The isomerization of diacetatobis(ethylenediamine)-cobalt(III) perchlorate in dimethylsulfoxide

The isomerization of diacetatobis(ethylenediamine)-cobalt(III) perchlorate in dimethylsulfoxide

INORG. NUCL. CHEM. THE LETTERS Vol. 8, pp. 167-171, 1972. Pergamon Press. P r i n t e d in Great Britain. I S O M E R I Z A T I O N OF D I...

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INORG.

NUCL.

CHEM.

THE

LETTERS

Vol.

8,

pp. 167-171,

1972.

Pergamon

Press.

P r i n t e d in Great Britain.

I S O M E R I Z A T I O N OF D I A C E T A T O B I S ( E T H Y L E N E D I A M I N E ) COBALT(III) P E R C H L O R A T E IN D I M E T H Y L S U L F O X I D E A r t h u r W. C h e s t e r

C e n t r a l R e s e a r c h D i v i s i o n L a b o r a t o r y , Mobil R e s e a r c h D e v e l o p m e n t C o r p o r a t i o n , Princeton, N e w J e r s e y 08540, (Received 4 Novem~r

Previously acetic

the

a c i d was

as w e r e

shown

similar

ascribed

isomerization

to f o r m a t i o n

due to a s t r u c t u r a l exchange

studies

occurred, ther

clarify

complex in the bears

the

of an a c e t a t e

isomerlzatlon the

aprotlc

no s p e c i a l

increases

documented

complex

is also

in p a r t

formed,

(in a n a l o g o u s

complexes

are

are due to f o r m a t i o n free

(4,5).

to a l i m i t i n g fraction

unreactive

ligand

exchange

with

(dmso)

solvent

To fur-

ion in the r e a c t i v i t y

of Co(en) 2X2 + c o m p l e x e s

the e q u i l i b r i u m

X-

Further

briefly

was

unreactive

intramolecular.

dimethylsulfoxide

as does

solvento

ion pair,

while

now been

ion),

The r e t a r d a t i o n

ions.

that,

lyate

s y s t e m has

has b e e n w e l l

merlzation

(lyate)

(the lyate

of

investigated

to w h i c h

acetate

relationship.

The b e h a v i o r

merization

(1,2).

i t s e l f was

role of the

solvent

by acetate

to free

(3) d e m o n s t r a t e d

ions the same

solvents

reactions

similarity

1971)

of cis-[Co(en) 2 ( O A c ) 2 ] C l O 4 in

to be r e t a r d e d

solvolysis

and U.S.A.

Cr(III)

formed

and o t h e r

The o v e r a l l as the

of the cis

isomer.

complexes, The

reactive

ions.

167

both

ion pairs

is added,

A cis-solvento for the iso-

cis-

increased

aprotic

rate of iso-

anion X-

as an i n t e r m e d i a t e

(6)L

of more

value

in dmso

and trans-

rates w i t h

added

from r e l a t i v e l y

168

DIACETATOBIS (ETHYLENEDIAMINE)-COBALT (lid PERCHLORATE

spectra

The

during

the

(OAC) 2]ClO 4 in d m s o w i t h in F i g u r e s

1 and

data

in T a b l e

with

added

isomer

2.

increases

isosbestic

0.00

points

and 0.01 M

Comparison

1, i n d i c a t e

acetate

Isomerization

added

throughout

acetate, the

solvento

intermediate

the rate

is r e t a r d e d

b y acetate,

constant

is c o n s t a n t

as a c e t a t e

intermediate

NaOAc

at 7 6 . 6 ° are s h o w n

figures,

as w e l l

(a) the i s o m e r i z a t i o n

(b) the e q u i l i b r i u m

with

of 0.01 M cis-[Co(en) 2

of these

that

concentration

and

indicate

By contrast, (b')

rate

increases

of the cls

although

of

no stable

in acetic

the c i s - t r a n s

is added,

as the

(c) the e x i s t e n c e

experiment

is formed.

Vol. 8, No. 2

acid

(a')

equilibrium (c')

no s o l v e n t o

is formed.

20

i6

u U Z

1.2

n., 0 03

m

0.8 28.9

0.4 I

2412 0 .........

1 30

228

[ 25 FREQUENCY, kK

FIG.

I ~'0

.-~ 15

1

I s o m e r i z a t i o n of 0.01 M c i s - [ C o ( e n ) ~ ( O A c ) _ ] C l O ~ in d m s o at 7 6 . 6 ° w i t h no NaOAc. I~i~-ral curve Is at M o p a~ 20 kK. Scans w e r e t a k e n at 9.6 m i n i n t e r v a l s . I s o s b e s t i c points are noted.

