Synthetic routes to a coordinatively unsaturated ruthenium complex supported by a tripodal, protic bis(N-heterocyclic carbene) phosphine ligand

Article abstract of DOI:10.1039/c7dt04333c

A facile, one pot synthesis of a coordinatively unsaturated ruthenium complex supported by a tripodal, protic bis(N-heterocyclic carbene) phosphine ligand is presented. A number of coordination complexes were discovered en route during this synthesis, revealing some of the unique aspects of complexes ligated by this type of tridentate, protic bis(NHC) ligand. Through a combination of 1D and 2D NMR spectroscopic analysis and single crystal X-ray diffraction, we reveal the intermediacy of phosphine-ligated bisimidazole complexes and show that abstraction of inner-sphere halide ions facilitates conversion to the desired tridentate bis(NHC) coordination mode. Ultimately the use of N-methyl-2-pyrrolidone is shown to enable the use of the extreme temperatures needed to facilitate the direct, thermally activated tautomerization reaction that gives rise to the bis(NHC) motif.

Full text of DOI:10.1039/c7dt04333c

View Article Online
View Journal
Dalton
Transactions
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: S. E. Flowers, M.
C. Johnson, Z. Pitre and B. Cossairt, Dalton Trans., 2017, DOI: 10.1039/C7DT04333C.
This is an Accepted Manuscript, which has been through the
Volume 45 Number
1 7 January 2016 Pages 1–398
Royal Society of Chemistry peer review process and has been
accepted for publication.
Dalton
Transactions
Accepted Manuscripts are published online shortly after
An international journal of inorganic chemistry
www.rsc.org/dalton
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1477-9226
PAPER
Joseph T. Hupp, Omar K. Farha et al.
Efficient extraction of sulfate from water using
framework
a Zr-metal–organic
rsc.li/dalton

Please do not adjust margins
Dalton Transactions
Page 1 of 9
View Article Online
DOI: 10.1039/C7DT04333C
Journal Name
ARTICLE
Synthetic Routes to a Coordinatively Unsaturated Ruthenium
Complex Supported by a Tripodal, Protic bis(N-heterocyclic
Carbene) Phosphine Ligand
Received 00th
January 20xx,
S. E. Flowersa, M. C. Johnsona, B. Z. Pitrea, and B. M. Cossairta*
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
A facile, one pot synthesis of a coordinatively unsaturated ruthenium complex supported by a tripodal, protic bis(N-
heterocyclic carbene) phosphine ligand is presented. A number of coordination complexes were discovered en route
during this synthesis, revealing some of the unique aspects of complexes ligated by this type of tridentate, protic bis(NHC)
ligand. Through a combination of 1D and 2D NMR spectroscopic analysis and single crystal X-ray diffraction, we reveal the
intermediacy of phosphine-ligated bisimidazole complexes and show that abstraction of inner-sphere halide ions
facilitates conversion to the desired tridentate bis(NHC) coordination mode. Ultimately the use of N-methyl-2-pyrrolidone
is shown to enable the use of the extreme temperatures needed to facilitate the direct, thermally activated
tautomerization
reaction
that
gives
rise
to
the
bis(NHC)
motif.
synthetic variants. This ligand is characterized by its strong
sigma donor character, neutral charge, and chemically tunable
backbone, which has led to its utilization as a ligand in many
different catalytic reactions including hydrogenation,19-22
alcohol amination,23 methylation of amines,24 and formic acid
dehydrogenation.25 Another well-established class of tripodal
ligands are tris(pyrazolyl)borate (Tp) and its synthetic variants.
Tp ligands are monoanionic, facially coordinating ligands, and
like Triphos are good sigma donors. Focusing solely on
ruthenium complexes supported by Tp ligands, these
complexes are effective catalysts for hydrogenation,26 coupling
chemistry,27 hydration of nitriles,28 hydroarylation,29 and
isomerization and cyclization reactions30.
Introduction
First introduced in 1968,1, 2 N-heterocyclic carbenes (NHCs)
are of interest to the organometallic community as useful
ligands for their tunable steric profiles and strongly electron
donating properties.3-5 Although methods of metalating
traditional NHCs with substituted NR wingtips have been
known for decades,6 the synthesis of protic NHCs (PNHCs) has
been far less studied. Protic NHCs are attractive because of
their tunable protonation state, which allows them to serve as
a proton relay, participate in substrate insertion reactions, and
ligate Lewis acids. Methods for making PNHC complexes have
been developed and are covered in several reviews,7-11 and
early metalation studies reveal thermodynamically controlled
formation of the desired carbene complexes for certain metal
Motivated by the exemplary catalytic performance of
catalysts ligated by tripodal ligands like Triphos and Tp, and
the attractive qualities of PNHCs, our group became interested
in developing a general strategy for the direct metalation of a
bis(imidazole)phosphine ligand to create novel catalyst
structures bearing tripodal PNHC ligands. To date we have
fragments including Ru(II).12, However, there are still very
13
few examples in the literature of chelating ligands containing
two PNHCs.14-18
Separately, organometallic complexes supported by facially
coordinating tripodal ligands have proven to be versatile and
effective catalysts for a variety of chemical transformations.
One of the most widely utilized, reviewed, and recognized
investigated
mono-
and
with
di-metallation
[Cp*RuCl]4
of
[(Me2benzimid)Et]2PPh
(L
)
and
[(bpy)(C6H6)Ru(OTf)](OTf) (Figure 1A-C),17, 18 however access to
a structure with only weakly bound ligands in the three
remaining facially disposed coordination sites has remained
elusive. In this work, we will discuss the one pot synthesis of
members
of
this
family
of
ligands
is
bis(diphenylphosphinoethyl)phenylphosphine (Triphos) and its
[(MeCN)3Ru(PNHC)2PPh]2+, complex
study of with [(arene)RuCl2]2, and preliminary CO2
hydrogenation catalysis results, demonstrating the potential of
and related complexes as active catalysts for this class of
transformations.
1, a detailed metalation
L
1
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 2 of 9
View Article Online
DOI: 10.1039/C7DT04333C
ARTICLE
Journal Name
A)
C)
Colorless crystals suitable for single crystal X-ray diffraction
were grown via slow diffusion of diethyl ether into
supersaturated solution of in acetonitrile at -35 °C. The
structure of (Figure 2) shows that the PNHC binds facially to
the ruthenium center. The bond lengths of the PNHCs in the
crystal structure of are within the range of structures we
have previously characterized.17,
OH2
2+
Cl
H
H
H
a
Cp*
H
N
N
N
N
1
Ru
Ru
P
N
N
1
N
N
N
N
P
1
18
The Ru-N(nitrile) bond
B)
D)
MeCN
N
Cl
lengths are similar for all three positions, ranging from
2.104(2) Å for Ru1-N6 to 2.115(2) Å for Ru1-N5.
