Stereochemistry of Optically Active Transition Metal Compounds

13 Phenyl Substituent Contributions in Circular Dichroism Spectra of Cobalt(III) Complexes of Ethylenediamine -N,N'-diacetate I o n Downloaded by UNIV OF CALIFORNIA SAN FRANCISCO on December 16, 2014 | http://pubs.acs.org Publication Date: May 27, 1980 | doi: 10.1021/bk-1980-0119.ch013

1

2

GARY G. HAWN , CHRIS MARICONDI , and BODIE E. DOUGLAS Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260 Additivity of Circular Dichroism Contributions The major contribution to the rotational strength of optical ly active complexes of transition metals is usually the chiral arrangement of chelate rings. The additivity of the contribu tions to the rotational strength was demonstrated (1) for com plexes of the type [Co(en) (aa)] (aa = amino acid anion). The Δ- and Λ- isomers of [Co(en) (S-pala)] are diastereoisomers, not enantiomers. The CD curves (Figure 1) are not mirror images. The sum of the 2 CD curves is the same as the CD curve for the unresolved complex, an active racemate. The contributions for the Δ and Λ arrangements of the chelate rings should cancel for this "vicinal effect" curve, giving twice the contribution of the coordinated S-phenylalaninate ligand. Subtraction of one-half of this CD curve from the curve for either Δ- or Λ- [(Co(en) (S-pala)] gives a curve which agrees well with the CD curve of one of the isomers of [Co(en) (gly)] . Since the chelate rings of the amino acid ligands are nearly planar, the contribution of an optically active amino acid ligand is expected to be primarily that of the asymmetric center, with l i t t l e conformational contribution. Yasui, Hidaka, and Shimura (2) found that the CD curve in the T (O ) band region for a series of "typical" optically active amino acid complex ions of the type [Co(NH ) (aa)] are similar to the "vicinal effect" CD curves of optically active amino acids in complex ions of the type [Co(en) (aa)]. Earlier Shimura (3) had observed the Cotton effect caused by the optically active ligand in the complex ion [Co(ΝΗ ) (S-leucinato)] and referred to this as a "vicinal" effect. Pfeiffer (4) introduced the term "vicinal" effect for Cotton effects caused by optically active ligands. In the case of S-propylenediamine, the methyl substituent causes the conformation of coordinated S-pn (l-pn) to be fixed so that the chiral conformation would make a contribution to the rotational strength also. The CD curves for (+)-[Co(en)(l-pn) ] (5) has a single broad peak in the T (O ) region while that for 2+

2

2+

2

2

2+

2+

2

1

1g

h

2+

3

4

2+

2

2+

3

4

3+

2

1

1g

1

2

h

Current address: Alcolac Inc., 3440 Fairfield Rd., Baltimore, MD 21226 Current address: Pennsylvania State University, McKeesport, PA 15123 0-8412-0538-8/80/47-119-255$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.

STEREOCHEMISTRY OF TRANSITION METALS

Downloaded by UNIV OF CALIFORNIA SAN FRANCISCO on December 16, 2014 | http://pubs.acs.org Publication Date: May 27, 1980 | doi: 10.1021/bk-1980-0119.ch013

256

. 600

λ(ΓΤΊΛί) 400

500

300

350

A-(+) -[Co(en) S - p a l a ] l 546

2

2

0.5 Δ€

0

-0.5 -1.0 -1.5 -2.0 -2.5 16

\

Unresolved Complex

\ \

J A-(-)

\

_l

5 4 6

/ I

I

ι

L_

ι

I

I

I

I

I

I

1_

18 20 22 24 26 28 30 32 34 i7(cnrr χ ΙΟ" ) 1

3

Inorganic Chemistry Figure 1.

CD curves for the two isomers of [Co(en) S-pah] complex (I) 2

+

and the unresolved


13.

HAWN ET AL.

