Synthesis of a series of new platinum organometallic complexes derived from bidentate Schiff-base ligands and their catalytic activity in the hydrosilylation and dehydrosilylation of styrene

Article abstract of DOI:10.1039/c5dt01407g

The synthesis and properties of a novel class of platinum complexes containing Schiff bases as O,N-bidentate ligands is described as are the solution and solid state properties of the uncomplexed ligands. The platinum complexes were prepared from [PtBr₂(COD)] (COD = 1,5-cyclooctadiene) and N-(2-hydroxy-1-naphthalidene)aniline derivatives in the presence of base (NaOBu^t). Instead of a substitution reaction to afford cationic species, the addition of the Schiff base ligands results in both the formal loss of two equivalents of bromide and addition of hydroxide to the COD ligand of the complexes. It is proposed that this reaction proceeds through a cationic platinum complex [Pt(N-O)(COD)]Br which then undergoes addition of water and loss of HBr. An example of a dinuclear platinum complex in which two cyclo-octene ligands are bridged by an ether linkage is also reported. The platinum complexes were evaluated as catalysts for the hydrogenative and dehydrogenative silylation of styrene, the resulting behaviour is substituent, time and temperature dependent.

Full text of DOI:10.1039/c5dt01407g

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Synthesis of a series of new platinum
organometallic complexes derived from bidentate
Schiff-base ligands and their catalytic activity in
the hydrosilylation and dehydrosilylation of
styrene†
Cite this: DOI: 10.1039/c5dt01407g
a,b
b
a
b
M. Belhadj Lachachi, Tayeb Benabdallah, Pedro M. Aguiar, M. Hadj Youcef,
a
a
Adrian C. Whitwood and Jason M. Lynam*
The synthesis and properties of a novel class of platinum complexes containing Schiff bases as
O,N-bidentate ligands is described as are the solution and solid state properties of the uncomplexed
ligands. The platinum complexes were prepared from [PtBr
2
(COD)] (COD = 1,5-cyclooctadiene) and
t
N-(2-hydroxy-1-naphthalidene)aniline derivatives in the presence of base (NaOBu ). Instead of a substi-
tution reaction to afford cationic species, the addition of the Schiff base ligands results in both the formal
loss of two equivalents of bromide and addition of hydroxide to the COD ligand of the complexes. It is
proposed that this reaction proceeds through a cationic platinum complex [Pt(N–O)(COD)]Br which then
undergoes addition of water and loss of HBr. An example of a dinuclear platinum complex in which two
cyclo–octene ligands are bridged by an ether linkage is also reported. The platinum complexes were eval-
uated as catalysts for the hydrogenative and dehydrogenative silylation of styrene, the resulting behaviour
is substituent, time and temperature dependent.
Received 14th April 2015,
Accepted 26th May 2015
DOI: 10.1039/c5dt01407g
www.rsc.org/dalton
ligands typically coordinate to transition metals through hard
nitrogen and oxygen donors and as such have principally
Introduction
Schiff bases represent a versatile and diverse class of ligands found application with first row and/or early transition
8
for transition metal compounds. The ligands are typically pre- metals. However, there are a number of complexes reported
pared from the condensation reaction of either an aldehyde or in which these ligands bind to softer metals such as ruthe-
9
ketone with a primary amine and, as such, it is possible to nium(II), rhodium(I), palladium(II) and platinum(II).
introduce a wide variety of steric and electronic features into
their structure. Traditional Schiff bases act as bidenatate N–O have found their principal application in oxidation/reductive
As expected from their hard nature, Schiff base ligands
1
1
0
donors to a single metal centre, however, there are additional reactions as well as catalysts for hydrolysis. However, includ-
examples in which the ligand may act as a tridentate N,O,O-, ing hard donor ligands into the coordination sphere of soft
N,O,N-, N,O,S- or tetradentate N,N,O,O-donor ligand permit- metal centres raises the possibility of introducing unusual
ting the synthesis of multinuclear complexes, including one- electronic features at a given metal and thus imparting novel
2
two- and three-dimensional metal organic frameworks. There- catalytic properties when compared to more traditional
fore, Schiff base ligands have found widespread application ligands for low oxidation state metals such as phosphines,
3
4
5
in catalysis, electrochemistry, nanotechnology, materials alkenes and carbon monoxide. In addition to creating such a
6
7
science and as potential therapeutic agents. Schiff base hard/soft mismatch, Schiff base ligands are attractive as it is
relatively straightforward to prepare a library of related ligands,
thus allowing structure/activity relationships to be readily
probed.
a
Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK.
E-mail: Jason.lynam@york.ac.uk; Tel: +44 (0)1904322534
b
The synthesis of some new platinum complexes which
Laboratory of Chemistry and Electrochemistry of Metallic Complexes, Department of
Organic Chemistry, Faculty of Chemistry, University of Sciences and Technology of
contain hard Schiff base ligands using [PtBr (COD)] as a pre-
2
Oran, BP 1505 El M’Naouar, Oran, 31000, Algeria
cursor is now described. The coordination of the Schiff base
promotes an unusual hydration reaction of the cyclo–octadiene
ligand. The new platinum complexes are catalysts for hydro-
genative and dehydrogenative silylation of styrene and the
†
Electronic supplementary information (ESI) available: Details of X-ray diffrac-
tion experiments, UV-vis, MS and NMR spectra. CCDC 1055267–1055271. For
ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c5dt01407g
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activity depends upon the nature of the substituents on the
Schiff base.
Results and discussion
Five naphthyl-substituted Schiff-base ligands, 3, were prepared
in good yield from the condensation of 2-hydroxy-1-naphthal-
dehyde, 1, with 4-substituted anilines 2 (Scheme 1) using the
1
1
method described by Salman and co-workers. In addition to
Fig. 1 Solid state structure of 3a, thermal ellipsoids are shown at the
characterisation by NMR spectroscopy, elemental analysis and 50% probability level, selected hydrogen atoms removed for clarity.
Selected bond lengths (Å) and angles (°) C(1)–O(1) 1.2683(14), C(11)–N(1)
mass spectrometry, the structures of 3a (Fig. 1), 3c (Fig. 2) and
1
1
.3321(14), C(12)–N(1) 1.3922(14), C(15)–N(2) 1.4500(14); N(2)–O(2)
.2305(13), N(2)–O(3) 1.2289(14); C(11)–N(1)–C(12) 127.54(10), O(1)–
3
d (Fig. 3) were determined by single crystal X-ray diffraction.
1
2
Compounds
3 exhibit a keto–enol tautomerisation
C(1)–C(10) 122.69(11).
