Ruthenium(II) complexes containing 2-diphenylphosphinobenzaldehyde: Synthesis and catalytic activity in transfer hydrogenation

Article abstract of DOI:10.1016/S0020-1693(03)00404-3

The reaction of dimers [Ru(η⁶-arene)(μ-Cl)Cl] ₂ (arene = C₆H₆ (2a); 1-ⁱPr-4-C ₆H₄Me (2b); 1,2,4,5-C₆H₂Me ₄ (2c); C₆Me₆ (2d)

Full text of DOI:10.1016/S0020-1693(03)00404-3

Inorganica Chimica Acta 356 (2003) 114Á120
/
www.elsevier.com/locate/ica
Ruthenium(II) complexes containing
2-diphenylphosphinobenzaldehyde: synthesis and catalytic activity in
transfer hydrogenation§
Pascale Crochet, Mariano A. Ferna´ndez-Zumel, Christel Beauquis, Jose´ Gimeno *
Departamento de Qu´ımica Orga´nica e Inorga´nica, Facultad de Qu´ımica, Instituto Universitario de Qu´ımica Organometa´lica ‘Enrique Moles’
(Unidad Asociada al CSIC), Universidad de Oviedo, E-33071 Oviedo, Spain
Received 3 March 2003; accepted 9 May 2003
Dedicated to Professor J.J.R. Frau´sto da Silva
Abstract
The reaction of dimers [Ru(h6-arene)(m-Cl)Cl]2 (areneꢀ
2-diphenylphosphinobenzaldehyde (1) yields the neutral complexes [Ru(h6-arene)Cl2(k1-P-2-Ph2PC6H4CHÄ
of compounds 3aÁ
d with one equivalent of AgSbF6 leads to the formation of the monocationic derivatives [Ru(h6-arene)Cl(k2-P,O-
2-Ph2PC6H4CHÄO)][SbF6] (4aÁd). When 3aÁd are treated with two equivalents of AgSbF6 in presence of acetone, the dicationic
complexes [Ru(h6-arene)(k1-O-Me2CÄO)(k2-P,O-2-Ph2PC6H4CHÄ C6H6 (5a); 1-iPr-4-C6H4Me (5b); 1,2,4,5-
O)][SbF6]2 (areneꢀ
C6H2Me4 (5c); C6Me6 (5d)) are obtained. Complexes 3Á5aÁd have proven to be active catalysts in transfer hydrogenation of
/
C6H6 (2a); 1-iPr-4-C6H4Me (2b); 1,2,4,5-C6H2Me4 (2c); C6Me6 (2d)) with
/
O)] (3aÁd). Treatment
/
/
/
/
/
/
/
/
/
/
acetophenone by propan-2-ol.
# 2003 Elsevier B.V. All rights reserved.
Keywords: (h6-Arene)Á
ruthenium(II) complexes; P,O-donor ligands; Transfer hydrogenation
/
1. Introduction
phorus ligand have proven to be efficient in this type of
catalytic transformations, i.e. bidentate or tridentate
phosphinooxazolines [6], pyridylphosphines [7], imino-
and aminophosphines [8], and iminophosphorane-phos-
phines [9]. In contrast, to the best of our knowledge only
very few studies employed catalysts with tridentate
P,N,O-donor ligands [7a,b,9b] and none with bidentate
P,O-donor ligands.
The coordination chemistry of 2-diphenylphosphino-
benzaldehyde (1) has been extensively studied with a
large variety of Rh, Pt, Mn, Re, Ni and Co fragments
[10], but, as far as we know, only the ruthenium(II)
The reduction of carbonyl compounds is an impor-
tant transformation in organic synthesis both from
academic and industrial points of view [1]. Hydrogen
transfer reactions are safer, highly selective and eco-
friendly compared to the commonly used reduction
processes which involve high hydrogen pressure or
hazardous reducing reagents [2]. Although phosphines
were historically the first type of ligands used in
transition metal catalyzed transfer hydrogenations [3],
it is now well-known that the use of nitrogen containing
ligands leads to an increased activity [4]. Thus, a wide
variety of ruthenium(II) derivatives bearing diamino or
derivative
trans,cis,cis-[RuCl2(k2-P,O-2-
O)2] has been reported to date (isolated
Ph2PC6H4CHÄ
/
aminoÁ
catalysts precursors [2,4,5]. In addition, many rutheniu-
m(II) complexes associated to a mixed nitrogenÁphos-
/alcohol ligands has been successfully used as
in 7% yield) [11]. With these precedents in mind, in this
paper we describe the preparation and catalytic activity
in transfer hydrogenation of ketones of novel neutral,
/
monocationic and dicationic (h6-arene)Á
/
ruthenium(II)
complexes bearing 2-diphenylphosphinobenzaldehyde
* Corresponding author. Tel.: ꢁ
/
34-98-5103 461; fax: ꢁ34-98-5103
/
446.
