Ruthenium complexes of CP3: A new carbon-centered polydentate podand ligand

Article abstract of DOI:10.1021/om200718j

A new tripodal, tetradentate, carbon-centered podand ligand based on HC(CH₂CH₂PPh₂)₃ (^HCP ₃) has been prepared. In the presence of [RuCl₂(PPh ₃)₃], ^HCP₃ dehydrogenates on heating to yield [Ru(C(CH₂CH₂PPh₂)₂(= CHCH₂PPh₂))Cl₂], where three phosphorus donors and a constrained alkene bind the metal. The metal-carbon bond is then formed by reduction with hydride in the presence of an ancillary ligand, to give [Ru(C(CH₂CH₂PPh₂)₃)LX] (L = ancillary ligand; X = H, Cl), where the metal has the full CP₃ donor set. The complex [Ru(CP₃)(CO)H] displays moderate catalytic activity for the transfer hydrogenation of acetophenone.

Full text of DOI:10.1021/om200718j

Article
pubs.acs.org/Organometallics
Ruthenium Complexes of CP3: A New Carbon-Centered Polydentate
Podand Ligand
Olivia R. Allen,† Leslie D. Field,*,† Alison M. Magill,† Khuong Q. Vuong,† Mohan M. Bhadbhade,‡
and Scott J. Dalgarno§
‡
†School of Chemistry and Mark Wainwright Analytical Centre, University of New South Wales, High Street, Kensington,
New South Wales 2052, Australia
§School of EPS-Chemistry, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, United Kingdom
S
* Supporting Information
ABSTRACT: A new tripodal, tetradentate, carbon-centered podand
ligand based on HC(CH2CH2PPh2)3 (HCP3) has been prepared. In
the presence of [RuCl2(PPh3)3], HCP3 dehydrogenates on heating
to yield [Ru(C(CH2CH2PPh2)2(CHCH2PPh2))Cl2], where three
phosphorus donors and a constrained alkene bind the metal. The
metal−carbon bond is then formed by reduction with hydride in the
presence of an ancillary ligand, to give [Ru(C(CH2CH2PPh2)3)LX]
(L = ancillary ligand; X = H, Cl), where the metal has the full CP3 donor set. The complex [Ru(CP3)(CO)H] displays moderate
catalytic activity for the transfer hydrogenation of acetophenone.
he pincer-type ligands1 are the best known of the carbon-
reported a C3-symmetric palladium(II) complex derived from a
CP3 podand which is an active catalyst for Suzuki couplings.12
Tcentered polydentate ligands. Metal complexes containing
In this paper, we report the synthetic approach to metal com-
plexes of a new CP3 ligand from tris[2-(diphenylphosphino)-
ethyl]methane) (1) as the ligand precursor. The precursor readily
dehydrogenates on heating in the presence of [RuCl2(PPh3)3], to
yield [Ru(C(CH2CH2PPh2)2(CHCH2PPh2))Cl2], where the
metal is bound by three phosphorus donors and a constrained
alkene. The metal−carbon bond is then formed by reduction with
K[Et3BH], to give [Ru(C(CH2CH2PPh2)3)LX] (L = ancillary
ligand; X = H, Cl), where the metal has the full CP3 donor set.
pincer ligands are among the most efficient catalysts for a range
of organic transformations and for the activation of small
2
2
molecules. Commonly, pincer complexes are of the ECsp E
type, where E is typically a neutral donor ligand such as PR2 or
NR2, and these are linked by a m-xylyl bridge. Complexes
3
featuring PCsp P pincer ligands, while currently much rarer, are
of increasing interest3 because the higher flexibility of the
alkane chelate rings, as well as the higher electron-donating
ability of the donor sp3 carbon atom, can result in complexes that
2
are, in some cases, more catalytically active than their PCsp P
RESULTS AND DISCUSSION
analogues.3a,4
■
The precursor to the new CP3 ligand is tris[2-(diphenylphosphino)-
ethyl]methane) (HCP3) (1). This compound was prepared via a
nucleophilic substitution of 3-(2-chloroethyl)-1,5-dichloropentane13
with lithium diphenylphosphide, prepared in situ from the
secondary phosphine and n-BuLi (Scheme 1) in a manner
Podand ligands, such as the trianionic tris(amido)amines5 [N-
(CH2CH2NR)3]3− or the Sacconi ligands [X(CH2CH2PR2)3]
(X = N, P),6 also provide rigid and well-defined coordination
geometries, which can lead to interesting chemical properties and
reactivity patterns.7 The metal complexes with podand ligands
have received much less attention than their pincer counterparts.
Even less well studied are complexes containing podand
ligands where the apical donor is an anionic group 14 element
(i.e., C, Si, Ge, Sn, and Pb)7,8 and there is a covalent metal−
element bond between the apical donor and the metal center.
Podands of this type may be thought of as tetradentate
Scheme 1
3
analogues of the ECsp E-type pincer ligands. Metal complexes
analogous to the reported synthesis of tris[(diphenylphosphino)-
methyl]methane.8c HCP3 (1) was obtained as a colorless solid,
which was purified by recrystallization from a THF/methanol
mixture.
with podand ligands with an anionic apical donor typically have
a strong bond between the apical donor and the metal, and this
serves as a concrete anchor point for the ligand. There is now
growing attention being paid to this class of ligands, and metal
complexes containing the SiP3 ligand, first reported by
Hendriksen et al.9 and Joslin and Stobart,10 are now of interest
in dinitrogen activation chemistry.11 Recently, Lahuerta et al.
Received: August 2, 2011
Published: November 14, 2011
© 2011 American Chemical Society
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The 31P{1H} NMR spectrum of HCP3 (1) shows a single
resonance at δ −15.55 ppm consistent with a symmetrical
compound with three equivalent phosphorus environments.
Scheme 3
1
The H NMR spectrum shows resonances for the protons on
the arms of the ligand at δ 1.40 and 1.78 ppm, and there is a
small one-proton multiplet resonance at δ 1.57 ppm that can be
attributed to the methine proton of the central carbon atom.
The aromatic protons display broad overlapping resonances at
δ 7.12−7.03 ppm.
The reaction of the ligand precursor HCP3 (1) with
Ru(PPh3)3Cl2 in toluene or dichloromethane at room temper-
ature initially produces a green product (2), and a precipitate
deposits slowly from the solution. This compound can be
isolated readily and has limited solubility in C6D6 and
dichloromethane-d2. Complex 2 crystallizes from dichloro-
methane-d2 as a tetramer, [RuCl2(HCP3)]4, with four metal
centers linked by four HCP3 ligands in a square arrangement
(Scheme 2).
