Ruthenium phenylindenyl complex as an efficient transfer hydrogenation catalyst

Article abstract of DOI:10.1002/adsc.201200411

An efficient and green protocol for the transfer hydrogenation of carbonyl and imine compounds is presented. The transformations are catalysed by the inexpensive and easily synthesised complex [RuCl(PPh₃)(3- phenylindenyl)]. Its catalytic activity was compared to that of the most commonly encountered ruthenium complexes in transfer hydrogenation reactions involving several protypical substrates. Copyright

Full text of DOI:10.1002/adsc.201200411

FULL PAPERS
DOI: 10.1002/adsc.201200411
Ruthenium Phenylindenyl Complex as an Efficient Transfer
Hydrogenation Catalyst
Simone Manzini,a Cꢀsar A. Urbina Blanco,a and Steven P. Nolana,*
a
EaStCHEM School of Chemistry, University of St Andrews, St Andrews, KY16 9ST, U.K.
Fax : (+44)-(0)1334-463-808; e-mail: snolan@st-andrews.ac.uk
Received: May 9, 2012; Published online: November 4, 2012
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201200411.
Abstract: An efficient and green protocol for the encountered ruthenium complexes in transfer hydro-
transfer hydrogenation of carbonyl and imine com- genation reactions involving several protypical sub-
pounds is presented. The transformations are cata- strates.
lysed by the inexpensive and easily synthesised com-
plex [RuCl
ACHTUNGTRENNUNG(PPh3)(3-phenylindenyl)]. Its catalytic ac- Keywords: alcohols; green chemistry; homogeneous
tivity was compared to that of the most commonly catalysis; ruthenium; transfer hydrogenation
Introduction
ruthenium complexes remain to date the best com-
promise between price and reactivity.[3d,6]
The increasing demand for evermore-selective chemi-
Amongst the numerous ruthenium complexes re-
cal transformations that avoid or reduce the amount ported[3c,7] for hydrogenation, one of the first
of waste produced has made it important to develop very
efficient
catalysts
was
the
complex
new environmentally friendly synthetic assembly tools [Ru2(CO) CHTUGNTRENNUNG
G
4A(m-H)(C4Ph4COHOCC4Ph4)] (1), synthes-
and protocols.[1] One of these “greener” processes is ised in 1984 by Shvo. This complex is also known as
the transfer hydrogenation reaction. This eco-friendly Shvoꢁs catalyst.[8] Many applications have been report-
methodology permits the reduction of ketones and ed with 1 in hydrogen transfer reactions.[9] In 2007,
imines to the corresponding alcohols and amines Frost reported an interesting variation, 3, of [Ru(Cl)-
through the transfer of two hydrogen atoms from
(indenyl)] (2),[10] first reported by Oro.[11]
ACHUTNGTREN(NUG PPh3)2ACHTUTGNRENNUGN
a
sacrificial alcohol, usually isopropyl alcohol Complex 3 is remarkably active in transfer hydroge-
(Scheme 1).[2]
Numerous transfer hydrogenation systems have
been reported in the literature, but most of them use
expensive metals (Ir/Rh complexes)[2e,3] or poorly
active and very unstable complexes (Fe complex-
es).[3d,4] Despite a recent report by Morris on highly
active iron-based transfer hydrogenation catalysts,[5]
Scheme 1. Transfer hydrogenation system.
Figure 1. Ruthenium complexes for transfer hydrogenation.
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Ruthenium Phenylindenyl Complex as an Efficient Transfer Hydrogenation Catalyst
Table 1. Base optimisation.[a]
Entry
Base
None
Conv. after
1 h [%][b}]
Conv. after
5 h [%][b]
1
0
0
2
3
4
5
6
7
8
9
K3PO4
Cs2CO3
NaOH
CsOH
KOH
NaOAc
NaOMe
NaO-t-Bu
KO-t-Bu
KO-t-Am
KHMDS
30
16
58
25
23
0
67
71
48
66
75
45
25
85
55
30
6
78
83
79
72
91
10
11
12
Scheme 2. One-pot synthesis of complex 6 and its activity in
chiral alcohol racemisation catalysis.
