Synthesis, structures and reactions of lithium complexes of [(o-RCHC6H4)PPh2NSiMe3]− (R = H, SiMe3) ligands

Abstract

N-Trimethylsilyl o-methylphenyldiphenylphosphinimine, (o-MeC₆H₄)PPh₂NSiMe₃ (1), was prepared by reaction of Ph₂P(Br)NSiMe₃ with o-methylphenyllithium. Treatment of 1 with LiBuⁿ and then Me₃SiCl afforded (o-Me₃SiCH₂C₆H₄)PPh₂NSiMe₃ (2). Lithiations of both 1 and 2 with LiBuⁿ in the presence of tmen gave crystalline lithium complexes [Li{CH(R)C₆H₄(PPh₂NSiMe₃)-2}·tmen] (3, R = H; 4, R = SiMe₃). From the mother liquor of 4, traces of the tmen-bridged complex [Li{CH(SiMe₃)C₆H₄(PPh₂NSiMe₃)-2}]₂(µ-tmen) (5) were obtained. Reaction of 2 with LiBuⁿ in Et₂O yielded complex [Li{CH(SiMe₃)C₆H₄(PPh₂NSiMe₃)-2}·OEt₂] (6). Reaction of lithiated 1 with Me₂SiCl₂ in a 2:1 molar ratio afforded dimethylsilyl-bridged compound Me₂Si[CH₂C₆H₄(PPh₂NSiMe₃)-2]₂ (7). Lithiation of 7 with two equivalents of LiBuⁿ in Et₂O yielded [Li₂{(CHC₆H₄(PPh₂NSiMe₃)-2)₂SiMe₂}·0.5OEt₂] (8·0.5OEt₂). Treatment of 4 with PhCN formed a lithium enamide complex [Li{N(SiMe₃)C(Ph)CHC₆H₄(PPh₂NSiMe₃)-2}·tmen] (9). Reaction of two equivalents of 5 with 1,4-dicyanobenzene gave a dilithium complex [{Li(OEt₂)₂}₂(1,4-{C(N(SiMe₃)CHC₆H₄(PPh₂NSiMe₃)-2}₂C₆H₄)] (10). All compounds were characterised by NMR spectroscopy and elemental analyses. The structures of compounds 2, 3, 5, 6 and 9 have been determined by single crystal X-ray diffraction techniques.