(Scheme 2) and the effects of the different substituents present
was probed by a number of different techniques. The UV-
visible spectra of the organic ligands were studied in a series
of solvents with different polarity ranging from protic, polar
1
3
aprotic to non-polar. The results indicate that the studied
Schiff bases are characterized by the presence of two tauto-
mers, a phenol–imine form and a keto–amine form. It was
also observed that the Schiff bases show two bands in the
visible region located above 400 nm (see ESI†) which were
1
1
assigned to the keto–amine form. The phenol–imine form
has no appreciable absorbance in this region. The UV-visible
spectra for the five Schiff base ligands indicates an increase in
the proportion of the keto–amine form as the solvent polarity
Fig. 2 Solid state structure of 3c, thermal ellipsoids are shown at the
increases. It was concluded that the phenol–imine form predo- 50% probability level. Selected bond lengths (Å) and angles (°) C(11)–N(1)
minates in non-polar aprotic solvents such as toluene and 1.2932(14), C(12)–N(1) 1.4143(14), C(1)–O(1) 1.3427(16); C(11)–N(1)–C(12)
119.71(10), O(1)–C(1)–C(10) 122.30(10).
cyclohexane, while the keto–amine form is predominant in
polar solvents, such as chloroform and ethanol. Indeed, in a
related system the keto–amine form has been shown to be
highly polar and a charge-density study supports a contri-
1
4
bution to the bonding from the proposed Lewis structure.
1
13
A comparison between the H and C NMR spectroscopic
data in both solution and solid state is given in Table 1, which
1
5
13
are consistent with previous reports. In the C CPMAS NMR
spectrum the chemical shifts of C-2 and C-α (see Scheme 2 for
Fig. 3 Solid state structure of 3d, thermal ellipsoids are shown at the
0% probability level. Selected bond lengths (Å) and angles (°) C(1)–Cl(1)
5
1
1
.7354(12), C(4)–N1 1.4039(16), C(7)–N(1) 1.3060(16), C(9)–O(1)
.3026(16); C(7)–N(1)–C(4) 124.16(11), O(1)–C(9)–C(8) 122.14(12).
labelling) are sensitive to the proton position and gives an
indication of the relative population of both tautomers. The
chemical shift of the C-2 carbon of 3a (δ 189.9) suggests that
the keto–amine form dominates in this structure. The data
from a single crystal X-ray diffraction study support this argu-
ment with the observation of short C(1)–O(1), 1.2683(14) Å,
and long C(11)–N(1), 1.3321(14) Å, bonds. In 3d, the chemical
1
3
Scheme 1 (i) EtOH, 2 hours, reflux.
shift of C-2 in the solid state C NMR is δ 172.9 suggesting a
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t
t
2
Scheme 3 (i) +NaO Bu, +H O, −NaBr, −HBr, −HO Bu, thf, 24 h.
Scheme 2 Keto–enol tautomerisation in compounds 3.
Table 1 Comparison between the solution and the solid state NMR for
1
13
the five bidentate Schiff bases (selected H and C chemical shifts)
NH/OH (ppm) C-2 (ppm) C-α (ppm)
CD Cl CD Cl
Entry
CD
Cl
2 2
Solid
2
2
Solid
2
2
Solid
a
3
3
3
3
3
a
b
c
d
e
14.88
15.62
15.46
15.2
11.9
16.3
14.2
15.2
15.2
193.9/168.8
167.8
169.4
167.5
167.9
189.9
169.9
180
172.9
170.1
158.2
154.9
155.5
157.3
155.2
141.7
149.5
145.1
148.2
148.9
15.59
a
Slow exchange between tautomers occuring.
greater contribution from the phenol–imine form and analysis
of the X-ray data of this compound, shows a longer C(9)–O(1)
1
.3026(16) and a shorter C(7)–N(1) 1.3060(16) bond. Unfortu-
nately, the correlation between the chemical shift of C-2 in the
1
3
solid state C NMR spectrum and the structure obtained by
X-ray diffraction does not hold for 3c, the latter technique pre-
dicts that the phenol–imine form should dominate (C(1)–O(1)
1
.3427(16) Å, C(11)–N(1) 1.2932(14) Å), but the resonance of
Fig. 4 Solid state structure of 4c (a) major component (79%) and (b)
minor component (21%). Thermal ellipsoids are shown at the 50% prob-
ability level, selected hydrogen atoms omitted for clarity. Selected bond
C-2 is actually less-shielded than that for 3d. However, it
should be noted that the two experiments report on the nature
of the chemical environment at two very different tempera- lengths (Å) and angles (°) in major form. Pt(1)–N(1) 2.106(4), Pt(1)–O(1)
tures, ca. 300 K for NMR versus 110 K for X-ray. In any event, it 2.028(4), Pt(1)–C(1) 2.136(7), Pt(1)–C(2) 2.149(7), Pt(1)–C(6) 2.011(6),
C(1)–C(2) 1.413(10), C(5)–C(6) 1.540(12), O(2)–C(5) 1.435(12); N(1)–
Pt(1)–C(1) 103.1(3), N(1)–Pt(1)–C(2) 95.7(2), O(1)–Pt(1)–N(1) 87.79(15),
O(1)–Pt(1)–C(1) 154.9(3), C(6)–Pt(1)–N(1) 175.3(2), C(6)–Pt(1)–O(1)
is clear that the substituent on the phenyl ring and the solvent
has a significant effect on the keto–enol tautomerisation.
In order to explore the coordination chemistry of ligands 3,
87.9(2), C(6)–Pt(1)–C(1) 81.5(3), C(6)–Pt(1)–C(2) 88.0(3). Selected bond
a
platinum-based precursor was employed. Reaction of lengths in minor form (Å) Pt(1)–C(1A) 2.206(17), Pt(1)–C(2A) 2.144(19),
t
[PtBr
2
(COD)] with ligands 3 in the presence of NaO Bu resulted Pt(1)–C(6A) 1.982(19).
in the formation of platinum complexes 4 (Scheme 3). Analysis
1
of the products by H NMR spectroscopy revealed that two pro-
ducts in approximately a 3.5 : 1 ratio were present, each with num through its nitrogen and oxygen atoms. However, the
an imine proton that exhibited platinum satellites, confirming structure determination demonstrated that the COD ligand
that the Schiff base ligand was coordinated to the metal. Evi- had been functionalised when compared to the precursor and
dence for a coordinated C
the number of resonances indicated that the complexes did elled as a hydroxyl group. The hydroxyl was disordered over
not contain a mirror plane.
two positions and thus explained the appearance in the NMR
8
ligand was also present, although an extra peak of electron density was present which was mod-
The identity of complexes 4 was confirmed by a single spectra of two imine resonances which were assigned to the
crystal X-ray diffraction study on 4c (Fig. 4). This study demon- two geometric isomers of 4. The bond lengths between the
strated that the Schiff-base ligand was coordinated to the plati- platinum and the three metal bound carbons are consistent
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t
t
2
Scheme 4 (i) +NaO Bu, −NaBr −HO Bu, (ii) +H O, −HBr, thf, 24 h.
with C(1) (2.136(7) Å), and C(2) (2.149(7) Å) binding as a
π-bound alkene, whereas C(6) (2.011(6) Å) is a typical plati-
num–carbon single bond.
