Modulating the steric, electronic, and catalytic properties of Cp* ruthenium half-sandwich complexes with β-diketiminato ligands

Article abstract of DOI:10.1021/om2006479

Five different types of β-diketiminate ligands, bearing electron-donating to strongly electron-withdrawing substituents, were synthesized and used in the synthesis of Cp* ruthenium complexes (Cp* = η⁵-C₅Me₅). One series consists of complexes with a covalent Ru^III-Cl bond, and the other series features a reduced Ru^II center, where the chloride is abstracted by treatment of the corresponding Ru^III compounds with Zn or Mg. All compounds were characterized by single-crystal X-ray diffraction, UV-visible spectroscopy, and cyclic voltammetry. In the case of Ru^II complexes, solution NMR techniques provided key information regarding the electronic and structural differences induced by the different β-diketiminate ligands employed. Capitalizing on the facile reduction-oxidation cycle of the Cp* ruthenium β-diketiminato complexes, catalytic atom transfer radical addition (ATRA) and cyclization (ATRC) reactions were performed on relevant substrates. The turnover rates are strongly dependent on the type of β-diketiminate used, where ligands with electron-withdrawing substituents, i.e., trifluoromethyl groups, provided complexes that efficiently catalyze the addition of CCl₄ or toluenesulfonyl chloride to styrene. In contrast, complexes with electron-donating substituents on the β-diketiminate promoted efficient ATR cyclization of N-allyl-N-phenyltrichloroacetamide and 2,2,2-trichloroethyl ether. Thus, the overall product conversion and yield are dependent on matching the ligand substitution pattern of the catalyst to the type of substrate.

Full text of DOI:10.1021/om2006479

Article
pubs.acs.org/Organometallics
Modulating the Steric, Electronic, and Catalytic Properties of Cp*
Ruthenium Half-Sandwich Complexes with β-Diketiminato Ligands
Andrew D. Phillips,†,‡ Katrin Thommes,† Rosario Scopelliti,† Claudio Gandolfi,§ Martin Albrecht,‡,§
Kay Severin,† Dominique F. Schreiber,‡ and Paul J. Dyson*,†
†Institut des Sciences et Ingen
‡School of Chemistry and Chemical Biology, University College Dublin, Belfield, Dublin 4, Ireland
§Department of Chemistry, University of Fribourg, Chemin du Musee
9, CH-1700 Fribourg, Switzerland
́ ́ ́
ierie Chimiques, Ecole Polytechnique Federale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
́
S
* Supporting Information
ABSTRACT: Five different types of β-diketiminate ligands, bearing electron-
donating to strongly electron-withdrawing substituents, were synthesized and
used in the synthesis of Cp* ruthenium complexes (Cp* = η5-C5Me5). One
series consists of complexes with a covalent RuIII−Cl bond, and the other series
features a reduced RuII center, where the chloride is abstracted by treatment of
the corresponding RuIII compounds with Zn or Mg. All compounds were
characterized by single-crystal X-ray diffraction, UV−visible spectroscopy, and
cyclic voltammetry. In the case of RuII complexes, solution NMR techniques
provided key information regarding the electronic and structural differences induced by the different β-diketiminate ligands
employed. Capitalizing on the facile reduction−oxidation cycle of the Cp* ruthenium β-diketiminato complexes, catalytic atom
transfer radical addition (ATRA) and cyclization (ATRC) reactions were performed on relevant substrates. The turnover rates
are strongly dependent on the type of β-diketiminate used, where ligands with electron-withdrawing substituents, i.e.,
trifluoromethyl groups, provided complexes that efficiently catalyze the addition of CCl4 or toluenesulfonyl chloride to styrene.
In contrast, complexes with electron-donating substituents on the β-diketiminate promoted efficient ATR cyclization of N-allyl-
N-phenyltrichloroacetamide and 2,2,2-trichloroethyl ether. Thus, the overall product conversion and yield are dependent on
matching the ligand substitution pattern of the catalyst to the type of substrate.
INTRODUCTION
■
Organoruthenium complexes promote a range of catalytic
reactions such as olefin metathesis,1 C−H activation,2 hydro-
genation,3 and oxidation.4 A key advantage of using Ru over
other metals is the strong preference for coordinating and
activating olefinic bonds,1b which in turn reduces or eliminates
the requirement for functional group protection. Although
complexes containing phosphine or carbene ligands currently
dominate the organoruthenium field, the past decade has
witnessed a renewed interest in complexes bearing strongly
donating nitrogen chelates.5 A well-known example is the Noyori
transfer hydrogenation catalyst, featuring the tosylethylenedi-
amine ligand.6 This expanding field now includes organometallic
species featuring anionic N,N′-chelates, where a number of
complexes with the amidinate ligand have been reported7
(Figure 1a). The five-membered β-diketiminates (Figure 1b)
have also received considerable attention8 and continue to be
successfully employed in stabilizing low-coordinate and highly
reactive main-group9 and transition-metal10 complexes. In
particular, this class of ligand exerts considerable steric effects
originating from the functional groups on the N-flanking
positions, normally aryl substituents. Thus, the β-diketiminate
ligand encloses and partially encapsulates the central metal,
preventing dimerization or oligomerization. In β-diketiminato
complexes featuring a higher metal coordination number,
Figure 1. Amidinates (a) and β-diketiminates (b) as anionic N,N′-
chelate ligands. The gray regions indicate the bite angle of the
corresponding ligand.
significant interligand repulsion is often observed. In contrast,
only minor steric interactions are encountered in species bearing
an amidinate ligand, where the N-flanking substituents are folded
away from the metal.
The chemistry of first-row transition metal based β-diketiminate
compounds is quite advanced, with numerous known examples,
while comparatively, the variety of complexes associated with
the second- and third-row d-block metals is far less explored.
Nevertheless, β-diketiminato complexes of Zr,11 Nb,12 Mo,13
Ag/Au,14 Pd/Pt,15,16 and Rh/Ir17,18 have recently emerged.
Concurrently a large expansion in the number of catalytic appli-
cations employing β-diketiminate transition-metal complexes
is in progress. In particular, the fields of polymerization,19
Received: July 19, 2011
Published: October 24, 2011
© 2011 American Chemical Society
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Scheme 1. Bifunctional Metal−Ligand Reactions of the η6-Arene β-Diketiminato Ruthenium Complex 1 with Acetylene,
Ethylene, Styrene, and Dihydrogen, Forming Species Featuring a Chelating β-Diimine Ligand
oxidation,20 olefin metathesis,13 hydrogenation,17a,21 and hydro-
amination22 have witnessed significant developments. Recently
we described the synthesis and characterization of the first
β-diketiminato ruthenium complexes supported by neutral
η6-arene ligands.23 The coordinatively unsaturated complex 1
(Scheme 1) was found to display an unusual metal−ligand
bifunctional character, as evidenced in reactions with alkenes
and alkynes, which undergo reversible metal−ligand cyclo-
additions. Furthermore, a rare example of heterolytic cleavage
of dihydrogen involving the nucleophilic β-carbon center of
the β-diketiminate was observed, resulting in an efficient
catalyst for the hydrogenation of highly substituted olefins,
including 1-methylcyclohexene and 4-isopropenyl-1-methylcy-
clohexene.
Herein, we expand the chemistry of organoruthenium
compounds bearing a β-diketiminate ligand, by describing a
new series of [Cp*RuIII(β-diketiminato)Cl] and [Cp*RuII(β-
diketiminato)] complexes. A detailed analysis of the steric
and electronic effects imparted by differently substituted
β-diketiminates and the influence of this ligand class on the
catalytic activity of the RuIII complexes in atom transfer radical
addition (ATRA) and cyclization (ATRC) reactions is also
described.
Subsequently, the series of β-diketiminato ruthenium(III)
complexes 7−11 were prepared using an established methodo-
logy previously employed in the synthesis of 1.23 A CH2Cl2
solution of the corresponding β-diketiminato lithium complex
(2−6) was added slowly to a solution of the dimer
[Cp*RuIIICl2]2 in CH2Cl2 (Scheme 3). During some reactions
the formation of a byproduct was observed, which was
particularly dominant in the case of 11 (Scheme 4). The
identity of this species 12, was confirmed by single-crystal X-ray
diffraction analysis, which showed a metal-coordinated neutral
1,2,3,4-tetramethylfulvene ligand, containing one exocyclic and
two internal CC bonds.26
The byproducts of type 12 formed in the synthesis of 7−11
were removed by washing with pentane, and residual
[Cp*RuIIICl2]2 was removed with diethyl ether. To increase
the yield of 11, an alternative method was employed. Recently,
the synthesis of the dimeric silver acetonitrile complex 18
(Scheme 5), featuring the fluorinated β-diketiminate 6, was
reported.14a Species 18 bearing the β-diketiminate 6 proved to be
a highly valuable and versatile ligand-transfer reagent. Reaction of
18 with [Cp*RuIIICl2]2 afforded 11 in 87% yield (Scheme 5)
without the formation of 12. Alternatively, transmetalation of
the fluorinated β-diketiminato thallium complex 19 with the
[Cp*RuIIICl2]2 dimer also provided 11 in high yield (Scheme 5).
