Stereochemistry of Optically Active Transition Metal Compounds

1

Research i n the Stereochemistry of Cobalt Complexes

Downloaded by UNIV OF CALIFORNIA SAN FRANCISCO on February 12, 2015 | http://pubs.acs.org Publication Date: May 27, 1980 | doi: 10.1021/bk-1980-0119.ch001

JOHN C. BAILAR, JR. School of Chemical Sciences, University of Illinois, Urbana, IL 61801

Stereochemistry, long the backbone of coordination chemistry, is s t i l l a major area for investigation and discovery. The methods of studying it have changed, and perhaps because of that, the emphasis on the topics under investigation has changed. Syn thetic chemistry has been displaced by, or better, augmented by, physical methods. Both approaches are important and both contri bute to the growth of our knowledge. It is most appropriate that we should hold a symposium on the stereochemistry of complexes and compare notes on what is being done in the countries which are represented at this meeting. In introducing the symposium, I should like to recount some developments of the nearly fifty years that I have been involved in this field. Most of the work which I shall describe was done by my students -- not that I think that their work is better than that of others, but because I know it better, and it serves to illustrate some interesting aspects of what I think of as the synthetic approach. Space alone would preclude discussing any more. My entrance into the field of inorganic stereochemistry was brought about in an unusual way. As an organic chemist, my in terest lay chiefly in isomerism and isomeric rearrangements. One day in a class in general chemistry which I was teaching, there was a discussion of the hydrolysis of antimony trichloride, which leads to the precipitation of the oxychloride, SbOCl. One of the students referred to this as "antimony hypochlorite". While I was correcting his impression that "0C1" always represents a hypochlorite, it occurred to me that the hypochlorite of a metal in the +1 oxidation state would be isomeric with the oxychloride of that metal in the +3 state. This was the first time I had ever imagined that inorganic compounds could exist in isomeric forms, and it was an exciting idea. That very day, I began efforts to prepare the two isomers of T10C1, only to discover that thallous hypochlorite cannot exist, for the cation is easily oxidized and the anion is a strong oxidizing agent. However, the idea of inorganic isomers persisted and my thinking and reading soon led to the postulation of many other cases; for example, 0-8412-0538-8/80/47-119-001$05.00/0 © 1980 American Chemical Society In Stereochemistry of Optically Active Transition Metal Compounds; Douglas, B., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.


2

STEREOCHEMISTRY OF

TRANSITION

METALS

s e l o n o s u l f a t e and t h i o s e l e n a t e , p h o s p h o n i u m n i t r a t e and ammonium m e t a p h o s p h a t e and h y d r o x y l a m i n e n i t r i t e and ammonium n i t r a t e . Of c o u r s e , one c a n n o t go v e r y f a r i n l o o k i n g f o r i s o m e r s i n i n organic chemistry without d i s c o v e r i n g the whole, r i c h f i e l d of c o o r d i n a t i o n compounds. And i f one c a n have i s o m e r i c r e a r r a n g e ments i n o r g a n i c m o l e c u l e s , why n o t i n t h e c o m p l e x e s o f c o b a l t , too? I t was t h u s t h a t I became an i n o r g a n i c c h e m i s t . The s t e r e o c h e m i s t r y o f c o o r d i n a t i o n compounds was a p a r t o f c h e m i c a l t h i n k i n g much e a r l i e r t h a n i s g e n e r a l l y assumed. For e x a m p l e , as e a r l y as 1875, v a n H o f f s u g g e s t e d t h a t compounds c o n t a i n i n g s i x g r o u p s a t t a c h e d t o a c e n t r a l m e t a l atom a r e a t t h e c o r n e r s o f an o c t a h e d r o n and t h a t g e o m e t r i c i s o m e r s s h o u l d e x i s t f o r s u i t a b l y s u b s t i t u t e d c a s e s (1). However, i t was A l f r e d W e r n e r who d e m o n s t r a t e d t h a t t h i s i s i n d e e d t h e c a s e , and a l s o t h a t t h e f o u r c o v a l e n t p l a t i n u m ( I I ) compounds a r e c o p l a n a r . In those e a r l y days, the m u l t i t u d e of s o p h i s t i c a t e d techniques which we now e n j o y was n o t known, and d e d u c t i o n s as t o s t r u c t u r e had t o be made m o s t l y on t h e b a s i s o f s y n t h e s i s and o t h e r c h e m i c a l e v i d e n c e . P r o g r e s s was s l o w , f o r t h i s k i n d o f s t r u c t u r e d e t e r m i n a t i o n r e q u i r e s a g r e a t d e a l o f i m a g i n a t i o n and more e x p e r i m e n t a l w o r k t h a n d e t e r m i n a t i o n o f s t r u c t u r e by modern m e t h o d s . C o n s i d e r , f o r example, Werner's i n g e n i o u s d e t e r m i n a t i o n o f t h e s t r u c t u r e s o f c i s - and t r a n s - [ P t ( N H ) 2 CI 2] ( 2 ) , and h i s d e m o n s t r a t i o n o f t h e o c t a h e d r a l s t r u c t u r e o f s i x - c o o r d i n a t e complexes through the o p t i c a l r e s o l u t i o n of [ C o ( e n ) 2 ( N H 3 ) X ] (X = C l , B r ) Ç3). We a r e now a b l e , by modern t e c h n i q u e s , n o t o n l y t o perform these demonstrations q u i c k l y , b u t , i n the case of c h i r a l c o m p l e x e s , t o show t h e a c t u a l c o n f i g u r a t i o n s o f t h e i s o m e r s (4,5) . A f t e r W e r n e r ' s d e a t h i n 1919, t h e r e was l i t t l e a c t i v i t y i n t h e f i e l d o f s t e r e o c h e m i s t r y o f c o o r d i n a t i o n compounds. An e x c e p t i o n i s f o u n d i n t h e w o r k o f Y u j i S h i b a t a , who had b e e n one o f W e r n e r ' s s t u d e n t s , and who c o n t i n u e d w i t h e x c e l l e n t s t e r e o c h e m i c a l w o r k when he r e t u r n e d t o J a p a n . H i s w o r k on t h e enzyme-like a c t i v i t y o f c o b a l t complexes f u r n i s h e s e s p e c i a l l y i n t e r e s t i n g e x a m p l e s o f s t e r e o s e l e c t i v i t y and o f t h e c a t a l y t i c a c t i o n o f s u c h compounds ( 6 ) . T. P. M c C u t c h e o n and V. L. K i n g , A m e r i c a n s who had done t h e i r t h e s e s on s t e r e o c h e m i c a l t o p i c s under Werner's g u i d a n c e , d i d not c o n t i n u e i n t h a t f i e l d . King, who a c t u a l l y p e r f o r m e d t h e f i r s t r e s o l u t i o n o f an a s y m m e t r i c c o m p l e x ( 7 ) , went i n t o i n d u s t r i a l w o r k . M c C u t c h e o n became a member o f t h e f a c u l t y a t t h e U n i v e r s i t y o f P e n n s y l v a n i a and d i d r e s e a r c h on c o m p l e x compounds, b u t n o t on t h e i r s t e r e o c h e m i s t r y . I n a l o n g p a p e r w h i c h he p u b l i s h e d i n 1912 (_8), Werner d e s c r i b e d many c i s - t r a n s r e a r r a n g e m e n t s w h i c h c o b a l t ( I I I ) compounds u n d e r g o d u r i n g r e p l a c e m e n t r e a c t i o n s . He a l s o d e s c r i b e d some r e a c t i o n s o f o p t i c a l l y a c t i v e c o m p l e x e s , w h i c h g i v e opt i c a l l y a c t i v e p r o d u c t s , s u c h as t h e one shown by t h e e q u a t i o n 3

