Synthesis and NMR investigation of Pt(CN)2(diphosphine) and [Pt(CN)(triphosphine)]Cl complexes

Article abstract of DOI:10.1016/S0020-1693(00)00042-6

Pt(CN)₂(Ph₂P(CH₂)(n)PPh₂) (n = 2,3,4) and Pt(CN)₂(P¹-P²) (P¹-P² = 1-diphenylphosphino-2,1'-[(1-diphenylphosphino)-1,3-propanediyl]-ferrocene, 1-diphenylphosphino-2,1'-[(1-dicyclohexylphosphino)-1,3-propanediyl]-ferrocen e) were synthesised by reacting potassium cyanide and the corresponding PtCl₂(diphosphine) complexes. PtCl(CN)(diphosphine) complexes were identified as minor products when KCN/PtCl₂(diphosphine) molar ratio was kept below 2. The use of KCN in excess resulted in the formation of K₂Pt(CN)₄. [Pt(CN)({Ph₂P(CH₂)₂}₂PPh)]⁺ complex cation and Pt(CN)₂)({Ph₂P(CH₂)₂}₂PPh) five-coordinate covalent complex of fluxional behaviour were obtained at KCN/Pt ratio of 1 and 2, respectively. The platinum-cyano complexes were characterised by NMR spectroscopy. The direct Pt-CN bond was proved by ¹J(¹⁹⁵Pt,³¹P), ²J(³¹P,¹³C) coupling constants by using sodium cyanide-¹³C for ligand exchange reactions. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(00)00042-6

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Inorganica Chimica Acta 303 (2000) 300–305
Note
Synthesis and NMR investigation of Pt(CN)2(diphosphine) and
[Pt(CN)(triphosphine)]Cl complexes
Gyo¨rgy Peto
3
cz a, La´szlo´ Ja´nosi a, Walter Weissensteiner b, Zsolt Cso´k c,
Zolta´n Berente d,e, La´szlo´ Kolla´r a,e,
*
a Department of Inorganic Chemistry, Janus Pannonius Uni6ersity, Ifjusag u. 6, PO Box 266, H-7624 Pe´cs, Hungary
b Institute of Organic Chemistry, Uni6ersity of Vienna, Wa¨hringer Straße 38, A-1090 Wien, Austria
c Department of Silicate Technology and Materials Science, Uni6ersity of Veszpre´m, PO Box 158, H-8201 Veszpre´m, Hungary
d Institute of Biochemistry, Uni6ersity Medical School, PO Box 99, H-7643 Pe´cs, Hungary
e Research Group for Chemical Sensors of the Hungarian Academy of Sciences, PO Box 266, H-7624 Pe´cs, Hungary
Received 15 July 1999; accepted 8 November 1999
Abstract
Pt(CN)2(Ph2P(CH2)nPPh2) (n=2,3,4) and Pt(CN)2(P1ꢀP2) (P1ꢀP2=1-diphenylphosphino-2,1%-[(1-diphenylphosphino)-1,3-
propanediyl]-ferrocene, 1-diphenylphosphino-2,1%-[(1-dicyclohexylphosphino)-1,3-propanediyl]-ferrocene) were synthesised by re-
acting potassium cyanide and the corresponding PtCl2(diphosphine) complexes. PtCl(CN)(diphosphine) complexes were identified
as minor products when KCN/PtCl2(diphosphine) molar ratio was kept below 2. The use of KCN in excess resulted in the
formation of K2Pt(CN)4. [Pt(CN)({Ph2P(CH2)2}2PPh)]+ complex cation and Pt(CN)2)({Ph2P(CH2)2}2PPh) five-coordinate cova-
lent complex of fluxional behaviour were obtained at KCN/Pt ratio of 1 and 2, respectively. The platinum–cyano complexes were
1
2
characterised by NMR spectroscopy. The direct PtꢀCN bond was proved by J(195Pt,31P), J(31P,13C) coupling constants by using
sodium cyanide-13C for ligand exchange reactions. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Platinum complexes; Cyano complexes
1. Introduction
derivatives. Some synthetic and structural details on
Pt(CN)2(diphosphine)-type complexes have already
been published, but the results are still sporadic. To the
best of our knowledge, in the Ph2P(CH2)nPPh2 ligand
series platinum–cyano complexes of dppm (bis(-
diphenylphosphino)methane, n=1) and dppp (1,3-bis(-
diphenylphosphino)-propane, n=3) have already been
published. While the various reaction pathways with
dppm furnished [Pt(dppm)(CN)2]2 and [Pt(dppm)(CN)]2
dinuclear complexes containing dppm bridges, which
The high trans influence of the cyano ligand in robust
squareplanar transition metal-bis(monodentate phos-
phine) complexes of Ni(II), Pd(II) and Pt(II) [1,2] as
well as its p-acceptor ability [3] is known for a long
time. Although even the catalytic activity of
Pd(CN)2(PPh3)2 and Pt(CN)2(PPh3)2 in olefin hydro-
genation has been tested [4], their coordination chem-
istry has remained relatively unexplored.
