Fully reversible cyclic dimerization of diphosphanylketenimines promoted by intramolecular C-H···N hydrogen bonds

Article abstract of DOI:10.1002/(SICI)1521-3773(20000515)39:10<1821::AID-ANIE1821>3.0.CO;2-H

Just by crystallization at room temperature the diphosphanylketenimine 1 is transformed into the unsymmetrical dimer 2 through a novel [2+3] cycloaddition reaction; a phosphanyl substituent is involved in the annelation process. This dimerization is fully reversible and appears to be promoted by intramolecular CH···N hydrogen bonds.

Full text of DOI:10.1002/(SICI)1521-3773(20000515)39:10<1821::AID-ANIE1821>3.0.CO;2-H

COMMUNICATIONS
[4] G. S. Wilson, H. L. Anderson, Chem. Commun. 1999, 1539 ± 1540; R.
Schlözer, J.-H. Fuhrhop, Angew. Chem. 1975, 87, 388; Angew. Chem.
Int. Ed. Engl. 1975, 14, 363; L. R. Nudy, H. G. Hutchinson, C.
Schieber, F. R. Longo, Tetrahedron 1984, 40, 2359 ± 2363.
[5] M. Uno, K. Seto, M. Masuda, W. Ueda, S. Takahashi, Tetrahedron Lett.
1985, 26, 1553 ± 1556.
[6] J. Diekmann, W. R. Hertler, R. E. Benson, J. Org. Chem. 1963, 28,
2719 ± 2724.
[7] R. Wagner, S. Berger, Magn. Reson. Chem. 1997, 35, 199 ± 202; J.
Kawabata, E. Fukushi, J. Mizutani, J. Am. Chem. Soc. 1992, 114,
1115 ± 1117.
Fully Reversible Cyclic Dimerization of
Diphosphanylketenimines Promoted by
À
Intramolecular C H ´´´ NHydrogen Bonds**
Javier Ruiz,* Fernando Marquínez, Víctor Riera,
Marilín Vivanco, Santiago García-Granda, and
M. Rosario Díaz
Ketenimines are important functional groups that show
enhanced reactivity in nucleophilic addition and cycloaddi-
tion reactions. Furthermore, compounds containing this
moiety are useful starting materials which have been applied
in heterocycle chemistry.[1] We recently reported the synthesis
[8] NOESY and HSQC-NOESY experiments were carried out witha
300 ms mixing time at 294 K on a Bruker DRX500 instrument. All
NOEs were negative.
[9] Crystals were grown by slow diffusion of n-pentane into a solution of
3 ´ 2C5H5N in CHCl3, over two weeks. Crystal data for 3 ´ 2C5H5N ´
0.5C5H12 ´ 3H2O: Mr ˆ 1901.05, monoclinic, space group P21/c, a ˆ
15.440(4), b ˆ 33.765(5), c ˆ 20.485(2) Š, b ˆ 94.64(2)8, Vˆ
ˆ ˆ
of the diphosphanylketenimines (PPh2)2C C NR (1a: R ˆ
Ph, 1b: R ˆ tBu) by metal-assisted coupling of a transient
10644.5(33) Š3, Z ˆ 4, Tˆ 150(2) K, 1calcd ˆ 1.186 gcmÀ3
,
m ˆ
diphosphanylcarbene with isocyanides (Scheme 1).[2] As these
0.508 mmÀ1, blue/green prisms 0.30 Â 0.20 Â 0.15 mm3, Enraf-Nonius
DIP2000 image plate diffractometer, radiation MoKa (l ˆ 0.71073 Š),
w scans, range 1.45 < q < 20; measured reflections: 4436; independent
reflections: 4436 (Rint ˆ 0.0000),
R
values (I < 2sI): R1 ˆ 0.1159,
wR2 ˆ 0.3212, all data: R1 ˆ 0.1628, wR2 ˆ 0.3711. Structure refine-
ment: full-matrix-block least-squares on F 2. max/min residual elec-
tron density 1.255/ À 0.393 eŠÀ3. Crystallographic data (excluding
structure factors) for the structure reported in this paper have been
deposited with the Cambridge Crystallographic Data Centre as
supplementary publication no. CCDC-139644. Copies of the data
can be obtained free of charge on application to CCDC, 12 Union
Road, Cambridge CB21EZ, UK (fax: (‡44)1223-336-033; e-mail:
deposit@ccdc.cam.ac.uk).
