NOTIZEN 973 Synthesis and Crystal Structure of
2-Chloro-4 - dimethy lamino - 6 - triphenylphosphazen-l'-yl-l,3,5-triazine
T. S t a n l e y C a m e r o n a n d K h . M a n n a n Chemistry Department, University of Ulster, Coleraine,
N. Ireland
M a l c o l m B i d d l e s t o n e and R o b e r t A. S h a w Department of Chemistry, Birkbeck College, University
of London, London W C 1E 7HY
(Z. Naturforsch. 30b, 9 73-974 [1975]; received August 4, 1975)
Asymmetric 1,3,5-Triazine, X -ray, Crystal Structure, Conformation, Triphenylphosphazenyl Group
The title compound was synthesized and its structure determined by X -ray crystallo
graphy. The NPPI13 substituent adopts a type I conformation with its nitrogen and phosphorus atoms coplanar with the ring.
The compound, the first asymmetric 1,3,5- triazine to be crystallographically investi
gated, shows significant variations in ring bond lengths and angles; these are discussed.
Basicity studies have shown1 that some triphenyl - phosphazenylcyclophosphazenes protonate on the ring and others on the side chain nitrogen atom.
This differences in behaviour is apparently the result of different substitutent conformations. X -ray crystallographic investigations have shown2 that when the protonation is on the ring the phosphorus and nitrogen atoms of the substituent are practically coplanar with the two nitrogen atoms of the local NPN ring segment; when protonation is exocyclic, the exocyclic phosphorus and nitrogen atoms together with the phosphorus atom of the ring make a plane that is perpendicular to that of the local ring segment3. The significance of these conforma
tions (termed type I and II respectively) have been discussed elsewhere4’5. The 1,3,5-triazine system has many similarities5 with the phosphazene, (the carbon atoms however carry only one, the phospho
rus atom, two substituents) and therefore the title compound was synthesised and its structure in
vestigated.
Experimental
Dichlorodimethylamino-1,3,5-triazine (0.01 mole) in benzene reacts with triphenylmonophosphazene (0.02 mole) in benzene on one hour at the b. p. of
Requests for reprints should be sent to Dr. T. S.
C a m e r o n , Physical Sciences Department, The New University of Ulster, Coleraine, County Londonderry, Northern Ireland.
the solution to give the title compound, m.p.
224 °C, (80% yield).
C25H21CIN5P
Calcd C 63.6 H 4.85 N 16.2, Found C 63.6 H 4.8 N 16.0.
The protons of the dimethylamino group show a temperature dependent XH NMR spectrum6.
The compound crystallized in the mono clinic spacegroup P2i/« with a = 15.06 ± 0 .0 1, b = 16.46 ± 0.01, c = 8.94 ± 0 .0 1 Ä, ß = 95.8 ± 0.2°;
V = 2204 Ä 3, Dcaic 1.306 g/cm3 for Z = 4, Dexp = 1.310, MW = 4 3 4 ; 854 independent reflections significantly above the background using Cuko radiation; i? = 0 .0 6 .
The bond lengths and angles within the triphenyl- phosphine group are as expected. The P-N bond length 1.622 ± 0.005 Ä (Fig. 1) is shorter than those
Figure. Selected interatomic distances, interbond angles ( ±1°) and a projection of the molecule along c.
often found7 where the nitrogen atom is conjugated to an aromatic system, but is longer8 than the mean distance of 1.558 ± 0.005 Ä in l,3,5-trinitro-2,4,6- tris(triphenylphosphoranilideneimino) benzene [C6(N02)3(Ph3PN)3] where considerable P-N double bond character was postulated; the P-N-C(tria- zine) plane makes an angle of 7° to the least squares best plane through the triazine ring, thus exhibiting type I conformation. The triazine ring itself is slight
ly boat-shaped with atoms N(l), C(2), C(l) and N(2) 0.006, 0.022, 0.012 and 0.022 Ä on one side of the least squares best plane throught the six atoms of the ring and C(3) and N(3) 0.027 and 0.062 Ä respectively on the other side. Most structures containing the C3N3 group that have been reported have had a symmetric substitution in the ring9. In this case the three different substituents produce uneven distortions from the regular hexagon. This is particularly noticeable in the interbond angles with N-C-N angles greater than, and the C-N-C less than 120°. Such distrotions are not unusual in substituted aromatic systems10 where they are normally explained in terms of repulsions between the electron in the sigma bonds8.