[a]
Reaction conditions: benzophenone (0.25 mmol),
6
(0.5 mol%) and base (10 mol%) dissolved in 1:1 toluene/
isopropyl alcohol (1 mL).
Conversion determined by H NMR from an average of
nation in formic acid. Casey has reported a novel
complex (4) bearing an OTMS-substituted indenyl
ligand, showing activity in transfer hydrogenation re-
actions (Figure 1).[12]
[b]
1
at least two runs.
In order to achieve an efficient hydrogenation
system using a relatively inexpensive metal complex,
we proceeded to evaluate the catalytic activity of the tries 8, 9, 10 and 11). The solubility of the base in the
complex [RuCl(PPh3)2(3-phenylindenyl)] complex (6) reaction medium appears to play an important role;
ACHTUNGTRENNUNG
recently reported. Complex 6 can be synthesised in there is a difference in activity when using NaOH,
a straightforward manner, starting from a propargylic KOH or CsOH even though they have similar basicity
alcohol and [RuCl2ACTHNUTRGNEUNG
(PPh3)3] (5).[13] Complex 6 is ex- (Table 1, entries 4, 5 and 6). Potassium hexamethylsi-
tremely active in the alcohol racemisation reaction, lazane (KHMDS) was found to be the best base for
which is formally a tandem hydrogenation/dehydro- the system examined (Table 1, entry 12). However,
genation process. Additionally, as shown before, Ru- even with less expensive bases such as NaOH, the cat-
indenyl systems have been extensively studied, dis- alytic activity remains remarkably high (Table 1,
playing interesting activity in hydrogen transfer. For entry 4).
these reasons, we hypothesized that complex 6 could
The loading of the base also plays an important
be a very active catalyst in transfer hydrogenation re- role in terms of catalytic activity (Table 2).
actions (Scheme 2).[14]
KHMDS alone cannot promote transfer hydrogena-
tion, even if used in stoichiometric amounts (Table 2,
entries 1 and 2). However, varying the base loading
can significantly influence the catalytic activity. In
fact, high and low loadings of base led to low conver-
Results and Discussion
Using the reduction of benzophenone as a benchmark sions. The best catalytic activity was achieved using
reaction, the hydrogenation conditions were opti- 2.5 mol% of base in the reaction (Table 2, entry 6).
mised by first screening various bases needed to assist The unusual reactivity at low loadings can be ex-
(or not) in the activation steps leading to catalytic ac- plained by the decrease of the rate of the bimolecular
tivity. As shown in Table 1, a base is necessary to acti- reaction necessary to generate the active species. On
vate the catalyst and the catalytic activity depends the other hand, at high loading of base, the desired al-
considerably on the base used (Table 1, entry 1). A cohols react with the base forming an alkoxide that
detailed analysis allows the nature of the various can be oxidised back to the ketone by the catalyst, as
tested bases to be rationalised. Stronger bases are sig- most of the newly formed alcohols are more acidic
nificantly more efficient in the catalysis; for example, than isopropyl alcohol.
NaOAc is not basic enough to activate the catalyst
This effect is slowed down at low catalyst loadings
(Table 1, entry 7), but stronger bases, such as alkox- due to high concentration of isopropyl alcohol com-
ides, show improved catalytic efficiency (Table 1, en- pared to the alcohol.
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Table 2. Base optimisation.[a]
Table 4. Hydrogen source screening.[a]
Entry
Catalyst
Base loading
Conv. [%][b]
Entry
Hydrogen source
Conv. [%][b]
1
2
3
4
5
6
7
8
none
none
100
10
100
10
5
2.5
1
0.5
0
0
1
2
3
4
i-PrOH
EtOH
HCOOH
H2
90
15
0
6
6
6
6
6
6
25
70
86
90
0
0[c]
[a]
Reaction conditions: benzophenone (0.25 mmol), com-
plex 6 (0.5 mol%), KHMDS (2.5 mol%) dissolved in tol-
uene (0.5 mL) and hydrogen source added.
