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A DFT analysis of the reaction of bpyNiEt2 with ArN3 was performed for para-tolyl-azide (Ar = pTol), 3,5-dimethyl-phenyl-azide (Ar = mXy) and ortho-tolyl-azide (Ar = oTol), and mesityl-azide (MesN3). Of particular interest were the different products obtained for the latter (ethylene, butane, azomesitylene, mesityl-ethylamine, etc.) versus the other reagents, i.e., (bpyNi(N(Ar)Et)(Et)). Calculated thermodynamics and kinetics for metal-free reactions did not differentiate MesN3 from the other aryl azides. Once (2)bpyNiEt• was generated via bond homolysis, formation of ethylene by ß-H elimination was facile, as was formation of nickel-imidyl (NR-•) intermediates by reaction of ArN3 with bpyNiEtx (x = 0-2). On the basis of computed energetics, three reactions of bpyNiEt2 were proposed to compete: Ni-C bond homolysis, reductive elimination of butane, and nucleophilic attack (NA) by ArN3. Inspection of their temperature dependence suggested that NA and Ni-Et bond homolysis dominated at lower and higher temperatures, respectively. Calculated Ni-N and Ni-C bond dissociation free energies (BDFEs) suggested the role of radical pathways in discriminating bpyNiEt2/ArN3 reactions, and implied that the concentration of radicals such as aminyl (ArN•(Et)), (2)bpyNiEt•, and Et• will be greatest for MesN3. [ABSTRACT FROM AUTHOR]

Keymechanistic features of the [Cp*MCl2]2(M =Ir, Rh, Co; all are in group 9) catalyzed C–H aminationof benzamides with organic azides were investigated with a strongemphasis on the metal effects on thereactionmechanism, revealing that the Rh- and Ir-catalyzedreactions follow a similar reaction profile, albeit with differentindividual kinetic and thermodynamic parameters. The observation thatthe Ir-based system was much superior in terms of the rates and efficiencyin comparison to Rh was attributed to the intrinsically strongrelativistic effects in iridium.While a cobalt system [Cp*CoIII] showed littlecatalytic activity formost azides examined, plausible [(BA)(Cp*)CoNR]+intermediatesof these reactions were characterized as a “Co(III)-nitrenoidradical” species with a weak (“one electron–twocenter type”) Co–NPh bond. Its Rh and Ir analogues arecharacterized as diamagnetic metal nitrenoids with a strong MNRdouble bond. The provided experimental and computational investigationsindicate that the rate-limiting step of the reaction resides in thefinal stage (protodemetalation) that takes place via a concerted metalation–deprotonation(CMD) mechanism. While experimental measurements of thermodynamicparameters were in good agreement with DFT calculations, theoreticalpredictions on the electronic nature of key intermediates and energybarriers were successfully used to rationalize the experimentallyobserved reactivity pattern. [ABSTRACT FROM AUTHOR]

Mechanistic details pertaining to the Pd0/PR3-catalyzed intermolecular arylation of a terminal β-C(sp3)-H bond aryl amide substrate (SM = EtCONH-Ar, where Ar = C6H5, C6F5 and CONH-Ar is a directing group (DG)) in the presence of CsF base were elucidated. Key mechanistic features of this reaction are (1) oxidative addition of the aryl halide PhI to Pd0/PR3, (2) deprotonation of SM by CsF to form DG' = [EtCON-Ar]Cs+ for subsequent coordination to intermediate I-PdII(PCy3)Ph (the substantially lower pKa of the EtCONHC6F5 in comparison to EtCONHC6H5 is instrumental for the presence of a larger population of the reactive deprotonated amides for Ar = C6F5), (3) "Cs2-I-F" cluster formation upon external (the second) CsF molecule approach to the active site of the I-PdII(PCy3)Ph(DG') intermediate, (4) "Cs2-I-F cluster" assisted β-C(sp3)-H bond activation via a concerted metalation-deprotonation (CMD) mechanism, and (5) reprotonation of the amide directing group to facilitate the C(sp3)-Ph reductive elimination. The energy barriers, ▵ G‡ (▵ G‡ disp), associated with the "Cs2-I-F cluster" mediated β-C(sp3)-H bond activation transition state are 6.5 (8.7) and 10.2 (12.9) kcal/mol when DG = CONHC6H5, CONHC6F5, respectively. It was shown that (a) the PCy3 ligand only semidissociates upon β-C(sp3)-H bond cleavage and (b) the I-to-F substitution in I-[PdII](Ph)(PCy3)(DG') is a facile process that makes the "direct-halide" assisted β-C(sp3)-H bond activation relatively less energy demanding and opens the possibility for a competing Ph-F bond formation reaction. It was shown that the "direct-I" assisted C-H bond activation TS, which associates with a relatively large energy barrier, is an H-atom insertion transition state into the Pd-I bond, while the "direct-F" assisted C-H bond activation TS, which occurs with a relatively low energy barrier (but still is much larger than that required for the "Cs2-I-F cluster" assisted pathway), is a direct proton abstraction transition state [ABSTRACT FROM AUTHOR]

