Multidentate Pyridyl-Aminophosphinite and Pyridyl-Phosphoramidite Ruthenium(II) Complexes: Synthesis, Structure and Application as Levulinic Acid Hydrogenation Pre-Catalysts

Article abstract of DOI:10.1002/ejic.201900640

Novel multidentate pyridyl-aminophosphinite (L1) and pyridyl-phosphoramidite (L2) ligands of N^{^}P^{^}P^{^}N-donor system have been synthesized via a series of simple steps. The ligands are symmetrical and as a result, their reactions with [Ru(p-cymene)Cl₂]₂ and [Ru(benzene)Cl₂]₂ lead to the formation of four monodentate bimetallic complexes (1–4) that retain the symmetry of the ligands. Meso and racemic mixtures (rac) of bidentate bimetallic complexes 5–8 were formed from the monodentate complexes through coordination of the pyridine nitrogen atoms to the two metal centers. The isomerism occurs at each metal center, which was evidenced by ³¹P{¹H}, ¹H NMR spectroscopy and single-crystal X-ray diffraction. The complexes were active towards hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) using formic acid as the hydrogen source. The complexes are active at relatively low temperatures and are able to perform the hydrogenation in the absence of any additional solvent apart from the reagents to give high TON of 3 600. The catalysts are recyclable up to the fourth cycle, following which 20 % loss of activity is seen.

Full text of DOI:10.1002/ejic.201900640

A Journal of
Accepted Article
Title: Multidentate pyridyl-aminophosphinite and pyridyl-
phosphoramidite ruthenium(II) complexes: Synthesis, structure
and application as levulinic acid hydrogenation pre-catalysts
Authors: Greshon Amenuvor, Charles K Rono, James Darkwa, and
Banothile C.E. Makhubela
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European Journal of Inorganic Chemistry
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Multidentate pyridyl-aminophosphinite and pyridyl-
phosphoramidite ruthenium(II) complexes: Synthesis, structure
and application as levulinic acid hydrogenation pre-catalysts
Gershon Amenuvor, [a] Charles K. Rono, James Darkwa*, and Banothile C. E. Makhubela*
[a]
[a]
[a]
Abstract: Novel multidentate pyridyl-aminophosphinite (L1) and
pyridyl-phosphoramidite (L2) ligands of N^P^P^N-donor system have
been synthesised via a series of simple steps. The ligands are
substrate. These ligand types are generally large in structure and
therefore form robust complexes with stable kinetic and
thermodynamic properties as compared to monodentate ligands.8
symmetrical and as a result, their reactions with [Ru(p-cymene)Cl
2 2
]
Due to their chelating ability, these ligands’ conformational
mobility is controlled effectively by choosing a suitable bridging or
linker size.1
and [Ru(benzene)Cl lead to the formation of four monodentate
2 2
]
bimetallic complexes (1-4) that retain the symmetry of the ligands.
Meso and racemic mixtures (rac) of bidentate bimetallic complexes 5-
In general, multidentate mixed-donor ligands that have been
reported comprise of phosphorus, nitrogen, sulphur and oxygen
donor atoms in different binding arrangements such as P^N^S
and P^N^N^P systems.9-11 An example of the latter is the
iminophosphorane-phosphine reported by Le Floch and co-
workers.12-13 Both iron(II) and rhodium(III) complexes of this ligand
have been found to be very effective in catalysing transfer
hydrogenation of acetophenone and its derivatives to the
respective alcohols. A year later, Sabo-Etienne and co-workers
8
were formed from the monodentate complexes through coordination
of the pyridine nitrogen atoms to the two metal centres. The isomerism
31
1
1
occurs at each metal center, which was evidenced by P{ H}, H NMR
spectroscopy and single crystal X-ray diffraction. The complexes were
active towards hydrogenation of levulinic acid (LA) to γ-valerolactone
(GVL) using formic acid as the hydrogen source. The complexes are
active at relatively low temperatures and are able to perform the
hydrogenation in the absence of any additional solvent apart from the
reagents to give high TON of 3 600. The catalysts are recyclable up
to the fourth cycle, following which 20% loss of activity is seen.
found
that
a
ruthenium(II)
complex
bearing
the
iminophosphorane-phosphine ligand was very effective in the
hydrogenation of both aromatic and aliphatic ketones.14 Worthy of
Introduction
2 2 2
attention is the extremely efficient trans-[RuCl ((S,S)-cyP (NH) ]
complex of P^N^N^P systems used for transfer hydrogenation of
aromatic ketones reported by Noyori and co-workers.15
The design of multidentate ligands containing mixed-donor atoms
to functionalise transition metal centres is a subject of growing
interest in coordination and organometallic chemistry.1-3
Tetradentate N^P^P^N type of mix-donor ligands are also
promising candidates for designing reactive transition metal
catalysts. In particular, very few examples of these ligands that
can coordinate to two metal centres through all four donor atoms
are known.4,16-17 One such ligand system is the 2-
Multidentate mixed-donor ligands function cooperatively in
stabilizing metal centres due to their different binding abilities and
bridging effect between two or more metal centres.4 These
synergistic effects are helpful in making complexes containing
2 2 n 2
PyCH (Ph)P(CH ) P(Ph)CH -2-Py (Py = pyridine, n = 2-4) (Figure
multidentate mixed-donor ligands very attractive for several
applications including catalysis.5-7 Catalytic activity of these
1 (a)) reported by Nakajima and co-workers, that bound to two
metal centres in a bidentate fashion providing a good platform for
homo- and hetero-dinuclear systems. The N^P^P^N system
ligands also results from easy dissociation of the weakly
coordinated donor atoms to create vacant site for the incoming
(
Figure 1(b)) reported by Mezzetti and co-workers forms a very
stable complex with iron(II) compared to P^N^N^P system due to
the hard N-donors (and its less bulkiness) at the terminals which
matches with the hard metal centre.17
[
a]
Dr G. Amenuvor, Mr C.K. Rono, Prof J Darkwa,
Dr B C. E. Makhubela
Chemistry Department
University of Johannesburg
Auckland Park Campus, 2006, South Africa
E-mail: bmakhubela@uj.ac.za
Our group has reported application of P^N pyrazolyl-phosphite
ruthenium(II) and pyrazolyl-phosphinite ruthenium(II) complexes
for LA hydrogenation and noticed the catalysts are effective and
selective for GVL formation using molecular hydrogen.18 By
Supporting information for this article is given via a link at the end of
the document.
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European Journal of Inorganic Chemistry
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FULL PAPER
carefully selecting phosphinocarboxylate ligands, we were able to
design another heterometallic Ru^Zn-based catalyst system.19a
This system outperformed the pyrazolyl-phosphite ruthenium(II)
and pyrazolyl-phosphinite ruthenium(II) system in LA
hydrogenation when formic acid was used as the hydrogen
source. LA is a product form cellulosic biomass hydrolysis →
dehydration → rehydration and has been identified as as one of
the top 12 building block chemicals.19b Hydrogenation of LA leads
to the formation of γ-valerolactone (GVL) which is useful as a bio-
solvent, fuel additive and an illuminating liquid fuel.19c-d
The uniqueness of these ligand systems is their variable
coordination modes, which can allow them to tolerate
coordination to two metal centres in either a mono- or bidentate-
fashion depending on reaction conditions. Single coordination
compounds with multiple metal ion sites can provide a unique set
of properties that may enhance their activity in catalytic
reactions.21 We report herein the synthesis and characterization
of pyridyl-aminophosphinite (L1) and pyridyl-phosphoramidite
(L2) N^P^P^N ligands and their bimetallic ruthenium(II)
complexes bearing benzene and p-cymene auxiliary ligands, and
studies of the catalytic activities of the resulting complexes in
hydrogenation of LA to GVL.
Of interest to us in this work are the pyridyl-phosphoramidite and
pyridyl-aminophosphinite P^N^N^P systems (which are less
explored in catalyst design) to stabilize two ruthenium metal
centres, forming a homonuclear bimetallic system. Having
nitrogen bonded directly to phosphorus might place the electronic
properties of these ligand systems between the traditional
phosphines and the phosphinites or phosphites. The π-acceptor
strength of the phosphorus in the pyridyl-phosphoramidite would
be lessened compared to the phosphite analogues, for instance,
the pyrazolyl-phosphite and pyrazolyl-phosphite systems.20 With
this modification, the properties and structures of their metal
complexes would differ from those of the phosphines and
phosphites analogues. It is envisaged that combination of the
weak π-acceptor phosphorus due to P-N bond and weak σ-donor
from the pyridine nitrogen could influence the catalytic activity of
the complexes containing these ligands.
Results and Discussion
Synthesis of ligands L1 and L2
1
2
The synthesis of N ,N -bis(pyridin-2-ylmethylene)ethane-1,2-
diamine (C1) was reported previously by several independent
authors. Oshima and co-workers22 reported the synthesis of this
compound by refluxing 2-pyridylcarboxaldehyde and 1,2-
ethylenediamine in ethanol for 1 h and obtained the product in
36% yield. El-Qisairi et al. also reported the synthesis of this
compound in a similar manner to obtain 48% yield but at a longer
reaction time of 24 h.23 Other attempts to synthesise C1 also lead
to low yields.24 We synthesised C1 under solvent-free condition,
o
where a mixture of the two reagents was stirred at 50 C for 1 h
to obtain over 99% yield without any work up. Reduction of the
diimine was carried out in methanol at reflux for 2 h, as reported
in literature25 using sodium borohydride to afford N ,N -
bis(pyridin-2-ylmethyl)ethane-1,2-diamine (C2) in 98% yield. The
bis(pyridyl-aminophosphinite) and bis(pyridyl-phosphoramidite)
ligands (L1 and L2) were synthesised as shown in Scheme 1 by
reacting C2 with two equivalents of chlorodiphenylphosphine and
diethyl chlorophosphite to obtain L1 and L2 respectively.
Compound L1 was obtained as a pale-yellow solid in 61% yield
whereas L2 was obtained as a pale-yellow viscous oil (83% yield)
at room temperature. The ligands were characterised using 1H,
1
2
3
1
1
13
1
P{ H} and C{ H} NMR spectroscopy. Both ligands show an
upfield shift in their 31P{ H} spectra with respect to the signals of
1
the original phosphine and phosphite reagents.
Figure 1. Example of N^P^P^N ligands previously reported and new ones
prepared by us.
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European Journal of Inorganic Chemistry
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FULL PAPER
spectrometry (HR-MS), infrared (IR) spectroscopy and elemental
analysis. The 31P{ H} NMR spectroscopy suggests that the two
phosphorus centres in the neutral bimetallic complexes are
magnetically equivalent. This is indicated by the appearance of a
single singlet in the 31P{ H} spectra of the complexes. There was
a considerable downfield shift in the 31P{ H} NMR spectra of
complexes 1 and 2. Complexes 3 and 4 experienced an upfield
shift of about 24 ppm in their 31P{ H} spectra compared to the free
ligand. This is possibly due to the electron withdrawing ability of
the ethoxy moieties on the phosphorus atom, which might
increase the π-acceptor ability of the phosphorus.
