CNC-Pincer Rare-Earth Metal Amido Complexes with a Diarylamido Linked Biscarbene Ligand: Synthesis, Characterization, and Catalytic Activity

In preparation of CNC-pincer rare-earth metal amido complexes with a diarylamido linked biscarbene ligand, it is found that conditions have a key influence on final products. Reaction of a THF suspension of bis­[2-(3-benzyl­imidazolium)-4-methyl­phenyl]­amine dichlorides (H₃<b>L</b>Cl₂) with [(Me₃Si)₂­N]₃­RE­(μ-Cl)­Li­(THF)₃ (RE = Yb, Eu, Sm) in THF at room temperature afforded the only unexpected fused-heterocyclic compound 8,9-dibenzyl-3,14-dimethyl-8<i>a</i>,9-dihydro-8<i>H</i>-benzo­[4,5]­imidazo­[2′,1′:2,3]­imidazo­[1,2-<i>a</i>]­imidazo­[2,1-<i>c</i>]­quinoxaline (<b>1</b>) containing an imidazolyl ring and a piperidyl ring, which formed through carbene C–C and C–N coupling. However, the reaction of H₃<b>L</b>Cl₂ with [(Me₃Si)₂­N]₃­Er­(μ-Cl)­Li­(THF)₃ in toluene afforded the CNC-pincer erbium amido complex incorporating a diarylamido linked biscarbene ligand <b>L</b>Er­[N­(SiMe₃)₂]₂ (<b>2</b>) in low yield and the above fused-heterocyclic compound <b>1</b>. The stepwise reaction of H₃<b>L</b>Cl₂ with strong bases (<i>n</i>-BuLi or LiCH₂SiMe₃) in THF for 4 h, followed by treatment with [(Me₃Si)₂­N]₃­RE­(μ-Cl)­Li­(THF)₃, generated zwitterion complexes [<b>L</b>₂RE]­[RECl­{N­(SiMe₃)₂}₃] (<b>L</b> = [4-CH₃-2-{(C₆H₄CH₂-[N­(CH)₂­CN]}­C₆H₃]₂N; RE = Y (<b>3</b>), Er (<b>4</b>), Yb (<b>5</b>)) in less than 20% yields together with fused-heterocyclic compound <b>1</b>. Additionally, the reaction of H₃<b>L</b>Cl₂ with 6 equiv of NaN­(SiMe₃)₂ in THF for 4 h, followed by treatment with YbCl₃, generated a novel discrete complex [<b>L</b>₂Yb]­[{Na­(μ-N­(SiMe₃)₂)}₅­(μ₅-Cl)] (<b>6</b>). The one-pot reaction of H₃<b>L</b>Cl₂ with <i>n</i>-BuLi, followed by reaction with [(Me₃Si)₂­N]₃­RE­(μ-Cl)­Li­(THF)₃ in THF at −78 °C, generated the CNC-pincer lanthanide bisamido complexes <b>L</b>RE­[N­(SiMe₃)₂]₂ (RE = Er (<b>2</b>), Y (<b>7</b>), Sm (<b>8</b>), Eu (<b>9</b>)) in moderate yields. These kinds of biscarbene supported pincer bisamido complexes could also be prepared by a one-pot reaction of bis­(imidazolium) salt (H₃<b>L</b>Cl₂) with 5 equiv of NaN­(SiMe₃)₂, followed by treatment with RECl₃, in good yields at −78 °C. Investigation of the catalytic activity of complexes <b>2</b> and <b>7</b>–<b>9</b> indicated that all complexes showed a high activity toward the addition of terminal alkynes to carbodiimides producing propiolimidines, which represents the first example of rare-earth metal CNC-pincer-type catalysts applied for catalytic C–H bond addition of terminal alkynes to carbodiimides at room temperature

Synthesis and Characterization of Rare-Earth Metal Complexes Supported by 2‑Imino or Amino Appended Indolyl Ligands with Diverse Hapticities: Tunable Selective Catalysis for Isoprene Polymerization

