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Honors Theses Student Work
6-1976
The preparation and kinetic studies of two stericallyhindered gold (III) complexesJames Forrest StevensUnion College - Schenectady, NY
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Recommended CitationStevens, James Forrest, "The preparation and kinetic studies of two sterically hindered gold (III) complexes" (1976). Honors Theses.2253.https://digitalworks.union.edu/theses/2253
THE PREPARATION AND KINETIC STUDIES - OF TWO STERICALLY HINDERED
GOLD(III) COMPLEXES
by JAMES F~VENS ft}, 5, t'1J fo Ill 1
This thesis is submitted in partial fulfillment of
the requirements for the degree of Master of Science in
Chemistry.
UNION COLLEGE
Schenectady, New York
July, 1975
Approved. _ _,.__('_~ L~uL~~~I_:_. -..;::;.U~~:....::..:::...'-=----- Approved~~.::....::;-=' _..._,CY)?'--+'~T-~~e-s~~=s~(/}1~A=~-v~i-s-o-r~~~~~~~~~~
Committee:ldn Graduate Studies
Date __ -7fg~fA/?1L~---+--'/ 1-+-Z-=-l _
This thesis is gratefully dedicated to my wonderful
wife, Rosemary, whose continual encouragement and under-
standing made this work possible.
ii
ACKNOWLEDGMENT
I heartfully thank my Research Advisor, Professor
Charles F. Weick, for his suggesting of this topic and
for his many evening and Saturday hours given in guidance,
assistance and encouragement towards its completion.
iii
TABLE OF CONTENTS
Acknowledgment
List of Figures
List of Tables
List of Abbreviations
Abstract
Introduction
Experimental
Materials
Analyses
Preparation of Complexes
Kinetic Studies
Results and Discussions
References and Bibliography
iii
v
vi
vii
ix
1
5
5
5
7
10
23
31
iv
LIST OF FIGURES
Figure Page
1.
2.
Absorbance of Auc14 vs Au Concentration at 313 nm
Absorption ~ectra of the ~romo and Chloro Species of4LAu(Me5dien)~ +at Concentrations of 4 x 10- M 13
6
3. Absoprtion S;>ectra of the Bromo and Chloro Species o~4LAu(MeEt4dien)~ 2+ at Concentrations of 4 x 10 M 14
4. A Typical Single Wavelength Scan of the Reaction of [Au(Me5dien)cg 2+ with 0.1 M Br
A Typical Scan for2ihe Reaction of C Au(MeEt4dien) c:g with 0. 05 M Br-
Graph of kb for t2~ Reaction of [ Au(MeEt4H:t~n)Cij with 0. 05 M Br-
Observed Rate Constant for [Au(Me5dien) qJ 2+
versus Bromide Concentration@ T - 25oc
Observed Rate Constant for [Au(MeEt4dien)C~ versus Bromide Concentration@ T = 25oc 21
16
5. 18
6. 19
7. 20
8. 2+
9. Observed Rate Constant for [Au(MeEt4dien)C1] 2+
versus Bromide Concentration@ T = 25°C and at wavelength 380 nm 22
10. R~action of [Au(M~Et4dien)CU 2+ with 0.05 M Br with respect to time 29
v
LIST OF TABLES
Table
I Pseudo First Order Rate Constants at 25°C
II First Order and Second Order Rate Constants
Page
2L~
25
vi
LIST OF ABBREVIATIONS
The following abbreviations will be used throughout
the text of this paper:
Abbreviation Name & Formula
amine any <lien or substituted <lien
amine-H the conjugate base of amine
dien Diethylenetriamine
dien-H
NH2CH2CH2NHCH2CH2NH2
the conjugate base of dien
NH2CH2CH2NCH2cH2NH2
1,1' ,7,7' - tetraethyldiethylene-
triamine
Et2dien
(C2H5)2NcH2cH2NHCH2cH2N(C2H5)2
the conjugate base of Et4dien
( C2H 5) 2NCH2CH2NCH2CH2N ( c2H5) 2 1,1'-diethydiethylenetriamine
Me4dien
(C2H5)2NCH2cH2NHCH2cH2NH2
the conjugate base of Et2dien
(C2H5) 2NCH2CH2NCH2CH2NH2-
l, l' , 7, 7' - tetramethyldiethylene-
triamine
Ma4dien-R
(CH3)2NcH2cH2NHCH2CH2N(CH3)2
the conjugate hase of Me4die.n
(CH) NCH0CH0NCH0CH N(CH3)0 3 2 e: Z.. L 2 IL
vii
Me2dien 1,1'-dimethyldiethylenetriamine
Me5dien
(CH3)2NCH2CH2NHCH2CH2NH2
the conjugate base of Me2dien
(CH3)zNCH2CH2NCHzCH2NH2
1,1' ,4,7,7'-pentamethyldiethylene-
triamine
(CH3)2NCH2CH2NCH3CH2CH2N(CH3)2
4-methyl-1,1' ,7,7'-tetraethyl-
diethylenetriamine
viii
ABSTRACT
Previous studies indicate substitution of bromide ion
for chloride ion in [Au(Et4dien~H)c.i] +occurs at a rate
almost independent of the bromide ion concentration, while
similar reactions with [Au(dien-H)Cl]+, [Au(Me2dien-H)c!]+
and [~u(Me4dien-H)c~+ show rates dependent on bromide ion
concentration as usually encountered for square planar
complexes. There is retardation of the reaction by steric
and electronic effects with increased N-alkyl substitution
of the triamine. It has also been postulated that substitu
tion of [Au(Et2dien-H)cJ]+ proceeds via a ring-opening
mechanism.
