Methane Activation by Titanium Monoxide Molecules:  A Matrix Isolation Infrared Spectroscopic and Theoretical Study

Abstract

Reactions of titanium monoxides with methane have been investigated using matrix isolation infrared spectroscopy and theoretical calculations. Titanium derivatives of several simple oxyhydrocarbons have been prepared and identified. The titanium monoxide molecules prepared by laser evaporation of bulk TiO2 target reacted with methane to form the TiO(CH4) complex in solid argon, which was predicted to have C3v symmetry with the oxygen atom coordinated to one hydrogen atom of the methane molecule. The complex rearranged to the CH3Ti(O)H titano-acetaldehyde molecule upon visible (lambda > 500 nm) irradiation. The titano-acetaldehyde molecule sustained further photochemical rearrangement to the CH2Ti(H)OH titano-vinyl alcohol molecule, which was characterized to be a simple carbene complex involving agostic bonding. The CH2Ti(H)OH molecule reacted with a second methane to form the (CH3)2Ti(H)OH titano-isopropyl alcohol molecule spontaneously on annealing. The (CH3)2Ti(H)OH molecule also can be produced via UV photon-induced rearrangement of the CH3Ti(O)H(CH4) complex.

Chemie mit Methan: Studieren geht über Probieren!

“…Werden isolierte Neutralatome (M = Fe, [70] Si, [71] B, [72] Be, [73] Mg, [73a] Sc, [74] Ti [75] oder Mn [70a] ) in einer Matrix durch thermische oder photochemische Anregung, kinetisch kontrolliert, mit Methanol zur Reaktion gebracht, dann erfolgt in den Begegnungskomplexen M(CH 3 OH) ausnahmslos die Aktivierung der stärkeren O-H-Bindung (Schema 4, Reaktionsweg A ) unter Bildung der jeweiligen [M]-OCH 3 -Spezies. [76] Wie nicht anders zu erwarten, verläuft die Methanoloxidation auf Sauerstoff-freien Oberflächen nach einem anderen Mechanismus.…”

Theoretical study on the gas‐phase reaction mechanism between palladium monoxide and methane

“…[31,32] They suggested that the trend in reactivity can be rationalized in terms of change in electrophilicity of MO x , the strength of the MAO bond, and the binding property of MO x to methyl or hydrogen as M and x are varied. [31,32] Zhou and coworkers [33][34][35][36][37] have investigated the MO þ CH 4 (M ¼ Fe, Mn, Nb, and Ta) and M þ CH 3 OH (M ¼ Sc, Ti, Mn, and Fe) model reactions, regarding the mechanism for the catalytic methane-to-methanol conversion process by quantum chemical calculations coupled with matrix isolation spectroscopy. For the late transition metals, Mn and Fe, the inserted CH 3 MOH is a critical intermediate in both MO þ CH 4 and M þ CH 3 OH reactions.…”

“…For the late transition metals, Mn and Fe, the inserted CH 3 MOH is a critical intermediate in both MO þ CH 4 and M þ CH 3 OH reactions. [33][34][35][36][37] For the group IV and V transition metals, the inserted CH 3 OMH and CH 3 M(O)H are the crucial intermediates. [33][34][35][36][37] For Sc, CH 3 ScOH is an important intermediate in the…”

“…[33][34][35][36][37] More recently, we have reported the gas-phase reaction mechanism of CH 4 with MO (M ¼ Mg, Ca, and Sr, Rh, and Ni). [38][39][40][41][42] For the alkaline-earth metals, Mg, Ca, and Sr, the products MOH þ CH 3 are more favorable than M þ CH 3 OH.…”

Theoretical study on the gas‐phase reaction mechanism between rhodium monoxide and methane for methanol production

“…18, 21 Zhou and coworkers have deliberately investigated the MO (M 5 Fe, Mn, Nb, Ta) 1 CH 4 and M (M 5 Sc, Ti, Mn, Fe) 1 CH 3 OH model reaction regarding the mechanism for the catalytic methane-to-methanol conversion process by quantum chemical calculations coupled with matrix isolation spectroscopy. 15,[37][38][39][40] It is proposed that for the late transition metals, Mn and Fe, the inserted CH 3 MOH molecule is a critical intermediate in both MO 1 CH 4 and M 1 CH 3 OH reactions; while for the group IV and V transition metals, the inserted CH 3 OMH and CH 3 M(O)H molecules are the crucial intermediates; and for Sc, the CH 3 ScOH molecule is an important intermediate in the ScO 1 CH 4 reaction, whereas the CH 3 OScH is a critical intermediate in the Sc 1 CH 3 OH reaction. 15,[37][38][39][40] Previously, we have reported the gas-phase reaction mechanism of CH 4 with MO (M 5 Mg, Ca, Sr), and put forward that the reaction may proceed via two kinds of important reaction intermediates, HOMCH 3 and HMOCH 3 , and the hydroxy intermediate HOMCH 3 is more preferable than the methoxy intermediate HMOCH 3 , while the products, MOH 1 CH 3 , are more favorable than M 1 CH 3 OH.…”