Stepwise assembly and structural characterization of oligonuclear ferrocene aggregates with boron-nitrogen backbone

The reaction of FcBBr(2) [1; Fc=(C5H5)Fe(C5H4)] with either 4-bromo-N,N-bis(trimethylsilyl)aniline or lithium N-tert-butyltrimethylsilylamide or sodium N,N-bis(trimethylsilyl)amide or 4-methoxyaniline in the appropriate stoichiometric ratio yields mononuclear {FcB(Br)N(SiMe3)(C6H4Br) (3); FcB(Br)N(SiMeACMe(3)) (4)}, dinuclear {[FcB(Br)](2)NSiMe3 (5); [FcBN(H)(C6H4OMe)](2)NC6H4OMe (6)}, trinuclear {[FcBN(C6H4OMe)](3) (7)} and tetranuclear {[FcB(Br)N(SiMe3)FcB](2)NH (8)} ferrocene complexes, which are held together by covalent boron-nitrogen bonds. All compounds 3-8 have been characterized by X-ray crystallography. Compound 7 features a puckered borazine core, while the BN backbone of 8 adopts a helical conformation. Treatment of 1,1'-fc(BBr2)(2) [10; fc = (C5H4)(2)Fe] with 4-bromo-N,N-bis(trimethylsilyl)aniline produces the 1,3-dibora-[3]ferrocenophane 13, in which a -B(Br)N(C6H4Br)B(Br)- bridge spans both cyclopentadienyl rings. Polymeric byproducts have not been observed. These results indicate a strong preference for the formation of intra molecular BNB ansa-bridges over intermolecular BNB crosslinks. (C) 2002 Elsevier Science B.V. All rights reserved.