Atom transfer radical addition (ATRA) of carbon tetrachloride and chlorinated esters to various olefins catalyzed by Cp′Ru(PPh 3)(PR3)Cl complexes

Article abstract of DOI:10.1016/j.ica.2011.11.008

C^pRu(PPh₃)(PR₃)Cl complexes, where PR ₃ = PMe₃, PPh₃, or PTA (PTA = 1,3,5-triaza-7-phosphaadamantane), were used to catalyze the atom transfer radical addition of chlorinated esters (CCl

Full text of DOI:10.1016/j.ica.2011.11.008

Inorganica Chimica Acta 380 (2012) 96–103
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Atom transfer radical addition (ATRA) of carbon tetrachloride and chlorinated
esters to various olefins catalyzed by Cp0Ru(PPh3)(PR3)Cl complexes
1
⇑
Radhika P. Nair , Jocelyn A. Pineda-Lanorio, Brian J. Frost
Department of Chemistry, University of Nevada, Reno, NV 89557-0216, United States
a r t i c l e i n f o
a b s t r a c t
Cp⁄Ru(PPh3)(PR3)Cl complexes, where PR3 = PMe3, PPh3, or PTA (PTA = 1,3,5-triaza-7-phosphaadaman-
tane), were used to catalyze the atom transfer radical addition of chlorinated esters (CCl3CO2Et,
CH2ClCO2Et) to styrene, and that of CCl4 to a variety of olefins. The monoadducts were obtained in mod-
erate to excellent yields. Moreover, high selectivities were obtained for the addition of CCl4 to internal
olefins. The activity of Cp⁄Ru(PTA)(PPh3)Cl and Cp⁄Ru(PTA)(PMe3)Cl were comparable to that of the
highly efficient ATRA catalyst, Cp⁄Ru(PPh3)2Cl. The addition of CCl3CO2Et to styrene catalyzed by
Cp0Ru(PPh3)(PR3)Cl (Cp0 = Dp, Ind, Cp, Tp) are also reported here. Two new compounds, 3-chloro-3-phe-
nyl-2-(trichloromethyl)-1-phenylpropan-1-one and 1,3,3,3-tetrachloro-1,2-diphenylpropane, resulting
from the addition of CCl4 to chalcone and cis-stilbene have been isolated and characterized by NMR spec-
troscopy and X-ray crystallography.
Article history:
Available online 13 November 2011
Young Investigator Award Special Issue
Keywords:
Atom transfer radical addition (ATRA)
Ruthenium(II) catalyst
Addition to olefin
Chlorinated ester
Carbon tetrachloride
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
ligands [14–16] among the most superior catalysts reported to date.
The use of 2,20-azobis(isobutyronitrile) (AIBN) in transition-metal-
The addition of halogenated compounds to olefins is one of the
fundamental reactions in organic synthesis and has gained consid-
erable attention over the years [1–5]. This simple reaction, reported
by Kharasch in 1938, is a classic example of anti-Markovnikov addi-
tion and is commonly referred to as atom transfer radical addition
(ATRA) [1]. The first successful examples of transition-metal-cata-
lyzed ATRA were the additions of CCl4 and CHCl3 to a variety of ole-
fins in the presence of iron and copper salts. Today, a variety of metal
complexes are known to catalyze ATRA reactions [4]. Amongst
them, nickel [5,6], copper [7,8], and particularly ruthenium based
systems [9–16] have displayed remarkable catalytic performance.
Intramolecular ATRA or atom transfer radical cyclization (ATRC) is
an effective tool for the synthesis of 5- or 6-membered carbocycles,
macrocyclic compounds, lactams and lactones, alkaloids, and other
functionalized ring systems [7a,17,18].
catalyzed ATRA was introduced by Severin and co-workers [15],
and has successfully been employed in ruthenium [15,16] and cop-
per [8b,c] catalyzed reactions, drastically increasing catalytic
activity.
We have recently reported the efficiency of
a series of
Cp0Ru(PR3)(PPh3)Cl complexes, where Cp0 = (
g
5-C5Me5ꢀ, Cp⁄), (g5ꢀ
-
C8H9ꢀ, Dp), ( 5-C9H7ꢀ, Ind), ( 5-C5H5ꢀ, Cp) or ( 3-HB(N2C3H3)3
g
g g ,
Tp); PR3 = 1,3,5-triaza-7-phosphaadamantane (PTA) or PMe3 to cat-
alyze various ATRA reactions in good to excellent yields [16]. Our
previous studies revealed that the electron-donating ability of the
ancillary ligand (Cp0) and the relative facility of dissociation of the
phosphine are crucial for good catalytic activity of the ruthenium
complexes. Among the series of complexes investigated, the Cp⁄
complexes Cp⁄Ru(PTA)(PPh3)Cl 1 and Cp⁄Ru(PMe3)(PPh3)Cl 2 exhib-
ited high activity, Fig. 1. We now report on the efficiency of catalytic
systems 1 and 2 for the addition of chlorinated esters to styrene, and
the addition of CCl4 to more challenging olefins in the presence of
AIBN, Scheme 1. For comparison, one of the best ruthenium cata-
lysts reported to date for ATRA [14a], Cp⁄Ru(PPh3)2Cl (3), has also
been employed under our reactions conditions.
