J. Am. Chem. SOC. 1991, 113, 2628-2634
2628
Syntheses and Structures of Cyclic and Short-Chain Linear Phosphazenes Bearing 4-Phenylphenoxy Side Groups Harry R. Allcock,*.t Dennis C. Ngo,+Masood Parvez,+Robert R. Whittle,+and William J. Birdsall’ Contribution from the Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, and Department of Chemistry, Albright College, Reading, Pennsylvania 19604. Received July 19, I990
Abstract: A series of cyclic and short-chain linear phosphazenes bearing the 4-phenylphenoxy side group has been synthesized. These compounds are models for the corresponding linear high polymer. The X-ray structures of [NP(O-C6H4-C6H5-p),], Compound 6 represents the first (I), [ N P ( O - C ~ H ~ - C & ~ S (2), - ~ ) ~and ] ~ O P ~ N ~ ( G C ~ H ~ - C ~(6) H Sare - ~ reported. )~ three-phosphorus linear oligomeric phosphazene-bearing aryloxy side group to be described. The molecular structure of 6 showed that the linear phosphazene skeleton assumes a distorted cis-trans conformation. Crystals of 1 are monoclinic with space group P2,lc with a = 23.296 (6) A, b = 7.162 (4) A, c = 34.666 (7) A, j3 = 90.14 (2)’, V = 6268.4 A’, and Z = 4. Crystals of 2 are triclinic of space group PI with u = 10.462 A, b = 16.433 A, c = 23.326 A, (Y = 94.25 (2)O, j3 = 91.03 (3)O, y = 103.59 (3)O, V = 3883.9 A’, and Z = 2. Finally, crystals of 6 are monoclinic with space group P2,ln with u = 10.413 (9) A, b = 23.425 (9) A, c = 36.359 (12) A, j3 = 96.27 (6)O, V = 8815.77 A3, and Z = 4.
High polymeric phosphazenes form a class of inorganic/organic macromolecules that possess a wide range of unusual properties.’ The type of side group attached to the polyphosphazene chain has a powerful effect on the physical and chemical characteristics., As part of our program to better understand the structureproperty relationships in poly(organophosphazenes), we have synthesized a series of small-molecule cyclic and linear phosphazenes as structural models for the corresponding high polymers. The value of small-molecule phosphazene models for devising synthetic routes for the high polymers, and as tools to probe the possible structure of polymers, has been illustrated previo~sly.~” In the present work, we report the syntheses of a series of cyclic and linear oligomeric phosphazenes that bear the 4-phenylphenoxy side group. In particular, the structures of [NP(O-C6H4-C6H5-p),], ( l ) , [ N P ( ~ 6 H 4 ~ 6 H S - P ) 2 1(21, 4 and OP3N2(M6H4x6H5-P)7 (6) are reported. The study of these compounds was guided by the following questions: (a) What is the effect of bulky aryloxy side groups on the bond lengths, bond angles, and conformation of a cyclophosphazene ring or a linear phosphazene backbone? (b) What is the preferred conformation of a linear phosphazene backbone? (c) Can evidence be found for the “stacking” of side groups in a way that might indicate possible liquid crystalline or nonlinear optical properties in related derivatives? (d) How closely will these model compounds mimic the structure and chemical properties of the high polymer? In this paper, the structural features of these compounds are compared and implications for the structure of the corresponding high polymer are discussed. Results and Discussion Syntheses. The reaction sequence used for the synthesis of the cyclophosphazenes is outlined in Scheme I. The cyclic model compounds were prepared by treatment of hexachlorocyclotriphosphazene or octachlorocyclotetraphosphazenewith sodium 4-phenylphenoxide to yield the cyclic phosphazenes 1 and 2, respectively. The reaction sequence for the synthesis of short-chain linear phosphazenes is summarized in Schemes I1 and 111. The linear species, pentachlorooxodiphosphazene (3) was prepared by the reaction of phosphorus pentachloride with ammonium ~ u l f a t e . ~ Heptachlorooxotriphosphazene (5) was prepared from 4 by use of a chain-building process.* Treatment of the respective chlorooxophosphazenes with sodium 4-phenylphenoxide gave compounds 4 and 6. Compound 7 was prepared by the reaction of [P4N3Cllo]+C1-with sodium 4-phenylphenoxide. Structural Characterization. The 31PN M R and mass spectra of compounds 1, 2, 4, 6, and 7 are listed in Table VII. Micro-
‘The Pennsylvania State University. Albright College.
