Electrochemical and Spectrochemical Studies of Biological Redox

12

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 8, 2013 | http://pubs.acs.org Publication Date: June 1, 1982 | doi: 10.1021/ba-1982-0201.ch012

Electrochemical and Spectroscopic Studies of Iron and Cobalt Porphodimethenes A Mononuclear Hydroxoiron(III) Tetrapyrrole Complex 1

ANDREAS BOTULINSKI, JOHANN WALTER BUCHLER , and KIONG LAM LAY—Institut für Anorganische Chemie, Technische Hochschule Darmstadt, D-6100 Darmstadt, Federal Republic of Germany JÜRGEN ENSLING—Institut für Anorganische und Analytische Chemie, Universität Mainz, D-6500 Mainz, Federal Republic of Germany HANS TWILFER—Abteilung Physiologische Chemie, Technische Hochschule Aachen, D-5100 Aachen, Federal Republic of Germany JOCHEN BILLECKE, HEIKO LEUKEN, and BERNHARD TONN Institut für Anorganische Chemie, Technische Hochschule Aachen, D-5100 Aachen, Federal Republic of Germany

Iron porphodimethenes (α,γ-dihydroporphyrins) repre sent a special class of sterically and electronically mod ified hemes in which both axial coordination sites show impaired accessibility, especially α , γ - d i - t e r t - b u t y l o c t a ethylporphodimethene. This feature allows the isolation of the first definitely identified mononuclear hydroxo iron(III) complex of a porphinoid ligand system, hy droxo [ α , γ - d i - t e r t - b u t y l - α , γ - d i h y d r o o c t a e t h y l p o r p h i n ato]iron(III). The hemin-like coordination group is char acterized by μ = 5.7 B.M., v = 3661 cm , g = 5.84, g = 2.00, δ= 0.314 mm/s (metallic Fe, 1.5 K), and ΔΕ = 0.56 mm/s in magnetic measurements and IR, ESR, and Mössbauer spectra. Instead of OH, a variety of other axial ligands can be bound by the di-tert-butylporphodimethene, for example, F, Cl, NO, N , NCS, OCN, and OMe. Notable exceptions are cyanide and carbon -1

eff

OH

Q

3

1

Author to whom correspondence should be addressed. 0065-2393/82/0201-0253$07.50 © 1982 A m e r i c a n C h e m i c a l Society

In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.

254

BO ILOGC IAL REDOX COMPONENTS


monoxide. The corresponding cobalt di-tert-butylporphodimethene shows a strongly diminished affinity toward dioxygen, although cyclic voltammetry indicates an easier metal oxidation in porphodimethenes than in porphyrins. " T \ u r i n g investigations to elucidate the influence o f the central metal on the h y d r o g é n a t i o n o f metalloporphyrins, various oxygen-sen sitive metal porphodimethenes ( α , γ - d i h y d r o p o r p h y r i n s ) were studied ( I , 2 , 3). A i r stable a , y - d i m e t h y l - a , y - d i h y d r o o c t a e t h y l p o r p h y r i n c o m p l e x e s , for e x a m p l e , t h e h e m i n F e ( O E P M e ) C l ( l A a , T a b l e I) ( 4 ) , or C o ( O E P M e ) ( l B b ) (5) w e r e o b t a i n e d i n a systematic s t u d y that r e v e a l e d the s p e c i a l e l e c t r o n i c a n d steric modification o f the porp h o d i m e t h e n e c o r e . P r o t o n N M R i n v e s t i g a t i o n s ( 2 , 6) a n d x - r a y c r y s t a l l o g r a p h y ( 7 , 8 , 9 ) d e m o n s t r a t e d t h e syn-axial-exo c o n f i g u r a t i o n of the t w o m e t h y l groups, w h i c h were i n t r o d u c e d b y a reductive m e t h y l a t i o n ( J O ) , a n d t h e m o r e firmly b o u n d a x i a l l i g a n d X , f o r example, i n N i ( O E P M e ) ( l C b ) (7), T i O ( O E P M e ) ( l D c ) (8), a n d O s ( O E P M e ) C O · P y ( l E d ) (9). T h e syn-axial-exo c o n f i g u r a t i o n m a y a l s o b e d e s c r i b e d as a roof like folded porphodimethene with both R a n d X i n " c h i m n e y posi t i o n s " ( 3 ) . T h i s c o n f i g u r a t i o n is s k e t c h e d for a g e n e r a l i r o n p o r p h o d i m e t h e n e F e ( O E P R ) X L ( A ) i n F i g u r e 1, I . B o t h a x i a l c o o r d i n a t i o n sites a r e i m p e d e d : X b y t h e t w o a l k y l g r o u p s , R a n d L b y t h e f o l d i n g o f t h e m a c r o c y c l e . T h e l a t t e r effect l e a d s t o a s o m e w h a t p r o l o n g e d axial O s - N b o n d i n l E d (9), whereas the former results i n a retarda t i o n o f t h e a c i d o l y s i s o f t h e μ - ο χ ο c o m p l e x l A e as c o m p a r e d w i t h t h e k n o w n /Lt-oxobisiron(III) p o r p h y r i n s ( 4 ) . 2

2

2

2

2

2

Basic hydrolysis o f hemins produces μ-οχο complexes i n a l l k n o w n cases f r o m p o r p h y r i n s ( I I ) , e v e n f r o m s t e r i c a l l y h i n d e r e d p o r p h y r i n s , for e x a m p l e , t h e " p i c k e t f e n c e " h e m e ( 1 2 ) . H y d r o l y s i s is i m m e d i a t e l y f o l l o w e d b y c o n d e n s a t i o n . T h i s r e a c t i o n is e x e m p l i f i e d b y i r o n p o r p h o d i m e t h e n e s as f o l l o w s ( R = C H , QH5, n - C H , i - C H ) : 3

3

7

3

7

condensation

H0O / H" 2

2 Fe(OEPR )Cl < Aa 2

[Fe(OEPR )] 0 Ae 2

2

H

C

1

2

(1)

acidolysis

T h u s , a linear extension o f R does not strongly increase the steric h i n d r a n c e o f X ( F i g u r e 1,1), a n d t h e r e s u l t i n g μ - ο χ ο c o m p l e x e s p r o b a b l y h a v e c o n f i g u r a t i o n I I ( F i g u r e 1); m o d e l s s h o w t h a t a μ - ο χ ο b r i d g e cannot b e formed u n d e r the roof (4). U s e o f tert-butyl as t h e a l k y l g r o u p ( R ) i n i r o n p o r p h o d i m e t h e n e s w a s n o t e d p r e v i o u s l y ( 1 3 , 14). T h e p r e s e n t p a p e r d e s c r i b e s t h e s p e c troscopic characterization o f the e x c l u s i v e l y mononuclear α,γ-di-tert-


255 12.

BOTULiNSKi E T AL.

