Inorganic Reaction MechanismsâPast, Present and Future

19 Inorganic Reaction Mechanisms—Past, Present

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and Future R A L P H G. WILKINS New Mexico State University, Department of Chemistry, Las Graces, N M 88003

Studies of inorganic reaction kinetics con tinue to develop in sophistication and scope. A number of important issues and areas of study which have not been emphasized in previous papers in this volume are singled out for discussion. Of particular importance is the application of techniques for the generation and detection of short-lived transient species of mechanistic in terest. A variety of combinations of laser flash photolysis or pulse radiolysis with resonance Ra man, epr, rapid scan spectrophotometry, etc., give hope for the characterization of reactive inter mediates of chemical significance. The further study of some slower substitution reactions has continued to reveal new reaction pathways and has demonstrated some weaknesses in established mecha nistic dogmas. Studies of complexes containing ligands designed to play a specific role are bound to reveal new and interesting mechanistic prob lems. Other classes of reactions continue to be elucidated. It remains surprising how little we understand about the reactivity of so simple a molecule as O . 2

Even a c u r s o r y examination o f t h e l a s t few issues o f a j o u r n a l such as " I n o r g a n i c Chemistry" w i l l convince t h e reader of t h e e x c i t i n g s t a t e o f t h e a r t o f i n o r g a n i c r e a c t i o n k i n e t i c s , both i n t h e s o p h i s t i c a t i o n o f the systems being examined and o f the methods being used t o measure r a t e s . I n t h i s ac count, some areas o f c u r r e n t and f u t u r e i n t e r e s t w i l l be s i n g l e d out, emphasizing those which have n o t been covered a t the Con ference . A s u b s t a n t i a l number o f r e a c t i o n s and processes i n v o l v i n g inorganic and b i o i n o r g a n i c molecules are r a p i d o r extremely 1

1

0097-6156/82/0198-0453$06.00/0 © 1982 American Chemical Society Rorabacher and Endicott; Mechanistic Aspects of Inorganic Reactions ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

MECHANISTIC


454

ASPECTS OF INORGANIC REACTIONS

r a p i d a t room temperature and r e q u i r e s p e c i a l i z e d techniques f o r t h e i r measurement ( 1 ) . Some t h a t a r e c u r r e n t l y a v a i l a b l e and the r e a c t i o n time range o f t h e i r u t i l i t y are shown i n F i g u r e 1. I t can be seen t h a t we a r e now down t o picosecond o b s e r v a t i o n times, which i s g e n e r a l l y the l i m i t o f i n t e r e s t t o the chemist. An e q u a l l y important development, I f e e l , i s t h e i n c r e a s i n g v a r i e t y o f m o n i t o r i n g methods which can now be l i n k e d t o the v e r s a t i l e flow and (simple) r e l a x a t i o n techniques. I t i s i n a p p r o p r i a t e t o l i s t here a l l t h e recent developments, b u t im p o r t a n t developments have i n v o l v e d the l i n k i n g o f flow methods to f l u o r e s c e n t and CD m o n i t o r i n g , t o c a l o r i m e t r y , t o NMR ( 2 ; 3+ s u c c e s s i v e replacement o f Al(DMSO)^ by the three donor n i t r o gens o f t e r p y r i d i n e , can be unambiguously viewed,^ from the r e l e a s e o f coordinated DMSO, u s i n g stopped-flow F.T. H NMR) and o f p u l s e r a d i o l y s i s combined w i t h EPR, Resonance Raman (3) o r r a p i d scan spectrophotometry ( 4 ) ; t h e s t r e a k camera recordings o f t r a n s i e n t s p e c t r a i n 200 ps i n t e r v a l s demonstrated two d i s t i n c t t r a n s i e n t s i n a p u l s e r a d i o l y t i c study o f the OH r a d i c a l reac t i o n with Cr(en) (SCH C00) ). Important i n f o r m a t i o n on the s t r u c t u r e and p r o p e r t i e s o f t r a n s i e n t s can now be o b t a i n e d , and t h i s approach i s l i k e l y t o be e x p l o i t e d f o r some time t o come. There i s a l s o the p o s s i b i l i t y o f u s i n g lowered temperatures t o study r e a c t i o n s , w i t h the advantages o f slower r a t e s and e a s i e r c h a r a c t e r i z a t i o n o f i n t e r m e d i a t e s . These were recognized e a r l y by a c o o r d i n a t i o n chemist (5,6) b u t e x p l o i t e d more r e c e n t l y by biochemists (7,8). +

