Oxidative addition to cyclometalated azobenzene platinum(II) complexes: A route to octahedral liquid crystalline materials

Article abstract of DOI:10.1021/om9808155

The 4,4′-disubstituted azobenzene ligands HL^a-d react with [(η³-C₄H₇)Pt(μ-Cl)]₂ to give the dinuclear cycloplatinated complexes [(L^a-d)Pt(μ-Cl)]₂, which are easily converted to t

Full text of DOI:10.1021/om9808155

2116
Organometallics 1999, 18, 2116-2124
Oxid a tive Ad d ition to Cyclom eta la ted Azoben zen e
P la tin u m (II) Com p lexes: A Rou te to Octa h ed r a l Liqu id
Cr ysta llin e Ma ter ia ls
Mauro Ghedini,* Daniela Pucci, Alessandra Crispini, and Giovanna Barberio
Dipartimento di Chimica, Universita` della Calabria, I-87030 Arcavacata (CS), Italy
Received September 29, 1998
The 4,4′-disubstituted azobenzene ligands HLa-d react with [(η3-C4H7)Pt(µ-Cl)]2 to give
the dinuclear cycloplatinated complexes [(La-d)Pt(µ-Cl)]2, which are easily converted to their
mononuclear Pt(II) acetylacetonate derivatives [(La-d)Pt(acac)]. Oxidative addition to the
square-planar Pt(II) complexes [(La-d)Pt(acac)] of electrophilic substrates such as I2 or CH3I
(RI)eventuallyledtothecorrespondingoctahedralPt(IV)[(La-d)Pt(acac)I2]and[(La-d)Pt(acac)(CH3)I]
products. Characterization by X-ray crystallography on model complexes [(La)Pt(acac)], [(La)-
Pt(acac)I2], and [(La)Pt(acac)(CH3)I] has been carried out, showing that the I2 or CH3I ligands
are bound to the Pt(IV) center at the apical positions. The presence of two ligands in apical
position led to the loss of the short intermolecular Pt- - -Pt distance of 3.311(1) Å observed
in the square-planar complex [(La)Pt(acac)]. Thermotropic mesomorphism is observed for
both the Pt(II) and Pt(IV) species with clearing temperatures, mainly lower than those of
the corresponding organic ligands. These products are the first examples of Pt(IV) octahedral
liquid crystalline species and suggest that oxidative addition to appropriate Pt(II) precursors
should be a convenient synthetic procedure for new hexacoordinated Pt(IV) mesogenic
materials.
In tr od u ction
nal planar [Hg(II)], and octahedral [Mn(I) and Re(I)] co-
ordination geometry and gives rise to a five-membered
metallacycle with a rodlike mesogenic ligand. Liquid
crystalline metallorganic complexes have not yet been
systematically explored, and further data are required
to single out how the topology of the metal environment
is related to the occurrence of thermotropic mesomor-
phism.
It has been observed that additional ligands placed
out of the plane where the mesogenic ligand lies are
beneficial in that they lower the transition temperatures
and improve the thermal stability of the resulting
mesophases.5d,8 Both these aspects are of interest with
reference to the processability of such materials, so that
mesogenic octahedral complexes may be relevant for
applicative purposes.
The only examples of hexacoordinated orthometalated
liquid crystals reported up to now are mononuclear
Mn(I) and Re(I) carbonyl complexes.7 Unfortunately,
these compounds require a rather involved synthetic
strategy. Indeed, they have been obtained reacting the
organic ligand with the unmodifiable, preexisting metal
complex fragment (i.e., [M(CO)4], M ) Mn, Re). There-
fore more versatile synthetic pathways to prepare
hexacoordinated metallomesogens are required.
Pt(II) chemistry is characterized by oxidative addition
reactions,9 and square-planar cycloplatinated species
could become suitable starting materials for the syn-
thesis of new octahedral Pt(IV) mesogens. In particular,
The metallomesogens1 are metal-containing liquid
crystalline materials whose chemical or physical proper-
ties can be fine-tuned by using the differences that each
metal center bring about. The synthesis of metallorganic
and coordination compounds that feature mesomor-
phism therefore represents a topic for material science.
Mesogenic coordination compounds involving transi-
tion metals are now widespread.2 On the contrary,
metallorganic species are less common, and the avail-
able data mainly concern cyclometalated Pd(II) imines
or azobenzenes3 and ferrocene derivatives.4 Other com-
plexes belonging to this class include some Pt(II) deriva-
tives with the same ligands,5 a few examples of Hg(II)
orthometalated azobenzenes,6 and Mn(I) or Re(I) cyclo-
metalated imines.7 With reference to the compounds
where the metal is σ-bonded to a carbon atom, the metal
center adopts a square-planar [Pd(II) and Pt(II)], trigo-
* Corresponding author. Fax: Int. code +(984)492044. E-mail:
m.ghedini@unical.it.
(1) (a) Serrano, J . L. Metallomesogens; VCH: Weinheim, 1996. (b)
Bruce, D. W. In Inorganic Materials, 2nd ed.; Bruce, D. W., O’Hare,
D., Eds.; Wiley: Chichester 1996.
(2) Espinet, P.; Esteruelas, M. A.; Oro, L. A.; Serrano, J . L.; Sola.
E. Coord. Chem. Rev. 1992, 117, 215.
(3) Hudson, S. A.; Maitlis, P. M. Chem. Rev. 1993, 93, 861.
(4) Deschenaux, R.; Goobdy, J . W. In Ferrocenes; Togni, A., Hayashi,
T., Eds.; VCH: Weinheim, 1995; p 471.
(5) (a) Praefcke, K.; Bilgin, B.; Usol’tseva, N.; Heinrich, B.; Guillon,
D. J . Mater. Chem. 1995, 5, 2257. (b) Buey, J .; Diez, L.; Espinet, P.;
Kitzerow, H. S.; Miguel, J . A. Chem. Mater. 1996, 8, 2375. (c) Ortega,
J .; Folcia, C. L.; Extebarria, J .; Ros, M. B.; Miguel, J . A. Liq. Cryst.
1997, 23, 285. (d) Ghedini, M.; Neve, F.; Pucci, D. Eur. J . Inorg. Chem.
1998, 501.
(6) Omenat, A.; Ghedini, M. J . Chem. Soc., Chem. Commun. 1994,
1309.
(7) (a) Bruce, D. W.; Liu, X. H. J . Chem. Soc., Chem. Commun. 1994,
729. (b) Bruce, D. W.; Liu, X. H. Liq. Cryst. 1995, 18, 165.
(8) (a) Bruce, D. W. Adv. Mater. 1994, 6, 699. (b) Ghedini, M.; Pucci,
D.; Neve, F. Chem. Commun. 1996, 137.
(9) Anderson, G. K. In Comprehensive Organometallic Chemistry;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press:
1995; Vol. 9.
10.1021/om9808155 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 05/04/1999

Octahedral Liquid Crystalline Materials
Organometallics, Vol. 18, No. 11, 1999 2117
Ch a r t 1. Stu ctu r e, P r oton Nu m ber in g Sch em e
a n d Mesom or p h ism of th e HLa -d Liga n d s (K )
Cr ysta l; N ) Nem a tic; Sm ) Sm ectic, I ) Isotr op ic)
this approach could be very useful to devise an alterna-
tive strategy to design complexes easily modulated as
far as the apical positions are concerned. The present
work has been planned in order to test a synthetic
procedure to obtain hexacoordinated Pt(IV) mesogens
by oxidative addition to cyclometalated azobenzene
Pt(II) complexes.
