Cross coupling reactions substituent effect study

Group 10 TM complexes (110) bearing allyl ligand were synthesized by breaking the corresponding dimer [MCI (R R -allyl) (2 (109) with two equivalents of free NHC ligand (equation 15). Aryloxy dimer [Ni(allyl)(OAr)]2 (Ar = 2,6-di-i5o-propylphenyl) has also been employed for the preparation of NHC-allyl Ni complexes.Since the [(NHC)PdCl(allyl)] complexes exhibited an excellent activity in palladium-catalyzed cross-coupling reactions,this series was extensively studied with special attention to allyl substituent effects. 

A series of tri- and tetrasubstituted alkenyldimethylsilanols were prepared to study the substituent effects on the stereochemical outcome of a subsequent cross-coupling reaction. The products were obtained in high geometrical purity by the combination of D3 and the geometrically defined alkenyllithium reagents generated by bromine-lithium exchange with f-butyllithium (Scheme 3). 

---