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5 Cyclophosphathiazenes Containing TwoThree-Coordinate Sulfur
or
N. BURFORD, T. CHIVERS, M. N. S. RAO, and J. F. RICHARDSON
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University of Calgary, Department of Chemistry, Calgary, Alberta T2N 1N4 Canada
The preparation, molecular and electronic struc tures, and some reactions of cyclophosphathiazenes containing two or three coordinate sulfur are de scribed. Inorganic heterocycles of general formu lae (R PN) (SN) or (R PN) (NSCl) are prepared by the reactions of S N with phosphorus(III) reagents [e.g. RPPR(R=Me,Ph) or Ph PH, n=1,2; or Ph PCl, x=2, y=1]. In addition to substitution at sulfur, (Ph PN) NSCl readily undergoes ring opening reac tions to give novel bicyclic, tricyclic, or spirocyclic PSN ring systems. X-ray crystallographic data and the results of MO calculations show that the excess of electrons may be accommodated by partial occupation ofπ*-levelsor by formation of transannular S-S bonds in these π-electron rich heterocycles. 2
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A w i d e v a r i e t y o f c y c l i c S-N compounds c o n t a i n i n g two o r t h r e e c o o r d i n a t e s u l f u r i s known ( l ) . The b i n a r y S-N r i n g s v a r y i n s i z e f r o m f o u r ( S N ) t o t e n (SsNs" ") atoms and e x a m p l e s o f a n i o n s ( S 3 N 3 " * ) and c a t i o n s ( S 3 N +, SJ+N3 , Si+Nt*"*") a r e known i n a d d i t i o n t o n e u t r a l m o l e c u l e s (_2). The e x c e s s o f e l e c t r o n s i n t h e s e p l a n a r , e l e c t r o n - r i c h h e t e r o c y c l e s i s o f t e n accommodated i n l o w l y i n g π* o r b i t a l s b u t , i n some c a s e s ( e . g . SifNi*, St*N5~), t h e number o f π* e l e c t r o n s i s r e d u c e d b y f o r m a t i o n o f t r a n s a n n u l a r S-S b o n d s t o g i v e c a g e s (.2,3.). An e v e n b r o a d e r r a n g e o f r i n g s i z e s i s f o u n d f o r t h e c y c l o phosphazenes ( R P N ) (X=3-1T) b u t t h e s e i n o r g a n i c h e t e r o c y c l e s a r e π-electron p r e c i s e ( i . e . t h e number o f π-electrons i s e q u a l t o t h e number o f a t o m i c c e n t e r s i n t h e r i n g s y s t e m ) . Although b o t h b i c y c l i c and c o n d e n s e d s t r u c t u r e s have b e e n i d e n t i f i e d , s i m p l e a n i o n s o r c a t i o n s o f c y c l o p h o s p h a z e n e s a r e unknown (k). The c o m b i n a t i o n o f t h e monomer u n i t s R P N a n d NS p r o v i d e s many p o s s i b i l i t i e s f o r i n o r g a n i c r i n g s y s t e m s c o n t a i n i n g p h o s p h o r u s , n i t r o g e n , and two c o o r d i n a t e s u l f u r . Thus one m i g h t a n 1
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0097-6156/83/0232-0081 $6.00/0. © 1983 American Chemical Society
Cowley; Rings, Clusters, and Polymers of the Main Group Elements ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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t i c i p a t e a h o m o l o g o u s s e r i e s ( R 2 P N ) ( S N ) i n w h i c h t h e f i r s t memb e r i s a s i x - m e m b e r e d r i n g ( l , n = l ) and t h e s e c o n d member i s an e i g h t - m e m b e r e d r i n g w i t h s t r u c t u r a l i s o m e r s (2 and 3 , n=2). In a d d i t i o n , l a r g e r r i n g s i z e s (n=3,4 e t c . ) are p o s s i b l e . S i m i l a r l y t h e c o m b i n a t i o n o f R2PN and NSC1 u n i t s a f f o r d s h e t e r o c y c l e s c o n t a i n i n g p h o s p h o r u s , n i t r o g e n and t h r e e c o o r d i n a t e s u l f u r ( e . g . k and 5) w h i c h may be c o n s i d e r e d as h y b r i d s o f t h e w e l l known r i n g s y s t e m s ( R 2 P Ï O 3 and ( N S C l ) 3 . T h i s p a p e r d e s c r i b e s t h e p r e p a r a t i o n , m o l e c u l a r and e l e c t r o n i c s t r u c t u r e s and some r e a c t i o n s o f compounds 1 - §, f o r w h i c h t h e g e n e r i c name c y c l o p h o s p h a t h i a z e n e s w i l l be u s e d . n
