Pivalate Research Articles

Photoreactions on a Single Isolated TiO2 Nanocrystal on Au(111): Photodecomposition of TMAA

An atomically resolved study of an adsorbate photoreaction on the surface of an isolated TiO2 nanocrystal is reported. The crystal is grown in situ on Au(111) in an ultrahigh-vacuum chamber. The experiments use scanning tunneling microscopy (STM) backed by temperature-programmed desorption (TPD) to determine the surface coverage of trimethylacetic acid (TMAA) on the nanocrystal surfaces before and after irradiation with monochromated 305 nm UV light. A detailed determination of the surface structure of the 1–3 nm thick and 10–30 nm wide nanocrystals is presented and the importance of moiré effects in controlling the reaction sites shown. The normalized TMAA photodesorption quantum efficiency from Au-supported TiO2 nanocrystals was found to be ∼4 times lower compared to the same reaction on rutile TiO2(110) surface, a result consistent with the lower fraction of light adsorbed in the nanocrystals.

Electronic Structure of a Mixed-Metal Fluoride-Centered Triangle Complex: A Potential Qubit Component.

A novel fluoride-centered triangular-bridged carboxylate complex, [Ni2Cr(μ3-F)(O2C(t)Bu)6(HO2C(t)Bu)3] (1), is reported. Simple postsynthetic substitution of the terminal pivalic acids in 1 with pyridine and 4-methylpyridine led to the isolation of [Ni2Cr(μ3-F)(O2C(t)Bu)6(C5H5N)3] (2) and [Ni2Cr(μ3-F)(O2C(t)Bu)6((4-CH3)C5H4N)3] (3). Structural and magnetic characterizations carried out on the series reveal a dominating antiferromagnetic interaction between the nickel and chromium centers leading to an S = (1)/2 ground state with a very unusual value of geff = 2.48.

Synthesis of Donor–Acceptor Polymers Containing Thiazolo[5,4-d]thiazole Units via Palladium-Catalyzed Direct Arylation Polymerization

This paper reports the synthesis of alternating donor–acceptor copolymers (DA polymers) containing thiazole units via palladium-catalyzed direct arylation polymerization (DArP), which has recently emerged as a viable alternative to conventional cross-coupling polycondensations. While thiazole-based C–H monomers such as benzodithiazole and thiazolothiazole are poorly reactive toward DArP, thiazolothiazoles (TzTz) capped with 5-bromothienyl and thienyl groups at the 2,5-positions, 2,5-bis[5-bromo-3-(2-octyldodecyl)thiophene-2-yl]thiazolo[5,4-d]thiazole (1-Br) and 2,5-bis[3-(2-octyldodecyl)thiophene-2-yl]thiazolo[5,4-d]thiazole (1-H), successfully react with C–H and C–Br monomers, respectively. The reactions proceed in THF at 100 °C in the presence of Pd2(dba)3 and P(2-MeOC6H4)3 (L1) as catalyst precursors and pivalic acid and Cs2CO3 as additives to afford TzTz-containing DA polymers with high molecular weight (Mn up to 88 100) and good solubility in almost quantitative yields. A high-temperature NMR analysi...

Synthesis, Structure, and Magnetic Properties of Phosphinate‐Bridged Hexanuclear FeIII Complexes Containing Two Butterfly‐Shaped Fe3O Cores

AbstractThe reaction of FeIII salts with 1,1,2,3,3‐pentamethyltrimethylenephosphinic acid [cycPO2H] or dicyclohexylphosphinic acid [(C6H11)2PO2H] along with pivalic acid in the presence of triethylamine leads to the formation of two hexanuclear iron(III) clusters: [FeIII6(μ3‐O)2(μ‐OH)2(μ‐cycPO2)6(μ‐tBuCO2)6(η1‐tBuCO2H)2]·4CH3CN·3CH2Cl2 (1) and [FeIII6(μ3‐O)2(μ‐OH)2{μ‐(C6H11)2PO2}6(μ‐tBuCO2)6(η1‐OH2)2]·2CH3CN·CH2Cl2 (2). These complexes are made up of two butterfly‐shaped {FeIII3O} subunits that are joined to each other by two bridging phosphinate ligands. In addition, the formation of 1 and 2 is assisted by μ3‐O, μ‐OH, and pivalate ligands. Variable‐temperature magnetic susceptibility measurements of complexes 1 and 2 reveal medium to strong antiferromagnetic interactions between the FeIII ions inside the Fe3O subunits and weak inter‐trinuclear antiferromagnetic interactions through the bridging phosphinate ligands. The triangular topology of the Fe3O subunits gives rise to competing antiferromagnetic interactions and spin frustration. The different relative magnitudes of the competing interactions leads to S = 5/2 and S = 1/2 ground spin states for the Fe3O subunits in 1 and 2, respectively.

