.1 Hz), 24.6, 25.0, 28.0 (CHMe2); 29.3, 29.6 (d, 5J(C,P)=
4.5 Hz) (CHMe2), 101.9 (g-C); 124.2, 126.5, 137.3, 144.1, 148.6,
168.5 ppm (NC, 2,6 iPr2C6H3); 29Si{1H} NMR (39.76 MHz, [D8]Tol,
1J(P,H)=144.1 Hz, 1H, PH), 0.40, 0.66, 1.05, 1.07, 1.16, 1.20, 1.37,
3
1.40 (each d, J(H,H)=6.8 Hz, 3H, CHMe2), 1.50 (s, 3H, NCMe), 2.11,
3
2.32 (each s, 3H, NHC (C(4,5)-Me)), 2.57, 2.72 (each sept, J(H,H)=
6.9 Hz, 1H, CHMe2), 2.82 (s, 1H, NCCHH’), 3.58 (s, 1H, NCCHH‘),
3.75, 4.15 (each s, 3H, NHC (N(1,3)-Me)) 3.80, 3.83 (each sept,
3J(H,H)=6.9 Hz, 1H, CHMe2), 5.37 (s, 1H, g-CH), 6.86–7.28 ppm (m,
6H, 2ꢃ2,6-iPr2C6H3); 13C{1H} NMR (100.61 MHz, C6H5F, lock-capillary:
[D6]C6H6, 258C): d=7.7, 8.0 (C(4,5)-Me); 24.6 (NCMe); 22.8, 23.4,
24.1, 24.6 (d, 6J(C,P)=3.7 Hz), 24.7, 25.5, 26.2, 26.5 (CHMe2); 27.9,
28.4, 29.3, 29.6 (CHMe2);33.5, 36.0 (N(1,3)-Me); 87.4 (NCCH2); 106.7
(g-C); 113.9–116.7, 121.9–125.4, 126.0, 126.8, 127.0, 127.3–131.6,
139.9, 141.3, 142.7, 143.6, 146.7, 147.4, 149.6, 150.0, 155.2, 161.5–
164.9 ppm (C6H5F, NC, 2,6 iPr2C6H3, NCN, C(4,5)); 29Si{1H} NMR
(79.49 MHz, C6H5F, lock-capillary: [D6]C6H6, 258C): d=ꢀ7.0 ppm (d,
1J(Si,P)=116.4 Hz); 31P{1H} NMR (81.01 MHz, [D8]THF, 258C): d=
ꢀ259.8 ppm (s, 1J(P,Si)=116.4 Hz); 31P NMR (81.01 MHz, [D8]THF,
258C):
d=ꢀ4.0 ppm
(d,
1J(Si,P)=15.0 Hz);
31P{1H} NMR
(161.97 MHz, [D8]Tol, 258C): d=ꢀ221.2 ppm (s, 1J(P,Si)=15.0 Hz);
31P NMR (161.97 MHz, [D8]Tol, 258C): d=ꢀ221.2 ppm (t, 1J(P,H)=
191.7, 1J(P,Si)=15.0 Hz); UV/Vis (toluene): lmax =356 nm; ESI-MS:
m/z calcd for C29H44N2PSSi: 511.2727 [M+H]+; found: 511.2715.
Compound 17: A solution of 8 (30.4 mg, 0.05 mmol) in toluene
(10 mL) at ꢀ258C was placed in a Schlenk tube and degassed by
a freeze–pump–thaw cycle. The reaction vessel was charged with
NH3 of normal pressure. After stirring for 30 min, the solution was
warmed to room temperature and stirred for a further 30 min. All
volatiles were removed in vacuo and the residue was extracted
three times with n-hexane (5 mL). The obtained colorless filtrate
was concentrated to 5 mL and left at ꢀ308C for three days to
afford colorless crystalline product, which was separated from the
mother liquor by filtration and dried in vacuo for 30 min. Yield:
16 mg (65%). 1H NMR (400.13 MHz, [D6]C6H6, 258C): d=0.86 (br,
NH2); 0.99, 1.03 (each dd, 1J(P,H)=189.3 Hz, 2J(H,H)=12.1 Hz, 1H,
1
258C): d=ꢀ289.8 ppm (d, J(P,H)=144.1 Hz); ESI-MS: m/z calcd for
C36H54N4PSi: 601.3850 [M+H]+; found: 601.3840.