The purpose of this research was to study further the
effect of steric hindrance on rates of substitution of two
additional gold(III) complexes. The complexes of Me5dien
and MeEt4dien with gold(III) were prepared and investigated,
As observed with other less methyl substituted gold(III)
dien complexes the substitution reaction of [Au(Me5dien)C:£j 2+
with bromide ion is dependent on the bromide ion concentra
tion. The results of the reaction rate studies on
[Au(MeEt4dien)CY Z+ with bromide ion can most easily be
rationalized in terms of the previously postulated ring-
opening mechanism.
ix
1
INTRODUCTION
Extensive quantitative studies on square planar, low
8 spin d complexes, especially those of Pt(II) and Pd(II),
have shown that these complexes generally undergo substi- 1
tution at rates that are reagent dependent.
Square planar substitution reactions of the form:
MA Xn+ + Y 3 > MA yn+ + X
3
are believed to follow a b~molecular displacement mechanism
which can be represented as:
-x > fast
-S fast +Y
- - y A3M<: - -.x -x )
fast 4
where Sis the solvent and k1 represents the solvent path
rate constant, Y is the substituting nucleophile and k2 is
the substituting nucleophile path rate constant. This
mechanism follows the two term rate law:
2
which under pseudo first order conditions with excess y-
reduces to:
Rate = k r MA Xn+l obs LI 3 -1
1
However, the square planar complexes of Pt(II), Pd(II)
and Au(III) with certain N-alkyl-substituted diethylenetri-
amines undergo substitution at rates that are almost indepen-
d f h . f h . 1· d 2•3•4 I ent o t e concentration o t e entering igan . t
has been suggested that the alkyl groups which occupy the
regions above and below the plane ·of the ion sterically
hinder the attack of the entering ligand.1
Studies of a
[Au(amine-H) CU+
series of reactions of the type
+ Br --~) · [Au(amine-H)B:cl + + Cl
with the amines having various degrees of alkyl substitution
reveal that the variation in the experimental bromide ion rate
dependence as a function of the amine is d i.eu-R> Me2dien-H>
Et2dien-H>Me4dien-H>.> Et4dien-H. However, examination of space
filling molecular models indicates that alkyl-group shielding of
the central Au(III) ion increases in the order; dien-H <: Me2dien-H < Me4dien-H <Etzdien-H < <Et4dien-H. Thus, if only
steric effects are considered the experimental rate dependence
should have shown Me4dien-H > Et2dien-H. 3' 5 To explain this anomaly between the molecular model
indications and the observed kinetics for (.Au(Et2dien-H)C~+
3
vs [Au(Me4dien-H)C1] +it has been suggested that the
substitution reaction of bromide with the [Au(Et2dien-H)C1] +
complex proceeds by the following ring-opening mechanism.6
(NEt2 N-Au--Br \_J
A similar ring-opening mechanism has been suggested for
the reaction of [Au(Et4dien-H)Clj +with N3-, 3
and for
[Pd(Et4dien)SeC~ with Br-. 7
4
To.investigate further the effects of alkyl substitution,
I J 2+ the gold(III) complexes, Au(Me5dien)Cl and
r . ] 2+ LAu(MeEt4dien)Cl have been prepared and their bromide
substitution reactions studied.
5
EXPERIMENTAL
Materials: Fine gold powder, purity better than 99.99%,
and ammonium hexafluorophosphate were obtained from Alfa
Inorganics, Inc. The 1,1' ,4,7,7'-pentamethyldiethylenetriamine
and the 4-methyl-1,1' ,7,7'-tetraethyldiethylenetriamine were
purchased from Ames Laboratories, Inc. All other chemicals
used were reagent grade.
Analyses: The gold analyses of the complexes, prepared as
the hexafluorophosphate salts, were performed by dissolving a
small accurately weighed quantity of complex in aqua regia fol
lowed by repeated evaporation with concentrated HCl to remove all
volatile nitrogen oxides. Throughout the evaporation the solutions
were not allowed to go to dryness, since dryness caused non-
reproducible results by volatilization of gold in the presence of
the hexafluorophosphate ion.3 The tetrachloroauric acid solutions
thus obtained were diluted with lM HCl to obtain solutions with
final concentrations in the range of 10-4 molar. The absorbance
of these solutions was measured at 314 nm using either a Perkin
Elmer Model 202.Recording Spectrophotometer or a Cary Recording
Spectrophotometer model 14MS .. The concentration of the gold was
then read from a standard curve of absorbance vs concentration
of HAuC14 prepared from pure gold. (Figure 1)
The chloride content of the complexes was determined by
the Mohr method.8
-N C'1")
N ,,....., N \.0 ,,....., Ji.< \.0 p...
