Synthesis of pincer ruthenium RuCl(CNN)(PP) catalysts from [RuCl(μ-Cl)(η6-p-cymene)]2

Article abstract of DOI:10.1021/om400280m

The cationic [RuCl(η⁶-p-cymene)(HCNN^a)]Cl (1a) (HCNN^a = 1-(6-arylpyridin-2-yl)methanamine) and the neutral RuCl ₂(η⁶-p-cymene)(HCNN^b) (1b) (HCNN ^b = 2-aminomethylbenzo[h]quinoline) complexes have been obtained by reaction of the precursor [RuCl(μ-Cl)(η⁶-p-cymene)] ₂ with the corresponding nitrogen ligand (HCNN^a and HCNN^b) in THF. Complex 1a reacts cleanly with monodentate (P = PPh₃) and bidentate phosphines (PP = dppb, dppf) in ethanol in the presence of NEt₃, affording the pincer catalysts RuCl(CNN ^a)(PPh₃)₂ (2) and RuCl(CNN^a)(PP) (PP = dppb 3, dppf 4). Similarly, the benzo[h]quinoline pincer derivative RuCl(CNN^b)(dppb) (5) is obtained from 1b and dppb. Complex 3 has also been prepared in a one-pot reaction from [RuCl(μ-Cl)(η⁶-p- cymene)]₂, HCNN^a, and dppb in ethanol. Similarly, the chiral complex RuCl(CNN^a)((R,S)-Josiphos) was isolated as a single stereoisomer by treatment of [RuCl(μ-Cl)(η⁶-p-cymene)] ₂ with HCNN^a and (R,S)-Josiphos in 1-butanol. Reaction of 1a and 1b with dppb affords cymene diphosphine species by displacement of the HCCN ligand.

Full text of DOI:10.1021/om400280m

Article
pubs.acs.org/Organometallics
Synthesis of Pincer Ruthenium RuCl(CNN)(PP) Catalysts from [RuCl(μ-
Cl)(η6‑p‑cymene)]2
Shuanming Zhang and Walter Baratta*
̀
Dipartimento di Chimica, Fisica Ambiente, Universita di Udine, Via Cotonificio 108, I-33100 Udine, Italy
S
* Supporting Information
ABSTRACT: The cationic [RuCl(η6-p-cymene)(HCNNa)]Cl
(1a) (HCNNa = 1-(6-arylpyridin-2-yl)methanamine) and the
neutral RuCl2(η6-p-cymene)(HCNNb) (1b) (HCNNb = 2-
aminomethylbenzo[h]quinoline) complexes have been ob-
tained by reaction of the precursor [RuCl(μ-Cl)(η6-p-
cymene)]2 with the corresponding nitrogen ligand (HCNNa
and HCNNb) in THF. Complex 1a reacts cleanly with
monodentate (P = PPh3) and bidentate phosphines (PP =
dppb, dppf) in ethanol in the presence of NEt3, affording the pincer catalysts RuCl(CNNa)(PPh3)2 (2) and RuCl(CNNa)(PP)
(PP = dppb 3, dppf 4). Similarly, the benzo[h]quinoline pincer derivative RuCl(CNNb)(dppb) (5) is obtained from 1b and
dppb. Complex 3 has also been prepared in a one-pot reaction from [RuCl(μ-Cl)(η6-p-cymene)]2, HCNNa, and dppb in ethanol.
Similarly, the chiral complex RuCl(CNNa)((R,S)-Josiphos) was isolated as a single stereoisomer by treatment of [RuCl(μ-
Cl)(η6-p-cymene)]2 with HCNNa and (R,S)-Josiphos in 1-butanol. Reaction of 1a and 1b with dppb affords cymene diphosphine
species by displacement of the HCCN ligand.
The preparation of these complexes entails the reaction of
RuCl2(PPh3)3 with a diphosphine and the HCNN ligand,
through orthometalation. It is worth noting that the arene
complexes [RuCl(μ-Cl)(η6-arene)]2 are the common precur-
sors used for the synthesis of the Noyori catalysts for both
hydrogenation and transfer hydrogenation reactions and
involve the formation of species containing the Ru(η6-
arene)(LL) moiety (LL = diphosphine, diamine).12
We report herein a new practical route for the preparation of
the CNN pincer catalysts starting from the commercially
available [RuCl(μ-Cl)(η6-p-cymene)]2 and from cationic and
neutral HCNN cymene ruthenium complexes.
