Benzazaphospholine-2-carboxylic acids: Synthesis, structure and properties of heterocyclic phosphanyl amino acids

Article abstract of DOI:10.1016/j.poly.2014.03.046

1,3-Dialkyl-1,3-benzazaphospholine-2-carboxylic acids 2a,b can be conveniently prepared by metalation and alkylation of N-methyl- and N-neopentyl-o-phosphanylaniline in liquid ammonia and cyclocondensation of the resulting N,P-disecondary phosphanylanilines 1a,b with glyoxylic acid hydrate (GAH) in ether. The primary neopentylphosphanylaniline reacts with two equivalents of GAH and forms a phosphanylbis(amino acid) 3 with toluidine. α-Branched P-substituents induce strongly preferred formation of trans-diastereoisomers with R,R- and S,S-configuration at P and C2, as shown by a crystal structure analysis of 2a, whereas a P-neopentyl (P-Np) group gives rise to trans/cis-diastereoisomeric mixtures. The trans-configuration exhibits the P lone-pair in cis-position to the COOH group, suitable for formation of five-membered chelate rings, as in diphenylphosphanylacetate nickel catalysts for ethylene oligomerization. Screening of 2a,b/Ni(COD)₂ solutions in THF by a batch procedure indeed showed formation of catalysts for conversion of ethylene to linear oligomers and waxy low-molecular weight polymers. The conversion depends strongly on the size of the N-alkyl group, being slow and limited for the N-Me catalyst 2a/Ni and much faster and more complete for the N-Np-substituted catalysts 2b/Ni and 2c/Ni (N-Np, P-tBu). Comparison of 2b/Ni with 2c/Ni shows that the more bulky P-substituent further increases the catalyst activity.

Full text of DOI:10.1016/j.poly.2014.03.046

Polyhedron 77 (2014) 10–16
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Benzazaphospholine-2-carboxylic acids: Synthesis, structure
and properties of heterocyclic phosphanyl amino acids
Mohammed Ghalib a, Joanna Lach a, Olga S. Fomina a,b, Dmitry G. Yakhvarov b,c, Peter G. Jones d,
Joachim Heinicke a,
⇑
a Institut für Biochemie (Anorganische Chemie), Ernst-Moritz-Arndt-Universität Greifswald, Felix-Hausdorff-Str. 4, 17487 Greifswald, Germany
b A.E. Arbuzov Institute of Organic and Physical Chemistry, Arbuzov str. 8, 420088 Kazan, Russian Federation
c Kazan (Volga Region) Federal University, Kremlevskaya str. 18, 420008 Kazan, Russian Federation
d Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Postfach 3329, 38023 Braunschweig, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
1,3-Dialkyl-1,3-benzazaphospholine-2-carboxylic acids 2a,b can be conveniently prepared by metalation
and alkylation of N-methyl- and N-neopentyl-o-phosphanylaniline in liquid ammonia and cyclocondensa-
tion of the resulting N,P-disecondary phosphanylanilines 1a,b with glyoxylic acid hydrate (GAH) in ether.
The primary neopentylphosphanylaniline reacts with two equivalents of GAH and forms a phosphanyl-
Received 26 January 2014
Accepted 25 March 2014
Available online 13 April 2014
bis(amino acid) 3 with toluidine.
a-Branched P-substituents induce strongly preferred formation of
Keywords:
Phosphanes
Heterocycles
Ligands
Catalysis
Ethylene
trans-diastereoisomers with R,R- and S,S-configuration at P and C2, as shown by a crystal structure analysis
of 2a, whereas a P-neopentyl (P-Np) group gives rise to trans/cis-diastereoisomeric mixtures. The trans-
configuration exhibits the P lone-pair in cis-position to the COOH group, suitable for formation of five-
membered chelate rings, as in diphenylphosphanylacetate nickel catalysts for ethylene oligomerization.
Screening of 2a,b/Ni(COD)2 solutions in THF by a batch procedure indeed showed formation of catalysts
for conversion of ethylene to linear oligomers and waxy low-molecular weight polymers. The conversion
depends strongly on the size of the N-alkyl group, being slow and limited for the N-Me catalyst 2a/Ni and
much faster and more complete for the N-Np-substituted catalysts 2b/Ni and 2c/Ni (N-Np, P-tBu). Compar-
ison of 2b/Ni with 2c/Ni shows that the more bulky P-substituent further increases the catalyst activity.
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
Ni(COD)2 [5]. To find out whether the higher activity of the ben-
zazaphospholine-2-carboxylate-based nickel catalysts is attribut-
Recent studies on the synthesis of bulky tert-butyl-substituted
heterocyclic phosphane ligands by addition of tert-butyllithium
at the P@C bond of aromatic phosphorus heterocycles have
included the discovery of a convenient route to 3-tert-butyl-1,3-
benzazaphospholine-2-carboxylic acids [1]. These possess the
same P-C-COOH structural unit as diphenylphosphanylacetic acid
[2], which is used in the generation of nickel catalysts for the eth-
ylene oligomerization in the SHOProcess [3], and also form highly
active catalysts for this reaction. The amino function did not inter-
fere with the catalytic conversion. This was observed also for
various acyclic alkylamino- and arylamino-diphenylphosphanyl-
acetic acids (phosphanylglycines) [4], whereas more closely related
heterocyclic 3-phenyl-1,3-azaphospholidine-2-carboxylic acids
(3-phenyl-phosphaprolines) without benzo-annulation required
activation by sodium hydride to form active catalysts with
able to the bulky P-tert-butyl substituent or to electronic effects
of the intrinsic o-aminophenyl group, a preliminary study of the
synthesis of less bulky P-alkyl-1,3-benzazaphospholine-2-carbox-
ylic acids and their performance as ligands in the nickel catalyzed
ethylene oligomerization was carried out.
2. Results and discussion
A well established strategy was chosen for the synthesis,
namely the cyclocondensation of 2-phosphanyl-substituted
amines, long since known for simple aldehydes and ketones [6].
