The mechanism of olefin exchange in platinum(0) pyridyl-methanimine and pyridyl-thioether complexes. A kinetic study

Article abstract of DOI:10.1039/b203608h

The complexes of type [Pt(η²-ol₁)(L-L′)] (ol₁ = dimethylfumarate (dmf), naphthoquinone (nq); L-L′ = pyridyl-methanimine (N-N′R′; R′ = Bu′, 4-MeOC₆H₄), pyridyl-thioether (N-SR; R = Bu′, Ph) ligands) were synthesised and fully characterised by means of spectrometric and spectroscopic techniques and elemental analysis. At variance with analogous palladium complexes which display a more complicated solution behaviour, the fluxional rearrangement of pyridyl-thioether platinum(o) olefin substrates occurs via inversion at sp³ sulfur only (L-L′ = N-SR). Moreover, the exchange olefin reactions between [Pt(η²-ol₁)(L-L′)] complexes and the entering olefi ol₂ [ol₂ = maleic anhydride (ma), fumaronitrile (fn), naphthoquinone (nq) and tetramethylethylenetetracarboxylate (tmetc)] were studied in CHCl₃ either under pseudo-first order or second order conditions. On the basis of the ensuing results and of the activation parameters, an associative reaction mechanism is proposed and a novel reactivity scale for the electron poor olefins acting as entering species is determined. The crystal structures of the complexes [Pt(η²-ol)(L-L′)] (ol= fn, ma, dmf) were also determined and compared with those of analogous platinum(o) and palladium(o) species.

Full text of DOI:10.1039/b203608h

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The mechanism of olefin exchange in platinum(0) pyridyl–
methanimine and pyridyl–thioether complexes. A kinetic study
Luciano Canovese,*a Fabiano Visentin,a Gavino Chessa,a Claudio Santo,a Paolo Uguagliati,a
Lucia Mainib and Marco Politob
a Dipartimento di Chimica, Università di Venezia, Calle Larga Santa Marta 2137, 30123 Venice,
Italy. E-mail: cano@unive.it
b Dipartimento di Chimica “G. Ciamician”, via Selmi 2, 40126 Bologna, Italy
Received 12th April 2002, Accepted 19th June 2002
First published as an Advance Article on the web 5th September 2002
The complexes of type [Pt(η2-ol1)(L–LЈ)] (ol1 = dimethylfumarate (dmf ), naphthoquinone (nq); L–LЈ = pyridyl–
methanimine (N-NЈRЈ; RЈ = But, 4-MeOC6H4), pyridyl–thioether (N-SR; R = But, Ph) ligands) were synthesised and
fully characterised by means of spectrometric and spectroscopic techniques and elemental analysis. At variance with
analogous palladium complexes which display a more complicated solution behaviour, the fluxional rearrangement
of pyridyl–thioether platinum() olefin substrates occurs via inversion at sp3 sulfur only (L–LЈ = N-SR). Moreover,
the exchange olefin reactions between [Pt(η2-ol1)(L–LЈ)] complexes and the entering olefin ol2 [ol2 = maleic anhydride
(ma), fumaronitrile (fn), naphthoquinone (nq) and tetramethylethylenetetracarboxylate (tmetc)] were studied in
CHCl3 either under pseudo-first order or second order conditions. On the basis of the ensuing results and of the
activation parameters, an associative reaction mechanism is proposed and a novel reactivity scale for the electron
poor olefins acting as entering species is determined. The crystal structures of the complexes [Pt(η2-ol)(L–LЈ)]
(ol = fn, ma, dmf ) were also determined and compared with those of analogous platinum() and palladium() species.
it being the only observable fluxional rearrangement taking
place. The complexes characterised and investigated and the
employed olefins are reported in the following Scheme 1.
Introduction
Low valent palladium and platinum complexes are often
invoked as precursors or active species in several catalytic reac-
tions involving C–C or C–N bond formation.1 A wealth of
papers dealing with Pd(), Ni() and Pt() olefin complexes is
available, but very few detailed mechanistic studies have
appeared in the recent literature.2 Our research group has been
systematically involved in studies on the mechanistic behaviour
and the determination of the related equilibrium constants
of olefin exchange in Pd() substrates containing pyridyl–
thioethers and pyridyl–methanimines as ancillary ligands.3 Our
investigations were unfortunately confined mostly to thermo-
dynamic determinations since the high reactivity of the pal-
ladium species renders the kinetic studies on olefin exchange
reactions difficult. In order to obtain some information on the
mechanism of such olefin exchange reactions we had to resort
to the use of the bulky tetramethylethylenetetracarboxylate
(tmetc) as entering or leaving olefin.3a,b The results we obtained,
while providing useful information on the intimate olefin
exchange mechanism, were necessarily incomplete, being based
in the case of pyridyl–thioether complexes on only few reacting
species. We therefore decided to extend our studies to the less
reactive Pt() substrates with the aim to generalise our previous
results by the use of several electron poor olefins as nucleo-
philes. We describe here the synthesis, the reactivity and in some
cases the structure of Pt() complexes of the type [Pt(η2-ol)-
(L–LЈ)] which undergo the exchange reaction:
Scheme 1
[Pt(η2-ol1)(L–LЈ)] ϩ ol2
[Pt(η2-ol2)(L–LЈ)] ϩ ol1 (1)
Results and discussion
where the ancillary ligand L–LЈ represents the pyridyl–
thioether or pyridyl–methanimine moiety and ol1 and ol2 are
electron poor olefins. To the best of our knowledge this study
represents the first kinetic investigation on entering olefins in
Pt() systems. Moreover, in the case of low valent pyridyl–
thioether platinum olefin complexes, the occurrence of inver-
sion of the sulfur’s absolute configuration was also investigated,
1. Synthesis of complexes
Zero valent olefin platinum complexes were synthesised in good
yield by reacting Pt(DBA)2 with the appropriate bidentate
ligand and the electron-poor olefin in THF. The temperature
and reaction time proved very important. With the less
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J. Chem. Soc., Dalton Trans., 2002, 3696–3704
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b203608h

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Table 1 Selected 1H NMR data recorded in CDCl3 at 223 K for platinum() olefin pyridyl–thioether complexes (coupling constants in Hz)
Isomeric
Complex
Olefinic protons
C–CH3
O–CH3
Ratio
[Pt(η2-dmf )(N–SBut)]
[Pt(η2-fn)(N–SBut)]
[Pt(η2-nq)(N–SBut)]
[Pt(η2-ma)(N–SBut)]b
[Pt(η2-tmetc)(N–SBut)]c
3.59 d (JHH = 8.3) 3.24 d (JHH = 8.3)
3.61 d (JHH = 8.3) 3.26 d (JHH = 8.3)
2.54 d (JHH = 7.8) 2.94 d (JHH = 7.8)
2.61 d (JHH = 7.8) 2.85 d (JHH = 7.8)
4.32 d (JHH = 6.2) 4.18 d (JHH = 6.2)
4.39 d (JHH = 6.4) 4.23 d (JHH = 6.4)
3.84 d (JHH = 3.7) 3.45 d (JHH = 3.7)
3.78 d (JHH = 3.7) 3.70 d (JHH = 3.7)
1.30 s
1.41 s
1.41 s
1.39 s
1.01 s
1.45 s
1.31 s
1.41 s
1.36 s
3.57 s 3.60 s
7 : 1
1.5 : 1
1 : 1
a
1.75 : 1
3.62 s 3.61 s
3.59 s 3.55 s
Complexes
Olefinic protons
–CH3
Isomeric ratio
[Pt(η2-fn)(N-SMe)]
[Pt(η2-ma)(N-SMe)]
2.97 d (JHH = 7.8) 2.64 d (JHH = 7.8)
2.98 d (JHH = 7.9) 2.70 d (JHH = 7.9)
3.71 d (JHH = 3.7) 3.50 d (JHH = 3.7)
3.81 d (JHH = 3.7) 3.49 d (JHH = 3.7)
2.58 s
2.41 s
2.38 s
2.39 s
1 : 1
1.2 : 1
Complexes
Olefinic protons
Isomeric ratio
[Pt(η2-fn)(N-SPh)]
[Pt(η2-ma)(N-SPh)]
2.96 d (JHH = 7.9) 2.73 d (JHH = 7.9)
2.97 d (JHH = 8.1) 2.77d (JHH = 8.1)
3.81 d (JHH = 3.7) 3.64 d (JHH = 3.7)
3.84 d (JHH = 3.7) 3.64 (JHH = 3.7)
1 : 1
1.2 : 1
a Obscured. b In CD2Cl2 at 208 K. c In CD2Cl2 at 213 K.
hindered olefins the optimised reaction time was 4 h at 45 ЊC
whereas the bulky olefin tmetc requires a reaction time of 24 h
at the same temperature; in this case decomposition depresses
the yield. The temperature and reaction time applied in the
synthesis of each complex are reported in the Experimental.
atoms and an asymmetric olefin (with substituents above and
below with respect to the main coordination plane) induces loss
of planarity and consequently chirality on the platinum atom.
