1,2,3,4-Tetramesityl-1,4-bis(tri-n-butyltin)tetraphosphane: Synthesis and molecular structure

Article abstract of DOI:10.1039/c3cc44571b

The reaction of [Na₂(thf)₄(P₄Mes ₄)] (1) with tributyltin chloride gives 1,2,3,4-tetramesityl-1,4- bis(tri-n-butyltin)tetraphosphane (2) which is stable towards disproportionation in solution at room temperature

Full text of DOI:10.1039/c3cc44571b

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1,2,3,4-Tetramesityl-1,4-bis(tri-n-butyltin)tetraphosphane:
synthesis and molecular structure†
Cite this: Chem. Commun., 2013,
49, 7355
Ivana Jevtovikj, Peter Lonnecke and Evamarie Hey-Hawkins*
¨
Received 18th June 2013,
Accepted 20th June 2013
DOI: 10.1039/c3cc44571b
www.rsc.org/chemcomm
The reaction of [Na2(thf)4(P4Mes4)] (1) with tributyltin chloride
gives 1,2,3,4-tetramesityl-1,4-bis(tri-n-butyltin)tetraphosphane (2)
which is stable towards disproportionation in solution at room
temperature.
Scheme 1 Synthesis of 1,2,3,4-tetramesityl-1,4-bis(tri-n-butyltin)tetraphosphane (2).
Homoatomic structures are well known for non-metals.1 Group
15 elements are always bound to three other atoms in their
homoatomic structures. These elements also have the tendency
to form homoatomic rings, chains and macromolecules, which
can be polyanions, polycations or neutral compounds.2 However,
most compounds with E–E bonds (E = P, As, Sb) typically
undergo a continuous dynamic reorganisation, which is more
pronounced for the higher homologues. Thus, it is possible to
obtain short-chain linear oligophosphanes, but not the analo-
gous oligoarsanes or stibanes.3 While diarsanes,4 distibanes5
and dibismutanes6 have been described, there are only few
examples of higher linear, single-stranded oligomers. Neutral
catena-stibanes such as tristibanes R2Sb–SbR0–SbR2 (R = Me,
Et, Ph; R0 = Me, Et, tBu, CH(SiMe3)2, Ph)7 and tetrastibanes
R02Sb–SbR–SbR–SbR02 (R = Et, R0 = Ph;7 R = CH2SiMe3, R0 =
Me, Ph)8 have been reported, but no crystal structures thereof.
To date, only a limited number of catena-phosphanes with
general formula X–(PnRn)–X (with X = H, SiMe3) have been reported,
where n = 2, R = Ph, 2,4,6-Me3C6H2 (Mes),9 n = 3, R = Ph,10 and n = 4,
R = tBu, Ph, Mes.11 One major problem is the sensitivity of these
compounds towards disproportionation, and thus only a few of
them have been fully characterised and further explored. The
disproportionation reactions of tetraphosphanes include rearrange-
ments that follow a four-centre mechanism predominantly
involving P–P bonds12 and lead to shorter linear primary or
secondary phosphanes as well as monocyclic phosphanes.13
We here report the synthesis of a stable and easier-to-handle
tetraphosphane, namely 1,2,3,4-tetramesityl-1,4-bis(tri-n-butyltin)-
tetraphosphane (2), which was obtained by reaction of
[Na2(thf)4(P4Mes4)]14 (1) with tributyltin chloride at ꢀ78 1C.
Recrystallisation from DME gave crystals of the pure compound
in 80% yield (Scheme 1).‡ Tetraphosphane 2 is stable in solution
at room temperature and stable towards disproportionation
reactions.
In the 31P NMR spectrum of the reaction mixture, two
multiplets (dP = ꢀ35.7 and ꢀ113.3 ppm) were observed indicating
an AA0BB0 spin system (if the coupling to 117Sn/119Sn is neglected;
1JPSn = 863.5 Hz), which is characteristic of compound 2 (Table 1).
