Photochemical and thermal reactions of a 2H-azaphosphirene complex with isonitriles

Article abstract of DOI:10.1021/om049014u

Photochemical ring opening of {2-[bis(tri-methylsilyl)methyl]-3-phenyl-2H- azaphosphirene-kP}-pentacarbonyltungsten(0) (1) in diethyl ether in the presence oftert-butyl isocyanide (2) yields the η¹-aza3-phosphaallene complex 4 at low temperature (-30°C), the formation of which is explained via a 1,1-addition of 2 with the transiently formed terminal phosphinidene complex 3. Complex 4 decomposed slowly at ambient temperature to furnish the [bis(trimethylsilyl)methyl]cyanophosphane complex 5 and isobutene. The same result was obtained via thermal ring opening of complex 1 at high temperature. In contrast, thermolysis of 1 in the presence of cyclohexyl isocyanide (7) afforded the N-cyclohexyl-substituted η¹-1-aza-3-phosphaallene complex 8. Complexes 4, 5, and 8 were unambiguously characterized by NMR and IR spectroscopy; the structure of complex 5 was established by X-ray crystal structure analysis. The structure of 5 and the energetics of its formation via decomposition of 4 were studied by DFT calculations, thus confirming the proposed reaction course.

Full text of DOI:10.1021/om049014u

Organometallics 2005, 24, 2237-2240
2237
Notes
Photochemical and Thermal Reactions of a
2H-Azaphosphirene Complex with Isonitriles
Emanuel Ionescu,† Gerd von Frantzius,† Peter G. Jones,‡ and Rainer Streubel*,†
Institut fu¨r Anorganische Chemie, Rheinische Friedrich-Wilhelms-Universita¨t Bonn,
Gerhard-Domagk-Strasse 1, D-53121 Bonn, Germany, and Institut fu¨r Anorganische und
Analytische Chemie, TU Braunschweig, Hagenring 30, D-38106 Braunschweig, Germany
Received December 13, 2004
Chart 1. Examples of η2-1-Aza-3-phosphaallene
Summary: Photochemical ring opening of {2-[bis(tri-
methylsilyl)methyl]-3-phenyl-2H-azaphosphirene-κP}-
pentacarbonyltungsten(0) (1) in diethyl ether in the
presence of tert-butyl isocyanide (2) yields the η1-1-aza-
3-phosphaallene complex 4 at low temperature (-30 °C),
the formation of which is explained via a 1,1-addition
of 2 with the transiently formed terminal phosphinidene
complex 3. Complex 4 decomposed slowly at ambient
temperature to furnish the [bis(trimethylsilyl)methyl]-
cyanophosphane complex 5 and isobutene. The same
result was obtained via thermal ring opening of complex
1 at high temperature. In contrast, thermolysis of 1 in
the presence of cyclohexyl isocyanide (7) afforded the
N-cyclohexyl-substituted η1-1-aza-3-phosphaallene com-
plex 8. Complexes 4, 5, and 8 were unambiguously
characterized by NMR and IR spectroscopy; the structure
of complex 5 was established by X-ray crystal structure
analysis. The structure of 5 and the energetics of its
formation via decomposition of 4 were studied by DFT
calculations, thus confirming the proposed reaction
course.
Complexes
agents. Very recently, the reaction of a nucleophilic
terminal titanium phosphinidene complex with tert-
butyl isocyanide was described, thus leading to a
η2-1-aza-3-phosphaallene complex (IIb) via formal in-
sertion of the isonitrile moiety into the Ti-P bond.4 To
the best of our knowledge, η1-1-aza-3-phosphaallene
complexes are still unknown.
