Phosphoric triamides. 31Phosphorus NMR chemical shift as a function of the P-N bond characteristics

Article abstract of DOI:10.1039/a704966h

Six phosphoric triamides in which amide nitrogens are incorporated into an increasing number (from 0 to 3) of the 1,3,2-diazaphospholidin-2-one rings have been prepared and their crystal structures have been determined. The structural changes from the non-cyclic to the mono-, di- and tri-cyclic systems result in the decrease of the N-P-N bond angles and the increase of the P-N bond distance. These changes are paralleled by a strong deshielding of the ³¹P nucleus, leading to an exceptionally high δ_p value for the tricyclic derivative. The δ_p-structural parameters relationship is discussed in terms of the changes in hybridization of phosphorus and the variation in the P-N bond order.

Full text of DOI:10.1039/a704966h

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3
1
Phosphoric triamides. Phosphorus NMR chemical shift as a
function of the P᎐N bond characteristics
,
a
b
,b
Susan A. Bourne,* Xavier Y. Mbianda, Tomasz A. Modro,*
a
b
Luigi R. Nassimbeni and Huijie Wan
a
Department of Chemistry, University of Cape Town, Rondebosch 7701, South Africa
Centre for Heteroatom Chemistry, Department of Chemistry, University of Pretoria,
b
Pretoria 0002, South Africa
Six phosphoric triamides in which amide nitrogens are incorporated into an increasing number (from 0
to 3) of the 1,3,2-diazaphospholidin-2-one rings have been prepared and their crystal structures have been
determined. The structural changes from the non-cyclic to the mono-, di- and tri-cyclic systems result in
the decrease of the N᎐P᎐N bond angles and the increase of the P᎐N bond distance. These changes are
31
paralleled by a strong deshielding of the P nucleus, leading to an exceptionally high ä value for the
P
tricyclic derivative. The ä –structural parameters relationship is discussed in terms of the changes in
P
hybridization of phosphorus and the variation in the P᎐N bond order.
3
1
The major contribution to the1 P NMR chemical shift results
from the paramagnetic term, not easily accessible by theor-
effect of the structural modifications on the shielding of the
phosphorus atom was then determined by P NMR spec-
31
2
etical calculations. The average excitation energy approxim-
troscopy, and the δ values were correlated with the molecular
P
ation leads to the equation linking the chemical shift with the
changes in bond overlap and hybridization. According to
Letcher and Van Wazer, the P chemical shift differences, ∆δ,
are dominated by three terms affected by structural variations,
eqn. (1), where ∆χ is the difference in electronegativity in the
parameters of the three P᎐N bonds of the triamide function.
3
31
Results and discussion
The representatives of the first three groups of substrates
studied (1, 2, 3) are interrelated by a sequence of 1,5-cyclization
reactions given in Scheme 1. The monocyclic phosphoric tri-
∆
δ = ϪC ∆χ ϩ k ∆n ϩ A ∆θ
(1)
X
π
P᎐X bond, ∆n the change in the π-electron overlap, ∆θ the
π
ArNH
O
Cl
change in the X᎐P᎐X σ bond angle, and C, k and A are con-
P
31
N
stants. In his extensive work on the applications of P NMR
ArNH
4
spectroscopy, Gorenstein focussed on the sensitivity of the
5
heavy-atom chemical shifts to bond angle changes and pro-
31
Cl
posed an empirical correlation between P chemical shifts and
the O᎐P᎐O bond angles in phosphates. According to that prin-
ciple, a decrease in the O᎐P᎐O bond angle results in a deshield-
ing of the phosphorus nucleus; ionization of the phosphate
function or the nature of the ester groups at phosphate oxygens
being of much lesser importance. As a consequence of the
relationship, cyclic five-membered ring phosphate esters, with
the endocyclic O᎐P᎐O bond angle less than 100Њ, are shifted
1
a Ar = Ph
i
Ph
ii
ArNH
O
Ar
Ar
N
O
Ar
P
Cl
Cl
P
N
N
N
N
6
downfield from their acyclic counterparts by up to 20 ppm. It is
well known that the same substrates are several orders of mag-
2
a Ar = Ph
c Ar = p-MeOC6H4
2b Ar = Ph
nitude more reactive in the nucleophilic cleavage of the P᎐O
7
31
bond than the acyclic analogues; the magnitude of the
P
NMR chemical shift can therefore be related to the reactivity of
the phosphoryl centre.