INTRODUCTION
■
The reduction of carbonyl compounds to alcohols is a versatile
organic transformation for the preparation of a number of
industrially relevant products.1 The catalytic hydrogenation2
and transfer hydrogenation3 of ketones can be achieved using
dihydrogen or hydrogen donor molecules, such as formic acid
or 2-propanol, mediated by transition-metal complexes based
on Rh, Ir, Os,4 and Ru, with ruthenium being the metal of
choice.2,3 On account of the ease of working, absence of the
risks associated with the use of H2, and the environmentally
friendly transformation, the catalytic transfer hydrogenation of
carbonyl compounds has become a valuable route for the
synthesis of alcohols. Following the pioneering works of Noyori
et. al on trans-RuCl2(PP)(1,2-diamine) (PP = diphosphine)5
and (η6-arene)RuCl(TsNCHPhCHPhNH2) (Ts = SO2C6H4-
CH3)6 for the hydrogenation and transfer hydrogenation of
ketones, respectively, several Ru catalysts have been developed
in the past decade. High rate ande chemo- and stereoselectivity
have been achieved using ligands containing the N−H function,
via bifunctional catalysis.7 The CNN pincer complexes
RuCl(CNN)(PP) (HCNN = 1-(6-arylpyridin-2-yl)-
methanamine,8 2-aminomethylbenzo[h]quinoline9), displaying
the NH2 function,7 are the most efficient catalysts for the
transfer hydrogenation of aldehydes and ketones. Outstanding
rate and productivity have been achieved, affording TOF and
TON values of 106 h−1 and 105, respectively, which meet the
requirements for industrial applications. These CNN pincer
complexes have also been found to be highly active in
hydrogenation of carbonyl compounds8c,9b and dehydrogen-
ation,10 racemization, and deuteration of alcohols11 and hold
promise for a broad use in a number of organic transformations.
RESULTS AND DISCUSSION
■
Treatment of [RuCl(μ-Cl)(η6-p-cymene)]2 with 2 equiv of 1-
(6-arylpyridin-2-yl)methanamine (HCNNa) in THF promptly
leads to the complex [RuCl(η6-p-cymene)(HCNNa)]Cl (1a),
which was isolated in 81% yield (Scheme 1).
1
The H NMR spectrum of 1a at 50 °C shows four doublets
for the aromatic p-cymene protons with two doublets for the
isopropyl moiety, whereas the two multiplets at δ = 4.50 are for
the two diastereotopic NCH2 protons. These data are
consistent with a cationic complex with a chloride as
counterion, as observed for analogous ruthenium complexes.13
While one N−H proton is at δ = 3.28 and appears as a broad
quartet, the second N−H is significantly low-field shifted at δ =
1
9.46 (broad triplet), as established through a H−1H COSY
experiment, and it is consistent with an interaction of the N−H
Received: April 4, 2013
© XXXX American Chemical Society
A
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Scheme 1. Synthesis of the Complexes 1a and 1b
Scheme 2. Synthesis of the Pincer Complexes 2−5
proton with the outer sphere chloride. In addition, the two
broad signals at δ = 7.25 and 7.90 of the aromatic tolyl protons
at 25 °C become sharper at 50 °C with a J(H,H) of 7.5 Hz,
suggesting that the slow rotation of the tolyl group is due to its
interaction with the p-cymene ligand. By contrast to HCNNa,
the reaction of 2-aminomethylbenzo[h]quinoline (HCNNb)
with [RuCl(μ-Cl)(η6-p-cymene)]2 leads to the formation of a
Scheme 3. One-Pot Synthesis of the Pincer Complexes 3
and 6
1
neutral complex 1b in 83% yield (Scheme 1). The H NMR
spectrum of 1b shows two doublets at δ = 5.20 and 5.06 for the
aromatic p-cymene protons, whereas the CH2 and NH2 groups
give two triplets at δ = 4.52 and 4.10, the latter N−H signal
being low-field shifted with respect to that of the free ligand (δ
= 2.90),8d in agreement with a benzo[h]quinoline acting as a
monodentate ligand through the NH2 group.14 The different
behaviors of the two HCNN ligands can be ascribed to the
steric properties of the nitrogen ligands, with the benzo[h]-
quinoline, which displays higher rigidity and hinders the
coordination of the heterocyclic nitrogen to the Ru p-cymene
moiety.