2+
H
NCMe
NCMe
NCMe
M
Cp*
H
N
N
Ru
P
Ru
P
N
N
N
N
N
B2
Figure 1. Examples of monometallic (A, C, D) and bimetallic (B)
complexes supported by a tripodal bis-PNHC ligand.
C32
C30
N5
C34
N3
N6
N7
Ru1
P1
N2
Results and Discussion
C2
N4
C1
N1
Complex
mixture of
1
can be prepared in one pot in 93% yield. A 2:1
L
and [(C6H6)RuCl2]2 is stirred at 170 °C in N-methyl-
2-pyrrolidone (NMP) for one hour, and the volatiles are
removed under reduced pressure. The resulting dark yellow
solid is dissolved in acetonitrile, 4 equivalents of AgBF4 are
added, and the mixture is stirred for one hour at ambient
B1
temperature. Upon further purification,
off-white powder (Scheme 1).
1 can be isolated as an
Figure 2. Single crystal X-ray diffraction structure of
1 with
thermal ellipsoids shown at the 50% probability level.
Hydrogen atoms are omitted for clarity. Selected interatomic
distances (Å): Ru1-N5 2.115(2), N5-C30 1.133(4), Ru1-N6
2.104(2), N6-C32 1.139(4), Ru1-N7 2.114(2), N7-C34 1.133(4),
Ru1-P1 2.2680(7), Ru1-C1 2.0063, Ru1-C2 2.003(3), C1-N1
1.355(4), C1-N2 1.360(4), C2-N3 1.355(3), C2-N4 1.360(3).
To understand the detailed coordination chemistry that
precedes the formation of
1, we investigated the metalation of
L
under more mild conditions. Sonication of a 2:1 mixture of
L
and [(C6H6)RuCl2]2 at room temperature in DMSO,
dichloromethane, or NMP leads to complete conversion to the
phosphine-ligated complex, (C6H6)Ru(L)Cl2 (2-benzene), within
one hour, as observed in situ by 1H NMR and 31P{1H} NMR
spectroscopy (Scheme 1). Complex 2-benzene is characterized
in DMSO-d6 by a 31P{1H} NMR singlet at 14 ppm, a downfield
shift from 31P{1H} NMR signal for
L at -34 ppm, and by several
distinctive 1H NMR signals including three aromatic singlets
corresponding to the aromatic protons on the imidazole units
at 8.1, 7.4, and 7.2 ppm respectively; two singlets
corresponding to the methyl groups on the benzimidazole at
3.0 and 2.3 ppm; and one singlet at 5.7 ppm corresponding to
the six equivalent protons on the η6-benzene ring suggesting
that benzene remains bound to the ruthenium center.
Similarly, the addition of [(p-cymene)RuCl2]2 (0.5 equiv) to a
Scheme 1. One-pot and step-wise synthesis of
[(MeCN)3Ru(PNHC)2PPh][BF4]2, complex
. Note, the structure
of complex is solvent (S) dependent, with evidence for
dimerization in non-coordinating solvent.
1
3
Complex
1
is characterized by a 31P{1H} NMR singlet at 44
1
ppm in CD2Cl2 and by several, distinctive H NMR signals: one
N-H singlet at 10.8 ppm, three phenyl group proton multiplets
at 7.8, 7.7, and 7.6 ppm; four multiplets for the diastereotopic
protons on the ethylene linker; two singlets for the protons on
the bound acetonitrile ligands trans to the NHCs at 2.2 ppm,
and one singlet corresponding to the acetonitrile unit trans to
the phosphorus at 2.6 ppm.
22 °C solution of
L in dichloromethane produces the bright
orange phosphine adduct, 2-cymene. The appearance of a
singlet at 11 ppm along with the simultaneous disappearance
of the free ligand resonance at -34 ppm in the 31P{1H} NMR
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 3 of 9
View Article Online
DOI: 10.1039/C7DT04333C
Journal Name
ARTICLE
spectra in CD2Cl2, suggests complete conversion to 2-cymene
In CD2Cl2, the 31P{1H} NMR spectrum of
singlet peak at 53 ppm, suggesting there is one phosphorus
3 reveals one
within one hour.
1
High quality orange hexagonal prisms suitable for single environment in the isolated molecule. The H NMR spectrum
crystal X-ray diffraction were grown via slow evaporation from in CD2Cl2 displays a single set of peaks for the phenyl group
a super-saturated solution of 2-benzene in dichloromethane attached to the phosphorus atom with multiplets at 8.12, 7.43,
and diethyl ether at -35 °C. The crystal structure of 2-benzene and 7.29 ppm. Although there is only one set of peaks
1
three-legged piano-stool geometry around the corresponding the phenyl group, the H NMR spectrum shows
shows
a
ruthenium center, with an η6-benzene ligand and with legs two inequivalent ethylene imidazole arms in this complex. In a
consisting of two chlorine atoms and bound to the ruthenium symmetric PNHC complex we would expect one singlet N-H
L
center by the phosphorus atom only (Figure 3). Coordination peak (2H), two aromatic C-H singlets (2H each), four multiplets
of [(arene)RuCl2]2 complexes with phosphine ligands to give corresponding to the two sets of diastereotopic protons on the
(arene)Ru(PR3)Cl2 complexes have been well reported in the ethylene linker (2H each), and two methyl singlets (6H each).17
1
literature.31-33
The H NMR spectrum of
3
in CD2Cl2 contains two singlet N-H
peaks at 11.0 ppm and 10.9 ppm (1H each); four aromatic
singlets at 7.3ppm, 7.1 ppm, 7.0 ppm, and 6.9 ppm (1H each);
eight multiplets corresponding to the diastereotopic ethylene
linker protons (1H each), and 4 methyl singlets at 2.5, 2.4, 2.3,
and 2.2 ppm (3H each). These results indicate that the
Ru1
P1
Cl2
Cl1
structure of
linkers, suggesting possible dimer formation in non-
coordinating solvent. Compound is soluble in
dichloromethane, acetonitrile and DMSO. When dissolved in a
coordinating solvent, the spectral features of drastically
change. For example, when
is dissolved in CD3CN the 31P{1H}
3 has two chemically distinct ethylene imidazole
N4
C2
3
N3
3
N2
3
C1
N1
NMR displays two separate peaks at 45 and 43 ppm, and a
1
distinct H NMR spectrum compared to the same complex in
CD2Cl2 (Figure S3).
Similarly, when
3
is dissolved in DMSO a new species,
3-DMSO), is observed. High
Figure 3. Single crystal X-ray diffraction structure of 2-benzene
with thermal ellipsoids shown at the 50% probability level.
Hydrogen atoms are omitted for clarity. Selected interatomic
distances (Å): Ru(1)-P(1) 2.3254(17), Ru(1)-Cl(1) 2.4061(15),
Ru(1)- Cl(2) 2.4192(16), C(2)-N(3) 1.298(8), C(2)-N(4) 1.368(7),
C(1)-N(1) 1.306(7), C(1)-N(2) 1.369(8).
