Solid-state distortions of linear mono-, bi-, and trimetallic bis(tri- n-butylphosphine) nickel and palladium complexes having 1,4-tetrafluorophenylene bridges as observed via 31P CP/MAS NMR spectroscopy

Abstract

31P CP/MAS NMR spectra were recorded for a series of eight linear mono-, bi-, and trimetallic bis(tri- n-butylphosphine) nickel and palladium complexes having 1,4-tetrafluorophenylene bridges. A 2 type spectra were obtained with Ni(PBu 3) 2(1,4-C 6F 4H) 2 ( I), Pd(PBu 3) 2(1,4-C 6F 2) ( V) and [Pd(PBu 3) 2(1,4-C 6F 4H)] 2(1,4-C 6F 4) ( VII). AB type spectra were obtained with Ni(PBu 3) 2(1,4-C 6F 4H)Br ( II), [Ni(PBu 3) 2(1,4-C 6F 4)Br 2 ( III) and [Pd(PBu 3) 2Cl] 2(1,4-C 6F 4) ( VI). The 2 J PP scalar coupling constants fell in the region of 300 to 450 Hz as expected for P-metal-P pairs in a trans configuration. The spectra of [Ni(PBu 3) 2] 3(1,4-C 6F 4) 2Br 2 ( IV) and [Pd(PBu 3) 2] 3(1,4-C 6F 4) 2Cl 2 ( VIII) consisted of overlapping A 2 and AB spins systems. Large upfield and downfield shifts were measured in the solid samples relative to the corresponding 31P NMR spectra in CDCl 3 solution. Correlating the 31P CP/MAS NMR data with reported X-ray crystallographic measurements revealed that both the chemical inequivalence and the solid versus solution resonance frequency shifts were the result of ring current effects brought about by distortions from square-planar geometry at the metal centre in the solid state.