Synthesis and characterisation of four-membered ring platinalactam complexes derived from 2-cyanoacetylurea; crystal structure of [Pt{N(CONH2)C(O)CH(CN)}(PPh3)2]

Article abstract of DOI:10.1016/S0020-1693(00)00237-1

The reactions of cis-[PtCl₂L₂] [L = PPh₃ or L₂ = dppe (Ph₂PCH₂CH₂PPh₂)] with cyanoacetylurea [NCCH₂C(O)NHC(O)NH₂] and triethylamine gives the platinalactam complexes [Pt{N(CONH₂)C(O)CH(CN)}L₂]. A single-crystal X-ray diffraction study on the triphenylphosphine complex confirms the presence of the four-membered platinalactam ring; the urea substituent is involved in intra- and intermolecular hydrogen bonding, forming a dimer in the solid state.

Full text of DOI:10.1016/S0020-1693(00)00237-1

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Inorganica Chimica Acta 310 (2000) 242–247
Note
Synthesis and characterisation of four-membered ring
platinalactam complexes derived from 2-cyanoacetylurea; crystal
¸¹¹¹¹¹¹¹¹¹¹¹º
structure of [Pt{N(CONH2)C(O)CH(CN)}(PPh3)2]
William Henderson a,*, Allen G. Oliver a,b, Clifton E.F. Rickard b
a Department of Chemistry, Uni6ersity of Waikato, Pri6ate Bag 3105, Hamilton, New Zealand
b Department of Chemistry, Uni6ersity of Auckland, Pri6ate Bag 92019, Auckland, New Zealand
Received 19 April 2000; accepted 30 June 2000
Abstract
The reactions of cis-[PtCl2L2] [L=PPh3 or L2=dppe (Ph2PCH2CH2PPh2)] with cyanoacetylurea [NCCH2C(O)NHC(O)NH2]
¸¹¹¹¹¹¹¹¹¹¹º
and triethylamine gives the platinalactam complexes [Pt{N(CONH2)C(O)CH(CN)}L2]. A single-crystal X-ray diffraction study on
the triphenylphosphine complex confirms the presence of the four-membered platinalactam ring; the urea substituent is involved
in intra- and intermolecular hydrogen bonding, forming a dimer in the solid state. © 2000 Elsevier Science B.V. All rights
reserved.
Keywords: Platinum; Lactam complexes; Crystal structures; Hydrogen bonding
reylene complexes have previously been synthesized
from ureas, by the same Ag2O methodology [5], and by
other routes [6–8].
1. Introduction
Four-membered rings which contain a metal atom
and an amide group in the ring system (metallalactam
complexes) are quite rare in the literature. A number of
four-membered ring metallalactam complexes of platin-
um(II) and palladium(II) 1, 2 have been synthesised by
reaction of halide complexes [MCl2L2] (L=phosphine
ligand or L2=cyclo-octadiene) with organic amides in
the presence of a base [silver(I) oxide]; amides investi-
gated to date are N-cyanoacetylurethane [1,2], acetoac-
etanilide [3] and 2-benzoylacetanilide [4]. In this Note
we extend our studies to the synthesis of platinalactam
complexes 3 from the more highly functionalised pre-
cursor cyanoacetylurea, NCCH2C(O)NHC(O)NH2.
This was of interest because of the possibility of form-
ing a platinaureylene complex 4, and for the nature of
the hydrogen bonding in the product formed. Platinau-
2. Results and discussion
2.1. Synthesis of platinalactam complexes
The reactions of the platinum(II) chloride com-
plexes cis-[PtCl2(PPh3)2] and [PtCl2(dppe)] (dppe=
Ph2PCH2CH2PPh2) with cyanoacetylurea and excess
triethylamine in refluxing methanol gives the platinalac-
tam complexes 3 in good yields. The reactions proceed
rapidly, and the products can be isolated from the
byproduct Et3NH+Cl− and excess Et3N simply by the
addition of excess water, in which the platinum com-
plexes are insoluble. Previous syntheses of platinalac-
tam complexes have used silver(I) oxide as a base [1–4],
so the triethylamine method is a viable alternative. It is
noteworthy that no ureylene complex 4 was observed;
presumably the PtꢀNH group of 4 is less stable than the
* Corresponding author. Tel.: +64-7-838 4656; fax: +64-7-838
4219.
E-mail address: w.henderson@waikato.ac.nz (W. Henderson).
