A NMR, X-ray, and DFT combined study on the regio-chemistry of nucleophilic addition to platinum(II) coordinated terminal olefins

Article abstract of DOI:10.1016/j.jorganchem.2008.05.040

The series of platinum complexes [PtCl(η²-CH₂{double bond, long}CH-C₆H₄-X)(tmeda)](ClO₄) (X = H, 1b; 4-OMe, 1c; 3-OMe, 1d; 4-CF₃, 1e; 3-CF₃, 1f; 3-NO₂, 1g; tmeda = N,N,N′,N′-tetramethyl-1,2-ethanediamine) has been considered. In the styrene complex (1b) both solution (NMR) and solid state (X-ray) data indicate a significant difference in the Pt-C bond lengths (the longer bond being that involving the olefin carbon atom carrying the phenyl ring). Such a difference increases when X is an electron donor group (EDG, 1c) and decreases when X is an electron withdrawing group (EWG, 1d-g). The attack of a nucleophile (MeO^-) to the substituted carbon (Markovnikov type, M) is by far the most favoured in the case of unsubstituted (1b) or EDG-substituted (1c) styrenes. The presence of an EWG (compounds 1d-g) levels off the probability of M and anti-M type of attack. DFT calculations on 1b,c and 1e were also performed. The NLMO analysis reveals the crucial role of the interaction between the filled π orbital of the olefin and the empty d orbital of platinum; the carbon with greater electron density becoming less susceptible of nucleophilic attack.

Full text of DOI:10.1016/j.jorganchem.2008.05.040

Journal of Organometallic Chemistry 693 (2008) 2819–2827
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
A NMR, X-ray, and DFT combined study on the regio-chemistry of nucleophilic
addition to platinum(II) coordinated terminal olefins
Carmen R. Barone a, Renzo Cini b, Eric Clot c, Odile Eisenstein c, Luciana Maresca a,
,
*
Giovanni Natile a, Gabriella Tamasi b
a Dipartimento Farmaco-Chimico, Università degli Studi di Bari, Via E. Orabona 4, 70125 Bari, Italy
b Dipartimento di Scienze e Tecnologie Chimiche e dei Biosistemi, Università degli Studi di Siena, Via A. Moro 2, 53100 Siena, Italy
c Institut Charles Gerhardt, UMR 5253 CNRS-UM2-ENSCM-UM1, Université Montpellier II, Bât. 15, case courrier-1501, Place Eugène Bataillon, 34095 Montpellier Cedex 05, France
a r t i c l e i n f o
a b s t r a c t
The series of platinum complexes [PtCl(g
2-CH2@CH–C6H4–X)(tmeda)](ClO4) (X = H, 1b; 4-OMe, 1c;
Article history:
3-OMe, 1d; 4-CF3, 1e; 3-CF3, 1f; 3-NO2, 1g; tmeda = N,N,N0,N0-tetramethyl-1,2-ethanediamine) has been
considered. In the styrene complex (1b) both solution (NMR) and solid state (X-ray) data indicate a sig-
nificant difference in the Pt–C bond lengths (the longer bond being that involving the olefin carbon atom
carrying the phenyl ring). Such a difference increases when X is an electron donor group (EDG, 1c) and
decreases when X is an electron withdrawing group (EWG, 1d–g). The attack of a nucleophile (MeOꢀ)
to the substituted carbon (Markovnikov type, M) is by far the most favoured in the case of unsubstituted
(1b) or EDG-substituted (1c) styrenes. The presence of an EWG (compounds 1d-g) levels off the proba-
bility of M and anti-M type of attack. DFT calculations on 1b,c and 1e were also performed. The NLMO
Received 18 March 2008
Received in revised form 28 May 2008
Accepted 29 May 2008
Available online 4 June 2008
Keywords:
Platinum
Arenes
NMR spectroscopy
X-ray diffraction
Density functional calculations
analysis reveals the crucial role of the interaction between the filled
p orbital of the olefin and the empty
d orbital of platinum; the carbon with greater electron density becoming less susceptible of nucleophilic
attack.
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
the higher will be the activation of the unsaturated ligand towards
nucleophiles). Therefore the energy of the LUMO appears to be a
The metal-olefin linkage plays a relevant role in organometallic
chemistry, being present in key steps of many useful processes of
polymerization and functionalization of organic molecules [1].
The metal–olefin bond is already well understood on the basis
of the model proposed by Duncanson, Chatt and Dewar [2]. It can
much better indicator of the olefin reactivity than other parame-
ters such as the overall charge of the complex. On this basis Hoff-
mann and Eisenstein could rationalize the striking different
behaviour of two isolobal complexes: [CpFe(CO)2(C2H4)]+ [4],
which is very reactive towards nucleophiles, and [Fe(CO)5(C2H4)]2+
[3], which is un-reactive.
The properties and reactivity of terminal olefins bring in an
additional issue: the site of attack of the nucleophile which can
be either the substituted or the unsubstituted olefinic carbon
(Markovnikov or anti-Markovnikov type of attack, respectively).
The work of Rosenblum on [CpFe(CO)2(CH2@CHOMe)]+, where
the coordinated olefin bears an electron donor substituent, did
show the complete regio-specificity of the nucleophilic addition
and the unique formation of the Markovnikov product [5]. The
X-ray structure of [CpFe(CO)2(CH2@CHOMe)]+ did show a longer
Fe–Colefin bond distance for the substituted carbon, indicative of a
certain degree of olefin ‘‘slippage” already in the ground state of
the complex molecule. The slippage was a consequence of the
be described as a continuum between two limiting situations:
donation of electrons of the olefin into a vacant d orbital of
the metal and
into a vacant orbital essentially based on the
r
p
r
p
back-donation from a filled d orbital of the metal
p
p
* orbital of the olefin.
A key feature of the coordinated olefin is its activation towards
nucleophiles which has been investigated in detail theoretically by
Hoffmann and Eisenstein in the early 1980s [3]. The authors found
that an ethylene symmetrically bound to a metal centre should un-
dergo nucleophilic attack less easily than in the free state, since in
the complex the LUMO is higher in energy than the p
* orbital of the
free olefin and less centred on it. In contrast, activation occurs if
the metal fragment slips along the C@C axis while the nucleophile
is approaching. This geometrical change induces a lowering of the
LUMO and favours its interaction with the filled orbital of the
donor (the lower in energy is the LUMO of the coordinated olefin,
greater localization of the
p orbital on the unsubstituted carbon.
The difference between the two Fe–Colefin distances becomes even
more pronounced when the substituent is an amino group but, in
spite of this, the reactivity of [CpFe(CO)2(CH2@CHNMe2)]+ towards
nucleophiles drops considerably. The explanation was found in an
* Corresponding author. Tel.: +39 080 5442759; fax: +39 080 5442230.
E-mail address: maresca@farmchim.uniba.it (L. Maresca).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.05.040

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C.R. Barone et al. / Journal of Organometallic Chemistry 693 (2008) 2819–2827
increased contribution of the limiting structure [CpFe(CO)2(CH2–
CH@NMe2)]+ which reduces the bond order between the two
carbon atoms [5]. Recent structural and computational studies
performed on this iron complex have come to the same conclusion
[6]. This interpretation has gained further support in a recent work
by Matchett [7].
Since the seminal paper of Hoffmann, correlations between
coordinated olefin parameters and observed reactivity have been
tracked over the years. Beyond X-ray structural data, a particular
attention has been paid to NMR parameters, olefinic proton and
carbon resonances being shifted upfield and the extent of the shift
4-CF3-styrene (e) or 3-CF3-styrene (f), leads to a solution of
[PtCl(
2-4-CF3-styrene)(tmeda)](ClO4) (1e) or [PtCl( 2-3-CF3-sty-
rene)(tmeda)](ClO4) (1f), while un-reacted 1g remains as precipi-
g
g
tate and can be removed by filtration.