The reaction of 2-(2,6-DippNHCH₂)­C₈H₅NH (Dipp = 2,6-^<i>i</i>PrC₆H₃, C₈H₅NH = indolyl) with 1 equiv of (Me₃SiCH₂)₃Yb­(THF)₂ at room temperature generated mononuclear ytterbium complex <b>1</b> having the indolyl ligands in η¹:η¹ mode with reduction of Yb³⁺ to Yb²⁺ and oxidation of the amino to imino group. In the case of Er and Y, the reactions produced dinuclear complexes <b>2</b> and <b>3</b> having the indolyl ligands in μ-η²:η²:η¹ modes with the central metals. When the rare-earth metal is dysprosium, the reaction afforded mixed ligated dinuclear complex <b>4a</b> having indolyl ligands in μ-η⁵:η¹:η¹ and μ-η⁶:η¹:η¹ modes with Dy, and its isomer <b>4b</b> having the indolyl ligands only in μ-η⁵:η¹:η¹ modes with Dy. However, when the rare-earth metal is Gd, the reaction only produced the mixed ligated dinuclear gadolinium complex [(μ-η⁵:η¹:η¹)-2-(2,6-DippNCH₂)­Ind­(μ-η⁶:η¹:η¹)-2-(2,6-DippNCH₂)­Ind]­[Gd­(CH₂SiMe₃)­(thf)]₂ (<b>5</b>), having indolyl ligands in μ-η⁵:η¹:η¹ and μ-η⁶:η¹:η¹ modes with Gd. In addition, treatment of 2-(2,6-DippNHCH₂)­C₈H₅NH with 1.25 equiv of (Me₃SiCH₂)₃Gd­(THF)₂ produced the alkoxido-bridged trinuclear gadolinium complex [(μ-η³:η²:η¹:η¹)-2-(2,6-DippNCH₂)­Ind­(μ-η²:η¹:η¹)-2-(2,6-DippNCH₂)­Ind<i>-</i>(η¹:η¹)-2-(2,6-DippNCH₂)­Ind]-Gd₃[(μ₃<i>-</i>O­(CH₂)₅SiMe₃)­(μ₂-O­(CH₂)₅SiMe₃)­(thf)₃] (<b>6</b>) having indolyl ligands in η¹:η¹, μ-η²:η¹:η¹, and μ-η³:η²:η¹:η ¹ modes with metals, respectively. In complex <b>6</b>, sp² C–H activation is observed at the 7-indolyl position producing unique 2-amido substituted indolyl-1,7-dianions having a μ-η³:η²:η¹:η¹ bonding modes with three metals. The O­(CH₂)₅SiMe₃ arises from the ring-opening of THF by attack of CH₂SiMe₃. Moreover, when 2-(2,6-DippNHCH₂)­C₈H₅NH was treated with 1 equiv of (Me₃SiCH₂)₃Sm­(THF)₂, a dinuclear samarium complex [μ-η³:η¹:η¹-2-(2,6-DippNCH₂)­Ind]₃Sm₂(thf)₃ (<b>7</b>) having a bridged indolyl ligand in μ-η³:η¹:η¹ hapticities was isolated. All structures of the complexes have been determined by X-ray crystallographic analyses. Dinuclear alkyl complexes <b>2</b>–<b>5</b> have been tested as isoprene polymerization initiators in the presence of Al^<i>i</i>Bu₃ and [Ph₃C]­[B­(C₆F₅)₄]. The regioselectivity for isoprene polymerization is tunable from 1,4-<i>cis</i> (up to 93.5%) to 3,4- (up to 86.2%) selectivity by these catalysts simply by adjusting the addition order of Al^<i>i</i>Bu₃ and [Ph₃C]­[B­(C₆F₅)₄]

Aromatic Ring Fused BOPHYs as Stable Red Fluorescent Dyes

Facile synthetic routes to a new class of red α-benzo-fused BOPHYs with 6,5,6,6,5,6-hexacyclic fused rings and β-thiophene-fused BOPHYs with 5,5,6,6,5,5-hexacyclic fused rings are presented. These dyes were characterized by NMR spectroscopy, HRMS, X-ray structure analysis, cyclic voltammetry, and optical measurements. Compared to parent BOPHY, significant red-shifts in the absorption (up to 600 nm in solution) and emission (up to 648 nm in solution and 717 nm in solid state), as well as high chemical stability and photostability, were found for these aromatic-ring-fused BOPHY dyes. As shown in cyclic voltammetry and DFT calculations, the aromatic ring fusions induced significantly increased HOMO energy levels, giving effective expansion of π-conjugation over these BOPHY dyes. These new molecular skeletons would be promising candidates for various applications in light of their unique structure and attractive photophysical properties

Aluminum Complexes Bearing N‑Protected 2‑Amino- or 2‑Imino-Functionalized Pyrrolyl Ligands: Synthesis, Structure, and Catalysis for Preparation of Pyrrolyl-End-Functionalized Polyesters

