Activation of a C-H bond in a pyridine ring. Reaction of 6-substituted 2,2′-bipyridines with the methyl and phenyl platinum(II) derivatives: N′,C(3)- rollover cyclometalation

Article abstract of DOI:10.1021/om0301583

The reaction of the electron-rich derivatives cis-[Pt(R)₂(DMSO)₂] (R = Me, Ph) with a series of 6-substituted-2,2′-bipyridines, HL, occurs with loss of methane or benzene, respectively, to yield cyclometalated platinum(II) species [Pt(R)(L)(DMSO)]where L is an anionic ligand N′,C(3) coordinated. The unusual C-H activation entails a consecutive reaction process through a detectable intermediate. The reaction is peculiar of 6-substituted ligands: for comparison no reaction occurs with 6,6′-Me₂-2,2′-bipy and an adduct, [Pt(R)₂(HL)], is obtained with 5-Me-2,2′-bipy.

Full text of DOI:10.1021/om0301583

4770
Organometallics 2003, 22, 4770-4777
Activa tion of a C-H Bon d in a P yr id in e Rin g. Rea ction
of 6-Su bstitu ted 2,2′-Bip yr id in es w ith Meth yl a n d P h en yl
P la tin u m (II) Der iva tives: N′,C(3)-“Rollover ”
Cyclom eta la tion
Giovanni Minghetti, Sergio Stoccoro, Maria Agostina Cinellu, Barbara Soro, and
Antonio Zucca*
Dipartimento di Chimica, Universita` di Sassari, Via Vienna 2, I-07100 Sassari, Italy
Received March 5, 2003
The reaction of the electron-rich derivatives cis-[Pt(R)2(DMSO)2] (R ) Me, Ph) with a series
of 6-substituted-2,2′-bipyridines, HL, occurs with loss of methane or benzene, respectively,
to yield cyclometalated platinum(II) species [Pt(R)(L)(DMSO)] where L is an anionic ligand
N′,C(3) coordinated. The unusual C-H activation entails a consecutive reaction process
through a detectable intermediate. The reaction is peculiar of 6-substituted ligands: for
comparison no reaction occurs with 6,6′-Me2-2,2′-bipy and an adduct, [Pt(R)2(HL)], is obtained
with 5-Me-2,2′-bipy.
In tr od u ction
[PdCl(L)]2 and [PtCl(L)(SMe2)], respectively4 (HL )
6-alkyl-2,2′-bipy). Furthermore the formation of Ar-H
in a process of thermal rearrangement of [Pt(Ar)2(bipy)]
derivatives was explained assuming activation of a C-H
bond of the bipy ligand.5
Cyclometalated complexes arising from direct C-H
activation of 6-substituted 2,2′-bipyridines are well
known: they include both N,N,C(sp2)-M as well as
N,N,C(sp3)-M species, the former ones being more
common.1
In contrast, although reported first several years ago,
still very rare is the direct metal-mediated activation
of a C-H bond of a pyridyl ring. As far as we know,
N′,C(3) five-membered rings have been observed in an
Ir(III) 2,2′-bipyridine (bipy) complex,2 in some platinum
derivatives with N-substituted-2,2′-bipyridines,3 and
quite recently in a palladium and a platinum species,
In platinum(II) chemistry examples of activation of a
C-H bond of the heterocyclic ring promoted by plati-
num(II) chlorides such as [PtCl4]2- or [PtCl2(L)2] ad-
ducts have not been reported. In the case of the
intermediates trans-[Pt(R)Cl(SMe2)2] (R ) Me, Ph) the
reaction with 6-substituted-2,2′-bipyridines, HL, mostly
gives adducts [Pt(R)Cl(HL)] or cyclometalated species
[PtCl(L)] where L is the anionic N,N,C ligand arising
from activation of a C-H bond of the substituent.6 Only
with HL ) 6-C(Me)3-2,2′-bipy does the methyl-chloro
intermediate trans-[Pt(Me)Cl(SMe2)2] give the afore-
mentioned rollover N′,C(3) cyclometalated species [PtCl-
(L)(SMe2)] with loss of methane.4 Here we report on the
reaction of the electron-rich [Pt(Me)2(DMSO)2] and
[Pt(Ph)2(DMSO)2] derivatives with 6-alkyl-, benzyl-, and
aryl-substituted 2,2′-bipyridines, HL, to give new “roll-
over” cyclometalated species [Pt(Me)(L)(DMSO)] and
[Pt(Ph)(L)(DMSO)] through methane or benzene elimi-
nation.
* Corresponding author. E-mail: zucca@uniss.it. Fax: +39 079
229559.
(1) N,N,C(sp2)-M derivatives: (a) Minghetti, G.; Cinellu, M. A.;
Chelucci, G.; Gladiali, S.; Demartin, F.; Manassero, M. J . Organomet.
Chem. 1986, 307, 107. (b) Constable, E. C.; Henney, R. P. G.; Leese,
T. A.; Tocher, T. A. J . Chem. Soc., Chem. Commun. 1990, 513. (c)
Constable, E. C.; Henney, R. P. G.; Leese, T. A.; Tocher, T. A. J . Chem.
Soc., Dalton Trans. 1990, 443. (d) Cheung, T. C.; Cheung, K. K.; Peng,
S. M.; Che, C. M. J . Chem. Soc., Dalton Trans 1996, 1645-1651. (e)
Sanna, G.; Minghetti, G.; Zucca, A.; Pilo, M. I.; Seeber, R.; Laschi, F.
Inorg. Chim. Acta 2000, 305/ 2, 189-205. N,N,C(sp3)-M derivatives:
(f) Newkome, G. R.; Evans, D. W.; Kiefer, G. E.; Theriot, K. J .
Organometallics 1988, 7, 2537-2542. (g) Stoccoro, S.; Chelucci, G.;
Cinellu, M. A.; Zucca, A.; Minghetti, G. J . Organomet. Chem. 1993,
450, C15. (h) Minghetti, G.; Cinellu, M. A.; Stoccoro, S.; Zucca A.;
Manassero, M. J . Chem. Soc., Dalton Trans. 1995, 777-781. (i) Zucca,
A.; Stoccoro, S.; Cinellu, M. A.; Minghetti, G.; Manassero, M.; Sansoni,
M. Eur. J . Inorg. Chem. 2002, 3336-3346. N,N,C(sp2)-M and N,N,C-
(sp3)-M derivatives: (j) Cinellu, M. A.; Zucca, A.; Stoccoro, S.; Minghetti,
G.; Manassero, M.; Sansoni, M. J . Chem. Soc., Dalton Trans. 1996,
4217. (k) Zucca, A.; Stoccoro, S.; Cinellu, M. A.; Minghetti, G.;
Manassero, M. J . Chem. Soc., Dalton Trans. 1999, 3431. (l) Zucca, A.;
Cinellu, M. A.; Pinna, M. V.; Stoccoro, S.; Minghetti, G.; Manassero,
M.; Sansoni, M.; Organometallics 2000, 199, 4295-4304.
A preliminary communication relevant to 6-Ph-2,2′-
bipy has been recently reported.7
Aspects of the reactivity of the new species will also
be discussed.
Resu lts a n d Discu ssion
The ligands HLn, shown in Scheme 1, include alkyl-,
benzyl-, and phenyl-6-substituted-2,2′-bipyridines.
