Synthesis and Characterization of Dysprosium and Lanthanum Bis(iminophosphorano)methanide and -methanediide Complexes

Attempts to prepare [Dy{C(PPh2NSiMe3)2}(I)(THF)2] (1) from in situ prepared “[Dy(Bn)2(I)(THF)3]” (“2”; Bn = C6H5CH2) and H2C(PPh2NSiMe3)2 resulted in the isolation of [Dy{CH(PPh2NSiMe3)2}(I)2(THF)] (3) and, on one occasion, a small quantity of [{Dy(CH[PPh2NSiMe3]2)(I)}2(μ-O)] (4). However, attempts to prepare 3 from [K{CH(PPh2NSiMe3)2}(THF) n ] and [Dy(I)3(THF)3.5] were unsuccessful. The corresponding reactions with [La(I)3(THF)4] were unsuccessful, and the reaction of [{Li2(C[PPh2NSiMe3]2)}2] and [La(I)3(THF)4] in a 1:1 ratio resulted in the isolation of [{La(μ-I)3Li(THF)2}2{μ-C(PPh2NSiMe3)2}] (5). However, the potassium methanide complex [K{CH(PPh2NMes)2}] (Mes = 2,4,6-Me3C6H2) was found to react with [La(I)3(THF)4] to give [La{CH(PPh2NMes)2}(I)2(THF)2] (6). Complex 6 reacts with 1 equiv of [K(Bn)] to afford the methanediide complex [La{C(PPh2NMes)2}(I)(THF)3] (7). A DFT study of 6 and 7 revealed an increased accumulation of charge at the endocyclic carbon following deprotonation and conversion of 6 to 7, and although the La−C bond indices increase substantially upon a second deprotonation, the bonding remains highly ionic and is dominated by carbon 2p contributions with little orbital contribution from lanthanum. Compounds 1−7 have been variously characterized by X-ray crystallography, NMR spectroscopy, FTIR spectroscopy, CHN microanalyses, room-temperature solution magnetic moments, and, for 6 and 7, DFT calculations.