[(DMSO)2ClRu(PNHC)2PPh][Cl]
(
quality crystals suitable for X-ray diffraction were grown in air
with a super saturated solution of 3-DMSO in a 1:1 mixture of
DMSO and CD2Cl2 (Figure 3). The crystal structure shows a
facially bound bis-PNHC ligand. The PNHCs are chemically
inequivalent in this structure because one is bound to the
ruthenium trans to chloride, while the other is bound trans to
a sulfur-coordinated DMSO molecule. In addition, there is a
second molecule of DMSO coordinated through an oxygen
atom to the ruthenium center trans to the phosphorus. The
carbene trans to the sulfur atom of DMSO shows a Ru-C bond
distance of 2.049(7) Å and the carbene trans to the chloride
has a Ru-carbon distance of 2.007(7) Å. There is one outer
sphere chloride that shows hydrogen bonding interactions
with the N-H moieties.
Heating 2-benzene at 170 °C for 45 minutes in NMP and
monitoring the reaction by 31P{1H} NMR spectroscopy
demonstrates the disappearance of the 2-benzene singlet at
13 ppm and the appearance of a new singlet corresponding to
a new species
3 at 55 ppm. Analysis with an internal standard
in NMP supported in situ conversion of 2-benzene to 3 in >60%
yield (Figure S1).
To further investigate this metalation reaction, 2-benzene
was heated at 140 °C in NMP and the reaction mixture was
monitored over time by 31P{1H} NMR spectroscopy. After five
hours at 140 °C the singlet for 2-benzene at 13 ppm decreased
and many new signals appeared in the 31P{1H} NMR spectrum.
Continued heating led to the disappearance of these peaks
Cl1
S1
Ru1
O2
and to the appearance of a single species, 3, at 55 ppm after
P1
23 hours at 140 °C (Scheme 1, Figure S2). These results
suggest that there may be multiple intermediates that form
N2
C2
N3
C1
N1
N4
between 2-benzene and
3. Compound 3 can also be
synthesized from [(p-cymene)RuCl2]2 in a similar manner but
requires 43 hours of heating at 140 °C, consistent with the
Cl2
expected relative lability of the arenes.34 Compound
3 can be
cleanly isolated from this reaction as a yellow-orange powder.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 4 of 9
View Article Online
DOI: 10.1039/C7DT04333C
ARTICLE
Journal Name
Figure 4. Single crystal X-ray diffraction structure of 3-DMSO
Since heating 2-benzene at 100 °C and base promoted
with thermal ellipsoids shown at the 50% probability level. tautomerization did not lead to formation of the desired PNHC
Hydrogen atoms and DMSO solvent molecule are omitted for complex, we were curious to see if different reactivity would
clarity. Selected interatomic distances (Å): Ru(1)-Cl(1) 2.508(2), be observed with 2-benzene following replacement of the
Ru(1)-O(2) 2.229(4), Ru(1)-S(1) 2.332(2), Ru(1)-C(1) 2.049(7), coordinated chlorides with non-coordinating counter anions.
C(1)-N(1) 1.365(8), C(1)-N(2) 1.376(9), Ru(1)-C(2) 2.007(7), The addition of 2 equivalents AgBF4 to a solution of 2-benzene
C(2)-N(3) 1.359(8), C(2)-N(4) 1.370(8).
in DMSO at 22 °C followed by five minutes of sonication led to
a change in the appearance of the solution from transparent
3
in orange to cloudy yellow. After thirty minutes 31P{1H} NMR
When two equivalents of AgBF4 are added to
acetonitrile and the resulting mixture is sonicated for ten spectral analysis reveals complete conversion to two new
minutes, complex
is produced as evidenced by NMR species, a major product 4a and minor product 4b with 31P{1H}
spectroscopy and crystallographic analysis (Scheme 1). NMR resonances at 17 ppm and 15 ppm, respectively, which
In previous reports, tautomerization or activation of the C- are present in a 100:33 ratio. Two singlets in the 1H NMR
H protons in was achieved by heating and [Cp*RuCl]4 at 100 spectrum located at 6.5 ppm and 5.9 ppm are associated with
°C.18 To see if these conditions would be applicable for the the η6-benzene proton signals, and are also present in a 100:33
synthesis of 2-benzene was heated at 100 °C for 17 hours in ratio (Figure S6). These data suggested the likely formation of
DMSO. The PNHC species was not observed, but conversion to mixture of dimerized diastereomers,
a DMSO adduct, (DMSO)3Ru(L)Cl2 2-DMSO), is proposed [(C6H6)(DMSO)Ru(L)]2[BF4]4, under these conditions as shown
1
L
L
1,
a
(
based on the in situ 1H NMR and 31P{1H} NMR spectra. The in Scheme 2. We had encountered both of the anticipated
time resolved 31P{1H} NMR spectra reveal that the singlet coordination environments separately in earlier experiments
associated with 2-DMSO, at 31 ppm, increases over time while with [RuCp*Cl]4 and related ligands,18 but only a single
the 31P{1H} NMR resonance at 14 ppm associated with 2- diastereomer is formed in each of these cases as evidenced by
1
benzene disappears. In the H NMR spectrum, the η6-benzene NMR spectroscopy and single crystal X-ray diffraction studies
singlet at 5.7 ppm decreases in intensity over time, indicating (Figure S7). In the case of Cp* coordination to ruthenium,
that benzene dissociates from the ruthenium center. Also, the steric effects may preclude observation of the other
1H NMR spectrum of species 2-DMSO has three singlets in the diastereomer.
aromatic region with chemical shifts of 8.2 ppm, 7.4 ppm, and
7.2 ppm, indicating that tautomerization or activation of the
N
Ph
N
Ph
N
N
C(1) proton has not occurred. The most dramatic shift in the
1H NMR spectrum of 2-DMSO is the methylene region
between 3-5 ppm which maintain four distinct signals
corresponding to the diastereotopic protons on the ethylene
linker. Similar results are obtained when heating complex 2-
cymene in DMSO, however the reaction proceeds at a slower
rate.
P
P
DMSO, 17 h, 100 °C
– C6H6
Cl
Cl
Ru
Cl
Ru
Cl
(DMSO)3
2
2
(2-benzene)
(2-DMSO)
2 AgBF4
DMSO, 30 min, 22 °C
– 2 AgCl
Another method for formation of PNHCs is base promoted
tautomerization. For example, in the presence of a suitable
metal precursor, the addition of a slight excess of KOtBu to
deprotonate the imidazole at the C1 position, followed by
addition of NH4PF6 to protonate the N-H wingtips generates
the desired PNHC complex.35, 36 When KOtBu was added to 2-
benzene in CD2Cl2, the appearance of multiple aromatic peaks
in the 1H NMR spectrum between 7.1 and 8.0 ppm and at least
five peaks between 2.3 and 2.5 ppm, corresponding to the
benzimidazole methyl substituents, suggest that the two
imidazole arms have become inequivalent. Additionally,
deprotonation of the ethylene linkers is probable as evidence
by the appearance of new multiplets in the olefinic region
between 6.0 and 6.3 ppm (Figure S4). With the addition of
NH4PF6, the 1H NMR spectrum simplifies to reveal a major
product similar to the starting material, 2-benzene. The
absence of the distinctive PNHC peak(s), as well as the
persistence of the C(1) imidazole peaks between 6.0 and 6.25
ppm, indicate that the base promoted tautomerization is not a
feasible method for achieving the desired PNHC complex in
this particular case (Figure S5).
