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}₂{GaMe(D)}₂] (D = Monodentate Donor) and [{Fe(η⁵-C₅H₄)₂}₂{GaMe}₂D] (D = Bidentate Donor)

Abstract

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.

Synthesis, Characterization and Reactivity of Dinuclear and Trinuclear Aluminum‐Bridged Ferrocenophanes

“…The most important results are summarized in Scheme 2. Independent of starting material 1, 2 or 3, the use of AlMe 3 or AlEt 3 resulted in the formation of 4a or 4b as the final products in solution. Compounds 4a and 4b could be isolated as crystalline solids.…”

“…We studied the reactivity of starting materials 1-3 [1] towards AlMe 3 and AlEt 3 , respectively, in order to form the pyridine adducts AlR 3 (py) and monitor the fate of the pyridine-free ferrocenediylaluminum compounds. The most important results are summarized in Scheme 2.…”

“…Their formation in equilibria is feasible, if it proves possible to offer another suitable acceptor for the pyridine ligands. It will be shown that AlMe 3 or AlEt 3 can play this role.…”

“…The re-sulting mixture contained 4b together with Et 3 Al, Et 3 Al(py) and several unidentified side products ( 1 H and 13 C NMR). The brown oil thus obtained was washed with hexane (2 mL), and the orange solid after removal of the hexane was dried in vacuo to give 108 mg of 4b (about 50 %) together with Et 3 Al(py) and Et 3 8 ]toluene (1.5 mL). Solid materials were separated by centrifugation, the supernatant liquid phase was collected and volatile materials were removed in vacuo.…”

“…In previous work, [1] we successfully introduced rational synthetic methods to prepare dipyridine adducts 1, 2 and 3 (Scheme 1), which, in contrast to their gallium congeners, [2][3][4][5] had not been known. Interestingly, other attempts in this field, in the absence of pyridine, have produced compounds such as 4 [6] and 5 [7] (Scheme 1), in which at least the central aluminum atoms possess rather unusual surroundings.…”