Synthesis and Characterization of Mononuclear and Dinuclear Manganese Bis-acetylide Complexes

The symmetric d5trans-bis-alkynyl complexes {Mn[(Me)2P(CH2)nP(Me)2]2(C≡CC6H4R)2} (n = 2, R = -C≡CTIPS (2a); n = 3, R = -C≡CTIPS (2b); n = 2, R = F (4); n = 3; -C≡CTIPS) were prepared by the reaction of [Mn(dmpe)2Br2] with two equivalents of the corresponding acetylide LiC≡CC6H4R (R = F, -C≡CTIPS). The reaction of compounds 2a, 2b and 4 with [Cp2Fe][PF6] yielded the corresponding d4 complexes {Mn[(Me)2P(CH2)nP(Me)2]2(C≡CC6H4R)2}[PF6] (n = 2, R = -C≡CTIPS, [2a]+; n = 3, R = -C≡CTIPS, [2b]+;n = 2, R = F, [4]+; n = 3; -C≡CTIPS). The unsymmetrically substituted trans-iodo-alkynyl complex [IMn(dmpe)2(C≡CC6H4-C≡CTIPS)] (5) was obtained by treating MeCpMn(dmpe)I with one equivalent of H-C≡CC6H4-C≡CTIPS in the presenceof dmpe. Deprotection of the TIPS group with TBAF gavecomplex [IMn(dmpe)2(C≡CC6H4C≡CH)] (6) in 94 % yield. The neutral dinuclear complexes MnII/MnII compounds {[Mn((Me)2P(CH2CH2)P(Me)2)2(C≡CC6H4R)]2(μ-C4)} (R = H, Me, n-pentyl, F) were prepared by the direct reaction of {[Mn((Me)2P(CH2CH2)P(Me)2)2I]2(μ-C4)} with the corresponding LiC≡CC6H4R (R = H, n-pentyl, F). These MnII/MnII dinuclear compounds were further oxidized to the mixed-valent complexes and the dicationic complexes using [Cp2Fe][PF6]. All complexes have been characterized by NMR, IR, and Raman spectroscopy. X-ray diffraction studies were carried out on complexes 1c, 2a, 4, [4]+, and 6.