Synthetic, spectral, structural, and catalytic aspects of some piano-stool complexes containing 2-(2-Diphenylphosphanylethyl)pyridine

Article abstract of DOI:10.1002/ejic.200901004

Reactions of the complexes [(η⁵-C₅H ₅)Ru(PPh₃)₂Cl], [{(η⁶a:rene) Ru(μ-Cl)Cl}₂] (η⁶-arene = C₆H ₆, C₁₀H₁₄, and C₆

Full text of DOI:10.1002/ejic.200901004

FULL PAPER
DOI: 10.1002/ejic.200901004
Synthetic, Spectral, Structural, and Catalytic Aspects of Some Piano-Stool
Complexes Containing 2-(2-Diphenylphosphanylethyl)pyridine
Prashant Kumar,[a] Mahendra Yadav,[a] Ashish Kumar Singh,[a] and
Daya Shankar Pandey*[a]
Keywords: Ruthenium / Rhodium / Iridium / N,P ligands / Hydrogen transfer
Reactions of the complexes [(η5-C5H5)Ru(PPh3)2Cl], [{(η6-
arene)Ru(µ-Cl)Cl}2] (η6-arene = C6H6, C10H14, and C6Me6)
and [{(η5-C5Me5)M(µ-Cl)Cl}2] (M = Rh, Ir) with 2-(2-di-
phenylphosphanylethyl)pyridine (PPh2Etpy) were investi-
gated. Neutral κ1-P-bonded complexes [(η5-C5H5)Ru(κ1-P-
PPh2EtPy)(PPh3)Cl] (1) and [(η6-arene)Ru(κ1-P-PPh2EtPy)Cl2]
[arene = C6H6, (2). C10H14, (3), and C6Me6, (4)] were isolated
from the reactions of [(η5-C5H5)Ru(PPh3)2Cl] and [{(η6-arene)-
Ru(µ-Cl)Cl}2] with PPh2EtPy. Treatment of 1–4 with NH4BF4/
NH4PF6 in methanol allows the synthesis of cationic κ2-P,N-
chelated complexes [(η5-C5H5)Ru(κ2-P,N-PPh2EtPy)(PPh3)]+
(5) and [(η6-arene)Ru(κ2-P-N-PPh2EtPy)Cl]+ [arene = C6H6,
(6), C6H14, (7), and C6Me6 (8)]. On the other hand, the dimers
[{(η5-C5Me5)M(µ-Cl)Cl}2] (M
= Rh or Ir) reacted with
PPh2EtPy in methanol to afford cationic κ2-P,N-chelated com-
plexes [(η5-C5Me5)M(κ2-P-N-PPh2EtPy)Cl]+ [M = Rh, (9); Ir,
(10)]. Complex 10 reacted with an excess amount of sodium
azide or sodium chloride to afford the complexes [(η5-C5Me5)-
Ir(κ1-P-PPh2EtPy)X2] (X = N3 11; Cl–, 12), establishing the
–
hemilabile nature of the coordinated PPh2EtPy. The com-
plexes were characterized by elemental analyses and various
physicochemical techniques. The molecular structures of 1,
5, 6, 9, and 10 were determined crystallographically, and the
catalytic potentials of 1–10 were evaluated towards transfer-
hydrogenation reactions under aqueous conditions.
hibits a versatile coordination behavior and a few transi-
tion-metal complexes based on it have been reported.[8c,8d]
It may coordinate to metal centers in three different coordi-
nation modes: P-monodentate, P,N-bridge, and P,N-chelate
mode.[8] In its chelating mode, PPh2EtPy forms a six-mem-
bered chelate ring in the “twist chair conformation” and
plays a significant role in the catalytic processes, for exam-
ple, in carbonylation of alkynes, oligomerization and poly-
merization of ethene, and in asymmetric transfer hydrogen-
ation.[9–12]
Furthermore, the ruthenium complex [(η5-C5H5)-
Ru(PPh3)2Cl] and the dimeric complexes [{(η6-arene)Ru(µ-
Cl)Cl}2] (η6arene = C6H6, C10H14, and C6Me6) and [{(η5-
C5Me5)M(µ-Cl)Cl}2] (M = Rh or Ir) play a vital role in
organometallic chemistry.[13–16] While the reactivity of these
precursors with a variety of ligands has been reported, its
reactivity with PPh2EtPy is yet to be explored. It is well
established that simple phosphane-containing ruthenium,
rhodium, and iridium complexes acts as active catalysts,
particularly in presence of a base and incorporation of the
η5-C5H5, η5-C5Me5, and η6-arene as spectator ligands in
the complexes boosts enantioselectivity of the respective re-
actions.[17,18] With the objective to expand the chemistry of
PPh2EtPy and to develop hydrogen-transfer catalysts con-
taining the [(η5-C5H5)Ru-/[(η6-arene)Ru-/[(η5-C5Me5)Rh-/
[(η5-C5Me5)Ir-] moieties and PPh2EtPy, we synthesized and
characterized a series of new neutral and cationic rutheni-
um(II) and rhodium(III)/iridium(III) complexes. These rep-
Introduction
Considerable current attention has been paid towards the
synthesis and characterization of complexes based on the
ligands containing P and N or O donor atoms because of
their interesting structural features, reactivity, and catalytic
applications.[1] Coordination compounds imparting hetero-
difunctional ligands possessing both the “soft” phosphorus
and “hard” nitrogen or oxygen donors exhibit hemilabile
behavior and are extremely useful in transition-metal catal-
ysis.[1–3] P,N donor ligands with π-acceptor phosphorus can
stabilize low oxidation states of the metals, and the σ-donor
ability of the nitrogen stabilizes higher oxidation states and
makes the metals more susceptible towards oxidative-ad-
dition reactions. The hard donor ligand easily detaches
from the metal center, creating a coordination site required
for binding of the substrate during the catalytic cycles.
Among the most widely studied P,N donor ligands a promi-
nent position is occupied by pyridyl phosphanes, including
chiral derivatives.[4–7] In this regard, 2-(2-diphenylphos-
phanylethyl)pyridine (PPh2EtPy) containing both P and N
donors have drawn special attention.[8] This phosphane ex-
[a] Department of Chemistry, Faculty of Science, Banaras Hindu
University,
Varanasi 221005 (U.P.), India
Fax: +91-542 2368174
E-mail: dspbhu@bhu.ac.in
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.200901004.
704
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Piano-Stool Complexes Containing 2-(2-Diphenylphosphanylethyl)pyridine
resent the first examples of complexes containing [(η5- N-chelated PPh2EtPy. The synthesis of complex 5 was also
C5H5)Ru-, [(η6-arene)Ru-, [(η5-C5Me5)Rh-, [(η5-C5Me5)Ir-] achieved by treatment of 1 with NH4BF4 in methanol whilst
moieties and PPh2EtPy. In this paper we present the synthe- stirring at room temperature (Scheme 1a). The ability of the
sis and spectral and structural characterization of some pi- chlorido-bridged arene ruthenium dimers [{(η6-arene)Ru(µ-
ano-stool ruthenium(II) and rhodium/iridium(III) com- Cl)Cl}2] to form mono- and binuclear complexes of the ge-
plexes imparting PPh2EtPy as a coligand. Also, we describe neral formula [(η6-arene)RuCl2L] and [{(η6-arene)-
herein catalytic applications of complexes 1–10 in the re- RuCl2}2(µ-L)] is well documented.[19] Reactions of the di-
duction of ketones to alcohol under aqueous and aerobic mers [{(η6-arene)Ru(µ-Cl)Cl}2] (η6-arene = C6H6, C10H14,
conditions.
and C6Me6) with PPh2EtPy in dichloromethane whilst stir-
ring at room temperature afforded the P-coordinated neu-
tral complexes [(η6-C6H6)Ru(κ1-P-PPh2EtPy)Cl2] (2), [(η6-
C10H14)Ru(κ1-P-PPh2EtPy)Cl2] (3), and [(η6-C6Me6)Ru(κ1-
P-PPh2EtPy)Cl2] (4). Complexes 2–4 upon treatment with
NH4PF6 in methanol under refluxing conditions allows N-
coordination of the PPh2EtPy to ruthenium, affording the
P,N-chelated cationic complexes [(η6-C6H6)Ru(κ2-P-N-
PPh2EtPy)Cl]PF6 (6), [(η6-C10H14)Ru(κ2-P-N-PPh2EtPy)-
Cl]PF6 (7), and [(η6-C6Me6)Ru(κ2-P-N-PPh2EtPy)Cl]PF6
(8) (Scheme 1b). On the other hand, rhodium and iridium
dimers [{(η5-C5Me5)M(µ-Cl)Cl}2] (M = Rh or Ir) reacted
Results and Discussion
Synthesis of the Complexes
The reaction of the complex [(η5-C5H5)Ru(PPh3)2Cl]
with PPh2EtPy in benzene under refluxing conditions af-
forded the P-coordinated neutral complex [(η5-C5H5)Ru(κ1-
P-PPh2EtPy)(PPh3)Cl] (1), whereas its reaction with
PPh2EtPy in methanol yielded the cationic complex [(η5-
C5H5)Ru(κ2-P-N-PPh2EtPy)(PPh3)]+ (5) containing κ2-P-
Scheme 1.
