Synthesis and characterisation of ruthenium dihydrogen complexes and their reactivity towards B-H bonds

Article abstract of DOI:10.1039/c3dt52037d

In this paper the synthesis and characterisation of ruthenium dihydrogen complexes bearing rigid aliphatic PNP pincer-type ligands are described. As one result hydride complexes were synthesised in good to high yields by a one-pot direct hydrogenation reaction. As another finding the dihydrogen complex, stabilised with a N-Me group in the ligand frame, can be converted with dimethylamine borane into a rare σ-boron complex [RuH₂(BH ₃)(Me-PNP)] with rapid B-N decoupling. Additionally, we present the first mass spectrometric analysis of the synthesised σ-complexes via liquid injection field desorption/ionisation technique (LIFDI-MS).

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DOI: 10.1039/C3DT52037D
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Paper
Synthesis and Characterisation of Ruthenium Dihydrogen Complexes
and their Reactivity towards B-H Bonds
Jong-Hoo Choi,a Nils E. Schloerer,a Josefine Berger,b and Martin H. G. Prechtl*a
Received (in XXX, XXX) 26th July 2013, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
In this paper synthesis and characterisation of ruthenium dihydrogen complexes bearing rigid aliphatic
PNP pincer-type ligands are described. As one result hydride complexes were synthesised in good to high
yields by one-pot direct hydrogenation reaction. As another finding the dihydrogen complex, stabilised
with a N-Me group in the ligand frame, can be converted with dimethylamine borane into a rare 휎-boron
10 complex [RuH2(BH3)(Me-PNP)] with rapid B-N decoupling. Additionally, we present the first mass
spectrometric analysis of the synthesised 휎-complexes via liquid injection field desorption/ionisation
technique (LIFDI-MS).
Introduction
The development of transition metal complexes is still a field of
15 increasing interest for application in homogeneous catalysis such
as hydrogenation,1 dehydrogenation,2 C-H bond3 or B-H bond
activation.4 Amongst the large and various numbers of transition
metal complexes, only a small collection is assigned to hydride
complexes as intermediates, much less molecular dihydrogen
20 complexes. Even though, Kubas et al. detected the molecular
dihydrogen complexes firstly in the 1980’s. This expanded the
45
diversity of complex chemistry.5-7 Since then, several dihydrogen
Figure 1 Representative selection of ruthenium dihydrogen complexes
and their bis(휎-B-H) aminoborane complexes.
transition metal complexes were reported.. Molecular dihydrogen
ligands are coordinated in a side-on arrangement to the metal
25 centre as 휎-complexes. This denotation is due to the interaction
between the electron donating 휎-orbital of the H2 bond and the
empty d-orbital at the metal centre and by the backdonation of the
metal’s d-orbitals into the empty 휎*-orbital of the hydrogen
molecule. This type of bonding is also considered as nonclassical
Ruthenium dihydrogen complexes can also be stabilised with
pincer ligands, for example complex 3 which was reported by
50 Leitner. Complex 3 is capable of H/D exchange, hydrogenation
or dehydrogenation and borylation of terminal alkynes.3,
16-18
Besides complex 3, Schneider et al. reported ruthenium hydride
complexes with an aliphatic, rigid PNP-pincer ligand, which have
been applied for homogeneous reduction of molecular dinitrogen
55 to ammonia.19 In his study, two polyhydride complexes (4 and 5)
have been assigned as hydride complexes as intermediates
(Figure 2). However, the spectroscopic evidence provided by
NMR relaxation time measurements was not convincing, since
the presented data did not allow the extraction of a clearly
60 defined T1min. The authors found for complex 4 a T1min of 113 ms
at 400 MHz, respectively 41 ms for complex 5, and calculated H-
H distances of 1.57 Å and 1.31 Å. Thus, they could be assumed
with certain security as elongated dihydrogen complexes.
Elongation of the hydrogen ligand in solution might have been
65 affected by the coordinative character of the deuterated solvent
THF. Therefore we used for T1 measurements of the dihydrogen
complexes deuterated toluene as solvent. Herein we display the
defined synthesis and characterisation of complex 4 and 5 and the
modified ruthenium hydride complex 6 bearing an aliphatic PNP
9
30 due to its 3-centre-2-electron (3c-2e) bonding character.8,
Besides molybdenum and tungsten, various ruthenium based
molecular dihydrogen complexes were reported, e.g., Chaudret et
al. focussed on ruthenium based molecular dihydrogen
complexes, stabilised by bulky ligands such as PCy3 (complex 1,
35 Figure 1).10-12 Moreover, the reactivity of molecular dihydrogen
complexes towards boryl adducts, such as amine boranes, turned
into a field of increasing research due to its potential in the
development of hydrogen storage systems. In recent reports,
Sabo-Etienne et al. showed the reactivity of dihydrogen
40 complex 1 in the presence of amine boranes by rapid hydrogen
evolution. As a consequence, the transformation of complex 1
into “true” bis(휎-B-H) complexes 2a-c was reported.13, 14 So far,
only a small number of “true” 휎-borane complexes have been
isolated yet.14, 15
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ligand with a methylated nitrogen compound, following a typical
synthetic protocol of ruthenium dihydrogen complexes.18
500 MHz (Supporting Information (SI), Figure S1). For
[Ru(H2)H(HPNP)] 5, the T1min value of 48 ms was matched at
Moreover, we report the reactivity of complex 6 towards B-H 40 207 K (SI, Figure S2). The H-H distance dHH for complex 4 has a
bonds. For each complex, we present the first mass spectra of air
and moisture sensitive small ruthenium dihydrogen complexes
which allowed us a deeper insight into the compositions of our
synthesised complexes.
calculated value of 1.17 Å and is assigned to the range of an
elongated dihydrogen complex (1.1-1.36 Å) defined by Kubas.12
In contrast to complex 4, the trihydride [Ru(H2)H(PNP)] 5 is
assigned to a nonclassical dihydrogen complex (0.8-1.0 Å),12
45 with a calculated H-H bond length of 0.99 Å.
5
The IR spectra of both complexes show (M-H) bands (SI, Figure
S5) between 2034 and 2000 cm-1 in a typical range of Ru-H
21
bonding.20,
For characteristic (M-H2) vibration, complex 4
shows significant Ru-H2 band at 1726 cm-1.7 Complex 5,
50 probably due to its pyramidal arrangement and amide-type
ligand, seems to have a shorter N-Ru bond length, an elongated
Ru-H2 distance and a shifted Ru-H2 band at 1975 cm-1 as a
shoulder of the bigger (M-H) band. The Isotope pattern of
complex 5 in the LIFDI-MS (Figure 3) appears to be different to
55 its simulated isotope pattern (SI, Figure S12). This can be
explained by the additional overlaps of isotope patterns of co-
existent [Ru(H2)H2(HPNP)], [RuH2(PNP)] and [RuH(PNP)]
species to the m/z isotope pattern of [Ru(H2)H(PNP)] generated
during the ionisation and analysis process under MS-conditions.
