Stoichiometric and Homogeneous-Catalytic Diboration of the NN Double Bond of Azobenzene

The diboration of the NN double bond of azobenzene was achieved by reaction of the [3]diboraplatinametalloarenophanes derived from ferrocene, [Fe(η5-C5H4)B(NMe2)Pt(PEt3)2B(NMe2)(η5-C5H4)], and bis(benzene)chromium, [Cr(η6-C6H5)B(NMe2)Pt(PEt3)2B(NMe2)(η6-C6H5)], with an excess of azobenzene in toluene at elevated temperature. The formation of the anticipated ansa-bis(boryl)hydrazines was substantiated by the determination of the molecular structure of the chromium derivative by X-ray diffraction. The synthesis of the ansa-bis(boryl)hydrazine derivative of ferrocene could also be accomplished under homogeneous catalysis conditions. Hence, reaction of the well-known [2]boraferrocenophane, [Fe(η5-C5H4)2B2(NMe2)2], and azobenzene in the presence of 5 mol % [Pt(PEt3)3] afforded the bis-borylated hydrazine derivative in good yields.