Iridium and rhodium "PNP" aminodiphosphine complexes used as catalysts in the oxidation of styrene

Article abstract of DOI:10.1039/c6ra01276k

Six PNP or aminodiphosphine ligands were synthesized and complexed to the transition metals iridium and rhodium to give [(η⁵-C₅Me₅)MCl{η²-P,P′-(PPh₂)₂NR}]PF₆, where M = Ir (1) an

Full text of DOI:10.1039/c6ra01276k

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DOI: 10.1039/C6RA01276K
Iridium and rhodium “PNP” aminodiphosphine
Cite this: DOI: 10.1039/x0xx00000x complexes used as catalysts in the oxidation of styrene
a
b
c
Dunesha Naicker Holger B. Friedrich and Pramod B. Pansuriya
Received 00th January 2012,
Accepted 00th January 2012
Six PNP or aminodiphosphine ligands were synthesized and complexed to the transition metals iridium
5
2
and rhodium to give [(η ꢀC Me )MCl{η ꢀP,P′ꢀ(PPh ) NR}]PF , where M= Ir (1) and Rh (2) and R=
5
5
2 2
6
DOI: 10.1039/x0xx00000x
cyclohexyl (a), isoꢀpropyl (b), pentyl (c), phenyl (d), chlorophenyl (e) and methoxyphenyl (f). These
complexes were fully characterized by NMR, elemental analyses and IR spectroscopy. Crystals of 1f and
www.rsc.org/
2
f were obtained, which showed a distorted octahedral geometry around the metal centers. These
complexes showed good activity in the oxidation of styrene using tertꢀbutyl hydroperoxide (TBHP) as
the oxidant. The iridium complexes were more active than the rhodium complexes. Higher yields to
benzaldehyde were achieved in comparison to styrene oxide for all catalysts.
Keywords: Aminodiphosphine; iridium; rhodium; styrene; oxidation
1
. Introduction
Significant quantities of feedstock, towards cheap starting materials, In this study, a new approach has been undertaken in using iridium
can be obtained from oils, which at present are burnt as fuel in the and rhodium aminodiphosphine complexes in the oxidation of
1
transport industry. The oxidation of hydrocarbons provides a costꢀ styrene. One of the early studies was carried out by Collman and coꢀ
effective method of converting these starting materials into bulk workers in 1967 using IrI(CO)(PPh3)2 in the oxidation of
31
chemicals and is an important transformation in the production of cyclohexene. In the early 1970’s iridium and rhodium compound
1
fine chemicals. The oxidation of alkenes to their corresponding catalysed olefin epoxidation was carried out using simple organic
epoxides and carbonyl compounds is important in the synthesis of salts, which performed poorly when compared to the Wacker
2
ꢀ14
32,33
fine and pharmaceutical grade chemicals.
Epoxides are important palladium oxidation.
Since then, less attention has been paid to
32ꢀ35
building blocks and are used as intermediates and precursors for these transition metals.
chemical production and in the preparation of resins and drugs.
Benzaldehyde is the second most important aromatic molecule and obtaining an 11% yield to benzaldehyde and phenyacetaldehyde.
More recently, Turlington and coꢀ
workers used half sandwich Ir complexes in the oxidation of styrene
9
3
6
has a widespread application in the agro chemical industries and
7
synthesis of dyes and perfumes.
The overꢀoxidation of
PF6
R
N
M
benzaldehyde results in the formation of benzoic acid which is
important in the food industry as a preservative inhibiting the growth
1
5
of mould, yeast and bacteria. Transition metalꢀbased systems are
Ph
Ph
1
6
able to catalyze epoxidation reactions, and the choice of catalyst
P
P
1
7
and oxidant can modify the course of the reaction. For selective
epoxidation, a suitable ligand system is required which is able to
Ph
Ph
1
7
Cp*
Cl
control the catalytic behaviour. One such system could include the
biꢀdentate or multidentate aminodiphosphine or “PNP” ligands,
which have been used extensively in ethylene oligomerization
Figure 1. General structure of the complexes used as catalysts in the
oxidation of styrene. (M=Ir (1) and Rh (2); R= cyclohexyl
1
8ꢀ24
studies.
The use of cobalt complexes with these ligands in the
2
5
oxidation of nꢀoctane was recently reported. These ligands are part
(
a), isoꢀpropyl (b), pentyl (c), phenyl (d), chlorophenyl (e)
and methoxyphenyl (f);
Cp* = η ꢀ pentamethylcyclopentadienyl).
of a system that displays high activity, stability and variability,
26ꢀ28
which makes them ideally suited for catalytic applications.
The
5
activity of the metal can be tailored through the modification of the
ligand backbone, by using different donor substituents or central
anionic atoms. The ligand then places a high demand on the
stereochemistry of the complex allowing the reactions of the metal
We herein report the synthesis and characterization of some new
iridium (1) and rhodium (2) aminodiphosphine complexes and their
application in the catalytic oxidation of styrene. Optimization of
solvent (acetonitrile (MeCN) and dichloroethane (DCE), oxidants
2
9,30
ions to be selective.
This journal is © The Royal Society of Chemistry 2013
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ARTICLE
6RA01276K
DOI: 10.1039Jo/Curnal Name
(
tertꢀbutyl hydroperoxide (TBHP), hydrogen peroxide (H O ), Nꢀ Calcd for C H ClIrNP 830.2423 . Found: 830.2417 NMR: (400
2
2
40 46
2
1
methyl morpholine Nꢀoxide (NMO)) and temperature (room MHz.; DMSO): H NMR δ 0.87ꢀ1.43 (m, 10H, cyclohexyl ring); δ
temperature (RT), 50 °C and 80 °C) were carried out. The 1.52 (s, 15H, Cp*); δ 3.59ꢀ3.69 (m, 1H, (cyclohexyl ring)); δ 7.44ꢀ
13
substituents on the nitrogen atom were varied by making use of six 7.77 (m, 20H, aromatic). C NMR δ 8.28 (Cp*); δ 33.82
different types of functional groups (Fig. 1), with the intention of (cyclohexyl ring); δ 24.30ꢀ24.94 (cyclohexyl ring); δ 127.51ꢀ133.39
31
observing if these groups have an effect on the catalytic activity and (aromatic); δ 64.57 (cyclohexyl ring). P NMR δ ꢀ152.99 − ꢀ131.04
selectivity to the products of oxidation. (PF ); δ 34.50.
6
+
-
Synthesis
of
[[Ph PN(C H )PPh ]IrCp*(Cl)] PF
6
(1b).
2
3
7
2
2
. Experimental
Compound 1b was synthesized according to the procedure described
for 1a except that [Ph PN(C H )PPh ] (0.250 mmol, 0.11 g) was
2
.1 Synthesis and characterization of the compounds
2
3
7
2
used. Yield: 88 %, 0.21 g. Melting point: 270ꢀ272 °C. IRν
max
All experiments were performed using standard Schlenk techniques
under inert conditions in moisture free reaction glassware with
anhydrous solvents. All solvents were analytical grade. To render
the reaction glassware moisture free, it was heated with a heat gun,
followed by cycles of vacuum and nitrogen pressure. The solvents
utilized were dry unless otherwise stated. Diethyl ether and hexane
were distilled from sodium benzophenoneketyl under nitrogen.
