Extremely bulky secondary phosphinoamines as substituents for sterically hindered aminosilanes

Article abstract of DOI:10.1039/c5dt02504d

The synthesis of a series of extremely bulky secondary amines with a phosphine function, Ar^?(PR₂)NH (Ar^? = C₆H₂{C(H)Ph₂}₂Prⁱ-2,6,4; R = Ph, NEt₂, NPr^i<

Full text of DOI:10.1039/c5dt02504d

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Extremely bulky secondary phosphinoamines as
substituents for sterically hindered aminosilanes†
Cite this: DOI: 10.1039/c5dt02504d
Tobias Böttcher* and Cameron Jones*
The synthesis of a series of extremely bulky secondary amines with a phosphine function, Ar†(PR2)NH (Ar† =
C6H2{C(H)Ph2}2Pri-2,6,4; R = Ph, NEt2, NPri2) is described. Deprotonation with either n-BuLi or KH yields
the respective alkali metal amides in some cases. Their reaction with the chlorosilanes SiCl4, HSiCl3,
Cl2SiPh2, Cl3Si–SiCl3 and Si5Cl10 allows access to monomeric molecular compounds bearing the extremely
bulky amino substituents via salt elimination. The products obtained may serve as precursors for subsequent
reduction reactions to access sterically protected low valent and low coordinate silicon compounds.
Received 1st July 2015,
Accepted 22nd July 2015
DOI: 10.1039/c5dt02504d
www.rsc.org/dalton
pounds as they perfectly meet the criteria for non-toxic, abun-
dant and inexpensive replacements for transition metal
Introduction
During the past three decades of main group chemistry, many complexes for use in chemical transformations, be they
compounds with hitherto unknown bonding motifs and oxi- stoichiometric or catalytic. However, access to low-coordinate
dation states have been discovered.1 Especially, low-coordi- silicon(II) species is a challenging endeavor and no example of
nate/low-oxidation state main group complexes have attracted a two-coordinate chloro or hydrido silylene has yet been
not only the attention of preparative chemists but also of theo- reported. Herein, new extremely bulky secondary amides with
reticians. The utilization of sterically demanding ligand a phosphine function, and their application as ligands for the
systems has allowed the stabilization of compounds which synthesis of aminosilane compounds, are presented. The latter
were previously thought to be too reactive to be isolated on a hold significant potential as precursors for two-coordinate
preparative scale. The further chemistry of these reactive com- low-oxidation state silicon systems.
plexes has also rapidly emerged in recent years. This is
perhaps best exemplified by the 2005 report by Power et al.,
which described the facile activation of hydrogen by a diger-
Results and discussion
myne, a reaction motif that is typical for late d-block metal
complexes.2 Further research revealed similar reactions for
Recently, our group reported a series of secondary amines,
other low oxidation state main group compounds, including
the activation of H2, NH3, CO and CO2.3 Many results in this
field were achieved by using polydentate ligand systems (e.g.
β-diketiminates), or additional Lewis-bases, to stabilize these
highly reactive compounds.4,5 However, within the research of
low-oxidation state group 14 element compounds, remarkable
results have been reported for unsupported and thus low-
valent species.6,7 Most recently, the synthesis of unsupported
two-coordinate amido germanium(II) and tin(II) hydrides using
the extremely bulky amido ligand (Ar†)(SiPri3)N–(Ar† = C6H2-
{C(H)Ph2}2Pri-2,6,4) allowed their application as highly
efficient catalysts for hydroboration reactions.7,8 A specific
focus of the research presented here is on related silicon com-
substituted with aryl and silyl groups of varying steric bulk of
the type (Ar)(SiR3)NH (Ar = Ar† or Ar* = C6H2{C(H)Ph2}2Me-
2,6,4; R3 = Me3, Ph3, Pri3, Ph2Me), in addition to their utiliz-
ation as pro-ligands for the stabilisation of two-coordinate
amido-group 14 halide complexes.9,10 The commercial avail-
ability of stable germanium(II), tin(II) and lead(II) chlorides
(ECl2, E = Ge, Sn or Pb) allowed for the straightforward substi-
tution of one chloride ligand on these precursors with a bulky
amino substituent via salt methathesis reactions using alkali
metal amide reactants. In contrast with the heavier homo-
logues, there is no commercial source of silicon(II) halides,
and instead low oxidation state silicon compounds are typi-
cally accessed via reduction of silicon(IV) precursor complexes
derived from SiCl4 and HSiCl3.4,11,12 With that said, the pre-
viously synthesized bulky aminosilanes (Ar*)(SiR3)N–SiCl3 and
(Ar*)(SiMe3)N–SiCl2H could not be reduced to lower oxidation
silicon compounds. To overcome these limitations, we pro-
posed to replace the silyl group of the ligand with a bulky
phosphine group. The resultant phosphinoamide system was
School of Chemistry, Monash University, P.O. Box 23, Melbourne, Victoria 3800,
Australia. E-mail: tobias.boettcher@ac.uni-freiburg.de, cameron.jones@monash.edu
†Electronic supplementary information (ESI) available. CCDC 1401422–1401434.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c5dt02504d
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Scheme 1 Synthesis of the pro-ligands 1–3 and their respective alkali
metal amides.
Fig. 1 Comparison between silylamido (A) and phosphinamido ligands
(B and C) coordinated to a tetrel fragment E. The P-lone pair of the
latter can coordinate E (D) or not (E), depending on steric and electronic
factors.
In order to access extremely bulky phosphinoamides, the
three amine pro-ligands Ar†(PR2)NH (R = Ph, NEt2, NPri2) were
synthesized using modifications of literature procedures
(Scheme 1).16,17
seen as offering both a different steric and electronic environ-
ment, as well as an additional, and potentially donating, lone
pair at the phosphorus adjacent to the nitrogen atom. In this
respect, it is well known that phosphinoamides have a signifi-
cantly shortened P–N bond with the negative charge mainly
located at the nucleophilic nitrogen-atom (B, Fig. 1). Accord-
ingly, this class of ligand has a long history in the coordination
chemistry of transition and alkali metals.13 However, there are
only few reports of bulky phosphinoamides being utilised for
the kinetic stabilization of low valent main group com-
pounds.14,15 The synthesis of phosphinoamides with even
greater steric bulk was an initial target of this study.
Compared with previously reported, and less sterically
demanding analogues, the extreme steric bulk of the Ar† group
did not negatively affect the yield of the products significantly.
The molecular structures of the phosphinoamines each show
the expected planar nitrogen and pyramidal phosphorus geome-
try (Fig. 2). Selected structural parameters are given in Table 1.
Compounds 1 and 2 were readily deprotonated using
n-BuLi or KH/HDMS, as monitored by 31P NMR spectroscopy,
and were used in situ for further reactions with no isolation or
purification necessary. The phosphinoamine 3 not only pro-
Fig. 2 Molecular structures of the amine pro-ligands 1, 2, 3. 2-K and 4 with the thermal ellipsoid plots at the 25% probability level. Hydrogen
atoms, except the N–H atoms, are omitted for clarity. Selected structural parameters are given in Table 1.
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Table 1 Selected bond lengths (Å) and angles (°) for compounds 1–3,
2-K and 4 and 31P{1H} NMR chemical shifts (δ)
1
2
3
2-K
4
N1–C1
N1–P1
N2–P1
N3–P1
N1–K
N3–K
C1–N1–P1
Ang. sum (P)
31P NMR
1.428(2)
1.711(2)
—
—
—
1.437(3)
1.709(2)
1.709(2)
1.691(2)
—
1.421(2)
1.723(1)
1.696(1)
1.695(1)
—
1.383(3)
1.649(3)
1.704(3)
1.751(3)
2.654(3)
2.954(3)
125.9(2)
310.0(2)
91.9
1.405(3)
1.561(2)
1.645(2)
—
—
—
124.8(2)
—
270.2
Scheme 3 Synthesis of compounds 5, 6, 7 and 9 by addition of 1-Li to
a solution of the respective chlorosilane via elimination of LiCl. (i) SiCl4;
(ii) HSiCl3; (iii) Ph2SiCl2; (iv) Cl3Si–SiCl3.
