Synthesis, properties and group 10 metal complexes of a bis(dipyridylphosphinomethyl)phenyl pincer ligand

Abstract

The synthesis, properties and coordination behaviour of the bis(dipyridylphosphinomethyl)phenyl pincer ligand 1,3-C6H4(CH2PPy2)2 (Py=2-pyridyl) are reported. The basicity of the phosphorus atoms in the ligand is explored through the synthesis of the phosphine selenide and a protonation study. The 1JPSe value of 742Hz indicates that this ligand is less basic than PPh3 and the protonation study confirms the nitrogen atoms are more basic than the phosphorus atoms. Protonation of the ligand also renders it water-soluble. The ligand reacts with [PtXY(hex)] (X=Y=Me; X=Cl Y=Me, hex=hexa-1,5-diene) at 50°C to give pincer [PtX(PCP)] complexes (X=Me, Cl). In contrast, when reaction with [PtXY(hex)] (X=Y=Me, Cl; X=Cl Y=Me) occurs at ambient temperature, dimeric complexes of the type [PtXY(μ-PP)]2 are observed in the NMR spectra. The presence of a methyl ligand appears to facilitate metalation: when there is no methyl ligand present formation of the platinum pincer complex does not occur even after prolonged thermolysis. However, reaction with [PdCl2(MeCN)2] proceeds readily at 50°C from the dimer to the [PdCl(PCP)] complex.