This short review describes paths to superphanes with metal-stabilized cyclobutadiene and cyclopentadienone rings in a one-pot and stepwise fashion. The stepwise synthesis also led to a new class of belt-like systems with large rings composed of CpCo-stabilized cyclobutadiene rings connected with propane chains. Finally, our research yielded the first beltenes composed of alternating four-and eight-membered conjugated rings.A superphane is a phane in which all hydrogen atoms of the cyclic conjugated rings are tethered by bridges. This definition goes back to Boekelheide and Hopf [1]. So far, a number of superphanes with benzene rings, heterocycles, and metal-stabilized π-systems have been prepared [2]. Our affair with superphanes started with the reaction of cyclodeca-1,6-diyne 1 with CpCoL 2 , which afforded in a onepot reaction the superphane 2 (Scheme 1) [3]. This reaction was first extended to other cyclic alkynes such as cyclotetradeca-1,8-diyne [4] and cyclooctadeca-1,10-diyne [5]. The superphanes proved to be excellent starting materials for bridged cage hydrocarbons [6] and model compounds to study the interactions between two metal centers separated by chains of different lengths [7]. This encouraged us to design also a path for a stepwise synthesis of superphanes with four-and five-membered [8-10] rings as summarized in Scheme 2. The resulting superphanes are stable at room temperature, and their molecular structures were investigated. The intermediates 5-7, which were cyclized in an intramolecular reaction to 2 and 8-11, stimulated us to look for higher oligomers.

A superphane consisting of one thiophene ring and one CpCo-stabilized cyclobutadiene ring, 8, was prepared in an eight-step synthesis from 5-cyclodecynol protected with tertbutyldimethylsilyl, 13. The first key step in this sequence was the reaction of 13 with zirconocene and subsequently with S 2 Cl 2 to yield the tricyclic thiophene derivative 12. The second key step was the ring closure of 11 with CpCo(COD) to give 8. X-ray structural investigations of 11 and 8 confirmed the structural assignments. Evidence for the close proximity of the CpCo-stabilized cyclobutadiene and the thiophene rings is also given by the electronic absorption spectrum of 8 and the oxidation potential (-0.07 V).

Adjustable belts: Selective synthesis of beltlike cyclophanes containing organometallic π systems is now possible. Intra‐ and intermolecular ring closure of the flexible ten‐membered ring units of 1 leads to tetramer 2 and octamer 3, respectively (see picture; cod=cyclooctadiene).

Keywords: Donor-acceptor systems / Phanes / Cyclic voltammetry / Electron transfer / CobaltThe synthesis of the tetrasilasuperphanes 10−18 can be achieved from 1,1,3,3-tetramethyl-1,3-disilacyclonona-4,8-diyne (7), 1,1,2,2-tetramethyl-1,2-disilacyclonona-3,8-diyne (8) or 1,1,4,4-tetramethyl-1,4-disilacyclodeca-5,9-diyne (9) by heating with [RCpCoL 2 ] [R = H, Si(CH 3 ) 3 , (CH 3 ) 5 , CO 2 CH 3 ; L 2 = COD, (CO) 2 , (C 2 H 4 ) 2 ]. The reaction of 7 with [RCpCo(CO) 2 ] [R = H, CH 3 , Si(CH 3 ) 3 , (CH 3 ) 5 ] produces the tricyclic cobalt-stabilized cyclobutadienediynes 20−23, whereas reaction with [RЈCpCo(L 2 )] [RЈ = H, (CH 3 ) 5 , CO 2 CH 3 ; L 2 = COD, (CO) 2 ] leads to the donor/acceptor superphanes 24−31. X-ray investigations on the superphanes

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