Probing the catalytic potential of chloro nitrosyl rhenium(i) complexes

Article abstract of DOI:10.1039/c0dt00842g

The reduction of the mononitrosyl Re(ii) salt [NMe₄] ₂[ReCl₅(NO)] (1) with zinc in acetonitrile afforded the Re(i) dichloride complex [ReCl₂(NO)(CH₃CN)₃] (2). Subsequent ligand substitution reactions with PCy₃, PiPr ₃ and P(p-tolyl)₃ afforded the bisphosphine Re(i) complexes [ReCl₂(NO)(PR₃)₂(CH₃CN)] (3, R = Cy a, iPr b, p-tolyl c) in good yields. The acetonitrile ligand in 3 is labile, permitting its replacement with H₂ (1 bar) to afford the dihydrogen Re(i) complexes [ReCl₂(NO)(PR₃) ₂(η²-H₂)] (4, R = Cy a, iPr b). The catalytic activity of 2, 3 and 4 in hydrogen-related catalyses including dehydrocoupling of Me₂NH·BH₃, dehydrogenative silylation of styrenes, and hydrosilylation of ketones and aryl aldehydes were investigated, with the main focus on phosphine and halide effects. In the dehydrocoupling of Me₂NH·BH₃, the phosphine-free complex 2 exhibits the same activity as the bisphosphine-substituted systems. In the dehydrogenative silylation of styrenes, 3a and 4a bearing PCy₃ ligands exhibit high catalytic activities. Monochloro Re(i) hydrides [Re(Cl)(H)(NO)(PR₃)₂(CH₃CN)] (5, R = Cy a, iPr b) were proven to be formed in the initiation pathway. The phosphine-free complex 2 showed in dehydrogenative silylations even higher activity than the bisphosphine derivatives, which further emphasizes the importance of a facile phosphine dissociation in the catalytic process. In the hydrosilylation of ketones and aryl aldehydes, at least one rhenium-bound phosphine is required to ensure high catalytic activity.

Full text of DOI:10.1039/c0dt00842g

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Dalton
Transactions
Cite this: Dalton Trans., 2011, 40, 2578
www.rsc.org/dalton
PAPER
Probing the catalytic potential of chloro nitrosyl rhenium(I) complexes†
Yanfeng Jiang, Olivier Blacque and Heinz Berke*
Received 14th July 2010, Accepted 2nd December 2010
DOI: 10.1039/c0dt00842g
The reduction of the mononitrosyl Re(II) salt [NMe4]2[ReCl5(NO)] (1) with zinc in acetonitrile afforded
the Re(I) dichloride complex [ReCl2(NO)(CH3CN)3] (2). Subsequent ligand substitution reactions with
PCy3, PiPr3 and P(p-tolyl)3 afforded the bisphosphine Re(I) complexes [ReCl2(NO)(PR3)2(CH3CN)] (3,
R = Cy a, iPr b, p-tolyl c) in good yields. The acetonitrile ligand in 3 is labile, permitting its replacement
2
with H2 (1 bar) to afford the dihydrogen Re(I) complexes [ReCl2(NO)(PR3)2(h -H2)] (4, R = Cy a, iPr b).
The catalytic activity of 2, 3 and 4 in hydrogen-related catalyses including dehydrocoupling of
Me2NH·BH3, dehydrogenative silylation of styrenes, and hydrosilylation of ketones and aryl aldehydes
were investigated, with the main focus on phosphine and halide effects. In the dehydrocoupling of
Me2NH·BH3, the phosphine-free complex 2 exhibits the same activity as the bisphosphine-substituted
systems. In the dehydrogenative silylation of styrenes, 3a and 4a bearing PCy3 ligands exhibit high
catalytic activities. Monochloro Re(I) hydrides [Re(Cl)(H)(NO)(PR3)2(CH3CN)] (5, R = Cy a, iPr b)
were proven to be formed in the initiation pathway. The phosphine-free complex 2 showed in
dehydrogenative silylations even higher activity than the bisphosphine derivatives, which further
emphasizes the importance of a facile phosphine dissociation in the catalytic process. In the
hydrosilylation of ketones and aryl aldehydes, at least one rhenium-bound phosphine is required to
ensure high catalytic activity.
[ReBr2(NO)(PR3)2(CH3CN)] (R = Cy a, iPr b)12 comprised of
Introduction
nitrosyl,13 the p-donor bromide, and the additional presence of
Hydrogen-related catalyses, including those with activation of
E–H (E = H,1,2 B,3 Si,4
s-donor phosphine ensure a certain degree of electron richness
and simultaneously ligand lability. Such species exhibited for
C
5) bonds as key elementary steps,
have attracted growing interest in both organic and inorganic
chemistry. Recent studies on chemical hydrogen storage are often
based on amine boranes,6 and these require such H–E bond
activation processes.7,3a So far, robust catalysts for such hydrogen-
related catalyses are mostly limited to early and late transition
metal compounds. In contrast, middle transition metal complexes
appear to be less active due to their high tendency to stay as
coordinatively saturated 18-electron species. The metal ligand
bonds are usually too strong to admit ligand lability. Such
drawbacks have to be overcome via the help of the ancillary
ligand sphere using for instance the cis-labilization effect of p-
donating ligands (e.g. Cl, Br) stabilizing dissociative transition
states or intermediates of low coordination numbers.8 A similar
labilization effect was expected to originate from the trans-effect
and trans-influencing ligands, like the NO moiety.9 With this
background our group has in recent years focused on the study
of the chemistry of the middle transition element rhenium,10 in
particular with respect to applications in homogeneous hydrogen
reactions.11 For example, the mononitrosyl rhenium dibromides
instance good catalytic activities toward the dehydrocoupling of
14
Me2NH·BH3
and highly selective dehydrogenative silylation
of alkenes,15 i.e. in more general terms the activation of E–H
bonds. Mechanistic studies implied the involvement of phosphine
dissociation which was either promoted by the substrate (e.g.
Me2NH·BH3) or induced by the ancillary ligand sphere (e.g.
in dehydrogenative silylation).16 Also the phosphine-free but
still p-donor and trans-influence/effect ligand containing Re(I)
dibromide [ReBr2(NO)(CH3CN)3] was found to be active in hy-
drosilylation of ketones and aldehydes.17 In extension of this work
with respect to ligand tuning, we report here the preparation of the
related mononitrosyl rhenium dichloride complexes bearing either
no phosphine or two phosphine ligands and their application in
the above-mentioned types of catalyses to trace the impact of
phosphine and halide substitution on the catalytic performance of
such mononitrosyl Re(I) systems.
Results and discussion
Synthesis of mononitrosyl Re(I) dichloride complexes
Anorganisch-chemisches Institut, Universita¨t Zu¨rich. Winterthurerstr. 190,
CH-8037, Zu¨rich, Schweiz. E-mail: hberke@aci.uzh.ch; Fax: +41 1 63 568
02; Tel: +41 1 63 546 81
† CCDC reference numbers 783380 and 783381. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/c0dt00842g
Chloride is a strong p-donor and therefore exerts a strong cis-
labilization effect on neighboring ligands, even stronger than
bromide.18 This could result in enhanced ligand replacements or
2578 | Dalton Trans., 2011, 40, 2578–2587
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
stabilization of unsaturated catalytic species. A synthetic pathway
to suitable mononitrosyl rhenium dichloride complexes is depicted
in Scheme 1, similar to the procedure in the preparation of related
Re(I) dibromides.11a
as shown in Fig. 1 and 2. Both molecules adopted a pseudo-
octahedral geometry around the rhenium center with two trans-
disposed phosphines. The two 2e ligands of 3c are slightly bent
toward one chloride with a P(1)–Re(1)–P(2) angle of 173.85(3)◦.
˚
˚
10a
The Re–Nacetonitrile distance is 2.0935(17) A in 3a and 2.075(3) A
˚
in 3c, close to the average value (2.098 A) for such bonds.
Apparently, the coordination mode of the phosphine, nitrosyl and
acetonitrile ligands do not depend much on the nature of the
halide, since only small variations of the Re–P, Re–N and NO
bond lengths are found with respect to the bromide derivative.
Scheme 1 Synthetic pathways to various chloro nitrosyl Re(I) complexes.
Starting from rhenium metal, a two-step procedure furnished
the mononitrosyl Re(II) salt [NMe4]2[ReCl5(NO)] (1) in 26% yield.
This compound was previously reported in a lower yield (15%)
by Guisto and co-workers via a complex procedure starting from
[K2][ReCl6].19 Compound 1 is well soluble in H2O but has a quite
poor solubility in CH3CN. Different from the bromide derivatives
bearing [NMe4]+ and [NEt4]+ counter-ions,19a 1 was found to be
insoluble in ethanol or methanol, even at elevated temperatures.
This prevented the preparation of Re(I) bisphosphine complexes
via a facile substitution route employing ethanol as both a solvent
and reductant.10b Therefore we modified this procedure adding
zinc as a reducing agent. Treatment of 1 with excess of zinc in
CH3CN at room temperature afforded within 5 days an orange so-
lution, from which the Re(I) complex mer-[ReCl2(NO)(CH3CN)3]
(2) was isolated in 51% yield. The IR spectra showed a strong
Fig.
