Cyano-stabilized triphenylphosphonium ylids

Article abstract of DOI:10.1107/S0108270106051201

Crystalline cyano-stabilized triphenylphosphonium ylids with keto or ester groups give rise to an extended electronic delocalization. In methyl 2-cyano-2-(trimethylphosphonio)-ethenoate, Ph₃P=C(CN)CO ₂CH₃ or C₂₂

Full text of DOI:10.1107/S0108270106051201

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
allow extensive electronic delocalization and interactions
between phosphorus and an acyl O atom. The conformations
should be similar in the solid and in solution, and we discuss
here the geometries of the following ylids in the crystal
ISSN 0108-2701
Cyano-stabilized triphenylphos-
phonium ylids
Fernando Castaneda,a* Clifford A. Bunton,b Ricardo
Ä
c
d
Â
Baggio and Marõa Teresa Garland
a
Â
Â
Â
Departamento de Quõmica Organica y Fisicoquõmica, Facultad de Ciencias,
Â
Â
Quõmicas y Farmaceuticas, Universidad de Chile, Casilla 233, Santiago, Chile,
bDepartment of Chemistry and Biochemistry, University of California, Santa Barbara,
CA 931060, USA, cDepartamento de Fõsica, Comision Nacional de Energõa Atomica,
Â
Â
Â
Â
d
structure. Complete details of the geometries in solution will
be given elsewhere. Crystalline methyl 2-cyano-2-(trimethyl-
phosphonio)ethenoate, (I), and 1-cyano-1-(trimethyl-
phosphonio)prop-1-en-2-olate, (II), have the molecular
structures and selected geometric parameters shown in Figs. 1
and 2, and Tables 1 and 3, respectively. In both ylids, the
con®gurations about the P atom are approximately tetra-
hedral, with phenyl groups forming a propeller-like arrange-
ment. For (I) and (II), the bond angles C31ÐP1ÐC11,
C21ÐP1ÐC11 and C31ÐP1ÐC21 are 107.42 (12),
107.44 (12) and 106.35 (12)ꢀ, and 108.17 (9), 105.79 (10) and
106.81 (9)ꢀ, respectively. The sums of the angles about the
ylidic C1 atom for (I) and (II) are 359.9 and 360ꢀ respectively,
consistent with sp2-hybridization in an almost trigonal±planar
geometry. It is well known that stabilized ylids have a longer
Â
Av. Gral Paz 1499, 1650 Buenos Aires, Argentina, and Departamento de Fõsica,
Â
Â
Facultad de Ciencias Fõsicas y Matematicas, and CIMAT, Universidad de Chile,
Santiago, Chile
Correspondence e-mail: fcastane@ciq.uchile.cl
Received 13 October 2006
Accepted 27 November 2006
Online 23 December 2006
Crystalline cyano-stabilized triphenylphosphonium ylids with
keto or ester groups give rise to an extended electronic
delocalization. In methyl 2-cyano-2-(trimethylphosphonio)-
ethenoate, Ph3P C(CN)CO2CH3 or C22H18NO2P, (I), and
1-cyano-1-(trimethylphosphonio)prop-1-en-2-olate, Ph3P C-
(CN)COÐCH3 or C22H18NOP, (II), the carbonyl groups are
oriented toward the cationoid P atom. Bond lengths and
angles, torsion angles and PÁ Á ÁO contact distances are
consistent with a dominant coplanar conformation where the
molecular structures are the result of a balance between intra-
and intermolecular interactions. The main interactions
presented by cyano-ester (I) and cyano-keto (II) are intra-
molecular interactions between the carbonyl O and the P
atoms. In addition, both compounds show other less important
intramolecular interactions between the carbonyl O and
phenyl H atoms, which could contribute to form a preferred
conformation in the crystal structure.
P
C bond as a result of the electronic delocalization caused
Comment
Electronic delocalization involving acyl keto and ester groups
stabilizes phosphonium ylids and is maximized by their taking
up planar conformations with favorable interactions between
anionoid O atoms and cationoid phosphorus (CastanÄeda et al.,
2001; CastanÄeda, Recabarren et al., 2003; CastanÄeda, Terraza
et al., 2003). However, in crystalline diethyl ester derivatives,
interference involving the trigonal ester groups leads to a
conformation where the acyl O atoms are anti to phosphorus,
and the acyl groups are twisted out of the ylidic plane
(CastanÄeda et al., 2005, 2007). The linear cyano group is
strongly electron withdrawing and should facilitate electronic
delocalization in a planar ylidic unit (see scheme).