This approach has been previously used to prepare Ni and Mo
β-diketiminato complexes.13,27 The procedure for preparing the
thallium precursor is based on that reported by Grubbs
et al.28 and others.29 Complex 19 was first prepared and isolated
from the reaction between TlOEt and 6 and subsequently
reacted with [Cp*RuIIICl2]2 in CH2Cl2 to afford 11 (Scheme 5)
without any evidence for the formation of 12.
RESULTS AND DISCUSSION
■
Synthesis and Reactivity of Complexes 7−17. The
protonated β-diketiminates used in this study are known
compounds and were prepared via reported literature
methods.24 In order to facilitate metal binding, deprotonation
of the ligand to the corresponding conjugate lithium salts 2−6
was accomplished using n-BuLi in n-pentane (see Scheme 2).25
In the solid state, all of the RuIII complexes are stable toward
O2, but when they are dissolved in nondegassed solvents, the
complexes decompose within hours, except for 10 and 11,
which are stable for several months even in solution.
Scheme 2. Synthetic Routes Used To Prepare the β-Diketiminate
Ligands with Electron-Donating (2, 3) or Electron-Withdrawing
Groups (4−6) and the Corresponding Lithium Salts
Complexes 7−11 are readily transformed into the corre-
sponding RuII species 13−17 in high yield by reduction with
zinc or magnesium in dry and degassed THF (Scheme 3).
Extraction with n-pentane and filtration through Celite
provided the RuII compounds in pure form, as determined
1
by H and 13C NMR spectroscopy. An alternative method for
the synthesis of a [Cp*RuII(β-diketiminato)] complex was
reported by Russell et al.30 and involves the direct reaction
of [Cp*RuIIICl2]2 with the protonated phenyl-substituted
β-diketiminate in the presence of excess K2CO3. The reaction
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Scheme 3. Synthesis of the RuIII Complexes 7−11 and the RuII Complexes 13−17
Scheme 4. Synthesis of the RuIII Complex 11 and the Corresponding Byproduct 12
Scheme 5. Alternative Routes to the Synthesis of Complex 11
presumably proceeds with the in situ formation of [Cp*RuII-
(μ2-OCH3)]2, a valuable precursor to a diverse range of
complexes bearing the Cp*RuII fragment. The synthesis is
completed by nucleophilic addition of the phenyl-substituted
β-diketiminate and loss of methanol.31
17, exhibiting increased shielding of the ring carbon atoms. For
all RuII complexes a single resonance for the methyl
substituents associated with the η5-C5Me5 ligand is observed,
indicating that in solution unhindered rotation occurs. The
combined effects for the induced structural distortions in the
η5-C5Me5 ligand and electronic influences imparted by the Ru-
β-diketiminate fragment are difficult to quantify separately.
Complex 17 has the greatest number of CF3 substituents on the
β-diketiminato ligand, which corresponds to the highest
shielded δ(1H) value of the Cp* methyl groups (Table 1).
Conversely, 14 has the sterically least hindered β-diketiminate,
with 3,5-bis-methylphenyl flanking aryls, and has the least shielded
δ(1H) values for CH3 groups associated with the Cp* ring,
indicating a decrease in electron density for this ligand in 14
compared to that in 17. For species 16 and 17 with CF3
substituents in the α-positions, a large increase for the δ(1H)
values of the β-CH position is observed, which correlates with
greater π-electron delocalization within the core atoms of the
β-diketiminate ligand. Since the extended π-type molecular orbitals
are orthogonal to the plane of the ligand, contraction of the
σ-bonding ligand framework, originating from electron-withdrawing
Upon exposure to chlorinated solvents such as CH2Cl2,
CHCl3, and CCl4, complexes 13−17 rapidly convert to the
original RuIII species 7−11, as determined by ESI-MS and UV−
visible experiments. Similar behavior has been observed for
other RuII complexes, including Cp*RuII amidinate complexes 32
and the family of Cp*RuII acetylacetone compounds.31 All five
β-diketiminato RuII complexes reported here are stable in wet
degassed hydrocarbon solvents: i.e., THF, Et2O, and pentane.
However, all RuII species react spontaneously with dioxygen,
both in the solid state and in nondegassed solutions, which
prevented accurate elemental analyses of the complexes.
Spectroscopic Characterization of Complexes 7−11
and 13−17. A comparison of the 1H and 13C NMR spectra of
13−17 reveals that the electronic effects exerted by the
different β-diketiminato ligands are readily distinguished, with
the compounds featuring electron-deficient ligands, i.e., 16 and
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a
1
Table 1. Selected H and 13C NMR Data for the RuII Complexes 13−17
Ar
R
δ(1H) β-CH
δ(13C) β-CH
δ(13C) α-C
δ(1H) (C5(CH3)5)
δ(13C) (C5(CH3)5)
δ(13C) (C5(CH3)5)
13
14
15
16
17
2,6-(CH3)2C6H3
3,5-(CH3)2C6H3
3,5-(CF3)2C6H3
3,5-(CH3)2C6H3
3,5-(CF3)2C6H3
CH3
CH3
CH3
CF3
CF3
5.455
5.553
5.294
7.080
6.714
98.86
98.13
99.28
90.24
91.33
157.52
157.36
157.97
145.78
146.27
0.938
1.243
0.864
0.973
0.476
9.98
10.03
9.67
77.16
77.74
78.15
83.42
84.39
9.25
8.81
a
Compounds were dissolved in C6D6 and spectra recorded at 25 °C.
inductive effects, results in an increased π-orbital overlap. Similarly,
CF3-substituted aryls have been used to decrease the atomic orbital
size of heavy main-group elements, resulting in strengthened PN
and AsN π-bonds.33
wavelength associated with λmax(A) is longer and corresponds
to less energetic d−d transitions. For 16 and 17 with α-CF3
substituents, the d−d transitions are significantly broadened
with no discernible maximum. For the RuIII complexes, a
second set of absorptions, labeled λmax(B), was observed when
the β-diketiminate has α-CF3 substituents. This band
corresponds to a charge transfer from the Cl ligand to the
metal center, termed XMCT, commonly seen in Ru complexes
featuring 1,3-diazabutadiene-type ligands.34a,35 Similarly, TD-
DFT calculations predict that this transition occurs at lower
wavelength for the RuIII−Cl complexes with α-CH3 sub-
stituents, i.e., 7−9, but are combined with other LMCT bands
associated with λmax(C). For the RuII series, λmax(B) is only
observed for complexes featuring CF3 α-substitution, i.e., 16
and 17, which according to the models corresponds to a MLCT
between the Ru center and the β-diketiminate ligand. The most
intense band present in the spectra of all complexes, labeled
λmax(C), is associated with LLCTs associated with the π system
of the β-diketiminate. However, some high-energy LMCTs are
also present and mixed with the LLCTs, especially for RuII and
RuIII complexes featuring α-CH3 groups on the β-diketiminate
ligand. In general, for both series of complexes, λmax(C)
undergoes a bathochromic shift corresponding to increasing
electron-withdrawing character of the β-diketiminate ligand,
where both the RuIII (11) and RuII (17) species feature less
energetic LMCTs. This is consistent with the TD-DFT
calculated models, which suggest that the nature of the
LUMO in the electron-donating CH3 α-substituted
β-diketiminate complexes, i.e., 7 and 13, are largely metal-
based, whereas for 11 and 17, featuring electron-withdrawing
CF3 groups, the LUMO is predominately built on contributions
from the π-type orbitals from core atoms of the β-diketiminate
ligand.
Solid-State Characterization of Complexes 7−17. Com-
prehensive structural characterization of all the complexes was
accomplished using X-ray diffraction methods. This enables a
detailed analysis of the influence imparted by different
substitution patterns for the β-diketiminate ligands employed
(Figures 2−7 and Tables 4 and 5). The RuIII species with an
additional Cl ligand, 7−11, feature a distorted three-legged
piano-stool geometry with the flanking aryl groups of the β-
diketiminate ligand positioned parallel with the plane of the η5-
C5Me5 group. Depending on the type of β-diketiminate ligand
used, some notable structural variations are observed, especially
for the RuIII complexes. Similarly to the previously reported
η6-C6H6 substituted chloro β-diketiminato RuII complexes,23c
two distinctive conformations of the coordinated β-diketimi-
nate ligand are apparent (Figure 8). The first type of
conformation, associated primarily with 7, and to a lesser
extent 8, shows the β-diketiminate ligand folded along the N−
N′ vector and, albeit less pronounced, orthogonally folded
A direct electronic comparison of the RuIII and RuII
complexes is possible using UV−visible spectroscopy. Spectra
of the blue and green RuIII complexes were measured in
CH2Cl2, while n-pentane was used for the more reactive
magenta and red RuII species. In both the RuIII series 7−11
(Table 2) and RuII series 13−17 (Table 3), depending on the
Table 2. UV−Visible Absorptions for the RuIII Complexes
a
7−11
103ε
103ε
103ε
λmax(A)
(nm)
(M−1
λmax(B)
(nm)
(M−1
λmax(C)
(nm)
(M−1
complex
cm−1
)
cm−1
)
cm−1
)
7
646
637
636
606
586
4.4
5.5
5.1
4.0
3.5
318
318
322
349
345
20.3
27.6
28.5
26.8
24.7
8
9
10
11
410
420
8.2
9.6
a
Spectra were recorded at 25 °C in CH2Cl2.
