Acceptorless dehydrogenation of alcohols on a diruthenium(II,II) platform

Article abstract of DOI:10.1021/acs.organomet.6b00085

The diruthenium(II,II) complex [Ru₂(L¹)(OAc)₃]Cl (1), spanned by a naphthyridine-diimine ligand and bridged by three acetates, has been synthesized. The catalytic efficacy of complex 1 has been evaluated for the acceptorless dehydrogenation (AD) of alcohols and for the dehydrogenative coupling reactions of alcohols with Wittig reagents. The diruthenium(II,II) complex is an excellent catalyst for AD of a diverse range of alcohols, and it is shown to be particularly effective for the conversion of primary alcohols to the corresponding aldehydes without undesired side products such as esters. Triphenylphosphonium ylides in a one-pot reaction with alcohols afforded the corresponding olefins in high yields with excellent E selectivity. The liberated dihydrogen gas was identified and measured to be 1 equiv with respect to alcohol. Deuteration studies with PhCD₂OH revealed the absence of isotope scrambling in the product, indicating the involvement of a Ru-monohydride intermediate. Kinetic studies and DFT calculations suggest a low-energy bimetallic β-hydride elimination pathway where rate-limiting intramolecular proton transfer from alcohol to metal-bound hydride constitutes the dehydrogenation step. The general utility of metal-metal bonded compounds for alcohol AD and subsequent coupling reactions is demonstrated here.

Full text of DOI:10.1021/acs.organomet.6b00085

Article
pubs.acs.org/Organometallics
Acceptorless Dehydrogenation of Alcohols on a Diruthenium(II,II)
Platform
Indranil Dutta, Abir Sarbajna, Pragati Pandey, S. M. Wahidur Rahaman, Kuldeep Singh,
and Jitendra K. Bera*
Department of Chemistry and Center for Environmental Sciences and Engineering, Indian Institute of Technology Kanpur, Kanpur
208016, India
S
* Supporting Information
ABSTRACT: The diruthenium(II,II) complex [Ru2(L1)(OAc)3]Cl (1), spanned by a
naphthyridine-diimine ligand and bridged by three acetates, has been synthesized. The
catalytic efficacy of complex 1 has been evaluated for the acceptorless dehydrogenation
(AD) of alcohols and for the dehydrogenative coupling reactions of alcohols with
Wittig reagents. The diruthenium(II,II) complex is an excellent catalyst for AD of a
diverse range of alcohols, and it is shown to be particularly effective for the conversion
of primary alcohols to the corresponding aldehydes without undesired side products
such as esters. Triphenylphosphonium ylides in a one-pot reaction with alcohols
afforded the corresponding olefins in high yields with excellent E selectivity. The
liberated dihydrogen gas was identified and measured to be 1 equiv with respect to
alcohol. Deuteration studies with PhCD2OH revealed the absence of isotope
scrambling in the product, indicating the involvement of a Ru-monohydride
intermediate. Kinetic studies and DFT calculations suggest a low-energy bimetallic
β-hydride elimination pathway where rate-limiting intramolecular proton transfer from
alcohol to metal-bound hydride constitutes the dehydrogenation step. The general utility of metal−metal bonded compounds for
alcohol AD and subsequent coupling reactions is demonstrated here.
environmentally benign synthetic methodology.8 Several cata-
INTRODUCTION
■
lysts based on N-heterocyclic carbene and phosphine ligands
The prospect of cooperative participation of metal ions renders
have been reported for AD reactions.9 The use of a metal−ligand
the bimetallic complexes as potential catalysts for organic
cooperation strategy in the ligand design has led to considerable
transformations.1 Metal−metal bonded complexes are partic-
improvement in the reaction conditions and selectivity.10
ularly interesting because of enforced proximity between the
However, these studies have focused primarily on a single
metals and the ability of the dimetal core to attain valence
metal center. A key step in the alcohol AD is β-hydride
delocalization.2 Elementary oxidative addition and reductive
elimination of a metal−alkoxide intermediate that proceeds via a
elimination processes are more favored on a bimetallic platform
four-membered agostic species (Scheme 1a).11 A metal−metal
than on a single-metal entity.3 Metal−metal singly bonded
bond provides an interesting possibility of an alternative pathway
dirhodium(II,II) systems are the most prominent catalysts for a
on a bimetallic platform (Scheme 1b). To assess this proposal, we
wide variety of organic reactions.4 Although the reactions almost
exclusively take place at one of the axial sites, the second metal
plays a significant role. A 3c/4e bonding manifold has been
proposed to explain the greater density of electronic states and
Scheme 1. β-Hydride Elimination on (a) Monometallic and
(b) Bimetallic Platforms
consequently diverse reactivity.5 Well-defined stoichiometric
reactions of small organic and inorganic molecules across the
metal−metal bonds have been widely reported.6 Catalytic
transformations on a bimetal platform utilizing equatorial sites
have been relatively less explored.7 Suitable ligands capable of
holding two metals in close proximity and accommodating
structural and electronic changes during the catalytic cycle are
vital to exploit the benefit of bimetallic cooperativity.
Acceptorless dehydrogenation (AD) is essentially a reaction
that removes one hydrogen molecule from ubiquitous yet
Special Issue: Organometallics in Asia
considerably less reactive alcohols to form carbonylsa more
potent synthon. Hydrogen is liberated without the use of
stoichiometric acceptor/oxidant, making AD a green and
Received: February 2, 2016
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.6b00085
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
have designed a diruthenium(II,II) acetate-bridged complex
incorporating a crescent-shaped naphthyridine-diimine ligand
and evaluated its catalytic utility for the AD of alcohols. The
catalyst is highly efficient for a range of alcohols and particularly
effective for primary alcohols, affording solely the corresponding
aldehydes. The AD methodology has been extended to the
catalytic olefination of alcohols. Mechanistic studies and DFT
calculations suggest a bimetallic pathway during the catalytic
cycle.
tetradentate ligand L1 ensures that two acetate units are disposed
opposite to each other, whereas the third acetate is trans to the
naphthyridine unit. The Ru1−Ru2 distance is 2.2953(8) Å and is
consistent with those in similar diruthenium(II,II) complexes.13
The imine nitrogens (axial) make longer Ru1−N3 (2.297(6) Å)
and Ru2−N4 (2.278(6) Å) bond distances in comparison to
naphthyridine nitrogens at the equatorial sites (Ru1−N1 =
2.019(6) Å and Ru2−N2 = 2.023(6) Å).