Orthoplatination, a reaction which for a long time was
not readily accomplishable,10 is now easily accessible
through an elegant synthetic method11 which involves
the use of [(η3-C3H5)Pt(µ-Cl)]2. The products obtained
from the reaction of azobenzenes with di-µ-chlorobis-
(η3-allylplatinum) or di-µ-chlorobis(η3-2-methylallylplat-
inum) are dinuclear chloro-bridged cyclometalated com-
plexes with a symmetric “H-shaped” molecular struc-
ture.5b,d With reference to the thermotropic properties,
the structurally similar Pd(II) products usually display
high transition temperatures. However, their mono-
nuclear derivatives, obtained from a bridge-splitting
reaction with a monoanionic chelating ligand such as
acetylacetonate, are unsymmetric “P-shaped” molecules
which show low-melting disordered mesophases12 and
rather exciting physical properties.5b-d,13 Accordingly,
for the aim of the present investigation, the “P-shaped”
acetylacetonate complexes were chosen as more ap-
propriate starting materials rather than the corre-
sponding chloro-bridged dimers.
Oxidative addition reactions have been extensively
performed on square-planar organoplatinum species,
but within this field orthoplatinated complexes have
been very seldom used.14 Relatively few examples of
Pt(IV) complexes prepared by the addition of X2 or RX
to Pt(II) precursors containing cyclometalated terden-
tate (NCN),15 (NNC),16 and (CNS)17 or bidentate (CN)
ligands18,19 have been found in the literature. Therefore,
the oxidative addition reaction on mononuclear cyclo-
platinated acetylacetonate complexes has to be tested.
The azobenzenes HLa-d selected for this study are
shown in Chart 1. In particular, the 4,4′-bis(methoxy-
azobenzene) ligand, HLa, has been chosen as a reference
compound to explore the synthetic procedures yielding
cycloplatinated complexes, while the homologous HLb-d
ligands are of interest in order to arrange a series of
mesomorphic ligands (thermotropic behavior in Chart
1) bearing an increasing number of aromatic rings.5d,8b
Herein, the synthesis, characterization, and meso-
morphic behavior of a series of dinuclear and mono-
nuclear Pt(II) complexes, [(La-d)Pt(µ-Cl)]2 and [(La-d)-
Pt(acac)], containing cyclometalated HLa-d azobenzene
ligands, are reported. Also described is the reactivity of
the mononuclear Pt(II) derivatives [(La-d)Pt(acac)] with
respect to the oxidative addition of iodine or methyl
iodide, with formation of Pt(IV) cyclometalated species
[(La-d)Pt(acac)I2] and [(La-d)Pt(acac)(CH3)I], respec-
tively. Moreover, the X-ray crystal structure determina-
tions of complexes [(La)Pt(acac)], 2a , [(La)Pt(acac)I2], 3a ,
and [(La)Pt(acac)(CH3)I], 4a , are presented.
(10) (a) Ryabov, A. D. Chem. Rev. 1990, 90, 403. (b) Ryabov, A. D.
In Perspectives In Coordination Chemistry; Williams, A. F., Floriani,
C., Merbach, A. E., Eds.; Verlag Helvetica Chimica Acta, Basel VCH:
Weinheim, 1992; p 271.
(11) Pregosin, P. S.; Wombacher, F.; Albinati, A.; Lianza, F. J .
Organomet. Chem. 1991, 418, 249.
(12) (a) Ghedini, M.; Pucci, D. J . Organomet. Chem. 1990, 395, 105.
(b) Baena, M. J .; Espinet, P.; Ros, M. B.; Serrano, J . L. Angew.
Chem., Int. Ed. Engl. 1991, 30, 711. (c) Ghedini, M.; Pucci, D.;
Cesarotti, E.; Francescangeli, O.; Bartolino, R. Liq. Cryst. 1994, 16,
373.
(13) (a) Cipparrone, G.; Versace, C.; Duca, D.; Pucci, D.; Ghedini,
M.; Umeton, C. Mol. Cryst. Liq. Cryst. 1992, 212, 217. (b) Scaramuzza,
N.; Pagnotta, M. C. Mol. Cryst. Liq. Cryst. 1994, 239, 263.
(14) Rendina, L. M.; Puddephatt, R. J . Chem. Rev. 1997, 97, 1735.
(15) (a) van Koten, G.; Terheijden, J .; van Beek, J . A. M.; Wehman-
Ooyevaar, I. C. M.; Muller, F.; Stam, C. H. Organometallics 1990, 9,
903. (b) Canty, A. J .; Honeyman, R. T. J . Organomet. Chem. 1990,
387, 247.
(16) (a) Anderson, C. M.; Crespo, M.; J ennings, M. C.; Lough, A. J .;
Ferguson, G.; Puddephatt, R. J . Organometallics 1991, 10, 2672. (b)
Anderson, C. M.; Crespo, M.; Ferguson, G.; Lough, A. J . G.; Puddephatt,
R. J . Organometallics 1992, 11, 1177.
(17) Chattopadhyay, S.; Sinha, C.; Basu, P.; Chakravorty, A. Orga-
nometallics 1991, 10, 1135.
(18) Crespo, M.; Solans, X.; Font-Bard`ıa, M. J . Organomet. Chem.
1994, 483, 187.
(19) Chassot, L.; von Zelewsky, A.; Sandrini, D.; Maestri, M.;
Balzani, V. J . Am. Chem. Soc. 1986, 108, 6084.
The new complexes [(Lb-d)Pt(acac)I2] and [(Lb-d)-
Pt(acac)(CH3)I] show thermotropic mesomorphism. Re-
markably, as far as we know, they are the first examples
of Pt(IV) hexacoordinated liquid crystalline compounds.
Resu lts a n d Discu ssion
Mod el Com p ou n d s. Syn th esis a n d Ch a r a cter iza -
tion of th e Cycloplatin ated HLa Com pou n ds: Com -
p lexes 1a -4a . The synthetic procedures leading to the
dinuclear Pt(II) and mononuclear Pt(II) or Pt(IV) com-
plexes have been tested for the ligand 4,4′-bis(methoxy-
azobenzene), HLa. The new compounds were character-
ized by elemental analyses, which accounted for the
1
expected products and IR and H NMR spectroscopies.
The optimized synthetic procedures are summarized in
Scheme 1.

2118 Organometallics, Vol. 18, No. 11, 1999
Ghedini et al.
Sch em e 1
F igu r e 1. Molecular structure and atomic labeling scheme
(40% probability thermal ellipsoids) (a); crystal packing
down the c axis showing the shortest Pt- - -Pt intemolecular
distance (b) of complex [(La)Pt(acac)], 2a .
The cycloplatinated chloro-bridged dimer [(La)Pt(µ-
Cl)]2, 1a , was prepared by treating HLa with 2 equiv of
[(η3-C4H7)Pt(µ-Cl)]2 in refluxing chloroform. The 1H
NMR spectrum (DMSO-d6) of 1a (Experimental Section)
accounts for an orthometalated azobenzene since in
the aromatic region signals attributable to two dif-
ferent phenyl rings are observed and the protons of the
Pt(II)-bonded ring are significantly upfield shifted with
reference to HLa (for example, for the H(5) proton, ∆δ
) 0.92 ppm). Moreover, the proton ortho to the ligand-
binding site, H(3), clearly shows a long-range coupling,
of about 48 Hz, with the 195Pt nuclei.
upfield shift of all the aromatic protons and a decreased
3
3
value of J Pt-H (from 39 to 20, for 3a , or to 25 Hz for
3
3
4a ). The J Pt-H data fall in the range characteristic for
Pt(IV) species, confirming that oxidation of Pt(II) to
Pt(IV) has actually occurred.20
Moreover, the 1H NMR spectrum of 4a shows a
CH3-Pt(IV) resonance, coupled to 195Pt, at 1.22 ppm
(2J Pt-H ) 65 Hz). Therefore, on the basis of this evidence,
a trans oxidative addition of methyl iodide is proposed.21
None of the compounds 1a -4a show mesomorphic
behavior, and all melt at temperatures that range from
180 °C (4a ) to 298 °C (1a ).