2 +

levo-cis-[Co(en)2CI2]CI + K C0 2

3

-> d e x t r o - [ C o ( e n ) C 0 ] C l 2

3

+

2KC1.

In Stereochemistry of Optically Active Transition Metal Compounds; Douglas, B., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.


1.

BAiLAR

Stereochemistry

of Cobalt

Complexes

3

He had no way o f k n o w i n g w h e t h e r t h i s r e a c t i o n i n v o l v e d a n i n v e r s i o n o f c o n f i g u r a t i o n , but on the b a s i s o f such s t u d i e s , he s u g g e s t e d a mechanism f o r t h e famous W a l d e n i n v e r s i o n o f o r g a n i c c h e m i s t r y , p o s t u l a t i n g t h a t t h e c e n t r a l atom o f a c h i r a l m o l e c u l e exerts a d i r e c t i v e influence. Some y e a r s l a t e r , R o b e r t A u t e n , a n u n d e r g r a d u a t e s t u d e n t a t the U n i v e r s i t y o f I l l i n o i s , a c h i e v e d an o p t i c a l i n v e r s i o n i n the r e a c t i o n j u s t mentioned ( 9 ) . P a t t e r n i n g h i s work on t h a t o f Walden, Auten used s i l v e r carbonate i n s t e a d o f potassium c a r b o n a t e and o b t a i n e d a l e v o - r o t a t o r y c a r b o n a t o complex. I t was soon found t h a t the c h o i c e o f carbonate i s not the i m p o r t a n t f a c t o r , a n d Dwyer, S a r g e s o n a n d R e i d , i n A u s t r a l i a , showed t h a t t h e pH o f t h e s o l u t i o n i s t h e d e c i d i n g f a c t o r ( 1 0 ) . After his i n i t i a l success, Auten looked f o r i n v e r s i o n s i n the r e a c t i o n s o f t h e d i c h l o r o c o m p l e x w i t h o x a l a t e and n i t r i t e , b u t d i d n o t f i n d them. I t i s most f o r t u n a t e t h a t he t r i e d t h e c a r b o n a t e r e a c t i o n f i r s t , f o r o t h e r w i s e , we w o u l d h a v e c o n c l u d e d t h a t o p t i c a l i n v e r s i o n s do n o t t a k e p l a c e i n t h e r e a c t i o n s o f c o b a l t c o m p l e x e s , and p r o b a b l y w o u l d n o t h a v e t r i e d c a r b o n a t e . W e r n e r ' s d i r e c t i o n s f o r t h e r e s o l u t i o n o f t h e d i c h l o r o comp l e x a r e v e r y s i m p l e a n d q u i t e s p e c i f i c , b u t when A u t e n r e p e a t e d them, he o b t a i n e d no c r y s t a l s o f t h e d i a s t e r e o i s o m e r a t a l l . S e v e r a l t r i a l s a l l gave n e g a t i v e r e s u l t s . Upon r e f l e c t i o n , A u t e n r e a l i z e d t h a t l a b o r a t o r i e s i n E u r o p e a r e n o t h e a t e d as much a s o u r s i n A m e r i c a , s o he r e p e a t e d W e r n e r ' s d i r e c t i o n s w i t h t h e s o l u t i o n c o o l e d t o 16°. T h i s gave a n e x c e l l e n t y i e l d o f p u r e product. E v e r y c h e m i s t knows t h a t sometimes r e p e t i t i o n o f a n o t h e r ' s w o r k does n o t g i v e good r e s u l t s ; many do n o t u n d e r s t a n d , h o w e v e r , t h a t t h e d i f f i c u l t y may l i e i n a m i n o r change i n c o n ditions . I t was s o o n f o u n d t h a t an i n v e r s i o n t a k e s p l a c e a l s o i n t h e reaction [Co(en) Cl ]Cl 2