(2) (a) Nord, G.; Hazell, A. C.; Hazell R. G.; Farver, O. Inorg. Chem.
1983, 22, 3429. (b) Spellane, P. J .; Watts, R. J .; Curtis, C. J . Inorg.
Chem. 1983, 22, 4060. (c) Braterman, P. S.; Heat, G. H.; Mackenzie, A
J .; Noble, B. C.; Peacock, R. D.; Yellowlees, L. J . Inorg. Chem. 1984,
23, 3425.
(3) (a) Dholakia, S.; Gillard, R. D.; Wimmer, F. L. Inorg. Chim. Acta
1983, 69, 179. (b) Castan, P.; Dahan, F.; Wimmer, F. L.; Wimmer, S.
J . Chem. Soc., Dalton Trans, 1990, 2971. (c) Castan, P.; Labiad, B.;
Villemin, D.; Wimmer, F. L.; Wimmer, S. J . Organomet. Chem. 1994,
479, 153-157.
(4) Minghetti, G.; Doppiu, A.; Zucca, A.; Stoccoro, S.; Cinellu, M.
A.; Manassero, M.; Sansoni, M. Chem. Heterocycl. Compd. (N.Y.) 1999,
35 (8), 992.
(5) Skapski, A. C.; Sutcliffe, V. F.; Young, G. B. Chem. Commun.
1985, 609.
(6) Doppiu, A.; Cinellu, M. A.; Minghetti, G.; Stoccoro, S.; Zucca,
A.; Manassero, M.; Sansoni, M. Eur. J . Inorg. Chem. 2000, 2555-2563.
(7) Zucca, A.; Doppiu, A.; Cinellu, M. A.; Minghetti, G.; Stoccoro,
S.; Manassero, M. Organometallics 2002, 21, 783-785.
10.1021/om0301583 CCC: $25.00 © 2003 American Chemical Society
Publication on Web 10/16/2003

N′,C(3)-“Rollover” Cyclometalation
Organometallics, Vol. 22, No. 23, 2003 4771
Ta ble 1. Selected 1H NMR Da ta a
Me
DMSO
H(4)
H(5)
H(6)
[Pt(Me)(L1)(DMSO)]
[Pt(Me)(L2)(DMSO)]
[Pt(Me)(L3)(DMSO)]
[Pt(Me)(L4)(DMSO)]
[Pt(Me)(L5)(DMSO)]
[Pt(Me)(L6)(DMSO)]
[Pt(Ph)(L3)(DMSO)]
[Pt(Ph)(L6)(DMSO)]
[Pt(Cl)(L3)(DMSO)]
[Pt(Cl)(L6)(DMSO)]
[Pt(Me)(L3)(CO)]
1a
2a
3a
4a
5a
6a
3b
6b
3c
6c
13
14
15
0.69 [82.0]
0.70 [82.0]
0.69 [82.3]
0.66 [82.0]
0.66 [82.0]
0.75 [81.8]
3.24 [19.3]
3.24 [18.3]
3.23 [18.1]
3.21 [18.1]
3.23 [18.1]
3.26 [18.3]
2.95 [17.6]
2.98 [17.6]
3.63 [24.7]
3.67 [24.2]
7.88 (8.0) [53.0]
7.88 (7.7) [52.6]
7.89 [51.9]
7.04 (8.0) [18.6]
6.98 (7.6) [18.9]
7.21 [18]
7.01 (7.8) [18.1]
6.84 (8.1) [17.6]
7.65 (8.1) [17.8]
6.94 (8.1) [16.6]
b
7.19 (8.3) [13.2]
7.55 (8.3) [13.0]
7.29 (7.8) [b]
7.13 (8.0) [11.4]
b
9.67 (5.9) [14.0]
9.66 (6.1) [14.1]
9.65 [13.8]
7.85 (7.8) [52.9]
7.75 (8.1) [51.8]
8.07 (8.1) [52.0]
6.77 (8.1) [61.0]
6.94 (7.8) [62.8]
8.53 (8.3) [41.0]
8.64 (8.3) [42.0]
7.96 (7.8) [45.9]
7.96 (8.0) [54.6]
8.31 (8.1) [46.5]
9.66 (6.6) [13.8]
9.58 (6.3) [13.7]
9.71 (5.6) [13.7]
9.56 (5.6) [12.6]
9.63 (5.4) [12.7]
9.57 (5.8) [35.4]
9.59 (5.8) [31.1]
8.61 (5.4) [19]
7.72 (5.4)
1.19 [86.2]
0.93 [84.0]
0.79 [83.0]
[Pt(Me)(L3)(3,5-(Me)2py)]
[Pt(Me)(L6)(PPh3)]
b
a
Room temperature, solvent CDCl3, chemical shifts in ppm from internal SiMe4, coupling constants in Hz, J (H-H) in parentheses,
J (Pt-H) in square brackets. bSignals partially overlapping.
small 3J (Pt-H) values, ca. 18 Hz, relative to the protons
Sch em e 1
of DMSO, are consistent with a ligand trans to a
C(sp2).7,10 The aromatic region shows six resonances: an
AB system due to H(4) and H(5) with satellites (e.g.,
3
compound 3a : δ (H4) 7.89, J (Pt-H) ) 51.9 Hz; δ (H5)
7.21, 4J (Pt-H) ) 18.0 Hz) confirms coordination of
platinum to the C(3) atom. The H(6′) proton is remark-
ably deshielded, ca. 9.6-9.7 ppm (see Table 1), and
3
coupled to 195Pt: the J (Pt-H) values, ca. 14 Hz, reflect
the high trans influence of the methyl group. The
The reaction of cis-[Pt(Me)2(DMSO)2] with the ligands
has been carried out both in acetone at room or reflux
temperature and in toluene at 70-90 °C with a Pt/L
1:1 molar ratio.
resonances of the aliphatic protons in the substituent,
which are far away from the platinum atom, are very
slightly affected by coordination. Compound 3a has been
fully characterized by means of 1H, 1H NOE difference,
13C{1H}, 13C APT, and 1H single frequency decoupled
13C NMR experiments, allowing a full assignment of 1H
1
and 13C resonances. Finally, H NOE difference experi-
ments agree with the proposed geometry of the complex
(e.g., irradiation of the Pt-Me at 0.69 ppm gives en-
hancement at 3.23 (coordinated DMSO) and 7.89 ppm
(H(4)).
In agreement with the 1H NMR data, the 13C{1H}
NMR spectrum of 3a shows an aromatic carbon atom
1
bonded to platinum at 141.31 ppm, with J Pt-C ) 1086
Hz, to be compared with previously reported data for
N,C(sp2) cyclometalated Pt(II) derivatives.11 In addition
the 13C APT spectrum shows in the aromatic region only
six tertiary and four quaternary carbon atoms, the
metalated one included. In the aliphatic region two
resonances, at -13.91 ppm (1J (13C-195Pt) ) 763.8 Hz))
and 43.69 ppm (2J (13C-195Pt) ) 42.5 Hz), give clear
evidence for coordinated Me and DMSO groups, respec-
tively.