The mononuclear Pt(II) acetylacetonate derivative,
[(La)Pt(acac)], 2a , was obtained by reaction of 1a with
2 equiv of [Tl(acac)], in dichloromethane solution, at
room temperature. The 1H NMR spectrum of 2a is
featured by the resonance at 5.50 ppm, assigned to the
methinic proton of the acetylacetonate ligand. Compari-
son between the aromatic regions of the spectra of 1a
and 2a shows two main differences, which confirm that
the molecular structure changes from dinuclear to
mononuclear: in 2a a sizable deshielding effect is
observed for all the aromatic protons (for example, for
Cr ysta l Str u ctu r e An a lysis of Com p lex [(La )P t-
(a ca c)], 2a . The overall view of the molecule of 2a , with
the atom-labeling scheme, is shown in Figure 1a.
Selected bond lengths and angles are listed in Table 1.
Complex 2a is essentially planar with the platinum
atom in a distorted square-planar geometry. The maxi-
mum deviation is represented by the “bite” angle N(1)-
Pt-C(1) of 79.0(3)°. This type of distortion is charac-
teristic of cyclometalated Pt(II) complexes (80.7° is the
mean N-Pt-C “bite” angle within the five-membered
cycloplatinated ring of Pt(II) complexes reported in the
literature). The bond distances and the other bond
3
the H(5) proton, ∆δ ) 0.26 ppm) and the J Pt-H
decreases to about 39 Hz.
Reaction of 2a with an equivalent amount of I2 or a
10 molar excess of CH3I, in acetone at room tempera-
ture, afforded the air-stable oxidative-addition platinu-
m(IV) products [(La)Pt(acac)I2], 3a (dark violet), and
[(La)Pt(acac)(CH3)I], 4a (brown-yellow), respectively.
The 1H NMR spectra of complexes 3a and 4a , compared
to the spectra of the starting material 2a , show a slight
(20) Monaghan, P. K.; Puddephatt, R. J . Organometallics 1985, 4,
1406.
(21) Clegg, D. E.; Hall, J . R.; Swile, G. A. J . Organomet. Chem. 1972,
38, 403.

Octahedral Liquid Crystalline Materials
Organometallics, Vol. 18, No. 11, 1999 2119
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p lexes 2a -4a
[(La)Pt(acac)], 2a
Pt-O(1)
1.985(6)
1.991(6)
1.295(10)
1.385(12)
Pt-O(2)
Pt-C(1)
N(2)-C(2)
2.078(6)
1.947(9)
1.405(9)
Pt-N(1)
N(1)-N(2)
C(1)-C(2)
O(1)-Pt-O(2)
O(2)-Pt-N(1)
O(2)-Pt-C(1)
90.3(2)
99.0(2)
176.3(3)
O(1)-Pt-N(1)
O(1)-Pt-C(1)
N(1)-Pt-C(1)
170.2(3)
91.5(3)
79.0(3)
[(La)Pt(acac)I2], 3a
Pt-I(1)
2.654(1)
Pt-I(2)
2.644(1)
2.133(6)
1.975(8)
1.370(12)
Pt-O(1)
Pt-N(1)
N(1)-N(2)
C(1)-C(2)
2.004(6)
2.021(6)
1.292(9)
1.412(11)
Pt-O(2)
Pt-C(1)
N(2)-C(2)
F igu r e 2. Molecular structure and atomic labeling scheme
(40% probability thermal ellipsoids) of complex [(La)Pt-
(acac)I2], 3a .
I(1)-Pt-I(2)
I(2)-Pt-O(1)
I(2)-Pt-O(2)
I(1)-Pt-N(1)
O(1)-Pt-N(1)
N(1)-Pt-C(1)
I(2)-Pt-C(1)
O(2)-Pt-C(1)
179.6(1)
91.6(2)
89.7(2)
90.0(2)
170.4(3)
79.7(3)
89.4(3)
177.8(3)
I(1)-Pt-O(1)
I(1)-Pt-O(2)
O(1)-Pt-O(2)
I(2)-Pt-N(1)
O(2)-Pt-N(1)
I(1)-Pt-C(1)
O(1)-Pt-C(1)
88.1(2)
90.1(2)
91.1(2)
90.3(2)
98.3(3)
90.8(3)
90.9(3)
[(La)Pt(acac)(CH3)I], 4a
Pt-I(1)
2.744(3)
Pt-C(20)
Pt-O(2)
Pt-N(1)
N(2)-C(2)
2.181(19)
2.156(15)
2.047(19)
1.386(31)
Pt-O(1)
Pt-C(1)
N(1)-N(2)
C(1)-C(2)
2.009(15)
1.986(24)
1.265(30)
1.427(32)
I(1)-Pt-N(1)
N(1)-Pt-O(1)
N(1)-Pt-O(2)
I(1)-Pt-C(1)
O(1)-Pt-C(1)
I(1)-Pt-C(20)
O(1)-Pt-C(20)
C(1)-Pt-C(20)
91.5(5)
169.1(7)
99.2(7)
90.9(6)
89.7(8)
178.1(5)
87.6(8)
90.3(8)
I(1)-Pt-O(1)
I(1)-Pt-O(2)
O(1)-Pt-O(2)
N(1)-Pt-C(1)
O(2)-Pt-C(1)
N(1)-Pt-C(20)
O(2)-Pt-C(20)
90.9(6)
91.7(5)
91.3(6)
79.6(8)
177.1(8)
90.2(7)
87.1(7)
F igu r e 3. Molecular structure and atomic labeling scheme
(40% probability thermal ellipsoids) of complex [(La)Pt-
(acac)(CH3)I], 4a .
angles within the cycloplatinated ring are comparable
with those found for the few structurally characterized
platinum(II) complexes containing azobenzene ligands.22
The coordination about the platinum atom is completed
by two oxygen atoms of the acac ligand. The trans effect
of the phenyl carbon C(1) bound to the Pt(II) center is
marked by the longer Pt-O(2) bond length [2.078(6) Å],
compared to the Pt-O(1) trans to the N(1) atom [1.985-
(6) Å]. This agrees with the trans influence of the
coordinated carbon center generally observed in ortho-
platinated complexes.23 The bond distances and angles
within the acac ligand are comparable with those found
in other acetylacetonate Pt(II) complexes.24 While the
acac plane and the five-membered cycloplatinated
ring are basically coplanar with a dihedral angle of
176.3(1)°, the rotationally free phenyl ring of the azo-
benzene ligand is twisted 32.0(8)° (average value) about
the N-C bond with respect to the plane of the remain-
der of the complex.
range 3.76-3.15 Å observed in dimers of cyclometalated
Pt(II) complexes.25 Within the dimeric unit the two
molecules are stacked along the y axis with an offset of
2.10 Å, and the distance between the five-membered
cycloplatinated ring and the six-membered ring formed
by the acac ligand is 3.40 Å.
Cr ysta l Str u ctu r e An a lysis of Com p lexes [(La )-
P t(a ca c)I2], 3a , a n d [(La )P t(a ca c)(CH3)I], 4a . The
crystal structures of 3a and 4a , with the pertinent atom-
labeling schemes, are shown in Figures 2 and 3,
respectively. Selected bond lengths and angles are listed
in Table 1. The coordination geometry at the Pt atom
is octahedral with the acetylacetonate and 4,4′-bis(meth-
oxyazobenzene) ligands in the equatorial plane. The two
iodine ligands in complex 3a and the iodine and the
methyl ligands in complex 4a are trans to each other
in the apical positions. Some distortion from regular
geometry results from the small ′bite′ of the 4,4′-bis-
(methoxyazobenzene) as previously discussed for com-
plex 2a (Table 1). The Pt-I bond lengths of complex 3a
are comparable with those in other Pt(IV) complexes
with trans iodide geometries,26 while the sligthly larger
value of 2.744(3) Å observed in complex 4a reflects the
In the crystal packing, compound 2a forms dimeric
units; the two molecules of the dimer are related to
one another by a center of inversion (Figure 1b). The
Pt- - -Pt distance of 3.311(1) Å implies some weak
interaction between the two molecules, being in the
(22) (a) Elder, R. C.; Cruea, R. D. P.; Morrison, R. F. Inorg. Chem.
