Selective Intermolecular C–H Bond Activation: A Straightforward Synthetic Approach to Heteroalkyl Yttrium Complexes Containing a Bis(pyrazolyl)methyl Ligand

The reactions of bis­(pyrazolyl)­methanes CH₂(C₃HN₂R₂-3,5)₂ (R = Me, <i>t</i>Bu) with Y­(CH₂SiMe₃)₃(THF)₂ and LY­(CH₂SiMe₃)₂­(THF)_<i>n</i> (L = amidopyridinate (Ap′), amidinate (Amd), tridentate amidinate bearing 2-methoxyphenyl pendant in a side arm (Amd^OMe) and pentamethylcyclopentadienyl (Cp*); <i>n</i> = 0, 1) were investigated. CH₂(C₃HN₂<i>t</i>Bu₂-3,5)₂ turned out to be inert in these reactions, while less bulky CH₂(C₃HN₂Me₂-3,5)₂ easily undergoes metalation by yttrium alkyls. The reaction of Y­(CH₂SiMe₃)₃(THF)₂ with CH₂(C₃HN₂Me₂-3,5)₂ regardless of the molar ratio of the reagents affords a homoleptic tris­(alkyl) species, Y­[CH­(C₃HN₂Me₂-3,5)₂]₃ (<b>1</b>). However, the reactions of equimolar amounts of LY­(CH₂SiMe₃)₂(THF)_<i>n</i> and CH₂(C₃HN₂Me₂-3,5)₂ occur selectively with replacement of a sole CH₂SiMe₃ fragment and afford the related heteroalkyl complexes LY­(CH₂SiMe₃)­[CH­(C₃HN₂Me₂-3,5)₂]­(THF)_<i>n</i> (L = Ap′, <i>n</i> = 1 (<b>6</b>); Amd, <i>n</i> = 0 (<b>7</b>); Amd^OMe, <i>n</i> = 1 (<b>8</b>); Cp*, <i>n</i> = 1 (<b>9</b>)) in good yields. The second equivalent of CH₂(C₃HN₂Me₂-3,5)₂ does not react with heteroalkyl yttrium complexes. The X-ray studies revealed that in complexes <b>1</b> and <b>6</b>–<b>9</b> the bis­(pyrazolyl)­methyl ligands are bound to the yttrium centers in a similar fashion via one covalent Y–C and two coordination Y–N bonds. Thermal decomposition of complexes <b>6</b>–<b>9</b> (C₆D₆, 80 °C) as evidenced by ¹H NMR spectroscopy resulted in SiMe₄ elimination, while no activation of the C–H bonds of bis­(pyrazolyl)­methyl ligands was detected. When <b>6</b> was treated with an equimolar amount of PhSiH₃, only the YCH₂SiMe₃ bond selectively underwent σ-bond metathesis and a dimeric yttrium alkyl-hydrido complex, {Ap′Y­[CH­(C₃HN₂Me₂-3,5)₂]­(μ²-H)}₂ (<b>10</b>), was formed. The reaction of <b>6</b> with 2,6-diisopropylaniline also resulted in the selective protonation of the YCH₂SiMe₃ bond and cleanly afforded alkyl-anilido complex Ap′Y­(NHC₆H₃<i>i</i>Pr₂-2,6)­[CH­(C₃HN₂Me₂-3,5)₂]­(THF) (<b>11</b>). The ternary catalytic systems <b>6</b>–<b>9</b>/borate/Al<i>i</i>Bu₃ (borate = [HNMe₂Ph]­[B­(C₆F₅)₄], [Ph₃C]­[B­(C₆F₅)₄]; [Ln]:[borate]:[Al<i>i</i>Bu₃] = 1:1:10) demonstrated moderate catalytic activity in isoprene polymerization; they allow quantitative conversion into polymer of up to 1000 equiv of monomer in 2–4 h. The best activity and 1,4-cis selectivity (83.5%) were demonstrated by amidinato complex <b>8</b>