0020-1693/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(00)00237-1

W. Henderson et al. / Inorganica Chimica Acta 310 (2000) 242–247
243
173.9) shows coupling to both 195Pt and 31P while the
urea carbonyl (l 156.0) shows coupling only to the
trans PPh3 ligand giving a doublet (J 5.6 Hz). Overall
the NMR spectroscopic features of 3a are comparable
to those of the related lactam complex 1 (M=Pt,
L=PPh3) [1].
Electrospray mass spectrometry has also been used to
characterise complexes 3a and 3b, which give strong
[MH]+ and weaker [2MH]+ ions in their positive-ion
electrospray mass spectra at low cone voltages (ca. 20
V) using MeCN–H2O as the mobile phase solvent. At
cone voltages of 40 V and higher, fragmentation occurs,
with the fragment ions [MHꢀNH3]+, [MHꢀHNCO]+,
and [L2Pt(NCO)]+ (L=PPh3 or L2=dppe) observed
for both complexes, formed by fragmentation of the
urea group and metalacycle. Thus, for complex 3a, the
ion [(Ph3P)2(NCO)]+ was observed at m/z 761. There
was no evidence for the alternative fragment ions
[L2Pt(CH2CN)]+, which for L=PPh3 would have m/z
759.
As with previously characterised platinalactam com-
plexes derived from N-cyanoacetylurethane (1) the IR
stretching frequency of the cyanide group shifts on
complex formation [1]. In cyanoacetylurea, the CN
stretch is observed at 2270 cm−1, while in 3a it is
observed at 2211 cm−1
.
PtꢀNꢀC(O) group in 3, where the PtꢀN bond is stabili-
sised by two electron-withdrawing carbonyl groups.
The attempted synthesis of the analogous bis(tri-
phenylphosphine) palladium complex was unsuccessful,
with 31P NMR showing the formation of a complex
mixture of products.
¸¹¹¹¹¹¹¹¹¹¹¹º
2.2. X-ray structure of [Pt{N(CONH2)C(O)CH(CN)}-
(PPh3)2] (3a)
Fig. 1 shows the atom labeling scheme for the com-
plex, and selected bond lengths and angles are given in
Table 1. The structure determination confirms the for-
mulation of the complex as a four-membered ring
platinalactam. The geometry about the platinum is a
distorted square plane; the N(1)ꢀPtꢀC(2) angle is acute
1
In the H NMR spectrum of 3a a broad resonance is
observed at l 4.5, assigned to the exchangeable urea
protons. The PtCH proton appears as a doublet of
doublets due to coupling to both P atoms, with 195Pt
satellites. The 31P{1H} NMR spectrum of 3a shows the
expected AB spin system of two nonequivalent PPh3
ligands, with the phosphorus trans to the higher trans
1
influence CH(CN) group showing the smaller J(PtP)
value (2543 versus 3742 Hz). Comparison of the 31P
NMR data of 3a and 3b with the corresponding
cyanoacetylureylene-derived complexes 1 [3] indicates
that the N(CO2Et) and N(CONH2) substituents have
very similar trans influences, but with the latter being
slightly higher, as shown by the smaller values of
1J(PtP) for P atoms trans to this group in 3a and 3b. In
the 13C{1H} NMR spectrum of 3a, the PtCH carbon (l
11.5) gives the expected doublet of doublets due to
phosphorus coupling, with additional coupling to 195Pt
(388 Hz). For comparison, in cyanoacetylurea, the CH2
carbon appears at l 30.6 (in DMSO-d6) indicating
shielding on platination. The cyano carbon (l 121.7,
c.f. l 119 in cyanoacetylurea) gives a doublet due to
phosphorus coupling, with additional platinum cou-
pling (3J(PC) 6.5, 2J(PtC) 49.4). The lactam carbonyl (l
¸¹¹¹¹¹¹¹¹¹¹º
Fig. 1. Molecular structure of [Pt{N(CONH2)C(O)CH(CN)}(PPh3)2]
(3a) showing the atom numbering scheme. Thermal displacement
ellipsoids are depicted at 50% probability. The phenyl hydrogen
atoms, dichloromethane and diethyl ether of crystallisation have been
omitted for clarity.

