Novel half-sandwich η5-Cp *-rhodium(III) and η5-Cp *-ruthenium(II) complexes bearing bis(phosphino)amine ligands and their use in the transfer hydrogenation of aromatic ketones

Article abstract of DOI:10.1002/aoc.3068

Two new half-sandwich η⁵-Cp*-rhodium(III) and η⁵-Cp*-ruthenium(II) complexes have been prepared from corresponding bis(phosphino)amine ligands, thiophene-2-(N,N- bis(diphenylphosphino)methylamine) or furfuryl-2-(N,N-bis(diphenylphosphino) amine). Structures of the new complexes have been elucidated by multinuclear one- and two-dimensional NMR spectroscopy, elemental analysis and IR spectroscopy. These Cp*-rhodium(III) and Cp*-ruthenium(II) complexes bearing bis(phosphino)amine ligands were successfully applied to transfer hydrogenation of various ketones by 2-propanol. Copyright

Full text of DOI:10.1002/aoc.3068

Full Paper
Received: 12 July 2013
Revised: 23 August 2013
Accepted: 23 August 2013
Published online in Wiley Online Library: 6 November 2013
(wileyonlinelibrary.com) DOI 10.1002/aoc.3068
5
Novel half-sandwich η -Cp *–rhodium(III) and
5
η -Cp *–ruthenium(II) complexes bearing bis
(phosphino)amine ligands and their use in the
transfer hydrogenation of aromatic ketones
Fatih Ok, Murat Aydemir, Feyyaz Durap and Akın Baysal*
Two new half-sandwich η5-Cp*–rhodium(III) and η5-Cp*–ruthenium(II) complexes have been prepared from corresponding bis
(phosphino)amine ligands, thiophene-2-(N,N-bis(diphenylphosphino)methylamine) or furfuryl-2-(N,N-bis(diphenylphosphino)
amine). Structures of the new complexes have been elucidated by multinuclear one- and two-dimensional NMR spectroscopy,
elemental analysis and IR spectroscopy. These Cp*–rhodium(III) and Cp*-ruthenium(II) complexes bearing bis(phosphino)
amine ligands were successfully applied to transfer hydrogenation of various ketones by 2-propanol. Copyright © 2013
John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: bis(phosphino)amine; Cp*; rhodium; ruthenium; transfer hydrogenation
proved to be versatile ligands and varying the substituents on
Introduction
both the P and N centers gives rise to the changes in the
P―N―P angles.[18] These bis(phosphino)amine ligands have
Bis(phosphino)amines which bear P―N―P fragments have
attracted considerable interest in recent years because of their
sophisticated coordination chemistry[1,2] and their potential use
in catalytic applications. To date, a number of bis(phosphino)
amine compounds have been synthesized and their transition
metal chemistry – especially nickel,[3] rhodium,[4] ruthenium,[5]
palladium, platinum and copper[6] – has been explored. The
applications of P―N―P ligands are extensive both in organome-
tallic chemistry and in homogeneous catalysis, as these ligands
can be used for fine adjustment of the activity and selectivity
of the catalyst,[5a] especially industrially important reactions
such as polymerization,[7] allylic alkylation,[8] the Mizoroki–Heck
reaction,[9] Suzuki–Miyaura coupling,[10] hydroformylation[11] and
hydrogenation of olefins.[12] In the recent years, Cp*
(pentamethylcyclopentadienyl) ligands have also emerged
as a promising class of arene ligands for metal-catalyzed
transfer hydrogenation.[4,13]
The hydrogenation of unsaturated ketones is a conceptually sim-
ple method for the preparation of saturated secondary alcohols,
but the transfer hydrogenation version of this process is a more at-
tractive route than H2 hydrogenation.[14] Ruthenium(II) or rhodium
(III) half-sandwich complexes bearing phosphorus-based ligands or
Cp* ligands have been successfully employed in transfer hydroge-
nation of ketones.[15] Formic acid/triethylamine (TEAF), isopropyl al-
cohol (IPA) and amine-borane adducts are the most used hydrogen
sources in transfer hydrogenation.[16] The advantages of transfer
hydrogenation using 2-propanol as a hydrogen source are well
documented in the literature.[17]
the advantages of being highly modular, relatively stable toward
air or moisture, facile synthesis, easily optimized and ability to
chelate transition metals such as ruthenium, rhodium, nickel,
palladium, platinum or copper. Considerable attention has been
focused on the preparation and properties of ruthenium and rho-
dium complexes due to their catalytic activities in transfer hydro-
genation. There is also continuing interest in the chemistry of