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C y c l o p h o s p h a t h i a z e n e s w i t h Two
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Preparation. The f i r s t r e p o r t o f a h e t e r o c y c l e o f t h i s t y p e ( l , R = Me3SiNH) i n v o l v e d t h e r e a c t i o n o f S^Ni* w i t h t h e p h o s p h o r us (V) r e a g e n t ( M e 3 S i ) P ( N S i M e 3 ) 2 ( 5 ) . The s t r u c t u r e o f t h i s deep b l u e compound c o n s i s t s o f a h i g h l y p u c k e r e d s i x - m e m b e r e d r i n g (6). The r e a c t i o n o f R2PPR2 w i t h Si+Nit p r o v i d e s a more g e n e r a l r o u t e t o such h e t e r o c y c l e s . Thus t r e a t m e n t o f St+Ni* w i t h t e t r a p h e n y l - o r t e t r a m e t h y l - d i p h o s p h i n e i n t o l u e n e a t r e f l u x p r o d u c e s 1 (R=Ph,Me) i n modest y i e l d s (15 - 20$, 1 , 8 ) . The Ph PPPh2/Si N» r e a c t i o n m i x t u r e was m o n i t o r e d b y Ρ nmr s p e c t r o s c o p y w h i c h r e v e a l e d t h e p r e s e n c e o f ( P h P N ) 3 , ( P h 2 P N K , and ( P h P S ) i n a d d i t i o n t o s e v e r a l o t h e r p r o d u c t s (£). Two o f t h e s e p r o d u c t s h a v e b e e n s e p a r a t e d b y 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 and i d e n t i f i e d as t h e s t r u c t u r a l i s o m e r s 2 and 3 (R=Ph,Me). The r e a c t i o n o f Ph2PH w i t h Si+Ni* a l s o p r o d u c e s ï - 3 and i s p r e f e r r e d f o r t h e p r e p a r a t i o n o f 1 and t h e 1 , 3 - i s o m e r , 2, b e c a u s e t h e p r o d u c t s a r e more r e a d i l y separated from P h P ( S ) H than from ( P h P S ) . However, t h e P h P H / SitNif r e a c t i o n g i v e s a v e r y l o w y i e l d o f t h e 1 , 5 - i s o m e r , 3 . 2
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M o l e c u l a r S t r u c t u r e s . An X - r a y s t r u c t u r a l d e t e r m i n a t i o n o f l ( R = P h ) shows t h a t t h e NSNSN s e q u e n c e o f t h e s i x - m e m b e r e d r i n g i s e s s e n t i a l l y p l a n a r b u t t h e p h o s p h o r u s atom i s t i l t e d 0. out o f t h i s p l a n e (8_) . The P-N and S-N b o n d d i s t a n c e s a r e c a . 1 . 6 2 and 1 . 5 T A , r e s p e c t i v e l y , compared t o c a . 1.60& f o r t h e P-N d i s t a n c e in (Ph PN) (10) and c a . I.60S f o r t h e S-N b o n d l e n g t h i n S 3 N 3 " (ll). These t r e n d s i n b o n d l e n g t h s a r e c o n s i s t e n t w i t h e x p e c t a t i o n s b a s e d on t h e v i e w t h a t ( P h 2 P N ) , P h 2 P S 2 N and S3N3"" a r e 6 , 8, and 10 π-electron s y s t e m s , r e s p e c t i v e l y (χ,.8). The s t r u c t u r e o f t h e o r a n g e 1 , 3 - i s o m e r o f t h e e i g h t - m e m b e r e d r i n g , g, r e s e m b l e s t h a t o f t h e s i x - m e m b e r e d r i n g i n t h a t t h e NSNSN u n i t i s e s s e n t i a l l y p l a n a r . The p h o s p h o r u s atoms l i e o u t and on o p p o s i t e s i d e s o f t h i s p l a n e b y c a . O.ToS (90 . The s t r u c t u r a l p a r a m e t e r s f o r 2, a r e g i v e n i n F i g u r e 1. In c o n t r a s t , the s t r u c t u r e of the p a l e y e l l o w 1 , 5 - i s o m e r , 3, c o n s i s t s o f a f o l d e d eight-membered r i n g w i t h a t r a n s a n n u l a r S-S bond (d(S-S)=2.53A, F i g u r e 2 ) . The two p l a n a r S N u n i t s i n t e r s e c t a t an a n g l e o f c a . Il6° and t h e p h o s p h o r u s atoms l i e c a . 2
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Cowley; Rings, Clusters, and Polymers of the Main Group Elements ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
Cyclophosphathiazenes
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BURFORD ET A L .