Compound 14: A solution of 4 (122 mg, 0.24 mmol) in n-hexane
(10 mL) at ꢀ908C was treated with TMEDA (42.9 mL) and subse-
quently a solution of ZnMe2 (0.22 mL, 1.2m in toluene) was added
dropwise. After stirring for 10 min, the solution was warmed to
room temperature and stirred for further 90 min. The resulting
orange solution was filtered and all volatiles of the filtrate were re-
moved in vacuo. The residue was dissolved in Et2O (2 mL) and left
at ꢀ308C for three days to afford a colorless crystalline product,
which was separated from the mother liquor by filtration and dried
in vacuo for 30 min. Yield: 115 mg (70%). 1H NMR (400.13 MHz,
3
PHH’); 1.17, 1.20, 1.23, 1.24, 1.37, 1.39, 1.43, 1.44 (each d, J(H,H)=
6.8 Hz, 3H, CHMe2); 1.50 (s, 3H, NCMe); 3.31 (s, 1H, NCCHH’); 3.40,
3
3.56, 3.63, 3.70 (each sept, J(H,H)=6.9 Hz, 1H, CHMe2); 3.94(s, 1H,
NCCHH’); 5.40 (s, 1H, g-CH), 7.04–7.25 ppm (m, 6H, 2ꢃ2,6-
iPr2C6H3); 13C{1H} NMR (100.61 MHz, [D6]C6H6, 258C): d=22.0
6
6
(NCMe); 24.3 (d, J(C,P)=5.5 Hz), 24.6, 24.9, 25.0, 25.1 (d, J(C,P)=
5
3.2 Hz) 25.5, 26.2, 26.7 (CHMe2); 28.2, 25.6, 28.8 (d, J(C,P)=2.0 Hz),
29.1 (d, J(C,P)=4.2 Hz) (CHMe2); 86.1 (NCCH2); 106.2 (g-C); 124.5,
1
5
[D6]C6H6, 258C): d=ꢀ1.03 (d, J(P,H)=173.1 Hz, 1H, PH), ꢀ0.71 (s,
3H, ZnMe), 0.94, 1.26, 1.38, 1.45, 1.47, 1.56, 1.63, 1.65 (each d,
3J(H,H)=6.8 Hz, 3H, CHMe2), 1.19 (s, 3H, Si-Me), 1.47 (4H,
NCH2CH2N), 1.62 (s, 3H, NCMe), 1.99 (br, 12H, NMe2); 3.26 (s, 1H,
124.5, 124.9, 125.0, 127.8, 128.3, 136.9, 138.0, 141.3, 148.3, 148.6,
148.7, 149.9, 149.0 ppm (NC, 2,6 iPr2C6H3); 29Si{1H} NMR (39.76 MHz,
[D6]C6H6, 258C): d=ꢀ26.5 ppm (d, 1J(Si,P)=7.9 Hz). 31P{1H} NMR
(161.97 MHz, [D6]C6H6, 258C): d=ꢀ253.8 ppm (s, 1J(P,Si)=7.9 Hz);
3
NCCHH’); 3.67, 3.70 (each sept, J(H,H)=6.9 Hz, 1H, CHMe2), 4.00 (s,
1H, NCCHH’), 4.19, 4.25 (each sept, 3J(H,H)=6.9 Hz, 1H, CHMe2),
5.56 (s, 1H, g-CH), 7.03–7.36 ppm (m, 6H, 2ꢃ2,6-iPr2C6H3);
13C{1H} NMR (100.61 MHz, [D6]C6H6, 258C): d=ꢀ9.8 (d, 2J(C,P)=
10.8 Hz, ZnMe); 8.6 (d, 2J(C,P)=1.2 Hz, SiMe); 22.8 (NCMe); 23.0,
23.7, 24.5, 25.3, 26.2, 26.4, 26.4, 26.5 (CHMe2); 28.0, 28.0, 29.2, 29.4
(CHMe2); 46.5 (NMe2), 56.4 (NCH2CH2N), 84.2 (NCCH2); 105.8 (g-C);
123.7, 124.1, 124.3, 124.9, 126.9, 126.9, 140.1, 140.9, 142.2, 148.6,
149.5, 149.7, 149.9, 149.9 ppm (NC, 2,6 iPr2C6H3); 29Si{1H} NMR
(79.49 MHz, [D6]C6H6, 258C): d=7.6 ppm (d, 1J(Si,P)=29.7 Hz);
31P{1H} NMR (161.97 MHz, [D6]C6H6, 258C): d=ꢀ304.6 ppm (s,
1J(P,Si)=29.7 Hz); 31P NMR (161.97 MHz, [D6]C6H6, 258C): d=
31P NMR (161.97 MHz, [D6]C6H6, 258C): d=ꢀ253.8 ppm (t, J(P,H)=
1
1
189.3, J(P,Si)=7.9 Hz); IR (KBr): n˜ =3482 (w, NꢀH), 3397 (w, NꢀH),
3056 (w), 2960 (s), 2924 (m), 2868 (m), 2286 (w, PꢀH), 1640 (m),
1540 (w), 1467 (m), 1438 (m), 1384 (s), 1351 (s), 1308 (m) 1257 (m),
1243 (m), 1195 (m), 1110 (w), 1098 (w), 1063 (m), 1054 (m),976 (w),
803 (s), 758 (m), 591 (w), 554 (w), 516 cmꢀ1 (w); ESI-MS: m/z calcd
for C29H45N3PSi: 494.3115 [M+H]+; found: 494.3115.
