SOLID-STATE DISTORTIONS OF LINEAR MONOMETALLIC, BIMETALLIC, AND TRIMETALLIC BIS(TRI-N-BUTYLPHOSPHINE) NICKEL AND PALLADIUM COMPLEXES HAVING 1,4-TETRAFLUOROPHENYLENE BRIDGES AS OBSERVED VIA P-31 CP/MAS NMR-SPECTROSCOPY

P-31 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. A2 type spectra were obtained with Ni(PBu3)2(1,4-C6F4H)2 (I), Pd(PBu3)2(1,4-C6F2) (V) and [Pd(PBu3)2(1,4-C6F4H)]2(1,4-C6F4) (VII). AB type spectra were obtained with Ni(PBu3)2(1,4-C6F4H)Br (II), [Ni(PBu3)2(1,4-C6F4)Br2 (III) and [Pd(PBu3)2Cl]2(1,4-C6F4) (VI). The 2J(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(PBu3)2]3(1,4-C6F4)2Br2 (IV) and [Pd(PBu3)2]3(1,4-C6F4)2Cl2 (VIII) consisted of overlapping A2 and AB spins systems. Large upfield and downfield shifts were measured in the solid samples relative to the corresponding P-31 NMR spectra in CDCl3 solution. Correlating the P-31 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.