tempo and carbene

Imidazolium salts bearing TEMPO groups react with commercially available copper powder affording Cu-NHC complexes. The in situ generated Cu-NHC-TEMPO complexes are quite efficient catalysts for aerobic oxidation of primary alcohols into aldehydes. The catalyst is easily available, and various primary alcohols were selectively converted to aldehydes in excellent yields.

Topics: Alcohols; Aldehydes; Catalysis; Copper; Cyclic N-Oxides; Heterocyclic Compounds; Methane; Molecular Structure; Organometallic Compounds; Oxidation-Reduction

The dinuclear and mononuclear nickel(I) thiolates, [Ni(PPh(3))(mu-SR)](2) (1a: R is 2,4,6-triisopropylphenyl (Tip), 1b: R is 1-adamantyl (Ad)), (DxpS)Ni(mu-SDxp)Ni(PPh(3)) (2) (Dxp is 2,6-dixylylphenyl), and Ni(SDmp)(PPh(3)) (3) (Dmp is 2,6-dimesitylphenyl), have been synthesized by the reaction of the nickel(I) amide Ni{N(SiMe(3))(2)}(PPh(3))(2) with the corresponding thiols. The two nickel centers of 1a and 1b are equivalent, and are linked by two thiolato sulfurs and a Ni-Ni bond, whereas the two inequivalent nickels of 2 are connected by a SDxp sulfur, a eta(2)/eta(3)-xylyl group of the other SDxp ligand, and a Ni-Ni bond. A slightly bulkier m-terphenyl thiolate, SDmp, prevents its nickel complex from forming a Ni-Ni bond, and the mononuclear nickel(I) center of 3 is bound to PPh(3) and SDmp through interactions with the sulfur and a eta(2)-mesityl. The coordinatively unsaturated nickel(I) complex 3 is reactive, and the reaction of 3 with TEMPO generated diamagnetic Ni(SDmp)(PPh(3))(O,N:eta(2)-TEMPO) (4). N-Heterocyclic carbenes, 1,3,4,5-tetramethylimidazolin-2-ylidene (IMe') and 1,3-bis-(2,4,6-trimethylphenyl)imidazolin-2-ylidene (IMes), also react with 3 to afford a dinuclear nickel(I) complex, [Ni(IMe')(mu-SDmp)](2) (5), and a mononuclear nickel(I) complex, Ni(SDmp)(IMes) (6), respectively. The reaction of 3 with 1 equiv of (t)BuNC afforded the dinuclear complex [Ni(CN(t)Bu)(mu-SDmp)](2) (7), whereas the analogous reaction with 1 equiv of CO resulted in a mixture of Ni(PPh(3))(2)(CO)(2) and Ni(CO)(SDmp)(2)(PPh(3)) (8).

Topics: Amides; Cyclic N-Oxides; Electrochemistry; Electron Spin Resonance Spectroscopy; Heterocyclic Compounds; Methane; Nickel; Organometallic Compounds; Sulfhydryl Compounds

Topics: Aldehydes; Biomimetics; Catalysis; Cyclic N-Oxides; Esters; Heterocyclic Compounds; Methane; Molecular Structure; Oxidation-Reduction; Stereoisomerism

Persistent triplet diphenylcarbenes with considerable stability have been shown to be trapped by tetramethylpiperidine N-oxides (TEMPOs) to give the corresponding benzophenones as major products along with tetramethylpiperidine, which indicates that the reaction pattern is essentially identical with that observed for parent triplet diphenylcarbene. The absolute rate constants for the quenching reaction were measured by a laser flash photolysis technique and compared with those for quenching by other typical triplet carbene quenchers. The results showed that the reactivity of TEMPOs toward triplet carbenes was lower than that of oxygen but higher than that of 1,4-cyclohexadiene. The advantages of TEMPOs as a triplet carbene quencher as opposed to the other quenchers are discussed, and TEMPOs are shown to be very convenient reagents to estimate the reactivity of triplet carbenes.

Topics: Benzene Derivatives; Cyclic N-Oxides; Diazomethane; Hydrocarbons; Kinetics; Lasers; Methane; Models, Chemical; Molecular Structure; Photolysis; Spectrophotometry, Ultraviolet; Thermodynamics