Dichloromethane (DCM) was distilled from P O and methanol from
ꢀ
1
(ATR)/cm : 833 (s) (PF ); 945 (m) (PꢀN); 1436 (m) (PPh ); 1482
6 2
(
w) (CH ). Anal. % Calcd for C H ClF IrNP : C: 47.5%; H: 4.5%;
3
37 42
6
3
N: 1.5%. Found: C: 47.0%; H: 4.3%; N: 2.0%. HRMS (ESI) Calcd
for C H ClIrNP 790.2110. Found: 790.2092. NMR: (400 MHz.;
3
7
42
1
2
2
DMSO): H NMR δ 0.94 (d, 6H, (CH ) ; J = 6.60 Hz); δ 1.54 (s,
3
2
1
5H, Cp*); δ 3.91ꢀ4.12 (m, 1H, CH); δ 7.41ꢀ7.78 (m, 20H,
13
aromatic). C NMR δ 8.27 (Cp*); δ 23.6 (CH ) ); δ 56.1 (CH); δ
1
3
3
2
2
5
31
28.31ꢀ133.07 (aromatic). P NMR δ ꢀ154.38 − ꢀ131.04 (PF ); δ
6
magnesium turnings. Deuterated solvents were used as received and
stored in a desiccator. The NMR spectra were recorded at 400 MHz
4.89.
1
13
31
(
H), 100 MHz ( C) and 162 MHz ( P) using a Bruker Ultrashield
+
-
Synthesis
of
[[Ph PN(C H )PPh ]IrCp*(Cl)] PF
6
(1c).
1
13
1
2
5
11
2
4
00 MHz spectrometer. H NMR and C{ H} NMR chemical shifts
Compound 1c was synthesized according to the procedure described
for 1a except that [Ph PN(C H )PPh ] (0.25 mmol, 0.11 g) was
are reported in parts per million (ppm) downfield from
1
13
1
2
5
11
2
tetramethylsilane.
H NMR and C{ H} NMR signals were
used. Yield: 54 %, 0.13 g. Melting point: 262ꢀ263 °C. IRν
max
referenced to the residual hydrogen and carbon signal of DMSO,
ꢀ
1
(
ATR)/cm : 751 (m) (CH ); 833 (s) (PF ); 999 (m) (PꢀN); 1437 (m)
3
1
2 6
(
2.50 ppm) and (39.52 ppm), respectively. P NMR chemical shifts
(
PPh ); 2930 (w) (CH ). Anal. % Calcd for C H ClF IrNP : C:
2 3 39 46 6 3
are reported in parts per million (ppm) from triphenylphosphine (ꢀ
4
8.6%; H: 4.8%; N: 1.5%. Found: C: 49.0%; H 4.3%; N 1.6%.
103
31
1
7.6 ppm). The 2D Rh and P NMR spectrum of compound 2c
HRMS (ESI) Calcd for C H ClIrNP 818.4185. Found: 818.2413.
3
9
46
1
2
was recorded using a Bruker Ultrashield 500 MHz spectrometer. The
FTꢀIR spectra were recorded using a Perkin Elmer Universal
Attenuated Total Reflection (ATR) sampling accessory attached to
an FTꢀIR series 100 spectrometer. The HRMS was recorded on a
Waters Micromass LCT Premier TOFꢀMS. All PNP ligands were
3
NMR: (400 MHz.; DMSO): H NMR δ 0.60 (t, 3H, CH ; J= 6.78
3
Hz); δ 0.92ꢀ0.97 (m, 4H, (CH ) ); δ 1.07ꢀ1.24 (m, 2H, CH ); δ 1.58
2
2
2
(
s, 15H, Cp*); δ 3.36ꢀ3.39 (m, 2H, CH ); δ 7.35ꢀ7.79 (m, 20H,
2
13
aromatic). C NMR δ 8.39 (Cp*); δ 13.38 (CH ); δ 21.26 (CH ); δ
3
2
2
8.02 (CH ); δ 29.15 (CH ); δ 51.59 (CH ); δ 128.25ꢀ133.34
2 2 2
2
0
synthesized with modification of literature procedure.
The
31
(aromatic). P NMR δ ꢀ152.99 −
ꢀ135.43 (PF ); δ
6
5
precursors [{MCl Cp*} ] (where M = Ir or Rh and Cp* = η ꢀ
2
2
3
4.19.
pentamethylcyclopentadienyl) were prepared according to reported
37ꢀ39
procedures.
+
-
Synthesis of [[Ph PN(Ph)PPh ]IrCp*(Cl)] PF (1d). Compound
2
2
6
1
d was synthesized according to the procedure described for 1a
+
-
Synthesis of [Ph PN(C H )PPh ]IrCp*(Cl)] PF (1a).
The
2
6
11
2
6
except that [Ph PN(Ph)PPh ] (0.25 mmol, 0.12 g) was used. Yield:
4
0
2
2
synthesis was adapted from a known procedure. To a 100 ml twoꢀ
neck round bottom flask, acetone (6 ml) was added and purged with
argon for 10 minutes. Thereafter, [Ph PN(C H )PPh ] (0.250
ꢀ
1
7
7 %, 0.19 g. Melting point: 249ꢀ251 °C. IRνmax (ATR)/cm : 827 (s)
(PF ); 946 (m) (PꢀN); 1439 (m) (PPh ); 1494 (w) (Ph). Anal. %
6
2
2
6
11
2
Calcd for C H ClF IrNP : C: 49.6%; H: 4.2%; N: 1.4%. Found: C:
40
40
6
3
mmol, 0.12 g) was added. Once completely dissolved, [{IrCl Cp*} ]
0.125 mol, 0.10 g) and NH PF (0.250 mmol, 0.04 g) were added to
2
2
4
8
1
3
1
3
9.1%; H: 4.0%; N: 2.9%. HRMS (ESI) Calcd for C H ClIrNP
40 40 2
(
4 6
1
24.1954. Found: 824.1945. NMR: (400 MHz.; DMSO): H NMR δ
the flask, followed by the addition of methanol (12 ml). The yellow
solution was allowed to stir for 6 h, after which DCM was added.
The solution was then filtered through celite and the solvent was
reduced to 2 ml. Upon addition of diethyl ether a yellow precipitate
formed, which was filtered using a Hirsch funnel. The yellow
powder was dried overnight in vacuo. Crystals were grown from
diethyl ether and dichloromethane. Yield: 78%, 0.19 g. Melting
2
.56 (s, 15H, Cp*); δ 6.64 (d, 2H, CH; J= 7.53 Hz); δ 7.14ꢀ7.21 (m,
13
H, CH); δ 7.41ꢀ7.77 (m, 20H, aromatic). C NMR δ 8.25 (Cp*); δ
31
24.08ꢀ133.54 (aromatic). P NMR δ ꢀ152.99 − ꢀ135.43 (PF ); δ
6
5.84
+
-
Synthesis
of [[Ph PN(C H Cl)PPh ]IrCp*(Cl)] PF
6
(1e).
2
6
4
2
Compound 1e was synthesized according to the procedure described
for 1a except that [Ph PN(C H Cl)PPh ] (0.25 mmol, 0.12 g) was
ꢀ
1
point: 295ꢀ296 °C. IRνmax (ATR)/cm : 762 (w) (CH rocking); 827
s) (PF ); 938 (m) (PꢀN); 1071 (m) (cyclohexyl ring vibrations);
6
436 (m) (PPh ). Anal. % Calcd for C H ClF IrNP : C: 49.3%; H:
.8%; N: 1.4%. Found: C: 49.6%; H: 4.8%; N: 1.6%. HRMS (ESI)
2n
2
6
4
2
(
used. Yield: 83%, 0.21 g. Melting point: 237ꢀ239 °C. IRν
max
1
4
ꢀ1
2
40 46
6
3
(ATR)/cm : 827 (s) (PF ); 900 (m) (PꢀN); 1439 (m) (PPh ); 1494
6 2
(
w) (Ph ). Anal. % Calcd for C H ClF IrNP : C: 47.9%; H: 3.9%;
2
40 39
6
3
2
| J. Name., 2012, 00, 1-3
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ART76ICLE
DOI: 10.1039/C6RA012 K
31
N: 1.4%. Found: C: 48.2%; H: 4.1%; N: 1.6%. HRMS (ESI) Calcd 128.14ꢀ133.37 (aromatic). P NMR δ ꢀ154.38 − ꢀ131.04 (PF ); δ
6
for C H Cl IrNP 858.1564. Found: 858.1555. NMR: (400 MHz.; 67.79 (d).
