Synthesis, Structural Characterization, and Catalytic Activity of Indenyl Tris(N-pyrrolyl)phosphine Complexes of Ruthenium

Article abstract of DOI:10.1002/ejic.201501381

The synthesis, characterization, and catalytic activity of new ruthenium complexes of the tris(N-pyrrolyl)phosphine ligand [P(pyr)₃] are described. The new ruthenium complexes [RuCl(ind)(PPh₃){P(pyr)₃}] and [RuCl(ind){P(pyr)₃}₂] (ind = indenyl, η⁵-C₉H₇^-) were synthesized in 73 and 63 % isolated yields, respectively, by thermal ligand exchange of [RuCl(ind)(PPh₃)₂] with P(pyr)₃. The electronic and steric properties of the new complexes were studied through analysis of the X-ray structures and cyclic voltammetry. The new complexes [RuCl(ind)(PPh₃){P(pyr)₃}] and [RuCl(ind){P(pyr)₃}₂] and the known complex [RuCl(ind){(PPh₃)₂}] differed only slightly in their steric properties, as seen from the comparable bond lengths and angles around the ruthenium centers. The oxidation potentials of [RuCl(ind)(PPh₃){P(pyr)₃}] and [RuCl(ind){P(pyr)₃}₂] of +0.34 and +0.71 V versus Cp₂Fe^0/+ (Cp = cyclopentadienyl) are substantially higher than that of [RuCl(ind)(PPh₃)₂] (-0.023 V), in accordance with the enhanced π-acidity of the P(pyr)₃ ligand. The new complexes are catalytically active in the etherification of propargylic alcohols and in the first ruthenium-catalyzed formation of known and new xanthenones from propargylic alcohols and diketones (18 to 72 h at 90 °C in ClCH₂CH₂Cl or toluene, 1-2 mol-% catalyst, 69-22 % isolated yields).

Full text of DOI:10.1002/ejic.201501381

DOI: 10.1002/ejic.201501381
Full Paper
Ruthenium Catalysts
Synthesis, Structural Characterization, and Catalytic Activity of
Indenyl Tris(N-pyrrolyl)phosphine Complexes of Ruthenium
Matthew J. Stark,[a] Michael J. Shaw,[b] Nigam P. Rath,[a,c] and Eike B. Bauer*[a]
Abstract: The synthesis, characterization, and catalytic activity ties, as seen from the comparable bond lengths and angles
of new ruthenium complexes of the tris(N-pyrrolyl)phosphine around the ruthenium centers. The oxidation potentials of
ligand [P(pyr)3] are described. The new ruthenium complexes [RuCl(ind)(PPh3){P(pyr)3}] and [RuCl(ind){P(pyr)3}2] of +0.34 and
[RuCl(ind)(PPh3){P(pyr)3}] and [RuCl(ind){P(pyr)3}2] (ind = ind- +0.71 V versus Cp2Fe0/+ (Cp = cyclopentadienyl) are substan-
–
enyl, η5-C9H7 ) were synthesized in 73 and 63 % isolated yields, tially higher than that of [RuCl(ind)(PPh3)2] (–0.023 V), in accord-
respectively, by thermal ligand exchange of [RuCl(ind)(PPh3)2] ance with the enhanced π-acidity of the P(pyr)3 ligand. The
with P(pyr)3. The electronic and steric properties of the new new complexes are catalytically active in the etherification of
complexes were studied through analysis of the X-ray structures propargylic alcohols and in the first ruthenium-catalyzed forma-
and cyclic voltammetry. The new complexes [RuCl(ind)(PPh3)- tion of known and new xanthenones from propargylic alcohols
{P(pyr)3}] and [RuCl(ind){P(pyr)3}2] and the known complex and diketones (18 to 72 h at 90 °C in ClCH2CH2Cl or toluene,
[RuCl(ind){(PPh3)2}] differed only slightly in their steric proper- 1–2 mol-% catalyst, 69–22 % isolated yields).
Introduction
powerful, they are somewhat limited at times, as they some-
times require lengthy syntheses, which hamper practical appli-
cations. Thus, the search for readily available phosphine ligands
with unique electronic properties is ongoing.
Transition-metal complexes of ruthenium are applied in broad
fields such as catalysis[1] and optical devices.[2] In medicinal or-
ganometallic chemistry, ruthenium complexes are increasingly
investigated as alternatives to platinum-based anticancer drugs
(which are limited by side-effects).[1a,3,4] A plethora of ruth-
enium complexes are known, as are attempts to modify them
to improve their performances in their respective applications.
The electronic properties of ruthenium complexes are most
commonly tuned through their ancillary ligands.[1c,4] Knowl-
edge of the effects of ligands on the electronic (and steric)
properties allows for the tailored synthesis of ruthenium com-
plexes with unique properties for specialized applications.
Phosphines are probably still the most widely utilized ligand
class in the synthesis and application of ruthenium com-
plexes,[5] albeit other ligands such as carbenes[6] and imines[7]
are increasingly utilized. Phosphine ligands bearing aryl and
alkyl groups are the most common ones used in the syntheses
of metal complexes, and their electronic modification is
achieved through the variation of the aryl substituents or the
nature of the alkyl groups.[8] Although the tuning options are
Tris(N-pyrrolyl)phosphine [P(pyr)3, pyr = N-pyrrolyl] is a read-
ily accessible ligand with electronic properties different from
those of the PPh3 ligand.[9] Research in the past decade has
shown that P(pyr)3 exhibits increased π-acidity[10] with elec-
tronic properties similar to those of CO.[9] IR νCO stretching fre-
quencies are utilized frequently to assess the electronic proper-
ties of a ligand, and the electron-withdrawing properties of
P(pyr)3 were demonstrated through the IR νCO stretching fre-
quencies of its rhodium chlorido carbonyl complex.[9] Further-
more, the oxidation potential, as determined by cyclic voltam-
metry, indicates the π-acidity of P(pyr)3.[11] Further electronic
tuning is possible by placing electron-withdrawing substituents
[13]
on the pyrrolyl ring.[12] A few ruthenium complexes of P(pyr)3
and their catalytic applications are known (Figure 1).[11] Never-
theless, the chemistry of P(pyr)3 complexes of ruthenium is far
less explored than that of PPh3 and its analogs. We think that
improved knowledge of the coordination chemistry of this li-
gand will open the pathway for its use in the synthesis of tai-
lored ruthenium complexes.
