A novel platinum methylene complex

Article abstract of DOI:10.1016/S0022-328X(99)00441-6

The dichlorobridged diplatinum organyls 4 and 5 undergo the expected chlorine-iodine exchange when treated with lithium iodide in diiodomethylene. Surprisingly, a second type of product, the triple-bridged (one methylene group plus two iodo units between

Full text of DOI:10.1016/S0022-328X(99)00441-6

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 592 (1999) 155–161
A novel platinum methylene complex
Klaus Praefcke a,1, Belkız Bilgin b,*, Joachim Pickardt a, Marina Borowski a
a Faculty of Chemistry, Technische Uni6ersita¨t Berlin, D-10623 Berlin, Germany
b
8
Department of Chemistry, Yıldız Teknik Uni6ersitesi, TR-80270, Sisli, Istanbul, Turkey
Received 7 July 1999; accepted 14 July 1999
Abstract
The dichlorobridged diplatinum organyls 4 and 5 undergo the expected chlorine–iodine exchange when treated with lithium
iodide in diiodomethylene. Surprisingly, a second type of product, the triple-bridged (one methylene group plus two iodo units
between the two Pt atoms) diplatinum complexes 7 and 8, respectively, are also formed in these unusual reactions. The formation
of these latter two interesting, novel compounds takes place via a change of configuration of their two ligand sections from anti
of their precursors (4 and 5, respectively) to syn present in 7 and 8; the mechanism of this process, however, is not yet clear. The
molecular structures of 7 and 8 are based on an X-ray crystal analysis of 7 and on their comparable characteristic NMR data.
© 1999 Elsevier Science S.A. All rights reserved.
Keywords: Anti/syn-transformation; Cycloplatination; Halogen exchange; Liquid crystal discussion; Overcrowded platinum organyls; Oxidative
addition; Platinum complexes of different oxidation states; Platinum methylene complexes; X-ray structure analysis
Here, we report not only the synthesis and character-
ization of two new planar diplatinum organyls (4 and
1. Introduction
6), but also the preparation of novel type m-methylene
The chemistry of cyclometallated complexes has at-
tracted much attention due to their applications in
organic synthesis. Whereas cyclometallated organopal-
bridged bis-metal complexes (7 and 8) formed by inter-
molecular oxidative addition reactions of di-
iodomethane onto cyclometallated diplatinum(II)
ladium compounds have been studied extensively, there
complexes.
are fewer studies of platinum(II) complexes with ortho-
metallated nitrogen donor ligands exhibiting liquid-
crystalline properties [1]. In particular, ortho-metallated
platinum(IV) complexes with nitrogen donor ligands
were unknown until recently and current knowledge is
2. Results and discussion
restricted to a few compounds synthesized by oxidative
addition of halogens or halocarbons to platinum(II)
precursors [2].
Since the discovery of the first example of metal
complexes with methylene bridged two metal atoms by
Herrmann et al. [3], such metal organyls have become
of special interest because of their affinity to methylene
groups on metal surfaces in heterogeneous reactions
[4,5].
The double-(chloro-)bridged platinum organyls 4 and
5 [6] containing two platinum atoms forming a flat
molecular core region were obtained by similar meth-
ods of ortho-metallation of diaryl imines — here 1 and
2 — as applied [6–8] for the syntheses of other equally
shaped dipalladium and diplatinum organyls with liq-
uid-crystalline properties (Scheme 1).
The exchange of the chloro-bridges in the diplatinum
organyl 4 with lithium iodide in dichloromethane–ace-
tone yielded not only the planar double-(iodo-)bridged
diplatinum(II) complex 6 but, surprisingly, also the
triple-bridged (methylene plus two iodo-bridges be-
tween the two Pt atoms) diplatinum(IV) organyl 7
(Scheme 1). Furthermore, this interesting and novel
* Corresponding author. Tel.: +90-212-2245000-1199; fax: +90-
212-2245013.
E-mail address: bilgin@yildiz.edu.tr (B. Bilgin)
1 Also corresponding author.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00441-6

156
K. Praefcke et al. / Journal of Organometallic Chemistry 592 (1999) 155–161
and free-radical reactions (chain- and nonchain-types)
bis-octahedral diplatinum methylene complex 7 could
be isolated exclusively under the same conditions but
using longer reaction times.
Alternatively, 7 can also be obtained from the reac-
tion of 4 with diiodomethane but in lower yields, see
Section 3.
