Dinuclear C,N,C cyclometalated platinum derivatives with bridging delocalized ligands. Fourfold deprotonation of 6,6'-diphenyl-2,2'-bipyridine, H4L, promoted by "Pt(R)2" fragments (R = Me, Ph). Crystal structures of [Pt2(L)(3,5-Me2py)2]

Article abstract of DOI:10.1021/om051075k

cis-[Pt(R)₂(DMSO)₂] (R = Me, Ph) reacts with 6,6'-diphenyl-2,2'-bipyridine (H₄) in a 2:1 molar ratio, giving the unusual, very slightly soluble dinuclear complex [Pt₂(L)(DMSO) ₂] (1). The reaction implies activation of four C-H bonds: in 1 a fourfold deprotonated H₄L links two Pt-DMSO fragments acting as a delocalized C,N,CC,N,C 12-electron donor. From 1 more soluble dinuclear [Pta(L)(L')₂] (L' = bulky 2-electron donors such as PR₃ and substituted pyridines) species, 2-6, and polynuclear {Pt₂(L)(L-L) }_n (L-L = Ph₂P(CH₂)_xPPh₂ (x = 1, dppm; x = 2, dppe; x = 3, dppp)) species, 7-9, have been obtained by substitution of the DMSO ligands. DMSO can also be displaced from 1 by CO, both in solution and in the solid state, to give the flat and completely insoluble complex [Pt₂(L)(CO)₂] (10). The structures of [Pt ₂(L)(3,5-Me₂-Py)₂] (5) and {Pt ₂(L)(dppe)}₂ (8) have been determined by single-crystal X-ray diffraction analysis, while a powder X-ray diffraction analysis has been performed on complex 10, [Pt₂(L)(CO)₂]. With a 1:1 Pt:L molar ratio a mononuclear complex, [Pt(H₂L)(DMSO)] (11), is obtained, where the twofold deprotonated ligand is C,N,C coordinated. Also, the DMSO can be displaced from 11 by neutral ligands, L', such as CO, PPh₃, and 3,5-Me₂-py to give [Pt(H₂L)(L')] (12-14). Compounds 11-14 further react with cis-[Pt(R)₂(DMSO)₂] to give dinuclear complexes. This two-step approach allows us to obtain species with different ligands around each platinum atom, [Pt₂(L)(L')(L'')] (15-18).

Full text of DOI:10.1021/om051075k

Organometallics 2006, 25, 2253-2265
2253
Dinuclear C,N,C Cyclometalated Platinum Derivatives with Bridging
Delocalized Ligands. Fourfold Deprotonation of
6,6′-Diphenyl-2,2′-bipyridine, H4L, Promoted by “Pt(R)2” Fragments
(R ) Me, Ph). Crystal Structures of [Pt2(L)(3,5-Me2py)2] and
{Pt2(L)(dppe)}2 (dppe ) 1,2-Bis(diphenylphosphino)ethane). X-ray
Powder Diffraction of [Pt2(L)(CO)2]
Antonio Zucca,* Giacomo Luigi Petretto, Sergio Stoccoro, Maria Agostina Cinellu, and
Giovanni Minghetti
Dipartimento di Chimica, UniVersita` di Sassari, Via Vienna 2, I-07100 Sassari, Italy
Mario Manassero,* Carlo Manassero, Louise Male, and Alberto Albinati
Dipartimento di Chimica Strutturale e Stereochimica Inorganica, UniVersita` di Milano, Centro CNR,
I-20133 Milano, Italy
ReceiVed December 16, 2005
cis-[Pt(R)2(DMSO)2] (R ) Me, Ph) reacts with 6,6′-diphenyl-2,2′-bipyridine (H4L) in a 2:1 molar
ratio, giving the unusual, very slightly soluble dinuclear complex [Pt2(L)(DMSO)2] (1). The reaction
implies activation of four C-H bonds: in 1 a fourfold deprotonated H4L links two Pt-DMSO fragments
acting as a delocalized C,N,C∧C,N,C 12-electron donor. From 1 more soluble dinuclear [Pt2(L)(L′)2]
(L′ ) bulky 2-electron donors such as PR3 and substituted pyridines) species, 2-6, and polynuclear
{Pt2(L)(L-L)}n (L-L ) Ph2P(CH2)xPPh2 (x ) 1, dppm; x ) 2, dppe; x ) 3, dppp)) species, 7-9, have
been obtained by substitution of the DMSO ligands. DMSO can also be displaced from 1 by CO, both
in solution and in the solid state, to give the flat and completely insoluble complex [Pt2(L)(CO)2] (10).
The structures of [Pt2(L)(3,5-Me2-Py)2] (5) and {Pt2(L)(dppe)}2 (8) have been determined by single-
crystal X-ray diffraction analysis, while a powder X-ray diffraction analysis has been performed on complex
10, [Pt2(L)(CO)2]. With a 1:1 Pt:L molar ratio a mononuclear complex, [Pt(H2L)(DMSO)] (11), is obtained,
where the twofold deprotonated ligand is C,N,C coordinated. Also, the DMSO can be displaced from 11
by neutral ligands, L′, such as CO, PPh3, and 3,5-Me2-py to give [Pt(H2L)(L′)] (12-14). Compounds
11-14 further react with cis-[Pt(R)2(DMSO)2] to give dinuclear complexes. This two-step approach allows
us to obtain species with different ligands around each platinum atom, [Pt2(L)(L′)(L′′)] (15-18).
studied as chemosensors,5 switches,6 metallomesogens,7 and
luminescent8 devices. Square-planar platinum(II) and palladium-
(II) species were also used as “building blocks” for complex
systems such as supramolecular entities or dendrimers.9
Introduction
Cyclometalated compounds of late transition metals with
nitrogen ligands are well-known.1 During the years they have
been the subject of continuous research, due to their numerous
potential applications in areas such as organic synthesis,2
homogeneous catalysis,3 medicinal and biological chemistry,4
and the design of novel materials with attractive properties.
Recently, cyclometalated derivatives of d8 metal ions have been
In addition to the classical N,C compounds, great attention
is now devoted to d8 complexes with terdentate ligands. Species
having an N,N,C or an N,C,N sequence of donor atoms are
common, whereas complexes with a C,N,C sequence are still
rare.10 The N,N,C cyclometalates having planar terdentate
ligands, such as those arising from 6-phenyl-2,2′-bipyridine,
imply a delocalized π system which can give rise to peculiar
photophysical and photochemical properties involving, inter alia,
weak noncovalent interactions such as d8-d8 or π-π interac-
tions.11
* To whom correspondence should be addressed. E-mail: zucca@uniss.it
(A.Z.); mario.manassero@unimi.it (M.M.).
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Our previous work in this field was concentrated on the
reactivity of d8 ions with 6-substituted 2,2′-bipyridines: plati-
num(II),12 gold(III),13 and palladium(II).12a,b,e,14 N,N,C cyclo-
metalated derivatives have been synthesized, with both metal-
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10.1021/om051075k CCC: $33.50 © 2006 American Chemical Society
Publication on Web 03/31/2006

2254 Organometallics, Vol. 25, No. 9, 2006
Zucca et al.
Scheme 1
C(sp2) and metal-C(sp3) bonds. The behavior of these ligands
is not easily predictable, especially in the case of palladium-
(II), the reaction often being driven toward unexpected results.
In the case of platinum(II) the results can be summarized as
follows.
(1) Inorganic Pt(II) derivatives such as [PtCl4]2- and
[(L′)2PtCl2] (L′ ) neutral monodentate ligand) react with
6-substituted bipyridines (bipyR) to afford 1:1 adducts, [PtCl2-
(bipyR)], or cyclometalated compounds, [PtCl(bipyR-H)]. The
metalation implies elimination of HCl (Scheme 1, reaction 1).
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Messori, L.; Mini, E.; Orioli, P.; Mazzei, T.; Cinellu, M. A.; Minghetti, G.
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E. J.; Merbach, A. E.; van Koten, G. Inorg. Chem. 2001, 40, 850-855.
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Cheung, K. K.; Peng, S. M.; Che, C. M. Inorg. Chem. 2000, 39, 255-
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M. Inorg. Chem. 1999, 38, 4046. (c) Lai, S. W.; Chan, C. W.; Cheung,
K. K.; Che, C. M. Organometallics 1999, 18, 3327, 3336. (d) Lin, Y.
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Y.; Wang, Y. Chem. Eur. J. 2003, 9, 1263-1272. (e) Lu, W.; Mi, B. X.;
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1220.

Dinuclear C,N,C Cyclometalated Platinum DeriVatiVes
Organometallics, Vol. 25, No. 9, 2006 2255
(2) With hybrid intermediates such as [PtCl(Me)(SMe2)2],
either 1:1 adducts, [PtCl(Me)(bipyR)], or metalated derivatives,
[PtCl(bipyR-H)] (R ) Ph, CH2Ph, C(Me)2Ph), were obtained.
In this case the metalation occurs with loss of CH4. With 6-tert-
butyl-2,2′-bipyridine an unexpected result was observed, prob-
ably due to the bulkiness of the substituent: the reaction
proceeds at room temperature through C-H activation and
methane elimination, but the activation does not involve a carbon
on the substituent but one of the substituted pyridine rings. In
compound C (Scheme 1, reaction 2) the bipyridine acts as a
bidentate N′,C(3) ligand (“rollover” metalation15 ) to give a five-
membered cycle.
the ligand was able to undergo a double “rollover” metalation,
the reaction with [Pt(Me)2(DMSO)2] was carried out with a
platinum/ligand molar ratio of 2/1, under conditions exactly like
those used in the case of 6-Ph-2,2′-bipy (toluene, 80 °C). The
reaction is slow and leads to the isolation of a yellow product
that is insoluble in the reaction medium, is stable in air, and
has high thermal stability.
(3) When electron-rich diorgano derivatives such as [Pt(R)2-
(DMSO)2] (R ) Me, Ph), are employed, the “rollover” meta-
lation proceeds under mild conditions with many 6-substituted
2,2′-bipyridines (Scheme 1, reaction 3). The unusual room-
temperature C-H activation is specific to 6-substituted bipy-
ridines; N′,C(3) metalated derivatives were not obtained with
the unsubstituted ligand or with a 6,6′-disubstituted bipy (R )
Me).15b
(4) The rollover species obtained from the ligand 6-Ph-2,2′-
bipy is able to react with a second molecule of [Pt(R)2(DMSO)2]
(Scheme 1, reaction 4) to give dinuclear species. The bridging
3-fold deprotonated bipy acts as a terdentate C,N,C ligand
toward one platinum and as a bidentate C∧N ligand toward the
second one.12g
The last reaction is a rare example of multiple C-H bond
activation, and the species obtained are unique in several
respects: (i) the two platinum atoms are connected through a
planar, delocalized, trianionic, 10-electron-donor ligand, derived
from a threefold deprotonated 6-phenyl-2,2′-bipyridine; (ii) three
five-membered C,N cycles are assembled in the same molecule;
(iii) the terdentate dianionic system has a rare C∧N∧C sequence
of donor atoms,10 a sequence obtained through direct C-H
activation only in a few cases; (iv) the neutral DMSO ligands
are trans to atoms with different trans influences and trans
effects. Moreover, the new organometallic species have a high
thermal stability.
Following our previous studies, here we report an investiga-
tion on the related ligand 6,6′-diphenyl-2,2′-bipyridine, similar
to 6-phenyl-2,2′-bipyridine but potentially able to undergo
additional C-H activations providing more complex delocalized
systems.
The solid obtained, yield ca. 80%, is almost insoluble in most
of the common organic solvents, so that characterization in
solution is hampered. The IR spectrum (Nujol mull) gives
evidence for a coordinated DMSO; the analytical data (C, H,
N) are in agreement with a ligand/platinum/DMSO molar ratio
of 1/2/2. The complex was tentatively formulated as [Pt2(L)-
(DMSO)2] (1), in which a fourfold deprotonated ligand bridges
the two platinum atoms. These should both be in an uncommon
C-N-C environment with a coordinated DMSO molecule to
fulfill square-planar coordination. On the whole, owing to the
highly delocalized bridging system, the molecule can be
predicted to be almost planar. Species of this type are usually
insoluble materials, due to association between the planes of
monomeric units by metal-metal or π-π interactions.
Results and Discussion
The ligand 6,6′-diphenyl-2,2′-bipyridine, H4L, was synthe-
sized according to literature methods.16 To ascertain whether
(9) (a) Lo´pez-Torres, M.; Ferna´ndez, A.; Ferna´ndez, J. J.; Sua´rez, A.;
Castro-Juiz, S.; Vila, J. M.; Pereira, M. T. Organometallics 2001, 20, 1350-
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Starting from complex 1, we planned to synthesize new
compounds, by substitution of the DMSO ligands, with two
(12) (a) Minghetti, G.; Cinellu, M. A.; Chelucci, G.; Gladiali, S.;
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2, 189-205. (d) Minghetti, G.; Cinellu, M. A.; Stoccoro, S.; Zucca, A.;
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G.; Doppiu, A.; Zucca, A.; Stoccoro, S.; Cinellu, M. A.; Manassero, M.;
Sansoni, M. Chem. Heterocyclic Compd. 1999, 8(386), 1127-1137. (f)
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Manassero, M.; Sansoni, M. Eur. J. Inorg. Chem. 2000, 2555-2563. (g)
Zucca, A.; Doppiu, A.; Cinellu, M. A.; Minghetti, G.; Stoccoro, S.;
Manassero, M. Organometallics 2002, 21, 783-785. (h) Zucca, A.;
Stoccoro, S.; Cinellu, M. A.; Minghetti, G.; Manassero, M.; Sansoni, M.
Eur. J. Inorg. Chem. 2002, 3336-3346. (i) Zucca, A.; Cinellu, M. A.;
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Marshall, W. J.; Wang, Y. Organometallics 2005, 24, 619-627.

2256 Organometallics, Vol. 25, No. 9, 2006
Zucca et al.
Scheme 2
each platinum atom, with a “rollover” double cyclometalation.
The two Pt atoms are connected by a planar bridging moiety,
which acts as a 12-electron donor. The resulting widely
delocalized system is quite original. The Pt atoms display an
essentially square-planar coordination, with a very slight
tetrahedral distortion, maximum deviations from the least-
squares plane being -0.027(5) Å for N(1) and +0.021(6) Å
for C(3). The Pt-N distances are normal,18 whereas the Pt-C
distances are elongated by the mutual trans influence. The
deviation from linearity of the C(3)-Pt-C(10) angle, 162.2°,
is obviously due to the bite of the terdentate ligand and has
been observed previously.18 The dihedral angle between the
metal coordination plane and the lutidine plane is 48.3(2)°. The
expected noncoplanarity of the lutidine ligand prevents the
formation of significant intermolecular interactions and deter-
mines the solubility of the species.
It is noteworthy that the parent compound 1 can be ob-
tained in one step through multiple activation of C-H
bonds of both phenyl and pyridyl rings, with the loss of four
molecules of methane. Complexes 2-6 are achieved by re-
placement of DMSO in compound 1 with neutral ligands. The
eight condensed rings form a highly delocalized bridging
motif where the two platinum atoms are connected by a sub-
stituted bipyridine unit which acts as a hexadentate, 12-electron
ligand.
divergent purposes: (i) to obtain more soluble species easily
characterizable in solution, and (ii) to obtain completely flat
molecules. To discourage association among monomeric units,
and thus obtain more soluble derivatives, rather bulky lig-
ands were chosen. Replacement of coordinated DMSO with
tertiary phosphines and heterocyclic sp2 nitrogen ligands was
successful, with compounds 2-6, [Pt2(L)(L′)2] (Scheme 2:
L′) Ph3P (2), Cy3P (3), Na3(4-SO3-C6H4)3P (4), 3,5-dimeth-
ylpyridine (5), quinoline (6)), being isolated in moderate to
good yields. With an amine such as 4-Me-C6H4-NH2 (N sp3)
or a nitrile (CH3CN; N sp), substitution of DMSO was not
observed.
Compounds 2-6 are soluble enough to be characterized by
1
NMR spectroscopy. The H spectra show only 6 resonances
In an alternative strategy designed to give soluble species,
compound 1 was reacted with bidentate ligands, which are able
to position themselves between two platinum atoms and so keep
the molecular planes apart.
for the 12 bipyridine protons, indicating that the species are
symmetric. Furthermore, only one set of signals is observed
for the ancillary ligands; for example, there is only one signal
in the 31P{1H} NMR spectra of compounds 2 and 3. The
195Pt-31P coupling constants are in agreement with those of a
phosphorus nucleus trans to a nitrogen atom.12i,17
Reaction of compound 1 with the diphosphines Ph2P(CH2)n-
PPh2 (n ) 1 (dppm), 2 (dppe), 3 (dppp)) in a 1:1 molar ratio
gives complete substitution of DMSO and isolation of three new
soluble complexes, 7 (n ) 1), 8 (n ) 2), 9 (n ) 3).
The 31P{1H} NMR spectra of compounds 7-9 show only
one resonance, with a chemical shift in the range expected for
a bridging ligand12d and coupling constants comparable to those
observed for compounds 2-4. The NMR spectra, indicative of
symmetric species, taken together with the analytical data, enable
us to assume that 7-9 are poly- or at least tetranuclear spe-
cies, the dinuclear units being connected by two diphosphines
(Chart 1).
Complex 5 has been characterized in depth in solution by
means of 13C, H NOE difference and COSY spectra and in
1
the solid state by X-ray diffraction. In the FAB mass spectrum
(positive ions), besides the molecular ion [M]+ at m/z 909, other
peaks at m/z 802 and 694 correspond to the loss of one and
two molecules of 3,5-Me2-py, respectively.
Red crystals of 5‚2CHCl3 suitable for single-crystal X-ray
diffraction analysis were isolated by diffusion of n-pentane into
a dilute chloroform solution. An ORTEP view of 5 is given in
Figure 1. Principal bond parameters are reported in the caption
of Figure 1.
For complex 8 (dppe) the tetranuclearity of the species was
.
confirmed by determination of the structure of 8‚1.5CHCl3 H2O
The structure consists of the packing of 5 and CHCl3
molecules in the molar ratio 1:2. The CHCl3 molecules are
partially disordered (see Experimental Section). The molecule
of 5 lies on a crystallographic inversion center. The structure
confirms that the ligand L behaves as a terdentate dianion toward
by single-crystal X-ray diffraction. The structure consists of the
packing of molecules of 8, CHCl3, and H2O in the molar ratio
1:1.5:1. The solvent molecules are disordered (see Experimental
Section). An ORTEP view of 8 is shown in Figure 2. Principal
bond parameters are reported in Table 2. As expected, the
molecule comprises two dinuclear units connected by two
diphosphines, which act as hexabidentate ligands. Each of the
four platinum atoms displays a square-planar coordination with
a slight tetrahedral distortion. Average bond lengths involving
the four Pt atoms are Pt-P ) 2.217 Å, Pt-N ) 2.025 Å,
Pt-C(phenyl) ) 2.075 Å, and Pt-C(pyridine) ) 2.115 Å. All
these values compare well with those found in [Pt2(L)Cl(PPh3)2]
(compound 19, H3L ) 6-phenyl-2,2′-bipyridine),12i where one
of the Pt atoms is in the same environment as the Pt atoms in
8; in 19 Pt-P ) 2.231(1) Å, Pt-N ) 2.024(3) Å, Pt-C(phenyl)
) 2.071(4) Å, and Pt-C(pyridine) ) 2.104(6) Å). The dihedral
angle between the least-squares planes of Pt(1) and Pt(2) is
8.9(6)°, and that between the least-squares planes of Pt(3) and
Pt(4) is 16.5(3)°. Therefore, in this case the two dinuclear units
(13) (a) Cinellu, M. A.; Zucca, A.; Stoccoro, S.; Minghetti, G.;
Manassero, M.; Sansoni, M. J. Chem. Soc., Dalton Trans. 1996, 4217-
4225. (b) Cinellu, M. A.; Minghetti, G.; Pinna, M. V.; Stoccoro, S.; Zucca,
A.; Manassero, M.; Sansoni, M. J. Chem. Soc., Dalton Trans. 1998, 1735-
1741. (c) Cinellu, M. A.; Minghetti, G.; Pinna, M. V.; Stoccoro, S.; Zucca,
A.; Manassero, M. Eur. J. Inorg. Chem. 2003, 12, 2304-2310. (d) Cinellu,
M. A.; Minghetti, G.; Pinna, M. V.; Stoccoro, S.; Zucca, A.; Manassero,
M. J. Chem. Commun. 1998, 2397-2398.
(14) (a) Zucca, A.; Cinellu, M. A.; Pinna, M. V.; Stoccoro, S.; Minghetti,
G.; Manassero, M.; Sansoni, M. Organometallics 2000, 19, 4295-4304.
(b) Stoccoro, S.; Soro, B.; Minghetti, G.; Zucca, A.; Cinellu, M. A. J.
Organomet. Chem. 2003, 679, 1-9.
(15) (a) Skapski, A. C.; Sutcliffe, V. F.; Young, G. B. Chem. Commun.
1985, 609-611. (b) Minghetti, G.; Stoccoro, S.; Cinellu, M. A.; Soro, B.;
Zucca, A. Organometallics 2003, 4770-4777.
(16) (a) Dietrich-Buchecker, C. O.; Marnot, P. A.; Sauvage, J. P.
Tetrahedron Lett. 1982, 23, 5291-5294. (b) Leadbeater, N. E.; Resouly,
S. M. Tetrahedron Lett. 1999, 40, 4253-4246.
(17) E.g.: Lu, W.; Chan, M. C. W.; Zhu, N.; Che, C. M.; Hui, L. Z. J.
Am. Chem. Soc. 2004, 126, 7639-7651.
(18) Lu, W.; Chan, M. C. W.; Cheung, K. K.; Che, C. M. Organome-
tallics 2001, 20, 2477-2486.

Dinuclear C,N,C Cyclometalated Platinum DeriVatiVes
Organometallics, Vol. 25, No. 9, 2006 2257
Figure 1. ORTEP view of compound 5. Ellipsoids are drawn at the 30% probability level. Selected bond lengths (Å) and angles (deg) in
5, with estimated standard deviations (esd’s) on the last figure in parentheses: Pt-N(1) ) 1.983(5), Pt-N(2) ) 2.037(5), Pt-C(3) )
2.054(6), Pt-C(10) ) 2.104(6); N(1)-Pt-N(2) ) 178.4(2), N(1)-Pt-C(3) ) 80.1(2), N(1)-Pt-C(10) ) 82.1(2), N(2)-Pt-C(3) )
99.9(2), N(2)-Pt-C(10) ) 98.0(2), C(3)-Pt-C(10) ) 162.2(2).
Chart 1
stitution of CO for DMSO occurs at room temperature, giving
complex 10, [Pt2(L)(CO)2].
are not completely planar, probably because of the π stacking
forces, and are staggered, not eclipsed, with respect to one
another. The distances between the two dinuclear units are in
the range 3.26(1)-3.58(1) Å.
We were eager to study how the length of the CH2 chain in
the diphosphine affects the nuclearity of derivatives 7 and 9, as
well as the overall dimension of the inside cage. Unfortunately,
however, crystals suitable for a X-ray analysis could not be
obtained.
For comparison, the reaction of the ligand 6,6′-diphenyl-2,2′-
bipyridine (H4L) has been carried out with cis-[Pt(Ph)2(DMSO)2]
(molar ratio 1:2) and found to give compound 1, isolated as an
almost insoluble solid that, by treatment with Ph3P, affords
compound 2 (NMR criterion). The double “rollover” cyclo-
metalation implies elimination of benzene instead of methane
in this case, proving that loss of methane is not an essential
condition for the multiple C-H activation. This reaction,
however, is less favored. Some decomposition to metal is
observed, and yields are lower:
The reaction also proceeds in solution starting from 5 and,
notably, even by passing a stream of CO over complex 1 in the
solid state. Yields are good, 75-85%. Complex 10 is a brick
red material which is completely insoluble in common solvents,
suggesting strong association of the planar dinuclear units. The
thermal stability is unusual for an organometallic species, the
complex not melting or decomposing in air up to 270 °C. The
IR spectrum shows a sharp absorption at 2063 cm-1, in the
region of terminal carbonyls, a reasonable value for a CO trans
to a nitrogen atom in a neutral platinum(II) complex.12i The
coordinated CO is easily displaced by Ph3P to give compound
2 but, surprisingly, not by 3,5-Me2-py. Samples of complex 10
suitable for a single-crystal X-ray diffraction analysis could not
be obtained. The structure was therefore studied by X-ray
powder diffraction.
2 cis-[Pt(Ph)2 (DMSO)2] (i) H L 8
4
(ii) PPh3
[Pt2(L)(PPh3)2] + 4C6H6 + 4DMSO
The structure of complex 10 was determined from powder
X-ray diffraction data by a direct space method, as implemented
in the software package Dash.19 The structural solution obtained
To synthesize a completely flat molecule, complex 1 was
reacted with carbon monoxide in a CH2Cl2 suspension. Sub-

2258 Organometallics, Vol. 25, No. 9, 2006
Zucca et al.
Figure 2. ORTEP view of compound 8. Ellipsoids are as in Figure 1. Only the first atoms of the phosphinic phenyl rings have been
shown, for clarity.
Table 1. Crystallographic Data
Table 2. Selected Bond Lengths (Å) and Angles (deg) in 8,
with Estimated Standard Deviations (Esd’s) on the Last
Figure in Parentheses
5‚2CHCl3
8‚1.5CHCl3‚H2O
C97.5H75.5Cl4.5N4OP4Pt4
2383.01
red
formula
Mr
color
cryst syst
space group
a/Å
C38H32Cl6N4Pt2
1147.60
red
Pt(1)-P(1)
Pt(1)-C(3)
Pt(2)-P(2)
Pt(2)-C(10)
Pt(3)-P(3)
Pt(3)-C(33)
Pt(4)-P(4)
Pt(4)-C(40)
2.217(2)
2.054(6)
2.227(2)
2.122(6)
2.209(2)
2.084(6)
2.213(2)
2.128(6)
Pt(1)-N(1)
Pt(1)-C(13)
Pt(2)-N(2)
Pt(2)-C(18)
Pt(3)-N(3)
Pt(3)-C(43)
Pt(4)-N(4)
Pt(4)-C(48)
2.027(5)
2.101(6)
2.038(5)
2.081(6)
2.006(5)
2.110(6)
2.028(5)
2.081(6)
orthorhombic
Pbca
11.710(1)
15.240(1)
21.610(2)
3856.5(6)
4
orthorhombic
P212121
16.140(1)
19.532(1)
27.911(2)
8798.8(1.0)
4
b/Å
c/Å
V/Å3
Z
P(1)-Pt(1)-N(1)
P(1)-Pt(1)-C(13)
N(1)-Pt(1)-C(13)
P(2)-Pt(2)-N(2)
P(2)-Pt(2)-C(18)
N(2)-Pt(2)-C(18)
P(3)-Pt(3)-N(3)
P(3)-Pt(3)-C(43)
N(3)-Pt(3)-C(43)
P(4)-Pt(4)-N(4)
P(4)-Pt(4)-C(48)
N(4)-Pt(4)-C(48)
174.3(1)
95.1(2)
81.3(2)
177.3(1)
103.5(2)
77.8(2)
174.4(1)
93.7(2)
81.6(2)
173.2(1)
102.5(2)
77.8(2)
P(1)-Pt(1)-C(3)
N(1)-Pt(1)-C(3)
C(3)-Pt(1)-C(13)
P(2)-Pt(2)-C(10)
N(2)-Pt(2)-C(10)
C(10)-Pt(2)-C(18)
P(3)-Pt(3)-C(33)
N(3)-Pt(3)-C(33)
C(33)-Pt(3)-C(43)
P(4)-Pt(4)-C(40)
N(4)-Pt(4)-C(40)
C(40)-Pt(4)-C(48)
105.2(2)
78.8(2)
159.4(2)
98.0(2)
80.9(2)
158.4(2)
106.3(2)
78.5(2)
159.8(2)
98.2(2)
81.6(2)
159.4(2)
F(000)
2184
1.976
150
4580
1.799
150
Dc/g cm-3
T/K
cryst dimens/mm
µ(Mo KR)/cm-1
min and max transmissn
factors
scan mode
frame width/deg
time per frame/s
no. of frames
detector-sample dist/cm 4.00
θ range/deg 3-27
reciprocal space explored full sphere
no. of rflns (total, indep)
Rint
0.22 × 0.23 × 0.33 0.20 × 0.22 × 0.44
77.8
66.7
0.631-1.000
0.479-1.000
ω
0.30
25
ω
0.30
15
2450
4.00
3-27
full sphere
122 297, 19 667
0.0637
0.051, 0.066
2450
slightly from planarity, with maximum deviations from the least-
squares plane through the non-hydrogen atoms of the molecule
of +0.1 and -0.1 Å for atoms O(1) and C(5), respectively.
The dihedral angle between the least-squares planes of the
platinum atoms is 6°.
52 032, 4222
0.0779
0.068, 0.090
final R2 and R2w
indicesa (F2, all rflns)
conventional R1 index
(I > 2σ(I))
0.037
0.027
As can be seen in Figure 3, the molecule that is formed from
the symmetrically equivalent halves in the refined solution is
chemically reasonable, with the bond distance C(3)-C(3_4)
being 1.45 Å. The bond distance Pt(1)-C(4_4) is 2.15 Å, which
is similar to equivalent Pt-C(pyridine) bond distances found
in the solid-state structures of 5 and 8 (see above). The geometry
around the platinum atom, which displays a square-planar coor-
dination with a slight tetrahedral distortion, is very similar to
that found in the structures of 5 and 8, with the C(7)-Pt(1)-
C(4_4) angle being 159°. All other geometrical parameters are
unremarkable and are within the corresponding ranges of values
as determined from related molecules found in the Cambridge
Structural Database (CSD).21
no. of rflns with I > 2σ(I) 3035
15 476
1063
0.98
no. of variables
244
1.05
goodness of fitb
a R2) [∑(|Fo - kFc |/∑Fo ], R2w) [∑w/(Fo - kFc )2/∑w(Fo )2]1/2
.
2
2
2
2
2
2
b [∑w(Fo2 - kFc2)2/(No - Nv)]1/2, where w ) 4Fo /σ(Fo ) , σ(Fo ) ) [σ2(Fo )
2
2 2
2
2
2
+ (pFo )2]1/2, No is the number of observations, Nv the number of variables,
and p, the ignorance factor, is 0.03 for 5‚2CHCl3 and 0.02 for
8‚1.5CHCl3‚H2O.
was subjected to rigid-body Rietveld refinement.20 The mol-
ecule, which lies on a 2-fold rotation axis in the structure, is
shown in Figure 3. As predicted, the molecule deviates only
(19) David, W. I. F.; Shankland, K. Dash, Program for Structure Solution
from Powder Diffraction Data; Cambridge Crystallographic Data Centre,
Cambridge, U.K., 2004.
(20) Rietveld, H. M. J. Appl. Crystallogr., 1969, 2, 65-71.

Dinuclear C,N,C Cyclometalated Platinum DeriVatiVes
Organometallics, Vol. 25, No. 9, 2006 2259
Figure 3. View of compound 10 showing the atomic numbering scheme.
deprotonation arises from a “rollover” metalation and a Ph-H
bond activation, with loss of methane:
Figure 4. Column of molecules formed along the (001) direction
through π-π interactions in the solid-state structure of compound
10.
As predicted, the planar nature of the molecules in this struc-
ture results in the formation of π-π interactions, as shown in
Figure 4. Columns of molecules are formed in the (001) direc-
tion, with the planes of the molecules being parallel and the
aromatic ring systems being offset, resulting in a favorable inter-
molecular interaction22 (see Figure 5). The interplanar distance
is 3.4 Å, corresponding to the closest Pt‚‚‚Pt distance of 3.4 Å.
Attempts to obtain another flat molecule by substitution of
CH3CN for DMSO or CO in 1 or 10 respectively, failed.
All the chemistry described up to this point has started from
the reaction of the ligand L with the platinum intermediates
[Pt(R)2(DMSO)2] in a 1:2 molar ratio. Building of the delocal-
ized bridging unit, involving C-H activation of both the phenyl
substituents, was achieved in a single step. To further investigate
the reactivity of the ligand H4L, the reaction was also carried
out with a 1:1 Pt:L molar ratio. Yields can be improved by
operating with an excess of H4L (see Experimental Section).
Multiple C-H bond activation occurs even in this case, giving
a mononuclear species, [Pt(H2L)(DMSO)] (11). The double
Complex 11, in contrast with 1, is soluble. This is likely to
be due to the presence of the nonmetalated phenyl ring which,
not being constrained in the coordination plane, discourages the
formation of interactions between planes. The 1H NMR spectrum
of 11 is more complex than those of the dinuclear species 2-6,
due to the lack of symmetry of the bipyiridine unit. The DMSO
3
signal (δ 3.68 ppm, JPt-H ) 26.8 Hz) is indicative of an
S-bonded ligand coordinated trans to a nitrogen atom.12g A 1H
1
COSY spectrum, in addition to H NOE difference spectra,
(21) Allen, F. H. Acta Crystallogr. 2002, B58, 380-388.
(22) Hunter, C. A.; Sanders, J. K. M. J. Am. Chem. Soc. 1990, 112,
5525-5534.
assisted us in the assignment of the proton signals. The NOE
difference spectra showed, inter alia, the presence of a strong

2260 Organometallics, Vol. 25, No. 9, 2006
Zucca et al.
Figure 5. Two views of a pair of molecules connected by π-π interactions in the solid-state structure of compound 10. The view on the
left is taken perpendicular to the least-squares plane through the non-hydrogen atoms of one of the molecules, and the view on the right is
taken along this plane.
Chart 2. Numbering Scheme for the Dinuclear and the
NOE contact between the DMSO methyl protons and the
Mononuclear Derivatives
adjacent protons H3′′ (7.62 ppm), and H4′ (8.27 ppm) (see Chart
3
2 for the numbering scheme). The H4′ proton shows a JPt-H
value of 18 Hz, in line with values previously observed.
Substitution of DMSO in 11 by CO, PPh3, and 3,5-Me2-py
gives [Pt(H2L)(CO)] (12), [Pt(H2L)(PPh3)] (13), and [Pt(H2L)-
(3,5-Me2-py)] (14), respectively. The IR spectrum of 12 in Nujol
shows an absorption at 2063 cm-1 (in CH2Cl2, 2065 cm-1), the
same value as that observed in the dinuclear complex 10. In
1
the H NMR spectra of 13 and 14 the signals of the H3′′ and
H4′ protons are shifted strongly upfield with respect to those
of compound 11, due, respectively, to the presence of the
adjacent PPh3 and 3,5-Me2-py ligands.
The mononuclear complex 11 reacts further with [Pt(Me)2-
(DMSO)2] to give complex 1, which implies that dinuclear
species can be obtained in two steps. Such a two-step approach
Conclusions
We have shown the remarkable ability of the electron-rich
derivatives [Pt(R)2(L′)2] to promote multiple C-H activations.
In the case of the reaction with 6,6′-diphenyl-2,2′-bipyridine, a
molecule poorly investigated in coordination chemistry thus far,
simultaneous activation of aryl and pyridyl C-H bonds occurs.
The outcome of this activation process, a “rollover” and an arylic
metalation, is the building up of deprotonated ligands able to
trap platinum ions in a C-N-C environment, an arrangement
not common and seldom achieved by direct C-H activation.
Depending on the ligand-to-platinum molar ratio, either di- or
mononuclear cyclometalated derivatives can be obtained. In the
dinuclear species the fourfold deprotonated substituted bipyri-
dine links the platinum atoms through a delocalized system
which acts as a 12-electron donor. With an appropriate choice
of the ancillary ligand L′, required to fulfill coordination around
the metal atom, it is possible to either favor or prevent
association between the monomeric units.With a ligand such
as CO an insoluble material is obtained, as expected for stacked
d8 planar complexes. In contrast, bulky ligands, e.g. PR3, hamper
association, allowing us to obtain soluble derivatives. Soluble
species with even higher nuclearity can be synthesized by using
bidentate L′ ligands suitable for bridging two monomeric units.
The solid-state structure of a tetranuclear complex has been
solved by single-crystal X-ray diffraction analysis.
Multiple C-H activation is also achieved with a 1:1 ligand-
to-platinum ratio. The mononuclear C,N,C cyclometalates
obtained can further react with another “PtR2” fragment to give
dinuclear derivatives. This two-step synthetic approach opens
up new prospects for assembling species with different environ-
ments around each of the platinum atoms and, consequently,
different properties.
Overall the results presented herein once again underline the
potential of the “Pt(R)2” fragments in the intramolecular
activation of C-H bonds. As shown, the synthesis of very
allows molecules with different environments around the two
platinum atoms to be synthesized (Scheme 3).
Comparison of the stretching vibration of the coordinated CO
in the dinuclear compounds 10, 17, and 18, νCO ∼2063, 2052,
2052 cm-1, respectively, indicates that the interaction between
the two platinum atoms through the delocalized bridging system
is not negligible.

Dinuclear C,N,C Cyclometalated Platinum DeriVatiVes
Organometallics, Vol. 25, No. 9, 2006 2261
Scheme 3
and vacuum-pumped to give the analytical sample as a green-yellow
solid. Yield: 458 mg, 83%. Mp: >270 °C. Anal. Calcd for
C26H24N2O2Pt2S2: C, 36.71; H, 2.84; N, 3.29. Found: C, 37.43;
H, 3.04; N, 3.29. IR (Nujol, cm-1): νmax 1013 (s), 1119 (s).
unusual molecules can be achieved whose properties deserve
further investigation. It is also worth noting that the reactivity
of these fragments is of paramount importance in intermolecular
C-H activation.23
Synthesis of [Pt2(L)(PPh3)2] (2). To a solution of PPh3 (30.8
mg, 0.117 mmol) in CH2Cl2 (40 mL) was added slowly, with
vigorous stirring, 50.0 mg of 1 (0.0588 mmol). The yellow
solution that formed was stirred for 1 h and then filtered over
Celite, concentrated to a small volume, and treated with diethyl
ether. The precipitate that formed was filtered, washed with diethyl
ether, and vacuum-pumped to give the analytical sample as a yellow
solid. Yield: 51.4 mg, 72%. Mp: >270 °C. Anal. Calcd for
C58H42N2P2Pt2‚H2O: C, 56.31; H, 3.58; N, 2.26. Found: C, 56.30;
H, 3.75; N, 2.04. 1H NMR (CD2Cl2): δ 5.82 (d, 2H, H4, H4′, JH-H
Experimental Section
The platinum complexes cis-[PtR2(DMSO)2] (R ) Me, Ph) were
prepared according to literature methods.24 The ligand 6,6′-diphenyl-
2,2′-bipyridine was synthesized according to ref 16. All the solvents
were purified and dried according to standard procedures.25 Ele-
mental analyses were performed with a Perkin-Elmer 240B
elemental analyzer by Mr. Antonello Canu (Dipartimento di Chim-
ica, Universita` degli studi di Sassari, Sassari, Italy). Infrared spectra
were recorded with a FT-IR Jasco 480P spectrometer using Nujol
mulls. 1H, 13C{1H}, and 31P{1H} NMR spectra were recorded with
a Varian VXR 300 spectrometer operating at 300.0, 75.4, and 121.4
MHz, respectively.1H NOE difference spectra and 2D 1H-1H
COSY spectra were recorded with a standard pulse sequence.
Chemical shifts are given in ppm relative to internal TMS (1H,
13C) and external 85% H3PO4 (31P). The mass spectrometric
measurements were performed on a VG 7070EQ instrument,
equipped with a PDP 11 250J data system and operating under
positive ion fast atom bombardment (FAB) conditions with 3-ni-
trobenzyl alcohol as the supporting matrix.
Synthesis of [Pt2(L)(DMSO)2] (1). To a solution of 6,6′-
diphenyl-2,2′-bipyridine (L; 200 mg, 0.65 mmol) in anhydrous
toluene (20 mL) was added with vigorous stirring 496 mg of cis-
[PtR2(DMSO)2] (R ) Me, Ph; 1.3 mmol): the solution rapidly
changed color to orange. The stirred solution, kept under an argon
atmosphere, was heated to 80 °C. During the heating, a yellow-
green precipitate was formed. After the mixture was cooled, the
precipitate was filtered off, washed with toluene and diethyl ether,
3
) 7.7 Hz. JPt-H ) 17.8 Hz); 6.21 (d, 2H, H3′′. H3′′′, JH-H ) 7.8
Hz, 3JPt-H ) 80 Hz); 6.51 (td, 2H, H4′′′. H4′′, JH-H ) 7.0, JH-H
)
1.4 Hz); 6.59 (dd, 2H, H5. H5′, JH-H ) 7.7 Hz, JH-H ) 1.4 Hz);
6.78 (t, 2H, H5′′. H5′′′, JH-H ) 7.0 Hz); 7.47 (d, 2H, H6′′, H6′′′,
JH-H ) 7.0 Hz); 7.41 (m, 18H, Hm, Hp (PPh3)); 7.82 (m, 12H, Ho
1
(PPh3)). 31P NMR (CD2Cl2): δ 24.9 (s, JPt-P ) 3949 Hz).
Synthesis of [Pt2(L)(PCy3)2] (3). Complex 3 was obtained by
following the same procedure used for complex 2, using PCy3
instead of PPh3. Yield: 48%. Mp: >270 °C. Anal. Calcd for
C58H78N2P2Pt2: C, 55.49; H, 6.26; N, 2.23. Found: C, 55.25; H,
1
6.27; N, 2.43. H NMR (CD2Cl2): δ 1.18-1.28 (m, 18H, CH2
(PCy3)); 1.55-1.83 (m, 30H, CH2 (PCy3)); 2.05-2.17 (m, 12H,
CH2 (PCy3)); 2.40-2.55 (m, 6H, CH (PCy3)); 6.93-7.04 (m, 6H,
H5′′, H4′′, H5); 7.29 (dd, 2H, H3′′, JH-H ) 7.1 Hz, JH-H ) 1.6 Hz);
7.54 (d, 2H, H4, JH-H ) 7.6 Hz); 7.75 (d, 2H, H5′′, JH-H ) 7.7
1
Hz). 31P NMR (CDCl3): δ 22.3 (s, JPt-P ) 3687 Hz).
Synthesis of [Pt2(L)(P(m-PhSO3Na)3)2] (4). To a solution of
P(m-PhSO3Na)3 (117.8 mg) in a 1:1 water/acetone mixture was
added with vigorous stirring under an argon atmosphere 70.5 mg
of 1 (0.083 mmol). The mixture was stirred at room tempera-
ture for 15 h. The yellow solution obtained was filtered, concen-
trated to small volume, and treated with acetone. The yellow
precipitate that formed was filtered off and washed with acetone
to give 4 in almost quantitative yield. Mp: >270 °C. Anal. Calcd
for C58H48N2Na6O24P2Pt2S6‚6H2O: C, 35.92; H, 2.49; N, 1.44;
Found: C, 35.86; H, 2.69; N, 1.38. 1H NMR (DMSO-d6): δ 5.84
(d, 2H, J ) 8.0 Hz); 5.99 (d, 2H, J ) 7.1 Hz); 6.42 (t, 2H, J ) ca.
7.5 Hz); 6.70 (t, 2H, J ) ca. 7.5 Hz); 6.77 (d, 2H, J ) 8.2 Hz);
(23) E.g.: (a) Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507-
514. (b) Shilov, A. E.; Shul’pin, G. B. Chem. ReV. 1997, 97, 2879-2932.
(c) Lersch, M.; Tilset, M. Chem. ReV. 2005, 105(6), 2471-2526. (d)
Crabtree, R. H. J. Organomet. Chem. 2004, 689, 4083-4091. (e) Driver,
T. G.; Day, M. W.; Labinger, J. A.; Bercaw, J. E. Organometallics 2005,
24, 3644-3654. (f) Fekl, U.; Goldberg, K. I. AdV. Inorg. Chem. 2003, 54,
259-320.
(24) (a) Eaborn, C.; Kundu, K.; Pidcock, A. J. Chem. Soc., Dalton Trans.
1981, 933. (b) Romeo, R.; Monsu` Scolaro, L. Inorg. Synth. 1998, 32, 153.
(25) Vogel’s Textbook of Practical Organic Chemistry, 5th ed.; Longman
Scientific and Technical: Harlow, U.K., 1989.

2262 Organometallics, Vol. 25, No. 9, 2006
Zucca et al.
1
7.34-8.04 (m, 26H). 31P NMR (DMSO-d6): δ 25.67 (s, JPt-P
)
Ho (PPh)); 7.88 (m, 8H, Ho (PPh)). 31P NMR (CD2Cl2): δ 23.95
1
3
3961 Hz).
(s, JPt-P ) 4010 Hz, JP-P ) 35.9 Hz). MALDI-TOF: m/z 1093
[Pt2(L)(dppe)]+.
Synthesis of [Pt2(L)(3,5-dimethylpyridine)2] (5). To a suspen-
sion of 1 (150 mg, 0.176 mmol) in CHCl3 (30 mL) was added
with vigorous stirring 0.40 mL of 3,5-lutidine (d ) 0.939 g/mL;
3.53 mmol, 10-fold excess). The mixture was heated to reflux for
5 h. After it was cooled, the mixture was filtered over Celite,
concentrated to small volume, and treated with Et2O. The precipitate
that formed was filtered, washed with Et2O, and vacuum-pumped
to give the analytical sample as an orange solid. Yield: 118 mg,
74%. Mp: >270 °C. Anal. Calcd for C36H30N4Pt2: C, 47.58; H,
3.33; N, 6.16. Found: C, 47.84; H, 3.28; N, 6.49. 1H NMR
(CD2Cl2): δ 2.41 (s, 12H, Me); 6.78 (dd, 2H, JH-H ) 7.3 Hz, JH-H
Synthesis of [Pt2(L)(dppp)]2 (9). Complex 9 was obtained by
following the same procedure used for complex 7, using dppp
instead of dppm. Total yield: 89%. Mp: >270 °C. Anal. Calcd
for C98H76N4P4Pt4: C, 53.17; H, 3.46; N, 2.53. Found: C, 53.51;
H, 3.63; N, 2.53. 1H NMR (CD2Cl2): δ 2.72-2.88 (m, 8H, CH2);
3.18-3.34 (m, 4H, CH2); 5.92 (d, 4H, JH-H ) 7.8 Hz, H5); 6.12
(dd, 4H, JH-H ) 7.8 Hz, JH-H ) 1.6 Hz, H4); 6.43 (d, 4H, JH-H
)
7.3 Hz, 4H, H3′′); 6.60 (td, 4H, JH-H ) 7.3 Hz, JH-H ) 1.4 Hz,
H4′′); 6.79 (td, 4H, JH-H ) 7.3 Hz, JH-H not resolved, H5′′); 6.88
(dd, 4H, JH-H ) 7.3 Hz, JH-H not resolved, H6′′); 7.27 (m, 12H,
Hm, Hp (dppp)); 7.38 (m, 12H, Hm, Hp (dppp)); 7.50 (m, 8H, Ho
(dppp)); 7.82 (m, 8H, Ho (dppp)). 31P NMR (CD2Cl2): δ 15.15 (s,
1JPt-P ) 3922 Hz).
3
) 1.4 Hz, JPt-H ) 27 Hz, H3′′, H3′′′); 6.97 (td, 2H, JH-H ) 1.4
Hz, JH-H ) 7.3 Hz, H5′′, H5′′′); 6.99 (d, 2H, JH-H ) 7.6 Hz, H5,
H5′); 7.05 (td, 2H, JH-H ) 1.4 Hz, JH-H ) 7.3 Hz, H4′′, H4′′′);
3
7.18 (d, 2H, JH-H ) 7.6 Hz, JPt-H ) 18 Hz, H4, H4′); 7.27 (dd,
Synthesis of [Pt2(L)(CO)2] (10). Method 1. In an acetone
suspension of 1 (50.0 mg, 0.0588 mmol) carbon monoxide was
bubbled with stirring at atmospheric pressure and room temperature.
The color of the mixture changed slowly from yellow-green to red.
After 1.5 h the red suspension was filtered and washed with diethyl
ether to give the analytical sample. Yield: 77%. Mp: >270 °C.
Anal. Calcd for C24H12N2O2Pt2‚3H2O: C, 35.79; H, 2.24; N, 3.48.
Found: C, 35.47; H, 1.97; N, 3.49. IR (Nujol, νmax/cm-1): 2063
(vs).
Method 2. In a dichloromethane solution of 5 (50.2 mg, 0.055
mmol) CO was bubbled with stirring at atmospheric pressure and
room temperature. After 1 h the suspension that formed was filtered
and washed with diethyl ether to give the analytical sample.
Yield: 35.5 mg, 85.5%.
2H, JH-H ) 7.3 Hz, JH-H ) 1.2 Hz, H6′′, H6′′′); 7.53 (s, 2H, H4
3
3,5-dimethylpyridine); 8.69 (s, 4H, JPt-H ) 43 Hz, H2 3,5-
dimethylpyridine). 13C NMR (CD2Cl2): δ 18.1 (CH3); 115.9 (CH);
122.6 (CH); 123.8 (CH); 128.6 (CH); 132.6 (CH); 135.5 (C, C3
3,5-dimethylpyridine); 137.9 (CH); 144.2 (CH); 149.9 (C); 151.1
(CH, C2 3,5-dimethylpyridine); 158.9 (C); 160.7 (C); 162.9 (C);
178.2 (C). MS-FAB (m/z): 909 [M]+, 802 [M - 3,5-dimethylpy-
ridine]+, 694 [M - 2(3,5-dimethylpyridine)]+, 501 [M - H -
2(3,5-dimethylpyridine) - Pt]+, 307 [L - H]+.
Synthesis of [Pt2(L)(quinoline)2] (6). To a suspension of 1 (50
mg, 0.059 mmol) in CHCl3 (20 mL) was added with vigorous
stirring 0.14 mL of quinoline (d ) 1.093 g/mL; 1.18 mmol, 10-
fold excess). The mixture was heated to reflux for 24 h. After it
was cooled, the mixture was filtered over Celite and evaporated to
dryness. The orange solid obtained was washed with n-hexane and
filtered off to give the analytical sample. Yield: 42%. Mp: >270
°C. Anal. Calcd for C40H26N4Pt2‚H2O: C, 49.49; H, 2.91; N, 5.77.
Found: C, 49.80; H, 3.02; N, 5.45. 1H NMR (CDCl3): δ 6.47 (dd,
2H, JH-H ) 6.1 Hz, JH-H not resolved); 6.75-7.05 (m, 6H); 7.22
(dd, 2H, JH-H ) 6.7 Hz, JH-H not resolved); 7.40-8.20 (m, 10H);
8.42 (d, 2H, JH-H ) 8.0 Hz); 9.32 (dd, 2H, JH-H ) 8.1 Hz, JH-H
) 5.6 Hz); 9.55 (d, 2H, JH-H ) 5.6 Hz).
Complex 10 is obtained also by passing a stream of CO over a
solid sample of compound 1 at room temperature.
Synthesis of [Pt2(L)(PPh3)2] from [Pt2(L)(CO)2]. To a suspen-
sion of 10 (7.5 mg, 0.01 mmol) in CHCl3 (20 mL) was added with
vigorous stirring 5.2 mg of PPh3 (0.02 mmol). The yellow solution
that formed was stirred for 1 h and then filtered over Celite,
concentrated to small volume, and treated with diethyl ether. The
precipitate that formed was filtered, washed with diethyl ether, and
vacuum-pumped to give the analytical sample as a yellow solid.
Yield: 10.4 mg, 86.2%.
Synthesis of [Pt2(L)(dppm)]2 (7). To a solution of dppm (22.6
mg, 0.059 mmol) in acetone (30 mL) was added slowly with stir-
ring 50.0 mg of 1 (0.059 mmol). The orange suspension was
stirred for 1 h at room temperature and then filtered to give
[Pt2(L)(dppm)]2 (7) as a reddish solid (36.0 mg); a second crop
(11.0 mg) was obtained from the mother liquor by concentration
to small volume followed by precipitation with diethyl ether and
filtration. Total yield: 47.0 mg, 74%. Mp: >270 °C. Anal. Calcd
for C95H70N4P4Pt4: C, 52.32; H, 3.18; N, 2.60. Found: C, 52.60;
H, 3.19; N, 3.04. 1H NMR (CD2Cl2): δ 4.30 (m, 4H, 4JPt-H ) ca.
30 Hz, CH2); 5.15 (dd, 4H, JH-H ) 7.8 Hz, H5 or H4); 5.22 (d, 4H,
JH-H ) 7.8 Hz, H5 or H4); 6.40 (d, 4H, H3′′, JH-H ) 7.3 Hz); 6.60
Synthesis of [Pt(H2L)(DMSO)] (11). To a solution of 6,6′-
diphenyl-2,2′-bipyridine (75.0 mg, 0.243 mmol) in toluene (50 mL)
was added with vigorous stirring 61.8 mg of [Pt(Me)2(DMSO)2]
(0.162 mmol). The solution was heated to 80 °C for 8 h, during
which time a small quantity of precipitate was formed. After the
mixture was cooled, the precipitate was filtered off and washed
with diethyl ether to give 14.8 mg of compound 1 as a green-yellow
solid. The filtered solution was concentrated to small volume and
treated with n-hexane. The precipitate that formed was fil-
tered, washed with n-hexane, and vacuum-pumped to give 11 as
an orange solid. Yield: 54%. Mp: dec at 210 °C. Anal. Calcd for
C24H20N2OPtS: C, 49.74; H, 3.48; N, 4.83. Found: C, 50.19; H,
(td, 4H, H4′′, JH-H ) 7.3 Hz, JH-H ) 1.4 Hz); 6.78 (t, 4H, JH-H
)
1
3
7.8 Hz, H5′′); 6.82 (dd, 4H, H6′′, JH-H ) 7.6 Hz, JH-H ) 1.4 Hz);
7.30 (m, 24H, Hm, Hp (PPh)); 7.35 (m, 8H, Ho (PPh)); 8.05 (m,
8H, Ho (PPh)). 31P NMR (CD2Cl2): δ 12.70 (s, 1JPt-P ) 4045 Hz,
2.99; N, 4.39. H NMR (CD2Cl2): δ 3.68 (s, 6H, JPt-H ) 26.8
Hz, CH3 (DMSO)); 7.16 (td, 1H, JH-H ) 7.5 Hz, JH-H ) 1.2 Hz,
H5′′); 7.29 (td, 1H, JH-H ) 7.5 Hz, JH-H ) 1.2 Hz, H4′′); 7.42 (t,
1H, JH-H ) ca. 7.5 Hz, H4′′′); 7.44 (1H, H3 (overlapping)); 7.47 (t,
2H, JH-H ) ca. 7.5 Hz, H3′′′, H5′′′); 7.54 (dd, 1H, JH-H ) 7.5 Hz,
JH-H ) 1.2 Hz, H6′′); 7.60 (d, 1H, JH-H ) 7.9 Hz, H5′); 7.62 (dd,
1H, JH-H ) 7.5 Hz, JH-H ) 1.2 Hz, JPt-H not resolved, H3′′); 7.74
3
2JP-P ) 30 Hz, JPt-P ) 72 Hz).
Synthesis of [Pt2(L)(dppe)]2 (8). Complex 8 was obtained by
following the same procedure used for complex 7, using dppe
instead of dppm. Total yield: 96%. Mp: >270 °C. Anal. Calcd
for C96H72N4P4Pt4: C, 52.98; H, 3.35; N, 2.55. Found: C, 52.81;
(t, 1H, JH-H ) 7.5 Hz, H4); 7.89 (dd, 1H, JH-H ) 7.5 Hz, JH-H
)
4
1
1.0 Hz, JPt-H ) 9 Hz, H5); 8.07 (d, 2H, JH-H ) 7.5 Hz, H2′′′,
H, 3.56; N, 2.34. H NMR (CD2Cl2): δ 3.60 (m, 4H, CH2); 3.75
H6′′′); 8.27 (d, 1H, JH-H ) 7.9 Hz, 3JPt-H ) 18 Hz, H4′). IR (Nujol,
(m, 4H, CH2); 5.69 (dd, 4H, JH-H ) 7.8 Hz, JH-H not resolved,
H5); 5.78 (d, 4H, JH-H ) 7.8 Hz, H4); 6.20 (d, 4H, JH-H ) 7.3 Hz,
ν
max/cm-1): 1013 (s), 1119 (s),
3JPt-H ) ca. 30 Hz, Hz, H3′′); 6.52 (d, 4H; JH-H ) 7.3 Hz, JH-H
)
Synthesis of [Pt(H2L)(CO)] (12). In a dichloromethane solution
1.4 Hz, H4′′); 6.72 (td, 4H, JH-H ) 7.3 Hz, JH-H not resolved, H5′′);
6.82 (dd, 4H, JH-H ) 7.3 Hz, JH-H ) 1.3 Hz, H6′′); 7.20 (m, 12H,
Hm + Hp (PPh)); 7.46 (m, 12H, Hm + Hp (PPh)); 7.76 (m, 8H,
of 11 (28.3 mg, 0.049 mmol) carbon monoxide was bubbled with
stirring at atmospheric pressure and room temperature for 1.5 h.
The red-orange solution obtained was concentrated to small volume

Dinuclear C,N,C Cyclometalated Platinum DeriVatiVes
Organometallics, Vol. 25, No. 9, 2006 2263
and treated with n-hexane. The precipitate that formed was filtered,
washed with n-hexane, and vacuum-pumped to give the analytical
sample as an orange solid in almost quantitative yield. Mp: dec at
235 °C. Anal. Calcd for C23H14N2OPt: C, 52.18; H, 2.67; N, 5.29.
Found: C, 52.04; H, 2.95; N, 5.12. 1H NMR (CDCl3): δ 7.15 (td,
1H, JH-H ) 7.5 Hz, JH-H ) 1.4 Hz, H5′′ or H4′′); 7.24 (td, 1H,
JH-H ) 7.5 Hz, JH-H ) 1.4 Hz, H5′′ Hz,or H4′′); 7.31 (dd, 1H,
JH-H ) 7.7 Hz, JH-H ) 1.4 Hz, H3); 7.38-7.53 (m, 5H, H5′, H3′′′,
H4′′′, H5′′′, H3′′, or H6′′); 7.64 (dd, 1H, JH-H ) 7.5 Hz, JH-H ) 1.4
Hz, H3′′ or H6′′); 7.69 (t, 1H, JH-H ) 7.7 Hz, H4); 7.75 (dd, 1H,
JH-H ) 7.7 Hz, JH-H ) 1.4 Hz, H5); 7.91 (d, 1H, JH-H ) 7.7 Hz,
3JPt-H ) 29 Hz, H4′); 8.05 (m, 2H, H2′′′, H6′′′). 1H NMR (CD2Cl2):
δ 7.17 (td, 1H, JH-H ) 7.5 Hz, JH-H ) 1.4 Hz, H5′′ or H4′′); 7.25
(td, 1H, JH-H ) 7.5 Hz, JH-H ) 1.4 Hz, H5′′ or H4′′); 7.35-7.52
NMR (CDCl3): δ 2.39 (s, 6H, CH3); 5.86 (d, 1H, JH-H ) 7.9 Hz);
6.13 (d, 1H, JH-H ) 7.6 Hz); 6.50-6.58 (m, 2H); 6.74-6.80 (m,
2H); 6.91-7.19 (m, 6H); 7.39-7.44 (m, 10H, H4 dimethylpyridin
e+ Hm + Hp PPh3); 7.82-7.89 (m, 6H, Ho PPh3); 8.72 (s, 2H,
JPt-H ) ca. 42 Hz, H2 dimethylpyridine).
Synthesis of [Pt2(L)(DMSO)(CO)] (17). To a solution of
12 (40.0 mg, 0.0755 mmol) in toluene (20 mL) was added
with vigorous stirring 28.8 mg of [Pt(Me)2(DMSO)2] (0.0755
mmol). The solution was stirred at 80 °C for 10 h. The pre-
cipitate that formed was filtered off and washed with diethyl ether
to give compound 17 as a dark red solid. Yield: 34 mg, 56%. Mp:
>260 °C. IR (Nujol, cm-1) νmax 2053 (s). Anal. Calcd for
C25H18N2O2SPt2‚2H2O: C, 35.89; H, 2.65; N, 3.35. Found: C,
35.25; H, 2.20; N, 3.02.
(m, 5H, H3, H3′′′, H4′′′, H5′′′, H3′′, or H6′′); 7.57 (d, 1H, JH-H
)
)
Synthesis of [Pt2(L)(3,5-dimethylpyridine)(CO)] (18). To a
suspension of 17 (30.0 mg, 0.0375 mmol) in CHCl3 (15 mL) was
added with vigorous stirring 0.04 mL of 3,5-dimethylpyridine (0.375
mmol). The suspension was heated to reflux for 8 h. After it was
cooled, the mixture was filtered. The solution obtained was
concentrated to small volume and treated with diethyl ether. The
precipitate that formed was filtered off, washed with diethyl ether,
and vacuum-pumped to give the analytical sample as a brick red
solid. Yield: 50.4% (15.7 mg). Mp: dec at 245 °C. IR (Nujol,
cm-1): νmax 2052 (s). Anal. Calcd for C30H21N3OPt2‚H2O: C, 42.50;
7.7 Hz, 4JPt-H ) 7 Hz, H5′); 7.63 (dd, 1H, JH-H ) 7.5 Hz, JH-H
3
1.4 Hz, JPt-H ) 35 Hz, H3′′ or H6′′); 7.76 (m, 2H, H4, H5); 7.94
3
(d, 1H, JH-H ) 7.7 Hz, JPt-H ) 29 Hz, H4′); 8.09 (m, 2H, H2′′′,
H6′′′). IR (Nujol, νmax/cm-1): 2063 (vs).
Synthesis of [Pt(H2L)(PPh3)] (13). To a solution of 11 (71.9
mg, 0.124 mmol) in 20 mL of CH2Cl2 was added, with vigorous
stirring, 65.1 mg of PPh3 (0.248 mmol). The orange solution was
stirred at room temperature for 1 h, the solvent was evaporated in
vacuo, and the solid was washed with n-hexane, filtered off, and
vacuum-pumped, to give the analytical sample as an orange solid.
Yield: 73.4 mg, 77.5%. Mp: dec at 265 °C. Anal. Calcd for
C40H29N2PPt‚H2O: C, 61.46; H, 4.00; N, 3.58. Found: C, 61.51;
1
H, 2.71; N, 4.95. Found: C, 42.49; H, 2.65; N, 4.33. H NMR
(CD2Cl2): δ 2.38 (s, 6H, CH3); 6.78 (dd, 1H, JH-H ) 7.1 Hz, JH-H
not resolved, H3”, see numbering scheme in Chart 2); 6.70-7.12
(m, 6H, aromatics); 7.25-7.30 (m, 3H, aromatics), 7.45 (dd, 1H,
JH-H ) 1.6 Hz, JH-H ) 7.1 Hz, H3”′, see numbering scheme in
H, 3.33; N, 3.52. 1H NMR (CDCl3): δ 6.29 (d, broad, 1H, JH-H
)
7.4 Hz, H3′′); 6.40 (d, 1H, JH-H ) 7.9 Hz, H4′); 6.70 (td, 1H, JH-H
) 7.4 Hz, JH-H ) 1.3 Hz, H4′′ or H5′′); 6.95 (td, 1H, JH-H ) 7.4
Hz, JH-H ) 1.2 Hz, H4′′ or H5′′); 7.04 (d, 1H, JH-H ) 7.9 Hz,
JPt-H ) ca. 8 Hz, H5′); 7.30-7.51 (m, 14H, H2′′′-H6′′′, Hm + Hp
PPh3); 7.71 (t, 1H, JH-H ) 7.8 Hz, H4); 7.82-7.94 (m, 7H, Ho
PPh3, H6′′); 8.02 (m, 2H, H3 + H5). 31P NMR (CDCl3): δ 28.58
(1JPt-P ) 4066 Hz).
Chart 2); 7.51-7.56 (m, 2H, aromatics); 8.64 (s, broad, JPt-H
43 Hz, H2 3,5-dimethylpyridine).
)
Single-Crystal X-ray Data Collections and Structure Deter-
minations. Crystal data are summarized in Table 1. The diffraction
experiments were carried out on a Bruker SMART CCD area-
detector diffractometer at 150 K, using Mo KR radiation (λ )
0.710 73 Å) with a graphite crystal monochromator in the incident
beam. No crystal decay was observed, so that no time-decay
correction was needed. The collected frames were processed with
the software SAINT,26 and an empirical absorption correction was
applied (SADABS)27 to the collected reflections. The calculations
were performed using the Personal Structure Determination Pack-
age28 and the physical constants tabulated therein.29 The structures
were solved by direct methods (SHELXS)30 and refined by full-
matrix least squares using all reflections and minimizing the
Synthesis of [Pt(H2L)(3,5-dimethylpyridine)] (14). To a solu-
tion of 11 (70.0 mg, 0.12 mmol) in 15 mL of CHCl3 was added,
with vigorous stirring, 0.14 mL of 3,5-lutidine (1.21 mmol, 10-
fold excess). The solution was refluxed for 12 h, the solvent was
evaporated in vacuo, and the solid was washed with n-hexane,
filtered off, and dried in vacuo to give the analytical sample as an
orange solid. Yield: 68.5 mg, 93%. Mp: dec at 216 °C. Anal. Calcd
for C29H23N3Pt‚H2O: C, 55.59; H, 4.02; N, 6.71. Found: C, 55.56;
H, 3.39; N, 6.15. 1H NMR (CDCl3): δ 2.42 (s, 6H, CH3
3,5-dimethylpyridine); 6.95 (dd, 1H, JH-H ) 7.1 Hz, JH-H ) 1.2
Hz, H3′′); 7.09 (td, 1H, JH-H ) 7.5 Hz, JH-H ) 1.4 Hz, H4′′ or
H5′′); 7.23 (td, 1H, JH-H ) 7.1 Hz, JH-H ) 1.2 Hz, H4′′ or H5′′);
function ∑w(Fo - kFc2)2 (refinement on F2). In 5‚2CHCl3 the
2
chloroform molecule is partially disordered, with the carbon atom
and one Cl atom ordered, while the other two Cl atoms are split
into four half-atoms with occupancy factors of 0.50 each. In 8‚
1.5CHCl3‚H2O there is a disordered chloroform half-molecule, with
an occupancy factor of 0.50, and two disordered water half-
molecules, with occupancy factors of 0.50 each. All the non-
hydrogen atoms were refined with anisotropic thermal factors. The
hydrogen atoms of the disordered solvent molecules were ignored.
All the other hydrogen atoms were placed in their ideal positions
(C-H ) 0.97 Å), with the thermal parameter B 1.10 times that of
the carbon atom to which they are attached, and were not refined.
In the final Fourier maps the maximum residuals were as follows:
for 5‚2CHCl3, 2.63(48) e Å-3 at 0.91 Å from Pt; for 8‚1.5CHCl3‚
H2O 2.72(70) e Å-3 at 1.36 Å from Pt(4). For noncentrosymmetric
7.34-7.46 (m, 5H, H2′′′-H6′′′); 7.36 (d, overlapping, 1H, JH-H
)
7.6 Hz, H4′); 7.50 (s, broad, overlapping, 1H, H4 3,5-dimethylpy-
ridine); 7.55 (d, partially overlapping, 1H, JH-H ) 7.5 Hz, H5′);
7.66 (t, 1H, JH-H ) 7.9 Hz, H4); 7.82 (dd, 1H, JH-H ) 7.8 Hz,
JH-H ) 1.2 Hz, H6′′); 8.07 (m, 2H, H3 + H5); 8.74 (s, broad, 2H,
JPt-H ) ca. 45 Hz, H2 3,5-dimethylpyridine).
Synthesis of [Pt2(L)(PPh3)(3,5-dimethylpyridine)] (16). To a
solution of 13 (65.0 mg, 0.085 mmol) in toluene (20 mL) were
added under vigorous stirring 32.4 mg of [Pt(Me)2(DMSO)2] (0.085
mmol). The solution was stirred at 80 °C for 14 h. The precipitate
that formed was filtered off, washed with diethyl ether (compound
15, 42 mg), and taken up with chloroform (20 mL). After addition
of 3,5-dimethylpyridine (0.3 mL, d ) 0.939 g/mL; 2.65 mmol) the
suspension was refluxed for 14 h. The suspension was cooled and
filtered. The filtered solution was concentrated to small volume
and treated with diethyl ether. The dark yellow precipitate that
formed was filtered off, washed with diethyl ether, and dried in
vacuo to give the analytical sample as a dark yellow solid. Yield
14.1 mg. Mp: >260 °C. Anal. Calcd for C47H36N3PPt2‚H2O: C,
(26) SAINT Reference Manual; Siemens Energy and Automation: Madi-
son, WI, 1994-1996.
(27) Sheldrick, G. M. SADABS, Empirical Absorption Correction
Program; University of Gottingen, Gottingen, Germany, 1997.
(28) Frenz, B. A. Comput. Phys. 1988, 2, 42.
(29) Crystallographic Computing 5; Oxford University Press: Oxford,
U.K., 1991; Chapter 11, p 126.
(30) Sheldrick, G. M. SHELXS 86: Program for the Solution of Crystal
Structures; University of Gottingen, Gottingen, Germany, 1985.
1
52.17; H, 3.54; N, 3.88. Found: C, 52.02; H, 3.01; N, 3.52. H

