Ruthenium(II) Arene complexes with asymmetrical guanidinate ligands: Synthesis, characterization, and application in the base-free catalytic isomerization of allylic alcohols

Article abstract of DOI:10.1021/om3009124

The ruthenium(II) arene dimer [{RuCl(μ-Cl)(η⁶-p-cymene)} ₂] readily reacted with 4 equiv of guanidines (ⁱPrHN) ₂C=NR (R = ⁱPr (1a), 4-C₆H₄ ^tBu (1b), 4-C₆H₄Br (1c), 2,4,6-C ₆H₂Me₃ (1d), 2,6-C₆H ₃ⁱPr₂ (1e)) in toluene at room temperature to generate the mononuclear complexes [RuCl{κ²N,N'-C(NR)(N ⁱPr)NHⁱPr}(η⁶-p-cymene)] (2a-e) and the easily separable guanidinium chloride salts [(ⁱPrHN) ₂C(NHR)][Cl] (3a-e). Compounds 2a-e and 3a-e were fully characterized by elemental analysis and IR and NMR spectroscopy. The structures of [RuCl{κ²N,N'-C(NⁱPr)₂NH ⁱPr}(η⁶-p-cymene)] (2a) and [RuCl{κ ²N,N'-C(N-4-C₆H₄^tBu)(N ⁱPr)NHⁱPr}(η⁶-p-cymene)] (2b) were also determined by X-ray diffraction analysis. Regardless of the steric requirements of the aromatic substituents, a nonsymmetric coordination of the guanidinate anions in 2b-e was observed, in complete accord with theoretical calculations (DFT) on the corresponding [RuCl{κ²N,N'-C(NR)(N ⁱPr)-NHⁱPr}(η⁶-p-cymene)] and [RuCl{κ²N,N'-C(NⁱPr)₂NHR} (η⁶-p-cymene)] models. Remarkably, complexes 2a-e were active catalysts for the redox isomerization of allylic alcohols in the absence of base, which represents the first catalytic application known for ruthenium guanidinate species.

Full text of DOI:10.1021/om3009124

Article
pubs.acs.org/Organometallics
Ruthenium(II) Arene Complexes with Asymmetrical Guanidinate
Ligands: Synthesis, Characterization, and Application in the Base-
Free Catalytic Isomerization of Allylic Alcohols
†
†
†
,†
,†
́
́
́
Rocío Garcıa-Alvarez, Francisco J. Suarez, Josefina Dıez, Pascale Crochet,* Victorio Cadierno,*
́
Antonio Antinolo,*,‡ Rafael Fernandez-Galan,‡ and Fernando Carrillo-Hermosilla‡
́
́
̃
†Laboratorio de Compuestos Organometal
ica, Instituto Universitario de Quımica Organometal
Clavería 8, E-33006 Oviedo, Spain
́
icos y Catal
́
isis (Unidad Asociada al CSIC), Departamento de Quımica Organ
́
ica e
́
́
́
Inorgan
́
́
ica “Enrique Moles”, Facultad de Quımica, Universidad de Oviedo, Julian
́
‡
́
́
́
Departamento de Quımica Inorganica, Organica y Bioquımica, Facultad de Ciencias Quımicas, Campus de Ciudad Real, Universidad
́
́
de Castilla-La Mancha, Campus Universitario, E-13071 Ciudad Real, Spain
S
* Supporting Information
ABSTRACT: The ruthenium(II) arene dimer [{RuCl(μ-
Cl)(η6-p-cymene)}2] readily reacted with 4 equiv of
i
t
guanidines (iPrHN)2CNR (R = Pr (1a), 4-C6H4 Bu (1b),
i
4-C6H4Br (1c), 2,4,6-C6H2Me3 (1d), 2,6-C6H3 Pr2 (1e)) in
toluene at room temperature to generate the mononuclear
complexes [RuCl{κ2N,N′-C(NR)(NiPr)NHiPr}(η6-p-cym-
ene)] (2a−e) and the easily separable guanidinium chloride
salts [(iPrHN)2C(NHR)][Cl] (3a−e). Compounds 2a−e and
3a−e were fully characterized by elemental analysis and IR and
NMR spectroscopy. The structures of [RuCl{κ2N,N′-C-
(NiPr)2NHiPr}(η6-p-cymene)] (2a) and [RuCl{κ2N,N′-C(N-
4-C6H4 Bu)(NiPr)NHiPr}(η6-p-cymene)] (2b) were also determined by X-ray diffraction analysis. Regardless of the steric
t
requirements of the aromatic substituents, a nonsymmetric coordination of the guanidinate anions in 2b−e was observed, in
complete accord with theoretical calculations (DFT) on the corresponding [RuCl{κ2N,N′-C(NR)(NiPr)-NHiPr}(η6-p-cymene)]
and [RuCl{κ2N,N′-C(NiPr)2NHR}(η6-p-cymene)] models. Remarkably, complexes 2a−e were active catalysts for the redox
isomerization of allylic alcohols in the absence of base, which represents the first catalytic application known for ruthenium
guanidinate species.
(NPh)2NHPh}3]7 and (ii) the half-sandwich ruthenium(II)
INTRODUCTION
■
arene complex [RuCl{κ2N,N′-C(NPh)2NHPh}(η6-p-cym-
ene)].8,9 Very recently, with our work already in progress, a
family of related chloride and azide (η6-p-cymene)RuII
derivatives bearing N,N′,N″-triarylguanidinates has been de-
scribed by Thirupathi and co-workers, along with a thorough
structural characterization in both solution and the solid state,
and reactivity studies of the azido complexes with activated
alkynes ([3 + 2] cycloaddition reactions).10 As in the preceding
cases, guanidinate monoanions generated from guanidines with
the symmetric substitution pattern (ArHN)2CNAr were
employed by Thirupathi. It is also worthy of note that, despite
the burgeoning role of ruthenium in catalytic organic synthesis,11
none of the ruthenium guanidinate complexes reported so far
have been explored in homogeneous catalysis. This fact contrasts
with the chemistry of related ruthenium amidinate systems,
which have found application in different catalytic trans-
formations.12
Guanidinate monoanions of the general formula [(RN)2CNR2]−
are closely related to the well-known amidinates, differing only in
that they contain an amino (R2N) substituent on the ligand’s
central carbon which results in a higher steric and electronic
tunability. Since the preparation of the first transition-metal
guanidinate complex by Lappert and co-workers in 1970,1 a huge
number of coordination complexes involving metals from across
the periodic table have been described.2,3 In these, the
guanidinate anions have exhibited many coordination modes,
but by far the two most common are when they act as delocalized
N,N′-chelating or bridging ligands (Figure 1).
Remarkably, despite the great variety of transition-metal
guanidinates reported to date in the literature, ruthenium
derivatives remain surprisingly rare. Thus, in addition to a series
of diruthenium complexes bridged by the N,N′,N″-triphenylgua-
nidinate monoanion described by Berry and co-workers,4 at the
beginning of our work in the field, only the following
mononuclear derivatives were known: (i) the octahedral species
[Ru{κ2N,N′-C(NPh)2NHPh}2(CO)(PPh3)],5 [RuH{κ2N,N′-
C(NPh)2NHPh}(CO)(PPh3)2],6 and [Ru{κ2N,N′-C-
Received: September 26, 2012
Published: November 5, 2012
© 2012 American Chemical Society
8301
dx.doi.org/10.1021/om3009124 | Organometallics 2012, 31, 8301−8311

Organometallics
Article
Figure 1. Guanidinate monoanions and their most common coordination modes.
Figure 2. Structure of the ruthenium(II) arene complexes synthesized in this work.
Scheme 1. Synthesis of the Mononuclear Ru(II) Complexes [RuCl{κ2N,N′-C(NR)(NiPr)NHiPr}(η6-p-cymene)] (2a−e)
To bridge this gap, herein we describe the preparation of the
novel ruthenium(II) arene complexes 2a−e (Figure 2),
generated from the reactions of the readily available guanidines
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Complexes [RuCl-
{κ2N,N′-C(NR)(NiPr)NHiPr}(η6-p-cymene)] (2a−e). The
i
t
(iPrHN)2CNR (R = Pr (1a), 4-C6H4 Bu (1b), 4-C6H4Br
novel ruthenium-guanidinate complexes [RuCl{κ2N,N′-C(NR)-
(1c), 2,4,6-C6H2Me3 (1d), 2,6-C6H3 Pr2 (1e))13 with the
i
(NiPr)-NHiPr}(η6-p-cymene)] (R = Pr (2a), 4-C6H4 Bu (2b),
i
t
dimeric precursor [{RuCl(μ-Cl)(η6-p-cymene)}2],14 and their
application in the catalytic isomerization of allylic alcohols to
carbonyl compounds.15 The present paper brings novelty since
(i) compounds 2b−e represent the first examples of ruthenium
complexes containing asymmetrical monoanionic guanidinate
ligands and (ii) unlike the majority of ruthenium catalysts
previously described for redox isomerizations of allylic alcohols,
complexes 2a−e operate without the assistance of base.15
i
4-C6H4Br (2c), 2,4,6-C6H2Me3 (2d), 2,6-C6H3 Pr2 (2e)) were
synthesized by following the same procedure reported by Bailey
and Thirupathi for the preparation of related symmetrical
[RuCl{κ2N,N′-C(NAr)2NHAr}(η6-p-cymene)] species.8,10
Thus, as shown in Scheme 1, treatment of [{RuCl(μ-Cl)(η6-p-
cymene)}2] with 4 equiv of guanidines (iPrHN)2CNR (1a−
e), in toluene at room temperature, led to the precipitation of the
corresponding guanidinium chloride salts [(iPrHN)2C(NHR)]-
8302
dx.doi.org/10.1021/om3009124 | Organometallics 2012, 31, 8301−8311

Organometallics
Article
Figure 3. ORTEP-type views of the structures of the ruthenium complexes 2a (left) and 2b (right) with the crystallographic labeling schemes. Hydrogen
atoms, except that on N(2), have been omitted for clarity in both structures. Thermal ellipsoids are drawn at the 10% probability level.
