Coordination chemistry of the soft chiral Lewis acid [Cp*Ir(TsDPEN)] +

Article abstract of DOI:10.1021/ic200160q

The paper surveys the binding of anions to the unsaturated 16e Lewis acid [Cp*Ir(TsDPEN)]⁺ ([1H]⁺), where TsDPEN is racemic H₂NCHPhCHPhNTs^-. The derivatives Cp*IrX(TsDPEN) were characterized crystallographically for X^- = CN^-, Me(C=NH)S^-, NO₂^-, 2-pyridonate, and 0.5 MoS₄^2-. [(1H)₂(μ-CN)]⁺ forms from [1H]⁺ and 1H(CN). Aside from 2-pyridone, amides generally add reversibly and bind to Ir through N. Thioacetamide binds irreversibly through sulfur. Compounds of the type Cp*IrX(TsDPEN) generally form diastereoselectively, although diastereomeric products were observed for the strong ligands (X = CN^-, H^- (introduced via BH ₄^-), or Me(C=NH)S^-). Related experiments on the reaction (p-cymene)Ru(TsDPEN-H) + BH₄^- gave two diastereomers of (p-cymene)RuH(TsDPEN), the known hydrogenation catalyst and a second isomer that hydrogenated acetophenone more slowly. These experiment provide new insights into the enantioselectivity of these catalysts. Diastereomerization in all cases was first order in metal with modest solvent effects. The diphenyl groups are generally diequatorial for the stable diastereomers. For the 2-pyridonate adduct, axial phenyl groups are stabilized in the solid state by puckering of the IrN₂C₂ ring induced by intramolecular hydrogen-bonding. Crystallographic analysis of [Cp*Ir(TsDPEN)]₂(MoS₄) revealed a unique example of a κ¹,κ¹-tetrathiometallate ligand. Cp*Ir(SC(NH)Me)TsDPEN) is the first example of a κ¹-S- thioamidato complex.

Full text of DOI:10.1021/ic200160q

ARTICLE
pubs.acs.org/IC
Coordination Chemistry of the Soft Chiral Lewis Acid [Cp*Ir(TsDPEN)]þ
Christopher S. Letko, Zachariah M. Heiden, Thomas B. Rauchfuss,* and Scott R. Wilson
School of Chemical Sciences, University of Illinois, Urbana, Illinois 61801, United States
S Supporting Information
b
ABSTRACT: The paper surveys the binding of anions to the unsaturated 16e Lewis acid
[Cp*Ir(TsDPEN)]þ ([1H]þ), where TsDPEN is racemic H2NCHPhCHPhNTsꢀ. The deri-
vatives Cp*IrX(TsDPEN) were characterized crystallographically for Xꢀ = CNꢀ, Me-
(CdNH)Sꢀ, NO2ꢀ, 2-pyridonate, and 0.5 MoS42ꢀ. [(1H)2(μ-CN)]þ forms from [1H]þ
and 1H(CN). Aside from 2-pyridone, amides generally add reversibly and bind to Ir through N.
Thioacetamide binds irreversibly through sulfur. Compounds of the type Cp*IrX(TsDPEN) generally form diastereoselectively,
although diastereomeric products were observed for the strong ligands (X = CNꢀ, Hꢀ (introduced via BH4ꢀ), or Me(CdNH)Sꢀ).
Related experiments on the reaction (p-cymene)Ru(TsDPEN-H) þ BH4ꢀ gave two diastereomers of (p-cymene)RuH(TsDPEN),
the known hydrogenation catalyst and a second isomer that hydrogenated acetophenone more slowly. These experiment provide
new insights into the enantioselectivity of these catalysts. Diastereomerization in all cases was first order in metal with modest
solvent effects. The diphenyl groups are generally diequatorial for the stable diastereomers. For the 2-pyridonate adduct, axial phenyl
groups are stabilized in the solid state by puckering of the IrN2C2 ring induced by intramolecular hydrogen-bonding.
Crystallographic analysis of [Cp*Ir(TsDPEN)]2(MoS4) revealed a unique example of a κ1,κ1-tetrathiometallate ligand. Cp*Ir(SC-
(NH)Me)TsDPEN) is the first example of a κ1-S-thioamidato complex.
’ INTRODUCTION
Scheme 1. Three States of Half-Sandwich Transfer
Hydrogenation Catalysts
Transfer hydrogenation catalysts often exist in one of two
states, an unsaturated metal center, usually stabilized by
π-interactions with amido (R2Nꢀ) ligands, and a saturated amino-
hydride state.1ꢀ5 Many such complexes are known, and a
popular ligand in this area is the monoanion [H2NCHPh-
CHPhNTs]ꢀ abbreviated TsDPENꢀ. For example, (p-cymene)-
RuH(S,S-TsDPEN) is useful for the enantioselective transfer
hydrogenation (TH) of ketones and imines.6 In the catalytic
cycle, this Ru(II) complex shuttles between hydro and dehydro states,
(p-cymene)RuH(TsDPEN) and (p-cymene)Ru(TsDPEN-H), re-
spectively. The present report focuses on a related complex, Cp*Ir-
(TsDPEN-H) (1), which is more amenable to detailed mechanistic
studies.7 Compound 1 is also catalytically active for TH but is more
robust than the (p-cymene)Ru derivative.8
A few years ago, our group and Ikariya’s, and Noyori’s groups
showed that a third state of the TH catalysts arises by protonation
of the dehydro state of these catalysts.9,10 Thus, protonation of 1
occurs at its NH center to afford the cation [Cp*Ir(TsDPEN)]þ
([1H]þ, Scheme 1).
In this report, we examine the binding of anionic ligands to
[1H]þ. Using a variety of anionic ligands, Ikariya and co-workers
have examined other derivatives of the type 1H(X). For example,
1 adds a variety of carbon-based ligands such as, for example,
nitromethane, acetone, malonate esters, and phenylacetylene.
The alkyl complexes (p-cymene)Ru(R)(TsDPEN) (R = Me, Et)
have also been prepared, although they are thermally labile.17 For
the carboxylate derivatives 1H(O2CR), crystallographic analysis
revealed intramolecular hydrogen-bonding between the carbox-
ylate and the amine center.18,19
The cation [1H]þ is a soft Lewis acid with distinctive pro-
perties.11,12 It is not poisoned by water or many related oxygenic
ligands, a property that is key to its reactivity toward H2 in polar
media.13ꢀ16 Adjacent to the vacant coordination site on the 16e
metal is an amine ligand, which is well positioned for hydrogen-
bonding to Lewis bases. These chiral complexes add H2 with high
diastereoselectivity, reflecting the influence of the phenyl sub-
stituents on the metal.
