Activation of nitriles by metal ligand cooperation. reversible formation of ketimido- and enamido-rhenium PNP pincer complexes and relevance to catalytic design

Article abstract of DOI:10.1021/ja4071859

The dearomatized complex cis-[Re(PNP^tBu*)(CO)₂] (4) undergoes cooperative activation of Ci - N triple bonds of nitriles via [1,3]-addition. Reversible C-C and Re-N bond formation in 4 was investigated in a combined experimental and c

Full text of DOI:10.1021/ja4071859

Article
pubs.acs.org/JACS
Activation of Nitriles by Metal Ligand Cooperation. Reversible
Formation of Ketimido- and Enamido-Rhenium PNP Pincer
Complexes and Relevance to Catalytic Design
Matthias Vogt,†,§ Alexander Nerush,†,§ Mark A. Iron,‡ Gregory Leitus,‡ Yael Diskin-Posner,‡
Linda J. W. Shimon,‡ Yehoshoa Ben-David,† and David Milstein*,†
‡
†Department of Organic Chemistry, and Department of Chemical Research Support, The Weizmann Institute of Science, Rehovot
76100, Israel
S
* Supporting Information
ABSTRACT: The dearomatized complex cis-[Re(PNPtBu*)-
(CO)2] (4) undergoes cooperative activation of CN triple
bonds of nitriles via [1,3]-addition. Reversible C−C and Re−
N bond formation in 4 was investigated in a combined
experimental and computational study. The reversible
formation of the ketimido complexes (5−7) was observed.
When nitriles bearing an alpha methylene group are used,
reversible formation of the enamido complexes (8 and 9) takes
place. The reversibility of the activation of the nitriles in the
resulting ketimido compounds was demonstrated by the displacement of p-CF3-benzonitrile from cis-[Re(PNPtBu−N
CPhpCF3)(CO)2] (6) upon addition of an excess of benzonitrile and by the temperature-dependent [1,3]-addition of pivalonitrile
to complex 4. The reversible binding of the nitrile in the enamido compound cis-[Re(PNPtBu−HNCCHPh)(CO)2] (9) was
demonstrated via the displacement of benzyl cyanide from 9 by CO. Computational studies suggest a stepwise activation of the
nitriles by 4, with remarkably low activation barriers, involving precoordination of the nitrile group to the Re(I) center. The
enamido complex 9 reacts via β-carbon methylation to give the primary imino complex cis-[Re(PNPtBu−HN
CC(Me)Ph)(CO)2]OTf 11. Upon deprotonation of 11 and subsequent addition of benzyl cyanide, complex 9 is regenerated
and the monomethylation product 2-phenylpropanenitrile is released. Complexes 4 and 9 were found to catalyze the Michael
addition of benzyl cyanide derivatives to α,β-unsaturated esters and carbonyls.
CO2.38−41 Recently, we and others have reported on C−C
INTRODUCTION
■
bond formation between the exo-cyclic methine carbon of our
Metal−ligand cooperation (MLC), in which both the metal
dearomatized pincer complexes and substrates bearing CO
center and a ligand undergo bond formation and cleavage
without a formal change in the oxidation state of the metal, has
become a powerful tool in bond activation chemistry and
“green” catalysis.1−7 In this regard, transition metal (TM)
complexes with pyridine- and acridine-based LNL′-type pincer
ligands are versatile in bond activation processes (for instance,
S−H,8,9 N−H,10,11 O−H,12 H−H,13−15 and C−H15−19 single
bonds). Among these examples, the aromatization/dearomati-
zation sequence of the pyridine-based pincer ligand is the key
step for MLC-promoted substrate activation. It is involved in
recently developed, atom-economic catalytic reactions, specif-
ically the acceptorless dehydrogenative coupling (DHC) of
alcohols to esters,20−23 the oxidation of alcohols to carboxylic
acids using water as oxidant,24 DHC of alcohols and amines to
amides,25−27imines,28 or pyrroles,29,30 the coupling of nitriles
with amines under hydrogen pressure to form imines,23 the
synthesis of primary amines directly from alcohols and
ammonia,31,32 the hydrogenation of esters to alcohols,33,34 the
direct hydrogenation of amides to alcohols and amines,35 the
hydrogenation of organic carbonates/cabamates36 or urea
derivatives37 to methanol, and the hydrogenation of
42−44
double bonds, specifically CO2
and aldehydes.45 MLC
plays a key role in these substrate activations, and we found
evidence for a concerted C−C and Ru−O bond formation
when CO2 binds to A (Scheme1). Along these lines, we now
report on the activation of CN triple bonds (i.e., nitriles)
triggered via MLC in a rhenium(I) PNP-pincer type complex
(Scheme 2). In contrast to the well-established ruthenium
pincer chemistry, rhenium PNP pincer-type complexes are
sparsely discussed in the literature. A few amino-bisphosphino
rhenium pincer compounds were previously reported,46−48 in
studies aimed at radio pharmaceutical applications.49−52 The
cleavage of dihydrogen promoted by MLC was shown by
Gusev and co-workers in the amido-bisphosphine complexes of
53
t
i
[ReH(NO)(N(C2H4PR2)2] (R = Bu or Pr). Pyridine-based
PNP rhenium pincer complexes are particularly rare. Walton
and co-workers prepared rhenium(III)-complexes with such a
ligand, furnishing Re−Re multiple bonds.54,55 Recently,
Received: July 14, 2013
Published: November 5, 2013
© 2013 American Chemical Society
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equivalent phosphorus nuclei. The 1H NMR spectrum has two
resonances for the pyridine backbone in the aromatic regime: a
virtual triplet (3JHH = 7.8 Hz) at 7.62 ppm assigned to the para-
CH proton and a doublet at 7.36 ppm (3JHH = 7.8 Hz),
integrating to two protons, for both meta-CH protons. The IR
spectrum exhibits strong absorptions characteristic of the CO
ligands at 1816 and 1900 cm−1 with a relative intensity of 1:1,
indicating an angle of 90° between both ligands. Large single
crystals of the bright yellow 3 were obtained from a n-pentane-
layered THF solution. The molecular structure derived from an
X-ray diffraction study is shown in Figure 1. (Selected bond
lengths for all X-ray structures are given in Table 1.) The
tridentate PNPtBu ligand binds to the Re(I) center in a
meridonal manner. The two CO ligands bind mutually cis, and
the axial chloride completes the octahedral coordination sphere.
Upon addition of KOtBu, the yellow THF solution of 3 turns
instantly deep green. Extraction with n-pentane and subsequent
slow evaporation of the solvent gives the dearomatized complex
4 as large green crystals. The 31P{1H} NMR spectrum of 4
indicates a reduced symmetry with an AB-spin system,
suggesting that the two phosphorus nuclei are inequivalent,
with doublets at 68.9 and 74.7 ppm (2JPP = 145 Hz). Likewise,
Scheme 1. Metal−Ligand Cooperative Activation of CO
Double Bonds and the Novel Activation of CN Triple
Bonds via M−N(O) and C−C Bond Formation
Scheme 2. Synthesis of the Dearomatized Complex 4 and
Subsequent Reactions with Nitriles Lacking an α-Methylene
Carbon (5−7) and with Aliphatic Nitriles (8, 9)
1
the H NMR spectrum of 4 has three signals for the pyridine
protons, signifying the reduction in symmetry, specifically the
loss of the mirror plane perpendicular to the pyridine ring.
These signals (see Experimental Section for details) are shifted
to lower frequencies, indicative of a dearomatized PNP ligand.
Deprotonation of the exo-cyclic methylene group results in two
pincer-“arm” resonances in the 1H NMR spectrum: a doublet at
2.74 ppm (2JHP = 9.2 Hz, 2H) for the two equivalent CH2
protons and a broad singlet at 4.06 ppm (1H) for the methine
CH proton. There is only one signal in the carbonyl regime of
the 13C{1H} NMR spectrum, suggesting the presence of a
symmetry plane through the PNP pyridine ring. This indicates
a trigonal bipyramidal geometry or rapid conversion on the
NMR time scale of two equivalent square pyramidal structures
in solution. However, dynamic exchange in solution could not
1
be concluded from phase-sensitive 2D H−1H NOESY NMR
1
spectroscopy. The H NMR resonances of the methylene CH2
and the methine CH protons do not share significant cross-
peaks, which would indicate mutual chemical exchange due to
interconversion of two pyramidal structures.
However, the IR spectrum of crystalline 4 in a KBr pellet
shows two intense bands at 1827 and 1906 cm−1 with a relative
intensity ratio of 1:1, implying a bond angle of 90°. Single
crystals of 4 suitable for X-ray diffraction studies were obtained
from a concentrated solution in n-pentane (Figure 1). The
structure reveals a distorted square pyramidal geometry around
structurally well-defined Re complexes have been reported by
Berke et al. and Klankermayer et al. as highly efficient catalyst
for (transfer) hydrogenation reactions.56−60
This work involves the synthesis of cis-[Re(PNPtBu)-
(CO)2Cl] (3, PNPtBu = 2,6-bis(di-tert-butylphosphinomethyl)-
pyridine, Scheme 2), a versatile rhenium(I) starting material,
which is readily deprotonated to give the dearomatized species
[Re(PNPtBu*)(CO)2] (4, the asterisk indicates a dearomatized
ligand). Significantly, complex 4 reacts with nitriles via
reversible C−C and Re−N bond formation to give [1,3]-
addition products (Scheme 2). This unprecedented mode of
activation of nitriles readily leads to ketimido and enamido
ligands and to catalysis based on this unusual mode of metal−
ligand cooperation.
RESULTS AND DISCUSSION
■
Complex 3 is readily prepared by the reaction of commercially
available [Re(CO)5 Cl] (2) and 2,6-bis(di-tert-
butylphosphinomethyl)pyridine (PNPtBu, 1) in THF at 80 °C
(Scheme 2). The 31P{1H} NMR spectrum of 3 exhibits a
characteristic singlet at 68.8 ppm indicating two chemically
Figure 1. ORTEP diagram of [Re(PNPtBu)(CO)2Cl] (3, left) and
[Re(PNPtBu*)(CO)2] (4, right) with ellipsoids at 50% probability. The
P(tert-butyl)2 groups are drawn as wire-frames, and hydrogen atoms
are omitted for clarity. Selected bond lengths are given in Table 1.
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Table 1. Selected Bond Lengths for the Crystal Structures of Complexes 3−5 and 7−11
bond lengths (Å)
3
4
5
7
8
9
10
11
Re1−N1
Re1−N2
Re1−C24
Re1−C25
Re1−P1
Re1−P2
C1−C2
C2−C3
C3−C4
C4−C5
C5−C6
C6−C7
N1−C2
N1−C6
P1−C1
2.183(3)
2.135(7)
2.183(4)
2.191(5)
1.902(6)
1.898(6)
2.414(1)
2.404(1)
1.494(8)
1.393(8)
1.376(9)
1.373(10)
1.387(8)
1.498(8)
1.356(7)
1.365(7)
1.878(5)
1.858(6)
1.260(7)
1.502(7)
1.574(8)
2.186(4)
2.168(4)
1.897(5)
1.906(5)
2.394(1)
2.409(1)
1.514(6)
1.391(6)
1.394(8)
1.366(8)
1.390(6)
1.501(7)
1.358(6)
1.360(6)
1.874(4)
1.863(5)
1.266(6)
1.545(6)
1.560(6)
2.178(4)
2.173(4)
1.889(5)
1.910(5)
2.403(1)
2.413(1)
1.487(6)
1.396(6)
1.368(7)
1.400(6)
1.388(6)
1.513(6)
1.355(6)
1.370(6)
1.866(5)
1.881(5)
1.348(6)
1.409(6)
1.543(6)
2.174(2)
2.173(3)
1.886(3)
1.909(3)
2.413(1)
2.4139(9)
1.502(5)
1.399(4)
1.378(5)
1.384(5)
1.389(4)
1.507(4)
1.351(4)
1.357(4)
1.881(3)
1.861(3)
1.349(4)
1.388(4)
1.545(4)
2.195(4)
2.232(4)
1.888(5)
1.897(6)
2.407(1)
2.454(1)
1.518(6)
1.362(8)
1.396(8)
1.382(8)
1.392(8)
1.501(7)
1.359(6)
1.357(6)
1.886(5)
1.854(5)
1.288(7)
1.488(7)
1.522(6)
1.478(6)
2.171(2)
2.168(2)
1.907(3)
1.904(2)
2.4107(9)
2.4113(9)
1.515(3)
1.382(3)
1.383(3)
1.377(4)
1.388(3)
1.505(3)
1.360(3)
1.354(3)
1.900(2)
1.858(2)
1.282(3)
1.511(3)
1.515(3)
1.899(4)
1.900(3)
2.4383(8)
2.4434(8)
1.505(4)
1.389(4)
1.375(5)
1.390(5)
1.388(4)
1.515(4)
1.358(4)
1.363(4)
1.855(3)
1.856(3)
1.866(10)
1.901(9)
2.417(2)
2.399(2)
1.402(12)
1.425(12)
1.355(13)
1.407(15)
1.365(14)
1.532(15)
1.409(11)
1.388(11)
1.772(9)
P2−C7
1.796(11)
N2−C26
C26−C27
C26−C1
a
b
c
X−Y
2.5238(8)
c
1.535(3)
a
b
Re1−Cl1. N2−C34. C27−C28.
298
the Re(I) center. The angle between the two CO ligands
(C24−Re1−C25) is 86°, and the angles between the pyridine
ligand and the CO moieties are 115° (N1−Re−C24) and 159°
(N1−Re1−C25). Selected bond lengths for all X-ray structures
are given in Table 1.
of
K = 0.021 was determined for the reaction 6 + Ph−CN
eq
⇌ 5 + pCF3Ph−CN (Scheme 3), indicating the higher
thermodynamic stability of the adduct of the electron poor
nitrile.
The reversibility of nitrile binding by MLC is best
t
Reaction with Nitriles. Complex 4 reacts in n-pentane
solution with aromatic and aliphatic nitriles (Scheme 2). Upon
addition of benzonitrile (PhCN), 4-(triflouromethyl)-
benzonitrile (pCF3PhCN), or pivalonitrile (tBuCN), ketimide
complexes 5−7 are formed. Remarkably, the CN triple bond
binds reversibly to give the [1,3]-addition product via C−C and
Re−N bond formation. Transition metal ketimide complexes
have drawn special attention as they can function as both σ- and
π-donors. They are stabilizing ligands in highly oxidized TM
complexes61−64 and for actinide metal centers.65,66 They have
been reported as ligands promoting strong M−M interactions67
and have found application as olefin polymerization catalysts
with group four metal centers.68−71
demonstrated with BuCN. Reacting the deep green n-pentane
solution of 4 at −38 °C with an excess of tBuCN produces large
red crystals after 24 h. The H and 31P{1H} NMR spectra of a
1
solution of the crystals in toluene-d8 at room temperature show
very broad signals. Upon stepwise cooling to −65 °C, these
resonances broaden further and eventually collapse while at the
same time sharp resonances appear (Figure 2), consistent with
Scheme 3. Reversible Binding of Nitriles to
a
[Re(PNPtBu*)(CO)2] (4)
The ketimide complexes cis-[Re(PNPtBu−NCPh)(CO)2]
(5) and cis-[Re(PNPtBu−NCPhpCF3)(CO)2] (6) have AB-
spin systems in their 31P{1H} NMR spectra at chemical shifts
characteristic for aromatized PNP ligand systems (86.6 and
128.2 ppm with 2JPP = 193.8 Hz for 5, and 86.6 and 129.4 ppm
2
1
with JPP = 191.9 Hz for 6). This is also reflected in the H
NMR chemical shifts of the pyridine hydrogen atoms, which
are in the aromatic regime (see the Experimental Section). For
the pincer CH2 arm, there are two sets of doublets of doublets
with large geminal couplings (2JHH = 15.50 Hz for 5 and 6) and
smaller phosphorus couplings (2JHP = 5.00 and 9.00 Hz for 5
and 6, respectively). The CH methine “arm” appears as a
doublet with a small phosphorus coupling (details in the
Experimental Section).
