107 Reactions of Triorganosilyl Halides with Esters of Tricoordinated and Tetracoordinated Phosphorus Downloaded via UNIV OF MASSACHUSETTS AMHERST on July 4, 2018 at 12:31:53 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
J. CHOJNOWSKI, M. CYPRYK, J. MICHALSKI, and L. WOZNIAK P o l i s h A c a d e m y o f Sciences, Centre o f M o l e c u l a r and M a c r o m o l e c u l a r Studies, 90-362 Łόdź, Boczna 5 P o l a n d
To get a broader concept of the nucleophi1ic reactivity of phosphorus acid derivatives towards organosilanes we studied me chanism of reactions of triorganosilyl halides with esters of tricoordinate and tetracoordinate phosphorus having the general formulae:
The reaction between a triorganosilyl halide and t r i a l k y l phosphite takes a course which departs from the Arbuzov scheme since i t leads to silyl esters of alkylphosphonic acids rather than to silylphosphonates (1, 2). The mechanism of this process was not understood although evidence for the possible transient formation of t r i o r g a n o s i l y l phosphites was presented (2). Recently we noticed that the reaction of alkyl phosphite with trimethylsilyl iodide involved various intermediates which were stable enough at lower temperatures to be identified and their formation and disappearance can be followed by PNMRspectroscopy. There fore the investigation of this process gives a deeper insight into the mechanism of the reaction of silyl halides with oxyesters of tricoordinated phosphorus. 31p MR studies over a 1arge temperature range revealed that two separate stages can be distinguished in this process. In the first stage, which can be conveniently followed in the temperatu re range - 2 0 ° - 0 ° C using methylene chloride as a solvent, only products of tricoordinated phosphorus are formed. The second sta ge including transformation of these tricoordinate Ρ intermediates to tetracoordinate phosphorus products ( t r i m e t h y l s i l y l esters of alkylphosphonic acid) in priniple does not occur at a s i g n i ficant rate in this temperature range. 31
0097-6156/81/0171-0521$05.00/0 © 1981 American Chemical Society Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
522
PHOSPHORUS CHEMISTRY
I n i t i a l l y t h e p r o c e s s 1eads t o a l m o s t e x c l u s i v e f o r m a t i o n o f di methyl î o d o p h o s p h i t e whi ch r e a c t s i n a c o n s e c u t i ve s t e p wi t h t h e o t h e r p r o d u c t t r i m e t h y l m e t h o x y s i1ane t o f o r m d i m e t h y l ( t r i m e t h y l s i l y l ) p h o s p h i t e a n d m e t h y l i o d i d e . The r e s u l t s a r e e x p i a i ned by f o u r - c e n t e r e d mechanism i n v o l v i n g t h e n u c l e o p h i 1 i c a t t a c k on p h o s p h o r u s a c c o r d i ng t o t h e f o l l o w i ng scheme MeO (MeO) +Me $î I 3
3
1+ (MeO) PI+Me SiOMe
MeO-P-··J
2
3
Meb-· · Si Me.
(1) " (MeO) PI+Me SiOMe 2
OMe »(MeO) P (0SiMe )+Mel
MeOP- ·· OSiMe.
3
2
3
1· · · Me The p o s s i b i l i t y o f t h e n u c l e o p h i 1 i c a t t a c k o f p h o s p h o r u s on s i 1 i con r e s u l t i ng i n t h e f o r m a t i o n o f a p h o s p h o n i urn o r p h o s p h o r a n e i n t e r m e d i a t e was e x c l u d e d by a c a r e f u l a n a l y s i s o f t h e r a t e o f f o r m a t i o n o f b o t h p h o s p h i t e p r o d u c t s as w e l l a s t h e a n a l y s i s o f t h e a n a l o g o u s r e a c t i o n o f ( M e O ^ P (OSiMe-) wi th M e ^ S ï I whi ch was s t u d i e d s e p a r a t e l y . The f i r s t r e a c t i o n o f scheme 1 i s r e v e r s i b l e , whi ch was p r o v e d by s t u d y i ng t h e r e a c t i on o f di p h e n y l î o d o p h o s p h i t e wi t h t r i methylmethoxys i1ane. In t h e c a s e o f m i x e d a l k y l a r y l e s t e r s t h e i o d o s i l a n e r e a c t s a l m o s t e x c l u s i v e l y wi th t h e a l k y l g r o u p . S i m i 1 a r l y i n t h e c a s e o f mi xed a l k y I s i l y l e s t e r s , t h e a l k o x y 1 g r o u p i s r e p l a c e d by iodi ne.