1
ORTEP drawing of [ReCl2(NO)(PCy3)2(CH3CN)] (3a) us-
ing 30% probability ellipsoids. The NO/Cl disorder and selected
˚
1
n(NO) absorption at 1697 cm-1. In the H NMR spectrum two
H
atoms are omitted for clarity. Selected bond lengths (A):
Re(1)–N(11), 1.768(6); Re(1)–N(2), 2.0935(17); Re(1)–Cl(1), 2.4183(10);
Re(1)–Cl(21), 2.4129(17); Re(1)–P(1), 2.5062(11); Re(1)–P(2), 2.5134(12);
N(11)–O(11), 1.185(8). Selected bond angles (deg): N(11)–Re(1)–N(2),
87.31(17); N(2)–Re(1)–Cl(1), 177.46(10); P(1)–Re(1)–P(2), 177.02(5);
O(11)–N(11)–Re(1), 176.4(5); N(11)–Re(1)–Cl(21), 174.43(15); N(11)–
Re(1)–P(1), 93.79(15); Cl(21)–Re(1)–Cl(1), 91.08(5).
resonances were observed for the Meacetonitrile groups at 3.00 and
2.93 ppm in a 1 : 2 ratio, confirming the mer-substitution pattern
of the acetonitrile ligands.
Complex 2 turned out to be a suitable precursor for vari-
ous ligand exchange reactions. Treatment of 2 with excess of
phosp◦hines such as PCy3, PiPr3 and P(p-tolyl)3 in acetonitrile
at 70 C afforded within 24 h the bisphosphine Re(I) dichloride
complexes of the type [trans-ReCl2(NO)(PR3)2(CH3CN)] (3, R =
Cy a, iPr b, p-tolyl c) in 50% (3a), 16% (3b) and 76% (3c) isolated
yield, respectively. Complexes 3a–c were fully characterized by
elemental analysis and various spectroscopic methods. In the IR
spectra the coordinated NO ligands gave rise to n(NO) bands at
1672 cm-1 (3a), 1668 cm-1 (3b) and 1688 cm-1 (3c), respectively.
The acetonitrile ligand of 3 is substitutionally labile. Treatment
of 3a with 1 bar of H2 in CH2Cl2 at room temperature afforded
within 24 h the dihydrogen Re(I) complex [ReCl2(NO)(PCy3)2(h -
2
H2)] (4a) in 85% isolated yield. Complex 4a was fully characterized
by elemental analysis, IR and 1H, 31P{ H}, 13C{ H} NMR
1
1
spectroscopy. The IR spectrum showed a strong n(NO) absorption
at 1674 cm-1. The 31P{ H} NMR spectra displayed a singlet at d
1
1
The 31P{ H} NMR spectra displayed singlet resonances at -11.10
14.5 ppm, which is shifted low-field in comparison with that of
1
(3a), -0.3 (3b) or -0.96 ppm (3c) accounting for the two chemically
3a. In the H NMR spectra, the resonance of the dihydrogen
1
equivalent trans-phosphorus nuclei. In the H NMR spectra the
ligand was observed as a broad triplet at 2.61 ppm (2J(PH)
=
Meacetonitrile groups were observed as singlets at 3.09 (3a), 3.07 (3b)
and 1.79 ppm (3c), which are comparable to those of the Re(I)
dibromide derivatives.11a The molecular structures of complexes 3a
and 3c were established by single-crystal X-ray diffraction studies,
18 Hz, T1 = 39 ms) due to coupling with the two phosphorus
nuclei.10b In the same manner 3b was also reacted with H2 but
affording a mixture containing 84% of the dihydrogen complex
2
[ReCl2(NO)(PiPr3)2(h -H2)] (4b) and 16% of the starting material
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 2578–2587 | 2579
©

View Article Online
Table 1 Dehydrocoupling of Me2NH·BH3 catalyzed by chloro nitrosyl
Re(I) complexesa
Entry
[Re]
T (◦C)
t (h)
Yield (%)b
TOF (h)
1
2
3
4
5
6
7
3a
3a
3a
3b
3c
4a
4a
2
23
23
85
85
85
45
85
85
80
80
24
4
4
4
4
2
4
4
4
14
25
97
93
95
7
79
96
11
<1
1
6
24
23
24
4
20
24
3
8
9c
10c
2
3a
4
—
a Reactions were performed with 0.25 mmol of Me2NH·BH3 in 0.5 mL of
dioxane. b On the basis of integration of 11B-NMR spectrum (96 MHz) of
the reaction mixture. c In acetonitrile.
adduct Cy3P·BH3. Similar results were obtained by applying 3b
and 3c as catalysts. Complex 4a turned out to be slightly less active,
probably due to its lower solubility in dioxane. In comparison with
the dibromide derivatives, the chloride complexes 3a and 3b did
not show higher activity. When the reaction catalyzed by 3a or 4a
was carried out at lower temperatures, such as 23 ◦C or 45 ◦C, the
TOFs decreased considerably.
Fig. 2 ORTEP drawing of [ReCl2(NO){P(p-tolyl)3}2(CH3CN)] (3c) using
30% probability ellipsoids. The NO/Cl disorder and all H atoms are
Interestingly, the phosphine-free Re(I) dichloride precursor 2
exhibited the same catalytic activity in the dehydrocoupling of
Me2NH·BH3 in dioxane. It should be noted that 2 is almost
insoluble in dioxane and during the catalysis it quickly turned from
orange to black within 15 min. The formed dark residue was found
to act as a heterogeneous catalyst in the dehydrocoupling reaction,
reaching a conversion of 96% within 4 h, which corresponds to a
TOF value of 24 h-1. The stoichiometric reaction between 2 and
Me2NH·BH3 (5 equiv.) demonstrated the formed black residue to
be insoluble in almost any organic solvent and only poorly soluble
in water. In the IR spectrum, a weak and broad absorption at
1644 cm-1 indicated the presence of a NO group.
˚
omitted for clarity. Selected bond lengths (A): Re(1)–N(12), 1.862(7);
Re(1)–N(2), 2.075(3); Re(1)–Cl(21), 2.360(2); Re(1)–Cl(1), 2.4137(8);
Re(1)–P(1), 2.4636(8); Re(1)–P(2), 2.4771(9); N(12)–O(12), 1.055(9). Se-
lected bond angels (deg): P(1)–Re(1)–P(2), 173.85(3); N(12)–Re(1)–Cl(21),
170.5(3); N(2)–Re(1)–Cl(1), 175.03(8); O(12)–N(12)–Re(1), 177.1(9);
Cl(1)–Re(1)–P(1), 87.37(3); Cl(21)–Re(1)–P(1), 88.50(6).
3b. T1 measurement was also carried out for the triplet signal at
2.49 ppm (2J(PH) = 18 Hz) of 4b in H NMR and the short T1
1
value of 87 ms indicated the coordination of dihydrogen ligand to
rhenium. No reaction at all occurred between 3c and H2 even at
elevated temperatures, presumably caused by the lower electron-
donating ability of the p-tolyl phosphine. H2 binding is known to
require a certain degree of electron richness of the metal center.1
The performance of the dehydrocoupling catalysis was found to
be quite solvent-dependent. When the reaction was catalyzed by
◦
2 in acetonitrile at 80 C for 4 h, only 11% of [Me2N–BH2]2 was
Application of chloro nitrosyl rhenium(I) complexes to
hydrogen-related catalysis
obtained along with the formation of 6% of (Me2NH)2BH. Under
the same conditions, the dehydrocoupling reaction catalyzed by
3a in acetonitrile afforded merely a trace amount of [Me2N–BH2]2
and (Me2NH)2BH (less than 1% of the total). These results suggest
the involvement of rhenium intermediates bearing vacant sites
regardless of the type of the coordinated ligand (PR3 or CH3CN).