1976, 15, 1623. (b) Chattopadhyay, S.; Sinha, C.; Basu, P.; Chakra-
vorty, A. J . Organomet. Chem. 1991, 414, 421.
(23) Mdleleni, M. M.; Bridgewater, J . S.; Watts, R. J .; Ford, P. C.
Inorg. Chem. 1995, 34, 2334.
(24) Katoh, H.; Miki, K.; Kai, Y.; Tanaka, N.; Kasai, N. Bull. Chem.
Soc. J pn. 1981, 54, 611.
(25) (a) Breu, J .; Range, K.-J .; von Zelewsky, A.; Yersin, H. Acta
Crystallogr. 1997, C53, 562. (b) Bandyopadhyay, D.; Bandyopadhyay,
L.; Chakravorty, A.; Cotton, F.; Falvello, L. R. Inorg. Chem. 1983, 22,
1315.

2120 Organometallics, Vol. 18, No. 11, 1999
Ghedini et al.
trans influence of the methyl ligand.27 The bond dis-
tances and angles within the five-membered cycloplati-
nated ring and the acac ligand in both complexes 3a
and 4a are similar to those found in complex 2a .
Mesogen ic Com p ou n d s. Syn th esis a n d Ch a r a c-
t er iza t ion of t h e Cyclop la t in a t ed H Lb -d Com -
p ou n d s: Com p lexes 1b-d t o 4b-d . The synthetic
procedures tested for HLa have been extended to the
series HLb-d (Chart 1) to obtain Pt(IV) complexes with
liquid crystalline properties. The 4,4′-disubstituted
azobenzenes HLb-d were prepared as previously re-
ported, while their cycloplatinated complexes 1b-d to
4b-d were synthesized as described for complexes 1a -
4a (Scheme 1).
Ta ble 2. Op tica l a n d Th er m a l P r op er ties of th e
Squ a r e-P la n a r P t(II) [(Lb-d )P t(µ-Cl)]2, 1b-d , a n d
[(Lb-d )P t(a ca c)], 2b-d , Com p lexes
compound
transitiona
T/°C
∆H/kJ mol-1 b
1b
1c
K-I
232c
206
253
275d
263
342c,d
129
109
87
124
131
196
202c
89
K-SmC
SmC-N
N-I
26.0
2.9
1d
2b
K-SmC
SmC-I
K-I
37.1
44.4
1.0
33.3
34.2
1.4
I-N
N-K
K-K′
K′-N
N-I
2c
1.4
I-N
All compounds, purified by recrystallization from
suitable solvents (Experimental Section), are air-stable
solids which give satisfactory elemental analyses and
N-K
K-N
N-I
27.4
36.2
2d
185
250c,d
1
were characterized by IR and H NMR spectroscopies.
a
b
K ) crystal, N ) nematic, Sm ) smectic, I ) isotropic. Data
The dinuclear chloro-bridged [(Lb-d)Pt(µ-Cl)]2 com-
from DSC for second heating cycle. c Data from optical observa-
tions. Decomposition.
1
plexes 1b-d display an H NMR spectral pattern ana-
d
logous to that of 1a , with the H(3) and H(5) protons
shielded about 0.2 and 0.3 ppm, respectively, with refer-
ence to the parent uncomplexed ligands. Moreover, the
1H NMR spectrum of 1c shows that the reaction product
is a 9:1 mixture of the two isomers, 1c(A) and 1c(B),
which form by a nonselective platination of the 4,4′-asym-
metrically substituted azobenzene HLc. Comparison of
Ta ble 3. Op tica l a n d Th er m a l P r op er ties of th e
Octa h ed r a l P t(IV) [(Lb-d )P t(a ca c)I2], 3b-d , a n d
[(Lb-d )P t(a ca c)(CH3)I], 4b-d , Com p lexes
compound
transitiona
T/°C
∆H/kJ mol-1 b
3b
3c
K-I
149c
125
60
178
180
134
108
230c,d
110c
142
270d
K-I
30.7
0.5
50.0
0.7
38.9
21.2
1
I-E
the H NMR spectra of 1c and 1d allows us to conclude
3d
K-N
N-I
that the major isomer is 1c(A). Thus in HLc metalation
preferably occurs at the more electron-rich phenyl ring.
4b
4c
K-I
K-N
N-I
4d
K-SmC
SmC-N
N-I
64.9
a
K ) crystal, E ) crystal, N ) nematic, Sm ) smectic, I )
isotropic. Data from DSC for second heating cycle. c Data from
optical observations. Decomposition.
b
d
ratio 1:100) was necessary to obtain 3d and 4d (Experi-
1
mental Section). The H NMR spectra of 2c, 3c, and 4c
account for a pure compound arising from the more
abundant isomer 1c(A). Moreover, in series 3 and 4,
3
3
the values of both the coupling constants J Pt-H and
2J Pt-H fall in the same range detected for 3a and 4a ;
thus all the obtained results agree well with the general
formula sketched in Scheme 1.
Mesogen ic Beh a vior of Com p lexes 1b-d to 4b-
d . The mesophases were first identified according to
their textures28 observed by polarized optical microscopy
and then investigated by differential scanning calorim-
etry. All the HLb-d are mesomorphic and exhibit an
enantiotropic nematic phase (N) which, in the case of
HLc and HLd, appears before the smectic C (SmC)
(Chart 1).
Tables 2 and 3 summarize the transition tempera-
tures, enthalpies, and types of mesophases observed for
the platinum complexes that the HLb-d ligands form.
The binuclear complex 1b, derived from 4,4′-bis-
(hexyloxyazobenzene) HLb, loses the liquid crystalline
behavior displayed by its organic precursor and, on
heating, directly melts (232 °C) to the isotropic liquid
The mononuclear square-planar â-diketonate com-
pounds, [(Lb-d)Pt(acac)], 2b-d give very similar 1H
3
3
NMR spectra and show a J Pt-H of about 36 Hz.
Complexes 2b and 2c react with a stoichiometric
amount of iodine or methyl iodide to give rise to
[(Lb-d)Pt(acac)I2] and [(Lb-d)Pt(acac)(CH3)I] derivatives,
3b,c and 4b,c, respectively. In similar reactions a large
excess of iodine (molar ratio 1:3) or methyl iodide (molar
(26) (a) van Beek, J . A. M.; van Koten, G.; Wehman-Ooyevaar, I. C.
M.; Smeets, W. J . J .; van der Sluis, P.; Spek, A. L. J . Chem. Soc., Dalton
Trans. 1991, 883. (b) Cheetham, A. K.; Puddephatt, R. J .; Zalkin, A.;
Templeton, D. H.; Templeton, L. K. Inorg. Chem. 1976, 15, 2997. (c)
Cook, P. M.; Dahl, L. F.; Hopgood, D.; J enkins, R. A. J . Chem. Soc.,
Dalton Trans. 1973, 294.
(28) (a) Demus, D.; Richter, L. Textures of Liquid Crystals; Verlag
Chemie: Weinheim-New York, 1978. (b) Gray, G. W.; Goodby, J . W.
Smectic Crystal Textures and Structures; Leonard Hill: Glasgow, 1984.
