Ru(0) and Ru(II) nitrosyl pincer complexes: Structure, reactivity, and catalytic activity

Article abstract of DOI:10.1021/ic401780p

Despite considerable interest in ruthenium carbonyl pincer complexes and their substantial catalytic activity, there has been relatively little study of the isoelectronic ruthenium nitrosyl complexes. Here we describe the synthesis and reactivity of several complexes of this type as well as the catalytic activity of complex 6. Reaction of the PNP ligand (PNP = 2,6-bis( ^tBu₂PCH₂)pyridine) with RuCl ₃(NO)(PPh₃)₂ yielded the Ru(II) complex 3. Chloride displacement by BAr^F- (BAr^F- = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) gave the crystallographicaly characterized, linear NO Ru(II) complex 4, which upon treatment with NaBEt ₃H yielded the Ru(0) complexes 5. The crystallographically characterized Ru(0) square planar complex 5·BF₄ bears a linear NO ligand located trans to the pyridilic nitrogen. Further treatment of 5·BF₄ with excess LiOH gave the crystallographicaly characterized Ru(0) square planar, linear NO complex 6. Complex 6 catalyzes the dehydrogenative coupling of alcohols to esters, reaching full conversion under air or under argon. Reaction of the PNN ligand (PNN = 2-(^tBu ₂PCH₂)-6-(Et₂NCH₂)pyridine) with RuCl₃(NO)(H₂O)₂ in ethanol gave an equilibrium mixture of isomers 7a and 7b. Further treatment of 7a + 7b with 2 equivalent of sodium isopropoxide gave the crystallographicaly characterized, bent-nitrosyl, square pyramidal Ru(II) complex 8. Complex 8 was also synthesized by reaction of PNN with RuCl₃(NO)(H₂O)₂ and Et₃N in ethanol. Reaction of the "long arm" PN²N ligand (PN ²N = 2-(^tBu₂PCH₂-)-6-(Et ₂NCH₂CH₂)pyridine) with RuCl ₃(NO)(H₂O)₂ in ethanol gave complex 9, which upon treatment with 2 equiv of sodium isopropoxide gave complex 10. Complex 10 was also synthesized directly by reaction of PN²N with RuCl ₃(NO)(H₂O)₂ and a base in ethanol. A noteworthy aspect of these nitrosyl complexes is their preference for the Ru(0) oxidization state over Ru(II). This preference is observed with both aromatized and dearomatized pincer ligands, in contrast to the Ru(II) oxidation state which is preferred by the analogous carbonyl complexes.

Full text of DOI:10.1021/ic401780p

Article
pubs.acs.org/IC
Ru(0) and Ru(II) Nitrosyl Pincer Complexes: Structure, Reactivity, and
Catalytic Activity
†
‡
†
†
‡
‡
Eran Fogler, Mark A. Iron, Jing Zhang, Yehoshoa Ben-David, Yael Diskin−Posner, Gregory Leitus,
‡
,†
Linda J. W. Shimon, and David Milstein*
†
‡
Department of Organic Chemistry and Department of Chemical Research Support, Weizmann Institute of Science, 234 Herzl
Street, Rehovot 76100, Israel
*
S Supporting Information
ABSTRACT: Despite considerable interest in ruthenium carbonyl pincer complexes and their substantial catalytic activity, there
has been relatively little study of the isoelectronic ruthenium nitrosyl complexes. Here we describe the synthesis and reactivity of
several complexes of this type as well as the catalytic activity of complex 6. Reaction of the PNP ligand (PNP = 2,6-
t
F−
F−
bis( Bu PCH )pyridine) with RuCl (NO)(PPh ) yielded the Ru(II) complex 3. Chloride displacement by BAr (BAr
=
2
2
3
3 2
tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) gave the crystallographicaly characterized, linear NO Ru(II) complex 4, which
upon treatment with NaBEt H yielded the Ru(0) complexes 5. The crystallographically characterized Ru(0) square planar
3
complex 5·BF bears a linear NO ligand located trans to the pyridilic nitrogen. Further treatment of 5·BF with excess LiOH gave
4
4
the crystallographicaly characterized Ru(0) square planar, linear NO complex 6. Complex 6 catalyzes the dehydrogenative
coupling of alcohols to esters, reaching full conversion under air or under argon. Reaction of the PNN ligand (PNN = 2-
t
(
Bu PCH )-6-(Et NCH )pyridine) with RuCl (NO)(H O) in ethanol gave an equilibrium mixture of isomers 7a and 7b.
2 2 2 2 3 2 2
Further treatment of 7a + 7b with 2 equivalent of sodium isopropoxide gave the crystallographicaly characterized, bent-nitrosyl,
square pyramidal Ru(II) complex 8. Complex 8 was also synthesized by reaction of PNN with RuCl (NO)(H O) and Et N in
3
2
2
3
2
2
t
ethanol. Reaction of the “long arm” PN N ligand (PN N = 2-( Bu PCH −)-6-(Et NCH CH )pyridine) with RuCl (NO)(H O)
in ethanol gave complex 9, which upon treatment with 2 equiv of sodium isopropoxide gave complex 10. Complex 10 was also
synthesized directly by reaction of PN N with RuCl (NO)(H O) and a base in ethanol. A noteworthy aspect of these nitrosyl
2
2
2
2
2
3
2
2
2
3
2
2
complexes is their preference for the Ru(0) oxidization state over Ru(II). This preference is observed with both aromatized and
dearomatized pincer ligands, in contrast to the Ru(II) oxidation state which is preferred by the analogous carbonyl complexes.
INTRODUCTION
electrophilicity of the system, presenting a possible strategy for
■
25,26
activation of an otherwise unreactive complex.
In cases of
Several pyridine-based ruthenium carbonyl pincer-type com-
bent M−N−O complexes, a pair of electrons originally assigned
plexes such as 1 and 2 (Scheme 1), developed in our
1
−3
to the metal center becomes a lone pair on nitrogen, i.e., the
laboratory,
are catalytically active in various reactions, such
+
−
25,27,28
as the dehydrogenative coupling of alcohols to form esters
electron-rich metal reduces NO to NO .
There are
1
−4
(
(
Scheme 1, eq 1),
hydrogenation of esters to alcohols
examples of complexes with both bent and linear NO ligands,
5
−7
Scheme 1, eq 2), coupling of alcohols with primary amines
and in some cases the linear and bent nitrosyl isomers are in
8
25,27,29,30
to form amides with liberation of H (Scheme 1, eq 3),
synthesis of imines from alcohols and amines with liberation of
2
equilibrium.
This equilibrium may provide a powerful
tool for catalysis. The linear-to-bent transition effectively
oxidizes the metal center by 2e and enables coordination of
an additional ligand, while the bent-to-linear transition
effectively reduces the complex by 2e and promotes
dissociation of a ligand by stabilizing the resulting com-
9
H , catalytic coupling of nitriles with amines to selectively
2
1
0
form imines, as well several other catalytic transforma-
9
,11−24
tions.
It was of interest to us to explore the structure,
reactivity, and catalytic activity of the isoelectronic nitrosyl
complexes toward dehydrogenative coupling of alcohols to
esters.
31−33
plex.