Table 3. UV−Visible Absorptions for the RuII Complexes
a
13−17
103ε
103ε
103ε
λmax(A)
(M−1
λmax(B)
(M−1
λmax(C)
(M−1
complex
(nm)
cm−1
1.1
)
(nm)
cm−1
)
(nm)
cm−1
)
13
531
306
322
308
314
317
318
40.2
40.1
50.1
53.0
34.0
36.0
14
15
16
17
516
517
b
1.8
1.9
387
447
448
6.3
7.7
8.5
b
a
b
Spectra were recorded at 25 °C in n-pentane. The λmax(A) band is
broad and is merged at the base with the λmax(B) transition.
substitution pattern of the β-diketiminate ligand, either two or
three sets of absorption maxima, λmax(A−C), were observed.
Assignment of the absorption bands to electronic transitions is
based on previous studies involving ruthenium coordination
compounds with unsaturated chelating nitrogen ligands, in
particular 1,3-diazabutadienes,34 and employing high-level time-
dependent density functional theory (TD-DFT) calculations
using the B3LYP level of theory (a full discussion is given in the
Supporting Information). The first set of absorptions, λmax(A)
in the RuIII series, corresponds to a mixture of d−d transitions
and LMCTs originating from the β-diketiminate ligand to the
metal center. In contrast, for the RuII complexes, these λmax(A)
bands are assigned as pure d−d-centered transitions, as
indicated by the relatively small molar extinction coefficients
in the range of (1.1−1.9) × 103 M−1 cm−1. For 13 and 14, the
along the Ru−C vector. The maximum amount of N−N′
β
folding, as indicated by the Ru−N,N′bisection−C β angle, defined
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Figure 2. ORTEP diagram of the RuIII complex 7 (left) and the RuII complex 13 (right) with the 2,6-(CH3)2C6H3-α-CH3 β-diketiminate, drawn with
30% probability ellipsoids. Disordered sections of the molecule and solvates are omitted for clarity.
Figure 3. ORTEP diagram of the RuIII complex 8 (left) and the RuII complex 14 (right) with the 3,5-(CH3)2C6H3-α-CH3 β-diketiminate, drawn with
30% probability ellipsoids. Disordered sections of the molecule and solvates are omitted for clarity.
Figure 4. ORTEP diagram of the RuIII complex 9 (left) and the RuII complex 15 (right) with the 3,5-(CF3)2C6H3-α-CH3 β-diketiminate, drawn with
30% probability ellipsoids. For 9, only one of the unique molecules in the unit cell is shown. Disordered sections of the molecule and solvates are
omitted for clarity.
by θ in Figure 8, is largest in species 7 due to the steric
hindrance originating from o-CH3 groups attached to the
flanking aryls. In contrast, complexes bearing CF3 substituents
at the α-position or aryl groups on the β-diketiminato ligand
have an essentially planar core framework, as indicated by θ >
170°. This structural dichotomy between the two types of RuIII
complexes defines the extent of π-electron delocalization
between the central atoms of the β-diketiminato ligand and
the Ru center. For example, in the case of 7, a more localized
allylic π-type interaction is envisaged between the pπ orbitals of
the N centers and the Ru dxz orbital. However, for species
9−11, an extended π-delocalized MO involving the metal and
the entire β-diketiminato framework, including the CN and
CC bonds, is apparent. The effect of adding electron-
donating or -withdrawing groups to the β-diketiminate ligand is
directly manifested in the magnitude of the Ru−Cl bond length
(Table 4), with 7 showing the longest distance within the
series. As expected, both 10 and 11 with the electron-with-
drawing α-positioned CF3 groups possess the shortest Ru−Cl
bonds of the series. Complex 9, with m-CF3 groups on the aryl
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Figure 5. ORTEP diagram of the RuIII complex 10 (left) and the RuII complex 16 (right) with the 3,5-(CH3)2C6H3-α-CF3 β-diketiminate, drawn
with 30% probability ellipsoids. Disordered sections of the molecule and solvates are omitted for clarity.
Figure 6. ORTEP diagram of the RuIII complex 11 (left) and the RuII complex 17 (right) with the 3,5-(CF3)2C6H3-α-CF3 β-diketiminate, drawn
with 30% probability ellipsoids. Disordered sections of the molecule and solvates are omitted for clarity.
substituents, has a slightly longer Ru−Cl bond distance than
the species with α-positioned CF3 groups. Similar trends for
Ru−Cl bond lengths are also observed for the (η 6-C6H6)RuCl
complexes with CF3-substituted β-diketiminates.23c
A number of reports have shown the strong steric influence
of the β-diketiminate ligand, and for the complexes described
herein, the Ru−Cp*(centroid) distance provides a useful
indicator for this steric interaction. Interestingly, species 11
has a Ru−Cp*(centroid) distance equal to that of 7, whereas
the Ru−N distances in 11 are significantly shorter than in 7
(Table 4), which suggests that steric interactions between the
Cp* ring and flanking aryl substituents of the β-diketiminate
ligand are maximized in this particular species. For those
complexes bearing CH3 α-substituted β-diketiminates, i.e., 7−9,
the N−Ru−N bond angles are smaller than those in 10 and 11
with α-CF3 groups. The internal Cβ−Cα bond lengths
associated with the β-diketiminate ligand are also significantly
decreased in 11 compared to the other compounds in the
series.
The secondary product 12, formed during the reaction
involving 11 (Scheme 2), was crystallized from n-pentane by
slow evaporation, and the crystals were found to contain both
11 and 17 in a ratio of 4:6. Consequently, the bond parameters
should be treated with caution. However, the structure of 17
(Figure 7) reveals the alternating CC double and C−C single
bonds associated with the fulvene ligand. Characteristically, the
exocyclic CH2 group is bent toward the Ru center, forming a
η2-Ru−CC π bond as observed in other related organo-
ruthenium systems bearing this ligand type.26
The corresponding series of reduced RuII complexes 13−17,
in which the Cl ligand is absent, are characterized by a planar
structure with C2v symmetry, when considering only the core
framework of the β-diketiminato ligand and chelated metal.
This topology is evident from the Ru−N,N′bisection−Cβ bond
angle θ, which for the entire RuII series is greater than 176°.
Moreover, the flanking aryl groups are positioned parallel to the
ring plane of the Cp* ligand. Similarly, cationic (η6-C6H6)RuII
β-diketiminate complexes such as 1 have structurally identical
features: i.e., a planar β-diketiminato ligand with an ortho-
gonally aligned η6-arene group.23b In comparison, the Cp*RuII
and p-cymene RuII complexes bearing the significantly less
bulky acetylacetone ligand feature a head-to-tail dimerization,
Figure 7. ORTEP diagram of RuII complex 12 featuring the
tetramethyl-substituted fulvene ligand, drawn with 50% probability
ellipsoids. Disordered sections of the molecule, including the overlap
of complex 11, are omitted for clarity.
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Figure 8. Comparison of the structure associated with the β-diketiminate ligands observed in the series of RuIII complexes 7−11: (left) envelope-
type conformation found in 7 (R = CH3, Ar = 2,6-dimethylphenyl) and 8 (R = CH3, Ar = 3,5-dimethylphenyl), where θ = 154.6(1) and 166.3(2)°,
respectively; (right) planar-type conformation found in 9 (R = CH3, Ar = 3,5-bistrifluoromethylphenyl), 10 (R = CH3, Ar = 3,5-dimethylphenyl),
and 11 (R = CF3, Ar = 3,5-bistrifluoromethylphenyl), where θ is equal to or greater than 171.6(2)°. In addition, 10 and 11 feature a second fold of
the β-diketiminate ligand along the Ru···β-CH axis. The Cp*(centroid)−Ru−Cl bond angle remains constant throughout the entire series.
Table 4. Selected Bond Lengths (Å) and Angles (deg) for the RuIII Complexes 7−11
a
7
8
9
10
11
Ru−N
N−Cipso
N−Cα
2.075(2)
2.089(2)
1.452(4)
1.453(4)
1.342(4)
1.347(4)
1.402(5)
1.399(5)
2.461(1)
1.890(1)
87.5(1)
2.051(4)
2.050(5)
1.451(7)
1.444(6)
1.332(7)
1.329(7)
1.381(8)
1.381(6)
2.451(1)
1.869(2)
87.8(2)
2.067(12)
2.055(4)
2.069(4)
1.470(7)
1.452(7)
1.331(6)
1.309(6)
1.384(8)
1.394(7)
2.431(1)
1.886(2)
90.2(2)
2.071(3)
2.070(3)
1.443(4)
1.440(4)
1.324(4)
1.329(4)
1.390(5)
1.395(6)
2.430(1)
1.881(2)
89.7(1)
1.432(17)
1.344(24)
1.387(23)
Cα−Cβ
Ru−Cl
2.437(2)
1.868(6)
87.6(4)
b
Ru−C
N−Ru−N
Ru−N−Cipso
120.8(2)
119.7(2)
124.0(2)
125.2(2)
123.7(3)
123.5(3)
127.4(3)
85.0(1)
115.9(3)
116.6(4)
127.6(3)
126.4(4)
123.2(4)
124.0(5)
128.1(5)
87.7(1)
116.3(10)
115.6(3)
116.8(3)
125.7(3)
124.4(4)
124.7(5)
126.0(5)
127.7(5)
86.7(1)
115.4(2)
116.5(2)
125.6(2)
125.7(2)
125.5(4)
125.2(3)
127.6(3)
85.0(1)
Ru−N−Cα
N−Cα−Cβ
128.5(9)
123.3(14)
Cα−Cβ−Cα
N−Ru−Cl
128.8(13)
88.4(3)
86.6(1)
86.2(1)
84.4(1)
85.7(1)
b
Cl−Ru−C
115.6(1)
160.2(1)
154.6(1)
115.5(1)
158.8(1)
166.3(2)
115.6(2)
156.7(4)
179.6(6)
116.06(8)
160.25(14)
114.4(6)
162.1(1)
173.0(2)
b
c
C −Ru−N
c
Ru−N −Cβ
171.6(2)
b
a
Four symmetry-independent molecules are found within the unit cell; the values reported are averaged. Refers to the centroid point of the
c
η5-C5Me5 ligand. Refers to the midpoint distance between the two nitrogen centers of the β-diketiminato ligand.
