Steric control in the metal-ligand electron transfer of iminopyridine-ytterbocene complexes

International audienceA systematic study of reactions between Cp*Yb-2(THF) (Cp* = eta(5)-C5Me5, 1) and iminopyridine ligands (IPy = 2,6-(Pr2C6H3N)-Pr-i=CH(C5H3N-R), R = H (2a), 6-C4H3O (2b), 6-C4H3S (2c), 6-C6H5 (2d)) featuring similar electron accepting properties but variable denticity and steric demand, has provided a new example of steric control on the redox chemistry of ytterbocenes. The reaction of the unsubstituted IPy 2a with 1, either in THF or toluene, gives rise to the paramagnetic species Cp*Yb-2(III)(IPy)(center dot-) (3a) as a result of a formal one-electron oxidation of the Yb-II ion along with IPy reduction to a radical-anionic state. The reactions of 1 with substituted iminopyridines 2b-d, bearing aryl or hetero-aryl dangling arms on the 6 position of the pyridine ring occur in a non-coordinating solvent (toluene) only and afford coordination compounds of a formally divalent ytterbium ion, coordinated by neutral IPy ligands Cp*Yb-2(II)(IPy)(0) (3b-d). The X-ray diffraction studies revealed that 2a-c act as bidentate ligands; while the radical-anionic IPy in 3a chelates the Yb-III ion with both nitrogens, neutral IPy ligands in 3b and 3c participate in the metal coordination sphere through the pyridine nitrogen and O or S atoms from the furan or thiophene moieties, respectively. Finally, in complex 3d the neutral IPy ligand formally adopts a monodentate coordination mode. However, an agostic interaction between the Yb-II ion and an ortho C-H bond of the phenyl ring has been detected. Imino-nitrogens in 3b-d are not involved in the metal coordination. Variable temperature magnetic measurements on 3a are consistent with a multiconfigurational ground state of the Yb ion and suggest that the largest contribution arises from the 4f(13)-radical configuration. For complexes 3b and 3c the data of magnetic measurements are indicative of a Yb-II-closed shell ligand electronic distribution. Complex 3d is characterized by a complex magnetic behavior which does not allow for an unambiguous estimation of its electronic structure. The results are rationalized using DFT and CSSCF calculations. Unlike diazabutadiene analogues, 3a does not undergo a solvent mediated metalligand electron transfer and remains paramagnetic in THF solution. On the other hand, complexes 3b-d readily react with THF to afford 1 and free IPy 2b-d

Metallacyclic yttrium alkyl and hydrido complexes: synthesis, structures and catalytic activity in intermolecular olefin hydrophosphination and hydroamination

International audienceMetallacyclic neutral and ionic yttrium alkyl complexes coordinated by a dianionic ene-diamido ligand ([2,6-iPr2C6H3NC(Me)[double bond, length as m-dash]C(Me)NC6H3iPr2-2,6] = L1) [L1]Y(CH2SiMe3)(THF)2 (2), {[L1]Y(CH2SiMe3)2}−{Li(THF)4}+ (3), [L1]Y(OEt2)(μ-Me)2Li(TMEDA) (4) were synthesized using a salt-metathesis approach starting from the related chloro complex [L1]Y(THF)2(μ-Cl)2Li(THF)2 (1) in 70, 85 and 72% yields respectively. The reactions of 2 with H2 or PhSiH3 afford the dimeric hydride {[L1]Y(THF)(μ-H)}2(μ-THF) (5) containing two μ-bridging hydrido and one μ-bridging THF ligands (91 and 85% yields). The X-ray studies of complexes 2, 3 and 5 revealed η2-coordination of the C[double bond, length as m-dash]C fragment of an ene-diamido ligand to a Y cation. DFT calculations were carried out to give an insight into the metal–ligand bonding and especially the interaction between the metal and the ene-diamido ligand. The observed bonding of the ene-diamido fragment is found to reflect the acidity of the metal center in the complex that is partially overcome by a better donation from the double bond (better overlap with an empty d orbital at the yttrium center). The treatment of complex 4 with DME resulted in the C–O bond cleavage of DME and afforded a three nuclear methoxide oxide complex [{[L1]Y}3(μ2-OMe)3(μ3-O)]2−[Li(DME)3]+2 (6). Complexes 2, 3, 5 and 7 proved to be efficient precatalysts for the intermolecular hydrophosphination of styrene, 4-vinylpyridine, and 1-nonene with PhPH2 and Ph2PH as well as hydroamination of styrene and pyrrolidine