The observed [1,3]-addition of nitriles to form complexes 5−
7 is a novel route for the synthesis of ketimido compounds,
complementary to those commonly used.68 This reactivity
mode is fully reversible. For instance, when a large excess of
benzonitrile is added to a solution of 6 in C6D6, the formation
of 5 and free pCF3Ph−CN is observed. An equilibrium constant
a
Top: Displacement of pCF3PhCN from 6 by an excess of PhCN.
Bottom: Displacement of PhCH2CN from 9 by CO.
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tively (Scheme 2). Complexes 8 and 9 are tautomers of the
corresponding ketimides via a formal [1,3]-proton shift. The
31P{1H} NMR spectra (C6D6, 25 °C) show the expected AB-
spin system with doublet resonances at 84.8 and 95.6 ppm (2JPP
= 191.0 Hz) for complex 8 and 82.9 and 98.9 ppm (2JPP = 186.6
Hz) for 9, indicative of two phosphorus nuclei in dissimilar
chemical environments.75
1
The H NMR spectra show the characteristic resonances for
the olefinic-CH protons for the enamido moieties: a quartet at
4.25 ppm (3JHH = 6.50 Hz) in 8 and a singlet at 5.32 ppm in 9.
The characteristic amido-NH proton is detected as a broad
singlet at 2.38 ppm in 8 and at 4.65 ppm in 9. The aromatic
resonances for the pyridine backbone in 8 and 9 are observed;
for full assignment, see the Experimental Section.
The reversible binding of benzyl cyanide to 4 was
demonstrated. Upon exposure of the coordinatively saturated
complex 9 in C6D6 to 1 atm of CO, the red solution slowly
changes to yellow, and the dearomatized tricarbonyl complex
mer-[Re(PNPtBu*)(CO)3] (12) is formed together with
detected free PhCH2CN (Scheme 3). This transformation
can be followed by 31P{1H} NMR spectroscopy (Figure 4):
after the addition of CO, complex 12 starts to form, and this
transformation is completed after 1 h at 65 °C.
Figure 2. Sections of the variable-temperature 31P{1H} NMR spectra
(298−208 K) of 7 in toluene-d8.
the formation of complex 7; see the Experimental Section for
full spectral assignments. Characteristically, the solution of 7 is
intense red at lower temperatures and deep green, typically
observed for solutions of the dearomatized complex 4, at
ambient temperature.72
The presence of the enamido moiety in 8 and 9 is supported
by a single-crystal X-ray diffraction study (Figure 5, Table 1).
The enamido moiety is characterized by a short CC double
bond between C26 and C27 (1.41 Å in 8 and 1.39 Å in 9).
Both structures have the amido ligand in an axial position with
the N2−C26 distances corresponding to N−C single bonds
adjacent to an sp2-carbon atom (N2−C26 = 1.35 Å in 8 and 9).
The newly formed C1−C26 bonds between the pincer arm and
enamido moiety are in the range of C−C single bonds (C1−
C26 = 1.54 Å in 8; C1−C26 = 1.55 Å in 9). The rhenium−
nitrogen bonds (Re1−N2 = 2.17 Å in 8 and 9) are comparable
to those found in ketimides complexes 5 and 7. The
rhenium(I) centers in both complexes have distorted
octahedral coordination spheres formed by the axial amido
moiety, two mutually cis CO ligands, and the meridional
tridentate PNPtBu pincer ligand.
Single crystals for complexes 5 and 7 were obtained from
concentrated n-pentane solutions. In the case of 7, the presence
of excess BuCN was necessary. The molecular structures
t
derived from single-crystal X-ray diffraction analyses are shown
in Figure 3. The structures of 5 and 7 are distorted octahedra
around the Re(I) centers with both CO ligands in mutually cis
positions. The ketimido ligands are bound in axial positions and
show characteristic NC double bond lengths (N2−C26 =
1.26 Å in 5; N2−C26 = 1.27 Å in 7) comparable to those of
previously reported ketimido complexes.61,62,73,74 The newly
formed C−C bond between the nitrile substrate and the exo-
cyclic carbon atom of the pincer ligand (C1−C26) is slightly
elongated by ∼0.06 Å (C1−C26 = 1.57 Å in 5; C1−C26 = 1.56
Å in 7) relative to the C6−C7 single bond. The Re1−N2 bond
lengths to the ketimide ligand (Re1−N2 = 2.19 Å in 5; Re1−
N2 = 2.17 Å in 7) are consistent with previously reported
complexes (e.g., in manganese complexes).67
DFT Calculations. To better understand the mechanism by
which this MLC activation occurs, the system was studied
computationally using density functional theory (DFT) at the
Substrates with a nitrile moiety adjacent to a methylene CH2
group, such as propiononitrile and benzyl cyanide, give the
enamido complexes cis-[Re(PNPtBu−HNCCHMe)(CO)2]
(8) and cis-[Re(PNPtBu−HNCCHPh)(CO)2] (9), respec-
Figure 3. ORTEP diagram of cis-[Re(PNPtBu−NCPh)(CO)2] (5,
left) and cis-[Re(PNPtBu−NCtBu)(CO)2] (7, right) with ellipsoids
at 30% probability. The P(tert-butyl)2 groups are drawn as wire-frames,
and hydrogen atoms are omitted for clarity. Selected bond lengths are
given in Table 1.
Figure 4. Sections of the 31P{1H} NMR spectra of 9 in C6D6 (bottom,
I), under 1 atm of CO for 15 min “(middle, II, * indicates resonances
correlated to 12), and under 1 atm CO at 65 °C for 1 h forming of 12
(top, III).
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Figure 5. ORTEP diagram of cis-[Re(PNPtBu−HNCCHMe)-
(CO)2] (8, left) and cis-[Re(PNPtBu−HNCCHPh)(CO)2] (9,
right) with ellipsoids at 30% probability. The P(tert-butyl)2 groups
are drawn as wire-frames, and hydrogen atoms, except partially for the
enamido moieties, are omitted for clarity. Selected bond lengths are
given in Table 1.
Figure 7. Transition state for the reaction of [Re(PNPtBu*)(CO)2]
(4) with PhCN; the transition states for the other nitriles are similar
in appearance. The P(tert-butyl)2 groups are drawn as wire-frames.
It is interesting to note that when PhCN is substituted in the
para position by either an electron-withdrawing (e.g., CF3) or
an electron-donating (e.g., NH2, not considered experimen-
tally) group, the products and associated transition states are
lower in energy than for PhCN. The low barrier and reaction
SMD(n-pentane)-DSD-PBEP86/cc-pV(D+d)Z//DF-PBE
+dv2/SDD(d) level of theory (see the Computational Methods
section for full details). Energies reported herein are ΔG298,sol
t
t
relative to 4 + R−CN (R = Et, Bu, Ph, PhCH2, pCF3Ph,
energy for the reaction with BuCN indicates a fast reversible
pNH2Ph). In a previous study, the reaction of a related
ruthenium complex with CO2 was investigated, and a concerted
CO2 addition mechanism was found where the Ru−O and C−
C bonds are formed in one concerted step.42
reaction. At room temperature, broad signals are observed in
1
the H and 31P{1H} NMR spectra, consistent with a rapid
equilibrium (on NMR time scale) between reactants and
product 7. Upon cooling, only the sharp resonances of 7 are
observed. Likewise, with pCF3PhCN, only product 6 is observed
by NMR spectroscopy, but the relatively low reverse barrier
The reaction with a number of nitriles was examined, and the
reaction profiles are shown in Figure 6. A concerted mechanism
was considered here, but the transition state found (Figure 7) is
associated with a Re−nitrile coordination complex prior to
activation. This coordination complex is slightly higher in
energy than the separated species and thus unlikely to be
observed experimentally. Nonetheless, this complex and the
subsequent transition state are sufficiently low to afford a very
rapid reaction (reaction barriers are all less than 15 kcal/mol).
⧧
(ΔG298 = 19.6 kcal/mol) indicates that the exchange is
possible, as experimentally observed when a large excess of
PhCN is added to 7. Two nitriles, EtCN and PhCH2CN, have
an α-hydrogen and can thus tautomerize to the enamide
complexes 8 and 9, respectively. It is not unreasonable to
assume that the reaction initially proceeds via the correspond-
ing ketimide complex. It was found that in the case of the
PhCH2CN, the enamide complex is lower in energy, while in
the case of EtCN the two complexes are, within the DFT error
estimate, practically isoergonic (Table 2.).
There are examples of iron(II) complexes with coordinated
1,3-diimine and nitrile ligands. Upon addition of base, both
ligands react giving C−C bond formation.76,77 In line with our
mechanistic considerations, an intramolecular mechanism has
been proposed for these systems entailing proton abstraction
by the base from the central methylene carbon of the 1,3-
diimine and subsequent nucleophilic attack at the α-carbon of
Table 2. Energies (ΔG298,sol, kcal/mol, at the SMD(n-
pentane)-DSD-PBEP86/cc-pV(D+d)Z//DF-PBE+dv2/
SDD(d) Level of Theory) of the Intermediates, Transition
States, and Products of the Reactions of 4 with Various
Nitriles
nitrile
RCN−[Re]
TS
ketimide
enamide
a
PhCN
tBuCN
pCF3PhCN
pNH2PhCN
EtCN
8.2
5.9
13.5
8.0
4.0
3.2
5.1
5.3
−7.3
−1.7
−15.6
−11.5
−6.4
−
a
−
a
0.0
−
a
−0.9
3.5
−
−6.1
−13.1
PhCH2CN
0.4
−10.4
Figure 6. Reaction profiles (ΔG298,sol, kcal/mol, at the SMD(n-
pentane)-DSD-PBEP86/cc-pV(D+d)Z//DF-PBE+dv2/SDD(d) level
of theory) for the reactions of 4 with various nitriles.
a
Not applicable.
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the coordinated nitrile. Reprotonation of the ketimido moiety,
bound to the Fe center, gives the final imino product. Electron-
withdrawing groups attached to the α-carbon of the nitrile
accelerate the reaction.78
studies (Figure 8, Table 1). Crystals of 10 were grown from a
dichloromethane solution layered with n-pentane. Complex 11
was crystallized from a concentrated benzene solution. Both
structures show cationic complexes with triflate counterions,
which were also observed by 19F{1H} NMR spectroscopy
(singlet at −79.6 ppm in acetone-d6 for 10; singlet at −80.1
ppm in CD3CN for 11). The rhenium(I) centers have distorted
octahedral coordination spheres with a meridional chelating
PNP pincer ligand. The two CO ligands bind to the metal in a
mutually cis orientation. The axial position is occupied in both
complexes by the (primary) imino ligands. The CN bond
lengths (N2−C26) are 1.288(7) Å for 10 and 1.282(3) Å for
11, indicating the formation of CN imino double bonds.
Reactivity of Complex 11. The primary imino complex 11
readily reacts with strong bases. In a NMR tube experiment, 11
was deprotonated with KOtBu in toluene-d8. The resulting
mixture contained two new major species with AB-spin systems
Reaction with Strong Electrophiles. Complexes 6 and 9
were reacted with methyl triflate in benzene (Scheme 4). The
ketimide complex 6 undergoes methylation of the ketimide
nitrogen atom to form the corresponding cationic imino
complex cis-[Re(PNPtBu−N(Me)CPhpCF3)(CO)2]OTf (10).
The 31P{1H} NMR in acetone-d6 exhibits an AB-spin system
consisting of two doublets with a large peak separation (89.3
and 149.7 ppm, 2JPP = 165.0 Hz). The 1H NMR spectrum has a
characteristic sharp singlet resonance with an integration value
equal to three protons for the introduced N-methyl group at
3.97 ppm. In contrast, the enamido complex 9 reacts with
methyl triflate to form the cationic primary imine compound
cis-[Re(PNPtBu−HNC−CH(Me)Ph)(CO)2]OTf (11) by
in the 31P{1H}NMR spectrum at 106.1 and 83.8 ppm (2JPP
=
1
methylation of the α-carbon atom (Scheme 4). The H NMR
189.5 Hz) and at 99.4 and 84.3 ppm (2JPP = 188.7 Hz). Upon
spectrum of 11 in CD3CN has a doublet resonance assigned to
the introduced methyl group at 1.47 ppm (3JHH = 7.0 Hz).
Significantly, the CNH proton resonance is detected as a
broad singlet at 9.96 ppm. The 31P{1H} NMR spectrum has the
expected AB-spin system with doublets at 88.9 and 147.5 ppm
(2JPP = 164.4 Hz). The IR spectra (KBr pellet) show two strong
absorption bands in a 1:1 ratio at 1924 and 1866 cm−1 for 10
and at 1921 and 1851 cm−1 for 11. The molecular structures of
10 and 11 were obtained from single-crystal X-ray diffraction
reaction with the base, the characteristic singlet resonance in
1
the H NMR spectrum for the primary imine proton CNH
at 9.96 ppm disappears, indicating deprotonation of the C
N−H proton rather than proton abstraction from the pincer
“arm”. Full assignment of the two in situ formed species was
challenging due to the multiple overlaps of peaks in the
aliphatic and aromatic regime of the 1H NMR spectra.
However, the smaller peak separation of the doublets in the
31P{1H} NMR spectrum, as observed for complex 9, suggests
two similar enamido species.
a
Scheme 4. Reaction with MeOTf
1
The H NMR spectrum exhibits two sets of signals in a
approximately 1:1 ratio, for methyl-, methylene-, methine-, and
amido moieties, suggesting the formation of two geometrical
isomers i-E and i-Z (Scheme 4B), which may result from the
initial formation of ketimido complex ii (not observed) and
subsequent tautomerization. Addition of benzyl cyanide to the
mixture of i-E/Z furnishes the starting complex 9 with release
of 2-phenylpropanenitrile, which was identified by GC−MS
analysis. It is reasonable to assume that the release of 2-
phenylpropanenitrile occurs via the ketimides ii, which is a
tautomeric form of i-E/Z. Essentially, the metal−ligand
Figure 8. ORTEP diagram of cis-[Re(PNPtBu−N(Me)CPhpCF3)-
(CO)2]OTf (10, left) and cis-[Re(PNPtBu−HNC−CH(Me)Ph)-
(CO)2]OTf (11, right) with ellipsoids at 30% probability. The P(tert-
butyl)2 groups are drawn as wire-frames. The OTf− counterions and
the hydrogen atoms, except for the H of the primary imino moiety in
11, are omitted for clarity. Selected bond lengths are given in Table 1.
a
(A) Stoichiometric reaction of 6. (B) A complete cycle for conversion
of PhCH2CN to 2-phenylpropanenitrile via complex 9.
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cooperative activation of benzyl cyanide by the dearomatized
complex 4 enables a methylation−deprotonation reaction
sequence, which allows for the selective monomethylation of
the substrate. However, this reaction cannot be run in a one-pot
reaction due to the incompatibility of MeOTf and KOtBu.