1
1
1
1
Scheme 1. Synthesis of bis(pyridyl-aminophosphinite) (L1) and bis(pyridyl-
phosphoramidite) (L2) ligands
.
The 31P{ H} signal of L1 was observed as a single peak at 64.9
ppm, suggesting the symmetrical nature of the ligand. Similarly, a
single major peak at 145.2 ppm in the 31P{ H} NMR spectrum of
L2 was observed. The symmetrical nature of the ligands supports
Balakrishna and co-workers’ findings on similar diphosphine
system that contains a benzyl pendant in place of the pyridyl
moiety.26 However, the N^P^P^N system reported by Nakajima
and co-workers have been found to exist as configurational
1
1
4
isomers due the stereogenic phosphorus centres. Formation of
L1 and L2 was further confirmed by 13C{ H} NMR spectroscopy.
1
In the 13C{ H} NMR spectra of the ligands, JCP and 2JCP couplings
between the phosphorus and the ethylene carbons were
observed. The coupling was observed for the methylene and 3o
carbons of the pyridine as well (Figure S3).
1
3
Scheme 2. Synthesis of mono- and bidentate bimetallic ruthenium(II)
complexes 1-8.
Further characterisation of the complexes with positive mode
electrospray ionization high resolution mass spectrometry, HR-
Synthesis and characterisation of complexes
Synthesis of the neutral complexes was accomplished as shown
in Scheme 2 by reacting ligands L1 and L2 with one molar
+
MS (ESI ), revealed that the complexes were both singly and
doubly (most stable fragments) charged in the mass spectrum
equivalent of the metal precursors [Ru(p-cymene)Cl
2 2
] and
(
e.g. Figure S9). The bidentate complexes were formed as shown
in Scheme 2, by treating the neutral complexes with two
equivalents of sodium tetraphenylborate (NaBPh ). Alternatively,
in situ generation of the neutral complexes in dichloromethane
followed by addition of two equivalents of NaBPh in 4 mL of
[
Ru(benzene)Cl in dichloromethane at room temperature to
2 2
]
afford monodentate bimetallic complexes 1-4. The ligand
coordination to the metal centre through the phosphorus atom is
a fast reaction that occurs in 1 to 2 h with no sign of coordination
of the pyridyl nitrogen as evidenced by changes observed in the
4
4
3
1
1
methanol at room temperature resulted in the formation of the
cationic complexes 5-8 in good yields. The bidentate coordination
of the ligands to the metal centres was established using several
P{ H} chemical shift. This sometimes requires
a halide
abstracting agent.27 The complexes have been characterised by
1
several characterisation techniques such as a combination of H,
1
31
1
13
1
3
1
1
13
1
techniques including H, P{ H} and C{ H} NMR spectroscopy
P{ H} and
C{ H} NMR spectra, high resolution mass
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European Journal of Inorganic Chemistry
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FULL PAPER
and single X-ray diffraction. Interestingly, two configurational
isomers (rac and meso compounds) were obtained from each
neutral complex upon coordination of the pyridyl nitrogen to the
centres assume a piano stool conformation as usual. With the
distorted boat conformation of the six-membered heterocyclic
rings the methylene hydrogens occupy equatorial and axial
positions. The axial hydrogen (H6A) points away from the nearby
pyridine and ethylene hydrogens (H4 and H7A). On the other
hand, H6B is pointed in the direction of H4 and H7A resulting in
close contact interaction with both H4 and H7A. The close contact
space-coupling is confirmed by the short distances observed for
ruthenium centres. The rac and meso compounds are present in
1
1
:1 ratio as determined by 31P{ H} and 1H NMR spectroscopy.
Isomers 5a, 5b, 6a and 6b have distinct solubility properties,
which make their separation possible via washing with
appropriate solvent or recrystallization.
…
…
Significant changes in chemical shifts have been observed in the
1H NMR spectra of the bimetallic complexes. Notably among
H4 H6B and H6B H7A (ca. 2.3 Å). The intramolecular close
…
contact H H distances found in 5a, 7b and 8b are listed in Table
these is the diastereotopicity of the methylene (CH
2
) protons
1. The distorted trigonal planar geometry of the sp3 nitrogen
atoms is observed also in the complexes (Figures 4 and 5). In
complexes 7b and 8b the sum of the three bond angles around
N2 are 358.8˚ and 354.8˚ respectively. Here, 7b seems to slightly
approach planarity at the sp3 nitrogen centre compared to 8b,
which has p-cymene at the metal centres. In 5a, however, the sp3
nitrogen centre is completely planar, giving a sum of the angles
around the nitrogen to be 360˚. There is no general trend in the
adjacent to the pyridyl group that split into an AB quartet (ABq)
fashion.28 HR-MS analysis in both positive and negative modes
also confirmed the formation of the cationic complexes. The
positive mode HR-MS analysis shows the doubly charged
fragments as the prominent peaks of the cationic portions of the
complexes.
3
Crystal structure determination by single crystal X-ray
crystallography
planarity at the sp nitrogen centre for all the complexes. However,
the nitrogen centre becomes more planar with increasing P(1)–
N(2)–C(6) bond angle for the complexes 5a, 7b and 8b. Complex
5a contains the largest P(1)–N(2)–C(6) bond angle of 120.7˚
followed by 7b (113.4˚) and 8b (113.2˚). This trend could be due
to possible strain on the non-planar heterocyclic ring formed
involving the P(1)–N(2)–C(6) bonds.
The crystal structures of the complexes show the presence of two
metal centres in which there is coordination between the
phosphorus atoms and metal centres. Close inspections of the
3
structure of 2 (Figure 2) revealed that the sp nitrogen atoms of
the complexes have lost their trigonal pyramidal geometry and
approach a trigonal planar geometry. This is true for some
substituted nitrogen containing compounds having P-N
bonds.26,29 The loss of pyramidality at the sp3 nitrogen centre
leads to an increase in bond angles around the nitrogen atoms.
For instance, the bond angles around N3 in the structure of 2 are
125.0(5)˚, 119.9(5)˚ and 114.4(6)˚ for P(2)–N(3)–C(26), P(2)–
N(3)–C(34) and C(26)–N(3)–C(34) respectively. The larger bond
angles around the sp3 nitrogen atom are those involving the
phosphorus atom. This is due to the larger size of phosphorus
compared to the size of carbon atom. The sum of the bond angels
around N3 is 359.3˚, which is just 0.7˚ less than 360˚. This
indicates that the N3 is slightly lying out of plane with its three
bonding partners.
The structures obtained from X-ray spectroscopy reveals the
configuration at the metal centres of the cationic complexes. In
the structure of 7b (Figure 4), for instance, there is coordination
of the pyridine nitrogen atoms to the two metal centres via chloride
exchange, resulting in the formation of six-membered heterocyclic
rings that assume a distorted boat conformation. The metal
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European Journal of Inorganic Chemistry
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FULL PAPER
Figure 2. Structure of complex 2 in the crystal as determined by X-ray diffraction.
Selected bond lengths (Å) and bond angles (˚): Ru(1)–Cl(1), 2.404(2); Ru(1)–
Cl(2), 2.415(2); Ru(1)–P(1), 2.359(2); Ru(1)–C(41), 2.211(9); Ru(1)–C(42),
2
.187(8); Ru(1)–C(43), 2.184(9); Ru(1)–C(44), 2.242(8); Ru(1)–C(45), 2.232(8);
Ru(1)–C(46), 2.231(8); P(1)–N(2), 1.668(6); N(2)–C(6), 1.452(10); N(2)–C(7),
.481(9); P(1)–Ru(1)–Cl(1), 85.64(7); P(1)–Ru(1)–Cl(2), 91.34(8); Cl(1)–Ru(1)–
1
Cl(2), 88.99(8); P(1)–N(2)–C(6), 125.0(5); P(1)–N(2)–C(7), 119.9(5); C(6)–
N(2)–C(7), 114.4(6).
Table 1. Short H…H close contact distances determined in the crystal structures
of the bimetallic complex.
Compound
d(H4…H6B)
d(H6B…H7A)
5a
7b
8b
2.3 Å
2.3 Å
2.3 Å
2.3 Å
2.4 Å
2.4 Å
Figure 4. Structure of 7b (meso) in the crystal as determined by X-ray diffraction.
Some hydrogen atoms and counterions are omitted for clarity. Selected bond
lengths (Å) and bond angles (˚): Ru(1)–Cl(1), 2.3863(10); Ru(1)–N(1), 2.148(3);
Ru(1)–P(1), 2.2629(10); Ru(1)–C(12), 2.189(4); Ru(1)–C(13), 2.185(4); Ru(1)–
C(14), 2.210(4); Ru(1)–C(15), 2.194(4); Ru(1)–C(16), 2.264(4); Ru(1)–C(17),
2.267(4); P(1)–N(2), 1.636(3); N(2)–C(6), 1.470(5); N(2)–C(7), 1.476(5); P(1)–
O(1), 1.582(3); P(1)–Ru(1)–Cl(1), 88.81(4); P(1)–Ru(1)–N(1), 89.33(9); N(1)–
Ru(1)–Cl(1), 84.90(9); P(1)–N(2)–C(6), 114.4(2); P(1)–N(2)–C(7), 126.4(3);
C(6)–N(2)–C(7), 118.0(3).
Figure 3. Structure of 5a (rac) in the crystal as determined by X-ray diffraction.
Some hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and
bond angles (˚): Ru(1)–Cl(1), 2.388(4); Ru(1)–N(1), 2.110(12); Ru(1)–P(1),
2.310(4); Ru(1)–C(39), 2.223(14); Ru(1)–C(40), 2.200(13); Ru(1)–C(41),
2.248(12); Ru(1)–C(42), 2.256(12); Ru(1)–C(43), 2.205(12); Ru(1)–C(44),
2.196(14); P(1)–N(2), 1.666(10); N(2)–C(6), 1.475(15); N(2)–C(7), 1.499(14);
P(1)–Ru(1)–Cl(1), 92.42(13); P(1)–Ru(1)–N(1), 87.3(3); N(1)–Ru(1)–Cl(1),
88.8(4); P(1)–N(2)–C(6), 120.7(8); P(1)–N(2)–C(7), 122.2(8); C(6)–N(2)–C(7),
117.1(9).
Figure 5. Structure of 8b (meso)in the crystal as determined by X-ray diffraction.
