Platinum(II), palladium(II) and gold(III) adducts and cyclometalated derivatives of 6-methoxy-2,2′-bipyridine: A comparative study

Article abstract of DOI:10.1016/j.jorganchem.2016.06.023

Reaction of 6-methoxy-2,2′-bipyridine (bpy^6OMe) with the electron-rich platinum(II) complex [Pt(Me)₂(DMSO)₂] gave the rollover cyclometalated complex [Pt(κ²-N,C-bpy^6OMe-H) (Me) (DMSO)] under mild conditions. The occurrence of rollover cyclometalation was demonstrated by single crystal X-ray diffraction structure determination. In contrast, reaction of bpy^6OMewith [Pt(Ph)₂(DMSO)₂] and [Pt(Cl)₂(DMSO)₂] under mild conditions gave only adduct species of the type [Pt(X)₂(bpy^6OMe)] (X = Ph, Cl). Under harsher conditions, activation of a C-H bond in the methoxy substituent yielded the terdentate cyclometalated complex [Pt (κ³-N,N,C-bpy^6OMe-H)Cl]. Finally, reaction of Pd(II) and Au(III) derivatives invariably gave adduct species, with the exception of the dimeric complex [Pd(κ²-N,C-bpy^6OMe-H) (OAc)]₂, which, however, was not isolated in pure form. The reactivity of bpy^6OMe, as emerged from this study, was compared with that of the corresponding disubstituted ligand 6,6′-dimethoxy-2,2′-bipyridine, previously studied by us.

Full text of DOI:10.1016/j.jorganchem.2016.06.023

Accepted Manuscript
Platinum(II), palladium(II) and gold(III) adducts and cyclometalated derivatives of 6-
methoxy-2,2′-bipyridine: A comparative study
Luca Maidich, Maria Agostina Cinellu, Fabio Cocco, Sergio Stoccoro, Mondina
Sedda, Simona Galli, Antonio Zucca
PII:
S0022-328X(16)30273-X
10.1016/j.jorganchem.2016.06.023
JOM 19540
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 9 March 2016
Revised Date: 5 June 2016
Accepted Date: 17 June 2016
Please cite this article as: L. Maidich, M.A. Cinellu, F. Cocco, S. Stoccoro, M. Sedda, S. Galli,
A. Zucca, Platinum(II), palladium(II) and gold(III) adducts and cyclometalated derivatives of 6-
methoxy-2,2′-bipyridine: A comparative study, Journal of Organometallic Chemistry (2016), doi: 10.1016/
j.jorganchem.2016.06.023.
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ACCEPTED MANUSCRIPT
Graphical Abstract
Rollover cyclometalation of 6-methoxy-2,2′-bipyridine
Luca Maidich, Maria Agostina Cinellu, Fabio Cocco, Sergio Stoccoro, Mondina Sedda, Simona
Galli and Antonio Zucca
Reaction of 6-methoxy-2,2′-bipyridine (bpy6OMe) with the electron-rich complex
[Pt(Me)
2
(DMSO)
] gave the rollover cyclometalated complex [Pt(bpy6OMe-H)(Me)(DMSO)]
2
under mild conditions. In contrast, electron poor Pt(II) complexes gave adduct species or
terdentate N,N,C complexes. Finally, Pd(II) and Au(III) derivatives gave adduct species in most
of the conditions studied.

ACCEPTED MANUSCRIPT
Platinum(II), palladium(II) and gold(III) adducts and cyclometalated
derivatives of 6-methoxy-2,2′-bipyridine: a comparative study
a
a,b
c
a,b
a
Luca Maidich, Maria Agostina Cinellu, Fabio Cocco, Sergio Stoccoro, Mondina Sedda,
d
a,b,
Simona Galli and Antonio Zucca
*
a) Dipartimento di Chimica e Farmacia, Università degli Studi di Sassari, Via Vienna 2, 07100
Sassari, Italy
b) Consorzio Interuniversitario Reattività Chimica e Catalisi (CIRCC), Italy
c) Dipartimento di Scienze Chirurgiche, Microchirurgiche e Mediche, Università degli Studi di
Sassari, Viale San Pietro 43/C, 07100 Sassari, Italy
d) Dipartimento di Scienza e Alta Tecnologia, Università dell′Insubria, via Valleggio 11, 22100
Como, Italy
Abstract
6
OMe
Reaction of 6-methoxy-2,2′-bipyridine (bpy
) with the electron-rich platinum(II) complex
2
6OMe
[
Pt(Me) (DMSO) ] gave the rollover cyclometalated complex [Pt(κ -N,C-bpy
-
2
2
H)(Me)(DMSO)] under mild conditions. The occurrence of rollover cyclometalation was
demonstrated by single crystal X-ray diffraction structure determination In contrast, reaction
with [Pt(Ph) (DMSO) ] and [Pt(Cl) (DMSO) ] under mild conditions gave only
.
6
OMe
of bpy
2
2
2
2
6
OMe
adduct species of the type [Pt(X) (bpy
)] (X = Ph, Cl). Under harsher conditions, activation
2
of a C-H bond in the methoxy substituent yielded the terdentate cyclometalated complex [Pt
3
6OMe
(
κ -N,N,C-bpy
-H)Cl]. Finally, reaction of Pd(II) and Au(III) derivatives invariably gave
2
6OMe
adduct species, with the exception of the dimeric complex [Pd(κ -N,C-bpy
-H)(OAc)]2,
6
OMe
which, however, was not isolated in pure form. The reactivity of bpy
, as emerged from
this study, was compared with that of the corresponding disubstituted ligand 6,6’-
dimethoxy-2,2′-bipyridine, previously studied by us.
Introduction
Cyclometalated compounds constitute one of the most important classes of organometallic
1
complexes. Their intrinsic stability, due to the chelated organometallic ligand, is at the basis
of their rich range of applications in traditional domains, such as catalysis, organic synthesis,
and C-H bond activation, as well as in advanced materials (e.g. anticancer agents, sensors,
1
,2
photophysiscal devices, switches, etc.)
1

ACCEPTED MANUSCRIPT
3
Unconventional cyclometalation reactions constitute interesting special cases, among which
4
the so-called “rollover cyclometalation” is attracting a growing interest; this behaviour is
shown by, but not limited to, bidentate heteroaromatic ligands able to undergo internal
rotation and activation of C-H bonds in remote positions. This reactivity, initially considered
rare, is receiving a remarkable attention due to applications in catalysis (with different
5
6
7
8
processes promoted by Pd(II), Rh(III), and Ru(II) ), organic synthesis, and as advanced
9
10
11
materials (e.g. chemosensors and chiroptical switches ) and anticancer agents. In
1
2
addition, a series of studies in the gas phase has envisaged further potential applications.
In recent years, we have directed our attention to rollover cyclometalation, investigating and
1
3
rationalizing the behaviour of a series of ligands and of the resulting complexes.
The peculiarity of rollover cyclometalated complexes is given by the presence of an
uncoordinated donor atom, usually a nitrogen atom, able to provide additional properties to
the complex. For example, protonation of the uncoordinated nitrogen atom affords
1
4
mesoionic species, also classified as abnormal-remote pyridylenes, allowing rollover
cyclometalated complexes to belong to the so-called “compounds with multiple
4
b,13c-d,15
personalities” class.
Most of the studies in rollover cyclometalation have been devoted to 2,2’-bipyridines, the
reactivity of which has shown to be strongly dependent on the nature of their substituents.
In the case of platinum(II), it has been postulated a nucleophilic behaviour of the metal
4
c, 16
centre in the cyclometalation process,
which is highly accelerated by electron-
1
7
withdrawing substituents on the ligand (e.g. CF ). Steric hindrance also plays a non
3
negligible role in the regioselectivity of the process: bulky substituents (e.g. t-butyl groups)
4
c
in position 6, i.e. α to a nitrogen atom, accelerate the process. The steric factor dominates
4
c
over the electronic one for electron releasing substituents such as CH3.
2