The transition-metal-promoted ATRA emerged in the early
1970’s with the discovery of RuCl2(PPh3)3 as a highly efficient and
versatile catalyst for ATRA [19,20]. The pioneering work of Sawam-
oto in RuCl2(PPh3)3 catalyzed controlled polymerization (ATRP) pro-
vided an impetus to the development of ruthenium-based ATRA
catalysts. A variety of ruthenium complexes are known to catalyze
ATRA reactions with half-sandwich ruthenium phosphine com-
2. Experimental
plexes bearing
g g
5-carborane [13] or 5-cyclopentadienyl-based
2.1. Materials and methods
⇑
Corresponding author. Tel.: +1 775 784 1993; fax: +1 775 784 6804.
E-mail address: frost@unr.edu (B.J. Frost).
Present address: Physical Science Department, Southern Utah University, Cedar
1
All reactions were performed under a dry nitrogen atmosphere,
using conventional Schlenk vacuum-line techniques and
City, UT 84720, United States.
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.11.008

R.P. Nair et al. / Inorganica Chimica Acta 380 (2012) 96–103
97
Table 1
Crystallographic data and structural refinement for compounds 19 and 20.
19
20
Formula
Formula weight
Color
C
16H12Cl4O
C15H12Cl4
334.05
colorless
100 (2)
0.71073
orthorhombic
Pna2(1)
11.7247(2)
19.7528(3)
6.09430(10)
90
362.06
light yellow
100 (2)
0.71073
monoclinic
P2(1)/c
10.83540(10)
8.01140(10)
18.1558(2)
90
T (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Fig. 1. Ruthenium complexes used as catalyst precursors for ATRA.
a
(°)
Cl
b (°)
97.5090(10)
90
1562.53(3)
4
90
90
1 mol% Cp'Ru(PR3)(PPh3)Cl
5 mol% AIBN, 60-85oC
X
X
Cl
c
(°)
R
V (Å3)
1411.41(4)
4
1.572
R
Z
Cl
(X
= CCl4, CCl3CO2Et, CH2ClCO2Et)
Dcalc (Mg mꢀ3
)
1.539
Absorption coefficient
0.752
0.820
Scheme 1. General reaction scheme for the atom transfer radical addition (ATRA) of
X–Cl to terminal olefins catalyzed by Cp0Ru(PR3)(PPh3)Cl complexes in the presence
of AIBN (PR3 = PPh3, PMe3, or PTA).
(mmꢀ1
)
F(000)
736
680
Crystal size (mm3)
2h Range (°)
0.56 ꢁ 0.23 ꢁ 0.12
1.90–32.56
ꢀ16 6 h 6 16,
ꢀ12 6 k 6 11,
ꢀ26 6 l 6 26
22693
0.518 ꢁ 0.065 ꢁ 0.06
2.02–31.01
ꢀ17 6 h 6 16,
ꢀ28 6 k 6 28,
ꢀ8 6 l 6 8
Index ranges
glove-box. Reagents were purchased from commercial suppliers,
and used as received. Solvents were dried with molecular sieves
and degassed with N2, prior to use. Column chromatography was
performed using Silicycle silica gel (60–200 mesh). Cp0Ru(P-
Me3)(PPh3)Cl [16] (Cp0 = Cp⁄, Dp, Cp, Tp), Cp⁄Ru(PTA)(PPh3)Cl
[16], Cp⁄Ru(PPh3)2Cl [21], IndRu(PMe3)(PPh3)Cl [22], Cp0Ru(P-
TA)(PPh3)Cl [23] (Cp0 = Dp, Cp, Ind), and TpRu(PTA)(PPh3)Cl [24]
were synthesized according to literature procedures. Kharasch
addition reactions were carried out under nitrogen in standard
NMR tube or in J-Young tube. Each catalytic run was repeated at
least twice to ensure reproducibility. The known Kharasch adducts
12 [12], 13 [11], 14 [8d], 15 [25,26], 16 [13a,14b], 17 [25], and 18
[11] were identified by comparison of their spectral data with
those reported in the literature. The new compounds 19 and 20
were isolated and fully characterized. NMR spectra were recorded
with a Varian NMR System 400 spectrometer with 1H and 13C NMR
spectra referenced to residual solvent relative to tetramethylsilane
(TMS). APPI-MS data were recorded on a Waters Micromass 20
mass spectrometer. X-ray crystallographic data was collected at
Number of reflections
collected
Number of independent 5613 (0.0247)
33086
4366 (0.0279)
4366/1/220
reflections (Rint
Number of data/
restraints/
)
5613/0/190
1.097
parameters
Goodness-of-fit (GOF)
1.064
on F2
Final R indices
[I > 2r(I)]
R indices (all data)
R1 = 0.0311,
wR2 = 0.0866
R1 = 0.0345,
wR2 = 0.0895
830022
R1 = 0.0195,
wR2 = 0.0530
R1 = 0.0200,
wR2 = 0.0534
830023
CCDC no.
