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.,