Flat and Efficient H CNN and CNN Pincer Ruthenium Catalysts for Carbonyl Compound Reduction

Article abstract of DOI:10.1021/acs.organomet.8b00919

The bidentate HCNN dicarbonyl ruthenium complexes trans,cis-[RuCl₂(HCNN)(CO)₂] (1-3) and trans,cis-[RuCl₂(ampy)(CO)₂] (1a) were prepared by reaction of [RuCl₂(CO)₂]_n with 1-[6-(4′-methylphenyl)pyridin-2-yl]methanamine, benzo[h]quinoline (HCNN), and 2-(aminomethyl)pyridine (ampy) ligands. Alternatively, the derivatives 1-3 were obtained from the reaction of RuCl₃ hydrate with HCO₂H and HCNN. The pincer CNN cis-[RuCl(CNN)(CO)₂] (4) was isolated from 1 by reaction with NEt₃. The monocarbonyl complexes trans-[RuCl₂(HCNN)(PPh₃)(CO)] (5-7) were synthesized from [RuCl₂(dmf)(PPh₃)₂(CO)] and HCNN ligands, while the diacetate trans-[Ru(OAc)₂(HCNN)(PPh₃)(CO)] (8) was obtained from [Ru(OAc)₂(PPh₃)₂(CO)]. Carbonylation of cis-[RuCl(CNN)(PPh₃)₂] with CO afforded the pincer derivatives [RuCl(CNN)(PPh₃)(CO)] (9-11). Treatment of 9 with Na[BAr^f]₄ and PPh₃ gave the cationic complex trans-[Ru(CNN)(PPh₃)₂(CO)][BAr^f₄] (12). The dicarbonyl derivatives 1-4, in the presence of PPh₃ or PCy₃, and the monocarbonyl complexes 5-12 catalyzed the transfer hydrogenation (TH) of acetophenone (a) in 2-propanol at reflux (S/C = 1000-100000 and TOF up to 100000 h^-1). Compounds 1-3, with PCy₃, and 6 and 8-10 were proven to catalyze the TH of carbonyl compounds, including α,β-unsaturated aldehydes and bulky ketones (S/C and TOF up to 10000 and 100000 h^-1, respectively). The derivatives 1-3 with PCy₃ and 5 and 6 catalyzed the hydrogenation (HY) of a (H₂, 30 bar) at 70 °C (S/C = 2000-10000). Complex 5 was active in the HY of diaryl ketones and aryl methyl ketones, leading to complete conversion at S/C = 10000.

Full text of DOI:10.1021/acs.organomet.8b00919

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Flat and Efficient HCNN and CNN Pincer Ruthenium Catalysts for
Carbonyl Compound Reduction
†
†
§
Steven Giboulot,†,‡ Salvatore Baldino,†,⊥ Maurizio Ballico, Rosario Figliolia, Alexander Pothig,
̈
Shuanming Zhang,†,∥ Daniele Zuccaccia,† and Walter Baratta*,†
†
̀
Dipartimento DI4A, Universita di Udine, Via Cotonificio 108, I-33100 Udine, Italy
⊥
̀
Dipartimento di Chimica, Universita di Torino, Via Pietro Giuria, 7, I-10125 Torino, Italy
‡Johnson Matthey, 28 Cambridge Science Park, Milton Road, Cambridge CB4 0FP, United Kingdom
§Department of Chemistry & Catalysis Research Center, Technical University of Munich, Lichtenbergstraße 4, 85747 Garching,
Germany
∥Jiangsu Industrial Technology Research Institute (JITRI), No. 699 Xuanwu Avenue, 210008 Nanjing, Jiangsu, People’s Republic of
China
S
* Supporting Information
ABSTRACT: The bidentate HCNN dicarbonyl ruthenium complexes trans,cis-
[RuCl2(HCNN)(CO)2] (1−3) and trans,cis-[RuCl2(ampy)(CO)2] (1a) were
prepared by reaction of [RuCl2(CO)2]n with 1-[6-(4′-methylphenyl)pyridin-2-
yl]methanamine, benzo[h]quinoline (HCNN), and 2-(aminomethyl)pyridine
(ampy) ligands. Alternatively, the derivatives 1−3 were obtained from the reaction
of RuCl3 hydrate with HCO2H and HCNN. The pincer CNN cis-[RuCl(CNN)-
(CO)2] (4) was isolated from 1 by reaction with NEt3. The monocarbonyl
complexes trans-[RuCl2(HCNN)(PPh3)(CO)] (5−7) were synthesized from
[RuCl2(dmf)(PPh3)2(CO)] and HCNN ligands, while the diacetate trans-[Ru-
(OAc)2(HCNN)(PPh3)(CO)] (8) was obtained from [Ru(OAc)2(PPh3)2(CO)].
Carbonylation of cis-[RuCl(CNN)(PPh3)2] with CO afforded the pincer derivatives
[RuCl(CNN)(PPh3)(CO)] (9−11). Treatment of 9 with Na[BArf]4 and PPh3 gave
the cationic complex trans-[Ru(CNN)(PPh3)2(CO)][BArf4] (12). The dicarbonyl
derivatives 1−4, in the presence of PPh3 or PCy3, and the monocarbonyl complexes
5−12 catalyzed the transfer hydrogenation (TH) of acetophenone (a) in 2-propanol at reflux (S/C = 1000−100000 and TOF
up to 100000 h−1). Compounds 1−3, with PCy3, and 6 and 8−10 were proven to catalyze the TH of carbonyl compounds,
including α,β-unsaturated aldehydes and bulky ketones (S/C and TOF up to 10000 and 100000 h−1, respectively). The
derivatives 1−3 with PCy3 and 5 and 6 catalyzed the hydrogenation (HY) of a (H2, 30 bar) at 70 °C (S/C = 2000−10000).
Complex 5 was active in the HY of diaryl ketones and aryl methyl ketones, leading to complete conversion at S/C = 10000.
industry for the production of a number of organic
compounds.5 A crucial breakthrough for the HY and TH
reactions has been the introduction of ligands with an NH
functionality, which led to highly active catalysts, entailing an
outer-sphere mechanism.6 The employment of the ampy
ligand,7 by us and other groups, has afforded the catalysts cis-
[RuCl2(ampy)(PP)] (PP = diphosphine), which allow the
reduction of a number of carbonyl compounds with high rate
and enantioselectiviy.8 Furthermore, the use of 6-aryl-function-
alized ampy ligands has led to cyclometalated pincer9 CNN
complexes [RuCl(CNN)(PP)] (HCNN = Hamtp),7,10 which
display superlative features for the TH and HY of carbonyl
compounds with TOF and TON values up to 106 h−1 and 105,
respectively (Figure 1).
INTRODUCTION
■
The search for more efficient transition-metal catalysts for the
synthesis of valuable organic compounds is an issue of current
relevance for both academia and industry. Among the different
metals, ruthenium has been deeply investigated because of its
high performance in several organic reactions.1 In the last few
decades great concern has been focused in academia on the
improvement of the catalyst (stereo)selectivity for achieving
clean organic transformations. Conversely, on account of
stringent regulations, industrial attention has been concen-
trated on atom economy and productivity of the catalysts,
which have to be employed at low loading and should display
moderate sensitivity against air and substrate impurities.
Therefore, robustness and deactivation of the ruthenium
species have to be carefully taken into account for the design of
a practical catalyst.2 The catalytic hydrogenation (HY)3 and
transfer hydrogenation (TH)4 of carbonyl compounds are
environmentally friendly and widely accepted methods in
Received: December 17, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.8b00919
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(CNN)(PPh3)(CO)] were found to be active in TH and HY
reactions, the dicarbonyl derivatives [RuCl2(HCNN)(CO)2]
and [RuCl(CNN)(CO)2] required the addition of a
phosphine, allowing the reduction at S/C values up to
100000 and TOF values up to 100000 h−1.
RESULTS AND DISCUSSION
■
Figure 1. 6-Aryl-functionalized ampy and benzo[h]quinoline CNN
ruthenium complexes.
Synthesis of Dicarbonyl Ruthenium Complexes.
Treatment of RuCl3·xH2O with formic acid in a sealed tube
at 110 °C for 2 h gave [RuCl2(CO)2]n, which reacted cleanly
with the Hamtp ligand7 in ethanol at 80 °C overnight,
affording the bidentate HCNN complex trans,cis-
[RuCl2(Hamtp)(CO)2] (1) isolated in 75% yield, in a one-
pot reaction (Scheme 1).
These pincer CNN complexes has also been found to be
active in other organic transformations, including dehydrogen-
ation,11 racemization, and deuteration of alcohols12 and imine
hydrogenation.13 Recently, we have demonstrated that benzo-
[h]quinoline pincer complexes [RuCl(CNN)(PP)] (CNN =
ambq7,14) are efficient catalysts for the HY and TH of
ketones10a,14,15 and aldehydes of commercial grade purity
(Figure 1).16 The reduction of aldehydes requires some
consideration, as several side reactions may occur during the
catalysis, with depletion of selectivity. Since the catalytically
active ruthenium hydride species6a,17 are generated in basic
alcohol media, aldehydes displaying reactive α-hydrogen atoms
can easily undergo aldol condensation,18 in addition to
Claisen−Tishchenko19 or Cannizzaro reactions20 for non-
enolizable substrates. Furthermore, aldehydes can also
decarbonylate with Ru21 and Os22 complexes, affording
metal carbonyl derivatives, resulting in deactivation and low
catalyst productivity.23 To avoid decarbonylation, employment
of carbonyl Ru catalysts has been investigated.23c,24 In the past
decade, monocarbonyl ruthenium complexes have been
successfully applied in a number of organic reactions, such as
TH and HY of carbonyl compounds,25 HY of carboxylic and
carbonic acid derivatives,26 alcohol dehydrogenation,27 and
C−X (X = C, N) forming reactions.28 Relevant examples of
monocarbonyl catalysts are [Ru(TFA)2(PPh3)2(CO)],29
[Ru(μ-OCOC2F4OCO)(diphosphine)(CO)]2,27e [Ru(OAc)-
(CCN)(CO)],30 Ru(CNO)(PPh3)2(CO)],31 [RuCl2(NNN)-
(CO)] and [RuCl(NNN)(HOCH3)(CO)]Cl,32 and those
reported by Milstein ([RuH(PNN)(CO)]),33 Gusev
([RuCl2(PNN)(CO)]),34 and Saito ([RuHCl(PNN)-
(CO)]).35 Moreover, we have described that the derivatives
[RuCl((2-CH2-6-MeC6H3)PPh2)(NN)(CO)]36 and [RuH-
(Ph2P(CH2)3PPh2)(NN)(CO)]Cl37 (NN = en, ampy7) are
active in ketone TH reactions. Dicarbonyl ruthenium
complexes have been proven to catalyze HY, TH, and
dehydrogenation (DHY) reactions involving carbonyl com-
pounds and alcohols, including dynamic kinetic resolution.38
Examples are [(η5-C5H4O)2HRu2H(CO)4],38b,39 [(η5-C5R5)-
RuCl(CO)2],40 [RuCl(PCP)(CO)2],41 [RuCl2(LL′)(CO)2]
(LL′ = PC, PP, PS),42 [RuBr(RCCCR)(CO)2]0/+ (RCCCR =
2,6-bis(1-alkylimidazolylidene)benzene),43 and [Ru(CP)-
(NN)(CO)2]Cl.44 In addition, [RuCl2(bpy)(CO)2] and
[Ru(bpy)2(CO)2][PF6]2 have been found to promote CO2
reduction45 and the water-gas shift reaction.7,46 It is also worth
pointing out that these ruthenium mono- and dicarbonyl
catalysts have usually been employed at a relatively low S/C
(≤103), thus limiting their application.
Scheme 1. Synthesis of HCNN Dicarbonyl Complexes
trans,cis-[RuCl2(HCNN)(CO)2] (1−3) and trans,cis-
[RuCl2(ampy)(CO)2] (1a)
1
Complex 1 in CDCl3 shows two triplets in the H NMR
spectrum at δ 4.78 and 4.19 for methylene and amino groups
of the HCNN ligand. The 13C{1H} NMR spectrum displays
two singlets at δ 195.5 and 190.3 for the CO groups and a
signal at δ 51.2 for the CH2N group, slightly shifted downfield
in comparison to the free ligand (δ 48.2),10e,48 suggesting a
configuration of 1 with two cis carbonyls and two trans
chlorine atoms. The strong IR νCO adsorption bands at 2067
and 1998 cm−1 can be attributed to the two cis CO groups.
These data are similar to those observed for the related
trans,cis-[RuCl2(ampy)(CO)2] (1a), which is prepared from
[RuCl2(CO)2]n and ampy7 in an ethanol/water (3/1 in
volume) mixture at reflux and isolated in 78% yield (Scheme
1). The triplets at δ 4.73 and 4.22 are for the CH2N and NH2
moieties, whereas the 13C{1H} NMR resonances of the two
CO groups appear at δ 195.9 and 192.7. In the IR spectrum
the two cis CO groups lead to two νCO adsorptions at 2054
and 1991 cm−1, close to those of the trans,cis-[RuCl2(bpy)-
(CO)2] derivative.49 Similarly to 1, complexes
[RuCl2(Hambq)(CO)2] (2) and [RuCl2(HambqPh)(CO)2]
(3), containing the more rigid benzo[h]quinoline HCNN
We report herein a straightforward synthesis of bidentate
HCNN and pincer CNN ruthenium complexes, with one and
two CO ligands, which display high catalytic activity and
productivity in the reduction of a number of aldehydes and
(bulky) ketones.47 While the monocarbonyl derivatives
[Ru(X)2(HCNN)(PPh3)(CO)] (X = Cl, OAc) and [RuCl-
B
DOI: 10.1021/acs.organomet.8b00919
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 2. Syntheses of the Cyclometalated Dicarbonyl Complex cis-[RuCl(amtp)(CO)2] (4)
Scheme 3. Synthesis of the HCNN Monocarbonyl Complexes trans-[RuCl2(HCNN)(PPh3)(CO)] (5−7)
ligands,50 were obtained by reaction of [RuCl2(CO)2]n with
Synthesis of Monocarbonyl Ruthenium Complexes.
The monocarbonyl ruthenium complex trans-[RuCl2(Hamtp)-
(PPh3)(CO)] (5) was synthesized in 68% yield by reaction of
the precursor [RuCl2(dmf)(PPh3)2(CO)] with Hamtp in
chloroform at 60 °C overnight (Scheme 3).
7
Hambq and HambqPh in ethanol at reflux and isolated in 49
and 72% yields, respectively (Scheme 1). The 1H NMR
spectrum of 2 in CD2Cl2 shows two broad resonances at δ 4.59
and 3.69 for the CH2 and the NH2 groups, whereas a doublet
of doublets at δ 9.07 is ascribed to the H-10 proton of the
benzo[h]quinoline moiety, indicating that the ligand is not
cyclometalated. The CO groups of 2 appear as singlets at δ
200.0 and 190.4 in the 13C{1H} NMR spectrum, while the
CH2N carbon is at δ 52.3. The IR spectrum reveals two
stretching bands at 2059 and 1985 cm−1 for the cis CO
1
The H NMR spectrum of 5 displays two triplets at δ 4.50
and 3.13 for the CH2 and the amino groups, whereas the
31P{1H} NMR resonance is at δ 54.5. These NMR data are
similar to those of trans-[RuCl2(ampy)(PPh3)(CO)],25a
displaying the CO trans to the NH2 moiety. For 5, the
13C{1H} NMR doublet at δ 200.5 (2J(C,P) = 21.5 Hz) is for
CO cis to the PPh3 group, whereas the doublet at δ 50.1 is for
the CH2N moiety. The CO ligand exhibits a stretching band at
1947 cm−1 in the IR spectrum, close to that of trans-
[RuCl2 (ampy)(PPh3 )(CO)].2 5 a Likewise, trans-
[RuCl2 (Hambq)(PPh3 )(CO)] (6) and trans-
[RuCl2(HambqPh)(PPh3)(CO)] (7) were obtained by the
reaction of [RuCl2(dmf)(PPh3)2(CO)] with Hambq and HCl·
HambqPh 51 with NBu3 in n-butanol at reflux overnight, leading
to the products in 93% and 44% yields, respectively (Scheme
3). The syntheses of 6 and 7 required higher temperature with
respect to that for 5, possibly due to the higher rigidity of the
benzo[h]quinoline ligands, in comparison to Hamtp, hindering
the coordination of the heterocyclic moiety. Complexes 6 and
7 show NMR and IR data similar to those observed for 5, with
31P{1H} NMR resonances at δ 53.4 and 53.5, whereas the
13C{1H} NMR carbonyl signals appear as doublets at δ 200.4
and 200.5, respectively. The aromatic H-10 protons for 6 and 7
are at δ 9.29 and 9.08, indicating no cyclometalation. Finally,
the IR spectra of 6 and 7 display a νCO band at 1920 and 1924
cm−1, respectively. The reaction between the acetate precursor
[Ru(OAc)2(PPh3)2(CO)] and the ligand Hamtp in toluene at
reflux for 48 h afforded the trans-[Ru(OAc)2(Hamtp)(PPh3)-
(CO)] (8) in 40% yield (eq 1).