2

2

Rapid S u b s t i t u t i o n Processes As we have seen, an area o f major importance and o f con s i d e r a b l e i n t e r e s t i s t h a t o f s u b s t i t u t i o n r e a c t i o n s o f metal complexes i n aqueous, nonaqueous and organized assemblies (par t i c u l a r l y m i c e l l a r systems). The accumulation o f a g r e a t d e a l of data on s u b s t i t u t i o n i n n i c k e l ( I I ) and c o b a l t ( I I ) i n s o l u t i o n (9) has f a i l e d t o shake t h e d i s s o c i a t i v e mechanism f o r s u b s t i t u t i o n and f o r these the statement "The mechanisms o f formation r e a c t i o n s o f s o l v a t e d metal c a t i o n s have a l s o been s e t t l e d , t h e m a j o r i t y t a k i n g p l a c e by the E i g e n - W i l k i n s interchange mechanism or by understandable v a r i a n t s o f i t " (10) seems a p p r o p r i a t e . Required, however, a r e more data f o r s u b s t i t u t i o n i n the other l a b i l e b i v a l e n t metal i o n s . F o r example, AV^ values f o r water 2+ 2+ exchange o f M n ^ and F e ^ suggest a degree o f a s s o c i a t i v e char a c t e r , which may show up as v a r i a b l e r a t e constants f o r l i g a t i o n (11,12). The p r a c t i c a l d i f f i c u l t i e s i n measuring these r a t e s may be circumvented by producing the b i v a l e n t complexes extreme l y r a p i d l y i n s i t u by t h e r e d u c t i o n o f t h e corresponding t e r -

Rorabacher and Endicott; Mechanistic Aspects of Inorganic Reactions ACS Symposium Series; American Chemical Society: Washington, DC, 1982.


WILKINS

Overview of Inorganic Reaction

FLOW

I

TEMPERATURE JUMP

I

ELECTRIC FIELD

UJ

σ

I

ULTRASONICS

I

LASER PHOTOLYSIS

ο

PULSE RADIOLYSIS NMR LINE BROADENING

I

I

EPR LINE BROADENING ELECTROCHEMICAL I

icr SECONDS 5

Figure 1.

455

I

PRESSURE JUMP

UJ

Mechanisms

I

I I 10r 10

Upper limit of measurable relaxation times for various techniques.


MECHANISTIC ASPECTS OF


456

INORGANIC REACTIONS

v a l e n t complexes, using pulse r a d i o l y s i s (13) or l a s e r p h o t o l y s i s (14) methods. The subsequent d i s s o c i a t i o n of the b i v a l e n t complex ( i n the ps to ms region) can be monitored by conduct i v i t y methods. Combination of the d i s s o c i a t i o n rate constants with s t a b i l i t y constants w i l l give the d e s i r e d formation r a t e constants. T r a n s i e n t Methods. The method of r a p i d generation of t r a n s i e n t s (even p o s s i b l e i n picoseconds), and subsequent i n s i t u examination of some property of the t r a n s i e n t , or of u t i l i z i n g i t s r e a c t i v i t y , has been a continuing theme i n t h i s Conference. I t w i l l continue to be e x p l o i t e d as f a c i l i t i e s f o r , and u t i l i t y o f , the approach becomes even more recognized. For example, a wide v a r i e t y of metal ions i n unusual o x i d a t i o n s t a t e s have been generated by p u l s e r a d i o l y s i s methods, and the rates of t h e i r subsequent r e a c t i o n s ( d i s p r o p o r t i o n a t i o n , r e a c t i o n with added s u b s t r a t e , etc.) determined (15,16). An i n t e r e s t i n g example of t h i s i s i n the use of the dye p y r i d i n e - 2 - a z o - p - d i m e t h y l a n i l i n e (PAD) to study metal complexing. The b i n d i n g of t h i s dye to p r o t e i n s , mediated by metal i o n s , had been examined i n the e a r l y 50' s (17). The value of PAD to examine the rates of r e a c t i o n with a number of metal ions was recognized i n some of the e a r l i e s t temperature-jump experiments (18). Most r e c e n t l y , the 2+ photochemical p e r t u r b a t i o n of the N i -PAD system has been studied (19). One of the r e l a x a t i o n times observed, f o l l o w i n g photochemical p e r t u r b a t i o n of the system, can be assigned to the r i n g c l o s u r e step (k^ç) of the unidentate complex (N-N = PAD): (H 0) Ni 2

