The reaction of 1,1‘-bis(trichlorostannyl)ferrocene with trimethylgallium results in the formation of Fe(C5H4GaMe2)2 (1), the first digallylferrocene. An X-ray crystal structure analysis of 1 reveals a polymeric structure. NMR data confirm a monomeric structure of [1·2 donor] in donor solvents. The reaction of 1 with phenazine results in the formation of the supramolecular polyferrocene [1·phenazine] n . Its rodlike structure is proven by X-ray crystallography.

Gentle warming of 1,1‘-bis(dimethylgallyl)ferrocene (1) leads to the formation of trimethylgallium and the thermolabile compound [{Fe(η5-C5H4)2}2{GaMe}2] (2), a [1.1]ferrocenophane featuring group 13 elements in bridging positions. While NMR data for 2 prove a dynamic structure in solution, X-ray data reveal an anti conformation of the ferrocenophane framework in the solid state. The anti conformation is maintained in the thermolabile adducts 2a−g, which are obtained from 2 and the donors diethyl ether (2a), pyridine (2b), pyrimidine (2c), quinoxaline (2d), DMSO (2e), pyrazine (2f), and dioxane (2g), by donor-exchange reactions (2b−g) or on gentle warming of the respective donor adducts of 1. Rodlike polymers are formed either by interaction of 2 with bidentate donors (2f,g) or by π-stacking effects of aromatic molecules acting as monodentate donors (2b−d). Steric requirements inhibit the complex formation between 2 and the donor phenazine. A cyclic voltammogram of 2b in pyridine reveals two reversible oxidation steps at −314 and −114 mV, indicating only weak electron delocalization in the cationic species. The formation of 2 from 1 has been shown to be reversible and thus is an example of an application of “dynamic covalent chemistry” as synthetic strategy.

A molecular carousel, that is the appearance of the structure of the title compound [1⋅2 py] (see picture), the first complex of a new structure type prepared by a highly selective condensation reaction from the equally new complex [Fe(C5H4GaMe2)2]. The first gallium bridged [m.m]ferrocenophane [{Fe(C5H4)2}2{GaMe(C5H5N)} 2] is formed as an intermediate; this compound can also be prepared in a planned synthesis and can be converted into [1⋅2 py] by warming. The complex [1⋅2 py] as well as [1⋅2 Et2O] and [1⋅2 DMSO], which were formed by donor exchange, offers various interesting properties, for example, [1⋅2 DMSO] can be reversibly oxidized to the mono‐, di‐, and trication.

No abstract

The trinuclear ferrocenophane [{Fe(eta(5)-C(5)H(4))(3)}(2)Ga(2)] (3) featuring two sp(2)-hybridized gallium atoms in bridging positions between three ferrocene-1,1'-diyl units represents a novel type of ferrocene derivative. Compound 3 is obtained by thermal treatment of 1,1'-bis(dimethylgallyl)ferrocene (1) in nondonor solvents or in diethyl ether as solvent and subsequent thermal decomplexation. The [1.1]ferrocenophane [{Fe(eta(5)-C(5)H(4))(2)}(2){GaMe}(2)] (2) is an intermediate in the formation of 3. The reaction of 3 with an excess of trimethylgallium leads back to 1 and proves the reversibility of the multistep reaction sequence. Theoretical calculations reveal a carousel-type D(3h) structure for 3. The compound can best be described as being composed of three only weakly interacting ferrocenediyl units covalently connected by gallium atoms without any pi-bond contribution in the Ga--C bonds. Owing to steric constraints 3 cannot be reduced to the dianion 3(2-), which would feature a Ga--Ga bond. Compound 3 represents a stereochemically rigid difunctional Lewis acid allowing the formation of the adducts 3 a-3 d possessing linear donor-aceptor-aceptor-donor arrangements. Crystal structure data for 3 a-3 d show a symmetry-reduced chiral ferrocenophane core (D(3h)-->D(3)). A polymeric rodlike structure is observed for 3 b and 3 d caused by pi-stacking effects (3 b) or by a difunctional donor-acceptor interaction (3 d). In solution, the chirality of the adducts is lost by rapid interconversion of the enantiomers. A cyclic voltammogram of 3 b in pyridine reveals three quasi-reversible oxidation steps at -356, -154, and 8 mV, indicating only weak electron delocalization in the cationic species. The redox potentials of the pyridine adduct 3 b are compared with those of other pyridine-stabilized gallyl-sustituted ferrocene derivatives and with ferrocene itself.