half-sandwich η5- Cp*–Rh(III) and η5-Cp*–Ru(II) metal complexes
because of their possible use in various catalytic reactions.[15,19]
The reactivity of η5-Cp*–Ru(II) with substituted P―N―P-based li-
gands have been reported by Balakrishna and co-workers[5]; how-
ever, to the best of our knowledge no reports of half-sandwich
Cp*–Rh(III) complexes containing P―N―P type ligands have
been reported so far. Recently, we also reported the synthesis
of η5-Cp*–Ru(II) complexes with P―N―P ligands derived from
2- or 4-CH(CH3)2-substituted aniline and their application in
ruthenium-catalyzed transfer hydrogenation.[15b] Following our
interest in the coordination chemistry of P―N―P ligands and
their use in transfer hydrogenation, we report herein the syn-
thesis and characterization of half-sandwich η5-Cp*–Rh(III)
and η5-Cp*–Ru(II) complexes derived from thiophene-2-(N,N-
bis(diphenylphosphino)methylamine), or furfuryl-2-(N,N-bis
(diphenylphosphino)amine). The catalytic behavior of these
*
Correspondence to: Akın Baysal, Department of Chemistry, Science Faculty,
Dicle University, TR-21280 Diyarbakır, Turkey. Email: akinb@dicle.edu.tr
Bis(phosphino)amine ligands with P―N―P fragments have
proved to be an effective arrangement for the construction of
chelate phosphorus complexes. P―N―P skeletons have also
Department of Chemistry, Science Faculty, Dicle University, TR-21280 Diyarbakır,
Turkey
Appl. Organometal. Chem. 2014, 28, 38–43
Copyright © 2013 John Wiley & Sons, Ltd.

Half sandwich Rh(III) and Ru(II) catalysts for reduction of ketones
complexes in transfer hydrogenation of acetophenone deriva-
tives is also discussed.
obtained in 92% or 89 % yield, respectively, as seen in Scheme 1.
The 31P-NMR spectra of neutral complexes [Ru((Ph2P)2NCH2-
C4H3S)(Cp*)Cl] 5 or [Ru((Ph2P)2NCH2–C4H3O)(Cp*)Cl] 6 show a sin-
glet at δ = 92.56 ppm or δ = 92.04 ppm, respectively, in line with
the values previously observed for similar compounds[15b]
(supporting information, Fig. S2). These spectra indicate that
cod has been replaced by the chelating bis(phosphino)amine.
Structures of 5 and 6 have also been elucidated by multinuclear
one- and two-dimensional NMR, elemental analysis and IR spec-
troscopy. Spectra of 5 and 6 display all signals of coordinated
ligands are in agreement with the structures proposed in the
Experimental section.
Results and Discussion
Synthesis of η5-Cp*–Rh(III) and η5-Cp*–Ru(II) Complexes
Bearing Bis(phosphino)amine Ligands
In our synthetic work, as the first aim, we synthesized the bis
(phosphino)amine ligands, ‘thiophene-2-(N,N-bis(diphenylphosphino)
methylamine), (Ph2P)2NCH2–C4H3S 1’, or ‘furfuryl-2-(N,N-bis
(diphenylphosphino)amine), (Ph2P)2NCH2–C4H3O 2’ according to
the literature procedure.[10c,20]
Treatment of [Rh(Cp*)Cl2]2 in THF solution with two equivalents
of bis(phosphino)amine ligand 1 or 2 yielded the half-sandwich
cationic Rh(III) complexes [Rh((Ph2P)2NCH2–C4H3S)(Cp*)Cl]Cl 3 or
[Rh((Ph2P)2NCH2–C4H3O)(Cp*)Cl]Cl 4, in 88% or 93% yield, respec-
tively, as seen in Scheme 1. Complexation reactions were straight-
forward, with coordination to rhodium being carried out at room
temperature, and compounds 3 and 4 were formed as air-stable
orange microcrystalline powders. The 31P-{1H} NMR spectra of free
ligands 1 and 2 show singlets at δ = 59.11 ppm and δ = 63.24 ppm,
respectively, due to the equivalent phosphorus nuclei of bis
(phosphinoamine) ligands.[2,10] In contrast to free ligands, the
phosphorus atoms of complexes 3 and 4 appeared as doublets
at δ = 71.45 (1JRhP = 119.9 Hz) and δ = 70.51 (1JRhP = 119.9 Hz), re-
spectively, and these spectra clearly indicate that both phospho-
rus atoms are bonded to the rhodium (supporting information,
Fig. S1). The chemical shifts and expected doublets with appropri-
ate Rh―P coupling constants in the 31P NMR spectra of both rho-
dium complexes are in accordance with the corresponding values
of chelate rhodium complexes with bis(phosphino)amines.[4] Fur-
thermore, structures of complexes 3 and 4 have been elucidated
by multinuclear one- and two-dimensional NMR, elemental analy-
sis and IR spectroscopy, and all spectra are in agreement with the
structures proposed in the Experimental section. To the best of
our knowledge, the half-sandwich Cp*–Rh(III) complexes of
P―N―P type ligands 3 or 4 were synthesized for the first time
in this study.