Iron and Cobalt Porphodimethenes


Table I. Structure and Numbering of Metal Dialkyloctaethylporphodimethenes

Lower case Letter"

X

a b c d e f

Lower case Letter

L

Cl

η ο

— Ο CO 0/2"

— OCH

g h i

OC H N NO NO Py Py e

3

j k 1 m

Py

Ρ q r s t u

6

— — — — — Py

OH 3

5

V X

w y ζ

Py

X

L

o Py F OAc OCN NCS OPhpBut CN CN l-Meim' 1-Meim Br Pip^ 2

o

2

— — — — — — CN — 1-Meim

c

6

Br Pip

α

In text, lowercase letters followed by prime (') indicate that X and L are reversed. pyridine acetate μ-οχο complex p-i-butylpnenoxide 1-methylimidazole piperidine b c

d

e f

9

butyloctaethylporphodimethenatoiron(III) complexes, F e ( O E P B u t ) X L 2 A a , 2 A f - 2 A j , 2 A p , a n d 2 A r - 2 A t (see T a b l e I ) . F o r t h e s e c o m p l e x e s , i n R e a c t i o n 1, h y d r o l y s i s stops at t h e stage o f t h e h y d r o x i d e , F e ( O E P B u t ) O H (2Af). S o m e e l e c t r o c h e m i c a l data a n d spectral prop erties o f other i r o n p o r p h o d i m e t h e n e s , F e ( O E P M e ) X L , a n d c o b a l t p o r p h o d i m e t h e n e s [ C o ( O E P R ) , l B b a n d 2 B b ] are also presented i n this chapter. 2

2

2

2



256


Figure 1. Presumed steric features of a mononuclear iron porphodi methene, Fe(OEPMe )XLJ[, and the μ-oxobislporphodimethenatoiron (III)] system, [Fe(OEPMe )]2 Ο, II. The porphodimethene core is approximated by a rectangle folded about the a,y-line (" roof-like folding", R,X in "chimney positions"). 2

2

T h e h y d r o x i d e F e ( O E P B u t ) O H (2Af) is t h e first f u l l y c h a r a c terized mononuclear hydroxoiron(III) complex of a porphinoid ligand s y s t e m , for w h i c h s p e c t r a l d a t a w e r e c o m m u n i c a t e d p r e v i o u s l y (14). I n more recent reports on iron p o r p h y r i n s w i t h steric h i n d r a n c e on b o t h sides o f the m o l e c u l a r p l a n e , isolated h y d r o x y l groups w e r e i d e n t i f i e d o n l y b y I R s p e c t r o s c o p y (J5, 16). A t h o r o u g h d e s c r i p t i o n o f the i n s t r u m e n t a l analysis o f m e t a l por p h o d i m e t h e n e s c a n b e f o u n d i n s e v e r a l s c i e n t i f i c t h e s e s (5, 17-22). 2

Experimental Preparation of Iron Porphodimethenes. Iron porphodimethenes were synthesized according to p r e v i o u s l y p u b l i s h e d procedures (4) from the corre s p o n d i n g α , γ - d i a l k y l o c t a e t h y l p o r p h o d i m e t h e n e s a n d iron pentacarbonyl (10, 17, 18). T h e hemins F e ( O E P R ) X (where X = O C H , O C H , N , F , CI, B r , O A c , O C N , N C S , a n d O P h p B u t ) were obtained b y acidolysis o f the μ-οχο complex l A e (Reaction 1) or esterification of the h y d r o x i d e 2 A f a n d were crys t a l l i z e d w i t h o u t chromatography i n the presence o f excess X ~ . Preparation of Hydroxo[ a,y-di-^eri-butyl-a,y-dihydrooctaethylporphinato]iron(III), F e ( O E P B u t ) O H (2Af) (13, 14). A 576-mg (1.12-mmol) sam p l e o f a,y-di-ferf-butyl-a,y-dihydrooctaethylporphyrin [ H ( O E P B u t ) , ob tained from zinc o c t a e t h y l p o r p h y r i n b y reductive alkylation (6,10) w i t h C ( C H ) I and demetalation] was refluxed 4 h w i t h 300 m g (1.17 m m o l ) o f I a n d 3 m L (21 mmol) o f F e ( C O ) i n 80 m L of toluene under nitrogen. After c o o l i n g a n d filtration, the solution was taken to dryness i n vacuo a n d the residue was chromatographed on a l u m i n a (grade I I I , neutral, 40 x 3 cm) w i t h toluene. T h e first b r o w n i s h fraction contained unreacted porphodimethene a n d some u n i d e n t i f i e d iron complexes. T h e second r e d fraction y i e l d e d the 2

3

6

5

3

2

2

3

2

3

2

5


257


12. BOTULN ISKI ET AL.

p r o d u c t 2 A f after e l u t i o n w i t h toluene-acetone ( 9 : 1 ) , evaporation o f the solvent, crystallization from cyclohexane, a n d d r y i n g at 4 5 ° C / 1 0 ~ m m . C o m p o u n d 2Af, a powder, reacts w i t h alcohols, concentrated acetone, a n d traces of acids (e.g., h y d r o c h l o r i c a c i d from d e c o m p o s i t i o n o f m e t h y l e n e chloride) to g i v e the corresponding hemins. Y i e l d : 394 m g (48.8%). A n a l y s i s o f C 4 H N F e O (719.9 g/mol): calculated, C , 73.41; H , 8.82; N , 7.78; O , 2.23; F e , 7.76%; found, C , 73.71; H , 9.00; N , 7.62; O , 2.35; F e , 7.15 (combustion res idue) % . Preparation of Cobalt Porphodimethenes l B b and 2 B b . T h e p o r p h o d i methene, H ( O E P R ) (0.5 m m o l ) , was refluxed under nitrogen w i t h C o 2 ( C O ) (1.4 m m o l ) a n d I (0.2 m m o l ) i n toluene for 1 h . T h e solution was taken to dryness i n vacuo; the residue was chromatographed on a l u m i n a (grade I I I , neutral) a n d e l u t e d w i t h c y c l o h e x a n e - t o l u e n e (9:1) under nitrogen. T h e first, y e l l o w - b r o w n fraction y i e l d e d C o ( O E P R ) [lBb: 221 m g , 6 7 % (5), 2 B b : 261 m g , 6 9 % (13, 21)] as b l a c k - b r o w n crystals after evaporation to dryness, recrystallization from cyclohexane, a n d d r y i n g at 4 5 ° C / 1 0 ~ m m . Analysis o f l B b , C H N C o (621.78 g/mol): calculated, C , 73.41; H , 8.10; N , 9.01; O , 0.00%; found. C , 73.31; H , 7.92; N , 9.13; O , 0.24%. Analysis o f 2 B b , ^ Η Ν 0 ) (705.94 g/mol): calculated, C , 74.86; H , 8.85; N , 7.94%; found, C , 74.73; H , 8.90; N , 8.05%. Preparation of Liganded Cobalt Porphodimethenes. T h e c o b a l t i c h r o m e salts [ C o ( O E P M e ) L ] P F , L = P y , 1 - M e i m , p i p e r i d i n e (lBm, Ι Β χ , l B z as cations, Table I) were o b t a i n e d b y treatment o f solutions o f l B b w i t h excess L , air, a n d N H P F i n (5). T h e corresponding octaethylporp h y r i n derivatives, [ C o ( O E P ) L ] P F , were prepared s i m i l a r l y (13, 14). Preparation of Hemichrome Salts. T h e o c t a e t h y l h e m i c h r o m e salts [ F e ( O E P ) L 2 ] P F ( L = P y , 3-chloropyridine, 1-Meim) a n d the corresponding porphodimethene h e m i c h r o m e salts, [ F e ( O E P M e ) L ] P F ( L = Py, 1-Meim) were o b t a i n e d from the chlorohemins b y b o i l i n g w i t h excess L a n d N H P F i n m e t h y l e n e c h l o r i d e a n d c r y s t a l l i z i n g (19, 20, 23). Instrumental Analysis. O p t i c a l spectra were recorded w i t h a U n i c a m S P 8 0 0 B spectrophotometer, I R spectra w i t h a P e r k i n - E l m e r 621 instrument ( K B r pellets), E P R spectra w i t h a B r u k e r B - E R 420 spectrometer (toluene glass), a n d proton N M R spectra w i t h a B r u k e r W H - 9 0 pulse F o u r i e r transform spectrometer (pulse w i d t h ~ l ^ s , 100 to 1000 scans, internal lock w i t h C D C 1 as solvent). T h e Mossbauer spectrometer was e q u i p p e d w i t h a C o - R h source (20 m C i ) at 295 K , an e l e c t r o m e c h a n i c a l vibrator, a 9 0 % K r - 1 0 % C 0 proportional counter, and a 400-channel analyzer (24, 25). Isomer shifts (δ) refer to m e t a l l i c iron. T h e values o f δ a n d the q u a d r u p o l e s p l i t t i n g , Δ Ε , were obtained b y a least-squares fit o f the measured spectra to L o r e n t z i a n l i n e shapes. T h e absorber samples contained F e i n natural abundance a n d were enclosed i n airtight perspex holders c o n t a i n i n g 0.2 m g o f F e / c m . M a g n e t i c measurements o f s o l i d 2 A f were performed w i t h a Faraday balance as d e s c r i b e d elsewhere (26). C y c l i c voltammograms were run w i t h P r i n c e t o n A p p l i e d Research e q u i p m e n t : a potentiostat 173 a n d u n i v e r s a l programmer 175, a P h i l i p s X Y recorder P M 8125, and a B e c k m a n p l a t i n u m button electrode. 3

