Arylation platinum catalysis

In addition to the synthetic route shown in Scheme 32, Armstrong approached the synthesis from the other direction, by converting the initial resin-bound iodide to a supported pinacolatoboronate 30 under platinum catalysis (Scheme 33). This was then coupled in the usual way with a solution-phase aryl iodide in high yield, and with much more satisfactory results than were obtained with the vinylboronates 29. This chemistry was later shown to be useful in solution for one-pot biaryl synthesis by genera-... 

It has been shown that using palladium or platinum catalysis the reaction of arenes with two molecules of ethyl propiolate may form 1-aryl-1,3-butadiene derivatives both regio- and stereo-selectively. ... 

Cyano compounds liquid crystals, 12, 278 in silver(III) complexes, 2, 241 Cyanocuprates, with copper, 2, 186 Cyano derivatives, a-arylation, 1, 361 Cyanosilanes, applications, 9, 322 Cyclic acetals, and Grignard reagent reactivity, 9, 53 Cyclic alkenes, asymmetric hydrosilylation, 10, 830 Cyclic alkynes, strained, with platinum, 8, 644 Cyclic allyl boronates, preparation, 9, 196 Cyclic allylic esters, alkylation, 11, 91 Cyclic amides, ring-opening polymerization, via lanthanide catalysis, 4, 145... 

Other Catalysts. Other catalysts with metals of rhenium and platinum have shown catalytic reactivities for cyclopropanation. Methylrhenium trioxide (MTO) was the first rhenium catalyst for catalytic cyclopropanation, with yields of 57-87% obtained for the cyclopropanation of alkyl or aryl alkenes with EDA (45). As for platinum, a number of complexes have been screened for cyclopropanation catalytic activity (46). PtCl4 was the most active, giving good yield (79%) of cyclopropane from styrene and EDA. However, all reactions had to proceed at elevated temperature. Nonmetal catalysts such as tris(4-bromophenyl)-aminium hexachloroantimonate have been utilized as catalysts for mechanistic studies of cyclopropanation of a series of raras-stilbenes with EDA (47). A cation radical mechanism for this catalysis has been proposed. 

A proposed mechanism [9] for the hydrosilylation of olefins catalyzed by platinum(II) complexes (chloroplatinic acid is thought to be reduced to a plati-num(II) species in the early stages of the catalytic reaction) is similar to that for the rhodium(I) complex-catalyzed hydrogenation of olefins, which was advanced mostly by Wilkinson and his co-workers [10]. Besides the Speier s catalyst, it has been shown that tertiary phosphine complexes of nickel [11], palladium [12], platinum [13], and rhodium [14] are also effective as catalysts, and homogeneous catalysis by these Group VIII transition metal complexes is our present concern. In addition, as we will see later, hydrosilanes with chlorine, alkyl or aryl substituents on silicon show their characteristic reactivities in the metal complex-catalyzed hydrosilylation. Therefore, it seems appropriate to summarize here briefly recent advances in elucidation of the catalysis by metal complexes, including activation of silicon-hydrogen bonds. 

The platinum-catalysed arylation of carbon-hydrogen bonds by diaryliodonium salts has been reported. Mechanistic studies indicate that reductive elimination from intermediates such as (143) is rate limiting. Interestingly, the site selectivity in naphthalenes, which is largely controlled by steric factors, is opposite to that observed using palladium catalysis. ... 

Other metals can catalyze Heck-type reactions, although none thus far match the versatility of palladium. Copper salts have been shown to mediate the arylation of olefins, however this reaction most probably differs from the Heck mechanistically. Likewise, complexes of platinum(II), cobalt(I), rhodium(I) and iridium(I) have all been employed in analogous arylation chemistry, although often with disappointing results. Perhaps the most useful alternative is the application of nickel catalysis. Unfortunately, due to the persistence of the nickel(II) hydride complex in the catalytic cycle, the employment of a stoichiometric reductant, such as zinc dust is necessary, however the nickel-catalyzed Heck reaction does offer one distinct advantage. Unlike its palladium counterpart, it is possible to use aliphatic halides. For example, cyclohexyl bromide (108) was coupled to styrene to yield product 110. 

Mixed phosphorus compounds, bearing at least two different tervalent phosphorus moieties have been developed and have found several applications in catalysis. Iri li described the synthesis of aminophosphine-phosphinite ligands 149 and 150, from the commercially available 3-piperidinemethanol and 3-(methylamino) pro-pan-l-ol. Their palladium and platinum complexes 151 and 152, containing metallocyclic rings, were obtained as air-stable compounds with high yields, and characterized by P, and NMR spectroscopy, FTIR spectroscopy and X-ray crystallography. The Pd complexes were effective catalysts on Suzuki-Miyaura cross-coupling reactions of various aryl chlorides and atyl bromides with phe-nylboronic acid. 

Recently, hydrosilanes are also employed for the silylation of aryl halides in the presence of a palladium,platinum, or rhodium catalyst. In view of atom efficiency, this procedure has an advantage. Palladium-catalyzed reactions are suitable for the silylation of electron-rich aryl halides, whereas rhodium-catalysis works well with a wide range of aryl halides (Scheme 3-17). Silylation of allyl halides with trichlorosilane proceeds in the presence of a copper catalyst. ... 

However, the most recent and useful applications of Pt catalysis to the hydrolysis of nitriles to amide were achieved with homogeneous platinum phosphinito catalysts [139, 140], The catalyst precursors are coordination compounds of Pt(ll) with secondary phosphine oxides and the results obtained with [PtH(PMe20H) (PMc2-0)2H] with aUcyl, alkenyl, and aryl nitriles are reported in Scheme 76. 

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