A silver-catalyzed radical hydroxyfluorination of styrenes with Selectfluor and H2O has been explored with exclusive anti-Markovnikov-type regioselectivity, thus affording vicinal fluorohydrins with regioselectivities opposite that of noncatalyzed processes. This reaction is operationally simple, scalable under mild conditions. The mechanism studies and DFT calculations revealed that the reaction go through a radical mechanism.Keywords: anti-Markovnikov; fluorohydrins; radical hydroxyfluorination; silver-catalyzed; styrenes;

Three types of (diphosphine)Pd- or Pt-bridged butterfly Fe/S cluster complexes have been prepared by a simple and convenient one-pot synthetic method. The first type of such complexes involves the linear (diphosphine)Pd- or Pt-bridged double-butterfly Fe/S clusters [(μ-RS)(μ-S═CS)Fe2(CO)6]2[M(diphosphine)] (1–12; M = Pd and Pt; R = Et, t-Bu, Ph, and p-MeC6H4; diphosphine = dppe, dppv, and dppf), which were prepared by sequential reactions of monoanions [(μ-RS)(μ-CO)Fe2(CO)6]– (formed in situ from Fe3(CO)12, RSH, and Et3N) with excess CS2, followed by treatment of the resulting monoanions [(μ-RS)(μ-S═CS)Fe2(CO)6]– with (diphosphine)MCl2. The second type of complexes involves the macrocyclic (diphosphine)M-bridged double-butterfly Fe/S clusters [μ-S(CH2)4S-μ][(μ-S═CS)Fe2(CO)6]2[M(diphosphine)] (13–16; M = Pd and Pt; diphosphine = dppe and dppv), which were prepared by sequential reactions of dianion [{μ-S(CH2)4S-μ}{(μ-CO)Fe2(CO)6}2]2– (generated in situ from Fe3(CO)12, dithiol HS(CH2)4SH, and Et3N) with excess CS2, followed by treatment of the resultant dianion [{μ-S(CH2)4S-μ}{(μ-S═CS)Fe2(CO)6}2]2– with (diphosphine)MCl2. In contrast, when dithiol HS(CH2)4SH was replaced by HS(CH2)3SH (a dithiol with a shorter carbon chain), the aforementioned sequential reactions afforded the third type of macrocyclic complexes which involves the (diphosphine)M-bridged quadruple-butterfly Fe/S clusters [{μ-S(CH2)3S-μ}{(μ-S═CS)Fe2(CO)6}2]2[M(diphosphine)]2 (17–20; M = Pd and Pt; diphosphine = dppe and dppv). While the two possible pathways are suggested for production of the two types of novel macrocyclic Fe/S clusters 13–20, respectively, all new complexes 1–20 have been characterized by elemental analysis, spectroscopy, and, for some of them particularly, DFT calculations and X-ray crystallography.

AbstractPalladium-catalyzed activation of remote meta-C−H bonds in arenes containing tethered alcohols was achieved with high regioselectivity by using a nitrile template. Computational studies on the macrocyclic transition state of the regioselectivity-determining C−H activation steps revealed that both the C-N-Ag angles and gauche comformations of phenyl ether play an extremely important role in the meta selectivity.

AbstractThe first example of a hypervalent iodine(III)-mediated oxidative fluorination of alkylsilanes by fluoride ions without the use of transition metals is demonstrated. This reaction is operationally simple, scalable, and proceeds under mild reaction conditions. Mechanistic studies suggest the involvement of a single-electron transfer resulting from the interaction of an organopentafluorosilicate and aryliodonium difluoride, which were generated in situ from the corresponding alkylsilane and iodosobenzene, respectively, in the presence of fluoride ions.

AbstractPalladium-catalyzed activation of remote meta-C−H bonds in arenes containing tethered alcohols was achieved with high regioselectivity by using a nitrile template. Computational studies on the macrocyclic transition state of the regioselectivity-determining C−H activation steps revealed that both the C-N-Ag angles and gauche comformations of phenyl ether play an extremely important role in the meta selectivity.

The mechanisms and reactivities of the [Cp*RhCl2]2 and [Cp*IrCl2]2 catalyzed oxidative annulation reaction of isoquinolones with alkynes have been investigated by combined experimental and computational studies. The results have disclosed that the low reactivity of [Cp*IrCl2]2 is attributed to the electron-richness and low electronegativity of Ir(III). These factors make Ir(III) difficult to reduce to Ir(I) and thus lead to a high activation energy of the reductive elimination step. The electronic and steric effects of alkyne substituents on the reactivities have been investigated. Small-sized and strong electron-donating substituents on alkynes should enhance the reactivity of the reaction for both catalysts by not only avoiding the steric repulsion between substrates but also facilitating the reductive elimination. The rate-determining steps for reactions involving [Cp*RhCl2]2 and [Cp*IrCl2]2 are alkyne insertion and reductive elimination, respectively. When an alkyne bearing a small-sized and strong electron-donating substituent NMe2 is employed as a substrate, C–H activation becomes rate determining for both catalysts.

