Low temperature neutron and X-ray diffraction study of imino(triphenyl)phosphorane

Article abstract of DOI:10.1016/S0022-328X(97)00551-2

The structure of imino(triphenyl)phosphorane, Ph₃PNH 1 has been determined by low-temperature X-ray and neutron diffraction. This dual study is the first such for an iminophosphorane. From the neutron diffraction data, the P-N bond length is 1.582(2) A and the P-N-H angle is 115.0(2)°.

Full text of DOI:10.1016/S0022-328X(97)00551-2

Journal of Organometallic Chemistry 550 Ž1998. 449–452
Short communication
Low temperature neutron and X-ray diffraction study of
1
ž
/
imino triphenyl phosphorane
Matthew G. Davidson a,), Andr e´ s E. Goeta , Judith A.K. Howard , Christian W. Lehmann ,
a
a,2
a
b
a
Garry M. McIntyre , Richard D. Price
UniÕersity of Durham, Department of Chemistry, Science Site, Durham, DHI 3LE, UK
a
b
Institut Laue LangeÕin, B.P. 156, Grenoble 38042, Cedex 9, France
Received 2 April 1997
Abstract
The structure of iminoŽtriphenyl.phosphorane, Ph PNH 1 has been determined by low-temperature X-ray and neutron diffraction. This
3
dual study is the first such for an iminophosphorane. From the neutron diffraction data, the P–N bond length is 1.582Ž2. A˚ and the
P–N–H angle is 115.0Ž2.8. q 1998 Elsevier Science S.A.
Keywords: Iminophosphorane; Phosphorus; X-ray and neutron diffraction
1
. Introduction
2. Experimental
During our work on the interactions of phosphonium
2
.1. Synthesis of imino(triphenyl)phosphorane 1
ylides and iminophosphoranes with s-block metals w1–3x
triphenyl phos-
and organic acids w4x, we isolated iminoŽ .
phorane, Ph PNH 1.
3
All solvents were freshly distilled over appropriate
drying agents prior to use.
Although iminophosphoranes are commonly repre-
sented with a P5N double bond 1a, their chemical and
structural similarity to isoelectronic phosphonium ylides
w5x suggests that a dipolar ylidic representation 1b is
Ph PNH was prepared by modification of a method
3
described previously w6x: 15 g
Ž
57.3 mmol
placed in a 1000 ml round-bottomed Schlenk vessel and
dried in vacuo before addition of acetonitrile 100 ml
.
Ph P were
3
equally valid Scheme 1 . The molecular structure of 1,
Ž .
Ž
.
.
shown in Fig. 1, is of interest in order to probe the
nature of this P–N bonding both by accurate structural
studies and by comparison with N-substituted, -com-
plexed, -protonated, and -metallated derivatives.
A total of 3 ml bromine in 45 ml acetonitrile were
added dropwise over a period of 45 min via a pressure-
equalising funnel and ammonia was then bubbled
through the reaction mixture for 4 h. The resulting
solution was stirred at ambient temperature overnight
and after removal of the solvent in vacuo the residue
was extracted with chloroform and the undissolved
NH Br removed by filtration. Precipitation by addition
4
)
Ž .
82% Ph PNH Br
Corresponding author. Fax: q44-0191-386-1127; e-mail:
of diethyl ether yielded 33.5 g
which was subsequently dried in vacuo and stored under
N . 15 g 42 mmol Ph PNH Br and 1.01 g 42 mmol
NaH were placed in a round-bottomed Schlenk vessel
3 2
m.g.davidson@durham.ac.uk.
1
Dedicated to Prof. Ken Wade on the occasion of his 65th
Ž
.
Ž
.
2
3
2
birthday with sincere thanks for stimulating and fruitful collabora-
tions in elucidation of the beautiful and complex structures that stem
from a unique and extensive chemistry.
under a dry N atmosphere and 50 ml toluene added.
2
2
Also corresponding author.
The reaction mixture was stirred at 1008C for 48 h and
0
022-328Xr98r$19.00 q 1998 Elsevier Science S.A. All rights reserved.