A possible pathway explaining the formation of complexes 4
t
is shown in Scheme 4. It is proposed that NaO Bu acts to
deprotonate the –OH group of 3 which then reacts with
+
[
PtBr (COD)] to give cationic intermediate [5] . Nucleophilic
2
attack of adventitious water onto the coordinated COD ligand
+
will then be enhanced by the cationic nature of [5] . Formal
loss of HBr will then afford the observed product. Further-
more, attempts to record mass spectra of complexes 4 exhibi-
+
ted a peak with a mass-to-charge ratio corresponding to [5] .
This may indicate that (at least in the mass spectrometer) loss Fig. 5 (a) Solid state structure of 6e, pentane of crystallisation omitted
−
of OH from 4 may occur.
for clarity (b) coordination environment of the two platinum atoms.
Thermal ellipsoids are shown at the 50% probability level, selected
hydrogen atoms omitted for clarity. Selected bond lengths (Å) and
angles (°) N(1)–Pt(1) 2.116(4), N(2)–Pt(2) 2.051(4), O(1)–Pt(1) 2.017(4),
O(4)–Pt(2) 2.091(3), C(22)–Pt(1) 2.103(5), C(23)–C(24) 1.474(7), C(23)–
Nucleophilic attack at COD ligands within the coordination
sphere of both neutral and cationic d -metal complexes is
a well-established process. Attack at neutral complexes with
1
6
17
8
alkoxide or malonate-based nucleophilies occurs directly at the Pt(1) 2.120(5), C(19)–Pt(1) 2.048(4), C(30)–Pt(2) 2.148(4), C(31)–C(32)
COD ligand, whereas in the case of Grignard reagents an 1.504(7), C(31)–Pt(2) 2.133(4), C(26)–O(3) 1.429(5), C(27)–O(3) 1.446(5),
C(34)–Pt(2) 2.058(4); O(1)–Pt(1)–N(1) 88.43(15), N(2)–Pt(2)–O(4)
89.09(13), C(19)–Pt(1)–N(1) 175.69(17), C(34)–Pt(2)–O(4) 173.07(15).
initial M–C bond formation is followed by migration of the
1
6d
organic group to COD.
Given that water is much poorer
nucleophile that many of those previously studied, we favour a
pathway involving the cationic intermediate with the exo attack
indicated in the structure of 4c indicating that direct addition
1
6d
to the COD has occurred.
On one occasion a further complex was obtained from an
attempt to re-crystallise complex 4e. In this instance, a single
crystal X-ray diffraction study demonstrated that a dimeric
species was obtained in which two complexes are bridged by a
single oxygen atom (Fig. 5).
The structural determination demonstrated that each plati-
num was in an approximately square-planar environment and
that in the case of Pt(1) the nitrogen atom was trans to the
alkyl-part of the modified COD ligands and the oxygen trans to
the carbon–carbon double bond. At Pt(2) the relative position
of the nitrogen and oxygen atoms with respect to the organic
+
ligand are interchanged. The bond metrics within the coordi- Scheme 5 (i) thf, −H .
nation environment of each platinum reflect these changes,
for example, when the heteroatom is trans to the hard alkyl
group the Pt–X bonds are lengthened, whereas the metal– Here, the hydroxyl-group of a complex 4e undergoes a further
heteroatom bonds are shortened when trans to the softer, reaction with putative 5 to give 6e (Scheme 5). Alternatively,
π-accepting, alkene group. The formation of 6e may be complexes 6 could be formed from the dehydration of two
explained on the basis of the initial mechanistic hypothesis. equivalents of 4. In any event, the exo attack indicated in the
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structure of 6e indicates that direct combination of the COD
ligands is occurring.
The ability of the platinum complexes to promote hydro-
silylation was then explored. The formation of Si–C bonds
remains a key industrial process and platinum-based systems,
such as Speier’s and Karstedt’s catalysts played an important
role in the development of transition metal mediated hydro-
1
8
silylation. More recently a number of other metal-based
1
9
systems have been shown to be active catalysts. Furthermore,
there are number of different competing pathways in a given
hydrosilylation reaction, including different regiochemical out-
2
0
comes and processes such as dehydrosilylation. Access to a Fig. 6 Catalyst activity over 12 h of complexes 4a–4e in the reaction
3
between HSiEt and styrene showing the formation of the 9 at 110 °C.
The lines shown are a guide to the eye.
number of related catalyst structures with various different
functional groups would allow for the effects of these substitu-
ents on the outcome of the reaction to be readily probed.
Our experiments focused on the ability of complexes 4 to
promote the addition of HSiEt , 8, to styrene, 7. When the
3
resulting reaction was monitored by GC-MS it was clear that in
addition to hydrosilylation occurring to give 9 (Scheme 6),
dehydrosilylation was competing to give 10. With this in mind,
the effects of a number of variables in the reaction such as the
nature of the catalyst, time and temperature on the outcome of
the reaction were explored. In order to achieve this, a number
8
of reactions were performed in NMR tubes using d -toluene as
2
1
solvent, 5 mol% of platinum catalyst and a 1 : 1 ratio of 7 to
1
8
. In addition to H NMR, reaction progress was monitored by
gas chromatography (GC), following the conversion of 7 to
products.
The data in Table 2 illustrate the conversion rate for the
hydrosilylation of styrene by triethysilane after 12 h, with
different catalyst precursors and temperature variation from
Fig. 7 Catalyst activity over 12 h of the complexes 4a–4e for the for-
mation of 10 from styrene and HSiEt at 110 °C. The lines shown are a
3
guide to the eye.
5
0 °C to 110 °C. It is clear that both of the catalysts 4b and 4e
have a better catalytic activity than the other platinum com-
Scheme 6 (i) toluene, 12 h, 4 (5 mol%).
