Surprising reactions of a 2H-azaphosphirene complex with a silylene

Article abstract of DOI:10.1039/b509567k

Reaction of the 2H-azaphosphirene complex 1 with the silylene 5 yielded the bicyclic carbene complex 9 as sole product at ambient temperature; the reaction was less selective at elevated temperatures; additionally, the synthesis and structure of the first 1,2,4,3-azadiphosphasilol-5-ene complex 11 is presented. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b509567k

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Surprising reactions of a 2H-azaphosphirene complex with a silylene{
Emanuel Ionescu,a Barbara Gehrhus,b Peter B. Hitchcock,b Martin Niegera and Rainer Streubel*a
Received (in Cambridge, UK) 6th July 2005, Accepted 9th August 2005
First published as an Advance Article on the web 5th September 2005
DOI: 10.1039/b509567k
the formation of complex 9 was independent on the stoichiometry
of 1 and 5. Unfortunately, we gained no further insight into the
reaction course and, therefore, we can only give a plausible
explanation as shown in Scheme 2.
Reaction of the 2H-azaphosphirene complex 1 with the silylene
5 yielded the bicyclic carbene complex 9 as sole product at
ambient temperature; the reaction was less selective at elevated
temperatures; additionally, the synthesis and structure of the
first 1,2,4,3-azadiphosphasilol-5-ene complex 11 is presented.
The primary formation of the Lewis acid–base adduct 6 seems
reasonable as well as to assume that a rearrangement of 6 to the
Recently, we reported on the formation of 2,3-dihydro-1,2,3-
azadiphosphete complexes 4a1 and 4b,2 which were obtained by
formal insertion of electrophilic terminal phosphinidene complexes
2a,b into the three-membered ring of 2H-azaphosphirene com-
plexes 1a,b3 (Scheme 1). Based on our assumptions that
zwitterionic complexes 3a,b are formed as intermediates, we
became interested to study the reactivity of 2H-azaphosphirene
complex 1a towards other formal six-electron species, e.g.,
silylenes.
Here, we report on the reaction of complex 1a3 with the
thermally stable silylene (NN)Si: (formula in Scheme 2),4 which
was successfully used recently by Lammertsma and Gehrhus to
achieve ring enlargement of 1H-phosphirene complexes.5
Reacting 2H-azaphosphirene complex 1a with silylene 5 in
benzene at ambient temperature furnished the bicyclic carbene
complex 9{ as major product, having a carbene carbon atom
connected to two heteroatoms as interesting structural motif
(Scheme 2). Complex 9 was isolated in good yield (61.9%) and was
characterized by NMR spectroscopy, MS spectrometry and X-ray
crystallography.§ 31P{1H} NMR reaction monitoring showed that
2-aza-4-phospha-1-silabutadiene complex
7 may take place.
Intramolecular attack of the nucleophilic nitrogen center in 7 to
yield the zwitterionic carbene complex 8, followed by rapid
reaction with one equiv. of 5 and ring closure would then furnish
complex 9. It is remarkable that the 2,3-dihydro-1,2,3-azapho-
sphasilete complex 10 was not detected.
Complex 9 was characterized by multinuclear NMR spectro-
scopy and X-ray crystallography. 9 displayed a 31P{1H} resonance
at 191.4 ppm (1JP,W 5 270.8 Hz) and a 13C{1H} resonance at
256.8 ppm for the carbene carbon atom, having a 2+3JP,C coupling
constant magnitude of 9 Hz. In addition, a resonance at 171.0 ppm
(1JP,C 5 41.2 Hz) was observed for the methylene carbon atom of
the phosphaalkene moiety. The molecular structure of 9 (Fig. 1)
contained the bicyclic structural unit with two folded five-
membered rings. Remarkable is the planar arrangement of the
W–C(5)–O(5)–Si(1) unit (torsion angle 179.2u).
The reaction between 1 and 5 was less selective at elevated
temperatures (75 uC). Apart from phosphorus-containing products
described earlier,1 we observed the formation of two unidentified
complexes as major products, with 31P{1H} resonances at 173.8
(1JP,W 5 272.1 Hz, ca. 33% by 31P NMR integration) and 42.3 ppm
(1JP,W 5 195.4 Hz, ca. 20%). The complex at 173.8 ppm was also
formed if a benzene solution of the bicyclic compound 9 was
heated, thus providing evidence that it relies on complex 9 as
Scheme 1 Ring-enlargement reactions of 1a,b using transient phosphi-
nidene complexes 2a,b (1a–4a: R 5 CH(SiMe3)2, 1b–4b: R 5 C5Me5).
aInstitut fu¨r Anorganische Chemie, Rheinische Friedrich-Wilhelms-
Universita¨t Bonn, Gerhard-Domagk-Strasse 1, 53121, Bonn, Germany.