Monomethylation of benzyl cyanide derivatives is an important
issue in the synthesis of ibuprofen and is the subject of recent
studies of environmentally benign methylations.79,80
Table 3. Catalytic Michael Additions of Benzyl Nitriles to
α,β-Unsaturated Esters and Ketones
a
Michael Addition Triggered by MLC. As shown above,
the dearomatized complex 4 readily reacts with benzyl cyanide
to form the enamido complex 9. Both 4 and 9 were found to
catalyze the Michael addition of benzyl cyanide to methyl
acrylate to give methyl 4-cyano-4-phenylbutanoate (13, Scheme
5) with no additional base.
Benzyl cyanide and methyl acrylate (0.4 mmol scale)
selectively react in THF in the presence of 2 mol% of complex
9 at 65 °C within 20 h to give 13 in 90% yield (NMR) (99%
conversion of methyl acrylate). Side reactions, such as
polymerization of methyl acrylate, were not observed. Stepwise
addition of a second equivalent of methyl acrylate, after the
reaction reached completion, resulted in a second Michael
addition sequence to give dimethyl 4-cyano-4-phenylheptane-
dioate (14). The double addition product 14 was also obtained
when the reaction was performed with 2.1 equiv of methyl
acrylate with respect to benzyl cyanide (0.66 mmol of benzyl
cyanide, 1.4 mmol of methyl acrylate, 1 mol % 9, 80 °C oil bath
temperature, 12 h, closed vessel, in THF).81
Other substrates can be used in the catalytic Michael
addition, and the results are summarized in Table 3. Different
α,β-unsaturated esters and ketones were used as Michael
acceptors and reacted with benzyl cyanide (entries 1−4).
Likewise, as the Michael donor, other benzyl cyanide
derivatives were used, including derivatives with electron-
donating (entry 5) and electron-withdrawing (entry 6)
substituents.
On the basis of our observations, we propose the catalytic
pathway in Scheme 6. The dearomatized complex 4 binds the
benzyl cyanide substrate via MLC to form the intermediate
enamido complex 9 (step I). Subsequently, 9 is attacked by
methyl acrylate to give the transient species A (step II), which
rearranges to the ketimides species B (step III). A tautomeric
[1,3]-H-shift gives complex C. The product 13 is released from
C by Re−N and C−C bond cleavage to give the
a
Conversion with respect to the Michael acceptor (determined by
GC); yield determined by NMR; 0.4 mmol nitrile, 0.4 mmol acceptor,
2 mol% catalyst [Re(PNPtBu−HNCCHPh)(CO)2] 9 (entries 1−4)
or [Re(PNPtBu*)(CO)2] 4 (entries 5−6); reaction time 20 h.
b
Michael addition product obtained as a 1:1 mixture of diastereomers.
c
0.2 mmol nitrile and 0.2 mmol acceptor.
dearmomatized complex 4, which completes the catalytic
cycle (step IV). A similar cycle is conceivable for the Michael
addition of 13 to methyl acrylate to yield 14.
Scheme 5. Michael Addition of Benzyl Cyanide to Methyl
Acrylate Catalyzed by 4 or 9 To Selectively Give the
Addition Products 13 and 14
SUMMARY AND CONCLUSION
■
We have demonstrated an unprecedented mode for activation
of nitriles, based on MLC, involving reversible C−C and M−N
bond formation in a rare Re(I) PNP pincer complex.
Depending on the nature of the substrate, ketimido complexes
are formed with nitriles lacking α-methylene groups, and
enamido complexes are formed with aliphatic nitriles. Electro-
philic attack occurs at nitrogen in the ketimido complex, and
selectively at the α-carbon in the enamido complex. Our
computational studies suggest a stepwise activation of the
nitriles by the dearomatized complex [Re(PNPtBu*)(CO)2] (4)
with remarkably low activation barriers, involving the
precoordination of the nitrile group to the rhenium(I) center.
A concerted activation, as previously found for the activation of
CO2 to a similar ruthenium PNP pincer complex ([Ru-
(PNPtBu*)(CO)(H)]), does not occur. The novel mode of
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equipped with a 30 m column (Restek 5MS, 0.32 mm internal
diameter) with a 5% phenylmethyl silicone coating (0.25 mm) and
helium as carrier gas. GC analysis were carried out using a Carboxen
1000 column on a HP 690 series GC system or HP-5 cross-linked 5%
phenylmethylsilicone column (30 m × 0.32 mm × 0.25 μm film
thickness, FID) on a HP 6890 series GC system using 1,3,5-tris-iso-
propyl benzene or mesitylen as an internal standard. Crystallographic
details are as follows. For complex 3, crystal data: C25H43ClNO2P2Re,
orange plate, 0.33 × 0.33 × 0.12 mm3, monoclinic P2(1)/c, a =
14.6158(2) Å, b = 12.1609(2) Å, c = 16.1492(2) Å, β = 101.0602(10)°
from 8178 reflections, T = 120(2) K, V = 2817.05(7) Å3, Z = 4, Fw =
673.19, Dc = 1.587 Mg m−3, μ = 4.543 mm−1. Data collection and
processing: Nonius KappaCCD diffractometer, Mo Kα (λ = 0.71073
Å), graphite monochromator, MiraCol optics, −20 ≤ h ≤ 20, −17 ≤ k
≤ 17, −22 ≤ l ≤ 22, frame scan width = 1.0°, scan speed 1.0° per 15 s,
typical peak mosaicity 0.46°, 42 412 reflections collected, 8571
independent reflections (R-int = 0.039). The data were processed
with DenzoHKL-Scalepack. Solution and refinement: Structure solved
with SHELXS. Full matrix least-squares refinement based on F2 with
SHELXL-97 on 295 parameters with no restraints gave final R1 =
0.0316 (based on F2) for data with I > 2σ(I) and R1 = 0.0398 on 8216
reflections, Goof on F2 = 1.036, largest electron density peak 4.039 e
Å−3. Largest hole −2.152 e Å−3. For complex 4, crystal data:
C25H42NO2P2Re, green/black prism, 0.28 × 0.20 × 0.17 mm3,
orthorhombic Pnaa, a = 11.3342(1) Å, b = 15.5145(3) Å, c =
30.5847(4) Å from 57 207 reflections, T = 120(2) K, V = 5378.2(2)
Å3, Z = 8, Fw = 636.74, Dc = 1.573 Mg m−3, μ = 4.659 mm−1. Data
collection and processing: Nonius KappaCCD diffractometer, Mo Kα
(λ = 0.71073 Å), graphite monochromator, MiraCol optics, 0 ≤ h ≤
13, 0 ≤ k ≤ 18, 0 ≤ l ≤ 36, frame scan width = 0.5°, scan speed 1.0°
per 20 s, typical peak mosaicity 0.58°, 24 275 reflections collected,
6742 independent reflections (R-int = 0.091). The data were
processed with Denzo HKL2000. Solution and refinement: Structure
solved with SHELXS. Full matrix least-squares refinement based on F2
with SHELXL-97 on 292 parameters with 0 restraints gave final R1 =
0.0587 (based on F2) for data with I > 2σ(I) and R1 = 0.0793 on 4870
reflections, Goof on F2 = 1.065, largest electron density peak 4.293 e
Å−3. Largest hole −1.429 e Å−3. For complex 5, crystal data:
C32H47N2O2P2Re, orange plate, 0.40 × 0.19 × 0.09 mm3, monoclinic
P2(1)/c, a = 8.9108(1)Å, b = 18.0558(4)Å, c = 20.9380(4)Å, β =
106.4490(14)° from 48 538 reflections, T = 120(2) K, V =
3230.87(10) Å3, Z = 4, Fw = 739.86, Dc = 1.5251 Mg m−3, μ =
3.890 mm−1. Data collection and processing: Nonius KappaCCD
diffractometer, Mo Kα (λ = 0.71073 Å), graphite monochromator,
MiraCol optics, −11 ≤ h ≤ 11, −22 ≤ k ≤ 23, −27 ≤ l ≤ 26, frame
scan width = 1.0°, scan speed 1.0° per 60 s, typical peak mosaicity
0.63°, 31 074 reflections collected, 7359 independent reflections (R-int
= 0.0646). The data were processed with Denzo HKL2000. Solution
and refinement: Structure solved with SHELXS. Full matrix least-
squares refinement based on F2 with SHELXL-97 on 364 parameters
with 0 restraints gave final R1 = 0.0434 (based on F2) for data with I >
2σ(I) and R1 = 0.0663 on 7359 reflections, Goof on F2 = 1.041, largest
electron density peak 1.764 e Å−3. Largest hole −1.425 e Å−3. For
complex 7, crystal data: C30H51N2O2P2Re + C5H9N, orange prism,
0.20 × 0.20 × 0.10 mm3, monoclinic P2(1)/n, a = 12.4882(2) Å, b =
22.7280(4) Å, c = 13.5870(2) Å, β = 104.861(1)° from 35 290
reflections, T = 120(2) K, V = 3725.79(11) Å3, Z = 4, Fw = 803.00, Dc
= 1.432 Mg m−3, μ = 3.380 mm−1. Data collection and processing:
Nonius KappaCCD diffractometer, Mo Kα (λ = 0.71073 Å), graphite
monochromator, MiraCol optics, 17 ≤ h ≤ 17, −32 ≤ k ≤ 29, −19 ≤ l
≤ 19, frame scan width = 1.0°, scan speed 1.0° per 20 s, typical peak
mosaicity 0.45°, 35 789 reflections collected, 11 162 independent
reflections (R-int = 0.088). The data were processed with Denzo
HKL2000. Solution and refinement: Structure solved with SHELXS.
Full matrix least-squares refinement based on F2 with SHELXL-97 on
376 parameters with 0 restraints gave final R1 = 0.0479 (based on F2)
for data with I > 2σ(I) and R1 = 0.0749 on 10 895 reflections, Goof on
F2 = 1.125, largest electron density peak 5.260 e Å−3. Largest hole
−1.739 e Å−3. For complex 8, crystal data: (2*(C28H47N2O2P2Re1) +
C5H12) orange plate, 0.09 × 0.08 × 0.03 mm3, monoclinic, P2(1)/c, a
Scheme 6. Possible Catalytic Cycle for the Michael Addition
of Benzyl Cyanide to Methyl Acrylate
nitrile activation via MLC was utilized in reactivity studies and
catalysis. A complete reaction cycle was developed for the
selective monomethylation of PhCH2CN to 2-phenylpropane-
nitrile (PhCH(Me)−CN) via complex 9. Complexes 4 and 9
are also active catalysts in Michael addition reactions with no
need for added base. We are currently extending the scope of
rhenium pincer-type complexes, and the activation of other
unsaturated substrates with dearomatized metal complexes is a
focal point of our ongoing research.
EXPERIMENTAL SECTION
■
All experiments were carried out under an atmosphere of purified
nitrogen in a M-BRAUN Unilab 1200/780 glovebox or using standard
Schlenk techniques. All solvents were purchased “reagent grade” or
better. Solvents, except methylene chloride, were refluxed over
sodium/benzophenone and distilled under an argon atmosphere.
Methylene chloride was used as received and dried over 4 Å molecular
sieves. Deuterated solvents were used as received and degassed with
argon and kept in the glovebox over 4 Å molecular sieves. The PNPtBu
ligand was prepared according to the literature procedure.83
Benzonitrile, propionitrile, pivalonitrile, and benzyl cyanide were
distilled prior to use. [Re(CO)5Cl], KOtBu, pCF3Ph−CN, and MeOTf
were used as received from Sigma-Aldrich without any further
purification. NMR spectroscopy: 1H, 13C{1H}, and 31P{1H} NMR
spectra were recorded on Bruker AMX-300, AMX-400, and AMX-500
NMR spectrometers. 1H, 13C{1H}, and 13C{1H} DEPTQ NMR
chemical shifts are reported in ppm referenced to tetramethylsilane
calibrated using residual solvent signals. 31P{1H} NMR chemical shifts
are reported in ppm referenced to an external 85% solution of
phosphoric acid in D2O. Elemental analyses were performed on a
Thermo Finnigan Italia S.p.A-FlashEA 1112 CHN Elemental Analyzer
by the Department of Chemical Research Support, Weizmann
Institute of Science. Mass spectra were recorded on MicromassPlat-
form LCZ 4000, using electro spray ionization (ESI) mode. GC−MS
was carried out on HP 6890 (flame ionization detector and thermal
conductivity detector) and HP 5973 (MS detector) instruments
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= 13.118(3), b = 14.918(3), c = 16.915(3) Å, β = 99.27(3)° from 20°
of data, T = 120(2) K, V = 3266.9(11) Å3, Z = 2, Fw = 1455.78, Dc =
1.480 Mg m−3, μ = 3.846 mm−1. Data collection and processing:
Nonius KappaCCD diffractometer, Mo Kα (λ = 0.71073 Å), graphite
monochromator, 13 983 reflections collected, −16 ≤ h ≤ 16, 0 ≤ k ≤
19, 0 ≤ l ≤ 21, frame scan width = 0.5°, scan speed 1.0° per 180 s,
typical peak mosaicity 0.69°, 7182 independent reflections (R-int =
0.0372). The data were processed with Denzo-Scalepack. Solution and
refinement: Structure solved by direct methods with SHELXS-97. Full
matrix least-squares refinement based on F2 with SHELXL-97. 382
parameters with 0 restraints, final R1 = 0.0389 (based on F2) for data
with I > 2σ(I) and R1 = 0.0623 on 7182 reflections, Goof on F2 =
1.026, largest electron density peak = 4.477 e Å−3, deepest hole −1.677
e Å−3. For complex 9, crystal data: (C33H49N2O2P2Re1 + C6H6),
spin-component scaled,90,91 second-order Møller−Plesset92 (SCS-
MP2)-like correlation, and an empirical dispersion correction,93−96
specifically Grimme’s third version of his empirical dispersion
correction (DFTD3)93,97 with Becke−Johnson (BJ) dampening.97,98
Two basis set-RECP (relativistic effective core potential) combinations
were used. The first, denoted SDD(d), is the combination of the
Huzinaga−Dunning double-ζ basis set99 on lighter elements with the
Stuttgart−Dresden basis set-RECP combination100 on transition
metals; polarization functions (i.e., the D95(d) basis set) were
added to second-row (i.e., phosphorus) atoms. The second is denoted
as cc-pV(D+d)Z-PP, which includes the Dunning cc-pVDZ basis
set101 on H, C, N, and O, Wilson’s cc-pV(D+d) on P,102 and
Peterson’s cc-pVDZ-PP basis set-RECP on Ru.103 Geometry
optimizations and frequency calculations were carried out using the
former basis set, while the energetics of the reaction were calculated at
these geometries with the latter basis set. When using the PBE
functional, density fitting basis sets, specifically the fitting sets
generated using the automatic generation algorithm implemented in
Gaussian 09, were used to speed up the calculations.104,105 The
accuracy of the DFT method was improved by adding the empirical
dispersion correction as recommended by Grimme.93,95 The older
version (DFTD2)95 is available, with analytical gradients and Hessians,
in Gaussian 09 and was used during geometry optimizations and
frequency calculations; our version of Gaussian 09 was locally modified
to allow for its use for any DFT functional rather than just the limited
set included in the commercially available version. As noted above,
DSD-PBEP86 includes, per definition, a DFTD3 correction with BJ-
scaling in its functional form, which was calculated using a program
written by Grimme.93 Bulk solvent effects were approximated by single
point energy calculations using a polarizable continuum model
(PCM),106−109 specifically the integral equation formalism model
(IEF-PCM)106,107,110,111 with n-pentane as the solvent as in the
experiments. Specifically, Truhlar’s empirically parametrized version
Solvation Model Density (SMD) was used.112 Geometries were
optimized using the default pruned (75,302) grid, while the “ultrafine”
(i.e., a pruned (99,590)) grid was used for energy and solvation
calculations.
yellow prism, 0.12 × 0.12 × 0.08 mm3, triclinic, P1, a = 12.124(2), b =
̅
13.337(3), c = 13.581(3) Å, α = 113.99(3)°, β = 91.15(3)°, γ =
106.97(2)° from 20° of data, T = 120(2) K, V = 1894.6(9) Å3, Z = 2,
Fw = 831.99, Dc = 1.458 Mg m−3, μ = 3.326 mm−1. Data collection and
processing: Nonius KappaCCD diffractometer, Mo Kα (λ = 0.71073
Å), graphite monochromator, 17 055 reflections collected, −15 ≤ h ≤
15, −17 ≤ k ≤ 16, 0 ≤ l ≤ 17, frame scan width = 1°, scan speed 1.0°
per 60 s, typical peak mosaicity 0.48°, 9007 independent reflections
(R-int = 0.0242). The data were processed with Denzo-Scalepack.
