First study of rhodium(I) complexes with chiral sulfur-containing terpenoids as catalytic systems for ketone hydrosilylation

Article abstract of DOI:10.1080/10426507.2019.1700376

Using a “chiral pool” approach, a number of chiral thiolate and sulfide ligands based on natural terpenes and terpenoids have been synthesized in a few simple steps. Two new Rh-thiolate complexes with the formula [Rh(CO)₂(μ-SR)]₂ were obtained. The influence of these complexes and catalytic systems formed by combining the synthesized ligands with [Rh(CO)₂(μ-Cl)]₂ and [Rh(cod)(μ-Cl)]₂, on the reaction rate, chemoselectivity, stereoselectivity and formation of tetraphenyldisiloxane in Rh-catalyzed asymmetric hydrosilylation of acetophenone as a model reaction have been studied. Mechanistic aspects of formation of silyl enol ether as a side product in the presence of S-containing ligands are presented.

Full text of DOI:10.1080/10426507.2019.1700376

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: https://www.tandfonline.com/loi/gpss20
First study of rhodium(I) complexes with chiral
sulfur-containing terpenoids as catalytic systems
for ketone hydrosilylation
Vladimir M. Uvarov & Dimitry A. de Vekki
To cite this article: Vladimir M. Uvarov & Dimitry A. de Vekki (2019): First study of rhodium(I)
complexes with chiral sulfur-containing terpenoids as catalytic systems for ketone hydrosilylation,
Phosphorus, Sulfur, and Silicon and the Related Elements, DOI: 10.1080/10426507.2019.1700376
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PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
https://doi.org/10.1080/10426507.2019.1700376
First study of rhodium(I) complexes with chiral sulfur-containing
terpenoids as catalytic systems for ketone hydrosilylation
Vladimir M. Uvarov
and Dimitry A. de Vekki
Department of Chemical Technology of Polymers, St. Petersburg State Institute of Technology, St. Petersburg, Russia
ABSTRACT
ARTICLE HISTORY
Received 20 August 2019
Accepted 29 November 2019
Using a “chiral pool” approach, a number of chiral thiolate and sulfide ligands based on natural
terpenes and terpenoids have been synthesized in a few simple steps. Two new Rh-thiolate com-
plexes with the formula [Rh(CO)2(l-SR)]2 were obtained. The influence of these complexes and
catalytic systems formed by combining the synthesized ligands with [Rh(CO)2(l-Cl)]2 and
[Rh(cod)(l-Cl)]2, on the reaction rate, chemoselectivity, stereoselectivity and formation of tetraphe-
nyldisiloxane in Rh-catalyzed asymmetric hydrosilylation of acetophenone as a model reaction
have been studied. Mechanistic aspects of formation of silyl enol ether as a side product in the
presence of S-containing ligands are presented.
KEYWORDS
Hydrosilylation; sulfides;
thiols; rhodium;
terpenoids; terpenes
GRAPHICAL ABSTRACT
Introduction
simple steps starting from readily available natural chiral
compounds—mono- and bicyclic terpenes. While the major-
ity of works are dedicated to bidentate N-, S- and/or P-
ligands, there is a lack of data on hydrosilylation of ketones
in the presence of simple chiral complexes with monoden-
tate sulfur-containing organic ligands, such as thiols and sul-
fides. A few works reported the promising application of
such an approach in the conversion of prochiral ketones to
chiral alcohols including use of lithium complexes with
derivatives of nopol,[5] camphor[6,7] and aminoterpene-based
systems.[8–10] These results predetermined our selection of
terpenes for the first study in the catalytic hydrosilylation of
prochiral ketones.
Chiral alcohols are important building blocks in the synthe-
sis of various classes of organic compounds and materials.[1]
Hydrosilylation of prochiral ketones is a valuable alternative
to reduction with metal and non-metal hydrides modified
by chiral ligands, as well as to catalytic asymmetric hydro-
genation owing to a number of advantages such as mild
reaction conditions (room temperature and atmospheric
pressure), use of relatively safe reagents, high chemoselectiv-
ity and direct synthesis of silylated (protected) alcohols,
which is especially important in multi-step syntheses.[2]
However, most of the existing catalytic systems are based on
complex organic ligands requiring laborious multistep syn-
theses, which significantly increase their costs and limit
availability.[3]
There are several ways of applying catalytic systems for
hydrosilylation: use of pre-formed metal complexes with
coordinated chiral ligands, in situ addition of chiral ligands
to simple non-chiral catalytically active metal complexes or
to metal complexes already containing chiral ligands in their
In order to address this problem and improve the avail-
ability of catalytic systems we used
a “chiral pool”
approach[4] for the synthesis of chiral ligands in a few coordination sphere.[11–13] Therefore, in this work we
CONTACT Vladimir M. Uvarov
vladi.uvarov@gmail.com
Department of Chemical Technology of Polymers, St. Petersburg State Institute of Technology,
Moskovsky av. 26, St. Petersburg 190013, Russia.
Supplemental data for this article is available online at https://doi.org/10.1080/10426507.2019.1700376.
ß 2019 Taylor & Francis Group, LLC