With the ligands HL1-6 the reaction is straightforward
and yields, at least in acetone solution, are fairly good.8
In toluene at 70-90 °C, partial decomposition to metal
occurs. The isolated species, 1a -6a , are stable in the
solid state, soluble in several organic solvents, and not
electrolytes in acetone. They have been fully character-
1
A series of H single frequency decoupled 13C NMR
spectra allowed us to assign the C resonances, showing
that the 195Pt-13C coupling constants of the carbon
atoms of the metalated pyridine are much larger than
those of the N-bonded pyridinic ring (e.g., C5, J (Pt-C)
) 59.7 Hz; C5′, J (Pt-C) ) 9.9 Hz).
The N′,C(3) metalation seems to be peculiar of electron-
rich derivatives. To point out the role of the substitution
of a methyl for a chloride, the behavior of the strictly
homologous species [Pt(Me)2(DMSO)2], [PtCl(Me)(DM-
1
ized by elemental analyses and by H NMR and FAB-
MS spectroscopy. In the FAB-MS spectra, besides the
molecular ions, [M]+, both the [M - Me]+ and [M -
DMSO]+ ions are observed (compounds 2a , 3a , 5a , and
1
6a ). The H NMR spectra provide evidence for only one
out of the two possible isomers. The resonance of the
methyl bonded to the platinum atom, at high field (δ
0.66-0.75, CDCl3 solution), is a singlet with satellites:
the 195Pt-H coupling constants, ca. 82 Hz, fit a methyl
trans to a nitrogen atom.9 On the other hand, the rather
(9) Monaghan, P. K.; Puddephatt, R. J . Inorg. Chim. Acta 1982, 65,
L59-L61.
(8) An additional ligand was investigated, namely, 6-(1-methylben-
zyl)2,2′-bipyridine: although 1H NMR spectra give evidence for N′,-
C(3) metalation, a number of other species are formed, hampering
isolation of a pure compound
(10) Doppiu, A.; Minghetti, G.; Cinellu, M. A.; Stoccoro, S.; Zucca,
A.; Manassero, M. Organometallics 2001, 20, 1148-1152.
(11) Chassot, L.; von Zelewsky, A. Inorg. Chem. 1987, 26, 2814-
18.

4772 Organometallics, Vol. 22, No. 23, 2003
Minghetti et al.
Sch em e 2
SO)2], and [PtCl2(DMSO)2] toward ligand HL1 has been
compared under the same conditions, Scheme 2. As can
be seen C(3)-H activation is achieved only with the
dimethyl derivative, at least under these experimental
conditions.
A substituent in 6 position is of paramount impor-
tance to achieve N′,C(3) metalation. By comparison, the
reaction of [Pt(Me)2(DMSO)2] with 5-Me-2,2′-bipyridine
(HL7) or the unsubstituted 2,2′-bipy (HL8), carried out
under the same experimental conditions (acetone, re-
flux), affords the adducts [Pt(Me)2(HLn)] (n ) 7, 8) (7,
8); with the disubstitued 6,6′-Me2-2,2′-bipyridine no
reaction occurs at room temperature, whereas heavy
decomposition is observed in refluxing acetone.
F igu r e 1. (a) 1H NMR progress of the reaction of
[Pt(Me)2DMSO2] with HL1 (1:1 molar ratio) in (CD3)2CO,
[Pt] ) [Pt(Me)2(DMSO)2]; (b) plot of ln[Pt(Me)2(DMSO)2]
vs time with a large excess of HL1.
The reaction is almost complete after 24 h. Conversion
of species i to complex 1a or 3a is relatively slow, but
not enough to allow isolation of the intermediates.
On the whole in the progress of the reaction only three
platinum(II) species are detected in solution: the reac-
tant ([Pt(Me)2(DMSO)2]), the final product ([Pt(L)(Me)-
(DMSO)]), and the new complex i. No other DMSO-
containing Pt(II) complex is observed.
1
The H NMR spectrum of the intermediate species i
shows only the signals of two Pt-Me groups and of a
coordinated HL unit. The resonances of the Pt-methyl
protons are very close, e.g., for HL1, δ 1.02, s, 2J (Pt-H)
2
) 89 Hz; 1.03, s, J (Pt-H) ) 87 Hz. Both the nitrogen
donors of the bipyridine seem to be coordinated: the
H(6′) proton is shifted to low field and coupled to
platinum (e.g., for HL1 δ 9.11 d, H6′, 3J (Pt-H) ) 23 Hz)
and the 6-Me protons resonate at δ 2.83, a value very
similar to that previously observed for the isomer of
[Pt(HL1)(Me)I], having the coordinated Me group close
to the 6-Me (δ 2.87). It is worth noting that in the
rollover species the chemical shift of the latter protons
is usually very similar to that of the free ligand (e.g.,
δ(Me): 1a , 2.46; HL1, 2.57). On the whole, the spectrum
of complex i strictly reminds us of those of the isolated
adducts 7 and 8 (see Experimental Section), so that we
feel confident to identify compound i as the adduct
[Pt(Me)2(HL1)]. Attempts to isolate the adduct by reac-
tion of [Pt(Me)2(COD)] with HL1 were unsuccessful: no
reaction occurs even at reflux temperature.
A plot of the concentrations of [Pt(Me)2(DMSO)2], i,
and 1a versus time (see Figure 1a) shows a pattern
consistent with a two-step consecutive reaction (Scheme
3). 1H NMR follow-up of the reaction with a large excess
of the ligand HL1 indicates that overall the reaction is
first order in [Pt(Me)2(DMSO)2] with kobs ) 0.16 s-1 at
18.5 °C. A plot of ln[Pt(Me)2(DMSO)2] versus time is
shown in Figure 1b.
The nature of the electronic and steric properties of
the 6-substituent of HLn does not remarkably affect the
reaction, which in most cases, e.g., n ) 1, 2, 3, and 6,
occurs even at room temperature.
The progress of the N′,C(3) metalation was investi-
1
gated following by H NMR spectroscopy the reaction
of [Pt(Me)2(DMSO)2] with the ligands HL1 and HL2 in
acetone at room temperature (see Experimental Sec-
tion).
The 1H NMR spectrum ((CD3)2CO) of the starting
complex [Pt(Me)2(DMSO)2] shows a sharp peak at δ 3.12
(12H) with 195Pt satellites (3J (Pt-H) ) 13.3 Hz), due to
the S-bonded Me2SO, and a singlet at δ 0.56 due to Pt-
Me (2J (Pt-H) ) 80.2 Hz). After addition of the ligand
HL1 a rapid decrease of these signals is observed; in the
aliphatic region of the spectra the signal of coordinated
DMSO, δ 3.12, partially converts into a singlet charac-
teristic of free DMSO, δ 2.52. At the same time a new
species, i, is formed, characterized by a H(6′) resonance
at low field (δ 9.11), with no coordinated DMSO. After
a few minutes after the mixing of the reactants, the
spectra show, in low concentration, the final reaction
products, [Pt(L1)(Me)(DMSO)] and methane (δ ) 0.16).
A plausible pathway for the conversion of the adduct
to the N′,C(3) cyclometalated species is shown in

N′,C(3)-“Rollover” Cyclometalation
Organometallics, Vol. 22, No. 23, 2003 4773
Sch em e 3
Sch em e 4
Accordingly, the cis-[Pt(Ph)2(DMSO)2] complex seems
to be somewhat less prone than the corresponding
dimethyl derivative to give N′-C(3) cyclometalation:
indeed this can be achieved under more severe condi-
tions such as refluxing acetone for HL3 or toluene at
90 °C for HL.6 Under mild conditions adducts, e.g.,
[Pt(Ph)2(HL6)] and [Pt(Ph)2(HL8)], are obtained.
