Triformylferrocenes, novel modules for organometallic scaffolds

Protection of formylferrocene with propanediol under acidic conditions furnishes its acetal. Metalation of the acetal occurs mainly in the ortho position at the same ring. Reaction with N-formylpiperidine leads to the semiprotected 1,2-diformylferrocene, and the monoacetal of 1,1′,2-triformylferrocene, which can be obtained upon acidic deacetalization. Further protection of the semiprotected 1,2-diformylferrocene with propanediol results in the corresponding bisacetal, which is metalated to give the title compound 1,2,3-triformylferrocene after quenching of the anion with N-formylpiperidine and acidic deprotection. The 1,1′,2-triformylferrocene undergoes an interesting solid-state reaction at 170 °C under cross-linking to yield a novel organometallic polycondensate, while 1,2,3-triformylferrocene melts undecomposed. 1,2-Diformylferrocene was transformed into 1,2-bisbutadiynylferrocene by treatment with Taberʹs reagent, followed by coupling of 1,2-diethynylferrocene to bromo-triisopropylsilylethyne under Cadiot–Chodkiewicz conditions in an overall 40% yield starting from diformylferrocene.