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P. Kumar, M. Yadav, A. Kumar Singh, D. Shankar Pandey
FULL PAPER
with PPh2EtPy in the presence of NH4PF6 in methanol to as a chelating P,N-donor ligand, forming a six-membered
afford the P,N-chelated cationic complexes [(η5-C5Me5)- chelate ring. The (η6-C6H6)-ruthenium complex 6 and (η6-
Rh(κ2-P-N-PPh2EtPy)Cl]PF6 (9) and [(η5-C5Me5)Ir(κ2-P- C5Me5)-rhodium and iridium complexes 9 and 10, respec-
N-PPh2EtPy)Cl]PF6 (10) in reasonably good yields tively are isostructural with complex 5. In complexes 5, 6,
(Scheme 1c).
9, and 10, the PPh2EtPy ligand is coordinated to the respec-
The hemilabile behavior of the coordinated PPh2EtPy in tive metal centers as a chelating P,N-donor ligand, forming
κ2-P-N-chelated complexes was established from the reac- a six-membered ring with bite angles of 93.98(2), 91.08(19),
tions of the representative complex [(η5-C5Me5)Ir(κ2-P-N- 84.2(2), and 84.57(10)°, respectively.
PPh2EtPy)Cl]PF6 with an excess amount of NaCl and
NaN3 in methanol whilst stirring. As expected, it gave neu-
tral complexes with the formulations [(η5-C5Me5)Ir(κ1-P-
PPh2EtPy)(N3)2] (11) and [(η5-C5Me5)Ir(κ1-P-PPh2EtPy)-
Cl2] (12), respectively. Taking into account the lability of
PPh2EtPy in complex 10, which allows coordination of a
chloride/azide ligand through the decoordination of the
-Ph2P-N moiety (Scheme 1d), we believe that complexes 5–
9 will also exhibit analogous behavior.
Characterization
Complexes 1–12 are air-stable, nonhygroscopic, crystal-
line solids soluble in halogenated solvents like chloroform
and dichloromethane, but insoluble in benzene, hexane, di-
ethyl ether, and petroleum ether. Characterization of the
complexes under study was achieved by standard spectro-
Figure 1. Molecular structure of complex 1 and selected bond
length [Å] and angles [°]: Ru1–Cl1 2.448(2), Ru1–P1 2.305(2), Ru1–
P2 2.327(2), Ru1–Cav(Cp) 2.206(8), Cg-Ru1 1.848, P1–Ru1–P2
97.84(8), P1–Ru1–Cl1 89.10(8), P2–Ru1–Cl1 90.56(8), Cl1–Ru1–Cg
123.9, P1–Ru1–Cg 123.5, P2–Ru1–Cg 122.7.
1
scopic techniques (IR, FAB-MS, H and 31P{1H} NMR,
electronic absorption spectral, and electrochemical studies)
as well as elemental analyses. All the complexes gave satis-
factory elemental analyses. Information about composition
of the complexes was also obtained from FAB mass spectral
studies. Resulting data along with their assignments are re-
corded in the Experimental Section; other data and spectra
of the complexes are shown in Figure S1–9 (Supporting In-
formation). The position of various peaks and overall frag-
mentation patterns in the FAB-MS of the respective com-
plexes conformed well to their respective formulations.
X-ray Crystallography
The molecular structures of complexes 1, 5, 6, 9, and 10
were determined crystallographically. ORTEP views at 30%
thermal ellipsoid probability along with the atom number-
ing scheme are shown in Figures 1, 2, 3, 4, and 5. Details
about the data collection, solution, and refinement are sum-
marized in the Experimental Section, and important geo-
metrical parameters (bond lengths and bond angles) are
summarized in the captions of Figures 1–5. A common
structural feature of these complexes is the typical piano-
stool geometry about the respective metal center with a
change in the η5-coordinated hydrocarbon ligands and κ1-
P-/κ2-P, N -coordinated PPh2EtPy. In complex 1, the coordi-
Figure 2. Molecular structure of complex 5 and selected bond
length [Å] and angles [°]: Ru1–N1 2.171(3), Ru1–P1 2.3270(8),
Ru1–P2 2.3160(8), Ru1–Cav(Cp) 2.213(3), Cg-Ru1 1.856, N1–Ru1–
P1 90.73(6), N1–Ru1–P2 93.98(7), P2–Ru1–P1 96.07(3), P1–Ru1–
Cg 124.9, P2–Ru1–Cg 123.7, N1–Ru1–Cg 119.4.
The hydrocarbon ligands (η5-C5H5, 1 and 5; η6-C6H6, 6;
nation geometry about the metal center ruthenium is com- η6-C5Me5, 9 and 10) are planar and various C–C bond
pleted by two P donors, one each from the PPh3 and lengths in these are normal.[19a,20] Metal-to-centroid dis-
PPh2EtPy, the chlorido group, and the cyclopentadienyl tances of the respective hydrocarbon ligands in complexes
ring in a η5-manner. An analogous arrangement of various 1, 5, 6, 9, and 10 are 1.848, 1.856, 1.711, 1.822, and 1.840 Å,
groups was observed in complex 5, except that in this com- respectively. These are comparable to the values reported in
plex the PPh2EtPy ligand is coordinated to the ruthenium the literature.[20] The Ru–Cl bond lengths in complex 1 and
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Piano-Stool Complexes Containing 2-(2-Diphenylphosphanylethyl)pyridine
Figure 5. Molecular structure of complex 10 and selected bond
length [Å] and angles [°]: Ir1–N1 2.121(3), Ir1–P1 2.308 (11), Ir1–
Cav(arene) 2.207(4), Ir1–Cl1 2.402 (8), Cg-Ir1 1.840, N1–Ir1–P1
84.57(10), N1–Ir1–Cl1 89.29(9), P1–Ir1–Cl1 90.59(4), Cl1–Ir1–Cg
121.5, P1–Ir1–Cg 133.2, N1–Ir1–Cg 124.6.
Figure 3. Molecular structure of complex 6 and selected bond
length [Å] and angles [°]: Ru1–N1 2.160(7), Ru1–P2 2.333(2), Ru1–
Cav(arene) 2.219(9), Ru1–Cl1 2.395(2), Cg-Ru1 1.711, N1–Ru1–P2
91.08(19), N1–Ru1–Cl1 83.72(18), P2–Ru1–Cl1 87.86(8), Cl1–Ru1–
Cg 126.0, P1–Ru1–Cg 128.6, N1–Ru1–Cg 125.8.
–
Figure 6. Counteranion (PF6 ) encapsulated in self-assembled cav-
ity of complex 2.
Figure 4. Molecular structure of complex 9 and selected bond
length [Å] and angles [°]: Rh1–N1 2.134(7), Rh1–P1 2.318(2), Rh1–
Cav(arene) 2.189(8), Rh1–Cl1 2.399(2), Cg-Rh1 1.822, N1–Rh1–P1
84.2(2), N1–Rh1–Cl1 91.0(2), P1–Rh1–Cl1 90.77(9), Cl1–Rh1–Cg
120.6, P1–Rh1–Cg 133.1, N1–Rh1–Cg 124.6.