1
moieties. Likewise, 3 displays a resonance at δ 9.42 in the H
NMR spectrum for the aromatic H-10 proton, whereas the two
13C{1H} NMR singlets at δ 201.2 and 194.4 are ascribed to the
CO ligands.
Treatment of 1 with an excess of triethylamine (10 equiv) in
n-butanol at 110 °C overnight afforded the cyclometalated
pincer CNN derivative cis-[RuCl(amtp)(CO)2] (4) in 58%
yield (Method A for compound 4 in the Experimental Section)
(Scheme 2). Alternatively, compound 4 was also obtained
directly through a one-pot synthesis from RuCl3·xH2O/
HCO2H (Method B for compound 4), followed by reaction
with Hamtp and triethylamine in n-butanol (Scheme 2). In the
1H NMR spectrum of 4 the diastereotopic methylene protons
of the CNN ligand appear as a doublet of doublets at δ 4.65
and a multiplet at δ 4.41, whereas the amino group give two
broad signals at δ 4.06 and 3.46. The 13C{1H} NMR spectrum
displays the CO signals at δ 200.4 and 194.0, while the
resonances at δ 164.2 and 52.3 are for the ortho-metalated
carbon and the CH2N moiety, respectively. The cis CO ligands
show two strong stretching bands in the IR spectrum at 2028
and 1958 cm−1. A comparison of the cyclometalation reaction
of Hamtp with [RuCl2(PPh3)3]50 and [RuCl2(PPh3)-
(dppb)],10e with respect to [RuCl2(CO)2]n, indicates that
the C−H activation occurs more easily with ruthenium
phosphine precursors.
1
The H NMR spectrum of 8 in CD2Cl2 shows a doublet of
doublets at δ 4.41 and a multiplet at δ 4.21 for the two
diastereotopic methylene protons. The NH2 group gives two
C
DOI: 10.1021/acs.organomet.8b00919
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
NBu3) failed, affording a mixture of 9 and uncharacterized
products.
Similarly to 9, the benzo[h]quinoline CNN derivative
[RuCl(ambq)(PPh3)(CO)] (10) was prepared by treatment
of the pincer precursor cis-[RuCl(ambq)(PPh3)2] with CO at
1
room temperature and isolated in 80% yield. The H NMR
spectrum of 10 resembles that of 9, with two signals at δ 4.51
and 3.70 for the diastereotopic CH2N protons, whereas the
NH2 resonances are at δ 4.03 and 2.86. The doublet at δ 8.02
is attributed to the CH proton close to the ortho-metalated
carbon atom. The 13C{1H} NMR signal of the CO ligand is a
doublet at δ 207.8 (2J(C,P) = 17.5 Hz), whereas the
cyclometalated carbon atom gives a doublet at δ 172.1
(2J(C,P) = 12.8 Hz). The 31P{1H} NMR spectrum of 10 shows
a singlet at δ 58.5, while the IR νCO adsorption band is at 1922
cm−1. The complex [RuCl(ambqPh)(PPh3)(CO)] (11) was
obtained from the pincer precursor cis-[RuCl(ambqPh)-
(PPh3)2] (11a), which was prepared following the procedure
described for the synthesis of 10. Thus, 11a was isolated in
88% yield by reaction of [RuCl2(PPh3)3] with HCl·
signals at δ 8.16 and 1.57; the low-field resonance is consistent
with an intramolecular N−H···O hydrogen bond interaction
with one acetate. The methyl signals of the acetate ligands are
at δ 2.07 and 1.20. In the 13C{1H} NMR spectrum the CO
appears as a doublet at δ 202.9 (2J(C,P) = 17.4 Hz), whereas
the acetate carbonyl shifts are at δ 180.5 and 177.7. The
31P{1H} NMR resonance of the PPh3 is at δ 54.4, very close to
the value observed for 5 (δ 54.5), while the IR νCO adsorption
band of the CO is at 1914 cm−1. Finally the infrared stretching
bands at 1597 and 1572 cm−1 are characteristic of νOCO of two
monodentate acetate ligands, the second slightly red shifted
due to the presence of a hydrogen bond with the amino
group.52 Therefore, the spectroscopic data for 8 are consistent
with the arrangement observed for 5, with one acetate ligand
interacting with the NH2 moiety.
51
HambqPh and 10 equiv of NEt3 in 2-propanol at reflux
(Scheme 4).
The 31P{1H} NMR spectrum of 11a in CDCl3 shows two
doublets at δ 57.3 and 50.8 with a 2J(P,P) value of 33.7 Hz. In
the 1H NMR spectrum, the signals for the diastereotopic
CH2N protons are at δ 4.31 and 3.61, whereas the NH2
resonances are at δ 4.02 and 3.02. The 13C{1H} NMR
spectrum of 11a exhibits a doublet at δ 177.9 (2J(C,P) = 3.9
Hz) for the cyclometalated carbon atom. Reaction of 11a with
CO (1 atm) in CH2Cl2 at room temperature afforded 11,
isolated in 83% yield, displaying much the same spectroscopic
data as the related derivative 10 (Scheme 4). The molecular
structure of 11 was confirmed by an X-ray single-crystal
diffraction measurement carried out at 123 K. An ORTEP style
drawing of 11 is displayed in Figure 2.
The pincer CNN monocarbonyl complex [RuCl(amtp)-
(PPh3)(CO)] (9) was easily prepared by treatment of cis-
[RuCl(amtp)(PPh3)2] with CO (1 atm) in CH2Cl2 at room
temperature overnight by PPh3 substitution and was isolated in
59% yield (eq 2).
The ruthenium center of 11 is in a pseudo-octahedral
environment with the cyclometalated CNN ligand bound to
the metal in a terdentate fashion, forming two five-membered
chelate rings. The Ru−N2 bond distance of the benzo[h]-
quinoline trans to the CO is significantly shorter (2.0719(17)
Å) than the Ru−N1 amino bond distance (2.2737(18) Å), in
agreement with the geometrical constraints of the terdentate
ligand showing narrow N2−Ru−C2 and N1−Ru−N2 bond
angles (80.78(7) and 74.45(6)°, respectively) and the higher
trans influence exerted by the aryl group. The amino nitrogen
N1 and the CHNH2 carbon are displaced by −0.182 and
+0.175 Å, respectively, from the best-fit plane through the
aromatic part of the CNN moiety. This arrangement is
characterized by one N−H and the Ru−Cl1 bonds that are
almost parallel (H−N1−Ru−Cl1 dihedral angle of about
−12.26°, with an H···Cl1 distance of 2.69 Å), suggesting a
possible intramolecular hydrogen bond interaction.54
The 31P{1H} NMR spectrum of 9 in CD2Cl2 shows a singlet
at δ 57.6, consistent with the PPh3 trans to chlorine,53 whereas
the CO ligand is trans to the pyridyl nitrogen. In the 1H NMR
spectrum the diastereotopic methylene protons appear as two
doublets of doublets at δ 4.25 and 3.41, while the amino group
is at δ 3.86 and 2.79. The 13C{1H} NMR doublet at δ 176.3
(2J(C,P) = 12.3 Hz) is for the cyclometalated carbon, whereas
the doublet at δ 207.5 (2J(C,P) = 18.2 Hz) is for the CO
moiety. For 9, the IR stretching band of CO is at 1905 cm−1.
Attempts to isolate 9 by cyclometalation of 5 in 2-propanol or
n-butanol at reflux and in the presence of a base (NEt3 or
Scheme 4. Synthesis of cis-[RuCl(ambqPh)(PPh3)2] (11a) and [RuCl(ambqPh)(PPh3)(CO)] (11)
D
DOI: 10.1021/acs.organomet.8b00919
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Reduction of Aldehydes and Ketones via TH and HY
Catalyzed by Carbonyl HCNN Ruthenium Complexes.
The catalytic activity of the complexes 1−12 was investigated
in the reduction of the model substrate acetophenone a via TH
and HY, in the presence of alkoxides. Complexes 1−4, with
phosphines, and the derivatives 5−11 efficiently catalyzed the
selective TH of different (bulky) ketones and (unsaturated)
aldehydes, in short times at S/C = 1000−100000 (Scheme 5).
The dicarbonyl HCNN complexes 1−4 (S/C = 1000) did
not show appreciable activity in the TH of a (0.1 M) in 2-
propanol at reflux in the presence of NaOiPr (2 mol %) with
less than of 2% of conversion in 2 h (Table S1 in the
Supporting Information). Addition of a phosphine, namely
PPh3 or PCy3 (2 equiv) in situ, drastically increased their
activity. Complex 1 in the presence of PPh3 afforded
quantitative reduction of a in 1 h with an S/C ratio of 1000
(TOF = 1000 h−1), whereas with PCy3 the TH occurred in less
than 1 min (Table 1, entries 1 and 2).
By employment of PCy3 at S/C = 10000, the reaction was
complete in 20 min (TOF = 100000 h−1), whereas at S/C =
50000−100000, quantitative reduction of a was achieved
within 4 h (Table 1, entries 3 and 4, and Table S1 in the
Supporting Information).
It is worth pointing out that the related complex trans,cis-
[RuCl2(ampy)(CO)2] (1a) was not active, and in the presence
of PCy3 the TH of a occurred in 2 h at a low rate (TOF = 800
h−1; Table 1, entry 5), indicating that the phenyl substituent in
the 6-position of the HCNN ligand is crucial to achieve high
catalytic activity.
Figure 2. ORTEP style plot of compound 11 in the solid state
(CCDC 1868440). Ellipsoids are drawn at the 50% probability level.
H atoms are omitted for clarity. Selected bond lengths (Å) and angles
(deg): Ru1−C1 1.847(2), Ru1−C2 2.042(2), Ru1−N2 2.0719(17),
Ru1−N1 2.2737(18), Ru1−P1 2.2763(5), Ru1−Cl1 2.4846(5); C1−
Ru1−C2 92.25(9), C1−Ru1−N2 172.74(8), C2−Ru1−N2 80.78(7),
C1−Ru1−N1 112.30(8), C2−Ru1−N1 154.78(7), N2−Ru1−N1
74.45(6), C1−Ru1−P1 88.70(6), C2−Ru1−P1 89.01(6), N2−Ru1−
P1 93.18(5), N1−Ru1−P1 96.94(5), C1−Ru1−Cl1 92.58(6), C2−
Ru1−Cl1 91.39(6), N2−Ru1−Cl1 85.61(5), N1−Ru1−Cl1
82.16(5), P1−Ru1−Cl1 178.643(19).
The benzo[h]quinoline derivatives 2 and 3 displayed a
similar behavior with S/C = 1000, affording 97% of reduction
of a in 1 h with PPh3, whereas in the presence of PCy3, 2 and 3
led to complete conversion in 15 and 30 min, respectively
(Table 1, entries 6−9). The cyclometalated pincer ruthenium
dicarbonyl derivative 4 in the presence of PCy3 afforded 97%
reduction of a in 20 min at S/C = 1000 (TOF = 4300 h−1),
indicating a lower activity with respect to 1 (entry 11). The
monocarbonyl HCNN derivative 5 displayed good perform-
ance (TOF = 12000 h−1), allowing quantitative reduction of a
in 20 min at S/C = 1000 (entry 12). An increase in the rate
was observed by addition of the strongly basic PCy3 to 5 (TOF
= 18700 h−1; entry 15). Complex 5 efficiently catalyzed the
TH of a also in the range of S/C 5000−50000, leading
quantitatively to 1-phenylethanol in 40 min (S/C = 10000,
TOF = 8000 h−1) and 42 h (S/C = 50000), proving that 5 was
a productive catalyst (entries 13 and 14 and Table S1 in the
Supporting Information). The benzo[h]quinoline complexes 6
and 7 led to 99% conversion of a at S/C 1000 in 10 and 20
min, respectively, with a rate comparable to that observed for 5
(TOF = 11000−12000 h−1). These catalysts were also active at
a lower loading (S/C 10000), with complete reduction of a in
2 h and 45 min for 6 and 7 (TOF up to 20000 h−1; entries 16−
19). The diacetate ruthenium derivative 8 gave 99%
conversion of a in 10 min and 1 h, at S/C = 1000 and
10000, respectively (TOF = 20000 and 17000 h−1; entries 20
and 21). The higher rate of 8 in comparison to that of 5 can be
attributed to the easier substitution of the acetate with the
isopropoxide, with respect to the chloride. A similar behavior
was observed for the [RuX(CNN)(dppb)] complexes (X = Cl,
OAc) which catalyze the TH of a with TOF values of 1100000
and 1800000 h−1 for the chloride and acetate derivative,
respectively.10e,53 Finally, the pincer CNN monocarbonyl
complexes 9−11 proven to be highly active catalysts for the
The cationic diphosphine complex trans-[Ru(amtp)-
(PPh3)2(CO)][BArf4] (12), isolated in 79% yield, was
promptly obtained by treatment of 9 with Na[BArf4] (Arf =
3,5-(CF3)2C6H3) and PPh3 in CH2Cl2 at room temperature, by
the replacement of chlorine with PPh3 (eq 3).
The 31P{1H} NMR spectrum of 12 in CD2Cl2 shows a
1
singlet at δ 35.5, while the H NMR signals at δ 3.53 and at δ
2.95 belong to the methylene and the amino groups,
respectively. The 13C{1H} NMR resonances of the CO and
the cyclometalated carbon atoms appear as triplets at δ 205.9
(2J(C,P) = 15.7 Hz) and 169.4 (2J(C,P) = 10.5 Hz),
respectively, indicating a trans arrangement of PPh3 ligands.
Finally, 12 shows a strong IR νCO adsorption band at 1914
cm−1. Thus, the NMR and IR data of the coordinated CO of
12 and 9 are much the same (Δδ = 1.6 and ΔνCO = 9 cm−1),
consistent with the presence of a trans pyridine nitrogen. It is
likely that the chlorine abstraction from 9 with Na[BArf4] may
led to a cationic species of the type [Ru(amtp)(PPh3)(CO)-
(solvent)n][BArf4] (n = 0, 1), which rapidly reacted with the
PPh3 to cleanly afford complex 12, also in accordance with the
isolated solvato complex [Ru(amtp)(dppb)(2-propanol)]-
[BArf4].55
E
DOI: 10.1021/acs.organomet.8b00919
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 5. TH of Ketones and Aldehydes Catalyzed by Ruthenium Carbonyl Complexes 1−12
Table 1. Catalytic TH of Acetophenone (0.1 M) with Complexes 1−12 in 2-Propanol at 82 °C in the Presence of 2 mol %
NaOiPr
a
b
entry
complex
S/C
ligand (2 equiv)
time (min)
conversn (%)
TOF (h−1
)
1
2
3
4
5
6
7
8
1
1
1
1
1a
2
2
3
3
4
4
5
5
5
5
6
6
7
7
8
8
9
9
10
10
11
12
12
1000
1000
10000
100000
1000
1000
1000
1000
1000
1000
1000
1000
10000
25000
1000
1000
10000
1000
10000
1000
10000
10000
50000
1000
1000
10000
1000
PPh3
PCy3
PCy3
PCy3
PCy3
PPh3
PCy3
PPh3
PCy3
PPh3
PCy3
60
1
20
240
120
60
15
60
30
60
20
20
40
1 day
20
10
120
20
45
10
60
20
240
15
30
60
10
240
960
480
10
99
99
99
99
99
97
96
97
99
99
97
99
99
99
97
99
99
99
99
99
98
99
99
96
95
99
99
98
90
91
99
1000
>30000
100000
95000
800
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
4300
12000
8000
2200
PCy3
18700
11600
10500
12000
20000
20000
17000
86000
55000
c
18000
45000
16000
120
480
49000
10000
1000
1000
[RuCl2(PCy3)2(CO)2]
[RuCl2(PCy3)2(CO)2]
[RuCl2(PCy3)2(CO)2]
ampy
Hamtp
1000
a
b
The conversions were determined by GC analysis. Turnover frequency (moles of ketone converted to alcohol per mole of catalyst per hour) at
c
50% conversion. Reaction was performed using 5 mol % K2CO3 as base.
