Synthesis and structural characterization of Ni(II) complexes with the chiral CpH(PN_Ment) tripod ligand

Abstract

Treatment of NiCl₂ with the tripod ligand (L_Ment,S_C)-1H led to (L_Ment,S_C)-[Cp(PN_Ment)NiCl] in which the potentially tridentate ligand coordinated to the metal center in a bidentate way via the cyclopentadienyl system and the phosphorus atom. In the presence of NH₄PF₆ [(L_Ment,S_C)-[Cp(PN_Ment)NiCl] readily underwent Cl/PPh₃ exchange to give (L_Ment,S_C)-[Cp(PN_Ment)NiPPh₃]PF₆. Reaction of (L_Ment,S_C)-[Cp(PN_Ment)NiCl] with 0.5 eq. of dppe afforded [{(L_Ment,S_C)-[Cp(PN_Ment)Ni]}₂dppe](PF₆)₂. (L_Ment,S_C)-[Cp(PN_Ment)NiPPh₃]PF₆ and [{(L_Ment,S_C)-[Cp(PN_Ment)Ni]}₂dppe](PF₆)₂ were characterized by NMR and MS spectroscopy, and also by single crystal X-ray diffraction. The cyclopentadienyl ligand of (L_Ment,S_C)-[Cp(PN_Ment)NiPPh₃]PF₆ shows a distortion intermediate between the ene-allyl and diene types, while the two cyclopentadienyl ligands of [{(L_Ment,S_C)-[Cp(PN_Ment)Ni]}₂dppe](PF₆)₂ have intermediate and diene distortions, respectively. According to the temperature dependent NMR spectra of (L_Ment,S_C)-[Cp(PN_Ment)NiPPh₃]PF₆ and [{(L_Ment,S_C)-[Cp(PN_Ment)Ni]}₂dppe](PF₆)₂ two different conformations of the tether in the Cp(PN_Ment)Ni system could be frozen out at low temperatures.

Keywords:

• Ni(II) complexes
• Chiral-at-metal complexes
• Tridentate ligand
• Crystal structure

Acknowledgment

We thank Mrs. Sato of A-Rabbit-Science Japan Co., Ltd. for the CHN analyses.