Figure 1. ORTEP drawing of 1,3-(Ph PNPPh )S N showing bond lengths (À) and angles (deg). All ORTEP figures are drawn with thermal ellipsoids at the 50% probability level, and only a-C atoms of the phenyl rings are shown. 2
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Cowley; Rings, Clusters, and Polymers of the Main Group Elements ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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0 . 2 l 8 "below t h e r e s p e c t i v e p l a n e s ( 9 . ) · The c o r r e s p o n d i n g d e r i v a t i v e , 3 (R=Me), h a s a v e r y s i m i l a r s t r u c t u r e e x c e p t t h e p h o s p h o r u s atoms l i e above and b e l o w t h e p l a n e s b y c a . and - 0 . r e s p e c t i v e l y , a p p a r e n t l y due t o a s o l i d s t a t e
methyl that +0.19 effect
(12).
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T h i s s t r u c t u r e may b e compared w i t h t h o s e o f t h e recently r e p o r t e d i s o e l e c t r o n i c c a r b o n a n a l o g u e s R C ( N S N ) 2 C R ( 1 3 , R=Me2N,Ph). I n t h e c a r b o n compounds t h e e f f e c t o f t h e e x o c y c l i c substituent on r i n g c o n f o r m a t i o n i s r e m a r k a b l e . Thus t h e p h e n y l d e r i v a t i v e i s c o m p l e t e l y p l a n a r and has s t r u c t u r a l p a r a m e t e r s c o n s i s t e n t w i t h a 10 π-electron s y s t e m w h i l e t h e d i m e t h y l a m i n o d e r i v a t i v e has a f o l d e d s t r u c t u r e w i t h a t r a n s a n n u l a r S-S d i s t a n c e o f 2.43& (Figure 3 ) . Electronic Structures. Ab i n i t i o HFS c a l c u l a t i o n s f o r 1 (R = H) h a v e c o n f i r m e d t h e c o n c l u s i o n s o f a n HMO a n a l y s i s t h a t t h e s i x - m e m b e r e d r i n g i s a n 8 π-electron s y s t e m i n w h i c h t h e HOMO i s a π* o r b i t a l ( 8 ) . These c a l c u l a t i o n s p r o v i d e t h e follow i n g a d d i t i o n a l i n s i g h t s i n t o the nature o f the bonding i n 1 (8). (i) The n o n - p l a n a r ( e x p e r i m e n t a l ) c o n f o r m a t i o n o f t h e PS2N3 r i n g i s s l i g h t l y l o w e r i n e n e r g y ( c a . 15 k c a l m o l " ) than the p l a n a r r i n g , but the o r d e r o f energy l e v e l s d o e s n o t change w i t h g e o m e t r y . (ii) The a v a i l a b i l i t y o f 3d o r b i t a l s o n p h o s p h o r u s l e a d s t o a s t a b i l i z a t i o n o f t h e π-system i n 1 compared t o S3N3", e s p e c i a l l y t h e π* l e v e l s . (iii) The s t r o n g v i s i b l e a b s o r p t i o n b a n d o b s e r v e d a t 5 ^ 5 58Ο nm f o r 1 (R = Me, P h , PhO, M e S i N H ) i s a s s i g n e d t o t h e Η0Μ0~(π*)^υΜ0(π*) t r a n s i t i o n ( c a l c u l a t e d va l u e c a . 