Synthesis of cis- and trans-dichloro(dimethylphenylphosphine)-(1-methyl-1,4,5,6-tetrahydropyrimidine) platinum(II) and their spectral and structural characterization

Article abstract of DOI:10.1016/S0022-328X(98)00471-9

Interaction of [{Pt(μ-Cl)Cl(PMe₂Ph)}₂] with 1-methyl-1,4,5,6-tetrahydropyrimidine, L (R=Me), in boiling toluene produced a mixture of cis- and trans- isomers of [PtCl₂(PMe₂Ph){N=CH(Me)CH₂CH₂CH ₂}]; trans-complex 2 isomerizes to give thermodynamically more stable corresponding cis-complex 1 in boiling ethanol. Spectroscopic and X-ray diffraction data permit generalizations about cis- and trans- isomeric pairs to be made. In addition, the trans influence of the ligand L is reliably assessed.

Full text of DOI:10.1016/S0022-328X(98)00471-9

Journal of Organometallic Chemistry 561 (1998) 7–11
Synthesis of cis- and
trans-dichloro(dimethylphenylphosphine)
×-(1-methyl-1,4,5,6-tetrahydropyrimidine)platinum(II)
and their spectral and structural characterization
a,
a
b
b
¸
8
8
Bekir Cetinkaya *, Ismail Ozdemir , M. Nawaz Tahir , Dinc¸er Ulku¨
a Department of Chemistry, Ino¨nu¨ Uni6ersity, 44069 Malatya, Turkey
b Department of Engineering Physics, Hacettepe Uni6ersity, Beytepe 06532 Ankara, Turkey
Received 9 June 1997; received in revised form 27 January 1998
Abstract
Interaction of [{Pt(v-Cl)Cl(PMe2Ph)}2] with 1-methyl-1,4,5,6-tetrahydropyrimidine, L (R=Me), in boiling toluene produced a
¸¹¹¹¹¹¹¹¹¹¹¹¹º
mixture of cis- and trans- isomers of [PtCl2(PMe2Ph){N=CH(Me)CH2CH2CH2}]; trans-complex 2 isomerizes to give thermody-
namically more stable corresponding cis-complex 1 in boiling ethanol. Spectroscopic and X-ray diffraction data permit
generalizations about cis- and trans- isomeric pairs to be made. In addition, the trans influence of the ligand L is reliably assessed.
© 1998 Elsevier Science S.A. All rights reserved.
Keywords: Tetrahydropyrimidine complexes; Platinum(II); Trans-influences; Cis-trans-isomerizations
1. Introduction
yn-1-ol into 2,3-dimethylfuran [10] or for the
cyclopropanation of ethyl diazoacetate and styrene
Nitrogen containing aromatic heterocycles coordi-
[11]. They also exhibit selective antimicrobial activity
nated to the platinum metals continue to play an
[12]. As a continuation of this work we describe in
important role both in catalysis [1,2] and in search
for effective antitumor drugs [3–5]. In this context, a
number of mononuclear metal systems have been
structurally characterized [6–9]. Recently, we have
been interested in synthesis and reactivity of the late
transition-metal complexes containing partially re-
duced rings such as L or L% as ligands.
this paper (i) the preparation; (ii) NMR spectro-
scopic characteri¸za¹ti¹o¹n¹o¹f¹c¹is¹- ¹a¹n¹dºtrans- isomers of
[PtCl2(PMe2Ph){NꢀCH(Me)CH2CH2CH2}] and (iii)
the single-crystal X-ray structures 1 and 2.
2. Results and discussion
Some of the resulting complexes behave as cata-
Di-v-chlorobis[chloro(trialkylphosphine)platinum(II)]
lysts for the cyclization of (Z)-3-methylpent-2-en-4-
has been used in the synthesis of mononuclear platinum
compounds via cleavage of the bridging Pt–Cl bonds
[11]. In a related way, we have used 1-methyl-1,4,5,6-te-
* Corresponding author.
trahydropyrimidine, L (R=Me), as a nucleophile.
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00471-9

