Branched tetrasilane substituted phosphines-synthesis and characterisation of PhSi(SiiPr2)3P and {PhSi(SiMe2) 3}2P14

Article abstract of DOI:10.1039/c4cc00165f

The branched trichlorotetrasilane PhSi(SiMe₂Cl)₃ reacts with P₇(SiMe₃)₃ leading to formation of a new oligophosphane {PhSi(SiMe₂)₃}₂P ₁₄ (1), which consists of two PhSi(SiMe₂)₃ substituted P₇ norbornane units. The phosphatetrasila[1.1.1]pentane derivative PhSi(SiiPr₂)₃P (3) was obtained from the reaction of PhSi(SiiPr₂Cl)₃ (2) with Li₃P. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4cc00165f

Volume 50 Number 34 4 May 2014 Pages 4385–4512
ChemComm
Chemical Communications
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COMMUNICATION
Michael Feierabend and Carsten von Hänisch
Branched tetrasilane substituted phosphines – synthesis and
characterisation of PhSi(SiiPr2)3P and {PhSi(SiMe2)3}2P14

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Branched tetrasilane substituted phosphines –
synthesis and characterisation of PhSi(SiiPr2)3P
and {PhSi(SiMe2)3}2P14†
Cite this: Chem. Commun., 2014,
50, 4416
Received 8th January 2014,
Accepted 22nd February 2014
Michael Feierabend and Carsten von Hanisch*
¨
DOI: 10.1039/c4cc00165f
www.rsc.org/chemcomm
The branched trichlorotetrasilane PhSi(SiMe2Cl)3 reacts with P7(SiMe3)3
leading to formation of a new oligophosphane {PhSi(SiMe2)3}2P14 (1),
which consists of two PhSi(SiMe2)3 substituted P7 norbornane units. The
phosphatetrasila[1.1.1]pentane derivative PhSi(SiiPr2)3P (3) was obtained
from the reaction of PhSi(SiiPr2Cl)3 (2) with Li3P.
Silicon–phosphorus compounds are still of considerable interest due
to their versatile molecular structures and bonding properties. More-
over, they are useful synthons for the formation of several other
phosphorus as well as silicon compounds.1 Silyl groups are also able
to stabilise highly reactive phosphorus species such as P73ꢀ, the
silylderivatives of which (e.g. P7(SiMe3)3 or P7{Si(SiMe3)3}3) are much
less reactive during oxidation or hydrolysis.2 As shown in recent
studies, bridging silyl substituents such as bidentate silyl or siloxane
groups have a major impact on the structures and properties of
oligophosphanes.3 Thus, we decided to investigate the extent to
which tripodal silyl groups are able to stabilise new Pn-compounds.4
Herein, we report on the application of the compound
PhSi(SiMe2Cl)3 as a substituent for P73ꢀ. Moreover, we present
the synthesis of the sterically demanding branched trichloro-
tetrasilane PhSi(SiiPr2Cl)3 as well as its reaction with Li3P.
After work-up of the reaction of P7(SiMe3)3 with PhSi(SiMe2Cl)3 in
DME, {PhSi(SiMe2)3}2P14 (1) was obtained as yellow crystals in 53%
yield. The latter was formed by dimerisation of the P7 cage through
substitution of the silyl groups and represents a silyl derivative of the
so far unknown Zintl anion P146ꢀ. The P14 framework of compound
1 consists of two P7 norbornane cages. In both P7 norbornane
subunits, one P5 ring is substituted by the branched silyl frame in
1, 2 and 4 positions (Fig. 1). These two P5Si4 fragments show the
same structure as the P9 cage in Hittorf’s phosphorus, and they are
Fig. 1 Molecular structure of 1; thermal ellipsoids represent a 50% probability
level, hydrogen atoms are not shown, selected bond lengths (pm) and angles (1):
Si1–Si2 233.5(4), Si1–Si3 232.9(5), Si1–Si4 234.24(4), Si2–P1 229.3(4), Si3–P2
229.9(4), Si4–P4 228.3(4), P1–P2 225.4(4), P1–P5 221.0(4), P2–P3 221.65(4),
P3–P4 217.6(4), P4–P5 219.9(4), P5–P6 218.6(4), P6–P7 229.4(4), P6–P70
224.0(4); Si2–Si1–Si3 98.88(16), Si2–Si1–Si4 107.90(14), Si3–Si1–Si4 106.70(15),
P1–Si2–Si1 102.70(15), P2–Si3–Si1 102.57(15), P4–Si4–Si1 110.70(16).
