Magnesium and potassium scorpionate complexes based on dihydrobis(pyrazolyl)borate

The first X-ray crystal structure is reported for [dihydrobis(pyrazol-1-yl)borato-κ²N,N']tris(tetrahydrofuran-κO)magnesium(II) tetrabenzylborate, [Mg(C₆H₈BN₄)(C₄H₈O)₃][B(C₇H₇)₄)], (I), which was obtained by reacting crude [K(C₆H₈BN₄)] with an equimolar amount of (PhCH₂)MgCl in tetrahydrofuran at room temperature and was isolated as a side product. The crystal structure analysis reveals the existence of a pronounced boat-shaped central Mg(N-N)₂B moiety with a weak pseudo-axial B-H...Mg interaction. The existence of a novel counter-ion, [B(C₇H₇)₄)]^-, has been demonstrated by the first evidence of reactivity between KBH₄ and (PhCH₂)MgCl (in a 1:4 molar ratio) to give a polymeric potassium tetrabenzylborate, poly[[μ₄-dihydrobis(pyrazol-1-yl)borato-κ²N,N']potassium(I)], [K{B(C₇H₇)₄}]_n, (II), with predominant (η⁶-C₆H₅)...K, and (η³-C₆H₅)...K interactions. Density functional theory (DFT) calculations were conducted to determine the energy, the frontier molecular orbitals (HOMO and LUMO) and the molecular electrostatic potential (MEP) in order to explain the stability of the structures in the experimental results for complexes (I) and (II).