4
50
M.G. DaÕidson et al.rJournal of Organometallic Chemistry 550 (1998) 449–452
Zs4. 6376 reflections, from which 2577 were unique
Ž
5
R s0.0282 , were collected to a maximum 2u of
.
int
18, y17-h-15, y10-k-10, y7-l-13; no
absorption correction was applied. The structure was
solved by direct methods and 2545 reflections were
Scheme 1.
1 was
used for the least squares refinement w8x. HŽ .
located from a difference Fourier map and freely re-
fined, all other H atoms were placed at calculated
positions and refined using a riding model with their
individual isotropic displacement parameter set to 1.2
then filtered hot to remove NaBr. Cooling the resulting
pale brown solution to room temperature overnight
yielded 7.7 g 66% colourless crystals of 1 which were
Ž .
times that of the attached C atom. Refinement was on
isolated and stored under N in a glove box. Crystals
2
2
F
and converged to a wR s0.1149, goodness of
for the diffraction studies were obtained by similar
reactions performed on a 5 mmol scale using 15 ml
toluene.
2
fits1.112 for all data, and conventional R s0.0479
1
for w2077 reflections with F)4s
Ž
F
.
x, 185 parameters.
y3
˚
Residual electron density, q0.14ry0.21 e A
.
2
.2. X-ray crystal and molecular structure determina-
tion of 1
2
.3. Neutron diffraction study of 1
The X-ray diffraction study was performed at 150
K on a Siemens SMART-CCD diffractometer w7x using
graphite-monochromated Mo–K a X-radiation
2
Ž .
The neutron diffraction experiment was performed
on the D10 four-circle diffractometer w9x at the Institut
Ž .
Ž
ls
.71073 A Unit cell parameters were obtained from
67 reflections 17 - u - 24 . Empirical formula:
˚
.
˚
0
2
Laue Langevin using a wavelength of 1.2658 4 A
obtained by a Cu 200 monochromator. The air-sensi-
Ž
.
Ž
.
C H NP, Ms277.29. A white crystal of 0.2=0.2=
tive crystals were manipulated in a glove-box under an
1
8
16
0
.1 mm was used. Space group P2 rc
Ž
Monoclinic
, A˚ , cs10.965
.
atmosphere of dry, oxygen-free N . A sample was
1
2
Ž
9
.
A˚ , bs9.597
Ž
6
.
Ž
7
.
,
mounted on an aluminium pin using a low temperature
with as14.587
3
y1
A, bs90.428 6 8, Vs1535 2 A , ms0.168 mm
Ž .
˚
Ž .
˚
Ž
4K epoxy glue Oxford Instruments, TRZ0004 and
. Ž .
Fig. 1. Ortep plot of 1 with thermal ellipsoids at 70% level Žderived from neutron diffraction data..