[Cl] (3a−e) and the clean formation of the mononuclear
complexes 2a−e, which were crystallized from the solution by
concentration, filtration of 3a−e, and cooling. Both complexes
2a−e and the guanidinium salts 3a−e were isolated as air-stable
solids in high yields (75−86% and 71−81%, respectively) and
characterized by elemental analysis and IR and NMR (1H and
13C{1H}) spectroscopy (details are given in the Experimental
Section). The asymmetric coordination of the guanidinate
anions in complexes 2b−e was clearly reflected in their 1H and
13C{1H} NMR spectra by the appearance of four well-
differentiated signals for the aromatic CH protons and carbons
of the η6-coordinated cymene ring, a typical situation in (η6-p-
cymene)ruthenium(II) complexes where the metal is a stereo-
genic center.16 In the case of the symmetric complex 2a, these
CH units are two-by-two equivalent, leading only to two signals
in the spectra. The expected resonances for the guanidinate
ligands were also observed in the 1H and 13C{1H} NMR spectra
of 2a−e, with a downfield singlet for the central CN3 carbon at δC
160.8−165.4 ppm being their most characteristic hallmark (for
the guanidinium salts 3a−e this carbon resonates at slightly
higher fields (δC 153.6−156.1 ppm)). It is also worthy of note
that for complexes 2d,e, containing the bulky aryl substituents
mesityl and 2,6-diisopropylphenyl, restricted rotation around the
N−Ar bond takes place in solution, as clearly evidenced in their
1H and 13C{1H} NMR spectra by the chemical inequivalence of
Table 1. Selected Bond Distances (Å) and Bond Angles (deg)
for 2a,b
a
2a
2b
Bond Distances
Ru−C*
Ru−Cl(1)
Ru−N(1)
Ru−N(3)
C(11)−N(1)
C(11)−N(2)
C(11)−N(3)
N(1)−C(12)
N(2)−C(15)
N(3)−C(18)
1.66433(17)
1.6655(2)
2.4147(9)
2.108(3)
2.085(3)
1.319(4)
1.375(4)
1.338(4)
1.469(4)
1.477(4)
1.396(4)
2.4284(6)
2.1196(19)
2.076(2)
1.340(3)
1.385(3)
1.322(3)
1.458(3)
1.454(3)
1.460(3)
Bond Angles
C*−Ru−Cl(1)
C*−Ru−N(1)
C*−Ru−N(3)
126.800(17)
134.97(5)
136.83(6)
87.86(6)
85.66(6)
62.19(8)
92.41(14)
135.56(16)
94.87(15)
138.85(17)
109.0(2)
124.4(2)
126.5(2)
123.4(2)
121.8(2)
125.6(2)
129.42(2)
135.12(8)
135.68(8)
85.33(8)
84.92(9)
62.3(1)
Cl(1)−Ru−N(1)
Cl(1)−Ru−N(3)
N(1)−Ru−N(3)
Ru−N(1)−C(11)
Ru−N(1)−C(12)
Ru−N(3)−C(11)
Ru−N(3)−C(18)
N(1)−C(11)−N(3)
N(1)−C(11)−N(2)
N(2)−C(11)−N(3)
C(11)−N(1)−C(12)
C(11)−N(2)−C(15)
C(11)−N(3)−C(18)
93.7(2)
136.4(2)
94.2(2)
132.0(2)
109.3(3)
125.0(3)
125.7(3)
122.3(3)
121.4(3)
129.7(3)
i
the Me and Pr groups located in the ortho positions of the
aromatic rings. This fact clearly reflects the high steric hindrance
between these aryl groups and the p-cymene ligand.
The structures of the symmetrical complex [RuCl{κ2N,N′-
C(NiPr)2NHiPr}(η6-p-cymene)] (2a) and the unsymmetrical
complex [RuCl{κ2N,N′-C(N-4-C6H4 Bu)(NiPr)NHiPr}(η6-p-
t
a
cymene)] (2b) were fully confirmed by means of X-ray
diffraction methods. Single crystals suitable for X-ray analysis
were obtained by slow diffusion of n-pentane into saturated
solutions of these compounds in diethyl ether. ORTEP views of
the molecules are shown in Figure 3, and selected structural
parameters are collected in Table 1.
C* denotes the centroid of the p-cymene ring (C(1), C(2), C(3),
C(4), C(5), and C(6)).
comparable to those previously found in the crystal structures
of [RuCl{κ2N,N′-C(NAr)2-NHAr}(η6-p-cymene)] (Ar = Ph,8 4-
10
C6H4Me,10 2-C6H4Me,10 2-C6H4OMe,10 2,4-C6H3Me2
)
A typical three-legged piano-stool geometry, with the
ruthenium atom surrounded by the η6-bonded p-cymene ligand,
a terminal chloride, and the corresponding chelating guanidinate
anion, is observed in both cases. The Ru−N(1) and Ru−N(3)
bond lengths, in the range 2.076(2)−2.1196(19) Å, are
(2.086(3)−2.149(3) Å). As observed for these complexes, the
CN3 cores of the guanidinate skeletons in 2a,b are perfectly
planar, as indicated by the sum of angles around the central
C(11) carbons of 359.9° (2a) and 360° (2b). Concerning the
bonding of the guanidinate anions to ruthenium, it is best
8303
dx.doi.org/10.1021/om3009124 | Organometallics 2012, 31, 8301−8311

Organometallics
Article
Figure 4. Resonance forms of the guanidinate ligands in complexes 2a−e.
i
described through the diazaallyl resonance form A (Figure 4).
The C−N bond distances between the metal-coordinated
nitrogen atoms N(1) and N(3) and the central carbon C(11)
of the ligand, very similar in both structures (1.319(4)-1.340(3)
Å) and significantly shorter than that of the C(11)−N(2) bond
(1.385(3) Å (2a) and 1.375(4) Å (2b)), are in complete accord
with the higher contribution of the delocalized form A over the
alternative resonance forms B−D to the bonding.
in comparison to the Pr group, which leads to a less compact
crystal packing.
As noted above, restricted rotation of the N−aryl bond in
complexes 2d,e was observed by NMR spectroscopy as a result of
the steric crowding in the metal environment. Despite this,
guanidinate rearrangement from the asymmetrical (complexes
2b−e) to the less congested symmetrical coordination
(complexes 2′b−e), via a formal 1,3-hydrogen shift, was not
observed in solution (Scheme 2).19 In order to account for the
preferred asymmetric coordination of the guanidinate anions, the
relative stability of complexes 2b−e vs 2′b−e was studied by
means of DFT calculations at the B3LYP/6-31G(d)+LANL2DZ
level of theory. For comparative purposes, the free anions 4b−e
and 4′b−e were also investigated (Figure 6).
The optimized structures of 2b−e, 2′b−e, 4b−e, and 4′b−e,
and their most relevant geometrical parameters, are given in the
Supporting Information.20 All of them were characterized as
minima on the potential energy surface, and their absolute and
relative energies are given in Table 2. According to our
calculations, the unsymmetrical complexes 2b−e are more stable
than the symmetrical complexes 2′b−e by 3.1−5.9 kcal/mol.
The smallest energy difference was observed for the 2e/2′e
couple, in which the most sterically demanding 2,6-diisopropyl-
phenyl group is present (3.1 kcal/mol). Concerning the free
guanidinate anions 4b−e and 4′b−e, the former was much more
stable than the latter, with energy differences ranging from 10.3
to 14.9 kcal/mol. In contrast to what is observed in the
complexes, the presence of the bulkiest 2,6-diisopropylphenyl
group results now in a marked preference for the nonsymmetric
structure 4e. All these theoretical predictions, which are in
complete accord with the experimental results, suggest that
electronic factors prevail over the steric factors to rationalize the
observed structures. The stabilization associated with the
electronic conjugation of the delocalized π electrons of the N−
C−N linkages with the aromatic rings may be evoked to explain
the higher thermodynamic stability of 2b−e vs 2′b−e and 4b−e
vs 4′b−e.