(1).
E-mail address: jgh@sauron.quimica.uniovi.es (J. Gimeno).
0020-1693/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0020-1693(03)00404-3

P. Crochet et al. / Inorganica Chimica Acta 356 (2003) 114Á
/120
115
2. Experimental
(83%). Anal. Found (Calc. for C29H29Cl2OPRu): C,
58.54 (58.39); H, 4.78 (4.90)%. 31P{1H} NMR, CDCl3,
1
d: 27.8 (s). H NMR, CDCl3, d: 10.31 (s, 1H, CHÄ
/
O),
2.1. General information
8.20Á7.27 (m, 14H, ArH), 5.33 and 4.86 (both d, 2H
/
3
each, JHH
ꢀ5.7, CH of cym), 2.98 (sept, 1H,
/
The manipulations were performed under an atmo-
sphere of dry nitrogen using vacuum-line and standard
Schlenk techniques. All reagents were obtained from
commercial suppliers and used without further purifica-
tion. Solvents were dried by standard methods and
distilled under nitrogen before use. The compounds
[Ru(h6-arene)(m-Cl)Cl]2 [12] and 2-Ph2PC6H4CHÄ
[13] were prepared by following the methods reported
in the literature. Infrared spectra (Nujol) were recorded
3JHH
ꢀ
/
6.8, CHMe2), 1.82 (s, 3H, ArMe), 1.24 (d, 6H,
6.8, CHMe2). 13C{1H} NMR, CDCl3, d: 193.0
3JHH
ꢀ
/
3
(d, JPC
ꢀ
/
6.1, CHÄ
4.9, Cq of cym), 97.9 (s, Cq of cym), 88.3 (d,
2.4, CH of cym),
/
O), 138.6Á128.1 (m, Carom), 112.7
/
2
(d, JPC
ꢀ
/
2JPC
ꢀ
/
4.9, CH of cym), 87.5 (d, 2JPC
ꢀ
/
30.4 (s, CHMe2), 22.0 (s, CHMe2), 18.0 (s, ArMe). IR,
nCÄO: 1686.
/
O
2.2.3. [Ru(h6-1,2,4,5-C6H2Me4)Cl2(k1-P-2-
on a PerkinÁ
frequencies are given in cmꢂ1. The C and H analyses
were carried out with a PerkinÁElmer 2400 micro-
/Elmer 1720-XFT spectrometer; absorption
Ph2PC6H4CHÄ
/
O)] (3c)
Following a similar procedure 3c was prepared as a
brown solid using 0.150 g (0.24 mmol) of 2c and 0.170 g
(0.59 mmol) of 1. Reaction time: 1 h. Yield: 0.239 g
(82%). Anal. Found (Calc. for C29H29Cl2OPRu): C,
/
analyzer. Conductivities were measured at r.t. with
approximately 10ꢂ3 mol dmꢂ3 acetone solutions, with
a Jenway PCM3 conductimeter. Gas chromatographic
58.25 (58.39); H, 4.97 (4.90)%. 31P{1H} NMR, CDCl3,
measurements were made on
a
HewlettÁPackard
/
1
d: 28.8 (s). H NMR, CDCl3, d: 10.19 (s, 1H, CHÄ
/
O),
HP6890 equipment; a HP-INNOWAX cross-linked
poly(ethylene glycol) column (30 m, 250 mm) was used.
NMR spectra were recorded on Bruker AV300 or
300DPX instrument at 300 MHz (1H), 121.5 MHz
(31P) or 75.4 MHz (13C) using SiMe4 or 85% H3PO4 as
standards. DEPT experiments have been carried out for
all the complexes. Coupling constants J are given in
Hertz. Abbreviations used: s, singlet; d, doublet; sept,
septuplet; m, multiplet; cym, 1-iPr-4-C6H4Me; Cq,
quaternary carbon; Ar, aromatic; Carom, aromatic
carbons.