iii
In our studies on the structure–reactivity relationship in
phosphoric amides, we attempted to relate the solvolytic
reactivity of the endo- vs. exo-cyclic P᎐N bond in cyclic phos-
O
Ar
Ar
P
N
N
N
15
8
phoric triamides to the N NMR parameters of the substrates.
All compounds studied there were however non-crystalline
oils), so their molecular parameters (bond distances and
3
a Ar = Ph
(
angles) were not easily accessible. In our recent preparation of
phosphoric triamides, we have synthesized several structurally
Scheme 1 Reagents and conditions: i MeONa–MeOH (95%); ii NaH,
PhCH Br, Bu NBr, C (77%); iii NaH, C (90%)
9
H
6
H
6 6
2
4
6
closely related, crystalline products, suitable for X-ray diffrac-
tion studies. Using our procedures, as well as some literature
methods, we have now prepared a series of phosphoric tri-
amides in which the main structural difference involves sequen-
tial incorporation of the triamide nitrogens into the five-
membered 1,3,2-diazaphospholidin-2-one ring systems. The
amide 2a was additionally N-benzylated to a crystalline deriv-
ative 2b in order to evaluate any possible effect of inter-
molecular hydrogen bonding on the molecular parameters in
10
the solid state. The tricyclic amidate 4 was prepared after
11
some modifications of the literature procedure (Scheme 2).
J. Chem. Soc., Perkin Trans. 2, 1998
83

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Table 1 Structural and spectroscopic data for amides 1–4
Compound
δP a
P᎐O/Å
᎐
P᎐N/Å
N᎐P᎐N/Њ
1
2
2
2
3
4
a
a
b
c
4.3
1.464(3)
1.477(2)
1.473(3)
1.477(2)
1.437(5)
1.481(4)
1.636(4)
106.7(2)
103.4(2)
107.0(2)
110.7(2)
111.6(2)c
94.3(2)
108.8(2)
109.0(2)c
93.3(2)
110.4(11)
111.2(11)c
93.6(11)
114.4(3)
96.2(3)
1
1
.638(4)
.644(4)
13.4
17.2
14.7
33.5
98.0
1.637(2)
b
1
.646(2)b
1
.656(2)
1.629(3)
b
1
1
.669(3)b
.644(3)
1.627(2)
b
1
1
.645(2)b
.660(2)
a
1.653(6)
1
1
.661(6)
.676(6)
95.7(3)
1.663(4)
101.0(2)
101.2(2)
100.5(2)
1
1
.678(4)
.680(4)
a
c
b
In CDCl , 30 ЊC; concentration 0.2 . Endocyclic P᎐N bond.
Endocyclic N᎐P᎐N bond angle.
3
H
N
H2N
NH2
i
3
1
Ts
N
Fig. 1 Effect of structural parameters on the P NMR chemical shift
Ts
N
of phosphoric triamides. ᭡, δ vs. P᎐N bond distance; , δ vs. N᎐P᎐N
P
P
bond angle.
ii
TsNH
NHTs
N
Since the nature of the atoms bonded to phosphorus
(N,N,N,O) is constant for all compounds studied, and since the
type of the nitrogen substitution (aromatic or aliphatic sub-
stituents) is the same for the first three types (1, 2, 3), it may be
concluded that the observed deshielding effect results not from
N
Ts
Ts
iii
any effective electronegativity changes [∆χ term in eqn. (1)],
x
but from the changes in the nature of the P᎐N bonding that
follow the changes in the molecular geometry. This conclusion
H
N
O
P
can be corroborated by a comparison of the δ value for 4 (98.0)
iv
P
N
N
with that of δ = 23.3 reported for hexaethylphosphoric tri-
N
P
14
N
amide, (Et N) PO. For that pair of phosphoric triamides any
N
H
2 3
H
differences in the polar effects of the substituents can certainly
be ignored, and the dramatic deshielding effect of 74.7 ppm
must reflect solely the difference in the geometries of the
molecules.