In dmso, and a more

then,

reactive

a free acetate

ion is p r e s e n t ion p a i r

when

no acetate

is f o r m e d w i t h

is added,

acetate

ion.

Vol. g, No. 2

DIACETATOBIS (ETHYLENEDIAMINE)-COBALT (lid PERCHLORATE

The behavior is "normal"

169

for this type of complex in an aprotic

solvent,

TABLE 1 Isomerization of 0.01 M cis-rCo(en) 2(OAc)23C104 in dmso--at----76.6° [NaOAc~,

0.0

M

104kobs,

sec -I

% cis

at e q u i l i b r i u m

i .4

29

0.01

13.

34

0.05

19.

42

although no solvento species if formed; the bulkiness of acetato ligands relative to halide ligands may be a factor in preventing formation of the solvento complex. 2.0

1.6

,~ 1.2

o

0.8

0.4

0 30

25 FREQUENCY,kK

FIG.

a

20

15

2

Isomerization of 0.01 M cis-[Co(en)9(OAc)?]ClO 4 in dmso 76.6 ° with 0.01 M NaOAc. Intltal curv~ is a~ top at 20 kK. were taken at 4.8 min intervals.

Scans

DIACETATOBIS (ETHYLENEDIAMINE)-COBALT (III) PERCHLORATE

170

Comparison acid

(1-3)

same

reactivity

the

free

pair the

data with

s h o w t h a t the a c e t a t e

acetate ions

acid,

(lyate)

the same

verifying ion p a i r

in o t h e r

in acetic

reactivity

that,

data

in d m s o has

ion p a i r

acid

in acetic roughly

the

acid,

and

as the a c e t a t e

ion

as p r e v i o u s l y

in acetic

solvents

previous

ion pair

as the p e r c h l o r a t e

ion in dmso has

in acetic

to free

of the p r e s e n t

Vol. 8, No. 2

contended

(1-3),

is s t r u c t u r a l l y

in that the a n i o n

charge

similar

is d_~e-

localized.

Investigation trans

isomer

reaction The

species

ylelded

occurred

reaction

of the

the u n e x p e c t e d

after

sequence

is p r o d u c e d

isomerization

the

initial

is s h o w n

with

starting

result

that

a third,

isomerization

in the s p e c t r a

relatively

w i t h the pure

intense

to e q u i l i b r i u m .

in Figure

maxima

slower

3.

A new

at 20.3 and

2.0

1.6

o

,~ 0 . 8

0

I 30

25

20

15

FREQUENCY, k K

FIG.

3

R e a c t i o n of 0.01 M t r a n s - r C o ( e n ) 9 ( O A c ) 9 ] C I O 4 w i t h 0.05 M NaOAc at 76.6 ° . R e a c t i o n s - - ~ n c e p r o c e e d s f~om b o t t o m to top~ w i t h scans taken at 4 . 8 m i n intervals. E x p e c t e d i s o s b e s t l c points are i n d i c a t e d

Vol. 8, No. 2

27.6 kK.

DIACETATOBIS (ETHYLENEDIAMINE)-COBALT (!11) PERCHLORATE

171

The new reaction I, which occurs at approximately i0~

the rate of the isomerization, by acetate ion.

is increased both in rate and extent

The direct dependence on acetate concentration

is inconsistent with solvolysis, A reasonable hypothesis

as acetate would be liberated.

involves deprotonation of an ethylenediamine

llgand by the basic acetate ion:

trans-[Co(en) 2(OAc)2 ]+

+

OAC-

~

[co(en) (en-H) (OAc) 2] + HOAc

Such a reaction is unusual for Co(III), but has been observed for Co(en) 3

3+

with potassium amide in liq. NH 3 (7).

The observed

spectrum may not be that of the deprotonated species, but of its decomposition product(s). mixture retards the rate,

Addition of acetic acid to the reaction further supporting the deprotonation

hypothesis.

REFERENCES i.

A. W. CHESTER,

Inorg. Chem.,

8, 1954

(1969).

2.

A. W. CHESTER,

Ibid.,

9, 1743

(1970).

3.

A. W. CHESTER,

Ibld.,

9, 1746

(1970).

4.

D. W. WATTS, Rec. Chem. Progress 29, 131 (1968).

5.

N. L. TOBE and D. W. WATTS,

6.

D. A. PALMER and D. W. WATTS, Aust. J. Chem.,

7.

G. W. WATT, P. W. ALEXANDER, 89, 6483 (1967).

I.

This reaction was not observed when starting with pure ci___ss although it probably occurs; the blurring of the high frequency Isosbestlc point in Fig. 2 may be a result of this reaction.

(Kresge-Hooper Sci. Library),

J. Chem. Soc.,

1964,

2991.

21, 2895

(1968).

and B. S. MANHAS, J. Am. Chem. Soc.,