Conformations of diester triphenyl-phosphonium ylides with an ylidic ester or keto and ester ylidic groups

Article abstract of DOI:10.1107/S0108270111027508

The structures of three related keto diester and diester ylides, namely diethyl 3-oxo-2-(triphenylphosphoranylidene)glutarate, C₂₇H ₂₇O₅P, (I), diethyl 3-oxo-2-(triphenylphosphoranylidene) glutarate acetic acid monosolvate

Full text of DOI:10.1107/S0108270111027508

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
tions of structures with a C P double bond are inadequate in
that they neglect electronic delocalization. The existence of
zwitterionic structures with extensive delocalization [part (b)
ISSN 0108-2701
Conformations of diester triphenyl-
phosphonium ylides with an ylidic
ester or keto and ester ylidic groups
Fernando Castaneda,a* Paul Silva,a Clifford A. Bunton,b
˜
c
d
´
Marıa Teresa Garland and Ricardo Baggio
a
´
´
´
Departamento de Quımica Organica y Fisicoquımica, Facultad de Ciencias
´
´
Quımicas y Farmaceuticas, Universidad de Chile, Casilla 233, Santiago, Chile,
bDepartment of Chemistry and Biochemistry, University of California, Santa Barbara,
c
´
´
CA 93106, USA, Departamento de Fısica, Facultad de Ciencias Fısicas y
´
Matematicas, Universidad de Chile, Casilla 487-3, Santiago de Chile, Chile, and
d
´
´
´
´
Departamento de Fısica, Comision Nacional de Energıa Atomica, Avenida Gral Paz
1499, 1650 Buenos Aires, Argentina
Correspondence e-mail: fcastane@ciq.uchile.cl
Received 12 January 2011
Accepted 8 July 2011
Online 22 July 2011
The structures of three related keto diester and diester ylides,
namely diethyl 3-oxo-2-(triphenylphosphoranylidene)glutar-
ate, C27H27O5P, (I), diethyl 3-oxo-2-(triphenylphosphoranyl-
idene)glutarate acetic acid monosolvate, C27H27O5PꢀC2H4O2,
(II), and diethyl 2-(triphenylphosphoranylidene)succinate,
C26H27O4P, (III), are presented. The syn-keto anti-ester
conformations in the crystalline keto diesters are governed
by electronic delocalization between the P—C and ylidic
bonds and an acyl group, and by intra- and intermolecular
interactions. There are also intramolecular attractive and
repulsive interactions of different types (C—Hꢀ ꢀ ꢀO and C—
Hꢀ ꢀ ꢀꢀ) controlling the molecular conformations. The mono-
ylidic diester (III) has an anti-ester conformation, while those
for (I) and (II) are related to pyrolytic formation of acetylene
derivatives. The terminal nonylidic ester group in (I) was
disordered over two sets of almost equally populated
positions.
of Scheme 1] provides due evidence of this fact (Bachrach,
1992). In addition, conformations with two acyl groups could
be syn–syn, syn–anti or anti–anti (Aitken et al. 2000) [part (c)
of Scheme 1].
Comment
The conformations of triphenylphosphonium ylides with a
single keto or ester group conjugated with the ylidic double
bond are best established by X-ray crystallography, provided
that suitable crystals can be isolated, or else are inferred from
NMR or IR spectroscopy (Bachrach & Nitsche, 1994). The
ylidic residue is typically close to planar, with electronic
delocalization involving the P atom, the ylidic C atom and the
associated acyl group. The conformations are designated as
syn or anti, depending on the orientation of the acyl group, viz.
either towards or away from the P atom (Aitken et al., 2000)
[part (a) of Scheme 1]. However, these classical representa-
Only syn–anti and anti–anti conformers of aliphatic diacyl
derivatives have been observed to date and the latter only
with a few diesters (Castan˜eda et al., 2001, 2005). The situation
Acta Cryst. (2011). C67, o319–o323
doi:10.1107/S0108270111027508
# 2011 International Union of Crystallography o319

organic compounds
Figure 1
Molecular diagrams for (I), showing (a) the atomic numbering scheme (singly and doubly primed atoms correspond to the disordered part of the
molecule) and (b) the nonbonding interactions. Narrow broken lines denote Pꢀ ꢀ ꢀO contacts, double broken lines intermolecular interactions and thick
broken lines intramolecular bonds. Displacement ellipsoids are drawn at the 40% probability level. [Symmetry codes: (i) x ꢂ 1, y, z; (ii) ꢂx + 1, ꢂy + 2,
ꢂz + 1; (iii) x + 1, y + 1, z; (iv) ꢂx, ꢂy + 1, ꢂz.]