4 BF4
4 BF4
N
N
N
N
N
Ph
DMSO
N
N
N
C6H6
Ru
P
Ph
N
DMSO
Ru
P
½
+
Ru
C6H6
DMSO
Ru
P
N
N
DMSO
C6H6
N
N
N
Ph
C6H6
P
N
N
Ph
(4)
DMSO, 12 h, 22 °C
– C6H6
4 BF4
4 BF4
N
N
N
N
N
N
Ph
DMSO
N
N
(DMSO)3
Ru
P
DMSO
Ph
DMSO
Ru
P
½
+
Ru
(DMSO)3
(DMSO)3
DMSO
Ru
P
N
N
N
N
Ph
(DMSO)3
P
N
N
N
N
Ph
(5)
Scheme 2. Synthesis of 2-DMSO
arene
, 4a/b, and 5a/b from complex 2-
.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 5 of 9
View Article Online
DOI: 10.1039/C7DT04333C
Journal Name
When the mixture of 4a and 4b is sonicated for one hour or
ARTICLE
Overall, the success of the one pot synthesis of
1 relies
left at room temperature overnight, complete conversion to upon the use of NMP as a solvent to access sufficient
5a and 5b is observed by 1H NMR and 31P{1H} NMR temperature needed to overcome the activation barrier
spectroscopy along with a colour change from yellow-orange associated with the demanding tautomerization reaction,
to pale yellow (Scheme 2). The 31P{1H} spectrum of 5a and 5b without base-mediated deprotonation of other acidic protons
displays two singlets, one at 35 ppm and the other at 33 ppm, on the ligand backbone. The addition of AgBF4 allows for
a downfield shift from the resonances of 4a and 4b, indicating chloride displacement and the clean formation of a single
the formation of two new species, which we propose to be the conformer of the desired tris-solvento platform.
result of ligand substitution with loss of the arene, resulting in
dimers of the general formulation [(DMSO)4Ru(L)]2[BF4]4 supported by tridentate ligands, as developed by Sanford37, 38
(Scheme 2). These new species also appear at a ratio of and Leitner,39 provided motivation for studying complex
as a
100:33 by integration of the 31P{1H} NMR spectrum, supporting catalyst for this transformation. Preliminary catalytic studies
the hypothesis that the dimers 5a and 5b remain intact during were performed with complex (53 µmol) in THF under 20 bar
Catalytic CO2 hydrogenation using ruthenium complexes
1
1
1
the ligand substitution reaction. The H NMR spectrum, along CO2 and 60 bar H2, yielding formate in the presence of excess
with COSY NMR studies, also supports the existence of K3PO4, with an initial, reproducible turn over number (TON) of
diastereomers 5a and 5b. A close examination of the 110 ± 6 with un-optimized reaction conditions (Scheme 3).
methylene region of both the 2D COSY spectrum and the 1D 1H Potassium formate precipitated out of solution, and the
NMR spectrum reveal that there are four inequivalent types of precipitate and solution were analysed separately for formate
methylene environments present in solution.
These formation using quantitative 1H and 13C NMR spectroscopy
diastereotopic ethylene linker resonances integrate to (Figure S12-16). Additionally, the pressure of the reaction
1:1:0.3:0.3, consistent with both the 31P{1H} NMR spectrum vessel steadily decreased over the four-day reaction time,
ratios and the proposed structures of 5a and 5b (Figure S8). suggesting slow but consistent gas consumption (Figure S17).
The aromatic region of the COSY spectrum also reveals that We hypothesize that further optimization of this class of
there are only two distinct types of phenyl groups in solution. complexes will result in robust catalytic activity. Optimization
This supports our conclusion that the solution consists of a of the catalytic conditions and mechanistic investigations are
mixture of diastereomers.
imilar to what is observed for the 2-benzene, when two
currently underway in our lab.
S
equivalents AgBF4 are added to a solution of 2-cymene in
DMSO or in acetonitrile, complete conversion to 4a-cymene
and 4b-cymene is observed after 30 minutes. The ratio of
major to minor product is 100:16 in DMSO and 100:30 in
acetonitrile and the p-cymene remains bound to the
ruthenium center after more than 24 hours. Heating the DMSO
reaction at 50 °C for 38 hours shows incomplete conversion to
5a and 5b, which increase simultaneously at a ratio of 100:36
suggesting that the dimer breaks apart in the presence of heat
and DMSO before p-cymene dissociates. The ratio of the major
to minor diastereomer changes based on the identity of the
coordinating solvent and the structure of the coordinated
aromatic ligand (p-cymene or benzene). We hypothesize that
the steric interactions of ligands around the metal center alter
the equilibrium between the two diastereomers in solution.
Continuous heating of 5a and 5b in DMSO lead to
decomposition of these complexes into multiple products as
seen by 31P-NMR spectroscopy (Figure S9).
O
C
cat. 1
CO2
+
H2
K3PO4 (86 eq.)
THF
140 °C, 4 days
H
O
K
20 bar
60 bar
TON = 110
Scheme 3. Hydrogenation of CO2 by [(PNHC)2PPh Ru(NCCH3)3][BF4]2
(1) under basic conditions.
Conclusions
We have explored the coordination chemistry and
reactivity of a facially coordinating tripodal bis(PNHC) ligand
and the arene dimer precursors [(C6H6)RuCl2]2 and [(p-
cymene)RuCl2]2.
[(MeCN)3Ru(PNHC)2PPh]2+
procedure using NMP as a solvent. We hypothesize that the
one pot synthesis of can be adapted for use as a general
Ultimately, the tris-solvento complex
(
1
) can be synthesized in a one pot
1
strategy to access a range of other transition metal complexes
ligated by the bis(PNHC) ligand. The use of NMP appears
critical for generating these bis-PNHC complexes due to its
polarity, hydrogen bonding ability, and high boiling point.
Using other solvents, such as DMSO, dichloromethane, and
acetonitrile we can access a series of phosphine-bound
monomer and dimer species with non-activated imidazole
In an attempt to isolate a single product, similar reaction
conditions to those used for the previously reported base
catalysed tautomerization of imidazole ligands to PNHCs were
tested with 5a and 5b 35, 36
When 5a and 5b are heated at 60
.