[a] Department of Chemistry and Biochemistry, University of Missouri –
St. Louis,
As part of our longstanding research program directed to-
wards the catalytic activation of propargylic alcohols,[14,15] we
were interested in investigating electron-poor ruthenium com-
plexes. Propargylic alcohols can be catalytically activated by
ruthenium complexes,[16] for example, through the formation of
One University Boulevard, St. Louis, MO 63121, USA
E-mail: bauere@umsl.edu
www.eike-bauer.net
[b] Department of Chemistry, Southern Illinois University Edwardsville,
Edwardsville, IL 62025, USA
[c] Center for Nanoscience, University of Missouri,
St. Louis, MO, USA
ruthenium allenylidene complexes [Ru=C=C=CR2]2+ [14,17]
and
,
we speculated that the reactivity of potential allenylidene inter-
mediates with nucleophiles would increase with decreased
electron density at the metal center. The known[18] ruthenium
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under http://dx.doi.org/10.1002/ejic.201501381.
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4 h, the mono(pyrrolylphosphine) complex [RuCl(ind)(PPh3)-
{P(pyr)3}] was isolated in 73 % yield as a red solid after chromat-
ographic workup (Scheme 1). In a second ligand-exchange reac-
tion, [RuCl(ind)(PPh3){P(pyr)3}] was heated with another equiva-
lent of P(pyr)3 in THF under reflux for 5 h. The bis(pyrrolyl-
phosphine) complex [RuCl(ind){P(pyr)3}2] was obtained in 63 %
yield as an orange-yellow solid after column chromatography.
Attempts to access [RuCl(ind){P(pyr)3}2] directly from
[RuCl(ind)(PPh3)2] in a double ligand-exchange reaction failed,
as the obtained mixtures of the mono- and disubstituted com-
plexes made workup difficult and lowered the yield.
Figure 1. Representative P(pyr)3 complexes of ruthenium.
indenyl complex [RuCl(ind)(PPh3)2] (ind = η5-C9H7 ) has been
utilized previously as a starting material for organometallic syn-
theses,[19] and ruthenium indenyl complexes are frequently ap-
plied in catalysis.[20] The increased reactivity of indenyl com-
plexes compared to the analogous cyclopentadienyl complexes
has been ascribed to the so-called “indenyl effect”.[21] The for-
mation of open coordination sites of the corresponding com-
plexes is facilitated through an η5–η3 ring slip. The effect has
been ascribed to increased aromaticity of the benzo portion of
the ligand through a ring slip[21e] or related to the lower M–C
bond energies of η5-indenyl complexes compared with those
of η5-cyclopentadienyl (Cp) complexes.[21b] We were interested
in synthesizing P(pyr)3 analogues of [RuCl(ind)(PPh3)2] to access
ruthenium complexes of increased Lewis acidity with improved
catalytic activity for the transformation of propargylic alcohols.
Herein, we describe the synthesis and characterization of the
ruthenium complexes [RuCl(ind)(PPh3){P(pyr)3}] and [RuCl(ind)-
{P(pyr)3}2]. We assess the electronic properties of the new com-
plexes through analysis of their X-ray structures and cyclic vol-
tammetry. Finally, we demonstrate that the new complexes are
catalytically active in the etherification of propargylic alcohols
and in the first ruthenium-catalyzed formation of xanthenones
from propargylic alcohols and diketones.
–
Scheme 1. Synthesis of P(pyr)3 complexes of ruthenium.
The new complexes were characterized by multinuclear NMR
spectroscopy, MS, IR spectroscopy, elemental analysis, and X-
ray diffraction. In [RuCl(ind)(PPh3){P(pyr)3}], the coordination of
one P(pyr)3 ligand and one PPh3 ligand is clearly indicated by
two distinct 31P{1H} NMR signals at δ = 122.8 and 40.4 ppm,
2
which exhibit a JP, P coupling constant of 144 Hz, as expected
for complexes with two magnetically different phosphorus at-
oms in the metal coordination sphere. Free P(pyr)3 resonates at
δ = 78.8 ppm in the 31P{1H} NMR spectrum, and the chemical
shifts for the complex indicate the coordination of the ligand.
The complex [RuCl(ind){P(pyr)3}2] exhibited only one signal in
its 31P{1H} NMR spectrum at δ = 122.2 ppm, as expected for
two identical phosphorus atoms coordinated to the ruthenium
center.
The indenyl ligand gives very distinct 1H and 13C{1H} NMR
signals for the three protons and the five carbon atoms of its
coordinated five-membered ring.[23] Owing to the unsymmetri-
cal substitution pattern with four different ligands in [RuCl(ind)-
(PPh3){P(pyr)3}], all of these carbons atoms and protons are dias-
tereotopic and give individual signals in the corresponding
NMR spectra. In [RuCl(ind){P(pyr)3}2], the complex is symmetric
as has two P(pyr)3 ligands, and the chemically equivalent pro-
tons and carbon atoms give only one set of signals for the
cyclopentadienyl portion of the complex, which simplifies the
1H and 13C{1H} NMR spectra.
Results and Discussion
Ligand and Ruthenium Complex Syntheses
Several syntheses of P(pyr)3 have been described previ-
ously.[9,10f] We prepared the ligand through a slightly modified
literature procedure,[9] which is provided in the Supporting In-
formation. In general, it is important to work under moisture-
free conditions and distill all starting materials immediately be-
fore use.
The precursor complex [RuCl(ind)(PPh3)2] has been used as a
starting material for the syntheses of ruthenium complex
X-ray Structures
through ligand-substitution reactions by us[13,15e,15f] and To establish the structure of the new ruthenium complexes un-
others.[22] Accordingly, when [RuCl(ind)(PPh3)2] was heated with equivocally, the X-ray structures of [RuCl(ind)(PPh3){P(pyr)3}] and
1.1 equiv. of P(pyr)3 in tetrahydrofuran (THF) under reflux for [RuCl(ind){P(pyr)3}2] were determined (Table 1 and Figure 2). Se-
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Table 1. Crystallographic parameters.