The new cationic compounds have been characterized via ele-
mental analysis, 1H and 13C NMR (1D and 2D) in solution, and
ESI mass spectrometry. We ought to mention that the use of meth-
anol (a classical solvent for ESI-MS experiments) leads to inconclu-
sive data, while much better results are obtained using acetonitrile
[11]. Although the latter solvent possesses good coordinating abil-
ity and reacts with complexes of type 1 by displacing the olefin, the
substitution reaction is rather slow at room temperature and goes
to completion in no less than 2 h. Therefore, it is sufficient to per-
form the ESI-MS determination experiment soon after dissolution
for observing a base peak corresponding to the molecular formula
of 1.
being related to the amount of
p back-donation [8,9]. Although
absolute values may depend also from the overall charge of the
complex and the nature of ancillary ligands, a high upfield shift
generally corresponds to a reduced electrophilicity of the coordi-
nated olefin. Furthermore, also the coupling between the metal
(when it has nuclear spin) and the olefinic carbons (1JM–C) can give
useful information on the geometry of the unsaturated ligand and
its propensity to undergo regiospecific nucleophilic addition.
Over the years some of us have investigated several olefin com-
The presence on the styrene phenyl ring of an electron with-
drawing substituent lowers the stability of the complexes, and
their tendency to release the olefin increases; a rough estimate of
the stability order is 1f (3-CF3-styrene) > 1g (3-NO2-styrene) > 1e
(4-CF3-styrene).
plexes of platinum having formula [PtCl(g
2-olefin)(tmeda)](ClO4),
1, (tmeda = N,N,N0,N0-tetramethyl-1,2-ethanediamine) which proved
to be highly electrophilic [10]. The nucleophilic addition of methox-
ide anion to a series of closely related styrene complexes has now
been investigated by combining experimental and computational
methods.
Relevant NMR parameters (13C, acetone-d6) for compounds 1
and for the corresponding free olefins are reported in Table 1.
The olefinic carbons undergo, upon coordination, an upfield shift
which is always more pronounced for the unsubstituted carbon
atom. As a consequence, in all considered cases the
the two olefinic carbon atoms is greater in the complex than in
the free olefin. The increase in d upon coordination is also mod-
Dd between
D
2. Results and discussion
ulated by the nature of the substituent on the phenyl ring (X), it
is close to 40% for the styrene derivative (1b), increases to >50%
for the 4-OMe-styrene (1c) and decreases to 35% for the styrenes
bearing electron withdrawing substituents (1e–g). Both the upfield
2.1. The complexes
The prototype compound [PtCl(g
2-CH2@CH2)(tmeda)](ClO4)
shift of the olefinic carbons and the increase of the
Dd upon coor-
(1a) can be directly prepared from Zeise’s salt [10a,b]; [PtCl(g2
-
dination have been related to the amount of charge transfer from
the metal to the olefin (back-donation) [9]. Coordinated olefins
CH2@CHMe)(tmeda)](ClO4) (1a0) can be obtained in quantitative
yield by substitution of propene for ethene in 1a [10c]; 1a0, in turn,
can be used as substrate for further olefin substitution (complexes
exhibiting a
Dd increase lower than 10% are considered to have a
very poor electrophilic character. Hahn has compared complexes
of formula [M(PNP)(CH2@CHPh)]n+ (M = Rh(I), n = 1; Pd(II) and
Pt(II), n = 2. PNP = 2,6-bis(diphenylphosphanylmethyl)pyridine))
differing for the electrophilicity of the olefin (very low in the case
of rhodium and high in the case of palladium and platinum) [12–
14]. The different behaviour has been explained on the basis of a
[PtCl(g
2-CH2@CH–C6H4–X)(tmeda)](ClO4) where X = H (1b), 4-
OMe (1c), or 3-OMe (1d) were obtained in this way [10g]). How-
ever, when the entering olefin is a styrene bearing a strong electron
withdrawing group on the phenyl ring (ligands 4-CF3-styrene (e),
3-CF3-styrene (f), and 3-NO2-styrene (g)), its coordinating ability
is lowered and the substitution of styrene for propene can be to-
tally impaired. Even in the latter unfavourable circumstances, the
metathetic reaction can still be performed by exploiting the differ-
ent solubilities of the compounds in CH2Cl2. In particular, the sol-
greater metal-to-olefin
p back-donation in the case of rhodium
(overall complex charge +1) than in the case of palladium and plat-
inum (total charge +2) [8]. The different situation is well described
by the 13C resonances of the olefin moiety. In the case of rhodium,
upon complexation, the shielding of the olefinic carbons increases
ubility of [PtCl(g
2-3-NO2-styrene)(tmeda)](ClO4) (1g) is so poor
in CH2Cl2 that it precipitates quantitatively from the reaction
medium when 1a0 is reacted with excess 3-NO2-styrene. In turn,
a suspension of 1g in dichloromethane, treated with an excess of
considerably but
of palladium and platinum there is a smaller increase in shielding
of the olefinic carbons but the increase of
Dd increases only by 10%; in contrast, in the case
D
d is nearly twice as
Table 1
Selected 13C NMR data for complexes [PtCl( 2-olefin)(tmeda)](ClO4), 1, in acetone-d6 at 21 °C
g
e
Olefin
@CH2
@CHR
D
dd
D
(1JPt–C
)
Freea
Coordb,c
Freea
Coordb,c
Freea
Coordb
Styrene (1b)
113.4
110.9
117.0
115.5
116.0
68.5 (174)
65.0 (187)
71.0 (n. d.)
70.0 (164)
70.5 (124)
137.0
136.6
136.0
135.5
135.0
103.2 (81)
104.5 (66)
96.5 (n. d.)
97.2 (137)
96.0 (139)
23.6
25.7
19
20
19
34.7
39.5
25.5
27.2
25.5
93
121
n. d.
27
ꢀ15
4ꢀOMeꢀstyrene (1c)
4ꢀCF3ꢀstyrene (1e)
3ꢀCF3ꢀstyrene (1f)
3ꢀNO2ꢀstyrene (1g)
a
free = free olefin.
b
coord = coordinated olefin.
c
1JPtꢀC (Hz) in parentheses.
d
D
D
d = d@CHR ꢀ d@CH2
.
e
(1JPt–C) = (1JPt–CH2) ꢀ (1JPt–CHR) (Hz).

C.R. Barone et al. / Journal of Organometallic Chemistry 693 (2008) 2819–2827
2821
much. Therefore it can be concluded that the greater electrophilic-
ity of the olefin in the palladium and platinum complexes stems
With the present work we were interested in unravelling the ki-
netic preference for the site of attack (Markovnikov or anti-Mark-
ovnikov) in compounds 1b–g. As a nucleophile we chose the
methoxide ion for two main reasons: its small size and the stability
of the kinetically determined addition product in basic medium
(Scheme 1) [10g]. Moreover, since the kinetic of addition reaction
can be influenced by steric effects, we selected a group of cationic
complexes having very similar steric requirements (1b–g).
from a smaller metal-to-olefin
p back-donation accompanied by
a greater asymmetry in olefin coordination.
In the case of platinum the asymmetry in olefin coordination
can also be sized by differences in 1JPt–C between the 195Pt nucleus
and the olefinic carbons, a greater value of 1JPt–C being indicative of
a carbon closer to the metal centre [8]. From inspection of Table 1,
it can be noted how
D
(1JP–C) is 93 Hz in the styrene complex (1b),
The methoxide addition reactions were performed by treating a
suspension of the olefinic complexes in chlorinated solvents (gen-
erally CH2Cl2) with a slight excess (+10%) of methanolic KOH. The
reaction products (2b–g) were obtained in practically quantitative
yields. The heterogeneous conditions (incomplete dissolution of
the starting substrate) are likely to influence the overall rate of
the reaction but not the relative rate of formation of the Markovni-
kov and anti-Markovnikov isomers. The isomeric ratio was evalu-
ated by integration of well separated 1H NMR signals pertaining
to the Pt–C H2CbH(OMe)(C6H4–X) and Pt–C H(C6H4–X)CbH2(OMe)
increases in the presence of an electron donor substituent (121 Hz
in 1c), while decreases in the presence of electron withdrawing
substituents (values in the range 20 Hz for 1e–g).