—
—
—
121.1(1)
303.6(1)
38.2
119.0(2)
307.0(1)
102.5
120.3(1)
312.1(1)
78.0
lone pair at the phosphorus atom in each (Fig. 3). The P-lone
pair in compounds 5 and 6 is pointing away from the silicon
center, whereas in compound 7 the lone pair is directed
towards it, but without P–Si coordination taking place. This
difference may be attributed to steric repulsion between the
phenyl groups at the phosphorus and at the SiPh2Cl fragment
in compound 7. It is of note that the change of the amide
ligand from that in Ar*(SiMe3)N–SiCl3 to that in Ar†(PPh2)N–
SiCl3 caused only minor structural changes. For example, the
N–Si (1.693(8) Å) and the mean Si–Cl (2.026(4) Å) bond lengths
in 5 are slightly longer compared to the respective bond
lengths in Ar*(SiMe3)N–SiCl3 (1.74(2) and 2.010(2) Å).
vides the extreme steric bulk of the Ar†-substituent, but
additional bulk comes from the –P(NPri2)2 group. Unfortu-
nately, it was not possible to deprotonate 3, following the
same synthetic protocols as used for 1 and 2. This result can
be attributed to the high demand of steric bulk around the
amine proton, rather than to electronic factors, as 2 and 3
share very similar electronic environments at the amine nitro-
gen atom. In an attempt to prepare a chloro-aminosilane(III),
the potassium salt of 2 (2-K) was slowly added to a solution of
Cl3Si–SiCl3 in toluene at −78 °C. A significant downfield shift
in the 31P NMR spectrum from δ 91.9 (2-K) to δ 270.2 ppm
(product) was observed. A single crystal XRD study of the
product revealed that it is not a silicon containing product, but
rather the phosphinoimine 4 (Fig. 2), presumably formed by an
elimination reaction. Similar elimination reactions have been
reported previously,18 although in this case the formation of 4
proceeds spontaneously at low temperatures and the product is
essentially stable as a solid. The mechanism of this reaction is
not fully understood, however, it was observed that the free
phosphinoamine 2 undergoes slow decomposition in solution,
in the absence of other reactants, to yield 4 via elimination of
HNEt2, as monitored by 31P NMR spectroscopy (Scheme 2). It
should be noted that related reactions of the lithium or potass-
ium salts of 2 with SiCl4 led to intractable product mixtures.
As the phosphinoamines 2 and 3, and alkali metal salts of
2, were found to be not suitable for the synthesis of sterically
protected aminosilanes, lithiated 1 was explored as a precursor
for salt metathesis reactions with chlorosilanes. In this
respect, addition of 1-Li to SiCl4, HSiCl3 and Ph2SiCl2 readily
yielded compounds 5, 6 and 7, respectively (Scheme 3).
Compounds 5, 6 and 7 were found to be surprisingly stable
towards several reducing agents. Attempts at reducing the
aminosilanes
with
{(MesNacnac)Mg}2
(
MesNacnac
=
[(MesNCMe)2CH]−, Mes = mesityl)19 or KC8 in toluene showed
no reaction, as determined by 31P NMR spectroscopy. When
elemental potassium or KC8 in thf were used, complete
decomposition of the starting materials was observed. The
addition of the N-heterocyclic carbene (NHC = 1,3,4,5-tetra-
methylimidazol-2-ylidene) as a dehydrochlorinating reagent to
a solution of 6 in toluene afforded the free phosphinoamine,
1, as the only phosphorus-containing compound. Attempts to
reduce 5 and 6 with potassium naphthalide led to no reaction.
On the other hand, addition of one equivalent of potassium
naphthalide to a solution of 7 showed consumption of ca. 50%
of the starting material and the formation of a new product
(31P NMR: δ −28.3 ppm).
Interestingly, crystallization of the reaction mixture yielded
only one phosphorus free product, that is the potassium
amide K[Ar†(SiPh2Cl)N], presumably formed via a P–N cleavage
reaction. Unfortunately, the XRD data for the crystal structure
of the potassium amide were not of publishable quality, but
the structure did confirm the gross atomic connectivity in the
salt. When the reaction was repeated using two equivalents of
potassium naphthalide, complete consumption of the starting
material was observed, according to Scheme 4. This allowed
assignment of the signal at δ −28.3 ppm in the 31P NMR spec-
trum of the reaction mixture, to the potassium phosphide,
K[PPh2], which arises from potassium induced P–N bond clea-
vage in 7.20 It is noteworthy that in the ESI mass spectrum of
7, a signal at m/z = 683.5 a.u. was detected and assigned to
[H2N(Ar†)(SiPh2Cl)]+, further supporting the facility of P–N
cleavage reactions for the aminosilane. Similar P–N cleavage
reactions provide a plausible explanation for the decompo-
While amido analogues of compounds of 5, 6, and phosphino-
amido analogues of 5 have been reported earlier,15 the com-
pound type represented by 7, appears without precedent.9 The
crystal structures of 5 and 7 revealed a different role of the
Scheme 2 Decomposition of 2 to yield 4.
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Fig. 3 Molecular structures of 5, 6 and 7 with the thermal ellipsoid plots at the 25% probability level. Hydrogen atoms, except the Si–H atom of 6,
are omitted for clarity. Selected bond lengths (Å) and angles (°) for 6: N1–C1 1.466(5), N1–P1 1.760(3), N1–Si1 1.707(4), Si1–Cl1 2.025(2), Si1–Cl2
1.980(2), C1–N1–P1 111.8(2), C1–N1–Si1 111.8(2), P1–N1–Si1 129.0(2), Σ angles at P 312.0(2). For 7: N1–C1 1.449(6), N1–P1 1.746(4), N1–Si1 1.753(4),
Si1–Cl1 2.049(2), C1–N1–P1 123.0(3), C1–N1–Si1 129.3(3), P1–N1–Si1 106.4(2), Σ angles at P 319.2(3). N.B. Structural parameters for 5 can be found
in Table 2.
Table 2 Selected bond lengths (Å) and angles (°) for compounds 5, 8, 9
and 10 and 31P{1H} NMR shifts (δ)
5
8
9
10
N1–C1
N1–P1
N1–Si1
Si1–Si2
Mean Si1–Cl
Mean Si2–Cl
P1–N1–Si1
Ang. sum (P)
31P NMR
1.456(11)
1.785(7)
1.693(8)
—
2.026(4)
—
129.9(4)
313.3(4)
65.7
1.440(2)
1.780(6)
1.713(2)
—
—
—
126.6(2)
308.6(4)
59.6
1.468(4)
1.758(3)
1.717(3)
2.345(2)
2.039(1)
2.042(2)
106.9(2)
317.9(2)
49.2
1.457(2)
1.731(2)
1.751(2)
2.3377(9)
—
Scheme 4 Observed P–N cleavage in the reaction of 7 with K[C10H8].
—
In an attempt to access a phosphinoamino–silicon(III) com-
pound, addition of 1-Li to Cl3Si–SiCl3 in toluene was carried
out, which afforded compound 9 in moderate yield after work-
up (Scheme 3). Compound 9 is stable as a solid under inert
atmosphere for at least several weeks. In ether solutions it
130.19(9)
310.1(1)
63.5
sition reactions observed in the attempted reductions of 5 and readily decomposes to yield 5 as the only product containing a
6. However, alkali metal amides derived from these reductions phosphorus atom. This formal elimination of SiCl2 is analo-
were never isolated.
gous to that previously observed for the iron(II) complex
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[Cp(CO)2Fe–SiCl2–SiCl3], which yielded [Cp(CO)2Fe–SiCl3] was detected. When the free N-heterocyclic carbene IPr (IPr =
under UV-irradiation.21
1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) was added to
For compound 9, the elimination process is apparently trig- a solution of 9 in C6D6 in an attempt to trap the SiCl2 fragment
gered by Lewis bases (Scheme 5). In non-coordinating solvents under formation of IPr–SiCl2,11 the reaction solution immedi-
(e.g. C6D6, toluene) the process is almost negligible. If the syn- ately showed only the resonance for 5 in its 31P NMR spectrum.
thesis of 9 was carried out in diethyl ether instead of toluene, Unfortunately, IPr–SiCl2 could not be determined as being
the yield decreased significantly and in thf only compound 5 present in the reaction mixture, based on the 1H and 29Si NMR
spectroscopic data of that mixture. Attempts at reducing 9 with
{
MesNacnacMg}2 or KC8, again only afforded compound 5.
So as to demonstrate the utility of the chlorosilanes 5 and 9
as precursors to the corresponding silicon hydride com-
pounds, they were treated with an excess of LiAlH4 in diethyl
ether which readily yielded the silanes (PPh2)(Ar†)N–SiH3
8
and (PPh2)(Ar†)N–SiH2SiH3 10 via Cl/H exchange processes.
Related Cl/H exchange reactions have been reported for
similar chlorosilanes.21,22 The molecular structures of com-
pounds 8, 9 and 10 were determined (Fig. 4), which in the case
Scheme 5 Lewis base induced formal elimination of SiCl2 from 9 to
give 5.
Fig. 4 Molecular structures of 8, 9 and 10 with the thermal ellipsoid plots at the 25% probability level. Hydrogen atoms, except the Si–H atoms, are
omitted for clarity. Selected structural parameters are given in Table 2.