Catalytic Transfer Hydrogenation of Aromatic Ketones
Catalytic transfer hydrogenation is one of the most basic but im-
portant reactions in organic chemistry. The activity of half-sand-
wich rhodium or ruthenium complexes is well known in this
catalytic reaction.[13d] In particular, in our previous studies we
reported that Rh(I) or Ru(II) complexes based on a P―N―P back-
bone are active catalysts in the transfer hydrogenation of aro-
matic ketones.[4,15b] But half-sandwich Cp*–Rh(III) complexes
based on the P―N―P backbone have not been reported in
transfer hydrogenation reactions so far. For these reasons, we de-
cided to investigate the catalytic behavior of these novel Cp*–Rh
(III) or Cp*–Ru(II) complexes bearing a P―N―P backbone in
transfer hydrogenation of aromatic ketones.
The catalytic activities of half-sandwich Rh(III) complexes
[Rh((Ph2P)2NCH2–C4H3S)(Cp*)Cl]Cl 3 or [Rh((Ph2P)2NCH2–C4H3O)
(Cp*)Cl]Cl 4, and half-sandwich Ru(II) complexes [Ru((Ph2P)
2NCH2–C4H3S)(Cp*)Cl] 5 or [Ru((Ph2P)2NCH2–C4H3O)(Cp*)Cl] 6,
were tested on the transfer hydrogenation of acetophenone de-
rivatives under variable conditions by 2-propanol (IPA), wherein
IPA is the hydrogen source, as seen in Scheme 2. It was found that
the factors acetophenone/complex/NaOH molar ratio and reac-
tion temperature appeared to be essential to achieve high con-
versions. These Rh(III) and Ru(II) complexes catalyzed the
reduction of acetophenone to 1-phenylethanol via hydrogen
transfer from IPA with IPA/NaOH as the reducing system, and
the results are summarized in Table 1.
Reaction of [Ru(cod)(Cp*)Cl)] (cod = 1,5-cyclooctadiene) with
bis(phosphino)amine ligand 1 or 2 in THF solution in a ratio of
1:1 at room temperature for 1 h gives a deep-red solution. After
this time, the solution of complex 5 or 6 was filtered and the sol-
vent was evaporated under vacuum; following recrystallization
from diethyl ether/CH2Cl2, air-stable brown crystals were
Initially, to an iso-PrOH solution of half-sandwich Rh(III) com-
plexes [Rh((Ph2P)2NCH2–C4H3S)(Cp*)Cl]Cl 3 or [Rh((Ph2P)2NCH2–
C4H3O)(Cp*)Cl]Cl 4, and half-sandwich Ru(II) complexes [Ru((Ph2P)2
NCH2–C4H3S)(Cp*)Cl] 5 or [Ru((Ph2P)2NCH2–C4H3O)(Cp*)Cl] 6, an
appropriate amount of acetophenone and NaOH/iso-PrOH
Scheme 1. Synthesis of half-sandwich [Rh((Ph2P)2NCH2-C4H3S)(Cp*)Cl]Cl 3 and [Rh((Ph2P)2NCH2-C4H3O)(Cp*)Cl]Cl 4, or Ru((Ph2P)2NCH2-C4H3S)(Cp*)Cl]
5 and [Ru((Ph2P)2NCH2-C4H3O)(Cp*)Cl] 6 complexes.
Appl. Organometal. Chem. 2014, 28, 38–43
Copyright © 2013 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

F. Ok et al.
of the catalytic reduction of acetophenone in 2-propanol
showed that high conversion was obtained with a base/catalyst
ratio of >5:1, and increasing the substrate-to-catalyst ratio does
not lower the conversion of the product in most cases. The cat-
alytic activity of half-sandwich Rh(III) complexes 3 or 4, and
half-sandwich Ru(II) complexes 5 or 6, was significantly im-
proved by an increase of reaction temperature from room tem-
perature to 82°C, giving almost quantitative conversions of
acetophenone. It should be noted that the catalytic activities
in the studied transfer hydrogenation reaction were generally
much higher for the half-sandwich Rh(III) complexes [Rh
((Ph2P)2NCH2–C4H3S)(Cp*)Cl]Cl 3 or [Rh((Ph2P)2NCH2–C4H3O)
(Cp*)Cl]Cl 4 than Ru(II) complexes [Ru((Ph2P)2NCH2–C4H3S)
Scheme 2. Hydrogen transfer from 2-propanol to acetophenone by half-
sandwich rhodium(III) complexes [Rh((Ph2P)2NCH2-C4H3S)(Cp*)Cl]Cl 3 or [Rh
((Ph2P)2NCH2-C4H3O)(Cp*)Cl]Cl 4, and ruthenium(II) complexes [Ru((Ph2P)
2NCH2-C4H3S)(Cp*)Cl] 5 or [Ru((Ph2P)2NCH2-C4H3O)(Cp*)Cl] 6, catalyst.
solutions were added, respectively, at room temperature
(acetophenone/cat./NaOH; 100:1:5 molar ratios). The solution
was stirred for 24 h and then examined by capillary GC analysis.