In a previous paper, we showed that [1H]þ and related
complexes bind a wide variety of charge-neutral Lewis bases such
as phosphines, CO, and ammonia.11 The Lewis base adducts
[1H(L)]þ were found to largely exist as single diastereoisomers.
Received: January 23, 2011
Published: May 16, 2011
r
2011 American Chemical Society
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Inorganic Chemistry
ARTICLE
Figure 1. Structures of the R- and β-isomers of Cp*Ir(X)(S,S-TsDPEN).
In this report we describe the synthesis and characterization of a
wide variety of Cp*Ir(X)(TsDPEN) adducts where X = CNꢀ, Me-
(CdNH)Sꢀ, Me(CdO)NHꢀ, NO2ꢀ, 2-pyridonate, and MoS4
.
2ꢀ
The diastereoselectivity of HX additions to 1 was also investigated,
along with the mechanism of diastereomerization. These findings
establish the versatility of [1H]þ as a Lewis acid. Compounds of the
type Cp*Ir(X)(TsDPEN) can exist as two diastereoisomers, depend-
ing on the relative configuration of the stereogenic Ir center and the
TsDPEN ligand. The stable diastereomer for all adducts features the
same relative disposition of ligands at metal and substituents on
the TsDPENꢀ ligand; this isomer is labeled R (Figure 1). The less
stable diastereomer, β, is observed in some cases.
Figure 2. Structure of R-Cp*Ir(CN)(TsDPEN). Thermal ellipsoids are
shown at the 50% probability level but are omitted on the Cp*, tosyl, and
phenyl groups for clarity.
A cyanide-bridged bimetallic complex can be readily prepared
from 1H(CN). Thus, treatment of R-1H(CN) with 1 equiv of
[1H]BF4 gave [(1H)2(μ-CN)]BF4. In the IR spectrum, the con-
version is indicated by a shift of νCN from 2107 to 2152 cmꢀ1
,
’ RESULTS AND DISCUSSION
which is in the region characteristic of a μ-CN ligand (eq 3).22 On
1
Cyanide. The complex Cp*Ir(CN)(TsDPEN) (1H(CN))
was prepared by the reaction of 1 and KCN in methanol
(eq 1). The solvent serves as the proton donor; reactions in
nonacidic solvents such as MeCN also proceed but are slower.
The origin of the proton from the solvent was verified by the
addition of Et4NCN to a solution of 1 in CD3CN under
anhydrous conditions, which slowly afforded 1D(CN). The IR
the basis of its H NMR spectrum, [(1H)2(μ-CN)]BF4 exists
mainly as a single diastereomer in CH2Cl2 solution. Using the
mixture of β-1H(CN) and R-1H(CN), we generated a pair of
diastereomers of [(1H)2(μ-CN)]BF4.
spectrum of Cp*Ir(CN)(TsDPEN) features νCN at 2107 cmꢀ1
,
which is typical for related cyanide complexes.20,21
The structure of 1H(CN) was verified crystallographically
(Figure 2). The Ir(1)ꢀC(32) distance is 1.990(8) Å, and
the C(32)ꢀN(3) distance was found to be 1.146(9) Å, both
of which are typical for related complexes.23 The IrꢀCꢀN
angle is 173.2°, tilted toward the NH2 group on the TsDPEN
backbone. Intermolecular hydrogen-bonds exist between
the IrCN and a neighboring H2NIr at 2.906(8) Å and
between a lattice water (H2O) and H2NIr at a distance of
3.062(18) Å.
Borohydride and Hydride. The synthesis of 1H(BH4) was
attempted by treatment of 1 with NaBH4 in methanolic
solution. A potentially related (BINAP)Ru(H)(BH4)(DPEN)
complex had been prepared in this way by Noyori et al.24 and
Morris et al.25 The reaction 1 þ NaBH4 was found, however,
to afford the well-known hydride 1H(H), the proton being
derived from solvent as proposed above for the cyanation.
The reaction of NBu4BH4 with CH2Cl2 solutions of 1 and
of 1H(Cl) also gave 1H(H). Treatment of a methanol solu-
tion of 1 with the milder reducing agent NaBH3CN resulted
in the formation of primarily 1H(CN) and some 1H(H).
The transfer of CNꢀ from NaBH3CN to metal centers is
known.21,26,27
Of course, 1H(CN) can also be prepared by salt metathesis
from 1H(Cl) and KCN, but the results were surprising. First, it is
important to note that solutions of 1H(Cl) in MeOH contain
significant amounts of [1H]þ, as indicated by the red color of
these solutions. In CD3OD, the 3J for the pair of doublets of the
TsDPEN backbone (CHPhCHPh) is 8.4 Hz versus 11.0 Hz in
CD2Cl2. The diminished coupling is consistent with a contribu-
tion from [1H]þ, wherein J is almost 0 Hz. According to H
NMR spectroscopy, salt exchange between 1H(Cl) and KCN
afforded a 50:50 mixture of R-1H(CN) and the β-diastereomer
(eq 2). Over the course of weeks, β-1H(CN) quantitatively
converts to R-1H(CN). At room temperature, isomerization of
β-1H(CN) to R-1H(CN) followed first order kinetics with a
half-life greater than 20 days. Similar behavior was observed for
the two isomers of Cp*Ir(CO)(TsDACH).11
3
1
The usual synthesis of 1H(H) by treating 1 with methanol
results in the formation of 0.8% of a minor isomer (298 K). The
reaction of NaBH4 and 1 was found to initially produce equal
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ARTICLE
Table 1. Rate Constants and Half-Life Data for the
Isomerization of the Unstable Diastereomer of 1H(H)
in Several Solvents at 298 K
solvent
kisom (sꢀ1
)
t1/2 (h)
CD2Cl2
CD3CN
C6D6
7.8 ꢁ 10ꢀ5
4.1 ꢁ 10ꢀ5
1.6 ꢁ 10ꢀ5
2.5
4.7
12
Figure 3. 1H NMR spectra in the hydride region for the reaction of a
mixture of R- and β-(p-cymene)RuH(R,R-TsDPEN) with acetophe-
none in CD2Cl2 solution at 23 °C. Equivalents of (initial) acetophenone
and reaction times are indicated on the spectra.
amounts of the two diastereomers of 1H(H). The 1H
NMR signals for the new isomer (β-1H(H)) match with
those for the minor hydride observed from the preparation of
1 and methanol. Crystals of the racemic mixture were
obtained, but they were featherlike and diffracted X-rays poorly.
