Platinum(II) complexes containing unsaturated ligands. Nucleophilic substitution versus nucleophilic attack to ligand: A stereochemistry driven outcome

Article abstract of DOI:10.1016/j.ica.2012.10.038

The reactivity of mixed complexes [PtCl₂(L)(L′)] (L = MeCN, EtCN, CO), L′ = PPh₃; L = η²-C ₂H₄, CO; L′ = MeCN, EtCN) towards diethylamine has been investigated. The processes are chemo- (substitution versus addition) and stereo-selective in dependence of the stereochemistry of the precursor. The structures of [SP4-4]-[PtCl(CONEt₂)(NHEt₂)(PPh ₃)], [SP4-4]-1, trans-[PtCl₂(NHEt₂)(PPh ₃)], trans-2, and cis-[PtCl₂{(E-)HNC(NEt ₂)Me}(PPh₃)], cis-3a, are reported.

Full text of DOI:10.1016/j.ica.2012.10.038

Inorganica Chimica Acta 395 (2013) 181–188
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Inorganica Chimica Acta
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Platinum(II) complexes containing unsaturated ligands. Nucleophilic
substitution versus nucleophilic attack to ligand: a stereochemistry driven outcome
⇑
Daniela Belli Dell’Amico , Claudio Broglia, Luca Labella, Fabio Marchetti, Daniele Mendola,
Simona Samaritani
Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Risorgimento 35, 1-56126 Pisa, Italy
a r t i c l e i n f o
a b s t r a c t
The reactivity of mixed complexes [PtCl2(L)(L0)] (L = MeCN, EtCN, CO), L0 = PPh3; L =
g
2-C2H4, CO;
Article history:
Received 20 July 2012
Accepted 24 October 2012
Available online 16 November 2012
L0 = MeCN, EtCN) towards diethylamine has been investigated. The processes are chemo- (substitution
versus addition) and stereo-selective in dependence of the stereochemistry of the precursor. The struc-
tures of [SP4-4]-[PtCl(CONEt2)(NHEt2)(PPh3)], [SP4-4]-1, trans-[PtCl2(NHEt2)(PPh3)], trans-2, and cis-
[PtCl2{(E-)HN@C(NEt2)Me}(PPh3)], cis-3a, are reported.
Keywords:
Ó 2012 Elsevier B.V. All rights reserved.
Substitution reactions
Addition reactions
Platinum
Unsaturated ligands
1. Introduction
C@C represents the alkene and L is a neutral ligand) with formation
of an alkyl zwitterionic species [4] where the positive and negative
Metal coordinated unsaturated ligands may undergo attack by
suitable nucleophiles, a reactivity widely exploited in coordination
and organometallic chemistry, as proved by the number of articles,
reviews and book chapters devoted to this topic [1]. Many exam-
ples describing the reactions of neutral platinum(II) PtCl2L2 (L =
CO; RCN) and PtCl2L(alkene) (L = neutral ligand) with primary
and/or secondary amines, have been reported and it is worth to re-
call here some of them. cis-[PtCl2(CO)2] reacts with NHiPr2 in
charges are localized on the nitrogen and platinum atoms, respec-
tively (Eq. (3)). Reaction 3 is an equilibrium reaction as the amine
attached to the alkene skeletal can be easily lost
½PtClꢁ ðC@CÞLꢁ þ NHR2 ꢀ ½PtꢀCl2ðC—C—NþHR2ÞLꢁ
ð3Þ
2
Recently Atwood et al. have re-examined the reactivity of a
series of platinum(II) neutral alkene complexes cis-[PtCl2(C@C)
(PPh3)], [5] reporting alkene substitution or nucleophilic attack to
the unsaturated ligand in dependence of the alkene nature (alkenes
with more than four carbon atoms being displaced by NHEt2) and
of the temperature (ligand substitution rather than nucleophilic
attack being observed also for the smaller alkenes if the reaction
mixture, initially at –75 °C, is allowed to reach room temperature
too rapidly). Ligand substitution reactions in platinum(II)
chemistry are strongly influenced by the ‘‘trans effect’’ [6],
exploited for synthetic goals to foresee or justify (with some pru-
dence) the outcome of a reaction [6] or the different behaviour of
two geometric isomers [7].
i
molar ratio 1:2 yielding the carbamoyl derivative [NH2 Pr2]cis-
[PtCl2(CONiPr2)(CO)] [2] (Eq. (1))
cis ꢀ ½PtCl2ðCOÞ ꢁ þ 2NHiPr2 ! ½NHi Pr2ꢁcis-½PtCl2ðCONiPr2ÞðCOÞꢁ
2
2
ð1Þ
Both, cis- and trans-[PtCl2(NCR0)2] react with excess of primary
or secondary amines yielding the bis-amidine derivatives cis- or
trans-[PtCl2{NH@C(R0)NR2}2], respectively (Eq. (2)) [3]
cis-½PtCl2ðNCR0Þ ꢁ þ 2NHR2 ! cis-½PtCl2fNH@CðR0ÞNR2g ꢁ
ð2aÞ
2
2
In order to gain a deeper insight into the reactivity towards dieth-
ylamine of neutral platinum(II) complexes, PtCl2LL0, containing at
least one unsaturated ligand, the present study was carried out with
the aim to find the conditions to favour selectively ligand attack or
ligand substitution. It appeared attractive to monitor both the che-
mo- and the regio-selectivity (attack to L versus L0 when both the
neutral ligands are unsaturated). The reactions of NHEt2 with both
geometrical isomers of [PtCl2(CO)(PPh3)], [PtCl2(NCR)(PPh3)] and
[PtCl2(C2H4)(NCR)] (R = Me, Et) and with trans-[PtCl2(CO)(NCEt)]
showed an outcome strictly dependent on the stereochemistry of
trans-½PtCl2ðNCR0Þ ꢁ þ 2NHR2 ! trans-½PtCl2fNH@CðR0Þ
2
ꢂ ðNR2g2ꢁ
ð2bÞ
Moreover, according to the earliest report by Orchin et al. and to
the extensive work by Panunzi and Green, amines attack the coor-
dinated alkene in platinum(II) complexes [PtCl2(C@C)L] (where
⇑
Corresponding author. Tel.: +39 0502219210.
E-mail address: belli@dcci.unipi.it (D. Belli Dell’Amico).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.10.038

182
D. Belli Dell’Amico et al. / Inorganica Chimica Acta 395 (2013) 181–188
the precursor. It appears surprising that clear and simple examples
correlating the precursor geometrical isomerism with the chemose-
lectivity of a process are quite rare in the literature [8].
0.82 (t) and 0.78 (t, 6H). 13C NMR (CDCl3): 167.7; 134.5 (d,
JC–P = 11 Hz); 130.5 (d, JC–P = 61 Hz); 130.4; 127.9 (d, JC–P = 11 Hz);
48.5; 47.7; 43.5; 38.7; 15.0; 14.0; 13.8. For the assignment see Sec-
tion 3. 31P NMR (CDCl3): 9.6 (1JP–Pt = 4310 Hz). 195Pt NMR (CDCl3):
1
~
ꢀ3949 (d, JPt–P = 4310 Hz). IR (ATR): 3212 (w,
m
N—H); 1556
2. Experimental
~
m
(m,
CO) cmꢀ1
.
