1050 Inorganic Chemistry, Vol. 50, No. 3, 2011
Berreau et al.
FTIR-8400 spectrometer. Elemental analyses were performed by
Atlantic Microlabs, Inc., Norcross, GA.
ratio. 1H NMR and GC-MS analysis of the products indicated
the presence of unreacted 1,3-diphenylpropanetrione (∼57%),
hydrated 1,3-diphenylpropanetrione (∼7%), and benzoic acid
(∼36%).
Stopped-Flow Kinetic Studies. Measurements were performed
using either a SF-61DX2 or a SF-43 multimixing anaerobic
cryogenic stopped-flow instrument (TgK Scientific, formerly
Hi-Tech Scientific, Salisbury, Wiltshire, U.K.) combined with either
a Hi-Tech Scientific KinetaScan diode-array or a J&M diode-
array spectrophotometer. All manipulations of I and [Me4N]-
[PhC(O)C(OH)C(O)Ph] and their solutions were performed in-
side an argon-filled glovebox. For stopped-flow kinetic studies
involving I, solutions of a known concentration of the complex
were prepared and then placed in a Hamilton gastight syringe,
which was loaded into the stopped-flow sample handling unit. To
Reaction of 1,3-Diphenylpropanetrione and H2O2 in the Pre-
sence of NEt3. The reaction mixture described above was pre-
pared. To this solution was added dry Et3N (5.9 μL, 4.2 ꢀ
10-5 mol). The mixture was then stirred for 24 h. Sampling of the
headspace gas of this reaction mixture indicated the formation
of CO/CO2 in a ∼12:1 ratio. After this time, the solvent was
removed under reduced pressure. 1H NMR and GC-MS analysis
of the products indicated the presence of benzoic acid/[Et3NH]-
[benzoate] (∼70%), unreacted 1,3-diphenylpropanetrione (∼30%),
and a trace amount of hydrated trione.
generate [Me4N][PhC(O)C(OH)C(O)Ph], solid Me4NOH 5H2O
3
was fully dissolved in dry acetonitrile (2 mM). A CH3CN solution
containing an equimolar amount of PhC(O)CH(OH)C(O)Ph was
then added, which resulted in the formation of a bright-orange
solution. After 30 min of stirring, the solution of [Me4N]-
[PhC(O)C(OH)C(O)Ph] was transferred to a gastight syringe and
diluted. Saturated solutions of O2 in CH3CN (8.2 mM) were
prepared by bubbling dry O2 through an argon-saturated solvent.
Solutions containing lower concentrations of O2 were prepared by
dilution of the 8.2 mM solution with argon-saturated CH3CN
using gastight syringes. For the kinetic runs of the O2 reactions of I
and [Me4N][PhC(O)C(OH)C(O)Ph] used to generate the Eyring
plot, the final concentrations were 0.3 mM (enolate complex or
salt) and 4.1 mM (O2). Data analysis was performed with the IS-2
or Kinetic Studio Rapid Kinetics Software (TgK Scientific).
Computational Experiments. All calculations were performed
by employing hybrid density functional theory with the B3LYP
exchange-correlation functional,19 as implemented in the Jaguar20
quantum chemistry program. Geometry optimizations and fre-
quency calculations were done with a standard valence double-ζ
basis set supplemented with a single set of polarization and diffuse
functions on non-hydrogen atoms, i.e., 6-31Gþ*. The solvent
corrections were calculated with the self-consistent-field reaction
method implemented in Jaguar.21 A dielectric constant of 37 and a
Preparation of [(6-Ph2TPA)Ni(CH3CN)(H2O)](ClO4)2 H2O
3
(IV). This complex is a solvation analogue of the previously
reported [(6-Ph2TPA)Ni(CH3CN)(CH3OH)](ClO4)2.16 An
admixture of 6-Ph2TPA (0.07 mmol) and Ni(ClO4)2 6H2O (0.07
3
mmol) in CH3CN (∼2 mL), followed by diffusion with diethyl
ether, yielded purple crystals (51 mg, 91%). The crystals were
crushed and dried under vacuum prior to elemental analysis. Anal.
Calcd for C32H33Cl2N5NiO10: C, 49.45; H, 4.28; N, 9.01. Found:
1
C, 49.39; H, 4.38; N, 8.92. The H NMR, UV-vis, and FTIR
features of this complex match those previously reported for
[(6-Ph2TPA)Ni(CH3CN)(CH3OH)](ClO4)2.16
Treatment of IV with 1,3-Diphenylpropanetrione. This reac-
tion was run in the presence and absence of O2 with no change in
the outcome. Complex IV (33 mg, 4.2ꢀ10-5 mol) was combined
with 1,3-diphenylpropanetrione (10 mg, 4.2 ꢀ 10-5 mol) in dry
acetontrile (∼2 mL, distilled from CaH2). The resulting mixture
was stirred for 6 h at ambient temperature. Sampling of the
headspace gas indicated primarily the formation of CO2 with only
a trace amount of CO (∼1:10 CO/CO2). After 6 h, the solvent was
removed under vacuum. The remaining residue was stirred with
1:1 hexanes/ethyl acetate (∼3 mL) for 1 h. This resulted in a yellow
solution and a pale-purple precipitate. The purple precipitate was
determined to be [(6-Ph2TPA)Ni(sol)2](ClO4)2 (sol = CH3CN
and/or water) by 1H NMR.16 Following filtration of the solution
through a Celiteplug, the filtrate was brought to dryness. The total
amount of organic products isolated was ∼8 mg. The organic
˚
probe radius of 2.18 A were used to model the solvent effects due
to acetonitrile. The thermal corrections were calculated for room
temperature (298.15 K) and a pressure of 1 bar from the Hessian
matrix using the standard rigid rotor and harmonic oscillator
approximations. The energies reported are thus relative Gibbs free
energies that include electronic energies, solvent, and thermal
corrections all calculated at the B3LYP/6-31Gþ* level of theory.