At ꢀ80 1C, a set of four additional multiplets (dP = ꢀ30.5, ꢀ47.4,
ꢀ114.3, ꢀ124.8 ppm) indicative of an ABCD spin system appeared
besides the signals of 2 as the main product and a signal of
PHMes(SnBu3)15 (Fig. 1).16 Assuming that the inversion at the
phosphorus atoms is slow on the NMR timescale, which is
plausible in the case of open-chain phosphanes at low temperature,
these additional multiplets could be assigned to a different
configurational isomer of 2. Considering the intensity of the
signals in the reaction mixture, the concentration of this
isomer is much lower than that of the main diastereomer of
Table 1 31P{1H} NMR parameters of (RP,RP,SP,SP)-P4Mes4(SnBu3)2 (2), (RP,SP,RP,SP)-
P4H2Mes4 and (RP,SP,RP,SP)-P4Ph4(SiMe3)2
(RP,SP,RP,SP)-
P4H2Mes4
(ref. 11f and 18)
(RP,SP,RP,SP)-
P4Ph4(SiMe3)2
(ref. 11a)
2a
dA
dB
ꢀ38.6 ppm
ꢀ119.6 ppm
ꢀ197.7(4) Hz
ꢀ169.2(3) Hz
+125.5(3) Hz
+24.6(3) Hz
ꢀ50.4 ppm
ꢀ104.9 ppm
ꢀ183.5 Hz
ꢀ170.4 Hz
+31.0 Hz
ꢀ27.6 ppm
ꢀ88.3 ppm
ꢀ140.31 Hz
ꢀ169.7 Hz
+128.1 Hz
+12.8 Hz
1
JAB = 1JA B
JBB
JAB = JA B
JAA
0
0
1
2
3
0
2
0
0
0
+11.8 Hz
¨
¨
Universitat Leipzig, Institut fur Anorganische Chemie, Johannisallee 29,
a
04103 Leipzig, Germany. E-mail: hey@uni-leipzig.de
The chemical shifts and coupling constants were calculated using the
† CCDC 936270. For crystallographic data in CIF or other electronic format see
DOI: 10.1039/c3cc44571b
simulation program SpinWorks 3 and are in good agreement with the
experimental data.17
c
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out by comparison with similar compounds, as well as by
considering steric and electronic effects. For example, the
silylated tetraphosphane P4Ph4(SiMe3)2 exists as four (of six
possible) different stereoisomers at low temperature, of which
the (RP,SP,RP,SP) diastereomer is the predominant isomer. This
stereoisomer corresponds to a meso form of the compound
with a coplanar arrangement of the phenyl groups at 1,3- and
2,4-positions, respectively, and the lone pairs of electrons have
an optimal trans orientation.11a Similar observations were
made for P4H2Mes4, which exists solely as a meso isomer, i.e.,
the (RP,SP,RP,SP) diastereomer.18 The 31P{1H} NMR parameters
for (RP,SP,RP,SP)-P4Ph4(SiMe3)2 and (RP,SP,RP,SP)-P4H2Mes4 and
those observed for the main isomer of 2, which was assigned as
a meso form, in this case the (RP,RP,SP,SP) diastereomer, are
listed in Table 1. The (RP,RP,SP,SP) diastereomer, in which the
bulky mesityl groups are positioned in the sterically least
hindered erythro,meso,erythro configuration, is also present in
the solid state. Compound 2 crystallises in the triclinic space
Fig. 1 31P{H} NMR spectrum of the reaction mixture in D8-THF at ꢀ80 1C
(B = (RP,RP,SP,SP)-2,
* = ABCD spin system (different diastereomer of 2),
‡ = cyclo-(P3Mes3), # = cyclo-(P4Mes4), J = PHMes(SnBu3), + = AB spin system
(not assigned), K = AB spin system (not assigned)).
P4Mes4(SnBu3)2 (2). In addition, two sets of doublets (AB spin
systems) at d = ꢀ102.6, ꢀ141.6 ppm (1JPP = 308.3 Hz) and
d = ꢀ109.7, ꢀ133.8 ppm (1JPP = 198.9 Hz) indicate that the P4
chain was cleaved to give two different compounds that contain
an unsymmetrical P2 moiety in which no coupling to tin is
observed. However, these resonances could not be further
assigned.
%
group P1 with one formula unit in the unit cell. The P4 chain
resides on an inversion centre, resulting in an anti-periplanar
arrangement (Fig. 3).