TH of a. [RuCl(amtp)(PPh3)(CO)] (9) afforded extremely
fast and quantitative reduction of a in 20 min at S/C = 10000
(TOF = 86000 h−1), whereas at S/C = 50000, complete
conversion was achieved in 4 h (TOF = 55000 h−1; entries 22
and 23). The benzo[h]quinoline ruthenium complexes 10 and
11 exhibited a lower activity, affording the reduction of a in 15
min for 10 (S/C = 1000) and in 1 h for 11 (S/C = 10000,
TOF = 18000 h−1; entries 24 and 26). Use of K2CO3 in place
of NaOiPr with 10 afforded quantitative reduction of a in
longer reaction times, this protocol being relevant for base-
sensitive substrates, such as aldehydes (entry 25).16b The
cationic complex 12 allowed reduction of a in 10 min at S/C =
F
DOI: 10.1021/acs.organomet.8b00919
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 2. TH of Ketones and Aldehydes (0.1 M) with Complexes 1−3, 6, and 8−10 in 2-Propanol at 82 °C in the Presence of 2
mol % NaOiPr
a
b
entry
complex
ligand (2 equiv)
substrate
S/C
time (min)
conversn (%)
TOF (h−1
)
1
2
3
4
5
6
7
8
1
1
1
1
1
1
1
2
2
3
3
PCy3
PCy3
PCy3
PCy3
PCy3
PCy3
PCy3
PPh3
PCy3
PPh3
PCy3
b
c
d
e
f
g
i
j
j
j
j
h
m
m
n
h
h
10000
10000
10000
10000
2000
10000
10000
1000
1000
1000
1000
10000
1000
10000
1000
1000
10000
1000
10000
10000
25000
10000
25000
1000
15
20
15
20
60
60
30
60
2
99
99
96
98
97
97
98
98
99
99
99
95000
75000
100000
75000
5000
20000
60000
1700
12000
1000
>30000
5600
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
60
1
c
d
6
8 h
10
8 h
30
30
56 h
10
90
10
30
40
90
40
30
60
99
99
99
c
6
6000
3300
c
6
c
e
f
6
99
99
81
99
c
g
8
8
8000
900
c
g
c
e
f
8
n
n
c
e
f
8
98
9
9
9
9
9
10
10
k
k
d
d
l
99
99
99
99
93
94
98
80000
65000
32000
25000
d
j
1000
1000
a
b
The conversions were determined by GC analysis. Turnover frequency (moles of ketone converted to alcohol per mole of catalyst per hour) at
c
d
50% conversion. Reactions were conducted employing 5 mol % K2CO3 as base. (−)-menthol/(+)-neomenthol/(+)-isomenthol/
e
f
g
(+)-neoisomenthol = 71/23/4/2. geranial/neral = 2/1. geraniol/nerol = 2/1. (−)-menthol/(+)-neomenthol/(+)-isomenthol/(+)-neo-
isomenthol = 75/18/4/3.
1000 (TOF = 45000 h−1) and was also active at lower loading
(S/C 10000), affording complete conversion in 4 h (entries 27
and 28), possibly through a displacement of a PPh3 group
under these catalytic conditions.
20 min, respectively, with the 1/PCy3 system at S/C = 10000
with TOF values of up to 95000 h−1 (Table 2; entries 1 and 2).
This catalytic system converted benzophenone d to
benzhydrol in 15 min at S/C = 10000 with TOF = 100000
h−1 (Table 2, entry 3). The sterically hindered dialkyl
pinacolone e and the cyclic (R)-camphor f were quantitatively
converted to pinacolyl alcohol and to an isoborneol/borneol
mixture (85/15) in 20 min and 1 h at S/C = 10000 and 2000,
respectively (TOF = 75000 and 5000 h−1; entries 4 and 5). It
is worth noting that bulky ketones were usually reduced at
considerably lower S/C on account of the difficulty of the
substrate to approach the metal center.57,58 Complex 1, in the
presence of PCy3, was proved to catalyze the TH of
cyclohexanone g in 1 h (97% conversion, S/C = 10000) and
allylacetone i in 30 min (98% conversion) to the
corresponding alcohols, with no reduction of the CC
bond (entries 6 and 7). Benzaldehyde j was completely and
rapidly reduced to benzyl alcohol by the benzo[h]quinoline
dicarbonyl ruthenium complexes 2 and 3 with PCy3 in a few
minutes (S/C = 1000, TOF up to 30000 h−1). Employment of
PPh3 instead of PCy3 afforded the TH of benzaldehyde j but
with longer reaction times (60 min; entries 8−11). The
benzo[h]quinoline derivative 6 quantitatively reduced
(−)-menthone h at S/C = 10000 in 8 h, with a good
stereoselectivity for (−)-menthol (71%; entry 12). ( )-β-
Citronellol was obtained from ( )-citronellal m in 99% yield
with 6 in 10 min and 8 h, respectively, at S/C 1000 and 10000
(entries 13 and 14). The commercial citral n, consisting of the
Since an acceleration effect was observed with the HCNN
complex 1 upon addition of PCy3, we carried out control
experiments starting from the well-known cis,trans,cis-
[RuCl2(PCy3)2(CO)2] precursor in the presence of HCNN.
The in situ generated catalyst, obtained by refluxing a 2-
propanol solution of [RuCl2(PCy3)2(CO)2] with Hamtp (2 h),
promoted the quantitative reduction of acetophenone in 10
min (TOF = 49000 h−1 at S/C 1000; Table 1, entry 31).
Conversely, using the ruthenium dicarbonyl precursor alone or
in the presence of ampy led to about 90% conversion of a with
much lower rates (TOFs = 120 and 480 h−1, respectively) and
with very long reaction times (16 and 8 h; entries 29 and 30).
These results clearly indicated that cis,trans,cis-
[RuCl2(PCy3)2(CO)2] displayed poor activity in the TH
reactions under our conditions, in agreement with the
literature data for the TH of cyclohexanone and HY of
aldehydes occurring at high temperature,56 and that the use of
HCNN ligands which allow cyclometalation is crucial to
achieve high rate and high productivity in the ketone TH (see
below).
The most active catalysts for the TH of a were tested in the
reduction of (bulky) ketones and aldehydes (Scheme 5).
Isobutyrophenone b and the bulky pivalophenone c were
quantitatively reduced to the corresponding alcohols in 15 and
G
DOI: 10.1021/acs.organomet.8b00919
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 6. HY of Ketones Catalyzed by Ruthenium Carbonyl Complexes 1−11
Table 3. HY of Ketones (2 M) with Complexes 1−3, 5, and 6 under H2 (30 bar) with KOtBu at 70 °C
a
entry
complex
ligand (2 equiv)
substrate
S/C
solvent
KOtBu (mol %)
time (h)
conversn (%)
1
2
3
4
5
6
7
8
1
1
1
PPh3
PCy3
PCy3
PCy3
PCy3
PCy3
a
a
a
a
a
a
a
a
d
o
p
q
r
2000
2000
2000
2000
2000
2000
2000
2000
500
10000
10000
500
10000
10000
EtOH
EtOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
2
2
5
5
5
5
5
5
5
2
5
5
5
5
16
16
16
16
16
16
16
16
16
16
16
16
16
34
46
99
99
99
99
63
99
99
46
99
99
99
63
b
1
2
3
5
6
5
5
5
5
5
5
9
10
11
12
13
14
s
16
a
b
HY was carried out in an eight-vessel Endeavor Biotage system, and the conversions were determined by GC analysis. Reaction was performed
employing 5 mol % KOH as base.
E and Z geranial and neral isomers in a ratio of about 2:1, was
converted to a mixture of the respective alcohols (geraniol and
nerol) with 6 in 30 min (99% conversion at S/C = 1000),
whereas the diacetate ruthenium complex 8 led to similar
results in 10 min (entries 15 and 18). K2CO3 was used instead
of NaOiPr for the TH of m and n to prevent aldol
condensation and CC hydrogenation side reactions in
strong basic media. Compound 8 proved to be active also at
lower loading, promoting the complete TH of n in 90 min at
S/C = 10000 (entry 19). Under these conditions, selective
reduction occurred only at the carbonyl group. The TH of the
conjugated CC bond began after longer reaction times,
affording 40% of citronellol in 30 h, at n/8 = 1000. With 8, h
was completely converted in 30 min with 75% of (−)-menthol
at S/C = 1000, whereas at S/C = 10000 only 81% conversion
was attained in 56 h (entries 16 and 17). Complex 9 promoted
the TH of benzophenone d with complete formation of
benzhydrol in 40 (S/C = 10000, TOF = 32000 h−1) and 60
min (S/C = 25000, TOF = 25000 h−1; entries 22 and 23),
whereas with 10, substrate d was reduced in 30 min (94%
conv) at S/C = 1000 (entry 25). Complexes 9 and 10
efficiently catalyzed the TH of aldehydes. Benzaldehyde j was
converted by 10 in 1 h at S/C = 1000 (entry 26), whereas the
derivative 9 quantitatively reduced 4-bromobenzaldehyde k in
10 and 30 min at S/C = 10000 and 25000, respectively, with
TOF up to 80000 h−1 (entries 20 and 21). Highly
chemoselective TH of (E)-2-methylcinnamaldehyde l was
achieved employing 9 (S/C = 1000) in 40 min, leading to 93%
of (E)-2-methylcinnamol (entry 24).
methanol in the presence of KOtBu at S/C up to 10000
(Scheme 6).
The dicarbonyl HCNN complexes 1−3 with 5 mol %
KOtBu showed no catalytic activity in the HY of a, as for the
TH reactions. Addition of 2 equiv of PPh3 or PCy3 to 1 (S/C =
2000) in ethanol led to 34% and 46% conversion, respectively,
after 16 h (Table 3; entries 1 and 2). Interestingly, quantitative
conversion was attained in methanol with PCy3 using KOtBu
or KOH as base (entries 3 and 4). A similar behavior was
observed with the benzo[h]quinoline derivatives 2 and 3 in the
presence of PCy3, affording quantitative reduction of a in
methanol and poor conversion in ethanol (entries 5 and 6 and
Table S3 in the Supporting Information). The monocarbonyl
complex 5 led to 63% conversion of a in methanol (16 h),
whereas with 6 quantitative formation of 1-phenylethanol was
obtained (entries 7 and 8). Conversely, the pincer CNN
derivatives 9−11 showed lower activity, with better results in
ethanol with respect to methanol. Complex 9 in the presence
of 2 mol % KOtBu gave 61% conversion of a in ethanol and
25% in methanol (16 h), and similar results were observed for
10 and 11 (Table S3 in the Supporting Information).
Complex 5 was tested in the HY of aryl methyl ketones with
different electronic properties (Scheme 6). Benzophenone d
was quantitatively converted to benzhydrol (99%) in 16 h (S/5
= 500; Table 3, entry 9). The HY of 2′-methylacetophenone o
led to 46% of conversion with a S/C = 10000 (entry 10),
whereas 2′-chloroacetophenone p and 4′-nitroacetophenone r
were quantitatively hydrogenated to the corresponding
alcohols in the presence of 5 mol % KOtBu (entries 11 and
13). In addition, 4′-methoxyacetophenone q afforded complete
conversion at S/5 = 500 (entry 12), while benzoin s gave 63%
of 1,2-diphenyl-1,2-ethanediol at S/5 = 10000, possibly due to
Complexes 1−11 were also studied in the HY of several
ketones (2 M) at 30 bar of H2 pressure at 70 °C in ethanol and
H
DOI: 10.1021/acs.organomet.8b00919
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
the chelate effect exerted by the diol product, resulting in
catalyst poisoning (entry 14). Therefore, these data indicated
that complex 5 displays a higher activity for methyl aryl
ketones containing Cl and NO2 electron-withdrawing groups
(p, r) with respect to acetophenone a and the corresponding
Me and OMe derivatives (o, q).
access of the substrate to the metal hydride. Furthermore,
these carbonyl complexes showed comparable or better
performance with respect to [RuCl(CNN)(PP)] for the
reduction of commercial grade aldehydes, with S/C values of
up to 25000.16b Finally, employment of HCNN ligands
afforded extremely active and productive catalysts with respect
to the bidentate ampy derivatives, 1a/PCy3 and trans-
[RuCl2(ampy)(PPh3)(CO)],25a on account of the formation
of more robust pincer complexes.
As regards the mechanism of the TH and HY reactions
involving ruthenium complexes, catalytically active mono- or
dihydride Ru species are generally formed from Ru−X (X = Cl,
carboxylate) precursors, by reaction with alkoxides or H2.17,59
In the TH with 2-propanol the Ru−H species are generated by
formation of acetone via an inner-sphere mechanism from a
Ru−OiPr complex. When a NH2 moiety is present cis to the
Ru−X center, the Ru−H species may be formed from a 16-
electron Ru−amide complex and alcohol through an outer-
sphere mechanism60 or a Ru−amine/alkoxide.6a,c,55,60a,61
Regarding the HY reactions, the Ru−H species are obtained
through a dihydrogen splitting from a labile Ru−X precursor in
basic alcohol (inner sphere) or from a 16-electron Ru−
amide6a,c or Ru−amine/alkoxide species (outer sphere).62
Therefore, is it reasonable that, in the TH promoted by the
pincer complexes 9−11, the reaction occurs through
substitution of the chloride with the isopropoxide, which
leads to the corresponding catalytically active hydride [RuH-
(CNN)(CO)(PPh3)]. This process is in line with the
mechanistic studies carried out on the analogous [RuX(CNN)-
(PP)] (X = Cl, H; HCNN = Hamtp; PP = dppb, (S,S)-
skewphos),55,61a in which the NH2 function accelerates TH
and HY reactions. Using the monocarbonyl phosphine
derivatives 5−8, pincer [RuX(CNN)(CO)(P)] (X = Cl, H)
can also be formed via cyclometalation under catalytic
conditions. With the bidentate dicarbonyl ruthenium deriva-
tives 1−3, it is likely that, in the presence of an added
phosphine, the first step in catalysis is the displacement of the
HCNN ligand with PR3, followed by CO elimination,
coordination of the HCNN ligand, and cyclometalation,
affording [RuX(CNN)(CO)(P)] species, a behavior which
has also been observed for the [RuCl(p-cymene)(Hamtp)]Cl/
phosphine catalytic system.50 Control 31P{1H} NMR experi-
ments showed that reaction of 1 with PCy3 (2 equiv) at room
temperature in CDCl3 afforded cis, trans, cis-
[RuCl2(PCy3)2(CO)2] (δ 27.7),63 in a small amount, as result
of Hamtp displacement. Heating of this solution at 90 °C (12
h) led to an increase in the dicarbonyl derivative, with the
formation of the monocarbonyl cis,trans-[RuCl2(PCy3)2(CO)]
(δ 34.5), in addition to the cyclometalated species [RuCl-
(amtp)(PCy3)(CO)] (see the Supporting Information).
Conversely, reaction of cis,trans,cis-[RuCl2(PCy3)2(CO)2]
with Hamtp in 2-propanol at reflux (2 h) and in the presence
of the base NEt3 led to the formation of several species,
including trans,cis-[RuHCl(PCy3)2(CO)2] and uncharacterized
ruthenium hydride species, in addition to [RuCl(amtp)-
CONCLUDING REMARKS
■
In conclusion, we reported the synthesis of bidentate HCNN
trans-[RuX2(HCNN)(L)(CO)] (X = Cl, OAc) and pincer
CNN [RuCl(CNN)(L)(CO)] (HCNN = Hamtp, Hambq,
HambqPh; L = CO, PPh3) carbonyl complexes starting from
RuCl3·xH2O, [RuCl2(CO)2]n, [RuCl2(PPh3)2(dmf)(CO)],
[Ru(OAc)2(PPh3)2(CO)], and cis-[RuCl(CNN)(PPh3)2] pre-
cursors. The monocarbonyl phosphine complexes and the
dicarbonyl derivatives, in the presence of phosphine (PPh3 or
PCy3), efficiently catalyzed the TH of ketones, including bulky
substrates, and the chemoselective TH of unsaturated
aldehydes in 2-propanol at reflux at S/C = 1000−100000
and TOF values of up to 100000 h−1. In addition, these
complexes were active catalysts for the HY of ketones (H2, 30
bar) in MeOH and EtOH at S/C values of up to 10000.
Formation of cyclometalated ruthenium carbonyl/phosphine
species represents a key issue for achieving highly productive
catalysts. Studies are ongoing to extend this synthetic protocol
to the preparation of CNN pincer carbonyl complexes and
apply these new systems for catalytic C−H activation organic
transformations.
EXPERIMENTAL SECTION
■
All reactions were carried out under an argon atmosphere using
standard Schlenk techniques. The solvents were dried by standard
methods and distilled under argon before use. The ruthenium
compound RuCl3·xH2O (x = 2.5) was purchased from Alfa/Aesar,
whereas all other chemicals were acquired from Aldrich and Strem
and used without further purification. The HCNN ligands Hamtp,10d
10a
Hambq,14b and HambqPh
and the complexes [RuCl2(CO)2]n,67
[RuCl2(dmf)(PPh3)2(CO)],68 [Ru(OAc)2(PPh3)2(CO)],69 cis-
[RuCl(amtp)(PPh3)2],50 and cis-[RuCl(ambq)(PPh3)2]14b were
prepared according to the literature procedures. NMR measurements
were recorded on a Bruker AC 200 spectrometer,and the chemical
shifts, in ppm, were relative to TMS for H and 13C{1H} and 85%
1
H3PO4 for 31P{1H}. Elemental analyses (C, H, N) were carried out
with a Carlo Erba 1106 elemental analyzer, whereas the GC analyses
were performed with a Varian GP-3380 gas chromatograph equipped
with a MEGADEX-ETTBDMS-β chiral column of 25 m length,
column pressure 5 psi, hydrogen as carrier gas, and flame ionization
detector (FID). The injector and detector temperature was 250 °C,
with initial T = 95 °C ramped to 140 °C at 3 °C/min−1 for a total of
20 min of analysis. The tR value of acetophenone was 7.03 min, while
the tR values of (R)- and (S)-1-phenylethanol were 9.93 and 10.15
min, respectively.
