Generation and Coupling of [Mn(dmpe)2(C≡CR)(C≡ C)]. Radicals Producing Redox-Active C4-Bridged Rigid-Rod Complexes

Francisco J. Fernández, Koushik Venkatesan, Olivier Blacque, Montserrat Alfonso, Helmut W. Schmalle, Heinz Berke

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The symmetric d5 trans-bis-alkynyl complexes [Mn(dmpe) 2(C≡ CSiR3)2] (R = Me, 1a; Et, 1b; Ph, 1c) (dmpe = 1,2-bis(dimethylphosphino)-ethane) have been prepared by the reaction of [Mn(dmpe)2Br2] with two equivalents of the corresponding acetylide LiC≡CSiR3. The reactions of species 1 with [Cp2Fe][PF6] yield the corresponding d4 complexes [Mn(dmpe)2(C≡CSiR3)2][PF 6] (R = Me, 2a; Et, 2b; Ph, 2c). These complexes react with NBu 4F (TBAF) at -10°C to give the desilylated parent acetylide compound [Mn(dmpe)2(C≡ CH)2][PF6] (6), which is stable only in solution at below 0°C. The asymmetrically substituted trans-bis-alkynyl complexes [Mn(dmpe)2(C≡CSiR 3)(C≡CH)] [PF6] (R = Me, 7a; Et, 7b) related to 6 have been prepared by the reaction of the vinylidene compounds [Mn(dmpe) 2(C≡CSiR3)(C=CH2)] (R = Me, 5a; Et, 5b) with two equivalents of [Cp2Fe][PF6] and one equivalent of quinuclidine. The conversion of [Mn(C5H4Me)(dmpe)I] with Me3SiC≡ CSnMe3 and dmpe afforded the trans-iodide-alkynyl d5 complex [Mn(dmpe)2(C≡ CSiMe3)I] (9). Complex 9 proved to be unstable with regard to ligand disproportionation reactions and could therefore not be oxidized to a unique MnIII product, which prevented its further use in acetylide coupling reactions. Compounds 2 react at room temperature with one equivalent of TBAF to form the mixed-valent species [(Mn(dmpe)2(C≡CH)) 2(μ-C4)] [PF6] (11) by C-C coupling of [Mn(dmpe)2(C≡CH)(C≡C.] radicals generated by deprotonation of 6. In a similar way, the mixed-valent complex [(Mn(dmpe) 2(C≡CSiMe3))2(μ-C 4)][PF6] [12]+ is obtained by the reaction of 7a with one equivalent of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene). The relatively long-lived radical intermediate [Mn(dmpe)2(C≡ CH)(C≡C.)] could be trapped as the MnI complex [Mn(dmpe)2(C≡CH)(≡C-CO2)] (14) by addition of an excess of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) to the reaction mixtures of species 2 and TBAF. The neutral dinuclear MnII/ Mn II compounds [(Mn(dmpe)2(C≡ CR3)) 2(μ-C4)] (R = H, 11; R = SiMe3, 12) are produced by the reduction of [11]+ and [12]+, respectively, with [FeCp(C6Me6)]. [11]+ and [12]+ can also be oxidized with [Cp2Fe][PF6] to produce the dicationic MnIII/MnIII species [(Mn(dmpe)2(C≡CR3))2(μ-C4)] [PF6]2 (R = H, [11]2+; R = SiMe3, [12]2+). Both redox processes are fully reversible. The dinuclear compounds have been characterized by NMR, IR, UV/Vis, and Raman spectroscopies, CV, and magnetic susceptibilities, as well as elemental analyses. X-ray diffraction studies have been performed on complexes 4b, 7b, 9, [12] +, [12]2+, and 14.

Original languageEnglish
Pages (from-to)6192-6206
Number of pages15
JournalChemistry - A European Journal
Issue number24
Publication statusPublished - 15 Dec 2003
Externally publishedYes


  • Mixed-valent compounds
  • Molecular devices
  • Molecular wire
  • Nanotechnology
  • Single-electron devices


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