Phenyl

Substituent

Contributions

257

+

( - ) - [ C o ( e n ) ( £ - p n ) 2 P shows two d i s t i n c t components ( F i g u r e 2 ) . The c o n t r i b u t i o n f r o m £-pn, o b t a i n e d b y a d d i n g t h e s e c u r v e s , shows a s t r o n g e r c o n t r i b u t i o n t o t h e ^ 2 ^ 3 ) component t h a n t o t h e ^-Είϋβ) component. The ^-E component i s much more i n t e n s e t h a n t h e I-A2 component f o r [ C o ( e n ) 3 ] 3 + . S u b t r a c t i o n o f t h e c o n t r i b u t i o n f r o m £-pn g i v e s " c o n f i g u r a t i o n a l e f f e c t " c u r v e s f o r b o t h i s o m e r s o f [Co(en)(£-pn)2]^ ( F i g u r e 3) w h i c h a r e s i m i l a r t o t h e CD c u r v e s o f t h e c o r r e s p o n d i n g i s o m e r s o f [ C o ( e n ) 3 ] 3 + . The same c o n t r i b u t i o n p e r £_-pn can be u s e d f o r [Co (en)2 (£-pn) ] 3 a n d [Co(£-pn)3]3 t o show t h a t t h e e f f e c t s a r e a p p r o x i m a t e l y additive. One m i g h t e x p e c t t h e c o n t r i b u t i o n s f r o m £-pn t o d i f f e r somewhat d e p e n d i n g o n t h e number o f £-pn l i g a n d s p r e s e n t b e c a u s e of s t e r i c e f f e c t s . O g i n o , Murano, a n d F u j i t a (6) showed t h a t t h e c o n t r i b u t i o n o f _£-pn i n t h e t r i s ( p r o p y l e n e d i a m i n e ) c o m p l e x i s r e m a r k a b l y s i m i l a r t o t h e CD c u r v e o f [Co ( ^ 3 ) 4 Çfc-pn) ] 3+. A d d i t i v i t y o f t h e v a r i o u s c o n t r i b u t i o n s h a s b e e n demons t r a t e d f o r many c o m p l e x e s . The c o n t r i b u t i o n s a r e f r o m t h e c h i r a l configuration of chelate rings (configurational e f f e c t ) , the c h i r a l c h e l a t e conformation ( c o n f o r m a t i o n a l e f f e c t ) , and t h e presence o f asymmetric c e n t e r s i n the l i g a n d s . As expected, t h e c o n t r i b u t i o n s a r e c o n s i d e r a b l y g r e a t e r f o r a s y m m e t r i c atoms w h i c h a r e c o o r d i n a t e d t o t h e chromophore t h a n f o r o t h e r s (see below). The c o n t r i b u t i o n s f r o m c h i r a l r i n g c o n f o r m a t i o n s a n d from asymmetric c e n t e r s on the l i g a n d s o f t e n a r e i n s e p a r a b l e . Complexes o f 2 , 2 ' - d i a m i n o b i p h e n y l (dabp) o f t h e t y p e [Co(dabp)(en)2]^ have b e e n o f i n t e r e s t Ç7, 8) s i n c e t h e c o o r d i n a t e d n o n - p l a n a r dabp i s c h i r a l w i t h o u t a n a s y m m e t r i c center.


+

+

+

+

C i r c u l a r Dichroism

o f E t h y l e n e d i a m i n e d i a c e t i c A c i d Complexes

I n g e n e r a l t h e r o t a t i o n a l s t r e n g t h o f a m e t a l c o m p l e x depends on t h e number o f c h e l a t e r i n g s a s w e l l a s t h e s i z e a n d r i g i d i t y of the r i n g s . E t h y l e n e d i a m i n e d i a c e t a t e (edda) i s a q u a d r i d e n t a t e l i g a n d w h i c h can f o r m two i s o m e r s ( F i g u r e 4) w i t h t h e o t h e r two c o o r d i n a t i o n s i t e s c i s . The s y m - c i s i s o m e r i s t h e one e a s i l y obtained. I n the case o f the s y m - c i s - [ C o ( e d d a ) X 2 ] complexes t h e CD s p e c t r a a r e r e m a r k a b l y i n s e n s i t i v e t o t h e n a t u r e o f t h e two X g r o u p s ( 9 , 1£, 11). They can be u n i d e n t a t e (NH3), o r bidentate w i t h v a r y i n g r i n g s i z e (ethylenediamine o r trimethyl e n e d i a m i n e ) ( F i g u r e 5) ( 1 1 ) , o r even t h e b i d e n t a t e o x y g e n l i g a n d s C 0 2 - , C2O4 -, a n d 0 C C H C 0 2 " ( 1 0 ) , o r amino a c i d s ( 9 ) . The h i g h CD i n t e n s i t i e s f o r s y m - c i s - [ C o ( e d d a ) e n ] a n d r e l a t e d c o m p l e x e s m i g h t be a t t r i b u t e d t o t h e r i g i d edda b a c k b o n e , b u t a l s o t h e c o o r d i n a t e d Ν atoms a r e a s y m m e t r i c . I f one r e p l a c e s t h e H s u b s t i t u e n t s o n t h e . Ν atoms by m e t h y l g r o u p s , t h e i n t e n s i t y o f t h e m a j o r CD p e a k d e c r e a s e s b y more t h a n a f a c t o r o f two ( 1 2 ) ( F i g u r e 6 ) . Replacement o f the methyl groups by e t h y l groups causes a f u r t h e r s l i g h t decrease. I t appears t h a t there i s a l a r g e c o n t r i b u t i o n from the c o o r d i n a t e d asymmetric n i t r o g e n s i n n +

