Reactivity and equilibrium thermodynamic studies of rhodium tetrakis(3,5-disulfonatomesityl)porphyrin species with H2, CO, and olefins in water

Article abstract of DOI:10.1021/ic0615022

Aqueous (D₂O) solutions of tetrakis(3,5-disulfonatomesityl) porphyrin rhodium(III) aquo/hydroxo complexes ([(TMPS)Rh^III(D ₂O)₂]^-7 (1), [(TMPS)Rh^III(OD)(D ₂O)]^-8 (2), and [(TMPS)Rh^III(OD) ₂]^-9 (3)) react with hydrogen (D₂) to form an equilibrium distribution with a rhodium hydride ([(TMPS)Rh-D(D ₂O)]^-8 (4)) and a rhodium(I) complex ([(TMPS)Rh ^I(D₂O)]^-9 (5)). Equilibrium constants (298 K) are measured that define the distribution for all five of these (TMPS)Rh species in this system as a function of the dihydrogen (D₂) and hydrogen ion (D⁺) concentrations. The hydride complex [(TMPS)Rh-D(D ₂O)]^-8 is a weak acid in D₂O (K_a(298 K) = 4.3 × 10^-8). Steric demands of the TMPS porphyrin ligand prohibit formation of a Rh(II)-Rh(II)-bonded complex, related rhodium(I)-rhodium(III) adducts, and intermolecular association of alkyl complexes which are prominent features of the rhodium tetra(p-sulfonatophenyl) porphyrin ((TSPP)Rh) system. The rhodium(II) complex ([(TMPS)Rh ^II(D₂O)]^-8) reacts with water to form hydride and hydroxide complexes and is not observed in D₂O. The (TMPS)Rh-OD and (TMPS)Rh-D bond dissociation free energies (BDFE) are virtually equal and have a value of approximately 60 kcal mol^-1. Reactions of [(TMPS)Rh-D(D₂O)]^-8 in water with CO and olefins produce rhodium formyl and alkyl complexes which have equilibrium thermodynamic values comparable to the values for the corresponding substrate reactions of [(TSPP)-Rh-D(D₂O)]^-4.

Full text of DOI:10.1021/ic0615022

Inorg. Chem. 2006, 45, 9884−9889
Reactivity and Equilibrium Thermodynamic Studies of Rhodium
Tetrakis(3,5-disulfonatomesityl)porphyrin Species with H2, CO, and
Olefins in Water
Xuefeng Fu, Shan Li, and Bradford B. Wayland*
Department of Chemistry, UniVersity of PennsylVania, Philadelphia, PennsylVania 19104-6323
Received August 9, 2006
Aqueous (D2O) solutions of tetrakis(3,5-disulfonatomesityl)porphyrin rhodium(III) aquo/hydroxo complexes
7
8
9
([(TMPS)RhIII(D2O)2]- (1), [(TMPS)RhIII(OD)(D2O)]- (2), and [(TMPS)RhIII(OD)2]- (3)) react with hydrogen (D2) to
8
form an equilibrium distribution with a rhodium hydride ([(TMPS)Rh
−
D(D2O)]- (4)) and a rhodium(I) complex
([(TMPS)RhI(D2O)]- (5)). Equilibrium constants (298 K) are measured that define the distribution for all five of
9
these (TMPS)Rh species in this system as a function of the dihydrogen (D2) and hydrogen ion (D+) concentrations.
8
The hydride complex [(TMPS)Rh
the TMPS porphyrin ligand prohibit formation of a Rh(II)
−
D(D2O)]- is a weak acid in D2O (Ka(298 K)
)
4.3
×
10-8). Steric demands of
rhodium(III)
−
Rh(II)-bonded complex, related rhodium(I)−
adducts, and intermolecular association of alkyl complexes which are prominent features of the rhodium tetra(p-
sulfonatophenyl)porphyrin ((TSPP)Rh) system. The rhodium(II) complex ([(TMPS)RhII(D2O)]-8) reacts with water to
form hydride and hydroxide complexes and is not observed in D2O. The (TMPS)Rh−OD and (TMPS)Rh−D bond
dissociation free energies (BDFE) are virtually equal and have a value of approximately 60 kcal mol-1. Reactions
8
of [(TMPS)Rh
−
D(D2O)]- in water with CO and olefins produce rhodium formyl and alkyl complexes which have
equilibrium thermodynamic values comparable to the values for the corresponding substrate reactions of [(TSPP)-
4
Rh−
D(D2O)]-
.
Introduction
areas of transition metal catalysis research. Our immediate
primary objectives in this area are to evaluate the reactivity
patterns of metalloporphyrins in water and to identify the
dominant energy terms that differentiate substrate reaction
behavior in organic and aqueous media.7-10 Prior papers in
this series have described reactions of tetra(p-sulfonatophe-
nyl)porphyrin rhodium ((TSPP)Rh) complexes in water with
H2/D2, D2O, CO, aldehydes, and olefins that form hydride,
hydroxide, formyl, R- and â-hydroxyalkyl, and alkyl
complexes.7-10 Equilibrium thermodynamic studies for this
wide range of (TSPP)Rh substrate reactions in water provide
one of the most comprehensive sets of thermodynamic
measurements for organometallic reactions.8-10 The (TSPP)-
rhodium(II) complex ([(TSPP)RhII(D2O)]-4) in water forms
Organometallic transformations in water1-10 and catalytic
processes in aqueous media11-14 are major contemporary
* To whom correspondence should be addressed. E-mail:
wayland@sas.upenn.edu.
