Ruthenium(II) N,S-heterocyclic carbene complexes and transfer hydrogenation of ketones

Article abstract of DOI:10.1039/c0dt00562b

A series of ruthenium(II) N,S-heterocyclic carbene (NSHC) complexes Ru ^IIX(RCOO)(PPh₃)₂(3-R′BzTh) (BzTh = benzothiazol-2-ylidene; R = Me, R′/X = Bz/Br (4), Prⁱ/I (6), Buⁱ/I (8); R = Et, R′/X = Bz/Br (

Full text of DOI:10.1039/c0dt00562b

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www.rsc.org/dalton | Dalton Transactions
Ruthenium(II) N,S-heterocyclic carbene complexes and transfer hydrogenation
of ketones†
Nini Dinga and T. S. Andy Hor*a,b
Received 28th May 2010, Accepted 30th July 2010
DOI: 10.1039/c0dt00562b
A series of ruthenium(II) N,S-heterocyclic carbene (NSHC) complexes RuIIX(RCOO)(PPh3)2(3-
R¢BzTh) (BzTh = benzothiazol-2-ylidene; R = Me, R¢/X = Bz/Br (4), Pri/I (6), Bui/I (8); R = Et,
R¢/X = Bz/Br (5), Pri/I (7), Bui/I (9)) have been synthesized and characterized. Single-crystal X-ray
structural analysis revealed that in each case the Ru(II) center adopts an essentially octahedral geometry,
coordinated by two trans-oriented PPh3 completed by an NSHC, chelating carboxylate and halide X
(X = Br (4–5), X = I (6–9)) ligands. Although thiazol-2-ylidiene Ru(II) complexes are established and
applied in metathesis, these benzothiazol-2-ylidene complexes (4–9) are the first of its kind. Their
catalytic activities towards transfer hydrogenation of ketones have been examined and discussed.
under mild conditions.11,12 Such methodology obviates the use of
Introduction
high hydrogen pressure and hazardous reducing agents. Although
Ruthenium(II) complexes have gained intense attention in re-
Ru(II) NHC complexes are known to be transfer hydrogenation
active,13–15 the activities of their NSHC counterparts are insofar
unknown.
cent years as powerful and efficient catalysts in an array
of organic transformations.1 Some of these catalysts have
proven to be superior or even indispensable for given types
of reactions.2,3 Recent examples include the N,S-heterocyclic
carbene-based ruthenium complexes RuCl2(3-R–DMeTh)( CH-
o-iPrO–Ph) (DMeTh = 4,5-dimethylthiazol-2-ylidene; R = phenyl,
2-methylphenyl, 2,4,6-trimethylphenyl, 2,6-diethylphenyl, 2,6-
diisopropylphenyl) and RuCl2(3-R–DMeTh)( CH–Ph)(PCy3)
(R = 2,4,6-trimethylphenyl, 2,6-diethylphenyl) developed by
Grubbs et al.2e Different from the majority of other N-heterocyclic
carbene (NHC) ligands,4 the NSHC ligand on these Ru(II) com-
plexes have only one exocyclic substituent. The aryl substituent
tends to protect the vacant site of the metal. This is in contrast with
their asymmetric NNHC counterparts which bear two exocyclic
(typically aryl with alkyl) substituents.5 Despite the lower steric
protection in a single-substituent ligand, these Ru(II) catalysts are
unexpectedly robust, and matching their NHC counterparts in
terms of stability and activity towards metathesis.6 Encouraged by
these, and as part of our study towards metal NSHC complexes,7
we have studied a new series of Ru–NSHC complexes, which are
different from Grubbs’ complexes in carrying the benzothiazol-2-
ylidene carbene. It remains to be explored if these two sub-groups