styrenewasobtainedbycolumnchromatographyonsilica(10%ethyl
acetate/hexanes) yielding 12 as a clear colorless liquid in 61% yield.
2.2.2. ATRA of CCl4 to various olefins
To a 1.5 mL vial was added 1 mol% catalyst (0.0138 mmol),
5 mol% AIBN (11.3 mg, 0.069 mmol), olefin (1.38 mmol), CCl4
100( 1) K on a Bruker APEX CCD diffractometer with MoKa radia-
tion (k = 0.71073 Å) and a detector-to-crystal distance of 4.94 cm.
Data collection was optimized utilizing the APEX2 software with
(533 lL, 5.52 mmol), and hexamethylbenzene as an internal stan-
a 0.5° rotation about
x between frames, and an exposure time of
dard (5 mg, 0.031 mmol). Toluene-d8 was added to bring the total
volume to 1 mL. The resulting solution was sealed in an NMR tube
and heated to 60–85 °C in an oil-bath. The formation of product
was monitored by 1H NMR spectroscopy at predetermined intervals.
10 s per frame. Data integration, correction for Lorentz and polari-
zation effects, and final cell refinement were performed using
SAINTPLUS, and corrected for absorption using SADABS. The structures
were solved using direct methods followed by successive least
squares refinement on F2 using the SHELXTL 6.10 software package
[27]. All non-hydrogen atoms were refined anisotropically and
hydrogen atoms placed in calculated positions. Crystallographic
data and data collection parameters are listed in Table 1.
2.3. Synthesis
2.3.1. Synthesis of 3-chloro-3-phenyl-2-(trichloromethyl)-1-
phenylpropan-1-one (19)
To a Schlenk tube with Teflon seal was added Cp⁄Ru(P-
TA)(PPh3)Cl (0.0288 g, 0.0414 mmol), AIBN (0.034 g, 0.207 mmol),
chalcone (0.862 g, 4.14 mmol), CCl4 (1.6 mL, 16.56 mmol), and
1.3 mL toluene-d8. The reaction was stirred at 85 °C under nitrogen
for 48 h. The reaction mixture was cooled to room temperature and
purified by chromatography on silica gel (toluene) yielding 19 as a
pale yellow crystalline solid in 29% yield (0.44 g). 1H NMR (CDCl3,
400 MHz) of major isomer: d 4.8 (d, 1H, CHCCl3, 3JHH = 10.0 Hz); 5.2
(d, 1H, CHCl, 3JHH = 10.0 Hz); 6.5–7.0 (m, 10H, PPh3); minor isomer:
d 4.55 (d, 1H, CHCCl3, 3JHH = 8.0 Hz); 5.4 (d, 1H, CHCl, 3JHH = 8.0 Hz);
6.5–7.0 (m, 10H, Ph). 13C{1H} NMR (CDCl3, 100 MHz) major
diastereomer: 62.14 (CHCl), 66.51 (CHCCl3), 95.55 (CCl3), 128.68–
129.09 (8 Ar–C); 129.60 (1 Ar–C), 133.89 (1 Ar–C), 137.71
2.2. Catalysis
2.2.1. ATRA of CCl3CO2Et or CH2ClCO2Et to styrene
Toa1.5 mLvialwasadded1 mol%catalyst(0.0138 mmol),5 mol%
AIBN (11.3 mg, 0.069 mmol), styrene (158
l
L, 1.38 mmol),
CCl3CO2Et (230 L, 1.66 mmol) or CH2ClCO2Et (177
l
lL, 1.66 mmol),
andhexamethylbenzeneasaninternalstandard(5 mg, 0.031 mmol).
