Lithiated amidines: syntheses and structural characterisations
Abstract
The reaction of a toluene solution of PhNC(Ph)NHPh
(N,N′-diphenylbenzamidine) with
n-butyllithium gave the toluene-solvated amidinolithium
compound {Li[PhNC(Ph)NPh]}
n
1. Similarly the same reaction performed in the presence
of the Lewis-base donors (Me
2
N)
3
PO (hmpa),
Me
2
N(CH
2
)
2
NMe
2
(tmen) or
[Me
2
N(CH
2
)
2
]
2
NMe (pmdien)
yielded the amidinolithium complexes
{Li[PhNC(Ph)NPh·hmpa]}
2
2,
{Li[PhNC(Ph)NPh]·tmen} 3 and
{Li[PhNC(Ph)NPh]·pmdien} 4 respectively. In
addition the reaction of a toluene solution of the related amidine
PhNC(Me)NHPh (N,N′-diphenylacetamidine) with
LiBu
n
in the presence of hmpa afforded
{Li[PhNC(Me)NPh]·hmpa}
2
5. The
solid-state structures of 2–5, which have been
resolved by single-crystal X-ray diffraction methods, show both
similarities and differences. The complexes 3 and 4,
which contain the di- and tri-dentate ligands tmen and pmdien
respectively, are monomeric, whilst use of the unidentate Lewis base
hmpa results in dimers 2 and 5. However, the way in
which dimerisation is achieved differs. The co-ordination geometry about
the lithium cation is clearly influenced by the choice of donor and as
such shows how a change in the denticity of the donor ligand utilised
can have a significant effect on the solid-state structure of the
system.
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