Platinum dimers catalysts

Diborations of 1,3-dienes are carried out in the presence of platinum(O) catalyst. In the Pt(PPh3)4-catalyzed dibora-tion of 1,3-dienes, 1,4-addition takes place to give (Z)-l,4-diboryl-2-alkenes stereoselectively (Equation (10)).62 In contrast, the Pt(dba)2-catalyzed reaction of 1,3-pentadiene affords 1,2-addition product, in which more substituted C=C bond is left intact (Scheme 5). The use of Pt(dba)2 as catalyst also enables the diborative dimerization of isoprene to occur (Equation (ll)).48... 

The first example of homogeneous transition metal catalysis in an ionic liquid was the platinum-catalyzed hydroformylation of ethene in tetraethylammonium trichlorostannate (mp. 78 °C), described by Parshall in 1972 (Scheme 5.2-1, a)) [1]. In 1987, Knifton reported the ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [Bu4P]Br, a salt that falls under the now accepted definition for an ionic liquid (see Scheme 5.2-1, b)) [2]. The first applications of room-temperature ionic liquids in homogeneous transition metal catalysis were described in 1990 by Chauvin et al. and by Wilkes et ak. Wilkes et al. used weekly acidic chloroaluminate melts and studied ethylene polymerization in them with Ziegler-Natta catalysts (Scheme 5.2-1, c)) [3]. Chauvin s group dissolved nickel catalysts in weakly acidic chloroaluminate melts and investigated the resulting ionic catalyst solutions for the dimerization of propene (Scheme 5.2-1, d)) [4]. 

Another approach for producing isoprene is the dimerization of propylene to 2-methyl-1-pentene. The reaction occurs at 200°C and about 200 atmospheres in the presence of a tripropyl aluminum catalyst combined with nickel or platinum. 

Oxides of Platinum Metals Anodes of platinum (and more rarely of other platinum metals) are used in the laboratory for studies of oxygen and chlorine evolution and in industry for the synthesis of peroxo compounds (such as persulfuric acid, H2S2O8) and organic additive dimerization products (such as sebacic acid see Section 15.6). The selectivity of the catalyst is important for all these reactions. It governs the fraction of the current consumed for chlorine evolution relative to that consumed in oxygen evolution as a possible parallel reaction it also governs the current yields and chemical yields in synthetic electrochemical reactions. 

Hydrogenation catalysts from non-platinum group have been also reported. For example, some organolanthanides of formula [ (r/5-C5Me5)2MH)2] are active catalyst for alkene hydrogenation.384 It has been proposed on the basis of kinetic studies that first the dimer dissociates according to (Equation (18)),... 

It should also be noted that in these mechanistic schemes it has been assumed that the platinum catalyst is monomeric. Evidence presented later (Section III,B,2) indicates that dimeric species are important in catalyzing H—D exchange. 

Only one paper has reported on catalytic asymmetric hydrogenation. In this study by Corma et al., the neutral dimeric duphos-gold(I)complex 332 was used to catalyze the asymmetric hydrogenation of alkenes and imines. The use of the gold complex increased the enantioselectivity achieved with other platinum or iridium catalysts and activity was very high in the reaction tested [195] (Figure 8.5). 

In addition to converting secondary alcohols into ketones, the platinum catalyst also converts toluene and other benzyl hydrocarbons into dimers. 

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... 

As shown in Scheme 45, DMSB can undergo polymerization or dimerization in the presence of similar platinum catalysts in good to excellent yields. The course of the reaction is apparently linked to the presence or absence of phosphine ligands platinum complexes that include added phosphines lead to dimerization, whereas polymerization usually occurred under ligandless conditions. Divinyltetramethyldisiloxane also serves as a ligand for the platinum-catalyzed dimerization of SCBs and disilacyclobutanes as reported by Chu and Frye <1993JOM(446)183>. 

Scheme 1 a The [2 + 2] cycloaddition product of prochiral trans 2-butene with Si dimers of the Si(100) surface leads to chiral adsorbate complexes, b Hydrogenation of prochiral a-keto esters over platinum is a heterogeneously catalyzed reaction leading to chiral alcohols. Using cinchonidin as chiral modifier makes this surface reaction enantioselective. In a similar fashion, TA-modified nickel is a highly enantioselective catalyst for /3-keto ester hydrogenation... 

Electrochemical catalyst regeneration was tested for addition reactions of perfluoroalkyl halides 41b to a-methylstyrene 42 (Fig. 8) [96], Dimers 43 were isolated in 50% and 70% yield, respectively, using 6-10 mol% of Ni(bipy)Br2 as the catalyst in a divided cell at -1.2 V at a platinum cathode. Under these conditions the Ni(II) complex is first reduced to Ni(0). 

Both amido and pinacol derivatives of B-Si compounds 125 and 126 added to terminal and internal alkynes in the presence of a palladium244-246 or platinum(O) catalyst247 by a mechanism involving an oxidative addition-insertion process (Equation (39)).248 On the other hand, phosphine-free nickel(O) catalyst resulted in the dimerization of alkynes giving a Z,Z-isomer of l-silyl-4-borylbutadiene derivatives.249 Since the palladium-catalyzed cross-coupling at the C-B bond is faster than the G-Si bond of 137, a silylboration-cross-coupling sequence provided a method for the synthesis of 1-alkenylsilanes.246... 

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