Cyclophosphathiazenes Containing Two- or Three-Coordinate Sulfur

Sep 30, 1983 - In addition to substitution at sulfur, (Ph2PN)2NSCl readily undergoes ring opening reactions to give novel bicyclic, tricyclic, or spir...
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5 Cyclophosphathiazenes Containing TwoThree-Coordinate Sulfur

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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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POLYMERS

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

1,5-Me NC(NSN) CNMe2 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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S t r u c t u r e o f (Ph2PN)2NSCI. A n X - r a y s t r u c t u r a l determinat i o n o f ( P h 2 P N ) 2 N S C l shows i t t o c o n s i s t o f a s i x - m e m b e r e d r i n g i n w h i c h t h e f i v e atom NPNPN u n i t i s p l a n a r t o w i t h i n O.O5S w h i l e

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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.4b,

-6-

5b, -8-

4b,

3b,__ 2α

-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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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

92

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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5.

BURFORD ET A L .

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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.