Valent Platinum Oxides

Complex Structure Oxidation State of Pt or Pd M—M A Conductivity C- cm-i Reference 

VALENCE LEVEL ENERGIES FOR VARIOUS PLATINUM OXIDES (77)  

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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... 

The activation of C—H bonds in hydrocarbons by oxidative addition to low-valent platinum group metal complexes is also feasible. This problem is discussed in more detail in Section III.D.3). 

The prior r -coordination is also proposed for oxidative addition of phenyl-propargyl halides to zero-valent platinum complex Pt(PPh3)4, where Pt(PPh3)2 and Pt(PPh3)3 are active species for the oxidative addition. Kinetic study reveals slow formation of Pt(r/ -PhC=CCH2X)(PPh3) n = 2, 3), from which... 

As a rare example, oxidative addition via ionic mechanism to give the cis product is also known [16,17,24]. Oxidative addition of propargyl halides to a zero-valent platinum complex results in cA-(halogeno)(j7 -propargyl)platinum(ll) complex as a kinetic product (Scheme 3.10). 

Oxidative addition of vinylic C-S bond to zero-valent platinum complex has recently been investigated in detail [139], The reaction of Pt(C2H4)(PPh3)2 with... 

Secondary phosphines are more reactive toward zero-valent complexes. When zero-valent platinum Pt(tran5-stilbene)(dppe) reacts with PHMesa (Mes = mesityl), competitive oxidative addition of P-H and P-C bonds takes place via a three-coordinate Pt(dppe)PHMes2 common intermediate (Scheme 3.84) [168]. Since the P-H bond cleavage product is converted to the P-C bond cleavage product, the former is regarded as a kinetic product and the latter is a thermodynamic one. 

Oxidative addition of other group 14 atom-tellurium bonds (Si-Te, Ge-Te, and Sn-Te) is also achieved (Eq. 3.47) [172]. Reactions of zero-valent platinum complex R(PEt3)3 with RTeMMcs (M = Se, Ge, Sn) at 25°C result in the formation of the tra 5 -Pt(TeR)(MMe2)(PEt3)2 within 10 min. 

Oxidative addition of transition metal-hydride and transition metal-carhon bonds to zero-valent transition metal complexes provides convenient method for preparation of homo- and heterodinuclear organometallic complexes. Oxidative addition of iron-hydride to zero-valent platinum complex giving Fe-Pt heterodinuclear complexes was demonstrated hy the reaction of HFe[Si(OMe)3](CO)3(/c -dppe) with zero-valent platinum complex such as Pt(C2H4)3 or Pt( 1,5-cod)2 giving eventually heterodinuclear ethyl or cyclooctenyl complex (Scheme 3.86) [175]. The resulting heterodinuclear structure is stahihzed hy the bridging dppe ligand and the siloxo moiety. 

The latter carbonylation involves the formation of PtH(SR)(PPh3)2 by the oxidative addition of RSH to the zero-valent platinum complex. A possible pathway may include the CO insertion into the S-Pt bond of PtH(SR)(PPh3)2. Then, acylplatination of alkynes generates p-thiocarbonyl-substituted vinylplatinum intermediate, which undergoes reductive elimination to give the a,p-unsaturated thioesters with regeneration of the catalyst. 

This chapter commences with a review of a limited number of ternary hydride systems that have two common features. First, at least one of the two metal constituents is an alkali or alkaline earth element which independently forms a binary hydride with a metal hydrogen bond that is characterized as saline or ionic. The second metal, for the most part, is near the end of the d-electron series and with the exception of palladium, is not known to form binary hydrides that are stable at room temperature. This review stems from our own more specific interest in preparing and characterizing ternary hydrides where one of the metals is europium or ytterbium and the other is a rarer platinum metal. The similarity between the crystal chemistry of these di-valent rare earths and Ca2+ and Sr2+ is well known so that in our systems, europium and ytterbium in their di-valent oxidation states are viewed as pseudoalkaline earth elements. 

Cyanide complexes of platinum occur most commonly in the divalent state, although there has been increasing interest in the complexes formed with platinum in a higher oxidation state. Among the complexes most recently studied have been the mixed valent complexes where platinum cyanides in the divalent state are partially oxidized. These complexes form one-dimensional stacks with Pt-Pt interactions. In the solid state these materials show interesting electrical conductivity properties, and these compounds are discussed by Underhill in Chapter 60. In this section the preparative procedures and spectroscopy of the complexes will be covered, but for solid state properties the reader is referred to Chapter 60. 

The chemistry of carbene complexes is a field which has developed in the past 20 years. The current interest is primarily centered on the chemistry of the early transition elements, but much of the early work was carried out at low valent, metal centers. The major complexes formed by platinum are those with the metal in a divalent oxidation state. 

Palladium(I) complexes are in general dimeric or oligomeric and consequently, although they have a d9 configuration, they are usually diamagnetic. The chemistry of this oxidation state is discussed in Section 51.3. Unlike most transition metals, the chemistry of low valent palladium is not dominated by carbonyls [Pd(CO)4] is only stable at 80 K in a matrix. As with platinum, the most common complexes are those containing phosphines, where complexes of the type [PdL ] (n = 2, 4) have been isolated. The chemistry of palladium(O) is dealt with in Section 51.2 and elsewhere.2... 

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