The complex trans-[Cr(CO)(3)(heptamethylindenyl)Rh(CO)(2)] (II) is a very efficient catalyst precursor in the cyclotrimerization reaction of dimethyl acetylenedicarboxylate (DMAD) to hexacarbomethoxybenzene. The formation of the ''true'' catalyst, likely to be the complex trans-[Cr(CO)(3)-Ind*-Rb(DMAD)(2)], is the slow step of the reaction and takes place during the induction period, the length of which is temperature dependent. After total consumption of the monomer two organometallic complexes were isolated from the inorganic residue, viz., the catalyst precursor II and the complex trans-[Cr(CO)(3)-Ind*-Rh(CO)(FADE)] (III; FADE = fumaric acid dimethyl ester), which turns out to be active in the trimerization reaction as II. The hydrogenation of DMAD to FADE is probably occurring via C-H bond activation of the solvent cyclohexane.
Heterobimetallic Indenyl Complexes. Mechanism of Cyclotrimerization of Dimethyl Acetylenedicarboxylate (DMAD) Catalyzed bytrans-[Cr(CO)3(Heptamethylindenyl)Rh(CO)2]†
CECCON, ALBERTO;SANTI, SAVERIO;
1997
Abstract
The complex trans-[Cr(CO)(3)(heptamethylindenyl)Rh(CO)(2)] (II) is a very efficient catalyst precursor in the cyclotrimerization reaction of dimethyl acetylenedicarboxylate (DMAD) to hexacarbomethoxybenzene. The formation of the ''true'' catalyst, likely to be the complex trans-[Cr(CO)(3)-Ind*-Rb(DMAD)(2)], is the slow step of the reaction and takes place during the induction period, the length of which is temperature dependent. After total consumption of the monomer two organometallic complexes were isolated from the inorganic residue, viz., the catalyst precursor II and the complex trans-[Cr(CO)(3)-Ind*-Rh(CO)(FADE)] (III; FADE = fumaric acid dimethyl ester), which turns out to be active in the trimerization reaction as II. The hydrogenation of DMAD to FADE is probably occurring via C-H bond activation of the solvent cyclohexane.
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