3-Phenylphosphaprolines – Synthesis, structure and properties of heterocyclic α-phosphanyl amino acids

Article abstract of DOI:10.1016/j.poly.2017.04.014

“Phenylphosphaprolines”, containing trivalent phosphorus within the five-membered ring of proline, were synthesized by cyclocondensation of 2-phenylphosphanyl ethylamines 1a,b with equimolar amounts of glyoxylic acid hydrate (GAH) or pyruvic acid in diethyl ether or 1,4-dioxane. Reaction monitoring revealed primary formation of acyclic intermediates that then converted more (1a) or less (1b) rapidly to the phosphanyl amino acids cis/trans-2a,b or cis/trans-4a,b. Ammonium-ethylphosphonium-bis(glycolate) impurities, e.g. 3b, were formed when an excess of GAH was applied. The conversion of 1a with phenylformic acid via the acyclic precursors 5a and 6a to the heterocyclic product cis/trans-7a was very slow, whereas heating of the mixture in 1,4-dioxane proceeded with decarboxylation to cis/trans-8a. The structures and diastereoisomer ratios of all new compounds were determined by ¹H, ³¹P and ¹³C solution NMR spectra. The cis/trans-ratio of 2a depends on the synthetic route, i.e. addition of the phosphanylethyl amine 1a to GAH (acidic medium) or of GAH to 1a (basic medium). Furthermore, this ratio changed slowly during storage of the solution of 2a in CD₃OD or methanol, indicating ring-opening ring-closure reactions and lower kinetic stability than for proline. XRD analyses established the structures of trans-2a and likewise of trans-4a and trans-8a, which from concentrated solutions crystallized in pure form.

Full text of DOI:10.1016/j.poly.2017.04.014

Polyhedron 130 (2017) 195–204
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
3-Phenylphosphaprolines – Synthesis, structure and properties of
heterocyclic a-phosphanyl amino acids
Kaleswara R. Basvani a, Markus K. Kindermann a, Holm Frauendorf b, Carola Schulzke a, Peter G. Jones c,
Joachim W. Heinicke a,
⇑
a Institut für Biochemie, Ernst-Moritz-Arndt-Universität Greifswald, Felix-Hausdorff-Str. 4, D-17489 Greifswald, Germany
b Institut für Organische und Biomolekulare Chemie, Zentrale Analytik/Massenspektrometrie, Georg-August-Universität Göttingen, Tammannstr. 2, D-37077 Göttingen, Germany
c Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Postfach 3329, D-38023 Braunschweig, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
‘‘Phenylphosphaprolines”, containing trivalent phosphorus within the five-membered ring of proline,
were synthesized by cyclocondensation of 2-phenylphosphanyl ethylamines 1a,b with equimolar
amounts of glyoxylic acid hydrate (GAH) or pyruvic acid in diethyl ether or 1,4-dioxane. Reaction mon-
itoring revealed primary formation of acyclic intermediates that then converted more (1a) or less (1b)
rapidly to the phosphanyl amino acids cis/trans-2a,b or cis/trans-4a,b. Ammonium-ethylphosphonium-
bis(glycolate) impurities, e.g. 3b, were formed when an excess of GAH was applied. The conversion of
1a with phenylformic acid via the acyclic precursors 5a and 6a to the heterocyclic product cis/trans-7a
was very slow, whereas heating of the mixture in 1,4-dioxane proceeded with decarboxylation to cis/
trans-8a. The structures and diastereoisomer ratios of all new compounds were determined by 1H, 31P
and 13C solution NMR spectra. The cis/trans-ratio of 2a depends on the synthetic route, i.e. addition of
the phosphanylethyl amine 1a to GAH (acidic medium) or of GAH to 1a (basic medium). Furthermore,
this ratio changed slowly during storage of the solution of 2a in CD3OD or methanol, indicating ring-
opening ring-closure reactions and lower kinetic stability than for proline. XRD analyses established
the structures of trans-2a and likewise of trans-4a and trans-8a, which from concentrated solutions crys-
tallized in pure form.
Received 9 March 2017
Accepted 18 April 2017
Available online 25 April 2017
Dedicated to Prof. Dr. Klaus Jurkschat on the
occasion of his 65 birthday
Keywords:
Phosphanes
Amino acids
P,N heterocycles
Structures
Isomerization
Catalyst ligand
Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction
glycines A (Chart 1), easily accessible by one-pot three-component
reaction of diphenylphosphane and primary amines with glyoxylic
Synthetic amino acids have attracted considerable attention
and have been used for various purposes in medicinal chemistry
and biochemistry or as substrates or organocatalysts in organic
chemistry [1]. Introduction of a N-phosphanylmethyl group into
acid hydrate in a suitable solvent such as diethyl ether at room
temperature [6]. A shortcoming is their kinetic lability in solution
which hampered reactivity studies. Well-defined transition metal
phosphanyl glycin(at)e complexes have not yet been isolated
except for few rather labile LM(CO)5 (M = W, Mo, Cr) species
[6b], but efficient ethylene oligomerization nickel catalysts were
formed from A and Ni(COD)2 in THF or toluene on slow heating
in the presence of ethylene [6]. Oligomer analysis proved the same
selectivity as phosphanyl acetate nickel chelate catalysts [7] and
suggest similar catalyst structures. For further investigations of
amino acids [2,3], use of BOC/FMOC-protected b- to e-Ph2P(S)-sub-
stituted amino acids and finally peptide libraries [4,5] have made
possible the generation of water-soluble or chiral amino-acid-
based transition metal complexes or catalysts. The goal of our stud-
ies was to find facile routes to amino acids bearing a phosphanyl
group at the
a
-carbon atom. Compounds with RR0P-CH(NHR00)-
COOH substructure might allow formation of chelate or hybrid
complexes with transition metals or introduction of protection
groups at the amino group for use in the preparation of phos-
phane-functionalized peptides or bioconjugates. Recently we
reported on a variety of N-monosubstituted diphenylphosphanyl
a-phosphanyl amino acids kinetically less labile representatives
would be desirable. Stabilization may be achieved in cyclic
moieties. P-Alkyl derivatives of recently studied phosphanylbis
(N-arylglycines)
B underwent spontaneous lactamization to
3-alkyl-1,3-azaphospholidine-5-one-2-carboxylic acids C, which
are more stable in solution [6e]. Previous reports on 1,3-
azaphospholidine-5-ones and 1,3-azaphospholidines, lacking
a
⇑
Corresponding author.
E-mail address: heinicke@uni-greifswald.de (J.W. Heinicke).
COOH or similar strong acidic substituent [8,9], gave no
a
http://dx.doi.org/10.1016/j.poly.2017.04.014
0277-5387/Ó 2017 Elsevier Ltd. All rights reserved.

196
K.R. Basvani et al. / Polyhedron 130 (2017) 195–204
HOOC
intermediates 2I⁄⁄a,b was established by characteristic proton
HOOC
pTol
and 13C doublets of the PCH(OH) fragment, e.g. for the 2I⁄⁄
a
R
COOH
N
N
*
*
*
*
H
diastereoisomers at d1H = 4.51, 4.53 (2JPH each ꢀ7 Hz) and
Ph2P
*
R'
P
*
R'
P
*
13C = 74.7 (1J = 25.2 Hz), 74.3 (1J ꢀ20 Hz). These values are typical
COOH
HN
R
d
O
Tol
R
NH
p
NH
of phosphanylglycolates [6a,c,d,11] and downfield from those of
cis/trans-2a. This suggests that the reactive intermediates
2I⁄⁄a,b are diastereoisomeric 2-(phenylphosphanyl)ethylammonium
glycolates. This is further supported by transient NCH2 and PCH2
doublets, which clearly differ from the downfield shifted ring
NCH2 and PCH2 signals of cis/trans-2a and disappear within a day
while the latter increase (Fig. S2). Finally, it should be mentioned
that the formation of 2b from the N-secondary amine 1b, either
still in ethereal suspension, in the NMR solvent or during
crystallization from methanol, is in clear contrast to the three-
component reactions of Ph2PH with GAH and N-secondary
amines. The latter stop at the stage of the organoammonium
phosphanylglycolates [6]. This different behavior might be
attributed to higher stability of the five-membered heterocyclic
structure. To emphasize the structural similarity to proline, the
new 1,3-azaphospholidine-2-carboxylic acids are also named
‘‘3-phenylphosphaprolines”. The NMR spectra provided no evi-
dence for alternative six-membered lactams with a P-CH(OH)-C
(O)-N substructure, even not as minor side products.
A (R = (hetero)aryl,
B (R = p-C6H4C(O)Me,
C (R' = Cy, iBu)
alkyl [zwitterionic])
R' = Ph)
Chart 1. Phosphanyl glycines A [6a–d] and B [6e] and 1,3-azaphospholidine-5-one-
2-carboxylic acids C [6e].
indications of kinetic lability in solution. This prompted us to
extend our studies to the hitherto unknown 1,3-azaphospho-
lidine-2-carboxylic acids, to examine their structure, properties
and stability in solution and to perform preliminary tests as cata-
lyst ligand.