60 Moreover, under MS conditions, we observed the formation of a
decomposition product with a mass ~101 units higher than
complex 5 which can be tentatively assigned to a complex
coordinating two Ru cores. The same observation has been made
with other ruthenium complex under MS conditions. In
65 consequence, summated intensities of ruthenium isotopes of
different complexes are observed in the LIFDI-MS, shifting the
m/z values of the collective pattern up to Δ2. However, exact
quantitative ratio of the existent ruthenium species could not be
defined, but it can be reported that ruthenium hydride subspecies
70 are co-existent in small amounts.
Figure 2 Ruthenium dihydrogen complexes [Ru(H2)H2(HPNP)] 4,
[Ru(H2)H(PNP)] 5 and [Ru(H2)H2(Me-PNP)] 6.
10
Results and Discussion
Synthesis and characterisation of ruthenium hydride 4 and 5
To synthesise the complexes 4 and 5, ruthenium precursor 7 and
PNP ligand 8 were pressurised with hydrogen gas to obtain a
15 product mixture in 90% yield, consisting of 43% of complex 4
and 57% of complex 5 (Scheme 1).
Scheme 1 Synthesis of ruthenium dihydrogen complexes 4 and 5 by one-
pot direct hydrogenation.
20 Starting with this product mixture, complex 5 was isolated but
complex 4 appears to be stable only in hydrogen atmosphere (see
experimental part). Therefore, the product mixture was
characterised by NMR and IR. The isolated complex 5 was
analysed separately by IR and NMR, and the collected data was
25 compared with the extracted data of the product mixture. The
similarity of both hydride species 4 and 5 allows differentiation
of the signals in the low field of 31P and in the high field of H
1
NMR. Complex 4 shows a singlet at 111.9 ppm in the 31P NMR
and a triplet at -8.26 ppm (2JPH = 14.7 Hz) in the 1H NMR
30 spectrum, while the singlet in 31P NMR for 5 appears at
114.3 ppm and its triplet signal in the 1H NMR spectrum at
-12.44 ppm (2JPH = 10.6 Hz). For assignment of the ruthenium
complexes to elongated and nonclassical hydrides (4-5), we
performed T1 relaxation time measurements of the complex
35 mixture between 298 K and 193 K at 500 MHz in deuterated
toluene. [Ru(H2)H2(PNP)] 4 passes through a substance specific
minimum (Θmin) at 223 K with a T1min value of 132 ms at
Figure 3 LIFDI-MS analysis of [Ru(H2)H(PNP)] 5 in toluene. Isotope
pattern areas: [RuH(PNP)] 457 – 466, [RuH2(PNP)] 458 - 467 and
[Ru(H2)H(PNP)] 459 – 468, [Ru(H2)H2(HPNP)] 461 – 470.
75 Equilibrium of ruthenium hydride 4 and 5
We assume that the lability of tetrayhdride 4 can be explained by
the cooperative properties of the H-PNP pincer backbone. The N-
H ligand module can be deprotonated to complex 5. The nitrogen
building block serves as proton donor and acceptor similar to the
80 benzylic position in pyridine based PNN or PNP pincer
2
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complexes.1, 22, 23 Therefore, shifting the equilibrium towards the 40 ligand vibration (M-H) between 1972 and 1923 cm-1 (SI, Figure
more stable complex 5 by removing one equivalent of H2 was
facile (Scheme 2), while the isolation of pure complex 4 was not
possible in argon atmosphere. Complex 5 in the presence of
isopropanol as hydrogen source in a closed system at 80 °C for
S5), and the vibration of the hydrides (M-H2) at 1776 cm-1,
similar to complex 4 with analogue octahedral complex
arrangement. Compared to the LIFDI-MS isotope pattern of
complex 5, the LIFDI-MS isotope pattern of complex 6 shows a
5
20 h emulates complex 4 until the equilibrium between the tetra- 45 relatively neat isotope pattern of ruthenium species
and trihydride complexes is restored. This process was monitored
via 1H and 31P NMR in deuterated benzene. Additionally, we
achieved the full regeneration of complex 4 by treatment of
[Ru(H2)H2(Me-PNP)] (Figure 4) and is in a good agreement of its
simulated isotope pattern (SI, Figure S17).
10 complex 5 dissolved in deuterated toluene with 2 bar of hydrogen
gas, the NMR showed the exclusive presence of the tetrahydride
4 which is stable only hydrogen atmosphere.
Figure 4 LIFDI-MS analysis of [Ru(H2)H2(Me-PNP)] 6 in toluene.
50 Isotope pattern areas: [RuH2(Me-PNP)] 473 - 482, [Ru(H2)H(Me-PNP)]
474 - 485 and [Ru(H2)H2(Me-PNP)] 475 - 484.
Scheme 2 Equilibrium between ruthenium dihydrogen complexes 4 and 5
15
in the presence of isopropanol as hydrogen source in a closed system
monitored via 1H- and 31P-NMR. Complex 5 is isolated through a constant
stream of argon.
Reactivity of [Ru(H2)H2(Me-PNP)] 6 towards B-H bonds
[Ru(H2)H2(Me-PNP)] 6 reacts sensitivley to B-H bonds with
rapid hydrogen evolution. In this work we particulary identified
55 the reaction with pinacolborane and dimethylamine borane
leading to ruthenium boryl complexes 10 and 11.
Synthesis and characterisation of [Ru(H2)H2(Me-PNP)] 6
Complex 6 was obtained by following the synthetic route of
20 complex 4 and 5 (Scheme 3). Contrary to ligand 8, ligand 9
contains methyl group blocking the nitrogen position.
a
Synthesis and characterisation of [RuH2(HBPin)(Me-
PNP)] 10
60 [RuH2(HBPin)(Me-PNP)] 10 was obtained in toluene with 1.0-
Therefore, cooperative properties acting as proton donor or
acceptor are avoided, thus a conversion of the tetrahydride into a
trihydride is not possible due to the absence of a neighbouring
25 proton source. The synthesis of complex 6 provides yields
between 64-67% as a powderous grey solid.
1.1 equivalents of pinacolborane under rapid hydrogen evolution
as a solid in 88% yield after removing the solvent (Scheme 4).
The IR spectrum of complex 10 shows the (M-H) band at
2024 cm-1 and the two bridging hydride bands (M-H-B) between
65 1973 – 1914 cm-1 and between 1744 – 1675 cm-1 (SI, Figure S7).