•A strong hydrogen bond between hypervalent iodine compounds and HF is found.•The hydrogen bonds between Ph(R)IF and HF are electrostatic-covalent in nature.•The stronger hydrogen bonds in complexes under study have higher covalency.•The favorable substituents enhance the electrostatic interaction of hydrogen bonds.•Altering oxidation states of the related atoms can help design new hydrogen bonds.For the first time, the intermolecular hydrogen bonding interactions between polyvalent iodine compounds and hydrogen fluoride (HF) have been studied using M06-2X/SDD-6-311++G(d, p) method. The computational results show that, compared with iodine(I) compound IF, both the iodine(III) compound Ph(Et)IF and the iodine(V) compound Ph(Et)3IF have strong hydrogen bonding interactions with HF and the binding energies are about -21.00 kcal/mol. Geometry analysis, natural bond orbital (NBO) analysis, energy decomposition analysis, electrostatic potential (ESP) analysis on molecular vdW surface and topological analysis for the bond critical points (BCPs) suggest that these strong interactions are not only electrostatic but also highly covalent in nature. In addition, our computational studies indicate that owing to the lower electronegativity of Cl and Br atoms relative to that of F atom, the compounds Ph(Et)ICl and Ph(Et)IBr have much weaker hydrogen bonding interactions with HF than Ph(Et)IF. Moreover, the electronic effects of substituents at the iodine center of the hypervalent iodine (III) compounds on the strength of the hydrogen bonds have also been studied and the results show that the alkyl groups such as methyl, ethyl, isopropyl and tert-butyl groups can enhance the hydrogen bonding interaction obviously relative to other types of substituents. And the hydrogen bond in complex Ph(iPr)IF⋯HF is very strong with binding energy of −22.44 kcal/mol.Download high-res image (122KB)Download full-size image

The first nickel-catalyzed intermolecular hydroacylation reaction of alkenes with simple aldehydes has been developed. This reaction offers a new approach to the selective preparation of branched ketones in high yields (up to 99%) and branched selectivities (up to 99:1). Experimental data provide evidence for reversible formation of acyl–nickel–alkyl intermediate, and DFT calculations show that the aldehyde C–H bond transfer to a coordinated alkene without oxidative addition is involved. The origin of the reactivity and regioselectivity of this reaction was also investigated computationally, which are consistent with experimental observations.

Samarium methoxide incorporating the ene-diamido ligand L(DME)Sm(μ-OMe)2Sm(DME)L (1; L = [DipNC(Me)C(Me)NDip]2–, Dip = 2,6-iPr2C6H3, and DME = 1,2-dimethoxyethane) has been prepared and structurally characterized. Complex 1 catalyzed the syndiospecific polymerization of styrene upon activation with phenylsilane and regioselective hydrosilylation of styrenes and nonactivated terminal alkenes. Unprecedented regioselectivity (>99.0%) for both types of alkenes has been achieved with the formation of Markovnikov and anti-Markovnikov products in high yields, respectively, whereas the polymerization of styrene resulted in the formation of syndiotactic silyl-capped oligostyrenes. The kinetic experiments and density functional theory calculations strongly support a samarium hydride intermediate generated by σ-bond metathesis of the Sm–OMe bond in 1 with PhSiH3. In addition, the observed regioselectvity for hydrosilylation and polymerization is consistent with the calculated energy profiles, which suggests that the bulky ene-diamido ligand and samarium hydride intermediate have important roles for regio- and stereoselectivity.

The mechanism of the rhodium-catalyzed cascade oxidative annulation of benzoylacetonitrile with alkynes is investigated using density functional theory calculations. The result shows that the reaction undergoes a stepwise annulation process, wherein the 1-naphthol acts as an intermediate. The first-step annulation involves the sp3 C–H bond cleavage, sp2 C–H bond cleavage, alkyne insertion into the Rh–C(sp2) bond, ketone enolization, and reductive elimination to produce the 1-naphthol intermediate. The second-step annulation involves the O–H cleavage, sp2 C–H bond cleavage, alkyne insertion into the Rh–C(sp2) bond, and C–O reductive elimination to generate the final product naphtho[1,8-bc]-pyran. The sp3 C–H bond cleavage rather than the sp2 C–H bond cleavage is found to be the rate-determining step of the catalytic cycle. The ketone enolization should occur before the reductive elimination. The substituent effects on the reactivities and regioselectivities of reactions are also analyzed. These calculation results shed light on some ambiguous suggestions from experiments.