56Ο nm) o n t h e b a s i s o f c a l c u l a t e d t r a n s i t i o n moments. (iv) M o s t o f t h e π-electron d e n s i t y i n 1 i s l o c a t e d o n t h e S2N3 u n i t s u g g e s t i n g t h a t t h e i n t e r n a l s a l t R 2 P S 2 N 3 " i s a r e a s o n a b l e m o d e l f o r t h e more q u a l i t a t i v e H u c k e l approach. J u s t i f i e d b y the s i m i l a r i t y o f the molecular s t r u c t u r e o f 2 w i t h t h a t o f 1 , t h e f o r m e r can b e c o n s i d e r e d t o c o n s i s t o f a n NSNSN" u n i t a c c o m m o d a t i n g δπ-electrons i n t e r a c t i n g w i t h t h e 2 π-electron u n i t Ph2P=N =PPh2. T h i s i n t e r a c t i o n l e a d s t o a s t a b i l i z a t i o n o f t h e HOMO (2a2) and LUMO ( U b i ) l e v e l s i n a manner s i m i l a r t o t h e l o w e r i n g o f t h e π-energy l e v e l s i n 1 w h i c h r e s u l t s from the i n t e r a c t i o n o f the 3d o r b i t a l s on phosphorus w i t h the π-type o r b i t a l s o f t h e NSNSN" u n i t ( F i g u r e k). Thus t h e eightmembered r i n g c a n b e d e s c r i b e d a s a 10 π-electron s y s t e m and, b y a n a l o g y w i t h 1 , i t seems r e a s o n a b l e t o s u g g e s t t h a t a s i m i l a r π*->π* t r a n s i t i o n i s r e s p o n s i b l e f o r t h e s t r o n g v i s i b l e a b s o r p t i o n b a n d a t c a . U60 nm and, h e n c e , t h e o r a n g e c o l o r o b s e r v e d f o r t h e 1,3-isomer. The e x i s t e n c e o f d i f f e r e n t c o n f o r m a t i o n s f o r t h e 1 , 5 - i s o m e r o f t h e e i g h t - m e m b e r e d r i n g s can be u n d e r s t o o d i n t e r m s o f HMO 1
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B U R F O R D ET A L .
Figure 3. Structures of1,5-PhC(NSN) CPh (top) and (bottom) (13). 2
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Cowley; Rings, Clusters, and Polymers of the Main Group Elements ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
RINGS, C L U S T E R S , A N D P O L Y M E R S
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c a l c u l a t i o n s f o r t h e two l i m i t i n g s t r u c t u r e s ( a ) a p l a n a r t e n πe l e c t r o n s y s t e m a n d ( b ) a f o l d e d s t r u c t u r e c o n s i s t i n g o f two i n d e p e n d e n t f o u r π-electron t h r e e c e n t e r u n i t s p l u s a n S-S σ-bond. F i g u r e 5 shows a c o r r e l a t i o n d i a g r a m f o r t h e s e t w o s t r u c t u r e s . As i l l u s t r a t e d b y G l e i t e r f o r Si+Ni* (Ik) , t h e HOMO ( a n a n t i - b o n d i n g π-level) o f t h e p l a n a r m o l e c u l e t r a n s f o r m s i n t o t h e b o n d i n g S-S σ-interaction o f t h e f o l d e d r i n g . Consequently, the b u t t e r f l y s t r u c t u r e w i l l b e a d o p t e d i f t h i s σ-interaction i s s u f f i c i e n t l y s t r o n g t o overcome t h e g r e a t e r π-delocalisation e n e r g y o f t h e p l a n a r r e l a t i v e t o t h e f o l d e d r i n g ( a s s u m i n g no s i g n i f i c a n t c h a n g e s i n t h e r e s t o f t h e σ f r a m e w o r k ) . The HOMO o f t h e p l a n a r r i n g i s t h e o r b i t a l most s e n s i t i v e t o c h a n g e s i n t h e e l e c t r o n e g a t i v i t y o f Ε a n d i t i s s t a b i l i z e d b y more e l e c t r o n e g a t i v e v a l u e s o f a g . Thus i t i s n o t u n r e a s o n a b l e t o f i n d t h a t t h e e l e c t r o n e g a t i v e s u b s t i t u e n t Ph f a v o r s t h e p l a n a r s t r u c t u r e i n RC(NSN)2CR, w h i l e t h e e l e c t r o n - r e l e a s i n g Me N g r o u p p r o d u c e s a folded conformation. The b u t t e r f l y s t r u c t u r e o f 3 i s p r o b a b l y a c o n s e q u e n c e o f t h e l o w e r e l e c t r o n e g a t i v i t y o f p h o s p h o r u s com pared t o carbon (12). 2