Solution and refinement: Structure solved by direct methods with
SHELXS-97. Full matrix least-squares refinement based on F2 with
SHELXL-97. 439 parameters with 1 restraints, final R1 = 0.0281 (based
on F2) for data with I > 2σ(I) and R1 = 0.0350 on 9007 reflections,
Goof on F2 = 1.100, largest electron density peak = 3.068 e Å−3,
deepest hole −1.199 e Å−3. For complex 10, crystal data:
C34H49F3N2O2P2Re + CF3O3S + CH2Cl2, yellow plate, 0.40 × 0.30
× 0.20 mm3, monoclinic P2(1)/c, a = 12.7580(1) Å, b = 9.2810(1) Å,
c = 35.6750(4) Å, β = 94.6930(4)° from 41 887 reflections, T =
120(2) K, V = 4210.01(7) Å3, Z = 4, Fw = 1056.89, Dc = 1.667 Mg
m−3, μ = 3.208 mm−1. Data collection and processing: Nonius
KappaCCD diffractometer, Mo Kα (λ = 0.71073 Å), graphite
monochromator, MiraCol optics, −15 ≤ h ≤ 15, −8 ≤ k ≤ 11, −42
≤ l ≤ 42, frame scan width = 0.5°, scan speed 1.0° per 14 s, typical
peak mosaicity 0.36°, 41 887 reflections collected, 17 455 independent
reflections (R-int = 0.112). The data were processed with Denzo
HKL2000. Solution and refinement: Structure solved with SHELXS.
Full matrix least-squares refinement based on F2 with SHELXL-97 on
364 parameters with 0 restraints gave final R1 = 0.0477 (based on F2)
for data with I > 2σ(I) and R1 = 0.0574 on 7681 reflections, Goof on
F2 = 1.097, largest electron density peak 5.936 e Å−3. Largest hole
−2.680 e Å−3. For complex 11, crystal data: (C34H52N2O2P2Re1 +
C1F3O3S1 + 1.5*C6H6) yellow plate, 0.15 × 0.08 × 0.02 mm3, triclinic,
cis-[Re(PNPtBu)(CO)2Cl] (3). A solution of 2,6-bis(di-tbutyl-
phosphinomethyl)pyridine) (870 mg, 2.20 mmol) in 4 mL of THF
was added to a stirred suspension of [Re(CO)5Cl] (800 mg, 2.20
mmol) in 4 mL of THF. The reaction mixture was transferred to a
pressure tube and heated at 80 °C overnight in the closed vessel. The
obtained yellow solution was then concentrated by partial evaporation
of the solvent in vacuo. The product 3 was crystallized by layering the
THF solution with n-pentane. The crystals were decanted, washed
1
with n-pentane, and dried in vacuo. Yield: 1037 mg, 70%. H NMR
3
(400.36 MHz, CD2Cl2, 25 °C) ∂: 1.33 (t, JPH = 6.30 Hz, 18H,
P1, a = 9.637(2), b = 12.321(3), c = 19.322(4) Å, α = 88.76(3)°, β =
̅
((CH3)3CP), 1.38 (t, 3JPH = 6.30 Hz, 18H, ((CH3)3CP), 3.61 (d, 2JHH
80.82(2)°, γ = 85.69(3)° from 20° of data, T = 100(2) K, V =
2258.3(8) Å3, Z = 2, Fw = 1035.15, Dc = 1.522 Mg m−3, μ = 2.865
mm−1. Data collection and processing: Bruker Apex2 KappaCCD
diffractometer, Mo Kα (λ = 0.71073 Å), graphite monochromator, 55
196 reflections collected, −12 ≤ h ≤ 12, −15 ≤ k ≤ 15, −25 ≤ l ≤ 25,
frame scan width = 0.5°, scan speed 1.0° per 40 s, typical peak
mosaicity 0.83°, 10 274 independent reflections (R-int = 0.0456). The
data were processed with Bruker Apex2. Solution and refinement:
Structure solved by direct methods with SHELXS-97. Full matrix least-
squares refinement based on F2 with SHELXL-97. 540 parameters with
0 restraints, final R1 = 0.0234 (based on F2) for data with I > 2σ(I) and
R1 = 0.0287 on 10 274 reflections, Goof on F2 = 1.027, largest electron
density peak = 1.012 e Å−3, deepest hole −0.956 e Å−3.
= 15.70 Hz, 2H, PCH2), 4.22 (d, 2JHH = 15.70 Hz, 2H, PCH2), 7.36 (d,
3
3JHH = 7.8 Hz, 2H, CHpyri(3,5)), 7.62 (t, JHH = 7.80 Hz, 1H, CHpyri(4)
)
ppm. 31P{1H} NMR (121.5 MHz, tol-d8, 25 °C) ∂: 68.8 (s, 2P) ppm.
13C{1H} QDEPT NMR (100.7 MHz, CD2Cl2, 25 °C) ∂: 32.1 (s, 3C,
(CH3)3CP), 32.9 (s, 3C, (CH3)3CP), 40.3 (m, 2C, (CH3)3CP)), 41.5
1
3
(t, JPC = 7.2 Hz, 2C, PCH2), 122.6 (t, JPC = 4.0 Hz, 2C, CHpyri(3,5)),
2
139.7 (s, 1C, CHpyri(4)), 166.9 (t, JPC = 3.5 Hz, 2C, Cpyri(2,6)), 203.7
(m, 1C, Re−CO), 210.6 (m, 1C, Re−CO) ppm. IR (KBr, pellet) ν
[cm−1]: 1816, 1900 (1:1 ratio). Anal. Calcd for C25H43ClNO2P2Re: C,
44.60; H, 6.44; N, 2.08. Found: C, 44.66; H, 6.35; N, 1.93.
[Re(PNPtBu*)(CO)2] (4). Complex 3 (200 mg, 0.30 mmol) was
dissolved in 4 mL of THF, and the yellow solution was cooled to −38
°C in the freezer. KOtBu (33 mg, 0.30 mmol) dissolved in 2 mL of
THF was added dropwise to the precooled solution. The deep green
solution was allowed to stir for 0.5 h at ambient temperature.
Subsequently, all volatiles were evaporated in vacuo, and the remaining
green solid was extracted with n-pentane (∼30 mL) and filtered
through a syringe filter (Teflon, 0.2 μm pore size). Large green crystals
formed upon concentration of the filtrate. The volume of the solution
was eventually reduced to ∼10 mL, via partial evaporation of the
solvent in vacuo, and allowed to finish the crystallization at −38 °C in
the freezer for 24 h. The crystals were decanted and dried in vacuo.
Computational Methods. All calculations were performed using
Gaussian 09 Revision C.01.84 Two density functional theory (DFT)
exchange-correlation functionals were used. Geometries were opti-
mized and vibrational frequencies were calculated using the Perdew−
Burke−Ernzerhof (PBE) generalized-gradient approximation (GGA)
functional.85,86 Accurate energies were calculated using one of the
latest double-hybrid functionals by Kozuch and Martin: DSD-
PBEP86.87 This double-hybrid functional incorporates the Perdew−
Burke−Ernzerhof (PBE),85,86,88 DFT exchange functional with “exact”
Hartree−Fock exchange, the Perdew-86 correlation functional89 with
17012
dx.doi.org/10.1021/ja4071859 | J. Am. Chem. Soc. 2013, 135, 17004−17018

Journal of the American Chemical Society
Article
1
3
3
Yield: 191 mg, 85%. H NMR (500.13 MHz, toluene-d8, 25 °C) ∂:
PCH), 6.29 (d, JHH = 7.50 Hz, 1H, CHpy), 6.64 (d, JHH = 7.50 Hz,
1H, CHpy), 6.81 (t, 3JHH = 7.50 Hz, 1H, CHpy(4)), 7.49 (d, 3JHH = 8.50
1.03 (d, 3JPH = 13.30 Hz, 18H, ((CH3)3CP), 1.32 (d, 3JPH = 13.30 Hz,
2
3
18H, ((CH3)3CP), 2.74 (d, JHP = 9.20 Hz, 2H, PCH2), 4.06 (s, 1H,
Hz, 2H, CHAr), 7.91 (d, JHH = 8.00 Hz, 2H, CHAr) ppm. 31P{1H}
PCH), 5.29 (d, 3JHH = 6.20 Hz, 1H, CHpyri(3)), 6.17 (m, 1H, CHpyri(4)),
NMR (202.5 MHz, C6D6, 25 °C) ∂: 86.6 (d, JPP = 192.2 Hz, 1P),
2
6.27 (d, JHH = 9.00 Hz, 1H, CHpyri(5)) ppm. 31P{1H} NMR (121.5
129.4 (d, JPP = 191.7 Hz, 1P) ppm. 13C{1H} QDEPT NMR (125.8
3
2
2
MHz, toluene-d8, 25 °C) ∂: 68.9 (d, JPP = 145.0 Hz, 1P, PCHC),
MHz, C6D6, 25 °C) ∂: 29.7 (d, br, 2JCP = 3.5 Hz, 3C, (CH3)3CP), 30.1
74.7 (d, JPP = 145.0 Hz, 1P, PCH2C)) ppm. 13C{1H} QDEPT NMR
(d, br, JCP = 1.8 Hz, 3C, (CH3)3CP), 30.9 (d, 3C, JCP = 3.4 Hz,
2
2
2
2
(100.7 MHz, CD2Cl2, 25 °C) ∂: 29.6 (d, JCP = 4.5 Hz, 3C,
(CH3)3CP), 32.1 (d, 3C, 2JCP = 3.6 Hz, (CH3)3CP), 36.1 (d, 1JCP = 7.4
2
1
1
3
(CH3)3CP), 30.0 (d, JCP = 3.9 Hz, 3C, (CH3)3CP), 36.2 (d, JCP
=
Hz, 1C, (CH3)3CP), 37.7 (dd, JCP = 10.6 Hz, JCP = 1.5 Hz, 1C,
(CH3)3CP), 38.0 (dd, JCP = 6.2 Hz, JCP = 6.0 Hz, 1C, (CH3)3CP), 38.5
(d, JCP = 21.0 Hz, 1C, (CH3)3CP), 40.1 (d, JCP = 16.9 Hz, 1C,
PCH2), 65.8 (d, 1JCP = 22.1 Hz, 1C, PCHCN), 116.9 (d, 3JPC = 6.8
Hz, 1C, CHpy), 117.8 (d, 3JPC = 6.5 Hz, 1C, CHpy), 125.3 (q (partially
obscured), 1JFC = 271.7 Hz, 1C, CF3), 125.7 (q, br, 3JFC = 3.8 Hz, 2C,
18.7 Hz, 1C, PCH2), 37.6 (d, 1JCP = 19.6 Hz, 1C, (CH3)3CP), 38.1 (d,
1JCP = 26.2 Hz, 1C, (CH3)3CP), 76.3 (d, JCP = 50.3 Hz, 1C, PCH
1
1
1
3
3
C), 99.7 (d, JPC = 10.2 Hz, 1C, CHpyri(3)), 118.4 (d, JPC = 16.6 Hz,
2
1C, CHpyri(5)), 131.6 (s, 1C, CHpyri(4)), 161.8 (t, JCP = 5.8 Hz, 1C,
Cpyri(6)), 175.1 (dd, 2,3JPC = 5.2 Hz, 17.4 Hz, 1C, Cpyri(2)), 208.4 (t, 2JCP
= 5.1 Hz, 2C, Re−CO) ppm. IR (KBr, pellet) ν [cm−1]: 1826, 1905
(νCO, 1:1 ratio). Anal. Calcd for C25H42NO2P2Re: C, 47.16; H, 6.65;
N, 2.20. Found: C, 47.19; H, 6.94; N, 1.95.
2
CHAr), 126.8 (s, 2C, CHAr), 129.3 (d, JFC = 32.0 Hz 1C, CAr), 135.8
(s, 1C, CHpy), 141.5 (s, 1C, CAr), 154.4 (dd, 2JPC = 16.4 Hz, 3JPC = 4.8
2
3
Hz, 1C, CN), 161.0 (dd, JPC = 5.0 Hz, JPC = 4.8 Hz, 1C, Cpy),
164.2 (m, br, 1C, Cpy), 210.8 (t, 2JCP = 5.0 Hz, 1C, Re−CO), 215.4 (t,
2JCP = 6.54 Hz, 1C, Re−CO) ppm. 19F{1H} NMR (282.4 MHz, C6D6,
25 °C) ∂: 62.6 (s, 3F, CF3) ppm. IR (KBr, pellet) ν [cm−1]: 1807,
1894 (νCO, 1:1 ratio). Anal. Calcd for C33H46F3N2O2P2Re: C, 49.06;
H, 5.74; N, 3.4. Found: C, 49.73; H, 5.84; N, 3.23. MS (ESI-TOF)
found M+ = 809.26 (6 + H+).
cis-[Re(PNPtBu−NCPh)(CO)2] (5). KOtBu (25 mg, 0.22 mmol, 1
equiv) was added to a stirred solution of 3 (150 mg, 0.22 mmol) in 3
mL of THF. After 1 h, all volatiles were evaporated in vacuo, and the
residue was extracted in n-pentane (2 × 15 mL) and filtered through a
syringe filter (Teflon, 0.2 μm pore size). The filtrate was split into two
20 mL vials, and subsequently to each vial two drops of benzonitrile
(excess) were added. Orange crystals separated from the orange-red
solution at −38 °C in the freezer within 48 h. The product was
decanted, washed with n-pentane, and dried in vacuo. For a second
and third crystallization, the mother liquor was each time concentrated
and allowed to crystallize at −38 °C. The obtained second and third
fractions were treated likewise. Yield of the combined fractions: 135
cis-[Re(PNPtBu−NCtBu)(CO)2] (7). KOtBu (10 mg, 0.09 mmol,
1 equiv) was added to a stirred solution of 3 (62 mg, 0.09 mmol) in 3
mL of THF in a 20 mL vial. After 20 min, all volatiles were evaporated
in vacuo, and the residue was extracted with n-pentane (15 mL) and
filtered through a syringe filter (Teflon, 0.2 μm pore size).