4
Scheme 2 Reagents and conditions: i TsCl, pyridine (75%); ii EtONa–
EtOH, then TsOCH CH OTs (94%); iii H SO , then aq. NaOH (65%);
iv P(O)Cl , Et N (16%)
2
2
2
4
3
3
31
A convincing trend of the P NMR downfield shift with the
The compound proved to be highly unstable and decomposed
easily, so the determination of its crystal structure presented
some problems (see Experimental section). The required
molecular parameters were however successfully determined,
and the reactivity of 4 will be published elsewhere. The struc-
tural and spectroscopic data required for the discussion are col-
lected in Table 1. The first obvious result is a rather powerful
decrease in the O᎐P᎐O bond angle in the PO tetrahedra has
4
been demonstrated by Gorenstein for a large number of sys-
6
tems, and associated with the changes in the hybridization
5
resulting from the bond angle changes. A much poorer corre-
12
lation involving a few selected substrates was reported for the
15
S᎐P᎐S bond angle variations, and, to our knowledge, in only
one case the downfield shift of the δ value in cyclic phos-
P


deshielding effect (∆δ = ϩ93.8 ppm) of the structural changes
phorus() triamides (P derivatives) upon moving from the
P
31
11
in the sequence 1→4 on the P NMR chemical shift. The typ-
ical range for the δP values observed for the compounds in
which the phosphoryl function is bonded to three nitrogen
atoms is between Ϫ5 andϩ26; the only exception reported in
six-membered to the five-membered system was reported.
Following these approaches, we have related the δ values for
P
compounds 1–4 to the average value of the three N᎐P᎐N bond
angles present in each molecule. The result is presented in Fig.
1. The results obtained for the P᎐N bonding case fully confirm
earlier observations derived from the phosphate systems, and
they demonstrate that even within a narrow range of structur-
ally closely related substrates, variations in the geometry can
lead to formidable changes in the shielding parameters at the
phosphoryl centre. The observed effect prompted us to analyse
the change in the molecular parameters within the series in
more detail.
31
a recent compilation of the P NMR data and including 23
1
3
examples, is compound 4, for which a value of δ = 41 was
P
11
reported by Verkade and co-workers. When preparing com-
pound 4, we have found however that the value of the P NMR
31
chemical shift for the product which was also used for X-ray
diffraction study is, in fact, δ = 98.0, much higher than that
P
11
reported in the literature. We have observed occasionally in
31
the P NMR spectra of crude 4 a signal of δ ≈ 40, probably
P
derived from the decomposition of 4 and taken by the authors
of the report as a true value for the tricyclic compound.
The N᎐P᎐N bond angle decreases along the series indicating
the shift of the hybridization of the phosphorus–nitrogen bond-
8
4
J. Chem. Soc., Perkin Trans. 2, 1998

View Article Online
Table
2
Typical P᎐N bond distances for organophosphorus
compounds containing nitrogen
the extrapolation of the plot to the non-bonded P᎐N distances
full removal of the P atom from the bonding sphere of nitro-
(
gens) should indicate the limiting δ value (highly positive)
for the PO ion, inaccessible for direct measurement, but a
P
Compound or class
of compounds
ϩ
Hybridization
P᎐N/Å
Reference
common species in the mass spectra of organophosphorus
Ϫ
ϩ a
3
3
22
HO P᎐NH3
P(O)᎐N
sp
sp –sp
1.77
17
18
19
20
compounds.