1
On the whole, the H NMR spectra of 3b and 6b are
similar to those of the corresponding methyl derivatives.
Evidence for the isomer having the phenyl trans to the
nitrogen atom is provided by the upfield shift with
respect to 3a and 6a (∆δ 1.12-1.13 ppm) of the
resonances of the H(4) protons, due to the shielding
effect of the adjacent phenyl ring.
In complexes 3a and 6a the platinum-C(sp3) bond
was cleaved by reaction with HCl in acetone at room
temperature (reaction 2):
Sch em e 5
Scheme 4. The steric hindrance due to the substitution
in 6 makes the adduct A unstable and allows the
cleavage of a Pt-N bond weakened by the strong trans
influence of the methyl group. Rotation of a pyridine
ring around the C(2)-C(2′) bond brings a C-H bond
close to the metal, B. The pseudo coordinatevely unsat-
urated intermediate B12 promotes the C(sp2)-H oxidative
addition to yield the pentacoordinated hydridoplati-
num(IV), C.13,14 From C, loss of methane eventually
leads to the platinum(II) N′-C(3) cyclometalated species
as the thermodynamically stable isomer D. An oxidative
addition from B to C is supported by the observation
that the formation of Ar-H in the thermal rearrange-
ment of [Pt(Ar)2(bipy)] is strongly favored in the case
of Ar ) 4-CMe3-C6H4 versus Ar ) 4-CF3-C6H4 (the
former reacts 62 times faster than the latter).5,15
The metal-carbon bond inside the five-membered
N,C cycle is unaffected. One isomer is selectively formed;
the correct assignment of the isomer can be attained
through the IR and NMR spectra. In the IR spectrum
(complex 3c) a strong absorption at 276 cm-1 is consis-
tent with the stretching vibration of a Pt-Cl bond trans
to a ligand with a high trans influence.16 In the 1H NMR
spectra the J (Pt-H) relevant to the methylic protons
of DMSO, 24.7 Hz, agrees with a DMSO trans to a
nitrogen atom.
The mononuclear chloride species are accompanied by
a minor product, [PtCl(L)]2, formed by elimination of
DMSO and poorly soluble, as often observed for this type
of chloro-bridged dimers. In its turn the bridge can be
opened by DMSO to restore the mononuclear complexes.
3
(12) The X-ray structure of a 14-electron platinum(II) complex
stabilized by an agostic interaction has been quite recently reported:
Baratta, W.; Stoccoro, S.; Doppiu, A.; Herdtweck, E.; Zucca, A.; Rigo,
P. Angew. Chem. 2003, 42 (1), 105-109.
(13) Puddephatt, R. J . Coord. Chem. Rev. 2001, 219-221, 157-185.
(14) Sixteen-electron platinum(IV) species have been recently char-
acterized by X-ray structure: (a) Fekl, U.; Kaminsky, W.; Goldberg,
K. I. J . Am. Chem. Soc. 2001, 123, 6423. (b) Reinartz, S.; White, P. S.;
Brookhart, M.; Templeton, J . L. J . Am. Chem. Soc. 2001, 123, 6425.
(15) Ryabov, A. D. Chem. Rev. 1990, 90, 403-424.
(16) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.
1973, 10, 335-422.

4774 Organometallics, Vol. 22, No. 23, 2003
Minghetti et al.
Reaction 2 is likely to occur through oxidative addition
of HCl followed by fast reductive elimination of CH4:
no hydrido-alkyl species is detected.13 The different
trans influence of the donors accounts for the isomer
having a trans Cl-Pt-C arrangement.
As shown, inter alia, by the reaction with HCl, the
N′,C(3) five-membered ring is rather robust, and a
variety of species can be obtained by substitution of
DMSO with neutral ligands, e.g., CO, 3,5-Me2pyridine,
and PPh3, reactions 3-5.
Finally it is worth mentioning that with the 6-alkyl-
and benzyl-substituted ligands, HL1-HL5, we were
unable to attain multiple C-H bond activation, as
recently reported in the case of 6-phenyl-2,2′-bipyridine,
HL.6,7 Nevertheless, the FAB mass spectra of com-
pounds 2a , 3a , and 5a provide evidence for dinuclear
species (e.g., 2a , m/z 613 [Pt2(L-2H]+) in the vapor
phase.
Exp er im en ta l Section
The ligands were prepared according to literature
methods.19
All the reactions were carried out under argon. The
solvents have been purified and dried according to
standard methods.20 Compounds cis-[Pt(Me)2(DMSO)2],
cis-[Pt(Ph)2(DMSO)2], and trans-[Pt(Me)Cl(DMSO)2] were
prepared according to literature procedures.21 Elemental
analyses were performed with a Perkin-Elmer 240B
elemental analyzer by Mr. A. Canu (Dipartimento di
Chimica, Universita` di Sassari). Infrared spectra were
recorded with a Perkin-Elmer 983 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.
Chemical shifts are given in ppm relative to internal
TMS (1H, 13C) and external 85% H3PO4 (31P). NOE
difference spectra were performed by means of standard
pulse sequences. 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-nitrobenzyl alcohol as supporting matrix.
P r ep a r a tion s. Gen er a l P r oced u r es for P r ep a r a -
tion of Com p ou n d s 1a -6a . Meth od A. To a suspen-
sion of cis-[Pt(Me)2(DMSO)2] (88 mg, 0.231 mmol) in
toluene (7 mL) were added under stirring 0.236 mmol
of HLn (n ) 1-6). The yellow solution was heated to
70-80 °C, then evaporated to dryness. The crude
product was dissolved in CH2Cl2, filtered over Celite,
and treated with pentane. The precipitate obtained was
filtered, washed with pentane, and vacuum-dried to give
the analytical sample as a pale yellow solid.
Reactions 3-5 occur in dichloromethane solution at
room temperature, i.e., in very mild conditions. Com-
pounds containing a single molecule of DMSO have been
reported to be rather inert17 to substitution; in com-
plexes such as 3a and 6a , the easy displacement of
DMSO by neutral ligands is promoted by the metal-
carbon σ-bond in trans position. Compounds 13-15
contain four different groups coordinated to the metal
center. Complex 13 in particular is not trivial, having
three different metal-carbon bonds, M-C(sp3), M-C-
(sp2), and M-C(sp), respectively. 1H NMR data are
consistent with the isomer having an N-Pt-Me ar-
rangement. A NOE difference experiment supports this
assignment: irradiation of the resonance of the methyl
bound to the platinum atom, δ 1.19, gives enhancement
of the signal of H(4), δ 7.96.
The present results point out that an interesting
intramolecular activation of a C-H bond of 6-substi-
tuted pyridine rings can be attained by reaction of
electron-rich platinum(II) derivatives. Although the
presence of a substituent in 6-position is crucial in
driving the reaction toward the N′,C(3) metalation, we
have evidence (1H NMR spectroscopy) that in the case
of [Pt(Me)2(DMSO)2] activation of a C-H bond of a
pyridine ring occurs even with the unsubstituted 2,2′-
bipyridine. However, the process requires harsh condi-
tions, e.g., refluxing toluene,5 and is accompanied by
heavy decomposition to metal. A dynamic behavior
implying dissociation-association of a nitrogen donor
has been previously observed in some palladium(II) 2,2′-
bipy complexes.18
Meth od B. To a solution of the ligand HLn (n ) 1-6,
0.30 mmol) in acetone (15 mL) was added under stirring
114 mg of cis-[Pt(Me)2(DMSO)2] (0.30 mmol). The yellow
solution was refluxed, then concentrated to small vol-
ume and treated with pentane. The precipitate obtained
was filtered, washed with pentane, and vacuum-dried
to give the analytical sample as a pale yellow solid.
[P t(Me)(L1)(DMSO)], 1a . Compound 1a was ob-
tained according to method B (5 h), yield 68%, mp 140-3
°C. Anal. Calcd for C14H18N2OPtS: C 36.76, H 3.97, N
6.12. Found: C 37.13, H, 3.65, N, 6.06. 1H NMR
2
(CDCl3): δ 0.69 (s, 3H, Me-Pt, J Pt-H ) 82.0 Hz), 2.52
3
(s, 3H, Me-bipy), 3.24 (s, 6H, Me(DMSO), J Pt-H
)
(19) (a) Kauffmann, T.; Konig, J .; Woltermann, A. Chem. Ber. 1976,
109, 3864. (b) Azzena, U.; Chelucci, G.; Delogu, G.; Gladiali, S.;
Marchetti, M.; Soccolini F.; Botteghi, C. Gazz. Chim. Ital. 1986, 116,
307. (c) Botteghi, C.; Chelucci, G.; Chessa, G.; Delogu, G.; Gladiali S.;
Soccolini, F. J . Organomet. Chem. 1986, 304, 217. (d) Polin, J .;
Schmohel, E.; Balzani, V. Synthesis 1998, 321-324.
(20) Vogel’s Textbook of Practical Organic Chemistry, 5th ed.;
Longman Scientific and Technical: Harlow, 1989.
(21) (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.
(17) (a) Monsu` Scolaro, L.; Mazzaglia, L.; Romeo, A.; Plutino, M.
R.; Castriciano, M.; Romeo, R. Inorg. Chim. Acta 2002, 330, 189-196.
(b) Romeo, R.; Cusumano, M. Inorg. Chim. Acta 1981, 49, 167.
(18) Markies, B. A.; Kruis, D.; Rietveld, M. H. P.; Verkerk, K. A.
N.; Boersma, J .; Kooijman, H.; Lakin, M. T.; Spek, A. L.; van Koten,
G. J . Am. Chem. Soc. 1995, 117, 5263-5274.

N′,C(3)-“Rollover” Cyclometalation
Organometallics, Vol. 22, No. 23, 2003 4775
19.3 Hz), 7.04 (d, 1H, H5, 3J H-H ) 8.0 Hz, 4J Pt-H ) 18.6
Me]+, 483 [M - DMSO]+, 467 [M - DMSO - CH4]+,
453 [M - DMSO - 2Me]+.
3
Hz), 7.31 (m, 1H, H5′), 7.88 (d, 1H, H4, J H-H ) 8.0 Hz,
3J Pt-H ) 53.0 Hz), 7.91 (td, 1H, H4′ (partially overlap-
[P t(Me)(L6)(DMSO)], 6a . Method A (2 h), yield 93%;
method B (1 h, reflux temp), yield 89%; mp 174-176
°C. Anal. Calcd for C19H20N2OPtS: C 43.93, H 3.88, N
5.39. Found: C 43.73, H 3.63, N 5.20. 1H NMR
3
ping)), 8.31 (d, 1H, H3′, J H-H ) 7.6 Hz), 9.67 (d, 1H,
3
3
H6′, J H-H ) 5.9 Hz, J Pt-H ) ca. 14 Hz).
[P t(Me)(L2)(DMSO)], 2a . Method A (80 °C, 16 h),
yield 60%; method B, yield 81%; mp 145 °C (dec). Anal.
Calcd for C18H26N2OPtS‚0.5DMSO: C 41.29, H 5.29, N
5.07. Found: C 40.98, H 5.12, N 5.11. 1H NMR
2
(CDCl3): δ 0.75 (s, 3H, Me-Pt, J Pt-H ) 81.8 Hz), 3.26
3
(s, 6H, (Me)2SO, J Pt-H ) 18.3 Hz), 7.32-7.54 (m, 4H,
3
4
aromatics), 7.65 (d, 1H, H5, J H-H ) 8.1 Hz, J Pt-H
)
4
3
2
17.8 Hz), 7.97 (dt, 1H, H4′, J H-H ≈ 1 Hz J H-H ) 7.8
(CDCl3): δ 0.70 (s, 3H, Me-Pt, J Pt-H ) 82.0 Hz), 0.96
Hz), 8.07 (d, 1H, H4, 3J H-H ) 8.1 Hz, 3J Pt-H ) 52.0 Hz),
(s, 9H, (Me)3C); 2.65 (s, 2H, CH2), 3.24 (s, 6H, Me-
3
3
3
8.14 (d, 2H, Ho (Ph), J H-H ) 7.8 Hz), 8.50 (ddd, 1H,
(DMSO) J Pt-H ) 18.3 Hz), 6.98 (d, 1H, H5, J H-H
)
3
3
4
H3′, J H-H ) 7.3 Hz), 9.71 (ddd, 1H, H6′, J H-H ) 5.6
7.6 Hz, J Pt-H ) 18.9 Hz) 7.32 (td, 1H, H5′) 7.88 (d, 1H,
Hz, J Pt-H ) 13.7 Hz). 13C NMR (DMSO-d6): δ -13.83
3
3
3
H4, J H-H ) 7.6 Hz, J Pt-H ) 52.6 Hz), 7.91 (1H, H4′
3
(s, J C-Pt ) 772.5 Hz), 120.06 (s, J C-Pt ) 60.0 Hz), 121.12
(s, J C-Pt ) 20.0 Hz), 125.09 (s), 125.93 (s), 128.46 (s),
128.67 (s), 138.87 (s, J C-Pt ) 90.6 Hz), 139.28 (s), 140.78
(s, J C-Pt ) 90.2 Hz), 145.52 (s), 149.86 (s), 151.35 (s,
J C-Pt ) 214.7 Hz), 161.65 (s, J C-Pt ) 56.4 Hz), 164.01
(s, J C-Pt ) 25.0 Hz). MS-FAB+ (m/z): 519 [M]+, 504
[M - Me]+, 441 [M - DMSO]+, 426 [M - DMSO - Me]+.
(overlapping)); 8.34 (d, 1H, H3′; J H-H ) 7.9 Hz), 9.66
(d, 1H, H6′, 3J H-H ) 6.1 Hz, 3J Pt-H )14.1 Hz). MS-FAB+
(m/z): 513 [M]+, 498 [M - Me]+, 435 [M - DMSO]+, 419
[M - DMSO - CH4]+, 403 [M - DMSO -2 CH4]+, 363
[M - DMSO - C(Me)3 - Me]+.
[P t(Me)(L3)(DMSO)], 3a . Method A (70 °C, 14 h),
yield. 61%; method B, yield 88%; mp 187 °C. Anal. Calcd
for C17H24 N2OPtS: C 40.87, H 4.84, N 5.61. Found: C
[P t(P h )(L3)(DMSO)], 3b. Complex 3b was obtained
according to method B (5 h) using [Pt(Ph)2(DMSO)2]
instead of [Pt(Me)2(DMSO)2], pale yellow, yield 44%; mp
225 °C. Anal. Calcd for C22H26N2OPtS: C 47.05, H 4.67,
N 4.99. Found: C 47.36, H 4.57, N 4.99. 1H NMR
(CDCl3): δ 1.32 (s, 9H, (Me)3C), 2.95 (s, 3H, Me(DMSO),
1
40.51, H 4.54, N 5.42. H NMR (CDCl3): δ 0.69 (s, 3H,
2
Me-Pt, J Pt-H ) 82.3 Hz), 1.38 (s, 9H, (Me)3C); 3.23
3
(s, 6H, Me(DMSO) J Pt-H ) 18.1 Hz); 7.21 (d, 1H, H5,
4
3J H-H ) 8.1 Hz, J Pt-H ) 18.0 Hz), 7.31 (ddd, 1H, H5′,
3
4
3J H-H ) 7.3 Hz, J H-H ) 5.6 Hz, J H-H ) 1.5 H), 7.89
3
3J Pt-H ) 17.6 Hz), 6.77 (d, 1H, H4, J H-H ) 8.1 Hz,
3
3
(d, 1H, H4, J Pt-H ) 51.9 Hz, J H-H ) 8.1 Hz), 7.91 (m,
1H, H4′ (overlapping)), 8.36 (d, 1H, H3′, 3J H-H ) 8.1 Hz),
9.65 (d, 1H, H6′, 3J Pt-H ) 19.8 Hz, 3J H-H ) 5.6 Hz). 13C-
{1H} NMR: δ -13.91 (CH3-Pt, 1J Pt-C ) 763.8 Hz), 30.21
(C-(CH3)), 43.69 (CH3 (DMSO), 2J Pt-C ) 42.5 Hz), 119.37
((C5), J Pt-C ) 59.7 Hz), 121.35 (C3′, J Pt-C ) 24.2 Hz),
124.07 (C5′, J Pt-C ) 9.9 Hz), 138.25 (C4′, J Pt-C ) n.r.),
140.21 (C4, J Pt-C ) 90.8 Hz), 141.31 (C3, 1J Pt-C ) 1086
Hz), 150.11 (C6′, J Pt-C ) 7.7 Hz). MS-FAB+ (m/z): 499
[M]+, 484 [M - Me]+, 421 [M - DMSO]+, 405 [M -
DMSO - CH4]+, 390 [M - DMSO - CH4 - Me]+,
375 [M - DMSO - 2Me - CH4]+, 349 [M - DMSO
-C(Me)3 - Me]+.
3
3J Pt-H ) 61.0 Hz), 6.94 (d, 1H, H5, J H-H ) 8.1 Hz,
4J Pt-H ) 16.6 Hz), 6.98-7.11 (m, 3H), 7.34 (m, 1H), 7.48
3
4
(dd, 2H, Ho (Ph), J H-H ) 8.1 Hz, J H-H ) 1.5 Hz,
3J Pt-H ) 66.9 Hz), 7.93 (td, 1H, H4′, J H-H ) 7.6 Hz,
3
4J H-H ) 1.4 Hz), 8.37 (dd, 1H, H3′, J H-H ) 7.6 Hz,
3
4J H-H ) 0.7 Hz), 9.56 (ddd, 1H, H6′, J Pt-H ) 12.6 Hz,
3
3J H-H ) 5.6 Hz,4J H-H ) 1.4 Hz, J H-H ) 0.7 Hz). MS-
5
FAB+ (m/z): 562 [MH]+, 483 [M - DMSO]+, 406 [M -
DMSO - Ph]+, 391 [M - DMSO - Ph - Me]+.
Syn th esis of [P t(P h )(L6)(DMSO)], 6b. Complex 6b
was obtained according to method A (90 °C, 8.5 h), using
[Pt(Ph)2(DMSO)2] instead of [Pt(Me)2(DMSO)2]; pale
yellow, yield 51%; mp 240 °C. Anal. Calcd for C24H22N2-
OPtS: C 49.56, H 3.81, N 4.82. Found: C 49.43, H 3.85,
[P t(Me)(L4)(DMSO)], 4a . Method B (1.5 h), yield
99%; mp 172-174 °C. Anal. Calcd for C22H26N2OPtS:
C 47.05, H 4.67, N 4.99. Found: C 46.72, H 4.39, N 5.38.
1
N 4.72. H NMR (CDCl3): δ 2.98 (s, 6H, Me(DMSO),
3
3J Pt-H ) 17.6 Hz), 6.94 (d, 1H, H4, J H-H ) 7.8 Hz,
2
1H NMR (CDCl3): δ 0.66 (s, 3H, Me-Pt, J Pt-H
)
3J Pt-H ) 62.8 Hz), 7.03-7.47 (m, 8H, aromatics), 7.51
(d, 2H, Ho (Ph-Pt), 3J H-H ) 6.8 Hz, 3J Pt-H 65.0 Hz), 7.98
82.0 Hz), 0.90 (t, 3H, MeCH2, 3J H-H ) 7.3 Hz), 2.08 (m,
1H, CH2), 2.37 (m, 1H, CH2), 3.21 (s, 6H, Me(DMSO),
3J Pt-H ) 18.1 Hz), 3.90 (t, 1H, CH, 3J H-H ) 7.7 Hz), 7.01
3
(t, 1H, H4′, J H-H ) 7.7 Hz), 8.02 (d, 2H, Ho Ph bipy,
3
3J H-H ) 7.8 Hz), 9.63 (d, 1H, H6′, J H-H ) 5.4 Hz,
3
4
3J Pt-H ) 12.7 Hz). MS-FAB+ (m/z): 503 [M - DMSO]+,
426 [M - DMSO - Ph]+.
(d, 1H, H5, J H-H ) 7.8 Hz, J Pt-H ) 18.1 Hz), 7.12-
3
7.37 (m, 6H, aromatics), 7.85 (d, 1H, H4, J H-H ) 7.8
3
3
[P t(Cl)(L3)(DMSO)] (3c) a n d [P t2(µ-Cl)2(L3)2] (3d ).
To a solution of 3a (157.0 mg, 0.315 mmol) in acetone
(20 mL) was added under stirring 3.2 mL of 0.1 M HCl
(0.320 mmol). The color of the solution changed im-
mediately to orange-yellow and a precipitate was formed.
The suspension was stirred for 4 h; after that the
precipitate was filtered and washed with acetone, to give
compound 3d as a yellow solid. The filtered solution was
concentrated to small volume. The precipitate formed
was filtered and washed with H2O, EtOH, and Et2O to
give compound 3c.
Hz, J Pt-H ) 52.9 Hz), 7.92 (td, 1H), H4′, J H-H ) 7.6
4
3
Hz, J H-H ) 1.5 Hz), 8.39 (d, 1H, H3′, J H-H ) 7.6 Hz),
3
3
9.66 (dd, 1H, H6′, J H-H ) 6.6 Hz, J Pt-H ) 13.8 Hz).
[P t(Me)(L5)(DMSO)], 5a . Method B (2.5 h): yield
73%; mp dec 155 °C. Anal. Calcd for C22H26N2OPtS: C
47.05, H 4.67, N 4.99. Found: C 46.55, H, 4.24, N, 5.10.
2
1H NMR (CDCl3): δ 0.66 (s, 3H, Me-Pt, J Pt-H
)
82.0 Hz), 1.77 (s, 6H, (Me)2C), 3.23 (s, 6H, Me(DMSO),
3J Pt-H ) 18.1 Hz), 6.84 (d, 1H, H5, J H-H ) 8.1 Hz,
3
4J Pt-H ) 17.6 Hz), 7.04-7.26 (m, 6H), 7.75 (d, 1H, H4,
3J H-H ) 8.1 Hz, J Pt-H ) 51.8 Hz), 7.83 (td, 1H, H4′,
3
3J H-H ) 7.8 Hz, J H-H ) 1.3 Hz), 8.27 (d, 1H, H3′,
4
3d , [P t2(µ-Cl)2(L3)2]: yield 15%; mp > 260 °C. Anal.
Calcd for C28H30Cl2N4Pt2‚H2O: C 37.32, H 3.55, N 6.22.
Found: C 36.73, H 3.20, N 5.93. IR (Nujol,νmax/cm-1):
3J H-H ) 7.8 Hz), 9.58 (d, 1H, H6′, J H-H ) 6.3 Hz,
3
3J Pt-H ) 13.7 Hz). MS-FAB+ (m/z): 561 [M]+, 546 [M -

4776 Organometallics, Vol. 22, No. 23, 2003
Minghetti et al.
1
330 (s), 347 (s), 371 (s), 393 (s). 1H NMR (CDCl3): δ 1.38
(s, 18H, (Me)3C), 7.06 (d, 2H), ca. 7.3 (2H, partially
hidden by the solvent), 7.58 (d, 2H), 7.91 (t, 2H, H4′),
8.08 (d, 2H), 8.80 (d + d, 2H, H6′). MS-FAB+ (m/z): 884
[M + 2H]+, 848 [MH - Cl]+, 441 [M/2]+, 405 [M/2 -
HCl]+, 390 [M/2 - HCl - Me]+.
3.93, N 4.64. H NMR (CD2Cl2): δ 6.34-8.17 (m, 21H,
aromatics), 8.38 (d, 1H, H6′).
[P t(P h )2(HL8)], 12. Complex 12 was obtained ac-
cording to method B, 30 min, room temperature, yield
95%. Spectroscopic data in agreement with those re-
ported in ref 23.23
[P t(Me)(L3)(CO)], 13. CO (1 atm) was bubbled for 3
h into a solution of 3a (81.9 mg, 0.164 mmol) in CH2Cl2
(15 mL). The solution was concentrated to small volume,
then Et2O was added. The precipitate formed was
filtered, washed with Et2O, and vacuum-dried to give
the analytical sample as a yellow solid. Yield: 75%; mp
160 °C. Anal. Calcd for C16H18N2OPt: C 42.76, H 4.04,
3c, [P t(Cl)(L3)(DMSO)] yield 60%; mp 210 °C. Anal.
Calcd for C16H21ClN2OPtS‚H2O: C 35.72, H 4.31, N
5.21. Found: C 35.47, H 3.99, N 4.95. IR (Nujol,νmax
/
1
cm-1): 276 (s), 316 (m). H NMR (acetone-d6): δ 1.38
3
(s, 9H, (Me)3C), 3.63 (s, 6H, Me(DMSO), J Pt-H ) 24.7
Hz), 7.19 (d, 1H, H5, 4J Pt-H ) 13.2 Hz, 3J H-H ) 8.3 Hz),
7.62 (m, 1H, H5′), 8.22 (td, 1H, H4′), 8.29 (dd, 1H, H3′),
8.53 (d, 1H, H4, 3J Pt-H ) 41.0 Hz, 3J H-H ) 8.3 Hz), 9.57
N 6.23. Found: C 42.69, H 3.70, N 6.04. IR (Nujol,νmax
/
3
3
cm-1): 1159 (w), 1259 (w), 1569 (m), 1608 (m), 2049 (s).
(d, 1H, H6′, J Pt-H ) 35.4 Hz, J H-H ) 5.8 Hz).
[P t(Cl)(L6)(DMSO)], 6c. To a solution of 6a (46.1 mg;
0.089 mmol) in acetone (15 mL) was added, under
vigorous stirring, 0.9 mL of 0.1 M HCl (0.09 mmol). The
color of the solution became immediately orange-yellow
and a precipitate formed. The suspension was stirred
for 6 h and concentrated to small volume. The precipi-
tate was filtered, washed with acetone, and vacuum-
dried to give the analytical sample. Yield 58%; mp 215
°C. Anal. Calcd for C18H17ClN2OPtS: C 40.04, H 3.17,
N 5.19. Found: C 39.86, H 3.12, N 5.27. 1H NMR
1H NMR (CDCl3): δ 1.19 (s, 3H, Me-Pt, J Pt-H ) 86.2
2
3
Hz), 1.38 (s, 9H, (Me)3C), 7.29 (d, 1H, H5, J H-H ) 7.8
Hz (partially overlapping)), 7.31 (m, 1H, H5′, (partially
3
overlapping)), 7.96 (d, 1H, H4, J Pt-H ) 45.9 Hz,
3J H-H ) 7.8 Hz), 8.00 (td, 1H, H4′, J H-H ) 7.8 Hz,
3
4J H-H ) 1.6 Hz), 8.39 (ddd, 1H, H3′, J H-H ) 8.0 Hz),
3
8.61 (ddd, 1H, H6′, 3J H-H ) 5.4 Hz, 3J Pt-H ) 19 Hz). MS-
FAB+ (m/z): 450 [MH]+, 434 [M - Me]+, 421 [M - CO],
405 [M - H - Me - CO]+, 391 [M - 2Me - CO]+.
[P t(Me)(L3)(3,5-(Me)2p y)], 14. To a solution of 3a
(70.6 mg; 0.141 mmol) in CH2Cl2 (15 mL) was added,
under vigorous stirring, 93.9 mg (0.876 mmol) of 3,5-
(Me)2py. The solution was stirred for 3.5 h, then con-
centrated to small volume and treated with hexane. The
precipitate formed was filtered, washed with hexane,
and vacuum-dried to give the analytical sample as a
yellow solid. Yield: 50%. Anal. Calcd for C22H27N3Pt: C
49.99, H 5.15, N 7.95. Found: C 49.60, H 4.82, N 7.66.
3
(CDCl3): δ 3.67 (s, 6H, Me(DMSO), J Pt-H ) 24.2 Hz),
3
7.38-7.51 (m, 4H, aromatics), 7.55 (d, 1H, H5, J H-H
)
8.3 Hz, 4J Pt-H ) 13.0 Hz), 8.01 (dt, 1H, H4′, 3J H-H ) 7.7
4
Hz, J H-H ) 1.5 Hz), 8.10 (d, 2H, Ho Ph), 8.39 (d, 1H,
3
3
H3′, J H-H ) 7.2 Hz), 8.64 (d, 1H, H4, J H-H ) 8.3 Hz,
3J Pt-H ) 42.0 Hz), 9.59 (ddd, 1H, H6′, J H-H ) 5.8
3
Hz,3J Pt-H ) 31.1 Hz).
[P t(Me)2(HL7)], 7. Method B: yield 90%; mp 152-
154 °C. Anal. Calcd for C13H16N2Pt: C 39.49, H 4.08, N
7.09. Found: C 39.13, H 4.34, N 6.77. 1H NMR
(CDCl3): δ 2.89 (s, 3H, bipy-Me), 0.94 (s, 3H, Pt-Me,
2J Pt-H ) ca. 85 Hz), 0.95 (s, 3H, Pt-CH3, 2J Pt-H ) ca. 85
Hz), 7.63 (m, 1H), 8.09 (d, 1H), 8.22-8.36 (m, 3H),
1H NMR (CDCl3): δ 0.93 (s, 3H, Me-Pt, J Pt-H ) 84.0
2
Hz), 1.37 (s, 9H, (Me)3C), 2.38 (s, 6H, Me (lutidine)), 7.08
(m, 1H, H5′), 7.13 (d, 1H, H5, 3J Pt-H ) 11.4 Hz, 3J H-H
)
8.0 Hz), 7.48 (s, 1H, H4 (lutidine)), 7.72 (d, 1H, H6′), 7.84
(td, 1H, H4′), 7.96 (d, 1H, H4, 3J Pt-H ) 54.6 Hz, 3J H-H
)
3
8.98 (s (br), 1H, H6, J Pt-H ) 21 Hz), 9.20 (dd, 1H, H6′,
8.0 Hz), 8.32 (d, 1H, H3′), 8.51 (s, 2H, H2(lutidine)
3J Pt-H ) 22 Hz).
3J Pt-H ) 21 Hz).
[P t(Me)2(HL8)], 8. Method B: 30 min, room temper-
ature, yield 92%. Spectroscopic data in agreement with
those reported in ref 22.22
[P t(Me)(L6)(P P h 3)], 15. To a solution of 6a (55.2 mg,
0.106 mmol) in CH2Cl2 (15 mL) was added, under
vigorous stirring, 28.6 mg of PPh3 (0.109 mmol). The
solution was stirred for 4 h, then concentrated to small
volume and treated with hexane. The precipitate formed
was filtered, washed with hexane, and vacuum-dried to
give the analytical sample as a pale yellow solid. Yield:
76%; mp 245 °C. Anal. Calcd for C35H29N2PPt‚0.5
CH2Cl2: C 57.15, H 4.05, N 3.75. Found: C 56.85, H
3.84, N 3.96. IR (Nujol,νmax/cm-1): 654 (s),774 (s), 1097
(s), 1569 (m), 1604 (m). 1H NMR (CDCl3): δ 0.79 (d, 3H,
[P t Cl2 (HL1)], 9. Complex 9 was obtained according
to method B (30 h) using [PtCl2(DMSO)2] instead of
[Pt(Me)2(DMSO)2]. Yield: 89%, mp: on heating a change
of color from yellow to brick red occurs at 230-232 °C;
no further decomposition up to 270 °C. Anal. Calcd for
C11H10Cl2N2Pt: C 30.29, H 2.31, N 6.42. Found: C 30.15,
1
H 2.39, N 6.20. H NMR (CDCl3): δ 3.18 (s, 3H, Me),
7.40 (dd, 1H), 7.48 (m, 1H), 7.91-7.99 (m, 3H), 8.13 (td,
3
1H), 9.69 (d, 1H, J Pt-H ) ca. 33 Hz).
Me-Pt, 2J Pt-H ) 83.0 Hz, 3J P-H ) 7.7 Hz), 6.68 (m, 1H),
3
[P tCl(Me)(HL1)], 10. Complex 10 was obtained ac-
cording to method B (30 h) using trans-[PtCl(Me)-
(DMSO)2] instead of [Pt(Me)2(DMSO)2]. Spectroscopic
and analytical data in agreement with those reported
in ref 6.
7.35-7.80 (m, 21H, aromatics), 8.15 (d, 2H, J H-H
)
)
)
)
3
4
7.6 Hz), 8.31 (dd, 1H, H4, J H-H ) 8.1 Hz, J P-H
3
3
5.1 Hz, J Pt-H ) 46.5 Hz), 8.53 (dd, 1H, H3′, J H-H
7.8 Hz). 31P{1H} NMR (CDCl3): δ 33.01 (s, J P-Pt
1
2233 Hz).
[P t(P h )2(HL6)], 11. Complex 11 was obtained ac-
cording to method B (2.5 h, at room temperature) using
[Pt(Ph)2(DMSO)2] instead of [Pt(Me)2(DMSO)2]. Yield:
90%; mp 180 °C (dec). Anal. Calcd for C28H22N2Pt‚
0.5DMSO: C 56.12, H 4.06, N 4.51. Found: C 56.10, H
NMR F ollow -Up Exp er im en ts. The rollover meta-
lation was monitored by 1H NMR spectroscopy. In a
typical experiment 10.0 mg of [Pt(Me)2(DMSO)2] and an
equimolar amount of HLn (n ) 1, 3) were dissolved in
1.0 mL of acetone-d6. The solution was rapidly mixed,
(22) Monaghan, P. K.; Puddephatt, R. J . Organometallics 1984, 3,
444-449.
(23) Rashidi, M.; Fakhroeian, Z.; Puddephatt, R. J . J . Organomet.
Chem. 1990, 406, 261-267.

N′,C(3)-“Rollover” Cyclometalation
Organometallics, Vol. 22, No. 23, 2003 4777
1
2
and H NMR spectra were recorded at regular intervals
[Pt(Me)2(HL1)]: 1H NMR δ 1.02 (s, Pt-Me, J Pt-H
)
until completion of the reaction at room temperature
(18.5 °C, HL1 and HL2) and at -60 °C (HL2). Selected
peaks (e.g., H(6′) or Pt-Me) were integrated, and the
values obtained were reported versus time.
The study was repeated with a large excess of ligand
in the case of HL1 (>10:1), and ln[Pt(Me)2(DMSO)2] was
plotted versus time, showing a pseudo-first-order rate.
In solution the presence of the starting reactants
([Pt(Me)2(DMSO)2] and HLn), the reaction products (the
rollover species [Pt(Me)(Ln)(DMSO)], free DMSO, and
methane (δ ) 0.16 ppm)), and a reaction intermediate,
formulated as the adduct species [Pt(Me)2(HLn)], was
observed.
89 Hz), 1.03 (s, Pt-Me, 2J (Pt-H) ) 87 Hz), 2.83 (s, Me),
8.06-8.29 (m, 4H, H3, H3′, H4, H4′), 7.56-7.63 (m, 2H,
3
H5, H5′), 9.11 (d, H6′, J (Pt-H) ) 23 Hz).
[Pt(Me)2(HL2)]: 1H NMR δ ca. 1.0 (m (signals overlap-
ping), Pt-Me, C(Me)3), 3.41 (s, CH2), 8.10-8.35 (m, 4H,
H3, H3′, H4, H4′), 7.56-7.63 (m, 2H, H5, H5′), 9.07 (d, H6′,
3J Pt-H ) 23 Hz).
Ack n ow led gm en t. Financial support from Univer-
sita` di Sassari is gratefully acknowledged. We thank one
of the reviewers for helpful suggestions.
OM0301583