Early transition metal complexes of carbene donors linked to cyclopentadienyl ring analogues or amidine/amidinate moieties

Abstract

The new indenyl-functionalised NHC potassium salt, 1-[3-(4, 7-dimethylindenylpropyl]-3-
(2,6-diisopropylphenyl)imidazol-2-ylidenepotassium, has been synthesised. Complexes of
titanium, zirconium and chromium containing this ligand and the two carbon bridge analogue,
1-[2-(4,7-dimethylindenyl)ethyl]-3-(2,6-diisopropylphenyl)imidazol-2 ylidene potassium,
have been synthesised and characterised by X-ray crystallographic techniques. The following
complexes were tested as catalysts for the oligomerisation of ethylene in the presence of
MAO: 3-(2,6-diisopropylphenyl)-1-[2-(4,7-dimethylindenyl)ethyl]-imidazol-2-ylidene(tertbutylimido)
titanium chloride, 3-(2,6-diisopropylphenyl)-1-[3-(4,7-
dimethylindenyl)propyl]imidazol-2-ylidene(tert-butylimido)titanium chloride, 3-(2,6-
diisopropylphenyl)-1-[3-(4,7-dimethylindenyl)propyl]imidazol-2-ylidenezirconium
trichloride, 3-(2,6-diisopropylphenyl)-1-[2-(4,7-dimethylindenyl)ethyl]imidazol-2-
ylidenezirconium trichloride, 3-(2,6-Diisopropylphenyl)-1-[2-(4,7-dimethylindenyl)ethyl]-
imidazol-2-ylidenechromium dichloride, 3-(2,6-diisopropylphenyl)-1-[3-(4,7-
(dimethylindenyl)propyl]imidazol-2-ylidene chromium dichloride, 3-(2,6-diisopropylphenyl)-
1-[3-(4,7-dimethylindenyl)propyl]-imidazol-2-ylidene chromium methyl chloride and 3-(2,6-
diisopropylphenyl)-1-[2-(4,7-dimethylindenyl)ethyl]-imidazol-2-ylidenevanadium dichloride.

The following alkyl chromium complexes containing 1-[2-(4,7-dimethylindenyl)ethyl]-3-(2,6-
diisopropylphenyl)imidazol-2 ylidene potassium have also been synthesised: 3-(2,6-
diisopropylphenyl)-1-[2-(4,7-dimethylindenyl)ethyl]-imidazol-2-ylidene chromium phenyl
chloride and 3-(2,6-diisopropyl-phenyl)-1-[2-(4, 7-dimethylindenyl)ethyl]-imidazol-2-ylidene
chromium dibenzyl. Chromium cations have been synthesised using as starting materials the
chromium alkyl complexes. The Cr(II) complex 3-(2,6-diisopropyl-phenyl)-1-[2-(4, 7-
dimethylindenyl)ethyl]-imidazol-2-ylidene chromium monochloride and a partially oxidised
dimerised product were also isolated. 5-(2-chloroethyl)- 1, 2, 3, 4-tetramethylcyclopentadiene
and 5-(3-chloropropyl) 1, 2, 3, 4-tetramethylcyclopentadiene were synthesised and isolated as
geminal isomers for the first time.

The trialkyl chromium complex, tribenzyl chromium tris(tetrahydrofuran) was synthesised
and also it was used as starting material for the complexes di(benzyl)chromium bis(1, 3-
diisopropylimidazol-2-ylindene) and tri(benzyl)chromium TACN. All complexes were
characterised by X-ray crystallography.

The imidazolium salt 3-(2.6-diisopropylphenyl)-1-[N, N-bis(2,6-
diisopropylphenyl)acetamidyl] imidazolium chloride was synthesised and used as a precursor
for the synthesis of amidinate-functionalised NHC zirconium and amidine-functionalised
NHC silver complexes. Double deprotonation of 3-(2,6-diisopropylphenyl)-1-[N, N’-bis(2,6-
diisopropylphenyl)acetamidyl] imidazolium chloride gave the amidinate-functionalised NHC
ligand, 3-(2.6-diisopropylphenyl)-1-[2-N, N’bis(2,6
diisopropylphenylamidinate)ethyl]imidazol-2-ylidenepotassium. Titanium, zirconium and
chromium complexes containing this ligand were synthesised and characterised by X-ray
crystallographic techniques. Transmetallation of the amidine-functionalised NHC silver
complex with [Rh(COD)Cl]2 and [Ir(COD)Cl]2 gave the corresponding species. Rh(amidinefunctionalised
NHC)(COD)Cl reacted with Na(BAr)4 (Ar = 3,5-CF3C6H3) to give the cation
Rh(amidine-functionalised NHC)(COD)]+[BAr4]-. These species were also characterised by
X-ray diffraction techniques.

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