Even the reaction of o-phosphanylaniline with pyruvic acid was
reported to give 2-methyl-1,3-benzazaphospholine-2-carboxylic
acid, but information on the properties and structure of this
compound, except for the detection of a P–H absorption in the
range 2240–2280 cmꢀ1, is not available [6c]. We used the conden-
sation with glyoxylic acid hydrate (GAH). This acid proved suffi-
ciently reactive at room temperature to undergo autocatalyzed
⇑
Corresponding author. Tel.: +49 864318; fax: +49 3834 864377.
E-mail address: heinicke@uni-greifswald.de (J. Heinicke).
http://dx.doi.org/10.1016/j.poly.2014.03.046
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

M. Ghalib et al. / Polyhedron 77 (2014) 10–16
11
three-component one-pot condensations with secondary phos-
phanes and primary alkyl- or arylamines to phosphanylglycines
[4] whereas aldehydes and ketones, including pyruvic and phenyl-
glyoxyl acid, do not undergo analogous condensations. The starting
phosphanes 1a,b were prepared from N-methyl- and N-neopentyl-
o-phosphanylaniline by P-alkylation. Attempts to achieve this via
lithiation of the primary precursors with butyllithium in diethyl
ether failed to give defined products, but metalation with sodium
in liquid ammonia provided sufficiently reactive phosphides for
preferred P-alkylation by isopropyl- and neopentylbromide,
respectively. The reaction is regioselective but not regiospecific
and also produced minor amounts of N-mono- and P-bisalkylated
side products, which, because of their similar boiling points, are
difficult to separate by distillation. For the subsequent cyclocon-
densation (Scheme 1) ethereal solutions of 1a,b were added to
GAH, dissolved in diethyl ether. The mixtures became turbid
instantaneously, but clear again after some minutes. Small
amounts of sticky precipitates were formed, identified as mixture
of products and phosphine oxides. Most of the products 2a and
2b was still in the filtrate, and they were isolated by removal of
ether as viscous oily mixtures, each consisting of two pairs of dia-
stereoisomers. In 2a, with a branched P-alkyl group and the small
methyl group at nitrogen, the isomers with trans-configuration of
the substituents in 2- and 3-position predominated (trans:cis ca.
9:1 by 1H NMR integration) and allowed slow formation of a solid
and finally crystallization, whereas 2b, with neopentyl groups at
both phosphorus and nitrogen, displayed a much lower trans/cis-
isomer ratio (ca. 3:2) and remained oily. The 31P NMR spectra of
crude 2a and 2b also indicated small impurity signals (up to
10 mol%) in the region of R2PCH(OH)COOH species [7]. These are
probably the primary condensation products and also formed in
small equilibrium amounts by hydrolysis with traces of moisture,
partial hydrolysis and attack by reactive OH species. The intrinsi-
cally Brønstedt acidic group may catalyze such reactions.
Reactions of P-primary o-phosphanylanilines with GAH are
more complicated. Condensation of N-neopentyl-o-phosphanylan-
iline with GAH did not provide a defined product, either in a 1:1 or
1:2 M ratio. Only in the presence of p-toluidine (molar ratio 1:2:2)
was a precipitate with defined composition obtained at room tem-
perature (Scheme 2). According to the elemental analysis and NMR
data it is a toluidinium salt (or hydrogen-bonded adduct with
toluidine) of a phosphanylbis(amino acid) 3, containing the ben-
zazaphospholine and phosphanylglycine skeleton. Because of the
rapid formation of phosphanylmono- and bis(glycolates) [7] and
subsequent conversion with amines to phosphanylmono- or
bis(glycines) [4] we assume primary reaction with two molecules
of GAH, followed by cyclization and substitution of OH by the
tolylamino group, rather than a stepwise reaction with GAH via
an intermediate PH-functional benzazaphospholin-2-carboxylate.
Structural aspects. The structure elucidation of the new com-
pounds is based on conclusive solution NMR data and for 2a addi-
tionally on crystal structure analysis. Characteristic features of the
phosphanes 1a and 1b are the PH doublets with one-bond P–H
coupling constants of 214–217 Hz whereas the benzazaphospho-
line-2-carboxylic acids display typical doublets for the CH protons
and carbon nuclei (Table 1). Small 2JPH coupling constants indicate
trans-orientation of the P lone-pair and H-2, and therefore also
trans-orientation of the P-substituent and the COOH group at C-
2, which is strongly preferred in 2a with its branched P-alkyl group
and is the only form in the related 3-tert-butyl-1-neopentyl-ben-
zazaphospholine-2-carboxylic acid (2c). The primary alkyl group
at phosphorus in 2b, despite the remote steric bulk of the tBu-
group in b-position, causes lower diastereoselectivity in the
ring-closure step, with only moderate preference for trans- over
cis-orientation (6:4). In compound 3 only trans-orientation of the
P-substituent and 2-COOH is indicated, while the additional asym-
metric carbon atom of the P-substituent gives rise to two pairs of
diastereoisomers in a 5:4 ratio (by intensity of 31P NMR signals).
as demonstrated in more detail for acyclic
a-phosphanyl amino
acids [4]. Purification was possible by flash chromatography on sil-
ica gel using hexane/ethyl acetate (30% for 2a, 2% for 2b), but with
a considerable loss of product by partial decomposition on reactive
sites of silica gel in the column. In contrast to 1,3-benzazaphosph-
olines without the COOH group, which were reported to be hydro-
lytically stable [6c], the carboxylic acid derivatives are sensitive to
1
The JPC coupling constant is less indicative with respect to cis/
trans-orientation, but proves the formation of the PCHN structural
unit, and the chemical shift of this doublet allows us to distinguish
R2
R2
3a
1. Na (-1/2H2)
2. R2Br
4
P3
(HO)2CHCOOH
PH2
PH
2
2
1
CH COOH
(liq.NH3, Et2O)
(Et2O)
NH
R1
NH
R1
1
N
R1
1a,b
2a,b
Scheme 1. Synthesis of 1a,b and cyclocondensation with GAH to the heterocyclic phosphanyl amino acids 2a (R1 = Me, R2 = iPr) and 2b (R1, R2 = neopentyl).
