Mononuclear Phenolate Diamine Zinc Hydride Complexes and Their Reactions With CO.

The synthesis, characterization, and zinc coordination chemistry of the three proligands 2--butyl-4-[-butyl ()/methoxy ()/nitro ()]-6-{[(2'-dimethylaminoethyl)methylamino]methyl}phenol are described. Each of the ligands was reacted with diethylzinc to yield zinc ethyl complexes -; these complexes were subsequently reacted with phenylsilanol to yield zinc siloxide complexes -. Finally, the zinc siloxide complexes were reacted with phenylsilane to produce the three new zinc hydride complexes -. The new complexes - have been fully characterized by NMR spectroscopy, mass spectrometry, and elemental analyses. The structures of the zinc hydride complexes have been probed using VT-NMR spectroscopy and X-ray diffraction experiments. These data indicate that the complexes exhibit mononuclear structures at 298 K, both in the solid state and in solution (-toluene). At 203 K, the NMR signals broaden, consistent with an equilibrium between the mononuclear and dinuclear bis(μ-hydrido) complexes. All three zinc hydride complexes react rapidly and quantitatively with carbon dioxide, at 298 K and 1 bar of pressure over 20 min, to form the new zinc formate complexes -. The zinc formate complexes have been analyzed by NMR spectroscopy and VT-NMR studies, which reveal a temperature-dependent monomer-dimer equilibrium that is dominated by the mononuclear species at 298 K.