1. Dehydrocoupling of Me2NH·BH3. The bisphosphine
dichloride complexes 3a–c and 4a were tested as catalysts in
the dehydrocoupling of Me2NH·BH3. The observed turnover
frequencies (TOFs) are listed in Table 1. In a typical run, 0.25 mmol
of Me2NH·BH3 and 1.0 mol% of 3a were mixed in 0.5 mL of
dioxane. The solution was kept at 85 ◦C with continuous release of
hydrogen. After 4 h, the 11B NMR spectra indicated the formation
of the dehydrocoupled cyclic product [Me2N–BH2]2 in 97% yield
displaying a characteristic triplet at 4.5 ppm (JBH = 112 Hz).14f
2. Dehydrogenative silylations of styrenes. Simultaneous ac-
tivation of sp2C–H and Si–H bonds by transition metal complexes
to form new Si–C bonds is one of the key steps of organosilicon
chemistry. Besides the well-developed hydrosilylation reaction,
which has found various industrial applications,20 the competitive
dehydrogenative silylation reaction, which permits the direct
production of unsaturated silyl compounds from olefins and
silanes, has drawn much attention during the last two decades.21
Hydrosilylations and dehydrogenative silylations are related by a
formal transfer hydrogenation process (eqns 1a and 1b). However,
Except for trace amounts of (Me2NH)2BH (d 28.0 ppm, d, JBH
=
132 Hz), no evidence was found for the formation of the cyclic
trimer [Me2N–BH2]3 or the linear dimer [Me2NH–BH2–NMe2–
BH3]. The stoichiometric reaction between 3a and 5 equiv. of
Me2NH·BH3 proved the formation of the phosphine-abstracted
2580 | Dalton Trans., 2011, 40, 2578–2587
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
Table 2 Dehydrogenative silylation of styrenes catalyzed by chloro nitrosyl Re(I) complexesa
Entry
R¢
R1
[Re]
T(◦C)
t (h)
Conv. (%)b
Ratio dehydro (E/Z) : hydroc
1
2
3
4
5
6
7
8
Et
Ph
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
Et
p-MeOC6H4
p-MeOC6H4
p-MeOC6H4
p-MeOC6H4
p-MeOC6H4
p-MeOC6H4
p-MeC6H4
p-MeC6H4
p-ClC6H4
p-FC6H4
3a
3a
3b
3b
3c
3c
3a
3c
3a
3a
3a
4a
4a
3a
3c
2
70
100
70
100
70
100
70
100
100
70
100
70
28
24
24
24
28
24
24
24
24
24
24
24
24
24
24
2
99
91
9
99 (99/1) : 2
95 (99/1) : 5
—
97 (98/2) : 3
—
96 (96/4) : 4
98 (>99/1) : 2
97 (99/1) : 3
96 (99/1) : 4
—
97 (99/1) : 3
98 (99/1) : 2
98 (>99/1) : 2
80 : 20
99
<5
92
87
97
99
39
98
99
99
99
99
99
99
71
56
99
66
51
99
69
64
98
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
p-FC6H4
p-MeOC6H4
p-MeC6H4
H
70
100
100
110
110
110
110
110
110
110
110
110
110
110
H
80 : 20
p-MeC6H4
p-MeOC6H4
Ph
94 (>99/1) : 6
93 (>99/1) : 7
95 (>99/1) : 5d
95 (>99/1) : 5
97 (>99/1) : 3
93 (>99/1) : 7
94 (>99/1) : 6
87 (>99/1) : 13
85 (>99/1) : 15
90 (>99/1) : 10
98 (>99/1) : 2
2
2
Et
Et
Et
Et
2
1.5
1.5
9
1.5
1.5
3
1.5
3
2
p-FC6H4
2
m-ClC6H4
m-MeC6H4
o-FC6H4
2
2
Et
2
Me2Phe
Me2Phe
Me2Phe
Ph
p-MeC6H4
m-MeC6H4
o-FC6H4
2
2
2
p-MeC6H4
2
a Reactions were carried out with 0.25 mmol of silane and 0.50 mmol of styrenes. b Calculated based on the silane consumption. c On basis of the
integration of the 1H NMR spectrum. d The selectivities decreased with prolonged reaction time. e With Me2PhSiH as the silane substrate.
a major drawback of the dehydrogenative silylation is that it is
usually accompanied by hydrosilylation byproduct. Thus highly
selective processes are desired.22,15a,15c–d
4 : 1) were observed. The reactions with the less hydridic Ph3SiH
catalyzed by 3a turned out to be sluggish at low temperature, but
could be accelerated at the higher temperature of 100 ◦C. All these
reactions, despite that trace amount of (Z)-vinylsilane products
were always found, showed no branched “side-products” of the
dehydrogenative silylations.
We also investigated the stoichiometric reactions of 3 in the
presence of Et3SiH. The reaction of 3a or 3b with Et3SiH in
toluene-d8 at 100 ◦C afforded within 1 h a deep-pink solution,
which quickly turned light-brown accompanied by some oily
residue when cooled to ambient temperature. The NMR spec-
tra indicated the formation of chloro Re(I) hydride complexes
[Re(Cl)(H)(NO)(PR3)2(CH3CN)] (5, R = Cy a, iPr b) in 98% (5a)
or 99% (5b) in situ yields. When the reactions were carried out at
70 ◦C, the conversions became rather poor, pointing to significant
catalyst degradation at longer reaction times. Both compounds 5a
In continuation of the exploration of the respective catalytic
potential, the performance of complexes 2, 3a–c and 4a in the
dehydrogenative silylation of styrenes was examined. Table 2 lists
the dehydrogenative silylation reactions studied under catalytic
conditions with various Re(I) dichlorides. For the sake of compar-
ison the reaction of Et3SiH (0.25 mmol) with p-methoxystyrene
(0.5 mmol) in toluene-d8 was carried out for at least 24 h in the
presence of 1.0 mol% of the Re(I) catalyst. Compared to the
dibromide analogues, the Re(I) dichlorides 3b and 3c bearing
PiPr3 or P(p-tolyl)3 ligands did not show improved activities.
Somewhat higher temperatures of 100 ◦C were required which,
however, did not affect the selectivities for the dehydrogenative
silylations over the hydrosilylations, with (E)-1-(p-methoxystyryl)-
2-(triethylsilyl)ethylene remaining the dominant product. In con-
trast, complexes 3a and 4a bearing PCy3 ligands turned out
to be better catalysts than the respective bromides, since the
reaction temperature could be decreased to 70 ◦C, affording even
slightly better selectivities. However, this positive tuning effect was
restricted to the case of p-methoxy and p-methylstyrene. Reactions
with substrates, such as p-chloro- and p-fluorostyrene, with silanes
using 3a or 4a as catalysts had to be carried out at 100 ◦C for the
benefit of both high conversions and selectivities. In the case of
ethylene, a high yield, but lower dehydro/hydro selectivities (about
1
and 5b were characterized in solution. For example, the 31P{ H}
NMR spectra showed singlets at d 21.2 for 5a and at 31.6 ppm
for 5b. In the 1H NMR spectra triplet resonances at d -1.51 ppm
(2J(HP) = 20.0 Hz) for 5a and -1.75 ppm (2J(HP) = 20.0 Hz) for
5b were assigned to the HRe proton. The Meacetonitrile groups were
observed as singlets at 1.11 ppm for 5a and 1.08 ppm for 5b.
Isolation of pure 5a and 5b was attempted, but elemental analyses
of the obtained solids were not satisfactory. In the IR spectra one
n(NO) band was observed at 1648 (5a) and at 1637 cm-1 (5b).◦In
contrast, no reaction occurred between 3c and Et3SiH at 100 C
even at longer times (48 h), which presumably can be attributed to
the lower electron-donating ability of the P(p-tolyl)3 ligands.
Interestingly, the phosphine-free complex 2 proved to be an even
better catalyst than those of type 3 and 4 in such silane catalyses.
For example, when a mixture of 0.50 mmol of p-methylstyrene and
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 2578–2587 | 2581
©

View Article Online
Table 3 Hydrosilylation of ketones and aryl aldehydes catalyzed by
0.25 mmol of Et3SiH were treated with 1.0 mo◦l% of 2 in toluene-
d8 and kept at the higher temperature of 110 C, conversions of
99% were achieved within 2 h accompanied by a high selectivity
of 94% for dehydrogenative silylation over hydrosilylation. Other
styrenes, such as p-methoxystyrene, m-methylstyrene also afforded
chloro nitrosyl Re(I) complexesa
◦
satisfactory conversions catalyzed by 2 at 110 C within 1.5–3 h
Carbonyl substrate
giving high selectivities of over 9 : 1 between dehydrogenative
silylations and hydrosilylations. The reactions of styrenes bearing
electron-withdrawing substituents such as p-fluorostyrene, m-
chlorostyrene and o-fluorostyrene were found to proceed slower
than those with electron-donating substituents of the aromatic
rings. Variations in the silanes were additionally tested in reactions
catalyzed by 2. While Ph3SiH still afforded reasonable conversions
and selectivities for dehydrogenative silylation, the reaction of
dimethylphenylsilane with various styrene derivatives afforded
somewhat lower selectivities (<9 : 1) under the same conditions as
in the cases of Ph3SiH and Et3SiH as the silyl component. It should
also be pointed out that in these catalyses of 2 always black residues
were formed, which were isolated and proved to be catalytically
inactive. The improved activity of 2 over 3 and 4 suggests that 3 and
4 are pre-catalysts which operate on the basis of loss of phosphine
ligands to form the active species. Phosphine dissociation might
even participate in the rate-determining step(s).12b
Entry R¢ R1
R2 [Re] T (◦C) t (h) Yield (%)b
1
2
Et Ph
Et Ph
Ph 3a
Ph 3a
Ph 3b
Ph 3c
Ph 4a
Me 3a
tBu 3a
3a
80
23
80
80
80
80
80
80
4
15
4
4
4
5
5
4
4
5
4
4
4
4
4
4
4
5
2
4
4
3
4
99
14
99
74
99
91
87
99
99
99
95
69
74
0
3
4
Et Ph
Et Ph
5
6
Et Ph
Et Ph
7
8
9
Et Me
Et Cyclohexanone
Et Cyclohexanone
Et p-MeC6H4
Et 1-Naph
Ph Ph
Ph Cyclohexanone
iPr Ph
iPr Cyclohexanone
Et Ph
Et Ph
3a
3a
3a
80
10
11
12
13
14
15
16
17
18
19
20
21
22
23
H
H
80
80
Ph 3a
3a
Ph 3a
3a
100
80
80
80
0
Ph
Me
tBu
H
H
H
2
2
2
2
2
2
2
2
110
110
110
110
110
110
110
110
34
81
47
99
99
95
96
87
Et Me
Et p-MeOC6H4
Et p-FC6H4
Et 1-Naph
Et Cyclohexanone
Et Cyclohexanone
The stoichiometric reaction of 2 with 5 equiv. of p-methylstyrene
afforded within 5 h at 110 ◦C a yellow solution, in which
the formation of p-methylstyrene-coordinated Re(I) complex
2
[ReCl2(NO)(CH3CN)2(h -CH2 CHPh(p-Me))] could be traced.