of NSHC ligands viz. thiazol-2-ylidene and benzothiazol-2-ylidene
would have any significant structural or catalytic differences. The
development of these heteroatomic carbenes (such as NSHC and
N,O-heterocyclic carbenes (NOHC))2e,7–10 obviously lag behind
those of NHC, or precisely, NNHC, ligands. We herein also
report their catalytic activites towards transfer hydrogenation,
which has been applied to ketones in the preparation of alcohols
Results and discussion
Synthesis and characterization of the ligand precursors and
complexes
The benzothiazolium salts 1–3 ([(C6H4)SCHNR]X (R and X =
Bz and Br (1); Pri and I (2); Bui and I (3)) undergo a one-pot
condensation reaction with Ru(RCOO)2(PPh3)2 (R = Me, Et)16 in
the presence of NaOOCR (R = Me, Et) to give the correspond-
ing mixed phosphine-carbene complexes RuIIX(RCOO)(PPh3)2(3-
R¢BzTh) (BzTh = benzothiazol-2-ylidene; R = Me, R¢/X = Bz/Br
(4), Pri/I (6), Bui/I (8); R = Et, R¢/X = Bz/Br (5), Pri/I (7),
Bui/I (9)) in moderate yield (40–61%) (Scheme 1). There is no
evidence of phosphine replacement by carbene. Instead, entry of
the latter, and chloride, is facilitated by the carboxylate departure
in form of carboxylic acid. Similar reaction of RuCl2(PPh3)3
with 1 and NaOAc in THF, which is a method adopted in the
preparation of Ru(II) NNHC complexes,17 only gave [1,3]-benzyl
migration18 product, but not the desired complex. Preparations
without addition of NaOAc also lead to incomplete reactions
aDepartment of Chemistry, National University of Singapore, 3 Science Drive
3, S117543, Singapore. E-mail: andyhor@nus.edu.sg
bInstitute of Materials Research and Engineering, Agency for Science,
Technology and Research, 3 Research Link, S117602, Singapore
† Electronic supplementary information (ESI) available: Additional fig-
ures. CCDC reference numbers 778716–778721. For ESI and crysta-
llographic data in CIF or other electronic format see DOI: 10.1039/
c0dt00562b
Scheme 1 Synthetic route of Ru(II)-(benzothiazol-2-ylidene) complexes
4–9.
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◦
˚
Table 1 Selected bond lengths (A) and angles ( ) for 4–9
4
5
6
7
8
9
Ru(1)–C(1)
Ru(1)–O(1)
Ru(1)–O(2)
Ru(1)–P(1)
1.970(6)
2.130(4)
2.241(4)
2.393(2)
2.374(2)
2.543(1)
173.63(6)
60.2(2)
106.6(5)
3.9
1.970(3)
2.163(2)
2.251(2)
2.3820(9)
2.3825(9)
2.5553(4)
169.03(3)
59.25(8)
106.5(2)
9.7
1.981(3)
2.283(2)
2.128(2)
2.3741(7)
2.3898(7)
2.7221(3)
164.55(2)
59.12(7)
107.7(2)
27.3
2.003(2)
2.149(2)
2.242(2)
2.3821(6)
2.3949(6)
2.7356(3)
171.09(2)
59.39(7)
106.8(2)
4.3
1.966(2)
2.135(1)
2.271(1)
2.3749(5)
2.4112(5)
2.556(2)
171.07(2)
59.29(5)
107.1(1)
24.8
1.976(2)
2.134(1)
2.241(2)
2.3846(6)
2.4031(6)
2.7412(4)
170.09(2)
59.55(6)
106.6(2)
26.6
Ru(1)–P(2)
Ru(1)–X(1)a
P(1)–Ru(1)–P(2)
O(1)–Ru(1)–O(2)
S(1)–C(1)–N(1)
Dihedral angleb
a X = Br for 4 and 5; X = I for 6–9; b dihedral angle between the [O1O2XC1] and N,S-heterocyclic planes.
and other side products. The products prepared are probably the
most stable complexes in this series because use of 2–3 fold excess
of 1–3 with Ru(RCOO)2(PPh3)2 did not yield any di-carbene or
phosphine displacement products.