2

3

2

2

2

+




258

^(-)-[CoU-pn) en] Cl - 2H£> 2

19

20

21

22

Ficrâ'îxlO"

3

23

24

25

26

3

Inorganic Chemistry Figure 2.

CD curves for (+)- and (—)-[Co(\-pn) en] + and the sum of the two curves (5) 2

3


HAWN E T AL.

Phenyl

Substituent

Contributions

259


λ(π\μ)

550

500

450

1

1

—ι

400 Τ"

i7(cm:')xlO-

3

Inorganic Chemistry Figure 3. The configurational effect curves for (+)- and (—)-[Co(\-pn) en] obtained by subtracting the vincinal contribution of 2 l-pn. The CD curve for (+)-[Co(en) ] * is shown for comparison (5). 2

3

3


3+


260

Ό


V-l

Ο ΤΝ-Η

Π Ι ) . Figure 4. Structures of the s-cis and uns-cis isomers of [Co(edda)X ] 2

Δ-i-cis

x

r-l

TV

E D A-uns-cis


h


H AWN E TAL.

Phenyl

Substituent

Contributions

- 1

r i c m ) χ ICT 16

18

/

/

20

22

24

261

3

26

28

, — [Co (edda) en]N0 -H 0

\

3

2

γ

^ / - [ C o (dmedda) en]CI-3H o| 2

'y/--[Co

(deedda) en] I · HgO

Inorganic Chemistry Figure 6. Absorption and CD spectra of s - c i s - [ C o ( e d d a ) e n ] N Ο · H 0 and ine corresponding complexes of Ν,Ν'-dimethyl and Ν,Ν'-diethyl ethylenediamine-N, N'-diacetic acid (12) 2




262

t h e u n s u b s t i t u t e d edda c o m p l e x e s where one o f t h e s u b s t i t u e n t s (H) on Ν i s much d i f f e r e n t f r o m t h e o t h e r two f i r s t n e i g h b o r s u b s t i t u e n t atoms ( b o t h CH2 o r one CH2 and one CH3). In the case o f a l k y l s u b s t i t u t e d edda c o m p l e x e s ( F i g u r e 7 ) , t h e CD s p e c t r a show t h e u s u a l dependence on t h e n a t u r e o f t h e o t h e r l i g a n d ( s ) (11). M a r i c o n d i and M a r i c o n d i (13) showed t h a t b e n z y l s u b s t i t u e n t s on t h e Ν atoms o f edda c a u s e d a s i g n i f i c a n t change i n CD i n t e n s i t i e s i n c o m p a r i s o n t o m e t h y l s u b s t i t u e n t s ( F i g u r e 8) and t h e " v i c i n a l " c o n t r i b u t i o n s o f -CH2C5H5 and -H s u b s t i t u e n t s a r e o f r e v e r s e d s i g n s i n c o m p a r i s o n t o -CH3 s u b s t i t u e n t s ( F i g u r e 9 ) . The c o m p a r i s o n i s e v e n more s t r i k i n g i n t h e c a s e o f [ C o ( e d 3 a ) N 0 2 ] ~ (ed3a = N , N , N - e t h y l e n e d i a m i n e t r i a c e t a t e i o n ) and t h e m e t h y l and b e n z y l s u b s t i t u t e d ed3a c o m p l e x e s ( F i g u r e 1 0 ) . T