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(<i>t</i>-Bu)­NH­(2,6-Me₂C₆H₃)}₂ (<b>1</b>) 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(<i>t</i>-Bu)­N­(2,6-Me₂C₆H₃)}₂]­Yb­(THF) (<b>2</b>) in 65% yield. Complex <b>2</b> features unusual κ¹amide, η⁶-arene coordination of both amidinate fragments to the ytterbium ion, resulting in the formation of a bent bis­(arene) structure. Oxidation of <b>2</b> by Ph₃SnCl (1:1 molar ratio) or (PhCH₂S)₂ (1:0.5) leads to the Yb^III species [C₆H₄-1,2-{NC­(<i>t</i>-Bu)­N­(2,6-Me₂C₆H₃)}₂]­YbCl­(1,2-dimethoxyethane) (<b>3</b>) and {[C₆H₄-1,2-{NC­(<i>t</i>-Bu)­N­(2,6-Me₂C₆H₃)}₂]­Yb­(μ-SCH₂Ph)}₂ (<b>4</b>), performing “classic” κ²N,N′-chelating coordination mode of ansa bis­(amidinate) ligand. By the reduction of <b>3</b> with equimolar amount of sodium naphthalide [C₁₀H₈^•–]­[Na⁺] in THF, complex <b>2</b> can be recovered and restored to a bent bis­(arene) structure. Complex <b>3</b> was also synthesized by the salt metathesis reaction of equimolar amounts of YbCl₃ and the dilithium derivative of <b>1</b> in THF

Reactions of Bis(alkyl)yttrium Complexes Supported by Bulky N,N Ligands with 2,6-Diisopropylaniline and Phenylacetylene

The reactions of bis­(trimethylsilylmethyl)yttrium complexes supported by bulky amidopyridinate (Ap) and amidinate (Amd) ligands (LY­(CH₂SiMe₃)₂(THF)_<i>n</i>: L = Ap, <i>n</i> = 1 (<b>1</b>); L = Amd, <i>n</i> = 1 (<b>2</b>)) with 2,6-diisopropylaniline and phenylacetylene were performed. The reaction of <b>1</b> with an equimolar amount of 2,6-diisopropylaniline occurs with TMS elimination and affords an yttrium alkyl anilido species which was isolated as a DME adduct, ApY­(CH₂SiMe₃)­(NH-2,6-ⁱPr₂C₆H₃)­(DME) (<b>3</b>). The protonolysis of <b>3</b> with phenylacetylene results in the alkynyl anilido derivative ApY­(CCPh)­(NH-2,6-ⁱPr₂C₆H₃)­(DME) (<b>6</b>). The treatment of complexes <b>3</b> and <b>6</b> with 2,2′-bipy leads to the formation of the bis­(anilido) derivative ApY­(NH-2,6-<i>i</i>Pr₂C₆H₃)₂(bipy) (<b>5</b>). The formation of a dimeric complex containing two ApY fragments linked by two μ₂-alkynyl groups and a μ-η²:η²-butatrienediyl fragment, [{AmdY­(μ₂-CCPh)}₂(μ₂-η²:η²-PhCCCCPh)] (<b>7</b>), was observed in the reaction of <b>2</b> with 2 equiv of phenylacetylene

Reactions of Bis(alkyl)yttrium Complexes Supported by Bulky N,N Ligands with 2,6-Diisopropylaniline and Phenylacetylene

The reactions of bis­(trimethylsilylmethyl)yttrium complexes supported by bulky amidopyridinate (Ap) and amidinate (Amd) ligands (LY­(CH₂SiMe₃)₂(THF)_<i>n</i>: L = Ap, <i>n</i> = 1 (<b>1</b>); L = Amd, <i>n</i> = 1 (<b>2</b>)) with 2,6-diisopropylaniline and phenylacetylene were performed. The reaction of <b>1</b> with an equimolar amount of 2,6-diisopropylaniline occurs with TMS elimination and affords an yttrium alkyl anilido species which was isolated as a DME adduct, ApY­(CH₂SiMe₃)­(NH-2,6-ⁱPr₂C₆H₃)­(DME) (<b>3</b>). The protonolysis of <b>3</b> with phenylacetylene results in the alkynyl anilido derivative ApY­(CCPh)­(NH-2,6-ⁱPr₂C₆H₃)­(DME) (<b>6</b>). The treatment of complexes <b>3</b> and <b>6</b> with 2,2′-bipy leads to the formation of the bis­(anilido) derivative ApY­(NH-2,6-<i>i</i>Pr₂C₆H₃)₂(bipy) (<b>5</b>). The formation of a dimeric complex containing two ApY fragments linked by two μ₂-alkynyl groups and a μ-η²:η²-butatrienediyl fragment, [{AmdY­(μ₂-CCPh)}₂(μ₂-η²:η²-PhCCCCPh)] (<b>7</b>), was observed in the reaction of <b>2</b> with 2 equiv of phenylacetylene