2.3. Complexes with type Z olefins and pyridyl–methanimine
ligands. These complexes are present as a pair of enantiomers
since, also in this case, the platinum atom is chiral owing to the
asymmetry of the pyridyl–methanimine ligand and the loss of
planarity induced by the asymmetric olefin (when coordinated).
2. NMR characterisation of complexes
1H and 13C{1H}-NMR spectral data recorded at RT for the
complexes are reported in the Experimental, whereas selected
1H NMR data at low temperature are listed in Table 1.
Since the spectral features of the species are strongly influ-
enced by the nature of the coordinated olefin, it is convenient to
distinguish among complexes on the basis of the symmetry of
the olefin itself which is classified as (i) symmetric (tmetc), (ii)
type E (dmf, fn), and (iii) type Z (ma, nq). However a general
feature of the ligands undergoing coordination is a down-field
shift of the non-olefinic ligand signals observed either in the 1H
or 13C{1H} NMR spectra. In particular, the shifts of H6 (pyrid-
2.4. Fluxional behaviour of pyridyl–methanimine complexes.
No fluxionality is observed in the case of pyridyl–methanimine
complexes since the recorded 1H NMR spectra remain substan-
tially unchanged at any safely attainable temperature.
2.5. Fluxional behaviour of pyridyl–thioether complexes.
Scheme 2 represents the diastereoisomers distribution when the
pyridyl–thioether species are used as ligands in Pt() olefin
systems.
The pyridyl–thioether species only undergo sulfur absolute
configuration inversion at temperatures comparatively higher
than those observed in analogous palladium systems. Appar-
ently, none of the other possible fluxional mechanisms
described in previous studies3b,4 is operative when palladium is
replaced by the less reactive platinum.
ine ring) in both classes of ligands, the CH᎐N iminic protons
᎐
in pyridyl–methanimine species and the endocyclic CH2–S
protons in the case of pyridyl–thioether moiety are significant.
H6, CH2S and iminic protons also display the characteristic
195Pt satellites. At variance, olefinic protons and carbons
upon coordination display a marked high-field shift (3–3.5 and
100–120 ppm respectively) in all the studied substrates. Olefinic
protons give rise to an AB system in the case of pyridyl–
methanimine species whereas an AX system is detected with
pyridyl–thioether complexes. 195Pt satellites are observed in
both cases.
The spectral features, in the case of inversion at sulfur, are
readily explained on the basis of molecular and olefin
symmetry.
2.6. Complexes with symmetric olefins and pyridyl–thioether
1
ligands. The H NMR spectrum in CD2Cl2 of the complex
[Pt(η2-tmetc)(N–S But)] at 213 K, among other less significant
signals, is characterised by the presence of four singlets between
3.50 and 3.65 ppm ascribable to the four different COOCH3
olefin protons. Meanwhile the endocyclic CH2-S protons give
rise to an AB system between 4.2 and 4.5 ppm, since the
presence of the “frozen” sulfur atom (chiral centre) induces
diastereotopicity on the thioether protons. At 296 K inversion
at sulfur becomes operative, the AB quartet reduces to a singlet
at 4.35 ppm (with the platinum satellites becoming evident) and
the four singlets turn into two singlets centred at 3.65 ppm.
2.1. Complexes with symmetric olefins and pyridyl–methan-
imine ligands. These complexes arise from coordination of a
symmetric olefin and of an asymmetric but planar ancillary
ligand (Cs symmetry). No chiral centres are therefore detectable
in these cases and the substrates are present as unique species.
2.2. Complexes with type E olefins and pyridyl–methanimine
ligands. These substrates are present in solution as a pair of
enantiomers; no symmetry planes are in fact detectable in this
case because the coordination of two non equivalent nitrogen
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Fig. 1 Olefinic protons in the 1H NMR spectrum of the complex
[Pt(η2-fn)(N–SBut)] in CDCl3 at 223 (a) and 296 K (b).
low temperature spectrum, while inversion at sulfur simplifies
the spectrum by increasing the complex symmetry since such
rearrangement corresponds to an effective interchange between
diastereoisomers.
As can be seen, diastereoisomers, when present, are often in
different concentrations. This peculiarity probably arises from
the mutual steric hindrance generated between bulky substit-
uent groups at the olefin and at the sulfur lying on the same
side of the main coordination plane.
Scheme 2
Inversion at sulfur, which was demonstrated to be independent
of the sample concentration, increases the symmetry of the
system under study and does not allow anymore the detection
of NMR signals due to COOCH3 protons at the same or at the
opposite side of the sulfur substituent. Such inversion process is
clearly intramolecular in nature and of widespread occurrence
in Pd() complexes.3 No hints of further reduction to one sing-
let of the couple of signals at 3.65 is detected at any attainable
temperature; apparently, no olefin rotation or pseudo-rotation
mechanisms are observable under our experimental conditions.
3. Determination of olefin exchange rates
The rates of olefin exchange [reaction (1)] were determined by
means of a conventional UV/vis spectrophotometer equipped,
when necessary, with a rapid mixing device. The spectral
changes of the reaction mixture, obtained by mixing appropri-
ate micro-aliquots of entering olefin with a pre-thermostatted
solution of the complex under study, were monitored at con-
stant temperature (25 ЊC) in the range 330–450 nm. At variance
with the analogous reactions of palladium pyridyl–thioether
and pyridyl–methanimine olefin species, no equilibrium
reactions could be observed when palladium is replaced with
the less reactive platinum. Moreover, the reaction rates con-
siderably decrease so that a wider number of exchanging
complexes and olefins could be studied. The results of such an
investigation are summarised in Table 2.
In order to ensure a suitable change in absorbance only
naphthoquinone and dimethylfumarate were used as leaving
olefins. In particular, naphthoquinone proved the more versatile
species thanks to its chromophoric properties but also because
the rates of displacement of this olefin are more accessible. The
reactivity of its complexes is in fact somewhat lower than that
of those bearing dimethylfumarate; moreover, in some cases
dmf complexes prevent the determination of the rate constants
in the case of the slower reactions involving tmetc since they
undergo extensive decomposition or do not show detectable
changes in absorbance.
2.7. Complexes with type E olefins and pyridyl–thioether lig-
ands. According to the isomer distribution reported in Scheme
2, the pyridyl–thioether platinum complexes bearing these
olefins (fn, dmf ) are present in solution at low temperature as a
1
couple of Si and Re diastereoisomers. The H NMR spectrum
in CDCl3 at 223 K of the complex [Pt(η2-fn)(N–S But)] is read-
ily interpretable on the basis of this situation. Fig. 1a shows
selected regions of the spectrum in which the olefinic protons
are detected as two pairs of AX doublets (2.5–3.0 ppm) ascrib-
able to the two different diastereoisomers present in solution at
different concentrations. The same difference in population is
confirmed in the region of t-butyl protons, C(CH3)3, at 1.4 ppm.