C o n t r i b u t i o n s of Stilbenediamine. The c o m p l e x [Co(edda)(£-stien)] (£-stien = ^ - s t i l b e n e d i a m i n e ) was p r e p a r e d (14) t o e s t i m a t e t h e c o n t r i b u t i o n f r o m t h e a s y m m e t r i c c a r b o n s o f stilbenediamine. T h e r e has been some c o n t r o v e r s y (15, 16, 17, 18) over the assignment of a b s o l u t e c o n f i g u r a t i o n f o r ^ - s t i e n , but a r e c e n t X - r a y d e t e r m i n a t i o n (19) e s t a b l i s h e d t h a t £-stien has t h e SS c o n f i g u r a t i o n and a d o p t s t h e 6 c o n f o r m a t i o n i n t h e t r i s c o m p l e x . The f o r m a t i o n o f [Co (edda) (£-stien)] was s t e r e o s e l e c t i v e , f a v o r i n g the f o r m a t i o n of the isomer (70% of p r o d u c t ) h a v i n g a d o m i n a n t n e g a t i v e CD peak ( F i g u r e 1 1 ) . This isomer i s a s s i g n e d t h e Δ-configuration b a s e d on t h e c l o s e s i m i l a r i t i e s t o t h e CD s p e c t r a o f o t h e r e d d a - d i a m i n e c o m p l e x e s ( 9 , 10, 11_, 12) . T h i s i s a l s o t h e i s o m e r w i t h more f a v o r a b l e s t e r i c i n t e r a c t i o n s as r e v e a l e d by e x a m i n a t i o n o f m o d e l s . The c o n t r i b u t i o n o f £-stien t o t h e CD c u r v e i s n e g a t i v e (14) t h r o u g h o u t t h e v i s i b l e r a n g e , w i t h a maximum c o n t r i b u t i o n o f a b o u t 0.6 (Δε). The edda l i g a n d s t i l l d o m i n a t e s t h e CD s p e c t r u m . The c o m p l e x [Co(£-sdda)en] (£-sdda = £-stilbenediaminedia c e t a t e i o n ) c o n t a i n s the ^ - s t i l b e n e d i a m i n e backbone, but each n i t r o g e n has as s u b s t i t u e n t s -CH2CO2, -H, and -CHC5H5). Only one i s o m e r o f [Co(£-sdda)en] was o b t a i n e d . Both [Co(edda)(_£-stien)] and [Co(£-sdda)en] w e r e shown (14) t o h a v e s - c i s g e o m e t r y f r o m t h e i r a b s o r p t i o n s p e c t r a and s i m p l e NMR spectra. I n e a c h c a s e t h e a b s o r p t i o n s p e c t r u m shows a s h o u l d e r i n t h e ^T^g(O^) band r e g i o n , i n d i c a t i n g two t e t r a g o n a l ( e f f e c t i v e 4 h ) components 0-E and I-A2). The s t e r e o s p e c i f i c i t y o f [Co 0 & - s d d a ) e n ] i s n o t s u r p r i s i n g s i n c e t h e p r e f e r r e d 6 - c o n f o r m a t i o n p e r m i t s t h e two l a r g e p h e n y l s u b s t i t u e n t s o f £-sdda t o occupy e q u a t o r i a l p o s i t i o n s . S i n c e t h e CD s p e c t r u m o f t h e one i s o m e r o f t h e [Co(£-sdda)en] ( F i g u r e 12) shows a p o s i t i v e dominant CD peak and an o v e r a l l CD c u r v e s i m i l a r t o t h a t o f (+)-s-cis-[Co(edda)(£s t i e n ) ] , i t m i g h t be e x p e c t e d t o have t h e A - c o n f i g u r a t i o n . However, t h e Λ-s-cis-configuration w o u l d r e q u i r e t h e ^ - s t i l b e n e d i a m i n e b a c k b o n e t o have t h e λ-conformation, f o r c i n g t h e l a r g e +

+

+

+

+

+

D

+

+

+



13.

HAWN E T AL.

Phenyl

Substituent

Contributions

263

λ (nm ) 600 550 500 450 —ι

J

1

I

I

16

18

1

I

I

20

1

I

I

I

22

400 1

—

I

I

24

I

I

26

I L

28

30

Ï7 ( k K ) Inorganic Chemistry Figure 7.

