Theoretical Study of the Oxidation of Alcohol to Aldehyde by d⁰ Transition-Metal−Oxo Complexes:  Combined Approach Based on Density Functional Theory and the Intrinsic Reaction Coordinate Method

Abstract

A combined density functional (DF) and intrinsic reaction coordinate (IRC) method has been applied to the mechanistic study of methanol oxidization to formaldehyde by the d0 transition-metal−oxo complexes MO2X2 (M = Cr, Mo, X = Cl; M = Ru, X = O). A two-step mechanism was investigated. The two steps involve addition of the methanol OH bond to an MO linkage to form a M−methoxy complex, MO2X2 + CH3OH = M(O)(OH)Cl2(OCH3) (step 1), and the elimination of formaldehyde from the M−methoxy complex to yield the final products, M(O)(OH)Cl2(OCH3) = M(OH)2X2 + CH2O (step 2). The calculated vibrational adiabatic intrinsic barriers were 23.7 kcal/mol (Cr), 16.2 kcal/mol (Mo), and 21.4 kcal/mol (Ru) for the addition process (1), as well as 23.1 kcal/mol (Cr), 33.3 kcal/mol (Mo), and 7.4 kcal/mol (Ru) for the elimination step (2). The enthalpies of the overall oxidation process were computed to be 3.1 kcal/mol (Cr), 41.9 kcal/mol (Mo), and −1.9 kcal/mol (Ru). The IRC trajectories revealed that reaction 1 is initiated by the formation of the weaker adduct CH3OH−MO2X2 between the initial reactants, whereas reaction 2 results in the strong adduct CH2O−M(OH)2X2 between final products. It is concluded that only the chromium and ruthenium oxo complexes are efficient reagents for the conversion of methanol to formaldehyde.

Matrix Isolation Study of the Thermal and Photochemical Reaction of OVCl3 with NH3: Spectroscopic and Theoretical Characterization of Cl2V(O)NH2

“…This agrees with theoretical calculations as well. 3,4 The second step in each system studied has been HCl elimination. In several cases, this was observed to occur thermally, in a merged jet system, whereas in other cases (including the present study), the reaction was photochemically induced.…”

Matrix isolation and theoretical investigation of the photochemical reaction of CrCl2O2 with benzenes substituted with electron withdrawing groups

“…Metal oxo compounds such as these have also been used as catalysts in organic or polymer synthesis and as models for the active sites in enzymes such as Cytochrome P-450 [8,9]. Extensive theoretical calculations of the potential energy surfaces for the reactions of CrCl 2 O 2 with small substrates have been conducted [10][11][12][13][14]. Finally, while much of the experimental work has been done in solution, a few studies have explored the reactions of CrCl 2 O 2 in the gas phase [5,6].…”

Kinetic study of 2-propanol and benzyl alcohol oxidation by alkaline hexacyanoferrate(III) catalyzed by a terpyridyl ruthenium complex

“…(27), (28), (29), and (26) for benzyl alcohol, 4-nitrobenzyl alcohol, and 4-methoxybenzyl alcohol. The values for k 1 are within experimental error of each other as would be expected for this mechanism.…”