(1) (a) Pryadun, R.; Sukumaran, D.; Bogadi, R.; Atwood, J. D. J. Am.
Chem. Soc. 2004, 126, 12414. (b) Helfer, D. S.; Phaho, D. S.; Atwood,
J. D. Organometallics 2006, 25, 410. (c) Lucey, D. W.; Helfer, D. S.;
Atwood, J. D. Organometallics 2003, 22, 826.
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1998, 37, 2181. (b) Stahl, S. S.; Labinger, J. A.; Bercaw, J. E. J. Am.
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9884 Inorganic Chemistry, Vol. 45, No. 24, 2006
10.1021/ic0615022 CCC: $33.50
© 2006 American Chemical Society
Published on Web 10/26/2006

Rh Tetrakis(3,5-disulfonatomesityl)porphyrin Species
1
droxo complex [(TMPS)RhIII(OD)2]-9 (3). H NMR of (TMPS)-
a RhII-RhII-bonded dimer [(TSPP)Rh(D2O)]2-8; [(TSPP)-
RhI(D2O)]-5 forms metal-metal-bonded RhI:RhIII-X adducts
with (TSPP)RhIII species, and the alkyl complexes ((TSPP)-
Rh-R) have a marked tendency to form oligomers in
solution. One of the objectives of this study is to evaluate
whether the use of the larger steric demand tetrakis(3,5-
disulfonatomesityl)porphyrin (TMPS) ligand will block oli-
gomer formation and prohibit formation of RhII-RhII. This
article reports on the aqueous solution reactivity patterns for
the (TMPS)Rh system and thermodynamics for substrate
reactions for comparison with results from the lower steric
demand (TSPP)Rh system.7-10
RhIII (360 MHz, neutral D2O): δ 8.87 (s, 8 H, pyrrole), 3.19 (s,
aq
12 H, p-methyl), 2.12 (s, 24 H, m-methyl).
[(TMPS)Rh-D(D2O)]-8 (4) and [(TMPS)RhI(D2O)]-9 (5). A
0.3 mL acidic D2O solution of (TMPS)RhIII (3 × 10-3 M, [D+]
aq
> 10-5 M) was put into a NMR tube with vacuum adaptor and
treated with three freeze-pump-thaw cycles to remove the
dissolved air. H2/D2 gas (300-500 Torr) was introduced into the
NMR tube, and the tube was then flame-sealed. The reaction
achieves equilibrium distributions of [(TMPS)RhIII(D2O)2]-7, H2/
D2, and [(TMPS)Rh-D(D2O)]-8 species within 2 months at 298
K. The equilibrium constant was evaluated from the intensity
1
integrations of H NMR signals for each species in combination
with D+ concentration measurement and the solubility data of H2/
D2 in water.18 A 0.3 mL basic D2O solution of (TMPS)RhIIIaq (3 ×
10-3 M, [D+] < 10-10 M) was pressurized with H2/D2 (300-500
Torr) using the same procedure. Complete conversion to [(TMPS)-
RhI(D2O)]-9 was achieved in 7 days at 298 K. 1H NMR of
[(TMPS)Rh-D(D2O)]-8 (4) (D2O, 360 MHz): δ 8.57 (s, 8H,
1
pyrrole), 3.16 (s, 12H, p-methyl), 2.13 (s, 24 H, m-methyl). H
NMR of [(TMPS)RhI(D2O)]-9 (5): δ 8.03 (s, 8H, pyrrole), 3.01
(s,12 H, p-methyl), 2.28 (s, 24 H, m-methyl).
Acid Dissociation Constant Measurements for [(TMPS)RhIII-
(D2O)2]-7 and [(TMPS)Rh-D(D2O)]-8 in Water. The method
developed for determining the acid dissociation constants of
[(TSPP)RhIII(D2O)2]-3 and [(TSPP)Rh-D(D2O)]-4 complexes8 was
used to measure the acid dissociation constants of [(TMPS)-
RhIII(D2O)2]-7 and [(TMPS)Rh-D(D2O)]-8 in D2O. The mole
fraction averaged pyrrole proton resonance for the equilibrium
distributions of 1, 2, and 3 as a function of the concentration of
D+ (δ1,2,3(obs)(pyr) ) (K1K2δ3(pyr) + K1[D+]δ2(pyr) + [D+]2δ1-
(pyr))/(K1K2 + K1[D+] + [D+]2) was used in the determination of
Experimental Section
General Procedures. All manipulations were performed on a
high-vacuum line equipped with a Welch Duo-Seal vacuum pump
or in an inert atmosphere box unless otherwise noted. Substrates
were degassed by freeze-pump-thaw cycles immediately before
use. Reagent grade hydrogen and carbon monoxide were purchased
from Matheson Gas Products and used without further purification.
1H NMR spectra were obtained on a Bruker AC-360 spectrometer
interfaced to an Aspect 300 computer at ambient temperature.
Chemical shifts were referenced to 3-trimethylsilyl-1-propane-
sulfonic acid sodium salt. The pD measurements were performed
with an Orion 9802 electrode connected to an Orion 410 pH meter.