8.20Á7.27 (m, 14H, ArH), 4.55 (s, 2H, C6H2Me4), 1.92
/
(s, 12H, C6H2Me4). 13C{1H} NMR, CD2Cl2, d: 193.4
3
(d, JPC
ꢀ
/
4.8, CHÄ
/
O), 138.8Á
/
128.5 (m, Carom), 98.5 (s,
4.8, Cq of C6H2Me4),
16.6 (s, C6H2Me4). IR, nCÄO: 1689.
2
CH of C6H2Me4), 93.8 (d, JPC
ꢀ
/
2.2.4. [Ru(h6-C6Me6)Cl2(k1-P-2-Ph2PC6H4CHÄ
(3d)
Following a similar procedure 3d was prepared as a
redÁbrownish solid using 0.100 g (0.15 mmol) of 2d and
/O)]
/
0.100 g (0.34 mmol) of 1. Reaction time: 1 h. Yield:
0.148 g (79%). Anal. Found (Calc. for C31H33Cl2OPRu):
C, 59.50 (59.62); H, 5.52 (5.33)%. 31P{1H} NMR,
CD2Cl2, d: 31.2 (s). 1H NMR, CD2Cl2, d: 10.17 (s,
2.2. Preparations
2.2.1. [Ru(h6-C6H6)Cl2(k1-P-2-Ph2PC6H4CHÄ
(3a)
A slurry of 2a (0.287 g, 0.57 mmol) and 1 (0.400 g,
1.38 mmol) in 50 ml of dichloromethane was stirred for
24 h at room temperature (r.t.). The reaction mixture
was then filtered through Kieselguhr and the filtrate
evaporated to dryness. The resulting residue was washed
/
O)]
1H, CHÄ
/
O), 8.19Á7.43 (m, 14H, ArH), 1.77 (s, 18H,
/
C6Me6). The low solubility of 3d prevented 13C{1H}
NMR measurements. IR, nCÄO: 1683.
2.2.5. [Ru(h6-C6H6)Cl(k2-P,O-2-Ph2PC6H4CHÄ
O)][SbF6] (4a)
/
twice with 10 ml of a mixture of hexaneꢁdiethyl ether
/
A slurry of 3a (0.316 g, 0.59 mmol) and AgSbF6 (0.20
g, 0.59 mmol) in 120 ml of dichloromethane was stirred
in the dark at r.t. for 1 h. The reaction mixture was then
filtered through Kieselguhr and the filtrate evaporated
to dryness. The resulting residue was washed 3 times
with 10 ml of diethyl ether and vacuum-dried to afford
an orange solid. Yield: 0.304 g (78%). Anal. Found
(Calc. for C25H21ClF6OPRuSb): C, 40.65 (40.54); H,
(1/1) and vacuum dried to afford a brown solid. Yield:
0.481 g (77%). Anal. Found (Calc. for C25H21Cl2OPRu):
C, 55.68 (55.57); H, 3.79 (3.92)%. 31P{1H} NMR,
1
CDCl3, d: 29.4 (s). H NMR, CDCl3, d: 10.45 (s, 1H,
CHÄ
/
O), 8.21Á6.98 (m, 14H, ArH), 5.97 (s, 6H, C6H6).
/
13C{1H} NMR, CD2Cl2, d: 193.5 (d, JPC
ꢀ
/
7.2, CHÄ
3.6, C6H6).
/
3
2
128.0 (m, Carom), 90.2 (d, JPC
O), 139.4Á
/
ꢀ
/
2.88 (2.86)%. Conductivity: 105 Vꢂ1 cm2 molꢂ1
.
IR, nCÄO: 1684.
31P{1H} NMR, acetone-d6, d: 37.5 (s). 1H NMR,
2.2.2. [Ru(h6-1-iPr-4-C6H4Me)Cl2(k1-P-2-
Ph2PC6H4CHÄO)] (3b)
4
acetone-d6, d: 9.97 (d, 1H, JPH
ꢀ
/
3.4, CHÄ
/
O), 8.35Á
/
3
7.60 (m, 14H, ArH), 6.19 (d, 6H, JPH
/
ꢀ
/
0.8, C6H6).
3
Following a similar procedure 3b was prepared as a
brown solid using 0.300 g (0.49 mmol) of 2b and 0.343 g
(1.18 mmol) of 1. Reaction time: 2 h. Yield: 0.486 g
13C{1H} NMR, acetone-d6, d: 204.6 (d, JPC
ꢀ
/
5.3,
3.0,
2
128.0 (m, Carom), 91.4 (d, JPC
CHÄ
/
O), 142.4Á
/
ꢀ
/
C6H6). IR, nCÄO: 1629.