6 are 2.448(2) and 2.395(2) Å, respectively, which are com-
parable to the Ru–Cl bond lengths in other related com-
plexes.[21,22] Similarly, the Rh–Cl bond length in 9 and the
Ir–Cl bond length in 10 are 2.399(2) and 2.402(8) Å, respec-
tively, and are consistent with the values reported in the
literature.[21,22] The Ru–P bond lengths in 1, 5, and 6 are
normal as the Rh–P and Ir–P bonds.[21–23] The Ru–N, Rh–
N, and Ir–N bond lengths in the respective complexes are
in the range of the reported values.[24]
Figure 7. (a) Space-filling representations of 10 showing C–H···F
interaction; (b) 1D ladder motif resulting from C–H···F interac-
tions in 10.
NMR Spectral Studies
The 1H and 31P{1H}NMR spectroscopic data of the
complexes is gathered in the Experimental Section along
Crystal structures of 1, 5, 6, 9, and 10 revealed the pres- with other characterization data. Coordination of
ence of extensive intra- and intermolecular C–H···X (X = PPh2EtPy to the ruthenium center is evident from the shifts
N, Cl, and F) and C–H···π interactions. These types of in- in the position of resonances corresponding to various pro-
teractions play significant roles in the building of huge sup- tons and 31P nuclei in comparison to the precursor com-
ramolecular moieties.[25] Interesting motifs resulting from plexes. The position and integrated intensity of various sig-
weak bonding interactions (C–H···π interaction) in 1, 5, 6, nals in the 1H NMR spectra of the complexes strongly sup-
9, and 10 are shown in Figures 6 and 7.
ported the proposed formulations. Formulation of the re-
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P. Kumar, M. Yadav, A. Kumar Singh, D. Shankar Pandey
FULL PAPER
spective complexes is further supported by 31P NMR spec- displayed transitions at ca. 612–540, 498–359, and ca. 288–
tral studies. Complex 1 in its 31P{1H}NMR spectrum dis- 246 nm, whereas the κ2-P-N bonded complexes 5–10 exhib-
played signals at δ = 44.79 and 37.19 ppm, corresponding ited transitions at 561–528, 492–351 and ca. 282–241 nm.
to the 31P nuclei of the coordinated PPh2EtPy and PPh3, On the basis of its intensity and position, the lowest-energy
respectively. The signal associated with 31P nuclei of absorptions in the visible region have tentatively been as-
PPh2EtPy exhibited a significant downfield shift upon co- signed to MLCT transition from ruthenium to π* orbitals
ordination to the metal center in comparison to the free of PPh2EtPy/PPh3/ηn bonded hydrocarbon ligands, whereas
ligand (δ =8.43 ppm). Similarly, complex 5 exhibited two the bands in the high-energy side have been assigned to the
signals at δ = 49.68 and 35.90 ppm, assignable to the 31P intra-ligand πǞπ*/ nǞπ* transitions.[26] One can see that
nuclei of the coordinated PPh2EtPy and PPh3, respectively. coordination of PPh2EtPy through both the P and N donor
The 31P{1H}NMR spectra of complexes 2–4 and 6–10 dis- sites in complexes 5–10 leads to blueshifting of the MdπǞL*
played singlets at δ = 48.4 (2), 47.6 (3), 46.9 (4), 37.7 (6), absorption bands compared to that in 1–4. It may be attrib-
36.6 (7), 33.5 (8), 10.69 (9), and 2.40 (10) ppm. Observed uted to the formation of more stable chelated complexes in
data suggested that the position of the resonances associ- the twist chair form, which significantly destabilizes the π*
ated with 31P nuclei of the ligand PPh2EtPy is sensitive to orbital of the hydrocarbon ligands (η5-C5H5, 1 and 5; η6-
the metal center and its coordination mode. Upfield shift C6H6, 6; η6-C5Me5, 9 and 10).
in the position of signals associated with 31P nuclei may be
attributed to the enhanced backdonation from the metal to
PPh2EtPy on going fd 12 exhibited a significant shift [δ =
20.71 (11) and 20.79 ppm (12)] from that in precursor com-
Electrochemistry
plex 10 (δ =2.40 ppm) and is in the range of P-coordinated
PPh2EtPy. This observation strongly supported decoordina-
tion of PPh2EtPy from the N-site.
Electrochemical properties of complexes 1, 2, 5, 6, and
10 were followed by cyclic voltammetry by using 0.1 
tetrabutylammonium perchlorate (TBAP) in dichlorometh-
ane as supporting electrolyte. The potential of the Fc/Fc+
couple under the experimental conditions was 0.10 V
(80 mv) vs. Ag/Ag+. Resulting data is summarized in
Table 1, and selected voltammograms are depicted in Fig-
ures 9, 10, and 11. Complexes 1 and 5 in their cyclic voltam-
mogram exhibited an oxidative response at 0.82 and
0.26(38) V, respectively, which has been assigned to RuII/III
oxidation. This oxidation is irreversible in 1 and reversible
in 5 (∆Ep ≈ 100 mV: ipa = ipc). This suggested that the phos-
phane PPh2EtPy in complex 5 is bonded to the metal center
in a chelating mode. The irreversible reduction peaks at –0.
85 (1) and –0.83 V (5) may be attributed to the ligand-based
redox process. Complexes 2 and 6 displayed irreversible and
reversible peaks, respectively, at 0.83 and 0.73 V. The redox
potential of the RuII/III couple in complex 6 is higher than
that observed in 5. It may be attributed to the lower elec-
tron-donating ability of the η6-arene ligand in 6 compared
to η5-C5H5 in 5. From the above observations it has been
concluded that PPh2EtPy in a chelating coordination mode
is a better stabilizer of the trivalent state of ruthenium com-
pared to the monodentate one. Complex 10 exhibits one
electron reversible oxidation corresponding to the IrIV/III re-
Electronic Spectroscopy
Electronic absorption spectra of complexes 1–10 were ac-
quired in dichloromethane (10–4 ) solution at room tem-
perature. Resulting data is summarized in the Experimental
Section, and the spectra of complexes 1–6 are depicted in
Figure 8. Ruthenium arene complexes in its absorption
spectra usually display intense peaks in the ultraviolet re-
gion, corresponding to ligand-based π–π* transitions with
overlapping metal-to-ligand (MLCT) transitions in the vis-
ible region. An analogous general trend has been observed
in the electronic absorption spectra of the complexes under
study. Complexes 1–4, containing κ1-P bonded PPh2EtPy
ox
dox couple at (E1/2 vs. Ag/Ag+) at ca. 1.15(77) V.[27] This
suggested that PPh2EtPy is a better stabilizer of the tetrava-
lent state of iridium in the chelating mode.
Table 1. Cyclic voltammetric data of the complexes.
0
0
Complex
E
/ V (∆E / mV)
E
/ V (∆E / mV)
ox
ox
1
0.82[a]
–0.85
–0.80
–0.83
–0.98
–0.86
2
0.83[a]
5
6
10
0.27(83)
0.73(54)
1.15(77)
Figure 8. Electronic absorption spectra of complexes 1, 2, 5, 6, 9,
and 10.
[a] Irreversible peak.
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Piano-Stool Complexes Containing 2-(2-Diphenylphosphanylethyl)pyridine
hydrogen transfer. Of particular interest was the compari-
son between the ruthenium, rhodium, and iridium com-
plexes and the effect of tethering the phosphane and cap-
ping group to make a highly chelating pocket. The reaction
chosen for comparison was hydrogen transfer from formate
to acetophenone, as this substrate has most commonly been
employed in this regard (Scheme 2).
Scheme 2.
Figure 9. Cyclic voltammogram of 5.
Complexes 1–10 were tested for the hydrogenation of
acetophenone by hydrogen transfer from formate
(3.2 mmol; Table 2) by using complexes (6.4 µmol) and the
ketone (0.64 mmol) in water (5 mL). The reactions were
carried out at 80 °C with a catalyst/substrate/formate (Cat/
S/formate) ratio of 1:100:500. The data indicate that com-
plexes 1–10 are all reasonably efficient hydrogen-transfer
catalysts under aerobic conditions. Conversion versus time
plot for PPh2EtPy containing precursor catalysts 1, 5, 7, 8,
9, and 10 is shown in Figure 12. The systems give ca. 50%
conversion after 1–4 h, and the relative activity sequence up
to ca. 14 h are 10 Ͼ 9 Ͼ 8 Ͼ 4 Ͼ 7 Ͼ 6 Ͼ 2 Ͼ 3 Ͼ 1 Ͼ 5.
The activities of these complexes have been explained on
the basis of electron releasing groups present on the aro-
matic ring and electronic effects about the metal center. It
was observed that the presence of electron releasing groups
on the aromatic ring increases the electron density on the
metal center and the rate of transfer hydrogenation.