ESI-MS exhibits a signal at m/z 800.0799, which is assigned to
1
[1 − Cl]+ (Figure 2). H NMR signals of 1 are broad and
RESULTS AND DISCUSSION
■
Syntheses and Structures. Synthesis of the naphthyridine-
diimine ligand 2,7-bis(N-mesitylmethylimino)-1,8-naphthyri-
dine (L1) was achieved by condensation of 1,8-napththyridine-
2,7-dicarbaldehyde with mesitylamine (Scheme S1 in the
Supporting Information). Treatment of L1 with Ru2(OAc)4Cl
in a 1:1 molar ratio in MeOH afforded [Ru2(L1)(OAc)3]Cl (1)
as a dark green solid in 79% yield (Scheme 2). A single-electron
5+
4+
reduction of Ru2 to Ru2 in methanol is consistent with the
literature reports.12
Scheme 2. Synthesis of Complex 1
Figure 2. Simulated (red line) and experimental mass distributions
(black line) for [1 − Cl]+ at m/z 800.0799 (z = 1).
featureless because of the paramagnetic nature of the complex.12c
The UV−vis spectrum of 1 shows intense absorption at 331 nm
(ϵ = 12000 M−1 cm−1, assigned to intraligand transitions) with
the appearance of a shoulder at 425 nm possibly due to
transitions from [Ru-Ru] dπ−dπ to ligand acceptor orbitals
(Figure S3 in the Supporting Information). Two additional
absorptions at 675 nm (ϵ = 6700 M−1 cm−1) and at 740 nm are
attributed to metal to ligand transitions. When a dichloro-
methane solution of 1 is excited at 331 nm, blue emissions are
observed at 406 and 428 nm (Figure S4 in the Supporting
Information). The cyclic voltammogram of 1 in 0.1 M TBAP/
acetonitrile shows a reversible one-electron, metal-centered
oxidation at 0.98 V vs Ag/AgCl (Figure S5 in the Supporting
Information). The oxidation observed for 1 represents the
formation of a formally mixed valence [Ru2]5+ species stable on
the cyclic voltammetry time scale.12a,c,14 The high potential of the
metal-based oxidation indicates a greater stability of the [Ru2]4+
relative to that of the [Ru2]5+ core in the presence of L1. Free L1
shows a single reversible two-electron reduction at −1.29 V,
which is split into two reversible one-electron reductions in 1 at
−0.32 and −1.16 V, indicating significant contribution from the
metal d orbitals. The effective magnetic moment of powdered 1
at 295 K is 2.81 μB, corresponding to two unpaired electrons per
molecule and is consistent with a σ2π4δ2δ*2π*2 electronic
configuration.12a,14
The molecular structure of 1 was confirmed by X-ray
crystallography, which revealed two very similar molecules in
the asymmetric unit. The salient features of only one molecule
are discussed here. The diruthenium(II,II) core is spanned by the
crescent-shaped L1, and three additional acetate ligands bridge
between the metal centers (Figure 1). Two imine nitrogen atoms
of L1 occupy sites trans to the Ru−Ru double bond. The
Catalytic Studies. A few reports of alcohol dehydrogenation
reactions on a diruthenium platform using O2 as oxidant have
appeared in the literature. Naota et al. reported that the aerobic
oxidation of alcohols in water could be performed efficiently in
the presence of a catalytic amount of Ru2(μ-OAc)3(μ-CO3)
under 1 atm of O2.15 The Tokii group synthesized phosphinato-
bridged diruthenium complexes and tested their catalytic
efficiency to oxidize cinnamyl alcohol under 1 atm of O2.16
The oxidation of alcohol was also achieved when iodide-bridged
diruthenium complexes were employed in the presence of
Figure 1. Molecular structure (40% probability thermal ellipsoids) of
the cationic unit in 1 with important atoms labeled. Hydrogen atoms are
omitted for the sake of clarity. Selected bond lengths (Å) and angles
(deg): Ru1−Ru2 2.2953(8), Ru2−N2 2.023(6), Ru2−O4 2.061(5),
Ru2−N4 2.278(6), Ru1−N1 2.019(6), Ru1−O3 2.072(5), Ru1−N3
2.297(6); N2−Ru2−O4 179.3(2), N2−Ru2−N4 74.7(2), O4−Ru2−
N4 105.0(2), N2−Ru2−Ru1 90.83(17), O4−Ru2−Ru1 89.40(14),
N4−Ru2−Ru1 163.13(15), N1−Ru1−O3 178.1(2), N1−Ru1−Ru2
89.61(17), O3−Ru1−Ru2 89.00(14), N1−Ru1−N3 75.2(2), O3−
Ru1−N3 106.2(2), Ru2−Ru1−N3 164.77(15).
B
DOI: 10.1021/acs.organomet.6b00085
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Ag2O.17 These studies, however, use oxidants, are limited in
substrate scope, and do not reflect on the mechanistic
implications. Complex 1 was tested for the acceptorless
dehydrogenation (AD) of benzyl alcohol at 1 mol % catalyst
loading in the presence of 10 mol % of KOH, which afforded
benzaldehyde in 89% yield (Table 1). Optimization studies
showed that KOH was the best choice among a variety of bases
(Table S2, entry 2, in the Supporting Information). The reaction
was not efficient at lower temperatures, and the best results were
obtained in toluene at 70 °C. Increasing the catalyst loading or
temperature did not affect the progress of the reaction.
a
Table 1. Acceptorless Dehydrogenation of Alcohol by 1
The substrate scope was then examined under the optimized
conditions. Electron-rich p-methoxybenzyl alcohol and p-
methylbenzyl alcohol gave excellent yields (93−98%; entries
1a,b) in comparison to benzyl alcohol (89%; Table 1, entry 1c).
However, electron-withdrawing groups attached to benzyl
alcohol reduced the yield of the corresponding aldehyde (61−
74%; entries 1d−f). The substrate scope was then extended to
polyaromatic and heterocyclic functionalized alcohols, and they
showed appreciable yields (80−97%; entries 1g−k). Diols
afforded corresponding lactones (86−94%, entries 1l,m) in
good yields. The reaction was extended to aliphatic alcohols such
as n-hexanol and n-octanol and showed moderate yields (45−
65%; entries 1n,o) after extending the reaction time to 24 h.
Natural products such as carveol and geraniol were also tested
under AD conditions, and they gave 42−48% yields of the
corresponding aldehyde (entries 1p,q). A significant amount of
hydrogenated products (15−20%) were also observed, which
could be accounted for on the basis of evolved hydrogen during
the reaction.
Unlike primary alcohols, secondary alcohols were poorly
dehydrogenated (38−45%; Table 1, entries 1r−t) to the
corresponding ketones. This is in contrast to reports where
secondary alcohols were dehydrogenated easily owing to their
low redox potentials.18 Furthermore, a review of literature
reports reveals that AD of primary alcohols invariably produces
esters as major products by a hemiacetalyzation followed by
dehydrogenation or by a Tischenko reaction.19 No such side
products were observed for the diruthenium catalyst. Catalyst 1 is
clearly a superior alternative for the AD of primary alcohols.