H
COOH
N
*
OH
2 (HO)2CH-COOH
+ 2 p-toluidine
H2N
PH2
NH
P CH
NH
P
*
COOH
COOH
*
2
-2 H2O
H
N
Ha
Me3C
CMe3
Hb
Me3C
2 TolNH2
3
(A:B 5:4)
Scheme 2. Synthesis of the heterocyclic phosphanyl bis(amino acid) 3.

12
M. Ghalib et al. / Polyhedron 77 (2014) 10–16
Table 1
Characteristic NMR data of 2a, 2b and 3, and comparison with those of 2c (R1 = Np, R2 = tBu) [1a] and N-p-tolyl-diphenylphosphanylglycine (TDPPG) [4b].
Compound; solvent
1H NMR (PCH)
13C NMR (PCH)
31P NMR
d ppm, (J, isomer)
d ppm, (J, isomer)
d in ppm
2a (trans/cis ca. 9:1); [D8]THF
2b (trans/cis ca. 6:4); CD3OD
4.33 (2.3 Hz, E)
4.32 (9.8 Hz, Z)
4.49 (2.6 Hz, E)
4.79 (17.0 Hz, Z)
4.54 (2.7 Hz, E)
4.25 (sh)
4.27 (br s)
4.73 (2.7 Hz)
4.98 (3.0 Hz)
4.73 (br s, superimp. by NH)
67.06 (23.9 Hz, E)
n.d. (minor amount)
71.37 (19.9 Hz, E);
68.66 (26.5 Hz, Z)
67.39 (25.7 Hz)
68.44 (23.0 Hz)
68.52 (23.9 Hz)
57.33 (25.4 Hz)
57.39 (25.2 Hz)
58.31 (17.6 Hz)
1.8 (E); ꢀ6.7 (Z),
ꢀ17.3 (E); ꢀ18 (Z),
2c; CD2Cl2
3; [D8]THF
19.5
ꢀ4.54; ꢀ6.10
TDPPG; [D8]THF
0.22
between acyclic and cyclic PCHN (more downfield shifted)
moieties. For comparison the respective data of N-p-tolyl-diphe-
nylphosphanylglycine (TDPPG) [4b] are included in Table 1. The
phosphorus resonances were found in the region of tertiary phos-
phanes, display downfield shift with increasing branching of the P-
alkyl group in the related compounds 2b < 2a < 2c, as is typical for
phosphanes [8] and show the number of diastereoisomers.
More detailed structure information gives the crystal structure
compared to those in P-tert-butyl- benzazaphospholine-2-carbox-
ylic acids with N-neopentyl (2c) [1a] and N-(1-arylethyl) substitu-
ents (aryl = p-anisyl, phenyl) [1b]. The screening was carried out
with precatalysts, formed from pure trans-2a and the trans/cis-
mixture of 2b, respectively, with Ni(COD)2 in THF, using a batch
procedure and reaction monitoring by pressure/time registration
(Fig. 3). After pressurizing the autoclave was heated up, at first to
70 °C (within 15–20 min). Whereas 2c (Fig. 3, plot c) and the
two recently tested 1-(aryl)ethyl-substituted P-tert-butyl-ben-
zazaphospholine-2-carboxylic acids formed highly active catalysts
ꢀ
analysis of 2a (Figs. 1 and 2). Single crystals (space group P1) were
obtained from the dominating trans-diastereoisomers after flash
chromatography by slow diffusion of hexane into the solution of
2a in [D8]THF. The unit cell contains two molecules with 2S,3S-
and 2R,3R-configuration, respectively. The P–C3a bond is some-
what longer and the P–C2 bond considerably longer than in the
benzazaphospholes, and the bond lengths are typical for P–C single
bonds to sp2 and sp3-carbon, respectively. The N–C7A distance is
still short in contrast to N–C2 or N–C8 and, together with the
sum of C–N–C angles, indicates sp2 hybridization at nitrogen and
conjugation with the benzene
p-system. The trans-configuration
offers ideal conditions for formation of P^Oꢀ-chelate complexes,
as the P lone-pair is on the same side as the COOH group.
Tests for formation of ethylene oligomerization catalysts. The
coordination behaviour towards transition metals was not studied
during this preliminary investigation of benzazaphospholine-
2-carboxylic acids, but the in situ generation of nickel catalysts
for ethylene oligomerization was tested for 2a and 2b in order to
evaluate the impact of the substituents at phosphorus and nitrogen
Fig. 2. Packing of dimers of 2a in the crystal. Hydrogen bond: O2–H02 0.87(2),
H02ꢁ ꢁ ꢁO1#1 1.77(2), O2ꢁ ꢁ ꢁO1#1 2.6397(12) Å, O2–H02ꢁ ꢁ ꢁ177.9(19)°.
80
60
a(e2)
a(e1)
40
20
b(e4)
b(e3)
c
0
0
5
10
15
time (h)
Fig. 1. Structure of the 2S,3S enantiomer of racemic 2a in the crystal (ellipsoids
with 50% probability). Selected bond lengths (Å) and angles (°): P3–C3A 1.8159(12),
C2–P3 1.8974(12), P3–C10 1.8629(12), N1–C7A 1.3790(15), N1–C2 1.4458(15), N1–
C8 1.4550(15); C3A–P3–C2 89.08(5), N1–C2–P3 107.44(7), C7A–N1–C2 115.31(9);
Fig. 3. Pressure–time plots for batch polymerization of ethylene with a) 2a/
Ni(COD)2 (entries 1, 2), (b) 2b/Ni(COD)2 (entries 3, 4) in THF at 100 °C and (c)
comparison with the P-tert-butyl-substituted trans-2c/Ni(COD)2 in THF at 70 °C
[1a].
R
(C–N–C) 356.9(9), R (C–P–C) 292.76(5).

