Ansa-metallocenes with BN and BP linkages: the importance of NH⋯FC hydrogen bonding in pentafluorophenyl boron compounds

The reaction of Cp′(CpB)ZrCl2 [CpB=η5-C5H4B(C6F5)2] with LiNHCMe3 gave Cp′(CpB)(μ-NHCMe3)ZrCl, with a constrained-geometry type CpBN chelate ligand. The 19F-NMR spectrum of the zirconium complexes, as well as that of the titanium analogue, reveals CF⋯HN hydrogen bonding to one of the ortho-F atoms of a C6F5 ring, strong enough to persist in solution at room temperature. The reaction of Cp′(CpB)TiCl2 with LiPPh2 affords the CpBP chelate complex Cp′(CpB)(μ-PPh2)TiCl, the first example of a crystallographically characterised Ti(IV) phosphido compound. A 19F-NMR study of a number of adducts of B(C6F5)3 with prim- and sec-amines demonstrates the importance of intramolecular hydrogen bonding to C6F5 in this class of compounds, while there are no such interactions in B(C6F5)3(PHR2) (R=Cy, Ph). The crystal structures of Cp′(CpB)(μ-PPh2)TiCl, B(C6F5)3(NHMe2) and B(C6F5)3(PHCy2) are reported.