4
0
39
1
2
2
2
DMSO): H NMR δ 1.55 (s, 15H, Cp*); δ 6.63 (d, 2H, CH; J= 8.84
Hz); δ 7.28 (m, 2H, CH; J= 8.88 Hz); δ 7.42ꢀ7.79 (m, 20H,
aromatic). C NMR δ 8.83 (Cp*); δ 125.46 ꢀ133.67 (aromatic).
+
-
2
Synthesis
Compound 2c was synthesized according to the procedure described
for 2a in that [Ph PN(C H )PPh ] (0.25 mmol, 0.13 g) was used.
of
[[Ph PN(C H )PPh ]RhCp*(Cl)] PF
(2c).
2
5
11
2
6
1
3
31
P
NMR δ ꢀ152.99 − ꢀ135.43 (PF ); δ 37.05
2
5
11
2
6
ꢀ
1
Yield: 95 %, 0.21 g. Melting point: 240ꢀ242 °C. IRνmax (ATR)/cm :
(1f). 750 (m) (CH ); 834 (s) (PF ); 999 (m) (PꢀN); 1436 (m) (PPh ); 2960
+
-
Synthesis
of
[[Ph PN(C H O)PPh ]IrCp*(Cl)] PF
2 7 7 2 6
2
6
2
Compound 1f was synthesized according to the procedure described (w) (CH ). Anal. % Calcd for C H ClF RhNP : C: 53.6%; H:
3
39 46
6
3
for 1a in that [Ph PN(C H O)PPh ] (0.25 mmol, 0.12 g) was used. 5.3%; N: 1.6%. Found: C: 53.8%; H: 4.9%; N: 2.0%. HRMS (ESI)
2
7
7
2
ꢀ
1
Yield: 87%, 0.22 g. Melting point: 239ꢀ242 °C. IRνmax (ATR)/cm : Calcd for C H ClRhNP 728.1849. Found: 728.1849. NMR: (400
8
39
46
1
2
3
32 (s) (PF ); 951 (m) (PꢀN); 1234 (m) (aromatic ether); 1437 (m) MHz.; DMSO): H NMR δ 0.59 (t, 3H, CH ; J= 6.74 Hz); δ 0.89ꢀ
6 3
(
4
PPh ); 1506 (w) (Ph ). Anal. % Calcd for C H ClF IrNOP : C: 0.97 (m, 4H, (CH ) ); δ 1.07ꢀ1.20 (m, 2H, CH ); δ 1.52 (s, 15H,
9.3%; H: 4.2%; N: 1.4%. Found: C: 49.0%; H 3.8%; N 1.7%. Cp*); δ 3.36ꢀ3.39 (m, 2H, CH ); δ 7.34ꢀ7.79 (m, 20H, aromatic). C
2
2 2 41 42 6 3 2 2 2
1
3
HRMS (ESI) Calcd for C H ClIrNOP
854.2059. Found: NMR δ 8.94 (Cp*); δ 13.38 (CH ); δ 21.26 (CH ); δ 27.98 (CH ); δ
3 2 2
4
0
42
2
1
31
8
54.2033. NMR: (400 MHz.; DMSO): H NMR δ 1.59 (s, 15H, 29.24 (CH ); δ 50.68 (CH ); δ 128.27ꢀ132.94 (aromatic). P NMR δ
2 2
2
Cp*); δ 3.66 (s, 3H, CH ); δ 6.60 (d, 2H, CH; J= 8.84 Hz); δ 6.78 ꢀ152.99 − ꢀ135.43 (PF ); δ 67.07 (d).
3
6
2
13
(
d, 2H, CH; J= 9.00 Hz); δ 7.31ꢀ7.78 (m, 20H, aromatic). C NMR
+
-
31
Synthesis of [[Ph PN(Ph)PPh ]RhCp*(Cl)] PF (2d). Compound
δ 8.34 (Cp*); δ 55.34 (CH ); δ 128.21 ꢀ133.42 (aromatic). P NMR
2
2
6
3
2
d was synthesized according to the procedure described for 2a
δ ꢀ152.99 − ꢀ135.43 (PF ); δ 37.05.
6
except that [Ph PN(Ph)PPh ] (0.25 mmol, 0.12 g) was used. Yield:
2
2
+
-
ꢀ1
Synthesis of [[Ph PN(Cy)PPh ]RhCp*(Cl)] PF
(2a). The 77 %, 0.19 g. Melting point: 249ꢀ251 °C. IRνmax (ATR)/cm : 827 (s)
synthesis was adapted from a known procedure. To a 100 ml twoꢀ (PF ); 941 (m) (PꢀN); 1439 (m) (PPh ); 1494 (w) (Ph ). Anal. %
2
2
6
4
0
6
2
2
neck round bottom flask, acetone (6 ml) was added and purged with Calcd for C H ClF RhNP : C: 54.6%; H: 4.6%; N: 1.6%. Found:
40
40
6
3
argon for 10 minutes. Thereafter, [Ph PN(Cy)PPh ] (0.250 mmol, C: 54.9%; H: 4.5%; N 1.2%.HRMS (ESI) Calcd for C H ClRhNP
2
2
40 40
1
2
0
.12 g) was added. Once completely dissolved, [{RhCl Cp*} ] 734.1380. Found: 734.1368 . NMR: (400 MHz.; DMSO): H NMR δ
2 2
(
0.125 mol, 0.08 g) and NH PF (0.250 mmol, 0.04 g) were added to 1.54 (s, 15H, Cp*); δ 6.65ꢀ6.67 (d, 2H, CH); δ 7.18ꢀ7.19 (m, 3H,
4 6
13
the flask, followed by the addition of methanol (12 ml). The yellow CH); δ 7.41ꢀ7.78 (m, 20H, aromatic). C NMR δ 8.83 (Cp*); δ
solution was allowed to stir for 6 h, after which DCM was added. 124.99ꢀ133.40 (aromatic). P NMR δ ꢀ152.99 − ꢀ135.43 (PF ); δ
31
6
The solution was then filtered through celite and the solvent was 68.42 (d).
reduced to 2 ml. Upon addition of diethyl ether an orange precipitate
+
-
formed, which was filtered using a Hirsch funnel. The orange Synthesis of [[Ph
powder was dried overnight in vacuo. Crystals were grown from Compound 2e was synthesized according to the procedure described
diethyl ether and dichloromethane. Yield: 90%, 0.20 g. Melting for 2a except that [Ph PN(C Cl)PPh ] (0.25 mmol, 0.12 g) was
point: 256ꢀ258 °C. IRνmax (ATR)/cm : 762 (w) (CH2 rocking); 829 used. Yield: 87%, 0.20 g. Melting point: 223ꢀ225 °C. IRνmax
PN(C
H
Cl)PPh
]RhCp*(Cl)] PF
(2e).