3
a
2
1.61–1.65
1.52–1.60
1.49
a
2
P(NR)᎐N
sp
b
P᎐N
sp
Experimental
᎐
a
b
Solvents and commercially available substrates were purified
by conventional methods. NMR spectra were recorded on a
Determined by X-ray diffraction. Determined by gas-phase spectro-
scopy.
Bruker AC 300 spectrometer in CDCl , and the chemical shift
3
1
values are given in ppm relative to the solvent ( H, δ 7.24), or to
3
3
31
ing orbitals from the sp towards the unhybridized, p (pyram-
idal) state. Such a trend should have a profound effect on other
properties of the P᎐N bonding, such as bond length, hence the
stability. For any covalent bond the less s-character in a hybrid
85% H PO ( P, δ 0.00) as external standard. J Values are given
3
4
in Hz.
Preparation of substrates
Preparation of 1a, 2a, 2c and 3a has been described before.
3-(2-Chloroethyl)-1-phenyl-2-(N-benzyl-N-phenylamino)-
16
9
atomic orbital (AO), the further it lies from the bonded nuclei.
Examination of the available data on the P᎐N bond distances in
various classes of organophosphorus compounds allowed us to
arrange them into groups according to the decreasing P᎐N
bond length resulting from the increasing s-character in the
bonding orbital (Table 2). The variations in the bond length are
large, and our value of the average P᎐N distance of 1.674 Å
obtained for 4 locates this compound beyond the usual range of
values observed for phosphoric triamides. The gradual decrease
in the N᎐P᎐N bond angles is paralleled therefore by the stretch-
ing of the P᎐N bond towards the value obtained for the ‘pure’
single bond in the zwitterionic form of phosphoramidic acid,
1,3,2-diazaphospholidin-2-one 2b. To a solution of 2a (0.50 g,
1.49 mmol) and phenylbromomethane (0.34 ml, 2.98 mmol) in
THF (15 ml), NaH (0.053 g, 2.23 mmol) and Bu NBr (0.025 g)
4
were added and the mixture was stirred overnight at room
temperature. The reaction mixture was poured on ice-cold aq.
NH Cl (30 ml) and extracted with CHCl3 (3 × 10 ml); the
4
chloroform solution was dried (MgSO ), evaporated and the
4
crude product was purified by column chromatography (SiO2,
diethyl ether). Yield 0.49 g (77%); colourless solid, mp 103–
104.5 ЊC. δ (CDCl ) 17.2; δ 2.95 (2H, m), 3.30 (4H, m), 4.42
P
3
H
Ϫ
ϩ
HO P᎐NH . A similar relationship between the bond angles
(1H, dd), 4.98 (1H, dd), 6.68 (2H, m), 6.97 (1H, t), 7.08 (7H, m),
7.16 (3H, m), 7.25 (2H, t) (Found: C, 64.83; H, 6.00; N, 9.86.
C H N ClOP requires: C, 64.86; H, 5.88; N, 9.87%).
3
3
and distances was reported before for a pair of cyclic phosphate
esters with the P᎐OAr group located in the equatorial or the
2
3
25
3
21
23
axial position. The contraction of the endocyclic O᎐P᎐O
bond angle in the equatorial stereoisomer (104.8 vs. 107.9Њ) was
followed by the endocyclic P᎐O bond distance increase to an
average of 1.565 relative to 1.554 Å in the axial isomer. When
the average P᎐N bond distances obtained for the series 1–4 were
used for the correlation with the δ values, a plot mirroring that
obtained for the N᎐P᎐N bond angle effect was obtained (Fig.
