The role of the atomic charges on the ligands and platinum(ii) in affecting the cis and trans influences in [PtXL(PPh3)2]+ complexes (X = NO3, Cl, Br, I; L = 4-substituted pyridines, amines, PPh3). A 31P NMR and DFT investigation

Article abstract of DOI:10.1039/c1dt10963d

One bond Pt-P coupling constants ¹J_PtP of a series of cationic complexes [PtXL(PPh₃)₂]⁺ (X = NO ₃, Cl, Br, I; L = 4-Z-pyridines, Z = electron withdrawing or releasing groups, 4a-k; or X = Cl, L = NH₃, PhCH₂NH ₂ and ⁱPrNH₂, 5a-c) have been used to establish the trans and cis influence sequences of X and pyridines. The crystal structure of compound 4f(BF₄) with Z = ^tBu has been resolved. In the pyridine complexes 4a-d (Z = H, variable X), both the trans and cis influence series of the anionic ligands X decrease along the same sequence I > Br > Cl > NO₃, as previously found for [PtX(PPh ₃)₃]⁺ (X = NO₃, Cl, Br, I, 3a-d), however in 4a-d the cis influence turns out to be more important than the trans. On the contrary, in [PtCl(4-Z-py)(PPh₃)₂]⁺ (4b,e-k) the sequence of the trans influence of the 4-Z-pyridines is opposite to that of the cis, the latter being Z = CN > CHO > Br > PhCO > H > Me > ^tBu > NH₂, i.e. the most basic pyridine gives rise to the lowest cis influence. This correlation was found to hold also for complexes 5a-c (L = amines). All the observed trends have been fully reproduced by B3LYP/def2-SVP DFT calculations, by looking at the relevant optimized bond lengths of selected complexes of type 3, 4 and 5. Subsequent evaluation of the atomic charges, by resorting to two independent methods, i.e., the Natural Bond Order analysis of the wavefunction and the Bader's Quantum Theory of Atoms in Molecules, allowed for rationalization of the origin of the cis and trans influences. The negative charge on the nitrogen atoms of free pyridines becomes more negative upon protonation and even more so when coordinated to the [PtCl(PPh₃)₂]⁺ moiety. The least negatively charged nitrogen atom of coordinated pyridines is that of 4-CN-py (the highest cis influencing pyridine derivative), which gives rise to the lowest positive charge on Pt, confirming the relationship between the lowering of the charge on the metal ion and a high cis influence. The trans influence can be described in terms of competition between the charges on the two trans donor atoms. In contrast with the behaviour of pyridines, the positive charge on the phosphorous atom of free PPh₃ increases upon coordination to Pt(ii), moreover the PPh₃ ligands acquire a substantial positive charge, thus efficiently delocalising the charge of the cationic complex. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c1dt10963d

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Dalton
Transactions
Cite this: Dalton Trans., 2011, 40, 10162
www.rsc.org/dalton
PAPER
The role of the atomic charges on the ligands and platinum(II) in affecting the
cis and trans influences in [PtXL(PPh3)2]+ complexes (X = NO3, Cl, Br, I; L =
4-substituted pyridines, amines, PPh3). A 31P NMR and DFT investigation†
Luca Rigamonti,a Michele Rusconi,a Alessandra Forni*b and Alessandro Pasini*a
Received 23rd May 2011, Accepted 21st July 2011
DOI: 10.1039/c1dt10963d
One bond Pt–P coupling constants 1JPtP of a series of cationic complexes [PtXL(PPh3)2]+ (X = NO3, Cl,
Br, I; L = 4-Z-pyridines, Z = electron withdrawing or releasing groups, 4a–k; or X = Cl, L = NH3,
PhCH2NH2 and iPrNH2, 5a–c) have been used to establish the trans and cis influence sequences of X
t
and pyridines. The crystal structure of compound 4f(BF4) with Z = Bu has been resolved. In the
pyridine complexes 4a–d (Z = H, variable X), both the trans and cis influence series of the anionic
ligands X decrease along the same sequence I > Br > Cl > NO3, as previously found for [PtX(PPh3)3]+
(X = NO3, Cl, Br, I, 3a–d), however in 4a–d the cis influence turns out to be more important than the
trans. On the contrary, in [PtCl(4-Z-py)(PPh3)2]+ (4b,e–k) the sequence of the trans influence of the
4-Z-pyridines is opposite to that of the cis, the latter being Z = CN > CHO > Br > PhCO > H > Me >
tBu > NH2, i.e. the most basic pyridine gives rise to the lowest cis influence. This correlation was found
to hold also for complexes 5a–c (L = amines). All the observed trends have been fully reproduced by
B3LYP/def2-SVP DFT calculations, by looking at the relevant optimized bond lengths of selected
complexes of type 3, 4 and 5. Subsequent evaluation of the atomic charges, by resorting to two
independent methods, i.e., the Natural Bond Order analysis of the wavefunction and the Bader’s
Quantum Theory of Atoms in Molecules, allowed for rationalization of the origin of the cis and trans
influences. The negative charge on the nitrogen atoms of free pyridines becomes more negative upon
protonation and even more so when coordinated to the [PtCl(PPh3)2]+ moiety. The least negatively
charged nitrogen atom of coordinated pyridines is that of 4-CN-py (the highest cis influencing pyridine
derivative), which gives rise to the lowest positive charge on Pt, confirming the relationship between the
lowering of the charge on the metal ion and a high cis influence. The trans influence can be described in
terms of competition between the charges on the two trans donor atoms. In contrast with the behaviour
of pyridines, the positive charge on the phosphorous atom of free PPh3 increases upon coordination to
Pt(II), moreover the PPh3 ligands acquire a substantial positive charge, thus efficiently delocalising the
charge of the cationic complex.
Studies on trans and cis influences have been performed for
Introduction
many years from their early observation1 to the present day,2 and
Coordination of a ligand L to an ML¢n fragment, to yield the
coordination compound LML¢n, occurs by donation of electron
density from the lone pair of L to the metal centre; the reorganiza-
tion of the charges on L, M and L¢, which follows such a process,
affects the M–L and M–L¢ bond properties (lengths and strengths),
as well as their reactivity. In the cases of planar and octahedral
compounds, these modifications are called cis and trans (static)
influences and cis and trans (kinetic) effects.
these concepts have been used in countless papers to rationalise
bond strengths, bond lengths and reactivity. In recent years these
topics have gained renewed interest because of some recently pub-
lished results. These include theoretical investigations,3–6 the study
of new, non classical, ligands, such as NHC’s,5,7 the relationship
between either influence with the stability of geometrical isomers,8
and with ligand reactivity9 related to aspects as different as the
chemistry of cisplatin analogues,10 the Shilov reaction,11 dioxygen
activation12 and the mechanism of ligand exchange.13 Finally, the
trans and cis influences have been documented to play a role also
in main group14 and lanthanide chemistry,15 indicating a general
validity of these aspects.