2
6
4
2
6
H
4
2
6
2
ꢀ
1
n
ꢀ
1
(
s) (PF ); 905 (m) (PꢀN); 1063 (m) (cyclohexyl ring vibrations); (ATR)/cm : 827 (s) (PF
6
); 901 (m) (PꢀN); 1439 (m) (PPh
). Anal. % Calcd for C40 RhNP : C: 52.5%; H: 4.3%;
H: 5.2%; N: 1.6%. Found: C: 54.0%; H 5.2%; N 1.8%. HRMS (ESI) N: 1.5%. Found: C: 52.3%; H: 4.6%; N: 2.0%. HRMS (ESI) Calcd
2
); 1494
6
1
435 (m) (PPh ). Anal. % Calcd for C H ClF RhNP : C: 54.2%; (w) (Ph
2
H
39ClF
6
3
2
40 46
6
3
Calcd for C H ClRhNP 740.1849 . Found: 740.1851 NMR: for C40
H
39Cl
RhNP 768.0990. Found: 768.0995. NMR: (400 MHz.;
4
0
46
2
2 2
1
1
2
(
400MHz; DMSO): H NMR δ 1.04ꢀ1.42 (m, 10H, cyclohexyl ring); DMSO): H NMR δ 1.51 (s, 15H, Cp*); δ 6.65 (d, 2H, CH; J= 8.92
2
δ 1.48 (s, 15H, Cp*); δ 3.63ꢀ3.72 (m, 1H, (cyclohexyl ring)); δ 7.43ꢀ Hz); δ 7.28 (d, 2H, CH; J= 6.88 Hz); δ 7.42ꢀ7.76 (m, 20H,
1
3
13
31
7
(
.80 (m, 20H, aromatic). C NMR δ 8.78 (Cp*); δ 24.27ꢀ33.87 aromatic). C NMR δ 8.83 (Cp*); δ 128.38ꢀ133.54 (aromatic).
cyclohexyl ring); δ 128.13ꢀ133.44 (aromatic); δ 64.57 (cyclohexyl NMR δ ꢀ152.99 − ꢀ135.43 (PF ); δ 69.69 (d).
P
6
31
ring). P NMR δ ꢀ152.99 − ꢀ131.04 (PF ); δ 67.62 (d).
6
+
-
Synthesis of [[Ph PN(C H O)PPh ]RhCp*(Cl)] PF
(2f).
(2b). Compound 2f was synthesized according to the procedure described
Compound 2b was synthesized according to the procedure described for 2a in that [Ph PN(C O)PPh ] (0.25 mmol, 0.12 g) was used.
for 2a in that [Ph PN(C H )PPh ] (0.13 mmol, 0.05 g) was used. Yield: 84%, 0.19 g. Melting point: 224ꢀ225 °C. IRνmax (ATR)/cm :
2
7
7
2
6
+
-
Synthesis
of
[[Ph PN(C H )PPh ]RhCp*(Cl)] PF
2 3 7 2 6
H
7
2
7
2
ꢀ
1
2
3
7
2
ꢀ
1
Yield: 94%, 0.09 g. Melting point: 242ꢀ244 °C. IRνmax (ATR)/cm : 833 (s) (PF
34 (s) (PF ); 949 (m) (PꢀN); 1436 (m) (PPh ); 1482 (w) (CH ). (PPh ); 1507 (w) (Ph
Anal. % Calcd for C H ClF RhNP : C: 52.5%; H: 5.0%; N: 1.7%. 54.1%; H: 4.7%; N: 1.5%. Found: C: 54.5%; H 4.3%; N 1.4%.
); 949 (m) (PꢀN); 1231 (m) (aromatic ether); 1436 (m)
6
8
2
2
). ). Anal. % Calcd for C41 RhNOP : C:
H
42ClF
6
3
6
2
3
3
7
42
6
3
Found: C: 53.0%; H: 5.0%; N: 2.2%. HRMS (ESI) Calcd for HRMS (ESI) Calcd for C40
H
39ClRhNOP
764.1485. Found:
2
1
C H ClRhNP 700.1536. Found: 700.1530. NMR: (400 Mhz.; 764.1478. NMR: (400 MHz.; DMSO): H NMR δ 1.56 (s, 15H,
3
7
42
2
1
2
2
DMSO): H NMR δ 0.94 (d, 6H, (CH ) J= 6.64 Hz); δ 1.48 (s, Cp*); δ 3.66 (s, 3H, CH
5H, Cp*); δ 4.05ꢀ4.19 (m, 1H, CH); δ 7.40ꢀ7.98 (m, 20H, (d, 2H, CH; J= 9.00 Hz); δ 7.32ꢀ7.59 (m, 20H, aromatic). C NMR
aromatic). C NMR δ 8.80 (Cp*); δ 23.77 (CH ) ); δ 55.6 (CH); δ δ 8.91 (Cp*); δ 55.34 (CH
); δ 6.60 (d, 2H, CH; J= 8.84 Hz); δ 6.77
3
2;
3
2
13
1
1
3
31
); δ 128.21 ꢀ133.42 (aromatic). P NMR
3
2
3
δ ꢀ152.99 − ꢀ135.43 (PF ); δ 69.86 (d).
6
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Table 1. Single crystal structural information of complexes 1f and 2f.
Compound
Mol. Formula
Mol. Weight
Temperature (k)
Wavelength (Å)
Crystal symmetry
Space Group
a (Å)
1f
2f
C H ClNOP Rh,F P
C H ClIrNOP ,F P
41
42
2
6
41 42
2
6
999.34
173
910.03
173
Mo Kα (0.71073)
Monoclinic
P21/c
Mo Kα (0.71073)
Monoclinic
P21/c
14.0391(9)
13.7146(8)
21.6343(14)
90, 105.8, 90
14.0480(4)
13.7160(6)
21.6798(9)
90, 105.8, 90
b (Å)
c (Å)
α, β, γ (°)
3
Volume (Å )
4007.4(4)
4
4017.5(3)
4
Z
3
Density (g/m )
1.656
1.505
ꢀ
1
3.580
0.673
1856
Absorption coefficient (mm )
F(000)
1984
0.13 x 0.19 x 0.22
1.5, 28.4
Crystal size (mm)
0.12 x 0.15 x 0.18
4.0, 27.5
Θ range for data collection
Reflection (collected, independent, Rint)
Observed Data [I > 2.0 sigma(I)]
Nref, Npar
118247, 10018, 0.080
8191
77581, 9164, 0.103
5603
10018, 493
9164, 493
R, wR2, S
0.0274, 0.0612, 1.01
0.0464, 0.1213, 1.03
ꢀ3
0.87, ꢀ0.93
0.96, ꢀ0.86
Largest diff. peak, hole (e.Å )
No of C—H···X interactions
3
2
3
2
No of CꢀH...π (CgꢀRing) interactions
No of π...π (Cgꢀ Cg) interactions
.2 Crystal structure analysis
24
24
2
refinement and data reduction were performed using the program
Singleꢀcrystal Xꢀray diffraction data of complex 1f were collected on
a Bruker KAPPA APEX II DUO diffractometer using graphiteꢀ
monochromated MoꢀKα radiation (λ = 0.71073 Å). Data collection
was carried out at 173(2) K (Table 1). Temperature was controlled
by an Oxford Cryostream cooling system (Oxford Cryostat). Cell
41
SAINT. The data were scaled and absorption correction performed
41
using SADABS. The structure was solved by direct methods using
SHELXSꢀ97 and refined by fullꢀmatrix leastꢀsquares methods based
2
42
on F using SHELXLꢀ97.
Xꢀray single crystal intensity data of
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4
8
complex 2f were collected on a Nonius KappaꢀCCD diffractometer, transfer as P is a 100% I= ½ nucleus with a high receptibility. The
2
31
103
31
also using graphite monochromated MoKα radiation (λ = 0.71073 Å
at 173 (2) K). Temperature was controlled by an Oxford Cryostream spectrum and is consistent with that shown in literature of similar
J( P,
Rh) value was calculated from the routine P NMR
48,49
2
cooling system. The data collection was evaluated using the Bruker compounds.
Nonius "Collect” program. Data were scaled and reduced using fact that two equivalent P nuclei are present which is consistent
DENZOꢀSMN software. Absorption correction was performed with the spectrum shown in Fig. 2. This constant is an indicator of
using SADABS. The program Olex2 was used to prepare the RhꢀP bond strength.
The J coupling constant ( J= 119.4 Hz) is due to the
3
1
4
3
50
41
48,51
Bulky ligands, such as the one present in
4
4
molecular graphic images. All nonꢀhydrogen atoms were refined this study, weaken the metalꢀphosphorous bond, which results in a
anisotropically. The ADP restraints and the rigid bond restraints slightly lower J values and is also noted in a series of RhꢀP
51
were used on all six fluorine atoms. All hydrogen atoms were placed complexes that bear such ligands.
in idealized positions and refined in riding models with Uiso assigned
values 1.2 or 1.5 times those of their parent atoms and the distances
of CꢀH were constrained to 0.95 Å for aromatic hydrogen atoms and
0
.98 Å for CH3.