From the previous observations it is possible to conclude that
the ground state of complexes 1b and 1c has a certain degree of
olefin slippage (contribution of the
g
1-limiting structure which
places a positive charge on the olefinic carbon farther from the me-
tal and a formal negative charge on the carbon attached to the me-
tal atom). A shift from the
g g
2- to the 1-coordination mode
a
a
generally occurs when an approaching nucleophile donates a lone
pair of electrons to the olefinic carbon which is moving away from
the metal. However, in the case of coordinated styrenes (particu-
larly those bearing an electron-donating substituent), a contribu-
moieties for the Markovnikov and anti-Markovnikov isomers,
respectively (Fig. 1).
Apart from performing the reaction on a preparative scale so to
isolate and fully characterize the addition products, the addition
reactions were also carried out in a NMR tube to directly evaluate
the isomeric ratio of the formed reaction products. Moreover, two
solvents were used: CDCl3 and acetone-d6; the results obtained are
listed in Table 2. While using CDCl3 the formation of the addition
reaction products was quantitative, in contrast, in the case of ace-
tone, the addition was accompanied by a side reaction with releas-
ing of free olefin.
Let us consider first the influence of the phenyl substituent X on
the isomeric composition of the addition products. As compared to
unsubstituted styrene, the Markovnikov/anti-Markovnikov ratio is
greater for a methoxy group in para position (3c), while is smaller
for a methoxy group in meta position (3d) or for a purely
withdrawing group either in meta or para position (3e–g). It can
be noticed how in this series of compounds the decrease of Mark-
tion of the
g
1-limiting structure to the ground state can be
fostered by delocalization over the phenyl ring of the positive
charge accumulating on the distal olefin carbon.
2.2. Regiochemistry of nucleophilic attack
In previous work we have examined the reactivity of 1a0 and 1b
towards several nucleophiles (OHꢀ, MeOꢀ, acetylacetonate, etc.)
and found a large preference for the Markovnikov type of attack
[10c]. More recently the investigation has been extended to
secondary amines and it has been found that there is always a ki-
netic preference for the Markovnikov addition product with an iso-
meric ratio close to 4:1. In chlorinated solvents the addition
products were found to undergo isomerization with a rate which
is strongly dependent upon the temperature. The equilibrium com-
position was shifted even more in favour of the Markovnikov iso-
mer (Markovnikov/anti-Markovnikov ratio > 9:1) in the case of
1a0, while in the case of 1b and 1c the shift was strongly in favour
of the anti-Markovnikov isomer (Markovnikov/anti-Markovnikov
ratio ꢁ 1:9 when the amine was NHEt2). Thus the thermodynami-
cally determined composition appeared to be strongly dependent
upon the nature of the olefin substituent. A methyl group favours
the Markovnikov isomer, whereas a phenyl group favours the
anti-Markovnikov form. Such a behaviour could be rationalized
on the basis of a phenyl stabilization and a methyl destabilization
of the high electron charge which accumulates on the carbon
bound to the metal atom [10h].
ovnikov/anti-Markovnikov ratio parallels the decrease in
D
Dd and
(1JPt–C) (Table 1). Therefore, it can be concluded that the reaction
kinetic is dominated by the degree of olefin slippage in the ground
state which is greatest for the 4-methoxy derivative (1c). In the last
compound the contribution of the
g
1-limiting structure, which
places a positive charge on the olefinic carbon atom further away
from the metal centre, is stabilized by the conjugative effect of
the OMe group in position 4 of the phenyl ring. It is noteworthy
that the same methoxy group in meta position (1d) is unable to
exert such a conjugative effect. As a result, a 3-OMe substituent
behaves as a purely electron withdrawing group disfavouring the
Markovnikov type of addition. The reaction medium appears to
have some influence upon the isomeric composition. In general,
Scheme 1. Nucleophilic addition of methoxide anion MeOꢀ to [PtCl( 2-CH2@CHR)(tmeda)]+.
g

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C.R. Barone et al. / Journal of Organometallic Chemistry 693 (2008) 2819–2827
Fig. 1. 1H NMR spectrum (300 MHz, CDCl3, 21 °C) of the addition product of CD3Oꢀ to [PtCl( 2-4-CF3-styrene)(tmeda)](ClO4) (1e).
g
Table 2
Kinetically controlled isomeric composition for the methoxide addition products
having Markovnikov (M), [PtCl{CH2CHR(OMe)}(tmeda)], or anti-Markovnikov (anti-
M), [PtCl{CHRCH2(OMe)}(tmeda)], configurations
Starting substrate
R
M (%)
anti-M (%)
1b
Ph
60
80
>90
>95
–
65
30
60
40
65
40
70
40
20
<10
<5
–
35
70
40
60
35
60
30
1c
1d
1e
1f
4-OMe–Ph
3-OMe–Ph
4-CF3–Ph
3-CF3–Ph
3-NO2–Ph
1g
Upper and lower entries refer to acetone-d6 and CDCl3 solvents, respectively.
Fig. 2. ORTEP drawing of the complex [PtCl(g
2-styrene)(tmeda)](ClO4), 1b (the
counter anion omitted for clarity). Data collection performed at 193 K. Ellipsoids
enclose 20% probability.
acetone appears to disfavour the Markovnikov addition as com-
pared to chloroform; the difference between acetone and chloro-
form may well depend upon the different solvation properties of
the two solvents. Acetone has better solvation capacity and, among
other things, this could affect the real size of the reactants [15]. An
increase in steric hindrance would disfavour the Markovnikov iso-
mer as compared to the anti-Markovnikov one.
2.3. X-ray crystallography
We obtained crystals suitable for X-ray investigation for some
of the considered complex species. Among the complexes of type
1, only the one with ethene (1a) has been structurally investigated
[10a,b]. The structures for the complex cations 1b and 1c are
reported in Figs. 2 and 3, respectively; significant bond lengths
and angles are reported in Table 3.
The olefin molecule binds to the platinum(II) centre in an
Fig. 3. ORTEP drawing of the complex [PtCl(g
2-4-OMe-styrene)(tmeda)](ClO4), 1c
(the counter anion omitted for clarity). Data collection performed at 193 K.
g
2-fashion and the coordination sphere has the usual square pla-
nar arrangement, when the chlorine atom, the two nitrogen atoms
Ellipsoids enclose 20% probability.