aUniversita` degli Studi di Milano, Dipartimento di Chimica Inorganica,
Metallorganica e Analitica ‘Lamberto Malatesta’, via Venezian 21, 20133,
Milano, Italy. E-mail: alessandro.pasini@unimi.it; Tel: +39-0250314381
bCNR-ISTM, via Golgi 19, 20133, Milano, Italy. E-mail: a.forni@istm.cnr.it
† CCDC reference number 822142. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/c1dt10963d
In spite of such a long story, some points remain to be
investigated. The sequences of both influences can be found in
10162 | Dalton Trans., 2011, 40, 10162–10173
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
1
any inorganic chemistry textbook, but a relevant question is their
relative importance: the trans influence is usually reported to be
more important than the cis,16,17 but to what extent is it? Moreover
the contrary has been observed in some instances.4 A related
problem concerns the possibility of quantifying these influences,
in other words obtaining the “influencing power” of a ligand,
i.e. a measure of how much a given ligand L is able to influence
the properties of a bond between a metal and another ligand L¢
trans, or cis, to L. Another important issue is the origin of these
influences. As for the trans influence, the common view ascribes it
to the competition between two trans ligands for the same hybrid
orbital of the metal centre.6,16 The cis influence, on the other hand,
is likely to depend on the ability of the influencing ligand of altering
the charge on the metal atom: a high cis influence (and effect) is
exhibited by ligands which lower the charge on the metal atom.4,18
We have been studying some of these points, analysing the
influences of some anionic ligands on the Pt–P bonds in neu-
tral and cationic Pt(II) complexes with triphenylphosphine 1–3,
Scheme 1.4,19,20 These studies were based on bond lengths (both
experimental and computed) and on one bond 195Pt–31P coupling
constants, which can be considered an estimate of the bond
strength between these two atoms.16,21 In agreement with this view,
a linear correlation between Pt–P bond lengths and 1JPtP values in
a series of Pt(II) phosphine complexes has recently been reported.22
the cis and trans influences of X and Y. Comparison of the JPtP
values and of some experimental and computed bond lengths of a
series of complexes 2, enabled us to discriminate the two influences;
it turned out that the cis influence, although of lower importance,
is by no means irrelevant and must be taken into account when
rationalising bond lengths and Pt–P coupling constants.4 iii) NMR
studies performed on complexes 3 showed that the cis and trans
series are little affected by the presence of a positive charge, with
the exception of the halides which were found to display the same
order of both influences, I > Br > Cl20 (the two series are usually
reported to be opposite). iv) In order to quantify either influence,
we have used the difference between 1JPtP of a complex with a given
X and that of the chloride derivative, as a means of evaluating the
weights of either influence of X with respect to Cl, which was
taken as a reference. We confirmed4,19,20 that both the cis and trans
weights are additive;23,24 we also found that in the cationic species
3, the trans weights are higher and the cis weights lower than
those displayed by the same ligands in the (neutral) complexes 1
and 2.20 v) A DFT study, performed on derivatives 2, allowed us
to rationalise the cis and trans series in terms of Pt–P bonding
and charge on Pt.4 In particular we confirmed that the highest cis
influence is displayed by ligands which decrease the charge on Pt.4
In the present paper we extend our investigation to the cationic
complexes cis-[PtX(4-Z-py)(PPh3)2]+ (4a–k) formally derived from
3 by substitution of a triphenylphosphine group cis to the anionic
ligand X (NO3, Cl, Br, I) by a 4-substituted pyridine, 4-Z-py, where
Z is either an electron withdrawing or releasing group (Z = CN,
t
CHO, Br, PhCO, H, Me, Bu, NH2, see Scheme 1). Complexes 4
have been chosen because, by comparison with 3, we can examine
whether a change of the nature of the coordination set affects the
sequences, or the weights of the cis and trans influences. Moreover,
by varying Z, we can fine-tune the charge on Pt, in order to
verify the role of such a charge. Some results on compounds cis-
[PtCl(amine)(PPh3)2]+ (5a–c, amine = NH3, PhCH2NH2, iPrNH2,
see Scheme 1) are also reported for comparison. In particular we
also extend the study of the role of the charges in affecting either
influence series derived from the 31P NMR spectra, and therefore
we have performed DFT calculations on selected complexes 3, 4
and 5 to obtain Pt–P bond lengths and, in particular, the charges
on Pt, donor atoms and ligands, through Natural Bond Order
(NBO) analysis. To our knowledge, the present analysis represents
the first attempts to rationalise the origin of the cis and trans
influences on the basis of a rigorous quantum mechanical study
of the charges on Pt, ligands and donor atoms.
Results and discussion
Syntheses and characterization
Scheme 1
Compounds 4b–k(BF4) and 5a–c(BF4) were prepared25 treat-
ing cis-[PtX2(PPh3)2] (X = Cl, Br, I) with one mole equiv-
alent of AgBF4, followed by addition of the appropriate
ligand L. cis-[Pt(NO3)(py)(PPh3)2](BF4), 4a(NO3), and cis-
[PtCl(py)(PPh3)2](BF4), 4b(BF4), were obtained also by reaction
of cis-[Pt(NO3)2(PPh3)2] and [PtCl(PPh3)3](BF4), 3a(BF4), respec-
tively, with pyridine. Compound 4a(NO3) was characterised in
solution through 31P NMR; it could not be isolated in the solid
state.
Our studies can be summarized as follows. i) In complexes 1,
the two PPh3 groups are trans to each other, consequently their
mutual trans influence can be considered constant, in the first
1
place, and the JPtP values reflect only the cis influences of the
anionic ligands X and Y.19 ii) On the other hand, in complexes 2
the mutual cis influence of the two cis-PPh3 groups can now be
assumed to be constant;4 these ligands experience, simultaneously,
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 10162–10173 | 10163
©

View Article Online
Table 1 31P NMR data of complexes cis-[PtX(4-Z-py)(PPh3)2]+ (4a–k)
PA (cis to 4-Z-py)
PB (trans to 4-Z-py)
d (ppm)
1JPtP (Hz)
1JPtP (Hz)
sp (Z)a
pKa
b
Complex
X
Z
d (ppm)
4a
4b
4c
4d
4e
4f
4g
4h
4i
NO3
Cl
Br
I
Cl
Cl
Cl
Cl
Cl
Cl
Cl
H
H
H
H
NH2
tBu
Me
PhCO
Br
CHO
CN
6.1
3892
3687
3632
3437
3744
3700
3696
3673
3673
3663
3648
3.9
4.5
2.7
-0.6
5.4
4.7
4.6
4.5
4.7
4.5
4.4
3344
3226
3198
3196
3142
3200
3207
3260
3266
3267
3318
0
0
0
0
5.25
5.25
5.25
5.25
9.9
6.0
6.1
—
—
4.7
1.90
15.7
16.1
14.5
15.8
15.7
15.6
15.4
15.4
15.4
15.3
-0.66
-0.20
-0.17
0.43
0.23
0.42
0.66
4j
4k
a Hammett sp constant of the substituent Z;26 b pKa value of the pyridine27
The cis configuration of the phosphine groups in complexes
4 and 5 is evinced by the presence, in the 31P NMR spectra, of
two doublets, due to two non-equivalent P nuclei (see Table 1).
This configuration was unambiguously determined for cis-[PtCl(4-
tBu-py)(PPh3)2](BF4), 4f(BF4), through X-ray crystallography (see
below). Assignment of the resonances was based on the similarity
of the chemical shifts of PA (trans to X) and 1JPtP(A) with those of cis-
[PtX2(PPh3)2].4 Confirmation of the assignment was achieved for
cis-[PtCl(py)(PPh3)2]+ (4b) and of cis-[PtCl(4-NH2-py)(PPh3)2]+
(4e) through two-dimensional 1H–31P HMBC experiments, which
showed a scalar coupling between PB and the a-hydrogens of
1
the pyridines. Moreover, the H–31P HOESY spectrum showed
a dipolar coupling between PA and the a-hydrogens of the nearby
pyridine, confirming that this ligand is cis to PA. The ligand 4-
NH2-py possesses two potential donor sites, the amino group and
the heterocyclic nitrogen atom. The scalar coupling between the
a hydrogen atoms of NH2-py and PB shows that this ligand is
coordinated via the heterocyclic N atom. In the 1H spectrum, the
resonance due to the a hydrogen atoms of NH2-py is complicated,
but it becomes a simple doublet by decoupling the resonance of the
b-hydrogen, because of the coupling with PB (trans to pyridine).
Fig. 1 ORTEP view of cis-[PtCl(4-tBu-py)(PPh3)2](BF4), 4f(BF4) (hy-
drogen atoms not shown for clarity). Ellipsoids are drawn at the 30%
probability level.
Crystal structure of cis-[PtCl(4-tBu-py)(PPh3)2](BF4), 4f(BF4)
The molecular structure of cis-[PtCl(4-tBu-py)(PPh3)2](BF4),
4f(BF4), is shown in Fig. 1 and selected bond lengths and angles
are reported in Table 2. The platinum atom displays a square-
planar coordination with a very slight tetrahedral distortion. The
maximum deviation from the best least-square plane through the
relatively weak C–H ◊ ◊ ◊ F bonds, the strongest one involving an
˚
H atom of pyridine (H5 ◊ ◊ ◊ F2[i] = 2.48(1) A; ∠ C5–H5 ◊ ◊ ◊ F2[i] =
167(1)◦, [i] = x–1/2, y–1/2, z).
˚
donor atoms P1, P2, N and Cl is 0.146(2) A for atom N. The metal
cis and trans influences of the anionic ligands X
˚
atom is placed at 0.0119(7) A from this plane. The pyridine ring
forms a dihedral angle of 76.5(1)◦ with the metal coordination
These influences can be reliably obtained from the data of the
four cis-[PtX(py)(PPh3)2]+ complexes (4a–d) (Table 1) because the
influence of pyridine is the same throughout. Both influences
follow the same order: I > Br > Cl > NO3, as found in the other
cationic type 3 complexes.20
-
plane. The BF4 counterion interacts with the complex through
◦
˚
Table 2 Selected bond lengths (A) and angles ( ) for compound cis-
[PtCl(4-tBu-py)(PPh3)2](BF4), 4f(BF4)
As in our preceding papers,4,19,20 we shall use the difference
between the 1JPtP value of a compound and that of the Cl derivative
as a means of evaluating the weight of the influences of X, relative
to those of Cl, i.e. how much more, or less, a given X influences the
properties of the Pt–P bonds, in comparison with Cl. The results
are reported in Table 3, where the weights of the anionic ligands
Pt–P1
Pt–P2
Pt–N
Pt–Cl
2.2588(9)
2.2818(9)
2.084(3)
Cl–Pt–N
Cl–Pt–P1
Cl–Pt–P2
N–Pt–P1
N–Pt–P2
P1–Pt–P2
85.54(9)
175.49(4)
88.35(4)
90.74(9)
171.32(9)
95.62(3)
2.3373(10)
10164 | Dalton Trans., 2011, 40, 10162–10173
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
Table 3 cis and trans weights (Hz) of X in complexes 1, 2, [PtX(PPh3)3]+ (3a–d) and in cis-[PtX(py)(PPh3)2]+ (4a–d) relative to Cl (a: X = NO3, b: X = Cl,
c: X = Br, d: X = I)
cis weights of X (Hz)
transweights of X (Hz)
X
119
24
320
4
219
34
4
NO3
Cl
Br
I
-130
0
34
-155
0
55
-122
0
19
-205
0
55
-171
0
4
-114
0
23
-118
0
28
75
228
28
250
-35
167
30
Fig. 2 Plot of 1JPtP vs. Hammett sp constants26 for a) PA and b) PB of complexes cis-[PtCl(4-Z-py)(PPh3)2]+ (4b,e–k).