2
.3 Oxidation of styrene
All reagents were weighed and handled in air. All products were
analyzed using a PerkinElmer Auto System gas chromatograph fitted
with a Flame Ionisation Detector (FID) set at 290 °C. A Varian DBꢀ
5
capillary column (25 m x 0.15 mm x 2ꢁm) was utilized with the
injector temperature set at 250 °C. The catalyst to substrate ratio was
kept constant at 1:100. A twoꢀnecked pear shaped flask was charged
with 5 mg of the respective catalyst, benzophenone (as an internal
standard), styrene, the respective oxidant and 10 ml of the solvent).
The flask was equipped with a reflux condenser, stirred, and heated
to the respective temperature. After intervals, an aliquot was
removed using a Pasteur pipette and (0.5 ꢁl) was injected into the
GC and quantified.
1
03
31
Figure 2. 2D Rh and P NMR spectrum of compound 2c.
The HRMS and elemental analyses match those of the calculated
values and the sharp melting points indicate that these complexes are
pure
.
3
.2 Description of crystal structures
Yellow and orange crystals of 1f and 2f, respectively, were obtained
by vapor diffusion of diethyl ether into a dichloromethane solution.
Structural views of complexes 1f and 2f are shown in Fig. 3. The
selected interatomic distances and angles for 1f and 2f are listed in
3
. Results and discussion
3
.1 Synthesis ad characterization of the compounds
The new complexes (1 and 2) were synthesized by adaptation of a Table 2. For both the complexes the iridium/rhodium centers are
4
0
reported general method. The respective PNP ligands were added distorted octahedrally and the chloro group is coordinated
to (2:1; v/v) methanol:acetone mixtures after which the metal perpendicular to the strained four membered chelate ring, whilst the
complex precursor and NH PF salt were added. For the iridium Cp* ligand is trans to the PNP nitrogen donor. Ir−Cl(1) and
4
6
complexes (1) a yellow precipitate formed after 1 h of stirring at Rh−Cl(1) bond lengths are 2.3855(9) Å and 2.3785(9) Å for 1f and
room temperature, whilst an orange precipitate formed for the 2f, respectively, and are comparable to the corresponding values
rhodium complexes (2). The complexes were characterized by observed for similar Ir and Rh complexes.4
5,46
The interatomic
NMR, IR, HRMS and in some cases single crystal xꢀray diffraction. distances of Ir···N and Rh···N bonds are 2.942 Å and 2.938 and the
3
1
A downfield shift is noted in the P NMR spectra of the rhodium P−N−P angles are 101.02(14)° and 101.82(16)° for 1f and 2f
31
complexes compared to the iridium complexes. Furthermore, the
P
respectively. These findings indicate that the phosphinoamine
NMR spectra for the rhodium complexes show a doublet resonance nitrogen atoms do not bind to the metal ions. In addition, the average
at ~ 67 ppm, while a singlet resonance is seen for the iridium P(1)···P(2) distances are 2.633 Å (1f) and 2.646 Å (2f). The P−N
complexes at ~34 ppm. This is consistent with literature for rhodium
bond lengths (~1.70 Å) obtained for compounds 1f and 2f lie in a
4
5,46
45,46,52,53
complexes of similar nature.
The substituents on the nitrogen
typical P−N single bond range.
The Rh−P bond lengths of
atom (aꢀf) have very little effect in the shift of the phosphorus peak,
as the peak shift is mainly influenced by the phenyl groups on the
nitrogen atom, and this is also noted in the νPPh2 of the free ligand
and the complex in the IR spectra. To show the correlation between
2
1
f are 2.2998(9) Å for Rh−P(1), 2.3079(9) Å for Rh−P(2), whilst for
f the bond length, Ir−P(1) is 2.2916(8) Å and 2.2958(8) Å for
Ir−P(2).These are similar to related rhodium and iridium
complexes.
45,46
1
03
31
the phosphorous and Rh metal, a 2D Rh and P NMR HMQC
experiment of compound 2c was carried out (Fig. 2). Transition The Rh–C(ring) and Ir–C(ring) distances are 2.188(4)ꢀ2.231(3) and
metal NMR has the advantage over normal proton NMR, in that the 2.197(3)ꢀ2.245(4) Å, respectively, and again are comparable with
transition metal nuclei offer very large shielding ranges, therefore those found in other pentamethylcyclopentadienyl compounds of
47
45,46
there is higher sensitivity to subtle structural perturbations. In this rhodium(III) and iridium(III).
case the phosphorous nuclei were used as a source of polarization
Although the nitrogen atom of the
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diphosphinoamine ligand is part of a tertiary amine, the nitrogen
atoms are located within the plane defined by two phosphorus and an
ipso carbon atoms.
Table 2. Selected bond lengths (Å) and bond angles (°) of
complexes 1f and 2f.
Bond
distances (Å)
MꢀP(1)
1f
2f
2.2916(8)
2.2998(9)
2.3079(9)
2.3785(9)
MꢀP(2)
MꢀCl(1)
2.2958(8)
2.3855(9)
MꢀCp*(1ꢀ5)
2.245(4), 2.227(3),
2.227(4), 2.214(4),
2.188(4), 2.231(3),
2.220(4)
2
.197(3), 2.237(3),
.233(3)
2
1
f
2f
P(1)ꢀN(1)
P(2)ꢀN(1)
P(1)ꢀC(11)
P(1)ꢀC(17)
P(2)ꢀC(30)
P(2)ꢀC(36)
N(1)ꢀC(23)
1.702(2)
1.709(2)
1.821(3)
1.808(3)
1.815(3)
1.817(3)
1.436(4)
1.703(3)
1.706(3)
1.821(4)
1.819(3)
1.813(3)
1.819(3)
1.449(4)
Figure 3. Structure of complexes 1f and 2f with labeling scheme.
The phenyl groups of P(2) are removed/omitted for
clarity.
3
.4 Oxidation of styrene
Both the iridium (1) and rhodium catalysts (2) were studied under
optimum conditions (previously determined by varying catalyst,
substrate and oxidant ratios) where a catalyst:substrate molar ratio of
:100 and substrate:oxidant molar ratio of 1:2.5 were used. When
,2ꢀdichloroethane (DCE) was used as a solvent, after 3 h, using
1
1
catalyst 1a, a 62% conversion was found, with a 15% yield to
benzaldehyde and a 1% yield to styrene oxide. When the reaction
was run for a further 6 h, the conversion increased to 96% and the
yield to benzaldehyde increased to 18% and styrene oxide to 2%.
When the solvent was changed to acetonitrile (MeCN), after 9 h,
Bond angles
1f
2f
(°)
P(1)ꢀMꢀP(2)
70.04(3)
101.02(14)
87.21(3)
70.10(3)
101.82(16)
87.58(3)
84.96(3)
P(1)ꢀN(1)ꢀ
P(2)
P(1)ꢀMꢀCl(1)
8
3% conversion was observed, with a 30% yield to benzaldehyde
and 24% yield to styrene oxide with the balance always being
benzoic acid. Higher catalytic activity in acetonitrile is attributed to
its polarity, where the different phases are uniform promoting mass
P(2)ꢀMꢀCl(1)
84.85(3)
2
10
The nitrogen atom is sp ꢀhybridized.
occasionally found in compounds with
Such hybridization is transfer.
54,55
a
P−N bond.
The Ir (1) catalysts are slightly more active than the Rh (2) catalysts
Additionally, the aromatic ring attached to the nitrogen atom is
largely twisted against the P−N−P plane (ca. 60−90°) as shown also
as shown by the reaction rates (Fig.4). This is due to the active oxo
3
4
4
5,46
Rh(III) complex having a lower affinity for the olefin. Such cases
in other Xꢀray crystal structures.