In deuterated cyclohexane, the characteristic signals appear in the
1
highfield region of H NMR at -5.64, -9.02 and -18.85 ppm as
broad singlets assigned to the bridging hydrides and the Ru-H
hydride. In contrast to complex 10, the comparable borylated
70 PNP complex with a pyridine backbone obtained by the
ruthenium dihydrogen complex 3 contains only one singlet signal
for the bridging hydrides in the 1H NMR spectrum, which is
presumably caused by the electronic effect of the ligand and the
generally vibrant system of the complex.17 In fact, only one signal
75 was detected in the 31P NMR spectrum at 92.1 ppm which
excludes the assumption of a second similar complex.
Scheme 3 Synthesis of ruthenium dihydrogen complexes 6 by one-pot
direct hydrogenation.
30 At room temperature, complex 6 shows a singlet signal at
108.7 ppm in the 31P NMR spectrum as well as a characteristic
triplet signal at -8.68 ppm (2JPH = 13.8 Hz) in the 1H NMR
spectrum, allocating two hydride ligands and one dihydrogen
ligand coordinated to ruthenium. The T1 measurement of
35 complex 6 resulted in a T1min value of 54 ms at 224 K in
deuterated toluene with a spectrometer frequency of 500 MHz. H-
H bond length of 1.01 Å was calculated which assigns complex 6
to a nonclassical dihydrogen complex (SI, Figure S3). IR
spectrum of [Ru(H2)H2(Me-PNP)] 6 indicates the dihydrogen
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(>95%) were obtained, thus THF traces were still visible in the
1H NMR. More interestingly, the synthetic route b adding 3-5
25 equivalents of dimethylamine borane led to the decoupling of the
N—B bond with the formation of the (휎-B-H)-ruthenium
complex 11 and loss of the dimethylamine in 91% yields. This
reactivity stays in contrast to previous reports by Sabo-Etienne
where the dihydrogen complex [Ru(PCy3)2(H2)(H2)2] 1 reacts
30 with amine boranes under dehydrogenation to bis-휎–borane
complexes 2a-c (Scheme 5). In their observation, two dihydrogen
휎-ligands were substituted by the borane with formations of 휎-B-
H bonds and simultaneously the B-N adduct were connected.
This observation might be related to slightly different electronic
35 properties of the ruthenium core in [Ru(PCy3)2(H2)(H2)2] 1
compared to [Ru(H2)H2(Me-PNP)] 6, which could be explained
by the different ligand types (monodentate ligands vs pincer
ligand).
Scheme 4 Reaction of 6 with pinacolborane to complex 10 with evolution
of hydrogen gas.
LIFDI-MS analysis confirmed structure 10 (m/z 602 – 610,
Figure 5). Furthermore, fragments of [RuH2(Me-PNP)] and
[RuH3(Me-PNP)] was detected in the MS. The approaching
simulated isotope pattern of [RuH3(Me-PNP)] (red) is in a good
agreement of the analysed fragment (black) which consists
mainly the [RuH3(Me-PNP)] species.
5
40 Scheme 5 Reaction of 6 to complex 11 with evolution of hydrogen gas.
Synthetic route a with THF borane complex, synthetic route b with
dimethylamine borane in comparison to complex 1 with amine boranes
leading to complex 2a-c.13
The 31P NMR spectrum of complex 11 shows a singlet signal at
45 84.9 ppm. At room temperature, the characteristic signals in the
1H NMR appear at 5.42 ppm as a broad singlet signal, attributed
to the terminal hydrogen atoms of boron. Broad singlet signals at
-5.69 and -19.76 ppm are assigned to the bridging hydrides. The
remaining hydride signal appears at -17.85 ppm as triplet of
50 doublets. At lower temperatures, the broad signals were
sharpened and the triplet of doublets at -17.85 ppm was adjusted
into a clear triplet (Figure 6). Also integral assignments of the
10
15
Figure 5 LIFDI-MS analysis of [RuH2(HBPin)(Me-PNP)] 10 in toluene.
Isotope pattern areas: [RuH2(HBPin)(Me-PNP)] 602 – 610. [RuH2(Me-
PNP)] 473 – 482 (black), [Ru(H2)H(Me-PNP)] 474 - 484 (black) in
comparison to the simulated isotope pattern of fragment [RuH3(Me-PNP)]
474 - 484 (red).
1
Synthesis and characterisation of (휎-B-H) complex
[RuH2(BH3)(Me-PNP)] 11
hydrogen atoms in the H NMR spectrum were more accurate at
temperatures below 278 K.
[RuH2(BH3)(Me-PNP)] 11 was obtained with different synthetic
routes (a-b, Scheme 5). Reaction of dihydrogen complex 6 with
20 2-3 equivalents of the THF borane complex (1M in THF) in a
mixture of toluene and pentane resulted in rapid hydrogen
evolution. Although, high yields (89%) and high conversions
4
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the Ru-B distance is 2.19(2) Å and thus in the range of previously
14
30 reported agostic ruthenium boron complexes.13, The bridging
hydrogen atom (H2), which replaced the position of the
molecular hydrogen ligand of complex 6, is located 1.69(2) Å
next to the ruthenium atom and 1.31(6) Å to the boron atom with
an angle (degree) of 92.76 for Ru1-H2-B1 on the trans axial
35 position to the terminal hydride (H1). This arrangement is in
agreement with a typical “true” (휎-B-H)-bonding to ruthenium
14
reported by Sabo-Etienne et al.13,
Moreover, H1 can be
attributed as a hydride, although the short Ru1-H5 distance of
1.48(8) Å is rarely known in literature, but throughout transition
40 metal – hydride distances of Ni-H, Fe-H, Pt-H or Ru-H around
1.5 Å or <1.5 Å have been already reported by others.27-31 More
interestingly the B1-H5 distance remains too stretched with
1.84(2) Å for a fixed B-H bonding mode. This fact encouraged us
to assume the coordinated boron as a 휎-BH3 adduct instead of the
-
45 originally considered η2-type BH4 adduct with expected
Figure 6 1H NMR signals (Ru-H, BH3) of [RuH2(BH3)] 11 at various
symmetric arrangement for both hydrides H2 and H5 with
distances of 1.67-1.85 Å to ruthenium and 1.25-1.3 Å to boron,
temperatures between 218.5 and 298 K in deuterated toluene (400 MHz).
