Chapter 25
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Skeletal Stabilization as the Basis for Synthesis of Novel Phosph(III)azane Oligomers and Polymers Elizabeth G. Bent, Joseph M . Barendt, R. Curtis Haltiwanger, and Arlan D. Norman Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309 Reactions of PhPCl or P(NR ) (R = alkyl) with orthoaminated benzenes yield new phosph(III)azanes which contain extended P(III)-N skeletons stabilized by bridging ο-C Η groups. The novel [(PhP)(C H N PPh)] is formed from the PhPCl - 1,2-(NH ) C Η reaction; the dimer (n = 2) is fully characterized. From 1,2-(NH ) C Η or 1,2,3-(NH ) C H reactions with P(NR ) (R = Me, Et), phosphazanes are obtained which contain P N or P N skeletal units stabilized around the arene rings. The intermediates C H (NH) (PNEt ) and C H (NH)[N(PNEt ) ](PNEt ) in the 1,2-(NH ) C Η - P(NEt ) reaction have been characterized. The two-phosphorus compound displays 1,4- A-B condensation monomer reactivity. Preliminary studies of its oligomer/polymer chemistry are reported. 2
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I n o r g a n i c polymers based on a l t e r n a t i n g main group e l e m e n t - n i t r o g e n s k e l e t o n s ( e . g . I - IV) are of i n t e r e s t f o r t h e i r p o t e n t i a l as elastomers, high-temperature o i l s , e l e c t r i c a l conductors, b i o l o g i c a l m o l e c u l e c a r r i e r s , and p r e c u r s o r s t o ceramic m a t e r i a l s (1_ - 6). \/ I - f - P=rN-4-η I
I I -f-P—Ν 4 η II
I I - ( - Β — Ν - ) -η III
, \ / I -f-Si—Ν-^-η N
IV
S i g n i f i c a n t r e c e n t advances have occured w i t h phosphazenes (J_) and t o a l e s s e r e x t e n t s i l i z a n e s ( 6 ) ; i n c o n t r a s t , polymers based on p h o s p h o r u s ( I I I ) and n i t r o g e n are v i r t u a l l y unknown. Because such systems o f f e r o p p o r t u n i t i e s f o r metal c o o r d i n a t i o n , and i n t h e i r o x i d i z e d forms c o u l d be v a l u a b l e polymer p r e c u r s o r s t o PON c e r a m i c s ( 2 ) , we have begun s y s t e m a t i c s t u d i e s of the s t r u c t u r a l and r e a c t i v i t y f a c t o r s necessary f o r t h e i r formation. Reactions that i n p r i n c i p l e could y i e l d l i n e a r phosph(III)azanes g e n e r a l l y do not 8 ) ; i n s t e a d they produce low m o l e c u l a r weight o l i g o m e r s . Among t h e s e , t h e four-membered r i n g 0097-6156/88/0360-0303$06.00/0 © 1988 American Chemical Society Zeldin et al.; Inorganic and Organometallic Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
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1 , 3 , 2 , 4 - d i a z a d i p h o s p h e t i d i n e s (V) are most common. Only w i t h s m a l l s u b s t i t u e n t s on phosphorus and n i t r o g e n (R and R = Me or E t ) have h i g h e r o l i g o m e r s ( e . g . V I ) been o b t a i n e d ( 9 ) . ?
μ
R R .P.
«< > P R
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V
%P
N
P
>" ~~ v RN PR
h
I
RP
N
H
P h
P h
Κ >
X
\
I
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.Ν
NR
V
Ν—Ρ
N
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P
h
< > Ν
/
Ν Ph
Ph
VI
P h
VII
R e a c t i o n s of PX3 w i t h RNH2 c o u l d form c y c l i c - l i n e a r polymers based on connected P2N2 r i n g s , e.g. [ P 2 ( N R ) 3 l ; however, so f a r o n l y the d i n u c l e a r o l i g o m e r V I I has been o b t a i n e d ( 8 ) . A p p a r e n t l y , a c o m b i n a t i o n of s m a l l bond angles around phosphorus and s t r o n g i n t e r g r o u p r e p u l s i o n s between s u b s t i t u e n t s on phosphorus and n i t r o g e n 0_, 7.» 8.» 10) s t r o n g l y f a v o r s m a l l r i n g o l i g o m e r s and d i s f a v o r polymers. I n no case has P ( I I I ) - N oligomer-polymer i n t e r c o n v e r s i o n , analogous t o what o c c u r s w i t h phosphazenes and s i l a z a n e s (1^, 6 ) , been seen. Recause low o l i g o m e r s of l i n e a r p h o s p h ( I I I ) a z a n e s appear t h e r m o d y n a m i c a l l y p r e f e r r e d at a l l r e a s o n a b l e t e m p e r a t u r e s , we have undertaken a s y n t h e t i c s t r a t e g y i n v o l v i n g s k e l e t a l s t a b i l i z a t i o n as a t e c h n i q u e t o o b t a i n these polymers. We seek t o c o n s t r u c t p h o s p h o r u s - n i t r o g e n s k e l e t o n s which c o n t a i n s t a b i l i z i n g u n i t s between a d i a c e n t n i t r o g e n atoms, f o r example as i n V I I I , c r e a t i n g r i g i d extended u n i t s which w i l l not n
a l l o w s m a l l r i n g f o r m a t i o n but w i l l f a v o r m o l e c u l a r e x t e n s i o n based on r i g i d 1,4- r e a c t i v e u n i t s . Thus we have sought t o s y n t h e s i z e r e a c t i v e A-B type i n t e r m e d i a t e monomers ( I X ) or o l i g o m e r s / p o l y m e r s ( V I I I ) d i r e c t l y based on such systems. Our s t u d i e s so f a r are p r o t o t y p i c a l and have c o n c e n t r a t e d m a i n l y on r e a c t i o n s t r a t e g i e s ; however, they i n d i c a t e the approach has c o n s i d e r a b l e p o t e n t i a l . Amine-Phosphorus(III)
H a l i d e Condensation
Reactions
Since amine-phosphorus(III) h a l i d e condensation r e a c t i o n s are w e l l - e s t a b l i s h e d low-energy r o u t e s to p h o s p h o r u s - n i t r o g e n bonds, they p r o v i d e a l o g i c a l s t a r t i n g p o i n t f o r e x a m i n a t i o n of s k e l e t a l l y s t a b i l i z e d molecule s y n t h e s i s . F o r our i n i t i a l s t u d i e s , r e a c t a n t s t h a t are phenyl s u b s t i t u t e d as opposed t o a l k y l s u b s t i t u t e d
Zeldin et al.; Inorganic and Organometallic Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
25.