The 1H NMR resonances of the alkene protons were observed as
two doublets of doublets at 4.85 and 3.81 ppm in a 1 : 2 ratio. The
signals of the two acetonitrile ligands were observed as two singlets
at 1.12 and 1.09 ppm suggesting their cis-position. The resonance
of free CH3CN ligand is detected as a singlet at 0.71 ppm.
Kinetic measurements were carried out for 2 (1.0 mol%)
catalyzed dehydrogenative silylation of p-methylstyrene and
Et3SiH. The rate law was determined, and showed first-order
dependence in the concentration of each substrate:
a Reactions were performed with 0.28 mmol of silane and 0.25 mmol of
ketones or aldehydes. b On the basis of the integration of the 1H-NMR
spectrum.
temperature. In the case of iPr3SiH, no conversion was observed
at all, presumably due to its steric congestion being too high.
In comparison to the dehydrogenative silylation reactions with 3
and 4, the phosphine-free compound 2 showed lower performance
in the hydrosilylation of ketones and aryl aldehydes. When the
reaction of benzophenone (0.25 mmol) and Et3SiH (0.28 mmol)
with 1 mol% of 2 was carried out at 80 ◦C, a conversion of less than
10% was achieved within 4 h. Raising the temperature to 110 ◦C
indeed accelerated the catalysis affording a yield of 34% within
4 h, which however is much lower than that from the catalyses
of 3 or 4 at 80 ◦C. Similar low activities were also observed
with 3,3-dimethylbutan-2-one and cyclopentanone as substrates.
Generally, the reactions with aryl aldehydes are faster than those
with ketones. A high yield of over 95% could be achieved at
110 ◦C within 2-4 h in the hydrosilylation of anisaldehyde, p-
fluorobenzaldehyde and 1-naphthaldehyde.
The catalytic behavior of 2 differing from 3 or 4 in the de-
hydrogenative silylations and hydrosilylations suggests divergent
underlying reaction paths. The stoichiometric reaction of 3a with
5 equiv. of acetophenone and Et3SiH afforded at 80 ◦C within
10 min the acetonitrile-coordinated Re(I) hydride 5a in 75%
yield, along with hydrosilylation products. The hydrosilylation was
completed at 80 ◦C within 1 h with 5a as the major remaining
organometallic species. This demonstrates that the Re(I) hydrides
5 are generated even in the initial pathway in bisphosphine Re(I)
dichloride catalyzed hydrosilylations. In contrast, the reaction of
2 with acetophenone and Et3SiH proceeded relatively slowly and
rate = 0.048 (min L mol-1) ¥ [Et3SiH][p-methylstyrene]
3. Hydrosilylation of ketones and aryl aldehydes. When ke-
tones andaryl aldehydes were employed as substrates, the reactions
with silane catalyzed by 3 and 4 furnished hydrosilylation and
formation of silyl ether products, as depicted in Table 3. When
benzophenone and 1.1 equiv. of Et3SiH were mixed with 1 mol%
of 3a in 0.5 mL of chlorobenzene-d5 and kept at 80 ◦C for 4 h, the
1H NMR spectra indicated almost complete hydrosilylation (yield
> 99%). Similar results were obtained using 3b and 4a as catalysts.
Complex 3c bearing P(p-tolyl)3 ligands led to only moderate yields
after 4 h, thus showing lower activity than the complexes bearing
alkylphosphine ligands. Other ketones, such as acetophenone, 3,3-
dimethylbutan-2-one, cyclopentanone and cyclohexanone also
afforded the corresponding hydrosilylation products in high yields
under similar conditions as for benzophenone. Aryl aldehydes,
including benzaldehyde and 1-naphthaldehyde, can also be re-
duced to silyl ethers by the reaction with Et3SiH. It was further
proven that the type of silane has a great influence on the catalytic
performance. Et3SiH turns out to be the most efficient silane source
for hydrosilylations. The reaction of Ph3SiH with benzophenone
or cyclopentanone afforded only moderate yields even at elevated
2582 | Dalton Trans., 2011, 40, 2578–2587
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
no obvious hydrosilylation occurred at 110 ◦C within 10 min.
Kinetic measurements for the hydrosilylation of acetophenone
with Et3SiH catalyzed by 2 (2.0 mol%) indicated a second-order
behavior, first-order with respect to both silane and ketone:
ated solvents were dried with sodium/benzophenone (toluene-
d8, benzene-d6) or CaH2 (CD2Cl2), and vacuum-transferred for
storage in Schlenk flasks fitted with Teflon valves. 1H NMR,
13C{ H} NMR, and 31P{ H} NMR data were recorded on a
Varian Gemini-300, Varian Mercury 200, or Bruker DRX 500
spectrometers using 5-mm diameter NMR tubes equipped with
Teflon valves, which allow degassing and further introduction of
gases into the probe. Chemical shifts are expressed in parts per
1
1
rate = 0.062 (min L mol-1) ¥ [Et3SiH][PhCOCH3]
It is most likely that in these hydrosilylations the rhenium
catalyst (5 or 2) functions as a Lewis acid coordinating the ketones
or aryl aldehydes, in which the activated carbon atom of the
1
million (ppm). 1H and 13C{ H} NMR spectra were referenced to
the residual proton or 13C resonances of the deuterated solvent. All
C
O bond is further attacked from “outside” by the hydride
1
chemical shifts for the 31P{ H} NMR data are reported downfield
of the silane affording the final hydrosilylation product.23 Another
possible pathway would be the initial activation of the Si–H bond
at the rhenium center, then the polarized silicon atom is attacked
by the carbonyl group.24 The rate-determining step is presumed to
be the dissociation of one acetonitrile ligand. This would explain
why the reactions catalyzed by 3 or 4 are faster than that by 2, as
the acetonitrile ligands in the bisphosphine Re(I) hydrides 5 are
more labile than those of 2.
in ppm relative to external 85% H3PO4 at 0.0 ppm. Signal patterns
are reported as follows: s, singlet; d, doublet; t, triplet; m, multiplet.
IR spectra were obtained by using ATR methods with a Bio-Rad
FTS-45 FTIR spectrometer. Microanalyses were carried out at
the Anorganisch-Chemisches Institut of the University of Zurich.
Et3SiH, Ph3SiH, Me2PhSiH, different styrene derivatives, ketones
and aryl aldehydes were purchased from Fluka and Aldrich and
used without further purification.
Caution: When generating hydrogen gas in Young-tap NMR
tubes, the tubes should be vented for safety reasons every 30 min
during experiments.
Conclusions
In summary, we have demonstrated synthetic access to chloro
nitrosyl Re(I) complexes and their utility in hydrogen-related catal-
yses including dehydrocoupling of Me2NH·BH3, dehydrogenative
silylation of styrenes, and hydrosilylation of ketones and aryl
aldehydes. An influence of the type of phosphine substitution and
a halide effect could be demonstrated. In the dehydrocoupling
of Me2NH·BH3, the phosphine-free Re(I) complex 2 exhibited
the same activities as the bisphosphine ones. In dehydrogena-
tive silylation reactions, the catalytic activities are only slightly
enhanced in the case of 3a and 4a when bromide and chloride
derivatives are compared. This might be interpreted in terms of
different cis-labilization effects exerted by different halide ligands
that facilitates phosphine dissociation. However, the substitution
of one halide by a hydride in the initiation step largely suppresses
this halide effect. Interestingly, 2 exhibited higher activity toward
dehydrogenative silylation than 3 or 4, which implies that two
acetonitrile ligands must dissociate from the rhenium center and
that such two-ligand dissociations are more reluctant to occur
with complexes of type 3 and 4. In the hydrosilylation of ketones
and aryl aldehydes, the phosphine-free complex 2 proved to be
less effective than the bisphosphine derivatives 3 and 4. The
different catalytic performance indicates a different mechanism.