2
V. M. UVAROV AND D. A. DE VEKKI
Ph3P,
H2O/Dioxane 1:4
SOCl2,
O
O
O
r.t.-75 oC, 2h
Reflux, 2h
SO2Cl
CH2
CH2
CH2
SO3H
SH
Scheme 1. Synthesis of (1S)-10-camphorthiol.
MeOH, Na
r.t., 30 min
R
SNa
R
SH
OTs
SR
R
SNa
MeOH
Reflux, 4h
R = Bn, Bu, Hex
Scheme 2. Synthesis of alkylnopyl sulfides.
synthesized a number of chiral thiolate and sulfide ligands sulfides. The solvents, DMF and DMA, were ruled out for
the same reason,[18] while the application of acetonitrile led
as well as new rhodium-based catalytic systems and studied
their efficiency in hydrosilylation of acetophenone with
diphenylsilane.
to poor conversion due to low solubility of the base.
Therefore, we developed a new one-pot protocol that is free
from coordinating high-boiling solvents. By taking advan-
tage of thiolates being more acidic and better nucleophiles
than alcohols, we converted the respective alkyl thiols into
thiolates using metallic sodium in methanol. The formed
thiolates were then reacted with nopol tosylate in the same
reaction vessel (Scheme 2). It should be noted that the reac-
tion has to be carried out under oxygen-free conditions in
order to prevent formation of disulfides and sulfones.[19]
This method readily afforded a series of (1R)-nopyl sul-
fides with overall yield of 64–67%. To the best of our know-
ledge, butyl- and hexylnopyl sulfides have not been
previously described. Butyl-, hexyl- and benzylnopyl sulfides
are abbreviated as BuSNpl, HexSNpl and BnSNpl
respectively.
Results and Discussion
Synthesis of ligands and metal complexes
The synthesis of (1S)-10-camphorthiol was performed in
two simple steps from readily available (1S)-10-camphorsul-
fonic acid as shown in Scheme 1. Chlorination of sulfonic
acid and reduction of the latter with triphenylphosphine in
aqueous 1,4-dioxane afforded the desired (1S)-10-camphor-
thiol (Scheme 1).[14]
According to the reported procedure,[14] purification of
10-camphorthiol is accomplished by column chromatog-
raphy, which could be a costly solution for larger-scale
applications. Therefore, we proposed an alternative isolation
method based on a one-pot extractive conversion of cam-
phorthiol into sodium thiolate followed by precipitation of
the product in an acidic medium. This approach allowed for
somewhat higher yield (66%) as in the case of chromatog-
The optical rotary dispersion of all three sulfides showed
almost no dependence of optical rotation angle on the alkyl
or benzyl substituents at the sulfur atom with angles being
within the range of [a]D ¼ –28.9 – –32.9j (Figure S1,
20
1
Supplemental material). Maximum rotation (absolute value)
is observed at 353 nm (ꢀ89.6j), 364 nm (ꢀ85.5j) and
376 nm (ꢀ86.5j) for (1R)-hexyl, benzyl and butylnopyl sul-
fides respectively.
raphy (60%).  NMR of the product shows two character-
istic doublets of CH2S (dH 2.81 and 2.85 ppm). Optical
rotation meets published data [a]D ¼ þ2.3j.[15] (1S)-neo-
20
menthylthiol was synthesized by the literature method[16]
from (1R)-menthol.
The 1H NMR spectra of all synthesized sulfides show
similar signals for protons of nopyl moiety, with characteris-
tic singlets of two CH3 groups (0.84 and 1.28 ppm) and a
broad singlet of the double bond ‘ (5.26 ppm). The four
protons of CH2SCH2 in butyl- and hexylnopyl sulfides are
equivalent and show a triplet at 2.50 ppm, while in benzyl-
nopyl sulfide these protons are nonequivalent (2.44, dt, 2,
The reported route of the synthesis of chiral sulfides of
nopol is based on a reaction between nopol tosylate and
benzyl thiolate in the presence of potassium hydroxide[5]
dissolved in dry DMSO. Since DMSO has a very high
coordination ability to late transition metals,[17] even trace
amounts remaining in the ligand may significantly affect the
structure of metal complexes formed from alkylnopyl CH2S, Npl, J ¼ 1.9, 7.1 Hz; 3.76 s, 2, PhCH2S).

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
3
H
+
+
S
H
S
CH
+
2
H
S
•
-RCH
-CH2=CHR'
2
R
R
m/z 61
R'
R' = Me, Pr
R =
,
Scheme 3. Formation of thiiranium cation in EI mass-spectra of alkylnopyl sulfides.
R
H C
3
CH
3
RSH
CO, DCM
r.t. 20 h
OC
OC
CO
CO
Cl
Cl
OC
OC
S
CO
O
HS
,
RSH =
Rh
Rh
Rh
Rh
CH SH
2
CO
S
R
Scheme 4. Synthesis of binuclear Rh(I) complexes with bridging thiolate ligands.
H2O, H+, 0-5 oC
CH3
H
H3C
H
H2C
O
H3C
O
O
O
[Rh] (0.025 - 1 mol%)
SiHPh2
Ph2HSi
SiHPh2
L (0 - 10 eq. Rh)
THF, 0 oC - r.t.
+
+
Ph2SiH2
+
(R)-isomer
(S)-isomer
[Rh], H2O or O2
H2O, H+, 0-5 oC
H+, H2O
polysiloxanes, silanols
(Ph2SiH)2O
CH3
HO
H3C
H
OH
H
+
(R)-isomer
(S)-isomer
Scheme 5. Hydrosilylation of acetophenone with diphenyl silane: products and side reaction.
1
Furthermore, the H NMR spectrum of benzylnopyl sulfide 28.63, 26.30, 30.07, 31.47 ppm respectively. It is noteworthy
features resonances of protons of an aromatic ring that in the case of butyl nopyl sulfide, the resonance at
a
at 7.27–7.38 ppm.
31.68 ppm overlaps ‘ signal of ‘CH2CH2S, while for hex-
The 13C NMR spectra of all the studied sulfides display
nearly identical shifts for carbon atoms of nopyl moiety.
The spectrum of benzyl nopyl sulfide contains characteristic
resonances of four nonequivalent aromatic carbon atoms
(126.93, 128.43, 128.86, 138.62 ppm), signal of benzylic pro-
ylnopyl sulfide, this atom has a resonance at 32.17 ppm. As
with the 13C spectrum of benzyl nopyl sulfide, ‘ signals of
b
‘CH2CH2S of butyl and hexylnopyl sulfides are shifted
downfield (37.12 and 37.28 ppm).
The mass spectra of alkylnopyl sulfides feature signature
tons SCH2Ph (29.37 ppm) and two carbon atoms of isotopic patterns,[20] along with molecular ion peaks (m/z
‘CH2CH2S (36.77 and 36.34 ppm). The spectra of butyl and 238, 266, 272 for butyl, hexyl and benzyl nopyl sulfides),
hexylnopyl sulfides display four and six signals of alkyl and [M þ 2]þ signals indicative of molecular ions containing
groups at 13.53, 21.86, 29.95, 31.68 ppm and 14.06, 22.59, isotope 34S. The main fragmentation path of the molecular