[10] A search of the Cambridge Structural Database showed that the
ˆ
average C C bond lengths in cumulenes are 1.34 and 1.25 Š for the
sp2-sp1 and sp1-sp1 bonds, respectively; D. A. Fletcher, R. F. McMeek-
ing, D. Parkin, J. Chem. Inf. Comput. Sci. 1996, 36, 746 ± 749; F. H.
Allen, O. Kennard, Chem. Design Autom. News 1993, 8, 31 ± 37.
[11] E. L. Eliel, S. H. Wilen, Stereochemistry of Organic Compounds,
Wiley, New York, 1994, pp. 544 ± 550; G. Märkl, M. Hafner, P.
Kreitmeier, C. Stadler, J. Daub, H. Nöth, M. Schmidt, G. Gescheidt,
Helv. Chim. Acta 1997, 80, 2456 ± 2476; J.-H. Fuhrhop, E. Baumgart-
ner, H. Bauer, J. Am. Chem. Soc. 1981, 103, 5854 ± 5861.
[12] S. Yamaguchi, T. Hanafusa, T. Tanaka, M. Sawada, K. Kondo, M. Irie,
H. Tatemitsu, Y. Sakata, S. Misumi, Tetrahedron Lett. 1986, 27, 2411 ±
2414.
Scheme 1. Metal-assisted synthesis of diphosphanylketenimines 1. In th e
case of R ˆ Phor p-tolyl, reversible dimerization takes place to form 2. 1a:
R ˆ Ph; 1b: R ˆ tBu; 1c: R ˆ p-tolyl; 1d: R ˆ xylyl; 2a: R ˆ Ph, X ˆ H; 2c:
R ˆ p-tolyl, X ˆ Me.
[13] N. Yoshida, H. Shimidzu, A. Osuka, Chem. Lett. 1998, 55 ± 56; A.
Nakano, H. Shimidzu, A. Osuka, Tetrahedron Lett. 1998, 39, 9489 ±
9492.
molecules combine the properties of diphosphanes with those
of ketenimines, it was anticipated that new reactivity patterns
could arise from them. Here we report a unique cyclic
dimerization of N-aryldiphosphanylketenimines involving a
new type of [2 ‡ 3] cycloaddition reaction to give an
azaphospha five-membered heterocycle featuring a phospho-
rus-ylide functionality. This dimerization is reversible under
mild conditions and appears to be promoted by nonconven-
tional CH ´´´ N hydrogen bonds.
[14] No 12C-HD to 13C-HD NOE was observed in 6, which is explained by
À
the larger HD
HD distance in 6 (calculated: 2.9 Š for D2 isomer; 2.6 Š
for C2h isomer) compared to that in 3 (crystallographic: 2.47 and
2.41 Š; calculated: 1.9 Š). The 1H and 13C NMR spectra of 6 were
assigned by assuming that the most shielded b-pyrrolic proton is HD.
[15] Molecular mechanics calculations were carried out using the
CAChe 4.1 software from Oxford Molecular Ltd. with augmented
MM2 parameters; MM3 gave similar results.
[*] Dr. J. Ruiz, F. Marquínez, Prof. Dr. V. Riera, Dr. M. Vivanco
Â
Â
Departamento de Química Organica e Inorganica
Facultad de Química, Universidad de Oviedo
33071 Oviedo (Spain)
Fax : (‡34)985-103-446
E-mail: jruiz@sauron.quimica.uniovi.es
Dr. S. García-Granda, Dr. M. R. Díaz
Departamento de Química Física y Analítica
Facultad de Química, Universidad de Oviedo
33071 Oviedo (Spain)
Â
[**] This work was supported by the Spanish Ministerio de Educacion y
Ciencia (project nos. DGE-96-PB-0317 and PB96-0556)
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The N-phenylketenimine 1a forms colorless solutions in
different organic solvents which are stable for weeks. How-
ever, when a solution of 1a in hexane is very slowly
concentrated to dryness under vacuum, and the process of
adding and removing hexane is repeated at least three times,
an orange solid corresponding to the unsymmetrical dimer 2a
is formed (Scheme 1). This dimerization is fully reversible,
and refluxing a solution of 2a in toluene for 10 min leads to
the quantitative formation of monomer 1a. By contrast, the
N-tert-butylketenimine 1b did not dimerize at all, showing the
strong influence of the substituent at nitrogen in this process.