Another example of this kind of triple-bridged plat-
inum complex is the diplatinum organyl 8 (Scheme 1),
now having eight longer alkoxy chains. This homologue
was obtained analogously from the liquid-crystalline
diplatinum organyl 5 (Cr 91.7°C {ND 54.4°C} Iso [6];
Cr=crystalline, ND=nematic discotic, Iso=isotropic
liquid) and lithium iodide excess in dichloromethane–
acetone. Numerous repetitions of this transformation
reaction yielded 8 as the only product.
have been found. However, the SN process is dominant
2
in reactions of alkyl halides or halogens and square-pla-
nar d8 complexes with ligands that do not block the
coordination sites above and below the coordination
plane [2,9,10]. These studies cited indicate that the
oxidative addition reactions of the related chloro-
bridged diplatinum(II) complexes forming the Pt(IV)
species 7 and 8 may proceed in an SN manner about
2
which details are yet unknown.
All the compounds described here were fully charac-
1
terized by H-, 13C-, and also (in part) by 195Pt-NMR
1
spectroscopy as well as by elemental analysis. The H-
and 13C-NMR data for the diplatinum organyls 4 and 6
are similar to those of the analogous anti-configurated,
proved by X-ray analysis [6], square-planar platinum
organyl 5. The l(195Pt) value of −3130.3 ppm for the
chloro-bridged platinum organyl 4 is well within the
range expected for organoplatinum(II) compounds
[6b,8] with ortho-metallated nitrogen donor ligands.
Oxidative addition of alkyl halides or halogens on
Pt(II) compounds can proceed via several mechanisms
[2]. Depending on the metal substrate, the alkyl halide,
or the halogen, and the reaction conditions both SN
2
Scheme 1.

K. Praefcke et al. / Journal of Organometallic Chemistry 592 (1999) 155–161
157
spectra for 7 and 8 display a single absorption at 6.55
and 6.52 ppm, respectively, for the CH2-bridges. The
interpretation of the 13C-NMR signals of the m-CH2
groups of the triple-bridged, bis-octahedral complexes 7
and 8 was possible on the basis of a 2D C–H COSY
spectrum. The 13C-NMR spectra of 7 and 8 showed a
triplet at 9.88 and at 9.80 ppm, respectively, for the
CH2-bridges.
Furthermore, for the bis-octahedral compounds 7
and 8 the resonance frequency of the iminic protons (l
8.36 and 8.33 ppm, respectively) was shifted to a lower
field relative to the bis-square-planar platinum(II) com-
pounds 4, 5 [6] and 6, cf. Section 3. The aforementioned
selected NMR data undoubtedly prove that 7 and 8 are
of identical basic molecular structure.
Suitable crystals of 7 as a model compound for an
X-ray analysis, due to its short substituents compared
with those of the homologue 8, were grown by slowly
evaporating its methanol–acetone solution. The molec-
ular structure of 7 including the atom labelling based
on that X-ray study is illustrated in Fig. 1.
Fig. 1. The crystal structure of 7.
The new organyl 7 crystallizes in the triclinic space
Table 1
Crystal and data collection parameters for 7 a
(
group P1. The crystal data, data collection and refine-
ment details are summarized in Table 1. Table 2 gives
the atomic coordinates and Table 3 a compilation of
selected bond lengths and angles.
Formula
C45H58I4N2O6Pt2
1620.74
0.05×0.2×0.5
Triclinic
Formula weight
Crystal size (mm)
Crystal system
Space group
Z
All atoms occupy general positions in the unit cell.
The two platinum atoms are each octahedrally coordi-
nated by a terminal iodine atom, two bridging iodine
atoms, and a methylene group (C45) as well as by a
nitrogen atom and a ring carbon (C19) of the
trimethoxyphenyl ring. The (nonbonding) distance
(
P1 (No. 2)
2
,
a (A)
10.543(7)
16.132(8)
17.156(29)
100.54(10)
95.89(11)
101.31(5)
2783.8
1.93
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
,
Pt1···Pt2 is 3.137(6) A. The iodine bridges are unsym-
,
metric with mean distances of 2.82(1) and 2.67(1) A,
3
most probably due to the trans-effects of the ligand
,
V (A )
dc (g cm−3
)
carbon versus the iodine atoms. The methylene bridge
,
Radiation u (A)
Mo–Ka, 0.71069
73.1
,
is symmetric with a mean PtꢀC distance of 2.08 A. The
v (cm−1
)
,
smallest intermolecular distance Pt···Pt is 8.74(2) A.
2qmax (°)
40.0
To the best of our knowledge, no dinuclear plati-
num(IV) compounds with methylene or related bridges
are known up until to now. However, there exists a
limited number of platinum(II) compounds of this type,
but, with the coordination number four, e.g.
hkl range
05h57, −155k515, −165l516
Scan type
ꢀ-scan
Min 1.0, max 29.3
4933
3194
Scan speed (deg min−1
No. of data measured
No. of unique data
)
I\2|(I)
1. [Pt2(m-CH2)(CH2PPh3)(m-dppm)2][PF6]
(dppm=
R
0.053
Ph2PCH2PPh2) with distances between PtꢀC 2.13(3)
Rw
w
0.055
1/[|2(F)+0.001951F2]
) −0.96/1.89
and Pt···Pt 3.12(2) A [11],
,
−3
,
Res. electron density (e A
Absorption correction
2. [Pt2(m-CH2)(m-Ph2PC2H4PPh2)2] with a PtꢀC dis-
Empirical, min/max corrections
0.710/1.459
,
tance of 2.08 A [12],
3. [Pt2W3(m-CC6H4Me-4)2(m3-CC6H4Me-4)(CO)6(h-
a Estimated standard deviations are given in parentheses.
