Yttrium and Neodymium Di- and Monohalide Complexes Based on Scorpionate (Poly(pyrazolyl)borate) Ligands

The syntheses of a series of well-characterized complexes of the type TpRYX2(solvent)n (1 and 2, R = H, X =
Br, Cl, solvent = THF, n = 2; 4, R = Me, X = Cl, solvent = THF, n = 1; 5, R = Me, X = Cl, solvent =
3,5-dimethylpyrazole, n = 1; 7, R = Ph, X = Cl, solvent = THF, n = 1) and the novel solvent-free bis(poly(pyrazolylborate) complexes [(TpR)(BpR‘)YX] (8, R = R‘ =Me, X = Cl; 9, R = H, R‘ = Ph, X = Br) are
presented. The data demonstrate that the steric, dynamic, and coordination behavior of these complexes are heavily
influenced by the choice of scorpionate ligand substituents, showing the versatility of this ligand system for
catalyst design. The coordinated THF solvent molecules of complexes 1, 2, and 4 are seen to undergo a dynamic
solvation/desolvation equilibrium in solution that is fast on the NMR time scale. The position of this equilibrium
is solvent-dependent and can be evaluated in complex 4 by observation of the line broadening of the 3-methyl
resonance in the 1H NMR spectra taken in different deuterated solvents. Complex 5, formed by slow hydrolysis
of 4, has been characterized by an X-ray diffraction structure determination and shown to adopt a distorted octahedral
geometry that is thought to be similar to that of complex 4. The Nd analogues of these complexes (3, R = H, X
= I, solvent = THF, n = 2; 6, R = Me, X = I, solvent = THF, n = 1) have been characterized by X-ray
diffraction structure determinations:  3 shows a distorted capped octahedral structure, and 6 a distorted octahedral
structure similar to that of 5. The solvent-free complex 8 is shown by 1H and 13C NMR spectroscopic analysis
to be nonfluxional in solution on the NMR time scale, although 9 appears able to weakly coordinate solvents
containing donor groups such as halides.