connected through a central P4 ring. Until now, no comparable P14
substructure has been observed in molecular compounds. The
known Zintl ion P14 consists of two P7 nortricyclan cages con-
¨
Fachbereich Chemie and Wissenschaftliches Zentrum fur Materialwissenschaften
4ꢀ
¨
(WZMW) of the Philipps-Universitat Marburg, Hans-Meerwein-Straße,
nected by one P–P bond.5 P14iPr4, consists – like compound 1 – of
two P7 norbornane units, which are connected by three P–P bonds
via P5 rings in 1, 2, and 4 positions (Scheme 1).6 The P14 unit in 1,
however, represents a part within the phosphorus strands in
[(CuI)8P12].7
D-35032 Marburg, Germany. E-mail: haenisch@chemie.uni-marburg.de
† Electronic supplementary information (ESI) available: DFT calculations, crystallo-
graphic data of compound 2, proposed mechanism for the formation of
compound 1 and 31PNMR spectrum of compound 1. CCDC 978105 (1), 978107
(2) and 978106 (3). For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c4cc00165f
4416 | Chem. Commun., 2014, 50, 4416--4419
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Scheme 1 Structurally characterised ionic/molecular compounds with
P14 units.
The 31P{1H} NMR spectrum of 1 shows four signals at 50.9,
9.1, 2.4 and ꢀ42.6 ppm corresponding to the four different
phosphorus positions within the molecule. Unfortunately,
these signals are broad, independent of the temperature and
solvent. So, the fine structure can be resolved only for the signal
at 50.9 ppm, which shows a triplet structure and represents the
symmetrically surrounded phosphorus atoms P4 and P40.
Some years ago, several groups reported on their attempts to
synthesise a 1-phospha-2,3,4,5-tetrasila[1.1.1]pentane.8 These
experiments, however, always led to the formation of other
bicyclic silylphosphines as shown in Scheme 2.
In order to avoid decomposition of the Si4 substructure, we
synthesised the sterically more demanding substituted branched
trichlorotetrasilane PhSi(SiiPr2Cl)3 (2) as starting compound. 2 was
obtained in a two-step synthesis by a reductive coupling of PhSiCl3
and iPr2SiHCl with elementary lithium and subsequent chlorination
with trichloroisocyanuric acid (TCCA) (Scheme 3).9
After work-up, the reaction of 2 with Li3P in THF provides the
target molecule as a white crystalline solid in small but reproducible
yields (Fig. 2). Other products could not be characterised to date. The
crystal structure analysis shows the strained molecular structure with
endocyclic bond angles all below 901: Si–Si–Si: 81.6–82.51, Si–Si–P:
80.2–80.61 and Si–P–Si: 83.3–83.61. The bond lengths in compound
3, however, are only slightly longer than the usual single bond
between these elements (Fig. 2). Worth mentioning are the short
distances between the atoms Si2, Si3 and Si4 (307.7(9)–309.0(12) pm)
and between Si1 and P (301.2(10) pm), which are significantly
shorter than the sum of the van der Waals radii.
Fig. 2 Molecular structure of 3; thermal ellipsoids represent a 50% probability
level, hydrogen atoms are not shown, selected bond lengths (pm) and angles
(1): Si1–Si2 235.46(8), Si1–Si3 235.01(14), Si1–Si4 233.61(12), Si2–P 230.05(14),
Si3–P 232.56(9), Si4–P 231.60(11); Si–Si1–Si 81.61(4)–82.52(4), Si1–Si–P
80.19(4)–80.68(4), Si–P–Si 83.30(4)–83.60(4).
The 31P NMR spectrum of compound 3 shows a typical
upfield shift for silylphosphines at ꢀ241.7 ppm. In the 29Si{1H}
NMR, two doublet signals can be observed at 15.4 and ꢀ58.2 ppm.
The signal at 15.4 ppm corresponds to the SiiPr2 groups and shows
1
a remarkably large JSi,P coupling constant of 53.2 Hz. This large
coupling constant suggests a high s-orbital contribution to the Si–P
s-bonds and matches the results of DFT calculations (see ESI†),
which show a high p-orbital character of the phosphorus lone pair
and a symmetric bonding orbital with significant contributions of
Si1–Si4 and P atomic s-orbitals. For comparison, the similar
substituted but planar compound P(SiiPr3)3 shows a 1JSi,P coupling
of only 9 Hz.10
All working procedures were conducted under rigorous exclusion
of oxygen and moisture using a Schlenk line and an argon atmo-
sphere. Solvents were dried and freshly distilled before use. NMR
spectra were recorded using a BRUKER AVANCE 300 or a BRUKER
DRX 400. The structural analysis was carried out using appropriate
single crystals on an automatic diffractometer (STOE-IPDS-2T, STOE-
IPDS-2 or BRUKER D8-Quest). The structures were solved and
refined using SHELXS-9711 and SHELXL-2013.12 The presentation
of crystal structures was effected by DIAMOND3.2. IR vibrational
spectra were recorded using the BRUKER ALPHA ATR-FT-IR. The
starting materials PhSi(SiMe2Cl)3,4 P7(SiMe3)3,2 and Li3P13 were
prepared by reported methods.