A few pincer-type ruthenium nitrosyl complexes are
known in the literature, such as a Ru(II) complex, synthesized
The majority of nitrosyl complexes bear a linear M−N−O
group, and in such cases the NO ligand generally behaves as a
+
+
2
e donor (NO ). Replacing CO by an NO ligand generates a
Received: July 10, 2013
complex with an extra positive charge, thus increasing the
©
XXXX American Chemical Society
A
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Scheme 1. Examples of Reactions Catalyzed by Complexes 1
and 2
RESULTS AND DISCUSSION
■
Synthesis and Properties of PNP−Ru Nitrosyl Com-
plexes. Ru(II) complexes 3 and 4 were synthesized according
to Scheme 2. Reaction of the PNP ligand (PNP = 2,6-
t
bis( Bu PCH )pyridine) ligand with RuCl (NO)(PPh ) in
2
2
3
3 2
refluxing toluene yielded complex 3. Upon reaction of 3 with
sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate (Na-
F
F
BAr ) replacement of the chloride by the BAr anion took
place to yield complex 4 with no change in the spectroscopic
data, indicating that the chloride anion in 3 was located in the
outer sphere and that the structures of 3 and 4 are essentially
identical. The fully characterized complexes 3 and 4 give rise to
a singlet at 66.7 ppm in the 31P{ H} NMR spectrum, and the
diastereotopic methylene groups of the ligand appear as a dt at
1
4
.80 ppm (JHH = 17 Hz, JHP = 4.5 Hz) and a dt at 4.46 ppm
1
(
JHH = 17 Hz, JHP = 3.6 Hz) in the H NMR spectrum. The
−1
NO stretch of 3 and 4 appears at 1867 cm in the IR
spectrum.
The entire amount of 4 was obtained as single crystals
suitable for X-ray diffraction. The X-ray structure of 4 (Figure
1
) reveals an octahedral structure containing two phosphorus
atoms trans to each other, a chloride trans to the pyridine
ligand, and a linear NO (Ru−N−O angle of 178.1°; Table 1)
located trans to the second chloride. The Ru−NO bond
distance of 1.775 Å is similar to the reported Ru(II)−NO bond
3
4
length of 1.737 Å for an analogous pincer complex
for structural studies, and a Ru(0), which was prepared during
+
34
(
II)
[
Ru (2,2′:6′,2″-terpyridine)Cl (NO)] . The Ru−P bond
35
2
research on N activation.
2
distances (2.444, 2.457 Å) are almost identical to the one
reported for an analogous [Ru ( Bu PCH SiMe ) N )(NO-
linear)(NO-bent)] pincer complex (2.45(2) Å), bearing a
In this work, we describe the synthesis, properties, reactivity,
and some catalytic activity of pyridine-based ruthenium nitrosyl
pincer complexes.
(II) t
−
2
2
2 2
36
+
−
linear NO ligand trans to the amide (N ) ligand.
Scheme 2. Synthesis of Complexes 3−5
B
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F
the only isolated product. Spectra of 5·BF and 5·BAr are
4
essentially identical.
Crystals of 5·BF suitable for X-ray diffraction analysis were
4
obtained by layering pentane over a concentrated dichloro-
methane (DCM) solution of 5·BF . The X-ray structure
4
(
Figure 2) exhibits a square planar structure containing two
phosphorus atoms trans to each other and a linear NO (Ru−
N−O angle of 176.4°) located trans to the pyridylic nitrogen,
Table 2. The short Ru−NO bond distance of 1.708 Å indicates
a stronger Ru−NO bond in the Ru(0) complex 5·BF than in
4
Ru(II) complex 4 (1.775 Å), a result of the expected higher
back-bonding in 5·BF . This is also in line with the lower
4
frequency of the NO stretch in the IR spectrum of 5·BF . The
4
reported Ru(0)−NO and Ru−P bond lengths of the analogous
(
0)
t
Ru (NO)( Bu PCH −SiMe ) N) pincer complex (1.721 Å
2
2
2 2
35
and 2.380 Å, respectively) are somewhat longer than those of
5
·BF (1.708 and 2.349 Å, respectively). The two hydrogen
4
atoms connected to C1 and C7A were located in the X-ray
structure, indicating that 5·BF is indeed an aromatic complex.
4
The ruthenium nitrosyl complex 5 adopts the aromatic
PNP−Ru(0) structure rather then the unobserved dearomat-
ized-PNP* Ru(II) hydride form 5′ (Figure 3), unlike the
analogous carbonyl complexes 1 and 2.
Figure 1. Structure of complex 4 (ellipsoids shown at 50% probability
level). Hydrogen atoms and the BAr the chloride counteranion are
omitted for clarity. t-Bu groups are presented as wireframe for clarity.
F
The aromatic structure of 5·BF is clearly evident in its
4
crystal structure, in which the two hydrogen atoms connected
to C1 and C7A were located. In addition, the pairs of bonds
C1−C2/C6−C7A, C2−C3/C5−C6, C3−C4/C4−C5, and
N1−C2/N1−C6 are (within experimental error) of the same
length, unlike the expected alternating bond lengths in the
putative Ru(II) dearomatized complex 5′.
Table 1. Selected Bond Lengths (Å) and Bond Angles (°) in
4
Ru1−N1
N1−O1
Ru1−P2
Ru1−N2
Ru1−Cl2
Ru1−P1
1.775(7)
1.123(8)
2.4566(7)
2.093(2)
2.300(2)
2.4437(7)
Ru1−Cl1
2.333(3)
163.94(2)
178.1(5)
96.4(2)
P1−Ru1−P2
Ru1−N1−O1
N2−Ru1−N1
N2−Ru1−Cl1
Cl2−Ru1−N1
Attempts to synthesize the dearomatized Ru(0) complex 6
by deprotonation of 5·BF4 with KOtBu (potassium tert-
butoxide) or KHMDS (potassium bis-hexamethyldisilazide)
led to decomposition of the complex. However, when 5·BF4
was reacted with a suspension of LiOH (large excess) in THF,
complex 6 was obtained as the sole product (Scheme 4).
172.6(3)
172.6(2)
Complexes 3 and 4 are relatively air stable (can be exposed
to air for a few minutes without decomposition); unfortunately,
they slowly decompose at room temperature, resulting in some
3
1
1
Complex 6 gives rise to two doublets in the P{ H}NMR
1
spectrum at 78.73 and 74.88 ppm (JPP = 200 Hz). In the H
1
NMR spectrum, the methylene groups of the ligand appear as a
doublet at 2.81 ppm (JPH = 8.7 Hz) and the “arm” vinylic
proton appears as a doublet (JHP = 3.6 Hz) at 3.81 ppm. The
unidentified decomposition products, as observed by H NMR.
Further treatment of complex 4 with NaBEt H in THF yielded
3
F
the square planar Ru(0) complex 5·BAr , which was separated
corresponding carbon exhibits a doublet at 67.8 ppm (J
=
and fully characterized. Complex 5 gives rise to a singlet at 80.6
CP
31
1
13
1
ppm in the P{ H} NMR spectrum, and the methylene groups
49.0 Hz) in the C{ H} NMR spectrum. The NO stretches in
−1
of the ligand appear as a triplet at 3.94 ppm (J = 3.5 Hz) in
the IR spectrum appear at 1916 cm . Single crystals of 6
suitable for X-ray diffraction were obtained by slow evaporation
of its etheral solution.
PH
1
−1
the H NMR spectrum. spectrum appears at 1759 cm .
