Synthesis and reactions of β-diketiminato heavy group 14 metal alkoxides and phosphanides

Abstract

Some low-valent, three-coordinated β-diketiminato heavy group 14 metal complexes have been synthesised and their reactions examined. Initially, our attention is focused on several β-diketiminatolead(II) alkoxides. The lead(II) alkoxides show different basic and nucleophilic reactivities from transition metal analogues. For example, the reaction between the lead(II) tert-butoxide and methyl iodide proceeds only under forcing conditions to give the lead(II) iodide and methyl tert-butyl ether. However, facile reversible carbon dioxide insertion into the lead-oxygen bond is observed. To investigate the steric effect of the bulky β-diketiminato ligand, compounds with various aromatic groups attached to nitrogen have been made. When either [(BDIPh)PbCl] (BDIPh = [HC{C(Me)N(C6H5)}2]−) or [(BDIIPP)PbCl] (BDIIPP = [HC{C(Me)N(4-iPrC6H4)}2]−) was treated with potassium tert-butoxide, the reactions gave the unexpected bis[β-diketiminato]lead(II) complexes. However, treatment of [(BDIDMP)PbCl] (BDIDMP = [HC{C(Me)N(2,6-Me2C6H3)}2]−) with AgOTf led to the expected β-diketiminatolead(II) triflate. These results suggest that the ortho-substituent on the N-aryl groups in the β-diketiminato ligand plays an important role in influencing the formation of bis[β-diketiminato]lead(II) complexes. A series of β-diketiminato heavy group 14 metal phosphanides was synthesised. The phosphorus is pyramidally coordinated in the compounds containing diphenyl- or dicyclohexylphosphanido ligands. In contrast, the geometry at phosphorus is planar in the germanium(II) and tin(II) bis(trimethylsilyl)phosphanides. The phosphorus in the lead(II) bis(trimethylsilyl)phosphanide is pyramidally coordinated. The observed conformations may be explained by the steric congestion from the β-diketiminato ligand and electronic effects in the phosphanido ligand. Reactions of the phosphanido complexes with one equivalent of elemental chalcogen give phosphinochalcogenoito complexes. Further reaction with elemental chalcogen gives phosphinodichalcogenoato complexes. In contrast, treatment of the germanium(II) dicyclohexylphosphanide with elemental chalcogen leads to the formation of germanium(IV) chalcogenide. The presence of NMR-active nuclei in these complexes makes possible detailed spectroscopic analysis