Conversion determined by H NMR from an average of
at least two runs.
0
[b]
[c]
1
[a]
Reaction conditions: benzophenone (0.25 mmol),
(0.5 mol%), KHMDS (X mol%) dissolved in 1:1 toluene/
isopropyl alcohol (1 mL).
Conversion determined by H NMR from an average of
6
Reaction performed in autoclave with a continuous pres-
sure of H2 (2 bar).
[b]
1
at least two runs.
hydrogenation in water is not efficient (Table 3,
entry 1). However, it is possible to use isopropyl alco-
The solvent choice also plays a role in defining the hol in a green system where a relatively inexpensive
catalytic activity. Solvents with boiling points greater and industrially acceptable[15] solvent performs also as
than or equal to 708C were considered (Table 3). a hydrogen source, reducing the amount of waste gen-
As shown above, catalyst 6 is efficient in polar and erated (Table 3, entry 2).
aprotic solvents, such as dimethoxyethane (DME) or
Complex 6 was studied in the presence of different
1,4-dioxane and in relatively non-polar solvents, for hydrogen sources, including H2 gas (Table 4). As ex-
example cyclohexane (C6H12) or toluene (Table 3, en- pected, primary alcohols are poorer hydrogen sources
tries 7, 8, 9 and 10.). Coordinating solvents, such as di- than secondary alcohols (Table 4, entries 1 and 2). In-
methylformamide
(DMF),
dimethyl
sulfoxide terestingly, complex 6 seems to be unreactive in the
(DMSO) and CH3CN led to poor conversions presence of gaseous H2 (Table 4, entry 4). Catalyst 6
(Table 3, entries 3, 4 and 5). Unfortunately transfer is also not active in the presence of formic acid
(Table 4, entry 3).
The effect of temperature was also studied
(Table 5). The results show that a minimum tempera-
Table 3. Solvent optimisation.[a]
ture of 408C is required to activate the catalyst
(Table 5, entry 3). The best results were achieved
Table 5. Temperature optimisation.[a]
Entry
Solvent
Conv. [%][b]
1
2
3
4
5
6
7
8
9
10
H2O
20
93
0
8
0
i-PrOH
DMSO
CH3CN
DMF
DCE
DME
toluene
dioxane
C6H12
Entry
Temp. [8C]
Conv. [%][b]
0
79
90
72
89
1
2
3
4
89 (reflux)
95
93
52
8
70
40
rt
[a]
[a]
Reaction conditions: benzophenone (0.25 mmol),
6
Reaction conditions: benzophenone (0.25 mmol),
6
(0.5 mol%), KHMDS (2.5 mol%) dissolved in 1:1 sol-
(0.5 mol%), KHMDS (2.5 mol%) dissolved in isopropyl
vent/isopropyl alcohol (1 mL).
Conversion determined by H NMR from an average of
alcohol (1 mL).
Conversion determined by H NMR from an average of
[b]
1
[b]
1
at least two runs.
at least two runs.
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Ruthenium Phenylindenyl Complex as an Efficient Transfer Hydrogenation Catalyst
Table 6. Low catalyst loading screening.[a]
products. Complex 6 showed good activity, achieving
almost complete hydrogenation of benzophenone (7)
to benzhydrol (8) with loadings as low as 0.05 mol%
in 48 h (Table 6, entry 5), reaching a maximum TON
of 1920.
To place these results into context, the catalytic ac-
tivity of 6 was compared with that of various rutheni-
um catalysts reported in the literature (Figure 2 and
Table 7).