2

+ NH

3

+ [Co(en) (NH )C1]C1 2

3

2

+

[Co(en) (NH ) ]Cl 2

3

2

3

t h e c o n f i g u r a t i o n o f t h e f i n a l p r o d u c t d e p e n d i n g upon t h e t e m p e r a t u r e at which the r e a c t i o n takes p l a c e (11). T h i s seems t o b e a somewhat more c o m p l i c a t e d r e a c t i o n t h a n t h e o n e w i t h c a r b o n a t e , f o r i t p r o c e e d s i n two d i s t i n c t l y v i s i b l e s t e p s w i t h s h a r p changes i n c o l o r , a n d i n e a c h s t e p t h e p r o d u c t may h a v e t h e o r i g i n a l c o n f i g u r a t i o n , t h e m i r r o r image one, o r t h e t r a n s c o n f i g u r a t i o n . The r o t a t i o n s o b s e r v e d f o r t h e diammine w e r e v e r y s m a l l , b u t w e r e c o n f i r m e d b y o b s e r v a t i o n s made b y s e v e r a l d i f f e r e n t p e o p l e a n d e v e n by s e c r e t l y h a v i n g t h e o b s e r v e r s c h e c k t h e same s a m p l e r e p e a t e d l y . The r e s u l t s a r e shown i n T a b l e I .


STEREOCHEMISTRY O F TRANSITION

4

Table I . R e a c t i o n o f Ammonia w i t h l e v o - [ C o ( e n ) 2 C I 2 ] C I [Co(en) (NH )2]Cl3 2


Reagent

Ratio cis/trans in product

[o]

D

-32° -22° +18° +38°

2.5/1 2.85/1 3.7/1 00

-77° -38° +25° +80°

3

to yield

3

Temperature

L i q u i d NH3 ( s o l u t i o n ) L i q u i d NH3 ( s o l u t i o n ) L i q u i d NH (solution) Gaseous NH3

METALS

In t h e r e a c t i o n a t 80°, t h e c o m p l e x r e m a i n e d s o l i d t h r o u g h o u t the r e a c t i o n . E v i d e n t l y v e r y l i t t l e r e a r r a n g e m e n t o f any s o r t took p l a c e , f o r the value o f f o r an a u t h e n t i c sample o f dextro [Co(en) (NH ) ]C1 was +50°. The d i s c o v e r y o f i n v e r s i o n i n t h i s r e a c t i o n was somewhat s u r p r i s i n g , e v e n t o t h e i n v e s t i g a t o r s , f o r i t h a d b e e n assumed t h a t t h e two s t e p s w o u l d f o l l o w t h e same m e c h a n i s m , s o t h a t any i n v e r s i o n t h a t t o o k p l a c e i n t h e f i r s t s t e p would be c o u n t e r b a l a n c e d by an i n v e r s i o n i n t h e second. However, E a r l Greenwood was n o t a b l e t o g e t an i n v e r s i o n i n t h e r e a c t i o n (12) 2

3

2

3

[Co(en) (NH )Cl]Cl 2

3

2

+ NH

+

3

[Co(en) (NH ) ]Cl 2

3

2

3

so i t was assumed t h a t i n v e r s i o n takes place only i n the r e placement o f t h e f i r s t c h l o r o group. R o n a l d A r c h e r l a t e r showed t h a t t h i s i s , i n d e e d , the case ( 1 3 ) . C l o s e l y r e l a t e d t o t h i s i s t h e much l a t e r w o r k o f E i s h i n Kyuno a n d L a u r e n c e B o u c h e r (14) , who s t u d i e d t h e r e a c t i o n s o f t h e t r i e t h y l e n e t e t r a m i n e c o m p l e x , [ C o ( t r i e n ) C l 2 ] C 1 . The c o m p l e x c a t i o n o f t h i s s u b s t a n c e e x i s t s i n t h r e e s t e r e o i s o m e r i c forms

β

trans

b o t h t h e a and β f o r m s b e i n g a s y m m e t r i c a n d r e s o l v a b l e . Treat ment w i t h b a s e c o n v e r t s t h e d e x t r o - a - f o r m i n t o i t s l e v o - 3 - i s o m e r . We o n c e t h o u g h t t h a t a l l o f t h e s e r e a r r a n g e m e n t s result f r o m t h e a b s t r a c t i o n o f a p r o t o n f r o m a c o o r d i n a t e d amine a n d t h e m o t i o n o f t h e r e s u l t i n g n e g a t i v e l y c h a r g e d amine group f r o m


1.