ACCEPTED MANUSCRIPT
The complex interplay of electronic and steric factors in the reactivity of platinum rollover
complexes is well exemplified by two processes involving the oxidative addition of Pt(II)
phosphane complexes of the kind [Pt(N,C)(Me)(PR )] (N,C = cyclometalated bipyridine, PR =
3
3
8
b, 18
PPh , PMe , PCy , etc.). The reaction with MeI showed to be dominated by steric factors,
3
3
3
whereas the “retrorollover process” (protonation of the uncoordinated nitrogen atom
1
3c
followed by H transfer to Pt and Pt-C bond rupture) is governed by electronic factors.
1
9
We have recently reported on the behaviour of 6,6’-dimethoxy-2,2’-bipyridine, the
reactivity of which is particularly rich, due to the presence of two methoxy substituents. In
particular, we were able to synthesize and isolate in the solid state the first rollover complex
2
0
of gold, and rollover cyclometalation was achieved for the first time with an electron poor
Pt(II) complex, [PtCl (DMSO) ]. In addition, regioselectivity could be controlled in order to
2
2
3
give terdentate N,N,C complexes through C(sp )-H bond activation of the methoxy
19
substituent.
With the aim of getting further insights into the influence of electronic and steric factors,
both in the rollover process and in the behaviour of the resulting rollover complexes, we
have decided to extend the study to 6-methoxy-2,2’-bipyridine, taking advantage of the
ambivalent nature of the methoxy group, being electron withdrawing by inductive effect (-I),
2
1
but electron releasing by mesomeric effect (+M).
Results and discussion
6
OMe
The ligand 6-methoxy-2,2′-bipyridine, bpy
, was synthesized through a Suzuki-Miyaura
reaction by coupling of 2-bromo-6-methoxypyridine with 2-pyridineboronic acid N-
2
2
phenyldiethanolamine ester in the presence of [Pd(PPh ) ] as catalyst.
3
4
21
As anticipated above, the OMe substituent has opposite inductive and mesomeric effects.
As a consequence, its influence on the coordinating behaviour of the closest nitrogen atom
and C-H bond activation in the pyridine ring might not be trivial.
In order to evaluate the electronic influence of the substituent on a 2,2’-bipyridine-type
ligand, we searched for literature data regarding monosubstituted pyridines. Proton affinity
and basicity data in the gas phase, as well as pKa values of the pyridinium ions are reported
in Table S1 of the supporting information. These data show that CH and CF have, as
3
3
expected, clear electron-donating and -withdrawing effects, respectively. The pKa values for
-, 3- and 4-methoxypyridinium are 3.28, 4.88 and 6.62, indicating that 2-methoxypyridine is
2
3

ACCEPTED MANUSCRIPT
significantly less basic than pyridine (pKa around 5.2), due to inductive effect, whereas 4-
methoxypyridine is more basic, likely due to mesomeric effect.
These data suggest that, in 6-methoxy-2,2’-bipyridine, the nitrogen atom of the substituted
ring should be a weak donor compared to 2,2’-bipyridine. In contrast, the position para to
3
the substituent, i.e. the C -H position, should have a higher electron density than in
unsubstituted bipyridine, a factor which should contrast rollover C-H bond activation in the
case of nucleophilic attack of the metal centre to the C-H bond.
Another factor to be considered is the value of ζ-angle, a useful parameter recently
1
7
developed by us, which accounts for the bulkiness of the substituted bipyridine ligand. In
fact, the value of 152.3 for the angle ζ for 6-methoxy-2,2’-bipyridine is somewhat
remarkable being only a few degrees below that for t-Bu (157.1) and almost 15 degrees
above that for CF , which showed to undergo rollover cyclometalation very easily. However,
3
it has to be noted that the reported value corresponds to the maximum hindrance of the
methoxy group; when the latter points away from the nitrogen atom, the ζ-angle is 109.3°,
i.e. still greater than the values for H (98.8°) and F (107.3°).
6
OMe
In order to investigate the organometallic reactivity of 6-methoxy-2,2’-bipyridine, bpy
,
8
we have chosen the d metal ions Pt(II), Pd(II) and Au(III), i.e. the only metal ions known to
1
9,20
be able to give rollover cyclometalation with 6,6’-dimethoxy-2.2’-bipyridine.
6
OMe
Reaction of bpy
with Pt(II) complexes gave different results depending on the electronic
properties of the starting complex (see Scheme 1).
4

ACCEPTED MANUSCRIPT
Scheme 1. Syntheses of the platinum(II) complexes reported in the present work
Methyl platinum(II) complexes experience facile cyclometallation reactions and their
2
3
behaviour has been extensively studied.
6
OMe
Reaction of the electron-rich complex [Pt(Me) (DMSO) ] with bpy
easily gives rollover C-
2
2
H bond activation even at room temperature, to yield the cyclometalated complex
6
OMe
[
Pt(bpy
-H)(Me)(DMSO)], 1. The reaction was followed in (CD ) CO at room temperature
3 2
1
by H NMR spectroscopy showing, in parallel to the formation of 1, the appearance of a
signal at 0.20 ppm due to free methane, confirming metalation. Only starting compounds
6
OMe
(
[Pt(Me) (DMSO) ] and bpy
) and reaction products (1 and methane) were detected in
2
2
1
2
solution: no intermediate species, such as the κ -N or κ -N,N adducts
6
OMe
6OMe
1
(
[Pt(Me) (bpy
)(DMSO)] or [Pt(Me) (bpy
)], respectively) were observed by H NMR,
, the cyclometalation process is extremely fast
even at room temperature. It follows that, in these conditions, the kinetic limiting step of the
2
2
6
OMe
indicating that, after coordination of bpy
6
OMe
reaction is the substitution of DMSO by bpy
, to give an adduct that was not detected in
solution due to its rapid conversion into the cyclometalated complex 1.
The influence of the methoxy substituent on the reaction rate is noteworthy, as 6-alkyl or
aryl-substituted 2,2’-bipyridines usually give the [Pt(N,N)(Me) ] adduct as intermediate,
2
4
c
easily detectable species.
Operating in acetone at 40 °C helps in completing the cyclometalation in 2 h. In this respect,
it is worth to remind that the analogous reaction with the unsubstituted 2,2’-bipyridine
4
d
occurs only in refluxing toluene with prolonged reaction times.
5

ACCEPTED MANUSCRIPT
Complex 1 was isolated in the solid state in high yields (ca. 80%) and thoroughly
1
13
1
1
1
13
characterised in solution by means of NMR spectroscopy ( H, C, H- H COSY, H- C HSQC
1
1
24
1
13
and H- H NOESY). All H and C signals were assigned.
1
In particular, in the aromatic region, the H NMR spectrum shows only 6 resonances, due to
3
4
5
the absence of the H proton and the presence of an AX system given by H and H , both
1
95
6’
coupled to Pt. In addition, the H proton is strongly deshielded and coupled to platinum,
3
indicating coordination of the external nitrogen atom (δ = 9.65 ppm, J
= 15 Hz).
Pt-H
2
Coordination of Me and DMSO is also confirmed: δCH3= 0.69 ppm, J = 82.0 Hz; δDMSO
=
Pt-H
3
3
.24 ppm, J = 18.2 Hz.
Pt-H
1
3
195
1
In the C NMR spectrum, a singlet at 136.76 ppm, strongly coupled to Pt ( J = 1092 Hz)
Pt-C
3
and attributable to the C carbon atom, proved metalation. In addition, two singlets with
1
2
satellites at δ = -14.08 ( J = 761 Hz) and 43.47 ppm ( J = 43 Hz) were assigned to the
Pt-C
Pt-C
coordinated methyl and DMSO, respectively.
1
1
The H- H NOESY spectrum highlighted the following through-space interactions: 0.69 ppm
4
6’
(
Pt-CH ) with 7.89 (H ) and 3.24 ppm (DMSO); 3.24 ppm (DMSO) with 9.65 (H , very weak,
3
6’
likely suggesting an H -O interaction, which stabilizes a conformation with the DMSO methyl
groups close in space to the coordinated CH ) and 0.69 ppm (Pt-CH ); 3.99 ppm (OCH ) with
3
3
3
5
3’
1
1
6
.71 (H ) and 8.21 ppm (H ) (sections of the H- H NOESY spectrum are reported in the
Supplementary Information, Figure S1).
1
6

