Formation and reactivity of a porphyrin iridium hydride in water: Acid dissociation constants and equilibrium thermodynamics relevant to Ir-H, Ir-OH, and Ir-CH2-bond dissociation energetics

Article abstract of DOI:10.1021/ic201553k

Aqueous solutions of group nine metal(III) (M = Co, Rh, Ir) complexes of tetra(3,5-disulfonatomesityl)porphyrin [(TMPS)M^III] form an equilibrium distribution of aquo and hydroxo complexes ([(TMPS)M ^III(D₂O)_2-n(OD)_n]^(7+n)-). Evaluation of acid dissociation constants for coordinated water show that the extent of proton dissociation from water increases regularly on moving down the group from cobalt to iridium, which is consistent with the expected order of increasing metal-ligand bond strengths. Aqueous (D₂O) solutions of [(TMPS)Ir^III(D₂O)₂]^7- react with dihydrogen to form an iridium hydride complex ([(TMPS)Ir-D(D₂O)] ^8-) with an acid dissociation constant of 1.8(0.5) × 10 ^-12 (298 K), which is much smaller than the Rh-D derivative (4.3 (0.4) × 10^-8), reflecting a stronger Ir-D bond. The iridium hydride complex adds with ethene and acetaldehyde to form organometallic derivatives [(TMPS)Ir-CH₂CH₂D(D₂O)] ^8- and [(TMPS)Ir-CH(OD)CH₃(D₂O)]^8-. Only a six-coordinate carbonyl complex [(TMPS)Ir-D(CO)]^8- is observed for reaction of the Ir-D with CO (P_CO = 0.2-2.0 atm), which contrasts with the (TMPS)Rh-D analog which reacts with CO to produce an equilibrium with a rhodium formyl complex ([(TMPS)Rh-CDO(D₂O)] ^8-). Reactivity studies and equilibrium thermodynamic measurements were used to discuss the relative M-X bond energetics (M = Rh, Ir; X = H, OH, and CH₂-) and the thermodynamically favorable oxidative addition of water with the (TMPS)Ir(II) derivatives.

Full text of DOI:10.1021/ic201553k

ARTICLE
pubs.acs.org/IC
Formation and Reactivity of a Porphyrin Iridium Hydride in Water: Acid
Dissociation Constants and Equilibrium Thermodynamics Relevant to
IrꢀH, IrꢀOH, and IrꢀCH2ꢀ Bond Dissociation Energetics
Salome Bhagan and Bradford B. Wayland*
Department of Chemistry, Temple University, 130 Beury Hall, 1901 North 13th Street, Philadelphia, Pennsylvania 19122, United States
S Supporting Information
b
ABSTRACT: Aqueous solutions of group nine metal(III) (M = Co, Rh, Ir) complexes
of tetra(3,5-disulfonatomesityl)porphyrin [(TMPS)MIII] form an equilibrium dis-
tribution of aquo and hydroxo complexes ([(TMPS)MIII(D2O)2ꢀn(OD)n](7+n)ꢀ).
Evaluation of acid dissociation constants for coordinated water show that the extent of
proton dissociation from water increases regularly on moving down the group from
cobalt to iridium, which is consistent with the expected order of increasing
metalꢀligand bond strengths. Aqueous (D2O) solutions of [(TMPS)IrIII(D2O)2]7ꢀ
react with dihydrogen to form an iridium hydride complex ([(TMPS)IrꢀD(D2O)]8ꢀ
)
with an acid dissociation constant of 1.8(0.5) ꢁ 10ꢀ12 (298 K), which is much smaller than the RhꢀD derivative (4.3 (0.4) ꢁ 10ꢀ8),
reflecting a stronger IrꢀD bond. The iridium hydride complex adds with ethene and acetaldehyde to form organometallic derivatives
[(TMPS)IrꢀCH2CH2D(D2O)]8ꢀ and [(TMPS)IrꢀCH(OD)CH3(D2O)]8ꢀ. Only a six-coordinate carbonyl complex [(TMPS)Irꢀ
D(CO)]8ꢀ is observed for reaction of the IrꢀD with CO (PCO = 0.2ꢀ2.0 atm), which contrasts with the (TMPS)RhꢀD analog which
reacts with CO to produce an equilibrium with a rhodium formyl complex ([(TMPS)RhꢀCDO(D2O)]8ꢀ). Reactivity studies and
equilibrium thermodynamic measurements were used to discuss the relative MꢀX bond energetics (M = Rh, Ir; X = H, OH, and CH2ꢀ)
and the thermodynamically favorable oxidative addition of water with the (TMPS)Ir(II) derivatives.
’ INTRODUCTION
for analogous reactions in hydrocarbon media with the exception
of addition of RhꢀH to alkenes where formation of highly
hydrophobic alkyl groups is much less favorable in water.28,84
Substrate reactions of (por)RhꢀH are generally much faster in
water compared to benzene which is ascribed to more versatile
reaction pathways and in particular the capability of water to
support ionic species and heterolysis routes.28,84
Water as a reaction medium and as a reactant for transition-
metal-induced transformations and catalysis is a major contem-
porary topic1ꢀ20 and a projected area for future growth.21ꢀ23
Our contributions in this area have been focused on the behavior
of group nine (Co, Rh, Ir) metal complexes with sulfonated
porphyrin ligands in water24ꢀ29 and methanol.30ꢀ35 Primary
objectives for these studies have encompassed defining the
nature and thermodynamic interrelationships for species in
solution, establishing the range of small molecule reactivity,
and identifying prominent reaction pathways.
This article reports on reactivity and thermodynamic studies
for aqueous solutions of tetra(3,5-disulfonatomesityl)porphyrin
iridium(III) aquo and hydroxo complexes ([(TMPS)MIII
(D2O)2ꢀn(OD)n](7+n)ꢀ) in D2O. The (TMPS)Ir system was
selected for study because the steric demands of the mesityl
derivative inhibit IrꢀIr bonding and suppress intermolecular
interactions that can occur for the less sterically demanding
tetra(p-sulfonatophenyl)porphyrin (TSPP) derivative. The Ir-
(III) complex reacts with H2(D2) to form a hydride complex
([(TMPS)IrIIIꢀD(D2O)]8ꢀ) that reacts with olefins and alde-
hydes to form iridium alkyl and α-hydroxyalkyl complexes, but
CO reacts to form only a carbon monoxide complex [(TMPS)Irꢀ
D(CO)]8ꢀ without observation of an iridium formyl species
(IrꢀCHO). Results from equilibrium thermodynamic studies
are used in discussing relative IrꢀH, IrꢀOH, and IrꢀCH2ꢀ
bond dissociation energetics in water and free energy favorable
(exergonic) oxidative addition of water with iridium(II)
porphyrins.
Rhodium porphyrins have a highly developed and extensive
reaction chemistry in diverse reaction media31,34,36ꢀ66 compared
with studies of the iridium derivatives,24,41,67ꢀ79 which are in a
relatively early stage of development. Prior studies in this series
have examined the equilibrium between group nine metallopor-
phyrin aquo and hydroxo complexes in water, reactions of
rhodium(III) with hydrogen to form equilibrium distributions
of RhꢀH and Rh(I) species, and the reactivity patterns and
thermodynamics for small molecule substrate reactions of Rh(I),
Rh(II), Rh(III), and RhꢀH derivatives.27,28,80ꢀ83
Oxidative addition of water to Rh(II)porphyrins, formation of
β-hydroxyalkyl complexes from reactions of olefins with Rh(III),
and reactions of the RhꢀH with olefins, aldehydes, and CO that
produce alkyl, α-hydroxyalkyl, and formyl (RhꢀCHO) com-
plexes are important types of transformations observed in
aqueous media. Free energy changes for most substrate reactions
of rhodium porphyrins in water are remarkably similar to those
Received: July 20, 2011
Published: October 14, 2011
r
2011 American Chemical Society
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dx.doi.org/10.1021/ic201553k Inorg. Chem. 2011, 50, 11011–11020
|

Inorganic Chemistry
ARTICLE
’ RESULTS AND DISCUSSION
function of [D+] (Figure 2) were used in determining the acid
dissociation constants for reactions 1 and 2 from nonlinear least-
squares curve fitting giving the expression δ2,3,4(obs)(pyr) =
Aquo and Hydroxo Complexes of (TMPS)IrIII in Water.