E-mail: r.streubel@uni-bonn.de; Fax: (+49)228-739616;
Tel: (+49)2285-735345
bDepartment of Chemistry, University of Sussex, Falmer, Brighton, UK
BN1 9QJ
{ Electronic supplementary information (ESI) available: Experimental
details. See http://dx.doi.org/10.1039/b509567k
Scheme 2 Proposed mechanism for the formation of 9.
4842 | Chem. Commun., 2005, 4842–4844
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Fig. 2 Molecular structure of 11 in the crystal (thermal ellipsoids at 50%
˚
Fig. 1 Molecular structure of 9 in the crystal (thermal ellipsoids at 50%
˚
probability). Selected bond lengths (A) and angles (u): P(1)–C(6) 1.847(2),
P(1)–Si(5) 2.341(1), P(2)–Si(5) 2.258(1); P(1)–Si(5)–P(2) 86.57(3), Si(5)–
probability). Selected bond lengths (A) and angles (u): W–C(5) 2.169(6),
P–C(6) 1.689(6), W–P 2.4392(16), O(5)–C(5) 1.381(6), N(5)–C(5) 1.366(7);
PC(6)N(5)Si(2) 2141.9, WC(5)N(5)C(6) 21.8, C(5)N(5)C(6)P 10.1,
Si(1)O(5)C(5)N(5) 22.9, O(5)C(5)N(5)Si(2) 227.3.
P(2)–C(20) 92.3(1), N(1)–P(1)–Si(5) 94.8(1).
We are grateful to the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie for financial support.
Notes and references
{ Satisfactory elemental analysis data were obtained for complexes 9 and
11. NMR data were recorded in C6D6 solutions on a Bruker AX 300
1
spectrometer for 9 (300.1 MHz for H, 75.0 MHz for 13C, 59.5 MHz for
29Si and 121.5 MHz for 31P) and on a Bruker AMX spectrometer for
11(500.1 MHz for 1H, 125.76 MHz for 13C, 99.3 MHz for 29Si and
202.5 MHz for 31P), using tetramethylsilane and 85% H3PO4 as standard
references. Chemical shifts d are given in ppm, coupling constant
magnitudes J in Hz. Selected NMR data of 9: 1H NMR (C6D6,
500.0 MHz): d 0.18 (s, 18H, SiMe3), 0.86 (s, 18H, C(CH3)3), 1.18 (s,
Scheme 3 Synthesis of complex 11.
precursor. Unfortunately, these complexes could not be isolated
using column chromatography. To get further insight into the
reaction course at elevated temperatures, we decided to investigate
the reactivity of complex 4a towards 5.
2
18H, C(CH3)3), 2.08 (d, 1H, JP,H 5 18.3 Hz, CH(SiMe3)2), 2.78 (d, 1H,
2
2JH,H 5 14.5 Hz, CH2C(CH3)3), 3.15 (d, 1H, JH,H 5 14.3 Hz,
2
CH2C(CH3)3), 3.33 (d, 1H, JH,H 5 14.5 Hz, CH2C(CH3)3), 3.51 (d, 1H,
2JH,H 5 14.3 Hz, CH2C(CH3)3), 6.30 (mc, 2H, Ph), 6.57 (mc, 2H, Ph), 6.71
(mc, 1H, Ph), 6.78 (mc, 4H, Ph), 6.85 (mc, 4H, Ph). 13C{1H} NMR (C6D6,
125.76 MHz): d 1.32 (s, SiMe3), 17.7 (d, 1JP,C 5 37.5 Hz, CH(SiMe3)2), 29.2
(s, C(CH3)3), 29.5 (s, C(CH3)3), 34.5 (s, C(CH3)3), 35.0 (s, C(CH3)3), 54.0 (s,
CH2), 54.4 (s, CH2), 110.0 (s, Carom), 111.9 (s, C-Ph), 118.3 (s, C-Ph), 118.7
(s, C-Ph), 126.8 (s, C-Ph), 128.3 (s, C-Ph), 128.8 (s, C-Ph), 138.0 (s, C-Ph),
Therefore, we reacted pure 4a with the silylene 5 in Et2O and
observed a clean reaction to the 1,2,4,3-azadiphosphasilol-5-ene
complex 11 (Scheme 3).{ Complex 11 was isolated in very good
yield (90.1%) and was characterized by NMR spectroscopy, MS
spectrometry and X-ray crystallography.§
1
The 31P{1H} NMR spectrum of 11 showed an AB-type spin
138.8 (s, C-Ph), 171.0 (d, JP,C 5 41.2 Hz, PLC), 205.7 (br, CO), 256.8
2+3
(
J
P,C
5 9 Hz, WLC). 29Si{1H} NMR (C6D6, 99.3 MHz): d 235.3 (s,
3 2
COSi), 230.7 (d, JP,Si 5 8.8 Hz, CNSi), 3.6 (d, JP,Si 5 5.9 Hz, SiMe3).