2. Results and discussion
2.1. Synthesis and isomerization
For the preparation of the envisaged heterocyclic a-phosphanyl
amino acids we studied the reactions of the N-primary and N-sec-
ondary 2-phosphanylethylamines 1a and 1b [9,10] with glyoxylic
acid hydrate (GAH) and with pyruvic acid, furthermore the reac-
tion of 1a with benzoylformic acid. Addition of ether solutions of
1a or 1b at room temperature to the solution of the keto carboxylic
acid led almost immediately to a white precipitate, as did the addi-
tions in reverse order. NMR reaction monitoring of the precipitates,
sampled after a minute, indicated in CD3OD solution the signals of
the heterocyclic products but also of reactive intermediates 2I⁄a,b
(each one signal set) and 2I⁄⁄a,b (each two signal sets). The signals
of the intermediates disappeared after some time (Scheme 1). Thus
the sample obtained from 1a and GAH displayed resonances of cis/
trans-2a, of P-tertiary phosphanyl intermediate 2I⁄⁄a and not fully
identified, partly P-deuterated P-secondary phosphane species
2I⁄a, integral ratio ca. 60:30:10, after 2 h ca. 80:12:8. After a week
only trace signals of the 2I⁄a intermediate were observable besides
the signals of cis/trans-2a. R. . .X of 2I⁄a might be H. . .OOC–CH(OH)2
but also CH(OH)-COO. The product cis/trans-2a displayed
partial H/D exchange at the C–H-acidic CH-2 site in CD3OD solution
(Fig. S1, supplementary data). The sample prepared from 1b and
GAH in diethyl ether revealed an analogous course of the cyclocon-
densation reaction. The nature of the more rapidly cyclizing
It is important to avoid an excess of GAH, since this causes con-
taminations. Reaction of 1b with two equivalents of GAH led to
considerable amounts of by-products with
d
31P = 40.2 and
40.7 ppm (CD3OD), identified by characteristic 13C NMR and HRMS
data as rac/meso-diastereoisomers of the ammonium-ethylphos-
phonium-bis(glycolate) 3b. Compounds of this type have been
obtained recently from secondary phosphanes, diethylamine and
two equivalents of GAH in ether [11]. P-Oxide species, formed by
unintentional air contact, were excluded. Direct exposure of cis/
trans-2b to air led to products with other 31P signals (Supporting
Information).
The cyclocondensation reactions of the phosphanylethylamines
1a,b with pyruvic acid in diethyl ether are slower, particularly for
the N-secondary 1b. 31P NMR monitoring of CDCl3 or CD3OD solu-
tions of the precipitate, formed at r. t. with 1b within 20 min, dis-
played signals of P-primary and P-tertiary phosphane
intermediates 4I⁄b and 4I⁄⁄b, which diminished within some hours
and finally disappeared in favor of the signals of cis/trans-4b
(Figs. S3 and S4). Minor transient PhPH/D 31P and MeC(O) proton
signals in CD3OD indicate salt formation (4I⁄b), while the stronger
intermediate phosphorus resonances in the range d = ꢁ6.6 to
ꢁ0.1 ppm suggest addition of PH at the keto group to 4I⁄⁄b as
the key step in the cyclocondensation. Trace amounts of phosphine
oxide by-products might be associated with rearrangements reac-
tions, in analogy to R2P-CHR0(OH) ? R2P(O)CH2R0 conversions,
reported for addition products of secondary phosphanes with aro-
matic aldehydes in HCl-acidic methanolic solution [12,13]. For
reactions carried out in CD3OD, the amount of the phosphine oxi-
des indeed became larger and particularly strong upon heating.
The cyclocondensation of the phosphanylethylamines with pyruvic
acid was accelerated by heating the mixtures in 1,4-dioxane
Scheme 1. Synthesis of cis/trans-2a,b and detection of the phosphonium-bis
(glycolates) rac/meso-3b by reaction with excess GAH.
Scheme 2. Synthesis of 4a,b.

K.R. Basvani et al. / Polyhedron 130 (2017) 195–204
197
(ca. 1 h, 90 °C). This led for 1a and 1b to good yields of 4a and 4b,
respectively (Scheme 2).
The keto group of benzoylformic acid is considerably less reac-
tive than that of pyruvic acid, so that at room temperature in
diethyl ether, even with 1a, after rapid precipitation of salts, the
further reaction steps were much slower. 31P{1H} and 13C{1H}
NMR reaction monitoring indicated the phenylphosphanyl-ethy-
lammonium benzoylformiate 5a as the major, the phosphanyl gly-
colate 6a as the minor primary product and only slow conversion
of both, 5a and 6a, to the phosphanyl amino acid cis/trans-7a
(Scheme 3, Fig. S5). Comparison of integral ratios of the PCH2,
NCH2 and PCH signals, which possess characteristic 13C chemical
shifts and P-C coupling constants (Fig. S6), allowed signal assign-
ment and unambiguous identification of these compounds. Indica-
tions of ring formation to cis/trans-7a are provided by the
Cq-doublets at d = 83.72 and 84.06 ppm with one-bond P-C cou-
plings of 30.5–31.8 Hz, close to those of the other phosphaprolines
(1JPC = 31.8–37.6 Hz), and the downfield shifted NCH2 signals with
small two-bond P-C couplings, likewise very similar to the values
of the other 1,3-azaphospholidin-2-carboxylic acids. The acyclic
diastereoisomers of 6a exhibit superimposed PCqO doublets
(d = 83.2, sh 83.6 ppm) with smaller P-C coupling constants
1JPC = 20–26 Hz, which are typical of phosphanylglycolates [6a,c,
d,11]. The NCH2 doublets of 6a appear upfield from those of 7a
and with larger two-bond P-C couplings. The NCH2 and PCH2
doublet signals of 5a were found close to those of the pivalate
salt (1apiv), synthesized for comparison (Supporting information).
The carbonyl signals at d = 196.92 and 173.77 ppm are consistent
with the phenylformate anion of 5a, whereas carbon signals of
imines or iminium salts (d = 150–164 ppm [14]), assumed as inter-
mediates in previous studies of non-functional azaphospholidines
[9], were undetectable. Since the solution of the initial precipitate
in CD3OD, even after a week at r. t., still displayed significant sig-
nals of unconverted 5a and 6a, the remaining precipitate was
added to the filtrate, the ether replaced by 1,4-dioxane and the
mixture heated for 2 h at 90 °C. However, workup of the resulting
solution did not afford cis/trans-7a but its decarboxylation product
cis/trans-8a (Scheme 3), which had previously been synthesized
from 1a and benzaldehyde [9a,b]. This showed that, in contrast
to the 2-methyl-3-phenyl-phosphaprolines cis/trans-4a and cis/
trans-4b, which were stable at this temperature, the 2-phenyl
compound underwent thermal cleavage of CO2.
Scheme 3. Reaction of 1a with benzoylformic acid and formation of 8a by thermal
decarboxylation.
H-2 towards the P-electron lone pair, observed in the 1H solution
2
NMR spectra by the small JPH coupling constant of H-2 (1.4 Hz)
[15,16]. The crystal packing involves classical hydrogen bonding
between the +NH2 and COO– groups, leading to a layer structure
(Fig. S8).
Crystals of racemic trans-4a grew during storage of a concen-
trated solution of cis/trans-4a in methanol. The monoclinic unit cell
contains four molecules, with 2R,3S- or 2S,3R-configuration (Fig. 2).
The C2-N1, C2-P3 and C2-C(COOꢁ) bond lengths and N1-C2-P3 and
C2-N1-C5 bond angles are slightly larger than in trans-4a but other
values are very similar. The conformation within the ring is practi-
cally the same, with an almost planar arrangement of N1-C2-P3-C4
(dihedral angle 3.41(10)°) and a slightly smaller deviation of C5
(dihedral angle C5-N1-C2-P3 24.43(13)°) towards the same side
as the 2-COOꢁ group, opposite to the 2-methyl and 3-phenyl
groups. The trans-configuration of the 3-phenyl towards the 2-
COO group is shown by the dihedral angle C7-C2-P3-C8 of
134.53(9)°, the cis-position towards 2-methyl by C6-C2-P3-
C8 = 11.49(11)°. With respect to the N1-C2-P3-C4 plane the P-phe-
nyl group is somewhat further rotated out of the axial position
(N1-C2-P3-C8 109.62(9)°) than in trans-2a, and, in contrast to the
latter, the phenyl ring plane is rotated around the P3-C8 axis with
C9 directed towards C5 (C2-P3-C8-C9 62.18(15)°, C4-P3-C8-C9
32.92(16)°). In the packing (Fig. S9) the molecules associate via
classical hydrogen bonds to form ladder-like tapes parallel to the
2.2. Structural aspects
a axis, with alternating rings of graph sets R22(10) and R44(12).
A crystal, selected from the cis/trans-8a crystal mixture in the
methanolic mother liquor, was found to crystallize with four mole-
cules of trans-8a with (2R,3S)-configuration (Fig. 3). Although the
space group is chiral, the bulk material is presumably a racemate;
indeed the structure was refined as an enantiomeric twin. The
structure determination confirmed the cyclic structure, the cleav-
age of the carboxylic group and trans-configuration of the two phe-
nyl groups. The N1-C and the P3-C4 bonds are slightly shorter than
in trans-2a and trans-4a, likewise the sum of the P-C angles, but the
other bond lengths and angles within the five-membered ring are
similar. The ring again displays an envelope conformation, in this
case, however, with the C5 atom displaced to the side of the axial
P-phenyl group at the N1-C2-P3-C4- skeleton. The distance of C5 to
the N1-C2-P3-C4 ‘plane’ is 0.60 Å and that of C12 is 1.68 Å on the
same side of this plane. In the packing, a bifurcated hydrogen bond
system consisting of C11-H11ꢂ ꢂ ꢂN1 and N1-H1Nꢂ ꢂ ꢂN1, both with
Hꢂ ꢂ ꢂN distances of 2.61 Å, connects the molecules to form chains
parallel to the a axis (Fig. S10).
The structures of the new heterocyclic
a-phosphanyl amino
acids were proved by conclusive solution NMR and HRMS data,
those of trans-2a, trans-4a and trans-8a additionally by crystal
structure analyses. Crystals of racemic trans-2a were obtained after
enrichment of these diastereoisomers in a methanolic solution of
crude cis/trans-2a by slow cis-to-trans isomerization (see Fig. S7
and below) and subsequent partial evaporation of the solvent.