C y c l o p h o s p h a t h i a z e n e s w i t h Three C o o r d i n a t e
Sulfur
Preparation. O n l y one example o f a c y c l o p h o s p h a t h i a z e n e o f the type (R2PN) (NSCl) has been r e p o r t e d . The compound ( C 1 P N ) N S C 1 ( 5 , R = C l ) was o b t a i n e d a s a c o l o r l e s s o i l b y t h e r e a c t i o n o f P C l ~ w i t h M e S i N S N S i M e 3 ( l ^ ) . The r e l a t e d c a t i o n ( C 1 P N ) N S , f o r m e d b y t r e a t m e n t o f t h i s o i l w i t h S b C l , was shown t o b e a p l a n a r s i x - m e m b e r e d r i n g b y X - r a y c r y s t a l l o g r a p h y (15). An a l t e r n a t i v e r o u t e t o h e t e r o c y c l e s o f t y p e 5 i s t h e r e a c t i o n o f Si+Nif w i t h t r i v a l e n t p h o s p h o r u s compounds c o n t a i n i n g P - C l b o n d s ( 1 6 ) · F o r e x a m p l e , t h e r e a c t i o n o f P h 2 P C l w i t h Si^Ni* i n a 3:1 m o l a r r a t i o i n CH3CN f o r 3h a t r e f l u x p r o d u c e s a n &5% y i e l d o f (Ph2PN)2NSCl a s m o i s t u r e - s e n s i t i v e , p a l e y e l l o w c r y s t a l s . The l i n e a r p r o d u c t [ P h P C l N P C l P h ] C l ~ i s a l s o obtained and t h e y i e l d o f t h i s m a t e r i a l increases s i g n i f i c a n t l y as t h e molar r a t i o Ph2PCl/S!,N i s i n c r e a s e d . A n o t h e r member o f t h e s e r i e s ( U , x = l , y=2) c a n b e o b t a i n e d b y t h e smooth o x i d a t i v e a d d i t i o n o f C l t o 1 u s i n g PÏ1ICI2 ( 1 7 ) . The d i c h l o r o compound k c a n b e c o n v e r t e d t o t h e b i c y c l i c m o l e c u l e 6 o n t r e a t m e n t w i t h Me3SiNSNSiMe3 ( F i g u r e 6 ) . R e l a t e d b i c y c l i c compounds w i t h f l u o r i n e ( o r P h a n d F ) s u b s t i t u e n t S o n p h o s p h o r u s h a v e p r e v i o u s l y b e e n o b t a i n e d f r o m t h e r e a c t i o n o f PF5 ( o r P h P F O w i t h M e S i N S N S i M e ( l 8 , 1 9 ) . The t h e r m a l d e c o m p o s i t i o n o f 6 i n t o l u e n e a t c a . 90°C f o r 3h r e g e n e r a t e s t h e six-membered r i n g ( l ) . x
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Cowley; Rings, Clusters, and Polymers of the Main Group Elements ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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BURFORD ET A L .
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-10
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-12-
2b, Ια lb,
-14-16
© o
M Figure
4. Orbital
•••••• ~
2
symmetry
^Cff
sMs
ΊΚ-'Ρ N ( ) N ' + ^ s"-'s ΝΚ-Λ' /
correlation diagram (R PNPR )S N . 2
2
2
for
R PS N 2
2
3
and
1,3-
3
A
2
Π7Γ
A,
Figure 5. Orbital symmetry correlation diagram for the planar (left) and folded (right) models of E(NSN) E, where a = a . 2
E
s
(Reproduced from Inorg. Chem. 1982, 21, 982.)