The two singlets are again clearly attributable to the two iso-
mers Si and Re. Increasing the temperature to 296 K promotes
inversion at sulfur and the concomitant spectral simplification
(Fig. 1b). Again, further increments in the temperature do not
induce other fluxional rearrangements. As a matter of fact, in
this case olefin rotation would leave the absolute configuration
of the platinum atom unchanged and the spectrum of the sub-
strate would display only one signal in the region of olefinic
protons but the persistence of an AB system ascribable to CH2S
protons which would remain diastereotopic because of the
chirality of the metal centre.3b
In almost all the cases examined, the observed rate law is:
rate = k2[complex][ol2]
(2)
The k2 values (Table 2) for the slower reactions were deter-
mined by regression analysis of the relationship
2.8. Complexes with type Z olefins and pyridyl–thioether
ligands. Complexes bearing Z olefins (ma, nq) give rise two
diastereoisomers (endo, exo) together with their undetectable
enantiomers (Scheme 2). The presence of the two diastereo-
isomers in different concentrations is clearly detectable in the
kobs = k2[ol2]
(3)
under pseudo-first order conditions (excess of ol2), where kobs
was derived from fitting a monoexponential reaction profile.
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Table 2 Second order rate constants for the reaction [Pt(η2-ol1)(L–LЈ)] ϩ ol2
k2 for ol2/molϪ1 dm3 sϪ1
[Pt(η2-ol2)(L–LЈ)] ϩ ol1 in CHCl3 at 25 ЊC
Complex
ma
fn
nq
tmetc
d
e
[Pt(η2-nq)(N–SBut)]
224 6a
40 2c
b
b
b
[Pt(η2-dmf )(N–SBut)]
[Pt(η2-nq)(N-SPh)]
1709 15a
1023 5a
451 6a
(5.8 0.2) × 10Ϫ3 f
[Pt(η2-nq)(N-NЈC6H4OMe-4)]
[Pt(η2-nq)(N-NЈBut)]
(2.1 0.1) × 10Ϫ2 f
b
d
1383 23a
344 1a
[Pt(η2-dmf )(N-NЈC6H4OMe-4)]
0.27 0.01g
b
b
b
a Measured under second order conditions. b Too fast to measure. c Measured under pseudo-first and second order conditions. d Too slow to measure
(decomposition). e No detectable changes in absorbance among reactants and products. f Measured under pseudo-first order conditions. g See text.
For the faster reactions, k2 values were computed from direct
analysis of absorbance data vs. time according to the customary
second order treatment ([complex] ≈ [ol2]). The experimental
data provide no evidence for the contribution of an olefin-
independent, first order path to the overall reaction rates. In
fact, the plots of kobs vs. [ol2] show no statistically significant
intercept, whereas under second order conditions bona fide k1
contributions, if any, would be masked by the manifold sources
of experimental error related to uncertainties in the initial
reactant concentrations combined with numerical uncertainties
in the fitting procedure arising from correlations between the
fitted parameters.
As a matter of fact, a second order treatment would be able
to reveal a first order path only when the latter contributes
substantially to the overall rate, which is not our case. More-
over, our experience in this field strongly supports the view that
the contribution of a first order (either dissociative or solvento-
mediated) path is to be ruled out in the case of these well known
bidentate ligand complexes, it only being observed when terden-
tate species are involved.3c Consistently, for the reaction of
[Pt(η2-nq)(N–S But)] with fn, for which both data treatments
are feasible, the computed k2 values for the two approaches are
superimposable within experimental error.
This reaction was also studied at variable temperature and
the rate constants k2 determined in the range 15–40 ЊC were
analysed according to a re-parameterised Eyring–Polanyi
It can be shown that the reaction profile for a mixed first-
second order process
equation.5 The ensuing activation parameters were ∆H≠
=
7.0 0.3 Kcal molϪ1 and ∆S≠ = Ϫ28 1 cal molϪ1 KϪ1. In
particular the low activation enthalpy and the largely negative
entropic value strongly suggest an associative pathway for these
olefin exchange reactions. As a matter of fact, the resulting
18-electron activated complex was proposed to govern the
activation process occurring in analogous reactions involving
palladium complexes.3a,b
Pt(ol1) ϩ ol2
Pt(ol1)
Pt(ol2) ϩ ol1 k2
Pt ϩ ol1 k1
Pt ϩ ol2
Pt(ol2) fast
is given by
[Pt(ol1)]t = M0 [k1 ϩ k2(ol0 Ϫ M0)]/((k1 ϩ
As can be seen the k2 values in Table 2 span an interval
of almost six orders of magnitude, indicating the prominent
influence of steric requirements of the entering olefin. The
predominant features which emerge from analysis of the data
in Table 2 might be summarised by the following points:
(i) Within homologous series the t-butyl substituent at sulfur
or at iminic nitrogen imparts a lower reactivity to the corre-
sponding complexes than the phenyl or 4-OMeC6H4 group.
(ii) The reactivity of the pyridyl–thioether complexes is lower
than that of the corresponding pyridyl–methanimine species.
(iii) Dimethylfumarate is a better leaving group than
naphthoquinone.
k2ol0)exp{t[k1 ϩ k2(ol0 Ϫ M0)]} Ϫ k2M0)
where M0 = [Pt]0, ol0 = [ol2]0.
The k1 and k2 rate constants can in principle be determined
by fitting concentration (or any instrumental response that is
proportional to concentration, such as absorbance etc.) to time
data by non-linear regression, with k1 and k2 being the param-
eters to be optimised. In practice, however, the results rely heav-
ily on the knowledge of the precise values of M0 and ol0 (which
may not be known with the desired accuracy in diluted solu-
tions) and the iterative convergence process is affected by the
high correlation between the parameters fitted. This situation
gives rise to large standard errors of estimate for the parameters
and to the difficulty of discriminating between the mixed first–
second order model and a purely second order path (k1 ≈ 0)
when the first order one does not make a substantial contribu-
tion to the overall mechanistic picture. Such is the situation
prevailing in the present work in which even residual analysis (a
customary tool of the trade in evaluating the adequacy of a
given model in regression analysis) provided no significant sup-
port to the contention that the reactions studied herein proceed
by a path more complicated than a purely second order mech-
anism. This is consistent both with the lack of an olefin-
independent term in the rate law determined under pseudo-first
order conditions and with our previous experience on related
olefin exchange processes involving palladium complexes with
bidentate ligands. On the other hand, a change in mechanism
on going from first- to second order conditions, albeit possible,
is not supported by any observable data, and we prefer to stick
to the old prescription that there is no merit in choosing a
mechanism more complicated than that demanded by experi-
mental evidence.
(iv) The reactivity order of the entering olefin is : ma > fn ≈
nq ӷ tmetc.
The first and second point can be easily discussed on taking
into consideration the associative nature of the reaction which
is expected to be strongly influenced by the steric hindrance of
the reagents. The bulkiness of the t-butyl group with respect to
the phenyl fragment depresses the substitution reaction rate
to a larger extent than its electronic characteristics would be
expected to do. It was in fact shown that in substitution reac-
tions between olefins in pyridyl–thioether palladium systems,
the difference in reactivity due to electronic reasons between
groups with analogous steric hindrance (Pri and Ph) was always
smaller than one order of magnitude, whereas the rate con-
stants can increase by more than three orders of magnitude if
the bulky t-butyl substituent at sulfur is replaced by the methyl
group.3b Analogously, the difference in reactivity among com-
plexes bearing the same substituent at sulfur or at iminic nitro-
gen can be traced back to the peculiar behaviour of the sp3
sulfur which, at room temperature, rapidly inverts its absolute
configuration, pushing the substituent up or down with respect
to the main coordination plane, thereby inducing some sort of
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permanent steric retardation. Again, no particular differences
in the electronic properties among pyridyl–thioether and
pyridyl–methanimine ligands were found in equilibrium studies
in which the latter were replaced by the former and vice versa.3b
Apparently, the π-antibonding orbitals of the sp2 iminic nitro-
gen behave similarly to the free d orbitals of the sp3 sulfur atom
since they are comparable in determining the extent of π-bond
back-donation. As for point three, according to the data
reported in Table 2 the dmf complex studied seems to be more
labile than the analogous nq, at variance with previous results
determined in palladium systems where dmf derivatives proved
less reactive than those bearing nq, essentially for entropic
reasons.3a However, accurate analysis of kinetic data suggests a
different interpretation for the reaction involving the complex
[Pt(η2-dmf )(N-NЈC6H4OMe-4)] with tmetc. The reaction pro-
file could be described as two consecutive steps leading to the
final species [Pt(η2-tmetc)(N-NЈC6H4OMe-4)], as can be shown
by the superimposability of the spectrum of a solution of an
authentic sample of [Pt(η2-tmetc)(N-NЈC6H4OMe-4)] with that
of the final reaction mixture at the same concentration. Since
we are dealing with two consecutive reactions, some sort of
stable intermediate species will accumulate before formation of
the products. Owing to the low activation enthalpy required by
these reactions we suggest the formation of an intermediate
bearing both the entering and the leaving olefin which can
either give the final species or revert to the initial one. This
situation is described by eqn. (4).