Amido Ln(II) Complexes Coordinated by Bi- and Tridentate Amidinate Ligands: Nonconventional Coordination Modes of Amidinate Ligands and Catalytic Activity in Intermolecular Hydrophosphination of Styrenes and Tolane

Heteroleptic Ln­(II) and Ca­(II) amides [<i>t</i>BuC­(NC₆H₃-<i>i</i>Pr₂-2,6)₂]­MN­(SiMe₃)₂(THF) (M = Yb (<b>1Yb</b>), Ca (<b>1Ca</b>)), [2-MeOC₆H₄NC­(<i>t</i>Bu)­N­(C₆H₃-<i>i</i>Pr₂-2,6)]­LnN­(SiMe₃)₂(THF) (Ln = Sm (<b>2Sm</b>), Yb (<b>2Yb</b>)), and [2-Ph₂P­(O)­C₆H₄NC­(<i>t</i>Bu)­N­(C₆H₃-Me₂-2,6)]­YbN­(SiMe₃)₂(THF) (<b>3Yb</b>) coordinated by bi- and tridentate amidinate ligands were obtained by the amine elimination reactions of M­[N­(SiMe₃)₂]­(THF)₂ (M = Yb, Sm, Ca) with parent amidines in good yields. Complex [<i>t</i>BuC­(NC₆H₃-<i>i</i>Pr₂-2,6)₂]­SmN­(SiMe₃)₂ can be obtained only by a salt metathesis reaction of [<i>t</i>BuC­(NC₆H₃-2,6-<i>i</i>Pr₂)₂]­SmI­(THF)₂ with NaN­(SiMe₃)₂. Unlike <b>1Yb</b> and <b>1Ca</b> in <b>1Sm</b> the amidinate ligand is coordinated to metal ion in κ¹-amido:η⁶-arene fashion preventing THF coordination. The derivatives of tridentate amidinate ligands bearing pendant donor 2-MeOC₆H₄ or 2-Ph₂P­(O)­C₆H₄N groups feature nonconventional κ¹-N,κ²-O,η⁶-arene coordination mode. Complexes <b>1Ca</b>, <b>1Sm</b>, <b>1Yb</b>, <b>2Sm</b>, <b>2Yb</b>, and <b>3Yb</b> proved to be efficient catalysts for styrene hydrophosphination with PhPH₂ and Ph₂PH. In styrene hydrophosphination with PhPH₂ all the catalysts perform excellent chemoselectivity and afford a monoaddition productsecondary phosphine (PhCH₂CH₂)­PhPH. Moreover, all the catalysts perform hydrophosphination reactions regioselectively with exclusive formation of the <i>anti-</i>Markovnikov addition product. Within the series of complexes coordinated by the same amidinate ligand catalytic activity decreases in the following order <b>1Ca</b> ≥ <b>1Sm</b>><b>1Yb</b>. The turnover frequencies were in the range of TOF ≈ 0.3–0.7 h^–1. However, application of tridentate amidinate ligand allowed one to increase catalytic activity significantly: for <b>2Sm</b> TOF was found to be 8.3 h^–1. For the addition of PhPH₂ to para-substituted styrenes catalyzed by <b>2Sm</b> it was found that electron-withdrawing substituents (Cl, F) do not affect the reaction rate while electron-donating groups (<i>t</i>Bu, OMe) noticeably slow down the reaction

Chloro and Alkyl Rare-Earth Complexes Supported by <i>ansa</i>-Bis(amidinate) Ligands with a Rigid <i>o</i>‑Phenylene Linker. Ligand Steric Bulk: A Means of Stabilization or Destabilization?