In comparison with all other ruthenium complexes
examined, complex 6 was found to be the most active
for the model transformation (Table 7, entry 1). Inter-
Entry Catalyst loading [mol%] Time [h] Conv. [%][b]
1
2
3
4
5
6
0.5
1
3
10
24
48
72
95
92
90
92
96
48
0.25
0.15
0.1
0.05
0.025
estingly, when changing from the simple RuCl2ACHTUNGTRENNUNG(PPh3)3
to complexes bearing a cyclopentadienyl or indenyl
ligand (complexes 5, 10 and 2, respectively), the reac-
tivity dramatically decreases (from 66% to 44% con-
version), but with complex 6 that bears a 3-phenylin-
denyl ligand this trend is not followed. Indeed on per-
forming this structural modification, there is an in-
crease in the catalytic activity (95% conversion). This
[a]
Reaction conditions: benzophenone (0.25 mmol),
(X mol%), KHMDS (2.5 mol%) dissolved in isopropyl
6
alcohol (1 mL).
Conversion determined by H NMR from an average of
[b]
1
at least two runs.
when the reaction was heated to 898C (Table 5, may very well be due to the electronic effect variation
entry 1). brought about by the presence of a phenyl substituent
With the aim of further improving the environmen- on the indenyl moiety, rendering the ruthenium
tal impact of our process and hopefully attaining centre slightly more electron rich. Of course, the
a more acceptable and greener level of catalyst use, steric mapping of the Ph-indenyl ligand being some-
the effect of further decreasing the catalyst loading what different than those of unsubstituted indenyl
was examined (Table 6).
counterparts cannot be completely excluded as
This achievement would lower the process costs, a cause for this improved catalyst activity. Various iso-
not only those associated with the catalyst but also electronic ruthenium complexes display low
with the removal of residual ruthenium from the or no reactivity. Of the 16 eÀ species, only the
Figure 2. Ruthenium complexes used for catalyst comparison.
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Table 7. Comparison of catalysts.[a]
The tolerance of the catalytic system to different
substrates bearing various structural motifs was exam-
ined and these result are presented in Table 8.
Entry
Base
Catalyst
Conv. [%][b]
Complex 6 shows very high activity in the hydroge-
nation of ketones, aromatic aldehydes and primary
imines[18] (Table 8, entries 1–10). Remarkably, catalyst
6 surpasses the catalytic activity of Shvoꢁs catalyst
under optimized conditions in the hydrogenation of
N-benzylideneaniline (22), achieving full conversion
in only 1 h [TOF (6)=200 hÀ1, TOF (1)=66 hÀ1]
(Table 8, entry 5).[19]
The catalytic hydrogenation system is very tolerant
to substrate variations. Increasing the steric bulk of
substrates causes the reaction to become more slug-
gish as expected, especially in the case of aliphatic
substituents (Table 8, entries 12, 13 and 15). Consider-
ing electronic effects, substrates with electron-with-
drawing substituents are less prone to hydrogenation,
especially if the substituent is in the para position
(Table 8, entries 16, 17, 18 and 19). Interestingly, the
hydrogenation is faster for aliphatic than for aromatic
1
2
3
4
5
6
7
8
KHMDS
none
6
9
9
2
10
5
11
12
13
14
15
1
95
3
KHMDS
KHMDS
KHMDS
KHMDS
KHMDS
KHMDS
KHMDS
none
53
44
62
66
15
1
53
0
0
9
10
11
12
KHMDS
KHMDS
27
[a]
Reaction conditions: benzophenone (0.25 mmol), catalyst
(0.5 mol%), KHMDS (2.5 mol%) dissolved in isopropyl
alcohol (1 mL).
Conversion determined by H NMR from an average of
at least two runs.
[b]
1
RuCl
ACHTUNGTRENNUNG(ICy)ACHTUNGTRENNUNG
conversions, achieving 53% conversion to 3 in 1 h.