Figure 10. Cyclic voltammogram of 6.
Table 2. Transfer hydrogenation of acetophenone catalyzed by ru-
thenium, rhodium, and iridium complexes.[a]
Catalyst M(arene)
Conv. / %
1
2
3
4
5
6
7
8
9
10
[(η5-C5H5)Ru(κ1-P-N-PPh2EtPy)(PPh3)Cl]
75
84
82
90
70
86
88
94
98
99
[(η6-C6H6)Ru(κ1-P-PPh2EtPy)Cl2]
[(η6-C10H14)Ru(κ1-P-PPh2EtPy)Cl2]
[(η6-C6Me6)Ru(κ1-P-PPh2EtPy)Cl2]
[(η5-C5H5)Ru(κ2-P-N-PPh2EtPy)(PPh3)]BF4
[(η6-C6H6)Ru(κ2-P-N-PPh2EPyt)Cl]PF6
[(η6-C10H14)Ru(κ2-P-N-PPh2EtPy)Cl]PF6
[(η6-C6Me6)Ru(κ2-P-N-PPh2EtPy)Cl]PF6
[(η5-C5Me5)Rh(κ2-P-N-PPh2EtPy)Cl]PF6
[(η5-C5Me5)Ir(κ2-P-N-PPh2EtPy)Cl]PF6
[a] Reaction carried out at 80 °C, in 5 mL water, acetophenone
(0.64 mmol), ratio catalyst/substrate/formate being 1:100:500.
Figure 11. Cyclic voltammogram of 10.
In the course of our studies on planar-chiral complexes
of late transition metals we prepared planar-chiral arene-
phosphane ruthenium/rhodium/iridium complexes (1, 5–10)
Catalytic Applications of 1–10 in the Transfer
Hydrogenation of Acetophenone under Aqueous Conditions
Hydrogen-transfer reactions of acetophenone using for- in which anchor phosphane prevents the rotation of the ar-
mate as the source of hydrogen were carried out under ene ring, constructing a good asymmetric environment
aqueous and aerobic conditions, and the reaction products around the metal center. Efficiency of the planar-chiral ar-
1
were analyzed by H NMR spectroscopy. Catalyst testing ene-phosphane ligand was proved by the induction of
was conducted to assess the effects of chelating phosphane metal-centered chirality with a high selectivity in the ligand
ligands on the ability of piano-stool complexes to catalyze exchange reactions with phosphane (PPh2EtPy) and an-
Eur. J. Inorg. Chem. 2010, 704–715
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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709

P. Kumar, M. Yadav, A. Kumar Singh, D. Shankar Pandey
FULL PAPER
Figure 12. Conversion vs. reaction time plots for complexes 1, 2, 6, 8, 9, and 10.
ionic/neutral ligands. Although, a tentative mechanism of chelating rings is observed. It is also clear from Table 3 that
these reactions is described here, a prior step involving for- shorting of the M–N and M–P bond lengths is in the same
mation of the hydrides was thought to be necessary. It is direction. This trend shows the effect of relative size and
reasonable that these hydrides can be formulated as [Ru- geometry of the coordinating metal on the bite angle and
(arene)H(L)]+. The partial decoordination of the M–N bond lengths. Furthermore, it is observed that the symmet-
bond is also necessary to allow coordination of the ketone ric deformation coordinates S4Ј[33] depends on the trans in-
in complex 5. On the basis of the behavior of complexes 1– fluence of ligands occupying a position trans to P coordina-
10 in solution and the synthesis as shown in Scheme 1, an tion sites and on the M–N bond lengths.
inner-sphere mechanism[28] is proposed for transfer hydro-
genation (TH) of the ketones catalyzed by chelated ηn com-
plexes. Complex 6 interacts with water to form RuII–OH2
(A), which upon further reaction with formate (source of
hydrogen) forms RuII carboxylate (B), which in turn results
in the formation of the Ru–H (D) intermediate with release
of CO2. Coordination of a ketone with D results in the for-
mation of alcohol (Scheme S1, Supporting Information).
Formation of Ru–H complexes from Ru–Cl precursors are
well documented,[29] and such in situ formed Ru–H species
can act as the active catalysts for TH of ketones.[29–32]
Conclusions
In summary, through this work we have developed a
range of piano-stool complexes of Ru, Rh, and Ir by im-
parting the heterodifunctional phosphane 2-(2-diphenyl-
phosphanylethyl)pyridine. From spectral and structural
studies it has been established that the coordinated
PPh2PyEt acts as both the unidentate and the chelating bi-
dentate ligand. In its chelating coordination mode 2-(2-di-
phenylphosphanylethyl)pyridine forms six-membered che-
late rings in the “twist chair” conformation. Furthermore, it
has been shown that the complexes under study moderately
catalyze reduction of acetophenone to 1-phenylethanol and
they serve as hydrogenating catalysts for use in water and
air and delivers faster rates in the absence of inert gas pro-
tection or substrate solubility in water.
Structural and Spectroscopic Correlation between
Complexes Containing Chelating P,N-PPh2EtPy
Crystallographic and 31P{1H}NMR spectroscopic data
of some reported complexes and those from the present
study involving P,N-chelates are recorded in the Table 3.
The literature reports on PPh2EtPy acting as a P,N-chelate
is rather scarce. Six-membered ruthenium chelate rings are
in “twist chair” conformation with slightly large bite angles.
Experimental Section
Reagents: All synthetic manipulations were performed under aero-
An increase in the P–M–N angle in the complexes with one bic conditions. The solvents were rigorously purified by standard
Table 3. Comparison of the structural and 31P NMR spectroscopic data of the metal complexes with one chelating P, N PPh2EtPy.[a]
M
Complex
S4Ј[b] / °
P-M–N / °
M–N / Å
M–P / Å
δ(P)[c] / ppm
Ref.
TW
Ru
Ru
Pd
Ni
6
5
33.29
37.69
27.78
22.60
91.08
93.98
95.03
98.03
2.159
2.172
2.223
2.024
2.333
2.316
2.196
2.302
37.7
35.9
36.3
–
TW
Pd(κ2-P-N-PPh2EtPy)(CH3)Cl
Ni(κ2-P-N-PPh2EtPy)Cl2
[8c]
[8c]
[a] (PN) chelating P,N-PPh2EtPy, TW = this work. [b] Angular symmetric deformation coordinate S4Ј defined as the sum of the M–P–
C angles minus the sum of the C–P–C angles. [c] δ (P) is a 31P chemical shift for a chelating phosphane.
710
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 704–715

Piano-Stool Complexes Containing 2-(2-Diphenylphosphanylethyl)pyridine
1
procedures prior to their use.[34] Hydrated ruthenium(III) chloride,
hydrated rhodium/iridium(III) chloride, dicyclopentadiene penta-
methylcyclopentadiene, α-phellandrene, hexamethylbenzene, 2-(2-
diphenylphosphanylethyl)pyridine (all Sigma–Aldrich) were used
as received without further purifications. The precursor complexes
(221) [(η6-C6H6)RuCl2]. H NMR: δ = 9.48 (dd, J = 5.2 Hz, 1 H,
py-H6), 7.74–7.70 (m, 5 H, py-H4 + Ph-H2), 7.48–7.32 (m, 6 H,
Ph-H3 + H4), 7.25–7.22 (m, 1 H, py-H5), 7.20 (d, J = 7.6 Hz, 1
H, py-H3), 5.68 (s, 6 H, C6H6), 3.20–3.16 (m, 2 H, py-CH2), 2.40–
2.37 (m, 2 H, P-CH2) ppm. 13C NMR: δ = 88.43 (C-C6H6), 154.3
(py-C2), 152.8 (py-C6), 136.4 (CH), 136.6 (CH), 129.6 (Ph-C1),
134.2 (CH), 131.0 (CH), 122.6 (s, CH), 123.2 (s, CH), 35.2 (py-
CH2), 25.1 (P-CH2) ppm. 31P{1H} NMR: δ = 48.48 (s, PPh2EtPy)
[(η5-C5H5)Ru(PPh3)2Cl], [{(η6-arene)Ru(µ-Cl)Cl}2] (η6-arene
=
C6H6, C10H14, and C6Me6) and [{(η5-C5Me5)M(µ-Cl)Cl}2] (M =
Rh or Ir) were prepared and purified following literature pro-
cedures.[35–37]
ppm. IR (KBr pellet): ν = 1648 (s), 1460 (s), 1440 (m), 1378 (m),
˜
1341 (s), 1245 (m), 1195 (m), 1033 (m), 993 (s), 889 (s), 807 (s), 722
(m), 670 (s), 528 (s), 473 (s) cm–1. UV/Vis: λ (ε, –1 cm–1) = 568
(1760), 482 (6850), 300 (27070), 246 (39300) nm.