M. Ghalib et al. / Polyhedron 77 (2014) 10–16
13
Table 2
Oligomerization of ethylene with catalysts formed from 2a,ba.
d
N
Catalyst (lmol)
C2H4 g (mol), conv. g (%), TON
(mol/mol)
Polymer (g),b mp. (°C), D
Polymer: MNMR (g molꢀ1),
Me/C@C
a
-olefin (%),
Linear a-olefines C6, C8, C10,
e
(g/cm3)c
C
12, C14
1
2
3
4
2a (93), Ni(COD)2 (182)
2a (76), Ni(COD)2 (84)
2b (81), Ni(COD)2 (89)
2b (78), Ni(COD)2 (86)
16.4 (0.58), 8.8 (54), 3373
16.6 (0.59), 8.4 (51), 3940
16.9 (0.60), 15.8 (93), 6953
14.7 (0.53), 14.1 (96), 6444
11.6, 107–112, -
-, -, -
6.8, 108–114, 0.939
-, -, -
MNMR 600, 86, 1.4
n.d.
MNMR 510, 91, 1.3
n.d.
13, 23, 21, 17, 6
11, 12, 8, 5, 3
33, 28, 10, 2, 0.2
30, 29, 12, 4, 0.6
a
b
c
Batch oligo/polymerization of ethylene in THF, pstart of C2H4 at r.t. ca. 45 bar, begin of conversion at ca. 100 °C.
Solid residue after flash distillation of volatiles, treatment with MeOH/aqueous conc. HCl (1:1), washing with MeOH and drying in a vacuum.
Density of tablets of the solid (pressed at 10 kbar) determined by the sinking method in H2O/EtOH.
d
e
MNMR based on 1H NMR integrals of CH2 and CH3 vs. =CH protons in swollen polymers at 100 °C.
GC peak area% of a-olefins in the flash distillate (1-butene not indicated by partial evaporation).
in liquid ammonia, by cyclocondensation with glyoxylic acid
hydrate (GAH) in diethyl ether at room temperature. The primary
o-phosphanylanilines prefer reaction with two equivalents of
GAH. Cocondensation with p-toluidine in a 1:2:2 M ratio furnished
a defined product with benzazaphospholine-2-carboxylic skeleton
and N-tolylglycinyl group at phosphorus. A branched alkyl group at
phosphorus gives rise to preferred formation of trans-diastereoiso-
mers with the P lone-pair and 2-COOH group at the same side. This
is suitable for formation of chelate complexes and led in combina-
tion with Ni(COD)2 in THF to formation of efficient catalysts for
conversion of ethylene to mixtures of liquid oligomers and waxy
low molecular weight polymers. Both oligomers and polymers dis-
R#
O
R2
Ni
P
C
H
O
C
N
R1
Fig. 4. Assumed catalyst species (R# = H or growing chain, h = ethylene coordina-
tion site).
under these conditions (p/t-plots see Ref. [1b]), the 2a/Ni and 2b/Ni
precatalysts remained still inactive. Catalysts were formed only at
100 °C , and the conversion of ethylene was much slower than in
the catalysis by 2c/Ni and incomplete for the 2a/Ni catalyst
(Table 2). Repeated experiments showed good reproducibility of
the ethylene conversion and only marginal influence of excess
Ni(COD)2 used in one conversion with 2a/Ni (entry 1).
play a strongly preferred linear
a-olefin architecture, typical for
ethylene conversion by neutral P^O-NiR chelate catalysts. Bulky
N-substituents at the benzazaphospholine-2-carboxylate ligand
are essential for high ethylene conversion and bulky P-substituents
increase the conversion rate.
Low molecular weight waxy polymers and liquid oligomers
were formed. The selectivity of the 2a/Ni and 2b/Ni catalysts for
4. Experimental
strongly preferred formation of linear a-olefin oligo- and polymers
General. All operations were performed under argon atmo-
sphere using freshly distilled ketyl-dried solvents. N-Methyl- [9]
and N-neopentyl-2-phosphanylaniline [1a] were prepared by
reduction of the corresponding diethylphosphonoanilines with
LiAlH4. Other chemicals were purchased and used without further
treatment. NMR spectra were measured on a multinuclear FT-NMR
spectrometer ARX300 (Bruker) at 300.1 (1H), 75.5 (13C), and 121.5
(Table 2) is the same as for phosphanylacetate, -benzoate, -enolate
or -phenolate nickel catalysts. This suggests that the mechanism is
the same as demonstrated for the former types in more detail,
involving formation of organonickel(II) P^Oꢀ chelate complexes
(Fig. 4) and generation of NiH starting species in the initiation
and chain-terminating b-hydride elimination [3].
The slow and rather incomplete conversion of ethylene in the
presence of 2a/Ni indicates that the substituent at nitrogen has a
decisive impact on the performance of the benzazaphospholine-
2-carboxylate nickel catalysts. A sufficiently bulky N-substituent
is necessary to achieve high ethylene conversion, probably by ste-
rically hindered coordination of the amino group at nickel. The size
of the alkyl group at phosphorus is less important for the total con-
version but affects the activation temperature and the conversion
rate. As only the trans-diastereoisomers of 2b can form P^Oꢀ nickel
chelate complexes, the lower activity of 2b/Ni compared to 2c/Ni
and N-(1-arylethyl)-benzazaphospholine-2-carboxylate nickel cat-
alysts [1] can be attributed in part to the presence of cis-diastere-
oisomers of 2b. The very marked decrease of the reaction rate and
shorter polymer chains compared to the results of catalysis with
trans-2c/Ni, however, is accounted for also by interfering side
reactions, which are allowed directly by the primary, b-branched
P-neopentyl group or indirectly by the sterically possible occur-
rence of the cis-diastereoisomeric ligand with other coordination
properties.