As a ruthenium hydride is oftentimes invoked as an matic substrates.
active catalytic species in such hydrogenation trans-
formations, the hydride derivative of 6, namely 9, was
synthesised by reacting 6 with NaOMe in methanol Conclusions
[Eq. (1)].
In conclusion, we report here a novel system capable
of mediating the hydrogenation of ketones and imines
using isopropyl alcohol as a hydrogen source. This
system shows high activity for the hydrogenation of
aldehydes, ketones and imines, and good compatibili-
ty with various bases and substrate functional groups.
To the best of our knowledge 6 represents one of the
most efficient ruthenium arene transfer hydrogena-
tion catalysts reported to date. Further studies are on-
going in our laboratory to evaluate the catalytic po-
tential of 6 in related reactions.
Unfortunately, complex 9 showed low catalytic ac-
tivity with and without addition of base (Table 7, en-
tries 2 and 3), suggesting that complex 9 is not the
active species in this transformation but may very
well be the catalyst resting state.[17] The active species
is most likely a 16 eÀ hydride species bearing only one
phosphine. A mechanistic study is presently ongoing
Experimental Section
General Considerations
to elucidate the exact nature of reaction intermediates All ketones, 22 and solvents were purchased from commer-
cial suppliers and used as received. Complexes 6, 10, 12, 13,
14 and 15 were synthesised according to previously de-
scribed procedures.[14,16b,20] Aldehydes 18 and 20 were puri-
fied according to the reported procedure.[21] Imines 24 and
26 were synthesised according to the procedure reported in
the literature.[22] Complexes 1 and 11 were purchased from
commercial suppliers and used as received. Flash column
chromatography was performed on silica gel 60 (230–400
in this transformation.
Pleasingly, catalyst 6 showed remarkable activity
compared to Shvoꢁs catalyst (1), one of the most
often used complexes for hydrogen transfer reactions
(Table 7, entries 1 and 9).[9a] Indeed, 6 reached almost
complete conversion in 1 h for the model reaction,
whereas 1 only achieved 30% in the same time, show-
ing that 6 can be a viable alternative to traditional
formic acid transfer hydrogenation with the Shvo cat-
alyst.
1
mesh). H, 13C, and 31P NMR spectra were acquired on an
Avance II 400 MHz spectrometer. All solvents except for
water were purchased from commercial suppliers as anhy-
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Ruthenium Phenylindenyl Complex as an Efficient Transfer Hydrogenation Catalyst
Table 8. Scope of the transfer hydrogenation reactions.[a]
Entry
Time [h]
Substrate
Product
Conv. [%][b]
95
Yield [%][c]
93
1
1
2
3
4
1
1
1
94
88
85
98
92
>99
5
6
1
1
95
88
86
83
7
8
1
1
80
75
81
>99
9
1
1
1
>99
90
78
87
66
10
11
73
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Simone Manzini et al.
FULL PAPERS
Table 8. (Continued)
Entry
Time [h]
Substrate
Product
Conv. [%][b]
90
Yield [%][c]
67
12
3
13
14
5
5
89
80
69
77
15
14
14
75
89
62
87
16[d]
17[d]
14
64
41
18[d]
14
14
34
11
n.d.
n.d.
19[d]
[a]
Reaction conditions: substrate (1 mmol), 6 (0.5 mol%), KHMDS (2.5 mol%) dissolved in isopropyl alcohol (2 mL).
Conversion determined by H NMR from an average of at least two runs.
Isolated yield.
Catalyst loading increased to 1 mol%.
[b]
[c]
[d]
1
drous and used as received. Distilled water was degassed
prior to use.
silica gel chromatography (pentane/ethyl acetate from 98:2
to 50:50).