A high-nuclearity [Cu6Cd4] antiferromagnet with a supertetrahedral configuration

A heterometallic coordination cluster with the formula of {[Cu6Cd4(HL)4(piv)8(H2O)6]·4MeOH} (1, H4L=pentaerythritol, Hpiv=pivalic acid) has been synthesized. Compound 1 crystallizes in the tetragonal space group I-4, and consists of a supertetrahedral cage with four Cd(II) and six Cu(II) ions held together by μ3-O bridges. Magnetic susceptibility exhibits that compound 1 is an antiferromagnet.

Two high-nuclearity homo-/hetero-metallic magnetic materials based on a tripodal alcohol

Two new polynuclear d-metal clusters based on pentaerythritol (H4L), [Mn12] (1) and [Mn10Cd2] (2) for short, were obtained from the reaction of H4L, transition-metal salt and pivalic acid (Hpiv) in the mixed solvent under ambient conditions. Compound 1 crystallizes in the triclinic space group P1¯, and consists of a dodecanuclear mixed-valent [MnIII4MnII8] cluster. When Cd(NO3)2·4H2O was introduced into the reaction, compound 2 was resulted in, which displays the similar structural feature as compound 1, fabricating a dodecanuclear heterometallic [MnIII4MnII6CdII2] cluster, but crystallizes in the monoclinic space group P21/c. Interestingly, there are two μ5-O bridges present in this structure, and it is rare. Magnetic susceptibilities of compounds 1 and 2 were measured, and antiferromagnetic interactions between metal centers were observed.

Nona- and undecanuclear nickel phosphonate cages

The bulky phosphonate ligands CarbmPO3H2 (((9H-carbazol-9-yl)methyl)phosphonic acid) and CarbePO3H2 ((2-(9H-carbazol-9-yl)ethyl)phosphonic acid) were employed to construct cages [Ni9{(py)2CO2}2(CarbmPO3)4(tBuCO2)6(tBuCO2H)2(CH3CN)2] 1 and [Ni11{(py)2CO2}2(CarbePO3)4(tBuCO2)10(CH3CN)2] 2 with (py)2CO (di-2-pyridyl ketone) and Hpiv (pivalic acid) as coligands under solvothermal conditions. The metallic cores of cages 1 and 2 display vertex-sharing tetragonal pyramidal and tetra-capped octahedral arrangements, respectively. Magnetic property measurements indicate the coexistence of antiferromagnetic and ferromagnetic interactions between nickel centers for both cages.

An Enantioselective Total Synthesis of (-)-Isoschizogamine.

A concise enantioselective total synthesis of (-)-isoschizogamine, a complex bridged polycyclic monoterpene indole alkaloid, was accomplished. N-Alkylation of an enantio-enriched imine with an alkyl iodide afforded an iminium salt, which, upon heating by microwave irradiation in the presence of pivalic acid, was converted into the hexacyclic structure of natural product by a complex but ordered domino sequence. The one-pot process leading to the formation of one C-C bond and three C-N bonds created three rings and three contiguous stereogenic centers with complete control of both the relative and absolute stereochemistry.

An Enantioselective Total Synthesis of (−)‐Isoschizogamine

AbstractA concise enantioselective total synthesis of (−)‐isoschizogamine, a complex bridged polycyclic monoterpene indole alkaloid, was accomplished. N‐Alkylation of an enantio‐enriched imine with an alkyl iodide afforded an iminium salt, which, upon heating by microwave irradiation in the presence of pivalic acid, was converted into the hexacyclic structure of natural product by a complex but ordered domino sequence. The one‐pot process leading to the formation of one CC bond and three CN bonds created three rings and three contiguous stereogenic centers with complete control of both the relative and absolute stereochemistry.