1
1,4,7-Tritosyl-1,4,7-triazaheptane. A solution of bis(2-
aminoethyl)amine (20.6 g, 0.20 mol) in pyridine (30 cm ) was
3
added dropwise to a solution of toluene-p-sulfonyl chloride
3
(115 g, 0.6 mol) in pyridine (300 cm ) at such a rate that the
temperature of the reaction mixture was maintained at 50–
60 ЊC. The solution was stirred at that temperature for an add-
itional 30 min, cooled to room temperature, and water (100
P
3
). It is, to our knowledge, the first direct correlation of a P᎐X
cm ) was slowly added. The mixture was stirred overnight,
31
bond distance with the P NMR shielding, and we propose it
as a better measure of the effect of structural parameters on the
NMR characteristics. The increase in the pyramidality of the
cooled in ice and the white precipitate was filtered off, washed
with ice-cold 95% ethanol and dried at 100 ЊC under reduced
pressure. Purified by crystallisation from acetonitrile. Yield 82.9
23
N P fragment of the phosphoric triamide tetrahedron results in
g (75%); mp 173–175 ЊC (lit. mp 174-175 ЊC).
1,4,7-Tritosyl-1,7-disodium-1,4,7-triazaheptane.
3
11,24
the increase of the P᎐N bonding distance (more ‘p’ character in
the bonding orbital), which in turn reduces the P᎐N bond order
by reducing the p→d π back-donation to the phosphoryl centre.
When not all nitrogen atoms are incorporated into the 1,3,2-
diazaphospholidin-2-one skeleton, the exocyclic P᎐N bond is
capable of compensating partially for the effect of the hybrid-
ization change of the endocyclic nitrogens by increasing the
conjugation of the exocyclic nitrogen lone pair with phos-
phorus. This can be clearly seen for substrates 2, for which the
exocyclic P᎐N bond is always significantly shorter than the two
endocyclic bonds. The extreme situation is achieved in 4 where
all three nitrogens are located in the bridgehead positions
shared by three phospholidine rings. In this molecule no ‘com-
pensation’ is possible, all N᎐P᎐N bond angles are small and all
A solu-
tion of tritosyl triamine (75 g, 0.132 mol) in anhydrous ethanol
3
(330 cm ) was heated to reflux, the heat source was removed and
a solution of sodium ethanolate (prepared from 34.5 g of
3
sodium in 260 cm of anhydrous ethanol) was added in an
atmosphere of dry nitrogen as rapidly as possible. The solution
was decanted and left overnight; the precipitated disodium
derivative was filtered off under nitrogen, washed with ice-cold
ethanol, then with diethyl ether and dried at 100 ЊC under
reduced pressure. Yield 79.1 g (98%). The product was used for
the next reaction without further purification.
24
1,4,7-Tritosyl-1,4,7-triazacyclononane. A solution of the
disodium derivative (79 g, 0.129 mol) in anhydrous DMF (530
3
cm ) was heated under dry nitrogen to 100 ЊC and a solution
3
P᎐N bond distances large (all nitrogens approach the ‘p ’ char-
of 1,2-bis(toluene-p-sulfonyl)ethane (prepared by tosylation of
acter), and no significant p→d π back-donation from nitrogens
ethane-1,2-diol with tosyl chloride in pyridine; 77%; 48.1 g,
0.129 mol) in DMF (270 cm ) was added slowly with stirring.
The solution turned turbid and yellow; it was stirred for an
3
can be expected. Such a geometry of a triamide is associated
31
with a dramatic deshielding of the P nucleus, as demonstrated
by the unusually high value of the chemical shift, well beyond
the range expected for the unstrained amides of phosphoric
acid.
additional 1 h at 100 ЊC, and cooled to room temperature. The
3
solution was then added to vigorously stirred water (2500 cm ),
3
the precipitate was filtered off, washed with water (500 cm ) and
It may be concluded therefore that the two last terms in eqn.
1) should not be treated independently, since the variations of
dried at 80 ЊC under reduced pressure. Yield 72 g (94%); mp
219–223 ЊC (lit. mp 217–223 ЊC); δH 2.41 (9H, s, 3 × Me of
24
(
the latter affect the former via the change in the π-electron over-
Ts), 3.40 (12H, s, 6 × CH ), 7.23 (12H, two d, 3 × C H ).