Synthesis of trans,cis-[RuCl2(Hamtp)(CO)2] (1). RuCl3·xH2O
(83.2 mg, 0.33 mmol) was added to formic acid (6 mL, 0.16 mol),
and the suspension was stirred in a sealed tube at 110 °C for 2 h, until
the mixture turned yellow and homogeneous, giving [RuCl2(CO)2]n.
The solvent was evaporated under reduced pressure, and the residue
was dissolved in distilled ethanol (6 mL). After addition of the ligand
Hamtp (78.1 mg, 0.39 mmol, 1.2 equiv), the solution was stirred at 80
°C overnight and then the solvent was evaporated under reduced
pressure. The residue was dissolved in chloroform (2 mL), and the
solution was stirred for 1 h at room temperature. The complex was
precipitated by addition of diethyl ether (10 mL). After filtration, the
1
(PCy3)(CO)], as inferred from H−1H COSY and 13C{1H}
NMR measurements.64 It is worth noting that for these types
of ruthenium carbonyl complexes the use of the bulky and
strongly basic phosphine PCy3 gave better catalytic perform-
ance, with respect to PPh3.65 In addition, bulky ketones, such
as pinacolone, pivalophenone, and camphor, were reduced
efficiently with the 1/PCy3 system, which appeared superior
with respect to the diphosphine derivatives [RuCl(CNN)-
(PP)]10e,14b and to the well-known arene complexes [(η6-
arene)RuCl(H2NCHPhCHPhNTs)].66 This is likely due to
the flatness of the pincer carbonyl system, allowing an easy
I
DOI: 10.1021/acs.organomet.8b00919
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
solid was washed with diethyl ether (2 × 5 mL) and n-pentane (5
mL) and dried under reduced pressure. Yield: 105.3 mg (75%). Anal.
Calcd for C15H14Cl2N2O2Ru: C, 42.27; H, 3.31; N, 6.57. Found: C,
42.19; H, 3.26; N, 6.59. IR (Nujol): 2067 (s), 1998 (s) cm−1 (νCO).
13C{1H} NMR (50.3 MHz, CD2Cl2, 20 °C): δ 201.2 (s; CO), 194.4
(s; CO), 161.7 (s; NCC), 157.2 (s; NCCH2), 150.4−118.2 (m;
aromatic carbon atoms), 46.4 (s; CH2N).
Synthesis of cis-[RuCl(amtp)(CO)2] (4). Method A. trans,cis-
[RuCl2(Hamtp)(CO)2] (1; 76.3 mg, 0.18 mmol) was suspended in n-
butanol (5 mL), and triethylamine (250 μL, 1.79 mmol, 10 equiv)
was added. The mixture was heated at 110 °C overnight, giving a
brown solution. The solvent was removed under reduced pressure,
and the residue was dissolved in dichloromethane (5 mL) and stirred
with K2CO3 (112 mg, 0.81 mmol, 4.5 equiv) for 2 h at room
temperature. The mixture was filtered, the filtrate was concentrated to
about 0.5 mL, and the product was precipitated by addition of n-
pentane (5 mL). The solid was filtered, washed with diethyl ether (2
× 2 mL) and n-pentane (2 × 5 mL), and dried under reduced
pressure. Yield: 41.6 mg (58%). Anal. Calcd for C15H13ClN2O2Ru: C,
46.22; H, 3.36; N, 7.19. Found: C, 46.25; H, 3.30; N, 7.11. IR
3
1H NMR (200.1 MHz, CDCl3, 20 °C): δ 7.79 (t, J(H,H) = 7.7 Hz,
1H; aromatic proton), 7.54 (d, 3J(H,H) = 8.2 Hz, 2H; aromatic
3
protons), 7.45−7.29 (m, 4H; aromatic protons), 4.78 (t, J(H,H) =
3
6.2 Hz, 2H; CH2N), 4.19 (t, J(H,H) = 5.9 Hz, 2H; NH2), 2.45 (s,
3H; CH3). 13C{1H} NMR (50.3 MHz, CDCl3, 20 °C): δ 195.5 (s;
CO), 190.3 (s; CO), 164.8 (s; NCC), 159.7 (s; NCCH2), 140.5−
120.2 (m, aromatic carbon atoms), 51.2 (s, CH2N), 21.5 (s; CH3).
Synthesis of trans,cis-[RuCl2 (ampy)(CO)2 ] (1a).
[RuCl2(CO)2]n (50.8 mg, 0.22 mmol) was suspended in an
ethanol/water mixture (3:1; 4 mL) and ampy (28 mL, 0.27 mmol,
1.2 equiv) was added to the slurry. The mixture was stirred at reflux
for 2 h, and then the solvent was removed under reduced pressure.
The residue was dissolved in dichloromethane (1 mL) and stirred for
30 min at room temperature. Addition of diethyl ether (5 mL)
afforded the precipitation of the complex, which was filtered, washed
with diethyl ether (2 × 2 mL) and n-pentane (2 mL) and finally dried
under reduced pressure. Yield 57.6 mg (78%). Anal. Calcd for
C8H8Cl2N2O2Ru: C, 28.59; H, 2.40; N, 8.33. Found: C, 28.55; H,
2.36; N, 8.39. IR (Nujol): 2054 (s), 1991 (s) cm−1 (νCO). 1H NMR
(200.1 MHz, CDCl3, 20 °C): δ 8.94 (dd, 3J(H,H) = 6.0 Hz, 4J(H,H)
1
(Nujol): 2028 (s), 1958 (s) cm−1 (νCO). H NMR (200.1 MHz,
3
CDCl3, 20 °C): δ 7.76 (d, J(H,H) = 7.4 Hz, 1H; aromatic proton),
7.73−7.63 (m, 1H; aromatic proton), 7.59 (d, 3J(H,H) = 8.0 Hz, 1H;
aromatic proton), 7.56−7.44 (m, 1H; aromatic proton), 7.10 (d,
3J(H,H) = 7.0 Hz, 1H; aromatic proton), 6.88 (d, 3J(H,H) = 7.7 Hz,
2
3
1H; aromatic proton), 4.65 (dd, J(H,H) = 16.4 Hz, J(H,H) = 6.5
Hz, 1H; NCH2), 4.41 (m, 1H; NCH2), 4.06 (m, 1H; NH2), 3.46 (m,
1H; NH2), 2.32 (s, 3H; CH3). 13C{1H} NMR (50.3 MHz, CDCl3, 20
°C): δ 200.4 (s, CO), 194.0 (s, CO), 164.2 (s, CRu), 162.6 (s, NCC),
157.6 (s, NCCH2), 142.8−117.1 (m; aromatic carbon atoms), 52.3
(s; NCH2), 21.7 (s; CH3).
3
4
= 1.5 Hz, 1H; o-C5H4N), 7.90 (td, J(H,H) = 7.8 Hz, J(H,H) = 1.4
Hz, 1H; p-C5H4N), 7.52−747 (m, 2H; m-C5H4N protons), 4.73 (t,
3J(H,H) = 5.9 Hz, 2H; CH2N), 4.22 (t, 3J(H,H) = 5.2 Hz, 2H; NH2).
13C{1H NMR (50.3 MHz, CD2Cl2, 20 °C): δ 195.9 (s; CO), 192.7 (s;
CO), 160.2 (s; NCCH2), 153.0 (s; C(6) of Py), 139.6 (s; C(4) of
Py), 125.2 (s; C(3) of Py), 122.5 (s; C(5) of Py), 50.6 (s; CH2N).
Synthesis of trans,cis-[RuCl2 (Hambq)(CO)2 ] (2).
[RuCl2(CO)2]n (203 mg, 0.89 mmol) was reacted with the ligand
Hambq (202.0 mg, 0.97 mmol, 1.1 equiv) in ethanol (10 mL), and
the suspension was stirred at 80 °C overnight. The solvent was
removed under reduced pressure, and the residue was dissolved in
dichloromethane (4 mL). The solution was stirred at room
temperature for 4 h, and then the volume was reduced to about 1
mL, with evaporation of the solvent under vacuum. The complex was
precipitated by addition of diethyl ether (10 mL). The obtained solid
was filtered, washed with diethyl ether (2 × 5 mL) and n-pentane (5
mL), and dried under reduced pressure. Yield: 190 mg (49%). Anal.
Calcd for C16H12Cl2N2O2Ru: C, 44.05; H, 2.77; N, 6.42. Found: C,
44.10, H, 2.78; N, 6.38. IR (Nujol): 2059 (s), 1985 (s) cm−1 (νCO).
Method B. RuCl3·xH2O (128.8 mg, 0.51 mmol) was suspended in
formic acid (7 mL, 0.186 mol), and the slurry was stirred at 110 °C
for 2 h. The solvent was evaporated under reduced pressure, and the
residue, dissolved in n-butanol (7 mL), was reacted with the ligand
Hamtp (111.0 mg, 0.56 mmol, 1.1 equiv) and triethylamine (1.4 mL,
10.0 mmol, 20 equiv). The solution was stirred at 110 °C overnight,
and then the solvent was evaporated under reduced pressure. The
residue was dissolved in CHCl3 (2 mL), stirred with K2CO3 (320 mg,
2.32 mmol, 4.5 equiv) for 2 h at room temperature, and filtered. The
filtrate was concentrated to about 1 mL, and the complex was
precipitated by addition of diethyl ether (10 mL). The obtained solid
was filtered, washed with diethyl ether (2 × 3 mL) and n-pentane (3
mL), and finally dried under reduced pressure. Yield: 61.2 mg (30%).
Synthesis of trans-[RuCl2(Hamtp)(PPh3)(CO)] (5).
[RuCl2(dmf)(PPh3)2(CO)] (282.3 mg, 0.36 mmol), suspended in
chloroform (15 mL), was reacted with the ligand Hamtp (78.4 mg,
0.40 mmol, 1.1 equiv), and the mixture was stirred at 60 °C overnight.
The obtained solution was concentrated to about 1 mL by solvent
evaporation under vacuum. The complex was precipitated by addition
of n-pentane (10 mL). The obtained solid was filtered, washed with
diethyl ether (2 × 5 mL) and n-pentane (5 mL), and dried under
reduced pressure. Yield: 160.3 mg (68%). Anal. Calcd for
C32H29Cl2N2OPRu: C, 58.19; H, 4.43; N, 4.24. Found: C, 58.20;
H, 4.40; N, 4.28. IR (Nujol): 1947 (s) cm−1 (νCO). 1H NMR (200.1
MHz, CDCl3, 20 °C): δ 7.69 (m, 10H; aromatic protons), 7.37 (m,
3
1H NMR (200.1 MHz, CD2Cl2, 20 °C): δ 9.07 (dd, J(H,H) = 4.4
Hz, 4J(H,H) = 1.0 Hz, 1H; aromatic proton), 8.29 (d, 3J(H,H) = 8.3
Hz, 1H; aromatic proton), 8.11−7.41 (m, 6H; aromatic protons),
1
4.59 (m, 2H; CH2N), 3.68 (br s, 2H; NH2). H NMR (200.1 MHz,
tetrachloroethane-d2, 20 °C): δ 9.04 (d, 3J(H,H) = 4.5 Hz, 1H;
3
aromatic proton), 8.23 (d, J(H,H) = 7.5 Hz, 1H; aromatic proton),
8.13−7.03 (m, 6H; aromatic protons), 4.61 (m, 2H; CH2N), 3.67 (br
s, 2H; NH2). 13C{1H} NMR (50.3 MHz, tetrachloroethane-d2, 20
°C): δ 200.0 (s; CO), 190.4 (s; CO), 160.0 (s; NCC), 156.5 (s;
NCCH2), 150.6−117.2 (m; aromatic carbon atoms), 52.3 (s; CH2N).
Synthesis of trans,cis-[RuCl2(HambqPh)(CO)2] (3).
[RuCl2(CO)2]n (227 mg, 1.00 mmol) suspended in ethanol (10
mL) was reacted with HCl·HambqPh (353 mg, 1.10 mmol, 1.1 equiv).
The suspension was stirred at 80 °C overnight, and the solvent was
evaporated under reduced pressure. The residue was dissolved in
dichloromethane (4 mL), and the mixture was stirred at room
temperature for 4 h. The solution was concentrated to about 1 mL,
with removal of the solvent under reduced pressure, and the complex
was precipitated by addition of diethyl ether (10 mL). The obtained
solid was filtered, washed with diethyl ether (2 × 5 mL) and n-
pentane (5 mL), and dried under reduced pressure. Yield: 370 mg
(72%). Anal. Calcd for C22H16Cl2N2O2Ru: C, 51.57; H, 3.15; N, 5.47.
Found: C, 51.49; H, 3.22; N, 5.51. IR (Nujol): 2055 (s), 1984 (s)
3
11H; aromatic protons), 7.15 (d, J(H,H) = 8.2 Hz, 1H; aromatic
3
3
proton), 4.50 (t, J(H,H) = 6.0 Hz, 2H; NCH2), 3.13 (t, J(H,H) =
5.9 Hz, 2H; NH2), 2.49 (s, 3H; CH3). 13C{1H} NMR (50.3 MHz,
CDCl3, 20 °C): δ 200.5 (d, 2J(C,P) = 21.5 Hz; CO), 165.3 (s; NCC),
3
161.2 (d, J(C,P) = 1.0 Hz; NCCH2), 140.3−119.6 (m; aromatic
3
carbon atoms), 50.1 (d, J(C,P) = 2.8 Hz; CH2N), 21.5 (s; CH3).
31P{1H} NMR (81.0 MHz, CDCl3, 20 °C): δ 54.5.
Synthesis of trans-[RuCl2(Hambq)(PPh3)(CO)] (6).
[RuCl2(dmf)(PPh3)2(CO)] (365 mg, 0.46 mmol), suspended in n-
butanol (5 mL), was reacted with the ligand Hambq (208 mg, 1.00
mmol, 2.2 equiv). The mixture was stirred at 130 °C overnight, and
then the solvent was evaporated under reduced pressure and the
residue was dissolved in chloroform (1 mL). The solution was stirred
for 1 h at room temperature, and the complex was precipitated by
addition of diethyl ether (10 mL). The solid was filtered, washed with
diethyl ether (2 × 3 mL) and n-pentane (3 mL), and finally dried
under reduced pressure. Yield: 291 mg (93%). Anal. Calcd for
C33H27Cl2N2OPRu: C, 59.11; H, 4.06; N, 4.18. Found: C, 59.20; H,
1
cm−1 (νCO). H NMR (200.1 MHz, CD2Cl2, 20 °C): δ 9.42 (d,
3J(H,H) = 7.4 Hz, 1H; aromatic proton), 8.22−7.03 (m, 11H;
aromatic protons), 4.68 (m, 2H; CH2N), 3.87 (m, 2H; NH2).
J
DOI: 10.1021/acs.organomet.8b00919
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
2
3
4.10; N, 4.16. IR (Nujol): 1920 (s) cm−1 (νCO). H NMR (200.1
6.5 Hz, 1H; CH2N), 2.79 (dd, J(H,H) = 8.6 Hz, J(H,H) = 6.6 Hz,
1H; NH2), 2.14 (s, 3H; CH3). 13C{1H} NMR (50.3 MHz, CD2Cl2,
20 °C): δ 207.5 (d, 2J(C,P) = 18.2 Hz; CO), 176.3 (d, 2J(C,P) = 12.3
Hz; CRu), 162.2 (s; NCC), 157.2 (s; NCCH2), 145.4−116.4 (m;
3
MHz, CD2Cl2, 20 °C): δ 9.29 (d, J(H,H) = 7.2 Hz, 1H; aromatic
proton), 8.10−6.87 (m, 21H; aromatic protons), 6.72 (d, J(H,H) =
8.3 Hz, 1H; aromatic proton), 4.27 (m, 2H; CH2N), 3.91 (m, 2H;
NH2). 13C{1H} NMR (50.3 MHz, CD2Cl2, 20 °C): δ 200.4 (d,
2J(C,P) = 18.4 Hz; CO), 160.3 (s; NCC), 155.0 (s; NCCH2), 142.6−
116.7 (m; aromatic carbon atoms), 49.5 (s; CH2N). 31P{1H} NMR
(81.0 MHz, CD2Cl2, 20 °C): δ 53.4.
3
3
aromatic carbon atoms), 51.2 (d, J(C,P) = 5.3 Hz; CH2N), 21.7 (s;
CH3). 31P{1H} NMR (81.0 MHz, CD2Cl2, 20 °C): δ 57.6.
Synthesis of [RuCl(ambq)(PPh3)(CO)] (10). Complex 10 was
prepared by following the procedure used for 9, employing cis-
[RuCl(ambq)(PPh3)2] (226 mg, 0.26 mmol) in place of cis-
[RuCl(amtp)(PPh3)2]. Yield: 132 mg (80%). Anal. Calcd for
C33H26CIN2OPRu: C, 62.51; H, 4.13; N, 4.42. Found: C, 62.55; H,
Synthesis of trans-[RuCl2(HambqPh)(PPh3)(CO)] (7).