3
Table 2 Total conversions/% for hydrosilylation reaction of HSiEt and
styrene (formation of 9) in the presence of 4a–e at different
temperatures
Fig. 8 Catalytic activity for complex 4b in the hydrosilylation of styrene
by HSiEt at different temperatures over 12 h. The lines shown are a
a
3
guide to the eye.
Temp. (°C)
Catalyst
50
70
90
110
plexes, except at 70 °C, where 4c and 4e have the highest
activity. In general, the activity of the catalysts may be divided
into two groups, the first containing electron withdrawing
groups, 4a and 4d, the other electron donatings groups, 4b
and 4e, with 4c is situated in the middle.
4
4
4
4
4
a
b
c
d
e
30
42
36
35
37
38
35
46
31
43
32
49
45
33
45
50
65
46
42
60
a
Reaction conditions: HSiEt
a–e (5 mol%), toluene (0.5 mL), 12 h. Product yields calculated by H
3
(8) (0.18 mmol), styrene (7) (0.18 mmol),
1
The catalytic data demonstrate that at 110 °C all of the plati-
NMR and verified by GC-MS (conversion relative to concentration of num complexes give excellent conversion to hydrosilylated pro-
4
3
HSiEt ).
ducts. The ratio of 9 to 10 varies depending on both the
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Table 3 Conversions/% to the hydrosilated 9 and the dehydrosilylated was dried over sodium and CD
product 10 by varying the time and the catalyst during the reaction of
HSiEt with styrene
3
2
Cl
2
used for NMR experiments
was dried over CaH2 and degassed with three freeze–pump–
thaw cycles. The solvent was then vacuum transferred into
NMR tubes fitted with PTFE J. Young’s taps. All other solvents
were used as received from Sigma-Aldrich UK. NMR spectra
a
1
h
2 h
3 h
4 h
12 h
Time
Product
b
b
b
b
b
b
b
b
b
b
9
10
9
10
9
10
9
10
9
10
1
were acquired on either a Jeol 400 (Operating Frequencies H
1
3
3
99.8 MHz, C 100.5 MHz) or a Bruker Avance 500 spectro-
Catalyst
1
13
13
4
4
4
4
4
a
b
c
d
e
12
11
7
4
9
25
17
33
29
13
20
25
16
14
22
31
23
40
35
23
25
32
20
25
36
32
24
46
41
28
29
56
25
31
42
34
26
51
48
33
50
65
46
42
60
50
35
54
58
40
meter ( H 500.2 MHz, C 125.8 MHz) at 295 K. C spectra
were recorded with proton decoupling. In some cases, the res-
onances for the coordinated COD ligands were complex multi-
plets that could not be assigned with certainty. Solid state
NMR spectra were acquired using a Bruker 4 mm HXY MAS
probe on an AvanceIII HD 400 spectrometer equipped with a
shielded widebore 9.4 T magnet. All spectra were acquired at a
set temperature of 285 K, which corresponds to sample temps
a
Reaction conditions: HSiEt
3
(6) (0.18 mmol), styrene (5) (0.18 mmol),
b
4
a–e (5 mol%), toluene (0.5 mL) at 110 °C. Product yields calculated
1
by H NMR and verified by GC-MS.
1
of ca. 298–300 K at the spinning rates employed. H MAS
spectra (400.3 MHz) were acquired at 14 kHz spinning rates
using a Bloch decay experiment (1 μs, 30 degree pulse), a
recycle delay of 20 s and are the sum of 8 co-added transients.
Chemical shifts are reported with respect to TMS and were
calibrated using adamantane as an external secondary refer-
reaction time and the nature of the catalyst (Fig. 6–8, Table 3).
In all cases, the greatest difference in the ratio of 9 to 10
was observed at short reaction times with 10 dominating
under these conditions. Over time the relative proportion of 9
increases in all cases with catalyst 4b favouring 9 (65%) and 4d
favouring 10 (58%).
1
3
ence (δ = 1.8 ppm). C{1H} CPMAS echo spectra (100.6 MHz)
were acquired at 12.5 kHz spinning rates with and without a
At this stage it is not clear what precise influence the substi-
tuent on the ligand is having on the catalytic cycle or indeed if
it is simply controlling the release of different catalytically-
active metal species. For example, the ligand effect may be due
to either a traditional structure–activity relationship influen-
cing the relative rates with a homogenous catalytic cycle. Alter-
natively (or additionally) the nature of the ligand might be
controlling the formation of the rate, extent and nature of cata-
1
dipolar-dephasing period (450 µs) and employing a H flip-
back pulse. Experiments employed a 1.5 ms contact pulse (lin-
1
early-ramped on H), recycle delay of 30–60 seconds, spinal-
6
6
4 heteronuclear decoupling (at υrf = 85 kHz) and consist of
4–448 co-added transients. Chemical shifts are reported
with respect to TMS, and were referenced using adamantane
δ(CH ) = 29.5 ppm) as an external secondary reference. High
(
2
2
2
resolution mass spectrometry was performed by the University
of York mass spectrometry service using the ESI technique on
a Thermo-Electron Corp LCQ Classic (ESI) instrument or
Waters GCT Premier Acceleration TOF MS (LIFDI). IR spectra
were acquired on a Thermo-Nicolet Avatar 370 FTIR spectro-
meter using either CsCl solution cells or as KBr discs. CHN
measurements were performed using an Exeter Analytical Inc.
CE-440 analyser. Single Crystal X-ray diffraction was carried
out on an Oxford Diffraction SuperNova diffractometer with
Mo-Kα radiation (λ = 0.71073 Å) using an EOS CCD camera.
The crystal was cooled with an Oxford Instruments Cryojet
lytically active nanoparticles. On the basis of the catalytic
data it is evident that the substituent on the ligand has an
effect on both the efficiency and selectivity of the reaction.
Conclusions
The incorporation of Schiff-bases based on the N-(2-hydroxy-1-
naphthalidene)aniline framework into the coordination sphere
of platinum may be readily achieved, even when a range of
different functional groups are present on the ligand. Coordi-
nation of these ligands appears to promote nucleophilic attack
by water onto a coordinated COD ligand, presumably via a cat-
ionic intermediate. The complexes are competent catalysts for
the hydrosilylation of styrene and the nature of the ligand
affects both the rate of the reaction and the distribution of pro-
ducts between hydrosilyation and dehydrosilyation.
and were kept at 110.00(10)
Using Olex2, the structures were solved with the Superflip
structure solution program using Charge Flipping except for
K during data collection.
2
3
24
2
0
3
a which was solved by direct methods and refined with
2
5
the ShelXL
refinement package using least squares
minimisation.
