Synthesis of the first fluoro(phosphanyl)- and diphosphanyl-stannanes and surprising formation of [P(SnMe3)4]+SiF 5- ?

Article abstract of DOI:10.1039/b308660g

Monophosphanylation of the difluorostannane Is₂SnF₂ (Is = 2,4,6-triisopropylphenyl) with Si(PH₂)₄ furnishes the first isolable fluoro(phosphanyl)stannane IS₂Sn(F)PH₂ 1, which readily underg

Full text of DOI:10.1039/b308660g

Synthesis of the first fluoro(phosphanyl)- and diphosphanyl-stannanes
and surprising formation of [P(SnMe3)4]+SiF5 †
2
Matthias Driess,* Klaus Merz and Christian Monsé
Chair of Inorganic Chemistry I: Cluster and Coordination Chemistry, Ruhr-University Bochum,
Universitätsstrasse 150, D-447801 Bochum, Germany. E-mail: matthias.driess@rub.de; Fax: 49 234 321
4378; Tel: 49 234 322 4153
Received (in Cambridge, UK) 28th July 2003, Accepted 3rd September 2003
First published as an Advance Article on the web 19th September 2003
Monophosphanylation of the difluorostannane Is2SnF2 (Is =
2,4,6-triisopropylphenyl) with Si(PH2)4 furnishes the first
isolable fluoro(phosphanyl)stannane Is2Sn(F)PH2 1, which
readily undergoes unique SiO2-assisted decompostion to
[Is2Sn(PH)]2 2 and HF, while further phosphanylation of 1
leads to the remarkably stable diphosphanylstannane
Is2Sn(PH2)2 3; the latter reacts with Me3SnF at the glass-wall
to give the first perstannylphosphonium pentafluorosilicate
[P(SnMe3) 4]+SiF52 4.
NMR, IR). The Sn2P2 heterocycle 2 crystallises in THF at room
temperature and the crystals have been fully characterised by
means of multinuclear NMR spectroscopy, mass spectrometry
and elemental analysis. ‡
X-Ray diffraction analysis§ revealed that 2 consists of a
puckered four-membered Sn2P2 ring with cis-configuration of
the hydrogen atoms at phosphorus (Fig. 1). This is in contrast to
the structure of the related Sn2P2 derivative (tBu2SnPH)2,8 or
9
(tBu2SnPtBu)2 which possess a planar Sn2P2 ring and trans-
configuration of the H atoms or tBu groups at phosphorus.
However, the Sn–P distances and Sn–P–Sn/P–Sn–P angles of 2
are unremarkable. Interestingly, while the cis-form of
(tBu2SnPH)2 represents a high temperature species which can
be observed by VT-NMR spectroscopy in solution at elevated
temperature, corresponding NMR investigations of 2 in xyly-
lene revealed that the cis-configuration is retained even at 130
°C.
Additional phosphanylation of 1 with Si(PH2)4 furnishes the
remarkably inert diphosphanylstannane derivative 3 in quantita-
tive yield (Scheme 1). Compound 3 has been fully characterised
‡ and represents the first diphosphanylstannane derivative
Polyphosphanyl-substituted compounds of the type RnE(PH2)m
(R = organo group; n = 0, 1,2; m > 2) with E = group 13, 14
and 15 metalloids and metals are rare and difficult to isolate
because they readily undergo oligomerization and condensation
reactions under evolution of PH3. However, they are valuable
non-basic reagents for mild nucleophilic PH2 transfer through
halogen/PH2 metathesis reactions. The tetraphosphanylalanate
complex-anion in [LiAl(PH2)4]1 has in the past four decades
been the only reliable polyphosphanyl compound of a main-
group element known to be capable for efficient nucleophilic
PH2 transfer but the anion is only stable in ethereal solutions.2
Therefore, several efforts have been undertaken to gain access
to molecular analogues which can be isolated in pure form.
Recently we succeeded in the synthesis of Si(PH2)4 and
3,4
Ge(PH2)4 which represent novel types of volatile, non-ionic
and mild PH2 transfer reagents with remarkable structural
features.5 However, attempts to synthesise analogous oligo-
phosphanylstannanes or stable halogen(phosphanyl)-stannanes
hitherto failed. Previous investigations revealed that even
monophosphanylstannanes of the type R3SnPH2 decompose
readily to P(SnR3)3 and PH3 if the PH2 group is not sufficiently
protected by sterically demanding substituents R at the tin
atom.6 We report here the straightforward stepwise phosphany-
lation reaction of the bulkily substituted difluorostannane
Is2SnF2 (Is = 2,4,6-triisopropylphenyl) with Si(PH2)4.
Reaction of Is2SnF2 with Si(PH2)4 in benzene at room
temperature furnishes Is2Sn(F)PH2 1 and volatile FSi(PH2)37 in
quantitative yield (31P NMR). Interestingly, Is2Sn(F)PH2 1 is
stable in solid state (up to 60 °C) as well as in solution in a
teflon-vessel but readily eliminates HF under silicate/SiO2-
assistance in a glass-vessel. The composition of 1 is evident
from its 31P, 19F, and 119Sn NMR spectroscopic data. The 31P
NMR spectrum of 1 shows a doublet [2J(P, F) = 2 Hz] of
triplets [1J(P, H) = 173 Hz] with 117/119Sn satellites at
characteristically high field (d = 2238.6),6 and the 19F NMR
spectrum gives a doublet [2J(P, F) = 2 Hz] with 117/119Sn-
satellites at d = 2184, while the 119Sn NMR spectrum reveals
consistently a doublet [1J(119Sn, F) = 2527 Hz] of doublets
[1J(119Sn, P) = 668 Hz] at d = 8.1. The decomposition of 1 in
solution at the glass-wall is concentration-dependent and
accelerated in a polar medium (e.g., THF), leading solely and
stereoselectively to the cis-1,3-distanna-2,4-diphosphetane 2
and HF (Scheme 1). However, due to HF-etching of the glass
wall, the HF is completely transformed into gaseous SiF4 (19F
Scheme 1 Synthesis of 1–3.
Fig. 1 Molecular structure of 2. Selected distances [pm] and angles [°]: Sn1–
P1 253.2(1), Sn1–P2 252.1(1), Sn2–P1 253.6(1), Sn2–P2 254.6(1), Sn1–C1
217.9(3), P1–H1 129(3), P2–H2 134(3); P1–Sn1–P2 93.31(4), P1–Sn2–P2
92.63(4), Sn1–P1–Sn2 83.48(4), Sn1–P2–Sn2 83.50(4).
† Electronic supplementary information (ESI) available: synthesis and
characterisation of 1, 2, 3 and 4. See http://www.rsc.org/suppdata/cc/b3/
b308660g/
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CHEM. COMMUN., 2003, 2608–2609
This journal is © The Royal Society of Chemistry 2003