2
6
4
lap between nitrogen and the phosphorus nuclei. The ∆δ vs.
P᎐N bond distance plot (Fig. 1) leads to speculation that
1,4,7-Triazacyclononane. The tritosyl derivative (20 g, 33.8
P
3
mol) was dissolved in conc. H SO (10 cm ) and the mixture was
2
4
J. Chem. Soc., Perkin Trans. 2, 1998
85

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Table 3 Crystal and data collection details
1
a
2b
3a
4
Empirical formula
Formula weight
C H Cl N OP
372.22
C H ClN OP
425.88
C H N OP
299.30
C H N OPH O
6 12 3 2
191.20
1
6
20
2
3
23 25
3
16 18
3
Space group
P2 /c
P2 /c
Pbca
6.235(3)
18.758(6)
25.688(9)
90
3004(2)
8
P2 /c
1
1
1
a/Å
b/Å
c/Å
β/Њ
11.785(2)
18.564(2)
8.70(1)
104.52(1)
1843(2)
4
9.176(2)
9.799(2)
24.913(4)
91.59(1)
2239.2(8)
4
23.109(9)
7.119(1)
10.901(2)
103.35(3)
1744.9(8)
8
3
V/Å
Z
F(000)
µ(Mo-Kα)/mm
776
0.446
896
0.261
1264
0.185
816
0.280
Ϫ1
Crystal dimensions/mm
D /g cm
c
0.20 × 0.20 × 0.20
1.341
0.15 × 0.15 × 0.18
1.263
0.15 × 0.15 × 0.25
1.323
0.10 × 0.12 × 0.30
1.455
Ϫ3
θ range scanned/Њ
Range of h, k, l
1–25
13, Ϫ22, ±10
2.8
1–25
±10, 11, 29
<1
1–25
7, 22, 30
1.2
1–25
27, Ϫ8, ±12
5.8
Decay of std refins (%)
Absorption correction:
Min, max, ave, correction
No. reflections collected
No. reflections with Irel > 2σIrel
No. parameters
0.953, 0.999, 0.983
3234
1977
0.952, 0.997, 0.971
3723
1487
a
2645
915
191
0.660, 0.999, 0.796
3071
1611
236
271
237
Max LS shift to esd
R1 (I > 2σI)
0.020
0.0674
0.2393
1.031
0.007
0.0547
0.1296
0.839
0.000
0.0898
0.2687
0.809
0.53, Ϫ0.75
0.114
0.0630
0.1798
0.941
wR2 (all data)
2
Goof on F
Ϫ3
Max, min residual electron density/e Å
0.55, Ϫ0.62
0.22, Ϫ0.24
0.36, Ϫ0.47
a
An absorption correction was not applied to this crystal.
heated with stirring at 120 ЊC for 120 h. After cooling the solu-
16Њ р θ р 17Њ. The ω/2θ mode was used at a maximum
recording time of 40 s. The scan width chosen was (0.85 ϩ 0.35
tan θ) and an aperture width of (1.12 ϩ 1.05 tan θ) and a verti-
cal aperture length of 4 mm were used. Three standard reflec-
tions were checked periodically for intensity and orientation
control. Data were corrected for Lorentz-polarization and
absorption effects.
tion was neutralized by slow addition of aq. NaOH (240 g in
3
5
00 cm water) and left overnight at 0 ЊC. The supernatant solu-
tion was decanted from the precipitated Na SO and extracted
2
4
3
in a continuous extraction apparatus with chloroform (350 cm )
for 3 days. Sodium sulfate was additionally extracted with
3
chloroform (200 cm ) and the combined chloroform solution
was evaporated on a rotary evaporator. The residue was dis-
solved in benzene (4 × 50 cm ), the combined benzene solution
Structure solution and refinement. Structures of 1a, 2b, 3a
3
27
and 4 were solved by direct methods using SHELXS86.