steric demand of the former and its more electron rich and
nucleophilic carbenic carbon resulting from its diminished
pp-pp interactions with the neighboring heteroatoms. The Ru–C
˚
bond lengths of the isopropyl analogues (6 (1.981(3) A) and
˚
These NSHC complexes are generally stable as solids (under
N2) but slowly decompose in solution. They are readily soluble
in CH2Cl2, THF and toluene and to a less extent Et2O. Their
formation is evidenced by the disappearance of the NCHS protons
7 (2.003(2) A)) are longest in this series, perhaps reflecting
˚
higher inter-ligand repulsions. The Ru–P lengths (2.374(2) A to
˚
˚
2.411(5) A) lie within the expected range of 2.40 0.05 A in
trans-RuII(PPh3)2 species.19 The chelating carboxylate oxygen,
carbenic carbon and halide ligands constitute a nearly perfect
1
in the H NMR spectra of 4–9 compared with their respective
˚ ˚
precursors 1–3, as well as the appearance of the diagnostic carbenic
carbon signals in the 226.0–230.1 ppm region in their 13C NMR
spectra.
equatorial plane (mean deviation, 0.0217 A (4); 0.0127 A (5);
˚
˚
˚
˚
0.0209 A (6); 0.0058 A (7); 0.0095 A (8); 0.0251 A (9)). Stronger
trans-influence20 of carbene compared to halide imparts a
significant disparity between the two Ru–O lengths (Ru1–O1
(2.128(2) to 2.163(2) A) being significantly stronger than Ru1–O2
(2.241(2) to 2.283(2) A)). The carboxylate ligands thus adopt
˚
Molecular structures of 4–9
˚
2
more an asymmetric h -chelating mode. The heterocyclic planes in
The structures of 4–9 were unequivocally elucidated by single-
crystal X-ray diffraction studies. They are invariably mononuclear
with trans-phosphine, as well as NSHC and halide trans to
chelating carboxylate in a distorted octahedral Ru(II) sphere
(Fig. 1 and Table 1). The phosphines in Ru(RCOO)2(PPh3)2
(R = Me, Et) are also trans oriented. The P–Ru–P alignments
are heavily distorted from linearity [P–Ru–P: 173.63(6)◦ (4);
169.03(3)◦ (5); 164.55(2)◦ (6); 171.09(2)◦ (7); 164.55(2)◦ (8);
170.08 (2)◦ (9)] which could reflect the non-bonding contacts
between the NSHC substituent with the phenyls PPh3. For
example, in 6, there are short H . . . H contacts between the
carbene N-substituent and phosphine phenyls, such as the methyl
4, 5, and 7 are nearly co-planar with the equatorial coordination
planes defined by O1O2XC1 (X = Br, I) whereas in 6, 8 and 9,
they are twisted to give unequivocally dihedral angles of 27.3◦
(6), 24.8◦ (8) and 26.6◦ (9). The latter rotations help to relieve
the short repulsive H . . . H contacts between methyl (6 and 9)
or methine group (8) with the phenyl ring, i.e., H9A and H6A
˚
˚
˚
(2.26 A (6)), H9 and H2D (2.06 A (8)) and H10C and H2B (1.86 A
(9)) (Fig. 1). The hydrogen atoms from benzyl ring in complexes
4 and 5 project to the center of phenyl ring and are therefore
shielded. Accordingly, the H10 and H14 of benzyl ring in 4 are
upfield shifted to 5.58 ppm. This shielding effect was confirmed
by 1H NMR and 2D 1H–1H correlation spectra (COSY). A closer
examination of the packing diagrams of the crystal structures
revealed that each mononuclear complex is associated with its
neighboring molecule(s) to form a two dimensional structure (4)
or dimeric species (5–9) (Supporting Information†).
˚
H9A and phenyl H6A (2.26 A) as well as the methine H8 and
˚
phenyl H2E (1.98 A) (Fig. 1). These complexes are static in
solution, each showing only a single dP resonance suggesting
˚
phosphine equivalence. The Ru–C bonds (1.966(2)–2.003(2) A) are
within the range between those reported Ru–NSHC complexes
such as RuCl2(3-R–DMeTh)( CH-o-iPrO–Ph) (DMeTh
4,5-dimethylthiazol-2-ylidene; R = phenyl) (1.944(1) A) and
=
˚
Transfer hydrogenation
RuCl2(3-R–DMeTh)( CH-o-iPrO–Ph) (R
= 2,4,6-trimethyl-
2e
˚
phenyl) (1.953(1) A) and Ru–NNHC complexes such as
Complexes 4–9 have been screened on their activities towards
transfer hydrogenation, using the reduction of p-methyl acetophe-
none to 1-(4-methylphenyl)ethanol in the presence of 2-propanol
as a model (Table 2). All catalysts tested give satisfactory yields
(77–91%) within 30 h at a catalyst loading of 1 mol%. Complex 4,
with benzyl substituent, generally gives better yield than the rest.
