Quantification of cis and trans influences in [PtX(PPh3) 3]+ complexes. A 31P NMR study

Article abstract of DOI:10.1016/j.ica.2010.07.002

In [PtX(PPh₃)₃]⁺ complexes (X = F, Cl, Br, I, AcO, NO₃, NO₂, H, Me) the mutual cis and trans influences of the PPh₃ groups can be considered constants in the first place, therefore the one bond Pt-P coupling constants of P _(cis) and P_{(trans )} reflect the cis and trans influences of X. The compounds [PtBr(PPh₃)₃](BF₄) (2), [PtI(PPh ₃)₃](BF₄) (3), [Pt(AcO)(PPh₃) ₃](BF₄) (4), [Pt(NO₃)(PPh₃) ₃](BF₄) (5), and the two isomers [Pt(NO ₂-O)(PPh₃)₃](BF₄) (6a) and [Pt(NO₂-N)(PPh₃)₃](BF₄) (6b) have been newly synthesised and the crystal structures of 2 and 4·CH ₂Cl₂·0.25C₃H₆O have been determined. From the ¹J_PtP values of all compounds we have deduced the series: I > Br > Cl > NO₃ > ONO > F > AcO > NO₂ > H > Me (cis influence) and Me > H > NO₂ > AcO > I > ONO > Br > Cl > F > NO ₃ (trans influence). These sequences are like those obtained for the (neutral) cis- and trans-[PtClX(PPh₃)₂] derivatives, showing that there is no dependence on the charge of the complexes. On the contrary, the weights of both influences, relative to those of X = Cl, were found to depend on the charge and nature of the complex.

Full text of DOI:10.1016/j.ica.2010.07.002

Inorganica Chimica Acta 363 (2010) 3498–3505
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Quantification of cis and trans influences in [PtX(PPh3)3]+ complexes.
A
31P NMR study
Luca Rigamonti a, Michele Rusconi a, Carlo Manassero b, Mario Manassero b,*, Alessandro Pasini a,
**
a Università degli Studi di Milano, Dipartimento di Chimica Inorganica, Metallorganica e Analitica ‘‘Lamberto Malatesta”, via Venezian 21, 20133 Milano, Italy
b Università degli Studi di Milano, Dipartimento di Chimica Strutturale e Stereochimica Inorganica, via Venezian 21, 20133 Milano, Italy
a r t i c l e i n f o
a b s t r a c t
In [PtX(PPh3)3]+ complexes (X = F, Cl, Br, I, AcO, NO3, NO2, H, Me) the mutual cis and trans influences of the
PPh3 groups can be considered constants in the first place, therefore the one bond Pt–P coupling con-
stants of P(cis) and P(trans) reflect the cis and trans influences of X. The compounds [PtBr(PPh3)3](BF4) (2),
[PtI(PPh3)3](BF4) (3), [Pt(AcO)(PPh3)3](BF4) (4), [Pt(NO3)(PPh3)3](BF4) (5), and the two isomers [Pt(NO2-
O)(PPh3)3](BF4) (6a) and [Pt(NO2-N)(PPh3)3](BF4) (6b) have been newly synthesised and the crystal struc-
tures of 2 and 4ꢀCH2Cl2ꢀ0.25C3H6O have been determined. From the 1JPtP values of all compounds we have
deduced the series: I > Br > Cl > NO3 > ONO > F > AcO > NO2 > H > Me (cis influence) and Me > H > NO2 > A-
cO > I > ONO > Br > Cl > F > NO3 (trans influence). These sequences are like those obtained for the (neutral)
cis- and trans-[PtClX(PPh3)2] derivatives, showing that there is no dependence on the charge of the com-
plexes. On the contrary, the weights of both influences, relative to those of X = Cl, were found to depend
on the charge and nature of the complex.
Article history:
Received 4 June 2010
Accepted 1 July 2010
Available online 7 July 2010
Keywords:
cis influence
trans influence
cis influence weight
trans influence weight
Platinum phosphine complexes
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
be considered an estimate of the M–L bond strength [1,13–19], but
this technique can be used only when both M and the donor atom
2
3
cis and trans influences of a ligand X can be defined as the ability
of that ligand to weaken the bond between a metal and a ligand L,
respectively, cis or trans to X [1–6]. The comprehension of these
influences is therefore important for understanding and rationalis-
ing some properties of square planar and octahedral transition me-
tal complexes. These include stability, occurrence of geometrical
isomers, bond strengths, as well as ligand reactivity (through the
link with the cis and trans effects) [1–5]. Because of such
importance, these influences have been the subject of many inves-
tigations from their early recognition [6] to the present days
[2,3,7–10]. Interestingly, the scope of these influences has recently
been expanded, since they were found to play a role also in main
group [11] and lanthanide chemistry [12].
These studies were mostly based on either X-ray crystallogra-
phy or spectroscopic (IR and NMR) investigations, although both
techniques suffer some limitations. Thus X-ray derived M–L bond
lengths may be affected by crystal packing and conformational ef-
fects and only few M–L bond stretches can be unambiguously as-
signed (M–H, certain M–Cl and few others); CO stretching
frequencies have also been used [13]. NMR investigations are usu-
ally based on the values of one bond coupling constants, which can
of L are NMR active (195Pt–31P, 103Rh–31P, etc.). JMC and JMH have
also been employed [1,20].
We have recently been studying cis and trans influences in Pt(II)
bis(triphenylphosphine) complexes. In a first paper [21] we have
used the one bond Pt–P coupling constants to evaluate the order
of cis influence of some anionic ligands X and Y in a series of
trans-[PtXY(PPh3)2] complexes (type A, see Scheme 1). In these
compounds the mutual trans influence of the two phosphine
groups can be considered constant throughout the series, conse-
1
quently JPtP of the various derivatives give an insight of the cis
influence of X and Y.