The reaction between cis-[PtCl2(CO)(PPh3)] and a slight excess
of Et2NH (molar ratio about 4) was carried out also starting from
2.1. General
1
a temperature of ꢀ30 °C in CD2Cl2 as solvent and monitored by
31P NMR spectroscopy. Resonances at 9.64, 8.71 and 7.67 ppm
(1JP–Pt = 4879, 4349 and 4926 Hz, respectively) were observed at
low temperature. Once at room temperature, those at 9.64 and
7.67 ppm progressively disappeared and only the signal due to
[SP4-4]-1 (8.71 ppm) was present after 5 h.
All manipulations were performed under a dinitrogen atmo-
sphere, if not otherwise stated. Solvents and liquid reagents were
dried according to reported procedures [9]. 1H-, 13C-, 31P and
195Pt NMR spectra were recorded with a Bruker ‘‘Avance DRX
400’’ spectrometer, in CDCl3 solution if not otherwise stated.
Chemical shifts were measured in ppm (d) from TMS by residual
solvent peaks for 1H and 13C, from aqueous (D2O) H3PO4 (85%)
for 31P and from aqueous (D2O) hexachloroplatinic acid for 195Pt.
A sealed capillary containing C6D6 was introduced in the NMR tube
to lock the spectrometer to the deuterium signal when non-deuter-
ated solvents were used. FTIR spectra in solid phase were recorded
with a Perkin–Elmer ‘‘Spectrum One’’ spectrometer, with ATR tech-
nique. FTIR spectra in solution were recorded with a Perkin–Elmer
‘‘Paragon 500’’ or a Perkin–Elmer ‘‘Spectrum 100’’ spectrometers. A
0.1 mm cell supplied with CaF2 windows was used. Elemental
analyses (C, H, N) were performed at Dipartimento di Scienze e
Tecnologie Chimiche, Università di Udine.trans-[PtCl2(C2H4)(NCEt)]
2.3. Reaction between cis-[PtCl2(NCMe)(PPh3)] and NHEt2
2.3.1. T = ꢀ30 °C. Formation of cis-[PtCl2{(E–)HN@C(NEt2)Me}(PPh3)],
cis-3a
A solution of 0.216 g (0.38 mmol) of cis-[PtCl2(NCMe)(PPh3)] in
MeCN (30 mL) was cooled (T = ꢀ30 °C), treated with 0.048 mL of
diethylamine (0.46 mmol, amine/Pt molar ratio = 1.2) and stirred
until room temperature (25 °C) was slowly reached (48 h). Solvent
and excess reagents were eliminated under vacuum, the solid res-
idue was dissolved in 1,2-dichloroethane (1,2-DCE) and treated
with heptane (15 mL). Pale yellow crystals were filtered, washed
with heptane and dried under vacuum (0.173 g, 71% yield). Single
crystals were selected for X-ray diffraction studies. Anal. Calcd. for
was prepared from trans-[Pt(l-Cl)Cl(C2H4)]2 according to the pro-
cedure described for trans-[PtCl2(C2H4)(NCMe)] [10,11]. cis-[PtCl2
(C2H4)(NCMe)] was prepared (54% yield) by reacting a suspension
of [Pt(l-Cl)Cl(C2H4)]2 with an excess of MeCN (11.5 mmol) in CH2-
C24H29Cl2N2PPt: C, 44.9; H, 4.6; N, 4.4%. Found: C, 44.6; H, 4.5; N,
Cl2 as solvent under argon atmosphere. trans-[PtCl2(C2H4)(NCMe)]
isomer is first obtained which slowly isomerizes to the sparingly
soluble cis-isomer (15 d at room temperature, solution about 1
M, 54% yield). 1H NMR (CD3CN + CDCl3): 4.64 (2JPt–H = 62 Hz; 4 H;
CH2 = CH2); 2.44 (4JPt–H = 13 Hz; 3 H; CH3CN). 13C NMR (CD3CN):
74.8 (1JPt–C = 163 Hz, CH2 = CH2); 4.6 (CH3CN) in agreement
with the literature data [12]. 195Pt NMR (CD3CN): ꢀ2883
(1JPt–N = 364 Hz). cis-[PtCl2(PPh3)(NCMe)], cis-[PtCl2(PPh3)(NCEt)]
and cis-[PtCl2(CO)(NCEt)] were prepared according to already re-
ported procedures.[13] cis-[PtCl2(CO)(PPh3)] [14] was prepared
(91% yield) by treatment of a propionitrile solution of cis-[PtCl2
(NCEt)(PPh3)] with CO (PCO ꢃ 1 atm) at room temperature until
complete conversion of the precursor was achieved (24 h, moni-
tored by 31P NMR spectroscopy). 31P NMR: 10.9 (1JP–Pt = 3030 Hz).
195Pt NMR: ꢀ4090 (1JP–Pt = 3030 Hz). 13C NMR: 156.4 (CO), 134.2
(d, JC–P = 10.7 Hz), 132.6 (s) 128.1 (d, JC–P = 12.0 Hz) 126.9 (d,
~
4.3%. 1H NMR (CDCl3, T = 50 °C): 7.80–7.35 (15H, aromatic hydro-
gens); 4.36 (s, 1H, NH@C(NEt2)CH3; 2.88 (m, 4H, NH@C[N(CH2-
CH3)2]CH3); 2.30 (s, 3H, NH@C(NEt2)CH3); 0.91 (t, 6H,
NH@C[N(CH2CH3)2]CH3). 13C NMR (CDCl3): 162.6 (s, N@C); 134.5
(d, JC–P = 11 Hz), 130.9, 128.7 (d, JC–P = 63 Hz) and 128.2 (d,
JC–P = 11 Hz) due to aromatic carbon nuclei; 43.7 (NH@C[N(CH2-
CH3)2]CH3); 22.6 (NH@C(NEt2)CH3); 13.0 (NH@C[N(CH2CH3)2]-
CH3). 31P NMR (1,2-DCE): 7.0 (1JP–Pt = 3950 Hz). 195Pt NMR (1,2-
1
~
m
DCE): ꢀ3421 (d, JP–Pt = 3950 Hz). IR (ATR): 3298 (m,
NH); 1592
(s, mC@ )cmꢀ1
.
~
N
2.3.2. T = 83 °C. Formation of trans-[PtCl2(NHEt2)(PPh3)], trans-2
A solution of 0.201 g (0.35 mmol) of cis-[PtCl2(NCMe)(PPh3)] in
10 mL of MeCN was refluxed (83 °C) and a solution of diethylamine
(0.43 mmol, NHEt2/Pt molar ratio = 1.2) in 5 mL of the same sol-
vent was slowly added under stirring. The solution turned deep
yellow and was refluxed until the complete conversion of the pre-
cursor was achieved (2 h, monitored by 31P NMR spectroscopy).