It is also worthy of note that the crystal packings of the two
molecules are different. Thus, while in the case of [RuCl{κ2N,N′-
C(N-4-C6H4 Bu)(NiPr)NHiPr}(η6-p-cymene)] (2b) no inter-
t
molecular interactions were found in the crystal lattice, the
N(2)−H unit of [RuCl{κ2N,N′-C(NiPr)2NHiPr}(η6-p-cym-
ene)] (2a) is involved in a hydrogen bond with the chloride
ligand of a neighboring molecule, thus leading to the formation of
dimeric aggregates in the solid state (see Figure 5).17 According
Catalytic Isomerization of Allylic Alcohols. The redox
isomerization of allylic alcohols represents an efficient, selective,
and atom-economical approach for the preparation of saturated
carbonyl compounds. The process involves the one-pot
migration of the CC bond of the allylic alcohol and subsequent
tautomerization of the resulting enol (Scheme 3). This catalytic
transformation has been extensively studied in academic
laboratories during the last two decades, as it conveniently
replaces the classical routes involving two-step sequential
oxidation and reduction reactions,15 and has found utility in
the pharmaceutical industry for the transformation of the
naturally occurring opiates morphine and codeine into the
more commonly prescribed narcotic analgesics hydromorphone
and hydrocodone.21
Figure 5. Hydrogen-bonding scheme for complex 2a. Hydrogen atoms,
except that on N(2), have been omitted for clarity. Distances (Å) and
angle (deg) for the intermolecular N(2)-H···Cl(1) hydrogen bond are
as follows: N(2)−H = 0.81; H−Cl(1) = 2.58; N(2)−Cl(1) = 3.354;
N(2)−H−Cl(1) = 161.64.
to the classification of Jeffrey,18 the distance and angle of the N−
H···Cl contact of 2.58 Å and 161.64°, respectively, allow it to be
classified as “weak” among the H bonds considered most
common in chemical systems. The absence of this weak
intermolecular interaction in the structure of 2b is probably
t
associated with the higher steric demand of the 4-C6H4 Bu group
8304
dx.doi.org/10.1021/om3009124 | Organometallics 2012, 31, 8301−8311

Organometallics
Article
Scheme 2. Potential Isomerization of the Unsymmetrical Complexes 2b−e into the Symmetrical Complexes 2′b−e
Figure 6. Structure of the guanidinate anions 4b−e and 4′b−e.
rhodium, and iridium complexes,15 with the first group being
particularly attractive due to their lower cost. In this context, a
huge number of ruthenium-based catalytic systems for this
relevant transformation have been described in recent years.22
Worthy of note, fast conversions are usually achieved in the
presence of a base, since deprotonation of the hydroxyl group of
the allylic alcohol is needed to enhance its coordinating ability.23
In marked contrast to this common trend, we have found that the
ruthenium guanidinate complexes [RuCl{κ2N,N′-C(NR)-
Table 2. Calculated Total (hartree) and Relative (kcal/mol)
Energies for Ruthenium Complexes 2b−e and 2′b−e and
a
Guanidinate Anions 4b−e and 4′b−e
2b
−1 772.588 602 12 (0.0)
−1 772.579 963 55 (5.4)
−4 186.140 932 31 (0.0)
−4 186.131 577 88 (5.9)
−1 733.281 334 09 (0.0)
−1 733.272 761 79 (5.4)
−1 851.206 685 05 (0.0)
−1 851.201 805 35 (3.1)
4b
−828.939 055 043 (0.0)
−828.922 596 635 (10.3)
−3 242.500 517 74 (0.0)
−3 242.480 911 75 (12.3)
−789.633 654 411 (0.0)
−789.614 214 617 (12.2)
−907.565 605 016 (0.0)
−907.541 868 079 (14.9)
2′b
2c
4′b
4c
2′c
2d
2′d
2e
4′c
4d
4′d
4e
i
t
(NiPr)NHiPr}(η6-p-cymene)] (R = Pr (2a), 4-C6H4 Bu (2b),
i
4-C6H4Br (2c), 2,4,6-C6H2Me3 (2d), 2,6-C6H3 Pr2 (2e)) are able
2′e
4′e
to promote the redox isomerization of allylic alcohols under base-
free conditions. In this sense, all of them were able to convert
selectively and almost quantitatively 1-octen-3-ol into octan-3-
one, in remarkably short times (10−15 min), with the catalytic
reactions being performed in THF (0.2 M solutions of the allylic
a
B3LYP/6-31G(d)+LANL2DZ-optimized geometries.
The most effective catalysts presently available for the redox
isomerization of allylic alcohols are based on ruthenium,
Scheme 3. Catalytic Redox Isomerization of Allylic Alcohols
8305
dx.doi.org/10.1021/om3009124 | Organometallics 2012, 31, 8301−8311

Organometallics
Article
Table 3. Catalytic Isomerization of 1-Octen-3-ol into Octan-3-one using [RuCl{κ2N,N′-C(NR)(NiPr)NHiPr}(η6-p-cymene)]
a
(2a−e) as Catalysts
b
entry
cat.
amt of Ru, mol %
solvent
temp, °C
time
yield, %
1
2a
2b
2c
2d
2e
2c
2c
2c
2c
2c
2c
2c
2c
1
THF
THF
THF
THF
THF
THF
THF
80
80
80
80
80
80
80
80
80
80
80
50
15 min
15 min
10 min
10 min
10 min
20 min
1 h
>99
>99
>99
>99
>99
>99
>99
99
2
1
3
1
4
1
5
1
6
0.5
0.1
1
7
8
toluene
1,2-dichloroethane
MeOH
2 h
9
1
20 min
3 h
99
10
11
12
1
52
1
H2O
3 h
15
1
THF
24 h
92
c
13
1
THF
80
2 h
>99
a
b
c
Reactions performed under an N2 atmosphere using 4 mmol of 1-octen-3-ol (0.2 M solutions). Yields determined by GC. Reaction performed in
the presence of 20 equiv (per Ru) of free p-cymene.
alcohol) at 80 °C with a metal loading of 1 mol % (entries 1−5 in
Table 3). Turnover frequencies of up to 540 h−1 were reached
under these conditions (entries 3−5). As shown in entries 6 and
7, lower catalyst loadings were tolerated without a drastic
increase in the reaction times. For example, using only 0.1 mol %
of [RuCl{κ2N,N′-C(N-4-C6H4Br)(NiPr)NHiPr}(η6-p-cym-
ene)] (2c), complete formation of octan-3-one took place in 1
h (TOF = 1000 h−1; entry 7). The isomerization of 1-octen-3-ol
into octan-3-one by means of complex 2c (1 mol %) was also
studied in other organic solvents (toluene, 1,2-dichloroethane,
and methanol), as well as in water, but none of them allowed us
to improve the result previously obtained in THF (entries 8−11
vs entry 3). The use of protic solvents (H2O and MeOH) turned
out to be particularly harmful due to the partial decomposition of
2c, a process clearly appreciable to the naked eye by a color
change of the solution from orange to black. Poorer results were
also obtained on lowering the reaction temperature (e.g., at 50
°C in THF, 24 h of heating was needed to attain a 92%
conversion; see entry 12). It is also important to note that, when
the isomerization of 1-octen-3-ol with complex 2c (1 mol %,
THF, 80 °C) was performed in the presence of 20 equiv of free p-
cymene, the performance shown by this catalyst was significantly
reduced (entry 13 vs 3). This fact seems to indicate that the
required vacant sites for coordination of the substrate may be
generated by release of the arene ligand, possibly as a result of the
steric hindrance between the bulky guanidinate substituents and
the coordinated p-cymene unit.
6−9). However, due probably to the steric congestion associated
with the presence a bulky Ar group in an α position with respect
to the alcohol unit, which disfavors their coordination to the
metal, longer reaction times (3−24 h) were in these cases
required to attain good conversions.24 In addition, a marked
influence of the electronic properties of the aryl rings on the
reaction rates was observed, with those substrates bearing
electron-withdrawing groups showing a remarkably lower
reactivity (entries 7 and 8 vs 9). Finally, it is also worthy of
note that the process is not restricted to allylic alcohols with a
monosubstituted carbon−carbon double bond, since the isomer-
ization of the disubstituted 3-penten-2-ol into pentan-2-one also
took place efficiently after a short heating period (1 h; entry 10).
The effectiveness shown by [RuCl{κ2N,N′-C(NR)(NiPr)-
NHiPr}(η6-p-cymene)] (2a−e) under base-free conditions
raised the question of a possible cooperative effect of the
pendant amino NHiPr group of the guanidinate ligands during
catalysis. This group could facilitate the generation of the more
coordinating oxo-allyl anion by deprotonation of the allylic
alcohol. To answer this question, we decided to prepare the
related amidinate complex [RuCl{κ2N,N′-C(NiPr)2Me}(η6-p-
cymene)] (5), by reacting [{RuCl(μ-Cl)(η6-p-cymene)}2] with
the lithium amidinate salt Li[(iPrN)2CMe]25 (details are given in
the Experimental Section), and explore its catalytic behavior
(Scheme 4).26 The remarkably lower catalytic activity shown by
this complex in the redox isomerization of the model substrate 1-
octen-3-ol seems to corroborate our hypothesis. More evidence
supporting the direct participation of the pendant amino NHiPr
group during the catalytic events is the fact that the activity of
[RuCl{κ2N,N′-C(N-4-C6H4Br)(NiPr)NHiPr}(η6-p-cymene)]
(2c) is drastically reduced in the presence of an acid. Thus, when
the catalytic isomerization of 1-octen-3-ol into octan-3-one by
means of 2c (1 mol %) was performed with 1 equiv of HCl (Et2O
solution) per Ru in the medium, 6.5 h of heating was needed to
achieve a quantitative conversion (13% after 1 h) of the substrate,
instead of the 10 min required under acid-free conditions (entry
1 in Table 4).
To define the scope of this catalytic transformation, other
allylic alcohols were subjected to the action of [RuCl{κ2N,N′-
C(N-4-C6H4Br)(NiPr)NHiPr}(η6-p-cymene)] (2c) (Table 4).