A second paper [14] dealt with the cis-[PtXY(PPh3)2] isomers
(type B of Scheme 1). Here each P atom experiences the cis influ-
ence of a PPh3 group, the trans influence of X and the cis influence
of Y (or the other way round). Assuming that the mutual cis influ-
1
ence of the two phosphine groups is constant, the JPtP values of
each P nucleus depends on the cis and trans influences of X and
Y. We have been able to discriminate the two influences, showing
that the former, although of lower importance, is by no means
1
irrelevant and must be taken into account when rationalising JPtP
as well as Pt–P bond distances. We could also justify the sequences
of both influences in terms of Pt–P bonding and charge on Pt [14].
We were also interested in quantifying the influences, i.e. to
ascertain ‘‘how much” a given X (or Y) ligand influences the Pt–P
bonds cis or trans to such ligand, in other words the cis or trans
* Corresponding author.
** Corresponding author.
E-mail address: alessandro.pasini@unimi.it (A. Pasini).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.07.002

L. Rigamonti et al. / Inorganica Chimica Acta 363 (2010) 3498–3505
3499
+
Ph
Ph
Ph
Ph
Ph
P1
Ph
Ph
Ph
Ph
Ph
Ph
Ph
P
Y
P
Y
X
P1
P2
Cl
P1
P2
P3
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Pt
Pt
Pt
Pt
Ph
Ph
P2
X
X
X
Ph
Ph
Ph
Ph
type A
type B
type C
Scheme 1.
weight of X (or Y). Since there is no possibility of obtaining the
absolute values of such ability, we used the cis and trans influences
of Cl as references, putting its abilities to zero. The difference be-
tween 1JPtP of the Cl derivative with that of a compound with a gi-
ven X, gives an estimate of such ability, i.e. how much X influences
the Pt–P bonds (either cis or trans) with respect of Cl [14,10–22].
Since these two investigations dealt with neutral compounds,
we wondered whether charged species would affect the cis and
trans sequences and/or their weights. Therefore we extended our
study to a series of cationic complexes of formula [PtX(PPh3)3](BF4)
(type C, Scheme 1: X = Cl, 1; Br, 2; I, 3; AcO, 4; NO3, 5; NO2-O, 6a;
NO2-N, 6b; F, 7; H, 8 and Me, 9). Besides the interest in the compar-
ison with the neutral compounds, the ligand X is trans to a phos-
phine (P1 in Scheme 1) and cis to two other phosphine groups
(P2 and P3, Scheme 1) therefore we can observe both influences
of X within the same complex. This can be done if we assume, in
the first place, that the mutual cis and trans influences of the three
PPh3 groups are constant.
2.2.2. Synthesis of [PtBr(PPh3)3](BF4) (2)
PPh3 (18.9 mg, 0.072 mmol) was added to a solution of [Pt2(
l-
Br)2(PPh3)4](BF4)2 (63.9 mg, 0.036 mmol) in nitromethane (2 mL)
and the mixture was stirred at room temperature for 30 min. Diiso-
propyl ether (40 mL) was added yielding a white solid (69.2 mg,
84% yield). 31P NMR (121 MHz, CDCl3, 25 °C): d = 12.5 (t,
1
2
2JPP = 18.0 Hz, JPtP = 3624 Hz, 1P, P(trans)), 19.4 (d, JPP = 18.0 Hz,
1JPtP = 2468 Hz, 2P, P(cis)). IR:
m
(BF4) 1053 cmꢁ1. Anal. Calc. for
C56H45BBrF4P3Pt: C, 56.46; H, 3.95. Found: C, 56.18; H 4.15%. Crys-
tals suitable for X-ray diffraction were obtained by slow diffusion
of diisopropyl ether into a dichloromethane solution.
2.2.3. Synthesis of [PtI(PPh3)3](BF4) (3) [27]
The reaction was performed under a nitrogen atmosphere with
the use of the Schlenk technique. A solution of AgBF4 (15.5 mg,
0.079 mmol) in acetone (5 mL) was added to a solution of trans-
[PtI2(PPh3)2] (76.6 mg, 0.079 mmol) in dichloromethane (10 mL);
the mixture was stirred at room temperature for 1 h, and then fil-
tered. The solvent was removed under reduced pressure and the
residue was dissolved in nitromethane and then PPh3 (53.2 mg,
0.20 mmol) was added. The mixture was stirred at room tempera-
ture for 2 h, concentrated and treated with diethyl ether, yielding a
yellow solid. (52.2 mg, 55% yield). 31P NMR (121 MHz, CDCl3,
2. Experimental
2.1. General
2
1
25 °C): d = 8.1 (t, JPP = 17.6 Hz, JPtP = 3480 Hz, 1P, P(trans)), 12.4
All chemicals were reagent grade. Solvents were used as re-
ceived. Elemental analyses were performed at the Microanalytical
Laboratory at the Università degli Studi di Milano. 1H and 31P{1H}
NMR spectra were recorded on a Bruker Advance DRX 300 at 300
and 121 MHz, respectively; dH values are in ppm versus external
2
1
(d, JPP = 17.6 Hz, JPtP = 2459 Hz, 2P, P(cis)). 31P NMR (121 MHz,
2
1
d6-acetone, 25 °C): d = 8.3 (t, JPP = 17.6 Hz, JPtP = 3511 Hz, 1P,
2
1
P
(trans)), 12.5 (d, JPP = 17.6 Hz, JPtP = 2474 Hz, 2P, P(cis)). IR: m(BF4)
1055 cmꢁ1. Anal. Calc. for C54H45BF4IP3Pt: C, 54.25; H, 3.79. Found:
1
C, 53.83; H 4.23%.
Me4Si, dP values are in ppm versus external H3PO4, JPtP coupling
constants (Hz) have been found reproducible to 3 Hz. Infrared
spectra were recorded from KBr disks with a JASCO FT-IR 410 spec-
trophotometer having 2 cmꢁ1 resolution.
