New, Simple Synthetic Route to Functional Mono- and Biferrocenes

Abstract

Visible-light photolysis using a simple 100 W lamp of the readily available precursors [(eta(5)-C(5)H(4)R)Fe(eta(6)-toluene)][PF(6)] (R = H, Me, Cl, COMe, CO(2)H, CO(2)Me, CO(2)CH(2)CCH, CONHCH(2)Ph, NHCH(2)Ph), or the bimetallic precursor [(mu(2),eta(5),eta'(5)-Fv)Fe(2)(eta(6)-toluene)(2)][PF(6)](2) (Fv = fulvalene) in the presence of a substituted cyclopentadienyl salt C(5)H(4)R'M (R' = COCH(3), CO(2)CH(3), PPh(2), SiMe(2)CH(2)Cl; M = Li or Na) or the dicyclopentadienyl salt 1,4-C(6)H(4)(CH(2)C(5)H(4))(2)Na(2) in dichloromethane, acetonitrile, or tetrahydrofuran under ambient conditions selectively yields 15 functional mono- and biferrocenes.

Why is Ferrocene so Exceptional?

“…The reduced Fe I forms are even stronger reductants than cobaltocene, and were designed as electron reservoirs paralleling fullerenes . Other practical reactions involve the visible‐light photolytic cleavage of the Fe–arene bond in [FeCp(η 6 ‐arene)] + salts, leading to functional ferrocenes [Equation ] and other organoiron cations, whereas thermal arene exchange in these neutral 19‐electron complexes proceeded at sub‐ambient temperature …”

“…[149,150] The reduced Fe I forms are even stronger reductants than cobaltocene [151,152] and were designed as electron reservoirs paralleling fullerenes. [153] Other practical reactions involve the visible-light photolytic cleavage of the Fe-arene bond in [FeCp(η 6 -arene)] + salts, leading to functional ferrocenes [Equation (5)] and other organoiron cations, [154][155][156][157] whereas thermal arene exchange in these neutral 19-electron complexes proceeded at sub-ambient temperature. [158] (5) With 1,1′-diacetylferrocene, only double ring exchange with polymethylbenzene derivatives was achieved, yielding [Fe(arene) 2 ] 2+ salts, a series of complexes isolobal to ferrocene with rich redox and arene activation properties.…”

Generation of Cyclopentadiene for Diels–Alder Reactions by Visible‐Light Irradiation of Iron Sandwich Complexes

“…Next, we briefly explored the possibility of the generation of substituted cyclopentadienes from the corresponding iron complexes. Complex [(C 5 H 4 COOMe)Fe(C 6 H 6 )]PF 6 ( 6 ) was chosen as a model compound, because its carboxylic group can be easily attached to various molecular fragments [35] . This complex was prepared in three steps following the Nesmeyanov method [36] from the commercially available diethyl‐ferrocene ( Scheme 5).…”

“…Complex [(C 5 H 4 COOMe)Fe(C 6 H 6 )]PF 6 (6) was chosen as a model compound, because its carboxylic group can be easily attached to various molecular fragments. [35] This complex was prepared in three steps following the Nesmeyanov method [36] from the commercially available diethyl-ferrocene (Scheme 5). Complex 6 can be also obtained from the unsubstituted ferrocene following the approach developed by Astruc et al [35,37] However, in our hands this method gave lower yields and was less convenient because of the complicated separation of [(C 5 H 5 )Fe(C 6 H 6 )]PF 6 and [(C 5 H 4 COOH)Fe-(C 6 H 6 )]PF 6 during the first step.…”

“…[35] This complex was prepared in three steps following the Nesmeyanov method [36] from the commercially available diethyl-ferrocene (Scheme 5). Complex 6 can be also obtained from the unsubstituted ferrocene following the approach developed by Astruc et al [35,37] However, in our hands this method gave lower yields and was less convenient because of the complicated separation of [(C 5 H 5 )Fe(C 6 H 6 )]PF 6 and [(C 5 H 4 COOH)Fe-(C 6 H 6 )]PF 6 during the first step. The structure of the intermediate complex [(C 5 H 4 COOH)Fe(C 6 H 6 )]PF 6 (5) was established by X-ray diffraction analysis (Figure 1), which revealed the formation of typical dimers with hydrogen bonds between the carboxylic groups.…”