k + J ) -*

2 +

1

6

(H 0) Ni 2

2 +

5

—Nil

+ H0 2

k-, f C

( H ^ N i

2

^ )

(unidentate complex)

+

H0 2

The value of k^^ i n d i c a t e s , as had been assumed, t h a t formation of the c h e l a t e i s mainly c o n t r o l l e d by the k^ step. Information on k^ cannot be e a s i l y obtained from temperature-jump measurements, s i n c e at e q u i l i b r i u m the c o n c e n t r a t i o n of the unidentate complex i s q u i t e s m a l l . These approaches cannot help but give i n s i g h t i n t o the d e t a i l s of c h e l a t i o n . c

S u b s t i t u t i o n i n I n e r t Complexes Simple methods can, and need t o , s t i l l be employed, however. The e f f e c t s of added ions on the rates of complex i o n r e a c t i o n s , discussed by Wahl at t h i s meeting, need to be f u r t h e r explored. In the s u b s t i t u t i o n area, the observations of i o n p a i r formation concommitant w i t h the s u b s t i t u t i o n r e a c t i o n s of M(NH ) OH 3

5

3+ 2

(M

=

Co,

Rh

and

Cr)

have

been

challenged


(20).

19.

WILKINS


457

Mechanisms

Even t h a t most sacred of mechanisms, the SÎCB f o r base h y d r o l y s i s , e s t a b l i s h e d a f t e r a long and f r u i t f u l r i v a l r y ( 2 1 ) , i s under some a t t a c k , a t l e a s t as a u n i v e r s a l mechanism (22-24). A concerted E2 mechanism i s suggested f o r the base h y d r o l y s i s of and

+

cis-Co(cyclen)Cl . 2

nously Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 21, 2016 | http://pubs.acs.org Publication Date: September 27, 1982 | doi: 10.1021/bk-1982-0198.ch019

Proton t r a n s f e r from a coordinated

N-H

cleavage of a Co-Cl bond are considered t o occur

synchro3+ i n t e r m e d i a t e Co(NH^)-

(24).

I s there a 5-coordinated 2+ i n induced r e a c t i o n s of Co(NH^)^X , and i f so what form does it take i n order t o e x p l a i n p u z z l i n g c o m p e t i t i o n r e s u l t s (25,26)? C l e a r l y more experiments are needed w i t h a wider range and type of r e a c t a n t s . These may be d i f f i c u l t t o conceive, c a r r y out and i n t e r p r e t . One s u b j e c t w i t h p o t e n t i a l r a m i f i c a t i o n s i n the m e t a l l o p r o t e i n area i s t h a t r e l a t e d t o the remark able enhancement of the l a b i l i t y of the M-OH^ bond by M-coordinated l i g a n d s . Coordinated H 0 i n F e ( I I I ) p o r p h y r i n complexes 4 5 i s some 10 -10 times more l a b i l e than t h a t i n the aqua ted i o n (27). Very s u r p r i s i n g , and needing more study, i s the e f f e c t of coordinated EDTA on the enhanced r a t e s of s u b s t i t u t i o n of M(EDTA)H 0" compared w i t h M ( N H ) H 0 f o r M = C r ( I I I ) , Ru(II) and O s ( I I I ) but not C o ( I I I ) nor R h ( I I I ) ! (28-30). Sometimes there are unexpected rewards f o r c a r r y i n g out a p p a r e n t l y r o u t i n e 3+ s t u d i e s . The a c i d h y d r o l y s i s of Ru(NH ) NH CH C00C H behaves q u i t e d i f f e r e n t l y from t h a t of the C o ( I I I ) analog, i n t h a t an unusual l i n k a g e isomerism i s observed (31). This i s a l e s s o n t h a t we should take t o h e a r t , f o r i t t e l l s us t h a t we are f a r away from a complete understanding of many "simple" i n o r g a n i c processes. o