C.R. Barone et al. / Journal of Organometallic Chemistry 693 (2008) 2819–2827
2823
Table 3
sized by the
planes [18]. This angle is 32° in Zeise’s anion [17] and in 1a
[10b], and close to 60° in 1b and 1c. A greater (0° is the value
a angle between the normals to the CH2 and CHR
Selected bond lengths (Å) and angles (°) for [PtCl(
g
2-styrene)(tmeda)](ClO4) (1b) and
[PtCl(
g
2-4-OMe-styrene)(tmeda)](ClO4) (1c)
a
Vector
1b
1c
for a perfectly planar olefin) indicates greater bending-back of
the olefin substituents and, in turn, greater electron back-donation
Pt–Cl(1)
Pt–N(1)
Pt–N(2)
Pt–C(1o)
Pt–C(2o)
N(1)–C(1)
N(2)–C(2)
C(1)–C(2)
C(1o)–C(2o)
C(2o)–C(3o)
2.297(3)
2.112(9)
2.097(4)
2.160(6)
2.223(6)
1.508(9)
1.498(7)
1.498(9)
1.395(9)
1.462(9)
2.3028(14)
2.083(5)
2.103(2)
2.145(2)
2.218(3)
1.511(5)
1.495(4)
1.494(5)
1.386(6)
1.469(4)
from the metal d to the olefin p* orbital. The phenyl ring is ori-
p
ented towards the chlorido ligand (syn orientation) and outward
with respect to the Me2N(1) group of tmeda (anti orientation);
such an orientation avoids steric repulsions that could occur if
the phenyl was syn to the Me2N(1) group. Moreover, the phenyl
ring is almost coplanar with the olefin, the C(1o)–C(2o)–C(3o)–
C(4o) torsion angles being –164.0(4)° and –162.7(2)° for 1b and
1c, respectively. Such an orientation, that leads to significant
non-bonding interactions between an ortho proton of the phenyl
ring and the olefin proton on C(2o) (HꢂꢂꢂH distances of 2.19(4)
and 2.15(3) Å for 1b and 1c, respectively), can be accounted for
on the basis of an electronic conjugation between the phenyl and
N(1)–Pt–N(2)
N(1)–Pt–C(1o)
N(1)–Pt–C(2o)
N(2)–Pt–C(1o)
N(2)–Pt–C(2o)
N(1)–Pt–Cl(1)
N(2)–Pt–Cl(1)
C(1o)–Pt–Cl(1)
C(2o)–Pt–Cl(1)
C(1)–N(1)–Pt
C(3)–N(1)–Pt
C(4)–N(1)–Pt
C(2)–N(2)–Pt
C(5)–N(2)–Pt
C(6)–N(2)–Pt
C(3)–N(1)–C(1)
C(4)–N(1)–C(1)
C(4)–N(1)–C(3)
C(2)–N(2)–C(6)
C(5)–N(2)–C(2)
C(5)–N(2)–C(6)
C(1o)–C(2o)–C(3o)
85.0(2)
97.8(2)
90.1(3)
160.2(2)
162.6(2)
174.8(2)
89.8(1)
84.7(1)
97.1(2)
90.6(1)
159.1(2)
163.8(1)
174.9(1)
90.2(1)
the olefin
between the oxygen lone pair of the methoxy substituent and the
phenyl system. Moreover, the short values of the O–Ph (1.352(4)
p systems. The X-ray structure also reveals a conjugation
87.1(2)
94.8(2)
87.8(2)
94.3(9)
p
Å) and O–Me (1.434(4) Å) bonds and the large value of the Me–O–
Ph angle (118.5(2)°) indicate that the oxygen atom has a sp2
hybridization and the O–Ph some double bond character. A similar
situation has been previously described in some iminoether com-
plexes of platinum [19] and leads to the conclusion that, whenever
an oxygen atom is adjacent to an unsaturated system, an oxygen
102.9(5)
110.4(5)
115.9(5)
106.9(3)
107.8(3)
115.5(3)
109.7(5)
106.7(6)
110.8(7)
107.7(4)
109.5(4)
109.3(4)
125.8(6)
104.5(3)
111.0(3)
117.3(3)
107.05(18)
107.04(19)
115.3(2)
108.8(3)
106.8(4)
108.1(3)
108.2(2)
109.8(3)
109.4(2)
125.7(4)
lone pair gets involved in the
p bond.
Hydrogen-bond type interactions are found between two
methyl groups from tmeda and the cis chlorine atom. Both in 1b
and 1c, the complex cations form columnar arrays with the per-
chlorate anions hosted in the holes. There are no stacking interac-
tions between the
p systems of the phenyl rings.
from tmeda, and the centroid of the olefin double bond are consid-
ered. In both cations the metal atom lies exactly in the plane de-
fined by the chlorine and nitrogen donors; the Pt–Cl(1), Pt–N(1)
(cis to the olefin), and Pt–N(2) (trans to the olefin) bond distances
are very close to the value found for the ethene derivative [10b]
when the estimated standard deviations are taken into account.
In the tmeda ligand N–C and C–C distances fall in the normal range.
The chelate ring is puckered and both k and d conformations are
present in the crystal; the puckering, comparable in the two com-
plexes, was measured by the q2 parameter of Cremer and Pople
[16] (0.481(9) and 0.468(5) Å for 1b and 1c, respectively).
2.4. DFT calculations
The geometries of the cations of 1b and 1c were optimized
starting from the X-ray structures (similar calculations were also
performed on 1e, using the coordinates of 1c for the initial guess).
The calculated metric values compare well to the experimental
data. For the bond lengths the average deviation is 0.05 Å, while
the greatest deviation is ꢁ0.1 Å and involves the Pt–C(2o) bond
in 1c. The metal–carbon bond distances happen to be the least
accurate as it can be judged from their large variation as a function
of the solvent. For the bond angles, the average deviation is 1°,
while the maximum deviation is 4° and it involves the C(1o)–
C(2o)–C(3o) bond angle of 1c. Geometry optimizations of the same
cations in the presence of solvents (CHCl3, CH2Cl2, (CH3)2CO, and
CH3OH), within the C-PCM approach [20], lead to similar results.
Therefore the calculations reproduce well the structural features
of these olefin complexes. In particular the calculations reproduce
the fact that not all olefins are symmetrically bonded to the metal
but a slippage is present in 1b and 1c [6].
Bond angles of the coordination sphere are close to the idealized
values of 90° and 180° when the Cl(1), N(1) and N(2) atoms are
considered, the largest deviation being that of the N(1)–Pt–N(2)
bond angle (close to 85°), which is governed by the bite angle of
the tmeda ligand. The dihedral angle between the least-square
planes defined by Pt, C(1o) and C(2o) and by Cl(1), N(1), and N(2)
(from now on referred to as coordination plane) deviates by ꢁ10°
from the ideal value of 90° (the corresponding deviation was only
2° in the case of the previously investigated [PtCl(
g
2-CH2@
In order to better analyze the effect of coordination to
[PtCl(tmeda)]+, we compared free and coordinated olefins. For
the three complexes here considered, upon coordination, the C–C
CH2)(tmeda)]+ (1a), where the olefin approached the idealized per-
pendicular orientation [10b]).
The distance between platinum and the unsubstituted olefinic
carbon is significantly shorter than that between platinum and
the olefinic carbon bearing the phenyl ring (Table 3); this could
be taken as an indication that in the two complexes there is a con-
bond elongates by 0.06–0.07 Å; while the a angle, which sizes
the bending-back of the olefin substituents, is 33–34° (similar to
the experimental values found in 1a and in Zeise’s anion but signif-
icantly smaller than those found in 1b and 1c). A Natural Bond
Orbital (NBO) analysis was carried out to study the bonding prop-
erties between the olefin and the metal. For the three complexes
the donation from the olefin to the metal is found to be signifi-
cantly stronger than the back-donation from the metal to the ole-
tribution of the
g
1-limiting formula to the ground state structure.
The C(1o)–C(2o) bond distance, similar for the two compounds,
is very close to the values found for the ethene derivative (1.376(3)
Å) [10b] and for the Zeise’s anion, [PtCl3(g
2-C2H4)]ꢀ, (1.375(4) Å)
[17]. Bond distances and angles involving the olefin are normal.
