or Three-Coordinate Sulfur - American Chemical Society

5 Cyclophosphathiazenes Containing TwoThree-Coordinate Sulfur

or

N. BURFORD, T. CHIVERS, M. N. S. RAO, and J. F. RICHARDSON

Downloaded by FUDAN UNIV on February 22, 2017 | http://pubs.acs.org Publication Date: September 30, 1983 | doi: 10.1021/bk-1983-0232.ch005

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

n

2

2

4

2

2

x

y

4

2

2

2

2

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

2

2

+

2

2

2

X

2

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.

82

RINGS, C L U S T E R S , A N D P O L Y M E R S

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


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

2

Coordinate

Sulfur

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

f

t

3

2

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2

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

3

3

3

2

2


Cyclophosphathiazenes


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

2

2

3


84

RINGS, C L U S T E R S , A N D

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).


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

3

+

+


85



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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86

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

2

2

5

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+

2

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5

+

2

2

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3

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


5.

BURFORD ET A L .

87


ο-

6b,— .3α

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2

4α

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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.)


88


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 ) .


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



B U R F O R D ET A L .


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.)


90



Figure 9. ORTEP

drawing of tricyclic compound obtained from and Me SiNSNSiMe (16). 3

(Ph PN) NSCl 2

3


2

5.

BURFORD ET A L .


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 . +


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


2

92


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


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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