The orthorhombic unit cell contains 16 molecules, representing a
racemate with (2S,3R)- and (2R,3S)-configuration. Fig. 1 displays
the four independent molecules, which were arbitrarily chosen
with (2S,3R)-configuration, all with similar bond length and angles.
Molecular dimensions may be regarded as normal; selected values
for molecule 1 are compiled in Table 1. The five-membered rings
display an envelope conformation with an effectively planar
arrangement of N1, C2, P3 and C4 (absolute dihedral angles
1.4 – 4.6°) whereas C5 lies outside this plane (dihedral angles
C5-N1-C2-P3 24–32°), to the same side as the carboxy group; O2
is synperiplanar to N1 along the C2-C6 bond. The phenyl group is
approximately perpendicular to the N1-C2-P3-C4 plane (absolute
N1-C2-P3-C7 97–108°) and trans to COOꢁ (C7-P3-C2-C6 = 132–
144°). The latter corresponds well with the trans-orientation of
While the crystal structures revealed only the molecules with
trans-configuration, the solution NMR spectra indicated clearly
cis- and trans-diastereoisomer pairs of 2a, 4a and 8a and also of

198
K.R. Basvani et al. / Polyhedron 130 (2017) 195–204
Fig. 1. The four independent molecules of trans-2a (all 2S,3R; ellipsoids with 50% probability) in the crystal. Dashed lines indicate hydrogen bonds.
Table 1
Selected bond lengths (Å) and angles (°) of trans-2a, trans-4a and trans-8a.
Item
trans-2aa
trans-4a
trans-8a
N1-C2
N1-C5
C2-P3
P3-C4
P3-Cipso(Ph)
C2-C(COOꢁ)
C4-C5
N1-C2-P3
C2-P3-C4
P3-C4-C5
C2-N1-C5
N1-C5-C4
1.487(3)
1.495(3)
1.884(2)
1.871(2)
1.833(2)
1.522(3)
1.516(3)
106.77(13)
91.38(9)
104.31(14)
108.85(16)
105.83(15)
298.24(9)
1.5051(17)
1.492(2)
1.465(7)
1.473(7)
1.926(6)
1.847(5)
1.835(6)
-
1.539(7)
107.5(4)
90.2(2)
105.9(4)
108.2(4)
107.3(4)
291.5(3)
1.9220(14)
1.8564(15)
1.8316(16)
1.5487(18)
1.524(2)
105.21(9)
91.37(6)
104.57(9)
111.34(11)
105.28(12)
299.73(7)
R
(P-C)
a
Values for molecule 1; for data from molecules 2–4 see deposited data (CCDC
1486897).
Fig. 3. Molecular structure of trans-(2R,3S)-8a in the crystal (ellipsoids with 30%
probability).
GAH in ether (acidic conditions) led to preference for trans-2a. This
indicates kinetically controlled and pH-dependent primary con-
densation. Furthermore it was observed that repeated 1H and 31P
records of the same sample in CD3OD solution after one, two and
seven days and long-term 13C{1H} and DEPT-135 NMR measure-
ments did not show constant cis/trans-ratios but depletion of cis-
2a in favor of trans-2a. 31P integration indicated an initial cis/trans
ratio of 61:39, diminished to 47:53 after 24 h and to 44:56 and
36:64 after 2 and 6 d, respectively. This trend was confirmed by
similar proton integral ratios of the cis- and trans-NCH2-multiplets
(d = 3.35–3.65 versus d = 3.25–3.50 and 3.65–3.90 ppm). The inte-
gral ratio of the H-2 proton doublets of cis/trans-2a,b diminished
stronger, from 52:48 to 32:68, 26:74 and 20:80 and gives evidence
that the isomerization in CD3OD solution was accompanied by
additional slow H-D exchange. The 31P NMR spectra confirm this
by increasing ratios of the D-2/H-2 isotopomer signals, in particu-
lar for the more rapidly exchanging cis-isomers (Fig. S7). A similar
isomerization behavior, though to a smaller extent, was observed
for cis/trans-2b and cis/trans-4a. The changes of the cis/trans-ratios
Fig. 2. Molecular structure of trans-4a in the crystal (2R,3S-molecule depicted,
ellipsoids with 50% probability).
2b and 4b. It was found that the cis/trans-ratio of freshly prepared
samples depends on the exact course of the synthesis. Thus, addi-
tion of an ether solution of GAH to 1a (basic conditions until com-
plete addition) favored cis-2a. The opposite order, addition of 1a to
mean that, despite the heterocyclic
a-phosphanyl amino acids
being less labile than acyclic phosphanylglycines [6], they are not

K.R. Basvani et al. / Polyhedron 130 (2017) 195–204
199
really kinetically stable. Thermodynamically driven conversions of
2.3. Preliminary catalytic tests
cis- to trans-diastereoisomers (or the reverse) require ring-opening
/ ring-closure reactions. These are slow but enabled by the intrin-
sically Brönstedt acidic carboxyl group, the resulting N- and P-pro-
tonation equilibria and an acetalic character of the k3P-C-N
moieties. The additional H-D exchange for cis/trans-2a,b indicates
The phenylphosphaprolines 2a,b and 4a,b possess a P-C-COOꢁ
substructure and are thus related to phosphanylacetic acids [18]
which are useful precursors of nickel catalysts for the ethylene
oligomerization step in the Shell Higher Olefin Process [7]. Ligand
screening of various N-aryl- or N-alkyl-substituted diphenylphos-
phanyl glycines [6] and also of 3H-1,3-benzazaphospholine-2-car-
furthermore
a-CH-acidity of the phosphanyl amino acids. Com-
pared to usual
a
-amino acids this is possibly increased by small
equilibrium amounts of concomitantly N- and P-protonated
boxylic acids [19] gave evidence that linear or heterocyclic a-
species.
amino-substituted phosphanylacetic acids likewise form ethylene
oligomerization catalysts with Ni(COD)2 in toluene or THF on heat-
ing in the presence of ethylene under pressure. This prompted us
to perform preliminary tests of the diastereoisomer mixtures of
2a and 4a as catalyst ligands. Precatalysts were prepared by addi-
tion of a solution of Ni(COD)2 in THF to equimolar amount of 2a or
4a in methanolic solution, removal of the solvent under vacuum
(to avoid catalyst deactivation by methanol), followed by addition
of THF or toluene. In contrast to the diphenylphosphanyl glycinate
and benzazaphospholine-2-carboxylate nickel catalysts excess
sodium hydride was required for activation of the 2a/Ni and 4a/
Ni pre-catalysts. Transfer of the greenish-yellow suspension, pres-
surizing with ethylene and heating to 100 °C led to catalyst forma-
tion and oligomerization of ethylene (Table 2). Pressure/time plots
(Fig. S12) showed for the catalyst system 2a/Ni/NaH in THF the
best performance within this series, but altogether rather slow
The isolation of pure trans-2a and sufficiently large distances
between the signals allowed still first-order stereochemical analy-
sis of the coupling pattern of the PCH2 and NCH2 protons and of the
solution structure (Fig. 4). The positions of the H atoms were
derived from the dependence of the JPH [15,16] and JHH [17] val-
ues on the dihedral angles H-C-P-lp u1 (lp lone electron pair) and
H–C–C–H u2, respectively. Signs of coupling constants were not
2
3
2
3
determined but it is known that values for JPH >5 Hz and JHH
are general positive. The small JPH(e) coupling (1.4 Hz) of He in 2-
2
position, easily assignable by its chemical shift in the heteroami-
nal-region [16], might be positive (70–80°) or negative (80–90°
or ca. 160°), but angles <90° are improbable. Therefore, it indicates
trans-orientation to the P electron lone pair. The 2-COOH and 3-
phenyl groups are then also trans to each other (trans-configura-
tion), like as found in the crystal. Hb exhibits a similar small P-H
2
coupling, JPH(b) ꢀ0 Hz, corresponding to u1ꢀ 80–90 or 180°
conversions. The selectivity for formation of mainly linear a-olefins
2
[15a], whereas the large value JPH(a) = 19.1 Hz of Ha shows that
(less than one methyl branching/100 CH2) with vinyl and methyl
end groups was similar to that of phosphanylacetate nickel cata-
lysts, so that complex formation and a related mechanism [7]
may be anticipated.
this atom is in cis-position to the P lone pair (u1 ꢀ20–30°). The
3
large vicinal coupling JH(a)H(d) = 11.7 Hz (u2 close to 180 or 0°)
suggests preferred axial trans-positions of Ha and Hd which
would be in accordance with the small value of JH(b)H(c) = 2.3 Hz
3
(u2 ꢀ60–70 or 110–120°) and preferred equatorial trans-positions
of Hb and Hc. The other vicinal coupling constants (3JH(a)H(c) = 7.2,
3JH(b)H(d) = 5.7 Hz) are found in the normal range, likewise the
3. Conclusions and outlook
2
amounts of the geminal couplings (2JH(a)H(b) = 15.1, JH(c)H
2-Phenylphosphanyl ethylamines 1a,b react with equimolar
amounts of glyoxylic acid hydrate (GAH) or pyruvic acid in diethyl
ether or 1,4-dioxane more or less rapidly to cis/trans-mixtures of
the 1,3-azaphospholidine-2-carboxylic acids 2a,b and 4a,b. The
cyclocondensation proceeds mainly via diastereoisomeric zwitteri-
onic phosphanylglycolates (2I⁄⁄a,b and 4I⁄⁄a,b) and to a minor
extent via not fully identified P-secondary phenylphosphanylethy-
lammonium intermediates (2I⁄a,b and 4I⁄a,b). The cyclization step
becomes slower if a substituent is present at the N-atom of 1 or at
(d) = 11.7 Hz), probably as usual with negative sign. The
assignment of the protons Ha-Hd in cis-2a (2JPH(e) = 15.8 Hz) was
achieved by difference analysis of a 1:1 cis/trans-2a mixture. For
cis/trans-4a the superimposed Ha-Hd protons are assigned in an
HH-COSY spectrum (Fig. S11).
the a-carbon atom of the keto-carboxylic acid or its hydrate, i.e. for
1b compared to 1a and for pyruvic acid compared to GAH. In the
case of arylformic acids, represented by PhC(O)COOH, the cyclo-
condensation is very slow, even with 1a. Heating in 1,4-dioxane,
suitable for the synthesis of 4a,b, leads here to decarboxylation,
possibly for steric reasons or because of the higher stability of an
aryl-substituted carbenium cation intermediate (M-effect). The
heterocyclic
than acyclic
a
-phosphanyl amino acids are kinetically more stable
a-phosphanyl amino acids (phosphanyl glycines), but
they are still able to isomerize slowly in solution in favor of the
trans-diastereoisomers (2a) or opposite (4a). This reaction requires
a ring-opening/ring-closure sequence, which is catalyzed by the
intrinsic acidic function and favored by a protic polar solvent.
