Molecular structures of M(Bu(t))3 (M = Al, Ga, In) using gas-phase electron diffraction and ab initio calculations: experimental and computational evidence for charge-transfer processes leading to photodissociation

The gas-phase structures of AI(Bu')3 and Ga(Bu')3 have been investigated by electron diffraction and are shown to consist of monomeric units with very slightly pyramidal geometries. Salient structural parameters (r(hl)) include r(A1-C) = 2.008(2) A and r(Ga-C) = 2.032(2) A. For both compounds the ligand orientations and geometries are controlled by interligand interactions. The structures of M(Bu(t))3 (M = Al, Ga, In) have been calculated ab initio and those for the aluminium and gallium derivatives are in good agreement with the electron-diffraction structures. Comparison of the ab initio calculated structure of In(Bu')3 with those of Al(Bu(t))3 and Ga(Bu(t))3 suggests that the significantly different photochemistry exhibited by the former does not result from structural factors. In fact the compounds undergo a charge-transfer process in the UV region, with the wavelength required calculated to be slightly longer for the indium compound than for the other two.     

Tetrathiophenalenyl radical and its disulfide-bridged dimer

The presence of two disulfide groups in the tetrathiophenalenyl radical TTPLY leads to a highly delocalized spin distribution and the lowest cell potential ever observed for a monofunctional phenalenyl derivative. While the heteroatom substituents successfully block C-C bond formation, TTPLY nonetheless associates in the solid state to afford the hypervalent S-S-bonded dimer (TTPLY)2.     

Efficient palladium/1,10-phenanthroline-catalyzed reductive carbonylation of mono- and dinitroarenes to urethanes in phosphonium salt ionic liquids

The highly reactive and selective reductive carbonylation of mono- and dinitroarenes to the corresponding mono- and diurethanes was carried out in the presence of a PdCl2/Phen catalytic system, using PSIL110[C14H29(C6H13)3P(+)PF6(-)] as the ionic liquid under mild reaction conditions. No cocatalyst is required.     

Accessing low denticity coordination modes of a high denticity tripodal ligand to complete its coordinative repertoire

New coordination complexes of the neutral tripodal tetra-amine Me(6)TREN with tBu(3)Ga or tBu(2)Zn have been synthesised and studied with their molecular structures revealing, for the first time, coordination to metal centres via an η(1) or η(2) mode, adding to previously reported η(3) and η(4) ligated examples.     

After-effects of lithium-mediated alumination of 3-iodoanisole: isolation of molecular salt elimination and trapped-benzyne products

Gaining a deeper understanding of the modus operandi of heterometallic lithium aluminate bases towards deprotonative metallation of substituted aromatic substrates, we have studied the reactions and their aftermath between our recently developed bis-amido base '(i)Bu(2)Al(μ-TMP)(2)Li'3 and 3-halogenated anisoles. Ortho-metallation of 3-iodoanisole with 3 results in a delicately poised heterometallic intermediate whose breakdown into homometallic species and benzyne cannot be suppressed, even at low temperature or in a non-polar solvent (hexane). Homometallic components [LiI·TMP(H)](4) (5) and (i)Bu(2)Al(TMP)·THF (6) have been isolated while the reactive benzyne intermediate has been trapped via Diels-Alder cyclization with 1,3-diphenylisobenzofuran yielding 1-methoxy-9-10-diphenyl-9-10-epoxyanthracene (7). In polar THF solution, nucleophilic addition of LiTMP across the benzyne functionality followed by electrophilic quenching with iodine yields the trisubstituted aromatic species 1-(2-iodo-3-methoxyphenyl)-2,2,6,6-tetramethylpiperidide (8). Compounds 5-8 have been characterized by single-crystal X-ray diffraction in the solid state and multinuclear NMR spectroscopy in solution. By considering these collated results, a plausible reaction mechanism has been proposed for the breakdown of the aforementioned intermediate bimetallic framework. Interestingly, the metallation reaction can be controlled by changing to 3-chloroanisole with an excess of base 3, as evidenced by electrophilically trapping the deprotonated aromatic with iodine to give 2-iodo-3-chloroanisole (9).     

Synthesis of High Molecular Weight Polyesters via In Vacuo Dehydrogenation Polymerization of Diols

The Milstein catalyst has proven to be highly effective for the conversion of alcohols to esters, as well as alcohols and amines to amides and polyamides. We have recently found that the catalyst's range can be extended to very efficient in vacuo dehydrogenation polymerization of α,ω‐diols to generate polyesters. The gaseous hydrogen byproduct that is produced is easily removed to drive the equilibrium toward product, which leads to the formation of high molecular weight polymer ( up to 145 000 g mol⁻¹). This optimized methodology works well to polymerize diols with a spacer of six carbons or more. Diols with fewer carbons are cyclized to lactone; the dividing point is the dehydrogenation of 1,5‐pentanediol, which leads to a mixture of polyester and lactone. Reported herein is the synthesis and characterization of five aliphatic polyesters prepared via this novel dehydrogenation polymerization approach.     

Measurement of volatile organic compounds emitted in libraries and archives: an inferential indicator of paper decay?

Background

A sampling campaign of indoor air was conducted to assess the typical concentration of indoor air pollutants in 8 National Libraries and Archives across the U.K. and Ireland. At each site, two locations were chosen that contained various objects in the collection (paper, parchment, microfilm, photographic material etc.) and one location was chosen to act as a sampling reference location (placed in a corridor or entrance hallway).