-
such as the PNP ruthenium η2-BH4 complex spotted by
The IR spectrum of complex 11 obtained with route a contains
traces of THF, but is congruent with the complex 11 obtained
with route b (Figure 7) Two strong bands appear at 2394 and
2330 cm-1 in a typical range of terminal B-H region.4, 15, 24-26 The
(M-H) was found at 2020 cm-1 and is in accord with previous
reports.4, 20, 21, 26 The band at 1693 cm-1 can be carefully assigned
Milstein.24 In our case, the rare type of 휎-boron complex 11 is
50 most comparable with the [IrH2(BH3)(POCOP)] complex
presented by Goldberg and Heinekey.15 Despite the different
transition metal, they reported a similar arrangement of the boron
and hydrides to the iridium centre. The [IrH2(BH3)(POCOP)]
complex also contains a bridging hydride in a 휎-B-H fashion with
55 a distance to ruthenium of around 1.90 Å and to boron of around
1.45 Å. The opposite Ru-H-B bonding distance of 1.74 Å (Ru-H
and H-B) is too stretched to be considered as a BH4- rather than a
BH3 adduct. All together, the similarity of [IrH2(BH3)(POCOP)]
5
10 to (Ru-H-B).15 No characteristic N-Me or N-H band of the
1
amine borane adduct was found neither in the H or 13C NMR
spectra nor in the IR spectrum in the region of 3000 cm-1 or
higher. Thus profoundly indicates that no ruthenium
dimethylaminoborane complex has been generated with route b,
15 but a 휎-B-H typed BH3 ruthenium complex instead.
-
to complex 11 clearly argues against the assumption of a η2-BH4
60 adduct, but emphasises the existence of a 휎-borane complex.
Figure 7 IR spectra of complex 11. Vibrational bands are identical beside
the THF traces independent from the different synthetic routes with
BH3THF (black) or BH3NMe2H (red).
Figure 8 ORTEP diagram of the single crystal structure of complex 11.
Ellipsoids are illustrated at 50% possibility. All hydrogen atoms are faded
out except for H1-H5 for clarity.
20 The single crystal X-ray analysis of the structure was determined
at 293 K (Figure 8, Table 1). Further refinement parameters and
collected data are listed in the Supporting Information. The
hydrogen atoms (H1-H5) were approached by electron densities
around the ruthenium and boron atoms. Thus we located
the
25 most likely electron density for H1 which contains a short
distanced Ru1-H1 bond length of slightly under <1.4 Å. Despite
the imprecise short bond length of Ru1-H1, the location of H1
confirms only the trans arrangement of the hydride. Furthermore
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Table 1. Selected bond distancesa and anglesb of complex 11.
Conclusion
Ru1-P1
Ru1-P2
Ru1-N1
Ru1-H1
Ru1-H5
Ru1-H2
Ru1-B1
B1-H2
2.32(7)
2.33(3)
2.18(9)
1.36(6)
1.48(8)
1.69(2)
2.19(2)
1.31(6)
1.84(2)
1.04(6)
1.15(7)
P1-Ru1-P2
Ru1-H2-B1
H1-Ru1-H2
H1-Ru1-P1
H1-Ru1-P2
N1-Ru1-B1
H3-B1-H4
163.06
92.76
170.78
63.28
65.96
143.08
108.16
In summary, we demonstrated an efficient and simple synthesis
30 of ruthenium dihydrogen complexes 4-6, stabilised with a rigid
aliphatic PNP backbone. These complexes have been
characterised via T1 spin lattice measurement as molecular
dihydrogen complexes (5 and 6) and as an elongated dihydrogen
complex 4. The methylated pincer ligand of complex 6 shows
35 major influence on its electron density and proved to be highly
active towards B-H groups, emphasising the formation of
complex 10 and the B-N decoupling of the dimethylamine borane
to a rare 휎-borane complex 11. All structures have been
confirmed by LIDS-MS analysis, which allowed us a good
40 insight into the complexes.
B1-H5
B1-H3
B1-H4
a Distances are given in Å. b Angles are reported in degrees.
Moreover the solid state structure of 11 confirms the bond
cleavage of the dimethylamine borane. The reactivity of
complex 6 towards THF borane complex or dimethylamine
borane, in route a and b, remains still uncleared, but regarding the
borane compounds as Lewis-pairs, it is plausible that THF or
dimethylamine is replaced by a stronger Lewis base system
(Figure 9). In this case, the methyl group of the PNP backbone of
10 complex 6 could electronically influence the ruthenium metal
centre by inducing Lewis-base character into the system. This
consideration would explain the possibility of a Lewis-pair
exchange during the synthesis of complex 11.
5
Experimental Section
General information
Reactions were generally prepared under argon atmosphere using
Schlenk techniques, flame-dried glassware and a Labmaster 200
45 glove-box from Mbraun. High-pressure hydrogen reactions were
performed in a Büchi Tinyclave (50 mL) glass autoclave. All
solvents and reagents were purchased from Acros, Merck, Sigma-
Aldrich, Fluka, Strem or were acquired from the institute stock.
Commercial anhydrous solvents and argon-gas packed reagents
50 were used as received and stored in the glove-box under argon
atmosphere. Non-anhydrous solvents were dried and distilled
(under vacuum or argon) prior to use, applying standard
procedures. The water content of solvents, alcohols and amines
has been quantified by Karl-Fischer titration.
15 Figure 9 Simplified Lewis pair exchange, THF or HNMe2 is replaced by a
55 Analytic methods
stronger Lewis base (complex 6).
1H, 13C, 11B, 31P NMR spectra were recorded on a Bruker Avance
II 300 and on a Bruker Avance II+ 600 spectrometer using
deuterated benzene, toluene, cyclohexane, THF and deuterium
oxide as solvents at room temperature. 1H NMR spectra
60 measurements at various temperatures were recorded on a Bruker
Avance 400 spectrometer. 1H shifts are reported in ppm (δH)
downfield from TMS and were determined by reference to the
residual solvent peaks (C6D6: 7.16 ppm, C7D8: 7.09 ppm, C6D12:
1.38 ppm, THF-d8: 3.58 ppm, D2O: 4.75 ppm.). Chemical shifts
65 are reported as singlet (s), doublet (d), triplet (t), quartet (q) and
multiplet (m). Coupling constants J were reported in [Hz]. 13C
NMR spectra were recorded using the APT or DEPTQ sequence.