(27) Albano, V. G.; Braga, D.; De Felice, V.; Panunzi, A.; Vitagliano,
A. Organometallics 1987, 6, 517.

Octahedral Liquid Crystalline Materials
Organometallics, Vol. 18, No. 11, 1999 2121
(I). Complex 1c, however, shows an SmC phase at 206
°C, with the typical schlieren texture, before giving way
to a N phase at 253 °C. Finally, complex 1d displays
only a SmC phase (exhibiting a schlieren texture), which
appears at 262 °C. For both 1c and 1d the transition
from liquid crystal to I (275 and 342 °C, respectively) is
accompanied by strong decomposition. With reference
to their parent ligands, a stabilization of the more
ordered SmC phase is observed for both 1c and 1d ,
while as the thermal properties are concerned, the
melting temperatures increase more than the clearing
ones, so that the mesomorphic range decreases.
which occurs between 142 and 270 °C. As a general
trend, it should be pointed out that substitution of I2
for CH3I in the oxidative addition to [(Lc-d)Pt(acac)]
complexes causes a large reduction in the melting
points. Contrarily, the corresponding clearing temper-
atures increase and a strong decomposition takes place
when the I phase forms. It is worth noting that both 4c
and 4d exhibit mesomorphism over a temperature range
(122 and 160 °C, respectively) that is much wider than
the corresponding square-planar homologous 2c and 2d
(65 °C). Furthermore, as confirmed by calorimetric and
1H NMR measurements carried out on melted samples
or after annealing experiments performed in the me-
sophase some degrees before the clearing temperature,
on heating, compounds 4b-d quantitatively revert to
the respective Pt(II) starting materials 2b-d . Thus, the
oxidative addition of methyl iodide to [(Lb-d)Pt(acac)]
complexes is a reversible process.
On going from the binuclear 1b-d to the mononuclear
2b-d Pt(II) complexes, it is evident (Table 2) that the
change in the molecular structure from “H-shaped” to
“P-shaped” (Scheme 1) promotes the mesomorphism. A
restoration of liquid crystallinity, which consists of a
monotropic N phase, stable from 109 to 87 °C, is indeed
observed for 2b. Moreover, for 2c and 2d , the enantio-
tropic SmC phase observed in the dimeric parents
becomes N (schlieren textures; range of stability: 2c,
131-196 °C; 2d : 185-250 °C), and the transition to the
I phase takes place with extensive decomposition. In
both compounds, by reducing the symmetry of the
molecules, the melting and the clearing points are
brought down in temperature, and for the 2d complex,
a broadening of the mesomorphism is achieved. It is
worth noting that species 2b-d show a less ordered
mesophase and clearing temperatures lower even than
those of the corresponding HLb-d ligands.
Con clu sion s
The HLa-d azobenzene ligands undergo orthometa-
lation by reaction with [(η3-C4H7)Pt(µ-Cl)]2 in mild
conditions. The ligand HLc, asymmetrically substituted
(Chart 1), preferentially underwent cyclometalation at
the most electron-rich azo-bonded aromatic ring. Thus
the orthoplatination of azobenzenes can be considered
electrophilic in character.29
The dinuclear species give rise to the corresponding
mononuclear derivatives [(La-d)Pt(acac)]. The molecular
structure of complex [(La)Pt(acac)], 2a , has been deter-
mined by single-crystal X-ray analysis, and the shortest
intermolecular Pt- - -Pt distance of 3.311(1) Å has been
found between two molecules related by a center of in-
version which form dimeric units in the crystal packing.
The mononuclear Pt(II) complexes undergo oxidative
addition reaction with I2 or CH3I. The trans-addition
has been confirmed by the X-ray crystal structure
analysis performed on the model compounds [(La)Pt-
(acac)I2], 3a , and [(La)Pt(acac)(CH3)I], 4a .
The addition of two ligands changes the coordination
geometry of the metal atom from square-planar to
octahedral so that, in the solid state, intermolecular
nonbonding Pt- - -Pt interactions are not observed.
These interactions may also be at work in the meso-
phases, and their disappearance should account for the
sizable lowering of the clearing temperatures the Pt-
(IV) mesogens show with reference to the respective Pt-
(II) parent complexes. Moreover, comparing the I2 with
the CH3I addition products, it should be pointed out
that, replacing an iodine atom with the bulkier methyl
group, the melting points decrease whereas the clearing
temperatures increase. Hence, by substitution of a CH3
group with an I atom, the mesophases become stable
over a wider temperature range.
The oxidative addition of CH3I to the [(Lb-d)Pt(acac)]
compounds is a process that can be made reversible on
heating. Both the starting Pt(II) and the final Pt(IV)
complexes are liquid crystals; interestingly, this outcome
could be of interest for the development of syntheses in
an oriented reaction media.
Liquid crystalline properties dramatically change by
oxidative addition of I2 and CH3I to acetylacetonate Pt-
(II) substrates. To promote mesomorphic behavior in
octahedral complexes,8a organic ligands of increasing
molecular length, fairly anisotropic in shape to com-
pensate for the structural perturbation induced by the
six-coordinate platinum center, were selected. Thus the
4,4′-bis(hexyloxyazobenzene) derivative 3b, which does
not have the appropriate molecular anisotropy to bal-
ance the introduction of two ligands in axial positions,
loses its mesomorphism and the microcrystalline solid
melts directly to an isotropic liquid at 149 °C. Upon
cooling from the I phase, 3b did not crystallize, but froze
in a glassy state which is stable over months. The
presence of a further aromatic ring in the mesogenic
ligand of compound 3c led to destabilization of the
mesomorphism of the square-planar Pt(II) parent com-
plex, transforming the enantiotropic N into the mono-
tropic E mesophase (mosaic texture). In addition, on
cooling, complex 3c retains the E ordering, giving a
glassy solid, stable for a long time. Interestingly, when
the azobenzene core of these hexacoordinated complexes
is symmetrically added onto by two benzoate groups,
the Pt(IV) diodio derivative, 3d , preserves the same
mesomorphic behavior of 2d and exhibits an enantio-
tropic N phase between 177 and 180 °C. The clearing
points of 3c and 3d are lower by about 70 °C than those
of 2c and 2d , and no decomposition was observed.
The [(Lb-d)Pt(acac)(CH3)I] compounds 4c and 4d
retain the mesophase which is shown by 2c and 2d ,
while 4b is not mesogenic at all. In particular, 4c forms,
at 108 °C, an enantiotropic N phase, exhibiting a
marbled texture, which is stable until 230 °C, and 4d
shows an SmC phase (at 110 °C), followed by the N one
Concluding, we succeded in the preparation of octa-
hedral Pt(IV) mesogens by oxidative addition to Pt(II)
(29) Cope, A. C.; Siekman, R. W. J . Am. Chem. Soc. 1965, 87, 3272.

2122 Organometallics, Vol. 18, No. 11, 1999
Ghedini et al.
[(La )P t(a ca c)], 2a . A mixture of 1a (113 mg, 0.12 mmol)
and [Tl(acac)] (73 mg, 0.24 mmol) in dichloromethane (15 mL)
was stirred at room temperature for 6 h. The reaction mixture
was filtered off and the solution evaporated under reduced
pressure. The solid was crystallized from methanol, filtered,
and dried under vacuum. A brown solid was obtained in 83%
yield (104 mg). Mp: 200 °C. Anal. Calcd for C19H20N2O4Pt: C,
acetylacetonate complexes. This synthetic procedure can
be extended to addenda other than I2 or CH3I, and in
principle, a wide family of differently functionalized
liquid crystalline Pt(IV), tailored for specific physical
properties, could become available.
Exp er im en ta l Section
1
42.62; H, 3.76; N, 5.23. Found: C, 42.32; H, 3.72; N, 4.66. H
NMR (CDCl3): δ (ppm) 7.89 (d, J ) 9.1 Hz, 2H; H2′,6′), 7.88 (d,
J ) 8.6 Hz, 1H; H6), 7.09 (d, J ) 2.8 Hz, 1H; H3), 6.96 (d, J )
9.1 Hz, 2H; H3′,5′), 6.74 (dd, J ) 8.6, 2.8 Hz, 1H; H5), 5.50 (s,
1H; CHdC(CH3)2), 3.94 (s, 3H; OCH3), 3.88 (s, 3H; OCH3), 2.06
Gen er a l Com m en ts. All the commercially available chemi-
cals were used as received. [K2(PtCl4)] was purchased from
J ohnson-Matthey Inc. Literature methods were used to pre-
pare [(η3-C4H7)Pt(µ-Cl)]230 and [Tl(acac)].31 The HLb , HLc , and
HLd ligands were synthesized as previously reported (refs 32,
8b, and 5d, respectively). The infrared spectra were recorded
on a Perkin-Elmer FT 2000, as KBr pellets. The 1H NMR
spectra were recorded on a Bruker WH-300 spectrometer in
CDCl3 or (CD3)2SO solutions, with TMS as internal standard.