Presumably the rhenium center operates as a Lewis acid to the
carbonyl group and the rate-determining step is the substitution
of acetonitrile ligand by the substrate. All these types of reactions
have in common a strong propensity of Re(NO) centers to activate
E–H bonds (E = B, Si), which in this respect resemble isoelectronic
RuL units (L = 2e- donor).
[NMe4]2[ReCl5(NO)] (1). In a 500 mL round-bottom flask,
H2O2 (20 mL, 30%) was added dropwise to Re powder (6.0 g,
32.2 mmol) at 0 ◦C. [NMe4]Cl (5.60 g, 51.09 mmol) was then added
and the mixture was stirred for 15 h at room temperature until the
solution became relatively homogenous. The mixture was dried
by rotary evaporation. After that, additional part of [NMe4]Cl
(5.60 g, 51.09 mmol) was added, and the mixture was dissolved in
220 mL of HCl (32%) and 10 mL of H3PO2 (50%). NO gas was
bubbled through the solution at 110 ◦C, and the solution turned
green after 2 h. 15 h later, the reaction mixture was cooled down
to room temperature and was filtered. The filtrate was dried by
rotary evaporation giving green solid, which was further washed
with acetone (3 ¥ 20 mL) and dried in vacuo. Yield: 4.50 g, 26%.
IR (ATR, cm-1): n (NO) 1715. Anal. Calcd for C8H24Cl5N3ORe
(541.77): C, 17.74; H, 4.47; N, 7.76. Found: C, 18.23; H, 4.35; N,
7.75.
mer-[ReCl2(NO)(CH3CN)3] (2). In a 250 mL round-bottom
flask, 1.14 g of 1 (2.10 mmol) was dissolved in 100 mL of
CH3CN. Then an excess of Zn (1.2 g, 18.46 mmol) was added
and the mixture was stirred at room temperature for 5 days. The
dark-orange supernatant solution was filtered and the solvent
was evaporated in vacuo. The residue was extracted with CH3CN
(5 ¥ 10 mL) to remove most of [NMe4]Cl and [NMe4]2[ZnCl4]
salt. The extracted solution was dried in vacuo and was further
extracted with CH2Cl2 (5 ¥ 20 mL) to afford orange solid.
1
Yield: 440 mg, 51%. IR (ATR, cm-1): n (NO) 1697. H NMR
(300.1 MHz, CD3CN, ppm): 3.00 (s, 3H, CH3CN), 2.93 (s, 6H,
CH3CN). 13C{ H} NMR (75.5 MHz, CD2Cl2, ppm): 134.2 (s,
1
Experimental details
CH3CN), 132.7 (s, CH3CN), 4.3 (s, CH3CN). Anal. Calcd for
C6H9Cl2N4ORe (410.27): C, 17.56; H, 2.21; N, 13.66. Found: C,
17.60; H, 2.53; N, 13.57.
General
All manipulations were performed under an atmosphere of dry
nitrogen using standard Schlenk techniques or in a glovebox
(M. Braun 150B-G-II) filled with dry nitrogen. Solvents were
freshly distilled under N2 by employing standard procedures and
were degassed by freeze–thaw cycles prior to use. The deuter-
[ReCl2(NO)(PCy3)2(CH3CN)] (3a). In a 50 mL Young-tap
Schlenk, 2 (82 mg, 0.2 mmol) and excess of PCy3 (280 mg,
1.0 mmol) were dissolved in 10 mL of CH3CN. The solution
was stirred at 70 ◦C for 15 h. During the reaction, a bright
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 2578–2587 | 2583
©

View Article Online
yellow precipitate was gradually formed. After cooling down to
room temperature, the supernatant solution was removed and
the precipitate was further washed with CH3CN (2 ¥ 10 mL)
and hexane (3 ¥ 5 mL), dried again in vacuo. Yield: 91 mg,
that 4b was formed in 84◦% yield with 16% of 3b remained. At
elevated temperatures (40 C), the yield of 4b doesn’t improve. 1H
NMR (300.1 MHz, CD2Cl2, ppm): 2.87 (m, 6H, P-CH(CH3)2),
2
2.49 (t, 2J(PH) = 18 Hz, T1 = 87 ms, h -H2), 1.33–1.43 (m, 36H, P-
1
1
50%. IR (ATR, cm-1): n (C–H) 2917, 2842, n (NO) 1672. H
CH(CH3)2).31P{ H} NMR (80.9 MHz, CD2Cl2, ppm): 23.7 (br).
NMR (300.1 MHz, CD2Cl2, ppm): 3.09 (s, 3H, CH3CN), 1.24–
IR (ATR, cm-1): n (C–H) 2929, 2852, n (CH3CN) 2259, n (Re–H)
2002, n (NO) 1648.
1
2.53 (m, 66H, P(C6H11)3). 13C{ H} NMR (75.5 MHz, CD2Cl2,
1
ppm): 34.3 (t, J(PC) = 10.1 Hz, P-C), 29.3, 28.6, 27.2. 31P{ H}
Preparation of [Re(Cl)(H)(NO)(PCy3)2(CH3CN)] (5a). In a
3 mL Young-tap NMR tube, 3a (24 mg, 0.027 mmol) and Et3SiH
(20 mL, 0.12 mmol) were dissolved in 0.5 mL of toluene-d8.
The solution was kept at 100 ◦C for 1 h affording a pink-violet
solution, which quickly turned light-brown when it was cooled
to room temperature. Some oily residue was also observed. NMR
spectroscopy indicated the formation of 5a in 98% yield with 2% of
free PCy3 ligand. 1H NMR (300.1 MHz, benzene-d6, ppm): 1.25–
NMR (121.5 MHz, CD2Cl2, ppm): -11.10 (s). Anal. Calcd for
C38H69Cl2N2OP2Re (889.03): C, 51.34; H, 7.82; N, 3.15. Found: C,
50.99; H, 7.56; N, 3.06.
[ReCl2(NO)(PiPr3)2(CH3CN)] (3b). In a 50 mL Young-tap
Schlenk, 2 (235 mg, 0.56 mmol) and excess of PiPr3 (0.50 mL,
2.20 mmol) were dissolved in 10 mL of CH3CN and the solu-
tion was stirred at 70 ◦C for 24 h. The resulting dark-brown
solution was dried in vacuo and the residue was extracted with
CH2Cl2/pentane (1/20 v/v, 5 ¥ 5 mL). The extracted yellow
solution was dried in vacuo. Yield: 57 mg, 16%. IR (ATR, cm-1):
n (NO) 1668. 1H NMR (300.1 MHz, CD2Cl2, ppm): 3.07 (s,
3H, CH3CN), 2.54 (m, 6H, P–CH(CH3)2), 1.34–1.43 (m, 36H,
2.59 (m, 66H, P(C6H11)3), 1.11 (s, 3H, CH3CN), -1.51 (t, 2J(PH)
=
1
20 Hz, 1H, Re–H). 13C{ H} NMR (75.5 MHz, benzene-d6, ppm):
35.1 (t, J(PC) = 10 Hz, P-C), 30.0 (s), 29.9 (s), 28.4 (m), 27.6 (s),
1
2.0 (s, CH3CN). 31P{ H} NMR (121.5 MHz, benzene-d6, ppm):
21.2 (s). IR (ATR, cm-1): n (C–H) 2929, 2852, n (CH3CN) 2259,
n (Re–H) 2002, n (NO) 1648.
1
P–CH(CH3)2). 13C{ H} NMR (75.5 MHz, CD2Cl2, ppm): 24.3
1
(t, J(PC) = 10.6 Hz, P–CH(CH3)2), 19.8 (s), 19.6 (s); 31P{ H}
Preparation of [Re(Cl)(H)(NO)(PiPr3)2(CH3CN)] (5b). In a
3 mL Young-tap NMR tube, 3b (20 mg, 0.03 mmol) and Et3SiH
(20 mL, 0.12 mmol) were dissolved in 0.5 mL of toluene-d8. The
solution was kept at 100 ◦C for 1 h affording a pink-violet solution,
which quickly turned light-brown when it was cooled to room
temperature. NMR spectroscopy indicated the formation of 5b in
NMR (121.5 MHz, CD2Cl2, ppm): -0.30 (s). Anal. Calcd for
C20H45Cl2N2OP2Re (648.19): C, 37.03; H, 6.99; N, 4.32. Found:
C, 37.20; H, 7.11; N, 4.13.
[ReCl2(NO){P(p-tolyl)3}2(CH3CN)] (3c). In a 50 mL Young-
tap Schlenk, 2 (126 mg, 0.3 mmol) and an excess of P(p-tolyl)3
(307 mg, 1.0 mmol) were dissolved in 10 mL of CH3CN and
the mixture was stirred at 70 ◦C for 8 h. During the reaction,
an orange-yellow precipitate was gradually formed. After cooling
down to room temperature, the supernatant solution was removed.