It has been described that ketenimines tend to dimerize, but
only upon prolonged thermolysis at high temperatures, and
through an ortho proton toward the exocyclic nitrogen atom
N(2), witha rather short H(2) ´´´ N(2) contact of 2.44(2) Š
À
(C H ´´´ N 141(1)8). A muchlonger contact exists between an
ortho proton of the phenyl group at N(2) and the endocyclic
nitrogen atom N(1) (H(1) ´´´ N(1) 2.94(2) Š) witha very
À
closed C H ´´´ N angle of 90(1)8. These two parameters
appear to indicate that this last interaction cannot be
considered as a real hydrogen bond, when taking into account
the cut-off of 2.7 Š based on van der Waals criteria and the
preference for a linear geometry.[7] However, it has been
shown that the electrostatic component of the hydrogen bond
also operates beyond the van der Waals separation, and that
directionality is blurred if other factors such as steric
restrictions comes into play.[8] Additionally, a structural
feature in favor of a hydrogen-bonding interaction is that
usually by [2‡2] cycloaddition reactions to give azetidines;[3]
[4]
related processes suchas base-induced dimerization
and
anodic oxidation[5] of ketenimines to give heterocyclic dimers
and trimers are also known. Therefore the present reaction is
a rare example of ketenimine dimerization occurring during
crystallization.
The 31P NMR spectrum of 2a revealed the presence of four
strongly coupled signals corresponding to the four inequiva-
lent phosphorus atoms of the molecule (see the Experimental
Section). The structure of 2a was definitively established by
X-ray crystallography[6] (Figure 1). The five-membered het-
erocycle C(1)-P(1)-C(3)-C(2)-N(1) is essentially planar. The
the H(1) N(1) vector is approximately directed toward the
À
sp3 lone pair of N(1).[9, 8a] Moreover, some cooperativity[8a]
could exist, as the two hydrogen bonds are interconnected
(the N(2)Ph group acts simultaneously as hydrogen-bond
donor and acceptor), resulting in an enhancement of the total
bond energy.
To assess the influence of the substituent at nitrogen in this
dimerization process, the new N-aryldiphosphanylketeni-
mines 1c (R ˆ 4-methylphenyl ˆ p-tolyl) and 1d (R ˆ 2,6-
dimethylphenyl ˆ xylyl) were prepared following the same
procedure used for the synthesis of 1a (Scheme 1). The N-p-
tolylketenimine 1c tends to dimerize under the same con-
ditions as 1a to give 2c, whereas the N-xylylketenimine 1d,
which lacks ortho hydrogen atoms for the substituent at N,
does not dimerize at all. This result suggests that not only the
H(2) ´´´ N(2) hydrogen bond but also the very weak inter-
action H(1) ´´´ N(1) could have some influence in the dime-
rization of 1a and 1c, although other factors such as steric
hindrance of the R substituent at nitrogen and packing forces
in the crystal must also be considered.
À
À
short C(2) C(3) (1.40(2) Š) and C(3) P(1) bonds (1.70(2) Š)
suggest that the negative charge at the ylide carbon atom C(3)
is strongly shared with the neighboring atoms. An important
feature of the structure of 2a is the presence of two
intramolecular CH ´´´ N hydrogen bonds. Thus, a phenyl ring
at phosphorus atom P(2) acts as a hydrogen-bond donor
The dimerization of diphosphanylketenimines described
here is noteworthy because: 1) it takes place under mild
conditions (room temperature), 2) it is reversible, 3) it
involves a new type of [2‡3] cycloaddition, and 4) it appears
to be promoted by intramolecular nonconventional CH ´´´ N
hydrogen bonds. Furthermore, the involvement of the phos-
phanyl substituent in the annelation process suggests an
enhancement of the synthetic potential of 1a ± d withrespect
to normal ketenimines. This is clearly shown in the reaction of
1a withtwo equivalents of dimethyl acetylenedicarboxylate,
which takes place instantaneously at room temperature to
give 3a (Scheme 2, see the Experimental Section).[10] This
unique bicyclic compound contains two fused five-membered
phosphaheterocycles resulting from two successive [2‡3]
cycloaddition reactions involving bothpohspohrus atoms
of the original ketenimine 1a.[11] Very likely this reac-
tion proceeds through the formation of the intermediate
species Ia, although it was not detected in the reaction
mixture (even at low temperature), suggesting an enhance-
ment of the reactivity after the first [2‡3] cycloaddition
process. Other preliminary studies show that 1a ± d react at
room temperature not only withelectron-poor alkynes but
also with heterocumulenes such as isocyanates and isothio-
cyanates.