2.2.4. Synthesis of [Pt(AcO)(PPh3)3](BF4) (4)
The reaction was performed under a nitrogen atmosphere with
the use of the Schlenk technique. A solution of AgBF4 (12.1 mg,
0.062 mmol) in acetone (2 mL) was added to a solution of cis-
[PtCl(AcO)(PPh3)2] (51.2 mg, 0.062 mmol) in dichloromethane
(5 mL) and the mixture was stirred at room temperature for 1 h,
then it was filtered. PPh3 (26.0 mg, 0.099 mmol) was added and
the solution was left under stirring for 1 h, and then treated with
diisopropyl ether (40 mL) yielding a white solid (44.0 mg, 63%
yield). 1H NMR (300 MHz, CDCl3, 25 °C): d = 0.28 (s, 3H, CH3). 31P
NMR (121 MHz, CDCl3, 25 °C): d = 3.5 (t, 2JPP = 19.8 Hz,
cis-[PtCl2(PPh3)2]
[14,23],
[Pt2(l
-Cl)2(PPh3)4](BF4)2
[24],
[PtCl(PPh3)3](BF4) (1) [25,26], cis-[PtBr2(PPh3)2] [14], cis-[PtCl(A-
cO)(PPh3)2] [14] and trans-[PtI2(PPh3)2] [14,21] were synthesised
as described in the literature. All reactions involving silver salts
were performed in the dark.
2.2. Preparation of complexes
2.2.1. Synthesis of [Pt2(
This reaction was performed under a nitrogen atmosphere
using the Schlenk technique. solution of AgBF4 (42.8 mg,
l-Br)2(PPh3)4](BF4)2
2
1
1JPtP = 3478 Hz, 1P, P(trans)), 22.7 (d, JPP = 19.8 Hz, JPtP = 2676 Hz,
2P, P(cis)). IR: (C@O) 1634, 1368, 1308,
m
m
(BF4), 1056 cmꢁ1. Anal.
A
Calc. for C56H48BF4O2P3Pt: C, 59.64; H, 4.29. Found: C, 59.71; H,
4.64%. Crystals suitable for X-ray diffraction were obtained by
slow diffusion of diisopropyl ether into
solution.
0.23 mmol) in acetone (3 mL) was added to a solution of cis-
[PtBr2(PPh3)2] (200.1 mg, 0.23 mmol) in dichloromethane (15 mL)
and the mixture was stirred at room temperature for 2 h and fil-
tered. The solution was concentrated by evaporation under re-
duced pressure, and treated with diisopropyl ether (40 mL)
a dichloromethane
yielding a white solid (112.7 mg, 55% yield). 31P NMR (121 MHz,
2.2.5. Synthesis of [Pt(NO3)(PPh3)3](BF4) (5) [26]
1
CDCl3, 25 °C): d = 16.1 (s, JPtP = 3747 Hz). IR:
m
(BF4) 1054 cmꢁ1
AgNO3 (8.4 mg, 0.049 mmol) was added to a solution of
Anal. Calc. for C72H60B2Br2F8P4Pt2: C, 48.78; H, 3.41. Found: C,
[PtCl(PPh3)3](BF4) (1) (31.1 mg, 0.028 mmol) in dichloromethane
49.27; H 3.73%.
(10 mL) and the mixture was refluxed for 2.5 h, hot filtered, the

3500
L. Rigamonti et al. / Inorganica Chimica Acta 363 (2010) 3498–3505
filtrate was concentrated under reduced pressure and treated with
diisopropyl ether (40 mL) yielding a white solid (18.1 mg, 57%
and the mixture was stirred at 50 °C for 30 min. The yellow solid
was filtered, washed with diisopropyl ether and dried in vacuo
(46.7 mg, 60% yield). 31P NMR (121 MHz, CDCl3, 25 °C): d = 20.3
(s, JPtP = 2596 Hz, 2P). Anal. Calc. for C36H30BrClP2Pt: C, 51.78; H,
3.62. Found: C, 51.67; H, 3.65%.
2
yield). 31P NMR (121 MHz, CDCl3, 25 °C): d = 2.7 (t, JPP = 19.2 Hz,
2
1
1
1JPtP = 3761 Hz, 1P, P(trans)), 22.2 (d, JPP = 19.2 Hz, JPtP = 2609 Hz,
2P, P(cis)). IR:
54H45BF4NO3P3Ptꢀ4H2O: C, 53.92; H, 4.40; N, 1.16. Found: C,
53.93; H, 4.27; N, 1.19%.
