Platinum complexes olefin exchanges

Although the transition state for the exchange reaction may be described as the critical complex for the conversion of the half-hydrogenated state to either a jr-complexed olefin or an eclipsed vicinal diadsorbed alkane, the stereochemistry of hydrogenation of cycloalkenes on platinum at low pressures can be understood if the transition state has a virtually saturated structure. 

A quite unique approach is also the complexation of chiral olefins by a ligand exchange type reaction with the chiral platinum(lV) complex (Table 1, entry 57). It is an equilibrium... 

Rearrangement of the olefin complexes L2PtCF2.CFBr and anion exchange gives a series of trifluorovinylplatinum complexes [267]. Parameters for two examples are given with the structure apart from the platinum-fluorine couplings, which were not observable even with CAT accumulation, the parameters for the other members of the series were very similar to those shown. (140) Parameters for the complexes... 

Depending on the nature of olefins, hydrosilanes, and catalysts, side reactions can also occur, such as H-Cl exchange in silanes as well as hydrogenation and olefin isomerization (144,145). In some cases, in the reaction catalyzed by some complexes of ruthenium, rhodium, iron, iridium, platinum, and nickel, alkenylsilanes have been obtained as a major product of the dehydrogenative... 

Alkenes.—Deuterium exchange of propene with MeOD homogeneously catalysed by complexes of platinum, rhodium, and nickel can be monitored by microwave spectroscopy. The results show considerable incorporation of deuterium at C-2, a result which cannot be accommodated by the 7t-allyl-metal hydride mechanism for exchange/isomerization of olefins. However, the n- or /i -allyl-metal hydride mechanism for olefin isomerization has received some useful supporting evidence. The compound (54) can be generated... 

Olefin-metal complexes are frequently labile, especially those of copper, silver and gold, and treatment of most olefin-metal complexes with ligands such as tertiary phosphines results in the displacement of the olefin. In the square-planar acetylacetonate complex (acac)Rh(C2H4)2 the ethylenes readily exchange with free ethylene - as is also found in the square-planar platinum-olefin complexes [17]. In these planar molecules exchange of olefins may involve olefin attack on the exposed metal atom, via a five-co-ordinated intermediate [65, 66]. 

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