The cationic complex 1a reacts promptly with the mono-
phosphine PPh3 in the presence of triethylamine in ethanol at
reflux, affording the pincer compound RuCl(CNNa)(PPh3)2
(2) through displacement of p-cymene and orthometalation of
the HCNN ligand (Scheme 2). Under the same experimental
conditions, 1a reacts with the diphosphine Ph2P(CH2)4PPh2
(dppb), leading to the pincer catalysts RuCl(CNNa)(dppb)
(3),8a whereas the use of 1,1′-bis(diphenylphosphino)ferrocene
(dppf) affords RuCl(CNNa)(dppf) (4),11 which were isolated
in high yield (Scheme 2).
molar ratio, respectively.15,16 Interestingly, by performing the
reaction in refluxing 1-butanol, which displays a boiling point
higher compared to ethanol (117 vs 78 °C), the chiral pincer
complex RuCl(CNNa)((R,S)-Josiphos) (6)8c was obtained as a
single stereoisomer and was isolated in 62% (Scheme 3).
Employment of toluene resulted in the formation of a mixture
of uncharacterized products, indicating that the solvent is
crucial for the synthesis of the pincer catalysts with (chiral)
bulky phosphines.
To elucidate the nature of the species involved in the
formation of the pincer complexes, we studied the reactivity of
the arene ruthenium complexes with HCNN and phosphine
ligands. It is well-established that the precursor [RuCl(μ-
Cl)(η6-p-cymene)]2 reacts promptly with phosphines, leading
to cationic or neutral complexes, depending on the stereo-
electronic features of the phosphines. As a matter of fact, the
reaction of [RuCl(μ-Cl)(η6-p-cymene)]2 with rigid diphos-
phines, such as BINAP, gave the cationic [RuCl(η6-p-
cymene)(BINAP)]Cl complex.17 Cationic species [RuCl(η6-p-
cymene)(PP)]+ (e.g., for PP = dppf)18 were easily prepared by
substitution of one chloride with low coordinating anions,
namely, PF6 or BF4, in polar solvent media. Reaction of
Conversely, the neutral benzo[h]quinoline derivative 1b
reacts cleanly with dppb in ethanol at reflux, affording the
pincer complex 59a in 80% yield (Scheme 2). It is worth
pointing out that the pincer complex RuCl(CNNa)(dppb) (3)
was also obtained in 64% yield by adding HCNNa and dppb to
the ruthenium precursor [RuCl(μ-Cl)(η6-p-cymene)]2 in
ethanol at reflux and in the presence of NEt3, through a one-
pot synthesis and without isolating the 1a intermediate
(Scheme 3).
Following this procedure, treatment of [RuCl(μ-Cl)(η6-p-
cymene)]2 with HCNNa and the chiral diphosphine (R,S)-
Josiphos in EtOH at refluxing conditions (8 h) results in the
formation of a mixture of two RuCl(CNNa)((R,S)-Josiphos)
diastereoisomers and the cationic arene phosphino intermedi-
ate [RuCl(η6-p-cymene)((R,S)-Josiphos)]Cl in about a 1:3:8
B
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[RuCl(μ-Cl)(η6-p-cymene)]2 with dppb led to the isolation of
the neutral dinuclear complex [RuCl2(η6-cymene)]2(μ-dppb),
regardless of the ruthenium/diphosphine stoichiometry, as
reported by Doherty et al.19 We found in this work that
[RuCl(μ-Cl)(η6-p-cymene)]2 reacts with dppb in dichloro-
methane, leading to an equilibrium between mononuclear and
dinuclear Ru complexes, according to eq 1
were recorded at 298 K on a Bruker AC 200 instrument at 200, 60,
and 80 MHz, respectively, whereas the chemical shifts are in parts per
million, using TMS or H3PO4 (85% in D2O) as external standards.