3 +

2

3

5

2

3

5

2

2

2

5

Metallo-Enzyme Models There have been some b e a u t i f u l l i g a n d syntheses, designed to form complexes w i t h a s p e c i f i c purpose, o f t e n t o simulate n a t u r a l l y o c c u r r i n g systems. S t r a i g h t to mind, of course, comes the i r o n complexes which model the behavior of the oxygenc a r r y i n g g l o b i n s (32) and the i r o n - s u l f u r p r o t e i n s (33). Two b i n u c l e a r c o p p e r ( I I ) complexes have been d e s c r i b e d , one w i t h (34), and one without (35) b r i d g i n g between the coppers. These are r e v e r s i b l y reduced t o the corresponding b i n u c l e a r copper(I) complexes by two monoelectronic steps which are simultaneous. I t i s c e r t a i n t h a t these types of s t u d i e s w i l l continue and t h a t i n v e s t i g a t i o n s of the dynamic aspects of these model complexes are l i k e l y t o f o l l o w those of the s y n t h e t i c and thermodynamic. This i s the u s u a l sequence, but too o f t e n there i s a c o n s i d e r able time gap between the thermodynamic and k i n e t i c s s t u d i e s .


MECHANISTIC ASPECTS OF INORGANIC REACTIONS

458

Rapid Conformational Changes and E l e c t r o n i c Spin R e l a x a t i o n One cannot help b u t be impressed by t h e e x p l o r a t i o n s i n the p a s t decade o f t h e r a t e s o f r a p i d changes i n conformation and i n c o o r d i n a t i o n number o f metal complexes (36-42). F o r example, e q u i l i b r i a between i n c l u s i v e (metal i o n completely enclosed) and e x c l u s i v e (metal i o n only p a r t l y surrounded by organic l i g a n d )


+

complexes o f C s w i t h t h e cryptand 2:2:2 have been examined by Cs-133 NMR (42). Some o f these processes are shown i n Table I . The r a t e s o f i n t e r s y s t e m - c r o s s i n g processes i n c e r t a i n C o ( I I ) , F e ( I I ) and F e ( I I I ) complexes have a l s o been measured (43-46) (Table I I ) . R e c e n t l y , t h e f i r s t h i g h s p i n £ low s p i n e q u i l i b r i a i n a C o ( I I I ) and i n a M n ( I I I ) complex have been c h a r a c t e r i z e d (47,48) and r a t e measurements on these may be a n t i c i p a t e d . These r a p i d processes r e q u i r e t h e s p e c i a l i z e d techniques r e f e r r e d t o i n F i g u r e 1. A s t a r t has been made by t h e o r e t i c a l chemists on t h e d e s c r i p t i o n and c a l c u l a t i o n o f t h e r a t e s i n Table I I (49). I t i s a f a i r guess t h a t the examination o f such fundamental processes, important i n biological systems (46,49,50), w i l l be continued. What i s t h e s p i n - e q u i l i b r i u m f u n c t i o n ( i f any) i n the i r o n p r o t e i n s ? E l e c t r o n T r a n s f e r Reactions E l e c t r o n t r a n s f e r r e a c t i o n s and theory have been h i g h l i g h t e d i n t h i s Conference. I t i s apparent t h a t d e t a i l e d char a c t e r i z a t i o n o f the e l e c t r o n t r a n f e r process both i n t h e ground and e x c i t e d s t a t e s w i l l be continued. The e m p i r i c a l and theo r e t i c a l c o r r e l a t i o n s o f redox r a t e parameters w i t h known proper t i e s o f t h e donor and acceptor c e n t e r s , t h e i n t e r s i t e d i s t a n c e f o r e l e c t r o n t r a v e l , and the nature o f the medium (51) w i l l con t i n u e t o be amassed. Such r e s u l t s have been, and promise t o be, important i n g r e d i e n t s f o r success w i t h b i o i n o r g a n i c systems (52-55). Photochemistry Some f u t u r e d i r e c t i o n s i n i n o r g a n i c photochemistry have been o u t l i n e d by Adamson ( 5 6 ) . A p e s s i m i s t i c p i c t u r e o f t h e p r a c t i c a l uses o f s o l a r energy conversion systems i s p a i n t e d , but a rosy view o f t h e academic f u t u r e o f t h e s u b j e c t i s h e l d . I t i s a n t i c i p a t e d t h a t there w i l l be f u r t h e r examination o f thermally e q u i l i b r a t e d excited (thexi) s t a t e s — t h e i r l i f e t i m e s , and s p e c t r o s c o p i c and s t r u c t u r a l p r o p e r t i e s — a n d an e x t e n s i o n o f present e f f o r t s t o o r g a n o m e t a l l i c s and m e t a l l o p r o t e i n s i s a l s o envisaged ( 5 6 ) . The i n t e r p r e t a t i o n o f s p e c t r o s c o p i c data from e x c i t e d s t a t e s w i l l continue t o be c o n t r o v e r s i a l and r e q u i r e f u t u r e experimentation (57).