4

e 3

4


2

2

8

2

2

3

3 8

5 0

4

6

2

4

2

6

2

4

6

CHCI3-CH3OH 2

6

6

2

2

e

4

6

3

5 7

2

0

5 7

5 7

2

Electrochemistry and Optical Spectra T h e cyclic voltammograms o f some octaethylhemichrome a n d the c o r r e s p o n d i n g p o r p h o d i m e t h e n e

salts

h e m i c h r o m e salts w e r e r e -


258


c o r d e d p r e v i o u s l y (20). S o m e results are c o m p a r e d i n F i g u r e 2 a n d T a b l e I I . T h e h e m i c h r o m e salts s h o w r e v e r s i b l e F e ( I I ) - F e ( I I I ) s t e p s o n l y i n the presence o f excess a x i a l l i g a n d L ; o t h e r w i s e the h e m i c h r o m e d i s s o c i a t e s i n s o l u t i o n ( 2 7 , 28). T h e c o b a l t i c h r o m e salts d e r i v e d from octaethylporphyrin a n d α , γ - d i m e t h y l o c t a e t h y l p o r p h o d i m e t h e n e a l s o w e r e s t u d i e d ( T a b l e I I ) ( 5 ) . T h e C o ( I I ) - C o ( I I I ) s t e p is i r r e v e r s i b l e i n a m o d e r a t e excess o f a x i a l base L ; a rather large n e g a t i v e s h i f t o f t h e p e a k p o t e n t i a l for r e d u c t i o n , E ( r e d ) , i n d i c a t e s d e s t a b i l i z a t i o n o f t h e r e d u c e d f o r m a n d a p r e f e r e n c e for p e n t a c o o r d i n a t i o n i n C o ( I I ) t e t r a p y r r o l e s . I r r e v e r s i b l e b e h a v i o r is f r e q u e n t l y f o u n d w i t h c o b a l t p o r p h y r i n s (29). G e n e r a l l y , t h e m e t a l i o n is m o r e easily o x i d i z e d i n p o r p h o d i m e t h e n e s than i n the p o r p h y r i n s y s t e m , a p p a r e n t l y b e c a u s e o f the s m a l l e r c e n t r a l N h o l e i n the p o r p h o d i m e t h e n e core (7). T h e a x i a l l i g a n d d e p e n d e n c e s h o w s the u s u a l t r e n d as e l a b o r a t e d w i t h o s m i u m p o r p h y r i n s e a r l i e r ( 3 0 ) , t h a t is, t h e i m i d a z o l e s y s t e m shifts t h e m e t a l ( I I - I I I ) s t e p to h i g h l y n e g a t i v e values.


p

4

-0.12

I

-0.29

J

-1.64

-1.43 Figure 2. Cyclic volt ammo grams of the dipyridine octaethylhemichrome salt, [Fe(OEP)Py ]PF (—), and the corresponding porphodi methene derivative, [Fe(OEPMe )Py ]PF (lAm) (—) (see Table II). 2

6

2

2

6


12.

259

ET AL.

BOTULiNSKi


Table II. Comparison of Metal (II/III) Oxidation-Reduction Potentials of Bisligand Octaethylporphyrin and Decaalkylporphodimethene Complexes L in Hemichrome

2

E (ox)

Salts"


[Fe(OEPMe )L ]PF

[Fe(OEP)L ]PF E (red)

p

3-Chloropyridine Pyridine 1-Methylimidazole

2

6

^1/2

p

E (ox)

E (red)

-0.22 -0.35

p

-0.03 -0.12

-0.41 -0.18

0.15

-0.16 -0.29

0.38

0.44

-0.41

-0.47

L in Cobaltichrome Salts*

[Co(OEP)L ]PF 2

E (ox)

6

ni2

p

(-0.19?) -0.32

-0.55

-0.51

[(Co(OEPMe )L ]PF 2

2

6

E (ox)

E (red)

0.22 -0.51 not m e a s u r e d

0.19 0.27

-0.61 -0.64

0.03

0.23

0.96

E (red)

p

Pyridine Piperidine 1-Methylimidazole

6

2

p

0.81

p

p

a

[Fe(OEP)L ]PF vs. [Fe(OEPMe )L ]PF [Co(OEP)L ]PF vs. [Co(OEPMe )L ]PF Note: Taken in acetonitrile with - 1 0 % L added; E[V] vs. Hg Cl /NaCl electrode, tetrabutylammonium hexaffuorophosphate as supporting electrolyte; É (ox) = peak po tential of anodic scan; E (red) = peak potential of cathodic scan; scan rate = 0.1 V/s. 2

e

2

2

e

2

e

2

2

e

6

2

2

p

p

T h e optical spectra o f the porphodimethene hemins (Figure 3, T a b l e I I I ) s h o w three b a n d s that are s o m e t i m e s not w e l l - r e s o l v e d . A h y p s o c h r o m i c s h i f t o c c u r s w i t h t h e b a n d at t h e s h o r t e s t w a v e l e n g t h as the π donor strength o f the axial l i g a n d X increases. W i t h Fe(II) c o m p l e x e s [ e . g . , t h e n i t r o s y l c o m p l e x e s l A j (4) a n d 2 A j ] t h e s p e c t r a o n l y s h o w o n e u n c h a r a c t e r i s t i c b a n d . H e n c e , a x i a l l i g a t i o n p h e n o m e n a , for e x a m p l e , d i o x y g e n b i n d i n g , are difficult to i n v e s t i g a t e . T h e greater ease o f m e t a l o x i d a t i o n expressed i n t h e e l e c t r o c h e m i c a l results s h o u l d favor i r r e v e r s i b l e o x i d a t i o n . T h e r e f o r e , i n s t e a d o f t r y i n g r e v e r s i b l e o x y g e n a t i o n , w e s t u d i e d t h e s t e r i c h i n d r a n c e i n t r o d u c e d b y t h e tertbutyl groups i n the h e n i i n 2 A a .

A Mononuclear Hydroxoiron(III) Porphodimethene As stated i n the introduction, the d i - £ e r £ - b u t y l p o r p h o d i m e t h e natoiron(III)

s y s t e m ( F i g u r e 1, I) i s s t e r i c a l l y h i n d e r e d a b o v e a n d

b e l o w the roof-like, f o l d e d tetrapyrrole system. T h i s steric h i n d r a n c e is f u r t h e r i l l u s t r a t e d i n F i g u r e 4 , w h i c h s h o w s t h e h y d r o x o i r o n ( I I I ) porphodimethene,

Fe(OEPBut )OH 2

(2Af), i n t w o possible configu-




260


261 12.

BOTULiNSKi E T AL.

Iron and Cobalt

Porphodimethenes

r a t i o n s , t h e syn-axial f o r m I I I , a n d t h e anti-axial f o r m I V . F o r m I V is f o r m e d f r o m a n y h e m i n F e ( O E P B u t ) X i n s t e a d o f a μ - o x o b i s iron(III) c o m p l e x o n exhaustive a l k a l i n e hydrolysis a c c o r d i n g to R e a c t i o n 1. 2

T h e syn-axial-exo c o n f i g u r a t i o n is a n a l o g o u s t o t h e p r o v e d s t r u c ture o f the c o m p o u n d T i O ( O E P M e 2 ) ( l D c ) a n d is further s u p p o r t e d b y the close relationship o f the T i O , F e C l , a n d F e O R c o o r d i n a t i o n groups i n m e t a l l o p o r p h y r i n s t e r e o c h e m i s t r y (31). H o w e v e r , a n x - r a y s t r u c t u r e determination o f a d i m e t h y l a c e t a m i d e solvate, F e ( O E P B u t ) O H · D M A , s h o w e d t h a t t h e anti-axial c o n f i g u r a t i o n I V is c o r r e c t (see N o t e a d d e d later).