(K1K2δ3(pyr) + K1[D+]δ2(pyr) + [D+]2δ1(pyr))/(K1K2
+
Dissolution of the hydrated tetra(3,5-disulfonatomesityl)porphyrin
iridium(III) complex (Na7[(TMPS)IrIII(D2O)2] 18D2O) in
K1[D+] + [D+]2) (K1(298 K) = 2.8 ꢁ 10ꢀ8, K2(298 K) =
2.5 ꢁ 10ꢀ11 and (δ1(pyr) = 8.63 ppm, δ3(pyr) = 8.27 ppm)
(Table 2).27,85 The equilibrium distribution of 1, 2, and3in D2Oasa
function of the hydrogen-ion concentration is illustrated in Figure 2b.
Comparison of Acid Dissociation Constants for Coordi-
nated D2O in [(TMPS)M(D2O)2]7ꢀ Complexes in Water (M =
Co, Rh, Ir). Results from evaluation of the acid dissociation
constants for coordinated water in aquo and hydroxo complexes of
[(TMPS)MIII] (M = Co, Rh, Ir) in D2O using 1H NMR are given
in Table 1. The relative acidities of the [(TMPS)MIII(D2O)2]7ꢀ
(M = Co, Rh, Ir) complexes increase regularly proceeding down
group nine from Co to Ir, which reflects the expected trend of
increasing metalꢀwater ligand bond strengths.86ꢀ88 Substitu-
tion of TMPS for TSPP results in a decrease in the correspond-
ing acid dissociation constants for [(TMPS)MIII(D2O)2]7ꢀ
(M = Co, Rh, Ir) (Table 1), which is consistent with the in-
creased electron-releasing property of TMPS and decreased
positive charge on the metal center relative to the TSPP complexes
(Table 1). Sensitivity of theacid dissociation constants to changing
the porphyrin from TMPS to TSPP decreases markedly going
down group nine from cobalt to iridium (Table 1).
3
D2O results in an equilibrium distribution of the bis-aquo
complex ([(TMPS)IrIII(D2O)2]7ꢀ) (1) with mono- and
bis-hydroxo complexes [(TMPS)IrIII(OD)(D2O)]8ꢀ (2) and
[(TMPS)IrIII(OD)2]9ꢀ (3) (eqs 1 and 2) (Figure 1). The axially
coordinated water and hydroxide ligands for 1, 2, and 3 in aqueous
media rapidly interchange protons with the bulk water (298 K),
which results in a single mole fraction averaged pyrrole 1H NMR
resonance for 1, 2, and 3 (Figure 2).
7ꢀ
8ꢀ
½ðTMPSÞIrIIIðD2OÞ2ꢂ h ½ðTMPSÞIrIIIðODÞðD2OÞꢂ þ Dþ
ð1Þ
8ꢀ
9ꢀ
½ðTMPSÞIrIIIðODÞðD2OÞꢂ h ½ðTMPSÞIrIIIðODÞ2ꢂ þ Dþ
ð2Þ
1H NMR spectra of the bis-aquo (1) and bis-hydroxo (3)
complexes are directly observed at limiting low and high pD,
respectively. The mole fraction averaged pyrrole 1H NMR
resonances for equilibrium distributions of 1, 2, and 3 as a
7ꢀ
½ðTMPSÞMIIIðD2OÞ2ꢂ þ ODꢀ
h
8ꢀ
½ðTMPSÞMIIIðODÞðD2OÞꢂ þ D2O
ð3Þ
8ꢀ
½ðTMPSÞMIIIðODÞðD2OÞꢂ þ ODꢀ
h
9ꢀ
½ðTMPSÞMIIIðODÞ2ꢂ þ D2O
ð4Þ
ð5Þ
D2O h Dþ þ ODꢀ
The free energy changes for displacement of water by hydro-
xide for [(TMPS)MIII(D2O)2]7ꢀ (M = Co, Rh,26 Ir) complexes
are derived using reactions 1 and 2 along with the free energy for
dissociation of D2O (eq 5) (ΔG3° = ΔG1° ꢀ ΔG5°, ΔG4° =
ΔG2° ꢀ ΔG5°ꢃ, where ΔG5° = 22.6 kcal molꢀ1) . The binding of
hydroxide is substantially more favorable than water in all cases,
and the difference increases when moving down group nine from
Figure 1. Water and hydroxide complexes of (TMPS) IrIII in water
(D2O).
1
Figure 2. (a) Observed limiting fast exchange mole fraction averaged pyrrole H NMR chemical shifts for [(TMPS)IrIII(D2O)2ꢀn(OD)n](7ꢀn)ꢀ
complexes 1, 2, and 3 in D2O. Points are experimentally determined values, and lines are calculated for K1(298 K) = 2.8 ꢁ 10ꢀ8 and K2(298 K) =
2.5 ꢁ 10ꢀ11.. (b) Equilibrium distributions of 1, 2, and 3 as a function of the hydrogen-ion concentration in D2O at 298 K calculated for K1(298 K) =
2.8 ꢁ 10ꢀ8 and K2(298 K) = 2.5 ꢁ 10ꢀ11; total [(TMPS)IrIII] = 1.0 ꢁ 10ꢀ3 M.
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Inorganic Chemistry
ARTICLE
Table 1. First and Second Acid Dissociation Constants of Water (K1, K2) (298 K) and Free Energy Changes (ΔG1°, ΔG2°)
(kcal/mol) (298 K) for [(L)MIII(D2O)]2]7ꢀ (L = TSPP, TMPS) (M = Co, Rh, Ir)a in D2O
TSPP
TMPS
MIII
K1
ΔG1°
K2
ΔG2°
K1
ΔG1°
K2
ΔG2°
Co
Rh
Ir
8.8 ꢁ 10ꢀ9
1.4 ꢁ 10ꢀ8
4.8 ꢁ 10ꢀ8
+10.9
+10.6
+9.90
7.1 ꢁ 10ꢀ13
2.8 ꢁ 10ꢀ12
2.6 ꢁ 10ꢀ11
+16.4
+15.6
+14.3
2.0 ꢁ 10ꢀ10
1.0 ꢁ 10ꢀ9
2.8 ꢁ 10ꢀ8
+13.2
+12.3
+10.3
2.5 ꢁ 10ꢀ14
2.8 ꢁ 10ꢀ13
2.5 ꢁ 10ꢀ11
+18.5
+17.1
+14.5
a References for previously reported values (TSPP)Rh,27 (TSPP)Ir,24 (TMPS)Rh.25
Table 2. Free Energy Changes (ΔG3°, ΔG4° (298 K)
(kcal/mol)) for Reactions 3 and 4 That Substitute
Hydroxide for Water in Complex [(L)MIII(D2O)]2]7ꢀ
(L = TSPP, TMPS; M = Co, Rh, Ir) in D2O
TSPP
TMPS
[(L)MIII(D2O)2]7ꢀ
ΔG3°
ΔG4°
ΔG3°
ΔG4°
Co
Rh
Ir
ꢀ11.7
ꢀ12.0
ꢀ13.7
ꢀ6.1
ꢀ6.8
ꢀ8.2
ꢀ9.4
ꢀ10.3
ꢀ12.3
ꢀ4.1
ꢀ5.5
ꢀ8.1
Figure 4. Hydrogen-ion dependence of the equilibrium of [(TMPS)IrIII-
(D2O)2]7ꢀ shown at 8.63 ppm and [(TMPS)IrꢀD(D2O)]8ꢀ shown at
8.36 ppm.