Recently, we have shown that 2H-azaphosphirene
complexes5 are effective precursors for highly reactive
electrophilic terminal phosphinidene complexes bearing
bulky substituents at phosphorus,6 which can be used
to access unusual three-membered phosphorus hetero-
cycles. More fascinating was the observation that ni-
trilium phosphane-ylide complexes can be generateds
via 1,1-addition of carbonitriles to the phosphorus center
of the electrophilic phosphinidene complexessand con-
sequently used as new building blocks in phosphorus
chemistry.7 Therefore, we became interested in studies
on the generation and synthetic potential of 1,1-adducts
of electrophilic phosphinidene complexes with π systems
possessing an element with an electron lone pair at the
terminal position. Herein, we describe the first examples
of 1,1-addition reactions of a transiently formed electro-
philic terminal phosphinidene complex with isocyanides,
Introduction
Since the first synthesis of a stable 1-aza-3-phos-
phaallene by Kolodiazhnyi and co-workers,1 the syn-
thesis of allenes or cumulenes of the general formula
EdCdE′, containing doubly bonded heavy elements
such as E ) P, As, Si, Ge, Sn and E′ ) C, N, P, As, O,
S, has become a new challenge in organoelement
chemistry.2 Access to stable 1-aza-3-phosphaalleness
and related compoundssrelies on the use of sterically
demanding substituents at the P and N atoms of the
PdCdN moiety and is most often achieved via base-
induced elimination reactions. Whereas the structures
and reactivity of 1-aza-3-phosphaallenes have been
intensively studied, very little is known about their
complexes. Usually, η2(P,C)-3 (I) and η2(N,C)-1-aza-3-
phosphaallene complexes (IIa,b)3,4 (Chart 1) are ob-
tained using 1-aza-3-phosphaallenes and complexing
(3) (a) David, M. A.; Alexander, J. B.; Glueck, D. S.; Yap, G. P. A.;
Liable-Sands, L. M.; Rheingold, A. I. Organometallics 1997, 16, 378.
(b) Alexander, J. B.; Glueck, D. S.; Yap, G. P. A.; Rheingold, A. I.
Organometallics 1995, 14, 3603.
* To whom correspondence should be addressed. Fax:
(49)228-739616. Tel: (49)2285-735345. E-mail: r.streubel@uni-bonn.de.
† Rheinische Friedrich-Wilhelms-Universita¨t Bonn.
‡ TU Braunschweig.
(1) (a) Kolodiazhnyi, O. I. Tetrahedron Lett. 1982, 23, 4933.
(b) Kolodiazhnyi, O. I. Zh. Obshch. Khim. 1982, 52, 2361.
(2) (a) Escudie, J.; Ranaivonjatovo, H.; Rigon, L. Chem. Rev. 2000,
100, 3639. (b) Eichler, B.; West, R. Adv. Organomet. Chem. 2001, 46,
1.
(4) Basuli, F.; Watson, L. A.; Huffmann, J. C.; Mindiola, D. J. Dalton
2003, 4228.
(5) Streubel, R. Coord. Chem. Rev. 2002, 227, 175.
(6) (a) Mathey, F.; Tran Huy, N. H.; Marinetti, A. Helv. Chim. Acta
2001, 84, 2938. (b) Lammertsma, K. Top. Curr. Chem. 2003, 229, 95.
(7) Streubel, R. Top. Curr. Chem. 2002, 223, 91.
10.1021/om049014u CCC: $30.25 © 2005 American Chemical Society
Publication on Web 03/23/2005

2238 Organometallics, Vol. 24, No. 9, 2005
Notes
Scheme 1. Photochemical and Thermal Reactions
of Complex 1 with Isonitriles 2 and 7a
Figure 1. The 1-aza-3-phosphaallene complex 4, its
resonance structure 4′ with a phosphanide-type phosphorus
center, and an adduct, the isocyanide phosphinidene
complex 4′′ (R ) CH(SiMe3)2).
Scheme 2. Thermolysis of Complex 1 in the
Presence of Cyclohexyl Isocyanide (R )
CH(SiMe3)2)
the η1-1-aza-3-phosphaallene complex 8 in a more clean
reaction. Interestingly, complex 8 was stable in solution
at room temperature, thus showing the necessity of a
(more) pendant group to promote H transfer and de-
composition (Scheme 1). However, also surprisingly, the
diphosphene complex 99susually not obtained in ther-
mal reactions of complex 1!swas also formed in this
reaction (Scheme 2). The reaction pathway to 9 is
unclear at the moment.