Scheme 2
Figure 1. ORTEP depiction of [Ru(C(CH2CH2PPh2)2(
CHCH2PPh2))Cl2] (3). Thermal ellipsoids are shown at the 50%
probability level, and hydrogen atoms are omitted for clarity.
While it is clear from the crystallographic analysis that the
constitution of the complex is correct, the structure could
not be fully refined (see the Supporting Information). Each
ruthenium center exhibits a very slightly distorted square
pyramidal geometry and is coordinated by two chloride ligands
in a mutually trans arrangement and three phosphorus atoms,
one of which occupies the apical position of the pyramid, with
the remaining two being mutually trans. At this stage in the
reaction sequence, the HCP3 ligand acts simply as a bridging
ligand, with two of the phosphorus donors coordinated to one
metal center, while the third arm bridges to a second metal
center. It is also unclear whether this tetrameric arrangement
persists in solution or is favored only in the solid state due to
packing forces.
Table 1. Selected Interatomic Bond Distances (Å) and Angles
(deg) for [Ru(C(CH2CH2PPh2)2(CHCH2PPh2))Cl2] (3)
and [Ru(C(CH2 CH2 PPh2 )2 (CHCH2 PPh2 ))-
(tBuNC)Cl]BPh4 (4a)
3
4a
Bond Lengths (Å)
2.3096(11)
2.4035(12)
2.3816(11)
2.261(7)
Ru(1)−P(1)
Ru(1)−P(2)
Ru(1)−P(3)
Ru(1)−C(1)
Ru(1)−C(2)
Ru(1)−Cl(1)
Ru(1)−L
2.4008(7)
2.3704(8)
2.3989(8)
2.247(3)
2.296(3)
2.4362(7)
2.298(5)
2.4246(12)
2.4840(10)
1.305(6)
When a solution of [RuCl2(HCP3)]4 (2) is heated at reflux in
mesitylene (165 °C), the color changes to brown-yellow and
after about 18 h the main product is [Ru(C(CH2CH2PPh2)2(
CHCH2PPh2))Cl2] (3), which precipitates from solution in
moderate yield (Scheme 3). In this case, one arm of the ligand
dehydrogenates and the metal is coordinated by two chlorides,
three phosphine donors, and a vinyl group, which is tightly
constrained in the coordination sphere.
The X-ray crystal structure of 3 (Figure 1 and Table 1)
confirms the mononuclear, octahedral geometry. The double
bond is disordered over two positions (effectively above and
below the equatorial plane of the complex). The Ru−C
distances are 2.298(5) Å for the central carbon atom and
2.261(7) Å for the CH carbon of the double bond. These Ru−
C distances are comparable to the Ru−C distances in Gusev’s
RuHCl[tBu2PCH2CH2((E)-CHCH)CH2PBut2];14 however,
a
b
2.007(3)
C(1)−C(2)
1.333(5)
Bond Angles (deg)
97.42(4)
P(1)−Ru(1)−P(2)
P(1)−Ru(1)−P(3)
P(2)−Ru(1)−P(3)
Cl(1)−Ru(1)−L
97.64(3)
95.76(3)
161.26(3)
95.00(4)
161.93(4)
a
b
85.75(4)
85.65(8)
a
b
L = Cl(1). L = C(3).
the CC length in Gusev’s complex is slightly longer at
1.401(13) Å compared to 1.305(6) Å in 3.
The 31P{1H} NMR spectrum of 3 displays three doublet of
doublets resonances at δ −54.3, 36.0, and 46.4 ppm. The
coupling constants are 360.3, 35.6, and 24.3 Hz, with the largest
coupling being between the two mutually trans phosphorus
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atoms. The resonance at δ −54.3 ppm is at very high field for a
complex of this type, and this unexpected shift can best be
rationalized by the presence of the magnetically anisotropic
double bond and the strong shielding effect this has on the
phosphorus atom that is constrained directly in the shielding
zone. This rationalization correlates with the X-ray structure,
where P(3) is physically constrained in close proximity to
1
the coordinated olefin. The H NMR spectrum of 3 displays
resonances for the phenyl protons in the usual range of
6.36−8.51 ppm. The olefinic proton appears as a multiplet
at δ 4.52 ppm and the two adjacent allylic protons display
resonances at δ 4.15 and 3.48 ppm. The other protons of the
ligand backbone resonate at shifts characteristic for this type of
complex between δ 1.95 and 2.88 ppm. In the 13C{1H} NMR
spectrum the quaternary carbon resonates at δ 104.6 ppm and
the other olefinic carbon resonates at δ 69.4 ppm, and this shift
compares well to those for other related olefin complexes of
ruthenium.14
The thermal dehydrogenation of long-chain bidentate
phosphines by transition-metal complexes, most notably rhodium
but also ruthenium, has been known for many years.14,15 It is
generally proposed that the reaction proceeds by initial trans-
bridging, bidentate coordination of the phosphorus atoms and
subsequent stepwise or simultaneous loss of hydrogen via mono-
or dihydride intermediates.15b
Figure 2. (a) Structure of the complex cation of [Ru(C-
(CH2CH2PPh2)2(CHCH2PPh2))(tBuNC)Cl]BPh4 (4a), with the
counterion, disordered solvate molecule, and hydrogen atoms omitted
for clarity, and cut-down view (b) along the CN−C(CH3)3 axis
showing the tert-butyl group “sandwiched” between two aromatic rings
and (c) perpendicular to the CN−C(CH3)3 axis.
of a coordinating ligand such as tBuNC, results in the formation
One chloride ligand of [Ru(C(CH2CH2PPh2)2(CHCH2-
of [Ru(C(CH2CH2PPh2)3)Cl(tBuNC)] (5) (Scheme 5), in
PPh2))Cl2] (3) may be displaced by the introduction of a
t
strong donor ligand, such as BuNC or CO, resulting in the
formation of [Ru(C(CH2CH2PPh2)2(CHCH2PPh2))-
(tBuNC)Cl]BPh4 (after anion exchange with NaBPh4) (4a)
and [Ru(C(CH2CH2PPh2)2(CHCH2PPh2))(CO)Cl]Cl
(4b), respectively (Scheme 4).
Scheme 5
Scheme 4
which the central carbon atom of the polydentate ligand is
covalently bound to the metal center.
The 31P{1H} NMR spectrum of [Ru(CP3)Cl(tBuNC)] (5)
displays two resonances: a doublet at δ 39.0 ppm, corresponding to
the two equivalent, mutually trans phosphorus atoms, and a triplet
at δ 30.3 ppm, corresponding to the unique axial phosphorus atom.