The counterions are omitted for clarity. Selected bond lengths (Å) and bond
angles (˚): Ru(1)–Cl(1), 2.3752(19); Ru(1)–N(1), 2.126(6); Ru(1)–P(1), 2.261(2);
Ru(1)–C(24), 2.225(8); Ru(1)–C(25), 2.229(8); Ru(1)–C(26), 2.242(7); Ru(1)–
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European Journal of Inorganic Chemistry
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FULL PAPER
C(27), 2.251(8); Ru(1)–C(28), 2.205(8); Ru(1)–C(29), 2.203(7); P(1)–N(2),
1
.648(7); N(2)–C(6), 1.471(10); N(2)–C(7), 1.475(9); P(1)–O(1), 1.594(5); P(1)–
Ru(1)–Cl(1), 87.17(7); P(1)–Ru(1)–N(1), 88.34(18); N(1)–Ru(1)–Cl(1),
4.93(18); P(1)–N(2)–C(6), 113.2(5); P(1)–N(2)–C(7), 124.2(5); C(6)–N(2)–
Table 2: Hydrogenation of LA using formic acid and 1-8a
8
C(7), 117.4(6).
Hydrogenation of LA with formic acid
Entry
Cat.
FA
Et
3
N
Conversion
(%)
GVL
The hydrogenation reaction was initially performed using LA (10
mmol), FA (10 mmol), triethylamine (10 mmol) and 0.01 mmol (0.1
(mol %)
(equiv)
(equiv)
selectivity
(
%)b
1c
2c
3
1 (0.1)
1 (0.1)
1 (0.1)
2 (0.1)
3 (0.1)
4 (0.1)
5a (0.1)
5b (0.1)
5 (0.1)
6a (0.1)
6b (0.1)
6 (0.1)
7 (0.1)
8 (0.1)
8 (0.1)
1
1
2
2
2
2
2
2
2
2
2
2
2
2
1
1
86
85
94
90
98
98
89
87
89
88
86
89
98
100
87
95
96
95
93
96
93
94
91
93
92
93
92
97
97
96
o
mol%) of pre-catalyst 1 at 120 C. Triethylamine was chosen as
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
the base for the reaction due to its effectiveness as reported
previously. 19,30 The reactions involving 1 and the rest of the
4
catalyst precursors were accompanied by CO
2
and H
2
generation
5
as observed previously.18-19,31 This was characterised by a rise in
6
7
the pressure gauge reading and prolonged fizzing of the reaction
mixture after opening the reactors. In a period of 12 h, 86%
conversion of LA was obtained with 95% GVL selectivity and the
rest being 4-hydroxyvaleric acid (4-HVA) (Table 2; entry 1). When
the amount of the base was reduced to 50 mol% in attempts to
optimize the reaction conditions, there was no significant change
in LA conversion, neither did this affect selectivity of GVL. This
indicates that the reaction does not require an equivalent amount
of base for complete deprotonation of the formic acid to formate
8
9
10
11
12
13
14
15
aConditions: LA 10.0 mmol; 8 h; 120 oC; bThe rest is 4-HVA; c12 h.
Conversions were determined by 1H NMR spectroscopy. Cat. 5, 6, 7 and 8
represent respective isomeric mixtures of 5a, 5b, 6a, 6b, 7a, 7b, 8a and 8b.
2 2
as the base is possibly regenerated when CO and H are formed
from the formic acid decomposition (a possible mechanistic
process that could be taking place concurrently with transfer
mechanism). This is further supported by the presence of two
The rest of the pre-catalysts (both those coordinted to the ligand
in a monodentate and bidentate manner ) were screened at these
optimized conditions and the results are summarized in Table 2.
All the pre-catalysts performed well, giving at least 90%
conversions within 8 h. Among the neutral complexes, 3 and 4
which contain the phosphoramidite ligands performed better than
their aminophosphinite analogues 1 and 2. Both 3 and 4 gave
98% conversion while 1 and 2 gave 94% and 90% conversions
respectively. Only traces of the intermediate 4-HVA were
observed in all the reactions. The catalytic activities of the
complexes 5-8 are very comparable with their monodentate
analogues 1-4. The isomers 5a, 5b, 8a and 8b demonstrate
similar catalytic activity with conversions between 85% and 90%.
This indicates that the configurations at the metal centres do not
really influence the catalysts performance in terms of conversion.
The isomeric mixtures of both 5 (5a and 5b) and 8 (8a and 8b)
gave 89% conversion, which is slightly lower compared to the
1
upfield signals in the H NMR spectrum of a mixture of isomers of
6a and 6b treated with formic acid at 120ºC for 30 minutes.
1
(
Figure S23). The the H NMR spectrum shows two signals at -
11.47 ppm and -14.43 ppm assigned to the Ru-H and the Ru-H
2
species respectively. The Ru-H is the catalytically active species
and is formed at both ruthenium centres, within the bimetallic
structure, and promotes the reaction simultaneoulsy. The reaction
pathway is likely similar to what we previously proposed.19a This
result together with our previous studies on LA hydrogenation
show that the catalytic reactions are less dependent on the
quantity of base used to initiate the reactions.19a,32 With two molar
equivalents of formic acid, there was an increase in the rate of the
catalytic reaction, giving 94% LA conversion at the lower base
concentration (50 mol%) and a shorter time of 8 h (Table 2; entry
3).
94% and 90% obtained with their respective neutral counterparts
1
and 2. This can be attributed to the extra stability associated
with the chelating system, which might hinder ligand dissociation
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European Journal of Inorganic Chemistry
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FULL PAPER
from the metal centre for facile formation of the active species.
Contrary to this, isomeric mixtures of 7 and 8 performed very
similarly to their neutral counterparts 3 and 4, giving 98% and
other homogeneous metal catalysts that have shown excellent
activities in LA hydrogenation to GLV using molecular hydrogen.44
The activity of the new bimetallic complexes is lower than that of
the Ru^Zn hexa-heterometallic complexes we reported recently.
100% conversions respectively. With one molar equivalent of FA,
1
9
the conversion with 8 decreased significantly to 87%, as observed
with 1. When comparing the current bimetallic catalysts with
similar monometallic systems which we previously used for LA
hydrogenation18,19a, it becomes clear that there is merit to
introducing two active sites in the catalyst structure. For example,
monometallic phosphorus-donor (phosphinite and phosphite)
ruthenium catalysts precurosor (at 0.1 mol% loading) showed
To verify the homogeneity of the catalysts, mercury poisoning test
was conducted using 4 and 8 as representatives of the neutral
and cationic bimetallic catalyst precursors respectively. At similar
conditions used previously in the presence of elemental mercury
(0.02 mmol; 4 mg), the pre-catalysts (4 and 8) performed well to
give 98% conversion each (Table 3; entries 5 and 6). This shows
that the catalytic reactions involving the pre-catalysts happened
with molecular complexes and no nanoparticles were involved
regardless of the mode of ligand coordination to the metal centre.
1
8
7
0% to 96 % conversion of LA in 16 hours , while similar
catalysts precursors (1-4) coordinated in a monodentate fashion
produced 93 % to 98 % conversion in half the time. Furthermore,
the latter required more base additive (20 mmol) while inthis
report we have established that lower base additive (5 mmol) is
sufficient. The observation is further highlighted when the
performance of monometallic cationic catalyst precursors, with
P^N donor ligands, are compare to the current bimetallic
systems (5-8). The former (at 0.1 mol % loading) displayed LA
Table 3: Catalyst loading investigation and homogeneity test
Entry
Cat. (mol %)
Conversion / %
GVL selectivity
TON
/
%b
1
2
8 (0.05)
8 (0.025)
8 (0.025)
8 (0.025)
4 (0.1)
90
34
66
90
98
99
95
1800
1360
2600
3600
980
100
100
95
3c
4d
5e
6e
1
8
conversions in the range of 37 % to 68 % in 16 hours , while in
this works the same loading of the pre-catalysts 5-8 gave
conversions in the range of 87 % to 100 % in 8 hours.
95
8 (0.1)
93
990
aConditions: LA 10.0 mmol; FA 10.0 mmol; Et
o
b
3
N LA 5.0 mmol; 8 h; 120 C; The rest is
4
-HVA; c140 oC; d24 h; eHg 0.02 mmol (4.0 mg). Conversions were determined by 1
H
NMR spectroscopy. Cat. 8 represents isomeric mixtures of 8a and 8b.
In general, the pre-catalysts bearing phosphoramidite ligands (3,
4, 7 and 8) performed better than those bearing aminophosphinite
Time and temperature dependent studies
ligands. This could be due to the electron withdrawing ability of
the ethoxy moieties on the phosphorus. As a result, the metal
centre becomes more electrophilic for the formate interaction prior
to decomposition.
Time dependent study was carried out on pre-catalysts 7 and 8.
Of note is that the activity of the catalysts was very minimal (13%
and 14% for 7 and 8 respectively) in the first hour of the reactions
The effect of catalysts loading on the catalytic reaction was
investigated using 8. As mentioned previously, 100% conversion
was obtained with pre-catalysts 8 at a catalyst loading of 0.1 mol%.
Under similar conditions and with a lower catalyst loading of 0.05
mol%, the catalyst’s performance was still very high; giving 90%
conversion (Table 3; entry 1), which correspond to TON of 1 800.
The conversion decreased drastically to 34% when the catalyst
loading was reduced further to 0.025 mol%. However, higher
conversion of 90% (3 600 TON) was observed with 0.025 mol%
catalyst loading when the reaction time was prolonged to 24 h
(
Figure 6). A plausible reason could be that formation of the
reactive catalyst species takes a relatively longer time to occur.
The progress of the reactions, especially with 8, became very
rapid after the first one hour. The evidence of this is the high
conversions obtained after the fourth hour into the reactions. Pre-
catalyst 8 delivered the highest conversion of 92% in 4 h, after
which the reaction proceeded gradually until the sixth hour where
99% was recorded. Pre-catalyst 7, on the other hand, gave 67%
conversion after 4 h and the reaction became faster between 4 h
and 6 h compared to the performance of 8 within these hours.
(
Table 3; entry 4). The catalyst performance is comparable to
most of the homogeneous metal catalysts reported for LA
hydrogenation using formic acid as the hydrogen donor and under
other similar conditions.31,33 It is important to note that there are
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European Journal of Inorganic Chemistry
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FULL PAPER
1
20
00
80
60
1
00
7
8
1
80
60
40
20
0
7
8
4
0
0
0
2
0
2
4
6
8
Time/ h
90
100
110
120
o
Temperature / C
Figure 6. Time dependent study of LA hydrogenation with FA. LA 10 mmol; FA
0 mmol; catalyst precursor 0.01 mmol (0.1 mol%); Et N 5.0 mmol; 120 °C.
2
3
Figure 7. Temperature dependent study of LA hydrogenation with FA. LA 10
mmol; FA 20 mmol; catalyst precursor 0.01 mmol (0.1 mol%); Et
h.