Toluene-d8 was added to bring the total volume to 1 mL. The result-
ing solution was sealed in an NMR tube and heated at 60 °C in an oil-
bath. The formation of product was monitored by 1H NMR spectros-
copy at predetermined intervals. The isolated yield for the
Cp⁄Ru(PPh3)2Cl catalyzed reaction of ethyl trichloroacetate with

98
R.P. Nair et al. / Inorganica Chimica Acta 380 (2012) 96–103
(C–CHCl), 138.10 (C–CO), 193.62 (C@O); minor diastereomer:
61.89 (CHCl), 65.18 (CHCCl3), 96.64 (CCl3), 128.90–129.15 (8 Ar–
C); 129.79 (1 Ar–C), 134.17 (1 Ar–C), 137.34 (C–CHCl), 137.63
(C–CO), 191.98 (C@O). APPI-MS: m/z Calc. 362.08. Found:
363.12% for [5ꢀH]+. M.P.: 77–85 °C. X-ray quality crystals were ob-
tained by slow evaporation of hexane solution of 19.
plexes 1 and 2 exhibited high reactivity with turnover frequencies
(TOF, defined as mol-product/mol-catalyst/h, calculated at 50–65%
conversion of styrene) of 251.6 and 132.1 hꢀ1, respectively. Contrary
to what was observed for the addition of CCl4, p-TsCl, and CHCl3 to
styrene [16], the activity of Cp⁄Ru(PTA)(PPh3)Cl 1 (TOF = 251.6 hꢀ1
)
was slightly higher than that of Cp⁄Ru(PPh3)2Cl 3 (TOF = 226 hꢀ1),
(Table 2, entries 1 and 3). Encouraged by these results, we also tested
the catalytic activity of the Dp, Cp, Ind, and Tp counterparts 4–11 (Ta-
ble 2, entries 4–12). As observed previously [16], the order of reactiv-
ity was proportional to the electron-donating ability of the ancillary
ligand Cp0, with the exception of Dp complexes 4 and 8 which were
slightly less efficient as compared to their Ind counterparts 5 and 9,
respectively, (Cp⁄ > Dp < Ind > Cp > Tp). Among the catalytic systems
(1–11) employed, the Tp-derivatives 7 and 11 were found to be the
least active with only 21–28% product formation after 24 h at 80 °C
(Table 2, entries 7 and 12). In the absence of Ru no reaction was ob-
served indicating that AIBN is not able to catalyze the reaction under
these conditions, Table 2 entry 13.
2.3.2. Synthesis of 1,3,3,3-tetrachloro-1,2-diphenylpropane (20)
To
TA)(PPh3)Cl (0.0288 g, 0.0414 mmol), AIBN (0.034 g, 0.207 mmol),
cis-stilbene (740 L, 4.14 mmol), CCl4 (1.6 mL, 16.56 mmol), and
750 L toluene-d8. The reaction was stirred at 85 °C under nitrogen
a
Schlenk flask with Teflon cap was added Cp⁄Ru(P-
l
l
for 3 days. The reaction mixture was cooled to room temperature
and purified via column chromatography (5% toluene/hexane)
yielding 20 as a pale yellow crystalline solid in 43% yield (0.6 g).
1H NMR (CDCl3, 400 MHz) major diastereomer: d 4.17 (d, 1H,
3
3
CHCCl3, JHH = 4.8 Hz); 5.91 (d, 1H, CHCl, JHH = 4.8 Hz); 7.0–7.6
(m, 10H, Ph); minor diastereomer: 4.48 (d, 1H, CHCCl3,
d
3JHH = 4.0 Hz); 5.76 (d, 1H, CHCl, JHH = 4.0 Hz); 7.0–7.6 (m, 10H,
Ph). 13C{1H} NMR (CDCl3, 100 MHz) major diastereomer: 62.29
(CHCl), 71.60 (CHCCl3), 100.90 (CCl3), 127.8–128.6 (8 Ar–C),
128.90 (1 Ar–C), 131.23 (1 Ar–C), 134.47 (C–CHCl), 140.09 (C–
CHCCl3); minor diastereomer: 62.47 (CHCl), 72.36 (CHCCl3),
101.05 (CCl3), 127.9–128.6 (8 Ar–C), 129.08 (1 Ar–C), 131.22 (1
Ar–C), 135.39 (C–CHCl), 138.98 (C–CHCCl3). APPI-MS: m/z Calc.
334.07. Found: 334.11%. M.P.: 62–70 °C. X-ray quality crystals
were obtained by slow evaporation of a hexane solution of 20.
The catalytic performance of PTA complexes was found to be
similar to that of their PMe3 analogues, except for Cp⁄Ru(P-
Me3)(PPh3)Cl (2) which displayed lower activity in comparison with
Cp⁄Ru(PTA)(PPh3)Cl (1) (Fig. 2). The Cp⁄Ru(PTA)(PPh3)Cl catalyzed
reaction obtained a 99% conversion within 80 min, as compared to
the 4 h completion time for (2). The decrease in activity was also
manifest in the lower TOF of 2 (132.1 hꢀ1) versus 1 (251.6 hꢀ1), Ta-
ble 2 entries 1 and 2. The high activity of the Cp⁄ complexes may be
related to the steric bulk and higher electron donating ability of the
Cp⁄ ancillary ligand which would stabilize the coordinatively unsat-
urated 16 eꢀ ruthenium center (Scheme 2) [16,28]. Compound 2
with the more electron donating PMe3 ligand (relative to PTA or
PPh3) may be too electron rich dropping activity slightly.