The generation of nickel catalysts for the oligomerization of ethy-
lene to linear a-olefins shows that complex formation occurs.
The here presented information on the synthesis, structures,
behavior in solution and the principal potential for transition metal
complex formation and catalysis of the ‘‘phenylphosphaprolines”
paves the way for further studies of their reactivity. Since 1,3-aza-
phospholidines without a COOH substituent [9,10] proved stable,
the kinetic lability of the novel
a-phosphanyl amino acids may
be overcome by formation of transition metal salts or complexes
Fig. 4. NMR spectrum of the 1,3-azaphospholidine ring protons of trans-2a.
or by introduction of N- or COO-protection groups. This may open

200
K.R. Basvani et al. / Polyhedron 130 (2017) 195–204
Table 2
Oligomerization of ethylene with catalysts formed from 2a/Ni and 4a/Ni.a
d
n
L/Ni (
NaH (mmol),
solvent
l
mol),
C2H4 g (mmol),
conv. g (%),
TON [mol/mol]
Polymer: g,b
mp. [°C],
MNMR [gꢂmol–1],
Volatile olefines
a
/internal olefin,
Me/C = C
lin.
lin.
a
a
/other olefines;
D [g/cm3]c
C4-C14 (%)e
1
2
3
4
2a/Ni (153/160),
(2.1), THF
2a/Ni (105/109),
(1.3), tol.
4a/Ni (99/109),
(1.0), THF
4a/Ni (135/123),
(1.0), tol.
12.2 (435),
9.5 (78), 2213
12.0 (428),
7.9 (66), 2682
11.6 (413),
7.0 (60), 2520
11.1 (396),
8.7,
MNMR 1600
73/27, 3.0
MNMR 3200
82/18, 3.9
MNMR 2760
89/11, 3.4
MNMR 2460
80/20, 3.2
72/28; 45, 33.4, 15,
5, 1.4, 0.1
69/31; 30, 30, 22,
13.6, 4, 0.3
90/10; 21, 39, 25,
10.5, 3.7, 0.8
80/20; 38, 31, 21,
8, 2
126–128, 0.91
7.5,
128–130, 0.91
5.0,
n.d.
8.4,
n.d.
9.0 (81), 2608
a
b
c
Batch oligo/polymerization of ethylene, pstart at r.t. 40–45 bar, start of conversion at 90–100 °C.
Residue after flash distillation of volatiles (10 mbar/ up to 150 °C), treatment with MeOH/aqueous conc. HCl (1:1), washing with MeOH and drying under vacuum.
Density of tablets of the solid (compressed at 10 kbar) determined by the sinking method in H2O/EtOH.
d
MNMR by proton NMR integral ratios of CH2 and CH3 versus @CH fragments in swollen polymers at 100 °C. [e] GC peak area% of olefins in flash distillate (butenes partially
evaporated, >C14 neglected).
a wide field for possible applications in coordination chemistry,
complex catalysis, medicinal chemistry or even inclusion in
P-containing peptide syntheses.
4.2. Syntheses
4.2.1. cis/trans-3-Phenyl-1,3-azaphospholidine-2-carboxylic acid (2a).
A solution of GAH (0.52 g, 5.65 mmol) in diethyl ether (20 mL)
was prepared using an ultrasound bath and slowly added to the
ether solution of 1a (0.85 mL, 5.77 mmol). A white precipitate
formed almost immediately. NMR monitoring of a precipitate sam-
ple, separated after a minute, displayed in CD3OD solution signals
at d31P = ꢁ10.7/1.3 (cis/trans), ꢁ14.1/ꢁ9.0 (cis/trans) and ꢁ59.4
(PH)/ꢁ60.9 (t, PD), integral ratio 43/14, 19/14 and 10 (sum of PH
and PD signals), after 2 h 60/20, 7/5 and 8. To allow for complete
conversion in ether the mixture was stirred for 1d. The precipitate
was separated by filtration, was washed with ether and dried
under vacuum to give 1.12 g (95%) of white powder. This was spar-
ingly soluble in chloroform or THF but soluble in methanol. IR
4. Experimental
4.1. General remarks
All operations were carried out under nitrogen or argon atmo-
sphere using Schlenk techniques and freshly distilled dry solvents.
Glyoxylic acid monohydrate (GAH), pyruvic acid and benzoyl-
formic acid were used as purchased. ClCH2CH2NHR (R = H, Et)
[20] and diethyl phenylphosphonate [21] were prepared by known
procedures. Phenylphosphane was synthesized by reduction of PhP
(O)(OEt)2 with LiAlH4 in analogy to o-diphosphanylbenzene or o-
phosphanylphenol [22] and, after reaction with sodium in liquid
ammonia, coupled with the chloroethylamines to give the starting
compounds 1a and 1b [9,10] (NMR data of 1a and 1b see Support-
ing information). NMR spectra were recorded at 25 °C on a multi-
nuclear FT-NMR spectrometer ARX300 (Bruker) at 300.1 (1H),
75.5 (13C), and 121.5 (31P) MHz. Chemical shifts (d in ppm) are
referred to tetramethylsilane for 1H and 13C and H3PO4 (85%) for
31P or to solvent signals calibrated with the aforementioned refer-
ence compounds. Coupling constants are JHH in 1H and JPC in 13C
NMR data unless indicated otherwise. Assignments refer to
nomenclature numbers or i-, o-, m-, p-position of the phenyl 13C
or H nuclei, cis or trans following the assignment indicate the con-
figuration of the diastereoisomer pairs (position of 3-phenyl rela-
tive to 2-COOꢁ group, in 8a to 2-Ph group). 31P NMR data were
measured immediately after the 1H NMR data to observe similar
cis/trans-diastereoisomer ratios in the case of cis/trans-isomeriza-
tion in solution. 31P NMR integrals (for AQ = 0.328 s and
D1 = 2.0s) are not quantitative, but 31P integral ratios for related
compounds with similar 31P relaxation time are still comparable
to 1H integral ratios. This was confirmed by comparison with
NCH2 integral ratios of trans-2a and used to evaluate trends in
reaction monitoring. Phosphorus analyses were carried out using
the method of Woy after oxidation of the sample with HNO3/HClO4
[23], CHN analyses with a LECO CHN analyser under standard con-
ditions. The elemental composition of air-sensitive compounds
was characterized by high resolution mass spectra (ESI in MeOH/-
formic acid or in MeOH), measured with a 7T Fourier transform ion
cyclotron resonance mass spectrometer APEX IV or an ESI-Qq-TOF
mass spectrometer micrOTOF (both Bruker Daltonics). LR mass
spectra were recorded on a single-focussing mass spectrometer
AMD40 (Intectra).
+
ꢀ
v
(KBr):
= 3437 (br), 3043 (st), 2704 (wm), 2400 (wm, NH ), 1619
(vst), 1586 (vst), 1375 (vst) cmꢁ1. Analysis calcd. for C10H12NO2P
(209.18): C 57.42, H 5.78, N 6.70; found: C 57.48, H 5.50, N 6.82.
HRMS (ESI in MeOH/FA): mass calcd. for [C10H12NO2P+H]+
210.06784; found 210.06792. MS (EI 70 eV, 150 °C): m/e (%) = 209
(11) [M]+, 165 (20), 164 (72) [M-COOH]+, 137 (15), 136 (22), 109
(44), 108 (100) [PhP]+, 107 (46), 44 (38). NMR data, measured in
CD3OD, indicated a mixture of cis- and trans-diastereoisomers of
2a, which underwent slow isomerization in favour of the trans-
diastereoisomer (see text). Slow concentration led within 3–4 days
to formation of crystals of racemic trans-2a. For selected bond
lengths and angles see Table 1, for crystal data Table 3.
trans-2a: 1H NMR (CD3OD, Ref. TMS): d = 2.19 (dddd,
-
2
2
3
3
JHaP = 19.1, JHaHb = 15.1, JHaHd = 11.7, JHaHc = 7.3 Hz, 1H, 4-Ha, cis
to P lone-pair), 2.54 (ddd, 2JHbHa = 15.1, 3JHbHd = 5.7, 3JHbHc = 2.3 Hz,
2
3
3
3
1H, 4-Hb), 3.20 (tdd, JHdHc = 11.8, JHdHa = 11.8, JHdHb = 5.8,
-
2
3
JPHd = 2.1 Hz, 1H, 5-Hd), 3.82 (dtd, JHcHd = 11.8, JHcHa
ꢀ
3JPHc = 7.1
3
2
(7.3 + 6.9), JHcHb = 2.3 Hz, 1H, 5-Hc), 4.53 (d, JPH = 1.4 Hz, 1H, 2-
H, trans to P-lone pair), 7.33–7.47 (m, 3H; Ph), 7.52–7.60 (m, 2H,
Ph). 31P{1H} NMR (CD3OD): d = 1.3. 13C{1H} and DEPT-135 NMR
(CD3OD): d = 24.98 (d, 1J = 19.8 Hz, PCH2), 49.04 (d, 2J = 5.3 Hz,
NCH2), 66.66 (d, 1J = 37.6 Hz, PCHN), 130.02 (s, p-CH), 130.24 (d,
3J = 4.3 Hz, 2 m-CH), 131.18 (d, 2J = 15.9 Hz, 2 o-CH), 137.17 (d, 1J
ꢀ 26 Hz, i-C); COO at noise level, data from cis/trans-mixture
172.60 (d, 2J = 13.2 Hz).
cis-2a (data from cis/trans-mixture): 1H NMR (CD3OD, Ref.
