Bifunctional Water Activation for Catalytic Hydration of Organonitriles

Treatment of [Rh­(COD)­(μ-Cl)]₂ with excess ^<i>t</i>BuOK and subsequent addition of 2 equiv of PIN·HBr in THF afforded [Rh­(COD)­(κC₂-PIN)­Br] (<b>1</b>) (PIN = 1-isopropyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)­imidazol-2-ylidene, COD = 1,5-cyclooctadiene). The X-ray structure of <b>1</b> confirms ligand coordination to “Rh­(COD)­Br” through the carbene carbon featuring an unbound naphthyridine. Compound <b>1</b> is shown to be an excellent catalyst for the hydration of a wide variety of organonitriles at ambient temperature, providing the corresponding organoamides. In general, smaller substrates gave higher yields compared with sterically bulky nitriles. A turnover frequency of 20 000 h^–1 was achieved for the acrylonitrile. A similar Rh­(I) catalyst without the naphthyridine appendage turned out to be inactive. DFT studies are undertaken to gain insight on the hydration mechanism. A 1:1 catalyst–water adduct was identified, which indicates that the naphthyridine group steers the catalytically relevant water molecule to the active metal site via double hydrogen-bonding interactions, providing significant entropic advantage to the hydration process. The calculated transition state (TS) reveals multicomponent cooperativity involving proton movement from the water to the naphthyridine nitrogen and a complementary interaction between the hydroxide and the nitrile carbon. Bifunctional water activation and cooperative proton migration are recognized as the key steps in the catalytic cycle

Effect of Ligand Structure on the Cu^II–R OMRP Dormant Species and Its Consequences for Catalytic Radical Termination in ATRP

The kinetics and mechanism of catalytic radical termination (CRT) of <i>n</i>-butyl acrylate (BA) in MeCN in the presence of Cu complexes with tridentate and tetradentate ligands was investigated both theoretically and experimentally. The tetradentate TPMA, TPMA*¹, TPMA*², TPMA*³, and the newly synthesized tridentate <i>N</i>-propyl-<i>N</i>,<i>N</i>-bis­(4-methoxy-3,5-dimethylpyrid-2-ylmethyl)­amine (BPMA*^Pr) as well as tridentate BPMA^Me were used as ligands. L/Cu^IIX₂ (X = Cl or OTf) complexes were characterized by cyclic voltammetry (CV), UV–vis–NIR, and X-ray diffraction. Polymerization of BA initiated by azobis­(iso­butyronitrile) (AIBN) in MeCN in the presence of a L/Cu^I complex showed higher rates of CRT for more reducing L/Cu^I complexes. The ligand denticity (tri- vs tetradentate) had a minor effect on the relative polymerization kinetics but affected the molecular weights in a way specific for ligand denticity. Quantification of the apparent CRT rate coefficients, <i>k</i>_CRT^app, showed larger values for more reducing L/Cu^I complexes, which correlated with the L/Cu^II–R (R = CH­(CH₃)­(COOCH₃)) bond strength, according to DFT calculations. The bond strength is mostly affected by the complex reducing power and to a lesser degree by the ligand denticity. Analysis of kinetics and molecular weights for different systems indicates that depending on the ligand nature, the rate-determining step of CRT may be either the radical addition to L/Cu^I to form the L/Cu^II–R species or the reaction of the latter species with a second radical

Ru–Zn Heteropolynuclear Complexes Containing a Dinucleating Bridging Ligand: Synthesis, Structure, and Isomerism