M.G. DaÕidson et al.rJournal of Organometallic Chemistry 550 (1998) 449–452
451
then, whilst still in the glove-box, sealed under a quartz
dome in order to maintain the inert atmosphere around
the crystal during subsequent transport and measure-
While Gr u¨ n et al. w11x mention the non-existence of
intermolecular N–H . . . N bridges, they omit to report
the existence of three intermolecular C–H . . . N contacts
ment. Data collection was carried out at 20
Ž
1
.
K using a
see Table 1 which form layers of molecules parallel to
Ž .
liquid-He flow cryostat. Unit cell parameters were de-
the bc-plane. One hydrogen bond forms chains along
the c-axis, while the other two intermolecular hydrogen
interactions form chains along b, the links of which are
tetrameric. Layers formed by the combination of these
interactions have a thickness of two molecules, approxi-
mately the length of the a-axis. One such layer is
shown in Fig. 2.
Ž
5
.
A˚ bs
Ž . Ž . Ž .
A˚ , cs10.686 A˚ , bs90.72
4 3 3 8, Vs
3
termined from 25 reflections, as14.301
9
1
.541
458
Ž
1
.
A˚ . A crystal of 3.5=3=1 mm was used to
collect 3412 reflections
y11-k-3, y7-l-12; 2716 unique reflections
R s0.023S were used for the refinement. Data were
corrected for absorption using a Gaussian grid integra-
tion w10x
. Heavy atom
umax s50.74 , y17-h-17,
Ž .
Ž
.
int
The molecular geometry of 1 is largely as expected
Ž
Tmax s0.83l8 and T s0.5878
.
Ž
values quoted for 1 are derived from the neutron
diffraction experiment . The P atom has a slightly dis-
torted tetrahedral geometry with C–P–N angles ranging
from 109.1 to 115.6 8. The P–N bond length in 1
w1.582
A˚ x is in the range of those reported for
N-substituted imino triphenyl phosphoranes: in
A˚
Ph PN p-BrC H the P–N bond length is 1.567
A˚ w16x. The P–N–H
8x is more acute than the
corresponding P–N–C angles in either of the above-
mentioned N-aryl substituted derivatives w124.2
8 and
130.4 8 for Ph PN p-BrC H and Ph PNPh, respec-
min
positions from the X-ray model were used as a starting
point for the refinement. Hydrogen atom positions were
located from subsequent difference Fourier maps. All
atoms were refined with anisotropic atomic displace-
.
Ž
1
.
1
Ž .
2
Ž .
2
ment parameters. Refinement w8x was on F and con-
Ž
.
verged to a wR s0.0435, goodness of fits1.149 for
Ž
.
4
6
Ž .
2
3
6
all data and conventional R s0.0389 for w2083 reflec-
3
w15x and in Ph PNPh, 1.602Ž .
1
3
tions with F)4s
Ž
F
.
x, 326 parameters.
2
bond angle in 1 w115.0Ž .
Lists of structure factors, anisotropic displacement
parameters, atomic coordinates and complete geometry
are available from the authors on request.
5
Ž .
Ž
3
.
Ž
.
4
3
6
3
tivelyx. Whether this is simply a steric effect or, more
significantly, indicative of pyramidalisation of N such
as it is found for the ylidic carbon atom in the isoelec-
tronic unsubstituted phosphonium ylide, Ph PCH w17x,
3
. Results and discussion
3
2
An X-ray structure of 1, determined at 203 K, has
remains unclear. The P–N bond length in 1 is also
also recently been reported by Gr u¨ n et al. w11x. Compar-
ison with that presented here shows a disagreement in
the cell parameters, in particular b and b. In order to
investigate the possibility of a phase transition occurring
between 203 and 150 K, we remeasured our cell param-
concordant with the decrease in P–X distance along the
isoelectronic and isonuclear series of Ph PX com-
3
3
pounds from Ph PBH to Ph PO wP–X distances for
3
3
3
XsBH w18x, CH w16x, NH
Ž
this work
.
and O w12–14x
and 1.494
3
2
are 1.917
Ž
average
.
, 1.661
Ž
average
.
, 1.582
Ž
2
.
eters of 1 at 203 K, obtaining as14.508
Ž
4
.
, bs
average
Ž .
A˚ , respectivelyx. This reduction in P–X bond
length from B to O can be attributed to a combination
of factors: a decrease in covalent radius; an increase in
9
.557 . We can, there-
Ž
2
.
, cs10.893
Ž
2
.
, bs90.29
Ž
1
.
fore, discount a phase transition as being responsible for
the discrepancy and instead attribute it to the characteri-
sation of two different polymorphs of Ph PNH. This
electronegativity
Ž
and a possible increase in the degree
; and a possible
of electrostatic shortening in the bond
.
3
possibility is supported by a number of observations.
Firstly, the ambiguous nature of the ylidic P–N bond in
increase in P–X multiple bonding. The relative contri-
bution of each of these factors, which is not necessarily
constant throughout the series, has yet to be satisfacto-
rily resolved.
To further elucidate the nature of the P–N bond in
iminophosphoranes in particular, and ylidic P–X where
Ž
1
is consistent with the existence of different molecular
geometries of similar energy: the main difference in the
geometries of the two polymorphs is in the length of the
P–N bond w1.524
Ž
3
.
and 1.582
Ž
2
.
A˚ , Gr u¨ n et al. w11x
and this neutron
Ž
. work, respectivelyx. Secondly, poly-
morphism has been observed in similar compounds: for
example, three polymorphs of Ph P5O, which is iso-
Table 1
3
electronic and isonuclear with 1 are known w12–14x.
Thirdly, samples of 1 were obtained by different syn-
thetic procedures and crystallised from different sol-
vents.
Geometries of intermolecular C–H...N contacts found in 1, derived
from neutron diffraction data
D–HPPPA
D–H
HPPPA DPPPA D–HPPPA
CŽ14.–HŽ14....NŽ1.i 1.082Ž3. 2.410Ž4. 3.331Ž2. 142.1Ž3.
ii
CŽ26.–HŽ26....NŽ1. 1.081Ž3. 2.484Ž3. 3.534Ž2. 163.5Ž3.
iii
CŽ34.–HŽ34....NŽl.
1.088Ž4. 2.599Ž4. 3.439Ž2. 133.4Ž3.
3
Cell parameters from Ref. w11x: as14.604Ž9., bs9.289Ž6.,
Symmetry Codes: Ži. 1y x, 0.5q y, 1.5y z; Žii. x, 0.5y y, 0.5q z;
Žiii. x, y0.5y y, 0.5q z.
cs10.966Ž6. A˚ , b s93.35Ž5.8 at T s203 K.