The 1H NMR spectrum also clearly reflects the higher symmetry of
the complex. Again, the tert-butyl protons undergo a significant
high-field shift (to δ 0.34 ppm), suggesting that the tert-butyl
groups are sandwiched between two aryl rings of the phosphine
ligand in a manner similar to that observed for complex 4.
This type of hydride-induced metal−carbon bond formation
has been occasionally reported in the past. Gusev and Lough3b
have demonstrated that the reaction of [RuHCl-
{tBu2PCH2CH2((E)-CHCH2)CH2PBut2}] with Li[Et3BH]
under N2 results in the formation of [RuH(N2){CH-
(CH2CH2PBut2)2}]. Similarly, the reaction of [RuHCl(Py)-
{tBu2PCH2CH2((E)-CHCH2)CH2PBut2}] (Py = pyridine)
with CO gives [RuCl(CO){CH(CH2CH2PBut2)2}]. Both
reactions presumably occur via insertion of the coordinated
olefin into a metal−hydride bond. It is likely that a similar
mechanism operates here, with substitution of a chloride ligand
by a hydride, followed by rapid insertion of the alkene into the
metal−hydride bond and coordination of the donor ligand
giving the observed product.
Complex 4a was characterized crystallographically. The
structure is a distorted octahedron with a structure very similar
to that of the parent complex 3 (Figure 2 and Table 1). The
double bond is again disordered over two positions, although in
this case, one element of the disorder is more heavily favored
over the other. The chloride ligand trans to the equatorial
t
phosphorus atom has been displaced, and the BuNC ligand
binds in its place.
The 31P{1H} NMR spectra of 4a,b are very similar to that of
the parent compound, with three distinct resonances
corresponding to three unique phosphorus environments, one
1
of which exhibits a significant shift to high field. In the H
NMR spectrum of 4a, the resonance corresponding to the
tBuNC protons also undergoes a significant shift to high field
from δ 1.45 ppm in the free ligand to δ 0.61 ppm. The reason
for this shift is clearly visible in the crystal structure, where the
tert-butyl group is neatly sandwiched in the shielding zone
between the faces of two of the aromatic substituents on the
coordinated phosphines (Figure 2b,c).
The reaction of [Ru(C(CH2CH2PPh2)2(CHCH2PPh2))-
Cl2] (3) with 1 equiv of K[Et3BH] in toluene, in the presence
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t
The reaction of 3 with an excess of K[Et3BH], in the
presence of a coordinating ligand such as tBuNC or CO results
in the formation of [Ru(C(CH2CH2PPh2)3)(H)(tBuNC)] (6a)
or [Ru(C(CH2CH2PPh2)3)(H)(CO)] (6b), respectively
(Scheme 5). The 31P{1H} NMR spectrum of 6a is similar to
that of 5, with the doublet resonance of the axial phosphines at
δ 67.2 ppm and the triplet resonance of the equatorial
The shift of the BuNC ligand from trans to phosphorus
in 5 to trans to carbon in 6a suggests that the substitution of
chloride probably proceeds via a five-coordinate intermediate
(Scheme 6).
Scheme 6
1
phosphine at δ 54.9 ppm. In the H NMR spectrum, there is a
phosphorus-coupled hydride resonance at δ −8.58 ppm which
appears as a doublet of triplets with coupling constants (2JPH)
of 73.9 Hz to the equatorial phosphine and 23.7 Hz to the two
equivalent axial phosphines. The difference in magnitude
between these two constants suggests that the hydride ligand
is positioned trans to the equatorial phosphine, in contrast to
the arrangement observed for 4 and 5. This proposal is further
Complexes 4a, 5, and 6a have νCN bands in their IR spectra at
2173, 2114, and 2019 cm−1, respectively. The νCN band is
1
t
16
observed at 2136 cm−1 for free BuNC. The shift of νCN to
higher frequencies upon complexation of an isocyanide to a metal
center is well precedented17 and therefore is not unexpected for 4a.
In the carbonyl complexes, νCO is at 2022 cm−1 for 4b and 1893
cm−1 for 6b. The quite dramatic reduction in νCN (6a) or νCO (6b)
is consistent with the geometry change observed upon formation of
these complexes. In 6a and 6b, the isonitrile and/or carbonyl ligand
is located trans to the coordinated central alkyl carbon of the CP3. A
strong, high-field σ-donor in the trans position provides strong π
back-donation of electron density from the metal into the anibonding
orbital of the carbonyl (or isonitrile) ligand, giving lower C−O (and
C−N) stretching frequencies.18
t
supported by the H NMR shift of the BuNC protons, which
are not highly shielded in this case and resonate at δ 1.55 ppm.
The NMR spectra of 6b are consistent with the proposed
structure, with the 31P{1H} spectrum being nearly indistin-
guishable from that of 6a. The hydride resonance is clearly
1
visible in the H NMR spectrum, and the coupling constants
again suggest that the hydride ligand occupies a position trans
to the equatorial phosphine ligand. The resonance for the
coordinated carbonyl ligand is clearly visible in the 13C{1H,31P}
NMR spectrum as a singlet at δ 208.1 ppm.
The X-ray structural analysis of 6a (Figure 3 and Table 2) confirms
that the hydride ligand occupies the site trans to the equatorial
Complex 5 has a νCN band similar to those of the
ruthenium(II) cyclopentadienyl complexes [(Cp)Ru(PPh3)X-
(tBuNC)] (X = Cl, 2108 cm−1; X = H, 2104 cm−1),19 while the
band for 6a is almost identical with that of [(Cp*)Ru(PPh3)-
H(tBuNC)] (νCN 2011 cm−1).20
Like complexes of the pincer ligands, the complexes of the
carbon-centered podands exhibit signs of being active catalysts for
a range of transformations. In the presence of isopropyl alcohol,
6b catalyzes the reduction of carbonyls to the corresponding
alcohols by transfer hydrogenation (Scheme 7 and Table 3).
Scheme 7
Figure 3. Structure of [Ru(C(CH2CH2PPh2)3)(H)(CNtBu)] (6a).
Selected hydrogen atoms are removed for clarity, and only a single
component of the disordered Bu group is shown.
With a catalyst loading of 2 mol %, acetophenone is reduced
almost quantitatively to 1-phenylethanol in 3.5 h in isopropyl
alcohol at reflux. Reducing the catalyst loading and reaction
time results in a decrease in catalyst performance. The addition
of the carbonyl-scavenging reagent Me3N·O appears to have a
detrimental effect on catalytic performance, while the presence
of base appears to be beneficial, although the reason for this is
unclear.
