Platinum hydrido

There is one interesting report of an inner sphere reductive migration in a platinum hydrido complex (equation 104). 

Addition of phenylacetylene to the platinum hydrido complexes R3Si PtH(PPh3)2 (entries 117 and 118) leads to reductive elimination of HSi R3 and formation of a Pt(0)-alkyne complex. A similar Pt(0) product is observed from the cyclic precursor in entry 119. 

In the early 1970s, Clark and Kurosawa [121] intensively investigated the mechanism of stoichiometric and catalytic isomerization of terminal and internal olefins (1-butene, allyl ethers) with phosphine-modified platinum hydrido complexes such as fcr ws-[HPt(PR3)2(acetone)]X. Later, Toniolo et cd. [122] showed that the isomerization rate is strongly dependent on the temperature. Hydroxy groups being a constituent of allyl alcohols may also control isomerization [121]. 

Thermal cure system. The thermal cure system is based on a hydrosilylation addition reaction between vinyl-functionalized and silicon-hydrido functionalized polysiloxanes [32,33,35], Unsaturated organic groups react with a Si-H functionality in the presence of a platinum-based catalyst (Scheme 10). 

Several hydrido(phenoxo) complexes of nickel, trans-[NiH(OPh)L2] (6) (a L= P Prs b L = PCys c L = PBnj), have been prepared by the metathesis reaction of NaOPh with trans-[NiHClL2] (Eq. 6.6). The complex 6c was obtained as the phenol-solvated complex whose structure was determined by X-ray analysis [9]. An analogous platinum complex trans-[PtH(OPh)(PEt3)2] (7) was prepared by the reaction of trans-[PtH(N03)(PEt3)2] with NaOPh (Eq. 6.7). The complex 7 is air-stable but thermally sensitive and decomposes at room temperature. The structure was elucidated by X-ray analysis [10]. 

In 1979, the first isolation of the hydrido(hydroxo) complex by oxidative addition of water to an electron-rich platinum(O) complex was accomplished by Yoshida and Otsuka [22]. Highly coordinatively unsaturated bis(triisopropylphosphine)platinum (24b) can activate water very easily at room temperature to give the hydrido(hydroxo)... 

Yoshida and Otsuka found that platinum(O) complexes [PtLj] (26) (a L = PEtj b L = P Prj) and rhodium hydrido complexes such as [RhHLj] (L = P Prs 33, PEts), [RhiHidr-NJlPCyslJ (34), tram-[RhH(N2)(PPh Bu2)J, and [RhH(P Bu3)J, all of which carry electron-donating alkylphosphine ligands, can catalyze the water gas shift reaction under fairly mild conditions (100-150°C CO 20 kg/cm ) (Eq. 6.32) [23, 60]. Among these complexes, [RhH(P Pr3)3] (33) was the most active catalyst precursor. Several complexes were isolated from or detected in the reaction mixture... 

Hydrido(hydroxo) complexes derived from the oxidative addition of HjO to [Pt(PR3)3] (26) are stronger bases than aqueous alkali in organic media. Platinum(O)... 

Platinum(II) Complexes with Hydrido and Dihydrogen Ligands 718... 

Protonation reactions of the related dimethyl(hydrido)platinum(IV) complex TpMe2PtMe2H (58) leading to rapid methane reductive elimination have also been reported (86). This protonation was shown to occur exclusively at the pyrazole nitrogen, presumably forming a five-coordinate Pt(IV) intermediate. This species should undergo C-H coupling, and while a Pt(II) methane complex is not observed, trapping with... 

The oxidative addition of alkane C-H bonds to Pt(II) has also been observed in these TpRa -based platinum systems. As shown in Scheme 19, methide abstraction from the anionic Pt(II) complex (K2-TpMe2)PtMe2 by the Lewis acid B(C6F5)3 resulted in C-H oxidative addition of the hydrocarbon solvent (88). When this was done in pentane solution, the pentyl(hydrido)platinum(IV) complex E (R = pentyl) was observed as a... 

The question of which pathway is preferred was very recently addressed for several diimine-chelated platinum complexes (93). It was convincingly shown for dimethyl complexes chelated by a variety of diimines that the metal is the kinetic site of protonation. In the system under investigation, acetonitrile was used as the trapping ligand L (see Fig. 1) which reacted with the methane complex B to form the elimination product C and also reacted with the five-coordinate alkyl hydride species D to form the stable six-coordinate complex E (93). An increase in the concentration of acetonitrile led to increased yields of the methyl (hydrido)platinum(IV) complex E relative to the platinum(II) product C. It was concluded that the equilibration between the species D and B and the irreversible and associative1 reactions of these species with acetonitrile occur at comparable rates such that the kinetic product of the protonation is more efficiently trapped at higher acetonitrile concentrations. Thus, in these systems protonation occurs preferentially at platinum and, by the principle of microscopic reversibility, this indicates that C-H activation with these systems occurs preferentially via oxidative addition (93). 

Fig. 4. Relevant structures for the discussion of methane activation by (bipyrimi-dine)PtCl2 Methane complex of Pt(II) (A) methyl(hydrido)platinum(IV) complex, the product of the oxidative addition (B) transition state for intramolecular deprotonation of the methane complex ( cr-bond metathesis , sometimes also called electrophilic , C) intermolecular deprotonation of the methane complex ( electrophilic pathway , D).

Section III.C A Hydrido(methyl)carbene Complex of Platinum(IV) (223) and Methyl(hydrido)platinum(IV) Complexes with Flexible Tridentate Nitrogen-Donor Ligands (224) are structurally related to the system shown in Scheme 13 and give additional information on how steric and electronic factors influence the stability of platinum(IV) methyl hydrides. 

An excess of ligand, including CO, will often inhibit isomerisation. HCo(CO)4, an unstable hydrido-carbonyl complex, belongs to the examples of catalysts also active in an atmosphere of CO. This is the only homogeneous catalyst being commercially applied, albeit primarily for its hydroformylation activity. Higher alkenes are available as their terminal isomers or as mixtures of internal isomers and the latter, the cheaper product, is mainly converted to aldehydes/alcohols by hydroformylation technology. Later we will see that the isomerisation reaction also plays a pivotal role in this system. Since 1990 several catalysts based on rhodium, platinum and palladium have been discovered that will also hydroformylate internal products to terminal aldehydes. 

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