The pD values were derived by adding 0.451 to the meter readings.
(pD ) pHreading + 0.451, (25 °C)).15
the acid dissociation constants (298 K) for [(TMPS)RhIII(D2O)2]-7
.
Similarly, the mole fraction averaged pyrrole proton resonance for
equilibrium distributions of 4 and 5 as a function of the concentra-
tion of D+ (δ4,5(obs)(pyr) ) (K5δ5(pyr) + [D+]δ4(pyr))/(K5 + [D+]))
was used to determine the acid dissociation constant (298 K) for
[(TMPS)Rh-D(D2O)]-8. The first and second acid dissociation
constants for [(TMPS)RhIII(D2O)2]-7 are K1 ) 1.0(0.2) × 10-9 and
K2 ) 9.7(0.3) × 10-13, respectively. The acid dissociation constant
Syntheses of (TMPS)RhIII ([(TMPS)RhIII(D2O)2]-7 (1),
aq
for [(TMPS)Rh-D(D2O)]-8 is K5 ) 4.3(0.5) × 10-8
.
[(TMPS)RhIII(OD)(D2O)]-8 (2), [(TMPS)RhIII(OD)2]-9 (3)),
[(TMPS)Rh-D(D2O)]-8 (4), and [(TMPS)RhI(D2O)]-9 (5)).
Tetramesitylporphyrin (TMP)16 and its sulfonated derivative Na8-
Reaction of [(TMPS)Rh-D(D2O)]-8 with CO. A 0.3 mL D2O
solution of (TMPS)RhIII (3 × 10-3 M, [D+] > 10-5 M) was
aq
pressurized with 0.8 atm of a mixture of H2 and CO gases (H2/CO
) 3:7). The rhodium formyl complex [(TMPS)Rh-CDO(D2O)]-8
(6) was produced and equilibrated with the hydride complex
[(TMPS)Rh-D(D2O)]-8. The equilibrium constant was evaluated
17
(TMPS)H2 were synthesized by literature methods.
(TMPS)RhIIIaq. A 15 mL methanol solution of Na8(TMPS)H2
(100 mg, 0.06 mmol) and [RhCl(CO)2]2 (14 mg, 0.04 mmol) was
refluxed overnight. After the reaction was cooled to room temper-
ature, two drops of 3% aqueous H2O2 solution was added to the
reaction which oxidizes rhodium(I) to rhodium(III). After the
reaction solution was stirred at room temperature for 10 min, the
solvent was removed, and the product was purified on a silica gel
column with methanol as the eluent. A greater than 90% isolated
yield of [Na7(TMPS)RhIII(L)2] complex (L ) coordinated methanol)
was obtained. Dissolution in D2O results in an equilibrium
distribution of the bisaquo complex [(TMPS)RhIII(D2O)2]-7 (1),
monohydroxo complex [(TMPS)RhIII(OD)(D2O)]-8 (2), and bishy-
1
from intensity integrations of the porphyrin pyrrole hydrogen H
NMR signals for rhodium hydride and rhodium formyl complexes,
which are at 8.58 and 8.64 ppm, respectively. 1H NMR (360 MHz,
D2O) for [(TMPS)Rh-CDO(D2O)]-8: δ 8.64 (s, 8H, pyrrole), 3.14
(s, 12H, p-methyl), 2.26 (s, 12H, m-methyl), 1.95 (s, 12H,
m′-methyl).
Reactions of [(TMPS)RhI(D2O)]-9 and [(TMPS)Rh-D(D2O)]-8
with Ethene and Propene. A 0.3 mL D2O solution of freshly
prepared [(TMPS)Rh-D(D2O)]-8/[(TMPS)RhI(D2O)]-9 (3 × 10-3
M) in a vacuum-adapted NMR tube was degassed followed by
vacuum transfer of ethene or propene (300-500 Torr) into the
solution, then dihydrogen gas (300-500 Torr) was reintroduced
(15) (a) Gary, R.; Bates, R. G.; Robinson, R. A. J. Phys. Chem. 1964, 68,
1186. (b) Gary, R.; Bates, R. G.; Robinson, R. A. J. Phys. Chem.
1964, 68, 3806. (c) Gary, R.; Bates, R. G.; Robinson, R. A. J. Phys.
Chem. 1965, 69, 2750.
(16) Lindsey, J. S.; Wagner, R. W. J. Org. Chem. 1989, 54, 828.
(17) Ashley, K. R.; Shyu, S. B.; Leipoldt, J. G. Inorg. Chem. 1980, 19,
1613.
(18) Fog, P. G. T.; Gerrard, W. Solubility of Gases in Liquids: A Critical
EValuation of Gas/Liquid Systems in Theory and Practice; Wiley:
Chichester, U.K., 1991.
Inorganic Chemistry, Vol. 45, No. 24, 2006 9885

Fu et al.
Scheme 1. Simultaneous Equilibria that Occur in the (TMPS)Rh(III)/
D2 System in Water
1
Table 1. Characteristic Pyrrole H NMR (D2O) Chemical Shifts for
(TMPS)Rh Species
(TMPS)Rh species
pyrrole
Figure 1. Observed limiting fast-exchange mole fraction-averaged pyrrole
1H NMR chemical shifts for compounds 1, 2, and 3 in D2O as a function
of -log [D+]. The solid line is the nonlinear least-squares best-fit line giving
K1(298 K) ) 1.0(0.2) × 10-9 and K2(298 K) ) 9.7(0.3) × 10-13. δ1(pyr)
) 8.87 ppm, δ2(pyr) ) 8.75 ppm, and δ3(pyr) ) 8.63 ppm;.