Although the PtX2(L) (X=Cl, Br, I; L=bidentate
ligand) complexes are among the most investigated
ones, surprisingly little is known about Pt(CN)2(L)-type
were
characterised
by
X-ray
crystallography
[5,6], Pt(CN)2(dppp) mononuclear complex was selec-
tively obtained with dppp [7]. With PtCl2(PhCN)2, the
dppm analogue 2,2-dppp (2,2-bis(diphenylphos-
phino)propane) possessing two methyl substituents at
the methylene carbon of dppm, affords the mononu-
clear complex PtCl2(2,2-dppp), which undergoes anion
* Corresponding author. Tel.: +36-72-327 622/4153; fax: +36-72-
501 527.
E-mail address: kollar@ttk.jpte.hu (L. Kolla´r)
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(00)00042-6

G. Peto
3
cz et al. / Inorganica Chimica Acta 303 (2000) 300–305
301
ligand exchange upon treatment with NaCN in ethanol
resulting in the formation of Pt(CN)2(2,2-dppp) [8].
Similar complexes have been described with the tripo-
dal ligand 1,1,1-triphos (1,1,1-tris(diphenylphosphino-
methyl)ethane) to form Pt(CN)2(1,1,1-triphos) wherein
two of the three phosphorus atoms of the ligand are
coordinated to platinum at low temperature and its
fluxional behaviour involving the corresponding five-co-
ordinate complex has been investigated [7,9].
2.3. Analytical data of the Pt(CN)2(diphosphine)
(1a–5a) and [Pt(triphos)(CN)]Cl (8a) complexes ( for
31P NMR data see Table 1)
1
1a: H NMR (l(ppm), CDCl3): 7.6 (m, 8H); 7.4 (m,
12H); 2.75 (m, 4H); 13C NMR (l (ppm), CDCl3): 136.7;
136.2; 131.5; 131.4; 129.8; 128.7; 128.6; 128.5; 28.4; IR
(KBr, cm−1): 2121 (w(CN)). Anal. Calc. for
C28H24N2P2Pt (M=645.54): C, 52.10; H, 3.75; N, 4.34.
Found: C, 52.45; H, 4.09; N, 4.17%. Yield: 78%.
We report our results on the systematic investigations
of the coordination chemistry of Pt(CN)2(diphosphine)
complexes as well as that of [Pt(CN)(triphos)]+ cation.
1
2a: H NMR (l (ppm), CDCl3): 7.6 (m, 8H); 7.4 (m,
12H); 2.67 (m, 4H); 1.85 (m, 2H); 13C NMR (l (ppm),
CDCl3): 133.2; 133.1; 131.8; 129.0; 28.5; 23.9; IR (KBr,
cm−1): 2189 (w(CN)). Anal. Calc. for C29H26N2P2Pt
(M=659.57): C, 52.81; H, 3.97; N, 4.25. Found: C,
52.97; H, 4.16; N, 4.14%. Yield: 80%.