As generally found in olefin complexes, there is a deviation of the
olefin moiety (CH2@CHR) from planarity. Such a deviation can be
fin. In particular the olefin
the metal fragment, while the back-donation to
0.3 electrons. Within the Perturbation Theory Energy Analysis, the
p
orbital donates almost 0.5 electrons to
p
* is no larger than

2824
C.R. Barone et al. / Journal of Organometallic Chemistry 693 (2008) 2819–2827
lowering in energy of the filled metal d orbital, consequent to the
4-CF3-substituted compound (1e) the two carbons contribute al-
most equally to the donation of the orbital to Pt and, as a conse-
quence, the observed regioselectivity is the lowest.
p
interaction with the empty olefin
rene (33.7 kcal/mol) to styrene (38.9 kcal/mol) and to 4-CF3-sty-
rene (40.6 kcal/mol), in good agreement with the Hammett
p
*, increases from 4-OMe-sty-
p
r
parameters. The donation from the olefin to the metal complex is
best understood by looking at the Natural Localized Molecular
Orbitals (NLMO) and in particular at the orbital describing the ole-
3. Conclusions
This investigation has shown that there is a significant partici-
pation of the g1 limiting formula to the ground state geometry
of styrene complexes 1b and 1c. This conclusion is supported by
several evidences: the terminal carbon of the olefin, as compared
to the one bearing the phenyl substituent, has a greater shielding,
a greater coupling with 195Pt, and a shorter distance from the metal
atom. This slippage of the olefin appears to stem from a phenyl sta-
bilization of the positive charge which accumulates on the distal
olefinic carbon (+M effect). The conjugation between the phenyl
finic
p bond (Table 4). This orbital has always a larger contribution
coming from the unsubstituted carbon and the difference between
unsubstituted and substituted carbon increases from 4-CF3-sty-
rene (6%), to styrene (8%), and to 4-OMe-styrene (13%). Since the
back-donation is almost equal for the two carbons, the
p donation
determines the difference between the electron densities on the
two carbons; the substituted carbon being the one with smaller
electron density. This analysis thus accounts for a slightly stronger
interaction between the metal and the unsubstituted carbon. This
difference in Pt–C interactions is however small and is largest in
the 4-methoxy substituted styrene for which the calculated differ-
ence between the contributions of the two carbons is the highest.
The computational analysis of selectivity requires, in principle,
the determination of the transition states for the competing reac-
tions. This is not feasible in the present case because in the gas
phase the addition of an anionic nucleophile to a cationic species
occurs without a transition state. Therefore, since the calculations
involving ionic species require the full consideration of all partners
(here two cations and two anions) as well as the participation of
the solvent, we resort to consider only the properties of the reac-
tants to rationalize the observations. This mode of reasoning has
been frequently used with success in particular for the regioselec-
tivity of addition to organic substrates [21]. The nucleophilic addi-
tion does not occur to a non-coordinated olefin, but only to olefins
coordinated to a metal fragment. The earlier work carried at the
extended Hückel level [3] gave a LUMO for the coordinated olefin
which was higher in energy than that of the free olefin. This is be-
cause the olefinic p* is destabilized by anti-bonding interaction
with occupied metal d orbitals. The explicit consideration of elec-
tron density and total charge, at the DFT level, yields a different re-
sult. The calculations show that, because of the positive charge on
the metal fragment, the LUMO of the complexed olefin is signifi-
cantly lower in energy than that of the free olefin. Even though
the energies of empty orbitals in DFT calculations should not be
considered quantitatively, they are qualitatively informative: low
lying empty orbitals clearly indicate an increased reactivity to-
and the olefin
p systems is revealed by the quasi planarity of the
styrene moiety; this planar conformation is attained notwithstand-
ing the repulsive interactions between the ortho protons of the
phenyl ring and a proton of the olefin moiety. The presence of a
methoxy substituent in para position of the phenyl ring (1c) sub-
stantially contributes to a further stabilization of the
form. The electron releasing ability of the 4-methoxy substituent
g
1-slipped
is promoted by an oxygen lone pair getting involved in conjugation
with the
p system of the phenyl ring. This is inferred by several
structural features such as the methoxy group coplanar with the
phenyl ring, the Me–O–Ph angle close to 120°, and the Me–O and
O–Ph distances slightly shorter than average values. In terms of
reactivity, the presence of a methoxy substituent in para position
is sufficient to shift the reaction towards the almost exclusive for-
mation of the Markovnikov addition product (addition of methox-
ide to the olefinic carbon bearing the phenyl ring). On the other
hand, the presence of an electron withdrawing substituent (com-
pounds 1d–g) reduces the +M effect of the phenyl ring (smaller dif-
ferences in shielding and coupling with 195Pt of the two olefinic
carbons) and in the reaction with MeOꢀ the Markovnikov and
the anti-Markovnikov addition products form in comparable
yields.
DFT calculations have revealed a significant slippage of the
g
2-bonded olefin (unsubstituted carbon closer to the metal center)
for the 4-OMe-styrene derivative and, to a lesser extent, for the
styrene derivative, in good agreement with the solid state struc-
tures. The reactivity of the complexed olefin towards an incoming
nucleophile stems from a lowering of the LUMO energy with re-
spect to that of the free olefin. Finally the regioselectivity can be
wards an incoming nucleophile [22]. In the present case, the g2
-
coordination activates the olefin towards nucleophilic addition.
The regioselectivity of the addition reaction is in accord with the
electron distribution associated with the NLMO analysis. The dona-
understood on the basis of the interaction between the olefinic
p
and the empty Pt d orbitals: the carbon which is closer to the metal
atom is more electron rich and less susceptible of nucleophilic at-
tack. Despite being only qualitative, this analysis has succeeded in
highlighting some principles which control the reactivity and
selectivity of nucleophilic addition to coordinated olefins.
tion from the olefinic
p orbital to platinum dominates over the
back-donation from platinum d orbitals to the olefin. In the dona-
p
tion the two carbons behave differently and the unsubstituted one,
which moves closer to platinum, remains more electron rich and
therefore becomes less susceptible of nucleophilic attack. This is
specifically the case of the 4-OMe-styrene complex (1c) for which
the observed regioselectivity is the highest (we refer to the results
in dichloromethane because it is a non coordinating solvent). In the
4. Experimental
4.1. Reagents and methods
Reagents and solvents were commercially available and used as
received without further purification. Elemental analyses were
performed with a CHN Eurovector EA 3011. 1H and 13C NMR spec-
tra were recorded with a 300 MHz Mercury Varian and a DPX-WB
300 Avance Bruker instruments equipped with probes for inverse
detection and with z gradient for gradient-accelerated spectros-
copy. 1H and 13C NMR spectra were referenced to TMS; the residual
Table 4
Contributions from the two vinyl carbon atoms in the orbitals involved in
) and back-donation (d Pt) as obtained by NLMO analysis
r
donation
(p
p
p
Complex
p
d Pt
p
%Cus
%Cs
%Cus
%Cs
1b
1c
1e
41.4
44.0
40.6
33.5
30.6
34.6
4.4
3.8
4.7
5.0
5.0
5.1
proton signal of the solvent was used as internal standard. 1H/13
C
inversely detected gradient-sensitivity enhanced heterocorrelated
2D NMR spectra for normal coupling (INVIEAGSSI) were acquired
C
us = C(1o), Cs = C(2o) of X-ray crystal structures.

C.R. Barone et al. / Journal of Organometallic Chemistry 693 (2008) 2819–2827
2825
using standard Bruker automation programs and pulse sequences.
Each block of data was preceded by eight dummy scans. The data
were processed in the phase-sensitive mode. The ESI-MS spectra
were recorded with an Agilent 1100 Series LC-MSD Trap System
VL.
51.24, and 53.12, tmeda CH3N; 62.54 and 66.94, tmeda CH2N; 65,
CH2@CHC6H4-4-CF3; 96.5, CH2@CHC6H4-4-CF3; 130.3, Cmeta; 125,
Cortho ppm.
[PtCl(g
2-3-CF3-styrene)(tmeda)](ClO4), 1f: Elemental Anal. Calc.
for C15H23Cl2F3N2O4Pt (618.33): C, 29.14; H, 3.75; N, 4.53. Found:
C, 29.44; H, 3.48; N, 4.72%. Peak of greatest intensity in ESI-MS:
m/z = 518.9 = [MꢀClO4]+. NMR (acetone-d6, 21 °C): d(1H) = 2.97 (s,
3H), 3.0 (s, 6H), and 3.41 (s, 3H), tmeda CH3N; 3.02 (m, 1H), 3.18
(m, 1H), 3.5 (m, 1H), and 3.58 (m, 1H), tmeda CH2N; 4.98 (d,
3JH–H cis = 10 Hz, 2JPt–H = 64 Hz, 1H) and 5.54 (d, 3JH–H trans = 14 Hz,
2JPt–H = 55 Hz, 1H), CH2@CHC6H4-3-CF3; 6.56 (m, 1H), CH2@
4.2. Syntheses
Cationic complexes [PtCl(g
2-olefin)(tmeda)](ClO4), 1, (ole-
fin = ethene, 1a; propene, 1a0; styrene, 1b; 4-OMe-styrene, 1c; 3-
OMe-styrene, 1d; 4-CF3-styrene, 1e; 3-CF3-styrene, 1f; 3-NO2-sty-
rene, 1g).
