Platinum complex, olefin oxidation

The shift in the C=C frequency, vi, for adsorbed ethylene relative to that in the gas phase is 23 cm-1. This is much greater than the 2 cm-1 shift that is observed on liquefaction (42) but is less than that found for complexes of silver salts (44) (about 40 cm-1) or platinum complexes (48) (105 cm-1). Often there is a correlation of the enthalpy of formation of complexes of ethylene to this frequency shift (44, 45). If we use the curve showing this correlation for heat of adsorption of ethylene on various molecular sieves (45), we find that a shift of 23 cm-1 should correspond to a heat of adsorption of 13.8 kcal. This value is in excellent agreement with the value of 14 kcal obtained for isosteric heats at low coverage. Thus, this comparison reinforces the conclusion that ethylene adsorbed on zinc oxide is best characterized as an olefin w-bonded to the surface, i.e., a surface w-complex. 

Since tetranuclear platinum-blues are oxidized by 02 to Pt(III) dinuclear complexes and are reversively reduced to the platinum-blues and further to the Pt(II) dinuclear complexes, an attempt was made to use these complexes as catalysts for olefin oxidation to ketones and epoxides. The catalysts used were a-pyrrolidonato-bridged Pt-tan [Pt4(NH3)8(C4H6N0)4](N03)6 -2H20 (19), pivalamidato-bridged Pt-blue [Pt4(NH3)8(C5H10NO)4](NO3)5 (57), a-pyrrolidonato-tan [Pt4(NH3)8... 

Since it is known that the tetranuclear mixed-valent platinum-blue complexes such as 19 and 57 undergo disproportionation and reduction by water as Eqs. (1)—(3) and (7)—(9) show (106, 113), all the species appearing in Eqs. (1)—(3) and (7)—(9) are present in the solution. However, only one or several of the four species in the solution may in fact be resposible for the catalytic olefin oxidation. To clarify this point, the effect of the Pt oxidation state in the platinum complexes was compared. The results are summarized in Table VII, which... 

Schiff bases -alkanolamines [ALKANOLAMINES - ALKANOLAMINESFROM OLEFIN OXIDES AND AMMONIA] (Vol 2) -from benzaldehyde [BENZALDEHYDE] (Vol 4) -platinum-group metal complexes of [PLATINUM-GROUP METALS, COMPOUNDS] (Vol 19)... 

Some attempts which I had made in 1946 to obtain PtPh2 or [PtPhJ from the reaction of phenylmagnesium bromide with [ PtCl2(C2H4)2 2] in ether had yielded biphenyl as the only pure solid product, and this served to confirm in my mind the belief that transition metals had no normal organometallic chemistry. I decided then to concentrate on the platinum(II)-olefin complexes. The first question was whether the olefin-metal bond used the d electrons normally involved in the oxidation of platinum(II) to platinum(IV) (valence d electrons) to bind the olefin, as required by such structures as (I), or whether, as was then generally believed, they were olefin coordination compounds formed independently of the presence of d electrons, even by Main Group element ions. 

T-Olefin platinum(O) complexes are important starting materials for oxidative addition see Oxidative Addition) or catalysts. Karstedt s catalysts, which are the most active ones for hydrosilylation, have been structurally characterized and found to show the structure of Pt2(M y M y )3 (9), wherein = divinyltetramethyldisiloxane." A styrene analogue Pt°(styrene)3 provides a convenient route to get an r-alkyne platinum complex by displacement (Scheme 27). DFT calculations indicate that aUcyne in the... 

Orchin and colleagues have studied (239, 325, 326, 514, 543-545) extensively the platinum complexes traws-(olefin)(4-ZC5H4NO)PtCl2 (212) in which the 4-substituent, Z, on pyridine-iV-oxide is OCH3, CH3, H, Cl, CO2CH3, CN, or NO2. The olefins have included ethylene (239), styrene, and 3- or 4-substituted styrenes (239, 544), 1-dodecene (544),... 

This hydrocarboration method is a valuable tool in industrial and laboratory synthesis, since it allows introduction of the one-carbon unit of carbon monoxide into unsaturated substrates and construction of new carbon skeletons with aldehyde functions or derivatives thereof formed by reduction, oxidation, condensation and other conversions. Hydroformylation, mainly catalyzed by cobalt, rhodium, or platinum complexes is an unsymmetrical 1,2-addition leading to linear and branched products if terminal olefins are used as the substrate. Since linear products are normally the industrial products wanted54, considerable efforts have concentrated on the control of regiochemistry. Other problems of the hydroformylation method arise from side reactions such as hydrogenation, double bond migration, and subsequent reactions of the products (e.g., condensation, reduction, dccarbonylation)54. 

Compounds containing Ad and 5d electron elements are generally more stable than those of 3d electron metals. The former compounds are characterized by greater thermal stability and by greater resistance to water and oxidizing agents. Many platinum group olefin complexes are air stable in the presence of water. This is a result of the character of the metal-olefin bond. 

It is well known that olefins may form complexes with some metals [80, 81]. Mercuric acetate can form complexes with polyolefins selectively, being removed by acid treatment [82]. Such complexes have been used in the separation of unsaturated fatty acids from mixtures [83]. Subbarao [84] has protected olefins aginst reduction using silver complexes, and Cope used reversible platinum complex formation [85, 86] for the resolution of medium ring trans olefins. Landesburg [87] used the iron tricarbonyl complex of the alcohol (13) to protect it during oxidation to the ketone (14) which was regenerated from the complex by photolysis [88a]. 

Interestingly, the catalytic activity of some platinum complexes toward decomposition of diazo compounds is influenced by the oxidation state of the metal and the type of diazo compound under study. For example, 9-diazofluorene is decomposed either catalytically or stoichiometrically, in the presence of the platinum (0) complex [Pt (C2H4) (PPhj)2], to the corresponding azine while the dicationic complex cis-[Pt (PPh3)2(CH2CN)2] [BF4]2 catalyzes the formation of the corresponding olefin. ... 

It is probable that during hydrosilylations these Ni(II) complexes are reduced to 7r-olefin Ni(0) species which then undergo an oxidative addition in an identical manner to that already discussed for the chloroplatinic acid case. There is current interest in such oxidations (83), and the platinum analog (Ph3P)2Pt(olefin) has been shown in one case (olefin = C2H4) to be an excellent hydrosilylation catalyst (240). In this system, intermediate low oxidation state Pt species have been isolated their nature is dependent on the electronegativity of the other groups attached to silicon. 

It has dso proved possible in the metal-olefin systems formed to isolate intermediates which have short lives in simpler systems for example, the complex PtBr4 (vp) can be seen as analogous to the unstable yellow oils sometimes reported in the oxidation of Zeise s salt to PtCU and 1,2 dichloroethane. Even weak interactions which affect the course of a reaction can be noted. Neither of the vinyl groups in PtBr2 (oS)2 is co-ordinated to the platinum atom, but bromine oxidation yields a Pt-carbon o-bond, indicating some interaction in the transition state at least. 

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