Suppression of unwanted heterogeneous platinum(0)-catalyzed reactions by poisoning with mercury(0) in systems involving competing homogeneous reactions of soluble organoplatinum compounds: thermal decomposition of bis(triethylphosphine)-3,3,4,4-tetramethylplatinacyclopentane

Abstract

Thermal decomposition of bis(trialkylphosphine)-3,3,4,4-tetramethylplatinacyclopentanes in hydrocarbon solvents yields two major products: 2,2,3,3-tetramethylbutane and 1-methyl-l-tert-butylcyclopropane. The former appears to be generated by heterogeneous process(es) catalyzed by platinum(0) (colloidal and/or solid) formed during the decomposition; the latter is the product of a homogeneous reaction sequence. The existence of competing heterogeneous and homogeneous reaction pathways complicates the study of this thermal decomposition. The addition of mercury(O) to the system selectively suppresses the heterogeneous reaction by poisoning the bulk platinum (0). This technique has been tested in one well-defined model system-the homogeneous hydrogenation of dirieopentylbis(triethylphosphine)platinum(II) to dihydridobis(triethylphosphine)platinum(lI) and neopentane in the presence of the heterogeneous platinum(0)-catalyzed hydrogenation of 1-methylcyclopentene to methylcyclopentane-and found to eliminate the heterogeneous reaction while leaving the homogeneous one essentially unaffected. Application of this technique to the thermal decomposition of 3,3,4,4-tetramethylplatinacyclopentane simplifies the reaction by eliminating 2,2,3,3-tetramethylbutane as a product. Similarly, addition of mercury(O) to solutions containing H2 and (l,5-cyclooctadiene)dimethylplatinum(II) in cyclohexane suppresses the autocatalytic, heterogeneous platinum-catalyzed conversion of the organoplatinum compound to (inter alia) cyclooctane, methane, and platinum(O). In other reactions examined-especially the high-temperature thermal decompositions of (l,5-cyclooctadiene)dineopentylplatinum(II) and of cts-bis(cyclopentyldimethylphosphine)dimethylplatinum(II) in hydrocarbon solvents-mercury poisoning does not successfully separate homogeneous and heterogeneous reactions. In the latter instance, an additional complicating processapparent reaction of mercury(O) with the organoplatinum compound-introduces reaction paths which seem to generate methyl radicals. The paper includes a simple preparation of l,4-dihalo-2,2,3,3-tetramethylbutane and illustrates the use of this material as a reagent for the preparation of 3,3,4,4-tetramethylmetallacyclopentanes via the corresponding di-Grignard reagents.

Physical‐Organic Chemistry: A Swiss Army Knife

“…These studies [30][31][32][33][34] , along with parallel, beautiful, studies by Bergman [35] , played a useful role in establishing the facility with which late transition metals could cleave (either intra-or intermolecularly) unactivated aliphatic C-H bonds. These studies were extensive, but involved conceptually straightforward examinations of products: the characterization of C-H bonds by examining the shuffling of deuterium in isotopically labeled species using NMR or mass spectroscopy [30] .…”

Rh(0) Nanoparticles: Synthesis, Structure and Catalytic Application in Suzuki–Miyaura Reaction and Hydrogenation of Benzene

“…The widely used test to identify the nature of the catalyst is mercury poisoning [43,44]. The inhibition of catalysis by Hg(0), which amalgamate the metal catalyst or adsorbs on its surface, is an evidence for heterogeneous catalysis as well as the presence of Rh (0) species in the system.…”

Immobilized Co/Rh Heterobimetallic Nanoparticle‐Catalyzed Pauson–Khand‐Type Reaction

“…The ability of added Hg(0) to poison metal(0) heterogeneous catalysts [25] by amalgamating the metal catalyst or adsorbing onto its surface is the single most widely used test of homogeneous versus heterogeneous catalysis. [26] The suppression of catalysis by Hg(0) is evidence for a heterogeneous catalyst; if Hg(0) does not suppress catalysis, the implication is that the catalysis is homogeneous.…”

“…The Hg(0)-poisoning experiment is easy to perform, but is not definitive by itself, and not universally applicable because Hg(0) reacts with some single-metal complexes. [25,26] Thus, this test inherently provides negative evidence (no poisoning) in cases where the catalyst is homogeneous.…”