The residue was washed with CH3CN (4 ¥ 5 mL) and dried
in vacuo. Yield: 215 mg, 76%. IR (ATR, cm-1): n (CH3CN): 2276,
n (NO) 1688. 1H NMR (300.1 MHz, CD2Cl2, ppm): 7.20–7.66 (m,
1
over 99% yield. H NMR (300.1 MHz, benzene-d6, ppm): 2.72
(m, 6H, CH), 1.33–1.48 (m, 36H, CH3), 1.08 (s, 3H, Re–CH3CN),
2
1
-1.75 (t, J(PH) = 20 Hz, 1H, Re–H). 13C{ H} NMR (75.5 MHz,
benzene-d6, ppm): 25.1 (t, J(PC) = 10 Hz, P-CH(CH3)2), 19.7 (s),
19.5 (s). 31P{ H} NMR (121.5 MHz, benzene-d6, ppm): 31.6 (s).
1
IR (ATR, cm-1): n (C–H) 2963, 2878, n (CH3CN) 2259, n (Re–H)
2106, n (NO) 1637.
1
24H, Ph), 2.37 (s, 18H, Ph–CH3), 1.79 (s, 3H, CH3CN); 13C{ H}
Catalytic dehydrocoupling of Me2NH·BH3 by chloro nitrosyl
Re(I) complexes. In a 3 mL Young-tap NMR tube, Me2NH·BH3
(15 mg, 0.25 mmol) and 0.0025 mmol of Re(I) chloride catalyst (2,
1.0 mg; 3a, 2.2 mg; 3b, 1.6 mg, 3c, 2.3 mg; 4a, 2.1 mg) were
mixed in 0.5 mL of dioxane or acetonitrile. The mixture was
stirred at the given temperatures (23, 45, 80, 85 ◦C) for appropriate
reaction times (2, 4, 24 h). When the reaction was carried out at
85 ◦C, bubbles of H2 were released vigorously during the reaction
and the NMR tube was vented every 30 min. After the reaction, the
yield of [Me2N–BH2]2 and other byproducts were determined by
the integration of the 11B NMR spectrum. 11B NMR (96.28 MHz,
ppm): d -14.4 (q, JBH = 96 Hz, Me2NH·BH3), 4.5 (t, JBH = 112 Hz,
[Me2N–BH2]2), 28.0 (d, JBH = 132 Hz, (Me2NH)2BH).
NMR (75.5 MHz, CD2Cl2, ppm): 140.6, 135.0, 129.2, 21.6, 3.5.
1
31P{ H} NMR (121.5 MHz, CD2Cl2, ppm): -0.96 (s). Anal. Calcd
for C44H45Cl2N2OP2Re (936.90): C, 56.41; H, 4.84; N, 2.99. Found:
C, 56.02; H, 4.43; N, 2.70.
[ReCl2(NO)(PCy3)2(g2-H2)] (4a). In a 50 mL Young-tap
Schlenk, 3a (58 mg, 0.065 mmol) was dissolved in 10 mL of
CH2Cl2. The nitrogen atmosphere was replaced with 1 bar of H2
by using a freeze–pump–thaw cycle. The mixture was stirred at
room temperature for 24 h. The resulting brown solution was
dried in vacuo and washed with toluene (1 ¥ 2 mL), dried again
in vacuo. Yield: 48 g, 85%. IR (ATR, cm-1): n (C–H): 2925, 2852, n
(NO) 1674. 1H-NMR (300.1 MHz, CD2Cl2, ppm): 2.61 (t, 2J(PH)
=
2
1
18 Hz, T1 = 39 ms, h -H2), 2.56–1.33 (m, 66H, P(C6H11)3). 13C{ H}
Dehydrogenative silylation of styrenes with silanes catalyzed by
chloro nitrosyl Re(I) complexes. In a 20 mL Young-tap Schlenk,
0.25 mmol of silane (Et3SiH, 38 mL; Me2PhSiH, 38 mL; Ph3SiH,
65 mg), 0.5 mmol of various styrenes (p-methoxystyrene, 67 mL;
p-methylstyrene, 66 mL; p-chlorostyrene, 60 mL; p-fluorostyrene,
60 mL; styrene, 57 mL; m-chlorostyrene, 63 mL; m-methylstyrene,
66 mL; o-fluorostyrene, 59 mL) and 0.0025 mmol of Re(I) chloride
catalyst (2, 1.0 mg; 3a, 2.2 mg; 3b, 1.6 mg, 3c, 2.3 mg; 4a, 2.1 mg)
were mixed in toluene-d8 (0.5 mL). The mixture was kept stir◦ring
in the closed system at the given temperatures (70, 100, 110 C).
NMR (75.5 MHz, CD2Cl2, ppm): 33.3 (t, J(PC) = 11 Hz, P–C), 29.6,
1
27.9, 26.8. 31P{ H} NMR (121.5 MHz, CD2Cl2, ppm): 14.5 (br).
Anal. Calcd for C36H68Cl2NOP2Re (865.03): C, 50.87; H, 8.06; N,
1.65; Found: C, 50.40; H, 7.56; N, 1.25.
Preparation of [ReCl2(NO)(PiPr3)2(g2-H2)] (4b). In a 3 mL
Young-tap NMR tube, 3b (13 mg, 0.02 mmol) was dissolved in
0.5 mL of CD2Cl2. The nitrogen atmosphere was replaced with 1
bar of H2 by using a freeze–pump–thaw cycle. The mixture was
kept at room temperature for 24 h. NMR spectroscopy indicated
2584 | Dalton Trans., 2011, 40, 2578–2587
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
After appropriate reaction times the yield and product distribution
were determined by 1H NMR spectroscopy according to the
characteristic chemical shifts (with typical coupling constants)
of (E)-CH CHSiR¢3, (Z)-CH CHSiR¢3, CH2 CHAr and -
CH2–CH2SiR¢3 moieties of known products. The data determined
by NMR were further verified by GC–MS and proved to be
quite reliable. The work-up procedures and spectroscopic data
of unreported products are listed below:
Hydrosilylation of ketones and aryl aldehydes with silanes
catalyzed by chloro nitrosyl Re(I) complexes. In a 3 mL Young-
tap NMR tube, 0.25 mmol of ketone (benzophenone, 45 mg;
acetophenone, 30 mL; 3,3-dimethylbutan-2-one, 31 mL; cyclopen-
tanone, 22 mL; cyclohexanone, 26 mL) or 0.25 mmol of aryl
aldehyde (p-tolualdehyde, 30 mL; 1-naphthaldehyde, 27 mL; p-
methoxybenzaldehyde, 30 mL; p-fluorobenzaldehyde, 27 mL) was
mixed with 0.28 mmol (1.1 equiv.) of silane (Et3SiH, 43 mL;
iPr3SiH, 57 mL; Ph3SiH, 73 mg) and 0.0025 mmol (1 mol% to
ketone or aryl aldehyde) of the Re(I) chloride complex (2, 1.0 mg;
3a, 2.2 mg; 3b, 1.6 mg, 3c, 2.3 mg; 4a, 2.1 mg) in chlorobenzene-d5
(0.5 mL). The mixture was kept at an appropriate temperature (23,
(E)-1-(m-methylstyryl)-2-(triethylsilyl)ethylene. In a 30 mL
Young-Schlenk tube, catalytic amount of 2 (4 mg, 0.01 mmol),
substrate Et3SiH (152 mL, 1.00 mmol) and m-methylstyrene
(264 mL, 2.00 mmol) were added. The solution was mixed in
toluene-d8 (0.8 mL) and kept stirring in the open system at
110 ◦C for 18 h. NMR spectroscopy indicated 100% conver-
sion of the starting material to the vinylsilane product. The
solvent was evaporated in vacuo and the residue was chro-
matographed on a silica gel column. Pure (E)-1-(m-methylstyryl)-
2-(triethylsilyl)ethylene was isolated (140 mg, 60%) as colorless
◦
1
80, 100, 110 C). Progress of the reaction was monitored by H
NMR spectroscopy.
Kinetic measurements. The kinetic test for 2 catalyzed dehy-
drogenative silylation was carried out in a Young–Schlenk flask
loaded with 4 mg of 2 and 1.5 mL of toluene-d8 and kept at
110 ◦C under N2. Solutions were prepared by mixing Et3SiH
and p-methylstyrene in different ratios: I (Et3SiH, 152 mL; p-
methylstyrene, 266 mL), II (Et3SiH, 152 mL; p-methylstyrene,
532 mL), III (Et3SiH, 304 mL; p-methylstyrene, 266 mL). Samples
were taken from the solution every 5 min and studied by 1H NMR
(CDCl3) to determine the ratios between reactants and products.