[RuCl2(dmf)(PPh3)2(CO)] (245 mg, 0.31 mmol) was reacted with
HCl·HambqPh (159 mg, 0.50 mmol, 1.6 equiv) and tributylamine (0.5
mL, 2.1 mmol, 6.8 equiv) in n-butanol (5 mL), and the mixture was
stirred at 130 °C overnight. The solvent was evaporated under
reduced pressure, and the residue was dissolved in chloroform (3
mL). After addition of K2CO3 (200 mg, 1.45 mmol, 4.7 equiv), the
mixture was stirred for 2 h at room temperature. The suspension was
filtered, and the solution was concentrated to about 1 mL by
evaporation of the solvent under reduced pressure. The complex was
precipitated by addition of diethyl ether (10 mL), filtered, washed
with diethyl ether (2 × 3 mL) and n-pentane (3 mL), and finally dried
under reduced pressure. Yield: 101 mg (44%). Anal. Calcd for
C39H31Cl2N2OPRu: C, 62.74; H, 4.19; N, 3.75. Found: C, 62.66; H,
4.10; N, 4.37. IR (Nujol): 1922 (s) cm−1 (νCO). H NMR (200.1
1
3
MHz, CD2Cl2, 20 °C): δ 8.02 (d, J(H,H) = 8.2 Hz, 1H; aromatic
proton), 7.90 (dt, 3J(H,H) = 6.6 Hz, 4J(H,H) = 1.3 Hz, 2H; aromatic
2
protons), 7.45−6.98 (m, 19H; aromatic protons), 4.51 (dd, J(H,H)
= 17.3 Hz, 3J(H,H) = 5.9 Hz, 1H; CH2N), 4.03 (dd, 2J(H,H) = 17.4
3
2
Hz, J(H,H) = 8.4 Hz, 1H; NH2), 3.70 (ddd, J(H,H) = 16.7 Hz,
3J(H,H) = 6.3 Hz, J(H,H) = 3.8 Hz, 1H; CH2N), 2.86 (pseudo t,
3
J(H,H) = 8.4 Hz, 1H; NH2). 13C{1H} NMR (50.3 MHz, CD2Cl2): δ
2
2
207.8 (d, J(C,P) = 17.5 Hz; CO), 172.1 (d, J(C,P) = 12.8 Hz;
CRu), 156.0 (s; NCC), 150.6 (s; NCCH2), 142.4−116.6 (m;
aromatic carbon atoms), 51.4 (s; CH2N). 31P{1H} NMR (81.0
MHz, CD2Cl2, 20 °C): δ 58.5.
1
4.10; N, 3.82. IR (Nujol): 1924 (s) cm−1 (νCO). H NMR (200.1
Synthesis of cis-[RuCl(ambqPh)(PPh3)2] (11a). The hydro-
chloride ligand HCl·HambqPh (183.5 mg, 0.57 mmol) and NEt3 (0.35
mL, 2.59 mmol) were added to [RuCl2(PPh3)3] (500 mg, 0.52 mmol)
in 2-propanol (5 mL), and the mixture was heated under reflux for 2
h. The resulting solution was concentrated (1 mL), and addition of n-
pentane (5 mL) afforded an orange precipitate. The solid was filtered,
washed with n-pentane (2 × 5 mL), and dried under reduced
pressure. The product was recrystallized from methanol (3 mL).
Yield: 432 mg (88%). Anal. Calcd for C56H45ClN2P2Ru: C, 71.22; H,
MHz, CD2Cl2, 20 °C): δ 9.08 (m, 1H; aromatic proton), 7.92−6.56
(m, 27H; aromatic protons), 4.16 (dd, 2J(H,H) = 10.3 Hz, 3J(H,H) =
4.9 Hz, 2H; CH2N), 3.88 (m, 2H; NH2). 13C{1H} NMR (50.3 MHz,
2
CD2Cl2, 20 °C): δ 200.5 (d, J(C,P) = 17.5 Hz; CO), 159.9 (s;
NCC), 155.1 (s; NCCH2), 148.7−117.2 (m; aromatic carbon atoms),
49.5 (s; CH2N). 31P{1H} NMR (81.0 MHz, CD2Cl2, 20 °C): δ 53.5.
Synthesis of trans-[Ru(OAc)2(Hamtp)(PPh3)(CO)] (8). [Ru-
(OAc)2(PPh3)2(CO)] (100.3 mg, 0.13 mmol) and the ligand Hamtp
(28.3 mg, 0.14 mmol, 1.1 equiv) were suspended in toluene (5 mL),
and the mixture was stirred at 110 °C for 2 days. The resulting
solution was concentrated to almost 0.5 mL, the solvent was
evaporated under reduced pressure, and the complex was precipitated
by addition of n-pentane (7 mL). The solid was filtered, washed with
n-heptane (2 × 5 mL) and diethyl ether (2 × 3 mL), and dried under
reduced pressure. Yield: 37.1 mg (40%). Anal. Calcd for
C36H35N2O5PRu: C, 61.10; H, 4.98; N, 3.96. Found: C, 61.02; H,
5.03; N, 3.89. IR (Nujol): 1914 (s) (νCO), 1597 (s) and 1572 cm−1
(s) (νCO). 1H NMR (200.1 MHz, CD2Cl2, 20 °C): δ 8.17 (d,
3J(H,H) = 7.9 Hz, 1H; NH2), 7.79−7.60 (m, 6H; aromatic protons),
7.46−7.37 (m, 6H; aromatic protons), 7.30−7.17 (m, 7H; aromatic
protons), 7.06 (m, 1H; aromatic proton), 6.91 (d, 3J(H,H) = 8.4 Hz,
1
4.80; N, 2.97. Found: C, 71.11; H, 4.73; N, 3.02. H NMR (200.1
3
4
MHz, CDCl3, 20 °C): δ 8.36 (dd, J(H,H) = 5.0 Hz, J(H,H) = 2.6
Hz, 1H; aromatic proton), 7.80−6.79 (m, 34H; aromatic protons),
6.69 (t, 3J(H,H) = 6.8 Hz, 6H; aromatic protons), 4.31 (dd, 2J(H,H)
= 16.0 Hz, 3J(H,H) = 3.6 Hz, 1H; CH2N), 4.02 (m, 1H; NH2), 3.61
(dt, 2J(H,H) = 16.1 Hz, 3J(H,H) = 7.6 Hz, 1H; CH2N), 3.02 (m, 1H;
NH2). 13C{1H} NMR (50.3 MHz, CDCl3, 20 °C): δ 177.9 (d,
2J(C,P) = 3.9 Hz; CRu), 161.3 (d, 3J(C,P) = 1.9 Hz; NCCH2),
155.1(s; NCC), 142.1−116.9 (m; aromatic carbon atoms), 50.8 (d,
3J(C,P) = 2.8 Hz; CH2N). 31P{1H} NMR (81.0 MHz, CDCl3, 20
2
2
°C): δ 57.3 (d, J(P,P) = 33.7 Hz), 50.8 (d, J(P,P) = 33.7 Hz).
Synthesis of [RuCl(ambqPh)(PPh3)(CO)] (11). Complex 11 was
prepared by following the procedure used for 9, employing cis-
[RuCl(ambqPh)(PPh3)2] (11a; 119.8 mg, 0.13 mmol) in place of cis-
[RuCl(amtp)(PPh3)2]. Yield: 76.6 mg (83%). Anal. Calcd for
C39H30ClN2OPRu: C, 65.96; H, 4.26; N, 3.94. Found: C, 66.01; H,
4.33; N, 4.02. IR (Nujol): 1920 cm−1 (νCO). 1H NMR (200.1 MHz,
3
3
1H; aromatic proton), 6.64 (dd, J(H,H) = 12.3 Hz, J(H,H) = 7.8
2
3
Hz, 1H; aromatic proton), 4.41 (dd, J(H,H) = 16.6 Hz, J(H,H) =
6.5 Hz, 1H; CH2N), 4.21 (m, 1H; CH2N), 2.14 (s, 3H; CH3), 2.07
(s, 3H; CH3CO), 1.57 (m, 1H; NH2), 1.23 (s, 3H; CH3CO).
13C{1H} NMR (50.3 MHz, CD2Cl2, 20 °C): δ 202.9 (d, J(C,P) =
2
17.4 Hz; CO), 180.5 (s; CH3CO), 177.7 (s; CH3CO), 163.5 (s;
NCC), 161.0 (s; NCCH2), 146.5−116.7 (m; aromatic carbon atoms),
52.2 (d, 3J(C,P) = 2.6 Hz; CH2N), 25.3 (s; CH3CO), 25.0 (s;
CH3CO), 21.6 (s; CH3). 31P{1H} NMR (81.0 MHz, CD2Cl2, 20 °C):
δ 54.4.
3
4
CD2Cl2, 20 °C): δ 7.96 (dd, J(H,H) = 6.0 Hz, J(H,H) = 1.0 Hz,
1H; aromatic proton), 7.66 (d, 3J(H,H) = 9.0 Hz, 1H; aromatic
proton), 7.61−7.48 (m, 5H; aromatic protons), 7.44 (t, 3J(H,H) = 2.6
Hz, 1H; aromatic proton), 7.36−7.30 (m, 2H; aromatic protons),
7.29−7.05 (m, 15H; aromatic protons), 7.03 (br s, 1H; aromatic
proton), 4.57 (dd, 2J(H,H) = 16.9 Hz, 3J(H,H) = 6.7 Hz, 1H;
Synthesis of [RuCl(amtp)(PPh3)(CO)] (9). cis-[RuCl(amtp)-
(PPh3)2] (251.9 mg, 0.29 mmol) was suspended in dichloromethane
(5 mL), and the mixture was stirred under a CO atmosphere (1 atm)
overnight at room temperature. The solvent was evaporated under
reduced pressure, and the residue was purified by flash chromatog-
raphy, using dichloromethane/diethyl ether as eluent (gradient 9/1 to
1/1). Yield: 106 mg (59%). Anal. Calcd for C32H28ClN2OPRu: C,
61.59; H, 4.52; N, 4.49. Found: C, 61.64; H, 4.61; N, 4.56. IR
2
3
CH2N), 4.14 (dd, J(H,H) = 17.4 Hz, J(H,H) = 7.6 Hz, 1H; NH2),
2
3
3.81 (dt, J(H,H) = 16.4 Hz, J(H,H) = 7.6 Hz, 1H; CH2N), 2.99
(pseudo t, J(H,H) = 7.9 Hz, 1H; NH2). 13C{1H} NMR (50.3 MHz,
2
CD2Cl2, 20 °C): δ 208.0 (d, J(C,P) = 17.4 Hz; CO), 172.6 (d,
2J(C,P) = 12.8 Hz; CRu), 155.8 (s; NCC), 150.9 (s; NCCH2), 148.7
(s; ipso-Ph), 142.7−117.2 (m; aromatic carbon atoms), 51.5 (s;
CH2N). 31P{1H} NMR (81.0 MHz, CD2Cl2, 20 °C): δ 58.0.
(Nujol): 1905 (s) cm−1 (νCO). H NMR (200.1 MHz, CD2Cl2, 20
1
Synthesis of trans-[Ru(amtp)(PPh3)2(CO)][BArf4] (12). Na-
[BArf4] (71.0 mg, 0.0801 mmol) was added to [RuCl(amtp)(PPh3)-
(CO)] (9; 50.0 mg, 0.0801 mmol) and PPh3 (21.0 mg, 0.0801 mmol)
in dichloromethane (5 mL). The reaction mixture was stirred for 30
min at room temperature and filtered to remove NaCl. The obtained
solution was concentrated (1 mL), and addition of n-heptane (5 mL)
afforded a light yellow precipitate that was filtered, washed with
°C): δ 7.78 (ddd, 3J(H,H) = 9.9 Hz, 3J(H,H) = 6.7 Hz, 4J(H,H) = 2.9
Hz, 2H; aromatic protons), 7.57−7.15 (m, 17H; aromatic protons),
6.69 (dd, 3J(H,H) = 6.6 Hz, 3J(H,H) = 1.9 Hz, 1H; aromatic proton),
3
4
4
6.62 (ddd, J(H,H) = 8.0 Hz, J(H,H) = 1.7 Hz, J(H,H) = 0.6 Hz,
2
3
1H; aromatic proton), 4.25 (dd, J(H,H) = 16.2 Hz, J(H,H) = 6.3
Hz, 1H; CH2N), 3.86 (dd, 2J(H,H) = 16.6 Hz, 3J(H,H) = 8.9 Hz, 1H;
2
3
3
NH2), 3.41 (ddd, J(H,H)= 16.5 Hz, J(H,H) = 10.0 Hz, J(H,H) =
K
DOI: 10.1021/acs.organomet.8b00919
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
pentane (2 × 3 mL), and dried under reduced pressure. Yield: 108.5
mg (79%). Anal. Calcd for C82H55BF24N2OP2Ru: C, 57.46; H, 3.23;
N, 1.63. Found: C, 57.52; H, 3.27; N, 1.62. IR (Nujol): 1914 cm−1
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00919.
■
S
1
(νCO). H NMR (200.1 MHz, CD2Cl2, 20 °C): δ 7.75 (m, 8H;
aromatic protons), 7.58 (s, 4H; aromatic protons), 7.44−7.32 (m,
8H; aromatic protons), 7.30−7.20 (m, 11H; aromatic protons),
3
7.19−7.06 (m, 15H; aromatic protons), 6.62 (d, J(H,H) = 7.9 Hz,
NMR data of the isolated complexes, X-ray crystallo-
graphic details of compound 11, and catalytic results of
the TH and HY reactions (PDF)
1H; aromatic proton), 6.42 (dd, 3J(H,H) = 7.6 Hz, 4J(H,H) = 0.5 Hz,
3
1H; aromatic proton), 3.53 (t, J(H,H) = 6.5 Hz, 2H; CH2N), 2.95
(m, 2H; NH2), 2.04 (s, 3H; CH3). 13C{1H} NMR (50.3 MHz,
CD2Cl2, 20 °C): δ 205.9 (t, 2J(C,P) = 15.7 Hz; CO), 169.4 (t,
2J(C,P) = 10.5 Hz; CRu), 162.1 (q, 1J(C,B) = 50.1 Hz; CB), 162.0 (s;
NCC), 156.3 (s; NCCH2), 144.6−116.8 (aromatic carbon atoms),
Accession Codes
CCDC 1868440 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
1
124.7 (q, J(C,F) = 271.8 Hz; CF3), 50.6 (s; CH2N), 21.7 (s; CH3).
31P{1H} NMR (81.0 MHz, CD2Cl2, 20 °C): δ 35.5.
Typical Procedure for TH of Ketones and Aldehydes. The
ruthenium catalyst solution used for TH was prepared by dissolving
the complexes 1−12 and cis,trans,cis-[RuCl2(PCy3)2(CO)2] (0.02
mmol) in 2-propanol (5 mL). The catalyst solution (250 μL, 1.0
μmol) and a 0.1 M solution of NaOiPr (200 μL, 20 μmol) in 2-
propanol were added subsequently to the ketone or aldehyde solution
(1.0 mmol) in 2-propanol (final volume 10 mL), and the resulting
mixture was heated under reflux. The reaction mixture was sampled
by removing an aliquot of it, which was quenched by addition of
diethyl ether (1/1 v/v), filtered over a short silica pad, and submitted
to GC analysis. The base addition was considered as the start time of
the reaction. The S/C molar ratio was 1000/1, whereas the base
concentration was 2 mol % with respect to substrate (0.1 M). The
same procedure was followed for TH reactions with other S/C values
(in the range 1000−100000) or with different base concentrations
(1−5 mol %), using the appropriate amount of catalysts, base, and 2-
propanol.
Typical Procedure for TH of Ketones and Aldehydes with in
Situ Prepared Catalysts from 1−11 and cis,trans,cis-
[RuCl2(PCy3)2(CO)2]. The catalyst solutions were prepared by adding
2-propanol (5 mL) to the complexes 1−11 (0.02 mmol) and the
corresponding ligand (PPh3 or PCy3, 0.04 mmol). The mixtures were
stirred for 30 min at reflux. The solutions of the in situ formed catalyst
were used in the TH reactions as described above.
AUTHOR INFORMATION
Corresponding Author
*E-mail for W.B.: walter.baratta@uniud.it.
ORCID
■
̈
Alexander Pothig: 0000-0003-4663-3949
Daniele Zuccaccia: 0000-0001-7765-1715
Walter Baratta: 0000-0002-2648-1848
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
̀
This work was supported by the Ministero dell’Universita e
della Ricerca (MIUR), PRIN 2015 program no.
20154X9ATP_005, and the Fellowship Program “Talents for
an International House (TALENTS UP)” (seventh R&D FP:
PEOPLE - Marie Curie Actions - COFUND) and AREA
Consortium of Trieste for a fellowship for S.G. We thank Mr.
Riccardo Bot for carrying out transfer hydrogenation tests, Mr.