2
2
3
3
TMS): d = 2.41 (ddt, JHaP = 19.6, JHaHb = 15.1, JHaHd = 8.9,
-
JHaHc = 8.5 Hz, 1H, 4-Ha, cis to P lone-pair), 2.61 (dddd, 2JHbHa = 15.1,
3
2
3JHbHc = 7.3, JHbHd = 4.8, JHbP = 1.5 Hz, 1H, 4-Hb), 3.51 (ddt,
2JHdHc = 12.0, JHdHa = 8.9, JHdHb
ꢀ
3JPHd = 4.7 Hz, 1H, 5-Hd), 3.72
3
3
2
3
3
3
(dddd, JHcHd = 12.0, JHcHa = 8.5, JHcHb = 7.4, JHcP = 2.3 Hz, 1H,
2
5-Hc), 4.54 (d, JPH = 15.8 Hz, 1H, 2-H, cis to
P lone-pair),

K.R. Basvani et al. / Polyhedron 130 (2017) 195–204
201
Table 3
Crystallographic data for trans-2a, trans-4a and trans-8a.
Identification code
trans-2a
10H12NO2P
209.18
100(2)
1.54184
trans-4a
trans-8a
Empirical formula
Formula weight
T (K)
Wavelength (Å)
Crystal system
Space group
C
C11H14NO2P
223.20
100(2)
1.54184
monoclinic
P21/n
C15H16NP
241.26
170(2)
0.71073
orthorhombic
P212121
orthorhombic
Pna21
Unit cell dimensions
a = 10.5503(3) Å,
a
= 90°
a = 5.8737(5) Å,
a
= 90°
a = 5.4961(11) Å, a = 90°
b = 17.0450(5) Å, b = 90°
b = 32.842(3) Å, b = 108.122(15)°
b = 10.233(2) Å, b = 90°
c = 22.4461(6) Å,
4036.5(2)
16
1.377
2.2
1760
0.16 ꢃ 0.15 ꢃ 0.04
3.3 to 71.0°
ꢁ12 ꢄ h ꢄ 12,
ꢁ20 ꢄ k ꢄ 20,
ꢁ25 ꢄ l ꢄ 26
56323
c
= 90°
c = 6.0495(8) Å,
1109.1(2)
4
1.337
2.0
472
c
= 90°
c = 22.726(5) Å, c = 90°
1278.1(4)
4
1.254
0.19
512
V (Å3)
Z
Density (calc.) (Mg/m3)
Absorption coefficient (mmꢁ1
F(000)
)
Crystal size (mm3)
0.08 ꢃ 0.03 ꢃ 0.03
0.44 ꢃ 0.06 ꢃ 0.05
Theta range for data collection
Index ranges
2.7 to 70.6°
1.8 to 24.8°
ꢁ6 ꢄ h ꢄ 7,
ꢁ6 ꢄ h ꢄ 5,
ꢁ39 ꢄ k ꢄ 40,
ꢁ6 ꢄ l ꢄ 7
ꢁ12 ꢄ k ꢄ 11,
ꢁ26 ꢄ l ꢄ 26
8558
Reflections collected
11078
Independent reflections
Completeness to theta
Absorption correction
Max. and min. transmission
Refinement method
7452 [R(int) = 0.042]
=67.50°, 99.9%
2040 [R(int) = 0.025]
=67.50°, 98.2%
Semi-empirical from equivalents
1.00 and 0.81
Full-matrix least-squares on F2
2040/0/145
2152 [R(int) = 0.145]
=25.00°, 95.8%
Numerical
Semi-empirical from equivalents
1.00 and 0.69
0.75 and 0.55
Full-matrix least-squares on F2
7452/457/531
Full-matrix least-squares on F2
2152/0/162
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
1.03
1.07
0.90
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0332,
wR2 = 0.0871
R1 = 0.0363,
R1 = 0.0298,
wR2 = 0.0768
R1 = 0.0348,
R1 = 0.0492,
wR2 = 0.0747
R1 = 0.1116,
wR2 = 0.0893
0.491(14)
wR2 = 0.0787
wR2 = 0.0907
0.43(18)
Absolute structure parameter
Largest diff. peak and hole (e.Åꢁ3
)
0.57 and ꢁ0.27
0.34 and ꢁ0.26
0.27 and ꢁ0.26
7.34–7.48 (m, 3H; Ph), 7.53–7.62 (m, 2H, Ph). 31P{1H} NMR
(CD3OD): d = ꢁ11.7. 13C{1H} and DEPT-135 NMR (CD3OD):
d = 24.55 (d, 1J = 17.7 Hz, PCH2), 47.47 (d, 2J = 3.8, NCH2), 66.56 (d,
1J = 35.5 Hz, PCHN), 129.75 (d, 3J = 6.5 Hz, m-CH), 130.73 (s, p-
CH), 133.69 (d, 2J = 18.4 Hz, 2 o-CH), 133.93 (d, 1J = 24.6 Hz, i-Cq),
169.47 (s, COO).
(d, 2J = 2.3 Hz, NCH2, cis), 57.42 (d, 2J = 5.0 Hz, NCH2, trans),
73.15 (d, 1J = 39.2 Hz, PCHN, trans), 73.17 (d, 1J = 35.6 Hz, PCHN,
cis), 129.62 (d, 3J = 6.6 Hz, 2 m-CH, cis), 130.07 (s, p-CH, trans),
130.35 (d, 3J = 5.3 Hz, 2 m-CH, trans), 131.05 (s, overlapped, p-
CH, cis), 131.12 (d, 2J = 15.9 Hz, 2 o-CH, trans), 133.93 (d, 1J =
25.2 Hz, i-Cq, cis), 134.44 (d, 2J = 19.9 Hz, 2 o-CH, cis), 137.03 (d,
1J = 26.5 Hz, i-Cq, trans), 168.55 (s, COO, cis), 172.28 (d, 2J = 13.4
Hz, COO, trans)
4.2.2. cis/trans-1-Ethyl-3-phenyl-1,3-azaphospholidine-2-carboxylic
acid (2b).
The decreased cis/trans ratios of the 13C-NMR methyl signal in
long-term DEPT-135 and 13C{1H} NMR measurements (48:52 and
33:67, on average 6 h and 18 h after the proton NMR measure-
ment) suggest slow isomerization of cis-2b in favour of trans-2b,
as also detected for cis/trans-2b by repeated 1H and 31P-measure-
ments. The solvent dependence of the 31P and characteristic 1H
and 13C NMR data is illustrated in Table S1 in the supporting
information.
Compound 1b (0.25 g, 1.38 mmol) was added at r. t. to the solu-
tion of GAH (0.13 g, 1.41 mmol) in diethyl ether (20 mL, ultrasound
bath) to give an immediate white precipitate. NMR monitoring of a
precipitate sample, separated after a minute, displayed signals of
cis/trans-2b and intermediates (d31P in CD3OD = ꢁ7.8/6.7,
ꢁ14.1/ꢁ7.4 and ꢁ58.8/ꢁ60.3 (t)) which slowly disappeared in
favor of product signals. The precipitate was then separated by fil-
tration, washed with additional ether and dried under vacuum to
give 0.29 g (89%) of an air-sensitive white powder. The crude pro-
duct was soluble in CD3OD, [D6]-DMSO, [D7]-DMF, D2O and even in
For the detection of 3b as side product in the reaction of 1b and
GAH in a 1:2 M ratio in diethyl ether see Supporting information.
+
ꢀ
v
CDCl3. IR (KBr):
= 3435 (br, vst), 2360, 2342 (m, NH ), 1636 (br,
4.2.3. cis/trans-2-Methyl-3-phenyl-1,3-azaphospholidine-2-carboxylic
acid (4a)
vst), 1374 (br, st) cmꢁ1. HRMS (ESI in MeOH/FA): mass calcd. for
[C12H16NO2P+H]+: 238.09914; found 238.09924. 1H NMR (CD3OD,
TMS): d = 1.27 (t, 3J = 7.3 Hz, 3H, CH3, trans), 1.35 (t, 3J = 7.3 Hz,
3H, CH3, cis), 2.15–2.35 (m, 1H, PCH2, trans), 2.37–2.62 (m, 3H,
PCH2, cis and trans), 2.95–3.28, 3.35–3.52, 3.95–4.10 (3 m, 8H,
a) A solution of pyruvic acid (0.5 mL, 7.19 mmol) in dry diethyl
ether (20 mL) was added to the ether solution of 1a (1.04 g,
6.79 mmol). Precipitation started after few seconds. NMR monitor-
ing of precipitate samples in CDCl3 solution displayed signals of
intermediates, strong at d = ꢁ6.6 to ꢁ6.0 and ꢁ0.1 ppm and weak
at d = ꢁ59, ꢁ9.5 and ꢁ4.0 ppm, which disappeared after 1–2 d in
favor of the product signals. The precipitate was then washed twice
with ether and dried under vacuum to give 1.52 g (95%) of a white
powder. This was moderately to well soluble in CDCl3 or CD3OD. IR
ꢀ
2
NCH2, cis and trans), 4.35 (d, JPH = 2.1 Hz, 1H, PCH, trans), 4.45
(d, 2JPH = 16.1 Hz, 1H, PCH, cis), 7.33–7.49 (m, 6H, Ph, cis and trans),
7.57–7.68 (m, 4H, Ph, cis and trans); cis/trans 57:43 (by 2-H inte-
gration). 31P{1H} NMR (CD3OD): d = ꢁ8.0 (cis), 6.5 (trans; integral
ratio 61:39). 13C{1H} and DEPT-135 NMR (CD3OD): d = 11.06 (s,
CH3, cis) and 11.48 (s, CH3, trans) – cis/trans 33:67 (by 13C methyl
integrals), 23.19 (d, 1J = 15.5 Hz, PCH2, cis), 24.31 (d, 1J = 17.9 Hz,
PCH2, trans), 52.80 (s, NCH2Et, trans), 53.50 (s, NCH2Et, cis), 55.30
(KBr):v = 3437 (br, vst), 3050 (st), 2977 (st), 2793 (w), 2714 (w),
1761 (sh), 1612 (vst), 1385 (st), 1349 (vst) cmꢁ1. Analysis calcd.