(
31P) MHz. Chemical shifts (d) are given in ppm relative to Me4Si
(or characteristic solvent signals calibrated with Me4Si) and
H3PO4 (85%), respectively. Coupling constants refer to JHH in 1H
and JPC in 13C NMR data unless stated otherwise. 1H NMR spectra
of polymers were measured at 100 °C, using concentrated solutions
of the polyethylene samples prepared by swelling for 1 d at 120 °C
under argon in C6D5Br (p-CH, d = 7.23 as reference). HRMS mea-
surements were performed in the Department Chemie, Ludwigs-
Maximilians-Universität München, using a MS700 (Jeol) (DEI)
and in the Institut für Organische Chemie, Universität Göttingen,
using a micrOTOF spectrometer (ESI in MeOH). Elemental analyses
were carried out with CHN analyser MICRO CUBE from Elementar
vario under standard conditions. The equipment and general
procedure for the ligand screening in the batch oligo- and polymer-
ization of ethylene was as reported earlier.[10] GC analyses of
flash-distilled oligomers were carried out using a gas chromato-
graph Hewlett Packard 5890, column HP-5 (30 m) (crosslinked
5% PhMe silicone), 40–150 °C, 10 min isotherm, 4 °C/min; FID.
3. Conclusions
4.1. N-Methyl-2-isopropylphosphanylaniline (1a)
1,3-Benzazaphospholine-2-carboxylic acids can be synthesized
from N,P-disecondary o-phosphanylanilines, accessible via metala-
tion and subsequent alkylation of P-primary o-phosphanylanilines
Sodium (181 mg, 7.87 mmol) was dissolved in ca. 30 mL liquid
ammonia at ꢀ60 °C. Then, a solution of N-methyl-2-phosphanylan-
iline (1.06 g, 7.62 mmol) in diethyl ether (ca. 10 mL) was added at

14
M. Ghalib et al. / Polyhedron 77 (2014) 10–16
the same temperature. Within 10 min the dark blue solution turned
via blue-green to yellow. Addition of a solution of isopropylbromide
(0.75 mL, 7.99 mmol) in ether (ca. 10 mL) at ꢀ50 °C and removal of
the cooling led to a colorless suspension after some minutes when
NH3 started to vaporize. After reaching room temperature the pre-
cipitate was filtered off, washed twice with ether (10 mL), and the
solvent removed in vacuum from the filtrate. NMR monitoring dis-
played ca. 85 mol% of 1a, ca. 10 mol% N,P-diisopropyl-N-methyl-2-
phosphanylaniline and ca. 5 mol% of another side product
(d31P = ꢀ18). Distillation at 10ꢀ3 mbar/51–53 °C gave 740 mg color-
less oil in a first fraction and 250 mg in a second fraction (53–54 °C).
NMR spectra indicated only marginal shifts in the composition
(85:11:4 and 83:8:9 mol%, respectively). This slightly contaminated
1a (corrected yield 61%) was used for the synthesis of 2a. 1H NMR
a solution of glyoxylic acid hydrate (111 mg, 1.205 mmol) in the
same solvent (20 mL). After stirring overnight the precipitate was
filtered off, washed with ether and the solvent removed from the
filtrate to give 260 mg crude oily product, which solidified after
some time. NMR monitoring showed a strong signal for the
trans-diastereoisomer of 2a, a weak signal for cis-2a (trans:cis ca.
90:10% by 1H NMR integration), trace signals of acyclic PCH(OH)-
COOH species and trace signals of a PH and P-oxide impurity
(d31P = 1.85, ꢀ6.69, 0.89, 5.16, ꢀ37.51, 51.52 ppm; relative intensi-
ties: 74:9:6:4:4:3 int.%), corresponding to ca. 75% yield of trans/cis-
2a. The compound is sensitive to air oxidation and also to reactive
sites in silica gel. Slow column chromatography led to extensive
decomposition but rapid column chromatography (within ca.
15 min) of an aliquot on silica gel using hexane/30% ethyl acetate
furnished ca. 50 mg pure trans-2a. 1H NMR ([D8]THF): d = 0.93
3
(CDCl3): d = 1.07 (dd, JPH = 25.7, 3J = 7.2 Hz, 3H, MeA), 1.12 (dd,
3JPH = 21.9, 3J = 6.8 Hz, 3H, MeB), 2.20 (m, 1H, PCH), 2.86 (s, 3H,
(dd, JPH = 14.2, 3J = 7.0 Hz, 3H, MeA), 1.07 (dd, JPH = 15.1,
3
3
1
3
NMe), 3.82 (dd, JPH = 216.8, 3J = 5.7 Hz, 1H, PH), 4.53 (br s, 1H,
3J = 6.8 Hz, 3H, MeB), 1.69 (sept d, 3J = 7, JPH = 2.8 Hz, 1H, PCH),
4
2
NH), 6.59 (br dd, 3J = 8.3, JPH = 3.8 Hz, 1H, H-6), 6.66 (br t, 3J = 7.5,
2.91 (s, 3H, NMe), 4.33 (d, JPH = 2.3 Hz, 1H, PCHtrans to lp), 6.41 (br
6.8 Hz, 1H, H-4), 7.26 (ddd, 3J = 8.3, 7.3, 4J = 1.5 Hz, 1H, H-5), 7.36
(td, 3J = 7.2, 4J = 1.5 Hz, 1H, H-3). 13C{1H} NMR (CDCl3): d = 21.99
(d, 2J = 18.6 Hz, MeA), 22.94 (d, 2J = 10.6 Hz, MeB), 23.82 (d,
1J = 5.3 Hz, PCH), 31.17 (s, NMe), 110.55 (br s, CH-6), 117.86 (d,
1J = 5.3 Hz, Cq-2), 117.91 (partly superimposed d, 3J = 4.0 Hz, CH-
4), 131.86 (CH-5), 138.54 (d, 2J = 8.0 Hz, CH-3), 153.31 (d,
2J = 13.3 Hz, Cq-1); for data in C6D6 see Fig. S1. 31P{1H} NMR (CDCl3):
d = ꢀ47.7 ppm. HRMS (DEI): C10H16NP (181.22), calcd. for [M]+
181.1020; found: 181.1011.
d, 3J = 8.0 Hz, 1H, H-7), 6.57 (tdd, 3J = 7.2, JPH = 2.3, 4J = 0.8 Hz,
4
1H, H-5), 7.14 (br td, 3J = 8.0, 4J ꢂ 1.5 Hz, 1H, H-6), 7.22 (ddd,
3
3J = 6.8, JPH = 5.3, 4J ꢂ 1.2 Hz, 1H, H-4), 10.3 (vbr s, 1H, COOH).