244
W. Henderson et al. / Inorganica Chimica Acta 310 (2000) 242–247
Table 1
,
Selected bond lengths (A) and bond angles (°) for
¸¹¹¹¹¹¹¹¹¹¹º
[Pt{N(CONH2)C(O)CH(CN)}(PPh3)2] (3a)
PtꢀN(1)
PtꢀP(1)
2.071(4)
2.2467(11)
1.371(6)
1.143(7)
1.220(6)
1.529(6)
1.826(5)
1.813(5)
1.841(5)
PtꢀC(2)
PtꢀP(2)
2.105(4)
2.3375(11)
1.401(6)
1.349(7)
1.230(6)
1.442(7)
1.834(5)
1.827(5)
1.826(5)
N(1)ꢀC(1)
N(2)ꢀC(3)
O(1)ꢀC(1)
C(1)ꢀC(2)
P(1)ꢀC(11)
P(1)ꢀC(31)
P(2)ꢀC(51)
N(1)ꢀC(4)
N(3)ꢀC(4)
O(2)ꢀC(4)
C(2)ꢀC(3)
P(1)ꢀC(21)
P(2)ꢀC(41)
P(2)ꢀC(61)
N(1)ꢀPtꢀC(2)
C(2)ꢀPtꢀP(1)
C(2)ꢀPtꢀP(2)
C(1)ꢀN(1)ꢀC(4) 124.5(4)
C(4)ꢀN(1)ꢀPt 135.9(3)
O(1)ꢀC(1)ꢀC(2) 126.7(4)
C(3)ꢀC(2)ꢀC(1) 112.4(4)
C(1)ꢀC(2)ꢀPt
65.94(17)
96.62(13)
165.48(13)
N(1)ꢀPtꢀP(1)
N(1)ꢀPtꢀP(2)
P(1)ꢀPtꢀP(2)
C(1)ꢀN(1)ꢀPt
O(1)ꢀC(1)ꢀN(1)
N(1)ꢀC(1)ꢀC(2)
C(3)ꢀC(2)ꢀPt
N(2)ꢀC(3)ꢀC(2)
O(2)ꢀC(4)ꢀN(1)
162.51(11)
99.97(11)
97.35(4)
98.6(3)
130.2(5)
103.1(4)
113.8(3)
178.9(6)
119.9(4)
92.2(3)
O(2)ꢀC(4)ꢀN(3) 123.0(5)
N(3)ꢀC(4)ꢀN(1) 117.2(4)
at 65.94(17)°, but is comparable to those found in
similar metallalactam structures (64–67°) [1,3]. The
P(1)ꢀPtꢀP(2) angle is more obtuse [97.35(4)°] to accom-
modate the steric bulk of the PPh3 ligands. The PtꢀP
bond lengths reflect the relative trans influences of the
¸¹¹¹¹¹¹¹¹¹¹º
Fig. 2. Hydrogen bonding in [Pt{N(CONH2)C(O)CH(CN)}(PPh3)2]
(3a); (a) plan view, (b) side view. Phenyl rings are omitted for clarity.
,
lent of O(2%) [O(2)···H(3b) 2.123 A], giving rise to a
,
trans atoms; PtꢀP(1) [2.2467(11) A] (trans to the low
loosely-bound dimeric species in the solid state (Fig.
2a), where the dimer is located about the crystallo-
graphic inversion center at coordinates (1, 0.5, 1). The
bond lengths for the cyanoacetylurea moiety are not
unusual. A side view of the intermolecular contacts
(Fig. 2b) shows that the hydrogen bonding is not in a
planar arrangement, but has the molecules lying
stepped to one another. Because of this intermolecular
interaction, H(3a) and H(3b) are not positioned oppo-
site each other. As can be seen in Fig. 2, H(3b) is bent
out of the plane of the platinalactam, oriented so that it
can more readily hydrogen bond to O(2%). A conforma-
tional calculation of the torsion angles [O(2)ꢀC(4)ꢀ
N(3)ꢀH] has H(3a) at 170.3° and H(3b) at 22.1°. If
H(3b) was directly opposite H(3a) a torsion angle of
about 10° for O(2)ꢀC(4)ꢀN(3)ꢀH(3b) might be ex-
pected. Hydrogenꢀbonded distances and angles are
summarised in Table 2.
trans influence nitrogen) is shorter than PtꢀP(2)
,
(2.3375(11) A), trans to the high trans influence C(2).
The coordination sphere around the platinum atom,
and the ring system, is highly planar, with no atom
,
lying more than 0.022(2) A from the least-squares
,
,
plane. The PtꢀN (2.071(4) A) and PtꢀC (2.105(4) A)
bonds of 3a are slightly longer than those of the related
¸¹¹¹¹¹¹¹¹¹¹º
cyanoacetylurethane complex [Pt{N(CO2Et)C(O)CH-
(CN)}(cod)] (cod=1,5-cyclo-octadiene) of type 1 [PtꢀN
,
2.016(6), PtꢀC 2.069(8) A] [1] due to the higher trans
influence of the PPh3 ligand compared to cod [9].
