Synthesis, crystal structure and rearrangement of a methylene(ylene)-phosphorane containing a CH2-moiety at an sp2-hybridized phosphorus(v) centre

Article abstract of DOI:10.1039/a607402b

The reaction of the iminophosphane, (Me₃Si)₃C-P=N-Mes *, with Me₂S=CH₂ affords the first methylenephosphorane containing a CH₂ moiety at an sp²-hybridized phosphorus(v) centre; the crystal

Full text of DOI:10.1039/a607402b

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Synthesis, crystal structure and rearrangement of a methylene(ylene)-
phosphorane containing a CH2-moiety at an sp2-hybridized phosphorus(v)
centre
Bernd Schinkels, Alexander Ruban, Martin Nieger and Edgar Niecke*
Anorganisch-Chemisches-Institut der Universita¨t Bonn, Gerhard Domagk Str.1, D-53121 Bonn, Germany
The reaction of the iminophosphane, (Me3Si)3C–PNN–Mes*,
with Me2SNCH2 affords the first methylenephosphorane
containing a CH2 moiety at an sp2-hybridized phosphorus(V)
centre; the crystal structure as well the rearrangement of
which is reported.
aryl substituent at N(1) is approximately orthogonal to the
central p-bond system (the angle between the plane P(1)–N(1)–
C(1)–C(2) and the aryl plane is 89°) and in an E-configuration
relative to the (Me3Si)3C substituent at P(1), as is found in the
iminophosphane 1 (Scheme 1). As compared to known
imino(methylene)phosphoranes,8 the P(1)–N(1)-bond length
[1.556(2) Å] in 2 is elongated which may be interpretated in
terms of the small P(1)–N(1)–C(12) angle [121.2(2)°], whereas
the P(1)–C(1) distance [1.612(3) Å] is significantly shorter.
Other bond lengths and angles do not show any peculiarities.
While compound 2 is stable at ambient temperatures it easily
isomerizes by heating a toluene solution of 2 at about 100 °C to
give the corresponding imino(methylene)phosphorane 3, which
was isolated by recrystallization from non-polar solvents as a
colourless powder (84.7% yield). The isomerization 2 ? 3 by
[1,3] silyl migration in the C–PNC triad results in chemical
equivalence and the shielding of the two hydrogens atoms, as
Methylenephosphoranes I, which may be formally regarded as
a phosphane stabilized methylene (CH2), are well established1
and their chemistry with respect to organic and organometallic
syntheses has long been known.2
In contrast, only one kinetically stable derivative of a
methylenephosphane,3 II, is known so far in which the CH2
moiety is linked to a phosphinidene unit. Methylene(ylene)-
phosphoranes III, which also contain an sp2-hybridized phos-
phorus centre as in II but with phosphorus(v) are known so far
only as transient species, and their existence has only been
inferred from trapping experiments.4 Here we report the
synthesis and X-ray structure of the first example of a stable
derivative of a methylenephosphorane of the type III (Fig. 1).
In a typical experiment, a THF solution of the iminophos-
phane, (Me3Si)3CPNNMes*, 1 [obtained by the treatment of
ClPNNMes*5 with an equimolar quantity of LiC(SiMe3)3 in
THF at 278 °C†] was added under stirring to an equimolar
quantity of Me2SNCH2 in THF at 240 °C.
1
2
shown by H NMR, (d 2.0, JPH 16.1 Hz), which reflects the
change in hybridization from sp2 to sp3. Furthermore the three
equivalent silyl groups in 2 split into a set of three resonances in
3. The tricoordinated phosphorus(v) centre maintains the
characteristic low field shift in the 31P NMR spectrum (d 129.5),
whereby the chemical shift of the methylene carbon in the 13
C
NMR spectrum (d 68.3, 1JPC 43.1 Hz) falls in the same spectral
The solvent was removed under vacuum and the residue was
taken up in 40 ml of hexane. The LiI present was removed by
filtration and the filtrate concentrated and the resulting residue
recrystallized from hexane to give 2 as pale colourless crystals
(82.6% yield).
Mes*
CH2
i
(Me3Si)3C
ii
P
P
N
N
Mes*
(Me3Si)3C
2
1
Compound 2 was shown to be a monomer from the
observation of the molecular ion in the high-resolution mass
spectrum at m/z 534 (6%). The formation of an imino(methyl-
ene)phosphorane and not of the valence isomeric azaphosphir-
ane6 is readily demonstrated by the low field 31P NMR chemical
shift (d 157.8), while the lowest field signal in the 13C NMR
CH2(SiMe3)
(Me3Si)2C
P
N
Mes*
3
Scheme 1 Reagents and conditions: i, Me2SCH2, THF, 240 °C, 82.6%; ii,
toluene, 1 h, reflux, 84.7%
1
spectrum (d 64.2, JCP 108.2 Hz) manifests the existence of a
methylene carbon atom attached to a phosphorus(v) centre. The
direct proximity of two chemical inequivalent hydrogens
attached to this atom (d d 3.07; dd 3.38, 2JPH 14.1, 2JHH 7.7 Hz)
unambiguously proves the presence of a ≤ PNCH2 moiety
≠
C(12)
Si(2)
(Scheme 1).
N(1)
The new methylenephosphorane 2 was conclusively charac-
terized by X-ray crystallography‡ for which suitable crystals
were obtained from hexane at room temperature (Fig. 2). As in
all structurally investigated bis(ylene)phosphoranes,7 the cen-
tral phosporus atom exhibits a trigonal planar environment (sum
of the angles at P = 360°). The methylene carbon atom, both the
hydrogen atoms bonded to it, and the atoms P(1)–N(1)–C(12)
are almost planar (mean deviation from plane = 0.005 Å). The
Si(3)
C(2)
P(1)
C(1)
Si(1)
Fig. 2 Molecular structure of 2. Disordered parts and methyl and aromatic
hydrogen atoms were omitted for clarity. Selected bond lengths (Å) and
angles (°): P(1)–C(1) 1.612(3), P(1)–N(1) 1.556(2), P(1)–C(2) 1.803(2);
C(1)–P(1)–N(1) 124.8(1), C(1)–P(1)–C(2) 118.6(1), N(1)–P(1)–C(2)
116.7(1), P(1)–N(1)–C(12) 121.2(2), C(1)–P(1)–N(1)–C(12) 2.6(3),
C(2)–P(1)–N(1)–C(12) 2178.5(2).
P
CH2
P
CH2
P
CH2
I
II
Fig. 1
III
Chem. Commun., 1997
293

