Synthesis and Characterization of Redox-Active C4-Bridged Rigid-Rod Complexes with Acetylide-Substituted Manganese End Groups

Abstract

The symmetric d 5 trans-bis(alkynyl) complexes [Mn(R'2PCH2CH2PR'2)2(C≡CR) 2 ] (R' = Me, R = SiEt 3 , 3a; R' = Me, R = Si i Pr 3 , 3b; R' = Me, R = Si( t Bu)Me 2 , 3c; R' = Et, R = SiEt 3 , 4a; R' = Et, R = Si i Pr 3 , 4b; R' = Et,R = Si( t Bu)Me 2 , 4c) can be prepared by the reaction of [Mn(R'2PCH2CH2PR'2)2Br2] (R' = Me, 1; R' = Et, 2) with 2 equiv of LiC≡CR (R = SiEt 3 , Si i Pr 3 , Si( t Bu)Me 2 ). The reactions of species 3 and 4 with [Cp 2 Fe] [PF 6 ] yield the corresponding d 4 complexes [Mn(dmpe) 2 (C≡CR) 2 ] [PF 6 ] (R' = Me, R = SiEt 3 , 5a; R' = Me, R = Si i Pr 3 , 5b; R' = Me, R = Si( t Bu)Me 2 , 5c; R' = Et, R = SiEt 3 , 6a; R' = Et, R = Si i Pr 3 , 6b; R' = Et, R = Si( t B u )Me 2 , 6c). The asymmetrically substituted trans-bis(alkynyl) complexes [Mn(dmpe) 2 -(C≡CR)(C≡CH)][PF 6 ] (R' = Me, R = SiEt 3 , lOa; R' = Me, R = Si i Pr 3 , lOb; R' = Me, R = Si( t Bu)Me 2 , lOc) are prepared by the reaction of the vinylidene compounds Mn(dmpe) 2 (C≡ CR)(C=CH 2 ) (R' = Me, R = SiEt 3 , 9a; R' = Me, R = Si i Pr 3 , 9b; R' = Me, R = Si( t Bu)Me 2 , 9c) with 2 equiv of [Cp 2 Fe] [PF 6 ] and 1 equiv of quinuclidine. The mixed-valent complexes [{Mn-(dmpe)2(C=CR)}2(μ-C4)][PF 6 ] [11] + are obtained by the reaction of 10 with 1 equiv of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene). The neutral dinuclear Mn(II)/Mn(II) compounds [{Mn-(dmpe) 2 (C≡CR)} 2 (μ-C4)] (R = SiEt 3 , 11a; R = Si i Pr 3 , lib; R = Si( t Bu)Me 2 , 11c) are synthesized by the reduction of [11] + with Co(C 5 Me 5 ) 2 . Complexes [11] + can also be oxidized with [Cp 2 -Fe] [PF 6 ] to produce the dicationic Mn(III)/Mn(III) species [{Mn(dmpe) 2 (C≡CR 3 )} 2 (μ-C 4 )] [PF 6 ] 2 (R = SiEt 3 , [11a] 2 + ; R = Si i Pr 3 , [11b] 2 + ; R = Si( t Bu)Me 2 , [11c] 2 + ). Both redox processes are fully reversible. The dinuclear compounds have been characterized by NMR, IR, and Raman spectroscopy, cyclic voltammetry, and elemental analyses. X-ray diffraction studies have also been performed on several complexes.