Ji.< .._, p... .._, q
-CO r;::::+ u N ,,....., u 0 ,,....._ Q,) 0 ·r-1 Q,) -e ·r-1 -cr -o .µ
l.J") w Q,) Q,)
@ ::<:: ::<:: .._, .._, -"" ;::l ::l C'1") ::l ~ ~
N
M ~ C'1") e 0 <l .µ ell
0 0 -r-i .µ -0 ell N H H .µ 0
Q,)
Q,) .µ
o •r-1
0 ..-=l M 0 u - w ::l r::i::< ;::l ;:::J ~ -'° ~ 0
~I ,....;
H Ji.<
eo s <r
M u ;::l ~ ~ _N 0 ,....;
Q,) o 0 qJ ,.D H 0 en ~ - co
6
0
M
co 0
<r 0
I N
0
aoueqz o sqv
0
7
~Preparation of Complexes: Tetrachloroauric acid was
prepared by dissolving a weighed quantity of fine gold powder
in a few ml of aqua regia followed by a repeated evaporation
with concentrated HCl to remove the volatile nitrogen oxides.
The solution was evaporated to a volume of 1-2 ml and allowed
to cool; crystals of tetrachloroauric acid then formed.
[Au(Me5dien)C1] (PF6)2: HAuC14, prepared as above,
equivalent to 0.5 g or 2.5 mmoles of gold was dissolved in
20 ml of cold H2o. The solution was cooled to 10°c. While
mechanically stirring the solution, 2.5 mmoles or approxi
mately 0.7 ml of 1,1' ,4,7,7'-pentamethyldiethylenetriamine
was added. A yellow precipitate of [Au(Me5dien)cl] [Auc14]2
immediately formed. While maintaining the solution at a
temperature below 10°c and monitoring the pH of the solution
with a Fischer Accumet model 120 pH meter, 0.15 M sodium
hydroxide was added dropwise not allowing the pH to go above
7. With the addition of the sodium hydroxide the pH first
increased and then slowly decreased as the added OH- reacted.
The yellow precipitate dissolved. The addition of the sodium
hydroxide was continued until the solution remained at pH 5
for five minutes. The solution was filtered and a clear
orange filtrate was obtained. The filtrate was cooled to less
thau 5°C and 1 g of NH4PF6 was added. A peach colored pre
cipitate formed which was then collected on filter paper and
washed with small portions of ice cold ethanol. This was
followed by a wash with cold ether and the product sucked
dry. The resulting cream colored crystals were then stored
8
over CaC12 in a refrigerated desiccator. A yield of 38%
was obtained (based on the weight of gold used).
Analysis: Calculated for [Au(Me5dien)C1] (PF6)2
Au, 28.3%; Cl, 5.11%. Found: Au, 28.1%; Cl, 5.2%.
[Au(MeEt4dien)C1] (PF6)2: HAuC14, prepared as stated
above, equivalent to 0.5 gor 2.5 mmoles of gold was dissolved
in 30 ml of H20 and cooled to 10°c. While mechanically stir
ring the solution, 2.5 rnmoles or approximately 0.7 ml of
4-methyl-1,1', 7, 7'-tetraethyldiethylenetriamine was added.
A yellow precipitate [Au(MeEt4dien)c1_] lAuclJ 2] immediately
formed. This precipitate was slowly dissolved with a dropwise
addition of 0.15 M sodium hydroxide, while monitoring the pH
and maintaining it below pH 7. The addition of the sodium
hydroxide caused the solution to darken to an orange color
and then to a gray, ,presumably because of some decomposition
of the yellow precipitate. Sodtum hydroxide was added until
a pH of 5.5 was maintained for five minutes. The solution and
dark residue were filtered to obtain a yellow-orange filtrate.
The f il tr ate was cooled to about 5°C and 1 g of NH4PF 6
was
added. The off-white precipitate produced was collected on
filter paper and washed with cold H2o, cold ethanol and
finally cold ether and sucked dry. The compound was stored
over CaC12 in a refrigerated desiccator. A yield of 33%
\(based on the weight of gold used) was obtained.
Analysis: Calculated for [Au(MeEt4dien)C1J (PF6)2
Au, 26.2%; Cl, 4.72%. Found: Au, 26.3%; Cl, 4.70%
9
Klthough these compounds were refrigerated in the absence
of light, they slowly darkened and became gummy. Recrystalli
zation was necessary after about one month. Recrystallization
was accomplished by dissolving the compound in a small quantity
of acetone and water. The mixture was then filtered and the
water-acetone filtrate collected. The acetone was removed by
vacuum. The resulting recrystallized compound-was collected
and washed with cold ethanol followed by cold ether and the
product sucked dry.
10
KINETIC STUDIES
Earlier studies of the aqueous solution chemistry of
Au(III) with various diens indicated that: (a) Au(III) dien-H
complexes undergo extensive hydrolysis in neutral aqueous
solutions; (b) an excess of halide ion represses hydrolysis
of these complexes in certain pH ranges; (c) the conjugate
acids of these complexes are stable in perchloric acid; and
(d) the conjugate acids of these complexes undergo decomposi
tion in hydrohalic acids. 3,5,9
Since [Au(Me5dien)C1] 2+ and [Au(MeEt4dien)Cl] 2+ are
complexes of the Au(III) dien cat~gory, their aqueous solu
tion chemistry was briefly examined to determine their
behavior at various pH's and to select suitable pH ranges
for kinetic study.