Complexes 4, 5, and 8 were unambiguously charac-
terized by NMR and IR spectroscopy, and additionally,
5 was characterized by X-ray diffraction studies. Com-
plex 4 displayed a 31P{1H} resonance at -136.6 ppm
and a 13C{1H} resonance for the carbon atom of the
t
a Legend: (i) diethyl ether, -30 °C, 120 min (R ) Bu) or
toluene, 75 °C, 45 min (R ) cyclohexyl); (ii) n-pentane, room
temperature, slow; (iii) toluene, 110 °C, 90 min.
thus giving the first η1-1-aza-3-phosphaallene com-
plexes; one of them (the N-tert-butyl-substituted com-
plex) exhibits an unprecedented reactivity pattern: i.e.,
ω-H transfer to the low-coordinated phosphorus center
with expulsion of isobutene.
Results and Discussion
Photochemical ring opening of the 2H-azaphosphirene
complex 1 in diethyl ether in the presence of tert-butyl
isocyanide (2) yielded selectively the η1-1-aza-3-phos-
phaallene complex 4 at low temperature. On the basis
of our earlier findings on the photochemistry of
2H-azaphosphirene complex 1,8 we assume that complex
4 is formed via a 1,1-addition of the isonitrile 2 with
the transiently formed terminal phosphinidene complex
3 (Scheme 1). 31P{1H} NMR reaction monitoring re-
1-aza-3-phosphaallene moiety at 195.5 ppm (1JP,C
)
3.9 Hz). The 31P{1H} resonance of 4 at high field and
the very small P,C coupling constant magnitude point
to a structural motive, which is characterized by an
enhanced negative charge at phosphorus (Figure 1),
thus explaining at the same time the chemical shielding
and the small tungsten-phosphorus coupling constant
1
vealed that complex 4 (δ -136.6, JP,W ) 194.5 Hz) is
1
of JW,P ) 194.5 Hz.
formed in Et2O at -30 °C, but after 48 h at ambient
temperature the amount of 4 had decreased in favor of
the [bis(trimethylsilyl)methyl]cyanophosphane complex
It has been recognized previously by Mathey et al.10
that negatively charged phosphorus centers of com-
plexes have a significant effect on various NMR param-
eters; very nice examples are the complex [(OC)5WPH3]
1
5 and isobutene. The latter was identified by H NMR
spectroscopy. Complex 5 was also obtained on subjecting
the 2H-azaphosphirene complex 1 to thermal ring
opening, but under these conditions 5 was formed
together with two minor products (<5%), 6 (δ(31P)
1
(δ(31P) -183, JW,P ) 216 Hz) and its dilithium phos-
phanide complex [(OC)5WP(Li)H2] (δ(31P) -273,
1JW,P ) 68 Hz).10 It should be also taken into account
that it is known from a series of η1 and η2 platinum
-104.7, JP,H ) 223.8 Hz) and 7 (δ(31P) -41.7, JP,W
)
1
1
1
1
216.6, JP,H ) 326.8 Hz). The product 6 could be
obtained as the main product, if the thermal reaction
with 5 was carried out at 70 °C in the presence of 1
equiv of 2. It should be noted that bis(tert-butyl)-1-aza-
3-phosphaallene is stable with regard to a ω-H transfer
reaction from the N-t-Bu group to phosphorus (it can
be purified through distillation).1
phosphaalkene complexes that the JPt,P coupling con-
stant magnitude can be seen as a proof for the coordina-
tion mode, because the value of the η1 mode is signifi-
cantly largersby roughly 1 order of magnitude.11
Although some η1 and η2 tungsten phosphaalkene
(9) Lang, H.; Huttner, G. J. Organomet. Chem. 1985, 291, 293.
(10) Nief, F.; Mercier, F.; Mathey, F. J. Organomet. Chem. 1987,
328, 349.
(11) (a) van der Knaap, Th. A.; Bickelhaupt, F. J. Am. Chem. Soc.
1982, 104, 1756. (b) Kroto, H. W.; Klein, S. I.; Meidine, M. F.; Nixon,
J. F.; Harris, R. K.; Packer, K. J.; Reams, P. J. Organomet. Chem. 1985,
280, 281.
For comparison, we carried out the thermolysis of 1
in the presence of cyclohexyl isocyanide (7) and obtained
(8) Streubel, R.; Wilkens, H.; Jones, P. G. Chem. Commun. 1999,
2127.