Figure 2
Molecular diagrams for (II), showing (a) the atomic numbering scheme and (b) the nonbonding interactions. Narrow broken lines denote Pꢀ ꢀ ꢀO contacts,
double broken lines intermolecular interactions and thick broken lines intramolecular bonds. Displacement ellipsoids are drawn at the 40% probability
level. [Symmetry codes: (i) x ꢂ 1, y, z; (ii) ꢂx + 1, ꢂy + 1, ꢂz + 1; (iii) ꢂx, ꢂy + 1, ꢂz; (iv) x + 1, y, z; (v) ꢂx, 1 ꢂ y, 1 ꢂ z.]
is more complicated with different acyl groups, but generally
in aliphatic keto esters the ester acyl group is anti and the keto
acyl group syn (Castan˜eda et al., 2001, 2003). In mixed ali-
phatic diesters, the smaller ester group is usually syn and the
large group anti with respect to P (Castan˜eda et al., 2009a,b).
These generalizations do not apply when aryl groups are
present in the ylidic residue, where electronic delocalization
and steric effects have to be considered, nor to some diylides
with bulky structures (Aitken et al., 2000).
The present work involves three triphenyl phosphonium
ylides: two keto diesters, diethyl 3-oxo-2-(triphenylphosphor-
anylidene)glutarate, (I), and diethyl 3-oxo-2-(triphenylphos-
phoranylidene)glutarate acetic acid monosolvate, (II), and
one diester, diethyl 2-(triphenylphosphoranylidene)succinate,
(III), with one ylidic and one nonylidic ester group [see
Scheme 2]. These ylides were prepared in order to examine
whether nonylidic external carboxylic ester groups affect the
conformations of the ylidic moieties in the crystal structures.
ꢁ
o320 Castaneda et al.
C27H27O5P, C27H27O5PꢀC2H4O2 and C26H27O4P
Acta Cryst. (2011). C67, o319–o323
˜

organic compounds
Figure 3
Molecular diagrams for (III), showing (a) the atomic numbering scheme and (b) the nonbonding interactions. Narrow broken lines (partially eclipsed by
atom C5) denote Pꢀ ꢀ ꢀO contacts and double broken lines intermolecular C—Hꢀ ꢀ ꢀO contacts. Displacement ellipsoids are drawn at the 40% probability
3
1
level. [Symmetry code: (i) ꢂx + , y ꢂ , z.]
2
2
Figs. 1(a), 2(a) and 3(a) show the corresponding molecular
views and atomic labelling schemes used for (I), (II) and (III),
respectively. These three ylides share common features, in
particular a slightly distorted tetrahedral arragement around
the P atom, with the phenyl groups in a propeller-like dispo-
sition, as observed for stabilized keto ester ylides (Castan˜eda
et al., 2001). The sums of the angles about ylidic atom C1 are
very near the ideal value of 360ꢃ, consistent with sp2 hybri-
dization [358.0 (4)ꢃ in (I), 358.6 (5)ꢃ in (II) and 359.9 (5)ꢃ in
(III)] in a near trigonal-planar geometry.
the van der Waals radii (Bondi, 1964), and favourable inter-
actions should stabilize the conformer. The ester groups in (I)–
(III) have the typical Z conformation (Eliel & Wilen, 1994)
and are approximately in the ylidic plane.
The keto diester ylide solvate, (II), was prepared because
acetic acid can promote the formation of good single crystals
(Abel et al. 1989) and new intermolecular interactions could
modify the syn-keto anti-ester conformation of ylide (I).
