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)(2)N](2)Yb(THF)(2) (THF = tetrahydrofuran) (toluene; room temperature) in a 1:1 molar ratio afforded a bis(amidinate) Yb-II complex [C6H4-1,2-{NC(t-Bu)N(2,6-Me2C6H3)}(2)]Yb(THF) (2) in 65% yield. Complex 2 features unusual kappa(1) amide, eta(6)-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 Yb-III 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(mu-SCH2Ph)}(2) (4), performing classic kappa N-2,N'-chelating coordination mode of ansa bis(amidinate) ligand. By the reduction of 3 with equimolar amount of sodium naphthalide [C10H8 center dot-][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.