The hydride-induced metal−carbon bond formation de-
scribed in this paper represents a powerful and direct route for
the preparation of the carbon-centered podands. The fact that we
now have an effective synthetic route to complexes of the carbon-
centered podands permits the chemistry of these pincer-type
complexes to be explored in more depth. We are currently
undertaking further studies to further probe the mechanisms of
the reactions described herein.
t
Table 2. Selected Interatomic Distances (Å) and Angles
(deg) for [Ru(C(CH2CH2PPh2)3)(H)(CNtBu)] (6a)
Bond Lengths (Å)
Ru(1)−C(1)
Ru(1)−C(2)
Ru(1)−H(1)
2.2354(16)
1.9540(18)
1.61(2)
Ru(1)−P(1)
Ru(1)−P(2)
Ru(1)−P(3)
2.2956(4)
2.3215(4)
2.2836(5)
Bond Angles (deg)
C(1)−Ru(1)−C(2)
C(1)−Ru(1)−H(1)
C(2)−Ru(1)−H(1)
175.75(7)
77.8(8)
C(2)−Ru(1)−P(2)
P(1)−Ru(1)−P(3)
101.13(5)
156.628(16)
98.0(8)
phosphine. The tert-butyl group, which is disordered equally across
two positions, is no longer sandwiched between aryl rings.
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Yield: 0.0411 g (85%). Anal. Found: C, 61.82; H, 5.36. Calcd for
Table 3. Transfer Hydrogenation of Ketones in Isopropyl
Alcohol using [Ru(CP3)H(CO)] (6b) as Catalyst
a
C
172H172P12Ru4Cl8·CH2Cl2: C, 61.40; H, 5.18.
[Ru(C(CH2CH2PPh2)2(CHCH2PPh2))Cl2] (3). A mixture of Ru-
cat. loading
(mol %)
additive
(amt (mol %))
time
(h)
conversn
(%)
(PPh3)3Cl2 (2.04 g, 2.15 mmol) and CP3 (1; 1.405 g, 2.15 mmol) in
mesitylene (100 mL) was heated to reflux. The mixture immediately
turned dark green, and reflux was continued for 18 h. The mixture was
cooled, and the yellow precipitate was collected by filtration, washed
with mesitylene (20 mL) and pentane (2 × 20 mL), and dried in
vacuo. Yield: 0.853 g (48%). Anal. Found: C, 62.71; H, 4.88, Calcd for
C43H41Cl2P3Ru: C, 62.78; H, 5.02. 31P{1H} NMR (C6D6, 121.5
MHz): δ −54.3 (dd, 2JPP = 360.3 and 35.6 Hz), 36.0 (dd, 2JPP = 360.3
substrate
b
acetophenone
2
1
1
1
KOH (40)
KOH (40)
KOtBu (11)
3.5
1
>99
b
66
c
2
41
c
KOtBu (11),
2
33
Me3N·O (2)
c
1
0
1
1
2
2
2
2
14
2
1
c
c
c
and 24.3 Hz), 46.4 (dd, JPP = 24.3 and 35.6 Hz) ppm. H NMR
(C6D6, 300 MHz): δ 1.95 (m, 1H, trans-PCH2CH2), 1.99 (m, 2H,
trans-PCH2CH2), 2.06 (m, 2H, cis-PCH2CH2), 2.34 (m, 1H, trans-
PCH2CH2), 2.78 (m, 1H, cis-PCH2CH2), 2.88 (m, 1H, cis-PCH2CH2),
3.48 (m, 1H, trans-PCH2CHC), 4.15 (m, 1H, trans-PCH2CHC), 4.52
(m, 1H, trans-PCH2CHC), 6.36−8.51 (30H, C6H5) ppm. 13C{1H}
NMR (C6D6, 75 MHz): δ 27.1 (m, trans-PCH2CH2), 32.1 (m, trans-
PCH2CHC), 33.0 (m, trans-PCH2CH2), 33.1 (m, cis-PCH2CH2), 36.6
(m, cis-PCH2CH2), 69.4 (m, trans-PCH2CHC), 104.6 (m, quarternary,
trans-PCH2CHC), 126.0−138.2 (m, PC6H5) ppm. Crystals suitable for
X-ray diffraction were grown by recrystallization from benzene.
[Ru(C(CH2CH2PPh2)2(CHCH2PPh2))(tBuNC)Cl]BPh4 (4a). A
solution of Ru(C(CH2CH2PPh2)2(CHCH2PPh2))Cl2 (3) (0.1251 g,
KOtBu (11)
KOtBu (11)
KOtBu (11),
Me3N·O (2)
7
55
50
cyclopentanone
a
i
Conditions: 10 mL of PrOH, 90 °C (oil bath temperature), 1.2
b
c
mmol of substrate. Determined by NMR. Determined by GC.
EXPERIMENTAL SECTION
■
General Information. All manipulations were carried out using
standard Schlenk techniques. Air-sensitive NMR samples were
prepared in an argon-filled glovebox, with solvent vacuum-transferred
into an NMR tube fitted with a concentric Teflon valve. Benzene-d6
and tetrahydrofuran-d8 were dried over sodium/benzophenone ketyl
and vacuum-distilled immediately prior to use. Dichloromethane-d2
was dried over molecular sieves. Tetrahydrofuran, pentane, dichloro-
methane, and toluene were dried using an Innovative Technology
solvent purification system. Hexane and mesitylene were dried over
and distilled from sodium. Ethanol was dried over and distilled from
diethoxymagnesium. All compressed gases were obtained from Linde
gases. 1H, 31P, and 13C NMR spectra were recorded on Bruker
DPX300, Avance III 400, Avance III 500, and Avance III 600 NMR
spectrometers; 31P NMR spectra were referenced using the unified
scale.21 Ru(PPh3)3Cl2 was prepared according to the literature
method.22
t
0.152 mmol) in DCM was treated with BuNC (36 μL, 0.318 mmol).
The mixture was stirred at room temperature for 40 min before the
solvent was removed under reduced pressure to give [Ru(C-
(CH2CH2PPh2)2(CHCH2PPh2))(tBuNC)Cl]Cl. Yield: quantita-
2
tive. 31P{1H} NMR (121 MHz, CD2Cl2): δ 29.83 (dd, JPP
=
2
285.7, 27.8 Hz, 1P), 25.86 (dd, JPP = 38.7, 27.8 Hz, 1P), −65.07
(dd, JPP = 285.7, 38.7 Hz, 1P) ppm. The complex was dissolved in
2
EtOH (20 mL), and NaBPh4 (0.0627 g, 0.318 mmol) was added as a
single solid portion. The resultant precipitate was filtered, washed with
EtOH (15 mL) and pentane (15 mL), and dried in vacuo.