AD of alcohol to aldehyde is accompanied by the concomitant
release of one molecule of hydrogen (Scheme 3). A volumetric
quantitative analysis of benzyl alcohol dehydrogenation using a
gas buret revealed near-quantitative formation of hydrogen
(∼92% of theoretical yield; Figure S6 in the Supporting
Information). The evolved hydrogen was identified by matching
the retention time with an authentic sample using a thermal
detector in GC. In another experiment, the AD reaction was
conducted in a flask that was connected through a rubber tube to
a second flask in which styrene and a catalytic amount of
RhCl(PPh3)3 in benzene were placed. After the reaction was
completed, ethylbenzene was produced in 76% yield in the
second flask, demonstrating that the hydrogen gas generated in
the AD reaction is responsible for styrene reduction (Scheme S2
and Figure S7 in the Supporting Information). This dual reaction
authenticated that hydrogen is produced during the course of the
reaction.10c When the AD reaction was done using benzyl
alcohol-α,α-d2 (PhCD2OH), GC-MS analysis of the product
showed a single peak at m/z 107, indicating monodeuterated
ethylbenzene formed by the in situ generated HD gas (Scheme
S3 and Figure S8 in the Supporting Information).
a
Conditions: 1 mmol of alcohol, 0.01 mmol of 1, 0.01 mol of KOH, 70
b
°C in toluene. Yields were determined by GC using 1 mmol of
dodecane as internal standard. A combined 15% yield of
monohydrogenated and dihydrogenated aldehydes (1:1). A com-
bined 20% yield of monohydrogenated and dihydrogenated aldehydes
c
d
(1:1).
Alcohols are common starting materials for many chemical
reactions, although they are largely unreactive. A convenient
approach toward alcohol activation/utilization is AD to a more
reactive carbonyl group.8 Acceptorless dehydrogenative coupling
C
DOI: 10.1021/acs.organomet.6b00085
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
mate, and only trace amounts of the Z isomer were present. The
substrate scope of the reaction was examined. Electron-rich p-
methoxybenzyl alcohol and p-methylbenzyl alcohol showed
better yields (81−88%; entries 2b,c), but in the presence of an
electron-withdrawing group such as p-nitrobenzyl alcohol, a
lesser yield was obtained (66%; entry 2d). However, the
selectivity of the reaction improved, yielding E products
exclusively. The reaction was expanded to another Wittig reagent
(triphenylphosphonium ethoxycarbonylmethylide), and similar
trends were obtained (entries 2f−i). Heterocyclic functionalized
alcohols such as 2-methyl-6-pyridinemethanol and ferrocenyl-
methyl alcohol were also notably tolerated under the reaction
conditions (entries 2e,j,k) to provide the corresponding (E)-
alkenes. Importantly, catalyst 1 exhibited higher E selectivity in
comparison with other catalysts.22
An AD reaction with Ru2(OAc)4Cl, having an accessible axial
site, yielded only 30% of benzaldehyde under identical reaction
conditions. The presence of a vacant axial site does not
necessarily lead to product formation. Rather, a suitably designed
framework renders trans ligands labile, and consequently those
equatorial sites can be accessed. We propose a mechanism that
involves both metals, and the reaction proceeds on the equatorial
platform (Scheme 4). Initially, the alkoxide moiety replaces the
Scheme 3. Alcohol Dehydrogenation and Olefination
(ADHC) reactions offer environmentally benign synthetic
routes for the preparation of a plethora of useful products such
as esters, amides, imines, and heterocycles by the direct reaction
of alcohol with an appropriate coupling reagent.20 Direct
reaction of an ylide/Wittig reagent with an alcohol to selectively
form an olefin, with the liberation of hydrogen gas and avoidance
of the use of oxidants, is a useful carbon−carbon bond forming
reaction (Scheme 3). Alkanes were obtained as major products
when iridium or ruthenium catalysts were used for similar
reactions.21 The product formation was explained on the basis of
hydrogenation of generated alkenes with the concomitantly
evolved hydrogen. The Milstein group has recently reported the
olefination of alcohols with Wittig salt precursors using an
Ru(II)-PNN pincer catalyst in an open system that allowed the
escape of hydrogen for the selective synthesis of alkenes.22
Catalyst 1 performs the same task with equal efficiency but at a
significantly lower temperature.
Scheme 4. Proposed Mechanistic Cycle for the AD Reaction
A mixture of benzyl alcohol, 1 mol % of 1, 10 mol % of KOH,
and triphenylphosphonium methoxycarbonylmethylide (Wittig
reagent, 1.5 equiv) was placed in a single vessel and heated to 70
°C in toluene for 6 h. Isolated yields were 80% (Table 2, entry
2a). NMR analysis showed predominantly (E)-methyl cinna-
Table 2. Catalytic Olefination of Alcohols by 1 using Wittig
a
Reagent
acetate group trans to the naphthyridine. A bimetallic β-hydride
elimination generates a Ru-hydride intermediate with the
concurrent formation of aldehyde. The aldehyde is extruded,
and an alcohol molecule binds to the metal. The catalytic cycle is
closed via a dehydrogenation step that involves an intramolecular
proton transfer from alcohol to the metal-bound hydride.
Kinetic Studies. To gain support for the proposed
mechanism, kinetic studies were performed. The initial rate of
reaction was monitored to determine the order with respect to
catalyst 1. Reactions were performed with varying concentrations
of 1 and equimolar amounts of benzyl alcohol and dodecane
(internal standard). The initial rate varied linearly with the
catalyst concentration, and the reaction was found to be first
order with respect to 1 (Figure 3a). Furthermore, equimolar
amounts of benzyl alcohol and dodecane (nalcohol = ndodecane) were
mixed with 1 mol % of catalyst 1 in 3 mL of toluene. Aliquots of
0.2 mL were taken out at regular time intervals, and the amount
of unreacted alcohol was measured using GC-MS against
dodecane. According to the integrated rate law for a reaction
of the type A → B with the restriction [A] = 1 and [B] = 0 at t = 0,
the ln[A] vs time plot fitted well to a first-order kinetics (Figure
3b). Both of these experiments suggest the involvement of
catalyst 1 and alcohol, one molecule each, in the rate-determining
a
Conditions: 1 mmol of alcohol, 0.01 mmol of 1, 0.01 mol of KOH,
1.5 mmol of Wittig reagent, 3 mL of toluene, 70 °C. All yields are
reported on isolation.
D
DOI: 10.1021/acs.organomet.6b00085
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
the slower steps of the reaction. The rate of the reaction was 4.94
0.02 times slower when PhCH2OD was used as a substrate
instead of PhCH2OH (Figure 4). The high kO−H/kO−D value
suggests that hydrogen elimination during the final stage of the
catalytic cycle is likely to be the rate-limiting step.
DFT Studies. DFT calculations at the M06 level of theory
were carried out to gain insight into the reaction pathway. All
DFT optimized structures of the intermediates and transition
states along with the energy profile of the reaction (kcal/mol) are
presented in Figures 5 and 6, respectively. A simplified system
Figure 3. (a) Dependence of initial rate on 1 and (b) decay of benzyl
alcohol vs time. Data are averaged over three runs.
step. As one molecule of the catalyst 1 consists of two ruthenium
centers, it is reasonable to assume that the reaction takes place on
the bimetallic assembly.23 Close proximity between the metals
aided by the ligand architecture allows the second metal to
participate in the β-hydride elimination step.