°C for two hours with excess NEt3 no change is seen by 31P{1H}
NMR or by 1H NMR spectroscopy (Figure S10). Furthermore,
addition of two equivalents of KOtBu to a DMSO solution of 5a
and 5b led to the formation of multiple species by 31P{1H} NMR
units. In the preliminary study of
1 as a CO2 hydrogenation
catalyst we observed a TON of 110 to formate, and we
anticipate that further optimization of the reaction conditions
1
and H NMR spectroscopy, similar to what we saw previously
in attempts to promote tautomerization using this base (Figure
S11).
will lead to robust catalytic activity from complex
derivatives.
1 and its
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 6 of 9
View Article Online
DOI: 10.1039/C7DT04333C
ARTICLE
Journal Name
Experimental Methods
Catalytic studies. The CO2 hydrogenation reaction was carried
out in a PFTE lined 45 ml Parr Instruments 5000 Multiple Reactor
system vessel. Under nitrogen atmosphere, 5 (45 mg, 53 µmol) and
K3PO4 (962 mg, 4.53 mmol, 86 eq) were dissolved in THF (5 ml) and
transferred to the Parr system vessel with a magnetic stir bar. The
vessel was pressurized with CO2 (20 bar) and H2 (60 bar) and heated
to 140 oC for four 4 days. The reaction solution was decanted away
from the resulting precipitate, and both were analyzed via 1H and
13C NMR. To the decanted solution, mesitylene (27.4 mg, 0.2280
mmol) was added as an internal standard. The precipitate was
dissolved in D2O, and dimethylformamide (DMF; 50.9 mg, 0.6964
mmol) was added as an internal standard. The spin-lattice
relaxation times (T1) were determined for standard solutions
containing known amounts of mesitylene and formic acid in DMSO-
d6 and of DMF and sodium formate in D2O in order to determine
the appropriate delay time for quantitative 1H NMR. For the
solution in DMSO-d6, the formate C-H proton T1 = 7.2 seconds, the
mesitylene arene-H T1 = 5.0 seconds, and the mesitylene methyl C-
H T1 = 2.3 seconds. For the D2O solution, the formate C-H T1 = 9.5
seconds, the DMF C-H T1 = 9.9 seconds, and the two inequivalent
DMF methyl C-H T1 = 8.3 seconds and 4.7 seconds (See SI for
details). These values are consistent with the literature.41 The delay
time for 1H NMR analysis of the reaction solutions was set to 30
seconds. Turn over numbers were calculated independently for the
solution and precipitate, and then added. An average of three runs
yielded a TON of 110 ± 6. For reference, the uncatalyzed reaction
run in the absence of complex 1 yielded about half as much
formate. Specifically, the formate to K3PO4 ratio in the catalyzed
reaction is 1.33:1 and for the uncatalyzed reaction is 0.68:1.
General remarks. All reactions were conducted under an inert
nitrogen atmosphere in a glove box or using standard Schlenk
techniques, unless otherwise indicated. Dichloromethane,
acetonitrile and diethyl ether were dried through columns of
activated alumina and molecular sieves under N2 gas. NMP, DMSO,
DMSO-d6, dichloro(p-cymene)ruthenium(II) dimer, and AgBF4 were
purchased anhydrous from Sigma Aldrich and were used without
further purification. CD2Cl2 and CD3CN were purchased from
Cambridge Isotope Labs, dried over calcium hydride, distilled before
use, and stored over molecular sieves under N2.
Dichloro(benzene)ruthenium(II) dimer was prepared according to a
published literature procedure.40 L was prepared using a modified
procedure from published in the literature.17 All NMR spectra were
taken on either a Bruker AV500, AV700, DRX500, or AV300
spectrometer at 298 K.
Synthesis of ((MeCN)3Ru(PNHC)2PPh)(BF4)2 (1).
One pot synthesis: In a N2 glovebox, a 100 ml thick-walled
Schlenk tube equipped with
a stir bar was charged with
dichloro(benzene)ruthenium(II) dimer (0.182 g, 0.363 mmol, 1 eq)
and L (0.334 mg, 0.734 mmol, 2 eq), and NMP (10 ml). The reaction
mixture was allowed to stir at room temperature for at least an
hour. The Schlenk tube was sealed, removed from the glove box,
connected to the Schlenk line, and heated outside the box at 170 °C
for one hour. The volatiles were then removed under reduced
pressure, at 100 °C on the Schlenk line, over the course of four
hours. The Schlenk tube was brought into the glove box and
acetonitrile (10 ml) and AgBF4 (0.284 g, 1.45 mmol, 4 eq) were
added to the reaction mixture. The solution immediately became
gray and cloudy. The resultant mixture was stirred for 1 hr before
being filtered through Celite and the captured solids were washed
with acetonitrile (3 x 5 ml). The volume of the extracts was reduced
by half under reduced pressure, and the product was precipitated
from solution with diethyl ether (30 ml). The resulting precipitate
was collected on a frit and was washed with diethyl ether (3 x 15
ml), and dried overnight under reduced pressure. The product was
collected as a white powder (0.583 g, 93% yield).
Synthesis of (C6H6)Ru(L)Cl2 (2-benzene). Ligand L (232 mg, 0.466
mmol, 1 eq) was dissolved in dichloromethane (15 ml) and the
resulting solution was transferred to a 20 ml vial charged with
dichloro(benzene)ruthenium(II) dimer and a stir bar. The solution
turned dark red and was allowed to stir for an hour at room
temperature. The solution was filtered through Celite and the Celite
was washed with dichloromethane (5 ml). The volatiles were
removed under vacuum until less than 1 ml of liquid remained. The
product was precipitated with 40 ml of filtered diethyl ether,
collected on a medium porosity frit, washed with diethyl ether (3 x
15 ml), and dried under vacuum overnight, producing a dark orange
powder (222 mg, 68% yield). High quality orange hexagonal prisms
suitable for single crystal X-ray diffraction were grown via slow
From Complex 3: Complex 3 (55.9 mg, 0.08374 mmol, 1 eq) was
suspended in CD3CN (1.5 ml) in a 20 ml vial and transferred to a vial
containing AgBF4 (19.5 mg, 0.101 mmol, 2 eq) via pipette. The
mixture immediately turned purple. After stirring for an hour, the
solution was filtered via syringe filter, washed two times with 2 ml
of acetonitrile and the product was precipitated out of solution with
35 ml of diethyl ether. The precipitate was collected on a medium
porosity frit and washed three times with 15 ml of diethyl ether,
dried under reduced pressure overnight, and was collected as a
white powder (56.9 mg, 80% yield).
evaporation of solvent from
a super-saturated solution in
dichloromethane and diethyl ether at -35°C. 1H NMR (500 MHz,
Methylene Chloride-d2) δ 7.95 – 7.83 (m, 2H, Ar-H), 7.68 – 7.58 (m,
3H, Ar-H), 7.55 (s, 2H, Ar-H), 7.45 (s, 2H, Ar-H), 7.07 (s, 2H, Ar-H),
5.42 (s, 6H, Ru-Benzene), 4.34 (dt, J = 15.9, 7.9 Hz, 2H, -CH2), 4.21
(dq, J = 15.8, 8.2 Hz, 2H, -CH2), 2.83 (q, J = 8.9 Hz, 4H, -CH2), 2.35 (s,
6H, -CH3), 2.32 (s, 6H, -CH3). 31P{1H} NMR (202 MHz, DMSO-d6) δ
13.7. 13C NMR (126 MHz, Benzene-d6) δ 142.9, 142.3, 134.3 , 132.8 ,
132.2 , 131.9 , 131.6 , 130.7 (d, J = 8.2 Hz), 129.9 (d, J = 9.5 Hz),
120.7 , 110.06 , 89.00 (d, J = 3.4 Hz), 40.6 , 26.3 (d, J = 25.4 Hz), 20.7
, 20.3. Anal. Calc. for C34H37Cl2N4PRu: C, 57.95; H, 5.29; N, 7.95.