Table 3). Dissolution of [(TMPS)IrꢀD(D2O)]8ꢀ (5) in
H2O/D2O (92:8) at pH 5ꢀ6 resulted in the observation of the
very high field iridium hydride 1H NMR resonance at ꢀ59.1 ppm,
which is permitted by the limiting slow exchange of IrꢀD with
Figure 3. Simultaneous equilibria that occur between iridium porphyrin
species from reaction of [(TMPS)Ir(D2O)2]7ꢀ with D2 in D2O solution.
1
D2O. Exceptionally high-field H NMR positions for iridium
hydrides compared to rhodium hydrides is one of the consequences
of larger relativistic effects for iridium complexes.90 Observation of
the inequivalence of the o-Me groups by 1H NMR of 5 is also a
manifestation of the slow proton exchange with water,50 which is
distinctly different from the fast proton exchange observed for
[(TMPS)RhꢀD(D2O)]8ꢀ complex in water (D2O).25
cobalt to iridium and is further increased for the less electron-
donating porphyrin (TSPP), where there is a larger net positive
charge on the metal center (Table 2).
Reaction of (TMPS)IrIII Species with H2/D2 in D2O. Aqueous
solutions of tetra(3,5-disulfonatomesityl)porphyrin iridium(III)
react with hydrogen to produce equilibrium distributions be-
tween five iridium species including iridium hydride, iridium(I),
and three iridium(III) aquo and hydroxo complexes that depend
on the hydrogen-ion and dihydrogen concentrations (Figure 3).
Equilibrium Constant To Form IrꢀD from Reaction of
[(TMPS)IrIII(D2O)2]7ꢀ with D2/H2 in D2O. The bisaquo complex
(1) reacts slowly with H2/D2 (P(H2) ≈ 0.6ꢀ0.9 atm) at
relatively high hydrogen-ion concentrations ([D+] > 10ꢀ3) to
produce an equilibrium distribution with the iridium hydride
[(TMPS)IrꢀD(D2O)]8ꢀ (5) (eq 6)
Equilibrium thermodynamics for reactions of [(TMPS)IrIII-
(OD)(D2O)]8ꢀ (2) (eq 7) and [(TMPS)IrIII(OD)2]9ꢀ (3) (eq 8)
with H2/D2 in water to form [(TMPS)IrꢀD(D2O)]8ꢀ (5) can
be derived (K7 = K6K1ꢀ1; K8 = K6K1ꢀ1K2ꢀ1) (Table 3). Reac-
tion of the iridium(III) complexes with hydrogen becomes more
exergonic in basic aqueous media.
8ꢀ
8ꢀ
½ðMIIIðODÞðD2OÞꢂ þ D2 h ½MꢀDðD2OÞꢂ þ D2O
ð7Þ
9ꢀ
8ꢀ
½ðMIIIðODÞ2ꢂ þ D2 þ Dþ h ½MꢀDðD2OÞꢂ þ D2O ð8Þ
Solutions of iridium(III) porphyrin in strongly basic D2O ([D+]
≈ 10ꢀ11) react with H2/D2 (P(H2) ≈ 0.5ꢀ0.6 atm) to form the
iridium(I) complex, [(TMPS)IrI(D2O)]9ꢀ (4). Complex 4 is
7ꢀ
½ðTMPSÞIrIIIðD2OÞ2ꢂ þ D2 h
8ꢀ
½ðTMPSÞIrꢀDðD2OÞꢂ þ Dþ þ D2O
ð6Þ
1
readily identified by a relatively high-field pyrrole H NMR
The equilibrium constant (298 K) for reaction 6 (K6 = 1.7 (1.0),
ΔG61° = ꢀ0.3 kcal/mol) was directly evaluated by integration of
the H NMR for 1 and 5 in combination with the proton
concentration [D+] and the solubility of D2 in water89 (Figure 4;
resonance (δ4 = 7.99 ppm) compared to iridium(III) complexes
(8.63ꢀ8.47 ppm), which is a characteristic that results from the
presence of the electron-rich metal site in the iridium(I) complex.
Nucleophilic substitution reactions for 4with alkyl halides that result
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Inorganic Chemistry
ARTICLE
Table 3. Measured (eqs 6 and 9) and Derived (eq 7, 8, and 11ꢀ13) Equilibrium Constants (Kn) and ΔG° (298 K) (kcal/mol) for
(TMPS)M Reactions in D2O (where M = Rh,25 Ir)
rxns of [(TMPS)M]
M = Rha
K6 = 18.2
M = Ir
K6 = 1.7(1)
7 ꢀ
8 ꢀ
½ðMIIIðD2OÞ2ꢂ
þ D2 h ½M ꢀ DðD2OÞꢂ
þ D þ þ D2O
eq 6
ΔG6° = ꢀ1.7
ΔG6° = ꢀ0.3(0.3)
K7 = 6.1 ꢁ 107
8 ꢀ
8 ꢀ
eq 7
K7 = 1.8 ꢁ 1010
½ðMIIIðODÞðD2OÞꢂ
þ D2 h ½M ꢀ DðD2OÞꢂ
þ D2O
ð7Þ
ð8Þ
ΔG7° = ꢀ14.0
K8 = 6.5 ꢁ 1022
ΔG7° = ꢀ10.6
K8 = 2.4 ꢁ 1018
9 ꢀ
8 ꢀ
½ðMIIIðODÞ2ꢂ
þ D2 þ D þ h ½M ꢀ DðD2OÞꢂ
þ D2O
eq 8
ΔG8° = ꢀ31.1
ΔG8° = ꢀ25.1
8 ꢀ
8 ꢀ
K9 = 4.3 ꢁ 10ꢀ8
K9 = 1.8(0.5) ꢁ 10ꢀ1
½M ꢀ DðD2OÞꢂ
h ½ðMIðD2OÞꢂ
þ D þ
eq 9
ΔG9° = +10.0
2ΔG9° = +16.0(0.3)
D þ þ D ꢀ h D2
ð10Þ
ð11Þ
ð12Þ
ð13Þ
eq 10
eq 11
eq 12
eq 13
K10 = 5.2 ꢁ 1037
ΔG10° = ꢀ53.2
7 ꢀ
8 ꢀ
11 = 9.5 ꢁ 1038
K11 = 8.8 ꢁ 1037
½ðMIIIðD2OÞ2ꢂ
½ðMIIIðD2OÞ2ꢂ
½ðMIIIðD2OÞ2ꢂ
þ D ꢀ h ½M ꢀ DðD2OÞꢂ
þ D2O
K
ΔG11° = ꢀ53.1
ΔG11° = ꢀ51.7
K12 = 2.3 ꢁ 104
7 ꢀ
7 ꢀ
9 ꢀ
8 ꢀ
8 ꢀ
12 = 2.3 ꢁ 10ꢀ2
þ ½ðMIðD2OÞꢂ
h ½ðMIIIðODÞðD2OÞꢂ ½M ꢀ DðD2OÞꢂ
K
ΔG12° = +2.2
K13 = 4.2 ꢁ 108
ΔG12° = ꢀ6.0
9 ꢀ
8 ꢀ
K13 = 1.4 ꢁ 1012
þ ½ðMIðD2OÞꢂ
þ D2 h 2½M ꢀ DðD2OÞꢂ
þ D2O
ΔG13° = ꢀ11.7
ΔG13° = ꢀ16.6
a (TMPS)Rh thermodynamic values derived from ref 25.
in forming alkyl complexes ([(TMPS)IrꢀR(D2O)]8ꢀ) is charac-
teristic of the iridium(I) species. The alkyl complexes are readily
1
identified in D2O solutions by characteristic high-field H NMR
resonances for the alkyl groups (Supporting Information).