Compound 18a: iPrNH2 (9.30 mL, 6.41 mg, 0.11 mmol) was added
through a syringe to a stirred solution of 8 (65.0 mg, 0.11 mmol) in
toluene (10 mL) at ꢀ808C. After stirring for 30 min, the solution
was warmed to room temperature and stirred for further 60 min.
All volatiles were removed in vacuo and the residue was extracted
three times with n-hexane (5 mL). All volatiles were removed in
vacuo and the residue was dissolved in [D6]C6H6 for NMR measure-
ments. Afterwards, again all volatiles were removed and dried in
vacuo for further characterization analyses. 1H NMR (400.13 MHz,
[D6]C6H6, 258C): d=0.43, 0.44 (each d, 3J(H,H)=6.2 Hz, 3H,
NCHMe2); 0.82 (dd, 3J(H,H)=10.5, 3J(P,H)=3.4 Hz, 1H, NꢀH); 1.20,
1
1
ꢀ304.6 ppm (d, J(P,H)=173.1, J(P,Si)=29.7 Hz); ESI-MS: m/z calcd
for C30H46N2PSi: 493.31624; found: 493.31503 [MꢀTMEDAꢀZnMe+
2H]+; MS (EI 70 eV): m/z (%)=492 (12, [MꢀTMEDAꢀZnMe+H]+),
477 (32, [MꢀTMEDAꢀZnMeꢀMe+H]+), 449 (43, [MꢀTMEDAꢀZn-
MeꢀiPr+H]+), 58 (100, 1/2 TMEDA: [Me2NCH2]+).
Compound 16: Gaseous H2S (2.57 mL, 0.11 mmol) was added
though a syringe to a stirred solution of 8 (59.6 mg, 0.10 mmol) in
toluene (10 mL) at ꢀ808C. After stirring for 90 min, the solution
was warmed to room temperature and stirred for further 30 min.
All volatiles were removed in vacuo and the residue was washed
3
1.23, 1.32, 1.33, 1.34, 1.37, 1.40, 1.44 (each d, J(H,H)=6.8 Hz, 3H,
CHMe2); 1.49 (s, 3H, NCMe);1.80, 1.86 (each dd, 1J(P,H)=190.2,
2J(H,H)=11.6, 2J(Si,H)=7.73 Hz, 1H, PHH’); 2.88 (m, 1H, NCHMe2);
Chem. Eur. J. 2014, 20, 1947 – 1956
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1954
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
1
3.34 (s, 1H, NCCHH’); 3.47, 3.58, 3.61, 3.81 (each sept, 3J(H,H)=
6.9 Hz, 1H, CHMe2); 3.98 (s, 1H, NCCHH’); 5.46 (s, 1H, g-CH), 7.04–
7.25 ppm (m, 6H, 2ꢃ2,6-iPr2C6H3); 13C{1H} NMR (100.61 MHz,
[D6]C6H6, 258C): d=22.5 (NCMe); 23.8, 24.9, 24.9, 25.4, 25.7 (d,
6J(C,P)=5.9 Hz), 26.2 (d, 6J(C,P)=3.2 Hz), 26.4, 26.9, 27.0, 27.2
(CHMe2, NCHMe2); 28.5 (d, 5J(C,P)=4.5 Hz), 28.3, 28.3, 28.9 (d,
5J(C,P)=5.0 Hz) (CHMe2); 43.8 (d, 3J(C,P)=5.4 Hz) (NCHMe2); 87.5
(NCCH2); 107.6 (g-C); 124.2, 124.3, 124.6, 125.5, 127.5, 127.9, 136.9,
138.0, 141.4, 148.2, 148.5, 148.7, 148.9, 149.0 ppm (NC, 2,6