It stills returns with a yield of 80% at a load down to 0.5 mol%
(Table 2, Entry 5). Its effect on different alkyl and aryl ketones was
hence further examined (Table 3). The results clearly show that
[RuCl3(NO)(NHC)]13 (NHC = 3-tert-butyl-1-(2-pyridyl)imidazol-
19d
˚
2-ylidene) (2.049(5) A), [RuF(H)(PPh3)2(CO)(NHC)] (NHC =
˚
1,3,4,5-tetramethylimidazol-2-ylidene) (2.170(2) A) and mer,
cis-[RuCl2(CO)(NHC)]14 (NHC
=
1,3-bis(2-diphenylpho-
˚
sphanylethyl)-3H-imidazol-2-ylidene) (2.038(3) A). There is no
crystallographic report on the literature phosphine containing
Ru(II)–NSHC complexes. The slightly shorter Ru–C in NSHC
compared to NNHC complexes could be attributed to a lower
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Fig. 1 Ortep diagrams of the structures of 4–9 with 50% probability ellipsoids and labelling scheme, and ortep diagrams of 6, 8 and 9 showing short
H ◊ ◊ ◊ H contacts.
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Table 2 Catalytic transfer hydrogenation of p-methyl acetophenone
catalysed by 4–9
viable and allows further ligand replacement to alter the electronic
and steric traits of the complexes. The study here suggests that
these complexes may be applied to area beyond metathesis. We
are actively exploring a wider catalytic scope of this and related
systems.
Entry
Catalyst
Time/h
Yield (%)
Experimental section
1
2
3
4
4
4
4
4
5
6
7
8
9
6
49
62
84
91
80
80
87
77
90
84
All manipulations were carried out under a nitrogen atmosphere
using standard Schlenk techniques. Preparation of the benzothia-
zolium salts required treatment of freshly distilled benzothiazole
and appropriate alkyl halide at room temperature (1) or 80 ◦C
(2–3) using a solvent-free method.8e Ru(RCOO)2(PPh3)2 (R = Me,
Et) were prepared according to the literature method.16 Other
commercially available reagents were purchased from Sigma-
Aldrich. All solvents were freshly distilled from standard drying
agents. 1H, 13C and 31P NMR spectra were recorded on a Bruker
18
26
30
30
30
30
30
30
30
4
5a
6
7
8
9
10
Experimental conditions: ketone, 1 mm◦ol; NaOBut, 0.1 mmol; Catalyst,
0.01 mmol; 2-propanol, 15 mL; temp, 82 C.a catalyst loading 0.005 mmol.
AMX 500 spectrometer, and chemical shifts (d) for 1H, 13C and 31
P
were recorded in ppm relative to the residual proton of CDCl3 (1H:
500.1 MHz; 13C: 125.8 MHz; 31P: 202.4 MHz). Elemental analyses
were performed on a Perkin-Elmer PE 2400 elemental analyzer.
The yields of hydrogenation products were determined by using
Hewlett Packard Series 6890 GC (Santa Clara, CA, USA) coupled
to a Hewlett Packard 5973 MS detector.
Table 3 Catalytic transfer hydrogenation of ketones catalysed by 4
Entry Substrate
Product
Yield (%)
1
2
3
4
5
6
cyclopentanone
acetophenone
4-chloroacetophenone 1-(4-chlorophenyl)ethanol
4-bromoacetophenone 1-(4-bromophenyl)ethanol 96
4-methoxyacetophenone 1-(4-methoxyphenyl)ethanol 14
benzophenone
cyclopentanol
1-phenylethanol
96
90
94
General procedures for the preparation of complexes (4–9)
diphenylmethanol
3
A
mixture of Ru(RCOO)2(PPh3)2 (0.25 mmol), NaOOCR
Experimental conditions: ketone, 1 mmol; NaOBut, 0.1 mmol; Catalyst,
0.01 mmol; 2-propanol, 15 mL; temp, 82 ◦C; time, 30 h.