Deuteration Studies. To garner further support in favor of
the proposed mechanism, isotope scrambling studies were
carried out with deuterated alcohol. A model AD reaction in
toluene-d8 did not afford deuterated product, thus ruling out the
possibility of isotope scrambling from the solvent. Reaction of
PhCD2OH showed deuterated benzaldehyde as the major
product (92/8 D/H observed by GC-MS analysis; Figure S9 in
the Supporting Information). An AD mechanism for a
monometal catalyst typically involves a RuII-dihydride species
generated by a sequence of elementary β-hydride elimination/
reductive elimination reactions (Scheme S4 in the Supporting
Information).24 Such a process necessarily leads to hydrogen
scrambling in the product. For example, for a Ru(II) catalyst
bearing an N-heterocyclic carbene based ligand, 42% hydrogen
incorporation was observed in deuterated imine products.25 The
absence of significant isotope scrambling for catalyst 1 strongly
suggests the intermediacy of a Ru-monohydride intermediate,
offering support to the proposed mechanism.26
Figure 5. DFT optimized structures of all intermediates and transition
states in the AD mechanism.
Kinetic Isotope Effects. The involvement of C−H bond
breaking in the rate-determining step of the catalysis is indicated
by the intermolecular kinetic isotope effect (KIE).27 A direct
comparison of two reactions, (a) PhCH2OH in toluene and (b)
PhCD2OH in toluene-d8, showed kC−H/kC−D = 2.71
(Figure 4). This proved that the C−H bond breaking is one of
0.04
Figure 6. Computed reaction profile for AD by catalyst 1. Energies are
shown in kcal/mol relative to A. Values in parentheses represent
activation barriers for the corresponding transition states.
was chosen where the mesityl group was replaced by methyl and
bridging acetates were replaced by formates. Methanol was
considered as the substrate to reduce the computational cost.
Replacement of one of the bridging formates trans to the
naphthyridine by alkoxide produces intermediate A. The
optimized structure B was subsequently computed where one
of the H atoms of the alkoxide is engaged in an agostic interaction
with the second ruthenium center.28 The computed Ru2···H1
distance is 2.04 Å, comparable to metal−hydrogen distances in
agostic complexes.29 Subsequent β-hydride elimination leads to
the metal−hydride intermediate C, which proceeds via the
transition state TSBC (ΔG⧧ = 12.42 kcal/mol, Figure 6). The
TSBC has a single imaginary frequency of 359i cm−1 and involves
movement of H1 toward Ru2, resulting in a decrease in Ru2···H1
(1.67 Å) and a simultaneous increase in C1−H1 (1.75 Å). An
alternate route involving a single metal center has also been
considered where β-hydride elimination occurs on Ru1, affording
Figure 4. Reaction rates for PhCH2OH, PhCD2OH, and PhCH2OD vs
time (min).
E
DOI: 10.1021/acs.organomet.6b00085
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
was purchased from Arora Matthey (India). The compounds
[Ru2(OAc)4Cl],30 1,8-naphthyridine-2,7-dicarboxaldehyde,31 and
PhCH2OD32 were synthesized following literature procedures.
X-ray Data Collection and Refinement. Single-crystal X-ray
structural studies were performed on a CCD Bruker SMART APEX
diffractometer equipped with an Oxford Instruments low-temperature
attachment. Data were collected at 100(2) K using graphite-
monochromated Mo Kα radiation (λα = 0.71073 Å). The frames were
indexed, integrated, and scaled using the SMART and SAINT software
package,33 and the data were corrected for absorption using the
SADABS program.34 The structure was solved and refined using the
SHELX suite of programs. All hydrogen atoms were included in the final
stages of the refinement and were refined with a typical riding model. All
non-hydrogen atoms were refined with anisotropic thermal parameters.
The “SQUEEZE” option in the PLATON program was used to remove
a disordered solvent molecule from the overall intensity data.35
Crystallographic data and pertinent refinement parameters for
compound 1 are summarized in Table S1 in the Supporting Information.
The crystallographic figures used in this paper have been generated
using Diamond 3.1e software.36 CCDC 1447839 contains supple-
mentary crystallographic data for this paper. These data can be obtained
free of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
F (Figure S10 in the Supporting Information). The energy of F is
18.63 kcal/mol higher than that of C. Clearly, a bimetallic β-
hydride elimination is a more energy efficient route than a
pathway involving a single metal. The next step is the liberation
of aldehyde from C followed by coordination of alcohol, a highly
downhill process to form the intermediate D. Proton transfer
from the alcohol to the metal-bound hydride gives the
dihydrogen-bound species E via the transition state TSDE
(ΔG⧧ = 14.64 kcal/mol, Figure 6). The endothermic nature of
the dehydrogenation step was validated by DFT calculations,
which revealed kC−H/kC−D = 2.68 and kO−H/kO−D = 3.73. These
results are in agreement with the experimental KIE values. The
final step is H2 liberation from E to regenerate A.
CONCLUSION
■
A diruthenium(II,II) complex incorporating a naphthyridine−
diimine ligand was synthesized. The ligand architecture offers
accessible sites trans to the naphthyridine unit. The title
compound is an excellent catalyst for AD of alcohols to the
corresponding carbonyl compounds. This diruthenium assembly
is remarkably effective for the clean conversion of primary
alcohols to the corresponding aldehydes without esters as side
products. A possible explanation is that the generated aldehyde is
rapidly extruded from the [RuRu] core and hence the
hemiacetalyzation is hindered. The same catalyst was further
exploited for catalytic olefination of alcohols using ylides to react
with the in situ produced aldehyde. Kinetic experiments, isotope
labeling studies, and DFT calculations point to a bimetallic
cooperative mechanism that operates on the equatorial platform.
A low-energy bimetallic β-hydride elimination makes dehydro-
genation process the rate-limiting step. This study underlines the
general utility of bimetallic catalysts in AD and ADHC reactions.
Synthesis of L1. 1,8-Naphthyridine-2,7-dicarboxaldehyde (250 mg,
1.34 mmol) was dissolved in 50 mL of methanol and placed in a 100 mL
round-bottom flask equipped with a stir bar. To this suspension was
introduced mesitylamine (370 mg, 2.71 mmol), and within a few
minutes a yellow precipitate appeared. This mixture was stirred
overnight. The yellow compound was collected by filtration and washed
with methanol followed by diethyl ether: yield 470 mg (84%); 1H NMR
(400 MHz, CDCl3) δ 8.60 (s, 1H), 8.56 (d, J = 8.24 Hz, 1H), 8.37 (d, J =
8.68 Hz, 1H), 6.93 (s, 2H), 2.19 (s, 9H); 13C NMR (100 MHz, CDCl3)
δ 163.4, 158.2, 147.5, 137.6, 134.2, 129.4, 129.2, 129.1, 127.1, 120.1,
20.9, 18.4 ppm; IR (KBr) ν 2949, 2914, 2856, 1636, 1597, 1505, 1479,
1373, 1206, 864, 852, 732 cm−1; ESI-MS (CH2Cl2) m/z 421.2453 [M +
H]+. Anal. Calcd for C28H28N4: C, 79.96; H, 6.72; N, 13.33. Found: C,
79.81; H, 6.53; N, 13.18.