Cowley; Rings, Clusters, and Polymers of the Main Group Elements ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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RINGS, C L U S T E R S , A N D P O L Y M E R S
t h e s u l f u r atom l i e s c a . 0 . 3 1 & o u t o f t h i s p l a n e ( F i g u r e 7 ) . The S-N b o n d d i s t a n c e s ( c a . I.56S) a r e somewhat s h o r t e r t h a n t h e c o r responding distances i n (NSCl) ( l . 6 0 - 1 . 6 l & ) ( 2 0 , ) , b u t t h e mean P-N d i s t a n c e i n t h e PNP u n i t ( c a . 1.592) i s t y p i c a l o f t h a t f o u n d f o r c y c l o p h o s p h a z e n e s (h). However, t h e P-N b o n d s l i n k i n g t h i s u n i t t o t h e NSN u n i t a r e c o n s i d e r a b l y l o n g e r ( 1 . 6 6 - 1 . 6 7 f t ) s u g g e s t i n g a t e n d e n c y t o w a r d s l o c a l i z a t i o n o f π-bonding a t o p p o s i t e ends of the molecule. A s i m i l a r d i f f e r e n c e i n S-N and P-N b o n d l e n g t h s i n P,N,S r i n g s c o n t a i n i n g f o u r c o o r d i n a t e s u l f u r has b e e n a t t r i buted t o the d i f f e r e n t e l e c t r o n e g a t i v i t i e s o f the phosphorus and s u l f u r c e n t e r s ( 2 1 ) . The S - C l d i s t a n c e ( 2 . 3 6 & ) i s s u b s t a n t i a l l y l o n g e r t h a n t h e c o r r e s p o n d i n g d i s t a n c e i n ( N S C l h ( 2 . 0 8 & ) . The c o r r e s p o n d i n g i o d i d e (Ph2PN)2NSI has v e r y s i m i l a r e n d o c y c l i c b o n d l e n g t h s a n d a n S-I d i s t a n c e o f c a . 2 . 7 2 Â ( 2 2 ) .
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3
R e a c t i o n s o f ( P h 2 P N ) 2 N S C I . The m o n o f u n c t i o n a l i t y o f 5 (R=Ph) p r o v i d e s a u n i q u e o p p o r t u n i t y t o i n v e s t i g a t e r e a c t i o n s a t t h e s u l f u r c e n t e r o f t h e P2SN3 r i n g and p r e l i m i n a r y r e s u l t s i n d i cates t h a t both d i r e c t s u b s t i t u t i o n and r i n g opening r e a c t i o n s can o c c u r . F o r e x a m p l e , t h e r e a c t i o n o f 5 w i t h K I i n CH3CN g i v e s a n a l most q u a n t i t a t i v e y i e l d o f d a r k r e d c r y s t a l s o f t h e corresponding i o d i d e , (Ph2PN)2NSI, w h i l e a v e r y m o i s t u r e - s e n s i t i v e a z i d e can b e o b t a i n e d u s i n g Me3SiN3 ( 2 2 ) . The t h e r m o l y s i s o f ( P h 2 P N ) N S C l above 200°C, o r o f t h e c o r responding i o d i d e a t lower temperatures (ca. lU0°C), produces c o l o r l e s s c r y s t a l s o f a v e r y s t a b l e compound w h i c h has b e e n shown b y X - r a y c r y s t a l l o g r a p h y t o have a s p i r o c y c l i c s t r u c t u r e i n w h i c h two s i x - m e m b e r e d r i n g s a r e j o i n e d a t a common s u l f u r atom ( F i g u r e 8). T h i s compound i s f r e q u e n t l y f o u n d a s a p r o d u c t o f t r a n s f o r mations i n v o l v i n g cyclophosphathiazenes. Each six-membered r i n g i s f o r m a l l y a s s o c i a t e d w i t h 6 π-electrons, i . e . π-electron p r e c i s e a n d i s o e l e c t r o n i c w i t h ( R 2 P N ) , and t h i s may a c c o u n t f o r t h e high s t a b i l i t y o f the s p i r o c y c l e . A n o t h e r i n t e r e s t i n g example o f a r i n g o p e n i n g r e a c t i o n o c c u r s when ( P h P N ) N S C l i s t r e a t e d w i t h M e S i N S N S i M e . A t r i c y c l i c compound, whose s t r u c t u r e i s i l l u s t r a t e d i n F i g u r e 95 i s f o r m e d i n c a . 20% y i e l d . T h i s m o l e c u l e c o n s i s t s o f two e i g h t - m e m b e r e d r i n g s ( 1 , 3 - i s o m e r , 2) f u s e d a t a common s u l f u r atom a n d l i n k e d b y a n S-S i n t e r a c t i o n ( S ( 2 ) - S ( 3 ) = 2.30&) t o g i v e a c e n t r a l f i v e - m e m b e r e d S3N2 r i n g . T h i s compound c a n b e f o r m a l l y d e r i v e d f r o m t h e s i x - m e m b e r e d s p i r o c y c l e b y i n s e r t i o n o f a n NS u n i t i n t o e a c h o f the six-membered r i n g s . Thus, each eight-membered r i n g would b e f o r m a l l y a s s o c i a t e d w i t h 9 ττ-electrons ( i . e . π-electron r i c h ) . The f o r m a t i o n o f t h e i n t e r - r i n g S-S b o n d p r o b a b l y has t h e e f f e c t o f c o n v e r t i n g two w e a k l y a n t i - b o n d i n g (IT*) e l e c t r o n s t o a n S-S σ - b o n d i n g e l e c t r o n p a i r ( c f . f o r m a t i o n o f t r a n s a n n u l a r S-S b o n d s in 3). I n t h e a t t e m p t e d c o u p l i n g o f t w o s i x - m e m b e r e d P2SN3 r i n g s t h r o u g h a n S-S b o n d b y t r e a t m e n t o f ( P h 2 P N ) N S C l w i t h P h S b a n 2
3
2
2
3
3
2
a
Cowley; Rings, Clusters, and Polymers of the Main Group Elements ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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B U R F O R D ET A L .