Notes
Organometallics, Vol. 24, No. 9, 2005 2239
complexes have been described, there is not much NMR
data available.12
In the IR spectra of uncomplexed 1-aza-3-phospha-
allenes a strong band between 1830 and 1915 cm-1 due
to the asymmetric stretch of the PdCdN unit has been
found to be characteristic for this class of compounds.2a
In the IR spectra of η2(P,C)- and η2(CN)-coordinated
1-aza-3-phosphaallene complexes a strong band in the
region 1800-2000 cm-1 is absent. Instead, a band at
1577 cm-1 (ν(CdN)) was found for [η2(P,C)-Mes*PdCd
NPh]Pt(Ph2P(CH2)2PPh2)3a and at 1505 cm-1 (ν(PdC))
for [η2(C,N)-Mes*PdCdNPh]Nb(Cl)(C5H4SiMe3)2.3b The
IR spectrum of 4 shows a very strong and broad band
at 1942 cm-1 and a strong band at 849 cm-1. A band in
the region 1500-1600 cm-1 was not observed. According
to the DFT frequency calculation13 (unscaled calculated
frequencies in brackets) the band at 1942 cm-1
(2020 cm-1) contains the asymmetric stretching vibra-
Figure 2. Molecular structure of 5 in the crystal state
(thermal ellipsoids at 50% probability). Selected bond
lengths (Å) and angles (deg): W-P, 2.4753(5); P-C(13),
1.816(2); P-C(6), 1.8129(18); N-C(13), 1.127(3); N-
C(13)-P, 176.91(19); C(13)-P-W, 114.40(6); C(6)-P-W,
123.84(6); C(6)-P-C(13), 102.82(8). For a comparison of
experimental and calculated structures see Figure 3.
tion of the CdN moiety; the band at 849 cm-1 (895 cm-1
)
can be assigned to the PdC stretching. These findings
are further strong evidence for the η1 coordination of
the 1-aza-3-phosphaallene ligand in 4, in agreement
with its NMR data.
(using DFT calculations) that the primary product has
the structure of a Lewis acid/base adduct rather than a
1-aza-3-silaallene.15a,b
The calculated structure of complex 4 (Figure 3)
exhibits a slightly pyramidalized phosphorus (sum of
bond angles at P 347°) and an almost linear PCN unit
(P-C-N ) 172°) with a P-C(N) distance 6% shorter
than in the cyanophosphane complex 5. In comparison
with complex 4 the calculated C-N stretching frequency
of 5 is shifted by 290 cm-1 toward greater wavenumbers.
With respect to the question of whether the structure
is that of a Lewis acid/base adduct, with a pseudo-
pyramidal phosphorus geometry, or that of a 1-aza-3-
phosphaallene complex, our results support the bonding
description of 4 (more) in terms of a 1-aza-3-phospha-
allene, as deduced from the NMR data. To attain a
better understanding of the proposed decomposition
reaction of complex 4, we calculated the enthalpy and
free energy of this process (Figure 3). According to our
calculations the release of isobutene from 4 is exother-
mal by 15 kJ/mol and exergonic by 60 kJ/mol.13
The cyanophosphane complex 5sthe first of its kinds
shows a 31P resonance at -69.9 ppm (1JW,P ) 242.9,
1JP,H ) 358.3 Hz) and a 1H resonance for the hydrogen
atom directly bonded to the phosphorus at δ 6.2, which
is low-field shifted versus uncomplexed derivatives of
t
the type RP(H)CN (R ) Me, δ(1H) 4.15; R ) Bu, δ(1H)
3.98).14 Nevertheless, some steric (and electronic)
effects can be taken into account if compared with
1,3,5-tBu3C6H2-P(H)CN (δ(1H) 5.95).14 The phosphane
6swhich could be converted into complex 5 by reaction
with [W(CO)5(thf)]sshows
a
31P resonance at
-104.8 ppm (1JP,H ) 224.8 Hz) and a 13C resonance of
the cyano group at 121.0 ppm (1JP,C ) 77.6 Hz). These
NMR parameters are in good agreement with the data
of 1,3,5-tBu3C6H2-P(H)CN (δ(31P) -101.6, JP,H
)
1
1
249.7 Hz, δ(13CCN) 121.2, JP,C ) 74.4 Hz).14
The structure of 5 was confirmed by single-crystal
X-ray crystallography (Figure 2).