formed through bonding between the metal and β-C
positions.36 This particular binding mode is not observed in
13−17. Therefore, the flanking aryl groups of β-diketiminate
ligands are highly effective in sterically preventing the
dimerization, which leads to stable complexes where the
coordination number of ruthenium is reduced.
Only a limited number of structural changes to the
β-diketiminate ligand were observed upon reduction of the
Cl-binding RuIII complexes, notably those parameters asso-
ciated with the Ru−N bond distances and N−Ru−N bond
angles. For example, the majority of RuII complexes feature
shorter Ru−N bonds, except in the case of 9 (Ar = 3,5-
(CF3)2C6H3), where the reduction from 9 to 15 leads to longer
Ru−N bonds. The larger N−Ru−N bond angles associated
with α-CF3 substitution found in 10 and 11 are retained in
the corresponding RuII species, 16 and 17. In comparison, the
metal−Cp*(centroid) distances are significantly shorter in the
RuII complexes than in the corresponding RuIII species, with
the greatest change occurring on reduction of 8 to 14 (Ar =
3,5-(CH3)2C6H3). The shortened Cp*−Ru distances indicate
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Table 5. Selected Bond Lengths (Å) and Angles (deg) for the RuII Complexes 13−17
a
13
14
15
16
17
Ru−N
N−Cipso
N−Cα
2.071(2)
2.060(1)
2.040(5)
2.050(2)
2.055(6)
2.056(6)
2.035(6)
2.025(6)
1.463(10)
1.437(9)
1.464(9)
1.455(9)
1.334(10)
1.367(10)
1.353(10)
1.372(10)
1.404(11)
1.388(12)
1.379(12)
1.373(12)
1.828(3)
1.821(3)
89.6(3)
2.060(3)
1.447(4)
1.452(4)
1.349(4)
1.348(4)
1.393(5)
1.396(5)
1.819(1)
87.2(1)
2.063(2)
2.046(4)
1.436(6)
1.436(6)
1.354(7)
1.352(7)
1.373(9)
1.387(9)
1.798(2)
87.4(2)
2.050(2)
1.457(3)
1.454(3)
1.346(3)
1.344(3)
1.391(3)
1.394(3)
1.824(1)
90.1(1)
1.446(2)
1.447(2)
1.347(2)
1.345(2)
Cβ−Cα
1.398(3)
1.398(3)
b
Ru−C
1.809(1)
N−Ru−N
87.92(6)
89.3(2)
Ru−N−Cipso
116.8(2)
117.0(2)
128.9(2)
129.3(2)
123.3(3)
123.1(3)
128.1(3)
179.4(1)
179.7(1)
115.92(11)
116.02(11)
128.46(12)
128.64(12)
123.48(16)
123.27(17)
128.05(17)
179.7(1)
116.8(3)
116.8(3)
129.2(4)
128.9(4)
122.9(5)
123.2(5)
128.2(5)
178.8(2)
178.4(3)
116.8(1)
116.2(1)
126.2(1)
126.3(1)
125.1(2)
125.0(2)
127.3(2)
179.8(1)
178.9(1)
117.0(5)
116.6(4)
117.0(4)
117.9(4)
126.9(5)
126.7(5)
127.3(5)
127.6(5)
125.1(7)
124.2(7)
124.0(7)
123.2(7)
127.4(7)
128.6(7)
179.3(2)
179.9(4)
179.0(5)
179.2(4)
Ru−N−Cα
N−Cα−Cβ
Cα−Cβ−Cα
b
c
C −Ru−N
c
Ru−N −Cβ
176.8(1)
a
b
c
Two symmetry-independent molecules are found within the unit cell. Refers to the centroid point of the η5-C5Me5 ligand. Refers to the midpoint
distance between the two nitrogen centers of the β-diketiminato ligand.
increased metal−ligand interactions and are correlated with a
more electron-rich β-diketiminato RuII fragment, donating into
the π* MOs associated with the Cp* ligand. A more detailed
and comprehensive comparison of the metal−ligand inter-
actions in the RuIII and RuII complexes as analyzed through
DFT-calculated models is discussed in the Supporting
Information.
parameters associated with the β-diketiminate ligand, partic-
ularly the N−Cβ and Cβ-Cα bond distances, show little variation
between oxidized 7 and reduced 13.
Both sets of RuII and RuIII complexes, incorporating
β-diketiminate CF3 groups, demonstrate crystal packing effects
more complicated than those observed in the other complexes.
In all cases involving CF3 groups, the spatial packing involving
complexes 9−11 and 15−17 maximizes the number of
intermolecular fluorine−fluorine interactions, as observed in
other organometallic complexes bearing fluorinated ligands37
and organic molecules.38 A more detailed discussion regarding
intermolecular interactions is provided in the Supporting
Information.
Interestingly, the shortened RuII−Cp*(centroid) distances
are not correlated with the Cipso−N-Ru bond angle, indicative
of the steric interaction between the flanking aryl of the
β-diketiminate ligand and the Cp* group. However, the 2,6-
dimethyl aryl substitution in 13 leads to the five CH3 groups of
the Cp* being significantly distorted out of the ring plane, as
indicated by an average Cp*(centroid)−C-C(Me) bond angle
of 172.48°. In contrast, for complex 14, which features a shorter
Cp*-Ru interaction, the out-of-plane bending of the CH3
substituents belonging to the Cp* are less than in 13, where
the average Cp*(centroid)−C-C(Me) bond angle is 173.51°,
the greatest in the RuII series. Comparison of other bond
Electrochemical Analysis of Complexes 7−11 and 13−
17. The redox properties of the RuIII complexes 7−11 and RuII
complexes 13−17 were characterized using cyclic and differ-
ential pulse voltammetry. Due to the propensity of the com-
plexes toward bond activation, [n-Bu4N]BArF was used as an
inert supporting electrolyte in all measurements (Table 6).
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a
behavior. In these complexes the reversible oxidation is not
paralleled by a similar process when starting from the
corresponding RuII analogues 15 and 17, respectively, suggesting
a more complicated electrochemically induced reaction sequence.
Evaluation of the RuIII Complexes 7−11 in Atom
Transfer Radical Addition Reactions. The atom transfer
radical addition (ATRA) of polyhalogenated compounds to
olefins (“Kharasch reaction”)40 is a versatile C−C coupling
reaction with importance in organic synthesis.41 In 1973 it was
discovered that RuIICl2(PPh3)3 is a potent catalyst for this
reaction.42 Since then, several ruthenium complexes with high
catalytic activity have been developed.43 Among them are half-
sandwich complexes with arene44 and cyclopentadienyl ligands45
and complexes bearing carborane,46 amidinate,32b,47 vinylidene,48
alkylidene,49 and N-heterocyclic carbene ligands,50 as well as
bimetallic complexes.44b,51 Not surprisingly, the nature of the
ligands is a decisive factor for the catalytic activity, and there is
evidence that the ATRA activity correlates with the redox
potential of the complexes.52 Consequently, the catalytic activity
of 7−11 in ATRA reactions was evaluated.
Ruthenium-catalyzed ATRA reactions are believed to
proceed via a RuII/RuIII redox couple, and RuII complexes are
generally used as catalyst precursors.43 Recently, however, it has
been shown that RuIII complexes can be used as the catalyst
precursors if combined with AIBN53 or Mg as a reducing
agent.51,54 The reducing agent generates and constantly
regenerates the active RuII species. The use of Mg is particularly
appealing, because it gives rise to low amounts of side products,
and it can easily be separated from the reaction mixture and was
thus chosen for the ATRA reactions with 7−11.
The addition of CCl4 to styrene, a commonly used
benchmark reaction, was initially investigated.43 All reactions
were performed at room temperature with a substrate to
catalyst ratio of 300:1. Since water-saturated solvents can be
beneficial for ATRA reactions,54d all reactions were carried out
in degassed “wet” deuterated toluene.
Complexes 7−11 were found to display very different
catalytic activities (Table 7), and 7−9, with a methyl
substituent on the β-diketiminato ligand, were almost inactive,
whereas 10 and 11, which carry the electron-withdrawing CF3
α-substituents, showed significantly higher activity. The highest
yield of 76% was obtained with 11 as the catalyst (Table 7,
entry 5).