[RuCl(ind)(PPh3){P(pyr)3}]
[RuCl(ind){P(pyr)3}2]
Xanthenone 7b
Empirical formula
Formula weight
C39H34ClN3P2Ru
743.15
C33H31ClN6P2Ru
710.10
C27H24O3
396.46
Temperature [K]/wavelength [Å]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
100(2)/0.71073
orthorhombic
Pbca
17.9518(15)
15.6316(12)
24.057(2)
100(2)/0.71073
monoclinic
P21/c
13.2598(6)
9.5844(4)
100(2)/0.71073
triclinic
P1
¯
10.1854(6)
12.5276(7)
17.3162(9)
105.980(3)
24.8271(11)
90
90
ꢀ [°]
90
99.205(2)
92.278(3)
γ [°]
90
90
107.377(3)
2009.2(2)4
1.311
0.084
Volume [Å3]/Z
6750.8(9)/8
1.462
0.672
3114.6(2)/4
1.514
0.726
Density (calculated) [Mg/m3]
Absorption coefficient [mm–1
F(000)
]
3040
1448
840
Crystal size [mm3]
0.346 × 0.235 × 0.076
1.924 to 27.161
–21 ≤ h ≤ 23
–20 ≤ k ≤ 15
–30 ≤ l ≤ 27
78357
0.256 × 0.151 × 0.135
1.556 to 36.325
–22 ≤ h ≤ 22
–15 ≤ k ≤ 14
–41 ≤ l ≤ 41
69845
0.298 × 0.275 × 0.243
1.234 to 30.571
–12 ≤ h ≤ 14
–17 ≤ k ≤ 17
–24 ≤ l ≤ 24
48129
θ range for data collection [°]
Index ranges
Reflections collected
Independent reflections
Absorption correction
Max. and min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
7471 [R(int) = 0.0733]
semiempirical from equivalents
0.7989 and 0.7989
7471/1/415
1.003
15058 [R(int) = 0.0603]
semiempirical from equivalents
0.8625 and 0.7561
15058/0/388
1.019
12106 [R(int) = 0.0413]
semiempirical from equivalents
0.8879 and 0.8189
12106/1/541
1.028
Final R indices [I > 2σ(I)]
R1 = 0.0319,
wR2 = 0.0.0604
R1 = 0.0596,
wR2 = 0.0706
0.479 and –0.511
R1 = 0.0361,
wR2 = 0.0745
R1 = 0.0559,
wR2 = 0.0831
0.759 and –0.683
R1 = 0.0525,
wR2 = 0.1314
R1 = 0.0892,
wR2 = 0.1546
0.365 and –0.324
R indices (all data)
Largest diff. peak and hole [e/Å3]
Figure 2. The molecular structures of [RuCl(ind)(PPh3){P(pyr)3}] (left) and [RuCl(ind){P(pyr)3}2] (right). Hydrogen atoms are omitted for clarity. The crystallographic
parameters are compiled in Table 1, and key bond lengths and angles are listed in Table 2.
lected bond lengths and angles are listed in Table 2, and for 99.008(14)°]; this suggests that some steric repulsion occurs be-
comparison purposes, the X-ray data for [RuCl(ind)(PPh3)2] are tween PPh3 and P(pyr)3 and between the two P(pyr)3 ligands,
also included.[24]
The bond angles for the monodentate ligands about the
ruthenium center range from 89.510(13) to 99.008(14)°. Thus,
the structures are best described as slightly distorted octahe-
respectively. Interestingly, the P(1)–Ru–P(2) angles for both
complexes are comparable; therefore, the P(pyr)3 and the PPh3
ligands have similar steric demands.
The Ru–P bond length for the P(pyr)3 ligand in
dra. For both complexes, the greatest deviation from the ideal [RuCl(ind)(PPh3){P(pyr)3}] [2.2323(15) Å] is only slightly shorter
90° angle is for the P(1)–Ru–P(2) angle [97.89(5) and than that found for the PPh3 ligand [2.2760(14) Å], which might
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Table 2. Selected bond lengths [Å] and angles [°].
[RuCl(Ind)(PPh3){P(pyr)3}]
[RuCl(Ind){P(pyr)3}2]
[RuCl(Ind)(PPh3)2]
Ru–P(1)
Ru–P(2)
Ru–Cl
2.2323(15) [P(Pyr)3]
2.2760(14) (PPh3)
2.4362(15)
1.712
1.831
97.89(5)
93.51(5)
91.79(5)
1.902
0.161
2.2042(4)
2.2716(4)
2.4251(4)
1.716
2.331
2.268
2.437
–
P(1)–N(X)[a] average
P(1)–C(X)[a] average
P(1)–Ru–P(2)
Cl–Ru–P(1)
Cl–Ru–P(2)
Ru–Cp[b]
–
–
99.008(14)
90.684(14)
89.510(13)
1.928
0.155
7.33
99.21
92.42
92.19
1.918
0.221
7.07
Δ Ru–C[c]
Fold angle[d]
7.06
[a] P(1)–N(X) corresponds to the P–N bonds of P(pyr)3. P(1)–C(X) corresponds to the P–C bonds of PPh3. [b] Distance between the Cp centroid of the indenyl
ligand and the ruthenium center. [c] Average difference between the Ru–C1, Ru–C2, and Ru–C9 bond lengths and the Ru–C3 and Ru–C8 bond lengths, see
Figure 3. [d] Angle between the planes formed by C1–C2–C9 and C2–C3–C8–C9, see Figure 3.
be due to increased backbonding from the ruthenium center ΔM–C is 0, and values of ca. 0.2 Å are typical for indenyl ligands
to the P(pyr)3 ligand.[11,13a] Furthermore, in [RuCl(ind){P(pyr)3}2], and indicate η5-coordination. The values for [RuCl(ind)(PPh3)-
the Ru–P bond lengths of both P(pyr)3 ligands are also slightly {P(pyr)3}] and [RuCl(ind){P(pyr)3}2] fall in this range. The fold an-
different [2.2042(4) and 2.2716(4) Å, respectively] but fall in the gle is the angle between the planes formed by C1–C2–C8 and
range found for other ruthenium P(pyr)3 complexes.[11,14e] Also, C2–C3–C8–C9 (Figure 3, top right); it takes the value 0 in an
the distances between the Cp centroids of the indenyl ligands ideal η5 coordination, and the values are typically below 10° for
and the ruthenium centers for both complexes are similar indenyl complexes. Again, [RuCl(ind)(PPh3){P(pyr)3}] and
(1.902 and 1.928 Å) and comparable to that for [RuCl(ind){P(pyr)3}2] fall in this range. An η3 coordination would
[RuCl(ind)(PPh3)2] (1.918 Å). Thus, the angles and bond lengths be indicated by a fold angle of ca. 60°.[21e]
for the P(pyr)3 ligand are comparable to the those for PPh3
ligand; overall, the geometric parameters for the two P(pyr)3
complexes and [RuCl(ind)(PPh3)2] are similar, and the Ru–P(pyr)3
bond lengths are at best slightly shorter than the Ru–P(pyr)3
bond lengths.