ACCEPTED MANUSCRIPT
In the solid state, the molecular structure of complex 1 was confirmed by single crystal X-ray
diffraction. 1 crystallizes in the triclinic space group P-1. The asymmetric unit is composed by
2
6OMe
two [Pt(κ -N,C-bpy
-H)(Me)(DMSO)] complexes lying in general positions. Selected bond
distances and angles for both complexes are gathered in Table S2 of the Supplementary
Information. The determination of the crystal structure confirmed the molecular features
suggested by solution NMR spectroscopy. As a matter of fact, both independent Pt(II) ions
possess a square planar stereochemistry of the kind cis-PtC NS, defined by the carbon atom
2
6
OMe
of one methyl group, the sulphur atom of one DMSO molecule and a C,N-chelating bpy
-
H ligand, which underwent cyclometalation. As expected on the basis of the so called trans-
6
OMe
influence rules, the nitrogen atom of bpy
-H and the sulphur atom of DMSO are trans to
3
the methyl group and to the coordinating carbon atom (C ) of the ligand, respectively.
Focusing the attention on the metallacycles, it is worth noting that, in both complexes, the
bond distances not involving the metal ion can be assimilated to those typical of a double
1
’
2’
2
3
2’
2
bond (N -C and C -C ) separated by that typical of a single bond (C -C ), this suggesting a
weak metalloaromaticity. Both complexes show only a slight deviation from planarity: the
angles between the root mean square (r.m.s.) plane describing the metallacycle and that
containing the Pt(CH )S fragment are lower than 9°; the angles between the r.m.s. plane
3
describing the ligand and that describing the coordination sphere of the metal centre are
less than 7°. The complexes pack, staggered, as dimers, along two different directions
(approximately [011] and [0-12]): no Pt-Pt interactions can be invoked.
7

ACCEPTED MANUSCRIPT
C2 C2’
1
N ’
Pt1
C3
CH3
S1
2
6OMe
Fig 1. Ortep representation of the molecular structure in [Pt(κ -N,C-bpy
-H)(Me)(DMSO)],
1
, at the 30% probability level (one of the two independent complexes has been arbitrarily
chosen). Colour code: carbon, grey; hydrogen, light grey; nitrogen, blue; oxygen, red;
1
3
platinum, fuchsia; sulphur, yellow. Selected bond distances (Å) and angles (°): Pt -C , 2.01(1);
1
1
1’
1
1
2
2’
2
3
2’ 1’
Pt -CH , 2.06(1); Pt -N , 2.125(8); Pt -S , 2.270(3); C -C , 1.46(2); C -C , 1.39(1); C -N ,
3
1
A
3A
1A
1A 1A’
1A 1A
2A 2A’
1
1
1
.35(1); Pt -C , 2.00(1); Pt -CH , 2.047(12); Pt -N , 2.13(1); Pt -S , 2.268(3); C -C ,
3
2
A
3A
2A’ 1A’
3
1
3
1
1’
1
1’
.46(2); C -C , 1.39(1); C -N , 1.35(1); C -Pt -CH , 91.4(5); C -Pt -N , 79.5(4); H C-Pt -N ,
3
3
3
1
1
1
1
1’
1
1
3A
1A
3A
69.8(4); C -Pt -S , 172.3(3); H C-Pt -S , 89.8(4); N -Pt -S , 99.8(2); C -Pt -CH , 90.6(5); C -
3
3
1
A
1A’
1A 1A’
3A
1A 1A
1A 1A
1A’
Pt -N , 79.6(4); H C-Pt -N , 170.1(4); C -Pt -S , 174.5(3); H C-Pt -S , 89.4(4); N -
3
3
1
A
1A
Pt -S , 100.5(3).
6
OMe
In contrast to the “Pt(Me )” analogue, reaction of [Pt(Ph) (DMSO) ] with bpy
does not
2
2
2
give cyclometalation, at least under the reaction conditions adopted. In acetone, only the
6
OMe
adduct [Pt(Ph) (bpy
)], 2, was obtained, which was characterized in solution by mono-
2
1
1
1
1
1
and bi-dimensional NMR experiments ( H NMR, H- H COSY, H- H NOESY). Cyclometalation
does not take place even in refluxing acetone.
8

ACCEPTED MANUSCRIPT
6
’
3
In particular, the H proton of 2 is downfield shifted (δ = 8.43 ppm, J = 21 Hz), likely due
Pt-H
1
95
1
to the shielding effect of the adjacent phenyl ring. The Pt- H coupling constant is in line
2
with a N-Pt-C(sp ) trans arrangement. The methoxy protons appear strongly shielded with
respect to the free ligand and complex 1 (3.28 vs 4.40 and 3.99 ppm, respectively), likely due
to the presence of one coordinated phenyl ligand in cis position.
1
1
The H- H NOESY spectrum shows correlations between the methyl group at 3.28 ppm and
1
95
the ortho hydrogens on the phenyl ring in cis position, which are coupled to Pt (δ = 7.44
3
6’
ppm, J = 72 Hz). The H proton (δ = 8.43 ppm) shows contacts with the ortho hydrogens
Pt-H
3
of the other phenyl ring (δ = 7.50 ppm, J = 79 Hz). These data confirm the chelating
Pt-H
coordination mode of bipyridine and the presence of two phenyl ligands. It is also interesting
0
to note that the ortho hydrogens (H ) of the two phenyl rings show different Pt-H coupling
3
1
constant values. The largest value ( J
= 79 Hz vs. 72 Hz) corresponds to N of the
Pt-H
substituted pyridine ring, suggesting a minor trans influence of this nitrogen atom, as a
consequence of its poorer donor ability due to the electron-withdrawing effect of the OMe
substituent. In addition to electronic factors, it should be noted that also the steric
1
hindrance of the methoxy group can play a non negligible role, elongating the Pt-N bond.
(
only one ortho hydrogen per phenyl ring is indicated for clarity)
6
OMe
The reaction of the electron poorer complex [PtCl (DMSO) ] with bpy
(acetone, rt, 3 h) is
2
2
6
OMe
1
very slow and affords the adduct [PtCl (bpy
)], 3, the H NMR spectrum of which shows,
2
6
’
inter alia, the H proton strongly deshielded, at 9.81 ppm, as expected due to the proximity
195
1
3
of the Cl ligand, with a Pt- H coupling constant ( J =39 Hz) in line with a nitrogen atom
Pt-H
coordinated in trans to Cl.
9

ACCEPTED MANUSCRIPT
At higher temperature and for longer reaction times (acetone 50 °C, 24 h), complex 3
remains the principal reaction product, even if, under prolonged reaction times (several
days), a second unidentified species appears in solution.
Under different experimental conditions (acetic acid, 100 °C, 7 d), reaction of [PtCl (DMSO) ]
2
2
6
OMe
with bpy
gives a different product, which was identified as the cyclometalated complex
3
6OMe
[
Pt(κ -N,N,C-bpy
-H)Cl], 4, resulting from activation of a C-H bond in the methoxy
1
substituent. H NMR data indicate a terdentate coordination of the bipyridine ligand, with an
N,N,C sequence of donor atoms: the absence of the methyl signals and the presence of a
1
95
2
singlet with satellites at 7.00 ppm, integrating 2 H and coupled with Pt ( J = 77 Hz), are
Pt-H
in agreement with this formulation, and are in line with those reported for the analogous
1
9
terdentate complex isolated with the 6,6’-dimethoxybipyridine ligand.
3
6’
4
The signals at 9.11 ppm (d with sat, J ca. 12 Hz, H ) and 7.44 ppm (d with sat, J = 11
Pt-H
Pt-H
5
Hz, H ) also support this formulation.
These results show that the cyclometalation reaction follows different paths depending on
the electronic properties of the platinum(II) precursor and also on the reaction conditions.
Rollover cyclometallation usually demands an electron-rich Pt(II) complex such as
[
Pt(Me) (DMSO) ]. The electron poorer complex [PtCl (DMSO) ] follows a different reaction
2 2 2 2
pathway, involving the activation of the methyl group. It is likely that different reaction
mechanisms are operating in the two cases.
6
OMe
For example, in the intermediate species, i.e. the adducts [Pt(bpy
)(Me) ] and
2
6
OMe
[
Pt(bpy
)Cl ], the lability of the Pt-N bonds may be very different, due to the different
2
trans effect of the CH and Cl ligands. In the first one the nitrogen atom of the substituted
3
pyridine may easily detach from the metal ion (both for electronc and steric factors)
6
OMe
facilitating the rollover process. However, this does not explain why the [Pt(bpy
)(Ph)2]
adduct does not give rollover metalation, showing to be very stable in solution (on the
6
OMe
contrary [Pt(bpy
)(Me) ] was not even detected in solution). In the case of [Pt(N,N)(Ph) ]
2 2
the last part of the reaction, which is likely an oxidative-addition/reductive-elimination
process, probably plays a fundamental role. It must be reminded, in addition, that the
analogous di-substituted ligand 6,6’-dimethoxy-2,2’-bipyridine gave rollover metalation (for
19
25
the first and only time) with [PtCl (DMSO) ], showing, once again, that the course of
2
2
intramolecular C-H bond activation is in large part unpredictable.
The DMSO ligand in complex 1 can be easily displaced at room temperature by good donors
6
OMe
such as triphenylphosphine to give the corresponding complex [Pt(bpy
-H)(Me)(PPh )], 5.
3
1
0

ACCEPTED MANUSCRIPT
OMe
OMe
N
4'
3'
N
acetone
5
'
5
PPh3
+
N
R.T.
N
4
6
'
Pt
Pt
DMSO
CH3
Ph P
CH3
3
1
5
31
Among the spectroscopic data supporting this formulation, the P NMR signal at 32.59 ppm,
1
with J = 2257 Hz, is fully consistent with a C-Pt-P trans arrangement. In the comparison
Pt-P
4
d
8b
with the corresponding complexes derived from 2,2’-bipyridine, 6-Me-2,2’-bipyridine,
1
7
and 6-CF -2,2’-bipyridine (complexes 6, 7 and 8, Scheme 2), although the differences are
3
not dramatic some trends can still be seen:
3
1
P NMR data for 6, 7 and 8 show only a slight chemical shift trend in line with the inductive
properties of the substituent on the bipyridine ligand: with respect to 6 and 7, R = H and CH3,
the P atom is slightly shielded with the electron attracting group CF . A second trend is given
3
3
1
195
1
by the P- Pt coupling constants: J = 2226 (7, R = CH ), 2229 (6, R = H), 2279 Hz (8, R
Pt-P
3
=
CF ). A similar trend was reported for Pt(II)-phosphane complexes with 4-substituted
3
2
6
pyridines. It was observed that substituents with high electronegativity on the pyridine ring
decrease the electron donation of the nitrogen atom coordinated to the metal ion and,
consequently, the platinum 6s orbital is more available for the platinum-phosphorus bond.
1
Stronger Pt-P bonds result in greater Pt-P coupling constants. In agreement with this, JPt-P
1
1

ACCEPTED MANUSCRIPT
values are greater for CF -substituted bipyridines (complex 8) and smaller for CH -
3
3
31
substituted ones (complex 7). The P NMR data for complexes 5 and 8 are comparable
(Scheme 2); this seems to indicate that, overall, the electron-attracting effect is the
predominant one for the methoxy substituent, as it is in the case of CF3.
1
In addition, the H NMR spectrum of 5 shows a doublet with satellites for the coordinated
2
3
methyl group; the values, δ = 0.73 ppm, J = 82.8 Hz and J = 7.8 Hz, are in agreement
Pt-H
P-H
4
d,17
1
with the proposed formulation.
In the case of the H NMR spectra, no meaningful
correlations were found for the Pt-CH protons in complexes 5-8, as the differences are very
3
small.
The electron rich complex 5 easily gives oxidative addition with CH I at room
3
6
OMe
temperature, affording the Pt(IV) complex [Pt(bpy
-H)(Me) I(PPh )], 9.
2 3
9
Reaction of cyclometalated Pt(II) complexes with MeI may result in the formation of
1
8
different isomers, depending on electronic and steric factors.
In this case, only one Pt(IV) species was observed in solution and isolated in the solid state:
all the spectroscopic data indicate the isomer with the PPh and one CH ligand in “axial”
3
3
3
1
position with respect to the cyclometalated plane. The P NMR spectrum shows a singlet
1
with satellites at δ = -10.84 ppm with J = 959 Hz.
Pt-P
1
The H NMR spectrum shows two doublets with satellites ascribable to the two methyl
3
2
groups: the resonance at 1.23 ppm ( J = 7.6 Hz, J = 60 Hz) is assigned to the one in axial
P-H
Pt-H
3
2
position, whereas the resonance at 1.67 ppm ( J = 8.0 Hz, J = 71 Hz) is assigned to the
P-H
Pt-H
8
b
6’
one trans to nitrogen in the plane of the cyclometalated bipyridine. The H proton is
strongly deshielded (δ = 9.59 ppm), as it is affected by the presence of an iodide ligand in
adjacent position.
8
6OMe
With the intention to extend the study to other d metals, the reactions of bpy
with a
series of Au(III) and Pd(II) metal salts were tested as a part of a preliminary study (Scheme
1
2

ACCEPTED MANUSCRIPT
3
).
Scheme 3. Syntheses of the palladium(II) and gold(III) complexes reported in the present
work
6
OMe
Reaction of bpy
with [Pd(OAc) ] in refluxing benzene gave a main species
2
6
OMe
1
characterized as the adduct [Pd(bpy
)(OAc) ], 10; the presence, in its H NMR
2
spectrum, of 7 resonances in the aromatic region and of resonances ascribable to two
acetate ligands supports this formulation.
1
1
1
1
1
In addition, a H- H COSY spectrum allowed a complete H NMR attribution and a H- H
NOESY spectrum (see Supplementary Information) showed cross peaks between the
methyl groups of the acetato moieties and the adjacent protons, i.e. 2.10 ppm (OAc cis to
6
’
OMe) with 3.94 ppm (OMe); 2.16 ppm (OAc trans to OMe) with 8.23 ppm (H ). In
addition a clear cross peak is observed between the methyoxy methyl (3.94 ppm) and the
5
adjacent H proton (6.85 ppm).
1
3

ACCEPTED MANUSCRIPT
Extraction with dichloromethane gave a second sample containing two species, in a 4:1
molar ratio, together with other impurities (NMR evidence). We were not able to obtain
1
these species in pure form; however, the H NMR spectrum supports their identification
6
OMe
as two geometric isomers of the dimeric rollover complex [Pd(bpy
1-t.
-H)(OAc)] , 11-c and
2
1
Proposed formulations for 11-c and 11-t
3
Our interpretation is supported, for both species, by the lack of the signal of the H
6
OMe
hydrogen and by the presence of an AX system compatible with a cyclometalated bpy
4
5
(
i.e. as in complex 1, vide supra) given by the H and H hydrogens. The coordination
around Pd is completed by two bridging acetate ligands in each species. Rollover
cyclometalation with Pd(II) acetate has been observed for other 6-substituted 2,2’-
2
5
bipyridines. In all cases, a mixture of species was formed, witnessing that the isolation in
pure form of these complexes is not always easy.
6
OMe
At variance, reaction of trans-[Pd(PhCN) Cl ] in CH Cl gave the adduct [PdCl (bpy
)],
2
2
2
2
2
1
2, isolated in the solid state and characterised.
1
4

ACCEPTED MANUSCRIPT
1
In particular, the H NMR spectrum shows seven aromatic protons, one of which is, as
6
’
expected, strongly deshielded (H , 9.20 ppm) due to proximity with one chloride ligand.
Complex 12 was obtained also by reaction of 10 with LiCl in acetone.
In the case of Au(III), two salts, NaAuCl and Au(OAc) , were used as starting material.
4
3
6
OMe
Reaction at room temperature of bpy
with NaAuCl in a MeCN/H O mixture gives the
4
2
6
OMe
6OMe
adduct [Au(bpy
)Cl ], 13, where bpy
likely acts as a monodentate ligand, as
3
2
7
previously observed with gold(III) adducts of 6-substituted 2,2’-bipyridines. The
1
characterization of 13 is based on analytical and NMR data (Fig. 2). In particular, the H
NMR spectrum shows that almost all the signals are downfield shifted with respect to the
6
’
free ligand (e.g. H from 8.65 to 9.03 ppm, OMe from 4.04 to 4.32 ppm). In contrast, the
3
3’
signals of the H and H protons are strongly shielded (ca -0.35 and -0.60 ppm).
-
1
The IR spectrum shows a band at 363 cm , due to Au-Cl stretching, in line with what
2
7
previously found for analogous Au(III) bipyridine adducts.
1
3
1
6OMe
Fig 2: Comparison of the H NMR spectra (aromatic region) of bpy
(a) and complex 13
(b).
1
5

ACCEPTED MANUSCRIPT
Treatment of the chlorido complex 13 with CH COONa and KPF in aqueous solution
3
6
6
Me
resulted in hydrolysis reaction affording the dinuclear oxo complex [Au(bpy )(µ-
O)] [PF ] , 14, in line with what previously observed, under analogous reaction conditions,
2
6 2
2
8
with similar gold(III) complexes of 6-substituted 2,2’-bipyridines; no C-H bond activation
1
was observed. The H NMR spectrum of 14 shows two set of signals in an approximate 4:1
molar ratio corresponding, respectively, to the trans, 14-t, and cis, 14-c, isomer. We were
not able to separate the two isomers in the solid state.
Proposed formulations for 14-c and 14-t
Complexes 14 c-t concur to enrich the small but interesting family of gold(III)-oxo
2
9
complexes. Indeed, these complexes have shown interesting reactivities both in
3
0
31
32
33
solution, in stoichiometric reactions and in catalysis, and in the gas phase. Also
3
4
noteworthy is their biological activity.
Unexpectedly, under the same reaction conditions recently used with 6,6’-dimethoxy-
6
OMe
2
,2’-bipyridine to give rollover cyclometalation, i.e. reaction of bpy
with Au(OAc)3
1
(
AcOH, 80 °C), no cyclometalation was achieved. The H NMR spectra indicate that, at
6
OMe
room temperature, the adduct [Au(bpy
)(OAc) ] is likely formed. In contrast to the
2
corresponding dimethoxy ligand, heating the solution resulted in heavy decomposition.
1
6

ACCEPTED MANUSCRIPT
Conclusions
Activation of C-H bonds by means of transition metal complexes is a topic still far to be
completely understood. In the case of substituted 2,2’-bipyridines, a delicate balance of
electronic and steric factors may drive the reaction towards unpredictable results. As a
part of our investigation on this class of ligands, we have reported here that the 6-
methoxy substituent promote a very easy bipyridine “rollover” activation and metallation
by reaction with the electron-rich Pt(II) precursor [Pt(Me) (DMSO) ]. In this case, the
2
2
process is very fast even at room temperature. Under different experimental conditions
the methoxy substituent is activated to give a terdentate N,N,C cyclometalated complex.
In all the other cases studied, starting from Au(III) and Pd(II) salts and other
[
PtX (DMSO) ] precursors (X = Ph, Cl), the rollover process did not occur or (in the case of
2 2
Pd(II) acetate) proceeds only in limited amount. This is likely ascribable to the peculiar
properties of the methoxy substituent, which has both electron withdrawing and
releasing properties (-I and +M, respectively).
6
OMe
The overall behaviour of 6-methoxy-2,2’-bipyridine, bpy
other 6-substituted-2,2’-bipyridines, as well as to the corresponding di-substituted ligand,
,6’-dimethoxy-2,2’-bipyridine.
Comparison with 6-substituted 2,2’-bipyridines (e.g. 6-CH , -CF , -t-but, -Ph, -CR Ph, etc)
, can be compared to that of
6
3
3
2
showed that, in the case of platinum(II), electron-withdrawing groups such as CF greatly
3
accelerate the rollover process. Also bulky substituents, such as t-butyl, facilitate the
6
OMe
process. In the case of bpy
the fast rollover activation is likely to be associated with
the inductive effect of the substituent on the nitrogen atom, as for CF3.
6
OMe
The comparison of bpy
with the corresponding disubstituted bipyridine is more
complex. In the case of platinum(II) an opposite behaviour was found for the two ligands:
6
OMe
in contrast to bpy
, the di-substituted ligand gives rollover metalation with the
electron-poor complex [Pt(DMSO) Cl ] and no reaction (or decomposition) with
2
2
[
Pt(DMSO) (Me) ]. At variance, both ligands activate the methoxy group in refluxing
2 2
acetic acid, to yield the corresponding terdentate N,N,C complex. As for palladium(II) and
gold(III), the disubstituted ligand showed an overall tendency to give an easier
6
OMe
metalation: with bpy
the palladium rollover complex was found only as a secondary
product and no gold(III) rollover complex was observed. In contrast, 6,6’-dimethoxy-2,2’-
bipyridine gave rollover metalation with both metals. As an example, under the same
reaction conditions (Au(OAc) , acetic acid, 80 °C), 6,6’-dimethoxy-2,2’-bipyridine gave
3
1
7

ACCEPTED MANUSCRIPT
rollover cyclometalation whereas 6-methoxy-2,2’-bipyridine gave an adduct at room
temperature and heavy decomposition under heating. The comparison is probably
complicated by the subtle balance between electronic and steric factors on both the
nitrogen donors and pyridine rings.
On the whole, a rationale of the reactivity of substituted 2,2’-bipyridines with noble
metals is still far to be reached and further investigations are needed to shed light into
the chemistry of this class of ligands.
Aknowledgements
Financial support from Università di Sassari and Università dell’Insubria (FAR) is gratefully
acknowledged. Regione Autonoma della Sardegna is gratefully acknowledged for the
financial support grant CRP-78365 “Complessi di Au e Pt derivanti da donatori calcogeni e
pnicogeni: applicazione quali antimicrobici”, L.R. 7 agosto 2007 n. 7, annualità 2013.
L.M. gratefully acknowledges a Ph.D. fund, financed on POR/FSE 2007-2013, from Regione
Autonoma della Sardegna.
Experimental Section
3
5
All the solvents were purified and dried according to standard procedures. Elemental
analyses were performed with a Perkin-Elmer 240B elemental analyzer by Mr. Antonello
Canu (Dipartimento di Chimica e Farmacia, Università degli Studi di Sassari, Italy). 6-
6
OMe
22
methoxy-2,2'-bipyridine (bpy
) was prepared by a Suzuki-Miyaura coupling.
Infrared spectra were recorded with a FT-IR Jasco 480P using Nujol mulls. Melting points
were measured in capillary tubes on a Büchi 530 melting points apparatus.
1
13
31
H, C, and P NMR spectra were obtained on a Bruker Avance III 400 spectrometer
operating at 400.0, 100.5 and 161.8 MHz, respectively. Chemical shifts are given in ppm
1
13
1
31
1
1
1
relative to internal TMS for H and C{ H} and external 85% H PO for P{ H}. H- H COSY,
3
4
1
1
1
13
H- H NOESY and H- C HSQC experiments were performed by means of standard pulse
3
6
sequences.
X-ray Crystal Structure Determination
The single crystal X-ray diffraction data for species 1 were acquired at room temperature
3
from a yellow, prismatic single crystal of approximate dimensions 0.2×0.2×0.3 mm , on an
1
8

ACCEPTED MANUSCRIPT
Enraf Nonius CAD4 automated diffractometer using graphite-monochromated Mo Kα
radiation (λ = 0.71073 Å). The unit cell was determined on the basis of the setting angles of
2
5 randomly distributed reflections in the range 9.2 < θ < 11.8°. The data collection was
performed in the range 3.0 < θ < 25.3° by applying the ω-scan mode [∆ω = 1.7 + (0.35tanθ)°].
A total of 5578 reflections, of which 3900 observed [I>2σ(I); R(int) = 0.029, R(sigma) = 0.059],
were collected and used for structure solution and structure refinement against 361
3
7
parameters. Prior to structure solution, the data were corrected for absorption. The
3
8
structure was solved by direct methods and it was refined by full-matrix least-squares on
2
39
F . All non-hydrogen atoms were assigned anisotropic temperature factors, while hydrogen
atoms were made riding their parent atoms with isotropic temperature factors 1.2 times
higher than those of their parent atoms.
Relevant crystallochemical data for 1, C H N O Pt S , FW = 946.86 g/mol: triclinic, space
2
8
36
4
4
2 2
group P-1, a = 10.569(5) Å, b = 11.537(5) Å, c = 13.680(7) Å,
α
= 82.52(4)°,
β = 83.75(4)°, γ =
3
3
6
8.22(3)°, V = 1540(1) Å , Z = 2, F(000) = 904, ρ = 2.04 g/cm , µ(Mo-Kα) = 9.25 1/mm. The R,
wR figures of merit reached final values of 0.045, 0.090 for the 3900 observed reflections,
and 0.079, 0.103 for all the 5578 reflections. The goodness of fit, highest peak and deepest
3
3
hole reached final values of 1.03, 1.60 e/Å and -1.05 e/Å , respectively.
Crystallographic data (excluding structure factors) for species 1 have been deposited with
the Cambridge Crystallographic Data Centre as supplementary publication number 1436235.
Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK, (fax: +44-(0)1223-336033 or e-mail: deposit@ccdc.cam.ac.uk).
6
OMe
[
Pt(bpy
To a solution of bpy
119.0 mg, 0.312 mmol) was added. The resulting solution, kept under inert atmosphere,
-H)(Me)(DMSO)], 1
6
OMe
(61.0 mg, 0.327 mmol) in acetone (15 mL) solid [Pt(Me) (DMSO) ]
2
2
(
was heated at 40 °C for 2 h under stirring; then it was concentrated under vacuum and n-
hexane was added. The precipitate formed was filtered off, washed with n-hexane and dried
to give the analytical sample as a yellow solid. Yield 80%. M.p. (dec) = 130 °C. Anal. Calcd. for
1
C H N OPtS (%): C, 35.50; H, 3.83; N, 5.92. Found: C, 35.38; H, 3.89; N, 5.63. H NMR
1
4 18 2
3
6’
(
CDCl , ppm): 9.65 (d with sat, 1H, J = 5.2 Hz, J = 14.9 Hz, H ), 8.21 (d, 1H, J = 7.6 Hz,
3 H-H Pt-H H-H
3
’
4’
3
4
H ), 7.90 (t, 1H, J = 7.6 Hz, H ), 7.88 (d with sat, 1H, J = 8.2 Hz, J = 50 Hz, H ), 7.30
H-H
H-H
Pt-H
5
’
4
5
(
m, 1H, JH-H = 7.6 Hz, JH-H = 5.2 Hz, H ), 6.71 (d with sat, 1H, J = 8.2 Hz, J = 15.8 Hz, H ),
H-H
Pt-H
3
2
4
.00 (s, 3H, OCH ), 3.24 (s with sat, 6H, J = 18.2 Hz, DMSO), 0.69 (s with sat, 3H, J = 82
3 Pt-H Pt-H
1
9

ACCEPTED MANUSCRIPT
1
3
2
Hz, Pt-CH ). C NMR (CDCl , ppm): 162.70 (s with sat, J = 58 Hz, C ), 162.13 (s with sat, J
Pt-C
3
3
Pt-C
2’
6
6’
=
6 Hz, C ), 161.42 (s, C ), 150.22 (s with sat, J = 7.6 Hz, C ), 142.96 (s with sat, J = 95
Pt-C Pt-C
4
4’
3
Hz, C ), 138.35 (s, C ), 136.76 (s with sat, J = 1092 Hz, C ), 123.33 (s with sat, J = 9 Hz,
Pt-C
Pt-C
5
’
3’
5
C ), 120.98 (s with sat, J = 24 Hz, C ), 111.15 (s with sat, J = 63 Hz, C ), 52.90 (s, OMe),
Pt-C
Pt-C
4
3.74 (s with sat, JPt-C = 42.5 Hz, DMSO), -14.08 (s with sat, JPt-C = 761 Hz, Pt-CH3).
1
1
1
1
1
13
Assignments based on H- H COSY, H- H NOESY, and H- C HSQC experiments.
6
OMe
[
Pt(Ph) (bpy
)], 2
2
6
OMe
To a solution of bpy
(18.3 mg, 0.098 mmol) in acetone (10 mL) solid [Pt(Ph) (DMSO) ]
2 2
(47.2 mg, 0.093 mmol) was added. The resulting solution was stirred under inert atmosphere
for 30 min. The precipitate formed was filtered off and dried under vacuum to give the
analytical sample as a yellow solid. From the filtered solution, a second crop (containing the
same product) was obtained after concentration and treatment with diethyl ether. Yield
6
0%. M.p. (dec) = 200 °C. Anal. Calcd. for C H N OPt (%): C, 51.59; H, 3.76; N, 5.23. Found:
23 20 2
1
C, 51.21; H, 4.02; N, 5.33. H NMR (CDCl ), δ (ppm): 8.43 (d, 1H, J = 5.7 Hz, JPt-H = 21 Hz,
3
H-H
6
’
3
4
4’
3’
H ), 7.99 (m, 2H, H +H ), 7.97 (t, 1H, part. overlapd., H ), 7.67 (d, 1H, J = 7.7 Hz, H ), 7.50
H-H
o
1
(
d with sat, 2H, JH-H = 8.2 Hz, JPt-H = 79 Hz, H Ph in trans to N ), 7.44 (d with sat, 2H, J = 8.2
H-H
o
1’
5’
m
1
Hz, JPt-H = 72 Hz, H Ph in trans to N ), 7.29 (m, 1H, H ), 6.97 (m, 2H, H Ph in trans to N ),
m
1’
p
1
6
1
.91 (m, 2H, H Ph in trans to N ), 6.85 (m, 1H, part. overlapd., H Ph in trans to N ), 6.82 (m,
5
p
1’
H, part. overlapd., H ), 6.67 (t, 1H, H Ph in trans to N ), 3.28 (s, 3H, OCH ). Assignments
3
1
1
1
1
13
based on H- H COSY and H- H NOESY experiments. C NMR (CDCl , ppm): 166.84 (s, Cq),
3
1
1
1
=
56.68 (s, Cq), 155.37 (s, Cq), 149.97 (s, CH), 144.06 (s, Cq), 143.57 (s, Cq), 140.68 (s, CH),
37.86 (s, CH), 137.55 (s, CH), 136.91 (s, CH), 127.10 (s, CH), 126.51 (s, CH), 126.01 (s, CH),
22.43 (s, CH), 121.56 (s, CH), 120.15 (s, CH), 114.49 (s, CH), 108.54(s, CH), 55.69 (s, CH ). Cq
3
quaternary carbon atom.
6
OMe
[
PtCl (bpy
)], 3
2
Solid [PtCl (DMSO) ] (73.5 mg, 0.1740 mmol) was added to 15 mL of an acetone solution of
2
2
6
OMe
bpy
(34.2 mg, 0.1836 mmol) under vigorous stirring. The resulting mixture was stirred
for 2 days at room temperature. The precipitate formed was filtered off and dried under
vacuum to give the analytical sample as a yellow solid. Yield 55 %. M.p.> 250 °C. Anal. Calcd.
1
for C H Cl N OPt (%): C, 29.22; H, 2.23; N, 6.19. Found: C, 29.69; H, 1.73; N 6.03. H NMR
11
10
2 2
2
0

ACCEPTED MANUSCRIPT
6
’
(
CD Cl , ppm): 9.81 (d with sat, 1H, J = 5.4 Hz, J =39 Hz, H ), 8.17 (t, 1H, J = 7.6 Hz, H4
2 2 H-H Pt-H H-H
4
4’
3’
3
or H ), 8.13 (t, 1H, J = 7.6 Hz, H or H ), 7.98 (d, 1H, J = 7.6 Hz, H or H ), 7.69 (d, 1H, J
4
’
H-H
H-H
H-H
3
3’
5’
5
=
4
7.6 Hz, H or H ), 7.57 (m, 1H, J = 7.8 Hz, H ), 7.06 (d, 1H, J = 7.8 Hz, JPt-H = 17 Hz, H ),
H-H
H-H
.13 (s, 3H, OCH3).
6
OMe
[
Pt(bpy
To a solution of bpy
88.8 mg, 0.210 mmol) was added. The resulting mixture was heated at 100 °C for 1 week.
-H)Cl], 4
6
OMe
(41.2 mg, 0.221 mmol) in acetic acid (15 mL) solid [PtCl (DMSO) ]
2
2
(
The precipitate formed was filtered off and dried to give the analytical sample as an orange
solid. Yield 20%. Anal. Calcd. for C H ClN OPt (%): C, 31.78; H, 2.18; N, 6.74. Found: C, 31.92;
1
1
9
2
1
3
H, 2.34; N, 6.57. H NMR (CDCl , ppm) = 9.11 (d with sat, 1H, J = 5.4 Hz, J ca. 12 Hz,
Pt-H
3
H-H
6
’
4
4’
3’
H ), 8.17 ppm (t, 1H, J = 7.8 Hz, H or H ), 8.03 (d, 1H, J = 7.8 Hz, H ), 7.96 (t, 1H, J =
H-H
H-H
H-H
4
4’
5’
3
4
7
.8 Hz, H or H ), 7.76 (m, 1H, J = 7.8 Hz, H ), 7.44 (d with sat, 1H, J = 7.6 Hz, J = 11
H-H
H-H
Pt-H
3
5
2
13
Hz, H ), 7.03 (d, 1H, J = 8.0 Hz, H ), 7.00 (s with sat, 2H, J
= 77 Hz, Pt-CH ). C NMR
H-H
Pt-H
2
(
CD Cl , ppm): 147.87 (s, CH), 138.61 (s, CH), 138.35 (s, CH), 127.11 (s, CH), 122.17 (s, CH),
2 2
1
12.99 (s, CH), 110.47 (s, CH), 70.88 (s, CH2).
6
OMe
[Pt(bpy
-H)(Me)(PPh )], 5
3
6
OMe
a) One pot synthesis: to a solution of bpy
(25.5 mg, 0.134 mmol) in acetone (7 mL)
[
Pt(Me) (DMSO) ] (48.1 mg, 0.126 mmol) was added. The resulting solution was heated at 40
2
2
°
C for 3 h under an inert atmosphere, then PPh (34.2 mg, 0.130 mmol) was added and left
3
to react for 1 h. The solution was concentrated to a small volume and treated with diethyl
ether. The precipitate formed was filtered off, washed with diethyl ether and dried to give
the analytical sample as a yellow solid. Yield 65%.
b) Complex 5 may also be obtained by reaction of complex 1 with PPh in a 1:1 molar ratio in
3
acetone at room temperature for 1 h. Yield 80%.
M.p. 230 °C. Anal. Calcd. for C H N OPPt (%): C, 54.79; H, 4.14; N, 4.26. Found: C, 54.69; H,
3
0 27 2
1
3
3
.56; N, 4.15. H NMR (CDCl , ppm): 8.27 (d, 1H, J = 7.9 Hz, H ), 8.15 (dd, 1H, J = 8.2 Hz,
3 H-H H-H
4
JP-H 4.8 Hz, JPt-H = 44 Hz, H ), 7.84 – 7.68 (m, 8H), 7.45 – 7.34 (m, 9H), 6.79 (d with sat, 1H, J
H-H
5
5’
=
8.2 Hz, JPt-H = 14 Hz, H ), 6.64 (m, 1H, J = 5.8, 6.2 Hz, H ), 3.99 (s, 3H, OMe), 0.73 (d with
H-H
3
1
sat, 3H, J = 7.8 Hz, J = 82.8 Hz, Pt-Me). P NMR (CDCl , ppm): 32.59 (s, J = 2257 Hz,
P-H
Pt-H
3
Pt-P
PPh3).
2
1

ACCEPTED MANUSCRIPT
1
3
C NMR (CDCl , ppm): 164.96 (d with sat, J = 49 Hz, J = 5 Hz, Cq), 161.65 (s, Cq), 150.47
3
Pt-C
P-C
3
’
(
d with sat, JPt-C = 976 Hz, JP-C = 22 Hz C ), 150.46 (s, CH), 150.38 (s, CH), 143.09 (d with sat,
JPt-C = 90 Hz, JP-C = 1 Hz), 137.33 (s, CH), 135.04 (d with sat, JPt-C = 17 Hz, JP-C = 12 Hz), 132.36
d with sat, JPt-C = 44 Hz, JP-C = 18 Hz, C-PPh3 ipso), 130.19 (d with sat, JP-C = 2 Hz, C-PPh3para),
28.25 (d with sat, JP-C = 10 Hz, C-PPh3meta), 123.27 (s with sat, JPt-C = 9.5 Hz), 121.21 (s with
(
1
sat, JPt-C = 19 Hz), 111.62 (d with sat, JPt-C = 56 Hz, JP-C = 6 Hz), 52.95 (s, OMe), -13.14 (d with
sat, JPt-C = 723 Hz, JP-C = 5 Hz, Pt-CH3).
6
OMe
[Pt(bpy
-H)(Me) (I)(PPh )], 9
2 3
To a solution of complex 5 (70 mg, 0.1064 mmol) in acetone (15 mL) MeI (32 μL) was added
in excess. The resulting solution was stirred for 3 h at room temperature under an inert
atmosphere, then it was concentrated to a small volume and treated with n-hexane. The
precipitate formed was filtered off, washed with n-hexane and dried to give the analytical
sample. Yield 65%. Anal. Calcd for C H IN OPPt (%): C, 46.57; H, 3.78; N, 3.50. Found: C,
3
1
30
2
1
4
7.71; H, 4.05; N, 3.67. H NMR (CDCl , ppm): 9.50 (d with sat, 1H, J = 5.4 Hz, JPt-H = 12 Hz,
3 H-H
6
’
3’
4’
H ), 8.14 (d, 1H, J = 8.1 Hz, H ), 7.74 (m, 1H, H ), 7.29 (m, 9H, PPh ), 7.18 (m, 6H, PPh ),
H-H
3
3
5
’
4
7
=
.09 (m, 1H, H ), 6.92 (d with sat, 1H, J = 8.2 Hz, JPt-H = 42 Hz, H ), 6.40 (d with sat, 1H, J
H-H
H-H
5
8.2 Hz, JPt-H = 11 Hz, H ), 4.02 (s, 3H, OCH ), 1.67 (d with sat, 3H, J = 7.9 Hz, JPt-H = 71 Hz,
3
H-H
31
Pt-Me), 1.23 (d with sat, 3H, JH-H = 7.6 Hz, JPt-H = 60 Hz, Pt-Me). P NMR (CDCl , ppm): -10.84
3
ppm (s with sat, JPt-P = 959 Hz, PPh3).
6
OMe
6OMe
[
Pd(bpy
To a solution of bpy
.50 mmol) was added. The resulting solution was heated at 80 °C for 1 h under stirring. The
precipitate formed was filtered off, washed with benzene and vacuum dried to give complex
0 as a creamy solid (Yield 80%). The filtered solution was concentrated to a small volume
and treated with diethyl ether to give a mixture of products. The main species were
)(OAc) ], 10, and Pd(bpy
-H)(OAc)] , 11-t + 11-c
2
2 ,
6
OMe
(93.0 mg, 0.50 mmol) in benzene (50 mL), solid Pd(OAc) (112 mg,
2
0
1
6OMe
identified as the trans and cis isomers of [Pd(bpy
-H)(OAc)] , 11-t and 11-c, present in 1:4
2
molar ratio.
6
OMe
[Pd(bpy
)(OAc) ], 10
2
Anal. Calcd for C H N O Pd (%): C, 43.86; H, 3.93; N, 6.82. Found: C, 43.72; H, 4.09; N, 6.57.
1
5 16 2 5
2
2

ACCEPTED MANUSCRIPT
1
3’
6’
H NMR (CDCl , ppm): 8.30 (d, 1H, J = 8.2 Hz, H ), 8.23 (d, 2H, J = 5.4 Hz, H ), 8.08 (m,
3
H-H
H-H
4
’
4
part. overlappd, JH-H = 7.7, 8.2 Hz, H ), 8.04 (m, part. overlappd, J = 7.7, 8.2 Hz, H ), 7.96
H-H
3
5’
5
(
d, 1H, JH-H = 7.7 Hz; H ), 7.34 (m, 1H, J = 7.8, 5.4 Hz, H ), 6.85 (d, 1H, J = 8.2 Hz; H ), 3.94
H-H H-H
6’
(
s, 3H; OMe), 2.16 (s, 3H; OAc cis to H ), 2.10 (s, 3H; OAc cis to OCH ). Assignments based on
3
1
1
1
1
H- H COSY and H- H NOESY experiments.
6
OMe
1
1
trans-[Pd(bpy
-H)(OAc)] , 11-t. H NMR (CDCl , ppm), selected H NMR signals: 8.03 (d,
2 3
6
’
4
5
2
H, JH-H = 5.5 Hz, H ), 7.07 (d, 2H, J = 8.4 Hz, H ), 6.32 (d, 2H, J = 8.4 Hz, H ), 3.84 (s, 6H,
H-H H-H
OCH ), 2.27 (s, 6H, CH COO).
3
3
6
OMe
1
1
Cis-[Pd(bpy
-H)(OAc)] , 11-c. H NMR (CDCl , ppm), selected H NMR signals: 7.86 (d, 2H,
2 3
6
’
4
5
JH-H = 5.5 Hz, H ), 6.87 (d, 2H, J = 8.4 Hz, H ), 6.20 (d, 2H, J = 8.4 Hz, H ), 3.84 (s, 6H,
H-H
H-H
OCH3).
6
OMe
[
Pd(bpy
a) To a solution of bpy
.50 mmol) was added. The mixture was stirred for 6 days at room temperature and then
)Cl ], 12
2
6
OMe
(93 mg, 0.50 mmol) in CH Cl (50 mL) trans-(PhCN)PdCl (192 mg,
2
2
2
0
filtered off and dried under vacuum. Recrystallization from MeCN–diethyl ether gave 12 as a
dark yellow crystalline product. Yield 90%.
b) To a solution of 10 (40 mg, 0.06 mmol) in acetone (30 mL) an excess of LiCl was added.
The mixture was stirred for 12 h at room temperature, then filtered off. The filtered solution
was concentrated to a small volume and treated with diethyl ether to give 12. Yield 90%.
Anal. Calcd. for C H Cl N OPd (%): C, 36.34; H, 2.77; N, 7.71. Found: C, 37.01; H, 2.38; N,
1
1
10
2 2
1
6’
4’
4
3’
7
.51. H NMR (CD CN, ppm): 9.20 (d, 1H, J = 5.5 Hz, H ), 8.16-8.10 (m, 3H, H H , H ), 7.82
3 H-H
3
5’
5
(
d, 1H, JH-H = 7.7 Hz, H ), 7.57 (dd, 1H, J = 5.0, 8.6 Hz, H ), 7.13 (d, 1H, J = 8.6 Hz, H ),
H-H H-H
3
.98 (s, 3H, Me).
6
OMe
[Au(bpy
)Cl ], 13
3
6
OMe
To a solution of bpy
(93 mg, 0.50 mmol) in MeCN (5 mL) an aqueous solution (30 mL) of
.
Na[AuCl ] 2H O (199 mg, 0.50 mmol) was added. The resulting yellow suspension was stirred
4
2
for 72 h at room temperature. During this period the colour of the suspension turned to dark
orange. The solid product was filtered off and air-dried under vacuum to give 13 (200 mg,
yield 81%). Recrystallization from chloroform–diethyl ether gave a dark orange crystalline
product, m.p. 170–171°C. Anal. Calcd for C H AuCl N O (%): C, 26.99; H, 2.06; N, 5.72.
1
1
10
3 2
1
6’
Found: C 27.19; H 1.84; N 5.63. H NMR (CDCl , ppm): 9.01 (dd, 1H, J = 5.6, 1.3 Hz; H ),
3
H-H
2
3

ACCEPTED MANUSCRIPT
3
’
3
8
0
=
.20 (td, 1H, JH-H = 7.7, 1.4 Hz, H ), 8.05 (dd, 1H, J = 7.9, 1.6 Hz, H ), 7.80 (td, 1H, J = 7.9,
H-H H-H
4’
4
5’
.6 Hz, H ), 7.71 (td, 1H, J = 6.7, 1.6 Hz, H ), 7.44 (d, 1H, J = 7.2 Hz, H ), 7.03 (d, 1H, J
H-H
H-H
H-H
5
-1
8.5 Hz, H ), 4.32 (s, 3H, Me). IR (Nujol): 363 cm , ν Au-Cl.
6
OMe
[
Au(bpy-
To a suspension of 13 (303 mg, 0.62 mmol) in MeCN (3 mL) and water (30 mL) solid KPF6
344 mg, 1.87 mmol) and an aqueous solution (15 mL) of MeCO Na (101 mg, 1.24 mmol)
)(µ-O)] [PF ] , 14
2
6 2
(
2
were added. The mixture was stirred for 6 days at room temperature and then filtered off
and dried under vacuum to give 14 as a mixture of the cis, 14-c, and trans, 14-t, isomers (421
mg, yield 72%). Recrystallization from acetonitrile/diethyl ether gave the analytical sample
as an orange solid, m.p. 198-200 °C. Anal. Calcd for C H Au F N O P (%); C, 24.28; H, 1.85;
2
2
20
2 12 4 4 2
1
N, 5.15. Found: C, 24.47; H, 1.38; N, 5.02. H NMR (CD CN, ppm) 14-t: 8.61 (d, 2H, J = 5.7
3
H-H
6
’
4’ 3’
,
4
Hz, H ), 8.44 (m, 4H, overlappd signals, H H ), 8.37 (t, 2H, J = 8.0 Hz, H ), 8.06 (m, 4H,
H-H
5
’
3
5
overlappd signals, H , H ), 7.46 (d, 2H, J = 8.7 Hz, H ), 4.24 (s, 6H, Me). 14-c: 8.76 (d, 2H,
H-H
6’
4’
3’
4
JH-H = 5.6 Hz, H ), 8.44 (m, 4H, overlappd signals, H , H ), 8.37 (t, 2H, J = 8.2 Hz, H ), 8.06
H-H
5
’
3
5
(
m, 4H, H , H ), 7.46 (d, J = 8.7 Hz, 2H, H ), 4.19 (s, 6H, Me).
H-H
2
4

ACCEPTED MANUSCRIPT
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Highlights
Highlights: rollover cyclometalation; C-H bond activation; bipyridine complexes; Pt(II), Pd(II)
and Au(III) cyclometalated complexes.
1