This complex was chosen because it could be easily crystallized
on a large scale. Reactions were performed in all cases in THF
(0.2 M solutions) at 80 °C using a Ru loading of 1 mol %. Thus,
as observed for 1-octen-3-ol (entry 1), related aliphatic substrates
AlkCH(OH)CHCH2 could also be efficiently converted into
the corresponding ketones after only 10−30 min of heating
(entries 2−5).
Complex 2c proved also effective in the isomerization of
aromatic allylic alcohols ArCH(OH)CHCH2, thus confirming
the generality of this base-free catalytic transformation (entries
8306
dx.doi.org/10.1021/om3009124 | Organometallics 2012, 31, 8301−8311

Organometallics
Article
Table 4. Catalytic Isomerization of Allylic Alcohols Using [RuCl{κ2N,N′-C(N-4-C6H4Br)(NiPr)NHiPr}(η6-p-cymene)] (2c) as
a
Catalyst
a
Reactions performed at 80 °C under N2 atmosphere using 4 mmol of the corresponding allylic alcohol (0.2 M solutions in THF). [substrate]:[Ru]
b
= 100:1. Yields determined by GC.
Scheme 4. Synthesis and Catalytic Behavior of the Ruthenium(II) Amidinate Complex 5
reaction of the dimer [{RuCl(μ-Cl)(η6-p-cymene)}2] with an
CONCLUSION
■
excess of the corresponding guanidines (iPrHN)2CNR, and
In summary, the novel ruthenium(II) guanidinate complexes
two of them, namely [RuCl{κ2N,N′-C(NiPr)2NHiPr}(η6-p-
[RuCl{κ2N,N′-C(NR)(NiPr)NHiPr}(η6-p-cymene)] (R = Pr
i
cymene)] (2a) and [RuCl{κ2N,N′-C(N-4-C6H4 Bu)(NiPr)-
t
t
(2a), 4-C6H4 Bu (2b), 4-C6H4Br (2c), 2,4,6-C6H2Me3 (2d), 2,6-
i
C6H3 Pr2 (2e)) have been synthesized in high yields from the
NHiPr}(η6-p-cymene)] (2b), were structurally characterized by
8307
dx.doi.org/10.1021/om3009124 | Organometallics 2012, 31, 8301−8311

Organometallics
Article
C of cym), 80.7, 79.3, 78.8, and 78.7 (s, CH of cym), 45.8 and 44.5 (s,
NCHMe2), 34.0 (s, CMe3), 31.4 (s, CHMe2 of cym), 31.3 (s, CMe3),
25.5, 24.8, 23.7, 22.9, 22.4, and 22.1 (s, NCHMe2 and CHMe2 of cym),
18.8 (s, Me of cym) ppm. Anal. Calcd for RuC27H42N3Cl: C, 59.48; H,
7.77; N, 7.71. Found: C, 59.60; H, 7.68; N, 7.83. 2c: yield 0.488 g (86%);
IR (KBr, cm−1) ν 3355 (N−H); 1H NMR (CDCl3) δ 7.29 and 7.04 (d,
2H each, 3JHH = 8.5 Hz, CHarom), 5.31 and 5.01 (d, 1H each, 3JHH = 5.5
Hz, CH of cym), 5.13 and 5.06 (d, 1H each, 3JHH = 5.7 Hz, CH of cym),
3.37−3.13 (m, 3H, NCHMe2 and NH), 2.65 (m, 1H, CHMe2 of cym),
means of single-crystal X-ray diffraction techniques. Compounds
2b−e represent the first examples of ruthenium complexes
containing asymmetrical monoanionic guanidinate ligands
reported to date in the literature. In addition, we have also
demonstrated that complexes 2a−e are efficient catalysts in the
redox isomerization of allylic alcohols into the corresponding
saturated ketones and that, unlike the majority of ruthenium
catalysts previously described for this catalytic transformation,
they are able to operate under base-free conditions. To the best
of our knowledge, this is the first catalytic application known for
ruthenium guanidinate species.
2.19 (s, 3H, Me of cym), 1.31, 1.29, 0.97, and 0.94 (d, 3H each, 3JHH
6.0 Hz, NCHMe2 or CHMe2 of cym), 1.24 and 1.20 (d, 3H each, 3JHH
=
=
7.0 Hz, NCHMe2 or CHMe2 of cym) ppm; 13C{1H} NMR (CD2Cl2) δ
160.8 (s, CN3), 149.9 and 111.6 (s, Carom), 131.0 and 123.7 (s, CHarom),
98.5 and 97.3 (s, C of cym), 80.6, 79.3, 79.0, and 78.6 (s, CH of cym),
45.7 and 44.8 (s, NCHMe2), 31.4 (s, CHMe2 of cym), 25.3, 24.7, 23.8,
22.7, 22.4, 22.0, and 18.8 (s, NCHMe2, CHMe2 of cym and Me of cym)
ppm. Anal. Calcd for RuC23H33N3BrCl: C, 48.64; H, 5.86; N, 7.40.
Found: C, 48.82; H, 5.79; N, 7.29. 2d: yield 0.435 g (82%); IR (KBr,
cm−1) ν 3343 (N−H); 1H NMR (CD2Cl2) δ 6.89 and 6.82 (s, 1H each,
CHarom), 5.04, 5.03, 4.99, and 4.82 (d, 1H each, 3JHH = 5.5 Hz, CH of
EXPERIMENTAL SECTION
■
Synthetic procedures were performed under an atmosphere of dry
nitrogen using vacuum-line and standard Schlenk techniques. Solvents
were dried by standard methods and distilled under nitrogen before use.
All reagents were obtained from commercial suppliers and used without
further purification, with the exception of the ruthenium(II) arene dimer
[{RuCl(μ-Cl)(η6-p-cymene)}2],14 guanidines (iPrHN)2CNR (1a−
e),13 the lithium amidinate salt Li[(iPrN)2CMe],25 and the allylic
alcohols 1-(4-fluorophenyl)-2-propen-1-ol,27 1-(4-chlorophenyl)-2-
propen-1-ol,28 and 1-(4-methoxyphenyl)-2-propen-1-ol,29 which were
prepared by following the methods reported in the literature. Infrared
spectra were recorded on a Perkin-Elmer 1720-XFT spectrometer. The
C, H, and N analyses were carried out with a Perkin-Elmer 2400
microanalyzer. NMR spectra were recorded on Bruker DPX300 and
AV400 instruments. Chemical shifts are given in ppm, relative to internal
tetramethylsilane. DEPT experiments have been carried out for all the
compounds reported in this paper. GC and GC/MSD measurements
were made on a Hewlett-Packard HP6890 apparatus (Supelco Beta-
DexTM 120 column, 30 m length, 250 μm diameter) and an Agilent
6890N apparatus coupled to a 5973 mass detector (HP-1MS column, 30
m length, 250 μm diameter), respectively.
3
cym), 3.45 (d, 1H, JHH = 10.2 Hz, NH), 3.20 and 2.82 (m, 1H each,
NCHMe2), 2.72 (m, 1H, CHMe2 of cym), 2.32, 2.28, and 2.27 (s, 3H
each, ArMe), 2.10 (s, 3H, Me of cym), 1.39, 1.26, and 0.91 (d, 3H each,
3JHH = 6.4 Hz, NCHMe2 or CHMe2 of cym), 1.31 (d, 3H, 3JHH = 6.8 Hz,
NCHMe2 or CHMe2 of cym), 1.29 (d, 3H, 3JHH = 7.5 Hz, NCHMe2 or
3
CHMe2 of cym), 0.74 (d, 3H, JHH = 5.3 Hz, NCHMe2 or CHMe2 of
cym) ppm; 13C{1H} NMR (CD2Cl2) δ 163.0 (s, CN3), 144.6, 133.4,
132.2, and 131.3 (s, Carom), 121.9 and 128.6 (s, CHarom), 101.5 and 92.4
(s, C of cym), 80.0, 79.4, 78.4, and 77.9 (s, CH of cym), 45.4 and 44.0 (s,
NCHMe2), 31.2 (s, CHMe2 of cym), 26.0, 25.4, 24.4, 22.9, 22.7, 22.1,
20.5, 20.2, 18.7, and 18.6 (s, NCHMe2, CHMe2 of cym, Me of cym and
ArMe) ppm. Anal. Calcd for RuC26H40N3Cl: C, 58.79; H, 7.59; N, 7.91.