palladium systems, one may argue that direct comparison
would not be warranted. However, it may be easily shown that
the complexes [M(η2-nq)(N-NЈC6H4OMe-4)] and [M(η2-nq)-
(N-SPh)] display a similar reactivity trend when they react with
tmetc independently of the metal (M = Pt, Pd), the ratios
between rate constants being 3.6 and 2 when M = Pt and Pd,
respectively. Apart some sort of levelling effect, the comparison
seems feasible. Platinum() complexes display a reactivity to
substitution which is three orders of magnitude less than that
of the corresponding palladium systems, thus confirming that
also in the case of low oxidation states the difference between
platinum and palladium is maintained.
4. X-Ray diffraction study
The molecular structures of complexes [Pt(η2-ol)(N-NЈBut)]
(ol = fn, ma, dmf ) have been confirmed by X-ray crystallo-
graphy. The ORTEP diagrams are shown in Fig. 2, 3 and 4
while the selected bond distances and angles are listed in
Table 3.
The customary approach to this problem6 allows the deter-
mination of only k2 by the regression analysis of (λ1 ϩ λ2)
vs. [ol2] where λ1 and λ2 are the observed combinations of
constants calculated by treating the above scheme by a bi-
exponential model. The sum of k1 ϩ kϪ1 (which is given as the
intercept of the linear regression analysis) does not allow separ-
ation of the two terms; however, the resulting value (k1 ϩ kϪ1
=
(1.53 0.01) × 10Ϫ2 sϪ1) suggests that since the overall dissoci-
ative path is slow the predominant part of the sum can be
traced back to the dissociation of dmf (kϪ1) which is by far the
less coordinating olefin.
Point four takes into account the different reactivity order
among entering olefins which, to the best of our knowledge,
was never determined before. At variance, the thermodynamic
stability induced by these electron poor alkenes was measured
in the case of Pd() substrates and was ascribed to the electron-
withdrawing capability of olefin substituents since the π-back-
donation from the metal to the alkene is assumed to be the most
important contribution to the overall bond strength.2a From the
kinetic point of view, the electron-withdrawing ability of alkene
substituents always plays an important role, but it is the steric
hindrance of the entering olefin that dictates its reactivity,
thereby overwhelming any other effect. As a matter of fact,
ma proved the most efficient olefin since its electronic features
are coupled with its modest Z-symmetry modulated steric
demand, which would drive the attack through the unsubsti-
tuted side of the olefin. Analogously, nq reacts almost as effi-
ciently as fn, although the latter results much more favoured
from the electronic point of view, as is shown by the high equi-
librium constants for olefin displacement by fn observed in
related systems.3 The case of tmetc is paradigmatic of the
importance of steric requirements. Although no direct evidence
is available, from a cross extrapolation of the existing rate con-
stants ma results about six orders of magnitude more efficient
than tmetc. The ratio between these olefin displacement equi-
librium constants for Pd() systems was shown to be confined
well within four orders of magnitude,3a,b indicating that the
electronic properties represent a minor contribution to the
overall rate constants. Since our conclusions take often into
account experimental results that we obtained with analogous
Fig. 2 ORTEP representation of [Pt(η2-fn)(N-NЈBut)] complex.
Fig. 3 ORTEP representation of [Pt(η2-ma)(N-NЈBut)] complex.
(4)
3700
J. Chem. Soc., Dalton Trans., 2002, 3696–3704

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Table 3 Selected bond lengths (Å) for [Pt(η2-fn)(N-NЈBut)], [Pt(η2-ma)(N-NЈBut)] and [Pt(η2-dmf )(N-NЈBut)]
[Pt(η2-fn)(N-NЈBut)]
[Pt(η2-ma)(N-NЈBut)]
[Pt(η2-dmf )(N-NЈBut)]
Pt–C
Pt(1)–C(12)
Pt(1)–C(13)
2.007(15)
2.014(14)
Pt(1)–C(12)
Pt(1)–C(13)
2.018(7)
2.061(6)
Pt(1)–C(14)
Pt(1)–C(13)
Pt(2)–C(30)
Pt(2)–C(29)
C(13)–C(14)
C(29)–C(30)
Pt(1)–N(1) 2.094(7)
Pt(1)–N(2)
2.044(9)
2.052(9)
2.043(7)
2.049(8)
1.465(12)
1.436(12)
C᎐C
᎐
C(12)–C(13)
1.43(2)
C(12)–C(13)
1.449(11)
Pt–N
Pt(1)–N(1)
Pt(1)–N(2)
2.105(15)
2.134(12)
Pt(1)–N(1)
Pt(1)–N(2)
2.082 (6)
2.101(5)
2.107(7)
2.081(7)
2.125(6)
Pt(2)–N(3)
Pt(2)–N(4)
The average Pt–C length in the case of the two complexes
bearing the two class E olefins (fn, dmf ) increases significantly
on going from [Pt(η2-fn)(N-NЈBut)] to [Pt(η2-dmf )(N-NЈBut)],
(2.011 vs. 2.047 Å, respectively) thereby supporting the
increased kinetic lability of the latter with respect to all the
Pt() complexes studied in this work.
Experimental
Preparation of ligands
The pyridyl–thioether (N-SR)9 and pyridyl–methanimine
(N-NЈRЈ)10 ligands were prepared according to published pro-
cedures. All other chemicals were commercial grade and were
purified or dried, where required, by standard methods.11
Preparation of complexes
All the complexes described herein were obtained by analogous
synthetic procedures. Therefore we report the detailed prepar-
ation of only one species. We however indicate analytical and
spectroscopic data together with the temperature and the time
of reaction for each substrate obtained. In particular the latter
are of paramount importance in obtaining pure samples since
the slower reactions lead often to extensive decomposition with
concomitant formation of platinum metal and the optimised
yield depends on a carefully balanced choice between time and
reaction temperature.
Fig. 4 ORTEP representation of [Pt(η2-dmf )(N-NЈBut)] complex.
Only one of the two independent molecules is shown.