<i>ansa</i>-Bis­(amidinate) ligands with a rigid <i>o</i>-phenylene linker, C₆H₄-1,2-{NC­(<i>t</i>Bu)­N­(2,6-R₂C₆H₃)­H}₂ (R = Me (<b>1</b>), <i>i</i>Pr (<b>2</b>)), were successfully employed for the synthesis of rare-earth chloro and alkyl species. The reaction of dilithium derivatives of <b>1</b> and <b>2</b> with LnCl₃ (Ln = Y, Lu) afforded the monomeric bis­(amidinate) chloro lanthanide complexes [C₆H₄-1,2-{NC­(<i>t</i>Bu)­N­(2,6-R₂C₆H₃)}₂]­Y­(THF)­(μ-Cl)₂Li­(THF)₂ (R = Me (<b>3</b>), <i>i</i>Pr (<b>5</b>)) and [C₆H₄-1,2-{NC­(<i>t</i>Bu)­N­(2,6-Me₂C₆H₃)}₂]­LuCl­(THF)₂ (<b>4</b>). Bis­(amidinate) ligands in complexes <b>3</b> and <b>4</b> are coordinated to the metal atoms in a tetradentate fashion, while the bulkier ligand in <b>5</b> is tridentate. The alkane elimination reactions of <b>1</b> and <b>2</b> with equimolar amounts of (Me₃SiCH₂)₃Ln­(THF)₂ (Ln = Y, Lu) allowed us to obtain the monoalkyl complexes [C₆H₄-1,2-{NC­(<i>t</i>Bu)­N­(2,6-R₂C₆H₃)}₂]­Ln­(CH₂SiMe₃)­(THF)_<i>n</i> (Ln = Y, R = Me, <i>n</i> = 1 (<b>6</b>); Ln = Lu, R = Me, <i>n</i> = 1 (<b>7</b>); Ln = Y, R = <i>i</i>Pr, <i>n</i> = 2 (<b>8</b>)). The kinetics of thermal decomposition of complexes <b>6</b>–<b>8</b> were measured, and for <b>6</b> the activation energy was obtained from the temperature dependence of the rate constants (<i>E</i>_a = 67.0 ± 1.3 kJ/mol). Complexes <b>6</b> and <b>7</b> turned out to be inert toward H₂ and PhSiH₃. Surprisingly, complex <b>8</b> was inert toward H₂ and PhSiH₃ but rapidly cleaved C–O bonds of DME. The reaction resulted in the formation of the methoxy complex {[C₆H₄-1,2-{NC­(<i>t</i>Bu)­N­(2,6-<i>i</i>Pr₂C₆H₃)}₂]­Y­(μ₂-OMe)]}₂(μ₂-DME) (<b>9</b>) and methyl vinyl ether

Amido Analogues of Nonbent Lanthanide (II) and Calcium Metallocenes. Heterolytic Cleavage of π‑Bond Ln–Carbazolyl Ligand Promoted by Lewis Base Coordination

Introduction of four <i>t</i>Bu groups into a carbazol-yl framework leads to switching of the metal–ligand bonding in the Ln­(II) and Ca complexes from σ to π. Complexes [(<i>t</i>Bu₄Carb)₂Ln] (Ln = Sm, Eu, Yb, Ca) are amido analogues of metallocenes, which adopt the sandwich structures with parallel disposition of the aromatic ligands and strong contribution of η³-mode into η⁵ metal–ligand bonding. The DFT calculations demonstrated that the geometry is due to steric effects (presence of the bulky <i>t</i>Bu groups) as well as the maximization of the overlap between the Sm ⁴f orbital and the π-type nitrogen lone pair of the carbazol-yl ligand. Coordination of DME to the metal centers in [(<i>t</i>Bu₄Carb)₂M] (M = Sm, Yb) results in the heterolytic dissociation of the metal–ligand π-bond and the formation of ionic complexes [<i>t</i>Bu₄Carb^–]₂­[Ln²⁺(DME)_<i>n</i>]

Amido Ln(II) Complexes Coordinated by Bi- and Tridentate Amidinate Ligands: Nonconventional Coordination Modes of Amidinate Ligands and Catalytic Activity in Intermolecular Hydrophosphination of Styrenes and Tolane