The kinetic test for 2 catalyzed hydrosilylation was carried out
in a Young–Schlenk flask loaded with 4 mg of 2 and 1.0 mL of
toluene-d8 and kept at 110 ◦C under N2. Solutions were prepared
by mixing Et3SiH and acetophenone in different ratios: I (Et3SiH,
86 mL; PhCOMe, 60 mL), II (Et3SiH, 86 mL; PhCOMe, 120 mL),
III (Et3SiH, 172 mL; PhCOMe, 60 mL). Samples were taken from
1
oil using 1 : 50 EtOAc/petroether mixture as eluent. H-NMR
(300.1 MHz, CDCl3, ppm): d 6.78–7.08 (m, 4H, ArH), 6.81 (d,
3
3J(HH)trans = 18 Hz, 1H, trans-Ar–CH CH), 6.36 (d, J(HH)trans
=
18 Hz, 1H, trans-CH CH–Si), 2.10 (s, 3H, Ar–CH3), 0.98
1
(t,3J = 6 Hz, 9H, CH3), 0.62 (q,3J = 6 Hz, 6H, CH2). 13C{ H}
NMR (50.3 MHz, CDCl3, ppm): d 144.9, 138.5, 138.0, 128.7,
128.4, 127.0, 125.6, 123.5, 21.4, 7.4, 3.5. GC-MS: m/z: 203.3
[M - Et]+·.
(E)-1-(m-chlorostyryl)-2-(triethylsilyl)ethylene. By a similar
procedure (Et3SiH, 152 mL; m-chlorostyrene, 252 mL; 110 ◦C,
24 h, 1 : 100 EtOAc/petroether), pure (E)-1-(m-chlorostyryl)-2-
(dimethylphenylsilyl)ethylene was isolated in 38% yield (96 mg).
1H-NMR (300.1 MHz, CDCl3, ppm): d 7.23–7.45 (m, 4H, ArH),
1
the solution every 5 min and studied by H NMR (CDCl3) to
determine the ratios between reactants and products.
3
6.84 (d, J(HH)trans = 19 Hz, 1H, trans-Ar–CH CH), 6.47 (d,
3J(HH)trans = 19 Hz, 1H, trans-CH CH–Si), 1.03 (t,3J = 6 Hz, 9H,
X-ray diffraction analyses
1
CH3), 0.72 (q,3J = 6 Hz, 6H, CH2). 13C{ H} NMR (75.4 MHz,
Relevant details about the structure refinements are given in
Table 4, and selected geometrical parameters are included in the
captions of the corresponding figures (Fig. 1 and 2). Intensity data
were collected at 183(2) K with an Oxford Xcalibur diffractometer
(4-circle kappa platform, Ruby CCD detector, and a single
CDCl3, ppm): d 143.2, 140.3, 134.5, 129.7, 128.0, 127.7, 126.2,
124.6, 7.4, 3.5. GC-MS: m/z: 223.1 [M - Et]+·.
(E)-1-(m-methylstyryl)-2-(dimethylphenylsilyl)ethylene. By
a
similar procedure (Me2PhSiH, 152 mL; m-methylstyrene, 264 mL;
110 ◦C, 24 h, 1 : 80 EtOAc/petroether), pure (E)-1-(m-
methylstyryl)-2-(dimethylphenylsilyl)ethylene was isolated in 75%
yield (192 mg). 1H-NMR (300.1 MHz, CDCl3, ppm): d 7.34–7.70
(m, 9H, ArH), 7.03 (d, 3J(HH)trans = 21 Hz, 1H, trans-Ar–CH CH),
wavelength Enhance X-ray source with MoKa radiation, l =
25
˚
0.71073 A). The selected suitable single crystals were mounted
using polybutene oil on the top of a glass fiber fixed on a go-
niometer head and immediately transferred to the diffractometer.
Pre-experiment, data collection, data reduction and analytical
absorption corrections 26 were performed with the Oxford program
suite CrysAlisPro.27 The crystal structures were solved with
3
6.68 (d, J(HH)trans = 21 Hz, 1H, trans-CH CH–Si), 2.46 (s, 3H,
1
Ar–CH3), 0.57 (s, 6H, CH3). 13C{ H} NMR (75.4 MHz, CDCl3,
ppm): d 145.5, 138.1, 134.0, 129.1, 129.0, 128.5, 127.9, 127.2, 126.8,
123.8, 21.5, -2.4. GC-MS: m/z: 252.2 [M]+·.
28
SHELXS-97 using direct methods. The structure refinements
were performed by full-matrix least-squares on F2 with SHELXL-
97.28 All programs used during the crystal structure determination
process are included in the WINGX software.29 The program
(E)-1-(o-fluorostyryl)-2-(dimethylphenylsilyl)ethylene. By
a
similar procedure (Me2PhSiH, 152 mL; o-fluorostyrene,
240 mL; 110 ◦C, 24 h, 1 : 80 EtOAc/petroether), pure (E)-1-(o-
fluorostyryl)-2-(dimethylphenylsilyl)ethylene was isolated in 47%
yield (119 mg).1H-NMR (300.1 MHz, CDCl3, ppm): d 7.15–7.65
(m, 9H, ArH), 7.25 (d, 3J(HH)trans = 19 Hz, 1H, trans-Ar–CH CH),
PLATON was used to check the result of the X-ray analyses.
30
CCDC 783380 (3a) and 783381 (3c) contain the supplementary
crystallographic data (excluding structure factors) for this paper.†
In the crystal structure of 3a, the trans-nitrosyl and chloride
ligand are substitutionally disordered over two positions with site-
occupancy factors of 0.747(3) and 0.253(3). The Checkcif report
detected additional pseudo-symmetry elements which would lead
to the space group P21/c. The Flack parameter of 0.521(6)
3
6.72 (d, J(HH)trans = 19 Hz, 1H, trans-CH CH–Si), 0.53 (s, 6H,
CH3). 13C{ H} NMR (75.4 MHz, CDCl3, ppm): d 161.9, 136.8,
1
133.9, 130.0, 129.5, 129.4, 129.2, 127.9, 126.8, 124.1, 115.9, 115.6,
-2.5. GC-MS: m/z: 241.2 [M - Me]+·.
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 2578–2587 | 2585
©

View Article Online
Table 4 Crystallographic data for compounds 3a and 3ca
3a
3c
Empirical formula
Formula weight (g mol-1)
Temperature (K)
C38H69Cl2N2OP2Re
889
183(2)
0.71073
Monoclinic, P21
9.5051(1)
16.2268(1)
13.0872(1)
90
95.074(1)
90
C44H45Cl2N2OP2Re
936.87
183(2)
˚
Wavelength (A)
0.71073
Triclinic, P1
¯
Crystal system, space group
˚
a (A)
10.8035(4)
12.5280(5)
15.6262(6)
79.631(3)
86.029(3)
75.399(3)
2012.59(14)
2, 1.546
3.268 mm
940
0.43 ¥ 0.28 ¥ 0.13
2.25 to 30.51
35 112
˚
b (A)
˚
c (A)
a (deg)
b (deg)
g (deg)
3
˚
Volume (A )
2010.63(3)
2, 1.468
3.265 mm
Z, density (calcd) (Mg m-3)
Abs coefficient (mm-1)
F(000)
916
Crystal size (mm3)
0.35 ¥ 0.25 ¥ 0.20
2.49 to 33.14
63 043
15 310/Rint = 0.031
100
Semi-empirical from equivalents
0.538 and 0.423
13 893/3/428
1.036
0.0296, 0.0635
0.0351, 0.0658
q range (deg)
Reflections collected
Reflections unique
Completeness to q (%)
Absorption correction
Max/min transmission
Data/restraints/parameters
Goodness-of-fit on F2
R1 and wR2 indices [I > 2s(I)]
R1 and wR2 indices (all data)
12 287/Rint = 0.049
99.9
0.654 and 0.369
8670/0/486
0.981
0.0345, 0.0733
0.0526, 0.0767
ꢀ
ꢀ
ꢀ
ꢀ
2
1/2
a The unweighted R-factor is R1 = (Fo - Fc)/ Fo; I > 2s(I) and the weighted R-factor is wR2 = { w(Fo - Fc2)2/ w(Fo2)2}
.
speaks also indicates a centrosymmetric space group. Nevertheless,
the solution in P21/c imposes the metal center to lie on a
crystallographic center of inversion and consequently the four
ligands in the equatorial plane (NO, 2Cl and NCCH3) to be
disordered over two positions with site-occupancy factor of 0.5.
The determination in P21 clearly shows that only the trans NO
and Cl ligands are disordered and in a ratio different than 0.5.
Furthermore, many atoms are non-positive definite in P21/c or
exhibit elongated ellipsoids. It seems to be a typical case of pseudo-
symmetry, and we consider ultimately that P21 is the best choice. In
the crystal structure of 3c, the trans-nitrosyl and chloride ligands
are also substitutionally disordered over two positions with site-
occupancy factors of 0.501(1) and 0.499(1). No classical hydrogen
bonding was found in both crystal structures.
4 (a) M. A. Brook, Silicon in Organic, Organometallic and Polymer
Chemistry, John Wiley and Sons, New York, 2000; (b) B. Marciniec,
Comprehensive Handbook on Hydrosilylation, Pergamon, Oxford, 1992,
ch. 2; (c) S. Diez-Gonzalez and S. P. Nolan, Acc. Chem. Res., 2008, 41,
349–358; (d) D. V. Gutsulyak, S. F. Vyboishchikov and G. I. Nikonov,
J. Am. Chem. Soc., 2010, 132, 5950.
5 (a) R. Giri, B. F. Shi, K. M. Engle, N. Maugel and J. Q. Yu, Chem.