β-1H(H) was found to convert to the R-diastereomer with
t1/2 = 4.7 h at room temperature. The rate of isomerization
was almost unaffected by solvent polarity (Table 1) as well as by
the addition of PPh3. A kinetic isotope effect of 1.2(3) was
determined for the isomerizations of 1H(H) and Cp*IrD-
(D2NCHPhCHPhNTs). The rate of isomerization was unaf-
fected when the tosyl group was replaced by a mesyl (MeSO2)
group.28 The temperature dependence of the rate constant over a
range of 22 °C revealed ΔSq = 138 J/mol K (see Supporting
Information).
In the absence of excess acetamide, the adduct was found to
slowly revert to the precursor (eq 4).
We previously found that the conformation of the diphenyl-
ethylene backbone of TsDPEN is readily analyzed by 1H NMR
spectroscopy by means of the coupling constants of the methine
protons.11 This analysis indicates that the phenyl groups in
β-1H(H) are diaxial: J = 4.7 Hz for CH(Ph)NH2 and a broad
singlet observed for CH(Ph)NTs. In contrast, the phenyl groups
are diequatorial in most pseudo-octahedral Cp*Ir(X)(TsDPEN)
complexes,11 including R-1H(H).
In CD3CN solution at 298 K, Keq is 3.3(1) ꢁ 102 Mꢀ1. Samples
of 1H(NHC(O)Me) can be precipitated from MeCN solution
but redissolve to afford a mixture of 1, MeC(O)NH2, and
1H(NHC(O)Me). A singlet at δ5.13 (CD3CN) is assigned to
MeC(O)NHIr, 0.4 ppm upfield of free acetamide. A broad triplet
1
The reaction of (p-cymene)Ru(TsDPEN-H) with NaBH4 was
also investigated, since this compound is more widely used as a
catalyst than the Cp*Ir derivative. We obtained two diastereomers
of (p-cymene)RuH(TsDPEN) in a 6:4 (β:R) ratio. The β-isomer
had previously been detected at a level of about 1% in samples of
(p-cymene)RuH(TsDPEN).3 To compare the reactivity of the
diastereomers in transfer hydrogenation, a 6:4 diastereomeric
mixture of β- and R-(p-cymene)RuH(R,R-TsDPEN) was trea-
ted with 3.3 equiv of acetophenone, and the consumption of
at δ11.24 in the H NMR spectrum is assigned to one of the
diastereomeric NH2 groups of the TsDPENꢀ ligand, the low-
field shift being consistent with intramolecular hydrogen-bonding
to the MeC(O)NHIr center. Ikariya and co-workers have
isolated the analogous (p-cymene)Ru(amidate)(MsDPEN)
(amidate = NHC(O)C(CN)(CH3)CH2C6H5, Ms = mesyl),
where the amidate NH coordinates to the Ru center. 1H NMR
resonances for the NH (δ6.00) and NH2 group of MsDPEN
(δ9.62) of Ikariya’s complex are similar to the corresponding
signals observed for 1H(NHC(O)Me).29 Several other com-
pounds feature N-bonded iridium amides.30ꢀ33 Qualitative tests
showed that formamide and benzamide also add to 1.
1
hydride isomers was monitored via H NMR. After 50 min at
room temperature, we observed the consumption of 95% of the
stable hydride isomer, but only 20% of the unstable isomer
(Figure 3). The organic product is 1-phenylethanol. This
experiment suggests that the β-hydride isomer is a less effective
TH catalyst compared to the R-isomer. Since the β-isomer of
(p-cymene)RuH(TsDPEN) is present in <1% quantity when
generated by treating (p-cymene)Ru(TsDPEN-H) with 2-pro-
panol, it is doubtful that this isomer has a significant role in TH
catalysis.
Compared to acetamide, thioacetamide was found to add
more strongly to 1. From the reaction of stoichiometric amounts
of 1 and the thioamide we obtained 1H(SC(NH)Me) in
analytical purity. Crystallographic analysis confirmed the pre-
sence of the S-bonded tautomer (Figure 4). The imine N was
found to engage in intermolecular hydrogen-bonding with the
H2N group of a neighboring Ir-adduct (dNꢀH N = 2.925(5) Å).
Two diastereomers of 1H(SC(NH)Me) we2re evident in fresh
solutions, but after a few hours a single diastereomer dominates.
Amides and Thioamides. Acetamide was found to add to 1 to
afford the corresponding amido-amine adduct, 1H(NHC(O)Me).
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ARTICLE
Figure 4. Structure of R-Cp*Ir(SC(NH)Me)(TsDPEN). The thermal
ellipsoids are shown at 50% probability level but are omitted on the Cp*
and phenyl rings for clarity.
These isomers are distinguished by imine NH signals at δ7.8 and
8.1 (CD2Cl2). One isomer exhibits sharp Cp* and TsDPEN
signals, whereas the other isomer features broadened signals
for the Cp* and TsDPEN. These signals remained unchanged
from ꢀ30 to 40 °C. These isomers are proposed to differ with
respect to coordination of the thioacetamide anion to the R- or
S-face of [1H]þ (eq 5).
Figure 5. Structure of (C5Me4H)Ir(NO2)(TsDPEN). The thermal
ellipsoids are shown at 50% probability level but are omitted on the
phenyl and tosyl groups for clarity.
nitro ligand (2.742(3) Å) (Figure 5). The coordination sphere
in 1H(NO2) is unexceptional, exhibiting equatorial phenyl
groups. Only a single diastereomer was observed via 1H NMR
spectroscopy.
2-Pyridone. 2-Pyridone, an amide that is known to engage in
strong H-bonding,36 adds to 1 as indicated by an immediate color
change from purple to yellow. 2-Pyridone is sufficiently acidic
(pKa = 8.26 in MeCN solution) relative to [1H(NCMe)]þ (pKa =
21 in MeCN) that a stable adduct of type 1H(2-pyridonate) is
anticipated.9,37 The binding is stronger than for acetamide: the
reaction only required stoichiometric amounts of the pyridone,
and the product did not dissociate detectably in solution.
Crystallography confirmed that the pyridonate is N-bonded
(Figure 6), as is typical for pyridonates of softer metals.38,39
The C(32)ꢀO(3) bond distance of 1.260(4) Å is similar to that
seen in other pyridonate complexes.40,41 Intramolecular hydro-
gen-bonding exists between the pyridonate carbonyl and the
TsDPEN amine, with a O(3)ꢀN(2) distance of 2.761(5) Å. The
pyridonate ring is coplanar with one of the phenyl rings.
