Synthesis of N‑Heterocycle Substituted Silyl Ligands within the Coordination Sphere of Iron

N-Heterocycle-substituted
silyl iron complexes have been synthesized
by nucleophilic substitution at trichlorosilyl ligands bound to iron.
The homoleptic (tripyrrolyl)- and tris­(3-methylindolyl)­silyl groups
were accessed from (Cl3Si)­CpFe­(CO)2 (Cl3SiFp) by substitution of chloride with pyrrolide or 3-methylindolide,
respectively. Analogously, nucleophilic substitution of Cl with pyrrolide
on the anionic Fe(0) synthon Cl3SiFe­(CO)4– generates the (tripyrrolyl)­silyl ligand, bound to
the iron tetracarbonyl fragment. The bulkier 2-mesitylpyrrolide substitutes
a maximum of 2 chlorides on Cl3SiFp under the same conditions.
The tridentate, trianionic nucleophile tmim (tmimH3 = tris­(3-methylindol-2-yl)­methane)
proves reluctant to perform the substitution in a straightforward
manner; instead, ring-opening and incorporation of THF occurs to form
the tris-THF adduct tmim­(C4H8O)3SiFe­(CO)4–. The bidentate, monoanionic nucleophile
2-(dipp-iminomethyl)­pyrrolide (DippIMP,
dipp = 2,6-diisopropylphenyl) shows chloride displacement and addition
of a second DippIMP moiety on the imine backbone. The heterocycle-based
silyl ligands were shown to be sterically and electronically tunable,
moderately electron-donating ligands. The presented approach to new
silyl ligands avoids strongly reducing conditions and potentially
reactive hydrosilane intermediates.