Alternatively, 5·BF was synthesized directly without the
4
need for separation of 3. Reaction of PNP with the Ru(II)
complex RuCl (NO)(H O) in refluxing ethanol in the
The X-ray structure of 6 (Figure 4) reveals a square planar
geometry with the two phosphorus atoms located trans to each
other and a linear nitrosyl group (Ru−N−O angle of 179.6°)
located trans to the dearomatized pyridine nitrogen, indicating
that 6 is a Ru(0) complex. Comparing the Ru(0)−NO bond
3
2
2
presence of Et N under reductive conditions (ethanol is
3
oxidized to acetone), followed by replacement of the chloride
with BF4− using AgBF , and filtration yielded complex 5·BF as
4
4
Scheme 3. Synthesis of 5·BF4
C
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Figure 4. X-ray structure of complex 6 (ellipsoids shown at 50%
probability level). Hydrogen atoms (except for the methylene and
vinylic protons) are omitted for clarity. t-Bu groups are presented as
wireframe for clarity.
Figure 2. X-ray structure of complex 5·BF (ellipsoids shown at 50%
probability level). Hydrogen atoms and counteranion are omitted for
clarity. t-Bu groups are presented as wireframe for clarity.
4
Table 2. Selected Bond Lengths (Å) and Bond Angles (°) in
5·BF4
Table 3. Selected Bond Lengths (Å) and Bond Angles (°) in
6
Ru1−N2
1.708(4)
1.157(6)
2.349(1)
2.349(1)
2.139(4)
1.511(7)
1.48(1)
C5−C6
C3−C4
C4−C5
N1−C2
1.366(7)
1.359(8)
1.360(8)
1.362(6)
1.358(6)
176.4(5)
165.24(5)
174.8(2)
Ru1−N1
N1−O1
Ru1−P1
Ru1−P2
Ru1−N2
C1−C2
C6−C7
P1−C1
P2−C7
1.721(3)
1.175(4)
2.3537(10)
2.3452(9)
2.098(3)
1.410(5)
1.463(5)
1.779(4)
1.817(3)
C2−C3
C5−C6
C3−C4
C4−C5
Ru1−N1−O1
P1−Ru1−P2
N2−Ru1−N1
P1−C1−C2
C6−C7−P2
1.423(5)
1.389(4)
1.371(5)
1.398(5)
179.6(4)
164.44(3)
178.3(1)
116.4(3)
114.5(3)
N2−O1
Ru1−P1
Ru1−P2
Ru1−N1
C1−C2
C6−C7A
C2−C3
N1−C6
Ru1−N2−O1
P2−Ru1−P1
N1−Ru1−N2
1.368(7)
However, when 6 was dissolved in dry methanol, it underwent
protonation to give 5 (and presumably methoxide as the
3
1
1
counteranion) as the only product as observed by P{ H}
NMR as a result of the large excess of the methanol solvent
(
Scheme 5). This reaction is fully reversible and upon
evaporation of the methanol solvent 6 was formed. This cycle
can be repeated several times.
Figure 3. Unobserved dearomatized complex 5′.
According to DFT calculations, 5′, the dearomatized isomer
of 5, is much less stable than 5 (ΔΔG = 30.0 kcal/mol). For
Scheme 4. Synthesis of 6
298
comparison, the CO analogue of 5′, the putative complex 2′, is
slightly less stable than the dearomatized complex 2a (2 with
t
P Bu ), ΔΔG = 2.2 kcal/mol, Scheme 6.
2
298
The likely explanation for this large difference in stability
between 5 and 5′ is the lower electron density at the metal
center in the nitrosyl complexes as compared with the
corresponding carbonyl complexes. This is indicated by the
more positive atomic polar tensor (APT) charges on the
ruthenium centers of the various complexes (Table 4).
Comparing complexes 2a and 5 (both with the PNP ligand),
the partial atomic charge on the ruthenium center is more
lengths of 6 and 5·BF shows a slightly longer Ru−NO in 6
4
(
1.721 vs 1.708 Å) and a slightly longer N−O bond length
1.175 vs 1.157 Å), Table 3. The difference in P1−C1 (1.779
(
Scheme 5. Protonation of 6 in MeOH Solution
Å) and P2−C7 (1.817 Å) indicates the contribution of a partial
P1C1 double bond to the resonance structure of complex 6.
Next, we explored the reactivity of 6 with water and
methanol. The NMR spectrum of complex 6 in a solution of
toluene saturated with water or in THF containing 10−15%
water (6 is insoluble in water, and adding more than 15% water
to a THF solution of 6 resulted in phase separation) was
identical to the spectrum of 6 in the absence of water, even
upon heating the THF/water solution to 50 °C for 14 h.
D
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−
1
Scheme 6. Free Energy Difference between 5 and 5′ and
between 2 and 2′
IR spectrum appear at 1855 and 1826 cm . The postulated
isomers, 7a and 7b, are probably in equilibrium. Thus, the ratio
of the peaks in the 31P{ H}NMR spectrum changed after
evaporation and replacement of the DCM solvent with EtOH.
A second evaporation of the EtOH and addition of the original
solvent (DCM) restored the original ratio between 7a and 7b.
In addition, in order to eliminate the possibility that outer-
sphere chloride is taking part in the equilibrium, we replaced
1
F
the chloride anion with the BAr anion, resulting in no change
in the spectra of 7a and 7b (but it increased their solubility in
ether).
The geometries of isomers 7a and 7b were optimized using
DFT. The energies in ethanol and benzene for each of the
complexes, relative to the most stable complex, are listed in
Table 5. In benzene, the energy difference between 7a and 7b is
very small (0.09 kcal/mol in favor of 7b). In ethanol, the energy
difference is 2.19 kcal/mol in favor of 7a. Therefore, an
equilibrium between 7a and 7b, as suggested by the
experimental results, is likely.
Table 4. DFT Partial (APT) Charges on Ru
APT charge
Reaction of the mixture of 7a + 7b with 2 equiv of sodium
isopropoxide gave the bent nitrosyl complex 8. Interestingly,
when the reaction was performed in a closed system 8 was not
complex
L
aromatic ligand
dearomatized
1
2
5
6
(PNN ligand)
CO
CO
NO
NO
−0.24
−1.21 (2′)
−0.56 (5)
0.25
a
−0.54 (2a)
0.16 (5′)
−0.49
obtained; hence, it is possible that liberation of H drives the
2
reaction. Perhaps substitution of the chlorides by isopropoxide
followed by β-H elimination yields a dihydride intermediate
which slowly loses H (3 days in refluxing ether) to give a
2
Ru(0) complex analogous to 5 which reacts with chloride to
give the Ru(II) complex 8, Scheme 8.
positive in the NO complex than in the CO complex; in fact,
the charge on the metal in the dearomatized CO complex 2a
Complex 8 gives rise to a singlet at 56.6 ppm in the
P{ H}NMR spectrum, and the phosphine methylene groups
(
5
−0.54) is similar to the charge in the aromatized NO complex
31
1
(−0.56). This is caused by the fact that the nitrosyl complex
of the ligand appear as a doublet at 3.27 ppm (J = 11 Hz) in
PH
is positively charged, and the nitrosyl ligand is a stronger π
acceptor. It is also notable that in the dearomatized Ru(0) NO
complex 6 the charge on Ru is similar to that in the Ru(II) 2a
and the cationic Ru(0) 5.
