ARTICLE DOI: 10.1002/zaac.200801423 Synthesis and Characterization of Mononuclear and Dinuclear Manganese Bis-acetylide Complexes Thorsten Fritz, [a] Helmut W. Schmalle, [a] Olivier Blacque, [a] Koushik Venkatesan, [a] and Heinz Berke* [a] Keywords: Mixed-valent compounds; Molecular devices; Molecular wires; Nanotechnology; Single-electron devices Abstract. The symmetric d 5 trans-bis-alkynyl complexes {Mn[(Me) 2 P(CH 2 ) n P(Me) 2 ] 2 (CCC 6 H 4 R) 2 } (n = 2, R = -CCTIPS (2a); n = 3, R = -CCTIPS (2b); n = 2, R = F(4); n = 3; -CCTIPS) were prepared by the reaction of [Mn(dmpe) 2 Br 2 ] with two equivalents of the corresponding acetyl- ide LiCCC 6 H 4 R (R = F, -CCTIPS). The reaction of com- pounds 2a, 2b and 4 with [Cp 2 Fe][PF 6 ] yielded the corresponding d 4 complexes {Mn[(Me) 2 P(CH 2 ) n P(Me) 2 ] 2 (CCC 6 H 4 R) 2 }[PF 6 ] (n = 2, R = -CCTIPS, [2a] + ; n = 3, R = -CCTIPS, [2b] + ; n = 2, R = F, [4] + ; n = 3; -CCTIPS). The unsymmetrically substituted trans-iodo-alkynyl complex [IMn(dmpe) 2 (CCC 6 H 4 - CCTIPS)] (5) was obtained by treating MeCpMn(dmpe)I with one equivalent of H-CCC 6 H 4 -CCTIPS in the presence Introduction The development of molecular devices requires the prep- aration of functional materials with suitable properties [1-3]. π-Conjugated “conducting” units containing electro- chemically active transition-metal end groups, such as L m M-(CC) n -ML m are basic constituents for electronic materials [4-6]. Research into the synthesis and electronic properties of metal alkynyl complexes and polymers con- tinues to develop as a key area of organometallic chemistry [7-17]. Owing to its high stability, ease of functionaliz- ation, and well-defined electrochemistry, transition-metal units have been widely used as redox-active centers that are linked together with a wide variety of structural units such as saturated and unsaturated carbon bridges, delocalized fused rings, and polymeric and dendritic backbones [18-56]. In particular, their rigid rod architectures and con- jugated backbones have been studied in the field of linear and non-linear optics, liquid crystallinity, and photovoltaic cells [24, 25]. We expect that electronic properties of materi- als with low energy work functions could be reasonably sat- isfied by molecular units with electron-rich phosphane sub- * Prof. Dr. H. Berke E-Mail: hberke@aci.uzh.ch [a] Institute of Inorganic Chemistry Winterthurerstraase 190 8057, Zürich, Switzerland Z. Anorg. Allg. Chem. 2009, 635, 1391-1401  2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1391 of dmpe. Deprotection of the TIPS group with TBAF gave complex [IMn(dmpe) 2 (CCC 6 H 4 CCH)] (6) in 94 % yield. The neutral dinuclear complexes Mn II /Mn II compounds {[Mn((Me) 2 P(CH 2 CH 2 )P(Me) 2 ) 2 (CCC 6 H 4 R)] 2 (μ-C 4 )} (R = H, Me, n-pentyl, F) were prepared by the direct reaction of {[Mn((Me) 2 P(CH 2 CH 2 )P(Me) 2 ) 2 I] 2 (μ-C 4 )} with the corresponding LiCCC 6 H 4 R (R = H, n-pentyl, F). These Mn II /Mn II dinuclear compounds were further oxidized to the mixed-valent complexes and the dicationic complexes using [Cp 2 Fe][PF 6 ]. All complexes have been characterized by NMR, IR, and Raman spectroscopy. X-ray diffraction studies were carried out on complexes 1c, 2a, 4, [4] + , and 6. stituted manganese end groups and a C 4 -spacer [26-29]. In addition to the above reasons, the L m Mn-C 4 -MnL m systems were selected as target molecules, because a build- up of Mn-di- and oligonuclears seemed to be synthetically feasible by acetylide substitution processes [27]. We have shown through our recent studies that systems of the type L m Mn-C 4 -MnL m can be achieved by coupling of Mn-C 2 units, such as Mn-alkynyl and Mn-vinylidene moieties. For instance, we have published the synthesis of redox-active dinuclear complexes of the type {[Mn(dmpe) 2 (X)] 2 (μ- C 4 )} n+ (X = I, CCH, CC-CCSiMe 3 and n = 0-2), which were either obtained by the reaction of two equiva- lents of [IMn(MeCp)(dmpe)] [dmpe = 1,2-bis(dimethyl- phosphanyl)ethane] with Me 3 Sn-C 4 -SnMe 3 and dmpe and subsequent acetylide substitution, or by an in situ C-C coupling of [Mn III (dmpe) 2 (CCH)(CC)] units similar to the Eglinton and McCrae oxidative coupling of acetylenic compounds [26-29]. We had earlier suggested from DFT calculations and experimental evidence that the terminal end group (X) in these kind of complexes {[Mn(dmpe) 2 (X)] 2 (μ-C 4 )} n+ (X = I, CCH, CC-CCSiMe 3 and n = 0-2), have less bearing or in- fluence on the communication between the two metal cen- ters [27]. However, the functionality and reactivity of the terminal end groups does matter considering the fact of further utilizing these molecules for the build up of longer oligonuclear and attaching these molecules to electrode sur- faces for single-molecule conductivity measurements [44].