Synthesis and structure of heteroleptic ytterbium (II) tetrahydroborate complexes

The synthesis and characterization of (TptBu,Me)Yb(BH4)(THF)n (n = 0, 3; n = 1, 4) complexes are reported. The compounds represent rare examples of lanthanide (II) tetrahydroborate complexes. The X-ray crystal structure of complex 4 has been determined and it shows a monomeric, formally seven coordinate ytterbium center, bearing one κ3 bonded TptBu,Me ligand, a tetrahydroborate ligand and a coordinated THF molecule. The tetrahydroborate ligand binds in a κ3 fashion, via three bridging hydrogen atoms. IR spectroscopy data are consistent with the solid-state structure and the corresponding BD4 analog of 4 shows the expected IR isotope shifts. The 1H NMR spectra of 3 and 4 shows one set of resonances each for the BH4 and the pyrazolylborate ligands indicating dynamic solution behavior. For complex 3, although X-ray quality crystals could not be obtained, the IR and NMR data are consistent with its formulation as the solvent-free analog of complex 4 with κ3-bonded BH4 ligand.