13C shifts are reported in ppm (δC) relative to the solvent
resonance (C6D6: 128.0 ppm, C7D8: 137.8 ppm, C6D12: 26.4 ppm,
70 THF-d8: 25.4 ppm). 31P NMR chemical shifts are reported in ppm
(δP) downfield from H3PO4 and referenced to an external 85%
solution of H3PO4 in D2O. For measurements of air sensitive
chemical compounds and for spin lattice relaxation time (T1)
experiments, Young-Teflon Capped NMR tubes from Wilmad
75 were used. T1 measurements were carried out at 500 MHz on a
Bruker DRX 500. Infrared spectra (IR) were measured at room
temperature under argon (Glovebox) with a Bruker Alpha
spectrometer equipped with a Diamond-ATR IR unit. Data is
reported as follows: absorption ṽ [cm-1], weak (w), medium (m),
Furthermore, the basic character of complex 11 could tend to
draw the more “protic” hydride H5 closer to the ruthenium
centre, which would explain the short distance of Ru1-H5 of
20 1.48(8) Å. LIFDI-MS analysis of [RuH2(BH3)(Me-PNP)] 11
confirms additionally the assumed structure (Figure 10) and is in
agreement of the simulated isotope pattern (SI, Figure S23).
Figure 10 LIFDI-MS analysis of [RuH2(BH3)(Me-PNP)] 11 in toluene.
25
Isotope pattern area: [RuH2(BH3)(Me-PNP)] 487 – 498.
80 strong
(s).
LIFDI-MS
(Liquid
Injection
Field
Desorption/Ionization-Mass Spectrometry) was performed on a
Waters micromass Q-ToF-2™ mass spectrometer equipped with
6
| Dalton Transaction, [2013], [vol], 00–00
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DOI: 10.1039/C3DT52037D
Page 7 of 10
Dalton Transactions
a LIFDI 700 ion source (Linden CMS).
δP [ppm] = 114.3 (s).
IR: ṽ[cm-1]=3291 (w), 2811 – 2950 (m), 2024 (m), 1471 (m),
60 1383 (w), 1361 (m), 1323 (m), 1204 (m), 1171 (m), 1151 (m),
1093 (w), 1058 (m), 1018 (m), 964 (w), 930 (w), 801 (m), 733
(m), 692 (m), 580 (m), 521 (m), 471 (s).
Synthesis of [Ru(H2)H2(PNP)] 4 and [Ru(H2)H(PNP)] 5
In an argon flushed Büchi glass autoclave, 320 mg (1.0 mmol,
1.0 eq.) [Ru(cod)(2-methylallyl)2] 7 were added to 400 mg
(1.1 mmol, 1.1 eq.) of PNP ligand 8 in 5 ml pentane. After the
autoclave was filled with H2 gas to 5 bar at room temperature, the
content was stirred for 48 h at 55 °C. With the increase in
5
Generation of dihydrogen complex 4 under H2 atmosphere
11 mg (1.0 eq., 0.023 mmol) of complex 5 dissolved in 0.1 mL
temperature to 55 °C, a H2 pressure of 7 bar was reached. After 65 deuterated toluene and introduced in an argon flushed NMR
the reaction mixture was cooled to room temperature, the
pressure tube. The NMR tube was pressurised with 2 bar of
hydrogen gas. After 60 h at room temperature, the colour of the
content turned from orange into yellow. Full conversion of
complex 5 into 4 was detected by NMR.
10 autoclave was depressurised and flushed twice with argon. After
separating the orange mother liquor with a cannula from the
yellow solid (mixture 4 and 5), the product mixture was washed
twice with pentane. The pentane was removed via cannula and 70 Spectral data of complex 4:
the product mixture was dried under argon and stored at -34 °C.
15 Yield: 397.0 mg (product mixture), 0.85 mmol, 85%.
Spectral data of complex 4:
1H NMR (600 MHz, toluene-d8): δH [ppm] = 4.55 (weak, 1H,
(H/D-exchange)), 2.92 – 2.88 (weak m, 2H, NCH2), 2.58 – 2.43
(m, 2H, NCH2), 1.94 – 1.88 (m, 2H, PCH2), 1.67 – 1.63 (m, 2H,
3
3
1H NMR (500 MHz, toluene-d8): δH [ppm] = 4.55 (weak s, 1H,
PCH2), 1,41 (t, 18H, JPH = 5.9 Hz PC(CH3)3), 1.30 (t, 18H, JPH
N-H (H/D-exchange)), 2.91 – 2.86 (m, 2H, NCH2), 2.54 – 2.44 75 = 5.9 Hz, PC(CH3)3), -8.25 (t, 4H, JPH = 14.5 Hz, Ru-H). 13C
2
(m, 2H, NCH2), 2.14 – 2.12 (m, 2H, PCH2), 1.67 – 1.63 (m, 2H,
NMR (75 MHz, toluene-d8): δC [ppm] = 55.7 (-CH2-), PC(CH3)3),
30.8 – 30.4 (PC(CH3)3), 27.4 (-CH2-). 31P NMR (121 MHz,
toluene-d8): δp [ppm] = 111.9 (s); Note to 13C-NMR: The
quaternary carbons between 34.7 – 32.1 (see synthesis of
3
3
20 PCH2), 1,41 (t, 18H, JPH = 6.1 Hz, PC(CH3)3), 1.36 (t, 18H, JPH
2
= 6.0 Hz, PC(CH3)3), -8.26 (t, 4H, JPH = 14.7 Hz, Ru-H). 13C
NMR (75 MHz, benzene-d6): δC [ppm] = 55.7 (-CH2-), 34.7 –
32.1 (PC(CH3)3), 30.8 – 30.5 (PC(CH3)3), 27.4 (-CH2-). 31P NMR 80 complex 4 and 5) were not detected due to low solubility of
(121 MHz, toluene-d8): δp [ppm] = 111.9 (s). T1 (500 MHz,
25 toluene-d8) = 298 K (312 ms), 258 K (184 ms), 238 K (148 ms),
228 K (135 ms), 221 K (132 ms), 208 K (141 ms), 198 K
(169 ms), 193 K (191 ms); (T1min = 132 ms, 223 K).
complex 5 in 0.1 mL deuterated toluene. Pointing out that the
NMR pressure tube has an inner measurable volume of 0.1 mL.
Synthesis of Me-PNP ligand 9
Synthesis of N-Methyl bis(2-chloroethyl)amine hydrochloride
85 17.0 g (0.096 mol) Bis(2-chloroethyl)amine hydrochloride and
10.0 g (0.2 mol) formic acid were added to 20 mL of a 37%
formaldehyde solution in a 500 mL round bottom flask equipped
with a reflux condenser. After the reaction mixture was refluxed
for 3 h at 100 °C and cooled to room temperature, the solvent was
90 removed in vacuo until a yellow white solid was obtained. For
further purification, the solid was dissolved in 100 mL THF.
After removing the solvent, the product was obtained as a white
solid which was directly used for the synthesis of PNP ligand 9
(18.41 g, 99%).