analysis data are listed in Table VIII. The 31PN M R spectra of the cyclic species were singlets, while those of the linear species were multiplets, reflecting the different chemical environment of the phosphorus atoms in these compounds. The chemical shifts of the -P(OR),- units in the linear species showed a close similarity to those in the high polymeric system, suggesting a strong correlation in structure between the linear models and the corresponding high polymer. However, the main structural characterization was by means of X-ray single-crystal analysis. Crystal and Molecular Structure Of [ N P ( O - C ~ H & H S - ~ ) ~ ] ~ (1). Compound 1 contains a cyclic trimeric phosphazene ring, with six 4-phenylphenoxy groups attached through P-0-C linkages to P(l), P(2), and P(3) of the phosphazene skeleton (Figure 1). The phosphazene ring is slightly puckered: the phosphorus atoms are located above and the nitrogen atoms are below the plane of the ring. (The displacements of the atoms from this plane are as follows: P(l), 0.089; P(2), 0.057; P(3), 0.043; N ( l ) , -0.085; N(2), -0.035, and N(3), -0.068 A.) By contrast, the phosphazene ring of [NP(OPh),], is planar.I2 Thus, extension of the side chains by one phenyl group, as in compound 1, appears to have only a minor effect on the conformation of the ring. However, the disposition of the biphenyl units is complex. On one side of the phosphazene ring, three side chains are aligned with their longest axes at right angles to the plane of the inorganic ring. On the other side of the phosphazene ring, three side chains are oriented so that their longest axes are slanted at approximately 68’ to the ring. While no direct stacking of side groups was detected within a molecule, intermolecular stacking of side groups is clearly shown in the packing diagram. The two phenyl rings of the 4-phenylphenoxy units are twisted relative to each other. The smallest angle of twist is for the C(49)-C(54) and C(55)-C(60) planes (2.58’). For the other side groups, the dihedral angles between planes of the rings in the biphenyl unit range between 18.02’ and (1) (2)
Allcock, H. R. Chem. Eng. News 1985,63,22-36. Allcock, H. R.; Mang, M. N.; Dembek, A. A,; Wynne, K.J. Macre
molecules 1989, 22, 4179. (3) Allcock, H. R.; Kugel, R. L.; Valan, K. J. Inorg. Chem. 1966,5, 1709. (4) Allcock, H. R. Acc. Chem. Res. 1979, 12, 351. (5) Allcock, H. R.; Fuller, T. J. Macromolecules 1980, 13, 1338. (6) Allcock, H. R.; Tollefson, N. M.; Arcus, R. A,; Whittle, R. R. J . Am. Chem. SOC.1985, 107, 5166. (7) Emsley, J.; Moore, J.; Udy, P. 8. J . Chem. SOC.A 1971, 2863. ( 8 ) Riesel, L.; Somieski, R. Z . Anorg. Allg. Chem. 1975, 411, 148. (9) Main, P.; Fiske, S. J.; Hull, S.; Lessinger, L.; Germain, G., Declercq, J. P.;Woolfson, M. M. MULTANE~;Universities of York England and Louvain: York, England, and Louvain, Belgium, 1982. (10) Cromer, D. T.; Mann, J. B. Acta Crysrallogr., Sect. A 1968, AZ4, 321. (1 1) Stewart, R. F.; Davidson, E. R.; Simpson, W. T. J. Chem. Phys. 1965, 42, 3175. (12) Marsh, W. C.; Trotter, J. J . Chem. Soc. A 1971, 169.
0002-7863/91/1513-2628%02.50/0 0 1991 American Chemical Society
Cyclic and Short- Chain Linear Phosphazenes
J. Am. Chem. SOC.,Vol. 113, No. 7, 1991 2629
scheme I
CI
CI
I
I
CI-P-N-P-CI
I
il
I
Naoc6n,.c6n,.p
I
-NaCI
N
CI-P-N-P-CI
I
*
N
N
I
CI
CI
2
scheme I1 PCI, + (NHJ,SO,
1
CI
m.UlmEblorUtI~m
CI
I I 0 =P - N = P I I CI CI
NHSIzM.,
CI
.CISIM.,
CI
I O=PI CI
3
I flfl
F-3,
N.0C,H4.C6Hs.p
0 OssP--N-P-0-
I OI
C1 N=
I -NHSIMe, I
P
CI
1
:%tM*
CI
CI
I
I I
O=P-N=P--N=P-CI
I
0
I
CI 5
CI
CI
I I
CI
/
Y $ j p Q
N.0C'H4.C'Hrp
. .