[Ru(C(CH2CH2PPh2)2(CHCH2PPh2))(tBuNC)Cl]BPh4 was re-
crystallized from acetone/methanol to yield a pale yellow powder.
Yield: 0.157 g (87%). Crystals suitable for X-ray diffraction were grown
by vapor diffusion of hexane into an acetone solution. Anal. Found: C,
71.89; H, 6.11; N, 1.15. Calcd for C72H70BClNP3Ru·C3H6O: C, 72.19;
H, 6.14; N, 1.12. 31P{1H} NMR (242 MHz, CD2Cl2): δ 29.56 (dd,
2JPP = 289.0, 27.9 Hz, 1P), 25.67 (dd, 2JPP = 39.6, 27.9 Hz, 1P), −65.66
(dd, 2JPP = 289.0, 39.6 Hz, 1P) ppm. 1H NMR (600 MHz, CD2Cl2): δ
8.20 (br, 1H, ArH), 8.08 (m, 2H, ArH), 7.62−7.51 (br m, 5H, ArH),
7.47−7.35 (m, 14H, ArH + BPh4), 7.12 (m, 10H, ArH + BPh4), 7.07−
6.98 (m, 3H, ArH), 6.98−6.90 (m, 5H, BPh4 + ArH), 6.89−6.78 (m,
8H, ArH), 6.62 (m, 2H, ArH), 3.81 (m, 3H, 3 × CHH), 3.34 (m, 2H,
2 × CHH), 2.87 (m, 2H, 2 × CHH), 2.42 (m, 2H, 2 × CHH), 2.14
(m, 1H, CHH), 1.82 (m, 1H, CHH), 0.61 (s, 9H, C(CH3)3) ppm.
Tris[(2-diphenylphosphino)ethyl]methane) (1; CP3). n-Butyl-
lithium (1.6 M in hexanes, 20 mL, 32 mmol) was added slowly to a
solution of diphenylphosphine (5.6 mL, 32 mmol) in tetrahydrofuran
(50 mL) at 0 °C. The red solution of lithium diphenylphosphide was
stirred at 0 °C for 1 h, and it was then added slowly to a solution of
3-[(2-chloroethyl)]-1,5-dichloropentane13 (2.04 g, 10.0 mmol) in
THF (80 mL) at 0 °C. The reaction mixture was stirred at 0 °C for 1 h
and then at room temperature overnight, during which time the red
color faded to light yellow. The solvent was completely removed
under reduced pressure to afford a white solid with some orange oil.
Deoxygenated water (20 mL) was added slowly to the residue,
followed by benzene (80 mL). The mixture was then transferred to a
separating funnel under nitrogen and the organic layer was separated,
washed with water (2 × 10 mL), and dried over magnesium sulfate.
After filtration to remove the drying agent, the solvent was removed
completely to afford a white solid. The crude solid product was
recrystallized from tetrahydrofuran/methanol to afford CP3 as a white
solid (5.32 g, 82%). Anal. Found: C, 78.94; H, 6.59. Calcd for
C43H43P3: C, 79.12; H, 6.64. ESI-MS (DCM) (m/z, %): 653.23 ([M +
H]+, 100%). 31P{1H} NMR (121.5 MHz, C6D6): δ −15.55 (s) ppm.
1H NMR (300 MHz, C6D6): δ 7.43−7.37 (m, 12H, ArH), 7.12−7.03
(m, 18H, ArH), 1.78 (m, 6H, PCH2), 1.57 (m, 1H, CH), 1.40 (m, 6H,
1
13C{1H} NMR (150 MHz, CD2Cl2): δ 164.50 (1:1:1:1 q, JBC = 49.5
Hz, Cipso BPh4), 145.03 (m, Ru−CN), 138.29 (dd, JPC = 34.7, 3.3 Hz,
ArC), 137.69 (dd, JPC = 45.0, 2.7 Hz, ArC), 136.40 (br, BPh4), 135.16
(dd, JPC = 39.2, 6.1 Hz, ArC), 134.53 (dd, JPC = 41.2, 2.3 Hz, ArC),
132.97 (dm, JPC = 34.5 Hz, ArC), 132.03 (d, JPC = 8.1 Hz, ArCH),
131.74 (d, JPC = 9.0 Hz, ArCH), 131.52 (d, JPC = 1.8 Hz, ArCH),
131.03 (d, JPC = 7.2 Hz, ArCH), 130.94 (d, JPC = 2.1 Hz, ArCH),
130.42 (br, ArCH), 130.40 (d, JPC = 8.1 Hz, ArCH), 130.21 (d, JPC
2.1 Hz, ArCH), 130.03 (d, JPC = 2.1 Hz, ArCH), 129.75 (dd, JPC
25.3, 5.9 Hz, ArC), 129.48 (d, JPC = 2.1 Hz, ArCH), 129.38 (d, JPC
=
=
=
9.9 Hz, ArCH), 129.24 (d, JPC = 9.5 Hz, ArCH), 129.20 (d, JPC = 2.2
Hz, ArCH), 129.07 (d, JPC = 9.2 Hz), 128.98 (d, JPC = 9.4 Hz, ArCH),
128.96 (d, JPC = 9.0 Hz, ArCH), 128.81 (d, JPC = 9.0 Hz, ArCH),
126.05 (m, BPh4), 122.19 (s, BPh4), 109.36 (m, CCH), 61.01 (d,
CHCH2) ppm. 13C{1H} NMR (75 MHz, C6D6): δ 140.20 (d, 1JP−C
=
15.3 Hz, ipso-C), 133.55 (d, JP−C = 18.9 Hz, o- or m-C of Ph), 129.04
(d, JP−C = 7.1 Hz, m- or o-C of Ph), 128.90 (s, p-C of Ph), 41.33 (q,
J
PC = 10.3 Hz, CCH), 58.83 (s, C(CH3)3), 34.77 (d, JPC = 28.1 Hz,
2
3JP−C = 12.4 Hz, CH), 28.55 (d, JP−C = 16.7 Hz, CHCH2), 24.75 (d,
CH2), 32.55 (d, JPC = 12.5 Hz, CH2), 32.15 (d, JPC = 6.6 Hz, CH2),
31.55 (d, JPC = 29.7 Hz, CH2), 29.01 (d, JPC = 31.3 Hz, CH2), 29.00 (s,
C(CH3)3) ppm. νCN (KBr): 2173 cm−1.