system with resonances at 3.1 and 242.7 ppm (1JP,W 5 225.5 Hz)
2+3
31P{1H} NMR (C6D6, 121.51 MHz): 191.4 (ssat 1JP,W 5 270.8 Hz).
,
with a
J
P,P
coupling constant magnitude of 211.1 Hz. In the
13C{1H} NMR spectrum, a doublet of doublets at 178.8 ppm
(JP,P 5 47.8 and 12.0 Hz) was observed for the ring carbon atom
of the azadiphosphasilolene ring. The molecular structure of 11 in
the crystal (Fig. 2) exhibited that, unlike in the precursor 5, the
bis(trimethylsilyl)methyl groups adopt cis-positions at the ring; this
points to a non-concerted mechanism of the insertion reaction.
A comparison of some distances of 11 with related bonds of the
dinuclear 2,3,4-triphenyl substituted 1,2,3,4-azatriphospholene
tungsten complex6 (12) suggest significant steric repulsions between
Selected NMR data for 11: 1H NMR (C6D6, 300.1 MHz): d 20.08 (s, 9H,
SiMe3), 20.03 (s, 9H, SiMe3), 0.29 (s, 9H, SiMe3), 0.41 (s, 9H, SiMe3), 1.15
(s, 9H, C(CH3)3), 1.20 (s, 9H, C(CH3)3), 1.96 (dd, 1H, JP,H 5 19.6,
2
4JP,H 5 2.1 Hz, CH(SiMe3)2), 2.25 (dd, 1H, JP,H 5 8.6, JP,H 5 1.0 Hz,
2
4
2
CH(SiMe3)2), 3.17 (d, 1H, JH,H 5 14.1 Hz, CH2C(CH3)3), 3.43 (d, 1H,
2JH,H 5 14.1 Hz, CH2C(CH3)3), 3.54 (d, 1H, JH,H 5 14.6 Hz,
CH2C(CH3)3), 4.15 (d, 1H, JH,H 5 14.6 Hz, CH2C(CH3)3), 6.7–6.9 (mc,
2
2
4H, H-Ph), 7.0–7.2 (mc, 5H, H-Ph). 13C{1H} NMR (C6D6, 75.0 MHz): d
20.5 (d, JP,C 5 6.5 Hz, SiMe3), 1.0 (d, JP,C 5 4.5 Hz, SiMe3), 2.5 (s,
3
3
3
1
SiMe3), 3.2 (d, JP,C 5 1.3 Hz, SiMe3), 17.8 (d, JP,C 5 17.8 Hz,
CH(SiMe3)2), 27.9 (d, 1JP,C 5 3.2 Hz, CH(SiMe3)2), 28.8 (s, C(CH3)3), 28.9
(s, C(CH3)3), 33.6 (s, C(CH3)3), 34.3 (s, C(CH3)3), 55.7 (s, CH2C(CH3)3),
57.6 (CH2C(CH3)3), 107.7 (s, C-Ph), 108.9 (s, C-Ph), 110.6 (s, C-Ph), 116.8
(s, C-Ph), 117.5 (s, C-Ph), 118.2 (s, C-Ph), 127.5 (s, C-Ph), 127.9 (s, C-Ph),
˚
the ring substituents at the P and Si centers in 11, e.g., 2.594(1) A
˚
for P(1)–W(1) in 11 vs. 2.5154(8) and 2.5361(7) in 12 and 1.863(2) A
128.4 (s, C-Ph), 138.7 (s, C-Ph), 139.5 (s, C-Ph), 140.5 (s, C-Ph), 178.8 (dd,
5 47.8, 2+3JP,C 5 12.0, PCNPSi), 195.7 (d, 2JP,C 5 21.7 Hz, trans-
4 1
for P(2)–C(13) vs. 1.827(3) and 1.845(3).
1+4
J
P,C
Studies on the reactivity of 2H-azaphosphirene complexes
towards other six-electron species such as carbenes are currently
underway.
CO), 197.8 (ddsat,
2JP,C 5 5.8, JP,C 5 1.9, JW,C 5 126.4 Hz, cis-CO).