The elemental analyses were carried out with a Carlo Erba 1106
elemental analyzer.
Synthesis of [RuCl(η6-p-cymene)(HCNNa)]Cl (1a). [RuCl(μ-
Cl)(η6-p-cymene)]2 (0.306 g, 0.5 mmol) was added to a solution of
HCNNa (0.198 g, 1.0 mmol) in THF (5 mL). The mixture was stirred
at room temperature for 10 min, affording a yellow precipitate that was
filtered, washed with THF, and dried under reduced pressure (0.410 g,
81% yield). mp 139 °C. Anal. Calcd for C23H28Cl2N2Ru (504.46): C,
[RuCl2(η6 ‐ p ‐ cymene)]2(μ ‐ dppb) + dppb
⇌ 2Rucl2(η6 ‐ p ‐ cymene)(η1 ‐ dppb)
1
(1)
54.76; H, 5.59; N, 5.55. Found: C, 54.65; H, 5.20; N, 5.40. H NMR
(CDCl3, 50 °C): δ 9.46 (br, 1H, NH2), 7.95−7.29 (m, 7H, aromatic
A K = 2.2 at 25 °C was determined through 31P{1H} NMR
measurements carried out with a Ru:diphosphine molar ratio of
1:1 to 1:3.20 As regards to the HCNN cymene derivatives,
complex 1b reacts promptly (5 min) with dppb in CD2Cl2 at
RT, affording RuCl2(η6-p-cymene)(η1-dppb) and [RuCl2(η6-p-
cymene)]2(μ-dppb) in equilibrium (eq 1), by displacement of
the HCNNb ligand. The reaction of the cationic complex 1a
gives the same phosphino complexes at 40 °C after 15 h. These
results clearly indicate that the neutral complex 1b is more
labile than the cationic 1a and that the diphosphine is a
stronger ligand compared to the neutral bidentate HCNNa and
HCNNb ligands. Therefore, the formation of the pincer
complexes from 1a and 1b involves the displacement of
HCNN with the phosphine, leading to the neutral or cationic
species Ru(η6-p-cymene)Cln(PP)0/+ (n = 1, 2). In alcohol
media and under reflux conditions, these species react with the
HCNN, affording RuCl2(HCNN)(PP) by elimination of p-
cymene and leading to the final RuCl(CNN)(PP) complex via
orthometalation. It is worth noting that employment of
diphosphines with a short backbone (i.e., dppe) leads to the
RuCl2(PP)2 species that show high stability and do not convert
into the pincer complexes. Thus, the preparation of RuCl-
(CNN)(PP) derivatives is accomplished with a suitable
combination of the HCCN and phosphine ligands. In addition,
although arene phosphine derivatives can be employed for the
synthesis of the pincer complexes, the Ru/phosphine
stoichiometry depends on the type of the phosphine used.
hydrogens), 5.96 (d, 1H, 3J(H,H) = 6.0 Hz, C6H4 of cymene), 5.24 (d,
3
3
1H, J(H,H) = 6.0 Hz, C6H4 of cymene), 4.98 (d, 1H, J(H,H) = 6.0
Hz, C6H4 of cymene), 4.80 (d, 1H, 3J(H,H) = 6.0 Hz, C6H4 of
cymene), 4.63 (m, 1H, NCH2), 4.40 (m, 1H, NCH2), 3.28 (br, 1H,
3
NH2), 2.72 (sept, 1H, J(H,H) = 7.0 Hz, CH(CH3)2), 2.49 (s, 3H,
CH3 of HCNNa), 1.93 (s, 3H, CH3 of cymene), 1.05 (d, 3H, 3J(H,H)
3
= 7.0 Hz, CH(CH3)2), 0.96 (d, 3H, J(H,H) = 7.0 Hz, CH(CH3)2).