However, (II) is a 1:1 ylide solvate with intermolecular
hydrogen-bond interactions and syn-keto anti-ester confor-
mations, as in (I).
The anti-ester conformations in crystalline ylides (I)–(III)
(Figs. 1–3) do not depend on the presence of a syn-keto group
and could be favoured by alkoxy Oꢀ ꢀ ꢀP interactions, an
attractive C—Hꢀ ꢀ ꢀꢀ effect (Nishio et al., 1995) or the absence
of nonbonded steric repulsion between alkoxy ylidic and
nonylidic ester groups. In the crystal structure and in solution,
the structures present one alkoxy group syn to P directed
towards the face of a phenyl group which is approximately
orthogonal to the ylidic C—P bond with a modestly stabilizing
C—Hꢀ ꢀ ꢀꢀ interaction (Nishio et al., 1995; Nishio & Hirota,
1989). The crystal structure of mono-ylidic diester (III) shows
an anti-ester conformation with a contact distance of
˚
The P1—C1 bond lengths [1.7196 (18)–1.758 (4) A] lie
between accepted values for single and double bonds (1.80–
˚
˚
1.83 A and 1.66 A, respectively; Howells et al., 1973) due to
electronic delocalization which shortens C1—C2 (in all three
structures) and C1—C3 [in (I) and (II)]. The ylidic keto
˚
carbonyl bonds are longer than the typical value of 1.21 A
˚
[C3—O4 = 1.239 (2)–1.254 (2) A] for keto-ester, diester and
diketo ylides (Castan˜eda et al., 2001, 2005).
In the crystalline stabilized ylides (I) and (II), the keto O
atom and the ylidic alkoxy groups are oriented towards P with
syn-keto and anti-ester conformations, respectively (Figs. 1
and 2). A syn-keto conformation is also established by
pyrolysis of diketo or keto ester-ylides, i.e. (I), where syn-keto
conformations are required to form keto or ester acetylenes,
respectively (Gough & Trippett, 1962; Chopard et al. 1965).
Coplanarity between the ylidic keto carbonyl and ester
carbonyl units in (I) and (II) is indicated by their torsion
angles. The P—C—C—O torsion angles are close to ꢂ2.5ꢃ for
the keto group and near to 167ꢃ for the ester carbonyl,
showing stronger delocalization of the keto group. The keto
and ester carbonyl groups in (I) and (II) have opposite
orientations, which reduces dipole–dipole repulsions, and the
˚
2.8177 (15) A between atoms P1 and O1.
The nonbonding interactions in (I), (II) and (III) are quite
different in all three structures. Compound (III) presents only
one close intramolecular Pꢀ ꢀ ꢀO contact [P1ꢀ ꢀ ꢀO1
=
˚
2.818 (2) A] and one moderate C—Hꢀ ꢀ ꢀO intermolecular
contact (Table 8), the remaining interactions being mostly van
der Waals. By contrast, (I) and (II) display a large number of
nonbonding contacts of diverse nature and strength. There are
two short intramolecular Pꢀ ꢀ ꢀO contacts in each [P1ꢀ ꢀ ꢀO1 =
˚
˚
˚
keto O atoms are within 2.88–2.91 A of P, i.e. within the sum of
2.877 (2) A and P1ꢀ ꢀ ꢀO4 = 2.879 (2) A in (I); P1ꢀ ꢀ ꢀO1 =
ꢁ
Acta Cryst. (2011). C67, o319–o323
Castaneda et al.
C27H27O5P, C27H27O5PꢀC2H4O2 and C26H27O4P o321
˜

organic compounds
˚
˚
Compound (I)
2.888 (2) A and P1ꢀ ꢀ ꢀO4 = 2.915 (2) A in (II)], many con-
ventional and nonconventional hydrogen bonds and C—
Hꢀ ꢀ ꢀꢀ contacts (both intra- and intermolecular) (Tables 2 and
5), and some ꢀ–ꢀ stacking interactions between aromatic rings
(Tables 3 and 6). All these contacts are presented schemati-
cally in Figs. 1(b), 2(b) and 3(b), and their inspection confirms
a final three-dimensional packing structure for (I) and (II), but
a much simpler one-dimensional (chain-like) structure for
(III).