2
was dried (Na SO ), and the solvent was removed under
They were refined by full matrix least squares on F using
2
4
28
reduced pressure. The crude product (viscous oil) was purified
by bulb-to-bulb distillation, oven temp. 40 ЊC/0.1 mm. Colour-
SHELXL93. All non-hydrogen atoms were refined aniso-
tropically. Unless otherwise stated, hydrogens were placed in
calculated positions and linked to common isotropic temper-
ature factors. The carbons of one chloroethyl chain in 1a were
disordered over two positions and were refined with site
occupancies of 0.61 and 0.39. Hydrogens attached to N(2)
and N(3) on this molecule were located in difference electron
density maps and modelled independently, but with a dis-
tance restraint on the N᎐H bond length. The benzyl hydro-
gens of 2b were located in a difference electron density map
and refined independently. Compound 4 crystallized with
two independent molecules and two water molecules in the
asymmetric unit. The water hydrogens were located in the
difference electron density map and allowed to refine
independently. Further details are given in Table 3.
less oil, 2.83 g (65%); δ 1.81 (3H, s, 3 × NH), 2.78 (12H, s,
H
25
6
× CH ). Lit. δH 1.83 (3H, s), 2.82 (12H, s).
2
4,10
11
1
0-Oxo-10-phospha-1,4,7-triazatricyclo[5.2.1.0 ]decane 4.
A solution of phosphoryl chloride (1.19 g, 7.8 mmol) in ben-
3
zene (24 cm ) was added over a period of 1 h with stirring to
an ice-cooled solution of 1,4,7-triazacyclononane (1.0 g, 7.7
mmol) and triethylamine (2.34 g, 23.2 mmol) in benzene (50
3
cm ). The mixture was stirred at room temperature for 2 h,
filtered under dry nitrogen, and the precipitate was washed with
3
benzene (200 cm ). The combined benzene solution was evap-
orated under reduced pressure yielding a crude product which
was purified by crystallization from boiling benzene–hexane–
CH Cl . White crystals, 0.21 g (16%); mp 212–215 ЊC (dec)
2
2
11
11
(
lit. mp 215 ЊC, dec); δ (CDCl ) 98.0; (C D ) 93.8 (lit. δP 41)
P 3 6 6
(
Found: C, 38.35; H, 7.36; N, 21.72. C H N OPؒH O requires
Molecular and crystal structures
6
12
3
2
C, 37.69; H, 7.38; N, 21.98%).
Full crystallographic details, excluding structure factor tables,
have been deposited at the Cambridge Crystallographic Data
Centre (CCDC). For details of the deposition scheme, see
‘Instructions for Authors’, J. Chem. Soc., Perkin Trans. 2, avail-
able via the RSC Web pages (http://chemistry.rsc.org/rsc/
p1pifa.htm). Any request to the CCDC for this material should
quote the full literature citation and the reference number 188/
109.
Fig. 2(a) shows the molecular structure of 1a. One of the
ethyl chains is disordered as shown. The molecule is held in a
fairly rigid conformation by two intramolecular hydrogen
bonds [C(22)᎐H(22) ؒ ؒ ؒ N(3) and C(32)᎐H(32) ؒ ؒ ؒ O(1)]. Mole-
cules pack in layers parallel to [001], held in place by N᎐H ؒ ؒ ؒ
O hydrogen bonding. These layers in turn pack head-to-tail
Structure determination
Crystal and molecular structures of 2a and 2c have been
26
described before.
Sample preparation and data collection. Single crystals of 1a,
b and 3a were selected and mounted on the end of a glass fibre
2
using cyanoacrylate glue. Compound 4 was very unstable in air
and was covered in glue before it was mounted in a Lindemann
capillary which was then sealed with glue. Data were collected
on an Enraf–Nonius CAD4 diffractometer at 293 K using
graphite monochromated Mo-Kα radiation (λ = 0.7107 Å).