C5H5)3] with distances between PtꢀC 2.02(3) and
,
Pt···Pt 2.95(2) A [13],
4. [Pt2(m-CꢁCHPh)(CꢂCPh)(PEt3)3I] with the following
The data given in the literature for the chemical shift
of CH2-bridges (3.43–8.03 ppm) [4,5] in related materi-
als differ considerably depending on the type of metal
atom as well as the nature of the ligands. The 1H-NMR
three distances: PtꢀC 2.10(9), Pt···Pt 2.72 (1) [14]
,
and PtꢀI 2.69(1) A.
A comparison of these excerpted measures shows
,
that the PtꢀC distance of 2.02(3) A in the third com-

158
K. Praefcke et al. / Journal of Organometallic Chemistry 592 (1999) 155–161
,
pound quoted here and the PtꢀI distance of 2.69(1) A in
Table 2
the fourth compound are in good agreement with those
Atom positions and Ueq values for 7 a
,
reported here for 7: 2.08(3) A and its shorter one of the
two PtꢀI distances of 2.67(1) and 2.82(1) A,
,
b
2
,
Atom
x
y
z
Ueq (A )
respectively.
Pt1
Pt2
I1
I2
I3
I4
O1
O2
O3
O4
O5
O6
N1
N2
C1
C2
C3
0.00964(12)
0.15141(12)
0.23563(21)
0.04860(23)
0.13227(21)
0.14016(7)
0.33419(7)
0.22968(12)
0.43236(13)
0.19761(12)
0.09400(13)
0.0882(13)
0.24473(7) 0.0373(5)
0.31135(7) 0.0388(5)
0.19765(12) 0.0500(8)
0.41369(12) 0.0595(9)
0.39491(11) 0.0506(8)
0.10058(12) 0.0605(9)
0.3736(12) 0.0648(58)
0.3997(14) 0.0767(60)
0.3492(15) 0.0799(61)
0.2250(12) 0.0679(58)
0.1161(12) 0.0719(58)
0.0979(13) 0.0799(60)
0.2397(11) 0.0448(56)
0.3598(12) 0.0371(56)
0.3000(18) 0.0564(64)
0.2895(14) 0.0443(61)
0.3101(16) 0.0433(62)
0.3470(14) 0.0403(61)
0.3642(15) 0.0407(61)
0.3386(18) 0.0573(65)
0.2743(15) 0.0523(64)
0.2141(17) 0.0544(62)
0.1399(18) 0.0563(65)
0.1156(19) 0.0649(65)
0.1654(18) 0.0486(65)
0.2340(16) 0.0421(64)
0.2589(17) 0.0476(64)
0.2546(15) 0.0396(61)
0.2095(18) 0.0549(65)
0.1608(18) 0.0518(64)
0.1533(16) 0.0561(64)
0.1921(15) 0.0525(64)
0.2477(15) 0.0321(59)
0.3163(17) 0.0605(64)
0.4158(14) 0.0364(61)
0.4025(17) 0.0385(64)
0.4600(20) 0.0557(66)
0.5281(17) 0.0484(65)
0.5414(18) 0.0552(65)
0.4831(16) 0.0479(65)
0.5937(20) 0.0744(81)
0.5544(22) 0.0887(89)
0.6230(19) 0.0699(79)
0.6714(22) 0.0886(89)
0.6239(25) 0.1076(97)
0.6815(24) 0.1069(96)
0.1416(20) 0.0719(80)
0.0572(33) 0.172(12)
0.0166(24) 0.0992(93)
Since the work presented in this paper originated
from our interest in novel materials and the relationship
between their molecular structures and thermomeso-
morphic properties, we want to comment on the follow-
ing observations with regard to the five platinum
organyls 4–8.
Whereas the flat 5 shows liquid-crystalline behaviour,
the four complexes 4 and 6–8 do not for different
reasons:
1. 4 and 6, although disc-like and flat, both carry too
short substituents,
2. 7 and 8 mainly due to their bulkiness and the fact
that they are bent too much, impressingly, as Fig. 1
and a ball-and-stick model demonstrate.
Surprisingly, in contrast to its precursor 4 the
‘dimeric’ product 7, model compound of our X-ray
study, adopts now syn-configuration! The interesting
anti–syn-transformation process involved here can not
yet be rationalized by us.
