Novel Catalytic Hunsdiecker−Heck (CHH) Strategy toward All-E Stereocontrolled Ferrocene-Capped Conjugated Push−Pull Polyenes

Abstract

Halodecarboxylation reaction of ferrocenylacrylic acid 1 and ferrocenyldienoic acid 3d with N-bromo-and N-iodosuccinimide in the presence of catalytic tetrabutylammonium trifluoroacetate at -40 °C and -78 °C affords the corresponding β-halovinylferrocenes 2a, 2b and δ-haloferrocenyldiene 4 in 37-72% yields. Heck reaction of β-iodovinylferrocene 2a with vinyl substrates (CH 2 dCH-Z where Z ) CO 2 Me, CO 2 Et, COMe, CO 2 H, CONH 2 , 4′-NO 2 C 6 H 4 ) in the presence of tri(4-tolyl)arsine/palladium acetate/lithium chloride/triethylamine in acetonitrile at 35-80 °C affords the corresponding ferrocenyldienes 3a-3f in 50-81% isolated yields. Similar reaction of δ-iodoferrocenyldiene 4 with vinyl substrates (CH 2 dCH-Z where Z ) CO 2 Me, CO 2 Et, CO 2 H, 4′-NO 2 C 6 H 4 ) affords the corresponding ferrocenyltrienes 5a-5d in 55-87% isolated yields. The ferrocene-capped conjugated dienes and trienes show excellent all-E stereoselectivity (vide NMR). The electronic, redox, and nonlinear optical properties of ferrocenylpolyenes have been evaluated. The data suggest that upon increasing the polyene chain length, (a) the absorption maxima shifts progressively to higher wavelength, (b) the oxidation potential of the Fc/Fc + couple (E 1/2 ) decreases, and (c) the HRS-derived secondorder NLO response (β) increases. From the insights derived from semiempirical calculation (ZINDO/1), a mechanism for the halodecarboxylation reaction has been proposed suggesting the prior formation of tetrabutylammonium salt of ferrocenylacrylic acid I. Attack of the halogenium atom at the π CdC in I leads to the formation of intermediate II, and the latter triggers the elimination of carbon dioxide.

Improved synthesis of diethyl ferrocenylphosphonate, crystal structure of (FcPO3Et2)2·ZnCl2, and electrochemistry of ferrocenylphosphonates, FcP(O)(OR)2, FcCH2P(O)(OR)2, 1,1′-fc[P(O)(OR)2]2 and [FcP(O)(OEt)2]2·ZnCl2 (Fc=(η5C5H5)Fe(η5C5H4), fc=(η5C5H4)Fe(η5C5H4), R=Et, H)

“…The change of the first ethyl group (entries 7, 8) gives rise to a greater variation (32 mV) than the second (entry 9) (10 mV). It is noteworthy that this variation decreases with the length of the spacer even for phosphonates containing p conjugated ferrocenyl units [20], and does not exist for ferrocenyl carboxylate [32]. A huge effect is observed during the neutralisation of the ferrocenylphosphonic acid, the salts being easier to oxidize than ferrocene (entries 3-5).…”

Syntheses, Structures and Nonlinear Optical Properties of Ferrocenyl Complexes with Arylethenyl Substituents

“…This is in good agreement with the greater stabilization of the positive charge corresponding to the more effective conjugation of the (E) isomers, and indicates a higher degree of charge transfer from the metal center to the polyene backbone. [5,6,15] The aldehydes 2 and 3 possess a much higher half-wave potential than the ferrocenyl complexes with one 4-nitrophenylethenyl or 4-cyanophenylethenyl substituent, [4Ϫ6] perhaps due to the electron-accepting nature of the aldehyde group. The substitution of the aldehyde group by the corresponding conjugated ligand to give 4 and 5, results in a shift to more cathodic potentials, probably as a consequence of the enhanced stabilization of the positive charge of the resultant ferrocenium species at the two conjugated ancillary ligands.…”

New pyridinium conjugated ferrocenes: Synthesis and electrochemical properties

“…The research for new conjugated ferrocenic compounds has not stopped because of the interest of these compounds in catalysis reactions, triggering electron transfer [1][2][3][4], as well as bringing interesting perspectives in the field of non-dipolar NLO [5][6][7][8][9]. In fact, with its almost always reversible one electron system, the ferrocene moiety can be switched from a good donor in the reduced state, to a weak attractor in the oxidized one.…”