.NCI
1
iI
O=P--N=P-N=P-O
'I m
I I
" Y q. j & q. j p Q. 6
28.70'. The unit cell contains four molecules arranged in such a manner that the longest axis of each molecule is pointed in the same direction. This orientation allows maximum stacking of side groups between neighboring molecules. The unit cell also contains four molecules of m-xylene, a solvent used for crystallization. The bond angles and bond distances for structure of 1 are shown in Table I. The average P-N bond distances range from 1.554 (7) to 1.602 (7) A with a mean value of 1.572 (7) A. The P-N-P angles range between 120.9 ( 5 ) O and 123.2 (4)O with an average value of 122.1 (4)O, and the N-P-N angles vary from 115.1 (4)O to 118.0 (4)' with a mean value of 116.5 (4)O. These values are similar to those found in [NP(OPh)2]3. The average P-0 bond distances range between 1.556 (6) and 1.592 (6) A with a mean value of 1.573 (6) A. This is shorter than the P-0 single bond
Table I. Bond Lengths (A) and Bond Angles (deg) for [NP(O-C6H4-CsH5-p),l, (1)'" O(1)-C(l) 1.363 (8) P(1)-0(1) 1.559 (6) 0(2)-C(13) 1.360 (8) 1.575 (6) P(1)-0(2) 0(3)-C(25) 1.355 (8) P(2)-0(3) 1.592 (6) 0(4)-C(37) 1.379 (8) P(2)-0(4) 1.556 (6) 0(5)-C(49) 1.369 (9) P(3)-0(5) 1.580 (6) 0(6)-C(61) 1.352 (8) P(3)-0(6) 1.578 (6) C(4)-C(7) 1.483 (9) P(1)-N(1) 1.561 (7) C(l6)-C(l9) 1.485 (9) P(l)-N(3) 1.581 (7) C(28)-C(31) 1.495 (10) P(2)-N(1) 1.568 (8) C(40)-C(43) 1.485 (9) P(2)-N(2) 1.602 (7) C(52)-C(55) 1.500 (10) P(3)-N(2) 1.554 (7) C(64)-C(67) 1.502 (9) P(3)-N(3) 1.570 (7)
N(l)-P(l)-N(3) 115.1 (4) 0(4)-P(2)-N(1) 107.2 (4) 1 1 1.0 (4) N(l)-P(2)-N(2) 116.4 (4) 0(4)-P(2)-N(2) N(2)-P(3)-N(3) 118.0 (4) 0(5)-P(3)-0(6) 97.8 (3) P(l)-N(l)-P(2) 123.2 (4) 0(5)-P(3)-N(2) 110.4 (4) P(2)-N(2)-P(3) 120.9 (5) 0(5)-P(3)-N(3) 109.6 (4) P(3)-N(3)-P(1) 122.3 (4) 0(6)-P(3)-N(2) 112.1 (4) O(l)-P(1)-0(2) 92.9 (3) 0(6)-P(3)-N(3) 107.0 (4) O(1)-P(1)-N(1) 122.4 (4) P(l)-O(I)-C(l) 131.2 (5) O(I)-P(l)-N(3) 110.5 (4) P(1)-0(2)-C(13) 120.6 (5) O(2)-P(1)-N(1) 111.8 (4) P(2)-0(3)-C(25) 126.0 (5) 0(2)-P(I)-N(3) 112.0 (4) P(2)-0(4)-C(37) 123.4 (5) 0(3)-P(2)-0(4) 98.3 (3) P(3)-0(5)-C(49) 120.2 (5) 0(3)-P(2)-N(l) 112.5 (4) P(3)-0(6)-C(61) 128.8 (5) 013kP(2bN(2) 109.9 (4) "Aromatic C-C distances were constrained to be 1.395 A. "Aromatic C-C-C angles were constrained to be 120.0'. Table 11. Angles between Phenyl Rings of Biphenyl Units in 1 angle between atoms in ring rings (deg) C( 1)-C(6) C(7)-C( 12) 28.70 C/ 13)-C(18) C(19kC/24) 25.55 c(25j-c(3oj c(31j c ( 3 6 j 18.02 C(37)-C(42) C(43)-C(48) 29.53 C(49)-C( 54) C(55)-C(60) 2.58 C(61)-C(66) C(67)-C(72) 27.73 (1.61 A), which suggests some exocyclic delocalization of electrons. The mean e P - 0 bond angles range from 92.9 (3)O to 97.8 ( 3 ) O and average to 96.3 (3)'. The angles of twist between the phenyl rings of the biphenyl units are listed in Table 11. Crystal and Molecular Structure of [ N P ( W S H 4 - C 6 H S - ~ ) 2 h (2). Molecules of [NP(O-C,&-C&-p)2]4 contain an eight-
Allcock et al.