(0.5 mmol) (R = Me, Et) and ligands 1–3 (0.30 mmol) was stirred
under vacuum at 50 ◦C for 1 h. Tetrahydrofuran was then added
and the suspension refluxed overnight. After cooling, the solvent
was removed under vacuum, leaving a dull yellow residue, which
was re-dissolved in toluene (20 mL) and filtered. The filtrate was
mixed with hexane (5 mL) and cooled to-20 ◦C to yield orange-red
crystals in 1–2 weeks.
complex 4 is an efficient catalyst except towards benzophenone
and 4-methoxyacetophenone (Entry 5 and 6), which is probably
attributed to the electronic and steric effects of the substituent on
the ketones.
The catalytic mechanism likely follows that established.11,12b
Easy opening of the carboxylate chelate, especially through cleav-
age of the Ru–O bond trans to the carbene, would create room for
entry of the ketone substrate. Exchange of halide (and carboxylate)
with proton would lead to the active hydride species needed for
hydrogenation transfer. These factors, coupled with the good
stability of these systems under redox conditions offer possible
reasons for the satisfactory catalytic activities shown. These could
be further improved by using polydentate carbene ligands which
tend to lend higher stability to the catalysts. For example, similar
reduction of acetophenone using catalytic [Ru(NO)(L)Cl3]13 (L =
3-tert-butyl-1-(2-pyridyl)imidazol-2-ylidene) can achieve a yield
of 96% within a shorter period of 4 h. A small catalyst loading
of 0.1 mol% fac-[Ru2(m-Cl)3Cl2(PCNHCP)2]Cl14 (PCNHCP = 1,3-
bis(2-diphenylphosphanylethyl)-3H-imidazol-2-ylidene) can also
catalyze the quantitative conversion of acetophenone to 1-
phenylethanol in 4.5 h.
RuBr(MeCOO)(PPh3)2(N-BzBzTh) (4)
1
Yield: 0.14 g (0.14 mmol, 56%). H NMR (500.1 MHz, CDCl3):
d 7.47–7.44 (m, 12H, Ar–H), 7.27–7.23 (m, 9H, Ar–H), 7.21–7.13
(m, 13H, Ar–H), 6,98 (m, 1H, Ar–H), 6.90 (m, 1H, Ar–H), 6.58
(d, 1H, Ar–H), 6.51 (m, 2H, Ar–H), 5.58 (s, 2H, CH2), 0.30 (s,
3H, CH3COO). 13C NMR (125.8 MHz, CDCl3): d 229.8 (NCS),
184.2 (CH3COO), 143.9, 136.7, 136.5, 135.2, 135.1, 132.5, 132.4,
132.2, 129.2, 128.7, 127.5, 127.4, 126.8, 126.0, 123.8, 122.2, 120.0,
112.1 (Ar–C), 53.0 (CH2), 22.2 (CH3COO). 31P NMR (202.4 MHz,
CDCl3): 36.90 (s). Anal. Calc for C52H44BrNO2P2RuS: C, 63.09;
H, 4.48; N, 1.42. Found: C, 63.14; H, 4.71; N, 1.26.