At room temperature no appreciable formation of 1-
phenylethanol was observed in any of the reactions (Table 1, en-
tries 1–4). Employed acetophenone/cat./NaOH molar ratios and
reaction temperatures were varied in order to find the optimal
transfer hydrogenation conditions. The presence of base is abso-
lutely necessary to observe appreciable conversions because base
presumably facilitates catalysis by promoting formation of possi-
bly [Ru]―H from the [Ru]―X (X: Cl, Br) pre-catalyst – transition
metal hydride species which are an active species in this reaction,
generated from alkoxide complexes.[16,21] A number of acceptable
mechanisms are summarized elsewhere with the metal-catalyzed
transfer hydrogenation reaction by metal hydride intermedi-
ates.[22,23] Kirchner and co-workers have also shown a reasonable
mechanism for the transfer hydrogenation of ketones with CpRu–
aminophosphine complexes.[22] According to this mechanism, after
Br- dissociation the alkoxide anion attacks the metal center,
giving alkoxide-bearing CpRu–aminophosphine complex, and
β-elimination from this complex yields the hydride-bearing
CpRu–aminophosphine complex and acetone.[22] It may also be
mentioned that the choice of base (KOH or NaOH) had little
influence on the conversion. As seen in Table 1, optimization studies
(Cp*)Cl]
5 or [Ru((Ph2P)2NCH2–C4H3O)(Cp*)Cl] 6 (Table 1,
entries 9–12).
Because of the encouraging catalytic results complexes 3
and 4 were extensively investigated with a variety of substrates.
The catalytic activities of complexes 3 and 4 significantly
improved the reduction rate by an increase of reaction
temperature from room temperature to 82°C, giving almost
quantitative conversions of acetophenone derivatives
(p-fluoroacetophenone, p-chloroacetophenone, p-bromoacetophenone,
p-methoxyacetophenone, o-methoxyacetophenone) in the range
98–99% in 2–20 h, respectively (Table 2). It is well known that the
electronic properties of substituents on the phenyl ring of
acetophenone also cause changes in the reduction rate. The
introduction of an electron-withdrawing group such as F, Cl or
Br to the p-position of the aryl ring of the ketone improved the
reduction rate, giving rise to easier hydrogenation (Table 2,
entries 1–3 and 8–10).[24] An o- or p-substituted acetophenone
with 2-methoxy or 4-methoxy (known as electron-donor substitu-
ent) is reduced more slowly than acetophenone, as seen in Table 2
(entries 6, 7, 13 and 14).
Finally, we extended our investigation to include the ef-
fect of bulkiness of the alkyl groups on catalytic activity. A
variety of simple aryl alkyl ketones were reduced to the cor-
responding secondary alcohols. It was found that the cata-
lytic activity highly depended on the steric hindrance of
the alkyl group, and transformation to secondary alcohol
gradually decreased by increasing the bulkiness of the alkyl
groups,[25] as seen in Table 3.
It is mentioned that, compared with our previous bis
(phosphino)amine cod-Rh(I) Rh(I)[4] or Cp*–Ru(II)[15b] complexes, for
the first time synthesized half-sandwich Cp*–Rh(III) complexes 3 or
4, and half-sandwich Cp*–Ru(II) complexes 5 or 6, provide higher
turnover frequency (TOF) values in Ru(II)-catalyzed transfer hydroge-
nation of acetophenone derivatives but lower TOF values in Rh(I)-
catalyzed transfer hydrogenation of acetophenone derivatives.
