New synthesis of diphenyl-N-(substituted)ketenimines from diaminophosphonium diazaylides

Article abstract of DOI:10.1016/S0022-328X(99)00094-7

Diaminophosphonium diazaylides 2 react under mild conditions with diphenylacetyl chloride, to afford diphenyl-N-(substituted)ketenimines 4 or, depending on the case, their transformation products: either the tautomer 8, or the dimer 9. The general reactio

Full text of DOI:10.1016/S0022-328X(99)00094-7

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 584 (1999) 68–72
New synthesis of diphenyl-N-(substituted)ketenimines from
diaminophosphonium diazaylides
Henri-Jean Cristau *, Isabelle Jouanin, Marc Taillefer 1
Ecole Nationale Supe´rieure de Chimie Montpellier, Laboratoire de Chimie Organique (ESA 5076 du CNRS) 8 rue de l’Ecole Normale,
F-34296 Montpellier, Cedex 5, France
Received 3 December 1998; received in revised form 25 January 1999
Abstract
Diaminophosphonium diazaylides 2 react under mild conditions with diphenylacetyl chloride, to afford diphenyl-N-(substi-
tuted)ketenimines 4 or, depending on the case, their transformation products: either the tautomer 8, or the dimer 9. The general
reaction seems to proceed firstly via an elimination step on the acid chloride followed then by an aza-Wittig reaction between the
resulting ketene 7 and the diaminophosphonium monoazaylide 6. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Diaminophosphonium diazaylide; Diphenylacetyl chloride; Ketenimine; Aza-Wittig reaction
1. Introduction
2. Results
In recent work, we have shown that phosphonium
diylides 1 are excellent tools in organic synthesis [1].
Indeed, these reagents, thanks to their reinforced car-
banionic activity, are more reactive than the corre-
sponding triphenylphosphonium monoylides and offer
a general method for the synthesis of numerous a,b-un-
saturated functions [1] (Scheme 1).
The corresponding nitrogen compounds, di-
aminophosphonium diazaylides 2, until now mainly
used in coordination chemistry [2], have been less stud-
ied in the field of organic synthesis. As a first applica-
tion example we have found that these reagents react as
equivalents of the synthon RNH−, thus allowing the
synthesis of primary or secondary amines [3]. The re-
sults reported here show another example of applica-
tion for nitrogen diazaylides 2: the synthesis of
diphenyl-N-(substituted)ketenimines 4.
We have studied the reaction between various diazayl-
ides 2, regardless of their stabilization, and diphenyl-
acetyl chloride (Scheme 2, Table 1).
Non-stabilized and semi-stabilized diazaylides 2 are
synthesized from the corresponding phosphonium salts
3 [3,4]. After the in situ addition, at −50°C, of one
equivalent of diphenylacetyl chloride the non-stabilized
diazaylide 2a (R=n-Bu) immediately disappears to
instantaneously give the corresponding phosphinic
amide 5a as sole organophosphorus product, as shown
by the 31P-NMR spectrum of the reaction mixture
(Table 1). Simultaneously the formation of the
diphenyl-N-n-butylketenimine 4a can be observed: the
IR spectrum of the reaction mixture exhibits a very
strong absorption at 2010 cm−1, characteristic of such
heterocumulenes. The yield in ketenimine 4a, which
1
then reaches 100% is determined by H-NMR titration.
It should be noted that this method corroborates the
yield, first determined by 31P-NMR, for the phosphinic
amide 5a.
Non-stabilized diazaylide 2b for which the substituent
on nitrogen is a more bulky group (R=i-Pr) also reacts
quickly with diphenylacetyl chloride to give
quantitatively the corresponding ketenimine 4b. With a
still more bulky group (R=t-Bu), the reaction is
* Corresponding author. Tel.: +33-4-67-144312; fax: +33-4-67-
144319.
E-mail address: cristau@cot.enscm.fr (H.-J. Cristau)
1 Also corresponding author.
E-mail address: taillefe@cit.enscm.fr (M. Taillefer)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00094-7

H.-J. Cristau et al. / Journal of Organometallic Chemistry 584 (1999) 68–72
69
With the semi-stabilized diazaylide 2f (R=Ph) the
reaction is slow, but affords the diphenylketene 7 to-
gether with the intermediate monoazaylide 6f (isolated
yield: 75%). This result further corroborates the pro-
posed mechanism.