X in complexes 1, 2 and 3 are included for comparison (higher
values mean higher influencing power). The absolute values of the
cis weights of X ligands in complexes 4a–d are higher than those
displayed by these ligands in the other cationic complexes 3a–d,
therefore substitution of a phosphine by pyridine enhances the
importance of the cis influencing power: there is an increase of
those of Br and I (compared to Cl) and a lowering of that of NO3.
The weights of the trans influence are similar to those of complexes
3; the exception is given by iodine, which was found to display a
rather anomalously high trans weight in type 3 complexes.20
Interestingly, the figures of Tables 1 and 3 show that in complexes
4 the weights of the cis influences of X towards PPh3 are more
important than those of the trans influences. Although the latter
influences (and effects) are usually reported to be more important,
the contrary has been observed in a few instances,4,23 therefore
substitution of a triphenylphosphine by pyridine reverses the
relative importance of the two influences.
The role of the substituents Z on the cis and trans influences of
pyridines
1
Comparison of the JPtP values (Table 1) of the complexes with
different pyridines and with X = Cl (4b,e–k) shows that the trans
influence increases along the series CN < CHO £ Br < PhCO
t
< Me < Bu < NH2, i.e. from the pyridine with the electron
withdrawing CN group to that with the electron releasing NH2.
1
The opposite trend is observed for the cis influence. Both JPtP
series correlate well with the Hammett sp constants26 of Z (Fig.
2), and with the pKa values of the pyridines27 (Fig. 3). The nature
of Z affects both influences only slightly: there is a difference
1
1
of about 100 Hz for JPtP(A) and 176 Hz for JPtP(B) from NH2-
py to CN-py (compare, for instance, the 455 Hz span induced
by X in the case of Z = H, see above, Tables 1 and 3). The
trans influences of pyridines are slightly more important than
the cis.
Fig. 3 Plot of 1JPtP vs. pKa of the pyridines27 for a) PA and b) PB of complexes cis-[PtCl(4-Z-py)(PPh3)2]+ (4b,e–g,i–k).
The Royal Society of Chemistry 2011 Dalton Trans., 2011, 40, 10162–10173 | 10165
This journal is
©

View Article Online
Table 4 31P NMR data of complexes cis-[PtCl(amine)(PPh3)2]+ (5a–c)
PA (cis to amine)
PB (trans to amine)
d (ppm)
1JPtP (Hz)
1JPtP (Hz)
pKa
a
Complex
amine
d (ppm)
5a
5b
5c
NH3
14.7
15.3
15.4
3681
3737
3752
5.3
7.2
6.0
3162
3242
3203
9.25
9.62
10.63
PhCH2NH2
iPrNH2
a pKa value of the amine27
+
˚
Table 5 Computed bond lengths (A) and charges q (e) in computed B3LYP/def2-SVP cis-[PtX(py)(PPh3)2] complexes (4a–d)
a
b
X
Pt–PA
Pt–PB
Pt–N
Pt–X
qnat
qQTAIM
NO3 (4a)
Cl (4b)
Br (4c)
I (4d)
2.314
2.335
2.350
2.367
2.354
2.352
2.355
2.356
2.148
2.143
2.145
2.148
2.097
2.382
2.520
2.721
0.364
0.253
0.223
0.179
0.370
0.258
0.207
0.134
a obtained by NBO analysis; b obtained by QTAIM.
Complexes cis-[PtCl(amine)(PPh3)2]+ (5a–c)
X-ray structure of cis-[PtCl(4-tBu-py)(PPh3)2]+ (4f) (in the hypoth-
esis that the coordination bond lengths are almost unvaried in the
presence of Me- or Bu-substituted pyridine), indicates that the
adopted B3LYP/def2-SVP method overestimates the interatomic
The cis influence series of the various pyridines is puzzling since,
in the preceding studies on complexes 1, 2 and 3, we showed that
the cis influence of a ligand is related to its ability to lower the
positive charge on Pt.4,19,20 In complexes 4 such a ligand should
be the most basic NH2-py. To check whether this inversion of
trend is due to some peculiarity of pyridines, such as the fact that
they are sp2 donors, we investigated some derivatives of formula
cis-[PtCl(amine)(PPh3)2]+ (5a–c) where the amine is an sp3 donor.
The 31P NMR data of these compounds (Table 4) show that in
this case also the cis influence decreases with increasing basicity
of the amine ligand, i.e. along the series NH3 > PhCH2NH2 >
iPrNH2.
t
˚
distances involving Pt by 0.05–0.08 A. This constitutes a typical
lengthening of metal–ligand bonds generally shown by gradient-
corrected DFT methods,30 comparable with results obtained in
our previous computational studies on complexes 2.4
Computed bond lengths
Let us consider first the cis-[PtX(py)(PPh3)2]+ (4a–d) derivatives.
˚
The Pt–PA distances, Table 5, increase by about 0.05 A along
the sequence X = NO3 < Cl < Br < I, in agreement with the
increasing cis influence series obtained by the 31P NMR spectra.
The Pt–PB bond lengths are essentially unchanged, in accordance
with the above-described low importance of the trans influence of
the anionic ligands in these complexes.
In the case of complexes 4b,e,g,k with the same anionic ligand,
Cl, and with different 4-Z-pyridines (Z = H, NH2, Me, CN,
respectively), the very slight differences of the Pt–P bond distances
are marginally affected by the nature of Z (Table 6) and are in
accordance with the 31P NMR derived influences. The Pt–N bond
lengths increase with the electron withdrawing power of Z. The
Pt–Cl distances are practically unaffected by the nature of Z. For
complexes 3, the two Pt–PB bond lengths cis to X (and trans to
each other) are different (Table 7). This difference is not surprising
since it was also found in the X-ray structure of some [PtX(PPh3)3]+
derivatives 3.20,31 The Pt–P bond distances, either cis or trans to X,
Computational studies
To try and rationalise the above described results we have
performed gas-phase B3LYP/def2-SVP geometry optimisations
of some investigated complexes. Atomic charges of the optimized
structures have then been determined through Natural Bond
Order (NBO) analysis.28 For some complexes, atomic charges have
also been computed by using the Quantum Theory of Atoms in
Molecules (QTAIM),29 in order to confirm the general validity
of our theoretical results on the atomic charges by resorting to
completely independent approaches. In all the cases examined,
both methods provided the same trend of atomic charges in the
different complexes (see Tables 5 and 6). Comparison between the
optimised structure of cis-[PtCl(4-Me-py)(PPh3)2]+ (4g) and the
+
˚
Table 6 Selected bond lengths (A) and Pt charges q (e) in computed B3LYP/def2-SVP cis-[PtCl(4-Z-py)(PPh3)2] complexes (4b,e,g,k)
a
b
Z
Pt–PA
Pt–PB
Pt–N
Pt–Cl
qnat
qQTAIM
NH2 (4e)
Me (4g)
H (4b)
2.332
2.334
2.335
2.338
2.356
2.354
2.352
2.347
2.131
2.138
2.143
2.151
2.384
2.386
2.382
2.382
0.258
0.254
0.253
0.247
0.268
0.260
0.258
0.248
CN (4k)
a obtained by NBO analysis; b obtained by QTAIM.
10166 | Dalton Trans., 2011, 40, 10162–10173
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
˚
Table 7 Selected bond lengths (A) in computed B3LYP/def2-SVP
iii) As for the role of the charges on the trans influence, in both
complexes 3 and 4 the charge on PA (trans to X) decreases from
X = NO3 to X = I, while the charge on X increases along the
same sequence (see Table 8), i.e. the highest influence is found in
complexes which display the lowest difference between the charges
of the two trans donor atoms. The trans influence is attributed to
the competition of the two trans ligands for the same hybrid orbital
of the metal centre.16 Our results suggest that, at least in the case of
X, such a competition can be described in terms of the difference
of the charges.