The NMR data of 8 are very similar to those of 4; 8
Conclusions
displays a 31P{1H} resonance at -141.4 ppm (1JP,W
)
The 1,1-additions of a transiently formed electrophilic
terminal phosphinidene complex to isonitriles yielded
the first η1-1-aza-3-phosphaallene complexes. Unexpect-
edly, it was also demonstrated that an unprecedented
reactivity pattern can emerge: i.e., ω-H transfer to a
low-coordinated phosphorus center. Interestingly, the
latter finding again demonstrates the close vicinity of
coordinatively unsaturated transition-metal and main-
group-element centers, which we soon hope to exploit
further in the field of activation of small molecules.
192.0 Hz) and a 13C{1H} resonance of the central carbon
atom of the 1-aza-3-phosphaallene unit at 195.4 ppm
with a low 1J(P,C) coupling constant magnitude of
8.7 Hz.
Because silylene derivatives and terminal electro-
philic phosphinidene complexes often show interesting
similarities in structure, bonding, and reactivity, it
seems interesting to compare our results with those
obtained from reactions of stable and/or transient di-
organosilylenes with isonitriles. For example, Tokitoh
et al. reported on a reaction of a silylene bearing
Experimental Section
t
sterically demanding arene substituents with BuNC,
All reactions and manipulations were carried out under an
atmosphere of deoxygenated dry argon, using standard Schlenk
techniques with conventional glassware, and solvents were
dried according with standard procedures under an argon
atmosphere. NMR spectra were recorded on a Bruker AX 300
spectrometer (121.5 MHz for 31P, 75.0 MHz for 13C, and
300.1 MHz for 1H) using C6D6 and CDCl3 as solvent and
internal standard; shifts are given relative to external tet-
from which a hydrocyanosilane derivative and isobutene
were obtained as final products.15a The same authors
also presented spectroscopic and theoretical evidence
(12) Holand, S.; Charrier, C.; Mathey, F.; Fischer, J.; Mitschler, A.
J. Am. Chem. Soc. 1984, 106, 826.
(13) B3LYP/6-311g(d,p) at C, H, N, P, O, Si and LanL2DZ (the ECP
by: Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270) at W. All
calculations were performed using GAUSSIAN03, Rev. B.02.
(14) Maraval, A.; Igau, A.; Lepetit, C.; Chrostowska, A.; Sotiropoulos,
J. M.; Pfister-Guillouzo, G.; Donnadieu, B.; Majoral, J.-P. Organo-
metallics 2001, 20, 33.
(15) (a) Takeda, N.; Kajiwara, T.; Suzuki, H.; Okazaki, R.; Tokitoh,
N. Chem. Eur. J. 2003, 9, 3530. (b) Takeda, N.; Suzuki, H.; Tokitoh,
N.; Okazaki, R.; Nagase, S. J. Am. Chem. Soc. 1997, 119, 1456.

2240 Organometallics, Vol. 24, No. 9, 2005
Notes
Figure 3. Calculated molecular structures (gas phase) of 4 and 5; ∆G for the decomposition of 4 to yield 5 and isobutene.
Selected bond lengths (Å) and angles (deg) are as follows. 4: W-P, 2.611; P-C(N), 1.690; P-C(H), 1.878; C(N)-N, 1.197;
N-C(P), 1.197; N-C-P, 171.88; C(N)-N-C, 137.59; C(N)-P-W, 114.48; C(H)-P-W, 125.08; C(H)-P-C(N), 107.48. 5
(deviations from the X-ray structure in percent are given in parentheses): W-P, 2.548 (+2.9); P-C(13), 1.802 (-0.8);
P-C(6), 1.852 (+2.1); N-C(13), 1.156 (+2.5); N-C(13)-P, 177.51 (+0.3); C(13)-P-W, 116.17 (+1.5); C(6)-P-W, 123.13
(-0.6); C(6)-P-C(13), 103.99 (+1.1).13
2
1
ramethylsilane (1H and 13C) and 85% H3PO4 (31P); only
coupling constant magnitudes are given. Electron impact
(EI, 70 eV) mass spectra were recorded on a Kratos MS 50
mass spectrometer. The IR spectrum of 4 (KBr pellet) was
recorded on a Perkin-Elmer 1600 FT-IR spectrometer. El-
emental analyses were performed with an Elementar Vario
EL analytical gas chromatograph.