3
N 5.0 mmol; 8
Further studies on the behaviour of the catalysts show that
temperature is very influential in their activity. As can be seen
Figure 7, the catalysts respond greatly to temperature changes
from 120 oC down to 90 oC. For catalyst 8, a decrease in
Effect of stirring on the catalytic reaction
Effect of stirring on the reaction kinetics has been studied using
pre-catalyst 8 (0.1 mol%), 10 mmol of LA, 2 molar equivalents of
FA, 0.5 molar equivalents of triethylamine at 120 oC and 8 h
reaction time. At low stirring speeds of 300 to 600 rpm, the LA
conversion was constant at 90% (Figure S22). The reaction rate
was enhanced at a higher stirring speed of 900 rpm, which
resulted in 95% LA conversion. The low reaction rate at low
stirring speed indicates that there is much resistance in mass
transport at lower stirring speeds. This is due to high viscosity of
the reaction mixture since the reactions were performed in the
absence of any additional solvent apart from the reagents. At low
stirring speeds, there is high resistance in the miscibility of the
reaction mixture with the hydrogen gas generated. A slight
increase of LA conversion (from 95 to 96%) was observed when
the mixing speed was increased to 1200 rpm. Further increase in
the stirring speed to 1500 rpm enhanced the reaction rate to give
complete conversion at same 8 h. Reactions performed in gas-
liquid36-37 and viscous liquid-liquid38-39 phases systems usually
encounter resistance to miscibility and mass transport.
o
o
temperature by 10 C (from 120 to 110 C) resulted in decrease
in LA conversion by 9%. Further reduction in temperature to 100
oC lowered the LA conversion further by 9%. Unexpectedly, the
activity of 8 became very poor giving only 10% conversion when
the temperature was dropped to 90 ℃. In contrast, there was 30%
o
conversion recorded with 7 at 90 C, which differs from 8 only by
the p-cymene auxiliary ligands on the metals instead of benzene.
The low activity of the catalysts at low temperature was
2 2
accompanied by less amount of the mixture of CO and H gases
generated during the reactions. The decomposition of the formate
at the metal centre could be less favoured at low temperature. As
a result, facile formation of the reactive catalytic species prior to
the LA reduction is hindered by the coordinated formate. Another
factor that could possibly play a role is solubility of hydrogen gas
generated in the reaction mixture at low temperature. It has been
reported that higher temperatures favour solubility of hydrogen
gas in organic liquids.35
Catalysts recyclability
Stability of the catalysts was studied using 8 by performing
recyclability experiments. The experiments were performed at the
o
optimum temperature of 120 C, catalyst loading of 0.1 mol% and
two molar equivalents of FA. The reactions were carried out for 6
h because 99% conversion was obtained with 8 after 6 h as
shown in Figure 6. The first run resulted in 99% conversion after
which GVL, water and triethylamine were removed from the
reaction mixture via vacuum distillation at 80 to 85 oC.40 The
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European Journal of Inorganic Chemistry
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FULL PAPER
recovered catalyst was transferred into the reactor followed by
addition of the appropriate amounts of LA, FA and triethylamine.
This procedure was repeated four times. Data for the recycling
experiment is summarized in Figure 8. The catalysts performance
was maintained after the first cycle giving 99% conversion.
However, its deactivation begun to occur gradually after the
second cycle. This resulted in a slight decrease in conversion to
Experimental Section
Experimental Details.
All reactions were performed under a dry, deoxygenated nitrogen
atmosphere using standard Schlenk techniques. All solvents were
of analytical grade and were dried using MBRAUN SPS-800
solvent drying system and or distilled prior to use. Compounds 2-
pyridinecarboxaldehyde (99%, Sigma-Aldrich), ethylenediamine
91% and 79% after the third and fourth cycles respectively.
(
99.5%, Sigma-Aldrich), sodium borohydride (96%, Sigma-
Aldrich), triethylamine (99%, Sigma-Aldrich),
chlorodiphenylphosphine Sigma-Aldrich), diethyl
1
00
80
60
40
20
0
(98%,
chlorophosphite (96%, Aldrich), 1,4-cyclohexadiene(97%, Sigma-
Aldrich), ruthenium(III) trichloride hydrate (99.98% trace metal
basis, Sigma-Aldrich) dichloro(p-cymene)ruthenium(II) dimer
(97%, Sigma-Aldrich), Levulinic acid (97%, Sigma-Aldrich) and
formic acid (95%, Sigma-Aldrich) were of reagent grades and
used as received. Dichloro(benzene)ruthenium(II) dimer was
synthesised following literature protocol.41 1H NMR, 13C{ H} NMR
and 31P{ H} NMR spectra were recorded on a Bruker Ultrashield
1
2
3
4
1
Number of cycles
1
Figure 8. Catalyst recyclability study usin 8: LA 10 mmol; FA 20 mmol; Catalyst
1
13
1
13
1
4
00 ( H NMR 400.17 MHz, C{ H} NMR 100.62 MHz and P{ H}
o
8
0.01 mmol (0.1 mol%); Et
3
N 5.0 mmol; 120 C; 6 h. Conversions and selectivity
1
1
NMR 161.99 MHz) or Bruker Ultrashield 500 ( H NMR 500.13
were determined by H NMR spectroscopy.
MHz, 13C{ H} NMR 125.75 MHz and P{ H} NMR 202.45 MHz) in
1
13
1
CDCl , DMSO-d and CD Cl as appropriate at room temperature.
3
6
2
2
Conclusions
FT-IR data was collected on PerkinElmer 83373. Elemental
analyses were performed on a Thermo Scientific FLASH 2000
CHNS-O analyzer. HRMS (ESI) spectra were recorded on a
Waters Synapt G2 spectrometer.
New multidentate ligands (L1 and L2) of N^P^P^N-donor system
that easily accommodate two metal centres leading to the
formation of bimetallic complexes were synthesised and
characterised. Reaction of the new ligands with [Ru(p-
All hydrogenation reactions were performed in TAIATSU
TECHNO high pressure reactor vessels with 200 °C and 10 MPa
capacities fitted into a high pressure autoclave reactor (PPV-
CTRO1-CE) with an in built heating, cooling and stirring systems.
Conversions and hydrogenation products were determined by
2 2 2 2
cymene)Cl ] and [Ru(benzene)Cl ] lead to the formation of four
neutral bimetallic complexes (1-4). Meso and rac cationic
bimetallic complexes (5-8) were formed from the monodentate
complexes through coordination of the pyridine nitrogen atoms to
the two metal centres. The new complexes are catalytically active
when screened for hydrogenation of LA to LA using formic acid
as the hydrogen source and triethylamine as base. Low catalyst
loadings of 0.025-0.1% resulted in over 90% selective conversion
of LA to GVL. Doubling the amount of formic acid increases the
catalytic conversion significantly while a decrease in the amount
of base by half equivalent has no significant effect on the LA
conversion. The complexes are active even at relatively low
temperatures and can perform the hydrogenation in the absence
of any additional solvent apart from the reagents. There is a loss
of 20% of catalyst activity in the fourth cycle.
1
Bruker Ultrashield 400 ( H NMR 400.17 MHz).
1
2
Synthesis of N ,N -bis(pyridin-2-ylmethylene)ethane-1,2-
diamine (C1)
Compound C1 was synthesised using a solvent-free approach.
Ethylenediamine (0.025 mol; 1.68 mL) was slowly added to 2-
pyridinecarboxaldehyde (0.05 mol; 4.80 mL) in a round bottom
o
flask and the mixture was stirred at 50 C for 1 h. After the reaction
time had elapsed, the flask was allowed to cool to room
temperature and the product was dried in vacuo and obtained as
an orange-brown solid in excellent yield. Yield: 5.96 g (> 99%).
Anal calcd. for C14
H
14
4
N : C 70.57, H 5.92, N 23.51%; found: C
1
7
0.49, H 5.33, N 23.26%. H NMR (CDCl
3
): δ 4.04 (s, CH
2
, 4H),
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European Journal of Inorganic Chemistry
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FULL PAPER
7
.29 (dd, 3JHH = 1.2 Hz, (CH)pyridyl, 2H), 7.72 (dd, 3JHH = 6.4 Hz,
CH)pyridyl, 2H), 7.96 (d, 3JHH = 8.0 Hz, (CH)pyridyl, 2H), 8.39 (s,
CH=N, 2H), 8.60 (d, 3JHH = 4.8 Hz, (CH)pyridyl, 2H).
7.30 (m, (CH)aromatic, 20H) , 7.42 (t, 3JHH = 1.6 Hz, (CH)pyridyl, 2H),
8.36 (d, 3JHH = 0.8 Hz, (CH)pyridyl, 2H). 13C{ H} NMR (100.6 MHz,
1
(
CDCl
2JCP = 21.0 Hz, (CH
28.1 (d, 2
CP = 5.9 Hz (CH)aromatic), 128.4 ((CH)aromatic), 132.0
((CH)aromatic), 132.2 ((CH)aromatic), 135.9 ((CH)pyridyl), 139.5 (d, JCP
3
): δ 50.8 (dd, 2JCP = 17.8 Hz, 3JCP = 4.8 Hz, CH
pyridyl), 121.5 ((CH)pyridyl), 121.8 ((CH)pyridyl),
2
), 57.4 (d,
2
)
1
J
1
2
N ,N -bis(pyridin-2-ylmthyl)ethane-1,2-diamine (C2)
=
Compound C2 was synthesised by adding four equivalents of
24.3 Hz, (C-Paromatic)), 148.9 ((CH=N)pyridyl), 159.8 (d, 3JCP = 4.8 Hz,
(C=N)pyridyl). 31P{ H} NMR (162 MHz, CDCl
1
): δ 64.9 (2P). FT-IR
NaBH
4
(0.1 mol; 3.78 g) to C1 (0.025 mol; 5.96 g) dissolved in 50
3
-1
mL of ethanol at room temperature. The reaction mixture was
(powder, cm ): ν(CH)pyridyl 3073-2983; ν(CH)aromatic 2900-2858;
ν(C=N) 1584.
o
stirred at room temperature for 30 min followed by reflux at 80 C
for 2 h. After the reaction time had elapsed, aqueous solution of
KOH (5.0 g in 50 mL water) was added to the crude mixture and
the product extracted from the aqueous mixture using100 mL of
ethyl acetate. The ethyl acetate extract was then washed with 50
Tetraethyl ethane-1,2-diylbis((pyridin-2-
ylmethyl)phosphoramidite) (L2)
Compound L2 was synthesised in a similar manner described for
L1. To a toluene solution (50 mL) containing C2 (2.54 mmol; 0.62
g) and stirring at 0-5 oC under argon atmosphere, was added
triethylamine (10.2 mmol; 1.4 mL). The mixture was stirred for
about 10 minutes followed by addition of diethyl chlorophosphite,
(5.1 mmol; 0.76 mL) in a dropwise manner. The mixture was
stirred at room temperature for 12 h and the mixture was filtered
off to remove the triethylamine hydrochloride salt. The filtrate was
dried in vacuo and the product was obtained as reddish-brown oil.
mL of water. The organic phase was dried over anhydrous MgSO
4
and filtered through a filter paper followed by evaporation of the
solvent to obtain a reddish-brown oil. Yield: 5.94 g (98%). Anal
calcd. for C14
H 7.27, N 23.06%. 1H NMR (CDCl
CH , 4H), 3.89 (s, (CH
H), 7.30 (d, 3JHH = 7.6 Hz, (CH)pyridyl, 2H), 7.62 (t, 3JHH = 6.0 Hz,
CH)pyridyl, 2H), 8.53 (d, 3JHH = 4.4 Hz, (CH)pyridyl, 2H).