Synthesis of 1. [Ru2(OAc)4(Cl)] (60 mg, 0.126 mmol) was placed
in a flame-dried Schlenk flask, and 10 mL of dry methanol was added to
form a brown suspension. Addition of L1 (53 mg, 0.12 mmol) resulted in
a deep green solution. The reaction mixture was stirred at room
temperature for 12 h. The solution was evaporated completely under
reduced pressure, and the residue obtained was redissolved in 0.5 mL of
dichloromethane. Diethyl ether was added with stirring to induce
precipitation. The solution was discarded by cannula filtration, and the
precipitate was further washed with diethyl ether (3 × 10 mL). Finally,
the precipitate was dried under vacuum to afford 1 as a green powder.
Yield: 73 mg (79%). Needle-shaped green crystals suitable for X-ray
diffraction were grown by layering hexane over a concentrated
dichloromethane solution of 1 inside an 8 mm o.d. vacuum−sealed
glass tube: IR (KBr) ν 2963, 1532, 1441, 1262, 1198, 1096, 1021, 800,
690 cm−1; MS (ESI; CH3CN) m/z 800.0799 [M − Cl]+. Anal. Calcd for
C34H37N4O6Ru2: C, 50.93; H, 4.65; N, 6.99. Found: C, 50.79; H, 4.45;
N, 6.83.
EXPERIMENTAL SECTION
■
General Procedures. All reactions were carried out under a
nitrogen atmosphere with the use of standard Schlenk-line techniques
unless stated otherwise. Glassware was flame-dried under vacuum prior
to use. 1H and 13C NMR spectra were obtained on JEOL JNM-LA 500
MHz and JEOL JNM-LA 400 MHz spectrometers. Chemical shift values
were referenced to the residual signals of the deuterated solvents. ESI-
MS were recorded on a Waters Micro mass Quattro Micro triple-
quadrupole mass spectrometer. Infrared spectra were recorded on a
Bruker Vertex 70 FTIR spectrophotometer in the range 400−4000
cm−1. Elemental analyses were performed on a Thermoquest EA1110
CHNS/O analyzer. The crystallized compound was washed several
times with dry diethyl ether, powdered, and dried under vacuum for at
least 48 h prior to elemental analyses. GC-MS experiments were
performed on an Agilent 7890A GC and 5975C MS system.
Cyclic voltammetric studies were performed on a BAS Epsilon
electrochemical workstation in acetonitrile with 0.1 M tetra-n-
butylammonium hexafluorophosphate (TBAPF6) as the supporting
electrolyte. The working electrode was a BAS Pt-disk electrode, the
reference electrode was Ag/AgCl, and the auxiliary electrode was a Pt
wire. The ferrocene/ferrocenium couple occurs at E1/2 = +0.51(70) V
versus Ag/AgCl under the same experimental conditions. The potentials
are reported in volts (V); the ΔE (Ep,a − Ep,c) values are in millivolts
(mV) at a scan rate of 100 mV s−1.
General Procedure for AD of Alcohols. A mixture of alcohol (1
mmol), 1 (0.01 mmol), potassium hydroxide (0.1 mmol), and dodecane
(1 mmol) in 3 mL of toluene was placed in an oven-dried reaction vessel.
The reaction mixture was heated to 70 °C with stirring for 6−24 h. The
reaction mixture was cooled, diluted with EtOAc, and passed through a
short column of silica for GC-MS analysis.
Volumetric Estimation of Evolved Hydrogen. Alcohol (1
mmol), 1 (0.01 mmol), and potassium hydroxide (0.1 mmol) in 3 mL
of toluene was placed in an oven-dried reaction vessel, and the reaction
mixture was heated to 70 °C. The headspace of the reaction vessel was
connected to a gas buret. The reaction was continued until evolution of
gas ceased. The experiment was repeated three times to get consistent
readings, and the number of moles of hydrogen evolved was calculated
by taking into account the vapor pressure of water at 293 K = 17.5424
Torr: volume of water displaced 22.6 mL, atmospheric pressure
UV−visible spectra were recorded using a JASCO V-670 UV/vis
absorption spectrophotometer. Emission spectra were recorded using a
Fluorolog FL3-21 (Horiba Jobin Yvon) spectrofluorometer equipped
with a xenon flash lamp and also using a PTI QuantaMaster Model QM-
4 scanning spectrofluorometer equipped with a 75 W xenon lamp,
emission and excitation monochromators, an excitation correction unit,
and a PMT detector for both visible and NIR regions.
Materials. Solvents were dried by conventional methods, distilled
under nitrogen, and deoxygenated prior to use. RuCl3·xH2O (39% Ru)
F
DOI: 10.1021/acs.organomet.6b00085
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
761.3126 Torr, R = 62.3635 L Torr K−1 mol−1, n(H2) = [(Patm − Pwater
V]/RT = 0.00092 mol, expected value 0.001 mol.
)
ACKNOWLEDGMENTS
■
Financial support from the Department of Science and
Technology (DST) of India and the Department of Atomic
Energy (DAE) is gratefully appreciated. J.K.B. thanks the DAE
for an SRC-OI fellowship. I.D. and P.P. thank the CSIR of India
for fellowships. A.S. and K.S. thank the UGC of India for
fellowships. I.D. thanks Mr. Vijay Kumar B. for providing one of
the Wittig reagents, Mr. Arunava Sengupta for magnetic
measurements, and Mr. Sooraj Kunnikuruvan for help in KIE
calculations.
Dual Reactions Involving Hydrogenation of Styrene. The
catalysis reaction using the catalyst 1 was conducted in a flask that was
connected through a rubber tube to another flask in which styrene (1
mmol) and a catalytic amount of RhCl(PPh3)3 (0.05 mmol) in benzene
were placed. Ethylbenzene was produced in the latter flask (76%).
Deuteration Studies with Styrene. A similar procedure was
followed using PhCD2OH as substrate. GC-MS analysis of the product
showed a signal for monodeuterated styrene (Scheme S3 in the
Supporting Information).
General Procedure for Catalytic Olefination of Alcohols using
Wittig Reagent. Alcohol (1 mmol), 1 (0.01 mmol), potassium
hydroxide (0.1 mmol), and Wittig reagent (1.5 mmol) were sequentially
added to 3 mL of toluene placed in an oven-dried reaction vessel. The
reaction mixture was heated to 70 °C with stirring for 6 h. After the
completion of the reactions, the products were purified by
chromatography on a silica gel column using hexane/EtOAc (9/1 v/
REFERENCES
■
(1) (a) Multimetallic Catalysts in Organic Synthesis; Shibasaki, M.,
Yamamoto, Y., Eds.; Wiley-VCH: Weinheim, Germany, 2004.
(b) Catalysis by Di- and Polynuclear Metal Cluster Complexes; Adams,
R. A., Cotton, F. A., Eds.; Wiley-VCH: Weinheim, Germany, 1998.
(c) Shibasaki, M.; Kanai, K.; Matsunaga, S.; Kumagai, N. Acc. Chem. Res.