BAiLAR

Stereochemistry

of Cobalt

5

Complexes

one c o r n e r o f t h e o c t a h e d r o n t o an a d j a c e n t one. T h i s may n o t b e the case, however, f o r A r c h e r and h i s s t u d e n t s a t t h e U n i v e r s i t y o f M a s s a c h u s e t t s h a v e o b s e r v e d a n i n v e r s i o n i n a r e a c t i o n o f an o c t a h e d r a l c o m p l e x i n w h i c h t h e r e a r e no a c i d i c p r o t o n s ( 1 5 ) . [Fe(o-phen) ]


3

3 +

+ 2CN~ + c i s - [ F e ( o - p h e n ) 2 ( C N ) 2 1

+

+ o-phen

Another s t e r e o c h e m i c a l problem concerns the p r e p a r a t i o n o f o c t a h e d r a l c o m p l e x e s o f known c o n f i g u r a t i o n . The R u s s i a n c h e m i s t s , who a r e m a s t e r s i n t h e m a n i p u l a t i o n o f p l a t i n u m c o m p l e x e s , h a v e done i n t e r e s t i n g w o r k i n t h i s a r e a . F o r e x a m p l e , C h e r n y a e v a n d K r a s o v s k a y a (16) p r e p a r e d a l l f i v e isomers o f [ P t ( N H ) C l B r ] : 3

2

2

2

II

III

D r . Anna Gel'man (now u s u a l l y t r a n s l i t e r a t e d a s Hel'man) a n d h e r c o l l e a g u e s h a v e a l s o done e l e g a n t w o r k o f t h i s t y p e a n d h a v e s u c c e e d e d i n m a k i n g t h e compound

I



6

STEREOCHEMISTRY OF

TRANSITION

METALS

i n w h i c h the p o s i t i o n o f each group i s f i r m l y e s t a b l i s h e d ( 1 7 ) . T h i s s u b s t a n c e i s c h i r a l , b u t e v i d e n t l y no a t t e m p t has b e e n made to r e s o l v e i t . P l a t i n u m l e n d s i t s e l f r e a d i l y t o these i n v o l v e d syntheses, f o r the t r a n s e f f e c t i n the r e a c t i o n s of p l a n a r p l a t i n u m ( I I ) complexes a l l o w s the p r e p a r a t i o n o f isomers w h i c h o f f e r good s t a r t i n g p l a c e s f o r t h e f o r m a t i o n o f t h e d e s i r e d o c t a h e d r a l p l a t i n u m ( I V ) compounds. I t i s u n f o r t u n a t e t h a t Dr. Hel'man has n o t c o n t i n u e d h e r v e r y i n t e r e s t i n g r e s e a r c h on t h e s y n t h e s i s o f compounds c o n t a i n i n g a m u l t i p l i c i t y o f u n i d e n t a t e g r o u p s , f o r i t i s e x c e l l e n t w o r k . F o r some y e a r s now she has been i n v o l v e d i n the c h e m i s t r y of a c t i n i d e elements. The p r e p a r a t i o n o f t h r e e i s o m e r s o f [ C o ( e n ) ( N H 3 ) 2 C I 2 ] C 1 by Peppard (18), I t h i n k , ranks i n importance w i t h those j u s t mentioned.

I n t h e s e s y n t h e s e s , P e p p a r d h a d t o r e l y on t h e v e r y weak t r a n s e f f e c t i n t h e c o b a l t c o m p l e x [Co (NH ) ( S 0 ) 2]"· The c i s dichloro-cis-diammineethylenediaminecobalt(III) i o n i s asymmetric, and P e p p a r d p a r t i a l l y r e s o l v e d i t i n t o i t s e n a n t i o m e r i c f o r m s by a d s o r p t i o n on q u a r t z g r o u n d t o 100 mesh. T h i s method o f r e s o l u t i o n i s f r e q u e n t l y , but not a l w a y s , e f f e c t i v e . B e f o r e i t can be f u l l y u t i l i z e d , we w i l l n e e d t o l e a r n a g r e a t d e a l more a b o u t the p r i n c i p l e s of a d s o r p t i o n . The p r e p a r a t i o n o f P e p p a r d ' s i s o m e r ' s i s p a r t i c u l a r l y i n t e r e s t i n g b e c a u s e c o b a l t ( I I I ) comp l e x e s r e a r r a n g e e a s i l y , w h e r e a s t h e p l a t i n u m compounds do n o t . A n o t h e r c a s e i n v o l v i n g c o b a l t c o m p l e x e s was s t u d i e d by Work (19) , who p r e p a r e d , among o t h e r s , a compound c o n t a i n i n g three d i f f e r e n t bidentate amines—ethylenediamine, trimethylened i a m i n e , and n e o p e n t a n e d i a m i n e , [ C o ( e n ) ( t n ) ( d a n ) ] C I 3 , by f o l l o w i n g and e x t e n d i n g a s y n t h e s i s f i r s t d e s c r i b e d by W e r n e r (20): 3

3

[Co(NH ) (N0 )3] -^>[Co(en)(NH )(N0 ) ]-^>[Co(en)(tn) (N0 ) ]N0 3

5£U

3

2

3

t r a n s - [Co (en) ( t n ) C l ] CI 2

2

3

2

2

2

[ Co (en) ( t n ) (dan) ] CI 3

The l a s t s t e p was a c c o m p l i s h e d t h r o u g h t h e c a t a l y t i c i n f l u e n c e o f d e c o l o r i z i n g c a r b o n , a method f i r s t u s e d by B j e r r u m (21) and d e v e l o p e d by Work ( 2 2 ) . D o u b t l e s s , t h i s s y n t h e s i s now c o u l d



1.