1JP−C = 12.4 Hz, PCH2) ppm.
[Ru(HC{CH2CH2PPh2}3)Cl2]4 (2). A solution of Ru(PPh)3Cl2
(0.0272 g, 0.0284 mmol) and CP3 (1; 0.0213 g, 0.326 mmol) in
CH2Cl2 (1 mL) was allowed to stand at room temperature for 10 days.
Large, dark green blocks of [Ru(HC{CH2CH2PPh2}3)Cl2]4 precipi-
tated from solution; these were collected and dried in vacuo.
[Ru(C(CH2CH2PPh2)2(CHCH2PPh2))(CO)Cl]Cl (4b). A J. Young
NMR tube was charged with Ru(C(CH2CH2PPh2)2(CHCH2-
PPh2))Cl2 (5) and CD2Cl2. The mixture was freeze−pump−thaw
degassed three times and then back-filled with carbon monoxide.
6437
dx.doi.org/10.1021/om200718j|Organometallics 2011, 30, 6433−6440

Organometallics
Article
The solvent was removed under reduced pressure to yield 4b as a pale
yellow powder. Yield: quantitative. Anal. Found for C44H41Cl2OP3Ru:
C, 59.71; H, 4.96. Calcd: C, 59.94; H, 4.69. 31P{1H} NMR (202 MHz,
CHH), 1.66 (m, 2H, CH2), 1.58 (m, 4H, 2 × CH2), 0.34 (s, 9H,
C(CH3)3) ppm. 13C{1H} NMR (125 MHz, CD2Cl2): δ 158.43 (Ru−
CN), 142.48 (ArC), 139.59 (ArC), 138.99 (ArC), 132.79 (br, ArCH),
131.40 (ArCH), 130.91 (ArCH), 128.87 (ArCH), 128.55 (ArCH),
128.32 (ArCH), 128.08 (ArCH), 128.04 (ArCH), 127.77 (ArCH),
55.64 (C(CH3)3), 55.48 (Ru−C), 46.89 (CH2), 42.47 (CH2), 32.48
(CH2), 29.15 (C(CH3)3), 26.68 (CH2) ppm. νCN (KBr): 2114 cm−1.
[Ru(C(CH2CH2PPh2)3)(H)(CNtBu)] (6a). A solution of [Ru(C-
(CH2CH2PPh2)2(CHCH2PPh2))Cl2] (3; 0.0519 g, 0.0631 mmol)
in DCM (10 mL) was treated with t-BuNC (12 μL, 0.107 mmol). The
mixture was stirred at room temperature for 30 min before the
volatiles were removed under reduced pressure. The residue was
suspended in toluene (5 mL) and treated dropwise with a solution of
K[Et3BH] (0.0200 g, 0.145 mmol) in toluene (5 mL). The solution,
which changed color to very pale yellow, was stirred at room
temperature for 1 h and then filtered and concentrated under reduced
pressure. The residue was extracted with pentane (2 × 20 mL),
filtered, and concentrated to give [Ru(C(CH2CH2PPh2)3)(H)-
(CNtBu)] (6a) as a white powder. Yield: 0.0267 g (51%). Crystals
suitable for X-ray analysis formed from a cooled saturated heptane
solution. Anal. Found: C, 68.80; H, 6.27; N, 1.59. Calcd for
C48H52NP3Ru: C, 68.89; H, 6.26; N, 1.67. 31P{1H} NMR (121
MHz, THF-d8): δ 67.2 (d, JPP = 16.0 Hz, 2P), 54.9 (t, 1P) ppm. H
NMR (600.13 MHz, THF-d8): δ 8.08 (m, 4H, ArH), 7.24 (m, 4H,
ArH), 7.18 (m, 2H, ArH), 7.12 (br m, 4H, ArH), 7.03 (m, 4H, ArH),
6.89 (m, 2H, ArH), 6.78 (m, 6H, ArH), 6.65 (m, 4H, ArH), 2.57−2.35
(m, 6H, CH2), 1.75−1.24 (m, 6H, CH2), 1.55 (s, 9H, C(CH3)3),
−8.58 (dt, 2JPH = 73.9, 23.7 Hz, 1H, Ru-H) ppm. 13C{1H} NMR (150
MHz, THF-d8): δ 145.01 (Ru−CN), 141.49 (ArC), 141.40 (ArC),
141.15 (ArC), 133.86 (ArCH), 130.30 (ArCH), 130.24 (ArCH),
127.70 (ArCH), 127.15 (ArCH), 126.86 (ArCH), 126.66 (ArCH),
126.61 (ArCH), 126.38 (ArCH), 67.57 (Ru−C), 54.78 (C(CH3)3),
46.65 (CH2), 43.10 (CH2), 35.73 (CH2), 34.73 (CH2), 30.99
(C(CH3)3) ppm. νCN (KBr): 2019 (νCN).