Evaluation of the IrꢀD Acid Dissociation Constant for
1
[(TMPS)IrꢀD(D2O)]8ꢀ in Water. The pyrrole H NMR reso-
nances for [(TMPS)IrI(D2O)]9ꢀ (4) (δ4 = 7.99 ppm) and
[(TMPS)IrꢀD(D2O)]8ꢀ (5) (δ5 = 8.36 ppm) are observed as
separate sharp peaks in D2O (Figure 5). The pyrrole resonance
positions for 4 and 5 are invariant to pH change, but the peak
intensities for the resonances of 4 and 5 change in accord with the
heterolytic dissociation equilibrium given by eq 9.
8ꢀ
9ꢀ
½ðTMPSÞIrꢀDðD2OÞꢂ h ½ðTMPSÞIrIðD2OÞꢂ þ Dþ
ð9Þ
In the pD range of 11ꢀ12, both species 4 and 5 are observed at
equilibrium. The acid dissociation constant of [(TMPS)Irꢀ
D(D2O)]8ꢀ (5) in D2O was determined directly by integration
1
of the H NMR (K9(298 K) = 1.8 ꢁ 10ꢀ12, ΔG°9(298 K) =
+16.0 kcal molꢀ1). The acid dissociation constant for the RhꢀD
analog25 of 5 is more than 4 orders of magnitude larger than the
iridium hydride (Table 3). The free energy change (298 K) for
heterolytic dissociation of D+ from [(TMPS)IrꢀD(D2O)]8ꢀ is
6 kcal molꢀ1 larger than that of [(TMPS)RhꢀD(D2O)]8ꢀ, which
primarily results from the larger iridium hydride bond energy.
Equilibrium constants and standard free energy changes
for displacement of water from complex 1 by hydroxide
(eq 3, ΔG3° = ΔG1° + ΔG5° = ꢀ12.3 kcal/mol) or by hydride
(eq 11, ΔG11° = ΔG6° + ΔG10° = ꢀ51.7 kcal/mol) are derived
from measured thermodynamic values (Table 3). The qualitative
interrelationships between the five species in simultaneous
equilibria shown in Figure 3 were quantitatively evaluated by
measuring the equilibrium constants. Results from thermody-
namic measurements for the (TMPS)Ir system are found in
Figure 5. 1H NMR (500 MHz) pyrrole resonances for aqueous
solutions of [(TMPS)IrI(D2O)]9ꢀ (4) and [(TMPS)IrꢀD(D2O)]8ꢀ
(5) in D2O at pD = (a) 9.8, (b) 10.2, (c) 11.7, and (d) 12.5.
Table 3 along with comparative values for the (TMPS)Rh
system. The free energy changes for this set of reactions for
group nine (Co, Rh, Ir) metalloporphyrins are shown in Figure 6
where the group nine (M = Co, Rh, Ir) bisaquo metalloporphyrin
complexes are set at zero to define the relative energy scale. The
free energy change associated with converting any given metal-
loporphyrin species to another species of the same metal in water
by reactions of D2, D+, and D2O is visually illustrated by Figure 6.
Utilizing the free energy change diagram (Figure 6), conversion
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Inorganic Chemistry
ARTICLE
7
Figure 6. Free energy change (ΔG°(298 K), kcal molꢀ1) interrelationships diagram between [(TMPS)MIII(D2O)2]h (M = Co, Rh, Ir) complexes in D2O.
of [(TMPS)MIII(D2O)(OD)]8ꢀ to [(TMPS)MI(D2O)]9ꢀ is
seen to be +3.4 and ꢀ5.4 kcal molꢀ1, respectively, for rhodium
and iridium and the increase in the energy of the systems by
deprotonation is readily visualized.
Table 4. Difference in BDFE (kcal molꢀ1) between
[(por)MꢀOD] and [(por)MꢀD)] (where por = TMPS,
TSPP and M = Rh, Ir)
(MꢀOD) ꢀ (MꢀD),
Evaluation of the Bond Dissociation Free Energy (BDFE)
Difference between IrꢀOD and IrꢀD in [(TMPS)IrꢀX(D2O)]8ꢀ
Complexes in D2O. The difference in the IrꢀOD and IrꢀD bond
dissociation free energies (BDFE) can be evaluated from the
standard free energy change for reaction 9, which is derived from
experimental values for reaction 7 and the reverse of reaction 1
(Tables 1 and 3) (K9 = K7/K1 = 6.1 ꢁ 107, ΔG9ꢃ = ꢀ10.6 kcal/
mol; Tables 1 and 3). Using the BDFEs in D2O for DꢀD (103.4
kcal molꢀ1) and DꢀOD (117.6 kcal molꢀ1) the difference in the
IrꢀD and IrꢀOD bond dissociation free energies is deduced by
considering the bonds formed and broken in reaction 9 (ΔG9ꢃ =
[IrꢀOD] + [DꢀD] ꢀ [IrꢀD] ꢀ [DꢀOD] and [IrꢀOD]ꢀ
[IrꢀD] = ΔG9° + [DꢀOD] ꢀ [DꢀD]). The BDFE difference
between (TMPS)IrꢀOD and (TMPS)IrꢀD is found to be
3.6 kcal molꢀ1, which compares with a difference of only
0.2 kcal molꢀ1 for (TMPS)RhꢀOD and (TMPS)RhꢀD.
(por)M
kcal molꢀ1
(TMPS)Ir
(TMPS)Rh
(TSPP)Rh
3.6
0.2
1.8
hydroxide oxygen π-donor orbitals is an interaction that could
account for the changes in the difference in ([MꢀOD ꢀ [MꢀD])
BDFEs. A lower energy position for the 6p orbitals of iridium
compared to rhodium and the corresponding stronger π bonding
with hydroxide could account for the increased spread of 3.4 kcal
molꢀ1 in ([MꢀOD] ꢀ [MꢀD]) BDFEs for the (TMPS)Ir
complex compared to the (TMPS)Rh system, Table 5. Larger
relativistic effects for iridium compared to rhodium result in a
differential lowering of the 6s and 6p orbitals of Ir compared to
Rh.91,92 The larger spread of ([RhꢀOD]ꢀ[RhꢀD]) for the
(TSPP)Rh compared to (TMPS)Rh system is consistent with a
higher effective positive charge and lower energy 5p orbitals for the
rhodium center in the (TSPP)Rh system.
8ꢀ
½ðTMPSÞIrIIIðODÞðD2OÞꢂ þ D2 h
8ꢀ
½ðTMPSÞIrꢀDðD2OÞꢂ þ D2O
ð9Þ
Implication for Oxidative Additions of Water with (TMPS)IrII.