Absorption and CD spectra of s-cis-[Co(deedda)tn]NO , (deedda)en]N0. and s-cis-[Co(deedda)(N H ) ]N Ο (II) s

1}

3

2

s-cis-[Co-

3




264

600

500

λ (ηm) 450 400

350

/

Αφ-Ν

/

3

y

R

2

/ ' / /

—

ί \

I

R = Η

Λ

\ \ \ ^ \

Δ€

R = CH

\ \

— ·— R =

3

Cg He>

\

0 -I

-2

I 16

I 18

I 20

I 22

I 24

I 26

! 28

Î7(KK) Inorganic Chemistry Figure 8.

Absorption and CD spectra of [Co(dbedda)en] and CD spectra of [Co(edda)en] and [Co(dmedda)enJ (13) +

+

+


HAWN ET AL.

Phenyl

Substituent

Contributions

265


Δ(Δ€)

ν (kK) Inorganic Chemistry Figure 9.

Difference CD curves: and Ae[Co(dbedda)en]

Ae[Co(dmedda)en]* ( Ae[Co(edda)en] — Ae[Co(dmedda)en] ( ) (13) +

+

)

+

λ (nm) 600

16

18

500

450

20

22

400

24

26

ï7(kK) Inorganic Chemistry Figure 10.

Absorption and CD spectra for the (-)ske isomers of [Co(edSa)N0 ]- and [Co(med3a)N0 ]- (13) 2

2




266



HAWN ET AL.

Figure 12.

Phenyl

Substituent

Contributions

Absorption and CD spectra for the one isomer of s-cis-[Co(l-sdda)en] obtained (14) +


267


2 6 8

s u b s t i t u e n t s i n t o unfavorable a x i a l p o s i t i o n s . The favored 6-conformation i s expected, r e q u i r i n g that the isomer of [Co(_£-sdda)en] have the Δ - c o n f i g u r a t i o n . Previous s t u d i e s (10, 11) have shown that the unsubstituted c h i r a l r i n g p a t t e r n f o r Δ - [ C o ( e d d a ) e n ] c o n t r i b u t e s approximately -2.5 to the CD i n t e n s i t y of the dominant peak. Furthermore, i t was seen that the c o n t r i b u t i o n from &-stien i s small, but negative. The maximum CD values f o r Δ - [ C o ( £ - s d d a ) e n ] i s +3.22. The a d d i t i o n a l c o n t r i b u t i o n to the r o t a t i o n a l strength i n t h i s case must be from the asymmetric n i t r o g e n atoms. In [Co(£-sdda)en] the asymmetric nitrogens must make very l a r g e p o s i t i v e c o n t r i b u t i o n s to the r o t a t i o n a l strength f o r the Ε t r a n s i t i o n . +