In all complexes the platinum() has a planar geometry. Two
sites of coordination are occupied by the bidentate ligand
N-NЈBut while the other positions are occupied by the double
bond of the olefin. In the CSD (October 2001) only one crystal
structure with Pt() coordinated to nitrogen and olefin is
reported.7 In all complexes described in this article the Pt()–N
distances are influenced by the nature of the nitrogen atom. In
fact, the pyridine nitrogen is closer to the Pt than the imine one
(see Table 3). The Pt()–C distances show differences among the
complexes, however they are slightly shorter than the complexes
with P-donors. Complexes with Pt() olefin and S-donors are
not present in the CSD. Pt() in [Pt(η2-fn)(N-NЈBut)] has the
shortest distances (2.007(15) and 2.014(14) Å), in [Pt(η2-ma)-
(N-NЈBut)] the Pt–C interactions exhibit a higher degree of
asymmetry than in [Pt(η2-fn)(N-NЈBut)] and [Pt(η2-dmf )-
(N-NЈBut)], Pt(1)–C(12) is 2.018(7) Å, comparable with the
interaction in [Pt(η2-fn)(N-NЈBut)], while Pt(1)–C(13) is
2.061(6) Å – the longest interaction observed in the complexes
reported. The average value 2.040 is comparable with those
observed in [Pt(η2-dmf )(N-NЈBut)]. The crystal structure of
[Pt(η2-dmf )(N-NЈBut)] shows two independent molecules. The
distances Pt–C are comparable in the two independent mole-
cules and are in the range of 2.043–2.052Å. In the complex
[Pt(η2-dmf )(dmphen)] reported by Albano et al.8 the Pt–C
distances are quite asymmetric (1.88(3) and 2.09(2)) but the
average value (1.99) is significantly shorter than that found in
[Pt(ꢀ2-ma)(N-SBut)]. To a solution of 0.206 g (0.31 mmol) of
Pt(DBA)2 12 in anhydrous THF, 0.0343 g (0.34 mmol) of maleic
anhydride (ma) and 0.3387 g (0.34 mmol) of N–SBut ligand
were added under inert atmosphere (N2). The resulting reaction
mixture was stirred for 24 h at 45 ЊC under nitrogen and the
initial deep violet colour turned to yellowish. The solution was
dried under reduced pressure, re-dissolved in CH2Cl2, treated
with activated charcoal and filtered on celite filter. Reduction
under small volume and addition of diethyl ether yielded
0.0775 g (0.16 mmol, 53% yield) of the title complex as cream-
coloured microcrystals (treact 24 h at 45 ЊC).
Found: C, 35.52; H, 3.74; N, 3.07; S, 6.52. C14H17NO3PtS
requires: C, 35.44; H, 3.61; N, 2.95; S, 6.76.
IR (KBr pellets, cmϪ1): νC᎐N 1603 (m); νC᎐O 1730, 1793.
᎐
1H NMR (in CDCl3, RT), δ (ppm): ᎐CH3 1.42 (9H, s);
HC᎐CH 3.55 (H, d, J = 3.7 Hz, J
= 82.2 Hz); HC᎐CH 3.87
᎐
᎐
H–Pt
(H, d, J = 3.7 Hz, JH–Pt = 82.2 Hz); CH2S 4.32 (2H, m); H5 7.27
(H, m); H3 7.64 (H, d, J = 7.7 Hz); H4 7.94 (H, td, J = 7.7 Hz,
J = 1.5 Hz); H6 9.17 (H, d, J = 5.5 Hz, JH–Pt = 30 Hz).
[Pt(ꢀ2-fn)(N-SBut)]. Cream-coloured microcrystals (69%
yield; treact 4.5 h at 45 ЊC or 17 h at RT).
[Pt(η2-dmf )(N-NЈBut)]. Consequently the average C᎐C bond
Found: C, 37.12; H, 3.86; N, 9.29; S, 7.25. C14H17N3PtS
requires: C, 37.00; H, 3.77; N, 9.25; S, 7.06.
᎐
length in the latter is higher than that found in [Pt (η2-dmf )-
(dmphen)] (1.450 vs. 1.420 Å, respectively). Moreover the C᎐C
IR (KBr pellets, cmϪ1): νC᎐N 1604 (m); νC᎐N 2202 (s).
᎐
᎐
᎐
bond distance in the complex [Pt(η2-ma)(N-NЈBut)] appears to
be significantly longer than those found in all the analogous
maleic anhydride platinum and palladium compounds.1p,2a,3b
1H NMR (in CDCl , RT), δ (ppm): CH 1.48 (9H, s); HC᎐
᎐
3 3
CH 2.62 (H, d, J = 7.7 Hz, JH–Pt = 85.9 Hz); HC᎐CH 3.00 (H, d,
᎐
J = 7.7 Hz, JH–Pt = 88.6 Hz); CH2S 4.36 (2H, m); H5 7.30 (H, dd,
J. Chem. Soc., Dalton Trans., 2002, 3696–3704
3701

View Article Online
J = 7.7 Hz, J = 4.75 Hz); H3 7.66 (H, d, J = 8.4); H4 7.97 (H, td,
J = 7.7 Hz, J = 1.8 Hz); H6 9.22 (H, d, J = 4.75 Hz, JH–Pt = 30.3
Hz).
[Pt(ꢀ2-fn)(N-SPh)]. Cream-coloured microcrystals (47%
yield; treact 4 h at 45 ЊC or 17 h at RT).
Found: C, 40.58; H, 2.67; N, 8.97; S, 6.89. C16H13N3PtS
requires: C, 40.50; H, 2.76; N, 8.86; S, 6.76.
13C NMR (in CDCl , RT), δ (ppm): HC᎐CH 4.04 (J
=
᎐
3
C–Pt
420.5 Hz); HC᎐CH 9.63 (J
= 410.3 Hz); C–(CH3)3 29.9
IR (KBr pellets, cmϪ1): νC᎐N 1605 (m); νC᎐N 2201 (s).
᎐
C–Pt
᎐
᎐
(JC–Pt = 21.5 Hz); CH2S 41.2 (JC–Pt = 24.9 Hz); C–(CH3)3 50.9;
1H NMR (in CDCl , RT), δ (ppm): HC᎐CH 2.80 (H, d,
᎐
3
5
C᎐N 122.0; C 123.5 (JC–Pt = 30.0 Hz); C3 125.1 (JC–Pt = 34.0 Hz);
J = 7.8 Hz, JH–Pt = 90 Hz); HC᎐CH 3.06 (H, d, J = 7.8 Hz,
᎐
᎐
᎐
C4 138.8; C6 154.97 (JC–Pt = 45.2 Hz); C2 160.9.
JH–Pt = 90 Hz); CH2S 4.59 (2H, bs); H5, Hb, Hd 7.30–7.41 (5H,
m); H3 7.57 (H, d, J = 6 Hz); Hc 7.72 (2H, bs); H4 7.95 (H, td,
J = 7.7, J = 1.6); H6 7.28 (H, d, J = 6 Hz, JH–Pt = 30 Hz).
[Pt(ꢀ2-dmf )(N-SBut)]. Cream-coloured microcrystals (53%
yield; treact 4 h at 45 ЊC or 17 h at RT).
[Pt(ꢀ2-nq)(N-SPh)]. Brown microcrystals (53% yield; treact 4 h
at 45 ЊC).
Found: C, 36.85; H, 4.58; N, 2.87; S, 6.28. C16H23NO4PtS
requires: C, 36.92; H, 4.45; N, 2.69; S, 6.16.
IR (KBr pellets, cmϪ1): νC᎐O 1686 (s); νC᎐N 1603 (m).
Found: C, 47.77; H, 3.21; N, 2.41; S, 5.89. C22H17NO2PtS
requires: C, 47.65; H, 3.09; N, 2.53; S, 5.78.
IR (KBr pellets, cmϪ1): νC᎐N 1589 (m); νC᎐O 1639 (s).
᎐
1H NMR (in CDCl3, RT)᎐, δ (ppm): CH3 1.41 (9H, s); OCH3
3.60 (3H, s); OCH 3.65 (3H, s); HC᎐CH 3.56 (H, d, J = 8.4 Hz,
᎐
3
᎐
᎐
1H NMR (in CDCl , RT), δ (ppm): HC᎐CH 4.51 (H, d,
JH–Pt = 89.5 Hz); HC᎐CH 3.85 (H, d, J = 8.4 Hz, J
=
᎐
H–Pt
᎐
3
88.4 Hz); CH2S 4.27 (2H, m); H5 7.22 (H, m); H3 7.56 (H, d,
J = 8.4); H4 7.86 (H, td, J = 7.7 Hz, J = 1.5 Hz); H6 9.23 (H, d,
J = 5.5 Hz, JH–Pt = 30.3 Hz).