In each half of this molecule the platinum atom, the
anellated heterobicyclic part of the ligand, the bridging
carbon C45, and one of the bridging iodine atoms (I-1
for Pt-1, I-3 for Pt-2) lie in a plane; the terminal iodine
and the remaining bridging iodine atom are stretching
perpendicularly out of this plane. The two planes about
the platinum atoms form an angle of approximately
65°, but the axes through the two heterobicyclic ligand
sections lie nearly perpendicular to each other. The two
substituted phenyl rings bound to the nitrogen atoms
are nearly coplanar to each other and tilted relative to
their flat N-bicyclic carriers by about 60°.
In summary, both 7 and 8 are repeatedly folded and
indeed very bulky, depicting a kind of spacious knot,
i.e. suffering from a heavily overcrowded molecular
situation, due to which it is not possible for thermo-
mesomorphism to be exhibited — not even when this
material (8) carries eight middle long chains: two hexyl
and six hexyloxy groups.
−0.12474(23)
−0.4478(22)
−0.4157(22)
−0.2038(22)
0.4384(22)
0.2418(22)
0.0000(23)
0.0621(24)
0.3522(20)
−0.1325(32)
−0.1446(29)
−0.2555(28)
−0.3468(30)
−0.3283(28)
−0.2233(31)
−0.0302(32)
0.1792(34)
0.2073(31)
0.3213(35)
0.4026(30)
0.3643(29)
0.2511(30)
0.2890(29)
0.3153(30)
0.2195(32)
0.0967(34)
0.0647(31)
0.1651(26)
0.3893(33)
0.4470(30)
0.5720(29)
0.6618(30)
0.6215(29)
0.4888(31)
0.4027(29)
0.7145(34)
0.7802(37)
0.8738(32)
0.9917(36)
1.0857(40)
1.1859(39)
0.5269(34)
0.5339(54)
0.4394(39)
0.4427(72)
0.3764(68)
0.3803(57)
−0.4898(34)
−0.3753(41)
−0.3131(39)
0.5058(39)
0.2243(44)
−0.1299(38)
−0.0323(27)
−0.0631(15)
−0.1298(14)
0.5950(13)
0.6208(13)
0.5264(15)
0.0142(13)
0.4098(14)
−0.0025(18)
0.0784(16)
0.1107(17)
0.0615(17)
−0.0179(19)
−0.0505(20)
−0.0317(18)
−0.0103(16)
0.0035(18)
−0.0201(18)
−0.0538(17)
−0.0660(16)
−0.0487(17)
0.4770(16)
0.5426(18)
0.5568(17)
0.5084(20)
0.4382(18)
0.4260(15)
0.4662(16)
0.3924(16)
0.3938(15)
0.3751(17)
0.3490(17)
0.3481(18)
0.3694(17)
0.3246(21)
0.2548(23)
0.2325(20)
0.2996(23)
0.3381(26)
0.4161(24)
−0.0686(21)
−0.1073(35)
−0.1827(25)
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
C16
C17
C18
C19
C20
C21
C22
C23
C24
C25
C26
C27
C28
C29
C30
C31
C32
C33
C34
C35
C36
C37
C38
C39
C40
C41
C42
C43
C44
C45
−0.2228(52) −0.0644(48) 0.283(13)
−0.2809(49) −0.1284(47) 0.256(13)
−0.3393(38) −0.1900(36) 0.199(12)
0.1530(21)
−0.0625(26)
−0.2021(25)
0.5876(25)
0.7013(28)
0.4728(24)
0.2621(16)
3. Experimental
1
The H- and 13C-NMR spectra were recorded with a
0.3390(21) 0.0803(85)
0.4738(25) 0.1119(98)
0.3073(24) 0.1039(95)
0.1524(24) 0.1059(95)
0.1521(27) 0.128(10)
0.0805(23) 0.0965(92)
0.2572(15) 0.0417(59)
Bruker WH 400 or AM 270 spectrometer, respectively,
in CDCl3 solutions; only structurally relevant data are
reported in the following. The 195Pt-NMR spectra were
run on a Bruker ARX 400 spectrometer (86.02 MHz) in
CDCl3 solutions using a separate reference sample (0.5
g Na2PtCl6 in 2 ml D2O). The MS spectrum was
recorded with a VARIAN MAT 711 spectrometer. The
melting points and enthalpies were obtained using dif-
a Estimated standard deviations are given in parentheses.
b Ueq=(1/3)ꢀiꢀjUija*a*aiaj.