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of 5 and 8, showed the conversion of the –SiCl3 moiety to the
an –SiH3 unit only slightly affects the molecular geometry of
the compounds. The lone pair at the phosphorus atom is
pointing away from the silicon atom in both compounds,
showing no P⋯Si intramolecular interaction. The N1–P1 and
N1–Si1 bond lengths increase on going from 5 to 8. The P1–
N1–Si1 angle is greater in 8, which can be attributed to its less
bulky –SiH3 group compared with –SiCl3 in 5. The 31P NMR
spectroscopic signal for 8 (δ 59.6 ppm) is shifted slightly
upfield compared with that for 5 (δ 65.7 ppm), which is in
accord with the positions of the 29Si NMR spectroscopic
signals for 5 (δ −29.4 ppm) and 8 (δ –47.1 ppm, 1JSiH = 218 Hz).
Moreover, the N–Si bond length in 8 (1.713(2) Å) compares
well with that found for the known silylhydrazine
H3SiMeNNMe2 (1.693(1) Å).23 The two higher silanes 9 and 10
show a different involvement of their phosphorus lone pairs.
In 9 the two phenyl groups at the phosphorus are turned
towards the bulky Ar† group, allowing a weak interaction
between P1 and Si2. That is, the P(donor)⋯Si(acceptor) dis-
tance is 3.555(1) Å, which is shorter than the sum of the van
der Waals radii (rvdw(Si–P) 3.90 Å),24 but significantly longer
than the sum of the covalent radii (2.08 Å).25 The N1–Si1 bond
length in 9 (1.717(3) Å) is shorter compared with 10 (1.751(2)
Å), whereas the Si1–Si2 bond length is slightly longer in 9
(2.345(2) Å) than the one found for 10 (2.3377(9) Å). Both Si–Si
bond lengths compare well with that for Ter–SiCl2–SiCl3
(2.358(2) Å) (Ter = 2,6-Mes2C6H3).26 The 31P NMR spectroscopic
signals for 9 (δ 49.2 ppm) and 10 (δ 63.5 ppm) are at similar
chemical shifts to those for the related aminosilanes described
in the Introduction. The 29Si NMR spectroscopic signal for Si1
Scheme 6 Synthesis of compounds 11 and 12.
in 9 (δ −29.4 ppm) is shifted significantly upfield compared
with that for Ter–SiCl2–SiCl3 (δ −4.24 ppm), whereas the signal
for Si2 in 9 (δ −2.1 ppm) is comparable with the one found for
Ter–SiCl2–SiCl3 (δ −3.54 ppm). For compound 10 the reso-
1
nances for Si1 (δ −38.6 ppm, JSiH = 208 Hz) and for Si2
1
(δ −99.8 ppm, JSiH = 196 Hz) compare well with the ones
detected for the iron complex [Cp(CO)2Fe–SiH2–SiH3] (–SiH2–:
1
1
δ −45.2 ppm, JSiH = 172 Hz and –SiH3–: δ −95.6 ppm, JSiH
=
184 Hz).21
To explore the chemistry of more silicon rich chloro-amino-
silanes, addition of one equivalent 1-Li to a solution of the cyclic
chlorosilane Si5Cl10 in toluene was carried out, and this afforded
11. When two equivalents of 1-Li were added to Si5Cl10, com-
pound 12 was obtained (Scheme 6). Both compounds were iso-
lated in moderate yields and were fully characterized.
If kept under an inert atmosphere, both 11 and 12 are
stable, however, in solution compound 10 slowly decomposes
and signals for 5 and the free amine, 1, were detected by 31P
NMR spectroscopy. In contrast, compound 12 is stable in solu-
tion for at least several days and does not undergo a similar
decomposition reaction. The 31P NMR spectroscopic signals
for 11 (δ 51.9 ppm) and 12 (δ 42.2 ppm) both appear as sing-
Fig. 5 Molecular structures of 11 and 12 with the thermal ellipsoid plots at the 25% probability level. Hydrogen atoms are omitted for clarity. All
carbon atoms are depicted using a “wire” representation. Selected bond lengths (Å) and angles (°) for 11: N1–C1 1.468(5), N1–P1 1.738(3), N1–Si1
1.719(3), Si1–Si2 2.366(2), Si2–Si3 2.347(2), Si3–Si4 2.351(2), Si4–Si5 2.370(2), Si1–Si5 2.398(2), Si1–Cl1 2.034(2), C1–N1–P1 123.8(2), P1–N1–Si1
101.9(2), Σ angles at P 318.7(2). And 12: N1–C1 1.460(1), N1–P1 1.740(9), N1–Si1 1.735(9), Si1–Si2 2.390(5), Si2–Si3 2.400(5), Si3–Si4 2.357(5), Si4–Si5
2.355(4), Si5–Si1 2.356(5), Si1–Cl1 2.040(4), N2–C48 1.46(2), N2–P2 1.721(9), N2–Si3 1.731(9), Si3–Cl4 2.044(4), C1–N1–P1 126.7(7), P1–N1–Si1
101.1(5), C48–N2–P2 127.4(7), P2–N2–Si3 102.8(5), Σ angles at P1 321.1(6) Σ angles at P2 321.4(5).
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lets. Both compounds possess three chemically inequivalent
silicon atoms and their 29Si NMR signals appear as doublets
due coupling to the phosphorus atom of the ligand. The
Experimental Section
General methods
2
4
decrease of the coupling constant on going from JPSi to JPSi All manipulations were carried out using standard Schlenk
allowed their assignment (see Experimental section). The high and glovebox techniques under an atmosphere of high purity
degree of kinetic stabilization of the Si5 ring in 12 not only pre- dinitrogen. THF, hexane and toluene were distilled over
vents its decomposition in solution, but also makes 12 inert molten potassium, while diethyl ether was distilled over Na/K
towards reduction using {MesNacnacMg}2 or KC8 in toluene (50 : 50) alloy. Deuterated benzene (C6D6) was dried and stored
(used either equimolar or in excess). Compound 11, substi- over sodium. 1H, 13C{1H}, 29Si{1H}, 31P{1H} NMR, and 1H/29Si
tuted with only one amido ligand, showed complete decompo- HMBC spectra were recorded on either a Bruker DPX300 or a
sition to as yet unidentified product mixtures following the Bruker AvanceIII 400 spectrometer and were referenced to the
same synthetic approaches.
resonances of the solvent used (1H and 13C NMR), external TMS
To date, only mono-aryl substituted cyclic, five-membered (29Si NMR) and external 85% H3PO4 (31P NMR). IR spectra were
chlorosilanes have been structurally characterized,22 and other recorded for solid samples, protected from the atmosphere by
related five-membered cyclic silianes were obtained by Nujol films, using an Agilent Cary 630 attenuated total reflec-
different synthetic approaches.27 The molecular structures of tance (ATR) spectrometer. Melting points were determined in
11 and 12 were successfully determined by single crystal XRD sealed glass capillaries under dinitrogen and are uncorrected.
(Fig. 5). The Si5 ring in 11 adopts a distorted envelope con- Microanalyses were carried out at the Science Centre, London
figuration with the Si2 atom being 0.89 Å out of the least Metropolitan University. The starting materials Ar†NH2,29 ClP
squares plane defined by Si1, Si3, Si4 and Si5. The ring in 12 (NEt2)2, ClP(NiPr2)2,30 and Si5Cl10
were prepared by pro-
31
shows a more puckered geometry with a less pronounced cedures reported in the literature. All other compounds were
envelope-like configuration. That is, the Si4 atom is only obtained from commercial sources and used as received.
