o r i e n t e d p r o p e r l y for the c y c l i z a t i o n s . Thus, c o m p l e x e s of the "sen" l i g a n d [18] c a n be cap p e d e i t h e r w i t h NH^ a n d C t ^ O to y i e l d [19] (methyl sep), or n i t r o m e t h a n e and C l ^ O to y i e l d the n i t r o m e t h y l cage [20] w i t h C a p i c e s (Scheme 4 ) . 2 *
Si m p l e o r g a n i c c h e m i s t r y c an be p e r f o r m e d at the C a p e x to vary the s u b s t i t u e n t s . R e d u c t i o n of the N O2 g r o u p w i t h Zn dust g ives the a m i n o m e t h y l sar. N i t r o s a t i o n in a q u e o u s s o l u t i o n gives b o t h the h y d r o x y and the c h loro ( c h l o r o m e t h y l s a r ) d e r i v a t i v e s in the p r e s e n c e of c h l o r i d e ion. The c h l o r o in t u r n can be s u b s t i t u t e d w i t h a p r o t o n by c a t a l y t i c h y d r o g e n a t i o n to g ive the pa r e n t (methy l s a r ) ion (Scheme 5). Similarly, r e d u c t i o n of the d i n i t r o - d e r i v a t i v e yie l d s the d i a m i n o a n a l o g u e w h i c h in turn can be c o n v e r t e d to the d i c h l o r o cage
1
a nd f i n a l l y the p arent cage [Co sar] . O t h e r s u b s t i t u e n t s in the a p i c a l p o s i t i o n w h i c h have b e e n r e p o r t e d i n c l u d e -NHOH, -NO, - N ( C H 3 )3+ , -Br, -I, -C00H, -C00R, - N H C 0 C H 3 , -CN, - C 0 N H 2 , - C H2O H. 2 2 ’ 2 3
In p r inciple, it s h o u l d be p o s s i b l e to e n l a r g e the size of the c a v i t y by c h a n g i n g the l i g a n d f r o m 1,2- d i a m i n o e t h a n e to 1 , 3 - d i a m i n o p r o p a n e . U n f o r t u n a t e l y , a t t e m p t s to cap the
O 1
[ C o ( I I I ) t r i s ( 1 , 3 - d i a m i n o p r o p a n e ) ] ion, [ C o ( t n ) 3 ] , (Scheme 6) have r\ /
not yet b e e n s u c c e s s f u l . The d i f f i c u l t y in a c h i e v i n g the d e s i r e d product, is b e l i e v e d to ar i s e f r o m the m o r e r a p i d l i g a n d loss of the
31
[ C o ( t n ) 3 ] i o n in the b asic a q u e o u s c o n d i t i o n s and less f a v o u r a b l e i m i n e o r i e n t a t i o n s for the i n t r a m o l e c u l a r c y c l i z a t i o n r e actions.
O 1
Some success has b e e n a c h i e v e d u s i n g [Rh(tn)^] as the p r e c u r s o r 2 S c o m p l e x w h e n the r e a c t i o n is c a r r i e d out in n o n - a q u e o u s media. Here the l arger Rh(III) ion o r i e n t s the c o m p o n e n t s for c y c l i z a t i o n e f f e c t i v e l y and loses l i gands less r e adily t han the Co(III) ion.
O t h e r p o l y a m i n e c o m p l e x e s of c o b a l t ( I I I ) s uch as [ C o ( 1 , 2 - d i a m i n o c y c l o h e x a n e ) 3 ] 3+ 26 an(j [ C o ( 1 , 2 - d i a m i n o p r o p a n e )3]3+ 27
C8