Anthony Linden

Santhanathan S Kumaravel

Setharampattu S Krishnamurthy

T Stanley Cameron

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J. CHEM. SOC. DALTON TRANS. 1990 1119 
Synthesis and X-Ray Crystal Structure of the Bis( imino) Cyclodiphosphazane, 
[ ( Ph N ) P( N Me,) ( N Ph)] , t4 
Santhanathan S. Kumaravel and Setharampattu S. Krishnamurthy * 
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore-560 0 12, India 
T. Stanley Cameron and Anthony Linden 
Department of Chemistry, Dalbousie University, Halifax, Canada B3H 4J3 
The reaction of trans- [ (PhN) P( NMe,)], (1 ) with 2 equivalents of phenyl a i d e  yields the bis( imino) 
derivative, trans-[(PhN)P(NMe,)(NPh)], (2). TheX-ray crystal structure of (2) reveals that the 
N,P, ring and the phenyl groups attached to the ring nitrogen atoms are coplanar. The ring 
nitrogen atoms as well as the nitrogen atoms of the dimethylamino groups display trigonal planar 
geometry. The bond length of 1.51 8 A for the exocyclic P=N bond indicates that this bond is not 
delocalised with the N,P, ring system. 
Structural features of four-membered N2P2 ring compounds in 
which the co-ordination number of phosphorus varies from 
three to five have attracted considerable attention in recent 
years.’-, Structural studies have been carried out on 1,3,2,4- 
diazadiphosphetidines containing exocyclic P=O, P=S, and 
P=Te bonds.2.”6 Although several 1,3,2,4diazadiphosphet- 
idines containing exocyclic P=N bonds have been reported in 
recent years,7 no X-ray crystal structure analysis has been 
reported. Only the X-ray crystal structures of an anionic 
cyclodiphosphazane,* [Re(CO),((RN),PZ(NR2)(NR),)I (R 7 
Me,Si), and a cationic derivative with an exocyclic P=N bond, 
[Me,Si(NR),P(NR),P(NR)(NHR)] + [Re,(CO),(p-Cl),] - 
(R = Me,Si), have been reported. We now report the synthesis 
and structural analysis of a bis(imino)cyclodiphosphazane and 
compare its structural features with those of [(Pri2N)2To=N]z, 
the first cyclodiphosphazene isolated by Baceiredo et al. 
Results and Discussion 
Reaction of trans-[(PhN)P(NMez)12, (l),” with PhN, in 
boiling toluene affords trans-[(PhN)P(NMe,)(NPh)], (2). The 
Ph 
(1) 
Ph 
I 
Table 1. Selected structural parameters (lengths in A, angles in ”) for 
C(Ph”NMe,)(NPh)l, (2) 
P-N( 1) 1.5 1 8(2) P-N(3) 1.625(2) 
P-N(2) 1.699(2) p . . . p /  2.574( 1) 
P-N(2’) 1.698(2) 
N(l)-P-N(2) 121.4(1) P-N(2)-C(21) 130.8(2) 
N(l)-P-N(3) 107.8(1) P-N( 2)-P’ 9 8 3  1) 
N(2)-P-N(3) 111.1(1) P-N(3)-C( 1) 123.3(2) 
N(2)-P-N(2’) 81.5(1) P-N( 3)-C(2) 1 2 1.3( 3) 
P-N(1)-C(11) 128.7(2) C(l)-N(3)<(2) 115.1(3) 
i.r. spectrum of (2) exhibits a band at 1365 cm-’ which is 
assigned to the exocyclic P=N vibration. The ‘H n.m.r. 
spectrum shows only a single doublet at 6 2.65 (JPH = 11 Hz) 
for “Me,’ protons indicating the presence of only one isomer. 
The 31P-(1H) n.m.r. spectrum consists of a singlet at 6 -23.6 
p.p.m. A single-crystal X-ray analysis reveals the trans configur- 
ation of the dimethylamino and consequently the phenylimino 
groups (see below). Thus the Staudinger reaction of the diaza- 
diphosphetidine (1) proceeds with net retention of configuration 
at the phosphorus centres. 
The structure of compound (2) is shown in the Figure and 
selected bond lengths and angles are given in Table 1. The 
molecule is centrosymmetric. The four-membered N2P2 ring is 
virtually planar. The phenyl rings attached to the ring nitrogen 
atoms are coplanar with the N,P, ring (dihedral angle 1.0”). 
The ring nitrogen atoms and the nitrogen atoms of the di- 
methylamino groups are trigonal planar, with the angles around 
each nitrogen atom summing to ca. 360”. The phosphorus 
atoms adopt a distorted tetrahedral geometry. Within the N2Pz 
ring, the P-N distances and P-N-P and N-P-N bond angles 
are close to those observed for cyclodiphosphazanes with 
exocyclic P=S bonds.’ 