Interestingly, the phenyl substituents on the TsDPEN ligand
are diaxial, an orientation that had not been previously observed
in pseudo-octahedral TsDPEN complexes, except for the meta-
stable hydride described above.
In one of the diastereomers, intramolecular hydrogen-bonding
between the imine and amine is strong, as indicated by the low
field H NMR signal at δ11.30. The NH2 group for the more
1
stable diastereomer does not display this low-field feature (δ7.48
and 4.06). At 23 °C, 1H(SC(NH)Me) was found to diastereo-
merize via a first order pathway with k = 1.5 ꢁ 10ꢀ4 sꢀ1 (t1/2
∼
1.3 h), slightly faster than the rates for the isomerization of
1H(H) and 1H(CN).
Nitrite. The nitro complex 1H(NO2) was prepared via anion
metathesis of 1H(Cl) and NaNO2 (eq 6).
1
Consistent with the crystallographic results, the H NMR
signals for the pyridonate CH groups appear in the region
(δ6ꢀ6.5) associated with vinylic protons, as is characteristic of
the pyridone tautomer.40,42 Further evidence for a pyridonate
description is evident in the 13C NMR spectrum, where reso-
nances were observed in the region for carbonyl centers at δ
172.7 and 173.3.40 The axial proton on the amine of 1H(2-
pyridonate) exhibits a 1H NMR signal at δ11.51, the downfield
shift resulting from hydrogen-bonding to the carbonyl. 1H NMR
data obtained on crystals dissolved at ꢀ18 °C displayed signals
for both diastereomers, both of which feature equatorial phenyl
We originally observed 1H(NO2) when 1H(H) was treated
with nitric oxide,34,35 even when this reaction was conducted
anaerobically.
Hydrogen-bonding between the amine of TsDPEN and the
1
nitrito ligand is indicated by the NH signal in the H NMR
spectrum at δ6.65 (δ4.42 for 1H(Cl)).11 On the basis of the
downfield shift of the NH signal, hydrogen-bonding in 1H(NO2)
is similar to that for the adducts of acetamide (δ11.24) and
2-hydroxypyridine (see below), and the previously reported
acetate and formate adducts (δ9.59, δ8.96).18 The C5Me4H
analogue of 1H(NO2) gave crystals suitable for X-ray diffrac-
tion. Crystallographic analysis verified the presence of a
hydrogen bond between the amine proton and O(3) of the
1
groups. H NMR spectra revealed a 5:4 isomer ratio (20 °C),
which was only slightly dependent on temperature (ΔH= 2.6 kJ/mol
and ΔS = 6.8 J/mol K over a 60 °C temperature range).
Indicative of the changeable isomer ratio, solutions were found
to be thermochromic: cold solutions appear yellow and warm
solutions are pink. No color changes were observed for solid
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Figure 7. Structure of [Cp*Ir(TsDPEN)]2MoS4. The thermal ellip-
soids are shown at 30% probability level but are omitted on the Cp*,
phenyl, and tosyl groups.
Crystallographic analysis of [1H]2MoS4 revealed a tetrahedral
Mo(VI) center linking two iridium centers. Diastereomers were
not observed. Similar diastereoselectivity had been observed for
[(1)2dppe]2þ 11
.
The MoꢀS bonds are of two distinct types: the
Figure 6. Structure of Cp*Ir(2-pyridonate)(TsDPEN), which crys-
tallizes as the β-diastereomer. The thermal ellipsoids are shown at
50% probability level but are omitted on the Cp* ring, phenyl, and
tosyl groups for clarity (inset: bond distances for the 2-pyridone
ring).
MoꢀSIr distances are 2.222(4) and 2.231(4) Å, whereas Moꢀ
S
terminal distances are 2.130(5) and 2.170(4) Å (Figure 7, Table 2).
The longer MoꢀSterminal bond is affected by hydrogen-bonding
to one amine proton on each of the Ir complexes (dS---NH2
=
3.508(8) Å). The dihedral angle between the planes generated
from Ir(1)ꢀS(3)ꢀMo(1) and Ir(2)ꢀS(4)ꢀMo(2) is 46.5°.
samples over a comparable temperature range (ꢀ30 to
120 °C).43 The second isomer is proposed to arise from the
attachment of 2-pyridonate to the opposite metal face (eq 7).11
Consistent with the crystallographic results, the 1H NMR signals
for the pyridonate CH groups appear in the vinyl region
(δ6ꢀ6.5), which is characteristic of the pyridone tautomer.40,42
’ CONCLUSIONS
In this work, we showed that [1H]þ binds a wide variety of
soft anionic ligands. Adducts were prepared in two ways: (i)
stable anions were combined directly with [1H]þ and (ii) for less
accessible anions, the corresponding conjugate acids were added
to 1. This methodology has afforded the first derivative of the
type MoS2(SR)246 and the first structurally characterized exam-
ple of a monodentate thioacetamido complex.49
In general, the initial binding of anions to [1H]þ is unselec-
tive, but the equilibrium diastereoselectivities are high. Support-
ing this view, basic ligands that would be expected to bind
strongly generate observable amounts of the β-diastereomer. In
contrast, weakly basic anions (e.g., nitrite, tetrathiomolybdate) or
ligands that eliminate readily (acetamide), gave only the more
stable R-isomer.
2ꢀ
Tetrathiomolybdate. Although the thioanions MoS4 and
WS4 have been well studied as “metalloligands”,44,45 com-
2ꢀ
plexes of the type (μ-κ1,κ1-MS4)(MLx)2 or esters such as
MoS2(SR)2 remain unknown.46ꢀ48 We prepared the first exam-
ple of such by the reaction of (Et4N)2MoS4 with 2 equiv of
[1H]BF4 (eq 8). Although thermally only slightly stable at room
temperature, dark purple [1H]2MoS4 was characterized by NMR
and IR spectroscopies, which indicated a single diastereomer.
Similar results were obtained for the green WS42ꢀ derivative.
