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.