WILKINS

19.

Table I .

459

Mechanisms

Rate Constants f o r Some Rapid Stereochemical Changes i n Metal Complexes. k ,s

System

C o n d i t i o n s Technique

k ,s

f

r

Ref.

Planar J tetrahedral Ρ

Ψ

2

4.5xl0

Cl Ni Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 21, 2016 | http://pubs.acs.org Publication Date: September 27, 1982 | doi: 10.1021/bk-1982-0198.ch019

2

5

6xl0

5

Photochemi c a l per turbation

36

20°,H 0

Nanosecond l a s e r photo lysis

38

25°,H 0

NMR and Tjump

40

25°,H 0

Laser Raman T-jump

39

25°,H 0

Ultrasonic absorption

41

23°,CH CN 3

Square pyramidal J planar Ni(L)H 0 l Ni(L) + H0

1.5xl0

2

7

4.5xl0

6

2

2

L = 2,2,4-trimethyl10,ll-benzo-l,5diaza-8,13-dithiacyclopentadeca-1, 10-diene Octahedral J P l a n a r Ni(L)(H 0) 2

2

*

Ni(L)H 0 j NiL + H 0 k r L = [12]aneN Z

9

Z

9

3.2xl0

4

5

2.5xl0

L = α,β,γ,δ-tetra

2

5

9

(4-N-Mepyridyl) porphine 5 J 6 coordinated EDTA 2

Co(EDTA) " + H 0 + 2

2

Co(EDTA)H 0 " 2

3xlO

c

9xlO

b

2



460


Table I I . Rate Constants f o r Intersystem-Crossing Processes i n C o ( I I ) , F e ( I I ) and F e ( I I I ) Complexes. ν

System

2

E(ls)Co(II) J

4

T(hs)Co(II) CH=NΝ

NHCH

Co CH=N

s' f'

1

k ,s r'

- 1

Conditions Technique Ref.

3

1/2

3.2xl0

6

9.1xl0

6

25°,CH CN/ Laser Raman TCH 0H Jump

43

20°,H 0

Laser Raman Tjump

44

25°,H 0

U l t r a s o n i c 45 absorption and Laser Raman T-jump

1°,H 0

Laser Raman 46 T-jump

3

3

NHCBL

^(lsiFeClI) J 5

A(hs)Fe(II)

Fe(6-Mepy)(py) 9

4xl0

D

8xl0

c

o

tren 2

T(ls)Fe(III) J

6

A(hs)Fe(III)

Fe a c a c ^ t r i e n

1.6x10* 3.2x10*

metmyoglobin hydroxide

3.9xl0

7

2.8xl0

7

2

2


19.