116
P. Crochet et al. / Inorganica Chimica Acta 356 (2003) 114Á120
/
2.2.6. [Ru(h6-1-iPr-4-C6H4Me)Cl(k2-P,O-2-
Ph2PC6H4CHÄO)][SbF6] (4b)
stirred in the dark at r.t. for 1 h. Then, 10 ml of acetone
were added to the reaction mixture. After filtration
through Kieselguhr, the filtrate was evaporated to
approximately 3 ml and 10 ml of diethyl ether were
added. The resulting precipitate was washed three times
with 10 ml of diethyl ether and vacuum-dried to afford
an ochre solid. Yield: 0.623 g (70%). Found (Calc. for
C28H27F12O2PRuSb2): C, 33.73 (33.66); H, 2.83 (2.72)%.
/
Following a similar procedure 4b was prepared as an
orange solid using 0.220 g (0.37 mmol) of 3b and 0.127 g
(0.37 mmol) of AgSbF6. Yield: 0.273 g (93%). Anal.
Found (Calc. for C29H29ClF6OPRuSb): C, 43.61
(43.72); H, 3.59 (3.67)%. Conductivity: 125 Vꢂ1 cm2
molꢂ1
.
31P{1H} NMR, acetone-d6, d: 36.0 (s). 1H
4
NMR, acetone-d6, d: 9.99 (d, 1H, JPH
Conductivity: 200 Vꢂ1 cm2 molꢂ1
.
acetone-d6, d: 41.0 (s). H NMR, acetone-d6, d: 10.19
31P{1H} NMR,
ꢀ
/
4.0, CHÄ
/O),
1
8.32Á7.45 (m, 14H, ArH), 6.39 and 6.21 (both d, 1H
/
each, 3JHH
ꢀ
ꢀ
/
6.5, CH of cym), 6.05 and 5.78 (both d, 1H
4
(dd, 1H, JPH
ꢀ
/
3.4, JHH
14H, ArH), 6.51 (d, 6H, JPH
ꢀ
/
0.7, CHÄ
/
O), 8.65Á7.60 (m,
/
3
each, JHH
/5.2, CH of cym), 2.46 (m, 1H, CHMe2),
3
ꢀ
/
1.0, C6H6). 13C{1H}
2.00 (s, 3H, ArMe), 1.10 and 0.79 (both d, 3H each,
6.8, CHMe2). 13C{1H} NMR, acetone-d6, d:
3
NMR, acetone-d6, d: 205.0 (d, JPC
ꢀ
/
6.8, CHÄ
/
O),
1
3JHH
204.8 (d, JPC
ꢀ
/
2
144.3Á
and 13C{1H} NMR spectra (acetone-d6): interchange
between (CH3)2CÄO and the solvent prevented the
/123.1 (m, Carom), 91.2 (d, JPC
ꢀ3.0, C6H6). H
/
3
ꢀ
/
5.3, CHÄ
/
O), 142.2Á
/
128.4 (m, Carom),
6.0, CH of cym),
6.8, CH of cym), 89.5
2
109.7 (s, Cq of cym), 98.2 (d, JPC
ꢀ
/
/
97.7 (s, Cq of cym), 92.8 (d, 2JPC
ꢀ
/
2
(d, JPC
2
observation of the signals corresponding to the coordi-
nated acetone ligand. IR, nCÄO: 1635 (aldehyde), 1651
(acetone).
ꢀ/1.5, CH of cym), 87.4 (d, JPC
ꢀ3.0, CH of
/
cym), 31.4 (s, CHMe2), 22.7 and 20.5 (both s, CHMe2),
18.1 (s, ArMe). IR, nCÄO: 1617.
2.2.7. [Ru(h6-1,2,4,5-C6H2Me4)Cl(k2-P,O-2-
2.2.10. [Ru(h6-1-iPr-4-C6H4Me)(k1-O-Me2CÄ
P,O-2-Ph2PC6H4CHÄO)][SbF6]2 (5b)
Following a similar procedure 5b was prepared as a
yellow solid using 0.300 g (0.50 mmol) of 3b and 0.688 g
(1.11 mmol) of AgSbF6. Yield: 0.502 g (95%). Anal.
Found (Calc. for C32H35F12O2PRuSb2): C, 36.38
(36.43); H, 3.24 (3.34)%. Conductivity: 193 Vꢂ1 cm2
/
O)(k2-
Ph2PC6H4CHÄ
/
O)][SbF6] (4c)
/
Following a similar procedure 4c was prepared as an
orange solid using 0.513 g (0.86 mmol) of 3c and 0.30 g
(0.86 mmol) of AgSbF6. Yield: 0.564 g (82%). Found
(Calc. for C29H29ClF6OPRuSb): C, 43.84 (43.72); H,
3.77 (3.67)%. Conductivity: 133 Vꢂ1 cm2 molꢂ1
.