H
18
N
4
: C 69.39, H 7.49, N 23.12%; found: C 69.17,
3
): δ 1.96 (s, NH, 2H), 2.79 (s,
2
2
) ,
pyridyl, 4H), 7.14 (t,3JHH = 5.2 Hz, (CH)pyridyl
2
(
Yield: 1.0 g (83%). Anal calcd. for C22
N 11.61%; found: C 54.81, H 7.55, N 11.53%. 1H NMR (400 MHz,
CDCl
): δ 1.17 (t, 3JHH = 6.8 Hz, CH , 12H), 2.99 (t, 3JHH = 5.2 Hz,
, 4H), 3.68 (m, 3JHH = 7.6 Hz, O-CH
CH , 8H), 4.21 (s, (CH
2H), 4.23 (s, (CH ,
pyridyl, 2H), 7.05 (dd, 3JHH = 4.8 Hz, (CH)pyridyl
36 4 4 2
H N O P : C 54.76, H 7.52,
1
2
1
2
N ,N -bis(diphenylphosphino)-N ,N -bis(pyridin-2-
ylmethyl)ethane-1,2-diamine (L1)
3
3
To a diethyl ether solution (50 mL) containing C2 (10.0 mmol; 2.5
g) and stirring at 0-5 oC under argon atmosphere, was added
triethylamine (40.0 mmol; 5.63 mL). The mixture was stirred for
2
2
2 pyridyl
) ,
2
)
2H), 7.28 (d, 3JHH = 8.0, (CH)pyridyl, 2H), 7.56 (dd, 3JHH = 6.0 Hz,
(CH)pyridyl, 2H), 8.43 (d,3JHH = 4.0 Hz, (CH)pyridyl, 2H). 13C{ H} NMR
1
about
10
minutes
followed
by
addition
of
chlorodiphenylphosphine, (20.0 mmol; 3.85 mL) in a dropwise
manner. The mixture was stirred at room temperature for 3 h and
the precipitates obtained were filtered off using a filter paper and
washed with 20 mL of diethyl ether. The precipitates were
dissolved in 50 mL of ethyl acetate and washed successively with
water (3 x 50 mL) to remove the triethylamine hydrochloride salt.
(100.6 MHz, CDCl
= 15.2 Hz, 3JCP = 3.0, CH
59.2 (d, 2JCP = 17.2 Hz, O-CH
3
): δ 16.9 (d, 3JCP = 6.0 Hz, CH
), 50.4 (d, 2JCP = 19.2 Hz, (CH
), 121.5 ((CH)pyridyl), 121.9
3
), 43.8 (dd, 2JCP
2
2
)pyridyl),
2
((CH)pyridyl), 136.1 ((CH)pyridyl), 148.9 ((CH=N)pyridyl), 160.1 (d, 3JCP
= 3.0, (C=N)pyridyl). 31P{ H} NMR (162 MHz, CDCl
1
): δ 145.2 (2P).
3
The organic phase was dried over anhydrous MgSO
4
and filtered
[{Ru(benzene)Cl
2 2
} L1] (1)
through a filter paper. The pure product was obtained as a pale-
A dichloromethane solution (15 mL) of [Ru(benzene)Cl ] (0.082
2 2
yellow solid upon evaporation of the solvent followed by drying in
mmol; 0.041 g) was mixed with a 15 mL dichloromethane solution
of ligand L1 (0.082 mmol; 0.05 g). The mixture was stirred at room
temperature for 2 h and the product precipitated with hexane after
concentrating the crude. The product was dried in vacuo to obtain
reddish-brown solids. Yield: 81.0 mg (89%). M.p: decomposes
vacuo. Yield: 3.87 g (61%). %). Anal calcd. for C38
4.74, H 5.94, N 9.17%; found: C 74.63, H 6.01, N 9.20%. 1H
NMR (400 MHz, CDCl , 2H), 2.99
): δ 2.98 (d, 3JHH = 3.6 Hz, CH
, 2H), 4.11 (s, (CH pyridyl, 2H), 4.13 (s,
pyridyl, 2H), 6.89 (d, 3JHH = 7.6 Hz, (CH)pyridyl, 2H), 7.02 (t, 3JHH
36 4 2
H N P : C
7
3
2
(
(
d, 3
CH
J
HH = 4.0 Hz, CH
2
2
)
2
)
without melting (onset at 189 °C). Anal calcd. for
5.2, (CH)pyridyl, 2H), 7.62 (t, 3JHH = 6.0 Hz, (CH)pyridyl, 2H), 7.19-
C
50.5
H49Cl
N
4
P
2
Ru
2
(1 0.5CH
.
Cl
2
): C 52.59, H 4.28, N 4.86%;
=
5
2
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European Journal of Inorganic Chemistry
10.1002/ejic.201900640
FULL PAPER
1
found: C 52.12, H 4.21, N 5.01%. H NMR (400 MHz, CDCl
3
): δ
room temperature for 2 h and the product precipitated with hexane
2
.41 (m, J = 9.2, CH
2
, 4H), 5.13 (s, (CH)benzene, 12H), 6.95 (d, 3JHH
7.6 Hz, (CH)pyridyl, 2H), 7.20 (t, 3JHH = 6.8 Hz, (CH)pyridyl, 2H), 7.22
after concentrating the crude. The product was dried in vacuo to
=
obtain
a reddish-brown solid. Yield: 0.35 g (97%). M.p:
(
(
m, (CH)aromatic, 12H), 7.59 (t, 3JHH = 7.6 Hz, (CH)pyridyl, 2H), 7.70
m, (CH)aromatic, 8H), 8.62 (d, 3JHH = 3.6 Hz, (CH)pyridyl, 2H). 13C{ H}
decomposes without melting (onset at 175 °C). Anal calcd. for
1
C
34
H48Cl
4
N
4
O
4
P
2
Ru
2
(3): C 41.56, H 4.92, N 5.70%; found: C
1
NMR (100.6 MHz, CD
2
Cl
2
): δ 47.1 (CH
2
), 55.4 ((CH
2
)
pyridyl), 89.8
41.83, H 4.90, N 5.74%. H NMR (400 MHz, CDCl
3
): δ 1.12 (t,
, 4H), 3.88
, 4H), 4.03 (m, 3JHH = 3.2 Hz, O-CH
, 4H),
pyridyl, 2H), 4.54 (s, (CH pyridyl, 2H), 5.70 (s,
(
(
(
(
d, 3JCP = 10.0 Hz, benzene-CH), 122.8 ((CH)pyridyl), 122.9
3JHH = 7.2 Hz, CH
(m, 3JHH = 3.2 Hz, O-CH
4.51 (s, (CH
3
, 12H), 3.35 (t, 3JHH = 4.4 Hz, CH
2
(CH)aromatic), 127.9((CH)pyridyl), 130.4 ((CH)aromatic), 133.1
2
2
(CH)aromatic), 136.9 ((CH)pyridyl), 150.0 ((CH=N)pyridyl), 159.9
2
)
2
)
C=N)pyridyl). 31P{ H} NMR (162 MHz, CDCl
1
): δ 75.9 (N-P-Ru, 2P).
(CH)benzene), 7.14 (dd, 3JHH = 5.2 Hz, (CH)pyridyl, 2H), 7.39 (d, 3JHH
= 7.6, (CH)pyridyl, 2H), 7.63 (dd, 3JHH = 6.8 Hz, (CH)pyridyl, 2H), 8.51
(d, 3JHH = 4.0 Hz, (CH)pyridyl, 2H). 13C{ H} NMR (100.6 MHz,
3
-1
FT-IR (powder, cm ): ν(CH)pyridyl 3058; ν(CH)aromatic 2954-2856;
+
2+
1
ν(C=N) 1588. HRMS (ESI ): m/z: 521.0454 [1-2Cl] .
CDCl pyridyl), 62.7 (O-CH
3
): δ 16.0 (CH
3
), 45.0 (CH
2
), 49.0 ((CH
2
)
2
),
[
{Ru(p-cymene)Cl
Complex 2 was synthesised in a similar manner described for 1
using L1 (0.082 mmol; 0.05 g) and [Ru(p-cymene)Cl (0.082
2
}
2
L1] (2)
90.2 (q, 2
JCP = 6.1 Hz, (CH)benzene), 122.1 ((CH)pyridyl), 122.7
((CH)pyridyl), 136.5 ((CH)pyridyl), 149.1 ((CH=N)pyridyl), 161.2 (d, 3JCP
1
2
]
2
= 3.0, (C=N)pyridyl). 31P{ H} NMR (162 MHz, CDCl
3
): δ 120.5 (N-P-
-
1
mmol, 0.05 g). The mixture was stirred in 30 mL of
dichloromethane at room temperature for 2 h. The product was
precipitated with hexane after concentrating the crude and dried
Ru, 2P). FT-IR (powder, cm ): ν(CH)pyridyl 3069-2977; ν(CH)aromatic
+
2+
2931; ν(C=N) 1590. HRMS (ESI ): m/z: 456.0316 [3-2Cl] .
under vacuum to obtain the pure product as a reddish-brown solid. [{Ru(p-cymene)Cl
2
}
2
L2] (4)
Complex 4 was synthesised in a similar manner described for 1
using L2 (0.68 mmol; 0.33 g) and [Ru(p-cymene)Cl (0.68 mmol;
0.43 g). The mixture was stirred in 40 mL of dichloromethane at
, 12H), room temperature for 2 h and the product precipitated with hexane
, 6H), 2.03 (m, 3JHH = 6.8 Hz, p-cym-
after concentrating the crude. The product was dried in vacuo to
), 2H), 2.20 (s, CH , 4H), 4.38 (s, (CH obtain reddish-brown solid. Yield: 0.71 (95%). M.p:
d, 3JHH = 5.2 Hz, p-cym-CH, 4H), 5.19 (d, 3JHH = 5.2 Hz, p-cym-
CH, 4H), 6.98 (d, 3JHH = 7.6 Hz, (CH)pyridyl, 2H), 7.23 (m, (CH)aromatic
Yield: 0.085 g (85%). M.p: decomposes without melting (onset at
.
1
90 °C). Anal calcd. for C58.5
H65Cl
5
N
4
P
2
Ru
2
(2 0.5CH
2
Cl
2
): C
2 2
]
5
5.52, H 5.18, N 4.43%; found: C 55.20, H 5.22, N 4.38%. 1
H
NMR (400 MHz, CD
.23 (s, p-cym-CH
CH(CH
2
Cl ): δ 0.88 (d, J = 6.8, p-cym-C-(CH
2
3 2
)
1
3
3
)
2
2
2
)
pyridyl, 4H), 5.09
a
g
(
decomposes without melting (onset at 180 °C). Anal calcd. for
.