Oxidative addition of water with transition-metal complexes is an
important underinvestigated process that is a growing focus of
attention.21 The ΔG° for oxidative addition of water (D2O) with
[(TMPS)RhII(OD)(D2O)]8ꢀ is ca. ꢀ2.4 kcal molꢀ1 (eq 14,
M = Rh).26
We previously reported the BDFE difference between
(TMPS)RhꢀOD and (TMPS)RhꢀD is 0.2 kcal molꢀ1, and the
corresponding difference for (TSPP)RhꢀOD and (TSPP)RhꢀD
is 1.8 kcal molꢀ1, Table 4. Evaluation of the difference in MꢀOD
and MꢀD for (M = Rh, Ir) ([MꢀOD]ꢀ[MꢀD]) = ΔG7ꢃ +
[(DꢀOD) ꢀ (DꢀD)] should be highly accurate because the
equilibrium measurement of ΔG9ꢃ is within (0.2 kcal molꢀ1 and
([DꢀOD]ꢀ[DꢀD]) is constant (+14.2 kcal molꢀ1). Table 5
provides values for the three systems where ([MꢀOD] ꢀ
[MꢀD]) have been evaluated. In every example the [MꢀOD]
BDFE in water is larger than the [MꢀD] BDFE but the difference
varies from 3.6 to 0.2 kcal molꢀ1 (Table 5). Variation in the
π-acceptor interaction of the empty 6p orbitals orbital with the filled
8ꢀ
2½ðTMPSÞMIIðD2OÞꢂ þ D2O h
8ꢀ
9ꢀ
½ðTMPSÞMꢀDðD2OÞꢂ þ ½ðTMPSÞMꢀODðD2OÞꢂ
ð14Þ
The larger (TMPS)IrꢀD compare to (TMPS)RhꢀD of ∼4ꢀ6 kcal
molꢀ1 and an increase of (TMPS)IrꢀOD relative to (TMPS)Rhꢀ
OD of 7ꢀ9 kcal molꢀ1 makes oxidative addition of water highly
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Inorganic Chemistry
ARTICLE
Table 5. Measured and Derived Equilibrium Constants and Free Energy Changes for Reactions (T = 298 K) of
[(TMPS)MꢀD(D2O)]8ꢀ (M = Rh,25 Ir) with Unactivated Olefins and Acetaldehyde and CO
(TMPS)M (M = Rh, Ir)
Kn
ΔG°n
ꢀ3.7
8 ꢀ
7 ꢀ
eq 15
eq 16
5.1 ꢁ 102
½Ir ꢀ DðD2OÞꢂ
þ C2H4 h ½Ir ꢀ CH2CH2DðD2OÞꢂ
8.7 ꢁ 101
8 ꢀ
7 ꢀ
½Ir ꢀ DðD2OÞꢂ
½Rh ꢀ DðD2OÞꢂ
þ C3H6 h ½Ir ꢀ CH2CHDCH3ðD2OÞꢂ
ꢀ0.67
ꢀ5.6
ꢀ2.7
5.7 ꢁ 103
8 ꢀ
7 ꢀ
þ C3H6 h ½Rh ꢀ CH2CHDCH3ðD2OÞꢂ
þ HCðOÞCH3 h ½Ir ꢀ CHðODÞCH3ðD2OÞꢂ
7 ꢀ
8 ꢀ
7 ꢀ
eq 19
eq 20
9.5 ꢁ 101
½Ir ꢀ DðD2OÞꢂ
9.5 ꢁ 103
ꢀ5.4
ꢀ4.4
8 ꢀ
½Ir ꢀ DðD2OÞꢂ
½Rh ꢀ DðD2OÞꢂ
þ CO h ½Ir ꢀ DðCOÞꢂ
þ D2O
1.7 ꢁ 103
8 ꢀ
7 ꢀ
þ CO h ½Rh ꢀ CDOðD2OÞꢂ
favorable (M = Ir, ΔG°14 ≈ ꢀ11 to ꢀ15 kcal molꢀ1) (eq 14).
Although [(TMPS)IrII(D2O)]8ꢀ and reaction 14 are not explicitly
observed, properties of this process can be deduced from observation
of reaction 12 and evaluation of thermodynamic values in Table 3 .
Substrate Reactions of [(TMPS)IrꢀD(D2O)]8ꢀ with Olefins,
Aldehydes, and Carbon Monoxide. Reaction of [(TMPS)Irꢀ
D(D2O)]8ꢀ with Olefins in Water. Reaction of the iridium hydride
(5) with terminal alkenes is very slow at acidic conditions
but becomes faster as the pD increases ([D+] ≈ 10ꢀ8ꢀ10ꢀ11).
Observation of higher reaction rates at basic conditions is ascribed to
partial deprotonation of 5 to form equilibrium quantities of the
reactive iridium(I) species [(TMPS)IrI(D2O)]9ꢀ. Aqueous solu-
tions of the iridium hydride ([(TMPS)IrꢀD(D2O)]8ꢀ) under
basic conditions ([D+] > 10ꢀ10 M) react with ethene and propene
to form measurable equilibrium concentrations of alkyl complexes
in a period of 10 days (eqs 15 and 16)
hydrogen (P(H2) = 500 Torr) results in the appearance of the
ethyl organometallic 6 (eq 15) and ethane in the H NMR.
1
Ethane is observed to be formed in a slow catalytic process in
which 2.4 turnovers occur during the first hour at 298 K. Only
qualitative conversion with time measurements could be
achieved with this experimental design because of complications
from producing a gaseous ethane product and the slow redis-
tribution of reagents between the gas and the solution phases
in the vacuum-adapted NMR tube. The process requires about
1 week to consume the hydrogen as the limiting reagent.
Catalytic hydrogenation of ethene probably occurs though the
intermediacy of the ethyl complex ([(TMPS)IrꢀCH2CH2D-
(D2O)]8ꢀ), which reacts either in a concerted manner by a σ-bond
metathesis type process with H2 (eq 17) or by stepwise protonation
and hydrogenation (eqs 18 and 6). The concerted pathway is
currently preferred because independent study of reaction 6 at acid
conditions indicates hydrogenation is far too slow to account for the
observed ethane formation. A concerted σ-bond metathesis-type
reaction for an iridium complex that does not have a readily available
cis-coordination site has been previously illustrated by Milstein.93
8ꢀ
½ðTMPSÞIrꢀDðD2OÞꢂ þ C2H4 h
8ꢀ
½ðTMPSÞIrꢀCH2CH2DðD2OÞꢂ
ð15Þ
8ꢀ
8ꢀ
½ðTMPSÞIrꢀDðD2OÞꢂ þ C3H6 h
½ðTMPSÞIrꢀCH2CH2DðD2OÞꢂ þ H2 h
8ꢀ
C2H5D þ ½ðTMPSÞIrꢀHðD2OÞꢂ þ Hþ
ð17Þ
ð18Þ
ð6Þ
8ꢀ
½ðTMPSÞIrꢀCH2CHDCH3ðD2OÞꢂ
ð16Þ
The porphyrin ring current shifted high-field Irꢀethyl resonances
of [(TMPS)IrꢀCH2CH2D(D2O)]7ꢀ (6) (δ(IrꢀCH2CH2D) =
ꢀ5.68 ppm, δ(IrꢀCH2CH2D) = ꢀ1.85 ppm) and Irꢀpropyl
peaks for [(TMPS)IrꢀCH2CHDCH3(D2O)]7ꢀ (7) (δ(Irꢀ
CH2CHDCH3) =ꢀ5.72 ppm, δ(IrꢀCH2CHDCH3) =ꢀ2.77 ppm,
δ(IrꢀCH2CHDCH3) = ꢀ1.74 ppm) groups provide convenient
observables to identify and quantify the Irꢀalkyl species in D2O.