General Procedure for the Hydrogenation of
Ketones, Imines and Aldehydes
General Procedure for Optimisation of Reactions and
Catalyst Comparison
In a vial fitted with a screw cap, the substrate (1 mmol), cat-
alyst 1 (0.005 mmol, 4.4 mg) and KHMDS (0.025 mmol,
4.8 mg) were charged inside the glovebox and dissolved in
isopropyl alcohol (2 mL). The solution was stirred at 898C
for the period of time indicated in Table 8. The reaction was
In a vial fitted with a screw cap, benzophenone (7)
(0.25 mmol), catalyst (0.00125 mmol) and the proper
amount of base were charged inside the glovebox and dis-
solved in organic solvent (0.5 mL). To this mixture the hy-
drogen source was added (0.5 mL). The solution was stirred
at the given temperature for 1 h hour (in the case of Table 1
the reactions are analysed for 1 h and 5 h). The solvent was
1
monitored by H NMR analysis of aliquots. The solvent was
removed under vacuum, and the product was purified by
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Ruthenium Phenylindenyl Complex as an Efficient Transfer Hydrogenation Catalyst
removed under vacuum and the crude reaction mixture was
analysed by 1H NMR.
Weinheim, 2008, pp 585–630; e) T. Ikariya, A. J. Black-
er, Acc. Chem. Res. 2007, 40, 1300–1308.
[3] a) O. Saidi, J. Williams, Iridium Catalysts, in: Topics in
Organometallic Chemistry, Vol. 34, (Ed.: P. G. Ander-
sson), Springer Verlag, Berlin/Heidelberg, 2011, pp 77–
106; b) C. Bianchini, L. Gonsalvi, M. Peruzzini, in: Iri-
dium Complexes in Organic Synthesis, Wiley-VCH,
Weinheim, 2009, pp 55–106; c) K. Sumi, H. Kumobaya-
shi, Organometallics in Process Chemistry, in: Topics in
Organometallic Chemistry, Vol. 6, Springer Verlag,
Berlin, Heidelberg, 2004, pp 63–95; d) M. C. Simpson,
D. J. Cole-Hamilton, Coord. Chem. Rev. 1996, 155,
163–207.
[4] a) R. H. Morris, Chem. Soc. Rev. 2009, 38, 2282–2291;
b) M. Darwish, M. Wills, Catalysis Science & Technolo-
gy 2012, 2, 243–255; c) S. Gaillard, J.-L. Renaud, Chem-
SusChem 2008, 1, 505–509; d) K. Junge, K. Schroder,
M. Beller, Chem. Commun. 2011, 47, 4849–4859.
[5] a) A. A. Mikhailine, M. I. Maishan, A. J. Lough, R. H.
Morris, J. Am. Chem. Soc. 2012, 134, 12266–12280;
b) P. O. Lagaditis, A. J. Lough, R. H. Morris, J. Am.
Chem. Soc. 2011, 133, 9662–9665.
[6] a) M. Kitamura, R. Noyori, in: Ruthenium in Organic
Synthesis, Wiley-VCH, Weinheim, 2005, pp 3–52; b) W.
Baratta, L. Fanfoni, S. Magnolia, K. Siega, P. Rigo, Eur.
J. Inorg. Chem. 2010, 2010, 1419–1423; c) W. Baratta, F.
Benedetti, A. Del Zotto, L. Fanfoni, F. Felluga, S. Mag-
nolia, E. Putignano, P. Rigo, Organometallics 2010, 29,
3563–3570; d) W. Baratta, G. Chelucci, S. Gladiali, K.
Siega, M. Toniutti, M. Zanette, E. Zangrando, P. Rigo,
Angew. Chem. 2005, 117, 6370–6375; Angew. Chem.
Int. Ed. 2005, 44, 6214–6219.
[7] a) W. Baratta, P. Rigo, Eur. J. Inorg. Chem. 2008, 2008,
4041–4053; b) S. Gladiali, E. Alberico, in: Transition
Metals for Organic Synthesis, Wiley-VCH, Weinheim,
2008, pp 145–166; c) C. Gunanathan, Y. Ben-David, D.
Milstein, Science 2007, 317, 790–792.