The solvent was eliminated under vacuum, the solid residue was
dissolved in 1,2-DCE (10 mL), treated with heptane (15 mL) and
cooled (ꢀ30 °C). Yellow crystals of solvated trans-[PtCl2(NHEt2)
(PPh3)] were obtained (about 60% yield) which were filtered and
dried under vacuum. Suitable single crystals were selected for
X-ray diffraction measurements and resulted to have the composi-
tion [PtCl2(NHEt2)(PPh3)]ꢄC2H4Cl2. Elemental analyses showed
different results in dependence of the length of the treatment
under vacuum. The partial loss of the lattice solvent is reasonably
responsible of the analytical results. Anal. Calcd. for [PtCl2(NHEt2)
(PPh3)]ꢄC2H4Cl2; C24H30Cl4NPPt: C, 41.1; H, 4.3; N, 2.0%. Anal. Calcd.
for [PtCl2(NHEt2)(PPh3)]ꢄ0.5C2H4Cl2; C23H28Cl3NPPt: C, 42.4; H, 4.3;
N, 2.1%. Anal. Calcd. for [PtCl2(NHEt2)(PPh3)], C22H26Cl2NPPt C,
43.9; H, 4.4; N, 2.3. Found sample a: C, 42.8; H, 4.3; N, 2.1%. Found
sample b: C, 43.9; H, 4.4; N, 2.4%. 1H NMR (CDCl3): 7.78–7.42 (15H,
aromatic protons); 3.63 (br, 1H, NH), 3.34 (m, 2H, CH2); 2.83 (m,
2H, CH2); 1.59 (t, 6H, CH3). 13C NMR (CDCl3): 134.8 (d,
JC–P = 10.5 Hz), 130.7 (d, JC–P = 2.7 Hz), 129.0 (d, JC–P = 63.0 Hz)
JC–P = 67.5 Hz). IR (ATR): 2104 (m .
CO) cmꢀ1
2.2. Reaction between cis-[PtCl2(CO)(PPh3)] and NHEt2 with formation
of [SP4-4]-[PtCl(CONEt2)(NHEt2)(PPh3)], [SP4-4]-1
A suspension of 0.683 g (1.23 mmol) of cis-[PtCl2(CO)(PPh3)] in
30 mL of toluene, under dinitrogen, was treated with a solution
of 0.520 mL of diethylamine (5.03 mmol, NHEt2/Pt molar ra-
tio = 4.09) in toluene (10 mL) under stirring. The liquid phase
turned deep yellow in minutes and a white solid appeared. When
the complete conversion of the substrate was achieved (2 h, mon-
itored by 31P NMR) the mixture was filtered under dinitrogen to
eliminate NH2Et2Cl, the filtrate was concentrated (15 mL) under
vacuum, treated with heptane (15 mL) and cooled (ꢀ30 °C).
Light-orange crystals separated out which were filtered and dried
under vacuum (0.522 g, 64% yield). Suitable single crystals were se-
lected for X-ray diffraction studies. Anal. Calcd. for C27H38ClN2-
OPPt: N, 4.2; C, 48.5; H, 5.7%. Found: N, 4.1; C, 48.8; H, 5.5%. 1H
NMR (CDCl3, T = 50 °C): 7.80–7.20 (15H); 4.30 (m, 1H); 3.78 (br s,
1H); 3.37–2.85 (m, 6H); 2.41 (m, 1H); 1.64 (t, 3H); 1.52 (t, 3H);

D. Belli Dell’Amico et al. / Inorganica Chimica Acta 395 (2013) 181–188
183
and 127.9 (d, JC–P = 10.6 Hz) due to the aromatic carbon nuclei;
47.4 (CH2); 14.9 (CH3). 31P NMR (CDCl3): 4.3 (1JP–Pt = 3560). 195Pt
complete conversion into the trans isomer was achieved (24 h,
monitored by 195Pt NMR spectroscopy: d ꢀ3426). The orange solu-
tion was treated with diethylamine (NHEt2/Pt molar ratio = 1.0)
and turned immediately yellow. The solvent was eliminated under
vacuum, the residue was dissolved in CDCl3 and NMR spectra were
recorded. 1H NMR: 3.65 (br, 1H, NH); 3.16 (m, 2H, CH2); 2.80 (m,
2H, CH2); 1.46 (t, 6H, CH3). 13C NMR: 153.5 (1JC–Pt = 1652 Hz, CO),
48.3 (NHCH2), 14.5 (NHCH2CH3). 195Pt NMR (1,2-DCE): ꢀ3421. IR
1
NMR (CDCl3): ꢀ3612 (d, JPt–P = 3560 Hz). IR (ATR): 3219 cmꢀ1
~
(m
N—H).
2.3.3. T = 25 °C
When the reaction was carried out at room temperature a mix-
ture of trans-2 and cis-3a was obtained.
(ATR): 2128 (s,
CO); 3226 (w,
m
NH)cmꢀ1. Elemental analyses were
~
~
m
2.4. Reaction of trans-[PtCl2(NCMe)(PPh3)] prepared ‘‘in situ’’ with
diethylamine at ꢀ30 °C. Formation of trans-[PtCl2(NHEt2)(PPh3)],
trans-2
unreliable for the extreme sensitivity of the product to moisture.
2.8. Reaction of trans-[PtCl2(NCR)(C2H4)] with NHEt2
trans-[Pt(l-Cl)Cl(PPh3)]2 (0.14 mmol of platinum) was sus-
Analogous results were obtained for MeCN and EtCN deriva-
tives. Experiments carried out with MeCN are described.
pended in 50.0 mL of MeCN at 0 °C. A yellow solution was formed
in 8 h (31P NMR: trans-[PtCl2(NCMe)(PPh3)], 4.3 ppm, 1JP–Pt = 4076 -
Hz; traces of the cis-isomer were present) [13]. The solution was
concentrated under vacuum (15 mL), cooled (ꢀ30 °C) and treated,
2.8.1. Amine/platinum molar ratio = 1
The treatment of [Pt(
l-Cl)Cl(C2H4)]2 (0.460 g; 0.78 mmol) with
under stirring, with 0.017 mL of diethylamine (0.17 mmol, NHEt /
acetonitrile (10 mL) afforded a yellow solution of trans-[PtCl2
2
Pt molar ratio = 1.2). The mixture was stirred until room tempera-
ture was reached, the solvent was eliminated under vacuum and
the solid residue was dissolved in CDCl3. 1H and 31P NMR spectra
revealed the formation of trans-2 as the largely prevalent product
(only traces of cis-3a were present).
(NCMe)(C2H4)] [10,11]. HNEt2 (155 ll; 1.49 mmol) was added
and after 15 min a 195Pt NMR spectrum was recorded on an aliquot
of the reaction mixture: a unique signal at –2987 ppm was ob-
served. After removing the volatiles in vacuum a yellow solid
was recovered (0.50 g, 86% yield as trans-[PtCl2(C2H4)(NHEt2)]
2
[10]. 1H NMR (CDCl3): 4.63 (s, CH2CH2, 4 H, JPt–H = 60 Hz); 3.3
2.5. Reaction between cis-[PtCl2(NCEt)(PPh3)] and diethylamine at
room temperature with formation of trans-[PtCl2(NHEt2)(PPh3)],
trans-2
and 2.9 (m, 4 H, NCH2); 1.54 (t, 6 H, NCH2CH3) in agreement with
1
the literature data [16]. 13C NMR (CDCl3):74.5 (CH2@CH2, JPt–
C = 158 Hz); 49.0 (PtNHCH2CH3); 14.7 (PtNHCH2CH3). 195Pt NMR
(CDCl3): ꢀ2986. Although the species has been already described
[16], at the best of our knowledge its 13C and 195Pt NMR data have
not been so far reported.