[PtX(PPh3)3]+ complexes (3a–d)
a
b
b
X
Pt–PA
Pt–PB
Pt–PB
Pt–Xc
NO3 (3a)
Cl (3b)
Br (3c)
I (3d)
2.328
2.353
2.370
2.391
2.465
2.462
2.469
2.477
2.423
2.423
2.427
2.432
2.104
2.385
2.521
2.722
a trans to X; b cis to X; c Pt–O for 3a
iv) The pyridine and phosphine ligands are positively charged
(Tables 8 and 9), as expected on the grounds of donation of electron
density from these (neutral) ligands to the metal centre. The
positive charge of the cationic complexes is therefore delocalised
on these ligands. Note, however, that qPt decreases on passing
from the (py)(PPh3)2 to the (PPh3)3 compounds, showing that
triphenylphosphine is able to relax the positive charge of the
cationic complex more efficiently than pyridines. Note also that
this finding suggests the absence (or at least a low relevance) of
P←Pt back donation in these cationic Pt(II) complexes.32 We can
also quantify the ability of such a charge relaxation: the decrease
of the charge on Pt from the complexes 4 to 3, with the same
anionic ligand, is constant, the average value being 0.142 e (0.139,
0.142, 0.143 and 0.144 e for X = NO3, Cl, Br and I, respectively).
This value represents the ability of triphenylphosphine to relax the
positive charge with respect to pyridine.
v) The charge of coordinated CN-py (0.216 e, Table 9) is lower
than that of NH2-py (0.264 e, Table 9); the ligand with the electron
releasing substituent donates more efficiently to Pt(II), as expected.
vi) Although coordinated pyridines are positively charged, their
N donor atoms are negative. Thus coordination of pyridines leaves
a substantial electron density on N, suggesting a relatively low
electron transfer from this atom to Pt. In fact the highest qPt is
found in the complex 4e, with 4-NH2-py, the ligand that bears
the highest positive charge and whose nitrogen atom is the most
negative in the series. See Table 9 and Scheme 2.
follow the cis and trans influence series, the latter is confirmed to
be more important than the cis influence.20
Atomic and ligand charges
The natural charges on platinum, pyridines, phosphines and on
the four donor atoms are collected in Tables 8 and 9. The
atomic charges of 4e, 4k, 3b and 5a together with those of free
pyridines, phosphine, ammonia and their protonated species, are
also displayed in Scheme 2 to allow a fast evaluation. These data
suggest the following considerations.
i) The natural charges on Pt both in cis-[PtX(py)(PPh3)2]+ (4a–d)
and in cis-[PtX(PPh3)3]+ (3a–d) (Table 8) decrease down the series
NO3 > Cl > Br > I, confirming that the highest cis influence is
displayed by the ligand (here I) which produces the lowest charge
on the metal atom. Further confirmation of this relationship is also
provided by qPt in the Z-py derivatives (Table 9): the lowest charge
on Pt is observed in the complex with the highest cis influencing
ligand, CN-py. It is, however, somewhat surprising that the highest
charge on Pt is found in the complex with the strongest donor
NH2-py; this point will be rationalised below (points v and vi).
ii) The anionic ligands bear a residual negative charge (Table
8), which becomes less negative from NO3 to I reflecting the
difference in X–Pt(II) interactions, from highly ionic, for NO3, to
an increasing covalent character for Cl < Br < I. Interestingly, such
a lowering is practically the same in complexes 3 and 4 (see DqPt in
Table 8), i.e. it is independent of the presence of three phosphines,
rather than two phosphines and a pyridine, indicating that the
donor ability of the anionic ligand is an intrinsic property of the
ligand itself.
vii) Comparison between the qN values of free and coordinated
NH2-py and CN-py shows an increase of electron density on N
following coordination (Table 9 and Scheme 2). Such an increase
seemed odd at first sight, since coordination involves donation of
Table 8 Selected atomic natural charges, q (e), in computed B3LYP/def2-SVP cis-[PtX(L)(PPh3)2]+ complexes (L = PPh3: type 3, L = py: type 4)
Computed charges (e)
X, L
q (Pt)
0.225
0.111
0.080
0.035
DqPt
q (X)
q (PAPh3)a
q (PA)a
1.082
1.050
1.039
1.021
q (PBPh3)b
q (PB)b
q (py)
—
3a
3b
3c
3d
NO3, PPh3
Cl, PPh3
Br, PPh3
I, PPh3
—
-0.647c
-0.450
-0.411
-0.335
0.497
0.448d
0.478e
0.420d
0.469e
0.419d
0.468e
0.410d
0.461e
0.549
0.522
0.521
0.512
1.020d
1.050e
1.013d
1.052e
1.009d
1.051e
1.000d
1.045e
1.112
1.107
1.103
1.095
0.114f
0.031g
0.045h
0.541
—
0.443
—
0.429
—
4a
4b
4c
4d
NO3, py
Cl, py
Br, py
I, py
0.364
0.253
0.223
0.179
—
-0.662i
-0.478
-0.411
-0.379
0.510
0.466
0.461
0.449
1.097
1.066
1.057
1.043
0.239
0.238
0.239
0.240
0.111f
0.030g
0.043h
a trans to X; b cis to X; c charge on O donor atom: -0.586 e; d with the longer Pt–P distance; e with the shorter Pt–P distance; f qPt in the NO3 derivative -
q
Pt in the Cl derivative; g
q
Pt in the Cl derivative - qPt in Br derivative; h
q
Pt in the Br derivative - qPt in the I compound; i charge on O donor atom - 0.605 e.
Dalton Trans., 2011, 40, 10162–10173 | 10167
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
Table 9 Selected atomic and ligand natural charges (e) in computed B3LYP/def2-SVP cis-[PtCl(4-Z-py)(PPh3)2]+ (4b,e,g,k) and [PtCl(PPh3)3]+ (3b)
complexes
Z
py
N
PA trans to Cl
PB cis to Cl
Cl
Pt
PPh3 (average)
PPh3 trans to Cl
PPh3 cis to Cl
4e
NH2
Me
H
CN
—
0.264
0.246
0.238
0.216
—
-0.558
-0.524
-0.517
-0.508
—
1.069
1.067
1.066
1.066
1.050
1.095
1.103
1.107
1.117
1.013
1.052
-0.482
-0.480
-0.478
-0.477
-0.450
0.258
0.254
0.253
0.247
0.116
0.480
0.490
0.494
0.507
0.447
0.462
0.467
0.466
0.472
0.451
0.498
0.513
0.522
0.541
0.420
0.469
4g
4b
4k
3ba
a [PtCl(PPh3)3]+, this complex is included in this Table for ease of comparison.
Scheme 2
some electron density from N to the metal centre and should de-
crease the negative charge on N. In order to ascertain whether this
observed increase is a characteristic of coordination of pyridines
to Pt (for instance, due to a particular bonding interaction with
Pt(II) or to Pt→N back donation), we calculated the charges
on protonated NH2-py and CN-py (Scheme 2). Protonation was
chosen because H+ is the simplest Lewis acid and because it
is incapable of back donation. We found that protonation also
enhances, although to a lesser extent, the negative charge on
N, thus the above described increase seems to be a feature of
pyridine-Lewis acids interaction. A likely explanation is that
electron donation to the proton withdraws electron density from
the whole pyridine backbone to the nitrogen atom. Clearly such
an electron flow is more relevant for the pyridine that possesses an
electron releasing, rather than an electron withdrawing group. It
is difficult, however, to quantify this electron flow; the charges on
the NH2 and CN groups increase upon protonation (see Scheme
2), but this can be due, at least in part, to the delocalisation
of the positive +1 charge of Z-pyH+, which, according to the
Pauling principle, should be spread along the periphery of the
10168 | Dalton Trans., 2011, 40, 10162–10173
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
molecule. Upon coordination to the [PtCl(PPh3)2]+ moiety, the
nitrogen donor atom becomes even more negative than in Z-
pyH+ (Scheme 2), presumably because the triphenylphosphines
efficiently delocalise the positive charge of the cationic complex,
causing an additional electron flow from the pyridine ring towards
the nitrogen atoms. The negative charge of the N atoms of the
pyridine ligands represents, therefore, the electron density which
is left on N after both the withdrawing or releasing properties of
Z, the N→Pt or N→H+ electron transfer and the delocalisation
of the positive charge are taken into account; the net result being
a balance between these electron flows.
viii) Noteworthy is the behaviour of ammonia: its nitrogen
atom becomes less negative upon interaction with either H+ or
with [PtCl(PPh3)2]+.33 We think this difference could be due to the
different hybridisation of the nitrogen in the two ligands: the sp3
hybridised nitrogen of ammonia is a better donor, at least towards
H+ and Pt(II).
ix) In sharp contrast with the behaviour of pyridines, the P donor
atoms of protonated and complexed triphenylphosphine not only
bear positive charges, but such charges are higher than that of P in
free PPh3 (0.822 e), suggesting a relevant P→Pt electron transfer.
