Synthesis of the diborylated ferrocene 1,1′-bis-(bis-pentafluorophenylboryl)ferrocene and the X-ray structure of its trimethylphosphine adduct

The diborylated ferrocene compound 1,1'-Fc[B(C6F5)(2)](2) (2) was prepared via a transmetallation reaction involving 1,1'-Fc(HgCl)(2) and two equivalents of ClB(C6F5)(2). Although this reaction is very clean spectroscopically, isolated yields of 2 were never greater than 40% owing to the high solubility of the compound in non-donor solvents. Compound 2 is similar in its properties to the related monoborylated complex FcB(C6F5)(2) (1) reported previously, particularly the UV-vis spectrum, which exhibits an intense charge transfer absorption (lambda (max) = 233 nm, epsilon = 1.64 x 10(4)) assignable to an Fedz2/dx2-y2 --> B-p transition. However, 2, is significantly more Lewis acidic than 1, reacting with weak donors such as acetonitrile at room temperature, and effecting methide abstraction from Cp2ZrMe2 under mild conditions. Complex 2 also forms a bis(trimethylphosphine) adduct (3), which was structurally characterized via X-ray crystallography.