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 [{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-H)]2 (1) with CuCl (1:2 molar ratio) and (PhCH2S)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 H2 and afford the dimeric Yb(II) species [{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-X)]2 (X = Cl (2), SCH2Ph (3)) in which a κ1-amido,η6-arene type of coordination of amidinate ligand is retained. Reaction of 1 with 2 equiv of (PhCH2S)2 results in oxidation of both Yb(II) and hydrido centers and leads to the formation of the Yb(III) complex [{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-SCH2Ph)2]2 (4). Complex 4 can be also synthesized by oxidation of 3 with an equimolar amount of (PhCH2S)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 κ1-amido, η6-arene to “classical” κ1,κ1-N,N-chelating. Unlike Yb(III) bis(alkyl) species supported by bulky amidopyridinate ligands, the reaction of [{tBuC(NC6H3-2,6-iPr2)2}Yb(CH2SiMe3)2(THF)] (6) with PhSiH3 (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 κ1,κ1-N,N to κ1-N, η6-arene. Oxidation of 1 by 2,6-iPr2C6H3N═C(H)C(H)═NC6H3-2,6-iPr2 was found to result in oxidation of the hydrido ligand and ytterbium ion and formation of the mixed-valent ion-pair complex [{tBuC(NC6H3-2,6-iPr2)2}Yb(DME)2]+[{2,6-iPr2C6H3NC(H)═C(H)NC6H3-2,6-iPr2}2Yb]− (5). The σ-bond metathesis reaction of 1 with Ph2PH allowed for the synthesis of the first mixed-ligand hydrido–phosphido Yb(II) species [{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-H)(μ-PPh2)Yb{tBuC(NC6H3-2,6-iPr2)2}] (7). The second hydrido ligand cannot be replaced by a phosphido ligand.