Also in these cases there is a decrease of charge, from 1.332 e to
about 1.01–1.09 e from Ph3PH+ to the complex, on account of
the above described delocalization of the positive charge of the
complex.
x) The opposite behaviours of P and N donor atoms upon
coordination (increase of electron density on N, decrease on P)
reflects the different electronegativities of the two elements, but we
think it may also arise from the better “matching” between the
soft (and second row) P, rather than the hard (and first row) N,
with Pt(II).
xi) The low electron transfer from py to Pt, evinced by the
presence of a significant negative charge on the N atoms of
pyridines, has little effect on the charge of the metal atom,
which becomes receptive to the donor properties of X. This is in
agreement with the observation that on passing from complexes
3 to 4, i.e. upon substitution of PPh3 by pyridine, the importance
of the cis influence of the anionic ligands is enhanced. The low
py→Pt electron transfer is also in agreement with the low cis
influence weights displayed by pyridines.
xii) A final comment concerns the possibility of back donation
from the filled d orbitals of Pt to the empty p* orbital of pyridines.
The lowering of the charges on pyridines in passing from py–H+
to py–PtCl(PPh3)2+ (see Scheme 2) could be due to the presence of
back donation. However from Scheme 2 we note that this lowering
(mean value 0.300 e) is of the same magnitude of that observed
in the series H3N–H+, H3N–PtCl(PPh3)2+ (0.296 e) where no back
donation is expected. Moreover, as previously stated, we think
back donation is unlikely in the case of cationic complexes.
that the cis influence is associated with the ability of a ligand to
lower the positive charge on the metal centre. Interestingly, this
series also parallels the decrease of the positive charge on the PA
atom, trans to X, by 0.061 e and 0.054 e for 3 and 4, respectively.
The origin of the trans influence has been discussed thoroughly
and the common view is that it is originated by the competition of
two ligands, trans to each other, for the same hybrid orbital. Our
results suggest that such a competition can be described in terms
of the charges of the two trans donor atoms (here X and PA): the
more negative is X, the more positive becomes PA.
The cis and trans influences of Z-py exhibit opposite orders, the
highest NMR-derived cis influence being displayed by CN-py and
the lowest by NH2-py. At first sight this finding is unexpected, on
the grounds of the hypothesis that a relevant cis influence should be
given by ligands which are able to lower the charge on Pt, i.e. NH2-
py. However DFT calculations show that the negative charge on
the nitrogen atoms of pyridines becomes more negative when these
ligands interact with either H+ or the [PtCl(PPh3)2]+ fragment, the
most negatively charged N atom being that of coordinated NH2-
py; moreover the Pt atom with this ligand bears the highest positive
charge in the series and, consistently, NH2-py displays the lowest
cis influence. Thus the relationship between the cis influence and
the charge on Pt is confirmed also in the case of the Z-pyridines.
The fact that the nitrogen atoms of pyridines become more
negative upon interaction with a Lewis acid is attributed to the
electron flow from the pyridine backbone towards the nitrogen
atom which occurs upon this interaction. However the existence
of such a high negative charge on N seems to suggest an incomplete
electron transfer from N to the Lewis acid. This fact is likely to be
due to the low basicity of the sp2 hybridized N atom of pyridine,
since the negative charge on the sp3 nitrogen atom of ammonia
becomes less negative both upon protonation and coordination to
Pt.
The behaviour of the P atoms of triphenylphosphine is opposite:
the positive charge on P in free PPh3 is increased both upon
protonation and complexation, on account of donation of electron
density to the Lewis acids. This different behaviour may be due
to the higher electronegativity of nitrogen, although in the case
of Pt complexes, it is tempting to ascribe such a difference also
to the unfavourable matching between the soft Pt(II) and the hard
(and second row) N in comparison with the softer (and third
row) P.
In conclusion we have illustrated the importance of the charge
distribution in ruling the properties of the ligand to metal bonds,
as well as their mutual influences. We are planning to study other
systems to ascertain the general validity of our findings.
Experimental
All chemicals were reagent grade. Solvents were used as re-
ceived. Elemental analyses were performed at the Microanalytical
Conclusions
1
Laboratory at the Universita` degli Studi di Milano. 31P{ H}
In this paper we have analysed the relationship between the charges
on the coordination set and the 31P NMR-derived cis and trans
influences of some anionic ligands X and of a series of 4-Z-
pyridines in cis-[PtX(4-Z-py)(PPh3)2]+ (4a–k) and [PtX(PPh3)3]+
(3a–d) complexes. It was found that both the cis and trans
influences of X follow the same order, i.e. NO3 < Cl < Br < I.
These series parallel the lowering of the charge on Pt, confirming
NMR spectra were recorded on a Bruker Advance DRX 300
1
at 121 MHz; dP values are in ppm versus external H3PO4, JPtP
coupling constants (Hz) have been found reproducible to 3 Hz.
Infrared spectra were recorded as KBr disks using a JASCO FT-
IR 410 spectrophotometer with a 2 cm-1 resolution. The syntheses
of cis-[PtCl2(PPh3)2],4,34 cis-[PtBr2(PPh3)2],4 trans-[PtI2(PPh3)2],4,19
cis-[Pt(NO3)2(PPh3)2],4,35 and [PtCl(PPh3)3](BF4),20 are reported in
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 10162–10173 | 10169
©

View Article Online
the literature. All reactions involving silver salts were performed in
the dark.
IR ◦(KBr): nmax/cm-1 1626 (CN), 1058 (BF4). dP (121 MHz; CDCl3;
2
1
25 C) -0.6 (1P, d, JPP = 15.0 Hz, JPtP = 3196 Hz, PB) and 14.5
(1P, d, 2JPP = 15.0 Hz, 1JPtP = 3437 Hz, PA).
Formation of cis-[Pt(NO3)(py)(PPh3)2](NO3), 4a(NO3), and
synthesis of cis-[Pt(py)2(PPh3)2](NO3)2
Synthesis of cis-[PtCl(4-NH2-py)(PPh3)2](BF4), 4e(BF4)
Pyridine (0.8 mL of a 0.134 mol L-1 solution in dichloromethane,
0.11 mmol) was added to a solution of cis-[Pt(NO3)2(PPh3)2]
(95.5 mg, 0.11 mmol) in dichloromethane (10 mL) and the mixture
was left under stirring at room temperature for 1 h. dP (121 MHz;
CH2Cl2; 25 ◦C) 0.7 (s, 1JPtP = 3311 Hz, cis-[Pt(py)2(PPh3)2](NO3)2),
3.6 (s, 1JPtP = 4013 Hz, cis-[Pt(NO3)2(PPh3)2]), 3.9 (d, 2JPP = 21.0 Hz,
This white product was obtained as above from AgBF4 (38.6 mg,
0.20 mmol), cis-[PtCl2(PPh3)2] (132.2 mg, 0.17 mmol) and 4-
aminopyridine (16.0 mg, 0.17 mmol) (33.6 mg, 22%). Found:
C, 51.17; H, 4.40; N, 2.94. Calc. for C41H36BClF4N2P2Pt·1.5H2O
(963.05): C, 51.13; H, 4.08; N, 2.91. IR (KBr): nmax/cm-1 3337 and
3242 (NH2), 1635 (CN), 1064 (BF4). dP (121 MHz; d6-acetone;
25 ◦C) 5.4 (1P, d, 2JPP = 18.8 Hz, 1JPtP = 3142 Hz, PB) and 15.8 (1P,
d, 2JPP = 18.8 Hz, 1JPtP = 3744 Hz, PA).
1JPtP = 3344 Hz, PB of cis-[Pt(NO3)(py)(PPh3)2]+) and 6.1 (d, 2JPP
=
21.0 Hz, 1JPtP = 3892 Hz, PA of cis-[Pt(NO3)(py)(PPh3)2]+). More
pyridine (1.5 mL, 18.6 mmol) was then added, and the reaction
mixture was left under stirring at room temperature for 4 h. The
white product was obtained by precipitation with diisopropyl ether
(88.2 mg, 90%). Found: C, 55.03; H, 3.89; N, 5.12. Calc. for
Synthesis of cis-[PtCl(4-tBu-py)(PPh3)2](BF4), 4f(BF4)
This white product was obtained as above from AgBF4 (32.3 mg,
0.17 mmol), cis-[PtCl2(PPh3)2] (105.3 mg, 0.14 mmol) and 4-
tert-butylpyridine (1.3 mL of a 0.126 mol L-1 solution in
dichloromethane, 0.16 mmol) (92.6 mg, 71%). Found: C, 51.22;
H, 5.21; N, 1.08. Calc. for C45H43BClF4NP2Pt·4H2O (1049.17):
C, 51.51; H, 4.90; N, 1.34. IR (KBr): nmax/cm-1 1616 (CN), 1055
C46H40N4O6P2Pt (860.75): C, 55.15; H, 4.02; N, 5.59. IR (KBr):
◦
n
max/cm-1 1435 (CC), 1381 (NO3). dP (121 MHz; CDCl3; 25 C)
0.7 (s, 1JPtP = 3311 Hz, cis-[Pt(py)2(PPh3)2](NO3)2).