[(TMPS)RhIII (D2O)2]-7 (1)
[(TMPS)RhIII(OD)(D2O)]-8 (2)
[(TMPS)RhIII(OD)2]-9 (3)
[(TMPS)Rh-D(D2O)]-8 (4)
[(TMPS)RhI(D2O)]-9 (5)
8.87
8.75
8.63
8.58
8.03
8.64
that are used in the identification of the (TMPS)Rh species
in D2O are listed in Table 1. The distribution of these
(TMPS)Rh species in D2O can be readily determined by
application of 1H NMR which provides a means to evaluate
equilibrium constants for each reaction.
Aquo and Hydroxo (TMPS)RhIII Complexes in Water.
Dissolution of (TMPS)RhIII in D2O results in solutions of
the bisaquo complex [(TMPS)RhIII(D2O)2]-7 (1) in equilib-
rium with mono- and bishydroxo complexes ([(TMPS)-
RhIII(OD)(D2O)]-8 (2) and [(TMPS)RhIII(OD)2]-9 (3)) (eqs
1 and 2). Rapid interchange of hydrogens from coordinated
water and hydroxide with bulk solvent water (T ) 275-
[(TMPS)Rh-CDO(D2O)]-8 (6)
into the sample to suppress the formation of (TMPS)RhIIIaq species.
Rhodium alkyl complexes [(TMPS)Rh-CH2CH2D(D2O)]-8 and
[(TMPS)Rh-CH2CHDCH3(D2O)]-8 were produced, respectively.
Reactions of the rhodium hydride with the olefins are completed
1
within the time needed to obtain H NMR spectra. Reactions of
[(TMPS)RhI(D2O)]-9 with the olefins are much slower and take as
long as two months to achieve equilibrium. The equilibrium
constants were evaluated from integration of the intensities of
1H NMR signals for rhodium alkyl and rhodium(I) complexes in
combination with concentrations of the small organic substrates in
water from solubility data18 and measurement of D+ concentration
which determines the equilibrium distributions of [(TMSP)Rh-
[(TMPS)RhIII(D2O)2]-7
[(TMPS)RhIII(OD)(D2O)]-8 + D+ (1)
h
D(D2O)]-8 and [(TMPS)RhI(D2O)]-9. H NMR (360 MHz, D2O)
1
of [(TMPS)Rh-CH2CH2D(D2O)]-8 (7): δ 8.52 (s, 8H, pyrrole),
3.16 (s, 12H, p-methyl), 2.28 (s, 12H, m-methyl), 2.02 (s, 12H,
m′-methyl), -2.18 (t, 2H, -CH2D, J1H-1H ) 8 Hz), -5.45 (t of d,
2H, -CH2, J1H-1H ) 8 Hz, J103Rh-1H ) 3 Hz). 1H NMR (360 MHz,
D2O) of [(TMPS)Rh-CH2CHDCH3(D2O)]-8 (8): δ 8.49 (s, 8H,
pyrrole), 3.14 (s, 12H, p-methyl), 2.22 (s, 12H, m-methyl), 2.02
(s, 12H, m′-methyl), -1.72 (d, 3H, -CH3, J1H-1H) 8 Hz), -4.31
(m, H, -CHD, J1H-1H ) 8 Hz), -5.38 (d of d, 2H, -CH2, J1H-1H
) 8 Hz, J103Rh-1H ) 3 Hz).
[(TMPS)RhIII(OD)(D2O)]-8
h
[(TMPS)RhIII(OD)2]-9 + D+ (2)
300 K) results in a single set of mole fraction averaged
porphyrin 1H NMR resonances for the equilibrium distribu-
tion of 1, 2, and 3 (Table 1). The mole fraction averaged
pyrrole proton resonance for equilibrium distributions of 1,
2, and 3 as a function of the concentration of D+ was used
in the determination of the acid dissociation constants (298
K) for 1 and 2 by nonlinear least-squares curve fitting to
the equation δ1,2,3(obs)(pyr) ) (K1K2δ3(pyr) + K1[D+]δ2(pyr)
+ [D+]2δ1(pyr))/(K1K2 + K1[D+] + [D+]2)8 (Figure 1)). The
acidities for 1 (K1 ) 1.0(0.2) × 10-9) and 2 (K2 ) 9.7(0.3)
× 10-13) are somewhat smaller than the values for
[(TSPP)RhIII(D2O)2]-3 and [(TSPP)RhIII(OD)(D2O)]-4 (K1 )
Reactions of [(TMPS)RhI(D2O)]-9 with RX (X ) I, Br, Cl;
R) CH3, CH2CH3, CH2CH2CH3) in D2O. Alkyl halides (1.2
equiv) were introduced by vacuum transfer into a 0.3 mL freshly
prepared D2O solution of [(TMPS)RhI(D2O)]-9 (3 × 10-3 M, [D+]
< 10-10 M) in a NMR tube with vacuum adaptor; rhodium alkyl
complexes [(TMPS)Rh-R(D2O)]-8 (R ) CH3, CH2CH3, CH2CH2-
CH3) were immediately formed and characterized by 1H NMR. 1H
NMR (360 MHz, D2O) of [(TMPS)Rh-CH3(D2O)]-8 (9): δ 8.51
(8H, pyrrole), 3.15 (16H, phenyl), 2.32 (s, 12H, m-methyl), 1.95
(s, 12H, m′-methyl), -6.2 (br, 3H, -CH3).