The slightly longer P–N bond lengths of the P(pyr)3 ligand
(1.712 and 1.716 Å) than the typical P–N bond lengths of phos-
phoramidite ligands R2NP(OR)2 (ca. 1.66 Å) suggest a substantial
P=N double-bond character in the phosphoramidite li-
gand.[13a,14a] The elongated P–N bond lengths in the P(pyr)3
ligand are in accordance with the aromatic delocalization of
the nitrogen lone pair into the five-membered pyrrolyl ring,
as described previously,[9] and this delocalization prevents the
formation of a double bond with the phosphorus atom.
As can be seen from the X-ray structures, the indenyl ligands
for both complexes are η5-coordinated, that is, all five carbon
atoms of the cyclopentadienyl units form bonds to the ruth-
Figure 3. Geometric parameters for indenyl complexes.
enium centers. However, as has been described previously, the
Ru–C bonds in the coordinated cyclopentadienyl units are not
However, what is interesting for the two complexes is which
all the same lengths in the two complexes described herein. As ligand takes the position trans to the C3 and C8 benzo carbon
illustrated in Figure 3 (top left) with some exaggeration, the atoms of the cyclopentadienyl unit. It has been demonstrated
cyclopentadienyl units in indenyl complexes are typically before that the ligand with the strongest trans influence takes
slipped in a way that the bond lengths of the two benzenoid the positon trans to the benzo unit, and this weakens the bond
carbon atoms are longer than the bond lengths to the other strength (and enlarges the bond length) of the two Ru–C bonds
three carbon atoms. This has been ascribed to a gain in reso- of the benzo unit.[21e] In [RuCl(ind){P(pyr)3}2], one of the two
nance energy for the aryl ring of the ligand.[21e] In an extreme P(pyr)3 ligands is located trans to the benzo ring; therefore,
case, only three of the five carbon atoms would bond to the P(pyr)3 has a stronger trans influence than the chlorido ligand
ruthenium center in an η3 fashion (Figure 3, top right).[21e] The (B in Figure 3). However, in [RuCl(ind)(PPh3){P(pyr)3}], the PPh3
degree of the slippage has previously been quantified by two ring is located in the trans position (A in Figure 3); therefore,
parameters taken from the X-ray data, the ΔM–C value and the PPh3 has a stronger trans influence than P(pyr)3. This observa-
fold angle.[21e,25] The ΔM–C value is the average difference be- tion might be ascribed to the higher σ-basicity of PPh3 com-
tween the Ru–C1, Ru–C2, and Ru–C9 bond lengths and the Ru– pared with that of P(pyr)3, which leads to a stronger trans influ-
C3 and Ru–C8 bond lengths in the structures in Figure 2. Ideally, ence.
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In the past, the basicity of ligands has been assessed through [RuCl(ind){P(pyr)3}2] only shows some reversibility at high scan
the νCO stretching frequencies of carbonyl complexes and, in- rates of 0.8 and 1.6 V/s with low ipc/ipa ratios of 0.7 to 0.8,
deed, the higher value for P(pyr)3 (ν = 2024 cm–1) than that for respectively, which indicate decomposition of the oxidized spe-
˜
PPh (ν = 1980 cm–1) in trans-[RhCl(CO)L ] [L = P(pyr) , PPh ] cies. The successive introduction of P(pyr)3 ligands apparently
˜
3
2
3
3
indicates the higher basicity of the latter.[9] Further evidence for increases the oxidation potential of the respective complexes,
the higher basicity of PPh3 compared to P(pyr)3 is provided by which is in line with the higher π-acidic electron demand of
the 31P–77Se coupling constants, which increase with decreas- that ligand. The presence of two P(pyr)3 ligands in
ing basicity of the phosphorus compound.[26] In accordance [RuCl(ind){P(pyr)3}2]
destabilize
the
oxidized
species
with the higher basicity of PPh3, Se=P(pyr)3 exhibits a JP, S e value [RuCl(ind){P(pyr)3}2]+, as can be seen from the decreased revers-
of ca. 970 Hz, which is significantly higher than the correspond- ibility of the oxidative cyclic voltammogram waves; this sug-
ing value for Se=PPh3 (735 Hz).[27]
gests that some decomposition occurs after oxidation, possibly
by attack of adventitious nucleophiles.
Overall, the combined X-ray diffraction, NMR spectroscopy,
and CV data demonstrate that the P(pyr)3 ligand shows π-acidic
behavior and is a weaker σ donor than PPh3. However, as can
be seen from the comparable bond lengths and angles for both
ligands around the ruthenium center, the P(pyr)3 ligand has
steric properties similar to those of PPh3, despite its profound
impact on the electron density at the metal center. Conse-
quently, P(pyr)3 can be utilized in the synthesis of complexes
with decreased electron density at the metal center but with
steric properties similar to those of their respective PPh3 deriva-
tives.
Cyclic Voltammetry
Overall, the solid-state structures of [RuCl(ind)(PPh3){P(pyr)3}]
and [RuCl(ind){P(pyr)3}2] revealed some similarities between
these two complexes and [RuCl(ind)(PPh3)2]. The structural pa-
rameters around the ruthenium center are comparable and cor-
roborate earlier statements that the PPh3 and P(pyr)3 ligands
are sterically similar. Electronic differences could be observed
through the stronger trans influence of PPh3 compared with
that of P(pyr)3 and through the higher JP, Se coupling constants
in Se=P(pyr)3. Cyclic voltammetry has been used before to char-
acterize the electronic properties of ruthenium phosphine com-
plexes.[28] To obtain further insights into the electronic proper-
ties of the new complexes, we recorded the cyclic voltammo-
grams of [RuCl(ind)(PPh3){P(pyr)3}] and [RuCl(ind){P(pyr)3}2] as
well as that of [RuCl(ind)(PPh3)2] for comparison. The traces for
a scan rate of 0.8 V/s are compiled in Figure 4.
Catalytic Applications
We then investigated the ability of the new complexes to acti-
vate propargylic alcohols catalytically[29] and chose the etherifi-
cation of propargylic alcohols
5
as test reactions
(Table 3).[15a,15c] The complexes [RuCl(ind)(PPh3){P(pyr)3}] and
[RuCl(ind){P(pyr)3}2] themselves did not show catalytic activity
for the reaction. However, after activation through chloride ab-
straction with Et3OPF6, we observed catalytic activity. After
some optimization efforts, we found that 1–2 mol-% of acti-
vated [RuCl(ind)(PPh3){P(pyr)3}] catalyzed the etherification of
several propargylic alcohols 5 to give the corresponding prop-
argyl ethers 6 in 42 to 27 % isolated yields (toluene solvent, 70
to 95 °C for 16–72 h). The complex [RuCl(ind){P(pyr)3}2] showed
no catalytic activity for the etherification reactions in Table 3,
even after activation through chloride abstraction. We do not
have a satisfactory explanation for the different catalytic activi-
ties of the two complexes in the etherification reactions; the
alcohol substrates for the etherification reaction possibly deac-
tivate the catalytically active species derived from
[RuCl(ind){P(pyr)3}2].
