The use of organotellurium heterocycles as precursors for novel organometallic compounds

Abstract

The reactions of group 16 heterocycles with organometallic reagents are described. Thiophenes have been used as models for organic sulfur in coal and their reactivity towards triiron dodecacarbonyl has been investigated. Reaction of unsubstituted thiophene with Fe₃(CO)₁₂ results in desulfurisation of the heterocycle, with the organic fragment being recovered in the form of the ferrole, C₄H₄.Fe₂(CO)₆. In addition a novel organometallic compound of iron is isolated, the formula of which is shown to be C₄H₄.Fe₃(CO)₈. Bezothiophene reacts with Fe₃(CO)₁₂ to yield benzothiaferrole, C₈H₆S.Fe₂(CO)₆, in which the sulfur is retained in the heterocycle. Dibenzothiophene, a more accurate model for organic sulfur in coal, displays no reactivity towards the iron carbonyl, suggesting that the more condensed systems will desulfurise less readily. Microwave methodology has been successful in accelerating the reactions of thiophenes with Fe₃(CO)₁₂. However, reaction of benzothiophene does not proceed to the desulfurisation stage while dibenzothiophene is unreactive even under microwave conditions.
Tellurophenes (Te analogues of thiophenes) are shown to mimic the behaviour of thiophenes towards certain organometallic reagents with the advantage that their greater reactivity enables recovery of products in higher yields. Hence, reaction of tellurophene with Fe₃(CO)₁₂ again affords the ferrole but with an almost ten-fold increase in yield over thiophene. More significantly, dibenzotellurophene is also detellurated by the iron carbonyl affording the previously inaccessible dibenzoferrole, C₁₂H₈.Fe₂(CO)₆, thereby demonstrating the mechanistic feasibility of dechalcogenation of the more condensed aromatic molecules. The potential of tellurium heterocycles to act as precursors for novel organometallics is also recognised owing to the relatively facile elimination of the heteroatom from these systems. Thus, 2-telluraindane reacts with Fe₃(CO)₁₂ to yield a novel organometallic compound of formula C₁₆H₁₆.Fe(CO)₃, arising from the unsymmetric dimerisation of two organic fragments.