A 1,2-DCE solution (20.0 mL) of cis-PtCl2(NCEt)(PPh3) [13]
(0.230 g, 0.40 mmol) was treated with 0.041 mL of diethylamine
(0.40 mmol, NHEt2/Pt molar ratio = 1.0) at room temperature. The
pale yellow solution turned immediately deep yellow and was
maintained under stirring at room temperature (3 h). The solution
volume was reduced to 7 mL, 15.0 mL of heptane were added and
the obtained solution was cooled (4 °C). Yellow crystals of trans-
2ꢄ1,2-DCE were obtained which were filtered, washed with
heptane (5.0 mL) and dried under vacuum (0.131 g, 55% yield).
Analytical and spectroscopic data (IR and NMR) corresponded to
those herein before reported.
2.8.2. Amine/platinum molar ratio P 2
In an experiment monitored by NMR spectroscopy [Pt(l-
Cl)Cl(C2H4)]2 (67 mg; 0.11 mmol) was dissolved in CD3CN
(1.0 mL) with formation of trans-[PtCl2(C2H4)(NCCD3)]. Diethyl-
amine (250 ll; 2.42 mmol; amine/Pt molar ratio = 11) was then
added. 1H and 13C NMR spectra of the solution showed signals
attributable to trans-[Pt(ꢀ)Cl2(CH2–CH2–N(+)HEt2)(NHEt2)]: 1H
NMR: 3.20 (q; Pt–CH2–CH2–NH–CH2–CH3); 2.89 and 2.64 (m;
CH2 of the platinum coordinated amine); 2.78 (t; Pt–CH2–CH2–
When the reaction was carried out at ꢀ30 °C a mixture of trans-
2 and cis-[PtCl2{(E–)HN@C(NEt2)Et}(PPh3)], cis-3b, was obtained.
2
N); 1.72 (t; JPt–H = 88.2; Pt–CH2–CH2–N); 1.33 (t; Pt–CH2–CH2–
NH–CH2–CH3); 1.28 (t; platinum coordinated amine CH3), in agree-
ment with the literature data [16]. 13C NMR: 59.5 (2JPt–C = 37 Hz;
Pt–CH2–CH2–N); 47.3 (s) and 47.1(s) (NH–CH2–CH3); 14.8(s) and
9.9(s) (NH–CH2–CH3); ꢀ11.3 (1JPt–C = 723 Hz; Pt–CH2–CH2–N).
2.6. Reaction of trans-[PtCl2(CO)(PPh3)] prepared ‘‘in situ’’ with
diethylamine: formation of trans-[PtCl2(NHEt2)(PPh3)], trans-2
A suspension of trans-[Pt(
l
-Cl)Cl(PPh3)]2 (21.0 mg, 4.0 ꢂ 10ꢀ2
-
The 195Pt NMR spectrum showed
a single resonance at
mmol of Pt) in 2.5 mL of CD2Cl2 was cooled (ꢀ35 °C) and the sus-
pension was saturated with CO. A yellow–orange solution was
obtained (1 h). The solution was frozen and saturated with N2 after
a treatment under vacuum (10ꢀ2 mmHg). A sample of the mixture
was analyzed by 31P NMR spectroscopy and showed a unique sig-
nal (15.2 ppm, 1JP–Pt = 3075 Hz), ascribable to trans-[PtCl2
(CO)(PPh3)] [15]. The solution was then treated under N2 atmo-
ꢀ3168 ppm, unchanged after 24 h.
In other experiments carried out in MeCN (amine/platinum mo-
lar ratio P 2) the 195Pt NMR spectrum of the reaction mixtures
showed a single platinum signal at ꢀ3168, due to trans-[Pt(ꢀ)Cl2
(CH2–CH2–N(+)HEt2)(NHEt2)]. In all the experiments, when the
solution was evaporated in vacuum and the solid residue was dis-
solved in CDCl3, 1H and 195Pt spectra showed the presence of both
sphere at ꢀ30 °C with a CD2Cl2 solution of Et2NH (5.0
ll in
trans-[Pt(ꢀ)Cl2(CH2–CH2–
0.30 mL) and immediately analyzed by 31P NMR: a signal at
4.35 ppm (1JP–Pt = 3568 Hz) was observed, due to trans-2, together
with minor signals at 9.64, 8.71 and 7.67 ppm (1JP–Pt = 4879, 4349
and 4926, respectively). Of the last three signals those at 9.64 and
7.67 ppm turned slowly into the one at 8.71 ppm, due to addition
product [SP4-4]-1.
trans-[PtCl2(C2H4)(NHEt2)]
and
N(+)HEt2)(NHEt2)].
2.9. NMR study of the reaction of cis-[PtCl2(C2H4)(NCMe)] with
diethylamine
Solutions of cis-[PtCl2(C2H4)(NCCH3)] in CD3CN were prepared
in NMR tubes under argon. Each solution was treated with a differ-
ent amount of diethylamine, in order to study the outcome of the
reactions with different amine/Pt molar ratios. Each sample was
monitored through 1H and 195Pt NMR spectra in order to follow
the evolution of the systems with time. The addition of the first
2.7. Reaction between trans-[PtCl2(CO)(NCEt)] and diethylamine.
Formation of trans-[PtCl2(CO)(NHEt2)], trans-4
A solution of 0.082 g (0.24 mmol) of cis-[PtCl2(CO)(NCEt)] [13]
in freshly distilled 1,2-DCE (10 mL) was stirred at 25 °C until the

184
D. Belli Dell’Amico et al. / Inorganica Chimica Acta 395 (2013) 181–188
Table 1
times while the other for the 33.2%. All hydrogen atoms were
Crystal data and structure refinements.
added in idealized positions. All non hydrogen atoms not involved
in disorder were refined with anisotropic displacement parame-
ters. The least squares refinements were done by using SHELXL97
programme [17]. Some other utilities contained in the WINGX
suite [18] were also used. The more relevant parameters of struc-
ture refinements are listed in Table 1.