Results

Of the locations surveyed, no measurable levels of sulfur dioxide were detected and low formaldehyde vapour (< 18???g?m^-3) was measured throughout. Acetic and formic acids were measured in all locations with, for the most part, higher acetic acid levels in areas with objects compared to reference locations. A large variety of volatile organic compounds (VOCs) was measured in all locations, in variable concentrations, however furfural was the only VOC to be identified consistently at higher concentration in locations with paper-based collections, compared to those locations without objects. To cross-reference the sampling data with VOCs emitted directly from books, further studies were conducted to assess emissions from paper using solid phase microextraction (SPME) fibres and a newly developed method of analysis; collection of VOCs onto a polydimethylsiloxane (PDMS) elastomer strip.

Conclusions

In this study acetic acid and furfural levels were consistently higher in concentration when measured in locations which contained paper-based items. It is therefore suggested that both acetic acid and furfural (possibly also trimethylbenzenes, ethyltoluene, decane and camphor) may be present in the indoor atmosphere as a result of cellulose degradation and together may act as an inferential non-invasive marker for the deterioration of paper. Direct VOC sampling was successfully achieved using SPME fibres and analytes found in the indoor air were also identified as emissive by-products from paper. Finally a new non-invasive, method of VOC collection using PDMS strips was shown to be an effective, economical and efficient way of examining VOC emissions directly from the pages of a book and confirmed that toluene, furfural, benzaldehyde, ethylhexanol, nonanal and decanal were the most concentrated VOCs emitted directly from paper measured in this study.     

Investigating magnetostructural correlations in the pseudooctahedral trans-[Ni(II){(OPPh2)(EPPh2)N}2(sol)2] complexes (E = S, Se; sol = DMF, THF) by magnetometry, HFEPR, and ab initio quantum chemistry

In this work, magnetometry and high-frequency and -field electron paramagnetic resonance spectroscopy (HFEPR) have been employed in order to determine the spin Hamiltonian (SH) parameters of the non-Kramers, S = 1, pseudooctahedral trans-[Ni(II){(OPPh(2))(EPPh(2))N}(2)(sol)(2)] (E = S, Se; sol = DMF, THF) complexes. X-ray crystallographic studies on these compounds revealed a highly anisotropic NiO(4)E(2) coordination environment, as well as subtle structural differences, owing to the nature of the Ni(II)-coordinated solvent molecule or ligand E atoms. The effects of these structural characteristics on the magnetic properties of the complexes were investigated. The accurately HFEPR-determined SH zero-field-splitting (zfs) D and E parameters, along with the structural data, provided the basis for a systematic density functional theory (DFT) and multiconfigurational ab initio computational analysis, aimed at further elucidating the electronic structure of the complexes. DFT methods yielded only qualitatively useful data. However, already entry level ab initio methods yielded good results for the investigated magnetic properties, provided that the property calculations are taken beyond a second-order treatment of the spin-orbit coupling (SOC) interaction. This was achieved by quasi-degenerate perturbation theory, in conjunction with state-averaged complete active space self-consistent-field calculations. The accuracy in the calculated D parameters improves upon recovering dynamic correlation with multiconfigurational ab initio methods, such as the second-order N-electron valence perturbation theory NEVPT2, the difference dedicated configuration interaction, and the spectroscopy-oriented configuration interaction. The calculations showed that the magnitude of D (～3-7 cm(-1)) in these complexes is mainly dominated by multiple SOC contributions, the origin of which was analyzed in detail. In addition, the observed largely rhombic regime (E/D = 0.16-0.33) is attributed to the highly distorted metal coordination sphere. Of special importance is the insight by this work on the zfs effects of Se coordination to Ni(II). Overall, a combined experimental and theoretical methodology is provided, as a means to probe the electronic structure of octahedral Ni(II) complexes.     

Synthesis and the thermal and catalytic dehydrogenation reactions of amine-thioboranes

A series of trimethylamine-thioborane adducts, Me(3)N·BH(2)SR (R = tBu [2a], nBu [2b], iPr [2c], Ph [2d], C(6)F(5) [2e]) have been prepared and characterized. Attempts to access secondary and primary amine adducts of thioboranes via amine-exchange reactions involving these species proved unsuccessful, with the thiolate moiety shown to be vulnerable to displacement by free amine. However, treatment of the arylthioboranes, [BH(2)-SPh](3) (9) and C(6)F(5)SBH(2)·SMe(2) (10) with Me(2)NH and iPr(2)NH successfully yielded the adducts Me(2)NH·BH(2)SR (R = Ph [11a], C(6)F(5) [12a]) and iPr(2)NH·BH(2)SR (R = Ph [11b], C(6)F(5) [12b]) in high yield. These adducts were also shown to be accessible via thermally induced hydrothiolation of the aminoboranes Me(2)N═BH(2), derived from the cyclic dimer [Me(2)N-BH(2)](2) (13), and iPr(2)N═BH(2) (14), respectively. Attempts to prepare the aliphatic thiolate substituted adducts R(2)NH·BH(2)SR' (R = Me, iPr; R' = tBu, nBu, iPr) via this method, however, proved unsuccessful, with the temperatures required to facilitate hydrothiolation also inducing thermal dehydrogenation of the amine-thioborane products to form aminothioboranes, R(2)N═BH(SR'). Thermal and catalytic dehydrogenation of the targeted amine-thioboranes, 11a/11b and 12a/12b were also investigated. Adducts 11b and 12b were cleanly dehydrogenated to yield iPr(2)N═BH(SPh) (22) and iPr(2)N═BH(SC(6)F(5)) (23), respectively, at 100 °C (18 h, toluene), with dehydrogenation also possible at 20 °C (42 h, toluene) with a 2 mol % loading of [Rh(μ-Cl)cod](2) in the case of the former species. Similar studies with adduct 11a evidenced a competitive elimination of H(2) and HSPh upon thermolysis, and other complex reactivity under catalytic conditions, whereas the fluorinated analogue 12a was found to be resistant to dehydrogenation.