3
3. Results and discussion
3.1. Catalytic activity
As shown in Scheme 2 triphenylphosphine likely dissociates
prior to the start of catalysis. Some evidence for this dissociation
was observed in a series of kinetics plots for the addition of
CCl3CO2Et to styrene catalyzed by CpRu(PPh3)(PMe3)Cl at various
PPh3 concentrations (Fig. 3). In the absence of excess of PPh3 there
We investigated the efficiency of complexes 1–3 towards the
addition of trichloroethyl acetate to styrene (Table 2, entries 1–3).
These reactions proceeded very efficiently at 60 °C and the desired
1:1 adduct 12 was obtained in quantitative yields within 1–2 h. Com-
Table 2
Atom transfer radical addition of CCl3CO2Et to styrene catalyzed by complexes 1–11.a
Cl
1 mol% [Ru]
5 mol% AIBN
Toluene, 60-80 C
CCl CO Et
2
2
CCl CO Et
3
2
o
12
Entry
Catalyst
Temp. (°C)
Time (h)
TOFb (hꢀ1
)
Yieldc (%)
1
2
3
4
5
6
7
8
Cp⁄RuCl(PTA)(PPh3) (1)
Cp⁄RuCl(PMe3)(PPh3) (2)
Cp⁄Ru(PPh3)2Cl (3)
60
60
60
60
60
60
80
60
60
60
60
80
60
1.5
2
1.5
3.25
3.5
4
251.6
132.1
226.0
40.6
61.6
34.7
–
51.7
54.5
38.6
14.8
–
99
98
98 (61)
98
99
98
21
98
99
99
59
28
–
DpRuCl(PTA)(PPh3) (4)
IndRuCl(PTA)(PPh3) (5)
CpRuCl(PTA)(PPh3) (6)
TpRuCl(PTA)(PPh3) (7)
DpRuCl(PMe3)(PPh3) (8)
IndRuCl(PMe3)(PPh3) (9)
CpRuCl(PMe3)(PPh3) (10)
CpRuCl(PMe3)(PPh3) (10)
TpRuCl(PMe3)(PPh3) (11)
–
24
3.25
9
5
4
4
24
30
10
11d
12
13e
–
a
b
c
All reactions were performed in toluene-d8, using 1 mol% catalyst and 5 mol% AIBN.
TOF is defined as mol-product/mol-cat/h, calculated at 50–65% conversion of styrene.
Yield is determined by 1H NMR spectroscopy of product vs. internal standard. The isolated yield is given in parenthesis.
d
e
Without AIBN.
Without Ru catalyst with 5 mol% AIBN.

R.P. Nair et al. / Inorganica Chimica Acta 380 (2012) 96–103
99
Fig. 2. Kinetics plots for the addition of CCl3CO2Et to styrene catalyzed by 1 mol% Cp⁄Ru(PMe3)(PPh3)Cl (ꢀ) or 1 mol% Cp⁄Ru(PTA)(PPh3)Cl (N) followed by 1H NMR
spectroscopy.
Cp'
RuII
PPh3
L
Cl
-PPh3
+PPh3
Cp'
RuII
Cl
R'
R
R-X
L
X
Cp'
Cp'
RuIII
R
RuIII
+
R'
X
L
+
X
L
R
R'
Cl
Cl
Scheme 2. General mechanism for Cp0Ru(L)(PPh3)Cl catalyzed ATRA reaction
(where L = PTA, PMe3, PPh3).
Fig. 3. Kinetics plots for the addition of CCl3CO2Et to styrene followed by 1H NMR
spectroscopy and catalyzed by 1 mol% CpRu(PPh3)(PMe3)Cl comparing the reaction
with no added PPh3 (ꢀ), with 10 mol% PPh3 (j), and 20 mol% PPh3 (N).
is no discernable induction period. At early time after the addition
of 10 or 20 mol% PPh3 an induction period was apparent. This
induction period was not easily observed in the Cp⁄ systems be-
cause the reaction is much faster (Fig. 4). Interestingly the induc-
tion period does not increase as [PPh3] was increased from 10 to
20 mol%. More surprising was that the addition of PPh3 increased
the rate of reaction as evidenced by the steeper slope in kinetics
plots of conversion versus time (Figs. 3 and 4). The rate increase
is observed with both CpRu(PPh3)(PMe3)Cl (Fig. 3) and
Cp⁄Ru(PPh3)(PMe3)Cl (Fig. 4) and is evidenced by a steeper slope
in both catalysts with addition of PPh3. At high [PPh3] (20 mol%)
a significant decrease in yield was observed for CpRu(PPh3)(P-
Me3)Cl, Fig. 3. These plots indicate that PPh3 has both an inhibitory
and promotive effect on catalysis. At this stage we assume that the
promotive effect comes from excess triphenylphosphine stabilizing
the catalyst from decomposition. Triphenylphosphine dissociation
from the Cp⁄ system appears quite fast (no induction period ob-
served) so there is little effect on overall yield with the addition
of PPh3. Triphenylphosphine dissociation from the Cp system is
much slower (as observed by the long induction period); therefore,
large amounts of PPh3 have a negative impact on the overall yield
of the reaction.