Cyclophosphathiazenes
Figure 6. Conversion of Ph PS N to the bicyclic molecule Ph PS N the reagents PhICl and Me SiNSNSiMe . 2
2
3
2
2
Figure 7. ORTEP
3
3
5
by using
3
drawing of (Ph PN) NSCl showing bond lengths (λ) and an gles (deg). 2
2
(Reproduced with permission from J. Chem. Soc, Chem. Commun. 1982, 982.)
Cowley; Rings, Clusters, and Polymers of the Main Group Elements ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
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RINGS, C L U S T E R S , A N D P O L Y M E R S
Figure 9. ORTEP
drawing of tricyclic compound obtained from and Me SiNSNSiMe (16). 3
(Ph PN) NSCl 2
3
Cowley; Rings, Clusters, and Polymers of the Main Group Elements ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
2
5.
BURFORD ET A L .
Cyclophosphathiazenes
91
i s o m e r o f t h e e x p e c t e d p r o d u c t was o b t a i n e d ( F i g u r e 1 0 ) . T h i s compound i s a twelve-membered r i n g w i t h a t r a n s a n n u l a r S-S b o n d o f 2.39& c f . d ( S - S ) = 2 . 5 3 8 i n 3 . I t c a n b e v i e w e d a s r e s u l t i n g f r o m t h e i n s e r t i o n o f a n a d d i t i o n a l Ph2PN u n i t i n t o e a c h h a l f o f 3. T h i s r i n g expansion causes t h e molecule t o t w i s t about t h e S-S b o n d . However, t h e mean S-N b o n d l e n g t h o f 1.598(2)8 i s s i m i l a r t o t h a t f o u n d f o r 3 ( 1 . 5 9 0 ( 3 ) 8 ) a n d t h e mean P-N b o n d l e n g t h s o f t h e NPNPN u n i t [ l . 5 8 2 ( 3 ) ( i n t e r n a l ) a n d 1.619(3)8 ( t e r m i n a l ) ] are i n d i s t i n g u i s h a b l e from those found f o r 2 [ l . 5 0 7 ( 3 ) and 1 . 6 l 3 (3)8, r e s p e c t i v e l y ] . Since a planar, monocyclic P i ^ S e r i n g w o u l d have Ik π-electrons ( c f . S N s , 2 3 ) , i t i s t e m p t i n g t o s u g g e s t t h a t t h e f o r m a t i o n o f a t r a n s a n n u l a r S-S b o n d p r o v i d e s a l a r g e r s t a b i l i z a t i o n t h a n t h e g r e a t e r π-delocalisation e n e r g y o f t h e p l a n a r twelve-membered r i n g ( c f . 3 ) . I t seems l i k e l y , how ever t h a t other f a c t o r s a l s o c o n t r i b u t e t o t h e observed geometry. F i n a l l y , i t s h o u l d b e p o i n t e d o u t t h a t t h i s twelve-membered r i n g b e l o n g s t o t h e homologous s e r i e s ( R 2 P N ) ( S N ) 2 (n=U) a n d t h u s t h e p r e d i c t i o n t h a t l a r g e r r i n g s i z e s may b e a n t i c i p a t e d i n t h i s s e r i e s has been v i n d i c a t e d . +
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5
n
Summary a n d C o n c l u s i o n s The f i r s t members o f a p o t e n t i a l l y e x t e n s i v e homologous s e r i e s o f c y c l o p h o s p h a t h i a z e n e s c o n t a i n i n g two c o o r d i n a t e sul f u r , (Ph2PN) (SN)2 (n=l,2,i|) have been p r e p a r e d and s t r u c t u r a l l y characterized. These h e t e r o c y c l e s a r e π-electron r i c h , i . e . t h e n
Figure 10. ORTEP
drawing of 12-membered ring obtained from and Ph Sb.
