Unusual transformations of a bipyridine ligand in attempts to trap a terminal chromium(III) alkylidene

Attempts to trap a terminal chromium alkylidene by reactions of dialkyl Cp* Cr(CH2SiMe3)(2) (Cp* = eta (5)-C5Me5) Or metallacycle Cp*(THF)Cr(CH2)(2)SiM e2 with the bidentate ligand 1,2-bis(dimethyphosphino)ethane (dmpe) lead to dinuclear paramagnetic chromium alkyls [Cp*Cr(CH2SiMe3)(2)](2) (mu-eta (1) :eta (1)-dmpe) (1) and [Cp*Cr(CH2)(2)Si(CH3)(2)](2)(mu-eta (1):eta (1)-dmpe ) (2), respectively. On the other hand, the unusual mononuclear chromium co mplex (eta (5)-pentamethylcyclopentadienyl)(2-(2",2"-dimeth 1,2-dihydro [2, 2] bipyridine-1,3"-diyl)chromium(III) (3) was obtained by a reaction of Cp* (THF)Cr(CH2)2SiMe(2) with 1 equiv of 2,2'-bipyridine (bipy). 3 is formed by carbon-carbon bond formation between one terminus of the metallacyle and t he 2-position of the bipy ligand, at the expense of the aromaticity of a py ridyl group. Single-electron oxidation of 3 with ferricenium hexafluorophos phate ([Cp2Fe]PF6) yielded 4, a dicationic dimer of 3 linked via a carbon-c arbon bond between the bipy backbones. 1-4 were structurally characterized by X-ray diffraction.