Found: C, 56.92; H, 5.43; N, 7.69 %.
High quality crystals suitable for X-ray diffraction were grown by
slow diffusion of diethyl ether into the CD3CN solution at -35°C. H
1
NMR (700 MHz, Methylene Chloride-d2) δ 10.78 (s, 2H, N-H), 7.85
(dd, J = 10.2, 7.7 Hz, 2H, Ph-H), 7.64 (td, J = 7.8, 2.1 Hz, 2H, Ph-H),
7.61 – 7.56 (m, 1H, Ph-H), 7.39 (s, 2H, Ar-H), 7.11 (s, 2H, Ar-H), 4.39
(dddd, J = 19.3, 13.2, 10.0, 2.5 Hz, 2H, -CH2), 4.25 (dddd, J = 26.2,
14.2, 7.3, 3.2 Hz, 2H, -CH2), 2.71 (tdd, J = 12.9, 7.1, 3.7 Hz, 2H, -CH2),
2.62 (s, 3H, NCCH3), 2.35 (s, 6H, -CH3), 2.33 (s, 6H, -CH3), 2.22 (s, 6H
NCCH3), 2.14 (tdd, J = 13.0, 9.6, 6.0 Hz, 2H, -CH2). 31P{1H} NMR (202
MHz, Acetonitrile-d3) δ 44.73 . 13C NMR (176 MHz, CD3CN) δ 189.05,
188.95, 134.87, 134.63, 134.07, 133.39, 133.11, 132.41, 131.90,
131.85, 131.44, 129.79, 129.74, 124.69, 118.31, 111.88, 110.58,
26.73, 26.53, 20.29, 20.04. Anal. Calc. for B2C34F8H40N4PRu: C, 47.91;
H, 4.73; N, 11.5. Found: C, 47.09; H, 4.65; N, 11.35 %.
Synthesis of (p-cymene)Ru(L)Cl2 (2-cymene). Ligand L (41.3 mg,
0.0909 mmol, 1 eq) was dissolved in dichloromethane (4 ml), and
the resulting solution was transferred to 20 ml vial charged with
dichloro(p-cymene)ruthenium(II) dimer (29 mg, 0.0468 mmol, 0.515
eq) and a stir bar. The solution immediately turned clear vibrant
orange. The solution was allowed to stir at room temperature for
90 min before the volatiles were removed via reduced pressure.
The product was isolated as a bright orange precipitate from a 1:10
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 7 of 9
View Article Online
DOI: 10.1039/C7DT04333C
Journal Name
ARTICLE
mixture of dichloromethane and diethyl ether. The orange powder
was collected on a medium porosity frit and was dried overnight
under vacuum (30.8 mg, 45% yield). H NMR (500 MHz, Methylene
Minor Diastereomer
1H NMR (500 MHz, Acetonitrile-d3) δ 8.27 (s, 1H, Ar-H), 8.10 (s,
1H, Ar-H), 8.00 (s, 1H, Ar-H), 7.89 – 7.81 (m, 3H, Ph-H), 7.45 (s, 1H,
Ar-H), 7.31 (s, 1H, Ar-H), 7.27 (s, 1H, Ar-H), 7.16 (s, 1H, Ar-H), 6.99
(s, 1H, Ar-H), 5.88 (d, J = 6.6 Hz, 1H, p-cymene Ar-H), 5.81 (d, J = 6.5
Hz, 1H, p-cymene Ar-H), 5.69 (d, J = 6.3 Hz, 1H, p-cymene Ar-H),
5.59 (d, J = 6.4 Hz, 1H, p-cymene Ar-H), 5.16 – 5.08 (m, 1H, -CH2),
4.18 (td, J = 16.9, 9.4 Hz, 1H, -CH2), 3.33 – 3.25 (m, 1H, -CH2), 3.24 –
3.18 (m, 1H, -CH2), 3.02 (tt, J = 15.5, 8.0 Hz, 1H, -CH2), 2.87 – 2.73
(m, 2H, -CH2), 2.38 (s, 3H, -CH3), 2.32 (s, 3H, -CH3), 2.27 (s, 3H, -CH3),
2.24 (s, 3H, -CH3), 1.84 (s, 3H, -CH3), 1.30 – 0.94 (m, 1H, -CH), 1.08
(d, J = 7.1 Hz, 3H, -CH3), 1.02 (d, J = 6.9 Hz, 3H, -CH3). 31P{1H} NMR
(202 MHz, CD3CN) δ 19.49.
1
Chloride-d2) δ 7.88 (tt, J = 6.9, 2.3 Hz, 2H, Ph-H), 7.66 (dt, J = 4.4, 2.2
Hz, 3H, Ph-H), 7.60 (s, 2H, Ar-H), 7.51 (s, 1H, Ar-H), 7.11 (s, 2H, Ar-
H), 5.29 – 5.18 (m, 4H, -CH2, Ar-H p-cymene), 4.42 – 4.22 (m, 4H, -
CH2), 3.08 (ddt, J = 13.7, 9.7, 6.7 Hz, 2H, -CH2), 2.83 (dddd, J = 14.8,
12.7, 9.4, 5.3 Hz, 2H, -CH2), 2.40 (s, 6H, -CH3), 2.37 (s, 6H, -CH3), 1.82
(s, 3H, -CH3), 1.11 (d, J = 6.9 Hz, 6H, -CH3). 31P{1H} NMR (283 MHz,
CD2Cl2) δ 10.8. 13C NMR (176 MHz, CD2Cl2) δ 142.9, 142.4, 134.3 (d,
J = 40.0 Hz), 132.7, 132.3, 131.6 131.6 , 130.4 (d, J = 7.5 Hz), 129.9
(d, J = 9.2 Hz), 120.7 , 110.0 , 109.1 , 97.4 , 89.3 , 86.2 , 40.4 , 30.7 ,
25.5 (d, J = 23.8 Hz), 22.1 , 20.7 , 20.3 , 18.0.