The diphosphinoamine ligands
3
4
also have been observed with Rh(C H ) (C H ) complexes. The
show a twist which may be due to steric interactions with the
nitrogen atom, and in cases where there is no coordinated metal it
has been shown to be due to intramolecular chargeꢀtransfer as noted
2
4 2
2
5
highest activities were exhibited by catalysts 1e (88%) and 2e (83%),
with the chlorophenyl group on the nitrogen atom. Catalysts 1c and
5
6ꢀ58
2
d were least active. Comparable activity between catalysts 1 and 2
in compounds such as pꢀdimethylaminobenzonitrile.
The crystal
with cyclohexyl (a) substituted and functionalized phenyl groups are
noted (e and f). The difference in the activity of the catalysts bearing
the different substituents could be attributed to their basicity. The
basic nature of the ligand is attributed to the substituent on the
nitrogen atom, which lowers the activity with an increase in basicity.
structures reveal that in all compounds, Cꢀbound H atoms are
involved in intermolecular C—H…halogen and πꢀπ interactions.
This links the fluorine of the counter ion to the compound via the
phenyl ring attached to the phosphorous atom.
2
0
6
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Catalysts 1ꢀ Conversion
Catalysts 1ꢀ Reaction Rate
Catalysts 2ꢀ Conversion
Catalysts 2ꢀ Reaction Rate
Catalysts with the cyclohexyl (a) and isopropyl (b) substituted
nitrogen atoms are comparable in terms of activity and yield to
benzaldehyde and styrene oxide and this comparable activity is also
noted in chromium catalysts bearing the same functional groups in
1
00
3
2
1
0
20
8
6
4
2
0
ethylene oligomerisation. This is due to these ligands having
similar basic properties. Increasing the chain length by at least four
carbons improves the selectivity, giving good selectivity to
0
0
0
0
20
benzaldehyde and poor selectivity to styrene oxide by catalyst 1c.
This again is likely due to the basic nature of catalyst 1c, since the
increase in carbon chain length increases the basic nature of the
catalyst. This controls the reaction whereby the metal goes from a
M(I) to M(III) species, thus controlling the selectivity to one product
a
b
c
d
e
f
Catalysts
(
benzaldehyde).
Figure 4. Conversion of styrene over catalysts 1 and 2 in MeCN.
Conditions: Catalyst:styrene (1:100); Styrene: TBHP
Table 3. Turnover numbers for catalysts 1 and 2 towards
(1:2.5); Temperature: 80 °C.
benzaldehyde and styrene oxide.
This basic substituent is likely to increase the electron density at the
metal center, which makes it easier for the oxidation process to
occur, where the oxidation state of the metal goes from a M(I) to
M(III) species (Scheme 1). However, the formation of the active
tertꢀbutoxy radical becomes more difficult, since the high basic
Turnover number (TON)
Catalysts
1
2
Benzaldehyde Styrene Benzaldehyde Styrene
III
Oxide
oxide
15
10
12
7
nature of the complex stabilizes the M oxidation state. Thus less
basic and electron withdrawing substituents such as 1e and 2e are
more active in comparison to 1c and 2c, where the alkyl substituent
increases the basic nature of the complex. The yields to
benzaldehyde for both catalysts are comparable, however, catalysts 1
are more selective to styrene oxide than catalysts 2 (Fig. 5). The
TONs towards benzaldehyde for catalysts 2 are slightly greater than
those of catalysts 1, however, the TONs towards styrene oxide are
higher for catalysts 1 (Table 3). This is an indication that deeper
oxidation is more prevalent when using catalysts 1, which also
reflects their high activity.
a
b
c
d
e
f
23
24
25
26
18
24
19
25
27
27
23
22
27
15
5
12
23
17
9
12
The catalyst with the chlorophenyl group (1e) is most selective to
styrene oxide, also giving the highest yield (28%) and TON (23).
The catalysts with the methoxy substituent (f) and the unsubstituted
phenyl group (d) exhibit similar activity and selectivity.
Unlike other studies reported, such as styrene oxidation carried out
by iridium cyclopentadienyl half sandwich complexes using PhIO as
an oxidant, where low yields to benzaldehyde (6ꢀ11%) and no
36
selectivity to styrene oxide was found, these systems achieve a
relatively good yield to both benzaldehyde and styrene oxide. In a
further comparison, bis(pyridylimino)isoindolatoꢀiridium complexes
gave a 55% conversion over a 48 h period with 50% yield to the
Catalysts 1ꢀBenzaldehyde
Catalysts 1ꢀstyrene oxide
Catalysts 2ꢀBenzaldehyde
Catalysts 2ꢀStyrene oxide
35
30
25
20
15
10
5
59
epoxide. Furthermore, triphenylphosphine complexes of Ir and Rh
used in the oxidation of styrene gave low yields to styrene
32,33
oxide.
. Using a PNNP system, Stoop et al. also reported low
60
conversions in the epoxidation of styrene. Early research by
Aneetha et al. using Ru(III) triphenylphosphine complexes reported
yields only to styrene oxide. Most studies involving ruthenium
61
ꢀ
complexes report higher yields to styrene oxide, but very little or no
a
b
c
d
e
f
62ꢀ66
yield to benzaldehyde under ambient conditions.
Few studies
Catalysts
have been reported on homogenous systems using cobalt, since
Figure 5. Yield to benzaldehyde and styrene oxide over catalysts 1
and 2 in MeCN.
much of the work has been done on heterogenizing these complexes
10,12,67,68
using supports such as zeolites.
conversion using cobaltꢀencapsulated zeolite
Li et al. reported a 63%
with higher
Conditions: Catalyst:styrene (1:100); Styrene: TBHP
Y
(1:2.5); Temperature: 80 °C.
67
selectivity to benzaldehyde than styrene oxide. With Schiff based
polymerꢀcobalt complexes, 20% selectivity to benzaldehyde was
69
found.
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The key feature of this system was the recovery of the catalyst. It has The conversion over catalyst 1c after cycle 1 decreased slightly from
been reported that when using phosphine based ligands the catalysts the original run (53% to 41%) and thereafter increased to be
70
are destroyed due to progressive oxidation of the ligands. The used essentially constant at 49% in cycle 2 and 48 % in cycle 3, results of
catalysts were recovered and characterized and the melting points which are probably within experimental error. Also, the repeat
(catalyst 1c recovered melting point: 263ꢀ264 °C) NMR (Fig. 6) and reactions were slightly more dilute. The yield to benzaldehyde is
single crystal XRD (Fig. 7) are comparable to those of the fresh comparable to the first run, however, the yield to styrene oxide
catalysts.
increases from cycle 1 (2%) to cycle 3 (6%). The recycled catalyst
c showed a decrease in conversion compared to the first run, but
2
Furthermore, the catalysts 1c and 2c were recovered and reꢀused
over 3 cycles (Fig. 8) (see supporting information). However, the
amount of catalyst recovered decreased over time, due to mechanical
loss and the small quantities involved.
significantly increased in cycle 3 (from 45 % to 65 %). This could be
due to concentration effects. The yield to benzaldehyde is
comparable to the first run, however, the yield to styrene oxide
decreased (from 15% to 5 %).
Recovered
Catalysts 1cꢀ Benzaldehyde
Catalyst 1cꢀ Styrene oxide
Conversion 1c
Catalyst 2cꢀ Benzaldehyde
Catalyst 2cꢀ Styrene oxide
Conversion 2c
40
30
20
10
ꢀ
80
60
40
20
0
Fresh
1
2
3
Cycle
Figure 8. Conversion of styrene by recovered catalysts over 1c and
c over three cycles in MeCN.
Conditions: Catalyst:styrene (1:100); Styrene: TBHP
1:2.5); Temperature: 80 °C.
