Spectroscopic data, platinum complexes

A number of comparative studies have been made of organogold compounds and related complexes of neighboring metals, notably platinum and mercury as well as the other group IB elements. These comparisons have included such aspects of their chemistry as thermal stability and reactivity, bonding modes, and spectroscopic data. 

Preparing trans-hydrido-alkyls or -aryls of platinum(II) does not require prior isolation of a hydroxo complex. The main routes we have used are shown in Equations 9-11, and selected spectroscopic data, including some from the literature, are in Table IV. 

All the compounds are crystalline solids, and with the exception of RuH(OCOCH3)(CO)[P(C6H5)3]2, can be manipulated in air briefly without decomposition. The platinum complex, ris[Pt(OCOCH3 )2 P(C 6H 5 )3 2] is soluble in chloroform, dichloromethane, and methanol but practically insoluble in benzene and acetone. The other complexes are soluble in chloroform and dichloromethane, moderately soluble in benzene and acetone, and almost insoluble in light alcohols. Analytical and spectroscopic data are given in the following table. Infrared data refer to mulls in Nujol XH nmr data were obtained at 90 MHz using solutions in chloroform-d and are referenced to TMS. 

The partial confusion arising after Dewar s and Chatt s reviews were published, was resolved after Chatt and Duncanson reported in 1953 in the Journal of the Chemical Society the results of infrared spectroscopic studies on a range of olefin platinum(II) complexes [38]. In this highly cited paper they proposed, with particular reference to Dewar s model, that in the olefin platinum(II) complexes the cr-type bond would be formed by overlap of the filled re-orbital of the olefin with a vacant 5d6s6p2 hybrid orbital of the platinum atom, and the re-type bond by overlap of a filled 5d6p hybrid orbital of the metal with the empty antibonding re-orbital of the olefin (Fig. 7.8). In addition, Chatt and Duncanson illustrated how the model could be used to interpret not only the physical properties of the olefin platinum compounds, such as the spectroscopic data and dipole moments, but also their reactivity and their greater stability compared to the olefin silver salts. 

Nickel, palladium and platinum - The low natural abundance of the 61Ni isotope means that there is a paucity of data on NMR spectroscopy of this element, although much useful information can be derived from spectra of ligand nuclei (e.g. Zschunke et al., 1992 Oik et al., 1992). In the case of 105Pd, the large value of the quadrupole moment presents additional difficulties for direct spectroscopic measurements and, as with nickel, NMR studies have concentrated on the characterisation of ligand nuclei. An example here is the application of two-dimensional NMR to investigate the structure of a nucleic acid palladium complex (Bichenkova et al., 1992). 

Bryce and co-workers reported that the crown-annulated TTF derivatives 98 and 99 were used for UV-Vis spectroscopic and electrochemical studies of metal complexation <1996J(P2)1587>. Solution electrochemical studies showed that metal complexation to the crown unit leads to a small anodic shift in the first oxidation potential of the TTF system. Langmuir-Blodgett films of amphiphilic 99 have been assembled on solid substrates by Y-type deposition. Compounds 100-104 were used to prepare self-assembled monolayers on gold and platinum surfaces <1998AM395, 2000JOC8269>. The self-assembled monolayers of 104 were the most stable in this series of TTF-crowns. Electrochemical data for the self-assembled monolayers of 100-104 in MeCN showed two reversible one-electron waves, typical of the TTF system. The self-assembled monolayers of 102-104 exhibited an electrochemical response in aqueous electrolyes, which was observed between 50 and 100 cycles. 

Hydride complexes of platinum have received considerable study since the preparation of PtHCl(PEt3)2- Spectroscopic studies by NMR techniques have been widely used because of the structural information which can be obtained from coupling constant data to Pt and other nuclei. Platinum is widely used as a heterogeneous catalyst, and vibrational studies on platinum hydride complexes have been useful for comparison of a hydrogen atom bonded to a single platinum with that bonded to a surface. Complexes of platinum have been used to catalyze hydrogenation, hydrosilylation and isomerization reactions with alkenes and alkynes, as well as H/D exchange reactions on alkanes. Hydride complexes are frequently proposed as intermediates in these reactions, and the pathways related to the known chemistry of hydride complexes. 

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