2630 J . Am. Chem. SOC.. Vol. 113, No. 7, 1991 Scheme 111 CI
CI \-0
J
L
0
7
Table 111. Bond Lengths
P(1)-0(2) P(1)-N(1) P(l)-N(4) P(2)-0(3) P(2)-0(4) P(2)-N(1) P(2)-N(2) P(3)-0(5) P(3)-O(6) P(3)-N(2) P(3)-N(3)
(A) and Bond Andes - (dea) . -. for
1.575 (8) 1.539 (9) 1.569 (8) 1.565 (8) 1.579 (9) 1.572 (9) 1.571 (8) 1.579 (7) 1.575 (8) 1.529 (9) 1.552 ( I S )
N(l)-P(l)-N(4) N(I)-P(2)-N(2) N(3)-P(3)-N(3) N(3)-P(4)-N(4) P(l)-N(l)-P(2) P(2)-N(2)-P(3) P(3)-N(3)-P(4) P(I)-N(4)-P(4) O(l)-P(I)-0(2) O(1)-P(1)-N(1) O(l)-P(l)-N(4) 0(2)-P(I)-N(l) 0(2)-P(I)-N(4) 0(3)-P(2)-0(4) 0(3)-P(2)-N(1) 0(3)-P(2)-N(2) P(3)-0(5)-C(501) P(4)-0(7)C(701)
121.4 ( 5 ) 121.3 ( 5 ) 119.5 ( 5 ) 120.5 ( 5 ) 133.1 ( 5 ) 138.7 (6) 132.1 (6) 132.5 (6) 102.5 (4) 106.4 ( 5 ) 108.5 (4) 110.1 (4) 106.5 (4) 104.6 (4) 110.5 (4) 104.9 ( 5 ) 126.0 (7) 122.5 (8)
P(4)-0(7) P(4)-0(8) P(4)-N(3) P(4)-N(4) O(I)-C(lOl) 0(2)-C(201) 0(3)-C(301) 0(4)-C(401) O(S)C(SOl)
0(6)-C(601) 0(7)-C(701) 0(8)-C(801) 0(4)-P(2)-N(1) 0(4)-P(2)-N(2) 0(5)-P(3)-0(6) 0(5)-P(3)-N(2) 0(5)-P(3)-N(3) 0(6)-P(3)-N(2) 0(6)-P(3)-N(3) 0(7)-P(4)-0(8) 0(7)-P(4)-N(3) 0(7)-P(4)-N(4) 0(8)-P(4)-N(3) 0(8)-P(4)-N(4) P(I)-0(I)C(101) P(1)-0(2)-C(201) P(2)-0(3)-C(301) P(2)-0(4)C(401) P(3)-0(6)C(601) P(4)-0(8)-C(801)
1.583 (9) 1.601 (7) 1.570 (16) 1.553 (9) 1.40 (1) 1.40 (2) 1.41 (1) 1.38 (1) 1.38 (1) 1.40 (1) 1.41 (1) 1.36 (1) 105.5 ( 5 )
109.0 (4) 99.1 (4) 109.7 ( 5 ) 105.6 (4) 112.1 (4) 108.7 ( 5 ) 99.0 (4) 109.2 (6) 107.0 (5) 112.3 ( 5 ) 106.6 ( 5 ) 121.7 (7) 129.8 (7) 130.6 (8) 123.7 (7) 126.1 (7) 124.3 (8)
membered phosphazene ring that assumes a boat conformation (Figure 2). Two 4-phenylphenoxy groups are attached to each phosphorus atom through P-O-C linkages. On one side of the phosphorus-nitrogen ring, three side chains from P(2), P(3), and P(4) are oriented with their longest axes approximately perpendicular to the ring. On the other side of the ring, three other side chains from P(l), P(2), and P(3) have their longest axes less than 90' to the plane of the inorganic ring. This conformation is very
Figure 1.