Finally, with the stabilized diazaylide 2g (R=
C(O)Ph), the reaction is also slow and the maximum
yield in ketenimine 4g, determined on the basis of the
phosphinic amide formed, only reaches 25%. The keten-
imine can be detected on the IR spectra only at the
beginning of the reaction, the corresponding signal
disappearing after 2 h. This observation is in accor-
dance with the results of the literature mentioning that
N-aroyldiphenylketenimines are very unstable (they are
characterized only by IR spectra) [6]. It should be noted
that the formation of the intermediates 6g and 7 can
also be observed.
Scheme 1. Lithium dialkyldiphenylphosphonium diylides 1 and nitro-
gen analogs 2.
slower, but a yield of 70% in ketenimine can be ob-
tained after 5 h at 65°C. At this time, the transforma-
tion ratio of the starting diazaylide 2c reaches 100%,
but only 60% of the phosphinic amide 5c is formed
(31P-NMR). Moreover, after the work-up of the reac-
tion mixture about 30% of the diaminophosphonium
monoazaylide 6c is isolated together with a significant
amount of ketene 7. This result is interesting from a
mechanistic point of view: in a first step, the diazaylide
deprotonates the diphenylacetyl chloride leading to the
concomitant formation of the corresponding ketene 7
and monoazaylide 6c; the second step consists of an in
situ aza-Wittig reaction between the two species giving
the ketenimine 4c and the phosphinic amide 5c (Scheme
2).
The mechanism proposed in Scheme 2 contains the
illustration for the three categories of diazaylides 2
(stabilized, non- and semi-stabilized). Accordingly, this
mechanism seems to be general, although we did not
observed the intermediate 6 and 7 in the case where the
reaction is particularly quick.
Starting from the diazaylide 2d (R=CH2Ph), the
formation of a high yield in ketenimine 4d was also
immediately observed. It is interesting to note that after
some time at 20°C, the product evolves continuously to
the major formation of the tautomer 8, which is ther-
modynamically more stable (Scheme 3).
As in the previous cases, the N-allylsubstituted diaza-
ylide 2e reacts at low temperature with diphenylacetyl
chloride immediately resulting in a good amount of the
corresponding ketenimine 4e. However, this compound
is quickly consumed, as shown by the disappearance of
the IR absorption at 2015 cm−1, to give quantitatively
the symmetric dimer 9 (Scheme 4).
The identification of dimer 9 was based on the spec-
troscopic data which allowed us to quickly discard the
two possible dissymetric structures. Between the two
possible remaining forms the diazetidine 9% was also
discarded on the basis of the 13C-NMR and by com-
parison with the results of the literature concerning a
structure close to cyclobutane 9 [5].
The reactivity of n-butylaminotriphenylphosphonium
monoazaylide 10 was also tested towards diphenyl-
acetyl chloride (Scheme 5). The ketenimine 4a is formed
but this method was not developed because of the
presence of two phosphorus by-products, 11 and 12,
and because of the lower reactivity of 10 in comparison
with the corresponding diazaylide 2a (60% yield after 1
h at 20°C with the monoazaylide, and 100% after 5 min
at −50°C with the diazaylide).
3. Conclusions
In conclusion, the study of the reactivity of di-
aminophosphonium diazaylides 2 affords a new method
for the synthesis, under mild conditions, of diphenyl-N-
(substituted)ketenimines, which are a family of not very
stable compounds, and of the cyclic dimer of the N-al-
lyldiphenylketenimine. These results represent an addi-
tional example of the potential of phosphonium diylides
in organic synthesis.
Scheme 2. Synthesis of diphenyl-N-(substituted)ketenimines 4 by reaction of diphenylacetyl chloride with various diaminophosphonium
diazaylides 2.

70
H.-J. Cristau et al. / Journal of Organometallic Chemistry 584 (1999) 68–72
Table 1
Synthesis of diphenyl-N-(substituted)ketenimines (4) by reaction of diaminophosphonium diazaylides 2 with diphenylacetyl chloride
Diazaylide
R
Reaction conditions
(°C)
2 tr (%) a
4
5 yield (%) d
Other products
b
IR (cm−1
)
CꢀCꢀN Yield (%) c
2a
2b
n-Bu
i-Pr
5 min/−50
1 h/20
12 h/20
12 h/20
5 h/65
22 h/65
5 min/−50
2 h/20
100
100
100
20
100
100
100
100
100
100
2010 vs
2000 vs
2000 vs
2005 s
2005 vs
2005 vs
2010 vs
2010 vs
2010 s
100
80
100
15
70
90
100
85
100
20
60
95
2c
2d
2e
t-Bu
6c: 30%
8: 60% c
CH2Ph
60
65
80
100
100
60
30 h/20
25
CH2CHꢀCH2 5 min/−50
2015 vs
70 e
f
1 h/0
6 h/20
2 h/20
1 h/20
24 h/20
100
100
100
–
80
2015 w
–
1995 m
2020 m
–
–
0
80
95
20
10
25
9: 100% e
6f: 75%
2f
Ph
25 g
10 g
0 (25 g)
f
2g
C(O)Ph
6g: 50%
a tr, transformation ratio of 2 determined by 31P-NMR.