2. Experimental
3a: 1H NMR (l (ppm), CDCl3): 7.62 (m, 8H); 7.4 (m,
12H); 2.64 (m, 4H); 1.65 (m, 4H); 13C NMR (l (ppm),
CDCl3): 133.0; 132.9; 131.7; 131.4; 131.1; 129.5; 129.4;
129.3; 28.4; 23.7; IR (KBr, cm−1): 2205 (w(CN)). Anal.
Calc. for C30H28N2P2Pt (M=673.59): C, 53.49; H, 4.19;
N, 4.16. Found: C, 53.67; H, 4.23; N, 4.06%. Yield: 77%.
4a: 1H NMR (l (ppm), CDCl3): 8.1 (m, 2H); 7.83 (m,
2H); 7.75 (m, 2H); 7.61 (m, 2H); 7.46 (m, 2H); 7.38 (m,
2H); 7.28 (m, 2H); 7.1 (m, 4H); 6.74 (m, 2H); 4.5 (m, 1H);
4.25 (m, lH); 4.16 (m, 1H); 4.03 (m, 1H); 3.83 (m, 1H);
3.46 (m, 1H); 3.42 (m, 1H); 2.95 (m, 1H); 2.50 (m, 1H);
2.35 (m, 1H); 2.15 (m, 1H); 1.56 (m, 1H); IR (KBr,
cm−1): 2231 (w(13CN). Anal. Calc. for C39H32N2P2FePt
(M=841.57): C, 55.66; H, 3.83; N, 3.33. Found: C,
55.81; H, 3.93; N, 3.20%. Yield: 84%.
The PtCl2(diphosphine)-type complexes were prepared
according to the literature [10]. The solvents were dried
by conventional methods [11], distilled and kept under
argon.
The 13C and 31P NMR spectra were recorded in CDCl3
with TMS (internal standard) and H3PO4 (85%) (external
standard), respectively. The spectra were recorded on a
Varian Unity 300 and a Varian Inova 400 spectrometers
at 75.4 and 100.58 MHz (13C NMR measurements) and
121.42 and 161.9 MHz (31P NMR measurements), re-
spectively.
2.1. The preparation of the [Pt(triphos)Cl]Cl complex
1
5a: H NMR (l (ppm), CDCl3): 8.0 (m, 2H); 7.6 (m,
A solution of 0.534 g (1 mmol) triphos in 3 ml of
benzene was added to the refluxing yellow solution of
0.472 g (1 mmol) PtCl2(PhCN)2. After a few minutes fine
white precipitate was formed. The mixture was stirred for
1 h then cooled to room temperature (r.t.). The solid was
filtered off, washed with benzene, and dried under
reduced pressure to give [Pt(triphos)Cl]Cl as white pow-
der.
Anal. Calc. for C34H33P3Cl2Pt (M=800.54): C, 51.01;
H, 4.15. Found: C, 51.18; H, 4.33%. Yield: 91%. 31P
NMR (CDCl3): 86.3 ppm (1J(Pt,P)=3035 Hz; 2J(P,P)=
2.6 Hz); 42.3 ppm (1J(Pt,P)=2477 Hz).
2H); 7.3 (m, 6H); 4.41 (m, 3H); 4.02 (m, 2H); 3.9 (m, 1H);
3.58 (m, 1H); 13C NMR (l (ppm), CDCl3): 135.4; 135.2;
133.7; 133.5; 132.3; 131.8; 131.7; 131.4; 131.0; 130.7;
128.3; 128.2; 128.0; 127.0; 97.9; 97.7; 86.0; 72.6; 72.2;
71.4; 69.8; 69.4; 41.4; 38.9; 30.8; 29.7; 27.6; 27.1; 26.2;
25.7; 24.0; IR (KBr, cm−1): 2095 (w(13CN). Anal. Calc.
for C39H44N2P2FePt (M=853.67): C, 54.87; H, 5.20; N,
3.28. Found: C, 55.07; H, 5.33; N, 3.05%. Yield: 83%.
8a: 1H NMR (l (ppm), CDCl3): 8.2 (dd; 7.2 Hz, 12 Hz;
2H); 7.8 (m, 9H); 7.5 (m, 14H); 3.9 (m, 2H); 3.2-3.4 (m,
2H); 2.65 (m; 2H); 2.2 (m; 2H); 13C NMR (l (ppm),
CDCl3): 139.3; 138.9; 137.6; 133.4; 132.8; 132.8; 129.2;
129.3; 128.6; 128.4; 24.5; 23.7; IR (KBr, cm−1): 2098
(w(13CN). Anal. Calc. for C35H33NP3ClPt (M=791.11):
C, 53.14; H, 4.20; N, 1.77. Found: C, 53.02; H, 4.08; N,
1.95%. Yield: 67%.