Figure 1. Molecular structure of 2a. Hydrogen atoms and phenyl groups,
except those involved in hydrogen bonds, are omitted for clarity (ellipsoids
at the 30% probability level). Selected bond lengths [Š] and angles [8]:
N(1)-C(1) 1.45(2), N(1)-C(2) 1.45(2), P(1)-C(1) 1.80(2), P(1)-C(3) 1.70(2),
C(2)-C(3) 1.40(2), N(1)-C(11) 1.45(2), C(1)-C(4) 1.38(2), C(2)-N(2) 1.27(2),
C(3)-P(2) 1.83(2), C(4)-P(3) 1.88(2), C(4)-P(4) 1.77(2), N(1) ´´´ H(1)
2.94(2), N(2) ´´´ H(2) 2.44(2), C(22) ´´´ N(1) 3.09(3), C(222) ´´´ N(2)
3.22(3); C(22)-H(1) ´´´ N(1) 90(1), C(222)-H(2) ´´´ N(2) 141(1), C(1)-P(1)-
C(3) 91(1), C(1)-N(1)-C(2) 111.(1), C(4)-C(1)-N(1) 126(2), C(4)-C(1)-P(1)
125(2), N(1)-C(1)-P(1) 108(4), N(1)-C(2)-N(2) 120(2), N(2)-C(2)-C(3)
129(2), N(1)-C(2)-C(3) 112(2), C(2)-C(3)-P(1) 114(1), C(2)-C(3)-P(2)
124(4), P(1)-C(3)-P(2) 122(1), C(1)-C(4)-P(4) 114(1), C(1)-C(4)-P(3)
115(1), P(3)-C(4)-P(4) 129(1).
1822
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Angew. Chem. Int. Ed. 2000, 39, No. 10

COMMUNICATIONS
[4] R. Gertzmann, R. Fröhlich, M. Grehl, E. Würthwein, Tetrahedron
1995, 51, 9031 ± 9044.
[5] J. Y. Becker, E. Shakkour, J. A. R. P. Sarma, J. Chem. Soc. Chem.
Commun. 1990, 1016 ± 1017; J. Y. Becker, E. Shakkour, J. A. R. P.
Sarma, J. Org. Chem. 1992, 57, 3716 ± 3720.
Ph
Ph
NPh
Ph
P
P
Ph
Ph
C
C
RC≡CR
C
C
C
NPh
C
R
P
P
Ph
Ph
Ph
R
[6] Crystal data for 2a (C64H50N2P4): Mr ˆ 970.94, orthorhombic, space
group P212121, a ˆ 10.609(7), b ˆ 13.36(1), c ˆ 36.06(2) Š, Vˆ
5111(7) Š3, Z ˆ 4, 1calcd ˆ 1.262 gcmÀ3, F(000) ˆ 2032, MoKa radiation
Ia
1a
RC≡CR
(l ˆ 0.71073 Š), m(MoKa) ˆ 0.191 mmÀ1
crystal dimensions 0.20 Â
;
0.20 Â 0.13. Diffraction data were collected on a Enraf-Nonius at
293 K. The structure was solved with direct methods and refined using
full-matrix least squares on F 2 withall non-hydrogen atoms aniso-
tropically defined. The hydrogen atoms were placed in calculated
positions, isotropically refined withcommon thermal parameters, and
allowed to ride on their parent carbon atoms. For 5590 unique
reflections and 632 parameters, R ˆ 0.063 and wR2 ˆ 0.109. Crystallo-
graphic data (excluding structure factors) for the structure reported in
this paper has been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication no. CCDC-136772. Copies
of the data can be obtained free of charge on application to CCDC, 12
Union Road, Cambridge CB21EZ, UK (fax: (‡44)1223-336-033;
e-mail: deposit@ccdc.cam.ac.uk).