for C11H14NO2P (223.21): C 59.19, H 6.32, N 6.28; found: C 59.34,

202
K.R. Basvani et al. / Polyhedron 130 (2017) 195–204
H
6.45,
N
6.37. HRMS (ESI in MeOH/FA): mass calcd. for
55.43 (d, 2J = 2.7 Hz, NCH2, trans), 74.70 (d, 1J = 39.8 Hz, PCqN,
trans), 78.78 (d, 1J = 33.2 Hz, PCqN, cis), 129.36 (d, 3J = 8.8 Hz, 2
m-CH, cis), 129.84 (d, 3J = 6.6 Hz, 2 m-CH, trans), 131.15 (s, p-CH,
cis), 131.24 (s, p-CH, trans), 133.68 (d, 1J = 29.2 Hz, i-Cq, trans),
134.61 (overlapped d, 1J ꢀ 21 Hz, i-Cq, cis), 134.53 (overlapped d,
2J ꢀ 21 Hz, 2 o-CH, trans), 134.83 (d, 2J = 21.2 Hz, 2 o-CH, cis),
170.90 (s, COO, cis), 175.76 (d, 2J = 15.9 Hz, COO, trans).
b) A solution of pyruvic acid (171 mg, 1.95 mmol) in 1,4-diox-
ane (2 mL) was added to a solution of 1b (439 mg, 2.42 mmol) in
1,4-dioxane (5 mL). Almost immediately a thick white precipitate
was formed. During heating the mixture for 70 min at 90 °C a large
amount of the insoluble material dissolved. After stirring overnight
at r. t., the mixture was filtered, the residual solid washed with
diethyl ether (111 mg white powder after drying) and discarded
because the NMR spectra in CD3OD indicated only a minor content
of cis- and trans-4b besides incompletely converted intermediates
with d31P = ꢁ60.4 (t, PD species), ꢁ5.2, ꢁ1.2 and a trace of a
P-oxide with d = 43.5. The major part of the product was still in
the filtrate. Removal of the solvent under vacuum gave 600 mg of
a sticky solid, still containing residual dioxane. It was dissolved
in a small amount of methanol and crystallized by storage of the
concentrated solution at +4 °C for few days. Separation of the
supernatant liquid (still containing 4b) and drying under vacuum
[C11H14NO2P+H]+: 224.08349; found 224.08356. MS (EI 70 eV,
135 °C): m/e (%) = 224 (8), 223 (21) [M]+, 195 (40) [M-C2H4]+, 178
(28) [M-COOH]+, 136 (11), 109 (18), 108 (26), 44 (100). 1H NMR
3
3
(CD3OD): d = 1.34 (d, JPH = 7.2 Hz, 3H, CH3, trans), 1.79 (d,
-
JPH = 17.7 Hz, 3H, CH3, cis), 2.30–2.75 (m, 4H, PCH2, cis- and trans),
3.53–3.98 (m, 4H, NCH2, cis- and trans), 7.35–7.41 (m, 3H, m- and
p-H, cis), 7.45–7.50 (m, 3H, m- and p-H, trans), 7.54–7.61 (m, 4
+ 4H, o-CH, cis and trans). 31P{1H} NMR (CD3OD): d = 7.2 (cis), 5.5
(trans); integral ratio 61:39. 13C{1H} and DEPT-135 NMR (CD3OD):
d = 20.29 (d, 2J = 2.4 Hz, 2-CH3, trans), 22.25 (DEPT d, 1J = 17.6 Hz,
PCH2, trans), 22.59 (DEPT d, 1J = 18.7 Hz, PCH2, cis), 22.57 (DEPT
d, 2J = 30.8 Hz, 2-CH3, cis), 46.84 (d, 2J = 3.0 Hz, NCH2, cis), 48.26
(d, 2J = 3.0 Hz, NCH2, trans), 73.16 (d, 1J = 37 Hz, PCqN, trans),
75.09 (d, 1J = 31.8 Hz, PCqN, cis), 129.71 (d, 3J = 6.6 Hz, m-CH, cis),
130.04 (d, 3J = 5.3 Hz, m-CH, trans), 131.09 (s, p-CH, cis), 131.14
(s, p-CH, trans), 132.96 (d, 1J = 27.9 Hz, i-Cq, trans), 134.07 (super-
imposed d, 2J ꢀ 20 Hz, o-CH, cis), 134.28 (d, 2J = 20 Hz, o-CH, trans),
134.34 (superimposed d, 1J ꢀ 25 Hz, i-Cq, cis), 172.44 (s, COO, cis),
175.82 (d, 2J = 15.9 Hz, COO, trans); cis:trans 54:46 (by integration
of the COOꢁ signals). Crystallization from a minimum amount
methanol, sufficient to dissolve the powder, led within 8–10 d at
room temperature to crystals of the trans-diastereoisomers of 4a
with (2R,3S)- and (2S,3R)-configuration. Selected bond lengths
and angles are compiled in Table 1, crystal data, in Table 3.
gave 190 mg (50%) cis/trans-4b. Anal. calcd. for
C13H18NO2P
(251.3): P 12.33; found: 12.38. The NMR data are in accordance
with those given above.
b) A solution of 1a (6.7 g, 43.8 mmol) in 1,4-dioxane (10 mL)
was slowly added to a solution of pyruvic acid (3.9 g, 44.3 mmol)
in dioxane (10 mL). After heating for 70 min at 80–100 °C the
precipitate was separated, washed with diethyl ether/EtOH (5:1)
and dried under vacuum to give 6.5 g (60%) white powder, m. p.
(dec.) 182–6 °C. Anal. calcd. for C11H14NO2P (223.2): P 13.88;
4.2.5. Detection of 5a, 6a and 7a in the reaction of 1a with phenyl
glyoxylic acid in diethyl ether and isolation of 2,3-diphenyl-1,3-
azaphospholidine (8a) after heating in dioxane
A solution of benzoylformic acid (584 mg, 3.89 mmol) in diethyl
ether (10 mL) was added to an ethereal solution of 1a (596 mg,
3.89 mmol; ca. 2 mL) at r.t. with shaking, resulting in a slightly
exothermic reaction and immediate formation of a thick precipi-
tate. This was separated after 20 min at r.t., washed with ether
and dried under vacuum to give 1.048 g of a white powder. 31P
and 13C NMR spectra in CD3OD indicated a mixture with slow con-
version of intermediate 5a and diastereoisomers of 6a to cis/trans-
7a (see Fig. S5). MS (EI 70 eV, 150 °C): m/e (%) = 285 (5) [M(7a)]+,
241 (16) [(7a)-CO2]+, 240 (12), 213 (42), 212 (40), 136 (18), 135
(40), 108 (21) [PhP]+, 77 (35), 44 (100). To accelerate the cyclocon-
densation, the residual crude precipitate (ca. 900 mg) was added to
the filtrate, diethyl ether evapoarated under vacuum and replaced
by 1,4-dioxane (10 mL) and the mixture heated at 90 °C for 2 h.
This led to complete dissolution of the solids. After cooling to r. t.
the solvent was removed under vacuum. The resulting pale-yellow
viscous liquid was crystallized from a small amount of methanol
(ca. 1 mL) to give 350 mg of a sticky crystal mixture of cis/trans-
8a. A considerable amount of this compound remained in the fil-
trate and formed a sticky material after addition of hexane
(5 mL). XRD analysis of a crystal selected from the crystal mixture
with mother liquor revealed trans-8a (selected bond lengths and
angles in Table 1, crystal data in Table 3). HRMS (ESI in CD3OH/
D): mass calcd. for [C15H16NP+H]+: 242.1093; found 242.1102;
mass calcd. for [C15H16NP+D]+: 243.1155; found 243.1155. cis/
trans-8a - 1H NMR (CD3OD): d = 2.05–2.51 (m, 4H, PCH2, cis and
trans), 2.87–3.07 (m, 2H, 2H, NCH2), 3.45–3.62 (m, 1H, NCH2),
found: 14.22. IR (Nujol):
m .
= 2600–2400, 1590, 1340 cmꢁ1 31P
{1H} NMR (CD3OD): d = 7.0 (cis), 5.9 (trans), integral ratio 42:58.
The isomer ratio changed by crystallization from hot concentrated
ethanolic solution in favour of the cis-diastereoisomers (cis:trans
ca. 55:45 by 31P integration and by 1H integration of 2-Me
doublets).