31P{1H} NMR, acetone-d6, d: 37.4 (s). 1H NMR,
molꢂ1
.
31P{1H} NMR, acetone-d6, d: 37.0 (s). 1H
4
acetone-d6, d: 10.03 (d, 1H, JPH
4
NMR, acetone-d6, d: 10.21 (d, 1H, JPH
ꢀ
/
4.0, CHÄ
/
O), 8.32Á
/
ꢀ
/
3.4, CHÄ
/
3
7.41 (m, 14H, ArH), 5.96 (s, 2H, C6H2Me4), 1.90 and
1.79 (both s, 6H each, C6H2Me4). 13C{1H} NMR,
O), 8.50Á
CH of cym), 6.62 (d, 1H, JHH
(d, 1H, 3JHH 6.3, CH of cym), 5.99 (d, 1H, 3JHH
CH of cym), 2.69 (m, 1H, CHMe2), 2.11 (s, 3H, ArMe),
/
7.74 (m, 14H, ArH), 6.88 (d, 1H, JHH
ꢀ
/
6.3,
5.7, CH of cym), 6.48
5.7,
3
ꢀ
/
3
acetone-d6, d: 205.0 (d, JPC
ꢀ
/
5.3, CHÄ
/
O), 142.0Á
/
ꢀ
/
ꢀ
/
125.9 (m, Carom), 100.6 (s, Cq of C6H2Me4), 100.4 (d,
2JPC
2
5.8, Cq of C6H2Me4), 95.8 (d, JPC
3
ꢀ
/
ꢀ5.3, CH of
/
1.25 and 0.95 both (d, 3H each, JHH
13C{1H} NMR, acetone-d6, d: 205.7 (d, JPC
CHÄO), 144.3Á124.5 (m, Carom), 108.7 (s, Cq of cym),
ꢀ6.8, CHMe2).
/
3
C6H2Me4), 16.4 and 16.3 (both s, C6H2Me4). IR, nCÄO
1622.
:
ꢀ6.8,
/
/
/
2
100.3 (s, Cq of cym), 94.3 (d, JPC
ꢀ6.0, CH of cym),
/
93.4 (d, 2JPC
of cym), 86.2 (d, JPC
ꢀ
/
3.0, CH of cym), 91.5 (d, 2JPC
ꢀ3.0, CH
/
2.2.8. [Ru(h6-C6Me6)Cl(k2-P,O-2-Ph2PC6H4CHÄ
O)][SbF6] (4d)
/
2
ꢀ1.5, CH of cym), 31.7 (s,
/
CHMe2), 22.9 and 20.6 (both s, CHMe2), 17.9 (s,
ArMe). 1H and 13C{1H} NMR spectra (acetone-d6):
Following a similar procedure 4d was prepared as an
orange solid using 0.120 g (0.19 mmol) of 3d and 0.066 g
(0.19 mmol) of AgSbF6. Yield: 0.134 g (86%). Anal.
Found (Calc. for C31H33ClF6OPRuSb): C, 44.96
(45.14); H, 4.21 (4.03)%. Conductivity: 128 Vꢂ1 cm2
interchange between (CH3)2CÄ/O and the solvent pre-
vented the observation of the signals corresponding to
the coordinated acetone ligand. IR, nCÄO: 1626 (alde-
hyde), 1652 (acetone).
molꢂ1
.
31P{1H} NMR, acetone-d6, d: 39.9 (s). 1H
4
NMR, acetone-d6, d: 9.95 (dd, 1H, JPH
ꢀ/4.0, JHH
ꢀ
/
2.2.11. [Ru(h6-1,2,4,5-C6H2Me4)(k1-O-Me2CÄ
P,O-2-Ph2PC6H4CHÄO)][SbF6]2 (5c)
/
O)(k2-
0.5, CHÄ
/
O), 8.21Á7.49 (m, 14H, ArH), 1.96 (d, 18H,
/
4JPH 0.8, C6Me6). 13C{1H} NMR, acetone-d6, d:
204.8 (d, JPC
ꢀ
/
/
3
ꢀ
/
4.3, CHÄ
/
O), 141.9Á
/
125.3 (m, Carom),
Following a similar procedure 5c was prepared as a
yellow solid using 0.250 g (0.42 mmol) of 3c and 0.320 g
(0.93 mmol) of AgSbF6. Yield: 0.386 g (87%). Anal.