Soc. Rev., 2009, 38, 3242–3272; (b) R. H. Crabtree, Chem. Rev., 1985,
85, 245–269; (c) R. H. Crabtree, Angew. Chem., Int. Ed. Engl., 1993,
32, 789–805; (d) A. E. Shilov and G. B. Shul’pin, Chem. Rev., 1997, 97,
2879–2932; (e) V. Ritleng, C. Sirlin and M. Pfeffer, Chem. Rev., 2002,
102, 1731–1769.
6 (a) C. W. Hamilton, R. T. Baker, A. Staubitz and I. Manners, Chem.
Soc. Rev., 2009, 38, 279–293; (b) F. H. Stephens, V. Pons and R. T. Baker,
Dalton Trans., 2007, 2613–2626; (c) T. B. Marder, Angew. Chem., Int.
Ed., 2007, 46, 8116–8118.
7 G. Alcaraz, L. Vendier, E. Clot and S. Sabo-Etienne, Angew. Chem.,
Int. Ed., 2009, 49, 918–920.
8 (a) T. C. Flood, J. K. Lim, M. A. Deming and W. Keung,
Organometallics, 2000, 19, 1166–1174; (b) M. A. Dewey and J. A.
Gladysz, Organometallics, 1990, 9, 1351–1353; (c) H. E. Bryndza and
W. Ta m , Chem. Rev., 1988, 88, 1163–1188; (d) N. M. Doherty and N. W.
Hoffman, Chem. Rev., 1991, 91, 553–573.
9 H. Berke and P. Burger, Comments Inorg. Chem., 1994, 16, 279–312.
10 (a) H. Jacobsen, H. W. Schmalle, A. Messmer and H. Berke, Inorg.
Chim. Acta, 2000, 306, 153–159; (b) D. Gusev, A. Llamazares, G. Artus,
H. Jacobsen and H. Berke, Organometallics, 1999, 18, 75–89; (c) Y. F.
Jiang, O. Blacque, T. Fox, C. M. Frech and H. Berke, Organometallics,
2009, 28, 4670–4680; (d) A. Choualeb, O. Blacque, H. W. Schmalle, T.
Fox, T. Hiltebrand and H. Berke, Eur. J. Inorg. Chem., 2007, 5246–5261.
11 (a) A. Choualeb, E. Maccaroni, O. Blacque, H. W. Schmalle and H.
Berke, Organometallics, 2008, 27, 3474–3481; (b) Y. F. Jiang, O. Blacque,
T. Fox, C. M. Frech and H. Berke, Organometallics, 2009, 28, 5493–
5504.
Acknowledgements
Financial support from the Swiss National Science Foundation,
Lanxess AG and the Funds of the University of Zu¨rich are
gratefully acknowledged.
References
1 (a) G. J. Kubas, Chem. Rev., 2007, 107, 4152–4205; (b) G. J. Kubas,
in Advances in Inorganic Chemistry – Including Bioinorganic Studies,
Vol. 56, Elsevier Academic Press Inc., San Diego, 2004, pp. 127–177;
(c) D. M. Heinekey, A. Lledos and J. M. Lluch, Chem. Soc. Rev., 2004,
33, 175–182; (d) D. M. Heinekey and W. J. Oldham, Chem. Rev., 1993,
93, 913–926; (e) R. H. Crabtree, Acc. Chem. Res., 1990, 23, 95–101.
2 H. Berke, ChemPhysChem, 2010, 11, 1837–1849.
3 (a) G. Alcaraz, M. Grellier and S. Sabo-Etienne, Acc. Chem. Res., 2009,
42, 1640–1649; (b) K. K. Pandey, Coord. Chem. Rev., 2009, 253, 37–55;
(c) Z. Y. Lin, in Contemporary Metal Boron Chemistry I: Borylenes,
Boryls, Borane, Springer-Verlag, Berlin, 2008, pp. 123–148.
12 (a) Y. Jiang and H. Berke, Chem. Commun., 2007, 3571–3573; (b) Y. F.
Jiang, O. Blacque, T. Fox, C. M. Frech and H. Berke, Chem. Eur. J.,
2009, 15, 2121–2128.
13 B. Machura, Coord. Chem. Rev., 2005, 249, 2277–2307.
14 (a) Y. Kawano, M. Uruichi, M. Shimoi, S. Taki, T. Kawaguchi, T.
Kakizawa and H. Ogino, J. Am. Chem. Soc., 2009, 131, 14946–14957;
2586 | Dalton Trans., 2011, 40, 2578–2587
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
(b) A. Friedrich, M. Drees and S. Schneider, Chem. Eur. J., 2009, 15,
10339–10342; (c) T. M. Douglas, A. B. Chaplin, A. S. Weller, X. Z.
Yang and M. B. Hall, J. Am. Chem. Soc., 2009, 131, 15440–15456;
(d) R. Dallanegra, A. B. Chaplin and A. S. Weller, Angew. Chem.,
Int. Ed., 2009, 48, 6875–6878; (e) T. M. Douglas, A. B. Chaplin and
A. S. Weller, J. Am. Chem. Soc., 2008, 130, 14432; (f) C. A. Jaska, K.
Temple, A. J. Lough and I. Manners, J. Am. Chem. Soc., 2003, 125,
9424–9434; (g) C. A. Jaska and I. Manners, J. Am. Chem. Soc., 2004,
126, 2698–2699.
20 (a) B. Marciniec and J. Gulinski, J. Organomet. Chem., 1993, 446,
15–23; (b) B. Marciniec, Hydrosilylation: A Comprehensive Review
on Recent Advances (Advances in Silicon Science), Springer Verlag,
2009.
21 B. Marciniec, Coord. Chem. Rev., 2005, 249, 2374–2390.
22 (a) S. Sabo-Etienne and B. Chaudret, Coord. Chem. Rev., 1998,
178, 381–407; (b) M. L. Christ, S. Saboetienne and B. Chaudret,
Organometallics, 1995, 14, 1082–1084; (c) Y. Seki, K. Takeshita, K.
Kawamoto, S. Murai and N. Sonoda, J. Org. Chem., 1986, 51, 3890–
3895.
23 I. Ojima, T. Kogure, M. Kumagai, S. Horiuchi and T. Sato,
J. Organomet. Chem., 1976, 122, 83–97.
24 (a) R. Sebastian and O. Martin, Angew. Chem., Int. Ed., 2008, 47,
5997–6000; (b) G. Z. Zheng and T. H. Chan, Organometallics, 1995,
14, 70–79; (c) D. J. Parks and W. E. Piers, J. Am. Chem. Soc., 1996,
118, 9440–9441; (d) D. J. Parks, J. M. Blackwell and W. E. Piers, J. Org.
Chem., 2000, 65, 3090–3098.
15 (a) F. Kakiuchi, Y. Tanaka, N. Chatani and S. Murai, J. Organomet.
Chem., 1993, 456, 45–47; (b) Y. Seki, K. Takeshita, K. Kawamoto, S.
Murai and N. Sonoda, J. Org. Chem., 1986, 51, 3890–3895; (c) M. L.
Christ, S. Sabo-Etienne and B. Chaudret, Organometallics, 1995, 14,
1082–1084; (d) R. Takeuchi and H. Yasue, Organometallics, 1996, 15,
2098–2102; (e) A. M. LaPointe, F. C. Rix and M. Brookhart, J. Am.
Chem. Soc., 1997, 119, 906–917.
16 Y. F. Jiang, O. Blacque, T. Fox, C. M. Frech and H. Berke, Chem. Eur. J.,
2010, 16, 2240–2249.
25 Xcalibur CCD System, Oxford Diffraction Ltd, Abingdon, UK,
2007.
17 H. L. Dong and H. Berke, Adv. Synth. Catal., 2009, 351, 1783–1788.
18 (a) J. D. Atwood and T. L. Brown, J. Am. Chem. Soc., 1976, 98, 3160–
3166; (b) S. A. Macgregor and D. MacQueen, Inorg. Chem., 1999, 38,
4868–4876; (c) A. Kovacs and G. Frenking, Organometallics, 2001, 20,
2510–2524; (d) J. K. Shen and F. Basolo, Russ. Chem. Bull., 1994, 43,
1451–1456.
19 (a) D. Giusto and G. Cova, Gazz. Chim. Ital., 1972, 102, 265; (b) G.
Ciani, D. Giusto, M. Manassero and M. Sansoni, Gazz. Chim. Ital.,
1977, 107, 429–430.
26 R. C. Clark and J. S. Reid, Acta Crystallogr., Sect. A: Found.
Crystallogr., 1995, A51, 887–897.
27 CrysAlisPro (version 1.171.32.4), Oxford Diffraction Ltd, Abingdon,
UK.
28 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2008,
64, 112–122.
29 L. J. Farrugia, J. Appl. Crystallogr., 1999, 32, 837.
30 A. L. Spek, J. Appl. Crystallogr., 2003, 36, 7–13.
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 2578–2587 | 2587
©