Platinum complexes carbon-donors

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]. 

The rates of substitution of the latter ligand by TU, DMTU and TMTU were followed as a function of nucleophile concentration, temperature and pressure by s.f. spectrophotometry. The reaction was first order in both platinum complex and nucleophile concentrations. From the form of the rate law and the negative entropies and volumes of activation it was concluded that the mechanism is an associ-atively activated substitution. It prevailed that substitution in the terpy parent ligand did not affect significantly the kinetic parameters. The reaction was slower when a carbon a-donor was in the cis position than when an N a-donor occupies this position, indicating a different situation from the effect of a Pt-C bond in the trans position. 

The availability of different metal ion binding sites in 9-substituted purine and pyrimidine nucleobases and their model compounds has been recently reviewed by Lippert [7]. The distribution of metal ions between various donor atoms depends on the basicity of the donor atom, steric factors, interligand interactions, and on the nature of the metal. Under appropriate reaction conditions most of the heteroatoms in purine and pyrimidine moieties are capable of binding Pt(II) or Pt(IV) [7]. In addition, platinum binding also to the carbon atoms (e.g. to C5 in 1,3-dimethyluracil) has been established [22]. However, the strong preference of platinum coordination to the N7 and N1 sites in purine bases and to the N3 site in pyrimidine bases cannot completely be explained by the negative molecular electrostatic potential associated with these sites [23], Other factors, such as kinetics of various binding modes and steric factors, appear to play an important role in the complexation reactions of platinum compounds. 

In addition to catalyzing hydroformylation, the platinum SPO complexes are excellent hydrogenation catalysts for aldehydes (as already demonstrated by the side products of hydroformylation), in particular, in the absence of carbon monoxide. Further, in ibis process, the facile heterolytic splitting of dihydrogen may play a role. The hydrogenation of aldehydes requires the presence of carboxylic acids, and perhaps the release of alkoxides from platinum requires a more reactive proton donor than that available on the nearby SPO. For example, 4 hydrogenates 2-methylpropanal at 95 °C and 40 bar of H2 to give the alcohol, with a TOF of 9000 mol moN h (71). 

PF3 is the strongest of the P-donor n acids and its ability to replace carbon monoxide in a zerovalent transition metal complex was realized in the 1940s by Chatt. However, WiUdnson was the first to isolate a homoleptic PF3 complex, viz. [Ni(PF3)4] see Homoleptic Compound), which turned out to be more thermally stable than [Ni(CO)4] subsequent research into the PF3 complexes of transition metals was carried out by Nixon. Bidentate ligands with two PF2 moieties have been prepared an example is F2P(l,2-cyclo-C6Hio)PF2. The volatility of the homoleptic PF3 transition metal species together with their relative stability has led to their use in MOCVD processes [Pt(PF3)4], for instance, has been used to deposit platinum films. ... 

Aqua ions are known but not very stable. Substitution of Pt in aqueous solution is sometimes zero-order in the added ligand, L, or can have both L-dependent and L-independent contributions to the rate, probably because intermediate formation of an unstable aqua complex is the rate-determining step for the L-independent pathway. A large number of O-donors, particularly anionic ones, give stable complexes, for example, carbonate, acetate, oxalate, acetylacetonate, and alkoxide. Tetrameric platinum(II) acetate is formed by formic acid reduction of Pt solutions in acetic acid. It does not appear to be a very useful synthetic precursor for Pt chemistry. The acetylacetonate [Pt(acac)2] is monomeric and square planar. 

Alternatively, since the platinum atom in trimethyl(nonane-2,4-dione)platinum(IV) is directly above the carbon atom, one could conceive of this as a pseudo-n-allylic complex over the three ring carbon atoms. A final description of bonding in these bridge-bonded complexes can be given in terms of valence-bond theory which suggests that there is a predominence of a third resonance contributing form (II) which enhances the donor ability of the unique ring carbon atom 27). 

Clark and Ward (45) obtained NMR parameters for a series of phenyl-platinum(2 +) complexes rrflns-[(C6H5)Pt(As(CH3)3)2L]+PF6, (IV), where L is a neutral donor ligand. Carbon-13 NMR parameters for IV are given in Tables XXVIII and XXIX. 

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