Reversible Switching of Coordination Mode of ansa bis(Amidinate) Ligand in Ytterbium Complexes Driven by Oxidation State of the Metal Atom

Reaction of bisamidine C6H4-1,2-{NC­(t-Bu)­NH­(2,6-Me2C6H3)}2 (1) and [(Me3Si)2N]2Yb­(THF)2 (THF = tetrahydrofuran) (toluene; room temperature) in a 1:1 molar ratio afforded a bis­(amidinate) YbII complex [C6H4-1,2-{NC­(t-Bu)­N­(2,6-Me2C6H3)}2]­Yb­(THF) (2) in 65% yield. Complex 2 features unusual κ1amide, η6-arene coordination of both amidinate fragments to the ytterbium ion, resulting in the formation of a bent bis­(arene) structure. Oxidation of 2 by Ph3SnCl (1:1 molar ratio) or (PhCH2S)2 (1:0.5) leads to the YbIII species [C6H4-1,2-{NC­(t-Bu)­N­(2,6-Me2C6H3)}2]­YbCl­(1,2-dimethoxyethane) (3) and {[C6H4-1,2-{NC­(t-Bu)­N­(2,6-Me2C6H3)}2]­Yb­(μ-SCH2Ph)}2 (4), performing “classic” κ2N,N′-chelating coordination mode of ansa bis­(amidinate) ligand. By the reduction of 3 with equimolar amount of sodium naphthalide [C10H8•–]­[Na+] in THF, complex 2 can be recovered and restored to a bent bis­(arene) structure. Complex 3 was also synthesized by the salt metathesis reaction of equimolar amounts of YbCl3 and the dilithium derivative of 1 in THF.