1.4(0.2) × 10-8 and K2 ) 2.8(0.3) × 10-12 7,8
)
and much
larger than the acid dissociation constant for pure D2O (eq
Results and Discussion
3) (K3(298 K) ) 2.44 × 10-17).19
Aqueous solutions of rhodium(III) tetrakis(3,5-disul-
fonatomesityl)porphyrin ((TMPS)RhIIIaq) complexes react
with dihydrogen to produce equilibrium distributions between
five rhodium species including a rhodium hydride, rhodium-
(I), and three rhodium(III) aquo and hydroxo complexes
(Scheme 1). The porphyrin pyrrole 1H NMR chemical shifts
D2O h D+ + OD-
(3)
Reactions of H2/D2 with Solutions of (TMPS)RhIII in
D2O. The bisaquo complex [(TMPS)RhIII(D2O)2]-7 (1) reacts
slowly with H2/D2 (PH ≈ 0.5-0.8 atm) in acidic D2O media
2
9886 Inorganic Chemistry, Vol. 45, No. 24, 2006

Rh Tetrakis(3,5-disulfonatomesityl)porphyrin Species
The aqueous acid dissociation constant of [(TMPS)Rh-
D(D2O)]-8 (K5 ) 4.3(0.5) × 10-8) is slightly smaller than
the value for [(TSPP)Rh-D(D2O)]-4 (K(298K) ) 8.0(0.5)
×10-8).7,8 The electron-releasing property of the mesityl
methyl groups and placement of the sulfonate groups in the
meta positions can be used to rationalize this observation.
The qualitative relationships between the (TMPS)Rh
species (Rh(III), Rh(II), Rh(I), and Rh-D) in D2O are
summarized by the pentagon shown in Scheme 1. Experi-
mentally measured quantitative relationships between the five
rhodium porphyrin species 1-8 depicted by reactions 1-8
are summarized in Table 2. The most prominent difference
between the (TMPS)Rh and (TSPP)Rh systems is that the
steric demands of the TMPS ligand preclude formation of a
RhII-RhII-bonded complex. Association of [(TSPP)Rh-alkyl-
(D2O)]-4 complexes in water and complex formation of
[(TSPP)RhI(D2O)]-5 with rhodium(III) species are also
blocked for (TMPS)Rh complexes by the large steric
demands of the TMPS ligand. The rhodium(II) complex
((TMPS)RhII) is not observed as a monomer in water because
of reaction with D2O that results in disproportionation into
(TMPS)RhI and (TMPS)RhIII species.
Figure 2. Limiting fast-exchange mole fraction-averaged 1H NMR
chemical shifts for [(TMPS)Rh-D(D2O)]-8 (4) and [(TMPS)RhI(D2O)]-9
(5) in D2O as a function of -log [D+]. The solid line is the nonlinear least
squares best fit line giving K5(298 K) ) 4.3(0.5) × 10-8: δ4(pyr) ) 8.58
ppm and δ5(pyr) ) 8.03 ppm.
([D+] > 10-6) to form the hydride complex [(TMPS)Rh-
D(D2O)]-8 (4) (eq 4). Reaction 4 achieves a conveniently
measurable equilibrium distribution of species. The equilib-
rium constant for reaction 4 (K4(298 K) ) 18.2(0.5)) was
evaluated by 1H NMR in combination with D+ concentration
Bond Dissociation Free Energy Difference between
Rh-OD and Rh-D. The difference in the Rh-OD and
Rh-D bond dissociation free energies (BDFE) can be
obtained by using reaction 9 in Table 3 ([(TMPS)-
RhIII(OD)(D2O)]-8 + D2 h [(TSPP)Rh-D(D2O)]-8 + D2O).
The difference in the (Rh-OD)aq and (Rh-D)aq bond
dissociation free energies (BDFE) is derived by expressing
∆G9° in terms of a BDFE for each bond formed or broken
[(TMPS)RhIII(D2O)2]-7 + D2 h
[(TMPS)Rh-D(D2O)]-8 + D+ + D2O (4)
measurements and the solubility of D2 in water. The
equilibrium constant for the reaction of (TMSP)RhIII with
dihydrogen is indistinguishable from the value for the
reaction of (TSPP)RhIII with dihydrogen.8
Solutions of (TMPS)RhIII in basic media ([D+] ≈ 10-8-
10-11 M), where the (TMPS)RhIII mono- and bishydroxo
complexes 2 and 3 predominate, give a much faster reaction
with H2/D2 than the reactions in acidic media and result in
formation of the rhodium(I) complex [(TMPS)RhI(D2O)]-9
(5).
Acid Dissociation Constant of [(TMPS)Rh-D(D2O)]-8.