Figure 1
The molecular structure of (I), showing the numbering scheme used. The
intramolecular hydrogen bond is shown as a double-dashed line and the
intermolecular CÐHÁ Á Áꢀ contacts as single-dashed lines. Displacement
ellipsoids are drawn at the 30% probability level. Symmetry codes are as
given in Table 2.
We therefore expected that the cyano group would favor
cyano-keto or -ester compounds taking up conformations that
Acta Cryst. (2007). C63, o65±o67
DOI: 10.1107/S0108270106051201
# 2007 International Union of Crystallography o65

organic compounds
by the stabilizing groups (Bachrach & Nitsche, 1994; Howells
et al. 1973). In cyano-ester ylid (I) and cyano-keto ylid (II), the
Ê
P1ÐC1 bond lengths are 1.730 (3) and 1.744 (2) A, respec-
no evidence of a CH interaction involving alkoxy and phenyl
groups (CastanÄeda, Terraza et al., 2003). The structures of (I)
and (II) have as a second intramolecular interaction CÐ
HÁ Á ÁO hydrogen bonds between phenyl donors and carbonyl
acceptors (Tables 2 and 4). These types of non-classical
interactions, despite being weak, could make a signi®cant
contribution to stabilizing conformations in the solid state.
Several intermolecular interactions with phenyl groups acting
as donors and acceptors are shown in Figs. 1 and 2. These
interactions could affect favorably the observed molecular
geometry and the packing conformations. The carbonyl IR
stretching frequencies in KBr for (I) (1650 cm 1) and (II)
(1584 cm 1) correlate with the crystallographic results,
indicating an extensive electronic delocalization for the
carbonyl groups.
tively. These values are between those reported for a PÐC
Ê
single bond (1.80±1.83 A; Howells et al., 1973) and P C
double bond (1.63±1.73 A; Howells et al., 1973) and they are
considerably longer than the P C bond in methylene-
Ê
Ê
triphenylphosphorane, Ph3P CH2 [1.661 (8) A; Bart, 1969],
where there is no opportunity for conjugation with other
groups. Electronic delocalization toward the carbonyl groups
shortens the C1ÐC3 and lengthens the C O carbonyl bonds.
Ê
In comparison with the normal value of 1.21 A, the keto
Ê
carbonyl bond is longer [1.239 (3) A] than the ester carbonyl
Ê
bond [1.212 (4) A], as was reported by CastanÄeda et al. (2001,
2005) for keto-esters, diesters and diketo ylides. However,
delocalization of the P C bond toward the cyano group is
Ê
small. Comparison of C N bond lengths for (I) [1.145 (4) A]
Ê
Ê
and (II) [1.150 (3) A] with a normal value of 1.140 A (Smith &
March, 2001) could indicate that the CN group is mainly acting
by inductive instead of resonance effects. Coplanarity between
the ylidic, carbonyl and cyano units is established by their
torsion angles (Tables 1 and 3). Ylids (I) and (II) present
nearly coplanar systems with the carbonyl O atoms oriented
syn to the P atoms, showing O1Á Á ÁP1 contact distances of
Experimental
(Cyanomethylene)triphenylphosphorane was prepared according to
a literature method (Trippet & Walker, 1959). Ylids (I) and (II) have
been reported previously (Horner & Oediger, 1958; Kobayashi et al.,
2000). In this work, both (I) and (II) were synthesized by reaction of
(cyanomethylene)triphenylphosphorane with methyl chloroformate
or acetyl chloride under transylidation conditions. A general
synthetic procedure was as follows: a solution of alkyl chloroformate
(9.1 mmol) or acetyl chloride (9.1 mmol) in dry benzene (5 ml) was
added slowly to (cyanomethylene)triphenylphosphorane (18.2 mmol)
dissolved in dry benzene (50 ml) under an inert atmosphere. The
stirred solution was maintained at room temperature for 6 h to allow
a white solid to separate. After ®ltration of (cyanomethyl)-
triphenylphosphonium chloride, the solvent was evaporated under
reduced pressure to give the products, which were crystallized from
ethanol. For (I): yield 75%, m.p. 485±486 K; 1H NMR (CDCl3): ꢁ 3.64
(s, 3H), 7.5±7.8 (m, 15H); IR (KBr): 2179 (±CN), 1650 (CO) cm 1. For
Ê
3.022 (2) and 2.928 (2) A, respectively. These attractive
intramolecular interactions between the acyl O atoms and the
cationoid P atoms lead to syn-preferred conformations where
the alkoxy or alkyl groups adopt an anti conformation to avoid
repulsive steric interactions with the phenyl groups. There is
(II): yield 65%, m.p. 478 K; 1H NMR (CDCl3): ꢁ 2.38 (s, 3H), 7.5±7.7
(m, 15H); IR (KBr): 2172 (±CN), 1584 (CO) cm
1
.