General Methods: Elemental analyses for C, H, and N on the com-
plexes were performed with an Exeter Analytical Inc. Model CE-
440 elemental analyzer. IR and far-IR in KBr disk form were re-
corded with a Varian 3300 FTIR spectrophotometer, and electronic
absorption spectra were recorded with a Shimadzu UV-1700 spec-
trophotometer. 1H (300 MHz), 13C (75.45 MHz), and 31P{1H}
(121.50 MHz) NMR spectra were acquired with a JEOL AL 300
FTNMR spectrometer at room temperature by using CDCl3 as sol-
vent and TMS as an internal reference for 1H and H3PO4 (85%)
as the external reference for 31P{1H}NMR spectra. FAB mass spec-
tra were recorded with a JEOL SX 102/Da-600 mass spectrometer.
Cyclic voltammetric measurements were performed with a CHI
620c electrochemical analyzer. A platinum working electrode, plati-
num wire auxiliary electrode, and Ag/Ag+ reference electrode were
used in a standard three-electrode configuration. Tetrabutylammo-
nium perchlorate (TBAP) was used as supporting electrolyte, and
the solution concentration was ca. 10–3.
[(η6-C10H14)Ru(κ1-P-PPh2EtPy)Cl2] (3): Prepared by following the
procedure for 2 by using [{(η6-C10H14)Ru(µ-Cl)Cl}2] (0.612 g,
1.0 mmol) and PPh2EtPy (0.291 g, 1.0 mmol). Yield: 0.532 g, 90%.
M.p. 140 °C. C29H32Cl2NPRu (597.53): calcd. C 58.29, H 5.40, N
2.34; found C 58.33, H 5.48, N 2.30. MS (FAB): m/z (calcd.) =
597.5 (596) [Ru(η6-C10H14)(κ1-P-N-PPh2EtPy)Cl2], 306.4 (306)
1
[(η6-C10H14)RuCl2]. H NMR: δ = 9.46 (dd, J = 5.0 Hz, 1 H, py-
H6), 7.76–7.68 (m, 5 H, py-H4 + Ph-H2), 7.46–7.34 (m, 6 H, Ph-
H3 + -H4), 7.25–7.22 (m, 1 H, py-H5), 7.16 (d, J = 7.6 Hz, 1 H, py-
H3), 5.22 [d, J = 5.8 Hz, 2 H, C10H14(C6H4)], 5.39 [d, J = 5.9 Hz, 2
H, C10H14(C6H4)], 3.18–3.16 (m, 2 H, py-CH2), 2.98 (sept., 1 H,
CH), 2.43–2.37 (m, 2 H, P-CH2), 2.23 (s, 3 H, CH3), 1.30 (d, J =
6.96 Hz, 6 H, CH3) ppm. 13C NMR: δ = 18.60 (C-CH3), 22.05
[CH(CH3)2], 30.60 [CH(CH3)2], 84.70 (C-C6H4), 100.49 (C-CH3),
102.16 (C-CHMe2), 159.5 (py-C2), 153.8 (py-C6), 138.5 (CH),
133.6 (CH), 131.6 (Ph-C1), 131.2 (CH), 129.0 (CH), 124.6 (s, CH),
123.2 (s, CH), 34.3 (py-CH2), 26.1 (P-CH2) ppm. 31P{1H}NMR: δ
[(η5-C5H5)Ru(κ1-P-PPh2EtPy)(PPh3)Cl] (1): To a suspension of
[(η5-C5H5)Ru(PPh3)2Cl] (0.5 g, 0.68 mmol) in benzene (25 mL) was
added PPh2EtPy (0.19 g, 0.68 mmol), and the contents of the flask
were heated under reflux for 8 h. After cooling to room tempera-
ture, the orange solution thus obtained was concentrated to dryness
under reduced pressure, and the residue was subjected to purifica-
tion by silica gel chromatography (CH2Cl2/ethyl acetate, 3:1). It
gave compound 1 as an orange solid, which was recrystallized from
CH2Cl2/petroleum ether (40–60 °C). Yield: 0.492 g, 89%. M.p.
145 °C. C42H38ClNP2Ru (755.24): calcd. C 66.79, H 5.07, N 1.87;
found C 66.58, H 5.14, N 1.74. MS (FAB): m/z (calcd.) = 755.1
(754) [(η5-C5H5)Ru(κ1-P-PPh2EtPy)(PPh3)Cl], 720.1 (719) [(η5-
C5H5)Ru(κ1-P-PPh2EtPy)(PPh3)]+, 458.2 (456) [(η5-C5H5)Ru(κ1-P-
= 47.65 (s, PPh EtPy) ppm. IR (KBr pellet): ν = 1626 (s), 1445 (s),
˜
2
1439 (s), 1394 (m), 1102 (m), 848 (s), 758 (s), 698 (s) cm–1. UV/Vis:
λ (ε, –1 cm–1) = 572 (3260), 495 (8770), 359 (7260), 277 (23080)
nm.
[(η6-C6Me6)Ru(κ1-P-PPh2EtPy)Cl2] (4): Prepared by following the
procedure for 2 except that [{(η6-C6Me6)Ru(µ-Cl)Cl}2] (0.668 g,
1.0 mmol) was used in place of [{(η6-C6H6)Ru(µ-Cl)Cl}2]. Yield:
0.743 g, 74%. C31H36Cl2NPRu (625.58): calcd. C 59.52, H 5.80, N
2.24; found C 59.58, H 5.78, N 2.26. MS (FAB): m/z (calcd.) =
625.5 (624) [(η6-C6Me6)Ru(κ1-P-PPh2EtPy)Cl2], 334.4 (334), [(η6-
1
C6Me6)RuCl2]. H NMR: δ = 9.48 (dd, J = 5.2 Hz, 1 H, py-H6),
1
PPh2EtPy)]+. H NMR: δ = 4.64 (s, 5 H, η5-C5H5), 9.52 (dd, J =
7.74–7.70 (m, 5 H, py-H4 + Ph-H2), 7.46–7.32 (m, 6 H, Ph-H3 +
-H4), 7.26–7.21 (m, 1 H, py-H5), 7.24 (d, J = 7.6 Hz, 1 H, py-H3),
3.26–3.17 (m, 2 H, py-CH2), 2.41–2.38 (m, 2 H, P-CH2), 2.08 (s,
18 H, C6Me6) ppm. 13C NMR: δ = 15.09 [η6-C6(CH3)6], 95.94
[C6(CH3)6], 159.5 (py-C2), 153.8 (py-C6), 138.5 (CH), 133.6 (CH),
131.6 (Ph-C1), 131.2 (CH), 129.0 (CH), 124.6 (s, CH), 123.2 (s,
CH), 34.3 (py-CH2), 26.1 (P-CH2) ppm. 31P{1H}NMR: δ = 46.95
5.2 Hz, 1 H, py-H6), 7.70–7.65 (m, 5 H, py-H4 + Ph-H2), 7.48–
7.38 (m, 6 H, Ph-H3 + -H4), 7.25–7.22 (m, 1 H, py-H5), 7.16 (d,
J = 7.6 Hz, 1 H, py-H3), 3.21–3.12 (m, 2 H, py-CH2), 2.33–2.27
(m, 2 H, P-CH2). 13C NMR: δ = 76.83 (s, Cp), 159.5 (py-C2), 153.8
(py-C6), 138.5 (CH), 133.6 (CH), 131.6 (Ph-C1), 131.2 (CH), 129.0
(CH), 124.6 (s, CH), 123.2 (s, CH), 128.05–138.72 (m, aromatic
carbon), 34.3 (py-CH2), 26.1 (P-CH2) ppm.1P{1H}NMR: δ = 44.79
(s, PPh EtPy) ppm. IR (KBr pellet): ν = 1668 (s), 1460 (s), 1437
˜
2
(s, PPh EtPy), 36.78 (s, PPh ) ppm. IR (KBr pellet): ν = 1626 (s),
˜
2
3
(m), 1378 (m), 1341 (s), 1245 (m), 1195 (m), 1033 (m), 993 (s), 889
1440 (s), 1394 (m), 1102 (m), 844 (s), 758 (s), 698 (s) cm–1. UV/Vis:
(s), 807 (s), 722 (m), 670 (s), 528 (s), 473 (s) cm–1. UV/Vis: λ (ε,
λ (ε, –1 cm–1) = 540 (7260), 468 (2680) 371 (6360), 288 (26270) nm.