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B. Cetinkaya et al. / Journal of Organometallic Chemistry 561 (1998) 7–11
8
Thus, reaction of the dimer with 2 mol equivalent of L
in boiling toluene leads to the rapid formation of a
mixture of 1 and 2 in essentially quantitative yield: the
ratio of the isomers formed is 1:2=40:60, based on
yields of the recovered material. This is somewhat
surprising because under identical conditions reaction of
related ligand L% (R=Et, or CH2Ph) with [{Pt(v-
Cl)Cl(PEt3)}2] has given only trans- isomer [11].
doublets which exclude tautomerization within the lig-
and. The H-NMR spectra indicate a significant differ-
1
ence between the isomers: All resonances assigned to the
protons on the ligand L of the trans- isomer have shifted
into low field in comparison with the cis- isomer. The
spectra of 1 and 2 show doublets at l 1.80 and 1.81
assigned to P–CH3. The presence of 195Pt satellites
[33.7% natural abundance, 3J(Pt–H)=37.1 and 25.2
Hz] demostrates that 1 and 2 are cis- and trans- isomers,
respectively [19]. Consistent with these, the 13C-NMR
spectra of complexes 1 and 2 give C2 signals with
coupling constants 3J(Pt–C)=54.3 and 32.6 Hz, respec-
tively.
While the complex 1 is white, 2 is yellow and both
products are stable towards oxygen and moisture. When
trans- complex 2 was heated (4 h) in ethanol under
reflux, the yellow colour was discharged to give white
cubic crystals of 1. In contrast, the cis-complex did not
isomerize in refluxing ethanol after 4h. It is noteworthy
that whereas cis“trans isomerizations are well known in
platinum chemistry (thermally [13], photochemically [14]
or in the presence of catalytic amount of bases [6,15]) the
reverse process is relatively novel [15–18]. The isomeric
pair have been characterized by elemental analysis (C, H,
N), IR and NMR spectroscopy and X-ray diffraction
techniques. The IR spectra of the products show a band
at ca. 1645 cm−1 attributable to w(CꢀN).
The 31P{H}-NMR spectra of 1 and 2 show singlets at
−23.8 and −18.2 ppm [relative to H3PO4] with 195Pt
1
satellites J(Pt–P)=3880 and 3251 Hz, respectively. In
¸¹¹¹¹¹¹¹¹º
the related trans-[PtCl2(NꢀCHN(R)CH2CH2)(PEt3)]
complexes, 1-alkyl-2-imidazoline (L%) nitrogen atom
showed coupling constants 1J (31P–195Pt)=3345 and
3314 Hz for R=Et and CH2Ph, respectively [11]. Vari-
ations in 1J(Pt–P) in platinum(II) complexes can be used
as a measure of the trans- influence of the ligand trans
C2 and C2–H of the heterocycle L and dimethyl-
phenylphosphine are effective probes for NMR spectro-
scopic studies (Tables 1 and 2). Thus, non-decoupled
13C-NMR spectra of 1 and 2 exhibit C2 carbon as
to P. In this procedure a high J(Pt–P) implies a low
1
trans- influence for the appropriate ligand [20]. Accord-
ingly, we should have the trans- influence order: PR3\
L\L%\Cl−.
Table 1
1H-NMR spectral data of the compounds La, 1 and 2 in CDCl3b
Compound
C2H
C4H2
C5H2
C6H2
N–CH3
P–CH3
C6H5
L
1
6.90 (s)
6.84 (t)
3.20 (m)
3.07 (t)
1.80 (q)
1.51 (q)
3.2 (m)
2.83 (t)
2.80 (s)
2.68 (s)
—
1.80 (d)
—
7.43 (m)
7.60 (m)
JPtH=45.5
JHH=5.6
JHH=5.8
J
HH=5.9
J
J
PH=11.6
PtH=37.1
2
7.44c
3.60 (t)
HH=5.3
1.93 (q)
HH=5.8
3.15 (t)
HH=6.0
2.97 (s)
1.81 (d)
7.44 (m)
7.86 (m)
J
J
J
J
J
PH=11.4
PH=25.2
a Included for the sake of comparison.
b Chemical shifts, l, are with reference to SiMe4 in CDCl3 solutions. Coupling constants, J, are in Hz.
c Obscured by the multiplets of the phenyl protons.