2
(
LMI
+
C(CH ) OOH
LMIIIꢀOꢀO + C(CH
3
3
) OH
3 3
(1)
1
c
2c
A
3
1
Figure 6. P NMR of the recovered and fresh catalysts 1c and 2c.
+
LMIIIꢀOꢀO
(2)
O
MIII
O
B
(3)
O
O
MIII
O
O
MIII
L
C
O
O
+
+
other products
other products
O
(
4)
O
O
O L
MIII
D
Figure 7. Structure of recovered complex 1c with labelling
scheme. The phenyl groups of P(2) are removed/omitted
for clarity.
LMI
Scheme 1. Proposed mechanism for the oxidation of styrene by
complexes 1 and 2.
8
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To elucidate the mechanism by which these two products form, Ahmad, A. L.; Koohestani, B.; Bhatia, S.; Ooi, S. B. Int. J Appl.
Ceram. Technol. 2012, 9, 588.
Patel, A.; Patel, K. Inorg. Chim. Acta 2014, 419, 130.
Karandikar, P.; Agashe, M.; Vijayamohanan, K.; Chandwadkar, A.
J. Appl. Catal. Aꢀ Gen. 2004, 257, 133.
Patil, N. S.; Jha, R.; Uphade, B. S.; Bhargava, S. K.; Choudhary,
V. R. Appl. Catal. Aꢀ Gen. 2004, 275, 87.
styrene oxide was used as a substrate with catalyst 1 under optimum
conditions. The reaction was monitored over 9 h, during which time
no conversion took place. When benzaldehyde was used as a
substrate, under the same conditions, the deeper oxidized product,
benzoic acid and the cleaved product benzene formed. On the basis
4
5
6
of this experimental work and the mechanism proposed by Li et al. 7 Patel, A.; Pathan, S. Ind. Eng. Chem. Res. 2011, 51, 732.
8
on a cobalt system, a probable mechanism is proposed in Scheme 1.
The metal complex (M(I)) can activate and bind to oxygen from the
oxidant (tꢀBuOOH) forming a peroxo M(III) species (A) (eqn 1)
which then reacts with styrene to form the intermediate (B) eqn
8 Li, Z.; Wu, S.; Ding, H.; Lu, H.; Liu, J.; Huo, Q.; Guan, J.; Kan, Q.
New J. Chem. 2013,37, 4220.
Ding, Y.; Gao, Q.; Li, G.; Zhang, H.; Wang, J.; Yan, L.; Suo, J. J.
Mol. Catal. Aꢀ Chem. 2004, 218, 161.
0 Hu, J.; Li, K.; Li, W.; Ma, F.; Guo, Y. Appl. Catal. Aꢀ Gen 2009,
9
1
1
1,67,71,72
(2).
Rearrangement of intermediate B to form C and
364, 211.
generation of the catalyst occurs (eqn 4). The formation of
benzaldehyde and styrene oxide via two different pathways occurs
1 Grigoropoulou, G.; Clark, J. H.; Elings, J. A. Green Chem. 2003,
5, 1.
12 Yang, Y.; Ding, H.; Hao, S.; Zhang, Y.; Kan, Q. Appl.
Organomet. Chem. 2011, 25, 262.
1,20,67,71ꢀ73
through D (eqn 4).
1
3 Duarte, T. A. G.; Estrada, A. C.; Simoes, M. M. Q.; Santos, I. C.
M. S.; Cavaleiro, A. M. V.; Neves, M. G. P. M. S.; Cavaleiro, J.
A. S. Catal. Sci. Technol. 2015, 5, 351.
4 Amanchi, S. R.; Patel, A.; Das, S. K. J. Chem. Sci. 2015, 126,
1641.
Conclusions
New iridium and rhodium complexes have been synthesized and
fully characterized and were used as catalysts in the oxidation of
styrene. The iridium catalysts are more active than the rhodium
1
catalysts. This could be due to the active oxo Rh(III) complex having 15 Warth A, D. Appl. Environ. Microbiol. 1991, 57, 3410.
1
6 Chiappe, C.; Sanzone, A.; Dyson, P. J. Green Chem. 2011, 13,
437.
7 Kanmani, A. S.; Vancheesan, S. Stud. Surf. Sci. Catal. 1998,
13, 285.
8 Teo, S.; Weng, Z.; Hor, T. S. A. Organometallics 2008, 27, 4188.
9 Blann, K.; Bollmann, A.; Dixon, J. T.; Hess, F. M.; Killian, E.;
Maumela, H.; Morgan, D. H.; Neveling, A.; Otto, S.; Overett, M.
J. Chem. Commun. 2005, 620.
0 Blann, K.; Bollmann, A.; de Bod, H.; Dixon, J. T.; Killian, E.;
Nongodlwana, P.; Maumela, M. C.; Maumela, H.; McConnel, A.
E.; Morgan, D. H.; Overette, M. J.; Pŕetorius, M.; Kuhlmann, S.;
Wasserscheid, P. J. Catal. 2007, 249, 244.
1 Overett, M. J.; Blann, K.; Bollmann, A.; Dixon, J. T.; Hess, F.;
Killian, E.; Maumela, H.; Morgan, D. H.; Neveling, A.; Otto, S.
Chem. Commun. 2005, 622.
a lower affinity for the olefin. The yield to benzaldehyde by both
catalysts is comparable and is much higher than that of styrene
oxide. However, the iridium catalysts give a higher yield to styrene
oxide. The catalysts bearing the chloro phenyl group on the nitrogen
atom is most active and gives the highest yield to styrene oxide. The
difference in the activity of the catalysts bearing the different
substituents on the nitrogen atom, of the ligand backbone, could be
attributed to the basicity of the ligand backbone. The catalysts were
recovered, characterized and recycled over 3 cycles. The activity and
yield to styrene oxide drops, however, the yield to benzaldehyde
remains constant. The work shows that, though somewhat neglected,
PNP complexes of Ir and Rh may indeed have considerable potential
in the selective oxidation of styrene.
1
1
1
1
1
2
2
2
2 Bollmann, A.; Blann, K.; Dixon, J. T.; Hess, F. M.; Killian, E.;
Maumela, H.; McGuiness, D. S.; Morgan, D. H.; Neveling, A.;
Otton, S.; Overette, M.; Slawin, A. M. Z.; Wassercheid, P.;
Kihlmann, S. J. Am. Chem. Soc. 2004, 126, 14712.
3 Bowen, L. E.; Haddow, M. F.; Orpen, A. G.; Wass, D. F. Dalton
Trans. 2007, 1160.
Acknowledgements
The authors gratefully acknowledge the financial support from NRF,
THRIP (Grant number 1208035643) and UKZN (URF).
2
Notes and references
24 Bowen, L. E.; Charernsuk, M.; Hey, T. W.; McMullin, C. L.;
a
School of Chemistry and Physics, University of KwaZuluꢀNatal,Durban,
Orpen, A. G.; Wass, D. F. Dalton Trans. 2010, 39, 560.
2
2
5 Naicker, D.; Friedrich, H. B.; Omondi, B. RSC Adv. 2015,
, 63123.
6 BenitoꢀGaragorri, D.; Alves, L. G. A.; Puchberger, M.; Mereiter,
K.; Veiros, L. F.; Calhorda, M. J.; Carvalho, M. D.; Ferreira, L.
P.; Godinho, M.; Kirchner, K. Organometallics 2009, 28, 6902.
7 BenitoꢀGaragorri, D.; Kirchner, K. Acc. Chem. Res. 2008, 41,
South Africa. Eꢀmail: duneshanaicker@gmail.com
School of Chemistry and Physics, University of KwaZuluꢀNatal,Durban,
b
5
South Africa. Eꢀmail: friedric@ukzn.ac.za
c
School of Chemistry and Physics, University of KwaZuluꢀNatal,Durban,
South Africa. Eꢀmail: pansuriya@ukzn.ac.za
2
†
Electronic Supplementary Information (ESI) available: [details of
2
01.
crystallographic data]. See DOI: 10.1039/b000000x/.