974 NOTIZEN
1379(7}
N(4)1 622(5) P.Ph,
C(4) 1 4 1 ( l \
i-48(i)y
C(5)
1-413(8) 7 N(1)--- C(2) 1343' nO- 'N(5)« H a c (3 )»»
1350(7)\
, ’’o
N(2) -
^36 3(8 )
no N (3)
/1 -3 3 5 ( 6 )
1-309(6)C(1)
vV795(5)
CI
In this compound the decrease in the C-N-C ring angles may be the result of a strong repulsion be
tween the sigma electrons of each of the N-C bonds and the lone pair electrons of the nitrogen atom which, since they are held close to the nitrogen atom, are more space-filling11. The increase in ring N-C-N bond angle can be explained by the attrac
tion of the sigma electrons towards the substituent atom in the exocyclic bond, thus reducing the repulsion between these electrons and those of ring C-N bonds. It would appear that for the sigma electrons NMe2 is a more powerful electron with
drawing group than NPPI13 while with the C-Cl bond the electron density, further attenuated by the longer bond length, produces the greatest dis
tortion in the N-C-N angle.
Moreover, the ring atom carrying the most electron withdrawing group (Cl) has adjacent to it the two shortest ring bonds, and that carrying the least electron withdrawing (NPPI13) the two longest.
This is probably the consequence of charge separa
tions around the ring; the nitrogen atoms carrying a partial negative charge, each of the carbon atoms slightly different partial positive charges. In the unsymmetric cyclotriphosphazatriene12, gem.
N3P3Cl3(NMe2)3 the correlation between electron withdrawing groups and bond length persists but in contrast to the triazine the mean P-N bond lengths of each P-N -P segment remains constant.
An observation, consistent with the Dawer P-N -P island model4-5 for the phosphazenes.
The C-N-PPI13 angle, 121°, is the smallest re
ported5 for this type of substituent, and its direction is such that the PPI13 group turns towards the chlorine atom and is as far as possible from the NMe2 group. This is the first indication5 of the direction adopted by an NPPI13 group with a type I conformation in an unsymmetric molecule. It re
mains to be seen how general this observations is and whether steric or polar effects are the main cause.
We thank the SRC for a grant (M.B. and R .A .S.), the Nuffield Foundation for a Travelling Fellowship (Kh.M.) and the University of Ulster Computing Centre for facilities.
1 M. B i d d l e s t o n e , S . N . N a b i , and R. A. S h a w ,
J.C .S . Dalton, in press.
2 G. J . B u l l e n and P. E. D a n n , personal communica
tion.
3 M. B i d d l e s t o n e , G. J . B u l l e n , P. E. D a n n , and R. A. S h a w , Chem. Commun. 1974, 56.
4 R. A. S h a w , Plenary Lecture, 2nd International (IUPAC) Symposium on Inorganic Phosphorus Compounds, Prague, Czechoslovakia, September, 1974; Pure Appl. Chem., in press.
5 R. A. S h a w , Plenary Lecture, 1st International (IUPAC) Symposium on the Chemistry of Inorganic Heterocycles, Besancon, France, June 1975; to be published.
6 M . Bi d d l e s t o n e, R. Ke a t, a n d R. A. Sh a w, u n p u b lis h e d r e s u lt s .
7 D. E. C . Co r b r i d g e, The Structural Chemistry of phosphorus, p. 290, Elzevier, Netherlands.
8 T. S. Ca m e r o n a n d C . K . Pr o u t, J . C h e m . Soc. (C) 1969, 2281.
9 G. J . Bu l l e n, D. J . Co r n e y, a n d F. S. St e p h e n s,
J. C. S. ( P e r k in II), 1972, 642 a n d r e f e r e n c e s t h e r e i n .
A. S. Ba i l e y a n d C . K . Pr o u t, J . C h e m . S o c . 1965, 4867.
11 R. J . Gi l l e s p i eand R. S. Ny h o l m, Quart. Rev. 11, 339 [1957].
12 F. R. Ah m e d and D. R. Po l l a r d. Acta Crystallogr.
B 28, 513 [1972].
