Catalysis platinum complex with

A New Class of Hydrido-Bridged Platinum Complex with Application in Catalysis... 

Platinum(O) phosphine complexes undergo a variety of oxidative addition reactions with compounds containing Group 14 elements. These reactions are of widespread interest because similar processes are probably involved in the catalysis by platinum complexes of reactions such as the hydrosilation of alkenes and the disilylation of dienes and alkenes. 

A closely related dicationic platinum complex has been shown to transform efficiently /3-citronellene into cis-thujane in a highly diastereoselective manner, which mimics terpene biosynthesis.362 Also, using platinum(n) catalysis, Widenhoefer has reported an intramolecular alkylation of indoles with unactivated olefins, which can be carried out in an enantioselective fashion (Scheme 99).363... 

The complex /rara-PtH(02CH)[PEt3]2 catalyzes the decomposition of formic acid in the presence of sodium formate. A mechanism based on the equilibria described in Scheme 2 has been proposed by Paonessa and Trogler (60). The role of formate ion is to promote catalysis by reaction with the platinum dimer (10) or the solvated complex [frans-PtH(S)L2]+, where S = acetone, to reform the catalytically active monomeric species 11 and 12. 

Attempts have been made to mimic proposed steps in catalysis at a platinum metal surface using well-characterized binuclear platinum complexes. A series of such complexes, stabilized by bridging bis(diphenyl-phosphino)methane ligands, has been prepared and structurally characterized. Included are diplati-num(I) complexes with Pt-Pt bonds, complexes with bridging hydride, carbonyl or methylene groups, and binuclear methylplatinum complexes. Reactions of these complexes have been studied and new binuclear oxidative addition and reductive elimination reactions, and a new catalyst for the water gas shift reaction have been discovered. 

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... 

There has been considerable interest in binuclear and polynuclear metal complexes as models for intermediates proposed to be formed during reactions which are heterogeneously catalysed by transition metals (1). Since platinum is one of the most versatile catalysts, we have begun an investigation into the synthesis, and chemical and catalytic properties of some binuclear organo-platinum complexes. In this article some hydrido and methyl complexes will be described, and a preliminary account of catalysis with binuclear complexes given. In addition, structural studies indicate that Pt-Pt bonding interactions may take several different forms in these complexes and so the nature of the Pt-Pt bond will also be discussed. 

Although the platinum-catalyzed reactions are not as practical as palladium used for the same purpose, several types of unique discoveries still are noteworthy. Besides electrophihc C-H activation, the platinum complexes are efficient catalysts for hydrosilation see Hydrosilation Catalysis) that is important to silicon polymer industry. Platinum carbene catalysts are prepared from Karstedt catalyst (9) and imidazolium salts. The trials of model hydrosilylation reactions show very high yields of regioselective products (<1% impurity) with remarkable TON (see Turnover) (<30ppm catalyst load) (Scheme 81). ... 

Studies with platinum(IV) complexes are complicated by platinum(II) catalysis 18). Some of the recent Russian work has considered this aspect 44) i but correlations are still being made without consideration of the catalytic problem 104)- The recent isolation of several optically active platinum(IV) complexes with all inorganic, monodentate ligands 35) should allow substantiation for older work which has always suggested retention, in agreement with the high A values for platinum(IV). 

The silicon hydrides do not spontaneously add to alkenes either. However, the hydrosilation, or hydrosilylation reaction, of olefins is of significant utility in the preparation of alkyl-subtituted silanes with the use of either radical or transition metal catalysis. The preferred metal catalysts for hydrosilation are platinum complexes. Chloro-platinic acid will catalyze hydrosilations with halosilanes, alkylarylhalosilanes, alkoxy-silanes, and siloxanes that in many cases are quantitative under ambient conditions. Yields and conversions are generally poorer for alkyl,- and arylsilanes. Many other coordination complexes have been found to catalyze the hydrosilation reaction, and these can provide certain advantages, particularly in regiochemistry. Some typical hydrosilation reactions are shown in Table... 

The mechanism of catalytic hydrosilylation is not well understood. Study of these reactions is hampered by their complexity induction periods are often involved, reaction conditions such as the nature of the catalyst and reacting groups are critical factors, and side-reactions, such as alkene rearrangements, are common. A widely accepted mechanism for homogeneous catalysis by platinum complexes is based on the work of Chalk and Harrod (Scheme 10)5,8,262. With Speier s catalyst, it appears that initially, and probably during the induction period, silane reduces the platinum to a Pt(0) or Pt(II) complex that is the active catalytic species265. 

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