2

T h e e l e m e n t a l a n a l y s i s o f 2Af c l e a r l y e x c l u d e d a μ - ο χ ο c o m p l e x b y the h i g h o x y g e n value. T h e presence o f a h y d r o x y 1 group is posi t i v e l y i n d i c a t e d b y a sharp v

0H

at 3 6 3 0 c m

- 1

i n the I R spectrum, part o f

w h i c h is s h o w n i n F i g u r e 5. F i g u r e 5 also shows t h e c o r r e s p o n d i n g spectral regions o f the m e t a l l o o c t a e t h y l p o r p h y r i n s , A l ( O E P ) O H (32), Si(OEP)(OH)

2

(33), a n d S n ( O E P ) ( O H )

2

(33) i n w h i c h the hydroxyl

groups are isolated a n d therefore have a rather h i g h h y d r o x y l v a l e n c e 1

frequency above 3600 c m " . A n o t h e r p r o o f o f t h e m o n o n u c l e a r c h a r a c t e r o f 2Af is i t s m a g n e t i c m o m e n t , μ^ = 5 . 7 Β . M . , m e a s u r e d i n t h e s o l i d state b e t w e e n 7 0 a n d 2 9 3 K . T h e s o m e w h a t r e d u c e d v a l u e (as c o m p a r e d w i t h t h e e x p e c t e d 5.9 B . M . ) i s e x p l a i n e d b y a q u a n t u m m e c h a n i c a l a d m i x t u r e o f 1 6 % o f 4

the

A i s p i n state t o t h e b a s i c 8 4 % o f t h e

6

A i s p i n state (34). μ - Ο χ ο

c o m p l e x e s s h o w a n t i f e r r o m a g n e t i c b e h a v i o r (26) n o t at a l l f o u n d w i t h 2Af.

F u r t h e r e v i d e n c e f o r t h e m o n o n u c l e a r state o f 2Af i s t h e E S R ,

M ô s s b a u e r , a n d proton N M R spectra. T w o t y p i c a l c h e m i c a l r e a c t i o n s (11) o f h e m e s o r h e m i n s ( t h e for mation o f c a r b o n y l hemes or d i c y a n o h e m i c h r o m e anions) p r o c e e d ac c o r d i n g to R e a c t i o n 2 w i t h F e ( I I ) p o r p h o d i m e t h e n e s (5) or R e a c t i o n 3

Figure 4.

Syn-axial (exo) or anti-axial (endo) configurations of 2Af ( see "Note added later ).

(III or IV)

y


In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982. 2

0H

CH

2

IR spectra of the octaethylporphyrin complexes Al(OEP)OH, Si(OEP)(OH) , and the porphodimethene complex, Fe(OEPBut )OH in the v /v region.

AK0ÉP)OH


2

Sn(OEP)(OH) ,

12.


BOTULINSKI E T A L .

263

w i t h F e ( I I I ) p o r p h o d i m e t h e n e s (17) for R = C H , b u t n o t at a l l (13,14, 18) for R = C ( C H ) . 3

3

3

Fe(OEPR )Py 2

2

+ CO

Fe(OEPR )CO · Py + Py 2

lAm (not 2Am) e

Fe(OEPR )Cl + 2 C N -» [Fe(OEPR )(CN) ] lAa(not2Aa') lAv 2


(

2

)

lAd 2

2

e

e

+ C l

(

3

)

I n t h e di-tert-butyl s e r i e s , n o t e v e n a m o n o c y a n i d e is s e e n . A p o s s i b l e e x p l a n a t i o n for t h i s m a y b e t h e f o l l o w i n g : R e a c t i o n s 2 a n d 3 w e r e r u n i n t h e p r e s e n c e o f p y r i d i n e , w h i c h b y a n a l o g y to t h e p r o v e d c o n f i g u r a tion o f 2 A f p r o b a b l y p r e f e r e n t i a l l y o c c u p i e s the position L u n d e r the roof. T h e r e f o r e , c a r b o n m o n o x i d e o r c y a n i d e c a n o n l y e n t e r t h e h e m o c h r o m e or the h e m i c h r o m e cation from the strongly h i n d e r e d p o s i t i o n X , i f at a l l . M a n y o b s e r v a t i o n s i n t h e d i - f e r f - b u t y l p o r p h o d i m e t h e n e series c a n b e u n d e r s t o o d i f o n e assumes that h e x a e o o r d i n a t e d species F e ( O E P B u t ) X L a r e n o t f o r m e d at a l l , a n d t h a t a l l p e n t a c o o r d i n a t e d species h a v e the configurations F e ( O E P B u t ) L or C o ( O E P B u t ) L . P e n tacoordinated compounds within the dimethylporphodimethene series, for e x a m p l e , F e ( O E P M e ) N O , C o ( O E P M e ) N O , o r t h e h e m i n s F e ( O E P M e ) X listed i n T a b l e I I I p r o b a b l y have the configurations l A j , l B j , or l A p etc. C o r r e s p o n d i n g species w i t h i n the d i - t e r f - b u t y l p o r p h o d i m e t h e n e series s h o u l d h a v e t h e o p p o s i t e c o n f i g u r a t i o n s , s u c h as, 2 A j ' , 2 B j ' , o r 2 A g ' t o 2 A j ' s h o w n i n T a b l e I I I . H o w e v e r , t h e s e configurations r e m a i n to b e c h e c k e d b y selected crystal structure de terminations. T h e c o b a l t c o m p l e x e s , C o ( O E P B u t ) P y or C o ( O E P B u t ) ( l - M e i m ) (2ΒΓ or 2 B w ' ) , cannot b e o x i d i z e d b y air to give the cobaltichrome c a t i o n s 2 B m o r 2 B x i n the p r e s e n c e o f e x c e s s P y o r M e i m . N e i t h e r t h e neutral d i l i g a n d species, 2 B m a n d 2 B x , nor t h e d i o x y g e n c o m p l e x , 2 B o ' , c a n b e f o r m e d ; t h e o x i d a t i o n is t h u s i m p e d e d . A p p l i c a t i o n o f s t r o n g e r o x i d a n t s r e m o v e s t h e tert-butyl g r o u p s , a n d c o b a l t o c t a e t h y l p o r p h y r i n s are o b t a i n e d . 2

2

2

2

2

2

2

2

Electron Spin Resonance Spectra T a b l e I V s u m m a r i z e s the results o f a n electron s p i n resonance s t u d y o f i r o n p o r p h o d i m e t h e n e s (21, 35, 36). R h o m b i c s y m m e t r y i s i n d i c a t e d for n e a r l y a l l c o m p l e x e s w i t h k i n k e d a x i a l l i g a n d s y s t e m s , t h a t is, t h e l a t t e r are p r e f e r e n t i a l l y o r i e n t e d a b o v e o n e o f t h e b o n d s b e t w e e n the central iron atom a n d a nitrogen atom o f the por phodimethene ligand. T h e only exceptions are the phenoxide, 2 A h ' , a n d t h e h y d r o x i d e , 2 A f (see F i g u r e 6 , u p p e r r i g h t ) . L a c k o f r h o m b i c i t y


264

BIOLOGICAL REDOX COMPONENTS

Table III. Electronic Absorption Spectra of Iron and Cobalt Porphodimethenes M ( O E P R ) X 2

Com pound


0

X

m a x

: Absorption maxima (log € in brackets)

Solvent*

c

lAp lAr lAi lAs 2Af ' 2Ag'

383 401 407 406 394 396

(4.51 s h ) , 4 2 6 (4.53), 4 4 1 (4.51 s h ) , 5 3 1 (3.99) (4.50), 4 4 7 ( 4 . 3 8 s h ) , 6 0 0 (3.47 sh) (4.57), 4 5 1 ( 4 . 4 0 s h ) , 6 0 3 (3.53 sh) (4.57), 4 4 6 ( 4 . 4 3 s h ) , 6 2 8 (3.51 sh) (4.46), 4 7 3 (4.46), 5 3 6 (3.27) (4.46), 4 7 3 (4.47), 5 4 1 (4.17)