Preparation of the bidentate Schiff base ligands
Experimental
The N-(2-hydroxy-1-naphthalidene) para-substituted anilines
1
1
All experimental procedures were performed under an atmos- ligands were prepared following the literature, by addition of
phere of dinitrogen using standard Schlenk Line and Glove equimolar quantities of the amine (aniline) in ethanol to a
Box techniques. Dichloromethane, acetonitrile, pentane and warm solution of 2-hydroxy-1-naphtaldehyde in ethanol and
hexane were purified with the aid of an Innovative Techno- the mixture was heated at reflux for two hours. After cooling,
logies anhydrous solvent engineering system. Diethyl ether the precipitated products were collected, recrystallized twice
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1
3
1
1
H, 2.7 Hz, α), 15.22 (d, 1H, 2.7 Hz, β). C{ H} NMR: (CD
δ 119.4 (8), 121.3 (3), 122.4 (11, 15), 124.0 (6), 128.5 (7), 129.9
5), 132.2 (12, 14), 136.5 (4), 157.3 (α), 167.5 (2); ESI-MS, posi-
tive ion: m/z 282.0674 (calculated for C17 13ClNO = 282.0680,
Δ = 0.6 mDa); elemental analysis: for C H NOCl Calc.
2 2
Cl )
(
H
1
7
12
C 72.47; H 4.29; N 4.97; rest 18.26% Found C 72.32; H 4.25;
N 4.88; rest 18.55% IR (KBr)/cm− 1618 (CvN), 3507 (X–H)(X =
1
O; N), 1181 (C–O phenolic).
1
Fig. 9 Structure and molecule numbering of the bidentate Schiff bases
derived from 2-hydroxy-1-naphtaldehyde and p-substituted anilines.
3e H NMR (CD
Cl
, 399.8 MHz, 293 K): 3.85 (s, 3H, σ), 7.01
2
2
(
d, 2H, 9.0 Hz, 11, 15), 7.10 (d, 1H, 9.1 Hz, 3), 7.36 (td, 1H, 7.7
Hz, 6), 7.39 (d, 2H, 9.0 Hz, 12, 14), 7.54 (t, 1H, 7.8 Hz, 7), 7.76
(
8
dt, 1H, 8.0 Hz, 5), 7.82 (d, 1H, 9.2 Hz, 4), 8.18 (d, 1H, 8.3 Hz,
), 9.42 (d, 1H, 2.8 Hz, α), 15.62 (d, 1H, 3.1 Hz, β); C{ H}
1
3
1
from ethanol and dried at 25 °C. They were obtained in a yield NMR: (CD Cl ) δ 56.1 (σ), 119.5 (8), 121.3 (3), 122.3 (11, 15),
2
2
approaching 80%. Labelling scheme is shown in Fig. 9.
124.1 (6), 128.5 (7), 130.0 (5), 133.5 (12, 14), 136.5 (4), 155.2
1
3
a H NMR (CD Cl , 399.8 MHz, 293 K): 7.15 (d, 1H, 9.2 Hz, (α), 167.9 (2); ESI-MS, positive ion: m/z 278.1165 (calculated for
2
2
3
), 7.41 (t, 1H, 7.6 Hz, 6), 7.16 (d, 2H, 9.1 Hz, 11, 15), 7.59 C H NO = 278.1176, Δ = 1.1 mDa); elemental analysis: for
18 16 2
(
4
1
t, 1H, 7.8 Hz, 7), 7.78 (dd, 1H, 7.8 Hz, 5), 7.90 (d, 1H, 9.2 Hz, C H NO Calc. C 77.96; H 5.45; N 5.05; rest 11.54% Found
18 15 2
−
1
), 8.18 (d, 1H, 8.2 Hz, 8), 8.33 (d, 2H, 9.2 Hz, 12, 14), 9.45 (d, C 77.71; H 5.41; N 4.97; rest 11.91%; IR (KBr)/cm 1620
1
3
1
H, 2.5 Hz, α), 14.89 (d, 1H, 2.6 Hz, β). C{ H} NMR: (CD
2
Cl
2
)
(CvN), 3488 (X–H)(X = O; N), 1246 (C–O phenolic).
δ 119.1 (8), 121.2 (3), 124.6 (11, 15), 125.4 (6), 126.3 (12, 14),
29.2 (7), 129.6 (5), 139.2 (4), 158.2 (α), 193.9 (2). ESI-MS, posi-
tive ion: m/z 293.0918 (calculated for C17 = 93.0921,
Δ = 0.2 mDa); elemental analysis: for C H N O Calc.
1
Synthesis of dibromo(1,5-cyclooctadiene)platinum(II)
13 2 3
H N O
1
7
12
2
3
Dibromo(1,5-cyclooctadiene)platinum(II) (2.16 g, 4.6 mmol,
C 69.86; H 4.14; N 9.58; rest 16.42% Found C 69.88; H 4.38;
95% yield) was obtained as green crystals from potassium tetra-
−
1
N 9.56; rest 16.18%; IR (KBr)/cm 1621 (CvN), 3431 (X–H)-
X = O; N), 1289 (C–O phenolic).
bromoplatinate (2.5 g, 6.0 mmol), glacial acetic acid (60 mL)
and 1,5-cyclooctadiene (2.5 mL, 20 mmol) in distilled water
(40 ml). The reaction mixture was stirred and heated to about
(
1
3
b H NMR (CD Cl , 399.8 MHz, 293 K): 1.42 (t, 3H, 7.0 Hz,
2 2
λ), 4.06 (q, 2H, 7.0 Hz, µ), 6.98 (d, 2H, 9.0 Hz, 11, 15), 7.10 (d,
90 °C over 30 min. The deep red solution slowly became pale
1
1
9
H, 9.2 Hz, 3), 7.35 (td, 1H, 7.5 Hz, 6), 7.37 (d, 2H, 9.0 Hz, 12,
4), 7.54 (t, 1H, 7.7 Hz, 7), 7.75 (dd, 1H, 7.8 Hz, 5), 7.81 (d, 1H,
.1 Hz, 4), 8.17 (d, 1H, 8.3 Hz, 8), 9.4 (d, 1H, 3.0 Hz, α), 15.64
yellow and fine crystals were deposited, washed in 50 ml por-
tions of water, ethanol and ether and then dried at 100 °C for
2
6
6
0 min. Labelling scheme is shown in Fig. 10.