4.2.4. cis/trans-1-Ethyl-2-methyl-3-phenyl-1,3-azaphospholidine-2-
carboxylic acid (4b)
a) A solution of pyruvic acid (0.24 g, 2.73 mmol) in diethyl ether
(20 mL) was added to the ether solution of 1b (0.50 g, 2.76 mmol),
resulting in immediate formation of a white precipitate. 31P NMR
monitoring of
a CDCl3 solution displayed strong signals at
d = ꢁ6.6 and ꢁ0.1, integrals 53 and 24%, and weak signals at
d = ꢁ59.0, ꢁ9.1, ꢁ8.4, ꢁ4.5, 18.0 and 21.1, integrals 2, 2, 1, 10, 4,
and 4%. Measurement after 30 h indicated conversion to cis- and
trans-4b, d = 21.6 and 18.2, integrals 50 and 31%, as the main
products. The solid was then washed with ether and dried under
ꢀ
vacuum to give 0.60 g white powder. IR (KBr):
v
= 3436 (br, vst),
. Anal. calcd. for
3055 (sh), 1625 (br, vst), 1357 (m) cmꢁ1
C13H18NO2P (251.26): C 62.14, H 7.22, N 5.57; found: C 61.93, H
7.50,
N 5.42. HRMS (ESI in MeOH/FA): mass calcd. for
[C13H18NO2P+H]+: 252.11479; found 252.11488. 1H NMR (CD3OD):
d = 1.07 (d, JPH = 5.7 Hz, 3H, 2-CH3, trans), 1.32 (t, 3J = 7.2 Hz, 3H,
3
CH3, trans), 1.37 (t, 3J = 7.5 Hz, 3H, CH3, cis), 1.79 (d, JPH = 20.0 Hz,
3
3H, 2-CH3, cis), 2.35–2.68 (m, 4H, PCH2, cis and trans), 3.01–3.19,
3.20–3.32, 3.32–3.59 (3 m, 6H, NCH2, cis and trans), 4.01–4.15,
4.18–4.33 (2 m, 2H, NCH2, cis and trans), 7.26–7.53, 7.54–7.75
(2 m, 10H, Ph, cis and trans); cis/trans 44:56 (by 2-Me proton inte-
gration). 31P{1H} NMR (CD3OD): d = 17.5 (cis-diastereoisomer), 18.9
(br, trans-diastereoisomer); integral ratio 46:54. 13C{1H} and
DEPT-135 NMR (CD3OD): d = 12.32 (s, 2 CH3(Et), cis and trans),
16.78 (s, 2-CH3, trans), 18.97 (d, 2J = 35.8 Hz, 2-CH3, cis), 20.15 (d,
1J ꢀ 16 Hz, PCH2, trans), 20.56 (d, 1J = 15.9 Hz, PCH2, cis), 47.32 (s,
NCH2(Et), trans), 49.04 (DEPT s, NCH2(Et), cis), 53.44 (s, NCH2, cis),
2
3.68–3.82 (m, 1H, NCH2), 4.41 (d, JPH = 20.4 Hz, 1H, 2-H, cis),
2
4.46 (d, JPH = 3.8 Hz, 1H, 2-H, trans), 6.80–7.53 (m, 11H, NH,
2-Ph, 3-Ph). 31P{1H} NMR (CD3OD): d = ꢁ1.9 (trans), ꢁ2.2 (cis[2D]),
ꢁ2.3 (cis), ꢁ2.7 (trans[2D]); 31P integrals 46, 22, 22, 10. 13C{1H}
and DEPT-135 NMR (CD3OD): d = 27.33 (d, 1J = 15.4 Hz, PCH2, cis),
29.61 (d, 1J = 14.6 Hz, PCH2, trans), 29.66 (d, 1J = 14.6 Hz, PCH2,
trans[2D]), 48.45 (DEPT, d, 2J = 3.3 Hz, NCH2, cis), 50.90 (d,
2J = 4.0 Hz, NCH2, trans), 69.54 (d, 1J = 22.6 Hz, PCHN, cis), 73.02
(d, 1J = 19.9 Hz, PCHN, trans), 127.10 (d, 3J = 4.0 Hz, 2 o-CH(CPh)
,

K.R. Basvani et al. / Polyhedron 130 (2017) 195–204
203
cis), 127.21 (d, 5J = 2 Hz, p-CH(CPh)
,
cis), 128.13 (d, 5J = 2 Hz,
Hydrogen atoms of NH2 groups were refined freely, but for trans-
2a with N–H distances restrained equal and with an overall U value
for the H atoms; methyls were refined as idealized rigid groups
allowed to rotate but not tip; other hydrogens were included using
a riding model starting from calculated positions. The structure of
trans-2a is pseudosymmetric; if the b axis is halved, the structure
can be refined in Pbca to an R value of 10%. However, the reflec-
tions corresponding to the longer b axis (those with odd k index)
are definitely present, if weak. There are also topological differ-
ences between the hydrogen bond systems; thus the asymmetric
three-center interaction from H02 to O1 and O2 has the longer
branch to O1, whereas that from H020 to O10 and O20 has the longer
branch to O20.
p-CH(CPh), trans), 128.45 (d, 3J = 8.8 Hz, 2 m-CH(PPh), trans), 128.79
(superimposed d, 3J = 6.6 Hz, 2 m-CH(PPh), cis), 128.80, 129.38
(two superimposed s, p-CH(PPh), trans and 2 m-CH(CPh), cis),
129.62 (superimposed s, 2 m-CH(CPh), trans, p-CH(PPh), cis), 129.81
(d, 3J = 5.5 Hz, 2 o-CH(CPh), trans), 131.87 (d, 2J = 16.5 Hz, 2 o-CH(PPh)
,
trans[2D]), 131.88 (d, 2J = 16.5 Hz, 2 o-CH(PPh), trans), 133.97 (d,
2J = 17.6 Hz, 2 o-CH(PPh), cis), 135.66 (d, 1J = 25.2 Hz, i-Cq(PPh), cis),
137.97 (s, i-Cq(CPh), cis[2D]), 138.03 (s, i-Cq(CPh), cis), 141.24 (d,
1J = 25.1 Hz, i-Cq(PPh)
, ,
trans), 142.94 (d, 2J = 17.3 Hz, i-Cq(CPh)
trans[2D]), 143.00 (d, 2J = 18.6 Hz, i-Cq(CPh), trans); C-phenyl assign-
ments tentative, based on different JPC in P-phenyl and P-benzyl
groups [24] and cis/trans integral ratios of roughly 1:2.
Characteristic 13C{1H} NMR data of intermediates (in CD3OD):
5a - d = 22.04 (d, 1J = 16.4 Hz, PCH2), 40.20 (d, 2J = 8.0 Hz, NCH2),
134.64 (d, 2J = 17.4 Hz, 2 o-CH), 173.77 (COO), 196.92 (CO); cis/
trans-6a - d = 21.98 (superimposed d, 1J ꢀ 17 Hz, PCH2), 22.52
(superimposed d, 1J ꢀ 20 Hz, PCH2), 38.57 (d, 2J = 9.3 Hz, NCH2),
38.97 (d, 2J = 8.0 Hz, NCH2), 83.20 (d, 1J = 20 Hz, PCq), 83.63 (super-
imposed d, 1J ꢀ 26 Hz, PCq), 135.45 (d, 2J = 19.9 Hz, 2 o-CH), 135.53
(d, 2J = 21.2 Hz, 2 o-CH); cis/trans-7a - d = 22.79 (d, 1J = 19.9 Hz,
PCH2), 24.02 (d, 1J = 18.0 Hz, PCH2), 47.20 (d, 2J = 2.7 Hz, NCH2),
47.53 (d, 2J = 2.7 Hz, NCH2), 83.72 (d, 1J = 31.8 Hz, PCqN), 84.06 (d,
1J = 30.5 Hz, PCqN), 133.37 (d, 2J = 15.9 Hz, 2 o-CH,), 134.57 (d,
2J = 19.9 Hz, 2 o-CH), 172.34 (br s with shoulders, COO, cis-7a),
172.63 (d, 2J = 13.3 Hz, COO, trans-7a); superimposition of COO
signals of 6a with those of 6a.
The data for trans-8a were recorded at 170 K on a STOE-IPDS 2T
diffractometer with graphite-monochromated Mo Ka-radiation
(k = 0.71073 Å). The structure was solved by direct methods (SIR-
92) [27] and refined by full-matrix least-squares techniques
(
SHELXL-2013) [26]. All non-hydrogen-atoms were refined with ani-
sotropic displacement parameters. The hydrogen atoms on C2 and
N1 were located and refined isotropically without any restraints or
constraints. All other hydrogen atoms were refined isotropically at
calculated positions using a riding model with their Uiso values
constrained to 1.2 Ueq of their pivot atoms.
Acknowledgments
We thank G. Thede and M. Steinich for numerous NMR and
mass spectroscopic measurements and G. Sommer-Udvarnoki
(Georg-August-Universität Göttingen, Institut für Organische und
Biomolekulare Chemie, Zentrale Analytik/Massenspektrometrie)
for HRMS measurements.
4.3. Ethylene oligomerization screening
A cold (5–10 °C) solution of Ni(COD)2 in THF (10 mL) was added
slowly to a solution of 2a or 4a in methanol (15 mL) at 20 °C.
Stirring for 10 min gave a greenish yellow solution. Then the sol-
vent was evaporated under vacuum to dryness, yielding a greenish
yellow solid. The precatalyst complex was then suspended in
freshly distilled THF or in toluene (20 mL), followed by addition
of NaH (1–2 mmol) at 0–5 °C. The suspension was stirred for about
15 min and transferred via a Teflon tube into a 75 mL stainless
steel autoclave, which was then pressurized with ethylene (mass
determined by difference weight) and heated at 100 °C in a silicon
oil bath. The oligomerization started after ca. 20 min (according to
a control measurement the internal temperature had then reached
90–100 °C) and was monitored by electronic pressure registration.
