Synthesis and structure of tris(4-ferrocenylphenyl)boroxine and its utility in cross-coupling reaction

The reaction of 4-bromophenylferrocene with butyllithium followed by treatment of the organolithium compound with tributyl borate afforded tris(4-ferrocenylphenyl)boroxine (2). X-ray diffraction study of the solvate 2·2C6H6 revealed an intermolecular stacking interaction between the boroxine ring and the Cp rings in the crystal structure. Cross-coupling of compound 2 with 4’-bromo-4-nitro-1,1’-biphenyl produced 4″-ferrocenyl-4-nitro-1,1’:4’,1″-terphenyl (3). X-ray diffraction study of terphenyl 3 showed that this compound crystallizes in the noncentrosymmetric space group P21. In the crystal, molecules 3 are packed in an antiparallel head-to-tail fashion, which is unfavorable for generation of strong nonlinear optical effects.