RuBr(EtCOO)(PPh3)2(N-BzBzTh) (5)
1
Yield: 0.15 g (0.15 mmol, 61%). H NMR (500.1 MHz, CDCl3):
d 7.47–7.45 (m, 12H, Ar–H), 7.27–7.21 (m, 10H, Ar–H), 7.19–
7.14 (m, 12H, Ar–H), 6.99 (m, 1H, Ar–H), 6.93 (m, 1H, Ar–H),
6.62 (d, 1H, Ar–H), 6.54 (m, 2H, Ar–H), 5.62 (s, 2H, CH2), 0.65
(m, 2H, CH3CH2COO), 0.02 (t, 3H, CH3CH2COO). 13C NMR
(125.8 MHz, CDCl3): d 230.1 (NCS), 187.0 (CH3CH2COO),
143.9, 136.8, 136.6, 135.1, 135.0, 132.7, 132.5, 132.4, 129.1, 128.7,
127.4, 126.8, 126.0, 123.8, 122.2, 120.0, 112.0 (Ar–C), 53.0 (CH2),
29.4 (CH3CH2COO), 7.8 (CH3CH2COO). 31P NMR (202.4 MHz,
Conclusions
Reported herein is a facile synthetic methodology that enables
the introduction of a NSHC carbene ligand to the [RuII(PPh3)2]
core. The presence of potentially labile and dissociable ligands on
these cores, such as carboxylate and halide, make this catalytically
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CDCl3): 36.69 (s). Anal. Calc for C53H46BrNO2P2RuS: C, 63.41;
H, 4.62; N, 1.39. Found: C, 63.73; H, 4.56; N, 1.34.
RuI(MeCOO)(PPh3)2(N-BuiBzTh) (8)
Yield: 0.13 g (0.13 mmol, 52%). 1H NMR (500.1 MHz, CDCl3): d
7.60–7.56 (m, 12H, Ar–H), 7.24–7.15 (m, 19H, Ar–H), 7.09–7.01
(m, 3H, Ar–H), 4.02 (d, 2H, JHH = 6.95 Hz, CH2CH(CH3)2),
RuI(MeCOO)(PPh3)2(N-PriBzTh) (6)
3
1.85 (m, 1H, CH2CH(CH3)2), 0.87 (s, 3H, CH3COO), 0.67 (d, 6H,
3JHH = 6.95 Hz, CH2CH(CH3)2). 13C NMR (125.8 MHz, CDCl3):
d 227.3 (NCS), 184.8 (CH3COO), 144.8, 137.7, 135.6, 135.2, 135.1,
133.7, 133.6, 133.4, 129.3, 129.0, 127.5, 127.3, 127.2, 123.5, 122.1,
122.0, 111.6 (Ar–C), 55.7 (CH2CH(CH3)2), 29.4 (CH2CH(CH3)2),
24.0 (CH3COO), 20.4 (CH2CH(CH3)2). 31P NMR (202.4 MHz,
CDCl3): 35.21 (s). Anal. Calc for C49H46INO2P2RuS: C,
58.68; H, 4.62; N, 1.40. Found: C, 58.45; H, 4.52;
N, 1.41.
1
Yield: 0.10 g (0.10 mmol, 40%). H NMR (500.1 MHz, CDCl3):
d 7.57–7.56 (m, 13H, Ar–H), 7.44 (d, 1H, Ar–H), 7.28, 7.21–7.14
(m, 18H, Ar–H), 7.09 (t, 1H, Ar–H), 7.03 (t, 1H, Ar–H), 5.70 (m,
1H, CH(CH3)2), 1.27 (d, 6H, CH(CH3)2), 0.50 (s, 3H, CH3COO).
13C NMR (125.8 MHz, CDCl3): d 226.0 (NCS), 184.5 (CH3COO),
142.4, 139.5, 135.4, 135.3, 135.0, 133.6, 133.5, 133.3, 129.2, 127.5,
127.4, 123.3, 121.8, 120.2, 112.8 (Ar–C), 53.7 (CH(CH3)2), 23.0
(CH3COO), 20.8 (CH(CH3)2). 31P NMR (202.4 MHz, CDCl3):