Protonation of [(TMPS)RhI(D2O)]-9 (5) produces the rhod-
ium hydride complex 4 by the reverse of eq 5. Aqueous
solutions that contain both 4 and 5 manifest a single mole
in reaction 9 (∆G9° ) -14.0 kcal mol-1 ) (Rh-OD)aq
+
(D-D)aq - (Rh-D)aq - (D-OD)aq; ((Rh-OD)aq - (Rh-
D)aq) ) -14.0 - (D-D)aq + (D-OD)aq) -14.0 - 103.4
+ 117.6 ) 0.2 kcal mol-1;19,20,21 (Rh-OH)aq - (Rh-H)aq
≈ 1.2 kcal mol-1).
The difference of ∼0.2 kcalmol-1 between the [(TMPS)-
Rh-OD]aq and [(TMPS)Rh-D]aq BDFE is slightly smaller
than the 1.8 kcal mol-1 BDFE difference between (TSPP)-
Rh-OD and (TSPP)Rh-D.8 A BDFE of 60(2) kcal mol-1
has been previously estimated for the (TSPP)Rh-D and the
(TMPS)Rh-D BDFE is undoubtedly also close to 60 kcal
mol-1.
[(TMPS)Rh-D(D2O)]-8 h [(TMPS)RhI(D2O)]-9 + D+
Reaction of [(TMPS)RhII(D2O)]-8 with D2O. The rhod-
ium(II) complex [(TMPS)RhII(D2O)]-8 is not observed by
1H NMR at the conditions where [(TSPP)RhII(D2O)]-4
(5)
fraction averaged 1H NMR resonance that results from rapid
proton interchange between 4 and 5. A plot of δ4,5(obs)(pyr)
for equilibrium distributions of 4 and 5 in D2O at a series of
hydrogen ion (D+) concentrations is illustrated in Figure 2.
dimerizes by RhII-RhII bonding to form [(TSPP)RhII(D2O)]2-8
.
The lack of observation of [(TMPS)RhII(D2O)]-8 is undoubt-
edly the result of reaction of the Rh(II) complex with water
(eq 17). Using BDFE value of 60 kcal mol-1 for the (TMPS)-
Rh-D and (TMPS)Rh-OD and 117.6 kcal mol-1 for the
BDFE of D-OD in water8 gives an estimate of -2.4 kcal
mol-1 for ∆G17° (298 K).
The mole fraction-averaged pyrrole proton resonances (δ4,5(obs)
-
(pyr)), as a function of the molar concentration of D+ was
used to determine the acid dissociation constant for the
hydride 4 at 298 K (K5 ) 4.3(0.5) × 10-8) by nonlinear
least-squares curve fitting to the relationship δ4,5(obs)(pyr) )
(K5δ5(pyr) + [D+]δ4(pyr))/(K5 + [D+]).
2 [(TMPS)RhII(D2O)]-8 + D-OD h
[(TMPS)Rh-D(D2O)]-8 + [(TMPS)Rh-OD(D2O)]-8 (17)
(19) Values are obtained from J. Phys. Chem. Ref. Data, 1982, 11,
supplement 2. Standard state used is 298.15 K and 0.1 MPa.
Inorganic Chemistry, Vol. 45, No. 24, 2006 9887

Fu et al.
Table 2. Measured and Calculated Equilibrium Constants (Kn) and ∆G°(298 K) (kcal mol-1) for (TMPS)Rh Reactions in D2Oa
Kn
(298 K)
∆G°
(kcal mol-1
)
(TMPS)Rh reactions
1
2
3
4
5
6
7
8
[RhIII(D2O)2]-7 h [RhIII(OD)(D2O)]-8 + D+
[RhIII(OD)(D2O)]-8 h [RhIII(OD)2]-9 + D+
D2O h OD- + D+
K1 ) 1.0(0.2) × 10-9
K2 ) 9.7(0.3) × 10-13
K3 ) 2.4 × 10-17
K4 ) 18.2(0.5)
+12.3(0.1)
+16.4(0.1)
+22.6b
[RhIII(D2O)2]-7 + D2 h [Rh-D(D2O)]-8 + D++ D2O
[Rh-D(D2O)]-8 h [RhI(D2O)]-9 + D+
[Rh-D(D2O)]-8 + CO h [Rh-CDO(D2O)]-8
D+ + D- h D2
-1.7(0.1)
+10.0(0.1)
-4.4(0.1)
-53.2c
K5 ) 4.3(0.5) × 10-8
K6 ) 1.7(0.1) × 103
K7 ) 5.2 × 1037
8 [Rh-D(D2O)]-8 + CH3-CHdCH2 h [Rh-CH2CHDCH3(D2O)]-8
K8 ) 5.7(0.1) × 103
-5.1(0.1)
a The reported K values correspond to equilibrium constant expressions that contain all constituents given in the chemical equation including water. b The
-log (ion product) of D2O (14.869) (K ) 1.35 × 10-15) and the D2O density (1.1044) were used to determine the K3 ) 2.44 × 10-17 at 298 K. c E°(2H+
+ 2e- h H2) ) 0.00 V and E°(2H- h H2 + 2e-) ) +2.23 V were used to evaluate ∆G°(H+ + H- h H2) ) -51.4 kcal mol-1 and ∆G°(D+ + D- h D2)
) - 53.2 kcal mol-1 (CRC Handbook of Chemistry and Physics, 71st ed.; Lide, D. R., Ed.; CRC Press: Boca Raton, FL, 1990-1991; pp 8-38, 6-11, and
8-17).