13C{1H} NMR (CDCl3): δ 164.7−119.4 (m, aromatic carbons), 103.7
(s, ipso-C6H4 of cymene), 90.1 (s, ipso-C6H4 of cymene), 83.8 (br,
C6H4 of cymene), 82.7 (br), 54.1 (s, NCH2), 30.7 (s, CH(CH3)2),
23.0 (s, CH3 of HCNNa), 21.4 (s, CH(CH3)2), 18.6 (s, CH3 of
cymene).
Synthesis of RuCl2(η6-p-cymene)(HCNNb) (1b). [RuCl(μ-Cl)-
(η6-p-cymene)]2 (0.306 g, 0.50 mmol) was added to a solution of
ligand HCNNb (0.208 g, 1.0 mmol) in THF (5 mL). The mixture was
stirred at room temperature for 10 min, affording an orange-yellow
precipitate that was filtered, washed with THF, and dried under
reduced pressure (0.427 g, 83% yield). mp 211 °C. Anal. Calcd for
C24H26Cl2N2Ru (514.45): C, 56.03; H, 5.09; N, 5.45. Found: C, 56.05;
1
H, 5.25; N, 5.31. H NMR (CD2Cl2): δ 7.44−9.33 (m, 8H, aromatic
hydrogens of HCNNb), 5.20 (d, 2H, 3J(H,H) = 6.0 Hz, C6H4 of
3
cymene), 5.06 (d, 2H, J(H,H) = 6.0 Hz, C6H4 of cymene), 4.52 (t,
2H, 3J(H,H) = 4.5 Hz, NCH2), 4.10 (t, 2H, 3J(H,H) = 4.5 Hz, NH2),
3
2.93 (sept, 1H, J(H,H) = 7.2 Hz, CH(CH3)2), 2.14 (s, 3H, CH3),
1.23 (d, 6H, 3J(H,H) = 7.2 Hz, CH(CH3)2). 13C{1H} NMR
(CD2Cl2): δ 156.0−120.7 (aromatic carbons), 102.7 (s, ipso-C6H4 of
cymene), 95.8 (s, ipso-C6H4 of cymene), 81.2 (s, C6H4 of cymene),
80.1 (s, C6H4 of cymene), 52.5 (s, NCH2), 31.1 (s, CH(CH3)2), 22.2
(s, CH(CH3)2), 18.7 (s, CH3 of cymene).
Synthesis of RuCl(CNNa)(PPh3)2 (2). PPh3 (0.216 g, 0.8 mmol)
and NEt3 (0.5 mL, 3.5 mmol) were added to a solution of complex
[RuCl(η6-p-cymene)(HCNNa)]Cl (1a) (0.200 g, 0.4 mmol) in
ethanol (5 mL). The resulting mixture was stirred under reflux for 2
h, whereupon a dark yellow precipitate formed that was filtered,
washed with ethanol, and dried under reduced pressure (0.284 g, 83%
yield). mp 158 °C. Anal. Calcd for C49H43ClN2P2Ru (858.35): C,
CONCLUDING REMARKS
■
In summary, we have described the isolation of ionic [RuCl(η6-
p-cymene)(HCNN]Cl and neutral RuCl2(η6-p-cymene)-
(HCNN) complexes, displaying a Ru/HCNN = 1, which can
be used as suitable precursors for the preparation of the pincer
catalysts RuCl(CNN)(PP) by reaction with the appropriate
phosphine ligand. Steric effects and the rigidity of HCNN are
responsible for the different coordination modes of these
ligands to the ruthenium center. Achiral and chiral pincer
complexes have also been prepared from [RuCl(μ-Cl)(η6-p-
cymene)]2, HCNN, and the appropriate (chiral) diphosphine
ligand, through a one-pot reaction using EtOH or 1-BuOH as
solvents. The straightforward synthesis of the pincer ruthenium
complexes holds promise for a broad use of them as catalysts in
organic transformations.