1
the H NMR spectrum (C symmetry for 8 was observed in the
H NMR due to fast conformational change; for more details
s
1
see DFT calculations below). The NO stretches in the IR
spectrum of the solid (NaCl plate) appear at 1928 and 1679
Synthesis and Properties of PNN Nitrosyl Complexes.
−1
t
cm , indicating the presence of both bent and linear NO in the
solid state (see DFT Calculations below).
Reaction of the PNN ligand (PNN = 2-( Bu PCH )-6-
2
2
(
Et NCH )pyridine) with RuCl (NO)(H O) in ethanol
2 2 3 2 2
Crystals of 8 suitable for X-ray diffraction analysis were
obtained by slow evaporation of ethanol from a concentrated
ethanol solution of 8. The X-ray structure (Figure 5 and Table
6) exhibits a square pyramidal structure with the phosphine
ligand located trans to the tertiary amine, a bent NO (Ru−N−
O angle of 130.2°) located cis to the pyridine-based ligand, and
an equatorial chloride.
followed by solvent evaporation led to a solid which is likely
a mixture of isomers 7a and 7b (Scheme 7). It exhibits two
singlets at 97.0 and 86.8 ppm in CD Cl (integration ratio of
2
2
0
.4:1) or two singlets at 96.2 and 87.0 ppm in EtOH
3
1
1
(
integration ratio of 0.24:1) in the P{ H}NMR spectrum.
The methylene groups of the phosphorus arm of the ligand
appear as multiplets at 3.32 and 3.63 ppm for 7a and at 3.45
1
ppm for 7b (see Experimental Section) in the H NMR
Distances and angles in 8 are similar to those of related
square pyramidal pincer Ru(II) nitrosyl complexes such as
spectrum (diastereotopic methylenes for 7a and nondiaster-
eotopic methylenes for 7b are consistent with the symmetry
across the meridional pincer plane). The NO stretches in the
(
II) t
+
36
[Ru ( Bu PCH SiMe ) N)(NO-linear)(NO-bent)] . The
2
2
2 2
Ru−NO bond distance is 1.837 Å, somewhat shorter than
Scheme 7. Synthesis of Complex 7
E
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present in the solid state (1928 cm− and 1679 cm ), although
1
−1
Table 5. Relative Energies (kcal/mol) of Isomers 7a and 7b
only one compound is observed in solution.
ΔG298, EtOH
ΔG298, C6H6
Complex 8 can also be synthesized by a simpler route
involving RuCl (NO)(H O) and PNN in refluxing ethanol to
7a
0.00
0.09
0.00
3
2
2
7b
2.19
form 7 in situ, which is further reduced to 8 by EtOH and Et N,
3
(
Scheme 10).
Synthesis and Properties of PN N Nitrosyl Complexes.
Next, we set out to prepare complexes of the “long arm” PNN
Scheme 8. Synthesis of Complex 8
2
2
t
ligand: PN N (2-( Bu PCH )-6-(Me NCH CH )pyridine).
2
2
2
2
2
First, we synthesized the Ru(II) dichloride complex 9 by
2
complexation of PN N with RuCl (NO)(H O) (Scheme 11).
3
2
2
The fully characterized complex 9 gives rise to a singlet at
4.3 ppm in the 31P{ H}NMR spectrum, and the phosphorus
1
9
methylene groups of the ligand appear as a double doublet at
1
5
.03 and 4.29 ppm (JHH = 17.1 Hz, JHP = 10.2 Hz) in the H
NMR spectrum. The NO stretch in the IR spectrum appears at
−
1
1
855 cm .
Crystals suitable for X-ray analysis were obtained by slow
evaporation of a concentrated CH Cl solution of 9. The X-ray
2
2
structure of 9 (Figure 6) exhibits an octahedral structure
containing phosphorus atoms trans to the tertiary amine, a
chloride trans to the pyridine ligand, and a linear NO (Ru−N−
O angle of 175.4°) trans to chloride. Bond lengths and angles
of 9 are similar to those of 4 (Table 7).
Comparing 9 to 4, the Ru(II)−NO bond length of 9 (1.744
Å) is shorter than that of 4 (1.775 Å) and the N−O distance in
9
(1.150 Å) is longer then in 4 (1.123 Å). This indicates more
back-donation to the NO ligand of 9. In addition, all Ru−ligand
distances are longer in 9 in comparison to 4.
Ru complex 10 was synthesized in two ways, as outlined in
Scheme 12: (a) reaction of complex 9 with NaO Pr as a hydride
Figure 5. Structure of complex 8 (ellipsoids shown at 50% probability
level). Hydrogen atoms and counteranion are omitted for clarity. t-Bu
and Et groups are presented as wireframe for clarity.
i
source (by β-H elimination after chloride substitution followed
by elimination) resulted in 30% yield and (b) by tandem
reaction in refluxing ethanol in which 9 was formed in situ,
resulting in higher yield (87%).
Table 6. Selected Bond Lengths (Angstroms) and Bond
Angles (degrees) of 8
Ru1−N3
N3−O1
Ru1−P1
Ru1−N1
Ru1−N2
1.837(5)
1.207(7)
2.265(2)
2.033(5)
2.269(5)
Ru1−Cl1
2.420(2)
130.2(4)
150.8(1)
168.9(1)
90.0(2)
The fully characterized complex 10 gives rise to a singlet at
Ru1−N3−O1
P1−Ru1−N2
N1−Ru1−Cl1
N1−Ru1−N3
1
5
6.9 ppm in the 31P{ H}NMR spectrum, and the phosphorus
methylene groups of the ligand appear as a doublet at 3.24 ppm
1
(
JHP = 10.8 Hz) in the H NMR spectrum (the reason we can
1
see C symmetry for 10 in the H NMR is probably due to fast
s
conformational change similar to 8). spectrum appears at 1589
cm , as expected for bent NO.
Dehydrogenative Coupling of Alcohols to Esters
Catalyzed by 6. Catalytic dehydrogenative coupling of
alcohols to esters is of central interest in organic synthesis.
The PNP and PNN pyridine-based ruthenium pincer
the reported Ru(II)−(bent NO) bond length of 1.910 Å for the
−1
(II) t
−
analogous pincer complex [Ru ( Bu PCH SiMe ) N )(NO-
2
2
2 2
+
linear)(NO-bent)] . The Ru−Cl bond is longer in 8 (2.420 Å)
than in 4 (2.300 and 2.333 Å), probably due to fast
conformational changes. DFT calculations on 8 indicate two
square pyramidal isomers, one with a bent NO in the apical
position (8) and another with a linear NO in the equatorial
position (8′) (Scheme 9). These isomers are very close in
energy; in both ethanol and benzene 8′ is slightly more stable
complexes 1 and 2 catalyze dehydrogenative coupling of
1−3
alcohols to esters and H (Scheme 1, eq 1).
Similarly, an
2
acridine-based PNP ruthenium carbonyl pincer-type complex
developed in our laboratory catalyzes (in the presence of base)
by ΔG
= −1.5 kcal/mol.
11
298,sol
conversion of alcohols to esters and H2. We now find that
These calculations are supported by the fact that according to
IR spectroscopy both linear and bent NO complexes are
complex 6 catalyzes this reaction as well. The reaction can be
Scheme 10. Alternative Synthesis of Complex 8
Scheme 9. Complexes 8 and 8′
F
dx.doi.org/10.1021/ic401780p | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Scheme 11. Synthesis of Complex 9
carried out under air, reaching full conversion and quantitative
yield after 12 h. Hexanol was chosen as a typical substrate
(
Scheme 13).
