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Mechanistic Study of the Oxidative Carbonylation of Methanol Catalyzed by Palladium Diphosphane Complexes with Nitrobenzene as Oxidant
Author(s) -
Mooibroek Tiddo J.,
Bouwman Elisabeth,
Drent Eite
Publication year - 2012
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201101354
Subject(s) - chemistry , carbonylation , palladium , oxidative addition , catalysis , medicinal chemistry , nitrobenzene , methanol , reductive elimination , steric effects , dimethyl carbonate , photochemistry , organic chemistry , carbon monoxide
The reactivity of Pd complexes having bidentate diarylphosphane ligands was studied in the oxidative carbonylation of CH 3 OH to dimethyl carbonate/oxalate (DMC/O) with PhNO 2 as the oxidant. Different ligands were employed with variation in backbone length and aryl ring substituent, and the acidity, CO pressure, or the partial pressure of H 2 was varied. At two different stages in the catalytic cycle, one equivalent of DMC/O may evolve for every equivalent of PhNO 2 reduced, which means that the efficiency with which nitrobenzene can function as the oxidant for the oxidative carbonylation of methanol ( E OC ) can potentially be 200 % relative to nitrobenzene conversion. The selectivity for DMC relative to DMO is thought to be determined by a species of the type [P 2 PdC(O)OCH 3 (R)]; the DMO/DMC ratio can be increased by increasing the CO pressure, by addition of an acid, or by using a ligand with a relatively large bite angle. On the basis of the collected results, we conclude that an ideal catalyst for oxidative carbonylation would have a relatively acidic palladium center and be sterically undemanding in the axial positions but sterically demanding in the equatorial positions of palladium. The Pd complex of bis(diphenylphosphanyl)ferrocene meets these criteria and was found to function most efficiently with PhNO 2 as oxidant for the oxidative carbonylation of methanol among the series of compounds studied, that is, with about 50 % of the theoretical maximum efficiency E OC .