The observation of metastable diastereomers of 1H(H) and
(p-cymene)RuH(TsDPEN) is noteworthy because of the utility
of these compounds as enantioselective catalysts for asymmetric
transfer hydrogenation.6,50 The high enantioselectivity arises
because (i) the catalysts form hydrides with high diastereoselec-
tivity from hydrogen donors (formate, alcohols, etc.) and (ii) the
resulting hydrides diastereoselectively transfer H2 to prochiral
substrates. We were surprised that using BH4ꢀ/ROH as a source
of H2 results in almost no diastereoselection, and the resulting
mixture of diastereomers is stable for many hours. The uncom-
mon diastereomer is competent for transfer hydrogenation, but is
slow. The differing rates probably arise because in the less stable
hydride substrate accessibility is hindered by the diaxial phenyl
groups. The diaxial orientation of the phenyl groups is proposed
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Table 2. Selected Bond Distances (Å) and Related Structural Features for New Compounds of the Type 1H(X)
compound
1 (ref 11)
[1H]BArF4 (ref 9)
1H(CN)
1H(SC(NH)Me)
[1H]2MoS4
1H(NO2)
1H(2-pyridonate)
IrꢀCp*(centroid)
IrꢀN(1)Ts
1.794(6)
2.058(5)
1.901(5)
1.782(6)
1.984(4)
2.096(5)
1.810(7)
2.151(5)
2.124(9)
1.990(1)
equatorial
1.818(4)
2.174(3)
2.112(5)
2.361(9)
equatorial
1.823(16), 1.800(14)
2.144(10), 2.137(10)
2.157(10), 2.091(11)
2.393(4), 2.406(4)
equatorial
1.830(4)
2.137(3)
2.106(3)
2.105(3)
equatorial
1.803(4)
2.168(3)
2.116(3)
2.114(3)
axial
IrꢀN(2)Hx (x = 1,2)
IrꢀX
phenyl group orientation
axial
axial
Scheme 2. Two Pathways for the Chelate-Ring-Opening
Mechanism Proposed for the Diastereomerization of 1H(H)
Figure 8. Proposed conformations of the R- and β-diastereomers of
Cp*IrH(S,S-TsDPEN). Similar conformations apply also to (p-cymene)-
RuH(TsDPEN).
to result from dihydrogen-bonding between the hydride ligand
and the amine group (Figure 8).51 Dihydrogen-bonding is
observed between NꢀH and RuꢀH in the stable isomer of (p-
cymene)RuH(TsDPEN).1
Although the binding of hard Lewis bases to [1H]þ is usually
unfavorable, binding affinities can be enhanced by intramolecular
hydrogen-bonding. This additional interaction is proposed to
influence the affinity of 1 for amides and 2-pyridone, even though
[1H]þ shows no affinity for pyridine itself.11 The influence of
hydrogen-bonding in the pyridonate adduct is sufficient to stabilize
the β-isomer of 1H(2-pyridonate), at least in the solid state. The
hydrogen-bonding interaction proposed to stabilize 1H(NHC(O)-
Me) is weaker than in the pyridonate complex, reflecting the
reduced tendency of simple amides to engage in hydrogen-bonds.52
We propose that diastereomerization occurs via two pathways.
For weakly basic ligands (acetamido, nitrito, chloride), only a
single diastereomer is observed. For these anions, we assume that
diastereomerization involves an elimination-readdition path-
way, either by dissociation of the anionic ligand or its conjugate
acid. More interesting is the isomerization mechanism for
tightly bound, basic ligands such as cyanide and hydride. In
these cases, dissociation of the anion is unlikely. A dissociative
pathway for the hydride is precluded because the rate of
addition of H2 to 1 is too slow, requiring days at 1 atm of H2.
Instead, diastereomerization is proposed to involve opening of
the Ir(TsDPEN) ring in a hemilabile manner. One can envision
dissociation of the amine or the tosylamido ligands followed
by reattachment of this group to the opposite face of the 16e-
intermediate (Scheme 2).
1 (Note: Cp*Ir(TsDPEN-H) was not initially dissolved in MeOH to
avoid formation of 1H(H) via hydrogen transfer). The resulting yellow
solution was allowed to stir for 5 min before solvent was removed under
reduced pressure. The pale red residue was recrystallized from CH2Cl2
solution with hexane to afford a pale yellow solid. Slow diffusion of a
CH2Cl2 solution of the solid into hexane gave pale yellow crystals
suitable for crystallographic analysis. Yield: 68 mg (66%). IR: νCN
(KBr) = 2107 cmꢀ1. 1H NMR (500 MHz, CDCl3): δ 1.86 (s, 15H, Cp*,
β) 1.94 (s, 15H, Cp*, R), 2.20 (s, 3H, SO2C6H4-4-CH3, β), 2.21 (s, 3H,
SO2C6H4-4-CH3, R), 3.60 (ddd, 2.5, 10.8, 13.0 Hz, 1H,
H2NCHPhCHPhNTs, R), 3.84 (br m, 1H, H2NCHPhCHPhNTs, β),
4.01 (br s, 4.13, HHNCHPhCHPhNTs, R), 4.19 (d, 1H, 11.0 Hz, H2N-
CHPhCHPhNTs, R), 4.39 (br m, 1H, HHNCHPhCHPhNTs, β), 4.58
(br m, 1H, HHNCHPhCHPhNTs, β), 4.60 (d, 9.0 Hz, H2NCHPhCH-
PhNTs, β), 4.84 (br m, 1H, HHNCHPhCHPhNTs, R), 6.62ꢀ7.46 (m,
28H, phenyl). The same compound was prepared by addition of 1 mL
of a 0.14 M KCN in MeOH solution that was 0.028 M in 1H(Cl).
Yield: 75 mg (74%). When 1 is treated with Et4NCN in CD3CN the
signal at δ 3.60 appears as a doublet assigned to the HDNCH(Ph)
proton. Anal. Calcd for C31H36IrN3O4S CH2Cl2 0.75H2O: C, 48.49; H,
’ EXPERIMENTAL SECTION
Materials and Methods. All synthetic manipulations were per-
formed in air unless noted. TsDPENH was prepared according Noyori
and co-workers.53 The preparations of Cp*Ir(TsDPEN-H) (1),
[Cp*Ir(TsDPEN)]BF4 ([1H]BF4), and (p-cymene)Ru(TsDPEN-H)
have been described.1,11,14 Other reagents were obtained from conven-
tional commercial sources or were prepared by standard methods.54 1H
and 13C NMR spectra were referenced to the residual solvent peaks.55
Cp*Ir(CN)(TsDPEN), 1H(CN). Two milliliters of a 0.072 M KCN
in MeOH solution were added to 100 mg (0.144 mmol) of solid
3
3
4.87; N, 5.14. Found: C, 48.29; H, 4.69; N, 4.98.
