Group 1 Bis(iminophosphorano)methanides, Part 2: N-Aryl Derivatives of the Sterically Demanding Methanes H2C(PPh2NR)2 (R = 2,4,6-trimethylphenyl or 2,6-diisopropylphenyl)

Treatment of H2C(PPh2NMes)2 (Mes = 2,4,6-trimethylphenyl) with 1 equiv of [Na(Bn)] (Bn = CH2C6H5) in THF gave the Lewis base adduct [Na{HC(PPh2NMes)2}(THF)2] (1). The heavy group 1 methanides [Rb{HC(PPh2NMes)2}(DME)2] (2) and [Cs{HC(PPh2NMes)2}]6 (3) were prepared by the reaction of [MOR] (M = Cs, Rb; OR = 2-ethylhexoxide) with [Li{HC(PPh2NMes)2}]. The Lewis base adduct 2 is monomeric, but 3 exists as a novel cyclic 2.9 nm hexamer in the solid state even though it was recrystallized from the strong donor solvent THF. The reaction of H2C(PPh2NDipp)2 (Dipp = 2,6-diisopropylphenyl) with [Na(Bn)] afforded [Na{HC(PPh2NDipp)2}(THF)] (4). The potassium congener [K{HC(PPh2NDipp)2}(THF)2] (5) was prepared by the reaction of the parent methane with KH. In 5, the methanide ligand is bound to potassium through one N center, the methanide center, and an η6-Dipp interaction. However, the THF molecules in 5 are loosely bound, as evidenced by the isolation of dimeric [{K[HC(PPh2NDipp)2](THF)}2] (6) from hexane. In 6, the potassium is bound to the two N centers of one methanide ligand, but no methanide–potassium interaction is observed, and a “loose” dimer is constructed by bridging K···CDipp interactions. The reaction of [MOR] (M = Rb, Cs) with [Li{HC(PPh2NDipp)2}] gave the heavy group 1 methanides [M{HC(PPh2NDipp)2}(THF)3] [M = Rb (7), Cs (8)]. The synthetic utility of these group 1 transfer agents has been demonstrated by the preparation of [Ln{HC(PPh2NMes)2}(I)2(THF)2] [Ln = Ce (9), Pr (10), Nd (11), Sm (12)] from [Ln(I)3(THF)n], employing a salt metathesis methodology. Complexes 1–12 have been characterized by X-ray crystallography, multielement NMR spectroscopy, FTIR spectroscopy, and CHN microanalyses.