49 Synthesis and Reactivity of (Silylamino)phosphines R O B E R T H . NEILSON, H. R A N D Y O ' N E A L
P A T T Y W I S I A N - N E I L S O N , D A V I D W. M O R T O N , and
Downloaded by UNIV OF SYDNEY on July 25, 2013 | http://pubs.acs.org Publication Date: November 11, 1981 | doi: 10.1021/bk-1981-0171.ch049
Department of Chemistry, Texas Christian University, Fort Worth, T X 76129
Compounds containing the Si-N-P linkage combine the structural and stereochemical diversity of phosphorus with the reactivity of the silicon-nitrogen bond. Indeed, much of the derivative chemistry and synthetic potential of these compounds, especially the (silylamino)phosphines such as (Me Si) NPMe2,is based on this difunctional character. We report here a general, "one-pot" synthesis of (silylamino)phosphines and describe their use in the preparation of several types of phosphorus-containing materials. Synthesis of (Silylamino)phosphines. In a typical preparation, addition of one molar equivalent of PCI to a stirred solution of LiN(SiMe ) in ether at -78°C followed by one or two equivalents of an alkyl Grignard or lithium reagent at 0°C gives the corresponding mono- or dialkylphosphine . This proce 3
3
2
3
(1)
n-BuLi
(2)
PCI3
>
(Me Si) NH 3
2
2
(Me Si) NPC1 3
2
R
RMgX > or R L i
(Me Si) N 3
2
2
CI
R
(MeoSi)oNPCl
2
= i-Pr,
t-Bu, CH SiMe
RMgX >(Me Si) NPR 3
R
2
2
2
= Me, E t , C H S i M e 2
0097-6156/81/0171-0239$05.00/0
©
1981 American Chemical Society
In Phosphorus Chemistry; Quin, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
3
3
240
PHOSPHORUS CHEMISTRY
dure routinely affords high yields (ca 75%) and large quantities (ca 100-200 g) of the phosphine product. Moreover, the method has been generalized to include the use of other silylamines, PhPCl instead of PCI , and different organometallic reagents. Synthesis of Polyphosphazenes. We are investigat ing a new, direct synthesis of phosphazene polymers which involves the thermally-induced elimination of silanes from suitably constructed N-silylphosphinimines. As a route to linear polyphosphazenes, this method Downloaded by UNIV OF SYDNEY on July 25, 2013 | http://pubs.acs.org Publication Date: November 11, 1981 | doi: 10.1021/bk-1981-0171.ch049
2
Me SiN
-«N=PV-
Me SiX
3
3
3
o f f e r s the d i s t i n c t advantage of i n c o r p o r a t i n g the d e s i r e d p h o s p h o r u s s u b s t i t u e n t s d i r e c t l y i n t o an easily-prepared s t a r t i n g m a t e r i a l , thereby e l i m i n a t i n g the need f o r p r e p a r i n g the d i h a l o polymers (X2PN) . Many o f t h e " s u i t a b l y c o n s t r u c t e d " phosphinimines (1) a r e p r e p a r e d v i a t h e b r o m i n a t i o n o f ( s i l y l a m i n o ) phosphines. The P-bromo compounds a r e e a s i l y convert ed t o t h e c o r r e s p o n d i n g d i a l k y l a m i n o o r a l k o x y d e r i v a tives . n
I
0°C (Me Si) NPRR 3
2
?
+ Br
>Me SiBr
2
+
3
Me S i N = P — R 3
R R,R
f
f
= Me, E t , P h , OCH2CF3
We f i n d t h a t t h e n a t u r e o f t h e l e a v i n g g r o u p ( X ) is important i n determining both the r e l a t i v e stability of t h e s t a r t i n g m a t e r i a l as w e l l as t h e degree o f o l i g o m e r i z a t i o n of t h e phosphazene products. For e x a m p l e , w h i l e t h e P-NMe a n d P-OMe p h o s p h i n i m i n e s are s t a b l e t o a t l e a s t 2 50°C, t h e P-Br a n a l o g u e s decompose a t lower t e m p e r a t u r e s (100-150°C) t o g i v e M e S i B r a n d c y c l i c p h o s p h a z e n e s ( R 2 P N ) w h e r e η = 3,4. Most s i g n i f i c a n t l y , however, p o l y m e r i c p h o s p h a z e n e s ( £ ) a r e o b t a i n e d a l m o s t e x c l u s i v e l y when t h e l e a v i n g group i s OCH2CF . The p r o d u c t s a r e t h e f i r s t f u l l y characterized polyphosphazenes containing only d i r e c t P-C b o n d e d s u b s t i t u e n t s . These m a t e r i a l s a r e s o l u b l e film-forming or elastomeric polymers with m o l e c u l a r w e i g h t s i n t h e 50-70,000 r a n g e . The 2
3
n
3
In Phosphorus Chemistry; Quin, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
49.