[Cp*2Ir2(TsDPEN)2(μ-CN)]BF4. A 6.4 mL aliquot of a 0.016 M
solution of [Cp*Ir(TsDPEN)]BF4 in CH2Cl2 was added to 11 mL of a
0.01 M solution of Cp*Ir(CN)(TsDPEN) in CH2Cl2. The resulting pale
red solution was allowed to stir for 5 min before the solvent was removed
under reduced pressure. The red residue was recrystallized from a
minimum volume of CH2Cl2 by the addition of hexane, affording a pale
1
yellow solid. Yield: 126 mg (81%). IR (KBr): νCN = 2152 cmꢀ1. H
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Inorganic Chemistry
ARTICLE
NMR (500 MHz, CD2Cl2): δ 1.91 (s, 15H, Cp*), 2.00 (s, 15H, Cp*),
2.177 (s, 3H, SO2C6H4-4-CH3), 2.18 (s, 3H, SO2C6H4-4-CH3), 3.68
(ddd, 2.7, 11.2, 13.2 Hz, 1H, H2NCHPhCHPhNTs), 3.75 (ddd, 2.7,
11.2, 13.2, 1H, H2NCHPhCHPhNTs), 4.54 (d, 11.2 Hz, 1H,
H2NCHPhCHPhNTs), 4.79 (d, 11.2 Hz, 1H, H2NCHPhCHPhNTs),
6.54ꢀ7.40 (m, 28 H).
added to 5 mL of a 0.03 M MeCN solution of 1. The resulting
yellow solution was allowed to stir for 5 min before removing the
solvent under reduced pressure. The resulting yellow solid was recrys-
tallized from CH2Cl2 solution by the addition of hexane to afford a deep
yellow solid. The resulting solid is air sensitive and will degrade upon
exposure to water. Slow diffusion of a CH2Cl2 solution of the solid
into hexane resulted in light yellow crystals suitable for crystallographic
Cp*IrH(TsDPEN) Isomers. Under an atmosphere of Ar, 0.5 g
(0.72 mmol) of 1 was treated with 68 mg (1.8 mmol) of NaBH4 in 5 mL
of MeOH. After 2 min, solvent was removed from the yellow mixture
under reduced pressure. The remaining residue was extracted into 3 ꢁ
10 mL of CH2Cl2. The combined extracts concentrated under reduced
pressure to afford a yellow solid. Yield: 330 mg (66%). 1H NMR
(500 MHz, CD2Cl2): δ ꢀ11.49 (s, 1H, IrꢀH, β), ꢀ10.12 (s, 1H, IrꢀH,
R), 1.63 (s, 15H, Cp*, β), 1.89 (s, 15H, Cp*, R), 2.28 (s, 3H, SO2C6H4-
4-CH3, β), 2.35 (s, 3H, SO2C6H4-4-CH3, R), 3.36 (d, 11 Hz, 1H,
HHNCHPhCHPhNTs, β), 3.58 (d, 10.2 Hz, 1H, HHNCHPhCH-
PhNTs, R), 3.69 (ddd, 3.2, 9.6, 12.6 Hz, 1H, H2NCHPhCHPhNTs, R),
3.77 (d, 4.7 Hz, 1H, H2NCHPhCHPhNTs, β), 4.10 (t, 11.5 Hz, 1H,
HHNCHPhCHPhNTs, R), 4.16 (d, 9.6 Hz, 1H, H2NCHPhCHPhNTs, R),
4.71 (s, 1H, H2NCHPhCHPhNTs, β), 4.73 (br s, 1H, HHNC-
HPhCHPhNTs, β), 6.80ꢀ7.75 (m, 28H). 1H NMR (500 MHz,
CD3CN): δ ꢀ11.75 (s, 1H, IrꢀH, β), ꢀ10.74 (s, 1H, IrꢀH, R), 1.64
(s, 15H, Cp*, β), 1.87 (d, 0.8 Hz, 15H, Cp*, R), 2.28 (s, 3H, SO2C6H4-4-
CH3, β), 2.38 (s, 3H, SO2C6H4-4-CH3, R), 3.68 (ddd, 3.6, 9.2, 12.1 Hz,
1H, H2NCHPhCHPhNTs, R), 3.73 (m, 1H, H2NCHPhCHPhNTs, β),
3.91 (d, 11.1 Hz, 1H, HHNCHPhCHPhNTs, β), 4.15 (d, 9.2 Hz, 1H,
H2NCHPhCHPhNTs, R), 4.24 (t, 11.2 Hz, 1H, HHNCHPhCHPh-
NTs, R), 4.40 (d, 10.6 Hz, 1H, HHNCHPhCHPhNTs, R), 4.57 (s, 1H,
H2NCHPhCHPhNTs, β), 4.91 (d, 8.7 Hz, 1H, HHNCHPhCHPhNTs, β),
6.85ꢀ7.74 (m, 28H).
1
analysis. Yield: 78 mg (71%). H NMR (500 MHz, CD2Cl2): δ 1.76
(s, 15H, Cp*, β), 1.81 (s, 15H, Cp*, R), 2.19 (s, 3H, β), 2.23 (s, 3H, R),
2.35 (s, 3H, β), 2.73 (d, 0.9 Hz, 3H, β), 3.22 (br d, 1H,
HHNCHPhCHPhNTs, β), 3.60 (m, 2H, H2NCHPhCHPhNTs, R þ
β), 4.06 (br d, 1H, HHNCHPhCHPhNTs, R), 4.20 (d, 11.1 Hz, 1H,
H2NCHPhCHPhNTs, R), 4.26 (d, 10.8 Hz, 1H, H2NCHPhCHPhNTs,
β), 6.53ꢀ7.33 (m, 28H, phenyl), 8.02 (br s, 1H, HHNCHPhCHPhNTs,
R), 7.48 (br t, 1H, HHNCHPhCHPhNTs, R), 7.84 (s, 1H, SC
(NH)Me, β), 8.06 (s, 1H, SC(NH)Me, R), 11.30 (br t, 1H,
HHNCHPhCHPhNTs, β). The 1H NMR spectrum was invariant from
ꢀ30 to 40 °C. Anal. Calcd for C33H40IrN3O2S2 CH2Cl2: C, 47.93; H,
3
4.96; N, 4.93. Found: C, 47.66; H, 4.83; N, 4.87.
Cp*Ir(NO2)(TsDPEN), 1H(NO2). Nitric oxide was bubbled
through a solution of 120 mg (0.18 mmol) of 1 in 10 mL of MeCN.
An immediate color change from pale orange to brown was observed. A
tan solid was obtained upon recrystallization from CH2Cl2/hexane.