Base-Free Lanthanoidocenes(II) Coordinated by Bulky Pentabenzylcyclopentadienyl Ligands

Metalation of Cp^Bn5H with PhCH₂K (1:1 molar ratio) and subsequent reactions with 0.5 equiv of LnI₂(THF)_<i>n</i> (Ln = Yb, Sm, Eu, <i>n</i> = 2, 3) (THF, 30 °C, 1 h) afforded new lanthanoidocenes (Cp^Bn5)₂Ln (Ln = Yb (<b>1</b>), Sm (<b>2</b>), Eu (<b>3</b>)), which were isolated in reasonable yields. The X-ray diffraction studies revealed that the obtained complexes adopt the structures of bent sandwiches (Cp_Centr–Ln–Cp_Centr = 141.8–142.9°). Complexes <b>1</b>–<b>3</b> do not contain coordinated Lewis base molecules directly after recrystallization from toluene at ambient temperature; however they feature short contacts between Ln­(II) ions and <i>o</i>-carbon atoms of two pendant Ph groups. The reaction of equimolar amounts of YbI₂(THF)₂ and Cp^Bn5K in DME afforded monocyclopentadienyl Yb­(II) complex [Cp^Bn5Yb­(DME)­(μ-I)]₂ (<b>4</b>). Complex <b>4</b> proved to be a centrosymmetric iodo-bridged dimer with trans-disposed cyclopentadienyl ligands, and no interactions of the Yb­(II) ion with pendant Ph groups were detected. Complexes <b>1</b>–<b>3</b> were inert toward Lewis bases (THF, DME, PMe₃, TMEDA), small molecules (H₂, SiH₄, N₂, CO), and molecules containing multiple C–C bonds (CH₂CH₂, PhCHCH₂, trans-PhCHCHPh, cis-PhCHCHPh, CH₂CH–CHCH₂, Ph–CHCH–CHCH–Ph, PhCCPh, Me₃SiCCSiMe₃). Among compounds <b>1</b>–<b>3</b> only the samarium derivative <b>1</b> reacts with bipy and phenazine, affording Sm^III complexes Cp^Bn5₂Sm­(bipy^–•) (<b>5</b>) and [(Cp^Bn5)₂Sm]₂[μ-η³:η³-(C₁₂H₈N₂)^2–] (<b>6</b>). Complex <b>4</b> when illuminated with natural light undergoes redox reaction and in 72 h transforms into the mixed-valent compound {[Cp^Bn5Yb^IIII₂(μ-OMe)]₂}₂­{Yb^II(DME)₃} (<b>7</b>), being a separated ion pair

Base-Free Lanthanoidocenes(II) Coordinated by Bulky Pentabenzylcyclopentadienyl Ligands

Metalation of Cp^Bn5H with PhCH₂K (1:1 molar ratio) and subsequent reactions with 0.5 equiv of LnI₂(THF)_<i>n</i> (Ln = Yb, Sm, Eu, <i>n</i> = 2, 3) (THF, 30 °C, 1 h) afforded new lanthanoidocenes (Cp^Bn5)₂Ln (Ln = Yb (<b>1</b>), Sm (<b>2</b>), Eu (<b>3</b>)), which were isolated in reasonable yields. The X-ray diffraction studies revealed that the obtained complexes adopt the structures of bent sandwiches (Cp_Centr–Ln–Cp_Centr = 141.8–142.9°). Complexes <b>1</b>–<b>3</b> do not contain coordinated Lewis base molecules directly after recrystallization from toluene at ambient temperature; however they feature short contacts between Ln­(II) ions and <i>o</i>-carbon atoms of two pendant Ph groups. The reaction of equimolar amounts of YbI₂(THF)₂ and Cp^Bn5K in DME afforded monocyclopentadienyl Yb­(II) complex [Cp^Bn5Yb­(DME)­(μ-I)]₂ (<b>4</b>). Complex <b>4</b> proved to be a centrosymmetric iodo-bridged dimer with trans-disposed cyclopentadienyl ligands, and no interactions of the Yb­(II) ion with pendant Ph groups were detected. Complexes <b>1</b>–<b>3</b> were inert toward Lewis bases (THF, DME, PMe₃, TMEDA), small molecules (H₂, SiH₄, N₂, CO), and molecules containing multiple C–C bonds (CH₂CH₂, PhCHCH₂, trans-PhCHCHPh, cis-PhCHCHPh, CH₂CH–CHCH₂, Ph–CHCH–CHCH–Ph, PhCCPh, Me₃SiCCSiMe₃). Among compounds <b>1</b>–<b>3</b> only the samarium derivative <b>1</b> reacts with bipy and phenazine, affording Sm^III complexes Cp^Bn5₂Sm­(bipy^–•) (<b>5</b>) and [(Cp^Bn5)₂Sm]₂[μ-η³:η³-(C₁₂H₈N₂)^2–] (<b>6</b>). Complex <b>4</b> when illuminated with natural light undergoes redox reaction and in 72 h transforms into the mixed-valent compound {[Cp^Bn5Yb^IIII₂(μ-OMe)]₂}₂­{Yb^II(DME)₃} (<b>7</b>), being a separated ion pair