X (2)
AlkO-P
Me SiI 3
/
\ PI
Me SiOAlk 3
X=Ar0, M e $ i O 3
On t h e o t h e r h a n d , t h e r e a c t ion o f t h e s i l y l i o d i d e w i t h a l k y l o r a r y l c h l o r o p h o s p h i t e s l e a d s f i r s t to the f u l 1 d i s p l a c e ment o f c h l o r i ne by i o d i n e . \ RO^P
C
(3)
1
Me SiI 3
RO j P
The r e a c t i on 3 may s e r v e as a c o n v e n i e n t a l k y l or aryl îodophosphi t e s .
Me SiCl 3
method o f
synthes i s o f
Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
107.
CHOJNOWSKI E T A L .
Reactions
of
Triorganosilyl
523
Halides
In a s h a r p c o n t r a s t t o p h o s p h i t e s , a l k y l e s t e r s o f t e t r a c o o r di n a t e p h o s p h o r u s r e a c t wi t h t r i o r g a n o s i l y l h a l i des ( a t 1 e a s t wi t h bromi de and i o d i de) a c c o r d i ng t o a mechani sm whi c h i s s i mi l a r t o t h e A r b u z o v scheme. The i n t e r a c t ion o f a p h o s p h o r y 1 g roup wi t h s i 1 i con 1eads t o t h e i o n i z a t i o n o f t h e s i 1 i c o n - h a l o g e n bond and t h e f o r m a t i o n o f t h e p h o s p h o n i urn s a l t i n t e r m e d i a t e . The sa 11 u n d e r g o e s decompos i t i o n Î n v o l v i ng d e a l k y 1 a t ion o f t h e p h o s phon i urn i o n by t h e c o u n t e r - i o n ( J ) .
OR (4)
1
fast
)P
+ R SÎX *
0
X=Cl, Br, I
ν + OR* Ρ 0SiR
slow X"
χ
x
!
R =alkyl
χ
•
3
J) .P( 0SiR
+
R'X
3
R=alkyl o r a r y l
The r e a c t i o n provî des an e a s y way f o r removal o f an a l ky 1 g roup f r o m e s t e r s o f p h o s p h o r u s and i t has f o u n d wi de app 1 i c a t ion i n the s y n t h e s i s o f b i o a c t i ve a c i ds o f p h o s p h o r u s (4). 11 may be a l s o u s e d f o r t h e s e l e c t i ve di s p i a c e m e n t o f t h e a l k y 1 g r o u p by t r i m e t h y 1 s i l y l g r o u p i n t h e p r e s e n c e o f some r e a c t i ve g r o u p s bonded t o p h o s p h o r u s 1i ke h a l o g e n , a m i n e , SR e t c . (5). The f a s t r e v e r s i b l e f o rmat ion o f t h e phosphon i urn s a l t a 1 s o d e s e r v e s a t t e n t i o n s i nee i t i s t h e f i r s t s t e p i n i m p o r t a n t r e a c t i o n s i n o r g a n o s i 1 i con chemi s t r y . As a c o n s e q u e n c e o f t h e p a r t i c u l a r l y h i g h s u s c e p t i b i 1 i t y o f t h e s i 1 i con i n t h e p h o s p h o n i urn i o n t o nucleophi1î c a t t a c k , p h o s p h o r y 1 compounds c a t a l y z e n u c l e o p h i 1 i c a t t a c k i n s u b s t i t u t ion a t s i1 i c o n (6). In o r d e r t o o b t a i η more i ηformat ion a b o u t t h e f a s t s t e p o f the r e a c t i o n ^ , t h e s i l y l e s t e r g roup e x c h a n g e ( r e a c t i o n 5) was studied. Κ Ph0 (5)
/OSiMe.