Spectral data of complex 5:
1H NMR (500 MHz, toluene-d8): δH [ppm] = 3.46 – 3.44 (m, 4H,
30 NCH2), 1.91 – 1.85 (m, 4H, PCH2), 1.30 (t, 36H, 3JPH = 12.1 Hz,
2
PC(CH3)3), -12.44 (t, JPH = 10.6 Hz). 13C NMR (75 MHz,
benzene-d6): δC [ppm] = 65.6 (-CH2-), 34.7 (PC(CH3)3), 29.6
(PC(CH3)3), 26.1 (-CH2-). 31P NMR (121 MHz, toluene-d8):
δP [ppm] = 114.3 (s). T1 (500 MHz, toluene-d8)
= 298 K
35 (138 ms), 258 K (97 ms), 238 K (69 ms), 228 K (59 ms), 221 K
(52 ms), 208 K (48 ms), 198 K (50 ms), 193 K (53 ms); (T1min
48 ms, 207 K).
=
IR ( 4 and 5): ṽ[cm-1]=3291 (w), 2852 – 2947 (m), 2034 - 1995
(m), 1726 (m), 1470 (m), 1383 (m), 1359 (m), 1202 (w), 1174
40 (m), 1053 (w), 1016 (m), 923 (m), 798 (s), 764 (w), 672 (m), 644
(w), 600 (m), 565 (m), 471 (s), 432 (m).
95 1H NMR (300 MHz, D2O): δH = 2.96 (s, 3H, NCH3), 3.63 (bs,
4H, -CH2CH2-), 3.93 (t, 4H, 2JHH = 5.8 Hz, -CH2CH2-).
Synthesis of Me-PNP 9
In a flame dried and argon flushed 500 mL Schlenk flask, 8.75 ml
(47.15 mmol, 2.3 eq.) di-tert-butyl phosphine was dissolved in
100 60 mL diethyl ether. After cooling to -78 °C, 18 mL of a 2M in
hexane butyl lithium solution was added dropwise to the content
under constant stirring. The reaction mixture was allowed to
reach room temperature, the Schlenk flask was equipped with a
reflux condenser and heated for 4 h at 50 °C under argon
105 atmosphere until a yellow solid of di-tert-butyl phosphine lithium
was obtained. In a flame dried and argon flushed 250 mL Schlenk
Isolation of dihydrogen complex 5
In an argon flushed Schlenk flask, 25 mg (1.0 eq., 0.054 mmol) of
the mixture of complex 4 and 5 were dissolved in 2 mL toluene.
45 The content was stirred for 1 h at room temperature under a slow
stream of argon. The brown-red coloured liquid was removed in
vacuo until a green solid 5 remained. The product was stored
under argon atmosphere at -34 °C. Yield: 18.0 mg, 0.04 mmol,
75%.
50 LIFDI-MS: m/z 468.0 (M+, 91.3), 470.1 (91.3), 466.0 (100),
465.0 (100), 464.0 (56.5), 462.9 (56.5), 462.0 (56.5), 461.0
(21.7), 460.9 (8.7), 460.0 (17.4), 459.0 (8.7).
flask
3.9 g
(20.5 mmol,
1.0 eq.)
N-Methyl
bis(2-
chloroethyl)amine hydrochloride was dissolved in 50 mL diethyl
ether and cooled to -78 °C. Under constant stirring, 8.16 mL of a
110 2M in hexane butyl lithium solution was added dropwise within
30 min to the content. After allowing the reaction mixture to
reach room temperature, the content was stirred for 2 h and
transferred slowly via transfer cannula to the precooled di-tert-
butyl phosphine lithium in the 500 mL Schlenk flask at -78 °C.
1H NMR (400 MHz, benzene-d6): δH [ppm] = 3.46-3.42 (m, 4H,
2
NCH2), 1.90 – 1.85 (m, 4H, PCH2), 1.22 (t, 36H, JPH = 6.0 Hz,
2
55 PC(CH3)3), -12.53 (t, JPH = 10.7 Hz). 13C NMR (75 MHz,
benzene-d6): δC [ppm] = 65.6 (-CH2-), 34.7 – 32.1 (PC(CH3)3),
29.6 (PC(CH3)3), 26.1 (-CH2-). 31P NMR (121 MHz, benzene-d6):
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DOI: 10.1039/C3DT52037D
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Page 8 of 10
Synthesis of complex [RuH2(HBPin)(Me-PNP)] 10
The unified reaction mixture was allowed to reach room
temperature and then refluxed over night at 60 °C under argon
atmosphere. The reaction mixture was allowed to reach room
temperature, the solution was separated in a flame dried and
argon flushed Schlenk tube from the solid lithium chloride via
centrifuge. The ether was removed in vacuo and replaced with
50 mL pentane. The content was extracted 3 times with degassed
water and dried over magnesium sulphate. After filtration, the
solvent was removed in vacuo to obtain a yellow oil (5.3 g,
10 14.15 mmol, 69% yield, purity 67%). Major impurities stemed
from the excess of di-tert-butyl phosphine. Ligand 9 was used
without further purification. For analytic data, the product was
dissolved in a solution of pentane and triethylamine (1:1). After
stirring the content for 30 min, the solvent mixture was removed
15 in vacuo to obtain a clearer oil with a purity of 80% or higher.
1H NMR (300 MHz, benzene-d6): δH = 2.91 - 2.84 (m, 4H, -
CH2CH2-), 2.40 (s, 3H, -CH3), 1.81 - 1.74 (m, 4H, -CH2CH2-),
1.23 (18 H, s), 1.20 (18 H, s). 13C NMR (75 MHz, benzene-d6):
δC = 58.9 – 58.4 (CH2), 41.8 (NCH3), 31.2 – 30.6 (P(C(CH3)3)),
20 29.7 - 29.5 (P(C(CH3)3)), 20.0 – 19.7 (CH2), 31P NMR (121 MHz,
benzene-d6): δP = 24.7 (s).
60 In an argon flushed Schlenk flask equipped with a bubbler,
100 mg (1.0 eq., 0.20 mmol) of complex 6 were dissolved in
6 mL toluene. 33 µL (1.1 eq, 0.22 mmol) pinacol borane were
added to the content and stirred for 2 h at room temperature. The
green coloured solvent was removed in vacuo until a green solid
65 (10) remained. The product was stored under argon atmosphere at
-34 °C. Yield: 111.0 mg, 0.176 mmol, 88%.