Table 1. Transfer hydrogenation of acetophenone with iso-PrOH
catalyzed by [Rh((Ph2P)2NCH2–C4H3S)(Cp*)Cl]Cl 3, [Rh((Ph2P)2NCH2–
C4H3O)(Cp*)Cl]Cl 4, [Ru((Ph2P)2NCH2–C4H3S)(Cp*)Cl] 5 and [Ru((Ph2P)
2NCH2-C4H3O)(Cp*)Cl] 6
e
Entry Catalyst S/C/NaOH
Time
Conversion (%)d TOF (hÀ1
)
1
3a
4a
5a
6a
3b
4b
5b
6b
3c
4c
5c
6c
100:1:5
100:1:5
100:1:5
100:1:5
100:1
1 h
1 h
1 h
1 h
2 h
2 h
2 h
2 h
3 h
3 h
6 h
6 h
Trace
Trace
Trace
Trace
<5
2
3
4
5
6
100:1
<5
7
100:1
<5
8
100:1
<5
9
100:1:5
100:1:5
100:1:5
100:1:5
98
99
98
99
33
33
16
17
Experimental
10
11
12
Materials and Methods
Unless otherwise stated, all reactions were carried out under an at-
mosphere of argon using conventional Schlenk glassware; solvents
were dried using established procedures and distilled under argon
immediately prior to use. Analytical-grade and deuterated solvents
were purchased from Merck. Chloro(pentamethylcyclopentadienyl)
(cyclooctadiene)Ru(II), pentamethylcyclopentadienyl-Rh(III) chloride
dimer, furfurylamine, thiophene-2-methylamine and Ph2PCl are pur-
Reaction conditions:
aAt room temperature; acetophenone/cat./NaOH, 100:1:5.
bRefluxing in iso-PrOH; acetophenone/cat. 100:1, in the absence
of base.
cRefluxing in iso-PrOH; acetophenone/cat./NaOH, 100:1:5.
dDetermined by GC (three independent catalytic experiments).
eReferred at the reaction time indicated in column; TOF = (mol
chased from Fluka and were used as received. 1H (at 400.1 MHz), 13
(at 100.6 MHz) and 31P-{1H} NMR (at 162.0 MHz) spectra were recorded
C
product/mol cat.) × hÀ1
.
wileyonlinelibrary.com/journal/aoc
Copyright © 2013 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2014, 28, 38–43

Half sandwich Rh(III) and Ru(II) catalysts for reduction of ketones
Table 2. Transfer hydrogenation results for substituted
acetophenones with complexes [Rh((Ph2P)2NCH2–C4H3S)(Cp*)Cl]Cl 3
or [Rh((Ph2P)2NCH2–C4H3O)(Cp*)Cl]Cl 4a
Syntheses and Characterization of Half-Sandwich [Rh((Ph2P)
2NCH2–C4H3S)(Cp*)Cl]Cl 3, [Rh((Ph2P)2NCH2-C4H3O)(Cp*)Cl]Cl
4, [Ru((Ph2P)2NCH2-C4H3S)(Cp*)Cl] 5 and [Ru((Ph2P)2NCH2-
C4H3O)(Cp*)Cl] 6 Complexes
Thiophene-2-(N,N-bis(diphenylphosphino)methylamine) (Ph2P)2
NCH2–C4H3S 1 and furfuryl-2-(N,N-bis(diphenylphosphino)amine)
(Ph2P)2NCH2–C4H3O 2 were synthesized according to the
literature procedure.[10c,20]
TOF (hÀ1
)
c
Entry
R
Time
Conversion (%)b
Synthesis of [Rh((Ph2P)2NCH2–C4H3S)(Cp*)Cl]Cl 3
A mixture of [Rh(Cp*)Cl2]2 (0.13 g, 0.20 mmol) and (Ph2P)2NCH2–
C4H3S 1 (0.19 g, 0.40 mmol) in 20 ml THF was stirred at room tem-
perature for 0.5 h. The volume of solvent was then reduced to
0.5 ml before addition of diethyl ether (10 ml). The precipitated
product was filtered and dried in vacuo, yielding [Rh((Ph2P)2NCH2–
C4H3S)(Cp*)Cl]Cl 3 as an orange microcrystalline powder (yield
Catalyst: [Rh((Ph2P)2NCH2–C4H3S)(Cp*)Cl]Cl 3
1
2
3
4
5
6
7
4-F
2 h
3 h
99
98
99
96
98
97
99
50
33
33
24
33
10
5
4-Cl
4-Br
3 h
2-F
4 h
2-Br
3 h
1
0.28 g, 88%); m.p. 190–191°C. H NMR (δ in ppm rel. to TMS, J Hz,
2-MeO
4-MeO
10 h
20 h
in CDCl3): 7.53–7.49 (m, 8H, o-protons of phenyls), 7.26–7.22 (m,
12H, m- and p-protons of phenyls), 7.09 (d, 1H, H-5, 3J= 4.6 Hz),
Catalyst: [Rh((Ph2P)2NCH2-C4H3O)(Cp*)Cl]Cl 4
3
3
6.50 (dd, 1H, H-4, J= 3.2 and 4.6 Hz), 6.32 (d, 1H, H-3, J= 3.2 Hz),
4.15 (dd, 2H, , CH2, 3J= 5.2 and 5.4 Hz), 1.38 (s, 15H, protons of
Cp*); 13C NMR (δ in ppm rel. to TMS, J Hz, in CDCl3): 138.74 (C-2),
8
4-F
2 h
3 h
98
98
98
94
96
99
98
49
33
33
16
24
10
5
9
4-Cl
10
11
12
13
14
4-Br
3 h
2
132.54 (d, o-carbons of phenyls, J= 4.3 Hz), 131.65 (p-carbons of
2-F
6 h
phenyls), 131.33 (d, i-carbons of phenyls, 1J = 10.1 Hz), 129.01
(d, m-carbons of phenyls,3J = 3.0 Hz), 128.33 (C-3), 127.56 (C-5),
126.77 (C-4), 90.56 (carbons Cp*), 47.08 (CH2), 9.82 (carbons
CH3―Cp*), assignment was based on 1H-13C HETCOR and
1H-1H COSY spectra; 31P-{1H} NMR (δ in ppm rel. to H3PO4, in
2-Br
4 h
2-MeO
4-MeO
10 h
20 h
aCatalyst (0.005 mmol), substrate (0.5 mmol), iso-PrOH (5 ml), NaOH
(0.025 mmol), 82°C, respectively; concentration of acetophenone
derivatives is 0.1 M.