x
A PhO
k + MeaNpPhSiCl
ϋ
J)
PhO ^'
v
k_
p' PhO
1
+ Me.SiCl 3
OSiMeaNpPh
The k i n e t i cs and e q u i l i b r i u m o f t h e r e a c t ion 5 i n ca rbon tetrachlorî de was i n v e s t i g a t e d by P NMR s p e c t r o s c o p y . The p r o c e s s fο 11ows t h e k i n e t i c 1 aw f o r a s e c o n d o r d e r r e v e r s î b l e r e a c t i o n ( f i r s t o r d e r i n b o t h the e s t e r and t h e s i l y l h a l i d e ) . V a l u e s o f r a t e and e q u i 1 i b r i urn c o n s t a n t s 25°C and o f a c t i v a t i o n p a r a m e t e r s a r e : k ^ O . 0 6 4 d m ^ m o l ~ s " , k -=0.048 dm^mol~ s ~ , X -ι X K=1.33, ΔΗ =21 k j mol , A S = - 3 9 e.u. These r e s u l t s a r e i n a c c o r d wi t h a p h o s p h o n i urn i n t e r m e d i a t e mechani sm. React ion 5 i s a c c o m p a n i e d by i n t e r m o l e c u l a r (6) and i n t r a m o l e c u l a r (7) s i l y l g r o u p mi g r a t i o n . 3 1
1
1
1
1
Τ
T
Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
1
PHOSPHORUS CHEMISTRY
524
R e a c t i o n 6 was d e t e c t e d u s i n g e s t e r s h a v i n g a d i f f e r e n t p h o s p h o r u s m o i e t y . T h i s r e a c t i o n may a l s o be r e s p o n s i b l e f o r t h e disappearance o f o p t i c a l a c t i v i t y i n the system d u r i n g r e a c t i o n 5 when t h e o p t i c a l l y a c t i v e i s o m e r o f MeotNpPhS i C1 i s u s e d . The r a c e m i z a t i o n f o l l o w s an i r r e g u l a r o p t i c a l r o t a t i o n - t i m e c u r v e and p r o c e e d s more s l o w l y t h a n r e a c t i o n 5, g i v i n g e v i d e n c e o f t h e s t e r e o s e l e c t i v e c o u r s e o f r e a c t i o n 5. The i n t r a m o l e c u l a r m i g r a t i o n 7 must l e a d t o t h e r a c e m i z a t i o n o f e s t e r s w i t h t h e c e n t e r o f c h i r a l i t y on the p h o s p h o r u s atom and i t i s t h e r e a s o n f o r t h e f a i 1 u r e t o i s o l a t e t h e o p t i c a l l y a c t i ve i somer h a v i ng Ρ ( O ) O S i M e j s t r u c t u r e . 11 does n o t seem, h o w e v e r , t o change c o n f i g u r a t i o n a t the s i 1i con a t o m .
Literature Cited 1. Malatesta, L.; Gazz. Chim. I t a l . (1950), 80, 527. 2. Bugerenko, E. F.; Tchernyshev, E. A . ; Popov, Ε. M . ; Izv. Acad. Nauk SSSR, ser. khim. (1966), 1391. 3. Borecka, B . ; Chojnowski, J.; Cypryk, M.; Michalski, J.; Zielińska, J.; J . Organometal. Chem. (1979), 171, 17. 4. McKenna, C. E . ; Higa, M. T.; Cheung, N. H . ; McKenna, M. C.; Tetrahedron Lett. (1977), 155. 5. Chojnowski, J.; Cypryk, M.; Michalski, J.; Synthesis (1978), 777. 6. Chojnowski, J.; Cypryk, M.; Michalski, J.; J . Organometal. Chem. (1978), 161 C 31-35. RECEIVED
July 7, 1981.
Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
