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

The symmetric d5 trans‐bis‐alkynyl complexes [Mn(dmpe)2(CCSiR3)2] (R = Me, 1 a; Et, 1 b; Ph, 1 c) (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...

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Published in:Chemistry : a European journal 2003-12, Vol.9 (24), p.6192-6206
Main Authors: Fernández, Francisco J., Venkatesan, Koushik, Blacque, Olivier, Alfonso, Montserrat, Schmalle, Helmut W., Berke, Heinz
Format: Article
Language:English
Subjects:
mixed-valent compounds
molecular devices
molecular wire
nanotechnology
single-electron devices
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Summary:The symmetric d5 trans‐bis‐alkynyl complexes [Mn(dmpe)2(CCSiR3)2] (R = Me, 1 a; Et, 1 b; Ph, 1 c) (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][PF6] (R = Me, 2 a; Et, 2 b; Ph, 2 c). These complexes react with NBu4F (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CSiR3)(CCH)][PF6] (R = Me, 7 a; Et, 7 b) related to 6 have been prepared by the reaction of the vinylidene compounds [Mn(dmpe)2(CCSiR3)(CCH2)] (R = Me, 5 a; Et, 5 b) 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‐C4)][PF6] [12]+ is obtained by the reaction of 7 a 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/MnII 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 perf
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.200305254