Reactivity of Ytterbium(II) Hydride. Redox Reactions: Ytterbium(II) vs Hydrido Ligand. Metathesis of the Yb–H Bond

Abstract

Oxidation reactions of the Yb(II) hydride [{ t BuC(NC 6 H 3 -2,6- i Pr 2 ) 2 }Yb(μ-H)] 2 ( 1 ) with CuCl (1:2 molar ratio) and (PhCH 2 S) 2 (1:1 molar ratio) revealed that the hydrido anion in 1 is a stronger reductant than the Yb(II) cation. Both reactions occur with evolution of H 2 and afford the dimeric Yb(II) species [{ t BuC(NC 6 H 3 -2,6- i Pr 2 ) 2 }Yb(μ-X)] 2 (X = Cl ( 2 ), SCH 2 Ph ( 3 )) in which a κ 1 -amido,η 6 -arene type of coordination of amidinate ligand is retained. Reaction of 1 with 2 equiv of (PhCH 2 S) 2 results in oxidation of both Yb(II) and hydrido centers and leads to the formation of the Yb(III) complex [{ t BuC(NC 6 H 3 -2,6- i Pr 2 ) 2 }Yb(μ-SCH 2 Ph) 2 ] 2 ( 4 ). Complex 4 can be also synthesized by oxidation of 3 with an equimolar amount of (PhCH 2 S) 2 . It was demonstrated that oxidation of the ytterbium center to the trivalent state leads to switching of the coordination mode of amidinate ligand from κ 1 -amido, η 6 -arene to “classical” κ 1,κ 1 -N,N-chelating. Unlike Yb(III) bis(alkyl) species supported by bulky amidopyridinate ligands, the reaction of [{ t BuC(NC 6 H 3 -2,6- i Pr 2 ) 2 }Yb(CH 2 SiMe 3 ) 2 (THF)] ( 6 ) with PhSiH 3 (1:2 molar ratio) occurs with reduction of ytterbium to a divalent state and affords 1 . Thus, reduction of Yb(III) to Yb(II) leads to a change of coordination mode from κ 1,κ 1 -N,N to κ 1 -N, η 6 -arene. Oxidation of 1 by 2,6- i Pr 2 C 6 H 3 N═C(H)C(H)═NC 6 H 3 -2,6- i Pr 2 was found to result in oxidation of the hydrido ligand and ytterbium ion and formation of the mixed-valent ion-pair complex [{ t BuC(NC 6 H 3 -2,6- i Pr 2 ) 2 }Yb(DME) 2 ] + [{2,6- i Pr 2 C 6 H 3 NC(H)═C(H)NC 6 H 3 -2,6- i Pr 2 } 2 Yb] − ( 5 ). The σ-bond metathesis reaction of 1 with Ph 2 PH allowed for the synthesis of the first mixed-ligand hydrido–phosphido Yb(II) species [{ t BuC(NC 6 H 3 -2,6- i Pr 2 ) 2 }Yb(μ-H)(μ-PPh 2 )Yb{ t BuC(NC 6 H 3 -2,6- i Pr 2 ) 2 }] ( 7 ). The second hydrido ligand cannot be replaced by a phosphido ligand.