13C{1H} NMR ([D8]THF): d = 18.18 (d, 2J = 15.9 Hz, MeA), 18.92 (d,
2J = 18.8 Hz, MeB), 27.73 (d, 1J = 18.6 Hz, PCH), 34.27 (s, NMe),
67.06 (d, 1J = 23.9 Hz, PCHN), 107.34 (CH-7), 116.94 (d,
4J = 8.0 Hz, CH-6), 123.26 (d, 1J = 11.9 Hz, Cq-3a), 131.08 (CH-5),
131.56 (d, 2J = 22.6 Hz, 4-CH), 155.32 (Cq-7a), 172.98 (d,
2J = 13.3 Hz, COOH); for data in CD3OD see Fig. S3. 31P{1H} NMR:
d = 1.8 ([D8]THF), 4.7 (CD3OD) ppm. HRMS (DEI): C12H16NO2P
(237.23), calcd. for [M]+ 237.0919; found: 237.0907. Characteristic
4.2. N-Neopentyl-2-neopentylphosphanylaniline (1b)
3
signals of cis-2a: 1H NMR ([D8]THF): d = 0.81 (dd, JPH = 11.0,
A
solution of N-neopentyl-2-phosphanylaniline (1.94 g,
3J = 7.2 Hz, MeA; MeB and CH superimposed), 2.81 (s, NMe), 4.32
2
9.94 mmol) in diethyl ether (ca. 10 mL) was added at ꢀ60 °C to a
solution of sodium (251 mg, 10.9 mmol) in ca. 50 mL liquid ammo-
nia. After the color had turned from dark blue to yellow, a solution
of neopentylbromide (1.37 mL, 10.9 mmol) in ether (ca. 10 mL)
was added at ꢀ55 °C. The reaction started only during evaporation
of NH3 and was slow. A colorless solution and precipitate was
formed after ca. 3 h at room temperature. The precipitate was then
filtered off and washed twice with ether (10 mL). The solvent was
removed in a vacuum. NMR monitoring of the crude product
(2.49 g) displayed 86 mol% of 1b (corrected yield 81%) along with
14 mol% unconverted N-neopentyl-2-phosphinoaniline, which
was removed by vacuum distillation into a Schlenk cooling trap.
The residue was then distilled at 10ꢀ2 mbar/90 °C (bath) to give a
viscous colorless oil (95% 1b). 1H NMR (CDCl3): d = 0.93 (s, 9H,
(d, JPH = 9.8 Hz, PCHcis to lp), aryl-H superimposed; characteristic
PCH signals of PCH(OH)COOH species in the crude product: 1H
2
NMR (CDCl3): d = 4.56 (d, JPH = 5.3 Hz, PCHtrans
lp), 4.72 d,
to
2JPH = 8.7 Hz, PCHcis
lp); 31P{1H} NMR: d = ꢀ6.7 ([D8]THF), ꢀ4.3
to
(CD3OD) ppm.
4.4. 1-Neopentyl-3-neopentyl-2,3-dihydro-1,3-benzazaphosphole-2-
carboxylic acid (2b)
An ethereal solution (5 mL) of 1b (120 mg, ca. 0.45 mmol) was
added at room temperature into a solution of glyoxylic acid
hydrate (42 mg, 0.46 mmol) in the same solvent (20 mL). After stir-
ring overnight the precipitate was filtered off using Celite and
washed with ether. Removal of the solvent gave 125 mg (85 %) oily
crude product. Rapid column chromatography on silica gel using
hexane/ethyl acetate (2 %) furnished a viscous oil. NMR monitoring
showed the signals for 2b, trans/cis-ratio in the major fraction ca.
58:42% (by 1H NMR integration), in a small second fraction ca.
80:20%. trans-2b: 1H NMR (CD3OD): d = 1.01 (s, 9H, NCCMe3),
1.08 (br s, 9H, PCCMe3), 1.32 (br d, 2J = 14.4 Hz, 1H, PCHA), 2.02
4
NCCMe3), 1.08 (dd, JPH = 0.8 Hz, 9H, PCCMe3), 1.63 (ddd,
2
2J = 13.6, 3J = 9.2, JPH = 2.1 Hz, 1H, PCHA), 2.12 (ddd, 2J = 13.6,
2
3J = 6.8, JPH = 6.0 Hz, 1H, PCHB), 2.80 (dd, 2J = 11.7, 3J = 6.4 Hz, 1H,
NCHA), 2.86 (dd, 2J = 11.7, 3J = 6.4 Hz, 1H, NCHB), 3.99 (ddd,
1JPH = 214.6, 3J = 9.2, 7.2 Hz, 1H, PH), 4.77 (vbr q, 3J = 5.7 Hz, 1H,
4
NH), 6.64 (br dd, 3J = 8.3, JPH = 3.8 Hz, 1H, H-6), 6.81 (br t,
3J = 7.5, 7.2 Hz, 1H, H-4), 7.31 (ddd, 3J = 8.3, 7.2, 4J = 1.5 Hz, 1H, H-
5), 7.56 (td, 3J = 7.2, 4J = 1.5 Hz, 1H, H-3). 13C{1H} NMR (C6D6):
d = 28.40 (s, CMe3), 31.11 (d, 3J = 9.3 Hz, CMe3), 31.72 (d,
2J = 10.6 Hz, CMe3), 32.41 (s, CMe3), 38.10 (d, 1J = 10.6 Hz, NCH2),
56.56 (s, NCH2), 111.14 (d, 3J = 2.7 Hz, CH-6), 118.90 (d,
1J = 6.6 Hz, Cq-2), 118.04 (d, 3J = 5.3 Hz, CH-4), 131.60 (CH-5),
137.79 (d, 2J = 8.0 Hz, CH-3), 152.45 (d, 2J = 13.3 Hz, Cq-1). 31P{1H}
NMR (C6D6): d = ꢀ86.8 ppm. HRMS (ESI): C16H28NP (265.37), calcd.
for [M+H]+ 266.2032; found: 266.2042.