To date, only one other mesityl-substituted tetraphosphane
with an anti-periplanar conformation, namely P4H2Mes4, has
been characterised. In contrast to the latter, the structurally
Starting with tetraphosphanes, the structural diversity of the
open-chain oligophosphanes becomes quite complex. Generally,
with increasing steric demand of the organic substituents on the
phosphorus atoms, the configurations and conformations of the
possible isomers are significantly influenced by steric factors in
addition to the tendency for gauche orientation of neighbouring
lone pairs of electrons. Theoretically, in the case of 1,2,3,4-tetra-
mesityl-1,4-bis(tri-n-butyltin)tetraphosphane (2), there are six possi-
ble configurational isomers. However, the experimentally observed
spectrum at room temperature shows that only the erythro,meso,
erythro (or RP,RP,SP,SP) diastereomer is formed due to the presence
of bulky mesityl substituents. In contrast to P4Ph4(SiMe3)2,11a in
which the –PPh(SiMe3) groups are the bulkiest substituents of the
two central phosphorus atoms, in 2, there is an obvious repulsion
between the bulky mesityl groups themselves, without any major
effect of the SnBu3 groups. Therefore, the erythro,meso,erythro
arrangement of the P4 chain is preferred (Fig. 2). The small amounts
of the other observed isomer are due to the less preferred orienta-
tion of the lone pairs of electrons of the terminal P–P bonds.
A helical structure of the P4 chain is also feasible.
characterised
silylated
tetraphosphane
P4tBu4(SiMe3)2
(ref. 11a), exhibits a syn-periplanar arrangement. The P–P bond
lengths of 2 [2.2178(5) and 2.2272(7) Å] are in the typical range
for P–P single bonds19 and also agree with those reported for
P4H2Mes4 (2.23 Å).11f The P–P bond lengths in P4tBu4(SiMe3)2
are slightly shorter and have an average value of 2.18 Å for the
terminal P–P bonds and 2.21 Å for the internal P–P bond.11c The
Sn–P bond length [2.5222(4) Å] is in the expected range of SnIV–P
single bonds, e.g. 2.520(1) and 2.503(1) Å (R = Me)20 or 2.545(3) and
2.536(3) Å (R = tBu)21 in the five-membered heterocycle cyclo-
(PtBu)4SnR2, 2.513(1), 2.533(2), 2.525(1) and 2.502(1) Å in the six-
membered heterocycle cyclo-1,4-{Sn(CH3)2(tBuP-PtBu)2}.20 SnII–P
bonds are typically longer (e.g. 2.640(2)–2.699(2) Å in the heteroleptic
The assignment of the spin systems observed in the 31P{1H}
NMR spectrum to the corresponding stereoisomer was carried
Fig. 3 Molecular structure of 1,2,3,4-tetramesityl-1,4-bis(tri-n-butyltin)tetraphos-
phane (2). H atoms are omitted for clarity. Selected bond lengths (Å) and angles (1):
P1–P2 2.2178(5), P2–P20 2.2272(7), Sn1–P1 2.5222(4); C23–Sn1–P1 101.08(7),
Sn1–P1–P2 106.28(2), C1–P1–P2 99.87(5), P1–P2–C10 107.47(5), P1–P2–P20
96.98(2) (ellipsoids are shown at 50% probability).
Fig. 2 Stereochemistry of 1,2,3,4-tetramesityl-1,4-bis(tri-n-butyltin)tetraphos-
phane (2).
c
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cage compound [(SnCl)4(FcP–PFc)2] [Fc = Fe(C5H4)(C5H5)],22
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toluene [PMDETA
= (Me2NCH2CH2)2NMe] and 2.578(2)–
2.884(2) Å in [{Sn(m3-Ppy)}3{Sn(m3,m1-pyP–Ppy)}3]ꢁ2.5THF (py =
2-pyridyl)23).
Surprisingly, 2 proved to be extremely unreactive in substi-
tution reactions (elimination of Bu3SnCl) and transmetallation
reactions.24 The stability of the Sn–P bond could be due to
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Support from the Deutscher Akademischer Austausch
Dienst (DAAD, doctoral grant for I.J.) and the COST Action
CM0802 PhoSciNet is gratefully acknowledged.
