Pt-Sn complexes

In the case of ethylene hydrogenation, the mechanism proposed by Parshall [61] involves the coordination of an alkene molecule through a five-coordinate intermediate (Eq. (13)) the subsequent alkene insertion into the Pt-H bond (Eq. (14)) and intervention of a second molecule of H2 (Eq. (15)) leads to the elimination of ethane and restoration of the catalytic active species [PtH(SnCl3)]2. However, in 1976 Yasumori and coworkers reported a kinetic analysis conducted on the hydrogenation of ethylene catalyzed by the Pt-Sn complex [(Me)4N]3[Pt(SnCl3)5] [70], under much milder conditions than those... 

The Pt-Sn complexes were studied extensively in the hydrogenation of vegetable oils to remove excessive unsaturation9. 

Pt-Sn Pt-Sn complex in acetone impregnated on A1203 / - / Reduced in situ at 375 °C at elevated H2 pressure. XPS... 

As noted in the Introduction, the Pt-Sn system has been studied extensively, both from the standpoint of the structure of the catalyst as well as the reason for the superior catalytic properties. Davis utilized Pt-Sn complexes, including Pt3Sn8Cl22, in an organic solvent to prepare supported catalysts (42). It was proposed that the reason for the superior activity of catalysts prepared in this manner was the formation of a PtSn alloy (48,49). 

The parent material for this particular hydrogenation, PtRu5(CO)jj(p-SnPhj) (Pg-C), was obtained from the reaction of Ph SnH with the hexanuclear cluster complex PtRUj(CO)jg(pg-C) - see Fig. 21.5b. The heterotrinuclear (Ru-Pt-Sn) complex was anchored to a mesoporous silica (38 A diameter) via the silanol groups, as previously described [49, 50]. 

The Pt-Sn complexes are quite inert to a number of reagents, including water and alcohols. 

The Pt—Sn complexes catalyze the hydrogenation of ethylene and some other olefinic compounds this action is doubtless connected with the ready dissociation of the complexes in solution, promoted by the trans-effect of SnClJ, which leaves vacant sites for coordination of olefin and of hydrogen (cf. also page 771). 

SCHEME 7.2 Coupled cycle mechanism for homogeneous WGS reaction over Pt-Sn complexes. Taken from Scheme 1 of C.H. Cheng, R. Eisenberg, J. Am. Chem. Soc. 102 (1978) 5968.)... 

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