Four (2,2′-bipyridyl)(ferrocenyl)boronium derivatives.

Crystal structures are reported for four (2,2′-bipyridyl)(ferrocenyl)boronium derivatives, namely (2,2′-bipyridyl)(ethenyl)(ferrocenyl)boronium hexafluoridophosphate, [Fe(C5H5)(C17H15BN2)]PF6, (I b), (2,2′-bipyridyl)( tert-butylamino)(ferrocenyl)boronium bromide, [Fe(C5H5)(C19H22BN3)]Br, (II a), (2,2′-bipyridyl)(ferrocenyl)(4-methoxyphenylamino)boronium hexafluoridophosphate acetonitrile hemisolvate, [Fe(C5H5)(C22H20BN3O)]PF6·0.5CH3CN, (III b), and 1,1′-bis[(2,2′-bipyridyl)(cyanomethyl)boronium]ferrocene bis(hexafluoridophosphate), [Fe(C17H14BN3)2](PF6)2, (IV b). The asymmetric unit of (III b) contains two independent cations with very similar conformations. The B atom has a distorted tetrahedral coordination in all four structures. The cyclopentadienyl rings of (I b), (II a) and (III b) are approximately eclipsed, while a bisecting conformation is found for (IV b). The N-H groups of (II a) and (III b) are shielded by the ferrocenyl and tert-butyl or phenyl groups and are therefore not involved in hydrogen bonding. The B-N(amine) bond lengths are shortened by delocalization of π-electrons. In the cations with an amine substituent at boron, the B-N(bipyridyl) bonds are 0.035 (3) Å longer than in the cations with a methylene C atom bonded to boron. A similar lengthening of the B-N(bipyridyl) bonds is found in a survey of related cations with an oxy group attached to the B atom. [ABSTRACT FROM AUTHOR]