Figure 4. Cyclic voltammograms of ruthenium indenyl complexes in 0.1
M
Bu4PF6/CH2Cl2 at 298 and recorded at scan rate of 0.8 V/s:
K
a
An excess of the alcohol nucleophile over the propargylic
alcohol is not required, and the catalyst load of 1–2 mol-% is
lower than those of other catalyst systems.[14] Some catalytic
[RuCl(ind)(PPh3)2] (solid line), [RuCl(ind)(PPh3){P(pyr)3}] (dotted line ···),
[RuCl(ind){P(pyr)3}2] (dashed line ---).
The cyclic voltammograms of [RuCl(ind)(PPh3)2] show a high systems perform the etherification reactions in Table 3 with the
degree of reversibility at different scan rates, as its ipc/ipa values alcohol nucleophile as the solvent.[14] We speculated that the
are close to 1 at all scan rates. The E°′ value for the oxidation is yields could be improved by running the reaction in neat alco-
–0.023 V (vs. Cp2Fe0/+), and the peak current ratio ipc/ipa is 1.0 hols, and we attempted this for the reactions in Table 3, En-
at a scan rate of 0.8 V/s. For [RuCl(ind)(PPh3){P(pyr)3}] and tries 3 and 4. In neat n-butanol, only trace quantities of the
[RuCl(ind){P(pyr)3}2], the E°′ values are significantly higher (+0.34 product were observed. In neat benzylic alcohol, conversion to
and +0.71 V, respectively). The oxidation of [RuCl(ind)(PPh3)- the product was detected by GC, but the starting material 5b
{P(pyr)3}] is still reversible at different scan rates, and the ipc/ipa was still present in the reaction mixture. Thus, the reaction is
ratio is 1.0 at 0.8 V/s. However, the oxidation of not more efficient with the alcohol nucleophile as the solvent,
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Table 3. Isolated yields.
might convert to acetic acid, which would make the catalyst
system more efficient. The identities of the xanthenones 7 were
established through X-ray analysis of product 7b (Figure 5). For
7a, E and Z isomers can form during catalysis, and we deter-
1
mined Z/E ratios of 4.1:1 and 8:1 by H NMR spectroscopy for
the transformations of 5b and 5c, respectively. We tentatively
assigned the Z configuration to the major isomer of this com-
pound by analogy to a closely related trisubstituted alkene.[31]
Product 7c is known,[32] and was isolated it as the pure E isomer,
as determined by NMR spectroscopy and comparison of the
chemical shifts with the literature values. The high reaction
temperatures and somewhat elongated reaction times might
promote the formation of the thermodynamically more stable
Table 4. Isolated yields.
[a] General conditions: propargylic alcohol (0.7 mmol) and alcohol R′–OH
(1 mmol) in toluene (2 mL) catalyzed by activated [RuCl(ind)(PPh3){P(pyr)3}]
(0.007 mmol). The products were isolated chromatographically. [b] 70 °C for
16 h. [c] 85 °C for 18 h. [d] 95 °C for 72 h.
and we tentatively ascribe this to the deactivation of the cata-
lyst by the alcohols.
We then turned our attention to carbon-centered nucleo-
philes in the form of diketones (Table 4), which have previously
been utilized for the substitution of the OH units of propargylic
alcohols.[14,29d,29e] When we subjected diketones to the same
reaction conditions as those in Table 3, we did not observe the
formation of the corresponding substitution products. Instead,
we detected xanthenone derivatives 7 in the crude reaction
mixtures when cyclohexane-1,3-dione was used as the diketone
substrate. Again, after some optimization efforts, we deter-
mined that the ruthenium complexes [RuCl(ind)(PPh3){P(pyr)3}]
and [RuCl(ind){P(pyr)3}2], after activation through chloride ab-
straction, catalyzed the synthesis of the xanthenone derivatives
7a–7c from propargylic alcohols and 2 equiv. of cyclohexane-
1,3-dione (80 to 95 °C, 72 h, 67–22 % isolated yields, Table 4).
For propargylic alcohol 5b, the corresponding propargylic acet-
ate 5c gave higher yields (Table 4, Entry 2). The higher yields
might be explained through the fact that the acetate group is
a better leaving group than OH. Furthermore, it has been re-
ported that carboxylic acids[30] or trifluoroacetic acid[16j,16k]
have beneficial effects on ruthenium-catalyzed isomerization
reactions. In line with these reports, the acetate leaving group
[a] Conditions: dione (2.5 equiv.) in ClCH2CH2Cl (2 mL) for 72 h at 80–95 °C.
The products were isolated chromatographically. [b] Catalyst 1–2 mol-%
[Ru(ind){P(pyr)3}2]+. [c] Catalyst 1–2 mol-% [Ru(ind)(PPh3){P(pyr)3}]+. [d] Condi-
tions: dione (2.5 equiv.) in cyclohexane (2 mL) for 16 h at 90 °C. The products
were isolated chromatographically. [e] Conditions: dione (2.5 equiv.) in
Cl2CH2CH2Cl (2 mL) for 18–48 h at 85–90 °C. The products were isolated
chromatographically. [f] Conditions: dione (2.5 equiv.) in ClCH2CH2Cl (2 mL)
for 18 h at 85 °C, 4 mol-% catalyst loading. The product was isolated chromat-
ographically.
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E isomer. The xanthenones 7a and 7b in Table 4 are new, and hexane-1,3-dione, 7b was isolated in a somewhat lower yield
xanthene derivatives exhibit pharmaceutical activity.[33]
of 32 % (Table 4, Entry 6), which suggests that the aldehyde
might be an intermediate for the reaction.
In principle, the formation of xanthenones from aldehydes
and diketones is known and has been achieved with Brøn-
sted[38] or Lewis acid catalysts,[35,39] catalyst-free,[36] or catalyzed
by iodine.[40] However, to the best of our knowledge, the chem-
istry shown in Table 4 and Scheme 2 represents the first exam-
ples of the ruthenium-catalyzed conversion of propargylic alco-
hols (not aldehydes) to xanthenones and the first ruthenium-
catalyzed version of the reaction. A gold-catalyzed conversion
of propargylic alcohols to xanthenones has been described pre-
viously.[41] Further investigations into the mechanism are under-
way.