5
LIFDI-MS: m/z 610.0 (M+, 0.6%), 609.0 (0.6), 608.0 (0.6), 607.4
(1.3), 607.3 (1.3), 606.5 (0.6), 606.4 (0.6), 606.3 (1.3), 605.3
(1.9), 604.4 (1.3), 603.1 (0.6), 602.2 (0.6), 601.3 (0.6), 484.8
70 (1.3), 482.1 (50.0), 481.9 (19.5), 481.1 (27.0), 480.2 (26.5), 480.1
(100), 480.0 (49.7), 479.1 (66.0), 479.0 (22.6), 478.1 (69.8),
478.0 (13.8), 477.1 (46.5), 477.0 (21.4), 476.0 (28.9), 476.0 (6.3),
475.1 (18.9), 475.0 (3.8).
1H NMR (300 MHz, C6D12): δH [ppm] = 2.61 – 2.54 (m, 2H,
75 NCH2), 2.59 (s, 3H, CH3), 2.44 – 2.38 (m, 4H, NCH2), 2.10 -
1.95 (m, 2H, PCH2), 1.84 – 1.72 (m, 2H, PCH2), 1.49 (t, 18H,
3JPH = 5.8 Hz, ), 1.41 (t, 18H, 3JPH = 6.1 Hz, ), 1.11 (12H, s, Pin),
-5.64 (bs, 1H, Ru-H-B), -9.02 (bs, 1H, Ru-H-B), -18.85 (bs, 1H,
Ru-H). 13C NMR (75 MHz, C6D12): δC [ppm] = 80.1 (Pin, Cq),
80 66.2 (CH2), 34.5 – 34.3 (P(C(CH3)3)), 32.5 – 32.2 (P(C(CH3)3))
29.2 (P(C(CH3)3)), 25.5 (CH2), 23.8 (Pin-CH3). 31P NMR:
(121 MHz, C6D12): δP [ppm] = 92.1 (s), 11B-NMR (160 MHz,
C6D12): 37.8 (s).
Synthesis of [Ru(H2)H2(Me-PNP)] 6
In an argon flushed Büchi glass autoclave, 240 mg (0.75 mmol,
1.0 eq.) [Ru(cod)(2-methylallyl)2] 7 were added to 413 mg
25 (regarding the purity grade of 67%, 1.1 mmol, 1.45 eq.) of
ligand 9 in 5 ml pentane. After the autoclave was filled with H2
gas to 5.5 bar at room temperature, the content was stirred for
48 h at 60 °C. With the increase in temperature to 60 °C, a H2
pressure of 6.5 bar was reached. After the reaction mixture was
30 cooled to room temperature, the autoclave was depressurised,
flushed twice with argon and stored under argon atmosphere at
-34 °C for 12 h. The dark red mother liquor was separated with a
cannula from the grey solid and the product was washed twice
with precooled pentane. The pentane was removed via cannula
35 and the product was dried under argon and stored at -34 °C.
Yield: 242 mg 0.50 mmol, 67%.
IR: ṽ[cm-1] = 2959 (m), 2897 – 2867 (m), 2032 (w), 1964 - 1924
85 (w), 1746 - 1688 (w), 1482 (m), 1461 (m), 1384 (m), 1360 (m),
1310 (w), 1268 (w),, 1218 (w), 1178 (m), 1160 (m), 1040 (s), 933
(w), 877 (m), 804 (s), 739 (m), 570 (m).
Synthesis of (휎-B-H)-complex [RuH2(BH3)(Me-PNP)] 11
Route a
90 In an argon flushed Schlenk flask equipped with a bubbler, 70 mg
(1.0 eq., 0.14 mmol) of complex 6 were dissolved in 5 mL
toluene. 0,36 mL (2.6 eq, 0.36 mmol) THF borane complex of a
1M THF solution were added to the content and stirred for 2 h at
room temperature. The solvent was removed in vacuo until a
95 yellow solid 11 remained. The product was stored under argon
atmosphere at -34 °C. Yield: 70.0 mg, 0.13 mmol, 92%.
Route b
In an argon flushed Schlenk flask equipped with a bubbler, 50 mg
(1.0 eq., 0.1 mmol) of complex 6 were dissolved in a mixture of
100 4 mL toluene and 2 mL pentane. 29 mg (5.0 eq, 0.5 mmol)
H3BNHMe2 were added to the content and stirred for 2 h at room
temperature. The solvent was removed in vacuo until a yellow
solid 11 remained. The product was stored under argon
LIFDI-MS: m/z 484.1 (M+,22.2), 483.1 (66.7), 483.0 (33.3),
482.0 (44.4), 481.1 (100), 480.0 (77.8), 479.1 (55.5), 479.0
(44.4), 478.1 (33.3), 478.1 (44.4), 478.0 (55.6), 477.1 (22.2),
40 477.0 (11.1), 476.1 (22.2), 476.0 (11.1), 475.1 (22.2), 475.0
(11.1).
1H NMR (300 MHz, toluene-d8): δH ppm = 2.52 – 2.43 (m, 2H,
NCH2), 2.4 (s, 3H, -CH3), 2.28 – 2.18 (m, 2H, NCH2), 1.81 -1.74
3
(m, 2H, PCH2), 1.64 – 1.58 (m, 2H, PCH2), 1.44 (t, 18H, JPH
=
=
3
2
45 6.1 Hz), 1.31 (t, 18H, JPH = 6.1 Hz), -8.68 (t, 4H, JPH
13.8 Hz). 13C NMR: (75 MHz, toluene-d8): δC [ppm] = 66.3 –
66.2 (CH2), 53.3 (CH3), 34.1 (P(C(CH3)3)), 31.9 (P(C(CH3)3)),
30.9 – 30.7 P(C(CH3)3)), 25.6 (CH2). 31P NMR: (121 MHz,
toluene-d8): δP [ppm] = 108.7 (s).
atmosphere at -34 °C. Yield: 44.0 mg, 0.082 mmol, 82%.
105 Preparation of [RuH2(BH3)(Me-PNP)] 11 for single crystal
analysis
In a headspace vial, 20 mg of complex 11 were dissolved in 3 mL
pentane and kept overnight at room temperature in argon
atmosphere. After the solvent was evaporated in the argon
110 atmosphere, the yellow crystals were stored in 3 mL pentane at
-34 °C.
50 T1 (500 MHz, toluene-d8) = 299 K (198 ms), 278 K (130 ms),
268 K (106 ms), 258 K (86 ms), 248 K (71 ms), 238 K (60 ms),
228 K (53 ms), 218 K (54 ms), 208 K (62 ms), (T1min = 54 ms,
224 K).
IR: ṽ[cm-1]=2985 (w), 2937 – 2856 (m), 1972 - 1923 (m), 1776
55 (m), 1475 – 1446 (m), 1415 (w), 1383 (m), 1362 (w), 1350 (m),
1317 (w), 1235 (w), 1207 (m), 1172 (m), 1039 (m), 1018 (m),
930 (w), 913 (w), 878 (m), 806 (s), 737 (m), 670 (m), 652 (m),
597 (m), 564 (m), 527 (w).
