Supramolecular engineering through temperature-induced chemical modification of 2H-tetraphenylporphyrin on Ag(111): flat phenyl conformation and possible dehydrogenation reactions

Scratching the surface: Formation of a monolayer of 2H-tetraphenylporphyrins (2H-TPP) on Ag(111), either by sublimation of a multilayer in the range 525-600?K or by annealing (at the same temperature) a monolayer deposited at room temperature, induces a chemical modification of the molecules. Rotation of the phenyl rings into a flat conformation is observed and tentatively explained, by using DFT calculations, as a peculiar reaction due to molecular dehydrogenation.     

S‐Alkylation of Soft Scorpionates

The alkylation reactions of soft scorpionates are reported. The hydrotris(S‐alkyl‐methimazolyl)borate dications (alkyl=methyl, allyl, benzyl), which were prepared by the reaction of Tm^Me anion and primary alkyl halides, have been isolated and structurally characterised. The reaction is, however, not universally successful. DFT analysis of these alkylation reactions (C?S versus B? H alkylation) indicates that the observed outcome is driven by kinetic factors. Extending the study to incorporate alternative imine thiones (mercaptobenzothiazole, bz; thiazoline, tz) led to the structural characterisation of di[aquo‐μ‐aquohydrotris(mercaptobenzothiazolyl)boratosodium], which contains sodium atoms in the κ³‐S,S,S coordination mode. Alkylation of Na[Tbz] and Na[tzTtz] leads to decomposition resulting in the formation of the simple S‐alkylated heterocycles. The analysis of the species involved in these reactions shows an inherent weakness in the B? N bond in soft scorpionates, which has implications for their use in more advanced chemistry.     

Stereodynamics of bond rotation in tertiary 1-naphthoic acid amides: a computational study

Computations sho that independent N-CO rotation is not possible in N,N-diethyl-1-naphthamide, and that the coalescence signal corresponding to methyl equivalence observed in the VT NMR spectrum of this system is caused by a complex process whose rate-determining step implies concerted N-CO, Ar-CO, and ethyl rotations. The calculated Gibbs energy barriers for these processes in solution are in good agreement with the experimental values.     

Cobalt-mediated [2+2+2] cycloaddition versus C-H and N-H activation of 2-pyridones and pyrazinones with alkynes: a theoretical study

DFT computations have been executed aimed at illuminating the variety of pathways by which pyridones react with alkynes in the presence of [CpCoL(2)]: NH-2-pyridones furnish N-dienylated ligands (N-H activation pathway), N-methyl-2-pyridones are converted into ligated cyclohexadienes ([2+2+2] cocycloaddition pathway), and N-alkynyl-2-pyridones may undergo either [2+2+2] cocycloaddition or C-dienylation (C-H activation), depending on the length of the tether. The calculations predict the formation of the experimentally observed products, including their regio- and stereochemical make up. In addition, the unusual regiochemical outcome of the all-intramolecular [2+2+2] cycloaddition of N,N'-dipentynylpyrazinedione was rationalized by computation, which led to the discovery of a new mechanism.     

Aldehyde‐Assisted Hydrogen Transfer during the Formation of Hydride–Iridafurans from Alkynes and Aldehydes

The bis(ethylene) Ir^I complex [TpIr(C₂H₄)₂] ( 1 ; Tp=hydrotris(3,5‐dimethylpyrazolyl)borate) reacts with two equivalents of aromatic or aliphatic aldehydes in the presence of one equivalent of dimethyl acetylenedicarboxylate (DMAD) with ultimate formation of hydride iridafurans of the formula [TpIr(H){C(R¹)?C(R²)C(R³)O }] (R¹=R²=CO₂Me; R³=alkyl, aryl; 3 ). Several intermediates have been observed in the course of the reaction. It is proposed that the key step of metallacycle formation is a C? C coupling process in the undetected Ir^I species [TpIr{η¹‐O‐R³C(?O)H}(DMAD)] ( A ) to give the trigonal‐bipyramidal 16 e^? Ir^III intermediates [TpIr{C(CO₂Me)?C(CO₂Me)C(R³)(H)O }] ( C ), which have been trapped by NCMe to afford the adducts 11 (R³=Ar). If a second aldehyde acts as the trapping reagent for these species, this ligand acts as a shuttle in transfering a hydrogen atom from the γ‐ to the α‐carbon atom of the iridacycle through the formation of an alkoxide group. Methyl propiolate (MP) can be used instead of DMAD to regioselectively afford the related iridafurans. These reactions have also been studied by DFT calculations.     