4
V. M. UVAROV AND D. A. DE VEKKI
SiHPh
2
Cl
Cl
Ph SiH
S(RR')
2
2
Cl
Rh
H
Rh
Rh
Rh
S(RR')
S(RR')
Cl
Ph
CH
O
3
SiHPh
2
H
H
Cl
S(RR')
Cl
Cl
S(RR')
H
Rh
H
Rh
H
H C
2
Rh
H
S(RR')
Ph
O
Ph
Ph
O
O
SiHPh
SiHPh
2
2
= solvent, ligand, vacant coordination site.
Scheme 6. Suggested mechanism of silyl ether of enol formation in the presence of sulfide ligands.
ions of alkylnopyl sulfides is the cleavage of the S-C bond diethyl ether and hexane, while they have good solubility in
THF, acetone, and dichloromethane.
from the side of the alkyl fragment leading to formation of
a NplSþ ion (m/z 181), the ion R-Sþ being characteristic for
organic sulfides.[21] Additionally, the presence of an alkyl
sulfide group in the structure is supported by the character-
istic thiiranium cation with m/z¼ 61 (Scheme 3),[21] while
this fragment is not observed for benzyl nopyl sulfide since
its formation is impossible in the presence of the benzyl
substituent. Instead, the benzyl nopyl sulfide spectrum
shows an intense peak of benzyl cation (m/z 91).
Consistent yields of alkylnopyl sulfides suggest generality
of the proposed method with regard to nopyl tosylate. By
contrast, use of myrtenol tosylate instead of nopyl did not
allow us to obtain the respective sulfides. The reaction gave
oils, which occur to be a complex mixture of products most
probably due to opening of the aliphatic cycle of the myrte-
nol moiety.
The IR spectra of the products feature a characteristic
shift of C ¼ O stretching frequencies to lower wavelength
f[Rh(CO)2(l-Cl)]2, ꢀ 2100, 2080, 2023 cmꢀ1, [Rh(CO)2(l-
SCmf)]2
ꢀ
2070, 2050, 1990, 1969 cmꢀ1; [Rh(CO)2(l-
SNmth)]2 ꢀ 2072, 2041, 2029, 2017 cmꢀ1g, which is in good
agreement with reported data for complexes with thiolate
ligands.[22] Measurement of optical rotation of the obtained
complexes was not possible due to intensive coloration of
their solutions, while circular dichroism spectroscopy was
not applicable due to the absence of chiral chromophores in
the molecule.
It should be noted that the reaction with camphorthiol,
where the SH group is bound to the terpene moiety via a
methylene “bridge”, proceeds much faster than in the case
of menthyl thiol with the SH group being directly attached
to the bulky substituent, therefore indicating that steric hin-
drance at the thiol sulfur has a negative effect on the coord-
ination of the ligand to the rhodium centre, but does not
lead to formation of detectable amounts of mono-
nuclear species.
Synthesis of metal complexes
In our earlier study[8] we reported a synthesis of mono-
nuclear carbonyl rhodium(I) complexes from [Rh(CO)2(l-
Cl)]2 and aminoterpenes. Unlike the reaction with amines,
interaction of [Rh(CO)2(l-Cl)]2 with organic thiols affords
binuclear bridge rhodium(I) complexes of general formula
[Rh(CO)2(l-SR)]2 (Scheme 4).
The addition of (1S)-10-camphorthiol (CmfSH) to
[Rh(CO)2(l-Cl)]2 in dichloromethane in a CO atmosphere
at the room temperature leads to a change in solution color
from pale-yellow to orange within a few minutes. The com-
plex was easily isolated in quantitative yield by removing the
solvent under vacuum. A reaction of (1S)-neomenthylthiol
(NmthSH) with [Rh(CO)2(l-Cl)]2 under these conditions
gave a red-brown oil, which crystallized after several weeks
forming a red powder with metallic shine (38% yield). The
Interestingly, no reaction took place in our attempt to pre-
pare platinum complexes with camphor, menthyl, benzyl,
hexyl or butyl nopylthiol starting from trans-[Pt(Py)2Cl2].
Reaction of cis-[Pt(Me2SO)2Cl2] with the listed thiols in
dichloromethane at the room temperature proceeded with
dissolution of the starting metal complex to give oils. Isolation
of respective products by standard means (trituration with
different solvents, chromatography, and freeze-thaw tech-
1
nique) was not successful. All the  NMR spectra show sig-
nals of both coordinated (3.54 ppm) and free (2.62 ppm)
dimethyl sulfoxide (ratio of integrals 1.2 ꢁ 1.4), which con-
firms the expected substitution of dimethyl sulfoxide ligand
with thiol rather than chlorine anion. However, signals of ter-
pene and aliphatic moieties of the respective thiols in the spec-
complexes are poorly soluble in non-polar solvents such as tra show a complex mixture of several species.

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
5
the catalytic system (Table 1, entry 5) and improves the
selectivity (Table 1, entry 5). Surprisingly, the carbonyl com-
plexes with preliminary coordinated camphor and neomen-
thylthiols show very different catalytic activity, but
comparable selectivity (Table 1, entries 6, 7). While
[Rh(CO)2(l-SNmth)]2 demonstrated good catalytic activity,
[Rh(CO)2(l-SCmf)]2 occurred to be even less active than
the catalytic system formed in situ with 10 eq. of camphor-
thiol. The observed difference may indicate a different
nature of the true catalyst. This hypothesis is also supported
by the fact that the chemoselectivity increases for
[Rh(CO)2(l-Cl)]2 þ 10 CmfSH, in contrast to [Rh(cod)(l-
Cl)]2 þ CmfSH and pre-synthesized rhodium carbonyl com-
plexes (see the mechanism discussion below).
The highest enantioselectivity is achieved in the presence
of [Rh(cod)(l-Cl)]2 and 2.1 eq. of camphorthiol with 1-(R)-
phenylethanol being the major product (17% ee) (Table 1,
entry 2). The increase of the thiol amount to 10 eq. does
not improve the stereoselectivity, while the use of
[Rh(CO)2(l-Cl)]2 and camphorthiol in situ or preformed
[Rh(CO)2(l-SCmf)]2 gave only a racemic mixture (Table 1,
entries 5, 6). At the same time, [Rh(CO)2(l-SNmth)]2
afforded 1-(R)-phenylethanol with an enantiomeric excess of
10% ee. Despite the low stereoselectivity, the obtained data
show the principle possibility of asymmetric induction with
terpene-based thiolate ligands.
Catalytic hydrosilylation
Model reaction
Hydrosilylation of acetophenone with diphenylsilane is con-
ventionally used as a model reaction for the estimation of
the catalytic properties of ketone hydrosilylation systems.[23]
The reaction yields silyl ether of 1-phenylethanol, which can
be easily hydrolyzed to the respective alcohol (Scheme 5). At
the same time the reaction can lead to the formation of silyl
ether of enol that regenerates acetophenone upon hydrolysis.
In earlier work we showed[8] that the main by-process
during catalytic hydrosilylation is conversion of diphenyl
silane into 1,1,3,3-tetraphenyldisiloxane giving higher
molecular weight phenyl siloxanes during hydrolysis of the
reaction mixture.
Therefore, in this work the efficiency of hydrosilylation
catalytic systems is compared with regard to the conversion
of acetophenone (activity), selectivity of formation of silyl
ether of 1-phenylethnol (chemoselectivity), yield of 1,1,3,3-
tetraphenyldisiloxane (selectivity towards hydrosilylation)
and
enantiomeric
excess
of
1-phenylethanol
(enantioselectivity).
Hydrosilylation in the presence of thiols
Hydrosilylation of acetophenone with diphenylsilane in the
presence of [Rh(cod)(l-Cl)]2 and (1S)-10-camphorthiol in
the ratio of 1:2.1 proceeds readily—100% ketone conversion
is achieved in less than 2 h, which is comparable to the
Hydrosilylation in the presence of alkylnopyl sulfides
activity of [Rh(cod)(l-Cl)]2 itself (Table 1, entries 1, 2).[24] First we investigated the influence of a precatalyst and hex-
The increase of the camphorthiol amount to 10 eq. leads to ylnopyl sulfide concentration at 20 and 0j C on the aceto-
a substantial decrease of both the reaction rate and selectiv- phenone conversion and reaction selectivity to establish the
ity (Table 1, entries 1–3). The use of [Rh(CO)2(l-Cl)]2 conditions, which could reveal the differences between the
instead of [Rh(cod)(l-Cl)]2 slightly increases the activity of studied alkylnopyl sulfides. Hydrosilylation of acetophenone
Table 1. Hydrosilylation of acetophenone with diphenylsilane in the presence of thiolsa.
Entry
Rh Cat.
L
L eq.
Time (h)
Conv.b (%)
Selectiv.b (%)
eec (%)
1
2
3
4
5
6
7
[Rh(cod)(l-Cl)]2
[Rh(cod)(l-Cl)]2
[Rh(cod)(l-Cl)]2
[Rh(CO)2(l-Cl)]2
[Rh(CO)2(l-Cl)]2
[Rh(CO)2(l-SCmf)]2
[Rh(CO)2(l-SNmth)]2
–
CmfSH
CmfSH
–
CmfSH
–
–
2.1
10
–
10
–
1
<2
77
1
51
90
1
95
100
75
81
85
90
90
80
64
39
70
89
44
48
–
17 (R)
11 (R)
–
0
0
–
–
10 (R)
aReaction conditions: AcPh : Ph2SiH2 : THF ¼ 1 : 1.25 : 1.4, CRh 1 mol%, 0 ꢂC.
bDetermined by H NMR by the Si-H signals of silyl ethers of 1-phenylethanol and enol (see experimental part).
1
cDetermined by H NMR after esterification with (S)-(þ)-a-methoxy-a-trifluoromethylphenylacetyl chloride (see experimental part).
1
Figure 1. Acetophenone conversion in the presence of [Rh(cod)(l-Cl)]2 and hexylnopyl sulfide: a) CRh 0.05 mol%, 20 j‘, 1—no sulfide; 2—1:2.1; 3—1:10; 4—1:5 b)
CRh 0.025 mol%, 20 j‘, 1—no sulfide; 2—1:10.1; 3—1:2.1; 4—1:50 c) CRh 0.1 mol%, 0 j‘, 1—no sulfide; 2—1:2.1; 3—1:10.

