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

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]

Indolyl-based Copper(I) Complex-Catalyzed Intermolecular Trifluoromethylazolation of Alkenes via Radical Process

Herein, we synthesized and characterized a binuclear copper(I) complex supported by the indolyl-based ligand. Employing this complex as catalyst, we have developed a three-component intermolecular trifluoromethylazolation of alkenes to deliver various trifluoromethylated azole derivatives. The method features exclusive chemo- and regioselectivity, a broad scope of alkenes and oxazoles, thiazoles, and good tolerance of functional groups under mild conditions. Preliminary mechanistic studies support a radical process for the transformation

Synthesis of Bis(NHC)-Based CNC-Pincer Rare-Earth-Metal Amido Complexes and Their Application for the Hydrophosphination of Heterocumulenes

The bis­(NHC) (NHC = N-heterocyclic carbene)-based CNC-pincer rare-earth-metal amido complexes <b>L</b>RE­[N­(SiMe₃)₂]₂ (<b>L</b> = 4-CH₃-2-{R-[N­(CH)₂CN]}­C₆H₃]₂N; <b>L</b>^<b>2</b>, R = CH₃; <b>L</b>^<b>3</b>, R = CH­(CH₃)₂) were synthesized and characterized, and their catalytic activities toward hydrophosphination of heterocumulenes were developed. Reactions of bis­[2-(3-methylimidazolium)-4-methylphenyl]­amine diiodide (H₃<b>L</b>^<b>2</b>I₂) or bis­[2-(3-isopropylimidazolium)-4-methylphenyl]­amine diiodide (H₃<b>L</b>^<b>3</b>I₂) with 5 equiv of NaN­(SiMe₃)₂ followed by treatment with 1 equiv of RECl₃ in THF at −78 °C afforded the bis­(NHC)-based CNC-pincer rare-earth-metal amido complexes <b>L</b>RE­[N­(SiMe₃)₂]₂ (<b>L</b>^<b>2</b> = [4-CH₃-2-{CH₃-[N­(CH)₂CN]}­C₆H₃]₂N, RE = Y (<b>1</b>), Eu (<b>2</b>), Er (<b>3</b>); <b>L</b>^<b>3</b> = [4-CH₃-2-{(CH₃)₂CH-[N­(CH)₂CN]}­C₆H₃]₂N, RE = Y (<b>4</b>), Er (<b>5</b>), Yb (<b>6</b>)). Complexes <b>4</b>–<b>6</b> can also be prepared by stepwise reactions of H₃<b>L</b>^<b>3</b>I₂ with <i>n</i>-BuLi in THF followed by reactions with [(Me₃Si)₂N]₃RE­(μ-Cl)­Li­(THF)₃. Stepwise reactions of H₃<b>L</b>^<b>2</b>I₂ with <i>n</i>-BuLi in THF followed by treatment with [(Me₃Si)₂N]₃RE­(μ-Cl)­Li­(THF)₃ generated the bis­(NHC)-based CNC-pincer rare-earth-metal amido complexes <b>L</b>^<b>2</b>RE­[N­(SiMe₃)₂]₂ (RE = Y (<b>1</b>), Er (<b>3</b>)) together with the fused-heterocyclic compound 3,8,9-trimethyl-8a,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>7</b>), which formed through carbene C–C and C–N coupling. Attempts to prepare complexes of the type <b>L</b>RE­[N­(SiMe₃)₂]₂ by reaction of H₃<b>L</b>^<b>3</b>I₂ with [(Me₃Si)₂N]₃Yb­(μ-Cl)­Li­(THF)₃ in THF, however, afforded mixed complexes of the bis­(NHC)-based CNC-pincer ytterbium complex <b>L</b>^<b>3</b>Yb­[N­(SiMe₃)₂]₂ (<b>6</b>) and the unexpected bis­(NHC)-based CNC-pincer monoamido ytterbium iodide <b>L</b>^<b>3</b>YbI­[N­(SiMe₃)₂] (<b>8</b>). Investigation of the catalytic activity of complexes <b>1</b>–<b>6</b> and <b>8</b> indicated that all complexes displayed high activity toward the addition of the phosphine P–H bond to heterocumulenes, producing the corresponding phosphaguanidines, phosphaureas, and phosphathioureas, which represents the first example of bis­(NHC)-based CNC-pincer type rare-earth-metal amido complexes as catalysts for the catalytic addition of the phosphine P–H bond to heterocumulenes with high efficiency in the presence of a low catalyst loading at room temperature