12
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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
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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-
In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
255 12.
BOTULiNSKi E T AL.
Iron and Cobalt Porphodimethenes
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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
In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
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256
BO ILOGC IAL REDOX COMPONENTS
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
In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
257
Iron and Cobalt Porphodimethenes
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
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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 -
In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
258
BO ILOGC IAL REDOX COMPONENTS
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.
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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
In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
12.
259
ET AL.
BOTULiNSKi
Iron and Cobalt Porphodimethenes
Table II. Comparison of Metal (II/III) Oxidation-Reduction Potentials of Bisligand Octaethylporphyrin and Decaalkylporphodimethene Complexes L in Hemichrome
2
E (ox)
Salts"
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[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-
In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
BO ILOGC IAL REDOX COMPONENTS
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260
In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
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).
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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.
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
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2
Sn(OEP)(OH) ,
12.
Iron and Cobalt Porphodimethenes
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
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(
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
In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
264
BIOLOGICAL REDOX COMPONENTS
Table III. Electronic Absorption Spectra of Iron and Cobalt Porphodimethenes M ( O E P R ) X 2
Com pound
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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.
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.
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In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
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).
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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.
Iron and Cobalt Porphodimethenes
BOTULINSKI E T A L .
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
In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
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
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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.
Iron and Cobalt Porphodimethenes
269
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BOTULINSKI E T
In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
270
BIOLOGICAL REDOX COMPONENTS
ICOoO
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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
In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
12.
Iron and Cobalt
BOTULINSKI E T A L .
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
In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
272
BIOLOGICAL REDOX
COMPONENTS
en ΣΤ.
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In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
12.
BOTULINSKI E T A L .
Iron and Cobalt Porphodimethenes
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
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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
In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
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274
BIOLOGICAL REDOX COMPONENTS
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
In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
12.
Iron and Cobalt
BOTULINSKI E T A L .
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
In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
276
BIOLOGICAL REDOX COMPONENTS
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
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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.
In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.
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12. BOTULINSKI ET AL.
Iron and Cobalt Porphodimethenes
277
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for review June 2, 1981.
ACCEPTED
August 17, 1981
In Electrochemical and Spectrochemical Studies of Biological Redox Components; Kadish, K.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.