A comprehensive theoretical study on the reactions of Sc+ with CnH2n+2 (n=1-3): structure,mechanism, and potential-energy surface

The reactions of Sc(+)((3)D) with methane, ethane, and propane in the gas phase were studied theoretically by density functional theory. The potential energy surfaces corresponding to [Sc, C(n), H(2n+2)](+) (n=1-3) were examined in detail at the B3LYP/6-311++G(3df, 3pd)//B3LYP/6-311+G(d,p) level of theory. The performance of this theoretical method was calibrated with respect to the available thermochemical data. Calculations indicated that the reactions of Sc(+) with alkanes are multichannel processes which involve two general mechanisms: an addition-elimination mechanism, which is in good agreement with the general mechanism proposed from earlier experiments, and a concerted mechanism, which is presented for the first time in this work. The addition-elimination reactions are favorable at low energy, and the concerted reactions could be alternative pathways at high energy. In most cases, the energetic bottleneck in the addition-elimination mechanism is the initial C--C or C--H activation. The loss of CH(4) and/or C(2)H(6) from Sc(+)+C(n)H(2n+2) (n=2, 3) can proceed along both the initial C--C activation branch and the Cbond;H activation branch. The loss of H(2) from Sc(+)+C(n)H(2n+2) (n=2, 3) can proceed not only by 1,2-H(2) and/or 1,3-H(2) elimination, but also by 1,1-H(2) elimination. The reactivity of Sc(+) with alkanes is compared with those reported earlier for the reactions of the late first-row transition-metal ions with alkanes.     

Thermal redistribution reactions in crosslinked polysiloxanes

The thermolysis under argon of various polysiloxane resins containing D, T, D^H, or T^H units was investigated using thermogravimetric analysis combined with mass spectroscopy (TG/MS analysis) and solid-state ²⁹Si-NMR. Redistribution reactions involving the exchange of Si? C/Si? O bonds or Si? H/Si? O bonds were evidenced in addition to the exchange of Si? O/Si? O bonds reported to date. These reactions significantly modify the initial siloxane units and lead to an escape of volatile silanes or siloxanes. The exchange of Si? H/Si? O bonds takes place at lower temperatures (300°C) than the exchange of Si? C/Si? O bonds (500°C).     

Synthesis,Characterization and Crystal Structure of Chlorodibenzyltin（Ⅳ） Complex with Dithiomorpholinocarba—mate Ligand

Chlorodibenzyltin (IV) complex with dithiomorpholinocarbamate ligand was synthesized by the reaction of dibenzyltin dichloride with dithiomorpholinocarbamate in 1:1 stoichiometry. The complex was characterized by elementary analysis, UV, BR and ¹H NMR spectra. The crystal structure was determined by X‐ray single crystal diffraction study. The crystallographic data are as follows: triclinic, space group P1 , a = 0.8723 (2) ran, b = 1.099 (2) nm, c = 1.1036 (3) nm, α = 86.498 (4)°, β = 89.697 (5)°, γ = 82.807 (5)°, Z = 2, V = 1.0479 (4) nm³, D_c= 1.580 g/cm^?3, μ = 1.553 mm^?1, F (000) = 500, R₁ = 0.0442, wR₂ = 0.0974. The crystal consists of discrete molecules containing five‐coordinate tin atoms in a distorted tigonal bipyramidal configuration. The molecules are packed in the unit cell in one‐dimensional chain structure through a weak interaction between the chlorine atom and sulfur atom, the sulfur atom and one of the sulfurs of an adjacent molecule.     

Synthese und Kristallstruktur der Spiro-Verbindung [(i-Pr)2P(S)NSiMe3]2SnCl2

Synthesis and Crystal Structure of the Spirocycle [(i-Pr)₂P(S)NSiMe₃]₂SnCl₂ The reaction of (i-Pr)₂P(S)N(SiMe₃)₂ ( 1 ) with SnCl₄ in 2:1 ratio yields under elimination of ClSiMe₃ the four-membered spirocycle [(i-Pr)₂P(S)NSiMe₃]₂SnCl₂ ( 2 ). The molecular structure of 2 was investigated by an X-ray structure analysis. Compound 2 crystallises in the monoclinic space group P2₁, Z = 2, a = 938.1(1), b = 1 424.1(2), c = 1 207.2(1) pm, β = 110.59(1)°, R = 2.05% for 4 102 reflexions. Compound 2 is a spirocycle with two Sn? N? P? S-rings joined at tin. The two rings are in cis-position.     

CN and CC Bond Formations in the Thermal Reactions of "Bare" Ni(NH(2) )(+) with C(2) H(4) : Mechanistic Insight on the Metal-Mediated Hydroamination of an Unactivated Olefin

Strike! While pure ammonia is out of luck, Ni(NH(2) )(+) gets one strike after another at the "ethylene bowling championship". In fact, Ni(NH(2) )(+) is so effective that no pin, not even at the neighboring lane, is safe from it.