0.63 Å out of the least squares plane defined by Si1, Si2, Si3
Preparation of Ar†(PPh2)NH (1). A solution of n-butyllithium
and Si5. The lone pairs at the phosphorus atoms of both 11 in hexane (7.6 ml, 12.20 mmol) was slowly added to a solution
and 12 display interatomic P⋯Si contacts with the silicon of Ar†NH2 (5.40 g, 11.6 mmol) in thf (80 ml) at −80 °C. The
atom substituted by the amide ligand (in 11 2.684(2) Å and 12 reaction mixture was allowed to reach room temperature
P1–Si1: 2.683(5) and P2–Si3: 2.698(4) Å), which are between the during a period of 1 hour and was subsequently cooled to
sum of the van der Waals radii (rvdw(Si–P) = 3.90 Å)24 and the −80 °C. Neat ClPPh2 (2.80 g, 12.70 mmol) was added and the
sum of the covalent radii (rcov(Si–P) = 2.08 Å),25 for the two reaction mixture was allowed to reach room temperature
elements. The mean Si–Si bond lengths in the ring systems during a period of 12 hours. All volatile components were
(11: 2.366(2) Å; 12: 2.372(5) Å) are only slightly longer than that removed under reduced pressure, and the residue then
for Si5Cl10·2MeCN (2.35 Å).28
extracted with toluene. The solvent was removed from the
extract under reduced pressure and the remaining pale yellow
solid was washed two times with hexane (20 ml). Drying
in vacuo gave Ar†(PPh2)NH (5.50 g, 8.44 mmol) as a pale yellow
Conclusion
1
solid. Yield: 73%. M.p.: 174–176 °C. H NMR (C6D6, 400 MHz,
3
In summary, a series of novel, extremely bulky secondary phos- 296 K), δ = 0.93 (d, 6H, JHH = 7 Hz, –CH(CH3)2), 2.46 (sept.,
phinoamines have been synthesised and compared with pre- 1H, JHH = 7 Hz, –CH(CH3)2), 3.65 (d, 1H, JPH = 8 Hz, N–H),
viously reported bulky aryl/silylamines. Deprotonation with 5.93 (d, 2H, JPH = 3 Hz, –CHPh2), 6.92–7.34 (m, 32H, Ar–H).
3
2
5
n-BuLi or KH afforded examples of the respective alkali metal 13C{1H} NMR (C6D6, 76 MHz, 296 K), δ = 24.1 (Ar†–CH(CH3)2),
amides, which proved to be suitable ligands for different chlor- 33.9 (Ar†–CH(CH3)2), 52.7 (CHPh2), 126.6, 128.5, 128.7, 128.8,
osilane fragments. These include compounds derived from 129.2, 130.2, 132.0 (d, JCP = 21 Hz), 139.6 (d, JCP = 3 Hz), 140.9
SiCl4, and the higher homologues, Cl3Si–SiCl3 and cyclic (d, JCP = 12 Hz), 142.7 (d, JCP = 15 Hz), 144.1 (d, JCP = 3 Hz),
Si5Cl10. Attempts at the reduction of the prepared chloro- 144.3 (Ar–C). 31P{1H} NMR (C6D6, 162 MHz, 296 K), δ = 38.2.
aminosilanes revealed them to display unexpected inertness. IR ν/cm−1 (ATR): 1598 (w), 1492 (m), 1446 (m), 1377 (w), 1354
Furthermore, by using more rigorous conditions, a P–N bond (w), 1264 (w), 1090 (w), 1075 (w), 1029 (w), 883 (w), 865 (w), 845
cleavage reaction of one amido ligand was observed. The (w), 745 (m), 726 (s), 692 (s). MS/EI m/z (%): 651.6 (M+, 62),
mono-amide substituted compounds derived from Cl3Si–SiCl3 466.4 (Ar†NH+, 46), 167.0 (Ph2CH+, 35). Anal. calc. (%) for
and Si5Cl10 decompose via an apparent Lewis-base triggered C47H42NP (Mr = 651.83): C, 86.60; H, 6.49; N, 2.15; Found:
eliminition of SiCl2. The bis-amide substituted Si5 ring is kine- C, 86.67; H, 6.53; N, 2.16.
tically protected by the high steric demand of two extremely
Preparation of Ar†(PPh2)NLi (1-Li). The lithium salt was pre-
bulky amido ligands. In addition, the amido-coordinated pared according to a procedure reported in the literature, i.e.
–SiCl3 and –SiCl2–SiCl3 functions can undergo Cl/H-exchange by reaction of 1 with a slight excess of n-butyllithium in
reactions to yield the respective stable silanes with –SiH3 and toluene.17 Compound 1-Li is highly sensitive towards air and
–SiH2–SiH3 fragments. The molecular structures of all species moisture and was therefore only prepared in situ for direct use.
were determined and discussed.
31P{1H} NMR (C6D6, 162 MHz, 296 K), δ = 64.3.
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Preparation of Ar†{P(NEt2)2}NH (2). A solution of n-butyl- for C47H60N3P (Mr = 697.99): C, 80.88; H, 8.66; N, 6.02; Found:
lithium in hexane (7.0 ml, 11.20 mmol) was slowly added to a C, 80.89; H, 8.71; N, 6.08.
solution of Ar†NH2 (5.00 g, 10.7 mmol) in thf (80 ml) at
Preparation of Ar†–N = PNEt2 (4). The ligand Ar†{P(NEt2)2}-
−80 °C. The reaction mixture was allowed to reach room temp- NH was deprotonated using KN(SiMe3) according to a pro-
erature during a period of 1 hour and was subsequently cooled cedure described in the literature, to give Ar†{P(NEt2)2}NK(thf)
to −80 °C. Neat ClP(NEt2)2 (2.50 g, 11.77 mmol) was added (73% yield).32 A solution of Ar†{P(NEt2)2}NK(thf) (1.0 g,
and the reaction mixture was allowed to reach room tempera- 1.33 mmol) in toluene (40 ml) was slowly added to a solution
ture during a period of 12 hours. All volatile components were of Si2Cl6 (0.36 g, 1.33 mmol) in toluene (10 ml) at −80 °C. The
removed under reduced pressure and the remaining pale reaction mixture was allowed to reach room temperature over a
yellow solid was extracted with hexane. The extract was kept at period of 12 hours to furnish a bright yellow solution. The
−30 °C to give pale yellow crystals of 2 (5.50 g, 8.57 mmol). reaction mixture was filtered through a glass fiber pad. All
Yield: 73%. M.p.: 101–103 °C. 1H NMR (400 MHz, C6D6, volatile components were removed from the filtrate under
3
296 K), δ = 0.84 (t, 12H, JHH = 7 Hz, –CH2–CH3), 0.93 (d, 6H, reduced pressure and the residue was washed with minimal
3
3JHH = 7 Hz, –CH(CH3)2), 2.47 (sept., 1H, JHH = 7 Hz, amounts of hexane. The product was dissolved again in
–CH(CH3)2), 2.89 (m, 8H, –CH2–CH3), 3.67 (s, 1H, N–H), 6.50 toluene, concentrated and kept at −30 °C to yield bright yellow
5
(d, 2H, JPH = 7 Hz, –CHPh2), 6.91–7.30 (m, 22H, Ar–H). crystals of 4 (0.40 g, 0.70 mmol). Yield: 53%. M.p.: 137–138 °C.
13C{1H} NMR (C6D6, 76 MHz, 296 K), δ = 15.4 (CH2–CH3), 1H NMR (400 MHz, C6D6, 296 K), δ = 0.60 (m, 3H, –CH3), 0.92
3
24.4 (Ar†–CH(CH3)2), 34.1 (Ar†–CH(CH3)2), 40.7 (N–CH2–), 53.3 (m, 3H, CH3), 1.05 (d, 6H, JHH = 7 Hz, –CH(CH3)2), 2.53 (m,
(CHPh2), 126.9, 128.7, 128.9, 130.6, 137.8, 140.0, 142.4 (Ar–C). 2H, N–CH2–), 2.56 (m, 1H, –CH(CH3)3), 3.38 (m, 2H, N–CH2–),
31P{1H} NMR (C6D6, 162 MHz, 296 K), δ = 102.5. IR ν/cm−1 5.86 (s, 2H, –CHPh2), 6.97–7.23 (m, 32H, Ar–H). 13C{1H} NMR
(ATR): 1598 (w), 1493 (m), 1446 (m), 1373 (w), 1340 (w), (C6D6, 76 MHz, 296 K), δ = 24.5 (Ar†–CH(CH3)2), 33.9 (Ar†–
3
1289 (w), 1264 (w), 1188 (m), 1172 (m), 1124 (w), 1092 (w), CH(CH3)2), 38.5 (m, –CH2–CH3), 40.3 (d, JCP = 38 Hz, PvN–
1007 (m), 910 (m), 897 (m), 878 (w), 866 (w), 830 (m), 785 (m), CH2–), 53.9 (CHPh2), 126.3, 126.7, 128.6, 130.5, 133.0 (d, JCP
=
763 (m), 730 (m), 697 (s). Anal. calc. (%) for C43H52N3P 7 Hz), 140.0, 144.8 (d, JCP = 14 Hz), 145.7 (Ar–C). 31P{1H}
(Mr = 641.88): C, 80.46; H, 8.17; N, 6.55; Found: C, 80.35; NMR (C6D6, 162 MHz, 296 K), δ = 270.2. IR ν/cm−1 (ATR):
H, 8.28; N, 6.49.
