The original reactivity of a phosphole-substituted Fischer carbene complex

Article abstract of DOI:10.1021/om400109h

In an unprecedented transformation, a phosphole-substituted Fischer carbene complex reacts with styrene to give an annelated phosphole derivative.

Full text of DOI:10.1021/om400109h

Communication
pubs.acs.org/Organometallics
The Original Reactivity of a Phosphole-Substituted Fischer Carbene
Complex
Kim Hong Ng, Yongxin Li, Rakesh Ganguly, and Francois Mathey*
Division of Chemistry & Biological Chemistry, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
S
* Supporting Information
ABSTRACT: In an unprecedented transformation, a phosp-
hole-substituted Fischer carbene complex reacts with styrene
to give an annelated phosphole derivative.
ischer carbene complexes are at the core of transition-
metal organometallic chemistry and display numerous uses
F
in organic synthesis.1 While a number of furan, thiophene, and
pyrrole derivatives of Fischer carbene complexes are known,2 to
the best of our knowledge, nothing is known about the
corresponding phosphole derivatives. In view of the rich
organic chemistry of Fischer carbene complexes,1 it seemed
quite attractive to prepare similar complexes derived from
phospholes, whose functional chemistry is still relatively
limited.3 The much lower aromaticity of the phosphole ring
in comparison with that of the other five-membered
heteroarenes4 could induce a greater conjugation between the
carbene and the diene unit of the heteroarene in the case of the
phosphorus ring. Hence, a significant perturbation of the
normal chemistry of Fischer carbene complexes could be
observed. This is indeed the case, as shown in this report.
In order to have an idea of what could be expected, we first
decided to compute the structure of the phosphole-substituted
free carbene 1 by DFT at the B3PW91/6-31G(d)-Lanl2dz(W)
level.5
Figure 1. Computed structure of phospholylcarbene (1). Main
distances (Å) and angles (deg): P−W = 2.520, P−Me = 1.849, P−
C1 = 1.802, P−C4 = 1.840, C4−C22 = 1.442, C22−O23 = 1.301,
C1−C2 = 1.354, C2−C3 = 1.475, C3−C4 = 1.377; C1−P−C4 = 91.0,
C4−C22−O23 = 120.1, O23−C22−C4−C3 = 68.5.
The structure is shown in Figure 1. As can be seen, the
carbene is not coplanar with the diene (O−C−CC dihedral
angle −68.5°), so that the overlap between the p orbital of the
carbene and the π orbitals of the diene is not maximal.
Nevertheless, a substantial conjugation between the two units
still exists, as shown by the relatively short C4−C22 bond
length of 1.442 Å. This is confirmed by the structure of the
LUMO (Figure 2), which is essentially a combination of the p
orbital of the carbene with the LUMO of the diene. The
structure of the carbene complex 1-W was also computed at the
same level. The repulsion between the two W(CO)5 groups
leads to a drastic change of the O−C−CC dihedral angle
from −68.5 to 68.8°. At 1.466 Å, the bond between the carbene
and the diene is longer than in 1 (1.442 Å). The back-bonding
of W to the p orbital of the carbene probably switches off the
conjugation with the diene. This means that the carbene−
tungsten bond will probably be rather easily cleaved to reinstall
Received: February 12, 2013
© XXXX American Chemical Society
A
dx.doi.org/10.1021/om400109h | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Communication
Figure 2. Computed HOMO and LUMO of 1 (Kohn−Sham).
the conjugation between the carbene and the diene. Indeed, the
dissociation energy of 1-W into 1 and singlet W(CO)5 is
computed to be 61.5 kcal mol−1, much lower than the De value
for (OC)5WCHOH at 81.9 kcal mol−1.6
Our starting point was the 2-lithiophosphole 4, prepared as
previously described.7 It was allowed to react with 2 equiv of
tungsten hexacarbonyl at −90 °C. The first equivalent reacts
with the carbanion, while the phosphole lone pair coordinates
to the second equivalent with elimination of CO. Subsequently,
in situ alkylation with MeOTf was carried out. The desired 2-
phospholylcarbene complex 28 was obtained in 30% yield after
purification by chromatography at −10 °C (eq 1).
