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.二价镱氢化物（Yb(II) hydride）[{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-H)]2（记为1）与氯化铜（CuCl，摩尔比1:2）以及二苄基二硫醚[(PhCH2S)2，摩尔比1:1]的氧化反应结果表明，1中的氢负离子还原剂活性强于二价镱阳离子。上述两个反应均伴随氢气（H2）逸出，得到二聚二价镱物种[{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-X)]2（X=Cl（2）、SCH2Ph（3）），该产物中脒基配体（amidinate ligand）仍保留κ1-酰胺基、η6-芳烯配位模式。当1与2当量的二苄基二硫醚反应时，二价镱中心与氢负离子均被氧化，生成三价镱配合物[{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-SCH2Ph)2]2（4）。配合物4也可通过3与等摩尔量的二苄基二硫醚氧化得到。研究表明，将镱中心氧化至三价态会使脒基配体的配位模式从κ1-酰胺基、η6-芳烯转变为“经典”的κ1,κ1-N,N双齿螯合模式。与大位阻酰胺吡啶基配体支撑的二(烷基)三价镱物种不同，配合物[{tBuC(NC6H3-2,6-iPr2)2}Yb(CH2SiMe3)2(四氢呋喃（THF）)]（记为6）与苯基硅烷（PhSiH3，摩尔比1:2）反应时，镱中心被还原为二价态，得到1。由此可见，三价镱还原为二价镱会使配位模式从κ1,κ1-N,N转变为κ1-N、η6-芳烯。1与2,6-二异丙基苯基氮杂烯丙基配体（2,6-iPr2C6H3N=C(H)C(H)=NC6H3-2,6-iPr2）的氧化反应会导致氢负离子配体与镱离子被氧化，生成混合价离子对配合物[{tBuC(NC6H3-2,6-iPr2)2}Yb(二甲氧基乙烷（DME）)2]+[{2,6-iPr2C6H3NC(H)=C(H)NC6H3-2,6-iPr2}2Yb]−（5）。1与二苯基膦（Ph2PH）的σ键复分解反应（σ-bond metathesis）可合成首例混合配体氢膦合二价镱物种[{tBuC(NC6H3-2,6-iPr2)2}Yb(μ-H)(μ-PPh2)Yb{tBuC(NC6H3-2,6-iPr2)2}]（7），且第二个氢负离子配体无法被膦基配体取代。