Diplatinum II Compounds

Several examples of diplatinum(II) compounds with Pt(II)-Pt(II) bonds have been reported since 2005, which was historically underdeveloped in contrast with the prevalent diplatinum(lll) compounds. Some examples of weak intermolecular metal-metal interactions were reported in the past few years [134]. But the intermolecular interaction, although it is intriguing from a structural perspective and has exhibited interesting physical properties, is outside the scope of the following section. 

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A phosphinito (R PO") bridging diplatinum(I) compound 177 and its protonation reactions were reported recently. Complex 177 was protonated by a variety of proton sources (HCl, HBr, HBF, PfOlHCyj) to produce a series of phosphide hydride bridged diplatinum(II) compounds, while two of the protonations are presented in Scheme 10.78 [128]. It was found that the protonation preferentially... 

Two hydride- and acetylide-bridging diplatinum(II) compounds (192,193) were characterized as products of reactions between Pt(II) and Pt(0) precursors via C-H bond activation and/or rearrangement (Scheme 10.80) [136]. 

Diplatinum(II) compounds (195, 196) with both intramolecular Pt(II)-Pt(II) bond and intermolecular Pt(II)-Pt(II) interactions were reported in the last decade (Figure 10.21) [138], The diplatinum(ll) paddlewheel monomer assembles into 1-D infinite chains through weak intermolecular Pt(ll)-Pt(ll) interactions, which were studied by a combination of spectroscopic and... 

As for the Pd(III)-Pd(III) moiety, 2-electron oxidation of diplatinum(II) compounds was proven to be a viable synthetic route toward Pt(lll)-Pt(III) bonds. A series of phosphido bridged diplat-inum(II) compounds were oxidized to form Pt(llI)-Pt(III) compounds 198 and 199 (Scheme 10.83) [140]. Complex 198 can further undergo reductive coupling to produce [CgFjPPhj] and Pt(II) species under mild conditions. It is noteworthy that Pd(II) compounds with identical ligand profiles were also tested for the same reaction condition, but no corresponding Pd(III)-Pd(III) moieties were obtained. 

Fig. 2. Schematic structures of compounds related to platinum blues . Diplatinum(II) species with HH (A-l) and HT (A-2) oriented amidate ligands, tetraplatinum(II) species (A-3), tetranuclear [Pt2 25]4 blues without (B-l) and with axial ligand (B-2), tetranuclear [Pt2 5]4 tans (C-l, C-2), and various types of diplatinum(III) species with HH (D-l, D-3) and HT (D-2) orientation of the bridging ligands. The amidate ligands are expressed with their N- and O-coordinating atoms only.

Recently compounds containing cyclic polyolefins coordinated to platinum or palladium have received considerable attention as a result of the unique bonding found in these compounds and their possible use as intermediates in a variety of reactions. Several methods have been reported for the synthesis of these compounds, and among these procedures the displacement of ethylene1 from di-Ju-chloro-dichlorobis(ethylene)diplatinum(II) and benzonitrile2 from dichlorobis(benzonitrile)palladium(II) are the most generally applied procedures. Both of these methods involve the preparation of intermediates before the isolation of the product, and in addition these intermediates tend to decompose upon storage. 

In 1982, novel diplatinum(II) diphosphite complexes were reported162. These compounds were readily generated by oxidative addition to the binuclear platinum(II) tet-rakis(diphosphite) complex, [Pt2(pop)4]4 (pop = P205H2 ), with halogens or methyl... 

It is probable that tetrachloro(diethyIene)diplatinum(II) was first prepared by Zeise by decomposition of trichloro-(ethylene)platinic(II) acid.1 Boiling hexachloroplatinic-(IV) acid with chloroform also gave the compound.2 However, it was first obtained in sufficient quantity for investigation by Anderson,3 who boiled an ethanolic solution of sodium hexachloroplatinate(IV) 6-hydrate until reduction to platinum(II) was complete. This procedure is tedious, and the yields are affected markedly by impurities in the platinum salt and by the presence of other platinum metals.4 Optimum yields of 75% are obtained only after much experience. The general method of Kharasch and Ashford,5 involving adding an olefin to a suspension of platinum(IV) chloride in warm benzene or glacial acetic... 

Potassium trichloro(ethylene)platinate(II) 1-hydrate can be isolated in about a 7-g. quantity by cooling to 0° the yellow aqueous solution obtained from flask A (Fig. 18) after absorption of ethylene is complete. Tetraehloro-(dipropylene)diplatinum(II) can be prepared by the same procedure used for the ethylene compound except that twice the time of shaking is needed for propylene absorption and that final evaporations must be carried out below 40°.6... 

Recendy, gtJlium(III) htilide was used to reduce Pd(II) and Pt(II) precursor in the presence of an arene, to afford arene-bridged diptJladium(I) or diplatinum(I) compounds (Scheme 10.58) [79]. For... 

Among all possible oxidation states, diplatinum(III) (Ptj ) compounds represents the vast majority and the quantity of compounds is second only to dirhodium(II) compounds among till metal-metal bonded moieties. In a comprehensive textbook chapter in 2005, the structure and chemistry of Pt-Pt bonded compounds were nicely reviewed by Murillo, which the reader is recommended to consult [2]. Therefore, an encyclopedic coverage of the literature is not the aim of the following section, and a representative selection of highlights made since 2005 will be introduced. 

The reaction between Pt(0) or Pt(II) hydride precursors and silane or germanes with E-H bonds (E = Si, Ge) can provide a variety of E-H bond activated products, for example, a series of silyl or germyl bridging diplatinum(I) compounds (Eigure 10.19) [130]. Further conversion of these compounds was possible including E-E bond coupling as well as the formation of Pt(II) silyl/germyl hydride. 

Platinum(II) salts behave similarly, although the range of cycloplatinated compounds is less extensive. Thus, chloride-bridged diplatinum complexes may be prepared with metallated N ligands such as azobenzene, 2-phenylpyridine, or 8-methylquinol-line . Tertiary phosphine and arsine complexes also may undergo metallation ... 

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