(a) ORTEP and (b) packing diagrams for [NP(O-
C6H4-C6H5-pP)213
similar to that of the trimeric analogue 1, which suggests that the side-chain conformation is not dependent on the size of the phosphazene ring. It is interesting to note that one of the side groups (from P(1)) is disposed so that it is coplanar with the phosphazene ring. As in 1, no intramolecular stacking of side groups was detected. However, the four molecules of 2 in the unit cell are arranged to permit long-range stacking of side groups between neighboring molecules. The bond angles and bond distances of compound 2 are shown in Table 111. The P-N bond distances range from 1.529 (9) to 1.571 (8) A with a mean of 1.554 (11) A. The P-N-P angles range from 132.1 (6)' to 138.7 (6)' with a mean value of 134.1 (6)', and the N-P-N angles vary between 119.5 (5)' and 121.4 (5)' with an average of 120.7 (5)'. The P - 0 distances range between 1.565 (8) and 1.601 (7) A with a mean of 1.582 (8) A. The 0-P-O angles are between 99.0 (4)' and 104.6 (4)' with an average of 101.3 (4)', which is significantly wider than that found in the cyclic trimeric species. As in 1, the phenyl rings of the biphenyl units are not coplanar. The dihedral
J . Am. Chem. SOC.,Vol. 113, No. 7, 1991 2631
Cyclic and Short-Chain Linear Phosphazenes Table IV. Angles between Phenyl Rings of Biphenyl Units in 2 angle between atoms in ring rings (deg) C(I )-C(6) C(7)-C(l2) 43.17 C( 13)-C( 18) C( 19)-C(24) 34.68 C(25)-C( 30) C(31)-C(36) 34.08 C(37)-C(42) C(43)-C(48) 32.44 C(49)-C(54) C(55)-C(60) 131.95 C(61)-C(66) C(67)-C(72) 36.00 C(73)-C(78) C(79)-C(84) 137.91 C(85)-C(90) C(91)-C(96) 135.02 Table V. Bond Lengths (A) and Bond Angles (deg) for (6)‘” OP3N2(=6Hi%Hi-P)7 P(1)-0(1) 1.483 (12) 0(3)-C(13) p(tj-o(zj 1.559 i i t j P(l)-0(3) 1.584 (11) P(I)-N(I) 1.571 (14) P(2)-N(I) 1.570 (13) P(2)-N(2) 1.533 (13) P(2)-0(4) 1.585 (10) P(2)-0(5) 1.592 (IO) P(3)-N(2) 1.524 (13) P(3)-0(6) 1.545 (1 1) P(3)-0(7) 1.532 (12) P(3)-0(8) 1.537 (11) 0(2)-C(I) 1.40 (2)
1.41 (2) 1.41 (2j 1.37 (2) 1.46 (2) 1.40 (2) 1.37 (2) 1.54 (2) 1.47 (2) 1.50 (2) 1.51 (2) 1.49 (2) 1.52 (2) 1.51 (2)
111.3 (6) N(I)-P(2)-N(2) 114.3 (7) 103.0 (6) P(l)-N(l)-P(2) 127.8 (8) 105.5 (7) P(2)-N(2)-P(3) 142.6 (IO) 103.2 (6) O(l)-P(l)-O(2) 103.6 (6) 115.9 (7) O(I)-P(l)-0(3) 112.8 (6) 117.4 (6) O(l)-P(l)-N(1) 124.0 (7) 123.6 (9) 0(2)-P(1)-0(3) 98.4 (6) 122.8 (9) 0(2)-P(I)-N(l) 108.1 (6) 123.1 (8) 0(3)-P(l)-N(l) 106.7 (7) 122.4 (9) 0(4)-P(2)-0(5) 100.2 (6) 119.0 (IO) 0(4)-P(2)-N(I) 116.1 (6) 129.5 ( I O ) 0(4)-P(2)-N(2) 108.4 (7) 125.2 (9) 0(5)-P(2)-N(I) 107.0 (6) 0(5)-P(2)-N(2) 109.7 (6) “Aromatic C-C constrained to be 1.395 A. *Aromatic C-C-C constrained to be 120.0°. angles between planes of the phenyl rings range between 32.44’ and 48.05O. The angles of twist between the phenyl rings of the biphenyl units are listed in Table IV. Crystal and Molecular Structure of OP3N2(&c&
