Synthesis of PhosphorusâNitrogen Polymers by Using Silicon

10 Synthesis of Phosphorus-Nitrogen Polymers by Using Silicon-Nitrogen-Phosphorus Reagents

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on August 20, 2015 | http://pubs.acs.org Publication Date: September 30, 1983 | doi: 10.1021/bk-1983-0232.ch010

PATTY WISIAN-NEILSON, AROOP K. ROY, ZE-MIN XIE, and ROBERT H. NEILSON Texas Christian University, Department of Chemistry, Fort Worth, TX 76129

Many small-molecule Si-N-P compounds of appropriate design can function as precursors to various oligomeric and polymeric P-N systems. For example, poly(dialkylphosphazenes), ( R P N ) , are r e a d i l y obtained v i a the thermal condensation-polymerization of c e r t a i n N-silylphosphinimines, Μe SiN=P(X)R . In a d d i t i o n , novel 3-coordinate phosphorus-V compounds including the b i s ( i m i n o ) phosphoranes, R P ( = N S i Μ e ) , can p o t e n t i a l l y lead to new polymers of formula (RPN) , the phosphorus analogs of e l e c t r i c a l l y conducting ( S N ) . The synthesis of polyphosphazenes and t h e i r precursors and the synthesis of p o t e n t i a l precursors to (RPN) are discussed. 2

n

3

3

2

2

n

n

n

The s t r u c t u r a l a n d c h e m i c a l d i v e r s i t y o f c o m p o u n d s c o n t a i n i n g t h e Si-N-P linkage i s a r e s u l t o fboth the v a r i e t y o f c o o r d i n a t i o n numbers w h i c h p h o s p h o r u s may assume and t h e r e a c t i v i t y o f t h e S i - N bond. The c o m b i n a t i o n o f t h e s e f e a t u r e s g i v e s S i - N - P compounds very promising synthetic u t i l i t y , p a r t i c u l a r l y i n the area o f inorganic polymer synthesis. T y p i c a l l y , t h e m o s t common p r e c u r s o r s t o n e w Si-N-P systems are simple si1y1aminophosphines (eq 1 ) . The d i f u n c t i o n a l c h a r a c t e r o f t h e s e c o m p o u n d s , w h i c h i s due t o t h e n u c l e o p h i l i c s i t e a t p h o s p h o r u s a n d a c o m p l e m e n t a r y e l e c t r o p h i 1 i c s i t e a t s i l i c o n , makes them very v e r s a t i l e reagents. They have been used i n a new s y n t h e s i s o f a l k y l and/or phenyl s u b s t i t u t e d phosphazenes ( R P N ) ( O and have l e d t o t h e p r e p a r a t i o n o f promising precursors t op o t e n t i a l l y electrically c o n d u c t i n g polymer systems o f general formula ( R P N ) . 2

n

n

0097-6156/83/0232-0167 $06.00/0 © 1983 American Chemical Society

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

168

RINGS,

Synthesis

of

CLUSTERS, A N D POLYMERS

Polyphosphazenes

Work i n t h e p o l y m e r s y n t h e s i s area has been e n h a n c e d by a c o n v e n i e n t " o n e - p o t " s y n t h e s i s w h i c h was d e v e l o p e d b y J . C . W i l b u r n (_2) ( e q 1 ) . Y i e l d s o f t h e p h o s p h i n e s p r e p a r e d i n t h i s manner a r e t y p i c a l l y 60 t o (Me Si) NH


3

2

(1 ) n - B u L i (2) P C 1 3

2RM gX >

(Me Si) N-P 3

2

N

R

[(Me Si) NPC1 ] — ( 3

2

(1 )

2

RMgX

R (Me Si) N-P^ CI y

3

or

RLi

2

t o 9 0 % a n d q u a n t i t i e s o f 250 t o 300 grams a r e e a s i l y obtained. The use o f P h P C l i n place of PC1 allows for the introduction of phenyl/alkyl s u b s t i t u t i o n at phosphorus · Many s i m p l e oxidation reactions of tertiary alkyl or a r y l p h o s p h i n e s a r e l e s s s t r a i g h t f o r w a r d i n p h o s p h i n e s w i t h s i l y l a m i n o s u b s t i t u e n t s (_3-8). Two such r e a c t i o n s have r e s u l t e d i n p r e c u r s o r s t o phosphazenes. The f i r s t o f t h e s e i s t h e r e a c t i o n o f b r o m i n e w i t h d i s u b s t i t u t e d s i l y l a m i n o p h o s p h i n e s (_7) t o g i v e M e S i B r and P - b r o m o - N - s i 1 y 1 p h o s p h i n i m i n e s ( e q2 ) . 2

3

3

R /R

B r

I

2

(Me Si) N-P 3

~->

2

^R

f

M e S i N = P-Br | R 3

-Me SiBr 3

(2)

1

R, R

1

= Me, E t , j . - P r , CH SiMe , 2

3

Ph , O C H C F , 2

3

CH Ph, 2

CH CH=CH , e t c . 2

2

The p h o s p h i n i m i n e s a r e t h e r m a l l y u n s t a b l e and r e a d i l y eliminate Me SiBr at temperatures of greater t h a n 100°C t o f o r m o n l y c y c l i c p h o s p h a z e n e s ( e q 3 ) . (_7) 3


10.