Small portions of each complex were dissolved in H2o,
to a final concentration of 4 x. l0-4M. The solutions were
placed in a water jacketed beaker and maintained at 2s0c by
circulating water through the jacket from a P.M. Tamson
constant temperature bath. The pH of these solutions was
measured with a Fischer Accumet pH meter previously calibrated
using Bechman pH 4.00 and pH 6.86 buffers. The pH was
decreased in small increments using HC104 and increased in
small increments using NaOH. The spectrum of aliquots of
each of the solutions at the various pH's was obtained by
using a Perkin-Elmer 202 spectrophotometer and scanning from
11
250 nm to 390 nm.
It was also of interest to examine the stability of the
bromide substituted complexes at various pH's. The examina-
tion was similar to that stated above except that the chloro
species was allowed to react with a sufficient amount of
bromide ion at 25°C before decreasing or increasing the pH
at small increments with HGl04 or NaOH respectively.
Whereas with previously studied gold(III) <liens it was
possible to form their· conjugate bases and measure the dis-
sociation constants, there are no acid-conjugate base
relationships with [Au(Me5dien)Cl] 2+ and [Au(MeEt4dien)C1] 2+
because all amine sites are completely substituted.
The pH of a 4 x 10-4 M solution of [Au(Me5dien)C1] 2+
in H20 was 5.5. The pH of a similar concentration of
(Au(MeEt4dien)C1] 2+ in H2o was 5.8.
Examination of the scans at the various pH's revealed
that the [Au(Me5dien)C1] 2+ complex was stable with the
addition of HClO 4 to an acidic pH of 1. 0, at which decomposi-
tion occurred with the formation of Aucl4 With the addition
of NaOH the complex was stable to a pH of 6.3, then the
hydroxide ion noticeably replaced the chloride ion. The
pH studies of the bromide substituted complex, [ Au(Me5dien)B~ 2+,
indicated that at a pH less than 5 there was unwrapping of
the ligand and replacement with bromide at the amine sites,
and at a pH greater than 6.3 hydrolysis takes· place. The
pH studies of the [Au(MeEt4dien)C1J 2+ complex indicated that it was less stable than the [Au(Me5dien)C1] 2+ complex.
12
Decomvosition occurred below a pH of 2.3 and hydrolysis took
place above pH 5.8. The bromide substituted species,
[Au(MeEt4dien)Br] 2+, was stable between pH 5.2 and pH 6.2.
Based on the above information it was decided to study
the kinetics of both complexes in a pH 5.8 buffer. A
Na2HP04~NaH2Po4 buffer was used. Two solutions of each
complex were prepared in pH 5.8 buffer, one containing
0.10 M Cl- and the other containing 0.10 M Br-. The spectrum
of each solution was then obtained. The results for
[Au(Me5dien)X] 2+ are shown in Figure 2. Examination of
these spectra show a large difference in absorbance at a
wavelength of 330 nm. Therefore, ·the wavelength of 330 nm
was selected as optimum for the kinetic study for the Me5dien
complex.
A wavelength of 340 nm was selected for the kinetic
study for the MeEt4dien complex by a similar procedure.
Pertinent spectra for these complexes are shown in Figure 3.
Solutions of the chloro complexes were prepared by
dissolving exact amounts of the solid [Au(amine)Cl] (PF6)2
in pH 5.8 phosphate buffer. Kinetic runs were carried out
by allowing 2 ml of this solution to react with 1 ml of a
solution containing bromide ion at various concentrations.
The b~omide solutions were prepared by dissolving exact amounts
of NaBr and NaCl04 in pH 5.8 buffer to produce, after mixing,
the desired bromide ion concentration and a total ionic
strength of NaBr and NaCl04equal to 0.10 M. The concentration
4-l 0 U) ~ (]) . .., <r o I (]) 0 o, .-I Cf.)
~ 0 1-1 <r 0 0
I.I")
.-I 4-l ('")
,.£:: 0 u
U) + + "d i:: N N i:: 0 r;:::;i ~
....... ell . .., §
.µ u l::Q 0 ell ....... ....... '-"
N s 1-1 i:: i:: 0 .µ (]) (]) ,.£::
[l:l 1-1 i:: . .., . .., .µ
~ l::Q (]) "d -e 00
:::::> o I.I") I.I") i:: c..') (]) i:: (]) (])
(])
H ,.£:: 0 ~ ~ .-I µ., .µ u <;» <:» (])
;::l ;::l :>- 4-l .µ L'.!. ~ ell o <1l ~ ell + <t: l::Q 1-1 N .µ
~ u (]) ....... c, i:: U) (]) . .., 0
i:: "d 0 0 I.I")
('")
• r-i (]) .µ ~ c, <;»
1-1 ;::l 0 L.. U) .0 <t:
13
0 0 -cr
0 I.I")
0 co <o ;.N
-cr N 0 . . . . .-I 0 0 0 0 0
aotraq.ro sqv
l-1 l-1 4-1 Cl) Cl)
0 ~ 4-1 4-1 4-1 4-1
CJ) -.:t ;:! ;:! (!) I ,Ll .o ·rl 0 CJ .-i 00 00 Cl) p. ~· l-1 LI') LI') U) (!)