Figure 3. X-ray crystal structure of the phosphole-substituted Fischer
carbene complex 2. Main distances (Å) and angles (deg): P−W =
2.5263(12), P−C14 = 1.821(5), P−C8 = 1.836(4), P−C13 =
1.789(5), C8−C9 = 1.359(7), C9−C11 = 1.486(7), C11−C13 =
1.340(7), C8−C6 = 1.475(6), C6−O6 = 1.332(5), C6−W1 =
2.173(4); C8−P−C13 = 90.7(2), O6−C6−C8 = 104.7(4), O6−C6−
W1 = 129.5(3), C8−C6−W1 = 124.1(3).
The most significant spectroscopic datum of 2 is the carbenic
13C resonance at 316.87 ppm (CDCl3). The structure was
established by X-ray crystal structure analysis (Figure.3). The
plane of the carbene (O6−C6−C8) makes an angle of 48.2°
with the plane of the diene. The bond between the carbene and
the diene (C6−C8) is longer than the corresponding computed
bond in 1 at 1.475(6) Å and very similar to those of thiophene
analogues.2 Overall, the structure is very close to that computed
for 1-W.
We tested three reactions of 2 in order to compare its
chemistry with the chemistry of standard Fischer carbene
complexes. The first reaction was the oxidation by DMSO (eq
2).
analysis (Figure 4). The ester and phosphole planes are
practically coplanar (angle 7.7°), and the C−C bond between
the diene and the ester remains at 1.475 Å. The ester group
appears at 163.24 ppm in the 13C NMR spectrum. The reaction
with water gave the aldehyde 68 (eq 3), which was
characterized by X-ray analysis (Figure 5). The aldehyde
group appears at 10.13 ppm (1H NMR) and 185.17 ppm (13C
NMR). Once again, a similar reactivity has previously been
described.9 A completely different picture emerged from the
reaction with neat styrene (eq 4).
Various reaction temperatures were tested from 50 to 90 °C.
Complete reaction was only achieved at 90 °C. The two
isomeric products 7a,b10 were obtained in a 1:1 ratio according
to the 31P NMR spectrum of the crude reaction mixture. 7a was
fully identified by an X-ray crystal structure analysis (Figure 6).
The 13C NMR spectra show that the cycloadditions leading to
7a,b have the same regiochemistry. In both cases, the styrenic
The reaction follows the normal course and gives the ester
5,8 which was fully characterized by an X-ray crystal structure
CH2 is not coupled to P, whereas the CHPh displays a JC−P
3
B
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Organometallics
Communication
Figure 6. X-ray crystal structure of bicyclic product 7. Main distances
(Å) and angles (deg): P−W = 2.5131(5), P−C22 = 1.8272(19), P−C6
= 1.7972(19), P−C14 = 1.8134(19), C6−C7 = 1.341(3), C7−C9 =
1.478(3), C9−C14 = 1.349(2), C9−C10 = 1.499(3), C10−C11 =
1.521(3), C11−C12 = 1.535(3), C12−C13 = 1.545(2), C13−C14 =
1.502(3), C13−O6 = 1.421(2); C6−P−C14 = 90.99(9), C14−C13−
O6 = 109.17(15), C13−C14−P = 126.79(13).
Figure 4. X-ray crystal structure of ester 5. Main distances (Å) and
angles (deg): P−W = 2.5196(7), P−C14 = 1.832(3), P−C6 =
1.794(3), P−C11 = 1.813(3), C6−C7 = 1.346(4), C7−C9 = 1.489(4),
C9−C11= 1.351(4), C11−C12 = 1.475(4), C12−O6= 1.211(3),
C12−O7 = 1.353(3); C6−P−C11 = 90.48(13), C11−C12−O6 =
127.3(3), C12−C11−P = 121.9(2), O6−C12−O7 = 123.23(3).
tetracoordinate 3,4-dimethylphospholes to the corresponding
3-methylene-4-methylphosphol-4-enes is also well-known.11 In
9, the 1,2-migration of H from C2 to the vicinal cyclopropyl
carbon would initiate the rearrangement into 7.
Finally, complex 2 was heated alone in toluene between 50
and 90 °C. No reaction was observed at temperatures lower
than 90 °C. However, at 90 °C, a messy 31P NMR spectrum
was obtained with complex 6 as the main product (due to the
trace amount of water present in toluene). Other dienophiles
such as alkynes (diphenylacetylene) were also tested under the
same reaction conditions. Promising results were obtained, but
the characterization of the products is still in progress.
