Discovery of Multicomponent Heterogeneous Catalysts via Admixture Screening: PdBiTe Catalysts for Aerobic Oxidative Esterification of Primary Alcohols

Abstract

In the present study, we demonstrate the utility of "admixture screening" for the discovery of new multicomponent heterogeneous Pd catalyst compositions that are highly effective for aerobic oxidative methyl esterification of primary alcohols. The identification of possible catalysts for this reaction was initiated by the screening of simple binary and ternary admixtures of Pd/charcoal in combination with one or two metal and/or metalloid components as the catalyst. This approach permitted rapid evaluation of over 400 admixture combinations for the oxidative methyl esterification of 1-octanol at 60 °C in methanol. Product yields from these reactions varied widely, ranging from 2% to 88%. The highest yields were observed with Bi-, Te-, and Pb-based additives, and particularly from those containing both Bi and Te. Validation of the results was achieved by preparing specific PdBiTe catalyst formulations via a wet-impregnation method, followed by application of response surface methodology to identify the optimal Pd-Bi-Te catalyst stoichiometry. This approach revealed two very effective catalyst compositions: PdBiTe/C (PBT-1) and PdBiTe/C (PBT-2). The former catalyst was used in batch aerobic oxidation reactions with different primary alcohols and shown to be compatible with substrates bearing heterocycle and halide substituents. The methyl ester products were obtained in >90% yield in nearly all cases. Implementation of the PBT-2 catalyst in a continuous-flow packed-bed reactor achieved nearly 60 000 turnovers with no apparent loss of catalytic activity.

The Use of Molecular Oxygen for Liquid Phase Aerobic Oxidations in Continuous Flow

“…The inclusion of promoters has been associated with mediating the adsorption and dissociation of O 2 , thus preventing over oxidation of the metal surface. Stahl and co-workers conducted an admixture screening in batch for the discovery of new heterogeneous Pd catalyst and promoter compositions [65]. Over 4000 catalyst compositions were explored for the oxidative methyl esterification of 1-octanol to methyl octanoate (Scheme 15a).…”

Additive-Mediated Selective Oxidation of Alcohols to Esters via Synergistic Effect Using Single Cation Cobalt Catalyst Stabilized with Inorganic Ligand

“…Aromatic alcohols containing electron-donating groups, such as p-methoxybenzyl alcohol, p-methylbenzyl alcohol, p-isopropylbenzyl alcohol, p-benzyloxybenzyl alcohol, 2-naphthalene methanol, and 2,4,6-trimethylbenzyl alcohol, all underwent completely oxidative esterification with excellent selectivity to provide the corresponding esters (compounds 2-9). Halogen-substituted aromatic alcohols were also amenable to the reaction conditions, giving the desired products in excellent yields without regard to the position of the substituents (compounds [10][11][12][13][14]. Strongly electronwithdrawing groups, such as -CF 3 and -NO 2 , were also tolerated under the standard conditions (compounds 15-17), but where the -NO 2 group locates on the phenyl ring resulted in totally different reactivity.…”

“…Both homogeneous and heterogeneous catalytic systems have been well established for the highly efficient oxidation of alcohols to esters. Some of the most effective examples uti-lize metal-based homogeneous catalysts supported by an organic ligand, such as ruthenium [5][6][7][8][9][10], palladium [11][12][13][14], gold [15], iridium [16,17], and rhodium [18], or rely on the use of toxic halide-based oxidants [19]. Heterogeneous catalysts generally employ functional ligands to modulate the catalytic performance (Figure 1(b)).…”

Cyclopentadienyl Ruthenium(II) Complex-Mediated Oxidation of Benzylic and Allylic Alcohols to Corresponding Aldehydes

“…Benzyl alcohol 1a is an important precursor for organic synthesis and a useful solvent because of its polarity, low toxicity, mildly pleasant aromatic odor, and low vapor pressure [52][53][54]. e chemoselective oxidation property of compound 1a was also very useful in functional transformations for the preparation of aldehydes [55,56] and their dicarboxyl analogues [57,58]. For these reasons, we carried out a plausible oxidation of benzyl alcohol 1a.…”