[SP4-4]-1
trans-
2ꢄC2H4Cl2
cis-3a
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C27H36ClN2OPPt C24H30Cl4NPPt
666.09
C24H29Cl2N2PPt
642.45
700.35
monoclinic
Cc (No. 9)
16.6781(5)
12.3373(4)
14.9107(5)
-
114.1040(10)
-
2800.55(16)
4
1.580
5.184
29272
6387 [0.0281]
302
triclinic
triclinic
ꢀ
ꢀ
P1 (No. 2)
P1 (No. 2)
9.3545(1)
9.5028(2)
16.6356(3)
99.930(1)
101.180(1)
100.443(1)
1393.29(4)
2
1.669
5.489
22017
6023 [0.0225]
259
8.624(1)
11.285(2)
13.963(2)
102.22(1)
107.86(1)
96.61(1)
1240.2(3)
2
1.720
5.950
6168
5112 [0.0243]
271
b (Å)
c (Å)
3. Results and discussion
a
(°)
The two geometrical isomers cis- and trans-[PtCl2(CO)(PPh3)]
react differently with NHEt2, the former with attack to CO and
the latter with substitution of CO (see Eqs. (4) and (5), respec-
tively). The reaction of cis-[PtCl2(CO)(PPh3)] with a small excess
of NHEt2 proceeds smoothly in toluene at room temperature under
dinitrogen without any evidence of CO evolution affording [SP4-4]-
[PtCl(CONEt2)(NHEt2)(PPh3)], [SP4-4]-1, and NH2Et2Cl (Eq. (4))
b (°)
c
(°)
U (Å3)
Z
Dcalc (Mg mꢀ3
)
l
(mmꢀ1
)
No. measured
No. unique (Rint
No. parameters
)
R1, wR2 [I > 2
r
(I)]a
0.0189, 0.0379
0.0229, 0.0390
0.0269, 0.0785
0.0326, 0.0892
1.075
0.0376, 0.0829
0.0513, 0.0881
1.035
cis-½PtCl2ðCOÞðPPh3Þꢁ þ 3NHEt2
R1, wR2 [all data]a
Goodness of fit on F2 0.988
a
! ½SP4-4ꢁ-½PtClðCONEt2ÞðNHEt2ÞðPPh3Þꢁ þNH2Et2Cl
ð4Þ
½SP4-4ꢁ-1
a
½
R(Fo) =
R
jjFoj–jFcjj/
R
jFoj; Rw(Fo2) = [
R
[w(Fo2e–Fc2)2]/
R
[
R
w(Fo2)2]]
;
w = 1/[r2
½
(Fo2) + (AQ)2 + BQ] where Q = [MAX(Fo2,0) + 2Fc2]/3; GOF = [
[w(Fo2--Fc2)2]/(N–P)]
,
where N, P are the numbers of observations and parameters, respectively.
trans-½PtCl2ðCOÞðPPh3Þꢁ þ NHEt2
! trans-½PtCl2ðPPh3ÞðNHEt2Þꢁ þCO
ð5Þ
trans-2
amine equivalent caused the fast formation of the zwitterionic
complex cis-[PtꢀCl2 (CH2CH2N+HEt2)(NCMe)]. A slow reaction,
monitored by 1H, 13C and 195Pt NMR spectra, followed the addition
of the second equivalent. Spectroscopic data suggest the addition
of the amine to the coordinated nitrile with formation of the ami-
dine complex cis-[Pt–Cl2(CH2CH2N+HEt2)(E-){NHC(NEt2)Me}]. For
the discussion of the spectra, see Section 3.
The crystalline product has been recovered in good yield and
characterized by elemental analysis, single crystal X-ray diffrac-
tion, IR and NMR spectra (see Table 3 for 31P and 195Pt NMR).
The molecular structure of [SP4-4]-1 is shown in Fig. 1 and selected
geometric parameters are listed in Table 2. The structure is similar
to that of the five Pt-carbamoyl derivatives reported in the chem-
ical literature [2,19]. The Pt(II) centre shows the usual square pla-
nar coordination geometry with the NCO group of the carbamoyl
ligand lying on a plane perpendicular to it. The Cl ligand trans to
the carbamoyl group shows in our compound a distance from the
platinum centre significantly longer than the mean value, 2.33 Å,
usually encountered in Pt(II) derivatives. No significant intermo-
lecular interactions are observed.
2.10. X-ray structure determinations
The X-ray diffraction experiments were carried out at room
temperature (T = 293 K) using Mo K
a radiation with the samples
sealed in glass capillaries under a dinitrogen atmosphere. Geomet-
ric and intensity data of cis-3a were collected by means of a Bruker
P4 diffractometer, those of [SP4-4]-1 and trans-2ꢄC2H4Cl2 by means
of a Bruker Smart Breeze 4 K CCD detector diffractometer. The
intensities were corrected for Lorentz and polarisation effects
and for absorption by means of a semi-empirical methods.1 The
more relevant crystal parameters for the three compounds are listed
in Table 1.
The structure solutions were obtained by means of the auto-
matic direct methods contained in SHELXS97 [17]. In the structure
of trans-2ꢄC2H4Cl2 a solvent molecule (1,2-DCE) was localised in a
cavity centred at 0.60, 0.60, 0.15. After the introduction of this mol-
ecule in the structural model several maxima were still present
around them in the difference Fourier map. This was considered
an evidence of disorder in this part of the structure and a second
orientation of the solvent molecule was added to the model super-
imposed to the first one by fixing to 1.0 the total occupancy of the
site. The following least squares refinement cycles were done with
constraints in the isotropic thermal factors of the atoms of disor-
dered solvent, but leaving free their occupancy factor. His final va-
lue suggested that one limit position was assumed for the 66.8% of
Table 2
Bond lenghts (Å) and angles (°) around Pt atoms in [SP4-4]-1.
Pt–Cl
Pt–P
Pt–C(19)
Pt–N(2)
Cl–Pt–P
Cl–Pt–N(2)
N(2)–Pt–C(19)
C(19)–Pt–P
P–Pt–N(2)
Cl–Pt–C(19)
2.4167(9)
2.2251(8)
2.002(4)
2.139(3)
92.88(3)
O–C(19)
C(19)–N(1)
N(1)–C(20)
N(1)–C(22)
Pt–N(2)–C(24)
Pt–N(2)–C(26)
Pt–C(19)–O
Pt–C(19)–N(1)
O–C(19)–N(1)
1.228(5)
1.367(5)
1.425(7)
1.482(7)
115.8(3)
115.9(3)
118.5(3)
121.5(3)
120.0(4)
83.34(9)
90.53(13)
93.09(10)
175.75(9)
172.48(11)
Table 3
31P and 195Pt NMR data.
Compound
195Pt d/ppm
31P d/ppm
1JPt–P/Hz
Solvent
[SP4-4]-1
10.5
9.6
8.7
4.3
7.0
7.4
–
4380
4310
4349
3560
3950
3860
–
toluene
CDCl3
CD2Cl2
CDCl3
1,2-DCE
CDCl3
1,2-DCE
CD3CN
CD3CN
ꢀ3949
trans-2
cis-3a
cis-3b
trans-4
cis-5
ꢀ3612
ꢀ3421
1
The absorption correction for the data of [SP4-4]-1 and trans-2ꢄC2H4Cl2 were done
by the multi-scan method (G.M. Sheldrick, SADABS, version 2008/2. Program for
Empirical Absorption Correction of Area Detector Data. Univ. of Göttingen: Göttingen,
Germany, 1996); those of cis-3a by a Psi-scan method (G.M. Sheldrick, XPREP, version
5.1/NT. Program for Redaction of Diffractometer Data. Bruker AXS Inc., Madison,
Wisconsin, USA, 2000).
