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.

The reaction of the low-spin d 5 complex Mn(dmpe) 2 (CtCSiMe 3 ) 2 (1) (dmpe ) 1,2-bis-(dimethylphosphino)ethane) with [NBu 4 ][Ph 3 F 2 M] (M ) Si or Sn) yields the SiMe 3 metathesis products Mn(dmpe) 2 (CtCMPh 3 ) 2 (M ) Si 2a, Sn 2b). When the Mn(II) species 1 was dissolved in MeOH in the presence of NaBF 4 , disproportionation occurred with formation of the Mn-(I) products Mn(dmpe) 2 (CtCSiMe 3 )(CdCH 2 ) (3a) and [Mn(dmpe) 2 (CtCSiMe 3 )(tC-CH 3 )]-[BF 4 ] (5a) and the cationic Mn(III) complex [Mn(dmpe) 2 (CtCSiMe 3 ) 2 ][BF 6 ] (4a). In a similar way 1 was transformed into [Mn(dmpe) 2 (CtCSiMe 3 ) 2 ][H 2 F 3 ] (4b) and [Mn(dmpe) 2 (Ct CSiMe 3 )(tC-CH 3 )][H 2 F 3 ] (5b) by its reaction with excess of HF‚pyridine. The reaction of 1 with Li or Na in toluene at 100 °C gave the new d 6 cis-bisalkynyl complexes [Mn(dmpe) 2 -(CtCSiMe 3 ) 2 ][M] (M ) Li 6a, Na 6b). The trans-alkynylvinylidene derivatives Mn(dmpe) 2 -(CtCSiMe 3 )(CdC(E)SiMe 3 ) (E ) H 3b, SnMe 3 3c) were obtained by the reaction of species 6 with stoichiometric MeOH or ClSnMe 3 . In MeOH/KOH solutions complex 3b or 3c was converted into the trans-alkynylvinylidene species 3a. The reaction of complex 3a with HBF 4 or HF‚pyridine produced the carbyne complexes [Mn(dmpe) 2 (CtCSiMe 3 )(tC-CH 3 )][A] (A ) BF 4 5a, H 2 F 3 5b). These new compounds have been characterized by NMR and IR spectroscopy and elemental analyses, and for 2a, 2b, 3a, 4b, and 6b X-ray diffraction studies have been performed.

Vinylidene species of the type Mn(C5H4CH3)[(H3C)2PCH2CH2P(CH3)2](CCR1R2) (R1 = R2 = H; R1 = H, R2 = Ph) can be fully reversibly coupled to yield the dinuclear complexes [(C5H4CH3)(dmpe)Mn⋮CC(R1)(R2)C(R1)(R2)C⋮Mn(dmpe)(C5H4CH3)][PF6]2 (R1, R2 = H; R1 = H, R2 = Ph) by an oxidation/reduction cycle involving formation and cleavage of a C−C σ bond.

The theoretically characterized (DFT) C4 cumulenic species Mn(C5H4R)(dmpe) [=C=C=C=C(SnPh3)2] was obtained by photolysis of the C(sp2)-Sn bond in the vinylidene complex Mn(C5H4R)(dmpe)[=C=C(SnPh3)-C[triple bond]CSnPh3], which in turn was prepared by a thermal reaction from MnC5H4R(dmpe)(C7H8) and Ph3Sn-C4-SnPh3.

The mononuclear vinylidene complexes of the type Mn(C5H4R‘)(R‘ ‘2PCH2CH2PR‘ ‘2)(CC(R1)(SnMe3)) were obtained by the reaction of Mn(C5H4R‘)(η6-cycloheptatriene) (R‘ = H, 1a; CH3, 1b) with 1 equiv of R1−C⋮C−SnMe3 (R1 = SnMe3, C6H5, C4H3S, C6H4CH3) and R‘ ‘2PCH2CH2PR‘ ‘2 (R‘ ‘ = CH3 (dmpe), C2H5 (depe)) in toluene at 50 °C for 3 h. The reactions of these tin-substituted complexes with 1 equiv of 1.0 M TBAF yielded the corresponding parent vinylidene species Mn(C5H4R‘)(R‘ ‘2PCH2CH2PR‘ ‘2)(CC(R1)(H)). Treatment of some of these vinylidene species with 1 equiv of [Cp2Fe][PF6] led to the oxidative coupling product [(C5H4R‘)(R‘ ‘2PCH2CH2PR‘ ‘2)Mn⋮C−CHR1−CHR1−C⋮Mn(R‘ ‘2PCH2CH2PR‘ ‘2)(C5H4R‘)][PF6]2 (R‘ = CH3, R‘ ‘ = CH3, R1 = H; R‘ = CH3, R‘ ‘ = CH3, R1 = C6H5; R‘ = CH3, R‘ ‘ = CH3, R1 = C4H3S; R‘ = H, R‘ ‘ = C2H5, R1 = H; R‘ = H, R‘ ‘ = C2H5, R1 = C6H5; R‘ = H, R‘ ‘ = C2H5, R1 = C4H3S). In some cases these products of oxidative coupling, [(C5H4R‘)(R‘ ‘2PCH2CH2PR‘ ‘2)Mn⋮C−CHR1−CHR1−C⋮Mn(R‘ ‘2PCH2CH2PR‘ ‘2)(C5H4R‘)][PF6]2, were accompanied by formation of dinuclear complexes of the type [(C5H4R‘)(R‘ ‘2PCH2CH2PR‘ ‘2)Mn⋮C−CR1CR1−C⋮Mn(R‘ ‘2PCH2CH2PR‘ ‘2)(C5H4R‘)][PF6]2 and of the cationic carbyne complexes [(C5H4R‘)(R‘ ‘2PCH2CH2PR‘ ‘2)Mn⋮C−CH2R1][PF6] obtained by proton transfer. Reduction of these dinuclear complexes with Cp2*Co yielded back the corresponding mononuclear precursor complexes involving a reductive decoupling process. Both the reductive coupling and the oxidative coupling are fully reversible, which is supported by DFT calculations. The mononuclear and the dinuclear compounds were characterized by NMR, IR, and cyclic voltammetric studies. X-ray diffraction studies have been performed on complexes 3a, 11, 13a, 15a, and 22b.