Synthesis of [(PNHC)2PPhRuCl]Cl (3). In a 20 ml scintillation vial
(C6H6)RuCl2 (64 mg, 0.217 mmol, 1 eq) was dissolved in NMP (2 ml)
and was transferred via pipette to a vial equipped with a stir bar
and the free L (123 mg, 0.433 mmol, 2 eq). The solution was
allowed to stir for 30 min at room temperature before being
transferred to a sealed tube. The sealed tube was heated for 23
hours at 140 °C. The sealed tube was brought back into the glove
box and the product was precipitated with 15 ml of diethyl ether,
collected on a medium porosity frit, washed 3 times with 10 ml of
diethyl ether and dried overnight under vacuum, and was collected
as an off-white powder (98.0 mg, 36% yield). 1H NMR (300 MHz,
Methylene Chloride-d2) δ 10.96 (s, 1H, N-H), 10.88 (s, 1H, N-H), 8.08
(dd, J = 9.9, 7.7 Hz, 2H, Ph-H), 7.39 (t, J = 7.4 Hz, 1H, Ph-H), 7.31 –
7.19 (m, 3H, Ar-H), 7.10 (s, 1H, Ar-H), 6.95 (d, J = 3.4 Hz, 2H, Ar-H),
4.92 – 4.71 (m, 1H, -CH2), 4.63 – 4.40 (m, 1H, -CH2), 4.30 (dddt, J =
87.5, 27.6, 14.1, 6.3, 3.6 Hz, 1H, -CH2), 3.89 – 3.71 (m, 1H, -CH2),
2.76 – 2.61 (m, 1H, -CH2), 2.37 (s, 3H, -CH3), 2.33 (s, 3H, -CH3), 2.28
(s, 3H, -CH3), 2.21 (s, 12H, -CH3). 31P{1H} NMR (121 MHz, CD2Cl2) δ
52.9.
[(DMSO)4Ru(L)]2 (BF4)4 (5a and 5b). The benzene dissociates
from 4a-benzene and 4b-benzene on prolonged exposure to DMSO
with gentle heating.
Major Diastereomer
1H NMR (700 MHz, DMSO-d6) δ 8.46 (s, 1H, Ar-H), 8.37 (s, 1H, Ar-
H), 8.08 – 8.03 (m, 2H), 7.63 (td, J = 7.4, 2.3 Hz, 2H, Ph-H), 7.58 –
7.56 (m, 1H, Ph-H), 7.58 (s, 1H, Ar-H), 7.56 (s, 1H, Ar-H), 7.52 (s, 1H,
Ar-H), 7.43 (s, 1H, Ar-H), 4.79 (ddt, J = 15.4, 10.4, 5.3 Hz, 1H, -CH2),
4.62 (m, 1H, -CH2), 4.45 – 4.36 (m, 1H, -CH2), 4.22 (ddt, J = 15.4,
10.8, 5.5 Hz, 1H, -CH2), 3.35 – 3.26 (m, 2H, -CH2), 3.21 – 3.02 (m,
2H, -CH2) 2.39 (s, 3H, -CH3)m2.36 (s, 3H, -CH3) 2.34 (s, 3H, -CH3) 2.32
(s, 3H, -CH3). 31P{1H} NMR (283 MHz, DMSO) δ 35.2.
Minor Diastereomer
1H NMR (700 MHz, DMSO-d6) δ8.39 (s, 1H, Ar-H), 8.25 (s, 1H, Ar-
H), 7.79 – 7.75 (m, 2H, Ph-H), 7.69 – 7.66 (m, 2H, Ph-H), 7.52 (s, 1H,
Ar-H), 4.67 – 4.57 (m, 1H, -CH2), 4.45 – 4.36 (m, 1H, -CH2), 4.50 (tq, J
= 15.3, 7.9, 7.1 Hz, 1H, -CH2), 4.32 (ddt, J = 15.3, 10.9, 5.8 Hz, 1H, -
CH2), 3.21 – 3.02 (m, 2H, -CH2), 2.87 (tt, J = 13.0, 6.3 Hz, 1H, -CH2),
2.76 (dq, J = 14.0, 6.8 Hz,1H, -CH2), 2.32 (s, 3H, -CH3), 2.17 (s, 3H, -
CH3). 31P{1H} NMR (283 MHz, DMSO) δ 32.9.
Synthesis of [(PNHC)2PPhRuCl(DMSO)2]Cl (3-DMSO). Complex 3
was dissolved in DMSO. High quality crystals suitable for X-ray
diffraction were grown in air with a super saturated solution in a 1:1
mixture of DMSO and dichloromethane.
Acknowledgements
Synthesis of [(p-cymene)(DMSO)Ru(L)]2(BF4)4 (4a-cymene and
4b-cymene). In a N2 glovebox, a J-Young tube was charged with
dichloro(p-cymene)ruthenium(II) dimer (9 mg, 0.014 mmol, 0.5 eq),
L (16 mg, 0.0291 mmol, 1 eq), and DMSO-d6 (1.4 ml). The J-Young
tube was sealed and the reaction vessel was sonicated for 28 min.
The J-Young tube was returned to the glove box and AgBF4 (11 mg,
0.583 mmol, 2 eq) was added to the reaction mixture. The tube was
again sealed and the mixture was sonicated. After five minutes of
sonication the orange solution turned cloudy and the color changed
from orange to yellow-orange. The reaction was judged complete
after 90 minutes of sonication.
The authors gratefully acknowledge the ACS Petroleum
Research Fund (54226-DNI3) and the David and Lucile Packard
Foundation for support of this research. The authors also
acknowledge assistance from Dr. Werner Kaminsky for
assistance with the X-ray crystallography data collection and
structure refinement, and Professor Douglas Grotjahn for
helpful discussions.
Notes and references
Major Diastereomer
1H NMR (500 MHz, Acetonitrile-d3) δ 9.21 (s, 1H, Ar-H), 8.65 (s,
1H, Ar-H), 7.98 (t, J = 8.9 Hz, 2H, Ph-H), 7.75 – 7.59 (m, 5H, Ar-H),
6.94 (s, 1H, Ar-H), 6.72 (s, 1H, Ar-H), 5.37 (d, J = 6.0 Hz, 1H, p-
cymene Ar-H), 5.09 – 4.95 (m, 1H, -CH2), 4.94 (d, J = 6.4 Hz, 1H, p-
cymene Ar-H), 4.45 (m, 1H, -CH2), 4.08 (d, J = 5.9 Hz, 1H, p-cymene
Ar-H), 3.98 (q, J = 14.9 Hz, 1H, -CH2), 3.83 (d, J = 6.4 Hz, 1H, p-
cymene Ar-H), 3.74 (dq, J = 15.0, 7.7, 7.0 Hz, 1H, -CH2), 3.50 (d, J =
15.9 Hz, 1H, -CH2), 3.36 (td, J = 13.5, 6.4 Hz, 1H, -CH2), 3.18 – 3.07
(m, 1H, -CH2), 2.36 (s, 6H, -CH3), 2.34 (s, 3H, -CH3), 2.34 (s, 3H, -CH3),
1.62 (s, 3H, -CH3), 1.30 – 0.94 (m, 1H, -CH), 0.86 (d, J = 6.9 Hz, 3H, -
CH3), 0.43 (d, J = 6.9 Hz, 3H, -CH3). 31P{1H } NMR (202 MHz, CD3CN) δ
13.2.
