Experimental Assessment of the Relative Affinities of Benzene and Ferrocene toward the Li+ Cation

In order to explore whether benzene or ferrocene presents a more attractive π face to Li+ ions, the lithium tetraorganylborate Li[BFc2Ph2] has been synthesized, which contains two phenyl rings as well as two ferrocenyl substituents as potential coordination sites (Fc = (C5H5)Fe(C5H4)). The compound crystallizes from toluene/dibutyl ether as the contact ion pair [Li(OBu2)][BFc2Ph2], with the Li+ ion located between the two borylated ferrocenyl cyclopentadienyl rings. This finding indicates ferrocene to be a stronger Li+ binder than benzene. In line with this conclusion, the hexaphenyl derivative [(Li(OBu2))2][1,1‘-fc(BPh3)2] was found to have each of its cyclopentadienyl substituents coordinated to one Li+ ion, thereby forming a multiple-decker sandwich complex in the solid state (fc = (C5H4)2Fe).