La reaction with propene is carried out in a laser-vaporization molecular beam source. Three Lahydrocarbon radicals are characterized by mass-analyzed threshold ionization (MATI) spectroscopy. One of these radicals is methylenelanthanum [La(CH 2)] (C s), a Schrock-type metal carbene. The other two are a five-membered 1-lanthanacyclopent-3-en [La(CH 2 CHCHCH 2)] (C s) and a tetrahedron-like trimethylenemethanelanthanum [La(C(CH 2) 3)] (C 3v). Adiabatic ionization energies and metal-ligand stretching and hydrocarbon-based bending frequencies of these species are measured from the MATI spectra, preferred structures and electronic states are identified by comparing the experimental measurements and spectral simulations, and reaction pathways for the formation of the metal-hydrocarbon radicals are investigated with density functional theory calculations. All three radicals prefer doublet ground electronic states with La 6s 1-based valence electron configurations, and singly charged cations favor singlet states generated by the removal of the La 6s 1 electron. The metal-carbene radical is formed via multi-step carbon-carbon cleavage involving metallacyclization, β-hydrogen migration, and metal insertion. The metal-carbene radical formed in the primary reaction reacts with a second propene molecule to form the five-membered-ring and tetrahedron-like isomers through distinct carbon-carbon coupling paths.

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Some initial acid‐catalytic reactions involved in the synthesis of the urea‐formaldehyde resin were theoretically investigated at B3LYP and MP2 levels with solvent effects included. The results suggest that the addition between urea and formaldehyde in neutral condition undergoes with a concerted mechanism represented by a four‐member ring transition state. For this reaction, a notable barrier (above 130 kJ/mol) was identified at all theoretical levels. The reactions between urea and different protonated forms of formaldehyde in acid solution were investigated. The reaction between protonated methanediol with urea can produce the methylol urea cation via an SN2 transition state with a lower barrier of 54.8 kJ/mol. With the mediation of a water molecule, the intra‐molecular proton transfer produces the stable methylol carbonium (NH2CONHCH2+), which plays an important role in the following formation of methylene and methylene ether linkages. Copyright © 2011 John Wiley & Sons, Ltd.

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The reactions of bare neutral palladium (Pd) and platinum (Pt) atoms with ethylene on both singlet and triplet surfaces were investigated at B3LYP and CCSD (T) levels of theory. The calculated potential energy profiles clearly show that Pt has higher reactivity than Pd toward ethylene. For both Pd and Pt, the reactions on singlet surfaces are energetically more favorable than those on triplet surfaces. However, notable barriers lie on the singlet and triplet surfaces for Pd +ethylene. This result rationalizes the experimental observation that Pd mainly forms π‐complex with ethylene. But under high‐energy condition, the reaction can proceed to yield dehydrogenation products, Pd‐CCH. and Pd (HCCH). For Pt, triplet‐singlet surface crossing was suggested to occur in the region where Pt forms π‐complex with ethylene to lead the reactions to the energetically more favorable singlet surfaces. For both the two metals, π‐complex and CH bond insertion species are the reaction intermediates and the H.‐elimination products are the final products. Copyright © 2010 John Wiley & Sons, Ltd.

The gas phase reaction of ground‐state yttrium (Y) with propene, previously examined by crossed molecular beams (CMBs) experiment, has been theoretically investigated in detail using B3LYP method. Three concerted and five stepwise pathways were found for H2 elimination. The calculated PESs indicate that the concerted mechanisms are energetically much more favorable than the stepwise mechanisms for the elimination of H2. Three isomers, Y‐propyne, Y‐allene, and Y(CHCHCH2), were assigned to the experimentally observed H2‐elimination product, YC3H4. Three pathways were identified for the CC bond cleavage products, YCH2 + C2H4. The energetically most favorable pathway involves the formation of a metallacyclobutane intermediate, which can decay to YCH2 + C2H4. The results of this study confirmed some previous inferences and provided more details for the title reaction. Copyright © 2010 John Wiley & Sons, Ltd.

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