which has been established by an X-ray diffraction analysis. §
The Sn atom in 3 is distorted tetrahedral coordinated with
characteristic Sn–P and Sn–C single bond distances (Fig. 2).10
In contrast to tBu2Sn(PH2)28 which readily decomposes at room
temperature, 3 remains unchanged even after heating in solution
at 180 °C.
the silicon atom in SiF4 versus the tin atom in the Me3Sn
groups.
Although the colourless large cubes of 4 have been unsuitable
for a satisfactory X-ray diffraction analysis due to disordering
of SiF52, the constitution of the separated [P(SnMe3)4]+SiF5
2
ion pair in 4 is proven by elemental analysis and the CP/MAS
31P NMR spectrum. ‡ In line with that, the CP/MAS 31P NMR
as well as the 31P and 119Sn NMR data of 4 in solution are
2 11
almost identical with that of [P(SnMe3)4]+BPh4
.
In summary, the unique fluoro(phosphanyl)stannane 1 under-
goes glass-assisted HF elimination to give the cis-distannadi-
phosphetane 2. Both the inert diphosphanylstannane 3 and the
tetrakis(trimethylstannyl)phosphonium cation in 4 represent
easily accessible and novel soft PH2 and Me3Sn+ transfer
2
reagents.
Notes and references
‡
For the synthesis and characterisation of 1, 2, 3 and 4 see ESI.† Selected
spectroscopic data
for 2: 31P NMR (300 K, C6D6): d = 266.0 (md, 1J(31P, 1H) = 121 Hz,
1J(31P, 117Sn) = 420.9 Hz, 1J(31P, 119Sn) = 440.5 Hz); 119Sn{1H} NMR:
d = 2140.7 (t, 1J(119Sn, 31P) = 440.5 Hz).
1
1
3: 31P NMR (300 K, C6D6): d = 2218.3 (mt, J(31P, H) = 172.8 Hz,
1J(31P, 117Sn) = 494.0 Hz, 1J(31P, 119Sn) = 518.5 Hz); 119Sn{1H} NMR:
d = 2136.7 Hz (t, 1J(119Sn, 31P) = 518.5 Hz).
4: 31P NMR (310 K, C6D6O): d = 2324.7 (s, w1/2 = 15 Hz); CP/MAS
31P NMR: d = 2301.6 (1J(31P, Sn) = 512 Hz); 119Sn{1H} NMR (310 K,
C6D6O): d = 38.6 (s, w1/2 = 840 Hz); 19F NMR: d = 2142.8 (s, w1/2 =
59 Hz).
Fig. 2 Molecular structure of 3. Selected distances [pm] and angles[°]: Sn1–
P1 252.4(3), Sn1–P2 253.1(2), Sn1–C1 216.7(5), Sn1–C16 218.6(6); C1–
Sn1–C16 103.0(2), C1–Sn1–P2 106.0(1), C16–Sn1–P2 105.9(2), C1–Sn1–
P1 119.2(1), P2–Sn1–P1 103.1(1).
§
Crystal data for 2: C60H94P2Sn2, M = 1114.67, triclinic, space group,
a = 10.538(4), b = 16.379(7), c = 17.760(7) Å, a = 103.08(3), b =
91.27(3), g = 101.45(3), V = 2919.4(19) Å3, Z = 2, 2qmax = 50°, 24 233
measured reflections, 585 parameters, m = 0.94 mm21, R1 = 0.0326 for
8356 observed reflections (I > 2s(I)), wR2 = 0.0789 for all reflections.
Solutions of the diphosphanylstannane 3 in THF are
remarkably inert towards air and water but they react slowly
with Me3SnF in THF to furnish Is2Sn(F)PH2 1 and Me3SnPH2
as initial products (31P NMR). Subsequently, the latter undergo
conversion to the Sn2P2 heterocycle 2 and surprising formation
of the tetrastannylphosphonium pentafluorosilicate [P(Sn-
¯
3: C30H50P2Sn, M = 591.36, triclinic, space group P1, a = 9.8122(18),
b = 10.394(2), c = 16.662(4) Å, a = 105.176(17), b = 96.941(15), g =
93.621(13), V = 1620.1(6) Å3, Z = 2, 2qmax = 45°, 3 999 measured
reflections, 298 parameters, m = 0.90 mm21, R1 = 0.0458 for 3609
observed reflections (I > 2s(I)), wR2 = 0.1592 for all reflections.
The intensity data were collected on a Bruker-axs-SMART 1000