Synthesis of cis-[PtCl(py)(PPh3)2](BF4), 4b(BF4)25
(BF4). dP (121 MHz; CDCl3; 25 ◦C) 4.7 (1P, d, 2JPP = 18.7 Hz, 1JPtP
=
3200 Hz, PB) and 15.7 (1P, d, 2JPP = 18.7 Hz, 1JPtP = 3700 Hz, PA).
First method: A solution of AgBF4 (26.5 mg, 0.14 mmol) in acetone
(3 mL) was added to a solution of cis-[PtCl2(PPh3)2] (105.5 mg,
0.13 mmol) in dichloromethane (10 mL). The reaction mixture was
stirred at room temperature for 1 h, and filtered to eliminate AgCl.
Pyridine (1.0 mL of a 0.134 mol L-1 solution in dichloromethane,
0.13 mmol) was added to the solution, which was stirred at room
temperature for 2 h. The white product, obtained by the addition
of diisopropyl ether, was filtered and dried in vacuo (44.0 mg,
37%). Second method: Pyridine (1.5 mL, 18.6 mmol) was added
to a solution of [PtCl(PPh3)3](BF4) (191.2 mg, 0.17 mmol). The
reaction mixture was stirred at room temperature for 4 h, and
treated with diisopropyl ether. The white product was filtered and
dried in vacuo (142.0 mg, 89%). Found: C, 53.47; H, 4.03; N, 1.67.
Calc. for C41H35BClF4NP2Pt (921.01): C, 53.47; H, 3.83; N, 1.52.
IR (KBr): nmax/cm-1 1607 (CN), 1057 (BF4). dP (121 MHz; CDCl3;
25 ◦C) 4.5 (1P, d, 2JPP = 18.7 Hz, 1JPtP = 3226 Hz, PB) and 15.7 (1P,
d, 2JPP = 18.7 Hz, 1JPtP = 3687 Hz, PA).
Synthesis of cis-[PtCl(4-Me-py)(PPh3)2](BF4), 4g(BF4)
This white product was obtained as above from AgBF4 (29.7 mg,
0.15 mmol), cis-[PtCl2(PPh3)2] (121.9 mg, 0.15 mmol) and
4-methylpyridine (8.1 mL of a 0.020 mol L-1 solution in
dichloromethane, 0.16 mmol) (100.0 mg, 69%). Found: C, 54.04;
H, 4.10; N, 1.30. Calc. for C42H37BClF4NP2Pt (935.04): C, 53.95;
H, 3.99; N, 1.50. IR (KB◦r): nmax/cm-1 1616 (CN), 1055 (BF4).
2
1
dP (121 MHz; CDCl3; 25 C) 4.6 (1P, d, JPP = 18.8 Hz, JPtP
=
3207 Hz, PB) and 15.6 (1P, d, 2JPP = 18.8 Hz, 1JPtP = 3696 Hz, PA).
Synthesis of cis-[PtCl(4-PhCO-py)(PPh3)2](BF4), 4h(BF4)
This white product was obtained as above from AgBF4 (26.0 mg,
0.13 mmol), cis-[PtCl2(PPh3)2] (101.5 mg, 0.13 mmol) and 4-
benzoylpyridine (35.5 mg, 0.19 mmol) (89.5 mg, 68%). Found: C,
55.74; H, 4.22; N, 1.31. Calc. for C48H39BClF4NOP2Pt (1025.11):
C, 56.24; H, 3.83; N, 1.37. IR (KBr): nmax/cm-1 1664 (CO), 1576
Synthesis of cis-[PtBr(py)(PPh3)2](BF4), 4c(BF4)
(CN), 1056 (BF4). dP (121 MHz; CDCl3; 25 ◦C) 4.5 (1P, d, 2JPP
18.8 Hz, 1JPtP = 3260 Hz, PB) and 15.4 (1P, d, 2JPP = 18.8 Hz, 1JPtP
3673 Hz, PA).
=
=
This white product was obtained as above from AgBF4 (25.5 mg,
0.13 mmol), cis-[PtBr2(PPh3)2] (101.0 mg, 0.12 mmol) and pyri-
dine (1.0 mL of a 0.134 mol L-1 solution in dichloromethane,
0.13 mmol) (34.1 mg, 27%). Found: C, 51.02; H, 4.02; N, 1.69.
Calc. for C41H35BBrF4NP2Pt (965.47): C, 51.01; H, 3.65; N, 1.45.
IR (KBr): nmax/cm-1 1610 (CN), 1058 (BF4). dP (121 MHz; CDCl3;
25 ◦C) 2.7 (1P, d, 2JPP = 17.3 Hz, 1JPtP = 3198 Hz, PB) and 16.1 (1P,
d, 2JPP = 17.3 Hz, 1JPtP = 3632 Hz, PA).
Synthesis of cis-[PtCl(4-Br-py)(PPh3)2](BF4), 4i(BF4)
This white product was obtained as above from AgBF4 (30.1 mg,
0.15 mmol), cis-[PtCl2(PPh3)2] (113.4 mg, 0.14 mmol) and 4-
bromopyridine (0.15 mmol, 5 mL of a solution obtained
from 4-Brpy·HCl, 58.3 mg, 0.30 mmol, dissolved in water,
treated with KHCO3, 30.0 mg, 0.30 mmol, and extracted with
dichloromethane, 10 mL) (84.1 mg, 59%). Found: C, 49.77; H,
3.52; N, 1.17. Calc. for C41H34BBrClF4NP2Pt (999.90): C, 49.25;
H, 3.43; N, 1.40. IR (KB◦r): nmax/cm-1 1593 (CN), 1056 (BF4).
Synthesis of cis-[PtI(py)(PPh3)2](BF4), 4d(BF4)
This white product was obtained as above from AgBF4 (21.4 mg,
0.11 mmol), trans-[PtI2(PPh3)2] (96.2 mg, 0.10 mmol) and pyri-
dine (0.8 mL of a 0.134 mol L-1 solution in dichloromethane,
0.11 mmol) (60.3 mg, 60%). Found: C, 49.11; H, 3.93; N, 1.48.
Calc. for C41H35BF4INP2Pt (1012.47): C, 48.64; H, 3.48; N, 1.38.
2
1
dP (121 MHz; CDCl3; 25 C) 4.7 (1P, d, JPP = 18.9 Hz, JPtP
=
3266 Hz, PB) and 15.4 (1P, d, 2JPP = 18.9 Hz, 1JPtP = 3673 Hz, PA).
10170 | Dalton Trans., 2011, 40, 10162–10173
This journal is The Royal Society of Chemistry 2011
©

View Article Online
compound
[PtCl(4-tBu-
Table 10 Crystallographic
py)(PPh3)2](BF4), 4f(BF4)
data
for
Synthesis of cis-[PtCl(4-CHO-py)(PPh3)2](BF4), 4j(BF4)
This white product was obtained as above from AgBF4 (29.9 mg,
0.15 mmol), cis-[PtCl2(PPh3)2] (110.1 mg, 0.14 mmol) and
4-formylpyridine (1.3 mL of a 0.138 mol L-1 solution in
dichloromethane, 0.18 mmol) (85.7 mg, 65%). Found: C, 52.88;
H, 4.16; N, 1.35. Calc. for C42H35BClF4NOP2Pt (949.02): C, 53.16;
H, 3.72; N, 1.48. IR (KBr): nmax/cm-1 1718 (CO), 1594 (CN), 1056
Crystal Data
Moiety formula
M
[C45H43ClNP2Pt](BF4)
977.09
Monoclinic
Cc
18.1703(11)
10.9178(7)
21.1239(13)
91.105(1)
4189.8(5), 4
1.549
9948
4.4–51.0
3.540
294(2)