Heteroleptic Ln­(II) and Ca­(II) amides [<i>t</i>BuC­(NC₆H₃-<i>i</i>Pr₂-2,6)₂]­MN­(SiMe₃)₂(THF) (M = Yb (<b>1Yb</b>), Ca (<b>1Ca</b>)), [2-MeOC₆H₄NC­(<i>t</i>Bu)­N­(C₆H₃-<i>i</i>Pr₂-2,6)]­LnN­(SiMe₃)₂(THF) (Ln = Sm (<b>2Sm</b>), Yb (<b>2Yb</b>)), and [2-Ph₂P­(O)­C₆H₄NC­(<i>t</i>Bu)­N­(C₆H₃-Me₂-2,6)]­YbN­(SiMe₃)₂(THF) (<b>3Yb</b>) coordinated by bi- and tridentate amidinate ligands were obtained by the amine elimination reactions of M­[N­(SiMe₃)₂]­(THF)₂ (M = Yb, Sm, Ca) with parent amidines in good yields. Complex [<i>t</i>BuC­(NC₆H₃-<i>i</i>Pr₂-2,6)₂]­SmN­(SiMe₃)₂ can be obtained only by a salt metathesis reaction of [<i>t</i>BuC­(NC₆H₃-2,6-<i>i</i>Pr₂)₂]­SmI­(THF)₂ with NaN­(SiMe₃)₂. Unlike <b>1Yb</b> and <b>1Ca</b> in <b>1Sm</b> the amidinate ligand is coordinated to metal ion in κ¹-amido:η⁶-arene fashion preventing THF coordination. The derivatives of tridentate amidinate ligands bearing pendant donor 2-MeOC₆H₄ or 2-Ph₂P­(O)­C₆H₄N groups feature nonconventional κ¹-N,κ²-O,η⁶-arene coordination mode. Complexes <b>1Ca</b>, <b>1Sm</b>, <b>1Yb</b>, <b>2Sm</b>, <b>2Yb</b>, and <b>3Yb</b> proved to be efficient catalysts for styrene hydrophosphination with PhPH₂ and Ph₂PH. In styrene hydrophosphination with PhPH₂ all the catalysts perform excellent chemoselectivity and afford a monoaddition productsecondary phosphine (PhCH₂CH₂)­PhPH. Moreover, all the catalysts perform hydrophosphination reactions regioselectively with exclusive formation of the <i>anti-</i>Markovnikov addition product. Within the series of complexes coordinated by the same amidinate ligand catalytic activity decreases in the following order <b>1Ca</b> ≥ <b>1Sm</b>><b>1Yb</b>. The turnover frequencies were in the range of TOF ≈ 0.3–0.7 h^–1. However, application of tridentate amidinate ligand allowed one to increase catalytic activity significantly: for <b>2Sm</b> TOF was found to be 8.3 h^–1. For the addition of PhPH₂ to para-substituted styrenes catalyzed by <b>2Sm</b> it was found that electron-withdrawing substituents (Cl, F) do not affect the reaction rate while electron-donating groups (<i>t</i>Bu, OMe) noticeably slow down the reaction

Chloro and Alkyl Rare-Earth Complexes Supported by <i>ansa</i>-Bis(amidinate) Ligands with a Rigid <i>o</i>‑Phenylene Linker. Ligand Steric Bulk: A Means of Stabilization or Destabilization?

