Dinuclear and Mononuclear Chromium Acetylide Complexes

Reaction of trans-Cl2Cr(dmpe)2 (1) [dmpe = 1,2-bis(dimethylphosphanyl)ethane] with 0.5 equiv. of Me3Sn–C≡C–C≡C–SnMe3 or Me3Sn–C≡C–C6H4–C≡C–SnMe3 afforded the dinuclear complexes trans-[Cl(dmpe)2Cr≡C–C≡C–C≡Cr(dmpe)2Cl] (2), trans-[Cl(dmpe)2Cr–C≡C–C≡C–Cr(dmpe)2Cl][SnMe3Cl2]2 (2[SnMe3Cl2]2), and trans-[Cl(dmpe)2Cr–C≡C–C6H4–C≡C–Cr(dmpe)2Cl][SnMe3Cl2]2 (3[SnMe3Cl2]2), which could be transformed to the 2[PF6]2 and 3[BPh4]2 salts. Substitutions of the chloride groups in 2 were carried out to achieve the corresponding iodo (4) and (trimethylsilyl)alkynyl (5) complexes. Utilizing similar reactions and treatment with only 1 equiv. of the corresponding alkynyl ligand [Me3Sn–C≡C–R (R = –SnMe3, –C6H5), Me3Sn–C≡C–C≡C–R (R = –SiMe3, –SnMe3), and Me3Sn–C≡C–C6H4–C≡C–SnMe3] allowed us to prepare a series of mononuclear monoacetylide complexes: trans-[Cl(dmpe)2Cr–C≡C–R] [R = –SnMe3(6),–C6H5(7)], trans-[Cl(dmpe)2Cr–C≡C–C≡C–R] [R = –SiMe3(8),–SnMe3(9)], and trans-[Cl(dmpe)2Cr–C≡C–C6H4–C≡C–SnMe3] (10), respectively. The complexes 2, 2[SnMe3Cl2]2, 2[PF6]2, 3[SnMe3Cl2]2, 3[BPh4]2, and 6–10 displayed paramagnetic behavior. Electrochemical studies performed on the dinuclear complexes (2), (2[SnMe3Cl2]2), (3[SnMe3Cl2]2), and (5) showed one two-electron redox wave revealing a class-I type behavior based on the Robin–Day classification, which is untypical for dinuclear complexes bridged by a butadiyne ligand. The complexes were characterized by NMR, ESI–MS, cyclic voltammetry, EPR spectroscopy, magnetic measurements, and exemplary single-crystal X-ray diffraction studies for 2, 2[SnMe3Cl2]2, 8, 9, and 10.