37.28 (s). Anal. Calc for C48H44INO2P2RuS: C, 58.30; H, 4.48; N,
1.42. Found: C, 57.97; H, 4.52; N, 1.20.
RuI(EtCOO)(PPh3)2(N-BuiBzTh) (9)
RuI(EtCOO)(PPh3)2(N-PriBzTh) (7)
Yield: 0.14 g (0.14 mmol, 56%). 1H NMR (500.1 MHz, CDCl3): d
Yield: 0.11 g (0.11 mmol, 45%). 1H NMR (500.1 MHz, CDCl3): d
7.58–7.51 (m, 13H, Ar–H), 7.45 (d, 1H, Ar–H), 7.28–7.26 (m, 4H,
Ar–H), 7.21–7.18 (m, 13H, Ar–H), 7.14 (d, 1H, JHH = 7.55 Hz,
7.60–7.57 (m, 12H, Ar–H), 7.24–7.14 (m, 18H, Ar–H), 7.10–7.01
3
(m, 4H, Ar–H), 4.04 (d, 2H, JHH = 7.55 Hz, CH2CH(CH3)2),
3
1.96 (m, 1H, CH2CH(CH3)2), 1.24 (m, 2H, CH3CH2COO),
0.69 (d, 6H, 3JHH = 6.30 Hz, CH2CH(CH3)2), 0.34 (t, 3H,
CH3CH2COO). 13C NMR (125.8 MHz, CDCl3): d 227.7 (NCS),
187.6 (CH3CH2COO), 144.8, 137.7, 135.6, 135.2, 135.1, 134.8,
133.9, 133.8, 133.6, 129.2, 129.0, 127.4, 127.3, 127.2, 123.4, 122.0,
119.7, 111.6 (Ar–C), 55.8 (CH2CH(CH3)2), 30.7 (CH3CH2COO),
29.2 (CH2CH(CH3)2), 20.4 (CH2CH(CH3)2), 7.9 (CH3CH2COO).
31P NMR (202.4 MHz, CDCl3): 35.22 (s). Anal. Calc for
C50H48INO2P2RuS: C, 59.05; H, 4.76; N, 1.38. Found: C, 59.10; H,
5.08; N, 1.39.
Ar–H), 7.10 (t, 1H, Ar–H), 7.03 (t, 1H, Ar–H), 5.78 (m, 1H,
CH(CH3)2), 1.27 (d, 6H, CH(CH3)2), 0.83 (m, 2H, CH3CH2COO),
0.08 (t, 3H, CH3CH2COO). 13C NMR (125.8 MHz, CDCl3): d
226.6 (NCS), 187.2 (CH3CH2COO), 142.5, 139.5, 137.8, 136.1,
135.4, 135.3, 133.8, 133.6, 133.5, 129.2, 129.1, 127.4, 127.3, 121.2,
120.2, 112.7 (Ar–C), 54.0 (CH(CH3)2), 30.0 (CH3CH2COO), 20.1
(CH(CH3)2), 7.7 (CH3CH2COO). 31P NMR (202.4 MHz, CDCl3):
37.17 (s). Anal. Calc for C49H46INO2P2RuS: C, 58.68; H, 4.62; N,
1.40. Found: C, 58.71; H, 4.74; N, 1.49.
Table 4 Summary of crystallographic parameters and refinement results for complexes 4–9
4
5
6
7
8
9
Formula
C62.50H56BrNO2P-
2RuS
C53H46BrNO2P-
2RuS
C55H52INO2P-
2RuS
C63H61INO2P-
2RuS
C49H46INO2P-
2RuS
C50H48INO2P-
2RuS
Fw
Cryst. syst.
