Syntheses, crystal structures, and electrochemical and spectroscopic properties of ruthenium complexes of the N,S-bidentate ligand 2-(2-pyridyl)benzenethiol
Abstract
Conversion of the amino group of 2-(2-aminophenyl)pyridine into a
thiol to give the N,S-donor chelating ligand 2-(2-pyridyl)benzenethiol
(HL) afforded the oxidised disulfide L–L which was
crystallographically characterised. It shows an interesting example of
an intermolecular
N · · · S–S
interaction (N · · · S
distances are 2.778 and 2.724 Å;
N · · · S–S angles are
both ca. 11°) in which the pyridyl lone pair interacts
weakly with the σ
* orbital of the S–S bond.
Reaction of L–L with
[Ru(bipy)
2
Cl
2
]·2H
2
O
(bipy = 2,2′-bipyridine) and
RuCl
3
·xH
2
O afforded
[Ru
II
(bipy)
2
L][PF
6
] 1 and
[Ru
III
L
3
] 2 respectively (following
in situ reduction of the disulfide) which have N
5
S
and mer-N
3
S
3
donor sets respectively (N
of pyridyl, S of benzenethiolate). Both were crystallographically
characterised and have the expected pseudo-octahedral geometries. An
interesting feature of both structures is that the relatively large
Ru–S distances (compared to the Ru–N) prevent the pyridyl
rings from approaching the metal centre as closely as they would if they
were not constrained, so the Ru–N distances are longer than usual.
Electrochemical studies show that the benzenethiolate ligands are more
effective electron donors to ruthenium (both +2 and +3) than are
phenolates: for example, the Ru
II
–Ru
III
couple of 1 is at -0.07 V vs.
ferrocene–ferrocenium, whereas the same couple of the related
N
5
O-co-ordinated complex (O from phenolate) was at +0.03 V.
Similarly the Ru
III
–Ru
IV
couple of
2 was at -0.21 V, compared to +0.14 V for the
N
3
O
3
-co-ordinated analogue. Complex 2
also shows a reversible ligand-based oxidation which is absent for
1, arising from stabilisation of the sulfur-based radical
cation by interaction with the lone pair on an adjacent sulfur atom in
the co-ordination sphere of the complex, which cannot happen for
1. Electronic spectral properties show that the sulfur donor of
1 weakens the ligand field with respect to
[Ru(bipy)
3
]
2+
, and that 2 has an intense
sulfur-to-Ru
III
ligand-to-metal charge-transfer band.
* orbital of the S–S bond.
Reaction of L–L with
[Ru(bipy)
2
Cl
2
]·2H
2
O
(bipy = 2,2′-bipyridine) and
RuCl
3
·xH
2
O afforded
[Ru
II
(bipy)
2
L][PF
6
] 1 and
[Ru
III
L
3
] 2 respectively (following
in situ reduction of the disulfide) which have N
5
S
and mer-N
3
S
3
donor sets respectively (N
of pyridyl, S of benzenethiolate). Both were crystallographically
characterised and have the expected pseudo-octahedral geometries. An
interesting feature of both structures is that the relatively large
Ru–S distances (compared to the Ru–N) prevent the pyridyl
rings from approaching the metal centre as closely as they would if they
were not constrained, so the Ru–N distances are longer than usual.
Electrochemical studies show that the benzenethiolate ligands are more
effective electron donors to ruthenium (both +2 and +3) than are
phenolates: for example, the Ru
II
–Ru
III
couple of 1 is at -0.07 V vs.
ferrocene–ferrocenium, whereas the same couple of the related
N
5
O-co-ordinated complex (O from phenolate) was at +0.03 V.
Similarly the Ru
III
–Ru
IV
couple of
2 was at -0.21 V, compared to +0.14 V for the
N
3
O
3
-co-ordinated analogue. Complex 2
also shows a reversible ligand-based oxidation which is absent for
1, arising from stabilisation of the sulfur-based radical
cation by interaction with the lone pair on an adjacent sulfur atom in
the co-ordination sphere of the complex, which cannot happen for
1. Electronic spectral properties show that the sulfur donor of
1 weakens the ligand field with respect to
[Ru(bipy)
3
]
2+
, and that 2 has an intense
sulfur-to-Ru
III
ligand-to-metal charge-transfer band.
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