b vs, very strong; s, strong; m, medium; w, weak.
c Yield determined after concentration of a sample of the reaction mixture by 1H-NMR titration with p-iodoanisole as internal standard
(isolated yields are given in Section 4).
d Yield determined by 1H-NMR titration and/or by 31P-NMR.
e Yield determined by 1H-NMR titration on the basis of the N-CH2 signal.
f Undetermined.
g Determined from the phosphinic amide yield.
4. Experimental
trometer. All solvents were distilled from drying agents
prior to use. The reactions were performed under nitro-
gen using Schlenk techniques. n-Butyllithium commer-
cial solutions in hexane (Aldrich) were titrated before
use [7]. Diaminophosphonium salts were prepared ac-
cording to the literature [4]. Commercial diphenylacetyl
chloride (Lancaster) and 4-iodoanisole (Aldrich) were
used without purification.
Melting points were determined using a Wild Leitz
350 and are given uncorrected. H-, 31P- and 13C-NMR
1
were recorded on a Bruker AC-200 spectrometer
(200.132, 81.0 and 50.323 MHz, respectively). IR spec-
tra were obtained with a Perkin–Elmer 377. Mass
spectra were measured with a Jeol JMS DX-300 spec-
Scheme 3. In situ formation of compound 8.
Scheme 4. In situ cyclodimerisation of the diphenyl-N-allylketenimine 4e.

H.-J. Cristau et al. / Journal of Organometallic Chemistry 584 (1999) 68–72
71
Scheme 5. Synthesis of the ketenimine 4a by reaction of two equivalents of n-butylaminotriphenylphosphonium monoazaylide 10 with
diphenylacetyl chloride.
4.1. Synthesis of diphenyl-N-(substituted)ketenimines 4
ketenimine 4 as a yellow solid. Reaction yield: 100%;
isolated yield: 65%.
4.1.1. General procedure
M.p. 49°C (recrystallization in petroleum ether (b.p.
45–60°C) at −30°C) {lit. [9] m.p. 45–46°C}. H-NMR
1
To 5 mmol of diaminodiphenylphosphonium bromide
3 in THF (20 ml) was added dropwise 10 mmol of
n-BuLi (4.35 ml, 2.3 M in hexane) at −50°C. Then
p-iodoanisole (1.17 g, 5 mmol) was added for the
1H-NMR titration. After 30 min at this temperature,
diphenylacetyl chloride (1.15 g, 5 mmol) was added
resulting in a yellow coloration of the solution. Depend-
ing on the diazaylide 2, the reaction mixture is then
allowed to warm up to room temperature or refluxed in
THF (see Table 1). When the reaction (monitored by
(CDCl3) [10]: l=1.38 (d, J=6.4 Hz, 6H, CH3), 3.94 (m,
J=6.4 Hz, 1H, CHN), 7.17–7.36 (m, 10H, 2C6H5).
13C{1H} (CDCl3): l=23.72 (s, 2C, CH3), 55.11 (s,
CHN), 79.10 (CꢀCꢀN), 125.82 (s, p-C, C6H5), 127.50 (s,
o-C, C6H5), 128.11 (s, m-C, C6H5), 135.21 (s, i-C, C6H5),
184.0 (s, CꢀCꢀN). MS (EI): m/z (%)=235 (36, M+),
193 (100), 166 (99). Anal. Calc. for C17H17N (235.33); C,
86.76; H, 7.28; N, 5.95. Found: C, 86.79; H, 7.23; N,
6.03%.
1
31P- and H-NMR) is stopped the THF is evaporated
and water is added (20 ml). The aqueous phase is then
extracted twice with methylene chloride (2×30 ml) and
the combined organic layers are dried on MgSO4, filtered
and concentrated under vacuum (at a temperature below
10°C). Then the work-up depends on the ketenimine.
4.1.4. Diphenyl-N-t-butylketenimine (4c)
From bis-t-butylaminodiphenylphosphonium bro-
mide 3c (2.04 g, 5 mmol). The work-up is performed and
the reaction stopped after 5 h at 65°C. After concentra-
tion of the organic layer, the residue is purified by
chromatography on basic alumina to give the corre-
sponding ketenimine 4c (yield: 50%). (The diaminophos-
phonium monoazaylide 6c is also obtained, not
completely pure, with a yield around 30%.)