Ylid (I)
Crystal data
C22H18NO2P
Mr = 359.34
Monoclinic, P21=c
Z = 4
Dx = 1.284 Mg m
Mo Kꢃ radiation
ꢄ = 0.16 mm
T = 297 (2) K
Plate, colorless
0.30 Â 0.24 Â 0.10 mm
3
1
Ê
a = 9.9601 (14) A
Ê
b = 9.0436 (13) A
Ê
c = 20.708 (3) A
ꢂ = 94.659 (3)ꢀ
V = 1859.1 (5) A
3
Ê
Data collection
Bruker SMART CCD
diffractometer
' and ! scans
14118 measured re¯ections
3659 independent re¯ections
2645 re¯ections with I > 2ꢅ(I)
Rint = 0.052
ꢆmax = 26.0ꢀ
Re®nement
Re®nement on F2
R[F2 > 2ꢅ(F2)] = 0.065
wR(F2) = 0.150
S = 1.07
3659 re¯ections
w = 1/[ꢅ2(F2o) + (0.0653P)2
+ 0.3502P]
Figure 2
where P = (F2o + 2Fc2)/3
(Á/ꢅ)max = 0.005
The molecular structure of (II), showing the numbering scheme used. The
intramolecular hydrogen bond is shown as a double-dashed line and the
intermolecular CÐHÁ Á Áꢀ contact as a single-dashed line. Displacement
ellipsoids are drawn at the 30% probability level. Symmetry codes are as
given in Table 4.
3
Ê
Áꢇmax = 0.36 e A
3
Ê
0.23 e A
236 parameters
H-atom parameters constrained
Áꢇmin
=
ꢁ
o66 Castaneda et al.
C22H18NO2P and C22H18NOP
Acta Cryst. (2007). C63, o65±o67
Ä

organic compounds
Table 1
Selected geometric parameters (A, ) for (I).
Table 3
Selected geometric parameters (A, ) for (II).
ꢀ
ꢀ
Ê
Ê
P1ÐC1
O2ÐC3
O2ÐC4
C2ÐN1
1.730 (3)
1.350 (4)
1.432 (4)
1.145 (4)
C2ÐC1
C1ÐC3
O1ÐC3
1.407 (4)
1.427 (4)
1.212 (4)
P1ÐC1
O1ÐC3
N1ÐC2
1.744 (2)
1.239 (3)
1.150 (3)
C1ÐC2
C1ÐC3
C3ÐC4
1.410 (3)
1.419 (3)
1.514 (3)
C2ÐC1ÐC3
C2ÐC1ÐP1
C3ÐC1ÐP1
N1ÐC2ÐC1
121.8 (2)
O1ÐC3ÐC1
O1ÐC3ÐC4
C1ÐC3ÐC4
121.6 (2)
119.4 (2)
119.0 (2)
C3ÐO2ÐC4
N1ÐC2ÐC1
C2ÐC1ÐC3
C2ÐC1ÐP1
117.0 (3)
179.2 (3)
120.8 (3)
120.3 (2)
C3ÐC1ÐP1
O1ÐC3ÐO2
O1ÐC3ÐC1
O2ÐC3ÐC1
118.8 (2)
122.5 (3)
126.0 (3)
111.5 (3)
120.27 (17)
117.95 (17)
178.4 (3)
C2ÐC1ÐC3ÐO1
P1ÐC1ÐC3ÐO1
177.0 (2)
3.3 (3)
C2ÐC1ÐC3ÐC4
3.3 (4)
C4ÐO2ÐC3ÐO1
C4ÐO2ÐC3ÐC1
C2ÐC1ÐC3ÐO1
4.1 (5)
175.0 (3)
173.5 (3)
P1ÐC1ÐC3ÐO1
C2ÐC1ÐC3ÐO2
4.4 (5)
7.5 (4)
Table 4
Non-bonding interactions and short contacts (A, ) in (II).
