The observed 1° isotope effect on 2° KIEs in H-transfer reactions has recently been explained on the basis of a H-tunneling mechanism that uses the concept that the tunneling of a heavier isotope requires a shorter donor-acceptor distance (DAD) than that of a lighter isotope. The shorter DAD in D-tunneling, as compared to H-tunneling, could bring about significant spatial crowding effect that stiffens the 2° H/D vibrations, thus decreasing the 2° KIE. This leads to a new physical organic research direction that examines how structure affects the 1° isotope dependence of 2° KIEs and how this dependence provides information about the structure of the tunneling ready states (TRSs). The hypothesis is that H- and D-tunneling have TRS structures which have different DADs, and pronounced 1° isotope effect on 2° KIEs should be observed in tunneling systems that are sterically hindered. This paper investigates the hypothesis by determining the 1° isotope effect on α- and β-2° KIEs for hydride transfer reactions from various hydride donors to different carbocationic hydride acceptors in solution. The systems were designed to include the interactions of the steric groups and the targeted 2° H/D's in the TRSs. The results substantiate our hypothesis, and they are not consistent with the traditional model of H-tunneling and 1°/2° H coupled motions that has been widely used to explain the 1° isotope dependence of 2° KIEs in the enzyme-catalyzed H-transfer reactions. The behaviors of the 1° isotope dependence of 2° KIEs in solution are compared to those with alcohol dehydrogenases, and sources of the observed "puzzling" 2° KIE behaviors in these enzymes are discussed using the concept of the isotopically different TRS conformations.

A variety of acyl protected phenols AcOAr participate in sp C-H etherification of substrates R-H to give alkyl aryl ethers R-OAr employing BuOOBu as oxidant with copper(I) β-diketiminato catalysts [Cu]. Although 1°, 2°, and 3° C-H bonds may be functionalized, selectivity studies reveal a preference for the construction of hindered, 3° C-OAr bonds. Mechanistic studies indicate that β-diketiminato copper(II) phenolates [Cu]-OAr play a key role in this C-O bond forming reaction, formed via transesterification of AcOAr with [Cu]-OBu intermediates generated upon reaction of [Cu] with BuOOBu.

Molecular catalysts for ammonia oxidation to dinitrogen represent enabling components to utilize ammonia as a fuel and/or source of hydrogen. Ammonia oxidation requires not only the breaking of multiple strong N–H bonds but also controlled N–N bond formation. We report a novel β-diketiminato copper complex [ i Pr2NNF6]CuI-NH3 ([CuI]-NH3 (2)) as a robust electrocatalyst for NH3 oxidation in acetonitrile under homogeneous conditions. Complex 2 operates at a moderate overpotential (η = 700 mV) with a TOFmax = 940 h–1 as determined from CV data in 1.3 M NH3–MeCN solvent. Prolonged (>5 h) controlled potential electrolysis (CPE) reveals the stability and robustness of the catalyst under electrocatalytic conditions. Detailed mechanistic investigations indicate that electrochemical oxidation of [CuI]-NH3 forms {[CuII]-NH3}+ (4), which undergoes deprotonation by excess NH3 to form reactive copper(II)–amide ([CuII]-NH2, 6) unstable toward N–N bond formation to give the dinuclear hydrazine complex [CuI]2(μ-N2H4). Electrochemical studies reveal that the diammine complex [CuI](NH3)2 (7) forms at high ammonia concentration as part of the {[CuII](NH3)2}+/[CuI](NH3)2 redox couple that is electrocatalytically inactive. DFT analysis reveals a much higher thermodynamic barrier for deprotonation of the four-coordinate {[CuII](NH3)2}+ (8) by NH3 to give the copper(II) amide [CuII](NH2)(NH3) (9) (ΔG = 31.7 kcal/mol) as compared to deprotonation of the three-coordinate {[CuII]-NH3}+ by NH3 to provide the reactive three-coordinate parent amide [CuII]-NH2 (ΔG = 18.1 kcal/mol) susceptible to N–N coupling to form [CuI]2(μ-N2H4) (ΔG = −11.8 kcal/mol).

Copper­(II) alkynyl species are proposed as key intermediates in numerous Cu-catalyzed C–C coupling reactions. Supported by a β-diketiminate ligand, the three-coordinate copper­(II) alkynyl [CuII]–CCAr (Ar = 2,6-Cl2C6H3) forms upon reaction of the alkyne H–CCAr with the copper­(II) tert-butoxide complex [CuII]–O t Bu. In solution, this [CuII]–CCAr species cleanly transforms to the Glaser coupling product ArCC–CCAr and [CuI]­(solvent). Addition of nucleophiles R′CC–Li (R′ = aryl, silyl) and Ph–Li to [CuII]–CCAr affords the corresponding Csp–Csp and Csp–Csp2 coupled products RCC–CCAr and Ph–CCAr with concomitant generation of [CuI]­(solvent) and {[CuI]–CCAr}−, respectively. Supported by density functional theory (DFT) calculations, redox disproportionation forms [CuIII]­(CCAr)­(R) species that reductively eliminate R–CCAr products. [CuII]–CCAr also captures the trityl radical Ph3C· to give Ph3C–CCAr. Radical capture represents the key Csp–Csp3 bond-forming step in the copper-catalyzed C–H functionalization of benzylic substrates R–H with alkynes H–CCR′ (R′ = (hetero)­aryl, silyl) that provide Csp–Csp3 coupled products R–CCR via radical relay with t BuOO t Bu as oxidant.

The effect of the bath chemistry and operating conditions on the chemical composition, microstructure and properties of Ni-W-B alloys deposited from tartrate baths on working electrode was studied for the first time by the pulsed current method. The investigations included the measurement of the current efficiencies and determination of the tungsten content in the electrodeposits. UV spectrometry was used for characterisation of complex formation. The grain size of deposits was determined by XRD. Also, the morphology of the deposits was studied by SEM. Amorphous Ni-W-B alloys were successfully obtained by electrodeposition from the tartrate bath. The corrosion behaviour of Ni-W-B coating on mild steel has been evaluated during exposure to 3?5%NaCl solution by electrochemical impedance spectroscopy. The electrochemical and corrosion behaviour of Ni-W-B alloy showed a good corrosion resistance in the 3?5%NaCl medium. The microhardness of nanocrystaline Ni-W-B is in the range between 700 and 850 HV.