Crystal data
C27H27O5P
Mr = 462.46
Triclinic, P1
a = 9.0348 (10) A
b = 10.3770 (11) A
˚
c = 13.8951 (15) A
ꢁ = 95.994 (2)ꢃ
ꢂ = 108.342 (2)ꢃ
ꢃ = 107.304 (2)ꢃ
3
˚
V = 1152.0 (2) A
Z = 2
˚
Mo Kꢁ radiation
ꢄ = 0.16 mmꢂ1
T = 150 K
0.46 ꢄ 0.26 ꢄ 0.19 mm
˚
Data collection
Bruker SMART CCD area-detector
diffractometer
Absorption correction: multi-scan
(SADABS; Sheldrick, 2001)
Tmin = 0.95, Tmax = 0.97
9669 measured reflections
4935 independent reflections
4077 reflections with I > 2ꢅ(I)
Rint = 0.021
Experimental
Diethyl 3-oxo-2-(triphenylphosphoranylidene)glutarate, (I) (m.p.
379 K, yield 68%), was prepared by reaction of ethyl 2-(triphenyl-
phosphoranylidene)acetate, Ph3P CH—CO2Et, with ethyl malonyl
chloride in dry benzene at room temperature. Recrystallization of (I)
from ethyl acetate–hexane (1:1 v/v) and then from acetic acid gave
the solvate (II) (m.p. 433 K, yield 72%). Diethyl 2-(triphenyl-
phosphoranylidene)succinate, (III) [m.p. 370 K, recrystallized from
ethyl acetate–hexane (1:1 v/v), yield 71%], was synthesized by
transylidation of Ph3P CH—CO2Et with ethyl 2-bromoacetate in
dry ethyl acetate at 313 K for 4 h. Elemental analyses using a Fisons
EA 1108 analyser agreed with the determined structures of ylides (I)–
(III).
Refinement
R[F2 > 2ꢅ(F2)] = 0.050
wR(F2) = 0.143
S = 1.09
4935 reflections
344 parameters
122 restraints
H-atom parameteꢂrs3 constrained
˚
Áꢆmax = 1.05 e A
Áꢆmin = ꢂ0.36 e A
ꢂ3
˚
Table 4
Selected bond lengths (A) for (II).
˚
P1—C1
1.758 (2)
1.806 (2)
1.812 (2)
1.817 (2)
1.343 (3)
O1—C4
O2—C2
O4—C3
C1—C3
C1—C2
1.450 (3)
1.212 (2)
1.255 (2)
1.417 (3)
1.455 (3)
Table 1
Selected bond lengths (A) for (I).
P1—C1A
P1—C1B
P1—C1C
O1—C2
˚
P1—C1
1.7546 (18)
1.8055 (19)
1.8106 (19)
1.8183 (19)
1.361 (2)
O1—C4
O2—C2
O4—C3
C1—C3
C1—C2
1.452 (2)
1.220 (2)
1.240 (2)
1.432 (3)
1.453 (3)
P1—C1A
P1—C1C
P1—C1B
O1—C2
Table 5
Hydrogen-bond geometry (A, ) for (II).
ꢃ
˚
Cg1 is the centroid of the C1A–C6A ring, Cg2 that of the C1B–C6B ring and
Cg3 that of the C1C–C6C ring.
Table 2
Hydrogen-bond geometry (A, ) for (I).
ꢃ
˚
D—Hꢀ ꢀ ꢀA
D—H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D—Hꢀ ꢀ ꢀA
Cg1 is the centroid of the C1A–C6A ring and Cg2 that of the C1B–C6B ring.