2
CD2Cl2): δ 19.0 (dd, 2JPP = 42.8, 30.8 Hz, 1P), 16.5 (dd, JPP1 = 254.2,
2
30.8 Hz, 1P), −77.6 (dd, JPP = 254.2, 42.8 Hz, 1P) ppm. H NMR
(500 MHz, CD2Cl2): δ 8.22 (m, 2H, ArH), 7.64 (m, 2H, ArH), 7.57
(m, 4H, ArH), 7.47 (m, 3H, ArH), 7.37 (m, 2H, ArH), 7.33 (m, 2H,
ArH), 7.26 (m, 4H, ArH), 7.09 (m, 2H ArH), 7.01 (m, 2H, ArH), 6.95
(m, 1H, ArH), 6.86 (m, 4H, ArH), 4.92 (m, 1H, CHH), 4.74 (m, 1H,
C  C H ) , 4 . 2 6 ( m , 1 H , C H H ) , 3 . 9 9 ( d b r m ,
JPH = 38.4 Hz, 1H, CHH), 3.65 (m, 1H, CHH), 3.29 (m, 1H,
CHH), 3.16 (m, 1H, CHH), 3.09−2.89 (m, 3H, 3 × CHH), 1.32 (m,
1H, CHH) ppm. 13C{1H} NMR (75 MHz, CD2Cl2): δ 196.3 (m,
CO), 136.94 (dd, JPC = 41.6, 2.4 Hz, ArC), 135.68 (d, JPC = 41.4 Hz,
ArC), 133.60 (m, ArC), 133.34 (m, ArC), 133.05 (m, ArC), 132.53
(dd, JPC = 9.9, 1.4 Hz, ArCH), 131.93 (dd, JPC = 9.7, 1.1 Hz, ArCH),
131.68 (d, JPC = 2.51 Hz, ArCH), 131.51 (d, JPC = 7.5 Hz, ArCH),
131.25 (d, JPC = 7.4 Hz, ArCH), 130.87 (d, JPC = 8.2 Hz, ArCH),
130.62 (d, JPC = 2.7 Hz, ArCH), 130.48 (m, 2 × ArCH), 130.23 (d, JPC
= 2.5 Hz, ArCH), 130.13 (d, JPC = 2.4 Hz, ArCH), 129.81 (d, JPC = 8.2
Hz, ArCH), 129.52−129.16 (m, 4 × ArCH), 128.87 (d, JPC = 9.2 Hz,
ArCH), 128.51 (d, JPC = 9.1 Hz, ArCH), 127.56 (m, ArC), 119.8 (m,
CCH), 66.49 (dd, JPC = 12.7, 1.1 Hz, CCH), 39.45 (dd, JPC = 8.2,
2
1
2.4 Hz, CH2), 35.67 (dd, JPC = 29.5, 0.7 Hz, CH2), 33.22 (dd, JPC
=
29.6, 3.1 Hz, CH2), 30.28 (d, JPC = 7.3 Hz, CH2), 29.64 (dd, JPC = 33.4,
2.4 Hz, CH2) ppm. νCO (Fluorolube): 2022 cm−1.
[Ru(C(CH2CH2PPh2)3)(Cl)(CNtBu)] (5). A solution of [Ru(C-
(CH2CH2PPh2)2(CHCH2PPh2))Cl2] (3; 0.0935 g, 0.114 mmol)
t
and BuNC (16 μL, 0.141 mmol) in DCM (10 mL) was stirred at
room temperature for 40 min before the volatiles were removed under
reduced pressure. The residue was suspended in toluene (10 mL), and
a solution of K[Et3BH] (0.0164 g, 0.119 mmol) in toluene (10 mL)
was added. The suspension rapidly cleared and the mixture was stirred
for a further 10 min. The volatiles were removed under reduced
pressure and the residue recrystallized from toluene to give
[Ru(C(CH2CH2PPh2)3)(Cl)(tBuNC)] as a pale yellow solid. Yield:
0.0627 g (63%). Anal. Found: C, 66.31; H, 5.80; N, 1.47. Calcd for
C48H51ClNP3Ru: C, 66.16; H, 5.90; N, 1.61. 31P{1H} NMR (202
[Ru(C(CH2CH2PPh2)3)(H)(CO)] (6b). A solution of [Ru(C-
(CH2CH2PPh2)2(CHCH2PPh2))Cl2] (3; 0.1866 g, 0.227 mmol)
in toluene (15 mL) was treated with a solution of K[Et3BH] (0.0747 g,
0.541 mmol) in toluene (5 mL). An initial color change to deep red-
brown was observed; the mixture then lightened slightly. After 5 min,
CO was bubbled through the mixture for a further 1 h. The mixture
was filtered, and the volatiles were removed under reduced pressure.
The oily residue was washed with pentane (2 × 20 mL) and dried in
vacuo to give [Ru(C(CH2CH2PPh2)3)(H)(CO)] (6b) as a pale yellow
2
2
MHz, CD2Cl2): δ 39.01 (d, JPP = 34.7 Hz, 2P), 30.25 (t, JPP = 34.7
1
Hz, 1P) ppm. H NMR (600 MHz, CD2Cl2): δ 8.29 (br, 4H, ArH),
7.40 (m, 4H, ArH), 7.30 (apparent t, 8H, ArH), 7.21 (apparent t, 2H,
ArH), 6.87 (apparent t, 2H, ArH), 6.79 (m, 6H, ArH), 6.69 (m, 4H,
ArH), 2.84 (m, 2H, 2 × CHH), 2.27 (m, 2H, CH2), 2.20 (m, 2H, 2 ×
Table 4
3
4a
6a
chem formula
formula mass/g mol−1
C55H53Cl2P3Ru
978.85
C75H76BClNOP3Ru
1247.61
C48H52NP3Ru
836.89
cryst syst
orthorhombic
15.501(3)
16.367(3)
17.976(3)
90
triclinic
monoclinic
10.9740(4)
20.8634(8)
18.2687(7)
90
a/Å
13.7351(12)
15.1183(6)
17.0756(7)
115.483(2)
99.362(3)
90.794(2)
3144.2(3)
155(2)
b/Å
c/Å
α/deg
β/deg
90
91.7040(10)
90
γ/deg
unit cell vol/Å3
90
4560.6(13)
100(2)
P212121
4
4180.9(3)
152(2)
P21/n
temp/K
space group
P1
̅
no. of formula units per unit cell, Z
no. of rflns measd
no. of indep rflns
Rint
2
4
47 778
10 073
0.0820
39 812
11 014
0.0820
0.0488
0.0819
0.0708
0.0885
831000
35 289
9085
0.0360
final R1 values (I > 2σ(I))
final wR2(F2) values (I > 2σ(I))
final R1 values (all data)
final wR2(F2) values (all data)
CCDC no.
0.0488
0.0245
0.0819
0.0639
0.0708
0.0315
0.0885
0.0704
830999
831001
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dx.doi.org/10.1021/om200718j|Organometallics 2011, 30, 6433−6440

Organometallics
Article
́
powder. Yield: 0.0997 g, (57%). Anal. Found: C, 67.33; H, 5.84. Calcd
for C44H43OP3Ru: C, 67.60; H, 5.54. 31P{1H} NMR (121 MHz, THF-
d8): δ 67.8 (d, 2JPP = 15.9 Hz, 2P), 55.0 (t, 1P) ppm. 1H NMR (300.3
MHz, THF-d8): δ 8.00 (m, 4H, ArH), 7.27 (m, 6H, ArH), 7.14 (m,
4H, ArH), 7.02 (m, 4H, ArH), 6.94 (m, 2H, ArH), 6.86 (m, 6H, ArH),
6.70 (m, 4H, ArH), 2.70−2.35 (br m, 6H, CH2), 1.90−1.41 (br m, 6H,
Quim. Mex. 2004, 48, 338−346. (g) Morales-Morales, D.; Jensen, C.
́
M. The Chemistry of Pincer Compounds; Elsevier: Amsterdam, 2007.
(h) Goldberg, K. I.; Goldman, A. S. Activation and Functionalization of
C−H Bonds; American Chemical Society: Washington DC, 2004.
