Facile Access to Redox-Active C 2 -Bridged Complexes with Half-Sandwich Manganese End Groups Sohrab Kheradmandan, Koushik Venkatesan, Olivier Blacque, HelmutW. Schmalle, and Heinz Berke* [a] Introduction The field of electronics using single-molecule components has recently received much attention as a possible new path for the continued miniaturization of electronics. Molecular wires are conceptually the simplest components and basic motifs of single electron devices. [1–5] Organometallic com- plexes consisting of a cumulenic spacer and transition-metal end groups were anticipated to appropriately serve the fun- damental requirements for the wire function. [1,4,5] Related polymers or oligomers consisting of dinuclear transition- metal units spaced by (CC) x  bridges were first reported by Hagihara etal. in the late 1970s. [7,8] Even though this earlierworkhasbeenjoinedbyextensivepreparativeexplo- rations, there is still lack of knowledge on appropriate  (L m M  C x  ML m ) n  species and even on their L m M  C x  ML m monomers.Inredoxwires [9–38] this electronic communication between the remote ends is related to the capability to un- dergo facile redox changes in conjunction with a strongly bound and electronically delocalized spacer. [6] Quite a few cases [10–15,25,32,39–78] have been studied, but there is still demand for further thorough explorations. Redox-active metal centers combined with C 2 bridges are expectedtoexhibitstrongthrough-bridgeinteractions.How- ever, such species have rarely been reported. [79–93] We there- foreinitiatedasearchforC 2 -bridged species with prominent redox and electron delocalization properties based on low- energy work functions. These requirements were anticipated to be well satisfied by half-sandwich molecular end groups with manganese centers bearing electron-donating phos- phane and cyclopentadienyl ligands. By analogy we were able to access related redox-active dinuclear complexes of the type [{Mn(dmpe) 2 (X)} 2 (m-C 4 )] n (X = I, C CH, C C C  CSiMe 3 and n = 0– + 2), [13,67,84] but the C 2 -bridged complex with,forinstance,X = Icouldnotbeisolated. Nevertheless, we then attempted the preparation of half- sandwich complexes of the type [(MeC 5 H 4 )(dmpe)Mn C  C Mn(dmpe)(MeC 5 H 4 )] n + (n = 0, 1, 2) starting from the substituted manganocene [(MeC 5 H 4 ) 2 Mn], [85,86] dmpe, and Me 3 SnC CSnMe 3 . The synthetic potential of manganocenes, in particular with regard to Cp or MeC 5 H 4 replacement, has [a] Dr.S.Kheradmandan,Dr.K.Venkatesan,Dr.O.Blacque, Dr.H.W.Schmalle,Prof.H.Berke Anorganisch-Chemisches Institut der Universität Zürich Winterthurerstrasse 190, 8057 Zürich, Switzerland Fax:(+ 41)163-56802 E-mail:hberke@aci.unizh.ch SupportinginformationforthisarticleisavailableontheWWW underhttp://www.chemeurj.org/orfromtheauthor. Abstract: The dinuclear mixed-valent complex [(MeC 5 H 4 )(dmpe)MnC 2 Mn- (dmpe)(C 5 H 4 Me)] + [(h 2 -MeC 5 H 4 ) 3 Mn]  [1] + [2]  (dmpe = 1,2-bis(dimethylphos- phanyl)ethane)waspreparedbythere- action of [Mn(MeC 5 H 4 ) 2 ] with dmpe andMe 3 SnCCSnMe 3 .Thereactionsof [1] + [2]  with K[PF 6 ] and Na[BPh 4 ] yielded the corresponding anion meta- thesis products [(MeC 5 H 4 )(dmpe)Mn- C 2 Mn(dmpe)(C 5 H 4 Me)][PF 6 ] ([1][PF 6 ]) and [(MeC 5 H 4 )(dmpe)MnC 2 Mn(dmpe)- (C 5 H 4 Me)][BPh 4 ] ([1][BPh 4 ]). These mixed-valent species can be reduced to the neutral form by reaction with Na/ Hg. The obtained complex [(MeC 5 H 4 )- (dmpe)MnC 2 Mn(dmpe)(C 5 H 4 Me)] (1) displays a triplet/singlet spin equilibri- um in solution and in the solid state, which was additionally studied by DFT calculations. The diamagnetic dication- ic species [(MeC 5 H 4 )(dmpe)MnC 2 Mn- (dmpe)(C 5 H 4 Me)][PF 6 ] 2 ([1][PF 6 ] 2 ) was obtained by oxidizing the mixed-valent complex [1][PF 6 ] with one equivalent of [Fe(C 5 H 5 ) 2 ][PF 6 ]. Both redox pro- cesses are fully reversible. The dinucle- ar compounds were characterized by NMR, IR, UV-visible, and Raman spectroscopy, cyclic voltammetry, and magnetic susceptibility measurements. X-ray diffraction studies were per- formed on [1][2], [1][PF 6 ], [1][BPh 4 ], and[1][PF 6 ] 2 . Keywords: alkyne ligands · density functional calculations · half-sand- wich complexes · manganese · mixed-valent compounds #2004Wiley-VCHVerlagGmbH&Co.KGaA,Weinheim DOI: 10.1002/chem.200400143 Chem. Eur. J. 2004, 10,4872–4885 4872 FULL PAPER