m
(NO3) 1516, 1265
m
(BF4) 1057 cmꢁ1. Anal. Calc. for
C
2.3. X-ray data collections and structure determinations
2.2.6. Synthesis of [Pt(NO2)(PPh3)3](BF4) (6a) and
[Pt(ONO)(PPh3)3](BF4) (6b)
The reaction was performed under a nitrogen atmosphere with
the use of the Schlenk technique. AgNO2 (13.7 mg, 0.089 mmol)
Crystal data are summarised in Table 1. The diffraction experi-
ments were carried out on a Bruker APEX II CCD area-detector dif-
fractometer, at 296 K for 2, and at 150 K for 4ꢀCH2Cl2ꢀ0.25C3H6O,
using Mo Ka radiation (k = 0.71073 Å) with a graphite crystal
was added to
a solution of [PtCl(PPh3)3](BF4) (1) (83.1 mg,
monochromator in the incident beam. No crystal decay was ob-
served, so that no time-decay correction was needed. The collected
frames were processed with the software SAINT [28], and an empir-
ical absorption correction was applied (SADABS) [29] to the collected
reflections. The calculations were performed using the Personal
Structure Determination Package [30] and the physical constants
tabulated therein [31]. The structures were solved by direct meth-
ods (SHELXS) [32] and refined by full-matrix least-squares, using all
0.075 mmol) in dichloromethane (20 mL) and the mixture was re-
fluxed for 7 h. The filtered solution was concentrated under re-
duced pressure and treated with diisopropyl ether (40 mL)
yielding a white solid (45.7 mg, 55% yield). 31P NMR (121 MHz,
CDCl3, 25 °C): d = ꢁ1.4 (t, 2JPP = 21.4 Hz, 1JPtP = 2838 Hz, 1P, P(trans)),
2
1
15.0 (d, JPP = 21.4 Hz, JPtP = 2692 Hz, 2P, P(cis)): [Pt(NO2)(PPh3)3]
2
1
(BF4) (6a); d = 3.5 (t, JPP = 18.4 Hz, JPtP = 3520 Hz, 1P, P(trans)),
2
1
2
2
reflections and minimising the function
R
wðF2o ꢁ kFc Þ (refinement
21.5 (d, JPP = 18.4 Hz, JPtP = 2633 Hz, 2P, P(cis)): [Pt(ONO)
(PPh3)3](BF4) (6b). 31P NMR (121 MHz, acetone-d6, 25 °C): d =
on F2). In the asymmetric unit of compound 4ꢀCH2Cl2ꢀ0.25C3H6O
there are two disordered half molecules of CH2Cl2, whose atoms
have occupancy factors of 0.50 each, and one disordered half mol-
ecule of C3H6O, whose atoms have also occupancy factors of 0.50
each (see Section 3). All the non-hydrogen atoms of these disor-
dered molecules, having occupancy factors of 0.50, have been re-
fined with isotropic thermal factors, and their hydrogen atoms
have been ignored. All the other non-hydrogen atoms of both com-
pounds have been refined with anisotropic thermal parameters,
and all their hydrogen atoms have been placed in ideal positions
(C–H = 0.970 Å), with the thermal parameter U being 1.10 times
that of the atom to which they are attached, and not refined. For
the non-centrosymmetric compound 2, both the inverted structure
models were fully refined: final R2 and R2w indices were 0.076 and
0.103 for the correct one, and 0.081 and 0.111 for the other. In the
final Fourier maps the maximum residuals were 3.44(1.32) e Åꢁ3 at
0.25 Å from Pt, and 2.54(46) e Åꢁ3 at 0.38 Å from Pt1, for 2 and
4ꢀCH2Cl2ꢀ0.25C3H6O, respectively. Minimum peaks (holes), in the
2
1
ꢁ1.4 (t, JPP = 22.3 Hz, JPtP = 2817 Hz, 1P, P(trans )), 14.9 (d,
1
2JPP = 22.3 Hz, JPtP = 2727 Hz, 2P, P(cis)): [Pt(NO2)(PPh3)3](BF4)
2
1
(6a); d = 3.6 (t, JPP = 19.0 Hz, JPtP = 3478 Hz, 1P, P(trans)), 21.4 (d,
2JPP = 19.0 Hz, JPtP = 2649 Hz, 2P, P(cis)): [Pt(ONO)(PPh3)3](BF4)
1
(6b). IR: m(NO) 1322, 1286, 1177, 886, 850, m
(BF4) 1056 cmꢁ1. Anal.
Calc. for C54H45BF4NO2P3Pt: C, 58.18; H, 4.07; N, 1.26. Found: C,
58.43; H, 4.13; N, 1.14%.
2.2.7. Synthesis of [PtBr2(CH3CN)2]
KBr (1000.2 mg, 8.40 mmol) was added to a solution of K2[PtCl4]
(155.7 mg, 0.38 mmol) in water (5 mL) and the solution was left at
room temperature for 15 min. Acetonitrile (2 mL) was added and
the mixture was refluxed for 2.5 h, then cooled. The yellow solid
was filtered, washed with water and dried in vacuo (76.1 mg,
46% yield). IR:
m
(C„N) 2337 cmꢁ1. Anal. Calc. for C4H6Br2N2PtꢀKBr:
C, 8.64; H, 1.08; N, 5.03. Found: C, 8.66; H, 1.01; N, 4.65%.
same order, were ꢁ2.84(1.32), and ꢁ1.47(46) e Åꢁ3
.
2.2.8. Synthesis of trans-[PtBr2(PPh3)2]
PPh3 (50.8 mg, 0.19 mmol) was added to
a solution of
[PtBr2(CH3CN)2] (54.9 mg, 0.099 mmol) in nitromethane (5 mL)
and the mixture was stirred at 50 °C for 30 min. The yellow solid
was filtered, washed with diisopropyl ether and dried in vacuo
(85.7 mg 99% yield). 31P NMR (121 MHz, CDCl3, 25 °C): d = 19.3
3. Results and discussion
3.1. Synthesis and characterisation
1
(s, JPtP = 2561 Hz, 2P)1. Anal. Calc. for C36H30Br2P2Pt: C, 49.17; H,
The synthetic paths to compounds C are outlined in Scheme 2.
All complexes were all isolated as their BF4 salts. Compound 2
was obtained through a reaction sequence similar to that reported
for 1 [24–26]: reaction of cis-[PtBr2(PPh3)2] with AgBF4 gives the
3.44. Found: C, 48.95; H 3.25%.
2.2.9. Synthesis of [PtBrCl(CH3CN)2]
KBr (180.9 mg, 1.52 mmol) was added to a solution of K2[PtCl4]
(157.7 mg, 0.38 mmol) in water (5 mL) and the mixture was stirred
at room temperature for 15 min. Acetonitrile (2 mL) was added, the
mixture was refluxed for 2.5 h, cooled and the yellow solid was fil-
tered, washed with water and dried in vacuo (52.8 mg, 35% yield).