Found: C, 58.65; H, 7.62; N, 7.78. 2e: yield 0.441 g (77%); IR (KBr,
cm−1) ν 3321 (N−H); 1H NMR (CD2Cl2) δ 7.15−7.09 (m, 3H,
CHarom), 5.23 and 5.12 (d, 1H each, 3JHH = 5.6 Hz, CH of cym), 5.03 and
4.96 (d, 1H each, 3JHH = 6.2 Hz, CH of cym), 4.00, 2.84, and 2.69 (m, 1H
each, NCHMe2, CHMe2 of cym or CHMe2 of Ar), 3.25 (m, 2H,
NCHMe2, CHMe2 of cym or CHMe2 of Ar), 3.07 (d, 1H, 3JHH = 10.8
Hz, NH), 2.15 (s, 3H, Me of cym), 1.42 (d, 3H, 3JHH = 7.4 Hz, NCHMe2,
CHMe2 of cym or CHMe2 of Ar), 1.36, 1.34, and 1.33 (d, 3H, 3JHH = 6.7
Hz, NCHMe2, CHMe2 of cym or CHMe2 of Ar), 1.31 (d, 3H, 3JHH = 7.0
Hz, NCHMe2, CHMe2 of cym or CHMe2 of Ar), 1.26 (d, 6H, 3JHH = 6.4
Hz, NCHMe2, CHMe2 of cym or CHMe2 of Ar), 1.05 (d, 3H, 3JHH = 7.1
Hz, NCHMe2, CHMe2 of cym or CHMe2 of Ar), 0.95 (d, 3H, 3JHH = 6.0
Hz, NCHMe2, CHMe2 of cym or CHMe2 of Ar), 0.60 (d, 3H, 3JHH = 5.8
Hz, NCHMe2, CHMe2 of cym or CHMe2 of Ar) ppm; 13C{1H} NMR
(CD2Cl2) δ 165.4 (s, CN3), 147.3, 145.3, and 144.5 (s, Carom), 123.9,
123.8, and 123.7 (s, CHarom), 102.0 and 92.9 (s, C of cym), 80.2, 79.4,
78.2, and 76.1 (s, CH of cym), 45.7 and 44.3 (s, NCHMe2), 31.4 (s,
CHMe2 of cym), 27.6 and 27.8 (s, CHMe2 of Ar), 26.9, 26.7, 26.4, 25.5,
25.4, 25.0, 24.1, 22.9, 22.5, and 22.3 (s, NCHMe2, CHMe2 of cym and
CHMe2 of Ar), 18.2 (s, Me of cym). Anal. Calcd for RuC29H46N3Cl: C,
60.76; H, 8.09; N, 7.33. Found: C, 60.69; H, 8.16; N, 7.21.
Reactions of the Dimer [{RuCl(μ-Cl)(η6-p-cymene)}2] with
i
t
Guanidines (iPrHN)2CNR (R = Pr (1a), 4-C6H4 Bu (1b), 4-
i
C6H4Br (1c), 2,4,6-C6H2Me3 (1d), 2,6-C6H3 Pr2 (1e)). A solution of
[{RuCl(μ-Cl)(η6-p-cymene)}2] (0.306 g, 0.5 mmol) in 30 mL of
toluene was treated with the appropriate guanidine 1a−e (2 mmol) at
room temperature for 2 h. The gradual appearance of a white solid
precipitate of the guanidinium chloride salts [(iPrHN)2C(NHR)][Cl]
(3a−e) was observed. The resulting suspension was then concentrated
to ca. 10 mL and filtered using a cannula. The white solid was washed
with hexanes (2 × 10 mL) and diethyl ether (5 mL) to afford 3a−e in
pure form. The filtrate was stored in a freezer at −20 °C for 24−48 h,
leading to complexes [RuCl{κ2N,N′-C(NR)(NiPr)NHiPr}(η6-p-cym-
ene)] (2a−e) as yellow-orange crystals, which were separated, washed
with hexanes (2 × 5 mL), and vacuum-dried. Characterization data for
2a−e are as follows. 2a: yield 0.364 g (80%); IR (KBr, cm−1) ν 3289
(N−H); 1H NMR (CD2Cl2) δ 5.42 and 5.18 (d, 2H each, 3JHH = 5.9 Hz,
CH of cym), 3.50−3.32 (m, 3H, NCHMe2), 2.87 (d, 1H, 3JHH = 10.8 Hz,
NH), 2.80 (sept, 1H, 3JHH = 7.0 Hz, CHMe2 of cym), 2.18 (s, 3H, Me of
cym), 1.30, 1.20, and 1.11 (d, 6H each, 3JHH = 6.4 Hz, NCHMe2), 1.27
(d, 6H, 3JHH = 7.0 Hz, CHMe2 of cym) ppm; 13C{1H} NMR (CDCl3) δ
163.6 (s, CN3), 97.9 and 96.7 (s, C of cym), 79.0 and 78.9 (s, CH of
cym), 46.7 and 46.6 (s, NCHMe2), 31.9 (s, CHMe2 of cym), 26.0, 25.0,
23.8, and 22.3 (s, NCHMe2 and CHMe2 of cym), 15.1 (s, Me of cym)
ppm. Anal. Calcd for RuC20H36N3Cl: C, 52.79; H, 7.97; N, 9.23. Found:
C, 52.66; H, 8.10; N, 9.17. 2b: yield 0.409 g (75%); IR (KBr, cm−1) ν
Characterization data for the guanidinium chloride salts 3a−e are as
follows. 3a:30 yield 0.175 g (79%); IR (KBr, cm−1) ν 3312 (N−H); 1H
NMR (CDCl3) δ 7.03 (broad s, 3H, NH), 3.97 (broad s, 3H, CHMe2),
1.39 (broad s, 18H, CHMe2) ppm; 13C{1H} NMR (CDCl3) δ 156.1 (s,
CN3), 46.9 (s, CHMe2), 23.9 (s, CHMe2) ppm. Anal. Calcd for
C10H24N3Cl: C, 54.16; H, 10.91; N, 18.95. Found: C, 54.01; H, 11.05; N,
18.85. 3b: yield 0.252 g (81%); IR (KBr, cm−1) ν 3411 (N−H), 3182
(N−H); 1H NMR (CD2Cl2) δ 10.05 (broad s, 1H, NH), 7.65 (broad s,
2H, NH), 7.41 and 7.21 (broad d, 2H each, 3JHH = 7.5 Hz, CHarom), 4.05
(broad s, 2H, CHMe2), 1.34 (s, 9H, CMe3), 1.20 (d, 12H, 3JHH = 6.0 Hz,
CHMe2) ppm; 13C{1H} NMR (CD2Cl2) δ 154.9 (s, CN3), 149.0 and
134.5 (s, Carom), 126.4 and 122.8 (s, CHarom), 45.7 (s, CHMe2), 34.4 (s,
CMe3), 31.0 (s, CMe3), 22.4 (s, CHMe2) ppm. Anal. Calcd for
C17H30N3Cl: C, 65.47; H, 9.70; N, 13.47. Found: C, 65.59; H, 9.87; N,
13.19. 3c: yield 0.251 g (75%); IR (KBr, cm−1) ν 3402 (N−H), 3221
(N−H); 1H NMR (CD2Cl2) δ 10.04 (broad s, 1H, NH), 7.74 (broad,
2H, NH), 7.41 and 7.13 (broad d, 2H each, 3JHH = 7.7 Hz, CHarom), 3.94
3338 (N−H); 1H NMR (CD2Cl2) δ 7.24 and 7.09 (d, 2H each, 3JHH
=
8.7 Hz, CHarom), 5.33 and 5.04 (d, 1H each, 3JHH = 6.1 Hz, CH of cym),
3
5.21 and 5.09 (d, 1H each, JHH = 5.5 Hz, CH of cym), 3.34 (m, 2H,
NCHMe2 and NH), 3.21 (m, 1H, NCHMe2), 2.71 (m, 1H, CHMe2 of
cym), 2.20 (s, 3H, Me of cym), 1.35 (s, 9H, CMe3), 1.32 and 1.29 (d, 3H
each, 3JHH = 6.3 Hz, NCHMe2 or CHMe2 of cym), 1.27 and 0.97 (d, 3H
each, 3JHH = 6.9 Hz, NCHMe2 or CHMe2 of cym), 1.23 (d, 3H, 3JHH = 6.6
Hz, NCHMe2 or CHMe2 of cym), 0.96 (d, 3H, 3JHH = 6.0 Hz, NCHMe2
or CHMe2 of cym) ppm; 13C{1H} NMR (CDCl3) δ 161.1 (s, CN3),
147.7 and 142.9 (s, Carom), 125.0 and 121.9 (s, CHarom), 98.3 and 96.8 (s,
8308
dx.doi.org/10.1021/om3009124 | Organometallics 2012, 31, 8301−8311

Organometallics
Article
(broad s, 2H, CHMe2), 1.17 (broad s, 12H, CHMe2) ppm; 13C{1H}
NMR (CD2Cl2) δ 154.7 (s, CN3), 136.1 and 119.0 (s, Carom), 132.6 and
124.0 (s, CHarom), 46.3 (s, CHMe2), 22.6 (s, CHMe2) ppm. Anal. Calcd
for C13H21N3BrCl: C, 46.65; H, 6.32; N, 12.55. Found: C, 46.54; H,
6.48; N, 12.69. 3d: yield 0.229 g (77%); IR (KBr, cm−1) ν 3393 (N−H),
3176 (N−H); 1H NMR (CDCl3) δ 9.37 (broad s, 1H, NH), 6.86 (s, 2H,
CHarom), 4.17 (broad s, 2H, CHMe2), 2.26 (s, 3H, ArMe), 2.17 (s, 6H,
ArMe), 1.15 (broad s, 12H, CHMe2) ppm; NHiPr signals not observed;
13C{1H} NMR (CDCl3) δ 153.6 (s, CN3), 141.1, 138.1, and 136.0 (s,
Images were collected at a 75 (2a) or 63 mm (2b) fixed crystal−detector
distance, using the oscillation method, with 1° oscillation and variable
exposure time per image (6−10 s for 2a and 1.5−5 s for 2b). Data
collection strategy was calculated with the program CrysAlisPro CCD.35
Data reduction and cell refinement was performed with the program
CrysAlisPro RED.35 An empirical absorption correction was applied
using the SCALE3 ABSPACK algorithm as implemented in the program
CrysAlisPro RED.35 The software package WINGX36 was used for space
group determination, structure solution, and refinement. The structures
were solved by Patterson interpretation and phase expansion using
SIR92.37
Carom), 129.8 (s, CHarom), 45.4 (s, CHMe2), 23.0 (s, CHMe2), 21.0 and
18.4 (s, ArMe) ppm. Anal. Calcd for C16H28N3Cl: C, 64.52; H, 9.47; N,
14.11. Found: C, 64.64; H, 9.38; N, 14.34. 3e: yield 0.241 g (71%); IR
(KBr, cm−1) ν 3391 (N−H), 3227 (N−H); 1H NMR (CDCl3) δ 9.57
(broad s, 1H, NH), 7.89 (broad s, 2H, NH), 7.32 (t, 1H, 3JHH = 7.3 Hz,
Isotropic least-squares refinement on F2 using SHELXL9738 was
performed. During the final stages of the refinements, all the positional
parameters and the anisotropic temperature factors of all the non-H
atoms were refined. The H atoms were geometrically located, and their
coordinates were refined riding on their parent atoms (except that on
N(2), which in both complexes was found from different Fourier maps
and included in a refinement with isotropic parameters). The function
3
CHarom), 7.17 (d, 2H, JHH = 7.3 Hz, CHarom), 4.43 (broad s, 2H,
NCHMe2), 3.00 (broad s, 2H, CHMe2), 1.16 (d, 12H, 3JHH = 6.0 Hz,
CHMe2), 1.14 (broad s, 12H, NCHMe2) ppm; 13C{1H} NMR (CDCl3)
δ 155.8 (s, CN3), 147.4 and 129.0 (s, Carom), 129.6 and 124.6 (s,
CHarom), 45.1 (broad s, NCHMe2), 28.3 (s, CHMe2), 24.5 (broad s,
NCHMe2), 22.9 (s, CHMe2) ppm. Anal. Calcd for C19H34N3Cl: C,
67.13; H, 10.08; N, 12.36. Found: C, 67.24; H, 9.90; N, 12.43.