2At' 2Ap' 2Ar' 2As' 2Ai' 2Aa' 2Aj' lBb 2Bb

400 400 402 409 410 410 446 420 425

(4.49), 4 7 7 ( 4 . 4 8 ) , 5 6 1 (4.09) (4.45), 4 7 5 (4.40), 5 6 3 (3.97) (4.59), 4 5 9 (4.41 s h ) , 5 9 8 ( 3 . 7 2 (4.60), 4 6 7 (4.31 s h ) , 5 8 9 ( 3 . 6 6 (4.57), 4 6 5 ( 4 . 4 0 s h ) , 5 9 3 (3.74 (4.65), 4 7 1 (4.41 s h ) , 6 2 3 ( 3 . 6 0 (4.51), 5 2 9 ( 4 . 1 9 sh) ( 4 . 6 0 s h ) , 4 5 6 (4.67), 4 9 8 (4.44 (4.43 s h ) , 4 6 1 (4.62), 5 0 2 (4.34

benzene 1%

CH3OH added

sh) sh) sh) sh) sh) sh)

toluene

a

See Table I for numbering system. The solvent was CH C1 unless otherwise stated. Shoulder. Note: Spectra of compounds lAa, lAe, lAg, lAh, lAj, lAq were published pre viously (4). 6

2

2

c

is e x p l a i n e d b y a s p e c i a l o r i e n t a t i o n o f t h e p h e n o x i d e g r o u p b e l o w t h e r o o f a l o n g t h e α , γ - l i n e i n 2Ah' a n d b y t h e m o b i l i t y o f t h e h y d r o x y l p r o t o n i n 2Af. T h e r e f o r e , a d i a g n o s t i c f e a t u r e o f t h e i s o l a t e d h y d r o x y l g r o u p is the axial E S R spectrum otherwise observed w i t h axially s y m m e t r i c a l s p e c i e s l i k e t h e c h l o r o h e m i n s l A a a n d 2Aa'. T h e m e t h o x i d e 2Ag' is e l e c t r o n i c a l l y c l o s e l y r e l a t e d t o t h e h y d r o x i d e 2Af (see F i g u r e 11), b u t s h o w s t h e l a r g e s t r h o m b i c i t y o b s e r v e d w i t h t h e h e m i n s (see F i g u r e 6, u p p e r left). R h o m b i c i t i e s o f t h e c o r r e s p o n d i n g o c t a e t h y l p o r p h y r i n s , F e ( O E P ) O M e or F e ( O E P ) O P h , are s o m e w h a t s m a l l e r t h a n those o f l A g or l A h a n d a m o u n t to 4 . 0 7 o r 2 . 7 8 % , r e s p e c t i v e l y (21). T h e E S R s p e c t r u m o f F e ( O E P B u t ) N O 2Aj' (see F i g u r e 6, l o w e r left) is c l o s e l y r e l a t e d to t h e E S R s p e c t r u m o f t h e m o n o m e r i c n i t r o s y l h e m o g l o b i n I o f Chironomus thumni thumni ( 3 7 ) , e s p e c i a l l y w h e n t h e l a t t e r is t r e a t e d w i t h s o d i u m d o d e c y l s u l f a t e (38). L i k e t h e l a t t e r m o d i f i e d h e m o g l o b i n , 2Aj' d o e s n o t a c c e p t a s e c o n d a x i a l l i g a n d . T h e s p e c t r u m is not a l t e r e d i n the p r e s e n c e o f a large excess o f p y r i d i n e . T h e s t e r i c a l l y u n h i n d e r e d F e ( O E P M e ) N O l A j has a s p e c t r u m s i m i l a r 2

2


In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982. Sx 5,91

5,56 5,70

gyy gzz(gll)

1,99 1,99 1,99 5,83 2,00 6,26 5,67 1,99 5,70 2,00 5,84 2,00 6,19 5,64 2,00 2,091 2,027 2,009 2,082 1,974 2,005 2,091 2,058 2,011 C o m p o u n d is n o t f o r m e d -— s p e c t r u m o f 2 A j ' o b s e r v e d .

6,39 6,27

gxx

1

e

d

c

1 4

1 4

1 4

0 5,19 3,56 0 5,56 0 0 3,44" a( NO) a( NO) a( NO)

g-Values of Iron Porphodimethenes

See Table I. " Rhombicity, R = [(É| « - & , ν ΐ 6 ] · 100[%]. 3% Methanol addec Taken at 3,6 Κ. Nitrogen hyperfine coupling constant [mT]. Taken in pyridine/toluene (1:9) Note: Bruker B-ER 420, X-band, 77 K, frozen solvent toluene (if not otherwise stated).

a

/

c

lAa lAg lAh 2Aa' 2Ag' 2Ah' 2Af 2Ai lAj IAk' 2Aj' 2Ak

Compound"

Table IV.



F i g u r e 6. 2

2

£ S R s p e c i r a ofFe(OEPBut )OMe Fe(OEPMe )NO

2

(2Ag), Fe(OEPBut )OH · Ft/ (lAk) (see Table

2

(2Af), Fe(OEPBut )NO IV).


9

(2Aj') and

Κ)

CS3

Ο g Ο Μ 25 Η

Ω

Μ α ο χ

δ r ο ο ο > r

2

Ο)

σ>

12.



1

to 2 A j ' w i t h a b e t t e r r e s o l u t i o n o f t h e a x i a l

4

267

N hyperfine splitting. O n

addition of pyridine, the spectrum changes to the one shown i n the lower

right

o f Figure

6, w h i c h is c l e a r l y a s s i g n e d

to F e ( O E P -

M e ) N O · P y l A k . T h e s p e c t r u m is s i m i l a r to that o f the 2

tetraphenyl-

p o r p h y r i n d e r i v a t i v e , F e ( T P P ) N O · P i p ( 3 9 ) , b u t is m u c h b e t t e r r e solved. Several researchers investigated

the reversible

oxygenation o f

cobalt p o r p h y r i n s a n d other cobalt chelates b y E S R analyses o f the Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 8, 2013 | http://pubs.acs.org Publication Date: June 1, 1982 | doi: 10.1021/ba-1982-0201.ch012

s p e c i e s i n v o l v e d (40-42). W e w e r e c u r i o u s t o see w h e t h e r t h e c o b a l t porphodimethenes

w o u l d u n d e r g o t h e s a m e r e a c t i o n s . T h i s is c l e a r l y

t h e c a s e f o r t h e α , γ - d i m e t h y l d e r i v a t i v e , as s h o w n i n T a b l e V a n d F i g u r e 7 , w h i c h c o r r e s p o n d s t o R e a c t i o n s 4 , 5 , a n d 6 , e s t a b l i s h e d at - 4 0 ° C a n d a n a l y z e d b y E S R spectra:

C o ( O E P M e ) «=* C o ( O E P M e ) P y (5) IBb 1B1 2

(4) 0

2

2

JJ - 4 0 P C

Co(OEPMe )0 2

(6) 0 2

2

JJ - 4 0 ° C

C o ( O E P M e ) P y ·0 2

IBn

2

IBo

T h e E S R parameters o f I B n correspond to the cobalt octaethylp o r p h y r i n s y s t e m (41). T h e E S R s p e c t r a o f C o ( O E P M e ) P y a n d C o ( O E P M e ) P y · 0 a r e v e r y s i m i l a r i n s h a p e to t h e p u b l i s h e d fea tures o f the analogous cobalt c o m p l e x e s o f the d i a c e t y l a c e t o n e e t h y l e n e i m i n e s y s t e m , C o ( a c a c e n ) P y a n d C o ( a c a c e n ) P y · 0 (42), b u t a r e better resolved. 2