Severin and co-workers [15] proposed that AIBN allows the
reduction of the Ru(III)-X back to the active Ru(II) catalyst
(Scheme 2). In the absence of AIBN the addition of CCl3CO2Et to
styrene is much slower (TOF = 14.8 hꢀ1; Table 2, entry 11) than
in the presence of 5 mol% AIBN (TOF = 33.6 hꢀ1; Table 2, entry
10). The percent conversion after 4 h for the CpRu(PPh3)(PMe3)Cl
catalyzed addition of ethyl trichloroacetate to styrene without
AIBN is 59% compared to 99% conversion obtained in the presence
of 5 mol% AIBN. Fig. 5 shows the effect of [AIBN] on the addition of
CCl3CO2Et to styrene catalyzed by CpRu(PPh3)(PMe3)Cl. Similar to
what we have reported previously for these compounds [16] as
the AIBN concentration is increased from 1 to 10 mol% the rate of
reaction increases. Above 10 mol% AIBN the reaction rate plateaus
(i.e. the rate at 10 mol% is the same as 15 mol%).
The reactivity of the compounds described here (except for the
Tp complexes 7 and 11) are high relative to those reported in the

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R.P. Nair et al. / Inorganica Chimica Acta 380 (2012) 96–103
slowly in comparison to the addition of the more halogenated ester
CCl3CO2Et, for which the same set of catalysts afforded quantitative
yields at 60 °C (Table 2, entry 1, 2, and 3). Similar results have been
reported previously for the RuCl2(PPh3)3 catalyzed addition of
CCl3CO2Et and CH2ClCO2Et to styrene [11]. Using Cp⁄ complexes
1–3, the reactivity of the halogenated substrates we have looked
at is CCl4 > CCl3CO2Et ꢂ CHCl3 > TsCl > CH2ClCO2Et [16].
3.1.1. Addition of CCl4 to terminal olefins
The substrate scope was further extended for catalyst
precursors 1, 2, and 3 by exploring the addition of CCl4 to a variety
of terminal olefins: 1-hexene, 1-decene, and n-butyl acrylate. With
1-hexene, the CCl4-adduct was obtained in 90–99% yield within
4–7 h at 60 °C (Table 3, entries 1–3). The Cp⁄Ru(PTA)(PPh3)Cl
catalyzed addition of CCl4 to 1-hexene proceeded rapidly (TOF
202 hꢀ1) as compared to the PMe3 and PPh3 analogues (53.3 and
100 hꢀ1, respectively). This is contrary to the results obtained for
CCl4 addition to styrene where Cp⁄Ru(PPh3)2Cl displayed highest
activity [14a,16]. The total turnovers (TTOs) obtained with all three
catalysts were impressive; with catalyst loadings of 0.001 mol%
(5 mol% AIBN), Cp⁄Ru(PTA)(PPh3)Cl (1) exhibited a TTO of 79000
in 48 h, Cp⁄Ru(PMe3)(PPh3)Cl (2) provided a TTO of 88000 after
48 h, and Cp⁄Ru(PPh3)2Cl (3) was the most active with a TTO of
92000 after 40 h. These are the highest TTOs reported to date. Prior
to this work, the highest TTO reported for ATRA was 44000 for the
addition of CCl4 to 1-hexene [15]. With 1-decene, a difficult sub-
strate for ATRA [10a,b,14a], the monoadduct 15 was obtained in
greater than 90% yield in under 4 h (Table 3, entries 4–6). n-Butyl
acrylate, an easily polymerizable substrate, also underwent a fast
and clean monoaddition with CCl4 affording the 1:1 adduct 16 in
>90% yield within 2.5–3.5 h (Table 3, entries 7–9). With 1-decene
and n-butyl acrylate, the reactivity of complexes 1, 2 and 3 was
comparable.
Fig. 4. Kinetics plots for the addition of CCl3CO2Et to styrene followed by 1H NMR
spectroscopy and catalyzed by 1 mol% Cp⁄Ru(PPh3)(PMe3)Cl comparing the reaction
with no added PPh3 (ꢀ), with 10 mol% PPh3 (j), and 20 mol% PPh3 (N).
Due to the exceptional activity of Cp⁄Ru(PPh3)2Cl (3) for ATRA
reactions, we performed the addition of CCl4 to 1-hexene, 1-de-
cene, and n-butyl-acrylate with complex 3 at room temperature.