Ph
NPh
Ph
C
C
P
C
P
C
R
R
R
C
C
Ph Ph
R
3a
Scheme 2. Two [2‡3] cycloaddition reactions of 1a withdimethyl acety-
lenedicarboxylate provide 3a. R ˆ CO2Me.
Experimental Section
[7] a) R. Taylor, O. Kennard, J. Am. Chem. Soc. 1982, 104, 5063 ± 5070;
b) G. R. Desiraju, Acc. Chem. Res. 1996, 29, 441 ± 449.
[8] a) T. Steiner, Chem. Commun. 1997, 727 ± 734; b) T. Steiner, B. Lutz, J.
van der Maas, A. M. M. Schreurs, J. Kroon, M. Tamm, Chem.
Commun. 1998, 171 ± 172.
[9] The H(1) atom, together with C(1), C(2), and C(11), completes a
virtual distorted tetrahedron around N(1): C(1)-N(1)-H(1) 1328, C(2)-
N(1)-H(1) 1078, C(11)-N(1)-H(1) 778, C(1)-N(1)-C(2) 1118, C(1)-
N(1)-C(11) 1118, C(2)-N(1)-C(11) 1158.
[10] A preliminary X-ray diffraction study of 3a confirms the proposed
bicyclic structure. Furthermore, 3a has been fully spectroscopically
characterized (see the Experimental Section).
2a: A solution of 1a (0.1 g, 0.2 mmol) in hexane (10 mL) was very slowly
evaporated to dryness under vacuum. Hexane (10 mL) was added to the
residue, giving an orange precipitate corresponding to the dimer 2a; th e
monomer 1a remained in solution. The solution was filtered off and then
retreated withhexane to afford a new fraction of 2a. The process was
repeated three times; yield 70% (0.07 g). The yield can be improved by
repeating the process as many times as possible. Crystals suitable for X-ray
diffraction were grown from a solution in CH2Cl2/hexane. Elemental
analysis calcd for C64H50N2P4: C 79.16, H 5.19, N 2.88; found: C 78.84, H
3
5.27, N 2.78; 1H NMR (300 MHz, CD2Cl2): d ˆ 7.90 (4H, dd, JP, H ˆ 13,
3
3JH,H ˆ 7 Hz), 6.4 ± 7.4 (44H, m), 5.85 (2H, d, JH,H ˆ 7 Hz); 31P{1H} NMR
2
3
3
(121.5 MHz, CD2Cl2): d ˆ 28.5 (ddd, JP, P ˆ 52, JP, P ˆ 24, JP,P ˆ 6 Hz), 14.3
[11] For other cycloaddition reactions involving phosphorus atoms, see for
3
3
3
3
2
(dd, JP, P ˆ 24, JP, P ˆ 4 Hz), 6.8 (dd, JP, P ˆ 4, JP, P ˆ 6 Hz), À22.8 (d, JP, P
ˆ
Â
instance G. Veneziani, R. Reau, F. Dahan, G. Bertrand, J. Org. Chem.
52 Hz).
1994, 59, 5927 ± 5929; J. Grobe, D. L. Van, B. Broschk, M. Hegemann,
B. Lüth, G. Becker, M. Böhringer, E. U. Würthwein, J. Organomet.
Chem. 1997, 529, 177 ± 187, and references therein.
2b: Compound 2b was prepared analogous to 2a. Elemental analysis calcd
for C66H54N2P4: C 79.35, H 5.45, N 2.80; found: C 79.26, H 5.32, N 2.75;
3
3
1H NMR (300 MHz, CD2Cl2): d ˆ 7.85 (4H, dd, JP, H ˆ 13, JH,H ˆ 7 Hz),
3
6.4 ± 7.4 (42H, m), 5.84 (2H, d, JH,H ˆ 7 Hz), 2.35 (3H, s), 2.12 (3H, s);
31P{1H} NMR (121.5 MHz, CD2Cl2): d ˆ 28.6 (m), 13.7 (m), 6.5 (s, br), À 23.8
(m).