2
2
minimized was [∑w(Fo2 − Fc2)/∑w(Fo )]1/2, where w = 1/[σ2(Fo ) +
2
(aP)2 + bP] (a and b values are given in Table S1) with σ(Fo ) from
counting statistics and P = (Max(Fo ,0) + 2Fc2)/3. The maximum
2
Preparation of the Amidinate Complex [RuCl{κ2N,N′-C-
(NiPr)2Me}(η6-p-cymene)] (5).26 The dimeric precursor [{RuCl(μ-
Cl)(η6-p-cymene)}2] (0.122 g, 0.2 mmol) and the lithium amidinate salt
Li[(iPrN)2CMe] (0.067 g, 0.45 mmol) were dissolved in 10 mL of dry
tetrahydrofuran at −78 °C, and the resulting mixture was warmed to
room temperature. The solvent was then removed under vacuum, the
crude product extracted with hexanes (ca. 30 mL), and the extract
filtered over Kieselguhr. Concentration of the resulting solution to ca. 5
mL resulted in the precipitation of a red solid, which was separated and
vacuum-dried. Yield: 0.110 g (67%). 1H NMR (C6D6): δ 5.08 and 4.81
(d, 2H each, 3JHH = 5.7 Hz, CH of cym), 3.41 (sept, 2H, 3JHH = 6.3 Hz,
NCHMe2), 2.74 (sept, 1H, 3JHH = 6.9 Hz, CHMe2 of cym), 2.16 (s, 3H,
residual electron density is in both cases located near heavier atoms.
Atomic scattering factors were taken from ref 39. Geometrical
calculations were made with PARST.40 The crystallographic plots
were made with PLATON.41
ASSOCIATED CONTENT
* Supporting Information
■
S
A CIF file and a table giving crystallographic data for compounds
2a,b and figures and tables giving optimized geometries and
Cartesian coordinates for 2b−e, 2′b−e, 4b−e, and 4′b−e. This
material is available free of charge via the Internet at http://pubs.
acs.org.
3
Me of cym), 1.52 (s, 3H, N2CMe), 1.25 (d, 12H, JHH = 6.3 Hz,
NCHMe2), 1.20 (d, 6H, 3JHH = 6.9 Hz, CHMe2 of cym) ppm. 13C{1H}
NMR (C6D6): δ 151.5 (s, NCN), 98.0 and 97.3 (s, C of cym), 78.9 and
78.3 (s, CH of cym), 47.8 (s, NCHMe2), 32.1 (s, CHMe2 of cym), 25.6
(s, NCHMe2), 22.5 (s, CHMe2 of cym), 19.0 (s, Me of cym), 13.1 (s,
N2CMe) ppm. Anal. Calcd for RuC18H31N2Cl: C, 52.48; H, 7.58; N,
6.80. Found: C, 52.59; H, 7.52; N, 6.95.
AUTHOR INFORMATION
Corresponding Author
■
*E-mail: crochetpascale@uniovi.es (P.C.); vcm@uniovi.es
(V.C.); Antonio.Antinolo@uclm.es (A.A.).
General Procedure for the Catalytic Isomerization of Allylic
Alcohols. In a sealed tube under a nitrogen atmosphere, the
corresponding ruthenium complex 2a−e (0.004−0.04 mmol; 0.1−1
mol % of Ru) was added to a solution of the corresponding allylic
alcohol (4 mmol) in tetrahydrofuran (20 mL), and the resulting mixture
was stirred at 80 °C for the indicated time (see Tables 3 and 4). The
course of the reaction was monitored by regularly taking samples of ca.
10 μL, which after dilution with THF (3 mL) were analyzed by GC. The
identity of the resulting carbonyl compounds was assessed by
comparison with commercially available pure samples (Aldrich
Chemical Co. or Acros Organics) and by their fragmentation in GC/
MS.
Computational Details. All theoretical calculations were per-
formed with the program package Gaussian03,31 at the density
functional theory (DFT) level by means of the hybrid B3LYP
functional.32 The molecular geometries were optimized, without any
molecular symmetry constraint, using Pople’s 6-31G(d) split valence
basis set for C, H, N, Cl, and Br elements33 and LANL2DZ for Ru, which
combines quasi-relativistic effective core potentials with a valence
double-basis set.34 Frequency calculations were performed to determine
whether the optimized geometries were minima on the potential energy
surface. Optimized geometries and Cartesian coordinates for all the
compounds studied can be found in the Supporting Information.
X-ray Crystal Structure Determination of Complexes 2a,b.
Crystals suitable for X-ray diffraction analysis were in both cases
obtained by slow diffusion of n-pentane into a saturated solution of the
complex in diethyl ether. The most relevant crystal and refinement data
are collected in Table S1 (Supporting Information). For both crystals,
data collection was performed on a Oxford Diffraction Xcalibur Nova
single-crystal diffractometer, using Cu Kα radiation (λ = 1.5418 Å).
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Spanish Ministry of Science and
Innovation (projects CTQ2010-14796/BQU, CTQ2009-09214,
and CSD2007-00006).
REFERENCES
■
(1) Chandra, G.; Jenkins, A. D.; Lappert, M. F.; Srivastava, R. C. J.
Chem. Soc. A 1970, 2550−2558.
(2) For reviews, see: (a) Bailey, P. J.; Pace, S. Coord. Chem. Rev. 2001,
214, 91−141. (b) Piers, W. E.; Emslie, D. J. H. Coord. Chem. Rev. 2002,
233−234, 131−155. (c) Edelmann, F. T. Adv. Organomet. Chem. 2008,
57, 183−352. (d) Edelmann, F. T. Chem. Soc. Rev. 2009, 38, 2253−2268.
(e) Jones, C. Coord. Chem. Rev. 2010, 254, 1273−1289. (f) Trifonov, A.
A. Coord. Chem. Rev. 2010, 254, 1327−1347. (g) Collins, S. Coord.
Chem. Rev. 2011, 255, 118−138.
(3) For very recent examples, see: (a) Kelley, M. R.; Rohde, J.-U. Chem.
Commun. 2012, 48, 2876−2878. (b) Yonke, B. L.; Keane, A. J.; Zavalij, P.
Y.; Sita, L. R. Organometallics 2012, 31, 345−355. (c) Elorriaga, D.;
Carrillo-Hermosilla, F.; Antinolo, A.; Lop
́
ez-Solera, I.; Menot, B.;
dez-Galan, R.; Villasenor, E.; Otero, A. Organometallics 2012, 31,
̃
Fernan
1840−1848. (d) Chlupaty, T.; Padel
́
́
̃
́
̌
kova, Z.; DeProft, F.; Willem, R.;
̊
̌
̌
Ruzicka, A. Organometallics 2012, 31, 2203−2211. (e) Chen, S.-J.;
Dougan, B. A.; Chen, X.-T.; Xue, Z.-L. Organometallics 2012, 31, 3443−
3446. (f) Willcocks, A. M.; Robinson, T. P.; Roche, C.; Pugh, T.;
Richards, S. P.; Kingsley, A. J.; Lowe, J. P.; Johnson, A. L. Inorg. Chem.