Phosphorus-Nitrogen Polymers

wisiAN-NEiLSON E T A L .

R

R

1

M e S i N = P-Br

1

Δ

Γ Ί ^ Ρ = Ν4η

3

R

169

1

+

Me3SiBr

R

(3)

η = 3 ,4


More i m p o r t a n t l y , t h e P-bromophosphiniraines react s m o o t h l y w i t h C F 3 C H 2 O H i n t h e p r e s e n c e o f ΕίβΝ t o f o r m P - ( t r i f l u o r o e t h o x y ) p h o s p h i n i m i n e s ( e q 4 ) (_7 ) . On h e a t ing i n e i t h e r sealed g l a s s ampoules or a s t a i n l e s s R I M e S i N =P-Br I R»

CF CH OH 3

2

>

3

Et N 3

R I Me3SiN =P-OCH CF3 I R 2

(4)

1

s t e e l bomb t h e s e p h o s p h i n i m i n e s r e a d i l y eliminate Me3SiOCH2CF3 ( e q 5) and form e x c l u s i v e l y p o l y m e r i c p h o s p h a z e n e s . (_1) R

R

M e S i N =P-OCH2CF3 3

I

Δ

>

R'

-Ρ"Ρ=Ν4Π

+

I

Me3SiOCH2CF3

(5)

R'

R

Me

Et

Ph

Ph

Ph

R'

Me

Et

Me

Et

Ch Ph 2

The p h y s i c a l p r o p e r t i e s o f t h e s e p o l y m e r s vary c o n s i d e r a b l y as t h e s u b s t i t u e n t s a t p h o s p h o r u s a r e changed. Po1 y ( d i m e t h y l p h o s p h a z e n e ) ( M e 2 P N ) i s a white f i l m - f o r m i n g polymer with a weight averaged m o l e c u l a r w e i g h t ( M ) o f 5 0 , 0 0 0 a s d e t e r m i n e d by l i g h t scatter ing. I t i s s o l u b l e i n C H 2 C I 2 , C H C I 3 , CH3CH2OH, a n d THF/H2O, a n d h a s a m e l t i n g p o i n t o f 158°C a n d a g l a s s t r a n s i t i o n t e m p e r a t u r e o f -42°C Q ) . The d i e t h y l analog ( E t 2 P N ) , on t h e o t h e r h a n d , i s q u i t e p e r p l e x i n g since i t s v i r t u a l i n s o l u b i l i t y i n a l l s o l v e n t s p r e c l u d e s most c h a r a c t e r i z a t i o n other than e l e m e n t a l a n a l y s i s . In c o n t r a s t t o t h e a l k y l s u b s t i t u t e d p o l y m e r s , t h e P-phenyl compounds, [ P h ( M e ) P N ] and [Ph(Εt)PN] , a r e b r i t t l e , brown c o l o r e d m a t e r i a l s which a r e q u i t e s o l u b l e i n THF a n d a r e r e a d i l y p l a s t i c i z e d by t r a c e amounts o f s o l v e n t . Determination of molecular weight n

w

n

n

n


170

RINGS, CLUSTERS, AND

POLYMERS

by g e l p e r m e a t i o n c h r o m a t o g r a p h y f o r [Ph(Me)PN] indicates M t o be 5 4 , 0 0 0 . I t s g l a s s transition t e m p e r a t u r e was f o u n d t o be 37°C Phosphazene copolymers have a l s o been p r e p a r e d by the t h e r m o l y s i s of e q u i m o l a r m i x t u r e s of the p h e n y l / a l k y l and d i a l k y l s u b s t i t u t e d P - t r i f l u o r o e t h o x y phosphinimines. n

n


Ph

R

= Me ,

Et

These m a t e r i a l s are g e n e r a l l y more e l a s t o m e r i c and r u b b e r - l i k e i n a p p e a r a n c e than e i t h e r of the corres ponding homopolymers. Such systems i n d i c a t e t h a t i t should be p o s s i b l e t o " c u s t o m d e s i g n " polyphosphazenes by c h o o s i n g p r e c u r s o r s with desirable substituents . I n s u m m a r y , t h i s new and g e n e r a l m e t h o d o f synthe s i z i n g b o t h c y c l i c and p o l y m e r i c phosphazenes (eq 6) R

R

1

1

Me SiN = P—X

>

3

R»

Me SiX 3

+

Γ 1 -|jP=N-Jn R

(6)