-cr 4-1 ::i::: ::i::: 0 4-1 p. c, l-1 4-1 ;:! _o 0 0 ,Ll p p LI')
.-i •rl •rl M
.r:: CJ) 00 u p ~ ?!
0 LI') '\j •rl M M ,....,. p .µ ::i::: 0 0 ~ (1j (1j p.
l-1 0 0 <;»
0 .µ p v " M a p •rl .r:: 0 (!) I I .µ
~ l-1 CJ + l-1 l-1 00 pq p N pq pq p
t5 0 r;::;1 (!)
(!) u CJ) CJ) ..-! H .r:: u ;:! ;:! (!)
J:;<.. .µ .µ ,-, ..-! ..-! :> (1j p p. p. (1j
4-1 (lJ + + ::;:
0 + •rl N 'CJ 1 N N
(1j GZ1 .µ -.:t r;::jl r;:n l-1 .µ »<; ~ u u CJ p Q) ,-, ,-, Q) (!) ?! p Q p. •rl '-' Q) (lJ U) '\j
~ •rl •rl
-.:t '\j '"d 0 Q .µ L-1 -.:t '::!" -o 0 w .µ .µ M ·rl Q) <11 w w .µ ?! (!) (!) p. '-' ?! ;:.:: l-1 ~
'-' "-./
0 ;:! ;:! CJ) l--1 ~ i..::!J ,Ll
<11 pq u
14
00
0
I
'° I
-.:t I
N
0 .
0 .
0
0 _o -.:t
0 - LI')
0 N . 0
15
-4 of the complex after mixing was 4 x 10 M. The reaction
occurring for [Au(Me5dien)Cl] (PF6)2 is as follows:
L 2+ ~u(Me5dien) Cl J + slow ) [Au(Me5dien)Br]2+ +Cl
Rates were determined using a Cary Recording Spectrophotometer
model 14 MS with 1 cm quartz cells in conjunction with a
Temptrol 153 waterbath from Precision Scientific Company that
pumped water through the cell compartment of the spectrophoto-
meter to keep the system at a constant temperature. The
scans obtained showed the change in absorbance at the specific
wavelength as a function of time. A typical scan is shown in
Figure 4. All reactions were performed at a temperature of
z5°c ~ 0.1°C. Bromide concentrations of 0.005 M, 0.01 M,
0.03 M, 0.05 M, 0.08 Mand 0.1 M were used for both complexes.
Additionally, [Au(MeEt4dien)Cl] Z+ was studied at 0. 02 M and
0.04 M bromide ion concentration; also the kinetics of this
complex were studied at a wavelength of 380 nm. For each
complex, replicate runs were performed at the various bromide
concentration levels. Reproducibility was better than 1%
absorbance.
Two methods for determining the pseudo-first order rate
constant were used:
1. The log of the difference in the absorbance
value (obtained from the scan) at time "t" (At)
and at the completion of the reaction (A) was (X)
plotted as a function of time.
16
0 -.::!" <r .-1
0 -N
C'f') .--1
0 -0
I N 1-1 ..-l ~ ~ .--1 (1) 0 . a - O'.) 0 'M 0
.µ ~ .--1 ..c: .µ ..c: -.::!" 'M .µ I ::: 'M 0 ::: .-1 0
+ - \.0 N s ~ °' r,:::jl- -.::!" u 0 ,,-., C'f') Cll i:: C'f') 'M (1) 'M .µ + _o "d Cl) N <r
LI') r-;::n CX)
(1) (1) ~ CJ u ...._, i:: ,,-., ;:l Cl) i:: CJ
<r ~ .0 (1) (1)
1-1 'M _o (})
i::il 0 "CJ N ~ 4-1 Cll LI') ....... i:: c> 0 .0 (1) 'M 0 <rl ~ H i:: ...._, (1)
Ji.< 0 p ;:l s 'M 'M ~
'M .µ _o ~ CJ (1) 0 Cl) Cll 4-1 , \.0 (1) Cl) 0 ~ (1)
1-1 i:: (1) CJ 0 ..c: (1) 'M .µ i::i .µ _o
Cl) CX)
1-1 Cl) 1-1 -.::!" 0 .µ 4-1 Cll i::
Cl) (1) i:: CJ Cd "d i:: CJ (1) 0 _o (/) ::: u \.0
0 C'f')
.--1 .-1 Cl) .-1 CJ 0 'M Ji.< P< :>. 0 ~ <r
N <rl
0 N .-I
I
°' 0
I CX) N
0
.-1
0 .
0 0 .
0 .
0
0 . 0
17
11 2. The Guggenheim method: The log of a A vs time
where a A equals the difference in absorbance
for a constant time interval at. For most runs
A t = 2 min.