(br dd, 2J = 14.4, JPH = 4.3 Hz, 1H, PCHB), 2.66 (br d, 2J = 15.1 Hz,
2
1H, NCHA), 3.45 (br d, 2J = 15.1 Hz, 1H, NCHB), 4.49 (d, 2JPH = 2.6 Hz,
1H, PCHtrans
lp), 6.59 (superimposed br d, 3J = 8.3 Hz, 1H, H-7),
to
4
6.63 (tdd, 3J = 8.3, 7.2, JPH = 2.6, 4J = 0.8 Hz, 1H, H-5), 7.16 (br td,
3J = 8.3, 7.2, 4J ꢂ 1.1 Hz, 1H, H-6), 7.27 (ddd, 3J = 7.2, JPH = 6.4,
3
4J ꢂ 1.1 Hz, 1H, H-4); COOH probably below solvent-OH). 13C{1H}
NMR (CD3OD): d = 28.76 (s, CMe3), 31.31 (d, 3J = 8.0 Hz, CMe3),
32.31 (d, 2J = 11.9 Hz, CMe3), 35.99 (s, CMe3), 46.80 (d,
1J = 23.9 Hz, PCH2), 60.50 (s, NCH2), 71.37 (d, 1J = 19.9 Hz, PCHN),
109.17 (CH-7), 118.14 (d, 4J = 9.3 Hz, CH-6), 125.38 (d, 1J = 8.6 Hz,
Cq-3a), 131.16 (CH-5), 131.68 (d, 2J = 25.2 Hz, 4-CH), 155.97 (Cq-
7a), 176.14 (d, 2J = 14.6 Hz, COOH). 31P{1H} NMR (CD3OD):
d = ꢀ17.3 ppm. cis-2b: 1H NMR (CD3OD): d = 0.97 (s, 9H, NCCMe3),
1.06 (br s, 9H, PCCMe3), 1.46, 1.47 (2 dd, 2J = 14.7, 2JPH = 5.1 Hz, 1H,
4.3. 1-Methyl-3-isopropyl-2,3-dihydro-1,3-benzazaphosphole-2-
carboxylic acid (2a)
A sample of the first fraction (219 mg, ca. 1.21 mmol 2a), dis-
solved in diethyl ether (5 mL) was added at room temperature into
PCHA), 1.85 (br dd, 2J = 14.7, JPH = 4.3 Hz, 1H, PCHB), 2.79 (br d,
2

M. Ghalib et al. / Polyhedron 77 (2014) 10–16
15
2J = 15.5 Hz, 1H, NCHA), 3.40 (br d, 2J = 15.5 Hz, 1H, NCHB), 4.79 (d,
2JPH = 17.0 Hz, PCHcis lp), 6.49 (br d, 3J = 8.3 Hz, 1H, H-7), 6.60
and slow reaction already at 90 °C). The reaction was allowed to
run overnight (ca. 15 h) with pressure registration. After cooling
to ca. 20 °C unconverted ethylene was released. Butenes and small
amounts of hexenes and THF were condensed in a cooling trap
(ꢀ20 °C). The remaining product was transferred to a flask, and
volatiles were flash distilled (80–100 °C/1 Torr) into a cooling trap
(ꢀ196 °C). Residual polymer waxes were stirred for 1 d with meth-
anol/hydrochloric acid (1:1), washed with methanol and dried in
vacuum. Conversion, characteristic data of polymers and composi-
tion of flash distilled oligomers are given in Table 2.
to
(superimposed tdd, 1H, H-5), 7.05 (br td, 3J = 8.3, 7.3, 4J ꢂ 1.5 Hz,
1H, H-6), 7.11 (superimposed br t, 1H, H-4); COOH probably below
solvent-OH). 13C{1H} NMR (CD3OD): d = 29.08, 29.12 (2s, CMe3),
31.27 (d, 3J = 9.3 Hz, CMe3), ca. 31.3 (superimposed d, CMe3),
35.45 (s, CMe3), 45.31 (d, 1J = 29.2 Hz, PCH2), 59.67 (s, NCH2),
68.66 (d, 1J = 26.5 Hz, PCHN), 108.74 (CH-7), 118.47 (d,
4J = 6.6 Hz, CH-6), 125.83 (d, 1J = 8.0 Hz, Cq-3a), 129.86 (d,
2J = 18.6 Hz, 4-CH), 130.21 (CH-5), 154.96 (d, 2J = 4.0 Hz, Cq-7a),
172.81 (s, COOH). 31P{1H} NMR (CD3OD): d = ꢀ17.9, ꢀ18.1 ppm.
(The occurrence of two close, similar intense signals for P, PCHA
and CMe3 of the N-Np group hints at hindered rotation in the cis-
diastereoisomers and slightly different signals of these nuclei if
the neopentyl groups are directed to the same or opposite sides
of the ring.) HRMS of trans/cis-2b (ESI): C18H28NO2P (321.39), calcd.
for [M+H]+ 322.1930; found: 322.1931.