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hydrogen atoms were refined anisotropically, H atoms localized by
difference electron density and refined using a ‘riding’ model. wR2 = 0.136
{R1 = 0.049 [I > 2s(I)]}. An empirical absorption correction on the basis
of Y-scans was applied. Selected bond lengths (Å) and angles (°):
P(1)–N(1) 1.566(3), P(1)–C(19) 1.837(3), N(1)–C(1) 1.429(4); P(1)–N(1)–
region as in 2. The composition of 3 was further deduced from
the high-resolution mass spectrum.
We thank the Deutsche Forschungsgemeinschaft, the Fonds
der Chemischen Industrie for generous financial support and the
Graduierten Kolleg for a grant (A. R.).
C(1) 120.2(2), C(19)–P(1)–N(1) 110.4(2), C(1)–N(1)–P(1)–C(19)–
–
178.7(2). For 2: C29H58NPSi3, M = 536.0, triclinic, space group P1 (no. 2),
yellow crystals, dimensions 0.60 3 0.70 3 0.80 mm3, a = 9.182(3),
Footnotes
b
g
=
=
13.539(5), c
82.42(3)°,
=
U
15.247(5) Å, a
=
65.59(3), b
= 84.94(3),
† Spectroscopic data for 1: Yield 76.1% mp 78–81 °C. 31P NMR (C6D6): d
500.4; 1H NMR (C6D6): d 0.53 (s, 27 H, SiMe3), 1.50 (s, 9 H, p-But), 1.68
(s, 18 H, o-But), 7.67 (s, 2 H, C6H2); 13C NMR (C6D6): d 5.4 (d, 3JPC 4.4
Hz, SiMe3), 32.2 (s, o-CCH3), 34.6 (d, JPC 2.6 Hz, p-CCH3), 34.9 (s,
=
1710(1) Å3, Dc
=
1.04 mg m23
,
Z = 2, m(MoKa) = 0.20 mm21, T = 293(2) K, F(000) = 592.6025
symmetry independent reflections were used for the structure solution
(direct methods) and refinement (full-matrix least-squares on F2, 444
parameters, 540 restraints). Non-hydrogen atoms were refined anisotrop-
ically, H atoms localized by difference electron density and refined using a
‘riding’ model, wR2 = 0.184 {R1 = 0.062 [I > 2s(I)]}. The p-But and the
C(SiMe3)3 group were disordered. Atomic coordinates, bond lengths and
angles, and thermal parameters have been deposited at the Cambridge
Crystallographic Data Centre (CCDC). See Information for Authors, Issue
No. 1. Any request to the CCDC for this material should quote the full
literature citation and the reference number 182/318.
1
p-CCH3), 37.2 (s, o-CCH3), 47.9 (d, JPC 100.3 Hz, p-CSi3), 122.7 (s,
m-Ar), 137.2 (d, 3JPC 11.7 Hz, o-Ar), 143.0 (s, p-Ar), 150.7 (d, 2JPC 15.7 Hz,
ipso-Ar). MS (20 eV, EI) m/z (%) 521 (7%) [M+], 290 (100) [PNMes*+].
For 2: Yield 82.6%, mp 86–90 °C. 31P NMR (C6D6): d 157.8; 1H NMR
(C6D6): d 0.56 (s, 27 H, SiMe3), 1.51 (s, 9 H, p-But), 1.84 (s, 18 H, o-But),