i
j

K. Praefcke et al. / Journal of Organometallic Chemistry 592 (1999) 155–161
159
Table 3
Selected bond distances (A) and angles (°) for 7
3.1. Preparation of the compounds 1, 2, 4–8
3.1.1. Synthesis of the imine ligands 1 and 2
a
,
Pt1ꢀI1
Pt1ꢀI3
Pt1ꢀI4
Pt1ꢀN1
Pt1ꢀC2
Pt1ꢀC45
Pt2ꢀI1
Pt2ꢀI2
Pt2ꢀI3
2.808(6)
2.673(5)
2.622(5)
2.20(2)
2.03(3)
2.08(3)
2.679(5)
2.610(5)
2.827(5)
2.22(2)
1.99(3)
2.08(3)
I1ꢀPt1ꢀI3
I1ꢀPt1ꢀI4
86.4(1)
95.2(1)
99.0(7)
174.6(7)
80.5(8)
174.6(1)
91.4(5)
88.2(7)
84.7(7)
93.4(5)
90.2(7)
90.5(7)
80.6(10)
176.1(9)
99.6(11)
174.7(1)
85.9(1)
92.6(6)
91.4(8)
83.7(8)
95.2(1)
92.2(6)
87.4(8)
91.4(8)
101.4(6)
177.2(8)
80.9(7)
79.6(9)
175.6(9)
98.0(11)
69.7(1)
69.5(1)
The imine 1 was prepared in the usual way by
p-toluenesulfonic acid (40 mg) catalyzed condensation
of 10 mmol (1.96 g) 2,3,4-tri(methoxy)benzaldehyde
with 12 mmol (2.13 g) 4-hexylaniline — both commer-
cially available — in 50 ml toluene and purified by
column chromatography on alkaline aluminium oxide
(eluent petroleum ether (b.p. 30–70°C)–ethyl acetate
10:1).
I1ꢀPt1ꢀN1
I1ꢀPt1ꢀC2
I1ꢀPt1ꢀC45
I3ꢀPt1ꢀI4
I3ꢀPt1ꢀN1
I3ꢀPt1ꢀC2
I3ꢀPt1ꢀC45
I4ꢀPt1ꢀN1
I4ꢀPt1ꢀC2
I4ꢀPt1ꢀC45
N1ꢀPt1ꢀC2
N1ꢀPt1ꢀC45
C2ꢀPt1ꢀC45
I1ꢀPt2ꢀI2
Pt2ꢀN2
Pt2ꢀC19
Pt2ꢀC45
The analogous preparation and spectroscopic data
for imine 2 is given in Ref. [6].
4-Hexylbenzene[2,3,4-tri(methoxy)benzal]imine (1):
yield 3.3 g (93%), yellow oil. 1H-NMR: l=8.74 (s;
HCꢁN), 7.89, 7.20, 7.14, 6.78 (4d, J:8 Hz each; 1, 2,
2 and 1 arom. Hs, respectively), 3.96, 3.93, 3.90 (3s; 3
OCH3 groups), 2.62 (t, J:7.5 Hz; a-CH2 group). —
13C-NMR: l=156.32, 154.50, 150.25, 141.74, 140.45,
123.03 (6s; 6 arom. Cs), 155.15 (d; HCꢁN), 128.97,
122.49, 120.83, 107.75 (4d; 2, 1, 2 and 1 arom. CH,
respectively), 61.96, 60.87, 56.02 (3q; 3 OCH3 groups),
35.43 (t; a-CH2 group). — C22H29NO3; MS: m/z=
355.2147 [M+], Calc. 355.2147.
I1ꢀPt2ꢀI3
I1ꢀPt2ꢀN2
I1ꢀPt2ꢀC19
I1ꢀPt2ꢀC45
I2ꢀPt2ꢀI3
I2ꢀPt2ꢀN2
I2ꢀPt2ꢀC19
I2ꢀPt2ꢀC45
I3ꢀPt2ꢀN2
I3ꢀPt2ꢀC19
I3ꢀPt2ꢀC45
N2ꢀPt2ꢀC19
N2ꢀPt2ꢀC45
C19ꢀPt2ꢀC45
Pt1ꢀI1ꢀPt2
Pt1ꢀI3ꢀPt2
3.1.2. Synthesis of the chloro-bridged dinuclear
platinum compounds 4 and 5
A solution of 2.05 mmol (0.73 g) of the imine 1 in 10
ml of dry methanol was added under Ar to a suspen-
sion of 1 mmol (0.57 g) of di-m-chloro-bis(h3-2-methyl-
allylplatinum) [20] (3) in 25 ml of dry methanol. After
stirring the reaction mixture at r.t. for 20 days a yellow
precipitate was filtered off. Crystallization from
methanol–acetone yielded the platinum organyl 4 as
yellow crystals.
a Estimated standard deviations are given in parentheses.
