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

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.