1600 (w) 1492 (w), 1464 (m), 1444 (s), 1379 (w), 1322 (m),
Preparation of Ar†{P(NEt2)2}NK (2-K). The potassium salt 1288 (w), 1262 (w), 1206 (m), 1176 (m), 1097 (w), 1075 (m),
was prepared according to a procedure reported in the litera- 1020 (s), 938 (m), 892 (w), 862 (w), 786 (m), 767 (m), 730 (m),
ture, i.e. by reaction of 1 with KH/HMDS.32 Compound 2-K is 697 (s).
highly sensitive towards air and moisture and was therefore
only prepared in situ for direct use. 31P{1H} NMR (C6D6, lithium in hexane (4.0 ml, 6.45 mmol) was slowly added to a
162 MHz, 296 K), δ = 91.9.
solution of Ar†(PPh2)NH (1) (4.00 g, 6.14 mmol) in thf (80 ml)
Preparation of Ar†(PPh2)N–SiCl3 (5). A solution of n-butyl-
Preparation of Ar†{P(NiPr2)2}NH (3). A solution of n-butyl- at −80 °C. The reaction mixture was allowed to reach room
lithium in hexane (7.0 ml, 11.20 mmol) was slowly added to a temperature during a period of 1 hour and was subsequently
solution of Ar†NH2 (5.00 g, 10.7 mmol) in thf (100 ml) at slowly added to a solution of SiCl4 (1.12 g, 6.60 mmol) in thf
−80 °C. The reaction mixture was allowed to reach room temp- (20 ml) at −80 °C. The reaction mixture was allowed to reach
erature during a period of 1 hour and was subsequently cooled room temperature during a period of 12 hours. All volatile
to −80 °C. A solution of ClP(NiPr2)2 (2.99 g, 11.20 mmol) in thf components were removed under reduced pressure and the
(30 ml) was added and the reaction mixture was allowed to remaining colorless solid was extracted with toluene. The
reach room temperature during a period of 12 hours. All vola- solvent was removed under reduced pressure and the remain-
tile components were removed under reduced pressure and ing solid was washed two times with hexane (20 ml). Drying
the remaining pale yellow solid was extracted with hexane. The in vacuo gave 5 (3.51 g, 4.47 mmol) as a fine colorless powder.
extract was kept at −30 °C to give pale yellow crystals of 3 Yield: 73%. M.p.: dec. > 181 °C. 1H NMR (400 MHz, C6D6,
3
(4.50 g, 6.45 mmol). Yield: 58%. M.p.: 136 °C. 1H NMR 296 K), δ = 0.88 (d, 6H, JHH = 7 Hz, –CH(CH3)2), 2.41 (sept.,
3
3
(400 MHz, C6D6, 296 K), δ = 0.93 (d, 6H, JHH = 7 Hz, –CH 1H, JHH = 7 Hz, –CH(CH3)2), 6.71 (s, 2H, –CHPh2), 6.59–8.16
(CH3)2), 0.97 (d, 12H, JHH = 7 Hz, –NCH(CH3)2), 1.17 (d, 12H, (m, 32H, Ar–H). 13C{1H} NMR (C6D6, 76 MHz, 296 K), δ = 23.7
3
3JHH = 7 Hz, –NCH(CH3)2), 2.48 (sept., 1H, JHH = 7 Hz, (Ar†–CH(CH3)2), 33.6 (Ar†–CH(CH3)2), 51.7 (CHPh2), 126.3,
3
3
–CH(CH3)2), 3.34 (m, 4H, JHH = 7 Hz, –NCH(CH3)2), 3.72 (s, 127.0, 128.3, 129.0 (d, JCP = 8 Hz), 130.2, 130.6, 130.9, 131.2,
1H, N–H), 6.50 (m, 2H, –CHPh2), 6.89–7.33 (m, 22H, Ar–H). 135.5 (d, JCP = 28 Hz), 142.6, 143.1 (d, JCP = 5 Hz), 146.8 (Ar–C).
2
13C{1H} NMR (C6D6, 76 MHz, 296 K),
δ
=
24.2 (m, 29Si{1H} NMR (C6D6, 80 MHz, 296 K), δ = −29.4 (d, JPSi
=
N–CH(CH3)2), 24.9 (Ar†–CH(CH3)2), 33.6 (Ar†–CH(CH3)2), 45.9 17 Hz). 31P{1H} NMR (C6D6, 162 MHz, 296 K), δ = 65.7. IR
(N–CH(CH3)2), 52.9 (CHPh2), 126.5, 127.8, 128.5, 130.4, 136.1, ν/cm−1 (ATR): 1599 (w), 1493 (m), 1444 (m), 1435 (m), 1377 (w),
139.9, 140.9, 145.0 (Ar–C). 31P{1H} NMR (C6D6, 162 MHz, 1362 (w), 1249 (w), 1196 (w), 1154 (w), 1114 (m), 1086 (w), 1030
296 K), δ = 78.0. IR ν/cm−1 (ATR): 1492 (w), 1446 (m), 1381 (w), (w), 1001 (w), 969 (w), 949 (s), 917 (w), 872 (w), 817 (m), 742
1174 (m), 1114 (w), 942 (m), 835 (w), 732 (w), 696 (s). MS/EI (m), 696 (s). MS/EI m/z (%): 785.5 (M+, 4), 467.4 (Ar†NH2 , 38),
+
m/z (%): 497 (Ar†NP+, 69), 167.1 (Ph2CH+, 100). Anal. calc. (%) 167.2 (Ph2CH+, 31). Anal. calc. (%) for C47H41Cl3NPSi (Mr =
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785.26): C, 71.89; H, 5.92; N, 1.61; Found: C, 71.88; H, 5.21; (m), 698 (s). MS/EI m/z (%): 867.7 (M+, 19), 217.1 (Ph2SiCl+,
N, 1.74.
58), 167.2 (Ph2CH+, 38%). Anal. calc. (%) for C59H51ClNPSi
Preparation of Ar†(PPh2)N–SiCl2H (6). A solution of n-butyl- (Mr = 868.57): C, 81.59; H, 5.92; N, 1.61; Found: C, 81.43;
lithium in hexane (1.8 ml, 2.91 mmol) was slowly added to a H, 5.87; N, 1.67.
solution of Ar†(PPh2)NH (1) (1.90 g, 2.91 mmol) in diethyl
Preparation of Ar†(PPh2)N–SiH3 (8). To a solution of LiAlH4
ether (80 ml) at −80 °C. The reaction mixture was allowed to (0.19 g, 4.97 mmol) in diethyl ether (20 ml) at −20 °C was
reach room temperature during a period of 1 hour. All volatiles added a solution of Ar†(PPh2)N–SiCl3 (1.30 g, 1.66 mmol) in
were removed under reduced pressure. The residue was dis- diethyl ether (40 ml). The reaction mixture was allowed to
solved in toluene and then slowly added to a solution of reach room temperature during a period of 12 hours. All vola-
HSiCl3 (0.41 g, 3.00 mmol) in toluene (20 ml) at −80 °C. The tile components were removed under reduced pressure and
reaction mixture was allowed to reach room temperature the residue was extracted with toluene. The solution was con-
during a period of 12 hours. The reaction mixture was filtered centrated and kept at −30 °C to give 8 (0.60 g, 0.88 mmol) as
through a glass fiber pad. The solvent was removed from the colorless crystals. Yield: 53%. M.p.: dec > 164 °C. 1H NMR
3
filtrate under reduced pressure and the remaining solid was (400 MHz, C6D6, 296 K), δ = 0.91 (d, 6H, JHH = 7 Hz,
3
washed two times with hexane (20 ml). Drying in vacuo gave –CH(CH3)2), 2.44 (sept., 1H, JHH = 7 Hz, –CH(CH3)2), 3.89 (s,
1
6 (0.85 g, 1.08 mmol) as a fine colorless powder. Yield: 31%. 3H, JSiH = 218 Hz, Si–H), 6.62 (s, 2H, –CHPh2), 6.97–7.95 (m,
M.p.: 168–169 °C. 1H NMR (400 MHz, C6D6, 296 K), δ = 0.87 (d, 32H, Ar–H). 13C{1H} NMR (C6D6, 76 MHz, 296 K), δ = 23.9 (Ar†–
3
3
6H, JHH = 7 Hz, –CH(CH3)2), 2.40 (sept., 1H, JHH = 7 Hz, CH(CH3)2), 33.8 (Ar†–CH(CH3)2), 51.8 (CHPh2), 126.6 (d, JCP
=
1
–CH(CH3)2), 5.12 (s, 1H, JSiH = 339 Hz, Si–H), 6.70 (s, 2H, 36 Hz), 128.4, 128.6, 128.7 (d, JCP = 7 Hz), 129.1, 129.9, 130.3,
–CHPh2), 6.97–8.14 (m, 32H, Ar–H). 13C{1H} NMR (C6D6, 130.6, 134.2 (d, JCP = 24 Hz), 140.2 (d, JCP = 21 Hz), 143.1 (d,
76 MHz, 296 K), δ = 23.7 (Ar†–CH(CH3)2), 33.6 (Ar†–CH(CH3)2), JCP = 4 Hz), 143.7, 146.3 (Ar–C). 1H/29Si HMBC NMR (C6D6,
51.8 (CHPh2), 127.7 (d, JCP = 49 Hz), 128.3, 128.6, 128.9 (d, 80 MHz, 296 K), δ = −47.1 (d, JSiH = 218 Hz). 31P{1H} NMR
1
JCP = 8 Hz), 130.0, 130.2, 130.9, 135.3 (d, JCP = 26 Hz), 136.5 (C6D6, 162 MHz, 296 K), δ = 59.6. IR ν/cm−1 (ATR): 1598 (w),
(JCP = 24 Hz), 143.1, 143.4 (d, JCP = 4 Hz), 146.5, 147.0 (Ar–C). 1493 (m), 1445 (m), 1381 (w), 1320 (w), 1248 (w), 1206 (w),
1
29Si{1H} NMR (C6D6, 80 MHz, 296 K), δ = −23.9 (d, JSiH
=
1160 (w), 1119 (m), 1089 (m), 1031 (w), 1001 (w), 975 (m), 930
339 Hz). 31P{1H} NMR (C6D6, 162 MHz, 296 K), δ = 63.1. IR (s), 882 (m), 843 (m), 765 (m), 742 (m), 696 (s). MS/EI m/z (%):
ν/cm−1 (ATR): 1599 (w), 1492 (m), 1458 (w), 1429 (m), 1380 (w), 681.6 (M+, 35), 496.4 (Ar†NP+, 12). Anal. calc. (%) for
1249 (w), 1202 (w), 1154 (w), 1122 (m), 1109 (m), 1029 (w), C47H44NPSi (Mr = 681.93): C, 82.78; H, 6.50; N, 2.05; Found:
998 (w), 922 (m), 867 (m), 831 (m), 765 (w), 744 (s), 696 (s). C, 82.63; H, 6.64; N, 2.12.
