Platinum-carbon bonds

Another interpretation of the 2045 cm" peak is the multiple bonding species formation. This frequency is comparable to the vibrational frequency of terminally-bonded CO in platinum carbonyl binary complexes Pt-(CO)n (n=l,2,3,4) synthesized by Ozin et al. by co-condensation of platinum atoms with carbon monoxide molecules in an argon matrix at very low temperature [22]. We prefer the assignment of this peak to the multiple bonded platinum carbon monoxide... 

The catalyst layer is the most expensive part of this fuel cell. It is made from a mixture of platinum, carbon powder, and PEM powder, bonded to a conductive carbon fiber cloth. We obtained ours from E-Tek Inc. The cost for an order of their ELAT catalyst cloth sheet includes a setup charge. So get together with others for a larger order if you want to keep costs down. We paid 360 for a piece of ELAT 15.2 centimeters by 15.2 centimeters [6 inches by 6 inches] including the 150 setup charge. This piece provides enough for about twelve disks. Each fuel cell requires two disks of ELAT and one larger disk of PEM to make the sandwich, so you can make six cells from this size... 

Chemically, the platinum-carbon bond in iodo(trimethyl)-platinum(IV) is relatively nonreactive and is unaffected by water or oxygen. The iodine atoms may be replaced by other ions through simple metathetical reactions. 

The triphenylphosphine complex 42 b reacts with bromine to give a platinum(IV) species 42f, assigned the cyclic structure with four platinum-carbon c-bonds. The reaction sequence here must begin with the attack of a bromine molecule on an uncoordinated olefin, as otherwise it is hard to see why two metal-carbon bonds are formed, and not one metal-carbon and one metal-bromine. 

This bonding to carbon atoms is again found in cyclopropane platinous chloride, which has recently been shown to contain a four-membered ring of three saturated carbon atoms and a platinum atom (la). The insolubility in noncoordinating media suggests that it is a polymer held together by... 

Contrary to previous reports suggesting colloidal metal as the active species in Pt-catalyzed hydrosilylations, the catalyst was found to be a monomeric platinum compound with silicon and carbon in the first coordination sphere.615 The platinum end product at excess olefin concentration contains only platinum-carbon bonds, whereas at high hydrosilane concentration, it is multinuclear and also contains platinum-silicon bonds. An explanation of the oxygen effect in hydrosilylation was also given to show that oxygen serves to disrupt multinuclear platinum species that are formed when poorly stabilizing olefins are employed. 

The reaction in Eq. 13.5 can be thought of as an electrophilic attack by HgtUiotvlhe platinum-carbon bond. The oxidative addition reaction shows oxidation of Pt(II) to Pt(lV) with simultaneous expansion of the coordination number of Pt from A to 6. 

Acetylacetone usually forms transition metal complexes by coordination through bidentate oxygens. Since platinum forms unusually strong bonds to carbon, acetylacetonato complexes of platinum(II) are frequently C-bonded. When Pt(acac)2 is treated with 1 mole of pyridine, a bidentate oxygen-bonded acetylacetonate ligand is converted to a y-carbon-bonded ligand. 

Platinum-carbon bond cleavage can be photoinduced. The photoinduced reductive elimination of cyanoalkanes from ftwis-PtH(R)(PPh3)2 (R = CH2CN, (CH2)2CN, (CH2)3CN) involves initial isomerization to the cis isomer prior to reductive elimination.563 Photolysis of platinacyclopentanes gives alkanes and alkenes.564... 

The complex (197) with a dithiocarboxylate ligand coordinated to platinum(II) bonded through both monodentate carbon and die chelating dithiocarboxylate ligand has been prepared from either the thiocarbonyl platinum(II) precursor or the carbon disulfide adduct of platinum(O).1796,1797 A cyclopentadienyl-substituted dithiocarboxylate ligand (198) can be used to prepared S,S-bonded platinum(II) and (IV) complexes Pt(C5H4CS2)2 and PtfCsKtCS 2-. The complexes show v(PtS) at 340 cm-1, and in each case electronic absorption bands of the Pt— L type are at 19 500 cm-1 and 29 500 cm-1.1798... 

The fact that the platinum-carbon-bond distances vary considerably suggests that there is some cr-bonded character between the /3 carbon and the metal (41, 42). The existence of this cr-bond character also supports the explanation for the anomalous NMR spectra of these complexes in polar solvents (44, 46). While the NMR spectrum of the 77-vinylsilyl ether complex (44) exhibits the expected ABX pattern for the vinyl protons in... 

In the former structure, two of the bonding electrons would be provided by the platinum, while in the latter the CO would be coordinated to the platinum. The force constant for the metal-carbon bond for CO on Cabosil-supported platinum was found to be 4 X 106 dynes/cm. On the simplest basis this force constant would indicate a single platinum-carbon bond. There is, however, considerable uncertainty in going from force constants to bond order so that a contribution, perhaps as high as 50 %, of the doublebond species could not be ruled out. The simple bridged structure... 

Study of the Metal-Carbon Bond of Carbon Monoxide Chemisorbed on Platinum... 

As already stated, benzonitrile is a very useful solvent for the insertion of platinum with PtCl2 (Eq. 8). Since the Pt atom in platinum acetylacetonate is bonded to carbon, it was not used for the insertion of this metal. 

The effect of hydrogen on naphthenic hydrocarbons is mainly that of ring scission followed by immediate saturation of each end of the fragment produced. The ring is preferentially broken at favored positions, although generally all the carbon-carbon bond positions are attacked to some extent. For example, methyl-cyclopentane is converted (over a platinum-carbon catalyst) to 2-methylpentane, 3-methylpentane, and n-hexane. 

Excitation to the LC states may also result in population of the CT-excited states, especially the LLCT states. These phenomena are frequently encountered in complexes containing both rc-acceptor (eg 1,10-phenantroline or 2,2 -bipyridyl) and 7r-donor ligands (eg aromatic thiols). Then the LC excitation can induce charge transfer between these ligands through central atom (LLCT) that leads to a photoredox reaction. Such reactions were reported in the case of heteroleptic organometallic compound [Rh CylLXCsHs)]3 [37], heteroleptic Re1 complex fac-[Re (L)(CO)3(bpy)]n+ [46] and metal-carbon-bonded platinum complexes [47]. 

Recent structural and spectroscopic investigations of organometallic complexes bonding two carbons of an allenic ligand to one rhodium 50 72> 87,95) or platinum atom 58,87,98,132) may have some pertinence to possible bridged intermediates proposed for various electrophilic additions to allenes, and the cr-iron-jr-iron complexes derived from allene and diiron... 

If the Kharasch-Ashford proposal had been correct, the existence of stereoisomers would be expected in the case of unsymmetrically substituted olefins [2, 3], Moreover, if a monosubstituted olefin were bound to platinum via a Pt—C cr-bond, the carbon atom containing the substituent would become a... 

In spite of the presence of metal-carbon o-bonds and carbon-carbon triple bonds in the backbone, the metal-poly-yne polymers are fairly stable to air in the solid state and show considerably good thermal stability (Table 6). The platinum-containing... 

Oxanickelacyclopentene can be prepared from the reaction of oxanickelacyclopropane with a terminal alkyne <2007EJ04981>. Substituted platinacyclopentane was prepared using a ring-expansion reaction, involving insertion into the platinum-carbon bonds <20070M1044>. 

---