Benzene, reactions with platinum clusters

Trevor D J, Whetten R L, Cox D M and Kaldor A 1985 Gas-phase platinum cluster reactions with benzene and several hexanes evidence of extensive dehydrogenation and size-dependent chemisorption J. Am. Chem. Soc. 107 518... 

Electrospray ionization will often produce ions that are fully coordinated, stable, and nonreactive in the gas phase. These ions may be probed by removal of ligands to form coordinatively unsaturated ions that are generally reactive. The chemical activity of metal cluster ions differs markedly and often shows size specific enhanced reactivity or lack of reactivity. Silver cluster ions Ag are fairly inert similar to Ag+. Platinum cluster ions PL are quite reactive similar to Pt+. Often, large cluster ions only appear to react with one donor molecule such as benzene this may be due to low concentrations of reactants or short reaction times. Similar clusters may react with a larger number of smaller molecules, and so until more information is available, rules for the coordination behavior of metal clusters are as yet not available. 

Dehydrocyclization of n-hexane to form benzene has been a subject of considerable academic and industrial interest since Bernard first reported that platinum clusters supported inside the channels of zeolite L catalyze the reaction with exceptional activity and selectivity (7). The nonacidic nature of the Pt-zeolite L catalyst and correlation of reaction rate with Pt content are consistent with the accepted view that the catalyst is monofunctional, depending solely on Pt metal for catalytic activity (7). However, comparison of aromatization reactivity over nonacidic Pt-zeolites to conventional non-zeolitic catalysts revealed that additional factors contribute to the unusual performance of Pt-zeolites (2). 

Figure 9. Time-of-flight mass spectrum of platinum clusters after reaction with perdeuteroben-zene. Products are labeled n, m to denote number of platinum atoms and benzene molecules, respectively. Vertical dashed line indicates a change in mass spectrometer transmission function and gain. (From Kaldor et al. )...

Little is known about the chemical nature of the recently isolated carbon clusters (C o> C70, Cg4, and so forth). One potential application of these materials is as highly dispersed supports for metal catalysts, and therefore the question of how metal atoms bind to C40 is of interest. Reaction of C o with organometallic ruthenium and platinum re nts has shown that metals can be attached directly to the carbon framework. Ihe native geometry of transition metal, and an x-ray difi action analysis of the platinum complex [(CgHg)3P]2Pt( () -C6o) C4HgO revealed a structure similar to that known for [(C4Hs)3P]2Pt( n -ethylene). The reactivity of C40 is not like that of relatively electron-rich planar aromatic molecules su( as benzene. The carbon-carbon double bonds of C40 react like those of very electron-deficient arenes and alkcnes. 

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