Elemental analyses were performed with a Perkin-Elmer 2400
analyzer. Optical observations were made with a Zeiss Axio-
scope polarizing microscope equipped with a Linkam C0 600
heating stage. The transition temperatures and enthalpies
were measured on a Perkin-Elmer DSC-7 differential scanning
calorimeter with a heating and cooling rate of 10 °C/min. The
3
(s, 3H; CH3CO), 1.97 (s, 3H; CH3CO); J (195Pt-H3) ) 39 Hz.
Colors, reaction times, yields, melting points, and analytical
and 1H NMR data for complexes 2b-d are as follows.
[(Lb)P t(a ca c)], 2b: red; 4.5 h; yield 97 mg (92%); thermo-
tropic behavior in Table 2. Anal. Calcd for C29H40N2O4Pt: C,
1
51.55; H, 5.97; N, 4.15. Found: C, 51.07; H, 6.01; N, 4.19. H
NMR (CDCl3): δ (ppm) 7.87 (d, J ) 9.0 Hz, 2H; H2′,6′), 7.86 (d,
J ) 8.6 Hz, 1H; H6), 7.06 (d, J ) 2.5 Hz, 1H; H3), 6.94 (d, J )
9.0 Hz, 2H; H3′,5′), 6.72 (dd, J ) 8.6, 2.5 Hz, 1H; H5), 5.50 (s,
1H; CHdC(CH3)2), 4.12 (t, 2H; OCH2), 4.02 (t, 4H; OCH2), 2.06
3
(s, 3H; CH3CO), 1.97 (s, 3H; CH3CO); J (195Pt-H3) ) 36 Hz.
apparatus was calibrated with indium (156.6 °C, 3.3 kJ mol-1
)
[(Lc)P t(a ca c)], 2c: red; 2.5 h; yield 73 mg (92%); thermo-
and tin (232.1 °C, 7.2 kJ mol-1). Two or more heating/cooling
cycles were performed on each sample.
tropic behavior in Table 2. Anal. Calcd for C42H56N2O6Pt: C,
1
57.32; H, 6.41; N, 3.18. Found: C, 57.29; H, 6.41; N, 3.59. H
P r ep a r a tion of [(La -d )P t(µ-Cl)]2 Com p lexes. The prepa-
ration of compound [(La)Pt(µ-Cl)]2, 1a , is described in detail;
all other homologues were prepared similarly.
NMR (CDCl3): δ (ppm) 8.17 (d, J ) 8.8 Hz, 2H; Ha′,d′), 7.98 (d,
J ) 8.9 Hz, 2H; H2′,6′), 7.91 (d, J ) 8.7 Hz, 1H; H6), 7.32 (d, J
) 8.9 Hz, 2H; H3′,5′), 7.09 (d, J ) 2.5 Hz, 1H; H3), 6.99 (d, J )
8.8 Hz, 2H; Hb′,c′), 6.75 (dd, J ) 8.7, 2.5 Hz, 1H; H5), 5.51 (s,
1H; CHdC(CH3)2), 4.14 (t, 2H; OCH2), 4.05 (t, 2H; OCH2), 2.08
(s, 3H; CH3CO), 1.99 (s, 3H; CH3CO).
[(La )P t(µ-Cl)]2, 1a . HLa ligand (121 mg, 0.50 mmol) was
added to a solution of [(η3-C4H7)Pt(µ-Cl)]2 (143 mg, 0.25 mmol)
in chloroform (15 mL). The mixture was heated at reflux for
35 h, cooled to room temperature, and filtered off; the dark-
red solid was crystallized from chloroform, filtered, and dried
under vacuum to give the pure product in 76% yield (180 mg).
Mp: 298 °C. Anal. Calcd for C28Cl2H26N4O4Pt2: C, 35.64; H,
2.78; N, 5.94. Found: C, 34.71; H, 2.66; N, 5.83. 1H NMR
((CD3)2SO): δ (ppm) 7.13 (d, J ) 8.5 Hz, 1H; H6), 6.90 (d, J )
1.9 Hz, 1H; H3), 6.72 (d, J ) 8.65 Hz, 2H; H2′,6′), 6.15 (d, J )
8.65 Hz, 2H; H3′,5′), 6.08 (dd, J ) 8.5, 1.9 Hz, 1H; H5), 3.02 (s,
[(Ld )P t(a ca c)], 2d : dark-red; 6 h; yield 114 mg (89%);
thermotropic behavior in Table 2. Anal. Calcd for C47H56N2O8-
Pt: C, 58.07; H, 5.81; N, 2.88. Found: C, 57.92; H, 5.70; N,
2.83. 1H NMR (CDCl3): δ (ppm) 8.19 (d, J ) 8.7 Hz, 2H; Ha′,d′),
8.17 (d, J ) 8.7 Hz, 2H; Ha,d), 8.08 (d, J ) 8.5 Hz, 1H; H6),
8.03 (d, J ) 8.9 Hz, 2H; H2′,6′), 7.42 (d, J ) 2.3 Hz, 1H; H3),
7.36 (d, J ) 8.9 Hz, 2H; H3′,5′), 7.09 (dd, J ) 8.5, 2.3 Hz, 1H;
H5), 6.99 (d, J ) 8.7 Hz, 4H; Hb,c,b′,c′), 5.50 (s, 1H; CHdC(CH3)2),
4.05 (t, 4H; OCH2), 2.06 (s, 3H; CH3CO), 1.99 (s, 3H; CH3CO);
3J (195Pt-H3) ) 32 Hz.
3
3H; OCH3), 2.98 (s, 3H; OCH3), J (195Pt-H3) ) 48 Hz.
Colors, solvent, reaction times, yields, melting points, and
analytical and 1H NMR data for complexes 1b-d are as
follows.
P r epar ation of [(La -d)P t(acac)I2] Com plexes. The prepa-
ration of compound [(La)Pt(acac)I2], 3a , is described in detail;
all other homologues were prepared similarly.
[(Lb)P t(µ-Cl)]2, 1b: red; chloroform; 26 h; yield 166 mg
(72%); mp 232 °C. Anal. Calcd for C48Cl2H66N4O4Pt2: C, 47.10;
H, 5.43; N, 4.58. Found: C, 47.50; H, 5.40; N, 4.47.
[(Lc)P t(µ-Cl)]2, 1c: red; toluene; 18 h; yield 89 mg (62%);
thermotropic behavior in Table 2. Anal. Calcd for C74Cl2H98N4O8-
Pt2: C, 54.44; H, 6.05; N, 3.43. Found: C, 54.55; H, 6.04; N,
3.30. 1H NMR (CDCl3), isomer A: δ (ppm) 8.15 (d, J ) 8.8 Hz,
2H; Ha′,d′), 7.81 (d, J ) 8.8 Hz, 2H; H2′,6′), 7.80 (d, J ) 8.7 Hz,
1H; H6), 7.35 (d, J ) 8.8 Hz, 2H; H3′,5′), 6.98 (d, J ) 8.8 Hz,
2H; Hb′,c′), 6.78 (d, 1H; H3), 6.71 (dd, 1H; H5), 4.05 (m, 4H;
OCH2).