Figure 5 shows a
l ;i 2+ Au(MeEt
4 <lien) ci]
typical scan for the reaction of
with 0.05 M Br-, followed as a decrease
in absorbance at 340 nm. Figure 6 shows a graph of kobs for
the reaction of [Au(MeEt dien)ci] 2+
with 0. 05 M Br-, c a I cu- 4
lated by the Guggenheim method.
From the linear plot obtained, the slope, or pseudo
first order rate constant, was calculated for the specific
bromide concentration being studi~d. Plots of replicate
runs yielded slopes which agreed within 10%. A straight
line was obtained from a plot of the observed rate constant
as a function of the bromide concentration with an intercept
equal to k1, the solvent path rate constant, and a slope of
k2, the bromide path rate constant. (See Figures, 7, 8, and
9)
The Guggenheim method was used because the absorbance
at time infinity is not needed to determine the observed
rate constant. The absorbance at time infinity was questioned
because of the hydrolysis that occurred with time. However,
comp~rison of the two methods showed no significant difference
in the calculated observed rate constant.
18
0 - C"')
I r-l H r:Q
;:E1 0 -N
ll"l r-l 0 QJ
;::;::: s 0 .,.,
.µ -:t 0 ,..c: I - r-l .µ ,..c: 0 r-l .,., .µ r-l ~ .,.,
~ ::;: + <r 0 N ~ -o r= CJ) r-l
u 0 .,., r<; <r + p C"') QJ N -o .,., .µ o-, "d Cil ~ -:t .µ QJ u P<:i (.) ,,-.... QJ p i:: -o e Cil QJ 00 (.)
ll"l .D .,., QJ ::l H "d CJ)
P<:i ~ 0 -:t ~ CJ) .µ i:: :::::> ~
P<:i -o .,., c.!) 4-1 QJ " H o· ;::;::: QJ µ., i:: ..._,, s p .,., ::l .,.,
0 di H .,., QJ -o .µ CJ) <o (.) Cil 4-1 Cil QJ 0 QJ H p ~ o
QJ 0 -o QJ "d .,., LI") ,..c: .µ .µ Cil Cil
H H CJ) .µ 0 Cil i:: -o 4-1 QJ <r
"d (.) p QJ i:: Cil ::;: 0 (.) 0 u ti) r-l -o
r-l C"') r-l 0 Cil µ., (.) .,., c, -o :>-. N H <t1
-o r-l
.- ,- 0 I I I I I I I
°' 00 " '° Lil -:t C"') N r-l 0 . . . . . . . 0 0 0 0 0 0 0 0 0 0
a::m~q:wsqv
<11 9.3 <l ~ 0
ee 0 H
9.2
9.6
9.5
9.4
9.1-
9.0-
19
FIGURE 6
Graph of kobs for the reaction of [Au(MeEt4dien)c~2+
with O. 05 M Br
Calculated by Guggenheim Method
2 -1 k calculated as 2.4 x 10 sec obs
Time in sec.
6.0- ,....; I
CJ Cl) Cl)
C"'l s.o- + 0 ,....;
~ "Cl Cl) 4.0- :> !-< Cl) Cl) ..Q 0 ~
3.0-
20
FIGURE 7
Observed Rate Constant for ~u(Me5dien)ci] 2+
versus Bromide Concentration@ T = 2s0c
Data obtained from change in Absorbance at 330 nm
9.0
0.10
8.0-
7.0-
2.0-
1.0-
Q,Q=-- I --'-~
0.01 0.02 0.03 0.04 I
0.08 I
0.09 I I
0.06 0.07 I
0.05
Moles I Liter Br
21
FIGURE 8
< [ 1l 2+ Observed Rate Constant for Au(MeEt4dien)C~
versus Bromide Concentration@ T = 25°C
Data Obtained from change in Absorbance at 340 nm
4.0
3.5-
..-l 2.5- I (J Q) rJ)
N + 0 2.0- ..-l
:< -e Q) :> H 1. 5- Q) CJ) ..0 0
.!:<I
1. 0-
0.5-
0.0-1-~~~-r,~~~....,...,~~~-....,~~~-r,~~~-.....,~~~-.....,~~~-...~ 0.01 0.02 0.03 0.04 0.05 0.06 0.07
moles/ Liter Br
4.0-
3. 0-
'"""" I (.) Q) 2.5- U)
N + 0 '"""" ~ 2.0- "O Q) :> ~ Q) U) .D 1. 5- 0 ~
22
FIGURE 9
Observed Rate Constant for [Au(MeEt4dien)C~ 2+
versus Bromide Concentration@ T = 25°C
Data obtained from change in absorbance at 380 nm
3.5-
1.0-
0.5-
0.01 0.02 0.03 0.04 0.05 0.06
moles/ Liter Br
23
. RESULTS AND DISCUSSION
The pseudo-first order rate constants obtained for the
reaction:
[Au(amine)Cl] 2+ + Br- ~ [Au(amine)BrJ 2+ + Cl
(where amine= (Me5dien), studied at wavelength 330 nm, and
(MeEt4dien), studied at 340 and 380 nm) are given in Table I.