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B. Cetinkaya et al. / Journal of Organometallic Chemistry 561 (1998) 7–11
9
Table 2
13C-NMR and 31P spectral data of the isomeric compounds in CDCl3a
Compound
C2H
C4H2
C5H2
C6H2
N–CH3
P–CH3
C6H5
lb (PMe2Ph)
L
1
162.8
155.6
32.6
21.6
51.4
47.9
54.7
44.9
35.4
41.2
—
12.7 (d)
—
129.2,
131.2,
—
−189.2
JPtP=38.5
129.1
131.0,
132.0
128.4,
131.2,
J
J
CH=194.1
PtC=54.3
JPC=43.8
2
154.5
20.9
45.6
43.6
40.8
12.6 (d)
PC=43.9
130.4,
132.2
−23.9
PtP=3283
J
J
CH=194.6
PtC=32.6
J
J
a Chemical shifts, l, are with reference to SiMe4.
b With reference to H3PO4; coupling constants, J, are in Hz.
complex has a more planar coordination plane than the
cis-isomer. The distance of the Pt2+ ion to the best
plane going through the coordination atoms Cl1, Cl2,
In order to confirm the above conclusion, we have
studied the structures of 1 and 2. It is worth noting that
although structural data on divalent platinum com-
plexes are becoming more available, such data on the
isomeric pairs are still rare [17,18]. The molecular struc-
tures of the isomers are illustrated in Figs. 1 and 2. For
a summary of crystal data, data collection and refine-
ment details, see Section 4. Cis- and trans- complexes
crystallize in triclinic and orthorhombic systems, re-
˚
˚
N1 and P is 0.0272(4) A for trans-and 0.0467(1) A for
cis-complex.The range of the bond angles in cis-and
trans-isomers are 87.32(3)–94.94(8)° and 88.7(2)–
92.7(0)° respectively.The trans-isomer has equal Pt–Cl
˚
˚
˚
distances[2.299(3) A] while the Pt–Cl1 [2.385(1) A] and
Pt–Cl2 [2.3115(9) A] bond lengths in cis-isomer differ
slightly from each other and they are longer than the
spectively,
composed
of
discrete
molecules,
Pt–Cl bond lengths observed in the trans-isomer.The
C12H21Cl2N2PPt. For a full listing of final coordinates
and temperature factors and the selected bond lengths
and angles, see Section 4. In both isomers the Pt2+ ion
has a slightly distorted square-planar coordination
(Figs. 1 and 2) involving two Cl atoms, the P atom of
the dimethylphenylphosphine ligand and an N atom of
the 1-methyltetrahydropyrimidine ligand. The trans-
˚
˚
Pt–N distances [2.015(3) A] for cis and [2.102(8) A] for
trans have values further apart than the Pt–P distances
˚
[2.2193(8)] and [2.237(3)] A, respectively. The phenyl
ring is planar with expected bond length and bond
angle values.The pyrimidine ring is not planar.The dis-
tances of the C3 atoms from the least squares plane
through the ring atoms N1, C1, N2, C2 for cis- and
˚
trans-complexes are 0.612(5) and 0.60(1) A, respec-
tively. The methyl C5 atoms are also out of the plane
˚
mentioned above, namely 0.278(5) A for cis- and
˚
0.06(1) A for trans-isomerDeviation from planarity for
C3 and C5 occur in opposite directions. For the cis-
and trans-complexes the interplanar-angles between the
coordination plane and the phenyl rings are 70.1(1) and
78.9(3)°, respectively.
In conclusion, the main differences between cis- and
trans- complexes, 1 and 2, are as follows: (i) cis- is
white, trans- is yellow; (ii) solubility in non-polar sol-
1
2
3
vents (trans\cis); (iii) J(Pt–P), J(Pt–C2) and J(Pt–
H) (cis\trans); (iv) w(CꢀN) (cis\trans); (v) l(Pt–P)
(trans\cis); (vi) l(Pt–N3) (trans\cis); (vii) l(C2–N3)
(transBcis). Many of these features are attributed to
the greater ionic character of the cis compared with the
trans complex, which in turn relates to the trans influ-
ence order.
3. Experimental
Fig. 1. ORTEPII drawing of the structure of the cis-complex 1,
showing the atomic numbering scheme. Displacement ellipsoids of
non-H atoms are shown at the 30% probability level and H atoms are
drawn as small circles of arbitrary radii.
All experiments were carried out under an atmo-
sphere of dry, purified argon. Glassware was dried and