Origin of Coverage Dependence in Photoreactivity of Carboxylate on TiO2(110): Hindering by Charged Coadsorbed Hydroxyls

The influence of reactant coverage on photochemical activity was explored using scanning tunneling microscopy (STM) and ultraviolet photoelectron spectroscopy (UPS). We observed diminished reactivity of carboxylate species (trimethyl acetate, TMA) on TiO2(110) as a function of increasing coverage. This effect was not linked to intermolecular interactions of TMA but to the accumulation of the coadsorbed bridging hydroxyls (HOb) deposited during (thermal) dissociative adsorption of the parent, trimethylacetic acid (TMAA). Confirmation of the hindering influence of HOb groups was obtained by the observation that HOb species originated from H2O dissociation at O-vacancy sites have a similar hindering effect on TMA photochemistry. Though HOb’s are photoinactive on TiO2(110) under ultrahigh vacuum conditions, UPS results show that these sites trap photoexcited electrons, which in turn likely (electrostatically) attract and neutralize photoexcited holes, thus suppressing the hole-mediated photoreactivity of TMA....

Decanuclear Ln10 Wheels and Vertex‐Shared Spirocyclic Ln5 Cores: Synthesis, Structure, SMM Behavior, and MCE Properties

The reaction of a Schiff base ligand (LH3) with lanthanide salts, pivalic acid and triethylamine in 1:1:1:3 and 4:5:8:20 stoichiometric ratios results in the formation of decanuclear Ln10 (Ln = Dy (1), Tb (2), and Gd (3)) and pentanuclear Ln5 complexes (Ln = Gd (4), Tb (5), and Dy (6)), respectively. The formation of Ln10 and Ln5 complexes are fully governed by the stoichiometry of the reagents used. Detailed magnetic studies on these complexes (1-6) have been carried out. Complex 1 shows a SMM behavior with an effective energy barrier for the reversal of the magnetization (Ueff) = 16.12(8) K and relaxation time (τo) = 3.3×10(-5) s under 4000 Oe direct current (dc) field. Complex 6 shows the frequency dependent maxima in the out-of-phase signal under zero dc field, without achieving maxima above 2 K. Complexes 3 and 4 show a large magnetocaloric effect with the following characteristic values: -ΔSm = 26.6 J kg(-1) K(-1) at T = 2.2 K for 3 and -ΔSm = 27.1 J kg(-1) K(-1) at T = 2.4 K for 4, both for an applied field change of 7 T.

Microwave synthesis of dirhenium paddlewheel complexes

Tetrakis(carboxylato)dihalidodirhenium (III,III) complexes were efficiently synthesized utilizing microwave irradiation. Re2(acetate)4X2, Re2(butyrate)4X2, and Re2(pivalate)4X2, where X = Cl or Br, were produced in under one hour in the microwave with comparable yields to traditional refluxes which take as long as four days. All reaction samples were prepared under inert gas and the septa caps of the microwave reaction vessels were sufficient to maintain this environment during the reaction. Re2(acetate)4X2 and Re2(butyrate)4X2 were synthesized from the (Bu4N)2[Re2X8] salt, the acid, the anhydride, and in some cases hexanes. Re2(pivalate)4X2, traditionally prepared via melt reactions, were synthesized from the (Bu4N)2[Re2X8] salt and pivalic acid combined in diglyme or diglyme and hexanes.

A bulky oxime for the synthesis of Mn(III) clusters

The reaction between Mn(OAc)2·4H2O and Br-saoH2 (=5-Br-salicylaldoxime) in EtOH in the presence of NMe4OH led to the formation of the hexanuclear cluster [Mn6O2(Br-sao)6(OAc)2(H2O)2(EtOH)2]·2.8H2O·2.2EtOH (1). Switching from Mn(OAc)2·4H2O to Mn(ClO4)2·6H2O, the same reaction upon addition of pivH (= trimethyl acetic acid) yielded [Mn6O2(Br-sao)6(piv)2(H2O)2(EtOH)2]·6EtOH (2 6EtOH), and finally upon changing pivH to NaO2CPh, we were able to isolate [Mn6Na2O2(Br-sao)6(O2CPh)4(H2O)2(EtOH)4]·6EtOH (3 6EtOH). Clusters 1 and 2 6EtOH describe “typical” [Mn6/oximate] complexes consisting of two {Mn3} oxo-centered triangular units bridged by oximate groups, while in 3 6EtOH these triangular motifs are separated by two sodium cations. An investigation into the magnetic properties of all three clusters revealed the presence of dominant antiferromagnetic interactions, leading to ground states of S = 4 and 2 for 1 and 3, respectively. Finally, cluster 2 6EtOH functions as a single-molecule magnet with Ueff = 27.54 K.

ChemInform Abstract: Palladium(II)‐Catalyzed Directed Trifluoromethylthiolation of Unactivated C(sp3)—H Bonds.