–1 cm–1) = 612 (1200), 577 (2720), 498 (8210), 331 (11380), 286
[(η6-C6H6)Ru(κ1-P-PPh2EtPy)Cl2] (2): To a stirred solution of
[{(η6-C6H6)Ru(µ-Cl)Cl}2] (0.50 g, 1.0 mmol) in dichloromethane
(25 mL) was added PPh2EtPy (0.34 g, 1.2 mmol), and the resulting
solution was stirred for 4 h at room temperature. The red solution
thus obtained was filtered to remove any solid impurities, and the
filtrate was concentrated to half its volume. The concentrated solu-
tion was saturated with petroleum ether (40–60 °C) and left in a
refrigerator for crystallization. Slowly, a microcrystalline product
separated, which was filtered, washed with diethyl ether, and dried
in vacuo. Yield: 0.421 g, 85%. C25H24Cl2NPRu (541.42): calcd. C
55.46, H 4.47, N 2.59; found C 55.58, H 4.54, N 2.68. MS (FAB):
(25140) nm.
[(η5-C5H5)Ru(κ2-P-N-PPh2EtPy)(PPh3)]BF4 (5)
Method 1: To a suspension of [(η5-C5H5)Ru(PPh3)2Cl] (0.5 g,
0.68 mmol) in methanol (25 mL) was added PPh2EtPy (0.196 g,
0.748 mmol) and NH4BF4 (0.078 g, 0.748 mmol), and the mixture
was stirred at room temperature for 2 h. It gave a yellow solution,
which was filtered to remove any solid impurities. The filtrate was
concentrated to half its volume and left for slow crystallization in
a refrigerator. Slowly, a microcrystalline product separated, which
was filtered, washed with diethyl ether, and dried in vacuo. Yield:
m/z (calcd.) = 513.3 (512) [(η6-C6H6)Ru(κ1-P-PPh2EtPy)Cl2], 222 0.432 g, 72%. M.p. 140 °C. C42H38BF4NP2Ru (806.59): calcd. C
Eur. J. Inorg. Chem. 2010, 704–715
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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711

P. Kumar, M. Yadav, A. Kumar Singh, D. Shankar Pandey
FULL PAPER
62.54, H 4.75, N 1.74; found C 62.58, H 4.72, N 1.64. MS (FAB):
CH), 35.6 (py-CH2), 26.4 (P-CH2) ppm. 31P{1H} NMR: δ = 36.65
m/z (calcd.)
=
719.7 (718) [Ru(η5-C5H5)(κ2-P-N-PPh2EtPy)- (s, PPh EtPy) ppm. IR (KBr pellet): ν = 1664 (s), 1440 (s), 1435
˜
2
(PPh3)]+, 457.7 (456) [(η5-C5H5)Ru(κ2-P-N- PPh2EtPy)]+. 1H (s), 1394 (m), 1244 (m), 1102 (m), 844 (s), 758 (s), 698 (s), 840
–
NMR: δ = 9.54 (dd, J = 5.5 Hz, 1 H, py-H6), 7.71–7.63 (m, 5 H, ν(PF6 ) cm–1. UV/Vis: λ (ε, –1 cm–1) = 545 (9560), 489 (17290),
py-H4 + Ph-H2), 7.48–7.38 (m, 6 H, Ph-H3 + -H4), 7.25–7.22 (m,
1 H, py-H5), 7.16 (d, J = 7.6 Hz, 1 H, py-H3), 4.68 (s, 5 H, η5-
C5H5), 3.21–3.12 (m, 2 H, py-CH2), 2.33–2.27 (m, 2 H, P-CH2)
ppm. 13C NMR: δ = 77.65 (s, Cp), 159.5 (py-C2), 153.8 (py-C6),
138.5 (CH), 133.6 (CH), 131.6 (Ph-C1), 131.2 (CH), 129.0 (CH),
124.6 (s, CH), 123.2 (s, CH), 130.15–136.27 (m, aromatic carbon),
34.3 (py-CH2), 26.1 (P-CH2) ppm. 31P{1H}NMR: δ = 35.90 (s,
352 (15900), 282 (39110) nm.
[(η6-C6Me6)Ru(κ2-P-N-PPh2EtPy)Cl]PF6 (8): Prepared by follow-
ing the procedure for 6 by using [(η6-C6Me6)Ru(κ1-P-PPh2EtPy)-
Cl2] (0.727 g, 1.0 mmol). Yield: 0.628 g, 80%. C31H36ClF6NP2Ru
(735.09): calcd. C 50.65, H 4.94, N 1.91; found C 50.68, H 4.98, N
1.92. MS (FAB): m/z (calcd.) = 590 (589) [(η6-C6Me6)Ru(κ2-P-N-
PPh2EtPy)Cl], 554.4 (554) [(η6-C6Me6)Ru(κ2-P-N-PPh2EtPy)],
263.4 (262) [(η6-C6Me6)RuCl]. 1H NMR: δ = 9.48 (dd, J = 5.2 Hz,
1 H, py-H6), 7.74–7.70 (m, 5 H, py-H4 + Ph-H2), 7.46–7.32 (m, 6
H, Ph-H3 + -H4), 7.26–7.21 (m, 1 H, py-H5), 7.24 (d, J = 7.6 Hz,
1 H, py-H3), 3.22–3.17 (m, 2 H, py-CH2), 2.41–2.38 (m, 2 H, P-
PPh EtPy), 49.68 (s, PPh ) ppm. IR (KBr pellet): ν = 1630 (s),
˜
2
3
1445 (s), 1394 (m), 1102 (m), 1040 (m), 844 (s), 758 (s), 698 (s)
cm–1. UV/Vis: λ (ε, –1 cm–1) = 519 (8090), 415 (1070), 359 (8490),
277 (30090) nm.
Method 2: To a suspension of [(η5-C5H5)Ru(κ1-P-PPh2EtPy)- CH2), 2.08 (s, 18 H, C6Me6) ppm. 13C NMR: δ = 15.03 [η6-
(PPh3)Cl] (1; 0.598 g, 1.0 mmol) in methanol (25 mL) was added
NH4PF6 (0.078 g, 0.748 mmol), and the mixture was stirred at
room temperature for 4 h. The clear orange yellow solution was
then concentrated. The residue was extracted with dichloromethane
and filtered to remove any insoluble material. From the filtrate, 5
was isolated in ca. 78% yield.
C6(CH3)6], 88.64 [C6(CH3)6], 155.5 (py-C2), 151.8 (py-C6), 136.4
(CH), 132.5 (CH), 132.3 (Ph-C1), 130.2 (CH), 128.4 (CH), 122.4
(s, CH), 120.2 (s, CH), 35.3 (py-CH2), 24.1 (P-CH2) ppm. 31P{1H}
NMR: δ = 33.54 (s, PPh EtPy) ppm. IR (KBr pellet): ν = 1648 (s),
˜
2
1460 (s), 1440 (m), 1378 (m), 1341 (s), 1245 (m), 1195 (m), 1033
(m), 993 (s), 889 (s), 807 (s), 722 (m), 670 (s), 528 (s), 473 (s) cm–1.
UV/Vis: λ (ε, –1 cm–1) = 550 (6770), 492 (14350), 351 (16060), 242
(38810) nm.
[(η6-C6H6)Ru(κ2-P-N-PPh2EtPy)Cl]PF6·CH2Cl2 (6): To a suspen-
sion of [(η6-C6H6)Ru(κ1-P-PPh2EtPy)Cl2] (0.720 g, 1.0 mmol) in
methanol (25 mL) was added NH4PF6 (0.062 g, 0.843 mmol), and [(η5-C5Me5)Rh(κ2-P–N-PPh2EtPy)Cl]PF6 (9): A mixture of [{(η5-
the mixture was heated to reflux for 4 h. The clear reddish yellow
solution was evaporated to dryness under reduced pressure. The
residue was extracted with dichloromethane and filtered to remove
any insoluble material. The filtrate was saturated with petroleum
ether and left for slow crystallization. It gave a fine crystalline prod-
uct, which was separated by filtration, washed a couple of times
with diethyl ether, and dried in vacuo. Yield: 0.611 g, 76%.