,
C
42.5
H65Cl
5
N
4
O
4
P
2
Ru
2
(4 0.5CH
2
Cl
2
): C 44.88, H 5.76, N 4.93%;
1
1
8
2H), 7.59 (t, 3JHH = 7.6, (CH)pyridyl, 2H), 7.70 (m, (CH)aromatic, 8H),
.64 (d, 3JHH = 2.4 Hz, (CH)pyridyl, 2H). 13C{ H} NMR (100.6 MHz,
found: C 45.13, H 5.72, N 5.01%. H NMR (400 MHz, CDCl
1.08 (t, 3JHH = 7.2 Hz, CH , 12H), 1.18 (d, 3JHH = 6.8, p-cym-C-
(CH , 6H), 2.08 (s,
, 6H), 1.22 (d, 3JHH = 6.8 Hz, p-cym-CH(CH
p-cym-CH ), 2H),
, 6H), 2.92 (m, 3JHH = 6.8 Hz, p-cym-CH(CH
3.31 (d, 3JHH = 2.8 Hz, CH , 4H), 3.99 (m, 3JHH = 6.4 Hz, O-CH
8H), 4.46 (d, 2JHH = 10.4 Hz, (CH pyridyl, 4H), 5.44 (d, 3JHH = 6.0
Hz, p-cym-CH, 4H), 5.53 (d, 3JHH = 6.0 Hz, p-cym-CH, 4H), 7.10
(dd, 3JHH = 5.6 Hz, (CH)pyridyl, 2H), 7.50 (d, 3JHH = 7.6, (CH)pyridyl
3
): δ
1
3
CD
cym-CH(CH
1.1 (p-cym-CH), 96.3 (p-cym-C
122.9
2
Cl
2
): δ 16.5 (p-cym-CH
), 46.9 (CH ), 54.3 ((CH
), 109.4 (p-cym-Cq), 122.6
127.8
3
,), 22.2 (p-cym-CH(CH
3
)
2
), 30.2 (p-
3
)
2
3 2
)
3
)
2
2
2
)
pyridyl), 86.0 (p-cym-CH),
3
3 2
)
9
q
2
2
,
(
(CH)aromatic),
((CH)pyridyl),
((CH)aromatic),
2
)
130.1((CH)pyridyl), 133.2 ((CH)aromatic), 136.8 ((CH)pyridyl), 149.9
3
1
1
(
(CH=N)pyridyl), 160.0 (C=N)pyridyl).
P{ H} NMR (162 MHz,
,
-1
2H), 7.61 (dd, 3JHH = 6.8, (CH)pyridyl, 2H), 8.48 (d, 3JHH = 4.4 Hz,
2 2
CD Cl ): δ 73.4 (N-P-Ru, 2P). FT-IR (powder, cm ): ν(CH pyridyl)
1
3
046-2962; ν(CH)aromatic 2924-2866; ν(C=N) 1587. HRMS (ESI+):
(CH)pyridyl, 2H). 13C{ H} NMR (100.6 MHz, CDCl
3
): δ 15.6 (CH
,), 21.4 (p-cym-CH(CH
), 30.4 (p-cym-CH(CH ), 45.8 (CH ), 46.2 (CH
pyridyl), 61.4 (d, 2JCP = 12.1 Hz, O-CH
), 89.9 (p-cym-CH), 90.9 (p-cym-CH), 91.2 (p-cym-
3
),
2
+
+
m/z: 576.1054 [2-2Cl] ; 1189.1929 [2-Cl] .
15.8 (CH
cym-CH(CH
52.3 ((CH
62.4 (O-CH
3
), 17.4 (p-cym-CH
3
3
)
2
), 21.9 (p-
3
)
2
3
)
2
2
2
),
[
{Ru(benzene)Cl
Complex 3 was synthesised in a similar manner described for 1
using L2 (0.37 mmol; 0.18 g) and [Ru(benzene)Cl (0.37 mmol;
.19 g). The mixture was stirred in 40 mL of dichloromethane at
2
}
2
L2] (3)
2
)
pyridyl), 52.7 ((CH
2
)
2
),
2
]
2
CH), 93.3 (p-cym-CH), 102.8 (d, 3JCP = 9.1 Hz, p-cym-Cq), 111.76
2
0
(p-cym-Cq), 124.4 ((CH)pyridyl), 126.0 ((CH)pyridyl), 139.4 ((CH)pyridyl),
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201900640
FULL PAPER
1
1
58.0 ((CH=N)pyridyl), 158.4 ((CH=N)pyridyl), 160.4 ((C=N)pyridyl).
70.23, H 5.28, N 3.34%; found: C 70.11, H 5.39, N 3.28%. H
NMR (400 MHz, Acetonitrile-d , 2H),
): δ 2.65 (t, 2JHH = 8.8 Hz CH
3.67-3.73 (q, 2JHH = 16.0 Hz, (CH pyridyl, 2H), 4.08-4.13 (dd, 2JHH
= 12.4 Hz; 2JHH = 3.6 Hz, (CH
pyridinyl, 2H), 5.40 (s, (CH)benzene
3
1
1
P{ H} NMR (162 MHz, CDCl
3
): δ 122.5 (N-P-Ru, 2P). FT-IR
3
2
-1
(
powder, cm ): ν(CH)pyridyl 3063-2972; ν(CH)aromatic 2926-2875;
2
)
ν(C=N) 1586. HRMS (ESI ): m/z: 513.0943 [4-2Cl]2+
+
1057.1572
,
;
2
)
[
4-Cl]+.
12H), 6.24 (t, 3JHH = 10.4 Hz, (CH)aromatic, 4H), 6.82 (t, 3JHH = 7.2
Hz, (CH)aromatic, 8H), 6.95-6.99 (m, (CH)BPh4, 16H), 7.25-7.26 (bm,
(CH)BPh4, 18H), 7.38 (t, 3JHH = 8.8 Hz, (CH)pyridyl, 2H), 7.45 (d, 3JHH
= 7.2 Hz, (CH)pyridyl, 2H), 7.71-7.84 (m, (CH)aromatic, 6H), 7.89 (t,
[
{Ru(benzene)Cl}
2 4
L1]2BPh (5a and 5b)
A dichloromethane solution (15 mL) of [Ru(benzene)Cl ] (0.164
2 2
mmol; 0.082 g) was mixed with a 15 mL dichloromethane solution
3JH-H = 7.6 Hz, (CH)pyridyl, 2H), 9.34 (d, 3JHH = 5.2 Hz, (CH)pyridyl
,
2H). 13C{ H} NMR (100.6 MHz, DMSO-d
1
): δ 48.9 (CH
of ligand L1 (0.164 mmol; 0.10 g). The mixture was stirred at room
6
2
), 49.9
2 2 2
(CH ), 57.6 ((CH )pyridyl), 57.8 ((CH )
pyridyl), 92.4 (q, 3JC-P = 6.5 Hz,
temperature for 2 h after which NaBPh
4
(0.33 mmol; 0.112 g) in 4
mL of methanol was added and stirred for 16 h. The crude was
washed with 20 mL portions of water three times and dried over
benzene-CH), 121.5 ((CH)aromatic), 121.5 ((CH)BPh4), 124.6
((CH)aromatic), 124.8 ((CH)pyridyl), 125.2-125.3 ((CH)BPh4), 127.9
((CH)BPh4,) 127.2 ((CH)aromatic), 127.4 ((CH)pyridyl), 128.3
((CH)aromatic), 129.9 ((Cq)BPh4,) 130.3 ((CH)pyridyl), 130.7
((CH)aromatic), 131.2 ((CH)aromatic), 132.5 ((Cq)aromatic), 133.4
((Cq)BPh4,), 135.5 ((CH)BPh4), 140.0 ((CH)pyridyl), 158.4 ((CH)aromatic),
4
anhydrous MgSO . The product in the dichloromethane solution
was then precipitated with diethyl ether as an orange-yellow solid
and dried under vacuum, resulting in a total yield of 0.26 g (95%).
Compound 5b was extracted into acetone by washing the mixture
with about 15 x 3 mL portions of acetone, leaving 5a behind. (5a):
Yield 0.11 g (40%); M.p: decomposes without melting (onset at
161.4 ((CH=N)pyridyl), 161.5 (C=N)pyridyl), 162.8 (q, JCB = 49.5 Hz,
(C-B)BPh4). 31P{ H} NMR (162 MHz, acetonitrile-d
1
3
): δ 85.8 (N-P-
-
1
2
05 °C). Anal calcd. for C98
N 3.34%; found: C 69.83, H 5.44, N 3.45%. H NMR (400 MHz,
Acetonitrile-d , 2H), 2.99-3.11 (q,
): δ 2.47 (t, 2JHH = 5.2 Hz CH
2JHH = 16.0 Hz, (CH pyridyl, 2H), 3.937-3.991 (dd, 2JHH = 10.4 Hz;
2JHH = 5.2 Hz, (CH
pyridinyl, 2H), 5.41 (s, (CH)benzene, 12H), 6.63 (t,
3JHH = 8.0 Hz, (CH)aromatic, 4H), 6.84 (t, 3JHH = 6.8 Hz, (CH)aromatic
2 4 2 2 2
H88Cl N P B Ru (5a): C 70.23, H 5.28, Ru, 1P). FT-IR (powder, cm ): ν(CH)pyridyl 3054-2987; ν(C=N)
1
+
2 4 2 2
1603. HRMS (ESI ): m/z: 521.0374 [C50H48Cl N P Ru
]2+; HRMS
-
-
3
2
(ESI ): m/z 319.1749 BPh
4
2
)
2
)
.
[{Ru(p-cymene)Cl}
Complexes 6a and 6b were synthesised in a similar manner
H), 6.959-6.99 (m, (CH)BPh4, 16H), 7.24-7.26 (bm, (CH)BPh4, 18H), described for 5a and 5b using L1 (0.33 mmol, 0.20 g), [Ru(p-
.38 (t, 3 HH = 8.8 Hz, (CH)pyridyl, 2H), 7.51 (d, 3
HH = 4.8 Hz, cymene)Cl (0.33 mmol, 0.20 g) and NaBPh (0.65 mmol, 0.224
2 4
L1]2BPh (6a and 6b)
,
8
7
J
J
2
]
2
4
(
CH)pyridyl, 1H), 7.69-7.71 (m, (CH)aromatic, 6H), 7.85 (t, 3JH-H = 7.6
g). The mixture of the isomers was obtained as an orange-yellow
solid after precipitation with diethyl ether with total yield of 0.51 g
(87%). Washing of the mixture with 30 mL of dichloromethane in
3 mL portions resulted in the separation of 6b from 6a. (6a): Yield:
Hz, (CH)pyridyl, 2H), 9.41 (d, 3JHH = 5.6 Hz, (CH)pyridyl, 2H). 13C{ H}
1
NMR (100.6 MHz, DMSO-d
(CH
pyridyl), 92.4 (q, 3JC-P = 6.5 Hz, benzene-
CH), 121.5 ((CH)aromatic), 121.5 ((CH)BPh4), 124.6 ((CH)aromatic),
24.8 ((CH)pyridyl), 125.2-125.3 ((CH)BPh4), 127.9 ((CH)BPh4,) 127.2
6 2 2
): δ 48.9 (CH ), 49.9 (CH ), 57.6
(
2 2
)pyridyl), 57.8 ((CH )
0.23 g (39%) M.p: decomposes without melting (onset at 226 °C).