+


+

+

C o n t r i b u t i o n s of Asymmetric Nitrogens. The homogeneity of the chemical environment of the asymmetric n i t r o g e n i s important i n determining the c o n t r i b u t i o n to the r o t a t i o n a l strength (12, 13). The s u b s t i t u e n t s on the asymmetric nitrogens of [Co Ç&-sdda)en] (methylene of the g l y c i n a t e r i n g , hydrogen, and benzyl) are more d i s s i m i l a r than i n the case of complexes of edda, dmedda, deedda, or dbedda and t h i s great d i s s i m i l a r i t y might cause the l a r g e c o n t r i b u t i o n . I t should be noted that the formal designations of absolute c o n f i g u r a t i o n s f o r nitrogens w i t h the same o v e r a l l arrangements of s u b s t i t u e n t s are (R,R) f o r the s - c i s isomers of Δ - [ C o ( e d d a ) e n ] and (S,S) f o r A-[Co(dbedda)en] and Δ-[Co(£-sdda)en]+. The d i f f e r e n c e s r e s u l t from changes i n p r i o r i t i e s of s u b s t i t u e n t s on N. The examination of a d d i t i v e c o n t r i b u t i o n s (_1, _3, .5, 6^ ) such as c o n f i g u r a t i o n a l , conformational, and v i c i n a l e f f e c t s of o p t i c a l l y a c t i v e l i g a n d s has been u s e f u l i n the c o r r e l a t i o n of stereochemical e f f e c t s and CD s p e c t r a . The l i g a n d - p o l a r i z a t i o n model (20, 21, 22, 24) of o p t i c a l a c t i v i t y depends upon the p o l a r i z a b i l i t y of the p e r t u r b i n g groups which c o n s t i t u t e the dissymmetric environment around the symmetric chromophore. Phenyl s u b s i t u t e n t s which have l a r g e a n i s o t r o p i c p o l a r i z a b i l i t y can make c o n t r i b u t i o n s with signs reversed from those expected (20). The o p t i c a l a c t i v i t y induced by s u b s t i t u e n t s on the l i g a n d can be s i g n i f i c a n t , and many e m p i r i c a l and t h e o r e t i c a l treatments have been developed which r e l a t e stereochemical c o n f i g u r a t i o n w i t h the signs and magnitude of CD curves. These are commonly r e f e r r e d to as r e g i o n a l or sector r u l e s (15, 24-29). The major d i f f i c u l t y with applying r e g i o n a l r u l e s r e s u l t s from assumptions which must be made about the e l e c t r o s t a t i c or p o l a r i z a b l e nature of the p e r t u r b i n g groups. Bosnien and Harrowfield (15) have pointed out the u n c e r t a i n t y concerning the s i g n of the p o t e n t i a l of hydrogen atoms which are bonded to donor n i t r o g e n s . Also, a n i s o t r o p i c p e r t u r b i n g groups, such as benzene r i n g s , can make c o n t r i b u t i o n s which are not r e a d i l y p r e d i c t a b l e (20). Maricondi and Maricondi (13) have shown that Mason's hexadecadal r e g i o n a l r u l e can be a p p l i e d to p r e d i c t the experimentally observed s i g n of the low energy CD t r a n s i t i o n f o r +

+

+


13.

HAWN ET AL.

Phenyl

Substituent

Contributions

269


+

s-cis-[Co(dbedda)en] where t h e n i t r o g e n s a r e s u b s t i t u t e d w i t h b e n z y l g r o u p s . Mason (29) assumed t h a t t h e e f f e c t o n t h e s i g n and m a g n i t u d e o f t h e r o t a t i o n a l s t r e n g t h p r o d u c e d b y Ns u b s t i t u t i o n i s l a r g e , w h i l e the e f f e c t from C - a l k y l s u b s t i t u t i o n i s s m a l l . The t h e o r e t i c a l t r e a t m e n t s o f S c h i p p e r ( 3 0 , 31) a n d R i c h a r d s o n (32) show p r o m i s e o f a d d i n g t o o u r u n d e r s t a n d i n g o f t h e c o r r e l a t i o n o f CD s p e c t r a a n d s t e r e o c h e m i s t r y a n d t h e additivity of chiral contributions. The s i g n s a n d m a g n i t u d e o f t h e CD c u r v e o f [ C o ( e d d a ) (£-stien)] a g r e e w i t h p r e v i o u s l y s t u d i e d C o ( I I I ) - e d d a c o m p l e x e s ( 1 1 , 1 2 , 1 3 ) , i n d i c a t i n g t h a t t h e edda p o r t i o n o f t h e c o m p l e x dominates and t h a t the benzene s u b s t i t u t i o n on the carbons has l i t t l e effect. However, f o r [Co(£-sdda)en] , t h e s i g n o f t h e l o w e n e r g y p e a k i n t h e CD s p e c t r u m i s o p p o s i t e t o what i s e x p e c t e d . E i t h e r t h e a s y m m e t r i c n i t r o g e n s make a l a r g e c o n t r i b u t i o n , o p p o s i t e t o t h a t from the c h i r a l arrangement o f c h e l a t e r i n g s to the r o t a t i o n a l s t r e n g t h , o r , c o n t r a r y t o the case f o r [Co(edda)(£-stien)] , t h e b e n z e n e s u b s t i t u e n t s o n t h e c a r b o n s are making a s i g n i f i c a n t c o n t r i b u t i o n t o the r o t a t i o n a l s t r e n g t h . The o t h e r p o s s i b i l i t y r e q u i r e s t h e o p p o s i t e (Λ) c o n f i g u r a t i o n w i t h the l a r g e p h e n y l s u b s t i t u e n t s i n unfavorable a x i a l p o s i t i o n s . +