diffractometer (Mo–Ka radiation, l = 0.71707 Å, T = 203 K).
Both structures were solved by direct methods and refined by full-matrix
least squares using SHELXTL-97. The PH2 hydrogens of compound 3 were
not visible in the electron density map. All non-hydrogen atoms were
refined using anisotropic thermal parameters. The atoms H1 and H2 in the
crystal structure of 2 were refined isotropically, while the other hydrogen
atoms were positioned geometrically, with C–H = 0.98–0.99 Å, and refined
as riding atoms. CCDC 216367 and 216368. See http://www.rsc.org/
suppdata/cc/b3/b308660g/ for crystallographic data in .cif or other elec-
tronic format.
Me3)4]+SiF5 4 which can be isolated in the form of cubic
2
crystals in 33% yield (Scheme 2). Compound 4 represents only
the second tetrastannylphosphonium salt hitherto known.11 The
mechanism is based on two independent reactions which have
been proven as follows: firstly, the reactive intermediate
Me3SnPH2 dismutates readily to P(SnMe3)3 and PH3 as proven
by alternative synthesis of Me3SnPH2 by reaction of Si(PH2)4
with Me3SnCl in the molar ratio of 1 : 4. Secondly, formation of
the strongly electrophilic stannylium salt Me3Sn+SiF52 occurs
by the reaction of SiF4 (formed from HF-etching of the glass-
wall) with Me3SnF. Subsequently, the stannylium salt can react
with the Lewis base P(SnMe3)3 to give 4.
This is consistent with the result of the reaction of P(SnMe3)3
with Me3SnF in THF in the presence of SiF4 which furnishes 4
in quantitative yield (Scheme 2). As expected, 4 is insoluble in
non-polar solvents but sparingly soluble in ethereal solvents and
can be re-crystallised from THF. The crystals are very sensitive
to moisture and readily lose SiF4 at room temperature. The
instability of 4 signals the competing fluoride acceptor ability of
1 A. E. Finholt, C. Helling, V. Imhof, L. Nielsen and E. Jacobsen, Inorg.
Chem., 1963, 2, 504.
2 Removal of the solvent leads to complete decomposition. Recently, we
synthesised iBu2AlPH2 which is suitable as a mild PH2 transfer reagent
and can be isolated in pure form: see ref. 4.
3 (a) M. Driess, C. Monsé, R. Boese and D. Bläser, Angew. Chem., 1998,
110, 2389; Angew. Chem., Int. Ed. Engl., 1998, 37, p. 2257; (b) M.
Driess, C. Monsé and K. Merz, Z. Anorg. Allg. Chem., 2001, 627,
1225.
4 M. Driess and C. Monsé, Z. Anorg. Allg. Chem., 2000, 626, 1091.
5 N. W. Mitzel, Angew. Chem., 1998, 110, 1767; Angew. Chem., Int. Ed.
Engl., 1998, 37, p. 1670.
6 D. Hänssgen and H. Aldenhoven, Chem. Ber., 1990, 123, 1833.
7 M. Driess, Ch. Monsé, D. Bläser, R. Boese, H. Bornemann, A. Kuhn and
W. Sander, J. Organomet. Chem., 2003, in print.
8 D. Hännsgen, H. Aldenhoven and M. Nieger, Chem. Ber., 1990, 123,
1837.
9 D. Hännsgen, H. Aldenhoven and M. Nieger, J. Organomet. Chem.,
1989, 367, 47.
10 D. Bongert, H. D. Hausen, W. Schwarz, G. Heckmann and H. Binder, Z.
Anorg. Allg. Chem., 1996, 622, 1167.
11 M. Driess, C. Monsé, K. Merz and C. van Wüllen, Angew. Chem., 2000,
39, 3838; Angew. Chem., Int. Ed. Engl., 2000, 39, p. 3684.
Scheme 2 Formation of 4.
CHEM. COMMUN., 2003, 2608–2609
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