Table 6. Electrochemical Data for 7−11 and 13−17
complex
aryl
α-R
E1/2 (V) ΔE (mV)
Epc (V)
7
2,6-(CH3)2C6H3
3,5-(CH3)2C6H3
3,5-(CF3)2C6H3
3,5-(CH3)2C6H3
3,5-(CF3)2C6H3
2,6-(CH3)2C6H3
3,5-(CH3)2C6H3
3,5-(CF3)2C6H3
3,5-(CH3)2C6H3
3,5-(CF3)2C6H3
CH3
CH3
CH3
CF3
CF3
CH3
CH3
CH3
CF3
CF3
0.39
0.30
0.56
0.48
−0.25
0.36
0.36
0.16
0.48
0.05
331
194
359
170
332
394
248
189
300
229
−1.07
8
−0.23
−0.81
−0.61
−1.58
9
cd
,
10
11
13
14
15
16
17
b
−0.72, 0.57
a
Conditions: in THF using [n-Bu4N]BArF (0.026 M) as supporting
electrolyte, potentials vs SCE referenced to external Fc+/Fc (E1/2
=
b
c
0.56 V), scan rate 250 mV s−1. Value from DPV. Only observed after
d
initial sample reduction. A second reversible oxidation is observed:
E1/2 = 0.74 V, ΔE = 222 mV.
Complexes 13−17 showed quasi-reversible oxidations between
+0.05 and +0.48 V. No clear correlation between the oxidation
potentials and the electronic effect imparted by the substituents
on the β-diketiminate was found. The electron-withdrawing
CF3 substituents tend to facilitate oxidation when located on
the aryl ring, although they lead to a higher oxidation potential
when positioned only within the β-diketiminato scaffold.
Possibly, stereoelectronic effects may account for a more
complex interplay between substituents and the metal center.
Such effects may include charge delocalization within the
six-membered β-diketiminato ruthenium unit entailing π back-
bonding,39 perhaps combined with a conformational rigidity of
the aryl fragments that is dependent on the α-positioned
substituents. The large variability of the oxidation potentials
within the series suggests that the redox reaction is not a purely
metal-centered process.
Compounds 7−11 display an irreversible reduction in
addition to a quasi-reversible oxidation. While again no clear
correlation is apparent, it is interesting to note that the redox
process in 7, 8, and 10 are closely related to the electrochemical
behavior of the corresponding analogues 13−15, respectively
(Figure 9). The irreversibility of the reduction implies a fast
Next, the ATRA of 4-toluenesulfonyl chloride (TsCl) to
styrene was investigated.55a The reactions were carried out at
room temperature using 1 mol % of the complexes, and the
results are summarized in Table 8. The relative catalytic
activities of the complexes differ from those observed for the
reaction with CCl4. The most active catalyst is 10, leading to a
yield of 87% (Table 8, entry 4), whereas 11, which was the
most active catalyst for CCl4, displays only moderate activity in
this reaction (Table 8, entry 5). However, the overall trend is
similar, with complexes bearing electron-withdrawing CF3
groups on the β-diketiminato ligand being more active.
Intramolecular ATRA reactions, often referred to as atom
transfer radical cyclization (ATRC) reactions, are particularly
interesting for organic synthesis, and several Cu and Ru
complexes have successfully been employed as catalysts for this
type of transformation.41,43 The catalytic properties of species
7−11 in ATRC reactions were evaluated for the cyclization of
N-allyl-N-phenyltrichloroacteamide (A)47,b and 2,2,2-trichloro-
ethyl ether (B)55 in the presence of Mg at room temperature.
Using 5 mol % of catalyst, all RuIII complexes showed some
Figure 9. Superimposed graphs from cyclic voltammetric measure-
ments of 7 (blue) and 13 (red), indicating the strong similarity of the
oxidation around +0.38 V and the irreversible reduction of species 7
around −1 V.
chemical transformation following the reduction. It seems
plausible that the electrochemically reduced complex 7− rapidly
undergoes chloride loss, thus forming 13. Notably, 9 and 11, both
featuring CF3 meta-substituted aryl groups, show a different
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Table 7. ATRA of CCl4 to Styrene Catalyzed by 7−11 in the
Table 9. ATRC Reactions Catalyzed by 7−11 in the Presence
a
a
Presence of Mg
of Mg
cat-
alyst
[catalyst]:
[olefin]
conversion
(%)
entry
yield (%)
1
2
3
4
5
7
1:300
1:300
1:300
1:300
1:300
5
8
3
6
8
9
8
6
10
11
60
78
56
76
cat-
alyst
conversion
(%)
a
Reactions were performed in the presence of activated Mg powder
entry
substrate
yield (%)
(100 mg) with D2O-saturated toluene-d8 as the solvent; [catalyst] =
4.6 mM, [styrene] = 1.38 M, [CCl4] = 5.52 M, [internal standard] =
270 mM. The conversion is based on the consumption of the olefin,
and the yield is based on the formation of the product determined by
1H NMR spectroscopy using the internal standard 1,4-bis-
(trifluoromethyl)benzene.
1
2
A
A
A
A
A
B
B
B
B
B
7
57
62
47
100
81
90
37
98
63
10
54
8
60
3
9
45
4
10
11
7
95
5
76
6
83
7
8
35
Table 8. ATRA of TsCl to Styrene Catalyzed by 7−11 in the
a
8
9
91 (86:14)
Presence of Mg
9
10
11
57
7
10
a
Reactions were performed in toluene-d8 (total volume 1000 μL,
[substrate] = 0.10 M, [Ru] = 5.0 mM). The conversion is based on the
consumption of the olefin, and the yield is based on the formation of
the product determined by 1H NMR spectroscopy after 24 h using 1,4-
bis(trifluoromethyl)benzene (50 mM) as the internal standard.
cat-
[catalyst]:
[olefin]
conversion
(%)
entry
alyst
yield (%)
1
2
3
4
5
7
1:100
1:100
1:100
1:100
1:100
13
26
18
89
43
8
22
14
87
37
8
EXPERIMENTAL SECTION
■
9
General Procedures. Synthesis of the starting materials was
carried out under a N2 atmosphere with standard Schlenk
techniques,57 whereas subsequent preparations and manipulations,
including catalytic reactions, were performed in a glovebox with a N2
atmosphere, containing less than 1 ppm of O2 and H2O. Unless
otherwise stated, all solvents were dried and degassed using
appropriate scavenging columns (Innovative Technologies Inc.) and
stored in Schlenk flasks equipped with Teflon stopcocks. Celite (541
grade, Aldrich) was dried at 180 °C before use. Benzene-d6 and
toluene-d8 were dried over potassium and distilled under a N2
atmosphere. Microwave reactions were performed using a Biotage
initiator 2.0 reactor using metal-capped pressurized microwave vials.
The protonated β-diketiminates 2−6, the corresponding lithium
10
11
a
Reactions were performed in the presence of activated Mg powder
(100 mg) with D2O-saturated toluene-d8 as the solvent; [catalyst] =
4.4 mM, [styrene] = 0.44 M, [TsCl] = 0.52 M, [internal standard] =
90 mM. The conversion is based on the consumption of the olefin,
and the yield is based on the formation of the product determined by
1H NMR spectroscopy after 24 h using the internal standard 1,4-
bis(trifluoromethyl)benzene.
level of activity, varying from moderate to very good (Table 9).
For the cyclization of substrate A, complex 10 was the most
active catalyst, leading to full conversion and a yield of 95%
after only 5 h (Table 9, entry 4). For the cyclization of 3,
however, the best yields were observed with 7 (83%, Table 9,
entry 6) and 9 (91%, Table 9, entry 8). The high activity of 7
and 9 is in sharp contrast to that observed for the ATRA
reactions with CCl4 (Table 1) and TsCl (Tables 7 and 8), in
which 7 and 9 were not very active.
The results obtained for the different ATRA and ATRC
reactions show that the complexes presented here, in com-
bination with Mg, are potent catalysts for ATR-type reactions,
leading to good yields under mild conditions. No simple
correlation between catalytic activity and the redox potential of
the complexes or the steric demand of the β-diketiminato
ligand was observed. In contrast, complexes with a low activity
for one reaction were found to be highly active for a different
one. The strong dependence of the relative catalytic activity on
the substrate parallels to some extent what has been observed
for ruthenium based metathesis catalysts,56 and should be
considered for future investigations in this area.
complexes, and [(η5-C5Me5)RuIIICl2]2 were prepared according to
24,58,59
literature procedures.
Mg powder (>99%) was obtained from
Fluka and was activated through agitation using a stirring bar under an
atmosphere of dry N2 for 10 days before use. All other reagents were
purchased from commercial sources and used as received. NMR
spectra were recorded on Bruker Avance instruments operating at 200
1
or 400 MHz. Where applicable, homo- and heteronuclear H (COSY,
NOE) and 13C (HMBC and HSQC) NMR correlation spectroscopy
1
was used to assign molecular connectivity. Chemical shifts for H and
1
13C spectra were referenced with respect to the H or 13C signal of
residual nondeuterated solvents in the sample, and 19F spectra were
referenced to CF3Cl. All NMR samples were prepared under a N2
atmosphere and stored in flame-sealed glass NMR tubes. Attenuated
transmitted reflectance FT-IR spectra were acquired on a Perkin-Elmer
Spectrum-One instrument with diamond-anvil configuration, or for
air-sensitive complexes, Nujol mull suspensions were kept between
KBr plates placed in a gasket-sealed sample holder. Elemental analyses
were obtained using an Exeter Analytical CE-440 elemental analyzer.