t 2,4-Bis(dimethylamino)-1,3-diphenyl-2,4-bis(phenylimino)- 
1,3,2h5,4h5-diazadiphosphetidine. 
1 A preliminary account of this work was presented at the 5th 
International Symposium on Inorganic Ring Systems, Amherst, 
Massachusetts, August 1988. 
Supplementary data available: see Instructions for Authors, J.  Chem. 
SOC., Dalton Trans., 1990, Issue 1, pp. xix-xxii. 
1120 J. CHEM. SOC. DALTON TRANS. 1990 
Figure. Perspective view of the molecule [(PhN)P(NMe,)(NPh>l2, (2) 
(H atoms omitted) 
It is worthwhile to compare the structural features of 
compound (2) with those of (3), the first stable cyclodiphos- 
phazene for which the X-ray structure is known." Both com- 
pounds contain phosphorus centres bonded to four nitrogen 
atoms. In the case of (3) the N,P, ring is planar and the 
exocyclic nitrogen atoms are trigonal planar. All endo- and 
exo-cyclic P-N bond lengths are equal (1.650 A) and it is 
(3) R = Pr' 
suggested that unsaturation is evenly delocalised over the ring 
skeleton and the exocyclic nitrogen atoms. By contrast, three 
different P-N bond lengths are observed for the bis(imino) 
derivative (2). The endocyclic P-N bonds are the longest 
(1.700 A) presumably as a result of the competition for the lone 
pair of electrons on the nitrogen by the aryl group; the exocyclic 
P-NMe, bonds are shorter (1.625 A) signifying appreciable 
multiple-bond character. The exocyclic P=N bonds are the 
shortest (1.518 %I) and this value indicates that the exocyclic 
P=N bond is not delocalised with the N2P, ring system. The 
effect of multiple bonding within the N,P2 ring in (3) is also 
reflected in the considerable widening of the endocyclic angle 
at phosphorus (N-P-N) and a corresponding decrease in the 
P-N-P angle (95.0 and 85.0" respectively) compared to the 
values for compound (2) (81.5 and 98.5" respectively). Such a 
trend (uiz. increase in the ring N-P-N angle and decrease in 
P-N-P angle with strengthening of skeletal n: bonding) is well 
documented for cyclotri- and cyclotetra-phosphazene deriv- 
atives, (NPX,), (n  = 3 or 4).', 
Experimental 
The i.r. spectrum (4 000--400 cm-') was recorded using a Carl- 
Zeiss UR-10 spectrometer, the 'H n.m.r. spectrum on a Bruker 
FT-270 (270 MHz) spectrometer with SiMe, as the internal 
standard, and the 31 P n.m.r. spectrum at 32.2 MHz on a Varian 
FT-80A spectrometer, chemical shifts downfield from the 
external standard, 85% H3P04, being assigned positive values. 
Elemental analyses were performed at the City University, 
London, by Dr. S. A. M a t h .  Phenyl azide', and trans- 
[(PhN)P(NMe,)], " were prepared by literature methods. 
Table 2. Atomic positional parameters for [(PhN)P(NMe,)(NPh)] 2, 
(2), with estimated standard deviations in parentheses 
Xla 
0.571 08(6) 
0.528 l(2) 
0.553 9(2) 
0.747 6(2) 
0.848 6(4) 
0.819 5(5) 
0.387 l(3) 
0.265 5(3) 
0.127 6(3) 
0.110 l(4) 
0.231 l(5) 
0.368 9(3) 
0.628 8(2) 
0.594 6(3) 
0.668 9(3) 
0.777 9(3) 
0.812 5(3) 
0.739 O(2) 
Ylb 
0.623 Ol(9) 
0.748 4(3) 
0.429 4(2) 
0.663 2(2) 
0.782 8(5) 
0.569 5(8) 
0.763 6(3) 
0.860 5(4) 
0.876 5(5) 
0.800 4(5) 
0.706 l(5) 
0.689 5(4) 
0.337 8(3) 
0.180 9(3) 
0.092 2(4) 
0.160 2(3) 
0.316 3(4) 
0.406 4(3) 
Z l C  
0.978 79(4) 
0.923 5(1) 
0.958 7(1) 
1.015 8(1) 
0.990 l(3) 
1.073 7(3) 
0.878 1(1) 
0.897 l(1) 
0.852 6(2) 
0.789 2(2) 
0.769 3(2) 
0.812 8(1) 
0.908 6(1) 
0.900 5(1) 
0.851 5(1) 
0.810 0(1) 
0.818 2(1) 
0.867 l(1) 
Synthesis of [(PhN)P(NMe,)(NPh)], (2).-Phenyl azide 
(0.72 g, 6 mmol) was added to a solution of [(PhN)P(NMe,)], 
(1) (1.0 g, 3 mmol) in toluene (15 cm3). After effervescence 
(caused by evolution of N2) had ceased (ca. 10 min), the solution 
was heated under reflux for 12 h and filtered. The filtrate was 
cooled to obtain the required compound (0.95 g, 61%) as 
colourless crystals. Recrystallisation from dichloromethane 
gave well formed crystals suitable for X-ray structure determin- 