Scheme 2 Reported attempts to synthesise a 1-phospha-2,3,4,5-tetrasila-
[1.1.1]pentane and the obtained products.8
%
Crystal data for 1: C24H46Si8P14ꢁ1.5 C7H8, 100 K, triclinic, P1,
a = 931.0(2), b = 1656.6(4), c = 1880.4(4) pm, a = 88.880(19)1, b =
87.593(19)1, g = 77.702(18)1, V = 2830.9(11) Å3, Z = 2, density =
1.327 g cm3, m = 0.619 mmꢀ1, F(000) = 1174, GOF = 0.742, theta
range: 1.26–24.001, 12 809 reflections collected, 8177 unique
(Rint = 0.1002). R1 (wR2) = 0.0716 (0.1586) for 530 parameters
and 3183 reflections with I 4 2s(I).
%
Crystal data for 3: C24H47Si4P1, 100 K, triclinic, P1, a = 916.4(3), b =
1020.7(3), c = 1644.1(9) pm, a = 92.88(4)1, b = 94.84(4)1, g = 110.34(2)1,
V = 1431.7(10) Å3, Z = 2, density = 1.111 g cm3, m = 0.273 mmꢀ1
,
Scheme 3 Synthesis pathway of compound 2.
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F(000) = 524, GOF = 1.036, theta range: 1.25–25.001, 9353 reflections (s, C6H5), 132.31 (s, C6H5), 138.85 (s, C6H5). 29Si{1H}-NMR
collected, 4731 unique (Rint = 0.0205). R1 (wR2) = 0.0247 (0.0657) for (C6D6): d/ppm = 33.4 (s, SiCH(CH3)2), ꢀ70.6 (s, SiC6H5).
262 parameters and 4266 reflections with I 4 2s(I).
MS(APCI+) m/z (%) calc.: 517.2126 [M+ ꢀ Cl], found: 517.2126
1: PhSi(SiMe2Cl)3 (0.42 g, 1.1 mmol) in dme (20 mL) was added [M+ ꢀ Cl] (100); IR [cmꢀ1]: 424(w), 463(s), 553(vs), 599(s),
dropwise to a solution of P7(SiMe3)3 (0.48 g, 1.1 mmol) in dme 621(m), 655(m), 700(m), 735(m), 760(w), 875(s), 991(m),
(20 mL) at ꢀ45 1C. The reaction mixture was allowed to warm up 1233(vw), 1365(w), 1427(w), 1461(m), 2867(m), 2948(m).
within 4 h to ambient temperature, the solvent was removed under
3: PhSi(SiiPr2Cl)3 (1.34 g, 2.42 mmol) in thf (10 mL) was
reduced pressure and the residue was dissolved in 5 mL toluene. added to a suspension of Li3P (0.13 g, 2.50 mmol) in thf
Subsequently, after 2 days yellow crystals of [{PhSi(SiMe2)3}2P14]ꢁ1.5 tol (100 mL) at ꢀ30 1C. Subsequently, the reaction mixture was
were obtained at 20 1C in a yield of 53% (0.29 g). Elemental analysis first warmed-up to room temperature and stirred for 16 hours
(%): calc. for C24H46Si8P14: C 29.03, H 4.67, found: C 29.09, H 5.07.
and then heated to reflux for 4 days. Thereafter, the solvent
1H-NMR (thf-d8): d/ppm = 0.35 (m, CH3, 12H), 0.78 (m, CH3, 12H), was removed under reduced pressure, and the residue was
0.92 (m, CH3, 12H), 7.28 (m, C6H5, 6H), 7.39 (m, C6H5, 4H). dissolved in n-pentane (25 mL). After filtration, the volume of
13C{1H}-NMR (thf-d8): d/ppm = 2.96 (m, CH3), 3.68 (m, CH3), the solution was reduced to 2 mL and cooled down to ꢀ30 1C.
128.24 (s, C6H5), 128.66 (s, C6H5), 129.11 (s, C6H5), 136.56 Compound 3 was obtained as colourless crystals within 4 days
(s, C6H5). 29Si{1H}-NMR (thf-d8): d/ppm = ꢀ4.3 (m, Si(CH3)2), in a yield of 8.8% (0.10 g). Elemental analysis (%): calc. for
ꢀ5.8 (m, Si(CH3)2), ꢀ77.5 (s, SiC6H5). 31P-NMR (thf-d8): d/ppm =
C
24H48Si4P: C 60.19, H 9.89, found: C 60.24, H 10.03.