Synthesis of 4a. Dibromo(1,5-cyclooctadiene)platinum(II)
50 mg, 0.11 mmol), N-(2-hydroxy-1-naphthalidene)-p-nitro-
1
3
1
(d, 1H, 3.1 Hz, β). C{ H} NMR: (CD Cl ) δ 15.0 (λ), 64.2 (µ),
2
2
1
1
2
19.4 (8), 121.7 (3), 122.1 (12, 14), 123.7 (6), 128.2 (7), 129.6 (5),
35.8 (4), 154.9 (α), 167.8 (2); ESI-MS, positive ion: m/z
92.1318 (calculated for C H NO = 292.1332, Δ = 1.4 mDa);
(
aniline (31 mg, 0.11 mmol) and sodium tert-butoxide (24 mg,
0.22 mmol) were stirred in THF (30 ml) for 16 hours under a
nitrogen atmosphere. The solution was then filtered under
nitrogen, and the filtrate dried under vacuum for 4 hours.
Complex 4a was obtained as red crystals (70 mg, 0.13 mmol,
1
9
18
2
elemental analysis: for C H NO Calc. C 78.33; H 5.88;
N 4.81; rest 10.98% Found C 78.17; H 5.83; N 4.73; rest
1
9
17
2
−
1
1
1.27%; IR (KBr)/cm 1616 (CvN), 3430 (X–H)(X = O; N),
1
248 (C–O phenolic).
60% yield).
1
3
c H NMR (CD
2
Cl
2
, 399.8 MHz, 293 K): 7.08 (d, 1H, 9.2 Hz,
3
), 7.31 (tt, 1H, 7.4 Hz, 13), 7.36 (td, 1H, 7.7 Hz, 6), 7.41 (dd,
2
H, 7.9 Hz, 11, 15), 7.49 (t, 2H, 7.9 Hz, 12, 14), 7.55 (td, 1H, 7.7
Hz, 7), 7.75 (dd, 1H, 8.2 Hz, 5), 7.84 (d, 1H, 9.2 Hz, 4), 8.17 (d,
1
3
1
1
H, 8.3 Hz, 8), 9.42 (s, 1H, α), 15.46 (s, 1H, β). C{ H} NMR:
(
(
1
CD Cl ) δ 119.1 (8), 120.5 (11, 15), 121.9 (3), 123.6 (6), 126.6
13), 128.2 (7), 129.7 (5), 133.3 (12, 14), 136.5 (4), 155.5 (α),
69.4 (2). ESI-MS, positive ion: m/z 248.1062 (calculated for
2
2
C H NO = 248.1070, Δ = 0.8 mDa); elemental analysis: for
1
7
14
C
17
H
13NO Calc. C 82.57; H 5.30; N 5.66; rest 6.47% Found
−
1
C 82.42; H 5.39; N 5.13; rest 7.06%; IR (KBr)/cm 1621 (CvN),
409 (X–H)(X = O; N), 1179 (C–O phenolic).
3
1
3
d H NMR (CD
Hz, 3), 7.35 (d, 2H, 8.9 Hz, 11, 15), 7.38 (t, 1H, 7.7 Hz, 6), 7.45
d, 2H, 9.0 Hz, 12, 14), 7.56 (t, 1H, 7.8 Hz, 7), 7.77(dt, 1H, 8.0
2 2
Cl , 399.8 MHz, 293 K): 7.12 (d, 1H, 9.1
Fig. 10 Structure and molecule numbering of the platinum(II) organo-
metallic complexes derived from 2-hydroxy-1-naphthaldehyde and 1,5-
(
Hz, 5), 7.86 (d, 1H, 9.1 Hz, 4), 8.17 (d, 1H, 8.2 Hz, 8), 9.43 (d, cyclooctadiene.
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4
a-major isomer. H NMR (CD
2
Cl
2
, 399.8 MHz, 293 K): 7.23 (td, 1H, 7.5 Hz, 14), 7.29 (dd, 2H, 8.4 Hz, 12, 16), 7.46 (dd,
δH 1.81 (m, 2H), 5.02 (m, 2H, 21 or 22), 6.91 (d, 1H, 9.6 Hz, 3), 2H, 7.1 Hz, 13, 15), 7.65 (dd, 1H, 8.1 Hz, 7), 7.76 (d, 1H,
7
2
.10 (d, 1H, 9.2 Hz, 6), 7.35 (dd, 2H, 8.3 Hz, 12, 16), 7.46 (dd, 9.2 Hz, 5), 7.88 (d, 1H, 8.6 Hz, 4), 7.93 (d, 1H, 8.6 Hz, 8), 9.08
3
13
1
H, 8.6 Hz, 13, 15), 7.64 (td, 1H, 7.8 Hz, 7), 7.72 (d, 1H, 8.2 Hz, (s, 1H,
2 2
JPt–H = 79.2 Hz, Pt–NvCH). C{ H} NMR: (CD Cl )
5
J
); 7.84 (d, 1H, 9.1 Hz, 4), 8.13 (d, 1H, 8.7 Hz, 8), 9.02 (s, 1H, δ 26.0 (23), 28.7 (19), 30.1 (20), 31.9 (24), 68.1 (17), 73.8 (18),
Pt–H = 76.2 Hz, Pt–NvCH). C{ H} NMR: (CD Cl ) δ 26.1 85.3 (21, 22), 110.6 (1), 119.5 (8), 123.3 (6), 123.3 (12, 16),
2 2
3
13
1
(
19), 28.6 (20), 31.5 (23), 32.4 (24), 68.2 (17), 73.8 (18), 75.8 (21, 125.9 (14), 128.0 (7), 128.2 (9), 129.2 (5), 129.8 (13, 15),
2
1
2), 111.9 (1), 119.3 (8), 123.5 (3), 124.3 (6), 124.9 (13, 15), 132.3 (10), 136.5 (4), 137.6 (11), 150.2 (3), 157.5 (#), 169.3 (2).
1
26.0 (9), 126.9 (12, 16), 127.8 (14), 128.6 (7), 129.1 (5), 135.3
4c-minor isomer. H NMR (CD
(s, 1H, JPt–H = 25.2 Hz, Pt–NvCH).
2
Cl
, 399.8 MHz, 293 K): 9.24
2
3
(
10), 138.4 (4), 140.3 (11), 153.2 (#), 169.7 (2).
1
4
a-minor isomer. H NMR (CD Cl , 399.8 MHz, 293 K): 9.21
LIFDI-MS, m/z 549.13 (calculated for C H NOPt [M]–OH =
2
2
25 24
3
(s, 1H, J
= 25.4 Hz, Pt–NvCH).
