Platinum complexes dimeric

The platinum complex is square planar, while the palladium dimer also has planar 4-coordination (for other examples of mercaptide bridges see section 3.8.3) [116]. 

A derivative of cyclopentyne has been trapped in a matrix. Although cycloheptyne and cyclohexyne have not been isolated at room temperatures, Pt(0) complexes of these compounds have been prepared and are stable." The smallest cyclic allene" so far isolated is l-/err-butyl-l,2-cyclooctadiene 107." The parent 1,2-cyclooctadiene has not been isolated. It has been shown to exist transiently, but rapidly dimerizes." " The presence of the rert-butyl group apparently prevents this. The transient existence of 1,2-cycloheptadiene has also been shown," and both 1,2-cyclooctadiene and 1,2-cycloheptadiene have been isolated in platinum complexes." 1,2-Cyclohexadiene has been trapped at low temperatures, and its structure has been proved by spectral smdies." Cyclic allenes in general are less strained than their acetylenic isomers." The cyclic cumulene 1,2,3-cyclononatriene has also been synthesized and is reasonably stable in solution at room temperature in the absence of air." ... 

The A-frame hydride [Pt2H2(/i-H)(/i-dppm)2] undergoes reductive elimination of H2 in the presence of tertiary phosphine ligands, L, to give the platinum(I) dimer, [Pt2HL(//-dppm)2]. Hill and Puddephatt have shown that this occurs via the intermediate [Pt2II2(/i-H)L(//-dppm)2] (14).99 Carbon monoxide reacts rapidly and reversibly with [PtH(/r-PP)2Pt(CO)]+, PP = R2P-CH2-PR2, R = Et or Ph, to give [PtH(/i-PP)2Pt(CO)2]+ and [PtH(CO)(/u-PP)2Pt(CO)2]+, the first reported mixed valence, platinum(0)-platinum(ll) complexes.100... 

Lippert and co-workers have reported a similar series of A-,O-bridged platinum(III) dimers in which the bridging ligands are the pyrimidines, 1-methyluracil, 1-methylthymine, or 1-ethylthy-mine. Chemical oxidation of dimeric platinum(II) complexes gave [Pt2XY(L)2(NH3)4]2+, X,Y = N03", N02, H20, Cl", or Br", L=l-MeU, 1-MeT, 1-EtT. 27 t30 They too found that the HT dimers are more stable than the HH.430... 

Visser and Ramakers [6] liberated 465 by the action of 2-methylthiirene 1,1-dioxide on the bis(triphenylphosphane)platinum complex 469 (Scheme 6.96) and observed a dimer, probably 474, or several dimers. The synthesis of 469 was accomplished by dehydrobromination of 468b in the presence of bis(triphenylphospha-ne)(ethylene)platinum and was believed to proceed via the trapping of 465 by the platinum complex. Jones et al. [185] doubted this opinion and regarded the reversed sequence as more likely, that is, the complexation of 468b by (PPh3)2Pt followed by the dehydrobromination. 

An attractive suggestion for the mechanism for multiple exchange, in the light of current knowledge, is the involvement of dimeric platinum complexes (53), the hydrocarbon interacting with both platinum atoms ... 

In the absence of triphenylphosphine a tris-SPO platinum complex forms when SPO is reacted with Pt(cod)2, which is insoluble and for which the structure is not known it could be either a hydride (4) or an oligomeric or a dimeric S PO complex (5) lacking one molecule of hydrogen. The reaction with alkene, CO and H2 gives complex 6, which was identified as the acyl tris-SPO complex by NMR. It shows an... 

A new preparative route to platinum(II) hydrides, particularly for those containing bulky phosphine ligands, involves the reaction of phosphines with bis[(2-methoxy-5-cyclooctenyl)chloroplatinum] in methanol. The reaction (equation 35) involves the use of 4 moles of phosphine per mole of dimeric platinum complex. 

Binuclear platinum complexes with the o -pyridinato ligand can be formed with the metals in a divalent oxidation state. Two such complexes are the head-to-tail dimer [Pt(QH4NO)(NH3)2]2+ and the head-to-head tetramer [Pt2(CsH4NO)2(NH3)4]2+. This tetrame-ric platinum(II)-(II) compound is prepared under experimental conditions where the pH is kept around neutrality to avoid the formation of the partially oxidized complex.1120 Platinum-195 NMR spectroscopy can be used to show that the head-to-head to head-to-tail isomerization of these complexes involves dissociation of one ligand arm followed by an intramolecular linkage isomerization. Finally bond formation occurs between the divalent platinum with the vacant coordination site and the uncoordinated end of the ligand.1121... 

For both the dipalladium and palladium-platinum complexes the metal-metal bond is unusually reactive and a number of small molecules undergo an insertion reaction with (9) to give (10 equation 8). The corresponding sulfide-bridged dipalladium dimer can be prepared from the reaction of S8 or MeCHCH2S with (9).83 A mixed rhodium-palladium dimer can also be prepared from (9) (see Scheme 6).84... 

Nevertheless, synthesis of the monocyclopropenylidene platinum complex cis-Cl2(Bu3P)Pt[C3(f-Bu)2] was achieved when 3,3-dichloro-l,2-di-f-butylcyclopropene was treated in refluxing benzene with the dimeric complex /i-[(Bu3P)Cl2Pt]2 in a 2 1 ratio, instead of Pt° (equation 275)351. The reaction may involve a dimer intermediate analogous to that obtained in the palladium series above (equation 273). 

Most recently, Milstein and coworkers reported a new type of homogeneous catalytic reaction that generates silanones from secondary silanols under extremely mild conditions. The platinum complex (dmpe)Pt(Me)OTf) (27) (dmpe = Me2PCH2CH2PMe2, OTf = OSO2CF3 was treated with an equimolar amount of the silanol, (i-PrhSilKOII) (28), in acetone to yield a new dimeric hydrido-bridged complex 29 and the trimer 30 of diisopropylsilanone, 31 (Scheme 12)29. 

Oxidative addition of the Si-aryl carbon bond in the silacyclobutene ring to Pt gives the optically active intermediate Pt-complex. Further coordination of (+)-l-methyl-l-(l-naphthyl)-2,3-benzosilacyclobut-2-ene to the complex and cr-bond metathesis will provide the cyclic dimer Pt-complex. Reductive elimination from the intermediate platinum complex gives cyclic polymers and oligomers. Preference of cr-bond metathesis over reductive elimination gives polymers of higher molecular weight. The presence of EtsSiH in the system results in the formation of linear products via cr-bond metathesis. 

As shown in Scheme 45, DMSB can undergo polymerization or dimerization in the presence of similar platinum catalysts in good to excellent yields. The course of the reaction is apparently linked to the presence or absence of phosphine ligands platinum complexes that include added phosphines lead to dimerization, whereas polymerization usually occurred under ligandless conditions. Divinyltetramethyldisiloxane also serves as a ligand for the platinum-catalyzed dimerization of SCBs and disilacyclobutanes as reported by Chu and Frye <1993JOM(446)183>. 

Platinum complexes 92 were successfully obtained from [PtCl2(PR3)2] and dipotassium cyanodiselenoimidocarbo-nate. The reaction of dipotassium cyanodiselenoimidocarbonate with an appropriate transition dimer 93 leads to four-membered rings 94 in. 39—42% yields (Scheme 9) <2005EJI209>. 

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