Synthesis And Characterization Of β-diketiminato Germanium Compounds

The synthesis of compounds containing low-valent and low-coordinate germanium is important branche of the main group chemistry.It also belongs to the frontier subject of inorganic synthesis field.The classical β-diketiminato ligands play a central role in stabilizing these compounds because of their unique steric and electronic effects.In previous work,our research group reported a new type of β-diketimine 4[MeC(PhCNDip)2H;Dip=2,6-iPr2C6H3]without active proton on the rest-groups of the back-bone,its features include steric and electronic effects.In addition,the possibility of losing protons in the skeleton is completely avoided.The β-diketiminato germylene chloride 6[MeC(PhCNDip)2GeCl]was selected as precursor compound during the master’s research work with soughting for synthesizing compounds such as germylene,gemanium(I)radical and germylene anion with novel structures.A new gemanium radical 7[MeC-(PhCNDip)2Ge]was synthesized through the reduction of β-diketiminato germylene chloride 6 by sodium naphthalene.The inductive effect of two phenyl groups leads to the backbone of ligand 4 being more electron deficient,and therefore the singly occupied molecular orbital(SOMO)of radical 7 is mainly composed of a л-antibonding orbital between the N and C atoms.Thus,the radical 7 is a two-coordinate germylene stabilized by an N-heterocyclic radical ligand.The β-diketiminato germylene azide 8[MeC(PhCNDip)2GeN3]was prepared through substitution reaction of β-diketiminato germylene chloride 6 with NaN3,The six-membered C3N2Ge-ring of compound 8 is not plane,and the three nitrogen atoms connected to Ge are in a linear structure.By reducingβ-diketiminato germylene azide 8 and 11[PhCH(PhCNDip)2Ge]with sodium naphthalenide,two unsymmetric substituted digermylene 10 LGe-GeL’(L=MeC(PhCNDip)2,L’=MeC(PhC)2NDip)and 12 L"Ge-GeL"(L"＝PhC(PhCNDip)2,L" PhC(PhC)2NDip)was afforded.Compounds 10 and 12 both possess trans-bent geometry and comprise a Ge-Ge single bond with a stereoactive lone pair on each germanium center.In contrast,the C3NGe rings in both compounds are planar,while the six-membered C3N2Ge rings are not planar.Reduction of β-diketiminato germylene chloride 6 with elemental lithium leding to cyclogermylidenide derivative in the form of its lithium salt 13 L’GeLi(THF)2(Et2O)(L’＝MeC(PhC)2NDip),the five-membered C3NGe-ring of compound 13 is almost planar,and the lithium atom is first observed to coordinate with germylene anion in an end mode.Ultra-large volume of amino potassium compound 16 ’Pr3Si(Dip)NK is a chain polymer.The structures of those molecules were confirmed by X-ray single crystal diffraction and nuclear magnetic resonance(NMR).To sum up,the β-diketiminato germanium radical complex 7 exhibited a remarkably different structure in comparison with the reported Ge(I)radical,the unpaired electron is mainly distributed on the NC3N backbone.The β-diketiminato germylene azide 8 was prepared in high yield.Two unsymmetric substituted digermylenes 10 and 12 were furnished in one step through the method of reduction for the first time.In compound 13 the lithium ion was first observed to coordinate with germylene anion in an end mode.The synthesis of these compounds had not only deepened the understanding of the bonding mode of the low-valent and low-coordinate germanium compounds,but also laid a solid foundation for further research.