2009, 42, 1117−1127.
v) as eluent. The isolated E products were characterized by 1H and 13
C
NMR spectra.
Experimental Procedure for Kinetics Studies. A mixture of
alcohol (1 mmol), 1 (0.01 mmol), potassium hydroxide (0.1 mmol), and
dodecane (1 mmol) in 3 mL of toluene was placed in an oven-dried
reaction vessel. The reaction mixture was heated to 70 °C. After
stipulated time intervals, small aliquots (0.2 mL) were taken out from
the reaction mixture, diluted with EtOAc, and passed through a short
column of silica for GC-MS analysis. The experiments were repeated in
triplicate with varying catalyst concentrations.
Experimental Procedure for Deuteration Studies and KIE.
Deuterated alcohol (1 mmol), 1 (0.01 mmol), NaOD (0.1 mmol), and
dodecane (1 mmol) in 3 mL of d8-toluene were placed in an oven-dried
reaction vessel. The reaction mixture was heated to 70 °C. After the
stipulated time intervals, small aliquots of 0.2 mL were taken out and
passed through silica column for GC-MS analysis.
Computational Details. Full geometry optimizations, without any
symmetry constraints, were carried out using the hybrid density
functional theory (DFT) method M0637 as implemented in the program
suite Gaussian 09.38 The Stuttgart−Dresden effective core potential
MWB28 and the corresponding basis set were invoked for Ru.39 The
ligand atoms H, N, C, and O were described using the 6-31+G(d,p) basis
sets.40 All structures were subjected to normal-mode vibrational analysis
calculated at the same level of theory as the corresponding geometry
optimization. All stationary points on the potential energy surface are
either local minima with no imaginary vibrational frequency or
transition states with one imaginary frequency. Solvent effects were
accounted for with the SMD model.41 Gas phase optimized structures
were taken as the initial geometries for optimization in solution.42,43 The
solvation energies were calculated in toluene (ε = 2.38). The reported
energies are Gibbs free energies in toluene using the M06 functional.
(2) (a) Esswein, A. J.; Veige, A. S.; Nocera, D. G. J. Am. Chem. Soc.
2005, 127, 16641−16651. (b) Gray, T. G.; Veige, A. S.; Nocera, D. G. J.
Am. Chem. Soc. 2004, 126, 9760−9768. (c) Teets, T. S.; Cook, T. R.;
McCarthy, B. D.; Nocera, D. G. Inorg. Chem. 2011, 50, 5223−5233.
(d) Pal, S.; Uyeda, C. J. Am. Chem. Soc. 2015, 137, 8042−8045.
(e) Steiman, T. J.; Uyeda, C. J. Am. Chem. Soc. 2015, 137, 6104−6110.
(f) Sarkar, M.; Doucet, H.; Bera, J. K. Chem. Commun. 2013, 49, 9764−
9766. (g) Patra, S. K.; Rahaman, S. M. W.; Majumdar, M.; Sinha, A.;
Bera, J. K. Chem. Commun. 2008, 2511−2513. (h) Dutta, I.; Sengupta,
G.; Bera, J. K. Reactivity and Catalysis at Sites Trans to the [Ru−Ru]
Bond. Top. Organomet. Chem. 2015, DOI: 10.1007/3418_2015_162.
(3) (a) Powers, D. C.; Ritter. Nat. Chem. 2009, 1, 302−309.
(b) Powers, D. C.; Ritter, T. Acc. Chem. Res. 2012, 45, 840−850.
(c) Li, C.; Widjaja, E.; Garland, M. J. Am. Chem. Soc. 2003, 125, 5540−
5548. (d) Broussard, M. E.; Juma, B.; Train, S. G.; Peng, W.-J.; Laneman,
S. A.; Stanley, G. G. Science 1993, 260, 1784−1788. (e) Majumdar, M.;
Sinha, A.; Ghatak, T.; Patra, S. K.; Sadhukhan, N.; Rahaman, S. M. W.;
Bera, J. K. Chem. - Eur. J. 2010, 16, 2574−2585.
(4) (a) Chifotides, H. T.; Saha, B.; Patmore, N. J.; Dunbar, K. R.; Bera,
J. K. Group 9 Metal-Metal Bonds. In Molecular Metal-Metal Bonds;
Liddle, S. T., Ed.; Wiley-VCH: Weinheim: Germany, 2015; pp 279−
324. (b) Doyle, M. P.; Duffy, R.; Ratnikov, M.; Zhou, L. Chem. Rev.
2010, 110, 704−724. (c) Doyle, M. P.; Forbes, D. C. Chem. Rev. 1998,
98, 911−936.
(5) Berry, J. F. Dalton Trans. 2012, 41, 700−713.
(6) (a) Basil, J. D.; Murray, H. H.; Fackler, J. P.; Tocher, J.; Mazany, A.
M.; Trzcinska-Bancroft, B.; Knachel, H.; Dudis, D.; Delord, T. J.; Marler,
D. O. J. Am. Chem. Soc. 1985, 107, 6908−6915. (b) Foo, S. J. L.; Jones,
N. D.; Patrick, B. O.; James, B. R. Chem. Commun. 2003, 988−989.
(c) Murahashi, T.; Kurosawa, H. Coord. Chem. Rev. 2002, 231, 207−228.
(d) Murahashi, T.; Okuno, T.; Nagai, T.; Kurosawa, H. Organometallics
2002, 21, 3679−3682. (e) Long, A. K. M.; Timmer, G. H.; Pap, J. S.;
Snyder, J. L.; Yu, R. P.; Berry, J. F. J. Am. Chem. Soc. 2011, 133, 13138−
13150. (f) Musch Long, A. K.; Yu, R. P.; Timmer, G. H.; Berry, J. F. J.
Am. Chem. Soc. 2010, 132, 12228−12230. (g) Timmer, G. H.; Berry, J. F.
Chem. Sci. 2012, 3, 3038−3052.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00085.
Experimental details and supporting figures (PDF)
Crystallographic data (CIF)
(7) Nishibayashi, Y.; Wakiji, I.; Hidai, M. J. Am. Chem. Soc. 2000, 122,
11019−11020. (b) Inada, Y.; Nishibayashi, Y.; Hidai, M.; Uemura, S. J.
Am. Chem. Soc. 2002, 124, 15172−15173. (c) Nishibayashi, Y.;
Yamanashi, M.; Takagi, Y.; Hidai, M. Chem. Commun. 1997, 859−
860. (d) Ammal, S. C.; Yoshikai, N.; Inada, Y.; Nishibayashi, Y.;
Nakamura, E. J. Am. Chem. Soc. 2005, 127, 9428−9438. (e) Tanaka, H.;
Arashiba, S.; Kuriyama, S.; Sasada, A.; Nakajima, K.; Yoshizawa, K.;
Nishibayashi, Y. Nat. Commun. 2014, 5, 3737. (f) Meyer, F.; Kaifer, E.;
Kircher, P.; Heinze, K.; Pritzkow, H. Chem. - Eur. J. 1999, 5, 1617−1630.