Found (Calc. for C32H35F12O2PRuSb2): C, 36.39
(36.43); H, 3.48 (3.34)%. Conductivity: 200 Vꢂ1 cm2
3
100.4 (d, JPC
1613.
ꢀ2.9, C6Me6), 15.7 (s, C6Me6). IR, nCÄO:
/
2.2.9. [Ru(h6-C6H6)(k1-O-Me2CÄ
O)][SbF6]2 (5a)
A slurry of 3a (0.481 g, 0.89 mmol) and AgSbF6
/
O)(k2-P,O-2-
Ph2PC6H4CHÄ
/
molꢂ1
.
31P{1H} NMR, acetone-d6, d: 38.6 (s). 1H
4
NMR, acetone-d6, d: 10.32 (d, 1H, JPH
ꢀ
/
2.9, CHÄ
/
(0.672 g, 1.96 mmol) in 120 ml of dichloromethane was
O), 8.54Á7.55 (m, 14H, ArH), 6.33 (s, 2H, C6H2Me4),
/

P. Crochet et al. / Inorganica Chimica Acta 356 (2003) 114Á
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117
4
2.15 (d, 6H, JPH
C6H2Me4). 13C{1H} NMR, acetone-d6, d: 206.1 (d,
3JPC
6.4, CHÄO), 144.1Á124.2 (m, Carom), 105.1 (d,
2JPC
2.9, Cq of C6H2Me4), 96.8 (s, Cq of C6H2Me4),
95.5 (d, JPC
(both s, C6H2Me4). 1H and 13C{1H} NMR spectra
(acetone-d6): interchange between (CH3)2CÄO and the
solvent prevented the observation of the signals corre-
ꢀ
/
1.1, C6H2Me4), 1.91 (s, 6H,
1). Compounds 3aÁ
/
d have been characterized by
elemental analyses, IR, and H, 13C{1H} and 31P{1H}
NMR spectroscopy being all the data fully consistent
with the proposed structures. In particular, the coordi-
nation of the phosphine is readily assessed in the
31P{1H} NMR spectra by a downfield shift of the
1
ꢀ
/
/
/
ꢀ
/
2
ꢀ4.3, CH of C6H2Me4), 16.3 and 16.2
/
Ph2P resonance with respect to the free ligand (dꢀ
29.4 (3a); 27.8 (3b); 28.8 (3c); 31.2 (3d) vs. ꢂ11.2 (1)
ppm). The IR spectra exhibit an absorption band in the
range 1683Á
1689 cmꢂ1, characteristic of a non-coordi-
nated aldehyde group [10f]. In addition, the free CHÄ
/
/
/
sponding to the coordinated acetone ligand. IR, nCÄO
1624 (aldehyde), 1646 (acetone).
:
/
/O
1
function gives rise in the H NMR spectra to a singlet
signal at approximately 10.2 ppm and in the 13C{1H}
NMR spectra to a doublet at approximately 193 ppm
due to the coupling with the phosphorus nuclei. These
chemical shifts are similar to those observed for the free
2.2.12. [Ru(h6-C6Me6)(k1-O-Me2CÄ
Ph2PC6H4CHÄO)][SbF6]2 (5d)
/
O)(k2-P,O-2-
/
Following a similar procedure 5d was prepared as an
ochre solid using 0.200 g (0.32 mmol) of 3d and 0.242 g
(0.70 mmol) of AgSbF6. Yield: 0.270 g (78%). Anal.
Found (Calc. for C34H39F12O2PRuSb2): C, 37.58
(37.70); H, 3.71 (3.63)%. Conductivity: 200 Vꢂ1 cm2
ligand 1. 1H NMR (CDCl3) d: 10.52 (d, 1H, 4JPH
CH Ä 18.9, CHÄ
O); 13C{1H} NMR, d: 191.7 (d, 4JPC
O). As far as we know, complexes 3aÁd represent the
first examples of ruthenium derivatives containing a
phosphinoÁaldehyde ligand coordinated in a monoden-
tate manner.
ꢀ
/
5.5,
/
ꢀ
/
/
/
molꢂ1
.
31P{1H} NMR, acetone-d6, d: 38.0 (s). 1H
4
NMR, acetone-d6, d: 10.40 (d, 1H, JPH
ꢀ
/
2.9, CHÄ
/
/
O), 8.62Á
1H and 13C{1H} NMR spectra (acetone-d6): interchange
between (CH3)2CÄO and the solvent prevented the
/7.43 (m, 14H, ArH), 1.90 (s, 18H, C6Me6).