2

2

2

Reaction 5 proceeds w i t h C o ( O E P B u t ) (2Bb), b u t R e a c t i o n 4 oc c u r s o n l y t o a v e r y m i n o r e x t e n t , a n d R e a c t i o n 6 w a s n o t o b s e r v e d (see T a b l e V ) . T h i s result is another e x a m p l e o f a b l o c k a d e o f the s e c o n d c o o r d i n a t i o n s i t e after t h e first o n e i s o c c u p i e d i n t h e d i - £ e r £ - b u t y l p o r p h o d i m e t h e n e series (see t h e n i t r o s y l 2 A j ' ) . 2

Môssbauer Spectroscopy M ô s s b a u e r spectra o f iron p o r p h y r i n s have attracted m u c h atten t i o n (43-46), a n d s p e c t r a s h o w n i n F i g u r e s 8 a n d 9 w e r e m e a s u r e d a n d d i s c u s s e d i n d e t a i l (21). T h e d i s c r i m i n a t i o n : m o n o n u c l e a r

hydroxo

c o m p l e x - b i n u c l e a r μ - ο χ ο c o m p l e x w i l l be elaborated here. T h e assign m e n t o f t h e s e c o n f i g u r a t i o n s f r o m t h e i s o m e r shifts δ a n d t h e

quadru-

p o l e s p l i t t i n g s AE is n o t p o s s i b l e i f o n e c o m p a r e s t h e n e w v a l u e s l i s t e d Q

i n T a b l e V I for the h y d r o x o c o m p l e x , F e ( O E P B u t ) O H ( 2 A f ) , a n d t h e 2

μ-οχο complexes,

[Fe(OEPMe )] 0 (lAe) and [Fe(ODM)] 0. T h e 2

2

2



d

d

d

2

2,559

gl

e

e

2,357

gyy

gzz(gll)

f

e

d

c

ô

&XX

2,015 11,54 2,011 — ? ? ? 2,096 ? ? ? 2,093 2,496 2,019 7,94 2,447 2,335 2,014 — O n l y a s m a l l f r a c t i o n o f 2Bn f o r m e d ' N o d i o x y g e n a d d u c t f o r m e d f r o m 2 Β Γ , n o t e v e n at - 7 0 ° C

2,455

gxx

g-Values of Cobalt Porphodimethenes

See Table I. Hyperfine coupling constants [mT]. Taken in pyriaine/toluene (1:9). Prepared by admitting 0 to solutions of lBb, 2Bb, 1B1 or 2B1 at - 4 0 ° C . Hyperfine structure not resolved. Spectrum not interprétable. Note: Conditions were as given in Table IV.

α

2Bo'

C

d

C

lBb 1B1 lBn lBo 2Bb 2B1' 2Bn'

0

Compound

Table V. yy

e

e

3,47

? ?

3,78

a


13,11 10,14 2,80 2,02 13,03 10,40

zz

a (aii)

1,02

1,40

I 4

a( NPy)»

3

s M

ο ο

Ο X

g Q

Ρ Ο Ξ Ρ

to oo

AL.


269


BOTULINSKI E T


270


ICOoO


98-0

10Q 0 o

98o0

96o0

lOOcO Ξ 98o0 ω

j)

Η 96o0 10

F 9^α0 _3 LU

ce

Figure 8. Môssbauer spectra of the hydroxoiron(III) complex, Fe(OEPBut )OH (2Af), at various temperatures. C o n t i n u e d on next page. 2

l a t t e r p o r p h y r i n d e r i v a t i v e is the f o r m a l α , γ - d e h y d r o g e n a t i o n p r o d u c t of l A e , /Lt-oxobis[a,y-dimethyloctaethylporphinatoiron(III)] (17). R e v i e w o f t h e l i t e r a t u r e for t h e o c t a e t h y l p o r p h y r i n c o m p l e x e s , F e ( O E P ) C l , F e ( O E P ) O M e , a n d [ F e ( O E P ) ] O (45, 46) d o e s n o t p r o v i d e s u p p o r t i n g data. z

T h e d i f f e r e n t t e m p e r a t u r e d e p e n d e n c e o f t h e h e m i n s a n d /x-oxo c o m p l e x e s l e a d s to a c l e a r d i s t i n c t i o n . A n a s y m m e t r i c b r o a d e n i n g o f t h e d o u b l e t at t e m p e r a t u r e s rising a b o v e a f e w Κ is a t y p i c a l f e a t u r e o f h e m i n s (43, 44), a n d j u s t t h i s effect is s e e n for F e ( O E P B u t ) O H ( F i g u r e 8). O n t h e o t h e r h a n d , μ - ο χ ο c o m p l e x e s d o n o t s h o w s u c h a n a s y m m e t r i c m a g n e t i c b r o a d e n i n g b e l o w r o o m t e m p e r a t u r e , as d o [ F e ( O E P M e ) ] 0 a n d [ F e ( O D M ) ] 0 ( F i g u r e 9). 2

2

2

2


12.

Iron and Cobalt


lOOoO

Porphodimethenes

271

\

96o0

Fe(0EPBut )0H 9

Τ = 7,0 K Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 8, 2013 | http://pubs.acs.org Publication Date: June 1, 1982 | doi: 10.1021/ba-1982-0201.ch012

92o0

lOOoO

96o0

Τ = 1,2 K

92o0

•A;

* lOOcO

I 96.0 CO

Τ - 1,5 Κ £ 92o0

-J Lu

ce

Figure

4.2

•2.1

2.1

-4.2

8. C o n t i n u e d . Môssbauer spectra of the hydroxoiron(III) complex, Fe(OEPBut )OH (2Af), at various temperatures. 2

Nuclear Magnetic Resonance Spectra T h e proton N M R spectra o f the α , γ - d i m e t h y l o e t a e t h y l p o r p h o dimethene hemins, F e ( O E P M e ) X (where X = O M e , F , N , O A c , O C N , C l , N C S , a n d B r ; S e r i e s 1) a n d o f t h e α , γ - d i - t e r i - b u t y l o c t a e t h y l p o r phodimethene hemins, F e ( O E P B u t ) X (where X = O M e , O H , O P h p B u t , F , N C S , N , C I , O C N , a n d B r ; S e r i e s 2) w e r e m e a s u r e d ( 1 8 ) . T h e p u r p o s e o f t h e p r e v i o u s w o r k (18) w a s t o find c o r r e l a t i o n s b e t w e e n t h e c o n f i g u r a t i o n s o f S e r i e s 1 a n d 2. A syn-axial-exo configu r a t i o n for t h e h e m i n s o f S e r i e s 1 i s r e a s o n a b l e b e c a u s e o f t h e i r s t r u c t u r a l r e l a t i o n t o T i O ( O E P M e ) ( l D c ) (8). T h e r e s u l t s o f t h e c r y s t a l s t r u c t u r e d e t e r m i n a t i o n o f F e ( O E P B u t ) O H (2Af) i n d i c a t e d t h a t a l l h e m i n s o f S e r i e s 2 h a v e t h e anti-axial c o n f i g u r a t i o n . 2

3

2

3

2

2


272

BIOLOGICAL REDOX

COMPONENTS

en ΣΤ.


•it

ο

Λ

5

ε ο -s s °

Ο

Ο

Ο

Ο

Ο

σ» οο πι N0ISSIUSIMVU1

in Ί3Η α

Ο Ο

ο ο

ο ο

ο ο ιπ ω x / IMOlSSIUSIMVbJ. ·Ί3Η ο

'S « β s S

CO

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ΣΖ ΣΤ

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( ΰ \ f ΙΜ Ο CP CD CH

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υ

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Γ· χ

σι σι

(η σι ο) œ

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12.