3a: To a solution of 1a (0.05 g, 0.1 mmol) in CH2Cl2 (10 mL) was added
dimethyl acetylenedicarboxylate (0.025 mL, 0.2 mmol). The color changed
to red instantly. After 5 min of stirring at room temperature the solvent was
evaporated to dryness, and the brown residue recrystallized from CH2Cl2/
hexane to afford red crystals; yield 85% (0.065 g). Elemental analysis calcd
for C44H37NO8P2: C 68.65, H 4.84, N 1.81; found: C 68.43, H 4.80, N 1.83;
Dianionic Homoleptic Biphosphinine
Complexes of Group 4 Metals**
Â
Patrick Rosa, Nicolas Mezailles, Louis Ricard,
1H NMR (300 MHz, CD2Cl2): d ˆ 7.99 (4H, dd, JP, H ˆ 14, JH,H ˆ 7 Hz),
6.8 ± 7.8 (19H, m), 6.52 (2H, d, 3JH,H ˆ 7 Hz), 3.50 (3H, s), 3.35 (3H, s), 3.27
(3H, s), 2.89 (3H, s); 31P{1H} NMR (121.5 MHz, CD2Cl2): d ˆ 8.97 (d,
2JP, P ˆ 71 Hz), À81.40 (d, 2JP,P ˆ 71 Hz); 13C NMR (75.5 MHz, CD2Cl2): d ˆ
3
3
François Mathey,* and Pascal Le Floch*
The stabilization of anionic transition metal centers is
generally associated withthe use of ancillary ligands possess-
ing strong p-acceptor properties. For the most part, it was
achieved with molecules such as CO,[1] isocyanides,[2] ethyl-
ene,[3] and arenes[4] which display a suitable synergistic effect
between s-donor and p-acceptor capabilities, and in rare
cases, by using tailored tertiary phosphanes.[5] However, only
little is known about the stabilizing effects provided by
199.43 (dd, JP,C ˆ 32, 22 Hz), 170.30 (dd, JP, C ˆ 25, 4 Hz), 170.05 (dd, JP, C
ˆ
14, 10 Hz), 169.15 (dd, JP, C ˆ 3, 1 Hz), 166.51 (dd, JP, C ˆ 6, 2 Hz), 162.41 (dd,
JP, C ˆ 16, 2 Hz), 159.52 (dd, JP, C ˆ 23, 13 Hz), 151.86 (d, JP, C ˆ 5 Hz), 131.28
(dd, JP,C ˆ 12, 7 Hz), 117.2 (dd, JP, C ˆ 93, 6 Hz), 52.60 (s, 1  CH3), 51.57 (s,
3 Â CH3); signals for phenyl groups not given.
Received: November 26, 1999 [Z14322]
[1] ªThe Chemistry of Ketenes, Allenes and Related Compoundsº: M. W.
Barker, W. E. McHenry in The Chemistry of Functional Groups, Part 2
(Ed.: S. Patai), Interscience, New York, 1980, chap. 17, pp. 701 ± 720;
G. Tennant in Comprehensive Organic Chemistry. The Synthesis and
Reactions of Organic Compounds, Vol. 2 (Eds.: D. Barton, W. D. Ollis,
I. O. Sutherland), Pergamon, Oxford, 1979, pp. 521 ± 527.
[2] J. Ruiz, V. Riera, M. Vivanco, M. Lanfranchi, A. Tiripicchio, Organo-
metallics 1998, 17, 3835 ± 3837.
Â
[*] Prof. F. Mathey, Dr. P. Le Floch, P. Rosa, Dr. N. Mezailles,
Dr. L. Ricard
   Â
Laboratoire ªHeteroelements et Coordinationº, Ecole Polytechnique
91128 Palaiseau Cedex (France)
Fax : (‡33)1-69-33-39-90
E-mail: francois.mathey@polytechnique.fr, lefloch@mars.
polytechnique.fr
[3] M. W. Barker, J. D. Rosamond, J. Heterocycl. Chem. 1972, 9, 1147 ±
1148; M. W. Barker, J. D. Rosamond, J. Heterocycl. Chem. 1972, 9,
1419 ± 1421.
[**] This work was supported by the CNRS and the Ecole Polytechnique.
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