1

involves properly designed N-si1ylphosphinimines which c o n t a i n a l e a v i n g g r o u p X and the d e s i r e d substituents R and R on p h o s p h o r u s . Such compounds eliminate s u b s t i t u t e d s i l a n e s M e S i X and form c y c l i c or polymeric phosphazenes. When X i s B r o r , as r e p o r t e d earlier ( £ ) , F, o n l y s m a l l r i n g c o m p o u n d s a r e f o r m e d , b u t w h e n X i s CF CH2Û, polymeric phosphazenes r e s u l t . In c o n t r a s t to the u s u a l methods of p r e p a r i n g inorganic polymers v i a ring opening polymerization, t h i s i s an unusual example of a c o n d e n s a t i o n - p o l y m e r i z a t i o n which g i v e s an i n o r g a n i c P-N polymer backbone. This method, t h e r e f o r e , has the advantage of a l l o w i n g the initial c o n s t r u c t i o n of s m a l l m o l e c u l e b u i l d i n g b l o c k s which incorporate desirable side groups. This is p a r t i c u l a r l y u s e f u l f o r the p r e p a r a t i o n of a l k y l and/or aryl substituted polyphosphazenes with direct carbon to phosphorus bonds, a system which i s d i f f i c u l t to a c h i e v e by o t h e r methods. f

3

3


10.

wisiAN-NEiLSON E T A L .

CCI4

Reactions of

Phosphorus-Nitrogen Polymers

171

(Silylamino)phosphines

Other N - s i l y l p h o s p h i n i m i n e s which are also s u i t a b l y c o n s t r u c t e d p h o s p h a z e n e p r e c u r s o r s , c a n be p r e p a r e d by a s e c o n d o x i d a t i o n r e a c t i o n o f s i l y l a m i n o phosphines. When t h e s e p h o s p h i n e s r e a c t w i t h c a r b o n t e t r a c h l o r i d e , t w o t y p e s o f P - c h l o r o p h o s p h i m i n i n e s may be f o r m e d b y e s s e n t i a l l y t w o p a t h w a y s ( e q 7 ) ( 8 ) .


R

I -CHCI3 >

H-C-SiMe I Me Q S i N = P - R 1

I

A CH R

CI

CCI4

2

(7)

( M e S i ) N-P, 3

3

R

2

I

R'

H-C-H | Me 3 S i N = P - R

-Me3SiCCl3 >

1

I

Β

CI R = S i M e 3 , Me, P h , Η R = C H S i M e 3 , Me, E t , _ i - P r , OCH CF 1

2

2

_t-Bu, Ph , N M e , 2

OMe ,

3

The e l i m i n a t i o n o f C H C I 3 as s h o w n i n p a t h w a y A o c c u r s i n s i m i l a r s y s t e m s w h i c h c o n t a i n a C-H m o i e t y α to p h o s p h o r u s . P r e s u m a b l y , i n i t i a l f o r m a t i o n o f an i o n p a i r i n t e r m e d i a t e ( R3PC 1 )( C C 1 3 ") (j_0) i s f o l l o w e d by a t t a c k o f t h e C C l 3 ~ a n i o n a t t h e h y d r o g e n on t h e α c a r b o n w i t h e l i m i n a t i o n o f CHCI3 g i v i n g y l i d e p r o d u c t s ( eq 8) (^,^_2_). However, i n systems which +

R* I R P-C-R" 2

R' CCI4 >

• / R P-C-R 2

Η

M

CCI3"

R •CHCI3 -> R P = C-R 2

I \

I

Cl

CI

H

contain a silylamino substitu are presumably intermediates [l,3]-silyl shift ( e q 9) ( 4 ) P - c h l o r o p h o s p h i n i m i n e s shown

!f

(8)

e n t , the analogous ylides which rearrange v i aa to give the i n p a t h w a y A.


172

RINGS, CLUSTERS, AND

POLYMERS

R

I CHR

H-C-SiMe-3

I (Me-iSi ) N-P-R'

Me 3 S i N =

>

2


I

(9)

ι P-R'

I

CI Cl An a l t e r n a t e p a t h w a y i s p o s s i b l e f o r s y s t e m s c o n t a i n i n g s i l y l a m i n o s u b s t i t u e n t s at p h o s p h o r u s . This most l i k e l y i n v o l v e s a t t a c k of the CCI3" a n i o n at the e l e c t r o p h i 1 i c s i l i c o n r e s u l t i n g i n e l i m i n a t i o n of M e 3 S i C C l 3 a s s h o w n i n p a t h w a y B. In the systems i n v e s t i g a t e d thus f a r , the r e a c t i o n pathway preference a p p e a r s t o be i n f l u e n c e d by: (1) s o l v e n t p o l a r i t y , and ( 2 ) s t e r i c and e l e c t r o n i c e f f e c t s o f t h e substituents at p h o s p h o r u s (8). Low-coordinate

Phosphorus

Systems

R e g a r d l e s s o f w h i c h Ν-si1y 1 p h o s p h i n i m i n e products are formed they a l l are p o t e n t i a l p r e c u r s o r s to phosphazenes v i a e l i m i n a t i o n of M e S i C l . Preliminary e v i d e n c e i n d i c a t e s t h a t the t h e r m a l e l i m i n a t i o n does i n d e e d o c c u r i n some c a s e s . The N-si1y 1phosphinimines are a l s o p o t e n t i a l p r e c u r s o r s to a n o t h e r type of novel Si-N-P compound, i . e . t h r e e - c o o r d i n a t e phosphoranes: 3

R-PC

>

Synthesis of PhosphorusâNitrogen Polymers by Using Silicon

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