dinuclear [Pt2(l
-Br)2(PPh3)4]2+, which, upon treatment with PPh3,
yields 2. Compounds 3 and 4 were prepared by similar methods
starting from trans-[PtI2(PPh3)2] and cis-[Pt(AcO)Cl(PPh3)2], respec-
tively, without isolating the dinuclear intermediates. The NO3 (5)
and NO2 (6a and 6b) complexes were obtained by metathesis reac-
tions, treating 1 with the appropriate silver salt. The reaction with
AgNO2 (performed under strict anaerobic conditions since nitrite is
easily oxidised under these conditions [14]) gave a solid which
analysed correctly for [Pt(NO2)(PPh3)2](BF4), whose IR spectrum
showed bands suggestive of the presence of the nitro and nitrito
linkage isomers [33] (see Section 2). The 31P NMR spectrum of this
material showed two sets of 31P triplets and doublets, in approxi-
mately 1:1 ratio. One set is assigned to [Pt(NO2-N)(PPh3)3]+ on
the grounds of the similarity of the chemical shifts and Pt–P cou-
pling constants (see Table 2) with those of trans-[PtCl(NO2-
IR:
m
(C„N) 2338 cmꢁ1. Anal. Calc. for C4H6BrClN2Ptꢀ1.5H2O: C,
11.46; H, 2.16; N, 6.68. Found: C, 11.46; H, 1.72; N, 6.38%.
2.2.10. Synthesis of trans-[PtBrCl(PPh3)2]
PPh3 (47.9 mg, 0.18 mmol) was added to
a solution of
[PtBrCl(CH3CN)2] (39.2 mg, 0.093 mmol) in nitromethane (10 mL)
1
Excess of PPh3 must be avoided, since it catalyses isomerisation to the cis isomer.
31P NMR (121 MHz, CDCl3, 25 °C): d = 14.3 (s, JPtP = 3614 Hz, 2P). This behaviour is
1
opposite to that of [PtI2(PPh3)2] which, in the presence of excess of PPh3 is converted
quantitatively to the trans isomer [14].
1
N)(PPh3)2] (d, 16.6 ppm; JPtP, 2760 Hz) and, particularly, with

L. Rigamonti et al. / Inorganica Chimica Acta 363 (2010) 3498–3505
3501
Table 1
Crystallographic data.
Compound
2
4ꢀCH2Cl2ꢀ0.25C3H6O
Formula
M
Colour
Crystal system
Space group
a (Å)
C
54H45BBrF4P3Pt
C231H203B4Cl8F16O9P12Pt4
4906.8
pale yellow
1148.69
colourless
orthorhombic
Pna21
20.1334(10)
18.1811(9)
13.0873(6)
90
90
90
4790.6(4)
4
triclinic
ꢀ
P1
12.8129(7)
21.0111(11)
21.7134(11)
70.270(1)
86.620(1)
75.770(1)
5331.7(5)
1
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
U (Å3)
Z
F(0 0 0)
Dcalc (g cmꢁ3
T (K)
2272
1.593
296
2453
1.528
150
)
k (Mo K
Crystal dimensions (mm)
(Mo K
) (cmꢁ1
a
)
0.71073
0.17 ꢂ 0.23 ꢂ 0.35
39.34
0.71073
0.09 ꢂ 0.38 ꢂ 0.46
29.03
l
a
)
Minimum and maximum transmission factors
Scan mode
0.763–1.000
x
0.691–1.000
x
Frame width (°)
0.50
0.50
Time per frame (s)
20
20
Number of frames
3300
3300
Detector-sample distance (cm)
5.00
5.00
h-range (°)
3.00–30.00
full sphere
163 445, 15 227
0.0322
0.076, 0.103
0.042
3.00–29.00
full sphere
181 579, 33 227
0.0413
0.060, 0.095
0.034
Reciprocal space explored
Number of reflections (total; independent)
Rint
Final R2 and R2w indices (F2, all reflections)
a
Conventional R1 index [I > 2r(I)]
Reflections with I > 2
r(I)
8229
22 448
Number of variables
576
0.985
1274
0.968
Goodness-of-fit (GOF)b
2
ðjF2o ꢁ kF2c jÞ=
R
F2o ꢃ, R2w ¼ ½
R
wðF2o ꢁ kFc Þ =
R
r
wðF2o Þ ꢃ
.
2
2
1=2
a
R2 ¼ ½
R
2
c
2
1=2
2
2
ðF2o Þ ¼ ½r2ðFo2Þ þ ðpFo2Þ ꢃ1=2, No is the number of observations, Nv the number of vari-
b
½
R
wðF2o ꢁ kF Þ =ðNo ꢁ N Þꢃ , where w ¼ 4F2o =
ðF2o Þ ,
r
v
ables, and p = 0.02 for 2, and =0.04 for 4ꢀCH2Cl2ꢀ0.25C3H6O.
1
those of cis-[Pt(NO2-N)2(PPh3)2] (d, ꢁ1.3 ppm; JPtP
,
3148 Hz)
cations, two crystallographic independent anions, one ordered
molecule of CH2Cl2 (occupancy factors = 1.00), two, intersected
and disordered, half molecules of CH2Cl2 (occupancy factors = 0.50
for each atom), and one half molecule of acetone (occupancy fac-
tors = 0.50 for each atom), disordered and lying near a crystallo-
graphic inversion centre. For ease of comparison, we have
labelled the inner core atoms of one of the two independent cat-
ions as Pt1, P1, P2, P3, O1, C1, O2, and C2 (cation 1 in Table 2),
and the corresponding atoms of the other cation (cation 2 in Table
[14,21]. The other set of resonances is assigned to the NO2-O iso-
mer: both the chemical shifts and the Pt–P coupling constants
are very similar to those of [Pt(NO3)(PPh3)3]+ and of [Pt(A-
cO)(PPh3)3]+ (Table 2), i.e. to compounds with a PtO(anionic)P3
coordination set. We were unable to isolate the two isomers be-
cause of the very similar physico-chemical properties. In the case
of 2 and 4 we could obtain crystals suitable for X-ray diffraction
studies (see Section 2).