<i>ansa</i>-Bis­(amidinate) ligands with a rigid <i>o</i>-phenylene linker, C₆H₄-1,2-{NC­(<i>t</i>Bu)­N­(2,6-R₂C₆H₃)­H}₂ (R = Me (<b>1</b>), <i>i</i>Pr (<b>2</b>)), were successfully employed for the synthesis of rare-earth chloro and alkyl species. The reaction of dilithium derivatives of <b>1</b> and <b>2</b> with LnCl₃ (Ln = Y, Lu) afforded the monomeric bis­(amidinate) chloro lanthanide complexes [C₆H₄-1,2-{NC­(<i>t</i>Bu)­N­(2,6-R₂C₆H₃)}₂]­Y­(THF)­(μ-Cl)₂Li­(THF)₂ (R = Me (<b>3</b>), <i>i</i>Pr (<b>5</b>)) and [C₆H₄-1,2-{NC­(<i>t</i>Bu)­N­(2,6-Me₂C₆H₃)}₂]­LuCl­(THF)₂ (<b>4</b>). Bis­(amidinate) ligands in complexes <b>3</b> and <b>4</b> are coordinated to the metal atoms in a tetradentate fashion, while the bulkier ligand in <b>5</b> is tridentate. The alkane elimination reactions of <b>1</b> and <b>2</b> with equimolar amounts of (Me₃SiCH₂)₃Ln­(THF)₂ (Ln = Y, Lu) allowed us to obtain the monoalkyl complexes [C₆H₄-1,2-{NC­(<i>t</i>Bu)­N­(2,6-R₂C₆H₃)}₂]­Ln­(CH₂SiMe₃)­(THF)_<i>n</i> (Ln = Y, R = Me, <i>n</i> = 1 (<b>6</b>); Ln = Lu, R = Me, <i>n</i> = 1 (<b>7</b>); Ln = Y, R = <i>i</i>Pr, <i>n</i> = 2 (<b>8</b>)). The kinetics of thermal decomposition of complexes <b>6</b>–<b>8</b> were measured, and for <b>6</b> the activation energy was obtained from the temperature dependence of the rate constants (<i>E</i>_a = 67.0 ± 1.3 kJ/mol). Complexes <b>6</b> and <b>7</b> turned out to be inert toward H₂ and PhSiH₃. Surprisingly, complex <b>8</b> was inert toward H₂ and PhSiH₃ but rapidly cleaved C–O bonds of DME. The reaction resulted in the formation of the methoxy complex {[C₆H₄-1,2-{NC­(<i>t</i>Bu)­N­(2,6-<i>i</i>Pr₂C₆H₃)}₂]­Y­(μ₂-OMe)]}₂(μ₂-DME) (<b>9</b>) and methyl vinyl ether

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 [{<i>t</i>BuC­(NC₆H₃-2,6-<i>i</i>Pr₂)₂}­Yb­(μ-H)]₂ (<b>1</b>) with CuCl (1:2 molar ratio) and (PhCH₂S)₂ (1:1 molar ratio) revealed that the hydrido anion in <b>1</b> is a stronger reductant than the Yb­(II) cation. Both reactions occur with evolution of H₂ and afford the dimeric Yb­(II) species [{<i>t</i>BuC­(NC₆H₃-2,6-<i>i</i>Pr₂)₂}­Yb­(μ-X)]₂ (X = Cl (<b>2</b>), SCH₂Ph (<b>3</b>)) in which a κ¹-amido,η⁶-arene type of coordination of amidinate ligand is retained. Reaction of <b>1</b> 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 [{<i>t</i>BuC­(NC₆H₃-2,6-<i>i</i>Pr₂)₂}­Yb­(μ-SCH₂Ph)₂]₂ (<b>4</b>). Complex <b>4</b> can be also synthesized by oxidation of <b>3</b> 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 [{<i>t</i>BuC­(NC₆H₃-2,6-<i>i</i>Pr₂)₂}­Yb­(CH₂SiMe₃)₂(THF)] (<b>6</b>) with PhSiH₃ (1:2 molar ratio) occurs with reduction of ytterbium to a divalent state and affords <b>1</b>. 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 <b>1</b> by 2,6-<i>i</i>Pr₂C₆H₃NC­(H)­C­(H)NC₆H₃-2,6-<i>i</i>Pr₂ was found to result in oxidation of the hydrido ligand and ytterbium ion and formation of the mixed-valent ion-pair complex [{<i>t</i>BuC­(NC₆H₃-2,6-<i>i</i>Pr₂)₂}­Yb­(DME)₂]⁺[{2,6-<i>i</i>Pr₂C₆H₃NC­(H)C­(H)­NC₆H₃-2,6-<i>i</i>Pr₂}₂Yb]⁻ (<b>5</b>). The σ-bond metathesis reaction of <b>1</b> with Ph₂PH allowed for the synthesis of the first mixed-ligand hydrido–phosphido Yb­(II) species [{<i>t</i>BuC­(NC₆H₃-2,6-<i>i</i>Pr₂)₂}­Yb­(μ-H)­(μ-PPh₂)­Yb­{<i>t</i>BuC­(NC₆H₃-2,6-<i>i</i>Pr₂)₂}] (<b>7</b>). The second hydrido ligand cannot be replaced by a phosphido ligand