Zinc, Cadmium, and Mercury Metallocenes Incorporating 1,2-Diaza-3,5-diborolyl Ligands

Sandwich compounds incorporating 1,2-diaza-3,5-diborolidine ligands have been prepared by metathesis reactions between zinc, cadmium, and mercury dihalides and M[cyclo-MeC(BR)₂(NiPr)₂] (M = Li, K; R = Me, Ph). The metallocenes M[cyclo-MeC(BR)₂(NiPr)₂)]₂ (M = Zn, R = Me (2a), Ph (2b); M = Cd, R = Me (3a), Ph (3b); M = Hg, R = Me (4a)) have been isolated and characterized by multinuclear NMR and mass spectrometry. The molecular structures of complexes 2a,b, 3a·BrLi(THF)₃, 3b, and 4a were determined by single-crystal X-ray diffraction and displayed strong similarities to the structures of their cyclopentadienyl analogues. All molecules are monomeric in the solid state, containing nearly parallel ligands featuring an η³ coordination mode in 2a and η¹ coordination modes in the remaining complexes. Spectroscopic evidence indicates that the solid-state structure is maintained in solution and that Lewis basic solvents have the ability to coordinate reversibly to the metal centers. For comparison, the σ-bonded analogues [cyclo-MeC(BR)₂(NiPr)₂]SiCl₃ (R = Me (5a), Ph (5b)) were prepared, and the structure of 5b was determined using single-crystal X-ray diffractometry.