1
68.56; H, 5.05; N, 3.26. Found: C, 68.35; H, 5.20; N, 3.07. H NMR
(CDCl3): δ 7.95−6.84 (m, 36H, aromatic), 4.52 (br, 1H, NCH2), 4.05
(br, 1H, NCH2), 3.45(br, 1H, NH2), 2.18 (s, 3H, CH3), 1.53 (br, 1H,
NH2). 31P{1H} NMR (CDCl3): δ 56.7 (d, 2J(P,P) = 33.6 Hz), 50.5 (d,
2J(P,P) = 33.6 Hz).
Synthesis of RuCl(CNNa)(dppb) (3). The synthesis of 3 was
carried out as described for 2 by addition of NEt3 (0.5 mL, 3.5 mmol)
and dppb (0.172 g, 0.4 mmol) in place of PPh3, to a solution of
[RuCl(η6-p-cymene)(HCNNa)]Cl (1a) (0.200 g, 0.4 mmol) in
ethanol (5 mL). The resulting mixture was stirred under reflux for 2
h, whereupon a yellow precipitate formed that was filtered, washed
with ethanol, and dried under reduced pressure (0.244 g, 80% yield).8a
Synthesis of RuCl(CNNa)(dppf) (4). The synthesis of 4 was
carried out as described for 2 by addition of NEt3 (0.5 mL, 3.5 mmol)
and dppf (0.216 g, 0.4 mmol) in place of PPh3, to a solution of
complex [RuCl(η6-p-cymene)(HCNNa)]Cl (1a) (0.200 g, 0.4 mmol)
in ethanol (5 mL). The resulting mixture was stirred under reflux for 2
h, whereupon a yellow precipitate formed that was filtered, washed
with ethanol, and dried under reduced pressure (0.284 g, 79% yield).11
Synthesis of RuCl(CNNb)(dppb) (5). The synthesis of 5 was
carried out as described for 2 by addition of NEt3 (0.5 mL, 3.5 mmol)
EXPERIMENTAL SECTION
■
All manipulations were carried out under an inert argon atmosphere,
using standard Schlenk-line conditions and dried and freshly distilled
solvents. The HCNN ligands 6-(4′-methylphenyl)-2-pyridylmethyl-
amine (HCNNa)8d and 2-aminomethylbenzo[h]quinoline (HCNNb)9a
were prepared according to literature procedures. All other chemicals
were purchased from Aldrich and used without further purification.
1
Unless otherwise stated, the H, 13C{1H}, and 31P{1H} NMR spectra
C
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Article
and dppb (0.172 g, 0.4 mmol) in place of PPh3, to a solution of
complex RuCl2(η6-p-cymene)(HCNNb) (1b) (0.204 g, 0.4 mmol) in
ethanol (5 mL). The resulting mixture was stirred under reflux for 2 h,
whereupon a yellow precipitate formed that was filtered, washed with
ethanol, and dried under reduced pressure (0.062 g, 80% yield).9a
One-Pot Synthesis of RuCl(CNNa)(dppb) (3). dppb (0.214 g, 0.5
mmol), HCNNa (0.100 g, 0.5 mmol), and NEt3 (0.2 mL, 1.4 mmol)
were added to a solution of complex [RuCl(μ-Cl)(η6-p-cymene)]2
(0.153 g, 0.25 mmol) in ethanol (3 mL). The resulting mixture was
stirred under reflux for 2 h, whereupon a dark yellow precipitate
formed that was filtered, washed with ethanol, and dried under
reduced pressure (0.243 g, 64% yield).
(7) (a) Yamakawa, M.; Ito, H.; Noyori, R. J. Am. Chem. Soc. 2000,
122, 1466. (b) Petra, D. G. I.; Reek, J. N. H.; Handgraaf, J. W.; Meijer,
E. J.; Dierkes, P.; Kamer, P. C. J.; Brussee, J.; Schoemaker, H. E.; van
Leeuwen, P. W. N. M. Chem.Eur. J. 2000, 6, 2818.
(8) (a) Baratta, W.; Chelucci, G.; Gladiali, S.; Siega, K.; Toniutti, M.;
Zanette, M.; Zangrando, E.; Rigo, P. Angew. Chem., Int. Ed. 2005, 44,
6214. (b) Baratta, W.; Siega, K.; Rigo, P. Adv. Synth. Catal. 2007, 349,
1633. (c) Baratta, W.; Chelucci, G.; Magnolia, S.; Siega, K.; Rigo, P.