WILKINS


Mechanisms

461

Oxyions


18 The measurement o f t h e l a b i l i t y o f oxyions from 0 ex change s t u d i e s has not been p a r t i c u l a r l y p o p u l a r , both because of the complexity o f the systems ( s e e , f o r example, t h e com p l e x i t y o f i s o t o p i c oxygen exchange between HÔ and V^Ô^g^ and the pH e f f e c t (58) and the tediousness o f the techniques ( t h e 18 r a p i d exchange ( t - ^ ' msec-secs) o f 0 between HÔ and 10^ needs t o be s t u d i e d by m u l t i - m i x e r , chemical quenching t e c h niques ( 5 9 ) ) . The burden o f measuring the extent o f exchange may be r e l i e v e d i n c e r t a i n i n s t a n c e s by i n s i t u examination o f NMR s p e c t r a , u s i n g i s o t o p e s h i f t s ( 6 0 ) ) . However, these a r e funda m e n t a l l y important r e a c t i o n s and steady progress i n r a t e meas urements can be a n t i c i p a t e d . A l s o l i k e l y t o occur i s i n c r e a s e d a t t e n t i o n t o other aspects o f the h e t e r o p o l y a n i o n f i e l d , such as l a r g e anion i n t e r c o n v e r s i o n s ( 6 1 ) , complexing o f metal ions by 28oxyanions, e.g., A S ^ W ^ O ^ Q l e a d i n g , i n t h i s case, t o a l l o s t e r i c behavior (62) and r e d u c t i o n o f heteropolyanions w i t h p r o d u c t i o n o f both f i r m l y trapped and even d i s t r i b u t i o n o f t h e added e l e c t r o n s (63,64). The mechanistic aspects o f these c l u s t e r molecules have been n e g l e c t e d , b u t they occur i n l a r g e v a r i e t i e s and t h e i r behavior i s r e l e v a n t t o t h a t o f s o l i d - s t a t e lattices. Work on these might represent the major i n c r e a s e d i n t e r e s t o f the 8 0 s . f

Volumes o f A c t i v a t i o n and Other Areas The values o f the volumes o f a c t i v a t i o n o f i n o r g a n i c pro cesses a r e becoming i n c r e a s i n g l y u s e f u l i n assignment o f mechan ism as more and more data accumulate (65,66). However, ambig u i t i e s i n i n t e r p r e t a t i o n s t i l l e x i s t (67-69), p a r t i c u l a r l y i n estimating

the c o n t r i b u t i o n

of solvation

d i s t i n c t from mechanistic e f f e c t s ( A V ^

i n t r

effects

) (70).

(AV^

as

Other c u r r e n t

controversies are also l i k e l y t o lead t o future studies. I n cluded i n these are the mechanisms o f g e o m e t r i c a l isomerism o f p l a n a r complexes (Π,72) (a number o f d i s t i n c t types have been promoted by v a r i o u s i n v e s t i g a t o r s ; 7 3 ) , the importance o f cov a l e n t h y d r a t i o n i n c e r t a i n r e a c t i o n s o f complex ions o f the b i p y r i d y l types (74,75), t h e i n t r i n s i c r e a c t i v i t y o f the z w i t t e r i o n l i g a n d i n complex formation (76-78), and the nature o f the intermediate i n induced r e a c t i o n s o f c o b a l t ( I I I ) complexes (22,23,25,26).


462


Oxygen Chemistry L e s t we become too complacent i n our assessment o f the marked progress t h a t has been made i n understanding i n o r g a n i c r e a c t i o n mechanisms, we should consider the simple and v e r y important redox systems: °2

+

e

E

" t °2~ +

0 " + e" + 2 H J H 0 Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 21, 2016 | http://pubs.acs.org Publication Date: September 27, 1982 | doi: 10.1021/bk-1982-0198.ch019

2

2

7

=

"°-

3

3

v

o

l

t

s

E° = +0.87 v o l t s

2

The thermodynamics are f a i r l y w e l l c h a r a c t e r i z e d (79,80) b u t , as so often happens i n c h e m i s t r y , the r a t e aspects are much l e s s w e l l understood. Only estimates from the a p p l i c a t i o n o f Marcus theory

for

the

0 , 2

0

electron

2

transfer

are

available

(81).

Although the f e a s i b i l i t y o f r e a c t i o n 1 (an important component of the Haber-Weiss mechanism f o r F e ( I I ) - m e d i a t e d decomposition of H 0 ) 2

2

°2

+

H

2 ° 2 * °2

+

0 H

~

+

0

H

(

has been questioned ( 7 9 , 8 0 , 8 2 ) , the r a t e constant has been termined and i t s low value has e l i m i n a t e d r e a c t i o n 1 as a t e n t i a l OH r a d i c a l source i n b i o l o g i c a l systems ( 8 3 ) . Given the i n g e n u i t y o f the i n o r g a n i c k i n e t i c i s t and a r r a y of measuring equipment now a v a i l a b l e , answers to these other problems w i l l s u r e l y emerge d u r i n g the remainder o f century.