Pierluigi Polese for the elemental analyses, and Dr. Paolo
Martinuzzi for NMR assistance. We also acknowledge Dr.
Antonio Zanotti-Gerosa for helpful discussions on hydro-
genation reactions and for giving the opportunity to S.G. to
perform hydrogenation tests at Johnson Matthey in Cam-
bridge.
In the case of cis,trans,cis-[RuCl2(PCy3)2(CO)2], the ampy or
Hamtp ligand was added to the ruthenium complex in 2-propanol
(ligand/catalyst ratio 2) and the mixture was refluxed for 2 h. The
solution of the in situ formed catalyst was used in the TH reactions as
described above.
Typical Procedure for HY of Ketones with 1−3, 5, 6, and 9−
11. The HY reactions were performed in an eight-vessel Endeavor
Biotage apparatus. The vessels were charged with the ruthenium
catalysts (2.5 μmol), loaded with 5 bar of N2, and slowly vented (five
times). The ketones (5 mmol), eventual ligand (PPh3 or PCy3, 5
μmol), and a KOtBu solution (1 mL, 0.1 mmol, 0.1 M) in methanol
or ethanol were added. Further addition of the solvent (methanol or
ethanol) led to a 2 M ketone solution. The vessels were purged with
N2 and H2 (three times each), and then the system was charged with
H2 (30 bar) and heated to 70 °C for the required time (16 h). The S/
C molar ratio was 2000/1, whereas the base concentration was 2 mol
%. A similar method was applied for the reactions with other S/C
values (in the range 500−10000) or with different base concen-
trations (5 mol %), using the appropriate amount of catalysts, base,
ligands (ligand/catalyst ratio 2), and solvent. The reaction vessels
were then cooled to room temperature, vented, and purged three
times with N2. A drop of the reaction mixture was then diluted with 1
mL of methanol and analyzed by GC.
Single-Crystal X-ray Crystallography Structure Determina-
tion of Compound 11. Single crystals of complex 11 were obtained
by slow cooling of a concentrated solution of the species in CH2Cl2.
X-ray diffraction data were collected with a Bruker APEX-II κ-CCD
diffractometer equipped with a rotating anode (Bruker AXS, FR591)
by using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å).
For additional details for the collection and refinement of data, see the
Supporting Information.
REFERENCES
■
(1) (a) Arockiam, P. B.; Bruneau, C.; Dixneuf, P. H. Ruthenium(II)-
Catalyzed C−H Bond Activation and Functionalization. Chem. Rev.
2012, 112, 5879−5918. (b) Asymmetric Catalysis on Industrial Scale:
Challenges, Approaches, and Solutions, 2nd ed.; Wiley-VCH:
Weinheim, Germany, 2010; Vol. 1, p 562. (c) Nolan, S. P.; Clavier,
H. Chemoselective Olefin Metathesis Transformations Mediated by
Ruthenium Complexes. Chem. Soc. Rev. 2010, 39, 3305−3316.
(d) Beller, M.; Kumar, K., Hydroformylation: Applications in the
Synthesis of Pharmaceuticals and Fine Chemicals. In Transition Metals
for Organic Synthesis, 2nd ed.; Beller, M.; Bolm, C., Eds.; Wiley-VCH:
Weinheim, Germany, 2004; Vol. 1, pp 28−55.
(2) Crabtree, R. H. Deactivation in Homogeneous Transition Metal
Catalysis: Causes, Avoidance, and Cure. Chem. Rev. 2015, 115, 127−
150.
(3) (a) Xie, X.; Lu, B.; Li, W.; Zhang, Z. Coordination Determined
Chemo- and Enantioselectivities in Asymmetric Hydrogenation of
Multi-Functionalized Ketones. Coord. Chem. Rev. 2018, 355, 39−53.
(b) Yoshimura, M.; Tanaka, S.; Kitamura, M. Recent Topics in
Catalytic Asymmetric Hydrogenation of ketones. Tetrahedron Lett.
2014, 55, 3635−3640. (c) Shang, G.; Li, W.; Zhang, X., Transition
Metal-Catalyzed Homogeneous Asymmetric Hydrogenation. In
L
DOI: 10.1021/acs.organomet.8b00919
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Catalytic Asymmetric Synthesis, 3rd ed.; Ojima, I., Ed.; Wiley:
Hoboken, NJ, 2010; Vol. 1, pp 343−436. (d) The Handbook of
Homogeneous Hydrogenation. Wiley-VCH: Weinheim, Germany, 2007;
Vols. 1−3, p 1568.
McLaren, D. B.; Moya, E.; Reynolds, S.; Sandham, K. S.; Martinuzzi,
P.; Baratta, W. Preparation of Pincer 4-Functionalized 2-
Aminomethylbenzo[h]quinoline Ruthenium Catalysts for Ketone
Reduction. Organometallics 2016, 35, 277−287. (b) Baratta, W.;
Benedetti, F.; Del Zotto, A.; Fanfoni, L.; Felluga, F.; Magnolia, S.;
Putignano, E.; Rigo, P. Chiral Pincer Ruthenium and Osmium
Complexes for the Fast and Efficient Hydrogen Transfer Reduction of
Ketones. Organometallics 2010, 29, 3563−3570. (c) Baratta, W.;
Siega, K.; Rigo, P. Fast and Chemoselective Transfer Hydrogenation
of Aldehydes Catalyzed by a Terdentate CNN Ruthenium Complex
[RuCl(CNN)(dppb)]. Adv. Synth. Catal. 2007, 349, 1633−1636.
(d) Baratta, W.; Bosco, M.; Chelucci, G.; Del Zotto, A.; Siega, K.;
Toniutti, M.; Zangrando, E.; Rigo, P. Terdentate RuX(CNN)(PP) (X
= Cl, H, OR) Complexes: Synthesis, Properties, and Catalytic Activity
in Fast Transfer Hydrogenation. Organometallics 2006, 25, 4611−
4620. (e) Baratta, W.; Chelucci, G.; Gladiali, S.; Siega, K.; Toniutti,
M.; Zanette, M.; Zangrando, E.; Rigo, P. Ruthenium(II) Terdentate
CNN Complexes: Superlative Catalysts for the Hydrogen-Transfer
Reduction of Ketones by Reversible Insertion of a Carbonyl Group
into the Ru-H Bond. Angew. Chem., Int. Ed. 2005, 44, 6214−6219.
(11) Baratta, W.; Bossi, G.; Putignano, E.; Rigo, P. Pincer and
Diamine Ru and Os Diphosphane Complexes as Efficient Catalysts
for the Dehydrogenation of Alcohols to Ketones. Chem. - Eur. J. 2011,
17, 3474−3481.
(4) (a) Wang, D.; Astruc, D. The Golden Age of Transfer
Hydrogenation. Chem. Rev. 2015, 115, 6621−6686. (b) Foubelo, F.;
́
Najera, C.; Yus, M. Catalytic Asymmetric Transfer Hydrogenation of
Ketones: Recent Advances. Tetrahedron: Asymmetry 2015, 26, 769−
790. (c) Ito, J.-i.; Nishiyama, H. Recent Topics of Transfer
Hydrogenation. Tetrahedron Lett. 2014, 55, 3133−3146. (d) Morris,
R. H. Asymmetric Hydrogenation, Transfer Hydrogenation and
Hydrosilylation of Ketones Catalyzed by Iron Complexes. Chem. Soc.
Rev. 2009, 38, 2282−2291. (e) Baratta, W.; Rigo, P. 1-(Pyridin-2-
yl)methanamine-Based Ruthenium Catalysts for Fast Transfer
Hydrogenation of Carbonyl Compounds in 2-Propanol. Eur. J.
Inorg. Chem. 2008, 2008, 4041−4053. (f) Wang, C.; Wu, X.; Xiao, J.
Broader, Greener, and More Efficient: Recent Advances in
Asymmetric Transfer Hydrogenation. Chem. - Asian J. 2008, 3,
̈
1750−1770. (g) Samec, J. S. M.; Backvall, J.-E.; Andersson, P. G.;
Brandt, P. Mechanistic Aspects of Transition Metal-Catalyzed
Hydrogen Transfer Reactions. Chem. Soc. Rev. 2006, 35, 237−248.
(5) Magano, J.; Dunetz, J. R. Large-Scale Carbonyl Reductions in the
Pharmaceutical Industry. Org. Process Res. Dev. 2012, 16, 1156−1184.
(6) (a) Clapham, S. E.; Hadzovic, A.; Morris, R. H. Mechanisms of
the H2-Hydrogenation and Transfer Hydrogenation of Polar Bonds
Catalyzed by Ruthenium Hydride Complexes. Coord. Chem. Rev.
2004, 248, 2201−2237. (b) Yamakawa, M.; Ito, H.; Noyori, R. The
Metal−Ligand Bifunctional Catalysis: A Theoretical Study on the
Ruthenium(II)-Catalyzed Hydrogen Transfer between Alcohols and
Carbonyl Compounds. J. Am. Chem. Soc. 2000, 122, 1466−1478.
(c) 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. Chiral Induction Effects in Ruthenium(II)
Amino Alcohol Catalysed Asymmetric Transfer Hydrogenation of
Ketones: An Experimental and Theoretical Approach. Chem. - Eur. J.
2000, 6, 2818−2829.
(12) Bossi, G.; Putignano, E.; Rigo, P.; Baratta, W. Pincer Ru and Os
Complexes as Efficient Catalysts for Racemization and Deuteration of
Alcohols. Dalton Trans. 2011, 40, 8986−8995.
(13) Solinas, M.; Sechi, B.; Baldino, S.; Baratta, W.; Chelucci, G.
Hydrogenation of Imines Catalyzed by 2-(Aminomethyl)pyridine-
Based Ruthenium and Osmium Complexes. ChemistrySelect 2016, 1,
2492−2497.
(14) (a) Baratta, W.; Fanfoni, L.; Magnolia, S.; Siega, K.; Rigo, P.
Benzo[h]quinoline Pincer Ruthenium and Osmium Catalysts for
Hydrogenation of Ketones. Eur. J. Inorg. Chem. 2010, 2010, 1419−
1423. (b) Baratta, W.; Ballico, M.; Baldino, S.; Chelucci, G.;
Herdtweck, E.; Siega, K.; Magnolia, S.; Rigo, P. New Benzo[h]-
quinoline-Based Ligands and their Pincer Ru and Os Complexes for
Efficient Catalytic Transfer Hydrogenation of Carbonyl Compounds.
Chem. - Eur. J. 2008, 14, 9148−9160.
(7) Abbreviations: ampy = 2-(aminomethyl)pyridine; en = 1,2-
ethylendiamine; bpy = 2,2′-bipyridine; Hamtp = 6-(4-methylphenyl)-
2-(aminomethyl)pyridine; amtp = anionic form of 6-(4-methylphen-
yl)-2-(aminomethyl)pyridine; Hambq = 2-(aminomethyl)benzo[h]
quinoline; ambq = anionic form of 2-(aminomethyl)benzo[h]
quinoline; HambqPh = 4-phenyl-2-(aminomethyl)benzo[h]quinoline;
ambqPh = anionic form of 4-phenyl-2-(aminomethyl)benzo[h]quino-
line; dppb = 1,4-bis(diphenylphosphine)butane.
(15) Chelucci, G.; Baldino, S.; Baratta, W. Ruthenium and Osmium
Complexes Containing 2-(aminomethyl)pyridine (Ampy)-based
Ligands in Catalysis. Coord. Chem. Rev. 2015, 300, 29−85.
(16) (a) Baldino, S.; Facchetti, S.; Nedden, H. G.; Zanotti-Gerosa,
A.; Baratta, W. Chemoselective Transfer Hydrogenation of Aldehydes
with HCOONH4 Catalyzed by RuCl(CNNPh)(PP) Pincer Com-
plexes. ChemCatChem 2016, 8, 3195−3198. (b) Baldino, S.; Facchetti,
S.; Zanotti-Gerosa, A.; Nedden, H. G.; Baratta, W. Transfer
Hydrogenation and Hydrogenation of Commercial-Grade Aldehydes
to Primary Alcohols Catalyzed by 2-(Aminomethyl)pyridine and
Pincer Benzo[h]quinoline Ruthenium Complexes. ChemCatChem
2016, 8, 2279−2288.
(8) (a) Putignano, E.; Bossi, G.; Rigo, P.; Baratta, W. MCl2(ampy)-
(dppf) (M = Ru, Os): Multitasking Catalysts for Carbonyl
Compound/Alcohol Interconversion Reactions. Organometallics
2012, 31, 1133−1142. (b) Baratta, W.; Chelucci, G.; Herdtweck,
E.; Magnolia, S.; Siega, K.; Rigo, P. Highly Diastereoselective
Formation of Ruthenium Complexes for Efficient Catalytic Asym-
metric Transfer Hydrogenation. Angew. Chem., Int. Ed. 2007, 46,
7651−7654. (c) Ohkuma, T.; Sandoval, C. A.; Srinivasan, R.; Lin, Q.;
́
(17) Espinet, P.; Albeniz, A. C., 1,2-Insertion and β-Elimination. In
Wei, Y.; Mun
̃
iz, K.; Noyori, R. Asymmetric Hydrogenation of tert-
Current Methods in Inorganic Chemistry; Kurosawa, H., Yamamoto, A.,
Eds.; Elsevier: Amsterdam, 2003; Vol. 3, pp 293−371.
Alkyl Ketones. J. Am. Chem. Soc. 2005, 127, 8288−8289. (d) Baratta,
W.; Herdtweck, E.; Siega, K.; Toniutti, M.; Rigo, P. 2-
(Aminomethyl)pyridine-Phosphine Ruthenium(II) Complexes:
Novel Highly Active Transfer Hydrogenation Catalysts. Organo-
metallics 2005, 24, 1660−1669.
(18) Smith, M. B. March’s Advances Organic Chemistry: Reactions,
Mechanisms and Structure, 7th ed.; Wiley: Hoboken, NJ, 2013; p 1141.
(19) (a) Werner, T.; Koch, J. Sodium Hydride Catalyzed
Tishchenko Reaction. Eur. J. Org. Chem. 2010, 2010, 6904−6907.
(b) Ekoue-Kovi, K.; Wolf, C. One-Pot Oxidative Esterification and
Amidation of Aldehydes. Chem. - Eur. J. 2008, 14, 6302−6315.
(20) Geissman, T. A. The Cannizzaro Reaction. In Organic
Reactions; Denmark, S. E., Ed.; Wiley: Hoboken, NJ, 1944; Vol. 2,
pp 94−113.
(9) (a) Younus, H. A.; Su, W.; Ahmad, N.; Chen, S.; Verpoort, F.
Ruthenium Pincer Complexes: Synthesis and Catalytic Applications.
Adv. Synth. Catal. 2015, 357, 283−330. (b) Gunanathan, C.; Milstein,
D. Bond Activation and Catalysis by Ruthenium Pincer Complexes.
Chem. Rev. 2014, 114, 12024−12087. (c) Albrecht, M. Cyclo-
metalation Using d-Block Transition Metals: Fundamental Aspects
and Recent Trends. Chem. Rev. 2010, 110, 576−623. (d) Djukic, J. P.;
Sortais, J. B.; Barloy, L.; Pfeffer, M. Cycloruthenated Compounds -
Synthesis and Applications. Eur. J. Inorg. Chem. 2009, 2009, 817−853.
(10) (a) Facchetti, S.; Jurcik, V.; Baldino, S.; Giboulot, S.; Nedden,
H. G.; Zanotti-Gerosa, A.; Blackaby, A.; Bryan, R.; Boogaard, A.;
(21) (a) Bolton, P. D.; Grellier, M.; Vautravers, N.; Vendier, L.;
Sabo-Etienne, S. Access to Ruthenium(0) Carbonyl Complexes via
Dehydrogenation of a Tricyclopentylphosphine Ligand and Decar-
bonylation of Alcohols. Organometallics 2008, 27, 5088−5093.
(b) Baratta, W.; Del Zotto, A.; Esposito, G.; Sechi, A.; Toniutti,
M.; Zangrando, E.; Rigo, P. RuCl2[(2,6-Me2C6H3)PPh2]2: A New
M
DOI: 10.1021/acs.organomet.8b00919
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Precursor for Cyclometalated Ruthenium(II) Complexes. Organo-
metallics 2004, 23, 6264−6272. (c) Coalter, J. N., III; Huffman, J. C.;
Caulton, K. G. Cleavage of H-C(sp2) and C(sp2)-X Bonds (X = Alkyl,
Aryl, OR, NR2): Facile Decarbonylation, Isonitrile Abstraction, or
Dehydrogenation of Aldehydes, Esters, Amides, Amines, and Imines
by [RuHCl(PiPr3)2]2. Organometallics 2000, 19, 3569−3578.
(22) Omura, S.; Fukuyama, T.; Murakami, Y.; Okamoto, H.; Ryu, I.
Hydroruthenation Triggered Catalytic Conversion of Dialdehydes
and Keto Aldehydes to Lactones. Chem. Commun. 2009, 6741−6743.