Attempts to catalyze similar reactions under the same
conditions using other complexes described in this work gave
disappointing results (for example, 8 gave 15% conversion of
hexanol to the corresponding acetal (1,1-bis(hexyloxy)hexane)
after 26 h). Therefore, we decided to suspend the inquiry of the
catalytic activity of these complexes for the present time.
CONCLUSION
■
We synthesized and characterized the ruthenium nitrosyl
aromatic complexes 3, 4, 5, 7, 8, 9, and 10 and the
dearomatized ruthenium nitrosyl complex 6. We found that
complex 6 catalyzes the dehydrogenative coupling of hexanol to
form hexyl hexanoate, reaching full conversion under either air
or argon. The nitrosyl complexes adopt the Ru(0) rather than
the Ru(II) oxidization state, in contrast to their carbonyl
analogs. This preference was observed with both aromatized
and dearomatized pincer ligands. DFT calculations show that
the partial charge on the Ru(0) of the nitrosyl complexes is
similar to their Ru(II) carbonyl analogs, suggesting that the
electron density at the metal center plays a major role in
determining the aromatic nature of the ligand and the overall
structure of the complex.
Figure 6. Structure of complex 9 (ellipsoids shown at 50% probability
level). Hydrogen atoms and counteranion are omitted for clarity. t-Bu
and Me groups are presented as wireframe for clarity.
Table 7. Selected Bond Lengths (Å) and Bond Angles (°) in
EXPERIMENTAL SECTION
General Procedures. All experiments with metal complexes and
phosphine ligands were carried out under an atmosphere of purified
nitrogen in a Vacuum Atmospheres glovebox equipped with a MO 40-
■
9
Ru1−N3
N3−O1
Ru1−P1
Ru1−N1
Ru1−N2
Ru1−Cl1
1.744(2)
1.150(3)
2.3940(7)
2.130(2)
2.268(2)
2.3877(7)
Ru1−Cl2
2.3313(6)
175.4(2)
174.46(6)
95.9(1)
Ru1−N3−O1
P1−Ru1−N2
N3−Ru1−N1
N1−Ru1−Cl1
N3−Ru1−Cl2
2
inert gas purifier or using standard Schlenk techniques. All solvents
were reagent grade or better. All nondeuterated solvents were refluxed
over sodium/benzophenone ketyl and distilled under argon
atmosphere. Deuterated solvents were used as received. All solvents
were degassed with argon and kept in the glovebox over 4 Å molecular
sieves. Commercially available reagents were used as received.
173.67(6)
176.29(7)
3
7
RuCl (NO)(PPh )
was prepared according to a literature
3
3 2
Scheme 12. Two Synthetic Routes to Complex 10
1
13
31
procedure. H, C, and P spectra were recorded at 400, 100,162,
and 376 MHz using Bruker AMX-300, AMX-400, and AMX-500
spectrometers. All spectra were recorded at 295 K unless otherwise
noted. H NMR and C{ H} NMR chemical shifts are reported in
ppm downfield from tetramethylsilane and referenced to the residual
signals of an appropriate deuterated solvent. 31P NMR chemical shifts
are reported in ppm downfield from H PO and referenced to an
1
13
1
3
4
external 85% solution of phosphoric acid in D O. ESI-MS spectros-
2
copy was performed by the Department of Chemical Research
Support, Weizmann Institute of Science. The nitrosyl complexes
described in this work were unstable toward light and air, and all
reactions were performed in the dark. Accurate elemental analysis
could not be obtained (elemental analysis results were not
reproducible even when single crystals (of 4) were used from the
same batch). HRMS was determined.
Scheme 13. Dehydrogenative Coupling of Hexanol to Hexyl Hexanoate Catalyzed by 6
G
dx.doi.org/10.1021/ic401780p | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1
2
Synthesis of 3. To a 10 mL flask equipped with a gas inlet were
P(C(CH ) ) ), 33.1 (d, J = 16.3 Hz, P(C(CH ) ) ), 30.2 (d, J
=
CP
3
3
2
CP
3
3
2
t
2
added RuCl (NO)(PPh ) (20 mg, 0.026 mmol), Bu-PNP (10.3 mg,
5 Hz, P(C(CH ) ) ), 29.6 (d, J = 5 Hz, P(C(CH ) ) ). IR: ν N−O
3
3
2
3
3
2
CP
3 3 2
−
1
+
0
.026 mmol), and toluene (1 mL) under nitrogen atmosphere. The
1916.0 cm . HRMS: m/z 527.1909 ((M + H) , calcd m/z 527.1894).
Reversible Protonation of 6 with Methanol (Scheme 5).
Analytically pure 6 (8.6 mg, 0.01636 mmol) was dissolved in MeOH
reaction mixture was stirred under reflux overnight, resulting in red
crystals of 3. The reaction mixture was allowed to cool to ambient
temperature and filtered. Crystals were rinsed with toluene (2 mL)
and pentane (2 mL) and dried under vacuum to give complex 3 as a
3
1
1
(1 mL) under nitrogen atmosphere at room temperature. P{ H}
NMR was taken showing only one peak, at 80.6 ppm, indicating
formation of the cationic complex 5 (presumably with methoxide
counteranion). Solvent was removed under vacuum, and the residue
was dissolved in C D , resulting in full restoration to the starting
material 6 as indicated by NMR. This procedure was repeated three
times using the same sample of 6.
Synthesis of 7. To a solution of RuCl (NO)(H O) (100 mg,
3
1
1
1
red solid in 97% yield. P{ H} NMR (CD Cl ): 66.7 (s). H NMR
2
2
3
3
(
CD Cl ): 8.18 (d, J = 7.8 Hz, 2H, Py-H3, H5), 8.09 (t, 1H, J
=
2
2
HH
HH
2
2
7
4
7
.8 Hz, Py-H4), 4.80 (dt, J = 17 Hz, J = 4.5 Hz, 2H, PCHHPy),
HH HP
6
6
2
2
3
.46 (dt, J = 17 Hz, J = 3.6 Hz, 2H, PCHHPy), 1.60 (d, J =
HP
HH
HP
3
.2 Hz, 18H, PC(CH ) , 1.55 (d, J = 7.2 Hz, 18H, PC(CH ) .
3
3
HP
3 3
1
3
1
C{ H} NMR (CD Cl ): 164.1 (s, Py-C2, C6) 142.9 (s, Py-C4),
2
2
3
2
2
1
1
1
6
25.4 (s, Py-C3, C5), 42.1 (t, J = 2.2 Hz, PC(CH ) ), 41.3 (t, J =
.7 Hz, PC(CH ) ), 38.0 (t, J = 8.7 Hz, PCH Py), 30.7 (bm,
PC(CH ) ). IR: ν N−O 1867 cm . HRMS: m/z 597.1295 (M , calcd
0.366 mmol) in ethanol (5 mL) was added PNN (118 mg, 0.366
mmol) under nitrogen atmosphere. The reaction mixture was stirred
for 5 h at room temperature, after which the solvent was removed
CP
3
3
CP
1
3
3
CP
2
−
1
+
3
3
m/z 597.1271).
under vacuum, the residue was extracted with 5 mL of CH
centrifuged, and the CH Cl solution was filtered and concentrated to
1 mL. Addition of pentane resulted in precipitation of pure 7 in 68%
Cl and
2 2
Synthesis of 4. To an ethereal suspension (4 mL) of 3 (20 mg,
2
2
F
0
.0316 mmol) was added 1 equiv of NaBAr (28 mg, 0.0316 mmol)
31
1
under nitrogen atmosphere. The reaction mixture was stirred for 2 h at
room temperature for reaction completion, and then the NaCl was
filtered off, and the solvent was slowly removed under vacuum, giving
yield. P{ H} NMR (CD Cl ): 97.0 (s, 0.4P, a), 86.8 (s, 1P, b).