6
V. M. UVAROV AND D. A. DE VEKKI
Figure 2. Chemoselectivity of hydrosilylation in the presence of [Rh(cod)(l-Cl)]2 and hexylnopyl sulfides: a) CRh 0.05 mol%, 20 j‘, 1—no sulfide; 2—1:10; 3—1:2.1;
4—1:5; b) CRh 0.025 mol%, 20 j‘, 1—1:10; 2—1:2.1; 3—no sulfide; 4—1:50 c) CRh 0.1 mol%, 0 j‘, 1—no sulfide; 2—1:2.1; 3—1:10.
Table 2. Hydrosilylation of acetophenone with diphenylsilane in the presence of hexylnopyl sulfidesa.
Conv.b (%)
Selectiv.b (%)
YieldSiOSi (%)
b
Entry
CRh, mol%.
L
L eq.
Temp.
Time (min)
1
2
3
4
5
6
7
8
0.025
0.025
0.025
0.025
0.05
0.05
0.05
0.05
0.1
–
–
2.1
10
50
–
2.1
5
10
–
2.1
10
20
20
20
20
20
20
20
20
0
180
180
240
210
180
210
120
210
240
210
210
66
60
63
37
83
82
73
82
84
81
64
76
76
80
65
74
69
55
70
84
65
48
31
42
43
23
28
18
13
16
31
22
30
HexSNpl
HexSNpl
HexSNpl
–
HexSNpl
HexSNpl
HexSNpl
–
9
10
11
0.1
0.1
HexSNpl
HexSNpl
0
0
aReaction conditions: AcPh : Ph2SiH2 : THF ¼ 1 : 1.25 : 1.4.
bDetermined by 1H NMR by the integration of Si-H signals of silyl ethers of 1-phenylethanol and enol, and Si-H signals of 1,1,3,3-tetraphenyldisiloxane (see
experimental part).
conversion and lower chemoselectivity (Figures 1b and 2b;
Table 2, entry 4).
At the lower temperature the effect of the in situ ligand
addition on the acetophenone conversion is detectable
already at 10 eq. of hexylnopyl sulfide (Figure 1c; Table 2,
entries 9–11), while the selectivity systematically decreases
with the increase in the amount of ligand (Figure 2c;
Table 2, entries 9–11).
The observed selectivity change trend is in line with the
results obtained for the thiols and opposite to the trend
observed for the amine ligands.[8] The possible reason of
this effect is discussed below.
The yield of 1,1,3,3-tetraphenyldisiloxane, which forma-
tion in the course of acetophenone hydrosilylation with
diphenylsilane was reported by us previously,[8] almost does
not depend on the temperature and [Rh(cod)(l-Cl)]2 con-
centration when no hexylnopyl sulfide is added (Table 2,
entries 1, 5, 9). However, in the presence of hexylnopyl sul-
fide its yield at the room temperature is reduced by the fac-
Figure 3. Yield of 1,1,3,3-tetraphenyldisiloxane in the presence of [Rh(cod)(l-
Cl)]2 precatalyst and alkylnopyl sulfides at 20 jC: ‘Rh: 3, 5, 6—0.05 mol%; 1, 2,
4—0.025 mol% Ratio [Rh(cod)(l-Cl)]2: alkylnopyl sulfide: 1, 5—1:2.1; 2, 6—1:10;
3—1:5; 4—1:50.
tor of 2 with the complex concentration increase from 0.025
to 0.05 mol% (Figure 3; Table 2, entries 1–8). Taking into
account the higher acetophenone conversion in the latter
case, this finding suggests that the addition of the sulfide
may facilitate hydrosilylation vs diphenylsilane transform-
ation, when a sufficient reaction rate is achieved. This trend
with diphenylsilane in the presence of alkylnopyl sulfides
proceeds with much higher rate than in the presence of
amines[24] and thiols. This allowed us to reduce the precata-
lyst concentration by 10–40 times (CRh 0.025-0.1 mol%
vs 1 mol%).
At the room temperature the addition of 2.1-10 eq. of can also be observed at the lower temperature (Table 2,
hexylnopyl sulfide to [Rh(cod)(l-Cl)]2 has almost no influ- entries 9–11), where less siloxane is formed in the presence
ence on the acetophenone conversion and reaction selectiv-
ity compared to [Rh(cod)(l-Cl)]2 alone (Figures 1a, b and
2a, b; Table 2, entries 1–3 and 5–8). However, the introduc-
of 2.1 eq. of hexylnopyl sulfide (faster reaction) or more in
the presence of 10 eq. (slower reaction).
In order to study the effect of the alkylnopyl sulfide
tion of 50-fold excess leads to the reduction of acetophenone nature on the hydrosilylation, we chose the metal complex