ASSOCIATED CONTENT
* Supporting Information
■
S
Text, figures, and CIF files giving experimental details and
characterization data, X-ray crystal structure analyses of
compounds 2 and 5−7, and the complete ref 5. This material
is available free of charge via the Internet at http://pubs.acs.org.
Figure 5. X-ray crystal structure of aldehyde 6. Main distances (Å) and
angles (deg): P−W = 2.4966(16), P−C13 = 1.837(6), P−C7 =
1.807(6), P−C12 = 1.802(6), C7−C8 = 1.352(9), C8−C11 =
1.488(9), C11−C12 = 1.335(9), C6−C7 = 1.456(9), C6−O6 =
1.221(8); C7−P−C12 = 89.9(3), C7−C6−O6 = 123.6(6), C6−C7−P
= 121.8(5).
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: fmathey@ntu.edu.sg.
Notes
The authors declare no competing financial interest.
coupling. Since the dissociation of 2 to the corresponding
carbene at 90 °C appears unlikely in view of the computed De,
we are obliged to admit the well-established formation of a
transient cyclopropane 8 (eq 5). The isomerization of
ACKNOWLEDGMENTS
■
We thank the Nanyang Technological University in Singapore
for the financial support of this work and Dr. Yunpeng Lu for
the computations on 1-W.
REFERENCES
■
(1) de Meijere, A.; Schirmer, H.; Duetsch, M. Angew. Chem., Int. Ed.
2000, 39, 3964. Barluenga, J.; Santamaria, J.; Tomas, M. Chem. Rev.
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2009, 253, 862.
C
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Organometallics
Communication
(2) See, for example: Metelkova,
́
R.; Tobrman, T.; Kvapilova,
́
H.;
JC−P = 2.2 Hz, PhP), 130.90 (d, JC−P = 43.5 Hz, PCH), 132.07 (d,
CH, JC−P = 12.5 Hz, PhP), 142.90 (s, PhC), 145.53 (d, JC−P = 41.3 Hz,
PC), 147.20 (d, JC−P = 13.8 Hz, CCH2), 149.29 (d, JC−P = 8.1 Hz,
CMe), 196.93 (d, JC−P = 6.9 Hz, W(CO)5 cis CO), 199.49 (d, JC−P
= 19.5 Hz, W(CO)5 trans CO). Exact mass: calcd C27H23O6PW,
658.0742; found 658.0746. 7b: eluted after 7a (20%). 31P NMR
(CDCl3): δ 16.1 ppm (JP−W = 216.7 Hz). 1H NMR (CD2Cl2): δ 1.93−
1.99 (m, 2H), 2.19 (d, 4JH−P = 1.2 Hz, 3H, Me), 2.55 (br, 2H), 2.60 (s,
3H, OMe), 2.92 (m, 1H, CH-Ph), 4.75 (d, JH−H = 8.7 Hz, CHOMe),
6.57 (d, 2JH−P = 36.2 Hz, 1H, CHP), 7.19−7.31 (m, 5H, Ph), 7.33−
7.40 (m, 3H, Ph), 7.55−7.60 (m, 2H, Ph). 13C NMR (CDCl3): δ
Hoskovskova, I.; Ludvik, J. Electrochim. Acta 2012, 82, 470. Lotz, S.;
́
van Jaarsveld, N. A.; Liles, D. C.; Crause, C.; Gorls, H.; Terblans, Y. M.
̈
Organometallics 2012, 31, 5371. van Jaarsveld, N. A.; Liles, D. C.; Lotz,
S. Dalton Trans. 2010, 39, 5777. Crause, C.; Gorls, H.; Lotz, S. Dalton
Trans. 2005, 1649.
(3) Quin, L. D. Curr. Org. Chem. 2006, 10, 43. Mathey, F. Acc. Chem.
̈
Res. 2004, 37, 954. Rea
Chemistry III; Elsevier: Oxford, U.K., 2008: Vol. 10, p 954.
́
u, R.; Dyer, P. W. Comprehensive Heterocyclic
(4) Cyranski, M. K.; Krygowski, T. M.; Katritzky, A. R.; Schleyer, P.
