New functionally substituted η5-cyclopentadienyl and
2-oxaallyl (η1-enolate) tungsten
complexes bearing an N-succinimidyl or an
N-sulfosuccinimidyl ester have been prepared
and fully characterized. The molecular structures of
[η5-((succinimidooxy)carbonyl)cyclopentadienyl]methyltricarbonyltungsten(II) (2) and
[η5-((succinimidooxy)carbonyl)cyclopentadienyl]iodotricarbonyltungsten(II) (5) were
solved by X-ray crystallography. The
reactivity of these activated esters toward a range of amines and amino
acids has been
studied. While the N-succinimidyl ester enolate was
found to be unreactive, N-succinimidyl-substituted cyclopentadienyl complexes were quite reactive, leading to
the expected stable
organometallic amides. Bovine serum albumin (BSA), a 66 kDa
molecular mass globular
protein, could be labeled with fair yields, and conjugates were
characterized by IR
spectroscopy of the CO ligands. Organotungsten
N-succinimidyl esters thus appear as
promising reagents for the labeling of proteins with heavy metals.
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