Low Catalyst Loading Procedure
In a vial fitted with a screw cap, inside the glovebox, an ali-
quot of 6, from a stock solution of catalyst 6 in dichlorome-
thane (2.6 mg in 5 mL) was added. The solvent was removed
under vacuum and the benzophenone (0.25 mmol), KHMDS
(0.0625 mmol, 1.2 mg) were added and dissolved in isopro-
pyl alcohol (1 mL). The solution was stirred at 898C for
a period of time indicated in Table 6. The solvent was re-
moved under vacuum and the crude reaction mixture was
analysed by 1H NMR.
Synthesis of [RuHACHTNUTRGNEUNG(PPh3)2(3-phenylindenyl)] (9)
In a round-bottomed flask, inside an argon-filled glovebox,
complex 6 (0.47 mmol, 400 mg) and NaOMe (0.47 mmol,
25 mg) were added and dissolved in methanol (23.5 mL).
The reaction mixture was stirred at room temperature for
3 h. The suspension was filtered and the solid collected was
washed with methanol (2ꢃ5 mL) and then with pentane
(5 mL). The solid was collected and dried under vacuum, af-
fording 9 as yellow solid; yield: 277 mg (77%). 1H NMR
(300 MHz, C6D6): d=À14.33 (t, J=31.2 Hz, 1H) 4.58–4.66
(m, 1H) 6.03 (s, 1H) 6.23 (dd, J=8.2, 3.6 Hz, 2H) 6.74–6.82
(m, 7H) 6.83–6.96 (m, 15H) 6.97–7.12 (m, 12H) 7.31 (ddd,
J=9.8, 7.1, 2.2 Hz, 6H) 7.81 (d, J=7.3 Hz, 2H); 13C NMR
(75 MHz, C6D6): d=74.24–75.14 86.79–87.69 88.72–89.49
106.63–107.08 110.88 119.87 125.27 125.46 125.82 126.97
127.08 127.35 127.47 127.90 128.55 129.52 139.19 139.43
139.94 140.85 141.37; 31P NMR (121 MHz, C6D6): d=62.78
(d J=25.5 Hz) 65.65 (d J=25.5 Hz); anal. calcd. for
C51H41P2Ru: C 74.99, H 5.06; found: C 74.83, H 4.95;
[8] Y. Shvo, D. Czarkie, Y. Rahamim, D. F. Chodosh, J.
Am. Chem. Soc. 1986, 108, 7400–7402.
Acknowledgements
[9] a) B. L. Conley, M. K. Pennington-Boggio, E. Boz, T. J.
Williams, Chem. Rev. 2010, 110, 2294–2312; b) M.
Warner, C. Casey, J.-E. Bꢄckvall, Bifunctional Moledul-
ra Catalysts, in: Topics on Organometallic Chemistry,
Vol. 37, (Eds.: T. Ikariya, M. Shibasaki), Springer
Verlag, Berlin, Heidelberg, 2011, pp 85–125; c) D. Holl-
mann, S. Bꢄhn, A. Tillack, M. Beller, Angew. Chem.
2007, 119, 8440–8444; Angew. Chem. Int. Ed. 2007, 46,
8291–8294; d) S. Bꢄhn, S. Imm, K. Mevius, L. Neubert,
A. Tillack, J. M. J. Williams, M. Beller, Chem. Eur. J.
2010, 16, 3590–3593.
We gratefully acknowledge support of this work through the
Seventh Framework Program (CP-FP 211468-2-EUMET).
Umicore AG is thanked for their generous donation of RuCl2
A
2ACHTUNGTRNEN(UNG PPh3)3 (5) and
CHTUNGTRENNUNG
Research Merit Award holder.
References
[10] C. A. Mebi, R. P. Nair, B. J. Frost, Organometallics
2006, 26, 429–438.
[1] a) R. A. Sheldon, in: Methods and Reagents for Green
Chemistry, John Wiley & Sons, Inc., Hobokon, 2007,
pp 189–199; b) P. T. Anastas, M. M. Kirchhoff, Acc.