Reactivity of N-protected 2-amino- or 2-imino-functionalized pyrroles with aluminum alkyls was investigated, resulting in the isolation of a series of aluminum alkyl complexes. Treatment of 2-imino-functionalized pyrrole with AlMe₃ produced only imino-coordinated aluminum complex 1-Bn-2-(2,6-^<i>i</i>Pr₂C₆H₃NCH)­C₄H₃NAlMe₃ (<b>1</b>), while reactions of N-protected 2-amino-functionalized pyrroles with aluminum alkyls produced the aluminum alkyl complexes {[η¹-μ-η¹:η¹-1-R₁-2-(2,6-^<i>i</i>Pr₂C₆H₃NCH₂)­C₄H₂N]­AlR}₂ (R₁ = Bn, R = Me (<b>2</b>); R₁ = Bn, R = Et (<b>3</b>); R₁ = R = Me (<b>4</b>); R₁ = Me, R = Et (<b>5</b>)), bearing 3-carbon bonded pyrrolyl ligands via C–H σ-bond metathesis reaction. Further reactions of complexes <b>2</b>–<b>5</b> with a stoichiometric amount of isopropyl alcohol (^<i>i</i>PrOH) afforded the corresponding aluminum alkoxide complexes [1-R₁-2-(2,6-^<i>i</i>Pr₂C₆H₃NCH₂)­C₄H₃NAlR­(μ-O^<i>i</i>Pr)]₂ (R₁ = Bn, R = Me (<b>6</b>); R₁ = Bn, R = Et (<b>7</b>); R₁ = R = Me (<b>8</b>); R₁ = Me, R = Et (<b>9</b>)) through selective cleavage of the Al–C (Pyr) bonds. The solid-state structures of the aluminum complexes <b>1</b>–<b>6</b> and <b>8</b> were confirmed by an X-ray diffraction study. These aluminum alkyl complexes exhibited notable activity toward the ring-opening polymerization of ε-caprolactone and l-lactide in the absence of alcohol. The end group analysis of the ε-CL oligomer gave strong support that the polymerization proceeded via a coordination–insertion mechanism involving a unique Al–C (Pyr) bond initiation, providing pyrrolyl-end-functionalized polyesters

<i>β-</i>Thiophene-Fused BF₂‑Azadipyrromethenes as Near-Infrared Dyes

A facile synthetic route to a new class of near-IR β-thiophene-fused BF₂-azadipyrromethenes (aza-BDTPs) is presented. Sharp absorption and fluorescence emission bands at around 800 nm were observed for these highly photostable aza-BDTPs, with a large absorption coefficient and very low absorptions in the visible range from 700 to 380 nm

Syntheses, Structures, and Catalytic Activities of the Anionic Heterobimetallic Rare-Earth Metal Complexes Supported by Pyrrolyl-Substituted 1,2-Diimino Ligands

A series of the anionic heterobimetallic rare-earth metal complexes supported by <i>trans-</i> or chiral pyrrolyl-substituted 1,2-diimino ligands were synthesized in good yields via reactions of [(Me₃Si)₂N]₃RE­(μ-Cl)­Li­(THF)₃ with the corresponding 1,2-diimino proligands. Reactions of [(Me₃Si)₂N]₃RE­(μ-Cl)­Li­(THF)₃ with 2 equiv of <i>trans</i>-1,2-bis­(pyrrol-2-ylmethylene)-1,2-diphenylethanediamine (<b>H</b>_<b>2</b><b>L</b>^<b>1</b>) afforded the discrete ion-pair rare-earth metal complexes [Li­(THF)₄]⁺[(<b>L</b>^<b>1</b>)₂RE]⁻ (RE = Sm­(<b>5</b>), Dy­(<b>6</b>), Er­(<b>7</b>)). Reactions of [(Me₃Si)₂N]₃RE­(μ-Cl)­Li­(THF)₃ with 2 equiv of (<i>R</i>,<i>R</i>)-1,2-bis­(pyrrol-2-ylmethylene)-1,2-diphenylethanediamine (<b>H</b>_<b>2</b><b>L</b>^<b>2</b>) gave the heterobimetallic rare-earth metal complexes (<b>L</b>^<b>2</b>)₂RELi­(THF)₂ (RE = Sm­(<b>8</b>), Y­(<b>9</b>)). When the rare-earth metal is Er, the chiral linear rare-earth coordination polymer {(<b>L</b>^<b>2</b>)₂ErLi}_<i>n</i> (<b>10</b>) was obtained. Reactions of [(Me₃Si)₂N]₃RE­(μ-Cl)­Li­(THF)₃ with 2 equiv of <i>trans</i>-1,2-bis­(pyrrol-2-ylmethyleneamino)­cyclohexane (H₂<b>L</b>^<b>3</b>) gave the heterobimetallic rare-earth metal complexes (<b>L</b>^<b>3</b>)₂RELi­(THF)₂ (RE = Pr (<b>11</b>), Sm­(<b>12</b>), Eu­(<b>13</b>)). Reactions of [(Me₃Si)₂N]₃RE­(μ-Cl)­Li­(THF)₃ with 2 equiv of (<i>R</i>,<i>R</i>)-1,2-bis­(pyrrol-2-ylmethyleneamino)­cyclohexane (H₂<b>L</b>^<b>4</b>) also gave the heterobimetallic rare-earth metal complexes (<b>L</b>^<b>4</b>)₂RELi­(THF)₂ (Ln = Pr­(<b>14</b>), Sm­(<b>15</b>)). All complexes were characterized by spectroscopic methods and elemental analyses, and complexes <b>5</b>–<b>11</b>, <b>13</b>, and <b>14</b> were further determined by single-crystal X-ray diffraction. The catalytic properties of racemic rare-earth metal complexes on cyanosilylation of ketones were examined, and results showed that the above complexes could effectively catalyze the cyanosilylation of ketones. Chiral rare-earth metal complexes as catalysts for the enantioselective epoxidation of α,β-unsaturated ketones were also examined to afford the chiral epoxides in high yields with moderate enantioselectivities