273

T a b l e V I . M o s s b a u e r Parameters o f the M o n o n u c l e a r H y d r o x o C o m p l e x 2 A f a n d the μ - Ο χ ο C o m p l e x e s l A e a n d [ F e ( O D M ) ] 0 2


Δ Ε (mm/s)

δ (mm/s)

Τ [Κ]

β

Compound 2Af 0.304 ± 0 . 1 0.314 0.294 0.304 0.314 0.304 0.304 0.314 Compound l A e 0 . 2 8 4 ± 0.01 0.284 0.284 0.284 [Fe(ODM)] 0 0.388 ± 0.005 0.453

170 80 30 20 10 7.0 4.2 1.5 30 10 4.2 1.5

0.54 ± 0 . 0 2 0.54 0.52 0.53 0.53 0.54 0.53 0.56 0 . 5 7 ± 0.01 0.57 0.58 0.58

2

78 4.2

0.523 ± 0.005 0.529

Note: δ = 0, metallic iron. T h e proton N M R spectra o f F e ( O E P M e ) N C S ( l A s ) and F e ( O E P B u t ) O H ( 2 A f ) a r e d i s p l a y e d i n F i g u r e 10. T h e h i g h field r e g i o n , 0 < δ < 10 p p m , c a n n o t b e f u l l y i n t e r p r e t e d . I n t e g r a t i o n o f t h e s p e c t r a s u g g e s t e d t h a t t h e first t w o h u m p s b e t w e e n 1 a n d 2 p p m r e p r e s e n t p a r t o f t h e m e t h y l or tert-butyl g r o u p s w i t h d i a s t e r e o t o p i c p r o t o n s . A n o t h e r p a r t is p r o b a b l y b u r i e d u n d e r t h e h u m p at ~ 6 p p m , w h i c h represents the 24 m e t h y l protons o f the p e r i p h e r a l e t h y l g r o u p s . S o m e v e r y b r o a d , flat s i g n a l s at 17 a n d 3 2 p p m i n t h e s p e c t r u m o f t h e t h i o c y a n a t e l A s c o u l d b e d u e t o t h e a,y~ or β , δ - p r o t o n s ; t h e β , δ - p r o t o n s , h o w e v e r , s h o u l d b e e x p e c t e d at m u c h h i g h e r field s t r e n g t h (47). 2

2

F o u r signals o f e q u a l intensity b e t w e e n 2 5 a n d 80 p p m i n the l o w - f i e l d r e g i o n a r e c h a r a c t e r i s t i c for a l l p o r p h o d i m e t h e n e s a n d a r e r e l i a b l y a s s i g n e d to t h e 16 m e t h y l e n e p r o t o n s o f t h e p e r i p h e r a l e t h y l g r o u p s . O c t a e t h y l h e m i n , F e ( O E P ) C l (47), h a s t w o d i a s t e r e o t o p i c ( a n d anisochronous) m e t h y l e n e protons ( C symmetry), a n d F e ( O E P R ) X (C s y m m e t r y ) , therefore, m u s t have four diastereotopic m e t h y l e n e p r o t o n s . I n F e ( O E P ) C l t h e s e p a r a t i o n is o n l y ~ 3 p p m , a n d i n t h e p o r p h o d i m e t h e n e i t c o u l d b e as l a r g e as 5 0 p p m i f t h e e x t r e m e set o f s i g n a l s b e l o n g s t o g e t h e r . T h u s a n a s s i g n m e n t o f the s i g n a l s to s p e c i f i c positions o f the p y r r o l e rings cannot b e m a d e . ( A n i n i t i a l p r o t o n N M R i n v e s t i g a t i o n o f i r o n p o r p h o d i m e t h e n e s (48) c a m e t o a s l i g h t l y differ4 v

2

2 v



274


80

*

70

60

50

40" """

30

'

20 «-t*"! 10

0

Figure 10. Proton NMR spectra of iron(III) complexes Fe(OEPBut )OH, 2Af (upper trace) and Fe(OEPMe )NCS, lAs (lower trace). 2

2

e n t c o n c l u s i o n . ) T h e s e f o u r s i g n a l s a r e v e r y s u s c e p t i b l e to a n y v a r i a t i o n o f t h e a x i a l l i g a n d a n d t h e a s s o c i a t e d c h a n g e i n s p i n d e n s i t y trans fer f r o m t h e m e t a l to t h e p o r p h o d i m e t h e n e c o r e b e c a u s e o f t h e i r l a r g e variation i n c h e m i c a l shift. T h e d e p e n d e n c e o f t h e c h e m i c a l shifts o f t h e m e t h y l e n e p r o t o n s i g n a l s o f t h e a x i a l l i g a n d s w i t h i n S e r i e s 1 a n d 2 is s c h e m a t i c a l l y r e p r e s e n t e d i n F i g u r e 11. B o t h series d e m o n s t r a t e a p r o g r e s s i v e s p r e a d o u t o f t h e f o u r s i g n a l s as t h e b a s i c i t y o f t h e a n i o n X d e c r e a s e s . T h e h y d r o x i d e i o n is i n a c l o s e p o s i t i o n to t h e m e t h o x i d e . T h e s e q u e n c e o f a n i o n s is n o t t h e s a m e i n b o t h s e r i e s ; s o m e r e p l a c e m e n t s o c c u r , e s p e c i a l l y w i t h t h e p s e u d o h a l i d e s , O C N " a n d N C S " . S e r i e s 2 has a s m a l l e r s p r e a d a n d l o o k s s o m e w h a t m o r e i r r e g u l a r t h a n S e r i e s 1. T h e s e d i f f e r e n c e s d o n o t s e e m m a j o r a n d c a n n o t b e u s e d to m a k e a n y c o n f i g u r a t i o n a l a s s i g n m e n t . T h e y m a y b e d u e to a d i f f e r e n t a n d variable angle o f f o l d i n g o f the t w o p y r r o m e t h e n e halves i n Series 1 a n d 2; i n a d d i t i o n , a v a r i a b l e s a d d l e - l i k e d e f o r m a t i o n s h o u l d a l s o b e c o n s i d e r e d . F i n a l l y , these differences c o u l d b e d u e to the s u s p e c t e d opposite configurations o f the t w o series. T h e f o l d i n g a n g l e b e t w e e n the n o r m a l s o f the p y r r o m e t h e n e halves i n l C b , l D c a n d l E d lies


12.

Iron and Cobalt


275

Porphodimethenes

between 38 a n d 52°, a n d the normals o f the pyrrole rings o f each p y r r o m e t h e n e h a l f m a y form angles b e t w e e n 1 a n d 2 3 ° (7, 8, 9). S u c h v a r i a t i o n s c e r t a i n l y affect t h e t r a n s f e r o f s p i n d e n s i t y f r o m t h e m e t a l t o the p e r i p h e r y w h e n they o c c u r i n iron(III) p o r p h o d i m e t h e n e s , a n d are more l i k e l y f o u n d w i t h the more sterically h i n d e r e d Series 2. Note added later: A f t e r s u b m i s s i o n o f t h i s c h a p t e r , a n x - r a y s t r u c t u r e d e t e r m i n a t i o n o f a d i m e t h y l a c e t a m i d e solvate o f the h y d r o x o i r o n ( I I I ) porphodimethene, F e ( O E P B u t ) O H · D M A , was performed b y W. R . Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 8, 2013 | http://pubs.acs.org Publication Date: June 1, 1982 | doi: 10.1021/ba-1982-0201.ch012

2

S c h e l d t a n d c o w o r k e r s (49). T h e c o m p o u n d has t h e anti-axial

config

u r a t i o n I V (see F i g u r e 4). T h i s s u r p r i s i n g r e s u l t n e c e s s i t a t e s f u r t h e r structure

determinations

of pentacoordinated

Fe(OEPMe )X, 2

C o ( O E P M e ) X , a n d C o ( O E P B u t ) X systems to determine w h i c h axial 2

2

positions are p r e f e r e n t i a l l y o c c u p i e d . I f the configurations o f a l l these systems w e r e k n o w n , t h e r e a c t i v i t y differences o f t h e α , γ - d i m e t h y l a n d t h e α,γ-di-tert-butyl

series w o u l d b e m o r e e a s i l y e x p l a i n e d .