The main feature of interest in the structure of 3a is
the urea substituent, which is coplanar with the platina-
cycle. The urea nitrogen N(3) oriented such that H(3a)
forms an intramolecular hydrogen bond to the lactam
,
oxygen O(1) [O(1)···H(3a) 1.988 A]. H(3b) forms an
intermolecular hydrogen bond to a symmetry equiva-
Table 2
¸¹¹¹¹¹¹¹¹¹¹º
b
Hydrogen bonds a (with H···ABr(A)+2.000 A) and angles (D···H···A angle\100°) for [Pt{N(CONH2)C(O)CH(CN)}(PPh3)2] (3a)
,
,
,
,
DꢀH
DꢀH (A)
H···A (A)
D···H···A (°)
D···A (A)
A
N(3)ꢀH(3a)
N(3)ꢀH(3b)
0.901
0.861
1.988
2.123
137.45
161.93
2.721
2.954
O(1)
O(2)
a DꢀH=H bond donor, A=H bond acceptor.
b Symmetry operator= [−x+2, −y+1, −z+2].

W. Henderson et al. / Inorganica Chimica Acta 310 (2000) 242–247
245
Table 3
¸¹¹¹¹¹¹¹¹¹¹º
Crystal, collection and refinement data for [Pt{N(CONH2)C(O)CH(CN)}(PPh3)2] (3a)
Empirical formula
Formula weight
Crystal system
C40H33N3O2P2Pt. CH2Cl2. 0.5(C2H5)2O
966.71
triclinic
(
Space group
Unit cell dimensions
P1
,
a (A)
10.9488(1)
12.8958(2)
17.5272(3)
72.796(1)
,
b (A)
,
c (A)
h (°)
i (°)
73.69(1)
k (°)
66.19(1)
2125.65(5)
2
3
,
V (A )
Z
Dc (g cm−3
)
1.510
Diffractometer
Siemens SMART CCD
,
Radiation, wavelength (A)
Temperature (K)
Mo Ka, u=0.71073
203(2)
Crystal size (mm)
0.45×0.40×0.30
q Range for data collection (°)
Reflections collected
1.76–27.49 (−135h514, −155k516, 05l522)
20978
Independent reflections
9205 [R(int)=0.0202]
3.541
Absorption coefficient (mm−1
)
Max., min. transmission factors
F(000)
0.4164, 0.2987
962
Solution by
direct methods
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I\2|(I)]
R indices (all data)
Weighting scheme
Largest difference peak (e A
Largest difference hole (e A
Programs used
full-matrix least-squares on F2
9205/3/481
1.141
R1=0.0348, wR2=0.0991
R1=0.0374, wR2=0.1013
w=1/[|2(Fo2)+(0.0520P)2+7.0112P] where P=(Fo2+2Fc2)/3
−3
,
,
)
2.881 [1.14 A from C(84)]
−2.719
−3
,
)
SHELXS-97 and SHELXL-97 [15]
Strong hydrogen bonding involving the urea sub-
stituent is not unexpected. Ureas are strongly hydro-
gen-bonded in the solid state [10] and platinum
complexes containing strongly hydrogen bonding lig-
ands are of interest for the diversity of hydrogen-
bonded motifs which are displayed [11].
Complex 3a crystallises with one molecule of
dichloromethane and one half of a diethyl ether; these
two solvent molecules occupy voids in the crystal lattice
[12], and the complexes cis-[PtCl2(PPh3)2] and
[PtCl2(dppe)] were synthesised from it by ligand substi-
tution with a stoichiometric quantity of the phosphine
in dichloromethane [13]. Cyanoacetylurea was used as
supplied from Aldrich.
¸¹¹¹¹¹¹¹¹¹¹¹º
3.2. Synthesis of [Pt{N(CONH2)C(O)CH(CN)}(PPh3)2]
(3a)
,
and have no contacts closer than C(70)ꢀO(2) (3.257 A)
A mixture of cis-[PtCl2(PPh3)2] (500 mg, 0.633
mmol), cyanoacetylurea (250 mg, 1.97 mmol) and tri-
ethylamine (ca. 0.5 ml) in methanol (25 ml) was
refluxed for 1 h to give a white suspension in a pale
yellow solution. The mixture was cooled to room tem-
perature, the white solid 3a was filtered, washed with
cold methanol (5 ml), water (10 ml) and diethyl ether
(10 ml) and dried to give 349 mg (65%) of 3a. Found:
C, 57.1; H, 4.0; N, 4.8. C40H33N3O2P2Pt requires: C,
56.9; H, 3.9; N, 5.0%. IR: w(CN) 2211(s), w(CO)
1683(s), 1652(s) cm−1. M.p. 274–276°C (dec.). 1H
NMR: l 7.54–7.03 (m, 30H, Ph), 4.50 (s, br, 2H, NH2),
,
and O(3)ꢀC(22) (3.532 A) with the platinalactam
complex.