Subsequently, a large excess of pivalonitrile (1 mL) was added to
the stirred solution, and a color change to brown was observed. A
bright red solution was observed at low temperature. The mixture was
allowed to crystallize for 24 h at −38 °C. The obtained red crystals
1
mg, 82%. H NMR (500.13 MHz, C6D6 25 °C) ∂: 0.78 (s, br, 9H,
(CH3)3CP), 1.09 (d, 3JPH = 11.50 Hz, 9H, (CH3)3CP), 1.32 (d, 3JPH
=
12.50 Hz, 9H, (CH3)3CP), 1.54 (d, 3JPH = 13.00 Hz, 9H, (CH3)3CP),
3.15 (dd, 2JHH = 15.50 Hz, 2JHP = 5.00 Hz, 1H, PCH2), 3.22 (dd, 2JHH
= 15.50 Hz, 2JHP = 9.10 Hz, 1H, PCH2), 6.19 (dd, 2JHP = 6.50 Hz, 4JHP
t
(suitable for X-ray diffraction analysis, BuCN cocrystallizes in lattice)
were decanted from the almost colorless supernatant solution, washed
with cold n-pentane, and dried in vacuo. Yield: 65 mg, 98%. Note: In
some cases, colorless crystals of excess BuCN are formed in the cold,
3
= 1.00 Hz, 1H, PCH), 6.27 (d, JHH = 7.00 Hz, 1H, CHpy), 6.68 (d,
3JHH = 7.50 Hz, 1H, CHpy), 6.74 (t, 3JHH = 7.50 Hz, 1H, CHpy(5)), 7.12
t
1
3
3
which are quickly dissolving upon warming to room temperature. H
(t, JHH = 7.50 Hz, 1H, CHAr), 7.27 (t, JHH = 7.50 Hz, 2H, CHAr),
3
8.05 (d, 3JHH = 8.00 Hz, 2H, CHAr) ppm. 31P{1H} NMR (202.5 MHz,
NMR (500.13 MHz, toluene-d8, −65 °C) ∂: −0.38 (d, br, 3H, JPH
=
2
2
10.00 Hz (CH3)3CP), 0.73 (s, 9H, (CH3)3C), 0.92 (s, br, 3H,
C6D6, 25 °C) ∂: 86.7 (d, JPP = 193.8 Hz, 1P), 128.2 (d, JPP = 193.8
Hz, 1P) ppm. 13C{1H} QDEPT NMR (125.8 MHz, C6D6, 25 °C) ∂:
29.8 (s, br, 3C, (CH3)3CP), 30.2 (s, br, 3C, (CH3)3CP), 30.9 (d, 3C,
(CH3)3CP), 1.19 (s, br, 9H, (CH3)3CP), 1.44 (d, 3JPH = 11.50 Hz, 9H,
(CH3)3CP), 1.54 (d, 3JPH = 12.00 Hz, 9H, (CH3)3CP), 1.95 (d, 3JPH
=
2
2JCP = 3.8 Hz, (CH3)3CP), 32.1 (d, 3C, JCP = 3.3 Hz, (CH3)3CP),
2
17.00 Hz, 3H, (CH3)3CP), 2.77 (d, br, JHH = 17.00 Hz, 1H, PCH2),
3.07 (dd, 2JHH = 15.50 Hz, 2JHP = 8.50 Hz, 1H, PCH2), 5.55 (d, 2JHP
=
1
1
36.1 (d, JCP = 7.5 Hz, 1C, (CH3)3CP), 37.7 (d, JCP = 10.6 Hz, 1C,
(CH3)3CP), 38.0 (t, JCP = 7.0 Hz, 1C, (CH3)3CP), 38.5 (d, 1JCP = 20.8
Hz, 1C, (CH3)3CP), 40.1 (d, 1JCP = 17.0 Hz, 1C, PCH2), 66.0 (d, 1JCP
= 23.0 Hz, 1C, PCHCN), 116.6 (d, 3JPC = 6.7 Hz, 1C, CHpy), 117.8
(d, 3JPC = 6.7 Hz, 1C, CHpy), 126.8 (s, 2C, CHAr), 128.3 (s, 1C, CHAr),
128.6 (s, 2C, CHAr), 135.6 (s, 1C, CHpy), 139.5 (s, 1C, CAr), 154.8
(dd, 2JPC = 16.5 Hz, 3JPC = 4.5 Hz, 1C, CN), 161.4 (t, br, 2JPC = 6.5
Hz, 1C, Cpy), 164.0 (d, 2JPC = 1.6 Hz, 1C, Cpy), 211.0 (t, 2JCP = 5.4 Hz,
5.50 Hz, 1H, PCH), 6.31 (d, 3JHH = 7.50 Hz, 1H, CHpy), 6.38 (d, 3JHH
3
= 7.00 Hz, 1H, CHpy), 6.88 (t, JHH = 7.50 Hz, 1H, CHpy(4)) ppm.
31P{1H} NMR (202.5 MHz, toluene-d8, −65 °C) ∂: 85.9 (d, JPP
=
2
2
195.3 Hz, 1P, PCH2), 132.3 (d, JPP = 195.3 Hz, 1P, PCH(NC))
ppm. 13C{1H} QDEPT NMR (125.8 MHz, toluene-d8, −65 °C) ∂:
27.6 (s, 3C, (CH3)3C), 27.1 (s, br, 1C, (CH3)3CP), 29.6 (s, br, partly
obscured, 3C, (CH3)3CP), 29.7 (s, br, 3C, (CH3)3CP), 30.3 (s, br, 1C,
(CH3)3CP), 30.8 (s, br, 3C, (CH3)3CP), 31.4 (s, br, 1C, (CH3)3CP),
34.9 (s, 1C, (CH3)3CP), 37.1 (d, 1JCP = 4.4 Hz, 1C, (CH3)3CP), 37.7
(d, JCP = 12.9 Hz, 1C, (CH3)3CP), 38.4 (m, JCP, 1C, (CH3)3CP), 39.5
2
1C, Re−CO), 215.4 (t, JCP = 5.5 Hz, 1C, Re−CO) ppm. IR (KBr,
pellet) ν [cm−1]: 1816, 1888 (νCO, 1:1 ratio). Anal. Calcd for
C32H47N2O2P2Re: C, 51.95; H, 6.40; N, 3.79. Found: C, 52.29; H,
6.30; N, 3.47. MS (ESI-TOF) found M+ = 638.23 (5 − PhCN) + H+.
cis-[Re(PNPtBu−NCPhpCF3)(CO)2] (6). KOtBu (10 mg, 0.09
mmol, 1 equiv) was added to a stirred solution of 3 (62 mg, 0.09
mmol) in 3 mL of THF in a 20 mL vial. After 20 min, all volatiles were
evaporated in vacuo, and the residue was extracted in n-pentane (15
mL) and filtered through a syringe filter (Teflon, 0.2 μm pore size).
Subsequently, 4-(trifluoromethyl)benzonitrile (24 mg, 0.14 mmol, 1.5
equiv) was added to the stirred solution, and an immediate color
change to orange occurred. Orange-brown crystalline flakes
precipitated upon stirring for further 15 min at ambient temperature.
The product was decanted from the almost colorless supernatant
solution, washed with n-pentane (10 mL), and dried in vacuo. Yield:
62 mg, 83%. 1H NMR (500.13 MHz, C6D6, 25 °C) ∂: 0.73 (s, br, 9H,
1
1
(d, JCP = 17.6 Hz, 1C, PCH2), 65.4 (d, JCP = 20.6 Hz, 1C, PCH),
3
3
116.5 (d, br, JPC = 3.8 Hz, 1C, CHpy), 119.9 (d, JPC = 5.7 Hz, 1C,
CHpy), 135.2 (s, br, 1C, CHpy(4)), 159.0 (dd, 2JPC = 15.6 Hz, 3JPC = 5.5
2
3
Hz, 1C, CN), 161.0 (dd, JPC = 5.0 Hz, JPC = 4.2 Hz, 1C, Cpy),
163.6 (d, br, 2JPC = 1.0 Hz, 1C, Cpy), 211.9 (m, br, 2JCP, 1C, Re−CO),
215.4 (m, br, 2JCP, 1C, Re−CO) ppm. IR (KBr, pellet) ν [cm−1]: 1800,
1876 (νCO, 1:1 ratio). Anal. Calcd for C30H51N2O2P2Re: C, 50.05; H,
7.14; N, 3.89. C, 49.59; H, 7.29; N, 4.03.
cis-[Re(PNPtBu−HNC−CHMe)(CO)2] (8). KOtBu (10 mg, 0.09
mmol, 1 equiv) was added to a stirred solution of 3 (62 mg, 0.09
mmol) in 3 mL of THF in a 20 mL vial. After 20 min, all volatiles were
evaporated in vacuo. The residue was extracted in n-pentane (15 mL)
and filtered through a syringe filter (Teflon, 0.2 μm pore size).
Subsequently, excess propiononitrile was added dropwise (0.5 mL) to
the stirred green solution, and a color change to red was observed. The
mixture was allowed to stay at −38 °C for 24 h to form large red
crystals (suitable for X-ray diffraction analysis). The almost colorless
(CH3)3CP), 1.07 (d, 3JPH = 11.50 Hz, 9H, (CH3)3CP), 1.26 (d, 3JPH
=
12.50 Hz, 9H, (CH3)3CP), 1.54 (d, 3JPH = 13.00 Hz, 9H, (CH3)3CP),
2.98 (dd, 2JH2H = 15.50 Hz, 2JHP = 5.00 Hz, 1H, PCH2), 3.21 (dd, 2JHH
2
= 15.50 Hz, JHP = 9.00 Hz, 1H, PCH2), 6.04 (d, JHP = 6.50 Hz, 1H,
17013
dx.doi.org/10.1021/ja4071859 | J. Am. Chem. Soc. 2013, 135, 17004−17018

Journal of the American Chemical Society
Article
supernatant solution was decanted, and the obtained product was
washed with cold n-pentane and dried in vacuo. Yield: 59 mg, 93%. 1H
NMR (500.13 MHz, toluene-d8, 25 °C) ∂: 0.78 (d, br, 3JPH = 11.50 Hz,
Excess methyl triflate (5 drops via Pasteur pipet) was added to the
stirred red solution until a color change to yellow was evident. After 15
min at ambient temperature, n-pentane was added to the mixture to
precipitate a yellow-orange solid, which was washed with n-pentane (5
mL) and dried in vacuo. Subsequently, the yellow residue was
dissolved in methylene chloride (3 mL), layered with n-pentane (15
mL), and allowed to crystallize for 24 h at ambient temperature. The
obtained orange crystals (suitable for X-ray diffraction analysis) were
3
9H, (CH3)3CP), 1.06 (d, JPH = 11.50 Hz, 9H, (CH3)3CP), 1.47 (d,
3
3JPH = 12.50 Hz, 9H, (CH3)3CP), 1.63 (d, JPH = 12.00 Hz, 9H,
3
(CH3)3CP), 1.64 (d, obscured, JHH, 3H, CH−CH3), 2.38 (s, br, 1H,
NH), 3.20 (d, 2JHH = 15.50 Hz, 2JHP = 5.50 Hz, 1H, PCH2), 3.38 (dd,
2JHH = 15.50 Hz, 2JHP = 9.00 Hz, 1H, PCH2), 4.25 (q, 3JHH = 6.50 Hz,
1
2
4
washed with n-pentane and dried in vacuo. Yield 30 mg, 92%. H
1H, CCH−Me), 4.31 (dt, JHP = 7.00 Hz, JHH = 2.00 Hz, 1H,
3
3
NMR (500.13 MHz, acetone-d6, 25 °C) ∂: 1.11 (s, br, partly obscured,
PCH), 6.50 (d, JHH = 7.50 Hz, 1H, CHpy), 6.79 (d, JHH = 7.50 Hz,
1H, CHpy), 6.93 (t, 3JHH = 7.50 Hz, 1H, CHpy(4)) ppm. 31P{1H} NMR
3
9H, (CH3)3CP), 1.16 (d, JPH = 13.00 Hz, 9H, (CH3)3CP), 1.66 (d,
3
3JPH = 13.00 Hz, 9H, (CH3)3CP), 1.70 (d, JPH = 13.50 Hz, 9H,
2
(202.5 MHz, toluene-d8, 25 °C) ∂: 84.8 (d, JPP = 190.4 Hz, 1P,
PCH2), 95.6 (d, JPP = 191.9 Hz, 1P, PCH(NC)) ppm. 13C{1H}
2
2
2
(CH3)3CP), 3.86 (dd, JHH = 16.50 Hz, JHP = 6.00 Hz, 1H, PCH2),
2
2
QDEPT NMR (100.7 MHz, toluene-d8, −65 °C) ∂: 11.7 (s, 1C, CH3),
29.5 (d, br, 3C, 3J = 2.4 Hz, (CH3)3C), 29.9 (s,br, 3C, (CH3)3CP),
3.97 (s, 3H, NCH3), 4.65 (ddd, JHH = 16.50 Hz, JHP = 9.50 Hz, J =
1.00 Hz, 1H, PCH2), 6.61 (dd, 2JHP = 6.50 Hz, J = 2.50 Hz, 1H, PCH),
30.2 (d, 3C, 3J = 3.3 Hz, (CH3)3CP), 30.4 (d, 3C, 3J = 3.7 Hz,
3
7.73 (d, JHH = 8.00 Hz, 2H, CHAr), 7.96 (m, JHP, JHH, 4H, overlay
3
(CH3)3CP), 36.5 (m, 1JCP, JCP overlay 2C, (CH3)3CP), 37.7 (d, JCP
=
CHpy + CHAr), 8.14 (t, JHH = 8.00 Hz, 1H, CHpy(4)) ppm. 31P{1H}
3
2
10.0 Hz, 1C, (CH3)3CP), 37.8 (d, JCP = 20.2 Hz, 1C, (CH3)3CP), 39.8
NMR (202.5 MHz, acetone-d6, 25 °C) ∂: 89.3 (d, JPP = 164.4 Hz,
1
1
1P), 149.7 (d, JPP = 165.0 Hz, 1P) ppm. 13C{1H} QDEPT NMR
2
(d, JCP = 18.2 Hz, 1C, PCH2), 63.1 (d, JCP = 13.9 Hz, 1C, PCH
CN), 78.1 (d, 1JCP = 3.8 Hz, 1C, CH−Me), 117.6 (d, 3JPC = 6.3 Hz,
(125.8 MHz, acetone-d6, 25 °C) ∂: one resonance for (CH3)3CP)
overlaid by acetone residual solvent peak, 30.2 (s, br, 3C, (CH3)3CP),
3
1C, CHpy), 118.0 (d, JPC = 7.1 Hz, 1C, CHpy), 136.4 (s, br, 1C,
2
4
2
2
CHpy(4)), 150.3 (dd, br, JPC = 7.5 Hz, JPC = 2.0 Hz, 1C, C−NH),
161.6 (dd, 2JPC = 4.6 Hz, 3JPC = 2.2 Hz, 1C, Cpy), 159.0 (dd, 2JPC = 7.2
Hz, 3JPC = 2.5 Hz, 1C, Cpy), 208.5 (dd, br, 2JCP = 8.0 Hz, 2JCP = 6.0 Hz,
1C, Re−CO), 208.8 (t, br, 2JCP = 5.2 Hz, 1C, Re−CO) ppm. IR (KBr,
pellet) ν[cm−1]: 1890, 1813 (νCO, 1:1 ratio). Anal. Calcd for
C28H47N2O2P2Re: C, 48.61; H, 6.85; N, 4.05. Found: C, 49.28; H,
7.07; N, 3.69.
