Syntheses, Characterization, and Redox Activity of Ferrocene-Containing Titanium Complexes

The chemistry of bis(π–η5:σ–η1-pentafulvene)titanium complexes
is characterized by a broad
range of E–H activation and Ti–C functionalization reactions,
whereas ferrocene derivatives are easily accessible and redox-active
compounds. The reaction of ferrocenealdehyde and -ketones with bis(π–η5:σ–η1-pentafulvene)titanium
complexes result in the formation of bimetallic complexes via insertion
of the CO double bond of the aldehyde/ketone into the Ti–Cexo bond of the pentafulvene moiety. The reaction of bis(π–η5:σ–η1-pentafulvene)titanium
complexes with ferrocenyl alcohols leads to alcoholate complexes via
deprotonation of the OH group by the pentafulvene ligand. Because
of the one remaining pentafulvene unit, further functionalization
of the complexes is possible. In this work, we proceeded with 1,1′-bifunctionalized
ferrocene derivatives for intramolecular follow-up reactions. 1,1′-Ferrocenedimethanol
reacts with bis(π–η5:σ–η1-pentafulvene)titanium complexes in a double O–H deprotonation
reaction to yield the dialcoholate complex. 1,1′-bis(phenylphosphine)ferrocene
reacts differently as the double P–H deprotonation reaction
results in the formation of a P–P linked phosphine. Therefore,
we studied the reactivity of 1,1′-bis(phenylphosphine)ferrocene
toward Rosenthal’s reagent. As Rosenthal’s reagent is
regarded as a masked titanocene(II) species, it undergoes redox reactions
toward H-acidic substrates, forming a paramagnetic Ti(III) complex.