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
7
j
Figure 4. Acetophenone conversion in the presence of [Rh(cod)(l-Cl)]2 and alkylnopyl sulfides, CRh 0.1 mol%, 0 ‘: a) 2.1 eq. of sulfide, 1—HexSNpl; 2—BuSNpl;
3—BnSNpl b) 10 eq. of sulfide, 1—BnSNpl; 2—BuSNpl; 3—HexSNpl.
Table 3. Hydrosilylation of acetophenone with diphenylsilane in the presence of [Rh(cod)(l-Cl)]2 and alkylnopyl sulfidesa.
Entry
L
L eq.
Time (min)
Conv.b (%)
Selectiv.b (%)
YieldSiOSi (%)
eec (%)
1
2
3
4
5
6
HexSNpl
HexSNpl
BuSNpl
BuSNpl
BnSNpl
BnSNpl
2.1
10
2.1
10
2.1
10
210
210
90
90
120
210
81
64
76
64
68
85
65
48
64
43
46
62
22
30
26
25
25
29
17 (R)
18 (R)
17 (R)
20 (R)
20 (R)
22 (R)
aReaction conditions: AcPh : Ph2SiH2 : THF ¼ 1 : 1.25 : 1.4. CRh 0.1 mol%, 0 ꢂC.
1
bDetermined by H NMR by the Si-H signals of silyl ethers of 1-phenylethanol and enol, and Si-H signals of 1,1,3,3-tetraphenyldisiloxane (see experimental part).
1
cDetermined by H NMR after esterification with (S)-(þ)-a-methoxy-a-trifluoromethylphenylacetyl chloride (see experimental part).
j
Figure 5. Chemoselectivity of hydrosilylation in the presence of [Rh(cod)(l-Cl)]2 and alkylnopyl sulfides, CRh 0.1 mol%, 0 ‘: a) 2.1 eq. of sulfide, 1—HexSNpl; 2—
BuSNpl; 3—BnSNpl b) 10 eq. of sulfide, 1—BnSNpl; 2—HexSNpl; 3—BuSNpl.
concentration of 0.1 mol% and reaction temperature of 0jC, 2, 4). However, the opposite effect is observed for benzyl-
since these conditions better revealed the influence of the in nopyl sulfide: increase from 2.1 to 10 eq. leads to a faster
situ ligand addition.
reaction and more complete ketone conversion (Figure 4b;
In the presence of 2.1 eq. of alkylnopyl sulfides the con- Table 3, entries 5, 6). The activity of the catalysts formed in
version of acetophenone is comparable within the first situ with 2.1 eq. of the sulfides increases in the following
30 min of the reaction (Figure 4a). The maximum achieved order BnSNpl < BuSNpl ꢃ HexSNpl, while with 10 eq.:
conversion 81% (210 min), 76% (90 min) and 68% (120 min) HexSNpl ꢃ BuSNpl < BnSNpl.
for hexyl, butyl, and benzylnopyl sulfides respectively
(Figure 4a; Table 3, entries 1, 3, 5).
For all three sulfides the chemoselectivity follows the
same trend as the conversion: lower values are observed at
Increasing the amount of butyl- and hexylnopyl sulfides higher concentrations of hexyl and butylnopyl sulfides, while
up to 10 eq. slows down the reaction and reduces the max- the opposite is true for benzylnopyl sulfide (Figures 5a, b;
imum acetophenone conversion (Figure 4b; Table 3, entries Table 2). Accordingly, the selectivity of acetophenone

8
V. M. UVAROV AND D. A. DE VEKKI
Cl
RSH, THF, no CO
CO
CO
RS
CO
CO
CO
Cl
Cl
Rh
Rh
Rh
SR
Scheme 7. Suggested structure of trans-dithiolato mononuclear Rh complex.
Figure 6. Yield of tetraphehyldisiloxane in the presence of [Rh(cod)(l-Cl)]2 and alkylnopyl sulfides, CRh 0.1 mol%, 0 j‘: a) 2.1 eq. of sulfide, 1—BuSNpl; 2—BnSNpl;
3—HexSNpl b) 10 eq. of sulfide, 1—HexSNpl; 2—BnSNpl; 3—BuSNpl.
hydrosilylation with 2.1 eq of sulfide increases as follows: with CO, which could cause elimination of the carbonyl lig-
BnSNpl < HexSNpl ꢃ BuSNpl, whereas the reverse order is and and formation of the trans-dithiolato rhodium complex
observed for 10-fold excess: BuSNpl ꢃ HexSNpl < BnSNpl. (due to relatively high trans-influence of the thiolate
ligands).[25] This hypothesis is supported by the finding of
In general, a longer reaction time favors hydrosilylation che-
Kingston et. al.,[26] who also observed the formation of simi-
moselectivity in the presence of all the studied sulfides.
lar complexes in an atmosphere of N2.
The decrease of chemoselectivity with the increase of the
sulfide or thiol concentration, observed in most of the cases,
may be explained based on our previous study of the reac-
tion mechanism in the presence of aminoterpene,[8,24] where
we have shown that the formation of enole silyl ether takes
place via b-hydride elimination from the coordinated aceto-
phenone. Sulfides and thiols have relatively high trans-influ-
ence,[25] which facilitates dissociation of the ligand in the
trans position (e.g. solvent) with the formation of a vacant
coordination site favoring b-elimination of the hydrogen
(Scheme 6). When a sulfide excess is present, the equilib-
rium between the free and coordinated sulfide is shifted
towards the latter and the probability of vacant coordination
site formation is increased. This hypothesis is supported by
the existence of the opposite effect in the case of amine
ligands, which show lower trans-influence,[25] on the
chemoselectivity.[8,24]
We hypothesize that the unusually high chemoselectivity
observed for [Rh(CO)2Cl]2 with 10 eq. of camphorthiol
added in situ compared to preformed catalysts (Table 1),
could be caused by a different structure of the true catalyst
compared to the preformed carbonyl thiolate complex as
shown in Scheme 7.
Indeed, the synthesis of the carbonyl thiolate complexes
was performed in a CO atmosphere, which is necessary to
prevent elimination of carbonyl ligands and obtain the
The sulfide ligand concentration was observed to have a
relatively small effect on the chemoselectivity of hydrosilyla-
tion at room temperature. This could be accounted for by a
higher rate of the target reaction compared to the silyl enol
ether formation, which is evidenced, in general, by higher
absolute values of selectivity at the room temperature even at
lower catalyst concentrations (Table 2). However, more
detailed kinetic studies are required to draw a firm conclusion.
Unlike the activity of the studied catalytic systems and
chemoselectivity of hydrosilylation, the enantioselectivty was
found to be almost independent of the amount and struc-
ture of the alkylnopyl sulfides being within the range of
17–22% ee. Notably, (R)-1-phenylethanol is formed predom-
inantly in all cases.
The yield of 1,1,3,3-tetraphenyldisiloxane in the presence
of all three sulfides falls within the range of 22–30% by the
end of the reaction (Figure 6; Table 3). As can be seen in
Figure 6, the formation of 1,1,3,3-tetraphenyldisiloxane is
affected to some extent by the structure of the sulfide ligand
only in the presence of 2.1 eq.
Experimental
1
13
 and ‘ NMR were recorded with Jeol JNM-ECX400A
and Bruker WŒ-400 spectrometers operating at 400 (1), 50
bridged structure. On the other hand, the addition of cam- (13‘) and 99.35 (29Si) MHz. NMR spectra were recorded in
phorthiol as a chiral auxiliary during the hydrosilylation CDCl3 or (CD3)2SO at þ25 ꢂC. 1H and 13C chemical shifts are
experiment was done without purging the reaction vessel given in parts per million downfield from TMS. IR spectra