1

)

de po the and the

Literature Cited

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19.

WILKINS

Overview of Inorganic Reaction Mechanisms

463

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464


39. Pasternack, R. F.; Sutin, N.; Turner, D. H. J. Am. Chem. Soc. 1976, 98, 1908. 40. Coates, J. H.; Hadi, D. Α.; Lincoln, S. F.; Dodgen, H. W.; Hunt, J. P. Inorg. Chem. 1981, 20, 707. 41. Harada, S.; Funaki, Y.; Yasunaga, T. J. Am. Chem. Soc. 1980, 102, 136. 42. Popov, A. I. Pure and Appl. Chem. 1979, 51, 101. 43. Simmons, M. G.; Wilson, L. J. Inorg. Chem. 1977, 16, 126. 44. Hoselton, Μ. Α.; Drago, R. S.; Wilson, L. J.; Sutin, N. J. Am. Chem. Soc. 1976, 98, 6967. 45. Binstead, R. Α.; Beattie, J. K.; Dewey, T. G.; Turner, D. H. J. Am. Chem. Soc. 1980, 102, 6442. 46. Dose, Ε. V.; Tweedle, M. F.; Wilson, L. J.; Sutin, N. J. Am. Chem. Soc. 1977, 99, 3886. 47. Gutlich, P.; McGarvey, B. R.; Kläui, W. Inorg. Chem. 1980, 19, 3704. 48. Sim, P. G.; Sinn, E. J. Am. Chem. Soc. 1981, 103, 241. 49. Buhks, E.; Navon, G.; Bixon, M.; Jortner, J. J. Am. Chem. Soc. 1980, 102, 2918. 50. Perutz, M. F.; Sanders, J. K. M.; Chenery, D. H.; Noble, R. W.; Pennelly, R. R.; Fung, L. W. M.; Ho, C.; Giannini, I.; Pörschke, D.; Winkler, H. Biochemistry 1978, 17, 3640. 51. Cannon, R. D. "Electron Transfer Reactions," Butterworths, London, 1980. 52. "Tunneling in Biological Systems," Chance, B.; deVault, D. C.; Frauenfelder, H.; Marcus, R. Α.; Schieffer, J. R.; Sutin, N., Eds., Academic Press, New York, 1979. 53. Armstrong, F. Α.; Henderson, R. Α.; Sykes, A. G. J. Am. Chem. Soc. 1980, 102, 6545. 54. Scott, R. Α.; Gray, Η. B.; J. Am Chem. Soc. 1980, 102, 3219. 55. Mauk, A. G.; Scott, R. Α.; Gray, H. B. J. Am. Chem. Soc. 1980, 102, 4360. 56. Adamson, A. W. Pure Appl. Chem. 1979, 51, 313. 57. Shipley, N. S.; Linck, R. G. J. Phys. Chem. 1980, 84, 2490. 58. Murmann, R. K.; Giese, K. C. Inorg. Chem. 1978, 17, 1160. 59. von Felten, H.; Gamsjäger, H.; Baertschi, P. J. Chem. Soc., Dalton 1976, 1683. 60. Risley, J. M.; Van Etten, R. L. J. Am. Chem. Soc. 1979, 101, 252. 61. Masters, A. F.; Gheller, S. F.; Brownlee, R. T. C.; O'Con nor, M. J.; Wedd, A. G. Inorg. Chem. 1980, 19, 3866. 62. Robert, F.; Leyrie, M.; Hervé, G.; Tézé, Α.; Jeannin, Y. Inorg.Chem. 1980, 19, 1746. 63. Kazansky, L. P.; Fedotov, M. A. Chem. Commun. 1980, 644. 64. Prados, R.; Pope, M. T. Inorg. Chem. 1976, 15, 2547. 65. Lawrance, G. Α.; Stranks, D. R. Accts. Chem. Res. 1979, 12, 403. 66. Palmer, D. Α.; Kelm, H. Coordn. Chem. Revs. 1981, 36, 89.


19.

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67. 68. 69. 70.

465

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