1128.06
1003.89
Monoclinic
P21/c
9.9427(4)
24.1566(10)
18.7354(7)
90
95.8130(10)
90
4476.8(3)
4
1.489
1.404
2048
31658
10257
0.0605
7837
1080.95
Monoclinic
P21/c
17.0266(6)
15.0002(6)
20.3236(7)
90
110.5390(10)
90
4860.7(3)
4
1.477
1.109
2192
57081
11151
0.0357
10310
1186.10
1002.84
1016.86
Triclinic
Triclinic
Triclinic
Triclinic
¯
¯
¯
¯
Space group
P1
P1
P1
P1
˚
a/A
11.359(4)
14.753(5)
17.270(6)
93.390(9)
104.451(8)
107.960(10)
2636.8(15)
2
10.7883(5)
13.8789(7)
18.6293(9)
90.8480(10)
94.2400(10)
96.8600(10)
2761.0(2)
2
11.1382(5)
12.3698(6)
18.7464(8)
74.5240(10)
81.5730(10)
63.4010(10)
2224.63(18)
2
11.5401(16)
12.3535(17)
17.615(3)
72.444(2)
76.977(2)
69.123(2)
2217.4(5)
2
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V (A )
Z
Dcalcd/g cm-3
m/mm-1
1.421
1.201
1158
28965
9311
0.1091
6098
1.427
0.983
1210
35988
12643
0.0315
11067
645
223(2)
0.0417
0.0931
1.082
1.088
-0.399
1.497
1.205
1012
28984
10201
0.0311
9528
517
223(2)
0.0270
0.0611
1.049
0.638
-0.0611
1.523
1.210
1028
28850
10157
0.0272
9304
F(000)
no. of reflns collected
no. of unique reflns
Rint
no. of observed reflns
Parameters
T/K
607
551
572
548
293(2)
0.1148
0.1570
1.017
0.883
-0.634
223(2)
0.0652
0.1075
0.991
1.268
-0.381
223(2)
0.0420
0.0861
1.127
0.798
-0.624
223(2)
0.0300
0.0658
1.041
0.618
-0.0658
a
R1 (all data)
wR2b(all data)
GOFc
-3
˚
˚
Drmax/e A
Drmin/e A
-3
1/2
a R1 = RꢀFo| - |Fcꢀ/R|Fo|. b wR2 = {wR(|Fo| - |Fc|)2/Rw|Fo|2}}
.
c GOF = {Rw(|Fo| - |Fc|)2/(n - p)}1/2, where n is the number of reflections
Dalton Trans., 2010, 39, 10179–10185 | 10183
and p is total number of parameters refined.
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General procedure for the transfer hydrogenation reaction
529; (c) R. Noyori and T. Ohkuma, Angew. Chem., Int. Ed., 2001, 40,
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1766; (h) A. Friedrich, M. Drees, J. Schmedt and S. Schneider, J. Am.
Chem. Soc., 2009, 131, 17552.
The transfer hydrogenation experiments were carried out using
standard Schlenk techniques. A mixture of appropriate amount
of ruthenium complexes 4–9 (1 mol%), and the ketone (1 mmol)
was dissolved in 2-propanol (20 mL). The solution was heated to
◦
82 C. When 0.1 M NaOBut (1 mL) was added, the reaction
commenced immediately. After refluxing for about 30 h, the
reaction mixture was directly passed through a pad of silica
gel with Et2O. The crude product was collected for GC-Mass
chromatography analysis.
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X-ray diffraction studies
Suitable crystals were mounted on quartz fibers and X-ray data
were collected on a Bruker AXS APEX diffractometer equipped
with a CCD detector, using graphite-monochromated Mo-Ka
˚
radiation (l = 0.71073 A). The data were corrected for Lorentz
and polarization effects with the SMART program suite and
for absorption effects with SADABS. The crystal structures were
solved by direct methods and refined by full-matrix least squares
on F2 using the SHELXTL program package.21 In complex 4,
one of the toluene solvates lies on the inversion center and
adopts a higher symmetry than the overall molecule. Such higher
symmetry is suppressed in the refinement and the toluene molecule
is treated by the disordered model with the occupancy factors
of its atoms fixed at 0.5 each. In 9, the isobutyl group adopts a
positional disorder and the ratio of the two disordered components
were refined to be 0.46/0.54. All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were calculated in ideal
geometries and refined isotropically. Selected crystal data for
complexes 4–9 are summarized in Table 4.
7 (a) S. K. Yen, L. L. Koh, F. E. Hahn, H. V. Huynh and T. S. A. Hor,
Organometallics, 2006, 25, 5105; (b) S. K. Yen, L. L. Koh, H. V. Huynh
and T. S. A. Hor, Dalton Trans., 2007, 3952; (c) S. K. Yen, L. L. Koh,
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Acknowledgements
We thank the National University of Singapore (NUS), Ministry
of Education and Agency for Science, Technology and Research
for financial support (Grant R-143-000-361-112) as well as the
staff at the CMMAC of NUS for technical assistance. We acknowl-
edge crystallographic assistance from G. K. Tan and L. L. Koh as
well as W. H. Zhang for helpful discussions.
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©