549.15); elemental analysis: for C H NO Pt Calc. C 53.00;
Pt–H
25 25
2
ESI-MS, positive ion: m/z 594.1329 (calculated for H 4.45; N 2.47; rest 40.08% Found C 53.19; H 4.48; N 2.72; rest
C H N O Pt [M]–O = 594.1353, Δ = 2.2 mDa); elemental ana- 39.61% IR (KBr)/cm− 1620 (CvN), 3498 (O–H), 1261 (C–O
1
2
5
23 2 3
lysis: for C H N O Pt calc. C 49.10, H 3.96, N 4.58, rest phenolic).
2
5
24 2 4
4
2.36%, found C 49.45; H 3.99; N 4.84, rest 41.72% IR (KBr)/
Synthesis of 4d. Dibromo(1,5-cyclooctadiene)platinum(II)
(50 mg, 0.108 mmol), N-(2-hydroxy-1-naphthalidene)-p-chloro-
−
1
cm 1579 (CvN), 3431 (O–H), 1262 (C–O phenolic).
Synthesis of 4b. Dibromo(1,5-cyclooctadiene)platinum(II) aniline (30 mg, 0.11 mmol) and sodium tert-butoxide (24 mg,
100 mg, 0.22 mmol), N-(2-hydroxy-1-naphthalidene)-p-ethoxy- 0.22 mmol) were stirred in THF (30 ml). The reaction mixture
(
aniline (63 mg, 0.22 mmol) and sodium tert-butoxide (50 mg, was left in a Schlenk tube under nitrogen and stirring over-
.43 mmol) were stirred in THF (30 ml). The reaction mixture night. The solution was then filtered under nitrogen, and
0
was left in a Schlenk tube under nitrogen and stirring over- dried under vacuum for 4 hours. The complex 4d was obtained
night. The solution was then filtered under nitrogen, and as yellow crystals (70 mg, 0.13 mmol, 60% yield).
1
dried under vacuum for 4 hours. The complex 4b was obtained
4d-major isomer. H NMR (CD
2
Cl
2
, 399.8 MHz, 293 K):
as yellow crystals (70 mg, 0.13 mmol, 60% yield).
H
δ 1.71 (m, 1H), 2.18 (m, 2H), 2.61 (m, 2H), 2.90 (m, 1H), 3.80
1
4
b-major isomer. H NMR (CD
2
Cl
2
, 399.8 MHz, 293 K): 1.43 (m, 1H), 4.05 (m, 1H), 4.98 (m, 2H, 21 and 22), 6.91 (d, 1H,
(t, 3H, 7.0 Hz, 26), 2.22 (m, 1H), 2.43 (m, 2H), 2.70 (m, 2H), 9.3 Hz, 3), 7.03 (dd, 1H, 8.6 Hz, 6), 7.25 (dd, 2H, 8.6 Hz, 12,
3
6
8
.61 (m, 1H), 4.08 (q, 2H, 7.2 Hz, 25), 4.96 (m, 2H, 21 and 22), 16), 7.44 (dd, 2H, 8.9 Hz, 13, 15), 7.65 (dd, 1H, 8.1 Hz, 7), 7.77
.88 (t, 2H, 7.2 Hz, 12, 16), 7.13 (d, 1H, 8.7 Hz, 3), 7.22 (td, 1H, (d, 1H, 9.4 Hz, 5), 7.86 (d, 1H, 8.5 Hz, 4), 7.91 (dd, 1H, 9.1 Hz,
3
13
1
.3 Hz, 6), 7.48 (m, 1H, 7.6 Hz, 7), 7.87 (d, 1H, 8.7 Hz, 5), 7.97 8), 9.03 (s, 1H, JPt–H = 69.4 Hz, Pt–NvCH). C{ H} NMR:
3
(d, 1H, 8.6 Hz, 4), 8.11 (d, 1H, 9.5 Hz, 8), 9.05 (s, 1H, JPt–H
=
(CD
2 2
Cl ) δ 27.6 (24), 28.4 (23), 31.3 (19), 33.8 (20), 68.2 (17),
1
3
1
7
2
7
1
1
1
7.8 Hz, Pt–NvCH). C{ H} NMR: (CD Cl ) δ 15.1 (26), 73.8 (18), 85.6 (21, 22), 110.2 (1), 119.5 (8), 123.1 (3), 123.1 (6),
2 2
6.0 (19), 27.5 (20), 28.6 (23), 31.5 (24), 64.3 (25), 68.3 (17), 125.1 (13, 15), 126.0 (12, 16), 126.4 (9), 127.3 (14), 128.0 (7),
3.9 (18), 84.6 (21, 22), 109.3 (1), 114.4 (12, 16), 119.4 (8), 129.2 (5), 132.3 (10), 136.7 (4), 137.6 (11), 157.6 (#), 169.4 (2).
1
21.6 (3), 125.3 (6), 126.9 (13, 15), 127.7 (9), 128.3 (7),
4d-minor isomer. H NMR (CD
2
Cl
2
, 399.8 MHz, 293 K): 9.21
3
29.1 (10), 129.7 (5), 135.8 (4), 137.0 (11), 155.0 (14), 157.8 (#), (s, 1H, JPt–H = 20.8 Hz, Pt–NvCH).
95.5 (2).
ESI-MS, positive ion, m/z 584.1181 (calculated for
b-minor isomer. H NMR (CD 23ClNOPt [M]–OH = 584.1191, Δ = 0.7 mDa). Elemental
analysis: for C H NO ClPt Calc. C 49.96; H 4.03; N 2.33; rest
1
4
2
Cl
= 25.8 Hz, Pt–NvCH).
2
, 399.8 MHz, 293 K): 9.24
25
C H
3
(s, 1H, J
Pt–H
25 24
2
ESI-MS, positive ion: m/z 593.1767 (calculated for 43.68% Found C 50.08; H 4.08; N 2.42; rest 43.42%; IR (KBr)/
−
1
C
27
H
28NO
2
Pt [M]–OH = 593.1765, Δ = −0.2 mDa); elemental cm 1580 (CvN), 3473 (O–H), 1261 (C–O phenolic).
Synthesis of 4e. Dibromo(1,5-cyclooctadiene)platinum(II)
9.81% Found C 53.57; H 4.81; N 2.75; rest 38.87% IR (KBr)/ (50 mg, 0.11 mmol), N-(2-hydroxy-1-naphthalidene)-p-methoxy-
analysis: for C H NO Pt Calc. C 53.11; H 4.79; N 2.29; rest
3
2
7
29
3
−
1
cm 1580 (CvN), 3433 (O–H), 1427 (C–O ether aromatic), aniline (30 mg, 0.11 mmol) and sodium tert-butoxide (24 mg,
261 (C–O phenolic). 22 mmol) in THF (30 ml). The reaction mixture was left in a
Synthesis of 4c. Dibromo(1,5-cyclooctadiene)platinum(II) Schlenk tube under nitrogen and stirring overnight. The solu-
1
(
(
50 mg, 0.11 mmol), N-(2-hydroxy-1-naphthalidene)aniline tion was then filtered under nitrogen, and dried under
26 mg, 0.11 mmol) and sodium tert-butoxide (10 mg, vacuum for 4 hours. Complex 4e was obtained as yellow crys-
0
.22 mmol) were stirred in THF (30 ml). The reaction mixture tals (70 mg, 0.13 mmol, 60% yield).