Yb(II) Triple-Decker Complex with the μ‑Bridging Naphthalene Dianion [Cp^Bn5Yb(DME)]₂(μ‑η⁴:η⁴‑C₁₀H₈). Oxidative Substitution of [C₁₀H₈]^2– by 1,4-Diphenylbuta-1,3-diene and P₄ and Protonolysis of the Yb–C₁₀H₈ Bond by PhPH₂

Two synthetic approaches to the new three-decker Yb­(II) complex [Cp^Bn5Yb­(DME)]₂[μ-C₁₀H₈] (<b>1</b>) were successfully employed: the reaction of [Cp^Bn5Yb­(DME)­(μ-I)]₂ (<b>2</b>) with 2 molar equiv of [C₁₀H₈]⁻·K in DME and the reaction of [YbI­(DME)₂]₂[μ-C₁₀H₈] (<b>3</b>) with Cp^Bn5K in a 1:2 molar ratio in DME. Complex <b>1</b> was proved to be a Yb­(II) binuclear triple-decker complex containing a dianionic naphthalene ligand bridging two Cp^Bn5Yb­(DME) fragments in a μ-η⁴:η⁴ fashion. An oxidative substitution of (C₁₀H₈)^2– by <i>trans</i>-(1<i>E</i>,3<i>E</i>)-1,4-diphenylbuta-1,3-diene afforded the three-decker Yb­(II) complex [Cp^Bn5Yb­(DME)]₂(μ-η⁴:η⁴ -PhCHCHCHCHPh) (<b>4</b>) with a dianionic μ-η⁴:η⁴-bridging diphenylbutadiene ligand and naphthalene. The reaction of <b>1</b> with excess P₄ also occurs with oxidation of (C₁₀H₈)^2–, whereas Yb remains divalent. The reaction results in the formation of the trinuclear Yb­(II) complex with a μ-bridging P₇^3– ligand [Cp^Bn5Yb­(DME)]₃(P₇) (<b>5</b>). Protonation of the Yb–C₁₀H₈ bond in <b>1</b> with PhPH₂ (1:2 molar ratio) afforded the dimeric phosphido complex [Cp^Bn5Yb­(THF)­(μ₂-PHPh)]₂ (<b>6</b>) in 64% yield, while an attempt to obtain a phosphinidene Yb­(II) species by reacting equimolar amounts of <b>1</b> and PhPH₂ in DME resulted in the isolation of the metallocene complex Cp^Bn5₂Yb­(DME) (<b>7</b>)

Yb(II) Triple-Decker Complex with the μ‑Bridging Naphthalene Dianion [Cp^Bn5Yb(DME)]₂(μ‑η⁴:η⁴‑C₁₀H₈). Oxidative Substitution of [C₁₀H₈]^2– by 1,4-Diphenylbuta-1,3-diene and P₄ and Protonolysis of the Yb–C₁₀H₈ Bond by PhPH₂