2.2. The preparation of a Pt(CN)2(diphosphine)
complex
The PtCl2(diphosphine) complex (0.5 mmol) was
added to the solution of potassium cyanide (1 mmol)
dissolved in 15 ml methanol. The powder did not dissolve
but was kept in suspension at 50°C with constant stirring
for 10 h. The white powder-like crystals were filtered,
washed with water, methanol and ether then dried. The
recrystallization was carried out in benzene–methanol
mixture.
3. Results and discussion
3.1. Synthesis of Pt(CN)2(diphosphine) complexes
For the preparation of platinum–cyano complexes
various homo- and heterobidentate diphosphines

302
G. Peto
3
cz et al. / Inorganica Chimica Acta 303 (2000) 300–305
PtCl2(P–P) +2KCN
“
Pt(CN)2(P−P)
+2KCl
P−P=dppe
P−P=dppp
P−P=dppb
P−P=6
1
2
3
4
5
1a
2a
3a
4a
5a
P−P=7
(1)
Fig. 1. The ferrocenyl diphosphines, 6 and 7.
In case of homobidentate ligands (dppe, dppp, dppb)
the ‘mixed anionic ligand’ complexes, PtCl(CN)-
(diphosphine) (e.g. 2b) were formed up to 5% yield,
when potassium cyanide was added at a ratio of Pt/
KCN=1/1 to the corresponding dichloro complex in
CDCl3. No further side-products were detected during
the ‘in situ’ NMR measurements, so even in these cases
the formation of 1a–3a were dominating while approx-
imately half of the starting dichloro complexes (1–3)
remained unchanged. However, a significant effect on
the formation of PtCl(CN)(diphosphine)-type com-
plexes was observed when 6 (two PPh2 groups in chem-
ically different positions) and 7 (PPh2 and PCy2 groups)
in 4a and 5a were used. The formation of the Pt-
Cl(CN)(diphosphine) complex was facilitated by the
larger difference in donor properties of the two phos-
phorus donors of the diphosphine ligand. The corre-
(dppe=1,2-bis(diphenylphosphino)ethane, dppp=1,3-
bis(diphenylphosphino)propane, dppb=1,4-bis(diphe-
nylphosphino)butane, 6=1-diphenylphosphino-2,1%-[(1-
diphenylphosphino)-1,3-propanediyl]-ferrocene,
7=
1-diphenylphosphino-2,1%-[(1-dicyclohexylphosphino)-
1,3-propanediyl]-ferrocene (Fig. 1)) were used which are
able to form five-, six- or seven-membered chelate rings.
While the Ph2P(CH2)nPPh2-type ligands are considered
as diphosphines forming flexible chelate rings, the two
ferrocenyl ligands possess rigid structure, and therefore
rigid platinum–diphosphine chelate.
The PtCl2(diphosphine) complexes (1–5) were re-
acted with potassium cyanide in methanol (See Section
2). The corresponding Pt(CN)2(diphosphine) complexes
(1a–5a) were separated as pure powder-like substances
in all cases.