Table 3. Equilibrium Constants (298 K) and the ∆G°(298 K) (kcal mol-1) for (TMPS)Rh Reactions Derived from Reactions in Table 2
∆G°
a
derived (TMPS)Rh reactions
Kn
(kcal mol-1
)
9
[RhIII(OD)(D2O)]-8 + D2 h [Rh-D(D2O)]-8 + D2O
[RhIII(OD)2]-9 + D2 h [RhI(D2O)]-9 + D2O
K9 ) K4/K1 ) 1.8 × 1010
K10 ) K4K5/(K1K2) ) 8.1 × 1014
K11 ) K1/K3 ) 4.1 × 107
K12 ) K4K7 ) 1.8 × 1040
K13 ) K4K6 /K1 ) 3.1 × 1013
K14 ) K3K6 /K5 ) 9.6 × 10-7
K15 ) K1 /K5 ) 2.3 × 10-2
K16 ) K4 /K5 ) 4.2 × 108
-14.0(0.1)
-20.4(0.1)
-10.4(0.1)
-54.9
10
11
12
13
14
15
16
[RhIII(D2O)2]-7 + OD- h [Rh(OD)(D2O)]-8 + D2O
[RhIII(D2O)2]-7 + D- h [Rh-D(D2O)]-8 + D2O
[RhIII(OD)(D2O)]-8 + D2 + CO h [Rh-CDO(D2O)]-8 + D2O
[RhI(D2O)]-9 + D2O + CO h [Rh-CDO(D2O)]-8 + OD-
[RhIII(D2O)2]-7 + [RhI(D2O)]-9 h [Rh(OD)(D2O)]-8 + [Rh-D(D2O)]-8
[RhIII(D2O)2]-7 + [RhI(D2O)]-9 +D2 h 2 [Rh-D(D2O)]-8 + D2O
-18.4(0.1)
8.2(0.1)
2.2(0.1)
-11.7
a The reported K values correspond to equilibrium constant expressions that contain all constituents given in the chemical equation including water (T )
298 K).
The absence of observable quantities of a (TMPS)RhII
species in D2O indicates that the average Rh-D and Rh-
OD BDFE must be at least 60 kcal mol-1. The capability
for a (TSPP)RhII species to occur at observable concentra-
tions in water is a result of the dimerization by RhII-RhII
Scheme 2. Reactivity Patterns of [(TMPS)Rh-D(D2O)]-8 in Water
bonding (∆G° ∼ -12(2) kcal mol-1) to form [(TSPP)-
-8
RhII(D2O)]2
.
Reactions of [(TMPS)RhI(D2O)]-9 and [(TMPS)Rh-
D(D2O)]-8 with CO and Olefins in Water. Reactions of
rhodium(III) porphyrins with hydrogen (H2/D2) in water
produce a rhodium hydride as part of a more complex set of
simultaneous equilibria involving a rhodium(I) complex and
several rhodium(III) species. Knowledge of the equilibrium
thermodynamic relationships between the solution species
in D2O permitted the establishment of conditions used in
this study where either the rhodium hydride (Rh-H) or
rhodium(I) complex is the only (TMPS)Rh species present
in observable concentrations. The thermodynamic objectives
have been advanced by directly measuring the equilibrium
distributions of species for each of the substrate reactions in
aqueous solution and evaluating the corresponding equilib-
rium constants.
The hydride complex ([(TMPS)Rh-D(D2O)]-8) is a weak
acid (Ka(298 K) ) 4.3(0.5) × 10-8) and reacts in water with
substrates such as CO and olefins to produce rhodium formyl
and rhodium alkyl complexes (Scheme 2). The quantitative
rates of reactions for [(TMPS)Rh-D(D2O)]-8 with CO and
olefins are similar to those for the less sterically demanding
and more acidic [(TSPP)Rh-D(D2O)]-4.9
Comparisons of Equilibrium Constants (Kn) and ∆Gn°
(kcal mol-1) for Substrate Reactions of (TSPP)Rh and
(TMPS)Rh in Water (298 K). The equilibrium constants
for reactions of [(TMPS)RhIII(D2O)2]-7 with D2 and [(TMPS)-
Rh-D(D2O)]-8 with CO and CH2dCHCH3 were directly
1
measured in water by H NMR. The reaction of [(TMPS)-
RhIII(D2O)2]-7 (298 K) with D2 has K4 ) 18.2(0.5) (∆G4°
) -1.7(0.1) kcal mol-1), which is the same as that previously
measured for the reaction of [(TSPP)RhIII(D2O)2]-3 with D2.8
The reaction of [(TMPS)Rh-D(D2O)]-8 with CO (298 K)
to form [(TMPS)Rh-CDO(D2O)]-8 (6) has an equilibrium
constant (K6 ) 1.7(0.1) × 103, ∆G6 ) -4.4(0.1) kcal mol-1)
which is close to the value previously measured for the
reaction of [(TSPP)Rh-D(D2O)]-4 with CO (K ) 3.0(0.3)
× 103, ∆G ) -4.7(0.1) kcal mol-1, T ) 298 K) in water.9
Comparisons of equilibrium constants (Kn) and ∆Gn° (kcal
mol-1) (298 K) for reactions of (TSPP)Rh and (TMPS)Rh
derivatives in water are listed in Table 4. The acid dissocia-
tion constants for the (TMPS)RhIII aquo/hydroxo complexes
(1 and 2) and the hydride [(TMPS)Rh-D(D2O)]-8 (4) are
(20) Blanksby, S. J.; Ellison, G. B. Acc. Chem. Res. 2003, 36, 255.