P{ H} NMR (EtOH): 96.2 (s, 0.24P, a), 87.0 (s, 1P, b). Two peaks
are observed due to isomers 7a and 7b. H NMR (CD Cl ): 8.30 (m,
1H, Py-H4 a + b,), 8.1 (bs, 1H, Py-H5 a + b), 7.77 (m, 1H, Py-H3 a +
b), 5.01 (bm, 1H, NCHHPy a), 4.78 (bm, 2H, NCH Py b), 4.67 (bm,
1H, NCHHPy a), 3.63 (m, 1H, PyCHHP a), 3.45 (m, 2H, PyCH P b),
3.32 (m, 1H, PyCHHP a), 1.59 (bm, 18H, P(C(CH ) ) a + b), 1.44
2 2
31
1
1
2
2
a red crystal of 4, suitable for X-ray analysis in 70% yield. HRMS: m/z
+
5
97.1272 (M , calcd m/z 597.1271). The rest of the spectra are
2
identical those of 3.
Reaction of 4 with NaBEt H to yield 5·BAr . To a solution of 4
36.5 mg, 0.025 mmol) in THF (5 mL) was added NaBEt H (56 μL,
2
F
3
3 3 2
1
3
1
(
∼
(bm, 2H, N(CH CH ) a + b), 1.25 (bm, 3H, N(CH CH ) . C{ H}
3
2 3 2 2 3 2
1 M solution, 0.05 mmol) under a nitrogen atmosphere at room
NMR (CD Cl ): 162.5 (s, Py-C2 A), 162.2 (s, Py-C2 B) 159.7 (s, Py-
2 2
C6 A), 159.5 (s, Py-C6 B), 143.3 (s, Py-C4 B), 142.7 (s, Py-C4 A),
125.8 (d, J = 8 Hz, Py-C3 A), 125.6 (d, J = 10 Hz, Py-C3 B),
123.3 (s, Py-C5 A), 122.9 (s, Py-C5 B), 67.8 (s, PyCH N A), 64.2 (s,
PyCH N B), 50.5 (s, N(CH CH )(CH CH ), A), 48.5 (s, N-
(CH CH )(CH CH ), A), 47.7 (s, N(CH CH ) ), B), 43.0 (d, J
temperature. The reaction mixture was stirred for 110 min, after which
the solvent was removed under vacuum and the residue was left under
vacuum for 2 h. The residue was extracted with pentane, and pentane
was removed under vacuum to yield pure 5 as a green solid in 10%
yield.
3
3
CP
CP
2
2
2
3
2
3
1
2
3
2
3
2
3
2
CP
F
1
13
1
1
For clarity, signals of BAr are omitted from H and C{ H} NMR.
= 14.9 Hz, P(C(CH ) )(C(CH ) ) A), 42.0 (d, JCP = 14.9 Hz,
3 3 3 3
3
1
1
1
1
P{ H} NMR (CD Cl ): 80.6(s). H NMR (CD Cl ): 7.79 (t, 1H,
P(C(CH ) )(C(CH ) ) A), 41.4 (d, J = 12.7 Hz, P(C(CH ) ) B),
3 3 3 3 CP 3 3 2
2
2
2
2
3J = 7.5 Hz, Py-H4), 7.47 (d, 2H, J = 7.5 Hz, Py-H3, H5), 3.94
3
1
1
HH
HH
38.3 (d, J = 23.3 Hz, PyCH P A), 37.2 (d, J = 24.6 Hz, PyCH2P
CP 2 CP
2
2
(
t, 4H, JPH = 3.5 Hz, Py-CH P), 1.53 (t, 36H, JPH = 7.5 Hz,
P(C(CH ) ) ). C{ H} NMR (CD Cl ): 167.1 (t, J = 6.9 Hz, Py-
B), 31.0 (bs, P(C(CH
3
)
3
)
2
B) 30.1 (s, P(C(CH
) A), 10.6 (s, N(CH
A), 10.3 (s, N(CH CH )(CH CH ) A), 8.3 (s, N((CH CH ) ) B). IR:
3
)
3
) (C(CH
3
)
3
) A),
2
13
1
30.0 (s, P(C(CH
)
)(C(CH
)
CH )(CH
CH
)
3
3
2
2
2
PC
3
3
3
3
2
3
2
3
C2, C6), 142.5 (s, Py-C4), 122.6 (t, JPC = 5.0 Hz, Py-C3, C5), 37.6 (t,
2
3
2
3
2
3 2
+
JPC = 8.8 Hz, P(C(CH ) ) ), 34.8 (t, J = 8.8 Hz, PyCH P), 29.9 (t,
ν N−O 1854.7, 1826.1. HRMS: m/z 524.0961 (M , calcd m/z
3
3
2
PC
2
−1
JPC = 2.7 Hz, P(C(CH ) ) ). IR: ν N−O 1759 cm . HRMS: m/z
27.1901 (M , calcd m/z 527.1894).
524.0938).
3
3 2
+
5
Synthesis of 8 from 7. To an ethereal suspension (3 mL) of 7 (20
mg, 0.048 mmol) at −34 °C was added a solution of iPrONa (7.55
mg, 0.092 mmol) in THF (2 mL) at the same temperature, resulting in
an immediate color change to green. The reaction mixture was stirred
for 40 min at the same temperature, 24 h at ambient temperature, and
3 days under reflux. The reaction was filtered, and the solvent was
removed under vacuum to give pure 8 in 29% yield. Crystals suitable
for X-ray analysis were obtained by slow evaporation of ethanol from a
Synthesis of 5·BF . To a solution of Ru(NO)Cl ·2H O (26 mg,
4
3
2
0
.1 mmol) in ethanol (10 mL) was added t-Bu-PNP (40 mg, 0.1
mmol) and NEt (30.3 mg, 0.3 mmol), and the mixture was heated at
3
7
8 °C for 4 h. Upon cooling to room temperature, the red-purple
solution was taken to dryness under vacuum and the residue was
extracted with THF (3 × 5 mL). To the combined THF solution was
added AgBF (19.5 mg, 0.1 mmol); the mixture was stirred in the dark
4
31
1
for 0.5 h and then filtered. The filtrate was concentrated to 2 mL, and
then 10 mL of diethyl ether was added slowly to precipitate a brown-
red solid of 5·BF (43 mg, 70%). Spectra of 5·BF are identical to
concentrated ethanol solution of 8. P{ H} NMR (C D ): 56.6 (s).
6 6
1
3
H NMR (C D ): 7.75 (d, 1H, J = 7.2 Hz, Py-H3), 7.32 (d, 1H,
6
6
HH
3J = 7.2 Hz, Py-H5), 7.21 (t, 1H, J = 7.2 Hz, Py-H4), 3.80 (s, 2H,
4
4
HH
HH
F
F
those of 5·BAr , except for the signals associated with BAr .