*
*
*
*
*
*
*
*
2) Pt1 , P1 , P2 , P3 , O1 , C1 , O2 , and C2 . An ORTEP view of the
asterisked cation is shown in Fig. 2. Selected bond parameters for
both cations are listed in Table 3. The conformations of the ligands
of the two independent cations are identical, as far as the phos-
phine moieties are concerned, including the phenyl carbon atoms
(the conformations of the corresponding ligands in the cation of
2 are not identical, but actually very similar, as can be seen com-
paring Figs. 1 and 2). On the contrary, the conformations of the
two acetato ligands are different. Atom Pt1 displays a square-pla-
nar coordination with a square-pyramidal distortion, maximum
displacements from the least-squares plane being +0.028(3) and
ꢁ0.042(1) Å for atoms O1 and Pt1, respectively. From the point
of view of planarity, the asterisked cation is different. Thus, atom
3.2. Description of the crystal and molecular structures of 2 and of
4ꢀCH2Cl2ꢀ0.25C3H6O
The structure of 2 consists of the packing of [PtBr(PPh3)3]+ cat-
ions and BF4 anions in the molar ratio 1:1 in the orthorhombic
ꢁ
non-centrosymmetric space group Pna21. An ORTEP view of the
cation is shown in Fig. 1. The metal atom displays a square-planar
geometry with a slight tetrahedral distortion, maximum displace-
ments from the least-square plane being +0.049(2) and
ꢁ0.061(3) Å for atoms Br and P3, respectively. Selected bond
lengths and angles are reported in Table 3, together with the cor-
responding values of 4ꢀCH2Cl2ꢀ0.25C3H6O (see below) and some
data adapted from the literature of [PtCl(PPh3)3](ClO4)ꢀ2CH2Cl2
(1ꢀ2CH2Cl2) [36], for comparison.
*
Pt1 adopts a square-planar coordination with a slight tetrahedral
distortion, maximum displacements from the least-squares planes
*
*
The structure of 4ꢀCH2Cl2ꢀ0.25C3H6O consists of the packing of
being +0.031(1) and ꢁ0.026(1) Å for atoms P3 and P1 , respec-
tively. The two acetato ligands are strictly planar. The dihedral an-
gles between the metal atom best planes and the planes of their
acetato ligands are 117.5(1) and 73.9(1)°, for cation 1 and the
asterisked cation, respectively.
[Pt(AcO)(PPh3)3]+ cations, BF4 anions, dichloromethane solvent
ꢁ
molecules, and acetone solvent molecules, in the molar ratio
1:1:1:0.25, in the triclinic space group P1. The asymmetric unit
of 4ꢀCH2Cl2ꢀ0.25C3H6O contains two crystallographic independent
ꢀ

3502
L. Rigamonti et al. / Inorganica Chimica Acta 363 (2010) 3498–3505
Br
Br
PPh3
PPh3
I
Br
Br
I
PPh3
PPh3
PPh3
PPh3
Ph3P
Br
PPh3
PPh3
PPh3
PPh3
Ph3P
Ph3P
Ph3P
Ph3P
AgBF4
-AgBr
2 PPh3
Pt
Pt
Pt
Pt
(BF4)2
Pt
Pt
Pt
(BF4)
(BF4)
2
[27]
Ph3P
I
Ph3P
I
AgBF4
-AgI
2 PPh3
(BF4)2
(BF4)
Pt
PPh3
I
3
Ph3P
I
acetone
PPh3
Pt
Cl
AcO
Ph3P
Cl
PPh3
PPh3
PPh3
PPh3
Ph3P
AcO
PPh3
PPh3
AgBF4
-AgCl
2 PPh3
intermediate(s) not isolated
and/or characterized
Pt
Pt
(BF4)
4
Ph3P
X
PPh3
PPh3
5
(X = ONO2)
6a (X = NO2)
6b (X = ONO)
AgX
Pt
Pt
(BF4)
(BF4)
-AgCl
1
Scheme 2.
Table 2
31P NMR data for [PtX(PPh3)3]+ (type C) complexes.a
P2 and P3 (cis to X)
P1 (trans to X)
X
d
1JPtP
d
1JPtP
I (3)
Br (2)
Cl (1)
ONO2 (5)
ONO (6b)
F (7) [34]
AcO (4)
NO2 (6a)
H (8) [35]
Me (9) [35]
12.4
19.4
23.4
22.2
21.5
26.5
22.7
15.0
22.5
28.4
2459
2468
2487
2609
2633
2640
2676
2692
2821
2931
8.3
12.5
12.8
2.7
3.5
3.0
3480
3624
3647
3761
3520
3701
3478
2838
2219
1919
3.5
ꢁ1.5
23.1
20.2
a
1
d values in ppm versus aqueous H3PO4, JPtP values in Hz.
In all the three cations, the steric hindrance of the three phos-
phine groups forces the two P(cis)–Pt–P(trans) angles to be greater
than 90°.
3.3. NMR studies
3.3.1. NMR Spectra
The 31P NMR spectra of type C complexes are reported in Table
2, where the compounds have been arranged in the order of
decreasing cis influence (see below). The spectra consist of a dou-
blet and a triplet, at higher fields, due to P(cis) and P(trans), respec-
2
Fig. 1. ORTEP view of cation [PtBr(PPh3)3]+ in compound [PtBr(PPh3)3](BF4) (2).
Ellipsoids are drawn at the 30% probability level. The BF4 anion and the hydrogen
atoms have been omitted for clarity.
tively. JPP values are in the 18–21 Hz range. There does not seem
ꢁ
to be a simple relationship between dP and the nature of X, except
for the halides derivatives, whose dPcis is shifted to lower fields
with increasing electronegativity.
3.3.2. cis and trans influences series
The former sequence is like that obtained in the case of type A
and B complexes [14,21] and similar to what is usually reported in
the literature [16,18,19], showing that this order is independent on
the charge of the complex. The trans sequence differs from that ob-
tained for type B complexes only for the position of I, which was
found lower than Cl, but was probably affected by some uncer-
tainty [14]. With this exception, also the trans influence sequence
can be considered independent on the charge of the complex.