ferential scanning calorimetry (Mettler TA 3000/DSC-
30 S with TA 72.5 software).
Single-crystal X-ray diffraction analysis: the determi-
nation of the lattice parameters and the data collection
were performed with a diffractometer Syntex P21 at
room temperature (r.t.). As only small, weakly diffract-
ing crystals could be obtained, the 2u-limit for the data
collection was set to 40°. Lorentz and polarisation
corrections as well as an empirical absorption correc-
tion (DIFABS [15]) were applied. The structure was
solved with the Patterson method using SHELXS-86 [16]
and completed by successive Fourier difference maps
using SHELX-76 [17]. The alkyl side chains proved to be
disordered and these atoms were included with
isotropic thermal parameters, as were the methyl group
C atoms, which were treated as rigid groups. The
remaining non-hydrogen atoms were included with an-
isotropic thermal parameters. Geometry calculations
and plots were obtained using PLATON and PLUTON
[18]. Atomic scattering factors and anomalous disper-
sion corrections were taken from the International Ta-
bles for X-ray Crystallograhy [19] or as supplied by
SHELX. All the hydrogen positions were introduced in
the last step of the refinement process in calculated
positions.
The analogues preparation and spectroscopic data
for compound 5 is given in Ref. [6].
1
Based on the H-NMR data for 4 we assume this
platinum organyl to be a mixture of two isomers, at
least in solutions, as reported in a previous paper for
the hexyloxy-substituted diplatinum analogue 5 [6].
This is probably due to the different orientations of the
two ligands i.e. parallel or antiparallel to each other, in
the molecule.
Di - m - chlorobis[3,4,5 - tris(methoxy) - 2 - {[(4 - hexyl-
phenyl)imino]methyl}phenyl-C,N]diplatinum(II)
(4):
yield 0.55 g (47%), m.p. 223.5°C (57.3 kJ mol−1) (at
:232.2°C decomposition). 1H-NMR: l=8.18, 8.16
[2s, ratio 1 (anti ):0.2 (syn); HCꢁN], 7.30, 7.19 as well as
:7.19, :7.08 (2×2d, J:8 Hz each; arom. Hs of
disubstituted rings), 6.67, 6.48 [2s, ratio 0.2 (syn):1
(anti ); arom. Hs of the platinated rings], 3.95, 3.82,
3.76 (3s; 3 types of OCH3), 2.63 (t, J:7.5 Hz; a-CH2
groups). — 13C-NMR: l=172.44 (d; 2HCꢁN), 157.34,
153.13, 146.53, 142.72, 137.21, 135.33, 130.80 (7s; 14
arom. Cs), 128.55, 123.51, 109.36 (3d; 4, 4, and 2 arom.

160
K. Praefcke et al. / Journal of Organometallic Chemistry 592 (1999) 155–161
It should be mentioned here that extending the reac-
tion time beyond 7 days lead exclusively to the
methylene-bridged platinum complex 7.
Alternatively, compound 7 can also be obtained from
the reaction of 0.1 mmol (0.12 g) of compound 4 either
with 10 ml diiodomethane or with lithium iodide (0.67
g) in 10 ml diiodomethane by stirring the reaction
mixture at r.t. for 15 days, however, with poorer yields
(25 and 22%, respectively).
Compound 8 was prepared by a procedure analogous
to that for compound 7. Starting from 0.1 mmol (0.16
g) of the chloro-bridged diplatinum organyl 5 [6], com-
pound 8 appeared in the form of orange crystals, which
were purified by crystallization from acetone–
methanol.
Di-m-iododiiodo-m-methylenebis[3,4,5-tris(hexyloxy)-
2 - {[(4 - hexylphenyl)imino]methyl}phenyl - C,N]dipla-
tinum(IV) (8): yield 0.12 g (60%), orange crystals, m.p.
117.5°C (42.8 kJ mol−1). 1H-NMR: l=8.33 (s;
2HCꢁN), 7.34, 7.19 (2d, J:8 Hz each; arom. Hs of the
disubstituted rings), 6.82 (s; arom. Hs of the platinated
rings), 6.52 (s; m-CH2), 4.29–4.10, 3.99–3.89 (2m; 6
OCH2 groups), 2.63 (t, J:7.5 Hz; 2 a-CH2 groups). —
13C-NMR: l=166.72 (d; 2HCꢁN), 157.34, 153.55,
146.30, 142.23, 138.14, 129.35, 128.95 (7s; 14 arom. Cs),
128.63, 123.61, 111.44 (3 d; 4, 4, and 2 arom. CH,
respectively), 74.73, 74.00, 69.13 (3t; 6 OCH2 groups),
35.49 (t; 2 a-CH2 groups), 9.80 (t; m-CH2). — Anal.
Calc. for C75H118I4N2O6Pt2 (2041.5): C, 44.12; H, 5.83;
N, 1.37. Found C, 43.54; H, 5.99; N, 1.33%.