+

+

S t e r e o s p e c i f i c i t y o f [Co(£-sdta)] . The c o m p l e x [Co(£-sdta)]" (_&-sdta = ^ - s t i l b e n e d i a m i n e t e t r a a c e t a t e i o n ) i s formed s t e r e o s p e c i f i c a l l y . The one i s o m e r o b t a i n e d (33) h a s a CD c u r v e o f t h e same f o r m a s t h o s e o f t h e ( - ) 5 4 6 - i s o m e r s o f [ C o ( e d t a ) ] " and [ C o ( 1 , 3 - p d t a ) ] " (1,3-pdta = 1,3-propaned i a m i n e t e t r a a c e t a t e i o n ) . The a b s o l u t e c o n f i g u r a t i o n s o f b o t h o f t h e s e c o m p l e x e s a r e known t o be (ΛΔΛ) (34, 3 5 ) . The ΛΔΛ i s o m e r o f [Co (£-sdta) ] " p e r m i t s t h e :S, S - s t i l b e n e d i a m i n e backbone r i n g t o adopt the s t a b l e δ c o n f o r m a t i o n w i t h b o t h p h e n y l g r o u p s e q u a t o r i a l . I f one removes t h e two " i n p l a n e " o r G a c e t a t e r i n g s t o g i v e a sym-sdda c o m p l e x , t h e a b s o l u t e c o n f i g u r a t i o n i s Δ (the r i n g s r e t a i n e d are those which g i v e the Δ c h i r a l p a i r f o r ΛΔΛ-[Co(£-sdta)]"). T h i s g i v e s s u p p o r t t o t h e Δ a b s o l u t e c o n f i g u r a t i o n a s s i g n e d above f o r [Co(£-sdda)en] , w h i c h was u n e x p e c t e d f r o m t h e CD c u r v e i n t h e l o w e n e r g y r e g i o n , a n d consequently i t supports the overwhelming c o n t r i b u t i o n from the c o o r d i n a t e d a s y m m e t r i c Ν atoms o f J l - s d d a . +

S u b s t i t u t e d d i b e n z y l e t h y l e n e d i a m i n e d i a c e t i c A c i d Complexes. A s e r i e s o f p a r a s u b s t i t u t e d dbedda a n a l o g s was p r e p a r e d t o study any p o s s i b l e e l e c t r o n i c e f f e c t s on asymmetric n i t r o g e n s w h i c h m i g h t be m a n i f e s t e d i n t h e CD s p e c t r a ( 1 4 ) . The s u b s t i t u t e d dbedda c o m p l e x e s w h i c h were p r e p a r e d w e r e t h e p a r a m e t h y l , c h l o r o a n d n i t r o d e r i v a t i v e s . These were compared t o t h e dbedda c o m p l e x (13) w h i c h c o n t a i n s a h y d r o g e n i n t h e p a r a position. A s s e e n f r o m t h e a b s o r p t i o n a n d CD d a t a shown i n F i g u r e 13, s u b s t i t u t i o n o f d i f f e r e n t g r o u p s i n t h e p a r a p o s i t i o n o f t h e b e n z e n e r i n g h a s no e f f e c t o n t h e p o s i t i o n o f t h e maxima




270

A(nm) 600

500 1

—ι

I

. 16

. 18

450

1

.

. 20

400

1

. 22

350 1—

1

. 24

• 26

I

28

v(kK) Inorganic Chemistry Figure 13. Absorption and CD spectra of s-cis-[Co(dbedda)en] ( ) s-cis[Co(dN0 bedda)en] ( ), s-cis-[Co(dClbedda)en] (---), and s-cis-[Co(dmbedda)en] (• · -)(14) +

2

+

+

+



13.

HAWN ET AL.