1
was left in a Schlenk tube under nitrogen and stirring over-
night. The solution was then filtered under nitrogen, and
4e-major isomer. H NMR (CD
2 2
Cl , 399.8 MHz, 293 K):
δ
H
1.81 (m, 1H), 2.15 (m, 2H), 2.60 (m, 2H), 2.90 (m, 2H), 3.84
dried under vacuum for 4 hours. The complex 4c was obtained (s, 3H, 27), 4.05 (m, 1H), 4.98 (m, 2H, 21 and 22), 6.91 (d, 1H,
as yellow crystals (70 mg, 0.13 mmol, 60% yield).
9.4 Hz, 3), 7.03 (dd, 1H, 8.5 Hz, 6), 7.25 (dd, 2H, 8.6 Hz, 12,
, 399.8 MHz, 293 K): 16), 7.44 (dd, 2H, 8.9 Hz, 13, 15), 7.65 (dd, 1H, 8.1 Hz, 7), 7.77
δH 1.69 (m, 2H), 3.84 (m, 1H), 4.08 (td, 1H, 8.8 Hz), 4.98 (m, (d, 1H, 9.3 Hz, 5), 7.86 (d, 1H, 8.5 Hz, 4), 7.91 (d, 1H, 8.9 Hz,
1
4
2 2
c-major isomer. H NMR (CD Cl
3
2
H, 21 and 22), 6.92 (d, 1H, 9.2 Hz, 3), 7.07 (dd, 1H, 8.4 Hz, 6), 8), 9.06 (s, 1H, JPt–H = 78.4
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1
3
1
Hz, Pt-NvCH). C{ H} NMR: (CD
2
Cl
2
) δ 26.0 (19), 27.3
4 Y. J. Hamada, IEEE Trans. Electron Devices, 1997, 44,
1208.
(
20), 28.6 (23), 31.2 (24), 55.9 (27), 68.2 (17), 73.9 (18), 84.8 (21,
2
1
2), 109.3 (1), 114.0 (12, 16), 119.6 (8), 122.1 (3), 123.0 (12),
23.8 (6), 124.4 (9), 124.5 (13, 15), 128.1 (7), 129.4 (5), 136.0
5 (a) F. Faridbod, M. R. Ganjali, R. Dinarvand, P. Norouzi
and S. Riahi, Sensors, 2008, 8, 1645; (b) H.-C. Wu,
P. Thanasekaran, C.-H. Tsai, J.-Y. Wu, S.-M. Huang,
Y.-S. Wen and K.-L. Lu, Inorg. Chem., 2006, 45, 295;
(c) C. Lordeiro and F. Pina, Coord. Chem. Rev., 2009, 253,
1353; (d) S. Khatua, S. H. Chol, J. Lee, J. O. Huh, Y. Do and
D. G. Churchlll, Inorg. Chem., 2009, 48, 1799.
(
10), 137.1 (4), 147.4 (11), 157.9 (#), 158.4 (14), 169.0 (2).
1
4
e-minor isomer. H NMR (CD Cl , 399.8 MHz, 293 K): 9.24
2 2
3
(s, 1H, JPt–H = 23.6 Hz, Pt–NvCH).
LIFDI-MS, m/z 579.16 (calculated for C H NO Pt [M]–OH
2
6
26
2
=
579.16). Elemental analysis: for C H NO Pt Calc. C 52.35;
26 27 3
H 4.56; N 2.35; rest 40.74% Found C 52.46; H 4.59; N 2.54; rest
4
phenolic), 1428 (C–O ether aromatic).
6 (a) A. K. Sutar, Y. Das, S. Pattnaik, N. Nath, P. Rath and
T. Maharana, Int. J. Mater. Sci. Appl., 2013, 2, 136;
(b) P. G. Cozzi, L. S. Dolci, A. Garelli, M. Montalti, L. Prodi
and N. Zaccheroni, New J. Chem., 2003, 27, 692;
0.41% IR (KBr)/cm− 1580 (CvN), 3458 (O–H), 1256 (C–O
1
General method for the hydrogenative and dehydrogenative
silylation of alkenes
(
c) A. V. Metelitsa, A. S. Burlov, S. O. Bezuglii,
I. G. Borodkina, V. A. Bren, A. D. Garnovskii and
V. I. Minkin, Russ. J. Coord. Chem., 2006, 32, 858.
(a) A. Garoufis, S. K. Hadjikakou and N. Hadjiliadis, Coord.
Chem. Rev., 2009, 253, 1384; (b) H. Q. Chen, S. Hall,
B. Zheng and J. Rhodes, BioDrugs, 1997, 7, 217;
Reaction with styrene. The appropriate complex 4, (5 mol%)
8
7
was dissolved in d -toluene (0.5 ml) and removed from the
glove-box. HSiEt
3
(0.18 mmol, 27 µl) and styrene (0.18 mmol,
2
0 µl) were added in a 1 : 1 molar ratio. The reaction mixture
(
c) R. Ramesh and M. Sivagamasundari, Synth. React. Inorg.
was kept at the stated temperature for 12 hours. The reactions
were performed in a range of different temperatures going
from 50 °C, 70 °C, 90 °C and 110 °C. The conversion to pro-
ducts and the ratio of the product isomers was determined by
Met.-Org. Chem., 2003, 33, 899.
(a) A. Sasmal, E. Garribba, C. J. Gómez-García,
C. Desplanches and S. Mitra, Dalton Trans., 2014, 43,
8
9
1
1
5958; (b) M. Padmaja, J. Pragathi and C. G. Kumari,
integration of the H NMR spectra, and confirmed by GC-MS.
J. Chem. Pharm. Res., 2011, 3, 602.
(a) B. De Clercq and F. Verpoort, Adv. Synth. Catal., 2002,
3
44, 639; (b) C. Janiak, A. C. Chamayou, A. K. M. Royhan
Notes and references
Uddin, M. Uddin, K. S. Hagen and M. Enamullah, Dalton
Trans., 2009, 3698.
1
2
(a) P. Guerriero, S. Tamburini and P. A. Vigato, Coord.
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