CH, respectively), 61.75, 60.73, 55.96 (3q; 6 OCH3
groups), 35.56 (t; 2 a-CH2 groups). — 195Pt-NMR:
l= −3130.3 (s). — Anal. Calc. for C44H56Cl2N2O6Pt2
(1170.0): C, 45.17; H, 4.82; N, 2.39. Found C, 45.12; H,
4.64; N, 2.49%.
3.1.3. Synthesis of the iodo-bridged dinuclear platinum
compounds 6, 7, and 8
To a solution of 0.1 mmol (0.12 g) of the chloro-
bridged platinum organyl 4 in 30 ml dichloromethane
and 15 ml acetone an excess of lithium iodide (8 mmol,
1.07 g), under Ar was added. This reaction mixture was
stirred at r.t. for 7 days. After filtration and evapora-
tion of the solvents under reduced pressure the crude
product was purified by repeated crystallization from
an acetone–methanol mixture.
The first crystallization step of the crude product
yielded the planar iodo-bridged diplatinum(II) com-
pound 6.
The platinum organyl 6 is also a mixture of two
isomers, at least in solution, as mentioned above for
compound 4.
Di-m-iodobis[3,4,5-tris(methoxy)-2-{[(4-hexylphenyl)-
imino]methyl}phenyl-C,N]diplatinum(II) (6): yield 0.03
g (22%), orange crystals, m.p. 158.4°C (decomposition).
1H-NMR: l=8.21, 8.19 [2s, ratio 1 (anti ):0.2 (syn);
HCꢁN], 7.27, 7.20 as well as 7.16, 7.09 (2×2 d, J:8
Hz each; arom. Hs of the disubstituted rings), 6.75, 6.57
[2s, ratio 0.2 (syn):1 (anti ); arom. Hs of the platinated
rings], 3.93, 3.82, 3.76 (3s; 3 types of OCH3), 2.64 (t,
J:7.5 Hz; a-CH2 groups). — 13C-NMR: l=172.52
(d; 2 HCꢁN), 157.24, 152.89, 146.70, 142.56, 136.63,
134.96, 131.12 (7 s; 14 arom. Cs), 128.48, 123.59, 110.20
(3d; 4, 4, and 2 arom. CH, respectively), 74.52, 73.46,
68.55 (3 q; 6 OCH3 groups), 35.60 (t; 2 a-CH2 groups).
— Anal. Calc. for C44H56I2N2O6Pt2 (1352.9): C, 39.06;
H, 4.17; N, 2.07. Found C, 39.44; H, 4.27; N, 2.13%.
Surprisingly, the second and slower crystallization
step of the crude product yielded the methylene-bridged
diplatinum(IV) compound 7.
4. Supplementary material
Crystallographic data have been deposited at the
Cambridge Data Center and may be obtained without
charge on quoting the depository number CCDC
120198 from CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (Fax: +44-1223-336033, e-mail: deposit@
ccdc.cam.ac.uk).
Di-m-iododiiodo-m-methylenebis[3,4,5-tris(methoxy)-
2 - {[(4 - hexylphenyl)imino]methyl}phenyl - C,N]dipla-
tinum(IV) (7): yield 0.05 g (31%), orange crystals, m.p.
127.4°C (decomposition). 1H-NMR: l=8.36 (s;
2HCꢁN), 7.35, 7.19 (2 d, J:8 Hz each; arom. Hs of
the disubstituted rings), 6.86 (s; arom. Hs of the plati-
nated rings), 6.55 (s; m-CH2), 4.05, 4.02, 3.85 (3s; 6
OCH3 groups), 2.63 (t, J:7.5 Hz; 2 a-CH2 groups). —
13C-NMR: l=166.61 (d; 2HCꢁN), 157.46, 153.86,
146.14, 142.39, 138.54, 129.43, 128.98 (7s; 14 arom. Cs),
128.65, 123.57, 110.56 (3 d; 4, 4, and 2 arom. CH,
respectively), 61.90, 61.31, 56.53 (3q; 6 OCH3 groups),
35.46 (t; 2 a-CH2 groups), 9.88 (t; m-CH2). — Anal.
Calc. for C45H58I4N2O6Pt2 (1620.7): C, 33.34; H, 3.60;
N, 1.72. Found C, 33.57; H, 3.41; N, 1.72%.
Acknowledgements
We are very grateful to Professor W.A. Herrmann,
Technische Universita¨t Mu¨nchen, Germany, for valu-
able information. Financial support of our liquid crys-
tal studies was also provided by the Deutsche
Forschungsgemeinschaft (Sonderforschungsbereich Sfb
335 ‘Anisotrope Fluide’, project C 6), the Fonds
der Chemischen Industrie, Frankfurt/Main, the
Gesellschaft von Freunden der Technischen Universita¨t
Berlin, and by the Technische Universita¨t Berlin. —
The supply of chemicals by the Degussa AG., Hanau,
Germany, is also gratefully acknowledged.

