Platinum-diphosphine complexes

Earle, M. J., McCormac, P. B. Seddon, K. R. Diels-Alder reactions in ionic liquids a safe recyclable green alternative to lithium perchlorate-diethyl ether mixtures. Green Chem., 1999, 1(1), 23-25 Doherty, S. Goodrich, P. Hardacre, C. et al. Marked enantioselectivity enhancements for Diels-Alder reactions in ionic liquids catalysed by platinum diphosphine complexes. Green Chem., 2004, 6(1), 63-67. 

Platinum-diphosphine complexes in [C4CiIm][PPg] have been studied via ip NMR [67,68]. Here, the insertion reaction of SnClj into the Pt-Cl bond of PtCljCbdpp) was observed, as well as the formation of an additional cationic complex. The structure of the catalyst could be elucidated via characteristic Jpp and Jpt p coupling constants. 

Rangits, G., Retocz, G., Berente, Z. et al, NMR investigation of platinum-diphosphine complexes in [bmim][RF5] ionic liquid, Inorg. Chim. Acta, 353, 301, 2003. 

The very first NMR investigation of elementary reactions involving transition metals was published by the group of Kollar [61, 62]. Focussing on the mechanisms of complex formation of platinum diphosphine complexes in [bmim]PF6, the authors found reactions being very similar to the ones in conventional solvents. They also observed a nowadays well-known effect, namely the partial decomposition of PF6 in the presence of water. 

Another method for enantioselective Baeyer-Villiger oxidations was developed by Strukul [28,29]. His catalytic system is based on cationic platinum-diphosphine complexes which activate H2O2 to oxidize cycHc ketones (Eq. 5). 

Kegl et al. used HP-NMR to investigate the behavior under syngas and CO pressure of three square-planar platinum diphosphine complexes with potential as hydroformylation catalysts. A platinum hydride and cationic platinum complexes were observed. 

Doherty, S., Goodrich, P., Hardacre, C., Luo, H. K., Rooney, D.W., Seddon, KR. Styring, P. (2004). Marked Enantioselectivity Enhancements for Diels-Alder reactions in Ionic Liquids Catalysed by Platinum Diphosphine Complexes, Green Chem., 6, pp. 63-67... 

Phosphine platinum complexes give active hydroformylation catalysts and both terminal and internal alkenes can be hydroformylated by selectively employing platinum-diphosphine complexes, often activated by an excess of tin chloride as the cocatalyst [25,26]. The combination of platinum chloride andtin(II) chloride leads to the formation of the trichlorostannate anion, which presumably acts as a weak coordinating anion, as tin-free catalyst systems have also been reported [27]. The group of Vogt found that the preformation of the catalyst also proved to be effective with only one equivalent of the tin source [28]. 

Carbene/diphosphine platinum(ll) complexes 141 or carbene/monophosphine platinum(ll) complex 142 were shown to be efficient for the cycloisomerisation of 1,6-enynes 140 (Scheme 5.37) [42]. The product 143 is obtained in higher yields and higher enantioselectivity when catalyst 142 is employed rather than catalyst 141. 

Mono and binuclear platinum(II) complexes with diphosphines have been reported as catalysts in the hydroformylation reaction. Dppp and related diphosphines are used as ligands in platinum/Sn systems for the hydroformylation of different substrates.99-107... 

Platinum(II) complexes with diphosphines based on DIOP (85),315-321 CHIRAPHOS (86),316,320 and bdpp (87)322-325 backbones have been prepared to be used, in the presence of SnCl2, as catalyst precursors in asymmetric hydroformylation of styrene and other alkenes. 

While apparently no metallasilsesquioxane complexes of nickel and palladium have yet been prepared, several literature reports have appeared on platinum compounds containing silsesquioxane ligands. Abbenhuis reported the synthesis and characterization of three platinum(II) complexes stabilized by the chelating diphosphine ligand dppe (= 1,2-bis(diphenylphosphino)ethane) as outlined in Scheme 63. ... 

Strukul and coworkers have carried out the catalytic epoxidation of a,/3-unsaturated ketones with H2O2 mediated by a series of platinum diphosphine based complexes, that confirm the ability of the Pt(II) center to increase the nucleophilicity of hydrogen peroxide . Interestingly, this transformation may be accomplished in enantioselective fashion when chiral diphosphines such as those in 53 are used (ee up to 63%). 

Notably, it is not just heteroatom-functionalized alkenes that can behave as dienophiles with metal-bound phospholes. It has been demonstrated that reaction of 2equiv of 3,4-dimethyl-l-phenylphosphole with a cationic platinum(n) complex of an enantiomerically pure cyclometallated A, A -dimethyl-l-(l-naphthyl)ethylamine ligand affords, following decomplexation with cyanide, the novel optically pure diphosphine (-f)-267 quantitatively as an air-sensitive oil (Scheme 93) <2000CC167>. The high-frequency chemical shift of one of the phosphoms centers (5 4.9 and 104.2 ppm (7pp = 43.9 Hz)) is indicative of rwt>-jy -stereochemistry. Similar reactivity has been... 

Scheme 4. Platinum(O) complexes containing various diphosphine ligands.

R. Sinigaglia, R. A. Michelin, F. Pinna, G. Strukul, Asymmetric epoxidation of simple olefins catalyzaed by chiral diphosphine-modified Platinum(II) complexes", Organometallics 6 (1987) 728. 

For instance, a cationic aqua complex/<2c-[PtMe3(OH2)3]" is indefinitely stable in aqueous solutions at elevated temperatures, whereas diphosphine - supported trimethyl platinum(lV) complexes such as/<2c-(dppbz)Pt Me3(OR) and/ac-(dppe) Pt MesCOR) shown in Fig. 5 undergo concurrent C-C and C-O reductive elimination at 120°C [21, 23, 24]. 

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