Lithiation and intermolecular exchange of tertiary methylphosphines in trans-[NiR2L2], where R = 2,6-dimethoxyphenyl

Abstract

2,6-Dimethoxyphenylnickel(II) complexes, trans-[NiR₂L₂][R = C₆H₃(OMe)₂-2,6; L = PMe₃, PMe₂Ph, and PMePh₂] and trans-[NiR(Cl)L₂](L = PMe₃, PMe₂Ph, and PPh₃) have been prepared from [NiCl₂L₂] and LiR. Reactions of n-butyl-lithium with trans-[NiR₂L₂](L = PMe₃ and PMe₂Ph) in diethyl ether resulted in the facile lithiation at the methyl carbon in the L ligands, giving trans-[NiR₂{PMe₂(CH₂SiMe₃)}₂] and trans-[NiR₂{ PMePh(CH₂SiMe₃)}₂], respectively, after treatment with SiMe₃Cl. The complexes trans-[NiR(C₆H₂Me₃-2,4,6)(PMe₃){PMe₂(CH₂SiMe₃)}] and trans-[Ni(C₆H₂Me₃-2,4,6)(C₆H₄Me-2){PMe₂(CH₂SiMe₃)}₂] were obtained from the corresponding PMe₃ complexes by analogous reactions in the presence of NNN′N′-tetramethylethylenediamine. Intermolecular tertiary phosphine exchanges have been observed between trans-[NiR₂L₂] complexes [L = PMe₃, PMe₂Ph, PMe₂(CH₂SiMe₃), and PMePh(CH₂SiMe₃)], as well as between trans-[NiR(Cl)L₂] complexes, on heating their benzene solutions or on treatment with carbon monoxide. The possible mechanisms are discussed briefly.