ꢀ3421
ꢀ3465
ꢀ3214
–
–
–
–
cis-6

D. Belli Dell’Amico et al. / Inorganica Chimica Acta 395 (2013) 181–188
185
In the IR spectrum (solid state) the product shows bands at
3212 cmꢀ1, attributable to the N–H stretching vibration of the
coordinated amine, and at 1556 cmꢀ1 due to the carbonyl stretch-
ing vibrations of the carbamoyl group. The 1H NMR spectrum re-
corded at 25 °C appeared rather complicated, probably for the
hindered rotation around the C(O)–NEt2 bond of the carbamoyl
group and the steric hindrance of the phosphine. The spectrum re-
corded at 50 °C showed the signals of the aromatic protons (7.80–
7.20 ppm), a broad resonance at 3.78 ppm, attributed to the NH
proton of the coordinated amine and complicated multiplets at
4.30 (1H), 3.11 (6H) and 2.41 (1H) that have been assigned to the
methylene protons of the ethyl groups of the carbamoyl moiety
and of the amine (methylene protons of the coordinated NHEt2
are diastereotopic). The two triplets at 1.64 and 1.52 (6H) ppm
are assigned to the methyl protons of the carbamoyl moiety, while
those at 0.82 and 0.78 (6H) ppm to the amine methyl protons.
Although the spectrum recorded at 50 °C shows a higher signal res-
olution, nevertheless the equivalence of the alkyl groups is not
reached. The 13C NMR spectrum recorded at room temperature
shows a signal at 167.7 ppm due to the carbamoyl (CON) and res-
onances of the aromatic nuclei at 134.5, 130.5, 130.4 and
127.9 ppm. Four signals at 48.5, 47.7, 43.5 and 38.7 ppm are due
to the CH2 of the four magnetically non equivalent ethyl groups,
while three resonances observed at 15.0, 14.0, 13.8 are assigned
to the four non-equivalent methyl carbon atoms, assuming the
overlapping of two signals.trans-[PtCl2(CO)(PPh3)] [15] was pre-
Fig. 1. View of the molecular structure of [SP4-4]-1. Thermal ellipsoids are at 20%
probability.
pared in situ by reacting trans-[PtCl(l-Cl)(PPh3)]2 with CO in CH2-
Cl2 at low temperature (Eq. (7)). It is the kinetic product of the
reaction and care has to be taken to avoid its isomerisation to
the more stable cis-isomer
Although three stereoisomers of 1 could be obtained, only the
isomer [SP4-4]-1 forms at room temperature as proved by the
31P NMR spectrum recorded on the reaction mixture, showing a
single signal at 10.5 ppm (1JPt–P = 4380 Hz). Reasonably the reac-
tion proceeds through NHEt2 nucleophilic attack to carbon monox-
ide followed by transfer of a proton to a second amine to get the
ionic intermediate a, [NH2Et2]cis-[PtCl2(CONEt2)(PPh3)] (Eq. (6a))
and subsequent substitution of a chloride by a third molecule of
amine (Eq. (6b)), favoured by the precipitation of [NH2Et2]Cl. The
geometric isomer [SP4-2]-1 (intermediate b), with an amine trans
to -CONEt2, is expected to be the kinetic product of the reaction
(the carbamoyl group should have a stronger trans effect than
PPh3, as usually carbon-donor ligands have [6]). Intermediate b
quickly converts to the more stable [SP4-4]-1 isomer (Eq. (6c)).
Such a proposal is reminiscent of what reported for the reaction
between cis-PtCl2(CO)2 and NHiPr2 (1:2 molar ratio) producing
trans-½PtClð -ClÞðPPh3Þꢁ2 þ 2 CO ! 2 trans-½PtCl2ðCOÞðPPh3Þꢁ ð7Þ
l
When it was reacted with an excess of NHEt2 at ꢀ30 °C trans-
[PtCl2(NHEt2)(PPh3)], trans-2, was obtained as the main product,
as reported in Eq. (5). Notwithstanding the low temperature, traces
of [SP4-4]-1 were observed, reasonably due to isomerisation of the
precursor, catalysed by the addition of the amine [15]. The main
product is easily recovered after work-up of the reaction mixture
and has been characterized in the course of this work by 31P and
195Pt NMR (see Table 3) and X-ray diffraction methods. Compounds
of the type trans-[PtCl2(PPh3)(amine)] are known [20] and the
i
structure of trans-[PtCl2(PPh3)(NH2 Pr)] has been reported [20b].
The molecular structure of trans-2 is shown in Fig. 2 and the bond-
ing geometry around the metal is listed in Table 4. The structure is
tightly related to that of [SP4-4]-1, the only difference being the
substitution of the carbamoyl moiety by the chloride ligand. The
Pt–Cl bond lengths have here the usual values. The diethylamine
orientation is very similar to that shown in [SP4-4]-1 with the
amine hydrogen lying approximately on the Pt coordination plane.
A quick look at CCDC database [21] shows that in all the diethyl-
amine coordination compounds of Pt(II) of known structure the
N–H bond makes small angles with the metal coordination plane.
Molecules are paired in couples related by inversion centres, point-
ing the NH hydrogen toward the Cl(1) atom of the partner (Fig. 3)
with a N–HꢄꢄꢄCl distance of 2.68 Å, slightly shorter than the sum of
the van der Waals radii.
It is worth to note that the Cl(1) atom involved in this interac-
tion shows a bond length from Pt significantly longer than Cl(2).
This interaction is reasonably responsible of the amine orientation.
The different reactivity of the two stereoisomers cis- and trans-
[PtCl2(CO)(PPh3)] can be justified with the stronger trans-effect of
the phosphine in comparison with that of the chloride, the dis-
placement of CO by NHEt2 in the trans-isomer being driven by
the lability of CO trans to PPh3.
[NH2 Pr2]cis-[PtCl2(CONiPr2)(CO)] [2]
i
cis-½PtCl2ðCOÞðPPh3Þꢁ þ 2 NHEt2
! ½NH2Et2ꢁcis-½PtCl2ðCONEt2ÞðPPh3Þꢁ
ð6aÞ
ð6bÞ
ð6cÞ
a
½NH2Et2ꢁcis-½PtCl2ðCONEt2ÞðPPh3Þꢁ þ NHEt2
! ½SP4-2ꢁ -½PtClðCONEt2ÞðNHEt2ÞðPPh3Þꢁ þ NH2Et2Cl
b
½SP4-2ꢁ-½PtClðCONEt2ÞðNHEt2ÞðPPh3Þꢁ
! ½SP4-4ꢁ-½PtClðCONEt2ÞðNHEt2ÞðPPh3Þꢁ
½SP4-4ꢁ-1
Furthermore, the presence of two intermediates in the course of
the reaction has been confirmed by monitoring the reaction carried
out at ꢀ30 °C by 31P NMR spectroscopy. Resonances at 9.6, 8.7 and
7.7 ppm (1JP–Pt = 4879, 4349 and 4926 Hz, respectively) were ob-
served. At room temperature those at 9.6 and 7.7 ppm progres-
sively disappeared and only the signal due to [SP4-4]-1 (8.7 ppm)
was present after 5 h.
The reactions of the two geometric isomers of [PtCl2(PPh3)
(NCR)] (R = Me, Et) [13] proceed with attack to or substitution of

186
D. Belli Dell’Amico et al. / Inorganica Chimica Acta 395 (2013) 181–188
Fig. 3. Pairing of molecules through hydrogen interaction in the structures of trans-
2 (above) and cis-3a (below).