1
3
51.0 (t, JPP = 328.1 Hz), 9.1 (m), 2.4 (m), ꢀ42.6 (m). MS(ESI+)
1H-NMR (C6D6): d/ppm = 1.36 (d, JHH = 7.5 Hz, CH(CH3)2,
m/z (%) calc.: 992.8153 [M+ + H], found: 992.8265 (45).
18H), 1.38 (d, JHH = 7.5 Hz, CH(CH3)2, 18H), 1.71 (sep, JHH =
3
3
PhSi(SiiPr2H)3: A solution of PhSiCl3 (12.63 g, 0.06 mol) and 7.5 Hz, CH(CH3)2, 6H), 7.09 (m, C6H5, 3H), 7.70 (m, C6H5, 2H).
2
iPr2HSiCl (44.96 g, 0.29 mol) in thf (250 mL) was slowly dropped 13C{1H}-NMR (C6D6): d/ppm = 18.91 (d, JCP = 5.2 Hz,
2
3
at ambient temperature to a vigorously stirred suspension of Li cuts CH(CH3)2), 20.92 (d, JCP = 1.1 Hz, CH(CH3)2), 21.36 (d, JCP
=
(3.32 g, 0.48 mol) in thf (250 mL) over 3 h, and stirring was continued 1.5 Hz, CH(CH3)2), 128.67 (s, C6H5), 129.22 (s, C6H5), 133.40
for 24 h. The suspension was poured into a mixture of ice and HCl (s, C6H5), 138.25 (s, C6H5). 29Si{1H}-NMR (C6D6): d/ppm =
1
2
(200 mL, 1 M) and n-pentane (100 mL) was added. The organic 15.4 (d, JSiP = 53.2 Hz, Si3P), ꢀ58.2 (d, JSiP = 8.5 Hz, SiC6H5).
phase was separated, the aqueous layer was extracted twice with 31P-NMR(C6D6): d/ppm = ꢀ241.7 (s). MS(APCIꢀ) m/z (%) calc.:
n-pentane (100 mL) and the combined organic phases were 479.2565 [M + H], found: 479.2560 [M + H] (30).
dried with MgSO4 and filtered. After evaporation of the solvents,
the raw product was distilled fractionally under vacuum to afford Forschungsgemeinschaft (DFG). The authors gratefully acknowledge
PhSi(SiiPr2H)3 (10ꢀ2 mbar, 120 1C) in a yield of 62.8% (16.9 g).
financial support from Evonik Industries AG, Creavis. The authors
1H-NMR (C6D6): d/ppm = 1.18 (d, 3JHH = 7.4 Hz, CH(CH3)2, 18H), thank Mr Gu¨nther Thiele for his help with the cover picture and the
This work was financially supported by the Deutsche
3
3
1.20 (d, JHH = 7.4 Hz, CH(CH3)2, 18H), 1.42 (d, sep, JHH = 7.4 Hz, DFT calculations.
3
and 2.7 Hz, CH(CH3)2, 6H), 4.18 (t, JHH = 2.7 Hz, SiH, 3H), 7.11
(m, C6H5, 3H), 7.80 (m, C6H5, 2H). 13C{1H}-NMR (C6D6): d/ppm =
Notes and references
13.96 (s, CH(CH3)2), 21.40 (s, CH(CH3)2), 22.98, (s, CH(CH3)2), 128.51
(s, C6H5), 129.29 (s, C6H5), 135.52 (s, C6H5), 138.42 (s, C6H5).
29Si-NMR (C6D6): d/ppm = ꢀ6.4 (d, m, 1JSiH = 172.3 Hz, SiCH(CH3)2),
ꢀ81,2 (s, SiC6H5). MS(APCI+) m/z (%) calc.: 449.2906 [M+ ꢀ H],
found: 449.2903 (15); IR [cmꢀ1]: 463(w), 584(w), 650(m), 698(s),
744(vs), 877(m), 917(m), 1003(m), 1067(m), 1233(vw), 1363(w),
1383(w), 1427(w), 1460(m), 2073(m, Si–H), 2861(m), 2940(m).
2: A solution of PhSi(SiiPr2H)3 (16.9 g, 0.038 mol) in thf (250 mL)
was cooled down to ꢀ20 1C. Afterwards, TCCA (10 g, 0.043 mol) was
slowly added and the solution was warmed up to ambient tempera-
ture. The solvent was removed under reduced pressure and the
residue was dissolved in n-pentane (60 mL). The insoluble white
precipitate was filtrated and washed two times with n-pentane
(25 mL). The volume of the combined filtrates was reduced to
50 mL. After 4 days at ꢀ8 1C, colourless crystals of PhSi(SiiPr2Cl)3
were obtained, the yield being 71.0% (14.9 g). Elemental analysis (%):
calc. for C24H47Si4Cl3: C 52.00, H 8.55, found C 52.01, H 8.97.
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