4.7. Crystal structure analysis of 2a
ꢀ
Crystal data: Triclinic, space group P1, a = 5.2089(4), b = 8.8838(4),
c = 13.5003(7) Å,
a
= 84.168(4),
b = 89.312(5),
c = 81.657(5)°,
V = 614.91(6) Å3, Z = 2, Dx = 1.281 Mg/m3,
l
= 1.870 mmꢀ1, F(000) =
252. A colourless tablet 0.20 ꢃ 0.15 ꢃ 0.08 mm was mounted on a
glass fibre in inert oil. A total of 25388 data (2547 unique, Rint 0.037)
were recorded at 100 K on an Oxford Diffraction Nova E diffractome-
4.5. 1-Neopentyl-3-(N-p-tolyl)glycinyl-2,3-dihydro-1,
3-benzazaphosphole-2-carboxylic acid (3)
ter using mirror-focussed Cu Ka radiation (k = 1.54184 Å) in the
range h = 3.3–75.7° (99.8% completeness to h = 75°). Absorption
corrections were semi-empirical from equivalents. The structure was
refined by full-matrix least-squares on F2 [11]. The OH hydrogen was
refined freely; other hydrogen atoms were included using a riding
model or rigid methyl groups. The final wR2 was 0.077 for 401
A solution of glyoxylic acid hydrate (500 mg, 5.43 mmol) in
diethyl ether (10 mL) was added slowly to a solution of N-neopen-
tyl-2-phosphanylaniline (53 mg, 2.73 mmol) and p-toluidine
(580 mg, 5.41 mmol) in diethyl ether (25 mL). After stirring for
24 h (to complete the conversion) the white precipitate was col-
lected, washed with small amounts of ether and dried in vacuum
to yield 0.77 g (68%) white powder. 1H NMR ([D8]THF, Ref. THF):
d = 0.84 (s, CMe3A) and 0.94 (s, CMe3B; A:B = 42:56%), 1.97 (s, p-
MeB), 2.03, 2.04, 2.05 (3s superimposed), 2.24 (s, p-MeA), 2.62 (d,
2J ꢂ 16 Hz, HAa), 2.67 (d, 2J ꢂ 15 Hz, HBa), 3.24–3.31 (m, CH2),
3.32 (d, 2J ꢂ 16 Hz, HAb), 3.39 (d, 2J = 15.1 Hz, HBb), 4.25 (sh) and
parameters and all reflections, with R1 (I > 2
r (I)) 0.029; S 1.05, max.
Dq
0.58 e Åꢀ3. Complete crystallographic data for 2a have been
deposited with the Cambridge Crystallographic Data Centre, CCDC
976535. Copies of the data can be obtained, free of charge, on
application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, (fax:
+44 (0)1223 336033 or e-mail: deposit@ccdc.cam.ac.uk).
2
2
4.27 (br s, PCH), 4.73 (d, JPC = 2.7 Hz, PCHA), 4.98 (d, JPC = 3.0 Hz,
PCHB), 5.06, 5.10 (br, sbr, NH and/or OH), 6.04 (m, 2 o-CH), 6.30–
6.77 (m, o- und m-CH), 7.00–7.23 (m, 4H, aryl), 7.78 (s, 1 HA, OH
oder NHAmid). 13C{1H} NMR and DEPT-135 ([D8]THF, ref. THF):
d = 20.20 (s, p-MeA), 20.31 (s, p-MeB), 28.35 (s, CMe3A), 28.42 (s,
CMe3B), 35.06 (s, CMe3), 57.33 (br d, 1J = 25.4 Hz, PCHB), 57.39 (br
d, 1J = 25.2 Hz, PCHA), 60.46 (s, NCH2A), 60.53 (s, NCH2B), 68.44 (d,
1J = 23.0 Hz, PCHAring), 68.52 (d, 1J = 23.9 Hz, PCHBring), 108.60 (s,
7-CHB), 108.95 (s, 7-CHA), 114.34 (2 superimposed s, o-CH),
Acknowledgments
Financial support by the Deutsche Forschungsgemeinschaft
(DFG) is gratefully acknowledged (HE1997/14-1). Dr. habil.
D.G.Yakhvarov and O.S.Fomina thank the Russian Foundation for
Basic Research (RFBR) and Tatarstan Academy of Sciences (research
project No. 12-03-97067-r_povolje_a) for support of this research
activity. We thank Dr. M. K. Kindermann, G. Thede and M. Steinich
for numerous NMR spectra, Prof. Dr. H.-C. Böttcher and B. Breiten-
stein (Department Chemie, Ludwig-Maximilians-Universität
München) for HRMS (DEI) and Dr. H. Frauendorf and G. Sommer-
Udvarnoki (Georg-August-Universität Göttingen, Institut für Organ-
ische und Biomolekulare Chemie) for HRMS (ESI) measurements.
114.89 (s, o-CHB
A), 117.29 (d, 3J = 8.7 Hz, 5-CH), 117.59 (d,
or
3J = 8.3 Hz, 5-CH), 120.10 (d, 1J = 13.7 Hz, 3-CqA), 120.40 (d,
1J = 12.0 Hz, 3-CqB), 122.15 (s, o-CHA), 125.65 (s, p-CqA), 127.04,
127.07 (2s, p-CqB), 129.54 (s, m-CHB
A), 129.76, 129.80 (2s, m-
or
CHB), 130.37 (s, m-CHA), 131.49 (s, 6-CHB), 131.54 (s, 6-CHA),
132.69 (d, 2J = 24.2 Hz, 4-CH), 133.32 (d, 2J = 23.9 Hz, 4-CH),
3
3
Appendix A. Supplementary data
146.36 (d, J ꢂ 7.3 Hz, i0-CqA), 146.53 (d, J ꢂ 7 Hz, i0-CqB), 151.35
(s, 7a-CqA), 156.86 (s, 7a-CqB), 172.28 (d, 2J = 12.0 Hz, COOHA),
172.50 (d, 2J = 13.3 Hz, COOHA), 172.72 (d, 2J = 12.0 Hz, COOHB).
31P{1H} NMR ([D8]THF): d = ꢀ4.54 ppm (A), ꢀ6.10 ppm (B), signal
intensity ratio A:B = 4:5 (43:57%). In solution slow decomposition
occurs, indicated by small signals at ꢀ21.9, ꢀ24.2, ꢀ24.9, ꢀ41.7
and ꢀ129.0 ppm after a long measuring time for 13C nuclei. Analy-
sis calcd. for C29H36N3O4P (521.59): C 66.78, H 6.96, N 8.06; found:
C 66.48, H 6.43, N 7.65.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.poly.2014.03.046.
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