The Trinuclear Gallium‐Bridged Ferrocenophane [{Fe(η⁵‐C₅H₄)₂}₃Ga₂]: Synthesis, Bonding, Structure, and Coordination Chemistry

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.

Suzuki–Miyaura coupling in the presence of (2,2,2-triferrocenylethyl)diphenylphosphane

“…These, together with its exceptional electrochemical properties, make ferrocenebased complexes promising candidates for the preparation of new materials with applications in organic synthesis, catalysis and material science [1]. Although a wide range of molecular structures containing more than one ferrocene unit have been described [2][3][4][5][6][7][8][9][10], triferrocenylmethyl derivates have been investigated little so far, and this is most likely because of the difficulties encountered in the synthesis of the triferrocenylmethyl scaffold. Triferrocenylmethanol has been previously synthesized by Pauson and Watts by the addition of ferrocenyllithium to diferrocenylketone.…”

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

“…Attempts to measure mass spectra (EI MS, 70 eV) did not reveal the respective molecular ions. Instead, the pattern of diferrocene (CpFeC 5 [a] of ferrocenophanes 4b and 4a [6] for comparison.…”

“…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.…”

[1.1]Ferrocenophane‐1,12‐dione as a Precursor of 1,12‐Di(cyclopenta‐2,4‐dienylidene)‐[1.1]ferrocenophane, a Doubly Bridged Difulvene

“…The incentive for this research was the possibility of an introduction of a third ferrocene unit in order to get an access to the symmetrical trinuclear ferrocenophane with two tris(cyclopentadienyl)methane ligands, a gallium analogue of which had earlier been prepared by Jutzi. [30,31] …”