Unlike CCl4 addition to styrene where the reaction goes to comple-
tion at room temperature [16], only 30–40% yield was observed in
all three cases after ꢂ10 min with no further reaction observed at
longer times. The short lifetime of the catalyst at room tempera-
ture is presumably due to the lack of AIBN activation at room tem-
perature (AIBN reverses catalyst deactivation).
Fig. 5. Kinetics plots for the addition of CCl3CO2Et to styrene catalyzed by 1 mol%
CpRu(PPh3)(PMe3)Cl at various [AIBN]: (ꢀ) no added AIBN, (j) 1 mol% AIBN, (N)
5 mol% AIBN, (d) 10 mol% AIBN, and (⁄) 15 mol% AIBN.
literature. For example, the CCl3CO2Et adduct of styrene was ob-
tained in 60% yield after 24 h with 1 mol% RuCl2(PPh3)3 at 75 °C
[11]. For the same reaction, 5 mol% Grubb’s catalyst P(Cy3)2-
Cl2Ru@CHPh afforded a 57% yield at 75 °C over 48 h [29]. It is note-
worthy that the CCl3CO2Et–styrene adducts are synthetically
interesting precursors as they can be cyclized to form lactones
[18]. ATRA addition of the more difficult substrate CH2ClCO2Et to
styrene was explored with the most active compounds 1, 2, and
3, Scheme 3. Due to poor reactivity, the reaction temperature
was increased to 85 °C. After 24 h, the monoadduct 13 was ob-
tained in modest yields with all three catalysts. Although the con-
version of styrene was high (>85%), only 21–28% of the addition
product 13 was formed, presumably due to competing polymeriza-
tion/oligomerization reactions. The reactions proceeded rather
3.1.2. Addition of CCl4 to internal olefins
It has been reported that the reaction of internal olefins with
CCl4 occurs with the preferential addition of the Cl atom to the
benzylic carbon [11,25]. We obtained similar results for the addi-
tion of CCl4 to trans-b-methyl styrene, benzylidene acetone, and
chalcone (Table 4, entries 1–9). The reaction of trans-b-methyl sty-
rene under the same experimental conditions afforded 17 in 91–
95% yield after 5–7 h (Table 4, entries 1–3). The monoadduct 17
was obtained as a mixture of anti/syn isomers (ꢂ3:1). The
a,b-
unsaturated ketones (benzylidene acetone and chalcone) were less
prone to undergo the addition of CCl4, yielding only 39–53% of 18
and 19 after 24 h at 60–85 °C (Table 4, entries 4–9). The addition of
CCl4 to cis-stilbene afforded 20 as a mixture of two diastereomers
in moderate yields after 24 h at 85 °C (Table 4, entries 10–12).
Interestingly, only subtle differences in the activities of catalytic
systems 1, 2 and 3 were observed with all four internal olefins em-
ployed. The more electron rich internal olefins were found to be
more active with trans-b-methyl styrene > benzylidene ace-
tone » chalcone ꢃ cis-stilbene. For trans-b-methyl styrene, all three
catalysts yielded >90% of the 1:1 adduct; however, <60% yield was
obtained with the less electron rich benzylidene acetone, chalcone,
and cis-stilbene. Chalcone and cis-stilbene were the least active
substrates requiring higher temperature (85 °C) relative to the
Scheme 3. Addition of CH2ClCO2Et to styrene catalyzed by Ru complexes 1–3.

R.P. Nair et al. / Inorganica Chimica Acta 380 (2012) 96–103
101
Table 3
Atom transfer radical addition of CCl4 to terminal olefins catalyzed by Cp⁄Ru(PTA)(PPh3)Cl (1), Cp⁄Ru(PMe3)(PPh3)Cl (2), and Cp⁄Ru(PPh3)2Cl (3).a
Entry
Catalyst
Olefins
Time (h)
Product
Yieldb (%)
1
2
3
1
2
3
4
7
4.5
93
99
92
Cl
n-C4H9
CCl3
hexene
n-C4H9
14
4
5
6
1
2
3
3.5
2.75
3.5
94
92
89
Cl
n-
C8H1
7
CCl3
decene
O
n-
C8H1
7
15
O
7
8
9
1
2
3
2.5
2.5
3.5
97
99
94
C4H9
C4H9
CCl3
O
O
Cl
n-butyl acrylate
16
a
All reactions were performed in toluene-d8 at 60 °C using 1 mol% catalyst and 5 mol% AIBN.
b
Yield is determined by 1H NMR spectroscopy of product vs. internal standard.
