DFT Mechanistic Insights into the Alkyne Insertion Reaction Affording Diiron μ-Vinyliminium Complexes and New Functionalization Pathways

Abstract

Insertion of propyne or 2-butyne into the Fe-carbyne bond belonging to the fragment [Fe2Cp2(CO)(µ-CO){µ-CNMe(R)}] + (R = Me or Xyl = 2,6-C6H3Me2) was DFT investigated, and plausible intermediates were identified along the formation of the vinyliminium complexes [Fe2Cp2(CO)(µ-CO){µ-η 1 :η 3 -C(Me)C(R′′)CN(Me)(R)}]SO3CF3, [2a-d] + , thus allowing to explain regio-and stereochemical features. The X-ray structure of [2a]SO3CF3 (R = Me, R′′ = H) was determined by single crystal X-ray diffraction. Novel C-C and C-S bond forming pathways involving the vinyliminium ligand were then explored. Thus, [2b]SO3CF3 (R = Xyl, R′′ = H) reacted with cyclopentadiene (or cyclopentene), triphenylphosphonium methylide and benzyl bromide, in tetrahydrofuran in the presence of sodium hydride, to give respectively [Fe2Cp2(CO)(µ-CO){µ-η 1 :η 2 -C(Me)C{C(CH)4}CN(Me)(Xyl)}], 3, [Fe2Cp2(CO)(µ-CO){µ-η 1 :η 2 -C(Me)C(CH2)CN(Me)(Xyl)}], 4, and [Fe2Cp2(CO)(µ-CO){µ-η 1 :η 3 -C(Me)C(CH2Ph)CN(Me)(Xyl)}]Br, [5]Br, in good yields. The unstable complex 4 (detected by IR spectroscopy) readily converted into [2c]SO3CF3 (R = Xyl, R′′ = Me) upon HSO3CF3 protonation of the methylide function. [5]Br was obtained as E/Z isomeric mixture, which was then quantitatively converted into the most stable Z form, by heating in methanol solution at 50 °C. The reactions of [2cd]SO3CF3 (R = Me, Xyl, R′′ = Me) with PhSSPh/NaH selectively yielded the aminoalkylidyne species [Fe2Cp2(SPh)(CO)(µ-CO){µ-CN(Me)(Xyl)}], 6, and the bis-alkylidene [Fe2Cp2(CO)(µ-CO){µ-η 1 :η 2 -C(Me)C(Me)(SPh)CN(Me)2}], 7, respectively, probably via the intermediacy of the radical compounds 2c-d. The structures of 3-7 and 2c-d were elucidated by DFT calculations, and the isolated products were characterized by analytical and spectroscopic methods.

Anticancer Potential of Diiron Vinyliminium Complexes

“…Compounds [ 7 – 13 ]CF 3 SO 3 and [ 17 – 18 ]CF 3 SO 3 were reported previously, whereas [ 1 – 6 ]CF 3 SO 3 , [ 14 – 16 ]CF 3 SO 3 and [ 19 ]CF 3 SO 3 are unprecedented. [ 18 ]CF 3 SO 3 was primarily obtained in its trans form (with respect to the geometry of the Cp ligands), before being quantitatively converted into the thermodynamically stable cis product upon gentle heating in methanol. The new products were characterized by IR, NMR (Figures S1–S37) and UV/Vis spectroscopy.…”

Constructing Organometallic Architectures from Aminoalkylidyne Diiron Complexes

“…The formation of new C 2 –C bonds has been achieved also by reactions of 29 (R = Xyl, R′ = Me) with NaH in the presence of, respectively, Ph 3 PCH 2 , cyclopentadiene, cyclopentene or benzyl bromide …”

“…The resulting cationic thiophenolate‐vinyliminium ( 68 ) can be modified by hydride addition into an efficient organometallic N,S ‐ligand ( 69 ), which makes possible the facile construction of heterometallic structures ( 70 ) . Alternatively to the synthesis of 68 , as a result of peculiar electronic/steric effects exerted by R/R′ groups, vinyliminium complexes 29 may react with PhSSPh/NaH affording the aminoalkylidyne 71 , via C 2 –C 1 bond cleavage and release of the C 2 C 3 unit (Scheme d) , …”

Bond Forming Reactions Involving Isocyanides at Diiron Complexes

“…This second synthetic route affords a more convenient and general access to diiron vinyliminium complexes (compounds 11) in that the net positive charge of 4 makes CO elimination viable via treatment with Me 3 NO, rather than with the less selective photochemical method. The need for CO removal has been explained by density functional theory (DFT) mechanistic investigation on the alkyne insertion reaction [72]. In both synthetic routes leading to 11, the overall remarkable result is the coupling of an alkyne with a bridging isocyanide, accompanied (assisted) by N alkylation.…”