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

Abstract

The symmetric d(5) trans-bis-alkynyl complexes [Mn(dmpe)(2)(C triple bond CSiR(3))(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)(2)Br(2)] with two equivalents of the corresponding acetylide LiC triple bond CSiR(3). The reactions of species 1 with [Cp(2)Fe][PF(6)] yield the corresponding d(4) complexes [Mn(dmpe)(2)(C triple bond CSiR(3))(2)][PF(6)] (R = Me, 2 a; Et, 2 b; Ph, 2 c). These complexes react with NBu(4)F (TBAF) at -10 degrees C to give the desilylated parent acetylide compound [Mn(dmpe)(2)(C triple bond CH)(2)][PF(6)] (6), which is stable only in solution at below 0 degrees C. The asymmetrically substituted trans-bis-alkynyl complexes [Mn(dmpe)(2)(C triple bond CSiR(3))(C triple bond CH)][PF(6)] (R = Me, 7 a; Et, 7 b) related to 6 have been prepared by the reaction of the vinylidene compounds [Mn(dmpe)(2)(C triple bond CSiR(3))(C=CH(2))] (R = Me, 5 a; Et, 5 b) with two equivalents of [Cp(2)Fe][PF(6)] and one equivalent of quinuclidine. The conversion of [Mn(C(5)H(4)Me)(dmpe)I] with Me(3)SiC triple bond CSnMe(3) and dmpe afforded the trans-iodide-alkynyl d(5) complex [Mn(dmpe)(2)(C triple bond CSiMe(3))I] (9). Complex 9 proved to be unstable with regard to ligand disproportionation reactions and could therefore not be oxidized to a unique Mn(III) 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 triple bond CH)](2)(micro-C(4))][PF(6)] (11) by C-C coupling of [Mn(dmpe)(2)(C triple bond CH)(C triple bond C*)] radicals generated by deprotonation of 6. In a similar way, the mixed-valent complex [[Mn(dmpe)(2)(C triple bond CSiMe(3))](2)(micro-C(4))][PF(6)] [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 triple bond CH)(C triple bond C*)] could be trapped as the Mn(I) complex [Mn(dmpe)(2)(C triple bond CH)(triple bond C-CO(2))] (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 Mn(II)/Mn(II) compounds [[Mn(dmpe)(2)(C triple bond CR(3))](2)(micro-C(4))] (R = H, 11; R = SiMe(3), 12) are produced by the reduction of [11](+) and [12](+), respectively, with [FeCp(C(6)Me(6))]. [11](+) and [12](+) can also be oxidized with [Cp(2)Fe][PF(6)] to produce the dicationic Mn(III)/Mn(III) species [[Mn(dmpe)(2)(C triple bond CR(3))](2)(micro-C(4))][PF(6)](2) (R = H, [11](2+); R = SiMe(3), [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 4 b, 7 b, 9, [12](+), [12](2+), and 14.

Mono‐ and Dinuclear High‐Spin Half‐Sandwich Manganese(II) Complexes Containing Acetylide and TMEDA Ligands

“…[74,75,101] We have also previously reported the synthesis and characterization of [I(dmpe) 2 MnCϵCϪCϵCMn(dmpe) 2 …”

“…These possibilities have been corroborated by recent studies in our group. [36,46,57,74,75,101] For instance, we have published the synthesis of redox-active dinuclear complexes of the type [{Mn(dmpe) 2 (X)} 2 (µ-C 4 …”

Chemistry of chromium bis-acetylide complexes

“…Transition metals such as manganese bearing bis alkynyl compounds have previously been accessed by reaction of Mn(dmpe) 2 Br 2 with the corresponding lithium acetylides [37][38][39][40]. Upon utilising similar reaction conditions, treatment of CrCl 2 (dmpe) 2 and CrCl 2 (depe) 2 [15] with two equivalents of R-C:C-Li (R = -SiMe 3 , -SiEt 3 , -SiiPr 3 , -SiPh 3 , -C:C-SiMe 3 , -C 6 H 5 -C 6 H 5 -C:C-SiiPr 3 , -SnBu 3 ) yielded the corresponding chromium(II)trans-bis(acetylide) complexes 1-16 quantitatively (Scheme 1).…”

New Access to Homodinuclear Half‐Sandwich Vinylidenemanganese Complexes

“…We recently reported the chemistry and reactivity of Mn II and Mn III half-sandwich Me 2 PCH 2 CH 2 PMe 2 (dmpe) alkynyl complexes and their conversion to (vinylidene)Mn I species. [21,23,24] The first conclusion of this study was that vinylidene complexes gained considerable stability through the presence of the bis(dimethylphosphanyl)ethane ligand (dmpe) in comparison with the reported CO-substituted 3 or L 1 = CO, L 2 = PRЈ 3 ). [25] Although the dinuclear complexes with the CO ligands were reported earlier, [26] these complexes are not ex-These dinuclear tin-substituted vinylidene complexes were further treated with an excess of MeOH to give the corresponding dinuclear parent vinylidene complexes of the type [{Mn(MeC 5 H 4 )(R 2 PCH 2 CH 2 PR 2 )=C=C(H)} 2 {X}] (X = {µ-1,4-C 6 H 4 }, R = Me, 6a; X = {µ-1,4-C 6 H 4 }, R = Et, 6b; X = {µ-1,3-C 6 H 4 }, R = Me, 7a; X = {µ-1,3-C 6 H 4 }, R = Et, 7b; X = {µ-4,4-C 6 H 4 -C 6 H 4 }, R = Me, 8a; X = {µ-4,4-C 6 H 4 -C 6 H 4 }, R = Et, 8b).…”

“…[23] In contrast, the complexes bearing electron-donating phosphane ligands can be expected to possess suitable electronic properties, i.e. a low energy work function.…”