4.1.2. Diphenyl-N-n-butylketenimine (4a)
From bis-n-butylaminodiphenylphosphonium bro-
mide 3a (2.05 g, 5 mmol). After concentration of the
organic layer, diphenyl-N-n-butylketenimine 4a is dis-
tilled under reduced pressure. Yellow liquid; reaction
yield: 100%; isolated yield: 80%.
1
M.p. 49°C (lit. [10] m.p. 50°C). H-NMR (CDCl3)
[10]: l=1.48 (s, 9H, t-C4H9), 7.04–7.36 (m, 10H,
2C6H5). 13C{1H}-NMR (CDCl3): l=29.75 (s, 3C,
CH3), 54.25 (s, N–C), 78.15 (CꢀCꢀN), 125.79 (s, p-C,
C6H5), 127.55 (s, o-C, C6H5), 128.21 (s, m-C, C6H5),
135.30 (s, i-C, C6H5), 183.55 (s, CꢀCꢀN). MS (EI): m/z
(%)=249 (4, M+), 193 (100), 165 (54), 57 (38).
B.p.0.5 90°C {lit. [8] 150–153 (16 mm)}. 1H-NMR
(CDCl3): l=1.03 (d, J=7.3 Hz, 3H, CH3), 1.40 (m,
J=7.3 Hz, 2H, CH2CH3), 1.80 (m, J=7.5 Hz, 2H,
CH2CH2CH3), 3.68 (t, J=7.3 Hz, 2H, CH2N), 7.33–
7.42 (m, 10H, 2 C6H5). 13C{1H}-NMR (CDCl3): l=
13.72 (s, CH3), 20.21 (s, CH2CH3), 32.44 (s,
CH2CH2CH3), 52.93 (s, CH2N), 78.60 (s, CꢀCꢀN),
125.89 (s, p-C, C6H5), 127.64 (s, o-C, C6H5), 128.75 (s,
m-C, C6H5), 135.20 (s, i-C, C6H5), 185.40 (s, CꢀCꢀN).
MS (EI): m/z (%)=249 (41, M+), 193 (100),165 (64),
57(4). Anal. Calc. for C18H19N (249.35); C, 86.70; H,
7.68; N, 5.62. Found: C, 87.21; H, 7.53; N, 5.62%.
4.1.5. Diphenyl-N-benzylketenimine (4d) and N-(2,2-
diphenylethenyl)benzenimine (8)
From bis-benzylaminodiphenylphosphonium bro-
mide 3d (2.38 g, 5 mmol). The work up is performed and
the reaction stopped after 30 h at 20°C, when the main
part of the ketenimine is transformed in the tautomer 8.
After concentration of the organic layer, petroleum ether
(20 ml) is added to the residue, affording a mixture of
phosphinic amide 5d and tautomer 8 as a yellow precip-
itate. After filtration the petroleum ether is eliminated
under vacuum to give the ketenimine 4d as a yellow oil
[11]. Yield: 25%. 1H-NMR (CDCl3) [11]: l=4.77 (s, 2H,
CH2), 7.10–7.42 (m, 15H, 3C6H5). MS (EI): m/z (%)=
283 (25, M+), 192 (35), 165 (38), 91 (100).
4.1.3. Diphenyl-N-i-propylketenimine (4b)
From bis-i-propylaminodiphenylphosphonium bro-
mide 3b (1.90 g, 5 mmol). After concentration of the
organic layer, petroleum ether (15 ml) is added to the
residue affording the phosphinic amide 5b as a white
precipitate. After filtration (5b is isolated in a 95% yield:
1.22 g) the organic layer is concentrated to give the

72
H.-J. Cristau et al. / Journal of Organometallic Chemistry 584 (1999) 68–72
The yellow precipitate is chromatographed on basic
13C{1H}-NMR (CDCl3): l=78.01 (CꢀCꢀN), 124.02
and 126.54 (2s, o-C and m-C, N–C6H5), 127.85 (p-C,
N–C6H5), 127.88 (o-C, C–Ph2), 128.89 (m-C, C–Ph2),
129.59 (p-C, C–Ph2), 134.0 (i-C, C–Ph2), 140.70 (i-C,
N–C6H5), 190.61 (CꢀCꢀN). MS (EI): m/z (%)=249
(84, M+), 192 (4), 165 (100). Anal. Calc. for C18H19N
(269.34); C, 89.18; H, 5.61; N, 5.20. Found: C, 88.89;
H, 5.22; N, 4.98%.
alumina ((a) AcOEt/Hexane:10/90 to obtain 8, and (b)
MeOH to recover 5d). Compound 8 is recrystallized in
petroleum ether as a yellow solid (yield: 45%).
