Synthetic, Structural, and Electrochemical Studies of 2‐Ferrocenyl‐ and2‐Cymantrenyl‐Functionalized 2,3‐Dihydro‐1 H ‐1,3,2‐diazaboroles and1,3,2‐Diazaborolidenes

Reaction of (dibromoboryl)ferrocene ( 1 ) with 1 equiv. of the diazabutadiene t BuN=CH–CH=N t Bu, and subsequent reduction of the obtained borolium salt 2 with sodium amalgam, affords the first ferrocenyl‐functionalized 1,3,2‐diazaborole ( 3 ). Similarly, 1,1′‐bis(dibromoboryl)ferrocene ( 4 ) can be transformed into compound 6 , which contains two diazaborolyl substituents at the ferrocene core. Treatment of precursors 1 and 4 with 1,2‐bis( tert ‐butylamino)ethane in the presence of Et 3 N gives rise to the formation of the diazaborolidine derivatives 13 and 14 . 1‐Dibromoboryl‐3‐methylcymantrene ( 7 ) was also treated with t BuN=CH–CH=N t Bu to give the borolium salt 8 , which was subsequently reduced to the 2‐cymantrenyl‐diazaborole 9 . Treatment of 7 with t BuN(H)CH 2 CH 2 N(H) t Bu in the presence of Et 3 N furnished the corresponding 2‐cymantrenyl‐diazaborolidine 15 . The novel compounds were characterized by elemental analyses and various spectroscopic techniques (IR; 1 H, 13 C, and 11 B NMR; MS). The molecular structures of 3 , 6 , and 15 were elucidated by X‐ray diffraction analyses. Cyclovoltammetric studies of the ferrocene derivatives at high scan rates show features of a quasireversible oxidation at the iron center. The heterocyclic groups serve as electron donors, considerably lowering the oxidation potential of the central iron atoms when compared to the parent compound ferrocene. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)