This document summarizes research into developing water-soluble organometallic catalysts for the activation of hydrogen peroxide. Diphenyl selenide and diphenyl telluride are investigated as potential catalysts. Kinetic experiments show that while diphenyl selenide does not significantly increase the reaction rate of hydrogen peroxide activation compared to the uncatalyzed reaction, diphenyl telluride provides a modest catalytic effect. Oxidizing diphenyl selenide also does not improve its catalytic activity. The goal of making water-soluble and stable organometallic catalysts for this reaction is discussed.

1. Green Catalytic Activation of H2O2 by Organometallic Compounds
Keilah M. Villines, Edwin Lozano, Michael D. Drake*
Department of Chemistry, California State University Stanislaus, Turlock, CA
Organoselenide and organotelluride compounds are
of great interest in “green” chemistry because of their
ability to activate hydrogen peroxide. Hydrogen
peroxide by itself is a slow oxidizing agent, but when
activated, it is kinetically useful. While the
organoselenide and telluride dendrimers prepared by
Detty and colleagues have shown significant catalytic
activation of H2O2, their catalysts were not water
soluble and were prone to selenoxide syn-elimination.
Various diphenyl selenide and diphenyl telluride species
are being investigated because they lack β-hydrogens,
and hold the potential to be water soluble when
structurally modified. Using gas chromatography, the
catalytic rate of H2O2 activation is evaluated with these
different species. A blank rate is determined initially in
order to standardize the efficiency of each catalyst.
Diphenyl selenide does not show an increased rate of
catalytic activity while diphenyl telluride shows a
modest degree of catalysis. Pre-oxidation of diphenyl
selenide results in no increase in the rate of H2O2
activation over the blank rate.
• Enzyme found in specific algae,
sponges, and other marine organisms
• Vanadium active site reacts with H2O2
• Oxidizes NaBr in sea water to “Br+”
species to make halogenated metabolites
• Mammalian antioxidant enzyme
containing a selenocysteine
active site
• Selenium active site reacts with
peroxides, ridding them from
the body
Scheerer, P.; Borchert, A.; Krauss, N.; Wessner, H.; Gerth, C.; Hohne, W.;
Kuhn, H.; Biochemistry, 2007, 46, 9041–9049.
Vanadium Bromoperoxidase (V-BrPO): Glutathione Peroxidase (GPx):
Littlechild, J.; Garcia-Rodriguez, E. Coordination Chemistry Reviews, 2003, 237, 65-76.
y = -5.90E-05x + 7.44E-01
R² = 9.93E-01
-0.2
0
0.2
0.4
0.6
0.8
0 5000 10000 15000
ln[1+2]
Time (sec.)
ln[1+2] vs. Time
(blank – no catalyst)
blank rate = kblank[H2O2]
ln[H2O2]t = -kblankt + ln[H2O2]0
ln[1+2]t = -kblankt + ln[1+2]0
y = (m)(x) + b
• the negative slope of the
line is the rate constant
kobs = Average of 5 trials = (4.17 ± 0.70) x 10-5 s-1
Reactions
Kinetics
kobs = Average of 3 trials = (4.77 ± 0.75) x 10-5 s-1
Two-phase system
NaBr, H2O2, cyclohexene, pH 6.0 buffer,
CH2Cl2 with internal standard, 25.0 °C
Br- is oxidized
“Br+” is captured by cyclohexene
internal
standard
CH2Cl2
• formation of 1 and 2 is monitored by GC
• samples are withdrawn every 5-10 minutes
Synthesis
Kinetics
Synthesis
Kinetics
1. Synthesis of Potentially Water Soluble Catalysts
kobs = Average of 3 trials = (8.15 ± 1.47) x 10-5 s-1
1. Francavilla, C.; Drake, M. D.; Bright, F. V.; Detty, M. R. J. Am. Chem. Soc. 2001, 123, 57-67.
2. Drake, M. D.; Bright, F. V.; Detty. M. R. J. Am. Chem. Soc. 2003, 125, 12558-12566.
3-SePh dendrimer
6-Se/TePh dendrimer
12-Se/TePh dendrimer
1-Se/TePh monomer
kcat = (9.66 ± 4.45) x 10-4M-2s-1
kcat = (1.26 ± 3.69) x 10-4 M-2s-1
0.00
0.20
0.40
0.60
0.80
1.00
1.20
0 3 6 9 12
kcat,M-2s-1
SePh groups/dendrimer
Oxidation of NaBr by Se Catalysts
measured rate constant
statistical expectation
0.00
0.20
0.40
0.60
0.80
0 3 6 9 12
kcat,M-2s-1
TePh groups/dendrimer
Oxidation of NaBr by Te Catalysts
measured rate constant
statistical expectation
But…
• Catalysts are not H2O soluble
• Catalysts are prone to elimination
Goal of the Project
1. Make Se and Te catalyst that are
H2O soluble
2. Make Se and Te catalysts that
do not possess b-hydrogens
• Reaction is first-order in H2O2, zero-order in NaBr
Observed rate of a
catalyzed reaction
blank reaction
rate +
catalyzed reaction
rate = kobs[H2O2]
• Diphenyl telluride is not commercially available, it must be synthesized
• Te oxidizes rapidly in H2O2, it was not pre-oxidized
• Diphenyl selenide is commercially available
• Se oxidizes slowly in H2O2, so it was pre-oxidized
• The loss of H2O2 (formation of “Br+”) is monitored by 1 and 2
=
California State University Stanislaus Research Scholarly & Creative Activities (RSCA) Grant: Fund G0106
underway:
planned:
selenium version
PEG-ylated catalysts
2. Incorporation Into a Dendrimer
= selenium or tellurium atom
0
0.2
0.4
0.6
0.8
1
1.2
0 20 40 60 80 100 120
mmole1and2
Time (min.)
mmole of 1 and 2 vs. Time
(with Ph-Te-Ph catalyst)
mmol 1
mmol 2
total mmol 1+2
0
0.2
0.4
0.6
0.8
1
1.2
0 50 100 150 200 250
mmole1and2
Time (min.)
mmole of 1 and 2 vs. Time
(with Ph-Se(O)-Ph catalyst)
mmol 1
mmol 2
total mmol 1+2
0
0.2
0.4
0.6
0.8
1
1.2
0 50 100 150 200 250
mmole1and2
Time (min.)
mmole of 1 and 2 vs. Time
(blank – no catalyst)
mmol 1
mmol 2
total mmol 1+2