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) Yb(II) complex [C6H4-1,2-{NC(t-Bu)N(2,6-Me2C6H3)}2]Yb(THF) (2) in 65% yield. Complex 2 features unusual κ(1)amide, η(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(μ-SCH2Ph)}2 (4), performing "classic" κ(2)N,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.