1.
2.
K. Öfele, J. Organomet. Chem., 1968, 12, P42-P43.
H. W. Wanzlick and H. J. Schönherr, Angew. Chem. Int.
Ed., 1968, 7, 141-142.
M. N. Hopkinson, C. Richter, M. Schedler and F. Glorius,
Nature, 2014, 510, 485-496.
W. A. Herrmann, Angew. Chem. Int. Ed., 2002, 41, 1290-
1309.
N. Marion, S. Díez-González and S. P. Nolan, Angew.
Chem. Int. Ed., 2007, 46, 2988-3000.
3.
4.
5.
6.
F. E. Hahn and M. C. Jahnke, Angew. Chem. Int. Ed., 2008,
47, 3122-3172.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Dalton Transactions
Page 8 of 9
View Article Online
DOI: 10.1039/C7DT04333C
ARTICLE
Journal Name
7.
F. E. Hahn, in Advances in Organometallic Chemistry and 34.
Catalysis, John Wiley Sons, Inc., 2013, DOI:
J. DePasquale, M. Kumar, M. Zeller and E. T. Papish,
Organometallics, 2013, 32, 966-979.
&
10.1002/9781118742952. Ch 9, pp. 111-132.
F. E. Hahn, ChemCatChem, 2013, 5, 419-430.
35.
J. Ruiz and B. F. Perandones, J. Am. Chem. Soc., 2007, 129,
9298-9299.
8.
9.
M. C. Jahnke and F. E. Hahn, Coord. Chem. Rev., 2015, 36.
293, 95-115.
J. M. C. and H. F. Ekkehardt, Chem. Lett., 2015, 44, 226- 37.
237.
S. Kuwata and T. Ikariya, Chem. Commun., 2014, 50, 38.
14290-14300.
R. J. Sundberg, R. F. Bryan, I. F. Taylor and H. Taube, J. Am. 39.
Chem. Soc., 1974, 96, 381-392.
G. Sini, O. Eisenstein and R. H. Crabtree, Inorg. Chem.,
2002, 41, 602-604.
A. S. El-Tabl, M. Mohamed Abd El-Waheed, M. A. Wahba 40.
and N. Abd El-Halim Abou El-Fadl, Bioinorg. Chem. Appl.,
J. Ruiz, D. Sol, J. F. Van der Maelen and M. Vivanco,
Organometallics, 2017, 36, 1035-1041.
C. A. Huff and M. S. Sanford, ACS Catal., 2013, 3, 2412-
2416.
N. M. Rezayee, C. A. Huff and M. S. Sanford, J. Am. Chem.
Soc., 2015, 137, 1028-1031.
S. Wesselbaum, V. Moha, M. Meuresch, S. Brosinski, K. M.
Thenert, J. Kothe, T. vom Stein, U. Englert, M. Holscher, J.
Klankermayer and W. Leitner, Chem. Sci., 2015, 6, 693-
704.
M. A. Bennett and A. K. Smith, J. Chem. Soc., Dalton
Trans., 1974, 0, 233-241.
10.
11.
12.
13.
14.
2015, 2015, 126023.
41.
I. D. Campbell and R. Freeman, J. Magn. Reson., 1973, 11,
143-162.
15.
16.
J. L. Gomez-Lopez, D. Chávez, M. Parra-Hake, A. T.
Royappa, A. L. Rheingold, D. B. Grotjahn and V. Miranda-
Soto, Organometallics, 2016, 35, 3148-3153.
D. C. Marelius, E. H. Darrow, C. E. Moore, J. A. Golen, A. L.
Rheingold and D. B. Grotjahn, Chem. Eur. J., 2015, 21,
10988-10992.
17.
18.
19.
M. R. Norris, S. E. Flowers, A. M. Mathews and B. M.
Cossairt, Organometallics, 2016, 35, 2778-2781.
S. E. Flowers and B. M. Cossairt, Organometallics, 2014,
33, 4341-4344.
G. A. Filonenko, M. J. B. Aguila, E. N. Schulpen, R. van
Putten, J. Wiecko, C. Müller, L. Lefort, E. J. M. Hensen and
E. A. Pidko, J. Am. Chem. Soc., 2015, 137, 7620-7623.
T. J. Korstanje, J. Ivar van der Vlugt, C. J. Elsevier and B. de
Bruin, Science, 2015, 350, 298-302.
20.
21.
J. Coetzee, D. L. Dodds, J. Klankermayer, S. Brosinski, W.
Leitner, A. M. Z. Slawin and D. J. Cole-Hamilton, Chem.
Eur. J., 2013, 19, 11039-11050.
22.
23.
24.
25.
A. A. N. Magro, G. R. Eastham and D. J. Cole-Hamilton,
Chem. Commun., 2007, 0, 3154-3156.
N. Nakagawa, E. J. Derrah, M. Schelwies, F. Rominger, O.
Trapp and T. Schaub, Dalton Trans., 2016, 45, 6856-6865.
Y. Li, I. Sorribes, T. Yan, K. Junge and M. Beller, Angew.
Chem. Int. Ed., 2013, 52, 12156-12160.
I. Mellone, M. Peruzzini, L. Rosi, D. Mellmann, H. Junge,
M. Beller and L. Gonsalvi, Dalton Trans., 2013, 42, 2495-
2501.
26.
27.
28.
29.
C. Yin, Z. Xu, S.-Y. Yang, S. M. Ng, K. Y. Wong, Z. Lin and C.
P. Lau, Organometallics, 2001, 20, 1216-1222.
Y. Arikawa, T. Asayama, Y. Moriguchi, S. Agari and M.
Onishi, J. Am. Chem. Soc., 2007, 129, 14160-14161.
C. W. Leung, W. Zheng, Z. Zhou, Z. Lin and C. P. Lau,
Organometallics, 2008, 27, 4957-4969.
N. A. Foley, M. Lail, J. P. Lee, T. B. Gunnoe, T. R. Cundari
and J. L. Petersen, J. Am. Chem. Soc., 2007, 129, 6765-
6781.
30.
31.
32.
33.
E. Becker, S. Pavlik and K. Kirchner, Adv. Organomet.
Chem., 2008, 56, 155-197.
H. Horvath, G. Laurenczy and A. Katho, J. Organomet.
Chem., 2004, 689, 1036-1045.
A. Demonceau, A. W. Stumpf, E. Saive and A. F. Noels,
Macromolecules, 1997, 30, 3127-3136.
I. Moldes, E. de la Encarnacion, J. Ros, A. Alvarez-Larena
and J. F. Piniella, J. Organomet. Chem., 1998, 566, 165-
174.
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 9 of 9
Dalton Transactions
View Article Online
DOI: 10.1039/C7DT04333C
39x19mm (300 x 300 DPI)