J = 6.0 Hz, JH–Pt = 72 Hz); CH S 4.47 (H, bs); HC᎐CH 4.63 (H,
᎐
2
d, J = 6.0 Hz, JH–Pt = 68 Hz); H5, Hb, Hc 7.08–7.55 (5H, m); H4
7.86 (H, t, J = 7.7 Hz); H6 9.63 (H, d, J = 6.3 Hz, JH–Pt = 31.2
Hz)
13C NMR (in CDCl , RT), δ (ppm): HC᎐CH 28.14 (J
=
᎐
3
C–Pt
375.3 Hz); HC᎐CH 35.04 (J
= 344.7 Hz); C–(CH3)3 29.56
᎐
C–Pt
[Pt(ꢀ2-tmetc)(N-SPh)]. Brown microcrystals (31% yield; treact
23 h at RT).
(JC–Pt = 21.5 Hz); CH2S 41.10 (JC–Pt = 26.0 Hz); C-(CH3)3 49.70;
OCH3 50.96; OCH3 50.74; C5 123.1 (JC–Pt = 26.0 Hz); C3 124.6
(JC–Pt = 35.0 Hz); C4 137.90; C6 154.10 (JC–Pt = 45.9 Hz); C2
Found: C, 40.37; H, 3.62; N, 2.24; S, 4.91. C22H23NO8PtS
requires: C, 40.25; H, 3.53; N, 2.13; S, 4.88.
160.77; C᎐O 174.65: C᎐O 176.67.
᎐
᎐
IR (KBr pellets, cmϪ1): νC᎐N 1605 (m); νC᎐O 1728 (s), 1703 (s),
[Pt(ꢀ2-nq)(N-SBut)]. Light-brown microcrystals (48% yield;
treact 4 h at 45 ЊC or 17 h at RT).
᎐
᎐
1693 (s).
1H NMR (in CDCl3, RT), δ (ppm): COOCH3 3.75 (6H, s);
COOCH3 3.76 (6H,s); CH2 S 4.58 (2H, m); H5, H3, Hb, Hc, He,
Hf 7.35–7.75 (7H, m); H4 7.86 (2H, t, J = 7.7Hz, J = 1.6 Hz);
He 7.97 (2H, bs); Hf 8.11(2H, m); H6 8.91 (H, d, J = 4 Hz,
JH–Pt = 31.5 Hz)
Found: C, 44.77; H, 3.84; N, 2.81; S, 6.23. C20H21NO2PtS
requires: C, 44.94; H, 3.96; N, 2.62; S, 6.00.
IR (KBr pellets, cmϪ1): νC᎐O 1637 (s), 1625 (s); νC᎐N 1589(m).
᎐
᎐
1H NMR (in CDCl3, RT), δ (ppm): CCH3 1.25 (9H, s); CH2S
4.18 (2H, m); HC᎐CH 4.38 (H, d, J = 6.2 Hz, JH–Pt = 70.9 Hz);
᎐
HC᎐CH 4.57 (H, d, J = 6.2 Hz, JH–Pt = 63.6 Hz); H5 7.32 (H, dd,
[Pt(ꢀ2-ma)(N-NЈC6H4OMe-4)]. Ochre microcrystals (53%
yield; treact 5 h at 45 ЊC).
᎐
J = 7.7 Hz, J = 5.5 Hz); Hf 7.48 (2H, m); H3 7.55 (H, d, J = 6.2);
H4 7.86 (H, td, J = 6.2 Hz, J = 1.5 Hz); He 8.05 (2H, m); H6 8.86
(H, d, J = 5.5 Hz, JH–Pt = 30.3 Hz).
Found: C, 40.52; H, 2.88; N, 5.46. C17H14N2O4Pt requires: C,
40.40; H, 2.79; N, 5.54.
IR (KBr pellets, cmϪ1): νC᎐O 1686 (s); νC᎐N 1597 (m).
[Pt(ꢀ2-tmetc)(N-SBut)]. Brown microcrystals (31% yield; treact
19 h at 45 ЊC or 48 h at RT).
᎐
᎐
1H NMR (in CDCl , RT), δ (ppm): HC᎐CH 3.66 (H, d,
᎐
3
J = 3.7 Hz, JH–Pt = 83.4 Hz); HC᎐CH 3.71 (H, d, J = 3.7 Hz,
᎐
Found: C, 37.68; H, 4.32; N, 2.28; S, 5.21. C20H27NO8PtS
requires: C, 37.74; H, 4.28; N, 2.20; S, 5.04.
JH–Pt =83.4Hz);OCH3 3.91(3H,s);H1 7.07(2H,d,J=8.9);H3,Hi
7.93–7.88 (H, m); H5 7.65 (H, d, J = 7.7 Hz, J = 5.5 Hz); 4H 8.17
IR (KBr pellets, cmϪ1): νC᎐N 1605 (m); νC᎐O 1727 (s), 1703 (s).
(H, td, J = 6.21, J = 1.3); 6H 9.25 (H, d, J = 5.5, JH–Pt = 32); HC᎐N
᎐
᎐
1H NMR (in CD2Cl2, RT), δ (ppm): CCH3 1.43 (9H, s);
OCH3 3.62 (3H,S); OCH3 3.65 (3H,S); CH2S 4.35 (H, bs,
J = 13.1 Hz); H5 7.29 (H, dd, J = 7.7 Hz, J = 5.2 Hz); H3 7.61
(H, d, J = 7.7 Hz); H4 7.93 (H, dd, J = 7.7 Hz, J = 1.5 Hz); H6
9.42 (H, d, J = 5.2 Hz, JH–Pt = 30.1 Hz).
᎐
9.27 (H, s, JH–Pt = 56.9).
[Pt(ꢀ2-fn)(N-NЈC6H4OMe-4)]. Dark-red microcrystals (47%
yield; treact 4 h at 45 ЊC).
Found: C, 42.14; H, 2.89; N, 11.75. C17H14N4OPt requires: C,
42.06; H, 2.91; N, 11.54.
[Pt(ꢀ2-fn)(N-SMe)]. Cream-coloured microcrystals (68%
yield; treact 4.5 h at 45 ЊC or 17 h at RT).
IR (KBr pellets, cmϪ1): νC᎐N 1597 (m); νC᎐N 2197 (s).
᎐
᎐
1H NMR (in CDCl , RT), δ (ppm): HC᎐CH 2.75 (H, d,
᎐
3
Found: C, 32.15; H, 2.80; N, 10.35; S, 7.71. C11H11N3PtS
requires: C, 32.04; H, 2.69; N, 10.19; S, 7.78.
J = 7.7 Hz, JH–Pt = 90 Hz); HC᎐CH 2.87 (H, d, J = 7.7 Hz,
᎐
JH–Pt = 92 Hz); PhOCH3 3.9 (3H, s); H1 7.09 (2H, d, J = 5.1); H5
7.68 (H, ddd, J = 6.7, J = 4.7, J = 1.3); H3 7.94 (H, d, J = 7.94);
Hi 7.90 (2H, d, J = 9.1); H4 8.17 (H, td, J = 6.21, J = 1.3); H6
IR (KBr pellets, cmϪ1): νC᎐N 1605 (m); νC᎐N 2204 (s), 2195 (s).
᎐
᎐
1H NMR (in CDCl , RT), δ (ppm): CH 1.23 (3H, s); HC᎐
᎐
3
3
CH 3.50 (H, d, J = 7.8 Hz, JH–Pt = 82 Hz); HC᎐CH 3.94 (H, d,
᎐
J = 7.8 Hz, JH–Pt = 84 Hz); CH2S 4.25 (2H, bs); H5 7.36 (H, bt);
H3 7.67 (H, d, J = 7.7 Hz); H4 8(H, td, J = 7.7 Hz, J = 1.5 Hz);
H6 8.27 (H, d, J = 6 Hz, JH–Pt = 30 Hz).
9.28 (H, d, J = 5.7, JH–Pt = 36); HC᎐N 9.27 (H, s, JH–Pt = 28).
᎐
[Pt(ꢀ2-dmf )(N-NЈC6H4OMe-4)]. Brick-red microcrystals
(67% yield; treact 2.5 h at RT).
[Pt(ꢀ2-ma)(N-SPh)]. Cream-coloured microcrystals (63%
yield; treact 4 h at 45 ЊC.).