Addition of the iridium hydride to propene occurs with anti-
Markovnikov regioselectivity, which places the iridium porphyrin
on the less sterically demanding terminal primary carbon center.
Reactions of the alkenes with 5 (eqs 15 and 16) achieve a 1H
NMR observable equilibrium which permitted evaluation of the
8ꢀ
½ðTMPSÞIrꢀCH2CH2DðD2OÞꢂ þ Dþ þ D2O h
7ꢀ
½ðTMPSÞIrðD2OÞ2ꢂ þ C2H4D2
7ꢀ
½ðTMPSÞIrðD2OÞ2ꢂ þ H2 h
8ꢀ
½ðTMPSÞIrꢀHðD2OÞꢂ þ Hþ þ D2O
Reaction of [(TMPS)IrꢀD(D2O)]8ꢀ with Acetaldehyde. Reac-
tion of acetaldehyde with basic solutions ([D+] > 10ꢀ10 M) of
[(TMPS)IrꢀD(D2O)]8ꢀ in D2O result in the H NMR ob-
1
servations of a doublet at ꢀ3.56 ppm and a broad resonance at
ꢀ2.83 ppm indicative of formation of [(TMPS)IrꢀCH(OD)-
CH3(D2O)]7ꢀ (9) within 1 h. The organometallic is observed to
be in equilibrium with 5 as shown in eq 19 (K19= 9.5 ꢁ 101,
ΔG19° = ꢀ2.7 kcal molꢀ1).
equilibrium thermodynamics at 298 K (K15 = 5.1 ꢁ 102, ΔG°15
=
ꢀ3.7 kcal molꢀ1; K16 =8.7 ꢁ 101, ΔG°16 = ꢀ0.67 kcal molꢀ1
;
Table 5). The free energy changes for reactions of alkenes with
the iridium hydride (IrꢀD) (5) are 4ꢀ5 kcal molꢀ1 less favorable
than comparable porphyrin rhodium hydride (RhꢀD) reactions
in water (Table 5).28 This is empirically associated with the
8ꢀ
increase in the iridium hydride BDFE (∼4ꢀ7 kcal molꢀ1
)
½ðTMPSÞIrꢀDðD2OÞꢂ þ HCðOÞCH3 h
7ꢀ
compared to rhodium hydride that is not fully compensated by
an increase in the IrꢀCH2ꢀ relative to the RhꢀCH2ꢀ.
Catalytic Hydrogenation of Ethene. A preformed sample of
½ðTMPSÞIrꢀCHðODÞCH3ðD2OÞꢂ
ð19Þ
[(TMPS)IrꢀD(D2O)]h(5) (5ꢁ 10ꢀ3 M) in acidic D2O(pD≈3)
Reaction of [(TMPS)IrꢀD(D2O)]8ꢀ with CO. The porphyrin
8
when pressurized with ethene (P(C2H4) = 600 Torr) and
pyrrole 1H NMR resonances for aqueous solutions of
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Inorganic Chemistry
ARTICLE
for addition of the iridium hydride to ethene and propene
compared to rhodium hydride by 4ꢀ5 kcal molꢀ1 illustrates
the larger increase in IrꢀH compared to IrꢀCH2ꢀ relative to the
rhodium derivative. The free energy change for reaction 21 to produce
1
an iridium formyl falls short of that needed to give observable H
NMR concentrations of [(TMPS)IrꢀCDO(D2O)]8ꢀ, but modestly
higher pressures of CO (∼50 atm) can be expected to give observable
concentrations of the elusive iridium formyl complex.
’ CONCLUSIONS
Aqueous solutions of group nine metal(III) (M = Co, Rh, Ir)
complexes of tetra(3,5-disulfonatomesityl)porphyrin [(TMPS)MIII]
form a hydrogen-ion-dependent equilibrium distribution of aquo
and hydroxo complexes ([(TMPS)MIII(D2O)2ꢀn(OD)n](7+n)ꢀ).
Evaluation of acid dissociation constants for coordinated water
show that the extent of proton dissociation from coordinated
water increases regularly on moving down the group from cobalt
to iridium, which is consistent with increasing metalꢀwater
ligand binding . Aqueous (D2O) solutions of [(TMPS)IrIII(D2O)2]7ꢀ
(1) react with dihydrogen to form an iridium hydride complex
([(TMPS)IrꢀD(D2O)]8ꢀ) (5) with an acid dissociation con-
stant of 1.8(0.5) ꢁ 10ꢀ12 that is much smaller than the RhꢀD
derivative (4.3 (0.4) ꢁ 10ꢀ8), reflecting a stronger IrꢀD bond.
The IrꢀD unit in 5 adds with ethene and acetaldehyde to
form organometallic derivatives [IrꢀCH2CH2D(D2O)]7ꢀ and
[IrꢀCH(OD)CH3(D2O)]7ꢀ. Only a six-coordinate carbonyl
complex [(TMPS)IrꢀD(CO)]8ꢀ is observed for reaction of
the hydride complex 5 with CO (0.2ꢀ2.0 atm), which contrasts
with the (TMPS)RhꢀD analog that forms a rhodium formyl
complex at equilibrium. Reactivity studies and equilibrium thermo-
dynamic measurements are used to deduce several features of the
relative MꢀH, MꢀOH, and MꢀCH2ꢀ BDFEs (M = Rh, Ir).
(TMPS)IrꢀD is approximately 4ꢀ6 kcal molꢀ1 larger than
(TMPS)RhꢀD. The spread of the IrꢀD, IrꢀOD, and IrꢀCH2ꢀ
BDFE values in water is substantially larger for the iridium system.
The difference in the ([(TMPS)IrꢀOH] ꢀ [(TMPS)IrꢀH)])
BDFEs and ([(TMPS)IrꢀCH2ꢀ] ꢀ [(TMPS)IrꢀD]), respec-
tively, differs by +3.4 and ꢀ4ꢀ5 kcal molꢀ1 from the corre-
sponding differences in BDFE values for the (TMPS)Rh system.
Oxidative addition of water with (TMPS)RhII has a ΔG° (298 K)
of ꢀ2 kcal molꢀ1, and the sum of the increases in the ((TMPS)Irꢀ
OH) and ((TMPS)IrꢀH BDFEs over those of the (TMPS)Rh
system are approximately 12ꢀ16 kcal molꢀ1, which permits
deducing that the oxidative addition of water with (TMPS)IrII is
Figure 7. 1H NMR of mole fraction average pyrrole resonances of
[(TMPS)IrꢀD(D2O)]8ꢀ and [(TMPS)IrꢀD(CO)]8ꢀ in D2O at var-
ious CO pressures.
[(TMPS)IrꢀD(D2O)]8ꢀ in contact with CO are observed to
shift regularly to lower field as the pressure of CO is increased.
Changes in the porphyrin pyrrole resonances as a function of CO
pressures are illustrated in Figure 7.
The pyrrole 1H NMR shifts are associated with mole fraction
averaged positions that result from limiting fast exchange between
[(TMPS)IrꢀD(D2O)]8ꢀ (5) and a CO complex ([(TMPS)-
IrꢀD(CO)]8ꢀ) (10), eq 20. The CO pressure dependence of the
1
pyrrole H NMR position is accurately fitted to the equilibrium
described by reaction 20 (T = 298 K; K20 = 9.5 ꢁ 103, ΔG°20=
ꢀ5.4 kcal molꢀ1) where the limiting pyrrole chemical shifts of 5
and 10 are 8.36 and 8.60 ppm, respectively.
8ꢀ
½ðTMPSÞIrꢀDðD2OÞꢂ þ CO h
8ꢀ
½ðTMPSÞIrꢀDðCOÞꢂ þ D2O
ð20Þ
free energy favorable by ∼14ꢀ18 kcal molꢀ1
’ EXPERIMENTAL SECTION
.
In the same range of CO and metal porphyrin concentra-
tions where [(TMPS)IrꢀD(D2O)]8ꢀ gives an equilibrium
with a CO complex [(TMPS)IrꢀD(CO)]8ꢀ, the rhodium
analog ([(TMPS)RhꢀD(D2O)]8ꢀ) gives an equilibrium with
General Considerations. D2O was purchased from Cambridge
Isotope Laboratory Inc. and degassed by three freezeꢀpumpꢀthaw
cycles before use. Proton NMR spectra were obtained on a Bruker
AvanceIII 500 MHz at 293 K. Chemical shifts were referenced to
3-trimethyl silyl-1 propane sulfonic acid sodium salt. Proton NMR spectra
were used to identify solution species and to determine the distribution of
species at equilibrium. pH measurements are performed on Thermo
Scientific XL15 m and Orion 9802 glass electrode94 precalibrated by Thermo
Orion buffer solutions of pH = 4.01, 7.00, and 10.01. Tetramesitylporphyrin
(TMP) was synthesized according to the reported methods.95ꢀ97
Sulfonation of meso-tetraphenylporphyrin sodium salt was achieved and
subsequentlypurifiedbythemethod ofSrivastava.98 Na8[(TMPS)H2] 1H
NMR (500 MHz, D2O) δ(ppm): 8.58 (s, 8H, pyrrole), 3.23 (s, 12H,
p-mesityl), 2.09 (s, 24H, o-mesityl), ꢀ2.35(s, br, 2H, ꢀNH).
a rhodium formyl complex [(TMPS)RhꢀCDO(D2O)]8ꢀ
,
K = 1.7 ꢁ 103, ΔG°= ꢀ4.4 kcal molꢀ1. Reaction of CO with
the iridium hydride to produce a formyl complex (eq 21) must
be thermodynamically less favorable than this process with the
corresponding rhodium hydride.
8ꢀ
8ꢀ
½ðTMPSÞIrꢀDðD2OÞꢂ þ CO h ½ðTMPSÞIrꢀCDOðD2OÞꢂ
ð21Þ
The BDFE for all IrꢀX units is larger than the corresponding
RhꢀX BDFE, but the increase in the iridium hydride compared
to the rhodium hydride is larger than the increase in IrꢀC
compared to RhꢀC. Less favorable equilibrium thermodynamics
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Inorganic Chemistry
ARTICLE
Concentration of Complexes and Ionic Strength of Aque-
ous Solutions. Thermodynamic studies of (TMPS)Ir complexes in
water were carried out at concentrations less than 2 ꢁ 10ꢀ3 M in order
to minimize molecular and ionic association. Most equilibrium constant
measurements were performed at a low ionic strength (μ ≈ 10ꢀ3) where
the ion activity coefficients approach unity.
samples of in D2O at a defined hydrogen-ion ([D+]) concentration,
and then dihydrogen was repressurized into the sample to suppress
formation of (TMPS)IrIII species.
Proton NMR was used to identify solution species and to determine
the distribution of each species at equilibrium. Equilibrium constants
1
were evaluated from the intensity integrations of H NMR for each
Synthesis of Na7[(TMPS)IrIII(D2O)2]7ꢀ. Na7[(TMPS)MIII
-
species in combination with D+ concentration measurement and the
solubility of the small organic substrate in water.22 Equilibrium con-
centrations of [(TMPS)IrꢀD(D2O)]8ꢀ for the substrate reactions were
determined from the averaged 1H NMR chemical shifts in combination
with the D+ ion concentration which determines the equilibrium
(D2O)2]7ꢀ (M = Co, Rh, Ir) was synthesized following the reported
methods by Ashley.13,14 [Na7(TMPS)Ir(D2O)2] was obtained by dis-
solving Na8(TMPS)H2 (100 mg, 0.06 mmol) and [Ir(COD)Cl]2 (210 mg,
0.3 mmol) into 15 mL of methanol and refluxed for 5 days until
complete metalation was determined by UVꢀvis. Two drops of 3%
H2O2 water solution was used to oxidize iridium(I) to iridium(III). The
solvent was removed under vacuum, and the product was purified on a
silica column with methanol eluent to remove unreacted [Ir(COD)Cl]2.
Dissolution of 1 in D2O results in solutions of the bis aquo complex
[(TMPS)IrIII(D2O)2]7ꢀ (1) in an equilibrium distribution with the mono-
and bis-hydroxo complexes, [(TMPS)IrIII(D2O)(OD)]8ꢀ (2) and
distribution of [(TMPS)IrI(D2O)]9ꢀ and [(TMPS)IrꢀD (D2O)]8ꢀ
.
Reaction of [(TMPS)IrꢀD (D2O)]8ꢀ with CO. A solution of
(TMPS)IrIII (10ꢀ3 M) was pressurized with a mixture of H2/CO containing
70% of CO (0.6 atm) to form [(TMPS)IrꢀD(CO)]8ꢀ. The equilibrium
constant is evaluated using least-squares averaging for the fast exchange
mole fraction averaged iridium hyridic carbonyl and iridium hydride with
1
limiting resonance H NMR shifts of 8.59 and 8.36 ppm, respectively.
1
[(TMPS)IrIII(OD)2]9ꢀ (3). Na7[(TMPS)IrIII(D2O)2] H NMR (500
[(TMPS)IrꢀCO(D2O)]8ꢀ 1H NMR (500 MHz, D2O) δ(ppm): 8.59
(s, 8H, pyrrole), 3.16 (s, 12H, p-methyl), 2.17 (s, 12H, o-methyl), 2.13 (s,
12H, o0-methyl).
MHz, D2O) δ(ppm): 8.63 (s, 8H, pyrrole), 3.17 (s,12 H, p-methyl).2.17
(s, 24 H, o-methyl).
Acid Dissociation Constant Measurement for [(TMPS)MIII-
(D2O)2]7ꢀ (M = Co, Ir) in Water. Samples of ([(TMPS)MIII-
(OD)2]7ꢀ) (M = Co, Ir) were prepared by a mixing standardized
D2O solution of NaOD with the stock solutions of complex 1 (0.5ꢀ
1.0 ꢁ 10ꢀ3 M) in NMR tubes. A series of DCl and NaOD deuterium
oxide solutions was used to tune the pH values. A plot of the pyrrole
hydrogen 1H NMR chemical shifts to pD value (pD = pH + 0.41) and fit
by nonlinear least-squares curve fitting to the equation
À
Reaction of [(TMPS)IrꢀD(D2O)]8ꢀ with Ethene, Propene,
and Acetaldehyde. A solution of [(TMPS)IrꢀD(D2O)]8ꢀ (3 ꢁ
10ꢀ3 M) reacts with ethene and propene to form [(TMPS)Irꢀ
CH2CH2D(D2O)]8ꢀ and [(TMPS)IrꢀCH2CHDCH3(D2O)]8ꢀ. Re-
actions of iridium hydride with all substrate olefins go to completion
within the time needed to run a 1H NMR. Thermodynamic equilibrium
constants are evaluated from integration of iridium alkyl complexes and
iridium(I) in combination with the proton concentration which deter-
mines the equilibrium concentration of [(TMSP)IrꢀD(D2O)]8ꢀ
.
