Calculations with Gaussian orbitals and periodic boundary conditions using several density functionals are carried out to study the proton-doping of polyaniline. We explore previously proposed mechanisms to explain the spectacular increase of the electrical conductivity of polyaniline upon protonation. The structural and spectroscopic theoretical predictions for both polaron and bipolaron lattices agree quite well with the experimental data, and we find that the bipolaron structure is lower in energy.

In order to achieve reproducibility during iridium-photoredox and nickel dual-catalyzed sp(3)-sp(2) carbon-carbon bond-forming reactions, we investigated the role that molecular oxygen (O2), solvent and light-source (CF lamp or blue LED) play in a variety of Ir-photoredox mediated transformations. The presence of O2 was discovered to be important for catalyst activation when air-stable Ni(II) precatalysts were used in DMF under CF lamp irradiation; however, O2 was not required for catalysis when conducted with Ni(COD)2 in the same reaction system. O2 is believed to promote rapid reduction of the Ni(II) precatalyst by Ir(II) to Ni(0). In addition to O2, the effects that solvent and light-source have on the dual-catalyzed decarboxylative cross-coupling reactions will be discussed. These findings have enabled us to develop a more robust dual-catalyzed decarboxylative cross-coupling protocol.

Simple 1,3-dienes undergo highly stereoselective hetero-Diels-Alder additions with SO2 at low temperature giving sultines. These reactions that are faster than the more exothermic cheletropic additions of SO2-producing sulfolenes. This has led to the invention of a new C-C bond-forming reaction combining electron-rich dienes and alkenes with SO2. The reaction cascade has been exploited to develop combinatorial, one-pot, four-component syntheses of polyfunctional sulfones, sulfonamides, and sulfonic esters. It also allows us to generate, in one-pot operations, enantiomerically enriched polypropionate fragments containing up to three contiguous stereogenic centers and a (E)-alkene unit. These fragments can be used directly in further C-C bond-forming reactions, such as cross-aldol condensations, thus permitting the expeditious construction of complicated natural products of biological interest (e.g., Baconipyrones, Rifamycin S, Apoptolidinone) and analogues. New ene reactions of SO2 have also been discovered; they open new avenues to organic synthesis.

Dirhodium-catalyzed C-H amination is hypothesized to proceed via Rh2-nitrene intermediates in either the Rh2(II,II) or Rh2(II,III) redox state. Herein, we report joint theoretical and experimental studies of the ground electronic state (GES), redox potentials, and C-H amination of [Rh2(II,III)(O2CCH3)4(L)n](+) (1_L) (L = none, Cl(-), and H2O), [Rh2(esp)2](+) (2), and Rh2(espn)2Cl (3) (esp = α,α,α',α'-tetramethyl-1,3-benzenedipropanoate and espn = α,α,α',α'-tetramethyl-1,3-benzenedipropanamidate). CASSCF calculations on 1_L yield a wave function with two closely weighted configurations, (δ*)(2)(π1*)(2)(π2*)(1) and (δ*)(2)(π1*)(1)(π2*)(2), consistent with reported EPR g values [Chem. Phys. Lett. 1986, 130, 20-23]. In contrast, EPR spectra of 2 show g values consistent with the DFT-computed (π*)(4)(δ*)(1) GES. EPR spectra and Cl K-edge XAS for 3 are consistent with a (π*)(4)(δ*)(1) GES, as supported by DFT. Nitrene intermediates 2N_L and 3N_L are also examined by DFT (the nitrene is an NSO3R species). DFT calculations suggest a doublet GES for 2N_L and a quartet GES for 3N_L. CASSCF calculations describe the GES of 2N as Rh2(II,II) with a coordinated nitrene radical cation, (π*)(4)(δ*)(2)(π(nitrene,1))(1)(π(nitrene,2))(0). Conversely, the GES of 3N is Rh2(II,III) with a coordinated triplet nitrene, (π*)(4)(δ*)(1)(π(nitrene,1))(1)(π(nitrene,2))(1). Quartet transition states ((4)TSs) are found to react via a stepwise radical mechanism, whereas (2)TSs are found to react via a concerted mechanism that is lower in energy compared to (4)TSs for both 2N_L and 3N_L. The experimental (determined by intramolecular competition) and (2)TS-calculated kinetic isotopic effect (KIE) shows a KIE ∼ 3 for both 2N and 3N, which is consistent with a concerted mechanism.