Anal. calc. (%) for C47H42Cl2NPSi (Mr = 750.82): C, 75.19;
Preparation of Ar†(PPh2)N–Si2Cl5 (9). A solution of n-butyl-
H, 5.64; N, 1.87; Found: C, 75.12; H, 5.70; N, 1.92.
lithium in hexane (1.0 ml, 1.61 mmol) was slowly added to a
Preparation of Ar†(PPh2)N–SiPh2Cl (7). A solution of n-butyl- solution of Ar†(PPh2)NH (1) (1.00 g, 1.54 mmol) in diethyl
lithium in hexane (2.2 ml, 3.45 mmol) was slowly added to a ether (40 ml) at −80 °C. The reaction mixture was allowed to
solution of Ar†(PPh2)NH (1) (2.14 g, 3.28 mmol) in diethyl reach room temperature during a period of 1 hour and was
ether (80 ml) at −80 °C. The reaction mixture was allowed to subsequently slowly added to a solution of Si2Cl6 (0.45 g,
reach room temperature during a period of 1 hour and was 1.61 mmol) in diethyl ether (10 ml) at −80 °C. The reaction
subsequently slowly added to a solution of Ph2SiCl2 (0.89 g, mixture was allowed to reach room temperature during a
3.50 mmol) in diethyl ether (20 ml) at −80 °C. The reaction period of 12 hours. All volatile components were removed
mixture was allowed to reach room temperature during a in vacuo and the residue was extracted with toluene. The
period of 12 hours. All volatile components were removed solvent was removed under reduced pressure and the remain-
under reduced pressure and the remaining colorless solid was ing solid was washed two times with hexane (10 ml). Drying
extracted with hot toluene. The solvent was removed under in vacuo gave 9 (0.94 g, 1.06 mmol) as a fine pale yellow solid.
reduced pressure and the remaining solid was washed two Yield: 66%. M.p.: dec > 138 °C. 1H NMR (400 MHz, C6D6,
3
times with hexane (20 ml). Drying in vacuo gave 7 (1.95 g, 296 K), δ = 0.96 (d, 6H, JHH = 7 Hz, –CH(CH3)2), 2.52 (sept.,
3
2.25 mmol) as a fine colorless powder. Yield: 68%. M.p.: 1H, JHH = 7 Hz, –CH(CH3)2), 6.08 (s, 2H, –CHPh2), 6.41–7.53
1
174–176 °C. H NMR (400 MHz, C6D6, 296 K), δ = 0.96 (d, 6H, (m, 32H, Ar–H). 13C{1H} NMR (C6D6, 76 MHz, 296 K), δ = 23.9
3
3JHH = 7 Hz, –CH(CH3)2), 2.51 (sept., 1H, JHH = 7 Hz, (Ar†–CH(CH3)2), 33.8 (Ar†–CH(CH3)2), 52.0 (CHPh2), 126.4 (d,
–CH(CH3)2), 6.62 (s, 2H, –CHPh2), 6.75–7.66 (m, 32H, Ar–H). JCP = 65 Hz), 128.0, 128.2, 128.5, 129.2 (d, JCP = 9 Hz), 129.6,
13C{1H} NMR (C6D6, 76 MHz, 296 K), δ = 23.9 (Ar†–CH(CH3)2), 130.4 (d, JCP = 30 Hz), 131.3 (d, JCP = 12 Hz), 136.0 (d, JCP = 22
33.6 (Ar†–CH(CH3)2), 51.3 (CHPh2), 125.7, 126.3, 127.9, 128.9, Hz), 142.6, 144.4, 145.3, 146.8 (Ar–C). 29Si{1H} NMR (C6D6,
2
128.5 (d, JCP = 8 Hz), 129.9, 130.2, 130.3, 130.6, 131.0, 135.0 (d, 80 MHz, 296 K), δ = −29.4 (d, JSiP = 62 Hz, –SiCl2–), −2.1 (d,
JCP = 23 Hz), 136.3, 136.8 (d, JCP = 22 Hz), 142.9, 144.2, 145.8, 3JSiP = 18 Hz, –SiCl3). 31P{1H} NMR (C6D6, 162 MHz, 296 K), δ =
146.8 (Ar–C). 29Si{1H} NMR (C6D6, 80 MHz, 296 K), δ = −14.5. 49.2. IR ν/cm−1 (ATR): 1493 (m), 1458 (m), 1434 (m), 1377 (m),
31P{1H} NMR (C6D6, 162 MHz, 296 K), δ = 56.8. IR ν/cm−1 1197 (w), 1157 (m), 1118 (m), 1081 (m), 1031 (w), 949 (m), 917
(ATR): 1492 (w), 1458 (m), 1429 (m), 1377 (w), 1202 (w), 1123 (w), 866 (w), 814 (m), 763 (w), 745 (s), 696 (s). MS/EI m/z (%):
(w), 1109 (m), 1029 (w), 923 (w), 867 (m), 831 (m), 765 (w), 744 167.2 (Ph2CH+, 100). Anal. calc. (%) for C47H41NCl5PSi2 (Mr =
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884.25): C, 63.84; H, 4.67; N, 1.58; Found: C, 63.92; H, 4.57; ether (40 ml) at −80 °C. The reaction mixture was allowed to
N, 1.62. reach room temperature during a period of 1 hour. All volatiles
Preparation of Ar†(PPh2)N–Si2H5 (10). To a solution of were removed under reduced pressure. The residue was dis-
LiAlH4 (0.10 g, 2.54 mmol) in diethyl ether (20 ml) at −20 °C solved in toluene and was then slowly added to a solution of
was added a solution of Ar†(PPh2)N–Si2Cl5 (0.45 g, 0.51 mmol) Si5Cl10 (0.24 g, 0.48 mmol) in toluene (10 ml) at −80 °C. The
in diethyl ether (40 ml). The reaction mixture was allowed to reaction mixture was allowed to reach room temperature
reach room temperature during a period of 12 hours. All vola- during a period of 12 hours. The reaction mixture was then fil-
tile components were removed under reduced pressure and tered through a glass fiber pad. The solvent was removed from
the residue was extracted with toluene. The extract was concen- the filtrate under reduced pressure and the remaining solid
trated and kept at −30 °C to give 10 (0.22 g, 0.31 mmol) as was washed two times with hexane (10 ml) at 0 °C. The impure
colorless crystals. Yield: 61%. M.p.: 176 °C. 1H NMR (400 MHz, product was dissolved in a minimum amount of toluene and
C6D6, 296 K), δ = 0.91 (d, 6H, 3JHH = 7 Hz, –CH(CH3)2), 2.40 (m, kept at −30 °C to give pale yellow crystals of 12 (0.50 g,
3
3H, SiH3), 2.44 (sept., 1H, JHH = 7 Hz, –CH(CH3)2), 4.58 (m, 0.29 mmol). Yield: 60%. M.p.: dec > 153 °C. 1H NMR
2H, –SiH2–), 6.57 (s, 2H, –CHPh2), 6.94–7.91 (m, 32H, Ar–H). (400 MHz, C6D6, 296 K), δ = 1.04 (m, 12H, –CH(CH3)2), 2.62
3
1H/29Si HMBC NMR (C6D6, 80 MHz, 296 K), δ = −99.8 (d, (sept., 2H, JHH = 7 Hz, –CH(CH3)2), 6.32–7.64 (m, 64H, CHPh2
1JSiH = 196 Hz, –SiH3), −38.6 (d, 1JSiH = 208 Hz, –SiH2–). 31P{1H} and Ar–H). 13C{1H} NMR (C6D6, 76 MHz, 296 K), δ = 23.9 (Ar†–
NMR (C6D6, 162 MHz, 296 K), δ = 63.5. IR ν/cm−1 (ATR): CH(CH3)2), 24.1 (Ar†–CH(CH3)2), 33.9 (Ar†–CH(CH3)2), 51.7
2118 (w), 1598 (w), 1492 (m), 1445 (m), 1380 (m), 1200 (w), (CHPh2), 125.7, 126.1 (d, JCP = 17 Hz), 126.6 (d, JCP = 9 Hz),
1158 (w), 1119 (m), 1088 (m), 1030 (w), 934 (m), 919 (m), 126.8, 128.6, 128.8, 129.3, 130.4 (d, JCP = 5 Hz), 130.6, 130.8,
893 (m), 878 (m), 832 (m), 812 (s), 761 (m), 737 (s), 695 (s). 131.2, 135.2, 135.4, 138.0, 143.4 (d, JCP = 34 Hz), 144.3, 144.7
MS/EI m/z (%): 452.3 (Ar†+, 12), 167.0 (Ph2CH+, 81). Anal. calc. (d, JCP = 20 Hz), 146.0 (d, JCP = 24 Hz), 146.9 (Ar–C). 29Si{1H}
(%) for C47H46NPSi2 (Mr = 712.04): C, 79.28; H, 6.51; N, 1.97; NMR (C6D6, 80 MHz, 296 K), δ = −38.3 (d, 2JPSi = 51 Hz), 4.1 (d,
4
Found: C, 79.19; H, 6.62; N, 2.01.