4
52
M.G. DaÕidson et al.rJournal of Organometallic Chemistry 550 (1998) 449–452
Fig. 2. Packing diagram of 1, viewed down the crystallographic c axis, showing one polymeric layer of molecules parallel to the bc plane.
H-atoms, except those involved in hydrogen bonding, omitted for clarity.
.
bonds in general, we plan to collect
w5x A.W. Johnson, Ylides and Imines of Phosphorus, Wiley, New
XsC, N or O
York, 1993.
X–ray diffraction data at 20 K using the Fddd high
intensity cryogenic diffractometer at Durham University
w19x to complement the neutron diffraction study re-
w6x H.J. Cristau, J. Kadoura, L. Chiche, E. Torreilles, Bull. Soc.
Chim. Fr. Ž1989. 515.
w7x Program used for data collection: SMART Ž1995.. Program
used for data reduction: SAINT Ž1995.. Siemens Analytical
ported here and thereby perform charge density studies
on 1.
X-ray Instruments, Madison, WI, USA.
w8x G.M. Sheldrick, SHELXTL, Ž1995.. Ver. 5.03rVMS, Siemens
Analytical X-ray Instruments, Madison, WI, USA.
w9x Program used for data collection: MAD. A. Barthelemy, Techni-
cal Report 84BA15T Ž1984.. Program used for data reduction:
COLL5N. M.S. Lehmann, S. Wilson. College V, Data Reduc-
Acknowledgements
tion System: Treatment of Reflection Profiles Ž1987.. Institut
A.E.G. and R.D.P thank EPSRC for a Postdoctoral
Fellowship and a Quota studentship, respectively.
J.A.K.H. thanks The Royal Society for a Leverhulme
Trust Senior Research Fellowship. The authors would
like to acknowledge the Institut Laue Langevin for the
beam time awarded in order to perform the neutron
measurement.
Laue Langevin, Grenoble, France.
w10x P. Coppens, DATAP, The Evaluation of Absorption and Extinc-
tion in Single-Crystal Structure Analysis, in: F.R. Ahmed ŽEd..,
Crystallographic Computing Ž1970. Munksgaard.
w11x M. Grun, K. Harms, R.M. zu Kocker, K. Dehnicke, H. Goes-
¨
¨
mann, Z. Anorg. Allg. Chem. 622 1996 1091.
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.
w12x G. Bandoli, G. Bartolozzo, D.A. Clemente, U. Croatto, C.
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w13x G. Ruban, V. Zabel, Cryst. Struct. Commun. 5 Ž1976. 671, first
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w14x A.L. Spek, Acta Crystallogr. C43 Ž1987. 1233, second mono-
clinic form.
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