Fulvalenyl Mono- and Diiron Complexes:  Photolytic and Electron-Transfer-Induced Substitution of the Benzene Ligands by Phosphines and CO in the Diiron Fulvalenyl Dibenzene Complexes [Fe₂Fv(C₆H₆)₂]^2+/0. Generation of the Average-Valence Species [Fe₂FvL₆]³⁺(L = Phosphine)

Abstract

The bi-sandwich complex [Fe2Fv(C6H6)2]2+(PF6 -)2 (1 2+; Fv = μ2-η5:η5-fulvalenyl, unless noted otherwise) synthesized from biferrocene, was photolyzed with visible light in acetonitrile in the presence of 1,2-bis(diphenylphosphino)ethane (dppe) or bis(diphenylphosphino)methane (dppm) at −15 °C to give [Fe2Fv(dppe)2(NCMe)2]2+(PF6 -)2 (2a 2+) or [Fe2Fv(dppm)2(NCMe)2]2+(PF6 -)2 (2b 2+). The complexes 2a 2+ and 2b 2+ reacted in refluxing 1,2-dichloroethane with CO to give [Fe2Fv(dppe)2(CO)2]2+(PF6 -)2 (3a 2+) and [Fe2Fv(dppm)2(CO)2]2+(PF6 -)2 (3b 2+), and 2a 2+ reacted similarly with PMe3 to give [Fe2Fv(dppe)2(PMe3)]2+(PF6 -)2 (4 2+). The direduced 38-electron (38e) complex 1 reacted at −15 °C with 1 atm of CO to give [Fe2(μ2-η4:η4-Fv)(CO)6] (7) and with PMe3 to give [Fe2Fv(PMe3)4] (9). When Na+PF6 - was present in stoichiometric amounts in THF, these reactions followed a different course and Na+PF6 - induced electron transfer (disproportionation) by irreversibly dislocating ion pairs: the reaction of 1 with 1 atm of CO gave [Fe(η5-Fv)(η6-C6H6), Na+PF6 -] (5), and that with PMe3 gave [Fe2Fv(PMe3)6]2+(PF6 -)2 (8 2+) and the known complex [Fe(PMe3)4] (10). The cyclic voltammograms (CV) of 2a 2+ and 2b 2+ contain irreversible oxidation and reduction waves, but the CVs of 3a 2+ and 3b 2+ showed two close reversible monoelectronic reduction waves (no oxidation wave). The CVs of the hexaphosphine complexes indicated partially or fully irreversible reduction waves, respectively, but two reversible waves at +0.71 and +0.95 V for 4 2+ and +0.70 and +1.08 V for 8 2+ (vs SCE, Pt, DMF, 0.1 M n-Bu4NBF4 −30 °C). The bielectronic reduction of 2a 2+ and the bielectronic oxidation of 4 2+ and 8 2+ using redox reagents led to decomposition, but the monoelectronic oxidation of 4 2+ and 8 2+ using (p-Br-C6H4)3N+SbCl6 - in CH2Cl2 gave the stable mixed-valence trications 4 3+ and 8 3+ , for which the Mössbauer spectra showed delocalized average valency on the Mössbauer time scale. These studies have opened the route to a variety of mono- and diiron fulvalenyl organometallic compounds, confirming the great importance of the presence of Na+PF6 -. This salt can change reaction pathways and, in particular, induce electron-transfer reactions, underlining the extraordinary electronic flexibility of the fulvalenyl ligand and its ability to transfer the electron flow between two metal centers.

A Novel Coordination Mode of the Fulvalene Ligand in Binuclear Ruthenium Complexes. Synthesis, Structure, and Some Reactivities of [(η5-Cp)Ru(μ2-η6:η6-C10H8)Ru(η5-Cp)](BF4)2

“…A similar redox process was observed in bis(ruthenocenyl)ethylenes . When the redox studies reported by Astruc are considered, a possible redox mechanism for RcRc can be proposed as follows. The stable 36-electron complex RcRc is first oxidized by two successive one-electron oxidation processes for each ruthenocene moiety to give the unstable 34-electron biradical ion [Ru III CpFvCpRu III ] 2+ (A ; see Scheme ), which is transformed to the unstable fulvalene complex B with the Ru II atoms.…”

“…The fulvalene (abbreviated as Fv) ligand is interesting because it provides the possibility of the simultaneous coordination of two metals. Thus, many M−Fv complexes have been reported. − In M−Fv complexes reported to date, two coordination modes have been found; one is the μ 2 -η 5 :η 5 form, which is the most typical, and the other is the μ 2 -η 4 :η 4 form, found in [Fe 2 Fv(CO) 6 ] 2+ and related cations. , Here, we report the synthesis and structure of the Ru−Fv complex 1 , which contains a third type of coordination mode (μ 2 -η 6 :η 6 ) for the Fv ligand. Reactions of 1 with Br 2 or PPh 3 are also described…”

Synthesis of Fulvalene-Bridged Bimetallic Compounds Containing a Substituted Cyclopentadienyl Group Based on Pauson−Khand Chemistry

“…When 4 was treated with BuLi and subsequently with FeCl 2 (THF) n , terferrocene 8 was obtained in 37% yield. The preparation and oxidation state properties of terferrocene have been reported by several groups. 10d,17c, Schottenberger et al reported the formation and some physical properties of heterotermetallocenes.…”

“…Many examples of fulvalene ligand (Fv)-bridged heterobimetallics are metallocene-based with the formulas [(C 5 H 5 )Fe(μ-η 5 :η 5 -Fv)M(C 5 R‘ 5 )] and [(C 5 H 5 )Fe(μ-η 5 :η 5 -Fv)ML x ] where ML x is not a metallocene. There are also many examples of fulvalene-bridged heterobimetallics [M‘L‘ y M(μ-η 5 :η 5 -Fv)M‘L x ] which are not based on metallocenes.…”

Electrochemical activation of reactions involving organometallic compounds

“…An interesting example of replacement of the arene ligand in binuclear fulvalene (Fv) complexes of iron has been reported. 29 The doubly reduced 38-electron complex readily reacts with CO or with different phosphine ligands.…”