BAiLAR

Stereochemistry

of Cobalt

7

Complexes

be p e r f o r m e d more e a s i l y t h r o u g h t h e e l e g a n t t r i s - c a r b o n a t o method d e v e l o p e d b y M o r i and h i s c o l l e a g u e s ( 2 3 ) . A g r e a t d e a l c o u l d be l e a r n e d by f u r t h e r s y n t h e t i c s t u d i e s o f u n u s u a l c o m p l e x e s o f p l a t i n u m and c o b a l t , a s w e l l a s o t h e r m e t a l s , but the s y n t h e s e s a r e l o n g and m u l t i s t e p and few chemists h a v e t h e p a t i e n c e t o a t t e m p t them. Knowledge g a i n e d b y w o r k o n t h e c o m p l e x e s o f one m e t a l c a n b e u s e d o n l y i n d i r e c t l y i n s t u d i e s of a n o t h e r ; the c h e m i s t r i e s o f the complexes o f c o b a l t ( I I I ) and c h r o m i u m ( I I I ) , f o r example, a r e q u i t e d i f f e r e n t , a l t h o u g h these substances c l o s e l y resemble each o t h e r i n p h y s i c a l p r o p e r t i e s . Another t o p i c o f i n t e r e s t i n the s t e r e o c h e m i s t r y o f coor d i n a t i o n compounds i s t h a t o f s t e r e o s e l e c t i v e r e a c t i o n s . The f i r s t c a s e o f t h i s was d i s c o v e r e d b y T s c h u g a e f f (Chugaev) a n d S o k o l o f f i n 19 07 ( 2 4 ) . They p r e p a r e d t h e t r i s - 1 , 2 - p r o p a n e d i a m i n e c o b a l t ( I I I ) complex from racemic p r o p y l e n e d i a m i n e and found t h a t the ions obtained contained molecules o f only the l e v o - o r o n l y the d e x t r o - base, and t h a t the presence o f t h e s e i n the complex f o r c e d a n o v e r a l l asymmetry upon i t . Thus, they o b t a i n e d [ D i l l ] and [Lddd] c o m p l e x e s , w h e r e t h e c a p i t a l l e t t e r s r e p r e s e n t t h e r o t a t i o n o f t h e complexes, and the s m a l l l e t t e r s , the r o t a t i o n of the molecules o f c o o r d i n a t e d base. Many p e o p l e h a v e w o r k e d i n t h i s f i e l d s i n c e , a n d a good d e a l has b e e n l e a r n e d . Dwyer, S a r g e s o n , and members o f t h e i r g r o u p s h a v e b e e n p a r t i c u l a r l y productive i n this f i e l d . The s u b j e c t was d i s c u s s e d i n d e t a i l b y J a e g e r ( 2 5 ) , who p r e p a r e d t r i s - ( t r a n s - 1 , 2 - c y c l o p e n t a n e d i a m i n e ) r h o d i u m ( I I I ) and c o b a l t ( I I I ) i o n s , and found t h a t , u s i n g the r a c e m i c b a s e , o n l y two o f t h e p o s s i b l e i s o m e r s , ( D i l l a n d L d d d ) , were formed i n e a c h c a s e . Even i f o n l y one o r two m o l e c u l e s o f the o p t i c a l l y a c t i v e base were used a l o n g w i t h a s y m m e t r i c a l base, as i n [ C o ( e n ) ( c p t d i n ) ] and [ C o ( e n ) ( c p t d i n ) ] , a s t e r e o s e l e c t i v e e f f e c t was o b s e r v e d . L i k e w i s e , e f f o r t s t o prepare t r a n s - [ C o ( 1 - c p t d i n ) ( d - c p t d i n ) C l ] were w i t h o u t a v a i l . Jaeger was o f t h e o p i n i o n t h a t t h i s s t e r e o s p e c i f i c i t y was d e p e n d e n t upon t h e symmetry o f t h e c o m p l e x e s — t h e more s y m m e t r i c a l t h e m o l e c u l e , the g r e a t e r i t s s t a b i l i t y . I t i s now g e n e r a l l y a g r e e d , h o w e v e r , t h a t t h e f o r m a t i o n o f some i s o m e r s i n p r e f e r e n c e t o o t h e r s depends upon t h e c o n f o r m a t i o n s o f t h e c h e l a t e r i n g s . This concept i s l a r g e l y due t o P r o f e s s o r E. J . C o r e y ( 2 6 ) . 3 +