Suitable elemental analyses for complexes 11−17 could not be
obtained, due to their high sensitivity to oxygen. Mass spectra were
recorded using ESI-MS under standard conditions employed for
organometallic compounds60 on a Thermo-Finnigan LCQ DECA XP
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Plus quadruple ion trap instrument set in positive mode: flow rate
5 μL per min; spray voltage 5 kV; capillary temperature 100 °C;
capillary voltage 20 V. UV−visible absorption spectra were recorded
using diluted stock solutions of n-pentane or CH2Cl2 and measured in
Teflon cap sealed quartz Suprasil cuvette (1 cm path length) on a
Jasco V-550 spectrometer at 25 °C. Electrochemical studies were
carried out using an EG&G Princeton Applied Research Model 273A
potentiostat employing a gas tight three-electrode cell under an argon
atmosphere. A saturated calomel electrode (SCE) was used as
reference; a Pt disk (3.14 mm2) and a Pt wire were used as the
working and counter electrodes, respectively. The redox potentials
were measured in THF (∼1 mM) with n-Bu4N(BArF) (0.026 M) as
the supporting electrolyte and ferrocene (E1/2 = 0.56 V vs SCE) as an
external standard. Crystallographic details and data tables are provided
in the Supporting Information.
(s); 1309 (w); 1283 (s); 1276 (s); 1218 (m); 1175 (s); 1165 (s); 1132
(s); 1112 (s); 1106 (s); 1017 (w); 1004 (w); 964 (m); 903 (w); 903
(m); 846 (m); 809 (w); 785 (w); 723 (m); 713 (m); 682 (s). ESI-MS
(positive mode; m/z): 651.3 [M+ − Cl− + H+]. UV−visible (25 °C,
CH2Cl2; λ (nm) [ε (cm−1 L mol−1)]): 606 [3954], 410 [8209], 349
[26 790].
Synthesis of (η5-C5(CH3)5)Ru(Cl)(3,5-(CF3)2C6H3NC(CF3))2CH
(11). Method A. This procedure is identical with that employed
for 7, using the following quantities: 0.522 g of Li[(3,5-
(CF3)2C6H3NC(CF3))2CH] (6-Li; 0.820 mmol), in 30 mL of
CH2Cl2 with 0.250 g of [(η5-C5(CH3)5)RuCl2]2 (0.407 mmol) in
2.5 mL of CH2Cl2. Yield: 60% (0.357 g).
Method B. The β-diketiminato silver precursor [Ag(3,5-(CF3)2C6H3NC-
(CF3))2CH)(MeCN)2]2 (18) was prepared by adding (3,5-
(CF3)2C6H3NC(CF3))2CH2 (6-H; 0.394 g, 0.629 mmol) to Ag2O
(0.150 g, 0.647 mmol) in 40 mL of degassed wet acetonitrile. This
solution was heated using a microwave reactor at 400 MW for 1 h. The
resulting red solution was filtered under N2 through a 1 cm pad of
Celite and the solvent removed under vacuum. The obtained brown-
yellow powder was washed with n-pentane and dried under vacuum,
protected from light. The final yield was 89% (0.432 g). Spectroscopic
data of the complex [Ag(3,5-(CF3)2C6H3NC(CF3))2CH)(MeCN)2]2
(18) are identical with those reported in the literature.14a
A 0.255 g portion of [Ag(3,5-(CF3)2C6H3NC(CF3))2CH)-
(MeCN)2]2 (18) was dissolved in 50 mL of CH2Cl2, and this solution
was added dropwise to a solution of [(η 5-C5(CH3)5)RuCl2]2 (0.101 g,
0.163 mmol) in 10 mL of CH2Cl2 over a period of 20 min. The
reaction mixture was stirred for 16 h with exclusion of light, after which
a mixture of a dark green solution and white-gray precipitate was
obtained. The solution was filtered through a 1 cm pad of Celite and
the solvent removed using vacuum. The dark green solid was washed
with 125 mL of n-pentane and then 75 mL of Et2O. Further purification
involved dissolving the crude complex in a minimal amount of CH2Cl2
(5 mL) and reprecipitating using 50 mL of n-pentane. The resulting
solid was collected, washed with 3 × 10 mL of n-pentane, and dried
under vacuum to afford complex 11 in 68% yield (0.100 g).
Synthesis of (η5-C5(CH3)5)Ru(Cl)(2,6-(CH3)2C6H3NC(CH3))2CH
(7). Li[(2,6-(CH3)2C6H3NC(CH3))2CH] (2-Li; 0.254 g, 0.813
mmol) was dissolved in CH2Cl2 (5 mL). This solution was added
dropwise to [(η5-C5(CH3)5)RuCl2]2 (0.250 g, 0.410 mmol) dissolved
in CH2Cl2 (5 mL). This mixture was stirred for 8 h and then filtered
through Celite. The solvent volume was reduced under vacuum,
and 25 mL of n-pentane was added to precipitate a blue solid that was
filtered and washed with 3 × 10 mL of n-pentane. Further purification
involved dissolving the crude complex in 25 mL of Et2O and filtering
through Celite. The solvent was removed under reduced pressure, and
the resulting solid was dried under high vacuum for 24 h. Yield: 84%
(0.389 g). Single crystals suitable for structural analysis by X-ray
diffraction were grown by slow diffusion of n-pentane into a saturated
CH2Cl2 solution containing 7.
Anal. Found (calcd): C, 63.80 (64.51); H, 7.08 (6.99); N, 4.67
(4.85). FT-IR (25 °C, solid; ν (cm−1)): 3071 (w); 2921 (w); 1590
(w); 1537 (m); 1507 (w); 1416 (m); 1432 (m); 1371 (m); 1346 (s);
1278 (m); 1266 (m); 1209 (m); 1186 (m); 1161 (w); 1096 (w); 1073
(w); 1018 (m); 986 (w); 919 (w); 849 (m); 812 (m); 769 (s);
705 (w). ESI-MS (positive mode; m/z): 543.3 [M+ − Cl−]. UV−
visible (25 °C, CH2Cl2; λ (nm) [ε (cm−1 L mol−1)]): 646 [4428], 318
[20 328].
Method C. A solution of (3,5-(CF3)2C6H3NC(CF3))2CH2) (6-H;
0.250 g, 0.397 mmol) dissolved in 30 mL of THF was combined with
TlOEt (0.109 g, 0.436 mmol), causing an instantaneous color change
from yellow to deep orange. The reaction mixture was stirred for 2 h
with the exclusion of light. Afterward, the solvent was removed under
Synthesis of (η5-C5(CH3)5)Ru(Cl)(3,5-(CH3)2C6H3NC(CH3))2CH
(8). The procedure is identical with that employed for 7, using the
following quantities: 0.254 g of Li[(3,5-(CH3)2C6H3NC(CH3))2CH]
(3-Li; 0.813 mmol), with 0.250 g of [(η 5-C5(CH3)5)RuCl2]2 (0.407
mmol). Yield: 59% (0.275 g), light blue complex. Anal. Found
(calcd): C, 64.52 (64.51); H, 7.31 (6.99); N, 4.62 (4.85). FT-IR
(25 °C, solid; ν (cm−1)): 2898 (w); 1599 (w); 1587 (m); 1541 (m);
1511 (w); 1442 (w, br); 1369 (w); 1346 (s); 1308 (w); 1286 (w);
1276 (w); 1161 (w); 1149 (w); 1115 (w, br); 1072 (w); 1027 (m);
912 (w); 848 (m); 792 (m); 758 (w); 693 (m). ESI-MS (positive
mode; m/z): 543.3 [M+ − Cl−]. UV−visible (25 °C, CH2Cl2; λ (nm)
[ε (cm−1 L mol−1)]): 637 [5535], 318 [27 621].
1
vacuum, resulting in an orange solid. H, 13C, and 19F NMR data for
Tl(3,5-(CF3)2C6H3NC(CF3))2CH) (19) are given below.
