84 Reactions of 2,4,6-Tri(t-butyl)phenyllithium with Phosphorus Halides Downloaded via UNIV OF CALIFORNIA SANTA BARBARA on July 20, 2018 at 11:55:39 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
M A S A A K I Y O S H I F U J I , I C H I R O S H I M A , and N A O K I I N A M O T O Department of Chemistry, Faculty of Science, The University of Tokyo, Hongo, Tokyo 113, Japan
S t e r i c a l l y hindered compounds have been of interest i n view of their protecting nature of reactive sites or molecules (1, 2, 3 ) . During the course of our studies of phosphorus-containing reactive intermediates ( 4 - 8 ) we have found the following interesting reac tions of 2,4,6-tri-t-butylphenyllithium (I) with some phosphorus halides.
The reaction of I with P(0)C1 gave a very crowded molecule, bis(2,4,6-tri-t-butylpheny 1)phosphinic chloride ( I I , mp 210 - 210.5° C) i n 49 % yield, together with 2,4,6-tri-t-butylchlorobenzene ( I I I , 29 % yield) (9), while the reaction of I with P(S)C1 gave mainly I I I i n 59 % yield. Compound I I has two very bulky 2,4,6tri-t-butylphenyl groups attached geminally on one element. The chlorine atom of I I resists toward the further nucleophilic attack and I I is quite insensitive to moisture. The X-ray analysis of I I 3
3
(II)
( I I I )
indicated that the molecule suffers a large steric congestion by the four ortho t-butyl groups to force it to take boat-shaped ben zene rings (10). Such distortions have previously found only i n the case of bridged benzene rings (11). The ab initio calculation 0097-6156/81/0171-0409$05.00/0 © 1981 American Chemical Society
Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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of t h e b o a t - b e n z e n e s k e l e t o n s o f I I i n d i c a t e d t h a t t h e m o l e c u l e I I c o n t a i n s 61.4 k c a l / m o l h i g h e r e n e r g y t h a n t h a t w i t h f l a t b e n z e n e rings. More i n t e r e s t i n g l y t h e ab initio c a l c u l a t i o n of boat b e n z e n e s u g g e s t e d t h a t b o a t - s h a p e d b e n z e n e i s more s t a b l e t h a n e n v e l o p e o r c h a i r - f o r m e d b e n z e n e , p r o b a b l y due t o t h e o v e r l a p o f 1,4-electrons (12). The r e a c t i o n o f I w i t h P C I 3 gave 2 , 4 , 6 - t r i - t - b u t y l p h e n y l p h o s phonous d i c h l o r i d e ( I V ) i n h i g h y i e l d , w h e r e a s t h e F r i e d e l - C r a f t s t y p e o f r e a c t i o n o f 1 , 3 , 5 - t r i - t - b u t y l b e n z e n e and P C I 3 i n t h e p r e s ence o f aluminum c h l o r i d e f a i l e d t o g i v e I V , but t h e r e a c t i o n i n v o l v i n g t h e m i g r a t i o n o f one o f t h e t - b u t y l g r o u p s t o t h e p h o s p h o r u s atom a f f o r d e d t - b u t y l - 3 , 5 - d i - t - b u t y l p h e n y l p h o s p h i n i c c h l o r i d e (V, mp 132.5 - 133.5°C, 86 %) a f t e r h y d r o l y s i s ( 1 3 ) .
PCI.
(IV) Compound I V i n r e f l u x i n g t o l u e n e i n t h e p r e s e n c e o f p y r i d i n e or P ( S ) C 1 gave a c y c l i c p r o d u c t , 5 , 7 - d i - t - b u t y l - l - c h l o r o - 3 , 3 - d i m e t h y l - l - p h o s p h a i n d a n ( V I , 64 %) o r i t s 1 - s u l f i d e ( V I I , 68 %) r e spectively. 3
(VII)
(VI)
Compound I V i n THF was a l l o w e d t o r e a c t w i t h magnesium t o g i v e surprisingly bis(2,4,6-tri-t-butylphenyl)diphosphene ( V I I I , mp 175 - 176 °C (decompn.)) i n 54 % y i e l d a s s t a b l e o r a n g e - r e d c r y s t a l s , w h i c h m i g h t be a d i m e r i z a t i o n p r o d u c t o f 2 , 4 , 6 - t r i - t - b u t y l -
(VIII)
/ ζ
(IX)
Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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YOSHiFUJi E T A L .