Phenyl

Substituent

Contributions

271

f o r t h e l o w e n e r g y (E) component and v e r y l i t t l e e f f e c t o n t h e intensities. O n l y t h e n i t r o s u b s t i t u t e d dbedda c o m p l e x h a s a maximum w h i c h c a n be c o n s i d e r e d t o be s i g n i f i c a n t l y d i f f e r e n t . However, s m a l l s h i f t s i n t h e p o s i t i o n s o f two a d j a c e n t CD p e a k s can r e s u l t i n changes i n p e a k i n t e n s i t i e s . Although the extent of o v e r l a p o f peaks i s d i f f i c u l t o r i m p o s s i b l e t o e v a l u a t e , i t may b e r e a s o n a b l e t h a t t h e n i t r o s u b s t i t u t e d dbedda c o m p l e x may show a l a r g e r t e t r a g o n a l s p l i t t i n g t h a n t h e o t h e r c o m p l e x e s . Generally, substitution at the para p o s i t i o n i s probably too f a r removed f r o m t h e chromophore t o p r o d u c e any s i g n i f i c a n t c h a n g e s . The p a r a p o s i t i o n was s e l e c t e d t o a v o i d s t e r i c e f f e c t s .

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.

Liu, C. T. and Douglas, Β. Ε., Inorg. Chem. (1964), 3, 1356. Yasui, T., Hidaka, J., and Shimura, Y . , Bull. Chem. Soc. Japan (1966), 39, 2417. Shimura, Υ., Bull. Chem. Soc. Japan (1958), 31, 315. Pfeiffer, P., Christeleit, W., Hesse, T., Pfitzner, Η., and Thielert, H . , J. Prakt. Chem. (1938), 150, 261. Douglas, Β. Ε . , Inorg. Chem. (1965), 4, 1813. Ogino, Κ., Murano, Κ., and Fujita, J., Inorg. Nucl. Chem. Letters (1968), 4, 351. Tanimura, T., Ito, Η., Fujita, J., Saito, K., Hirai, S., and Yamasaki, K., J. Coord. Chem. (1973), 3, 161. Jordan, W. T., Lin, C.-Y., and Douglas, Β. E . , J. Coord. Chem. (1973), 3, 1. Legg, J. I . , Cooke, D. W., and Douglas, Β. Ε . , Inorg. Chem. (1967), 6, 700. Van Saun, C. W. and Douglas, Β. Ε., Inorg. Chem. (1969), 8, 115. Jordan, W. T. and Douglas, Β. Ε . , Inorg. Chem. (1973), 12, 403. Maricondi, C. W. and Douglas, Β. Ε., Inorg. Chem. (1972), 11, 688. Maricondi, C. W. and Maricondi, C., Inorg. Chem. (1973), 12, 1524. Hawn, G. G., Maricondi, C., and Douglas, Β. E . , Inorg. Chem. (1979), 18, in press. Bosnich, B. and Harrowfield, J., J. Am. Chem. Soc. (1972), 94, 3425. Gillard, R. D., Tetrahedron (1965), 21, 503. Fereday, R. L. and Mason, S. F . , Chem. Commun. (1971), 1314. Mason, S. F. and Seal, R. H . , Chem. Commun. (1973), 422. Kuroda, R. and Mason, S. F . , J. Chem. Soc. Dalton (1977), 1016. Höhn, E. G. and Weigang, O. Ε., J r . , J. Chem. Phys. (1968), 48, 1127. Kirkwood, J. G., J. Chem. Phys. (1937), 5, 479. Mason, S. F. and Seal, R. Η., Chem. Commun. (1975), 331.


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25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35.


Mason, S. F. and Seal, R. H . , Mol. Phys. (1976), 31, 755. Hawkins, G. J . and Larsen, Ε., Acta. Chem. Scand. (1965), 19, 185, 1969. Schellman, J . Α., Acc. Chem. Res. (1968), 1, 144. Schäffer, C. Ε . , Pure Appl. Chem. (1970), 24, 361. Mason, S. F . , J . Chem. Soc. A (1971), 667. Richardson, F. S., Inorg. Chem. (1972), 11, 2366. Hearson, J . Α., Mason, S. F . , and Seal, R. Η., J. Chem. Soc. (Dalton) (1977), 1026. Schipper, P. E . , J . Am. Chem. Soc. (1978), 100, 1433. Schipper, P. Ε . , This volume. Richardson, F. S., This volume. Hawn, G. G., Chang, C. Α., and Douglas, Β. Ε . , Inorg. Chem. (1979), 18, 1266. Okamoto, Κ., Tsukihara, T., Hidaka, J., and Shimura, Υ., Chem. Lett. Japan (1973), 145. Nagao, R., Marumo, F . , and Saito, Y . , Acta. Cryst. (1972), B28, 1852.

RECEIVED September 13, 1979.


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