As a part of our interest in C-C bond forming reactions1 and ongoing investigations on the reactivity of the μ-aminoalkylidyne complexes [Fe2{mu-CNMe(R)}(mu-CO)(CO)(NCMe)(Cp)2]SO3CF3 (1; R=Me, -CH2Ph, 2,6Me2C6H3) 2,3, we decided to examine the reactions with alkynes. Replacement of the acetonitrile with a chloride (2) and subsequent addition of AgCF3SO3 provides a formal unsaturation on the metal atom, which allows the insertion of mono and di-substituted acetylenes, into the metal –mu-carbyne carbon, leading to the formation of novel bridging iminium-vinyl diiron complexes 3 (see scheme). The X ray crystal structure of [Fe2{mu-C(SiMe3)CHCN(Me)(Me2C6H3)}(mu-CO)(CO)(Cp)2]SO3CF3 has been determined and shown in figure. Structural and NMR data indicate that the insertion is stereospecific, leading to the isomeric form in which the biggest substituent of the inserted alkyne is situated on the carbon adjacent to the Fe atom. Compounds 3 are cationic and characterised by a bridging unsaturated ligand: the study of the reactivity towards nucleophiles has showed different behaviours according to the nature of R. If R=Me or -CH2Ph, nucleophilic attacks are directed to the alpha-carbon of the ring. Otherwise, with the more hindered substituent (R=2-6Me2C6H3), steric and electronic effects play important roles: hydride addition occurs at the beta-carbon, and, in case of monosubstituted alkynes, deprotonation of the inserted alkyne easily occurs, so generating a terminal acetylide.
SYNTHESIS AND REACTIVITY OF NOVEL BRIDGING-IMMINIUM-VINYL DIIRON COMPLEXES
MARCHETTI, FABIO;
2002-01-01
Abstract
As a part of our interest in C-C bond forming reactions1 and ongoing investigations on the reactivity of the μ-aminoalkylidyne complexes [Fe2{mu-CNMe(R)}(mu-CO)(CO)(NCMe)(Cp)2]SO3CF3 (1; R=Me, -CH2Ph, 2,6Me2C6H3) 2,3, we decided to examine the reactions with alkynes. Replacement of the acetonitrile with a chloride (2) and subsequent addition of AgCF3SO3 provides a formal unsaturation on the metal atom, which allows the insertion of mono and di-substituted acetylenes, into the metal –mu-carbyne carbon, leading to the formation of novel bridging iminium-vinyl diiron complexes 3 (see scheme). The X ray crystal structure of [Fe2{mu-C(SiMe3)CHCN(Me)(Me2C6H3)}(mu-CO)(CO)(Cp)2]SO3CF3 has been determined and shown in figure. Structural and NMR data indicate that the insertion is stereospecific, leading to the isomeric form in which the biggest substituent of the inserted alkyne is situated on the carbon adjacent to the Fe atom. Compounds 3 are cationic and characterised by a bridging unsaturated ligand: the study of the reactivity towards nucleophiles has showed different behaviours according to the nature of R. If R=Me or -CH2Ph, nucleophilic attacks are directed to the alpha-carbon of the ring. Otherwise, with the more hindered substituent (R=2-6Me2C6H3), steric and electronic effects play important roles: hydride addition occurs at the beta-carbon, and, in case of monosubstituted alkynes, deprotonation of the inserted alkyne easily occurs, so generating a terminal acetylide.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