̃
v. R. J. Org. Chem. 2002, 67, 1333.
3
17.03 (d, JC−P = 10.3 Hz, Me), 25.78 (d, JC−P = 8.5 Hz, CH2), 30.76
(5) Frisch, M. J. et al. Gaussian 03, revision B.05; Gaussian, Inc.,
(s, CH2), 47.08 (d, JC−P = 6.3 Hz, CHPh), 57.06 (s, OMe), 81.90 (d,
JC−P = 9.5 Hz, CHOMe), 127.04 (s, CH, PhC), 127.92 (s, CH, PhC),
128.71 (d, CH, JC−P = 10.7 Hz, PhP), 128.97 (s, CH, PhC), 130.50 (d,
C, JC−P = 41.2 Hz, PhP), 130.59 (d, JC−P = 46.7 Hz, PCH), 130.87
(d, CH, JC−P = 2.2 Hz, PhP), 133.08 (d, CH, JC−P = 13.1 Hz, PhP),
Pittsburgh, PA, 2003.
(6) Vyboishchikov, S. F.; Frenking, G. Chem. Eur. J. 1998, 4, 1428.
(7) Deschamps, E.; Mathey, F. Bull. Soc. Chim. Fr. 1992, 129, 486.
(8) 2: purified by chromatography on silica gel at −10 °C with
hexane/dichloromethane (7/3); deep red solid (30%). 31P NMR
1
144.30 (s, PhC), 144.84 (d, JC−P = 37.3 Hz, PC), 148.92 (d, JC−P
=
=
(CH2Cl2): δ 23.4 (JP−W = 221 Hz). H NMR (500 MHz, CDCl3): δ
4
12.7 Hz, CCH2), 149.69 (d, JC−P = 8.5 Hz, CMe), 197.05 (d, JC−P
2.31 (d, JH−P = 1.4 Hz, 3H, Me), 2.36 (s, 3H, Me), 4.53 (s, 3H,
2
6.7 Hz, W(CO)5 cis CO), 199.08 (d, JC−P = 18.4 Hz, W(CO)5 trans
OMe), 6.72 (d, JH−P = 36.6 Hz, 1H, CHP), 7.39−7.53 (m, 5H,
Ph). 13C NMR (CDCl3): δ 17.79 (d, JC−P = 9.7 Hz, Me), 17.99 (d,
3
CO).
3JC−P = 8.0 Hz, Me), 69.63 (s, OMe), 128.04 (d, JC−P = 38.4 Hz,
PC(Ph)), 129.43 (d, JC−P = 10.3 Hz, Ph), 132.03 (s, Ph), 133.06 (d,
JC−P = 13.1 Hz, Ph), 133.15 (d, JC−P = 41.1 Hz, PCH), 148.47 (d,
JC−P = 15.3 Hz, CMe), 151.08 (d, JC−P = 8.5 Hz, CMe), 162.99 (d,
JC−P = 23.1 Hz, PC), 196.73 (d, JC−P = 6.3 Hz, PW(CO)5 cis C
O), 197.00 (s, CW(CO)5 cis CO), 198.42 (d, JC−P = 21.6 Hz,
PW(CO)5 trans CO), 203.32 (s, CW(CO)5 trans CO), 316.87 (s,
CW). Exact mass: calcd C24H15O11PW2Na, 900.9268; found,
900.9276. 5: purified by chromatography with hexane/dichloro-
methane (4/1); yellow oil (70%). 31P NMR (CH2Cl2): δ 17.7 ppm
(11) Ciric, A.; Mathey, F. Organometallics 2010, 29, 4785 and
references cited therein.