Fig. 2. View of the molecular structure of trans-2. Thermal ellipsoids are at 20%
probability.
trans-½PtCl2ðNCMeÞðPPh3Þꢁ þ NHEt2
! trans-½PtCl2ðNHEt2ÞðPPh3Þꢁ þ MeCN
ð10Þ
trans-2
Table 4
To check if the trans-isomer reacts with nitrile substitution also
at low temperature, an experiment was performed where trans-
[PtCl2(NCMe)(PPh3)] was produced in situ by reacting the dinucle-
Bond lenghts (Å) and angles (°) around Pt atoms in trans-2.
Pt–Cl(1)
Pt–N
Cl(1)–Pt–N
Cl(1)–Pt–P
Cl(2)–Pt–N
2.3071(13)
2.134(4)
86.30(13)
90.90(5)
Pt–Cl(2)
Pt–P
Cl(2)–Pt–P
Cl(1)–Pt–Cl(2)
N–Pt–P
2.2891(12)
2.2368(11)
94.29(5)
174.77(5)
177.15(12)
ar trans-[PtCl(l-Cl)(PPh3)]2 with MeCN at 0 °C. The solution,
containing only traces of cis-[PtCl2(NCMe)(PPh3)], was cooled at
ꢀ30 °C and treated with NHEt2. The reaction was monitored by
31P NMR: trans-2 was obtained as final product with only traces
of cis-3a. Results comparable with those obtained with cis-[PtCl2
(NCMe)(PPh3)] were observed for the reaction of the propionitrile
derivative cis-[PtCl2(NCEt)(PPh3)] with NHEt2, with the difference
that the temperature threshold to avoid isomerisation of the pre-
cursor was lower, and also at ꢀ30 °C some trans-2 was formed to-
gether with cis-[PtCl2{(E)-HN@C(NEt2)Et}(PPh3)], cis-3b, while at
room temperature complete conversion to trans-2 was observed.
cis-3a was recovered in good yield and characterized by elemental
analysis, single crystal X-ray diffraction, IR and NMR spectra. Sig-
nificant bands in its IR spectrum at 1592 and 3298 cmꢀ1 are attrib-
utable to the C@N and N–H stretching vibrations, respectively. Its
1H NMR spectrum shows, besides the signals due to the phosphine
aromatic protons, a broad singlet at 4.36 ppm, due to the amidine
HN@C proton and a singlet at 2.30 ppm due to the amidine N@C–
CH3 methyl group, in the region typical of the E configuration of the
ligand [3c]. The two magnetically equivalent ethyl groups produce
two signals at 2.88 (CH2) and 0.91 (CH3) ppm. The 13C NMR spec-
trum shows signals of aromatic nuclei, a resonance due to HN@C
at 162.6 ppm, and a resonance attributable to the N@C–CH3 methyl
at 22.6 ppm. Signals due to the ethyl groups are at 43.7 (CH2) and
13.0 (CH3) ppm. The molecular structure of cis-3a is shown in Fig. 4
and the geometrical parameters of the metal bonding are listed in
Table 5. The N–C@N–H plane of amidine ligand is almost perpen-
dicular (81.5°) to the platinum coordination plane and this orienta-
tion can be explained, besides the steric hindrance of the
phosphine, by the intermolecular interaction requirements. The
cis-3a molecules are, in fact, packed in pairs related by inversion
centres (Fig. 3). Each molecule of a pair points its N–H toward
88.51(13)
the unsaturated ligand for the cis- and the trans isomer, respec-
tively. The geometric isomers of the precursor, at variance with
those of [PtCl2(PPh3)(CO)], present a quite similar stability and
are usually both present in equilibrium in solution with similar
concentrations: solutions of a pure isomer can be obtained only
if care is taken to avoid isomerisation. By operating at an initial
temperature of ꢀ30 °C, cis-[PtCl2(NCMe)(PPh3)] isomerisation is
inhibited and it reacts with a slight excess of NHEt2 in MeCN as sol-
vent, with addition of the nucleophile to the coordinated nitrile
and formation of the amidino-complex cis-[PtCl2{(E)-HN@C(NEt2)-
Me}(PPh3)], cis-3a (Eq. (8))
cis-½PtCl2ðNCMeÞðPPh3Þꢁ þ NHEt2
! cis-½PtCl2fðEÞ-HN@CðNEt2ÞMegðPPh3Þꢁ
ð8Þ
cis-3a
If the reaction is carried out at about 80 °C only trans-[PtCl2
(NHEt2)(PPh3)], trans-2, is obtained, as observed by monitoring
the system by 31P NMR. Finally, by operating at room temperature
a mixture of trans-2 and cis-3a is produced. As at high temperature
the cis isomer of the precursor is still largely prevalent (cis/trans
molar ratio about 95/5), reasonably both the precursor isomerisa-
tion (Eq. (9)) and the substitution reaction on the trans-isomer (Eq.
(10)) have to be faster than the amine addition to the cis-isomer
(Eq. (8)). At room temperature the reaction rates are probably sim-
ilar with formation of the mixture of products
cis-½PtCl2ðNCMeÞðPPh3Þꢁ ꢀ trans-½PtCl2ðNCMeÞðPPh3Þꢁ
ð9Þ

D. Belli Dell’Amico et al. / Inorganica Chimica Acta 395 (2013) 181–188
187
and 195Pt NMR), substitution is expected to occur with retention of
configuration, as usual for platinum(II) complexes, producing the
trans-isomer, trans-4
trans-½PtCl2ðNCEtÞðCOÞꢁ þ NHEt2
! trans-½PtCl2ðNHEt2ÞðCOꢁ þ EtCNÞ
ð13Þ
trans-4
The IR spectrum of the product in solid phase shows bands at
3226 and 2128 cmꢀ1 attributable to N–H and C–O stretching vibra-
tions, respectively. For instance the C–O stretching vibration in
trans-PtCl2(CO)(amine) is reported at 2139, 2123 and 2121 cmꢀ1
with amine = NH3, py, PhNH2 [22a] and in the range 2128–
2147 cmꢀ1 when the amine is a para-substituted pyridine [22b].
In the 1H NMR spectrum the signals due to the coordinated amine
are observed. The broad singlet at 3.65 ppm is assigned to NH, the
multiplets at 3.16 and 2.80 ppm to the diastereotopic CH2 and the
triplet at 1.46 ppm to methyl protons. The 13C NMR spectrum
shows the signal due to coordinated CO at 153.5 (1JC–Pt = 1652 Hz)
Fig. 4. View of the molecular structure of cis-3a. Thermal ellipsoids are at 30%
probability.
to be compared with the data 151.10 ppm ( JC–Pt = 1670 Hz) re-
1
ported for PtCl2(CO)py [22c]. For 195Pt NMR data see Table 3.
Preliminary results have been obtained for the system cis-
[PtCl2(MeCN)(C2H4)]/NHEt2. The reactions were performed in CD3-
CN at room temperature and monitored by 195Pt , 13C and 1H NMR.
The addition of the first equivalent of the amine produced the fast
formation of the zwitterionic complex cis-[Pt–Cl2(NCMe)(CH2CH2-
N+HEt2)], cis-5 (Eq. (14)). After 1 h from the amine addition the
the Cl(2) atom of the coupled molecule with a N–HꢄꢄꢄCl(2) distance
of 2.74 Å and the Pt–Cl(2) bond length is significantly longer than
Pt–Cl(1) one.