The zero energy level corresponds to separated substrates, speci-
fically triplet O2 and the monoanion [PhC(O)C(OH)C(O)Ph]- (1)
in the singlet ground state. Structures of all intermediates and TSs
were fully optimized, and the character of the stationary point was
confirmed by a frequency analysis; i.e., minima and TSs have zero
or one imaginary frequency, respectively.
1
products identified by GC-MS and H NMR were unreacted
1,3-diphenylpropanetrione, hydrated 1,3-diphenylpropanetrione,
benzil, and benzoin. The combined yield of benzil and benzoin in
this reaction was ∼30-35% (determined by 1H NMR).
Treatment of IV with 1,3-Diphenylpropanetrione and H2O2.
Complex IV (33 mg, 4.2 ꢀ 10-5 mol) was mixed with 1,3-
diphenylpropanetrione (10 mg, 4.2 ꢀ 10-5 mol) in ∼2 mL of
dry acetonitrile. The resulting mixture was stirred until everything
had dissolved, which gave a light-yellow solution. Aqueous H2O2
(4.2 μL of 31% solution, 4.2 ꢀ 10-5 mol) was introduced, and the
reaction was stirred for 24 h, during which time the intensity of the
yellow color diminished. Sampling of the headspace gas of this
reaction mixture indicated the formation of CO/CO2 in a ∼3:1
ratio. Following removal of the solvent under vacuum, the residue
was extracted with hexanes/ethyl acetate (1:1) for 1 h, and the
soluble portion was brought to dryness (4.4 mg). The species
present in this product were identified by 1H NMR and GC-MS
as benzoic acid (major) and small amounts of unreacted 1,3-
diphenylpropanetrione and benzil. 1H NMR analysis of the
nickel(II) complex residue indicated the presence of [(6-Ph2-
TPA)Ni(sol)2](ClO4)2 (sol = CH3CN and/or H2O).16
Caution! Perchlorate salts of metal complexes with organic
ligands are potentially explosive. Only small amounts of material
should be handled with great care.22
Reaction of 1,3-Diphenylpropanetrione and H2O2. 1,3-Diphe-
nylpropanetrione (10 mg, 4.2ꢀ10-5 mol) was combined with
aqueous H2O2 (4.2 μL of 31% solution; 4.2 ꢀ 10-5 mol) in ∼1 mL
of dry acetonitrile. This produced a yellow solution. The reaction
mixture was stirred for 24 h. Sampling of the headspace gas of this
reaction mixture indicated the formation of CO/CO2 in a ∼12:1
(18) Allen, T. H.; Root, W. S. J. Biol. Chem. 1955, 216, 319–323.
(19) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652. (b) Lee, C.; Yang,
W.; Parr, R. G. Phys. Rev. B 1988, 37, 785–789.
Reaction of IV with 1,3-Diphenylpropanetrione, H2O2, and
NEt3. Complex IV (33 mg, 4.2 ꢀ 10-5 mol) was mixed with 1,3-
diphenylpropanetrione (10 mg, 4.2 ꢀ 10-5 mol) in ∼2 mL of dry
acetonitrile. The resulting mixture was stirred until everything had
dissolved, which gave a yellow solution. To this solution was
added dry Et3N (5.9μL, 4.2 ꢀ 10-5 mol), and the reaction mixture
remained yellow. Aqueous H2O2 (4.2 μL of 31% solution, 4.2 ꢀ
10-5 mol) was introduced, and the reaction was stirred for 24 h,
€
(20) Jaguar, version 7.6; Schrodinger, LLC: New York, 2009.
(21) (a) Tannor, D. J.; Marten, B.; Murphy, R.; Friesner, R. A.; Sitkoff,
D.; Nicholls, A.; Honig, B.; Ringnalda, M.; Goddard, W. A., III J. Am.
Chem. Soc. 1994, 116, 11875–11882. (b) Marten, B.; Kim, K.; Cortis, C.;
Friesner, R. A.; Murphy, R. B.; Ringnalda, M. N.; Sitkoff, D.; Honig, B. J. Phys.
Chem. 1996, 100, 11775–11788.
(22) Wolsey, W. C. J. Chem. Educ. 1973, 50, A335–A337.