A novel cyclization of 3-acyloxy-1,5-enynes is developed in the presence of PtI2 for the synthesis of substituted unsymmetrical m-terphenyls in good to excellent yields. Two unique steps are involved in this transformation, which includes the elimination of HOAc and benzyl group migration. DFT calculations indicated that the rate-determining step is the migration of the benzylic carbocation to form a zwitterionic intermediate followed by the elimination of HOAc. The subsequent cyclopropanation of the zwitterionic intermediate is the regioselectivity-determining step.

The first theoretical study on the mechanism of [RhCl(CO)2]2-catalyzed [5 + 1] cycloadditions of 3-acyloxy-1,4-enyne (ACE) and CO has been performed using density functional theory (DFT) calculations. The effect of ester on reactivity of this reaction has been investigated. The computational results have revealed that the preferred catalytic cycle involves the sequential steps of 1,2-acyloxy migration, CO insertion, reductive elimination to form ketene intermediate, 6π-electroncyclization, and aromatization to afford the resorcinol product. The 1,2-acyloxy migration is found to be the rate-determining step of the catalytic cycle. The electron-rich p-dimethylaminobenzoate substrate promotes 1,2-acyloxy migration and significantly increases the reactivity by stabilizing the positive charge building up in the oxocyclic transition state.The first theoretical study on the mechanism of [RhCl(CO)2]2-catalyzed [5 + 1] cycloadditions of 3-acyloxy-1,4-enyne (ACE) and CO has been performed using density functional theory (DFT) calculations. The electron-rich p-dimethylaminobenzoate substrate promotes 1,2-acyloxy migration and significantly increases the reactivity by stabilizing the positive charge building up in the oxocyclic transition state.

The ruthenium-Cp* picolyl-NHC complexes catalyzed transfer hydrogenation reaction has been investigated with the aid of density functional theory calculations at the B3LYP level of theory. Two kinds of “hydridic route” (inner sphere mechanism) and one “direct hydrogen transfer route” (Meerwein–Ponndorf–Verley mechanism) have been examined. From the results we conclude that the stepwise inner sphere mechanism would be favored from the energetic point of view. The hemilability of the picolyl group plays an important role in determining which mechanism the transfer hydrogenation reaction should be followed. And the effect of agostic interaction has also been discussed.

The mechanism of Rh-catalyzed (5+2) cycloadditions of 3-acyloxy-1,4-enyne (ACE) and alkynes is investigated using density functional theory calculations. The catalytic cycle involves 1,2-acyloxy migration, alkyne insertion, and reductive elimination to form the cycloheptatriene product. In contrast to the (5+2) cycloadditions with vinylcyclopropanes (VCPs), in which alkyne inserts into a rhodium–allyl bond, alkyne insertion into a Rh–C(sp2) bond is preferred. The 1,2-acyloxy migration is found to be the rate-determining step of the catalytic cycle. The electron-rich p-dimethylaminobenzoate substrate promotes 1,2-acyloxy migration and significantly increases the reactivity. In the regioselectivity-determining alkyne insertion step, the alkyne substituent prefers to be distal to the forming C–C bond and thus distal to the OAc group in the product.

Rh(I) carbenes were conveniently generated from readily available ynamides. These metal carbene intermediates could undergo metathesis with electron-rich or neutral alkynes to afford 2-oxopyrrolidines or be trapped by tethered alkenes to yield 3-azabicyclo[3.1.0]hexanes, a common skeleton in numerous bioactive pharmaceuticals. Although the scope of the former is limited, the latter reaction tolerates various substituted alkenes.