(23) (a) Saudan, L. A.; Saudan, C. M.; Debieux, C.; Wyss, P.
Dihydrogen Reduction of Carboxylic Esters to Alcohols under the
Catalysis of Homogeneous Ruthenium Complexes: High Efficiency
and Unprecedented Chemoselectivity. Angew. Chem., Int. Ed. 2007,
46, 7473−7476. (b) Wu, X.; Liu, J.; Li, X.; Zanotti-Gerosa, A.;
Hancock, F.; Vinci, D.; Ruan, J.; Xiao, J. On Water and in Air: Fast
and Highly Chemoselective Transfer Hydrogenation of Aldehydes
with Iridium Catalysts. Angew. Chem., Int. Ed. 2006, 45, 6718−6722.
(c) Beck, C. M.; Rathmill, S. E.; Park, Y. J.; Chen, J.; Crabtree, R. H.;
Liable-Sands, L. M.; Rheingold, A. L. Aldehyde Decarbonylation
Catalysis under Mild Conditions. Organometallics 1999, 18, 5311−
5317.
(28) (a) Figliolia, R.; Baldino, S.; Nedden, H. G.; Zanotti-Gerosa,
A.; Baratta, W. Mild N-Alkylation of Amines with Alcohols Catalyzed
by the Acetate Ru(OAc)2(CO)(DiPPF) Complex. Chem. - Eur. J.
2017, 23, 14416−14419. (b) Watson, A. J. A.; Atkinson, B. N.;
Maxwell, A. C.; Williams, J. M. J. Ruthenium-Catalyzed Remote
Electronic Activation of Aromatic C-F Bonds. Adv. Synth. Catal. 2013,
355, 734−740. (c) Zbieg, J. R.; McInturff, E. L.; Krische, M. J.
Allenamide Hydro-Hydroxyalkylation: 1,2-Amino Alcohols via
Ruthenium-Catalyzed Carbonyl anti-Aminoallylation. Org. Lett.
2010, 12, 2514−2516. (d) Denichoux, A.; Fukuyama, T.; Doi, T.;
Horiguchi, J.; Ryu, I. Synthesis of 2-Hydroxymethyl Ketones by
Ruthenium Hydride-Catalyzed Cross-Coupling Reaction of α,β-
Unsaturated Aldehydes with Primary Alcohols. Org. Lett. 2010, 12,
1−3. (e) Nixon, T. D.; Whittlesey, M. K.; Williams, J. M. J. Transition
Metal Catalysed Reactions of Alcohols Using Borrowing Hydrogen
Methodology. Dalton Trans. 2009, 753−762. (f) Burling, S.; Paine, B.
M.; Nama, D.; Brown, V. S.; Mahon, M. F.; Prior, T. J.; Pregosin, P.
S.; Whittlesey, M. K.; Williams, J. M. J. C-H Activation Reactions of
Ruthenium N-Heterocyclic Carbene Complexes: Application in a
Catalytic Tandem Reaction Involving C-C Bond Formation from
Alcohols. J. Am. Chem. Soc. 2007, 129, 1987−1995.
(29) (a) Creswell, C. J.; Dobson, A.; Moore, D. S.; Robinson, S. D.
Complexes of the Platinum Metals. 17. Molecular Dynamics of the
Species [M(O2CR)2(CO)(PPh3)2] (M = Ruthenium, R = Methyl,
Trifluoromethyl, Pentafluoroethyl, Pentafluorophenyl; M = Osmium,
R = Methyl, Trifluoromethyl). Inorg. Chem. 1979, 18, 2055−2059.
(b) Dobson, A.; Robinson, S. D. Complexes of the Platinum Metals.
7. Homogeneous Ruthenium and Osmium Catalysts for the
Dehydrogenation of Primary and Secondary Alcohols. Inorg. Chem.
1977, 16, 137−142.
(30) Ito, J.-i.; Sugino, K.; Matsushima, S.; Sakaguchi, H.; Iwata, H.;
Ishihara, T.; Nishiyama, H. Synthesis of NHC-Oxazoline Pincer
Complexes of Rh and Ru and Their Catalytic Activity for
Hydrogenation and Conjugate Reduction. Organometallics 2016, 35,
1885−1894.
(31) (a) Ramesh, M.; Kumar, M. D.; Jaccob, M.; Therrien, B.;
Venkatachalam, G. Cyclometalated Ruthenium(II) Carbonyl Com-
plexes Containing 2-(biphenylazo)phenolate Ligands: Synthesis,
Structure, DFT Study and Catalytic Activity Towards Oxidation
and Transfer Hydrogenation. Inorg. Chim. Acta 2018, 477, 40−50.
(b) Ramesh, M.; Prabusankar, G.; Venkatachalam, G. Ru(II)
Mediated CH Activation of 1-(biphenylazo)naphthol: Synthesis and
Catalytic Evaluation for Transfer Hydrogenation of Ketones. Inorg.
Chem. Commun. 2017, 79, 89−94.
(24) Miecznikowski, J. R.; Crabtree, R. H. Hydrogen Transfer
Reduction of Aldehydes with Alkali-Metal Carbonates and Iridium
NHC Complexes. Organometallics 2004, 23, 629−631.
(25) (a) Cavarzan, D. A.; Fagundes, F. D.; Fuganti, O.; da Silva, C.
W. P.; Pinheiro, C. B.; Back, D. F.; Barison, A.; Bogado, A. L.; de
Araujo, M. P. Mixed Phosphine/Diimines and/or Amines Ruthenium
Carbonyl Complexes: Synthesis, Characterization and Transfer-
Hydrogenation. Polyhedron 2013, 62, 75−82. (b) Prabhu, R. N.;
Ramesh, R. Synthesis, Structural Characterization, Electrochemistry
and Catalytic Transfer Hydrogenation of Ruthenium(II) Carbonyl
Complexes Containing Tridentate Benzoylhydrazone Ligands. J.
Organomet. Chem. 2012, 718, 43−51. (c) Ito, J.-i.; Teshima, T.;
Nishiyama, H. Enhancement of Enantioselectivity by Alcohol
Additives in Asymmetric Hydrogenation with Bis(oxazolinyl)Phenyl
Ruthenium Catalysts. Chem. Commun. 2012, 48, 1105−1107.
(d) Sarmah, B. J.; Dutta, D. K. Chlorocarbonyl Ruthenium(II)
Complexes of Tripodal Triphos {MeC(CH2PPh2)3}: Synthesis,
Characterization and Catalytic Applications in Transfer Hydro-
genation of Carbonyl Compounds. J. Organomet. Chem. 2010, 695,
781−785. (e) Zhang, J.; Leitus, G.; Ben-David, Y.; Milstein, D.
Efficient Homogeneous Catalytic Hydrogenation of Esters to
Alcohols. Angew. Chem., Int. Ed. 2006, 45, 1113−1115.
(26) (a) Dub, P. A.; Ikariya, T. Catalytic Reductive Transformations
of Carboxylic and Carbonic Acid Derivatives Using Molecular
Hydrogen. ACS Catal. 2012, 2, 1718−1741. (b) Fogler, E.;
Balaraman, E.; Ben-David, Y.; Leitus, G.; Shimon, L. J. W.;
Milstein, D. New CNN-Type Ruthenium Pincer NHC Complexes.
Mild, Efficient Catalytic Hydrogenation of Esters. Organometallics
2011, 30, 3826−3833. (c) Balaraman, E.; Gunanathan, C.; Zhang, J.;
Shimon, L. J. W.; Milstein, D. Efficient Hydrogenation of Organic
Carbonates, Carbamates and Formates Indicates Alternative Routes
to Methanol Based on CO2 and CO. Nat. Chem. 2011, 3, 609−614.
(27) (a) Muthaiah, S.; Hong, S. H. Acceptorless and Base-Free
Dehydrogenation of Alcohols and Amines using Ruthenium-Hydride
Complexes. Adv. Synth. Catal. 2012, 354, 3045−3053. (b) Johnson, T.
C.; Morris, D. J.; Wills, M. Hydrogen Generation from Formic Acid
and Alcohols Using Homogeneous Catalysts. Chem. Soc. Rev. 2010,
39, 81−88. (c) Dobereiner, G. E.; Crabtree, R. H. Dehydrogenation
as a Substrate-Activating Strategy in Homogeneous Transition-Metal
Catalysis. Chem. Rev. 2010, 110, 681−703. (d) Zhang, J.; Gandelman,
M.; Shimon, L. J. W.; Milstein, D. Electron-Rich, Bulky PNN-type
Ruthenium Complexes: Synthesis, Characterization and Catalysis of
Alcohol Dehydrogenation. Dalton Trans. 2007, 107−113. (e) van
Buijtenen, J.; Meuldijk, J.; Vekemans, J. A. J. M.; Hulshof, L. A.;
Kooijman, H.; Spek, A. L. Dinuclear Ruthenium Complexes Bearing
Dicarboxylate and Phosphine Ligands. Acceptorless Catalytic
Dehydrogenation of 1-Phenylethanol. Organometallics 2006, 25,
873−881.
(32) Shi, J.; Hu, B.; Chen, X.; Shang, S.; Deng, D.; Sun, Y.; Shi, W.;
Yang, X.; Chen, D. Synthesis, Reactivity, and Catalytic Transfer
Hydrogenation Activity of Ruthenium Complexes Bearing NNN
Tridentate Ligands: Influence of the Secondary Coordination Sphere.
ACS Omega 2017, 2, 3406−3416.
(33) (a) Balaraman, E.; Gnanaprakasam, B.; Shimon, L. J. W.;
Milstein, D. Direct Hydrogenation of Amides to Alcohols and Amines
under Mild Conditions. J. Am. Chem. Soc. 2010, 132, 16756−16758.
(b) Gunanathan, C.; Ben-David, Y.; Milstein, D. Direct Synthesis of
Amides from Alcohols and Amines with Liberation of H2. Science
2007, 317, 790−792. (c) Zhang, J.; Leitus, G.; Ben-David, Y.;
Milstein, D. Facile Conversion of Alcohols into Esters and
Dihydrogen Catalyzed by New Ruthenium Complexes. J. Am.
Chem. Soc. 2005, 127, 10840−10841.
(34) Spasyuk, D.; Gusev, D. G. Acceptorless Dehydrogenative
Coupling of Ethanol and Hydrogenation of Esters and Imines.
Organometallics 2012, 31, 5239−5242.
(35) Kuriyama, W.; Matsumoto, T.; Ogata, O.; Ino, Y.; Aoki, K.;
Tanaka, S.; Ishida, K.; Kobayashi, T.; Sayo, N.; Saito, T. Catalytic
Hydrogenation of Esters. Development of an Efficient Catalyst and
Processes for Synthesising (R)-1,2-Propanediol and 2-(l-Menthoxy)-
ethanol. Org. Process Res. Dev. 2012, 16, 166−171.
(36) (a) Sun, R.; Chu, X.; Zhang, S.; Li, T.; Wang, Z.; Zhu, B.
Synthesis, Structure, Reactivity, and Catalytic Activity of Cyclo-
metalated (Phosphine)- and (Phosphinite)ruthenium Complexes.
N
DOI: 10.1021/acs.organomet.8b00919
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Eur. J. Inorg. Chem. 2017, 2017, 3174−3183. (b) Baratta, W.; Da Ros,
P.; Del Zotto, A.; Sechi, A.; Zangrando, E.; Rigo, P. Cyclometalated
Ruthenium(II) Complexes as Highly Active Transfer Hydrogenation
Catalysts. Angew. Chem., Int. Ed. 2004, 43, 3584−3588. (c) Lewis, L.
N.; Smith, J. F. Catalytic Carbon-Carbon Bond Formation via ortho-
Metalated Complexes. J. Am. Chem. Soc. 1986, 108, 2728−2735.
(d) Lewis, L. N. Enhancement of Catalytic Activity Through
Orthometalation. Synthesis, Structure, and Catalytic Activity of a
New Orthometalated Ruthenium Complex. J. Am. Chem. Soc. 1986,
108, 743−749.
Gas Shift Reactions Catalyzed by [Ru(bpy)2(CO)Cl]+ and [Ru-
(bpy)2(CO)2]2+. Organometallics 1986, 5, 724−730.
́
(46) (a) Aguirre, P.; Lopez, R.; Villagra, D.; Azocar-Guzman, I.;
Pardey, A. J.; Moya, S. A. Synthesis of Ruthenium Complexes with
Carbonyl and Polypyridyl Ligands Derived from Dipyrido[3,2-a:2′,3′-
c]phenazine: Application to the Water Gas Shift Reaction. Appl.
Organomet. Chem. 2003, 17, 36−41. (b) Luukkanen, S.; Haukka, M.;
Kallinen, M.; Pakkanen, T. A. The Low-Temperature Water-Gas Shift
Reaction Catalyzed by Sodium-Carbonate-Activated Ruthenium
Mono(bipyridine)/SiO2 Complexes. Catal. Lett. 2000, 70, 123−125.
(37) Zhang, S.; Baldino, S.; Baratta, W. Synthesis of [RuX(CO)-
(dppp)(NN)]Cl (X = H, Cl; NN = en, ampy) Complexes and Their
Use as Catalysts for Transfer Hydrogenation. Organometallics 2013,
32, 5299−5304.
̈ ̈
(c) Haukka, M.; Venalainen, T.; Kallinen, M.; Pakkanen, T. A.
Chemically Activated Ruthenium Mono(bipyridine)/SiO2 Catalysts
in Water-Gas Shift Reaction. J. Mol. Catal. A: Chem. 1998, 136, 127−
134.
̈
(38) (a) Warner, M. C.; Backvall, J.-E. Mechanistic Aspects on
(47) (a) Baratta, W.; Baldino, S.; Giboulot, S.; Zhang, S. Dicarbonyl
Ruthenium and Osmium Catalysts. WO2017/134620A1, February
03, 2017. (b) Baratta, W.; Baldino, S.; Giboulot, S. Monocarbonyl
Ruthenium and Osmium Catalysts. WO2017/134618A1, August 10,
2017.
Cyclopentadienylruthenium Complexes in Catalytic Racemization of
Alcohols. Acc. Chem. Res. 2013, 46, 2545−2555. (b) Conley, B. L.;
Pennington-Boggio, M. K.; Boz, E.; Williams, T. J. Discovery,
Applications, and Catalytic Mechanisms of Shvo’s Catalyst. Chem.
Rev. 2010, 110, 2294−2312. (c) Ahn, Y.; Ko, S.-B.; Kim, M.-J.; Park,
J. Racemization Catalysts for the Dynamic Kinetic Resolution of
Alcohols and Amines. Coord. Chem. Rev. 2008, 252, 647−658.
(48) Baratta, W.; Chelucci, G.; Magnolia, S.; Siega, K.; Rigo, P.
Highly Productive CNN Pincer Ruthenium Catalysts for the
Asymmetric Reduction of Alkyl Aryl Ketones. Chem. - Eur. J. 2009,
15, 726−732.
̈
(39) (a) Warner, M. C.; Casey, C. P.; Backvall, J.-E., Shvo’s Catalyst
in Hydrogen Transfer Reactions. In Bifunctional Molecular Catalysis;
Ikariya, T., Shibasaki, M., Eds.; Springer-Verlag: Berlin, Heidelberg,
2011; Topics in Organometallic Chemistry Vol. 37, pp 85−125.
(b) Shvo, Y.; Czarkie, D.; Rahamim, Y.; Chodosh, D. F. A New Group
of Ruthenium Complexes: Structure and Catalysis. J. Am. Chem. Soc.
1986, 108, 7400−7402.
(49) Black, D. S. C.; Deacon, G. B.; Thomas, N. C. Ruthenium
Carbonyl Complexes. I. Synthesis of [Ru(CO)2(bidentate)2]2+
Complexes. Aust. J. Chem. 1982, 35, 2445−2453.
(50) Zhang, S.; Baratta, W. Synthesis of Pincer Ruthenium
RuCl(CNN)(PP) Catalysts from [RuCl(μ-Cl)(η6-p-cymene)]2. Orga-
nometallics 2013, 32, 3339−3342.
(40) (a) Stewart, B.; Nyhlen, J.; Martin-Matute, B.; Backvall, J.-E.;
Privalov, T. A Computational Study of the CO Dissociation in
Cyclopentadienyl Ruthenium Complexes Relevant to the Racemiza-
tion of Alcohols. Dalton Trans. 2013, 42, 927−934. (b) Warner, M.
(51) The hydrochloride salt of HambqPh (HCl·HambqPh) is more air
stable than the HCNN ligand.
(52) (a) Koike, T.; Ikariya, T. Mechanistic Aspects of Formation of
Chiral Ruthenium Hydride Complexes from 16-Electron Ruthenium
Amide Complexes and Formic Acid: Facile Reversible Decarbox-
ylation and Carboxylation. Adv. Synth. Catal. 2004, 346, 37−41.