BENT ET AL.
Novel Phosph(III)azane Oligomers and Polymers
on phosphorus were chosen, so as to maximize the p o s s i b i l i t y of obtaining c r y s t a l l i n e products. R e a c t i o n of P h P C l w i t h 1,2-(NH ) 2 6 i+ t o l u e n e i n the presence of E t N to remove hydrogen c h l o r i d e proceeds smoothly a t r e f l u x as: c
2
H
i
n
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+ η 1,2-(NH ) C ^ J^ ^* 3
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1/n
[(PhP)(C H N PPh)] 6
4
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(1)
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X The c h a r a c t e r of p r o d u c t X depends on r e a c t i o n d i l u t i o n . Oligomers (n _> 2)/polymers form; dimer f o r m a t i o n i s minimized at h i g h r e a c t a n t concentrations. The s t r u c t u r e of dimer XI (X, where η = 2 ) , o b t a i n e d by x - r a y s i n g l e c r y s t a l a n a l y s i s ( F i g u r e 1), shows t h a t the d e s i r e d s k e l e t a l s t a b i l i z a t i o n based upon 1,4- c o n d e n s a t i o n u n i t s has been a c h i e v e d . XI i s a c y c l o p h a n e type m o l e c u l e which c o n t a i n s an e i g h t membered r i n g of a l t e r n a t i n g phosphorus and n i t r o g e n atoms. A d j a c e n t n i t r o g e n atoms are b r i d g e d by o-CgH^ u n i t s i n t o d i a z a p h o s p h o l e r i n g s . The C symmetry of the m o l e c u l e i s m a i n t a i n e d i n s o l u t i o n a l s o , s i n c e t h e P(31) NMR spectrum e x h i b i t s two temperature independent t r i p l e t s ( J = 17.2 Hz) at 85.0 pom and 112.0 ppm. 2 v
In a d d i t i o n to b e i n g a s k e l e t a l l y s t a b i l i z e d m o l e c u l e , XI c o n t a i n s an u n u s u a l r i n g s t r u c t u r e . The r i n g has f o u r n i t r o g e n and two phosphorus atoms i n a p l a n e w i t h the two r e m a i n i n g phosphorus atoms above the r i n g , which a l o n g w i t h the o r i e n t e d phenyl groups forms a w e l l - d e f i n e d c a v i t y i n a boat shaped e i g h t membered r i n g . T h i s geometry i s undoubtedly imposed by the s k e l e t a l s t a b i l i z i n g unit. Other e i g h t membered p h o s p h o r u s ( I I I ) - n i t r o g e n r i n g s , (MePNMe)i* (9) and (PrNCH CH NP)i (11) are crown shaped c o n t a i n i n g a l l c h e m i c a l l y e q u i v a l e n t phosphorus atoms. I n X I , because the phosphorus atoms are of two s e t s and one s e t i s i n a h i g h l y p r o t e c t e d environment, the p o s s i b i l i t y of s e l e c t i v e , " c a v i t a n d , " c o o r d i n a t i o n at phosphorus s i t e s e x i s t s . D e t a i l e d c h a r a c t e r i z a t i o n of the o l i g o m e r / p o l y m e r p r o d u c t s (X) 2
2
X
+
XIII
from E q u a t i o n 1 are i n p r o g r e s s . The p r o d u c t s are v i s c o u s o i l s , s o l u b l e i n h y d r o c a r b o n s o l v e n t s , c o n s i s t e n t w i t h t h a t expected o f l i n e a r oligomer/polymers· They e x h i b i t broad a p p r o x i m a t e l y e q u a l a r e a P(31) resonances at 95 - 102 ppm and 114 - 120 ppm, c o n s i s t e n t w i t h phosphorus environments of b r i d g i n g and d i a z a p h o s p h o l e t y p e s . G i v e n the p h y s i c a l p r o p e r t i e s and the c o r r e l a t i o n of P(31) and H ( l ) NMR s p e c t r a l parameters between dimer XI and the h i g h e r o r d e r p r o d u c t s , we i n f e r X has the c y c l i c - l i n e a r s t r u c t u r a l p r o p e r t i e s c h a r a c t e r i s t i c of X I . S t u d i e s of the o l i g o m e r / p o l y m e r p r o d u c t s to
Zeldin et al.; Inorganic and Organometallic Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
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M
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