Infrared Spectrum of the CH3−PtH Complex in Solid Argon Prepared in the Oxidative C−H Insertion of Methane by Laser-Ablated Pt Atoms

Probing the binding and activation of small molecules by gas-phase transition metal clusters via IR spectroscopy

Isolated transition metal clusters have been established as useful models for extended metal surfaces or deposited metal particles, to improve the understanding of their surface chemistry and of catalytic reactions. For this objective, an important milestone has been the development of experimental methods for the size-specific structural characterization of clusters and cluster complexes in the gas phase. This review focusses on the characterization of molecular ligands, their binding and activation by small transition metal clusters, using cluster-size specific infrared action spectroscopy. A comprehensive overview and a critical discussion of the experimental data available to date is provided, reaching from the initial results obtained using line-tuneable CO₂ lasers to present-day studies applying infrared free electron lasers as well as other intense and broadly tuneable IR laser sources.

Selective Activation of the C-H Bond in Methane by Single Platinum Atomic Anions

Mass spectrometric analysis of the anionic products of interaction between platinum atomic anions, Pt^- , and methane, CH₄ and CD₄ , in a collision cell shows the preferred generation of [PtCH₄ ]^- and [PtCD₄ ]^- complexes and a low tendency toward dehydrogenation. [PtCH₄ ]^- is shown to be H-Pt-CH₃ ^- by a synergy between anion photoelectron spectroscopy and quantum chemical calculations, implying the rupture of a single C-H bond. The calculated reaction pathway accounts for the observed selective activation of methane by Pt^- . This study presents the first example of methane activation by a single atomic anion.

Computational insights into CH3MX (M = Cu, Ag and Au; X = H, F, Cl, Br and I)

The thermodynamically stability of CH₃MX with respect to CH₃X + M is CH₃CuX > CH₃AuX > CH₃AgX. Some stable CH₃MX have not been identified experimentally because their vibrational fingerprints (ν_C−M and v_M−X) are too low to be detected.

Investigation of spin-flip reactions of Nb + CH3CN by relativistic density functional theory

In order to explore the details of the reaction mechanisms of Nb atoms with acetonitrile molecules, the sextet, quartet, and doublet spin state potential energy surfaces have been investigated. Density functional theory (DFT) with the relativistic zero-order regular approximation at the PW91/TZ2P level has been applied. The complicated minimum energy reaction path involves four transition states (TS), stationary states (1) to (5) and two intersystem crossings from spin sextets to quartets to doublets (indicated by ⇒): (6)Nb + NCCH3→(6)Nb η(1)-NCCH3 ((6)1) →(6)TS1/2⇒(4)Nb η(2)-(NC)CH3 ((4)2) →(4)TS2/3→(4)NbH η(3)-(NCCH2) ((4)3) →(4)TS3/4→ CNNbCH3 ((4)4) ⇒(2)TS4/5→ CN(NbH)CH2 ((2)5). The minimum energy crossing points were determined with the help of the DFT fractional-occupation-number approach. The first spin inversion leads from the sextet to an energetically low intermediate quartet ((4)2) with final insertion of Nb into the C-C bond. The second one from the quartet to the doublet state facilitates the activation of a C-H bond, lowering the rearrangement-barrier by 44 kJ mol(-1). The overall reaction is calculated to be exothermic by about 170-180 kJ mol(-1). All intermediate and product species were frequency and NBO analyzed. The species can be rationalized with the help of Lewis type formulas.

Infrared spectra of CH2=M(H)NC, CH3-MNC, and eta2-M(NC)-CH3 produced by reactions of laser-ablated group 5 metal atoms with acetonitrile

Methylidene isocyanides, methyl isocyanides, and eta(2)-nitrile-pi-complexes are observed in the matrix IR spectra from reactions of Group 5 metals with acetonitrile isotopomers. The primary isocyanide products with no trace of cyanide complexes are consistent with the reaction path proposed in the analogous Zr study. The major products (CH(2)=Ta(H)NC, CH(3)-NbNC, eta(2)-Nb(NC)-CH(3), and eta(2)-V(NC)-CH(3)) after codeposition and reaction of metal with CH(3)CN clearly show the increasing preference for the higher oxidation-state complex on going down the group column, and the subsequent photochemistry provides further information for molecular rearrangements. The Group 5 metal methylidene isocyanides exhibit more agostic distortion than the Zr counterparts and are comparable to the previously studied Group 5 metal methylidene hydrides and halides. The computed structures and observed frequencies indicate that the effects of metal conjugation (C=Ta-N=C:) are minor.