ation, m.p. 186-194 "C (decomp.) (Found: C, 64.5; H, 6.3; 
N, 16.2. C,,H,,N,P, requires C, 65.4; H, 6.2; N, 16.3%). 1.r. 
spectrum (Nujol mull): 1 595s, 1495s, 1365s, 1 285s, 1 275s, 
1 205w, 1 195w, 1 115s, 1095m, 1080w, 1040w, 1015s, 1 OlOs, 
965s, 930s, 905w, 770m, 705w, 550w, 530w, and 480s cm-'. 
N.m.r.: 'H (CDCI,), 6 2.65 (d with virtual coupling, JPH = 11 
Hz) and 6.70-7.50 (m); ,'P-{ 'H) (CHCI,), 6 - 23.6 (s) p.p.m. 
Crystallographic Studies.-Crystal data. C,,H,,N,P,, A4 = 
514, monoclinic, space group P2,/n (alternative P2,lc, no. 14), 
a = 8.405(2), b = 8.536(1), c = 18.844(3) A, p = 94.51(2)", 
U = 1347.8 A3, 2 = 2, D, = 1.268 g cm-,, F(OO0) = 544, 
h = 0.709 26 A, p(Mo-K,) = 1.942 cm-', crystal size = 
0.4 x 0.3 x 0.3 mm. 
Data collection. An Enraf-Nonius CAD-4 four-circle diffract- 
ometer with graphite-monochromatised Mo-K, radiation was 
used to measure the unit-cell dimensions and to collect the data. 
The unit-cell constants were obtained by least-squares analysis 
of the diffractometer setting angles of 25 well centred reflections 
with 20 < 28 < 28". The intensities of 3 213 reflections with 
4 < 28 < 50" were recorded using -28 scans. Of these, 2 364 
reflections were unique and 1424 had Z > 20 ( I ) .  The 
intensities were reduced to a standard scale using routine 
procedures. l4 Corrections for Lorentz and polarisation factors 
were applied, but not for absorption. Scattering factors for 
neutral atoms were taken from ref. 15 and were corrected for 
the real and imaginary parts of anomalous dispersion. 
Structure solution and rejinement. The structure was solved 
by direct methods (MULTAN 80)', from which phosphorus, 
nitrogen, and most carbon atom positions were obtained. The 
remaining non-hydrogen-atom positions were determined from 
a Fourier difference synthesis. Refinement was carried out by 
using the SHELX 76 system.I7 The structure was refined 
initially by a full-matrix least-squares procedure with indepen- 
dent isotropic thermal parameters for the heavy atoms. Only the 
hydrogen atoms of the phenyl rings could be seen in a Fourier 
difference synthesis, and all hydrogen atoms were placed in their 
J. CHEM. SOC. DALTON TRANS. 1990 1121 
geometrically correct positions (C-H 1.08 A). The hydrogen 
atoms were then allowed to refine freely with satisfactory 
results. The final refinements were with anisotropic thermal 
parameters for the non-hydrogen atoms and isotropic 
parameters for the hydrogen atoms and the positions of all 
atoms free to refine. A three-block-matrix least-squares method 
was employed minimising ZwAF2 where w-’ = 021FoI + 
O.0O11F,J2. The refinement converged at R = 0.036, R’ = 0.035 
for 1 413 unique observed reflections [ I  > 20(1) ]  and 229 least- 
squares parameters. Eleven reflections were omitted because of 
suspected extinction. The final difference maps were flat, 
without recognisable residual features. The final atomic 
positional parameters of the non-hydrogen atoms are given in 
Table 2. 
Additional material available from the Cambridge Crystallo- 
graphic Data Centre comprises H-atom co-ordinates, thermal 
parameters, and remaining bond distances and angles. 
Acknowledgements 
Thanks are due to the Council of Scientific and Industrial 
Research, New Delhi, India for a fellowship (to S .  S .  K.) and the 
International Organisation of Chemical Sciences in Develop- 
ment (IOCD) (City University, London) for elemental analyses. 
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Received 12th May 1989; Paper 9/01997T 


Synthesis and X-Ray Crystal Structure of the Bis( imino) Cyclodiphosphazane, [ ( Ph N ) P( N Me,) ( N Ph)] , t4

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Synthesis and X-Ray Crystal Structure of the Bis( imino) Cyclodiphosphazane, [ ( Ph N ) P( N Me,) ( N Ph)] , t4

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