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phenylphosphinidene (IX) as a r e a c t i v e i n t e r m e d i a t e . Compound V I I I i s t h e f i r s t i s o l a t e d m o l e c u l e w i t h a l o c a l i z e d P=P b o n d , i n w h i c h s t e r i c h i n d r a n c e makes an i m p o r t a n t c o n t r i b u t i o n t o t h e s t a b i l i z a t i o n (14). D i p h e n y l d i p h o s p h e n e o r p h o s p h o b e n z e n e was an e r r o n e o u s s t r u c t u r a l f o r m u l a r e p o r t e d i n 1877 (15) and a b o u t 70 y e a r s l a t e r i t turned out t o r e p r e s e n t c y c l o p o l y p h o s p h i n e s (PhP)n ( n = 4 , 5 , 6 ) by m o l e c u l a r w e i g h t d e t e r m i n a t i o n (16) and X - r a y a n a l y s i s (17, 18). S i n c e t h e n i t has b e e n t h o u g h t t h a t " p h o s p h o b e n zene" never e x i s t s as a s t a b l e m o l e c u l e ( 1 9 ) . However, Compound V I I I i s f a i r l y s t a b l e t o a i r and m o i s t u r e and c a n be c h a r a c t e r i z e d by *H, C , and P NMR, mass , UV, and IR s p e c t r a l a n a l y s i s and a l s o by m o l e c u l a r w e i g h t d e t e r m i n a t i o n . *H NMR ( C C I Ο δ 7.30 ( s , 4H, a r o m . ) , 1.45 ( s , 36H, o - t - B u ) , 1.35 ( s , 18H, p - t - B u ) ; P NMR ( C D ) 6 -59.0 ppm ( f r o m e x t e r n a l 85% H 3 P O O ; mass s p e c t r u m m/e c a l c d : 552.4012; f o u n d ; 552.4012; UV ( C H C 1 ) Amax (ε) 2 8 4 ( 1 5 6 6 0 ) , 340 ( 7 6 9 0 ) , 460 (1360) nm; m o l e c u l a r w e i g h t ( v a p o r p h a s e osmometr i c ) : 552.1 ( i n C H ) . A n a l . ( C 3 6 H 5 8 P 2 ) C, H. The X - r a y c r y s t a l l o g r a p h i c a n a l y s i s of V I I I i n d i c a t e d that the s t r u c t u r e i s s i m i l a r t o t h a t o f a n t i - a z o b e n z e n e and t h a t t h e bond d i s t a n c e b e t w e e n t h e two p h o s p h o r u s atoms i n V I I I ( 2 . 0 3 4 ( 2 ) A) i s s h o r t e r than the average v a l u e observed i n cyclopolyphosphines (14). 1 3
3 1
3 1
6
6
2
6
2
6
Compound V I I I g a v e 2 , 4 , 6 - t r i - t - b u t y l p h e n y l p h o s p h o n i c c h l o r i d e (X) by t h e r e a c t i o n w i t h c h l o r i n e i n c a r b o n t e t r a c h l o r i d e f o l l o w e d by h y d r o l y s i s i n a l m o s t q u a n t i t a t i v e y i e l d .
S u c h s t e r i c a l l y h i n d e r e d and u n u s u a l p h o s p h o r u s compounds d e s c r i b e d h e r e m i g h t s e r v e a s good m o d e l compounds f o r t h e t h e o r e t i c a l s t u d i e s as w e l l as s t u d i e s i n o r g a n i c o r i n o r g a n i c chemis try. Acknowledgment s T h i s w o r k was s u p p o r t e d i n p a r t by t h e S c i e n t i f i c R e s e a r c h G r a n t o f t h e M i n i s t r y o f E d u c a t i o n , S c i e n c e , and C u l t u r e o f J a p a n (Nos. 3 8 4 0 2 9 , 4 6 4 1 6 3 , and 5 4 3 0 0 8 ) . Literature Cited
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