Chem. Res. 2002, 35, 686–694; c) E. S. Beach, Z. Cui,
P. T. Anastas, Energy Environ. Sci. 2009, 2, 1038–1049.
[2] a) R. Noyori, S. Hashiguchi, Acc. Chem. Res. 1997, 30,
97–102; b) J. S. Cha, Org. Process Res. Dev. 2006, 10,
1032–1053; c) C. F. de Graauw, J. A. Peters, H. van
Bekkum, J. Huskens, Synthesis 1994, 1994, 1007,1017;
d) D. Klomp, U. Hanefeld, J. A. Peters, in: The Hand-
book of Homogeneous Hydrogenation, Wiley-VCH,
[11] L. A. Oro, M. A. Ciriano, M. Campo, C. Foces-Foces,
F. H. Cano, J. Organomet. Chem. 1985, 289, 117–131.
[12] C. P. Casey, H. Guan, Organometallics 2011, 31, 2631–
2638.
[13] Complex 6 was originally isolated as a decomposition
product of an olefin metathesis catalyst precursor. This
is an example of the age-old saying “making lemonade
out of lemons”.
[14] S. Manzini, C. A. Urbina-Blanco, A. Poater, A. M. Z.
Slawin, L. Cavallo, S. P. Nolan, Angew. Chem. 2012,
Adv. Synth. Catal. 2012, 354, 3036 – 3044
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
3043

Simone Manzini et al.
FULL PAPERS
124, 1066–1069; Angew. Chem. Int. Ed. 2012, 51, 1042–
1045.
[15] R. K. Henderson, C. Jimenez-Gonzalez, D. J. C. Con-
stable, S. R. Alston, G. G. A. Inglis, G. Fisher, J. Sher-
wood, S. P. Binks, A. D. Curzons, Green Chem. 2011,
13, 854–862.
[16] a) J. Bosson, A. Poater, L. Cavallo, S. P. Nolan, J. Am.
Chem. Soc. 2010, 132, 13146–13149; b) J. Bosson, S. P.
Nolan, J. Org. Chem. 2010, 75, 2039–2043.
[17] For other examples in which the correspondent hydride
is inactive in transfer hydrogenations see: a) R. J.
Lundgren, M. A. Rankin, R. McDonald, G. Schatte, M.
Stradiotto, Angew. Chem. 2007, 119, 4816–4819;
Angew. Chem. Int. Ed. 2007, 46, 4732–4735; b) W. W. N.
O, A. J. Lough, R. H. Morris, Organometallics 2011, 30,
1236–1252.
[18] Unfortunately, complex 1 shows less or no activity with
secondary imines.
[19] J. S. M. Samec, J.-E. Bꢄckvall, Chem. Eur. J. 2002, 8,
2955–2961.
[20] a) P. Nun, G. C. Fortman, A. M. Z. Slawin, S. P. Nolan,
Organometallics 2011, 30, 6347–6350; b) N. Ahmad, J. J.
Levison, S. D. Robinson, M. F. Uttlky, E. R. Wonchoba,
G. W. Parshall, in: Inorganic Syntheses, John Wiley &
Sons, New York, 2007, pp 45–64; c) M. I. Bruce, C. Ha-
meister, A. G. Swincer, R. C. Wallis, S. D. Ittel, in: Inor-
ganic Syntheses, John Wiley & Sons, New York, 2007,
pp 270–272.
[21] W. L. F. Armarego, C. L. L. Chai, in: Purification of
Laboratory Chemicals, 6th edn., Butterworth-Heine-
mann, Oxford, 2009, pp 88–444.
[22] J. L. Garcꢅa Ruano, J. Alemꢆn, I. Alonso, A. Parra, V.
Marcos, J. Aguirre, Chem. Eur. J. 2007, 13, 6179–6195.
3044
asc.wiley-vch.de
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2012, 354, 3036 – 3044