Tris(trimethylsilyl)silanes and germanes in Pd-catalyzed cross-couplings

ORGN 135

Zhizhong Wang, and Stanislaw F. Wnuk, Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199
The E and Z vinyl tris(trimethylsilyl)silanes 1 and germanes 2 under oxidative conditions serve as good transmetalation agents in coupling reactions. Thus, treatment of the germane 2(E) (R = Ph) with H2O2 in aqueous NaOH/THF (or t-butylperoxide in dried KH/THF) followed by addition of aryl iodides or bromides and Pd(PPh3)4 gave E stilbene 4 (37-83%)Analogous coupling (H2O2/NaOH/THF/TBAF) of TTMS-silanes 1(E) with aryl halides also provided E stilbene 4 (75-98%). Fluoride ion was necessary to promote the coupling of silanes 1. The reaction has the general character and a variety of the conjugated and unconjugated TTMS-silanes 1 and germanes 2 undergo coupling with aryl and alkenyl halides. The coupling of Z- isomers 1 and 2 occurred with lessen stereoselectivity to produce E/Z mixture of products 4. Couplings with the (a-fluoro)vinyl TTMS-germanes 3 appeared to occur easier than with the corresponding (a-fluoro)vinyl stannanes and silanes since no addition of an extra ligand as well as activation with CuI or fluoride is required.