K. Praefcke et al. / Journal of Organometallic Chemistry 592 (1999) 155–161
161
[9] (a) M.F. Lappert, P.W. Lednor, Adv. Organomet. Chem. 14
(1976) 345. (b) J.P. Collman, L.S. Hegedus, in: A. Kelly (Ed.),
Principles and Application of Organotransition Metal Chem-
istry, University Science Books, Mill Valley, 1980, Ch. 4.
[10] (a) G. Ferguson, M. Parvez, P.K. Monaghan, R.J. Puddephatt,
J. Chem. Soc. Chem. Commun. (1983) 267. (b) R.J. Puddephatt,
J.D. Scott, Organometallics 4 (1985) 1221. (c) G. Ferguson, P.K.
Monaghan, M. Parvez, R.J. Puddephatt, Organometallics 4
(1985) 1669.
[11] K.A. Azam, A.A. Frew, B.R. Lloyd, L. Manojlovic-Muir, K.W.
Muir, R.J. Puddephatt, Organometallics 4 (1985) 1400.
[12] D.P. Arnold, M.A. Bennett, G.M. McLaughlin, G.B. Robertson,
J. Chem. Soc. Chem. Commun. (1983) 34.
[13] G.P. Elliot, J.A.K. Howard, T. Mise, I. Moore, C.M. Nunn,
F.G.A. Stone, J. Chem. Soc. Dalton Trans. (1986) 2091.
[14] E. Baralt, E.A. Boudreaux, J.N. Demas, P.G. Lenhert, C.M.
Lukehart, A.T. McPhail, D.R. McPhail, J.B. Myers, L. Sackst-
eder, W.R. True, Organometallics 8 (1989) 2417.
[15] N. Walker, D. Stuart, DIFABS, Acta Crystallogr. Sect. A 39
(1983) 158.
[16] G.M. Sheldrick, SHELXS-86, Program for crystal structure solu-
tion, University of Go¨ttingen, Germany, 1986.
References
[1] (a) A.-M. Giroud-Godquin, P.M. Maitlis, Angew. Chem. 103
(1991) 370; Angew. Chem. Int. Ed. Engl. 30 (1991) 375. (b) P.
Espinet, M.A. Esteruelas, L.A. Oro, J.L. Serrano, E. Sola,
Coord. Chem. Rev. 117 (1992) 215. (c) D.W. Bruce, in: D.W.
Bruce, D. O’Hare, (Eds.), Inorganic Materials, Wiley,
Chichester, 1992, Ch. 8. (d) S.A. Hudson, P.M. Maitlis, Chem.
Rev. 93 (1993) 861. (e) J.L. Serrano (Ed.), Metallomesogens,
Synthesis, Properties, and Applications, VCH, Weinheim,
1996.
[2] L.M. Rendina, R.J. Puddephatt, Chem. Rev. 97 (1997) 1735.
[3] W.A. Herrmann, B. Reiter, H. Biersack, J. Organomet. Chem.
97 (1975) 245.
[4] Review: W.A. Herrmann, Adv. Organomet. Chem. 20 (1982)
159.
[5] Review: J.E. Hahn, Progr. Inorg. Chem. 31 (1984) 205.
[6] (a) K. Praefcke, B. Bilgin, J. Pickardt, M. Borowski, Chem. Ber.
127 (1994) 1543. (b) B. Bilgin, Ph.D. Dissertation, Faculty
5/Chemistry, Technische Universita¨t Berlin, Germany, 1996.
[7] (a) K. Praefcke, D. Singer, B. Gu¨ndog˘an, Mol. Cryst. Liq. Cryst.
223 (1992) 181. (b) B. Gu¨ndog˘an, K. Praefcke, Chem. Ber. 126
(1993) 1253. (c) K. Praefcke, D. Singer, B. Gu¨ndog˘an, K.
Gutbier, M. Langner, Ber. Bunsenges. Phys. Chem. 98 (1994)
118. (d) N. Usol’tseva, K. Praefcke, D. Singer, B. Gu¨ndog˘an,
Liq. Cryst. 16 (1994) 601.
[17] G.M. Sheldrick, SHELXS-76, Program for crystal structure deter-
mination, University of Cambridge, UK, 1976.
[18] A.L. Spek, The Euclid Package, in: D. Sayre (Ed.), Computa-
tional Crystallography, Clarendon Press, Oxford, 1982, p. 528.
[19] International Tables for X-ray Crystallography, Vol. IV, Kynoch
Press, Birmingham, 1974.
[8] K. Praefcke, B. Bilgin, N. Usol’tseva, B. Heinrich, D. Guillon, J.
Mater. Chem. 5 (1995) 2257.
[20] D.J. Mabbott, B.E. Mann, P.M. Maitlis, J. Chem. Soc. Dalton
Trans. (1977) 294.
.