C6A—H6Aꢀ ꢀ ꢀO5
C5—H5Eꢀ ꢀ ꢀCg2
0.95
0.98
0.859 (10)
0.99
0.95
0.98
0.95
0.98
2.57
2.97
1.85 (2)
2.47
2.59
2.41
2.85
2.86
3.498 (4)
3.820 (3)
2.636 (3)
3.430 (3)
3.377 (3)
3.345 (4)
3.711 (4)
3.744 (4)
165
146
152 (4)
163
140
160
152
150
D—Hꢀ ꢀ ꢀA
D—H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D—Hꢀ ꢀ ꢀA
O2D—H2Dꢀ ꢀ ꢀO4
C10—H10Bꢀ ꢀ ꢀO1D
C2A—H2Aꢀ ꢀ ꢀO1Di
C2D—H2DBꢀ ꢀ ꢀO5ii
C4B—H4Bꢀ ꢀ ꢀCg3iii
C9—H9Bꢀ ꢀ ꢀCg1iv
C10—H10Aꢀ ꢀ ꢀO2
C2A—H2Aꢀ ꢀ ꢀO2i
0.99
0.95
0.95
0.95
0.98
0.95
2.23
2.54
2.48
2.38
2.74
2.79
2.853 (3)
3.189 (3)
3.327 (5)
3.245 (3)
3.712 (4)
3.604 (2)
120
126
150
151
172
144
i
C3B—H3Bꢀ ꢀ ꢀO50
C4A—H4Aꢀ ꢀ ꢀO4ii
C90—H90Aꢀ ꢀ ꢀCg1iii
C4C—H4Cꢀ ꢀ ꢀCg2iv
Symmetry codes: (i) x ꢂ 1; y; z; (ii) ꢂx þ 1; ꢂy þ 1; ꢂz þ 1; (iii) ꢂx; ꢂy þ 1; ꢂz; (iv)
Symmetry codes: (i) x ꢂ 1; y; z; (ii) ꢂx þ 1; ꢂy þ 2; ꢂz þ 1; (iii) x þ 1; y þ 1; z; (iv)
x þ 1; y; z.
ꢂx; ꢂy þ 1; ꢂz.
Table 3
ꢀ–ꢀ contacts (A) for (I).
Table 6
ꢀ–ꢀ contacts (A) for (II).
˚
˚
CCD is the centroid–centroid distance and PCD is the (mean) centroid to
opposite plane distance; for details, see Janiak (2000). Cg1 is the centroid of
the C1A–C6A ring and Cg3 that of the C1C–C6C ring. The rings are parallel
by symmetry.
CCD is the centroid–centroid distance and PCD is the (mean) centroid to
opposite plane distance; for details, see Janiak (2000). Cg1 is the centroid of
the C1A–C6A ring and Cg2 that of the C1B–C6B ring. The rings are parallel
by symmetry.
˚
CCD (A)
˚
PCD (A)
˚
CCD (A)
˚
PCD (A)
Group 1/group 2
Group 1/group 2
Cg1ꢀ ꢀ ꢀCg1ii
3.8512 (12)
3.9326 (12)
3.5410 (8)
3.6424 (8)
Cg1ꢀ ꢀ ꢀCg1v
3.762 (2)
3.814 (2)
3.520 (2)
3.630 (2)
Cg3ꢀ ꢀ ꢀCg3iv
Cg2ꢀ ꢀ ꢀCg2iii
Symmetry codes: (ii) ꢂx + 1, ꢂy + 2, ꢂz + 1; (iv) ꢂx, ꢂy + 1, ꢂz.
Symmetry codes: (v) ꢂx, ꢂy + 1, ꢂz + 1; (iii) ꢂx, ꢂy + 1, ꢂz.
Acta Cryst. (2011). C67, o319–o323
ꢁ
o322 Castaneda et al.
C27H27O5P, C27H27O5PꢀC2H4O2 and C26H27O4P
˜

organic compounds
Table 7
Selected bond lengths (A) for (III).
Compound (II)
˚
Crystal data
P1—C1
1.7196 (18)
1.8073 (19)
1.8172 (18)
1.8186 (18)
1.404 (3)
C1—C10
C2—O2
C2—O1
C4—O1
1.511 (3)
1.230 (2)
1.374 (2)
1.435 (2)
C27H27O5PꢀC2H4O2
ꢃ = 64.285 (6)ꢃ
3
P1—C1B
P1—C1A
P1—C1C
C1—C2
˚
Mr = 522.51
Triclinic, P1
V = 1340.7 (9) A
Z = 2
˚
a = 9.957 (4) A
Mo Kꢁ radiation
ꢄ = 0.15 mmꢂ1
T = 150 K
0.46 ꢄ 0.38 ꢄ 0.32 mm
˚
b = 10.589 (4) A
˚
c = 14.928 (6) A
ꢁ = 78.191 (6)ꢃ
ꢂ = 71.505 (6)ꢃ
Table 8
Hydrogen-bond geometry (A, ) for (III).