Synthesis of 6. To a solution of 5·BF (125 mg, 0.267 mmol) in
2
3
PyCH N), 3.27 (d, J = 11 Hz, 2H, PCH Py), 2.47 (q, 4H, J = 7
Hz, CH CH N), 1.08 (d, 18H, J = 13 Hz, P(C(CH ) ) ), 0.98 (t,
H, J = 6.9 Hz, NCH CH ). C{ H} NMR (C D ): 160.2 (s, Py-
C6), 154.4 (d, J = 6 Hz, Py-C2) 136.0 (s, Py-C4), 123.6 (s, Py-C5),
20.3 (s, Py-C3), 59.8 (s, PyCH N), 47.3 (s, NCH CH ), 35.9 (d, J
58 Hz, P(C(CH ) ) ), 32.9 (s, J = 58 Hz, PCH Py), 26.6 (bs,
3 3 2 CP 2
P(C(CH ) ) ), 12.1 (s, NCH CH ). IR: ν N−O 1928.3, 1679 cm .
HRMS: m/z 454.1571 (M , calcd m/z 454.1561).
Synthesis of 8 from Ru(NO)Cl ·2H O. To a solution of
Ru(NO)Cl ·2H O (27.2 mg, 0.1 mmol) and PNN (32.2 mg, 0.1
3 2
mmol) in ethanol (3 mL) was added Et N (30.3 mg, 0.3 mmol) under
nitrogen atmosphere, and the reaction mixture was stirred under reflux
for 19 h. The reaction mixture was allowed to cool to ambient
temperature, and the solvent was removed under vacuum. The residue
was extracted with 5 mL of THF and filtered, the solvent was removed
under vacuum, and the residue was extracted with 1 mL of benzene.
Evaporation of the solvent under vacuum gave pure 8 in 18% yield.
2
HP
2
HH
3
PH
13
4
3
2
3 3 2
THF (4 mL) was added LiOH (125 mg, 5.22 mmol) under nitrogen
atmosphere at room temperature. The suspended reaction mixture was
stirred for 1 h and 30 min, after which the solvent was removed under
vacuum. The residue was extracted with pentane (3 × 5 mL), and the
solvent was removed under vacuum to yield pure 6 as a black/blue
solid in 63% yield. Single crystals of 6 suitable for X-ray diffraction
3
1
6
HH
2
3
6
6
2
CP
1
1
=
2 2 3 CP
1
−1
3
3
2
2
3
+
31
1
were obtained by slow evaporation of an etheral solution. P{ H}
3
2
2
2
NMR (C D ): 78.7 (d, 1P, J = 200 Hz), 74.9 (d, 1P, J = 200 Hz).
6
6
PP
PP
1
H NMR (C D ): 6.06 (bd, 2H, Py-H3 + H5), 5.03 (m, 1H, Py-H5),
6
6
3
2
2
3
.81 (d, J = 3.6 Hz, 1H, PyCHP), 2.81 (d, J = 8.7 Hz, 2H,
H,P HP
3
PCH Py), 1.63 (d, 18H, J = 12.6 Hz, P(C(CH ) ) ), 1.27 (d, 18H,
2
PH
3 3 2
3
13
1
JPH = 12.6 Hz, P(C(CH ) ) ). C{ H} NMR (toluene-d ): 173.2 (d,
3
3
2
8
2JCP = 21.4, 5 Hz, Py-C2), 160.8 (m, Py-C6) 131.7 (s, Py-C4), 116.4
3
3
1
(
4
d, J = 18.8 Py-C3), 98.4 (d, J = 11.3 Py-C5), 67.8 (d, J
9.0, PyCHP), 37.4 (d, J = 22.6, PyCH P), 36.2 (d, J = 15.1 Hz,
=
CP
CP
CP
1
1
CP 2 CP
H
dx.doi.org/10.1021/ic401780p | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
a
Table 8. Experimental Data Regarding X-ray Diffraction
4
5·BF4
6
8
9
formula
C H Cl N OP Ru + C H BF
C H N OP Ru + C H N OP Ru
C H ClN OPRu
2C H Cl N OPRu + C NORu
18 33 2 3 l5
+ 2CH Cl2
2
2
+
3
43
2
2
2
32 12
24
23 43
BF4
2
2
23 42
2
2
19 35
3
C H O
4
10
diffractometer
cryst description
cryst size, mm3
fw, g mol−
space group
cryst syst
a, Å
Bruker APEX - II
green plate
Bruker APEX - II
orange blue prism
Nonius
Bruker APEX - II
red needle
Nonius
orange prism
brown prism
0.50 × 0.30 × 0.10
1534.85
0.25 × 0.20 × 0.18 0.08x 0.05 × 0.05 0.35 × 0.13 × 0.11 0.45 × 0.15 × 0.08
1
613.41
P1
525.60
488.99
1499.01
P1
P2 /c
1
̅
Pbca
P3 21
1
̅
monoclinic
13.7611(5)
23.5911(7)
20.3726(6)
triclinic
8.0668(5)
12.3986(7)
15.5505(8)
108.203(3)
102.593(3)
92.010(3)
1432.98(14)
2
orthorhombic
11.908(2)
15.530(3)
28.001(6)
trigonal
triclinic
14.945(2)
8.30100(10)
10.90700(10)
16.9480(2)
92.6710(10)
95.3230(10)
106.7980(10)
1458.30(3)
1
b, Å
c, Å
20.484(4)
α, deg
β, deg
97.092(2)
γ, deg
cell vol., Å3
6563.1(4)
4
5178.3(18)
8
3962.3(15)
6
Z
density(calcd, g cm−3) 1.553
1.422
1.348
1.230
1.707
μ, mm−
1
0.480
0.703
0.745
0.766
1.459
no. of reflns
no. of unique reflns
Θmax
121 182
25 096
33.29
25 268
42 864
6401
33 334
5530
26 236
5327
6650
25.50
28.28
26.73
27.48
Rint
0.0528
1016(48)
0.0498
0.0431
274(0)
0.0620
238(0)
0.0326
no. of params
368(35)
310(0)
(restraints)
final R for data with I > 0.0531
σ(I)
0.0485
0.0490
0.0483
0.0332
2
final R for all data
0.0982
1.024
0.0745
1.068
0.0740
1.072
0.0640
0.871
0.0410
1.070
goodness of fit
a
Crystals were coated in Paratone oil and mounted on a fiber loop.
Synthesis of 9. To a solution of Ru(NO)Cl ·2H O (136.5 mg, 0.5
the same temperature, 24 h at ambient temperature, and 65 °C
overnight. The reaction mixture was allowed to cool to ambient
temperature and then filtered, and the solvent was removed under
3
2
2
mmol) in ethanol (7 mL) was added PN N (154 mg, 0.5 mmol) under
nitrogen atmosphere, and the mixture was stirred for 1.5 h at room
temperature. Solvent was removed under vacuum, and the residue was
extracted with 100 mL of CH Cl and filtered. Solvent was removed
31
1
vacuum to yield pure 10 in 30% yield. P{ H} NMR (C D ): 56.9 (s).