30.4 (d, br, JCP = 3.3 Hz, 3C, (CH3)3CP), 31.4 (d, br, 3C, JCP = 3.5
1
3
Hz, (CH3)3CP), 37.5 (dd, JCP = 8.3 Hz, JCP = 5.4 Hz, 1C,
(CH3)3CP), 39.0 (d, JCP = 16.4 Hz, 1C, (CH3)3CP), 39.7 (d, obscured,
1
1
1C, (CH3)3CP), 39.8 (d, JCP = 20.8 Hz, 1C, PCH2), 40.3 (d, JCP
=
3.1 Hz, 1C, (CH3)3CP), 52.6 (s, 1C, N−CH3), 66.3 (d, 1JCP = 6.8 Hz,
1C, PCH), 122.3 (d, 3JPC = 4.8 Hz, 1C, CHpy), 122.9 (d, 3JPC = 6.7 Hz,
1C, CHpy), 125.1 (q, very weak, (partially obscured) 1C, CF3), 126.6
cis-[Re(PNPtBu−HNC−CHPh)(CO)2] (9). KOtBu (10 mg, 0.09
mmol, 1 equiv) was added to a stirred solution of 3 (62 mg, 0.09
mmol) in 3 mL of THF in a 20 mL vial. After 20 min, all volatiles were
evaporated in vacuo. The residue was extracted in n-pentane (15 mL)
and filtered through a syringe filter (Teflon, 0.2 μm pore size).
Subsequently, excess benzyl cyanide (1 mL) was added dropwise to
the stirred green solution. The red mixture was allowed to stay at −38
°C for 24 h to form a red precipitate. The supernatant solution was
decanted, and the obtained product was washed with cold n-pentane.
Recrystallization from a benzene (3 mL)/n-pentane (15 mL) layered
solution at −38 °C gave large red crystals (suitable for X-ray diffraction
analysis), which were subsequently washed with n-pentane and dried
(q, br, 3JFC = 3.5 Hz, 2C, CHAr), 130.0 (s, 2C, CHAr), 132.6 (d, 2JFC
=
33.1 Hz, 1C, CAr), 136.5 (s, 1C, CAr), 141.2 (s, 1C, CHpy), 158.9 (dd,
2JPC = 7.4 Hz, 3JPC = 4.2 Hz, 1C, Cpy), 166.5 (s, br, 1C, Cpy) 178.8 (d,
2
2
br, JPC = 7.9 Hz, 1C, CN(Me)), 207.4 (m, br, JCP, 1C, Re−CO),
209.8 (s, br, 1C, Re−CO) ppm. 19F{1H} NMR (282.4 MHz, acetone-
d6, 25 °C) ∂: −79.6 (s, 3F, O3SCF3), 64.6 (s, 3F, CF3) ppm. IR (KBr,
pellet) ν [cm−1]: 1925, 1851 (νCO, 1:1 ratio). Anal. Calcd for
C35H49F6N2O5P2ReS: C, 43.25; H, 5.08; N, 2.8. Found: C, 44.76; H,
5.43; N, 2.51.
cis-[Re(PNPtBu−HNC−CH(Me)Ph)(CO)2]OTf (11). Complex 9
(45 mg, 0.06 mmol) was dissolved in 4 mL of benzene in a 20 mL vial.
Methyl triflate (MeOTf) was added dropwise to the blood-red
solution until a color change to yellow was observed (3 drops via
Pasteur pipet). n-Pentane (5 mL) was added to the solution to
precipitate a yellow solid, which was decanted and dissolved in a
minimum of THF. Subsequent precipitation with n-pentane gave the
desired product 11 as a yellow microcrystalline powder, which was
separated from the supernatant solution by decantation and dried in
vacuo. Yield: 50 mg, 91%. Single crystals suitable for X-ray diffraction
1
in vacuo. Yield: 45 mg, 67%. H NMR (400.36 MHz, toluene-d8, 25
3
3
°C) ∂: 0.73 (d, br, JPH = 11.61 Hz, 9H, (CH3)3CP), 1.05 (d, JPH
=
12.01 Hz, 9H, (CH3)3CP), 1.45 (d, 3JPH = 12.81 Hz, 9H, (CH3)3CP),
1.58 (d, 3JPH = 12.80 Hz, 9H, (CH3)3CP), 3.12 (dd, 2JHH = 15.61 Hz,
2JHP = 5.61 Hz, 1H, PCH2), 3.31 (dd, 2JHH = 15.61 Hz, 2JHP = 9.20 Hz,
2
1H, PCH2), 4.41 (dt, JHP = 6.81 Hz, JHH = 2.00 Hz, 1H, PCH), 4.65
3
(s, br, 1H, NH), 5.32 (s, 1H, Ph(H)CC), 6.45 (d, JHH = 7.60 Hz,
3
3
1H, CHpy), 6.81 (d, JHH3 = 8.00 Hz 1H, CHpy), 6.87 (t, JHH = 7.21
1
analysis were obtained from a concentrated solution in benzene. H
3
Hz, 1H, CHAr), 6.92 (t, JHH = 7.61 Hz, 1H, CHpy(4)), 7.22 (t, JHH
=
3
NMR (500.13 MHz, CD3CN, 25 °C) ∂: 0.73 (d, br, JPH = 12.50 Hz,
7.61 Hz, 2H, CHAr), 7.34 (d, 3JHH = 7.21 Hz, 2H, CHAr) ppm. 31P{1H}
NMR (162.1 MHz, toluene-d8, 25 °C) ∂: 82.9 (d, 2JPP = 186.7 Hz, 1P),
3
9H, (CH3)3CP), 1.11 (d, JPH = 12.50 Hz, 9H, (CH3)3CP), 1.44 (d,
3JPH = 13.50 Hz, 9H, (CH3)3CP), 1.47 (d, 3JHH = 7.00 Hz, 3H, CH3),
1.53 (d, 3JPH = 13.50 Hz, 9H, (CH3)3CP), 3.57 (dd, 2JHH = 17.00 Hz,
98.9 (d, JPP = 186.6, 1P) ppm. 13C{1H} QDEPT NMR (100.7 MHz,
2
toluene-d8, 25 °C) ∂: 29.5 (d, br, 3C, 2JCP = 4.1 Hz (CH3)3C), 30.0 (d,
2
2
2JHP = 5.50 Hz, 1H, PCH2), 3.31 (ddd, JHH = 16.80 Hz, JHP = 10.00
2
br, 3C, JCP = 3.1 Hz (CH3)3C), 30.4 (2d, br, obscured, 6C, JCP
,
Hz, J = 1.00 Hz, 1H, PCH2), 4.45 (q, 3JHH = 7.00 Hz, 1H, (Me)CH),
4.41 (dt, JHP = 6.50 Hz, JHH = 1.50 Hz, 1H, PCH), 7.13 (d, JHH
8.00 Hz, 2H, CHAr), 7.42 (m, JHH, overlaid, 3H, CHAr), 7.61 (d, 3JHH
1
3
(CH3)3C), 36.4 (dd, JCP = 7.8 Hz, JCP = 5.5 Hz, 1C, (CH3)3CP),
36.8 (dd, 1JCP = 11.7 Hz, 3JCP = 1.7 Hz, 1C, (CH3)3CP), 37.4 (d, 1JCP
9.4 Hz, 1C, (CH3)3CP), 38.0 (d, 1JCP = 20.3 Hz, 1C, (CH3)3CP), 39.9
2
4
3
=
=
=
=
3
3
1
1
8.00 Hz, 1H, CHpy), 7.90 (d, JHH = 7.50 Hz, 1H, CHpy), (t, JHH
(d, JCP = 18.0 Hz, 1C, PCH2), 65.7 (d, JCP = 13.1 Hz, 1C, PCH),
8.00 Hz, 1H, CHpy(4)), 9.96 (s, br, 1H, CNH) ppm. 31P{1H} NMR
3
3
90.5 (d, JCP = 3.7 Hz, 1C, Ph(H)CC), 118.0 (d, br, JPC = 6.1 Hz,
1C, CHpy), 118.2 (d, 3JPC = 6.9 Hz, 1C, CHpy), 120.1 (s, 1C, CHAr,para),
123.7 (s, 2C, CHAr,ortho), 128.2 (s, 2C, CHAr,meta), 136.6 (s, 1C,
CHpy(4)), 142.9 (s, 1C, CAr, ipso), 153.5 (dd, JPC = 8.2 Hz, JPC = 2.0
Hz, 1C, C−NH), 162.1 (dd, JPC = 4.3 Hz,, JPC = 1.9 Hz, 1C, Cpy),
2
(202.5 MHz, CD3CN 25 °C) ∂: 88.9 (d, JPP = 162.6 Hz, 1P), 147.5
(d, JPP = 166.2, 1P) ppm. 13C{1H} QDEPT NMR (125.8 MHz,
2
2
2
4
CD3CN, 25 °C) ∂: 18.0 (s, 1C, CH3), 29.2 (d, br, 3C, JCP = 4.3 Hz
(CH3)3C), 29.8 (d, br, 3C, 2JCP = 2.1 Hz (CH3)3C), 30.2 (2 d, br, 2JCP
= 3.6 Hz, 3C, (CH3)3C), 30.7 (2 d, 2JCP = 3.9 Hz, 3C, (CH3)3C), 37.6
(dd, 1JCP = 11.2 Hz, 3JCP = 4.9 Hz, 1C, (CH3)3CP), 38.8 (d, 1JCP = 21.6
2
3
2
3
2
162.1 (dd, JPC = 6.8 Hz,, JPC = 3.1 Hz, 1C, Cpy), 208.2 (t, JCP,= 5.0
Hz, 1C, Re−CO), 208.4 (t, 2JCP = 6.5 Hz, 1C, Re−CO) ppm. IR (KBr,
pellet) ν [cm−1]: 1899, 1821 (νCO, 1:1 ratio). Anal. Calcd for
C33H49N2O2P2Re: C, 52.57; H, 6.55; N, 3.72. Found: C, 53.21; H,
6.29; N, .
1
3
Hz, partly overlaid, 1C, (CH3)3CP), 38.9 (dd, JCP = 14.5 Hz, JCP
=
1.3 Hz, 1C, (CH3)3CP), 39.4 (m, partly obscured, JCP = 3.8 Hz, 1C,
1
3
(CH3)3CP), 39.6 (d, JCP = 20.5 Hz, 1C, PCH2), 50.0 (d, JCP = 1.8
cis-[Re(PNPtBu−N(Me)CPhpCF3)(CO)2]OTf (10). Complex 6 (27
Hz, 1C, (Me)CH), 61.4 (d, 1JCP = 5.2 Hz, 1C, PCH), 122.1 (d, 3JPC
7.0 Hz, 1C, CHpy), 123.1 (d, JPC = 6.9 Hz, 1C, CHpy), 129.0 (s, 2C,
=
3
mg, 0.03 mmol) was dissolved in 3 mL of benzene in a 20 mL vial.
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Article
CHAr), 129.1 (s, 1C, CHAr,para), 129.9 (s, 2C, CHAr), 137.0 (s, 1C,
Phenyl 4-Cyano-4-phenylbutanoate (15). 1H NMR (500.13
MHz, CDCl3, 25 °C): 2.26 (q, 3JHH = 7.4 Hz, 2H, (CH2)CHCN), 2.67
2
3
CAr,ipso), 140.1 (s, 1C, CHpy(4)), 158.5 (dd, JPC = 6.4 Hz,, JPC = 4.5
Hz, 1C, Cpy), 165.8 (t, br, 2JPC = 2.6 Hz, 1C, Cpy), 189.7 (dd, 2JPC = 8.2
(m, 2H, (CH2)CO), 3.98 (t, JHH = 7.4 Hz, 1H, CHCN), 6.98 (d,
3
4
Hz,, JPC = 2.9 Hz, 1C, CNH), 208.0 (m, JCP, 2C, superimposed
2H, C6H5(acrylate)), 7.18 (br, 1H, CHar (cyanide)), 7.31 (m, 7H,
CHar (acrylate+cyanide)). 13C{1H} QDEPT NMR (125.8 MHz, CDCl3, 25
°C): 31.00 (s, 1C, (CH2)CHCN), 31.43 (s, 1C, (CH2)CO), 36.63
(s, 1C, CHCN), 120.56 (s, 1C, CN), 121.77 (s, 2C, CHar 5(acrylate‑ortho)),
126.43 (s, 1C, CHar5), 127.69 (s, 2C, CHar), 128.81 (s, 1C, CHar5),
129.66 (s, 2C, CHar), 129.88 (s, 2C, CHar), 135.18 (s, 1C, C6H5-ipso)
150.71 (s, 1C, C6H5-ipso), 171.09 (s, 1C, CO).
Re−CO moieties) ppm. 19F{1H} NMR (282.4 MHz, CD3CN, 25 °C)
∂: −80.1 (s, 3F, O3SCF3), 64.6 (s, 3F, CF3) ppm. IR (KBr, pellet) ν
[cm−1]: 1921, 1851 (νCO
, 1:1 ratio). Anal. Calcd for
C35H52F3N2O5P2ReS: C, 45.79; H, 5.71; N, 3.05. Found: C, 46.29;
H, 5.70; N, 2.50.
mer-[Re(PNPtBu*)(CO)3] (12). In an experiment performed in a J.
Young NMR tube fitted with a Kontes valve, complex 9 (10 mg, 0.01
mmol) was dissolved in 0.5 mL of C6D6. The red solution was
degassed in a freeze−pump−thaw cycle and pressurized with 1 atm of
CO gas. After 15 min at ambient temperature, ∼10% of complex 12
was formed. The reaction was brought to completion by heating the
NMR tube for 1 h at 65 °C in an oil bath. To verify the nature of 12 as
mer-[Re(PNPtBu*)(CO)3], a control experiment was performed in a J.
Young NMR tube fitted with a Kontes valve: The dearomatized
complex 4 (10 mg, 0.015 mmol) was dissolved in 0.5 mL of C6D6 and
pressurized with 1 atm CO gas. The initial green solution turned
5-Oxo-2-phenylhexanenitrile (16). 1H NMR (500.13 MHz,
CDCl3, 25 °C): 2.09 (s, 3H, (CH3)CO), 2.10 (m, 2H,
2,3
(CH2)CHCN), 2.52 (ddd,
J
= 18.5, 7.3, 5.9 Hz, 1H, (CH2)C
HH
2,3
O), 2.58 (dvt,
J
= 18.4, 7.4 Hz, 1H, (CH2)CO), 3.88 (dd, 3JHH
HH
3
= 8.8 Hz, JHH= 6.2 Hz, 1H, CHCN), 7.27 (br, 3H, C6H5), 7.30 (br,
2H, C6H5). 13C{1H} QDEPT NMR (125.8 MHz, CDCl3, 25 °C):
29.78 (s, 1C, CH2CHCN), 30.48 (s, 1C, CH3), 36.46 (s, 1C, CHCN),
40.25 (s, 1C, (CH2)CO), 120.81 (s, 1C, CN), 127.6 (s, 2C, CHar),
128.61 (s, 1C, CHar), 129.53 (s, 2C, CHar), 135.57 (s, 1C, C6H5-ipso),
207.21 (s, 1C, CO).