(3) (a) Leis, W.; Mayer, H. A.; Kaska, W. C. Coord. Chem. Rev. 2008,
252, 1787−1797. (b) Gusev, D. G.; Lough, A. J. Organometallics 2002,
21, 5091−5099. (c) Errington, R. J.; Mcdonald, W. S.; Shaw, B. L. J.
Chem. Soc., Dalton Trans. 1982, 1829−1835. (d) Castonguay, A.;
Beauchamp, A. L.; Zargarian, D. Organometallics 2008, 27, 5723−5732.
(e) Zhao, J.; Goldman, A. S.; Hartwig, J. F. Science 2005, 307, 1080−
1082. (f) Olsson, D.; Arunachalampillai, A.; Wendt, O. F. Dalton
Trans. 2007, 5427−5433. (g) McLoughlin, M. A.; Keder, N. L.;
Harrison, W. T. A.; Flesher, R. J.; Mayer, H. A.; Kaska, W. C. Inorg.
Chem. 1999, 38, 3223−3227. (h) Kuznetsov, V. F.; Lough, A. J.;
Gusev, D. G. Inorg. Chim. Acta 2006, 359, 2806−2811.
2
CH2), −8.07 (dt, JPH = 76.2, 22.2 Hz, 1H, Ru-H) ppm. 13C{1H,31P}
NMR (125.7 MHz, C6D6): δ 208.1 (CO), 143.9 (ArC), 140.1 (ArC),
139.9 (ArC), 134.4 (ArCH), 131.1 (ArCH), 130.9 (ArCH), 129.4
(ArCH), 128.5 (ArCH), 128.35 (ArCH), 128.29 (ArCH), 128.1
(ArCH), 127.9 (ArCH), 71.6 (Ru-C), 47.3 (CH2), 43.9 (CH2), 36.3
(CH2), 35.5 (CH2) ppm. νCO (Fluorolube): 1893 cm−1.
Transfer Hydrogenation. All catalytic reactions were carried out
under N2. The transfer hydrogenation of acetophenone in the
presence of KOtBu is given as a representative example. [Ru(C-
(CH2CH2PPh2)3)(H)(CO)] (6b; 0.0287 g, 0.0367 mmol) and KOtBu
(0.0454 g, 0.809 mmol) were dissolved in isopropyl alcohol.
Acetophenone (167 μL, 1.43 mmol) was added and the mixture
placed in a preheated oil bath at 90 °C for the required time. The
solvent was distilled at atmospheric pressure and the residue analyzed
(4) (a) Castonguay, A.; Sui-Seng, C.; Zargarian, D.; Beauchamp, A.
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̈
Andersson, C. Dalton Trans. 2002, 1396−1400. (c) Ohff, M.; Ohff, A.;
van der Boom, M. E.; Milstein, D. J. Am. Chem. Soc. 1997, 119,
11687−11688.
1
by H NMR spectroscopy. Where GC was used for the analysis, the
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reaction mixture was cooled and 1,4-dioxane (20 μL) was added as an
internal standard. The mixture was then analyzed by GC on a SGE
Sol-Gel Wax column.
(6) Stoppioni, P.; Mani, F.; Sacconi, L. Inorg. Chim. Acta 1974, 11,
227−230.
X-ray Structure Determinations. Single crystals of 2, 4a, and 6a
were attached, with Exxon Paratone N, to a short length of fiber
supported on a thin piece of copper wire inserted in a copper
mounting pin. The crystal was quenched in a cold nitrogen gas stream
from an Oxford Cryosystems Cryostream. A Bruker Kappa APEXII
area detector diffractometer employing graphite-monochromated Mo
Kα radiation generated from a fine-focus sealed tube was used for the
data collection. The data integration and reduction were undertaken
with APEX2,23 and subsequent computations were carried out with
the X-Seed24 graphical user interface. The structures were solved by
direct methods with SHELXS-9725 and extended and refined with
SHELXL-97.25 The non-hydrogen atoms in the asymmetric unit were
modeled with anisotropic displacement parameters. A riding atom
model with group displacement parameters was used for the hydrogen
atoms.
(7) Kuzu, I.; Krummenacher, I.; Meyer, J.; Armbruster, F.; Breher, F.
Dalton Trans. 2008, 5836−5865.
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Zsolnai, L.; Kremer, R. Angew. Chem., Int. Ed. 1991, 30, 303−304.
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Asam, A.; Walter, O.; Buechner, M.; Zsolnai, L. Chem. Ber. 1995, 128,
63−70. (e) Seitz, T.; Asam, A.; Huttner, G.; Walter, O.; Zsolnai, L. Z.
Naturforsch. B 1995, 50, 1287−1306. (f) Urtel, K.; Frick, A.; Huttner,
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Inorg. Chem. 2000, 33−50. (g) Mautz, J.; Heinze, K.; Wadepohl, H.;
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504−505.
(11) (a) Takaoka, A.; Mendiratta, A.; Peters, J. C. Organometallics
2009, 28, 3744−3753. (b) Whited, M. T.; Mankad, N. P.; Lee, Y. H.;
Oblad, P. F.; Peters, J. C. Inorg. Chem. 2009, 48, 2507−2517.
(c) Mankad, N. P.; Whited, M. T.; Peters, J. C. Angew. Chem., Int. Ed.
2007, 46, 5768−5771. (d) Lee, Y.; Mankad, N. P.; Peters, J. C. Nat.
Chem. 2010, 2, 558−565.
All calculations were performed using the crystallographic and
structure refinement data summarized in Table 4.
ASSOCIATED CONTENT
* Supporting Information
■
S
A CIF file giving crystallographic data for 3, 4a, and 6a and a
figure showing the molecular structure of 2. This material is
available free of charge via the Internet at http://pubs.acs.org.
(12) Ciclosi, M.; Lloret, J.; Estevan, F.; Lahuerta, P.; Sanau, M.;
Perez-Prieto, J. Angew. Chem., Int. Ed. 2006, 45, 6741−6744.
(13) Baumeister, J. M.; Alberto, R.; Ortner, K.; Spingler, B.;
Schubiger, P. A.; Kaden, T. A. Dalton Trans. 2002, 4143−4151.
(14) Gusev, D. G.; Lough, A. J. Organometallics 2002, 21, 2601−
2603.
AUTHOR INFORMATION
Corresponding Author
*Tel: (+61) 2 9385 2700. Fax: (+61) 2 9385 8008. E-mail:
L.Field@unsw.edu.au.
■
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ACKNOWLEDGMENTS
We acknowledge the Australian Research Council and the
University of New South Wales for funding.
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