3JPSi = 29 Hz), 9.2 (d, JPSi = 19 Hz). 31P{1H} NMR (C6D6,
Preparation of Ar†(PPh2)N–Si5Cl9 (11). A solution of n-butyl- 162 MHz, 296 K), δ = 42.2 (br). IR ν/cm−1 (ATR): 1599 (w), 1492
lithium in hexane (0.4 ml, 0.60 mmol) was slowly added to a (m), 1449 (m), 1433 (m), 1378 (w), 1200 (w), 1158 (w), 1120 (m),
solution of Ar†(PPh2)NH (1) (0.39 g, 0.60 mmol) in diethyl 1077 (m), 1031 (w), 934 (w), 866 (m), 822 (m), 743 (m), 696 (s).
ether (30 ml) at −80 °C. The reaction mixture was allowed to Anal. calc. (%) for C94H82Cl8N2P2Si5 (Mr = 1725.68): C, 65.43;
reach room temperature during a period of 1 hour. All volatiles H, 4.79; N, 1.62; Found: C, 65.31; H, 6.85; N, 1.62.
were removed under reduced pressure. The residue was dis-
X-ray crystallography
solved in toluene and then slowly added to a solution of
Si5Cl10 (0.30 g, 0.61 mmol) in toluene (10 ml) at −80 °C. The Single crystals of compounds 1, 2, 2-K, 3, 4, 5, 6, 7, 8, 9, 10, 11
reaction mixture was allowed to reach room temperature and 12 suitable for X-ray structural determination were
during a period of 12 hours. The reaction mixture was then fil- mounted in silicone oil. Crystallographic measurements for
tered through a glass fiber pad. The solvent was then removed compounds 1, 2, 3, 5, 6 and 9 were carried out on either a
from the filtrate under reduced pressure and the remaining Bruker X8 Apex and an Oxford Gemini Ultra diffractometer
solid was washed two times with hexane (10 ml) at 0 °C. using a graphite monochromator with Mo Kα radiation (λ =
Drying in vacuo gave 11 (0.35 g, 0.32 mmol) as a pale yellow 0.71073 Å), and for compounds 2-K, 4, 7, 8, 10, 11 and 12 the
1
solid. Yield: 53%. M.p.: dec > 80 °C. H NMR (400 MHz, C6D6, MX1 beamline of the Australian Synchrotron (λ = 0.71090 Å).
3
296 K), δ = 0.87 (d, 6H, JHH = 7 Hz, –CH(CH3)2), 2.41 (sept., The software package Blu-Ice33 was used for synchrotron data
1H, 3JHH = 7 Hz, –CH(CH3)2), 6.23 (d, 2H, 5JPH = 7 Hz, –CHPh2), acquisition, while the program XDS34 was employed for syn-
6.36 (s, 2H, Ar–H), 6.83–7.42 (m, 32H, Ar–H). 13C{1H} NMR chrotron data reduction. The structures were solved by direct
(C6D6, 76 MHz, 296 K), δ = 23.7 (Ar†–CH(CH3)2), 33.5 (Ar†– methods and refined on F2 by full matrix least squares
CH(CH3)2), 51.6 (CHPh2), 126.1, 127.2, 128.7, 129.3 (d, JCP
9 Hz), 129.7, 130.3 (d, JCP = 31 Hz), 131.7, 133.0, 135.4 (d, JCP
=
=
(SHELX97)35 using all unique data. Hydrogen atoms have been
included in calculated positions (riding model) for all struc-
18 Hz), 143.4, 144.1, 145.3 (Ar–C). 29Si{1H} NMR (C6D6, tures. The asymmetric unit of the crystal structure of com-
2
3
80 MHz, 296 K), δ = −38.2 (d, JPSi = 57 Hz), 0.4 (d, JPSi
=
pound 8 was found to exhibit site disorder between a 50 : 50
4
26 Hz), 1.7 (d, JPSi = 4 Hz). 31P{1H} NMR (C6D6, 162 MHz, ratio of a molecule of the protonated ligand (Ar†(PPh2)NH) and
296 K), δ = 51.9. IR ν/cm−1 (ATR): 1493 (w), 1449 (m), 1436 (m), 8, sitting on the molecular same site. This disorder was suc-
1385 (w), 1198 (w), 1157 (w), 1120 (m), 1102 (w), 1031 (w), 940 cessfully modelled. For the crystal structure of compound 12,
(m), 864 (w), 819 (m), 745 (m), 698 (s). MS/EI m/z (%): 651.5 only a low value (20.96°) for Ɵmax for the diffraction data could
(Ar†(PPh2)NH+, 100), 466.3 (Ar†NH+, 42), 167.1 (Ph2CH+, 31). be attained. This arose from the data above that angle being
Anal. calc. (%) for C47H41Cl9NPSi5 (Mr = 1110.30): C, 50.84; H, too weak to observe. Hence, the software used to integrate the
3.72; N, 1.26; Found: C, 50.83; H, 3.81; N, 1.28.
diffraction data at the Australian Synchrotron discarded these
Preparation of Ar†{(PPh2)N}2Si5Cl8 (12). A solution of data. This resulted in the poor quality of the crystal structure.
n-butyllithium in hexane (0.6 ml, 0.96 mmol) was slowly added Although the metrical parameters for the compound should
to a solution of Ar†(PPh2)NH (1) (0.62 g, 0.96 mmol) in diethyl not be considered as accurate, the gross molecular connectivity
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of the compound is unambiguous. Crystal data, details of data
collections and refinement are given in Table S1 in the ESI.†
K. Junold, J. A. Baus, C. Burschka and R. Tacke, Angew.
Chem., Int. Ed., 2012, 51, 7020–7023.
13 M. Alajarín, C. López-Leonardo and P. Llamas-Lorente,
Top. Curr. Chem., 2005, 250, 77–106; Z. Fei and P. J. Dyson,
Coord. Chem. Rev., 2005, 249, 2056–2074.
14 A. Stasch, Angew. Chem., Int. Ed., 2012, 51, 1930–1933;
A. L. Hawley and A. Stasch, Eur. J. Inorg. Chem., 2015, 2015,
258–270.
