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

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

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

Amido Ca and Yb(II) Complexes Coordinated by Amidine-Amidopyridinate Ligands for Catalytic Intermolecular Olefin Hydrophosphination

A series of amido Ca and Yb­(II) complexes LM­[N­(SiMe₃)₂]­(THF) (<b>1Yb</b>, <b>1–4Ca</b>) coordinated by amidine-amidopyridinate ligands <b>L</b>^{<b>1</b>–<b>4</b>} were synthesized via a transamination reaction between proligands <b>L</b>^{<b>1</b>–<b>4</b>}<b>H</b> and bisamido complexes M­[N­(SiMe₃)₂]₂­(THF)₂ (M = Yb, Ca). The reactions of Yb­[N­(SiMe₃)₂]₂­(THF)₂ with proligands <b>L</b>^<b>2</b><b>H</b>-<b>L</b>^<b>4</b><b>H</b> containing CF₃ and C₆H₄F fragments do not allow for preparing the target Yb­(II) complexes, while the Ca analogues were synthesized in good yields. Complexes <b>1Yb</b> and <b>1</b>–<b>4Ca</b> were evaluated as precatalysts for hydrophosphination of styrene, <i>p</i>-substituted styrenes, α-Me-styrene, and 2,3-dimethylbutadiene with various primary and secondary phosphines (PhPH₂, 2,4,6-Me₃C₆H₂PH₂, 2-C₅NH₄PH₂, Ph₂PH, Cy₂PH). Complexes <b>1Yb</b>, <b>1</b>–<b>4Ca</b> performed high catalytic activities in styrene hydrophosphination with PhPH₂ and Ph₂PH and demonstrated high regioselectivity affording exclusively the anti-Markovnikov addition products. For primary PhPH₂ the reactions (1:1 molar ratio of substrates) catalyzed by <b>1Yb</b>, <b>1Ca</b>, and <b>2Ca</b> proved to be highly chemoselective affording the secondary phosphine Ph­(PhCH₂CH₂)­PH; however, complexes <b>3Ca</b> and <b>4Ca</b> led to the formation of both secondary and tertiary phosphines in 80:20 and 86:14 ratios. Styrene hydrophosphinations with 2,4,6-Me₃C₆H₂PH₂ and 2-pyridylphosphine for all complexes <b>1Yb</b> and <b>1–4Ca</b> proceeded much more slowly compared to PhPH₂. Addition of 2-C₅NH₄PH₂ to styrene catalyzed by complex <b>1Yb</b> turned out to be non-regioselective and led to the formation of a mixture of Markovnikov and anti-Markovnikov addition products, while all Ca complexes enabled regioselective anti-Markovnikov addition. Complexes <b>1Ca</b> and <b>1Yb</b> containing catalytic centers featuring similar ionic radii performed different catalytic activity: the ytterbium analogue proved to be a more active catalyst for intermolecular hydrophosphination of styrene with Cy₂PH, 2-C₅NH₄PH₂, and PhPH₂, but less active with sterically demanding 2,4,6-Me₃C₆H₂PH₂. Styrenes containing in <i>p</i>-position electron-donating groups (Me, tBu, OMe) performed with noticeably lower rates in the reactions with PhPH₂ compared to styrene. Complexes <b>1Yb</b>, <b>1Ca</b>, <b>2Ca</b>, <b>3Ca</b>, and <b>4Ca</b> enabled addition of PhPH₂ toward the double CC bond of α-Me-styrene, and the reaction rate for this substrate is noticeably lower; however quantitative conversions were reached in ∼40 h. Complexes <b>1Ca</b> and <b>2Ca</b> promoted 1,2-addition of PhPH₂ to 2,3-dimethyl butadiene with excellent regio- and chemoselectivity to afford linear secondary phosphines. Hydrophosphination of inert 1-nonene with Ph₂PH with 40% conversion becomes possible due to the application of complex <b>2Ca</b> (40 h, 70 °C). The rate law for the hydrophosphination of styrene with Ph₂PH catalyzed by <b>1Ca</b> was found to agree with the idealized equation: <i>v</i> = <i>k</i>[styrene]¹[<b>1Ca</b>]¹

Divalent Heteroleptic Ytterbium Complexes – Effective Catalysts for Intermolecular Styrene Hydrophosphination and Hydroamination

New heteroleptic Yb­(II)–amide species supported by amidinate and 1,3,6,8-tetra-<i>tert</i>-butylcarbazol-9-yl ligands [2-MeOC₆H₄NC­(<i>t</i>Bu)­N­(C₆H₃-<i>i</i>Pr₂-2,6)]­YbN­(SiMe₃)₂(THF) (<b>6</b>) and [1,3,6,8-<i>t</i>Bu₄C₁₂H₄N]­Yb­[N­(SiMe₃)₂]­(THF)_<i>n</i> (<i>n</i> = 1 (<b>7</b>), 2 (<b>8</b>)) were synthesized using the amine elimination approach. Complex <b>6</b> features an unusual κ¹-<i>N</i>,κ²-<i>O</i>,η⁶-arene coordination mode of the amidinate ligand onto Yb­(II). Complexes <b>7</b> and <b>8</b> represent the first examples of lanthanide complexes with π-coordination of carbazol-9-yl ligands. Complexes <b>6</b> and <b>7</b>, as well as the amidinate–Yb­(II)–amide [<i>t</i>BuC­(NC₆H₃-<i>i</i>Pr₂-2,6)₂]­YbN­(SiMe₃)₂(THF) (<b>5</b>), are efficient precatalysts for the intermolecular hydrophosphination and hydroamination of styrene with diphenylphosphine, phenylphosphine, and pyrrolidine to give exclusively the anti-Markovnikov monoaddition product. For both types of reaction, the best performances were observed with carbazol-9-yl complex <b>7</b> (TONs up to 92 and 48 mol/mol at 60 °C, respectively)