C26H26Cl3F6NP2Ru (735.87): calcd. C 42.45, H 3.57, N 1.91; found
C 42.48, H 3.62, N 1.86. MS (FAB): m/z (calcd.) = m/z 506.3 (505)
C5Me5)Rh(µ-Cl)Cl}2] (0.668 g, 1.0 mmol) and PPh2EtPy (0.291,
1.0 mmol) in methanol (25 mL) was heated under reflux for 8 h.
After cooling to room temperature, methanol was removed under
reduced pressure to one-fourth its volume and a saturated solution
of NH4PF6 was added. It gave a red solid, which was recrystallized
from
CH2Cl2/petroleum
ether.
Yield:
0.542 g,
86%.
C29H33ClF6NP2Rh (709.88): calcd. C 49.07, H 4.69, N 1.97; found
C 49.12, H 4.64, N 1.92. MS (FAB): m/z (calcd.) = 564.9 (564) [(η5-
C5Me5)Rh(κ2-P-N-PPh2EPyt)Cl], 273.9 (273) [(η5-C5Me5)RhCl].
[(η6-C6H6)Ru(κ2-P-N-PPh2EtPy)Cl]+, 471.3 (470) [(η6-C6H6)- 1H NMR: δ = 9.56 (dd, J = 5.2 Hz, 1 H, py-H6), 7.74–7.72 (m, 5
Ru(κ2-P-N-PPh2EtPy)]2+. 1H NMR: δ = 9.78 (dd, J = 5.8 Hz, 1 H,
py-H6), 7.76–7.66 (m, 5 H, py-H4 + Ph-H2), 7.42–7.36 (m, 6 H, (m, 1 H, py-H5), 7.24 (d, J = 7.6 Hz, 1 H, py-H3), 3.22–3.17 (m,
H, py-H4 + Ph-H2), 7.46–7.32 (m, 6 H, Ph-H3 + -H4), 7.26–7.21
Ph-H3 + -H4), 7.27–7.24 (m, 1 H, py-H5), 7.18 (d, J = 7.8 Hz, 1
H, py-H3), 4.64 (s, 5 H, η5-C5H5), 3.24–3.16 (m, 2 H, py-CH2),
2.36–2.28 (m, 2 H, P-CH2) ppm. 13C NMR: δ = 88.43 (C-C6H6),
2 H, py-CH2), 2.41–2.36 (m, 2 H, P-CH2), 1.51 (s, 15 H, C5Me5)
ppm. 13C NMR: δ = 8.53 (C-CH3), 94.72 (C5Me5), 159.6 (py-C2),
154.5 (py-C6), 138.4 (CH), 132.5 (CH), 130.3 (Ph-C1), 127.2 (CH),
154.3 (py-C2), 152.8 (py-C6), 136.4 (CH), 136.6 (CH), 129.6 (Ph- 126.4 (CH), 120.4 (s, CH), 116.3 (s, CH), 37.3 (py-CH2), 28.2 (P-
C1), 134.2 (CH), 131.0 (CH), 122.6 (s, CH), 123.2 (s, CH), 35.2
(py-CH2), 25.1 (P-CH2) ppm. 31P{1H} NMR: δ = 37.71 (s,
PPh2PyEt) ppm. UV/Vis: λ (ε, –1 cm–1) = 558 (5470), 377 (5610),
279 (23630) nm.
CH2) ppm. 31P{1H} NMR: δ = 10.69 (s, PPh2EtPy) ppm. IR (KBr
pellet): ν = 1648 (s), 1460 (s), 1440 (m), 1378 (m), 1341 (s), 1245
˜
(m), 1195 (m), 1033 (m), 993 (s), 889 (s), 807 (s), 722 (m), 670 (s),
528 (s), 473 (s) cm–1. UV/Vis: λ (ε, –1 cm–1) = 539 (6310), 487
(12000), 354 (10950), 281 (35090) nm.
[(η6-C10H14)Ru(κ2-P-N-PPh2EtPy)Cl]PF6 (7): Prepared by follow-
ing the procedure for
6
starting from [(η6-C10H14)Ru(κ1-P-
[(η5-C5Me5)Ir(κ2-P-N-PPh2EtPy)Cl]PF6 (10): Prepared by follow-
ing the procedure for 9 by using [{(η5-C5Me5)Ir(µ-Cl)Cl}2] (0.795 g,
1.0 mmol) instead of [{(η5-C5Me5)Rh(µ-Cl)Cl}2]. Yield: 0.695 g,
78%. C29H33ClF6IrNP2 (799.20): calcd. C 43.58, H 4.16, N 1.75;
found C 43.62, H 4.10, N 1.82. MS (FAB): m/z (calcd.) = 654.2
(654) [(η5-C5Me5)Ir(κ2-P-N-PPh2EtPy)Cl], 363.2 (364) [(η5-C5Me5)
PPh2EtPy)Cl2] (0.755 g, 1.0 mmol). Yield: 0.634 g, 86%. M.p.
140 °C. C29H32ClF6NP2Ru (707.04): calcd. C 49.26, H 4.56, N 1.98;
found C 49.30, H 4.64, N 1.84. MS (FAB): m/z (calcd.) = 562.04
(562) [(η6-C10H14)Ru(κ2-P-N-PPh2EtPy)Cl]+, 526.5 (526) [(η5-
C10H14)Ru(κ2-P-N-PPh2EtPy)]2+, 235.4 (235) [(η5-C10H14)Ru]2+
.
1H NMR: δ = 9.46 (dd, J = 5.0 Hz, 1 H, py-H6), 7.76–7.68 (m, 5
IrCl]. H NMR: δ = 9.56 (dd, J = 5.2 Hz, 1 H, py-H6), 7.74–7.72
1
H, py-H4 + Ph-H2), 7.46–7.34 (m, 6 H, Ph-H3 + -H4), 7.25–7.22 (m, 5 H, py-H4 + Ph-H2), 7.46–7.32 (m, 6 H, Ph-H3 + -H4), 7.26–
(m, 1 H, py-H5), 7.16 (d, J = 7.6 Hz, 1 H, py-H3), 5.24 [d, J = 7.21 (m, 1 H, py-H5), 7.24 (d, J = 7.6 Hz, 1 H, py-H3), 3.22–3.17
5.8 Hz,
C10H14(C6H4)], 3.18–3.16 (m, 2 H, py-CH2), 2.96 (sept., 1 H), 2.43– C5Me5) ppm. 13C NMR: δ = 8.38 (C-CH3), 86.69 (C5Me5), 162.5
2.37 (m, 2 H, P-CH2), 2.28 (s, 3 H, CH3), 1.34 (d, J = 6.92 Hz, 6 (py-C2), 155.8 (py-C6), 140.5 (CH), 136.6 (CH), 134.6 (Ph-C1),
H, CH3) ppm. 13C NMR: δ = 18.65 (C-CH3), 22.12 [CH- 134.2 (CH), 129.0 (CH), 124.6 (s, CH), 123.2 (s, CH), 35.6 (py-
2 H, C10H14(C6H4)], 5.42 [d, J = 5.9 Hz, 2 H, (m, 2 H, py-CH2), 2.41–2.36 (m, 2 H, P-CH2), 1.56 (s, 15 H,
(CH3)2], 32.60 [CH(CH3)2], 85.70 (C6H4), 102.54 (C-CH3), 104.61
(C-CHMe2), 162.5 (py-C2), 155.8 (py-C6), 140.5 (CH), 136.6 (CH),
CH2), 26.4 (P-CH2) ppm. 31P{1H} NMR: δ = 2.40 (s, PPh2EtPy)
ppm. IR (KBr pellet): ν = 1648 (s), 1464 (s), 1434 (m), 1378 (m),
˜
134.6 (Ph-C1), 134.2 (CH), 129.0 (CH), 124.6 (s, CH), 123.2 (s, 1341 (s), 1245 (m), 1192 (m), 1036 (m), 996 (s), 890 (s), 806 (s), 720
712 Eur. J. Inorg. Chem. 2010, 704–715
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Piano-Stool Complexes Containing 2-(2-Diphenylphosphanylethyl)pyridine
(m), 674 (s), 526 (s), 478 (s) cm–1. UV/Vis: λ (ε, –1 cm–1) = 540
(17120), 489 (96560), 357 (94000), 241 (36330) nm.