/
3.2. Synthesis and characterization of complexes [Ru(h6-
arene)Cl(k2-P,O-2-Ph2PC6H4CHÄ
O)][SbF6] (4aÁd)
observation of the signals corresponding to the coordi-
nated acetone ligand. The low solubility of 5d prevented
13C{1H} NMR measurements. IR, nCÄO: 1625 (alde-
hyde), 1643 (acetone).
/
/
Treatment of dichloromethane solutions of 3aÁ
one equivalent of AgSbF6 yields (78Á93%) the cationic
derivatives [Ru(h6-arene)Cl(k2-P,O-2-Ph2PC6H4CHÄ
O)][SbF6] (areneꢀ
C6H6 (4a); 1-iPr-4-C6H4Me (4b);
/d with
/
/
2.3. General procedure for catalytic transfer
hydrogenation of acetophenone
/
1,2,4,5-C6H2Me4 (4c); C6Me6 (4d)), which are readily
formed via abstraction of one chloride ligand and O-
coordination of the aldehyde group (Scheme 1). Char-
Under inert atmosphere acetophenone (0.60 g, 5
mmol), the ruthenium catalyst precursor (0.01 mmol,
0.2 mol%), and 45 ml of propan-2-ol were introduced in
a Schlenk tube fitted with condenser and heated at 82 8C
for 15 min. Then NaOH was added (5 ml of a 0.048 M
solution in propan-2-ol, 4.8 mol%) and the reaction
monitored by gas chromatography. GC measurements
are effectued each 5 min till conversion reachs 50% in
order to obtain the half-reaction time and the TOF50
values with the better precision. TOF50 values are given
acterization of compounds 4aÁd was achieved by means
/
of standard spectroscopic techniques as well as elemen-
tal analyses and conductance measurements. The
31P{1H} NMR spectra of complexes 4aÁ
d display a
singlet signal at 37.5 (4a), 36.0 (4b), 37.4 (4c) and 39.9
(4d) ppm which appear at lower fields (ca. 10 ppm) when
/
compared to their neutral precursors 3aÁ
nation of the aldehyde group on the ruthenium centre is
evidenced by: (i) (IR) the n(CÄO) absorptions (in the
range 1613Á
1629 cmꢂ1) which are red-shifted in com-
parison with those observed for complexes 3aÁd and
that of the free ligand 1, and (ii) (13C{1H} NMR
spectra) the downfield shifting of the CÄO resonance
(d ca. 205 ppm). In addition, conductance measure-
/
d. The coordi-
/
with a precision of 9
10 hꢂ1. Acetone and 1-pheny-
lethanol were the only products detected in all cases.
/
/
/
/
3. Results and discussion
ments in acetone confirm that compounds 4aÁd are 1:1
/
electrolytes (LM between 105 and 133 Vꢂ1 cm2 molꢂ1).
3.1. Synthesis and characterization of complexes [Ru(h6-
arene)Cl2(k1-P-2-Ph2PC6H4CHÄ
/
O)] (3aÁ
/
d)
3.3. Synthesis and characterization of complexes [Ru(h6-
arene)(k1-O-Me2CÄ
O)][SbF6]2 (5aÁd)
/
O)(k2-P,O-2-Ph2PC6H4CHÄ
/
Dimers [Ru(h6-arene)(m-Cl)Cl]2 (2aÁ
equivalents of 2-diphenylphosphinobenzaldehyde (1), in
dichloromethane at room temperature, to afford neutral
/d) react with two
/
The treatment of complexes [Ru(h6-arene)Cl2(k1-P-2-
Ph2PC6H4CHÄO)] (3aÁd) with a twofold excess of
AgSbF6, in dichloromethane and further addition of
complexes [Ru(h6-arene)Cl2(k1-P-2-Ph2PC6H4CHÄ
/
O)]
C6H6 (3a); 1-iPr-4-C6H4Me (3b); 1,2,4,5-
C6H2Me4 (3c); C6Me6 (3d)) in 77Á83% yield (Scheme
/
/
(areneꢀ
/
/

118
P. Crochet et al. / Inorganica Chimica Acta 356 (2003) 114Á
/120
Scheme 1.
acetone, leads to the formation of the dicationic
derivatives
[Ru(h6-arene)(k1-O-Me2CÄO)(k2-P,O-2-
Ph2PC6H4CHÄO)][SbF6]2 (areneꢀ
C6H6 (5a); 1-iPr-4-
C6H4Me (5b); 1,2,4,5-C6H2Me4 (5c); C6Me6 (5d)) (75Á
95% yield; Scheme 1). Alternatively, complexes 5aÁ
can be prepared in similar yields starting from 4aÁd and
(0.2 mol%) and NaOH (4.8 mol%) were added to a 0.1
M solution of acetophenone in propan-2-ol at reflux
temperature, the reaction being monitored by gas
chromatography. The results are summarized in Table 1.