1.06 (d, 1H, JP,H ) 7.1 Hz, CH(SiMe3)2), 3.70 (d, 1H, JP,H )
224.8 Hz, PH); 13C{1H} NMR δ 121.0 (d, 1JP,C ) 77.6 Hz, PCN);
31P NMR -104.5 (1JP,H ) 224.8 Hz).
Synthesis of 8. An 84 mg portion (0.77 mmol) of cyclohexyl
isocyanide (7) and 475 mg (0.77 mmol) of 1 were dissolved in
1.2 mL of toluene and heated for 45 min at 75 °C. Subsequent
evaporation of the solvent (ca. 0.01 mbar) and column chro-
matography (silanized silica gel, -50 °C, n-pentane) yielded
8 in the second fraction as a red oil. Yield: 285 mg (59.6%).
The first eluted fraction yielded 9 (NMR data are in accord
with the literature data).9 Anal. Calcd for 8: C, 36.60; H, 4.85;
N, 2.25. Found: C, 36.42; H, 4.78; N, 2.22. Selected NMR data
for 8: 13C{1H} NMR δ 0.0 (d, 1J(P,C) ) 2.9 Hz, SiMe3), 1.1
(d, 1J(P,C) ) 3.2 Hz, SiMe3), 22.9 (s, 2 × Cy CH2), 24.0 (s, Cy
CH2), 26.5 (d, 1J(P,C) ) 24.2 Hz, CH(SiMe3)2), 32.0 (s, 2 × Cy
t
Synthesis of 4. A 91 mg portion (1.1 mmol) of BuNC and
617 mg (1 mmol) of 1 were dissolved in 400 mL of diethyl ether
and irradiated for 2 h at -30 °C (low-pressure Hg lamp;
λ 254 nm). Subsequent evaporation of the solvent (ca.
0.01 mbar) and column chromatography (silanized silica gel,
-50 °C, n-pentane) yielded 4 as a red oil (first eluted fraction)
as a 4:1 mixture with 5. Selected NMR data of 4: 13C{1H} NMR
δ -0.8 (d, 3JP,C ) 4.2 Hz, SiMe3), -0.5 (d, 3JP,C ) 2.9 Hz, SiMe3),
27.8 (d, 1JP,C ) 24.9 Hz, CH(SiMe3)2), 61.2 (d, 3JP,C ) 12.9 Hz,
CH2), 60.3 (d, J(P,C) ) 12.8 Hz, NCH), 195.4 (d, 1J(P,C) )
3
2
PCNC), 28.1 (s, C(CH3)3), 195.3 (d, JP,C ) 3.2 Hz, cis-CO),
8.7 Hz, PCN), 196.5 (d, 2J(P,C) ) 3.2 Hz, cis-CO), 200.1
195.5 (d, 1JP,C ) 3.9 Hz, PCN), 200.0 (d, 2JP,C ) 24.2 Hz, trans-
CO); 31P{1H} NMR δ -136.6 (s, 1JP,W ) 194.5 Hz). Selected IR
data of 4 (KBr): ν˜ 848.5 (ν(PdC)), 1880.0-1942.0 (broad,
(d, 2J(P,C) ) 24.9 Hz, trans-CO); 31P{1H} NMR δ -141.4
1
(s, J(P,W) ) 192.0 Hz). Selected MS data for 8 (EI, 70 eV):
m/z 623.1 [M+, 34].
ν(CO) and ν(CdN)), 2069.6 (ν(CO)) cm-1
.
Crystal Structure Determination of 5, C13H20NO5PSi2W.