2
1H NMR (30 °C, 399.8 MHz, C6D6; δ (ppm)): 0.94 (t, JHH = 7
2
Hz, 3H, CH3CH2OH), 3.35 (q, JHH = 7 Hz, 2H, CH3CH2OH), 5.89
(s, 1H, β-CH), 7.21 (s, 4H, Ar o-CH), 7.58 (s, 2H, Ar p-CH). 13C
NMR (30 °C, 100.5 MHz, C6D6; δ (ppm)): 19.2 (s, CH3CH2OH),
3
58.4 (s, CH3CH2OH), 90.9 (m, β-CH), 117.8 (sept, JCF = 3.8 Hz,
1
p-CH), 121.8 (q, JCF = 289.1 Hz, α-CF3), 122.9 (s, o-CCH3), 124.0
1
2
Synthesis of (η5-C5(CH3)5)Ru(Cl)(3,5-(CF3)2C6H3NC(CH3))2CH
(9). The procedure is identical with that employed for 7, using the
following quantities: 0.425 g of Li[(3,5-(CF3)2C6H3NC(CH3))2CH]
(4-Li; 0.805 mmol), with 0.250 g of [(η 5-C5(CH3)5)RuCl2]2
(0.407 mmol). Yield: 72% (0.582 g), light blue solid. Anal. Found
(calcd): C, 46.95 (46.61); H, 3.56 (3.57); N, 3.48 (3.53). FT-IR
(25 °C, solid); ν (cm−1)): 1543 (w); 1517 (w); 1465 (w); 1433 (w);
1373 (m); 1348 (m); 1277 (s); 1262 (w); 1196 (m); 1173 (m); 1127
(s); 1105 (m); 1069 (w); 1037 (w); 1019 (w); 983 (m); 931 (w);
921 (w); 899 (m); 885 (w); 847 (m); 805 (w); 718 (m); 705 (w);
682 (s). ESI-MS (positive mode; m/z): 759.4 [M+ − Cl− + H+]. UV−
visible (25 °C, CH2Cl2; λ (nm) [ε (cm−1 L mol−1)]): 636 [5067], 322
[28 512].
(q, JCF = 273.0 Hz, m-CF3), 133.4 (q, JCF = 33.3 Hz, Ar m-CCF3),
151.2 (s, Ar i-C), 151.4 (q, JCF = 25.9 Hz, α-CF3C). 19F NMR
1
(30 °C, 376.1 MHz, C6D6; δ (ppm)): −62.79 (s, 12F, m-CF3), −60.23
(s, 6F, α-CF3).
Complex 19 was dissolved in 30 mL of CH2Cl2 and added dropwise
to a solution of [(η5-C5(CH3)5)RuCl2]2 (0.122 g, 0.198 mmol) in
25 mL of CH2Cl2. The solution was stirred for 14 h with exclusion of
light. Afterward the reaction mixture was filtered through a 1 cm pad
of Celite and the solvent removed using vacuum. The residue was
washed with 125 mL of n-pentane and then 75 mL of Et2O. The
product was purified by dissolving the crude complex in a minimal
amount of CH2Cl2 (10 mL) and precipitated with 150 mL of
n-pentane. The resulting solid was collected on a frit, washed with 3 ×
10 mL of n-pentane, and dried under vacuum, to afford complex 11
(0.301 g) in 84% yield.
Single crystals suitable for structural analysis by X-ray diffraction
were grown by slow diffusion of n-pentane into a saturated CH2Cl2
solution of 11 kept at 4 °C.
Anal. Found (calcd): C, 42.07 (41.32); H, 2.82 (2.46); N, 3.01
(3.11). FT-IR (25 °C, solid; ν (cm−1)): 3004 (w); 2909 (w); 1605
(w); 1592 (w); 1559 (w); 1527 (w); 1483 (w); 1446 (w); 1417 (m);
Synthesis of (η5-C5(CH3)5)Ru(Cl)(3,5-(CH3)2C6H3NC(CF3))2CH
(10). The procedure is identical with that employed for 7, using the
following quantities: 0.176 g of Li[(3,5-(CH3)2C6H3NC(CF3))2CH]
(5-Li; 0.419 mmol), in 10 mL of CH2Cl2 with 0.250 g of [(η5-
C5(CH3)5)RuCl2]2 (0.407 mmol) in 12 mL of CH2Cl2. Yield: 58%
(0.287 g), pale green microcrystalline solid. Anal. Found (calcd): C,
54.54 (54.35); H, 5.35 (5.00); N, 3.89 (4.09). FT-IR (25 °C, solid; ν
(cm−1)): 1619 (w); 1567 (w); 1485 (w); 1471 (w); 1415 (w); 1366
6129
dx.doi.org/10.1021/om2006479|Organometallics 2011, 30, 6119−6132

Organometallics
Article
1382 (w); 1374 (w); 1352 (w); 1313 (m); 1293 (m, sh); 1278 (w);
1260 (w); 1208 (m); 1187 (s); 1156 (s); 1130 (s); 1108 (m); 1072
(w); 1026 (m); 999 (w); 972 (w); 955 (w); 863 (w); 853 (m); 796
(m); 766 (w); 715 (m); 704 (m); 699 (m). ESI-MS (positive mode;
m/z): 867.2 [M+ − Cl− + H+]. UV−visible (25 °C, CH2Cl2; λ (nm)
[ε (cm−1 L mol−1)]): 586 [3532], 420 [9552], 345 [24 675].
Synthesis of (η 5-C5(CH3)5)Ru(3,5-(CH3)2C6H3NC(CF3))2CH
(16). The procedure is identical with that employed for 13, except
the following quantities were used: 0.313 g of (η 5-C5(CH3)5RuCl(3,5-
(CH3)2C6H3NC(CF3))2CH) (10; 0.457 mmol), in 20 mL of THF
with 0.172 g of Zn (2.63 mmol). The reaction mixture was stirred for
14 h. Yield: 84% (0.297 g), red solid. Single crystals suitable for
structural analysis by X-ray diffraction were grown by slow evaporation
of saturated benzene solution containing 16. 1H NMR (25 °C, 400 MHz,
C6D6; δ (ppm)): 0.973 (s, 15H, η5-C5(CH3)5); 2.340 (s, 12H, Ar m-
CH3); 6.819 (s, 2H, Ar p-CH); 7.080 (s, 1H, β-CH); 7.143 (s, 4H, Ar o-
CH). 13C NMR (25 °C, 101 MHz, C6D6; δ (ppm)): 9.25 (s, η5-
C5(CH3)5); 20.95 (s, Ar m-CH3); 83.42 (s, η5-C5(CH3)5); 90.24 (s, β-
CH); 123.05 (q, 1JCF = 295 Hz, α-CCF3); 123.88 (s, Ar o-CH); 126.74 (s,
Synthesis of (η 5-C5(CH3)5Ru(2,6-(CH3)2C6H3NC(CH3))2CH
(13). (η 5-C5(CH3)5RuCl(2,6-(CH3)2C6H3NC(CH3))2CH) (7;
0.327 g, 0.567 mmol) was dissolved in THF (10 mL). To this solution
was added activated zinc filings (0.108 g, 1.65 mmol, approximately 3
mol excess) directly to the flask, and the mixture was stirred for 14 h.
Gradually the solution changed from dark blue to dark red. Afterward,
the solvent was removed using vacuum and the residue was extracted
with 40 mL of n-pentane and passed through Celite. The solvent was
removed using vacuum, affording a magenta solid, which was dried
2
Ar p-CH); 136.34 (s, Ar m-CCH3); 145.78 (q, JCF = 25 Hz, α-CCF3);
155.81 (s, Ar i-C). 19F NMR (25 °C, 181 MHz, C6D6; δ (ppm)): −55.97
1
1
under vacuum for 10 h. Yield: 89.3% (0.274 g). H NMR (25 °C, 400
(s, JFC = 295 Hz, α-CCF3). FT-IR (25 °C, Nujol mull, KBr disks; ν
MHz, C6D6; δ (ppm)): 0.938 (s, 15H, η5-C5(CH3)5), 1.734 (s, 6H, α-
(cm−1)): 1626 (w); 1605 (w); 1592 (m); 1565 (m); 1430 (s); 1309 (s);
1289 (m); 1272 (m), 1201 (s); 1167 (s); 1148 (s); 1136 (s); 1105 (m);
1074 (w); 1026 (m); 859 (w); 849 (m); 813 (m); 809 (w); 713 (m); 559
CH3), 2.187 (s, 12H, Ar o-CH3), 5.455 (s, 1H, β-CH), 7.066 (t, 3JHH
7.32 Hz, 2H, Ar p-CH), 7.212 (t, 3JHH = 7.32 Hz, 4H, Ar m-CH). 13
=
C
NMR (25 °C, 101 MHz, C6D6; δ (ppm)): 9.982 (s, η5-C5(CH3)5),
19.78 (s, α-CH3), 23.93 (s, Ar o-CH3), 77.16 (s, η5-C5(CH3)5), 98.86
(s, β-CH), 124.39 (s, Ar p-CH), 132.14 (s, Ar m-CH), 131.58 (s, Ar o-
C), 157.53 (s, α-CCH3), 157.854 (s, Ar i-C). FT-IR (25 °C, Nujol
mull, KBr disks; ν (cm−1)): 1546 (s); 1509 (m); 1283 (w); 1263 (m);
1239 (w); 1214 (w); 1191 (m); 1160 (m); 1089 (w); 1072 (w); 1029
(m); 1018 (m); 984 (w); 846 (w); 786 (w); 763 (s); 722 (w); 709
(w). UV−visible (25 °C, n-pentane; λ (nm) [ε (cm−1 L mol−1)]): 306
[40 26].
(w); 474 (w). UV−visible (25 °C, n-pentane; λ (nm) [ε (cm−1
L
mol−1)]): 447 [7669], 317 [33 984].