1
Remembering the definition of influence and that higher JPtP
values correspond to stronger Pt–P bonds, the coupling constants
reported in Table 2 give the sequences:
I > Br > Cl > NO3 > ONO > F > AcO > NO2 > H > Me (cis influence)
Me > H > NO2 > AcO > I > ONO > Br > Cl > F > NO3
influence)
(trans

L. Rigamonti et al. / Inorganica Chimica Acta 363 (2010) 3498–3505
3503
Table 3
Selected bond lengths (Å) and angles (°) for 1ꢀ2CH2Cl2a, 2 and 4ꢀCH2Cl2ꢀ0.25C3H6O, with Estimated Standard Deviations (Esd’s) on the last figure in parentheses.
1ꢀ2CH2Cl2 (X = Cl)a
2 (X = Br)
4ꢀCH2Cl2ꢀ0.25C3H6O (X = AcO)
Cation 1
Cation 2
2.264(1)
Pt–P1
Pt–P2
Pt–P3
Pt–Cl/Br/O1
P1–Pt–P2
P1–Pt–P3
P1–Pt–Cl/Br/O1
P2–Pt–Cl/Br/O1
P3–Pt–Cl/Br/O1
P2–Pt–P3
2.266(2)
2.359(2)
2.368(2)
2.360(2)
98.91(8)
95.87(8)
169.58(10)
83.77(9)
83.43(9)
162.27(8)
2.295(1)
2.347(1)
2.363(1)
2.440(1)
96.34(5)
94.44(5)
176.00(4)
87.62(4)
81.65(4)
168.37(6)
2.265(1)
2.355(1)
2.370(1)
2.068(2)
98.41(3)
94.45(3)
172.99(8)
87.51(7)
79.52(7)
166.95(3)
2.342(1)
2.373(1)
2.070(2)
95.05(3)
95.93(3)
175.73(7)
88.89(7)
80.18(7)
168.95(3)
a
adapted from ref. [36].
which, being both
r and p donors to Pt(II) [40], decrease effica-
ciously the positive charge on the metal [22,41].
3.3.3. Weights of the cis and trans influences
Having established that the sequences are not charge-depen-
dent, we wondered whether their abilities are affected by the
charge of the complexes.
To do so we adopted the same approach used in the preceding
papers. If we subtract 1J(cis) (or 1J(trans)) of each compound from the
corresponding values of the Cl derivative, we obtain the weight (in
Hz) of the influences of each X ligand relative to weight of Cl, which
is set to 0 and used as the reference. Since we subtract the J value of
a given compound from that of the Cl derivative, a negative value
means a lower influence of that ligand with respect to that of Cl.
The weights of the cis influence of the various X in type C com-
plexes are collected in column A of Table 4. These weights decrease
from I to Me, following the cis influence sequence. The absolute
values are all lower than those found in the preceding studies for
neutral complexes trans-[PtClX(PPh3)2] (type A) and cis-
[PtClX)PPh3)2] (type B) (Table 4, columns D and E, respectively)
[14,21], meaning a decreased relevance of the cis influence in cat-
ionic complexes C. We think that this is a consequence of the posi-
tive charge of the complex. In fact the cis influence is related to the
ability of a ligand of lowering the positive charge on Pt [21]. In
Pt(II) complexes Pt–P back donation can be considered marginally
relevant [42] and it is likely to be negligible in cationic complexes,
thus the Pt(II)–P bond can be described, mainly, as donation from
the lone pair of P to Pt, which becomes weaker as the positive
charge on Pt decreases [21]. Such decrease is of lower importance
in cationic than in neutral complexes, since in the former Pt carries
a residual and substantial positive charge.
Fig. 2. ORTEP view of the asterisked cation [Pt(AcO)(PPh3)3]+ in compound
4ꢀCH2Cl2ꢀ0.25C3H6O (see text). Ellipsoids are drawn at the 30% probability level.
ꢁ
The other independent cation, the two BF4 anions, the solvent molecules, and the
hydrogen atoms have been omitted for clarity.
The trans sequence of the halides is in accordance with the sugges-
tion that there is an inverse correlation between the trans influence
of a ligand and its electronegativity [37,38].
The two sequences are only roughly opposite: the order
I > Br > Cl holds for both sequences [2,16,18] and their position is
higher than those of F and NO3 in both sequences. The fact that
there seems to be little relationship between the two series con-
firms that the two phenomena are originated by different
mechanisms.
In fact the trans influence is believed to be due to the competi-
tion of two ligands, trans to each other, for the same hybrid orbital
of the metal centre [1,2,10,38,39], i.e. to the competition between
two trans ligands for the opportunity to donate electron density
to Pt [2]. Thus the higher trans influence is displayed by ligands
with a relevant covalent character of their Pt–X bond.
On the other hand the cis influence is related to the ability of the
influencing ligand to lower the positive charge on the metal [21], a
mechanism confirmed also by our 31P NMR and DFT investigations
[14,21]. Thus the strongest cis influence is displayed by I, Br and Cl
Column B of Table 4 reports the weights of the trans influence of
the various X, relative to that of Cl, in compounds C. With the
exception of Me, these figures are higher, than those obtained in
the case of (neutral) cis-[PtClX(PPh3)2] [14], reported in column F,
showing that the charge plays a role also in this case. Such an in-
crease of weight induced by the positive charge is in accordance
with the view that the trans influence is due to the competition
of two trans ligands for the same metal hybrid orbital: a positive
charge on the metal centre enhances X ? Pt donation, weakening
donation of the ligand trans to X. The low trans ability of NO3
may have this origin: its interaction with Pt(II) has a rather high io-
nic character [14], making the Pt orbitals available for a strong
interaction in the trans position. As for the low trans weight of F,
besides its high electronegativity (see above [37,38]), one could
envisage that its bond with Pt involves a 2s–6s interaction, origi-
nating a rather weak Pt–F bond (compound 7 is little stable
[34]), allowing a strong interaction in the trans position.