3.10 (d, 2JHH 7.7 Hz, 2JPH < 1.0 Hz, 1 H, PNCH2), 3.38 (dd, 2JHH 7.7, 2JPH
14.1 Hz, 1 H, PNCH2), 7.65 (d, 6JPH 2.2 Hz, 2 H, C6H2); 13C NMR (C6D6):
d 6.0 (d, 3JPC 3.1 Hz, SiMe3), 17.2 (d, 1JPC 28.5 Hz, P-CSi3), 32.3 (d, 7JPC
5
6
1.7 Hz, p-CCH3), 33.2 (d, JPC 1.4 Hz, o-CCH3), 35.0 (d, JPH 1.9 Hz,
p-CCH3), 37.5 (d, 4JPH 2.3 Hz, o-CCH3), 64.2 (d, 1JPC 108.2 Hz, PNCH2),
123.0 (d, 4JPH 5.7 Hz, m-Ar), 141.5 (d, 3JPC 11.8 Hz, o-Ar), 142.2 (d, 5JPH
6.5 Hz, p-Ar), 146.2 (d, 2JPC 13.4 Hz, ipso-Ar). The CH2 group is confirmed
by a DEPT 135 experiment. MS (20 eV, EI) m/z (%) 535 (4) [M+], 73 (100)
[(CH3)3Si+] (Found: M+, 535.3614. C29H58N1:Si3P1 requires 535.3620).
For 3: Yield 84.7%, mp 82–84 °C. 31P NMR (C6D6): d 129.5; 1H NMR
(C6D6): d 0.29 (s, 9 H, SiMe3), 0.31 (s, 9 H, SiMe3), 0.39 (s, 9 H, SiMe3),
References
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1993.
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2
1.51 (s, 9 H, p-But), 1.74 (s, 18 H, o-But), 2.0 (d, JPH 16.1 Hz, 2 H,
SiMe3CH2), 7.55 (d, 6JPH 2.2 Hz, 2 H, C6H2); 13C NMR (C6D6): d 1.14 (d,
3JPC 3.4 Hz, PNCSiMe3), 4.37 (d, 3JPC 4.9 Hz, PNCSiMe3), 5.6 (d, 3JPC 5.0
1
7
Hz, SiMe3CH2), 21.7 (d, JPC 62.3 Hz, P–C(SiMe3)H2), 32.1 (d, JPC 1.2
Hz, p-CCH3), 32.3 (d, 5JPC 1.7 Hz, o-CCH3), 35.0 (d, 6JPH 1.5 Hz, p-CCH3),
37.0 (d, 4JPH 1.9 Hz, o-CCH3), 68.3 [d, 1JPC 43.1 Hz, PNC(SiMe3)2], 122.5
(d, 4JPH 4.2 Hz, m-Ar), 140.0 (d, 3JPC 10.3 Hz, o-Ar), 142.2 (d, 5JPH 5.0 Hz,
2
6 E. Niecke, A. Seyer and D.-A. Wildbredt, Angew. Chem., 1981, 93, 687;
Angew. Chem., Int. Ed. Engl., 1981, 20, 675.
p-Ar), 144.7 (d, JPC 10.3 Hz, ipso-Ar). MS (20 eV, EI) m/z (%) 535(3)
[M+], 73 (100) [(CH3)3Si+].
–
7 M. Regitz and O. J. Scherer, Multiple Bonds and Low Coordination in
Phosphorus Chemistry, Thieme Verlag, New York, 1989.
8 W. Schilbach, V. von der Go¨nna, D. Gudat, M. Nieger and E. Niecke,
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982.
‡ Crystal data for 1: C28H56NPSi3, M = 522.0, triclinic space group P1 (no.
2), red crystals, dimensions 0.10 3 0.20 3 0.38 mm3, a = 9.814(3),
b
g
=
=
13.580(5), c
79.20(3)°, U
=
=
14.113(4) Å, a
=
=
64.38(3), b
=
82.94(2),
2,
1664(1) Å3, Dc
1.04 mg m23, Z
=
m(CuKa) = 1.87 mm21, T = 200(2) K, F(000) = 576.5647 symmetry
independent reflections were used for the structure solution (direct methods)
and refinement (full-matrix least-squares on F2, 316 parameters). Non-
Received, 30th October 1996; Com. 6/07402B
294
Chem. Commun., 1997