.
1
Anal calcd. for C106.5
H105Cl
3
N
4
P B
2 2
Ru
2
(6a 0.5CH
2
Cl
2
): C 69.78, H
(
(
(
(
(
(CH)aromatic), 127.4 ((CH)pyridyl), 128.3 ((CH)aromatic), 129.9
(Cq)BPh4,) 130.3 ((CH)pyridyl), 130.7 ((CH)aromatic), 131.2
(CH)aromatic), 132.5 ((Cq)aromatic), 133.4 ((Cq)BPh4,), 135.5
(CH)BPh4), 140.0 ((CH)pyridyl), 158.4 ((CH)aromatic), 161.4
5.77, N 3.06%; found: C 69.53, H 5.74, N 2.88%. 1H NMR (400
MHz, Acetone-d6): δ 0.96 (d, 3JHH = 6.8 Hz, p-cym-C-(CH
, 6H),
1.19 (d, 3JHH = 6.8 Hz, p-cym-C-(CH
, 6H), 1.67 (s, p-cym-CH
6H), 2.28 (bd, 3JHH = 7.0 Hz, (CH ), 2H), 2.63 (m, 3JHH = 6.8 Hz,
p-cym-CH(CH ), 2H), 3.551-
), 2H), 2.72 (bd, 3JHH = 8.0 Hz, (CH
3.664 (q, 2JHH = 15.6 Hz, (CH pyridyl, 2H), 4.24-4.29 (dd, 2JHH
10.0 Hz; 5.6 Hz, (CH
pyridyl, 2H), 5.04 (d, 3JHH = 6.4 Hz, p-cym-CH,
3 2
)
3
)
2
3
,
2
(CH=N)pyridyl), 161.5 (C=N)pyridyl), 162.8 (q, JCB = 49.5 Hz, (C-
3
)
2
2
B)BPh4). 31P{ H} NMR (162 MHz, acetonitrile-d
1
): δ 85.8 (N-P-Ru,
)
=
3
2
-1
1
P). FT-IR (powder, cm ): ν(CH)pyridyl 3054-2987; ν(C=N) 1603.
2
)
+
2+
-
2H), 5.09 (d, 3JHH = 6.4 Hz, p-cym-CH, 2H), 5.42 (d, 3JHH = 6.0 Hz,
p-cym-CH, 2H), 5.94 (d, 3JHH = 6.0 Hz, p-cym-CH, 2H), 6.72-6.78
(m, (CH)aromatic, 12H), 6.92 (t, 3JHH = 7.6 Hz, ((CH)BPh4, 16H), 7.21-
7.24 (m, (CH)aromatic, 4H), 7.26 (t, 3JHH = 2.4 Hz, (CH)pyridyl, 2H),
HRMS (ESI ): m/z: 521.0374 [C50
H48Cl
2
N
4 2 2
P Ru ] ; HRMS (ESI ):
m/z 319.1749 BPh4-.
(
(
5b): Yield: 0.094 g (34%); M.p: decomposes without melting
onset at 202 °C); Anal calcd. for C98
H
2 4 2 2 2
88Cl N P B Ru (5b): C
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201900640
FULL PAPER
-1
7
7
.30-7.34 (bm, (CH)BPh4, 20H), 7.60 (t, 3JHH = 8.4, (CH)pyridyl, 2H),
(N-P-Ru, 2P). FT-IR (powder, cm ): ν(CH)pyridyl 3055-2984;
ν(CH)aromatic 2900-2858; ν(C=N) 1605. HRMS (ESI+): m/z:
.60-7.66 (m, (CH)aromatic, 4H), 7.75-7.76 (m, (CH)aromatic, 6H), 7.95
2+
-
(
t, 3JHH = 6.0 Hz, (CH)pyridyl, 2H), 9.44 (d, 3JHH = 5.2 Hz, (CH)pyridyl
,
576.1051 [C58
BPh4-.
2 4 2 2
H64Cl N P Ru ] ; HRMS (ESI ): m/z 319.1746
1
2
2
H). 13C{ H} NMR (100.6 MHz, DMSO-d
1.0 (p-cym-CH(CH ), 21.1 (p-cym-CH(CH
), 54.9 (CH ), 55.9 ((CH pyridyl), 88.3 (p-cym-CH), 91.7
p-cym-CH), 92.4 (p-cym-CH), 93.9 (d, 3JC-P = 6.1 Hz, p-cym-CH),
00.0 (p-cym-C ), 113.0 (p-cym-Cq), 121.5 ((CH)aromatic), 124.7
6
): δ 16.9 (p-cym-CH
3
,),
3
)
2
3 2
) ), 30.2 (p-cym-
CH(CH
3
)
2
2
2
)
2 4
[{Ru(p-benzene)Cl} L2]2BPh (7a and 7b)
(
Complexes 7a and 7b were synthesised in a similar manner
described for 5a and 5b using L2 (0.46 mmol; 0.22 g),
1
q
(
(
(CH)pyridyl), 125.2-125.3 ((CH)BPh4), 127.3 ((CH)BPh4), 127.9
(Cq)BPh4,) 129.1 ((CH)aromatic), 130.4((CH)pyridyl), 130.6 ((CH)pyridyl),
[Ru(benzene)Cl
2 2 4
] (0.46 mmol; 0.23 g) and NaBPh (0.92 mmol;
0.31 g). The pure product was obtained as an orange-yellow solid
131.3 ((CH)aromatic), 132.3 ((CH)aromatic), 133.0 ((Cq)aromatic), 135.5
in good yield. Yield: 0.62
g
(87%); Anal calcd. for
.
(
(
(Cq)BPh4,), 140.1 ((CH)pyridyl), 158.6 ((CH)aromatic), 161.4
C
82.5
H89Cl
3
N
4
O
4
P
2
B
2
Ru
2
(7 0.5CH
2
Cl
2
): C 62.21, H 5.63, N 3.52%;
1
(CH=N)pyridyl), 161.5 (C=N)pyridyl), 164.1 (q, JCB = 49.5 Hz, (C-
found: C 62.15, H 5.68, N 3.51%; M.p: (152.4-153.1 °C). H NMR
B)BPh4). 31P{ H} NMR (162 MHz, acetone-d6): δ 87.6 (N-P-Ru, 2P). (400 MHz, DMSO-d6): δ 1.35 (t, 3JHH = 4.4 Hz, CH
1
, 6H), 1.44 (t,
, 2H), 2.80 (d, CH , 2H), 3.88
pyridyl, 2H), 3.96-4.17 (m, 3JHH = 5.2 Hz, O-
HH = 14.0 Hz, (CH pyridyl, 2H), 5.95 (s,
3
-
1
3JHH = 7.2 Hz, CH
(dd, 3JHH = 5.6 Hz, (CH
CH
, 8H), 4.31 (dd, 3
FT-IR (powder, cm ): ν(CH)pyridyl 3055-2984; ν(CH)aromatic 2900-
858; ν(C=N) 1605. HRMS (ESI+): m/z: 576.1044
3
, 6H), 2.49 (d, CH
2
2
2
2
)
2
+
-
-
[
C
58
H64Cl
2
N
4
P
2
Ru
2
] ; HRMS (ESI ): m/z 319.1746 BPh4 .
2
J
2
)
(
6b): Yield: 0.21 g (35%) M.p: decomposes without melting (onset
(CH)benzene), 6.80 (d, 3JHH = 5.2 Hz, (CH)BPh4, 8H), 6.93 (t, 3JHH
4.8 Hz, (CH)BPh4, 16H), 7.18 (bs, (CH)BPh4, 16H), 7.39 (dd, 3JHH
=
=
.
at 225 °C); Anal calcd. for C106.5
H105Cl
3
N
4
P
2
B
2
Ru
2
(6b 0.5CH
2
Cl
2
):
1
10.0 Hz, (CH)pyridyl, 2H), 7.72 (d, 3JHH = 5.6, (CH)pyridyl, 2H), 8.02
C 69.78, H 5.77, N 3.06%; found: C 69.53, H 5.74, N 2.88%. H
NMR (400 MHz, Acetone-d6): δ 0.96 (d, 3JHH = 7.2 Hz, p-cym-C-
(dd, 3JHH = 5.6 Hz, (CH)pyridyl, 2H), 9.29 (d, 3JHH = 11.6 Hz,
1
(
CH
p-cym-CH
6.8 Hz, p-cym-CH(CH
H), 3.91-4.02 (q, 2JHH = 15.6 Hz, (CH
2JHH = 11.6 Hz; 4.4 Hz, (CH pyridyl, 2H), 4.98 (d, 3JHH = 6.0 Hz, p-
cym-CH, 2H), 5.06 (d, 3JHH = 6.4 Hz, p-cym-CH, 2H), 5.27 (d, 3JHH
6.4 Hz, p-cym-CH, 2H), 5.88 (d, 3JHH = 5.6 Hz, p-cym-CH, 2H),
.39 (q, 3 HH = 8.4 Hz, (CH)aromatic, 4H), 6.78 (t, 3JHH = 7.2 Hz,
3
)
2
, 6H), 1.18 (d, 3JHH = 6.8 Hz, p-cym-C-(CH
, 6H), 2.27 (m, 3JHH = 7.6 Hz, (CH ), 2H), 2.60 (m, 3JHH
), 2H), 2.91 (dd, 3JHH = 8.8 Hz, (CH
),
pyridyl, 2H), 4.30-4.35 (dd,
3
)
2
, 6H), 1.71 (s,
(CH)pyridyl, 2H). 13C{ H} NMR (100.6 MHz, DMSO-d
6
): δ 15.6 (CH
pyridyl), 61.3 (d, 2JCP = 11.1 Hz,
), 92.4 (d, 2JCP = 3.0 Hz, (CH)benzene), 121.5
3
),
3
2
15.9 (CH
3 2 2
), 45.6 (CH ), 52.3 ((CH )
=
3
)
2
2
O-CH ), 62.6 (O-CH
2
2
2
2
)
((CH)BPh4), 124.1 ((CH)pyridyl), 125.3 ((CH)BPh4), 128.3 ((CH)pyridyl),
135.5 ((CH)BPh4), 139.3 ((CH)pyridyl), 158.7 ((CH=N)pyridyl), 160.3
((C=N)pyridyl), 164.1 (q, JCB = 49.5 Hz, (C-B)BPh4). 31P{ H} NMR
2
)
1
=
6
(162 MHz, DMSO-d ): δ 129.3 (N-P-Ru, 1P), 129.9 (N-P-Ru, 1P).