Table 1
NMR data of Pt(CN)2(diphosphine) and [Pt(triphos)(CN)]+ complexes a
Complexes
l(31P)
1J(31P,195Pt)
2J(31P,31P)
l(13C) b
1J(13C,195Pt)
2J(13C,31P)
(ppm)
(Hz)
(Hz)
(ppm)
(Hz)
(Hz)
PtCl2(dppe)
Pt(CN)2(dppe)
PtCl2(dppp)
Pt(CN)2(dppp)
PtCl(CN)(dppp)
1
1a
2
2a
2b
43.0
41.2
3634
2462
3408
c
c
−4.9
−9.8
−5.7
−8.8
10.7
9.0
−2.0
34.4
−3.0
29.5
−0.4
30.8
−0.4
47.0
−2.3
39.0
2368
(122.9)
(1047)
d
26.7
d
PtCl2(dppb)
Pt(CN)2(dppb)
PtCl2(6)
3
3a
4
3538
2263
3375
3715
2321
2562
2100 d
3560 d
3570
3527
2408
2435
2452
3334
2383
2205
19.5
25.5
23.0
16
Pt(CN)2(6)
4a
4b
5
n.d.
n.d.
(25.6; 121.2)
(26.0; 123.1)
PtCl(CN)(6)
PtCl2(7)
Pt(CN)2(7)
5a
5b
8a
23.5
19.8
6.0
(125.1)
(121.2)
(998)
(1059)
(12.9; 114.0)
(14.1; 121.8)
PtCl(CN)(7)
[Pt(CN)(triphos)]+
1.0
45.9
41.0 e
90.8
n.d.
n.d.
(11.9)
(102.4)
a Solvent: CDCl3; 31P NMR and 13C NMR spectra were recorded at 121.4 MHz (161.9 MHz) and 75.4 MHz (100.6 MHz), respectively.
b Chemical shift of the CN carbon (the data in parenthesis are obtained with 13C enriched 13CN complexes).
c The 2J(13C,31P) coupling constants are obtained from the AA%XX% second-order 31P NMR spectra of the Pt(13CN)2(PꢀP) complex.
d Due to the Pt-satellites of very low intensity, the 1J(Pt,P) coupling constants could not be determined exactly.
e The doublet at higher field (41.0 ppm) corresponds to two equivalent phosphorus.

G. Peto
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cz et al. / Inorganica Chimica Acta 303 (2000) 300–305
303
Table 2
Coupling constants of AA%XX% second order system
Complex
2J(PA,PA%) (Hz)
2J(CX,CX%) (Hz)
2J(PA,CX) (Hz)
2J(PA,CX%) (Hz)
Pt(13CN)2(dppe)
Pt(13CN)2(dppp)
9.6
32.7
6.7
2.0
123.8
121.9
−12.9
−14.3
sponding chloro-cyano complexes were obtained in 14
and 30% yields by using ligands 6 and 7, respectively.
However, even the application of the slight excess (up
to 25%) of potassium cyanide (Pt/KCN=1/2.5) results
in the partial substitution of the diphosphine ligand.
The appearance of the signal of the free ligand was
observed by ‘in situ’ 31P NMR measurements (Eq. (2)).
Surprisingly, the papers published in this topic did
not mention this consecutive reaction and potassium
cyanide is used in slight excess in all cases. As a
consequence of that, a part of the platinum must have
been ‘lost’ as potassium-tetracyano-platinate(II).
Pt(CN)2(P−P)+2KCN“K2[Pt(CN)4]+P−P
1a−5a
(2)
3.2. NMR characterisation of Pt(CN)2(diphosphine)
complexes
The most remarkable feature of the 31P NMR of the
1
above complexes is the surprisingly small J(195Pt,31P)
coupling constant (Table 1). With the exception of
1J(195Pt, 31P) for one of the phosphorus of Pt(CN)2(6),
all values fall below 2500 Hz.
Fig. 2. 31P NMR spectrum of Pt(13CN)2(7). (The upper spectrum is
the enlargement of the upfield region.)
The direct PtꢀCN bond has been proved by 31P and
13C NMR investigation of the corresponding 13C la-
belled complexes. The Pt(13CN)2(ligand)-type com-
plexes of both homobidentate and heterobidentate
ligands were prepared which show the presence of two
equivalent and non-equivalent cyano ligands, respec-
tively. It was proved unequivocally by 31P and 13C
NMR (Tables 1 and 2). (Instead of potassium cyanide
the labelled reagent sodium cyanide-13C (enrichment in
13C was higher than 99.5%) was used in all cases and
has shown similar reactivity.)