Two synthetic approaches to the new three-decker Yb­(II) complex [Cp^Bn5Yb­(DME)]₂[μ-C₁₀H₈] (<b>1</b>) were successfully employed: the reaction of [Cp^Bn5Yb­(DME)­(μ-I)]₂ (<b>2</b>) with 2 molar equiv of [C₁₀H₈]⁻·K in DME and the reaction of [YbI­(DME)₂]₂[μ-C₁₀H₈] (<b>3</b>) with Cp^Bn5K in a 1:2 molar ratio in DME. Complex <b>1</b> was proved to be a Yb­(II) binuclear triple-decker complex containing a dianionic naphthalene ligand bridging two Cp^Bn5Yb­(DME) fragments in a μ-η⁴:η⁴ fashion. An oxidative substitution of (C₁₀H₈)^2– by <i>trans</i>-(1<i>E</i>,3<i>E</i>)-1,4-diphenylbuta-1,3-diene afforded the three-decker Yb­(II) complex [Cp^Bn5Yb­(DME)]₂(μ-η⁴:η⁴ -PhCHCHCHCHPh) (<b>4</b>) with a dianionic μ-η⁴:η⁴-bridging diphenylbutadiene ligand and naphthalene. The reaction of <b>1</b> with excess P₄ also occurs with oxidation of (C₁₀H₈)^2–, whereas Yb remains divalent. The reaction results in the formation of the trinuclear Yb­(II) complex with a μ-bridging P₇^3– ligand [Cp^Bn5Yb­(DME)]₃(P₇) (<b>5</b>). Protonation of the Yb–C₁₀H₈ bond in <b>1</b> with PhPH₂ (1:2 molar ratio) afforded the dimeric phosphido complex [Cp^Bn5Yb­(THF)­(μ₂-PHPh)]₂ (<b>6</b>) in 64% yield, while an attempt to obtain a phosphinidene Yb­(II) species by reacting equimolar amounts of <b>1</b> and PhPH₂ in DME resulted in the isolation of the metallocene complex Cp^Bn5₂Yb­(DME) (<b>7</b>)

Yb(II) Triple-Decker Complex with the μ‑Bridging Naphthalene Dianion [Cp^Bn5Yb(DME)]₂(μ‑η⁴:η⁴‑C₁₀H₈). Oxidative Substitution of [C₁₀H₈]^2– by 1,4-Diphenylbuta-1,3-diene and P₄ and Protonolysis of the Yb–C₁₀H₈ Bond by PhPH₂

Two synthetic approaches to the new three-decker Yb­(II) complex [Cp^Bn5Yb­(DME)]₂[μ-C₁₀H₈] (<b>1</b>) were successfully employed: the reaction of [Cp^Bn5Yb­(DME)­(μ-I)]₂ (<b>2</b>) with 2 molar equiv of [C₁₀H₈]⁻·K in DME and the reaction of [YbI­(DME)₂]₂[μ-C₁₀H₈] (<b>3</b>) with Cp^Bn5K in a 1:2 molar ratio in DME. Complex <b>1</b> was proved to be a Yb­(II) binuclear triple-decker complex containing a dianionic naphthalene ligand bridging two Cp^Bn5Yb­(DME) fragments in a μ-η⁴:η⁴ fashion. An oxidative substitution of (C₁₀H₈)^2– by <i>trans</i>-(1<i>E</i>,3<i>E</i>)-1,4-diphenylbuta-1,3-diene afforded the three-decker Yb­(II) complex [Cp^Bn5Yb­(DME)]₂(μ-η⁴:η⁴ -PhCHCHCHCHPh) (<b>4</b>) with a dianionic μ-η⁴:η⁴-bridging diphenylbutadiene ligand and naphthalene. The reaction of <b>1</b> with excess P₄ also occurs with oxidation of (C₁₀H₈)^2–, whereas Yb remains divalent. The reaction results in the formation of the trinuclear Yb­(II) complex with a μ-bridging P₇^3– ligand [Cp^Bn5Yb­(DME)]₃(P₇) (<b>5</b>). Protonation of the Yb–C₁₀H₈ bond in <b>1</b> with PhPH₂ (1:2 molar ratio) afforded the dimeric phosphido complex [Cp^Bn5Yb­(THF)­(μ₂-PHPh)]₂ (<b>6</b>) in 64% yield, while an attempt to obtain a phosphinidene Yb­(II) species by reacting equimolar amounts of <b>1</b> and PhPH₂ in DME resulted in the isolation of the metallocene complex Cp^Bn5₂Yb­(DME) (<b>7</b>)