Accurate cell parameters were obtained by least-squares
analysis of the setting angles of 24 reflections in the range
8
6
J. Chem. Soc., Perkin Trans. 2, 1998

View Article Online
Fig. 2 Molecular structures of 1a, 2b, 3a and 4
Table 4 Intra- and inter-molecular contacts
D ؒ ؒ ؒ A/Å D᎐H/Å
cup-shaped conformation. Details are given in Table 4. The
molecules pack in herringbone fashion.
D᎐H ؒ ؒ ؒ A/Å
Compound 4 was unusual in this series because it was found
to be very unstable. The crystal structure revealed another
unusual feature—the inclusion of water molecules in the solid
stucture.† Fig. 2(d) shows the molecular structure of 4. As
expected, this molecule is very rigid. Each five-membered ring
is in the envelope conformation, with C(1), C(3) and C(6) the
atoms out-of-plane of each ring respectively. The molecules
pack in layers parallel to [001] with a layer of water molecules
interleaved between the layers of 4. The structure is held
together by an infinite network of O᎐H ؒ ؒ ؒ O hydrogen bonds.
Details are given in Table 4.
1
a
a
N(2)᎐H(2) ؒ ؒ ؒ O(1)
2.857(5)
3.350(6)
2.509(5)
2.80(4)
0.816(35)
0.930(7)
0.930(7)
0.97(5)
164(4)
C(22)᎐H(22) ؒ ؒ ؒ N(3)
C(32)᎐H(32) ؒ ؒ ؒ O(1) a
C(14)᎐H(14) ؒ ؒ ؒ Cl(2)b
C(34)᎐H(34) ؒ ؒ ؒ Cl(2)
119.5(1)
129.3(1)
155.0(6)
158.5(2)
2.968(7)
0.930(9)
2
b
C(4)᎐H(4) ؒ ؒ ؒ O(1)
2.941(5)
0.92(3)
116(2)
3
a
C(16)᎐H(16) ؒ ؒ ؒ O(1)
C(32)᎐H(32) ؒ ؒ ؒ O(1)
3.165(9)
3.114(9)
0.93(1)
0.93(1)
131.3(7)
130.2(8)
Acknowledgements
Financial assistance from the University of Pretoria, University
of Cape Town, and the Foundation for Research Development
is gratefully acknowledged.
4
O(1W)᎐H(1W) ؒ ؒ ؒ O(1A)
O(1W)᎐H(2W) ؒ ؒ ؒ O(2W)
O(2W)᎐H(3W) ؒ ؒ ؒ O(1B)
O(2W)᎐H(4W) ؒ ؒ ؒ O(1W)
2.883(6)
2.992(8)
2.909(6)
2.949(8)
0.95(8)
1.16(8)
1.16(9)
0.94(9)
172(6)
165(6)
156(6)
145(8)
c
† The relationship between the molecular structure of 4 and its chem-
1
2
ical behaviour will be published separately.
a
b
c
via x, ¹ Ϫ y, z Ϫ ¹. via 1 Ϫ x, y Ϫ ¹, ¹ Ϫ z. via x, 1¹ Ϫ y, z Ϫ ¹.
¯
²
¯
²
¯ ¯
² ²
¯
²
¯
²
References
parallel to [010], with two weaker intermolecular contacts
between layers [C(14B)᎐H(14D) ؒ ؒ ؒ Cl(2) and C(34)᎐H(34) ؒ ؒ ؒ
Cl(2)]. Details of the intermolecular contacts are given in
Table 4.
Compound 2b also contains one intramolecular C᎐H ؒ ؒ ؒ O
hydrogen bond, involving one of the benzyl hydrogens [Fig.
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Paper 7/04966H
Received 10th July 1997
Accepted 25th September 1997
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J. Chem. Soc., Perkin Trans. 2, 1998