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B. Cetinkaya et al. / Journal of Organometallic Chemistry 561 (1998) 7–11
10
Fig. 2. ORTEPII drawing of the structure of the trans-complex 2, showing the atomic numbering scheme. Displacement ellipsoids of non-H atoms
are shown at the 30% probability level and H atoms are drawn as small circles of arbitrary radii.
filled with argon, and solvents were distilled and kept
under argon. Instruments: NMR, Bruker AC300P FT
spectrometer operating at 300.13 MHz (1H), 121.50
MHz (31P) and 75.47 MHz (13C), SiMe4 as internal
standart; IR, spectra were recorded in the 4000–400
cm−1 region on a Pye Unicam spectrometer. Starting
materials were either commercially available or were
mer deposited. The crystals were filtered off, washed
with ether and dried in vacuo (0.05 g). They were
identified by H-NMR spectroscopy.
The cis-complex did not change in refluxing ethanol
after 4 h.
1
3.3. X-ray crystallography
prepared
following
literature
procedures:
¸¹¹¹¹¹¹¹¹¹¹¹º
NꢀCH(Me)CH2CH2CH2 [21], [Pt(v-Cl)Cl(PMe2Ph)]2
Suitable single crystals for X-ray diffraction were
grown by cooling the CH2Cl2/Et2O solution and the
isomers were separated manually. The weighting
scheme used was w=1/|2(F) and w=1/[|2(F)+
(0.02)2+1.0] except w=0 if F2B6|2F for cis- and
trans complexes, respectively. All non-H atoms were
refined with anisotropic displacement parameters. H
atoms of the phenyl ring were placed geometrically
[19,22].
3.1. Synthesis of complexes 1 and 2
A solution of the tetrahydropyrimidine (0.18 g, 1.84
mmol) in toluene (10 ml) and [Pt(v-Cl)Cl(PMe2Ph)]2
(0.61 g, 0.75 mmol) were heated for 2 h under reflux.
n-Hexane (15 ml) was added to the solution in order to
obtain pale-yellow product. Recrystallization from
CH2Cl2 (5 ml)/Et2O (10 ml) at −25°C, gave white and
yellow crystals of 1 and 2 which were manually sepa-
rated. The ratio of cis/trans-isomers was ca. 40/60 and
total yield 0.66 g (89%).
˚
0.950 A from their parent atoms. Other H atoms were
refined for a few cycles.For all H atoms a riding
model was used with Beq(H)=1.3Beq(C). For data
collection CAD4-Express, [23] for data reduction,
structure solution and refinement MoIEN [24], for
molecular graphics ORTEPII [25] programs were
used.
1: M.p. 203–204°C. w(CꢀN, KBr, cm−1)=1649.
Anal.Found: C, 30.99; H, 4.32; N, 5.55.
C12H21N2Cl2PPt (490.271). Calc.: C, 31.13; H, 4.22; N,
5.59. 2: m.p. 152–153°C. w(CꢀN, KBr, cm−1)=1643.
Anal.Found: C, 30.95; H, 4.30; N, 5.50.
4. Supplementary material available
Crystal data, data collection and refinement details,
final coordinates, temperature factors, and selected
bond lengths and angles are available on request from
the author.
3.2. Isomerization of 2 into 1
The trans-complex (0.06 g) was heated in refluxing
ethanol for 4 h. Upon cooling white crystals of cis-iso-

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B. Cetinkaya et al. / Journal of Organometallic Chemistry 561 (1998) 7–11
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