The gas-phase reactivity of methyl fluoride with selected first-row transition metal monocations (Sc(+), Ti(+), V(+), and Zn(+)) has been theoretically investigated. Our thermochemical and kinetics study shows that early transition-metal cations exhibit a much more active chemistry than the latest transition metal monocation Zn(+). The strong C-F bond in methyl fluorine can be activated by scandium, titanium, and vanadium monocations yielding the metal fluorine cation, MF(+). However, the rate efficiencies vary dramatically along the period 0.73 (Sc), 0.91 (Ti), and 0.028 (V) in agreement with the experimental observation. The kinetics results show the relative importance of the entrance and exit channels, apart from the "inner" bottleneck, to control the global rate constant of these reactions. At the mPW1K/QZVPP level our computed kglobal (at 295 K), 1.99 × 10(-9) cm(3) molecule(-1) s(-1) (Sc(+)), 1.29 × 10(-9) cm(3) molecule(-1) s(-1) (Ti(+)), and 3.46 × 10(-10) cm(3) molecule(-1) s(-1) (V(+)) are in good agreement with the experimental data at the same temperature. For the reaction of Zn(+) and CH3F our predicted value for kouter, at 295 K, 3.79 × 10(-9) cm(3) molecule(-1) s(-1), is in accordance with the capture rate constant. Our study suggests that consideration of the lowest excited states for Ti(+) and V(+) is mandatory to reach agreement between calculations and experimental measurements.

Recently, a small number of diverse iridium complexes have been shown to catalyze unusual atom transfer C-H functionalization reactions. To further our understanding and enhance the utility of iridium complexes for C-H functionalization, we report the design and synthesis of a family of iridium(III)-bis(oxazolinyl)phenyl complexes. The ability to tune the ligand environment around the metal in these systems is exploited to design complexes with the ability to catalyze the asymmetric insertion of donor/acceptor iridium carbenoids into activated C-H bonds. Low catalyst loadings (0.5 mol%) routinely lead to excellent reaction yields (51-99%) and enantioselectivities (83-99%). Density functional theory calculations provide compelling evidence that in these complexes the carbene binds to the iridium cis to the phenyl group of the bis(oxazolinyl)phenyl ligand. This finding is vital for understanding the observed stereochemical induction and is of particular significance in the field of enantioselective transition metal-catalysed atom transfer reactions utilizing oxazoline-X-oxazoline tridentate ligands, as previously employed stereochemical models for these ligand sets are based on the assumption that reactive ligands and Lewis bases bind trans to the central X ligand.

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Polysulfone- and diphenyldisulfone-catalyzed alkene isomerizations are much faster for 2-alkyl-1-alkenes than for linear, terminal alkenes. The mechanism of these reactions has been investigated experimentally for the isomerization of methylidenecyclopentane into 1-methylcyclopentene, and theoretically [CCSD(T)/6-311++G(d,p)//B3LYP/6-311++G(d,p) calculations] for the reactions of propene and 2-methylpropene with a methanesulfonyl radical, MeSO2*. On heating, polysulfones and (PhSO2)2 equilibrate with sulfonyl radicals, RSO2*. The latter abstract allylic hydrogen atoms in one-step processes giving allylic radical/RSO2H pairs that recombine within the solvent cage producing the corresponding isomerized alkene and RSO2*. The sulfinic acid, RSO2H, can diffuse out from the solvent cage (H/D exchange with MeOD,D2O) and reduce an allyl radical. Calculations did not support other possible mechanisms such as hydrogen exchange between alkenes, electron transfer, or addition/elimination process. Kinetic deuterium isotopic effects measured for the (PhSO2)2-catalyzed isomerization of methylidenecyclopentane and deuterated analogues and calculated for the H abstraction from 2-methylpropene and deuterated analogues by CH3SO2* are consistent also with the one-step hydrogen transfer mechanism. The high chemoselectivity for this reaction is not governed by an exothermicity difference but by a difference in ionization energies of the alkenes. Calculations for CH3SO2* + propene and CH3SO2* + 2-methylpropene show a charge transfer of 0.34 and 0.38 electron, respectively, from the alkenes to the sulfonyl radical in the transition states of these hydrogen abstractions.