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
9
were recorded with Shimadzu FTIR-8400S (4000–400 cmꢀ1
)
(1S)-Camphorsulfonic acid chloride was synthesized
from 16 g (69 mmol) of (1S)-camphorsulfonic acid following
the protocol[14] with the yield of 95%. 1H NMR (CDCl3,
300 MHz): d ppm 0.91 (s, 3H), 1.13 (s, 3H), 1.40–1.53 (m,
1H), 1.72–1.81 (m, 1H), 2.00 (d, J ¼ 18.5 Hz, 1H), 2.05–2.12
(m, 1H), 2.12–2.17 (m, 1H), 2.35–2.48 (m, 2H), 3.73 (d, J ¼
14.5 Hz, 1H), 4.31 (d, J ¼ 14.5 Hz, 1H).
in KBr pellets. Elemental analysis was performed on a Leco
CHN-932 analyser. Specific optical rotation was measured
with Perkin Elmer 241MC polarimeter in quartz temperature-
controlled cuvettes (10 cm, 25 ꢂC, 589 nm). Chromatographic
analysis was performed at Agilent 6890N equipped with
Agilent 5973N (EI 70 eV) mass detector and DB Petro 100
(100 m ꢄ 0.25 mm, film 0.5 lm) capillary column under the
following conditions: injection temperature 280 j‘, split ratio
1:20, injection volume 1 lL, temperature program 100 to 290
(1S)-10-camphorthiol (CmfSH) was obtained from (1S)-
10-Camphorsulfonic acid chloride (9.5 g, 38 mmol) as
described in [14]. Upon completion of the reaction, the solv-
ent was removed under vacuum, the precipitate was dis-
solved in toluene under argon and 20% solution of NaOH
was added to the mixture. Aqueous layer was separated and
acidified with 15% HCl. Formed white precipitate was iso-
lated by filtration and dried in high vacuum to give pure
product with the yield of 66%. Mp. 63–65ꢂ‘ ꢂ (Lit.,[28]
j
j
‘ at 3 ‘/min, carrier gas—helium, interface temperature
j
1
290 ‘. The Supplemental Materials contains sample H and
13C NMR spectra of the products (Figures S2–S13,
Supplemental material).
Enantiomeric excess of 1-phenylethanol was determined
1
by  NMR after esterification with (S)-(þ)-a-methoxy-
65–66 ꢂC). [a]D ¼ þ2.3j (c 0.15, EtŽ, Lit. þ2.6 [15]). H
NMR (CDCl3, 300 MHz): d ppm 0.88 (s, 3H), 0.99 (s, 3H),
1.33–1.40 (m, 1H), 1.64–1.72 (m, 1), 1.88 (m, 1H), 1.92
(m, 1), 1.87–1.99 (m, 2H); 2.06 (m, 1), 2.30–2.33 (m,
1H), 2.34–2.36 (m, 1H), 2.81–2.86 (dd, J ¼ 14.0 Hz, 1H).
20
1
a-trifluoromethylphenylacetyl chloride according to the pro-
cedure.[27] Enantiomeric excess was calculated by the ratio
of doublets of methyl groups of the obtained diastereomers
at d 1.65 ppm [J 6.6 Hz, (S,S)-isomer] and 1.58 ppm [J

6.6 Hz, (S,R)-isomer], which corresponds to (S)- and (R)-iso-
mers of 1-phenylethanol respectively.
13C NMR (CDCl3, 50 MHz): d ppm 19.84 (‘ ‘‘3),
3
20.32 (‘ ‘‘3), 21.41 (CCH2CH2), 26.64 (CCH2CH2),
3
Methanol, diethyl ether, tetrahydrofuran, toluene, aceto-
27.06 (CH2CO), 43.30 (SCH2), 43.67 (CH2CHCH2), 47.87
(CH3C), 60.66 (SCH2C), 217.93 (CCO).
phenone,
(1S)-camphorsulfonic
acid,
(1R)-menthol,
(1R)-Nopol, 1-butanethiol, 1-hexanethiol, benzylthiol, were
purchased from Aldrich; (S)-(þ)-a-methoxy-a-trifluorome-
thylphenylacetyl chloride, diphenylsilane were purchased
from Acros; [Rh(COD)Cl]2 and [Rh(CO)2(l-Cl)]2 were pur-
chased from Fluka and used as received. All reagents were
used without further purification.
(1S)-neomenthylthiol (NmthSH) was prepared from (1R)-
menthol according to the procedure[16] with overall yield of
ꢂ
50%. [a]D ¼ þ52.8j (c 0.3, CHCl3, Lit. þ53.2 [16]). 1H NMR
20
(CDCl3, 300 MHz): 0.55–2.15 (m, 9 H); 3.45 (m, 1H)
Tosylate of (1R)-Nopol. Triethylamine (29 g, 290 mmol)
was added to (1R)-Nopol (25.7 g, 154 mmol), the mixture
was stirred for 5 min followed by the addition of tosyl chlor-
ide (33.7 g, 176 mmol). Upon the addition, the mixture was
stirred for 2 h and then acidified with 1N HCl, diluted with
diethyl ether (150 mL), and washed with water (2x100 mL).
The aqueous layer was back extracted with (2x100 mL),
combined organic layers were washed with brine, dried over
MgSO4 and concentrated under vacuum until formation of
white precipitate. The residue was treated with hexane
(100 mL) and solid was filtered-off, rinsed with hexane
(100 mL), collected and dried in vacuum to give 35.5 g
(72%) of product, which was used without further purifica-
General procedure of hydrosilylation
The hydrosilylation of acetophenone with diphenylsilane
was carried out in an anhydrous tetrahydrofuran with molar
ratio acetophenone: Ph2SiH2: THF ¼ 1: 1.25: 1.4. The reac-
tion vessel was charged with a desired amount of a metal
complex (0.025–1 mol%), tetrahydrofuran and chiral ligand
(0–50 eq. with respect to metal complex), and the mixture
was stirred for 15 min at the room temperature followed by
addition of acetophenone. The mixture was then cooled
down to 0–5 ꢂC and diphenylsilane was added in two equal
portions over 10 min. The reaction progress was monitored
1
tion. H NMR (CDCl3, 300 MHz): d ppm 0.76 (s, 3H), 1.07
(d, J ¼ 8.8 Hz, 1), 1.23 (s, 3H), 1.93 (m, 1H), 2.05 (m,
1H), 2.12–2.24 (m, 2H), 2.24–2.33 (m, 3H), 2.45 (s, 3H),
4.02 (t, J ¼ 7 Hz, 2H), 5.23 (s, 1H), 7.34 (d, J ¼ 8.1 Hz, 2H),
7.78 (d, J ¼ 8.1 Hz, 2H).
1
by H NMR (CDCl3, d, ppm): silyl ether of 1-phenylethanol:
1.53 d (3H, CH3, J 6.63 Hz) 5.02 q (1H, CH, J 6.38 Hz),
5.44 s (1H, SiH); 7.30–8.00 m (10H, Ph); silyl ether of enol:
4.55 d (1H, CH2, J 2.20 Hz), 4.96 d (1H, CH2, J 2.13 Hz),
(1R)-Butylnopyl sulfide (BuSNpl). To 18 mL of methanol
under argon was added 1.5 g (0.065 mol) of sodium and
6.2 g (0.068 mol) mol of butylthiol. The reaction mixture was
stirred for 30 min followed by addition of 18.9 g (0.059 mol)
of nopyl tosylate. The resulting solution was refluxed for 4 h.
Upon completion, the reaction was quenched with 30 mL of
water and the product extracted with diethyl ether (3 x
50 mL). Organic phase was dried with MgSO4, and concen-
5.76 s (1H, SiH), 7.30–8.00
m
(10H, Ph); 1,1,3,3-
Tetraphenyldisiloxane: 5.63 s (2H, SiH); 7.33 m (12H, Ph);
7.55 m (8H, Ph), 29Si (CDCl3, d, ppm): –19.21 s. Isolation of
1-phenylethanol for enantiomeric excess determination was
done by addition of 1 mL of methanol and, after 1 h, 5 mL
of 1N solution of HCl, the mixture was extracted with
diethyl ether, the extract was dried over MgSO4, passed
through a short silica column, and the solvent was removed
on a rotary evaporator. Enantiomeric composition analysis
j
trated. Vacuum distillation (Bp. 92 ‘ at 2 mm Hg) afforded
9 g (64%) of pure butylnopyl sulfide. [a]D ¼ –32.9j (c 0.2,
20
1
was carried out by H NMR as described above.
CHCl3). 1H NMR (CDCl3, 300 MHz): d ppm 0.82 (s, 3H,