Mononuclear complexes <i>in</i>- and <i>out</i>-[Ru­(Cl)­(trpy)­(Hbpp)]⁺ (<i><b>in</b></i><b>-0</b>, <i><b>out</b></i><b>-0</b>; Hbpp is 2,2′-(1<i>H</i>-pyrazole-3,5-diyl)­dipyridine and trpy is 2,2′:6′,2″-terpyridine) are used as starting materials for preparation of Ru–Zn heterodinuclear <i>out</i>-{[Ru­(Cl)­(trpy)]­[ZnCl₂]­(μ-bpp)} (<i><b>out</b></i><b>-2</b>) and heterotrinuclear <i>in,in</i>- and <i>out,out</i>-{[Ru­(Cl)­(trpy)]₂(μ-[Zn­(bpp)₂])}²⁺ (<i><b>in</b></i><b>-3</b>, <i><b>out</b></i><b>-3</b>) constitutional isomers. Further substitution of the Cl ligand from the former complexes leads to Ru–aqua <i>out,out</i>-{[Ru­(trpy)­(H₂O)]₂(μ-[Zn­(bpp)₂])}⁴⁺ (<i><b>out</b></i><b>-4</b>) and the oxo-bridged Ru–O–Ru complex <i>in,in</i>-{[Ru^III(trpy)]₂(μ-[Zn­(bpp)₂(H₂O)]­μ-(O)}⁴⁺ (<i><b>in</b></i><b>-5</b>). All complexes are thoroughly characterized by the usual analytical techniques as well as by spectroscopy by means of UV–vis, MS, and when diamagnetic NMR. CV and DPV are used to extract electrochemical information and monocrystal X-ray diffraction to characterize complexes <i><b>out</b></i><b>-2</b>, <i><b>in</b></i><b>-3</b>, <i><b>out</b></i><b>-3</b>, and <i><b>in</b></i><b>-5</b> in the solid state. Complex <i><b>out</b></i><b>-3</b> photochemically isomerizes toward <i><b>in</b></i><b>-3</b>, as can be observed by NMR spectroscopy and rationalized by density functional theory based calculations

Bifunctional Water Activation for Catalytic Hydration of Organonitriles

Treatment of [Rh­(COD)­(μ-Cl)]₂ with excess ^<i>t</i>BuOK and subsequent addition of 2 equiv of PIN·HBr in THF afforded [Rh­(COD)­(κC₂-PIN)­Br] (<b>1</b>) (PIN = 1-isopropyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)­imidazol-2-ylidene, COD = 1,5-cyclooctadiene). The X-ray structure of <b>1</b> confirms ligand coordination to “Rh­(COD)­Br” through the carbene carbon featuring an unbound naphthyridine. Compound <b>1</b> is shown to be an excellent catalyst for the hydration of a wide variety of organonitriles at ambient temperature, providing the corresponding organoamides. In general, smaller substrates gave higher yields compared with sterically bulky nitriles. A turnover frequency of 20 000 h^–1 was achieved for the acrylonitrile. A similar Rh­(I) catalyst without the naphthyridine appendage turned out to be inactive. DFT studies are undertaken to gain insight on the hydration mechanism. A 1:1 catalyst–water adduct was identified, which indicates that the naphthyridine group steers the catalytically relevant water molecule to the active metal site via double hydrogen-bonding interactions, providing significant entropic advantage to the hydration process. The calculated transition state (TS) reveals multicomponent cooperativity involving proton movement from the water to the naphthyridine nitrogen and a complementary interaction between the hydroxide and the nitrile carbon. Bifunctional water activation and cooperative proton migration are recognized as the key steps in the catalytic cycle

Olefin Oxygenation by Water on an Iridium Center

Oxygenation of 1,5-cyclooctadiene (COD) is achieved on an iridium center using water as a reagent. A hydrogen-bonding interaction with an unbound nitrogen atom of the naphthyridine-based ligand architecture promotes nucleophilic attack of water to the metal-bound COD. Irida-oxetane and oxo-irida-allyl compounds are isolated, products which are normally accessed from reactions with H₂O₂ or O₂. DFT studies support a ligand-assisted water activation mechanism

Olefin Oxygenation by Water on an Iridium Center

Oxygenation of 1,5-cyclooctadiene (COD) is achieved on an iridium center using water as a reagent. A hydrogen-bonding interaction with an unbound nitrogen atom of the naphthyridine-based ligand architecture promotes nucleophilic attack of water to the metal-bound COD. Irida-oxetane and oxo-irida-allyl compounds are isolated, products which are normally accessed from reactions with H₂O₂ or O₂. DFT studies support a ligand-assisted water activation mechanism

Catalytic Conversion of Alcohols to Carboxylic Acid Salts and Hydrogen with Alkaline Water

A [RuH­(CO)­(py-NP)­(PPh₃)₂]Cl (<b>1</b>) catalyst is found to be effective for catalytic transformation of primary alcohols, including amino alcohols, to the corresponding carboxylic acid salts and two molecules of hydrogen with alkaline water. The reaction proceeds via acceptorless dehydrogenation of alcohol, followed by a fast hydroxide/water attack to the metal-bound aldehyde. A pyridyl-type nitrogen in the ligand architecture seems to accelerate the reaction