Conclusions
The synthesis of the first tris(N-pyrrolyl)phosphine indenyl ruth-
enium complexes [RuCl(ind)(PPh3){P(pyr)3}] and [RuCl(ind)-
{P(pyr)3}2] is described. As determined through X-ray analysis
and cyclic voltammetry, the P(pyr)3 ligand is more π-acidic and
less σ-donating than PPh3. However, the steric properties of
both ligands in the solid state are comparable, as can be seen
from the bond lengths and angles associated with the ruth-
enium centers derived from X-ray data. After chloride abstrac-
tion, the new complexes are catalytically active in the etherifica-
tion of propargylic alcohols and in a tandem isomerization–
condensation sequence to give xanthenones.
Figure 5. Molecular structure of xanthenone 7b.
When pentane-2,4-dione was used as the diketone (Table 4,
Entry 5), a related reaction occurred in which the diketone con-
densed with the rearranged propargylic alcohol to give the
known conjugated allylidene dione 8, which has previously
been synthesized by utilizing catalytic p-toluenesulfonic acid
under reflux conditions.[34]
In contrast to the etherification reactions in Table 3, it
seemed that activated [RuCl(ind)(PPh3){P(pyr)3}] and [RuCl(ind)-
{P(pyr)3}2] gave comparable yields with diketones.
Although the exact mechanism of the reactions is still to be
investigated, the reactions can be viewed as tandem isomeriza-
tion–condensation sequences (Scheme 2).[35,36] Propargylic al-
cohols undergo acid-catalyzed Meyer–Schuster rearrangements
to their corresponding aldehydes 9 (Scheme 2).[14,37] The alde-
hydes formed from the propargylic alcohols in Table 4 can then
undergo double aldol condensations with the enol tautomers
of the diones followed by a hemiacetal formation/dehydration
sequence, as suggested by others.[35,36] Indeed, when 3,3-di-
phenylacrylaldehyde (9) was utilized in the reaction with cyclo-
Experimental Section
General: All reactions were performed under an inert N2 atmos-
phere by using standard Schlenk techniques. All chemicals were
used as supplied from Sigma–Aldrich unless otherwise noted. The
complex [RuCl(ind)(PPh3)2] was synthesized by following the litera-
ture procedure.[18] THF was distilled from Na/benzophenone under
N2. Ethyl acetate, hexane, toluene, CH2Cl2, and ClCH2CH2Cl were
used as received. Pyrrole was vacuum-distilled from CaCl2 before
use. All propargylic alcohols, alcohols, and ketones were obtained
and used as provided from Sigma–Aldrich. 1-Phenyl-2-propyn-1-ol
and propargyl acetate (5c) were synthesized according to literature
procedures.[42,43]
The NMR spectra for characterization were collected at room tem-
perature with a Varian Unity 300 MHz or Bruker Avance 300 MHz
instrument; all chemical shifts (δ) are reported in ppm and are refer-
enced to a residual solvent signal. The IR spectra were recorded
with a Thermo Nicolet 360 FTIR spectrometer. The FAB and exact
mass data were collected with a JEOL MStation (JMS-700) mass
spectrometer. Melting points were determined with a Thomas
Hoover uni-melt capillary melting point apparatus. Elemental analy-
ses were performed by Atlantic Microlab Inc., Norcross, GA, USA.
[RuCl(ind)(PPh3){P(pyr)3}]:
A
Schlenk
flask
containing
[RuCl(ind)(PPh3)2] (0.658 g, 0.848 mmol), P(pyr)3 (0.214 g,
0.932 mmol), and THF (8 mL) was heated gently under reflux for
4 h under nitrogen. The solvent was removed in vacuo. The com-
plex was isolated as a red solid (0.462 g, 0.622 mmol, 73 %) by
column chromatography (silica gel 2 × 15 cm, CH2Cl2 as eluent);
m.p. 120–122 °C (dec.). 1H NMR (300 MHz, CDCl3): δ = 7.51–7.45 (m,
6 H, arom.), 7.33–7.13 (m, 13 H, arom.), 6.14 (br s, 6 H), 6.03 (br s, 6
Scheme 2. Tandem isomerization–condensation sequence to give xanthen-
ones 7.
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H), 4.86 (s, 1 H, ind), 4.75 (s, 1 H, ind), 4.54 (s, 1 H, ind) ppm. 13C{1H}
NMR (75 MHz, CDCl3): δ = 136.9 (d, JC,P = 42.6 Hz), 133.5 (d, JC,P
10 Hz), 129.8 (s), 129.6 (s), 129.5 (s), 128.2 (d, JC,P = 9.5 Hz), 124.9
(s), 124.4 (s), 124.2 (d, JC,P = 6 Hz), 114.8 (s), 114.7 (s), 111.2 (d, JC,P
δ = 163.9 (s), 142.6 (s), 138.0 (s), 128.3 (s), 127.9 (s), 127.3 (s), 126.4
(s), 116.5 (s), 42.3 (s), 38.3 (s), 37.1 (s), 27.8 (s), 27.2 (s), 26.3 (s), 21.9
(s), 20.3 (s) ppm.
=
=
From propargyl acetate 5c (Table 4, Entry 2). To a small screw-cap
vial containing 2-phenyl-3-butyn-2-acetate (5c, 0.175 g,
0.934 mmol), 1,3-cyclohexanedione (0.265 g, 2.36 mmol) was
added, along with ClCH2CH2Cl (2 mL). The activated catalyst was
added (0.010 g, 0.012 mmol, 1.3 mol-%), and the mixture was
heated at 80 °C for 72 h. The product was isolated by column chro-
matography (silica gel, 1.5 × 15 cm, 2:5 ethyl acetate/hexane) as an
off-white solid (0.145 g, 0.435 mmol, 46 %) as an 8:1 mixture of
Z/E isomers, as assessed by NMR spectroscopy. The spectroscopic
data matched those reported above.
6.5 Hz), 93.9 (s), 70.5 (d, JC,P = 7.5 Hz), 68.3 (d, JC,P = 6.0 Hz) ppm.
31P{1H} NMR (121 MHz, CDCl3): δ = 122.81 (d, JP, P = 144 Hz), 40.37
(d, JP, P = 144 Hz) ppm. IR (neat, solid): ν = 3133 (w), 3052 (w), 2962
˜
(w), 2359 (w), 1454 (m), 1437 (m), 1287 (w), 1178 (s), 1056 (s), 1036
(s), 732 (s), 696 (m), 623 (m) cm–1. HRMS: calcd. for C39H34N3P2102Ru
[Ru(ind){P(pyr)3}2]+ 708.1249; found 708.1282. C39H34ClN3P2Ru
(743.09): calcd. C 63.03, H 4.61; found C 62.77, H 4.59.
