Mononuclear Phenolate Diamine Zinc Hydride Complexesand Their Reactions With CO2

摘要

The synthesis, characterization, and zinc coordination chemistry of the three proligands 2-tert-butyl-4-[tert-butyl (>1)/methoxy (>2)itro (>3)]-6-{[(2′-dimethylaminoethyl)methylamino]methyl}phenol are described. Each of the ligands was reacted with diethylzinc to yield zinc ethyl complexes >4–>6; these complexes were subsequently reacted with phenylsilanol to yield zinc siloxide complexes >7–>9. Finally, the zinc siloxide complexes were reacted with phenylsilane to produce the three new zinc hydride complexes >10–>12. The new complexes >4–>12 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 (d8-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 quantitativelywith carbon dioxide, at 298 K and 1 bar of pressure over 20 min, toform the new zinc formate complexes >13–>15. The zinc formate complexes have been analyzed by NMR spectroscopyand VT-NMR studies, which reveal a temperature-dependent monomer–dimerequilibrium that is dominated by the mononuclear species at 298 K.