1
instantly yellow to form 12 quantitatively. H NMR (300.13 MHz,
2-(3-Oxocyclohexyl)-2-phenylacetonitrile (17). The product
was obtained as a 1:1 diastereomeric mixture. Analytical data have
been previously reported.82
3
C6D6, 25 °C) ∂: 1.09 (d, JPH = 13.20 Hz, 18H, (CH3)3CP), 1.44 (d,
2
3JPH = 13.20 Hz, 18H, (CH3)3CP), 2.83 (d, JHH = 8.10 Hz, 1H,
1
3
Methyl 4-(4-Aminophenyl)-4-cyanobutanoate (18). H NMR
(300.13 MHz, CDCl3, 25 °C): 2.11 (dd, JHH = 7.0, 14.2 Hz, 2H,
PCH2), 4.01 (s, br, 1H, PCH), 5.46 (d, JHH = 6.30 Hz, 1H, CHpy),
3
3
3
6.31 (d, JHH = 8.70 Hz, 1H, CHpy), 6.44 (t, br, JHH = 8.10 Hz, 1H,
CHpy(4)) ppm. 31P{1H} NMR (121.5 MHz, C6D6, 25 °C) ∂: 53.2 (d,
(CH2)CHCN), 2.40 (m, 2H, (CH2)CO), 3.56 (s, 2H, NH2), 3.61
3
3
2JPP = 113.2 Hz, 1P), 67.2 (d, JPP = 117.5 Hz, 1P) ppm. 13C{1H}
2
(s, 3H, OCH3), 3.77 (t, JHH = 7.3 Hz, 1H, CHCN), 6.60 (d, JHH
=
3
2
7.9 Hz, 2H, C6H4−NH2), 7.03 (d, JHH = 7.8 Hz, 2H, C6H4−NH2).
13C{1H} QDEPT NMR (100.7 MHz, CDCl3, 25 °C): 30.92 (s, 2C,
CH2), 35.65 (s, 1C, CHCN), 51.95 (s, 1C, OCH3), 115.61 (s, 2C,
C6H4−NH2), 120.86 (s, 1C, CN), 124.54 (s, 1C, C6H4-ipso), 128.42
(s, 2C, C6H4−NH2), 146.55 (s, 1C, C6H4-ipso), 172.74 (s, 1C, CO).
QDEPT NMR (100.7 MHz, C6D6, 25 °C) ∂: 29.8 (d, JPC = 3.7 Hz,
6C, (CH3)3CP), 30.6 (d, 2JPC = 3.8 Hz, 6C, (CH3)3CP), 37.2 (d, 1JCP
1
= 17.6 Hz, 2C, (CH3)3CP), 39.2 (d, JCP = 24.3 Hz, 2C, (CH3)3CP),
1
1
39.9 (d, JCP = 29.7 Hz, 1C, PCH), 69.5 (d, JCP = 50.5 Hz, 1C,
3
3
PCH2), 100.3 (d, JPC = 8.3 Hz, 1C, CHpy), 113.7 (d, JPC = 15.4 Hz,
1C, CHpy), 131.2 (s, 1C, CHpy(4)), 157.9 (s, br, 1C, Cpy), 172.5 (dd,
1
Methyl 4-(3-Bromophenyl)-4-cyanobutanoate (19). H NMR
2JPC = 14.0 Hz, JPC = 3.2 Hz, 1C, Cpy), 199.4 (t, JCP = 7.9 Hz, 2C,
3
2
(300.13 MHz, CDCl3, 25 °C): 2.14 (m, 2H, (CH2)CHCN), 2.44 (m,
3
2
2H, (CH2)CO), 3.63 (s, 3H, CH3), 3.90 (t, JHH = 7.54 Hz, 1H,
Re−CO), 202.0 (m, br, JCP 1C, Re−CO) ppm.
CHCN), 7.20 (m, 2H, C6H4−Br), 7.42 (m, 2H, C6H4−Br). 13C{1H}
QDEPT NMR (100.7 MHz, CDCl3, 25 °C): 30.76 (s, 2C, CH2),
36.00 (s, 1C, CHCN), 52.05 (s, 1C, OCH3), 119.67 (s, 1C, CN),
123.28 (s, 1C, C6H4-ipso), 126.09 (s, 1C, CHar), 130.50 (s, 1C, CHar),
130.86 (s, 1C, CHar), 131.7 (s, 1C, CHar), 137.28 (s, 1C, C6H4-ipso),
172.40 (s, 1C, CO).
Deprotonation of 11 To Form (i-E and -Z) and Formation of
9 via Addition of Benzyl Cyanide (Scheme 4). Complex 11 (27
mg, 0.03 mmol) was suspended in toluene-d8 (1 mL) in a 20 mL vial,
and KOtBu (4 mg, 1.3 equiv) was added to the vigorously stirred
mixture. The greenish solution was filtered through a syringe filter
(Teflon, 0.2 μm pore size) and transferred to a J. Young NMR tube
and investigated in situ by NMR spectroscopy. Addition of excess
benzyl cyanide (10 μL, d20 = 1.02 g/cm3, 3 equiv) via microsyringe
gave complex 9 and free 2-phenylpropanenitrile, which was identified
by GC−MS analysis.
Catalyzed Michael Additions− Experiments of Table 3.
General Procedure. The specific benzyl cyanide derivative (amounts
are specified in Table 3) was dissolved in 0.5 mL of THF in a 20 mL
vial, and 1 equiv of the specific acceptor was dissolved in 0.5 mL of
THF and added to the cyanide solution. The catalyst (2 mol %,
complex 9 or 4, respectively, as specified) was added to the substrate
mixture, and the solution was transferred to a Schlenk tube and heated
in an oil bath to the specified temperature for the indicated time
period. After the reaction vessel was cooled to room temperature, all
volatiles were evaporated in vacuo. The resulting residue was dissolved
in CDCl3. An appropriate standard was added to the solution to
determine the yields via 1H NMR spectroscopy via relative comparison
of the integration values with standard compound. For details, see the
Supporting Information. The product was purified for NMR
characterization using a preparative TLC sheet (scale, 15−30 mg of
compound; eluent, n-hexane:ethyl acetate 4:1).
Double Additions of Methyl Acrylate to Benzyl Cyanide.
Complex 9 (5 mg, 0.0066 mmol, 1 mol %) dissolved in 1 mL of THF
was added to a solution of benzyl cyanide (78 mg, 0.66 mmol) and
methyl acrylate (120 mg, 1.4 mmol, 2 equiv) in 1 mL of THF. The
mixture was heated in a closed Schlenk tube at 80 °C for 12 h. After
the reaction vessel was cooled to room temperature, all volatiles were
removed in vacuo to yield dimethyl 4-cyano-4-phenylheptanedioate
(14) in quantitative yield (NMR). Alternatively, 14 was obtained via
the stepwise addition of 2 equiv of methyl acrylate. Benzyl cyanide (47
mg, 0.4 mmol) was dissolved in 0.5 mL of THF in a 20 mL vial; 1
equiv of methyl acrylate (35 mg, 0.4 mmol) was dissolved in 0.5 mL of
THF and added to the benzyl cyanide solution. The catalyst (complex
9, 6 mg, 0.008 mmol, 2 mol %) was added to the substrate mixture,
and the solution was transferred to a Schlenk tube and heated in an oil
bath at 65 °C for 20 h. Subsequently, another equivalent of methyl
acrylate (35 mg, 0.4 mmol) was added, and the mixture was heated at
80 °C for another 10 h. After the reaction vessel was cooled to room
temperature, a sample was taken for GC analysis. Conversion with
respect to methyl acrylate was >99% GC. Quantitative formation gave
dimethyl 4-cyano-4-phenylheptanedioate (14).
Methyl 4-Cyano-4-phenylbutanoate (13). 1H NMR (500.13
MHz, CDCl3, 25 °C): 2.15 (q, 3JHH = 7.4 Hz, 2H, (CH2)CHCN), 2.42
(m, 2H, CH2)CO), 3.60 (s, 3H, OCH3), 3.90 (t, 3JHH = 7.5 Hz, 1H,
CHCN), 7.27 (br, 3H, C6H5), 7.30 (br, 2H, C6H5). 13C{1H} QDEPT
NMR (125.8 MHz, CDCl3, 25 °C): 30.80 (s, 1C, CH2CO), 30.83
(s, 1C (CH2)CHCN), 36.35 (s, 1C, CHCN), 51.95 (s, 1C, OCH3),
120.32 (s, 1C, CN), 127.37 (s, 2C, CHar), 128.40 (s, 1C, CHar), 129.27
(s, 2C, CHar), 135.02 (s, 1C, C6H5-ipso), 172.55 (s, 1C, CO).
Dimethyl 4-Cyano-4-phenylheptanedioate (14). 1H NMR
(500.13 MHz, C6D6, 25 °C): 1.94 (m, 6H, (CHHCH2)CO), 2.30
(m, 2H, (CHH, CH2)CO), 3.20 (s, 6H, OCH3), 6.93 (br, 3H,
3
C6H5), 7.07 (dd, JHH = 8.0 Hz, 2H, C6H5). 13C{1H} QDEPT NMR
(125.8 MHz, C6D6, 25 °C): 30.12 (s, CH2CO), 35.81 (s,
(CH2)CHCN), 46.93 (s, CCN), 51.13 (s, OCH3), 121.06 (s, CN),
126.09 (s, CHar), 128.12 (s, CHar), 129.30 (s, CHar), 137.04 (s, C6H5-
ipso), 171.79 (CO).
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Journal of the American Chemical Society
Article
Control Experiments. Complex 4 as Catalyst. Benzyl cyanide
(47 mg, 0.4 mmol) was dissolved in 0.5 mL of THF in a 20 mL vial,
and 1 equiv of methyl acrylate (35 mg, 0.4 mmol) was dissolved in 0.5
mL of THF and added to the cyanide solution. Complex 4 (5.5 mg,
0.008 mmol, 2 mol %) was added to the substrate mixture, and the
solution was transferred to a Schlenk tube and heated in an oil bath for
20 h at 65 °C. After the reaction vessel was cooled to room
temperature, all volatiles were evaporated in vacuo. The resulting
residue was dissolved in CDCl3. Ferrocene as standard was added to
(11) Khaskin, E.; Iron, M. A.; Shimon, L. J. W.; Zhang, J.; Milstein, D.
J. Am. Chem. Soc. 2010, 132, 8542−8543.
(12) Kohl, S. W.; Weiner, L.; Schwartsburd, L.; Konstantinovski, L.;
Shimon, L. J. W.; Ben-David, Y.; Iron, M. A.; Milstein, D. Science 2009,
324, 74−77.
(13) Schwartsburd, L.; Iron, M. A.; Konstantinovski, L.; Ben-Ari, E.;
Milstein, D. Organometallics 2011, 30, 2721−2729.
(14) Schwartsburd, L.; Iron, M. A.; Konstantinovski, L.; Diskin-
Posner, Y.; Leitus, G.; Shimon, L. J. W.; Milstein, D. Organometallics
2010, 29, 3817−3827.
1
the solution to determine the yields via H NMR spectroscopy via
relative comparison of the integration values with standard compound.
Yield: 87%. Catalytic use of KOtBu: Benzyl cyanide (47 mg, 0.4 mmol)
was dissolved in 0.5 mL of THF in a 20 mL vial; 1 equiv of methyl
acrylate (35 mg, 0.4 mmol) was dissolved in 0.5 mL of THF and
added to the benzyl cyanide solution. Potassium tert-butoxide (1 mg,
0.008 mmol, 2 mol %) was added to the substrate mixture, and the
solution was transferred to a Schlenk tube and heated in an oil bath for
20 h at 65 °C. After the reaction vessel was cooled to room
temperature, all volatiles were evaporated in vacuo. The resulting
residue was dissolved in CDCl3. Ferrocene as a standard was added to
(15) Ben-Ari, E.; Leitus, G.; Shimon, L. J. W.; Milstein, D. J. Am.
Chem. Soc. 2006, 128, 15390−15391.
(16) Prechtl, M. H. G.; Holscher, M.; Ben-David, Y.; Theyssen, N.;
̈
Loschen, R.; Milstein, D.; Leitner, W. Angew. Chem., Int. Ed. 2007, 46,
2269−2272.
(17) Kloek, S. M.; Heinekey, D. M.; Goldberg, K. I. Angew. Chem.,
Int. Ed. 2007, 46, 4736−4738.
(18) Hanson, S. K.; Heinekey, D. M.; Goldberg, K. I. Organometallics
2012, 27, 1454−1463.
(19) de Boer, S. Y.; Gloaguen, Y.; Lutz, M.; van der Vlugt, J. I. Inorg.
Chim. Acta 2012, 380, 336−342.
1
the solution to determine the yields via H NMR spectroscopy via
relative comparison of the integration values with standard compound.
Conversion with respect to methyl acrylate was >99% GC. Yield of
products: 37% (13), 26% (14), and nonidentified byproducts.
(20) Hunsicker, D. M.; Dauphinais, B. C.; Mc Ilrath, S. P.;
Robertson, N. J. Macromol. Rapid Commun. 2011, 33, 232−236.
(21) Friedrich, A.; Schneider, S. ChemCatChem 2009, 1, 72−73.
(22) Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D. J. Am. Chem.
Soc. 2005, 127, 10840−10841.
ASSOCIATED CONTENT
■
(23) Srimani, D.; Balaraman, E.; Gnanaprakasam, B.; Ben-David, Y.;
Milstein, D. Adv. Synth. Catal. 2012, 354, 2403−2406.
(24) Balaraman, E.; Khaskin, E.; Leitus, G.; Milstein, D. Nat. Chem.
2013, 5, 122−125.
S
* Supporting Information
Figures giving NMR spectra, coordinates for the DFT
optimized geometries, and CIF files for all structures. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(25) Gunanathan, C.; Ben-David, Y.; Milstein, D. Science 2007, 317,
790−792.
(26) Gnanaprakasam, B.; Milstein, D. J. Am. Chem. Soc. 2011, 133,
1682−1685.
AUTHOR INFORMATION
■
(27) Zeng, H.; Guan, Z. J. Am. Chem. Soc. 2011, 133, 1159−1161.
(28) Gnanaprakasam, B.; Zhang, J.; Milstein, D. Angew. Chem., Int.
Ed. 2010, 49, 1468−1471.
Corresponding Author
david.milstein@weizmann.ac.il
Author Contributions
(29) Michlik, S.; Kempe, R. Nat. Chem. 2013, 5, 140−144.
(30) Srimani, D.; Ben-David, Y.; Milstein, D. Angew. Chem., Int. Ed.
2013, 52, 4012−4015.
§These authors contributed equally.
Notes
(31) Gunanathan, C.; Gnanaprakasam, B.; Iron, M. A.; Shimon, L. J.
W.; Milstein, D. J. Am. Chem. Soc. 2010, 132, 14763−14765.
(32) Gunanathan, C.; Milstein, D. Angew. Chem., Int. Ed. 2008, 47,
8661−8664.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
(33) Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D. Angew. Chem.
Int. Ed. 2006, 45, 1113−1115.
(34) Balaraman, E.; Fogler, E.; Milstein, D. Chem. Commun. 2012, 48,
1111−1113.
(35) Balaraman, E.; Gnanaprakasam, B.; Shimon, L. J. W.; Milstein,
D. J. Am. Chem. Soc. 2010, 132, 16756−16758.
(36) Balaraman, E.; Gunanathan, C.; Zhang, J.; Shimon, L. J. W.;
Milstein, D. Nat. Chem. 2011, 3, 609−614.