Found: C, 41.50; H, 3.75; N, 5.26. C19H20N2O5Pt requires: C,
41.38; H, 3.66; N, 5.08.
Found: C, 38.93; H, 2.73; N, 2.95; S, 6.52. C16H13NO3PtS
requires: C, 38.87; H, 2.65; N, 2.83; S, 6.49.
IR (KBr pellets, cmϪ1): νC᎐N 1597 (m); νC᎐O 1686 (s).
᎐
᎐
1H NMR (in CDCl , RT), δ (ppm): HC᎐CH 3.74 (H, d,
᎐
3
IR (KBr pellets, cmϪ1): νC᎐N 1603 (m); νC᎐O 1796 (s), 1730 (s).
J = 8.8 Hz, JH–Pt = 73.1 Hz); HC᎐CH 3.84 (H, d, J = 8.7 Hz,
᎐
᎐
᎐
1H NMR (in CDCl , RT), δ (ppm): HC᎐CH 3.60 (H, d,
JH–Pt = 9.28 Hz); PhOCH3 3.59 (3H, s); OCH3 3.67 (3H, s); OCH3
3.88 (3 H, s); H1 6.90 (2H, d, J = 8.77); H5 7.43 (H, bt); Hi
6.90 (2H, d, J = 8.77); H3 7.94 (H, d, J = 7.68); H4 8.06 (H,
᎐
3
J = 3.7 Hz, JH–Pt = 82 Hz); HC᎐CH 3.94 (H, d, J = 3.7 Hz,
᎐
JH–Pt = 84 Hz); CH2S 4.56 (2H, bs); H5, Hb, Hd 7.31–7.38 (5H,
m); H3 7.57 (H, d, J = 7.7 Hz); Hc 7.64 (H, m); H4 7.93 (H, td,
J = 7.7 Hz, J = 1.6 Hz); H6 9.20 (H, d, J = 4 Hz, JH–Pt = 30 Hz)
td, J = 6.21, J = 1.5); H6 9.06 (H, bs); HC᎐N 9.31 (H, s,
᎐
JH–Pt = 53.7).
3702
J. Chem. Soc., Dalton Trans., 2002, 3696–3704

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13C NMR (in CDCl , RT), δ (ppm): HC᎐CH 24.91 (J
=
C–Pt
[Pt(ꢀ2-dmf )(N-NЈBut)]. Ochre microcrystals (52% yield; treact
4.5 h at RT).
᎐
3
415.0 Hz); HC᎐CH 25.99 (J
= 387.0 Hz); OCH3 50.51;
᎐
C–Pt
OCH3 50.81; PhOCH3 55.28; C1 113.61; Ci 126.03 (JC–Pt = 17.8
Hz); C5 127.13 (JC–Pt = 5.6 Hz); C3 127.73 (JC–Pt = 36.8 Hz); C4
137.19; Cm 140.11; C6 151.54 (JC–Pt = 76.0 Hz); Ch 156.46; C2
Found: C, 38.25; H, 4.52; N, 5.51. C16H22N2O4Pt requires: C,
38.32; H, 4.42; N, 5.59.
IR (KBr pellets, cmϪ1): νC᎐N 1587 (m); νC᎐O 1680 (s).
᎐
᎐
160.93; C᎐N 156.84; C2 160.93; C᎐O 177.0 (J
= 62.5); C᎐O
1H NMR (in CDCl , RT), δ (ppm): CH = 1.63 (9H, S); HC᎐
᎐
3 3
᎐
᎐
᎐
C–Pt
176.5 (JC–Pt = 60.5).
CH 3.68 (H, d, J = 8.8 Hz, JH–Pt = 91.4 Hz); HC᎐CH 3.85 (H, d,
᎐
J = 9.1 Hz, JH–Pt = 91.4 Hz); H5 7.55 (H, dd, J = 7.7, J = 1.5); H3
7.69 (H, d, J = 7.7); H4 8.06 (H, td, J = 7.6, J = 1.5); HC᎐N 9.00
[Pt(ꢀ2-nq)(N-NЈC6H4OMe-4)]. Brown microcrystals (81%
yield; treact 1 h at 40 ЊC).
᎐
(H, s, JH–Pt = 57.0); H6 9.31 (H, d, J = 4.7, JH–Pt = 30.7).
13C NMR (in CDCl , RT), δ (ppm): HC᎐CH 24.96 (J
=
C–Pt
᎐
3
Found: C, 48.66; H, 3.09; N, 5.09. C23H18N2O3Pt requires: C,
48.85; H, 3.21; N, 4.95.
418.2 Hz); HC᎐CH 25.20 (J
= 373.0 Hz); C–(CH3)3 29.54;
᎐
C–Pt
OCH3 50.38; OCH3 50.76; C-(CH3)3 63.03; C5 126.14; C3
128.54 (JC–Pt = 35.0 Hz); C4 137.57; C6 152.24 (JC–Pt = 74.6 Hz);
C2 156.57; C᎐N 158.68; C᎐O 176.34; C᎐O 177.01.
IR (KBr pellets, cmϪ1): νC᎐N 1587 (m); νC᎐O 1632 (s).
᎐
᎐
1H NMR (in CDCl , RT), δ (ppm): HC᎐CH 2.75 (H, d,
᎐
3
᎐
᎐
᎐
J = 7.7 Hz, JH–Pt = 90 Hz); HC᎐CH 2.87 (H, d, J = 7.7 Hz,
᎐
JH–Pt = 92 Hz); PhOCH3 3.9 (3H, s); H1 7.09 (2H, d, J = 5.1);
H5 7.68 (H, ddd, J = 6.7, J = 4.7, J = 1.3); H3 7.94 (H, d,
[Pt(ꢀ2-nq)(N-NЈBut)]. Dark-red microcrystals (72% yield;
treact 3 h at RT).
J = 7.94); Hi 7.90 (2H, d, J = 9.1); H 8.17 (H, td, J = 6.21,
4
6
J = 1.3); H 9.28 (H, d, J = 5.7, JH–Pt = 36); HC᎐N 9.27 (H, s,
Found: C, 46.69; H, 3.81; N, 5.71. C20H20N2O2Pt requires: C,
46.60; H, 3.91; N, 5.43.
᎐
JH–Pt =28).
IR (KBr pellets, cmϪ1): νC᎐N 1585 (m), νC᎐O 1630 (s).
᎐
᎐
1H NMR (in CDCl , RT), δ (ppm): CH 1.53 (9H, s); HC᎐
[Pt(ꢀ2-tmetc)(N-NЈC6H4OMe-4)]. Ochre microcrystals (22%
yield; treact 22 h at RT).
3
3
᎐
CH 4.50 (H, d, J = 6.2 Hz, JH–Pt = 73.6 Hz); HC᎐CH 4.55 (H, d,
᎐
J = 6.2 Hz, JH–Pt = 73.1 Hz); Hf 7.45 (H, m); H5 7.61 (H, dd,
Found: C, 41.39; H, 3.75; N, 4.33. C23H24N2O9Pt requires: C,
41.38; H, 3.62; N, 4.20.
J = 6.7, J = 4.7, J = 1.3); H3 7.73 (H, d, J = 7.7); He, H4 8.02–
8.09 (3H, m); HC᎐N 8.83 (H, s, J
= 68.0); H6 9.05 (H, d,
H–Pt
IR (KBr pellets, cmϪ1): νC᎐N 1598 (m); νC᎐O 1696 (s).
᎐
1H NMR (in CDCl3, RT),᎐δ (ppm): OCH3 3.63 (6H, s); OCH3
3.75 (6 H, s); PhOCH3 3.85 (3H, s); H1 6.90 (2H, d, J = 10);
H5 7.50 (H, m); H3 7.89 (H, d, J = 8); H4–Hi 7.99–8.10
᎐
J = 6.0, JH–Pt = 30.4).