2
2
8 van der Boom, M. E.; Milstein, D. Chem. Rev. 2003, 103, 1759.
9 Xu, X.; Xi, Z.; Chen, W.; Wang, D. J. Coord. Chem. 2007, 60,
2
297.
30 Albrecht, M.; van Koten, G. Angew. Chem. Int. Ed. 2001, 40,
750.
References
3
1
2
Bruin, de B.; Budzelaar, P. H. M.; Gal, A. W. Angew. Chem. Int.
Ed. 2004, 43, 4142.
31 Collman, J. P.; Kubota, M.; Hosking, J. W. J. Am. Chem .Soc.
1967, 89, 4809.
Tada, M.; Muratsugu, S.; Kinoshita, M.; Sasaki, T.; Iwasawa, Y. J. 32 Takao, K.; Wayaku, M.; Fujiwara, Y.; Imanaka, T.; Teranishi, S.
Am. Chem. Soc. 2009, 132, 713.
3
B. Chem. Soc. Jpn. 1970, 43, 3898.
3
3 Takao, K.; Fujiwara, Y.; Imanaka, T.; Teranishi, S. B. Chem. Soc.
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 9

RSC Advances
Page 10 of 11
View Article Online
ARTICLE
6RA01276K
DOI: 10.1039Jo/Curnal Name
Jpn. 1970, 43, 1153.
4 Farrar, J.; Holland, D.; Milner, D. J. Dalton Trans. 1975, 815.
5 Suzuki, T. Chem. Rev. 2011,111, 1825.
6 Turlington, C. R.; Harrison, D. P.; White, P. S.; Brookhart, M.;
Templeton, J. L. Inorg. Chem. 2013, 52, 11351.
66 Moghadam, M.; Mirkhani, V.; Tangestaninejad, S.;
3
3
3
MohammadpoorꢀBaltork, I.; Kargar, H.; Sheikhshoaei, I.; Hatefi,
M. J. Iran. Chem. Soc. 2011, 8, 1019.
67 Li, Z.; Wu, S.; Ma, Y.; Liu, H.; Hu, J.; Liu, L.; Huo, Q.; Guan, J.;
Kan, Q. Transit. Metal Chem. 2013, 38, 243.
3
3
7 Kang, J. W.; Moseley, K.; Maitlis, P. M. J. Am. Chem .Soc. 1969, 68 Luo, Y.; Lin, J. Micropor. Mesopor. Mat. 2005, 86, 23.
9
1, 5970.
69 Demetgül, C.; Delikanlı, A.; Sarıbıyık, O. Y.; Karakaplan, M.;
Serin, S. J. Am. Chem.Soc. 2012, 15, 75.
8 Ball, R. G.; Garaham, W. A. G.; Heinekey, D. M.; Hoyano, J. K.;
McMaster, A. D.; Mattson, B. M.; Michel, S. T. Inorg. Chem.
70 Bressan, M.; Morvillo, A. Inorg. Chem. 1989, 28, 950.
71 Tang, Q.; Zhang, Q.; Wu, H.; Wang, Y. J. Catal. 2005, 230, 384.
72 Valand, J.; Parekh, H.; Friedrich, H.B. Catal. Commun. 2013, 40,
149.
73. Cui, H.; Zhang, Y.; Zhao, L.; Zhu, Y. Catal. Commun. 2011, 12,
417.
1
990, 29, 2023.
3
4
9 White, C.; Yates, A.; Maitlis, P. M. Inorg. Synth. 1992, 29.228.
0 Govindaswamy, P.; Mozharivskyj, Y. A.; Kollipara, M. R.
Polyhedron 2005, 24, 1710.
1 Sheldrick, G. M.; 2.05 ed.; SHELXSꢀ97, SHELXLꢀ97 and
SADABS version 2.05, University of Göttingen, Germany: 1997.
2 Sheldrick, G. Acta Crystallogr., Sect. A:. 2008, 64, 112.
3 Otwinowski, Z and Minor, Z. Processing of Xꢀray Diffraction
Data Collected in Oscillation Mode, Methods in Enzymology,
Macro. Cryst. A, 1997, 276, 307. C.W. Carter, Jr. and R. M.
Sweet, Eds., Academic Press (New York).
4
4
4
4
4
4
4 Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A.
K.; Puschmann, H. J. Appl. Crystallogr. 2009, 42, 339.
5 Valderrama, M.; Contreras, R.; Boys, D. J. Organomet. Chem.
2
003, 665, 7.
6 SimónꢀManso, E.; Valderrama, M. J. Organomet. Chem. 2006,
91, 380.
6
4
4
7 von Philipsborn, W. Chem. Soc. Rev. 1999, 28, 95.
8 Elsevier, C. J.; Ernsting, J. M.; de Lange, W. G. J. J. Chem. Soc.
Chem. Commun. 1989, 585.
4
5
9 Carlton, L. Magn. Reson. Chem. 1997, 35, 153.
0 Ernsting, J. M.; Gaemers, S.; Elsevier, C. J. Magn. Reson. Chem
2
004, 42, 721.
1 Elsevier, C. J.; Kowall, B.; Kragten, H. Inorg. Chem. 1995, 34,
836.
2 Appleby, T.; Derek Woollins, J. Coord. Chem. Rev. 2002, 235,
21.
5
5
4
1
5
5
3 Fei, Z.; Dyson, P. J. Coord. Chem. Rev. 2005, 249, 2056.
4 Albright, T. A.; Burdett, J. K. Problems in Molecular Orbital
Theory. 1992, 103. Oxford University Press: New York.
5 Browning, C. S.; Farrat, D. H.; Frankel, D. C. Acta Cryst. Sec. C
5
5
5
1
992, C48, 806.
6 Grabowski, Z. R.; Rotkiewicz, K.; Rettig, W. Chem. Rev. 2003,
03, 3899.
1
7 Druzhinin, S. I.; Dubbaka, S. R.; Knochel, P.; Kovalenko, S. A.;
Mayer, P.; Senyushkina, T.; Zachariasse, K. A. J. Phys. Chem. A
2
008, 112, 2749ꢀ2761.
5
8 Ganesamoorthy, C.; Balakrishna Ms Fau ꢀ Mague, J. T.; Mague Jt
Fau ꢀ Tuononen, H. M.; Tuononen, H. M. Inorg. Chem. 2008, 47,
7
035.
5
6
6
6
6
6
6
9 Camerano, J. A.; Sämann, C.; Wadepohl, H.; Gade, L. H.
Organometallics 2011, 30, 379.
0 Stoop, R. M.; Bachmann, S.; Valentini, M.; Mezzetti, A.
Organometallics 2000, 19, 4117.
1 Aneetha, H.; Padmaja, J.; Zacharias, P. S. Polyhedron 1996, 15,
2
445.
2 Antony, R.; Tembe, G. L.; Ravindranathan, M.; Ram, R. N.
Eur. Polym. J. 2000, 36, 1579.
3 Barf, G. A.; van den Hoek, D.; Sheldon, R. A. Tetrahedron 1996,
5
2, 12971.
4 Chatterjee, D.; Basak, S.; Riahi, A.; Muzart, J. J. Mol. Catal. Aꢀ
Chem. 2006, 255, 283.
5 Cheng, W.ꢀC.; Fung, W.ꢀH.; Che, C.ꢀM. J. Mol. Catal. Aꢀ
Chem. 1996, 113, 311.
1
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DOI: 10.1039/C6RA01276K
O
O
TBHP, MeCN, 80 °C
New Ir and Rh “PNP” aminidiphoshphine complexes have been synthesised, characterised and used
as catalysts in styrene oxidation with tert-butyl hydroperoxide as the oxidant. The Ir catalysts were
more active than the Rh catalysts with high yields to benzaldehyde in comparison to styrene oxide.