3
CHC6H4-3-CF3; 7.63 (t, 1H, JH–H = 8.0 Hz), Hmeta; 7.79 (d, 1H),
Complexes 1a [10a], 1a0 [10c] and 1b,c [10g] were prepared
according to already reported procedures. Complexes 1d,g were
prepared similarly to 1b,c by olefin exchange starting from the cat-
ionic complex [PtCl(g2-propene)(tmeda)](ClO4), 1a0. In a typical
experiment 1a0 (250 mg, 0.5 mmol) was suspended in dichloro-
methane (3 mL) and treated with a 10 molar excess of the incom-
ing olefin (d = 3-OMe-styrene or g = 3-NO2-styrene). After 24 h
stirring at room temperature, the solid was recovered on a sintered
glass filter, washed with diethyl ether, and dried; it turned to be
the desidered compound.
H
ortho; 8.04 (s, 1H), Hortho; 8.11 (d, 1H), Hpara ppm. d(13C) = 49.6,
50.4, 51.1, and 53.3, tmeda CH3N; 62.4 and 66.9, tmeda CH2N;
70.5 (1JPt–C = 164 Hz), CH2@CHC6H4-3-CF3’; 97.3 (1JPt–C = 137 Hz),
CH2@CHC6H4-3-CF3; 125.98, Cortho; 126.42, Cpara; 129.43, Cmeta
;
133.77, Cortho ppm.
4.3. Addition products with methoxide anion
The addition product 2b has already been reported [10c]. Com-
pounds 2c–g have been prepared as hereafter described. A few mL
of CH2Cl2 and a known amount of a methanolic solution of KOH
[PtCl(
ferred to platinum, was 95% (282 mg). Elemental Anal. Calc. for
15H26Cl2N2O5Pt (580.36): C, 31.04; H, 4.52; N, 4.83. Found: C,
g
2-3-OMe-styrene)(tmeda)](ClO4), 1d: the isolated yield, re-
(0.12 mmol, 120 lL of a 1 M solution) were placed in a reaction
C
vessel and treated with a stoichiometric amount (0.12 mmol) of
the appropriate cationic complex. In the case of unstable starting
complexes (1e–g) the reaction vessel was precooled in an ice bath.
The mixture was kept under stirring for 2 h during that time disso-
lution of the cationic complex and precipitation of KClO4 were ob-
served. The organic phase was repeatedly washed with water
(4 ꢃ 0.5 ml), diluted with CH2Cl2 up to 20 mL and kept for some
hours over anhydrous Na2SO4, filtered, and finally evaporated to
dryness under vacuum. Trituration with diethyl ether of the ob-
tained sticky residue gave a solid powder of the addition product,
which was a mixture of the Markovnikov and anti-Markovnikov
isomers. The yield, referred to platinum, was nearly quantitative.
2c, Elemental Anal. Calc. for C16H29ClN2O2Pt (511.94): C, 37.54;
H, 5.71; N, 5.47. Found: C, 38.1; H, 5.92; N, 5.68%. NMR (CDCl3,
31.33; H, 4.44; N, 4.45%. Peak of greatest intensity in ESI-MS:
m/z = 481 = [MꢀClO4]+. NMR (acetonitrile-d3, 21 °C): d(1H) = 3.2–2.7
(16H), CH3N and CH2N of tmeda; 3.83 (s, 3H), CH2@CHC6H4OCH3;
3
2
3
4.7 (d, JH–H cis = 8 Hz, JPt–H = 61 Hz, 1H), and 5.3 (bd, JH–H trans =
15 Hz, 1H), CH2@CHC6H4-3-OCH3; 6.3 (bm, 1H), CH2@CHC6H4-3-
OMe; 7–7.4, aromatic H ppm.
[PtCl(
ferred to platinum, was 95% (295 mg). Elemental Anal. Calc. for
14H23Cl2N3O6Pt (595.3): C, 28.24; H, 3.89; N, 7.06. Found: C,
g
2-3-NO2-styrene)(tmeda)](ClO4), 1g: the isolated yield, re-
C
28.52; H, 3.98; N, 7.10%. Peak of greatest intensity in ESI-MS: m/
z = 495.9 = [MꢀClO4]+. NMR (acetone-d6, 21 °C): d(1H) = 2.97 (s,
3H), 3.01 (s, 6H), 3.48 (s, 3H), tmeda CH3N; 3.01 (m, 1H), 3.23
(m, 1H), 3.5 (m, 1H), and 3.57 (m, 1H), tmeda CH2N; 5.05 (d,
3JH–H cis = 8.2 Hz, 2JPt–H = 65 Hz, 1H), and 5.62 (d, 3JH–H
21 °C): [PtCl{g
1-CH2-CH(OCH3)(C6H4-4-OCH3)}(tmeda)], d(1H) = 1.92
2
3
trans = 15.2 Hz, JPt–H = 57 Hz, 1H), CH2@CHC6H4-3-NO2; 6.61 (m,
(s, JPt–H = 50 Hz, 3H), 2.66 (s, 3H), 2.68 (s, 3H), and 2.71 (s, 3H),
3
2
1H), CH2@CHC6H4-3-NO2; 7.7 (t, JH–H = 8.0 Hz, 1H), Hmeta; 8.23
tmeda CH3N; 2.6–2.9 (m, 4H), tmeda CH2N; 1.19 (t, JH–H and
2
3
(d, 1H), Hortho; 8.31 (d, 1H), Hpara; 8.54 (s, 1H), Hortho ppm.
d(13C) = 49, 50, 51, and 52, tmeda CH3N; 62 and 65, tmeda CH2N;
70.5 (1JPt–C = 124 Hz), CH2@CHC6H4-3-NO2; 96.0 (1JPt–C = 139 Hz),
CH2@CHC6H4-3-NO2; 123, Cortho; 124, Cpara; 129, Cmeta; 136, Cortho
ppm.
3JH–H = 9.5 Hz, JPt–H = 90 Hz, 1H) and 2.23 (dd, JH–H = 5.0 Hz, 1H),
Pt–CH2-CH(OCH3)(C6H4-4-OCH3); 3.27 (s, 3H), Pt–CH2-CH(OCH3)-
(C6H4-4-OCH3); 3.74 (s, 3H), Pt–CH2-CH(OCH3)(C6H4-4-OCH3);
3
4.56 (dd, 1H), Pt–CH2-CH(OCH3)(C6H4-4-OCH3); 6.77 (d, JH–H
=
8.5 Hz, 2H), 2Hmeta; 7.55 (d, 2H), 2Hortho ppm. In this case the
anti-Markovnikov isomer was very minor (<5%).
Complexes 1e,f were prepared by olefin exchange starting from
the cationic complex 1g. In a typical experiment 1g (150 mg,
0.25 mmol), was suspended in dichloromethane (3 mL), and trea-
ted with a 13-fold excess of the incoming olefin (e = 4-CF3-styrene
or f = 3-CF3-styrene). After 24 h stirring at room temperature, the
reaction mixture was filtered on a sintered glass filter to remove
un-reacted 1g. The mother liquor was evaporated to dryness under
vacuum and the sticky residue after trituration with diethyl ether
gave a yellowish solid which was 1e or 1f. The isolated yield, al-
ways referred to platinum and after the indicated stirring time,
was ca. 50%.
