Catalysts cubane

A cationic molybdenum sulfide cluster [Mo3S4(H20)9] " with incomplete cubane-type structure and a cationic nickel-molybdenum mixed sulfide cluster [Mo3NiS4Cl(H20)9p " with complete cubane-type structure were introduced into zeolites NaY, HUSY and KL by ion exchange. Stoichiometry of the ion exchange was well established by elemental analyses. The UV-visible spectra and EXAFS analysis data exhibited that the structure of the molybdenum cluster remained virtually intact after ion exchange. MoNi/NaY catalyst prepared using the molybdenum-nickel sulfide cluster was found to be active and selective for benzothiophene hydrodesulfurization. 

The electrochemical results described above indicate that unlike in the cases of other cobalt-catalyzed oxidation processes where the Co /Co redox couple is invariably involved [19b,38], in the present case where cubane clusters of the general formula Co4(p3-0)4( J,-02-CR)4(L)4 are to be employed as catalysts for the air/02 or TBHP oxidation of alkylaromatics, alcohols, etc., we have a catalytic system wherein the oxidation states of cobalt cycle between +3 and +4. The kinetic inertness of Co(lll) coupled with the inadequately explored reactivity of Co(lV) thus make the catalysts based on C04O4 cubanes quite interesting [36]. We shall now discuss the resulting materials prepared by supporting the cubane-like cobalt(lll)-oxo clusters discussed above in this section by following the chemical route in which the carboxylate anion derived from CMS-CH2CH2CO2H binds the in situ or preformed cobalt(III)-oxo tetramers at elevated temperatures. 

There is an important class of rearrangements of strained cyclic a-bonded systems to give less strained ir-bonded qrstems which occur under the influence of transition metal catalysts although the uncatalysed proce is Woodward-Hoffman forbidden and slow. Examples are the conversion of cubanes XXII and bis-homocubanes XXIll to syn-tricyclooctadienes XXIV and related species XXV and of quadricyclene (XXVI) to norbomadiene (XXVII) [Ag, however, converted cubane and related species to the previously unrecognised species cuneane (XXVIII) and its relatives as do some electrophiles with incompletely filled d-subshells ... 

Heterometal alkoxide precursors, for ceramics, 12, 60-61 Heterometal chalcogenides, synthesis, 12, 62 Heterometal cubanes, as metal-organic precursor, 12, 39 Heterometallic alkenes, with platinum, 8, 639 Heterometallic alkynes, with platinum, models, 8, 650 Heterometallic clusters as heterogeneous catalyst precursors, 12, 767 in homogeneous catalysis, 12, 761 with Ni—M and Ni-C cr-bonded complexes, 8, 115 Heterometallic complexes with arene chromium carbonyls, 5, 259 bridged chromium isonitriles, 5, 274 with cyclopentadienyl hydride niobium moieties, 5, 72 with ruthenium—osmium, overview, 6, 1045—1116 with tungsten carbonyls, 5, 702 Heterometallic dimers, palladium complexes, 8, 210 Heterometallic iron-containing compounds cluster compounds, 6, 331 dinuclear compounds, 6, 319 overview, 6, 319-352... 

A metal sulfide cluster Cp2Mo2Co2(CO)4 S3 (6), potentially having some structural features of a sulfided Co-Mo/AI2O3 catalyst surface, reacts with thiophene at 150°C under 15 atm of H2 (equation 18) to give an essentially quantitative yield of the cubane cluster Cp2Mo2Co2(CO)2S4 (7). The thiophene sulfur is incorporated into the cluster, and the hydrocarbon portion is converted to a mixture of Ci-4 alkanes and alkenes. The mechanism of this reaction may involve initial S-coordination of thiophene to (6). 

A better example for the possible intervention of a distinct intermediate was recently disclosed in a study of the valence isomerization of cubane (79) to syw-tricyclooctadiene 20) using various rhodium (I) catalysts. 

Rhodium(I) complexes are efficient catalysts for the valence isomerizations of cubane (23a equation 7) and its derivatives to the corresponding iy/j-tricyclo[4.2.0.CF ]octa-3,7-dienes. When a stoichiometric amount of [ RhQ(CO)2)2l is added to a chloroform solution of cubane, the organorhodium compound (24) is obtained in about yield. Treatment of (24) with a stoichiometric amount of triphenylphos-phine gives, in about 90% yield, the polycyclic ketone (25) together with a small amount (5-10%) of cy-clooctatetraene. A similar reaction is also reported for the methoxycarbonyl derivative (23b). 

Rearrangements of strained skeletal rearrangements of highly strained orbital symmetry restrictions.4 Thus treatment of homo-cubane(l) in dilute CDC13 or acetone-4 solution with catalytic amounts of silver fluoroborate results in quantitative conversion into (2), pentacyclo[4.3.0.02-4. (F-MF- nonane, within 1 day at 25°. In the absence of silver ion, (1) is stable to 2400.5... 

Dismukes, G. C. Brimblecombe, R. Felton, G. A. N. Pryadun, R. S. Spiccia, L. Swiegers, G. F. Development of Bioinspired M114O4—Cubane Water Oxidation Catalysts Lessons from Photosynthesis. Acc. Chem. Res., 2009,42, 1935-1943. 

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