Cumulene sp-carbon molecular wires C 2 [Fc(Ph)CdC(Ph)Fc] up to C 7 [Fc(Ph)CdCdCd CdCdCdC(Ph)Fc] endcapped by two electroactive ferrocenyl groups are presented in this report. Synthetically, ferrocenyl cumulenes can be built-up by a modular strategy using C 1 synthon ferrocenyl(phenyl)ketone as starting material with various acetylenic/propargylic/ homopropargylic C 2 -C 5 reagents, taking into account and exploiting the efficient stabilization of an electron-deficient carbenium center by an adjacent ferrocenyl moiety. With increasing cumulene chain length the reactivity of cumulenes increases considerably, indicating steric protection as the main requirement for bulk stability. Even cumulenes C 2 , C 4 , and C 6 are conjugated "molecular wires" effecting electronic communication between the terminal ferrocenyl substituents, whereas odd cumulenes C 3 , C 5 , and C 7 are nonconjugated and electronically decoupled due to their orthogonal terminal π-systems. Electrochemically, separate redox waves can be detected up to a C 6 cumulene spacer, but the electronic communication between the endcapping redox-active ferrocenyl substituents decreases with increasing cumulene length.

Synthetically established methods for methylation of phenols and demethylation of methyl phenyl ethers rely in general on hazardous reagents or/and harsh reaction conditions and are irreversible. Consequently, alternative regioselective methods for the reversible formation and breakage of CO ether bonds to be performed under mild and sustainable conditions are highly desired. Here we present a biocatalytic shuttle concept making use of corrinoiddependent methyl transferases from anaerobic bacteria. The two-component enzymatic system consists of a corrinoid protein carrying the cofactor and acting as methyl group shuttle, and a methyltransferase catalyzing both methylation and demethylation in a reversible fashion. Various phenyl methyl ethers are successfully demethylated and serve in addition as sustainable methylating agents for the functionalization of various substituted catechols. Therefore, this methyl transfer approach represents a promising alternative to common chemical protocols and a valuable add-on for the toolbox of available biocatalysts.

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The ether functionality represents a very common motif in organic chemistry and especially the methyl ether is commonly found in natural products. Its formation and cleavage can be achieved via countless chemical procedures. Nevertheless, since in particular the cleavage often involves harsh reaction conditions, milder alternatives are highly demanded. Very recently, we have reported on a biocatalytic shuttle catalysis concept for reversible cleavage and formation of phenolic O-methyl ethers employing a corrinoid-dependent methyl transferase system from the anaerobic organism Desulfitobacterium hafniense.Here we report the technical study of this system, focusing on the demethylation of guaiacol as model reaction. The optimal buffer-, pH-, temperature-and cofactor-preferences were determined as well as the influence of organic co-solvents. Beside methyl cobalamin also hydroxocobalamin turned out to be a suitable cofactor species, although the latter required activation. Various O-methyl phenyl ethers were successfully demethylated with conversions up to 82% at 10 mM substrate concentration.