3 +

2

2

+

2

The c o m p l e x e s o f p r o p y l e n e d i a m i n e ( 1 , 2 - p r o p a n e d i a m i n e ) o f f e r a somewhat more c o m p l i c a t e d p i c t u r e t h a n t h o s e o f t r a n s - c y c l o ρentanediamine, f o r t h e p r o p y l e n e d i a m i n e m o l e c u l e n o t o n l y c o n t a i n s an asymmetric carbon atom, but i s a l s o u n s y m m e t r i c a l . Werner r e p o r t e d t h e i s o l a t i o n o f a l l e i g h t o f t h e p o s s i b l e i s o m e r s o f c i s - [ C o ( e n ) ( p n ) ( N 0 ) ] , a n d t h i s was s u p p o r t e d b y t h e w o r k o f C o o l e y a n d L i u ( 2 7 ) , who o b t a i n e d f o u r i s o m e r s o f c i s [ C o ( e n ) ( 2 , 3 - b n ) ( N 0 ) ] and f o u r c i s - [ C o ( e n ) ( i s o - b n ) ( N 0 ) ] . (2,3-bn = r a c e m i c N H C H ( C H ) C H ( C H ) N H ; i s o - b n = N H C ( C H ) C H N H ) . The i s o m e r s c o n t a i n i n g 2 , 3 - b u t y l e n e d i a m i n e p r o v e d t o b e o f u n equal s t a b i l i t y — i n f a c t , i n the e a r l y experiments, only three +

2

2

+

2

+

2

2

2

3

3

2

2

3

2

2


2

2

STEREOCHEMISTRY OF TRANSITION METALS

8

i s o m e r s were o b t a i n e d , a n d , t o i s o l a t e t h e f o u r t h , t h e e x p e r i m e n t had t o be r e p e a t e d , u s i n g m i l d e r c o n d i t i o n s . In t h e e a r l y b e l i e f t h a t t h e s e r e a c t i o n s were c o m p l e t e l y s t e r e o s p e c i f i c , we f e l t t h a t t h e r e a c t i o n o f [ C o ( 1 - p n ) 2 C I 2 ] w i t h c a r b o n a t e c o u l d n o t g i v e an o p t i c a l i n v e r s i o n u n d e r any e x p e r i mental c o n d i t i o n s . T h i s i s , o f c o u r s e , n o t t r u e , a s was s o o n shown by t h e w o r k o f M c R e y n o l d s (28) and S i s t e r Mary M a r t i n e t t e Hagan (29) . I n a c o b a l t c o m p l e x c o n t a i n i n g a s y m m e t r i c l i g a n d s , one f o r m i s p r e f e r r e d , b u t b o t h forms c a n and do e x i s t . In the same b e l i e f , we hoped t h a t s t e r e o s p e c i f i c e f f e c t s c o u l d be u s e d i n the r e s o l u t i o n of racemic p o t e n t i a l l i g a n d s . T h i s does g i v e p a r t i a l r e s o l u t i o n , as shown by t h e w o r k o f J o h n s o n ( 3 0 ) , J o n a s s e n and G o t t (31,32) and H a m i l t o n ( 3 3 ) . H a m i l t o n ' s r e s u l t s , shown i n T a b l e I I , i n d i c a t e t h i s c l e a r l y .


+

[Co a ~ p n )

Table I I . ( 1 - t a r t ) ] + + d - t a r t " -> [Co (1-pn) 2 ( d - t a r t ) ] Ba + t a r t " -> B a ( t a r t ) 2

2

2 +

+

1-tart

2

2

Time o f S t a n d i n g with B a (hours)

[α]ρ o f R e c o v e r e d Tartaric Acid

Y i e l d of Ba t a r t (g)

2 +

0 0.2 0.5 2 4 18 72

-6° 0° +7.5° +7.5° +7.5° +12° +10°

4.7 1.5 0.6 0.9 1.6 0.5 0.2 10.0 (theoretical)

He t r e a t e d [ C o ( 1 - p n ) 2 C O 3 ] C 1 w i t h a 100% e x c e s s o f r a c e m i c t a r t a r i c a c i d t o form the complex [ C o ( 1 - p n ) 2 t a r t ] . The a d d i t i o n o f an e x c e s s o f b a r i u m h y d r o x i d e t o t h e s o l u t i o n gave an i m m e d i a t e p r e c i p i t a t e o f b a r i u m t a r t r a t e w h i c h was removed f r o m t h e s o l u t i o n , and w h i c h was shown t o c o n t a i n an e x c e s s o f 1 - t a r t r a t e . The f i l t r a t e , upon s t a n d i n g , gave more p r e c i p i t a t e , w h i c h was removed a t i n t e r v a l s , and was f o u n d t o c o n t a i n t a r t r a t e o f v a r y i n g r o t a t o r y power, but always d e x t r o . Attempts t o improve the s t e r e o s e l e c t i v i t y by u s i n g v e r y b u l k y a s y m m e t r i c l i g a n d s , s u c h as p h e n y l e t h y l e n e d i a m i n e , h a v e n o t i m p r o v e d t h e s i t u a t i o n ( 3 4 ) . The f i r s t s t e r e o s e l e c t i v e s y n t h e s e s o f c o o r d i n a t i o n com pounds w e r e p e r f o r m e d by J o n a s s e n and Huffman (35) who t r e a t e d [Co(en)2C0 ] with d-tartaric acid. T h i s gave a m i x t u r e o f Dand L - [ C o ( e n ) 2 d - t a r t ] , w h i c h , upon t r e a t m e n t w i t h e t h y l e n e d i a m i n e a t 50°, gave a 70% y i e l d o f D - [ C o ( e n ) 3 ] . E i t h e r t h e two t a r t r a t o i s o m e r s w e r e f o r m e d i n u n e q u a l amounts, o r t h e l e s s +

3

+

3 +


1.