1
CDCl3): 71.45 (d, NPP, JRhP = 119.9 Hz); selected IR (KBr pellet,
in cm-1): υ (P―N―P): 996, (P―Ph): 1436; Anal. Calcd for
bPurity of compounds is checked by NMR and GC (three
independent catalytic experiments); yields are based on
methyl aryl ketone.
C
39H40NSCl2P2Rh: calcd C 59.25, H 5.10, N 1.77; found C 59.12,
H 5.06, N 1.72%.
cTOF = (mol product/mol cat.) × hÀ1
.
Synthesis of [Rh((Ph2P)2NCH2–C4H3O)(Cp*)Cl]Cl 4
To a solution of [Rh(Cp*)Cl2]2 (0.13 g, 0.21 mmol) in THF, a solution
(THF, 30 ml) of (Ph2P)2NCH2–C4H3O, 2 (0.19 g, 0.42 mmol) was
added. The resulting reaction mixture was stirred at room temper-
ature for 0.5 h. After this time, the solution was filtered and the sol-
vent evaporated under vacuum. The solid residue thus obtained
was washed with diethyl ether (3 × 10 ml) and then dried under
vacuum. Following recrystallization from diethyl ether/CH2Cl2, a
yellow crystalline powder [Rh((Ph2P)2NCH2–C4H3O)(Cp*)Cl]Cl 4
on a Bruker Avance 400 spectrometer, with tetramethylsilane (TMS) as
an internal reference for 1H NMR and 13C NMR or 85% H3PO4 as ex-
ternal reference for 31P-{1H} NMR. IR spectra were recorded on a
Mattson 1000 ATI UNICAM FT-IR spectrometer as KBr pellets. El-
emental analysis was carried out on a Fisons EA 1108 CHNS-O in-
strument. Melting points were recorded by a Gallenkamp model
apparatus with open capillaries. Analyses by gas chromatogra-
phy (GC) were performed on a Shimadzu 2010 Plus gas chro-
matograph equipped with a capillary column (5% biphenyl,
95% dimethylsiloxane) (30 m × 0.32 mm × 0.25 μm).
1
was obtained (yield 0.30 g, 93%); m.p. 181–182°C. H NMR (δ in
ppm rel. to TMS, J Hz, in CDCl3): 7.54–7.48 (m, 8H, o-protons of
phenyls), 7.28–7.24 (m, 12H, m- and p-protons of phenyls), 6.77
(br, 2H, H-5), 5.15 (br, 2H, H-4), 5.47 (br, 2H, H-3), 3.89 (br, 4H,
CH2), 1.41 (s, 15H, protons of Cp*); 13C NMR (δ in ppm rel. to
TMS, J Hz, in CDCl3): 152.00 (br, C-2), 142.04 (C-5), 133.45 (i-carbons
of phenyls), 132.47 (o-carbons of phenyls), 131.51 (p-carbons of
phenyls), 128.95 (m-carbons of phenyls), 110.56 (C-4), 109.81
(C-3), 90.12 (carbons Cp*), 43.23 (―CH2), 9.76 (carbons CH3―Cp*);
assignment was based on the 1H-13C HETCOR and 1H-1H COSY
spectra; 31P-{1H} NMR (δ in ppm rel. to H3PO4, in CDCl3): 70.51
(d, NPP, JRhP = 119.9 Hz); Selected IR (KBr pellet, in cmÀ1): υ
(P―N―P): 924, (P―Ph): 1435; Anal. Calcd. for C39H40NOCl2P2Rh:
calcd C 60.48, H 5.21, N 1.81; found C 60.42, H 5.16, N 1.78%.
