Electronic effects on the reactivity of cross-conjugated carbonyl systems with Fe2(CO)9

Abstract

Neste trabalho foram estudados os efeitos eletrônicos induzidos por p-substituintes no anel fenilico de diversos compostos carbonílicos conjugados [4-p-R-fenil-1-(1,3-ditiolano-2-ilideno)-3E-buteno-2-ona, onde R=NO 2 , Cl, Br, OMe, NEt 2 (2-6)], e sua reatividade frente a Fe 2 (CO) 9 usando o diagrama de Hammett. A estrutura dos compostos (3 e 4b) foi totalmente estabelecida por análise de difração de raio-X.The electronic effects induced by p-substituents on the phenyl ring of several novel crossconjugated carbonyl compounds [4-p-R-phenyl-1-(1,3-dithiolane-2-ylidene)-3E-butene-2-one, where R= NO 2 , Cl, Br, OMe, NEt 2 (2-6),] and their reactivity towards Fe 2 (CO) 9 have been studied using a Hammett plot. The structure of two compounds (3 and 4b) was fully established by X-ray diffraction analysis.

A Rationale for the Linear Correlation of Aryl Substituent Effects in Iron(0) Tricarbonyl Complexes Containing α,β-Unsaturated Enone (Chalcone) Ligands

“…Representative complexes 2g and 2l are illustrated in Figures and . The chalcone ligands exhibit the expected s-cis (single-bond geometry connecting the enone) conformation, and the bond lengths within the C−C−C−O framework exhibit the changes that are predicted on the basis of the bonding models described above; namely, the O 1 −C A and C B −C C bonds show significant lengthening on coordination to the metal, whereas C A −C B exhibits shortening, compared to the free ligand. ,− An examination of the bond angles around the iron indicates that the complexes are best considered to be six-coordinate octahedral species with three coordination sites occupied by the carbonyl ligands, with the remaining position occupied by O 1 , C C , and the center of the C A −C B bond. The mean bond angles around the iron for all six complexes are shown in Figure .…”

“…Considerable substituent effects are also observed in the NMR spectra of the complexes and ligands; indeed, in the free ligand a linear correlation has been observed between the resonance for C C and the electronic properties of suitable substituents …”

C−S Bond Activation of Two Novel Asymmetric α-azo-Ketenedithioacetals Using Fe2(CO)9

“…Complex 5a was obtained in a trace amount. This compound has been obtained by other methods 13 and as subproduct of α,β-unsaturated ketone analogues in reactions brought about under similar conditions. , The novel complexes 5b and 5c are the principal products, and they arise from the C−S bond activation of 5 . This activation is not selective, as compared with complexes 2 and 3 .…”

“…Thus, when α,β-unsaturated ligands with a dithiol group react with diiron nonacarbonyl, they generate dinuclear complexes 1 . However, ligands that contain an additional conjugated double bond, such as 4-phenyl-1-(1,3-dithiolane-2-ylidene)-3 E -butenone, produce dinuclear Fe(0) complex 2 displaying C−S bond activation . We previously reported that this activation depends on the electronic density of the heterodienic moiety 3b.…”

“…However, ligands that contain an additional conjugated double bond, such as 4-phenyl-1-(1,3-dithiolane-2-ylidene)-3 E -butenone, produce dinuclear Fe(0) complex 2 displaying C−S bond activation . We previously reported that this activation depends on the electronic density of the heterodienic moiety 3b. An attempt to understand the activation mechanism of these systems led us to the synthesis of α,β-unsaturated ketones with a sulfoxide group in β-position, which were regioselectively reacted with Fe 2 (CO) 9 , leading to dinuclear Fe(0) complexes 3 .…”