10
V. M. UVAROV AND D. A. DE VEKKI
CH3CCH3); 0.91 (t, J ¼ 7.4 Hz, 3, ‘ ‘2), 1.15 (d, J ¼ (‘CHCH2CH), 36.34 (‘CH2CH2S), 36.77 (‘CH2CH2S),
3
8.1 Hz, 1, ‘CHCHHCH), 1.26 (s, 3H, CH3CCH3), 1.41 38.02 (CH3CCH3), 40.79 (C ¼ CHCH2CH), 45.68 (CCHC),
(m, 2, ‘ ‘2), 1.56 (m, 2, ‘ ‘ ‘2), 2.01 (m, 117.33 (CH2CCH), 126.93 (Ph), 128.43 (Ph), 128.86 (Ph),
3
3
2
1, CCHC), 2.07 (m, 1H, C ¼ CHCH2CH); 2.22–2.25 (m, 138.62 (Ph), 146.63 (Ph). EI-MS: m/z (Ir (%)): 274 (0.8)
2, ‘CH2CH2S), 2.23 (m, 2, C ¼ CHCH2), 2.35 (m, 1, [M þ 2]þ, 272 (18) [M]þ, 207 (12), 181 (100) [M-C7H7]þ,
147 (31), 135 (13) [C10H15]þ, 133 (8) [C10H12]þ, 121 (28),
‘CHCH2CH), 2.50 (m, 4, CH2SCH2), 5.24 (br. s., 1,
119 (13), 105 (29), 103 (8) [C4H9SCH2]þ, 93 (19) [C7H9]þ,
91 (91) [C7H7]þ, 79 (22) [C6H7]þ, 77 (15) [C6H5]þ, 65 (17)
[C5H5]þ, 55 (11) [C4H7]þ, 41 (27) [C3H5]þ, 29 (8) [C2H5]þ,
27 (4) [C2H3]þ. Anal cald. for C17H30S (266.48): C, 76.62;
H, 11.35; S, 12.03. Found: C, 76.66; H, 11.38; S, 12.76.
‘‘‘2). 13C NMR (CDCl3, 50 MHz): d ppm 13.53
(‘ ‘2), 21.05 (CH3CCH3), 21.86 (‘ ‘2), 26.15
3
3
(CH3CCH3), 29.95 (‘ ‘ ‘2), 31.11 (C ¼ CHCH2)),
3
2
31.51 (‘CHCH2CH), 31.68 (CH2CH2‘H2S), 37.12
(‘CH2CH2S), 37.85 (CH3CCH3), 40.65 (C ¼ CHCH2CH),
45.58 (CCHC), 116.99 (CH2CCH), 146.70 (‘H2CCH). EI-
MS: m/z (Ir (%)): 240 (0.3) [M þ 2]þ, 238 (6) [M]þ, 207 (2),
195 (4) [M-C3H7]þ, 181 (68) [M-C4H9]þ, 169 (19), 148 (9),
135 (45) [C10H15]þ, 133 (59) [C10H12]þ, 119 (14), 105 (100),
103 (8) [C4H9SCH2]þ, 93 (19) [C7H9]þ, 91 (32) [C7H7]þ, 79
(22) [C6H7]þ, 77 (16) [C6H5]þ, 61 (34) [C2H5S]þ, 55 (11)
[C4H7]þ, 41 (27) [C3H5]þ, 29 (11) [C2H5]þ, 27 (5) [C2H3]þ.
Anal cald. for C15H26S (238.43): C, 75.76; H, 10.99; S, 13.45.
Found: C, 75.80; H, 10.97; S, 14.05.
Bis-l-di[(1)-10-camphrothiolato]dicarbonylrhodium(I)
[Rh(CO)2(l-SCmf)]2. The flask equipped with a capillary
was charged with 5 mL of DCM and the solvent was satu-
rated with freshly generated CO (H2SO4 þ formic acid) for
15 min. Then 79.8 mg (0.205 mmol) of [Rh(CO)2Cl]2 was
added and CO was bubbled for another 20 min followed by
addition of 75.65 mg (0.41 mmol) of (1S)-10-camphorthiol
(the red solution almost immediately turned yellow-orange).
The mixture was stirred for 50 min at r.t. with constant flow
of CO. Removal of solvent and volatiles under vacuum
(1R)-Hexylnopyl sulfide (HexSNpl). Reaction was carried
out as described for butylnopyl sulfide. Vacuum distillation
(Bp. 116 j‘ at 2 mm Hg) afforded 10.2 g (65%) of pure hexyl-
20
afforded ꢂ126.8 mg (90%) of orange-brown complex. [a]D
1
¼ þ54.5 (c 0.0067, CHCl3). Mp. ¼ 135 ꢂC (decomp.). H
nopyl sulfide. [a]D ¼ –28.9j (c 0.3, CHCl3). 1H NMR
20
NMR (CDCl3, 300 MHz): d ppm 0.86 (s, 3H, ‘ ‘‘3),
3
1.03 (s, 3H, ‘ ‘‘3), 1.34–1.40 (m, 1H, CCHHCH2),
(CDCl3, 300 MHz): d ppm 0.84 (s, 3H, CH3CCH3); 0.88 (t, J
3
1.55–1.62 (m, 1, CCH2CCHH), 1.83 (d, J ¼ 18.4 Hz, 1H,
CHHCO), 1.92–2.05 (m, 2, CCHHCHH), 2.19–2.26 (m,
1H, CH2CHCH2); 2.32 (d, J ¼ 18.4 Hz, 1H, CCHHCO), 3.10
(d, J ¼ 14.0, 1H, SCHH), 3.48 (d, J ¼ 14.0, 1H, SCHH). 13C
¼ 6.6 Hz, 3, ‘ ‘2), 1.16 (d, J ¼ 8.1 Hz, 1,
3
‘CHCH2CH), 1.28 (s, 3H, CH3CCH3), 1.37 (m, 2, ‘
3
‘2), 1.56 (m, 2, ‘ ‘ ‘2), 1.99 (m, 1, CCHC), 2.06
3
2
(m, 1H, C ¼ CHCH2CH), 2.19–2.22 (m, 2, ‘CH2CH2S),
2.23 (m, 2, C ¼ CHCH2), 2.35 (m, 1, ‘CHCH2CH), 2.52
(m, 4, CH2SCH2), 5.26 (br. s., 1, ‘‘‘2). 13C NMR
NMR (CDCl3, 50 MHz): d ppm 20.07 (‘ ‘‘3), 20.50
3
(‘ ‘‘3), 25.65 (CCH2CH2), 26.83 (CH2CO), 33.30
3
(CCH2CH2), 42.90 (SCH2), 43.43 (CH2CHCH2), 48.10
(CH3C), 61.90 (SCH2C), 184.09, 185.5 (RhCO), 215.77
(CCO). IR, cmꢀ1: 2954, 2923, 2887 (ꢀ ‘-); 2070, 2050,
2014, 1990, 1969 (ꢀ ‘-Ž); 1743; 1657, 1601, 1514, 1453,
1415, 1390, 1320, 1244, 1061, 1043, 1023, 961, 815 (d ‘-H);
576; 511; 488. Anal Cald. for C24H30O6Rh2S2 (684.43): C,
42.12; H, 4.42; S, 9.37. Found: C, 42.17; H, 4.44; S, 11.12.
Bis-l-di[(1)-neomenthylthiolato]dicarbonylrhodium(I)
[Rh(CO)2(l-SNmth)]2. The flask equipped with a capillary
was charged with 4 mL of DCM and the solvent was saturated
with freshly generated CO (H2SO4 þ formic acid) for 15 min.
Then 28.2 mg (0.072 mmol) of [Rh(CO)2Cl]2 was added and
CO was bubbled for another 20 min followed by addition of
25 mg (0.145 mmol) of (1S)-neomenthylthiol (the red solution
gradually turned red-orange). The mixture was stirred for 20h
at r.t. with constant flow of CO. Removal of solvent and vola-
tiles under vacuum afforded 19 mg (38%) of orange-brown
oil, which crystallized upon standing. Mp. ¼ 166–168 ꢂC. IR,
cmꢀ1: 2949, 2922, 2867, 2840 (ꢀ ‘-); 2072, 2029, 2017 (ꢀ
‘-Ž); 1836; 1454, 1378, 1366, 1279, 1260, 1089, 1026, 1017 (d
‘-H); 805. Anal Cald. for C24H38O4Rh2S2 (660.49): C, 42.73;
H, 5.61; S, 9.92. Found: C, 42.78; H, 5.63; S, 11.35.
(CDCl3, 50 MHz):
(CH3CCH3), 22.59 (‘ ‘2), 26.30 (CH3CCH3), 28.63
d
ppm 14.06 (‘ ‘2), 21.22
3
3
(‘ ‘ ‘2), 29.67 (‘ ‘ ‘ ‘2), 30.07 (S‘
2
3
2
3
2
2
‘ ‘2), 31.25 (C ¼ CHCH2), 31.47 (S‘ ‘ ‘2), 31.50
2
2
2
(‘CHCH2CH), 32.17 (‘CH2CH2S), 37.28 (‘CH2CH2S),
37.99 (CH3CCH3), 40.77 (C ¼ CHCH2 CH), 45.69 (CCHC),
117.14 (CH2CCH), 146.81 (‘H2CCH). EI-MS: m/z (Ir (%)):
268 (0.5) [M þ 2]þ, 266 (9) [M]þ, 207 (2), 198 (23) [M-
C5H8]þ, 181 (87) [M-C6H13]þ, 148 (17), 135 (58) [C10H15]þ,
133 (67) [C10H12]þ, 131 (8) [C6H13SCH2]þ, 119 (16), 105
(100), 93 (21) [C7H9]þ, 91 (32) [C7H7]þ, 79 (22) [C6H7]þ, 77
(16) [C6H5]þ, 61 (23) [C2H5S]þ, 55 (23) [C4H7]þ, 43 (31)
[C3H7]þ, 41 (30) [C3H5]þ, 29 (7) [C2H5]þ, 27 (5) [C2H3]þ.
Anal cald. for C18H24S (272.44): C, 79.35; H, 8.88; S, 11.77.
Found: C, 79.40; H, 8.85; S, 12.34.
(1R)-Benzylnopyl sulfide (BnSNpl). Reaction was carried
out as described for butylnopyl sulfide. Vacuum distillation
j
(Bp. 140 ‘ at 2 mm Hg) afforded 10.8 g (67%) of pure hex-
ylnopyl sulfide. [a]D ¼ –29.5j (c 0.6, CHCl3). 1H NMR
20
(CDCl3, 300 MHz): d ppm 0.86 (s, 3H, CH3CCH3), 1.18 (d,
J ¼ 8.1 Hz, 1, ‘CHCH2CH), 1.30 (s, 3H, CH3CCH3), 2.00
(m, 1, CCHC), 2.07 (m, 1H, C ¼ CHCH2CH), 2.19–2.23
(m, 2, ‘CH2CH2S), 2.35 (m, 1, ‘CHCH2CH), 2.44 (d.t.,
J ¼ 1.9, 7.1 Hz, 2, CH2S, Npl), 3.76 (s, 2, PhCH2S), 5.26
(br. s., 1, ‘‘‘2), 7.27–7.38 (m, 5H, Ph). 13C NMR
Conclusions
(CDCl3, 50 MHz):
d
ppm 21.27 (CH3CCH3), 26.34 In summary, we have shown the first example of catalytic
(CH3CCH3), 29.37 (SCH2Ph), 31.30 (C ¼ CHCH2), 31.69 systems for hydrosilylation of ketones based on rhodium