General Procedure for the Transfer Hydrogenation of
Ketones
The typical procedure for the catalytic hydrogen transfer reaction
was as follows. A solution of complexes [Rh((Ph2P)2NCH2–C4H3S)
(Cp*)Cl]Cl 3, [Rh((Ph2P)2NCH2–C4H3O)(Cp*)Cl]Cl 4, [Ru((Ph2P)
2NCH2–C4H3S)(Cp*)Cl] 5, [Ru((Ph2P)2NCH2-C4H3O)(Cp*)Cl] 6,
NaOH (0.025 mmol) and the corresponding ketone (0.5 mmol) in
degassed iso-PrOH (5 ml) were refluxed until the reactions were
completed. After this period a sample of the reaction mixture
was removed, diluted with acetone and analyzed immediately
by GC. Conversions obtained were related to the residual
unreacted ketone.
Synthesis of [Ru((PPh2)2NCH2–C4H3S)(Cp*)Cl] 5
To a solution of [Ru(cod)(Cp*)Cl)] (0.15 g, 0.38 mmol) in 10 ml THF,
a
solution (THF, 15 ml) of (PPh2)2NCH2–C4H3S 1 (0.18 g,
0.38 mmol) was added. The resulting reaction mixture was
Appl. Organometal. Chem. 2014, 28, 38–43
Copyright © 2013 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/aoc

F. Ok et al.
Table 3. Transfer hydrogenation results for substituted alkylphenylketones with the complex [Rh((Ph2P)2NCH2–C4H3S)(Cp*)Cl]Cl 3 or [Rh((Ph2P)
2NCH2–C4H3O)(Cp*)Cl]Cl 4a
TOF (hÀ1
)
c
Entry
Catalyst
Time
Substrate
Product
Conversion (%)b
1
3
4
3
4
3
4
3
4
3
4
3
4
3
4
4 h
4 h
Ph–CO–Et
Ph–CO–Et
Ph–CHOH-Et
Ph–CHOH-Et
98
97
99
98
99
98
99
99
92
95
91
97
99
98
25
24
17
16
10
10
<5
<5
12
14
15
16
12
12
2
3
6 h
Ph–CO–Pr
Ph–CHOH-Pr
4
6 h
Ph–CO–Pr
Ph–CHOH-Pr
5
10 h
10 h
24 h
24 h
8 h
Ph–CO–i-Pr
Ph–CHOH–i-Pr
6
Ph–CO–i-Pr
Ph–CHOH–i-Pr
7
Ph–CO–t-but
Ph–CO–t-but
CH3C(O)(CH2)3CH3
CH3C(O)(CH2)3CH3
CH3C(O)CH(CH3)2
CH3C(O)CH(CH3)2
CH3C(O)(CH2)2Ph
CH3C(O)(CH2)2Ph
Ph–CHOH–ter-but
Ph–CHOH–ter-but
CH3C(OH)(CH2)3CH3
CH3C(OH)(CH2)3CH3
CH3C(OH)CH(CH3)2
CH3C(OH)CH(CH3)2
CH3C(OH)(CH2)2Ph
CH3C(OH)(CH2)2Ph
8
9
10
11
12
13
14
7 h
6 h
6 h
8 h
8 h
aCatalyst (0.005 mmol), substrate (0.5 mmol), iso-PrOH (5 ml), NaOH (0.025 mmol), 82°C, respectively; concentration of alkylphenylketones is 0.1 M.
bPurity of compounds is checked Àb1y NMR and GC (three independent catalytic experiments); yields are based on methyl aryl ketone.
cTOF = (mol product/mol cat.) × h
.
allowed to proceed under stirring at room temperature for 1 h. (s, 15H, protons of Cp*); 13C NMR (δ in ppm rel. to TMS, J in Hz, CDCl3):
After this time, the solution was filtered and the solvent evapo- 151.29 (C-2), 141.30 (C-5), 134.78 (o-carbons of phenyls), 133.91 (i-car-
rated under vacuum. The solid residue thus obtained was washed bons of phenyls), 129.49 (p-carbons of phenyls), 126.73 (m-carbons of
with diethyl ether (3 × 15 ml) and then dried under vacuum. Fol- phenyls), 110.38 (C-4), 109.29 (C-3), 90.03 (carbons Cp*), 45.93 (CH2),
lowing recrystallization from diethyl ether/CH2Cl2, a brown crys- 9.89 (carbons CH3―Cp*); assignment was based on 1H-13C HETCOR
talline powder [Ru((PPh2)2NCH2–C4H3S)(Cp*)Cl] 5 was obtained and 1H-1H COSY spectra; 31P-{1H} NMR (δ in ppm rel. to H3PO4, CDCl3):
(yield 0.27 g, 92%); m.p. 168–169°C. 1H NMR (δ in ppm rel. to 92.04 (s, NPP); selected IR (KBr pellet, in cmÀ1): υ (P―N―P): 924,
3
TMS, J Hz, in CDCl3): 7.72 (dd, 8H, o-protons of phenyls, J = 7.2 (P―Ph): 1434; Anal. Calcd for C39H40NOP2RuCl: C 63.54, H 5.47,
and 13.6 Hz), 7.54 (dd, 4H, p-protons of phenyls, 3J = 6.6 and N 1.90; found: C 63.42, H 5.41, N 1.85%.