[(La )P t(a ca c)I2], 3a . A solution of 33 mg of I2 (0.13 mmol)
in acetone (3 mL) was added to a suspension of 2a (72 mg,
0.13 mmol) in acetone (6 mL). The solution immediately turned
yellow and was allowed to stir, at room temperature, for 75
min. The solvent volume was reduced, and a dark-violet solid
was filtered off and dried under vacuum to give the pure
product in 90% yield (96 mg). Mp: 246 °C. Anal. Calcd for
C19H20I2N2O4Pt: C, 28.91; H, 2.55; N, 3.55. Found: C, 28.86;
H, 2.56; N, 3.00. 1H NMR (CDCl3): δ (ppm) 8.13 (d, J ) 8.5
Hz, 1H; H6), 8.04 (d, J ) 8.6 Hz, 2H; H2′,6′), 7.02 (d, J ) 2.5
Hz, 1H; H3), 7.00 (d, J ) 8.6 Hz, 2H; H3′,5′), 6.87 (dd, J ) 8.5,
2.5 Hz, 1H; H5), 5.60 (s, 1H; CHdC(CH3)2), 4.03 (s, 3H; OCH3),
3.92 (s, 3H; OCH3), 2.17 (s, 3H; CH3CO), 2.15 (s, 3H; CH3CO);
3J (195Pt-H3) ) 20 Hz.
[(Ld )P t (µ-Cl)]2, 1d : red; toluene; 16 h; yield 175 mg
(65%); thermotropic behavior in Table 2. Anal. Calcd for
C84Cl2H98N4O12Pt2: C, 55.53; H, 5.44; N, 3.08. Found: C, 55.97;
H, 5.51; N, 2.70. 1H NMR (CDCl3): δ (ppm) 8.10 (d, J ) 9.1
Hz, 2H; Ha′,d′), 8.07 (d, J ) 9.1 Hz, 2H; Ha,d), 7.96 (d, J ) 8.4
Hz, 1H; H6), 7.86 (d, J ) 8.8 Hz, 2H; H2′,6′), 7.39 (d, J ) 8.8
Hz, 2H; H3′,5′), 7.13 (d, J ) 2.0 Hz, 1H; H3), 7.09 (dd, J ) 8.4,
2.0 Hz, 1H; H5), 6.94 (d, J ) 9.1 Hz, 2H; Hb′,c′), 6.89 (d, J ) 9.1
Hz, 2H; Hb,c), 4.04 (t, 2H; OCH2), 4.00 (t, 2H; OCH2).
P r ep a r a tion of [(La -d )P t(a ca c)] Com p lexes. The prepa-
ration of compound [(La)Pt(acac)], 2a , is described in detail;
all other homologues were prepared similarly.
Colors, reaction times, yields, melting points, and analytical
and 1H NMR data for complexes 3b-d are as follows.
[(Lb)P t(a ca c)I2], 3b: red; 75 min; crystallization from
methanol; yield 62 mg (90%); mp 149 °C. Anal. Calcd for
C
29H40I2N2O4Pt: C, 37.47; H, 4.34; N, 3.01. Found: C, 37.99;
H, 4.37; N, 3.07. 1H NMR (CDCl3): δ (ppm) 8.10 (d, J ) 8.9
Hz, 1H; H6), 8.01 (d, J ) 9.1 Hz, 2H; H2′,6′), 6.99 (d, J ) 2.5
Hz, 1H; H3), 6.97 (d, J ) 9.1 Hz, 2H; H3′,5′), 6.84 (dd, J ) 8.9,
2.5 Hz, 1H; H5), 5.59 (s, 1H; CHdC(CH3)2), 4.20 (t, 2H; OCH2),
4.05 (t, 2H; OCH2), 2.17 (s, 3H; CH3CO), 2.14 (s, 3H; CH3CO);
3J (195Pt-H3) ) 20 Hz.
(30) Mabbot, D. J .; Mann, B. E.; Maitlis, P. M. J . Chem. Soc., Dalton
Trans. 1977, 294.
(31) Taylor, E. C.; Hawks, G. H.; Mckillop, A. J . Am. Chem. Soc.
1968, 90, 2421.

Octahedral Liquid Crystalline Materials
Organometallics, Vol. 18, No. 11, 1999 2123
Ta ble 4. Cr ysta llogr a p h ic Da ta for Com p lexes 2a -4a
[(La)Pt(acac)], 2a
[(La)Pt(acac)I2], 3a
[(La)Pt(acac)(CH3)I], 4a
empirical formula
fw
C
536.5
19H21N2O4Pt
C19H21I2N2O4Pt
790.3
C20H24IN2O4Pt
678.4
cryst syst
space group
a, Å
b, Å
triclinic
P1h
triclinic
P1h
orthorombic
P212121
10.335(3)
13.015(9)
16.386(4)
90
90
90
2204(2)
4
9.390(3)
9.830(4)
10.366(3)
96.62(3)
100.08(2)
94.62(3)
930.7(5)
2
7.687(3)
10.155(3)
15.604(6)
95.59(3)
94.08(3)
109.75(2)
1133.9(7)
2
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
F(000)
518
1.914
75.64
730
2.315
39.36
1284
2.044
77.94
F(calc.), g/cm3
µ, cm-1
transmission factors
T, °C
0.068/0.103
25
0.271/0.898
25
0.030/0.073
25
λ, Å
0.710 73
3.5-50.0
3558
3250 [R(int) ) 0.0502]
3003/0/235
0.032
0.710 73
3.5-50.0
4305
3979 [R(int) ) 0.0486]
3202/0/253
0.043
0.710 73
3.5-50.0
2229
2209 [R(int) ) 0.000]
2077/0/253
0.064
2θ range for data collection
no. of reflns collected
no. of ind reflns
no. of data/restraints/params
Ra [I > 2σ(I)]
R1b
0.040
0.047
0.071
goodness-of-fit
0.50
1.39
1.85
a
b
2
R ) Σ||Fo| - |Fc||/Σ|Fo|. R1 ) [Σw(|Fo| - |Fc|)2/Σw|Fo| ]1/2
.
[(Lc)P t(a ca c)I2], 3c: red; 1 h; crystallization from metha-
nol; yield 47 mg (89%); thermotropic behavior in Table 3. Anal.
Calcd for C42H56I2N2O6Pt: C, 44.49; H, 4.98; N, 2.47. Found:
C, 44.77; H, 5.01; N, 2.81. 1H NMR (CDCl3): δ (ppm) 8.18-
8.10 (m, 5H; Ha′,d′,2′,6′,6), 7.37 (d, J ) 8.9 Hz, 2H; H3′,5′), 7.02-
6.98 (m, 3H; H3,b′,c′), 6.87 (dd, J ) 8.8, 2.2 Hz, 1H; H5), 5.60 (s,
1H; CHdC(CH3)2), 4.22 (t, 2H; OCH2), 4.05 (t, 2H; OCH2), 2.18
(s, 3H; CH3CO), 2.15 (s, 3H; CH3CO).
(t, 2H; OCH2), 2.14 (s, 3H; CH3CO), 2.09 (s, 3H; CH3CO), 1.21
(s, 3H; CH3Pt); J (195Pt-H3) ) 30 Hz; J (195Pt-H) ) 65 Hz.
[(Lc)P t(a ca c)(CH3)I], 4c: 50 equiv of CH3I; yellow; 6 days;
crystallization from acetone/methanol; yield 43 mg (52%);
thermotropic behavior in Table 3. Anal. Calcd for C43H59IN2O6-
Pt: C, 50.54; H, 5.82; N, 2.74. Found: C, 50.65; H, 5.66; N,
3.56. 1H NMR (CDCl3): δ (ppm) 8.16 (d, J ) 8.9 Hz, 4H;
Ha′,d′,2′,6′), 8.07 (d, J ) 8.4 Hz, 1H; H6), 7.34 (d, J ) 8.9 Hz, 2H;
H3′,5′), 7.05 (d, J ) 2.3 Hz, 1H; H3), 6.99 (d, J ) 8.9 Hz, 2H;
Hb′,c′), 6.91 (dd, J ) 8.4, 2.3 Hz, 1H; H5), 5.54 (s, 1H; CHd
C(CH3)2), 4.19 (m, 2H; OCH2), 4.06 (t, 2H; OCH2), 2.15 (s, 3H;
3
2
[(Ld )P t(a ca c)I2], 3d : 3 equiv of I2; dark-red; 30 min; yield
24 mg (60%); thermotropic behavior in Table 3. Anal. Calcd
for C47H56I2N2O8Pt: C, 46.05; H, 4.60; N, 2.28. Found: C,
3
CH3CO), 2.09 (s, 3H; CH3CO), 1.22 (s, 3H; CH3Pt); J (195Pt-
1
45.65; H, 4.50; N, 2.35. H NMR (CDCl3): δ (ppm) 8.35 (d, J
2
H3) ) 32 Hz; J (195Pt-H) ) 64 Hz.