(37) Balaraman, E.; Ben-David, Y.; Milstein, D. Angew. Chem., Int. Ed.
2011, 50, 11702−11705.
(38) Tanaka, R.; Yamashita, M.; Nozaki, K. J. Am. Chem. Soc. 2011,
131, 14168−14169.
(39) Tanaka, R.; Yamashita, M.; Chung, L. W.; Morokuma, K.;
Nozaki, K. Organometallics 2011, 30, 6742−6750.
(40) Langer, R.; Diskin-Posner, Y.; Leitus, G.; Shimon, L. J. W.; Ben-
David, Y.; Milstein, D. Angew. Chem., Int. Ed. 2011, 50, 9948−9952.
(41) Huff, C. A.; Sanford, M. S. J. Am. Chem. Soc. 2012, 133, 18122−
18125.
(42) Vogt, M.; Gargir, M.; Iron, M. A.; Diskin-Posner, Y.; Ben-David,
Y.; Milstein, D. Chem.-Eur. J. 2012, 18, 9194−9197.
(43) Huff, C. A.; Kampf, J. W.; Sanford, M. S. Organometallics 2012,
31, 4643−4645.
This research was supported by the European Research Council
under the FP7 framework (ERC No. 246837). D.M. holds the
Israel Matz Professorial Chair of Organic Chemistry. M.V.
would like to thank the Swiss Friends of the Weizmann
Institute for a postdoctoral fellowship.
REFERENCES
■
(1) Albrecht, M.; Lindner, M. M. Dalton Trans. 2011, 40, 8733.
(2) Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed. 2001, 40,
3750−3781.
(3) Gunanathan, C.; Milstein, D. Acc. Chem. Res. 2011, 44, 588−602.
(4) Gunanathan, C.; Milstein, D. Top. Organomet. Chem. 2011, 37,
55−84.
(5) van der Vlugt, J. I. Eur. J. Inorg. Chem. 2012, 2012, 363−375.
(6) van der Vlugt, J. I.; Reek, J. N. H. Angew. Chem., Int. Ed. 2009, 48,
8832−8846.
(7) The Chemistry of Pincer Compounds; Morales-Morales, D., Jensen,
M. C., Eds.; Elsevier: New York, 2007; pp 1−467.
(8) van der Vlugt, J. I.; Pidko, E. A.; Bauer, R. C.; Gloaguen, Y.; Rong,
M. K.; Lutz, M. Chem.-Eur. J. 2011, 17, 3850−3854.
(9) van der Vlugt, J. I.; Lutz, M.; Pidko, E. A.; Vogt, D.; Spek, A. L.
Dalton Trans. 2009, 1016−1023.
(44) Vogt, M.; Rivada-Wheelaghan, O.; Iron, M. A.; Leitus, G.;
Diskin-Posner, Y.; Shimon, L. J. W.; Ben-David, Y.; Milstein, D.
Organometallics 2013, 32, 300−308.
(10) Feller, M.; Diskin-Posner, Y.; Shimon, L. J. W.; Ben-Ari, E.;
Milstein, D. Organometallics 2012, 31, 4083−4101.
17016
dx.doi.org/10.1021/ja4071859 | J. Am. Chem. Soc. 2013, 135, 17004−17018

Journal of the American Chemical Society
Article
(45) Montag, M.; Zhang, J.; Milstein, D. J. Am. Chem. Soc. 2012, 134,
10325−10328.
are observed as doublets (3JHP = 11.0 Hz) at 1.54 and 1.44 ppm, and a
broad singlet at 1.19 ppm with integration equal to nine protons each.
(73) Scepaniak, J. J.; Wu, G.; Hayton, T. W. Dalton Trans. 2012, 41,
7859−7861.
(46) Ozerov, O. V.; Watson, L. A.; Pink, M.; Caulton, K. G. J. Am.
Chem. Soc. 2007, 129, 6003−6016.
(74) Soriaga, R. A. D.; Javed, S.; Hoffman, D. M. J. Cluster Sci. 2010,
21, 567−575.
(47) Michos, D.; Luo, X. L.; Crabtree, R. H. J. Chem. Soc., Dalton
Trans. 1992, 1735−1738.
(75) Upon cooling a solution of 8 in toluene-d8, a second minor
(10% at −65 °C) species is detected. The 31P{1H}NMR shows an AB-
spin system with large separation of the two doublets at 86.4 and 125.8
ppm (2JPP = 194.0 Hz) typically observed for the ketimido complexes
(e.g., the analogue complex 7). However, a reliable assignment of the
NMR data to such a species could not be made with certainty due to
overlapping NMR resonances.
(76) Goto, M.; Ishikawa, Y.; Ishihara, T.; Nakatake, C.; Higuchi, T.;
Kurosaki, H.; Goedken, V. J. Chem. Soc., Dalton Trans. 1998, 1213−
1222.
(77) Goto, M.; Ishikawa, Y.; Ishihara, T.; Nakatake, C.; Higuchi, T.;
Kurosaki, H.; Goedken, T. L. V. L. Chem. Commun. 1997, 539−540.
(78) Kurosaki, H.; Ishikawa, Y.; Ishihara, T.; Yamamoto, T.;
Yamaguchi, Y.; Goto, M. Dalton Trans. 2005, 1086−1092.
(79) Selva, M.; Marques, C. A.; Tundo, P. J. Chem. Soc., Perkin Trans.
1 1994, 1323.
(48) Marchi, A.; Marvelli, L.; Rossi, R.; Magon, L.; Uccelli, L.;
Bertolasi, V.; Ferretti, V.; Zanobini, F. J. Chem. Soc., Dalton Trans.
1993, 1281−1286.
(49) Bolzati, C.; Boschi, A.; Uccelli, L.; Tisato, F.; Refosco, F.;
Cagnolini, A.; Duatti, A.; Prakash, S.; Bandoli, G.; Vittadini, A. J. Am.
Chem. Soc. 2002, 124, 11468−11479.
(50) Bolzati, C.; Benini, E.; Cazzola, E.; Jung, C.; Tisato, F.; Refosco,
F.; Pietzsch, H. J.; Spies, H.; Uccelli, L.; Duatti, A. Bioconjugate Chem.
2004, 15, 628−637.
(51) Porchia, M.; Tisato, F.; Refosco, F.; Bolzati, C.; Cavazza-
Ceccato, M.; Bandoli, G.; Dolmella, A. Inorg. Chem. 2005, 44, 4766−
4776.
(52) Kim, Y. S.; He, Z.; Hsieh, W. Y.; Liu, S. Bioconjugate Chem.
2006, 17, 473−484.
(53) Choualeb, A.; Lough, A. J.; Gusev, D. G. Organometallics 2007,
26, 3509−3515.
(80) Selva, M.; Perosa, A. Green Chem. 2008, 10, 457−464.
(81) The double addition product 14 is observed in low
concentration (<10%) at the end of the reaction of benzyl cyanide
and methyl acrylate in 1:1 ratio to form 13 (see GC traces in the
Supporting Information). The first Michael addition step to form 13
proceeds more selectively under milder conditions (65 °C, 1:1 ratio).
Hence, the first Michael addition is considerably faster than the
second. The double addition product was obtained upon stepwise
addition of benzyl cyanide or starting from a 1:2 ratio at higher
temperature (80 °C). A control experiment has shown that catalytic
amounts of KOtBu catalyze the Michael addition between benzyl
cyanide and methyl acrylate. However, a significantly lower selectivity
for the monoaddition product 13 was observed; see GC traces and
Supporting Information Table S1 in the Experimental Section.
(82) Shimizu, S.; Shirakawa, S.; Suzuki, T.; Sasaki, Y. Tetrahedron
2001, 57, 6169−6173.
(54) Lang, H.-F.; Fanwick, P. E.; Walton, R. A. Inorg. Chim. Acta
2002, 329, 1−8.
(55) Kuang, S.-M.; Fanwick, P. E.; Walton, R. A. Inorg. Chem. 2002,
41, 405−412.
(56) Landwehr, A.; Dudle, B.; Fox, T.; Blacque, O.; Berke, H. Chem.-
Eur. J. 2012, 18, 5701−5714.
(57) Jiang, Y.; Hess, J.; Fox, T.; Berke, H. J. Am. Chem. Soc. 2010,
132, 18233−18247.
(58) Dudle, B.; Rajesh, K.; Blacque, O.; Berke, H. J. Am. Chem. Soc.
2011, 133, 8168−8178.
(59) Jiang, Y.; Schirmer, B.; Blacque, O.; Fox, T.; Grimme, S.; Berke,
H. J. Am. Chem. Soc. 2013, 135, 4088−4102.
(60) Schleker, P. P. M.; Honeker, R.; Klankermayer, J.; Leitner, W.
ChemCatChem 2013, 5, 1762−1764.
(61) Lewis, R. A.; Wu, G.; Hayton, T. W. Inorg. Chem. 2013, 50,
4660−4668.
(83) Hermann, D.; Gandelman, M.; Rozenberg, H.; Shimon, L. J. W.;
Milstein, D. Organometallics 2002, 21, 2−818.
(62) Lewis, R. A. R.; Wu, G. G.; Hayton, T. W. T. J. Am. Chem. Soc.
2010, 132, 12814−12816.
(84) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.;
Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega,
N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; ,Salvador, P.;
Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.;
Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09,
revision C.01; Gaussian, Inc.: Wallingford, CT, 2009.
(63) Soriaga, R. A. D. R.; Nguyen, J. M. J.; Albright, T. A. T.;
Hoffman, D. M. D. J. Am. Chem. Soc. 2010, 132, 18014−18016.
(64) Lewis, R. A.; George, S. P.; Chapovetsky, A.; Wu, G.; Figueroa,
J. S.; Hayton, T. W. Chem. Commun. 2013, 49, 2888−2890.
(65) Seaman, L. A.; Wu, G.; Edelstein, N.; Lukens, W. W.; Magnani,
N.; Hayton, T. W. J. Am. Chem. Soc. 2012, 134, 4931−4940.
(66) Kiplinger, J. L.; Morris, D. E.; Scott, B. L.; Burns, C. J.
Organometallics 2002, 21, 3073−3075.
(67) Lewis, R. A.; Morochnik, S.; Chapovetsky, A.; Wu, G.; Hayton,
T. W. Angew. Chem., Int. Ed. 2012, 51, 12772−12775.
(68) Ferreira, M. J.; Martins, A. M. Coord. Chem. Rev. 2006, 250,
118−132.
(69) Henderson, K. W.; Hind, A.; Kennedy, A. R.; McKeown, A. E.;
Mulvey, R. E. J. Organomet. Chem. 2002, 656, 63−70.
(70) Martins, A. M.; Marques, M. M.; Ascenso, J. R.; Dias, A. R.;
Duarte, M. T.; Fernandes, A. C.; Fernandes, S.; Ferreira, M. J.; Matos,
(85) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996, 77,
I.; Conceica̧ o Oliveira, M.; Rodrigues, S. S.; Wilson, C. J. Organomet.
̃
3865−3868.
Chem. 2005, 690, 874−884.
(86) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1997, 78,
1396.
(71) Ferreira, M. J.; Matos, I.; Ascenso, J. R.; Duarte, M. T.; Marques,
M. M.; Wilson, C.; Martins, A. M. Organometallics 2007, 26, 119−127.
(87) Kozuch, S.; Martin, J. M. L. Phys. Chem. Chem. Phys. 2011, 13,
1
(72) The H NMR spectrum at −65 °C in toluene-d8 has three
20104−20107.
distinct resonances for the CH3 groups of the P−tBu moiety in vicinity
(88) Adamo, C.; Barone, V. J. Chem. Phys. 1999, 110, 6158−6170.
(89) Perdew, J. Phys. Rev. B: Condens. Matter 1986, 33, 8822−8824.
(90) Szabados, A. J. Chem. Phys. 2006, 125, 214105.
to the axial ketimido nitrogen atom. Broad peaks integrating to three
3
protons are found for the methyl groups at −0.38 ppm (br, d, JHP
=
16.5 Hz), 0.92 ppm (br, s), and 1.95 ppm (br, d, 3JHP = 10.7 Hz). We
hypothesize that this splitting into three resonances is due to
hindrance of the free rotation of the P−tBu group upon [1,3]-addition
of the pivalonitrile to 4. The other resonances for the P−tBu groups
(91) Grimme, S. J. Chem. Phys. 2003, 118, 9095−9102.
(92) Møller, C.; Plesset, M. S. Phys. Rev. 1934, 46, 618−622.
(93) Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. J. Chem. Phys.
2010, 132, 154104.
17017
dx.doi.org/10.1021/ja4071859 | J. Am. Chem. Soc. 2013, 135, 17004−17018

Journal of the American Chemical Society
Article
(94) Schwabe, T.; Grimme, S. Acc. Chem. Res. 2008, 41, 569−579.
(95) Schwabe, T.; Grimme, S. Phys. Chem. Chem. Phys. 2007, 9,
3397−3406.
(96) Grimme, S. J. Comput. Chem. 2006, 27, 1787−1799.
(97) Grimme, S.; Ehrlich, S.; Goerigk, L. J. Comput. Chem. 2011, 32,
1456−1465.
(98) Johnson, E. R.; Becke, A. D. J. Chem. Phys. 2006, 124, 174104.
(99) Dunning, T. H., Jr.; Hay, P. J. In Modern Theoretical Chemistry 3.
Methods of Electronic Structure Theory; Schaefer, H. F., III, Ed.; Plenum
Press: New York, 1976; Vol. 3, pp 1−28.
(100) Dolg, M. In Modern Methods and Algorithms of Quantum
Chemistry; Grotendorst, J., Ed.; John von Neumann Institute for
Computing: Julich, 2000; Vol. 3, pp 507−540.
̈
(101) Dunning, T. H., Jr. J. Chem. Phys. 1989, 90, 1007−1023.
(102) Wilson, A. K.; Woon, D. E.; Peterson, K. A.; Dunning, T. H.,
Jr. J. Chem. Phys. 1999, 110, 7667−7676.
(103) Peterson, K. A.; Figgen, D.; Dolg, M.; Stoll, H. J. Chem. Phys.
2007, 126, 124101.
(104) Dunlap, B. I. J. Chem. Phys. 1983, 78, 3140−3142.
(105) Dunlap, B. I. J. Mol. Struct. (THEOCHEM) 2000, 529, 37−40.
(106) Mennucci, B.; Tomasi, J. J. Chem. Phys. 1997, 106, 5151−5158.
(107) Cances
3032−3041.
̀
, E.; Mennucci, B.; Tomasi, J. J. Chem. Phys. 1997, 107,
(108) Cossi, M.; Barone, V.; Mennucci, B.; Tomasi, J. Chem. Phys.
Lett. 1998, 286, 253−260.
(109) Cossi, M.; Scalmani, G.; Rega, N.; Barone, V. J. Chem. Phys.
2002, 117, 43−54.
(110) Mennucci, B.; Cances
101, 10506−10517.
(111) Tomasi, J.; Mennucci, B.; Cances
(THEOCHEM) 1999, 464, 211−226.
̀
, E.; Tomasi, J. J. Phys. Chem. B 1997,
̀
, E. J. Mol. Struct.
(112) Marenich, A. V.; Cramer, C. J.; Truhlar, D. G. J. Phys. Chem. B
2009, 113, 6378−6396.
17018
dx.doi.org/10.1021/ja4071859 | J. Am. Chem. Soc. 2013, 135, 17004−17018