8309
dx.doi.org/10.1021/om3009124 | Organometallics 2012, 31, 8301−8311

Organometallics
Article
́
Rodrıguez, M. A. Inorg. Chem. 2003, 42, 3293−3307. (b) Cadierno, V.;
2012, 51, 246−257. (g) Rai, V. K.; Nishiura, M.; Takimoto, M.; Zhao, S.;
Liu, Y.; Hou, Z. Inorg. Chem. 2012, 51, 822−835. (h) Chiarella, G. M.;
Cotton, F. A.; Dalal, N. S.; Murillo, C. A.; Wang, Z.; Young, M. D. Inorg.
́
́
́
́
́
Crochet, P.; Dıez, J.; Garcıa-Alvarez, J.; Garcıa-Garrido, S. E.; Garcıa-
́
Granda, S.; Gimeno, J.; Rodrıguez, M. A. Dalton Trans. 2003, 3240−
́
Chem. 2012, 51, 5257−5263. (i) Fernan
́
dez-Galan
́
, R.; Antinolo, A.;
́
́
̃
3249. (c) Cadierno, V.; Dıez, J.; Garcıa-Alvarez, J.; Gimeno, J.;
Carrillo-Hermosilla, F.; Lopez-Solera, I.; Otero, A.; Serrano-Laguna, A.;
́
Calhorda, M. J.; Veiros, L. F. Organometallics 2004, 23, 2421−2433.
(d) Cadierno, V.; Dıez, J.; Garcıa-Alvarez, J.; Gimeno, J. Organometallics
́
Villasenor, E. J. Organomet. Chem. 2012, 711, 35−42. (j) Zhang, X.;
̃
́
́
́
Qian, C.; Wang, C.; Zhang, Y.; Wang, Y.; Yao, Y.; Shen, Q. Eur. J. Inorg.
́
́
2004, 23, 3425−3436. (e) Cadierno, V.; Dıez, J.; Garcıa-Alvarez, J.;
Chem. 2012, 847−858. (k) Neuhauser, C.; Reinmuth, M.; Kaifer, E.;
̈
Gimeno, J. Organometallics 2005, 24, 2801−2810. (f) Cadierno, V.;
́
Himmel, H.-J. Eur. J. Inorg. Chem. 2012, 1250−1260. (l) Zelga, K.;
́
́
Dıez, J.; Garcıa-Alvarez, J.; Gimeno, J. J. Organomet. Chem. 2005, 690,
́
Leszczyn
H.; Lewin
́
ski, M.; Justyniak, I.; Kornowicz, A.; Cabaj, M.; Wheatley, A. E.
́
2087−2096. (g) Cadierno, V.; Garcıa-Alvarez, J.; Gimeno, J.; Rubio-
́
́
ski, J. Dalton Trans. 2012, 41, 5934−5938. (m) Wang, Y.; Luo,
́
́
Garcıa, J. J. Organomet. Chem. 2005, 690, 5856−5862. (h) Dıaz-Alvarez,
Y.; Chen, J.; Xue, H.; Liang, H. New J. Chem. 2012, 36, 933−940.
(n) Chiarella, G. M.; Melgarejo, D. Y.; Fackler, J. P., Jr. Inorg. Chim. Acta
2012, 386, 13−16.
A. E.; Crochet, P.; Zablocka, M.; Cadierno, V.; Duhayon, C.; Gimeno, J.;
́
́
Majoral, J.-P. New J. Chem. 2006, 30, 1295−1306. (i) Dıaz-Alvarez, A. E.;
Crochet, P.; Zablocka, M.; Cadierno, V.; Vendier, L.; Gimeno, J.;
(4) Pap, J. S.; Snyder, J. L.; Piccoli, P. M. B.; Berry, J. F. Inorg. Chem.
2009, 48, 9846−9852.
́
Majoral, J.-P. Polyhedron 2007, 26, 933−940. (j) Cadierno, V.; Dıez, J.;
́
́
́
Garcıa-Alvarez, J.; Gimeno, J.; Rubio-Garcıa, J. Dalton Trans. 2008,
(5) Holman, K. T.; Robinson, S. D.; Sahajpal, A.; Steed, J. W. J. Chem.
Soc., Dalton Trans. 1999, 15−18.
́
́
́
5737−5748. (k) Cadierno, V.; Dıez, J.; Garcıa-Alvarez, J.; Gimeno, J.
Organometallics 2008, 27, 1809−1822. (l) Cadierno, V.; Dıez, J.; Garcıa-
́
́
(6) Robinson, S. D.; Sahajpal, A.; Steed, J. Inorg. Chim. Acta 2000, 303,
265−270.
́
Alvarez, J.; Gimeno, J. Dalton Trans. 2010, 39, 941−956.
(17) Metal-bound chlorine atoms are well-known hydrogen-bond
(7) Bailey, P. J.; Grant, K. J.; Mitchell, L. A.; Pace, S.; Parkin, A.;
Parsons, S. Dalton Trans. 2000, 1887−1891.
́
acceptors: Aullon, G.; Bellamy, D.; Brammer, L.; Bruton, E. A.; Orpen,
A. G. Chem. Commun. 1998, 653−654.
(18) (a) Jeffrey, G. A. In An Introduction to Hydrogen Bonding; Oxford
University Press: Oxford, U.K., 1997. (b) Steiner, T. Angew. Chem., Int.
Ed. 2002, 41, 48−76.
(8) Bailey, P. J.; Mitchell, L. A.; Parsons, S. J. Chem. Soc., Dalton Trans.
1996, 2839−2841.
(9) An isolated example of a ruthenium complex containing a
coordinated guanidinate dianion, namely [Ru{κ2-(N,N′)-C(NAc)2
NAc}(η6-p-cymene)(PPh3)], has also been described: Dinger, M. B.;
Henderson, W.; Nichloson, B. K. J. Organomet. Chem. 1998, 556, 75−88.
(10) Singh, T.; Kishan, R.; Nethaji, M.; Thirupathi, N. Inorg. Chem.
2012, 51, 157−169.
(19) Related rearrangements in both free guanidines and guanidinate
complexes have been described. See ref 10 and: (a) Mullins, S. M.;
Duncan, A. P.; Bergman, R. G.; Arnold, J. Inorg. Chem. 2001, 40, 6952−
6963. (b) Zhang, J.; Cai, R.; Weng, L.; Zhuo, X. Organometallics 2004,
23, 3303−3308. (c) Qian, C.; Zhang, X.; Li, J.; Xu, F.; Zhang, Y.; Shen,
Q. Organometallics 2009, 28, 3856−3862. (d) Zhang, X.; Wang, C.;
Qian, C.; Han, F.; Xu, F.; Shen, Q. Tetrahedron 2011, 67, 8790−8799.
(20) The optimized bond distances for 2b are in good agreement with
those experimentally obtained by X-ray diffraction (Table 1), deviating
only ca. 0.5 Å (e.g., Ru−N(1) = 2.147 Å, Ru−N(3) = 2.095 Å, C(11)−
N(1) = 1.337 Å, C(11)−N(2) = 1.381 Å, C(11)−N(3) = 1.340 Å). The
calculated bond angles are also in complete accord with those found
experimentally (e.g., N(1)−C(11)−N(3) = 109.37°, N(1)−Ru−N(3)
= 61.99°).
(11) For selected reviews, accounts, and books on the field, see:
(a) Bruneau, C.; Dixneuf, P. H. Chem. Commun. 1997, 507−512.
(b) Naota, T.; Takaya, H.; Murahashi, S.-I. Chem. Rev. 1998, 98, 2599−
2660. (c) Trost, B. M.; Toste, F. D.; Pinkerton, A. B. Chem. Rev. 2001,
101, 2067−2096. (d) Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001,
34, 18−29. (e) Ritleng, V.; Sirlin, C.; Pfeffer, M. Chem. Rev. 2002, 102,
1731−1770. (f) Ruthenium in Organic Synthesis; Murahashi, S.-I., Ed.;
Wiley-VCH: Weinheim, Germany, 2004. (g) Ruthenium Catalysts and
Fine Chemistry; Bruneau, C., Dixneuf, P. H., Eds.; Springer: Berlin, 2004.
(h) Trost, B. M.; Frederiksen, M. U.; Rudd, M. T. Angew. Chem., Int. Ed.
́
(21) Díaz-Alvarez, A. E.; Cadierno, V. Recent Patents Catal. 2012, 1,
́
2005, 44, 6630−6666. (i) Bruneau, C.; Derien, S.; Dixneuf, P. H. Top.
43−50 and patents cited therein.
(22) See, for example: (a) Ito, M.; Kitahara, S.; Ikariya, T. J. Am. Chem.
Organomet. Chem. 2006, 19, 295−326. (j) Bruneau, C.; Dixneuf, P. H.
Angew. Chem., Int. Ed. 2006, 45, 2176−2203. (k) Cadierno, V.; Crochet,
́
Soc. 2005, 127, 6172−6173. (b) Cadierno, V.; Garcıa-Garrido, S. E.;
́
P.; Garcıa-Garrido, S. E.; Gimeno, J. Curr. Org. Chem 2006, 10, 165−
́
Gimeno, J.; Varela-Alvarez, A.; Sordo, J. A. J. Am. Chem. Soc. 2006, 128,
dez-Zumel, M. A.; Gimeno, J.;
183. (l) Cadierno, V.; Crochet, P. Curr. Org. Synth. 2008, 5, 343−364.
(m) Murahashi, S.-I.; Zhang, D. Chem. Soc. Rev. 2008, 37, 1490−1501.
(n) Bruneau, C.; Renaud, J.-L.; Demerseman, B. Pure Appl. Chem. 2008,
80, 861−871. (o) Kondo, T. Bull. Chem. Soc. Jpn. 2011, 84, 441−458.