M.p. 129°C (petroleum ether: b.p. 45–60°C) (lit. [12]
m.p. 131.5–133.5°C). IR (KBr): w=3420, 1620 (CꢀN),
1
1550, 1480, 1440, 1380 cm−1. H-NMR (CDCl3): l=
7.33–7.54 (m, 13H, 2 C6H5 and m- and p- from CH–
C6H5), 7.77–7.80 (m, 3H, 2H o- from CH–C6H5 and
CHꢀCPh2), 8.42 (s, 1H, CH–N). 13C{1H}-NMR
(CDCl3): l=127.5 and 127.53 (2 s, p-C, Ph2C), 127.77
(s, o-C, CH–C6H5), 128.32 and 128.68 (2s, o-C, Ph2C),
128.81 and 128.87 (2s, m-C, Ph2C), 130.94 (s, p-C,
CH–C6H5), 131.74 (s, m-C, CH–C6H5), 136.71 (s, i-C,
CH–C6H5), 138.74 and 140.96 (2s, i-C, Ph2C), 140.0
(CHꢀCPh2), 141.75 (CHꢀCPh2), 161.33 (CHꢀN). MS
(EI): m/z (%)=283 (62, M+), 206 (100), 178 (32), 165
(24).
6f is recrystallized in THF (yield: 75%).
M.p. 178–180°C (THF). IR (KBr): w=3400, 3020,
2920, 2820, 1600, 1580, 1480, 1430, 1310–1300 (PꢀN),
1280, 1230 cm−1 31P{1H}-NMR (CDCl3): l= −1.6
.
ppm. 1H-NMR (CDCl3): l=6.83–7.12 (m, 10H,
2C6H5), 7.42–7.52 (m, 6H, Ph2P), 7.88–7.99 (m, 4H,
Ph2P). 13C{1H}-NMR (DMSOD): l=125.13 (p-C, N–
2
C6H5), 126.03 (d, JPC=11.3 Hz, o-C, Ph2P), 133.65 (d,
3JPC=14.1 Hz, m-C, Ph2P), 133.79 (m-C, N–C6H5),
1
136.33 (d, JPC, i-C, Ph2P), 136.99 (p-C, Ph2P), 137.08
(d, 3JPC=9.8 Hz, o-C, N–C6H5), 149.75 (i-C, N–
C6H5). MS (FAB: GT): m/z=369 (M+1).
4.1.6. 2,2,4,4-Tetraphenyl cyclobutane-1,3-bis-N-
allylimine (9)
From bis-allylaminodiphenylphosphonium bromide
3e (1.88 g, 5 mmol). After concentration of the organic
layer the residue is distillated under reduced pressure to
give 9. Yellow oil; yield: 85%.
Acknowledgements
We thank S. Maurin, for the contribution to this
work.
B.p.0.3 142°C. IR (NaCl/film): w=3060, 3037, 2962,
2940, 1740, 1667, 1617, 1510, 1467, 1208, 945 cm−1
.
1H-NMR (CDCl3): l=3.14 (dt, J=6.9 Hz, J=1.1
Hz, 4H, CH2N), 5.15–5.26 (m, 4H, CHꢀCH2), 5.65–
5.87 (m, 2H, CHꢀCH2), 7.26–7.42 (m, 20H, 4C6H5).
13C{1H}-NMR (CDCl3): l=44 (CH2N), 51.84 (CPh2),
120.45 (CHꢀCH2), 122.08 (CꢀN), 127.10 (m-C, C6H5),
128 (p-C, C6H5), 128.91 (o-C, C6H5), 131.92
(CHꢀCH2), 139.80 (i-C, C6H5). MS (EI): m/z (%)=233
(12), 192 (100), 165 (90). FAB+ (NBA) m/z=467
(M+1).
3
4
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From bis-phenylaminodiphenylphosphonium bro-
mide 3f (2.39 g, 5 mmol). After concentration of the
organic layer the intermediate monoylide 6f is precipi-
tated by addition of petroleum ether (40 ml). After
filtration the organic layer is concentrated to give 4f as
a yellow solid (yield: 20%).
M.p. 52°C (recrystallization in petroleum ether (b.p.
1
45–60°C), 3 days at −20°){lit. [13] m.p. 55°C}. H-
NMR (CDCl3): l=7.22–7.44 (m, 15H, 3C6H5).
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