2d, Elemental Anal. Calc. for C16H29ClN2O2Pt (511.94): C, 37.54;
H, 5.71; N, 5.47. Found: C, 37.01; H, 6.02; N, 5.95%. NMR (CDCl3,
21 °C): [PtCl{g
1-CH2-CH(OCH3)(C6H4-3-OCH3)}(tmeda)], d(1H) = 1.92
3
(s, JPt–H = 50 Hz, 3H), 2.67 (s, 3H), 2.69 (s, 3H), and 2.71 (s, 3H),
2
tmeda CH3N; 2.6 ꢄ 2.9 (m, 4H), tmeda CH2N; 1.22 (t, JH–H and
2
3
3JH–H = 9.6 Hz, JPt–H = 90 Hz, 1H), and 2.21 (dd, JH–H = 5.0 Hz,
1H), Pt–CH2–CH(OCH3)(C6H4-3-OCH3); 3.28 (s, 3H), Pt–CH2–
CH(OCH3)(C6H4-3-OCH3); 3.76 (s, 3H), Pt–CH2–CH(OCH3)(C6H4-3-
OCH3); 4.58 (dd, 1H), Pt–CH2–CH(OCH3)(C6H4-3-OCH3); 6.66, (dd,
4
3JH–H = 8.2 Hz, JH–H = 2.8 Hz, 1H), Hpara; 6.95, (s, 1H), Hortho; 7.14,
3
[PtCl(
g
2-4-CF3-styrene)(tmeda)](ClO4), 1e: Elemental Anal. Calc.
(d, JH–H = 7.6 Hz, 1H), Hortho; 7.2, (m, 1H), Hmeta ppm. [PtCl{g1
-
for C15H23Cl2F3N2O4Pt (618.33): C, 29.14; H, 3.75; N, 4.53. Found:
C, 29.49; H, 3.66; N, 4.37%. Peak of greatest intensity in ESI-MS:
m/z = 518.9 = [MꢀClO4]+. NMR (acetone-d6, 21 °C): d(1H) = 2.97 (s,
3H), 3.02 (s, 6H), 3.48 (s, 3H), tmeda CH3N; 3.04 (m, 1H), 3.16
CH(C6H4-3-OCH3)-CH2(OCH3)}(tmeda)], d(1H) = 2.60 (s, 3H), 2.64 (s,
3H), 2.76 (s, 3H), and 2.84 (s, 3H), tmeda CH3N; 2.6–2.9 (m, 4H),
3
tmeda CH2N; 3.09 (dd, JH–H = 4.1 and 10.5 Hz, 1H), Pt–CH(C6H4-
3-OCH3)-CH2(OCH3); 3.27 (s, 3H), Pt–CH(C6H4-3-OCH3)–CH2-
3
(m, 1H), 3.48 (m, 1H), 3.54 (m, 1H), tmeda CH2N; 5.0 (d, JH–H
(OCH3); 3.74 (s, 3H), Pt–CH(C6H4-3-OCH3)–CH2(OCH3); 3.86 (dd,
3
cis = 9 Hz, 1H), and 5.54 (d, JH–H trans = 15 Hz, 1H), CH2@CHC6H4-
2JH–H = 10.5 Hz, 1H), and 4.0 (t, 1H), Pt–CH(C6H4-3-OCH3)–
3
3
4-CF3; 6.56 (m, 1H), CH2@CHC6H4-4-CF3; 7.72 (d, JH–H = 8.7 Hz,
CH2(OCH3); 6.56, (d, JH–H = 6.6 Hz, 1H), Hpara; 6.95, (s, 1H), Hortho
;
2H), 2Hortho; 7.99 (d, 2H), 2Hmeta ppm. d(13C) = 49.86, 50.61,
7.14, (d, JH–H = 7.64 Hz, 1H), Hortho; 7.2, (m, 1H), Hmeta.
3

2826
C.R. Barone et al. / Journal of Organometallic Chemistry 693 (2008) 2819–2827
Table 5
2e, Elemental Anal. Calc. for C16H26ClF3N2OPt (549.92): C, 34.95;
H, 4.77; N, 5.09. Found: C, 34.80; H, 4.52; N, 5.12%. NMR (CDCl3,
21 °C): [PtCl{
1-CH2-CH(OCH3)(C6H4-4-CF3)}(tmeda)], d(1H) = 1.89
Selected crystal data and structure refinement parameters for [PtCl(g
2-styrene)(tme-
da)](ClO4) (1b) and [PtCl(
g
2-4-OMe-styrene)(tmeda)](ClO4) (1c)
g
3
Parameter
Value
(s, JPt–H = 50 Hz, 3H), 2.66 (s, 3H), 2.69 (s, 3H), and 2.71 (s, 3H),
2
tmeda CH3N; 2.6–2.9 (m, 4H), tmeda CH2N; 1.19 (t, JH–H and
1b
1c
2
3
3JH–H = 9.6 Hz, JPt–H = 90 Hz, 1H), and 2.21 (dd, JH–H = 5.0 Hz,
1H), Pt–CH2-CH(OCH3)(C6H4-4-CF3); 3.28 (s, 3H), Pt–CH2–CH-
(OCH3)(C6H4-4-CF3); 4.69 (dd, 1H), Pt–CH2–CH(OCH3)(C6H4–4-
Empirical formula
Formula weight
Temperature (K)
Crystal system, space group
a (Å)
C
14H24Cl2N2O4Pt
C15H26Cl2N2O5Pt
580.37
550.34
193(2)
193(2)
3
3
Monoclinic, Cc
16.059(2)
11.2805(16)
12.8872(19)
90
Monoclinic, Cc
16.0319(19)
11.4831(13)
13.0220(15)
90
CF3); 7.48 (d, JH–H = 8.0 Hz, 2H), 2Hortho; 7.79 (d, JH–H = 8.2 Hz,
2H), 2Hmeta ppm. [PtCl{g
1-CH(C6H4-4-CF3)–CH2(OCH3)}(tmeda)],
b
c
d(1H) = 2.60 (s, 3H), 2.84 (s, 3H), 2.9 (s, 3H), and 2.94 (s, 3H), tmeda
3
CH3N; 2.6–2.9 (m, 4H), tmeda CH2N; 3.18 (dd, 1H, JH–H = 4.0 and
a
(°)
b (°)
127.124(2)
90
126.6400(10)
90
10.5 Hz), Pt–CH(C6H4-4-CF3)–CH2(OCH3); 3.27 (s, 3H), Pt–
2
c
(°)
CH(C6H4-4-CF3)–CH2(OCH3); 3.88 (dd, JH–H = 10.5 Hz, 1H), and
Volume (Å3)
1861.5(5)
4, 1.964
1923.6(4)
4, 2.004
3
4.07 (t, 1H), Pt–CH(C6H4-4-CF3)–CH2(OCH3); 7.3 (d, JH–H
=
Z, Calculated density (Mg mꢀ3
)
3
Absorption coefficient (mmꢀ1
Crystal size (mm)
)
7.844
7.600
8.23 Hz, 2H), 2Hortho; 7.52 (d, JH–H = 8.0 Hz, 2H), 2Hmeta ppm.
0.24 ꢃ 0.22 ꢃ 0.13
12,587/4604
[0.0399]
0.43 ꢃ 0.25 ꢃ 0.18
13,608/4687
[0.0265]
2f, Elemental Anal. Calc. for C16H26ClF3N2OPt (549.92): C, 34.95;
Reflections collected/unique [Rint
]
H, 4.77; N, 5.09. Found: C, 34.65; H, 4.55; N, 5.23%. NMR (CDCl3,
21 °C): [PtCl{g
1-CH2-CH(OCH3)(C6H4-3-CF3)}(tmeda)], d(1H) = 1.77
Data/restraints/parameters
Final R indices [I > 2
4369/2/208
R1, 0.0269; wR2,
0.0630
4562/2/226
R1, 0.0157; wR2,
0.0369
3
(s, JPt–H = 50 Hz, 3H), 2.65 (s, 3H), and 2.68 (s, 6H), tmeda CH3N;
r(I)]
2
3
2.6 ꢄ 2.9 (m, 4H), tmeda CH2N; 1.07 (t, JH–H and JH–H = 9.5 Hz,
3
2JPt–H = 90 Hz, 1H), and 2.27 (dd, JH–H = 4.5 Hz, 1H), Pt–CH2-
R indices (all data)
R1, 0.0288; wR2,
0.0639
R1, 0.0162; wR2,
0.0371
CH(OCH3)(C6H4-3-CF3); 3.28 (s, 3H), Pt–CH2-CH(OCH3)(C6H4-3-
CF3); 4.72 (dd, 1H), Pt–CH2-CH(OCH3)(C6H4-3-CF3); 7.35 (m, 2H),
Absolute structure parameter
Largest difference in peak and hole
(e Åꢀ3
0.071(8)
1.226 and ꢀ0.858
ꢀ0.003(4)
0.932 and ꢀ0.571
H
meta and Hortho; 7.8 (d, 3JH–H = 7.2 Hz, 1H), Hpara; 8.17 (s, 1H), Hortho
)
ppm. [PtCl{g
1-CH(C6H4-3-CF3)-CH2(OCH3)}(tmeda)], d(1H) = 2.59 (s,
The wavelength was 0.71073 Å for all data collection.