) 8.6 Hz, 1H; H6), 8.19 (d, J ) 8.9 Hz, 2H; H2′,6′), 8.18 (dd, J
) 8.9 Hz, 2H; Ha,d,a′,d′), 7.45 (d, J ) 2.3 Hz, 1H; H3), 7.42 (d, J
) 8.9 Hz, 2H; H3′,5′), 7.34 (dd, J ) 8.6, 2.3 Hz, 1H; H5), 7.01 (d,
J ) 8.9 Hz, 2H; Hb′,c′), 7.00 (d, J ) 8.9 Hz, 2H; Hb,c), 5.63 (s,
1H; CHdC(CH3)2), 4.07 (t, 4H; OCH2), 2.19 (s, 3H; CH3CO),
[(Ld )P t(a ca c)(CH3)I], 4d : 100 equiv of CH3I; yellow; 5
days; crystallization from diethyl ether/petroleum ether; yield
41 mg (55%); thermotropic behavior in Table 3. Anal. Calcd
for C48H59IN2O8Pt: C, 51.75; H, 5.34; N, 2.51. Found: C, 51.83;
H, 5.30; N, 2.27. 1H NMR (CDCl3): δ (ppm) 8.27 (d, J ) 8.6
Hz, 1H; H6), 8.23 (d, J ) 9.0 Hz, 2H; H2′,6′), 8.18 (d, J ) 8.9
Hz, 2H; Ha′,d′), 8.17 (d, J ) 9.0 Hz, 2H; Ha,d), 7.47 (d, J ) 2.3
Hz, 1H; H3), 7.38 (d, J ) 9.0 Hz, 2H; H3′,5′), 7.34 (d, J ) 8.6
Hz, 2.3 Hz, 1H; H5), 7.01 (d, J ) 9.0 Hz, 2H; Hb′,c′), 7.00 (d, J
) 9.0 Hz, 2H; Hb,c), 5.57 (s, 1H; CHdC(CH3)2), 4.07 (t, 2H;
OCH2), 4.06 (t, 2H; OCH2), 2.15 (s, 3H; CH3CO), 2.11 (s, 3H;
CH3CO), 1.58 (s, 3H; CH3Pt); 3J (195Pt-H3) ) 25 Hz; 2J (195Pt-
H) ) 63 Hz.
3
2.17 (s, 3H; CH3CO); J (195Pt-H3) ) 18 Hz.
P r ep a r a tion of [(La -d )P t(a ca c)(CH 3)I] Com p lexes. The
preparation of compound [(La)Pt(acac)(CH)3I], 4a , is described
in detail; all other homologues were prepared similarly.
[(La )P t(a ca c)(CH3)I], 4a . CH3I (1.71 mmol) was added to
a suspension of 2a (90 mg, 0.17 mmol) in acetone (10 mL) and
stirred for 4 days. Concentration of the resulting yellow
solution followed by addition of diethyl ether resulted in the
formation of a brownish solid, which was filtered off and dried
under vacuum. Yield: 91 mg (80%). Mp: 180 °C. Anal. Calcd
for C20H23IN2O4Pt: C, 35.46; H, 3.42; N, 4.13. Found: C, 35.16;
H, 3.39; N, 4.34. 1H NMR (CDCl3): δ (ppm) 8.09-8.02 (m, 3H;
H2′,6′,6), 7.06 (d, J ) 2.3 Hz, 1H; H3), 6.98 (d, J ) 8.6 Hz, 2H;
H3′,5′), 6.91 (dd, J ) 8.5, 2.3 Hz, 1H; H5), 5.55 (s, 1H; CHd
C(CH3)2), 4.01 (s, 3H; OCH3), 3.91 (s, 3H; OCH3), 2.15 (s, 3H;
X-r a y Str u ctu r e Deter m in a tion s of [(La )P t(a ca c)], 2a ,
[(La )P t(a ca c)I2], 3a , a n d [(La )P t(a ca c)(CH3)I], 4a . Diffrac-
tion measurements were carried out on a Siemens R3m/V
automated four-circle diffractometer equipped with graphite-
monochromated Mo KR radiation (λ ) 0.710 73 Å). The data
were corrected for Lorentz, polarization, and X-ray absorption
effects, and an empirical absorption correction was applied
using a method based upon azimuthal (Ψ) scan data.33 Details
of crystal data collection are listed in Table 4. The structures
were solved by Patterson and Fourier methods and refined by
full-matrix least-squares. The weighting scheme used in the
3
CH3CO), 2.11 (s, 3H; CH3CO), 1.22 (s, 3H; CH3Pt); J (195Pt-
2
H3) ) 25 Hz; J (195Pt-H) ) 65 Hz.
Colors, reaction times, yields, melting points, and analytical
and 1H NMR data for complexes 4b-d are as follows.
[(Lb)P t(a ca c)(CH3)I], 4b: 50 equiv of CH3I; brownish; 6
days; crystallization from n-hexane; yield 76 mg (75%); mp
133.8 °C. Anal. Calcd for C30H43IN2O4Pt: C, 44.07; H, 5.30;
2
last refinement cycle was w-1 ) σ2|Fo| + q|Fc| , with q ) 0.0133
for complex 2a , q ) 0.0010 for complex 3a , and q ) 0.0020 for
1
N, 3.43. Found: C, 43.70; H, 5.44; N, 3.71. H NMR (CDCl3):
(32) Ghedini, M.; Morrone, S.; Neve, F.; Pucci, D. Gazz. Chim. It.
1996, 126, 511.
(33) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.,
Sect. A 1968, 24, 351.
δ (ppm) 8.07-8.00 (m, 3H; H2′,6′,6), 7.02 (d, J ) 2.1 Hz, 1H;
H3), 6.95 (d, J ) 9.1 Hz, 2H; H3′,5′), 6.88 (dd, J ) 8.6, 2.1 Hz,
1H; H5), 5.53 (s, 1H; CHdC(CH3)2), 4.17 (m, 2H; OCH2), 4.04

2124 Organometallics, Vol. 18, No. 11, 1999
Ghedini et al.
complex 4a , respectively. All the non-hydrogen atoms were
refined anisotropically, and the hydrogen atoms were included
as idealized atoms riding on the respective carbon atoms with
C-H bond lengths appropriate to the carbon atom hybridiza-
tion. The isotropic displacement parameter of each hydrogen
atom was fixed at U ) 0.08 Å2. Convergences for 3003, 3202,
and 2077 observed reflections [I > 2σ(I)] and 235 and 253
parameters respectively for complexes 2a , 3a , and 4a were
reached at R ) 0.032, 0.043, and 0.064, R′ ) 0.040, 0.047, and
0.071. All calculations were performed with SHELXTL PLUS34
and PARST35 programs. Atomic scattering factors were as
implemented in the SHELXTL PLUS program.
Ack n ow led gm en t. The present work was supported
by the Italian Ministero dell’Universita` e della Ricerca
Scientifica e Tecnologica (MURST) and Consiglio Na-
zionale delle Ricerche (CNR).
Su p p or tin g In for m a tion Ava ila ble: Atomic coordinates
and Ueq, intramolecular bond distances and angles, hydrogen
coordinates and isotropic displacement parameters, anisotropic
displacement parameters for 2a , 3a , and 4a (Tables S1-S12).
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM9808155
(34) SHELXTL PLUS, Version 4.21; Siemens Analytical X-ray
Instruments Inc.: Madison, WI, 1990.
(35) Nardelli, M. Comput. Chem. 1983, 7, 95.