colourless, rhombic prism
0.50 ¥ 0.35 ¥ 0.03
Crystal system
Space group
˚
a/A
(BF4). dP (121 MHz; CDCl3; 25 ◦C) 4.5 (1P, d, 2JPP = 18.8 Hz, 1JPtP
=
˚
b/A
3267 Hz, PB) and 15.4 (1P, d, 2JPP = 18.8 Hz, 1JPtP = 3663 Hz, PA).
˚
c/A
b/◦
3
˚
V/A , Z
Synthesis of cis-[PtCl(4-CN-py)(PPh3)2](BF4), 4k(BF4)
Dx/Mg m-3
Reflns for cell determination
2q/◦ for cell determination
m/mm-1
T/K
Color, habit
This white product was obtained as above from AgBF4 (26.0 mg,
0.13 mmol), cis-[PtCl2(PPh3)2] (103.5 mg, 0.13 mmol) and 4-
cyanopyridine (13.8 mg, 0.13 mmol) (100.9 mg, 81%). Found:
C, 53.68; H, 3.81; N, 2.57. Calc. for C42H34BClF4N2P2Pt (946.01):
C, 53.33; H, 3.62; N, 2.96. IR (KBr): nmax/cm-1◦2239 (C N), 1616
Dimensions/mm
Data Collection
(C N), 1055 (BF4). dP (121 MHz; CDCl3; 25 C) 4.4 (1P, d, 2JPP
18.9 Hz, 1JPtP = 3318 Hz, PB) and 15.3 (1P, d, 2JPP = 18.9 Hz, 1JPtP
3648 Hz, PA).
=
=
˚
radiation, l/A
Mo-Ka, 0.71073
j and w
54.9
-23→23
-14→14
-27→27
None
33401
9491
8849
0.042
Scan type
◦
2qmax
/
h range
k range
l range
Synthesis of cis-[PtCl(NH3)(PPh3)2](BF4), 5a(BF4)
Intensity decay (%)
Measured reflns
Independent reflns
Reflns with I > 2s(I)
Rint
This white product was obtained as above from AgBF4 (29.2 mg,
0.15 mmol), cis-[PtCl2(PPh3)2] (110.2 mg, 0.14 mmol) and ammo-
nia (2.0 mL of a 0.5 mol L-1 solution in 1,4-dioxane, 1.00 mmol)
(86.5 mg, 72%). Found: C, 50.84; H, 3.90; N, 1.53. Calc. for
C36H33BClF4NP2Pt (858.95): C, 50.34; H, 3.87; N, 1.63. IR (KBr):
Refinement on F2
R[F2>2s(F2)], wR[F2>2s(F2)]
S
0.0240, 0.0517
0.907
0.004(4)
530, 27
0.001
0.626, -0.494
n
max/cm-1 3257 and 3055 (NH), 1059 (BF4). dP (121 MHz; CDCl3;
Flack parameter
Parameters, restraints
(D/s)max
25 ◦C) 5.3 (1P, d, 2JPP = 18.8 Hz, 1JPtP = 3162 Hz, PB) and 14.7 (1P,
d, 2JPP = 18.8 Hz, 1JPtP = 3681 Hz, PA).
-3
˚
Drmax, Drmin/e A
Synthesis of cis-[PtCl(PhCH2NH2)(PPh3)2](BF4), 5b(BF4)
This white product was obtained as above from AgBF4 (28.1 mg,
0.14 mmol), cis-[PtCl2(PPh3)2] (108.6 mg, 0.14 mmol) and benzy-
lamine (1.0 mL of a 0.142 mol L-1 solution in dichloromethane,
0.14 mmol) (89.0 mg, 69%). Found: C, 54.81; H, 4.44; N, 1.29. Calc.
for C43H39BClF4NP2Pt (948.06): C, 54.42; H, 4.14; N, 1.48. IR
(KBr): nmax/cm-1 3292 and 3243 (NH2), 1056 (BF4). dP (121 MHz;
CDCl3; 25 ◦C) 7.2 (1P, d, 2JPP = 19.0 Hz, 1JPtP = 3242 Hz, PB) and
15.3 (1P, d, 2JPP = 19.0 Hz, 1JPtP = 3737 Hz, PA).
are summarised in Table 10. Intensity data were collected on
a Bruker Apex CCD area detector at room temperature, using
graphite monochromated Mo-Ka radiation. No crystal decay
was observed, so no time-decay correction was needed. Data
reduction was performed with SAINT, and absorption corrections
based on multiscan were obtained with SADABS.36 The structure
was solved by direct methods with SHELXS-9737 and refined by
SHELXL-97.37 The program ORTEPIII was used for graphics.38
Anisotropic thermal parameters were used for all non-hydrogen
atoms. The isotropic thermal parameters of H atoms were fixed at
1.2 (1.5 for methyl groups) times those of the atom to which they
were attached. All H atoms were placed in calculated positions
and refined by a riding model. The methyl groups of the tert-
butyl moiety present large disorder, which was partially resolved
by splitting such groups in two positions, labelled by adding the
letters A and B to the numbering scheme. Some restraints on
distances and thermal parameters (SADI and SIMU instructions,
respectively) were required during the refinement in order to obtain
a satisfactory geometry.
Synthesis of cis-[PtCl(iPrNH2)(PPh3)2](BF4), 5c(BF4)
This white product was obtained as above from AgBF4
(25.3 mg, 0.13 mmol), cis-[PtCl2(PPh3)2] (102.8 mg, 0.13 mmol)
and isopropylamine (1.6 mL of a 0.082 mol L-1 solution in
dichloromethane, 0.13 mmol) (84.7 mg, 72%). Found: C, 52.90; H,
4.68; N, 1.31. Calc. for C39H39BClF4NP2Pt·0.5C6H14O (952.10): C,
52.98; H, 4.87; N, 1.47. IR (KBr): nmax/cm-1 3287 and 3233 (NH2),
1056 (BF4). dP (121 MHz; CDCl3; 25 ◦C) 6.9 (1P, d, 2JPP = 19.0 Hz,
1JPtP = 3203 Hz, PB) and 15.4 (1P, d, 2JPP = 19.0 Hz, 1JPtP = 3752 Hz,
PA).
X-ray crystal structure determination
Computational details
Crystals of 4f(BF4) suitable for X-ray diffraction experiments
were obtained from slow diffusion of diisopropyl ether into
a CDCl3 solution. Crystal data and details of data collection
Calculations were performed with the Gaussian 03 program
package.39 All geometries were fully optimized using the B3LYP
functional40 and the def2-SVP split valence basis set with
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 10162–10173 | 10171
©

View Article Online
polarization functions on all atoms.41,42 In particular, an extra set
of f functions with exponent 0.66813 has been used for Pt. Iodine
and platinum have been treated as 25- and 18-electron systems,
respectively, with relativistic effective core potentials (ECPs) taken
from the literature.43,44 The natural bond orbital (NBO) analysis28
and the Quantum Theory of Atoms in Molecules (QTAIM)29 were
used for evaluating the atomic charges. QTAIM partitioning of the
computed charge density distribution has been performed with the
AIMPAC program.45
O. Krizanovic, M. Lutterbeck, M. Schuermann, E. C. Fusch and B.
Lippert, Dalton Trans., 2009, 10774–10786.
11 H. J. Zhu and T. Ziegler, Organometallics, 2008, 27, 1743–1749.
12 L. T. Haar, K. P. Jensen, J. Boesen and H. E. M. Christensen, J. Inorg.
Biochem., 2010, 104, 136–145.
13 J. Goodman, V. V. Grushin, R. B. Larichev, S. A. MacGregor, W.
J. Marshall and D. C. Roe, J. Am. Chem. Soc., 2010, 132, 12013–
12026.
14 (a) M. Ochiai, T. Sueda, K. Miyamoto, P. Kiprof and V. Zhdankin,
Angew. Chem., Int. Ed., 2006, 45, 8203–8206; (b) E. M. Shustorovidh
and Yu. A. Buslaev, Inorg. Chem., 1976, 15, 1142–1147.
15 (a) K. Krogh-Jespersen, M. D. Romanelli, J. H. Melman, T. J. Emge
and J. G. Brennan, Inorg. Chem., 2010, 49, 552–560; (b) T. J. Emge, A.
Komienko and J. G. Brennan, Acta Crystallogr., Sect. C: Cryst. Struct.
Commun., 2009, 65, m422–m425.
Acknowledgements
16 T. G. Appleton, H. G. Clark and L. E. Manzer, Coord. Chem. Rev.,
1973, 10, 335–422.
17 D. Jaganyi, D. Reddy, J. A. Gertenbach, A. Hofmann and R. van Eldik,
Dalton Trans., 2004, 33, 299–304.
18 See, for instance, A. Hoffmann, L. Dahlenburg and R. van Eldik, Inorg.
Chem., 2003, 42, 6528–6538.
We thank the Italian Ministry of Education and Scientific
Research for financial support. A. F. acknowledges CASPUR for
computational resources within the project “Standard HPC Grant
2011”.
19 L. Rigamonti, C. Manasseo, M. Rusconi, M. Manassero and A. Pasini,
Dalton Trans., 2009, 38, 1206–1213.
20 L. Rigamonti, M. Rusconi, C. Manassero, M. Manassero and A. Pasini,
Inorg. Chim. Acta, 2010, 363, 3498–3505.
21 C. J. Jamson, in Multinuclear NMR, ed. J. Mason, Plenum Press, New
York, 1987, pp. 89–131.
References
1 (a) A. Pidcock, R. E. Richards and L. M. Venanzi, J. Chem. Soc. (A),
1966, 1007–1710; (b) L. M. Venanzi, Chem. Brit., 1968, 4, 162–167;
(c) F. H. Allen and A. Pidcock, J. Chem. Soc. (A), 1968, 2700–2704;
(d) F. H. Allen and S. N. Sze,, J. Chem. Soc. (A), 1971, 2054–2056.