Fe(OEPMe )X

|

2

I I I I I I I i

|

|

I I

i

ι

I l I I δ [PPm]

80

I I I

70

60

Fe(OEPBut )X

50

I I

I I

I

I

N

OAc

OCN

20

I

I I I l I l II

I II

OH OPhpBut

I

F

I

10

OfAe ,

I

II

I I

y

Br

I

I

3

c«

I I

I I

F

30

I

OMe

NCS -

40

|

2

I I I ι

I I

|

I

\ x

\

NCS

N 3

ci , - ' II O C N I I Br

Figure 11. Comparison of the chemical shifts, &[ppm], of the four low-field proton NMR signals (see Figure 10) for the porphodimethene hemin series FeiOEPMe^X and Fe(OEPBut )X for a variation ofX(X = anion as indicated). 2


276


Acknowledgments T h e authors thank K . G e r s o n d e (Aachen), J . G r o b e (Darmstadt), a n d P . G i i t l i c h ( M a i n z ) for t h e u s e o f t h e i r E S R , N M R , a n d M ô s s b a u e r e q u i p m e n t a n d H . A . O . H i l l ( O x f o r d ) for i n i t i a l h e l p w i t h N M R spectra. F i n a n c i a l support o f the D e u t s c h e Forsehungsgemeinschaft, the Fonds d e r C h e m i s c h e n Industrie, a n d the V e r e i n i g u n g v o n F r e u n d e n d e r T e c h n i s c h e n H o c h s c h u l e D a r m s t a d t is g r a t e f u l l y

acknowl


e d g e d . W e t h a n k W . R . S c h e l d t for i l l u m i n a t i n g d i s c u s s i o n s a n d for t h e determination o f the crystal a n d m o l e c u l a r structure o f the hydroxoiron(III) porphodimethene.

Literature Cited 1. Buchler, J. W.; Schneehage, H. H. Angew. Chem. 1969, 81, 912; Int. Ed. Engl. 1969, 8, 893. 2. Buchler, J. W.; Schneehage, H. H. Tetrahedron Lett. 1972, 3803. 3. Buchler, J. W.; Puppe, L.; Rohbock, K.; Schneehage, H. H. Ann. Ν. Y. Acad. Sci. 1973, 206, 116. 4. Buchler, J. W.; Lay, K. L. Z. Naturforsch. 1975, 30b, 385. 5. Tonn, B., Ph.D. Dissertation, Technische Hochschule Aachen, 1979. 6. Buchler, J. W.; Puppe, L. Liebigs Ann. Chem. 1974, 1046. 7. Dwyer, P. N.; Buchler, J. W.; Scheidt, W. R. J. Am. Chem. Soc. 1974, 96, 2789. 8. Dwyer, P. N.; Puppe, L.; Buchler, J. W.; Scheidt, W. R. Inorg. Chem. 1975, 14, 1782. 9. Buchler, J. W.; Lay, K. L.; Smith, P. D.; Scheidt, W. R.; Rupprecht, G. Α.; Kenny, J. A. J. Organomet. Chem. 1976, 110, 109. 10. Buchler, J. W.; Puppe, L. Liebigs Ann. Chem. 1970, 740, 142. 11. Buchler, J. W. In "The Porphyrins"; Dolphin, D., Ed.; Academic: New York, 1978; Vol. 1, pp. 389-483. 12. Collman, J. P.; Gagne, R. R.; Reed, C. Α.; Halbert, T. R.; Lang, G.; Robin son, W.Τ.J.Am. Chem. Soc. 1975, 97, 1427. 13. Buchler, J. W.; Lay, K. L., unpublished data. 14. Buchler, J. W. Angew. Chem. 1978, 90, 425; Angew. Chem., Int. Ed. Engl. 1978, 17, 407. 15. Cense, J.-M.; Le Quan, R. M. Tetrahedron Lett. 1979, 3725-3728. 16. Groves, J. T.; Haushalter, R. C.; Nakamura, M.; Nemo, T. E.; Evans, B.J.J. Am. Chem. Soc. 1981, 103, 2884-2885. 17. Lay, K. L., Ph.D. Dissertation, Technische Hochschule Aachen, 1975. 18. Botulinski, A. Diplomarbeit, Technische Hochschule Darmstadt, 1981. 19. Tonn, M. Diplomarbeit, Technische Hochschule Aachen, 1975. 20. Tonn, B. Diplomarbeit, Technische Hochschule Aachen, 1976. 21. Billecke, J., Ph.D. Dissertation, Technische Hochschule Aachen, 1980. 22. Puppe, L., Ph.D. Dissertation, Technische Hochschule Aachen, 1972. 23. Hill, H. A. O.; Skyte, P. D.; Buchler, J. W.; Lueken, H.; Tonn, M.; Gregson, A. K.; Pellizer, G. J. Chem. Soc., Chem. Commun. 1979, 151. 24. Gütlich, P.; Link, R.; Trautwein, A. "Mössbauer Spectroscopy and Transi tion Metal Chemistry"; Springer: Berlin, 1978. 25. Ensling, J., Ph.D. Thesis, Technische Hochschule Darmstadt, 1970. 26. Lueken, H.; Buchler, J. W.; Lay, K. L. Z. Naturforsch. 1976, 31b, 1596. 27. Truxillo, L. Α.; Davis, D. G. Anal. Chem. 1975, 47, 2260. 28. Constant, L. Α.; Davis, D. G. J. Electroanal. Chem. 1976, 74, 85.



12. BOTULINSKI ET AL.


277

29. Fuhrhop, J. H.; Kadish, Κ. M.; Davis, D. G. J. Am. Chem. Soc. 1973, 95, 5140. 30. Buchler, J. W.; Kokisch, W.; Smith, P. D. Struct. Bonding (Berlin) 1978, 34, 80-134. 31. Scheidt, W. R. In "The Porphyrins"; Dolphin, D., Ed.; Academic: New York, 1978; Vol. 3, pp. 463-511. 32. Inhoffen, H. H.; Buchler, J. W. Tetrahedron Lett. 1968, 2057. 33. Buchler, J. W.; Puppe, L., unpublished data. 34. Lueken, H., unpublished data. 35. Billecke, J.; Buchler, J. W.; Lay, K. L.; Twilfer, H. Biophys. Struct. Mech. 1980, 6(Suppl.),26. 36. Ibid., 27. 37. Overkamp, M.; Twilfer, H.; Gersonde, Κ. Z. Naturforsch. 1976, 31c, 524. 38. Twilfer, H., Ph.D. Dissertation, Technische Hochschule Aachen, 1979. 39. Wayland, Β. B.; Olson, L. W. J. Am. Chem. Soc. 1974, 96, 6037. 40. Walker, F. A. J. Am. Chem. Soc. 1970, 92, 4235. 41. Walker, F.A.J. Magn. Res. 1974, 15, 201. 42. Jones, R. D.; Summerville, D. Α.; Basolo, F. Chem. Rev. 1979, 79, 139179. 43. Hambright, P.; Bearden, A. J. In "Porphyrins and Metalloporphyrins"; Smith, K. M., Ed.; Elsevier: Amsterdam, 1975; pp. 539-553. 44. Sams, J. R.; Tsin, T. B. In "The Porphyrins"; Dolphin, D., Ed.; Academic: New York, 1979; Vol. 4, pp. 425-478. 45. Dolphin, D. H.; Sams, J. S.; Tsin, T. B.; Wong, K. L. J. Am. Chem. Soc. 1978, 100, 1711. 46. Tang, S. C.; Koch, S.; Papaefthymiou, G. C.; Foner, S.; Frankel, R. B.; Ibers, J. Α.; Holm, R. H. J. Am. Chem. Soc. 1976, 98, 2414. 47. La Mar, G. N.; Walker (Jensen), F. A. In "The Porphyrins"; Dolphin, D., Ed.; Academic: New York, 1979; pp. 61-157. 48. Skyte, P. D., Ph.D. Dissertation, University of Oxford, 1978. 49. Scheidt, W. R., personal communication; Buchler, J. W.; Lay, K. L.; Lee, Y. J.; Scheidt, W. R. Angew. Chem. Suppl. 1982, in press. RECEIVED

for review June 2, 1981.

ACCEPTED

August 17, 1981


Electrochemical and Spectrochemical Studies of Biological Redox

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