Aluminum Alkyl Complexes Supported by Bidentate N,N Ligands: Synthesis, Structure, and Catalytic Activity for Guanylation of Amines

The reactions of AlMe₃ or AlEt₃ with 2-pyridyl- or indolyl-substituted imines were studied, leading to the formation of different organoaluminum complexes. While the reactions of the iminopyridine Cy­[NCMe-2-(C₅H₄N)]₂ (<b>L</b>^<b>1</b>) derived from 1-(pyridin-2-yl)­ethanone and <i>trans</i>-1,2-cyclohexanediamine with AlEt₃ gave the aluminum complex Cy­[NC­(Me)­(Et)-2-(C₅H₄N)­AlEt₂]₂ (<b>1</b>), in which the two ketimine groups of the ligand were transformed into the amido functionality through the addition of two ethyl groups, the reaction of <b>L</b>^<b>1</b> with AlMe₃ afforded the aluminum complex Cy­[NC­(CH₂)-2-(C₅H₄N)­AlMe₂]₂ (<b>2</b>) via a sp³ C–H activation with elimination of two methane molecules. The reactions of indolyl-2-aldimines (2-(RNCH)­C₈H₅NH (R = ^<i>t</i>Bu (<b>L</b>^<b>2</b><b>H</b>), C₆H₅ (<b>L</b>^<b>3</b><b>H</b>), 2,6-Me₂C₆H₃ (<b>L</b>^<b>4</b><b>H</b>)) with AlMe₃ or AlEt₃ afforded only the deprotonated indolyl aluminum complexes [2-(RNCH)­C₈H₅N]­AlMe₂ (R = ^<i>t</i>Bu (<b>3</b>), C₆H₅ (<b>4</b>), 2,6-Me₂C₆H₃ (<b>5</b>)) and [2-(2,6-Me₂C₆H₃NCH)­C₈H₅N]­AlEt₂ (<b>6</b>), respectively. The structures of complexes <b>2</b>–<b>6</b> were characterized by spectral methods and X-ray crystallographic analyses. These aluminum complexes showed a high catalytic activity in the addition of amines to carbodiimides to form guanidines. The mechanism of the catalytic process was studied by control experiments and ¹H NMR monitoring. Together with the isolation of the complex [2-(2,6-Me₂C₆H₃NCH)­C₈H₅N]­[CyNC­(4-MeC₆H₃N)­(NHCy)]­AlMe (<b>7</b>), a probable mechanism for the guanylation reaction was proposed

Regioselective and Stepwise Syntheses of Functionalized BODIPY Dyes through Palladium-Catalyzed Cross-Coupling Reactions and Direct C–H Arylations

Regioselective and stepwise syntheses of a series of functionalized BODIPY dyes through palladium-catalyzed cross-coupling reactions and direct C–H arylations have been developed. In particular, this method allows the straightforward synthesis of 2,6-dibromo-3,5-diarylBODIPYs and 2-bromo-3-arylBODIPYs from polybrominated BODIPYs. The X-ray structure of intermediates <b>5a</b>–<b>c</b> indicated that the palladium was first inserted into the C–Br bonds at 3,5-positions of brominated BODIPYs. The resulting 2,6-dibromo-substituted BODIPYs are potential long wavelength photosensitizers which are not easily accessible using previous methods