Crystal data: triclinic, space group P1h, a ) 6.9618(4) Å,
b ) 9.6073(8) Å, c ) 16.1541(9) Å, R ) 73.219(3)°, â ) 89.975-
(3)°, γ ) 81.823(3) °, U ) 1022.98(12) Å3, Z ) 2, T ) -140 °C.
Data collection: a crystal with dimensions ca. 0.16 × 0.15 ×
0.08 mm was used to register 19 997 intensities (Mo KR
radiation, 2θmax ) 60°) on a Bruker SMART 1000 CCD
diffractometer. An absorption correction was performed with
SADABS. Structure refinement: full-matrix least squares on
F2 (program SHELXL-97)16 to wR2 ) 0.0346 and R1 ) 0.0159
for 218 parameters, 21 restraints (to displacement parameters
to the light atoms), and 5954 independent reflections. The
phosphane hydrogen H0 was refined freely; other H atoms
were included using a riding model or rigid methyl groups.
See http://www.rsc.org/suppdata for crystallographic data in
CIF or other electronic format (the structure was deposited
with the number 246853).
t
Synthesis of 5. A 91 mg portion (1.1 mmol) of BuNC and
617 mg (1 mmol) of 1 were dissolved in 2 mL of toluene and
heated at 75 °C for 45 min. The solvent was evaporated (ca.
0.01 mbar), and the remaining solid was washed twice with
2 mL of n-pentane and twice with 2 mL of diethyl ether and
dried under vacuum (ca. 0.01 mbar); air-stable colorless solid,
yield 450 mg (83.2%), mp 153 °C dec. Anal. Calcd for 5: C,
28.85; H, 3.72; N, 2.59. Found: C, 28.32; H, 3.72; N, 2.54.
1
Selected NMR data of 5: H NMR δ 0.28 (s, 9H, SiMe3), 0.37
2
(s, 9H, SiMe3), 0.63 (d, 1H, JP,H ) 2.8 Hz, CH(SiMe3)2), 6.20
1
3
(d, 1H, JP,H ) 358.3 Hz, PH); 13C{1H} NMR δ -0.21 (d, JP,C
) 3.3 Hz, SiMe3), 1.04 (d, 3JP,C ) 4.1 Hz, SiMe3), 12.23 (d, 1JP,C
1
) 7.3 Hz, CH(SiMe3)2), 116.8 (d, JP,C ) 1.9 Hz, PCN), 193.8
2
1
2
(d, JP,C ) 5.8 Hz, JW,C ) 126.1 Hz, cis-CO), 195.9 (d, JP,C
)
27.2 Hz, trans-CO); 31P{1H} NMR δ -69.9 (s, JP,W ) 242.9
Hz). Selected MS data for 5 (EI, 70 eV): m/z 541 [M+, 68].
Selected IR data of 5 (KBr): ν˜ 1900.0-1950.0 (broad, ν(CO)),
1
Acknowledgment. We are grateful to the Deutsche
Forschungsgemeinschaft and the Fonds der Chemischen
Industrie for financial support and the John von Neu-
mann Institute of Computing; Mr. A. Weinkauf regis-
tered the X-ray data for 5.
Supporting Information Available: Crystallographic
data (CIF file) for 5. This material is available free of charge
via the Internet at http://pubs.acs.org.
1991.6 (ν(CO)), 2080.6 (ν(CO)) cm-1
.
Attempted Synthesis of 6. A 20.8 mg portion (0.25 mmol)
t
of BuNC and 135.3 mg (0.25 mmol) of 5 were dissolved in
2 mL of toluene and heated at 110 °C for 90 min. The solvent
was evaporated (ca. 0.01 mbar) and the residue subjected to
column chromatography (silica gel, -50 °C, n-pentane)sbut
this proved unsuccessful (!), as 6 decomposed during the
column chromatography. 31P NMR spectroscopic analysis of
the crude residue showed a 20:1 mixture of 6 and 5 (by
integration) and contained, most probably, small amounts of
OM049014U
1
some carbonyl complexes. Selected NMR data of 6: H NMR
(16) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen, Go¨ttin-
gen, Germany, 1997.
4
δ -0.02 (d, 9H, JP,H ) 1.1 Hz, SiMe3), 0.66 (s, 9H, SiMe3),