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=?5-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