Chem.Eur. J. 2009, 15, 726. (d) Baratta, W.; Bosco, M.; Chelucci,
G.; Del Zotto, A.; Siega, K.; Toniutti, M.; Zangrando, E.; Rigo, P.
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Zotto, A.; Fanfoni, L.; Felluga, F.; Magnolia, S.; Putignano, E.; Rigo, P.
Organometallics 2010, 29, 3563.
One-Pot Synthesis of RuCl(CNNa)((R,S)-Josiphos) (6). (R,S)-
Josiphos (0.320 g, 0.5 mmol), HCNNa (0.100 g, 0.5 mmol), and NEt3
(0.5 mL, 3.5 mmol) were added to a solution of complex [RuCl(μ-
Cl)(η6-p-cymene)]2 (0.156 g, 0.25 mmol) in 1-butanol (4 mL). The
resulting mixture was stirred under reflux for 4 h, the resulting dark red
solution was concentrated to 0.5 mL, and pentane (5 mL) was added.
Compound 6 was obtained as a dark yellow solid through filtration
and dried under reduced pressure (0.301 g, 62% yield).8c
(9) (a) Baratta, W.; Ballico, M.; Baldino, S.; Chelucci, G.; Herdtweck,
E.; Siega, K.; Magnolia, S.; Rigo, P. Chem.Eur. J. 2008, 14, 9148.
(b) Baratta, W.; Fanfoni, L.; Magnolia, S.; Siega, K.; Rigo, P. Eur. J.
Inorg. Chem. 2010, 1419.
(10) Baratta, W.; Bossi, G.; Putignano, E.; Rigo, P. Chem.Eur. J.
2011, 17, 3474.
(11) Bossi, G.; Putignano, E.; Rigo, P.; Baratta, W. Dalton Trans.
2011, 40, 8986.
ASSOCIATED CONTENT
* Supporting Information
The NMR spectra of 1a and of the Ru(p-cymene)/dppb
system. This material is available free of charge via the Internet
at http://pubs.acs.org.
(12) (a) Noyori, R.; Ohkuma, T. Angew. Chem., Int. Ed. 2001, 40, 40.
(b) Noyori, R.; Hashiguchi, S. Acc. Chem. Res. 1997, 30, 97.
■
S
(13) (a) Turkmen, H.; Kani, I.; Çetinkaya, B. Eur. J. Inorg. Chem.
̈
2012, 4494. (b) Zobi, F.; Mood, B. B.; Wood, P. A.; Fabbiani, F. P. A.;
Parsons, S.; Sadler, P. J. Eur. J. Inorg. Chem. 2007, 2783.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: walter.baratta@uniud.it.
Notes
■
(15) 31P{1H} NMR in CDCl3: δ 78.3 and 40.3 (d, 2J(P,P) = 43.2 Hz,
2
diastereomer of 6), 68.7 and 44.3 (d, J(P,P) = 42.8 Hz, complex 6),
49.1 and 28.3 (d, 2J(P,P) = 59.2 Hz, [RuCl(η6-p-cymene)((R,S)-
Josiphos)]Cl).
(16) Zanetti, N. C.; Spindler, F.; Spencer, J.; Togni, A.; Rihs, G.
Organometallics 1996, 15, 860.
The authors declare no competing financial interest.
(17) (a) den Reijer, C. J.; Dotta, P.; Pregosin, P. S.; Albinati, A. Can.
J. Chem. 2001, 79, 693. (b) Mashima, K.; Kusano, K. H.; Sate, N.;
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ACKNOWLEDGMENTS
This work was supported by the Ministero dell’Universita
della Ricerca (MIUR) and the Talents program of the AREA
Science Park of Trieste for a fellowship for S.Z. We thank
Johnson-Matthey/Alfa Aesar for a generous loan of ruthenium
and Mr. P. Polese for carrying out the elemental analyses.
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dx.doi.org/10.1021/om400280m | Organometallics XXXX, XXX, XXX−XXX