ꢃ
˚
Data collection
D—Hꢀ ꢀ ꢀA
C4B—H4Bꢀ ꢀ ꢀO2i
Symmetry code: (i) ꢂx þ ; y ꢂ ; z.
D—H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D—Hꢀ ꢀ ꢀA
Bruker SMART CCD area-detector
diffractometer
Absorption correction: multi-scan
(SADABS; Sheldrick, 2001)
Tmin = 0.93, Tmax = 0.95
11211 measured reflections
5728 independent reflections
4037 reflections with I > 2ꢅ(I)
Rint = 0.112
0.95
2.46
3.389 (3)
165
3
2
1
2
Refinement
program(s) used to refine structure: SHELXL97 (Sheldrick, 2008);
molecular graphics: SHELXTL (Sheldrick, 2008); software used to
prepare material for publication: SHELXTL and PLATON (Spek,
2009).
R[F2 > 2ꢅ(F2)] = 0.058
wR(F2) = 0.171
S = 0.93
5728 reflections
341 parameters
1 restraint
H atoms treated by a mixture of
independent and constrained
refinement
ꢂ3
˚
Áꢆmax = 0.49 e A
ꢂ3
˚
Áꢆmin = ꢂ0.36 e A
The authors acknowledge the Spanish Research Council
(CSIC) for providing a free-of-charge licence to the
Cambridge Structural Database (Allen, 2002).
Compound (III)
Crystal data
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: GT3033). Services for accessing these data are
described at the back of the journal.
3
˚
V = 4688.9 (9) A
Z = 8
C26H27O4P
Mr = 434.45
Orthorhombic, Pbca
Mo Kꢁ radiation
ꢄ = 0.15 mmꢂ1
T = 150 K
0.57 ꢄ 0.47 ꢄ 0.06 mm
˚
a = 8.7357 (10) A
˚
b = 16.8280 (18) A
References
˚
c = 31.896 (4) A
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36723 measured reflections
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R[F2 > 2ꢅ(F2)] = 0.052
wR(F2) = 0.139
S = 0.91
280 parameters
H-atom parameteꢂrs3 constrained
˚
Áꢆmax = 0.44 e A
ꢂ3
˚
5370 reflections
Áꢆmin = ꢂ0.22 e A
All H atoms were located from difference Fourier maps but were
treated differently in refinement. H atoms bonded to C atoms were
re-positioned at their geometrically expected locations and allowed
˚
to ride, with C—H = 0.95–0.99 A. The acetic acid H atom bonded to
˚
O in (II) was refined with a restrained O—H distance of 0.85 (1) A
Chopard, P. A., Searle, R. J. G. & Devitt, F. H. (1965). J. Org. Chem. 30, 1015–
1019.
and free Uiso values; in all remaining cases, Uiso(H) = 1.2 or
1.5Ueq(host). The terminal nonylidic ester group in (I) appeared to be
disordered over two sets of positions which were almost equally
populated. They were refined with restraints on interatomic distances
and displacement factors [SAME/SADI and SIMU instructions in
SHELXL97 (Sheldrick, 2008)], and refinement of the occupancies
converged to 0.522 (3):0.478 (3).
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8665–8701.
¨
Sheldrick, G. M. (2001). SADABS. University of Gottingen, Germany.
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Spek, A. L. (2009). Acta Cryst. D65, 148–155.
For all compounds, data collection: SMART (Bruker, 2001); cell
refinement: SAINT (Bruker, 2001); data reduction: SAINT;
program(s) used to solve structure: SHELXS97 (Sheldrick, 2008);
ꢁ
Acta Cryst. (2011). C67, o319–o323
Castaneda et al.
C27H27O5P, C27H27O5PꢀC2H4O2 and C26H27O4P o323
˜