Potential precursors for terminal ytterbium(ii) imide complexes bearing the hydrotris(3-tert-butyl-5-methylpyrazolyl)borato ligand

Abstract

Monomeric, divalent ytterbium primary amides Tp^tBu,MeYb(NHR)(thf)_x (R = C₆H₃iPr₂-2,6 = Ar^iPr = Dipp, C₆H₃(CF₃)₂-3,5 = Ar^CF3, SiPh₃) supported by the bulky hydrotris(3-tBu-5-Me-pyrazolyl)borato scorpionate ligand are synthesized acccording to salt metathesis and protonolysis protocols, respectively. Yb(II) precursors comprise YbI₂(thf)₂, Yb[N(SiMe₃)₂]₂(thf)₂ and Tp^tBu,MeYb[N(SiMe₃)₂]. Complexes Tp^tBu,MeYb(NHR)(thf)_x readily engage in donor (thf) exchange with nitrogen donors like DMAP (4-dimethylaminopyridine) and pyridine. Treatment of Tp^tBu,MeYb(NHAr^CF3)(thf)₂ with the Lewis acids AlMe₃ and GaMe₃ results in the heterobimetallic complexes Tp^tBu,MeYb(NHAr^CF3)(MMe₃) (M = Al, Ga). Reactions of Tp^tBu,MeYb(NHR)(thf)_x (R = Ar^iPr, Ar^CF3) with the halogenating agents C₂Cl₆ and TeBr₄ give access to trivalent complexes [Tp^tBu,MeYb(NHR)(X)] (X = Cl, Br). The ytterbium(II) complexes under study display ¹⁷¹Yb NMR chemical shifts in the range 582 ppm for Tp^tBu,MeYb(NHAr^CF3)(GaMe₃) to 954 ppm for Tp^tBu,MeYb(NHSiPh₃)(dmap). The salt-metathesis route is also applicable for the synthesis of complexes Tp^tBu,MeLn(NHAr^iPr)(thf) (Ln = Sm, Eu) and Tp^tBu,MeYb(NHAr^Me) (Ar^Me = C₆H₃Me₂-2,6).