[RuCl(ind){P(pyr)3}2]: A Schlenk flask containing [RuCl(ind)(PPh3)-
{P(pyr)3}] (0.140 g, 0.188 mmol), P(pyr)3 (0.086 g, 0.380 mmol), and
THF (5 mL) was heated gently under reflux for 5 h under nitrogen.
The solvent was removed in vacuo. The complex was isolated as an
orange-yellow solid (0.083 g, 0.117 mmol, 62 %) by column chroma-
tography (silica gel 2 × 15 cm, CH2Cl2 as eluent); m.p. 126–128 °C
(dec.). 1H NMR (300 MHz, CDCl3): δ = 7.19–7.16 (m, 4 H, arom.), 6.40
(d, JH,H = 1.8 Hz, 12 H), 6.17 (d, JH,H = 1.8 Hz, 12 H), 5.21 (br s, 2 H,
ind), 4.75 (br s, 1 H, ind) ppm. 13C{1H} NMR (75 MHz, CDCl3): δ =
131.1 (s), 124.4 (s), 124.2 (s), 112.9 (s), 112.4 (s), 96.1 (s), 70.8 (s)
ppm. 31P{1H} NMR (121 MHz, CDCl3): δ = 122.2 (s) ppm. IR (neat,
9-(2,2-Diphenylvinyl)-3,4,5,6,7,9-hexahydro-1H-xanthene-
1,8(2H)-dione (7b): To a small screw-cap vial containing 1,1-di-
phenylprop-2-yn-1-ol (5d, 0.110 g, 0.528 mmol), 1,3-cyclohexanedi-
one (0.212 g, 1.35 mmol) was added, along with ClCH2CH2Cl (2 mL).
The activated catalyst was added (0.010 g, 0.014 mmol, 2.2 mol-%),
and the mixture was heated at 85 °C for 72 h. The product was
isolated by column chromatography (silica gel, 1.5 × 15 cm, 2:5
ethyl acetate/hexane) as an off-white solid (0.144 g, 0.363 mmol,
1
69 %). H NMR (300 MHz, CDCl3): δ = 7.32–7.21 (m, 3 H, Ph), 7.06–
solid): ν = 3127 (w), 3106 (w), 1453 (m), 1176 (s), 1083 (m), 1055 (s),
˜
7.04 (m, 2 H, Ph), 6.08 (d, JH,H = 9 Hz, 1 H), 4.32 (d, JH,H = 9 Hz, 1
H), 2.23 (m, 8 H), 1.82 (m, 4 H) ppm. 13C{1H} NMR (75 MHz, CDCl3):
δ = 196.6 (s), 164.3 (s), 143.4 (s), 142.1 (s), 139.9 (s), 130.4 (s), 130.3
(s), 127.9 (s), 127.7 (s), 127.4 (s), 127.0 (s), 126.9 (s), 116.1 (s), 36.9
(s), 27.2 (s), 26.7 (s), 20.6 (s) ppm. C27H24O3 (396.48): calcd. C 81.79,
H 6.10; found C 81.63, H 6.12.
1033 (s), 736 (s), 712 (s), 703 (m), 614 (m) cm–1. HRMS: calcd. for
C33H31N6P2102Ru [Ru(ind)(PPh3){P(pyr)3}]+ 675.1138; found 675.1140.
C33H31ClN6P2Ru (710.08): calcd. C 55.82, H 4.40; found C 55.80, H
4.32.
Activation of [RuCl(ind)(PPh3){P(pyr)3}] through Chloride Ab-
straction: [RuCl(ind)(PPh3){P(pyr)3}] was placed in a Schlenk tube
with triethyloxonium hexafluorphosphate (1 equiv.) and CH2Cl2. The
mixture was stirred under N2 for 2–4 h, and the solvent was re-
moved in vacuo to afford the activated catalyst as a dark tan solid.
(E)-9-Styryl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione
(7c):[32] To a small screw-cap vial containing 1-phenylprop-2-yn-1-
ol (5a, 0.133 g, 1.01 mol), 1,3-cyclohexanedione (0.292 g,
2.60 mmol) was added, along with cyclohexane (3 mL). The acti-
vated catalyst was added (0.016 g, 0.018 mmol, 1.8 mol-%), and the
mixture was heated at 90 °C for 16 h. The product 7c was isolated
by column chromatography (silica gel, 1.5 × 15 cm, 2:5 ethyl acet-
ate/hexane) as an off-white solid (0.095 g, 0.296 mmol, 29 %). 1H
NMR (300 MHz, CDCl3): δ = 7.43–7.18 (m, 5 H, Ph), 6.27 (s, 2 H), 4.72
(s, 1 H), 2.52 (m, 8 H), 2.12 (m, 4 H) ppm. 13C{1H} NMR (75 MHz,
CDCl3): δ = 196.7 (s), 164.8 (s), 137.5 (s), 131.4 (s), 130.2 (s), 128.5
(s), 127.3 (s), 126.6 (s), 115.7 (s), 37.2 (s), 28.2 (s), 27.4 (s), 20.6 (s)
ppm.
[2-(Benzyloxy)but-3-yn-2-yl]benzene (Representative Example
for the Catalysis Reactions in Table 3): From 2-phenyl-3-butyn-2-
ol (5b, Table 3, Entry 3). To a small screw-cap vial containing 2-
phenyl-3-butyn-2-ol (5b, 0.105 g, 0.72 mmol), benzyl alcohol
(0.154 g, 1.4 mmol) was added, along with toluene (2 mL). The
activated catalyst was added (0.010 g, 0.007 mmol, 1 mol-%), and
the mixture was heated at 100 °C for 72 h. The product 6c was
isolated by column chromatography (silica gel, 1.5 × 15 cm, 2:1 hex-
ane/CH2Cl2) as a dark yellow oil (0.071 g, 0.30 mmol, 42 %). The
spectroscopic data for all products in Table 3 are given in the Sup-
porting Information and matched the literature values.[15c]
3-(3,3-Diphenylallylidene)pentane-2,4-dione (8): To
a small
screw-cap vial containing 1,1-diphenylprop-2-yn-1-ol (5d, 0.111 g,
0.532 mmol), 2,4-pentanedione (0.146 g, 1.45 mmol) was added,
along with ClCH2CH2Cl (2 mL). The catalyst was added (0.010 g,
0.012 mmol, 2.4 mol-%), and the mixture was heated at 85 °C for
16 h. The product was isolated as a tan oil by column chromatogra-
phy (silica gel, 1.5 × 12 cm, 2:5 ethyl acetate/hexane). The tan oil
was dried in vacuo and dissolved in warm hexanes. As the solution
cooled, the product formed as an orange-white solid (0.054 g,
(Z)-9-(2-Phenylprop-1-en-1-yl)-3,4,5,6,7,9-hexahydro-1H-
xanthene-1,8(2H)-dione (7a): From propargyl alcohol 5b (Table 4,
Entry 1). To a small screw-cap vial containing 2-phenyl-3-butyn-2-ol
(5b, 0.138 g, 0.943 mmol), 1,3-cyclohexanedione (0.267 g,
2.381 mmol) was added, along with ClCH2CH2Cl (2 mL). The acti-
vated catalyst was added (0.010 g, 0.012 mmol, 1.3 mol-%), and the
mixture was heated at 80 °C for 72 h. The product was isolated by
column chromatography (silica gel, 1.5 × 15 cm, 2:5 ethyl acetate/
hexane) as an off-white solid (0.066 g, 0.197 mmol, 21 %) as a 4.2:1
Z/E mixture of isomers, as assessed by NMR spectroscopy. C22H22O3
(334.16): calcd. C 79.02, H 6.63; found C 79.27, H 6.64.