1H(NO2) can also be prepared from a CD3CN solution of 1H(Cl) and
NaNO2. Nitric oxide was purified by passage through a saturated
1
aqueous NaOH solution. Yield: 75 mg (56%). H NMR (500 MHz,
CD3CN): δ 1.78 (s, 15H, Cp*), 2.25 (s, 3H, SO2C6H4-4-Me), 3.72
(ddd, 1 H, H2NCHPhCHPhNTs), 4.23 (d, 1H, H2NCHPhCHPhNTs),
5.18 (br d, 1H, HHNCHPhCHPhNTs), 6.65 (br t, 1H, HHNCHPh-
CHPhNTs), 6.70ꢀ7.23 (m, 14H). Anal. Calcd for C31H36IrN3O4S: C,
50.39; H, 4.91; N, 5.69. Found: C, 50.07; H, 5.09; N, 5.43. FD-MS:
m/z = 693 (MHþ). The Cp* system tended to form long needles that
did not diffract well. The related (C5Me4H)Ir(NO2)(TsDPEN) was
prepared as described above (55% yield) and readily crystallized as the
CH2Cl2 solvate. 1H NMR (500 MHz, CD3CN): δ 1.76 (s, 3H,
C5Me4H), 1.80 (s, 3H, C5Me4H), 1.83 (s, 3H, C5Me4H), 1.91 (s, 3H,
C5Me4H), 2.25 (s, 3H, SO2C6H4-4-Me), 3.84 (ddd, 3.3, 11, 12.7 Hz, 1 H,
H2NCHPhCHPhNTs), 4.36 (d, 11 Hz, 1H, H2NCHPhCHPhNTs),
4.84 (br d, 7 Hz, 1H, HHNCHPhCHPhNTs), 6.47 (br t, 10 Hz, 1H,
HHNCHPhCHPhNTs), 6.70ꢀ7.23 (m, 14H).
(p-Cymene)RuH(R,R-TsDPEN) Isomers. The preparation fol-
lowed the procedure for R- and β-1H(H) (preceding procedure) starting
with 100 mg (0.17 mmol) of (p-cymene)Ru(R,R-TsDPEN-H) to afford a
mixture of (p-cymene)RuH(R,R-TsDPEN) R and β isomers as a brown
1
solid. Yield: 28 mg (28%). H NMR (500 MHz, CD2Cl2): δ ꢀ6.13
(s, 1H, RuꢀH, β), ꢀ5.82 (s, 1H, RuꢀH, R), 1.27 (d, 6.6 Hz, 3H,
CH(CH3)2, β), 1.29 (d, 6.9 Hz, 3H, CH(CH3)2, R), 1.29 (d, 6.9 Hz, 3H,
CH(CH3)2, β), 1.34 (d, 6.9 Hz, 3H, CH(CH3)2, R), 1.95 (s, 3H, CH3
cymene, β), 2.30 (s, 3H, SO2C6H4-4-CH3, β), 2.33 (s, 3H, CH3 cymene,
R), 2.37 (s, 3H, SO2C6H4-4-CH3, R), 2.61 (m, 1H, CH(CH3)2, β), 2.71
(m, 1H, CH(CH3)2, R), 3.22 (t, 12.1 Hz, 1H, HHNCHPhCHPhNTs,
R), 3.31 (m, 1H, HHNCHPhCHPhNTs, β), 3.51ꢀ3.60 (m, 2H, HHN-
CHPhCHPhNTs, R þ β), 3.72 (m, 1H, H2NCHPhCHPhNTs, β), 3.81
(d, 9.8 Hz, 1H, H2NCHPhCHPhNTs, R), 4.06 (ddd, 3.1, 9.9, 12.9 Hz, 1H,
H2NCHPhCHPhNTs, R), 4.37 (dd, 1.0, 5.8 Hz, 1H, C6H4 cymene, β),
4.73 (d, 3.6 Hz, 1H, H2NCHPhCHPhNTs, β), 4.82 (dd, 0.8, 5.8 Hz, 1H,
C6H4 cymene, R), 4.86 (d, 5.7 Hz, 1H, C6H4 cymene, β), 5.00 (dd, 1.0,
5.7 Hz, 1H, C6H4 cymene, R), 5.26 (d, 5.7 Hz, 1H, C6H4 cymene, β),
5.34 (d, 5.7 Hz, 1H, C6H4 cymene, R), 5.41ꢀ5.44 (m, 2H, C6H4 cymene,
R þ β), 6.75ꢀ7.48 (m, 28H).
Cp*Ir(2-pyridonate)(TsDPEN), 1H(2-pyridonate). A solution
of 0.14 g (0.21 mmol) of 1 in 10 mL of MeCN was treated with 5 mL of
0.041 M (0.21 mmol) MeCN solution of 2-hydroxypyridine. The
addition resulted in an instantaneous color change from reddish-purple
to yellow-orange. The solution was stirred for 5 min, and the solvent was
removed under reduced pressure. The yellow solid was recrystallized by
dissolution in 2 mL of MeCN followed by the addition of 30 mL of Et2O.