iPr2C6H3); 29Si{1H} NMR (79.49 MHz, [D6]C6H6, 258C): d=ꢀ27.7 ppm
(d, 1J(Si,P)=4.0 Hz); 31P{1H} NMR (161.97 MHz, [D6]C6H6, 258C): d=
ꢀ254.7 ppm (s); 31P NMR (161.97 MHz, [D6]C6H6, 258C): d=
(400.13 MHz, [D6]C6H6, 258C): d=1.21,1.23 (each dd, J(P,H)=191.5,
2J(H,H)=11.7 Hz, 1H, PHH’);1.09, 1.18, 1.21, 1.29, 1.30, 1.34, 1.36,
1.39 (each d, J(H,H)=6.8 Hz, 3H, CHMe2); 1.49 (s, 3H, NCMe); 3.37
3
(s, 1H, NCCHH’); 3.44, 3.47, 3.59, 3.61 (each sept, 3J(H,H)=6.9 Hz,
1H, CHMe2); 3.97 (s, 1H, NCCHH’); 4.01 (br, NꢀH); 4.78 (br, NꢀH);
5.43 (s, 1H, g-CH); 6.95–7.27 ppm (m, 6H, 2ꢃ2,6-iPr2C6H3); 13C NMR
(100.61 MHz, [D6]C6H6, 258C): d=21.9 (NCMe); 24.0, 24.3 (d,
6J(C,P)=5.3 Hz), 24.9, 25.1, 25.1 (d, J(C,P)=2.5 Hz), 25.2, 26.5, 26.9
6
(CHMe2); 28.3, 28.4, 28.6, 29.1 (d, 5J(C,P)=3.6 Hz) (CHMe2); 87.8
(NCCH2); 107.3 (g-C); 124.6, 124.8, 125.1, 125.3, 127.5, 127.8, 128.1,
128.3, 128.3, 128.4, 136.1, 137.1, 142.2, 148.0, 148.4, 148.5, 148.5,
148.8 ppm (C6F5, NC, 2,6 iPr2C6H3); 19F{1H} NMR (188.31 MHz,
[D6]C6H6, 258C): d=ꢀ156.2 (br d, 3J(F,F)=22.5 Hz, 2F, ortho-F);
1
ꢀ254.7 ppm (t, J(P,H)=190.2 Hz); IR (KBr): n˜ =3391 (w, NꢀH), 3113
3
3
(w), 3056 (w), 2962 (s), 2925 (m), 2862 (m), 2284 (w, P-H), 1635 (m),
1535 (w), 1462 (m), 1439 (m), 1380 (s), 1353 (s), 1306 (m) 1252 (m),
1238 (m), 1198 (m), 1176 (m), 1165 (m), 1128 (m), 1111 (w), 1098
(w), 1060 (m), 1044 (m), 1031 (w), 976 (w), 926 (m), 918 (w), 804 (s),
774 (m), 757 (m), 591 (w), 596 (w), 509 cmꢀ1 (w); ESI-MS: m/z calcd
for C32H51N3PSi: 536.3584 [M+H]+; found: 536.3583.
ꢀ164.5 (2ꢃt, J(F,F)=22.3 Hz, 2F, meta-F), ꢀ167.7 ppm (tt, J(F,F)=
22.2, J(F,F)=4.3 Hz, 1F, para-F); 29Si{1H} NMR (79.49 MHz, [D6]C6H6,
4
258C): d=ꢀ23.1 ppm; 31P{1H} NMR (161.97 MHz, [D6]C6H6, 258C):
d=ꢀ263.9 ppm (t, J(P,F)=7.5 Hz); 31P NMR (161.97 MHz, [D6]C6H6,
6
1
6
258C): d=ꢀ263.9 ppm (tt, J(P,H)=191.5, J(P,F)=7.5 Hz); IR (KBr):
n˜ =3351 (w, NꢀH), 3059 (w), 2963 (s), 2921 (m), 2864(m), 2290 (w,
PꢀH), 1621 (s), 1551 (s), 1526 (s), 1518 (s), 1461 (m), 1439 (m), 1380
(s), 1361 (w), 1323 (m), 1275 (m), 1253 (w), 1176 (m), 1100 (m),
1059 (m), 1018 (m), 992 (m), 963 (w), 932 (w), 804 (m), 759 cmꢀ1
(m); APCI-MS: m/z calcd for C36H51N3PSi: 675.3066 [M+H]+; found:
675.3067.