ChemInformVolume 46, Issue 35 Preparative Organic Chemistry ChemInform Abstract: Palladium(II)-Catalyzed Directed Trifluoromethylthiolation of Unactivated C(sp3)—H Bonds. Heng-Ying Xiong, Heng-Ying Xiong INSA Rouen, CNRS UMR, Univ. Rouen, F-76821 Mont Saint Aignan, Fr.Search for more papers by this authorTatiana Besset, Tatiana Besset INSA Rouen, CNRS UMR, Univ. Rouen, F-76821 Mont Saint Aignan, Fr.Search for more papers by this authorDominique Cahard, Dominique Cahard INSA Rouen, CNRS UMR, Univ. Rouen, F-76821 Mont Saint Aignan, Fr.Search for more papers by this authorXavier Pannecoucke, Xavier Pannecoucke INSA Rouen, CNRS UMR, Univ. Rouen, F-76821 Mont Saint Aignan, Fr.Search for more papers by this author Heng-Ying Xiong, Heng-Ying Xiong INSA Rouen, CNRS UMR, Univ. Rouen, F-76821 Mont Saint Aignan, Fr.Search for more papers by this authorTatiana Besset, Tatiana Besset INSA Rouen, CNRS UMR, Univ. Rouen, F-76821 Mont Saint Aignan, Fr.Search for more papers by this authorDominique Cahard, Dominique Cahard INSA Rouen, CNRS UMR, Univ. Rouen, F-76821 Mont Saint Aignan, Fr.Search for more papers by this authorXavier Pannecoucke, Xavier Pannecoucke INSA Rouen, CNRS UMR, Univ. Rouen, F-76821 Mont Saint Aignan, Fr.Search for more papers by this author First published: 13 August 2015 https://doi.org/10.1002/chin.201535073Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume46, Issue35September, 2015 RelatedInformation

Ability ofTiO2(110)surface to be fully hydroxylated and fully reduced

Many $\mathrm{Ti}{\mathrm{O}}_{2}$ applications (e.g., in heterogeneous catalysis) involve contact with ambient atmosphere and/or water. The resulting hydroxylation can significantly alter its surface properties. While the behavior of a single, isolated OH species on the model metal oxide surface of rutile $\mathrm{Ti}{\mathrm{O}}_{2}(110)$ is relatively well understood, much less is known regarding highly hydroxylated surfaces and/or whether $\mathrm{Ti}{\mathrm{O}}_{2}(110)$ could be fully hydroxylated under ultrahigh vacuum conditions. Here we report the in situ formation of a well-ordered, fully hydroxylated $\mathrm{Ti}{\mathrm{O}}_{2}(110)\ensuremath{-}(1\ifmmode\times\else\texttimes\fi{}1)$ surface using an enhanced photochemical approach, the key parts of which are predosing of water and multistep dissociative adsorption and subsequent photolysis of the carboxylic (trimethyl acetic) acid. Combining scanning tunneling microscopy, ultraviolet photoelectron spectroscopy, and density functional theory results, we show that the attained ``super OH'' surface is also fully reduced, as a result of the photochemical charging of electron traps associated with the OH groups.

Engineered and Native Coenzyme B12-dependent Isovaleryl-CoA/Pivalyl-CoA Mutase

Adenosylcobalamin-dependent isomerases catalyze carbon skeleton rearrangements using radical chemistry. We have recently demonstrated that an isobutyryl-CoA mutase variant, IcmF, a member of this enzyme family that catalyzes the interconversion of isobutyryl-CoA and n-butyryl-CoA also catalyzes the interconversion between isovaleryl-CoA and pivalyl-CoA, albeit with low efficiency and high susceptibility to inactivation. Given the biotechnological potential of the isovaleryl-CoA/pivalyl-CoA mutase (PCM) reaction, we initially attempted to engineer IcmF to be a more proficient PCM by targeting two active site residues predicted based on sequence alignments and crystal structures, to be key to substrate selectivity. Of the eight mutants tested, the F598A mutation was the most robust, resulting in an ∼17-fold increase in the catalytic efficiency of the PCM activity and a concomitant ∼240-fold decrease in the isobutyryl-CoA mutase activity compared with wild-type IcmF. Hence, mutation of a single residue in IcmF tuned substrate specificity yielding an ∼4000-fold increase in the specificity for an unnatural substrate. However, the F598A mutant was even more susceptible to inactivation than wild-type IcmF. To circumvent this limitation, we used bioinformatics analysis to identify an authentic PCM in genomic databases. Cloning and expression of the putative AdoCbl-dependent PCM with an α2β2 heterotetrameric organization similar to that of isobutyryl-CoA mutase and a recently characterized archaeal methylmalonyl-CoA mutase, allowed demonstration of its robust PCM activity. To simplify kinetic analysis and handling, a variant PCM-F was generated in which the αβ subunits were fused into a single polypeptide via a short 11-amino acid linker. The fusion protein, PCM-F, retained high PCM activity and like PCM, was resistant to inactivation. Neither PCM nor PCM-F displayed detectable isobutyryl-CoA mutase activity, demonstrating that PCM represents a novel 5'-deoxyadenosylcobalamin-dependent acyl-CoA mutase. The newly discovered PCM and the derivative PCM-F, have potential applications in bioremediation of pivalic acid found in sludge, in stereospecific synthesis of C5 carboxylic acids and alcohols, and in the production of potential commodity and specialty chemicals.