Major Z isomer: 1H NMR (300 MHz, CDCl3): δ = 7.53–7.09 (m, 5 H,
Ph), 5.17 (d, JH,H = 9.9 Hz, 1 H), 4.62 (d, JH,H = 9.9 Hz, 1 H), 2.45 (m,
11 H), 1.97 (m, 4 H) ppm. 13C{1H} NMR (75 MHz, CDCl3): δ = 196.7
(s), 164.5 (s), 144.1 (s), 136.3 (s), 128.7 (s), 128.1 (s), 126.7 (s), 126.1
(s), 116.1 (s), 37.2 (s), 27.4 (s), 26.2 (s), 20.6 (s), 16.3 (s) ppm.
1
0.186 mmol, 34 %). H NMR (300 MHz, CDCl3): δ = 7.53–7.46 (m, 4
H, Ph), 7.41–7.32 (m, 4 H, Ph), 7.32–7.25 (m, 2 H, Ph), 7.19 (d, JH,H
=
11.8 Hz, 1 H), 7.07 (d, JH,H = 11.8 Hz, 1 H), 2.46 (s, 3 H, CH3), 2.20 (s,
3 H, CH3′) ppm. 13C{1H} NMR (75 MHz, CDCl3): δ = 203.6 (s), 197.5
(s), 155.5 (s), 141.9 (s), 140.8 (s), 140.3 (s), 138.2 (s), 130.6 (s),129.6
(s), 129.0 (s), 128.7 (s), 128.5 (s), 128.5 (s), 122.2 (s), 31.9 (s), 26.3 (s)
ppm. C20H18O2 (290.26): calcd. C 82.73, H 6.25; found C 82.28, H
6.24.
Cyclic Voltammetry: The voltammograms were recorded with a
three-electrode BAS electrochemical cell in a Vacuum Atmospheres
Minor E Isomer: 1H NMR (300 MHz, CDCl3, partial): δ = 5.56 (d, JH,H
8.7 Hz), 4.24 (d, JH,H = 8.7 Hz) ppm. 13C{1H} NMR (75 MHz, CDCl3):
=
HE-493 drybox under an atmosphere of argon with samples in 0.1
M
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NBu4PF6/CH2Cl2 at 298 K. A 1.6 mm Pt disk electrode was used as
the working electrode, a platinum wire was used as the auxiliary
electrode, and a silver wire was used a pseudoreference electrode.
The potentials were calibrated against the Cp*2Fe0/+ (Cp* = penta-
methylcyclopentadienyl) couple, which occurs at –0.548 V versus
the Cp2Fe0/+ couple for this solvent.[44] The potentials in this paper
can be changed to saturated calomel electrode (SCE) reference val-
ues by the addition of 0.56 V. The voltammograms were collected
at scan rates of 0.05–1.6 V/s with an EG&G PAR 263A potentiostat
interfaced to a computer operated with the EG&G PAR Model 270
software.
NMR spectrometer (CHE-9974801), the ApexII diffractometer
(MRI, CHE-0420497), and the mass spectrometer (CHE-9708640)
is acknowledged.
Keywords: Phosphane ligands · Ligand effects · Ruthenium ·
Structure elucidation · Homogeneous catalysis · Oxidation
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X-ray Structure Determination for [RuCl(ind)(PPh3){P(pyr)3}],
[RuCl(ind){P(pyr)3}2], and 7b: Crystals of the metal complexes of
appropriate dimension were obtained by the slow diffusion of hex-
anes into a CH2Cl2 solution of the compounds, and crystals of 7b
were obtained by layering an ethyl acetate solution of the com-
pound with hexanes. The crystals were mounted on MiTeGen cryo-
loops in random orientations. Preliminary examination and data col-
lection were performed with a Bruker X8 Kappa Apex II charge-
coupled device (CCD) detector system single-crystal X-ray diffrac-
tometer equipped with an Oxford Cryostream LT device. All data
were collected with graphite-monochromated Mo-Kα radiation (λ =
0.71073 Å) from a fine-focus sealed-tube X-ray source. The prelimi-
nary unit-cell constants were determined with a set of 36 narrow-
frame scans. Typical data sets consisted of combinations of ω and
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The final cell constants were determined by global refinement of
reflections harvested from the complete data set. The collected data
were corrected for systematic errors by SADABS on the basis of the
Laue symmetry by using equivalent reflections.[45]
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The crystal data and intensity data collection parameters are listed
in Table 1. Structure solutions and refinements were performed
with the SHELXTL-PLUS software package.[46] The structures were
solved by direct methods and refined successfully in the space
groups, Pbca, P2 /c, and P1 for [RuCl(ind)(PPh ){P(pyr) }], [RuCl(ind)-
¯
1
3
3
{P(pyr)3}2], and 7b, respectively. Full-matrix least-squares refine-
2
2 2
ments were performed by minimizing Σw(Fo – Fc ) . The non-
hydrogen atoms were refined anisotropically to convergence. All
hydrogen atoms were treated with an appropriate riding model
(AFIX m3). The final residual values and structure refinement param-
eters are listed in Table 1.
CCDC 1053440 (for 7b), 1053441 (for [RuCl(ind){P(pyr)3}2]), and
1053442 (for [RuCl(ind)(PPh3){P(pyr)3}]) contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre.
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Acknowledgments
The National Science Foundation (NSF) is thanked for financial
support (grant to E. B. B.: CHE-1300818, grant to M. J. S.: CHE-
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Eur. J. Inorg. Chem. 2016, 1093–1102
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© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Received: November 25, 2015
Published Online: January 29, 2016
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© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim