Cyclometalation of 2,2 -bipyridine. mono- and dinuclear C,N platinum(II) derivatives

Article abstract of DOI:10.1021/om801033g

Reaction of the electron-rich derivative cis-[Pt(Me)₂(DMSO) ₂] with 2,2 -bipyridine (L) affords the mononuclear "rollover" N,C(3) cyclometalate [Pt(L-H)(Me)(DMSO)] (la) or the unusual dinuclear species [Pt₂(μ-L-2H)(Me)₂(DMSO) ₂] (2a), depending on the Pt/L molar ratio. The latter complex, 2a, can be obtained either directly from cis-[Pt(Me)₂(DMSO)₂] or by a two-step process through complex la. The synthesis of 2a implies a double C - H bond activation, with loss of two molecules of methane: the 2-fold deprotonated 2,2 -bipyridine links two [Pt(Me)(DMSO)] fragments, acting as a Π-delocalized C,NLN,C eight-electron donor. From la and 2a displacement of DMSO with two-electron-donor ligands such as PPh₃, (b), CO (c), and 3,5-Me₂py (d) gives two series of complexes, lb - d and 2b - d, respectively. Reaction of la and 2a with HC1 affords the corresponding chlorides [Pt(L-H)(Cl)(DMSO)] (3a) and [Pt₂(H-L-2H)(Cl) ₂(DMSO)₂] (4a), from which complexes 3b - d and 4b,d can be obtained by substitution of DMSO. The crystal structures of the mono- and dinuclear complexes [Pt(L-H)(Cl)(PPh₃)] (3b) and [Pt ₂(μ-L-2H)(Cl)₂(PPh₃)₂] (4b) have been solved by X-ray diffraction. Protonation of the uncoordinated nitrogen atom in la can be achieved by reaction with 18-crown-6 · HBF₄: [Pt(L^*)(Me)(DMSO)][BF₄] (5), where the zwitterionic ligand L^* is still N - C(3) bonded to platinum(II), can be isolated in the solid state. Taking advantage of the two-step approach used for the synthesis of complex 2a, unsymmetric species where the platinum atoms are in different environments, e.g. [(DMS0)(Cl)Pt(μ-L-2H)Pt-(Me)(DMSO)] (6), [(PPh₃)(Me)Pt(μ-L-2H)Pt(Me)(DMSO)] (7), and [(C0)(Cl)Pt(μ-L-2H) Pt(Me)(DMS0)] (8), can be prepared in good yields. Attempts to build up a platinum(II) - gold(III) species by reaction of 3a with NaLAuC1μ] failed: no platinum - gold derivative was obtained but a platinum(IV) complex, [Pt(L-H)(C1)₃(DMSO)] (9), likely due to the strong oxidative capability of gold(III).

Full text of DOI:10.1021/om801033g

2150
Organometallics 2009, 28, 2150–2159
Cyclometalation of 2,2′-Bipyridine. Mono- and Dinuclear C,N
Platinum(II) Derivatives
Antonio Zucca,*,† Giacomo Luigi Petretto,† Sergio Stoccoro,† Maria Agostina Cinellu,†
Mario Manassero,*,‡ Carlo Manassero,‡ and Giovanni Minghetti†
Dipartimento di Chimica, UniVersita` di Sassari, Via Vienna 2, I-07100 Sassari, Italy, and Dipartimento di
Chimica Strutturale e Stereochimica Inorganica, UniVersita` di Milano, Centro CNR, Via Venezian 21,
I-20133 Milano, Italy
ReceiVed October 27, 2008
Reaction of the electron-rich derivative cis-[Pt(Me)2(DMSO)2] with 2,2′-bipyridine (L) affords the
mononuclear “rollover” N′,C(3) cyclometalate [Pt(L-H)(Me)(DMSO)] (1a) or the unusual dinuclear species
[Pt2(µ-L-2H)(Me)2(DMSO)2] (2a), depending on the Pt/L molar ratio. The latter complex, 2a, can be
obtained either directly from cis-[Pt(Me)2(DMSO)2] or by a two-step process through complex 1a. The
synthesis of 2a implies a double C-H bond activation, with loss of two molecules of methane: the
2-fold deprotonated 2,2′-bipyridine links two [Pt(Me)(DMSO)] fragments, acting as a π-delocalized
C,N∧N,C eight-electron donor. From 1a and 2a displacement of DMSO with two-electron-donor ligands
such as PPh3, (b), CO (c), and 3,5-Me2py (d) gives two series of complexes, 1b-d and 2b-d, respectively.
Reaction of 1a and 2a with HCl affords the corresponding chlorides [Pt(L-H)(Cl)(DMSO)] (3a) and
[Pt2(µ-L-2H)(Cl)2(DMSO)2] (4a), from which complexes 3b-d and 4b,d can be obtained by substitution
of DMSO. The crystal structures of the mono- and dinuclear complexes [Pt(L-H)(Cl)(PPh3)] (3b) and
[Pt2(µ-L-2H)(Cl)2(PPh3)2] (4b) have been solved by X-ray diffraction. Protonation of the uncoordinated
nitrogen atom in 1a can be achieved by reaction with 18-crown-6 · HBF4: [Pt(L*)(Me)(DMSO)][BF4]
(5), where the zwitterionic ligand L* is still N′-C(3) bonded to platinum(II), can be isolated in the solid
state. Taking advantage of the two-step approach used for the synthesis of complex 2a, unsymmetric
species where the platinum atoms are in different environments, e.g. [(DMSO)(Cl)Pt(µ-L-2H)Pt-
(Me)(DMSO)] (6), [(PPh3)(Me)Pt(µ-L-2H)Pt(Me)(DMSO)] (7), and [(CO)(Cl)Pt(µ-L-2H)Pt(Me)(DMSO)]
(8), can be prepared in good yields. Attempts to build up a platinum(II)-gold(III) species by reaction of
3a with Na[AuCl4] failed: no platinum-gold derivative was obtained but a platinum(IV) complex, [Pt(L-
H)(Cl)3(DMSO)] (9), likely due to the strong oxidative capability of gold(III).
Chart 1
Introduction
In the chemistry of transition metals with heterocyclic
nitrogen ligands, 2,2′-bipyridines have been very popular since
the early days of coordination chemistry.1 The title of a recent
review, “bipyridine: the most widely used ligand...”,2 gives an
idea of their importance.
Mostly they were, and still are, found as neutral N,N′ ligands
bonded to early and late transition metals, in a variety of
oxidation states, low states included.3 As the years went by and
interest in heterocyclic nitrogen molecules grew, the potential
role of the 2,2′-bipyridines was thoroughly investigated: in the
case of the late transition metals they now appear to be involved
* To whom correspondence should be addressed. E-mail: zucca@uniss.it
(A.Z.); mario.manassero@unimi.it (M.M.).
† Universita` di Sassari.
‡ Universita` di Milano.
in a number of species with applications spanning from
medicinal chemistry4 to novel materials.5
Of the two possible coplanar conformations, cis and trans
(Chart 1, a and b), which differ in several aspects such as dipole
moment and charge distribution, it is well-known that the most
(1) Reedijk, J. In ComprehensiVe Coordination Chemistry; Wilkinson,
G., Gillard, R. D., McCleverty, J. A., Eds.; Pergamon Press: Oxford, U.K.,
1987; Vol. 2, p 73.
(2) Kaes, C.; Katz, A.; Hosseini, M. W. Chem. ReV. 2000, 100, 3553.
(3) Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry, 5th
ed., Wiley: New York, 1988; pp 348-350.
(4) For example: (a) Elwell, K. E.; Hall, C.; Tharkar, S.; Giraud, Y.;
Bennett, B.; Bae, C.; Carper, S. W. Bioorg. Med. Chem. 2006, 14, 8692–
8700. (b) Chan, H.-L.; Ma, D.-; Yang, M.; Che, C.-M. J. Biol. Inorg. Chem.
2003, 8, 761–769.
(5) (a) Marder, S. R. In Inorganic Materials; Bruce, D. W., O’Hare,
D., Eds.; Wiley: New York, 1997; p 115. (b) Sun, W.; Zhu, H.; Barron,
P. M. Chem. Mater. 2006, 18, 2602–2610.
10.1021/om801033g CCC: $40.75
2009 American Chemical Society
Publication on Web 03/16/2009

Cyclometalation of 2,2′-Bipyridine
Organometallics, Vol. 28, No. 7, 2009 2151
stable form, both in the solid state and in solution, is the trans
species, b.6 The cis coplanar form may be disfavored by
H- - -H steric interactions and Coulombic repulsions of the
nitrogen lone pairs.
In spite of this, the common graphic representation of 2,2′-
bipy is that corresponding to the cis conformation, a, because
as a neutral ligand 2,2′-bipy almost invariably acts as an N,N′
chelating ligand (c), whereas derivatives such as d (monoden-
tate), e (bridging), and f (N′-C bonded tautomeric form) are
rare or extremely rare. The type b conformation, however, may
play a role favoring, with an appropriate metal intermediate,
activation of a C-H bond of a pyridine ring, forming an
N′-C(3) five-membered cyclometalated ring, g.
To the best of our knowledge, this behavior of 2,2′-bipyridine
is unprecedented in platinum chemistry and, on the whole,
extremely rare, an example being an iridium(III) derivative that
was a matter of long debate and was reported many years ago10
Results and Discussion
This peculiar metalation was first observed in a reaction with
platinum derivatives by Young and co-workers many years ago
and reported in a preliminary communication:7 few experimental
details were given, and no mononuclear derivative was isolated.
In recent years we have found that in the case of 6-substituted
2,2′-bipyridines electron-rich platinum intermediates containing
a “Pt(R)2” fragment readily promote N′,C(3) cyclometalation.
Platinum(II) complexes, [Pt(L-H)(X)(L′)] (L ) 6-substituted
2,2′-bipyridine; X ) Me, Ph, Cl; L′ ) neutral two-electron
ligand), were isolated in the solid state and fully characterized,8
in some cases also by X-ray diffraction. In contrast, in the course
of our studies, we were unable to isolate analogous derivatives
from the reaction of the unsubstituted 2,2′-bipyridine, though
some faint NMR evidence suggested their presence in solution.8b
Herein we report that under definite conditions even meta-
lation of 2,2′-bipyridine is promoted by the platinum(II)
intermediates [Pt(Me)2(L′)2]: the first cyclometalated derivatives
of 2,2′-bipyridine, [Pt(L-H)X(L′)] (L ) 2,2′-bipy; X ) Me, Cl),
have been isolated and fully characterized. The 2-(pyridyl)py-
ridine forms a five-membered cyclometalated ring reminiscent
of that of the most common 2-(phenyl)pyridine, a ligand
widespread in the chemistry of late transition metals.9 In addition
to a likely different charge distribution inside the ligand, a
remarkable difference between the two systems is the presence
in the (pyridyl)pyridine species of an uncoordinated nitrogen
atom potentially available for protonation, further coordination,
or other chemical reactions or weak interactions. Taking
advantage of the uncoordinated nitrogen atom, a two-step
approach allowed us to build up dinuclear platinum species,
both symmetric and nonsymmetric: [Pt2(µ-L-2H)(X)2(L′)2] (X
) Me, Cl).
With the exception of the preliminary communication by
Young and co-workers on the reaction of cis-
[Pt(Ph)2(DMSO)2],7 platinum(II) C-3 metalation of the unsub-
stituted 2,2′-bipyridine was never reported. As mentioned above,
in the course of our previous investigations we were unable to
isolate cyclometalated derivatives of the unsubstituted 2,2′-
bipyridine: to force metalation, we decided to operate under
conditions more severe than those previously used. In toluene
at 110 °C, the reaction of cis-[Pt(Me)2(DMSO)2] with 2,2′-bipy
(L) results in C(3)-H bond activation and metalation in high
yields. To avoid decomposition, the reaction requires strictly
controlled conditions: e.g., anhydrous solvents and nitrogen
atmosphere.
The outcome of the reaction depends on the Pt/L molar ratio.
When a bipyridine excess is employed, a mononuclear complex,
[Pt(L-H)(Me)(DMSO)] (1a), is formed. The reaction, which
occurs with loss of methane, proceeds in almost quantitative
yield. At variance, with Pt/L ) 2/1, a dinuclear species, [Pt2(µ-
L-2H)(Me)2(DMSO)2] (2a), can be isolated and characterized.
With a 1/1 Pt/L molar ratio a mixture of 1a and 2a is obtained:
the mono- and dinuclear species can be separated by taking
advantage of their different solubilities.
Mononuclear Complexes. Complex 1a, the first mononuclear
platinum N′-C(3) derivative of 2,2′-bipy, is a yellow air- and
moisture stable compound, which was characterized by elemen-
tal analyses and NMR spectroscopy.
Protonation of one of the mononuclear species with 18-crown-
6 · HBF4 gives a cationic complex, isolated in the solid state,
where a neutral bipyridine acts as a zwitterionic N,C endo-
bidentate ligand.
1
In particular, in the H NMR spectrum the absence of the
C(3)-H resonance and the strong coupling to platinum of the
3
H(4) proton (dd, δ 8.01, JPt-H ) 56.0 Hz) confirm the
(6) Goller, A. H.; Grummt, U. W. Chem. Phys. Lett. 2002, 354, 233–
242.
(7) Skapski, A. C.; Sutcliffe, V. F.; Young, G. B. J. Chem. Soc., Chem.
Commun. 1985, 609–611.
(8) (a) Minghetti, G.; Doppiu, A.; Zucca, A.; Stoccoro, S.; Cinellu,
M. A.; Manassero, M.; Sansoni, M. Chem. Heterocycl. Compd. 1999, 35,
992–1000. (b) Minghetti, G.; Stoccoro, S.; Cinellu, M. A.; Soro, B.; Zucca,
A. Organometallics 2003, 4770–4777.
(9) For example: (a) Omae, I. Coord. Chem. ReV. 2004, 248, 995–1023.
(b) Craig, C. A.; Garces, F. O.; Watts, R. J.; Palmans, R.; Frank, A. J.
Coord. Chem. ReV. 1990, 97, 193–208. (c) Mdeleni, M. M.; Bridgewater,
J. S.; Watts, R. J.; Ford, P. C. Inorg. Chem. 1995, 34, 2334–2342. (d) Okada,
T.; El-Mehasseb, I. M.; Kodaka, M.; Tomohiro, T.; Okamoto, K. I.; Okuno,
H. J. Med. Chem. 2001, 44, 4661–4667. (e) Niedermair, F.; Waich, K.;
Kappaun, S.; Mayr, T.; Trimmer, G.; Mereiter, K.; Slugovc, C. Inorg. Chim.
Acta 2007, 360, 2767–2777. (f) Mamtora, J.; Crosby, S. H.; Newman, C. P.;
Clarkson, G. J.; Rourke, J. P. Organometallics 2008, 27, 5559–5565. (g)
Yagyu, T.; Ohashi, J.; Maeda, M. Organometallics 2007, 26, 2383–2391,
and references therein.
metalation. A singlet at δ 3.25, flanked by satellites (3JPt-H
)
18.3 Hz), is consistent with an S-bonded DMSO trans to an sp2
carbon atom;11 the chemical shift and coupling constant (δ 0.70,
3JPt-H ) 82 Hz) of the coordinated methyl are in line with a
Me trans to a nitrogen atom.11 The geometry of the complex
has been confirmed by a NOE difference spectrum (see the
Experimental Section). In the 13C NMR spectrum direct evidence
(10) (a) Spellane, P. J.; Watts, R. J.; Curtis, C. J. lnorg. Chem. 1983,
22, 4060–4062. (b) Braterman, P. S.; Heat, G. H.; Mackenzie, A. J.; Noble,
B. C.; Peacock, R. D.; Yellowlees, K. J. Inorg. Chem. 1984, 23, 3425.
(11) (a) Owen, J. S.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc.
2004, 126, 8247–8255. (b) Zucca, A.; Doppiu, A.; Cinellu, M. A.; Minghetti,
G.; Stoccoro, S.; Manassero, M. Organometallics 2002, 21, 783–785. (c)
Doppiu, A.; Minghetti, G.; Cinellu, M. A.; Stoccoro, S.; Zucca, A.;
Manassero, M. Organometallics 2001, 20, 1148–1152.

2152 Organometallics, Vol. 28, No. 7, 2009
Zucca et al.
Table 1. Selected NMR and IR Data for Mononuclear Speciesa
compd
H6
8.65
8.36
H5
7.21
7.17
7.22
7.24 (17.4)
7.07
7.08 (16.5)
6.42
7.06 (18)
6.88
H4
7.73
8.01 (56.0)
8.24 (48)
8.06 (46.0)
8.10 (60.4)
8.60 (42)
6.85 (49)
7.78 (62.7)
6.70 (48.3)
H6′
H5′
H4′
H3′
CH3
other data
Lb
1a
1b
1c
1d
3a
3b
3c
3d
8.42 (H3)
9.71 (14)
d
7.36
6.67
7.35
7.14
7.40
d
7.95
8.29
8.31
0.70 (82)
0.74 (83)
1.19 (85.7)
0.94 (84.2)
3.25 (18.3)c
33.6 (2229)e
8.40
d
8.40
8.65 (19.8)
7.76 (20)
9.59 (36)
9.85 (31)
9.50 (34)
9.67 (39.5)
8.03 (17.4)
7.88
7.98
8.00
8.07
8.33
2044 IR (νCO
8.51 (23.1)f
3.65 (24.2)c
23.6 (4285)e
2107 IR (νCO
8.61 (23.4)f
)
ca. 8.25d
8.37
ca. 8.25d
8.22
8.17
8.45
8.30
8.26
8.26
8.10
7.53
7.30
)
7.92
a Conditions for 1H NMR: 300 MHz, room temperature, solvent CDCl3. JPt-H and JPt-P, in parentheses, are given in Hz. b See ref 26. c In DMSO.
e
d Signals overlapping. Conditions for 31P NMR: 121.4 MHz, PPh3. f Ho py.
Table 2. Selected NMR and IR Data for Dinuclear Speciesa
compd
H6
H5
H4
Pt-CH3
other data
2a
2b
2c
2d
4a
4b
4d
9.14
7.14
6.57
7.20
6.88
7.07
6.51
6.78d
8.05 (51.3)
8.13 (42.0)
8.16 (45)
8.05 (54.6)
6.64
0.67 (80.8)
0.62 (81.4)
1.17 (83.8)
0.91 (82.8)
3.23 (18.7) DMSO
33.29 (2347)c
ca. 7.4b
8.27 (22)
7.25b
2048 IR (νCO
)
8.52 (23.4) Ho py
3.27 (23.0) DMSO
19.55 (4135)c
8.95
9.06
8.90 (39)
6.81 (44.8)
6.78d
8.86 (41.7) Ho py
a Conditions for 1H NMR: 300 MHz, solvent CDCl3, room temperature. JPt-H and JPt-P, in parentheses, are given in Hz. b Partially overlapping.
c Conditions for 31P NMR: 121.4 MHz, PPh3. d Signals overlapping.
for the metalation is given by a quaternary carbon at δ 145.10,
The cyclometalated ring in complex 1a is rather robust and,
at least under mild conditions, e.g. at room temperature, it is
not attacked by HCl or neutral two-electron ligands. The reaction
of 1a with HCl (1/1 Pt/HCl molar ratio) gives the chloride
complex [Pt(L-H)(Cl)(DMSO)] (3a) with loss of methane (eq
3).
1
with JPt-C ) 1090 Hz, a value that fits previously reported
data11a for sp2 carbons bonded to platinum. Two signals in the
aliphatic region, δ -13.38 (JPt-C ) 763 Hz) and δ 43.73 (JPt-C
) 42.1 Hz), are assignable to the Pt-CH3 and the Pt-DMSO
carbons, respectively.
The adduct [Pt(L)(Me)2] is the first and only product formed
when [Pt(DMSO)2(Me)2] is reacted with 2,2′-bipyridine at room
temperature.8b Heating the adduct in toluene in the absence of
DMSO results in partial decomposition to metal and a mixture
of unidentified products. In toluene at 90 °C, in the presence of
a small amount of DMSO, the rollover species [Pt(L-
H)(Me)(DMSO)] is formed, providing evidence for the role of
[Pt(L)(Me)2] as an intermediate in the formation of the rollover
species.
From complex 1a a series of mononuclear compounds can
be synthesized by substitution of neutral ligands for DMSO (eq
2). The reaction occurs under mild conditions, likely favored
by the lability of DMSO coordinated trans to a carbon atom.12
Under our reaction conditions, neither protonation of the free
nitrogen atom nor cleavage of the Pt-C(sp2) bond is observed.
Reaction 3 occurs with isomerization to a trans Cl-Pt-C
arrangement, as previously observed with related species.8b
1
Assignment of the geometry mainly rests on the H NMR
spectra. The H6′ resonance is strongly deshielded (δ 9.59), as
expected, due to the close proximity of the chloride.13 Further
3
evidence is provided by the JPt-H value of the DMSO methyl
protons, 24.2 Hz, typical of a DMSO coordinated trans to a
pyridine nitrogen atom.8b
At variance with reaction 3, which leads to the corresponding
chloride 3a as the main product (yield ca. 70%), reaction of 1a
with excess HCl gives a mixture of products that was not further
pursued. To shed some light on the behavior of the nitrogen
atom toward protonation, the reaction of 1a was carried out
with HBF4 · 18-crown-6, having a noncoordinating anion. Sur-
prisingly, no attack at the platinum-methyl bond occurs, only
selective protonation of the uncoordinated nitrogen to give
[Pt(L*)(Me)(DMSO)][BF4] (5), where the zwitterionic ligand
L* is still N,C bonded to platinum.
Complexes 1b-d, [Pt(L-H)(Me)(L′)], are air-stable com-
pounds and have been characterized by analytical and spectro-
scopic methods (see Table 1 and the Experimental Section). In
particular in the 1H NMR spectra the values of 2JPt-H, relevant
to the methyl protons, are all in the range 82-86 Hz, typical
for a methyl trans to a nitrogen atom,11 while the chemical shifts
depend on the nature of the cis ligand L′. The effect of L′ is
also observed on the H6′ and H4 protons. As expected (see
Complex 5 is an interesting compound due to the nature of
the ligand L* which can be envisaged as a tautomeric form of
the neutral 2,2′-bipyridine. Its characterization mainly rests on
NMR, IR, and analytical data. In particular, the 1H NMR
3
Table 1), the H6′ resonances have similar JPt-H values but
chemical shifts dependent on L′. In contrast, the chemical shifts
3
of the H4 protons are almost invariant, whereas JPt-H is
dependent on L′ and reflects its trans influence.
In addition to the 1H NMR, the 31P NMR of 1b (δ 33.6, 1JPt-P
(12) In this series, obtained by direct substitution of DMSO, we isolated
also the carbonyl complex 1c, in contrast with the behavior of the analogous
phenylpyridine cyclometalated complex.11a
) 2229 Hz) and the IR spectrum of 1c (νCO 2044 cm-1 11c also
)
support the proposed geometry.

Cyclometalation of 2,2′-Bipyridine
Organometallics, Vol. 28, No. 7, 2009 2153
spectrum clearly shows a broad signal at δ ca. 13, due to the
N-H proton. Complex 5 is rather stable in solution. After 24 h
at room temperature or 1 h at 50 °C in CDCl3 no decomposition
is observed by 1H NMR. Heating in acetone results in methane
loss (from NH+ and Pt-CH3) and unidentified species are
formed.
From 3a other complexes can be obtained by substitution of
DMSO with PPh3 (b), CO (c), and 3,5-(Me)2-py (d): [Pt(L-
H)(Cl)(PPh3)] (3b), [Pt(L-H)(Cl)(CO)] (3c), and [Pt(L-H)(Cl)(3,5-
(Me)2-py)] (3d).
Figure 1. ORTEP view of molecule 1 in 3b. Ellipsoids are drawn
at the 30% probability level.
Table 3. Selected Bond Distances (Å) and Angles (deg) in the Two
Independent Molecules of 3b, with Estimated Standard Deviations
(Esd’s) on the Last Figure Given in Parentheses
1
In the H NMR spectra the H6′ resonance is observed in all
cases at very low field, due to the proximity of the coordinated
chloride. The H4 proton is shielded in 3b,d, owing to the effect
of the aromatic rings in PPh3 and 3,5-(Me)2-py, respectively.
In the IR spectrum of 3c, νCO is observed at 2107 cm-1, as
expected at higher wavenumber, in comparison to 2044 cm-1
in 1c.
molecule 1
molecule 2
Pt-Cl
2.380(1)
2.233(1)
2.097(2)
2.008(3)
1.349(3)
1.463(4)
1.416(4)
2.379(1)
2.228(1)
2.091(2)
2.002(3)
1.348(3)
1.467(4)
1.413(4)
Pt-P
Pt-N1
Pt-C7
N1-C1
C1-C6
C6-C7
The crystal structure of complex 3b has been determined by
X-ray diffraction. It consists of the packing of 3b molecules
with no unusual van der Waals contacts. In the asymmetric unit
there are two crystallographically independent 3b molecules,
hereinafter called molecule 1 and molecule 2. Molecules 1 and
2 are very similar to each other (see Table 3). An ORTEP14
view of molecule 1 is shown in Figure 1. Selected bond lengths
and angles for both molecules are reported in Table 3. In both
molecules the platinum atom displays a square-planar coordina-
tion with a slight tetrahedral distortion. Maximum distances from
the best planes are +0.043(2) and -0.050(3) Å for atoms N1
and C7, respectively, in molecule 1 and +0.071(1) and -
0.105(2) Å for atoms Cl and N1, respectively, in molecule 2.
Bond parameters reported in Table 3 can be compared with
corresponding parameters found in [PtCl(L1)(SMe2)] (HL1 )
6-tert-butyl-2,2′-bipyridine),8a the only “rollover” mononuclear
bipyridine complex so far characterized by X-ray analysis. In
the latter species, having a sulfur atom in place of a phosphorus,
Pt-Cl ) 2.395(2) Å, Pt-N ) 2.042(4) Å, and Pt-C7 )
1.990(5) Å. The agreement with the values reported in Table 3
is good, with the exception of the present average Pt-N,
2.094(2) Å, which can be considered elongated by the higher
trans influence of phosphorus with respect to that of sulfur. The
present average Pt-P distance, 2.230(1) Å, is statistically
Cl-Pt-P
92.75(2)
90.77(6)
170.97(7)
176.24(6)
95.80(7)
80.77(10)
93.35(2)
91.51(6)
171.59(7)
171.86(5)
94.68(8)
80.82(9)
Cl-Pt-N1
Cl-Pt-C7
P-Pt-N1
P-Pt-C7
N1-Pt-C7
coincident with the average value of 2.228(1) Å found in
[Pt2(L2)Cl(PPh3)2] (H3L2 ) 6-phenyl-2,2′-bipyridine15).
Dinuclear Complexes. When the reaction of [Pt(Me)2-
(DMSO)2] with 2,2′-bipy is carried out with a 2/1 Pt/L molar
ratio, a double C-H bond activation occurs and the dinuclear
species [Pt2(µ-L-2H)(Me)2(DMSO)2] (2a) is obtained. The
second metalation appears to be slightly favored with respect
to the first one, as complex 2a is also produced with a 1/1 Pt/L
molar ratio.
(13) For example: (a) Byers, P. K.; Canty, A. J. Organometallics 1990,
9, 210. (b) Sanna, G.; Minghetti, G.; Zucca, A.; Pilo, M. A.; Seeber, R.;
Laschi, F. Inorg. Chim. Acta 2000, 305, 189–205.
(14) Johnson, C. K.; ORTEP, Report No. ORNL-5138; Oak Ridge
National Laboratory, Oak Ridge, TN, 1976.
Alternatively, 2a can be obtained by a two-step approach:

2154 Organometallics, Vol. 28, No. 7, 2009
[Pt(Me)2(DMSO)2] + 2, 2′-bipy f
Zucca et al.
[Pt(L-H)(Me)(DMSO)]
(1)
(5)
1a
[Pt(L-H)(Me)(DMSO)] + [Pt(Me)2(DMSO)2] f
[Pt2(µ-L-2H)(Me)2(DMSO)2]
2a
The second step of the synthesis underlines the potential
ability of the mononuclear derivate to act as a Lewis base, at
least toward [Pt(Me)2(DMSO)2].
1
In the H NMR spectrum the presence of one set only of
signals and the absence of the C(3)-H protons support a
symmetric 2-fold metalated structure for 2a. Also in this case
the geometry has been definitively confirmed by NOE difference
experiments (see the Experimental Section).
Substitution of DMSO in [Pt2(µ-L-2H)(Me)2(DMSO)2] (2a)
with PPh3, CO, and 3,5-(Me)2-py is straightforward, giving
complexes 2b-d, respectively:
[Pt2(µ-L-2H)(Me)2(DMSO)2] + L′f
2a
Figure 2. ORTEP view of 4b. The molecule lies on a crystal-
lographic inversion center. Ellipsoids are as in Figure 1.
[Pt2(µ-L-2H)(Me)2(L′)2]
Table 4. Selected Bond Lengths (Å) and Angles (deg) in 4b, with
Estimated Standard Deviations (Esd’s) on the Last Figure Given in
Parentheses
2b, L′ ) PPh3
2c, L′ ) CO
(6)
2d, L′ ) 3,5-(Me)2-py
Pt-Cl1
Pt-N
N-C(1)
C1′-C2′
2.351(1)
2.107(2)
1.349(3)
1.401(3)
Pt-P
Pt-C2′
C1-C1′
2.236(1)
2.016(2)
1.439(3)
The reaction of 2a with HCl is also comparable to that of
the corresponding mononuclear derivative 1a: also in this case
only the Pt-CH3 bond is attacked.
Cl1-Pt-P
Cl1-Pt-C2′
P-Pt-C2′
93.41(2)
170.56(6)
94.89(6)
Cl1-Pt-N
P-Pt-N
N-Pt-C2′
90.41(5)
176.03(5)
81.40(7)
[Pt2(µ-L-2H)(Me)2(DMSO)2] + 2HClf
2a
The crystal structure of the complex 4b · 2CHCl3 consists of
the packing of 4b and CHCl3 molecules in the molar ratio 1/2
with no unusual van der Waals contacts. An ORTEP14 view of
4b is shown in Figure 2. Selected bond distances and angles
are reported in Table 4. Molecule 4b lies on a crystallographic
inversion center. The platinum atom displays a square-planar
coordination with a tetrahedral distortion. Maximum distances
from the best plane are +0.068(2) and -0.055(2) Å for atoms
C(2′) and N(2), respectively. The two fused pentaatomic rings
Pt-N-C2′-C1′-C1-N′-Pt′-C2 are quasi-planar, maximum
distances from the best plane being +0.019(2) and -0.019(2)
Å for atoms C2 and C2′, respectively. Bond parameters reported
in Table 5 can be compared with corresponding parameters
found in [Pt2(L2)Cl(PPh3)2] (H3L2 ) 6-phenyl-2,2′-bipyridine),15
where the atom Pt(1) is in the same environment found here:
Pt1-Cl1 ) 2.347(1) Å, Pt1-P1 ) 2.225(1) Å, Pt1-N2 )
2.119(3) Å, and Pt1-C3 ) 2.010(4) Å. An inspection of Table
4 shows that in all cases the agreement is very good.
Reaction 5, i.e. the second step in the synthesis of these
dinuclear derivatives, calls attention to the capability of the
mononuclear species to act as a Lewis base, at least toward
the [Pt(Me)2(DMSO)2] precursor. It is worthy of note that in
the case of 6-substitued 2,2′-bipyridines this chemical behavior
is not common. With most of the substituents studied (Me,
C(Me)3, CH2Ph, etc.) the second rollover metalation was not
observed. Only in the case of a phenyl substituent did the
reaction proceed to give C,N,C pincer complexes.11b,17 The
peculiar reactivity of the uncoordinated nitrogen atom in
the 2,2′-bipyridine mononuclear derivatives makes the two-step
[Pt2(µ-L-2H)(Cl)2(DMSO)2] + 2CH4
(7)
4a
Exchange of L′ for DMSO allows us to obtain other dinuclear
derivatives: [Pt2(µ-L-2H)(Cl)2(PPh3)2] (4b) and [Pt2(µ-L-
2H)(Cl)2(3,5-(Me)2-py)2] (4d).
Complexes 2 and 4 are not trivial species: the 2-fold
deprotonated 2,2′-bipyridine acts on the whole as an eight-
electron, tetradentate dianionic ligand. The bridging organic
moiety comprises two fused five-membered cyclometalated rings
in addition to the pyridine rings.16
(15) Zucca, A.; Cinellu, M. A.; Minghetti, G.; Stoccoro, S.; Manassero,
M. Eur. J. Inorg. Chem. 2004, 4484–4490.
(16) Comparison of the 1H NMR spectra of 1a and 2a deserve comments
with regard to the resonances of the H6/H6′ protons. In the mononuclear
species 1a, coordination to the metal leads to an opposite effect in the two
rings: in comparison with the free ligand, H6′ is strongly deshielded, with
∆δ (δcomplex-δligand) ) ca. 1.1 ppm, and H6 slightly shielded, with ∆δ )
ca.-0.25 ppm. The deshielding of H6′ has been previously observed in
analogous cyclometalates involving 6-substituted 2,2′-bipyridines: ∆δ is
known to be mainly dependent on the nature of the ligand close to H6′.
The upfield shift of H6 is obviously observed here for the first time. In 2a
the protons close to the nitrogen atoms, H6, are equivalent and less
deshielded, ∆δ ) ca. 0.55 ppm, than H6′ in 1a, even though the chemical
environment around the platinum atoms in 2a is the same as in 1a. The
opposite effects on the charge distribution inside the bridging ligand,
observed in the mononuclear 1a, are roughly averaged in the dinuclear 2a.
The same is also observed comparing the corresponding chlorides 3a and
4a. A recent work6 has pointed out that in 2,2′-bipyridine rotation around
the C2-C2′ bond on going from the anti to the cis conformation inherently
entails a change in the charge distribution inside the rings.

Cyclometalation of 2,2′-Bipyridine
Organometallics, Vol. 28, No. 7, 2009 2155
Chart 2
approach a synthetic strategy of great potential. Indeed, in
addition to the symmetric species 2a-d and 4a-d, taking
advantage of the two-step approach, it is also possible to build
up dinuclear unsymmetric systems where the platinum atoms
are in different environments, e.g. the complexes [(DMSO)-
(Cl)Pt(µ-L-2H)Pt(Me)(DMSO)] (6; different anions, Me and Cl),
[(PPh3)(Me)Pt(µ-L-2H)Pt(Me)(DMSO)] (7; different ligands,
PPh3 and DMSO), and [(CO)(Cl)Pt(µ-L-2H)Pt(Me)(DMSO)] (8;
different anions and ligands), obtained according to reactions
8-10.
[Pt(L-H)(Cl)(DMSO)] + [Pt(Me)2(DMSO)2] f
[(DMSO)(Cl)Pt(µ-L-2H)Pt(Me)(DMSO)]
(8)
(9)
6
[Pt(L-H)(Me)(PPh3)] + [Pt(Me)2(DMSO)2] f
[(PPh3)(Me)Pt(µ-L-2H)Pt(Me)(DMSO)]
7
[Pt(L-H)(Cl)(CO)] + [Pt(Me)2(DMSO)2] f
[(CO)(Cl)Pt(µ-L-2H)Pt(Me)(DMSO)]
(10)
8
Compounds 6-8 can be isolated in reasonable yields and
are stable in air: they have been characterized by elemental
analyses and, for 6 and 7, by NMR spectra. The 1H NMR spectra
of 6 and 7 give clear evidence of the lack of symmetry,
exhibiting six well-separated resonances for the aromatic
protons. Characterization in solution of compound 8 is hampered
by its solubility: in the IR spectra νCO is observed at 2090 cm-1,
a value consistent for a carbonyl in a platinum-chloride system.
In a first attempt to study the coordinating behavior of the
second nitrogen atom toward a different metal,we studied the
reaction of 3a with Na[AuCl4]. The reaction did not afford
platinum-gold derivatives but, likely due to the strong oxidative
capability of gold(III), gave a platinum(IV) complex, [Pt(L-
H)Cl3(DMSO)] (9), which was isolated and characterized.
same strategy can successfully be applied to the synthesis of
noteworthy heterodinuclear derivatives.18
Experimental Section
[Pt(Me)2(DMSO)2] was synthesized according to ref 19.
All the solvents were purified and dried according to standard
procedures.20 Elemental analyses were performed with a Perkin-
Elmer 240B elemental analyzer by Mr. Antonello Canu (Diparti-
mento di Chimica, Universita` degli studi di Sassari, Sassari, Italy).
Infrared spectra were recorded with a FT-IR Jasco 480P instrument
1
using Nujol mulls. H, 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. Chemical shifts are given in
ppm relative to internal TMS for 1H and 13C{1H} and external 85%
H3PO4 for 31P{1H}. J values are given in Hz. NOE difference, 2D-
COSY, and 2D-HETCOR experiments were performed by means
of standard pulse sequences. Conductivities were measured with a
Philips PW 9505 conductimeter. The ESI mass spectrometric
measurements were performed on a quadrupole time-of-flight nano
ESI-Q-TOF instrument (Q-Tof Ultima, Waters, Manchester, U.K.)
equipped with a nanoelectrospray ion source, calibrated in positive
mode. Compounds 1a-d, 2a-d, 3a-d, and 4a-c are shown in
Chart 2, and the numbering scheme used is given in Chart 3.
Synthesis of [Pt(L-H)(Me)(DMSO)] (1a). To a solution of 2,2′-
bipyridine (430 mg, 2.75 mmol) in anhydrous toluene (50 mL) was
added 350 mg of cis-[Pt(Me)2(DMSO)2] (0.918 mmol): the color
of the solution rapidly changed to red. The stirred solution, kept
under a nitrogen atmosphere, was heated to 110 °C. During the
heating, the solution color changed from red to yellow. After 3 h
the mixture was cooled to room temperature, concentrated to a small
volume, and treated with n-hexane to form a yellow precipitate.
The solid was filtered off, washed with n-hexane, and vacuum-
Conclusions
In the present study we have described aspects of the
reactivity of 2,2′-bipyridine, one of the most common ligands
in the coordination chemistry of transition metal ions; we have
shown the following.
(i) Under specific conditions, direct C(3) metalation of 2,2′-
bipy can be achieved by reaction with adducts of the “Pt(Me)2”
fragment. Series of mononuclear, [Pt(bipy-H)(X)(L)], and
dinuclear, [Pt2(bipy-2H)(X)2(L)2], cyclometalates (X ) Me, Cl;
L ) neutral ligands) have been synthesized and characterized
in solution and, in two cases, in the solid state (X-ray analysis).
(ii) In the mononuclear derivatives protonation of the
uncoordinated nitrogen atom can be accomplished. Reaction
with an acid having a noncoordinating anion allowed, at least
in one case, isolation and characterization of a cationic species
where the N′-C(3) coordinated zwitterionic ligand can be
envisaged as a tautomeric form of 2,2′-bipyridine.
(iii) Dinuclear derivatives can be built up by a two-step
approach to get species with different anions and different
ligands on each platinum center. This strategy allows us to tune
the electronic and steric properties of the environment around
each platinum atom, making the dinuclear species good
substrates for studies relevant, for example, to oxidative addition
reactions.18 Furthermore, preliminary results indicate that the
(17) Zucca, A.; Petretto, G. L.; Stoccoro, S.; Cinellu, M. A.; Minghetti,
G.; Manassero, M.; Manassero, C.; Male, L.; Albinati, A. Organometallics
2006, 25, 2253–2265.
(18) Work in progress.
(19) (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.
(20) Vogel’s Textbook of Practical Organic Chemistry, 5th ed.; Longman
Scientific and Technical: Harlow, U.K., 1989.

2156 Organometallics, Vol. 28, No. 7, 2009
Zucca et al.
Chart 3
yellow solid. Yield: 66%. Mp: 215 °C dec. Anal. Calcd for
C18H19N3Pt: C, 45.76; H, 4.05; N, 8.89. Found: C, 45.51; H, 3.86;
1
N, 8.92. H NMR (CDCl3): δ 8.51 (s, 1H, JPt-H ) 23.1 Hz, Ho
lutidine), 8.29-8.24 (m, 2H, H6 + H3′), 8.10 (dd, 1H, JH-H ) 1.5
Hz, JH-H ) 7.8 Hz, JPt-H ) 60.4 Hz, H4), 7.88 (broad td, 1H, JH-H
) 7.8 Hz, H4′), 7.76 (d, 1H, JH-H ) 5.4 Hz, JPt-H ) ca. 20 Hz,
H6′), 7.50 (s, 1H, Hp lutidine), 7.14 (t, 1H, JH-H ) 5.4 Hz, H5′),
7.07 (dd, 1H, JH-H ) 4.8 Hz, JH-H ) 7.6 Hz, H5), 2.39 (s, 6H,
CH3 3,5-lutidine), 0.94 (s, 3H, JPt-H ) 84.2 Hz, CH3-Pt).
Synthesis of [Pt2(L-2H)(Me)2(DMSO)2] (2a). To a solution of
2,2′-bipyridine (61.5 mg, 0.394 mmol) in anhydrous toluene (25
mL) was added 300 mg of cis-[Pt(Me)2(DMSO)2] (0.787 mmol):
the color of the solution rapidly changed to red. The stirred solution,
kept under a nitrogen atmosphere, was heated to 110 °C. During
the heating, the color of the solution changed from red to yellow.
After 8 h the mixture was cooled to room temperature, concentrated
to a small volume, and treated with diethyl ether to form a yellow
precipitate. The solid was filtered off, washed with diethyl ether,
and vacuum-pumped to give the analytical sample as a yellow solid
in almost quantitative yield. Mp: >260 °C. Anal. Calcd for
C16H24N2O2Pt2S2: C, 26.30; H, 3.31; N, 3.83. Found: C, 26.56; H,
pumped to give an analytical sample as a yellow solid in almost
quantitative yield. Mp: 95 °C. Anal. Calcd for C13H16N2OPtS: C,
1
35.21; H, 3.64; N, 6.32. Found: C, 35.49; H, 3.20; N, 6.42. H
NMR (CDCl3): δ 9.71 (dd, 1H, JH-H ) 5.2 Hz, JPt-H ) 14 Hz,
H6′), 8.36 (dd, 1H, JH-H ) 5.4 Hz, JH-H ) 1.2 Hz, H6), 8.29 (d,
1H, JH-H ) 7.5 Hz, H3′), 8.01 (dd, 1H, JPt-H ) 56.0 Hz, JH-H
)
1.5 Hz, JH-H ) 7.8 Hz, H4), 7.95 (td, 1H, JH-H ) 7.5 Hz, H4′),
7.36 (m, 1H, JH-H ) 5.2 Hz, JH-H ) 7.5 Hz, JH-H ) 1.5 Hz, H5′),
7.17 (dd, 1H, JH-H ) 4.5 Hz, JH-H ) 7.8 Hz, H5), 3.25 (s, 6H,
JPt-H ) 18.3 Hz, Me(DMSO)), 0.70 (s, 3H, JPt-H ) 82 Hz, Me-
Pt). NOE difference spectrum (CDCl3): irradiation at δ 0.70
(CH3-Pt) gives enhancement of the signals at δ 8.01 (dd, H4) and
3.25 (coordinated DMSO). 13C NMR (75.4 MHz; CDCl3): δ -13.4
(CH3-Pt, JPt-C ) 763 Hz), 43.73 (DMSO, JPt-C ) 42.1 Hz), 121.17
(CH), 123.87 (CH), 124.50 (CH), 138.51 (CH), 140.26 (CH), 145.10
(C-Pt, 1JPt-C ) 1090 Hz), 145.76 (CH), 150.33 (CH), 162.50 (Cq,
JPt-C ) 55 Hz), 164.80 (Cq, JPt-C ) 24 Hz).
1
3.19; N, 3.78. H NMR (CDCl3): δ 9.14 (dd, 2H, JH-H ) 5.2 Hz,
JH-H ) 1.3 Hz, H6/H6′), 8.05 (dd, 2H, 3JH-H ) 7.8 Hz, 4JH-H ) 1.3
3
3
Hz, JPt-H ) 51.3 Hz, H4/H4′), 7.14 (dd, 2H, JH-H ) 5.2, 7.8 Hz,
H5/H5′), 3.23 (s, 6H, 3JPt-H ) 18.7 Hz, CH3 (DMSO)), 0.67 (s, 3H,
2JPt-H ) 80.8 Hz, CH3-Pt). NOE difference spectrum (CDCl3):
irradiation at δ 0.67 (s, CH3-Pt) gives enhancement of the signals
at δ 8.05 (dd, H4) and 3.23 (s, coordinated DMSO). 13C NMR (75.4
Synthesis of [Pt(L-H)(Me)(PPh3)] (1b). To a solution of 1a
(50.6 mg, 0.12 mmol) in CH2Cl2 (15 mL) was added 31.6 mg of
PPh3 (0.12 mol): the solution was stirred and kept under a nitrogen
atmosphere. After 2 h the solution was concentrated to a small
volume under reduced pressure and treated with n-hexane to form
a precipitate. The solid was filtered off, washed with n-hexane, and
vacuum-pumped to give the analytical sample as a yellow solid.
Yield: 67%. Mp: 215 °C. Anal. Calcd for C29H25N2PPt · 1/2H2O: C,
MHz; CDCl3): δ 15.2 (JPt-C ) 740.2 Hz, CH3-Pt), 43.83 (JPt-C
)
45.7 Hz, DMSO), 123.75 (JPt-C ) 61.9 Hz, CH), 141.9 (J ) 87.5
Hz, CH), 141.6 (Cq), 145.9 (CH), 173.2 (Cq).
Synthesis of [Pt2(L-2H)(Me)2(PPh3)2] (2b). To a solution of
2a (30.0 mg, 0.041 mmol) in CH2Cl2 (10 mL) was added 21.5 mg
of PPh3 (0.082 mmol): the solution was stirred under a nitrogen
atmosphere for 2 h. During the reaction a yellow precipitate was
formed. The solid was filtered off, washed with diethyl ether, and
vacuum-pumped to give the analytical sample as a yellow solid.
Yield: 71%. Mp: >260 °C. Anal. Calcd for C48H42N2P2Pt2 · H2O:
C, 51.61; H, 3.97%; N, 2.51. Found: C, 51.56; H, 3.12; N, 2.48.
1
54.72; H, 4.12; N, 4.40. Found: C, 54.67; H, 3.79; N, 4.51. H
NMR (CDCl3): δ 8.40 (m, 1H, H6), 8.31 (dd, 1H, JH-H ) 8.0 Hz,
JH-H ) 1.5 Hz, H3′), 8.24 (ddd, 1H, JH-H ) 1.8 Hz, JH-H ) 5.4
Hz, JH-H ) 7.5 Hz, JPt-H ) 48 Hz, H4), 7.79-7.72 (m, 7H, H4′ +
Ho PPh3), 7.46-7.35 (m, 10H, H6′ + Hm+p PPh3), 7.22 (ddd, 1H,
JH-H ) 1.7 Hz, JH-H ) 7.8 Hz, JH-H ) 7.5 Hz, H5), 6.67 (td, 1H,
JH-H ) 1.5 Hz, JH-H ) 5.4 Hz, H5′), 0.74 (d, 3H, JP-H ) 7.7 Hz,
JPt-H ) 83 Hz, Me-Pt). 31P NMR (121.4 MHz; CDCl3; H3PO4): δ
33.59 (s, JPt-P ) 2229 Hz, PPh3).
1H NMR (CDCl3): δ 8.13 (m, 2H, JPt-H ) 42 Hz, JH-H ) JP-H
)
ca. 6.5 Hz, H4/4′), 7.76 (m, 12H, Ho PPh3), 7.40 (m, 20H, Hp + Hm
(PPh3) + H6/6′), 6.57 (m, 2H, JH-H ) 5.4 Hz, JH-H ) 7.5 Hz, JP-H
) 2.1 Hz, H5/5′), 0.62 (d, 6H, JP-H ) 7.4 Hz, JPt-H ) 81.4 Hz,
CH3-Pt). 31P NMR (121.4 MHz; CDCl3): δ 33.29 (1JPt-P ) 2347
Hz).
Synthesis of [Pt(L-H)(Me)(CO)] (1c). In a solution of 1a (50.0
mg, 0.113 mmol) in 15 mL of CH2Cl2, CO was bubbled at room
temperature. After 3 h the solution was concentrated to a small
volume under reduced pressure and treated with n-hexane. The
precipitate that formed was filtered, washed with n-hexane, and
vacuum-pumped to give the analytical sample as a dark solid. Yield:
41%, Mp: 137 °C dec. Anal. Calcd for C12H10N2OPt: C, 36.65; H,
2.56; N, 7.12. Found: C, 36.42; H, 2.31; N, 6.98. 1H NMR (CDCl3):
δ 8.65 (dd, 1H, JH-H ) 5.1 Hz, JPt-H ) 19.8 Hz, H6′), 8.40 (dd,
1H, JH-H ) 1.5 Hz, JH-H ) 4.8 Hz, H6), 8.33 (d, 1H, JH-H ) 8.0
Hz, H3′), 8.06 (dd, 1H, JPt-H ) 46 Hz, JH-H ) 1.6 Hz, JH-H ) 7.8
Synthesis of [Pt2(L-2H)(Me)2(CO)2] (2c). In a solution of 2a
(25.0 mg, 0.034 mmol) in 15 mL of CH2Cl2, CO was bubbled at
room temperature. After 3 h the solution was concentrated to a
small volume in vacuo and treated with diethyl ether. The precipitate
that formed was filtered, washed with n-pentane, and vacuum-
pumped to give the analytical sample as a red solid. Yield: 90%.
Mp: 255 °C dec. Anal. Calcd for C14H12N2O2Pt2: C, 26.67; H, 1.92;
1
N, 4.44. Found: C, 26.62; H, 1.64; N, 4.23. H NMR (CDCl3): δ
8.27 (dd, 2H, JH-H ) 5.2 Hz, JH-H ) 1.4 Hz, JPt-H ) 22 Hz, H6/6′),
8.16 (dd, 2H, JH-H ) 7.4 Hz, JH-H ) 1.3 Hz, JPt-H ) 45 Hz, H4/4′),
7.20 (m, 2H, overlapping with the solvent, H5/5′), 1.17 (s, 6H, JPt-H
) 83.8 Hz, CH3-Pt). FT-IR (Nujol; cm-1): 2048, s.
Hz, H4), 8.03 (ddd, 1H, JH-H ) 7.6 Hz, JH-H ) 8.0 Hz, JH-H
)
1.6 Hz, JPt-H ) 17.4 Hz, H4′), 7.35 (ddd, 1H, JH-H ) 1.5 Hz, JH-H
) 5.1 Hz, JH-H ) 7.6 Hz, H5′), 7.24 (dd, 1H, JPt-H ) 17.4 Hz,
JH-H ) 4.8 Hz, JH-H ) 7.8 Hz, H5), 1.19 (s, 3H, JPt-H) 85.7 Hz,
CH3-Pt). FT-IR (Nujol; cm-1): 2044, s.
Synthesis of [Pt2(L-2H)(Me)2(3,5-Me2Py)2] (2d). To a solution
of 2a (50.0 mg, 0.068 mmol) in 15 mL of acetone was added 1.37
mmol of 3,5-Me2Py. The solution was stirred and heated to reflux.
After 8 h the solvent was concentrated to a small volume under
reduced pressure and treated with n-pentane. The precipitate that
formed was filtered, washed with n-pentane, and vacuum-pumped
to give the analytical sample as a yellow solid. Yield: 76%. Mp:
>260 °C. Anal. Calcd for C26H30N4Pt2: C, 39.59; H, 3.83; N, 7.10.
Synthesis of [Pt(L-H)(Me)(3,5-Me2-pyridine)] (1d). To a
solution of 1a (50 mg, 0.113 mol) in acetone (15 mL) was added
0.06 mL of 3,5-Me2-pyridine (0.56 mmol, d ) 0.939 g/mL, ca.
5-fold excess): the solution was stirred and heated to reflux under
a nitrogen atmosphere. After 2 h the solvent was concentrated to a
small volume under reduced pressure and treated with n-hexane to
form a precipitate. The solid obtained was filtered off, washed with
n-hexane, and vacuum-pumped to give the analytical sample as a
1
Found: C, 39.17; H, 3.54; N, 6.80. H NMR (CDCl3): δ 8.52 (s,
4H, JPt-H ) 23.4 Hz, Ho lutidine), 8.05 (dd, 2H, JH-H ) 1.2 Hz,

Cyclometalation of 2,2′-Bipyridine
Organometallics, Vol. 28, No. 7, 2009 2157
1
JH-H ) 7.7 Hz, JPt-H ) 54.6 Hz, H4/4′), 7.47 (s, 2H, Hp lutidine),
7.25 (m, partially overlapping with the solvent, H6/6′), 6.86 (dd,
2H, JH-H ) 5.1 Hz, JH-H ) 7.7 Hz, H5/5′), 2.38 (s, 12H, CH3 3,5-
lutidine), 0.91 (s, JPt-H ) 82.8 Hz, 6H, CH3-Pt).
H, 3.27; N, 8.53. Found: C, 41.33; H, 3.03; N, 8.64. H NMR
(CDCl3): δ 9.67 (s, 1H, JPt-H ) 39.5 Hz, JH-H ) 5.2 Hz, H6′), 8.61
(s, 2H, JPt-H ) 23.4 Hz, Ho lutidine), 8.31 (dd, 1H, JH-H ) 4.9 Hz,
H6), 8.09 (d, 1H, JH-H ) 8.0 Hz, H3′), 7.92 (t, 1H, JH-H ) 7.6 Hz,
JH-H ) 8.0 Hz, H4′), 7.49 (s, 1H, Hp lutidine), 7.30 (m, 1H,
overlapping with CDCl3, H5′), 6.88 (dd, 1H, JH-H ) 4.9 Hz, JH-H
) 7.8 Hz, H5), 6.68 (dd, 1H, JPt-H ) 48.3 Hz, JH-H ) 7.8 Hz, H4),
2.38 (s, 6H, CH3 3,5-lutidine).
Synthesis of [Pt2(L-2H)(Cl)2(DMSO)2] (4a). To a suspension
of 2a (84.0 mg, 0.115 mmol) in 40 mL of acetone were added 2
mL of DMSO and 2.3 mL of 0.1 M aqueous HCl (0.23 mmol).
The suspension was stirred for 8 h, and then the solvent was
concentrated to a small volume. Complex 4a was extracted with
CH2Cl2, dried with Na2SO4, and concentrated to a small volume.
The residue was then treated with diethyl ether to form a precipitate
which was filtered and washed with diethyl ether to give the
analytical sample as a yellow solid. Yield: 70%. Mp: >260 °C.
Anal. Calcd for C14H18Cl2N2O2Pt2S2: C, 21.80; H, 2.35; N, 3.63%.
Synthesis of [Pt(L-H)(Cl)(DMSO)] (3a). To a solution of 1a
(200 mg, 0.451 mmol) in 50 mL of acetone were added with
vigorous stirring 2 mL of DMSO and 4.5 mL of aqueous 0.1 M
HCl (0.451 mmol). After 8 h the solution was concentrated to a
small volume: complex 3a was extracted with CH2Cl2, dried with
Na2SO4, and concentrated to a small volume. The residue was then
treated with n-hexane to form a precipitate which was filtered,
washed with n-hexane, and vacuum-pumped to give the analytical
sample as a yellow solid. Yield: 70%. Mp: 142 °C. Anal. Calcd
for C12H13N2ClOPtS: C, 31.07; H, 2.82; N, 6.04. Found: C, 31.41;
1
H, 2.89; N, 5.86. H NMR (CDCl3): δ 9.59 (dd, 1H, JH-H ) 0.8,
1.6, 5.2 Hz, JPt-H ) 36 Hz, H6′), 8.60 (dd, 1H, JH-H ) 1.5, 8.0 Hz,
JPt-H) 42 Hz, H4), 8.37 (dd, 1H, JH-H ) 1.5, 4.8 Hz, H6), 8.22 (d
br, 1H, JH-H ) 7.7 Hz, H3′), 7.98 (td, 1H, JH-H ) 1.6, 7.7 Hz, H4′),
1
7.40 (m, 1H, JH-H ) 1.6, 5.2, 7.7 Hz, H5′), 7.08 (dd, 1H, JH-H
4.8, 8.0 Hz, JPt-H ) 16.5 Hz, H5), 3.65 (s, 6H, JPt-H ) 24.2 Hz,
CH3(DMSO)). 13C NMR (75.4 MHz; CDCl3): δ 47.02 (JPt-C
)
Found: C, 21.94; H, 1.72; N, 3.53. H NMR (CDCl3): δ 8.95 (d,
2H, JH-H ) 5.2 Hz, H6/6′), 6.64 (d, 2H, JH-H ) 7.6 Hz, H4/4′), 7.07
(dd, 2H, JH-H ) 5.2 Hz, JH-H ) 7.6 Hz, H5/5′), 3.27 (s, 12H, JPt-H
) 23.0 Hz, CH3 (DMSO)).
)
59.8 Hz, CH3 DMSO); 121.4 (JPt-C ) 41.2 Hz, C3′), 123.8 (JPt-C
) 31.8 Hz, C5′), 124.6 (JPt-C ) 45.8 Hz, C5), 136.5 (JPt-C ) 1102.9
Hz, C3-Pt), 140.8 (n.o., C4′), 141.2 (JPt-C ) 48.9 Hz, C4), 145.6
(n.o., C6), 149.3 (JPt-C ) 21.0 Hz, C6′), 162.1 (JPt-C ) 59.5 Hz),
163.4 (JPt-C ) 74.1 Hz) (C2 and C2′). 1H and 13C assignments were
made on the basis of 1H-1H COSY and1H-13C HETCOR spectra.
Synthesis of [Pt(L-H)(Cl)(PPh3)] (3b). To a solution of 3a (140
mg, 0.304 mmol) in CH2Cl2 (25 mL) was added 79.6 mg of PPh3
(0.304 mol): the solution was stirred and kept under a nitrogen
atmosphere for 2 h. The solvent was concentrated to a small volume
under reduced pressure and treated with n-hexane to form a
precipitate which was filtered off, washed with n-hexane, and
vacuum-pumped to give the analytical sample as a yellow solid.
Yield: 88%. Mp >260 °C. Anal. Calcd for C29H25N2PPt: C, 55.50;
Synthesis of [Pt2(L-2H)(Cl)2(PPh3)2] (4b). To a suspension of
4a (56.1 mg, 0.073 mmol) in CH2Cl2 (20 mL) was added 38.2 mg
of PPh3 (0.146 mmol). The suspension was stirred under a nitrogen
atmosphere for 2 h. The solution that was obtained was concentrated
to a small volume under reduced pressure 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 yellow solid. Yield: 75%. Mp: >260 °C. Anal. Calcd for
C48H36N2Cl2P2Pt2: C, 48.47; H, 3.18; N, 2.46. Found: C, 48.61; H,
2.79; N, 2.37. 1H NMR (CDCl3): δ 9.06 (m, 2H, H6/6′), 7.81-7.75
(m, 12H, Ho PPh3), 7.47-7.37 (m, 18H, Hp+m PPh3), 6.81 (d, 2H,
JH-H ) 7.9 Hz, JPt-H ) 44.8 Hz, H4/4′), 6.51 (m, 2H, JH-H ) 7.9
Hz, H5/5′). 31P NMR (121.4 MHz; CDCl3; H3PO4): δ 19.55 (s, JPt-P
) 4135 Hz, PPh3).
1
H, 4.02; N, 4.46. Found: C, 55.18; H, 3.87; N, 4.71. H NMR
(CDCl3): δ 9.85 (m, 1H, broad, JPt-H ) 31 Hz, H6′), 8.26 (d, 1H,
JH-H ) 8.2 Hz, H3′), 8.17 (dd, 1H, JH-H ) 4.8 Hz, H6), 8.0 (t, 1H,
JH-H ) 6.6 Hz, JH-H ) 7.6 Hz, H4′), 7.82-7.62 (m, 6H, Ho PPh3),
7.46-7.36 (m, 10H, H5′ + Hm+p PPh3), 6.85 (dd, 1H, JH-H ) 8.0
Hz, JPt-H ) 49 Hz, H4), 6.42 (dd, 1H, JH-H ) 4.8 Hz, JH-H ) 8.0
Synthesis of [Pt2(L-2H)(Cl)2(3,5-Me2-pyridine)2] (4d). To a
suspension of 4a (35 mg, 0.045 mmol) in 20 mL of acetone was
added 0.45 mmol of 3,5-Me2Pyridine (10-fold excess). The suspen-
sion was stirred and heated to reflux for 8 h and then concentrated
to a small volume under reduced pressure and treated with
n-pentane. The precipitate that formed was filtered, washed with
diethyl ether, and vacuum-pumped to give the analytical sample
as a yellow solid. Yield: 82%. Mp: >260 °C. Anal. Calcd for
C24H24Cl2N4Pt2: C, 34.75; H, 2.92; N, 6.75. Found: C, 34.06; H,
Hz, H5). 31P NMR (124.8 MHz; CDCl3; H3PO4): δ 23.6 (s, JPt-P
)
4285 Hz, PPh3).
Synthesis of [Pt(L-H)(Cl)(CO)] (3c). In a solution of 3a (80
mg, 0.17 mmol) in 25 mL of CH2Cl2, CO was bubbled at room
temperature. After 3 h the solution was concentrated to a small
volume under reduced pressure and treated with n-hexane. The
precipitate that formed was filtered, washed with n-hexane, and
vacuum-pumped to give the analytical sample as a yellow solid.
Yield: 74%. Mp: 248 °C dec. Anal. Calcd for C11H7ClN2OPt: C,
1
2.75; N, 6.34. H NMR (CDCl3): δ 8.90 (d, 2H, JH-H ) 4.8 Hz,
JPt-H ) 39 Hz, H6/6′), 8.86 (s, 4H, JPt-H ) 41.7 Hz, Ho), 7.50 (s,
2H, Hp lutidine), 6.78 (d, overlapping 4H, H4/4′, H5/5′), 2.38 (s, 12H,
CH3 3,5-lutidine).
Synthesis of [Pt(L*)(DMSO)(Me)][BF4] (5). To a solution of
1a (55.5 mg, 0.125 mmol) in acetone was added with stirring 18-
crown-6 · HBF4 · H2O in a 1/1 molar ratio. The solution was stirred
for 3 h and then concentrated to a small volume and treated with
diethyl ether. The precipitate that formed was filtered and washed
with diethyl ether to give the analytical sample in almost quantitative
yield. Mp: 110 °C dec. Anal. Calcd for C13H17BF4N2OPtS: C, 29.39;
1
31.93; H, 1.71; N, 6.77. Found: C, 32.25; H, 1.04; N, 6.75. H
NMR (CDCl3): δ 9.50 (dd, 1H, JH-H ) 5.2 Hz, JPt-H ) 34 Hz,
H6′), 8.45 (dd, 1H, JH-H ) 1.5 Hz, JH-H ) 5.2 Hz, H6), 8.26 (dd,
1H, JH-H ) 7.9 Hz, H3′), 8.07 (td, 1H, JH-H ) 1.8 Hz, JH-H ) 7.9
Hz, H4′), 7.78 (dd, 1H, JPt-H ) 62.7 Hz, JH-H ) 1.8 Hz, JH-H
7.8 Hz, H4), 7.53 (m, 1H, JH-H ) 1.5 Hz, JH-H ) 5.2 Hz, JH-H
7.9 Hz, H5′), 7.06 (dd, 1H, JPt-H ) 18 Hz, JH-H ) 5.2 Hz, JH-H
7.8 Hz, H5). FT-IR (CH2Cl2, cm-1): 2107, s.
)
)
)
1
H, 3.23; N, 5.27. Found: C, 29.28; H, 3.09; N, 4.98. H NMR
(CDCl3): δ 13.8 (broad, 1H, NH), 9.95 (dd, 1H, JH-H ) 4.8 Hz,
JPt-H ) ca. 15 Hz, H6′), 8.75 (dd, 1H, JH-H ) 8.1 Hz), 8.68 (dd,
1H, JH-H ) 5.4 Hz), 8.51 (d, 1H, JH-H ) 8.1 Hz), 8.24 (td, 1H,
7.4 Hz), 7.72-7.60 (m, 2H), 3.30 (s, 6H, JPt-H ) 20.5 Hz, CH3
DMSO), 0.78 (s, 3H, JPt-H ) 81 Hz, CH3-Pt). IR (Nujol; cm-1):
3295 m, 3190 m, 1087 s br.
Synthesis of [Pt2(L-2H)(Cl)(Me)(DMSO)2] (6). To a solution
of 3a (90.0 mg, 0.194 mmol) in 35 mL of toluene was added 73.9
mg of [Pt(Me)2(DMSO)2] (0.194 mmol). The solution was heated
to 80 °C and stirred for 24 h and then evaporated to dryness. The
Synthesis of [Pt(L-H)(Cl)(3,5-Me2-pyridine)] (3d). To a solu-
tion of 3a (130 mg, 0.28 mmol) in acetone (25 mL) was added
0.12 mL of 3,5-Me2-pyridine (1.23 mmol, d ) 0.939 g/mL, ca.
4-fold excess): the solution was stirred and heated to reflux under
a nitrogen atmosphere. After 4 h the solvent was concentrated to a
small volume under reduced pressure and treated with n-hexane.
The precipitate that formed was filtered off, washed with n-hexane,
and vacuum-pumped to give the analytical sample as a yellow solid.
Yield: 92%. Mp: 210 °C Anal. Calcd for C17H16ClN3Pt: C, 41.43;

2158 Organometallics, Vol. 28, No. 7, 2009
Zucca et al.
Table 5. Crystallographic Data
3b
4b · 2CHCl3
formula
Mr
color
C28H22ClN2PPt
648.02
yellow
C48H38Cl8N2P2Pt2
1378.60
yellow
cryst syst
space group
triclinic
P1
monoclinic
P21/n
j
a/Å
b/Å
c/Å
10.8349(6)
13.6678(7)
17.7696(9)
101.229(1)
100.839(1)
106.739(1)
2386.8(2)
4
9.7794(5)
23.9415(12)
10.3588(5)
90
90.000(1)
90
R/deg
ꢀ/deg
γ/deg
U/Å3
2425.3(2)
2
Z
F(000)
1256
1.803
1324
1.888
Dc/g cm-3
T/K
150
295
cryst dimens (mm)
µ(Mo KR)/cm-1
min-max transmissn factors
scan mode
frame width/deg
time per frame/s
no. of frames
0.12 × 0.21 × 0.23
0.12 × 0.14 × 0.23
61.4
63.7
0.768-1.000
ω
0.30
10
3660
0.720-1.000
ω
0.30
20
3360
detector-sample dist/cm
θ range/deg
6.00
3-27
6.00
3-28
reciprocal space explored
no. of rflns (total; indep)
Rint
full sphere
44 199; 12 219
0.0285
0.030, 0.040
0.020
9719
595
0.96
full sphere
42 242; 6439
0.0217
0.025, 0.040
0.018
5423
280
0.98
final R2 and R2w indicesa (F2, all rflns)
conventional R1 index (I > 2σ(I))
no. of rflns with I > 2σ(I)
no. of variables
goodness of fitb
a
b
2
2
2
2
2
2
2
2
2
R2 ) [∑(|Fo - kFc2|)/∑Fo ]. R2w ) [∑w/(Fo - kFc2)2/∑w(Fo )2]1/2
.
[∑w(Fo - kFc2)2/(No - Nv)]1/2, where w ) 4Fo /σ(Fo )2, σ(Fo ) ) [σ2(Fo ) +
2
(pFo )2]1/2, No is the number of observations, Nv is the number of variables, and p ) 0.02.
residue was recrystallized from CH2Cl2/n-pentane to give the
analytical sample as a green solid. Yield: 63%. Mp: >260 °C. Anal.
Calcd for C15H21ClN2O2Pt2S2: C, 23.99; H, 2.82; N, 3.73. Found:
C, 24.14; H, 2.42; N, 3.66. 1H NMR (CDCl3): δ 9.13 (d, 1H, JH-H
7.15 (dd, 1H, JH-H ) 5.2 Hz, JH-H ) 7.8 Hz, H5 cis PPh3), 6.57
(m, 1H,, H5′ cis DMSO), 3.23 (s, 6H, JPt-H ) 19.2 Hz, DMSO),
0.67 (s, 3H, JPt-H ) 80 Hz, Pt-Me), 0.62 (d, 3H, JPt-H ) 81 Hz,
JP-H ) 7.5 Hz, Pt-Me cis PPh3).
) 5.0 Hz, JPt-H ) ca. 10 Hz, H6′ trans Me), 8.98 (d, 1H, JH-H
)
Synthesis of [Pt2(L-2H)(Me)(Cl)(DMSO)(CO)] (8). To a solu-
tion of 3c in toluene (82.8 mg, 0.20 mmol, 30 mL) was added with
vigorous stirring 76.3 mg of [Pt(DMSO)2Me2] (0.20 mmol). The
solution was refluxed for 4 h. The precipitate that formed was
filtered and washed with toluene and diethyl ether to give the
analytical sample as a dark yellow solid. Yield: 90%. Mp: >260
°C. Anal. Calcd for C14H15ClN2O2Pt2S: C, 23.99; H, 2.16; N, 4.00.
Found: C, 23.65; H, 2.08; N, 3.76. IR (Nujol; cm-1): 2090, s. NMR:
insoluble in common organic solvents.
7.8 Hz, JPt-H ) 42 Hz, H4 trans DMSO), 8.61 (dd, 1H, JH-H ) 5.0
Hz, JPt-H ) 41 Hz, H6 trans DMSO), 8.06 (d, 1H, JH-H ) 7.8 Hz,
JPt-H ) 50 Hz, H4′ trans Cl), 7.15 (dd, 1H, JH-H ) 5.0 Hz, JH-H
)
7.8 Hz, H5 or H5′), 7.06 (dd, 1H, JH-H ) 5.0 Hz, JH-H ) 7.8 Hz,
H5 or H5′), 3.62 (s, 6H, JPt-H) 22.8 Hz, DMSO trans N), 3.23 (s,
6H, JPt-H ) 19.5 Hz, DMSO trans C), 0.71 (s, 3H, JPt-H ) 81.3
Hz, Pt-Me).
Synthesis of [Pt2(L-2H)(Me)2(DMSO)(PPh3)] (7). To a solution
of 1b (65.8 mg, 0.105 mmol) in 20 mL of toluene was added 40.0
mg of [Pt(Me)2(DMSO)2] (0.105 mmol). The solution was heated
to reflux and stirred for 4 h and then evaporated to dryness. The
residue was recrystallized from CH2Cl2/Et2O to give the analytical
sample as a yellow solid. Yield: 60%. Mp: >250 °C. Anal. Calcd
for C32H33N2OPPt2S · H2O: C, 41.20; H, 3.78; N, 3.00. Found: C,
Synthesis of [Pt(L-H)(Cl)3(DMSO)] (9). To a solution of 3a
(79.9 mg, 0.236 mmol) in MeCN (10 mL) was added with stirring
an aqueous solution of NaAuCl4 (0.236 mmol in 10 mL, obtained
from HAuCl4 and NaHCO3 in a 1/1 molar ratio). The mixture was
heated to 100 °C for 8 h. The suspension that formed was filtered
off, washed with water, dried, and recrystallized from CH2Cl2/Et2O
to give the analytical sample as a cream-colored solid. Yield: 65%.
Anal. Calcd for C12H13Cl3N2OPtS · H2O: C, 26.07; H, 2.74; N, 5.07.
Found: C, 25.74; H, 2.30; N, 4.79. 1H NMR (CD2Cl2): δ 9.71 (dd,
1H, JH-H ) 4.9 Hz, JPt-H ) 25 Hz, H6′), 5.86 (dd, 1H, JH-H ) 8.1
Hz, JH-H ) 1.2 Hz, JPt-H ) 18 Hz, H4), 8.46 (dd, 1H, JH-H )4 .8
41.33; H, 3.58; N, 2.97. 1H NMR (CDCl3): δ 9.14 (d, 1H, JH-H
)
5.2 Hz, H6′ cis DMSO), 8.13 (m, JPt-H broad, H4′ trans PPh3), 8.05
(dd, JH-H ) 7.8 Hz, JPt-H ) 42 Hz, H4 trans DMSO), 7.78-7.73
(m, 6H, Ho PPh3), 7.42-7.33 (m, 10H, Hm+p PPh3 + H6 cis PPh3),
(21) SAINT Reference Manual; Siemens Energy and Automation,
Madison, WI, 1994-1996.
(22) Sheldrick, G. M. SADABS, Empirical Absorption Correction
Program,; University of Gottingen, Gottingen, Germany, 1997.
(23) Frenz, B. A. Comput. Phys. 1988, 2, 42.
(24) Crystallographic Computing 5; Oxford University Press: Oxford,
U.K., 1991; Chapter 11, p 126.
(25) Sheldrick, G. M. SHELXS 86: Program for the Solution of Crystal
Structures; University of Gottingen, Gottingen, Germany, 1985.
(26) Castellano, S.; Gu¨nther, H.; Eberaole, S. J. Phys. Chem. 1965, 69,
4166.
Hz, JH-H ) 1.2 Hz, H6), 8.40 (dd, 1H, JH-H ) 8.0 Hz, JH-H )
1.4 Hz), 8.13 (td, JH-H ) 7.8 Hz, JH-H ) 1.4 Hz, H4′), 7.60 (m,
1H, H5′), 7.30 (ddd, JH-H ) 8.4 Hz, JH-H ) 4.8 Hz, JPt-H ) 7 Hz,
H5), 3.93 (s, JPt-H ) 14.3 Hz, CH3 DMSO). ESI-MS (CH2Cl2):
m/z 498 [M - Cl]+.
X-ray Data Collection and Structure Determination. Crystal
data are summarized in Table 5. The diffraction experiments were
carried out on a Bruker SMART CCD area-detector diffractometer
at 150 K for 3b and at 295 K for 4b · 2CHCl3, using Mo KR

Cyclometalation of 2,2′-Bipyridine
Organometallics, Vol. 28, No. 7, 2009 2159
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,21 and an empirical absorption
correction was applied (SADABS)22 to the collected reflections.
The calculations were performed using the Personal Structure
Determination Package23 and the physical constants tabulated
therein.24 The structures were solved by direct methods
(SHELXS)25 and refined by full-matrix least squares using all
reflections and minimizing the function ∑w(Fo2 - kFc2)2 (refinement
on F2). All the non-hydrogen atoms were refined with anisotropic
thermal factors. The hydrogen atoms were placed in their ideal
positions (C-H ) 0.97 Å), with the thermal parameter U being
1.10 times that of the carbon atom to which they are attached, and
not refined. In the final Fourier maps the maximum residuals were
as follows: for 3b, 0.91(35) e Å-3 at 0.95 Å from Pt′; for
4b · 2CHCl3, 0.85(16) e Å-3 at 0.12 Å from Cl(4). CCDC Nos.
696077 (3b) and 696078 (4b) contain the supplementary crystal-
lographic data for this paper.
Acknowledgment. Financial support from the Universita`
di Sassari (FAR) and Ministero dell’Istruzione, dell’Universita`
e della Ricerca (MIUR, PRIN 2007) is gratefully acknowl-
edged. We thank Johnson Matthey for a generous loan of
platinum salts.
Supporting Information Available: CIF files giving crystal data
for 3b and 4b. This material is available free of charge via the
Internet at http://pubs.acs.org.
OM801033G