All the complexes are active leading to nearly
quantitative conversions to 1-phenylethanol. Both in
the neutral and the monocationic series the benzene
(3a,b) and p-cymene (4a,b) derivatives are the most
active (entries 1, 2, 5 and 6). Nevertheless, this trend is
no longer observed for the dicationic complexes, being
5c (1,2,4,5-C6H2Me4) the faster catalyst. This seems to
indicate that the catalytic activity does not depend
exclusively on the steric or electronic properties of the
arene ligand.
/
/
/
/
/
d
/
one equivalent of AgSbF6 in a mixture dichloro-
methane/acetone as solvent. These compounds have
been obtained as yellowÁbrownish air stable solids,
/
being slightly soluble in chloroform or dichloromethane
but highly soluble in acetone. Analytical and spectro-
scopic data support the proposed formulation. In
particular, the presence of the coordinated acetone is
assessed by an IR absorption at approximately 1650
cmꢂ1. The spectroscopic features corresponding to the
Different types of the active catalytic species have
been proposed in the literature, the requirements being a
coordinated ligand 2-Ph2PC6H4CHÄ
/
O are very similar
to those observed for the complexes 4aÁ
/d, confirming
metalÁhydride function and a free coordination site [14].
/
once again the chelate coordination of the 2-diphenyl-
phosphinobenzaldehyde ligand. Remarkable features
are: (i) (1H NMR) a doublet signal at approximately
10.2 ppm attributable to the aldehydic proton, (ii)
(13C{1H} NMR) a doublet resonance at approximately
205 ppm assignable to the aldehydic carbon, and (iii)
In our case, no mechanistic studies have been per-
formed. Nevertheless, we can propose that the hydride
formation results probably from the substitution of a
chloride ligand (3aÁ
/
d, 4aÁ
/
d), or the coordinated acetone
(5aÁ
/
d),1 by the isopropoxide anion,2 followed by b-
elimination. The generation of a vacancy can be
provided by (i) substitution of the arene [15] or (ii)
partial dissociation of the chelate ligand [8d], as
proposed previously for similar catalyst precursors.
The former proposition can be discarded here since
(IR) an absorption band for the CHÄ
1624 and 1635 cmꢂ1. Conductance measurements in
acetone confirm that compounds 5aÁd are 1:2 electro-
lytes (LM ca. 200 Vꢂ1 cm2 molꢂ1).
/
O group between
/
3.4. Catalytic transfer hydrogenation of acetophenone
1
Treatment of complex [Ru(h6-1-iPr-4-C6H4Me)Cl(k2-P,O-2-
The catalytic activity of complexes 3aÁ
/
d, 4aÁd and
/
Ph2PC6H4CHÄ
propanol leads after 5 min to the formation of three new species
31P{1H NMR, in 2-propanol/capilar D2O, d: 49.8, 52.8 and 54.8 ppm)
which can tentatively be attributed to [Ru(h6-1-iPr-4-C6H4Me)H(k2-
P,O-2-Ph2PC6H4CHÄ
O)][SbF6], [Ru(h6-1-iPr-4-C6H4Me)H2(k1-P-2-
Ph2PC6H4CH Ä
O)] and [Ru(h6-1-iPr-4-C6H4Me)ClH(k1-P -2-
Ph2PC6H4CHÄO)]. The mixture rapidly decomposes avoiding
/
O)][SbF6] with 24 equiv. of NaOH in refluxing 2-
5aÁd in transfer hydrogenation of acetophenone by
/
propan-2-ol has been investigated (Scheme 2). In a
typical experiment, the ruthenium(II) catalyst precursor
(
/
/
/
further characterization.
2
The isopropoxide anion is generated from 2-propanol and base.
No activity is observed in absence of base.
Scheme 2.

P. Crochet et al. / Inorganica Chimica Acta 356 (2003) 114Á
/120
119
Table 1
Transfer hydrogenation of acetophenone
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60
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