Cerium(IV) Hexanuclear Clusters from Cerium(III) Precursors: Molecular Models for Oxidative Growth of Ceria Nanoparticles.

Reactions of cerium(III) nitrate, Ce(NO3 )3 ⋅6 H2 O, with different carboxylic acids, such as pivalic acid, benzoic acid, and 4-methoxybenzoic acid, in the presence of a tridentate N,N,N-donor ligand, diethylenetriamine (L(1) ), under aerobic conditions yielded the corresponding cerium hexamers Ce6 O8 (O2 CtBu)8 (L(1) )4 (1), Ce6 O8 (O2 CC6 H5 )8 (L(1) )4 (2), and Ce6 O8 (O2 CC6 H4 -4-OCH3 )8 (L(1) )4 (3). Hexamers 1, 2, and 3 contain the same octahedral Ce(IV) 6 O8 core, in which all interstitial oxygen atoms are connected by μ3 -oxo bridging ligands. In contrast, treatment of the Ce(IV) precursor (NH4 )2 Ce(NO3 )6 (CAN) with pivalic acid and the ligand L(1) under the same conditions afforded Ce6 O4 (OH)4 (O2 CtBu)12 (L(1) )2 (4), exhibiting a deformed octahedral Ce(IV) 6 O4 (OH)4 core containing μ3 -oxo and μ3 -hydroxo moieties in defined positions. In contrast to the formation of 1-3, the use of N-methyldiethanolamine (L) in the reaction with Ce(NO3 )3 ⋅6 H2 O and pivalic acid afforded a previously reported Ce(III) dinuclear cluster, Ce2 (O2 CtBu)6 L2 , even in the presence of dioxygen. ESI-MS analysis of the reaction mixture clearly indicated the importance of the ligand L(1) in promoting oxidation of the Ce(III) aggregates, [Cen (O2 CtBu)3n (L(1) )2 ], which is necessary for the formation of Ce(IV) hexamers.

Efficient Palladium-Catalyzed C-H Fluorination of C(sp3)-H Bonds: Synthesis of β-Fluorinated Carboxylic Acids.

A novel and facile process for direct fluorination of unactivated C(sp3)-H bonds at the β position of carboxylic acids was accomplished by a palladium(II)-catalyzed C-H activation. The addition of Ag2O and pivalic acid was found to be crucial for the success of this transformation. This reaction provides a versatile strategy for the synthesis of β-fluorinated carboxylic acids.

Nickel-Catalyzed Insertion of Alkynes and Electron-Deficient Olefins into Unactivated sp(3) C-H Bonds.

Insertion of unsaturated systems such as alkynes and olefins into unactivated sp(3) C-H bonds remains an unexplored problem. We herein address this issue by successfully incorporating a wide variety of functionalized alkynes and electron-deficient olefins into the unactivated sp(3) C-H bond of pivalic acid derivatives with excellent syn- and linear- selectivity. A strongly chelating 8-aminoquinoline directing group proved beneficial for these insertion reactions, while an air-stable and inexpensive Ni(II) salt has been employed as the active catalyst.

Pd/Pivalic Acid Mediated Direct Arylation of 2‐Pyrones and Related Heterocycles

AbstractDirect arylation represents a favourable alternative to traditional cross‐coupling reactions and has found widespread use with simple aryls and robust heterocycles. Herein a direct arylation protocol has been optimised and applied to more delicate, privileged biological motifs. The intramolecular direct arylation of 2‐pyrones, 2‐coumarins, 2‐pyridones and 2‐quinolones occurs in very good to excellent yields using a Pd0 source and pivalic acid as a crucial additive. Preliminary mechanistic investigations were also carried out.