Synthesis and structural characterisation of mono- and bi-nuclear cobalt(II) alkyls
Abstract
Treatment of CoCl
2
with the organolithium compounds
[(LiR
1
)
2
],
[{LiR
2
(tmen)}
2
],
[{LiR
3
(tmen)}
2
] and
[LiR
4
(tmen)]
[R
1
= C(SiMe
3
)
2
(C
5
H
4
N-2),
R
2
= CPh(SiMe
3
)(C
5
H
4
N-2),
R
3
= CH(SiMe
3
)(C
9
H
6
N-8), R
4
=
CH(SiBu
t
Me
2
)(C
5
H
4
N-2);
tmen = Me
2
NCH
2
CH
2
NMe
2
] afforded the corresponding cobalt(II) dialkyls
[C![[upper bond 1 start]](https://www.rsc.org/images/entities/char_e010.gif)
o{C(SiMe
3
)
2
(C
5
H
4
N-2![[upper bond 1 end]](https://www.rsc.org/images/entities/char_e011.gif)
)}
2
] 1,
[Co{CPh(SiMe
3
)(C
5
H
4
N-2
)}
2
] 2,
[Co{CH(SiMe
3
)(C
9
H
6
N-8
)}
2
] 3 and
[{Co[CH(SiBu
t
Me
2
)(C
5
H
4
N)]
2
}
2
]
4. X-Ray diffraction analyses revealed that
1–3 are four-co-ordinated mononuclear compounds,
each cobalt(II) centre adopting a square-planar environment
with a pair of alkyl ligands bound in a trans chelating
fashion. In contrast 4 is a four-co-ordinated binuclear
compound, with one pair of alkyl ligands forming two interligand bridges
between the tetrahedral cobalt centres to give an eight-membered
‘chair’ conformation. The cobalt to α-carbon and
cobalt to nitrogen distances are in the ranges 2.01–2.13 and
1.90–2.10 Å, respectively. Magnetic moment
measurements of 1–3 are consistent with a
low-spin d
7
electronic configuration having one unpaired
electron, whilst 4 showed antiferromagnetic coupling between
two cobalt(II) centres. The electrochemical behaviour of
these cobalt(II) compounds was studied by cyclic
voltammetry.
o{C(SiMe
3
)
2
(C
5
H
4
N-2 )}
2
] 1,
[Co{CPh(SiMe
3
)(C
5
H
4
N-2
)}
2
] 2,
[Co{CH(SiMe
3
)(C
9
H
6
N-8
)}
2
] 3 and
[{Co[CH(SiBu
t
Me
2
)(C
5
H
4
N)]
2
}
2
]
4. X-Ray diffraction analyses revealed that
1–3 are four-co-ordinated mononuclear compounds,
each cobalt(II) centre adopting a square-planar environment
with a pair of alkyl ligands bound in a trans chelating
fashion. In contrast 4 is a four-co-ordinated binuclear
compound, with one pair of alkyl ligands forming two interligand bridges
between the tetrahedral cobalt centres to give an eight-membered
‘chair’ conformation. The cobalt to α-carbon and
cobalt to nitrogen distances are in the ranges 2.01–2.13 and
1.90–2.10 Å, respectively. Magnetic moment
measurements of 1–3 are consistent with a
low-spin d
7
electronic configuration having one unpaired
electron, whilst 4 showed antiferromagnetic coupling between
two cobalt(II) centres. The electrochemical behaviour of
these cobalt(II) compounds was studied by cyclic
voltammetry.
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