Analysis of the electronic structureof PdO complexes is reportedutilizing multiconfigurational self-consistent field (MCSCF) theory.Models include hard (N) and soft (Cl) donors to mimic proposed Pdoxo intermediates. Calculations argue against formulation of a PdIVoxo intermediate as posited in earlier experimental studiesof PdII-mediated oxy insertion: i.e., a square-pyramidalcomplex with a basal oxo ligand. However, low-energy structures withother coordination geometries (trigonal bipyramidal) and isomerism(basal O) were identified. The supporting ligand plays a role in stabilizationof the PdO bond as indicated by calculations on the PdOCl2fragment and LPdOCl2(L = model diimine ligand). [ABSTRACT FROM AUTHOR]

The reactivity of a series of oxidants with [(tbpy)Pt(Ph)(L)]+ and [(tbpy)2Rh(Me)(OTf)]+ [tbpy = 4,4′-di- tert-butyl-2,2′-bipyridine, L = thf or triflate (OTf)] complexes was investigated. The PtII and RhIII complexes [(tbpy)Pt(Ph)(ONMe3)][BAr′4], [(tbpy)Pt(Ph)(OPy)][BAr′4], [(tbpy)2Rh(Me)(ONMe3)][BAr′4][OTf], and [(tbpy)2Rh(Me)(OPy)][BAr′4][OTF] (Ar′ = 3,5-(CF3)2C6H3, OPy = pyridine N-oxide) have been isolated and characterized by 1H, 13C, and 19F NMR spectroscopy as well as elemental analysis. In addition, single-crystal X-ray diffraction studies of the complexes [(tbpy)Pt(Ph)(OPy)][BAr′4], [(tbpy)2Rh(Cl)2][BAr′4], [(tbpy)2Rh(Me)2][BAr′4], [(tbpy)2Rh(Me)( I)][BAr′4], and [(tbpy)2Rh(Me)(OPy)][BAr′4][OTf] are reported. DFT calculations computationally model the conversions of Pt-Ph and Rh-Me species to the corresponding Pt-OPh and Rh-OMe complexes, providing insight into activation barriers for the oxygen-atom insertion into PtII-R and RhIII-R bonds. [ABSTRACT FROM AUTHOR]

Transition-metal-mediated oxy insertion into metal–carbonbonds is useful for the development of catalytic cycles for selectivehydrocarbon oxidation. However, there are few bona fide examples ofnet oxy insertion with transition-metal complexes. An extremely rareexample of a 3d metal mediating oxy insertion into metal–carbonbonds is a series of NiIIalkyl complexes reacting withnitrous oxide (N2O) reported by Hillhouse and co-workers;however, the mechanism was never fully elucidated. A computationalstudy has been performed on bipyridyl nickel metallacycles that formnickel alkoxides upon reaction with N2O to attain insightinto future catalyst design for oxygen atom transfer reactions. Twopossible mechanisms are explored. Of the two pathways, the computationssuggest that the preferred mechanism proceeds through a Ni–oxylintermediate followed by alkyl migration of the nickel–carbonbond to form an alkoxide. Oxyl formation was found to be the rate-determiningstep, with a free energy barrier of 29.4 kcal/mol for bpyNiII(cyclo-(CH2)4). Complexes that contain sp2-hybridized molecules at the β-carbon site within themetallacycle ring do not undergo oxy insertion due to elevated barriers.While exploring insertion with another oxidant, namely pyridine N-oxide, we found that N2O is critical for netoxy insertion with this complex due to the substantial thermodynamicadvantage of N2expulsion. Reaction with pyridine N-oxide necessitated expulsion of a “worse”leaving group, resulting in much higher barriers (ΔG⧧= 49.7 kcal/mol) for the oxyl formationstep. [ABSTRACT FROM AUTHOR]

A correction to the article "Impact of d-Orbital Occupation on Metal-Carbon Bond Functionalization" that was published in the Vol. 53, 2014 issue is presented.