2264 Organometallics, Vol. 25, No. 9, 2006
Zucca et al.
Figure 6. Fit between the observed (solid line) and calculated (dotted line) powder X-ray diffraction patterns and difference plot from the
rigid-body Rietveld refinement on compound 10.
8‚1.5CHCl3‚H2O full refinement of the correct enantiomer led to
R2 ) 0.051 and R2w ) 0.066, full refinement of the wrong
enantiomer led to R2 ) 0.069 and R2w ) 0.101. Supplementary
crystallographic data for this paper have been submitted as
Supporting Information and have been deposited with the CCDC.
Powder X-ray Diffraction Structure Determination. Data
collection was carried out on a sample of complex 10 in a 0.4 mm
diameter borosilicate glass capillary on a Bruker D8 ADVANCE
diffractometer in Debye-Scherrer geometry equipped with a copper
X-ray source and Go¨ebel mirrors. Data were collected twice, in
steps of 0.01° (5° e 2θ e 63.5°), for 10 s/step in the first instance
and 29.8 s/step in the second. These two runs were added together
in DIFFRACplus EVA31 to give the final dataset.
set described the valence electrons.37 For all other atoms the 6-31G
basis set was used.39 The resulting model was symmetric about a
2-fold rotation axis at the molecular center of mass, and thus the
model of the ASU used during structure solution was one of the
symmetrically equivalent halves.
Structure solution was carried out using the Dash19 program, by
a global optimization technique employing a simulated annealing
(SA) algorithm40 to determine the position, orientation, and
conformation, within the unit cell, of the ASU model. Each variation
of these parameters gives rise to a trial structure, and powder
diffraction patterns generated from the trial structures are compared
with the observed data using the intensity ø2 factor, defined as
The data were indexed in Treor90,32 which is part of the
Crysfire33 suite. The unit cell obtained was tetragonal with a )
16.8251 Å and c ) 6.7371 Å. The unit cell volume (1907.2 Å3)
and symmetry indicated that the asymmetric unit (ASU) comprises
half the molecule (Z′ ) 0.5). The space group was identified as
P4h21c using the program Extinction Symbol.34 Integrated intensities
were extracted from the observed data by a Pawley refinement
procedure (the ø2 value was 4.70).35
A model of the molecule was made by geometry optimization
at the DFT/B3LYP level36 in GAUSSIAN 03.37 Effective core
potentials (ECP) were used to represent the innermost electrons of
the platinum atoms,38 while a standard double-ú LANL2DZ basis
2
2
ø2 )
[(Ih - c|Fh| )(V -1)hk(Ik - c|Fk| )]
∑∑
h
k
(37) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K.
N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,
S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A.
D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A.
G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.;
Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham,
M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian
03, revision C.02; Gaussian, Inc.: Wallingford, CT, 2004.
(31) DIFFRACplus EVA; Bruker AXS, Karlsruhe, Germany, 2002.
(32) Werner, P.-E.; Eriksson, L.; Westdahl, M. TREOR, a semi-
exhaustive trial-and-error powder indexing program for all symmetries. J.
Appl. Crystallogr. 1985, 18, 367-370.
(33) Shirley, R. The Crysfire 2002 System for Automatic Powder
Indexing, User’s Manual; The Lattice Press: Guildford, U.K., 2002.
(34) Markvardsen, A. J.; David, W. I. F.; Johnson, J. C.; Shankland, K.
Acta Crystallogr. 2001, A57, 47-54.
(35) Pawley, G. S. J. Appl. Crystallogr. 1981, 14, 357-361.
(36) (a) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. ReV. B 1988, 37,
785-789. (b) Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652. (c)
Stephens, P.; Devlin, F.; Chabalowski, C.; Frisch, M. J. Phys. Chem. 1994,
98, 11623-11627.
(38) (a) Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284-298. (b)
Hay, P. J.; Wadt W. R. J. Chem. Phys. 1985, 82, 299-310.
(39) Hehre, W.; Ditchfie, R.; Pople, J. J. Chem. Phys. 1972, 56, 2257-
2261.
(40) Press: W. H.; Flannery, B. P.; Teukolsky, S. A.; Vetterling, W. T.
Numerical Recipes; Cambridge University Press: Cambridge, U.K., 1986;
pp 274-277 and 326-331 (ISBN 0521308119).

Dinuclear C,N,C Cyclometalated Platinum DeriVatiVes
Organometallics, Vol. 25, No. 9, 2006 2265
where Ih,k values are the integrated intensities extracted from the
observed data and Vhk is the covariance matrix, both determined
from the Pawley refinement, c is the scale factor, and Fh,k values
are structure factors calculated from the trial structure. The success
of a SA run can be monitored by use of a profile ø2 factor. The
consistency of the solutions obtained from several runs gives a
further indication of success.
Solutions from initial SA runs were all highly consistent. In all
cases the molecule was formed successfully from two ASU’s, which
were arranged symmetrically about a twofold rotation axis. Thus,
in subsequent SA runs the molecular center of mass was fixed on
the special position related to this axis and the resulting structural
solutions were all identical with one another and extremely similar
to those from the initial runs. The intensity and profile ø2 values
from the best run were 539.01 and 27.23, respectively.
A rigid-body Rietveld refinement20,41 was carried out in Dash
in which the background, profile shape, zero point, and unit cell
parameters (a ) 16.8067 Å and c ) 6.7323 Å) from the Pawley
refinement were used. The refined parameters were as follows: a
global isotropic temperature factor, the single variable torsion angle
of the ASU, ASU orientation parameters, and the positional
parameter z. The molecular center of mass was held fixed on the
special position, and thus x and y were not refined. The resulting
intensity and profile ø2 values were 327.95 and 28.03, respectively.
The final fit between the observed data and the powder diffraction
pattern calculated from the refined solution is shown in Figure 6.
Although the overall fit is good, the first peak is not well described.
An excellent fit can only be obtained if it is described as two
overlapping peaks at 7.07 and 7.41° 2θ, but indexing is only
possible when only the largest peak at 7.41° is included. This
indicates that the minor peak at 7.07° arises from an impurity in
the sample.
The unit cell parameters were subjected to a Rietveld refine-
ment in GSAS.42 The background, the profile shape (pseudo-Voigt),
the particle size and microstrain, the scale factor, and θ0 were
the refined parameters. The final unit cell parameters are a )
16.799(1) Å and c ) 6.7283(4) Å, values that are very close to
those obtained from Pawley refinement.
Acknowledgment. Financial support from the Universita` di
Sassari is gratefully acknowledged. A.A. and L.M. wish to
acknowledge financial support from HYDROCHEM, a Research
Training Network funded by the European Commission’s 5th
Framework Improving Human Potential program, and useful
discussions with Dr. E. Pidcock and Dr. S. Motherwell of the
Cambridge Crystallographic Data Centre, Cambridge, U.K.,
Prof. A. Lledo´s and Dr. O. Maresca of the Universitat Auto`noma
de Barcelona, Barcelona, Spain, and Dr. H. Nowell of Diamond
Light Source, Didcot, U.K.
Supporting Information Available: Figures and a table giving
additional information on crystal structures and CIF files giving
crystal data for 5, 8, and 10. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM051075K
(42) (a) Larson, A. C.; Von Dreele, R. B. General Structure Analysis
System (GSAS); Los Alamos National Laboratory Report LAUR; Los
Alamos National Laboratory, Los Alamos, NM, 2004; pp 86-748. (b) Toby,
B. H. EXPGUI, a graphical user interface for GSAS. J. Appl. Crystallogr.
2001, 34, 210-213.
(41) Leach, A. R. Molecular Modelling: Principles and Applications,
Longman: Harlow, U.K., 1996; pp 1-3 (ISBN 0582239338).