29Si{1H} NMR (C6D6, 59.5 MHz): d 20.8 (d, 2JP,Si 5 12.0 Hz, SiMe3), 0.8
(dd, 1+4JP,Si 5 48.7, 1+4JP,Si 5 6.2 Hz, PSiP), 2.6 (pt, 2JP,Si 5 6.9 Hz, SiMe3),
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2
4.1 (d, JP,Si 5 7.4 Hz, SiMe3), 4.4 (dd, JP,Si 5 19.4, JP,Si 5 1.8 Hz,
2
4
for 543 parameters, 17 restraints and 12333 unique reflections; max./min.
Dr 1.577/21.488 e A23. The hydrogens were refined using a riding model.
CCDC 278009 and 278010. See http://dx.doi.org/10.1039/b509567k for
crystallographic data in CIF or other electronic format.
SiMe3). 31P NMR (C6D6, 121.5 MHz): d 3.1 (dsat
,
J
5 211.1,
5
2+3
˚
P,P
1JP,W 5 225.5, 2JP,H 5 18.6 Hz, s4-P), 242.7 (d, 2+3JP,P 5 211.1, 2JP,H
3.8 Hz, s3-P).
§ Crystal structure determination for 9: C51H76N5O5PSi4W. Crystal data:
orthorhombic, space group P212121 (no. 19), a 5 12.9763(2), b 5 17.5048(3),
1 E. Ionescu, P. G. Jones and R. Streubel, Chem. Commun., 2002, 2204.
2 R. Streubel, M. Bode, U. Schiemann, C. Wismach, P. G. Jones and
A. Monsees, Z. Anorg. Allg. Chem., 2004, 630, 1215.
3 R. Streubel, A. Kusenberg, J. Jeske and P. G. Jones, Angew. Chem., 1994,
106, 2564; R. Streubel, A. Kusenberg, J. Jeske and P. G. Jones,
Angew. Chem., Int. Ed., 1994, 33, 2427: for a review on
2H-azaphosphirene complexes see: R. Streubel, Coord. Chem. Rev.,
2002, 227, 175.
4 B. Gehrhus, M. F. Lappert, J. Heinicke, R. Boese and D. Bla¨ser, J. Chem.
Soc., Chem. Commun., 1995, 1931.
5 J. C. Slootweg, F. J. J. de Kanter, M. Schakel, A. W. Ehlers, B. Gehrhus,
M. Lutz, A. M. Mills, A. L. Spek and K. Lammertsma, Angew. Chem.,
2004, 116, 3556; J. C. Slootweg, F. J. J. de Kanter, M. Schakel,
A. W. Ehlers, B. Gehrhus, M. Lutz, A. M. Mills, A. L. Spek and
K. Lammertsma, Angew. Chem., Int. Ed, 2004, 43, 3471.
6 N. Hoffmann, C. Wismach, P. G. Jones, R. Streubel, N. H. Tran Huy
and F. Mathey, Chem. Commun., 2002, 45.
3
˚
˚
c 5 25.6015(4) A, U 5 5815.3(2) A , Z 5 4, T 5 223(2) K. Data collection:
a red crystal ca. 0.10 6 0.10 6 0.05 mm was used to record 25183
intensities on a Nonius KappaCCD diffractometer (Mo-Ka radiation,
2hmax 5 50u). Absorption corrections were applied using MULTISCAN.
Structure refinement: the structure was refined full-matrix least squares on
F2 (SHELXL-97, G. M. Sheldrick, Univ. Go¨ttingen) to wR2 5 0.076, R1
50.055 for 604 parameters, 0 restraints and 9729 unique reflections;
S 5 20.026(6), max./min. Dr 0.53 and 20.58 e A23. The hydrogens were
˚
refined using a riding model. Crystal structure determination for 11:
C42H69N3O5P2Si5W?0.5Et2O. Crystal data: monoclinic, space group P21/n
˚
(no. 14), a 5 11.3153(1), b 5 19.0877(2), c 5 25.1500(3) A, b 5 93.196(1)u,
U 5 5423.53(10) A , Z 5 4, m(Mo-Ka) 5 2.342 mm21, T 5 123(2) K. Data
3
˚
collection: a yellow crystal ca. 0.30 6 0.20 6 0.15 mm was used to record
43997 intensities on a Nonius KappaCCD diffractometer (Mo-Ka
radiation, 2hmax 5 60u). An empirical absorption correction was applied
(min./max. transmission 5 0.55337/0.65097). Structure refinement: the
structure was refined as above to wR2 5 0.0647, R1 5 0.0275 (for I . 2s(I))
4844 | Chem. Commun., 2005, 4842–4844
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