The values shown fork b are reproducible within 10% 0 s
and are the average of from four to eight replicate runs.
The estimated values of the first and second order rate
[ 2+ constants for Au(Me5dien)Clj and [Au(MeEt4dien)Cl] 2+
are listed in Table II, these represent rate constants for
the solvent and bromide paths, respectively. Also listed in
Table II are the data for the substitution reactions of Br-
for Cl in the complexes of [Au(dien)Cl] 2+, [Au(dien-H)Cl] +
[Au(Me2dien-H)C1]+, [Au(Me4dien-H)Cl] + [Au(Et2dien-H)Cl] +
and [Au(Et4dien-H)Cl] +
As has been stated previously, examination of molecular
models indicates that the shielding of the Au(III) by the
amine increases in the following order: dien-H < Me2dien-H < Me4dien-H<Et2dien-H <<Et4dien-H.
6 Examination of the
molecular models of Me5dien. and MeEt4dien indicates the
Me5dien shields the Au(III) slightly more than the Me4dien-H
and the MeEt4dien shields slightly more than the Et4dien-H.
However, it should be noted that Me5dien and J1eEt4dien com
plexes are divalent positive ions. Thus the slight shielding
24
TABLE I
Pseudo First Order Rate Constants at ?:5° C for:
[Au(amine)Cl] 2+ + Br- ~~)~ [Au(amine)Br] 2+ +Cl-
amine= Me5dien
Br- concentration
0.10 M
0.08 M
0.05 M
0.03 M
0.01 M
0.005 M
kobs x 103 at 330 nm
8.3 sec-1
7.0
5.0
4.1
3.0
2.5
amine = MeEt4dien
Br - concentration kobsX 102 at 340 nm kohsx 102 at 380 nm
0.05 M 2.4 -1 2.4 sec-1 sec
0.04 M 2.2 2.2
0.03 M 1. 8 1. 8
0.02 M 1. 6 1. 6
0.01 M 1. 5 1. 5
0.005 M 1. 2 1. 2
25
TABLE II
First Order and Second Order
Rate Constants for the Reactions:
+ [Au(amine-H)Cl] + Br
~u(~mine)clJ 2+
+Br
Complex
~u(dien) CU 2+
~u(dien-H)Ctj +
~u(Me2dien-H)c1] +
~u(Me4 dien-H) c]J +
~u(Me5dien)C1] 2+
. ~(Et2dien-H)CLJ +
~u(Et4dien-H)cfj +
~u(MeEt4dien)c!} 2+
) [Au(amine-H)Br] + + Cl
and
) [Au (amine) Br] 2+ + Cl
k1 (sec-1) kz (M-lsec-1) Reference
0 380 5
0.6 190 5
0.20 44 6
0.062 0.76 6
0.002 0.058 this work
0.023 3.8 6
0.00012 0.0085 6
0.01 0.26 this work
The rate constants for the reactions were determined
at 25° "±" o.1°c.
26
effect" of the additional methyl group might be offset by
the increased charge of the Me5dien and the MeEt4dien
complexes.
The data in Table II shows that the bromide substitu
tion of chloride in [Au(Me5dien)C1] 2+
proceeds via the
solvent path 30 times slower and via the bromide path 10
times slower than the same reactions for [Au(Me4dien-H)CJ] +
This decrease in rate can be attributed to the steric
blocking of the 5th methyl group. This decrease due to the
steric effect would presumably be larger but is offset by
the increased charge of the complex. Note that H 0 entry 2
is decreased by a larger factor than Br entry, because
ion-dipole interaction is less than ion-ion interaction.
However, the same phenomenon is not observed in the examina-
tion of the data in Table II for the MeEt4dien vs the
Et dien-H complexes. The br omi.de substitution of the 4 .
chloride in [Au(MeEt dien)ci] 2+ proceeds via the solvent 4
path approximately 100 times faster and via the bromide path
approximately 30 times faster than with [Au(Et4dien-H)C1J +
Also, by comparison [Au(MeEt 4 <lien) cl] 2+ reacts two times
slower via the solvent path and 15 times slower via the
bromide path than [Au(Et2dien-H)ci] +. While steric
hindrance can be invoked to rationalize the slower reaction
of [Au(MeEt4dien)Cl] Z+ over [Au(Et2dien-H)Cl] +, such a
rationalization is not consistent with the increase in rate
observed for ~u(MeEt4dien)C1] 2+ over [Au(Et4dien-H)Cl] +
27
. Furthermore, this latter increase cannot be explained in
terms of increased charge since this should cause increased
Br entry to a greater extent than H2o entry as was observed
for the methyl substituted complexes. This anomaly can be
rationalized in terms of the postulated ring-opening mechanism.
Evidence for ring-opening is apparent in the equilibrium
studies. The gold(III) complexes of Me2dien and Me4dien were
found stable in 1 Macidic chloride and bromide solutions.
A similar behavior was observed for the gold(III) Me5dien
complex. On the other hand, the complexes of gold(III)
containing Et2dien and Et4dien broke up in 1 M acidic chloride
solutions to yield Auc14- and in 1 M acidic bromide solutions - 6
to yield AuBr4. A similar behavior was also observed for
the gold(III) MeEt4dien complex. Therefore, in the acidic
solutions the ethyl groups on the terminal nitrogens of the
chelate exert a specific effect leading to ring-opening.