1
4
(JP−W = 221 Hz). H NMR (CD2Cl2): δ 2.24 (d, JH−2P = 1.4 Hz, 3H,
Me), 2.55 (s, 3H, Me), 3.68 (s, 3H, OMe), 6.71 (d, JH−P = 34.4 Hz,
1H, CHP), 7.36−7.53 (m, 5H, Ph). 13C NMR (CD2Cl2): δ 15.14
3
3
(d, JC−P = 6.4 Hz, Me), 16.70 (d, JC−P = 9.7 Hz, Me), 50.98 (s,
OMe), 128.17 (d, JC−P = 36.9 Hz, PC(Ph)), 128.40 (d, JC−P = 10.5 Hz,
Ph), 130.53 (d, JC−P = 2.3 Hz, Ph), 131.63 (d, JC−P = 12.9 Hz, Ph),
133.73 (d, JC−P = 43.7 Hz, PCCO2Me), 135.13 (d, JC−P = 41.5 Hz,
PCH), 149.80 (d, JC−P = 6.2 Hz, CMe), 161.63 (d, JC−P = 12.7 Hz,
CMe), 163.24 (d, JC−P = 16.9 Hz, CO), 195.89 (d, JC−P = 6.6 Hz,
W(CO)5 cis CO), 198.29 (d, JC−P = 20.1 Hz, W(CO)5 trans CO).
Exact mass: calcd C19H15O7PW, 570.0065; found 570.0068. 6: purified
by chromatography with hexane/dichloromethane (4/1); yellow oil
(70%). 31P NMR (CH2Cl2): δ 14.9 ppm (JP−W = 219 Hz). H NMR
1
(CD2Cl2): δ 2.29 (d, 4JH−P = 1.4 Hz, 3H, Me), 2.51 (s, 3H, Me), 6.94
2
(d, JH−P = 34.8 Hz, 1H, =CH-P), 7.39−7.57 (m, 5H, Ph) 10.13 (d,
3JH−P = 16.5 Hz, 1H, CHO). 13C NMR (CDCl3): δ 14.29 (d, JC−P
=
3
6.8 Hz, Me), 17.08 (d, 3JC−P = 9.4 Hz, Me), 129.17 (d, JC−P = 41.8 Hz,
PC(Ph) ipso) 129.14 (d, JC−P = 10.7 Hz, Ph), 131.08 (s, Ph), 131.80
(d, JC−P = 12.6 Hz, Ph), 137.85 (d, JC−P = 40.6 Hz, PCH), 142.92
(d, JC−P = 35.9 Hz, PCCHO), 150.23 (d, JC−P = 5.6 Hz, CMe), 162.37
(d, JC−P = 12.3 Hz, CMe), 185.17 (d, JC−P = 12.1 Hz, CHO), 196.04
(d, JC−P = 6.6 Hz, W(CO)5 cis CO), 198.61 (d, JC−P = 20.2 Hz,
W(CO)5 trans CO);. Exact mass: calcd C18H13O6PW, 539.9959;
found 539.9962.
(9) Aumann, R.; Hinterding, P.; Kruger, C.; Goddard, R. J.
̈
Organomet. Chem. 1993, 459, 145.
(10) 7a: purified by chromatography with hexane/dichloromethane
(1/1); yellow solid (40%). 31P NMR (CDCl3): δ 13.1 ppm (JP−W
=
=
217.8 Hz). 1H NMR (CD2Cl2): δ 2.01−2.07 (m, 2H), 2.17 (d, 4JH−P
1.4 Hz, 3H, Me), 2.28−2.36 (m, 1H), 2.49−2.59 (m, 1H), 2.85 (s, 3H,
OMe), 3.07−3.14 (m, 1H, CHPh), 3.90 (d, JH−H = 6.3 Hz, CHOMe),
6.54 (d, 2JH−P = 37.6 Hz, 1H, CHP), 6.97−6.99 (m, 2H, Ph), 7.13−
7.19 (m, 3H, Ph), 7.41−7.43 (m, 3H, Ph), 7.51−7.57 (m, 2H, Ph). 13C
NMR (CDCl3): δ 16.92 (d, 3JC−P = 10.3 Hz, Me), 24.23 (d, JC−P = 7.7
Hz, CH2), 27.88 (s, CH2), 44.70 (d, JC−P = 4.0 Hz, CHPh), 59.10 (s,
OMe), 80.33 (d, JC−P = 8.3 Hz, CHOMe), 126.67 (s, CH, PhC),
127.76 (s, CH, PhC), 128.47 (s, CH, PhC), 129.12 (d, CH, JC−P
=
10.1 Hz, PhP), 129.93 (d, C, JC−P = 38.5 Hz, PhP), 130.88 (d, CH,
D
dx.doi.org/10.1021/om400109h | Organometallics XXXX, XXX, XXX−XXX