A systematic investigation of all possible isomers of fullerene derivatives C50X2 (X = H, F, Cl, Br, OH) has been performed using the semiempirical AM1 method. The equilibrium geometrical structures, heats of formation, HOMO–LUMO energy gaps, ionization potentials, electronic affinities, strain and aromaticity have been studied. The results indicate that the selection rule for two groups adding to fullerene C50 is independent of the type of functional group. The isomer-78, which corresponds to a 1,4-addition at the six-membered ring located on the equator, is the most stable isomer for C50X2 (X = H, F, Cl, Br, OH). The driving force governing the stabilities of the presently studied C50X2 isomers is the strain inherent in the C50 cage. The contribution of the conjugation effect to the stabilization is not able to compete with that of the strain. The more stable C50X2 isomers have larger ionization potentials and smaller electronic affinities compared with C50, which suggests that it is more difficult to oxidize and reduce C50X2 than to oxidize and reduce C50. Energies as well as HOMO–LUMO gaps of isostructural C50X2 (X = H, F, Cl, Br, OH) isomers are almost parallel, i.e., energy differences between isostructural isomers of any two kinds of C50X2 derivatives are constant. This phenomenon can be called H/F/Cl/Br/OH parallels, which may result from the same degree of perturbation for addition of different functional groups to the structure of the parent carbon cage. H/F parallels are generalized characteristics among not only isostructural isomers of fullerenes but also isostructural isomers of carbon nanotubes. Furthermore, it is predictable that general H/F/Cl/Br/OH… parallels may exist among various derivatives of other fullerenes and carbon nanotubes.

The 1,3-dipolar cycloaddition of methyl azide to C50 and the subsequent nitrogen elimination from the formed triazoline intermediate to yield the aziridine adduct have been studied using semiempirical AM1 methods. The results show that the cycloaddition of methyl azide to a [5,5] bond of C50 leading to a closed [5,5]-triazoline intermediate takes place through two stepwise pathways a and b: both of them starting from the formation of one C–N bond followed by the formation of the other C–N bond. The two pathways are competitive and the activation energy of each path is about 22 kcal mol−1. The subsequent thermal loss of N2 from the closed [5,5]-triazoline takes place through two paths, I and II: path I includes three steps while path II includes two steps. And path I is the preferred one with a total activation energy of approximately 41 kcal mol−1. There is also a pathway without the formation of triazoline, in which the formation of C–N bond between N3CH3 and C50 to give an intermediate is followed by the elimination of N2 together with the formation of the other C–N bond to form the closed [5,6]-C50NCH3, which is the preferred pathway among all the pathways with a total activation energy of about 14.5 kcal mol−1. It is expected that the closed [5,6]-C50NCH3 is the main product from addition of N3CH3 to C50. The closed [5,6]-C50NCH3 isomer is more stable than its closed [5,5] isomer. The isomerization activation energy from the closed [5,6] isomer to the [5,5] isomer is 53.6 kcal mol−1, and that for the reverse isomerization is 35.7 kcal mol−1. This result indicates that the conversion of the two isomers can hardly take place at room temperature and some day both of them can have the chance to be actually isolated experimentally.

A novel cyclization of 3-acyloxy-1,5-enynes is developed in the presence of PtI2 for the synthesis of substituted unsymmetrical m-terphenyls in good to excellent yields. Two unique steps are involved in this transformation, which includes the elimination of HOAc and benzyl group migration. DFT calculations indicated that the rate-determining step is the migration of the benzylic carbocation to form a zwitterionic intermediate followed by the elimination of HOAc. The subsequent cyclopropanation of the zwitterionic intermediate is the regioselectivity-determining step.

A systematic investigation of all possible isomers of fullerene derivatives C50X2 (X = H, F, Cl, Br, OH) has been performed using the semiempirical AM1 method. The equilibrium geometrical structures, heats of formation, HOMO–LUMO energy gaps, ionization potentials, electronic affinities, strain and aromaticity have been studied. The results indicate that the selection rule for two groups adding to fullerene C50 is independent of the type of functional group. The isomer-78, which corresponds to a 1,4-addition at the six-membered ring located on the equator, is the most stable isomer for C50X2 (X = H, F, Cl, Br, OH). The driving force governing the stabilities of the presently studied C50X2 isomers is the strain inherent in the C50 cage. The contribution of the conjugation effect to the stabilization is not able to compete with that of the strain. The more stable C50X2 isomers have larger ionization potentials and smaller electronic affinities compared with C50, which suggests that it is more difficult to oxidize and reduce C50X2 than to oxidize and reduce C50. Energies as well as HOMO–LUMO gaps of isostructural C50X2 (X = H, F, Cl, Br, OH) isomers are almost parallel, i.e., energy differences between isostructural isomers of any two kinds of C50X2 derivatives are constant. This phenomenon can be called H/F/Cl/Br/OH parallels, which may result from the same degree of perturbation for addition of different functional groups to the structure of the parent carbon cage. H/F parallels are generalized characteristics among not only isostructural isomers of fullerenes but also isostructural isomers of carbon nanotubes. Furthermore, it is predictable that general H/F/Cl/Br/OH… parallels may exist among various derivatives of other fullerenes and carbon nanotubes.