Presumably, these complexes are in equilibrium with low con-
centrations of ions containing the triamine as a bidentate
ligand.
Additional evidence for ring-opening, can be seen in
the kinetic studies. Spectral changes during the bromide
substitution for chloride in [Au(MeEt4dien)cD z+ showed that for a concentration of bromide ion in the range 0.001 M
2+ to 0.03 M the substitution product was [Au(MeEt4dien)B~
Concentrations greater than 0.03 M Br- $howed unwrapping of
the ligand to form various substitution products presumably
28
l}uBT J-, [AuBr 3oig-, [AuBr 2 (OH) 2 J - , [ AuBr (OH3)J - and
[ Au(OH) 41-. A typical example of one spectrum obtained
is shown in Figure 3.
At 340 nm it was difficult to determine whether decom-
position had any effect on the kinetic results since the
absorbances of the [Au(MeEt4dien)BrJ 2+ and the decomposition products were essentially the same. Therefore, repetitive
scans from 320 nm to 390 nm were run on the reaction of
[Au(MeEt4dien)c1] 2+ with 0.05 M Br-. These are shown in
Figure 8. As can be seen, the Lscsbes.r Lc points at 323 nm
and 367 nm indicate that the formation of [Au(MeEt4dien)BrJ 2+
occurred before further unwrapping of the ligand took place.
Furthermore, when 0.1 M Br- was added dropwise to the product
of the reaction of [Au(MeEt4dien)C1] 2+ with 0.03 M Br
spectral changes indicated that unwrapping of the ligand took
place.
To substantiate the kinetic rate values obtained from
the studies at 340 nm kinetic runs with the various concentra-
tions of bromide ion were also carried out at 380 nm. Since
the [Au(MeEt4dien)Br.J 2+ and the decomposition products have
different absorbances at 380 nm, the Guggenheim method was
used to calculate rate constants from these runs. The results
obtained at 380 nm were essentially the same as those obtained
at 340 nm.
Therefore, the kinetic results for the bromide substitu
tions for chloride in [Au(MeEt dien)clJ z+ can be rationalized 4
I I-< 0 u P'.:l 0 P'.:l " 0\
i::; ("I)
?! 'M a l1") 0 r-f
0
,.i:;: P'.:l .µ 'M ~ (!) a + 'M
N .µ
r:;i 0 0 .-'I u II ,-.. ,-.. r>::i i::; <t: !§ ~ (!) t> 'M 0 <;»
0 "d l1") H <r (!) ("I) ,..c:: l't-< .µ a .µ
r>::i 'M en . (!) .µ i::; ?! (!) '-' 0 r-f :l .µ (!)
6 ::> .µ rd o ::SC (!)
4-l p.. 0 C/J
(!) i::; I-< 0 'M .c .µ .µ u 'M rd ~ (!) ~
29
0 0 ("I)
0
r-f
0 N
0 .
0 .
0
~30
. in t~rms of the following ring-opening mechanism:
(NEt2
MeN Au~~-Cl -. NEt2
-: MeN Au--Cl
~NEt 2
(I) (R)
(NEtz
MeN-- Au-- Br -. NEt2
The bidentate species (I) is much more susceptible to
bromide ion and solvent attack. Therefore, it is reason-
able that bromide ion substitution should occur at a rate
greater than observed for ~u(Me5dien)ci] 2+ The faster
rate observed for ~u(MeEt4dien)c.i] 2+ over_ ~u(Et4dien-H)cI]+
is presumably the result of the increased charge of the
former ion.
31
. REFERENCES AND BIBLIOGRAPHY
1. Fred Basolo and Ralph G. Pearson, "Mechanisms of
Inorganic Reactions," Second Edition, John Wiley &
Sons, Inc., New York, N. Y. (1967)
2. W. H. Baddley and F. Basolo, Journal of the American
Chemical Society, 88, 2944 (1966)
3. C. F. Weick and Fred Basolo, Inorganic Chemistry,
5, 576 (1966)
4. John R. Goddard and Fred Basolo, Inorganic Chemistry,
L. 936 (1968)
5. William H. Baddley and Fred Basolo, Inorganic
Chemistry, ~. 1089 (1964)
6. David L. Fant and C. F. Weick, Inorganic Chemistry,
12, 1964 (1973)
7. John L. Burmeister and John C. Lim, Chemical
Communications, 19, 1154. (1969)
8. William Reiman, III, Jacob D. Neuss, and Barnet Naiman,
Quantitative Analysis , McGraw-Hill Book Company, Inc.,
New York, N.Y. (1951)
9. W. H. Baddley, Fred Basolo, Harry B. Gray, Clarita
N8lting, and A. J. P8e, Inorganic Chemistry, 2, 923
(1963)
32
. 10. F~ed Basolo and Ronald Johnson, Coordination Chemistry,
W. A. Benjamin, Inc., New York, N. Y. (1964)
11. E. A. Guggenheim, Philadelphia Magazine, z, 538 (1926)