(21) (a) Han, P.; Bartels, D. M. J. Phys. Chem. 1990, 94, 7294. (b) Schwarz,
H.; Dodson, R. W. J. Phys. Chem. 1984, 88, 3643. (c) Hamad, S.;
Lago, S.; Mejias, J. A. J. Phys. Chem. A 2002, 106, 9104.
9888 Inorganic Chemistry, Vol. 45, No. 24, 2006

Rh Tetrakis(3,5-disulfonatomesityl)porphyrin Species
Table 4. Equilibrium Constants (Kn) and ∆Gn° (kcal mol-1) for Substrate Reactions of (TSPP)Rh and (TMPS)Rh in Water (298 K)
(TSPP)Rh
(TMPS)Rh
(por)Rh reactionsa
Kn
∆Gn°
Kn
∆Gn°
[RhIII(D2O)2]-n h [RhIII(OD)(D2O)]-(n+1) + D+
1.4 × 10-8
+10.7
+15.8
-1.7
+9.7
-4.7
-6.2
1.0 × 10-9
+12.3
+16.4
-1.7
[RhIII(OD)(D2O)]-(n+1) h [RhIII(OD)2]-(n+2) + D+
[RhIII(D2O)2]-n + D2 h [Rh-D(D2O)]-(n+1) + D+ + D2O
[Rh-D(D2O)]-(n+1) h [RhI(D2O)]-(n+2) + D+
2.8 × 10-12
9.7 × 10-13
18.2
18.2
8.0 × 10-8
3.0 × 103
3.7 × 104
4.3 × 10-8
1.7 × 103
5.7 × 103
+10.0
-4.4
[Rh-D(D2O)]-(n+1) + CO h [Rh-CDO(D2O)]-(n+1)
[Rh-D(D2O)]-(n+1) + CH2dCHCH3 h [Rh-CH2CHDCH3(D2O)]-(n+1)
-5.1
a n ) 3 (TSPP); n ) 7 (TMPS).
all smaller than the values for the (TSPP)Rh system.8,9 The
reduced capability of (TMPS)Rh to stabilize negative charge
compared to (TSPP)Rh is consistent with the electron-
releasing character of the o,p-methyl groups and placement
of the sulfonate groups in the meta positions in the TMPS
ligand.
(TMPS)Rh-CDO BDFE. Reaction of the hydride 4 with
CO (eq 6) produces the rhodium formyl complex 6 with a
∆G6° (298K) of -4.4(0.1) kcal mol-1. The thermodynamic
cycle gives 44(3) kcal mol-1 for the Rh-CDO BDFE in
(TMPS)Rh-CDO which is indistinguishable from the value
previously determined for (TSPP)Rh-CDO (Rh-CDO
BDFE ) 44(3) kcal mol-1).9
butions of rhodium hydride and rhodium(I) complexes. Acid
dissociation constants for the (TMPS)Rh aquo and hydride
complexes are somewhat smaller than the corresponding
values for the (TSPP)Rh derivatives which indicates that
TSPP can stabilize negative charge better than the TMPS
ligand. The Steric demands of the TMPS porphyrin ligand
prohibit formation of a Rh(II)-Rh(II)-bonded dimer species,
related rhodium(I) complexes with rhodium(III) species, and
intermolecular association of alkyl complexes which are
prominent features of the rhodium tetra(p-sulfonatophenyl)-
porphyrin ((TSPP)Rh) system. Reactions of the hydride
complex [(TMPS)Rh-D(D2O)]-8 in water with CO and
olefins produce rhodium formyl and alkyl complexes.
Equilibrium thermodynamic values for substrate reactions
of (TMPS)Rh-D in water are comparable to the values for
the reactions of (TSPP)Rh-D. A (TMPS)RhII complex is
not observed in D2O because of the thermodynamically
favorable reaction with D2O which is anticipated from bond
dissociation free-energy (BDFE) values for (TMPS)Rh-D
(60 kcal mol-1), (TMPS)Rh-OD (60 kcal mol-1), and
D-OD (117 kcal mol-1).8 The difference in the (TMPS)-
Rh-OD and (TMPS)Rh-D bond dissociation free energies
(BDFE) is negligible (∼0.2 kcal mol-1) and slightly smaller
than the difference of ∼1.8 kcal mol-1 measured for the
(TSPP)Rh system.
Conclusions
Acknowledgment. This research was supported by the
Department of Energy, Division of Chemical Sciences, Office
of Science through grant DE-FG02-86ER-13615.
Aqueous (D2O) solutions of tetrakis(3,5-disulfonatomesi-
tyl)porphyrin rhodium(III) aquo/hydroxo complexes ((TMPS)-
RhIIIaq) react with dihydrogen to produce equilibrium distri-
IC0615022
Inorganic Chemistry, Vol. 45, No. 24, 2006 9889