13C NMR (in CDCl3, RT), δ (ppm): C–(CH3)3 29.31;
HC᎐CH 41.54 (J
= 372.99 Hz); HC᎐CH 42.95 (JC–Pt = 308.6
᎐
᎐
C–Pt
Hz); C-(CH3)3 64.22; C5 126.25 (JC–Pt = 13.6 Hz); C3 128.68
(3H, m); HC᎐N 9.18 (H, s, JH–Pt = 56.3); 6H 9.06 (H, d, J = 5.5,
᎐
(JC–Pt = 35.0 Hz); Ce 124.9; Ce 125.3; Cf 130.86; Cf 130.95; C4
JH–Pt = 24.9).
138.09; C6 150.19 (JC–Pt = 63.3 Hz); C2 156.55; C᎐N 158.66; Cn
13C NMR (in CDCl , RT), δ (ppm): C᎐C 41.39; C᎐C 41.50;
᎐
᎐
᎐
3
186.94; Cn 177.01.
OCH3 52.04; OCH3 52.35; PhOCH3 55.59; Cl 114.03; Ci
126.58; C5 126.92; C3 128.47 (JC–Pt = 36.3 Hz); C4 138.35; C6
153.36 (JC–Pt = 67.8 Hz); Ch 156.34; C᎐N 158.14; C2 161.42;
᎐
UV/vis, IR and NMR measurements
C᎐O 171.24; C᎐O 174.63.
᎐
᎐
UV/vis spectra were recorded on a Perkin Elmer λ 40 spectro-
photometer at the designed temperature. The reactions were
studied by addition of known micro-aliquots of the entering
olefin (ol2) to a solution of the complex under study ([Pt]0 ≈
1 × 10Ϫ4 mol dmϪ3) in CHCl3 and recording spectral changes
in the wavelength region 330–450 nm or at a suitable fixed
wavelength.
[Pt(ꢀ2-ma)(N-NЈBut)]. Ochre microcrystals (61% yield; treact
3 h at RT).
Found: C, 36.77; H, 3.75; N, 6.23. C14H16N2O3Pt requires: C,
36.93; H, 3.54; N, 6.15.
IR (KBr pellets, cmϪ1): νC᎐N 1588 (m); νC᎐O 1795 (s); 1776 (s),
᎐
᎐
1720 (s).
1
The IR spectra and the H and 13C{1H}-NMR spectra were
1H NMR (in CDCl , RT), δ (ppm): HC᎐CH 3.67 (H, d,
᎐
3
recorded on a Nicolet Magna 750 spectrophotometer and on
J = 3.7 Hz, JH–Pt = 82.6 Hz); HC᎐CH 3.74 (H, d, J = 3.7 Hz,
᎐
a Bruker AC 200 spectrometer, respectively.
JH–Pt =82.6Hz);H5 (H,ddd,J=6.7,J=4.7,J=1.3);H3 7.83(H,d,
The temperature-dependent 1H-NMR spectra were analysed
using the SWAN program.13
J=6.0);H4 8.13(H, td, J=8, J=1.6);HC᎐N9.00(H, s, JH–Pt =62)
᎐
H6 9.25 (H, d, J = 4, JH–Pt = 28).
Mathematical and statistical data analysis were carried
out on a personal computer equipped with a locally adapted
version of Marquardt’s algorithm.14
13C NMR (in CDCl , RT), δ (ppm): HC᎐CH 23.68 (J
=
C–Pt
᎐
3
418.2 Hz); HC᎐CH 24.83 (J
= 384.3 Hz); C–(CH3)3 29.59
᎐
C–Pt
(JC–Pt = 9.9); C-(CH3)3 64.13; C5 126.95 (JC–Pt = 14.7 Hz); C3
129.43 (JC–Pt = 38.4 Hz); C4 138.86; C6 153.32 (JC–Pt = 79.1 Hz);
C2 156.56; C᎐N 160.35; C᎐O 174.86; C᎐O 174.75.
X-Ray structural analysis
᎐
᎐
᎐
All X-ray diffraction data collections were carried out on a
NONIUS CAD-4 diffractometer equipped with an Oxford
Cryostream liquid-N2 device. Crystal data and details of
measurements are reported in Table 4. Diffraction data were
corrected for absorption by azimuthal scanning of high-χ
reflections. The SHELX-9715 package was used for structure
solution and refinement based on F 2. ORTEP-316 was used for
the graphical representation of the results. Common to all
compounds: Mo Kα radiation, λ = 0.71069 Å, monochromator
graphite. All non-H atoms in [Pt(η2-ma)(N-NЈBut)] were
refined anisotropically. In all cases hydrogen atoms were placed
in calculated positions and thereafter allowed to ride on their
parent atoms.
[Pt(ꢀ2-fn)(N-NЈBut)]. Ochre microcrystals (57% yield; treact
3 h at RT).
Found: C, 38.51; H, 3.82; N, 12.99. C14H16N4Pt requires: C,
38.62; H, 3.70; N, 12.87.
IR (KBr pellets, cmϪ1): νC᎐N 1593 (m); νC᎐O 2203 (s).
᎐
᎐
1H NMR (in CDCl , RT), δ (ppm): CH = 1.69 (9H, S); HC᎐
᎐
3
3
CH 2.78 (H, d, J = 8.0 Hz, JH–Pt = 90.6 Hz); HC᎐CH 2.83
᎐
(H, d, J = 8.0 Hz, JH–Pt = 90.6 Hz); H5 7.64(H, m); H3 7.94 (H, d,
J = 7.7); H4 (H, td, J = 7.6, J = 1.5); HC᎐N 9.01 (H, s,
᎐
JH–Pt = 60) H6 9.29 (H, d, J = 4.7, JH–Pt = 30).
13C NMR (in CDCl , RT), δ (ppm): HC᎐CH Ϫ1.28 (J
=
C–Pt
᎐
3
438.5 Hz); HC᎐CH 0.54 (J
= 481.5 Hz); C–(CH3)3 29.81;
᎐
C–Pt
᎐
C-(CH3)3 63.86; C᎐N 124.16 (J
= 72.3 Hz); C5 126.50
CCDC reference numbers 183322–183324.
See http://www.rsc.org/suppdata/dt/b2/b203085n/ for crystal-
lographic data in CIF or other electronic format.
᎐
C–Pt
(JC–Pt = 13.6 Hz); C3 129.06 (JC–Pt = 37.3 Hz); C4 138.54; C6
153.25 (JC–Pt = 78 Hz); C2 156.15; C᎐N 159.74.
᎐
J. Chem. Soc., Dalton Trans., 2002, 3696–3704
3703

View Article Online
Table 4 Crystallographic data for complexes [Pt(η2-fn)(N-NЈBut)], [Pt(η2-ma)(N-NЈBut)] and [Pt(η2-dmf )(N-NЈBut)]
[Pt(η2-fn)(N-NЈBut)]
[Pt(η2-ma)(N-NЈBut)]
[Pt(η2-dmf )(N-NЈBut)]
Empirical formula
Formula weight
C14H16N4Pt
435.40
C14H16N2O3Pt
455.38
C16H22N2O4Pt
501.45
T /K
System
Space group
293(2)
Monoclinic
P21/a
293(2)
Monoclinic
P21/c
293(2)
Triclinic
¯
P1
Z
a/Å
b/Å
c/Å
α/Њ
β/Њ
4
4
4
9.338(2)
8.706(2)
18.463(3)
8.362(3)
10.045(3)
16.811(3)
8.969(3)
12.776(4)
15.380(4)
92.92(3)
95.15(2)
94.92(3)
1745.8(9)
8.058
6369
6122
0.0299
0.0764
96.046(17)
93.47(2)
γ/Њ
V/Å3
1492.8(6)
9.392
2700
2618
0.0434
0.1189
1409.5(7)
9.963
3812
2465
0.0276
0.0656
µ(Mo Kα)/mmϪ1
Measured reflections
Unique reflections
R1[on F, I > 2σ(I )]
wR2 (F 2, all data)
17, 4634; ( f ) M. Tschoerner, G. Trabesinger, A. Albinati and
P. S. Pregosin, Organometallics, 1997, 16, 3447.
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J. Chem. Soc., Dalton Trans., 2002, 3696–3704