(b) Kuznetsov, V. F.; Yap, G. P. A.; Alper, H. Chiral Ruthenium
Complexes with P,N-Ligands Derived from (S)-Proline. Organo-
metallics 2001, 20, 1300−1309. (c) Wong, W.-K.; Lai, K.-K.; Tse, M.-
S.; Tse, M.-C.; Gao, J.-X.; Wong, W.-T.; Chan, S. Reactivity of
Ru(OAc)2(Ph3P)2 Toward Chelating Diphosphine Ligands. X-ray
Crystal Structures of fac-Ru(OAc)2(Ph3P)(dppm) and trans-Ru-
(OAc)2(P2N2H4). Polyhedron 1994, 13, 2751−2762.
̈
C.; Verho, O.; Backvall, J.-E. CO Dissociation Mechanism in
Racemization of Alcohols by a Cyclopentadienyl Ruthenium
Dicarbonyl Catalyst. J. Am. Chem. Soc. 2011, 133, 2820−2823.
́
̈
(c) Nyhlen, J.; Privalov, T.; Backvall, J.-E. Racemization of Alcohols
Catalyzed by [RuCl(CO)2(η5-pentaphenylcyclopentadienyl)]: Mech-
anistic Insights from Theoretical Modeling. Chem. - Eur. J. 2009, 15,
5220−5229.
(41) Musa, S.; Fronton, S.; Vaccaro, L.; Gelman, D. Bifunctional
Ruthenium(II) PCP Pincer Complexes and Their Catalytic Activity in
Acceptorless Dehydrogenative Reactions. Organometallics 2013, 32,
3069−3073.
(53) Baratta, W.; Ballico, M.; Del Zotto, A.; Herdtweck, E.;
Magnolia, S.; Peloso, R.; Siega, K.; Toniutti, M.; Zangrando, E.; Rigo,
P. Pincer CNN Ruthenium(II) Complexes with Oxygen-Containing
Ligands (O2CR, OAr, OR, OSiR3, O3SCF3): Synthesis, Structure, and
Catalytic Activity in Fast Transfer Hydrogenation. Organometallics
2009, 28, 4421−4430.
(42) (a) Humphries, M. E.; Pecak, W. H.; Hohenboken, S. A.;
Alvarado, S. R.; Swenson, D. C.; Domski, G. J. Ruthenium(II)
Supported by Phosphine-Functionalized N-heterocyclic Carbene
Ligands as Catalysts for the Transfer Hydrogenation of Ketones.
Inorg. Chem. Commun. 2013, 37, 138−143. (b) Deb, B.; Sarmah
Podma, P.; Dutta Dipak, K. Synthesis of Dicarbonylruthenium(II)
Complexes of Functionalized P,S-Chelating Diphosphane Ligands
and Their Catalytic Transfer Hydrogenation. Eur. J. Inorg. Chem.
2010, 2010, 1710−1716. (c) Deb, B.; Borah, B. J.; Sarmah, B. J.; Das,
B.; Dutta, D. K. Dicarbonylruthenium(II) Complexes of Diphosphine
Ligands and their Catalytic Activity. Inorg. Chem. Commun. 2009, 12,
868−871.
(43) Naziruddin, A. R.; Huang, Z.-J.; Lai, W.-C.; Lin, W.-J.; Hwang,
W.-S. Ruthenium(II) Carbonyl Complexes Bearing CCC-Pincer bis-
(carbene) Ligands: Synthesis, Structures and Activities Toward
Recycle Transfer Hydrogenation Reactions. Dalton Trans. 2013, 42,
13161−13171.
(44) Giboulot, S.; Baldino, S.; Ballico, M.; Nedden, H. G.;
Zuccaccia, D.; Baratta, W. Cyclometalated Dicarbonyl Ruthenium
Catalysts for Transfer Hydrogenation and Hydrogenation of Carbonyl
Compounds. Organometallics 2018, 37, 2136−2146.
(45) (a) Kobayashi, K.; Tanaka, K. Approach to Multi-Electron
Reduction Beyond Two-Electron Reduction of CO2. Phys. Chem.
Chem. Phys. 2014, 16, 2240−2250. (b) Ishida, H.; Tanaka, K.;
Morimoto, M.; Tanaka, T. Isolation of Intermediates in the Water
(54) (a) Brammer, L. Metals and Hydrogen Bonds. Dalton Trans.
2003, 3145−3157. (b) Steiner, T. The Hydrogen Bond in the Solid
́
State. Angew. Chem., Int. Ed. 2002, 41, 48−76. (c) Aullon, G.;
Bellamy, D.; Guy Orpen, A.; Brammer, L.; Bruton, E. A. Metal-Bound
Chlorine Often Accepts Hydrogen Bonds. Chem. Commun. 1998,
653−654.
(55) Baratta, W.; Ballico, M.; Esposito, G.; Rigo, P. Role of the NH2
Functionality and Solvent in Terdentate CNN Alkoxide Ruthenium
Complexes for the Fast Transfer Hydrogenation of Ketones in 2-
Propanol. Chem. - Eur. J. 2008, 14, 5588−5595.
(56) (a) Strohmeier, W.; Holke, K. Selektive Bulkhydrierung von
̈
̈
α,β-Ungesattigten Aldehyden zu Ungesattigten Alkoholen mit
Homogenen Ruthenium-Katalysatoren. J. Organomet. Chem. 1980,
̈
193, C63−C66. (b) Graser, B.; Steigerwald, H. Aktivitaten von Ru-
Komplexen in der Homogenen Bulk-H2-Transfer Reaktion. J.
Organomet. Chem. 1980, 193, C67−C70.
(57) (a) Parekh, V.; Ramsden, J. A.; Wills, M. Ether-Tethered
Ru(II)/TsDPEN Complexes; Synthesis and Applications to Asym-
metric Transfer Hydrogenation. Catal. Sci. Technol. 2012, 2, 406−414.
(b) Matsunaga, H.; Ishizuka, T.; Kunieda, T. Highly Efficient
Asymmetric Transfer Hydrogenation of Ketones Catalyzed by Chiral
O
DOI: 10.1021/acs.organomet.8b00919
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
‘Roofed’ cis-diamine-Ru(II) Complex. Tetrahedron Lett. 2005, 46,
3645−3648. (c) Palmer, M. J.; Kenny, J. A.; Walsgrove, T.;
Kawamoto, A. M.; Wills, M. Asymmetric Transfer Hydrogenation of
Ketones Using Amino Alcohol and Monotosylated Diamine
Derivatives of Indane. J. Chem. Soc., Perkin Trans. 1 2002, 416−
427. (d) Rhyoo, H. Y.; Yoon, Y.-A.; Park, H.-J.; Chung, Y. K. Use of
amino amides derived from proline as chiral ligands in the
ruthenium(II)-catalyzed transfer hydrogenation reaction of ketones.
Tetrahedron Lett. 2001, 42, 5045−5048. (e) Jiang, Y.; Jiang, Q.;
Zhang, X. A New Chiral Bis(oxazolinylmethyl)amine Ligand for Ru-
Catalyzed Asymmetric Transfer Hydrogenation of Ketones. J. Am.
Chem. Soc. 1998, 120, 3817−3818.
Ketones Catalyzed by trans-Dihydrido(diamine)ruthenium(II) Com-
plexes. J. Am. Chem. Soc. 2002, 124, 15104−15118. (d) Alonso, D. A.;
Brandt, P.; Nordin, S. J. M.; Andersson, P. G. Ru(arene)(amino
alcohol)-Catalyzed Transfer Hydrogenation of Ketones: Mechanism
and Origin of Enantioselectivity. J. Am. Chem. Soc. 1999, 121, 9580−
9588.
(62) (a) Dub, P. A.; Gordon, J. C. The Mechanism of
Enantioselective Ketone Reduction with Noyori and Noyori-Ikariya
Bifunctional Catalysts. Dalton Trans. 2016, 45, 6756−6781. (b) Dub,
P. A.; Henson, N. J.; Martin, R. L.; Gordon, J. C. Unravelling the
Mechanism of the Asymmetric Hydrogenation of Acetophenone by
[RuX2(diphosphine)(1,2-diamine)] Catalysts. J. Am. Chem. Soc. 2014,
136, 3505−3521.
̈
(58) (a) Slagbrand, T.; Kivijarvi, T.; Adolfsson, H. Bimetallic
(63) Beach, N. J.; Dharmasena, U. L.; Drouin, S. D.; Fogg, D. E.
Improved Syntheses of Versatile Ruthenium Hydridocarbonyl
Catalysts Containing Electron-Rich Ancillary Ligands. Adv. Synth.
Catal. 2008, 350, 773−777.
Catalysis: Asymmetric Transfer Hydrogenation of Sterically Hindered
Ketones Catalyzed by Ruthenium and Potassium. ChemCatChem
2015, 7, 3445−3449. (b) Pannetier, N.; Sortais, J. B.; Issenhuth, J. T.;
Laurent, B.; Sirlin, C.; Holuigue, A.; Lefort, L.; Panella, L.; de Vries, J.
G.; Pfeffer, M. Cyclometalated Complexes of Ruthenium, Rhodium
and Iridium as Catalysts for Transfer Hydrogenation of Ketones and
Imines. Adv. Synth. Catal. 2011, 353, 2844−2852. (c) Jerphagnon, T.;
Haak, R.; Berthiol, F.; Gayet, A. J. A.; Ritleng, V.; Holuigue, A.;
Pannetier, N.; Pfeffer, M.; Voelklin, A.; Lefort, L.; Verzijl, G.;
Tarabiono, C.; Janssen, D. B.; Minnaard, A. J.; Feringa, B. L.; de Vries,
J. G. Ruthenacycles and Iridacycles as Catalysts for Asymmetric
Transfer Hydrogenation and Racemisation. Top. Catal. 2010, 53,
1002−1008. (d) Xing, Y.; Chen, J.-S.; Dong, Z.-R.; Li, Y.-Y.; Gao, J.-
X. Highly Efficient Chiral PNNP Ligand for Asymmetric Transfer
Hydrogenation of Aromatic Ketones in Water. Tetrahedron Lett. 2006,
47, 4501−4503. (e) Morris, D. J.; Hayes, A. M.; Wills, M. The
“Reverse-Tethered” Ruthenium(II) Catalyst for Asymmetric Transfer
Hydrogenation: Further Applications. J. Org. Chem. 2006, 71, 7035−
7044. (f) Matharu, D. S.; Morris, D. J.; Clarkson, G. J.; Wills, M. An
Outstanding Catalyst for Asymmetric Transfer Hydrogenation in
Aqueous Solution and Formic Acid/Triethylamine. Chem. Commun.
2006, 3232−3234. (g) Hayes, A. M.; Morris, D. J.; Clarkson, G. J.;
Wills, M. A Class of Ruthenium(II) Catalyst for Asymmetric Transfer
Hydrogenations of Ketones. J. Am. Chem. Soc. 2005, 127, 7318−7319.
(h) Nordin, S. J. M.; Roth, P.; Tarnai, T.; Alonso, D. A.; Brandt, P.;
Andersson, P. G. Remote Dipole Effects as a Means to Accelerate
[Ru(amino alcohol)]-Catalyzed Transfer Hydrogenation of Ketones.
Chem. - Eur. J. 2001, 7, 1431−1436. (i) Alonso, D. A.; Nordin, S. J.
M.; Roth, P.; Tarnai, T.; Andersson, P. G.; Thommen, M.; Pittelkow,
U. 2-Azanorbornyl Alcohols: Very Efficient Ligands for Ruthenium-
Catalyzed Asymmetric Transfer Hydrogenation of Aromatic Ketones.
1
(64) Relevant NMR data for [RuCl(amtp)(PCy3)(CO)]: H NMR
(400.1 MHz, CDCl3, 20 °C) δ 4.94 (m, NH2), 3.95 (m, CH2N), 3.82
(m, CH2N), 2.97 (m, NH2); 13C{1H} NMR (100.1 MHz, CDCl3, 20
2
°C) δ 208.5 (d, J(C,P) = 17.2 Hz; CO), 179.3 (m; CRu), 51.2 (s;
CH2N); 31P{1H} NMR (162.0 MHz, CDCl3, 20 °C) δ 57.9.
(65) (a) Poe, A. J. Pendent Group Effects, PGEs, in P-donor
Ligands. New J. Chem. 2013, 37, 2957−2964. (b) Snelders, D. J. M.;
van Koten, G.; Klein Gebbink, R. J. M. Steric, Electronic, and
Secondary Effects on the Coordination Chemistry of Ionic Phosphine
Ligands and the Catalytic Behavior of Their Metal Complexes. Chem.
- Eur. J. 2011, 17, 42−57. (c) Crabtree, R. H. The Organometallic
Chemistry of the Transition Metals, 5th ed.; Wiley: Hoboken, NJ, 2009;
Vol. 1, p 520. (d) White, D.; Taverner, B. C.; Leach, P. G. L.; Coville,
N. J. Quantification of Substituent and Ligand Size by the Use of
Solid Angles. J. Comput. Chem. 1993, 14, 1042−1049. (e) Coville, N.
J.; Loonat, M. S.; White, D.; Carlton, L. Steric Measurement of
Substituted Cyclopentadiene Ligands and the Synthesis and Proton
NMR Spectral Analysis of [(η5-C5H4R)Fe(CO)(L)I] Complexes with
Variable R. Organometallics 1992, 11, 1082−1090. (f) Tolman, C. A.
Steric Effects of Phosphorus Ligands in Organometallic Chemistry
and Homogeneous Catalysis. Chem. Rev. 1977, 77, 313−348.
(66) Haack, K.-J.; Hashiguchi, S.; Fujii, A.; Ikariya, T.; Noyori, R.
The Catalyst Precursor, Catalyst, and Intermediate in the RuII-
Promoted Asymmetric Hydrogen Transfer between Alcohols and
Ketones. Angew. Chem., Int. Ed. Engl. 1997, 36, 285−288.
(67) Anderson, P. A.; Deacon, G. B.; Haarmann, K. H.; Keene, F. R.;
Meyer, T. J.; Reitsma, D. A.; Skelton, B. W.; Strouse, G. F.; Thomas,
N. C.; Treadway, J. A.; White, A. H. Designed Synthesis of
Mononuclear Tris(heteroleptic) Ruthenium Complexes Containing
Bidentate Polypyridyl Ligands. Inorg. Chem. 1995, 34, 6145−6157.
(68) James, B. R.; Markham, L. D.; Hui, B. C.; Rempel, G. L.
S y n t h e s i s a n d C a t a l y t i c P r o p e r t i e s o f s o m e
Carbonyltriphenylphosphineruthenium(II) Complexes. J. Chem. Soc.,
Dalton Trans. 1973, 2247−2252.
J. Org. Chem. 2000, 65, 3116−3122. (j) Muller, D.; Umbricht, G.;
̈
Weber, B.; Pfaltz, A. C2-Symmetric 4,4′,5,5′-Tetrahydrobi(oxazoles)
and 4,4′,5,5′-Tetrahydro-2,2′-methylenebis[oxazoles] as Chiral Li-
gands for Enantioselective Catalysis: Preliminary Communication.
Helv. Chim. Acta 1991, 74, 232−240.
(59) Wiedner, E. S.; Chambers, M. B.; Pitman, C. L.; Bullock, R. M.;
Miller, A. J. M.; Appel, A. M. Thermodynamic Hydricity of Transition
Metal Hydrides. Chem. Rev. 2016, 116, 8655−8692.
(69) Spencer, A.; Wilkinson, G. Reactions of μ3-oxo-Triruthenium
Carboxylates with π-acid Ligands. J. Chem. Soc., Dalton Trans. 1974,
786−792.
(60) (a) Sandoval, C. A.; Ohkuma, T.; Muniz, K.; Noyori, R.
̃
Mechanism of Asymmetric Hydrogenation of Ketones Catalyzed by
BINAP/1,2-Diamine-Ruthenium(II) Complexes. J. Am. Chem. Soc.
2003, 125, 13490−13503. (b) Noyori, R.; Yamakawa, M.;
Hashiguchi, S. Metal-Ligand Bifunctional Catalysis: A Nonclassical
Mechanism for Asymmetric Hydrogen Transfer between Alcohols and
Carbonyl Compounds. J. Org. Chem. 2001, 66, 7931−7944.
(61) (a) Baratta, W.; Baldino, S.; Calhorda, M. J.; Costa, P. J.;
Esposito, G.; Herdtweck, E.; Magnolia, S.; Mealli, C.; Messaoudi, A.;
Mason, S. A.; Veiros, L. F. CNN Pincer Ruthenium Catalysts for
Hydrogenation and Transfer Hydrogenation of Ketones: Experimen-
tal and Computational Studies. Chem. - Eur. J. 2014, 20, 13603−
13617. (b) Baratta, W.; Siega, K.; Rigo, P. Catalytic Transfer
Hydrogenation with Terdentate CNN Ruthenium Complexes: The
Influence of the Base. Chem. - Eur. J. 2007, 13, 7479−7486.
(c) Abdur-Rashid, K.; Clapham, S. E.; Hadzovic, A.; Harvey, J. N.;
Lough, A. J.; Morris, R. H. Mechanism of the Hydrogenation of
P
DOI: 10.1021/acs.organomet.8b00919
Organometallics XXXX, XXX, XXX−XXX