Notes and references
¨
( f ) R. Wolf, S. Gomez-Ruiz, J. Reinhold, W. Bohlmann and
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‡ 2: a solution of Bu3SnCl (0.15 mL, 0.55 mmol) in toluene (5 mL) was
carefully added dropwise at ꢀ78 1C to an orange solution of
[Na2(thf)4P4Mes4]14 (0.25 g, 0.26 mmol) in toluene (50 mL). The result-
ing yellow solution was allowed to warm to room temperature over 2 h
and then stirred for an additional 2 h. The solvent was removed under
vacuum and the resulting yellow oil was extracted with Et2O (2 ꢂ
30 mL). The yellow Et2O solution was filtered and Et2O was evaporated.
The remaining crystalline yellow solid was dissolved in DME (1 mL) and
the solution stored at ꢀ20 1C. Yellow crystals of 2 formed within one
day. Yield: 0.25 g (80%). 1H NMR (25 1C, 400.13 MHz, D8-THF), d =
0.8–1.0 (br m, 18H, CH3 in Bu), 1.1–1.6 (br m, 36H, CH2 in Bu), 1.9–2.8
(br m, 36H, CH3 in Mes), 6.2–6.8 (br m, 8H, 3,5-H in Mes); 13C{1H} NMR
(25 1C, 100.61 MHz, D8-THF), d = 11.8 (s, CH3 in Bu), 12.7 (s, CH2 in Bu),
20.0 (s, CH2 in Bu), 128.3 (s, 3,5-C in Mes–PB), 129.5 (s, 3,5-C in Mes–PA),
136.4 (s, 4-C in Mes–PA), 138.2 (s, 4-C in Mes–PB), 143.5 (s, 2,6-C in Mes–
PA), 144.7 (m, 1-C in Mes), 146.1 (s, 2,6-C in Mes–PB); 31P NMR (25 1C,
161.98 MHz, D8-THF), see Table 1; 119Sn NMR (25 1C, 149.21 MHz, D8-
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1
THF), d = ꢀ5.8 (d, JSnP = 863.5 Hz); elemental analysis: found, C
16 31P{1H} NMR (ꢀ80 1C, 161.98 MHz, D8-THF), d = ꢀ38.6 (m, PAA in 2),
0
58.51%, H 8.41%, calcd for C60H98Sn2P4, C 61.03%, H 8.37%. Crystal
0
ꢀ119.6 (m, PBB in 2), ꢀ50.5 (s, cyclo-(P4Mes4)), ꢀ114.1 (d, PA from
%
data for 2: C60H98Sn2P4, FW = 1180.64, triclinic, space group P1, Z = 1,
1
cyclo-(P3Mes3), JPP = 182.6 Hz), ꢀ149.9 (t, PB from cyclo-(P3Mes3),
a = 9.5430(2), b = 13.0225(4), c = 14.6643(4) Å, a = 110.296(2)1, b =
1JPP = 182.6 Hz), ꢀ191.2 (s, 1JPSn = 621.7 Hz), ꢀ30.5, ꢀ47.4, ꢀ114.3,
99.499(2)1, g = 106.251(2)1, V = 1569.89(7) Å3, m(Mo-Ka) = 0.931 mmꢀ1
,
rcalc = 1.249 Mg mꢀ3, T = 200(2) K. Data were collected on an Agilent
GEMINI CCD diffractometer. Of a total of 34 675 reflections, 9560 were
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(Sir-92)25 and refined by full-matrix least-square method on F2. Final
R1 = 0.0349 (all data) and wR2 = 0.0671 (all data). CCDC 936270 (2).
ꢀ124.8 (m, ABCD spin system, different isomer of 2), ꢀ102.6,
1
ꢀ141.6 (d, AB spin system, JPP = 308.3 Hz), ꢀ109.7, ꢀ133.8
1
(d, JPP = 198.9 Hz).
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´
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24 Compound 2 was reacted with a variety of transition metal(II)
complexes, such as [Pd(cod)Cl2] (cod
= 1,5-cyclooctadiene),
[RhCl(CO)2]2, [RhCl(cod)]2, [FeBr2(CO)4] or main group metal
halides such as PbCl2, SnCl2. The reactions were usually performed
in refluxing THF and toluene. No reaction occurred under these
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6 G. Becker and O. Mundt, Unkonventionelle Wechselwirkungen in der
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¨
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c
This journal is The Royal Society of Chemistry 2013
Chem. Commun., 2013, 49, 7355--7357 7357