Compound 18b: A solution of p-toluidine (6.08 mg, 0.06 mmol) in
toluene (5 mL) at ꢀ708C was added through a teflon cannula to
a stirred solution of 8 (34 mg, 0.06 mmol) in toluene (10 mL) at
ꢀ708C. After stirring for 60 min, the solution was warmed to room
temperature and stirred for further 3 h. All volatiles were removed
in vacuo and the residue was extracted three times with n-hexane
(5 mL). All volatiles were removed in vacuo and the residue was
dissolved in [D6]C6H6 for NMR measurements. Afterwards, again all
volatiles were removed and dried in vacuo for further characteriza-
tion analyses. 1H NMR (400.13 MHz, [D6]C6H6, 258C): d=0.84, 0.88
(each dd, 1J(P,H)=188.8, 2J(H,H)=12.0, 2J(Si,H)=8.4 Hz 1H, PHH’);
Computational methods
DFT calculations were performed at the B97-D/cc-pVTZ(PCM=Ben-
zene)//B97-D/6-31G* level of theory.[68–72] Stationary points on the
potential energy surface (PES) were characterized by harmonic vi-
brational frequency calculations. Transition states, with one imagi-
nary frequency, were confirmed by intrinsic reaction coordinate
(IRC) calculations. Calculations were carried out using Gaussian 09
program.[73]
3
0.89, 0.99, 1.02, 1.18, 1.28, 1.46, 1.47, 1.48 (each d, J(H,H)=6.8 Hz,
3H, CHMe2); 1.51 (s, 3H, NCMe); 2.12 (s. 3H, Ph-CH3); 3.32 (s, 1H,
NCCHH’); 3.34, 3.43, 3.64, 3.81 (each sept, 3J(H,H)=6.9 Hz, 1H,
CHMe2); 3.96 (s, 1H, NCCHH’); 3.78 (br, 1H, NꢀH); 5.54 (s, 1H, g-
3
3
CH), 6.74 (d, J(H,H)=8.1 Hz, 2H, NCCHCH); 6.97 (d, J(H,H)=8.1 Hz,
2H, NCCHCH); 7.00–7.26 ppm (m, 6H, 2ꢃ2,6-iPr2C6H3); 13C NMR
(100.61 MHz, [D6]C6H6, 258C): d=20.1 (PhꢀCH3) 22.1 (NCMe); 24.4,
24.5, 24.6, 24.9 (d, 6J(C,P)=5.0 Hz), 25.2, 25.2, 25.8, 26.5 (CHMe2);
27.1, 27.8, 29.1, 29.2 (d, 5J(C,P)=4.3 Hz, CHMe2); 86.8 (NCCH2);
105.6 (g-C); 118.1 (NCCH2CH2); 129.8 (NCCH2CH2);124.5, 124.8,
124.8, 125.3, 127.9, 128.1, 129.9, 136.8, 137.8, 142.2, 142.9, 148.1,
149.0, 149.0, 149.2, 150.3 ppm (NCCH2CH2C, NC, 2,6 iPr2C6H3);
29Si{1H} NMR (39.76 MHz, [D6]C6H6, 258C): d=ꢀ31.4 ppm (d,
1J(Si,P)=6.4 Hz); 31P{1H} NMR (161.97 MHz, [D6]C6H6, 258C): d=
ꢀ254.3 ppm (s, 1J(Si,P)=6.4 Hz); 31P NMR (161.97 MHz, [D6]C6H6,
Acknowledgements
We are grateful to the Cluster of Excellence “UniCat” (spon-
sored by the Deutsche Forschungsgemeinschaft and adminis-
tered by the TU Berlin), and the Deutsche Forschungsgemein-
schaft (DR 226/17-2); T.S. thanks The New Szꢄchenyi Plan
TAMOP-4.2.2/B-10/1–2010-0009 for generous support. We
thank Prof. Dr. S. Inoue and Dipl.-Chem. M. Stoelzel for fruitful
discussions and Dr. S. Enthaler for UV/Vis measurements.
1
258C): d=ꢀ254.3 ppm (t, J(P,H)=188.8 Hz); IR (KBr): n˜ =3401 (w,
NꢀH), 3176 (w), 3153 (w), 3054 (w), 3013 (w), 2961 (s), 2925 (m),
2918 (m), 2865 (m), 2285 (w, PꢀH), 1638 (m), 1603 (s), 1515 (s),
1462 (m), 1438 (m), 1372 (s), 1352 (s), 1306 (m), 1279 (s), 1252 (w),
1240 (w), 1226 (m), 1199 (m), 1177 (m), 1165 (m), 989 (w), 926 (m),
900 (w), 805 (s), 760 (m), 588 (w), 559 (w), 540 (w), 519 cmꢀ1 (w);
ESI-MS: m/z calcd for C36H51N3PSi: 584.3584 [M+H]+; found:
584.3575.
Keywords: phosphinidine · phosphorus · silanes · silicon ·
zwitterions
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Chem. Eur. J. 2014, 20, 1947 – 1956
www.chemeurj.org
1956
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim