Ruthenium-mediated selective activation of a C–H bond. Direct
aromatic thiolation in the complexes
[RuII{o-SC6H3(R)N![[double bond, length as m-dash]](https://www.rsc.org/images/entities/char_e001.gif)
NC
5H4N}2] (R = H, Me or
Cl)
Abstract
The reaction of the complexes
ctc-[Ru
II
L
2
Cl
2
]
(L = arylazopyridine,
RC
6
H
4
NNC
5
H
4
N, where
R = H, m-Me, p-Me or p-Cl;
ctc = cis-trans-cis with respect to
chlorides, pyridine and azo nitrogens respectively) with
KS
2
COR′ (R′ = Me, Et, Pr
n
,
Bu
n
or CH
2
Ph) in boiling dimethylformamide afforded
[Ru
II
{o-SC
6
H
3
(R)NNC
5
H
4
N}
2
] where the o-carbon
atom of the pendant phenyl ring of both ligands L has been selectively and
directly thiolated. The newly formed tridentate thiolated ligands are bound
in a meridional fashion. When one methyl group is present at the
meta position of the pendant phenyl ring of L the reaction
resulted in two isomeric complexes due to free rotation of the singly
bonded meta-substituted phenyl ring with respect to the azo group.
The molecular geometry of the complexes in solution has been determined by
1
H NMR spectroscopy. This revealed the presence of an intimate
mixture of the two isomers in solution in a 2∶1 ratio. In the visible
region the complexes exhibit two metal-to-ligand charge-transfer
transitions at ≈700 and ≈560 nm respectively and in the UV region
intraligand (π–π*, n–π*) transitions. In acetonitrile
solution the complexes exhibit one reversible
ruthenium(II) ruthenium(III)
oxidation couple near 0.4 V and an irreversible oxidative response near 1 V
due to oxidation of the co-ordinated thiol group. Reduction of the
co-ordinated azo groups occurs at ca. -0.8 and -1.4 V
respectively. Coulometric oxidation of the complexes
[Ru
II
{o-SC
6
H
3
(R)NNC
5
H
4
N}
2
] at 0.6 V versus the
saturated calomel electrode in dichloromethane produced unstable
ruthenium(III) congeners. When R = p-Me,
the presence of trivalent ruthenium in the oxidised solution was evidenced
by a rhombic EPR spectrum having
g
1
= 2.359,
g
2
= 2.300 and
g
3
= 1.952.
NC
5
H
4
N, where
R = H, m-Me, p-Me or p-Cl;
ctc = cis-trans-cis with respect to
chlorides, pyridine and azo nitrogens respectively) with
KS
2
COR′ (R′ = Me, Et, Pr
n
,
Bu
n
or CH
2
Ph) in boiling dimethylformamide afforded
[Ru
II
{o-SC
6
H
3
(R)NNC
5
H
4
N}
2
] where the o-carbon
atom of the pendant phenyl ring of both ligands L has been selectively and
directly thiolated. The newly formed tridentate thiolated ligands are bound
in a meridional fashion. When one methyl group is present at the
meta position of the pendant phenyl ring of L the reaction
resulted in two isomeric complexes due to free rotation of the singly
bonded meta-substituted phenyl ring with respect to the azo group.
The molecular geometry of the complexes in solution has been determined by
1
H NMR spectroscopy. This revealed the presence of an intimate
mixture of the two isomers in solution in a 2∶1 ratio. In the visible
region the complexes exhibit two metal-to-ligand charge-transfer
transitions at ≈700 and ≈560 nm respectively and in the UV region
intraligand (π–π*, n–π*) transitions. In acetonitrile
solution the complexes exhibit one reversible
ruthenium(II) ruthenium(III)
oxidation couple near 0.4 V and an irreversible oxidative response near 1 V
due to oxidation of the co-ordinated thiol group. Reduction of the
co-ordinated azo groups occurs at ca. -0.8 and -1.4 V
respectively. Coulometric oxidation of the complexes
[Ru
II
{o-SC
6
H
3
(R)NNC
5
H
4
N}
2
] at 0.6 V versus the
saturated calomel electrode in dichloromethane produced unstable
ruthenium(III) congeners. When R = p-Me,
the presence of trivalent ruthenium in the oxidised solution was evidenced
by a rhombic EPR spectrum having
g
1
= 2.359,
g
2
= 2.300 and
g
3
= 1.952.
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![[double bond, length as m-dash]](https://www.rsc.org/images/entities/h2_char_e001.gif)
NC
5H4N}2] (R = H, Me or
Cl)