Yield: 73.3 mg (44%). 1H NMR (500 MHz, CD3CN): δ 1.61 (s, 15H,
Cp*), 1.63 (s, 15H, Cp*), 2.16 (s, 3H, SO2C6H4-4-CH3), 2.21 (s, 3H,
SO2C6H4-4-CH3), 3.57 (dt, 6.0, 11.3 Hz, 1 H, H2NCHPhCHPhNTs),
3.73 (ddd, 4.6, 10.9, 15.9 Hz, 1 H, H2NCHPhCHPhNTs), 3.79 (d, 11 Hz,
1H, H2NCHPhCHPhNTs), 3.98 (br t, 9.7 Hz, 1H, HHNCHPhCHPh-
NTs), 4.36 (d, 11 Hz, 1H, H2NCHPhCHPhNTs), 4.68 (br dd, 5.0,
10.9 Hz, 1H, HHNCHPhCHPhNTs), 6.10ꢀ6.15 (m, 2H, pyridone
ring), 6.20 (dd, 1.3, 8.6 Hz, 1H, pyridone ring), 6.35 (dt, 1.5, 6.5 Hz, 1H,
pyridone ring), 6.37ꢀ6.56 (m, 9 H), 6.58 (tt, 1.3, 7.2 Hz, 1H, pyridone
ring), 6.66 (m, 1H), 6.68 (d, 7.8 Hz, 1H, SO2C6H4-4-Me), 6.80 (d,
8.4 Hz, 1H, SO2C6H4-4-Me), 6.69ꢀ7.25 (m, 18H), 7.26 (ddd, 2.2, 6.6,
8.7 Hz, 1H, pyridone ring), 7.32 (ddd, 2.2, 6.6, 8.7 Hz, 1H, pyridone
ring), 8.52 (dd, 2.2, 6.1 Hz, 1H, pyridone ring), 8.76 (dd, 2.0, 6.1 Hz, 1H,
pyridone ring), 9.79 (br t, 7.8 Hz, 1H, HHNCHPhCHPhNTs), 11.51
(br t, 11.1 Hz, 1H, HHNCHPhCHPhNTs). 13C NMR (500 MHz,
CD3CN): δ 9.29, 9.67, 68.92, 72.03, 72.99, 73.88, 87.12, 87.43, 108.52,
108.96, 117.78, 118.20, 127.21, 127.22, 127.44, 127.66, 127.99, 128.01,
Cp*Ir(NH(CO)Me)(TsDPEN), 1H(NH(CO)Me). A MeCN solu-
tion of acetamide (1.2 mL, 0.14 M) was added to a flask containing 100
mg (0.14 mmol) of solid 1. The purple solution was allowed to stir
overnight, affording a yellow precipitate. The precipitate was filtered off and
washed with hexane. Yield: 50 mg (46%). 1H NMR (500 MHz, CD3CN): δ
1.73 (s, 15H, Cp*), 1.98 (s, 3H, H3CCONHIr), 2.18 (s, 3H, SO2C6H4-4-
CH3), 3.61 (ddd, 3.4, 11.4, 12.5 Hz, 1H, H2NCHPhCHPhNTs), 4.17 (br d,
1H, HHNCHPhCHPhNTs), 4.26 (d, 11.2 Hz, 1H, H2NCHPhCHPhNTs),
5.12 (br s, 1H, H3CCONHIr), 6.59ꢀ7.62 (m, 14H), 11.24 (br t, 11 Hz, 1H,
HHNCHPhCHPhNTs). Upon dissolving the sample in CD3CN, the yellow
solution turned purple concomitant with the appearance of signals for 1 in the
1H NMR spectrum.
Cp*Ir(SC(NH)Me)(TsDPEN), 1H(SC(NH)Me). Under an atmo-
sphere of Ar, 1.6 mL of a 0.09 M MeCN solution of thioacetamide was
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Inorganic Chemistry
ARTICLE
128.40, 128.88, 128.95, 128.97, 129.02, 129.55, 130.75, 131.09, 138.80,
138.85, 138.87, 138.88, 140.15, 140.32, 140.95, 141.74, 144.00, 144.54,
153.61, 155.60, 172.72, 173.34, 175.85. Anal. Calcd for C31H36IrN3O4S:
C, 50.39; H, 4.91; N, 5.69. Found: C, 50.07; H, 5.09; N, 5.43.
[Cp*Ir(TsDPEN)]2(MoS4), [1H]2MoS4. Five milliliters of a
0.01 M (50 mmol) solution of (Et4N)2MoS4 in MeCN was added to
71 mg (100 mmol) of [Cp*Ir(TsDPEN)]BF4 in 10 mL of MeCN at
0 °C. The color changed instantly from pale yellow to a dark purple. The
solution was stirred for 5 min before removing the solvent under
reduced pressure. The product was recrystallized by diffusion of 60 mL
of Et2O into a solution of the purple residue in 2 mL of acetone
at ꢀ20 °C. Large colorless crystals of Et4NBF4 were removed manually,
leaving a purple solid. Yield: 71 mg (88%). 1H NMR (500 MHz,
CD3CN): δ 1.80 (s, 30H, Cp*), 2.29 (s, 6H, SO2C6H4-4-CH3), 3.86
(br t, 13 Hz, 2H, H2NCHPhCHPhNTs), 4.02 (d, 11 Hz, 2H,
H2NCHPhCHPhNTs), 5.10 (br s, 2H, HHNCHPhCHPhNTs), 5.82
(br t, 13 Hz, 2H, HHNCHPhCHPhNTs), 6.60ꢀ7.43 (m, 28H, phenyl).
UVꢀvis (MeCN): 463 (ε = 1.06 ꢁ 104 Mꢀ1 cmꢀ1), and 500 nm
(ε = 1.11 ꢁ 104 Mꢀ1cmꢀ1).
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The synthesis of [1H]2MoS4 was also achieved by the reaction of
2 equiv of 1H(Cl) and (Et4N)2MoS4. Above 0 °C, solutions degraded
over the course of a day as evidenced by precipitation of a black solid and
observation of free HTsDPEN by 1H NMR spectroscopy. Solid samples
degraded after several hours at room temperature.
[Cp*Ir(TsDPEN)]2(WS4). A green product was obtained using the
preceding procedure but using (Et4N)2WS4 in place of (Et4N)2MoS4.
[1H]2WS4 was found to degrade at room temperature, but more slowly
1
than the MoS4 derivative. Yield: 71 mg (94%). H NMR (500 MHz,
CD2Cl2): δ 1.79 (s, 30H, Cp*), 2.15 (s, 6H, SO2C6H4-4-CH3), 3.75 (br
t, 11.8 Hz, 2H, H2NCHPhCHPhNTs), 4.20 (br d, 2H, H2NCHPh-
CHPhNTs), 6.00 (br s, 2H, HHNCHPhCHPhNTs), 6.60ꢀ7.45 (m,
30H, phenyl). UVꢀvis (MeCN): 405 (ε = 3.01 ꢁ 104 Mꢀ1 cmꢀ1).
’ ASSOCIATED CONTENT
(26) Borch, R. F.; Hassid, A. I. J. Org. Chem. 1972, 37, 1673–1674.
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S
Supporting Information. NMR spectra, kinetic mea-
b
surements for the isomerization of 1H(CN), 1H(H), and 1H-
(SC(NH)Me), Eyring and van’t Hoff plots for the isomerization
of 1H(H), details for acetophenone hydrogenation by (p-cymene)-
RuH(R,R-TsDPEN), calculation of Keq for 1H(NHC(O)Me),
variable temperature data and van’t Hoff plot for the isomeriza-
tion of 1H(2-pyridonate) and crystallographic information files (cif)
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Corresponding Author
*E-mail: rauchfuz@illinois.edu.
’ ACKNOWLEDGMENT
This research was supported by the Division of Basic Energy
Sciences, Office of Science of the U.S. Department of Energy
through contract DEFG02-90er14146.
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