-1
6
J
FT-IR (powder, cm ): ν(CH)pyridyl 3055-2983; ν(CH)aromatic 2900;
(
(
CH)aromatic, 12H), 6.92 (t, 3JHH = 7.6 Hz, ((CH)BPh4, 16H), 7.06-7.10
m, (CH)aromatic, 4H), 7.26 (t, 3JHH = 7.6 Hz, (CH)pyridyl, 2H), 7.32-
ν(C=N)
1606.
Ru
HRMS
(ESI+):
m/z:
456.0303
2+
-
-
[C36
H56Cl
2
N
4
O
4
P
2
2
] ; HRMS (ESI ): m/z 319.1671 BPh4 .
7
7
9
.33 (bm, (CH)BPh4, 20H), 7.52 (t, 3JHH = 6.4, (CH)pyridyl, 2H), 7.81-
.87 (m, (CH)aromatic, 10H), 7.96 (t, 3JHH = 6.4 Hz, (CH)pyridyl, 2H),
.36 (d, 3JHH = 5.6 Hz, (CH)pyridyl, 2H). 13C{ H} NMR (100.6 MHz,
2 4
[{Ru(p-cymene)Cl} L2]2BPh (8a and 8b)
1
Complexes 8a and 8b were synthesised in a similar manner
described for 7a and 7b using L2 (0.64 mmol; 0.31 g), [Ru(p-
Acetone-d6): δ 17.6 (p-cym-CH
p-cym-CH(CH ), 31.5 (p-cym-CH(CH
3JC-P = 4.0 Hz, (CH
pyridyl), 88.5 (p-cym-CH), 92.8 (p-cym-CH),
3.9 (p-cym-CH), 94.6 (d, 3JC-P = 7.0 Hz, p-cym-CH), 100.8 (p-
cym-C ), 116.5 (p-cym-Cq), 122.1 ((CH)aromatic), 125.8-125.9
(CH)BPh4), 126.1 ((CH)pyridyl), 128.4 ((CH)aromatic), 130.1((CH)pyridyl),
3
3 2
,), 21.8 (p-cym-CH(CH ) ), 22.0
(
3
)
2
3
)
2
), 51.0 (CH ), 58.6 (dd,
2
2 2 4
cymene)Cl ] (0.64 mmol; 0.39 g) and NaBPh (1.28 mmol; 0.44
2
)
g). The pure product was obtained as a dark-brown solid after
9
precipitation with diethyl ether. Yield: 0.87 g (82%); M.p: (129.6-
.
q
130.8 °C); Anal calcd. for C90.5
H105Cl
3
N
4
O
4
P
2
B
2
Ru
2
(8 0.5CH
2
Cl
2
):
1
(
C 63.76, H 6.21, N 3.29%; found: C 63.90, H 5.85, N 3.20%. H
NMR (400 MHz, DMSO-d
): δ 0.96 (d, 3JHH = 6.8, p-cym-C-(CH
6H), 1.13 (d, 3JHH = 6.8 Hz, p-cym-C-(CH , 6H), 1.24 (t, 3JHH
8.0 Hz, CH , 6H), 1.80 (s, p-cym-
, 6H), 1.35 (t, 3JHH = 4.8 Hz, CH
CH , 3H), 1.82 (s, p-cym-CH
, 3H), 2.27 (t, 3JHH = 7.6 Hz, CH
131.7 ((CH)pyridyl), 134.1 ((CH)aromatic), 134.7 ((CH)aromatic), 136.9
6
3 2
) ,
(
(
(Cq)aromatic), 136.9 ((Cq)BPh4,), 140.9 ((CH)pyridyl), 159.7
3
)
2
=
(CH)aromatic), 161.6 ((CH=N)pyridyl), 161.7 (C=N)pyridyl), 165.5 (q, JCB
3
3
49.3 Hz, (C-B)BPh4). 31P{ H} NMR (162 MHz, acetone-d6): δ 87.3
1
=
3
3
2
,
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European Journal of Inorganic Chemistry
10.1002/ejic.201900640
FULL PAPER
2
2
H), 2.65 (t, 3JHH = 8.4 Hz, p-cym-CH(CH
H), 3.81-3.98 (m, (CH
pyridyl, 4H), 4.00-4.281 (m, 3JH-H = 5.2 Hz,
, 8H), 5.90 (d, 3JHH = 6.4 Hz, p-cym-CH, 2H), 5.97 (d, 3JHH
6.8 Hz, p-cym-CH, 4H), 6.07 (d, 3JHH = 5.2 Hz, p-cym-CH, 2H),
.80 (t, 3 HH = 7.2 Hz, (CH)BPh4, 8H), 6.94 (t, 3
H-H = 7.2 Hz,
CH)BPh4, 16H), 7.18 (bs, (CH)BPh4, 16H), 7.43 (dd, 3JHH = 7.2 Hz,
CH)pyridyl, 2H), 7.55 (d, 3JHH = 7.6, (CH)pyridyl, 1H), 7.70 (d, 3JHH
.2, (CH)pyridyl, 1H), 7.97 (dd, 3JHH = 7.2 Hz, (CH)pyridyl, 1H), 8.03
dd,3JHH = 8.0 Hz, (CH)pyridyl, 1H), 9.20 (d, 3JHH = 6.0 Hz, (CH)pyridyl
3
)
2
), 2H), 2.78 (t, CH
2
,
coefficients. All hydrogen atoms were placed in geometrically
idealised positions and constrained to ride on their parent atoms.
Crystallographic data has been deposited with the Cambridge
Crystallographic Data Center with CCDC 1843031 (2), 1843033
(5a), 1843032 (7b) and 1843034 (8b). Copies of this information
may be obtained free of charge from the Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax: +44 1223 336063;
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
2
)
O-CH
2
=
6
J
J
(
(
=
7
(
,
H), 9.21 (d, 3JHH = 6.4 Hz, (CH)pyridyl, 1H). 13C{ H} NMR (100.6
): δ 15.6 (CH ), 15.8 (CH ), 17.4 (p-cym-CH ,),
1.4 (p-cym-CH(CH ), 21.9 (p-cym-CH(CH ), 30.4 (p-cym-
CH(CH ), 45.8 (CH ), 46.2 (CH ), 52.3 ((CH
pyridyl), 61.4 (d, 2JCP = 12.1 Hz, O-CH
), 62.4 (O-CH
1
General procedures for the hydrogenation reactions
1
MHz, DMSO-d
6
3
3
3
An autoclave reactor was charged with levulinic acid (10 mmol)
catalyst (0.01 mmol / 0.1 mol%), formic acid (10 mmol) and
triethylamine (10 mmol). The reactor was purged several times
with nitrogen gas and the mixture was stirred at 120 °C for 8 h.
2
3
)
2
3 2
)
3
)
2
2
2
2
)pyridyl), 52.7
(
(
(CH
2
)
2
2
), 89.9
p-cym-CH), 90.9 (p-cym-CH), 91.2 (p-cym-CH), 93.3 (p-cym-CH), After the reaction time had elapsed, the mixture was cooled to
1
02.8 (d, 3
J
CP = 9.1 Hz, p-cym-Cq), 111.76 (p-cym-Cq), 121.5
(CH)BPh4), 124.4 ((CH)pyridyl), 125.3 ((CH)BPh4), 126.0 ((CH)pyridyl),
35.5 ((CH)BPh4), 139.4 ((CH)pyridyl), 158.0 ((CH=N)pyridyl), 158.4
room temperature and the gas generated in the course of the
(
reaction was released. A sample of the reaction mixture was
1
1
taken, diluted with MeOD-d
4
or CDCl
3
and analysed by H NMR
(
(CH=N)pyridyl), 160.4 ((C=N)pyridyl), 164.1 (q, JCB = 25.3 Hz, (C-
spectroscopy at 64 scans (5.38 min.).
B)BPh4). 31P{ H} NMR (162 MHz, DMSO-d
1
): δ 129.5 (N-P-Ru, 1P),
6
-1
1
30.1 (N-P-Ru, 1P). FT-IR (powder, cm ): ν(CH)pyridyl 3055-2983;
Acknowledgments
ν(C=N)
1604.
Ru
HRMS
(ESI+):
m/z:
513.0938
2
+
-
-
[
C
42
H64Cl
2
N
4
O
4
P
2
2
] ; HRMS (ESI ): m/z 319.1495 BPh4 .
We gratefully acknowledge funding for this project from the
National Research Foundation of South Africa (Grant Numbers:
Data collection, structure resolution and refinement
9
9269 and 117989), The Royal Society and African Academy of
Sciences Furture Leaders - African Independent Reseachers
FLAIR) Scheme (Fellowship ref: 191779) and the University of
Single crystals suitable for X-ray diffraction analysis for
compounds 2, 5a, 7b and 8b, were grown and used to determine
the structures for the respective compounds. In a typical
(
Johannesburg Centre for Synthesis and Catalysis. Our profound
gratitude also goes to Prof. Ilia A. Guzei, Dr. Frederick Malan and
Dr. Banele Vatsha for their help with the single crystal X-ray data
experiment, an orange crystal of 7b with approximate dimensions
3
0
.55 x 0.44 x 0.32 mm was selected under ambient conditions.
The crystal was mounted in a stream of cold nitrogen at 150 K
and centreed in the X-ray beam using a video camera on the
diffractometer. The crystal evaluation and data collection were
performed using Quazar multi-layer optics monochromated Mo
Kα radiation (λ = 0.71073 Å) on a Bruker D8 Venture kappa
geometry diffractometer with duo Is sources, a Photon 100
CMOS detector and APEX II control software.40 All X-ray
diffraction measurements were performed at 150(2) K and
diffractometer to crystal distance of 4.00 cm. Data reduction was
performed using SAINT+, and the intensities were corrected for
absorption using SADABS.42
collection.
Keywords: aminophosphinite • phosphoramidite • ruthenium(II)
complexes • levulinic acid • γ-valerolactone
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European Journal of Inorganic Chemistry
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FULL PAPER
Aminophosphinite and
*Phosphorus-based ligands
II
phosphoramidite based Ru neutral
bimetallic complexes form with
retention of symmetry. These
complexes readily transform into
cationic P^N^N^ P complexes
following halide abstraction, giving
isomers with R,S and S,S
Gershon Amenuvor, Charles K. Rono,
James Darkwa*, and Banothile C. E.
Makhubela*
Multidentate pyridyl-aminophosphinite
and pyridyl-phosphoramidite
configurations. The complexes are
good catalysts for levulinic acid
hydrogenation into γ-valerolactone
ruthenium(II) complexes: Synthesis,
structure and application as levulinic
acid hydrogenation pre-catalysts.
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