6
6
1
3
2
2
H NMR (C D ): 7.68 (d, 1H, J = 7.8 Hz, Py-H3), 7.12 (t, 1H, J
= 7.8 Hz, Py-H4), 6.69 (d, 1H, J = 7.8 Hz, Py-H5), 3.24 (d, J
6
6
HH
HH
3
2
under vacuum, and the residue was washed with CH Cl (2 mL) to
=
2
2
HH
HP
3
give pure 9 in 62% yield. Crystals suitable for X-ray analysis were
obtained by slow evaporation of a concentrated CH Cl solution of 9.
10.8 Hz, 2H, PCH Py), 2.94 (t, 2H, J = 7.3 Hz, PyCH CH N),
2 HH 2 2
3
2
2
2.72 (t, 2H, J = 7.3 Hz, PyCH CH N), 2.15 (s, 6H, NCH ), 1.15
HH
2
2
3
3
13
1
Single crystals of 9 used for X-ray analysis were obtained with
(d, 18H, J = 12.9 Hz, P(C(CH ) ) ). C{ H} NMR (C D ): 159.7
PH 3 3 2 6 6
2
−
31
1
1
RuCl NO as counteranion. P{ H} NMR (CD Cl ): 94.3 (s). H
5
2
2
(s, Py-C2) 154.9 (s, Py-C6), 135.7 (s, Py-C4), 123.0 (s, Py-C5), 120.5
3
NMR (CD Cl ): 8.40 (d, 1H, J = 7.5 Hz, Py-H3), 8.06 (t, 1H, J
7.5 Hz, Py-H4), 7.70 (d, 1H, J = 7.5 Hz, Py-H5), 5.03 (dd, J
17.1 Hz, J = 10.2 Hz, 1H, PCHHPy), 4.29 (dd, J = 17.1 Hz,
HP HH
2
2
HH
HH
(s, Py-C3), 67.5 (s, PyCH CH N), 45.5 (s, NCH ), 45.2 (s, NCH ),
2
2
3
3
3
2
=
HH
HH
36.1 (s, P(C(CH ) ) ), 35.7 (s, P(C(CH ) ) ), 33.1 (m, PCH Py),
3 3 2 3 3 2 2
2
2
=
29.9 (s, PyCH CH N), 27.2 (bs, P(C(CH ) ) ). IR: ν N−O 1589.1
−1 +
2
2
3 3 2
2
JHP = 10.2 Hz, 1H, PCHHPy), 3.65 (m, 1H, PyCHHCH N), 3.43 (m,
2
cm . MS: m/z 475.13 (M , calcd m/z 475.11). HRMS: m/z 440.1418
3
− +
1
H, PyCHHCH N), 3.04 (d, 3H, J = 2 Hz, NCH ), 2.96 (m, 1H,
((M − Cl ) , calcd m/z 440.1405).
2
HP
3
PyCH CHHN), 2.84 (m, 4H, PyCH CHHN and NCH ), 1.67 (d, 9H,
Synthesis of 10 from Ru(NO)Cl ·2H O. To a solution of
2
2
3
3
2
3
3
2
JPH = 15.5 Hz, P(C(CH ) ) ), 1.37 (d, 9H, JPH = 13 Hz,
P(C(CH ) ) ). H{ P} NMR (CD Cl ): 8.40 (d, 1H, J = 7.5
Hz, Py-H3), 8.06 (t, 1H, J = 7.5 Hz, Py-H4), 7.70 (d, 1H, J = 7.5
Hz, Py-H5), 5.09 (d, J = 17.1 Hz, 1H, NCHHPy), 4.34 (d, J
Ru(NO)Cl ·2H O (136.5 mg, 0.5 mmol) and PN N (154 mg, 0.5
3 2
3
3
2
1
31
3
mmol) in ethanol (15 mL) was added Et N (0.506 g, 5 mmol) under
3
3
2
2
2
HH
3
3
nitrogen atmosphere. The reaction mixture was stirred under reflux for
3 h. Solvent was removed under vacuum and remained under vacuum
for 2 h. THF (15 mL) was added, and the reaction mixture was stirred
under argon overnight (to allow hydrogen escape). Solvent was
removed under vacuum, and crude 10 was extracted once with ether
(15 mL) and twice with benzene (15 mL). The ethereal and benzene
solutions were combined, filtered, and evaporated to yield pure 10 in
87% yield.
Catalytic Dehydrogenation of Alcohols. A solution of 6 (13.1
mg, 0.025 mmol) and n-hexanol (255.4 mg, 5 mmol) was stirred at
reflux under argon atmosphere in an open system for 12 h to yield
pure hexyl hexanoate in quantitative yield.
HH
HH
2
2
=
HH
HH
1
7.1 Hz, 1H, PCHHPy), 3.65 (m, 1H, PyCHHCH N), 3.51 (m, 1H,
2
PyCHHCH N), 3.10 (s, 3H, NCH ), 3.04−2.94 (m, 4H,
2
3
PyCH CHHN and PyCH CHHN), 2.84 (s, 3H, NCH ), 1.67 (bd,
2
2
3
3
13
1
9
H, J = 7 Hz, P(C(CH ) ) ), 1.39 (bs, 9H, P(C(CH ) ) ). C{ H}
PH 3 3 2 3 3 2
NMR (CD Cl ): 164.4 (s, Py-C2) 160.3 (s, Py-C6), 142.3 (s, Py-C4),
2
2
3
1
26.6 (s, Py-C5), 126.1 (d, JCP = 9 Hz, Py-C3), 58.5 (s,
1
PyCH CH N), 49.6 (s, NCH ), 49.2 (s, NCH ), 40.9 (d, J = 5.6
2
2
3
3
CP
1
Hz, P(C(CH ) ) ), 40.8 (d, J = 5.6 Hz, P(C(CH ) ) ), 36.0 (s,
3
3
2
CP
3 3 2
1
PyCH CH N), 35.7 (d, JCP = 24 Hz, PCH Py), 30.4 (bs,
2
2
2
−1
P(C(CH ) ) ), 30.1 (bs, P(C(CH ) ) ). IR: ν N−O 1854.7 cm .
3
3
2
3 3 2
+
HRMS: m/z 510.0792 (M , calcd m/z 510.0782).
Catalytic Dehydrogenative Coupling of Hexanol to Ethyl
Acetate under Air. A solution of 6 (13.1 mg, 0.025 mmol), n-
hexanol (255.4 mg, 5 mmol), and m-xylene (1.5 mL) was stirred at
reflux under air in an open system overnight to yield hexyl hexanoate
Synthesis of 10 from 9. A THF solution (2 mL) of iPrONa (20
mg, 0.0367 mmol) was added to a THF solution (3 mL) of 9 (20 mg,
.0367 mmol) at −34 °C. The reaction mixture was stirred for 1 h at
0
I
dx.doi.org/10.1021/ic401780p | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
in quantitative yield. According to GC-MS a trace of hexanal was also
formed (>0.5%).
ACKNOWLEDGMENTS
■
This research was supported by the European Research Council
under the FP7 framework (ERC No 246837). D.M. is the
holder of the Israel Matz Professorial Chair of Organic
Chemistry.
Computational Details. All calculations were carried out using
3
8
39
Gaussian 03 Revision E.01 and Gaussian 09 Revision C.01. The
40
former was locally modified with the MNGFM patch; this patch
from the University of Minnesota adds the Minnesota-06 family of
DFT exchange-correlation functionals to the commercial version. Two
members of the Minnesota-06 family of DFT functional were used:
M06, a meta-hybrid functional containing 27% HF exchange, and
41
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4
(
1
(
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