Table 4
Atom transfer radical addition of CCl4 to internal olefins catalyzed by Cp⁄Ru(PTA)(PPh3)Cl (1), Cp⁄Ru(PMe3)(PPh3)Cl (2), and Cp⁄Ru(PPh3)2Cl (3).a
Entry
Catalyst
Olefins
Temp. (°C)
Time (h)
Product
Yieldb (%)
1
2
3
Cp⁄Ru(PPh3)2Cl
60
60
60
5
6
7
94 (77:23)c
95 (77:23)c
91 (76:24)c
Cl
Cp⁄Ru(PTA)(PPh3)Cl
Cp⁄Ru(PMe3)(PPh3)Cl
trans- -methyl styrene
CCl3
O
17
4
5
6
Cp⁄Ru(PPh3)2Cl
60
60
60
24
24
24
49 (83:17)c
53 (87:13)c
39 (85:15)c
O
Cl
Cp⁄Ru(PTA)(PPh3)Cl
Cp⁄Ru(PMe3)(PPh3)Cl
CCl3
Benzylidene acetone
O
18
7
8
9
Cp⁄Ru(PPh3)2Cl
85
85
85
24
24
24
41 (70:30)c
58 (80:20)c
44 (73:27)c
O
Cl
Cp⁄Ru(PTA)(PPh3)Cl
Cp⁄Ru(PMe3)(PPh3)Cl
CCl3
Chalcone
19
10
11
12
Cp⁄Ru(PPh3)2Cl
85
85
85
24
24
24
43 (74:26)d
41 (73:27)d
28 (61:39)d
Cl
CCl3
Cp⁄Ru(PTA)(PPh3)Cl
Cp⁄Ru(PMe3)(PPh3)Cl
cis-Stilbene
20
a
b
c
All reactions were performed in toluene-d8 using 1 mol% catalyst and 5 mol% AIBN, CCl4/olefin is 4:1.
Yield is determined by 1H NMR spectroscopy of product vs. internal standard.
The ratio of anti/syn isomers was determined from the 1H NMR spectrum.
The diastereomeric ratio was determined from the 1H NMR spectrum.
d
other substrates (60 °C). Despite the superior catalytic perfor-
mance of 3 for the ATRA of CCl4 to styrene [14,16], the activity of
3 towards the addition of CCl4 to the aforementioned substrates
was in general lower than that of 1 and 2. Complex 2 was slightly
more active for addition of CCl4 to benzylidene acetone (53% yield)
versus 49% and 39% for 1 and 3, respectively. For the addition of
CCl4 to chalcone, 2 was also the most active providing a 58% yield
versus 41% and 44% for 1 and 3, respectively. The reaction of cis-
stilbene with CCl4 provided the lowest yields with 1 and 2 the most
active with yields of 43% and 41%, respectively; 3 was again the
least active at 28% yield. These results indicate that the rate of
the reaction varies with small changes to the catalyst, but also with
the nature of the substrate.
Compounds 17–20 contain two stereogenic centers; a mixture
of diastereomers with predominantly trans product was obtained
for 17, 18, and 19. Using catalysts 1, 2, and 3 only minor variations
in diastereomeric ratio were observed. The diastereomeric ratios
for 17 (ꢂ75:25) and 18 (ꢂ85:15) (Table 4, entries 1–6) were
slightly higher than previously reported for 17 (2:1) and 18
(64:36) [11,25]. In the case of the chalcone–CCl4 adduct (19), both
% yield and isomeric ratio for the Cp⁄Ru(PTA)(PPh3)Cl catalyzed
reaction were slightly higher than those of PMe3 and PPh3 ana-
logues. The differences in stereoselectivity may be due to differ-
ences in the sterics of the catalysts. PTA being the smallest of the
ligands used, but in the middle with respect to electronics, pro-
vides the highest diastereoselectivity.

102
R.P. Nair et al. / Inorganica Chimica Acta 380 (2012) 96–103
Fig. 6. Thermal ellipsoid (50% probability) representation of the RR diastereomer of 19 with the atomic numbering scheme, both the RR and SS enantiomers are present in the
structure.
of Cp⁄Ru(PTA)(PPh3)Cl (1) and Cp⁄Ru(PMe3)(PPh3)Cl (2) were com-
parable to that of Cp⁄Ru(PPh3)2Cl (3), which is the current standard
in Kharasch chemistry.
Acknowledgments
We gratefully acknowledge financial support from the National
Science Foundation CAREER Program (NSF CHE-0645365). Finan-
cial support from the NSF is also acknowledged for X-ray (CHE-
0226402) and NMR (CHE-0521191) facilities.
Appendix A. Supplementary material
CCDC 830022 and 830023 contain the supplementary crystallo-
graphic data for 19 and 20. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2011.11.008.
Fig. 7. Thermal ellipsoid (50% probability) representation of the SS diastereomer of
20 with the atomic numbering scheme, hydrogen atoms have been omitted for
clarity, both the RR and SS enantiomers are present in the structure.
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