ꢀ
Ê
Table 2
Non-bonding interactions and short contacts (A, ) in (I).
ꢀ
Ê
Cg1 is the centroid of ring C11±C16.
Cg2 and Cg3 are the centroids of rings C21±C26 and C31±C36, respectively.
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
C16ÐH16Á Á ÁO1
C34ÐH34Á Á ÁCg1i
P1Á Á ÁO1
Symmetry code: (i) x; y ‡ 1; z.
0.93
0.93
±
2.34
2.91
±
3.130 (3)
3.703 (3)
2.928 (2)
142
144
±
C32ÐH32Á Á ÁO1
C14ÐH14Á Á ÁCg3i
C16ÐH16Á Á ÁCg2ii
P1Á Á ÁO1
0.93
0.93
0.93
±
2.51
2.93
2.99
±
3.294 (4)
3.738 (3)
3.835 (3)
3.022 (2)
142
146
153
±
Symmetry codes: (i) x; y 1; z; (ii) x ‡ 1; y ‡ 12; z ‡ 21.
The authors acknowledge CONICYT±FONDAP (grant No.
11980002), and the Spanish Research Council (CSIC) for
providing us with a free-of-charge license to the CSD
system.
Ylid (II)
Crystal data
C22H18NOP
Mr = 343.34
Z = 4
Dx = 1.256 Mg m
Mo Kꢃ radiation
ꢄ = 0.16 mm
T = 298 (2) K
Plate, colorless
0.42 Â 0.32 Â 0.14 mm
3
Monoclinic, P21=c
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: SQ3045). Services for accessing these data are
described at the back of the journal.
1
Ê
a = 10.1144 (11) A
Ê
b = 8.9938 (10) A
Ê
c = 19.968 (2) A
ꢂ = 91.744 (2)ꢀ
V = 1815.6 (3) A
3
Ê
References
Data collection
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Bruker SMART CCD
diffractometer
' and ! scans
13496 measured re¯ections
3569 independent re¯ections
2789 re¯ections with I > 2ꢅ(I)
Rint = 0.038
ꢆmax = 26.0ꢀ
Re®nement
Re®nement on F2
R[F2 > 2ꢅ(F2)] = 0.054
wR(F2) = 0.143
S = 1.03
3569 re¯ections
w = 1/[ꢅ2(F2o) + (0.0819P)2
+ 0.1374P]
where P = (F2o + 2Fc2)/3
(Á/ꢅ)max = 0.009
3
Ê
Áꢇmax = 0.45 e A
3
Ê
0.27 e A
227 parameters
H-atom parameters constrained
Áꢇmin
=
H atoms were placed at idealized positions [CÐH = 0.93
Ê
(aromatic) and 0.96 A (methyl)] and allowed to ride on the corre-
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sponding host, with Uiso(H) values of xUeq(C) [x = 1.2 (aromatic) and
1.5 (methyl)].
For both ylids, data collection: SMART-NT (Bruker, 2001); cell
re®nement: SAINT-NT (Bruker, 2001); data reduction: SAINT-NT;
program(s) used to solve structure: SHELXS97 (Sheldrick, 1997);
program(s) used to re®ne structure: SHELXL97 (Sheldrick, 1997);
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prepare material for publication: SHELXTL-NT and PLATON
(Spek, 2003).
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ꢁ
Acta Cryst. (2007). C63, o65±o67
Castaneda et al.
C22H18NO2P and C22H18NOP o67
Ä