(Ph PN) NSCl 2
3
Cowley; Rings, Clusters, and Polymers of the Main Group Elements ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
2
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RINGS, C L U S T E R S , A N D P O L Y M E R S
number o f π-electrons e x c e e d s t h e number o f a t o m i c c e n t e r s i n t h e r i n g s y s t e m , a n d t h e e x c e s s e l e c t r o n s may b e accommodated e i t h e r by p a r t i a l o c c u p a t i o n o f TT*-levels o r , i n f a v o u r a b l e c a s e s , b y t h e f o r m a t i o n o f t r a n s a n n u l a r S-S b o n d s . Cyclophosphathiazenes containing three coordinate s u l f u r , w h i c h a r e h y b r i d s o f (Ph2PN)3 a n d ( N S C l ) , h a v e a l s o b e e n p r e pared. The i n o r g a n i c h e t e r o c y c l e ( P h 2 P N ) 2 N S C l r e a d i l y u n d e r g o e s r i n g o p e n i n g t o g i v e t h e π-electron p r e c i s e s p i r o c y c l e (Ph2PN)itS^2 or b i c y c l i c and t r i c y c l i c molecules i n which i n t e r - o r i n t r a - r i n g S-S σ-bonds a r e a d o m i n a n t s t r u c t u r a l f e a t u r e . 3
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Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
Roesky, H.W. Adv. Inorg. Chem. Radiochem. 1979, 22, 239. Gleiter, R. Angew. Chem., Int. Ed. Engl. 1981, 20, 444. Chivers, T.; Oakley, R.T. Top. Curr. Chem. 1982, 102, 117. Krishnamurthy, S.S.; Sau, A.C.; Woods, M. Adv. Inorg. Chem. Radiochem. 1978, 21, 41. Appel, R.; Halstenberg, M. Angew. Chem., Int. Ed. Engl. 1976, 15, 696. Weiss, J. Acta Crystallogr., Sect. Β 1977, B33, 2272. Burford, N; Chivers, T.; Oakley, R.T.; Cordes, A.W.; Swepston, P.N. J. Chem. Soc., Chem. Commun. 1980, 1204. Burford, Ν.; Chivers, T.; Cordes, A.W.; Laidlaw, W.G.; Noble, M.C.; Oakley, R.T.; Swepston, P.M. J. Am. Chem. Soc. 1982, 104, 1282. Burford, Ν.; Chivers, T.; Richardson, J.F. Inorg. Chem. 1983, 22, in press. Ahmed, F.R.; Singh, P.; Barnes, W.H. Acta Crystallogr., Sect. Β 1969, B25, 316. Bojes, J.; Chivers, T.; Laidlaw, W.G.; Trsic, M. J. Am. Chem. Soc. 1979, 101, 4517. Burford, N.; Chivers, T.; Codding, P.W.; Oakley, R.T. Inorg. Chem. 1982, 21, 982. Ernest, I,; Holick, W.; Rihs, G.; Schomburg, G.; Shokam, G.; Wenkert, D.; Woodward, R.B. J. Am. Chem. Soc. 1981, 103, 1540. Gleiter, R. J. Chem. Soc. A 1970, 3174. Pohl, S.; Peterson, O.; Roesky, H.W. Chem. Ber. 1979, 112, 1545. Chivers, T.; Rao, M.N.S.; Richardson, J.F. J. Chem. Soc., Chem. Commun. 1982, 982. Oakley, R.T. personal communication. Appel, R.; Ruppert, I.; Milker, R.; Bastian, V. Chem. Ber. 1974, 107, 380. Weiss, J.; Ruppert, I.; Appel, R. Z. Anorg. Allg. Chem. 1974, 406, 329.
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20. Wiegers, G.A.; Vos, A. Acta Crystallogr., Sect. B 1966, B20, 192. 21. Van de Grampel, J.C. Rev. Inorg. Chem. 1981, 3, 1. 22. Chivers, T.; Rao, M.N.S.; Richardson, J.F. umpublished re sults. 23. Bartetzko, R.; Gleiter, R. Inorg. Chem. 1978, 17, 995. April 15, 1983
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RECEIVED
Cowley; Rings, Clusters, and Polymers of the Main Group Elements ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