22.571(2) Å, α = 90°, β = 108.903(9)°, γ = 90°, V = 3557.3(4) Å3,
Z = 4, Dcalcd. = 1.506 gcm–3, µ = 0.585 mm–1, T = 150(2) K, λ =
0.71073 nm, R(all) = 0.0484, R[IϾ2σ(I)] = 0.0373, wR2 = 0.1026,
wR2[IϾ2σ(I)] = 0.0970, GooF = 1.081.
[(η5-C5Me5)Ir(κ1-P-PPh2EtPy)(N3)2] (11): To a solution of com-
plex 10 (0.39 g, 0.5 mmol) in methanol (40 mL) was added sodium
azide (0.52 g, 8.0 mmol), and the mixture was stirred at room tem-
perature for 8 h. The resulting solution was evaporated to dryness,
and the residue was extracted with dichloromethane and filtered
through Celite. The filtrate was saturated with diethyl ether and left
undisturbed for slow crystallization. Slowly, it gave a yellow solid,
which was filtered, washed with diethyl ether, and dried in air.
Yield: 0.30 g, 77% (11). C29H33IrN7P (702.82): calcd. C 49.56, H
Complex 6: Formula = C26H26Cl3F6NP2Ru, Mr = 735.84, ortho-
rhombic space group P212121, a = 9.4603(7) Å, b = 11.7153(9) Å,
c = 25.822(3) Å, α = 90°, β = 90°, γ = 90°, V = 2861.9(4) Å3, Z =
4, Dcalcd. = 1.708 gcm–3, µ = 0.998 mm–1, T = 150(2) K, λ =
0.71073 nm, R(all) = 0.0705, R[IϾ2σ(I)] = 0.0621, wR2 = 0.1598,
wR2[IϾ2σ(I)] = 0.1571, GooF = 1.111.
1
4.73, N 13.95; found C 49.60, H 4.75, N 13.92. H NMR: δ = 8.56
Complex 9: Formula = C29H33ClF6NP2Rh, Mr = 709.86, triclinic
¯
(d, J = 5.2 Hz, 1 H, py-H6), 7.74–7.72 (m, 5 H, py-H4 + Ph-H2),
7.46–7.32 (m, 6 H, Ph-H3 + -H4), 7.26–7.21 (m, 1 H, py-H5), 7.24
(d, J = 7.6 Hz, 1 H, py-H3), 3.22–3.17 (m, 2 H, py-CH2), 2.41–
2.36 (m, 2 H, P-CH2), 1.56 (s, 15 H, C5Me5) ppm. 31P{1H}NMR:
space group P1,
a = 8.3137(5) Å, b = 12.0488(8) Å, c =
14.5773(10) Å, α = 96.302(5)°, β = 92.148(5)°, γ = 94.089(5)°, V =
1446.18(16) Å3, Z = 2, Dcalcd. = 1.630 gcm–3, µ = 0.853 mm–1, T =
150(2) K, λ = 0.71073 nm, R(all) = 0.0881, R[IϾ2σ(I)] = 0.0753,
wR2 = 0.2127, wR2[IϾ2σ(I)] = 0.2079, GooF = 1.138.
δ = 20.71 (s, PPh EtPy) ppm. IR (KBr pellet): ν = 2024 (s), 1624
˜
2
(s), 1460 (s), 1432 (m), 1378 (m), 1344 (s), 1235 (m), 1192 (m), 1036
(m), 996 (s), 720 (m), 674 (s), 526 (s), 478 (s) cm–1.
Complex 10: Formula = C29H33ClF6IrNP2, Mr = 799.15, triclinic
¯
space group P1,
a = 8.3872(2) Å, b = 12.0166(4) Å, c =
[(η5-C5Me5)Ir(κ1-P-PPh2EtPy)Cl2] (12): Prepared by following the
procedure for 11 except that NaCl (0.46 g, 8.0 mmol) was used in
place of NaN3. Yield: 0.32 g, 82%. C29H33Cl2IrN (658.71): calcd.
C 52.88, H 5.05, N 2.13; found C 52.85, H 5.08, N 2.18. 1H NMR:
δ = 8.46 (d, J = 4.6 Hz, 1 H, py-H6), 7.68–7.71 (m, 5 H, py-H4 +
Ph-H2), 7.40–7.30 (m, 6 H, Ph-H3 + -H4), 7.22–7.18 (m, 1 H, py-
H5), 7.26 (d, J = 7.7 Hz, 1 H, py-H3), 3.20–3.16 (m, 2 H, py-CH2),
2.39–2.36 (m, 2 H, P-CH2), 1.56 (s, 15 H, C5Me5) ppm. 31P{1H}
NMR: δ = 20.79 (s, PPh2EtPy) ppm.
14.5758(4) Å, α = 96.887(2)°, β = 91.915(2)°, γ = 93.709(2)°, V =
1454.12(7) Å3, Z = 2, Dcalcd. = 1.825 gcm–3, µ = 4.853 mm–1, T =
150(2) K, λ = 0.71073 nm, R(all) = 0.0277, R[IϾ2σ(I)] = 0.0246,
wR2 = 0.0628, wR2[IϾ2σ(I)] = 0.0621, GooF = 1.082.
Supporting Information (see footnote on the first page of this arti-
cle): FAB spectra of 1–6 and 8–10; cyclic voltammograms of 1 and
2; π···π interactions in 1; motifs resulting from various C–H···F
weak bonding interactions in 6; C–H···π interactions in 9; mono-
hydride inner-sphere mechanism for hydrogen transfer from formic
acid to a ketone.
Catalytic Experiments: Hydrogen-transfer experiments for the hy-
drogenation of acetophenone (0.64 mmol) were carried out in water
(5 mL) at 80 °C for 8–14 h in the presence of complexes 1–10
(6.4 µmol), sodium formate (3.2 mmol), and HCOOH/HCOONa
buffer (pH 4.0). The reactions were quenched at 0 °C, and the prod-
ucts were extracted with diethyl ether and separated by silica gel
chromatography. These were analyzed by 1H NMR spectroscopy
in CDCl3 and the yields of the respective processes were calculated
considering relative integral of the ketones and alcohol.
Acknowledgments
We gratefully acknowledge financial support from the Department
of Science and Technology, Ministry of Science and Technology,
New Delhi, India (Grant No. SR/SI/IC-15/2007). Thanks are also
due to Prof. P. Mathur, In-charge, National Single Crystal X-ray
Diffraction Facility, Indian Institute of Technology, Mumbai, for
providing single-crystal X-ray data. Further, we are grateful to the
Head, Department of Chemistry, Faculty of Science, Banaras
Hindu University, Varanasi, for extending laboratory facilities.
Crystallographic Studies: Suitable crystals for single X-ray diffrac-
tion analyses for complexes 1, 5, 6, 9, and 10 were obtained by slow
diffusion of petroleum ether (40–60 °C) into the dichloromethane
solution of the respective complexes at room temperature. Prelimi-
nary data on the space group and unit-cell dimensions as well as
intensity data were collected with an Oxford Diffraction
XCAUBER-SЈ diffractometer by using graphite monochromated
Mo-Kα radiation. The structures were solved by direct methods and
refined by using SHELX-97[38] Non-hydrogen atoms were refined
with anisotropic thermal parameters. All the hydrogen atoms were
geometrically fixed and allowed to refine by using a riding model.
The computer program PLATON was used for analyzing the inter-
action and stacking distance.[38] CCDC-742869 (for 1), -742870 (for
5), -742871 (for 6), -742872 (for 10), and -742873 (for 9) contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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Complex 1: Formula = C42H38ClNP2Ru, Mr = 755.19, triclinic
¯
space group P1, a = 9.423(2) Å, b = 9.704(2) Å, c = 19.907(4) Å, α
= 89.961(17)°, β = 78.293(18)°, γ = 71.93(2)°, V = 1690.7(6) Å3, Z
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Eur. J. Inorg. Chem. 2010, 704–715
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
713

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Received: October 14, 2009
Published Online: December 22, 2009
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