(p) Bruneau, C.; Achard, M. Coord. Chem. Rev. 2012, 256, 525−536.
(12) For a review on the catalytic applications of ruthenium-
amidinates, see: Nagashima, H.; Kondo, H.; Hayashida, T.;
Yamaguchi, Y.; Gondo, M.; Masuda, S.; Miyazaki, K.; Matsubara, K.;
Kirchner, K. Coord. Chem. Rev. 2003, 245, 177−190.
1360−1370. (c) Crochet, P.; Fernan
́
́
Scheele, M. Organometallics 2006, 25, 4846−4849. (d) Bouziane, A.;
Carboni, B.; Bruneau, C.; Carreaux, F.; Renaud, J.-L. Tetrahedron 2008,
́
64, 11745−11750. (e) Lastra-Barreira, B.; Dıez, J.; Crochet, P. Green
Chem. 2009, 11, 1681−1686. (f) Servin, P.; Laurent, R.; Gonsalvi, L.;
Tristany, M.; Peruzzini, M.; Majoral, J.-P.; Caminade, A. M. Dalton
́
Trans. 2009, 4432−4434. (g) Gonzalez, B.; Lorenzo-Luis, P.; Serrano-
́
̋
Ruiz, M.; Papp, E.; Fekete, M.; Csepke, K.; Osz, K.; Joo, F.; Romerosa, A.
́
́
J. Mol. Catal. A: Chem. 2010, 326, 15−20. (h) Pontes da Costa, A.; Mata,
J. A.; Royo, B.; Peris, E. Organometallics 2010, 29, 1832−1838. (i) Azua,
A.; Sanz, S.; Peris, E. Organometallics 2010, 29, 3661−3664.
(13) Alonso-Moreno, C.; Carrillo-Hermosilla, F.; Garces
́
, A.; Otero,
́
A.; Lop
2010, 29, 2789−2795.
́
ez-Solera, I.; Rodrıguez, A. M.; Antinolo, A. Organometallics
̃
́
́
(j) Fernandez-Zumel, M. A.; Lastra-Barreira, B.; Scheele, M.; Dıez, J.;
(14) Bennett, M. A.; Huang, T.-N.; Matheson, T. W.; Smith, A. K.
Inorg. Synth. 1982, 21, 74−78.
Crochet, P.; Gimeno, J. Dalton Trans. 2010, 39, 7780−7785. (k) Liu, P.
N.; Ju, K. D.; Lau, C. P. Adv. Synth. Catal. 2011, 353, 275−280.
(l) Brown, C. J.; Miller, G. M.; Johnson, M. W.; Bergman, R. G.;
Raymond, K. N. J. Am. Chem. Soc. 2011, 133, 11964−11966.
(15) For reviews and accounts on this catalytic transformation, see:
́ ́
(a) Uma, R.; Crevisy, C.; Gree, R. Chem. Rev. 2003, 103, 27−51. (b) van
der Drift, R. C.; Bouwman, E.; Drent, E. J. Organomet. Chem. 2002, 650,
1−24. (c) Cadierno, V.; Crochet, P.; Gimeno, J. Synlett 2008, 1105−
1124. (d) Mantilli, L.; Mazet, C. Chem. Lett. 2011, 40, 341−344.
(e) Mazet, C. Chimia 2011, 65, 802−805. (f) Ahlsten, N.; Bartoszewicz,
A.; Martín-Matute, B. Dalton Trans. 2012, 41, 1660−1670. (g) Lorenzo-
Luis, P.; Romerosa, A.; Serrano-Ruiz, M. ACS Catal. 2012, 2, 1079−
1086.
́
́
́
(m) Garcıa-Alvarez, J.; Gimeno, J.; Suarez, F. J. Organometallics 2011,
30, 2893−2896. (n) Putignano, E.; Bossi, G.; Rigo, P.; Baratta, W.
Organometallics 2012, 31, 1133−1142. (o) Bizet, V.; Pannecoucke, X.;
Renaud, J.-L.; Cahard, D. Angew. Chem., Int. Ed. 2012, 51, 6467−6470.
́
́ ́
(p) Bellarosa, L.; Dıez, J.; Gimeno, J.; Lledos, A.; Suarez, F. J.; Ujaque,
G.; Vicent, C. Chem. Eur. J. 2012, 18, 7749−7765. (q) Udvardy, A.;
́
́
́
(16) See, for example: (a) Cadierno, V.; Crochet, P.; Dıez, J.; Garcıa-
Ben
́
yei, A. C.; Katho,
́
́
A. J. Organomet. Chem. 2012, 717, 116−122.
́
́
́
Alvarez, J.; Garcıa-Garrido, S. E.; Gimeno, J.; Garcıa-Granda, S.;
(r) Dıez, J.; Gimeno, J.; Lledos, A.; Suarez, F. J.; Vicent, C. ACS Catal.
́
́
8310
dx.doi.org/10.1021/om3009124 | Organometallics 2012, 31, 8301−8311

Organometallics
Article
̌
̌ ́ ̌ ̌
2012, 2, 2087−2099. (s) Schulz, J.; Císarova, I.; Stepnicka, P. Eur. J.
Inorg. Chem. 2012, 5000−5010.
(23) The use of water as solvent has allowed, in some cases, the
reactions to be carried out in the absence of base. The high polarity of
this medium favors the deprotonation of the alcohol to form the
corresponding oxo-allyl anion. See, for example, refs 22b,f,i,m,p,r.
(24) Previous studies have already pointed out this effect. See, for
́
́
example, ref 22c and: (a) Crochet, P.; Dıez, J.; Fernandez-Zumel, M. A.;
́
́
Gimeno, J. Adv. Synth. Catal. 2006, 348, 93−100. (b) Dıaz-Alvarez, A.
E.; Crochet, P.; Zablocka, M.; Duhayon, C.; Cadierno, V.; Gimeno, J.;
Majoral, J. P. Adv. Synth. Catal. 2006, 348, 1671−1679. (c) Cadierno, V.;
Francos, J.; Gimeno, J.; Nebra, N. Chem. Commun. 2007, 2536−2538.
́
(d) Cadierno, V.; Crochet, P.; Francos, J.; Garcıa-Garrido, S. E.;
Gimeno, J.; Nebra, N. Green Chem. 2009, 11, 1992−2000.
(25) Coles, M. P.; Swenson, D. C.; Jordan, R. F.; Young, V. G., Jr.
Organometallics 1997, 16, 5183−5194.
(26) The amidinate complex 5 has been previously mentioned in a
patent. However, neither details on its isolation nor characterization data
were given in the document: Shenai-Khatkhate, D. V.; Wang, Q. M. U.S.
Pat. Appl. Publ. US 20080026578, 2008.
(27) Marion, N.; Gealageas, R.; Nolan, S. P. Org. Lett. 2007, 9, 2653−
2656.
(28) Brown, R. C. D.; Fisher, M. L.; Brown, L. J. Org. Biomol. Chem.
2003, 1, 2699−2709.
(29) Laabs, S.; Munch, W.; Bats, J. W.; Nubbemeyer, U. Tetrahedron
̈
2002, 58, 1317−1334.
(30) Said, F. F.; Ong, T.-G.; Yap, G. P. A.; Richeson, D. Cryst. Growth
Des. 2005, 5, 1881−1888.
(31) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K.
N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa,
J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.;
Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.;
Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.;
Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.;
Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels,
A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.;
Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham,
M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; and Pople, J. A.
Gaussian 03, Revision C.01; Gaussian, Inc., Wallingford, CT, 2004.
(32) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 1372−1377. (b) Becke,
A. D. J. Chem. Phys. 1993, 98, 5648−5652. (c) Lee, C.; Parr, R. G.; Yang,
W. Phys. Rev. B 1988, 37, 785−789. (d) Stephens, P. J.; Devlin, J. F.;
Chabalowski, C. F.; Frisch, M. J. J. Phys. Chem. 1994, 98, 11623−11627.
(33) Henre, W. J.; Radom, L.; Schleyer, P. v. R.; Pople, J. A. In Ab Initio
Molecular Orbital Theory; Wiley: New York, 1986.
(34) (a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270−283.
(b) Ehlers, A. W.; Boehme, M.; Dapprich, S.; Gobbi, A.; Hoellwarth, A.;
Jonas, V.; Koehler, K. F.; Stegmann, R.; Veldkamp, A.; Frenking, G.
Chem. Phys. Lett. 1993, 208, 111−114.
(35) CrysAlisPro CCD & CrysAlisPro RED; Oxford Diffraction Ltd.,
Oxford, U.K., 2008.
(36) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837−838.
(37) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435−436.
(38) Sheldrick, G. M. SHELXL97: Program for the Refinement of Crystal
Structures; University of Gottingen, Gottingen, Germany, 1997.
̈
̈
(39) International Tables for X-Ray Crystallography; Kynoch Press:
Birminghan, U.K., 1974; Vol. IV (present distributor: Kluwer Academic
Publishers, Dordrecht, The Netherlands)
(40) Nardelli, M. Comput. Chem. 1983, 7, 95−97.
(41) Spek, A. L. PLATON: A Multipurpose Crystallographic Tool;
University of Utrecht, Utrecht, The Netherlands, 2007.
8311
dx.doi.org/10.1021/om3009124 | Organometallics 2012, 31, 8301−8311