A digalla[1.1]ferrocenophane and its coordination chemistry:: Synthesis and structure of [{Fe(η5-C5H4)2}2{GaMe}2] and of the adducts [{Fe(η5-C5H4)2}2GaMe(D)}2] (D = monodentate donor) and [Fe(η5-C5H4)2}2{GaMe}2D] (D = bidentate donor)

Gentle warming of 1,1'-bis(dimethylgallyl)ferrocene (1) leads to the formation of trimethylgallium and the thermolabile compound [{Fe(eta(5)-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 :pi-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.