Synthesis and Properties of[NiCp*(2,5-tBu_2PC_4H_2)],a 20-Valence-Electron Phosphanickelocene

摘要

The reaction of the bulky phospholide salt Li(2,5-fBu_2PC_4H_2)-2THF(1;THF = tetrahy-drofuran)with[NiCp*(acac)](HCp* = pentamethylcyclopentadiene,Hacac = acetylacetone)gives the green air-sensitive phosphanickelocene[NiCp*(2,5-tBu_2PC_4H_2)](2)in yields of about 85%.An X-ray structural determination of 2 shows long Ni-ring bonds and "delocalised" ring P-C and C-C bonds characteristic of a classical 20-valence-electron(ve)nickelocene.The electronic structure of 2 has been clarified through a combined Amsterdam density functional(ADF)and photoelectron spectroscopic study,which indicates that the higher lying semi-occupied molecular orbital(SOMO)(-5.82 eV)has a' symmetry and that the phosphorus "lone pair" is energetically low-lying(-8.15 eV).Oxidation of phosphanickelocene 2 by AgBF_4 occurs quantitatively to give the corresponding air-sensitive orange phosphanickel-ocenium salt[NiCp*(2,5-fBu_2PC_4H_2)]-[BF_4](3).This complex has also been characterised by an X-ray crystallo-graphic study,which reveals long Ni- C_alpha and short C_alpha-C_beta bonds in the phos-pholyl ligand indicative of a SOMO having a" symmetry.PMe_3 reacts with 2 at room temperature to provoke a ring-slip reaction that gives the 18ve complex[NiCp*eta~1-(2,5-tBu_2PC_4H_2)-(PMe_3)](4),but shows no reaction with the phosphanickelocenium salt 3 under the same conditions.