Heating was stopped after 17 h, the autoclave cooled to ca. 5–10 °C,
unconverted C2H4 released, the difference weight (of converted
ethylene) determined and the residual content transferred into a
round-bottom flask. Volatiles were flash distilled under vacuum
(1 mbar / heating up to 100 °C) into a cooling trap. The solid resi-
due was stirred in MeOH/conc. HCl (1:1) for 1 d at r. t., washed
Appendix A. Supplementary data
CCDC 1486897, 898645 and 1483643 contain the supplemen-
tary crystallographic data for trans-2a, trans-4a and trans-8a. These
data can be obtained free of charge via http://dx.doi.org/10.1016/j.
poly.2017.04.014, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data
associated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.poly.2017.04.014.
References
[1] (a) P. Jana, S. Maity, D. Haldar, Adv. Org. Synth. 5 (2013) 355;
(b) S. Kotha, D. Goyal, A.S. Chavan, J. Org. Chem. 78 (2013) 12288;
(c) I. Avan, C.D. Hall, A.R. Katritzky, Chem. Soc. Rev. 43 (2014) 3575;
(d) A.F.M. Noisier, M.A. Brimble, Chem. Rev. 114 (2014) 8775;
(e) A. Stevenazzi, M. Marchini, G. Sandrone, B. Vergani, M. Lattanzio, Bioorg.
Med. Chem. Lett. 24 (2014) 5349;
(f) A.E. Metz, M.C. Kozlowski, J. Org. Chem. 80 (2015) 1;
(g) J.C. Maza, T.H. Jacobs, D.M. Uthappa, D.D. Young, Synlett 27 (2016) 805.
[2] (a) P.W. Lednor, W. Beck, H.G. Fick, H. Zippel, Chem. Ber. 111 (1978) 615;
(b) K. Kellner, A. Tzschach, Z. Nagy-Magos, L. Markó, J. Organomet. Chem. 268
(1984) 175;
with methanol and ether and dried under vacuum. The a/internal
olefin ratio, molecular weight (MNMR) and methyl/C = C ratio was
determined by 1H, the microstructure (polymer of entries 1 and
2) by 13C NMR measurement, both at 100 °C of swollen polymers
(8 h at 100 °C in C6D5Br), the density by the sinking method of
tablets, compressed at 10 kbar (at r. t.) in ethanol/water. The flash
distillate was analyzed by GC. Details of the equipment were
described earlier [25]. Conversion, characteristic data of polymers
and composition of flash distilled oligomers are given in Table 2.
(c) A.M.Z. Slawin, J.D. Woollins, Q. Zhang, J. Chem. Soc., Dalton Trans. (2001)
621.
[3] (a) A.A. Karasik, I.O. Georgiev, O.G. Sinyashin, E. Hey-Hawkins, Polyhedron 19
(2000) 1455;
(b) A.A. Karasik, I.O. Georgiev, E.I. Musina, O.G. Sinyashin, J. Heinicke,
Polyhedron 20 (2001) 3321;
(c) Review: E.I. Musina, A.A. Karasik, O.G. Sinyashin, G.N. Nikonov, in: E.F.V.
Scriven, C.A. Ramsden (Eds.), Advances in Hetero-cyclic Chemistry, Academic
Press, 2015, pp. 83–130.
4.4. Crystal structure analyses
Suitable crystals of trans-2a and trans-4a, respectively, were
mounted on a glass fiber in inert oil and measured at 100 K on
an Oxford diffractometer using mirror-focussed Cu K
[4] (a) S.R. Gilbertson, Prog. Inorg. Chem. 50 (2001) 433;
(b) A. Agarkov, S.J. Greenfield, D. Xie, R. Pawlick, G. Starkey, S.R. Gilbertson,
Biopolymers 84 (2006) 48;
a radiation
(c) C. Malan, T.R. Ward, in: A. Boerner (Ed.), Phosphorus Ligands in
Asymmetric Catalysis, Vol. 3, Wiley-VCH, Weinheim, 2008, pp. 1103–1131;
(d) L.-W. Xu, ChemCatChem 5 (2013) 2775.
(k = 1.54184 Å). Crystal data are compiled in Table 3. The structures
were refined anisotropically by full-matrix least-squares on F2 [26].

204
K.R. Basvani et al. / Polyhedron 130 (2017) 195–204
[14] H.-O. Kalinowski, S. Berger, S. Braun, 13C NMR-Spektroskopie, Thieme,
[5] (a) C. Meyer, M. Scherer, H. Schönberg, H. Rügger, S. Loss, V. Gramlich, H.
Grützmacher, Dalton Trans. (2006) 137;
Stuttgart, 1984, p. 95.
(b) S. Burck, S.G.A. van Assema, B. Lastdrager, J.C. Slootweg, A.W. Ehlers, J.M.
Otero, B. Dacunha-Marinho, A.L. Llamas-Saiz, M. Overhand, M.J. van Raaij, K.
Lammertsma, Chem. Eur. J. 15 (2009) 8134;
[15] (a) J.P. Albrand, G. Gagnaire, J.B. Robert, J. Chem. Soc., Chem. Commun. (1968)
1469;
(b) Review: W.G. Bentrude, W.N. Setzer, in: J.G. Verkade, L.D. Quin (Eds.),
Phosphorus-31 NMR Spectroscopy in Stereochemical Analysis, Methods in
Stereochemical Analysis, Vol 8, VCH, Weinheim, 1987, p. 365.
[16] (a) A. Zschunke, A. Hauser, H. Oehme, J. Tauchnitz, Org. Magn. Res. 6 (1974)
568;
(c) J. Tauchman, I. Cisarova, P. Stepnicka, Eur. J. Org. Chem. (2010) 4276.
[6] (a) J. Heinicke, N. Peulecke, P.G. Jones, Chem. Commun. (2005) 262;
(b) J. Lach, C.-Y. Guo, M.K. Kindermann, P.G. Jones, J. Heinicke, Eur. J. Org.
Chem. (2010) 1176;
(c) O.S. Fomina, D.G. Yakhvarov, J. Heinicke, O.G. Sinyashin, Uchenye zapiski
Kazanskogo Universiteta, 153–154, Proceedings of the Kazan University, 2012,
p. C13;
(d) J. Lach, N. Peulecke, M.K. Kindermann, G.J. Palm, M. Köckerling, J.W.
Heinicke, Tetrahedron 71 (2015) 4933;
(b) A. Zschunke, A. Hauser, H. Oehme, Z. Chem. 13 (1973) 310.
[17] M. Karplus, J. Am. Chem. Soc. 85 (1963) 2870.
[18] K. Issleib, G. Thomas, Chem. Ber. 93 (1960) 803.
[19] M. Ghalib, J. Lach, O.S. Fomina, D.G. Yakhvarov, P.G. Jones, J. Heinicke,
Polyhedron 77 (2014) 10.
(e) J. Lach, G.J. Palm, P.G. Jones, J.W. Heinicke, Eur. J. Inorg. Chem. (2016) 3417.
[7] (a) M. Peuckert, W. Keim, Organometallics 2 (1983) 594;
(b) W. Keim, R.P. Schulz, J. Mol. Catal. 92 (1994) 21;
(c) P. Kuhn, D. Semeril, D. Matt, M.J. Chetcuti, P. Lutz, Dalton Trans. (2007) 515.
[8] H. Oehme, K. Issleib, E. Leißring, Phosph. and the Related Group V Elements 3
(1973) 159.
[20] (a) V.P. Wystrach, D.W. Kaiser, F.C. Schäfer, J. Am. Chem. Soc. 77 (1955) 5915;
(b) K. Ward, J. Am. Chem. Soc. 57 (1935) 914.
[21] F. Simeon, P.A. Jaffres, D. Villemin, Tetrahedron 54 (1998) 10111.
[22] (a) K. Issleib, E. Leissring, M. Riemer, Z. Anorg. Allg. Chem. 519 (1984) 75;
(b) J. Heinicke, I. Böhle, A. Tzschach, J. Organomet. Chem. 317 (1986) 11.
[23] (a) R. Woy, Chem. Ztg. 20 (1897) 441;
[9] (a) K. Issleib, H. Oehme, Tetrahedron Lett. (1967) 1489;
(b) K. Issleib, H. Oehme, Chem. Ber. 100 (1967) 2685;
(c) K. Issleib, H. Oehme, R. Kümmel, E. Leißring, Chem. Ber. 101 (1968) 3619.
[10] K. Issleib, R. Kümmel, H. Oehme, I. Meißner, Chem. Ber. 101 (1968) 3612.
[11] N. Peulecke, M.K. Kindermann, M. Köckerling, J. Heinicke, Polyhedron 41
(2012) 61.
(b) E.P. Clark, Semimicro Quantitative Organic Analysis, Academic Press, New
York, 1943, pp. 65–67.
[24] A.W. Verstuyft, D.A. Redfield, L.W. Cary, J.H. Nelson, Inorg. Chem. 16 (1977)
2776.
[25] J. Heinicke, M. Köhler, N. Peulecke, M. He, M.K. Kindermann, W. Keim, G. Fink,
Chem. Eur. J. 9 (2003) 6093.
[12] (a) A.A. Buckler, J. Am. Chem. Soc. 82 (1960) 4215;
(b) M. Epstein, A.A. Buckler, Tetrahedron 18 (1962) 1231;
(c) S. Tripett, J. Chem. Soc. (1961) 2813.
[26] (a) G.M. Sheldrick, Acta Crystallogr., Sect. 64 (2008) 112;
(b) G.M. Sheldrick, SHELXL-97, University of Göttingen, Germany.
[27] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M.C. Burla, G. Polidori,
M. Camalli, J. Appl. Crystallogr. 27 (1994) 435.
[13] W. Wolfsberger, Chem. Ztg. 109 (1985) 317.