Synthesis of (η 5-C5(CH3)5)Ru(3,5-(CF3)2C6H3NC(CF3))2CH
(17). The procedure is identical with that employed for complex
13, except the following quantities were used: 0.295 g of (η 5-
(C5(CH3)5)RuCl(3,5-(CF3)2C6H3NC(CF3))2CH) (11; 0.327 mmol),
in 15 mL of THF with 0.152 g of Zn (2.32 mmol). Yield: 91.3% (0.259
g), red solid. Single crystals suitable for X-ray diffraction were grown
1
by slow evaporation of a saturated benzene solution of 17. H NMR
Synthesis of (η 5-C5(CH3)5)Ru(3,5-(CH3)2C6H3NC(CH3))2CH
(14). The procedure is identical with that employed for 13, except
the following quantities were used: 0.278 g of (η 5-C5(CH3)5RuCl(3,5-
(CH3)2C6H3NC(CH3))2CH) (8; 0.482 mmol), in 15 mL of THF
with 0.182 g of Zn (2.78 mmol). Yield: 87% (0.226 g), magenta solid.
Single crystals suitable for structural analysis by X-ray diffraction were
grown by slow evaporation of a saturated n-pentane solution
(25 °C, 400 MHz, C6D6); δ (ppm)): 0.476 (s, 15H, η5-C5(CH3)5);
6.714 (s, 1H, β-CH); 7.681 (s, 2H, Ar p-CH); 7.684 (s, 4H, Ar o-CH).
13C NMR (25 °C, 101 MHz, C6D6; δ (ppm)): 8.81 (s, η5-C5(CH3)5);
84.39 (s, η5-C5(CH3)5); 91.33 (s, β-CH); 119.00 (s, Ar p-CH); 122.27
1
1
(q, JCF = 271 Hz, α-CCF3); 123.74 (q, JCF = 324 Hz, Ar m-CCF3);
126.00 (s, Ar o-CH); 130.91 (q, 2JCF = 33 Hz, Ar m-CCF3); 146.27 (q,
2JCF = 25 Hz, α-CCF3); 155.65 (s, Ar i-C). 19F NMR (25 °C, 181
1
containing 14. H NMR (25 °C, 400 MHz, C6D6; δ (ppm)): 1.243
1
(s, 15H, η5-C5(CH3)5); 2.136 (s, 6H, α-CH3); 2.377 (s, 12H, Ar
m-CH3); 5.553 (s, 1H, β-CH); 6.844 (s, 2H, Ar p-CH); 7.030 (s, 4H,
Ar o-CH). 13C NMR (25 °C, 101 MHz, C6D6; δ (ppm)): 10.03 (s,
η5-C5(CH3)5); 21.23 (s, Ar m-CH3); 24.91 (s, α-CH3), 77.74 (s,
η5-C5(CH3)5); 98.13 (s, β-CH); 123.71 (s, Ar o-CH), 125.22 (s, Ar
p-CH); 137.42 (s, Ar m-CCH3); 157.36 (s, α-CCH3); 159.66 (s, Ar
i-C). FT-IR (25 °C, Nujol mull, KBr disks; ν (cm−1)): 1604 (m); 1589
(m); 1541 (s); 1507 (m); 1457 (s); 1366 (s); 1307 (m); 1278 (m);
1161 (w); 1146 (m); 1070 (w); 1028(m br.); 998 (w); 947 (w); 901
(w); 880 (w); 845 (m); 851 (m); 767 (w); 759 (w); 692 (m); 600
(w); 589 (w); 571 (w); 546 (w). UV−visible (25 °C, n-pentane; λ
(nm) [ε (cm−1 L mol−1)]): 308 [50 199].
MHz, C6D6; δ (ppm)): −56.59 (s, JFC = 271 Hz, α-CF3); −63.05 (s,
1JFC = 324 Hz, Ar m-CF3). FT-IR (25 °C, Nujol mull, KBr disks; ν
(cm−1)): 1634 (w); 1620 (w); 1611 (w); 1567 (m); 1424 (m); 1308
(s); 1278 (s); 1247 (s); 1221 (s); 1127 (s); 1023 (m); 1003 (w); 984
(w); 966 (s); 918 (w); 918 (w); 901 (m); 897 (m); 891 (m); 847
(m); 817 (m); 804 (w); 722 (s); 710 (s); 683 (s); 582 (w); 539 (w);
476 (w). UV−visible (25 °C, n-pentane; λ (nm) [ε (cm−1 L mol−1)]):
448 [8481], 318 [36 035].
General Procedures for the Catalytic ATRA and ATRC
Reactions. An aliquot of a stock solution containing the appropriate
catalyst 7−11 in toluene-d8 was added to a 1.5 mL vial containing Mg
powder (100 mg). This mixture was stirred for 10 min. A stock
solution of substrate was prepared in the following manner: D2O
(20 μL) was added to a freshly prepared toluene-d8 solution
containing the substrate (CCl4, TsCl, A or B), styrene (only for
ATRA reactions), and an internal standard, 1,4-bis(trifluoromethyl)-
benzene. This mixture was shaken for 1 min to saturate the solu-
tion with D2O. An aliquot of this stock solution was added to the
reaction vial, and the total volume was completed to 1000 μL with
toluene-d8. After the mixture was stirred for 24 h at 25 °C, a sample
(ATRA, 20 μL; ARTC, 40 μL) was removed from the reaction
Synthesis of (η 5-C5(CH3)5)Ru(3,5-(CF3)2C6H3NC(CH3))2CH
(15). The procedure is identical with that employed for 13, except
the following quantities were used: 0.360 g of (η 5-C5(CH3)5RuCl(3,5-
(CF3)2C6H3NC(CH3))2CH) (9; 0.454 mmol), in 35 mL of THF with
0.125 g of Zn (1.91 mmol). Yield: 92% (0.317 g), magenta solid.
Single crystals suitable for structural analysis by X-ray diffraction were
grown by slow evaporation of a saturated benzene solution containing
1
13. H NMR (25 °C, 400 MHz, C6D6; δ (ppm)): 0.864 (s, 15H, η5-
C5(CH3)5); 1.632 (s, α-CH3); 5.294 (s, 1H, α-CH); 7.651 (s, 4H, Ar
o-CH); 7.806 (s, 2H, Ar p-CH). 13C NMR (25 °C, 101 MHz, C6D6; δ
(ppm)): 9.67 (s, η5-C5(CH3)5); 25.20 (s, Ar o-CH3); 78.15 (s, η5-
1
mixture, diluted with CDCl3 (500 μL), and analyzed by H NMR
spectroscopy. Table 10 details the concentration of each reagent in the
reactions.
3
C5(CH3)5); 99.28 (s, β-CH); 117.35 (q, JCF = 3.9 Hz, Ar p-CH);
123.87 (q, 1JCF = 272 Hz, Ar m-CCF3); 125.55 (q, 3JCF = 2.7 Hz, Ar o-
CH); 131.87 (q, 2JCF = 35 Hz, m-CCF3); 157.97 (s, α-CCH3); 159.58
(s, Ar i-C). 19F NMR (25 °C, 181 MHz, C6D6; δ (ppm)): −62.91 (s,
1JFC = 272 Hz, Ar m-CF3). FT-IR (25 °C, Nujol mull, KBr disks; ν
(cm−1)): 1618 (w); 1605 (w); 1547 (m); 1512 (m); 1436 (m); 1431
(m); 1276 (s); 1220 (w); 1169 (s); 1126 (s); 1104 (m); 1092 (w);
1059 (m); 1023 (m); 1003 (w); 983 (m); 917 (m); 891 (s); 872 (w);
847 (m); 783 (w); 767 (w); 760 (w); 718 (m); 704 (m); 683 (s).
UV−visible (25 °C, n-pentane; λ (nm) [ε (cm−1 L mol−1)]): 387
[6300], 314 [53 019].
Table 10. Concentration of the Components Used in the
ATRA and ATRC Reactions
reaction
type
[cat.]
(mM)
[substrate]
(M)
[styrene] [internal std]
substrate
(M)
(mM)
ATRA
ATRA
ATRC
CCl4
4.6
4.4
5.0
5.52
0.52
0.10
1.38
0.44
n/a
270
90
TsCl
A or B
50
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dx.doi.org/10.1021/om2006479|Organometallics 2011, 30, 6119−6132

Organometallics
Article
W. J.; Qian, B. X.; Baek, S. W.; Smith, M. R.; Motry, D. H. Inorg. Chem.
1999, 38, 5964−5977.
ASSOCIATED CONTENT
* Supporting Information
■
S
(12) Tomson, N. C.; Yan, A.; Arnold, J.; Bergman, R. G. J. Am. Chem.
Soc. 2008, 130, 11262−11263.
Computational analysis describing electronic molecular orbital
structure and simulation of UV−visible spectra with band
assignment for complexes 7, 11, 13, and 17. A detailed
discussion regarding the solid-state packing. Experimental
details for the crystallographic analysis of complexes 7−17.
The accompanying CIF contains additional crystallographic
data. This material is available free of charge via the Internet at
http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: paul.dyson@epfl.ch.
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ACKNOWLEDGMENTS
■
This research was supported by grants from the European
Commission Marie Curie Action (ADP, MEIF-CT-2005-
025287, CARCAS), the Swiss National Science Foundation,
the Ecole Polytechnique Federale de Lausanne, and University
́ ́
College Dublin. A.D.P. thanks the Science Foundation Ireland
(SFI) for a Stokes Lectureship at UCD.
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