δ
2, 3, 4ðobsÞðpyrÞ ¼ K1K2δ3ðpyrÞ þ K1½Dþꢂ2ðpyrÞ
1H NMR ([(TMPS)IrꢀCH2CH2D(D2O)]8ꢀ) (500 MHz, D2O)
δ(ppm): 8.29 (s, 8H, pyrrole), 3.20 (s, 12H, p-methyl), 2.16 (s, 24H,
o-methyl), ꢀ1.85 (br, 2H,-CH2), ꢀ5.68 (br, 2H, ꢀCH2D).
ꢀ
ꢁ
Á
2
2
þ ½Dþꢂ δ1ðpyrÞ = K1K2 þ K1½Dþꢂ þ ½Dþꢂ
1
([(TMPS)IrꢀCH2CHDCH3(D2O)]8ꢀ) H NMR (500 MHz, D2O)
Synthesis of [(TMPS)IrꢀD(D2O)]8ꢀ/[(TMPS)IrI(D2O)]9ꢀ. A
0.4 mL amount of [(TMPS)IrIII(D2O)2]7ꢀ D2O stock solutions (1.2ꢀ1.8 ꢁ
10ꢀ3 M, [D+] > 10ꢀ3 M) was added into a vacuum-adapted NMR
tube. The NMR tubes were then degassed by three cycles of freezeꢀ
pumpꢀthaw, and 500ꢀ700 Torr H2/D2 was pressurized into the
NMR tube. Reaction of [(TMPS)IrIII(D2O)2]7ꢀ with H2/D2 produ-
cing [(TMPS)IrꢀD]8ꢀ in acidic solution achieves equilibrium dis-
tributions of (TMPS)IrIII and [(TMPS)IrꢀD]8ꢀ species. The
equilibrium constant was evaluated from the intensity integrations
δ(ppm): 8.33 (s, 8H, pyrrole), 3.15 (s, 12H, p-methyl), 2.20(s, 24H, o-
methyl), ꢀ5.72 (br, 2H, ꢀCH2CHDCH3),ꢀ2.77 (br, 2H, ꢀCH2CHDCH3),
ꢀ1.74 (br, 2H, ꢀCH2CHDCH3). ([(TMPS)IrꢀCH(OD)CH3-
1
(D2O)]8ꢀ) H NMR (500 MHz, D2O; 292 K) δ(ppm): 8.35 (s, 8H,
pyrrole), 3.14 (s, 12H, p-methyl), 2.23 (s, 24H, o-methyl), ꢀ2.83 (br,
2H, ꢀCH), ꢀ3.56(d, 3H, ꢀCH3, J1Hꢀ H
1
= 6.3 Hz).
Reactions of [(TMPS)IrI(D2O)]9ꢀ with RI (R= CH3, CH2CH3,
(CH2)4CH3) in Water. [(TMPS)IrꢀR(D2O)]9ꢀ (R = CH3, CH2CH3,
(CH2)4CH3) was produced through transferring alkyl halide into the
vacuum line-adapted NMR tube containing [(TMPS)IrI(D2O)]9ꢀ
solutions.
1
of H NMR of each species in combination with D+ concentration
measurement and the solubility of H2/D2 in water.16 Following the
same procedure, (TMPS)IrIII complexes completely converted to
[(TMPS)IrꢀCH3(OD)]9ꢀ 1H NMR (500 MHz, D2O) δ(ppm):
8.26 (8H, pyrrole), 3.19 (s,12H, p-methyl), 2.38(s, 12H, o-methyl),
2.15(s, 12H, o0-methyl), ꢀ7.11 (br, 3H, CH3).
[(TMPS)IrI]9ꢀ in basic D2O solution ([D+]
<
10ꢀ12 M).
[(TMPS)IrꢀD(D2O)]7ꢀ 1H NMR (5) (D2O, 500 MHz) δ(ppm):
8.36 (s, 8H, pyrrole), 3.15 (s, 12H, p-methyl), 2.24 (s, 12 H, o-
methyl), 2.15 (s, 12 H, o0-methyl). [(TMPS)IrI(D2O)]7ꢀ 1H NMR
(4) (D2O, 500 MHz) δ(ppm): 7.95 (s, 8H, pyrrole), 3.13 (s,12 H, p-
methyl) 2.43 (s, 24 H, o-methyl).
[(TMPS)IrꢀCH2CH3(OD)]9ꢀ 1H NMR (500 MHz, D2O) δ(ppm):
8.24 (8H, pyrrole), 3.19 (s,12H, p-methyl), 2.38(s, 12H, o-methyl), 2.15
(s, 12H, o0-methyl), ꢀ6.07 (br, 2H, CH2), ꢀ3.96 (br, 3H, CH3).
[(TMPS)Irꢀ(CH2)4CH3(OD)]9ꢀ 1H NMR(500MHz, D2O) δ(ppm):
8.23 (8H, pyrrole), 3.19 (s,12H, p-methyl), 2.40(s, 12H, o-methyl),
Acid Dissociation Constant Measurements for [(TMPS)Irꢀ
D(D2O)]8ꢀ in Water. The acid dissociation constant of [(TMPS)Irꢀ
D(D2O)]8ꢀ was measured in water by direct observation of [(TMPS)Irꢀ
D(D2O)]8ꢀ and [(TMPS)IrI(D2O)]9ꢀ concurrently between [D+]
10ꢀ10.5 and 10ꢀ12 in 1H NMR. Integration of the peak areas of 4and 5against
a standard of known concentration was used to calculate the acid dissociation
of eq 7 to give K7 = 1.8(0.5) ꢁ 10ꢀ12, ΔG7ꢃ = +16.0(0.3) kcal/mol.
Substrate Reactions of [(TMPS)IrꢀD(D2O)]8ꢀ and [(TMPS)IrI-
(D2O)]9ꢀ with Olefins, Aldehydes, and CO in Water. Substrate
reactions of [(TMPS)IrꢀD]8ꢀ and [(TMPS)IrI]9ꢀ with CO, aldehydes,
and olefins in water were carried out by vacuum transfer of the
substrate to vacuum line-adapted NMR tubes containing preformed
2.13(s, 12H, o0-methyl), ꢀ6.16 (t, 2H, CH2ꢀ(CH2)3CH3, J1Hꢀ H
1
= 7 Hz),
ꢀ4.5 (t of d, 2H, CH2ꢀCH2ꢀ(CH2)2CH3, J1Hꢀ H
1
= 7 Hz, J1Hꢀ H
1
=
6.3 Hz), ꢀ1.33 (t, 2H, (CH2)2ꢀCH2ꢀCH2CH3, J1Hꢀ H
1
= 6.3 Hz),
ꢀ0.43 (br, 2H, (CH2)3-CH2CH3), ꢀ0.32 (br, 3H, (CH2)4CH3).
’ ASSOCIATED CONTENT
S
Supporting Information. Calculations of equilibrium
b
constants, tables and representative NMR spectra. This ma-
terial is available free of charge via the Internet at http://pubs.
acs.org.
11018
dx.doi.org/10.1021/ic201553k |Inorg. Chem. 2011, 50, 11011–11020

Inorganic Chemistry
ARTICLE
’ AUTHOR INFORMATION
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Corresponding Author
*E-mail: bwayland@temple.edu.
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’ ACKNOWLEDGMENT
This research was supported by the Department of Energy,
Division of Chemical Sciences and Office of Science through
Grant DE-FG02-09ER-16000.
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