NEILSON ET A L .
OCH CF 2
241
(Silylamino)phosphines
3
180-190°. C Me SiN=P—R > j 2-5 d a y s R R,R = Me,Et,Ph 3
Me SiOCH CF 3
2
1 I -4N=P> | R
+
3
f
f
Downloaded by UNIV OF SYDNEY on July 25, 2013 | http://pubs.acs.org Publication Date: November 11, 1981 | doi: 10.1021/bk-1981-0171.ch049
1
c o m p l e t e c h a r a c t e r i z a t i o n of t h e s e and r e l a t e d m a t e r i als i s under a c t i v e i n v e s t i g a t i o n . N u c l e o p h i l i c R e a c t i o n s of (Silylamino)phosphines. The r e a c t i o n s o f ( s i l y l a m i n o ) p h o s p h i n e s w i t h simple a l d e h y d e s and k e t o n e s p r o c e e d v i a n u c l e o p h i l i c a t t a c k by p h o s p h o r u s f o l l o w e d by a [ 1 , 4 ] s i l y l m i g r a t i o n f r o m n i t r o g e n t o o x y g e n t o y i e l d new N-silylphosphinimines Ο). With a,3-unsaturated c a r b o n y l compounds, 1 , 4 - a d d i R
f
I 0 (Me Si) NPMe 3
I R-C-R
+
2
R-C-OSiMe CH C1 2
I Me SiN=PMe
2
1
>
3
3
2
0°C tion occurs hydrolysis,
producing s i l y l enol ethers which, y i e l d γ-carbonyl phosphine o x i d e s .
upon
0
I (Me Si) NPMe 3
2
+
2
CH "= CH
C
2
R C H C H = C. I OSiMe. Me SiN=PMe 2
X
H 0 2
J
3
>
2
o°c R
>
° g Κ I Me PCH CH CR 2
2
2
(Silylamino)phosphines also react with various h a l i d e s i n c l u d i n g e t h y l bromoacetate, a l l y l bromide, and c h l o r o f o r m â t e s . The i n i t i a l l y - f o r m e d p h o s p h o n i u m s a l t s e l i m i n a t e s i l y l h a l i d e s to a f f o r d f u n c t i o n a l i z e d p h o s p h i n i m i n e s M e S i N = P (R)Me2 w h e r e R = -CH2C (0) O E t , - C H 2 C H = C H 2 , and - C ( 0 ) 0 R . Two-coordinate (Silylamino)phosphines. Certain chlorο(silylamino)phosphines bearing a t r i m e t h y l s i l y l m e t h y l g r o u p c a n be d e h y d r o h a l o g e n a t e d t o y i e l d s t a b l e (methylene)phosphines. The v e r y low f i e l d (δ 309. 9) 31p s h i f t c o n f i r m s t h e t w o - c o o r d i n a t e n a t u r e of t h i s compound w h i l e t h e low f i e l d (δ 7.09) H s i g n a l shows i t t o be t h e P=CH r a t h e r t h a n t h e P=N isomer. Three modes o f r e a c t i v i t y o f t h i s ( m e t h y l e n e ) p h o s p h i n e h a v e been o b s e r v e d : a d d i t i o n t o t h e P=C b o n d , o x i d a t i v e 3
f
1
In Phosphorus Chemistry; Quin, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
242
PHOSPHORUS
a d d i t i o n at phosphorus, tion metal centers.
and c o m p l e x a t i o n w i t h
CI I (Me Si)2N-P-CH SiMe3 3
base >
2
(Me Si) N-P 3
2
-HC1
CHEMISTRY
transi-
-