Comparison of columns A, B, D, E and F show that the values of
the weights depend on the nature of the complex, i.e. on the metal

3504
L. Rigamonti et al. / Inorganica Chimica Acta 363 (2010) 3498–3505
Table 4
gands. It turns out that the sequences of both influences are unaf-
Weights of the cis and trans influences.a
fected by the charge, since they are the same as those obtained for
the neutral cis- and trans-[PtXY(PPh3)2] complexes. On the con-
trary, we found a charge-dependence of the weights of either influ-
ence. The trans weights are higher than those obtained for the
neutral complexes, whereas the cis weights are lower. These latter
findings are a clear evidence of the role of the charge, as explained
above.
An interesting point concerns the relative importance of the
two influences. We have previously found that in type B complexes
the cis influence of the halides is higher than their trans influence
[14] but in the case of compounds C, the data of column C of Table
4 suggest that the cis influence is about one third less relevant than
the trans influence throughout the series. This different behaviour
can be due to both the different charge and the different coordina-
tion environments of Pt in B and C. In particular in (neutral) com-
pounds B there is a cis-PtXYP2 coordination set, and the cis and
trans influences of both X and Y operate simultaneously in a con-
certed way.
X
A
B
C
D
E
F
I
Br
Cl
ONO2
ONO
F
AcO
NO2
H
28
19
0
167
23
0
ꢁ114
127
ꢁ54
169
809
1428
1728
ꢁ1021
ꢁ1156
ꢁ1160
ꢁ1152
ꢁ887
ꢁ1061
ꢁ802
ꢁ146
602
75
34
0
253
55
0
ꢁ10
8
0
ꢁ122
ꢁ146
ꢁ153
ꢁ189
ꢁ205
ꢁ344
ꢁ444
ꢁ130
ꢁ169
ꢁ185
–
–
–
–
–
–
ꢁ223
ꢁ243
ꢁ389
ꢁ517
ꢁ283
ꢁ276
–
ꢁ827
113
799
–
Me
1012
1946
a
A, weight of the cis influence of X referred to that of Cl in type C complexes; B,
trans weight of X referred to that of Cl in type C complexes; C, 1JPtP(cis) 1JPtP(trans) of
ꢁ
type C complexes; D, cis weight calculated in the case of trans-[PtClX(PPh3)2] (type
A) derivatives [21], signs are inverted to be in accordance with those used in the
present paper, the Br derivative was not included in that paper and has been newly
synthesised, see Section 2; E, cis weight calculated for cis-[PtClX(PPh3)2] (type B)
[14]; F, trans weight calculated for the same compounds B [14].
Finally throughout this and the preceding papers we have used
the working hypothesis that the mutual cis and trans influences of
the phosphines are constant within each type of compound, and
our results seem to be consistent with such hypothesis. An evalu-
ation of the weights of these influences remains, however, is still
an open question.
The results here presented pose a number of new problems, like
understanding how the mutual influences of the ligands operate.
Moreover, although the cis and trans sequences are in line with
those usually accepted and reported on textbooks, we wonder
how their weights are affected by different co-ligands (for instance
amines instead of phosphines) or in complexes of different metal
ions. These problems require further studies, which will be under-
taken in the near future.
environment (trans-PtXYP2, cis-PtXYP2, or PtXP3). Interestingly,
however, the various weights display a clear analogy in the three
compounds. All the NO3 weights are negative, for AcO, NO2-N, H
and Me the cis weights are negative and the trans weights positive;
the Br weights are all positive. The exception to this trend is given
by I. Its trans weight is rather high and positive in compounds C,
but negative in type B cis-[PtClI(PPh3)2]. This is somewhat puz-
zling. It is tempting to attribute this behaviour to the softness of
I, which may destabilise the Pt–P bond in trans through antisymbi-
osis [43–46] (an inverse relationship between trans influence and
ligand hardness has been proposed [10]). This does not occur in
B, because in this compound P2 (trans to I, Scheme 1, X = Cl,
Y = I) is cis to the highly cis influencing Cl, thus the actual influenc-
ing ability of a ligand depends on the metal environment (i.e. its
coordination set). However we must remember that both the posi-
tion and the weight of I in B may be affected by some uncertainty,
as stated above.
Acknowledgements
This work has been supported by the Italian Ministero della
Pubblica Istruzione. We thank Alberto Ferrandi for some experi-
mental work.
3.3.4. Relative importance of the cis and trans influences
The cis influence has usually been reported to be of lower
importance [1,18,47], although there are examples where the con-
trary has been observed. For instance, in type B compounds the cis
influences of the halides are higher than their trans influences [14]
and van Eldik reported that in certain Pt(II) complexes the kinetic
cis effect is more dominant than the trans effect [22].
Appendix A. Supplementary data
CCDC 771161 and 771162 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif
In compounds C, there is a span of about 500 and 1500 Hz for
1
1JPtP(cis) and JPtP(trans), respectively (see Table 3), showing that the
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2010.07.002.
trans influence is about three times more effective. The greater
importance of the trans influence is also revealed by the values
of column B of Table 4 (trans weights), which are higher than those
1
1
of column A (cis weights). Moreover the differences Jcis ꢁ Jtrans
(column C, Table 4), are negative and increase (i.e. the Pt–P bonds
cis to X become stronger) in the order halides to Me (the same or-
der of decreasing cis influence) becoming positive for H and Me.
Thus in type C complexes the trans influences is more relevant
for X from I to NO2, but less important for H an Me. The fact that
in type B compounds the cis influence of the halides is higher than
their trans influence, is likely to be due to the presence of a cis-PtXY
moiety, where both influences of X and Y operate in a concerted
way. In other words the importance of both influences depend
on the coordination set.
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