3. Experimental
3.1. General
General procedures and instrumentation were as pre-
viously described [4]. All reactions and recrystallisations
were carried out in solvents that were distilled prior to
use but were not deoxygenated. The complex
[PtCl2(cod)] was synthesised by the literature procedure
3
3
2
1.65 [dd, 1H, PtCH, J(PHtrans) 8, J(PHcis) 3, J(PtH)
3
61]. 13C{1H} NMR: l 173.9 [d, ring CO, J(PC) 6.2,

246
W. Henderson et al. / Inorganica Chimica Acta 310 (2000) 242–247
3
2J(PtC) ca. 120], 156.0 [d, urea CO, J(PC) 5.6], 134.7–
127.5 (m, Ph), 121.7 [d, CN, 3J(PC) 6.5, 2J(PtC) 49.4] 11.5
[dd, PtCH, 2J(PCtrans) 74, 2J(PCcis) 2, 1J(PtC) 388].
model resulted in unreasonable thermal motion parame-
ters for the nearby atoms. It is likely that this residual
density is due to disorder of the diethyl ether. Crystal data,
together with collection and refinement details are given
in Table 3.
31P{1H} NMR: AB spin system, l 17.2 [d, J(PtP trans
1
C) 2530, 2J(PP) 18], 11.8 [d, 1J(PtP trans N) 3722, 2J(PP)
18]. ESMS (cone voltage 20 V, MeCNꢀH2O solution)
[MH]+ (m/z 845, 100%), [2MH]+ (m/z 1689, 10%); cone
voltage 40 V, [(Ph3P)2Pt(NCO)]+ (m/z 761, 60%),
[MHꢀHNCO]+ (m/z 802, 15%), [MHꢀNH3]+ (m/z 828,
15%), [MH]+ (845, 100%).
4. Supplementary material
Crystallographic data (excluding structure factors) for
the structure described in this paper have been deposited
with the Cambridge Crystallographic Data Center,
CCDC No. 151652. Copies of this information can be
obtained free of charge from The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax: +44-1223-
336033; e-mail deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
¸¹¹¹¹¹¹¹¹¹¹¹º
3.3. Synthesis of [Pt{N(CONH2)C(O)CH(CN)}(dppe)]
(3b)
Following the method for 3a, [PtCl2(dppe)] (88 mg, 0.13
mmol), cyanoacetylurea (18 mg, 0.15 mmol) and triethy-
lamine (ca. 0.5 ml) gave 3b (68 mg, 73%). The product
was recrystallised from dichloromethane–diethyl ether
and dried under vacuum prior to elemental analysis.
Found: C, 49.6; H, 4.0; N, 5.7. C30H27N3O2P2Pt requires:
C, 50.1; H, 3.8; N, 5.9%. IR: w(CN) 2202(s), w(CO) 1616
(br, s) cm−1. M.p. 151–154°C (dec.). 31P{1H} NMR: AB
spin system, l 45.1 [s, 1J(PtP trans C) 2525, 2J(PP)
Acknowledgements
We thank the Universities of Waikato and Auckland,
and the New Zealand Lottery Grants Board for financial
support of this work, including a scholarship (to AGO).
We also thank Johnson Matthey plc for a generous loan
of platinum, and Dr Maarten Dinger for assistance with
NMR experiments.
1
2
unresolved], 38.6 [s, J(PtP trans N) 3432, J(PP) unre-
solved]. ESMS (cone voltage 20 V, MeCNꢀH2O solution):
[MH]+ (m/z 719, 100%). [2MH]+ (m/z 1437, 50%); cone
voltage 40 V, [(dppe)Pt(NCO)]+ (m/z 635, 25%),
[MHꢀHNCO]+ (m/z 676, 20%), [MHꢀNH3]+ (702, 40%),
[MH]+ (m/z 719, 100%).
¸¹¹¹¹¹¹¹¹¹¹¹º
3.4. X-ray structure of [Pt{N(CONH2)C(O)CH(CN)}-
(PPh3)2] (3a)
References
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