Enantioselective C–H Bond Addition of Pyridines to Alkenes Catalyzed by Chiral Half-Sandwich Rare-Earth Complexes

Cationic half-sandwich scandium alkyl complexes bearing monocyclopentadienyl ligands embedded in chiral binaphthyl backbones act as excellent catalysts for the enantioselective C–H bond addition of pyridines to various 1-alkenes, leading to formation of a variety of enantioenriched alkylated pyridine derivatives in high yields and excellent enantioselectivity (up to 98:2 er)

Enantioselective C–H Bond Addition of Pyridines to Alkenes Catalyzed by Chiral Half-Sandwich Rare-Earth Complexes

Cationic half-sandwich scandium alkyl complexes bearing monocyclopentadienyl ligands embedded in chiral binaphthyl backbones act as excellent catalysts for the enantioselective C–H bond addition of pyridines to various 1-alkenes, leading to formation of a variety of enantioenriched alkylated pyridine derivatives in high yields and excellent enantioselectivity (up to 98:2 er)

PNP-Ligated Heterometallic Rare-Earth/Ruthenium Hydride Complexes Bearing Phosphinophenyl and Phosphinomethyl Bridging Ligands

The reaction of rare-earth bis­(alkyl) complexes containing a bis­(phosphinophenyl)­amido pincer (PNP), LnPNP_<i>i</i>Pr(CH₂SiMe₃)₂ (<b>1-Ln</b>, Ln = Y, Ho, Dy), with ruthenium trihydride phosphine complexes, Ru­(C₅Me₅)­H₃PPh₃ and Ru­(C₅Me₅)­H₃PPh₂Me, gave the corresponding bimetallic Ln/Ru complexes bearing two hydride ligands and a bridging phosphinophenyl (μ-C₆H₄PPh₂-κ<i>P</i>:κ<i>C</i>¹, <b>2a-Ln</b>) or a bridging phosphinomethyl ligand (μ-CH₂PPh₂-κ<i>P</i>:κ<i>C</i>, <b>2b-Ln</b>), respectively. Reaction of <b>2a-Y</b> with CO gas at 1 atm and at 20 °C in toluene-<i>d</i>₈ afforded the complex <b>3a-Y</b>, which bears a bridging pseudooxymethylene ligand (μ-OCH­(<i>o</i>-C₆H₄)­PPh₂-κ<i>P</i>:κ<i>O</i>) and a bridging hydride ligand on the Y/Ru centers. Computational studies by the DFT method suggested that <b>3a-Y</b> was formed in two steps: first the coordination of CO (Δ<i>G</i>(B3PW91) = 22.9; Δ<i>G</i>(M06) = 14.9 kcal/mol) and migratory insertion of the Y–C₆H₄ group (Δ<i>G</i>^⧧(B3PW91) = 13.3; Δ<i>G</i>^⧧(M06) = 16.7 kcal/mol), followed by a rapid intramolecular hydride migration to the resulting acyl group. Complex <b>2b-Y</b> reacted with organic nitriles (<i>t</i>BuCN, CH₃CN, PhCN), an aldimine (PhNCHPh), an isonitrile (<i>t</i>BuNC), and group IX transition-metal carbonyls (M­(C₅Me₅)­(CO)₂, M = Rh, Ir) via insertion of the reactive Y–CH₂ group into the unsaturated bond. These reactions afforded complexes with new ligand scaffolds, including a bridging alkylideneamidophosphine (<b>4b-Y</b>), an amidophosphine (<b>7b-Y</b>), an η²-iminoacylphosphine (<b>8b-Y</b>), and oxycarbenephosphine (<b>9b-Y</b> and <b>10b-Y</b>) ligands at the binuclear Y/Ru core. All of these reaction products were structurally characterized by X-ray crystallography, NMR spectroscopy, and elemental analyses

PNP-Ligated Heterometallic Rare-Earth/Ruthenium Hydride Complexes Bearing Phosphinophenyl and Phosphinomethyl Bridging Ligands

The reaction of rare-earth bis­(alkyl) complexes containing a bis­(phosphinophenyl)­amido pincer (PNP), LnPNP_<i>i</i>Pr(CH₂SiMe₃)₂ (<b>1-Ln</b>, Ln = Y, Ho, Dy), with ruthenium trihydride phosphine complexes, Ru­(C₅Me₅)­H₃PPh₃ and Ru­(C₅Me₅)­H₃PPh₂Me, gave the corresponding bimetallic Ln/Ru complexes bearing two hydride ligands and a bridging phosphinophenyl (μ-C₆H₄PPh₂-κ<i>P</i>:κ<i>C</i>¹, <b>2a-Ln</b>) or a bridging phosphinomethyl ligand (μ-CH₂PPh₂-κ<i>P</i>:κ<i>C</i>, <b>2b-Ln</b>), respectively. Reaction of <b>2a-Y</b> with CO gas at 1 atm and at 20 °C in toluene-<i>d</i>₈ afforded the complex <b>3a-Y</b>, which bears a bridging pseudooxymethylene ligand (μ-OCH­(<i>o</i>-C₆H₄)­PPh₂-κ<i>P</i>:κ<i>O</i>) and a bridging hydride ligand on the Y/Ru centers. Computational studies by the DFT method suggested that <b>3a-Y</b> was formed in two steps: first the coordination of CO (Δ<i>G</i>(B3PW91) = 22.9; Δ<i>G</i>(M06) = 14.9 kcal/mol) and migratory insertion of the Y–C₆H₄ group (Δ<i>G</i>^⧧(B3PW91) = 13.3; Δ<i>G</i>^⧧(M06) = 16.7 kcal/mol), followed by a rapid intramolecular hydride migration to the resulting acyl group. Complex <b>2b-Y</b> reacted with organic nitriles (<i>t</i>BuCN, CH₃CN, PhCN), an aldimine (PhNCHPh), an isonitrile (<i>t</i>BuNC), and group IX transition-metal carbonyls (M­(C₅Me₅)­(CO)₂, M = Rh, Ir) via insertion of the reactive Y–CH₂ group into the unsaturated bond. These reactions afforded complexes with new ligand scaffolds, including a bridging alkylideneamidophosphine (<b>4b-Y</b>), an amidophosphine (<b>7b-Y</b>), an η²-iminoacylphosphine (<b>8b-Y</b>), and oxycarbenephosphine (<b>9b-Y</b> and <b>10b-Y</b>) ligands at the binuclear Y/Ru core. All of these reaction products were structurally characterized by X-ray crystallography, NMR spectroscopy, and elemental analyses