BAiLAR

Stereochemistry

of Cobalt

9

Complexes

s t a b l e o n e was c o n v e r t e d t o t h e more s t a b l e one d u r i n g t h e r e a c t i o n w i t h ethylenediamine. S i m i l a r l y , treatment o f the mixed t a r t r a t o complexes w i t h h y d r o c h l o r i c a c i d o r w i t h c a l c i u m n i t r i t e gave a p r e p o n d e r a n c e o f d e x t r o - r o t a t o r y - c i s - [ C o ( e n ) 2 C I 2 ] o r dextro-rotatory-cis-[Co(en) (N0 ) 2] , respectively. One o t h e r t o p i c s h o u l d b e m e n t i o n e d — t h e s y n t h e s i s o f com p l e x e s i n w h i c h a c h e l a t i n g l i g a n d s p a n s t r a n s p o s i t i o n s . Werner assumed t h a t a c h e l a t i n g l i g a n d must o c c u p y c i s - p o s i t i o n s i n a complex and f o r o r d i n a r y l i g a n d s t h i s i s c e r t a i n l y c o r r e c t . However, s e v e r a l i n v e s t i g a t o r s have p r e s e n t e d e v i d e n c e t h a t u n d e r some c o n d i t i o n s a s i n g l e c h e l a t i n g g r o u p c a n r e a c h a c r o s s t h e t r a n s - p o s i t i o n s o f a p l a n a r complex. S c h l e s i n g e r ( 3 6 ) , and I s s l i e b and H o h l f e l d (37) u s e d b i d e n t a t e l i g a n d s w h i c h were l o n g enough t o r e a c h a c r o s s t h e d i a g o n a l o f a s q u a r e p l a n a r c o m p l e x of Cu(II) o r N i ( I I ) . V e n a n z i a n d h i s s t u d e n t s (38,39) s y n t h e s i z e d a r i g i d l i g a n d which can e a s i l y adapt i t s e l f t o t h e d i a g o n a l o f a p l a t i n u m ( I I ) s q u a r e , but not t o the edge: +

+


2

2

M a t t e r n a n d M o c h i d a (40) u s e d q u i t e a d i f f e r e n t a p p r o a c h , a t t a c h i n g a t r i d e n t a t e amine t o p l a t i n u m ( I V ) a n d t h e n d e s t r o y i n g t h e b o n d b e t w e e n t h e m e t a l a n d t h e n i t r o g e n atom i n t h e c e n t e r o f the t r i d e n t a t e l i g a n d by r e d u c i n g the m e t a l t o p l a t i n u m ( I I ) , thus l o w e r i n g t h e c o o r d i n a t i o n number f r o m s i x t o f o u r .

A

Β

B e f o r e t h e e x p e r i m e n t was t r i e d , t h e r e was no a s s u r a n c e i n a n y one's m i n d t h a t t h e d e s i r e d bonds w o u l d b r e a k when t h e m e t a l was r e d u c e d , b u t i t was h o p e d t h a t t h e t r a n s e f f e c t o f t h e c h l o r i d e a n d t h e s e c o n d a r y n a t u r e o f t h e c e n t r a l amine n i t r o g e n


10



w o u l d l o o s e n t h o s e atoms f r o m t h e m e t a l . H a p p i l y , t h a t i s what occurred. On r e p e a t e d c r y s t a l l i z a t i o n f r o m w a t e r , t h e r e d u c e d p r o d u c t l o s t ammonia a n d c h l o r i d e , y i e l d i n g

Compound B, i n b o i l i n g h y p o c h l o r i c a c i d , was c o n v e r t e d t o t r a n s dichlorodiamine platinum(II). Efforts to place a trans-spanning c h e l a t e on e a c h s i d e o f t h e p l a t i n u m p l a n e h a v e n o t y e t s u c c e e d e d (41). T h e r e i s c e r t a i n l y no d e a r t h o f i n t e r e s t i n g a n d s i g n i f i c a n t s t e r e o c h e m i c a l problems a w a i t i n g s o l u t i o n . Many f u n d a m e n t a l q u e s t i o n s r e m a i n t o be a n s w e r e d . A l s o , t h e growth o f b i o i n o r g a n i c c h e m i s t r y , t h e u s e o f m e t a l c o m p l e x e s i n c a n c e r chemotherapy, and t h e w i d e s p r e a d c o n c e r n o v e r p o l l u t i o n have opened up a r e a s w h i c h w i l l k e e p a l l o f us b u s y f o r many y e a r s t o come.

