Substitution reactions platinum-catalyzed alkylation

Contrasting results are obtained for the peralkylated disilanes RMe2SiSi-Me2R (R = Me, "Bu, Bu), which yield only trace amounts of the 1,4-addition products under the same reaction conditions. Attempts to increase double silylation yields by use of other platinum or palladium catalyst precursors under carbon monoxide pressure or inert atmosphere were also unsuccessful for these peralkylated disilanes. Additionally, the reaction of tetramethyl-l,2-divinyldisilane results in conversion to an intractable product mixture, with no incorporation of the 1,3-diene. Phenyl-substituted disilanes are also effective reagents in the Pt(dba)2-catalyzed double silylation of phenylacetylene, but again, the alkylated disilanes and the vinyl-substituted disilane do not give double silylation products. 

A considerable number of pyrroles 30 with alkyl, alkenyl, or aryl substituents were synthesized by spontaneous cyclization of the enyne precursors 31 (when R = H, Ph, CH2OTHP), or upon treatment of 31 with the catalytic system PdCV KCl (when = H), or alternatively, by treatment of 31 with CuCb (when R H) <03JOC7853>. Treatment of y-ketoalkynes with amines in the presence of catalytic amounts of platinum dichloride constitutes a new route to 1,2,3,5-substituted pyrroles <03AG(E)2681>. An intramolecular rhodium(lI)-catalyzed N-H insertion reaction of 5-amino-7,Y-difluoro-a-diazo-P-ketoesters has been used for the synthesis of a series of 3-fluoropyrroles <03OL745>. 

Extensive mechanistic studies have been performed on reactions catalyzed by rhodium and platinum complexes containing enantiopure C2-symmetric diphosphine ligands.As discussed above, (1) the formation of the Tr-olefin-Rh(H) complex 19, (2) stereospecific cis addition of the hydridorhodium to the coordinated olefin to form the alkyl-Rh complex 20 (and then 2, and (3) the migratory insertion of a carbonyl ligand giving the acyl-Rh complex 17 with retention of configuration, have been established in the hydroformylation of 1-alkenes or substituted ethenes. Thus, it is reasonable to assume that the enantioselectivity of the reaction giving a branched aldehyde is determined at the diastereomeric (1) TT-olefin-Rh complex 19 formation step, (2) alkyl-Rh complex 20 formation step, or (3) acyl-Rh complex 17 formation step. 

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