3.3. Synthesis and characterization of
[Pt(triphos)(CN)]+ complex cation
The [Pt(triphos)Cl]Cl (8) ionic complex (where
triphos (9) stands for bis(2-diphenylphosphinoethyl)-
phenylphosphine) has been synthesized by the usual
‘benzonitrile method’ (See Section 2). Unlike the ‘1,1,1-
triphos’ (1,1,1-tris(diphenylphosphinomethyl)-ethane),
the ‘linear triphos’ forms a well-defined square-planar
ionic complex without a dangling arm, observed before
with palladium [12]. [Pt(triphos)(CN)]+ (8a) complex
cation was obtained selectively in a facile reaction by
the addition of one equivalent of KCN only. Both in 8
and 8a all the three phosphorus atoms of the ligand are
coordinated to platinum (Table 1).
Upon addition of a further equivalent of potassium
cyanide to 8a in CDCl3 a rather complex mixture was
obtained. In addition to the signals of 8a a sharp
doublet of quartet (dq)-type pattern appeared at 47.6
ppm (1J(Pt,P)=2549 Hz) and a signal of exactly dou-
ble intensity (based on the integration) was situated at
As a typical example, the 31P and 13C NMR spectra
of Pt(13CN)2 (7) are shown in Figs. 2 and 3, respec-
tively. The 31P NMR shows an eight-line multiplet for
both non-equivalent phosphorus flanked by platinum
satellites. This pattern is arising from the coupling of
the phosphorus with the carbon of the cyano ligands
both in cis and trans positions as well as with the
neighbouring phosphorus atom in cis position. A clear
13C NMR spectrum of similar structure was obtained,
as expected (Fig. 3).
Both Pt(13CN)2(dppp) and Pt(13CN)2(dppe) com-
plexes show typical AA%XX% second order 31P NMR
spectra. The calculated values of 2J(PA, PA%), 2J(CX,
2
2
CX%), J(PA, PX), and J(PA, PX%) are in Table 2.

304
G. Peto3 cz et al. / Inorganica Chimica Acta 303 (2000) 300–305
Fig. 3. 13C NMR spectrum of Pt(13CN)2(7). The 1/4/1 patterns (central line and platinum satellites) for the carbons of the two non-equivalent
cyano ligands are indicated by ꢀ and ×. (The rest of the peaks are due to the aromatic carbons of the ligand 7.)
of this signal at 243 K indicating a situation near to
coalescence, no separation of the lines could be
achieved and some complex precipitated due to low
solubility at this temperature. It is worth noting,
that similar behaviour has been obtained in
Fig. 4. The proposed structure of the Pt(triphos)(CN)2 complex.
CD2Cl2; no line separation has been reached even at
223 K.
14.5 ppm (1J(Pt,P):1350 Hz) as an extremely broad
1/4/1 pattern.
Acknowledgements
This phenomenon can be explained by the presence
of a square pyramidal covalent Pt(13CN)2(triphos)
complex (Fig. 4). The dq pattern can be assigned to
the most basic ‘middle’ phosphorus (P2) of the ligand
bound strongly to the platinum in equatorial position
(with a cyano ligand trans to it). It couples with the
The authors thank T. Lora´nd for the IR measure-
ments. L.K. thanks the Hungarian National
Science Foundation for financial support (OTKA
T23525) and the Ministry of Education for grant
FKFP 0242.
two
cyano
carbons
(2Jcis(31P,13C)=14
Hz;
2Jtrans(31P,13C)=121 Hz) and with the other two
phosphorus (2J(P,P)=ca. 14 Hz). The two 2J(P,P)
coupling constants could be equal in case of the fast
interchange of diphenylphosphino moieties of the
equatorial and apical positions (P1 and P3). The inter-
change could be fast in the NMR timescale. It may
result in the extremely broad ‘upfield’ signal at 14.5
ppm which also refers to the fluxional behaviour of
the five-coordinate complex. Although the low-tem-
perature measurements show the further broadening
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