Literature Cited 1.

van't Hoff, J . H. Maandblad voor Natuurwetenschappen, 1895, 6, 37. 2. Werner, A. Z. anorg. Chem., 1893, 3, 310. 3. Werner, A. Ber., 1911, 44, 1887. 4. Saito, Yoshihiko. Topics in Stereochemistry, Volume 10, pages 95-174, Ernest L. Eliel and Norman L. Allinger, Eds. John Wiley and Sons, New York (1978). 5. Igi, Kozo; Douglas, Bodie E. J. Coordination Chem., 1978, 7, 155-161 and many other earlier articles in the series by Douglas and his students. 6. Shibata, Y.; Yamasaki, Kazuo. J. Chem. Soc. Japan, 1933, 54, 1207, and several preceding articles. 7. King, V. L. J . Chem. Educ., 1942, 19, 345. 8. Werner, Alfred. Ann., 1912, 386, 1. 9. Bailar, John C., J r . ; Auten, Robert W. J. Am. Chem. Soc., 1934, 56, 774. 10. Dwyer, Francis P.; Sargeson, Alan M.; Reid, Ian K. J. Am. Chem. Soc., 1963, 85, 1215. 11. Bailar, John C., J r . ; Haslam, John H.; Jones, Eldon M. J. Am. Chem. Soc., 1936, 58, 2226. 12. Greenwood, Earl L . , B. S. Thesis, University of Illinois, 1936.


1.

BAILAR

Stereochemistry of Cobalt Complexes

13.


J.

11

Archer, Ronald D.; Bailar, John C., Jr. J . Am. Chem. Soc., 1961, 83, 812. 14. Kyuno, Eishin; Boucher, L. J.; Bailar, John C . , Jr. J . Am. Chem. Soc., 1965, 87, 4458. 15. Archer, Ronald D.; Suydam, L. Jill; Dollberg, Donald D. Am. Chem. Soc., 1971, 93, 6837. 16. Chernyaev, I. I.; Krasovskaya, Ν. N. Russian J . Inorg. Chem., 1959, 4, 455 (in English). 17. Gel'man, A. D.; Essen, L. N. Doklady Akad. Nauk. S.S.S.R., 1950, 75, 693; C. Α., 1951, 45, 3279h. 18. Bailar, John C., J r . ; Peppard, D. F. J. Am. Chem. Soc., 1940, 62, 105. 19. Bailar, John C., J r . ; Work, J . B. J . Am. Chem. Soc., 1946, 68, 232. 20. Werner, Alfred. Helv. Chim. Acta, 1918, 1, 10. 21. Bjerrum, J . "Metal Amine Formation in Aqueous Solutions. Theory of Reversible Step Reactions"; P. Hasse and Son: Copenhagen, Denmark, 1941. 22. Bailar, John C., J r . ; Work, J . B. J . Am. Chem. Soc., 1945, 67, 176. 23. Mori, M.; Shibata, M.; Kyuno, E . ; Adachi, T. Bull. Chem. Soc. Japan, 1956, 29, 883. See also a review by Shibata, Muraji Proc. Japan Acad., 1974, 50, 779 and the references therein; Bauer, H. F . ; Drinkard, W. C. J . Am. Chem. Soc., 1960, 82, 5031. 24. Tschugaeff, L . ; Sokoloff, W. Ber., 1907, 40, 177; 1909, 42, 55. 25. Jaeger, F. M. "Optical Activity and High Temperature Measurements"; McGraw-Hill: New York, 1930. This contains references to similar work by Lifschitz and by Smirnoff. 26. Corey, E. J.; Bailar, John C., Jr. J . Am. Chem. Soc., 1959, 81, 2620. 27. Cooley, William E . ; Liu, Chui-Fan; Bailar, John C., Jr. J. Am. Chem. Soc., 1959, 81, 4189. 28. Bailar, John C., J r . ; McReynolds, J. P. J. Am. Chem. Soc., 1939, 61, 3199. 29. Sister Mary Martinette, B.V.M.; Bailar, John C., Jr. J . Am. Chem, Soc., 1952, 74, 1054. 30. Johnson, Roy D., Thesis, University of Illinois, 1948. 31. Jonassen, Η. B.; Bailar, John C., J r . ; Gott, A. D. J . Am. Chem. Soc., 1952, 74, 3131. 32. Gott, A. D.; Bailar, John C., Jr. Ibid., 1952, 74, 4820. 33. Hamilton, Nathan, Thesis, University of Illinois, 1947. 34. Hryhorczuk, Lew, Thesis, University of Illinois, 1972. 35. Jonassen, Hans B.; Bailar, John C . , J r . ; Huffman, Ε. H. J. Am. Chem. Soc., 1948, 70, 756. 36. Schlessinger, N. Ber., 1925, 58, 1877. 37. Isslieb, K.; Hohlfeld, G. Z. anorg. allgem. Chem., 1961, 312, 169.



12

38. 39. 40.


41.

Stefano, N. J.; Johnson, D. Κ.; Lane, R. M.; Venanzi, L. M. Abst. American Chem. Soc. Meeting (Boston, Mass., April 9-14, 1972) INOR 150. Stefano, N. J.; Johnson, D. K.; Venanzi, L. M. Angew. Chem., Int. Ed. Eng., 1974, 13, 133. Mochida, Isao; Mattern, J . Arthur; Bailar, John C., Jr. J. Am. Chem. Soc., 1975, 97, 3021. Fry, Fred; Bailar, John C., J r . ; unpublished work.

RECEIVED September 11, 1979.


Stereochemistry of Optically Active Transition Metal Compounds

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