(g) Teets, T. S.; Nocera, D. G. J. Am. Chem. Soc. 2011, 133, 17796−
17806. (h) Teets, T. S.; Nocera, D. G. Dalton Trans. 2013, 42, 3521−
3527.
Cartesian coordinates of all computed molecules (XYZ)
AUTHOR INFORMATION
■
Corresponding Author
*E-mail for J.K.B.: jbera@iitk.ac.in.
Notes
The authors declare no competing financial interest.
G
DOI: 10.1021/acs.organomet.6b00085
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(8) (a) Watson, A. J. A.; Williams, J. M. J. Science 2010, 329, 635−636.
(b) Gunanathan, C.; Milstein, D. Science 2013, 341, 1229712.
2009, 351, 2643−2649. (e) Muthaiah, S.; Ghosh, S. C.; Jee, J.−E.; Chen,
C.; Zhang, J.; Hong, S. H. J. Org. Chem. 2010, 75, 3002−3006. (f) Kang,
B.; Fu, Z.; Hong, S. H. J. Am. Chem. Soc. 2013, 135, 11704−11707.
(g) Gunanathan, C.; Milstein, D. Acc. Chem. Res. 2011, 44, 588−602.
(h) Allen, C. L.; Williams, J. M. J. Chem. Soc. Rev. 2011, 40, 3405−3415.
(i) Gnanaprakasam, B.; Zhang, J.; Milstein, D. Angew. Chem., Int. Ed.
2010, 49, 1468−1471. (j) Michlik, S.; Kempe, R. Nat. Chem. 2013, 5,
140−144. (k) Srimani, D.; Ben-David, Y.; Milstein, D. Angew. Chem., Int.
Ed. 2013, 52, 4012−4015. (l) Shan, S. P.; Xiaoke, X.; Gnanaprakasam,
B.; Dang, T. T.; Ramalingam, B.; Huynh, H. V.; Seayad, A. M. RSC Adv.
2015, 5, 4434−4442. (m) Xie, X.; Huynh, H. V. ACS Catal. 2015, 5,
4143−4151.
(21) (a) Edwards, M. G.; Williams, J. M. J. Angew. Chem., Int. Ed. 2002,
41, 4740−4743. (b) Edwards, M. G.; Jazzar, R. F. R.; Paine, B. M.;
Shermer, D. J.; Whittlesey, M. K.; Williams, J. M. J.; Edney, D. D. Chem.
Commun. 2004, 90−91. (c) Burling, S.; Paine, B. M.; Nama, D.; Brown,
V. S.; Mahon, M. F.; Prior, T. J.; Pregosin, P. S.; Whittlesey, M. K.;
Williams, J. M. J. J. Am. Chem. Soc. 2007, 129, 1987−1995. (d) Nixon, T.
D.; Whittlesey, M. K.; Williams, J. M. J. Dalton Trans. 2009, 753−762.
(e) Black, P. J.; Edwards, M. G.; Williams, J. M. J. Eur. J. Org. Chem. 2006,
2006, 4367−4368.
(9) (a) Valencia, M.; Muller-Bunz, H.; Gossage, R. A.; Albrecht, M.
̈
Chem. Commun. 2016, 52, 3344−3347. (b) Polukeev, A. V.; Petrovskii,
P. V.; Peregudov, A. S.; Ezernitskaya, M. G.; Koridze, A. A.
Organometallics 2013, 32, 1000−1015. (c) Donnelly, K. F.; Segarra,
C.; Shao, L.-X.; Suen, R.; Muller-Bunz, H.; Albrecht, M. Organometallics
̈
2015, 34, 4076−4084. (d) Chakraborty, S.; Piszel, P. E.; Brennessel, W.
W.; Jones, W. D. Organometallics 2015, 34, 5203−5206. (e) Chakra-
borty, S.; Lagaditis, P. O.; Forster, M.; Bielinski, E. A.; Hazari, N.;
̈
Holthausen, M. C.; Jones, W. D.; Schneider, S. ACS Catal. 2014, 4,
3994−4003. (f) Tseng, K.-N. T.; Kampf, J. W.; Szymczak, N. K. ACS
Catal. 2015, 5, 5468−5485. (g) Oldenhuis, N. J.; Dong, V. M.; Guan, Z.
Tetrahedron 2014, 70, 4213−4218. (h) Musa, S.; Fronton, S.; Vaccaro,
L.; Gelman, D. Organometallics 2013, 32, 3069−3073. (i) Tseng, K.-N.
T.; Kampf, J. W.; Szymczak, N. K. Organometallics 2013, 32, 2046−2049.
(j) van Buijtenen, J.; Meuldijk, J.; Vekemans, J. A. J. M.; Hulshof, L. A.;
Kooijman, H.; Spek, A. L. Organometallics 2006, 25, 873−881.
(k) Shahane, S.; Fischmeister, C.; Bruneau, C. Catal. Sci. Technol.
2012, 2, 1425−1428. (l) Muthaiah, S.; Hong, S. H. Adv. Synth. Catal.
2012, 354, 3045−3053.
(10) (a) Gunanathan, C.; Milstein, D. Chem. Rev. 2014, 114, 12024−
12087. (b) Khusnutdinova, J. R.; Milstein, D. Angew. Chem., Int. Ed.
2015, 54, 12236−12273. (c) Kawahara, R.; Fujita, K.-i.; Yamaguchi, R. J.
Am. Chem. Soc. 2012, 134, 3643−3646. (d) Fujita, K.-i.; Tanino, N.;
Yamaguchi, R. Org. Lett. 2007, 9, 109−111. (e) Kawahara, R.; Fujita, K.-
i.; Yamaguchi, R. Angew. Chem., Int. Ed. 2012, 51, 12790−12794.
(f) Zeng, G.; Sakaki, S.; Fujita, K.; Sano, K.; Yamaguchi, R. ACS Catal.
2014, 4, 1010−1020.
(22) Khaskin, E.; Milstein, D. Chem. Commun. 2015, 51, 9002−9005.
(23) (a) Lewis, W. G.; Magallon, F. G.; Fokin, V. V.; Finn, M. G. J. Am.
Chem. Soc. 2004, 126, 9152−9153. (b) Rodionov, V. O.; Presolski, S. I.;
Gardinier, S.; Lim, Y. H.; Finn, M. G. J. Am. Chem. Soc. 2007, 129,
12696−12704. (c) Saha, S.; Kaur, M.; Bera, J. K. Organometallics 2015,
34, 3047−3054.
(24) Sølvhøj, A.; Madsen, R. Organometallics 2011, 30, 6044−6048.
(25) Maggi, A.; Madsen, R. Organometallics 2012, 31, 451−455.
(11) (a) Clapham, S. E.; Hadzovic, A.; Morris, R. H. Coord. Chem. Rev.
2004, 248, 2201−2237. (b) Samec, J. S. M.; Backvall, J. E.; Andersson, P.
G.; Brandt, P. Chem. Soc. Rev. 2006, 35, 237−248.
̀
(26) (a) Pamies, O.; Backvall, J.-E. Chem. - Eur. J. 2001, 7, 5052−5058.