Elementary analysis calculated for C21H52BNP2Ru (493.47) C
51.22, H 10.64, B 2.20, N 2.84, P 12.58, Ru 20.52; found: C
50.88, H 9.71, B 2.20, N 2.50, P 12.58, Ru 20.52. Found atom
115 ratio by CHN: C20.9H47.5N0.9B1.0P2.0Ru1.0.
LIFDI-MS: m/z 496.2 (M+, 7.1), 496.1 (14.3), 495.2 (42.9), 495.0
8
| Dalton Transaction, [2013], [vol], 00–00
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DOI: 10.1039/C3DT52037D
Page 9 of 10
Dalton Transactions
(7.1), 494.5 (7.1), 494.1 (57.1), 493.2 (14.2), 493.1 (100), 493.0
11. Y. Guari, A. Castellanos, S. Sabo-Etienne and B. Chaudret, J. Mol.
Catal. A, 2004, 212, 77 - 82.
(35.7), 492.1 (92.9), 492.0 (28.6), 491.1 (35.7), 491.0 (50.0),
490.1 (42.9), 490.0 (7.3), 489.2 (14.3), 488.1 (7.1), 487.1 (28.6),
487.0 (14.3).
12. G. J. Kubas, Metal–dihydrogen and sigma-bond coordination: the
consummate extension of the Dewar–Chatt–Duncanson model
for metal–olefin pi bonding, J. Organomet. Chem., 2001.
13. G. Alcaraz and S. Sabo-Etienne, Angew. Chem.-Int. Edit., 2010, 49,
7170-7179.
60
5
1H NMR: (400 MHz, toluene-d8): δH [ppm] = 5.42 (bs, 2H, BH2),
2.19 (s, 3H, CH3), 2.10 – 2.02 (m, 2H NCH2), 2.01 – 1.93 (m, 2H,
NCH2), 1.68 – 1.61 (m, 2H, PCH2), 1.52 (bt, 18H, 3JPH = 4.9 Hz),
3
1.48 – 1.45 (m, overlapped, 2H, PCH2), 1.40 (t, 18H, JPH
=
=
14. G. Alcaraz, A. B. Chaplin, C. J. Stevens, E. Clot, L. Vendier, A. S.
Weller and S. Sabo-Etienne, Organometallics, 2010, 29, 5591-
5595.
2
6.1 Hz), -5.69 (bs, 1H, 휎-Ru-H-B), -17.85 (td, 1H, JPH
65
10 19.22 Hz, JBH = 3.52 Hz, Ru-H), -19.76 (bs, 1H, Ru-H-B). 13C
NMR: (75 MHz, toluene-d8): δC [ppm] = 67.0 (CH2), 51.4 (), 35.1
(P(C(CH3)3)), 33.9 (P(C(CH3)3)), 30.2 (P(C(CH3)3)), 24.13
2
15. T. J. Hebden, M. C. Denney, V. Pons, P. M. B. Piccoli, T. F. Koetzle,
A. J. Schultz, W. Kaminsky, K. I. Goldberg and D. M.
Heinekey, J. Am. Chem. Soc., 2008, 130, 10812-10820.
(CH2). 31P NMR: (121 MHz, toluene-d8): δP [ppm] = 84.9 (s). 11
B
NMR (160 MHz, toluene-d8): 19.2 (s).
70 16. M. Hölscher, M. H. G. Prechtl and W. Leitner, Chem.-Eur. J., 2007,
13, 6636-6643.
15 IR: ṽ[cm-1]=2966 - 2861 (m), 2394 (m), 2330 (m), 2020 (m),
1815 (w), 1693 (m), 1472 (m), 1441 (m), 1384 (w), 1363 (w),
1326 (w), 1257 (m), 1097 (w), 1039 - 1033 (m), 927 (w), 907
(w), 870 (m), 805 (m), 740 (m), 672 (m), 600 (m), 573 (m), 529
(w), 478 (m).
17. C. Gunanathan, M. Hölscher, F. Pan and W. Leitner, J. Am. Chem.
Soc., 2012, 134, 14349-14352.
18. M. H. G. Prechtl, Y. Ben-David, D. Giunta, S. Busch, Y. Taniguchi,
75
W. Wisniewski, H. Goerls, R. J. Mynott, N. Theyssen, D.
Milstein and W. Leitner, Chem.-Eur. J., 2007, 13, 1539-1546.
19. B. Askevold, J. T. Nieto, S. Tussupbayev, M. Diefenbach, E.
Herdtweck, M. C. Holthausen and S. Schneider, Nature
Chem., 2011, 3, 532-537.
20 Acknowledgements
We acknowledge the Ministerium für Innovation, Wissenschaft
und Forschung NRW (MIWF-NRW) for financial support within
the Energy Research Program for the Scientist Returnee Award
for M. H. G. Prechtl (NRW-Rückkehrerprogramm). For access
25 to LIFDI-MS analysis, we gratefully acknowledge Prof. Dr.
T. Braun (Humboldt-University of Berlin, Germany). J-H. Choi
wants to thank C. Hegemann, M. Keßler and S. Sahler for helpful
discussion.
80 20. P. G. Jessop and R. H. Morris, Coordin Chem Rev, 1992, 121, 155-
284.
21. T. Arliguie, B. Chaudret, R. H. Morris and A. Sella, Inorg Chem,
1988, 27, 598-599.
22. J. Zhang, M. Gandelman, L. J. W. Shimon, H. Rozenberg and D.
85
Milstein, Organometallics, 2004, 23, 4026-4033.
23. J. Zhang, G. Leitus, Y. Ben-David and D. Milstein, J. Am. Chem.
Soc., 2005, 127, 12429-12429.
Notes and references
30 a Department of Chemistry, University of Cologne, Greinstr.6,50939
Cologne, Germany. Fax: +49 221 470 1788; Tel: +49 221 470 1981; E-
mail: martin.prechtl@uni-koeln.de Web: www.catalysislab.de
b Institute of Chemistry, Humboldt University at Berlin, Brook-Taylor-
Straße 2, D-12489 Berlin, Germany.
24. J. Zhang, E. Balaraman, G. Leitus and D. Milstein, Organometallics,
2011, 30, 5716-5724.
90 25. D. A. Addy, J. I. Bates, M. J. Kelly, I. M. Riddlestone and S.
Aldridge, Organometallics, 2013, 32, 1583-1586.
35 † Electronic
DOI: 10.1039/b000000x/
‡ For limited spectral and crystallographic data see ESI.
Supplementary
Information
(ESI)
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