15 J. Wang, R. Liu, W. Ruan, Y. Li, K. C. Mondal,
H. W. Roesky and H. Zhu, Organometallics, 2014, 33,
2696–2703.
Acknowledgements
C.J. acknowledges funding from the Australian Research
Council. T.B. greatfully acknowledges a Feodor Lynen Stipend
by the Alexander von Humboldt Foundation. Part of this
research was carried out at the Australian Synchrotron.
16 H. Sisler and N. Smith, J. Org. Chem., 1961, 26, 611–613.
17 N. Poetschke, M. Nieger, M. A. Khan, E. Niecke and
M. T. Ashby, Inorg. Chem., 1997, 36, 4087–4093.
Notes and references
18 E. Niecke and W. Flick, Angew. Chem., Int. Ed. Engl., 1973,
12, 585–586; O. J. Scherer and N. Kuhn, Angew. Chem., Int.
Ed. Engl., 1974, 13, 811–812; S. Pohl, Chem. Ber., 1979, 112,
3159–3165; E. Niecke and D. Gudat, Angew. Chem., Int. Ed.
Engl., 1991, 103, 251–270; A. N. Chernega, A. A. Korkin and
V. D. Romanenko, Zh. Obshch. Khim. (Russ. J. Gen. Chem.),
1995, 65, 1823–1833; K. Miqueu, J.-M. Sotiropoulos,
G. Pfister-Guillouzo, V. L. Rudzevich, H. Gornitzka,
V. Lavallo and V. D. Romanenko, Eur. J. Inorg. Chem., 2004,
2004, 2289–2300.
1 J. Arnold, Dalton Trans., 2008, 4334–4335; C. Jones and
G. A. Koutsantonis, Aust. J. Chem., 2013, 66, 1115–1117.
2 Y. Peng, M. Brynda, B. D. Ellis, J. C. Fettinger, E. Rivard
and P. P. Power, Chem. Commun., 2008, 6042–6044.
3 Y. Peng, B. D. Ellis, X. Wang and P. P. Power, J. Am. Chem.
Soc., 2008, 130, 12268–12269; G. D. Frey, J. D. Masuda,
B. Donnadieu and G. Bertrand, Angew. Chem., Int. Ed.,
2010, 49, 9444–9447; R. C. Fischer and P. P. Power, Chem.
Rev., 2010, 110, 3877–3923; P. P. Power, Nature, 2010, 463,
171–177; D. Martin, M. Soleilhavoup and G. Bertrand, 19 S. P. Green, C. Jones and A. Stasch, Science, 2007, 318,
Chem. Sci., 2011, 2, 389–399; P. P. Power, Acc. Chem. Res.,
2011, 44, 627–637; M. Asay, C. Jones and M. Driess, Chem.
Rev., 2011, 111, 354–396.
1754–1757; C. Jones and A. Stasch, Top. Organomet. Chem.,
2013, 45, 73–101.
20 F. Dornhaus, M. Bolte, H.-W. Lerner and M. Wagner,
Eur. J. Inorg. Chem., 2006, 2006, 1777–1785.
4 R. S. Ghadwal, R. Azhakar and H. W. Roesky, Acc. Chem.
Res., 2013, 46, 444–456; S. S. Sen, S. Khan, S. Nagendran 21 W. Malisch, H. Jehle, S. Möller, G. Thum, J. Reising,
and H. W. Roesky, Acc. Chem. Res., 2012, 45, 578–587.
5 S. Yao, Y. Xiong and M. Driess, Organometallics, 2011, 30,
1748–1767.
A. Gbureck, V. Nagel, C. Fickert, W. Kiefer and M. Nieger,
Eur. J. Inorg. Chem., 1999, 1999, 1597–1605.
22 H. Stueger, T. Mitterfellner, R. Fischer, C. Walkner, M. Patz
and S. Wieber, Inorg. Chem., 2012, 51, 6173–6179.
6 J. Li, C. Schenk, F. Winter, H. Scherer, N. Trapp, A. Higelin,
S. Keller, R. Pottgen, I. Krossing and C. Jones, Angew. 23 N. W. Mitzel, Chem. – Eur. J., 1998, 4, 692–698.
Chem., Int. Ed., 2012, 51, 9557–9561; J. Li, M. Hermann, 24 A. Bondi, J. Phys. Chem., 1964, 68, 441–451.
G. Frenking and C. Jones, Angew. Chem., Int. Ed., 2012, 51, 25 B. Cordero, V. Gomez, A. E. Platero-Prats, M. Reves,
8611–8614; M. Hermann, C. Goedecke, C. Jones and
G. Frenking, Organometallics, 2013, 32, 6666–6673.
J. Echeverria, E. Cremades, F. Barragan and S. Alvarez,
Dalton Trans., 2008, 2832–2838.
7 T. J. Hadlington, M. Hermann, J. Li, G. Frenking and 26 R. S. Simons, S. T. Haubrich, B. V. Mork,
C. Jones, Angew. Chem., Int. Ed., 2013, 52, 10199–10203.
8 T. J. Hadlington, M. Hermann, G. Frenking and C. Jones,
M. Niemeyer and P. P. Power, Main Group Chem.,
1998, 2, 275–283.
J. Am. Chem. Soc., 2014, 136, 3028–3031; T. J. Hadlington 27 T. J. Drahnak, R. West and J. C. Calabrese, J. Organo-
and C. Jones, Chem. Commun., 2014, 50, 2321–2323.
9 J. Li, A. Stasch, C. Schenk and C. Jones, Dalton Trans.,
2011, 40, 10448–10456.
10 E. W. Y. Wong, D. Dange, L. Fohlmeister, T. J. Hadlington
and C. Jones, Aust. J. Chem., 2013, 66, 1144–1154.
met. Chem., 1980, 198, 55–69; H. Stüger, P. Lassacher
and E. Hengge, Z. Anorg. Allg. Chem., 1995, 621, 1517–
1522; U. Oöschl, H. Siegl and K. Hassler, J. Organo-
met. Chem., 1996, 506, 93–100; H. Wagner, A. Wallner,
J.
Fischer,
M.
Flock,
J.
Baumgartner
and
11 R. S. Ghadwal, H. W. Roesky, S. Merkel, J. Henn and
D. Stalke, Angew. Chem., Int. Ed., 2009, 48, 5683–5686.
12 M. Denk, R. Lennon, R. Hayashi, R. West, A. V. Belyakov,
H. P. Verne, A. Haaland, M. Wagner and N. Metzler, J. Am.
Chem. Soc., 1994, 116, 2691–2692; S. S. Sen, A. Jana,
H. W. Roesky and C. Schulzke, Angew. Chem., Int. Ed., 2009,
C. Marschner, Organometallics, 2007, 26, 6704–6717;
K. Abersfelder, A. Russell, H. S. Rzepa, A. J. White,
P. R. Haycock and D. Scheschkewitz, J. Am. Chem.
Soc., 2012, 134, 16008–16016; X. Q. Xiao, H. Zhao,
Z. Xu, G. Lai, X. L. He and Z. Li, Chem. Commun.,
2013, 49, 2706–2708.
48, 8536–8538; S. S. Sen, H. W. Roesky, D. Stern, J. Henn 28 X. Dai, K. J. Anderson, D. L. Schulz and P. Boudjouk,
and D. Stalke, J. Am. Chem. Soc., 2010, 132, 1123–1126;
Dalton Trans., 2010, 39, 11188–11192.
This journal is © The Royal Society of Chemistry 2015
Dalton Trans.

View Article Online
Paper
Dalton Transactions
29 G. Berthon-Gelloz, M. A. Siegler, A. L. Spek, B. Tinant, 33 T. M. McPhillips, S. E. McPhillips, H.-J. Chiu,
J. N. Reek and I. E. Marko, Dalton Trans., 2010, 39, 1444–1446.
30 P. G. Chantrell, C. A. Pearce, C. R. Toyer and R. Twaits,
J. Appl. Chem., 2007, 14, 563–564.
31 E. Hengge and D. Kovar, J. Organomet. Chem., 1977, 125,
C29–C32.
A. E. Cohen, A. M. Deacon, P. J. Ellis, E. Garman,
A. Gonzalez, N. K. Sauter, R. P. Phizackerley,
S. M. Soltis and P. Kuhn, J. Synchrotron Radiat., 2002,
9, 401–406.
34 W. Kabsch, J. Appl. Crystallogr., 1993, 26, 795–800.
32 D. Dange, J. Li, C. Schenk, H. Schnöckel and C. Jones, 35 G. M. Sheldrick, Acta Crystallogr., Sect. A: Fundam. Crystal-
Inorg. Chem., 2012, 51, 13050–13059. logr., 2008, 64, 112–122.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2015