Characterization of the Low-Energy Electronic Excited States of Benzoyl-Substituted Ferrocenes

Abstract

Resonance Raman spectroscopy has been employed to probe the excited-state distortions associated with the low-energy electronic transition of benzoylferrocene and 1,1'-dibenzoylferrocene. Resonance intensity enhancement of in-plane ligand modes, in general, and the carbonyl stretching mode, in particular, supports the proposal that the excited state populated by this transition contains appreciable metal-to-ligand charge transfer character. The redistribution of charge that occurs upon populating this state weakens the metal-ring bonding and facilitates the loss of a benzoylcyclopentadienide anion. This photochemical reaction has been investigated by an on-line electrospray ionization mass spectrometry technique that allows direct detection of primary and secondary products with solution lifetimes down to the millisecond range.

Photoinduced iron–cyclopentadienyl (Fe–Cp) bond cleavage reactions and photocontrolled polymerizations of strained [1]ferrocenophanes

“…Based on their work, Kutal and co-workers have also proposed that excitation near the MLCT energy was believed to weaken the Fe-Cp bond by reducing the hapticity of one of the Cp rings from g 5 to g 4 (Fig. 2) [29][30][31]. This was also accompanied by an increase in the electrophility of the Fe centre and thus facilitated coordination by an incoming ligand such as a weakly donating solvent (L).…”

“…In 1998, Kutal and coworkers demonstrated that 1,1 0 -dibenzoylferrocene can effectively function as photoinitiator in the anionic polymerization of ethyl-a-cyanoacrylate [28]. During the investigation to identify the mechanism for this process, Kutal et al had also carried out detailed studies on the solution photochemistry of benzoyl-substituted ferrocenes by resonance Raman and UV-Vis spectroscopy as well as electrospray ionization mass spectrometry [29,30]. The analysis led to the following major conclusions.…”

“…The analytical data strongly suggested that the photochemical reaction of 1, 1 0 -dibenzoylferrocene in the presence of a coordinating solvent L led to Fe-Cp bond dissociation, yielding the benzoylcyclopentadienide anion with concomitant formation of the half-sandwich Fe(II) complex stabilized by L (Scheme 2). The former was believed to be the photoinitiator in the anionic polymerization of ethyl-a-cyanoacrylate [29][30][31].…”

Photoinitiation of multifunctional acrylates via ferrocene-alkyl chloride charge transfer complexes

“…Titanocenes and ferrocenes are numbered among the successfully implemented organometallic photoinitiators. [11][12][13][14][15][16][17][18][19][20][21][22][23] In a review article authored by Yang and Kutal,20 the mechanism of titanocene and ferrocene photoinitiation is delineated; however, in this research, the ferrocene photoinitiators, specifically involving free-radical initiation, will be explored in detail.…”

“…21 The use of either ferrocene or 1,1 0 -dibenzoylferrocene has also been shown to initiate anionic photopolymerization in certain cases. [21][22][23] Thus, the utility of ferrocene or ferrocene-like derivatives to initiate a broad range of monomers is very apparent.…”