3H), 2.64 (s, 3H), 2.83 (s, 3H), and 2.88 (s, 3H), tmeda CH3N;
3
2.6 ꢄ 2.9 (m, 4H), tmeda CH2N; 3.17 (dd, JH–H = 4.2 and 10.5 Hz,
1H), Pt–CH(C6H4-3-CF3)-CH2(OCH3); 3.27 (s, 3H), Pt–CH(C6H4-3-
the atoms to which they are attached. The non-hydrogen atoms
were refined as anisotropic, and the hydrogen atoms were treated
as isotropic with thermal factors equal to 1.2 times those of the
correspondent heavier atoms. Twenty-four cycles of least-squares
calculations gave a nice convergence for the model of each of the
two structures. The conventional R1 and wR2 factors converged to
0.0269 and 0.0630 for 1b, and 0.0157 and 0.0361 for 1c. The anal-
ysis of molecular geometry parameters was performed through
PARST-97 [27] and the molecular graphics was carried out through
ORTEP-32 [28]. All the calculations were performed by using Pen-
tium IV personal computers operating through the Windows-XP
system. All data for the structures here reported have been depos-
ited with the Cambridge Crystallographic Data Centre as CCDC ref-
erence numbers: 665827 (1b) and 665825 (1c).
2
CF3)–CH2(OCH3); 3.87 (dd, JH–H = 10.5 Hz, 1H), and 4.05 (t, 1H),
Pt–CH(C6H4-3-CF3)–CH2(OCH3); 7.23 (m, 2H), Hmeta and Hortho; 7.6
3
(s, 1H), Hortho; 7.67 (d, JH–H = 6.9 Hz, 1H), Hpara ppm.
2g, Elemental Anal. Calc. for C15H26ClN3O3Pt (526.92): C, 34.19;
H, 4.97; N, 7.97. Found: C, 37.96; H, 5.12; N, 5.08%. NMR (CDCl3,
21 °C): [PtCl{g
1-CH2-CH(OCH3)(C6H4-3-NO2)}(tmeda)], d(1H) = 1.77
3
(s, JPt–H = 50 Hz, 3H), 2.66 (s, 3H), and 2.68 (s, 6H), tmeda CH3N;
2
3
2.6 ꢄ 2.9 (m, 4H), tmeda CH2N; 1.08 (t, JH–H and JH–H = 9.5 Hz,
3
2JPt–H = 90 Hz, 1H), and 2.28 (dd, JH–H = 4.7, 1H), Pt–CH2-
CH(OCH3)(C6H4-3-NO2); 3.31 (s, 3H), Pt–CH2–CH(OCH3)(C6H4-3-
NO2); 4.75 (dd, 1H), Pt–CH2-CH(OCH3)(C6H4-3-NO2); 7.31 (m,
3
2H), Hmeta and Hortho; 7.79 (d, 1H, JH–H = 7.2 Hz), Hpara; 8.17 (s,
1H), Hortho ppm. [PtCl{g
1-CH(C6H4-3-NO2)-CH2(OCH3)(tmeda)}],
d(1H) = 2.58 (s, 3H), 2.60 (s, 3H), 2.84 (s, 3H), and 2.89 (s, 3H), tme-
3
da CH3N; 2.6–2.9 (m, 4H), tmeda CH2N; 3.18 (dd, JH–H = 4.1 and
4.5. Computational details
10.5 Hz, 1H), Pt–CH(C6H4-3-NO2)–CH2(OCH3); 3.30 (s, 3H), Pt–
2
CH(C6H4-3-NO2)–CH2(OCH3); 3.87 (dd, JH–H = 10.5 Hz, 1H), and
The calculations were performed with the GAUSSIAN03 package
[29] at the B3PW91 level [30]. Platinum and chlorine atoms were
represented by the relativistic effective core potentials (RECP) from
the Stuttgart group and their associated basis sets (SDDALL
keyword in GAUSSIAN03) [31], augmented by a f polarization function
4.06 (t, 1H), Pt–CH(C6H4-3-NO2)–CH2(OCH3); 7.26 (m, 2H), Hmeta
and Hortho; 7.6 (s, 1H), Hortho; 7.69 (d, 3JH–H = 7.2 Hz, 1H), Hpara ppm.
4.4. X-ray crystallography
for Pt (a = 0.993) [32a] and a d for Cl (a = 0.64) [32b]. A 6-31G(d,p)
The data sets for compounds 1b and 1c were collected through
a Bruker SMART CCD area detector diffractometer located at X-ray
Crystallography Laboratory, Emory University, Atlanta, Georgia,
USA, at 193 2 K. Selected crystallographic data are reported in Ta-
ble 5. The original data sets were corrected for Lorentz-polarization
effects through SAINT32 [23] (1b,1c) computer packages. The
basis set was used for all the other atoms (C, N, H, O, F) [33]. The
geometry optimizations were performed without any symmetry
constraint followed by analytical frequency calculations to confirm
that a minimum had been reached. Geometry optimizations were
performed at the B3PW91 level either in the gas phase or within
the C-PCM methodology (UAKS radii were used) [20]. Natural
bonding orbital analysis [34] was performed with the NBO 5.0 ver-
sion implemented in GAUSSIAN03.
absorption effects were corrected through the
w-scan techniques
by using the SADABS [24] for 1b and 1c. The structure solution was
performed through the direct methods implemented in the SHEL-
XS-97 software [25a] under WINGX [26]. All the atoms of the coordi-
nation sphere and most of the other non-hydrogen atoms were
located from the structure solution whereas the remaining atoms
were located from subsequent cycles of Fourier-difference synthe-
sis and least-squares calculations. The hydrogen atoms were lo-
cated via the HFIX options of SHELXL-97 [25b] and left riding on
Acknowledgments
Prof. Kenneth Hardcastle from Emory University, Department of
Chemistry, is gratefully acknowledged for the X-ray data collection
at Emory for compound 1b and 1c. We thank the financial support
of the Universities of Siena and Bari, and of the Italian Ministero

C.R. Barone et al. / Journal of Organometallic Chemistry 693 (2008) 2819–2827
2827
(h) G. Lorusso, N.G. Di Masi, L. Maresca, C. Pacifico, G. Natile, Inorg. Chem.
Commun. 9 (2006) 500–503;
(i) G. Lorusso, C.R. Barone, N.G. Di Masi, C. Pacifico, L. Maresca, G. Natile, Eur. J.
Inorg. Chem. (2007) 2144–2150.
dell’Università e Ricerca (MUR, Cofin. No. 2005032730). EC and OE
thank the CNRS and the Ministère de l’Enseignement Supérieur et
de la Recherche for financial support.
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1807–1818.
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Appendix A. Supplementary material
CCDC 665827 and CCDC 665825 contain the supplementary
crystallographic data for this paper. 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
associated with this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2008.05.040.
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