2 Examples of recent studies: (a) A. Abbassi, M. Yu. Skripkin, L. Erikson
and N. Torapava, Dalton Trans., 2011, 40, 1111–1118; (b) F. D. Rochon,
C. Bensimon and C. Tessier, Inorg. Chim. Acta, 2008, 361, 16–28; (c) C.
Hansson, M. Lindqvist and A. Oskarsson, Acta Crystallogr., Sect.
B: Struct. Sci., 2008, B64, 187–195; (d) S. Schmidt, S. Angel and Z.
Kramer, J. Coord. Chem., 2007, 60, 1809–1816; (e) P. H. Russel, M. A.
Meyer, M. D. Tawa, A. J. Ward, A. Williamson, A. L. Rheingold and
L. N. Zakharov, Inorg. Chem., 2004, 43, 747–756; (f) Y. Yamaguchi-
Teresaki, T. Fujihara and S. Kaizaki, Eur. J. Inorg. Chem., 2007, 3394–
3399; (g) J. C. Toledo, B. S. Lima Neto and D. W. Franco, Coord. Chem.
Rev., 2005, 249, 419–431; (h) M. A. Bennett, S. K. Suresh, S. H. Priver
and A. C. Willis, Eur. J. Inorg. Chem., 2008, 3467–3481.
3 (a) P. K. Sajith and C. H. Suresh, Dalton Trans., 2010, 39, 815–822;
(b) A. E. Anastasi and R. J. Deeth, J. Chem. Theory Comput., 2009,
5, 2339–2352; (c) P. N. Kapoor and R. Kakkar, THEOCHEM, 2004,
679, 149–156; (d) H. Terao, S. Ninomiya, M. Hashimoto and K. Eda,
J. Mol. Struct., 2010, 965, 68–73; (e) J. Kuta, J. Wuerges, L. Randaccio
and P. M. Kozlowski, J. Phys. Chem., 2009, 113, 11604–11612; (f) O.
Picazo, I. Alkorta, J. Elguero, M. R. Sundberg and J. Valo, Eur. J. Inorg.
Chem., 2007, 324–332.
22 P. G. Waddell, A. M. Slawin and J. D. Woollins, Dalton Trans., 2010,
39, 8620–8625.
23 D. Jaganyi, A. Hofmann and R. van Eldik, Angew. Chem., Int. Ed.,
2001, 40, 1680–1683.
24 F. Yamashita, H. Kuniyasu, J. Terrao and N. Kambe, J. Chem. Soc.,
Dalton Trans., 1989, 1149–1159.
25 G. K. Anderson, H. C. Clark and J. A. Davies, Inorg. Chem., 1983, 22,
434–438.
26 C. Hansch, A. Leo and R. W. Taft, Chem. Rev., 1991, 91, 165–195.
27 D. D. Perrin, Dissociation constants of organic bases in aqueous solution,
Butterworths, London, 1965.
28 A. E. Reed, L. A. Curtiss and F. Weinhold, Chem. Rev., 1988, 88,
899–926.
29 R. F. W. Bader, Atoms in molecules—A Quantum Theory, Oxford
University Press, Oxford, 1990.
30 W. Koch and M. C. Holthausen, A Chemist’s Guide to Density
Functional Theory, Wiley-VCH, New York, 2nd Edition, 2000.
31 P. J. Stang, M. H. Kowalski, M. D. Schiavelli and D. Longford, J. Am.
Chem. Soc., 1989, 111, 3347–3356.
1
32 In Pt(II) complexes there is a neat correlation between JPtP and the
donor power of arylphosphines, suggesting that p back donation to
P is negligible, see, for instance, J. C. Cobley and P. G. Pringle, Inorg.
Chim. Acta, 1997, 265, 107–115.
4 L. Rigamonti, A. Forni, M. Manassero, C. Manassero and A. Pasini,
Inorg. Chem., 2010, 49, 123–135.
33 A. Forni, L. Rigamonti and A. Pasini, unpublished results.
34 F. R. Hartley, Organomet. Chem. Rev., Sect. A, 1970, 6, 119–137.
35 M. Alesi, S. Fantasia, M. Manassero and A. Pasini, Eur. J. Inorg. Chem.,
2006, 1429–1435.
5 M. P. Mitoraj, H. Zhu, A. Michalak and T. Ziegler, Int. J. Quantum
Chem., 2009, 109, 3379–3386.
6 (a) Z. Chval, M. Sip and J. V. Burda, J. Comput. Chem., 2008, 29, 2370–
2381; (b) A. Yu. Sokolov and O. V. Sizova, Russ. J. Gen. Chem., 2010,
80, 1223–1231.
7 (a) J. A. Dimmer, H. Schubert and L. Wassermann, Chem.–Eur. J.,
2009, 15, 10613–10619; (b) J. Zhu and Z. Lin, Inorg. Chem., 2005,
44, 9384–9390; (c) S. Subramanium and L. M. Slaughter, ACS Natl.
Meeting, March 2011, Book of abstracts and L. M. Slaughter, personal
communication; (d) Y. A. Wanniarachchi, K. Yuri and L. M. Slaughter,
Organometallics, 2008, 27, 21–24; (e) K. A. Netland, A. Krivokapic and
M. Tilset, J. Coord. Chem., 2010, 63, 2909–2927; (f) M. S. Datt, J. J.
Nair and S. Otto, J. Organomet. Chem., 2005, 690, 3422–3426.
8 For instance: (a) J. N. Harvey, K. M. Heslop, A. G. Orpen and P. G.
Pringle, Chem. Commun., 2003, 278–279; (b) G. K. Anderson and R. J.
Cross, Chem. Soc. Rev., 1980, 9, 185–215; (c) O. O. Lubimova and O.
V. Sizova, Russ. J. Coord. Chem., 2005, 31, 575–579.
9 (a) H. J. Haller, M. J. Page, S. Erhardt, S. A. MacGregor, M. F. Mahon,
A. M. Nasser, A. Velez and M. K. Whittlesey, J. Am. Chem. Soc., 2010,
113, 18408–18416; (b) S. de Visser and W. Nam, J. Phys. Chem., 2008,
112, 12887–12895.
10 (a) E. I. Montero, J. Y. Zhang, J. J. Moniodis, S. J. Bernes-Price and N.
P. Farrell, Chem.–Eur. J., 2010, 16, 9175–9185; (b) A. Galstyan, W. Z.
Shen and B. Lippert, Z. Naturforsch., B: Chem. Sci., 2009, 64, 1653–
1661; (c) P. J. Sanz Miguel, M. Roitzsch, L. Yin, P. M. Lax, L. Holland,
36 Bruker, SMART, SAINT and SADABS, Bruker AXS Inc., Madison,
Wisconsin, USA, 1997.
37 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2008,
A64, 112–122.
38 M. N. Burnett and C. K. Johnson, ORTEP-III: Oak Ridge Thermal
Ellipsoid Plot Program for Crystal Structure Illustrations, Oak Ridge
National Laboratory Report ORNL-6895, 1996.
39 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb,
J. R. Cheeseman, Jr., J. A. Montgomery, T. Vreven, K. N. Kudin, J. C.
Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci,
M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji, M.
Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.
Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox,
H. P. Hratchian, J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts,
R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J.
W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J.
J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C.
Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B.
Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski,
B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.
L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A.
10172 | Dalton Trans., 2011, 40, 10162–10173
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, C. Gonzalez and J. A. Pople, Gaussian 03, Revision B.04,
Gaussian, Inc., Pittsburgh, PA, 2003.
Chase, J. Li and T. L. Windus, J. Chem. Inf. Model., 2007, 47, 1045–
1052.
43 K. A. Peterson, D. Figgen, E. Goll, H. Stoll and M. Dolg, J. Chem.
40 (a) C. T. Lee, W. T. Yang and R. G. Parr, Phys. Rev. B, 1988, 37, 785–789;
Phys., 2003, 119, 11113–11123.
(b) A. D. Becke, J. Chem. Phys., 1993, 98, 5648–5652.
44 D. Andrae, U. Haeussermann, M. Dolg, H. Stoll and H. Preuss, Theor.
Chim. Acta, 1990, 77, 123–141.
41 F. Weigend and R. Ahlrichs, Phys. Chem. Chem. Phys., 2005, 7, 3297–
3305.
45 R. F. W. Bader, AIMPAC: A set of programs for the theory of atoms
in molecules, McMaster University, Hamilton, Ontario, Canada L8S
4M1, 1994.
42 (a) D. Feller, J. Comput. Chem., 1996, 17, 1571–1586; (b) K. L.
Schuchardt, B. T. Didier, T. Elsethagen, L. Sun, V. Gurumoorthi, J.
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 10162–10173 | 10173
©