The systems PtCl2LL0/NHEt2 with both L and L0 unsaturated li-
gands (L = CO, C2H4; L0 = MeCN, EtCN) revealed to be rather com-
plex, not only because the outcome of the reactions depends on
the amine/precursor molar ratio, but also because the involved
complexes, especially carbonyl complexes, are quite air sensitive.
Nevertheless specific points have been established. When trans-
[PtCl2(NCR)L] [L = C2H4, CO] is reacted with diethylamine in molar
ratio 1, in principle four outcomes are possible: (a) L substitution,
(b) nitrile substitution, (c) nucleophilic attack to L, (c) nucleophilic
attack to nitrile. By reacting trans-[PtCl2(NCR)(C2H4)] [11] with a
stoichiometric amount of NHEt2 at room temperature in RCN as
solvent, nitrile substitution is observed with formation of trans-
[PtCl2(NHEt2)(C2H4)] (Eq. (11)) as single product. The high trans-ef-
fect of the alkene justifies this outcome. Further addition of NHEt2
causes the already reported [4c] nucleophilic attack to the coordi-
nated ethylene with formation of the alkyl zwitterionic complex
(Eq. (12))
1
195Pt resonance due to the precursor (ꢀ2883 ppm, JPt–N 364 Hz,
4JPt–H 13 Hz) is not observable anymore while a broad signal attrib-
utable to the product appears at ꢀ3465 ppm
cis-½PtCl2ðNCMeÞðC2H4Þꢁ
þ NHEt2 ꢀ cis-½Pt-Cl2ðNCMeÞðCH2CH2NþHEt2Þꢁ
ð14Þ
cis-5
Selected 13C and 1H NMR signals are reported, with their attri-
bution, in Table 6. The coordinated nitrile does not exchange with
the solvent and the platinum–hydrogen coupling (4JPt–H) is ob-
served. Furthermore, signals due to coordinated ethylene are not
present anymore while the resonances at 2.95 and 1.57 ppm in
the 1H spectrum and those at 54.4 and –12.7 ppm in the 13C spec-
trum can be assigned to the methylene nuclei of the fragment Pt–
CH2CH2–N. The high field signal due to Ca (see scheme in Table 6)
reveals a coupling constant to the 195Pt nucleus of 638 Hz, as ex-
trans-½PtCl2ðNCRÞðC2H4Þꢁ þNHEt2
R@Me; Et
! trans-½PtCl2ðNHEt2ÞðC2H4Þꢁ þ RCN
ð11Þ
pected for an a-carbon atom of a platinum-alkyl group [23]. Ha nu-
clei produce a triplet with satellites showing coupling to platinum.
When the solution is treated in vacuo equilibrium 14 is displaced to
the left, preventing the product isolation.
The addition of an excess of NHEt2 to cis-[PtCl2(C2H4)(NCMe)]
(molar ratio 4) causes the rapid formation of the zwitterionic
complex cis-5 followed by a slower reaction. Spectroscopic data
suggest that the amidino complex cis-[Pt–Cl2{NH@C(Me)NEt2}
(CH2CH2N+HEt2)], cis-6 (Eq. (15)) is formed
trans-½PtCl2ðNHEt2ÞðC2H4Þꢁ þ NHEt2 ꢀ trans-½PtꢀCl2ðNHEt2ÞðCH2-CH2NþHEt2Þꢁ
ð12Þ
Similarly, the reaction of trans-[PtCl2(EtCN)(CO)] with NHEt2
(molar ratio 1), carried out at room temperature in 1,2-dichloro-
ethane (1,2-DCE) or CH2Cl2 as solvent, proceeds with nitrile substi-
tution affording a single platinum complex containing NHEt2 and
CO as ligands, [PtCl2(NHEt2)(CO)], 4 (Eq. (13)). Since no isomerisa-
tion evidence was detected by monitoring the reaction mixture (IR
cis-½PtCl2ðNCMeÞðCH2CH2NHEt2Þꢁ þ NHEt2
! cis ꢀ ½PtꢀCl2NH ¼ CðMeÞNEt2ðCH2CH2NþHEt2Þꢁ
ð15Þ
cisꢀ6
In the 195Pt NMR spectrum the initial signal at –3465 ppm, due
to cis-5, slowly (24 h) disappears with concomitant formation of a
signal at ꢀ3214 ppm assigned to cis-6. Selected 13C and 1H NMR
resonances with their attribution are reported in Table 6. Signals
due to coordinated nitrile have disappeared and new resonances
at 163.6 ppm and 23.2 ppm in the 13C spectrum are assigned to
the NH@C–CH3 unsaturated and saturated carbon atoms, respec-
tively. The signal at 2.52 ppm in the 1H spectrum is attributable
to the methyl protons of the same group; its chemical shift value
suggests the E configuration for the amidino [3c]. Attempts to
Table 5
Bond lenghts (Å) and angles (°) around Pt atoms in cis-3a.
Pt–Cl(1)
Pt–Cl(2)
Pt–N(1)
Pt–P
Cl(1)–Pt–Cl(2)
Cl(1)–Pt–P
Cl(2)–Pt–N(1)
P–Pt–N(1)
Cl(1)–Pt–N(1)
2.3170(16)
2.3540(18)
2.016(6)
2.2069(17)
90.64(7)
N(1)–C(1)
C(1)–C(2)
C(1)–N(2)
1.316(9)
1.497(10)
1.337(9)
Cl(2)–Pt–P
175.52(7)
126.5(5)
122.4(7)
118.5(6)
119.0(7)
87.57(6)
Pt–N(1)–C(1)
N(1)–C(1)–N(2)
N(1)–C(1)–C(2)
C(2)–C(1)–N(2)
87.69(18)
94.11(17)
178.32(18)

188
D. Belli Dell’Amico et al. / Inorganica Chimica Acta 395 (2013) 181–188
Table 6
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Selected 1H and 13C NMR signals of cis-5 (see Eq. (14)) and cis-6 (see Eq. (15)) in
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4. Conclusions
Geometrical isomers of neutral complexes PtCl2LTL where LT is a
ligand with a rather strong trans-effect and L is an unsaturated li-
gand have different reactivity towards diethylamine. While trans-
PtCl2LTL complexes (LT = PPh3, L = CO, MeCN, EtCN; LT = CO,
L = EtCN; LT = C2H4, L = MeCN) react with substitution of L by the
amine, the cis-isomers (LT = PPh3, L = CO, MeCN) react with attack
to the unsaturated ligand. Moreover, cis-PtCl2(CH2@CH2)(NCMe)
reacts with a fast attack to the alkene followed by a slow attack
to the nitrile. This straightforward behaviour is respected unless
partial isomerisation of the precursor takes place before the reac-
tion occurs. Therefore, the stereo-isomerism of the precursor ap-
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We gratefully acknowledge the Ministero dell’Università e della
Ricerca Universitaria (MIUR), Progetti di Ricerca di Rilevante Interesse
Nazionale (PRIN 2007) for financial support. We thank Chimet
S.p.A., I–52041 Badia al Pino (Arezzo), for a loan of platinum.
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Appendix A. Supplementary material
(b) P. Ganis, I. Orabona, F. Ruffo, A. Vitagliano, Organometallics 17 (1998) 2646.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.ica.2012.10.038.