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

Attempts to prepare [Dy{C(PPh 2 NSiMe 3 ) 2 }(I)(THF) 2 ] ( 1 ) from in situ prepared “[Dy(Bn) 2 (I)(THF) 3 ]” (“ 2 ”; Bn = C 6 H 5 CH 2 ) and H 2 C(PPh 2 NSiMe 3 ) 2 resulted in the isolation of [Dy{CH(PPh 2 NSiMe 3 ) 2 }(I) 2 (THF)] ( 3 ) and, on one occasion, a small quantity of [{Dy(CH[PPh 2 NSiMe 3 ] 2 )(I)} 2 (μ-O)] ( 4 ). However, attempts to prepare 3 from [K{CH(PPh 2 NSiMe 3 ) 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 [{Li 2 (C[PPh 2 NSiMe 3 ] 2 )} 2 ] and [La(I) 3 (THF) 4 ] in a 1:1 ratio resulted in the isolation of [{La(μ-I) 3 Li(THF) 2 } 2 {μ-C(PPh 2 NSiMe 3 ) 2 }] ( 5 ). However, the potassium methanide complex [K{CH(PPh 2 NMes) 2 }] (Mes = 2,4,6-Me 3 C 6 H 2 ) was found to react with [La(I) 3 (THF) 4 ] to give [La{CH(PPh 2 NMes) 2 }(I) 2 (THF) 2 ] ( 6 ). Complex 6 reacts with 1 equiv of [K(Bn)] to afford the methanediide complex [La{C(PPh 2 NMes) 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.