12.4 Hz), 7.32 (m, 8H, m-protons of phenyls), 7.00 (d, 1H, H-5,
3
3J = 5.2 Hz), 6.66 (dd, 1H, H-4, J = 3.8 and 5.2 Hz), 6.39 (d, 1H, H-
3
3
3, J = 3.8 Hz), 4.45 (t, 2H, CH2, J = 11.6 Hz), 1.38 (s, 15H, protons
of Cp*); 13C NMR (d in ppm rel. to TMS, J Hz, in CDCl3): 140.54
(C-2), 134.31 (t, o-carbons of phenyls, 2J = 5.5 Hz), 132.83 (t,
p-carbons of phenyls, 4J = 6.0 Hz), 129.84 (d, i-carbons of phe-
Conclusions
We have synthesized new half-sandwich η5-Cp*–Rh(III) and η5-
Cp*–Ru(II) complexes bearing bis(phosphino)amine ligands.
Cp*–Rh(III) complexes 3 and 4, based on a P―N―P backbone,
were easily synthesized for the first time from the [Rh(Cp*)Cl2]2
and bis(phosphino)amine ligands 1 or 2, at room temperature,
respectively. η5-Cp*–Rh(III) and η5-Cp*–Ru(II) complexes were
used for transfer hydrogenation of aromatic and aliphatic
substituted ketones. We have found that these Cp*–Rh(III) and
Cp*–Ru(II) complexes are efficient homogeneous catalytic
systems that can catalyze the reduction of various ketones via hy-
drogen transfer from 2-propanol and readily lead to secondary al-
cohols from high yields. The procedure is simple and efficient
towards various aryl ketones. Furthermore, the modular construc-
tion of these catalysts and their flexibility toward transfer hydro-
genation make these systems to pursue.
1
nyls, J = 57.3 Hz), 127.86 (C-3), 127.41 (t, m-carbons of phenyls,
3J = 4.0 Hz), 126.55 (C-4), 125.32 (C-5), 91.13 (carbons Cp*),
47.68 (CH2), 9.88 (carbons CH3―Cp*); assignment was based
on 1H-13C HETCOR and 1H-1H COSY spectra; 31P-{1H} NMR
(δ in ppm rel. to H3PO4, in CDCl3): 92.56 (s, NPP); selected IR
(KBr pellet, in cmÀ1): υ (P―N―P): 986, (P―Ph): 1442; Anal. Calcd
for C39H40NSP2RuCl: C 62.18, H 5.35, N 1.86; found: C 62.08, H
5.29, N 1.82%.
Synthesis of [Ru((PPh2)2NCH2–C4H3O)(Cp*)Cl] 6
To a solution of [Ru(cod)(Cp*)Cl)] (0.13 g, 0.33 mmol) in 10 ml THF, a
solution (THF, 30 ml) of (PPh2)2NCH2–C4H3O, 2 (0.15 g, 0.33 mmol)
was added. The resulting reaction mixture was stirred at room tem-
perature for 1 h. After this time, the solution was filtered and the sol-
vent evaporated under vacuum. The solid residue thus obtained was
washed with diethyl ether (3 × 15 ml) and then dried under vacuum.
Following recrystallization from diethyl ether/CH2Cl2, a dark-brown
crystalline powder [Ru((PPh2)2NCH2–C4H3O)(Cp*)Cl] 6 was obtained
(yield 0.21 g, 89%); m.p. 169–171°C. 1H NMR (δ in ppm rel.
to TMS, J in Hz, CDCl3) 7.45–7.47 (br, 8H, o-protons of phenyls),
Acknowledgements
Partial support from Dicle University (Project number: DUBAP-12-FF-11)
is gratefully acknowledged.
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version of this article at the publisher’s web site.
Figure S1. The 31P-{1H} NMR spectra of half-sandwich [Rh((Ph2P)2
NCH2-C4H3S)(Cp*)Cl]Cl 3 or [Rh((Ph2P)2NCH2-C4H3O)(Cp*)Cl]Cl 4,
complexes.
Figure S2. The 31P-{1H} NMR spectra of half-sandwich [Ru((Ph2P)2
NCH2-C4H3S)(Cp*)Cl] 5 or [Ru((Ph2P)2NCH2-C4H3O)(Cp*)Cl] 6
complexes.
Appl. Organometal. Chem. 2014, 28, 38–43
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