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
11
Rus. J. Gen. Chem. 2010, 80, 35–46. DOI: 10.1134/
S107036321001007X.
complexes with monodentate chiral sulfide and thiolate
ligands readily available in a few simple synthetic steps from
naturally occurring chiral substrates (i.e. no need for asym-
metric synthesis). Unfortunately, the thiolate-based rhodium
carbonyl complexes [Rh(CO)2(l-SR)]2 showed low chemo-
and enantioselectivity despite good catalytic activity. On the
other hand, catalysts based on [Rh(cod)(l-Cl)]2 and nopyl
sulfides provide to be more efficient. Among the studied
systems [Rh(cod)(l-Cl)]2 with 2.1 eq. of butylnopyl sulfide
or 10 eq. of benzylnopyl sulfide showed the best results.
Despite modest enantioselectivities obtained in these first
experiments, we have shown that the addition in situ of the
nopylsulfide ligands as chiral auxiliaries under proper condi-
tions does not impair catalytic properties of [Rh(cod)(l-
Cl)]2 and, at the same time, provides asymmetric induction,
which makes the suggested approach a promising candidate
for the development of active and simple catalytic systems.
[9] de Vekki, D. A.; Uvarov, V. M.; Reznikov, A. N.; Skvortsov,
N. K. Synthesis of Platinum Complexes Containing (þ)-bornyl
and (–)-menthylammonium in the Outer Coordination Sphere
and their Catalytic Activity in Hydrosilylation Reactions. Rus.
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008-0054-3.
[10] Borovinskaya, E. S.; Uvarov, V. M.; Schael, F.; de Vekki, D. A.;
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Vladimir M. Uvarov
http://orcid.org/0000-0002-0470-3278
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