Survey of Strategies for Switching Off Base Stations in Heterogeneous Networks for Greener 5G Systems

Reactivity and Properties of Metal Complexes Enabled by Flexible and Redox-Active Ligands with a Ferrocene Backbone

“…We were able to synthesize a series of inverse sandwich metal arene or alkene metal complexes, such as naphthalene, anthracene, 57 biphenyl, p-terphenyl, 1,3,5-triphenylbenzene, 29 and (E)-stilbene, 45 with a general formula [(NN TBS )M(THF) x ] 2 (-arene)[K(solvent)] y (for arene = naphthalene, anthracene, and (E)-stilbene, y = 0, x = 0 for M = Sc or x = 1 for other rare-earth metals; for arene = biphenyl, p-terphenyl, 1,3,5-triphenylbenzene, y = 2 and x = 0). For the doubly reduced arene in [(NN TBS )M(THF) x ] 2 (-arene), the negative charges were delocalized over two or more phenyl rings and thus the metal ions coordinated to different rings, in agreement with an ionic interaction with the rare-earth metal.…”

“…The rare-earth metal ions also played an important role in the stabilization of the quadruply reduced benzene tetraanion as DFT calculations revealed a covalent interaction between the metal orbitals and the * orbitals of benzene with  symmetry. 29 . We hypothesized that the tighter binding between the ferrocene backbone and scandium provided an additional protection around the scandium center and thus allowed the formation of a unique realgar-type P 8 tetraanion.…”

“…The synthesis of rare-earth metal complexes supported by ferrocene-based ligands can be divided into two groups based on the type of ligand: for the ferrocene diamide ligands NN fc , an alkane elimination reaction between H 2 (NN fc ) and rare-earth metal tribenzyl precursors was found to be the most straightforward route without contamination of side products for most rare-earth metals (except the redox active europium and ytterbium); 29,41,46,65,81,82 for the tetradentate ligands OEEO fc , various methods, including amine or alcohol elimination and salt metathesis, could be employed to obtain the desired rare-earth metal complexes. 43,59,78 (NN fc ): Initially, we sought out to employ salt metathesis between K 2 (NN fc ) and MX 3 (THF) y (M = rare-earth metal, X = Cl or Br, y = 3-4) and found that the reaction was poorly reproducible and usually accompanied by a side product, the bis-ligand-adduct K[(NN fc ) 2 M], which was difficult to remove.…”

“…35 Our group has taken a different approach in order to achieve the goal of coordination flexibility and redox activity (Chart 1g, h). [27][28][29] Instead of using a purely organic ligand, we reasoned that an organometallic ligand should serve as an excellent candidate. Such a ligand needs to fulfill the following requirements: (1) the organometallic part should be chemically inert under common reaction conditions; (2) the metal should be redox active; (3) the organometallic fragment should be able to act as a weak donor.…”

“…28 In some cases, a metal-toligand charge transfer can result in partial reduction of the arene and, thus, provide an electron reservoir for the metal. 29,30 Therefore, in theory, arenes could serve as flexible and redox non-innocent ligands. In practice, because the arene-metal interaction is usually not robust enough, the arene is usually incorporated into the backbone of the supporting ligand.…”