̈
(b) Saha, B.; Rahaman, S. M. W.; Daw, P.; Sengupta, G.; Bera, J. K.
Chem. - Eur. J. 2014, 20, 6542−6551.
(12) (a) Binamira-Soriaga, E.; Keder, N. L.; Kaska, W. C. Inorg. Chem.
(27) (a) Wiberg, K. B. Chem. Rev. 1955, 55, 713−743. (b) Bell, R. P.
Chem. Soc. Rev. 1974, 3, 513−544. (c) Simmons, E. M.; Hartwig, J. F.
Angew. Chem., Int. Ed. 2012, 51, 3066−3072.
1990, 29, 3167−3171. (b) Campos-Fernan
Dunbar, K. R. Inorg. Chem. 2000, 39, 2432−2433. (c) Campos-
Fernandez, C. S.; Thomson, L. M.; Galan-Mascaros, J. R.; Ouyang, X.;
Dunbar, K. R. Inorg. Chem. 2002, 41, 1523−1533.
(13) (a) Dikarev, E. V.; Filatov, A. S.; Clerac, R.; Petrukhina, M. A.
́
dez, C. S.; Ouyang, X.;
(28) Brookhart, M.; Green, M. L. H.; Parkin, G. Proc. Natl. Acad. Sci. U.
S. A. 2007, 104, 6908−6914.
́
́
́
(29) (a) Toner, A. J.; Grundemann, S.; Clot, E.; Limbach, H.-H.;
́
̈
Inorg. Chem. 2006, 45, 744−751. (b) Miyasaka, H.; Motokawa, N.;
Matsunaga, S.; Yamashita, M.; Sugimoto, K.; Mori, T.; Toyota, N.;
Dunbar, K. R. J. Am. Chem. Soc. 2010, 132, 1532−1544. (c) Miyasaka,
H.; Motokawa, N.; Atsuumi, R.; Kamo, H.; Asai, Y.; Yamashita, M.
Dalton Trans. 2011, 40, 673−682. (d) Kosaka, W.; Yamamoto, N.;
Miyasaka, H. Inorg. Chem. 2013, 52, 9908−9914. (e) Kosaka, W.; Itoh,
M.; Miyasaka, H. Dalton Trans. 2015, 44, 8156−8168. (f) Brown, T. R.;
Donnadieu, B.; Sabo-Etienne, S.; Chaudret, B. J. Am. Chem. Soc. 2000,
122, 6777−6778. (b) Oxgaard, J.; Goddard, W. A. J. Am. Chem. Soc.
2004, 126, 442−443. (c) Chen, Y.; Wang, M.; Fang, S.; Wang, T.; Liu, J.
Organometallics 2015, 34, 4864−4870.
(30) Mitchell, R. W.; Spencer, A.; Wilkinson, G. J. Chem. Soc., Dalton
Trans. 1973, 846−854.
(31) Vu, C.; Walker, D.; Wells, J.; Fox, S. J. Heterocycl. Chem. 2002, 39,
829−832.
(32) Mahadevan, V.; DuBois, J. L.; Hedman, B.; Hodgson, K. O.; Stack,
T. D. P. J. Am. Chem. Soc. 1999, 121, 5583−5584.
(33) SAINT+ Software for CCD Diffractometers; Bruker AXS, Madison,
WI, 2000.
́
Dolinar, B. S.; Hillard, E. A.; Clerac, R.; Berry, J. F. Inorg. Chem. 2015, 54,
8571−8589.
(14) Angaridis, P. Ruthenium Compounds. In Multiple Bonds between
Metal Atoms, 3rd ed.; Cotton, F. A., Murillo, C. A., Walton, R. A., Eds.;
Springer Science: New York, 2005; pp 377−430.
(34) (a) SHELXTL Package v. 6.10; Bruker AXS, Madison, WI,, 2000.
(b) Sheldrick, G. M. SHELXS-86 and SHELXL-97; University of
(15) Komiya, N.; Nakae, T.; Sato, H.; Naota, T. Chem. Commun. 2006,
4829−4831.
Gottingen, Gottingen, Germany, 1997.
(16) Koga, K.; Yamada, Y.; Koikawa, M.; Tokii, T. J. Coord. Chem.
2007, 60, 143−151.
̈
̈
(35) Spek, A. L. PLATON; University of Utrecht, Utrecht, The
(17) Do, Y.; Ko, S.-B.; Hwang, I.-C.; Lee, K.-E.; Lee, S. W.; Park, J.
Organometallics 2009, 28, 4624−4627.
Netherlands, 2001.
(36) Bradenburg, K. Diamond, version 3.1e; Crystal Impact GbR, Bonn,
Germany, 2005.
(18) (a) Adkins, H.; Elofson, R. M.; Rossow, A. G.; Robinson, C. C. J.
Am. Chem. Soc. 1949, 71, 3622−3629. (b) Baratta, W.; Bossi, G.;
Putignano, E.; Rigo, P. Chem. - Eur. J. 2011, 17, 3474−3481.
(19) (a) Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D. J. Am. Chem.
Soc. 2005, 127, 10840−10841. (b) Musa, S.; Shaposhnikov, I.; Cohen,
S.; Gelman, D. Angew. Chem., Int. Ed. 2011, 50, 3533−3537. (c) Spasyuk,
D.; Gusev, D. G. Organometallics 2012, 31, 5239−5242. (d) Friedrich,
A.; Schneider, S. ChemCatChem 2009, 1, 72−73.
(37) Zhao, Y.; Truhlar, D. G. Theor. Chem. Acc. 2008, 120, 215−241.
(38) 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.;
(20) (a) Nielsen, M.; Junge, H.; Kammer, A.; Beller, M. Angew. Chem.,
Int. Ed. 2012, 51, 5711−5713. (b) Gunanathan, C.; Ben-David, Y.;
Milstein, D. Science 2007, 317, 790−792. (c) Nordstrøm, L. U.; Vogt,
H.; Madsen, R. J. Am. Chem. Soc. 2008, 130, 17672−17673. (d) Ghosh,
S. C.; Muthaiah, S.; Zhang, Y.; Xu, X.; Hong, S. H. Adv. Synth. Catal.
H
DOI: 10.1021/acs.organomet.6b00085
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
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.
(39) Andrae, D.; Haussermann, U.; Dolg, M.; Stoll, H.; Preuss, H.
̈
Theor. Chim. Acta 1990, 77, 123−141.
(40) Binkley, J. S.; Pople, J. A.; Hehre, W. J. J. Am. Chem. Soc. 1980, 102,
939−947.
(41) Marenich, A. V.; Cramer, C. J.; Truhlar, D. G. J. Phys. Chem. B
2009, 113, 6378−6396.
(42) Tomasi, J.; Mennucci, B.; Cammi, R. Chem. Rev. 2005, 105,
2999−3094.
(43) Tomasi, J.; Persico, M. Chem. Rev. 1994, 94, 2027−2094.
I
DOI: 10.1021/acs.organomet.6b00085
Organometallics XXXX, XXX, XXX−XXX